Generation of Free Radicals from Hydrogen Peroxide and Lipid Hydroperoxides in the Presence of Cr(III)

Free radical generation from H₂O₂ and lipid hydroperoxides in the presence of Cr(III) was investigated by electron spin resonance (ESR) spin trapping methodology. Incubation of Cr(III) with H₂O₂ at physiological pH generated hydroxyl (·OH) radical, the yield of which reached saturation level in about 6 min. Deferoxamine reduced the ·OH radical yield by only about 20%, diethylenetriamine pentaacetic acid (DTPA) reduced it by about 70%, while cysteine, glutathione, and NADH exhibited no significant effect. The yield of ·OH radical formation also depended on the pH being 15 times higher at pH 10 than that at pH 7.2. At pH 3.0, ·OH radical generation became nondetectable, and addition of H₂O₂ to Cr(III) solution did not affect the intensity of the Cr(III) ESR signal while at pH 10, addition of H₂O₂ reduced the Cr(III) intensity by about 40%, showing that reaction of Cr(III) with H₂O₂ occurred only at higher pH. Incubation of Cr(III) with the model lipid hydroperoxides, cumene hydroperoxide and t-butyl hydroperoxide, generated lipid hydroperoxide-derived free radicals. Addition of deferoxamine or DTPA had a minor inhibitory effect on that generation. These results show that Cr(III) is capable of producing free radicals from H₂O₂ and lipid hydroperoxides, which may have significant implications regarding the mechanism of chromium-induced carcinogenesis.