Regulation of drug metabolism and toxicity by multiple factors of genetics, epigenetics, lncRNAs, gut microbiota, and diseases: a meeting report of the 21International Symposium on Microsomes and Drug Oxidations (MDO)

Variations in drug metabolism may alter drug efficacy and cause toxicity; better understanding of the mechanisms and risks shall help to practice precision medicine. At the 21International Symposium on Microsomes and Drug Oxidations held in Davis, California, USA, in October 2-6, 2016, a number of speakers reported some new findings and ongoing studies on the regulation mechanisms behind variable drug metabolism and toxicity, and discussed potential implications to personalized medications. A considerably insightful overview was provided on genetic and epigenetic regulation of gene expression involved in drug absorption, distribution, metabolism, and excretion (ADME) and drug response. Altered drug metabolism and disposition as well as molecular mechanisms among diseased and special populations were presented. In addition, the roles of gut microbiota in drug metabolism and toxicology as well as long non-coding RNAs in liver functions and diseases were discussed. These findings may offer new insights into improved understanding of ADME regulatory mechanisms and advance drug metabolism research.

17-Estradiol up-regulates UDP-glucuronosyltransferase 1A9 expressionestrogen receptor

UDP-glucuronosyltransferase 1A9 (UGT1A9) is a major phase II enzyme responsible for elimination of drugs and endogenous molecules. Clinical data have shown increased elimination of UGT1A9 substrates in pregnant women or oral contraceptive users, but the role of estrogen in the regulation of UGT1A9 expression remains unknown. In this study, we investigated the effect of 17-estradiol (E2) on UGT1A9 expression and the role of ERin the transcriptional regulation of UGT1A9. E2 significantly increased UGT1A9 promoter activity in HepG2 cells in the presence of ER. UGT1A9 induction by E2 was abrogated by antiestrogen ICI182,780 in HepG2 cells that constitutively express ER. Results from transient transfection of ERmutants into HepG2 cells demonstrated that mutation at DNA-binding domain of ERabrogates increased UGT1A9 promoter activity by E2. Deletion and mutation assays of UGT1A9 promoter revealed a putative ERE located within -2262/-1987 region. Examination of healthy human liver tissues revealed significantly higher UGT1A9 expression in women as compared to men. Together, these findings provide a mechanistic basis for the previous clinical reports and may shed a light on identifying sources for inter-individual variability in UGT1A9-mediated drug metabolism.