Reduced microvascular thrombosis and improved outcome in acute murine stroke by inhibiting GP IIb/IIIa receptor-mediated platelet aggregation.

Abstract

Treatment options in acute stroke are limited by a dearth of safe and effective regimens for recanalization of an occluded cerebrovascular tributary, as well as by the fact that patients present only after the occlusive event is established. We hypothesized that even if the site of major arterial occlusion is recanalized after stroke, microvascular thrombosis continues to occur at distal sites, reducing postischemic flow and contributing to ongoing neuronal death. To test this hypothesis, and to show that microvascular thrombosis occurs as an ongoing, dynamic process after the onset of stroke, we tested the effects of a potent antiplatelet agent given both before and after the onset of middle cerebral arterial (MCA) occlusion in a murine model of stroke. After 45 min of MCA occlusion and 23 h of reperfusion, fibrin accumulates in the ipsilateral cerebral hemisphere, based upon immunoblotting, and localizes to microvascular lumena, based upon immunostaining. In concordance with these data, there is a nearly threefold increase in the ipsilateral accumulation of 111 In-labeled platelets in mice subjected to stroke compared with mice not subjected to stroke. When a novel inhibitor of the glycoprotein IIb/IIIa receptor (SDZ GPI 562) was administered immediately before MCA occlusion, platelet accumulation was reduced 48%, and fibrin accumulation was reduced by 47% by immunoblot densitometry. GPI 562 exhibited a dose-dependent reduction of cerebral infarct volumes measured by triphenyltetrazolium chloride staining, as well as improvement in postischemic cerebral blood flow, measured by laser doppler. GPI 562 caused a dose-dependent increase in tail vein bleeding time, but intracerebral hemorrhage (ICH) was not significantly increased at therapeutic doses; however, there was an increase in ICH at the highest doses tested. When given immediately after withdrawal of the MCA occluding suture, GPI 562 was shown to reduce cerebral infarct volumes by 70%. These data support the hypothesis that in ischemic regions of brain, microvascular thrombi continue to accumulate even after recanalization of the MCA, contributing to postischemic hypoperfusion and ongoing neuronal damage. ( J. Clin. Invest. 1998. 102:1301-1310.)

Platelet Recruitment to the Inflamed Glomerulus Occurs via an αIIbβ3/GPVI-Dependent Pathway

“…In an in vivo ferric chloride thrombosis model, a localized thrombus is formed by the microinjection of 6% ferric chloride. In this model, the GPIb␣-binding venom protein, alboaggregin B, prevented primary platelet adhesion, whereas GPI562, which has been demonstrated to be a potent and selective inhibitor of ␣ IIb ␤ 3 , 36,45 prevented platelet aggregation (see Supplemental Figure S1 and Supplemental Video 1 at http://ajp.amjpathol.org). In addition, alboaggregin B prevented platelet attachment to collagen under high shear flow conditions in vitro (see Supplemental Figure S2 at http://ajp.amjpathol.org), interactions previously found to be GPIb␣/vWF-dependent.…”

“…To inhibit ␣ IIb ␤ 3 , GPI562 (4 mg/kg), a small molecule ␣ IIb ␤ 3 antagonist, was used. 35,36 Alboaggregin-B (280 g/kg), a GPIb␣-binding venom protein purified as a 25-kDa heterodimer from C.h. horridus (rattlesnake venom) as previously described (kindly provided by A/Prof.…”

Recognition of the Importance of Embolization in Atherosclerotic Vascular Disease

“…69 Perhaps a key further explanation is the lack of attention to relieving microvascular obstruction, which would potentially be exacerbated by fibrinolytic therapy alone. In a recent experimental stroke model, Choudhri et al 70 showed marked sparing of brain infarction and relief of microvascular obstruction using a platelet GP IIb/IIIa inhibitor. Initial experience with GP IIb/IIIa blockade in acute stroke management had indeed been quite favorable.…”

Cerebral Microvasculature

“…117 A significant dose-dependent increase in debilitating hemorrhage within the ischemic regions can occur with these agents. 117,118 In keeping with the observation that specific integrin ␣ IIb ␤ 3 blockade can produce hemorrhage within the ischemic territory in animal models, a prospective phase III trial of the pan-␤ 3 inhibitor of platelet ␣ IIb ␤ 3 in ischemic stroke patients has been terminated because of safety concerns. 119 This suggests that despite salutary effects of integrin blockade at the vascular interface a more complete understanding of the mechanisms whereby adhesive events regulate blood-brain barrier integrity and leukocyte trafficking across the microvessel permeability barrier is required.…”