A Glutamate Receptor Antagonist, S-4-Carboxyphenylglycine (S-4-CPG), Inhibits Vasospasm After Subarachnoid Hemorrhage in Haptoglobin 2 to 2 Mice

Abstract

Vasospasm contributes to delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage (SAH). Glutamate concentrations increase after SAH and correlate with vasospasm in experimental SAH. The haptoglobin (Hp) 2-2 genotype is associated with higher risk of vasospasm after SAH. We tested the efficacy of (S)-4-carboxyphenylglycine (S-4-CPG), a metabotropic glutamate receptor inhibitor, for the treatment of vasospasm after SAH in Hp 2-2 and Hp 1-1 mice. To evaluate the effect on vasospasm and neurobehavioral scores after SAH of systemic S-4-CPG, as well as its toxicity, and phosphorylation of vasodilator-stimulated phosphoprotein (VASP) in Hp 2-2 mice. Western blot was used to assess changes in VASP phosphorylation in response to glutamate with and without S-4-CPG. A pharmacokinetics study was done to evaluate S-4-CPG penetration through the blood-brain barrier in vivo. Toxicity was assessed by administering increasing S-4-CPG doses. Efficacy of S-4-CPG assessed the effect of S-4-CPG on lumen patency of the basilar artery and animal behavior after SAH in Hp 1-1 and Hp 2-2 mice. Immunohistochemistry was used to evaluate the presence of neutrophils surrounding the basilar artery after SAH. Exposure of human brain microvascular endothelial cells to glutamate decreased phosphorylation of VASP, but glutamate treatment in the presence of S-4-CPG maintains phosphorylation of VASP. S-4-CPG crosses the blood-brain barrier and was not toxic to mice. S-4-CPG treatment significantly prevents vasospasm after SAH. S-4-CPG administered after SAH resulted in a trend toward improvement of animal behavior. S-4-CPG prevents vasospasm after experimental SAH in Hp2-2 mice. S-4-CPG was not toxic and is a potential therapeutic agent for vasospasm after SAH.