[Apoptosis induced by excitatory sulfur amino acids in primary cultured rat immature cerebral neurons].

In the neural tissue of patients with amyotrophic lateral sclerosis (ALS), the elevation of taurine, the final product of the metabolic pathway of sulfur amino acids (SAAs), has been reported, suggesting that excitatory SAAs, the intermediates of this pathway, could also be increased. This study was undertaken to evaluate whether excitatory SAAs have the ability to inhibit cystine uptake. Since immature neurons have not yet expressed the receptor channels, they are not susceptible to excitotoxicity. Inhibition of cystine transport leads to a depletion of glutathione, and results in cell death due to oxidative stress. Cell cultures were obtained from the cerebral cortex of fetal Wistar rats. Cytotoxicity studies were performed 48 hours after plating by addition of the culture medium containing SAAs; cysteine sulfinic acid, cysteic acid, homocysteine sulfinic acid (HCSA), homocysteic acid (HCA) and S-sulfocysteine. Cell death was quantified by the release of the cytosolic enzyme lactate dehydrogenase, and single cell assessment of apoptosis was carried out by staining cells with acridine orange, DNA isolation and agarose gel electrophoresis were also performed. Protection of cycloheximide, a protein synthesis inhibitor, against non-receptor mediated excitatory SAA cytotoxicity was also assessed. HCA and HCSA showed cytotoxicity, the morphology and biochemistry of which were compatible to apoptosis. It will be a subject for future study to examine whether this mechanism of cell death is primarily present in ALS.