Nitidine Chloride Is a Mechanism-Based Inactivator of CYP2D6

Abstract

Nitidine chloride (NC) is a benzophenanthridine alkaloid isolated from the roots of (Roxb.) DC, a widely used traditional herbal medicine. Several reports have revealed NC's multiple pharmacologic properties. The inhibitory effects of NC on human cytochrome P450 enzymes were investigated in the present study. We found that NC caused time- and concentration-dependent inhibition of CYP2D6, and more than 50% of CYP2D6 activity was suppressed after a 15-minute incubation with NC at 100M in the primary incubation mixtures, with of 4.36M, of 0.052 minute, and a partition ratio of approximately 290. Moreover, the loss of CYP2D6 activity required the presence of NADPH. Superoxide dismutase/catalase and glutathione showed minor protection against the NC-induced enzyme inhibition. Quinidine as a competitive inhibitor of CYP2D6 slowed down the inactivation by NC. Trapping experiments using -acetylcysteine demonstrated that quinone and/or carbene intermediate(s) were/was generated in human liver microsomal incubations with NC. In addition, potassium ferricyanide prevented the enzyme from the inactivation mediated by NC, which provided evidence that inhibition of CYP2D6 resulted from heme destruction by the formation of a carbene-iron complex. CYP1A2 was found to be the major enzyme involved in the generation of NC quinone metabolites. In conclusion, NC is a mechanism-based inactivator of CYP2D6. The generation of a carbene intermediate might be mainly responsible for the enzyme inactivation.

Identification of the metabolite of ophiopogonanone A by liquid chromatography/quadrupole time‐of‐flight mass spectrometry

“…Sitaxentan serves as an example 21 . In addition, these intermediates can interact with P450 enzymes, resulting in P450 enzymes inactivation, and amplify the potential of drug–drug interactions 11,16 . Therefore, further studies need to be performed to evaluate the safety of OPA.…”

“…OPA contains a methylenedioxyphenyl moiety, which is a well‐known alert functional group that can be readily bioactivated into ortho ‐quinone intermediate 11,16 . To trap the reactive intermediate, GSH was incorporated in the microsomal incubations.…”

“…G1, G2, G3, and G4 were detected at the retention times of As indicated by previous publications, 1,3-benzodioxole moiety can be bioactivated into carbene and ortho-quinone species. 10,11,16 These species are highly reactive and can covalently bind to proteins, leading to protein dysfunction. Sitaxentan serves as an example.…”

“…It has been well documented that the methylenedioxyphenyl moiety is ready to undergo cytochrome P450 enzyme–catalyzed metabolism, resulting in the formation of catechol derivative 10 . Such biotransformation may lead to reactive metabolites carbene and ortho ‐quinone intermediates that may bring some unwanted side effects 11–16 . Therefore, it is necessary to identify and profile the metabolites of OPA, especially the identification of reactive metabolites.…”

“…10 Such biotransformation may lead to reactive metabolites carbene and ortho-quinone intermediates that may bring some unwanted side effects. [11][12][13][14][15][16] Therefore, it is necessary to identify and profile the metabolites of OPA, especially the identification of reactive metabolites.…”