Unusual reactivity in a commercial chromium supplement compared to baseline DNA cleavage with synthetic chromium complexes

Commercially available chromium supplements were tested for their DNA cleavage ability compared with synthetic chromium(III) complexes, including chromium(III) tris-picolinate [Cr(pic) 3], basic chromium acetate [Cr 3O(OAc) 6] +, model complexes, and recently patented Cr-complexes for use in supplements or therapy. Four different supplements ( P1– P4) were tested for their DNA cleaving activity in the presence and the absence of H 2O 2, dithiothreitol (DTT) or ascorbate. One supplement, P1, showed nicking of DNA in the absence of oxidant or reductant at 120 μM metal concentration. Different lot numbers of P1 were also tested for DNA cleavage activity with similar results. Commercial supplements containing Cr(pic) 3 nicked DNA at ⩾120 μM metal concentrations in the presence of 5 mM ascorbate or with excess hydrogen peroxide, analogous to reactions with synthetic Cr(pic) 3 reported elsewhere. Another chromium (non-Cr(pic) 3) supplement, P2, behaves in a comparable manner to simple Cr(III) salts in the DNA nicking assay. Chromium(III) malonate [Cr(mal) 2] and chromium(III) acetate [Cr(OAc)] can nick DNA in the presence of ascorbate or hydrogen peroxide, respectively, only at higher metal concentrations. The Cr(III) complexes of histidine, succinate or N-acetyl- l-glutamate do not nick DNA to a significant degree.