Submitted to: Free Radicals in Biology and Medicine
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/7/2007
Publication Date: 6/15/2007
Citation: Hininger, I., Benaraba, R., Osman, M., Faure, H., Marie Roussel, A., Anderson, R.A. 2007. Safety of trivalent chromium complexes: no evidence for DNA damage in human HaCaT keratinocytes. Free Radicals in Biology and Medicine. 42 (12):1759-65. Interpretive Summary: Type 2 diabetes, one of the leading causes of morbidity and mortality, is increasing at an alarming rate. Experimental and clinical studies demonstrate that the essential nutrient, chromium, often improves the signs and symptoms of diabetes including elevated blood sugar, fats and insulin. Recent studies, using isolated DNA, have reported that chromium may cause DNA damage. Our study was designed to test the safety of chromium supplements under more normal conditions in intact cells. We demonstrated that not only did chromium not cause DNA damage but it functions as an antioxidant and protects cells from DNA damage. This work demonstrates that studies assessing chromium toxicity involving isolated or unprotected DNA are misleading and are not an accurate measure of toxicity in cells, experimental animals and humans. This work will be of importance to the medical community but also the millions of people who take supplements that contain chromium.
Technical Abstract: While the toxicity of hexavent chromium is well established, trivalent Cr is an essential nutrient with very low toxicity. Several studies have demonstrated beneficial effects of supplemental Cr in subjects with reduced insulin sensitivity but recent studies have questioned the potential toxicity of trivalent chromium. The objective of this study was to evaluate the cytotoxic and genotoxic potential of the Cr(III) complexes (histidinate, picolinate and chloride) as compared with Cr(VI) dichromate. The cytotoxic and genotoxic potential of the Cr complexes were assessed in human HaCaT keratinocytes by determining the concentrations of Cr required to decrease cell viability assessed by determining the ability of a keratinocyte cell line (HaCaT) to reduce a tetrazolium dye. DNA damage using Comet assay and the production of 8-hydroxy-2'-deoxyguanosine (8-OHdG) were also determined with and without hydrogen peroxide-induced stress. The LD50 for human cultured HaCaT keratinocytes, was 50µM for hexavalent sodium dichromate, and more than 120-fold higher for Cr chloride (6mM) and Cr histidinate (10mM). For Cr picolinate, at saturating solution (120 µM), the LD50 was not attained. High Cr(III) concentrations, 250µM Cr as Cr chloride and Cr histidinate and 120 µM Cr picolinate (highest amount soluble in the system, not only did not result in oxidative DNA damage but exhibited protective antioxidant effects when cells were exposed to hydrogen peroxide-induced oxidative stress. These data demonstrate the lack of genotoxicity of Cr(III) forms used as dietary supplements and highlight the methodological limits of the studies using free cell systems or purified DNA to demonstrate the potential toxicity of nutritional supplements. 7/27/05