UGT1A6

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Curtis D Klaassen - One of the best experts on this subject based on the ideXlab platform.

  • induction of mouse udp glucuronosyltransferase mrna expression in liver and intestine by activators of aryl hydrocarbon receptor constitutive androstane receptor pregnane x receptor peroxisome proliferator activated receptor α and nuclear factor eryt
    Drug Metabolism and Disposition, 2009
    Co-Authors: David B Buckley, Curtis D Klaassen
    Abstract:

    UDP-glucuronosyltransferases (UGTs) catalyze the addition of UDP-glucuronic acid to endo- and xenobiotics, enhancing their water solubility and elimination. Many exogenous compounds, such as microsomal enzyme inducers (MEIs), alter gene expression through xenobiotic-responsive transcription factors, namely, the aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR), pregnane X receptor (PXR), peroxisome proliferator-activated receptor α (PPARα), and nuclear factor erythroid 2-related factor 2 (Nrf2). These transcription factors regulate xenobiotic-inducible expression of hepatic and intestinal biotransformation enzymes and transporters. The purpose of this study was to determine hepatic and intestinal inducibility of mouse Ugt mRNA by MEIs. Male C57BL/6 mice were treated for four consecutive days with activators of AhR [2,3,7,8-tetrachlorodibenzodioxin (TCDD), polychlorinated biphenyl 126, and β-naphthoflavone], CAR [1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP), phenobarbital, and diallyl sulfide], PXR [pregnenolone-16α-carbonitrile (PCN), spironolactone, and dexamethasone], PPARα (clofibrate, ciprofibrate, and diethylhexylphthalate), and Nrf2 (oltipraz, ethoxyquin, and butylated hydroxyanisole), respectively. Ugt1a1 mRNA expression in liver was induced by activators of all five transcription factor pathways, Ugt1a5 by Nrf2 activators, UGT1A6 by all the pathways except CAR, and Ugt1a9 by all the pathways except Nrf2. Ugt2b35 mRNA in liver was induced by AhR activators and Ugt2b36 by CAR and PPARα activators. Throughout the small and large intestine, the AhR ligand TCDD increased UGT1A6 and Ugt1a7 mRNA. In small intestine, the PXR activator PCN increased Ugt1a1, UGT1A6, Ugt1a7, Ugt2b34, and Ugt2b35 mRNA in the duodenum. In conclusion, chemical activation of AhR, CAR, PXR, PPARα, and Nrf2 in mouse results in induction of distinct Ugt gene sets in liver and intestine, predominantly the Ugt1a isoforms.

  • induction of mouse udp glucuronosyltransferase mrna expression in liver and intestine by activators of aryl hydrocarbon receptor constitutive androstane receptor pregnane x receptor peroxisome proliferator activated receptor α and nuclear factor eryt
    Drug Metabolism and Disposition, 2009
    Co-Authors: David B Buckley, Curtis D Klaassen
    Abstract:

    UDP-glucuronosyltransferases (UGTs) catalyze the addition of UDP-glucuronic acid to endo- and xenobiotics, enhancing their water solubility and elimination. Many exogenous compounds, such as microsomal enzyme inducers (MEIs), alter gene expression through xenobiotic-responsive transcription factors, namely, the aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR), pregnane X receptor (PXR), peroxisome proliferator-activated receptor α (PPARα), and nuclear factor erythroid 2-related factor 2 (Nrf2). These transcription factors regulate xenobiotic-inducible expression of hepatic and intestinal biotransformation enzymes and transporters. The purpose of this study was to determine hepatic and intestinal inducibility of mouse Ugt mRNA by MEIs. Male C57BL/6 mice were treated for four consecutive days with activators of AhR [2,3,7,8-tetrachlorodibenzodioxin (TCDD), polychlorinated biphenyl 126, and β-naphthoflavone], CAR [1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP), phenobarbital, and diallyl sulfide], PXR [pregnenolone-16α-carbonitrile (PCN), spironolactone, and dexamethasone], PPARα (clofibrate, ciprofibrate, and diethylhexylphthalate), and Nrf2 (oltipraz, ethoxyquin, and butylated hydroxyanisole), respectively. Ugt1a1 mRNA expression in liver was induced by activators of all five transcription factor pathways, Ugt1a5 by Nrf2 activators, UGT1A6 by all the pathways except CAR, and Ugt1a9 by all the pathways except Nrf2. Ugt2b35 mRNA in liver was induced by AhR activators and Ugt2b36 by CAR and PPARα activators. Throughout the small and large intestine, the AhR ligand TCDD increased UGT1A6 and Ugt1a7 mRNA. In small intestine, the PXR activator PCN increased Ugt1a1, UGT1A6, Ugt1a7, Ugt2b34, and Ugt2b35 mRNA in the duodenum. In conclusion, chemical activation of AhR, CAR, PXR, PPARα, and Nrf2 in mouse results in induction of distinct Ugt gene sets in liver and intestine, predominantly the Ugt1a isoforms.

  • tissue and gender specific mrna expression of udp glucuronosyltransferases ugts in mice
    Drug Metabolism and Disposition, 2007
    Co-Authors: David B Buckley, Curtis D Klaassen
    Abstract:

    UDP-glucuronosyltransferases (UGTs) catalyze phase II biotransformation reactions in which lipophilic substrates are conjugated with glucuronic acid to increase water solubility and enhance excretion. Currently, little information regarding tissue- or gender-specific expression of mouse UGTs is available. Mice are increasingly popular models in biomedical research, and therefore, thorough characterization of murine drug metabolism is desired. The purpose of the present study was to determine both tissue- and gender-specific UGT gene expression profiles in mice. RNA from 14 tissues was isolated from male and female C57BL/6 mice and UGT expression was determined by the branched DNA signal amplification assay. UGTs highly expressed in mouse liver include Ugt1a1, Ugt1a5, UGT1A6, Ugt1a9, Ugt2a3, Ugt2b1, Ugt2b5/37/38, Ugt2b34, Ugt2b35, and Ugt2b36. Several isoforms were expressed in the gastrointestinal (GI) tract, including UGT1A6, Ugt1a7c, Ugt2a3, Ugt2b34, and Ugt2b35. In kidney, Ugt1a2, Ugt1a7c, Ugt2b5/37/38, Ugt2b35, and Ugt3a1/2 were expressed. UGT expression was also observed in other tissues: lung (UGT1A6), brain (Ugt2b35), testis and ovary (UGT1A6 and Ugt2b35), and nasal epithelia (Ugt2a1/2). Male-predominant expression was observed for Ugt2b1 in liver, Ugt2b5/37/38 in kidney, and UGT1A6 in lung. Female-predominant expression was observed for Ugt1a1 and Ugt1a5 in liver, Ugt1a2 in kidney, Ugt2b35 in brain, and Ugt2a1/2 in nasal epithelia. UDP-glucose pyrophosphorylase was highly expressed in liver, kidney, and GI tract, whereas UDP-glucose dehydrogenase was highly expressed in the GI tract. In conclusion, marked differences in tissue- and gender-specific expression patterns of UGTs exist in mice, potentially influencing drug metabolism and pharmacokinetics.

  • tissue mrna expression of the rat udp glucuronosyltransferase gene family
    Drug Metabolism and Disposition, 2003
    Co-Authors: Melinda K Shelby, Nathan J Cherrington, N R Vansell, Curtis D Klaassen
    Abstract:

    UDP-Glucuronosyltransferases (UGTs) are phase II biotransformation enzymes that glucuronidate numerous endobiotic and xenobiotic substrates. Glucuronidation increases the water solubility of the substrate and facilitates renal and biliary excretion of the resulting glucuronide conjugate. UGTs have been divided into two gene families, UGT1 and UGT2. Tissue distribution of UGTs has not been thoroughly examined, and such data could provide insight into the importance of individual UGT isoforms in specific tissues and to the pharmacokinetics and target organ toxicity of UGT substrates. Therefore, the aim of this study was to determine mRNA levels of rat UGT1 and UGT2 family members in liver, kidney, lung, stomach, duodenum, jejunum, ileum, large intestine, cerebellum, and cerebral cortex, as well as nasal epithelium for UGT2A1. Tissue levels of UGT mRNA were detected using branched DNA signal amplification analysis. Three UGT isoforms, UGT1A1, UGT1A6, and UGT2B12, were detected in many tissues, whereas distribution of other UGT isoforms was more tissue-specific. For example, UGT2A1 was detected predominantly in nasal epithelium. Additionally, UGT1A5, UGT2B1, UGT2B2, UGT2B3, and UGT2B6 were detected primarily in liver. Furthermore, detection of UGT1A2, UGT1A3, UGT1A7, and UGT2B8 was somewhat specific to gastrointestinal (GI) tract. However, not all of these UGTs were detected in all portions of the GI tract. UGT1A8 was unique in that it was barely detectable in any of the tissues examined. In conclusion, some UGT isoforms were expressed in multiple tissues, whereas other UGT isoforms were predominantly expressed in a certain tissue such as nasal epithelium, liver, or GI tract.

Chantal Guillemette - One of the best experts on this subject based on the ideXlab platform.

  • in vitro glucuronidation of fenofibric acid by human udp glucuronosyltransferases and liver microsomes
    Drug Metabolism and Disposition, 2009
    Co-Authors: Jelena Tojcic, Marieodile Enoitbiancamano, Robert J. Straka, Michael H Cou, Chantal Guillemette
    Abstract:

    Fenofibric acid (FA), the active moiety of fenofibrate, is an agonist of the peroxisome proliferator-activated nuclear receptor α that modulates triglyceride and cholesterol profiles. Lipid response to fenofibrate and FA serum concentrations is highly variable. Although FA is reported to be almost exclusively inactivated by UDP-glucuronosyltransferases (UGTs) into FA-glucuronide (FA-G), the contribution of UGT isoenzymes has never been systematically assessed. Heterologously expressed human UGT1A and UGT2B and their coding variants were tested for FA glucuronidation using liquid chromatography/mass spectrometry. Recombinant UGT2B7 presented the highest Vmax/Km value (2.10 μl/min/mg), 16-fold higher than the activity of other reactive UGTs, namely, UGT1A3, UGT1A6, and UGT1A9 (0.13, 0.09, and 0.02 μl/min/mg, respectively). UGT2B7.1 (His268) and UGT2B7.2 (Tyr268) enzyme activity was similar, whereas UGT1A3.2 (R11A47), UGT1A3.3 (Trp11), and UGT1A9.3 (Thr33) showed 61 to 96% reduced Vmax/Km values compared with the respective (1) reference proteins. FA-G formation by a human liver bank (n = 48) varied by 10-fold, but the rate of formation was not associated with common genetic variations in UGT1A3, UGT1A6, UGT1A9, and UGT2B7. Correlation with activities for the probe substrates zidovudine (UGT2B7; r2 = 0.75), mycophenolic acid (UGT1A9; r2 = 0.42), fulvestrant (UGT1A3; r2 = 0.36), but not serotonin (UGT1A6; r2 = 0.06) indicated a primary role for UGT2B7 and lesser roles of UGT1A9 and UGT1A3 in hepatic FA glucuronidation. This was confirmed by a strong correlation of FA-G formation with UGT2B7 protein content and inhibition by fluconazole, a known UGT2B7 selective inhibitor. Additional studies are required to identify genetic factors contributing to the observed FA glucuronidation variability.

  • hepatic expression of the ugt1a9 gene is governed by hepatocyte nuclear factor 4α
    Molecular Pharmacology, 2005
    Co-Authors: Olivier Barbier, Franck J Gonzalez, Helene Duez, Yusuke Inoue, Akihide Kamiya, Jean Charles Fruchart, Chantal Guillemette, Lyne Villeneuve, Hugo Girard, Bart Staels
    Abstract:

    UDP-glucuronosyltransferase (UGT) enzymes catalyze the glucuronidation reaction, which is a major pathway in the catabolism and elimination of numerous endo- and xenobiotics. Among the UGT enzyme family members, the UGT1A7, UGT1A8, UGT1A9, and UGT1A10 isoforms are issued from a single gene through differential splicing. However, these enzymes display distinct tissue-specific expression patterns. Indeed, UGT1A7, UGT1A8, and UGT1A10 are exclusively expressed in extrahepatic tissues, whereas UGT1A9 transcripts are found at high concentrations in liver. In the present study, we report that the liver-enriched hepatocyte nuclear factor 4 (HNF4)-α controls the hepatic expression of the UGT1A9 enzyme. Liver-specific disruption of the HNF4 α gene in mice drastically decreases liver UGT1A9 mRNA levels. Furthermore, an HNF4α response element (HNF4α RE) was identified in the promoter of human UGT1A9 at position -372 to -360 base pairs by transient transfection, electrophoretic mobility shift assays, and chromatin immunoprecipitation experiments. It is interesting that this response element is absent in the proximal UGT1A7, UGT1A8, and UGT1A10 gene promoters. In conclusion, the present study identifies HNF4α as a major factor for the control of UGT1A9 hepatic expression and suggests that the absence of UGT1A7, UGT1A8, and UGT1A10 expression in the liver is caused by, at least in part, a few base pair changes in their promoter sequences in the region corresponding to the HNF4α RE of the UGT1A9 gene.

  • novel functional polymorphisms in the ugt1a7 and ugt1a9 glucuronidating enzymes in caucasian and african american subjects and their impact on the metabolism of 7 ethyl 10 hydroxycamptothecin and flavopiridol anticancer drugs
    Journal of Pharmacology and Experimental Therapeutics, 2003
    Co-Authors: Lyne Villeneuve, Jeanfrancois Gagne, Louis-charles Fortier, Hugo Girard, Chantal Guillemette
    Abstract:

    In vitro metabolic studies revealed that along with UDP-glucuronosyltransferase (UGT) 1A1, the hepatic UGT1A9 and the extrahepatic UGT1A7 are involved in the biotransformation of the active and toxic metabolite of irinotecan, 7-ethyl-10-hydroxycamptothecin (SN-38). Variant UGT1A1 and UGT1A7 alleles have been reported but the polymorphic nature of the UGT1A9 gene has not been revealed yet. To further clarify the molecular determinants of irinotecan-induced toxicity, we have identified and characterized the functionality of novel UGT1A9 polymorphisms and determined whether additional missense polymorphisms exist in UGT1A7. Using direct DNA sequencing, four single nucleotide polymorphisms (SNPs) were identified in the first exons of UGT1A7 and UGT1A9. One of the two amino acid substitutions found in the UGT1A9 gene, UGT1A9*3 (M33T), results in a dramatic decrease in SN-38 glucuronide formation, with 3.8% of the activity of the UGT1A9*1 allele. In turn, the glucuronidation of flavopiridol, an anticancer drug biotransformed predominantly by UGT1A9, remains unaffected, indicating a substrate-dependent impact of this variant. UGT1A9*3 is detected only in Caucasians and 4.4% of the population tested was found heterozygous (*1/*3). Two additional UGT1A7 SNPs were found exclusively in African-American subjects and generate five alleles (UGT1A7*5 to *9) when combined to the four known SNPs present in UGT1A7*2, *3, and *4. Upon functional analysis with SN-38, five out of nine UGT1A7 allozymes exhibited much lower SN-38 glucuronidation activities compared with UGT1A7*1, all having in common the mutational changes at codons 115 or 208. Results suggest that these low SN-38 glucuronidating alleles may represent additional molecular determinants of irinotecan-induced toxicity and warrant further investigations.

  • common human ugt1a polymorphisms and the altered metabolism of irinotecan active metabolite 7 ethyl 10 hydroxycamptothecin sn 38
    Molecular Pharmacology, 2002
    Co-Authors: Jeanfrancois Gagne, Patrick Bélanger, Valerie Montminy, Kim Journault, Genevieve Gaucher, Chantal Guillemette
    Abstract:

    7-Ethyl-10-hydroxycamptothecin (SN-38) is the pharmacologically active metabolite of irinotecan, in addition to being responsible for severe toxicity. Glucuronidation is the main metabolic pathway of SN-38 and has been shown to protect against irinotecan-induced gastrointestinal toxicity. The purpose of this study was to determine whether common polymorphic UDP-glucuronosyltransferase (UGT) affects SN-38 glucuronidation. First, kinetic characterization of SN-38-glucuronide (SN-38-G) formation was assessed for all known human UGT1A and UGT2B overexpressed in human embryonic kidney 293 cells. To assess the relative activity of UGT isoenzymes for SN-38, rates of formation of SN-38-G were monitored by liquid chromatography/mass spectrometry analysis and normalized by level of UGT cellular expression. Determination of intrinsic clearances predicts that hepatic UGT1A1 and UGT1A9 and the extrahepatic UGT1A7 are major components in SN-38-G formation, whereas a minor role is suggested for UGT1A6, UGT1A8, and UGT1A10. In support of the involvement of UGT1A9, a strong coefficient of correlation was observed in the glucuronidation of SN-38 and a substrate, mainly glucuronidate, by UGT1A9 (flavopiridol) by human liver microsomes (coefficient of correlation, 0.905; p = 0.002). In vitro functional experiments revealed a negative impact of the UGT1A1 allelic variants. Residual activities of 49, 7, 8, and 11% were observed for UGT1A1*6 (G71R), UGT1A1*27 (P229Q), UGT1A1*35 (L233R), and UGT1A1*7 (Y486D), respectively. Common variants of UGT1A7, UGT1A7*3 (N129K;R131K;W208R), and UGT1A7*4 (W208R), displayed residual activities of 41 and 28% compared with the UGT1A7*1 allele. Taken together, these data provide the evidence that molecular determinants of irinotecan response may include the UGT1A polymorphisms studied herein and common genetic variants of the hepatic UGT1A9 isoenzyme yet to be described.

David B Buckley - One of the best experts on this subject based on the ideXlab platform.

  • induction of mouse udp glucuronosyltransferase mrna expression in liver and intestine by activators of aryl hydrocarbon receptor constitutive androstane receptor pregnane x receptor peroxisome proliferator activated receptor α and nuclear factor eryt
    Drug Metabolism and Disposition, 2009
    Co-Authors: David B Buckley, Curtis D Klaassen
    Abstract:

    UDP-glucuronosyltransferases (UGTs) catalyze the addition of UDP-glucuronic acid to endo- and xenobiotics, enhancing their water solubility and elimination. Many exogenous compounds, such as microsomal enzyme inducers (MEIs), alter gene expression through xenobiotic-responsive transcription factors, namely, the aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR), pregnane X receptor (PXR), peroxisome proliferator-activated receptor α (PPARα), and nuclear factor erythroid 2-related factor 2 (Nrf2). These transcription factors regulate xenobiotic-inducible expression of hepatic and intestinal biotransformation enzymes and transporters. The purpose of this study was to determine hepatic and intestinal inducibility of mouse Ugt mRNA by MEIs. Male C57BL/6 mice were treated for four consecutive days with activators of AhR [2,3,7,8-tetrachlorodibenzodioxin (TCDD), polychlorinated biphenyl 126, and β-naphthoflavone], CAR [1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP), phenobarbital, and diallyl sulfide], PXR [pregnenolone-16α-carbonitrile (PCN), spironolactone, and dexamethasone], PPARα (clofibrate, ciprofibrate, and diethylhexylphthalate), and Nrf2 (oltipraz, ethoxyquin, and butylated hydroxyanisole), respectively. Ugt1a1 mRNA expression in liver was induced by activators of all five transcription factor pathways, Ugt1a5 by Nrf2 activators, UGT1A6 by all the pathways except CAR, and Ugt1a9 by all the pathways except Nrf2. Ugt2b35 mRNA in liver was induced by AhR activators and Ugt2b36 by CAR and PPARα activators. Throughout the small and large intestine, the AhR ligand TCDD increased UGT1A6 and Ugt1a7 mRNA. In small intestine, the PXR activator PCN increased Ugt1a1, UGT1A6, Ugt1a7, Ugt2b34, and Ugt2b35 mRNA in the duodenum. In conclusion, chemical activation of AhR, CAR, PXR, PPARα, and Nrf2 in mouse results in induction of distinct Ugt gene sets in liver and intestine, predominantly the Ugt1a isoforms.

  • induction of mouse udp glucuronosyltransferase mrna expression in liver and intestine by activators of aryl hydrocarbon receptor constitutive androstane receptor pregnane x receptor peroxisome proliferator activated receptor α and nuclear factor eryt
    Drug Metabolism and Disposition, 2009
    Co-Authors: David B Buckley, Curtis D Klaassen
    Abstract:

    UDP-glucuronosyltransferases (UGTs) catalyze the addition of UDP-glucuronic acid to endo- and xenobiotics, enhancing their water solubility and elimination. Many exogenous compounds, such as microsomal enzyme inducers (MEIs), alter gene expression through xenobiotic-responsive transcription factors, namely, the aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR), pregnane X receptor (PXR), peroxisome proliferator-activated receptor α (PPARα), and nuclear factor erythroid 2-related factor 2 (Nrf2). These transcription factors regulate xenobiotic-inducible expression of hepatic and intestinal biotransformation enzymes and transporters. The purpose of this study was to determine hepatic and intestinal inducibility of mouse Ugt mRNA by MEIs. Male C57BL/6 mice were treated for four consecutive days with activators of AhR [2,3,7,8-tetrachlorodibenzodioxin (TCDD), polychlorinated biphenyl 126, and β-naphthoflavone], CAR [1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP), phenobarbital, and diallyl sulfide], PXR [pregnenolone-16α-carbonitrile (PCN), spironolactone, and dexamethasone], PPARα (clofibrate, ciprofibrate, and diethylhexylphthalate), and Nrf2 (oltipraz, ethoxyquin, and butylated hydroxyanisole), respectively. Ugt1a1 mRNA expression in liver was induced by activators of all five transcription factor pathways, Ugt1a5 by Nrf2 activators, UGT1A6 by all the pathways except CAR, and Ugt1a9 by all the pathways except Nrf2. Ugt2b35 mRNA in liver was induced by AhR activators and Ugt2b36 by CAR and PPARα activators. Throughout the small and large intestine, the AhR ligand TCDD increased UGT1A6 and Ugt1a7 mRNA. In small intestine, the PXR activator PCN increased Ugt1a1, UGT1A6, Ugt1a7, Ugt2b34, and Ugt2b35 mRNA in the duodenum. In conclusion, chemical activation of AhR, CAR, PXR, PPARα, and Nrf2 in mouse results in induction of distinct Ugt gene sets in liver and intestine, predominantly the Ugt1a isoforms.

  • tissue and gender specific mrna expression of udp glucuronosyltransferases ugts in mice
    Drug Metabolism and Disposition, 2007
    Co-Authors: David B Buckley, Curtis D Klaassen
    Abstract:

    UDP-glucuronosyltransferases (UGTs) catalyze phase II biotransformation reactions in which lipophilic substrates are conjugated with glucuronic acid to increase water solubility and enhance excretion. Currently, little information regarding tissue- or gender-specific expression of mouse UGTs is available. Mice are increasingly popular models in biomedical research, and therefore, thorough characterization of murine drug metabolism is desired. The purpose of the present study was to determine both tissue- and gender-specific UGT gene expression profiles in mice. RNA from 14 tissues was isolated from male and female C57BL/6 mice and UGT expression was determined by the branched DNA signal amplification assay. UGTs highly expressed in mouse liver include Ugt1a1, Ugt1a5, UGT1A6, Ugt1a9, Ugt2a3, Ugt2b1, Ugt2b5/37/38, Ugt2b34, Ugt2b35, and Ugt2b36. Several isoforms were expressed in the gastrointestinal (GI) tract, including UGT1A6, Ugt1a7c, Ugt2a3, Ugt2b34, and Ugt2b35. In kidney, Ugt1a2, Ugt1a7c, Ugt2b5/37/38, Ugt2b35, and Ugt3a1/2 were expressed. UGT expression was also observed in other tissues: lung (UGT1A6), brain (Ugt2b35), testis and ovary (UGT1A6 and Ugt2b35), and nasal epithelia (Ugt2a1/2). Male-predominant expression was observed for Ugt2b1 in liver, Ugt2b5/37/38 in kidney, and UGT1A6 in lung. Female-predominant expression was observed for Ugt1a1 and Ugt1a5 in liver, Ugt1a2 in kidney, Ugt2b35 in brain, and Ugt2a1/2 in nasal epithelia. UDP-glucose pyrophosphorylase was highly expressed in liver, kidney, and GI tract, whereas UDP-glucose dehydrogenase was highly expressed in the GI tract. In conclusion, marked differences in tissue- and gender-specific expression patterns of UGTs exist in mice, potentially influencing drug metabolism and pharmacokinetics.

Peter I. Mackenzie - One of the best experts on this subject based on the ideXlab platform.

  • coexpression of human hepatic uridine diphosphate glucuronosyltransferase proteins implications for ontogenetic mechanisms and isoform coregulation
    The Journal of Clinical Pharmacology, 2020
    Co-Authors: Yuejian Liu, Peter I. Mackenzie, Michael W H Coughtrie, Justine Badee, Ryan H Takahashi, Stephan Schmidt, Neil Parrott, Stephen Fowler, Abby C Collier
    Abstract:

    Uridine diphosphate glucuronosyltransferases (UGTs) catalyze glucuronidation to facilitate systemic and local clearance of numerous chemicals and drugs. To investigate whether UGT expression is coregulated in human liver, we analyzed the protein expression of UGTs 1A1, 1A3, 1A4, 1A6, 1A9, 2B7, 3A1, and 3A2 using western blots from 164 healthy human liver samples, comparing expression with age and sex. UGT1A6 levels were significantly higher in children than adults, and UGT3A1 and 3A2 expression significantly increased with age from childhood to age >65 yearas. In children aged 18 years. UGT1A3 expression was always significantly correlated with other UGT1A isoforms in all adults aged >18 years. In individuals aged ≥12 years, expression of UGT1A1/1A4, UGT1A1/1A6, UGT1A1/1A9, and UGT1A4/1A6 significantly correlated, which was not observed in children aged <12 years. In contrast, UGT1A4/2B7 showed significant correlation in children aged <12 years, but not in individuals aged ≥12 years, and this was observed in female but not male individuals. Expression of UGT1A6/1A9 and UGT3A1/3A2 correlated in the entire sample population, but UGT3As did not correlate with other UGTs. These correlations were sex dependent, as UGT1A3/1A1, UGT1A4/2B7 and UGT3A1/3A2 correlated more highly in male than female individuals, while UGT1A4/1A6 protein correlated more significantly in female than male individuals. This is the first report on the ontogeny of UGT3A isoforms, showing maximal expression in the elderly, and is the first demonstration that UGT isoforms commonly coexpress in vivo, in both age-dependent and sex-dependent manners.

  • inhibition of human udp glucuronosyltransferase enzymes by lapatinib pazopanib regorafenib and sorafenib implications for hyperbilirubinemia
    Biochemical Pharmacology, 2017
    Co-Authors: John O Miners, Kathleen M. Knights, Peter I. Mackenzie, Andrew Rowland, Nuy Chau, Kushari Burns, Ross A Mckinnon, G T Tucker, Ganessan Kichenadasse
    Abstract:

    Kinase inhibitors (KIs) are a rapidly expanding class of drugs used primarily for the treatment of cancer. Data relating to the inhibition of UDP-glucuronosyltransferase (UGT) enzymes by KIs is sparse. However, lapatinib (LAP), pazopanib (PAZ), regorafenib (REG) and sorafenib (SOR) have been implicated in the development of hyperbilirubinemia in patients. This study aimed to characterise the role of UGT1A1 inhibition in hyperbilirubinemia and assess the broader potential of these drugs to perpetrate drug-drug interactions arising from UGT enzyme inhibition. Twelve recombinant human UGTs from subfamilies 1A and 2B were screened for inhibition by LAP, PAZ, REG and SOR. IC50 values for the inhibition of all UGT1A enzymes, except UGT1A3 and UGT1A4, by the four KIs were <10μM. LAP, PAZ, REG and SOR inhibited UGT1A1-catalysed bilirubin glucuronidation with mean IC50 values ranging from 34nM (REG) to 3734nM (PAZ). Subsequent kinetic experiments confirmed that REG and SOR were very potent inhibitors of human liver microsomal β-estradiol glucuronidation, an established surrogate for bilirubin glucuronidation, with mean Ki values of 20 and 33nM, respectively. Ki values for LAP and PAZ were approximately 1- and 2-orders of magnitude higher than those for REG and SOR. REG and SOR were equipotent inhibitors of human liver microsomal UGT1A9 (mean Ki 678nM). REG and SOR are the most potent inhibitors of a human UGT enzyme identified to date. In vitro-in vivo extrapolation indicates that inhibition of UGT1A1 contributes significantly to the hyperbilirubinemia observed in patients treated with REG and SOR, but not with LAP and PAZ. Inhibition of other UGT1A1 substrates in vivo is likely.

  • effects of amino acid substitutions at positions 33 and 37 on udp glucuronosyltransferase 1a9 ugt1a9 activity and substrate selectivity
    Biochemical Pharmacology, 2012
    Co-Authors: Porntipa Korprasertthaworn, Krongtong Yoovathaworn, Benjamin C Lewis, Peter I. Mackenzie, Andrew Rowland, John O Miners
    Abstract:

    Abstract UGT1A9 contributes to the glucuronidation of numerous drugs and xenobiotics. There is evidence to suggest that the Met33Thr substitution, as occurs in the polymorphic variant UGT1A9*3, variably affects xenobiotic glucuronidation. The equivalent position in UGT1A4 is also known to influence enzyme activity, whilst an N-terminal domain histidine (His37 in UGT1A9) is believed to function as the catalytic base in most UGT enzymes. To elucidate the roles of key amino acids and characterise structure–function relationships, we determined the effects of amino acid substitutions at positions 33 and 37 of UGT1A9 on the kinetics of 4-methylumbelliferone (4-MU), mycophenolic acid (MPA), propofol (PRO), sulfinpyrazone (SFZ), frusemide (FSM), ( S )-naproxen (NAP) and retigabine (RTB) glucuronidation, compounds that undergo glucuronidation at either a phenolic (4-MU, MPA, PRO), carboxylate (FSM, NAP), acidic carbon (SFZ) or amine (RTB) function. Substitution of Met33 with Val, Ile, Thr, and Gln, as occur in UGT1A1, UGT1A3, UGT1A4 and UGT1A6 respectively, variably affected kinetics and catalytic efficiency. Whilst K m values were generally higher and V max and CL int values were generally lower than for wild-type UGT1A9 with most substrate-mutant pairs, the pattern and the magnitude of the changes in each parameter differed substantially. Moreover, exceptions occurred; CL int values for MPA and FSM glucuronidation by the position-33 mutants were the same as or higher than that of UGT1A9. Mutation of His37 abolished activity towards all substrates, except RTB N-glucuronidation. The data confirm the importance of single amino acids for UGT enzyme activity and substrate selectivity, and support a pivotal role for residue-33 in facilitating substrate binding to UGT1A9.

  • influence of n terminal domain histidine and proline residues on the substrate selectivities of human udp glucuronosyltransferase 1a1 1a6 1a9 2b7 and 2b10
    Drug Metabolism and Disposition, 2009
    Co-Authors: Oranun Kerdpin, Kushari Bowalgaha, Peter I. Mackenzie, Moshe Finel, John O Miners
    Abstract:

    An N-terminal domain histidine [corresponding to position 39 of UDP-glucuronosyltransferase (UGT) 1A1] is conserved in all UGT1A and UGT2B subfamily proteins except UGT1A4 (Pro-40) and UGT2B10 (Leu-34). Unlike most UGT1A and UGT2B xenobiotic-metabolizing enzymes, UGT1A4 and UGT2B10 lack the ability to glucuronidate 4-methylumbelliferone (4MU) and 1-naphthol (1NP), both planar phenols, and naproxen (a carboxylic acid). However, only UGT1A4 glucuronidates the tertiary amines lamotrigine (LTG) and trifluoperazine (TFP). In this study, we sought to elucidate the influence of specific N-terminal histidine and proline residues on UGT enzyme substrate selectivity. The conserved N-terminal domain histidine of UGT1A1, UGT1A6, UGT1A9, and UGT2B7 was mutated to proline and leucine 34 of UGT2B10 was substituted with histidine, and the capacity of the wild-type and mutant proteins to glucuronidate 4MU, 1NP, LTG, TFP, and naproxen was characterized. Whereas UGT1A1(H39P), UGT1A6(H38P), and UGT1A9(H37P) lacked the ability to metabolize 4MU, 1NP, and naproxen, all glucuronidated LTG. K(m) values for UGT1A1(H39P) and UGT1A9(H37P) were 774 and 3812 microM, respectively, compared with 1579 microM for UGT1A4. UGT1A1(H39P) also glucuronidated TFP with a V(max)/K(m) value comparable to that of UGT1A4. In contrast to the wild-type enzyme, UGT2B10(L34H) glucuronidated 4MU and 1NP with respective K(m) values of 260 and 118 microM. UGT2B7(H35P) lacked activity toward all substrates. The data confirm a pivotal role for an N-terminal domain proline in the glucuronidation of the tertiary amines LTG and TFP by UGT1A subfamily proteins, whereas glucuronidation reactions involving proton abstraction generally, although not invariably, require a histidine at the equivalent position in both UGT1A and UGT2B enzymes.

  • The Configuration of the 17-Hydroxy Group Variably Influences the Glucuronidation of β-Estradiol and Epiestradiol by Human UDP-Glucuronosyltransferases
    Drug Metabolism and Disposition, 2008
    Co-Authors: Katrina Itaaho, Shin Ichi Ikushiro, Peter I. Mackenzie, John O Miners, Moshe Finel
    Abstract:

    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.

John O Miners - One of the best experts on this subject based on the ideXlab platform.

  • inhibition of human udp glucuronosyltransferase enzymes by lapatinib pazopanib regorafenib and sorafenib implications for hyperbilirubinemia
    Biochemical Pharmacology, 2017
    Co-Authors: John O Miners, Kathleen M. Knights, Peter I. Mackenzie, Andrew Rowland, Nuy Chau, Kushari Burns, Ross A Mckinnon, G T Tucker, Ganessan Kichenadasse
    Abstract:

    Kinase inhibitors (KIs) are a rapidly expanding class of drugs used primarily for the treatment of cancer. Data relating to the inhibition of UDP-glucuronosyltransferase (UGT) enzymes by KIs is sparse. However, lapatinib (LAP), pazopanib (PAZ), regorafenib (REG) and sorafenib (SOR) have been implicated in the development of hyperbilirubinemia in patients. This study aimed to characterise the role of UGT1A1 inhibition in hyperbilirubinemia and assess the broader potential of these drugs to perpetrate drug-drug interactions arising from UGT enzyme inhibition. Twelve recombinant human UGTs from subfamilies 1A and 2B were screened for inhibition by LAP, PAZ, REG and SOR. IC50 values for the inhibition of all UGT1A enzymes, except UGT1A3 and UGT1A4, by the four KIs were <10μM. LAP, PAZ, REG and SOR inhibited UGT1A1-catalysed bilirubin glucuronidation with mean IC50 values ranging from 34nM (REG) to 3734nM (PAZ). Subsequent kinetic experiments confirmed that REG and SOR were very potent inhibitors of human liver microsomal β-estradiol glucuronidation, an established surrogate for bilirubin glucuronidation, with mean Ki values of 20 and 33nM, respectively. Ki values for LAP and PAZ were approximately 1- and 2-orders of magnitude higher than those for REG and SOR. REG and SOR were equipotent inhibitors of human liver microsomal UGT1A9 (mean Ki 678nM). REG and SOR are the most potent inhibitors of a human UGT enzyme identified to date. In vitro-in vivo extrapolation indicates that inhibition of UGT1A1 contributes significantly to the hyperbilirubinemia observed in patients treated with REG and SOR, but not with LAP and PAZ. Inhibition of other UGT1A1 substrates in vivo is likely.

  • effects of amino acid substitutions at positions 33 and 37 on udp glucuronosyltransferase 1a9 ugt1a9 activity and substrate selectivity
    Biochemical Pharmacology, 2012
    Co-Authors: Porntipa Korprasertthaworn, Krongtong Yoovathaworn, Benjamin C Lewis, Peter I. Mackenzie, Andrew Rowland, John O Miners
    Abstract:

    Abstract UGT1A9 contributes to the glucuronidation of numerous drugs and xenobiotics. There is evidence to suggest that the Met33Thr substitution, as occurs in the polymorphic variant UGT1A9*3, variably affects xenobiotic glucuronidation. The equivalent position in UGT1A4 is also known to influence enzyme activity, whilst an N-terminal domain histidine (His37 in UGT1A9) is believed to function as the catalytic base in most UGT enzymes. To elucidate the roles of key amino acids and characterise structure–function relationships, we determined the effects of amino acid substitutions at positions 33 and 37 of UGT1A9 on the kinetics of 4-methylumbelliferone (4-MU), mycophenolic acid (MPA), propofol (PRO), sulfinpyrazone (SFZ), frusemide (FSM), ( S )-naproxen (NAP) and retigabine (RTB) glucuronidation, compounds that undergo glucuronidation at either a phenolic (4-MU, MPA, PRO), carboxylate (FSM, NAP), acidic carbon (SFZ) or amine (RTB) function. Substitution of Met33 with Val, Ile, Thr, and Gln, as occur in UGT1A1, UGT1A3, UGT1A4 and UGT1A6 respectively, variably affected kinetics and catalytic efficiency. Whilst K m values were generally higher and V max and CL int values were generally lower than for wild-type UGT1A9 with most substrate-mutant pairs, the pattern and the magnitude of the changes in each parameter differed substantially. Moreover, exceptions occurred; CL int values for MPA and FSM glucuronidation by the position-33 mutants were the same as or higher than that of UGT1A9. Mutation of His37 abolished activity towards all substrates, except RTB N-glucuronidation. The data confirm the importance of single amino acids for UGT enzyme activity and substrate selectivity, and support a pivotal role for residue-33 in facilitating substrate binding to UGT1A9.

  • characterization of niflumic acid as a selective inhibitor of human liver microsomal udp glucuronosyltransferase 1a9 application to the reaction phenotyping of acetaminophen glucuronidation
    Drug Metabolism and Disposition, 2011
    Co-Authors: John O Miners, Kushari Bowalgaha, Pawel Baranczewski, David J. Elliot, Kathleen M. Knights
    Abstract:

    Enzyme selective inhibitors represent the most valuable experimental tool for reaction phenotyping. However, only a limited number of UDP-glucuronosyltransferase (UGT) enzyme-selective inhibitors have been identified to date. This study characterized the UGT enzyme selectivity of niflumic acid (NFA). It was demonstrated that 2.5 μM NFA is a highly selective inhibitor of recombinant and human liver microsomal UGT1A9 activity. Higher NFA concentrations (50–100 μM) inhibited UGT1A1 and UGT2B15 but had little effect on the activities of UGT1A3, UGT1A4, UGT1A6, UGT2B4, UGT2B7, and UGT2B17. NFA inhibited 4-methylumbelliferone and propofol (PRO) glucuronidation by recombinant UGT1A9 and PRO glucuronidation by human liver microsomes (HLM) according to a mixed (competitive-noncompetitive) mechanism, with Ki values ranging from 0.10 to 0.40 μM. Likewise, NFA was a mixed or noncompetitive inhibitor of recombinant and human liver microsomal UGT1A1 (Ki range 14–18 μM), whereas competitive inhibition (Ki 62 μM) was observed with UGT2B15. NFA was subsequently applied to the reaction phenotyping of human liver microsomal acetaminophen (APAP) glucuronidation. Consistent with previous reports, APAP was glucuronidated by recombinant UGT1A1, UGT1A6, UGT1A9, and UGT2B15. NFA concentrations in the range of 2.5 to 100 μM inhibited APAP glucuronidation by UGT1A1, UGT1A9, and UGT2B15 but not by UGT1A6. The mean Vmax for APAP glucuronidation by HLM was reduced by 20, 35, and 40%, respectively, in the presence of 2.5, 50, and 100 μM NFA. Mean Km values decreased in parallel with Vmax, although the magnitude of the decrease was smaller. Taken together, the NFA inhibition data suggest that UGT1A6 is the major enzyme involved in APAP glucuronidation.

  • influence of n terminal domain histidine and proline residues on the substrate selectivities of human udp glucuronosyltransferase 1a1 1a6 1a9 2b7 and 2b10
    Drug Metabolism and Disposition, 2009
    Co-Authors: Oranun Kerdpin, Kushari Bowalgaha, Peter I. Mackenzie, Moshe Finel, John O Miners
    Abstract:

    An N-terminal domain histidine [corresponding to position 39 of UDP-glucuronosyltransferase (UGT) 1A1] is conserved in all UGT1A and UGT2B subfamily proteins except UGT1A4 (Pro-40) and UGT2B10 (Leu-34). Unlike most UGT1A and UGT2B xenobiotic-metabolizing enzymes, UGT1A4 and UGT2B10 lack the ability to glucuronidate 4-methylumbelliferone (4MU) and 1-naphthol (1NP), both planar phenols, and naproxen (a carboxylic acid). However, only UGT1A4 glucuronidates the tertiary amines lamotrigine (LTG) and trifluoperazine (TFP). In this study, we sought to elucidate the influence of specific N-terminal histidine and proline residues on UGT enzyme substrate selectivity. The conserved N-terminal domain histidine of UGT1A1, UGT1A6, UGT1A9, and UGT2B7 was mutated to proline and leucine 34 of UGT2B10 was substituted with histidine, and the capacity of the wild-type and mutant proteins to glucuronidate 4MU, 1NP, LTG, TFP, and naproxen was characterized. Whereas UGT1A1(H39P), UGT1A6(H38P), and UGT1A9(H37P) lacked the ability to metabolize 4MU, 1NP, and naproxen, all glucuronidated LTG. K(m) values for UGT1A1(H39P) and UGT1A9(H37P) were 774 and 3812 microM, respectively, compared with 1579 microM for UGT1A4. UGT1A1(H39P) also glucuronidated TFP with a V(max)/K(m) value comparable to that of UGT1A4. In contrast to the wild-type enzyme, UGT2B10(L34H) glucuronidated 4MU and 1NP with respective K(m) values of 260 and 118 microM. UGT2B7(H35P) lacked activity toward all substrates. The data confirm a pivotal role for an N-terminal domain proline in the glucuronidation of the tertiary amines LTG and TFP by UGT1A subfamily proteins, whereas glucuronidation reactions involving proton abstraction generally, although not invariably, require a histidine at the equivalent position in both UGT1A and UGT2B enzymes.

  • The Configuration of the 17-Hydroxy Group Variably Influences the Glucuronidation of β-Estradiol and Epiestradiol by Human UDP-Glucuronosyltransferases
    Drug Metabolism and Disposition, 2008
    Co-Authors: Katrina Itaaho, Shin Ichi Ikushiro, Peter I. Mackenzie, John O Miners, Moshe Finel
    Abstract:

    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.