Use of a human liver microsome bank in drug glucuronidation studies

A bank of readily available, well characterized human hepatic microsomal fractions (29 samples from different livers) has been established. The enzymatic characteristics of each microsome sample were determined using three specific UDP-glucuronosyltransferase (UDPGT) substrates (p-nitrophenol for UDPGT(1), 4-hydroxybiphenyl for UDPGT(2)A and monodigitoxoside digitoxigenin (DT(1)) for UDPGT(7)). After characterization, the bank was used to study the phase II biotransformation processes of two drugs: an antiviral, zidovudine (AZT), and an intermediate metabolite of digoxin, monodigitoxoside digoxigenin (DG(1)). Results showed a wide interindividual variability for the glucuronidation rate of 4-hydroxybiphenyl, DT(1), AZT and DG(1). Surprisingly, this variability was lower for p-nitrophenol. No significant correlation was found between the various activities except between DG(1) and DT(1) UDPGT activities and 4-hydroxybiphenyl and AZT UDPGT activities. For AZT, further experiments showed that glucuronidation of this antiviral compound was inhibited by 4-hydroxybiphenyl and chloramphenicol but not by morphine, p-nitrophenol, acetaminophen, or bilirubin. Finally, the results strongly suggest the respective involvement of UDPGT(2)A and UDPGT(7) in the glucuronidation of AZT and DG(1).