Role of insulin in Cr(VI)-mediated genotoxicity in Neurospora crassa

Aims: Chromium (III) is an insulinomimetic agent whose biological and/or environmental availability is frequently in the form of Cr(VI), which is known to be toxic. Wall-less mutant of Neurospora crassa (FGSC stock no. 4761) is known to possess insulin receptor in its cell membrane and hence is a good model for Cr toxicity studies. This study explores the toxicity of Cr(VI) and the possible consequences on simultaneous exposure to insulin in N. crassa. Methods and Results: Comet assay of N. crassa cells treated with 100 mu mol l(-1) Cr(VI) showed up to 50% reduction in comet tail lengths when incubated simultaneously with 0.4 U insulin. Fluorescence measurement in Cr(VI)-treated cells using DCFH-DA showed six-to eightfold increase in free radical generation, which was reduced to fourfold by 0.4 U insulin. Annexin-V/PI Flow cytometry analysis indicated necrotic cell death up to 28.7 +/- 3.6% and 68.6 +/- 2.5% on Cr(VI) exposure at concentrations 100 and 500 mu mol l(-1) which was reduced by 68.3 +/- 3.2% and 48.9 +/- 3.6%, respectively, upon addition of insulin. Conclusion: Insulin-mediated protection from DNA damage by Cr(VI) is because of scavenging of free radicals liberated during exposure to Cr(VI). Significance and Impact of the Study: Overall, Cr(VI) toxicity depends upon available insulin, indicating that Cr(VI) toxicity may be a serious issue in insulin-deficient individuals with diabetes.