Association of Factor V Secretion with Protein Kinase B Signaling in Platelets from Horses with Atypical Equine Thrombasthenia.

BACKGROUND: Two congenital bleeding diatheses have been identified in Thoroughbred horses: Glanzmann thrombasthenia (GT) and a second, novel diathesis associated with abnormal platelet function in response to collagen and thrombin stimulation. HYPOTHESIS/OBJECTIVES: Platelet dysfunction in horses with this second thrombasthenia results from a secretory defect. ANIMALS: Two affected and 6 clinically normal horses. METHODS: Ex vivo study. Washed platelets were examined for (1) expression of the αIIb-ß3 integrin; (2) fibrinogen binding capacity in response to ADP and thrombin; (3) secretion of dense and α-granules; (4) activation of the mammalian target of rapamycin (mTOR)-protein kinase B (AKT) signaling pathway; and (5) cellular distribution of phosphatidylinositol-4-phosphate-3-kinase, class 2B (PIK3C2B) and SH2 containing inositol-5'-phosphatase 1 (SHIP1). RESULTS: Platelets from affected horses expressed normal amounts of αIIb-ß3 integrin and bound fibrinogen normally in response to ADP, but bound 80% less fibrinogen in response to thrombin. α-granules only released 50% as much Factor V as control platelets, but dense granules released their contents normally. Protein kinase B (AKT) phosphorylation was reduced after thrombin activation, but mTOR Complex 2 (mTORC2) and phosphoinositide-dependent kinase 1 (PDK1) signaling were normal. SH2-containing inositol-5'-phosphatase 1 (SHIP1) did not localize to the cytoskeleton of affected platelets and was decreased overall consistent with reduced AKT phosphorylation. CONCLUSIONS AND CLINICAL SIGNIFICANCE: Defects in fibrinogen binding, granule secretion, and signal transduction are unique to this thrombasthenia, which we designate as atypical equine thrombasthenia.

Platelet activation in cats with hypertrophic cardiomyopathy.

BACKGROUND: Cats with hypertrophic cardiomyopathy (HCM) are at risk for development of systemic thromboembolic disease. However, the relationship between platelet activation state and cardiovascular parameters associated with HCM is not well described. OBJECTIVES: To characterize platelet activation by flow cytometric evaluation of platelet P-selectin and semiquantitative Western blot analysis of soluble platelet-endothelial cell adhesion molecule-1 (sPECAM-1). ANIMALS: Eight normal healthy cats (controls) owned by staff and students of the School of Veterinary Medicine and 36 cats from the UC Davis Feline HCM Research Laboratory were studied. METHODS: Platelet-rich plasma (PRP) was used for all flow cytometry studies. Platelet surface CD41 and P-selectin expression were evaluated before and after ADP stimulation. sPECAM-1 expression was evaluated by Western blot analysis of platelet-poor plasma that had been stabilized with aprotinin. Standard echocardiographic studies were performed. RESULTS: Resting platelets from cats with severe HCM had increased P-selectin expression compared to controls, and expressed higher surface density of P-selectin reflected by their increased mean fluorescence intensities (MFI). Stimulation with ADP also resulted in significantly increased P-selectin MFI of platelets from cats with severe HCM. Increased P-selectin expression and MFI correlated with the presence of a heart murmur and end-systolic cavity obliteration (ESCO). sPECAM-1 expression from cats with moderate and severe HCM was significantly increased above those of control cats. CONCLUSIONS AND CLINICAL IMPORTANCE: P-selectin and sPECAM expression may be useful biomarkers indicating increased platelet activation in cats with HCM.

Clinical characterization of canine platelet procoagulant deficiency (Scott syndrome).

BACKGROUND: Platelet function defects are rare causes of bleeding diatheses; however, disease prevalence might be underestimated because diagnosis requires assessment of specific parameters of platelet activation. OBJECTIVES: The goal of this study was to characterize the clinical presentation of canine Scott syndrome (CSS), an intrinsic platelet function defect first identified in a closed colony of German Shepherds (GSD). ANIMALS: Eleven (n = 6 female) client-owned GSD affected with CSS that sought veterinary care for one or more episodes of abnormal bleeding. METHODS: Retrospective review of all cases of CSS diagnosed through the Comparative Coagulation Laboratory at Cornell University between 2005 and 2011. The diagnosis of CSS was based on 2 measures of platelet procoagulant activity: serum prothrombin consumption and flow cytometric detection of platelet phosphatidylserine externalization after in vitro activation. RESULTS: Postoperative hemorrhage was the most common sign of CSS, whereas petechiae were not found in any dog. Although most GSD responded to platelet transfusion, refractory epistaxis in 2 GSD was managed by nasal arterial embolization. The CSS trait was not restricted to a single pedigree of related GSD or to a single geographic region. CONCLUSIONS AND CLINICAL IMPORTANCE: Unlike thrombocytopenia and platelet aggregation defects, petechiae and other capillary hemorrhage are not typical features of CSS. After preliminary screening to rule out more common causes of hemorrhage, CSS should be considered in the differential diagnosis of recurrent hemorrhage in GSD, and potentially other breeds of dog. Definitive diagnosis of CSS requires specific tests of platelet procoagulant activity.

Exposure of mice to concentrated ambient particulate matter results in platelet and systemic cytokine activation.

Increasingly, evidence suggests a role for a systemic procoagulant state in the pathogenesis of cardiac dysfunction subsequent to inhalation of airborne particulate matter. The authors evaluated blood cell parameters and markers of platelet activation in mice exposed to concentrated ambient particulate matter (CAPs) from the San Joaquin Valley of California, a region with severe particulate matter (PM) pollution episodes. The authors exposed mice to an average of 88.5 microg/m(3) of CAPs in a size range less than 2.5 microm for 6 h/day for 5 days per week for 2 weeks. Platelets were analyzed by flow cytometry for relative size, shape, aggregation, fibrinogen binding, P-selectin, and lysosomal-associated membrane protein-1 (LAMP-1) expression. Serum cytokines were analyzed by bead-based immunologic assays. CAPs-exposed mice had elevations in macrophage inflammatory protein (MIP)-1 alpha, MIP-1 beta, interleukin (IL)-6, IL-10, tumor necrosis factor alpha (TNFalpha), macrophage colony-stimulating factor (M-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), platelet-derived growth factor (PDGF)-bb, and RANTES (regulated upon activation, normally T-expressed, and presumably secreted). Platelets were the only peripheral blood cells that were significantly elevated in number in CAPs-exposed mice. Flow cytometric analysis of unstimulated platelets from CAPs-exposed mice indicated size and shape changes, and platelets from CAPs-exposed animals had a 54% increase in fibrinogen binding indicative of platelet priming. Stimulation of platelets by thrombin resulted in up-regulation of LAMP-1 expression in CAPs-exposed animals and an increased microparticle population relative to control animals. These findings demonstrate a systemic proinflammatory and procoagulant response to inhalation of environmentally derived fine and ultrafine PM and suggests a role for platelet activation in the cardiovascular and respiratory effects of particulate air pollution.

Treatment of cervical artery dissection: a systematic review and meta-analysis.

BACKGROUND AND PURPOSE: Cervical dissection is an important cause of stroke in the young. This paper presents a systematic review and a meta-analysis to assess the effectiveness of different treatment approaches: antithrombotic drugs, thrombolysis and stenting. METHODS: Medline and PubMed were searched from 1966 to 8 April 2007. Reference lists were reviewed. Separate searches were performed for treatment with anticoagulation and antiplatelet therapy during the acute phase (within 1 month of symptoms), thrombolysis and stenting. RESULTS: There were only sufficient data for meta-analysis for the comparison of antiplatelet versus anticoagulation therapy. No randomised trials were identified. 34 non-randomised studies included 762 patients. There was no significant difference in risk of death (antiplatelet 5/268 (1.8%), anticoagulation 9/494 (1.8%), p = 0.88); stroke (antiplatelet 5/268 (1.9%), anticoagulant 10/494 (2.0%), p = 0.66), or stroke and death. Four non-randomised studies of thrombolysis provided insufficient data for assessment of efficacy but complication rates were no greater than thrombolysis for other ischaemic stroke. Six studies included 96 patients undergoing stenting for both acute dissection and chronic complications, providing insufficient data for assessment of efficacy, although complication rates appeared similar to those published for carotid atherosclerosic stenosis. CONCLUSIONS: There are no data to support the therapeutic superiority of anticoagulants over antiplatelet agents. Thrombolysis in dissection appears safe but more data on efficacy are required. Stenting is technically possible but there are no data to demonstrate efficacy. There is little evidence to support current treatment approaches in cervical dissection. Randomised controlled prospective trials, particularly assessing anticoagulation versus antiplatelet agents, are required.

Seizures after stroke: a prospective multicenter study.

BACKGROUND: Studies of seizures after stroke have largely been retrospective, with small patient numbers and limited statistical analysis. Much of the doctrine about seizures after stroke is not evidenced based. OBJECTIVE: To determine the incidence, outcome, and risk factors for seizures after stroke. DESIGN: International, multicenter, prospective, analytic inception cohort study conducted for 34 months. PATIENTS AND SETTING: There were 2021 consecutive patients with acute stroke admitted to university teaching hospitals with established stroke units. After exclusion of 124 patients with previous epilepsy or without computed tomographic diagnosis, 1897 were available for analysis. Mean follow-up was 9 months. MAIN OUTCOME MEASURES: Occurrence of 1 or more seizures after stroke, stroke disability, and death after stroke. RESULTS: Seizures occurred in 168 (8.9%) of 1897 patients with stroke (28 [10.6%] of 265 with hemorrhagic and 140 [8.6%] of 1632 with ischemic stroke). On Kaplan-Meier survival analysis, patients with hemorrhagic stroke were at significantly greater risk of seizures (P =.002), with an almost 2-fold increase in risk of seizure after stroke (hazard ratio [HR], 1.85; 95% confidence interval [CI], 1.26-2.73; P =.002). On multivariate analysis, risk factors for seizures after ischemic stroke were cortical location of infarction (HR, 2.09; 95% CI, 1. 19-3.68; P<.01) and stroke disability (HR, 2.10; 95% CI, 1.16-3.82; P<.02). The only risk factor for seizures after hemorrhagic stroke was cortical location (HR, 3.16; 95% CI, 1.35-7.40; P<.008). Recurrent seizures (epilepsy) occurred in 47 (2.5%) of 1897 patients. Late onset of the first seizure was an independent risk factor for epilepsy after ischemic stroke (HR, 12.37; 95% CI, 4.74-32.32; P<. 001) but not after hemorrhagic stroke. CONCLUSIONS: Seizures occur more commonly with hemorrhagic stroke than with ischemic stroke. Only a small minority later develop epilepsy. Patients with a disabling cortical infarct or a cortical hemorrhage are more likely to have seizures after stroke; those with late-onset seizures are at greater risk of epilepsy.

Diagnostic strategies in young patients with ischemic stroke in Canada.

BACKGROUND: A preliminary national survey of ischemic stroke in the young (15-45 years) undertaken by the Canadian Stroke Consortium indicated that in 44% of 356 patients, no cause was found. OBJECTIVE: To determine the reason for this high incidence of diagnostic uncertainty in young patients with ischemic stroke. METHODS: Neurologists in the ten Canadian stroke centers completed a detailed questionnaire for patients aged 15-45 years admitted to hospital between January 1993 and December 1997. Using a stepwise diagnostic algorithm incorporating clinical, neuroimaging, neurovascular and laboratory data, we divided patients into three groups: (1) those with established cause for the ischemic stroke, (2) those who remained unexplained despite adequate investigation, (3) those who remained unexplained but were, in our opinion, under-investigated. RESULTS: In 197 patients (56%), an identified cause was established including cardioembolic sources (14%), extracranial arterial dissection (13%), lacunar infarcts (8%) atherosclerosis (6%). A miscellaneous group of 15%, included cerebral venous thrombosis, coagulopathies, vasculitis and others. In 159 patients (44%) with no apparent cause for their stroke, we considered only 81 (23%) adequately investigated, and 78 (21%) inadequately investigated. CONCLUSION: About one in five young patients was inadequately investigated by a stroke-oriented group of neurologists. The major problem appears to be restriction of investigations to neuroimaging alone (usually computerized cerebral tomography), without further tests such as cerebral angiography and cardiac imaging.

Cerebral microembolism in acute myocardial infarction.

BACKGROUND AND PURPOSE: This study was undertaken to determine the frequency of cerebral microemboli (high-intensity transient signals; HITS) detected by transcranial Doppler (TCD) in patients with acute myocardial infarction (AMI) and to relate them to the various putative risk factors and clinical embolic events. METHODS: We investigated 112 consecutive patients within 72 hours of admission to an acute coronary care unit using TCD to monitor for cerebral microemboli. Twelve patients were excluded because of failure of ultrasound insonation. All patients had 2-dimensional echocardiograms within the study period. RESULTS: HITS were detected in 17% of patients, with significantly higher frequency in patients with reduced (<65%) left ventricular (LV) ejection fraction (P=0. 019), akinetic LV segments (P=0.002), and LV thrombus (P=0.015). A marginally significant (P=0.059) increase of HITS was found in patients with anterior AMI. Stroke was significantly more frequent in patients with cerebral microemboli (P=0.01). CONCLUSIONS: HITS were detected in 17% of patients in spite of adequate antithrombotic therapy and were increased in patients with reduced LV function, akinetic myocardial segments, and LV thrombus. They were present in all 3 patients with stroke and may represent a predictor of clinical embolic events.