Mercury induces cell cytotoxicity and oxidative stress and increases beta-amyloid secretion and tau phosphorylation in SHSY5Y neuroblastoma cells

Concentrations of heavy metals, including mercury, have been shown to be al tered in the brain and body fluids of Alzheimer's disease (AD) patients. To explore potential pathophysiological mechanisms we used an in vitro model system (SHSY5Y neuroblastoma cells) and investigated the effects of inorgan ic mercury (HgCl2) on oxidative stress, cell cytotoxicity, beta-amyloid pro duction, and tau phosphorylation. We demonstrated that exposure of cells to 50 mu g/L (180 nM) HgCl2 for 30 min induces a 30% reduction in cellular gl utathione (GSH) levels (n = 13, p < 0.001). Preincubation of cells for 30 m in with 1 mu M melatonin or premixing melatonin and HgCl2 appeared to prote ct cells from the mercury-induced GSH loss, Similarly, 3-(4,5-dimethylthiaz ol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity assays revealed that 50 mu g/L HgCl2 for 24 h produced a 50% inhibition of MTT reduction ( n = 9, p < 0.001). Again, melatonin preincubation protected cells from the deleterious effects of mercury, resulting in MTT reduction equaling control levels. The release of beta-amyloid peptide (A beta) 1-40 and 1-42 into ce ll culture supernatants after exposure to HgCl2 was shown to be different: A beta 1-40 showed maximal (15.3 ng/ml) release after 4 h, whereas A beta 1 -42 showed maximal (9.3 ng/ml) release after 6 h of exposure to mercury com pared with untreated controls (n = 9, p < 0.001), Preincubation of cells wi th melatonin resulted in an attenuation of A beta 1-40 and A beta 1-42 rele ase. Tau phosphorylation was significantly increased in the presence of mer cury (n = 9, p < 0.001), whereas melatonin preincubation reduced the phosph orylation to control values, These results indicate that mercury may play a role in pathophysiological mechanisms of AD.