Glucuronidation of drugs in humanized UDP ‐glucuronosyltransferase 1 mice: Similarity with glucuronidation in human liver microsomes

Abstract Uridine 5′‐diphosphate ‐glucuronosyltransferases ( UGTs ) are phase II drug‐metabolizing enzymes that catalyze glucuronidation of various endogenous and exogenous substrates. Among 19 functional human UGTs , UGT1A family enzymes largely contribute to the metabolism of clinically used drugs. While the UGT1A locus is conserved in mammals such as humans, mice, and rats, species differences in drug glucuronidation have been reported. Recently, humanized UGT1 mice in which the original Ugt1 locus was disrupted and replaced with the human UGT 1 locus ( hUGT 1 mice) have been developed. To evaluate the usefulness of hUGT 1 mice to predict human glucuronidation of drugs, UGT activities, and inhibitory effects on UGT s were examined in liver microsomes of hUGT 1 mice as well as in those of wild‐type mice and humans. Furosemide acyl‐glucuronidation was sigmoidal and best fitted to the Hill equation in hUGT 1 mice and human liver microsomes, while it was fitted to the substrate inhibition equation in mouse liver microsomes. Kinetic parameters of furosemide glucuronidation were very similar between hUGT 1 mice and human liver microsomes. The kinetics of S ‐naproxen acyl‐glucuronidation and inhibitory effects of compounds on furosemide glucuronidation in hUGT 1 liver microsomes were also slightly, but similar to those in human liver microsomes, rather than in wild‐type mice. While wild‐type mice lack imipramine and trifluoperazine N ‐glucuronidation potential, hUGT 1 mice showed comparable N ‐glucuronidation activity to that of humans. Our data indicate that hUGT 1 mice are promising tools to predict not only in vivo human drug glucuronidation but also potential drug‐drug interactions.