New research indicates that chromium (III) is even more genotoxic than chromium (VI)

Background:
Chromium (III) is often discussed as an essential element that is believed to play a beneficial role in the glucose metabolism and therefore is included in some food supplements and health products. However, naturally available food sources used in well-balanced diets are capable to cover the requirement of trivalent chromium completely and Cr deficiency cases are therefore extremely rare. While evidence-based biochemical justification for artificial source needed additionally to standard foods has not been provided in the literature,  some commercial organisations promote Cr3+ nutrient supplements. During the last decades, chromium has become the second most popular dietary supplement after calcium in the United States with sales amounting to approximately 100 million dollars annually. While chromium supplements are mainly used for weight loss, some patients with diabetes also use these supplements to improve their glycemic control. However, efficacy of chromium to improve glycemic control has not been established. On the other side, hexavalent chromium  is classified to be carcinogenic. Therefore, during the last decade, a bunch of rules and legislation has been established, meant to restrict the exposure of humans to hexavalent chromium (see EVISA's Link database).

The new study:
In this new study, chinese researchers compared the effects of Cr(VI) (i.e., CrO₃) and Cr(III) (i.e., CrCl₃) on DNA damage both in vivo and in vitro using yeast and human T cell leukemia Jurkat cells as well as animal cells. Their  in vivo results suggest that both Cr(VI) and Cr(III) significantly induce genetic mutation in yeast and cause DNA damage within both yeast and Jurkat cells and that both can act as genotoxic compounds. In addition, the ability of CrCl₃ to generate DNA damage is significantly greater than that of CrO₃.

The researchers conclude "Based on our results, we conclude that Cr(III) can directly cause genotoxicity in vivo."   

Chromium III and chromium VI render toxicity via different mechanisms.  Previous studies on chromium genotoxicity mainly focused on the formation of chromium-DNA adducts. The researchers found that chromium III interferes with base pair stacking and causes DNA cleavage and degradation of DNA. Cr(VI) was previously suggested to interact with DNA via two modes of interaction: inducing structural changes and DNA compaction. Results obtained from the new study further indicates that Cr(VI) can intercalate into the planes between DNA base pairs and cause DNA structural changes and degradation.