Enzyme kinetics of ligustilide metabolism in rat liver microsomes

To study the enzyme kinetics of ligustilide metabolism and the effects of selective CYP450    inhibitors on the metabolism of ligustilide in liver microsomes of rat, a LC-MS method was established for  quantitative analysis of ligustilide in liver microsomes incubation system with nitrendipine as internal standard.  The determination m/z for ligustilide was 173, and for nitrendipine, 315.  An optimum incubation system was found and various selective CYP inhibitors were used to investigate their inhibitory effects on the metabolism of ligustilide.  The results showed that enzyme kinetics of ligustilide could be significantly inhibited by ketoconazole, trimethoprim and α-naphthoflavon but scarcely inhibited by omeprazole, 4-methylpyrazole and quinidine.  Therefore, CYP3A4, CYP2C9 and CYP1A2 are the major isoenzyme participated in in vitro metabolism of ligustilide.