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Human Microsomes (human + microsome)
Selected AbstractsMetabolism of methoxymorpholino-doxorubicin in rat, dog and monkey liver microsomes: comparison with human microsomesFUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 6 2001Dominique Beulz-Riche The morpholino anthracycline, methoxymorpholino-doxorubicin (MMDx) is a novel anticancer agent. The metabolism of this highly lipophilic doxorubicin analogue is not fully elucidated. MMDx is metabolically activated in vivo, resulting in an 80-fold increase in potency over the parent drug. In this study, MMDx in vitro metabolism was compared in rat, dog, monkey and human liver microsomes. When microsomal fractions were incubated with MMDx, 6,8 metabolites were formed depending on the species and on the substrate concentrations. Among these eight metabolites, three comigrated with authentic standards, namely MMDx-ol, PNU156686 and PNU159682, and the five others are in the process of being characterized. Quantitatively, monkey and human metabolize MMDx with a higher rate than rat and dog. Qualitatively, MMDx metabolic profile in dog microsomes was different from the three other species. MMDx-ol was predominant in dog and only minor in other species. In conclusion, MMDx metabolism was species-different. Rat and monkey liver microsomes may be used as models to study MMDx metabolism in humans. Dog liver microsomes may be a good model for studying the formation of MMDx-ol. [source] Structure elucidation of aplidine metabolites formed in vitro by human liver microsomes using triple quadrupole mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2005Esther F. A. Brandon Abstract The cyclic depsipeptide aplidine is a new anti-cancer drug of marine origin. Four metabolites of this compound were found after incubation with pooled human microsomes using gradient high-performance liquid chromatography with ultraviolet detection. After chromatographic isolation, the metabolites have been identified using nano-electrospray triple quadrupole mass spectrometry. A highly specific sodium-ion interaction with the cyclic structure opens the depsipeptide ring, and cleavage of the amino acid residues gives sequence information when activated by collision-induced dissociation in the second quadrupole. The aplidine molecule could undergo the following metabolic reactions: hydroxylation at the isopropyl group (metabolites apli-h 1 and apli-h 2); C-dealkylation at the N(Me)-leucine group (metabolite apli-da); hydroxylation at the isopropyl group and C-dealkylation at the N(Me)-leucine group (metabolite apli-da/h), and C-demethylation at the threonine group (metabolite apli-dm). The identification of these metabolites formed in vitro may greatly aid the elucidation of the metabolic pathways of aplidine in humans. Copyright © 2005 John Wiley & Sons, Ltd. [source] Lack of appreciable species differences in nonspecific microsomal bindingJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2010Ying Zhang Abstract Species differences in microsomal binding were evaluated for 43 drug molecules in human, monkey, dog and rat liver microsomes, using a fixed concentration of microsomal protein. The dataset included 32 named drugs and 11 proprietary compounds encompassing a broad spectrum of physicochemical properties (11 acids, 24 bases, 8 neutral, c,log,D ,1 to 7, MW 200 to 700 and free fraction <0.001 to 1). Free fractions (fu,mic) in monkey, dog, rat and human microsomes were highly correlated, with linear regression correlation coefficients greater than 0.97. The average fold-difference in fu,mic between monkey, dog, or rat, and human was 1.6-, 1.3-, and 1.5-fold, respectively. Species differences in fu,mic were also assessed for a range of microsomal protein concentrations (0.2,2,mg/mL) for midazolam, clomipramine, astemizole, and tamoxifen, drugs with low to high microsomal binding. The mean fold species-difference in fu,mic for midazolam, clomipramine, astemizole, and tamoxifen was 1.1-, 1.2-, 1.3-, and 2.0-fold, respectively, and was independent of normalized microsomal protein concentration. For a fixed concentration of microsomal protein, greater than 76% and 90% of drugs examined in this study had preclinical species fu,mic within 1.5- and 2-fold, respectively, of experimentally measured human values. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:3620,3627, 2010 [source] In vitro Metabolism of Genistein and Tangeretin by Human and Murine Cytochrome P450sBASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 1 2003Vibeke M. Breinholt Analysis of the metabolic profile from incubations with genistein and human liver microsomes revealed the production of five different metabolites, of which three were obtained in sufficient amounts to allow a more detailed elucidation of the structure. One of these metabolites was identified as orobol, the 3,-hydroxylated metabolite of genistein. The remaining two metabolites were also hydroxylated metabolites as evidenced by LC/MS. Orobol was the only metabolite formed after incubation with CYP1A2. The two major product peaks after incubation of tangeretin with human microsomes were identical with 4,-hydroxy-5,6,7,8-tetramethoxyflavone and 5,6-dihydroxy-4,,7,8-trimethoxyflavone, previously identified in rat urine in our laboratory. By comparison with UV spectra and LC/MS fragmentation patterns of previously obtained standards, the remaining metabolites eluting after 14, 17 and 20 min. were found to be demethylated at the 4,,7-, 4,,6-positions or hydroxylated at the 3,- and demethylated at the 4,-positions, respectively. Metabolism of tangeretin by recombinant CYP1A2, 3A4, 2D6 and 2C9 resulted in metabolic profiles that qualitatively were identical to those observed in the human microsomes. Inclusion of the CYP1A2 inhibitor fluvoxamine in the incubation mixture with human liver microsomes resulted in potent inhibition of tangeretin and genistein metabolism. Other isozymes-selective CYP inhibitors had only minor effects on tangeretin or genistein metabolism. Overall the presented observations suggest major involvement of CYP1A2 in the hepatic metabolism of these two flavonoids. [source] Resveratrol is efficiently glucuronidated by UDP-glucuronosyltransferases in the human gastrointestinal tract and in Caco-2 cellsBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 4 2006Nicole Sabolovic Abstract Resveratrol (3, 5, 4,-trihydroxy- trans -stilbene), a natural polyphenol present in grapes and peanuts, has been reported to exert a variety of potentially therapeutic effects. The aim of this study was to determine the contribution of the gastrointestinal (GI) tract to the glucuronidation of this compound and its cis -isomer, which also occurs naturally. For this purpose, glucuronidation of the two resveratrol isomers was investigated in human microsomes prepared from: stomach, duodenum, four segments of the remaining small intestine (S-1 to S-4) and colon, and from the human intestinal cell lines Caco-2 and PD-7. cis - and trans -Resveratrol were efficiently glucuronidated in the GI tract with the formation of both 3- O - and 4,- O -glucuronides, however, the two stereoisomers were glucuronidated at different rates depending on the donor and the segment considered. Microsomes prepared from Caco-2 and PD-7 cells also efficiently glucuronidated cis -resveratrol and, to a lesser extent, the trans -isomer, however, only the 3- O -glucuronide was formed. Among the UDP-glucuronosyltransferases (UGT) that are known to be expressed in the GI tract, the isoforms UGT1A1, 1A6, 1A8, 1A9 and 1A10 were active in glucuronidating trans - and/or cis -resveratrol. The results demonstrate that the GI tract may contribute significantly to the first pass metabolism of these naturally occurring polyphenols. Copyright © 2006 John Wiley & Sons, Ltd. [source] Equally potent inhibitors of cholesterol synthesis in human hepatocytes have distinguishable effects on different cytochrome P450 enzymesBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 9 2000L.H. Cohen Abstract Six 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (the present cholesterol-lowering drugs known as statins), lovastatin (L), simvastatin (S), pravastatin (P), fluvastatin (F), atorvastatin (A) and cerivastatin (C) are shown to be potent inhibitors of cholesterol synthesis in human hepatocytes, the target tissue for these drugs in man. All six inhibited in the nM range (IC50 values: 0.2,8.0 nM). As daily used cholesterol-lowering drugs they are likely coadministered with other drugs. While several cytochrome P450 (CYP) enzymes are involved in drug metabolism in the liver and thus play an important role in drug,drug interaction it was investigated which of these enzymes are influenced by the active forms of the six statins. These enzyme activities were studied in human liver microsomal preparations, and in simian and human hepatocytes in primary culture. The following CYP reactions were used: nifedipine aromatization (CYP3A4), testosterone 6,-hydroxylation (CYP3A4), tolbutamide methylhydroxylation (CYP2C9), S -mephenytoin 4-hydroxylation (CYP2C19), bufuralol 1,-hydroxylation (CYP2D6), aniline 4-hydroxylation (CYP2E1), coumarin 7-hydroxylation (CYP2A6) and 7-ethoxyresorufin O -dealkylation (CYP1A1/2). In the human liver microsomes the statins (concentrations up to 400 µM) did not influence the CYP1A1/2 activity and hardly the CYP2A6 and CYP2E1 activities. Except P, the other five statins were stronger inhibitors of the CYP2C19 activity with IC50 values around 200 µM and the same holds for the effect of A, C and F on the CYP2D6 activity. L and S were weaker inhibitors of the latter enzyme activity, whereas P did not influence both activities. About the same was observed for the statin effect on CYP2C9 activity, except that F was a strong inhibitor of this activity (IC50 value: 4 µM). Using the assay of testosterone 6,-hydroxylation the CYP3A4 activity was decreased by L, S and F with IC50 values of about 200 µM and a little more by C and A (IC50 around 100 µM). P had hardly an effect on this activity. To a somewhat less extent the same trend was seen when CYP3A4 activity was measured using nifedipine as substrate. The inhibitory effects observed in microsomes were verified in suspension culture of freshly isolated hepatocytes from Cynomolgus monkey (as a readily available model) and of human hepatocytes. In general the same trends were seen as in the human microsomes, except that in some cases the inhibition of the CYP activity was less, possibly by the induction of the particular CYP enzyme by incubation of the cells with a particular statin. F remained a strong inhibitor of CYP2C9 activity in human and monkey hepatocytes. A induced the CYP2C9 in monkey hepatocytes but was an inhibitor of the CYP2C9 in human hepatocytes. A, S, L and C were moderate inhibitors in both cellular systems of CYP3A4. P was not affecting any of the CYP activities in the three systems studied. It is concluded that different CYP enzymes interact with different statins and therefore differences in between these drugs are to be expected when drug,drug interaction is considered. Copyright © 2000 John Wiley & Sons, Ltd. [source] | |||||||||||||