This project investigates the role of free radical reactions in cellular injury caused by mineral particles and metal ions. (A) Tetrandrine, catalase, sodium formate and deferoxamine inhibited silica-induced activation of the nuclear transcription factor NFkappaB. Tetrandrine also inhibited NFkappaB activation induced by 12-O-tetradecanoylphorbol-13- acetate and by lipopolysaccharide. The results indicate that hydroxyl radicals, generated by metal-mediated Fenton-like reactions, play an important role in the mechanism of silica-induced NFkappaB activation. Since NFkappaB regulates the expression of several protooncogenes, including c-myc, it is possible that tetrandrine, antioxidants and metal chelators may inhibit silica-induced carcinogenesis by inhibiting silica-induced NFkappaB activation. The results also support the role of silica-mediated free radical reactions in the mechanism of silica-induced carcinogenesis and fibrosis. (B) Cr(IV)-glutathione (GSH) was synthesized as a model compound to study the role of Cr(IV) and its related free radical generation in the mechanism of Cr(VI) carcinogenesis. The Cr(IV)-GSH compound was identified by ESR and magnetic susceptibility measurements. This compound is able to generate hydroxyl radical upon reaction with aqueous medium in the presence of molecular oxygen. Catalase inhibited hydroxyl radical generation while hydrogen peroxide enhanced it. Molecular oxygen was consumed during hydroxyl radical generation. Deferoxamine attenuated hydroxyl radical generation with concomitant generation of deferoxamine-derived free radicals. The results imply that Cr(IV) may play an important role in the mechanism of Cr(VI)-induced carcinogenesis and Cr(IV)-GSH can be used as a model Cr(IV) compound. (C) Direct low frequency electron spin resonance (ESR) in conjunction with a surface coil was used to study the metabolism of Cr(VI) on rat skin. It was shown that reduction of Cr(VI) by rat skin generated reactive Cr(IV) intermediate, which reacts with hydrogen peroxide to generate hydroxyl radical. The results not only clarify the mechanism of Cr(VI) carcinogenesis, but also demonstrate that ESR can be used to study metal metabolism in a large living animal.