Glucuronide formation is a major route of xenobiotic and endobiotic metabolism in humans. UDP-glucuron-osyltransferases (UGTs), protein products of a supergene family, mediate these reactions whereby hydrophobic compounds (aglycones) are conjugated to glucuronic acid, forming metabolites which are rapidly excreted by the kidney or liver. Four areas of research are planned. First, the significance of the polymorphic isoforms of UGT2B7 in the metabolism of certain substrates (losartan and zidovudine) will be explored using HK293 cell lines stable expressing these proteins. Using hepatic microsomes from individuals homozygous for these polymorphic isoforms, studies will address the question of whether inter-individual variation in AZT glucuronidation can be predicted base don the genotype of the individual. mRNA and glucuronidation activities for UGT2B7 and UGT1A6 have been found in human brain. Studies are proposed to use immunohistochemical localization to identify the cell types that express these proteins in the brain. Since immunohistochemical localization to identify the cell types that express these proteins in the brain. Since UGT2B7 catalyzes the formation of morphine-6-glucuronide (which is 50 times more potent that morphine as an analgesic) it is important to know where in the rain morphine-6-glucuronide can be formed because its local formation may account for part of the mechanism of action of morphine. Studies determining the substrate specificities of UGTs expressed in intestine, 1A8 and 1A5, are proposed. These isoforms are not expressed in liver and, therefore, may play an important role in xenobiotic and endobiotic metabolism in the intestine. UGT1A4 is an important enzyme because it catalyzes the glucuronidation of tertiary amines (e.g., anti-histamines) and progestins, whereas UGT1A3 catalyzes the glucuronidation of estrogens and NSAIDs. Studies are proposed that will investigate how the protein structure of UGT1A3 and UGT1A4 affects the function of the expressed enzymes. Chimeric proteins and amino acid substitutions will examine the aglycone binding sites for substrates which are unique to each protein and which are common for each UGT.
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