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Identifying and applying a highly selective probe to simultaneously determine the O-glucuronidation activity of human UGT1A3 and UGT1A4.

ABSTRACT: Glucuronidation mediated by uridine 5'-diphospho (UDP)-glucuronosyltransferase is an important detoxification pathway. However, identifying a selective probe of UDP- glucuronosyltransferase is complicated because of the significant overlapping substrate specificity displayed by the enzyme. In this paper, desacetylcinobufagin (DACB) 3-O- and 16-O-glucuronidation were found to be isoform-specific probe reactions for UGT1A4 and UGT1A3, respectively. DACB was well characterized as a probe for simultaneously determining the catalytic activities of O-glucuronidation mediated by UGT1A3 and UGT1A4 from various enzyme sources, through a sensitive analysis method.

SUBMITTER: Jiang L

PROVIDER: S-EPMC4401096 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:INTRODUCTION:Clozapine (CLZ) is an FDA approved second-generation antipsychotic for refractory schizophrenia, and glucuronidation is an important pathway in its metabolism. The aim of this study was to fully characterize the CLZ glucuronidation pathway and examine whether polymorphisms in active glucuronidating enzymes could contribute to variability in CLZ metabolism. METHODS:Cell lines overexpressing wild-type or variant uridine diphosphate-glucuronosyltransferase (UGT) enzymes were used to determine which UGTs show activity against CLZ and its major active metabolite N-desmethylclozapine (dmCLZ). Human liver microsomes (HLM) were used to compare hepatic glucuronidation activity against the UGT genotype. RESULTS:Several UGTs including 1A1 and 1A4 were active against CLZ; only UGT1A4 showed activity against dmCLZ. UGT1A1 showed a 2.1-fold (P <0.0001) higher V(max)/K(M) for formation of the CLZ-N?-glucuronide than UGT1A4; UGT1A4 was the only UGT for which CLZ-5-N-glucuronide kinetics could be determined. The UGT1A4(24Pro/48Val) variant showed a 5.2-, 2.0-, and 3.4-fold (P < 0.0001 for all) higher V(max)/K(M) for the formation of CLZ-5-N-glucuronide, CLZ-N?-glucuronide, and dmCLZ-5-N-glucuronide, respectively, as compared with that of wild-type UGT1A4(24Pro/48Leu). There was a 37% (P< 0.05) decrease in the rate of CLZ-N?-glucuronide formation in HLM with the UGT1A1 (*28/*28)/UGT1A4 (*1/*1) genotype, and a 2.2- and 1.8-fold (P < 0.05 for both) increase in the formation of CLZ-5-N-glucuronide and CLZ-N?-glucuronide in UGT1A1 (*1/*1)/UGT1A4 (*3/*3) HLM compared with UGT1A1 (*1/*1)/UGT1A4 (*1/*1) HLM. The UGT1A1*28 allele was a significant (P = 0.045) predictor of CLZ-N?-glucuronide formation; the UGT1A4*3 allele was a significant (P < 0.0001) predictor of CLZ-5-N-glucuronide and dmCLZ-glucuronide formation. CONCLUSION:These data suggest that the UGT1A1*28 and UGT1A4*3 alleles contribute significantly to the interindividual variability in CLZ and dmCLZ metabolism.

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Identifying and applying a highly selective probe to simultaneously determine the O-glucuronidation activity of human UGT1A3 and UGT1A4.

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