Abstract
Hexavalent chromium [Cr(VI)] compounds are Group‐I human carcinogens. Cr(VI)‐induced DNA–protein crosslinks (DPCs) have been implicated in the mutagenic and carcinogenic effects of Cr(VI). Although multiple mechanisms have been suggested for Cr(VI)‐induced DNA–protein crosslinking, the mechanism of formation of DNA–protein crosslinks is not well understood. In this study, we explored the hypothesis that Cr(VI)‐induced DPCs could be formed via generation of protein carbonyls and malonaldehyde (MDA) through protein oxidation and lipid peroxidation, respectively. Treatment of human leukemic T‐lymphocyte MOLT4 cells with potassium chromate induced the formation of protein carbonyls and DPCs within 2 h, but increased the level of MDA only after 4 h, in a dose‐dependent manner. Chromate treatment of MOLT4 cell homogenates also resulted in increased formation of MDA and protein carbonyls in a dose‐dependent manner. EPR spectrometry in combination with spin trapping techniques revealed that reaction of Cr(VI) with biological reductants such as NADPH, glutathione reductase or H~2~O~2~ generates Cr(V) and ^•^OH radicals. Pretreatment of cells with antioxidants such as α‐tocopherol or Tiron inhibited chromate‐induced increase in formation of protein carbonyls, MDA and DPCs, but pretreatment of cells with riboflavin or 3‐aminotriazole, a catalase inhibitor, had the opposite effect. Our results, for the first time, demonstrate that Cr(VI) exposure increases the cellular level of protein carbonyls and that Cr(VI)‐induced DPCs may be formed, at least in part, via generation of protein carbonyls. Copyright © 2008 John Wiley & Sons, Ltd.