Journal articles: 'Human liver microsomes'

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Minoda, Yuko, and Evan D. Kharasch. "Halothane-dependent Lipid Peroxidation in Human Liver Microsomes Is Catalyzed by Cytochrome P4502A6 (CYP2A6)." Anesthesiology 95, no. 2 (August 1, 2001): 509–14. http://dx.doi.org/10.1097/00000542-200108000-00037.

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Background Halothane is extensively (approximately 50%) metabolized in humans and undergoes both oxidative and reductive cytochrome P450-catalyzed hepatic biotransformation. Halothane is reduced under low oxygen tensions by CYP2A6 and CYP3A4 in human liver microsome to an unstable free radical, and then to the volatile metabolites chlorodifluoroethene (CDE) and chlorotrifluoroethane (CTE). The free radical is also thought to initiate lipid peroxidation. Halothane-dependent lipid peroxidation has been shown in animals in vitro and in vivo but has not been evaluated in humans. This investigation tested the hypothesis that halothane causes lipid peroxidation in human liver microsomes, identified P450 isoforms responsible for halothane-dependent lipid peroxidation, and tested the hypothesis that lipid peroxidation is prevented by inhibiting halothane reduction. Methods Halothane metabolism was determined using human liver microsomes or cDNA-expressed P450. Lipid peroxidation was quantified by malondialdehyde (MDA) formation using high-pressure liquid chromatography-ultraviolet analysis of the thiobarbituric acid-MDA adduct. CTE and CDE were determined by gas chromatography-mass spectrometry. Results Halothane caused MDA formation in human liver microsomes at rates much lower than in rat liver microsomes. Human liver microsomal MDA production exhibited biphasic enzyme kinetics, similar to CDE and CTE production. MDA production was inhibited by the CYP2A6 inhibitor methoxsalen but not by the CYP3A4 inhibitor troleandomycin. Halothane-dependent MDA production was catalyzed by cDNA-expressed CYP2A6 but not CYP3A4 or P450 reductase alone. CYP2A6-catalyzed MDA production was inhibited by methoxsalen or anti-CYP2A6 antibody. Conclusions Halothane causes lipid peroxidation in human liver microsomes, which is catalyzed by CYP2A6, and inhibition of halothane reduction prevents halothane-dependent lipid peroxidation in vitro.

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Myllynen, P., P. Pienimäki, H. Raunio, and K. Vähäkangas. "Microsomal metabolism of carbamazepine and oxcarbazepine in liver and placenta." Human & Experimental Toxicology 17, no. 12 (December 1998): 668–76. http://dx.doi.org/10.1177/096032719801701204.

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Metabolism of both carbamazepine (CBZ) and oxcarbaze-pine (OCBZ) were catalyzed by human liver microsomes and microsomes from livers of CBZ-induced or non-induced C57BL/6 mice. Human placental microsomes metabolized only OCBZ. Mouse liver microsomes metabolized CBZ to carbamazepine-10,11-epoxide (CBZ-E), 10- hydroxy-10,11-dihydro-carbamazepine (10-OH-CBZ), 3- hydroxy-carbamazepine (3-OH-CBZ), 10,11-trans-dihydroxy-10,11-dihydro-carbamazepine (10,11-D) and to an unidentified metabolite. CBZ-pretreatment of mice increased both ethoxyresorufin O-deethylase activity in the liver and the amount of CBZ-E in microsomal incubations regardless of the age of mice. Human liver microsomes catalyzed the formation of CBZ to 9-hydroxymethyl-10-carbamoyl acridan (9-AC) in addition to CBZ-E, 3-OH-CBZ and 10-OH-CBZ. OCBZ was metabolized to its active metabolite in all incubations. An unknown metabolite was also present in some of the incubations. Human liver microsomes catalyzed only minute covalent binding of CBZ and OCBZ to DNA. Binding of OCBZ was, however, one order of magnitude greater than binding of CBZ. Human placental micro-somes from the mothers on CBZ therapy did not catalyze CBZ metabolism. The same microsomes catalyzed OCBZ metabolism to 10-OH-CBZ and to an unknown metabolite. These results indicate autoinduction in CBZ metabolism in mouse liver. Due to the higher binding of OCBZ than CBZ to DNA in vitro, further studies on the potential mutagenicity of OCBZ may be warranted.

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Barnes, T. S., M. D. Burke, and W. T. Melvin. "Differences in adult and foetal human cytochrome P-450 forms recognized by monoclonal antibodies with specificity for the P450III family." Biochemical Journal 260, no. 3 (June 15, 1989): 635–40. http://dx.doi.org/10.1042/bj2600635.

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Six murine monoclonal antibodies raised against a major human adult liver cytochrome P-450 (P-450) of the PCN family (P450III) detected a protein in human foetal liver microsomes (microsomal fractions) which had an approx. 1 kDa higher molecular mass on SDS/polyacrylamide-gel electrophoresis than the protein recognized in human adult liver microsomes. Although each of the antibodies recognized both the adult and the foetal forms, antibody HL4 showed higher affinity for the foetal form. Recognition by the monoclonal antibodies of peptides generated by proteolytic cleavage of microsomal proteins showed different patterns for the adult and foetal forms. It is concluded that the foetal P-450 form recognized by antibodies to the major human adult liver form P450hA7, although structurally similar, is either a distinct P-450 isoenzyme or that the adult and foetal proteins have different covalent modification. Immunoquantification experiments showed comparable levels of the P-450 forms in adult and foetal liver, although there appeared to be less inter-individual variation in foetal livers.

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George, R., P. J. Davis, L. Luong, and M. J. Poznansky. "Cholesterol-mediated regulation of HMG-CoA reductase in microsomes from human skin fibroblasts and rat liver." Biochemistry and Cell Biology 68, no. 3 (March 1, 1990): 674–79. http://dx.doi.org/10.1139/o90-097.

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3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity was determined in microsomes from human skin fibroblasts and rat liver that had been variously manipulated in vivo or in tissue culture to up- and down-regulate the enzyme. The cholesterol content of these microsomal preparations was then altered by depletion to or enrichment from either cholesterol-free or cholesterol-rich lipid vesicles. Microsomes from human skin fibroblasts responded to cholesterol depletion by increasing HMG-CoA reductase activity and by decreasing it in response to cholesterol enrichment. This was independent of the initial enzyme activity or the tissue culture conditions. Alterations in cholesterol content of rat liver microsomes in vitro failed to demonstrate any significant changes in HMG-CoA reductase activity whether the microsomes started with low enzyme activity (cholesterol-fed rats) or with high enzyme activity (cholestyramine-treated rats). The results are discussed in relation to previously published data and in respect to differences in the control of the human skin fibroblast and rat liver enzymes.Key words: cholesterol, HMG-CoA reductase, microsomes, fibroblasts, rat liver.

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Nguyen, Ngoc, Ngoc Cao, Thi Nguyen, Thien-Kim Le, Gun Cha, Soo-Keun Choi, Jae-Gu Pan, Soo-Jin Yeom, Hyung-Sik Kang, and Chul-Ho Yun. "Regioselective Hydroxylation of Phloretin, a Bioactive Compound from Apples, by Human Cytochrome P450 Enzymes." Pharmaceuticals 13, no. 11 (October 22, 2020): 330. http://dx.doi.org/10.3390/ph13110330.

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Phloretin, the major polyphenol compound in apples and apple products, is interesting because it shows beneficial effects on human health. It is mainly found as a form of glucoside, phlorizin. However, the metabolic pathway of phloretin in humans has not been reported. Therefore, identifying phloretin metabolites made in human liver microsomes and the human cytochrome P450 (P450) enzymes to make them is interesting. In this study, the roles of human liver P450s for phloretin oxidation were examined using human liver microsomes and recombinant human liver P450s. One major metabolite of phloretin in human liver microsomes was 3-OH phloretin, which is the same product of a bacterial CYP102A1-catalyzed reaction of phloretin. CYP3A4 and CYP2C19 showed kcat values of 3.1 and 5.8 min−1, respectively. However, CYP3A4 has a 3.3-fold lower Km value than CYP2C19. The catalytic efficiency of a CYP3A4-catalyzed reaction is 1.8-fold higher than a reaction catalyzed by CYP2C19. Whole-cell biotransformation with CYP3A4 was achieved 0.16 mM h−1 productivity for 3-OH phlorein from 8 mM phloretin at optimal condition. Phloretin was a potent inhibitor of CYP3A4-catalyzed testosterone 6β-hydroxylation activity. Antibodies against CYP3A4 inhibited up to 90% of the microsomal activity of phloretin 3-hydroxylation. The immunoinhibition effect of anti-2C19 is much lower than that of anti-CYP3A4. Thus, CYP3A4 majorly contributes to the human liver microsomal phloretin 3-hydroxylation, and CYP2C19 has a minor role.

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Court, Michael H., Su X. Duan, Leah M. Hesse, Karthik Venkatakrishnan, and David J. Greenblatt. "Cytochrome P-450 2B6 Is Responsible for Interindividual Variability of Propofol Hydroxylation by Human Liver Microsomes." Anesthesiology 94, no. 1 (January 1, 2001): 110–19. http://dx.doi.org/10.1097/00000542-200101000-00021.

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Background Oxidation of propofol to 4-hydroxypropofol represents a significant pathway in the metabolism of this anesthetic agent in humans. The aim of this study was to identify the principal cytochrome P-450 (CYP) isoforms mediating this biotransformation. Methods Propofol hydroxylation activities and enzyme kinetics were determined using human liver microsomes and cDNA-expressed CYPs. CYP-specific marker activities and CYP2B6 protein content were also quantified in hepatic microsomes for correlational analyses. Finally, inhibitory antibodies were used to ascertain the relative contribution of CYPs to propofol hydroxylation by hepatic microsomes. Results Propofol hydroxylation by hepatic microsomes showed more than 19-fold variability and was most closely correlated to CYP2B6 protein content (r = 0.904), and the CYP2B6 marker activities, S-mephenytoin N-demethylation (r = 0.919) and bupropion hydroxylation (r = 0.854). High- and intermediate-activity livers demonstrated high-affinity enzyme kinetics (K(m) < 8 microm), whereas low-activity livers displayed low-affinity kinetics (K(m) > 80 microm). All of the CYPs evaluated were capable of hydroxylating propofol; however, CYP2B6 and CYP2C9 were most active. Kinetic analysis indicated that CYP2B6 is a high-affinity (K(m) = 10 +/- 2 microm; mean +/- SE of the estimate), high-capacity enzyme, whereas CYP2C9 is a low-affinity (K(m) = 41 +/- 8 microm), high-capacity enzyme. Furthermore, immunoinhibition showed a greater contribution of CYP2B6 (56 +/- 22% inhibition; mean +/- SD) compared with CYP2C isoforms (16 +/- 7% inhibition) to hepatic microsomal activity. Conclusions Cytochrome P-450 2B6, and to a lesser extent CYP2C9, contribute to the oxidative metabolism of propofol. However, CYP2B6 is the principal determinant of interindividual variability in the hydroxylation of this drug by human liver microsomes.

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Milewich, L., P. C. MacDonald, and B. R. Carr. "Activity of 17β-hydroxysteroid oxidoreductase in tissues of the human fetus." Journal of Endocrinology 123, no. 3 (December 1989): 509–18. http://dx.doi.org/10.1677/joe.0.1230509.

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ABSTRACT The interconversion of oestrone and oestradiol, androstenedione and testosterone, and dehydroepi-androsterone and 5-androstene-3β,17β-diol in mammalian tissues is catalysed by 17β-hydroxysteroid oxidoreductase (17β-HSOR). To identify tissue sites of 17β-HSOR activity in the human fetus, microsomal fractions from 15 different fetal tissues obtained from first and second trimester pregnancies were used for evaluation of enzymatic activity by use of [17α-3H] oestradiol as the substrate and NADP+ as the co-factor. With these reagents, the enzyme-catalysed reaction led to the production of both non-radiolabelled oestrone and NADP3H in equimolar amounts; the radioactivity associated with NADP3H was used to quantify 17β-HSOR activity. Activity of 17β-HSOR was present in microsomes of all the tissues evaluated. The specific activity of the enzyme was highest in liver and placental microsomes. The interconversion of oestradiol and oestrone in microsomal fractions of nine different fetal tissues was studied by the use of substrates labelled with tritium at stable nuclear positions ([6,7-3H]oestradiol and [6,7-3H]oestrone). The products, [3H]oestrone and [3H]oestradiol, were quantified by the use of established techniques; other metabolites formed in these incubations were not identified. The reductive pathway of metabolism (oestrone to oestradiol) appeared to be favoured in microsomal fractions prepared from placenta, fetal zone of the adrenal gland and, possibly, lung. The oxidative pathway (oestradiol to oestrone) appeared to be favoured in microsomes prepared from liver, intestine, stomach, kidney, brain and heart. 17β-HSOR activity in fetal liver also was assessed by the use of fresh and frozen-thawed tissue, homogenate, subcellular fractions, and, also, in primary hepatocytes maintained in culture; the specific activity of the enzyme was highest in the microsomal fraction of liver tissue and 17β-HSOR activity in liver microsomes was linear with time of incubation up to 1 h. In hepatocytes, the enzymatic activity was linear with time of incubation up to 2 h and with cell number up to 2·5 × 105 cells/ml; the apparent Michaelis constant of hepatocyte 17β-HSOR for oestradiol was 11 μmol/l. The specific activity of 17β-HSOR did not change after pretreatment of hepatocytes for 24 h with insulin, glucagon or dexamethasone. Journal of Endocrinology (1989) 123, 509–518

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Wang, Li, Zhe Wang, Meng-ming Xia, Ying-ying Wang, Hai-yun Wang, and Guo-xin Hu. "Inhibitory effect of silybin on pharmacokinetics of imatinib in vivo and in vitro." Canadian Journal of Physiology and Pharmacology 92, no. 11 (November 2014): 961–64. http://dx.doi.org/10.1139/cjpp-2014-0260.

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The objective of this work was to investigate the effect of orally administered silybin on the pharmacokinetics of imatinib in rats and the metabolism of imatinib in human liver microsome and rat liver microsomes. Eighteen healthy male SD rats were randomly divided into 3 groups: group A (control group), group B (received multiple doses of 50 mg·kg−1 silybin for 15 consecutive days), and group C (received a single dose of 50 mg·kg−1 silybin). A single dose of imatinib was administered orally 30 min after administration of silybin (50 mg·kg−1). Imatinib plasma levels were measured by UPLC-MS/MS, and pharmacokinetic parameters were calculated by DAS 3.0 software (Bontz Inc., Beijing, China). In addition, human and rat liver microsome were performed to determine the effects of silybin metabolism of imatinib in vitro. The multiple doses or single dose of 50 mg·kg−1 silybin significantly decreased the area under the curve (0-t) of imatinib (p < 0.01). And the half-life (t1/2) of imatinib is significantly increased (p < 0.05 and p < 0.01, respectively). Also, silybin showed inhibitory effect on human and rat microsomes, the IC50 of silybin were 26.42 μmol·L−1 and 49.12 μmol·L−1 in human and rat liver microsomes, respectively. These results indicate that more attention should be paid to when imatinib is administrated combined with silybin.

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Senler, T. I., W. L. Dean, L. F. Murray, and J. L. Wittliff. "Quantification of cytochrome P-450-dependent cyclohexane hydroxylase activity in normal and neoplastic reproductive tissues." Biochemical Journal 227, no. 2 (April 15, 1985): 379–87. http://dx.doi.org/10.1042/bj2270379.

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It is well established that liver microsomal cytochrome P-450 participates in steroid metabolism and probably also in the metabolism of anti-oestrogens such as tamoxifen (Nolvadex). Thus it is possible that variations in cytochrome P-450 levels may influence the responsiveness of human breast and endometrial carcinomas to endocrine therapy. Therefore a simple sensitive spectrophotometric assay for determining levels of cytochrome P-450-dependent cyclohexane hydroxylation activity in breast and uterine microsomes (microsomal fractions) has been developed. Cyclohexane was chosen as a substrate because of the relatively high levels of cyclohexane hydroxylase activity in tumour microsomes and because cyclohexane serves as a substrate for several forms of cytochrome P-450. As previously described [Senler, Dean, Pierce & Wittliff (1985) Anal. Biochem. 144, 152-158], a direct method utilizing isotope-dilution/gas chromatography-mass spectrometry was also developed in order to confirm the results of the spectrophotometric assay. The average activity (cyclohexane-dependent NADPH oxidation) for 139 human breast-tumour microsome preparations was 1.34 nmol/min per mg, which is in the range of that found in untreated mammalian liver (1-3 nmol/min per mg). Also, high enzyme activity was demonstrated in human ovary, normal uterus as well as uterine leiomyomas. Endocrine status appeared to influence enzyme levels, in that mammary tissue from virgin rats contained significantly (P less than 0.025) higher amounts of activity than did tissues from either pregnant or lactating rats. Furthermore, carbon monoxide, as well as an antibody against rat liver cytochrome P-450, completely inhibited NADPH oxidation by breast-carcinoma microsomes. These results strengthen our hypothesis that tumours with high levels of cytochrome P-450 may have a reduced response to additive endocrine therapy.

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Svobodová, Martina, Markéta Martínková, Eva Frei, and Marie Stiborová. "Identification of human enzymes oxidizing a human metabolite of carcinogenic 2-nitroanisole, 2-nitrophenol. Evidence for its oxidative detoxification by human cytochromes P450." Collection of Czechoslovak Chemical Communications 75, no. 6 (2010): 703–19. http://dx.doi.org/10.1135/cccc2010023.

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2-Nitrophenol (2-NP) is the major detoxification metabolite of an important industrial pollutant and a potent carcinogen, 2-nitroanisole (2-NA). Here, we characterized the product of 2-NP metabolism catalyzed by human, rat, rabbit and mouse hepatic microsomes containing cytochromes P450 (CYPs) and identified the major human CYP enzymes participating in this process. The 2-NP metabolite was characterized by mass spectrometry and co-chromatography on HPLC with a synthetic standard, 2,5-dihydroxynitrobenzene (2,5-DNB) to be 2,5-DNB. No nitroreductive metabolism leading to the formation of N-(2-hydroxyphenyl)hydroxylamine or o-aminophenol was evident by all tested hepatic microsomes. Likewise, no DNA binding of 2-NP metabolite(s) measured with the 32P-postlabeling technique was detectable in hepatic microsomes. Therefore, hepatic microsomal CYP enzymes participate in 2-NP metabolism that does not lead to its activation to species binding to DNA. Selective inhibitors of human CYPs were used to characterize CYPs oxidizing 2-NP in human livers. Based on these inhibitory studies, we attribute most of 2-NP oxidation in human liver to CYP2E1, 3A4, 2A6, 2C and 2D6. Among recombinant human CYP enzymes tested in this study, CYP2E1, 2A6 and 2B6 were the most effective enzymes oxidizing 2-NP. Oxidation of 2-NP by human CYP2E1 exhibits the Michaelis-Menten kinetics, having the Km value of 0.21 mM. The results found in this study, the first report on the metabolism of 2-NP by human hepatic microsomes and human CYP enzymes, demonstrate that CYP2E1 is the major enzyme oxidizing this compound in human.

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Wallin, R., S. D. Patrick, and L. F. Martin. "Vitamin K1 reduction in human liver. Location of the coumarin-drug-insensitive enzyme." Biochemical Journal 260, no. 3 (June 15, 1989): 879–84. http://dx.doi.org/10.1042/bj2600879.

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The antidotal effect of vitamin K in overcoming poisoning by coumarin anticoagulant drugs is mediated by a vitamin K-reducing enzyme of the endoplasmic reticulum [Wallin & Martin (1987) Biochem. J. 241, 389-396]. With microsomes obtained from human liver biopsies, we have investigated the localization and the transverse orientation of this enzyme in the endoplasmic reticulum and compared its orientation to that of the other enzymes of the vitamin K-dependent carboxylation system. All enzymes were protected by the microsomal membrane and thus appear to have a luminal orientation in the endoplasmic reticulum, consistent with their role in the vitamin K-dependent modification of secretory glycoproteins. Separation of rough and smooth microsomes showed that vitamin K-dependent carboxylase activity was 6-fold higher in rough than in smooth microsomes. Vitamin K1 reduction by the coumarin-drug-sensitive (pathway I) and -insensitive (pathway II) enzymes of the vitamin K-dependent carboxylation system was the same in rough and smooth microsomes. The data suggest a close association between the pathway I and II enzymes in the endoplasmic reticulum. These pathways may be partial reactions of multienzyme complex which carries out the various activities associated with the vitamin K-dependent carboxylation system.

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Möllenberg, Alexander, and Gerhard Spiteller. "Transformations of 12,13-Epoxy-ll-hydroxy-9-octadecenoic Acid and 4,5-Epoxy-N-acetylsphingosine by Incubation with Liver Homogenate and Liver Microsomes." Zeitschrift für Naturforschung C 55, no. 11-12 (December 1, 2000): 981–86. http://dx.doi.org/10.1515/znc-2000-11-1222.

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Transformation of 12,13-epoxy-11-hydroxy-9-octadecenoic acid and 4,5-epoxy-N-acetylsphingosine by addition of porcine liver homogenate and human liver microsomes, respectively was investigated. Both epoxides were converted to corresponding dioles by porcine liver homogenate, but not by human liver microsomes, suggesting location of the hydrolyzing enzymes not in the microsomes, but within the cell wall.

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Crosbie, Sarah J., PG Blain, and Faith M. Williams. "Metabolism of n-hexane by rat liver and extrahepatic tissues and the effect of cytochrome P-450 inducers." Human & Experimental Toxicology 16, no. 3 (March 1997): 131–37. http://dx.doi.org/10.1177/096032719701600301.

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1 The in vitro metabolism ofn-hexane was studied in rat liver, lung, brain and skeletal muscle microsomes and in microsomes prepared from cell lines expressing human cytochrome P-450 2E1 or 2B6. The hydro xylated metabolites ofn-hexane were quantified by gas chromatography-mass spectometry. 2 Rat liver and extensor digitorum longus (EDL, fast- twitch skeletal muscle) microsomes and the CYP 2B6 microsomes produced the pre-neurotoxic metabolite of n-hexane, 2-hexanol as a major metabolite in contrast to the other rat tissues examined. 3 Inhibition of 2- and 3-hexanol production from n- hexane by rat lung microsomes using metyrapone, an inhibitor of cytochrome P-450 2B1 activity, resulted in almost complete inhibition of lung microsomal activ ity. 4 Production of all three hexanols was significantly increased with phenobarbital-induced rat liver micro somes, with a 10-fold increase in 2- and 3-hexanol production. A slight increase in 2-hexanol production with phenobarbital-induced rat EDL and brain micro somes was observed. No increase in n-hexane meta bolism was noted following induction with β- naphthoflavone or with ethanol.

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Tateishi, Tomonori, Pavel Soucek, Yoseph Caraco, F. Peter Guengerich, and Alastair J. J. Wood. "Colchicine biotransformation by human liver microsomes." Biochemical Pharmacology 53, no. 1 (January 1997): 111–16. http://dx.doi.org/10.1016/s0006-2952(96)00693-4.

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Miners, John O., Kerry J. Smith, Richard A. Robson, Michael E. McManus, Maurice E. Veronese, and Donald J. Birkett. "Tolbutamide hydroxylation by human liver microsomes." Biochemical Pharmacology 37, no. 6 (March 1988): 1137–44. http://dx.doi.org/10.1016/0006-2952(88)90522-9.

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Bangchang, Kesara Na, Juntra Karbwang, and David J. Back. "Mefloquine metabolism by human liver microsomes." Biochemical Pharmacology 43, no. 9 (May 1992): 1957–61. http://dx.doi.org/10.1016/0006-2952(92)90638-y.

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Li, Yan, Yanyan Zhou, Nan Si, Lingyu Han, Wei Ren, Shaokun Xin, Hongjie Wang, et al. "Comparative Metabolism Study of Five Protoberberine Alkaloids in Liver Microsomes from Rat, Rhesus Monkey, and Human." Planta Medica 83, no. 16 (April 11, 2017): 1281–88. http://dx.doi.org/10.1055/s-0043-108249.

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AbstractProtoberberine alkaloids including berberine, palmatine, jatrorrhizine, coptisine, and epiberberine are major components in many medicinal plants. They have been widely used for the treatment of cancer, inflammation, diabetes, depression, hypertension, and various infectious areas. However, the metabolism of five protoberberine alkaloids among different species has not been clarified previously. In order to elaborate on the in vitro metabolism of them, a comparative analysis of their metabolic profile in rat, rhesus monkey, and human liver microsomes was carried out using ultrahigh-performance liquid chromatography coupled with a high-resolution linear trap quadrupole-Orbitrap mass spectrometer (UHPLC-electrospray ionization-Orbitrap MS) for the first time. Each metabolite was identified and semiquantified by its accurate mass data and peak area. Fifteen metabolites were characterized based on accurate MS/MS spectra and the proposed MS/MS fragmentation pathways including demethylation, hydroxylation, and methyl reduction. Among them, the content of berberine metabolites in human liver microsomes was similar with those in rhesus monkey liver microsomes, whereas berberine in rat liver microsomes showed no demethylation metabolites and the content of metabolites showed significant differences with that in human liver microsomes. On the contrary, the metabolism of palmatine in rat liver microsomes resembled that in human liver microsomes. The content of jatrorrhizine metabolites presented obvious differences in all species. The HR-ESI-MS/MS fragmentation behavior of protoberberine alkaloids and their metabolic profile in rat, rhesus monkey, and human liver microsomes were investigated for the first time. The results demonstrated that the biotransformation characteristics of protoberberine alkaloids among different species had similarities as well differences that would be beneficial for us to better understand the pharmacological activities of protoberberine alkaloids.

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Barnes, T. S., P. M. Shaw, M. D. Burke, and W. T. Melvin. "Monoclonal antibodies against human cytochrome P-450 recognizing different pregnenolone 16α-carbonitrile-inducible rat cytochromes P-450." Biochemical Journal 248, no. 1 (November 15, 1987): 301–4. http://dx.doi.org/10.1042/bj2480301.

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Six murine monoclonal antibodies against human hepatic cytochrome P-450 have been raised, using human liver microsomes (microsomal fractions) or semi-purified human cytochrome P-450 as immunogen. All six antibodies recognized the same highly purified of human liver cytochrome P-450 of molecular mass 53 kDa and gave rise to a single band at 53 kDa on immunoblots of human liver microsomes from 11 individuals. The antibodies also recognized proteins at 52 kDa and 54 kDa on immunoblots of control and induced male-rat liver microsomes, showing four different banding patterns. Antibodies HL4 and HP16 recognized a 52 kDa protein that was only weakly expressed in untreated rats and which was strongly induced by pregnenolone 16 alpha-carbonitrile (PCN) but not by phenobarbitone (PB), 3-methylcholanthrene (3MC), isosafrole (ISF), Aroclor 1254 (ARO), clofibrate or imidazole. HP10 and HL5 recognized a constitutive 52 kDa protein that was weakly induced by PCN but not by the other agents and was suppressed by 3MC and ARO. HP3 recognized a 54 kDa protein that was undetectable in control rats but was strongly induced by PB, PCN, ISF and ARO. HL3 appeared to recognize a combination of the proteins recognized by the other antibodies plus a 54 kDa protein that was weakly expressed in control rats. The constitutive proteins recognized were male-specific.

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Miles, J. S., A. W. McLaren, L. M. Forrester, M. J. Glancey, M. A. Lang, and C. R. Wolf. "Identification of the human liver cytochrome P-450 responsible for coumarin 7-hydroxylase activity." Biochemical Journal 267, no. 2 (April 15, 1990): 365–71. http://dx.doi.org/10.1042/bj2670365.

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1. We have constructed a full-length human liver cytochrome P450IIA cDNA from a partial-length clone by oligonucleotide-directed mutagenesis, and subcloned it into the monkey kidney (COS-7) cell expression vector, pSVL. 2. The cDNA encodes a 49 kDa protein with coumarin 7-hydroxylase (COH) activity which cross-reacts with antisera to the mouse cytochrome P-450 isoenzyme responsible for COH activity and comigrates with a human liver microsomal protein. 3. Western blot analysis of a panel of human livers indicates that the level of the 49 kDa protein, detected using antisera to either the mouse COH P-450 or rat P450IIA1 protein, correlates very highly with COH activity. 4. Antisera to the rat P450IIA1 protein can inhibit COH activity in human liver microsomes. Taken together, these data indicate that a member of the P450IIA subfamily is responsible for most, if not all, of the COH activity in human liver.

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Williams, FM, E. Mutch, KW Woodhouse, D. Lambert, and MD Rawlins. "Ethoxyresorufin O-deethylation by human liver microsomes." British Journal of Clinical Pharmacology 22, no. 3 (September 1986): 263–68. http://dx.doi.org/10.1111/j.1365-2125.1986.tb02885.x.

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McManus, M. E., D. S. Davies, A. R. Boobis, P. H. Grantham, and P. J. Wirth. "Guanethidine N-oxidation in human liver microsomes." Journal of Pharmacy and Pharmacology 39, no. 12 (December 1987): 1052–55. http://dx.doi.org/10.1111/j.2042-7158.1987.tb03163.x.

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MIYAZAWA, Mitsuo, Atsushi SUGIE, and Masaki SHINDO. "Biotransformation of (−)-Verbenone by Human Liver Microsomes." Bioscience, Biotechnology, and Biochemistry 66, no. 11 (January 2002): 2458–60. http://dx.doi.org/10.1271/bbb.66.2458.

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MIYAZAWA, Mitsuo, and Kyousuke NAKANISHI. "Biotransformation of (−)-Menthone by Human Liver Microsomes." Bioscience, Biotechnology, and Biochemistry 70, no. 5 (May 23, 2006): 1259–61. http://dx.doi.org/10.1271/bbb.70.1259.

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Wandel, C., R. Bocker, A. Browne, H. Bohrer, and E. Martin. "METABOLISM OF DIAZEPAM IN HUMAN LIVER MICROSOMES." Anesthesiology 81, SUPPLEMENT (September 1994): A395. http://dx.doi.org/10.1097/00000542-199409001-00394.

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25

Paibir, Sheela G., William H. Soine, Diana F. Thomas, and Robert A. Fisher. "Phenobarbital N-glucosylation by human liver microsomes." European Journal of Drug Metabolism and Pharmacokinetics 29, no. 1 (March 2004): 51–59. http://dx.doi.org/10.1007/bf03190574.

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Kobayashi, Tsutomu, Judith E. Sleeman, Michael W. H. Coughtrie, and Brian Burchell. "Molecular and functional characterization of microsomal UDP-glucuronic acid uptake by members of the nucleotide sugar transporter (NST) family." Biochemical Journal 400, no. 2 (November 14, 2006): 281–89. http://dx.doi.org/10.1042/bj20060429.

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Transport of the co-substrate UDPGA (UDP-glucuronic acid) into the lumen of the endoplasmic reticulum is an essential step in glucuronidation reactions due to the intraluminal location of the catalytic site of the enzyme UGT (UDP-glucuronosyltransferase). In the present study, we have characterized the function of several NSTs (nucleotide sugar transporters) and UGTs as potential carriers of UDPGA for glucuronidation reactions. UDPGlcNAc (UDP-N-acetylglucosamine)-dependent UDPGA uptake was found both in rat liver microsomes and in microsomes prepared from the rat hepatoma cell line H4IIE. The latency of UGT activity in microsomes derived from rat liver and V79 cells expressing UGT1A6 correlated well with mannose-6-phosphatase latency, confirming the UGT in the recombinant cells retained a physiology similar to rat liver microsomes. In the present study, four cDNAs coding for NSTs were obtained; two were previously reported (UGTrel1 and UGTrel7) and two newly identified (huYEA4 and huYEA4S). Localization of NSTs within the human genome sequence revealed that huYEA4S is an alternatively spliced form of huYEA4. All the cloned NSTs were stably expressed in V79 (Chinese hamster fibroblast) cells, and were able to transport UDPGA after preloading of isolated microsomal vesicles with UDPGlcNAc. The highest uptake was seen with UGTrel7, which displayed a Vmax approx. 1% of rat liver microsomes. Treatment of H4IIE cells with β-naphthoflavone induced UGT protein expression but did not affect the rate of UDPGA uptake. Furthermore, microsomes from UGT1-deficient Gunn rat liver showed UDPGA uptake similar to those from control rats. These data show that NSTs can act as UDPGA transporters for glucuronidation reactions, and indicate that UGTs of the 1A family do not function as UDPGA carriers in microsomes. The cell line H4IIE is a useful model for the study of UDPGA transporters for glucuronidation reactions.

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Benga, Gheorghe, and William Ferdinand. "Amino acid composition of rat and human liver microsomes in normal and pathological conditions." Bioscience Reports 15, no. 2 (April 1, 1995): 111–16. http://dx.doi.org/10.1007/bf01200145.

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The amino acid composition of proteins from liver microsomes has been studied in rats and in human subjects with normal liver, with obstructive jaundice or liver cirrhosis. The pattern of the amino acid composition of microsomes appeared to be species-specific. Phenylalanine, threonine, serine, proline, histidine and [aspartic acid plus asparagine] were increased, while alanine, tyrosine, glycine and arginine were decreased in the human compared to the rat microsomes. In patients with obstructive jaundice of short duration (less than two months) only a slight decrease in leucine and phenylalanine could be noticed, while in the case of liver cirrhosis amino acid composition was markedly changed.

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Richard, Kerry, Robert Hume, Ellen Kaptein, Jo P. Sanders, Hans van Toor, Wouter W. de Herder, Jan C. den Hollander, Eric P. Krenning, and Theo J. Visser. "Ontogeny of Iodothyronine Deiodinases in Human Liver1." Journal of Clinical Endocrinology & Metabolism 83, no. 8 (August 1, 1998): 2868–74. http://dx.doi.org/10.1210/jcem.83.8.5032.

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abstract The role of the deiodinases D1, D2, and D3 in the tissue-specific and time-dependent regulation of thyroid hormone bioactivity during fetal development has been investigated in animals but little is known about the ontogeny of these enzymes in humans. We analyzed D1, D2, and D3 activities in liver microsomes from 10 fetuses of 15–20 weeks gestation and from 8 apparently healthy adult tissue transplant donors, and in liver homogenates from 2 fetuses (20 weeks gestation), 5 preterm infants (27–32 weeks gestation), and 13 term infants who survived up to 39 weeks postnatally. D1 activity was determined using 1μ m [3′,5′-125I]rT3 as substrate and 10 mm dithiothreitol (DTT) as cofactor, D2 activity using 1 nm [3′,5′-125I]T4 and 25 mm DTT in the presence of 1 mm 6-propyl-2-thiouracil (to block D1 activity) and 1 μm T3 (to block D3 activity), and D3 activity using 10 nm [3,5-125I]T3 and 50 mm DTT, by quantitation of the release of 125I−. The assays were validated by high performance liquid chromatography of the products, and kinetic analysis[ Michaelis-Menten constant (Km) of rT3 for D1: 0.5 μm; Km of T3 for D3: 2 nm]. In liver homogenates, D1 activity was not correlated with age, whereas D3 activity showed a strong negative correlation with age (r −0.84), with high D3 activities in preterm infants and (except in 1 infant of 35 weeks) absent D3 activity in full-term infants. In microsomes, D1 activities amounted to 4.3–60 pmol/min/mg protein in fetal livers and to 170–313 pmol/min/mg protein in adult livers, whereas microsomal D3 activities were 0.15–1.45 pmol/min/mg protein in fetuses and <0.1 pmol/min/mg protein in all but one adult. In the latter sample, D3 activity amounted to 0.36 pmol/min/mg protein. D2 activity was negligible in both fetal and adult livers. These findings indicate high D1 and D3 activities in fetal human liver, and high D1 and mostly absent D3 activities in adult human liver. Therefore, the low serum T3 levels in the human fetus appear to be caused by high hepatic (and placental) D3 activity rather than caused by low hepatic D1 activity. The occasional expression of D3 in adult human liver is intriguing and deserves further investigation.

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Kim, Sin-Eun, Hyung-Ju Seo, Yeojin Jeong, Gyung-Min Lee, Seung-Bae Ji, So-Young Park, Zhexue Wu, Sangkyu Lee, Sunghwan Kim, and Kwang-Hyeon Liu. "In Vitro Metabolism of Donepezil in Liver Microsomes Using Non-Targeted Metabolomics." Pharmaceutics 13, no. 7 (June 23, 2021): 936. http://dx.doi.org/10.3390/pharmaceutics13070936.

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Donepezil is a reversible acetylcholinesterase inhibitor that is currently the most commonly prescribed drug for the treatment of Alzheimer’s disease. In general, donepezil is known as a safe and well-tolerated drug, and it was not associated with liver abnormalities in several clinical trials. However, rare cases of drug-related liver toxicity have been reported since it has become commercially available. Few studies have investigated the metabolic profile of donepezil, and the mechanism of liver damage caused by donepezil has not been elucidated. In this study, the in vitro metabolism of donepezil was investigated using liquid chromatography–tandem mass spectrometry based on a non-targeted metabolomics approach. To identify metabolites, the data were subjected to multivariate data analysis and molecular networking. A total of 21 donepezil metabolites (17 in human liver microsomes, 21 in mice liver microsomes, and 17 in rat liver microsomes) were detected including 14 newly identified metabolites. One potential reactive metabolite was identified in rat liver microsomal incubation samples. Metabolites were formed through four major metabolic pathways: (1) O-demethylation, (2) hydroxylation, (3) N-oxidation, and (4) N-debenzylation. This study indicates that a non-targeted metabolomics approach combined with molecular networking is a reliable tool to identify and detect unknown drug metabolites.

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KRAMER, Werner, Hans-Joerg BURGER, William J. ARION, Daniel CORSIERO, Frank GIRBIG, Claudia WEYLAND, Horst HEMMERLE, Stefan PETRY, Paul HABERMANN, and Andreas HERLING. "Identification of protein components of the microsomal glucose 6-phosphate transporter by photoaffinity labelling." Biochemical Journal 339, no. 3 (April 26, 1999): 629–38. http://dx.doi.org/10.1042/bj3390629.

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The glucose-6-phosphatase system catalyses the terminal step of hepatic glucose production from both gluconeogenesis and glycogenolysis and is thus a key regulatory factor of blood glucose homoeostasis. To identify the glucose 6-phosphate transporter T1, we have performed photoaffinity labelling of human and rat liver microsomes by using the specific photoreactive glucose-6-phosphate translocase inhibitors S 0957 and S 1743. Membrane proteins of molecular mass 70, 55, 33 and 31 kDa were labelled in human microsomes by [3H]S 0957, whereas in rat liver microsomes bands at 95, 70, 57, 54, 50, 41, 33 and 31 kDa were detectable. The photoprobe [3H]S 1743 led to the predominant labelling of a 57 kDa and a 50 kDa protein in the rat. Stripping of microsomes with 0.3% CHAPS retains the specific binding of T1 inhibitors; photoaffinity labelling of such CHAPS-treated microsomes resulted in the labelling of membrane proteins of molecular mass 55, 33 and 31 kDa in human liver and 50, 33 and 31 kDa in rat liver. Photoaffinity labelling of human liver tissue samples from a healthy individual and from liver samples of patients with a diagnosed glycogen-storage disease type 1b (GSD type 1b; von Gierke's disease) revealed the absence of the 55 kDa protein from one of the patients with GSD type 1. These findings support the identity of the glucose 6-phosphate transporter T1, with endoplasmic reticulum protein of molecular mass 50 kDa in rat liver and 55 kDa in human liver.

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Park, Ria, Eun Jeong Park, Yong-Yeon Cho, Joo Young Lee, Han Chang Kang, Im-Sook Song, and Hye Suk Lee. "Tetrahydrofurofuranoid Lignans, Eudesmin, Fargesin, Epimagnolin A, Magnolin, and Yangambin Inhibit UDP-Glucuronosyltransferase 1A1 and 1A3 Activities in Human Liver Microsomes." Pharmaceutics 13, no. 2 (February 1, 2021): 187. http://dx.doi.org/10.3390/pharmaceutics13020187.

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Eudesmin, fargesin, epimagnolin A, magnolin, and yangambin are tetrahydrofurofuranoid lignans with various pharmacological activities found in Magnoliae Flos. The inhibition potencies of eudesmin, fargesin, epimagnolin A, magnolin, and yangambin on six major human uridine 5′-diphospho-glucuronosyltransferase (UGT) activities in human liver microsomes were evaluated using liquid chromatography–tandem mass spectrometry and cocktail substrates. Eudesmin, fargesin, epimagnolin A, magnolin, and yangambin inhibited UGT1A1 and UGT1A3 activities, but showed negligible inhibition of UGT1A4, UGT16, UGT1A9, and UGT2B7 activities at 200 μM in pooled human liver microsomes. Moreover, eudesmin, fargesin, epimagnolin A, magnolin, and yangambin noncompetitively inhibited UGT1A1-catalyzed SN38 glucuronidation with Ki values of 25.7, 25.3, 3.6, 26.0, and 17.1 μM, respectively, based on kinetic analysis of UGT1A1 inhibition in pooled human liver microsomes. Conversely, the aforementioned tetrahydrofurofuranoid lignans competitively inhibited UGT1A3-catalyzed chenodeoxycholic acid 24-acyl-glucuronidation with 39.8, 24.3, 15.1, 37.6, and 66.8 μM, respectively in pooled human liver microsomes. These in vitro results suggest the necessity of evaluating whether the five tetrahydrofurofuranoid lignans can cause drug–drug interactions with UGT1A1 and UGT1A3 substrates in vivo.

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Pennanen, S., A. Kojo, M. Pasanen, J. Liesivuori, RO Juvonen, and H. Komulainen. "CYP enzymes catalyze the formation of a terminal olefin from 2-ethylhexanoic acid in rat and human liver." Human & Experimental Toxicology 15, no. 5 (May 1996): 435–42. http://dx.doi.org/10.1177/096032719601500512.

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1 The metabolism of 2-ethylhexanoic acid (2-EHA) was studied in rat, mouse and human liver microsomes in vitro. The metabolites of 2-EHA were identified as methylated derivatives by gas chromatography-mass spectrometry. 2 2-Ethyl-1,6-hexanedioic acid was the main metabolite produced in rat, mouse and human liver microsomes. Unsaturated 2-ethyl-5-hexenoic acid, a terminal ole fin, was produced only in human liver microsomes and phenobarbital-induced rat liver microsomes. The cytochrome P450 (CYP) inhibitors metyrapone, SKF 525A, triacetyloleandomycin (TAO), quinidine and the cytochrome P450 reductase antibody abolished its formation both in rat and human microsomes. 3 The metabolites were analyzed also in vivo in urine of 2-EHA-exposed rats and in urine of sawmill workers exposed occupationally to 2-EHA. Both rat and human urine contained 2-ethyl-1,6-hexanedioic acid as the main metabolite and also 2-ethyl-5-hexenoic acid. Metyrapone, SKF 525A and TAO all decreased drastically the formation of 2-ethyl-5-hexenoic acid in the rat. 4 The data indicate that (1) several CYP families (CYP2A, CYP2B, CYP2D and CYP3A) could be responsible for the hepatic metabolism of 2-EHA, (2) the same metabolites were formed in rats and man and (3) an unsaturated terminal olefin, 2-ethyl-5-hexenoic acid is formed in the liver.

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Venkataramanan, Raman, Shimin Zang, Timothy Gayowski, and Nina Singh. "Voriconazole Inhibition of the Metabolism of Tacrolimus in a Liver Transplant Recipient and in Human Liver Microsomes." Antimicrobial Agents and Chemotherapy 46, no. 9 (September 2002): 3091–93. http://dx.doi.org/10.1128/aac.46.9.3091-3093.2002.

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ABSTRACT The purpose of this study was to assess the effect of voriconazole on the blood tacrolimus concentration in a liver transplant recipient and to examine the interaction between voriconazole and tacrolimus by using human liver microsomes. Two subjects were enrolled in the clinical study: one received voriconazole, and the other received a placebo. Tacrolimus metabolism was evaluated in human liver microsomes at various concentrations in the absence and presence of various concentrations of voriconazole. Coadministration of voriconazole and tacrolimus resulted in elevated (nearly 10-fold-higher) trough tacrolimus blood concentrations in the liver transplant patient. In the in vitro study, voriconazole at a concentration of 10.4 ± 4.3 μg/ml inhibited the metabolism of tacrolimus by 50%. Clinically relevant concentrations of voriconazole inhibited the metabolism of tacrolimus in human liver microsomes. Close monitoring of the blood concentration and adjustment in the dose of tacrolimus are warranted in transplant recipients treated with voriconazole.

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Trapnell, C. B., C. Jamis-Dow, R. W. Klecker, and J. M. Collins. "Metabolism of rifabutin and its 25-desacetyl metabolite, LM565, by human liver microsomes and recombinant human cytochrome P-450 3A4: relevance to clinical interaction with fluconazole." Antimicrobial Agents and Chemotherapy 41, no. 5 (May 1997): 924–26. http://dx.doi.org/10.1128/aac.41.5.924.

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Rifabutin and fluconazole are often given concomitantly as therapy to prevent opportunistic infections in individuals infected with the human immunodeficiency virus. Recent reports have shown increased levels of rifabutin and its 25-desacetyl metabolite, LM565, in plasma when rifabutin is administered with fluconazole. Since fluconazole is known to inhibit microsomal enzymes, this study was undertaken to determine if this rifabutin-fluconazole interaction was due to an inhibition of human hepatic enzymes. The metabolism of both rifabutin and LM565 was evaluated in human liver microsomes and recombinant human cytochrome P-450 (CYP) 3A4 in the presence of fluconazole and other probe drugs known to inhibit CYP groups 1A2, 2C9, 2D6, 2E1, and 3A. The concentrations of rifabutin (1 microg/ml), LM565 (1 microg/ml), and fluconazole (10 and 100 microg/ml) used were equal to those observed in plasma after the administration of rifabutin and fluconazole at clinically relevant doses. High-performance liquid chromatography was used to assess the metabolism of rifabutin and LM565. Rifabutin was readily metabolized to LM565 by human microsomes, but the reaction was independent of NADPH and was not affected by the P-450 inhibitors. No rifabutin metabolism by recombinant CYP 3A4 was found to occur. LM565 was also metabolized by human microsomes to two products, but metabolism was dependent on NADPH and was affected by certain P-450 inhibitors. In addition, LM565 was readily metabolized by the recombinant CYP 3A4 to the same two products found with its metabolism by human microsomes. Therefore, rifabutin is metabolized by human microsomes but not via cytochrome P-450 enzymes, whereas LM565 is metabolized by CYP 3A4.

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Buchmueller, Julia, Florian Kaltner, Christoph Gottschalk, Maria Maares, Albert Braeuning, and Stefanie Hessel-Pras. "Structure-Dependent Toxicokinetics of Selected Pyrrolizidine Alkaloids In Vitro." International Journal of Molecular Sciences 23, no. 16 (August 16, 2022): 9214. http://dx.doi.org/10.3390/ijms23169214.

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Phytochemicals like pyrrolizidine alkaloids (PAs) can affect the health of humans and animals. PAs can occur for example in tea, honey or herbs. Some PAs are known to be cytotoxic, genotoxic, and carcinogenic. Upon intake of high amounts, hepatotoxic and pneumotoxic effects were observed in humans. This study aims to elucidate different toxicokinetic parameters like the uptake of PAs and their metabolism with in vitro models. We examined the transport rates of differently structured PAs (monoester, open-chained diester, cyclic diester) over a model of the intestinal barrier. After passing the intestinal barrier, PAs reach the liver, where they are metabolized into partially instable electrophilic metabolites interacting with nucleophilic centers. We investigated this process by the usage of human liver, intestinal, and lung microsomal preparations for incubation with different PAs. These results are completed with the detection of apoptosis as indicator for bioactivation of the PAs. Our results show a structure-dependent passage of PAs over the intestinal barrier. PAs are structure-dependently metabolized by liver microsomes and, to a smaller extent, by lung microsomes. The detection of apoptosis of A549 cells treated with lasiocarpine and monocrotaline following bioactivation by human liver or lung microsomes underlines this result. Conclusively, our results help to shape the picture of PA toxicokinetics which could further improve the knowledge of molecular processes leading to observed effects of PAs in vivo.

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Waddell, I. D., H. Scott, A. Grant, and A. Burchell. "Identification and characterization of a hepatic microsomal glucose transport protein. T3 of the glucose-6-phosphatase system?" Biochemical Journal 275, no. 2 (April 15, 1991): 363–67. http://dx.doi.org/10.1042/bj2750363.

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A 52 kDa polypeptide in rat liver microsomes was identified as a glucose-binding protein by its ability to weakly bind cytochalasin B and by its cross-reactivity to an antibody raised against the human erythrocyte glucose transport protein. The microsomal glucose binding polypeptide was purified by affinity chromatography and an antibody was raised against it. The inhibitory effect of this antibody on rat microsomal glucose-6-phosphatase activity and on glucose transport out of microsomal vesicles indicates that this protein is a microsomal glucose transport protein.

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He, Kan, Bing He, James E. Grace, Baomin Xin, Donglu Zhang, Donald J. Pinto, Joseph M. Luettgen, et al. "Preclinical Pharmacokinetic and Metabolism of Apixaban, a Potent and Selective Factor Xa Inhibitor." Blood 108, no. 11 (November 16, 2006): 910. http://dx.doi.org/10.1182/blood.v108.11.910.910.

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Abstract Apixaban is a potent, orally available, highly selective, and reversible factor Xa inhibitor, and currently under development for prevention and treatment of thrombosis. The preclinical pharmacokinetic and metabolism attributes of apixaban feature a small volume of distribution, a low systemic clearance, good oral bioavailability, multiple elimination pathways and minimal potential for drug-drug interactions. Apixaban is well absorbed in chimpanzees, dogs and rats with a mean oral bioavailability of 51, 88 and 34%, respectively. The mean volume of distribution of apixaban is 0.17, 0.29 and 0.31 L/kg in chimpanzees, dogs and rats, respectively, suggesting apixaban is primarily distributed (30–50%) to blood where the therapeutic action resides. The small volume is not due to extensive plasma protein binding, but possibly attributed to limited extravascular tissue distribution, given that the unbound fraction is approximately 13, 5, 8 and 4% in human, chimpanzee, dog and rat serum, respectively. The systemic clearance is <3% of hepatic blood flow in chimpanzees (0.018 L/h/kg) and dogs (0.052 L/h/kg), and <10% in rats (0.26 L/h/kg). Consistent with this low clearance, the in vitro metabolic clearance of apixaban is low, as indicated by the lack of significant metabolism in human liver microsomes and hepatocytes, and in chimpanzee and dog liver microsomes. The primary metabolite identified in vitro is the O-demethylated product which is formed mainly by CYP3A4 in human liver microsomes. The elimination of apixaban involves multiple pathways including renal and intestinal excretion of the parent and metabolism. The biliary clearance is low in dogs, accounting for approximately 2% of the systemic clearance. Apixaban did not inhibit CYP1A2, 2C8, 2C9, 2C19, 2D6 and 3A4 activities in cDNA-expressed enzyme systems and human liver microsomes, nor induced 1A2, 2B6 and CYP3A4 in human hepatocytes. No glutathione adduct with apixaban was formed in dog and rat, and in human hepatocytes and liver microsomal incubation in the presence of glutathione, suggesting low potential for the formation of reactive metabolites. In conclusion, apixaban shows excellent pharmacokinetic and metabolic properties for clinical development.

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Moreira da Silva, Rodrigo, Cristiane de Gaitani, Lucas Marques, Karina Fraige Baraco, Alberto Cavalheiro, Luiz de Moraes, Norberto Lopes, and Anderson de Oliveira. "Characterization of Casearin X Metabolism by Rat and Human Liver Microsomes." Planta Medica 85, no. 04 (October 29, 2018): 282–91. http://dx.doi.org/10.1055/a-0765-9523.

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AbstractCasearin X (CAS X) is the major clerodane diterpene isolated from the leaves of Casearia sylvestris and has been extensively studied due to its powerful cytotoxic activity at low concentrations. Promising results for in vivo antitumor action have also been described when CAS X was administered intraperitoneally in mice. Conversely, loss of activity was observed when orally administered. Since the advancement of natural products as drug candidates requires satisfactory bioavailability for their pharmacological effect, this work aimed to characterize the CAS X metabolism by employing an in vitro microsomal model for the prediction of preclinical pharmacokinetic data. Rat and human liver microsomes were used to assess species differences. A high-performance liquid chromatography with diode-array detection (HPLC-DAD) method for the quantification of CAS X in microsomes was developed and validated according to European Medicines Agency guidelines. CAS X was demonstrated to be a substrate for carboxylesterases via hydrolysis reaction, with a Michaelis-Menten kinetic profile. The enzyme kinetic parameters were determined, and the intrinsic clearance was 1.7-fold higher in humans than in rats. The hepatic clearance was estimated by in vitro-in vivo extrapolation, resulting in more than 90% of the hepatic blood flow for both species. A qualitative study was also carried out for the metabolite identification by mass spectrometry and indicated the formation of the inactive metabolite CAS X dialdehyde. These findings demonstrate that CAS X is susceptible to first-pass metabolism and is a substrate for specific carboxylesterases expressed in liver, which may contribute to a reduction in antitumor activity when administered by the oral route.

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Chen, Hui, Ya Zhang, Xiaoying Wu, Candong Li, and Huan Wang. "In Vitro Assessment of Cytochrome P450 2C19 Potential of Naoxintong." Evidence-Based Complementary and Alternative Medicine 2012 (2012): 1–6. http://dx.doi.org/10.1155/2012/430262.

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The effects of Buchang Naoxintong Capsules (BNCs) on S-mephenytoin 4′-hydroxylation activities in human liver microsomes in vitro were assessed. Human liver microsome was prepared by different ultracentrifugation. Human liver microsome incubation experiment was carried out to assay BNC on S-mephenytoin 4′-hydroxylation activities. The 4′-hydroxylation of S-mephenytoin, a representative substrate toward CYP2C19, was increased by phenytoin sodium (positive control). After the incubation, the metabolites of the substrates (4′-OH-mephenytoin) were determined by HPLC. Results showed that both phenytoin sodium and BNC showed obvious increase effect on CYP2C19. The enzymatic reaction of BNC was observed with concentrations ranging from 5 μg/mL to 250 μg/mL. Compared to blank, the increase effect of BNC showed significant difference from the beginning of concentration of 150 μg/mL (P<0.001). The conclusion was that BNC showed obvious increase effect on the catalytic activities of drug-metabolising CYP2C19 enzyme.

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Dai, Ziru, Guibo Sun, Jiada Yang, Jie Hou, Ping Zhou, Weijie Xie, Guangbo Ge, Xiaobo Sun, and Ling Yang. "Interspecies Variation in NCMN-O-Demethylation in Liver Microsomes from Various Species." Molecules 24, no. 15 (July 30, 2019): 2765. http://dx.doi.org/10.3390/molecules24152765.

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NCMN (N-(3-carboxy propyl)-4-methoxy-1,8-naphthalimide), a newly developed ratiometric two-photon fluorescent probe for human Cytochrome P450 1A (CYP1A), shows the best combination of specificity and reactivity for real-time detection of the enzymatic activities of CYP1A in complex biological systems. This study aimed to investigate the interspecies variation in NCMN-O-demethylation in commercially available liver microsomes from human, mouse, rat, beagle dog, minipig and cynomolgus monkey. Metabolite profiling demonstrated that NCMN could be O-demethylated in liver microsomes from all species but the reaction rate varied considerably. CYP1A was the major isoform involved in NCMN-O-demethylation in all examined liver microsomes based on the chemical inhibition assays. Furafylline, a specific inhibitor of mammalian CYP1A, displayed differential inhibitory effects on NCMN-O-demethylation in all tested species. Kinetic analyses demonstrated that NCMN-O-demethylation in liver microsomes form rat, minipig and cynomolgus monkey followed biphasic kinetics, while in liver microsomes form human, mouse and beagle dog obeyed Michaelis-Menten kinetics, the kinetic parameters from various species are much varied, while NCMN-O-demethylation in MLM exhibited the highest similarity of specificity, kinetic behavior and intrinsic clearance as that in HLM. These findings will be very helpful for the rational use of NCMN as a practical tool to decipher the functions of mammalian CYP1A or to study CYP1A associated drug-drug interactions in vivo.

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Skjelbo, E., and K. Brosen. "Inhibitors of imipramine metabolism by human liver microsomes." British Journal of Clinical Pharmacology 34, no. 3 (September 1992): 256–61. http://dx.doi.org/10.1111/j.1365-2125.1992.tb04133.x.

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Kang, Ping, Deepak Dalvie, Evan Smith, Sue Zhou, Alan Deese, and James A. Nieman. "Bioactivation of Flutamide Metabolites by Human Liver Microsomes." Drug Metabolism and Disposition 36, no. 7 (April 14, 2008): 1425–37. http://dx.doi.org/10.1124/dmd.108.020370.

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Zhang, Mei, J. Paul Fawcett, Julia M. Kennedy, and John P. Shaw. "Stereoselective glucuronidation of formoterol by human liver microsomes." British Journal of Clinical Pharmacology 49, no. 2 (February 2000): 152–57. http://dx.doi.org/10.1046/j.1365-2125.2000.00133.x.

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McLure, James A., John O. Miners, and Donald J. Birkett. "Nonspecific binding of drugs to human liver microsomes." British Journal of Clinical Pharmacology 49, no. 5 (May 2000): 453–61. http://dx.doi.org/10.1046/j.1365-2125.2000.00193.x.

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Kharasch, Evan D., and Rita Labroo. "Metabolism of Ketamine Stereoisomers by Human Liver Microsomes." Anesthesiology 77, no. 6 (December 1, 1992): 1201–7. http://dx.doi.org/10.1097/00000542-199212000-00022.

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García-Agúndez, Jose Augusto, Antonio Luengo, and Julio Benítez. "Aminopyrine N-demethylase activity in human liver microsomes." Clinical Pharmacology and Therapeutics 48, no. 5 (November 1990): 490–95. http://dx.doi.org/10.1038/clpt.1990.184.

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Miyazawa, Mitsuo, and Masaki Shindo. "Biotransformation of 1,8-Cineole by Human Liver Microsomes." Natural Product Letters 15, no. 1 (January 2001): 49–53. http://dx.doi.org/10.1080/10575630108041257.

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Hoskins, J., G. Shenfield, M. Murray, and A. Gross. "Characterization of moclobemideN-oxidation in human liver microsomes." Xenobiotica 31, no. 7 (January 2001): 387–97. http://dx.doi.org/10.1080/00498250110055488.

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Wynalda, M. A., K. M. Wynalda, B. M. Amore, P. E. Fagerness, and L. C. Wienkers. "Characterization of bropirimineO-glucuronidation in human liver microsomes." Xenobiotica 33, no. 10 (October 2003): 999–1011. http://dx.doi.org/10.1080/00498250310001602757.

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Mckillop, D., A. D. Mccormick, G. S. Miles, P. J. Phillips, K. J. Pickup, N. Bushby, and M. Hutchison. "In vitrometabolism of gefitinib in human liver microsomes." Xenobiotica 34, no. 11-12 (January 2004): 983–1000. http://dx.doi.org/10.1080/02772240400015222.

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Journal articles on the topic 'Human liver microsomes'

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