Abstract
BACKGROUND AND PURPOSE: Pyruvate is known to be cytoprotective through antioxidant and anti-inflammatory mechanisms. We tested the hypothesis that pyruvate protects the brain against ischemia-reperfusion injury by inducing endogenous erythropoietin (EPO) expression. METHODS: Pyruvate's protective effect was evaluated in C6 glioma cells and HT22 neuronal cells subjected to transient oxygen glucose deprivation. Cell viability (calcein AM assay) and expression of hypoxia-inducible factor-1α, EPO, Akt and Erk (immunoblot), and EPO receptor (reverse transcription-polymerase chain reaction) were analyzed. Transient focal cerebral ischemia in rats was induced by 2 hours middle cerebral artery occlusion followed by 24 hours reperfusion. Pyruvate or saline was infused from 60 minutes occlusion until 30 minutes reperfusion. Lesion volume and DNA fragmentation were assessed by 2,3,5-triphenyltetrazolium staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay, respectively. Immunoblots were conducted to determine cerebral EPO contents. RESULTS: Pyruvate increased cell viability, hypoxia-inducible factor-1α, EPO, and Akt phosphorylation. Small interfering RNA suppression of hypoxia-inducible factor-1α and EPO abolished pyruvate-induced cytoprotection. In the rat stroke model, pyruvate reduced lesion volume by 84% and DNA fragmentation by 77% versus controls; increased EPO content paralleled these cerebroprotective actions of pyruvate. CONCLUSIONS: Pyruvate activation of the hypoxia-inducible factor-1α-EPO signaling cascade in neurons and glia could protect the brain from ischemia-reperfusion injury.