Inorganic mercury causes pancreatic beta-cell death via the oxidative stress-induced apoptotic and necrotic pathways

Mercury is a well-known highly toxic metal. In this study, we characterize and investigate the cytotoxicity and its possible mechanisms of inorganic mercury in pancreatic beta-cells. Mercury chloride (HgCl2) dose-dependently decreased the function of insulin secretion and cell viability in pancreatic beta-cell-derived HIT-T15 cells and isolated mouse pancreatic islets. HgCl2 significantly increased ROS formation in HIT-T15 cells. Antioxidant N-acetylcysteine effectively reversed HgCl2-induced insulin secretion dysfunction in HIT-T15 cells and isolated mouse pancreatic islets. Moreover, HgCl2 increased sub-G1 hypodiploids and annexin-V binding in HIT-T15 cells, indicating that HgCl2 possessed ability in apoptosis induction. HgCl2 also displayed several features of mitochondria-dependent apoptotic signals including disruption of the mitochondrial membrane potential, increase of mitochondrial cytochrome c release and activations of poly (ADP-ribose) polymerase (PARP) and caspase 3. Exposure of HIT-T15 cells to HgCl2 could significantly increase both apoptotic and necrotic cell populations by acridine orange/ethidium bromide dual staining. Meanwhile, HgCl2 could also trigger the depletion of intracellular ATP levels and increase the LDH release from HIT-T15 cells. These HgCl2-induced cell death-related signals could be significantly reversed by N-acetylcysteine. The intracellular mercury levels were markedly elevated in HgCl2-treated HIT-T15 cells. Taken together, these results suggest that HgCl2-induced oxidative stress causes pancreatic beta-cell dysfunction and cytotoxicity involved the co-existence of apoptotic and necrotic cell death.