Metabolic Activation and Cytotoxicity of Propafenone Mediated by CYP2D6

Propafenone (PPF) is a class I_C antidysrhythmic drug, which is commonly used for the treatment of atrial fibrillation and other supraventricular arrhythmias. It is also a β-adrenoceptor antagonist that can cause bradycardia and bronchospasm. Hepatotoxicity is one of the adverse reactions reported, with clinical manifestations including acute cholestasis and hepatocyte necrosis. However, the mechanism of PPF-induced hepatotoxicity remains unclear. The present study was conducted to identify reactive metabolite(s) to determine related metabolic pathways and define the possible association of the bioactivation with PPF cytotoxicity. An O-demethylation phase I metabolite (M1), a further position C5 hydroxylation (para-position of the benzene ring) metabolite (M2), glutathione (GSH) conjugates (M3 and M4), and N-acetylcysteine (NAC) conjugates (M5 and M6) were detected in rat liver microsomal incubations containing PPF and GSH or NAC as trapping agents. The corresponding GSH conjugates and NAC conjugates were found in the bile and urine of rats after PPF administration, respectively. The observed GSH and NAC conjugates indicate that a quinone metabolite was generated in vitro and in vivo. Recombinant P450 enzyme incubations showed that CYP2D6 was the principal enzyme catalyzing this metabolic activation. Quinidine, a selective inhibitor of CYP2D6, attenuated the susceptibility of hepatocytes to the cytotoxicity of PPF. The results suggest that PPF was metabolized to a p-quinone intermediate which may be involved in PPF-induced hepatotoxicity.