Cadmium (Cd), a toxic environmental contaminant, induces neurodegenerative diseases. Recently we have shown that Cd elevates intracellular free calcium ion ([Ca2+]i) level, leading to neuronal apoptosis partly by activating mitogen-activated protein kinases (MAPK) and mammalian target of rapamycin (mTOR) pathways. However, the underlying mechanism remains to be elucidated. Here we show that the effects of Cd elevated [Ca2+]i on MAPK and mTOR network as well as neuronal cell death are through stimulating phosphorylation of calcium/calmodulin-dependent protein kinase II (CaMKII). This is supported by the findings that chelating intracellular Ca2+ with BAPTA/AM or preventing Cd-induced [Ca2+]i elevation using 2-aminoethoxydiphenyl borate (2-APB) blocked Cd activation of CaMKII. Inhibiting CaMKII with KN93 or silencing CaMKII attenuated Cd activation of MAPK/mTOR pathways and cell death. Furthermore, inhibitors of mTOR (rapamycin), JNK (SP600125) and Erk1/2 (U0126), but not of p38 (PD169316), prevented Cd-induced neuronal cell death in part through inhibition of [Ca2+]i elevation and CaMKII phosphorylation. The results indicate that Cd activates MAPK/mTOR network triggering neuronal cell death, by stimulating CaMKII. Our findings underscore a central role of CaMKII in the neurotoxicology of Cd, and suggest that manipulation of intracellular Ca2+ level or CaMKII activity may be exploited for prevention of Cd-induced neurodegenerative disorders.

Aims This study explores the neuroprotective effects and mechanisms of N-acetyl-L-cysteine (NAC) in mice exposed to cadmium (Cd). Methods NAC (150 mg/kg) was intraperitoneally administered to mice exposed to Cd (10-50 mg/L) in drinking water for 6 weeks. The changes of cell damage and death, reactive oxygen species (ROS), antioxidant enzymes, as well as Akt/mammalian target of rapamycin (mTOR) signaling pathway in brain neurons were assessed. To verify the role of mTOR activation in Cd-induced neurotoxicity, mice also received a subacute regimen of intraperitoneally administered Cd (1 mg/kg) with/without rapamycin (7.5 mg/kg) for 11 days. Results Chronic exposure of mice to Cd induced brain damage or neuronal cell death, due to ROS induction. Co-administration of NAC significantly reduced Cd levels in the plasma and brain of the animals. NAC prevented Cd-induced ROS and significantly attenuated Cd-induced brain damage or neuronal cell death. The protective effect of NAC was mediated, at least partially, by elevating the activities of Cu/Zn-superoxide dismutase, catalase and glutathione peroxidase, as well as the level of glutathione in the brain. Furthermore, Cd-induced activation of Akt/mTOR pathway in the brain was also inhibited by NAC. Rapamycin in vitro and in vivo protected against Cd-induced neurotoxicity. Conclusions NAC protects against Cd-induced neuronal apoptosis in mouse brain partially by inhibiting ROS-dependent activation of Akt/mTOR pathway. The findings highlight that NAC may be exploited for prevention and treatment of Cd-induced neurodegenerative diseases.

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CD is an independent risk factor for the inability to initiate and sustain breastfeeding. It is desirable to reduce the CD rate and provide specific breastfeeding support during early postpartum period to CD mothers.