Inhibitory effect of vitamin C on the mutagenicity and covalent DNA binding of the electrophilic and carcinogenic metabolite, 6-sulfooxymethylbenzo[a]pyrene

Abstract

6-Sulfooxymethylbenzo[a]pyrene has recently been shown to be a strong hepatocarcinogen in infant male B6C3F(1) mice (Y.-J.Surh et al., Biochem. Biophys. Res. Commun., 172, 85-91, 1990) and appears to be an ultimate carcinogenic metabolite of 6-hydroxymethylbenzo[a] pyrene and possibly of benzo[a]pyrene and 6-methylbenzo[a]pyrene. It produced high levels of aralkyl DNA adducts in the livers of B6C3F(1) mice and also exhibited strong direct mutagenicity toward Salmonella typhimurium TA98 without metabolic activation. In the present study we found that ascorbic acid significantly reduced the bacterial mutagenicity and in vitro covalent DNA binding of 6-sulfooxymethylbenzo[a]pyrene. Ascorbic acid forms a mutagenically inactive covalent adduct with 6-sulfooxymethylbenzo[a]pyrene, which appears to account for its novel protective mechanism against this reactive sulfuric acid ester. It seems likely that the formation of this adduct involves aralkylation of an ascorbic acid anion by a presumed carbo cation derived from the electrophilic sulfuric acid ester.