To investigate the toxic mechanism of hexavalent chromium Cr(VI) and search for an antidote for Cr(VI)-induced cytotoxicity, a study of mitochondrial dysfunction induced by Cr(VI) and cell survival by recovering mitochondrial function was performed. In the present study, we found that the gene expression of electron transfer flavoprotein dehydrogenase (ETFDH) was strongly downregulated by Cr(VI) exposure. The levels of coenzyme 10 (CoQ10) and mitochondrial biogenesis presented by mitochondrial mass and mitochondrial DNA copy number were also significantly reduced after Cr(VI) exposure. The subsequent, Cr(VI)-induced mitochondrial damage and apoptosis were characterized by reactive oxygen species (ROS) accumulation, caspase-3 and caspase-9 activation, decreased superoxide dismutase (SOD) and ATP production, increased methane dicarboxylic aldehyde (MDA) content, mitochondrial membrane depolarization and mitochondrial permeability transition pore (MPTP) opening, increased Ca²⁺ levels, Cyt c release, decreased Bcl-2 expression, and significantly elevated Bax expression. The Cr(VI)-induced deleterious changes were attenuated by pretreatment with CoQ10 in L-02 hepatocytes. These data suggest that Cr(VI) induces CoQ10 deficiency in L-02 hepatocytes, indicating that this deficiency may be a biomarker of mitochondrial dysfunction in Cr(VI) poisoning and that exogenous administration of CoQ10 may restore mitochondrial function and protect the liver from Cr(VI) exposure.

Background: Hexavalent chromium [Cr(VI)] and its compounds (e.g. chromates), which are extensively used in numerous industrial processes including leather tanning and steel manufacturing, are considered as priority pollutants. There is growing evidence supporting that Cr(VI) could be a human carcinogen that induces primary liver cancer after oral exposure, and this sheds light on the importance of the investigation of Cr(VI)-induced hepatotoxicity. Although it is known that mitochondria are major targets for heavy metals, the mechanisms of electron transfer chain (ETC) dysfunction involved in Cr(VI)-induced cytotoxicity are unclear. Methods: In the present study, by using mitochondrial respiratory chain complex (MRCC) I inhibitor rotenone (ROT) and its substrates glutamate/malate (Glu/Mal), MRCC III inhibitor antimycin A (AA) and its substrate coenzyme Q (CoQ), and the antioxidant Vitamin C (Vit C), we aimed to elucidate the role of mitochondrial ETC dysfunction in Cr(VI)-induced cytotoxicity. Results: We found that Cr(VI) targeted and inhibited MRCC I and III to induce ETC dysfunction, which played an important role in Cr(VI)-induced cytotoxicity. Conclusion: Our current data provides novel important insight into the mechanisms of mitochondrial ETC dysfunction in Cr(VI)-induced cytotoxicity in the hepatocytes, and we will be poised to develop new methods in the prevention and treatment of liver diseases involving mitochondrial ETC dysfunction for the occupational exposure population.

Background: Hexavalent chromium (Cr(VI)) overdose causes hepatocellular injuries by inducing mitochondrial damage and subsequent apoptosis in animals and humans. Autophagy can selectively remove damaged organelles, especially impaired mitochondria, and in turn, protects against mitochondria-dependent cell death. The present study was designed to explore the effects of autophagy on the Cr(VI)-induced hepatotoxicity. Methods: L-02 hepatocytes were incubated with different concentrations of Cr(VI) for 24h and several indicators for evaluating mitochondrial damage and hepatocellular apoptosis were measured. Then effects of ROS scavenger NAC on ROS production and calcium overload during Cr(VI)-induced hepatotoxicity were examined. Finally, the study further investigated the role of autophagy played in repairing mitochondrial damage and subsequent hepatocyte injuries. Results: After exposed to different concentrations of Cr(VI) for 24h, cell viability, mitochondria membrane potential, ATP content were significantly decreased and caspase-3 activities and apoptosis rates increased in L-02 hepatocytes. The treatment of NAC reduced ROS formation and Ca²⁺ content, restored CRAC channel activities and further diminished mitochondrial injuries. Furthermore, autophagy inducer, rapamycin is beneficial for repairing mitochondrial function and limiting hepatocytes damage, and pharmacological inhibition of autophagy by 3-methyladenine further exacerbated Cr(VI)-induced hepatotoxicity. Conclusions: ROS production is a critical reason for Cr(VI)-induced mitochondria-dependent apoptosis. And activation of autophagy could repair mitochondria function to protect hepatocytes potentially by removing damaged mitochondria.

Hexavalent chromium [Cr(VI)] and its compounds have extensive applications in many industries and are widely known to cause occupational diseases as well as carcinogenic effects in humans. Mitochondrial damage, which is important in Cr(VI)‑induced cytotoxicity, may be characterized by the opening status of the permeability transition pore, the maintenance of the mitochondrial membrane potential and the level of malondialdehyde. The formation of DNA‑protein crosslinks (DPCs) in target tissues appears to be the direct and primary genotoxic effect of Cr(VI) exposure, and the lymphocytic DPCs may be viewed as a biomarker of internal Cr(VI) accumulation. It is well known that vitamin C (vit C) is an important biological reducing agent in humans and animals, which is capable of reducing Cr(VI). Regardless of the evidence from cell culture and in vivo experiments of the protective effect of the antioxidant, vit C, following exposure to Cr(VI), no studies have been conducted to date to demonstrate the time‑order effects of vit C on Cr(VI)‑induced mitochondrial damage and DPC formation. In the present study, by using peripheral blood lymphocytes from Sprague‑Dawley rats, we demonstrated that vit C pre‑ and co‑treatment have a protective effect against Cr(VI)‑induced loss of cell viability and mitochondrial damage, while only vit C co‑treatment has a protective effect against the Cr(VI)‑induced increase in DPCs. The mechanistic investigation revealed that cellular reactive oxygen species levels are correlated with Cr(VI)‑induced mitochondrial damage, and that p53 expression is correlated with the Cr(VI)‑induced increase in DPCs. We concluded that vit C exerts different time‑order effects on Cr(VI)‑induced mitochondrial damage and DPC formation, and that biomarkers, including DPC and p53, may be used in the assessment of the development of Cr(VI)‑induced cancer. These findings facilitate more detailed follow‑up of the Cr(VI)‑exposure populations for secondary prevention.

Background: Hexavalent chromium (Cr(VI)) is a common environmental pollutant. Cr(VI) exposure can lead to severe damage in the liver, but the preventive measures to diminish Cr(VI)-induced hepatotoxicity need further study. Acid sphingomyelinase (ASMase) is responsible for the production of ceramide via the hydrolysis of sphingomyelin. The present study was designed to investigate effects of desipramine (DES), as an ASMase inhibitor, on Cr(VI)-induced hepatotoxicity. Methods: L-02 hepatocytes were incubated with different concentrations of Cr(VI) for 24h, and ASMase activities and ceramide levels were measured. Moreover, the study investigated the role of DES played in ASMase activities and ceramide levels. Finally, effects of DES on mRNA and protein expressions of the components of mitochondrial permeability transition pore (PTP) and PTP opening were detected. Results: The ASMase activities and ceramide contents increased in L-02 hepatocytes treated with Cr(VI). The results demonstrated that apoptosis rates, ASMase activities and ceramide content decreased in groups treated with the combination of DES and Cr(VI) compared to Cr(VI) groups. Furthermore, DES inhibited Cr(VI)-induced mitochondrial PTP opening by intervening the mRNA and protein expressions of the components of mitochondrial PTP. Conclusions: DES may exert protective effects on Cr(VI)-induced hepatocellular apoptosis probably by inhibiting ceramide channel formation and mitochondrial PTP opening.