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 hydroxy anisole 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 d amage, biological inactivation of single-stranded bacteriophage phiX-1 74 DNA, as well as induction of 7-hydro-8-oxo-2'-deoxyguanosine (8-oxo dG) in dG by these compounds was studied in vitro, in the presence and absence of peroxidases. Both test systems showed that BHA and TBQ (pr obably due to lack of reductase activity in vitro) were not capable of inducting oxidative DNA damage. TBHQ, however, appeared to be a stron g inactivator of phage DNA as well as a potent inducer of 8-oxodG form ation. Addition of radical scavengers showed that this damage was due to formation of superoxide anion, hydrogen peroxide and hydroxyl radic als. Addition of iron chelators and metal ions showed that the one-ele ctron oxidations of TBHQ via the semiquinone radical into TBQ are toxi c via the formation of oxygen radicals and are not directly due to the hydroquinone itself or the formation of semiquinone radicals. Althoug h peroxidation of TBHQ by prostaglandin H synthase (PHS) is indicated to result in a superoxide anion burst, this is not accompanied by an i ncrease in oxidative DNA damage in vitro. This might be due to the use of hydrogen peroxide as a substrate by PHS itself, consequently resul ting in less formation of hydroxyl radicals. Oxidation of TBHQ by lipo xygenases 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 yi elding reactive oxygen species may induce a carcinogenic potential, si nce the BHA metabolite TBHQ, appeared to be a strong inducer of oxidat ive DNA damage.