Chemical Interaction of Protein Cysteine Residues with Reactive Metabolites of Methyleugenol

Methyleugenol (ME), an alkenylbenzene compound, is a natural ingredient of several herbs and is used as flavoring agent in foodstuffs and fragrance in cosmetics. The hepatotoxicity, cytotoxicity, and carcinogenesis of ME have been well documented, and metabolic activation has been suggested to involve in ME-induced toxicities. The objective of this study was to identify chemical identity of interactions of protein with reactive metabolites of ME. Modification of cysteine residues of protein was observed in microsomal incubations and mice after exposure to ME. Three types of protein modification derived from the corresponding epoxide, α,β-unsaturated aldehyde, and carbonium ion of ME were detected in vitro and in vivo. The protein adduction took place in time- and dose-dependent manners. Dexamethasone, ketoconazole, and l-buthionine sulfoximine increased the protein modification induced by ME, which was proportional to the hepatotoxicity of ME. The findings facilitate the understanding of mechanism action of ME toxicities.