The Role of Prostaglandin H Synthase-mediated Metabolism in the Induction of Oxidative DNA Damage by BHA Metabolites

The carcinogenicity of the phenolic food antioxidant butylated hydroxyanisole may be related to its oxidative biotransformation in vivo. In order to determine the ability of BHA, 2-tert-butyl(1,4)hydroquinone (TBHQ) and 2-tert-butyl(1,4)paraquinone (TBQ) to induce oxidative DNA damage, biological inactivation of single-stranded bacteriophage phi X-174 DNA, as well as induction of 7-hydro-8-oxo-2'-deoxyguanosine (8-oxodG) in dG by these compounds was studied in vitro, in the presence and absence of peroxidases. Both test systems showed that BHA and TBQ (probably due to lack of reductase activity in vitro) were not capable of inducting oxidative DNA damage. TBHQ, however, appeared to be a strong inactivator of phage DNA as well as a potent inducer of 8-oxodG formation. Addition of radical scavengers showed that this damage was due to formation of superoxide anion, hydrogen peroxide and hydroxyl radicals. Addition of iron chelators and metal ions showed that the one-electron oxidations of TBHQ via the semiquinone radical into TBQ are toxic via the formation of oxygen radicals and are not directly due to the hydroquinone itself or the formation of semiquinone radicals. Although peroxidation of TBHQ by prostaglandin H synthase (PHS) is indicated to result in a superoxide anion burst, this is not accompanied by an increase in oxidative DNA damage in vitro. This might be due to the use of hydrogen peroxide as a substrate by PHS itself, consequently resulting in less formation of hydroxyl radicals. Oxidation of TBHQ by lipoxygenases showed that no semiquinone radicals or oxygen radicals were formed, probably due to a two-electron oxidation of TBHQ directly into TBQ. The present results indicate that metabolic activation of BHA yielding reactive oxygen species may induce a carcinogenic potential, since the BHA metabolite TBHQ, appeared to be a strong inducer of oxidative DNA damage.