Chromium(III) and DNA damage.

In their paper, “Chromium(III)-Induced 8-Hydroxydeoxyguanosine in DNA and Its Reduction by Antioxidants: Comparative Effects of Melatonin, Ascorbate, and Vitamin E,” Qi et al. (1) reported on a cellfree system and confirmed results from other laboratories that Cr(III) may react with peroxide to form reactive intermediates causing oxidative DNA damage. However, their conclusions on reactions in living systems are entirely speculative. Compounds of trivalent chromium are very weakly, if at all, carcinogenic (2–6). The authors misled readers when they cited Tsou et al. (7) and Lloyd et al. (8) as evidence for “the carcinogenic mechanisms of Cr(III).” The mechanism that Qi et al. (1) demonstrated by treating isolated DNA with Cr(III) plus 0.5 mM hydrogen peroxide does not apply to cells with a peroxide concentration of 10–9–10–8 M, but it does apply to cells that are subject to inflammation or other stress conditions in which the peroxide levels are increased. Nevertheless, the results of Qi et al. (1) should be taken as a warning that chromium(III) may be more harmful to living cells than thought previously, if it acts in combination with agents that cause the generation of reactive oxygen species. However, I question the final recommendation of the authors that melatonin should be applied against Crinduced genotoxicity for two reasons: a) the supreme goal should be to avoid exposure to toxic chromium exposure, and b) reducing agents combined with Cr(VI) may create similar toxic intermediate oxidation states of Cr as does the oxidation of Cr(III) (9).