Abstract TP318: Ethyl Pyruvate Treatment Increases Post-ischemic Levels of Selected Metabolites Detected by Labelled Cerebral Microdialysis

Abstract

Introduction: Metabolic perturbations associated with mitochondrial function are common after transient cerebral ischemia and are detectable using cerebral microdialysis (CMD). Several putative neuroprotective treatments including ethyl pyruvate (EP) target mitochondrial energy metabolism, but continuous real-time effects have not been described. Using 13 C-succinate labelled CMD with Liquid Chromatography - Mass Spectrometry (LC-MS) we hypothesized that effects of EP treatment on mitochondrial function after transient ischemia could be monitored in vivo. Methods: Adult Sprague Dawley rats (n=11) were subjected to transient ischemia by stereotaxic microinjection of vasoconstricting endothelin-1 (ET-1) and monitored for 5 hours after reperfusion with trace amount labelled 13 C-succinate CMD during intravenous treatment with EP (40 mg/kg) or vehicle (Ringer’s solution). Using mixed effect linear regression, values of labelled and endogenous energy metabolites after reperfusion were compared to baseline. Results: ET-1 induced vasoconstriction resulted in transient depression of glucose and elevation of lactate. After reperfusion labelled malate and endogenous xanthine displayed significantly higher concentrations in the EP-group compared to the placebo-group: (mean±SEM) 39.5±14.9%, p<0.01 and 93.9±28.3%, p<0.001 respectively. Endogenous glucose-6-phosphate, pyruvate, succinate, fumarate, malate and isocitrate showed larger variance and no significant difference. Neither did labelled pyruvate, lactate fumarate or isocitrate. Conclusions: EP treatment potentiates mitochondrial de novo synthesis of malate after transient cerebral ischemia. Differences compared to other Krebs’ cycle intermediates may be explained by a pronounced labelling ratio difference influenced by proximity to labelling source in the metabolic pathway. Increased amounts of endogenous xanthine may be explained by ROS scavenging effects of EP maintaining a beneficial NAD + /NADH ratio required for efficient purine metabolism. Labelled CMD combined with LC-MS enables detailed temporal monitoring of energy metabolites aiding evaluation of putative neuroprotective treatments in vivo.