Gotowa bibliografia na temat „Novel glycolipids”

The addition of polyoxyethylene sorbitan monooleate (Tween 80) to a culture of mycobacteria greatly influences cell permeability and sensitivity to antibiotics but very little is known regarding the underlying mechanism. Here we show thatCorynebacterium matruchotii(surrogate of mycobacteria) converts Tween 80 to a structural series of polyoxyethylenic acids which are then used to form novel series-2A and series-2B glycolipids. Minor series-3 glycolipids were also synthesized. The polyoxyethylenic acids replaced corynomycolic acids in the cell wall. Correspondingly the trehalose dicorynomycolate content was reduced. MALDI mass spectrometry, MS-MS,1H-NMR, and13C-NMR were used to characterize the series-2 glycolipids. Series-2A glycolipid is trehalose 6-C36:2-corynomycolate-6′-polyoxyethylenate and series-2B glycolipid is trehalose 6-C36:2-corynomycolate-6′-furan ring-containing polyoxyethylenate.Mycobacterium smegmatisgrown in the presence of Tween 80 also synthesizes series-2 type glycolipids. The synthesis of these novel glycolipids in corynebacteria and mycobacteria should result in gross changes in the cell wall permeability and drug sensitivity.

Crude extracts of the North Sea marine sponge Pachymatisma johnstonia showed promising activity in a new assay for inhibitors of bacterial type III secretion. Bioassay-guided fractionation resulted in the isolation of the pachymosides, a new family of sponge glycolipids. A major part of the structural diversity in this family of glycolipids involves increasing degrees of acetylation and differing positions of acetylation on a common pachymoside glycolipid template. All of the metabolites with these variations in acetylation pattern were converted into the same peracetylpachymoside methyl ester (2) for purification and spectroscopic analysis. Pachymoside A (1) is the component of the mixture that has natural acetylation at the eight galactose hydroxyls and at the C-6 hydroxyls of glucose-B and glucose-D. Chemical degradation and transformation in conjunction with extensive analysis of 800 MHz NMR data was used to elucidate the structure of pachymoside A (1). Key words: Pachymatisma johnstonia, marine sponge, pachymoside, glycolipid.

Glycolipid biosurfactants are natural amphiphiles and have gained particular interest recently in their biodegradability, diversity, and bioactivity. Microbial infection has caused severe morbidity and mortality and threatened public health security worldwide. Glycolipids have played an important role in combating many diseases as therapeutic agents depending on the self-assembly property, the anticancer and anti-inflammatory properties, and the antimicrobial properties, including antibacterial, antifungal, and antiviral effects. Besides, their role has been highlighted as scavengers in impeding the biofilm formation and rupturing mature biofilm, indicating their utility as suitable anti-adhesive coating agents for medical insertional materials leading to a reduction in vast hospital infections. Notably, glycolipids have been widely applied to the synthesis of novel antimicrobial materials due to their excellent amphipathicity, such as nanoparticles and liposomes. Accordingly, this review will provide various antimicrobial applications of glycolipids as functional ingredients in medical therapy.

Glycolipids are found mainly in photosynthetic organisms (plants, algae, and cyanobacteria), Gram-positive bacteria, and a few other bacterial phyla. They serve as membrane lipids and play a role under phosphate deprivation as surrogates for phospholipids.Mesorhizobium lotiaccumulates different di- and triglycosyl diacylglycerols, synthesized by the processive glycosyltransferase Pgt-Ml, and two so far unknown glycolipids, which were identified in this study by mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy asO-methyl-digalactosyl diacylglycerol (Me-DGD) and glucuronosyl diacylglycerol (GlcAD). Me-DGD is a novel glycolipid, whose synthesis depends on Pgt-Ml activity and the involvement of an unknown methyltransferase, while GlcAD is formed by a novel glycosyltransferase encoded by the open reading frame (ORF)mlr2668, using UDP-glucuronic acid as a sugar donor. Deletion mutants lacking GlcAD are not impaired in growth. Our data suggest that the different glycolipids inMesorhizobiumcan mutually replace each other. This may be an adaptation mechanism to enhance the competitiveness in natural environments. A further nonphospholipid inMesorhizobiumwas identified as a hydroxylated form of an ornithine lipid with the additional hydroxy group linked to the amide-bound fatty acid, introduced by the hydroxylase OlsD. The presence of this lipid has not been reported for rhizobia yet. The hydroxy group is placed on the C-2 position of the acyl chain as determined by NMR spectroscopy. Furthermore, the isolated ornithine lipids contained up to 80 to 90%d-configured ornithine, a stereoform so far undescribed in bacteria.

A novel Gram-stain-negative, aerobic and rod-shaped halophilic archaeon, designated HD8-45T, was isolated from the red brine of salted brown alga Laminaria produced at Dalian, PR China. According to the results of 16S rRNA gene and rpoB′ gene sequence comparisons, strain HD8-45T showed the highest sequence similarity to the corresponding genes of Salinirussus salinus YGH44T (95.1 and 85.2 % similarities, respectively), Halovenus aranensis EB27T (91.2 and 86.0 % similarities, respectively). The low sequence similarity and the phylogeny implied the novel generic status of strain HD8-45T. Genomic relatedness analyses showed that strain HD8-45T were clearly distinguished from other species in the order Halobacteriales , with average nucleotide identity, amino acid identity and in silico DNA–DNA hybridization values not more than 75.1, 65.6 and 21.5 %. The polar lipid pattern contained phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, two major glycolipids and two minor glycolipids. The two major glycolipids and a minor glycolipid were chromatographically identical to disulfated mannosyl glucosyl diether, sulfated mannosyl glucosyl diether and mannosyl glucosyl diether, respectively. The major respiratory quinones were menaquinone MK-8 and MK-8(H2). The DNA G+C content was 62.0 mol% (Tm ) and 61.9 mol% (genome). All these results showed that strain HD8-45T represents a novel species of a new genus in the order Halobacteriales , for which the name Salinibaculum litoreum gen. nov., sp. nov. is proposed. The type strain of Salinibaculum litoreum is HD8-45T (=CGMCC 1.15328T=JCM 31107T).

Abstract Invariant natural killer T cells are known to have marked immunomodulatory capacity due to their ability to produce copious amounts of effector cytokines. In this study, we report the first crystal structures of a novel class of strong Th1 biasing structural analogues of α-galactosylceramide by addition of aromatic structures on the 6-OH position of galactose. They are characterized by marked Th1 polarized cytokine patterns that are highly conserved between mice and men, and marked tumour protection in vivo. The strength of the Th1 response correlates well with enhanced lipid binding to CD1d as a result of an induced fit mechanism that binds the aromatic substitution as a third anchor, in addition to the two lipid chains. This induced fit is in contrast to another Th1 biasing glycolipid, α-C-GalCer, whose CD1d binding follows a conventional key-lock principle. These findings highlight the previously unexploited flexibility of CD1d in accommodating galactose-modified glycolipids and broaden the range of glycolipids that can stimulate iNKT cells. We speculate that glycolipids can be designed that induce a similar fit, thereby leading to superior and more sustained iNKT cell responses in vivo.

The Phytomonas spp. are trypanosomatid parasites of plants. A polar glycolipid fraction of a Phytomonas sp., isolated from the plant Euphorbia characias and grown in culture, was fractionated into four major glycolipid species (Phy 1-4). The glycolipids were analysed by chemical and enzymic modifications, composition and methylation analyses, electrospray mass spectrometry and microsequencing after HNO2 deamination and NaB3H4 reduction. The water-soluble headgroup of the Phy2 glycolipid was also analysed by 1H NMR. All four glycolipids were shown to be glycoinositol-phospholipids (GIPLs) with phosphatidylinositol (PI) moieties containing the fully saturated alkylacylglycerol lipids 1-O-hexadecyl-2-O-palmitoylglycerol and 1-O-hexadecyl-2-O-stearoylglycerol. The structures of the Phy 1-4 GIPLs are: Man alpha 1-2Man alpha 1-6Man alpha 1-4GlcN alpha 1-6PI, Glc alpha 1-2(NH2-CH2CH2-HPO4-)Man alpha 1-2Man alpha 1-6Man alpha 1-4GlcN alpha 1-6PI, [formula: see text] Glc alpha 1-2(NH2CH2CH2-HPO4-)Man alpha 1-2Man alpha 1-6Man alpha 1-4(NH2-CH2CH2-HPO4-)GlcN alpha 1-6PI [formula: see text] and Glc alpha 1-2Glc alpha 1-2(NH2CH2-CH2-HPO4-)Man alpha 1-2Man alpha 1-6Man alpha 1-4(NH2CH2CH2-HPO4-)-GlcN alpha 1-6PI. [formula: see text] The Phytomonas GIPLs represent a novel series of structures. This is the first description of the chemical structure of cell-surface molecules of this plant pathogen. The Phytomonas GIPLs are compared with those of other trypanosomatid parasites and are discussed with respect to trypanosomatid phylogenetic relationships.

In synthetic biology approaches, lipid vesicles are widely used as protocell models. While many compounds have been encapsulated in vesicles (e.g. DNA, cytoskeleton and enzymes), the incorporation of glycocalyx components in the lipid bilayer has attracted much less attention so far. In recent years, glycoconjugates have been integrated in the membrane of giant unilamellar vesicles (GUVs). These minimal membrane systems have largely contributed to shed light on the molecular mechanisms of cellular processes. In this review, we first introduce several preparation and biophysical characterization methods of GUVs. Then, we highlight specific applications of protocells investigating glycolipid-mediated endocytosis of toxins, viruses and bacteria. In addition, we delineate how prototissues have been assembled from glycan-decorated protocells by using lectin-mediated cross-linking of opposed glycoreceptors (e.g. glycolipids and glycopeptides). In future applications, glycan-decorated protocells might be useful for investigating cell–cell interactions (e.g. adhesion and communication). We also speculate about the implication of lectin–glycoreceptor interactions in membrane fusion processes.

The glycolipid α-galactosyl ceramide, α-GalCer, has been shown to stimulate the proliferation of murine spleen cells and activate the immune system. Stimulation occurs through binding of the glycolipid to the protein CD1d. Subsequent presentation of the CD1d−glycolipid complex to invariant Natural Killer T cells (iNKT cells) initiates the proliferation of a host of cytokines leading to an immune response The therapeutic potential of α-GalCer is currently being explored; however the induction of both Th1 and Th2 cytokines by this agent is likely to limit its therapeutic application. Significantly, analogues of α-GalCer have been shown to induce iNKT cell-derived cytokines more selectively through a skewed Th1-Th2 response. To date, very few alterations around the amide bond have been explored. To investigate its importance in iNKT cell stimulation, a range of α-GalCer and threitol ceramide (ThrCer) analogues has been synthesised in which the amide functionality in these two leads has been replaced with different carbonyl functional groups. These compounds have been tested for iNKT cell induction and in particular their Th1/Th2 response, which determined their therapeutic potential. Labelled derivatives of α-GalCer and ThrCer have also been designed and synthesised to find application in lipid trafficking studies.

New glycolipids and a benzylammonium lipid were rationally designed by varying the chemical structure of a D-glucose-derived hit compound active as lipid A antagonist. We report the synthesis of these compounds, their in vitro activity as lipid A antagonists on HEK cells and the capacity to inhibit LPS-induced septic shock in vivo. The lack of toxicity and the good in vivo activity suggest the use of some compounds of the panel as hits for anti-sepsis drug development. In addition in the studies presented in this PhD thesis new classes of natural compounds are tested for their ability to interact with TLR4 receptor complex.

NKT cells are an important part of human immune system and recognize a specific set of antigens called glycolipids. Only a handful of "natural" NKT cell antigens are known till date. Although NKT cells play a protective role against pathogenic organisms, imbalances in NKT cell functions are implicated in many diseases including asthma. Allergic asthma, a Th2 driven inflammation of airways, is primarily caused by inhalation of environmental allergens. In the last decade, inhaled allergen Aspergillus fumigatus has been under scrutiny for the presence of NKT cell antigens that might trigger asthma. We successfully isolated, characterized and synthesized a "natural" antigenic glycolipid which activates NKT cells in CD1d dependent manner. When this glycolipid is administered intranasally to mice, WT but not CD1d-/- mice developed airway hyperreactivity (AHR), which is a cardinal feature of asthma. Our results indicate that this glycolipid also triggers the production of key cytokines responsible for development of airway hyperreactivity, namely IL-4 and IL-13. Widespread use of antibiotics has convoluted the problem of antimicrobial resistance. Our research group has developed a novel class of antimicrobial peptide mimics called Ceragennins. These cholic acid based antimicrobial compounds have many desirable properties including low MICs, effectiveness against biofilms, and relatively low manufacturing cost. In order to advance the clinical development of Ceragennins, we developed analytical methods for qualitative and quantitative determination of these compounds in complex biological matrices. These methods were also used for carrying out the stability studies of Ceragenins under varying pH and temperatures

Invariant NKT (iNKT) cells are a subset of T lymphocytes that express an invariant \(\alpha\) \(\beta\) T cell receptor (TCR) as well as an NK1.1 marker. They play an important role in autoimmune diseases, such as type I diabetes and lupus. In contrast to conventional CD4+ and CD8+ T lymphocytes that recognise foreign peptides bound to the major histocompatibility complex (MHC) class I or MHC class II, iNKT cells recognise a range of foreign lipids and glycolipids bound to CD1d proteins. \(\alpha\) \(\beta\)-Galactosyl Ceramide (\(\alpha\) \(\beta\)GalCer), originally isolated from a marine sponge, is a powerful agonist of CD1d capable of triggering an immune response that results in the proliferation of a range of regulatory cytokines, including IFN-\(_y\) (Th1), as well as IL-4 (Th2). This mixed cytokine response (i.e. Th1 and Th2), combined with the “unresponsive state” of iNKT cells after activation with \(\alpha\)GalCer, limits the therapeutic potential of this agonist. To address some of these issues, we have also synthesised an \(\alpha\)GalCer analogue, namely Threitol Ceramide (ThrCer), that exhibits attenuated activity relative to \(\alpha\)GalCer. ThrCer is a truncated analogue of \(\alpha\)GalCer that conserves the stereochemistry of the hydroxyl functions present in \(\alpha\)GalCer and that exhibit a much stronger ether bond under acidic hydrolysis linking the sugar moiety with ceramide than the glycosidic bond in \(\alpha\)GalCer. We have labelled ThrCer with a biotin residue and with a 14C radiolabel, and our collaborators have used these derivatives to show that ThrCer behaves similarly to \(\alpha\)GalCer in endogenous lipid trafficking and its tissue distribution in vivo. We have also made advances towards the stereoselective synthesis of recently discovered natural agonists of iNKT cells from pathogenic origin, namely \(\alpha\)-galactosyl diacylglycerol (\(\alpha\)GalDAG).

The development of novel medicinal agents is becoming increasingly important in solving several serious healthcare issues. Tuberculosis (TB) is among one of the world’s most serious health threats, especially in developing countries, and although treatment is available, current methods take 6 – 24 months. Prolonged treatment times often result in noncompliance and subsequently result in selection for drug resistance. As there are several multidrug resistant strains of Mycobacterium tuberculosis current treatment methods are proving inadequate, and it is becoming more and more essential to develop novel drugs to control the incidence and spread of TB; alongside other pathogenic bacterial species of clinical importance. Three major approaches towards the creation of novel antitubercular and antimicrobial agents and treatment regimens through the use of carbohydrate-based chemistry were explored within this project; (i) structure-based drug design and synthesis of novel competitive inhibitors targeting mycolic acid synthesis of M. tuberculosis (Chapter 1 & 2); (ii) modification of aminoglycosides (AGs) through amphiphilic substitution, aimed to restore activity towards resistant bacteria or create agents with novel mechanisms of action (Chapter 3 & 4); (iii) the development of novel liposomal drug carriers to selectively deliver therapeutics towards severe intracellular respiratory infections (Chapter 5 & 6). Mycolic acids are essential for the growth and survival of M. tuberculosis, making mycolic acid inhibition a highly promising drug target for treating TB. Recently, a novel pathway of fatty acid synthesis has been identified as a promising drug target. FadD32, a fatty acyl-AMP ligase (FAAL) involved in the progression of TB represents a promising target for novel drug design. A family of sulfonylacetamide compounds have shown promising preliminary results in treating TB, however these failed within in vivo experiments due to their poor pharmacokinetic properties. Further development of these lead compounds with a rational structure-based drug design approach, led to the design and synthesis of compounds directly targeting the FadD32 biosynthetic pathway. This synthesised library of compounds were evaluated for their antitubercular inhibitory effect and several lead structures were identified. The most potent derivatives synthesised within this study displayed an MIC90 of 13 – 16 μg/mL towards M. tuberculosis (H37Rv) within a normoxic resazurin reduction microplate assay. Structural modification of the AG scaffold has historically remained a successful approach towards creating novel antibiotics. This approach led to the discovery of amikacin, a potent AG that is used for the treatment of TB today. Recently, a new class of antibiotics derived from the AG scaffold has produced several promising lead compounds that have revived antimicrobial activities against drug resistant bacterial species of clinical importance. This new class of antimicrobial agents are derived from conjugation of hydrophobic groups to AGs, creating semi-synthetic amphiphilic aminoglycosides (AAGs). AAGs have shown promising preliminary results against several drug resistant bacterial strains, including mycobacteria by evading common mechanisms of resistance and exerting novel mechanisms of action. A variety of novel and structurally diverse AAGs have been synthesised within this study providing lead structures with promising activity for the development of antimicrobial agents. A series of AAGs synthesised from the scaffolds of amikacin, kanamycin and neomycin were synthesised by conjugation of several hydrophobic groups to the AG scaffold. Derivatives were prepared by utilizing either the active functionality from the sulfonylacetamides conjugated via amide or triazole linkers; or by an alternative prodrug-based strategy utilizing long alkyl chains conjugated via ester linkages. Due to AGs broad-spectrum antibacterial activities, these compounds were evaluated for their antimicrobial inhibitory effect towards M. tuberculosis and S. aureus. Several structures were identified to display potent antitubercular activities. One of the kanamycin-based prodrugs was found to exert an increased antitubercular activity in comparison to the parent scaffold (MIC90 3 μg/mL), while amikacin derivatives maintained significant inhibitory effect (MIC90 3 – 6 μg/mL). The most active AAG utilizing the active functionality of the sulfonylacetamides was an amide-linked conjugate of amikacin (MIC90 22 μg/mL). Intracellular infections from bacterial pathogens such as M. tuberculosis are the causative agents of several serious diseases worldwide. Although the mononuclear phagocyte system primarily consists of macrophages, and constitutes the primary line of defence against infections, several bacterial pathogens have evolved the ability to survive and reproduce within intracellular host organelles. Intracellular infections are difficult to eradicate through traditional chemotherapeutic approaches due to the poor intracellular penetration of antibiotics. Moreover, the resulting low intracellular concentration of antibiotics is often ineffective against intracellular pathogens and furthermore promotes the development of drug resistance. Consequently, novel approaches to improve therapeutic effectiveness must be considered to advance treatment towards persistent intracellular bacterial infections. Nanoparticle-based drug delivery systems are one such approach; enabling improved antibiotic bioavailability and targeted site-specific drug delivery, offering the ability to overcome the less than desirable effects most antibiotics display towards intracellular pathogens. Liposomal drug delivery vectors are the most established and investigated nanocarriers, offering nontoxic biological delivery systems that can enhance the antimicrobial efficiency and therapeutic index of various chemotherapeutics. Liposomes provide unique delivery systems for antibiotics, such as AGs, as they can enhance efficiency whilst decreasing toxicity. Liposomal encapsulated AGs have demonstrated enhanced bactericidal activity towards intracellular infections in vitro and in vivo. Liposomal encapsulated amikacin has demonstrated its effectiveness in clinical trials and is currently FDA approved for the treatment of Mycobacterium avium complex. Within this study, amphiphilic-based prodrug derivatives of amikacin and mannosylated targeting ligands were utilized to formulate novel liposomal preparations for the treatment of pulmonary infections. Amphiphilic derivatization of amikacin allowed passive drug loading of the active therapeutic within the lipid bilayer, providing improved drug loading capacities compared to conventional approaches of loading amikacin within the aqueous core. Additionally, incorporation of the therapeutic AAG within the bilayer resulted in vesicles with improved membrane stability and more desirable physiochemical properties compared to conventional formulations. To test these liposomal formulations as a delivery system against intracellular pathogens in vitro, a murine macrophage cell line expressing mannose receptor (RAW264.7) was infected with S. aureus and bacterial inhibition was determined. All formulations displayed concentration-dependent killing efficiencies, while some were capable of complete intracellular bacterial inhibition at higher concentrations. The lipid derivatized amikacin-based prodrug delivery systems provide a novel liposomal delivery platform for intracellular infections, whilst offering the potential to overcome the shortcomings of current liposomal formulations such as poor stability and drug leakage. Once realized, this application could improve treatment towards serious intracellular pulmonary infections such as M. tuberculosis.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Institute for Glycomics
Griffith Health
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Development and design of sustainable cosmetic products is a key R&D priority across all the cosmetic and personal care companies. This is primarily due to the focus on addressing the strong consumer driver for cosmetic products that do not have a negative environmental footprint. This has led to the rapid development of new formulations where traditional ingredients such as synthetic surfactants, polymers, silicone oils etc are being replaced by more sustainable alternatives such as biosurfactants, biobased surfactants, biopolymers, natural oils. This replacement of traditional ingredients by more sustainable alternatives however is not trivial as re-building the performance of traditional ingredients is highly challenging. This is specifically true of oil-in-water and water-in-oil based emulsion systems which constitute a large majority of cosmetic products. The stability, texture/rheology/sensory has to be re-engineered in these sustainable formulations. This re-engineering of the formulations however does additionally present opportunities to build in new performance attributes and to additionally engineeer in smart or stimuli responsive behavior.This study will report on the formulation design of several novel sustainable emulsion systems-a thermo-responsive whey protein/chitosan oil-in-water emulsion system, a glycolipid/silica particle water-in-oil emulsion system, a thermo-responsive methylcellulose/chitosan hydrogel system incorporating an EGF (epidermal growth factor). The ability to tune the rheology and rheological response to external stimuli to deliver performance benefits will be illustrated.