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Karl Walter Bock - One of the best experts on this subject based on the ideXlab platform.
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Human UDP-glucuronosyltransferases: Feedback loops between substrates and ligands of their transcription factors
Biochemical Pharmacology, 2012Co-Authors: Karl Walter BockAbstract:Expression profiles of human adult and fetal hepatic and intestinal UDP-glucuronosyltransferases (UGTs), information about their endo- and xenobiotic substrates, and their transcriptional regulation suggests regulatory circuits between some UGT substrates and ligands of their transcription factors. For examples: (i) bilirubin is solely conjugated by UGT1A1 and activates its transcription factors Ah receptor, PXR and CAR. (ii) Hepatotoxic lithocholic acid (LCA) is oxidized to hyodeoxycholic acid, the latter conjugated by UGT2B4 and UGT2B7. LCA is also an agonist of FXR and PPARα, which are controlling these UGTs. (iii) Similar feedback loops possibly exist between some eicosanoids, PPARα and UGTs. (iv) Regulatory circuits may also have evolved between dietary polyphenols, which are efficient substrates of UGTs and activators of the Ah receptor. Although many newly developed drugs are conjugated by promiscuous UGTs, the discussed regulatory circuits may provide hints to evolutionary important UGT substrates.
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Human UDP-glucuronosyltransferases: Feedback loops between substrates and ligands of their transcription factors
Biochemical Pharmacology, 2012Co-Authors: Karl Walter BockAbstract:Expression profiles of human adult and fetal hepatic and intestinal UDP-glucuronosyltransferases (UGTs), information about their endo- and xenobiotic substrates, and their transcriptional regulation suggests regulatory circuits between some UGT substrates and ligands of their transcription factors. For examples: (i) bilirubin is solely conjugated by UGT1A1 and activates its transcription factors Ah receptor, PXR and CAR. (ii) Hepatotoxic lithocholic acid (LCA) is oxidized to hyodeoxycholic acid, the latter conjugated by UGT2B4 and UGT2B7. LCA is also an agonist of FXR and PPARα, which are controlling these UGTs. (iii) Similar feedback loops possibly exist between some eicosanoids, PPARα and UGTs. (iv) Regulatory circuits may also have evolved between dietary polyphenols, which are efficient substrates of UGTs and activators of the Ah receptor. Although many newly developed drugs are conjugated by promiscuous UGTs, the discussed regulatory circuits may provide hints to evolutionary important UGT substrates. © 2012 Elsevier Inc.
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Functions and transcriptional regulation of adult human hepatic UDP-glucuronosyl-transferases (UGTs): mechanisms responsible for interindividual variation of UGT levels.
Biochemical Pharmacology, 2010Co-Authors: Karl Walter BockAbstract:Abstract Ten out of 19 UDP-glucuronosyltransferases (UGTs) are substantially expressed in adult human liver (>1% of total UGTs); 5 UGT1 isoforms (UGT1A1, 1A3, 1A4, 1A6 and 1A9) and 5 UGT2 family members (UGT2B4, 2B7, 2B10, 2B15 and 2B17) (Izukawa et al. [11] ). Surprisingly, UGT2B4 and UGT2B10 mRNA were found to be abundant in human liver suggesting an underestimated role of the liver in detoxification of their major substrates, bile acids and eicosanoids. Among factors responsible for high interindividual variation of hepatic UGT levels (genetic diversity including polymorphisms and splice variants, regulation by liver-enriched transcription factors such as HNF1 and HNF4, and ligand-activated transcription factors) nuclear receptors (PXR, CAR, PPARα, etc.), and the Ah receptor are discussed. Unraveling the mechanisms responsible for interindividual variation of UGT expression will be beneficial for drug therapy but still remains a major challenge.
Moshe Finel - One of the best experts on this subject based on the ideXlab platform.
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clopidogrel carboxylic acid glucuronidation is mediated mainly by ugt2b7 UGT2B4 and ugt2b17 implications for pharmacogenetics and drug drug interactions
Drug Metabolism and Disposition, 2018Co-Authors: Helina Kahma, Moshe Finel, Anne M Filppula, Mikko Neuvonen, Katriina E Tarkiainen, Aleksi Tornio, Mikko T Holmberg, Matti K Itkonen, Pertti J Neuvonen, Mikko NiemiAbstract:The antiplatelet drug clopidogrel is metabolized to an acyl- β -d-glucuronide, which causes time-dependent inactivation of CYP2C8. Our aim was to characterize the UDP-glucuronosyltransferase (UGT) enzymes that are responsible for the formation of clopidogrel acyl- β -d-glucuronide. Kinetic analyses and targeted inhibition experiments were performed using pooled human liver and intestine microsomes (HLMs and HIMs, respectively) and selected human recombinant UGTs based on preliminary screening. The effects of relevant UGT polymorphisms on the pharmacokinetics of clopidogrel were evaluated in 106 healthy volunteers. UGT2B7 and UGT2B17 exhibited the greatest level of clopidogrel carboxylic acid glucuronidation activities, with a CL int,u of 2.42 and 2.82 µ l⋅min −1 ⋅mg −1 , respectively. Of other enzymes displaying activity (UGT1A3, UGT1A9, UGT1A10-H, and UGT2B4), UGT2B4 (CL int,u 0.51 µ l⋅min −1 ⋅mg −1 ) was estimated to contribute significantly to the hepatic clearance. Nonselective UGT2B inhibitors strongly inhibited clopidogrel acyl- β -d-glucuronide formation in HLMs and HIMs. The UGT2B17 inhibitor imatinib and the UGT2B7 and UGT1A9 inhibitor mefenamic acid inhibited clopidogrel carboxylic acid glucuronidation in HIMs and HLMs, respectively. Incubation of clopidogrel carboxylic acid in HLMs with UDPGA and NADPH resulted in strong inhibition of CYP2C8 activity. In healthy volunteers, the UGT2B17*2 deletion allele was associated with a 10% decrease per copy in the plasma clopidogrel acyl- β -d-glucuronide to clopidogrel carboxylic acid area under the plasma concentration-time curve from 0 to 4 hours (AUC 0–4 ) ratio ( P β -d-glucuronide is impaired in carriers of the UGT2B17 deletion. These findings may have implications regarding the intracellular mechanisms leading to CYP2C8 inactivation by clopidogrel.
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The Configuration of the 17-Hydroxy Group Variably Influences the Glucuronidation of β-Estradiol and Epiestradiol by Human UDP-Glucuronosyltransferases
Drug Metabolism and Disposition, 2008Co-Authors: Katrina Itaaho, Peter I Mackenzie, Shin Ichi Ikushiro, John O. Miners, Moshe FinelAbstract:The glucuronidation of 17β-estradiol (β-estradiol) and 17α-estradiol (epiestradiol) was studied to elucidate how the orientation of the 17-OH group affects conjugation at the 3-OH or the 17-OH of either diastereomer. Recombinant human UDP-glucuronosyltransferases (UGTs) UGT1A1, UGT1A3, UGT1A7, UGT1A8, and UGT1A10 conjugated one or both diastereomers, mainly at the 3-OH. The activity of UGT1A4 was low and unique because it was directed merely toward the 17-OH of both aglycones. UGT1A10 exhibited particularly high estradiol glucuronidation activity, the rate and affinity of which were significantly higher in the case of β-estradiol than with epiestradiol. UGT1A9 did not catalyze estradiol glucuronidation, but UGT1A9-catalyzed scopoletin glucuronidation was competitively inhibited by β-estradiol. UGT2B4, UGT2B7, and UGT2B17 exclusively conjugated the estradiols at the 17-OH position in a highly stereoselective fashion. UGT2B4 was specific for epiestradiol; UGT2B7 glucuronidated both diastereomers, with high affinity for epiestradiol, whereas UGT2B17 only glucuronidated β-estradiol. UGT2B15 glucuronidated both estradiols at the 3-OH, with a strong preference for epiestradiol. Human UGT2A1 and UGT2A2 glucuronidated both diastereoisomers at both hydroxyl groups. Microsomal studies revealed that human liver mainly yielded epiestradiol 17- O -glucuronide, and human intestine primarily yielded β-estradiol 3- O -glucuronide, whereas rat liver preferentially formed β-estradiol 17- O -glucuronide. Of the three recombinant rat UGTs that were examined in this study, rUGT2B1 was specific for the 17-OH of β-estradiol, rUGT2B2 did not catalyze estradiol glucuronidation, whereas rUGT2B3 exhibited high activity toward the 17-OH in both diastereoisomers. The results show that although many UGTs can catalyze estradiol glucuronidation, there are marked differences in their kinetics, regioselectivity, and stereoselectivity.
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substrate specificity of the human udp glucuronosyltransferase UGT2B4 and ugt2b7 identification of a critical aromatic amino acid residue at position 33
FEBS Journal, 2007Co-Authors: Lydia Barre, Pierre Netter, Moshe Finel, Jacques Magdalou, Sylvie Fournelgigleux, Mohamed OuzzineAbstract:The human UDP-glucuronosyltransferase (UGT) isoforms UGT2B4 and UGT2B7 play a major role in the detoxification of bile acids, steroids and phenols. These two isoforms present distinct but overlapping substrate specificity, sharing common substrates such as the bile acid hyodeoxycholic acid (HDCA) and catechol-estrogens. Here, we show that in UGT2B4, substitution of phenylalanine 33 by leucine suppressed the activity towards HDCA, and impaired the glucuronidation of several substrates, including 4-hydroxyestrone and 17-epiestriol. On the other hand, the substrate specificity of the mutant UGT2B4F33Y, in which phenylalanine was replaced by tyrosine, as found at position 33 of UGT2B7, was similar to wild-type UGT2B4. In the case of UGT2B7, replacement of tyrosine 33 by leucine strongly reduced the activity towards all the tested substrates, with the exception of 17-epiestriol. In contrast, mutation of tyrosine 33 by phenylalanine exhibited similar or even somewhat higher activities than wild-type UGT2B7. Hence, the results strongly indicated that the presence of an aromatic residue at position 33 is important for the activity and substrate specificity of both UGT2B4 and UGT2B7.
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Substrate specificity of the human UDP-glucuronosyltransferase UGT2B4 and UGT2B7
FEBS Journal, 2007Co-Authors: Lydia Barre, Pierre Netter, Moshe Finel, Sylvie Fournel-gigleux, Jacques Magdalou, Mohamed OuzzineAbstract:The human UDP-glucuronosyltransferase (UGT) isoforms UGT2B4 and UGT2B7 play a major role in the detoxification of bile acids, steroids and phenols. These two isoforms present distinct but overlapping substrate specificity, sharing common substrates such as the bile acid hyodeoxycholic acid (HDCA) and catechol-estrogens. Here, we show that in UGT2B4, substitution of phenylalanine 33 by leucine suppressed the activity towards HDCA, and impaired the glucuronidation of several substrates, including 4-hydroxyestrone and 17-epiestriol. On the other hand, the substrate specificity of the mutant UGT2B4F33Y, in which phenylalanine was replaced by tyrosine, as found at position 33 of UGT2B7, was similar to wild-type UGT2B4. In the case of UGT2B7, replacement of tyrosine 33 by leucine strongly reduced the activity towards all the tested substrates, with the exception of 17-epiestriol. In contrast, mutation of tyrosine 33 by phenylalanine exhibited similar or even somewhat higher activities than wild-type UGT2B7. Hence, the results strongly indicated that the presence of an aromatic residue at position 33 is important for the activity and substrate specificity of both UGT2B4 and UGT2B7.
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Prominent but Reverse Stereoselectivity in Propranolol Glucuronidation by Human UDP-Glucuronosyltransferases 1A9 and 1A10
Drug Metabolism and Disposition, 2006Co-Authors: Taina Sten, Leena Luukkanen, Risto Kostiainen, Saana Qvisen, Päivi Uutela, Moshe FinelAbstract:Propranolol is a nonselective β-adrenergic blocker used as a racemic mixture in the treatment of hypertension, cardiac arrhythmias, and angina pectoris. For study of the stereoselective glucuronidation of this drug, the two propranolol glucuronide diastereomers were biosynthesized, purified, and characterized. A screen of 15 recombinant human UDP-glucuronosyltransferases (UGTs) indicated that only a few isoforms catalyze propranolol glucuronidation. Analysis of UGT2B4 and UGT2B7 revealed no significant stereoselectivity, but these two enzymes differed in glucuronidation kinetics. The glucuronidation kinetics of R-propranolol by UGT2B4 exhibited a sigmoid curve, whereas the glucuronidation of the same substrate by UGT2B7 was inhibited by substrate concentrations above 1 mM. Among the UGTs of subfamily 1A, UGT1A9 and UGT1A10 displayed high and, surprisingly, opposite stereoselectivity in the glucuronidation of propranolol enantiomers. UGT1A9 glucuronidated S-propranolol much faster than R-propranolol, whereas UGT1A10 exhibited the opposite enantiomer preference. Nonetheless, the Km values for the two enantiomers, both for UGT1A9 and for UGT1A10, were in the same range, suggesting similar affinities for the two enantiomers. Unlike UGT1A9, the expression of UGT1A10 is extrahepatic. Hence, the reverse stereoselectivity of these two UGTs may signify specific differences in the glucuronidation of propranolol enantiomers between intestine and liver microsomes. Subsequent experiments confirmed this hypothesis: human liver microsomes glucuronidated S-propranolol faster than R-propranolol, whereas human intestine microsomes glucuronidated S-propranolol faster. These findings suggest a contribution of intestinal UGTs to drug metabolism, at least for UGT1A10 substrates.
André Bélanger - One of the best experts on this subject based on the ideXlab platform.
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Glucuronidation of arachidonic and linoleic acid metabolites by human UDP-glucuronosyltransferases.
Journal of lipid research, 2003Co-Authors: David Turgeon, Patrick Bélanger, Sylvie Chouinard, Jean-françois Labbé, Serge Picard, Pierre Borgeat, André BélangerAbstract:Arachidonic acids (AA) and linoleic acids (LAs) are metabolized, in several tissues, to hydroxylated metabolites that are important mediators of many physiological and pathophysiological processes. The conjugation of leukotriene B4 (LTB4), 5-hydroxyeicosatetraenoic acid (HETE), 12-HETE, 15-HETE, and 13-hydroxyoctadecadienoic acid (HODE) by the human UDP-glucuronosyltransferase (UGT) enzymes was investigated. All substrates tested were efficiently conjugated by human liver microsomes to polar derivatives containing the glucuronyl moiety as assessed by mass spectrometry. The screening analyses with stably expressed UGT enzymes in HK293 showed that glucuronidation of LTB4 was observed with UGT1A1, UGT1A3, UGT1A8, and UGT2B7, whereas UGT1A1, UGT1A3, UGT1A4, and UGT1A9 also conjugated most of the HETEs and 13-HODE. LA and AA metabolites also appear to be good substrates for the UGT2B subfamily members, especially for UGT2B4 and UGT2B7 that conjugate all HETE and 13-HODE. Interestingly, UGT2B10 and UGT2B11, which are considered as orphan enzymes since no conjugation activity has so far been demonstrated with these enzymes, conjugated 12-HETE, 15-HETE, and 13-HODE. In summary, our data showed that several members of UGT1A and UGT2B families are capable of converting LA and AA metabolites into glucuronide derivatives, which is considered an irreversible step to inactivation and elimination of endogenous substances from the body.
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3'-Azido-3'-deoxythimidine (AZT) is glucuronidated by human UDP- glucuronosyltransferase 2B7 (UGT2B7)
Drug Metabolism and Disposition, 2000Co-Authors: Olivier Barbier, David Turgeon, D W Hum, Caroline Girard, Thomas R. Tephly, M.d. Green, André BélangerAbstract:3'-Azido-3'-deoxythymidine (AZT) is frequently prescribed to patients infected with the human immunodeficiency virus. After absorption, AZT is rapidly metabolized into 3'-azido-3'-deoxy-5'-glucuronylthy- midine by UDP-glucuronosyltransferase (UGT) enzymes. Using la- beled [14C]UDP-glucuronic acid and microsomal preparations from human kidney 293 cells stably expressing the different human UGT2B isoenzymes, it was demonstrated that AZT glucuronidation is cata- lyzed specifically by human UGT2B7. The identity of the metabolite formed was confirmed as AZT-G by liquid chromatography coupled with mass spectrometry. UGT2B7 is encoded by a polymorphic gene and kinetic analysis of AZT glucuronidation by the two allelic variants UGT2B7(H268) and UGT2B7(Y268), yielded apparent Km values of 91.0 and 80.1 microM, respectively. Normalization to protein levels yielded glucuronidation efficiency ratios (Vmax/Km) of 21.3 and 11.0 microl* min-1*mgprotein-1 for UGT2B7(H268) and UGT2B7(Y268), respec- tively. It remains possible that otherUGTenzymes are also involved in AZT conjugation; however, the glucuronidation of AZT by UGT2B7, which is a UGT2B protein expressed in the liver, is consistent with previous findings and supports the physiological relevance of this enzyme in AZT conjugation.
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Isolation and characterization of a novel cDNA encoding a human UDP-glucuronosyltransferase active on C19 steroids.
The Journal of biological chemistry, 1996Co-Authors: Mario Beaulieu, D W Hum, Esther Lévesque, André BélangerAbstract:To isolate cDNA clones encoding novel UGT2B enzymes, human prostate and LNCaP cell cDNA libraries were screened using a pool of steroid-specific UGT2B cDNA probes. In approximately 10(6) recombinants, we isolated 3 cDNA clones of 2.1 kilobases that encode a novel UGT2B enzyme. UGT2B17 is 95% identical with UGT2B15 and 91% identical with UGT2B8. Primary structure analysis of UGT2B17 based on the nucleotide sequence revealed a putative amino-terminal membrane insertion signal peptide, a carboxyl-terminal membrane-spanning region, and three potential asparagine-linked glycosylation sites. UGT2B17 cloned in the pBK-CMV expression vector was transfected into HK293 cells to obtain a stable clonal cell line expressing a high level of the active 53-kDa UGT2B17 enzyme. Of the over 60 endogenous and exogenous substances tested, 25 compounds revealed reactivity. The major substrates are eugenol > 4-methylumbelliferone > dihydrotestosterone > androstane-3alpha, 17beta-diol (3alpha-diol) > testosterone > androsterone (ADT). The apparent Km values obtained with tritiated steroids in intact cells were 0.4 microM for ADT, 0.7 microM for dihydrotestosterone, 1.0 microM for 3alpha-diol, and 3.4 microM for testosterone. Southern blot analysis of reverse transcription-polymerase chain reaction products revealed expression of UGT2B17 mRNA in various tissues including the liver, kidney, testis, uterus, placenta, mammary gland, adrenal gland, skin, and prostate. UGT2B17 is the first human uridine diphosphoglucuronosyltransferase enzyme expressed in extrahepatic tissues to have a specificity for ADT as well as testosterone, dihydrotestosterone, and 3alpha-diol.
Xiaopu Yuan - One of the best experts on this subject based on the ideXlab platform.
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UDP-glucuronosyltransferase and sulfotransferase polymorphisms, sex hormone concentrations, and tumor receptor status in breast cancer patients.
Breast Cancer Research, 2004Co-Authors: Rachel Sparks, Jeannette Bigler, Cornelia M. Ulrich, Shelley S. Tworoger, Yutaka Yasui, Kumar B. Rajan, Peggy L. Porter, Frank Z. Stanczyk, Rachel Ballard-barbash, Xiaopu YuanAbstract:Introduction UDP-glucuronosyltransferase (UGT) and sulfotransferase (SULT) enzymes are involved in removing sex hormones from circulation. Polymorphic variation in five UGT and SULT genes – UGT1A1 ((TA)6/(TA)7), UGT2B4 (Asp458Glu), UGT2B7 (His268Tyr), UGT2B15 (Asp85Tyr), and SULT1A1 (Arg213His) – may be associated with circulating sex hormone concentrations, or the risk of an estrogen receptor-negative (ER-) or progesterone receptor-negative (PR-) tumor.
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UDP-glucuronosyltransferase and sulfotransferase polymorphisms, sex hormone concentrations, and tumor receptor status in breast cancer patients
Breast Cancer Research, 2004Co-Authors: Rachel Sparks, Jeannette Bigler, Cornelia M. Ulrich, Shelley S. Tworoger, Yutaka Yasui, Kumar B. Rajan, Frank Z. Stanczyk, Rachel Ballard-barbash, Peggy Porter, Xiaopu YuanAbstract:Introduction UDP-glucuronosyltransferase (UGT) and sulfotransferase (SULT) enzymes are involved in removing sex hormones from circulation. Polymorphic variation in five UGT and SULT genes – UGT1A1 ((TA)_6/(TA)_7), UGT2B4 (Asp^458Glu), UGT2B7 (His^268Tyr), UGT2B15 (Asp^85Tyr), and SULT1A1 (Arg^213His) – may be associated with circulating sex hormone concentrations, or the risk of an estrogen receptor-negative (ER^-) or progesterone receptor-negative (PR^-) tumor. Methods Logistic regression analysis was used to estimate the odds ratios of an ER^- or PR^- tumor associated with polymorphisms in the genes listed above for 163 breast cancer patients from a population-based cohort study of women in western Washington. Adjusted geometric mean estradiol, estrone, and testosterone concentrations were calculated within each UGT and SULT genotype for a subpopulation of postmenopausal breast cancer patients not on hormone therapy 2–3 years after diagnosis ( n = 89). Results The variant allele of UGT1A1 was associated with reduced risk of an ER^- tumor ( P for trend = 0.03), and variants of UGT2B15 and SULT1A1 were associated with non-statistically significant risk reductions. There was some indication that plasma estradiol and testosterone concentrations varied by UGT2B15 and SULT1A1 genotypes; women with the UGT2B15 Asp/Tyr and Tyr/Tyr genotypes had higher concentrations of estradiol than women with the Asp/Asp genotype ( P = 0.004). Compared with women with the SULT1A1 Arg/Arg and Arg/His genotypes, women with the His/His genotype had elevated concentrations of testosterone ( P = 0.003). Conclusions The risk of ER^- breast cancer tumors may vary by UGT or SULT genotype. Further, plasma estradiol and testosterone concentrations in breast cancer patients may differ depending on some UGT and SULT genotypes.
Nobumitsu Hanioka - One of the best experts on this subject based on the ideXlab platform.
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Glucuronidation of mono(2-ethylhexyl) phthalate in humans: roles of hepatic and intestinal UDP-glucuronosyltransferases.
Archives of Toxicology, 2016Co-Authors: Nobumitsu Hanioka, Yu Kinashi, Toshiko Tanaka-kagawa, Takashi Isobe, Hideto JinnoAbstract:Mono(2-ethylhexyl) phthalate (MEHP) is an active metabolite of di(2-ethylhexyl) phthalate (DEHP), which is an endocrine-disrupting chemical. In the present study, MEHP glucuronidation in humans was studied using recombinant UDP-glucuronosyltransferases (UGTs) and microsomes of the liver and intestine. Among the recombinant UGTs examined, UGT1A3, UGT1A7, UGT1A8, UGT1A9, UGT1A10, UGT2B4, and UGT2B7 glucuronidated MEHP. The kinetics of MEHP glucuronidation by UGT1A3, UGT1A7, UGT1A8, UGT1A10, UGT2B4, and UGT2B7 followed the Michaelis–Menten model, whereas that by UGT1A9 fit the negative allosteric model. CLint values were in the order of UGT1A9 > UGT2B7 > UGT1A7 > UGT1A8 ≥ UGT1A10 > UGT1A3 > UGT2B4. The kinetics of MEHP glucuronidation by liver microsomes followed the Michaelis–Menten model. Diclofenac (20 µM) and raloxifene (20 µM) decreased CLint values to 43 and 36 % that of native microsomes, respectively. The kinetics of MEHP glucuronidation by intestine microsomes fit the biphasic model. Diclofenac (150 and 450 µM) decreased CLint values to 32 and 13 % that of native microsomes for the high-affinity phase, and to 28 and 21 % for the low-affinity phase, respectively. Raloxifene (2.5 and 7.0 µM) decreased CLint values to 35 and 4.1 % that of native microsomes for the high-affinity phase, and to 48 and 53 % for the low-affinity phase, respectively. These results suggest that MEHP glucuronidation in humans is catalyzed by UGT1A3, UGT1A9, UGT2B4, and/or UGT2B7 in the liver, and by UGT1A7, UGT1A8, UGT1A9, UGT1A10, and/or UGT2B7 in the intestine, and also that these UGT isoforms play important and characteristic roles in the detoxification of DEHP.
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Effect of aflatoxin B1 on UDP-glucuronosyltransferase mRNA expression in HepG2 cells.
Chemosphere, 2012Co-Authors: Nobumitsu Hanioka, Yuko Nonaka, Keita Saito, Tomoe Negishi, Keinosuke Okamoto, Hiroyuki Kataoka, Shizuo NarimatsuAbstract:Aflatoxin B1 (AFB1) is a potent mycotoxin that induces hepatocellular carcinoma in many animal species, including humans. In this study, we examined the effects of AFB1 on UDP-glucuronosyltransferase (UGT) mRNA expression in HepG2 cells (human hepatocellular carcinoma cell line). The cells were treated with AFB1 for 48 h at a concentration of 10 μM, and their viability (87%) was not significantly different from that of control cells. Reverse transcription polymerase chain reaction (RT-PCR) analysis demonstrated that the mRNAs of four UGT1As (UGT1A1, UGT1A3, UGT1A4 and UGT1A9) and seven UGT2Bs (UGT2B4, UGT2B7, UGT2B10, UGT2B11, UGT2B15, UGT2B17 and UGT2B28) are expressed in HepG2 cells. The mRNAs of aryl hydrocarbon receptor (AhR), pregnane X receptor (PXR), retinoid X receptor (RXR) and glucocorticoid receptor (GR) as transcriptional regulators were also detected. AFB1 significantly increased mRNA levels of UGT1A3, UGT2B10, UGT2B15 and UGT2B17 in HepG2 cells to 2.5-, 2.0-, 1.9- and 1.5-fold, respectively, whereas the mRNA levels of transcriptional regulators were hardly affected by AFB1. These findings suggest that AFB1 induces UGT2B isoforms rather than UGT1A isoforms in HepG2 cells, and that the change may closely contribute to the toxicity of AFB1.
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Human UDP-glucuronosyltransferase isoforms involved in bisphenol A glucuronidation.
Chemosphere, 2008Co-Authors: Nobumitsu Hanioka, Takanori Naito, Shizuo NarimatsuAbstract:Bisphenol A (BPA) is one of a number of potential endocrine disruptors which may affect normal hormonal function. In this study, human UDP-glucuronosyltransferase (UGT) isoforms involved in BPA glucuronidation were studied by kinetic analyses using human liver microsomes and recombinant human UGTs expressed in insect cells (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B4, UGT2B7, UGT2B15 and UGT2B17). BPA glucuronidation was catalyzed by UGT1A1, UGT1A3, UGT1A9, UGT2B4, UGT2B7 and UGT2B15 as well as by human liver microsomes. Among these UGTs, UGT2B15 showed the highest activity of BPA glucuronidation at low- (1.0 μM) and high- (20 μM) substrate concentrations. Kinetic analyses of BPA glucuronidation were performed by constructing Michaelis–Menten and Eadie–Hofstee plots. The kinetic profile of BPA glucuronidation by pooled human liver microsomes and UGT2B15 was monophasic, the Km and Vmax values were 6.39 μM and 4250 pmol min−1 mg−1 protein for pooled human liver microsomes, and 8.68 μM and 873 pmol min−1 mg−1 protein for UGT2B15, respectively. The Km values for BPA glucuronidation by pooled human liver microsomes and UGT2B15 were similar. These findings demonstrate that BPA is mainly glucuronidated by UGT2B15 in human liver microsomes, and suggest that this UGT isoform plays important roles in the detoxification and elimination of BPA.
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stereoselective glucuronidation of propranolol in human and cynomolgus monkey liver microsomes role of human hepatic udp glucuronosyltransferase isoforms ugt1a9 UGT2B4 and ugt2b7
Pharmacology, 2008Co-Authors: Nobumitsu Hanioka, Keiko Hayashi, Takeshi Shimizudani, Kenjiro Nagaoka, Akiko Koeda, Shinsaku Naito, Shizuo NarimatsuAbstract:The stereoselective glucuronidation of propranolol (PL) in human and cynomolgus monkey liver microsomes, and the roles of human hepatic UDP-glucuronosyltransferase (UGT) isofoms involved in the enanti
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Human UDP-glucuronosyltransferase isoforms involved in bisphenol A glucuronidation
Chemosphere, 2008Co-Authors: Nobumitsu Hanioka, Takanori Naito, Shizuo NarimatsuAbstract:Bisphenol A (BPA) is one of a number of potential endocrine disruptors which may affect normal hormonal function. In this study, human UDP-glucuronosyltransferase (UGT) isoforms involved in BPA glucuronidation were studied by kinetic analyses using human liver microsomes and recombinant human UGTs expressed in insect cells (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B4, UGT2B7, UGT2B15 and UGT2B17). BPA glucuronidation was catalyzed by UGT1A1, UGT1A3, UGT1A9, UGT2B4, UGT2B7 and UGT2B15 as well as by human liver microsomes. Among these UGTs, UGT2B15 showed the highest activity of BPA glucuronidation at low- (1.0 μM) and high- (20 μM) substrate concentrations. Kinetic analyses of BPA glucuronidation were performed by constructing Michaelis-Menten and Eadie-Hofstee plots. The kinetic profile of BPA glucuronidation by pooled human liver microsomes and UGT2B15 was monophasic, the Km and Vmax values were 6.39 μM and 4250 pmol min-1 mg-1 protein for pooled human liver microsomes, and 8.68 μM and 873 pmol min-1 mg-1 protein for UGT2B15, respectively. The Km values for BPA glucuronidation by pooled human liver microsomes and UGT2B15 were similar. These findings demonstrate that BPA is mainly glucuronidated by UGT2B15 in human liver microsomes, and suggest that this UGT isoform plays important roles in the detoxification and elimination of BPA. © 2008 Elsevier Ltd. All rights reserved.
