%0 Journal Article %A Hyunyoung Lee %A Jae-Kyung Heo %A Ga-Hyun Lee %A So-Young Park %A Su Nyeoung Jang %A Hyun-Ji Kim %A Mi Jeong Kwon %A Im-Sook Song %A Kwang-Hyeon Liu %T Ginsenoside Rc is a new selective UGT1A9 inhibitor in human liver microsomes and recombinant human UGT isoforms %D 2019 %R 10.1124/dmd.119.087965 %J Drug Metabolism and Disposition %P dmd.119.087965 %X Ginseng is known to have inhibitory effects on UGT1A9 activity. However, little is known about the inhibitory effects of ginsenosides, the major active compounds in ginseng, on UGT1A9 activity. In vitro investigation of UGT1A9 inhibition by ginsenosides was carried out using human liver microsomes (HLMs). Among ten ginsenosides, ginsenoside Rc was the strongest inhibitor of UGT1A9-mediated mycophenolic acid glucuronidase activity. Further inhibition kinetic studies using HLMs suggested that ginsenoside Rc competitively and noncompetitively inhibited UGT1A9-mediated propofol and mycophenolic acid glucuronidation activities with Ki values of 2.83 and 3.31 μM, respectively. Next, to investigate whether the inhibitory effect of ginsenoside Rc is specific to the UGT1A9 isoform, we studied the inhibitory potency of ginsenoside Rc on nine human UGT activities using recombinant human UGT isoforms. Ginsenoside Rc exhibited a 12.9-fold selectivity (which was similar to niflumic acid at 12.5-fold) for UGT1A9 inhibition. Ginsenoside Rc at 50 μM also inhibited none of the other UGT isoform-specific activities above 12.0%, except for UGT1A9 (>91.5%) in HLMs, indicating that ginsenoside Rc might be used as a selective UGT1A9 inhibitor in reaction phenotyping studies of new chemical entities. Considering lower plasma concentrations (0.01 μM) of ginsenoside Rc in healthy subjects and no induction potential on UGT isoforms, ginsenoside Rc does not cause pharmacokinetic drug interactions with other co-administered drugs metabolized by UGT1A9.SIGNIFICANCE STATEMENT Ginsenoside Rc selectively inhibited UGT1A9-mediated propofol and mycophenolic acid glucuronidation activities in human liver microsomes and recombinant UGT isoforms. It exhibited a 12.9-fold selectivity for UGT1A9 inhibition. Therefore, ginsenoside Rc might be used as a selective UGT1A9 inhibitor in reaction phenotyping studies of new chemical entities such as niflumic acid. %U https://dmd.aspetjournals.org/content/dmd/early/2019/10/02/dmd.119.087965.full.pdf