Comparative Studies of Tri- and Hexavalent Chromium Cytotoxicity and Their Effects on Oxidative State of Saccharomyces cerevisiae Cells

Chromium is a significant mutagen and carcinogen in environment. We compared the effects of tri- and hexavalent chromium on cytotoxicity and oxidative stress in yeast . Cell growth was inhibited by Cr 3+ or Cr 6+ , and Cr 6+ significantly increased the lethal rate compared with Cr 3+ . Both Cr 3+ and Cr 6+ can enter into the yeast cells. The percent of propidium iodide permeable cells treated with Cr 3+ is almost five times as that treated with the same concentration of Cr 6+ . Levels of TBARS, O 2 − , and carbonyl protein were significantly increased in both Cr 6+ - and Cr 3+ -treated cells in a concentration- and time-dependent manner. Moreover, the accumulation of these stress markers in Cr 6+ -treated cells was over the Cr 3+ -treated ones. The decreased GSH level and increased activity of GPx were observed after 300 μM Cr 6+ -exposure compared with the untreated control, whereas there was no other change of GSH content in cells treated with Cr 3+ even at very high concentration. Exposure to both Cr 3+ and Cr 6+ resulted in the decrease of activities of SOD and catalase. Furthermore, the effect of Cr 6+ is stronger than that of Cr 3+ . Null mutation sensitivity assay demonstrated that the gsh1 mutant was sensitive to Cr 6+ other than Cr 3+ , the apn1 mutant is more sensitive to Cr 6+ than Cr 3+ , and the rad1 mutant is sensitive to both Cr 6+ and Cr 3+ . Therefore, Cr 3+ can be concluded to inhibit cell growth probably due to the damage of plasma membrane integrality in yeast. Although both tri- and hexavalent chromium can induce cytotoxicity and oxidative stress, the action mode of Cr 3+ is different from that of Cr 6+ , and serious membrane damage caused by Cr 3+ is not the direct consequence of the increase of lipid peroxidation.