Targeting Platelets in Acute Experimental Stroke

Abstract

Background-Ischemic stroke is a frequent and serious disease with limited treatment options. Platelets can adhere to hypoxic cerebral endothelial cells by binding of their glycoprotein (GP) Ib receptor to von Willebrand factor. Exposure of subendothelial matrix proteins further facilitates firm attachment of platelets to the vessel wall by binding of collagen to their GPVI receptor. In the present study, we addressed the pathogenic role of GPIb, GPVI, and the aggregation receptor GPIIb/IIIa in experimental stroke in mice. Methods and Results-Complete blockade of GPIb␣ was achieved by intravenous injection of 100 g Fab fragments of the monoclonal antibody p0p/B to mice undergoing 1 hour of transient middle cerebral artery occlusion. At 24 hours after transient middle cerebral artery occlusion, cerebral infarct volumes were assessed by 2,3,5-triphenyltetrazolium chloride staining. In mice treated with anti-GPIb␣ Fab 1 hour before middle cerebral artery occlusion, ischemic lesions were reduced to Ϸ40% compared with controls (28.5Ϯ12.7 versus 73.9Ϯ17.4 mm 3 , respectively; PϽ0.001). Application of anti-GPIb␣ Fab 1 hour after middle cerebral artery occlusion likewise reduced brain infarct volumes (24.5Ϯ7.7 mm 3 ; PϽ0.001) and improved the neurological status. Similarly, depletion of GPVI significantly diminished the infarct volume but to a lesser extent (49.4Ϯ19.1 mm 3 ; PϽ0.05). Importantly, the disruption of early steps of platelet activation was not accompanied by an increase in bleeding complications as revealed by serial magnetic resonance imaging. In contrast, blockade of the final common pathway of platelet aggregation with anti-GPIIb/IIIa F(ab) 2 fragments had no positive effect on stroke size and functional outcome but increased the incidence of intracerebral hemorrhage and mortality after transient middle cerebral artery occlusion in a dose-dependent manner. Conclusions-Our data indicate that the selective blockade of key signaling pathways of platelet adhesion and aggregation has a different impact on stroke outcome and bleeding complications. Inhibition of early steps of platelet adhesion to the ischemic endothelium and the subendothelial matrix may offer a novel and safe treatment strategy in acute stroke.

Stroke‐induced chronic systolic dysfunction driven by sympathetic overactivity

“…Focal cerebral ischemia was induced by a 30‐minute tMCAO, as previously described 15. Briefly, mice were anesthetized with 2% isoflurane in O 2 .…”

Importance of T Lymphocytes in Brain Injury, Immunodeficiency, and Recovery after Cerebral Ischemia

“…The net impact of the accumulated platelets in the postischemic microcirculation remains unclear; however, inhibition of platelet tethering and adhesion to vascular endothelial cells (the early phases of platelet activation) has produced reductions in cerebral infarct volume (Elvers et al, 2010;Kleinschnitz et al, 2007Kleinschnitz et al, , 2009Zhao et al, 2009). Furthermore, inhibition of early platelet adhesion and activation maintains cerebral blood flow during reperfusion (Pham et al, 2011).…”

Neutrophil infiltration to the brain is platelet‐dependent, and is reversed by blockade of platelet GPIbα

“…Therefore, to assess whether platelet‐dependent neutrophil infiltration could be blocked, in a manner with less potential systemic effects and therefore more relevant therapeutically and without reducing platelet numbers, we administered anti‐GPIb α antibody in the context of LPS‐induced brain inflammation. Anti‐GPIb α antibody has been shown previously to protect mice from ischaemic brain injury in an experimental stroke model without an increase in bleeding complications 14. Here, anti‐GPIb α antibody had no effect on numbers of circulating platelets compared with IgG‐injected controls (Fig.…”

“…Indeed, neutrophils have neurotoxic effects on neurons in vitro ,16 an effect that appears dependent on phenotypic changes that occur during neutrophil cerebrovascular infiltration 17. Targeting various aspects of platelet activation reduces stroke injury 3, 14, 18. This, together with platelet‐dependent neutrophil infiltration mechanisms3 and the relevance of these in different tissues shown here, suggests that platelet‐targeted therapies may be beneficial after CNS injury.…”