Inhibitory mechanism of tetrahydropalmatine enantiomers on cytochrome P450 in human liver microsomes / 中草药

ABSTRACT

Objective: To investigate the inhibition of tetrahydropalmatine (THP) enantiomers on main cytochrome P450 (CYP450) in human liver microsomes and the mechanism. Methods: The effects of (-)-THP and (+)-THP on the activies of main phase I metabolic enzymes in human liver microsomes, CYP1A2, CYP2C9, CYP2C19, CYP3A1, CYP2E1, and CYP2D6 were investigated using Cocktail probe drugs method; The effect of preincubation with (-)-THP on the CYP2D6 substrate dextromethorphan demethylation activity in human liver microsomes were investigated using a two-step incubation scheme and study its inhibitory mechanism was studied; The enzyme inhibitory kinetic parameters of CYP2D6 by (-)-THP were investigated using time-dependent incubation with human liver microsomes. Results: The inhibitory effect of (+)-THP on CYP450 subtype was not significant, while.CYP2D6 activity was significantly inhibited by (-)-THP (IC50 = 0.46 μmol/L). The value of IC50 preincubation with or without NADPH were 2.40 and 0.46 μmol/L, respectively, IC50 (-) NADPH/IC50 (+) NADPH = 5.22. And the enzyme inhibitory kinetic parameters of Ki and Kinact were 0.690 μmol/L and 0.0846 min-1, respectively. Conclusion: (-)-THP has a strong inhibition on CYP2D6, and the type of inhibition is mechanism-based inhibiton (MBI), which should indicate a potential metabolic drug-drug interaction mediated by (-)-THP in clinical application.