Low levels of selenium compounds are selectively toxic for a human neuron cell line through ROS/RNS increase and apoptotic process activation

Organic and inorganic selenium compounds were used to examine whether low selenium concentration is able to trigger apoptotic degeneration in a human neuron cell line in vitro and to explore changes in reactive oxygen and nitrogen species and antioxidant protein content during the apoptotic processes. The results indicated that: (1) SKNBE neuroblastoma cells treated with sodium selenite, sodium selenate and seleno-methionine (0.1, 0.5 and 0.5 μM, respectively) for 24 h exhibited a viability decrease, unlike kidney or prostatic cells; (2) the PARP (poly-ADP-ribose-polymerase) degradation and caspase activation detected by Western blot and flow cytometry fluorimetric examination showed induction of apoptosis; (3) during selenium treatment, a ROS/RNS increase occurred despite the GSH increment, as revealed by fluorimetric analysis; (4) the RNS production could be blocked by a peroxynitrite scavenger; (5) after exposure to selenium compounds, the concentration of nitric oxide synthase, manganese superoxide dismutase (SOD2), P-NF-kB (phospho nuclear factor kB), glutathione reductase and glutathione peroxidase increased, whereas that of P-ERK (phospho extracellular signal-regulated kinase) decreased; (6) selenium presence induced copper/zinc superoxide dismutase (SOD1) translocation into mitochondria, in a way similar to what is observed in amyotrophic lateral sclerosis (ALS). This study supports epidemiologic studies showing the possibility that excess environmental exposure to Se represents a risk factor for a devastating human neurodegenerative disease.