UDP-glucuronosyltransferase 1A1 is the principal enzyme responsible for puerarin metabolism in human liver microsomes

Puerarin has multiple pharmacological effects and is widely prescribed for patients with cardiovascular diseases, including hypertension, cerebral ischemia, myocardial ischemia, diabetes mellitus, and arteriosclerosis. While puerarin is a useful therapeutic agent, its mechanisms of action have not been well defined. Understanding puerarin metabolism, in particular its interactions with metabolizing enzymes, will contribute to our understanding of its toxic and therapeutic effects and may help to elucidate potential negative drug–drug interactions. In this study, the major metabolite of puerarin was obtained from the urine of rats administered puerarin, by a semi-preparative high-performance liquid chromatography method. The major metabolite was identified as puerarin-7-O-glucuronide. In vitro, we used a UDP-glucuronosyltransferase (UGT) reaction screening method with 12 recombinant human UGTs to demonstrate that formation of puerarin-7-O-glucuronide was catalyzed by UGT1A1, 1A9, 1A10, 1A3, 1A6, 1A7, and 1A8. UGT1A1, 1A9, and 1A10 significantly catalyzed puerarin-7-O-glucuronide formation, and the activity of UGT1A1 was significantly higher than those of 1A9 and 1A10. The V _max of UGT1A1 was two- to threefold higher than the levels of UGT1A9 or 1A10, with a lower K _m value and a higher V _max/K _m value. The kinetics of puerarin-7-O-glucuronide formation catalyzed by UGT1A1 were similar to those of the pooled human liver microsomes (HLMs), with V _max values of 186.3 and 149.2?pmol/min/mg protein, and K _m values of 811.3 and 838.9?μM, respectively. Furthermore, bilirubin and β-estradiol, probe substrates for UGT1A1, significantly inhibited the formation of puerarin-7-O-glucuronide in HLMs.