Mutagenicity of tocopheryl quinones: evolutionary advantage of selective accumulation of dietary alpha-tocopherol.

ABSTRACT

We have shown that phenolic antioxidant tocopherols are oxidized to nonarylating alpha-tocopheryl quinone (alpha-TQ) and arylating gamma- and delta-TQ electrophiles. The arylating quinones stimulate apoptosis and are highly cytotoxic in mammalian cells. Some xenobiotic phenolic antioxidants are mutagens, and it has been suggested that their arylating quinone metabolites are the active agents in mutagenesis related to carcinogenesis. We found that neither alpha- nor gamma-TQ was directly genotoxic in supercoiled-to-nicked circular DNA conversions, but these agents interacted with the cytomegalovirus reporter-driven plasmid and enhanced luciferase transfection, with gamma-TQ > alpha-TQ. The Ames test, using gamma-TQ and a number of Salmonella strains, showed no evidence of bacterial mutagenesis. gamma-TQ was highly cytotoxic and alpha-TQ slightly cytotoxic in eukaryocyte AS52 cells. A guanosine phosphoribosyltransferase gene assay showed that gamma-TQ was highly mutagenic and alpha-TQ slightly mutagenic in AS52 cells. A review of the literature identified associations where a decrease in dietary gamma-tocopherol (gamma-T) diminishes and an increase in dietary gamma-T and its quinone enhances carcinogenicity. Humans and other omnivores selectively accumulate alpha-tocopherol, even though gamma-T is their principal dietary tocopherol. We suggest that this selectivity confers an evolutionary advantage by limiting tissue gamma-T, a putative precursor of the mutagen gamma-TQ.