Sulbactam improves binding property and uptake capacity of glutamate transporter-1 and decreases glutamate concentration in the CA1 region of hippocampus of global brain ischemic rats.

Abstract

Glutamate transporter-1 (GLT-1) removes most glutamate in the synaptic cleft. Sulbactam confers neuronal protection against ischemic insults in the hippocampal CA1 region accompanied by the upregulation of GLT-1 expression in rats. The present study further investigates the effect of sulbactam on the binding property and uptake capacity of GLT-1 for glutamate, and the change in extracellular glutamate concentration in the hippocampal CA1 region of rats with global brain ischemia. The binding property and uptake capacity of GLT-1 were measured using a radioligand binding and uptake assay, respectively, with L-3H-glutamate. The extracellular glutamate concentration was detected using microdialysis and high-performance liquid chromatography-mass spectrometry. Neuropathological evaluation was performed based on thionin staining. It was shown that sulbactam pre-treatment changed GLT-1 binding property, including increased Bmax and decreased Kd values, increased GLT-1 uptake capacity for glutamate, and inhibited the elevation of extracellular glutamate concentration in rats with global cerebral ischemia. These effects of sulbactam were accompanied by its neuronal protection on the hippocampal CA1 neurons against delayed neuronal death resulted from ischemic insult. Furthermore, administration of GLT-1 antisense oligodeoxynucleotides, which inhibited the expression of GLT-1, blocked the aforementioned sulbactam-related effects, which suggested that GLT-1 upregulation mediated the above effect although other mechanisms independent of the upregulation of GLT-1 expression could not be excluded. It could be concluded that sulbactam improves the binding property and uptake capacity of GLT-1 for glutamate and then reduces the glutamate concentration and excitotoxicity during global cerebral ischemia, which contributes to the neuroprotection of sulbactam against brain ischemia.