The Hydrogen Sulfide Donor AP39 Reduces Glutamate-mediated Excitotoxicity in a Rat Model of Brain Ischemia

The vast majority of stroke cases are classified as ischemic stroke, but effective pharmacotherapy strategies to treat brain infarction are still limited. Glutamate, which is a primary mediator of excitotoxicity, contributes to neuronal damage in numerous pathologies, including ischemia. The aim of this study was to investigate the effect of the hydrogen sulfide donor AP39 on excitotoxicity. AP39 was administered as a single dose of 100 nmol/kg b.w. i.v. 10 min after the restoration of blood flow and 100 min after middle cerebral artery occlusion (MCAO) in male Sprague-Dawley rats. Neurological deficits by Phillips's score, and infarct volume by TTC staining were evaluated (n = 8). LC-MS was used to determine the extracellular glutamate concentration in microdialysates collected intrasurgically and from freely moving animals 24 h and 3 days after reperfusion (n = 6). The expression of proteins involved in the regulation of glutamatergic transmission was investigated 24 h after reperfusion by Western-blot analysis (n = 6). The results were verified by double-immunostaining of brain cryosections (n = 6). The results showed a significant longitudinal decrease in extracellular glutamate concentrations in the motor cortex and hippocampus in MCAO + AP39 rats compared to MCAO rats. Moreover, the administration of AP39 increased the content of the GLT-1 transporter and reduced the content of VGLUT1 in the ischemic core. Upregulation of the GLT-1 transporter responsible for glutamate reuptake from the synaptic cleft, and downregulation of VGLUT1, which regulates glutamate transport to synaptic vesicles, indicate that these are important mechanisms by which AP39 reduces extracellular glutamate concentrations and, consequently, excitotoxicity after ischemia.