Species Differences in Ezetimibe Glucuronidation

Abstract ID 95840 Poster Board 432 Authors: Shalom Emmanuel, MPH; Eric Asare, PharmD; Gao Song, Ph.D.; and Ting Du, Ph.D. Department of Pharmaceutical Science, College of Pharmacy and Health Sciences, Texas Southern University, Houston, TX, USA Background: Ezetimibe is a potent cholesterol absorption inhibitor that is primarily metabolized by uridine diphospate glucuronosyltransferase (UGT), specifically UGT1A1 in the liver and intestine. Studies have revealed that Ezetimibe is rapidly and extensively metabolized to its glucuronide, Ezetimibe Phenoxy beta-d-glucuronide, in the intestine after oral administration. The study aimed to characterize the impact of species differences in Ezetimibe glucuronidation in the intestines of rats, mice, monkeys, and dogs. Method: Ezetimibe glucuronidation was fitted to the Michaelis-Menten model using intestinal microsomes from rats, monkeys, mice, and dogs. The glucuronidation metabolism reaction was conducted in vitro using ezetimibe as the substrate. An enzyme kinetic study was carried out by assaying 0.01 mg/mL of intestinal microsomes from the different species and incubating them at 37oC with varying substrate concentrations for 1 hour. Ultra-performance liquid chromatography was used to quantify the metabolites formed, and GraphPad prism was used to generate the Michaelis-Menten plot to determine enzyme kinetic activity and kinetics (Km and Vmax). Results: The maximum velocity was higher in monkeys (Vmax = 3.86 nmol/mg/min) than in dogs (Vmax = 1.18 nmol/mg/min), but was similar between mice and rats (Vmax = 2.23 nmol/mg/min and Vmax = 2.35 nmol/mg/min, respectively). There were also differences in the rate of ezetimibe metabolism in monkey intestinal microsomes (Km = 8.00 uM), rat intestinal microsomes (Km = 3.33 uM), mouse intestinal microsomes (Km = 0.57 uM), and dog intestinal microsomes (Km = 2.59 uM). Conclusion: This study revealed that species differences exist in the metabolism of ezetimibe and have an impact on ezetimibe glucuronidation in the intestine. When analyzing the pharmacodynamics and pharmacokinetics of ezetimibe, these species differences must be taken into consideration. Keywords: Ezetimibe, enzyme kinetic study, species differences, glucuronidation, UGT