Metabolic Activation of trans-Anethole Plays a Role in Hepatic Cytotoxicity in Mice

trans-Anethole (1-methoxy-4-[1(E)-propenyl]benzene, tAT) is the main ingredient in the essential oil extracted from star anise fruits. The double bonds in the side chain of tAT are a type of alert structure that can be metabolized into epoxides possibly causing liver damage. This work investigated and identified the reactive metabolites of tAT that are chemically reactive to biothiols, such glutathione (GSH), N-acetyl-l-cysteine (NAC), and cysteine residues of proteins. Four GSH conjugates (M2–M5) and two NAC conjugates (M6 and M7), which are derived from epoxide metabolite of tAT, were found in bile and urine, respectively. Four cysteine adducts (M8–M11) were found in proteolytic liver proteins isolated from mice administered tAT. The formation of protein adduction exhibited a dose-dependent pattern. Cytochrome P450 1A (CYP1A) dominated the side chain epoxidation of tAT. Exposure to tAT induced cytotoxicity in cultured mouse primary hepatocytes. Pretreatment of hepatocytes with α-naphthoflavone decreased the susceptibility of the cells to tAT cytotoxicity.