ABSTRACT
It has been postulated that cellular glutamate is released into the extracellular fluid when the energy supply of the brain is compromised (i.e., anoxia or oxygen/glucose deprivation), and there the amino acid triggers the so-called excitotoxic cascade, causing neuronal death. Several mechanisms for this release have been postulated, and, by using glutamate transporter inhibitors, several authors have established that reversed uptake is the major mechanism through which glutamate is released in acute oxygen/glucose deprivation. We have studied the effect of the slowly transported glutamate analogue L-trans-pyrrolidine-2,4-dicarboxilic acid (PDC) preload on glutamate release and cell death in an in vitro model of oxygen plus glucose deprivation with differentiated PC12 cells. As expected, we found that PDC preload inhibits glutamate release induced by oxygen/glucose deprivation, supporting the conclusion that it occurs via reverse transport. In addition, we show that PDC preload but not the nontransportable glutamate uptake inhibitor DL-threo-beta-benzyloxyaspartate (TBOA) protects cells against the death induced by oxygen/glucose deprivation, indicating that PDC entry into the cell is necessary for this protective effect. This protection does not correlate with the extracellular glutamate concentration or changes in proteins synthesis rate and eukaryotic initiation 2 phosphorylation. Oxygen/glucose deprivation induces a significant increase in glutathione levels in both unloaded and PDC-preloaded cells, but this increase is not due to up-regulation of glutamate cysteine ligase levels. Intracellular glutathione disulfide (GSSG) significantly increased after oxygen/glucose deprivation. It was also interesting that intracellular GSSG levels in PDC-preloaded cells under oxygen/glucose deprivation strongly correlate with the protection exerted by this compound against cell death.
