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 μmol 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 μmol 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.