Abstract WP256: Serum Glutamate Level but Not NMDAR Antibody - A Potential Biomarker of Early Ischemia in Rat Stroke Model

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Introduction: Identifying a biomarker for early detection of ischemia is indispensable as millions of stroke patients are in dire need of a screening tool that is fast in diagnosis whilst obviating the need of expensive neuroimages.

Hypothesis: A key element in ischaemic cascade is the failure of energy dependent ion channels that leads to influx of calcium ions. This influx triggers multifold release of Glutamate - an Excitatory Neurotransmitter that activates NMDA receptor which further augments the spread of depolarization from ischaemic core to the viable penumbra. We assessed the hypothesis that Glutamate is a credible early biomarker of ischaemic insult to the brain. This proposition was trialed on an animal stroke model.

Methods: The stroke model was created through permanent Middle Cerebral Artery Occlusion(pMCAO) on 39 male Wistar Albino rats (250-300g). The rats were divided into Stroke group(n 24) and Sham/Control group(n 15). The blood samples were collected 0 hour (before stroke induction/sham procedure) and also at 1, 3 or 6 hours post procedure. The serum was tested for Glutamate and anti-NR2 Antibody using ELISA assay.

Results: Serum Glutamate increased 4-fold at 1 hour of stroke induction (from 0.24+0.3nmol to 3.7+0.8nmol(p<0.0001))(Fig. 1A). No significant difference in Glutamate levels were observed between two groups at 3 or 6 hour(Fig. 1B & 1C). Serum Glutamate of Stroke rats at 3 different time-point showed that it can be detected as early as 1 hour of stroke induction but plummets to pre-stroke level at 3 to 6 hours(Fig. 2).

The levels of anti-NR2 antibody were below detectable limits in both Stroke and Sham Control rats throughout the experiments.

Conclusions: Serum Glutamate level rose significantly within 1 hour of stroke in our rat pMCAO model, but no detectable antibody was obtained for NR2 subunit of NMDAR indicating delay in antibody formation. Translational research can validate Glutamate as marker of early ischaemia. ischaemia.

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