Mechanism-based inhibition of human liver microsomal cytochrome P450 2D6 (CYP2D6) by alkamides of Piper nigrum

Nineteen alkamides isolated from Piper nigrum L. were tested for their mechanism-based inhibition on human liver microsomal dextromethorphan O-demethylation activity, a prototype marker for cytochrome P450 2D6 (CYP2D6). All compounds increased their inhibitory activity with increasing preincubation time. Among them, 15 and 17 showed more than 50% decrease of the CYP2D6 residual activity after 20 min preincubation. Further investigations on 15 and 17 showed that the characteristic time and concentration-dependent inhibition, which required a catalytic step with NADPH, was not protected by nucleophiles, and was decreased by the presence of a competitive inhibitor. The kinetic. parameters for inactivation (k(inact) and k(I)) were 0.028 min(-1) and 0.23 mu M for 15 and 0.064 min(-1) and 0.71 mu M for 17, respectively, which were stronger than the known mechanism-based inhibitor, paroxetine (a positive control). Thus, 15 and 17 are potent mechanism-based inhibitors of CYP2D6.