Oxygen–glucose deprivation decreases glutathione levels and glutamate uptake in rat hippocampal slices

Abstract

Ischemia is a transitory or permanent reduction of blood flow that may provoke an excessive release of glutamate. In that condition, increased reactive oxygen species generation and/or decreased cerebral antioxidant capacity may induce cell death. Antioxidant enzymes and thiols play an important role in the cellular defenses against oxidative stress. The purpose of this study was to evaluate cell viability, glutamate uptake and antioxidant status in rat hippocampal slices exposed to oxygen–glucose deprivation (OGD), an in vitro model of ischemia. After 15 min or 1 h of OGD, hippocampal slices showed a significant reduction of cell viability. Reperfusion during 1 or 2 h did not increase cell death. In this condition, the activities of antioxidant enzymes catalase, glutathione reductase, and peroxidase did not change. However, slices exposed to 15 min OGD and reperfused for 1 or 2 h showed higher superoxide dismutase activity. A significant reduction of glutathione levels was observed after 1 or 2 h of reperfusion in slices previously exposed to 1 h of OGD, although the protein-thiol content was unchanged. Slices exposed to 1 h of OGD and reperfused for 2 h showed reduced sodium-dependent l-[ 3H]glutamate uptake. The reduction of glutamate uptake was partially reversed by dl-dithiothreitol (DTT), a thiol-reducing agent, which may reduce thiol groups in glutamate transporters. Therefore, higher glutamate levels in the synaptic cleft could promote transporter reversal and impair glutamate uptake. Increased extracellular glutamate levels associated with decreased glutathione levels might exacerbate cell damage induced by oxygen and glucose deprivation.