Glucuronidation, catalyzed by the UDP-glucuronosyltransferase (UGT) enzymes, is an important metabolic pathway involved in the inactivation and excretion of a multitude of drugs, toxins, potential carcinogens and endobiotics. The long-term objectives of this research are to elucidate the molecular determinates of individual variability in UGT1A6 function. In doing so, it may then be possible to identify individuals within a population that may be at high risk for adverse drug reactions and interactions, susceptibility to environmental toxins and carcinogens, as well as those with inborn errors of endogenous metabolism. UGT1A6 preferentially glucuronidates planar phenolic xenobiotics and substantially contributes to the biotransformation of acetaminophen. Acetaminophen glucuronidation in humans appears to be heterogenous and the molecular basis for this phenomenon is currently unknown. There is evidence for functionally relevant polymorphisms in the human UGT1A6 gene, which may affect either substrate affinity or enzyme content. Furthermore, recent studies suggest that UGT isoforms can form heterodimers which could modulate UTG1A6-mediated glucuronidation through protein-protein interactions.
Three specific aims are proposed: (1) To utilize acetaminophen as a probe substrate for UTG1A6-mediated glucuronidation which will be substantiated by comparative activity and enzyme kinetic determinations using currently available cDNA-expressed UGT isoforms, and by isoform-specific immunoinhibition of acetaminophen glucuronidation in human liver microsomes: (2) To investigate the influence of polymorphisms in the UGT1A6 gene on isoenzyme content and specific activity ascertained by comparisons of expressed wild-type and variant UGT1A6, and by phenotypic-genotypic analyses using human liver microsomes and (3) To investigate the potential role for protein-protein interactions in modulating UGT1A6-mediated glucuronidation by identifying interacting proteins with the yeast two-hybrid expression system, and substantiating the functional significance of these interactions by coexpression studies.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Pharmacology A Study Section (PHRA)
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Okita, Richard T
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Tufts University
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Court, Michael H; Zhu, Zhaohui; Masse, Gina et al. (2017) Race, Gender, and Genetic Polymorphism Contribute to Variability in Acetaminophen Pharmacokinetics, Metabolism, and Protein-Adduct Concentrations in Healthy African-American and European-American Volunteers. J Pharmacol Exp Ther 362:431-440
Court, Michael H; Almutairi, Fawziah E; Greenblatt, David J et al. (2014) Isoniazid mediates the CYP2B6*6 genotype-dependent interaction between efavirenz and antituberculosis drug therapy through mechanism-based inactivation of CYP2A6. Antimicrob Agents Chemother 58:4145-52
Haas, David W; Kwara, Awewura; Richardson, Danielle M et al. (2014) Secondary metabolism pathway polymorphisms and plasma efavirenz concentrations in HIV-infected adults with CYP2B6 slow metabolizer genotypes. J Antimicrob Chemother 69:2175-82
Court, Michael H; Peter, Inga; Hazarika, Suwagmani et al. (2014) Candidate gene polymorphisms in patients with acetaminophen-induced acute liver failure. Drug Metab Dispos 42:28-32
Kwara, Awewura; Cao, Lei; Yang, Hongmei et al. (2014) Factors associated with variability in rifampin plasma pharmacokinetics and the relationship between rifampin concentrations and induction of efavirenz clearance. Pharmacotherapy 34:265-71
Court, Michael H (2013) Feline drug metabolism and disposition: pharmacokinetic evidence for species differences and molecular mechanisms. Vet Clin North Am Small Anim Pract 43:1039-54
Court, Michael H; Freytsis, Marina; Wang, Xueding et al. (2013) The UDP-glucuronosyltransferase (UGT) 1A polymorphism c.2042C>G (rs8330) is associated with increased human liver acetaminophen glucuronidation, increased UGT1A exon 5a/5b splice variant mRNA ratio, and decreased risk of unintentional acetaminophen-induce J Pharmacol Exp Ther 345:297-307
Molter, Christine M; Court, Michael H; Cole, Gretchen A et al. (2013) Pharmacokinetics of meloxicam after intravenous, intramuscular, and oral administration of a single dose to Hispaniolan Amazon parrots (Amazona ventralis). Am J Vet Res 74:375-80
Hanley, Michael J; Masse, Gina; Harmatz, Jerold S et al. (2013) Effect of blueberry juice on clearance of buspirone and flurbiprofen in human volunteers. Br J Clin Pharmacol 75:1041-52
Court, Michael H (2013) Canine cytochrome P-450 pharmacogenetics. Vet Clin North Am Small Anim Pract 43:1027-38

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