FK419, a nonpeptide platelet glycoprotein IIb/IIIa antagonist, ameliorates brain infarction associated with thrombotic focal cerebral ischemia in monkeys: comparison with tissue plasminogen activator

A pilot behavioural and neuroimaging investigation on photothrombotic stroke models in rhesus monkeys

BACKGROUND

Ischemic stroke leads to a long-term disability in humans and no efficient clinical therapy exists to date. The middle cerebral artery occlusion (MCAO) model in non-human primates has shown to be of value for translational stroke research. New method In the current study, a photothrombotic (PT) stroke model was established in rhesus monkeys with either a proximal or distal segment of middle cerebral artery (MCA) thrombosis. This study is the first that compares the two approaches of PT stroke in monkeys using behavioral and physiological measurements and MRI scans.

RESULTS

The experiment found that infarct occurred in the MCA target regions, with all monkeys having impaired behavior reflected by deficits in neurologic function, and motor and cognition in object retrieval detour (ORD) task. The monkeys with distal MCA thrombosis developed with sequential photo-irritations of the Sylvian fissure zone, adjacent central anterior gyrus and central posterior gyrus, had similar impairments with respect to behavior and showed a tendency of a small edema volume with proximal MCA thrombosis at days 4 and 7 post PT stroke.

COMPARISON WITH EXISTING METHODS

The distal MCA thrombosis developed with sequential photo-irritations might provide a consistent and well-tolerated focal ischemia in rhesus monkeys, compared with other PT stroke models which usually were singly conducted on the animal's motor cortex and had a temporal effect.

CONCLUSIONS

The sequentially photo-irritated PT stroke model is a promising ischemic stroke model in rhesus monkey for studying human stroke pathology and physiology and for new therapies development.

Thromboinflammation: challenges of therapeutically targeting coagulation and other host defense mechanisms

Thrombosis with associated inflammation (thromboinflammation) occurs commonly in a broad range of human disorders. It is well recognized clinically in the context of superficial thrombophlebitis (thrombosis and inflammation of superficial veins); however, it is more dangerous when it develops in the microvasculature of injured tissues and organs. Microvascular thrombosis with associated inflammation is well recognized in the context of sepsis and ischemia-reperfusion injury; however, it also occurs in organ transplant rejection, major trauma, severe burns, the antiphospholipid syndrome, preeclampsia, sickle cell disease, and biomaterial-induced thromboinflammation. Central to thromboinflammation is the loss of the normal antithrombotic and anti-inflammatory functions of endothelial cells, leading to dysregulation of coagulation, complement, platelet activation, and leukocyte recruitment in the microvasculature. α-Thrombin plays a critical role in coordinating thrombotic and inflammatory responses and has long been considered an attractive therapeutic target to reduce thromboinflammatory complications. This review focuses on the role of basic aspects of coagulation and α-thrombin in promoting thromboinflammatory responses and discusses insights gained from clinical trials on the effects of various inhibitors of coagulation on thromboinflammatory disorders. Studies in sepsis patients have been particularly informative because, despite using anticoagulant approaches with different pharmacological profiles, which act at distinct points in the coagulation cascade, bleeding complications continue to undermine clinical benefit. Future advances may require the development of therapeutics with primary anti-inflammatory and cytoprotective properties, which have less impact on hemostasis. This may be possible with the growing recognition that components of blood coagulation and platelets have prothrombotic and proinflammatory functions independent of their hemostatic effects.

Prasugrel reduces ischaemic infarct volume and ameliorates neurological deficits in a non-human primate model of middle cerebral artery thrombosis

Several clinical trials have demonstrated the benefits of thienopyridine monotherapy in ischaemic stroke patients. Non-human primate models of ischaemic stroke have been used for various antithrombotic agents; however, to the best of our knowledge, there is no data on the effects of P2Y12 antagonists in models, such as the thrombotic middle cerebral artery occlusion (MCAO) monkey model. Accordingly, it remains unclear what level of inhibition of platelet aggregation (IPA) is required for optimal treatment of ischaemic stroke. In the present study, we investigated the effects of prasugrel, a third-generation thienopyridine antiplatelet drug, on platelet aggregation, thrombus formation and cerebral infarct volume in a non-human primate model. Daily oral administration of prasugrel resulted in significant and stable platelet inhibitory effects on Day 3, with IPA values ranging from 31% to 36% at 0.3mg/kg/day and from 44% to 50% at 1mg/kg/day. These IPA levels encompassed values observed in clinical trials of clopidogrel, and were thus selected for further study. In the thrombotic MCAO model, prasugrel increased MCA patency in a dose-dependent manner and significantly reduced ischaemic infarct volume by approximately 70% at 0.3mg/kg/day and 90% at 1mg/kg/day without increasing haemorrhagic infarction. Prasugrel also significantly reduced neurological deficit scores by 60% at 0.3mg/kg/day and 80% at 1mg/kg/day. In conclusion, prasugrel treatment resulted in effective reduction of ischaemic infarction and an associated improvement in neurological function without increasing haemorrhagic infarction. These data suggest that prasugrel monotherapy would be effective for the prevention of thrombotic stroke.

Safety of tirofiban for patients with acute ischemic stroke in routine clinical practice

The aim of the present study was to investigate the safety of tirofiban alone and in combination with various treatments in acute ischemic stroke (AIS). A total of 120 patients with AIS were included in the study, and these patients were divided into three treatment groups: Group A (tirofiban alone, n=68), group B (tirofiban plus thrombolytic therapy, n=26), and group C (tirofiban as a 'bridging therapy', n=26). Risk factors, stroke severity, initial imaging, treatment regimens, complications and long-term outcomes were analyzed. In total, eight patients (6.7%) [six patients (23.1%) in group B and two patients (7.7%) in group C] had hemorrhage during or subsequent to treatment. Sixteen patients (six in group A, eight in group B and two in group C) succumbed during the hospital admission period. The mortality rate was 13.3% (8.8% for group A, 30.7% for group B and 7.7% for group C) in the acute phase. A favorable outcome (modified Rankin Scale score, 0-2) in the first three months after stroke was only observed in 43.3% of patients (44.1% in group A, 46.7% in group B and 36.4% in group C). The mean Barthel index was 72.3 in group A, 84.4 in group B and 56.8 in group C (total patient population, 71.0). The results of the present study have shown that stroke treatment with tirofiban is safe in AIS. A large randomized controlled trial in the future is required to decrease the incidence of the minor bleeding complications associated with tirofiban therapy.

SMTP-7, a novel small-molecule thrombolytic for ischemic stroke: a study in rodents and primates

SMTP-7 (Stachybotrys microspora triprenyl phenol-7), a small molecule that promotes plasminogen activation through the modulation of plasminogen conformation, has excellent therapeutic activity against cerebral infarction in several rodent models. Detailed evaluations of SMTP-7 in a primate stroke model are needed for effective, safe drug development. Here we evaluated SMTP-7 in a monkey photochemical-induced thrombotic middle cerebral artery (MCA) occlusion model (n=6), in which MCA occlusion was followed by recanalization/reocclusion. SMTP-7 (10 mg/kg, intravenous infusion) significantly increased the postinfusion MCA recanalization rate (32.5-fold, P=0.043) and ameliorated the post-24-h neurologic deficit (by 29%, P=0.02), cerebral infarct (by 46%, P=0.033), and cerebral hemorrhage (by 51%, P=0.013) compared with the vehicle control animals. In normal monkeys, SMTP-7 did not affect general physiologic or hemostatic variables, including coagulation and platelet parameters. Investigations in rodent models of transient and permanent focal cerebral ischemia, as well as arterial thrombosis and bleeding tests, suggest a role for SMTP-7's regulated profibrinolytic action and neuroprotective properties in the monkey MCA occlusion model. In conclusion, SMTP-7 is effective in treating thrombotic stroke in monkeys. SMTP-7 is thus a promising candidate for the development of alternative therapy for ischemic stroke.

Outcome after systemic thrombolysis is predicted by age and stroke severity: an open label experience with recombinant tissue plasminogen activator and tirofiban

Stroke patients can recover upon intravenous thrombolysis but remain impaired in lacking recanalization. We sought to investigate the clinical effect of systemic thrombolysis with an intravenous bolus of 20 mg recombinant tissue plasminogen activator (rtPA) and an infusion of body-weight adjusted tirofiban for 48 hours in acute stroke. This prospective, open label study, included 192 patients (68±13 years, 50% males) treated between 1 January 2005 and 31 December 2007. The neurological deficit was assessed with the National Institutes of Health stroke scale (NIHSS). Follow-up was performed using a telephone interview of modified Rankin Scale (mRS) and Barthel index. The site of cerebral artery occlusion was determined by computed tomography or magnetic resonance angiography. Data were analyzed by descriptive statistics and multiple regression analyses. Eighty-one percent of the patients had an infarct in the middle cerebral artery (MCA) territory and were severely affected with a median NIHSS of 10. During treatment on the Stroke Unit the patients improved (P<0.0001) except for patients who deceased due to malignant infarction (n=10) or cerebral haemorrhage (n=6); 18 percent deceased within 100 days which was predicted by older age (76 + 10 years, P<0.05) and more severe affection on admission (P<0.0001). Also, these patients more frequently had atrial fibrillation (P<0.03) than the surviving patients. The surviving patients had more frequently distal MCA occlusions and improved further (P<0.0001). At follow-up 48% of the patients had a mRS of 0 and 1. Similarly to intravenous thrombolysis with body-weight adjusted rtPA, poor prognosis was predicted by higher age, more severe neurological deficit at stroke admission, and a proximal MCA occlusion. Half of the surviving patients improved to no or minimal impairment.

A novel inhibitor of plasminogen activator inhibitor-1 provides antithrombotic benefits devoid of bleeding effect in nonhuman primates

Inhibition of plasminogen activator inhibitor (PAI)-1 is useful to treat several disorders including thrombosis. An inhibitor of PAI-1 (TM5275) was newly identified by an extensive study of structure-activity relationship based on a lead compound (TM5007) which was obtained through virtual screening by docking simulations. Its antithrombotic efficacy and adverse effects were tested in vivo in rats and nonhuman primates (cynomolgus monkey). TM5275, administered orally in rats (1 to 10 mg/kg), has an antithrombotic effect equivalent to that of ticlopidine (500 mg/kg) in an arterial venous shunt thrombosis model and to that of clopidogrel (3 mg/kg) in a ferric chloride-treated carotid artery thrombosis model. TM5275 does not modify activated partial thromboplastin time and prothrombin time or platelet activity and does not prolong bleeding time. Combined with tissue plasminogen activator, TM5275 improves the latter's therapeutic efficacy and reduces its adverse effect. Administered to a monkey model of photochemical induced arterial thrombosis, TM5275 (10 mg/kg) has the same antithrombotic effect as clopidogrel (10 mg/kg), without enhanced bleeding. This study documents the antithrombotic benefits of a novel, more powerful, PAI-1 inhibitor in rats and, for the first time, in nonhuman primates. These effects are obtained without adverse effect on bleeding time.

Targeting Platelets in Acute Experimental Stroke

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 GPIbα was achieved by intravenous injection of 100 μg 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-GPIbα Fab 1 hour before middle cerebral artery occlusion, ischemic lesions were reduced to ≈40% compared with controls (28.5±12.7 versus 73.9±17.4 mm 3 , respectively; P <0.001). Application of anti-GPIbα Fab 1 hour after middle cerebral artery occlusion likewise reduced brain infarct volumes (24.5±7.7 mm 3 ; P <0.001) and improved the neurological status. Similarly, depletion of GPVI significantly diminished the infarct volume but to a lesser extent (49.4±19.1 mm 3 ; P <0.05). 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.

Therapeutic time window of tacrolimus (FK506) in a nonhuman primate stroke model: Comparison with tissue plasminogen activator

Tacrolimus (FK506), an immunosuppressive drug, has been shown to exert a potent neuroprotective activity when administered immediately after occlusion of the middle cerebral artery (MCA) in a nonhuman primate model of stroke. Here, we assessed the neuroprotective efficacy of tacrolimus with delayed treatment using the same model and compared with that of recombinant tissue plasminogen activator (rt-PA). Ischemic insult was induced by photochemically induced thrombotic occlusion of MCA in cynomolgus monkeys, and tacrolimus (0.2 mg/kg) and/or rt-PA (1.0 mg/kg) was intravenously administered 2 h after MCA occlusion. In another experiment, tacrolimus (0.1 mg/kg) was administered 4 h after MCA occlusion. Neurological deficits were monitored for 28 days after the ischemic insult and cerebral infarct volumes were measured with brain slices. With drug administration 2 h after the ischemic insult, tacrolimus significantly reduced neurological deficits and infarct volumes in the cerebral cortex without affecting the recanalization pattern in the MCA, however, rt-PA did not significantly improve neurological deficits or infarct volumes, even though it increased the recanalization rate of the occluded MCA. Combined treatment with tacrolimus and rt-PA exerted additional protection. Administration of tacrolimus 4 h after the ischemic insult still showed significant amelioration of neurological deficits. These results suggested that tacrolimus had a wider therapeutic time window than rt-PA in the nonhuman primate stroke model.