The influence of ginsenosides on cytochrome P450 reductase

Our previous studies had shown that some naturally occurring ginsenosides or their metabolites exhibited inhibition of cytochrome P450 isoforms (P450) activities to different extent. Considering that cytochrome P450 reductase (CPR) is the electron donator in P450 catalytic cycle, the fluctuation of CPR activity might result in a variation of P450 metabolic activity. In this study, the effects on the CPR activity of ginsenosides Rb1, Rb2, Rc, Rd, Re, Rg1, Rg2, R-Rg3, S-Rg3, Rh1, F1, Ppt, Ppd, and C-K were further investigated in human liver microsomes. The CPR activity was indicated by its specific reaction, MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) oxidation. The inhibitive effects of ginsenosides on CPR activity were assayed. The results demonstrated that ginsenosides Rg1 and Rc of 100μM inhibited the CPR activity with the reduction of CPR activity by 25% and 20% respectively, while the other ginsenosides exhibited no significant inhibition (<5%). The further inhibitory kinetics studies showed that with the non-linear regression analysis, the Ki values of Rg1 and Rc were calculated to be 151.1±1.3 μM and 178.9±1.1 μM, respectively. In addition, their inhibition types to CPR activity were different. Rg1 non-competitively inhibited CPR activity, while the inhibition type of Rc on CPR activity was un-competitive. The discrepant inhibitive models might be correlated with their different molecular structures.