Increased vulnerability of neuronal cell lines to sodium nitroprusside-mediated toxicity is caused by the decreased level of nitric oxide metabolites

Nitric oxide (NO) is an unstable radical produced during the oxidative deam ination catalyzed by NO synthase (NOS) that converts L-arginine to L-citrul line. NO is also generated nonenzymatically from a group of compounds, call ed NO donors, such as sodium nitroprusside (SNP). NO directly or through it s metabolites has been implicated in several disorders, including Alzheimer 's disease (AD). Since NO is a highly labile unstable free gas, we measured the stable end products, nitrite and nitrate (NOx). Here, we investigated the effect of SNP-mediated NO release in different cell types and its effec t on the beta-amyloid precursor protein (beta APP). When different cell typ es were induced with SNP, a significant level of NOx was detected in a time and dose-dependent manner over the spontaneous release of NOx by SNP. The astrocytes, glial, and epithelial cell lines released significantly higher level of NOx as compared to neuronal cells following the exposure of SNP. T he latter group of cells was more sensitive to NO-mediated cytotoxicity, as demonstrated by the lactate dehydrogenase assay. The SNP-mediated toxicity is known to be caused by the accumulation of cyanide ions and we report th at the ability of cells to protect against it depends on the levels of nitr ic oxide metabolites. Cell lines, such as astrocytic and epithelial, that p roduce more NQx are better protected against the SNP-induced toxicity than the less NOx-protecting neuronal cell lines. The possibility of differentia l susceptibility of neurons and astrocytes resulting from the different con tent of reduced glutathione is also discussed. The release of NOx was preve nted by cotreatment with a NO scavenger and superoxide dismutase but not by a NOS inhibitor. The activity of NOS was decreased when cytosolic extracts were incubated with SNP. In the conditioned medium of SNP-induced cells, t he level of soluble beta APP (sAPP) was decreased, and this decrease was mo re apparent in neuronal than astrocytic cell lines. Taken together, these r esults suggest that the SNP-derived NO release is independent of the NOS pa thway, that various cell types metabolize SNP differently, and that neurona l cell lines are more vulnerable With SNP treatment with lowered sAPP secre tion. Since the neuronal cell lines lack a nitric-oxide-generated protectiv e mechanism, we speculate that these cells may be the first targets of neur odegeneration by several toxic agents, including the cyanides and peroxynit rites.