Abstract
Ionic liquids (ILs) as a green replacement for volatile organic solvents are increasingly used in large-scale commercial applications. A good understanding of the toxic mechanisms and environmental impact of ILs is neede to reduce the risk for human health and the environment. For this purpose, we aimed to evaluate the possible impacts of 1-methyl-3-octylimidazolium bromide ([C8mim]Br) exposure on human hepatocellular carcinoma (HepG2) cells as to elucidate the cytotoxic mechanism of [C8mim]Br. Biochemical assays revealed that [C8mim]Br exposure altered the protein levels of heat shock protein 70 (HSP70) and HSP90, generally inhibiting total antioxidative capacity (T-AOC), depleting heme oxygenase-1 (HO-1) and increasing transcription and activity of inducible nitric oxide synthase (iNOS) in HepG2 cells. These results indicated that [C8mim]Br may induce biochemical disturbances and cause oxidative stress in HepG2 cells. Moreover, increased phosphorylation of p53, mitochondrial membrane disruption, cyclooxygenase-2 activation, Bcl-2 family protein modulation, cytochrome c and Smac/DIABLO release, and inhibition of apoptosis inhibitory protein-2 (c-IAP2) and survivin were also observed in [C8mim]Br-treated cells, suggesting that [C8mim]Br-induced apoptosis might be mediated by the mitochondrial pathway. Further research showed that [C8mim]Br exposure increased tumour necrosis factor α (TNF-α) transcription and content and promoted the expression of Fas and FasL, indicating that TNF-α and Fas/FasL are involved in the apoptosis induced by [C8mim]Br. Additionally, [C8mim]Br cytotoxicity was partly inhibited by N-acetyl-cysteine (NAC), and NAC reversed [C8mim]Br-mediated mitochondrial dysfunction and blocked apoptotic events by inhibiting the generation of reactive oxygen species (ROS). This work first demonstrated that the ROS-mediated mitochondrial and death receptor-initiated apoptotic pathway is involved in [C8mim]Br-induced HepG2 cell apoptosis.