CrPic induces DNA damage in Chinese Hamster Ovary Cells

Brooke Baker
Northern Arizona University

The manufacture and sales of chromium trispicolinate (CrPic) as a popular dietary supplement has become a multimillion-dollar industry. This readily available form of chromium can be found in a variety of multi-vitamins, sports drinks, and chewing gum and has recently even been patented for treatment of Type II Diabetes. It is known that long-term exposure to Cr6+, another stable form of chromium, leads to an increased risk of developing human lung cancer. Unfortunately, the molecular mechanism behind chromium-induced cancer is not well understood. We are using CrPic, which is a bio-available form of Cr(III), to explore the possible role that Cr(III) may have in Cr(VI)-induced cancer. CrPic has been shown to cause chromosomal aberrations and mutations at the hprt locus, and to induce apoptosis in Chinese hamster ovary (CHO) cells. The focus of this current work is to characterize the types of DNA lesions found in cells after exposure to CrPic. Chromium-DNA adducts were measured by ICP mass spectrometry and UV/visible spectroscopy. CrPic produced less Cr-DNA adducts in CHO cells than did chromic chloride and potassium dichromate. Results from the single cell gel electrophoresis (comet assay) suggested the presence of DNA crosslinks in CrPic treated CHO cells. Comparison of the effects of MMS and proteinase K on percent DNA in tail and DNA tail length of cells exposed to CrPic, cis-platin and formaldehyde suggest that DNA-protein crosslinks were more prevalent crosslinks in CrPic treated cells. The observation of crosslinks in the comet assay was consistent with extents of cell survival in a series of CHO cells deficient in DNA repair. CrPic was most toxic in the CHO UV135 line and least toxic in the parental AA8 lone with the following order observed: UV135 < UV41 < UV5 = EM9 < UV20 < AA8. The free ligand, picolinic acid, produced the opposite trend, with cell survival being greater in the repair deficient lines: AA8 < EM9 = UV20 < UV135 < UV5 < UV41. Equivalent doses of chromic chloride were non-cytotoxic in all lines tested. Understanding the mechanism behind CrPic-induced DNA damage will be necessary before genotoxicity results can be extrapolated to humans ingesting dietary supplements.