Glutamate-induced modulation in energy metabolism contributes to protection of rat cortical slices against ischemia-induced damage

Abstract

Objectives: Glutamate excitotoxicity contributes to neurodegeneration during cerebral ischemia. Recent studies in the protective effect of glutamate against ischemia and hypoxia have shown the need for questioning the role of glutamate in energy metabolism during ischemia. Current study investigates the effect of glutamate on energy substrate metabolites such as alpha-ketoglutarate, lactate, and pyruvate release during control, oxygen-glucose deprivation (OGD), and reoxygenation (REO) conditions. Methods: The effects of 0.5 and 2 mM glutamate on spontaneous alpha-ketoglutarate, lactate, and pyruvate release were tested in vitro, on acute rat cortical slices. Alpha-ketoglutarate, lactate, and pyruvate levels were determined by HPLC with UV detector. Results: We observed that glutamate added into medium significantly increased alpha-ketogluarate release under control conditions. Although OGD and REO also had a glutamate-like effect, only REO-induced rise further enhanced by glutamate. In contrast to alpha-ketoglutarate, both OGD and REO conditions caused significant declines in pyruvate and lactate outputs. While OGD and REO-induced declines in pyruvate outputs were further potentiated, lactate output was not altered by glutamate added into the medium. Glutamate and alpha-ketoglutarate, moreover, also ameliorated OGD- and REO-induced losses in 2,3,5-triphenyltetrazolium chloride staining with a similar degree. Conclusion: These results indicate that glutamate probably increases alpha-ketoglutarate production as an alternative energy source for use in the TCA cycle under energy-depleted conditions. Thus, increasing the alpha-ketoglutarate production may represent a new therapeutic intervention for neurodegenerative disorders, including cerebral ischemia.