PHENOXYL RADICAL-INDUCED THIOL-DEPENDENT GENERATION OF REACTIVE OXYGEN SPECIES - IMPLICATIONS FOR BENZENE TOXICITY

Mechanisms of phenoxyl radical-induced generation of oxygen radicals p otentially involved in toxicity of benzene were studied. We hypothesiz ed that phenoxyl radical intermediates formed from phenolic metabolite s of benzene by oxidative enzymes (e.g., peroxidases, tyrosinase) are able to damage biomolecules via (i) oxidation of low-molecular-weight thiols and protein thiols and (ii) thioI-dependent generation of oxyge n radicals and subsequent oxidation of DNA. Phenoxyl radicals were gen erated by the oxidation of phenol by myeloperoxidase + H2O2, horseradi sh peroxidase + H2O2, or tyrosinase. The reaction of phenol-phenoxyl r adicals with GSH and dihydrolipoic acid was studied. Our HPLC measurem ents showed that both thiols reduced the phenoxyl radical back to phen ol. This reaction was accompanied by the formation of thiyl radicals ( detected by ESR as 5,5-dimethyl-1-pyrroline-N-oxide/glutathione thiyl radical spin adducts) and of superoxide radicals (measured by their ch emiluminescence response in the presence of lucigenin). Hydroxylation of 2'-deoxyguanosine to 8-oxo-7,8-dihydro-2'deoxyguanosine was demonst rated in the course of the tyrosinase-catalyzed oxidation of phenol in the presence of dihydrolipoic acid and Fe(III)-EDTA. Redoxcycling of phenoxyl radicals by thiols produces oxygen radicals which can be resp onsible for the oxidative damage of DNA by radical intermediates of be nzene metabolism. (C) 1995 Academic Press, Inc.