Increased Plasma Glutamate in Stroke Patients Might Be Linked to Altered Platelet Release and Uptake

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Abstract
Experimental studies have shown the role of excitotoxicity in the pathogenesis of ischemic brain lesions, and glutamate levels have been found to be elevated in CSF and plasma from patients, early after stroke. In this study, we investigated whether platelets could be involved in the mechanism of altered plasma glutamate levels after stroke. Forty four patients, from 6 hours to 9 months after ischemic stroke, 15 age-related healthy controls and 15 controls with stroke risk factors or previous transient ischemic attack were enrolled. Glutamate plasma levels, platelet glutamate release after aggregation and platelet glutamate uptake were assessed. Plasma glutamate levels were increased up to 15 days after the ischemic event in stroke patients, and the levels at day 3 were inversely correlated with the neurologic improvement between day 3 and 15. Ex vivo platelet glutamate release was decreased by 70% in stroke patients, suggesting previous in vivo platelet activation. Moreover, platelet glutamate uptake in these patients was decreased by 75% up to 15 days and was still reduced 90 days after stroke. Our data show a prolonged increase of glutamate in plasma after stroke, which might presumably be linked to altered platelet functions, such as excessive release of the amino acid or impaired uptake.