Cr(VI) induces cytotoxicity in vitro through activation of ROS-mediated endoplasmic reticulum stress and mitochondrial dysfunction via the PI3K/Akt signaling pathway

The occupational and environmental toxicant hexavalent chromium [Cr(VI)] can cause severe damage to the liver; however, the exact mechanisms associated with its toxicity have not been thoroughly demonstrated. In the present study, the underlying mechanisms of Cr(VI)-induced hepatotoxicity were investigated. Our results showed that Cr(VI) inhibited the growth and proliferation of L-02 hepatocytes. Further study revealed that Cr(VI) significantly induced S-phase cell cycle arrest and apoptosis accompanying with the overproduction of reactive oxygen species (ROS). Cr(VI)-induced apoptosis could be prevented by inhibiting ROS with N-acetyl-l-cysteine (NAC). Additionally, our data showed that Cr(VI)-induced endoplasmic reticulum (ER) stress and mitochondrial dysfunction were concentration- and time-dependent. Moreover, inhibition of C/EBA homologous protein (CHOP) expression by siRNA partially prevented Cr(VI)-induced cell apoptosis, mitochondrial dysfunction and ROS generation. We also found that Cr(VI) treatment inhibited the PI3K/Akt pathway in a concentration- and time-dependent manner. After using IGF-1 (50 ng/mL), the specific agonist of the PI3K/AKT signaling pathway, the facilitating effects of Cr(VI) were depressed. This finding demonstrated the relationship between the PI3K/Akt pathway, ER stress and mitochondrial dysfunction. Collectively, these findings indicated that Cr(VI) increased ROS production. Increased ROS production may account for inhibition of the PI3K/Akt pathway and lead to ER stress and mitochondrial dysfunction, which consequently induces apoptosis in L-02 hepatocytes. This study provides novel insights into the molecular mechanisms of Cr(VI)-induced cytotoxicity.