In Vitro and in Vivo Studies of the Electrophilicity of Physcion and its Oxidative Metabolites.

Physcion (1,8-dihydroxy-3-methoxy-6-methyl-9,10-anthracenedione) is a bioactive component found in Polygoni Multiflori Radix (PMR), which has been widely used as traditional Chinese medicine. Unfortunately, studies showed hepatotoxicity of PMR during its clinical use. The mechanisms of its toxic action remain unknown. The major objectives of this study were to characterize oxidative metabolites of physcion in vitro and in vivo and to determine the electrophilicity of the parent compound and its oxidative metabolites. Five oxidative metabolites (M1-M5) were detected in rat liver microsomal incubations after exposure to physcion, and the formation of the metabolites was NADPH dependent. M1-M4 were monohydroxylation metabolites, and M5 was O-demethylation metabolite. A total of three N-acetylcysteine (NAC) conjugates (M6-M8) were observed in rat liver microsomes fortified with NAC as a trapping agent. M6 was derived from M4 conjugated with a molecule of NAC; M7 and M8 originated from parent compound physcion adducted with a molecule of NAC, respectively. M1-M8 were also observed in urine of rats given physcion. HLM incubations produced four oxidative metabolites and two NAC conjugates. The structures of M3, M7, and M8 were characterized by LC-Q-TOF MS and NMR. Recombinant P450 enzyme incubations demonstrated that CYPs2C19, 1A2, 2B6, and 3A4 were mainly involved in hydroxylation of physcion. The metabolism study assisted us to better understand the mechanisms of physcion-induced hepatotoxicity.