Cytotoxicity of safrole in HepaRG cells: studies on the role of CYP1A2-mediated ortho-quinone metabolic activation

1. Safrole is a natural compound categorized as a group 2B carcinogen extracted from sassafras oil or certain other essential oils. The hepatotoxicity of safrole has always been highly concerned. So, the purpose of this study was to evaluate the role of cytochrome P450 (CYP450)-mediated reactive metabolites (RMs) formation and its induced cytotoxicity in HepaRG cells.

2. Safrole belongs to the methylenedioxyphenyl structure which could be activated to RMs. Two metabolites (M1, M2) and three new glutathione conjugates (M3–M5) of safrole ortho-oquinone RMs were found in HepaRG cells. Using human recombinant CYP450 enzymes and chemical inhibitor method, the metabolism of safrole RMs was predominantly carried out through the CYP1A2 with minor contributions by CYP2E1.

3. Induction of CYP1A2 by omeprazole (OME) enhanced safrole-induced cytotoxicity, compared with treatment with safrole alone, whereas inhibition of CYP1A2 by alpha-naphthoflavone (α-NAP) decreased the cytotoxicity. The cytotoxicity of cell induced by safrole was related to the amount of RMs formation. Besides, pretreatment with L-buthionine sulfoximine (BSO) to deplete intracellular GSH markedly enhanced safrole-induced cytotoxicity. OME induced the safrole-induced GSH exhaustion, and GSH depletion by safrole was not via oxidation of GSH and occurred prior to the increase in ROS. Furthermore, mitochondrial membrane potential (ΔΨm) could be aggravated by the inducer of CYP1A2 together with safrole. Collectively, these data suggest that the ortho-quinone RM may mediate safrole hepatotoxicity, and CYP1A2 was the core enzyme in ortho-quinone RMs-mediated safrole hepatotoxicity.