Relationship between intracellular Ca²⁺ and ROS during fluoride-induced injury in SH-SY5Y cells

The mechanisms underlying the neurotoxicology of endemic fluorosis still remain obscure. To explore lactate dehydrogenase (LDH) leakage, intracellular Ca²⁺ concentration ([Ca²⁺]i ) and reactive oxygen species (ROS) production induced by fluoride, human neuroblastoma (SH-SY5Y) cells were incubated with sodium fluoride (NaF, 20, 40, 80 mg/L) for 24 h, with 40 mg/L NaF for 3, 6, 12, 18, 24 h, and N-acetyl-L-cysteine (NAC), ethyleneglycol-bis-(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester (BAPTA-AM) alone or combined with fluoride (40 mg/L) respectively for 12 h in vitro. The results showed that the LDH levels in the 40 and 80 mg/L fluoride-treated groups were significantly higher than that of the control group (in the test level of 0.05, the difference were statistical significance). [Ca²⁺]i and ROS reached a peak at 3 h and 12 h respectively after exposure to 40 mg/L fluoride. Fluoride coincubated with NAC (antioxidant) dramatically decreased ROS and LDH levels compared with the fluoride only group (in the test level of 0.05, the difference were statistical significance). However, fluoride-induced increase in [Ca²⁺]i was not affected by NAC. BAPTA-AM (intracellular calcium chelator) markedly lowered fluoride-induced increase of [Ca²⁺]i , ROS and LDH levels while EGTA (extracellular calcium chelator) have no effects on them. These results indicate that fluoride-related Ca²⁺ release from the site of intracellular calcium storage causes the elevation of ROS contributing to the cytotoxicity in SH-SY5Y cells.