Carcinogenic chromium(VI)-induced protein oxidation and lipid peroxidation: implications in DNA-protein crosslinking.
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 alpha-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.
Mattagajasingh
Subhendra N
SN
Cardiovascular Institute, University of Pittsburgh Medical Center, Pittsburgh, PA 15213, USA. snm16@pitt.edu
Misra
Bhaba R
BR
Misra
Hara P
HP
D020003:1-Octanol / Q000737:chemistry; D002273:Carcinogens; D045744:Cell Line, Tumor; D002840:Chromates / Q000737:chemistry / Q000493:pharmacokinetics; D017608:Chromium Compounds / Q000493:pharmacokinetics / Q000633:toxicity*; D002860:Chromium Radioisotopes; D003432:Cross-Linking Reagents; D004247:DNA / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D017665:Hydroxyl Radical / Q000378:metabolism; D015227:Lipid Peroxidation / Q000187:drug effects*; D010084:Oxidation-Reduction; D017680:Potassium Compounds / Q000737:chemistry / Q000493:pharmacokinetics; D050050:Protein Carbonylation / Q000187:drug effects; D011506:Proteins / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D012997:Solvents
D002273:Carcinogens; D002840:Chromates; D017608:Chromium Compounds; D002860:Chromium Radioisotopes; D003432:Cross-Linking Reagents; D017680:Potassium Compounds; D011506:Proteins; D012997:Solvents; D017665:Hydroxyl Radical; C027373:potassium chromate(VI); D004247:DNA; D020003:1-Octanol; C023600:chromic oxide