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Maitland, Vivien. "Isozyme-specific induction of cytochrome P450 in rat hepatocyte cultures." Thesis, University of Aberdeen, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302485.
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The aim of this study was to investigate the induction of CYP1A by DMSO, to determine whether DMSO induced other P450 isozymes (CYP2B) and to compare the effects of DMSO and another differentiating agent, sodium butyrate. Induction of CYP1A-dependent ethoxyresorufin-O-deethylase (EROD) was observed in the presence of increasing concentrations of DMSO. All concentration investigated (1%, 1.5% and 2%) caused induction (2-3 fold), and enhanced BA-induction of EROD. Enhancement of BA-induction was greater with 1% and 1.5% DMSO (2.5-3 fold over BA alone) than with 2% (1.8-fold). DMSO alone did not increase CYP1A1 RNA levels. Hepatocytes treated with BA and DMSO together exhibited a 1.3-fold greater increase in RNA levels than with BA alone. Western blotting indicated that CYP1A1 protein was increased by inducers (BA, DMSO and isosafrole), but that CYP1A2 was not. This indicates that the CYP1A1 isozyme is responsible for EROD activity in these cultures, and that the CYP1A2-induction mechanism is lost in rat hepatocytes cultured under the conditions of these experiments. This observation was confirmed by the lack of CYP1A2-dependent phenacetin-O-deethylase (POD) activity in culture. The substituted benzimidazole omeprazole has been shown to induce CYP1A isozymes in human hepatocyte cultures. In this study omeprazole was not effective in inducing EROD activity in rat hepatocytes or in vivo in the rat. This confirms that rat hepatocytes are not a good model for CYP1A induction in man. DMSO appears to be isozyme specific, since CYP2B-dependent pentoxyresorufin-O-dealkylase (PROD) activity was not increased by DMSO, and phenobarbitone (PB) induction of PROD was enhanced only slightly by DMSO on day 3 of culture (4-fold over control; 1.5-fold over PB alone). Sodium butyrate and DMSO were both shown to induce differentiation of rat hepatocyte, with maintenance of low level of γ-glutamyl transferase activity, and maintenance of a more rounded morphology.
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Wurden, Colleen J. "Metabolism of carbamazepine and inhibitory drug interactions /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/7977.
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Bradshaw, Jennifer Jean. "Isoflurane : interaction with hepatic microsomal enzymes." Doctoral thesis, University of Cape Town, 1992. http://hdl.handle.net/11427/27138.
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lsoflurane interacts with cytochrome P-450 in rat and human hepatic microsomes and the Δ6- and Δ5-desaturases in rat hepatic microsomes. The interaction of isoflurane with cytochrome P-450 results in its metabolism to fluoride ion and organofluorine metabolites. The cytochrome P-450 isozymes catalysing the defluorination of isoflurane were assessed in hepatic microsomes from phenobarbital-, β-naphthoflavone- and pregnenolone-16α-carbonitrilepretreated and untreated rats. One or more of the cytochrome P-450 isozymes induced by phenobarbital and pregnenolone-16α-carbonitrile appear to defluorinate isoflurane, but those induced by β-naphthoflavone do not. From a comparison of the extent of defluorination of isoflurane in hepatic microsomes from phenobarbital- and pregnenolone-16α-carbonitrile-pretreated rats, and their Kₘ and Vₘₐₓ values, it appears that isoflurane is defluorinated by one or more isozymes induced by both phenobarbital and pregnenolone-16α-carbonitrile. The major isozyme is probably cytochrome P-450PCN1. The metabolites of isoflurane were identified in human and phenobarbital-induced rat hepatic microsomes. In microsomes from phenobarbital-pretreated rats, isoflurane is metabolised to fluoride ion and trifluoroacetaldehyde; trifluoroacetic acid is not produced in measureable amounts. The trifluoroacetaldehyde produced binds to microsomal constituents. In human hepatic microsomes, the organofluorine metabolite is identified as trifluoroacetic acid. It is proposed that isoflurane is metabolised by different pathways in human and phenobarbital-induced rat hepatic microsomes. The interaction of isoflurane with the cyanide-sensitive factors was assessed by several criteria. Firstly, using the reoxidation of cytochrome b₅ as an index of fatty acid desaturase activity, isoflurane appears to interact with the Δ6- and/or Δ5-desaturases, but not the Δ9-desaturase. Secondly, these results were confirmed and clarified by the use of direct assays to measure the fatty acid desaturase activity. Using the direct assay, we confirmed that isoflurane did not inhibit the Δ9-desaturase and inhibited Δ6-desaturation of linoleic acid, but not the Δ6-desaturation of α-linolenic acid. The inhibition of the Δ6-desaturation of linoleic acid occurred at low millimolar concentrations of isoflurane. lsoflurane inhibits the Δ5-desaturation of eicosa-8, 11, 14-trienoic acid to a small extent which is only apparent at much higher concentrations of isoflurane than that which inhibits the Δ6-desaturase. Further studies focussed on measurement of the activity of Δ6-desaturase in order to attempt to study the kinetics of the inhibition of the Δ6-desaturase by isoflurane: Δ6-desaturase activity was assessed using hepatic microsomes as the source of the enzyme and linoleic acid as substrate precursor. In the course of these studies, we identified a number of factors that affected the apparent activity of the Δ6-desaturase in hepatic microsomes. These included significant levels of endogenous substrate and competing reactions in the hepatic microsomes. Endogenous substrate levels were quantified and corrected for. We then resorted to computer modelling to extract the kinetics of the Δ6-desaturase free of contributions from acyl-CoA synthetase and lysophospholipid acyltransferase, as well as enzyme decay. The kinetics of isoflurane inhibition of the Δ6-desaturase were then superimposed and studied by computer modelling.
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Uusitalo, J. (Jouko). "The role of drug metabolism in drug discovery and development:case ospemifene." Doctoral thesis, Oulun yliopisto, 2015. http://urn.fi/urn:isbn:9789526210223.
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Abstract Drug metabolism is one of the most important events a drug faces after administration. Traditionally, drug metabolism has only been considered as a major clearance and elimination step in the pharmacokinetics of a drug. However, drug metabolism is also one of the important factors behind safety and toxicity issues in drug discovery and development. Some of the mechanisms behind metabolism-related toxicity we do understand well while others, especially the role of reactive metabolites, need further research. The thesis reviews the role of drug metabolism in the drug discovery and development process from the point of view of metabolism and metabolites. Special emphasis is put on reviewing the metabolism behind human toxicity and safety, and the roles of circulating and reactive metabolites in particular. Ospemifene is a nonsteroidal selective estrogen receptor modulator recently approved for the treatment of vulvar and vaginal atrophy in postmenopausal women with moderate to severe dyspareunia. The present study characterized the in vitro and in vivo metabolism and potential drug interactions of ospemifene. The principal human metabolites were identified and the adequacy nonclinical animal exposure was evaluated. The major human cytochrome P450 enzymes involved in the formation of principal metabolites were also identified and the clinical consequences assessed. Finally, the interaction potential of ospemifene as a cytochrome P450 enzyme inducer or inhibitor was investigated. As a result, ospemifene was considered to be safe drug from a metabolic interaction point of view. This study was part of the drug development program of ospemifene and practically all of the in vitro study data were included in the marketing authorization application of ospemifene. Ospemifene was also a case molecule in the development of new methodologies to study drug metabolism and drug-drug interactionsTiivistelmä Lääkeainemetabolia on lääkeaineen farmakokinetiikassa tärkeä puhdistuma- ja eliminaatioaskel, jonka rooli on ymmärretty varsin hyvin. Lääkeainemetabolialla on myös merkittävä vaikutus lääkeaineen toksisuuteen ja lääkkeen käytön turvallisuuteen. Osa lääkeainemetaboliaan liittyvistä toksisuusmekanismeista selvitetty hyvin, mutta erityisesti reaktiivisiin metaboliitteihin liittyvä osa vaatii vielä tutkimusta. Tämän työn kirjallisuusosassa katselmoidaan lääkeainemetabolian merkitystä lääkekehitysprosessissa painottaen erityisesti lääkeainemetabolian sekä reaktiivisten ja verenkierrossa kiertävien metaboliatuoteiden vaikutusta toksisuuteen ihmisellä ja merkitystä turvalliseen lääkkeiden käyttöön. Ospemifeeni on uusi ei-steroidinen selektiivinen estrogeenireseptorimodulaattori, joka on hyväksytty yhdynnänaikaisesta kivusta kärsivien postmenopausaalisten naisten vulvan ja vaginan limakalvojen kuivumisen hoitoon. Tässä tutkimuksessa selvitettiin ospemifeenin lääkeainemetaboliaa ihmisellä ja koe-eläimillä sekä mahdollisia lääkeinteraktioita. Tutkimuksessa tunnistettiin tärkeimmät metaboliitit ihmisellä ja arvioitiin eläinkokeissa käytettyjen koe-eläinten altistumisen kattavuus niille. Työssä selvitettiin myös tärkeimmät päämetaboliitteja katalysoivat sytokromi P450 -entsyymit ja arvioitiin löydösten kliinistä merkitystä. Lisäksi tutkittiin aiheuttaako ospemifeeni lääkeinteraktioita muille lääkeaineille indusoimalla tai inhiboimalla sytokromi P450 -entsyymejä. Tutkimustulosten perusteella ospemifeenia voidaan pitää lääkeainemetabolian suhteen turvallisena lääkkeenä. Tämä tutkimus oli osa ospemifeenin lääkekehitysohjelmaa ja käytännössä kaikki tutkimustyön in vitro -tietoaineisto oli mukana ospemifeenin myyntilupa-hakemuksissa lääketurvallisuusviranomaisille. Ospemifeenia käytettiin tutkimustyön aikana myös yhtenä esimerkkimolekyylinä kehitettäessä uusia menetelmiä lääkeainemetabolian ja lääkeinteraktioiden tutkimiseen
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Turpeinen, M. (Miia). "Cytochrome P450 enzymes—in vitro, in vivo, and in silico studies." Doctoral thesis, University of Oulu, 2006. http://urn.fi/urn:isbn:9514282205.
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Abstract
Metabolism is a major determinant of the pharmacokinetic properties of most drugs and is often behind bioavailability problems, drug-drug interactions, and metabolic idiosyncrasies. Cytochrome P450 (CYP) enzymes are a superfamily of microsomal hemoproteins catalysing the metabolic reactions of several exogenous compounds. The majority of crucial steps within drug metabolism are in connection with CYP enzymes.
In the present study, in vivo, in vitro, and in silico approaches were applied and characterised to evaluate the effects of chemical entities on CYP-mediated metabolism. CYP2B6 was used as a target enzyme for these studies.
For evaluation of the CYP inhibition potential of new chemical entities, a novel in vitro test system utilising the n-in-one approach was developed. This method proved to be robust and applicable to screening purposes. Validation of the n-in-one assay was done by comparing its performance to commonly used in vitro techniques using six structurally diverse drugs. All assay types yield remarkably similar results with the majority of the CYP forms tested.
Several chemicals were screened in vitro and in silico in order to find potent and selective chemical inhibitors for CYP2B6. Ticlopidine, thioTEPA and 4-(4-chlorobenzylpyridine) were found to be highly effective inhibitors of CYP2B6. The selectivity of thioTEPA proved to be very high, whereas ticlopidine and 4-(4-chlorobenzylpyridine) also inhibited other CYPs. At a concentration level of 1 μM for ticlopidine and 0.1 μM for 4-(4-chlorobenzylpyridine), the inhibitory effect towards other CYPs was negligible.
Due to wide clinical use and relevance, clopidogrel and ticlopidine were selected for further in vivo interaction studies. Both clopidogrel and ticlopidine significantly inhibited the CYP2B6-catalysed bupropion hydroxylation and patients receiving either clopidogrel or ticlopidine are likely to need dose adjustments when treated with drugs primarily metabolised by CYP2B6. The effect of impaired kidney function on CYP2B6 activity and on bupropion pharmacokinetics was also explored. In patients with kidney disease, the bupropion AUC and Cmax were significantly higher and the apparent oral clearance of bupropion was notably lower compared to healthy controls.
The present results indicate that the in silico and in vitro methods used are helpful in predicting in vivo drug-drug interactions. The effective utilisation of these models in the early phases of drug discovery could therefore help to target the in vivo studies and to eliminate metabolically unfavourable drug candidates.
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Lundahl, Anna. "In vivo Pharmacokinetic Interactions of Finasteride and Identification of Novel Metabolites." Doctoral thesis, Uppsala universitet, Institutionen för farmaci, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-129362.
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The general aim of this thesis was to improve the understanding of the in vivo pharmacokinetics and, in particular, the metabolism of finasteride, a 5α-reductase inhibitor used in the treatment of enlarged prostate glands and male pattern baldness. CYP3A4 has been identified as the major enzyme involved in the sequential metabolism of finasteride to ω-OH finasteride (M1) and ω-COOH finasteride (M3). The consequences of induced and inhibited metabolism on the pharmacokinetics of finasteride and its metabolites were investigated in humans and pigs. Both studies included bile collection. The collected human and pig samples were used for the metabolite identification. As expected, induced metabolism led to reduced plasma exposure of finasteride and inhibited metabolism had the opposite effect. The interactions were investigated in detail and included examination of the biliary pharmacokinetics of finasteride and its metabolites. In pigs, the study included monitoring of the hepatic extraction over time, deconvolution and the development of a semi-physiological model for comparison of the effects on the gut wall and liver metabolism. For M3, the concentration ratios of bile to plasma and the renal clearance indicated that carrier-mediated processes are involved in the biliary and urinary excretion. This was not, however, the case for finasteride. The metabolite, M1, could not be quantified either in humans or pigs. Instead, two other OH metabolites, M1 isomers, were identified in humans. These metabolites were found to undergo glucuronide conjugation. In humans, one glucuronide was identified intact and in pigs, both glucuronides were identified intact in bile and in urine. In addition, a glucuronide of M3 was identified in human bile. In conclusion, advances have been made in the understanding of the pharmacokinetics of finasteride, in particular in relation to the metabolism. Hopefully, the findings of this comprehensive investigation can be applied to other drugs and novel chemical entities.
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Vicente, David Gil Marques Borrero. "An overview of the role of cytochrome P450 enzyme system in food-drug interactions and possible applications in veterinary medicine." Bachelor's thesis, Universidade Técnica de Lisboa. Faculdade de Medicina Veterinária, 2009. http://hdl.handle.net/10400.5/1003.
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Dissertação de Mestrado Integrado em Medicina VeterináriaCytochrome P450 enzymes (CYP) are hemoproteins belonging to the group of monooxygenases and one of the main enzymatic systems responsible for drug metabolism. In the present study, in vitro approach was applied to evaluate the relation of CYP-catalyzed activities between human, rabbit, minipig and mouse, using single substrate assays (MultiCYP 7-ethoxycoumarin 0-deethylase (ECOD), CYP1A1/2 7-ethoxyresorufin 0- deethylase (EROD), CYP2A6 coumarin 7-hydroxylase (COH), CYP3A4 midazolam 1- hydroxylase (OH-MDZ), and CYP2E1 chlorzoxazone 6-hydroxylase (OH-CLZ)). It was also studied plant extracts (Pinus sylvestris, Angelica archangelica, Mentha sp., Citrus grandis) and phytochemicals (8-Hydroxybergapten, 5,6-dihydroxyangelicin, α, β-Thujone, α-Thujone, angelicin, bergamottin, bergapten, bergaptol, cnidilin, imperatorin, isobergapten, isopimpinellin, lanatin, phellopterin, psoralen, sphondin, xanthotoxin) as potential inhibitors in CYP-related activities of hepatic human microsomes (CYP1A1/2 (EROD), CYP2A6 (COH), CYP3A4 (OH-MDZ)). This study showed that the lowest ECOD activity was detected in humans and there was no similarity between other species. CYP1A1/2 showed equivalent activities. The highest CYP activities in humans were found for CYP2A6 and CYP3A4. In CYP2E1 activity, two similar groups were recognized: human and mouse versus rabbit and minipig. EROD reaction was the most inhibited CYP-mediated reaction. COH reaction was inhibited by few compounds. The highest inhibition was detected among angular furocoumarins. Linear furocoumarins group had the lower inhibitory concentration of CYP3A4. Thujone showed weak inhibition of CYP activities.
RESUMO - As enzimas do sistema citocromo P450 (CYP) são hemoproteinas pertencentes ao grupo das monoxigenases e um dos principais sistemas enzimáticos responsáveis pela metabolização de fármacos. Neste estudo foi avaliada a relação da actividade catalítica de diferentes CYPs entre humanos, coelhos, minipig e murganhos, recorrendo a substratos como sondas individuais in vitro para mensurar reacções especificas (MultiCYP 7-etoxicumarina 0-deetilase (ECOD), CYP1A1/2 7-etoxiresorufina 0-deetilase (EROD), CYP2A6 cumarina 7-hidroxilase (COH), CYP3A4 midazolam 1-hidroxilase (OH-MDZ), e CYP2E1 clorozoxazona 6-hidroxilase (OH-CLZ)). Também foram estudados extractos de plantas (Pinus sylvestris, Angelica archangelica, Mentha sp., Citrus grandis) e fitoquímicos (8-hidroxibergaptem, 5,6-dihidroxiangelicina, α, β-tujona, α-tujona, angelicina, bergamottin, bergapteno, bergaptol, cnidilina, imperatorina, isobergapteno, isopimpinelina, lanatin, felopterina, psoraleno, sphondin, xantotoxina) como potenciais inibidores da actividade catalítica dos CYPs microssomais hepáticos humanos (CYP1A1/2 (EROD), CYP2A6 (COH), CYP3A4 (OH-MDZ)). Neste estudo não foram detectadas actividades similires entre espécies na reacção ECOD e a actividade mais baixa foi detectada nos humanos. A reacção EROD dos CYP1A1/2 demonstrou actividades similares entre as diferentes espécies. As maiores actividades cataliticas verificadas nos humanos correspondem aos CYP2A6 e CYP3A4. No estudo da reacção do CYP2E1 foram determinados dois grupos distintos com actividades cataliticas similares: 1) humanos e murganhos, 2) coelhos e minipigs. No estudo de potenciais inibidores dos CYPs, a reacção EROD foi a mais inibida. Pelo contrário, a reacção COH foi inibida por poucos compostos. A maioria das inibições ocorreu por exposição a furocumarinas angulares. O grupo de furocumarinas lineares teve a menor concentração inibitória da reacção OH-MDZ do CYP3A4. Os fitoquímicos α, β-tujona e α- tujona demonstraram ter um fraco poder inibitório na actividade dos CYPs analisados.
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Kabulski, Jarod L. "Development of Au-immobilized P450 platform for exploring the effect of oligomer formation on P450-mediated metabolism for In vitro to In vivo drug metabolism predictions." Morgantown, W. Va. : [West Virginia University Libraries], 2010. http://hdl.handle.net/10450/10892.
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Thesis (Ph. D.)--West Virginia University, 2010.Title from document title page. Document formatted into pages; contains xiv, 180 p. : ill. (some col.). Includes abstract. Includes bibliographical references.
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Habenschus, Maísa Daniela. "Estudos de inibição das enzimas do citocromo P450 pelo produto natural (-)-grandisina utilizando microssomas hepáticos de humanos." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/59/59138/tde-06072016-095943/.
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A (-)- grandisina (GRA) é um produto natural da classe das lignanas e é encontrada em muitas espécies de plantas das regiões Norte e Nordeste do Brasil. Por apresentar diversas propriedades biológicas, como atividade tripanocida, anti-inflamatória, antinociceptiva, e principalmente atividade antileucêmica e antitumoral contra tumores de Ehrlich, a GRA pode ser considerada um potencial candidato a fármaco. Porém, para que a GRA se torne um fármaco são necessárias diversas etapas de estudos, incluindo estudos pré-clínicos de interações medicamentosas (DDI). As DDI ocorrem principalmente devido a inibições diretas e tempo-dependentes das enzimas do citocromo P450 (CYP450), uma superfamília de enzimas responsável por metabolizar cerca de 75% dos fármacos em uso. Os estudos pré-clínicos de DDI envolvem o conhecimento do potencial inibitório do candidato a fármaco sobre essas enzimas e esses estudos podem ser realizados empregando diversos modelos in vitro, como, por exemplo, microssomas hepáticos de humanos (HLM). Assim, nesse estudo foi avaliado o efeito inibitório da GRA sobre a atividade das principais isoformas do CYP450 e também foram determinadas as isoformas que contribuem para a formação dos metabólitos da GRA. Os resultados demonstraram que múltiplas isoformas participam da formação dos metabólitos da GRA, com destaque para a CYP2C9, que participa da formação de todos os metabólitos. Em relação aos estudos de inibição, foi possível concluir que a GRA é um inibidor fraco da CYP1A2 e CYP2D6, com valores de IC50 maiores do que 200 µM e 100 µM, respectivamente, e um inibidor moderado e competitivo da CYP2C9, com IC50 igual a 40,85 µM e Ki igual a 50,60 µM. Para a CYP3A4 o potencial inibitório da GRA foi avaliado utilizando dois substratos distintos. A GRA demonstrou ser tanto um inibidor dose-dependente moderado e competitivo dessa isoforma, quanto um inibidor tempo-dependente baseado em mecanismo com potencial de inativação equiparável ao do irinotecano, inibidor baseado em mecanismo clinicamente significativo. Utilizando a nifedipina como substrato os valores de IC50 e Ki foram 78,09 µM e 48,71 µM, respectivamente. Já os valores dos parâmetros cinéticos de inativação foram KI= 6,40 µM, kinact= 0,037 min-1 e Clinact= 5,78 mL min-1 µmol-1. Para os ensaios empregando o midazolam os valores de IC50 e Ki foram 48,87 µM e 31,25 µM, respectivamente, e os valores dos parâmetros cinéticos de inativação foram KI= 31,53 µM, kinact= 0,049 min-1 e Clinact= 1,55 mL min-1 µmol-1. Com relação a CYP2E1, por sua vez, foi possível observar que a GRA tem capacidade de aumentar a atividade dessa isoforma significativamente a partir da concentração de 4 µM. Portanto, conclui-se que não há risco da GRA apresentar interações medicamentosas com fármacos metabolizados pela CYP1A2 e CYP2D6, enquanto que para a CYP2C9, apesar da GRA ser um inibidor moderado dessa isoforma, o risco é baixo. Já para medicamentos metabolizados pela CYP2E1 e CYP3A4 o risco de DDI existe e isso deve ser cuidadosamente monitorado in vivo, principalmente porque a CYP3A4 é a isoforma responsável por catalisar o metabolismo da maioria dos fármacos.(-)-grandisin (GRA) is a lignanic natural product found in many species of plants from North and Northeast of Brazil. This compound has several biological properties, such as trypanocide, anti-inflammatory, antinociceptive, antileukemia activity and antitumor activity against Ehrlich tumor. Because of these biological properties, GRA is considered a potential drug candidate, however, before becoming a new drug, GRA has to undergo various tests, including preclinical drug-drug interactions (DDI) studies. Most of the times, DDI occur because of direct and time-dependent inhibitions of cytochrome P450 (CYP450) enzymes, an enzyme superfamily responsible for metabolizing the vast majority of drugs administered. Preclinical drug-drug interactions studies involve the evaluation of the potential of a drug candidate to inhibit this superfamily of enzymes and these studies can be conducted using in vitro models, such as human liver microsomes (HLM). Therefore, in this project, the inhibitory effect of GRA on the activity of some CYP450 isoforms was evaluated and the isoforms that catalyze the formation of GRA\'s metabolites were also determined. Results showed that multiple CYP450 isoforms participate in the GRA\'s metabolites formation, highlighting CYP2C9, which catalyzes the formation of all metabolites. The inhibition studies showed that GRA is a weak inhibitor of CYP1A2 and CYP2D6, with IC50 values greater than 200 µM and 100 µM, respectively, and a moderate and competitive inhibitor of CYP2C9, with IC50 value equal to 40.85 µM and Ki value equal to 50.60 µM. The capability of GRA to inhibit CYP3A4 was evaluated using two different substrates. GRA showed to be a moderate and competitive dose- dependent inhibitor of this isoform and also a mechanism-based time-dependent inhibitor with potential of inactivation comparable to irinotecan, a clinically significant mechanism-based inhibitor. IC50 and Ki values obtained using nifedipine as substrate were 78.09 µM and 48.71 µM, respectively, and inactivation kinetics parameters were KI= 6.40 µM, kinact= 0,037 min-1 e Clinact= 5.78 mL min-1 µmol-1. On the other hand, IC50 and Ki values using midazolam as substrate were 48.87 µM and 31.25 µM, respectively, and the values of inactivation kinetics parameters were KI= 31.53 µM, kinact= 0,049 min-1 and Clinact= 1.55 mL min-1 µmol-1. With respect to CYP2E1, it was observed that GRA increases its activity significantly from a concentration of 4 µM. Therefore, it is possible to conclude that there is no risk of DDI between GRA and drugs metabolized by CYP1A2 and CYP2D6, while for CYP2C9, although GRA is a moderate inhibitor of this isoform, the risk is low. Finally, for drugs metabolized by CYP3A4 and CYP2E1 there is risk of DDI and this should be carefully monitored in humans, mainly because CYP3A4 is an isoform responsible for catalyzing the metabolism of most drugs in use.
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Nguyen, San. "Inhibitory Properties of Functional Food Plants on CYP Enzymes and Cree Traditional Medicines on Aldose Reductase." Thèse, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/20070.
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This thesis examines the cytochrom P450 (CYP) drug metabolizing enzyme inhibition and antimicrobial properties of 46 common food plants available in the Canadian Market and the inhibitory properties of 17 traditional Cree antidiabetic medicines on aldose reductase. Inhibitory activity profiles of CYP 3A4, 3A5, 3A7 and 2D6 were created for the 46 samples. The most active plants in the CYP inhibition assay were the spices, belonging to the Apiaceae and Lamiaceae. Similarly, the most active plants in the antimicrobial assay were also the Apiaceae and Lamiaceae. Swine lens homogenate was tested as a novel model for the aldose reductase inhibition assay. Several Cree plants selected for the aldose reductase study showed a high activity, primarily in samples which also contained high levels of phenolics. A positive correlation was observed between total phenolics content and aldose reductase inhibition r2=0.44, p=0.05. Crude extracts of Rhododendron groenlandicum exhibited inhibitory activities of 35.11 ± 0.16 %. The subfractionation and HPLC analysis of R. groenlandicum revealed high levels of phenolics compounds including, catechin, epicatechin, quercetin and quercetin glycosides. This study found that medicinal and food plants contain phytochemicals that may have both beneficial and detrimental biological effects.Nous avons étudié dans cette thèse les capacités de 46 plantes comestibles, disponibles sur le marché canadien, à inhiber le cytochrome P450 (CYP), enzyme responsable du métabolisme des médicaments, les propriétés antimicrobiennes, et les propriétés inhibitrices de l'aldose réductase à partir de 17 médicaments antidiabétiques traditionnellement utilisés par les Cris. Les profils de l'activité inhibitrice du CYP 3A4, 3A5, 3A7 et 2D6 ont été réalisés pour les 46 plantes à l'étude. Les plantes les plus actives dans le test d'inhibition du CYP furent les épices, plantes appartenant aux familles des Apiaceae et Lamiaceae. De même, les plantes les plus actives dans le bioessai antimicrobien furent aussi les plantes de ces deux mêmes familles. Un homogénat de cristallin de porc a été utilisé comme modèle nouveau pour le test d'inhibition de l'aldose réductase. Plusieurs plantes, utilisées par la nation Cri, qui ont été sélectionnées pour l'étude ont montré une forte activité inhibitrice de l’aldose réductase, principalement dans les échantillons qui contenaient des teneurs élevées en composés phénoliques. Une corrélation positive a été observée entre la teneur totale en composés phénoliques et l'inhibition de l'aldose réductase (r2 = 0.44, p = 0.05). Des extraits bruts de Rhododendron groenlandicum ont montré des activités inhibitrices de 35.11 ± 0.16%. Le sous-fractionnement et l'analyse HPLC de R. groenlandicum ont aussi révélé des teneurs élevées des composés phénoliques, incluant la catéchine, l'épicatéchine, la quercétine et les glycosides de quercétine. Cette étude a montré que les plantes médicinales et alimentaires contiennent des composés phytochimiques qui peuvent avoir à la fois des effets biologiques bénéfique et préjudiciable.
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Sanford, Jonathan Christian. "Pharmacogenetics of Drug Metabolizing Enzymes Involved in Cardiovascular Drug Treatment." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1405518187.
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Chan, C. Y. "Assessment of degradation rate constants for quantitative predictions of drug-drug interactions arising from CYP450 drug metabolising enzymes." Thesis, University of Liverpool, 2018. http://livrepository.liverpool.ac.uk/3020976/.
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The first-order degradation rate constant (kdeg) of drug metabolising enzymes (DMEs) is a known source of uncertainty in the prediction of time-dependent drug-drug interactions (DDIs) in physiologically-based pharmacokinetic (PBPK) modelling. There is a large disparity or paucity of published kdeg and related half-life (t1/2) values for DMEs. Physiologically-relevant kdeg values should ideally be derived in vivo to facilitate accurate DDI predictions. However, direct measurement of DME degradation in humans is not routinely possible and indirect measurements utilising changes in levels of specific endogenous substrates have only been described for a few DMEs. This thesis aims to develop an in vitro method of measuring DME protein degradation rates to improve the prediction accuracy of time-dependent DDIs. One in vitro approach of measuring protein degradation rates involves inhibiting de novo protein synthesis, followed by tracking residual protein or activity decline over time. Pharmacological protein synthesis inhibitor agents are commonly used for this purpose but may cause cytotoxicity. Four commonly used inhibitor agents were assessed for their capacity to inhibit protein synthesis without overt cytotoxicity. However, all selected compounds were too cytotoxic for subsequent use in kdeg studies. Small-interfering ribose nucleic acid (siRNA) can be added to in vitro systems to initiate gene-specific silencing by inhibiting messenger RNA (mRNA) translation. It was hypothesised that siRNA would inhibit de novo protein synthesis with less cytotoxicity owing to its specificity. CYP3A4 is the most widely studied cytochrome P450 (CYP) enzyme in terms of DDIs because of its well-recognised role in xenobiotic metabolism. Primary human hepatocytes were treated with CYP3A4-specific siRNA to suppress mRNA translation, followed by the tracking of enzyme activity and protein loss over time to derive kdeg. CYP3A4 kdeg was calculated at 0.019 (± 0.044) and 0.020 (± 0.0003) h-1 from protein and activity loss, respectively. These values were in good agreement with existing published values. The siRNA approach was subsequently applied to determine CYP2B6 kdeg. The CYP2B6 kdeg values derived from siRNA-treated hepatocytes were 0.081 (± 0.009) h-1 from protein loss and 0.058 (± 0.010) and 0.062 (± 0.006) h-1 from activity loss, which were assessed by different methods. The CYP2B6 kdeg values derived from untreated hepatocytes were similar to values in literature. This novel approach can now be used for other less well-characterised DMEs that are associated with time-dependent DDIs. Cellular protein abundance is a balance between synthesis and degradation. Dysregulation of the lysosomal or proteasomal protein degradation mechanisms affects steady-state protein levels and impacts on overall cellular functions. It was hypothesised that single nucleotide polymorphisms (SNPs) in the CYP3A4 protein degradation machinery could affect CYP3A4 protein abundance and downstream activity. Five SNPs were investigated for associations with plasma atazanair (ATV) concentrations, which was a surrogate measure for CYP3A4 activity. No associations were found and this was likely due to the lack of clear understanding of the specific mechanisms that commits CYP proteins for degradation. Further work in this field will identify targets that may be exploited in the future for more accurate measurements of DME kdeg. The data presented in this thesis enhances the understanding of methods used to study protein degradation and this can be applied to multiple fields of cellular research. Importantly, work herein has generated a novel approach to measuring kdeg of proteins that can be applied to other less-well characterised enzymes for better prediction of time-dependent DDIs.
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Coutts, Jane M. "Characterisation of mammalian cytochrome P450 enzymes by their metabolic activities." Thesis, Robert Gordon University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296198.
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Heydari, Amir. "Prediction of in vivo drug-drug interactions involving metabolism from in vitro data incorporating population variability." Thesis, University of Sheffield, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425594.
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Youssef, Amir Samaan Bishara. "Improvement of Gastroparesis Management By Addressing Challenges in Drug Metabolism: Studies with Metabolite Identification, Reaction Phenotyping and In Vitro Drug-Drug Interactions." Diss., Temple University Libraries, 2013. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/231985.
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Pharmaceutical SciencesPh.D.
Gastroparesis is a disorder characterized by delayed gastric emptying due to chronic abnormal gastric motility. Prokinetic agents such as domperidone and metoclopramide are the cornerstone in treatment of gastroparesis. Although these medications have been used for decades, essential information about their metabolism is not available. Lack of knowledge about the metabolites formed in the body upon administration of the aforementioned medications as well as the enzymes involved in their metabolism limits key information needed to make sound medical decisions. Accurate and comprehensive identification of the metabolites along with reaction phenotyping of prokinetic agents will ensure safe and effective use of these drugs and hence enhance the clinical outcome. The thesis starts with an introductory chapter which comprises a comprehensive literature review on gastroparesis and the available pharmacological treatment options. The chapter also emphasizes the importance of metabolic profiling of prokinetic agents (domperidone and metoclopramide) and its impact on enhancing the safety and efficacy of these medications. Chapter 2 of this project was aimed to determine phase oxidative and conjugative metabolites of domperidone in the plasma and urine of gastroparesis patients using tandem mass spectrometry. First, the metabolites were identified in in-vitro human subcellular fractions. The knowledge gained in this experiment helped identifying the metabolites in the biological fluids of patients. In total, 12 metabolites including 7 new metabolites were identified, 5 of which were not reported previously. Chapter 3 aimed to identify the cytochrome P450 (CYP) enzymes responsible for the metabolism of metoclopramide. The parent depletion approach was used and a novel LC-MS/MS method was developed and validated to enable metoclopramide quantification. CYP2D6 was showed to the predominant isoform in metoclopramide metabolism; other isoforms also contribute to a minor extent. Chapter 4 discusses the possibility of potential drug-drug interaction (DDI) in the current management practice of gastroparesis. We identified and investigated some frequently used drug combinations that are known to share common metabolic pathways. Domperidone in combination with pioglitazone and ondansetron was evaluated. Results showed that pioglitazone inhibited domperidone metabolism in-vitro. Our experiments did not predict a DDI for the domperidone - ondansetron combination. In summary, the ultimate goal of this thesis was to improve the management of gastroparesis by increasing information about the metabolic disposition of prokinetic agents and to investigate the magnitude of putative drug combinations. The knowledge provided by this work will help in making more effective and less hazardous clinical decisions which will ultimately lead to more successful gastroparesis management.
Temple University--Theses
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Sall, Carolina. "In vitro-in vivo assessment of repaglinide metabolism and drug-drug interactions : towards a physiologically-based pharmacokinetic model." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/in-vitroin-vivo-assessment-of-repaglinide-metabolism-and-drugdrug-interactionstowards-a-physiologicallybased-pharmacokinetic-model(1b8eca49-bc68-484e-b921-2e324b4c5f00).html.
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Repaglinide is currently recommended as an in vivo CYP2C8 probe by the U.S. Food and Drug Administration (FDA), but the kinetic characterisation and enzymes involved in the elimination of this drug have not been fully delineated. In addition to its complex metabolism, polymorphism in the SLCO1B1 gene encoding for the hepatic uptake transporter organic anion transporting polypeptide 1B1 (OATP1B1) has been shown to impact repaglinide pharmacokinetics, further complicating the prediction of repaglinide clearance and drug-drug interactions (DDIs). The aim of this thesis was to firstly perform a systematic analysis of repaglinide metabolic pathways and thereby assess the contribution of specific enzymes to its clearance, and to secondly increase the understanding of repaglinide as a victim drug by implementing obtained in vitro metabolism data together with reported hepatic uptake parameters into a physiologically-based pharmacokinetic (PBPK) model. Furthermore, reported repaglinide DDIs, repaglinide AUC in different SLCO1B1 genotype groups and repaglinide P450 metabolite ratios were collated and critically analysed. The metabolism of repaglinide was characterised using a range of in vitro systems, namely pooled cryopreserved human hepatocytes, human liver microsomes (HLMs), human S9 fractions and recombinant P450 enzymes. The impact of in vitro systems on the analysis of repaglinide metabolic pathway was investigated and the importance of individual metabolic pathways studied. Definite differences in formation clearance ratios were found between CYP3A4 and CYP2C8 for the formation of M1 and M4 metabolites, resulting in a 60- and 0.05-fold M1:M4 ratio in recombinant CYP3A4 and CYP2C8, respectively. A major system difference was seen in clearances for the formation of M2, which is suggested to be a main metabolite of repaglinide in vivo. An approximately 7-fold higher unbound intrinsic clearance was observed in hepatocytes and S9 fractions in comparison to microsomes; the involvement of aldehyde dehydrogenase in M2 formation was shown for the first time. This systematic analysis revealed a comparable in vitro contribution from CYP2C8 and CYP3A4 to the metabolism of repaglinide.
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Sane, Rucha S. "Differential Induction of Drug Metabolizing Enzymes and Drug Transporters by Tamoxifen molecular mechanisms and clinical implications /." Cincinnati, Ohio : University of Cincinnati, 2006. http://www.ohiolink.edu/etd/view.cgi?acc%5Fnum=ucin1143410615.
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Thesis (Ph. D.)--University of Cincinnati, 2006.Title from electronic thesis title page (viewed Aug. 9, 2006). Includes abstract. Keywords: Tamoxifen; CYP3A4; Cytochrome P450; Enzyme induction; drug metabolism; human hepatocytes; UDP-glucuronosyl transferase; P-glycoprotein; Pregnane X Receptor; PXR; LS174T. Includes bibliographical references.
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Wen, Xia. "In vitro approaches in evaluation and prediction of drug-drug interactions involving the inhibition of cytochrome P450 enzymes." Helsinki : University of Helsinki, 2002. http://ethesis.helsinki.fi/julkaisut/laa/kliin/vk/wen/.
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Woodland, Cindy Lisa Patricia. "The role of the kidney in human toxicology, p-glycoprotein-mediated drug interactions and intrarenal drug metabolism." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq49967.pdf.
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Oscarson, Mikael. "Genetic polymorphism of human drug metabolising enzymes : structural and functional studies /." Stockholm, 1999. http://diss.kib.ki.se/1999/91-628-3717-6/.
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Merrell, Matthew David. "Xenosensor Regulation of Enzymes and Transporters in Drug Exposure and Disease." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/194051.
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A large and varied array of xenobiotics (foreign chemicals) enters into our bodies every day. In order to prevent toxicity resulting from xenobiotic accumulation, the body has developed a complex and integrated network of enzymes and transporters to promote and control the metabolism and excretion of drugs and other compounds. Drug metabolizing enzymes are classified as oxidative (Phase I) or conjugative (Phase II), and generally result in increased hydrophilicity of their substrates. Drug transporters actively route xenobiotics into (Phase 0) or out of (Phase III) the cells. The expression of the proteins involved in drug metabolism and transport are coordinately regulated by xenosensing transcription factors, including the constitutive androstane receptor, the pregnane X receptor, the aryl hydrocarbon receptor, and Nrf2. Through the activation of these xenosensors, chemical exposure itself induces the processes which help to remove the xenobiotics from the body. The liver is the major organ of drug metabolism in the body. Chronic hepatic diseases impact the activity of xenosensors and the expression of their enzyme and transporter gene targets. Nonalcoholic fatty liver disease (NAFLD) is the most prevalent liver disease in the United States, affecting 20-30% of the populations. This profoundly underdiagnosed disease has significant effects on hepatic gene expression and may increase the risk of adverse drug reactions and xenobiotic toxicity in affected patients. This manuscript presents original research which contributes to our understanding of xenosensor function in the contexts of chemical exposure and liver disease. Manuscripts in this dissertation investigate 1) the induction profile and mechanisms of the experimental therapeutic agent oltipraz, 2) the xenosensor-regulated mechanisms of induction of the drug transporter ABCC3, 3) the impact of NAFLD on the expression of major drug metabolizing enzymes, and 4) the utility of altered drug disposition as a biomarker for NAFLD progression. The findings of these studies highlight the clinical importance of xenosensor activation and the potential pharmacological and toxicological consequences of hepatic disease.
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Ventura, Ventanachs Verònica. "In vitro metabolism and drug-drug interaction potential of irosustat, a steroidal sulfatase inhibitor." Doctoral thesis, Universitat de Barcelona, 2013. http://hdl.handle.net/10803/124483.
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Irosustat is a first-generation, irreversible, steroid sulfatase inhibitor currently in development for hormone-dependent cancer therapy. Its structure is a tricyclic coumarin-based sulfamate that undergoes desulfamoylation in aqueous solution, yielding the sulfamoyl-free derivative, 667-coumarin.
The first aim of the present work was to study the in vitro metabolism of irosustat, including its metabolic profile in liver microsomes and hepatocytes, the potential species differences, and the identification of the main metabolites. And the second aim of the present work was to predict potential drug-drug interactions between irosustat and possible concomitantly administered medications through the investigation in vitro of the enzymes participating in the metabolism of irosustat and its inhibition/induction potential with the main drug-metabolizing enzymes. The interaction of aromatase inhibitors in the in vitro metabolism of irosustat was also studied.
Irosustat was extensively metabolized in vitro, showing similar metabolite profiles among rat, dog, monkey, and humans (both sexes). In liver microsomes, the dog was the species that metabolized irosustat most similarly to metabolism in humans. Marked differences were found between liver microsomes and hepatocytes, meaning that phase I and phase II enzymes contribute to irosustat metabolism. Various monohydroxylated metabolites of irosustat and of 667-coumarin were found in liver microsomes, which mostly involved hydroxylations at the C8, C10, and C12 positions in the cycloheptane ring moiety. 667-Coumarin was formed by degradation but also by non-NADPH-dependent enzymatic hydrolysis, probably catalyzed by microsomal steroid sulfatase. The main metabolites formed by hepatocytes were glucuronide and sulfate conjugates of 667-coumarin and of some of its monohydroxylated metabolites.
The major cytochrome P450 enzymes involved in the transformation of irosustat were CYP2C8, CYP2C9, CYP3A4/5, and CYP2E1. Moreover, various phase II enzymes (UDP-glucuronosyltransferases and sulfotransferases) were capable of conjugating many of the metabolites of irosustat and 667-coumarin; however, the clinically relevant isoforms could not be elucidated.
Irosustat inhibited CYP1A2 activity in human liver microsomes through the formation of its desulfamoylated degradation product and metabolite 667-coumarin. CYP1A2 inhibition by 667-coumarin was competitive, with a K(i) of 0.77 μM, a concentration exceeding by only 5-fold the maximal steady-state concentration of 667-coumarin in human plasma with the recommended dose of irosustat. In addition, 667-coumarin metabolites enhanced the inhibition of CYP1A2 activity. Additional clinical interaction studies of irosustat with CYP1A2 substrate drugs are strongly recommended. 667-Coumarin also appeared to be a competitive inhibitor of CYP2C19 (K(i) = 5.8 μM) in human liver microsomes, and this inhibition increased with assessment in human hepatocytes. Inhibition of CYP2C19 enzyme activity was not caused by repression of CYP2C19 gene expression. Therefore, additional mechanistic experiments or follow-up studies with clinical evaluation are recommended. Irosustat neither inhibited CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2D6, CYP2E1, CYP3A4/5, or UDP-glucuronosyltransferase 1A1, 1A4, or 2B7 activities nor induced CYP1A2, CYP2C9, CYP2C19, or CYP3A4/5 at clinically relevant concentrations. Results from human liver microsomes indicated that no changes in irosustat pharmacokinetics in vivo are expected as a result of inhibition of irosustat metabolism in cases of concomitant medication administration or irosustat-aromatase inhibitor combination therapy with letrozole, anastrozole, or exemestane.Irosustat és un inhibidor irreversible de la sulfatasa esteroidal, de primera generació, actualment en desenvolupament per al tractament del càncer dependent d'hormones. Els objectius d'aquest treball van ser estudiar el metabolisme in vitro d'irosustat, incloent el seu perfil metabòlic en microsomes hepàtics i hepatòcits, les diferències entre espècies, així com la identificació dels principals metabòlits. I també predir les possibles interaccions fàrmac-fàrmac entre irosustat i possibles medicaments administrats de forma concomitant, a través de la investigació in vitro dels enzims que participen en el metabolisme de irosustat i el seu potencial d'inhibició / inducció dels principals enzims metabolitzants de fàrmacs. La interacció dels inhibidors de l'aromatasa en el metabolisme in vitro del irosustat també es va estudiar. Irosustat és extensament metabolitzat in vitro, mostrant perfils metabòlics similars entre rates, gossos, micos i humans (ambdós sexes). En microsomes de fetge, el gos va ser l'espècie que metabolitza irosustat de forma més similar al metabolisme en humans. 667-coumarin es va formar per degradació, però també per hidròlisi enzimàtica no dependent de NADPH, probablement catalitzada per la sulfatasa esteroidal microsomal. Es van trobar grans diferències entre els perfils metabòlics de microsomes hepàtics i de hepatòcits, significant que tant enzims de fase I com de fase II contribueixen al metabolisme del irosustat. Els principals metabòlits formats pels microsomes de fetge van ser monohidroxilats del irosustat i de la 667-coumarin, mentres que en hepatòcits van ser conjugats glucurònids i sulfats de 667-coumarin i d'alguns dels seus metabòlits monohidroxilats. Els principals enzims del citocrom P450 involucrats en la transformació del irosustat van ser CYP2C8, CYP2C9, CYP3A4/5, i CYP2E1. D'altra banda, diversos enzims de fase II (UDP-glucuronosiltransferasas i sulfotransferasas) eren capaços de conjugar molts dels metabòlits de irosustat i 667-coumarin, però, les isoformes clínicament rellevants no es van poden dilucidar. Irosustat inhibeix les activitats dels CYP1A2 i CYP2C19 en microsomes de fetge humà a través de la formació de 667-coumarin. Es recomanen estudis clínics addicionals d'interacció entre irosustat i substrats del CYP1A2. Pel CYP2C19, aquesta inhibició va augmentar amb l'avaluació en hepatòcits humans, tot i que no va ser causada per la repressió de l'expressió del gen CYP2C19. Per tant, es recomanen experiments mecanistics addicionals o estudis de seguiment amb avaluació clínica. Irosustat no inhibeix CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2D6, CYP2E1, CYP3A4/5, UGT1A1, UGT1A4 ni UGT2B7. Tampoc indueix CYP1A2, CYP2C9, CYP2C19 o CYP3A4/5, a concentracions clínicament rellevants. Els resultats dels microsomes hepàtics humans van indicar que no s'espera canvis en la farmacocinètica del irosustat com a resultat de la inhibició del seu metabolisme en els casos d'administració concomitant d’inhibidors de l’aromatase: letrozole, anastrozole, o exemestane.
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Böttiger, Ylva. "Metabolic drug interactions in man : methodological aspects on in vivo studies /." Stockholm, 2000. http://diss.kib.ki.se/2000/91-628-4207-2/.
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Xu, Cong. "Mechanisms and quantitative prediction of efavirenz metabolism, pharmacogenetics and drug interactions." Thesis, Indiana University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3666233.
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The antiretroviral drug efavirenz remains a cornerstone for treatment-naïve HIV patients. Subsequent to the demonstration that efavirenz is a substrate of cytochrome P450 (CYP) 2B6, a number of clinical studies found that the CYP2B6*6 allele is significantly associated with higher efavirenz exposure and/or adverse reactions. However, the mechanism of reduced efavirenz metabolism by this genetic variant is not fully understood and whether this variant exhibits differential susceptibility to metabolic inhibition is also unknown. Ths use of efavirenz is further complicated by the drug interactions associated with it. Therefore, I hypothezised that 1) the CYP2B6*6 allele reduces efavirenz metabolism by altering catalytic properties of CYP2B6; 2) efavirenz alters the pharmacokinetics of co-administered drugs by inhibiting drug metabolizing enzymes. A series of studies was carried out in hepatic microsomal preparations to determine the functional consequences of the CYP2B6*6 allele and to assess inhibition potency of efavirenz on 8 CYPs. The major findings for these studies include: 1) the CYP2B6*6 allele reduces efavirenz metabolism by decreasing substrate binding and catalytic efficiency; 2) functional consequences of the CYP2B6*6 allele appear to be substrate- and cytochrome b5-dependent; 3) the CYP2B6*6 allele confers increased susceptibility to metabolic inhibition; and 4) efavirenz inhibits the activities of CYP2B6, 2C8, 2C9 and 2C19 at therapeutically relevant concentrations. In addition, I explored the hypothesis that the incorporation of in vitro mechanism by which the CYP2B6*6 allele reduced efavirenz metabolism predicts the genetic effect of this allele on efavirenz clearance after a single oral dose by modeling approach. A pharmacogenetics-based in vitro-in vivo extrapolation (IVIVE) model was developed to predict human efavirenz clearance. Taken together, results from this dissertation provide new mechanistic information on how the CYP2B6*6 allale alters substrate metabolism and drug interactions; demonstrate new mechanisms of efavirenz-mediated inhibition interactions; and demonstrate the utility of a pharmacogenetics-based predictive model that can serve as a basis for future studies with efavirenz and other CYP2B6 substrates. Overall these data provide improved understanding of genetic and non-genetic determinant of efavirenz disposition and drug interactions associated with it.
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Nishihara, Mitsuhiro. "Investigation of Drug Metabolism by Non-Cytochrome P450 Enzymes and Its Clinical Relevance." Kyoto University, 2014. http://hdl.handle.net/2433/189328.
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Saadatmand, Ali Reza [Verfasser], Jürgen [Akademischer Betreuer] Brockmöller, Gerhard [Akademischer Betreuer] Burckhardt, and Nicolas von [Akademischer Betreuer] Ahsen. "OCT1-mediated cellular drug uptake and interactions between drug transport and drug metabolism / Ali Reza Saadatmand. Gutachter: Jürgen Brockmöller ; Gerhard Burckhardt ; Nicolas von Ahsen. Betreuer: Jürgen Brockmöller." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://d-nb.info/1042846219/34.
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Meldrum, J. A. "Kinetic and metabolic studies on some substituted-imidazoles using hepatic microsomal monooxygenases." Thesis, University of Strathclyde, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382416.
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Damanhouri, Z. A. "Drug interactions with the anticancer drug aminoglutethimide and related compounds : A study of aminoglutethimide and pyridoglutethimide as inducers and inhibitors of hepatic metabolism." Thesis, Cardiff University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379192.
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Liu, Rui. "Effects of Selected Natural Health Products on Drug Metabolism: Implications for Pharmacovigilance." Thesis, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/19818.
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Seventeen Cree anti-diabetic herbal medicines and eight Traditional Chinese Medicines have been examined for their potential to cause interactions with drugs, which is considered as a major reason for adverse drug effects. Specifically, the effect of these natural health products was examined on major Phase I drug metabolism enzymes including cytochrome P450, human carboxylesterase-1 and flavin-containing monooxygenases. Several of these natural health products have the potential to cause adverse drug effect through the inhibition of major drug metabolism enzymes. The results indicated that 7 Cree medicines plant extracts inhibited CYP3A4 activity, and 3 of them have been proven to cause potent mechanism-based inactivation of CYP3A4. Seven of eight Traditional Chinese Medicines have been identified as strong CYP3A4 inhibitors; the ethanol extract of Goji has identified as a potent inhibitor for CYP2C9 and 2C19. Goji juice showed universal inhibitory effects on most of the tested enzymes except flavin-containing monooxygenases 3.
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Geitmann, Matthis. "Biosensor Studies of Ligand Interactions with Structurally Flexible Enzymes : Applications for Antiviral Drug Development." Doctoral thesis, Uppsala universitet, Institutionen för naturvetenskaplig biokemi, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5797.
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The use of a surface plasmon biosensor fills a missing link in kinetic studies of enzymes, since it measures directly the interaction between biomolecules and allows determination of parameters that are determined only indirectly in activity assays. The present thesis deals with kinetic and dynamic aspects of ligand binding to two viral enzymes: the human cytomegalovirus (HCMV) protease and the human immunodeficiency virus type 1 reverse transcriptase (HIV-1 RT). The improved description of interactions presented herein will contribute to the discovery and development of antiviral drugs. The biosensor method provided new insights into the interaction between serine proteases and a peptide substrate, as well as substrate-induced conformational changes of the enzymes. The direct binding assay served as a tool for characterising the binding mechanism of HCMV protease inhibitors. Kinetic details of the interaction between HIV-1 RT and non-nucleoside reverse transcriptase inhibitors (NNRTIs) were unravelled. The recorded sensorgrams revealed several forms of complexity. A general binding model for the analysis was derived from the data, describing a two-state mechanism for the enzyme and a high- and a low-affinity interaction with the inhibitor. Interaction kinetic constants were determined for the clinically used NNRTIs and several investigational inhibitors. The established method was applied to investigate the mechanism of resistance against NNRTIs. Amino acid substitutions in the NNRTI-binding site resulted in both decreased association rates and increased dissociation rates for the inhibitors. The K103N and the L100I substitution also interfered with the formation of the binding site, thereby facilitating inhibitor binding and unbinding. Finally, thermodynamic analysis revealed that, despite the hydrophobic character of the interaction, NNRTI binding was mainly enthalpy-driven at equilibrium. Large entropy contributions in the association and dissociation indicated that binding is associated with a dynamic effect in the enzyme.
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Chan, Lauretta Man Sum. "Interactions between intestinal metabolic and secretory efflux systems." Thesis, University of Newcastle Upon Tyne, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366781.
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Abu-Omar, Ghada M. "Drug interactions and metabolism of cyclosporin A and steroids by human liver microsomes in vitro." Thesis, University of Aberdeen, 1992. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU545502.
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1) The purpose of this work is to study the enzymology of cyclosporin A (CsA) metabolism by human liver in vitro , in particular investigating the basis for interindividual variations and drug interactions involving CsA metabolism, and to apply this knowledge to the development of a non-invasive test for predicting an individual's ability to metabolise CsA in vivo . The ultimate aim is to help to improve CsA therapy by understanding the factors which determine its metabolism in patients. 2) Human liver microsomes metabolised cyclosporin A (Km 25M) to eight identifiable metabolites, which were detected following incubation with [3H]-CsA in the presence of NADPH and aerobic O2. An interindividual variation in the generation of CsA metabolites was also observed. In addition, the formation rates of primary and secondary CsA metabolites were induced to different extents by 2 and 4 fold respectively, in liver microsomes prepared from patients treated with anticonvulsant treatment. Metabolite M1 formation was also induced by anticonvulsant treatment. 3) A significant correlation was observed between the total rate of CsA metabolism and cytochrome P-450IIIA concentration as measured by Western blot analysis, in 9 human liver microsomal preparations; 6 were obtained from untreated individuals and 3 from anticonvulsant-treated patients. This correlation was also present when the primary and the secondary metabolite profiles were considered separately. The kinetics of CsA metabolism by human liver microsomes demonstrated different Km and Vmax values for the formation rates of primary and secondary CsA metabolites. This suggests the possible involvement of two enzymes within the P-450IIIA family, responsible for the formation of primary and secondary metabolites, respectively. 4) Anti P-450IIIA antibodies inhibited the total rate of CsA metabolism in microsomal preparations from anticonvulsant-treated patients but to a lesser extent than those from untreated individuals. This suggests an involvement of other form(s) of P-450in CsA metabolism, responsible for between 20-30&'37 of CsA metabolic activity in human liver microsomes. However, these are unlikely to be P-450IIB1, P-450IA1 or P-450IIC, as none of the antibodies raised against these P450s significantly inhibited the metabolism of CsA. 5) From induction, inhibition and correlation studies, cytochrome P-450IIIA has been confirmed as being responsible for the major part of CsA metabolism in human and rat liver microsomes.
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Taavitsainen, P. (Päivi). "Cytochrome P450 isoform-specific in vitro methods to predict drug metabolism and interactions." Doctoral thesis, University of Oulu, 2001. http://urn.fi/urn:isbn:9514259009.
Full textAbstract:
Abstract
Cytochromes P450 (P450, CYP) are a superfamily of enzymes that participate
especially in the oxidative metabolism of various xenobiotics and endogenous
compounds.
The major goal of this study was to characterise suitable methods for routine
preclinical in vitro testing of new chemical entities (NCE)
and to test the methods for the affinity screening of selected drugs.
In vitro methods used involve the utilisation of human
liver microsomes for studies with P450-selective reference inhibitors,
inhibitory antibodies and cDNA-expressed enzymes in cytochrome P450-catalysed
activities and for studying the reactions of selegiline and entacapone.
In this project, the CYP-catalysed oxidative in vitro
biotransformation of selegiline into its primary metabolites desmethylselegiline
and l-methamphetamine and the transformation of entacapone
into its in vitro metabolite
N-desethylentacapone were studied. The affinities of
selegiline, desmethylselegiline, l-methamphetamine,
entacapone, candesartan, eprosartan, irbesartan, losartan and valsartan to P450
enzymes were also elucidated, and the selectivity of tranylcypromine as a
CYP2A6-selective reference inhibitor was characterised.
The most important findings were that the methodology developed during this work
is suitable for preclinical in vitro testing of NCEs and
that the results obtained for the studied compounds are in line with the
available in vivo data.
By the in vitro testing methodology, it is possible to
target the in vivo interaction studies to the relevant
groups of compounds. The in vitro methods presented in this
thesis could also make the early phases of drug development more cost-effective.
Further, the number of animals used for in vivo testing in
preclinical metabolism and interaction studies can be markedly reduced by
effectively using this methodology.
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Morrison, Roxanne. "The development of an in vitro system for the production of drug metabolites using microsomal enzymes from bovine liver." Thesis, Rhodes University, 2011. http://hdl.handle.net/10962/d1007698.
Full textAbstract:
Drug metabolism is a specialised subset of xenobiotic metabolism, pertaining to the breakdown and elimination of pharmaceutical drugs. The enzymes involved in these pathways are the cytochrome P450 family of isozymes. Metabolism is an important factor in determining the pharmacological effects of drugs. The main aim of this study was to develop a system whereby the major metabolites of drugs can be produced in vitro. An in vitro system was developed and optimised using commercially prepared microsomes from rat liver and coumarin (by monitoring its conversion to 7-hydroxycoumarin) as a model. The optimum running conditions for the incubations were 50 μM coumarin, 50 μg protein/ml microsomes, 1 mM NADP⁺, 5 mM G6P and 1U/ml G6PDH incubated for 30 minutes at 38℃. The HPLC method for the detection of coumarin and 7-hydroxycoumarin was also validated with respect to linearity, reproducibility, precision, accuracy and lower limits of detection and quantification. The system developed was then tested using microsomes prepared from fresh bovine liver on these ten drugs of interest in doping control in horse racing: diazepam, nordiazepam, oxazepam, promazine, acepromazine, chlorpromazine, morphine, codeine, etoricoxib and lumiracoxib. The bovine liver microsomes were prepared using differential centrifugation and had activity on a par with the commercial preparations. This in vitro system metabolised the drugs and produced both phase I and II metabolites, similar to those observed in humans and horses in vivo. For example, the major metabolites of the benzodiazepine drug, diazepam, nordiazepam, temazepam and oxazepam as well as the glucuronidated phase II products were all found after incubations with the bovine liver microsomes. The metabolism of the drugs was also investigated in silico using the computational procedure, MetaSite. MetaSite was able to successfully predict known metabolites for most of the drugs studied. Differences were observed from the in vitro incubations and this is most likely due to MetaSite using only human cytochrome P450s for analysis.
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Wagmann, Lea [Verfasser], and Hans Hilarius [Akademischer Betreuer] Maurer. "Psychoactive substances as substrates or inhibitors of enzymes in drug metabolism and transport / Lea Wagmann ; Betreuer: Hans Hilarius Maurer." Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2018. http://d-nb.info/119993285X/34.
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Tantipolphan, Ruedeeporn, and n/a. "Characterisation of protein-phospholipid interactions in implantable delivery systems." University of Otago. School of Pharmacy, 2007. http://adt.otago.ac.nz./public/adt-NZDU20071218.162425.
Full textAbstract:
Purpose: This thesis aimed to gain a better understanding of the effects of salts in modifying in vitro phase behaviour of lecithin and cholesterol solid implants and to obtain further information on in vitro protein release and stability.
Methods: Raman spectroscopy and partial least squares regression (PLSR) were used to investigate lecithin-cholesterol molecular interactions as a function of method of preparation. Lipid-salt interactions were studied by attenuated total reflectance Fourier transform infrared (ATR-FTIR) and Raman spectroscopy using principal component analysis (PCA). In vitro release of bovine serum albumin (BSA), a model protein, from lecithin and lecithin:cholesterol implants comprising 10 and 30% NaCl and CaCl₂ were performed. Size exclusion (SE) HPLC was used for quantitative and qualitative analysis of the released BSA. On hydration, changes in phase behaviour and implant morphology were studied by ATR spectroscopy and light microscopy. SE-HPLC, ATR and fluorescence spectroscopy were used to evaluate the structure of unreleased BSA. Protein adsorption on lipid films was studied by flow through ATR spectroscopy. Increased amide II peak area upon recirculation of BSA in salt solutions over hydrated lecithin and lecithin:cholesterol films cast on ZnSe prisms was used to quantify the deposition of BSA onto the lipid surfaces.
Results: Shifts in the Raman spectra suggested the lecithin headgroup may be involved in lecithin-cholesterol interactions. Greater R� and root mean square error of cross validation in the calibration curves of physical mixing and heating (120�C) methods reflected poor mixing in these preparations. The mean absolute residue and mean Mahalanobis distance values from the physical mixing and granulation methods indicated their spectral similarity and comparable level of lecithin-cholesterol interactions. Calcium exhibited stronger affinity for phospholipids than sodium and it induced headgroup hydration and reorganisation upon binding. PCA of ATR spectra was sensitive to cholesterol addition, calcium binding and method of preparation whilst PCA of Raman spectra only differentiated the presence of cholesterol. In vitro release of BSA from implants produced from wet granulation mixtures of lecithin and lecithin:cholesterol in the absence of salt showed retention of a high monomer content and the release profiles were similar to the literature. Cholesterol increased the swelling, induced phase transformation of lecithin and, subsequently, reduced the BSA release. Salts only slightly modified the BSA release from the lecithin implants. In contrast, for lecithin:cholesterol matrices salts greatly enhanced implant swelling, induced the formation of hydrated lecithin of heterogeneous size and inhibited the in vitro BSA release. Analyses of the protein showed increased aggregation of BSA with a high retention of native structure while retained within the swollen matrices. ATR spectra suggested that salts promoted protein adsorption onto hydrated lecithin surfaces and the effects depend on salt types (NaCl > CaCl₂) and concentration (0.1 M > 1.0 M) but not on lecithin:cholesterol surfaces.
Conclusion: PLSR and PCA can be used to investigate molecular interactions in the solid lipid matrices. In lecithin:cholesterol implants, salts modified the phase behaviour of lecithin which resulted in enhanced swelling, formation of hydrated lecithin of altered morphology and inhibition of in vitro BSA release.
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Lam, Maria Shuk Mun. "Genetic polymorphisms in AH receptor and cytochrome P450 drug-metabolizing enzymes in relation to estradiol metabolism and breast cancer susceptibility." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0021/MQ54164.pdf.
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Wang, Jun-Sheng. "In vivo and in vitro studies on drug metabolism and interactions involving mibefradil, isradipine, lidocaine, selegiline and metronidazole." Helsinki : University of Helsinki, 2001. http://ethesis.helsinki.fi/julkaisut/laa/kliin/vk/wang/.
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Darwich, Adam Saed. "Physiologically-based pharmacokinetic modelling and simulation of oral drug bioavailability : focus on bariatric surgery patients and mechanism-based inhibition of gut wall metabolism." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/physiologicallybased-pharmacokinetic-modelling-and-simulation-of-oral-drug-bioavailability-focus-on-bariatric-surgery-patients-and-mechanismbased-inhibition-of-gut-wall-metabolism(182c1e87-670c-4430-82ba-b335f6c13887).html.
Full textAbstract:
Understanding the processes that govern pre-systemic drug absorption and elimination is of high importance in pharmaceutical research and development, and clinical pharmacotherapy, as the oral route remains the most frequently used route of drug administration. The emergence of systems pharmacology has enabled the utilisation of in silico physiologically-based pharmacokinetic (PBPK) modelling and simulation (M&S) coupled to in vitro-in vivo extrapolation in order to perform extrapolation and exploratory M&S in special populations and scenarios were concerns regarding alterations in oral drug exposure may arise, such as following gastrointestinal (GI) surgery or metabolic drug-drug interactions (DDIs).Due to the multi-factorial physiological implications of bariatric surgery, resulting in the partial resection of the GI tract, the inability to rationalise and predict trends in oral drug bioavailability (Foral) following surgery present considerable pharmacotherapeutical challenges. PBPK M&S is a highly implemented approach for the prediction of DDIs. Reoccurring issues have emerged with regards to predictions of the magnitude of mechanism-based inhibition (MBI) where overestimations of DDIs have repeatedly been reported for drugs exhibiting high intestinal extraction. The aim of this thesis was to explore the interplay between oral drug absorption and metabolism occurring in the GI tract through the exploration of the impact of bariatric surgery on oral drug exposure and by theoretically examining the nesting and hierarchy of enterocyte and enzyme turnover and its impact on MBIs in the small intestine. This would be carried out by utilising a systems pharmacology PBPK M&S approach under a general model development framework of identification and characterisation of critical intrinsic factors and parameters, model implementation and validation. Developed post bariatric surgery PBPK models allow a framework to theoretically explore physiological mechanisms associated with altered oral drug exposure pre to post surgery, which could be assigned to the interplay between dissolution, absorption and gut-wall metabolism, where dissolution and formulation properties emerged as the perhaps most important parameters in predicting the drug disposition following surgery. Model validation identified missing critical factors that are essential for additional model refinement. Developed post bariatric surgery PBPK models have the potential of aiding clinical pharmacotherapy and decision-making following surgery. A mechanistic PBPK model was developed to describe the hierarchical dependency of enzyme and enterocyte turnover in the small intestine. Predicted enzyme recovery using the nested enzyme-within-enterocyte turnover model may potentially account for reported overpredictions of mechanism-based inhibition. Developed models in this thesis showcase the advantage of PBPK M&S in the extrapolation of oral drug exposure to special population and the potential of a PBPK approach in understanding underlying the underlying mechanism governing Foral and additionally highlight the need for generation of interdisciplinary data to support model development.
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Cece, Esra Nurten 1984. "Metabolite identification in drug discovery : from data to information and from information to knowledge." Doctoral thesis, Universitat Pompeu Fabra, 2017. http://hdl.handle.net/10803/403648.
Full textAbstract:
Drug metabolism studies provide the opportunity to enhance metabolic properties of new drugs. The overall aims of the drug metabolism studies are to (1.) optimize pharmacokinetic properties of the drug candidates, (2.) characterize the polymorphic enzyme contribution to clearance, and (3.) support the selection of safe drugs with respect to bioactivation potentials.
The ultimate goal in drug metabolism assays in early drug discovery is to translate analytical data to build final knowledge. By contribution of this translation, metabolism scientists can rationalize how structures of new drug compounds could be changed and how metabolic pathways could be better understood. Analytical techniques, such as High Resolution Mass Spectrometry (HRMS), have progressed and now it is possible to generate large datasets through High Throughput Screening (HTS) assays in drug metabolism laboratories. However, the transformation of these data into information and information into knowledge is insufficient. In-depth data inspection is necessary to support the generation of high quality results which are consistent across experiments. For this purpose, innovative software solutions can be utilized to process analytical data. In this respect, by applying standardized and fully automated data evaluation tools, it is possible to (1.) enable comprehensive data analysis, (2.) accelerate structure-based information handling, (3.) eliminate human error and finally (4.) improve chemical features of lead molecules in terms of biotransformation properties.
This thesis research aimed to use a novel automated workflow within HRMS to identify the drug metabolites and their structures. Final results confirmed that this new workflow can be used to translate HRMS data into information, which is required for building useful and ultimate knowledge in drug metabolism.Los estudios de metabolismo de fármacos ofrecen la oportunidad de mejorar las propiedades metabólicas de nuevos fármacos. Los objetivos generales de los estudios de metabolismo de fármacos son: (1.) optimizar las propiedades farmacocinéticas de los fármacos candidatos, (2.) caracterizar la contribución de las enzimas polimórficas a la elimicación y (3.) apoyar la selección de fármacos seguros con respecto a los potenciales bioactivación. El objetivo final en los ensayos de metabolismo de fármacos es traducir los datos analíticos para construir conocimiento final. Mediante la aportación de esta traducción, los científicos que trabajan en metabolismo pueden racionalizar cómo las estructuras de los nuevos compuestos de fármacos podrían ser cambiadas y cómo las vías metabólicas podrían ser mejor entendidaa. Las técnicas analíticas, como la espectrometría de masas de alta resolución (HRMS), han progresado y ahora es posible generar grandes volúmenes de datos a través de ensayos masivos (HTS) en laboratorios de metabolismo de fármacos. Sin embargo, la transformación de estos datos a información y la información a conocimiento es insuficiente. Es necesario un estudio en profundidad de los datos para ayudar a la generación de resultados de alta calidad que sean consistentes con los experimentos. Para este propósito, las soluciones innovadoras de software pueden ser utilizados con el objetivo de procesar los datos analíticos. A este respecto, mediante la aplicación de datos estandarizados y totalmente automatizados herramientas de evaluación, es posible (1.) permitir el análisis de datos completos, (2.) acelerar el manejo de información basada en la estructura, (3.) eliminar el error humano y finalmente (4.) mejorar las características químicas de las moléculas en términos de sus propiedades metabólicas. La investigación de esta tesis tuvo el objetivo que utilizar una novedoso y automatizado “sistema de trabajo” dentro HRMS para identificar los metabolitos de compuestos así como sus estructuras. Los resultados finales se confirmaron que se pueden utilizar herramientas de software para convertir los datos en información de HRMS, necesario para la construcción del conocimiento útil en el metabolismo de fármacos
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Hikuam, Willem Christoph. "Modulation of the redox status, phase 2 drug metabolizing enzymes and fumonisin-induced cancer promotion in rat liver by selected Southern African medicinal plants." Thesis, Cape Peninsula University of Technology, 2014. http://hdl.handle.net/20.500.11838/1524.
Full textAbstract:
Thesis submitted in fulfilment of the requirements for the degree
Doctor of Technology: Biomedical Technology
in the
Faculty of Health and Wellness Sciences
at the
Cape Peninsula University of Technology
2014According to the World Health Organization, cancer is the leading cause of death in the developed world, while it is the second leading cause of death in the developing world. In particular, liver cancer is the fifth most commonly diagnosed cancer in men, however, it is the second most frequent cause of death, responsible for an estimated 700,000 deaths annually. General limited access to health services, including treatment and the overall management of cancer in developing countries often contribute to the increased mortality rates when compared to developed countries. For centuries, medicinal plants have been used to prevent, and to a certain extent, treat cancer as a readily available and affordable alternative. In many instances, the curative or preventative claims still remain anecdotal. However, increasing evidence suggest that polyphenolic components of plants possess antioxidant activities, which are credited with curative/beneficial properties of medicinal plants. The curative properties could either be related to the primary compounds present in the plant itself, or the bio-activation products of plant components affecting hepatic drug metabolising and antioxidant enzymes systems related to carcinogen metabolism and maintaining oxidative homeostasis, respectively. Similarly, chronic consumption of medicinal plants could also result in hepatotoxicity, either caused by the primary plant components or bio-activation products. Due to these observations it is paramount to understand the mechanisms involved in the metabolism of plant components to critically assess beneficial versus potential harmful properties associated with chronic consumption. The focus of the current study was aimed at elucidating the bio-activity of four multipurpose indigenous plants to Southern Africa, i.e. Adansonia digitata, Agathosma betulina, Siphonochilus aethiopicus and Myrothamnus flabellifolius. Traditionally, A. digitata has been used as an immunostimulant, anti-inflammatory and analgesic agent, while also as an antipyretic agent in the treatment of diarrhoea and dysentery. Similarly, traditional medicinal uses of A. betulina include treatment cholera, haematuria, calculus, kidney diseases, as well as infections of the bladder, urethra, and prostate among others. S. aethiopicus was traditionally employed to treat infections associated with pains and fevers, whereas M. flabellifolius served as treatment of conditions ranging from respiratory ailments, backache, kidney problems, haemorrhoids, chest pain, and asthma. In the first part of this study, the polyphenolic contents and antioxidant capacities of the four plants were characterised. The emphasis was placed on using different solvents, namely water, ethanol and acetone for the extraction of the plant material and different methodologies to assess the antioxidant contents and -capacities of the various extracts as both these factors can influence the outcome. When considering the antioxidant contents, total polyphenols, flavanols, and flavonols of the different solvent extracts prepared from the four plants were determined, whereas three different assays were used for the antioxidant capacities, i.e. oxygen radical absorbance capacity (ORAC), trolox equivalent antioxidant capacity (TEAC) and ferric-reducing antioxidant power (FRAP) assays. The A. digitata acetone extract had the highest (7.121 mg gallic acid equivalent (GAE)/milligram (mg) soluble solids), whereas the water extract of the same plant had the lowest total phenolic content (0.008 mg GAE/mg soluble solids). In general, the acetone extracts demonstrated the highest total polyphenol, flavanol, and flavonol contents, followed by the ethanol extracts, with the water extracts having the lowest contents. M. flabellifolius was the only distinct deviation from this rule, where the water extract demonstrated the highest total polyphenol content. Considering antioxidant capacities, the acetone extracts provided the highest antioxidant capacities for all plants when assessed using the TEAC (8.56-32.68 milimole (mmole) trolox equivalent (TE)/mg soluble solids) and FRAP (5.69-37.39 mmole ascorbic acid equivalent/mg soluble solids) antioxidant assays, with the exception of M. flabellifolius where the water extract demonstrated the highest activity (22.73 mmole ascorbic acid equivalent/mg soluble solids). Antioxidant capacity determinations with TEAC and FRAP assays followed similar patterns, which were different from capacities determined by the ORAC (0.46-533.54 mmoleTE/mg of soluble solids) assay. Corroborating the antioxidant content findings, the acetone extracts also demonstrated the highest antioxidant capacities (140.41-533.54 mmoleTE/mg of soluble solids), followed by ethanol (94.62-151.29 mmoleTE/mg of soluble solids) and water (0.46-134.02 mmoleTE/mg of soluble solids). Only M. flabellifolius (TEAC and FRAP) and S. aethiopicus (FRAP) deviated from this trend. Correlations between the polyphenolic contents and antioxidant capacities indicated that acetone and ethanol were more effective in extracting polyphenolic compounds than water, while also providing extracts with superior antioxidant activities. Furthermore, ORAC assay was the antioxidant capacity determining assay of choice for the aqueous plant extracts, whereas the TEAC and FRAP assays were more suitable when determining the antioxidant capacities of the acetone and ethanol plant extracts. These results confirm the notion that no single assay can comprehensively determine the antioxidant activities of plant extracts and that a battery of assays should be used, as the various antioxidant capacity determination techniques use different substrates with different targets for measurement. The second part of this study comprised an in vivo experimental animal model to assess the potential toxicity, antioxidant status and modulation of the hepatic phase 2 drug metabolising enzymes following chronic consumption of the various plant extracts in male Fisher rats. Rats consumed aqueous extracts of the various plants (2% and 5% (w/v)) as the sole source of drinking fluid for 90 days, and the serum chemical pathology parameters for monitoring liver and kidney function conducted. These included alkaline phosphatase (ALP), aspartate transaminase (AST), alanine transaminase (ALT), total iron (Fe), and creatinine (CREA). Parameters for blood and hepatic redox status included total polyphenols, ORAC, reduced glutathione (GSH), oxidised glutathione (GSSG), their ratio (GSH:GSSG), conjugated dienes (CD) and thiobarbituric acid reactive substances (TBARS). Assessment of the phase 2 hepatic xenobiotic metabolising enzymes included glutathione S-transferase (GST) and activity in the cytosolic fraction and, UDP-glucuronosyltransferase (UDP-GT) activity in liver microsomes. When considering the liver and kidney function none of the plant extracts induced any significant toxicity, while 2% A. digitata significantly increased serum Fe. When considering the redox status, the whole blood and liver samples yielded similar results, with significant decreases in oxidised glutathione (GSSG) in rats consuming the 2% M. flabellifolius (82.76 mole/L) and 5% A. digitata (90.42 mole/L) with a resultant significant increase in the glutathione redox status (GSH:GSSG ratio of 5.69 and 5.64, respectively) when compared to rats consuming water (4.77). The GSH:GSSG ratio was also significantly increased by consumption of 2% A. betulina (8.45) and 5% S. aethiopicus (5.99). The consumption of all plant extracts, except 5% A. betulina and M. flabellifolius, significantly increased lipid peroxidation in the plasma CDs assay. These results indicated an increased antioxidant capacity in the liver with/without an associated reduced cellular oxidative stress status, which could be interpreted as a reduced susceptibility to oxidative damage. When considering the phase 2 hepatic enzymes, none of the plant extracts caused any significant changes in GST, GST or UDP-GT activities. The third part investigated the chemoprotective properties against cancer promotion in the liver utilising diethylnitrosamine (DEN) as cancer initiator and maize culture material of Fusarium verticillioides, containing the fumonisin B mycotoxins, as promoters in male Fischer rats. The rats consumed 2% (w/v) aqueous extracts of A. digitata, A. betulina, and S. aethiopicus over 28 days after cancer initiation and liver sections subjected to glutathione-S-transferase placental form positive GSTP+ staining and pre-cancerous liver foci categorised according to size. In addition, blood and liver analyses were done as described in the chronic feeding study above. Consumption of the A. digitata and, to a certain extent, S. aethiopicus extracts, altered the oxidative stress status in the liver as indicated by the increased lipid peroxidation, as determined by significantly increased liver CDs and the decreased GSH:GSSG ratio in the blood. This can be related to a subchronic toxicity due to the high total polyphenol intake as mentioned above. These underlying sub chronic toxic effects of A. digitata and S. aethiopicus are likely to be responsible for the observed inhibitory effect on the proliferation of GSTP+ minifoci in the liver. Hepatic phase 2 metabolising enzyme activities were not significantly altered by A. digitata and S. aethiopicus consumption, while GST activity was significantly increased by A. betulina treatment. Based on the findings of the current study, aqueous extracts of A. digitata, A. betulina, and S. aethiopicus may serve as hepatoprotectors with a potential to modulate liver carcinogenesis, specifically cancer promotion. To our knowledge, no other studies have attempted to describe the possible chemoprevention mechanisms of these indigenous medicinal plants. Assessments of phase 1 hepatic enzymes and other antioxidant enzymes are suggested for future studies to further describe biochemical and molecular mechanisms associated with consumption of these extracts. Additionally, identifying main compounds present in the plant extracts could culminate in development of drugs and novel nutraceuticals. It is also recommended that increasing concentrations of the plant extracts and/or the ethanol extracts to be used in future studies to better describe dose-responses of the different plants in liver carcinogenesis.
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Rosmarin, Daniel Norris. "Germline determinants of 5-fluorouracil drug toxicity and patient survival in colorectal cancer." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:d5e2c306-689c-4c53-b4c3-2c1001b04ec6.
Full textAbstract:
Despite a decade of publications investigating the effect of germline polymorphisms on both toxicity related to treatment with 5-fluorouracil-based (5-FU) chemotherapy and prognosis following diagnosis with colorectal cancer (CRC), few genetic biomarkers have been identified convincingly. For 5-FU toxicity and CRC prognosis, in four results chapters, this thesis aims to validate previously-reported genetic biomarkers, identify new markers, determine the mechanistic basis of associated polymorphisms, and expand upon methods in the field. The first three results chapters investigate genetic biomarkers for the prediction of toxicity caused by 5-FU-based treatment, particularly for the 5-FU prodrug capecitabine (Xeloda®, Roche). In the first, a systematic review and meta-analysis is performed for all variants that have been previously studied for an association with toxicity caused by any 5-FU-based drug regimen. 16 studies are analysed, including 36 previously-studied variants. Four variants show strong evidence of affecting a patient’s risk of global (any) 5-FU-related toxicity upon analysis of both the existing data and over 900 patients from the QUASAR2 trial of capecitabine +/- bevacizumab (Avastin®, Roche/Genentech): DPYD 2846, DPYD *2A, TYMS 5’VNTR and TYMS 3’UTR. Next, 1,456 polymorphisms in 25 genes involved in the activation, action or degradation of 5-FU are investigated in 1,046 patients from QUASAR2. At a Bonferroni-corrected p-value threshold of 3.43e-05, three novel associations with capecitabine-related toxicity are identified in DPYD (rs12132152, rs7548189, A551T) and the previously-identified TYMS 5’VNTR and 3’UTR toxicity polymorphisms are refined to a tagging SNP (rs2612091) downstream of TYMS and intronic to the adjacent ENOSF1, the latter of which appears to be functional. Finally, a genome-wide investigation of 4.77 million directly genotyped or imputed SNPs identifies one variant (rs2093152 on chr20) as significantly associated with capecitabine-related diarrhoea (p<5e-08), though no associations meet this threshold for global toxicity. In the study of CRC prognosis, a severe left truncation to the VICTOR trial is defined and shown to probably reduce statistical power but not bias effect estimates. Applying standard and novel genome-wide analysis approaches, a set of 43 SNPs are prioritised for future work. With over one million new CRC cases annually, this work helps define biomarkers that could become broadly applicable in the clinical setting.
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Patel, Jignesh Mitra Ashim K. "P-glycoprotein mediated efflux and CYP3A4 mediated metabolism of HIV-protease inhibitor, ritonavir, and its interaction with pure herbal constituents." Diss., UMK access, 2004.
Find full textAbstract:
Thesis (Ph. D.)--School of Pharmacy and Dept. of Chemistry. University of Missouri--Kansas City, 2004."A dissertation in pharmaceutical science and chemistry." Advisor: Ashim K. Mitra. Typescript. Vita. Description based on contents viewed Feb. 27, 2006; title from "catalog record" of the print edition. Includes bibliographical references (leaves 175-199). Online version of the print edition.
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Alandas, Mohammed N. "An investigation into the metabolic activation of novel chloromethylindolines by isoforms of cytochrome P450. Targeting drug metabolising enzymes in cancer: analysis of the role and function of selected cytochrome P450 oxidising novel cancer prodrugs." Thesis, University of Bradford, 2012. http://hdl.handle.net/10454/6289.
Full textAbstract:
Introduction Cytochromes P450 (CYPs) are the major family of enzymes responsible for detoxification and metabolism of a wide range of both endogenous and xenobiotics chemicals in living organisms. The use of CYPs to activate prodrugs to cytotoxins selectively in tumours has been explored including AQ4N, Phortress and Aminoflavone. CYP1A1, CYP1B1, CYP2W1, and CYP4F11 have been identified as expressed in tumour tissue and surrounding stroma at high frequency compared to most normal tissues.
Aim is to investigate the differential metabolism of novel chloromethylindoline by high frequency expressed CYPs in tumours. This differential may be exploited to elicit a selective chemotherapeutic effect by metabolising inert small molecules to potent cytotoxins within the tumour environment.
Materials and Methods Sensitive and specific LC/MS/MS techniques have been developed to investigate the metabolism of chloromethylindolines. Recombinant enzymes and transfected cell lines were used to investigate the metabolic profiles with a focus on production of the cytotoxic derivatives of chloromethylindolines. Results Detailed metabolic studies show that (1-(Chloromethyl)-1,2-dihydropyrrolo
[3,2-e]indol-3(6H)-yl)(5-methoxy-1H-indol-2-yl) methanone (ICT2700) and other chloromethylindolines are converted by CYP1A1 mediated hydroxylation at the C-5 position leading to highly potent metabolites. In vitro cytotoxicity studies showed differentials of up to 1000-fold was achieved between CYP1A1 activated compared to the non-metabolised parent molecules. The reactivity of metabolites of ICT2700 was also explored using glutathione as a nucleophile. The metabolites were identified by a combination of LC/MS and LC MS/MS techniques. Investigations using mouse and human liver microsomes show that a large number of metabolites are created though none were shown to be associated with a potential anticancer effect. Studies focused on CYP2W1 show that this isoform metabolised ICT2706 to a cytotoxic species and a pharmacokinetic study showed a good distribution of ICT2706 into mouse tissues including tumour. However metabolism of ICT2726 by CYP2W1 resulted only in a non-toxic metabolite profile and may have potential as a biomarker for functional CYP2W1 in tissues. Preliminary studies show that palmitic acid hydroxylation is a useful marker of functional CYP4F11. Summary and conclusion The in vitro results show that the chloromethylindolines are a novel class of agent with potential as prodrugs that following specific hydroxylation by CYP1A1 and CYP2W1 are converted to ultra-potent cytotoxins. Other metabolites are also evident which are not cytotoxic. Studies in vivo show that selected chloromethylindolines possess a good pharmacokinetic profile and show potential as prodrug anticancer agents that require activation by CYP1A1 or CYP2W1. The methods, results, progress and suggestions for future work are presented in this thesis.
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Alandas, Mohammed Nasser. "An investigation into the metabolic activation of novel chloromethylindolines by isoforms of cytochrome P450 : targeting drug metabolising enzymes in cancer : analysis of the role and function of selected cytochrome P450 oxidising novel cancer prodrugs." Thesis, University of Bradford, 2012. http://hdl.handle.net/10454/6289.
Full textAbstract:
Introduction: Cytochromes P450 (CYPs) are the major family of enzymes responsible for detoxification and metabolism of a wide range of both endogenous and xenobiotics chemicals in living organisms. The use of CYPs to activate prodrugs to cytotoxins selectively in tumours has been explored including AQ4N, Phortress and Aminoflavone. CYP1A1, CYP1B1, CYP2W1, and CYP4F11 have been identified as expressed in tumour tissue and surrounding stroma at high frequency compared to most normal tissues. Aim is to investigate the differential metabolism of novel chloromethylindoline by high frequency expressed CYPs in tumours. This differential may be exploited to elicit a selective chemotherapeutic effect by metabolising inert small molecules to potent cytotoxins within the tumour environment. Materials and Methods: Sensitive and specific LC/MS/MS techniques have been developed to investigate the metabolism of chloromethylindolines. Recombinant enzymes and transfected cell lines were used to investigate the metabolic profiles with a focus on production of the cytotoxic derivatives of chloromethylindolines. Results: Detailed metabolic studies show that (1-(Chloromethyl)-1,2-dihydropyrrolo [3,2-e]indol-3(6H)-yl)(5-methoxy-1H-indol-2-yl) methanone (ICT2700) and other chloromethylindolines are converted by CYP1A1 mediated hydroxylation at the C-5 position leading to highly potent metabolites. In vitro cytotoxicity studies showed differentials of up to 1000-fold was achieved between CYP1A1 activated compared to the non-metabolised parent molecules. The reactivity of metabolites of ICT2700 was also explored using glutathione as a nucleophile. The metabolites were identified by a combination of LC/MS and LC MS/MS techniques. Investigations using mouse and human liver microsomes show that a large number of metabolites are created though none were shown to be associated with a potential anticancer effect. Studies focused on CYP2W1 show that this isoform metabolised ICT2706 to a cytotoxic species and a pharmacokinetic study showed a good distribution of ICT2706 into mouse tissues including tumour. However metabolism of ICT2726 by CYP2W1 resulted only in a non-toxic metabolite profile and may have potential as a biomarker for functional CYP2W1 in tissues. Preliminary studies show that palmitic acid hydroxylation is a useful marker of functional CYP4F11. Summary and conclusion: The in vitro results show that the chloromethylindolines are a novel class of agent with potential as prodrugs that following specific hydroxylation by CYP1A1 and CYP2W1 are converted to ultra-potent cytotoxins. Other metabolites are also evident which are not cytotoxic. Studies in vivo show that selected chloromethylindolines possess a good pharmacokinetic profile and show potential as prodrug anticancer agents that require activation by CYP1A1 or CYP2W1. The methods, results, progress and suggestions for future work are presented in this thesis.
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Kirchheiner, Julia. "Arzneitherapieempfehlungen auf pharmakogenetischer Basis." Doctoral thesis, [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972661018.
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Saadatmand, Ali Reza. "OCT1-mediated cellular drug uptake and interactions between drug transport and drug metabolism." Doctoral thesis, 2012. http://hdl.handle.net/11858/00-1735-0000-000D-EF89-B.
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Xu, Cong. "Mechanisms and quantitative prediction of Efavirenz metabolism, pharmacogenetics and drug interactions." Thesis, 2013. http://hdl.handle.net/1805/4212.
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Indiana University-Purdue University Indianapolis (IUPUI)The antiretroviral drug efavirenz remains a cornerstone for treatment-naïve HIV patients. Subsequent to the demonstration that efavirenz is a substrate of cytochrome P450 (CYP) 2B6, a number of clinical studies found that the CYP2B6*6 allele is significantly associated with higher efavirenz exposure and/or adverse reactions. However, the mechanism of reduced efavirenz metabolism by this genetic variant is not fully understood and whether this variant exhibits differential susceptibility to metabolic inhibition is also unknown. Ths use of efavirenz is further complicated by the drug interactions associated with it. Therefore, I hypothezised that 1) the CYP2B6*6 allele reduces efavirenz metabolism by altering catalytic properties of CYP2B6; 2) efavirenz alters the pharmacokinetics of co-administered drugs by inhibiting drug metabolizing enzymes. A series of studies was carried out in hepatic microsomal preparations to determine the functional consequences of the CYP2B6*6 allele and to assess inhibition potency of efavirenz on 8 CYPs. The major findings for these studies include: 1) the CYP2B6*6 allele reduces efavirenz metabolism by decreasing substrate binding and catalytic efficiency; 2) functional consequences of the CYP2B6*6 allele appear to be substrate- and cytochrome b5-dependent; 3) the CYP2B6*6 allele confers increased susceptibility to metabolic inhibition; and 4) efavirenz inhibits the activities of CYP2B6, 2C8, 2C9 and 2C19 at therapeutically relevant concentrations. In addition, I explored the hypothesis that the incorporation of in vitro mechanism by which the CYP2B6*6 allele reduced efavirenz metabolism predicts the genetic effect of this allele on efavirenz clearance after a single oral dose by modeling approach. A pharmacogenetics-based in vitro-in vivo extrapolation (IVIVE) model was developed to predict human efavirenz clearance. Taken together, results from this dissertation provide new mechanistic information on how the CYP2B6*6 allale alters substrate metabolism and drug interactions; demonstrate new mechanisms of efavirenz-mediated inhibition interactions; and demonstrate the utility of a pharmacogenetics-based predictive model that can serve as a basis for future studies with efavirenz and other CYP2B6 substrates. Overall these data provide improved understanding of genetic and non-genetic determinant of efavirenz disposition and drug interactions associated with it.
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Makume, Mantha Thandiwe. "Detection of drug metabolizing enzyme gene (DMEs) polymorphisms among the Zulu population of South Africa." Thesis, 2007. http://hdl.handle.net/10413/2524.
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The ability to metabolise drugs and achieve positive therapeutic outcomes is dependent on both genetic and environmental factors. The focus of this study was to determine the distribution and frequency of clinically relevant DME alleles and to assess the impact of these DME alleles on therapeutic outcomes in a cohort of 50 HIV-TB co-infected Zulu participants. PCR-RFLP was used to generate a genotypic profile of CYPIA2, 2C9, 2C19, 2E1, 3A4, MDR-1 and NAT-2. The distributions of the allelic frequencies were as follows. The CYPIA2 (A) - 50.7%, CYP2C9*2 — 100% and *3 — 56.2%, CYP2C19*2 — 35.4%, CYP2E1 (C2) — 28.4%, CYP3A4*1B (G) — 58.2%, MDR-1 (C3435T) - 16% and NAT-2 slow acetylators — 6.5%. Seventy-three percent of participants had prolonged TB therapy. Within this group, 82.9% of patient displayed wild type and 17.2% variant allele for CYP2E1 gene (p= 0.04) profile. In addition, all the slow acetylators in this study had prolonged TB therapy. In the MDR-1 gene, 87.5% showed wild type allele and 12.5% displayed the variant allele. Unsuccessful TB outcomes were also noted in 22% of this study population. In this group the variant allele was found to be dominant in CYPIA2, CYP3A4 and NAT-2, the opposite was seen in CYP2E1 and MDR-1. It was also interesting to note a similar genetic profile in the group that showed successful TB therapy outcomes. All participants had positive ARV treatment outcomes despite DME genotypic variations. However, 26% of all study participants experienced liver enzyme abnormalities. These findings concur with other studies regarding the ethnic distribution of DME alleles and evidence of an association between ART and TB therapeutic outcomes and DME genotype variation was inconclusive.Thesis (M.Med.Sc.)-University of KwaZulu-Natal, Durban, 2007.
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Li, Yilan. "Botanical-drug interactions soy isoflavones and drug metabolism /." 2005. http://etd.nd.edu/ETD-db/theses/available/etd-08192005-160319/.
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