Marker proteins of platelet activation in patients with cerebrovascular disease

Intense exercise at high altitude causes platelet loss across the brain in humans

Platelets are known primarily for their role in blood clotting; however, it is becoming clear that they play diverse roles beyond that of haemostasis. Exercise has been shown to activate platelets and stimulate neurogenesis, neuroplasticity and improve cognitive function, highlighting a potentially powerful link between platelet function and brain health. Despite this clear link between platelets and the brain, very little is known about the behaviour of platelets through the cerebral circulation in humans. We examined platelet concentration across the brain in exercising humans at sea level (340 m) and high altitude (6-8 days at 3800 m; a stimulus known to modify platelet function). During intense exercise at sea level, platelet concentration increased similarly by 27 ± 17% in the arterial and internal jugular venous circulations (exercise: P < 0.001, interaction: P = 0.262), indicating no uptake or release of platelets into/from the brain. At high altitude, resting platelet concentrations were similar to sea level values in both the arterial and jugular venous circulations (P = 0.590); however, intense exercise at high altitude caused a 31 ± 35% decrease in platelet concentration across the brain (P = 0.016). This divergent response across the brain was not observed in any other haematological or metabolic variables. These data highlight a unique situation where the combination of intense exercise and high altitude hypoxia cause a decrease in platelet concentration across the cerebral circulation. The physiological implications and mechanisms that might influence platelet function across the brain during exercise at high altitude remain to be established. KEY POINTS: Platelets are known primarily for their role in blood clotting; however, it is becoming clear that they play diverse roles beyond that of haemostasis. Exercise has been shown to activate platelets, which in turn stimulate neurogenesis, neuroplasticity and improve cognitive function, highlighting a powerful link between platelet function and brain health. At sea level, platelet concentration in blood going into and out of the brain was similar at rest, during maximal exercise and in recovery from exercise. During maximal exercise at high altitude, platelet concentration was 31% lower in the blood exiting the brain; the final destination of these platelets is unknown. The physiological implications and mechanisms that might influence platelet function across the cerebral circulation during exercise at high altitude remain to be established.

The Impact of Treatment with IL-17/IL-23 Inhibitors on Subclinical Atherosclerosis in Patients with Plaque Psoriasis and/or Psoriatic Arthritis: A Systematic Review

Accumulating evidence considers psoriasis a systemic inflammatory disorder that is associated with comorbidities such as psoriatic arthritis, cardiovascular disease, and metabolic syndrome. Although the precise pathogenetic links between psoriasis and atherosclerosis warrants further investigation, it is believed that chronic systemic inflammation along with the T helper (Th)-1 and Th17 polarization are associated with endothelial dysfunction and subsequent acceleration of atherosclerosis. Considering the above, several studies have evaluated if optimal control of the inflammation in psoriasis by inhibiting interleukins targeting the Interleukin (IL)-23/Th17 axis could subsequently reduce the atherosclerotic process during anti-psoriatic treatment by using a variety of surrogate markers of subclinical atherosclerosis. This systematic review summarizes current knowledge on the pathogenetic mechanisms and diagnostic evaluation of atherosclerosis in the context of psoriasis and provides a systematic review of the literature on the impact of treatment with biologics targeting the IL-23/Th17 axis on subclinical atherosclerosis in patients with plaque psoriasis and/or psoriatic arthritis.

Short-term associations of ambient air pollution with hospital admissions for ischemic stroke in 97 Japanese cities

The short-term association between ambient air pollution and hospital admissions for ischemic stroke is not fully understood. We examined the association between four regularly measured major ambient air pollutants, i.e., sulfur dioxide (SO₂), nitrogen dioxide (NO₂), photochemical oxidants (O_x), and particulate matter with aerodynamic diameters ≤ 2.5 μm (PM_2.5), and hospital admissions for ischemic stroke by analyzing 3 years of nationwide claims data from 97 cities in Japan. We first estimated city-specific results by using generalized additive models with a quasi-Poisson regression, and we obtained the national average by combining city-specific results with the use of random-effect models. We identified a total of 335,248 hospital admissions for ischemic stroke during the 3-year period. Our analysis results demonstrated that interquartile range increases in the following four ambient air pollutants were significantly associated with hospital admissions for ischemic stroke on the same day: SO₂ (1.05 ppb), 1.05% (95% CI: 0.59-1.50%); NO₂ (6.40 ppb), 1.10% (95% CI: 0.61-1.59%); O_x (18.32 ppb), 1.43% (95% CI: 0.81-2.06%); and PM_2.5 (7.86 μg/m³), 0.90% (95% CI: 0.35-1.45%). When the data were stratified by the hospital admittees' medication use, we observed stronger associations with SO₂, NO₂, and PM_2.5 among the patients who were taking antihypertensive drugs and weaker associations with SO₂, NO₂, and O_x among those taking antiplatelet drugs. Short-term exposure to ambient air pollution was associated with increased hospital admissions for ischemic stroke, and medication use and season may modify the association.

High on-clopidogrel platelet reactivity in ischaemic stroke or transient ischaemic attack: Systematic review and meta-analysis

OBJECTIVES

To assess the prevalence of high on-clopidogrel platelet reactivity (HCPR) in patients with ischaemic stroke or transient ischaemic attack (IS/TIA), their outcome and genetic basis of on-treatment response variability in IS/TIA patients.

METHODS

We conducted a comprehensive search of PubMed and EMBASE from their inceptions to March 9, 2019. Studies that reported absolute numbers/percentages of HCRP at any time point after IS/TIA onset evaluated with any type of platelet function tests, clinical outcomes and genotyping data were included.

RESULTS

Among 21 studies of 4312 IS/TIA patients treated with clopidogrel, the pooled prevalence of HCPR was 28% (95%CI: 24-32%; high heterogeneity: I² = 88.2%, p < 0.001). Heterogeneity degree diminished across groups defined by the HCPR testing method. Clopidogrel non-responder IS/TIA patients had poorer outcome compared to responders (RR = 2.09, 95%CI: 1.61-2.70; p = 0.036; low heterogeneity across studies: I² = 27.4%, p = 0.210). IS/TIA carriers of CYP2C19*2 or CYP2C19*3 loss of function alleles had a higher risk of HCPR compared to wild type (RR = 1.69, 95%CI: 1.47-1.95; p < 0.001; I² = 0.01%, p = 0.475).

CONCLUSIONS

This systematic review shows a high prevalence of clopidogrel resistance in IS/TIA and poor outcome in these patients. CYP2C19 polymorphisms may potentially influence clopidogrel resistance.

Assessment of platelet function in patients with stroke using multiple electrode platelet aggregometry: a prospective observational study

Background

There is a link between high on-treatment platelet reactivity (HPR) and adverse vascular events in stroke. This study aimed to compare multiple electrode platelet aggregometry (MEA), in healthy subjects and ischaemic stroke patients, and between patients naive to antiplatelet drugs (AP) and those on regular low dose AP. We also aimed to determine prevalence of HPR at baseline and at 3–5 days after loading doses of aspirin.

Methods

Patients with first ever ischaemic stroke were age and sex-matched to a healthy control group. Three venous blood samples were collected: on admission before any treatment given (baseline); at 24 h and 3–5 days after standard treatment. MEA was determined using a Mutliplate® analyser and agonists tested were arachidonic acid (ASPI), adenosine diphosphate (ADP) and collagen (COL).

Results

Seventy patients (mean age 73 years [SD 13]; 42 men, 28 women) were age and sex-matched to 72 healthy subjects. Thirty-three patients were on antiplatelet drugs (AP) prior to stroke onset and 37 were AP-naive. MEA results for all agonists were significantly increased in AP-naive patients compared to healthy subjects: ADP 98 ± 31 vs 81 ± 24, p < 0.005; ASPI 117 ± 31 vs 98 ± 27, p < 0.005; COL 100 ± 25 vs 82 ± 20, p < 0.005. For patients on long term AP, 33% (10/30) of patients were considered aspirin-resistant. At 3–5 days following loading doses of aspirin, only 11.1% were aspirin resistant based on an ASPI cut-off value of 40 AU*min.

Conclusions

Many patients receiving low dose aspirin met the criteria of aspirin resistance but this was much lower at 3–5 days following loading doses of aspirin. Future studies are needed to establish the causes of HPR and potential benefits of individualizing AP treatment based on platelet function testing.

Platelet activation: a link between psoriasis per se and subclinical atherosclerosis--a case-control study

BACKGROUND

Pathomechanisms of both psoriasis and atherosclerosis may involve platelet activation. Activated platelets show increased P-selectin; CD62 expression, and mean platelet volume (MPV). Impaired brachial artery flow-mediated dilatation (FMD) is related to atherosclerosis.

OBJECTIVES

To determine the presence of subclinical atherosclerosis in patients with psoriasis (without overt cardiovascular complications or traditional cardiovascular disease risk factors), compared with controls.

METHODS

In this case-control study, 25 patients with psoriasis and 25 age- and gender-matched healthy individuals were subjected to assessment of MPV, CD62 expression using flow cytometry, and brachial artery FMD and transthoracic echocardiography by cardiac ultrasound scanner.

RESULTS

A statistically highly significant increased CD62 expression, but not MPV, was found in cases compared with controls, and in patients with moderate/severe psoriasis compared with either mild cases or controls (P < 0.001). CD62 expression was statistically significantly positively correlated with the Psoriasis Area and Severity Index (PASI) score (P < 0.001), baseline brachial artery diameter (P = 0.03) but not FMD and aortic root diameter (ARD; P = 0.03). ARD was statistically significantly higher in patients with moderate/severe psoriasis compared with controls (P = 0.017). Stepwise simple linear regression analysis revealed that PASI score was the most important factor affecting CD62 expression (P < 0.001).

CONCLUSIONS

Our study showed increased atherosclerosis risk in patients with psoriasis, particularly those with moderate/severe disease, as evidenced by increased expression of platelet CD62 compared with healthy controls. Moreover, we found a positive correlation between CD62 expression and ARD (another possible marker of atherosclerosis), with positive correlation to the PASI score; the most important factor influencing CD62 expression. However, our data on MPV and FMD do not support the use of either value for diagnosing subclinical atherosclerosis in patients with psoriasis in further studies.

Simultaneous assay of activated platelet count and platelet-activating capacity by P-selectin detection using K2-EDTA-treated whole blood for antiplatelet agents

INTRODUCTION

It is well recognized that examinations of activated platelets (aPLTs) and platelet-activating capacity are very important to observe and prevent embolic diseases (events) such as ischemic stroke and myocardial infarction. Previously, we reported an appropriate measurement technique of aPLT for clinical assay. In this paper, we investigated stable conditions for measurement of activating capacity of platelets.

METHODS

Blood samples were taken from healthy volunteers using anticoagulants of 2K-EDTA, sodium citrate and heparin, and platelets were stimulated with adenosine diphosphate (ADP) or collagen. We demonstrated platelet-activating capacity by detection of scattering light, absorbance, microscopic observation, and P-selectin (CD62P) expression. We also performed basic experiments in seven healthy volunteers to test the clinical application of these assays with monitoring aspirin therapy.

RESULTS

We judged that samples of whole blood with 2K-EDTA were suitable for CD62P expression assay as functional assessments of platelet activity, because platelets treated with anticoagulants such as sodium citrate and heparin were extremely damaged after stimulation, and it was difficult to measure the CD62P expression by flow cytometry. For optimal results, samples should be tested within 1 h after the drawing of blood and stimulated with ADP or collagen for 10 min. The CD62P-positive platelet value of blood from volunteers who had taken aspirin was decreased, and platelet activation was inhibited as well.

CONCLUSION

The simultaneous assay of aPLT and platelet-activating capacity by CD62P detection using whole blood treated with the K2-EDTA anticoagulant was useful for the monitoring of antiplatelet drugs.

Mean platelet volume predicting carotid atherosclerosis in atherothrombotic ischemic stroke

BACKGROUND

Platelets are involved in atherosclerosis. Mean platelet volume (MPV) could be a marker of platelet activation. We aim to determine whether MPV levels were correlated with the presence of atherosclerotic disease in carotid arteries of patients with stroke.

METHODS

We recruited 215 patients with atherothrombotic stroke. All the participants underwent ultrasonographic evaluation of their extracranial carotid arteries. MPV was measured in automated hematology analysis system. The subjects were divided according to plaques and severity of carotid stenosis. Univariate and multivariate statistical analyses and a ROC curve to predict carotid stenosis were performed.

RESULTS

Univariate analysis showed a positive relationship between MPV and the degree of carotid atherosclerosis (p < 0.00007), and with carotid intima to media thickness (p < 0.00002). In ROC curve, a MPV cut-off of 11.25 fl was obtained for a sensibility of 70% and a specificity of 71% (p < 0.02). Multivariate analysis showed significant correlation with severity of carotid stenosis, when MPV was higher than 11.25 fl (OR: 2.9, p < 0.00007).

CONCLUSIONS

Our results indicate that an elevated MPV could be an easily measurable marker of severity of carotid stenosis in patients with atherothrombotic stroke.

Time Course of Platelet Activation and von Willebrand Factor in Patients With Non-Valvular Atrial Fibrillation After Ischemic Stroke Evaluation of Prognostic Determinants

BACKGROUND

The present study investigated serial changes in platelet activation (expressed by CD62p) and von Willebrand factor (VWF), and the correlation between increased CD62p expression, VWF and brain infarct volume (BIV: measured by magnetic resonance imaging), and prognostic determinants in non-valvular atrial fibrillation (NVAF) patients after acute ischemic stroke (IS).

METHODS AND RESULTS

CD62p expression and plasma VWF concentrations were serially measured (<48 h, on days 7, 21 and 90) using flow cytometry and enzyme-linked immunosorbent assay, respectively after acute IS in 61 NVAF patients. CD62p expression and VWF concentrations were also examined in 50 NVAF-risk control and 30 healthy individuals. The VWF concentration had no significant changes at 4 intervals among the patients and did not differ among 3 groups at acute stroke phase. CD62p expression was significantly higher in the acute phase after IS than in both control groups (both p<0.0001). However, CD62p expression declined to a significantly lower level on day 7 and to a substantially lower level thereafter (p<0.0001). CD62p expression did not differ on day 90 in the 3 groups (both p>0.5). Linear regression analysis showed that BIV and modified Rankin scale score (>3) were independently associated with increased CD62p expression (<48 h) (both p<0.01). Furthermore, the Cox proportional hazards model showed that BIV was the only independent predictor of intermediate-term (8.8+/-4.4 months) combined recurrent stroke and death.

CONCLUSIONS

The CD62p expression, which reflected increased BIV, was significantly increased in NVAF patients in acute-phase IS and substantially declined thereafter. The BIV was predictive of unfavorable intermediate-term clinical outcomes.

Link between platelet activity and outcomes after an ischemic stroke

BACKGROUND

Platelets play an important role in atherosclerosis and thromboembolic events. We examined the relationship between platelet activity and outcomes after an ischemic stroke.

METHODS

Using flow cytometry, we serially measured the fractions of circulating platelet activity (CD62p expression) after an ischemic stroke in early (<48 h), recent (day 7), convalescent (day 21) and chronic (day 90) phases in 92 consecutive patients with an ischemic stroke. Patients were classified into high (CD62p expression >3.16%) and low (CD62p expression < or =3.16%) platelet activity groups according to the median value of CD62p expression in the early phase of a stroke.

RESULTS

The composite end point--death, recurrent stroke and severe neurological impairment (alive in care), defined as a score of >13 on the National Institutes of Health Stroke Scale--within the first 30 days and at an interval of 8.2 +/- 1.5 months of follow-up was determined for each group. In the first 30 days, the composite end point occurred in 37.0% of patients in the high platelet activity group as compared with 6.5% in the low platelet activity group (p = 0.0004). At a mean follow-up of 8.2 +/- 1.5 months, the composite end point occurred in 36.6% of patients in the high platelet activity group as compared with 10.9% in the low platelet activity group (p = 0.0044). Multiple stepwise logistic regression analysis displayed that high platelet activity (p = 0.011), age (p = 0.013) and the presence of coronary artery disease (p = 0.021) were independently associated with adverse outcomes at the intermediate-term follow-up.

CONCLUSIONS

Results of this study showed that high platelet activity is strongly associated with adverse clinical outcomes after an early ischemic stroke.

Characterization of a novel thrombotic middle cerebral artery occlusion model in monkeys that exhibits progressive hypoperfusion and robust cortical infarction

In an attempt to establish a thrombotic middle cerebral artery (MCA) occlusion model using cynomolgus monkeys, we measured the blood flow in the main MCA tract and cerebral cortex, brain damage, and neurological deficits, and compared them with those of mechanical MCA occlusion model. Thrombotic occlusion was induced photochemically by green light application on the MCA following rose bengal treatment; mechanical occlusion was induced by MCA clipping for 3h. Patency of the main MCA tract showed two patterns in the thrombotic model: permanent occlusion or cyclical flow reduction (CFR). Regional cerebral blood flow (rCBF) decreased during occlusion followed by post-ischemic hyperperfusion in the clipping model, whereas rCBF reduction expanded time-dependently in the thrombotic occlusion model. Brain infarction and neurological scores in the thrombotic occlusion model were significantly larger than those in the clipping occlusion model. In histological assessment, microthrombi containing myeloperoxidase- and fibrinogen-positive cells were observed in the cortex following the thrombotic but not clipping occlusion. These results collectively suggest that this thrombotic MCA occlusion model, because it shows impairment of cerebral microcirculation, could provide a vital platform for understanding progressive ischemia as well as for evaluating potential therapeutic drugs.

Analysis of combined treatment of embolic stroke in rat with r-tPA and a GPIIb/IIIa inhibitor

Suppression of platelet activation improves the efficacy of thrombolytic therapy for stroke. Thus, combination treatment with recombinant tissue plasminogen activator (r-tPA) and 7E3 F(ab')2, a GPIIb/IIIa inhibitor that binds the platelet to fibrin, may improve the efficacy of thrombolytic therapy in embolic stroke. Magnetic resonance imaging (MRI) was used to monitor treatment response in rats subjected to embolic middle cerebral artery (MCA) occlusion (MCAo). Animals were randomized into treated (n=12) and control (n=10) groups and received intravenous combination therapy or saline, respectively, 4 hours after MCAo. Magnetic resonance imaging (MRI) measurements performed 1 hour after MCAo showed no difference between groups. However, an increased incidence (50%) of MCA recanalization was found in the treated group at 24 hours compared with 20% in the control group. The area of low cerebral blood flow at 24 and 48 hours was significantly smaller in the combination treatment group, and the lesion size, as indicated from the T2 and T1 maps, differed significantly between groups. Fluorescence microscopy measurements of cerebral microvessels perfused with fluorescein isothiocyanate-dextran and measurements of infarct volume revealed that the combination treatment significantly increased microvascular patency and reduced infarct volume, respectively, compared with the control rats. The efficacy of combination treatment 4 hours after ischemia is reflected by MRI indices of tissue perfusion, MCA recanalization, and reduction of lesion volume. The treatment also reduced secondary microvascular perfusion deficits.

Course of platelet activation markers after ischemic stroke

BACKGROUND AND PURPOSE

The aim of this study was to evaluate the time course of platelet activation after ischemic stroke and to investigate whether platelet activation and inflammation are correlated with each other.

METHODS

We serially determined expression of p-selectin (CD62p) and lysosome-associated membrane protein (CD63) by platelets using flow cytometry at 10 time points between days 1 and 90 in patients after ischemic stroke (n=50), in healthy subjects (n=30), and in risk factor control subjects (n=20). Furthermore, we correlated leukocyte count, C-reactive protein, and fibrinogen levels with platelet activation markers.

RESULTS

CD62p and CD63 expression was higher on day 1 after stroke than in both control groups (P<0.005 for both). CD62p expression rapidly declined, whereas CD63 expression remained significantly elevated until day 90. Stroke severity and different medication for secondary stroke prevention did not influence CD62p or CD63 expression. Platelet activation markers and inflammatory parameters were not correlated with each other at any time point after stroke.

CONCLUSIONS

The initial increase in both CD62p and CD63 expression by platelets is followed by a differential regulation of both parameters after stroke. The rapid decrease in CD62p expression may be caused by shedding from the cell surface. Its persistent elevation makes CD63 a good candidate for studies on predictors for stroke recurrence. Our findings suggest that the expression of CD62p and CD63 by platelets is regulated independently from inflammatory indexes.

Dynamic platelet accumulation at the site of the occluded middle cerebral artery and in downstream microvessels is associated with loss of microvascular integrity after embolic middle cerebral artery occlusion

Information is lacking regarding dynamic platelet accumulation at the site of the occluded middle cerebral artery (MCA) and the relationship between platelet aggregation in downstream cerebral microvessels and loss of perfusion and vascular integrity of these microvessels. In the present study, we employed a model of embolic MCA occlusion in the rat to simultaneously measure temporal and spatial profiles of platelet accumulation at the site of the embolus occluding the MCA and within downstream cerebral microvessels. We also measured the integrity of microvessels and matrix metalloproteinase (MMP) activity in ischemic brain. Rats (n=36) were subjected to embolic MCA occlusion. Immunohistochemistry was used to detect microvascular integrity, plasminogen activator inhibitor 1 (PAI-1) and the deposition of fibrin. SDS-PAGE zymography was used to measure MMP2 and MMP9 activities. Accumulation of platelets and increases in PAI-1 immunoreactivity at the site of the embolus occluding the MCA were detected 1 h (n=7) and 4 h (n=7) after ischemia, respectively, and numbers of GPIIb/IIIa immunoreactive downstream cerebral microvessels increased significantly (209+/-59; n=7; P<0.05) 4 h after ischemia, suggesting dynamic platelet aggregation. A significant (n=7; P<0.01) diffuse loss of type IV collagen immunoreactivity in microvessels was temporally associated with platelet GPIIb/IIIa immunoreactivity within the vessels. Triple immunostaining revealed that microvessels containing platelet aggregates exhibited loss of type IV collagen immunoreactivity and both intra- and extra-vascular fibrin deposition, suggesting that intravascular platelet aggregation is associated with decreases in the integrity of the microvascular basal lamina and blood-brain barrier leakage. A significant increase (P<0.05) in MMP9 was detected at 4 h (n=3) and 24 h (n=3) after ischemia but levels of MMP2 were not significantly changed in ischemic brain. Our data suggest that dynamic platelet aggregation in ischemic brain may contribute to time-dependent resistance to fibrinolysis. In addition, platelet deposition and increased MMP9 coincided with degradation of type IV collagen and loss of vascular integrity. These data suggest an important role for post-occlusive distal platelet deposition in the pathophysiology of stroke.

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

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 111In-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.

Inhibition of collagen-induced platelet aggregation by argatroban in patients with acute cerebral infarction

Platelet aggregation induced by collagen is enhanced in patients with cerebral thrombosis [1], and platelet aggregates and activation products such as beta-thromboglobulin appear in the circulation, particularly during the acute phase [2]. It is known that the presence of activated platelets markedly amplifies thrombin generation by the prothrombinase complex. Platelet aggregation, for which thrombin is the most potent stimulator, is effected by the activation of the thrombin receptor. Activated platelets likely provide the principal surfaces on which intrinsic coagulation factors and prothrombinase assemble in vivo. Moreover, the blood coagulation cascade is simultaneously enhanced during the acute phase of cerebral infarction, resulting in thrombin production and fibrin formation [3]. Cerebral arterial thrombosis is thought to be initiated by rupture of atherosclerotic plaque. Platelets adhere to the constituents of the plaque, and platelet aggregation and the formation of thrombin occur rapidly. The presence of activated platelets involving thrombin generation in cerebral infarction remains to be further clarified. The present study in patients with acute cerebral infarction was undertaken to determine whether argatroban, a direct thrombin inhibitor, is effective in inhibiting collagen-induced platelet aggregation. It is well known that argatroban inhibits not only thrombin cleavage of fibrinogen with a Ki of 19 nM, but also thrombin-mediated platelet activation with a Ki of 40 nM [4]. We evaluated whether the sensitivity of platelets to collagen is increased in the presence of a trace amount of thrombin associated on platelets, at a concentration that does not induce platelet aggregation in acute cerebral infarction. The study also measured the inhibitory effect, if any, of the addition of argatroban during platelet hyperactivation induced by collagen.

Modification of platelet aggregation by leukocytes in acute ischemic stroke

BACKGROUND AND PURPOSE

Platelet aggregation plays an important role in the pathogenesis of thromboembolic cerebrovascular disease. Leukocytes can efficiently stimulate as well as inhibit platelet aggregability. We studied the influence of leukocytes on collagen-induced platelet aggregation in patients with acute ischemic stroke.

METHODS

We investigated 23 patients within 2 days after stroke and 23 healthy age- and sex-matched control subjects and determined collagen-induced platelet aggregation in platelet-rich plasma with or without addition of polymorphonuclear or mononuclear leukocytes.

RESULTS

Platelet aggregation without leukocytes tended to be lower in patients than in control subjects (P = .06). Mononuclear leukocytes reduced (P = .018) and polymorphonuclear leukocytes tended to reduce (P = .06) platelet aggregation in patients. Leukocytes did not significantly alter platelet aggregation in control subjects. In the presence of either mononuclear or polymorphonuclear leukocytes, platelet aggregation was significantly lower in patients than in control subjects (P = .004 and P = .008). The ratio of polymorphonuclear leukocytes to platelets in venous blood was higher in patients than in control subjects (P < .001).

CONCLUSIONS

Mononuclear--and less clearly polymorphonuclear-leukocytes possess a platelet aggregation-inhibiting potential in the early stages after ischemic stroke, a feature with possible antithrombotic effects.

Hematologic abnormalities occur in both cortical and lacunar infarction

BACKGROUND AND PURPOSE

Primary hematologic abnormalities are a rare but established cause of ischemic stroke. In addition, activation of hemostatic parameters is often present during the acute phase of stroke. However, it is uncertain whether these abnormalities occur in both cortical and lacunar infarction; this study aimed to further assess this issue.

METHODS

Hematologic parameters (prothrombin, activated partial thromboplastin, thrombin clotting, and euglobulin lysis times; and fibrinogen, fibrinopeptide A, antithrombin III, protein C, protein S, and plasminogen levels) were measured in 19 patients within 48 hours of the onset of acute cerebral infarction. These patients included 10 with cortical infarcts and 9 with lacunar infarcts, as determined by standard clinical and radiological criteria.

RESULTS

Five patients with lacunar infarction and 7 patients with cortical infarction demonstrated raised fibrinopeptide A levels, indicating enhanced thrombin activity. Fibrinolysis, assessed by the euglobulin lysis time, was impaired in 6 of 9 patients with lacunar infarction and in 2 of 10 patients with cortical infarction. Lupus anticoagulants were detected in 3 patients with lacunar infarction and in 1 patient with cortical infarction. Three patients in each group displayed decreased antithrombin III function, and 1 patient with a lacunar infarction had a low protein C level.

CONCLUSIONS

Primary hematologic disorders and secondary hemostatic derangements may occur in patients with either cortical or lacunar infarction.

Increased thromboxane biosynthesis in patients with acute cerebral ischemia

BACKGROUND AND PURPOSE

Clinical and experimental studies suggest that platelets have a major role in the pathogenesis of cerebral ischemia. However, ex vivo both platelet aggregation studies and measurements of platelet-derived products in patients with cerebral ischemia have shown inconsistent results. The present study was designed to resolve this inconsistency.

METHODS

We have measured the urinary excretion of a thromboxane metabolite, 11-dehydro-thromboxane B2, by a previously validated radioimmunoassay technique in 51 patients with acute cerebral ischemia who had experienced either a transient ischemic attack (14 patients) or an ischemic stroke (37 patients) and in 20 control patients with nonvascular neurological disorders. The median time between the onset of symptoms and urine sampling was 24 hours (range, from 2 hours to 8 days).

RESULTS

The excretion rate of immunoreactive 11-dehydro-thromboxane B2 ranged between 39 and 478 pmol/mmol creatinine in patients with a transient ischemic attack and between 23 and 5,916 pmol/mmol creatinine in stroke patients, with 29% (p = 0.18) and 51% (p = 0.004) of the urine samples, respectively, exceeding the upper limit of the control samples (251 pmol/mmol creatinine [mean +/- 2 SD]) (p = 0.01). In stroke patients, metabolite excretion was not related to the type (cortical or "lacunar") or site of cerebral infarction. Low-dose aspirin (50 mg per day for 7 days) reduced the urinary excretion by approximately 85% in 11 consecutive stroke patients.

CONCLUSIONS

We conclude that 1) episodes of enhanced thromboxane biosynthesis are detected infrequently in patients with a transient ischemic attack, 2) aspirin-suppressible episodes of increased thromboxane formation can be detected during the early phase of acute ischemic stroke, and 3) this finding may provide a rationale for testing the efficacy and safety of this drug in this setting.

The topography of microthrombi in ischemic brain infarct

Following cerebral ischemia a tendency to increased coagulation can be detected. Vascular occlusion may develop either as a result of local thrombus formation or from emboli caused by circulating platelet aggregates. We studied the localization of microthrombi and their effects on tissue in double-hemisphere sections. Fresh brain infarcts showed a large number of microthrombi limited to the ischemic region. In more advanced infarcts they were found mainly at the border of the necrosis and diffusely distributed over both hemispheres. Older, subsiding infarcts showed only isolated microthrombi limited to the area of the necrosis. This indicates that great importance must be attached to microthrombi in infarct progression.

Headache in transient or permanent cerebral ischemia. Dutch TIA Study Group

We studied headache features in 3,126 patients with acute cerebral or retinal ischemia. Headache occurred in 18% of these patients (in 16% of all patients with transient ischemic attacks, in 18% of patients with reversible ischemic neurologic deficits, and in 19% of patients with minor strokes) and was mostly continuous in all types of attacks. Headache was present in 16% of patients with monocular visual symptoms. The occurrence of headache was not related to the mode of onset, mode of disappearance, or duration of the attack. Patients with headache more often were known to have heart disease. Headache was less frequent in patients with small deep infarcts, who were more often hypertensive, and in patients with infarcts in the anterior circulation; headache was more frequent in patients with cortical infarcts and in patients with infarcts in the posterior circulation. Patients with a relevant small deep infarct on computed tomographic scan and accompanying headache relatively often reported symptoms compatible with cortical ischemia, such as language disorders or a visual field defect. We conclude that headache is a frequent accompanying symptom in patients with acute cerebral and retinal ischemia and that the occurrence of headache is partly related to the underlying cause of the ischemic lesion.

Plasma 11-dehydrothromboxane B2: a reliable indicator of platelet hyperfunction in patients with ischemic stroke

The plasma level of 11-dehydrothromboxane B2 (11-dehydroTXB2) is free from artifactual increase during blood sampling, and it can be reliable indicator of TXA2 production in vivo. We have estimated plasma 11-dehydroTXB2 in patients with ischemic stroke. Subjects studied were 29 patients with cerebral thrombosis (62 +/- 9 years old) and 41 healthy controls (61 +/- 7 years old). Plasma 11-dehydroTXB2 and TXB2 were determined by radioimmunoassay. Plasma 11-dehydroTXB2 levels in patients and controls were 5.4 +/- 2.5 and 1.8 +/- 0.9 pg ml, respectively, and the difference was significant (p less than 0.001). Plasma TXB2 also was higher in patients than in controls: 401 +/- 61 vs 311 +/- 51 pg/ml (p less than 0.05). However, the 11-dehydroTXB2 was found to be a more effective parameter to distinguish between stroke patients and controls. Estimation of plasma 11-dehydroTXB2 levels is a reliable method to detect platelet hyperfunction in stroke patients.

Platelet volume, aggregation, and adenosine triphosphate release in cerebral thrombosis

We compared whole blood platelet aggregation, adenosine triphosphate release, platelet count, platelet crit (percentage volume of platelets), and mean platelet volume during the acute, subacute, and chronic periods of cerebral thrombosis in 22 patients with value in 29 controls. During the acute and subacute periods, platelet aggregation, platelet count, platelet crit, and mean platelet volume were significantly less in the patients than in the controls (p less than 0.05-0.01) while the adenosine triphosphate release rate per volume of platelets was significantly greater (p less than 0.05). During the acute period, infarct size showed a significant positive correlation with platelet aggregation (r = 0.59, p less than 0.01) and adenosine triphosphate release rate (r = 0.70, p less than 0.001) but a negative correlation with platelet count (r = -0.44, p less than 0.05). Our results suggest that platelet aggregation is reduced during the acute period due to the consumption of platelets during thrombogenesis but that the remaining individual platelets are hyperactive. Platelet consumption during the acute period increases with infarct size. During the chronic period, platelet crit and mean platelet volume were significantly less in the patients than in the controls (p less than 0.01) while the adenosine triphosphate release rate was significantly greater (p less than 0.01), suggesting sustained platelet consumption and chronically enhanced secretion of individual platelets.

Prognostic significance of fibrinopeptide A in survivors of cerebral infarction

We measured levels of fibrinopeptide A, beta-thromboglobulin, and fibrinogen in the plasma of 27 patients 2 months after their first stroke. Concentrations of fibrinopeptide A, a sensitive index of in vivo hypercoagulability, were significantly higher in the 18 ischemic stroke patients than in 40 age- and sex-matched controls and in the six patients who experienced recurrence within 5 years than in the 12 who remained asymptomatic. On the contrary, fibrinopeptide A levels had no prognostic significance among the nine patients with hemorrhagic stroke. Concentrations of beta-thromboglobulin, an index of platelet activation, were higher in the 27 stroke patients than in the 40 controls, but this index was not associated with stroke recurrence. Fibrinogen levels were not significantly higher in stroke patients than in controls. In a multivariate regression analysis of hemostatic and clinical variables, only fibrinopeptide A levels of greater than 4 ng/ml were significantly related to cerebral infarction. Our results support the role of hypercoagulability in the recurrence of ischemic stroke and may allow identification of subjects at high risk for it. If confirmed in more patients, our results could provide a rationale for clinical trials of anticoagulant therapy in such patients.

Platelet count, mean platelet volume and their relation to prognosis in cerebral infarction

The study was performed on patients with ischaemic cerebral infarction in order to obtain information on serial changes of some platelet parameters and to test their prognostic significance. Platelet count, obtained within 48 h after cerebral infarction, was significantly lower than in the control group (213,611 +/- 65,652 mm-3 vs. 299,525 +/- 60,611 mm-3, P less than 0.001), reaching the normal level on the ninth day and thereafter. The mean platelet volume was significantly greater than in the controls (11.26 +/- 1.29 fl vs. 8.93 +/- 0.93 fl, P less than 0.001), and normalization generally occurred on the forty-fifth day. The mean platelet count was significantly lower in the patients who died than in those who survived (P less than 0.025 and P less than 0.05 respectively on the first to second and fourth day after infarction). The reduction of platelet count and the increase of mean volume appear to be related to an increased platelet consumption in the infarction area, associated with an in vivo platelet activation, as larger platelets are more responsive to platelet activity and aggregability tests. The lower mean platelet count observed in the patients who died suggests that the platelet value might be considered as a prognostic index of cerebral infarction.

Evaluation of platelet changes in completed ischemic stroke

In a retrospective study we evaluated the platelet count in 45 patients mean age 73 +/- 9 years, with cerebral infarction (C.I.) documented by CT, and 45 age and sex-matched controls randomly selected. In 12 patients changes in platelet count were examined prospectively, starting from the acute event for 30 days. In the retrospective study the mean platelet count in C.I. was significantly lower than that found in controls: 260, 220 +/- 86,076/mm3 and 302, 422 +/- 65,747/mm3 (p less than 0.05) respectively. In the prospective study the mean count was 213,330 +/- 79,930/mm3. A progressive increase up to the 9-12th day was observed, achieving a mean of 305,630 +/- 83,470/mm3 (p less than 0.01), not statistically different from controls. The 40-45% decrease of platelet count shows that about half of the circulating platelets had rapidly disappeared from the systemic circulation, presumably related to an increase in vivo platelet activation and aggregation.

Protein C in acute stroke

The plasma concentrations of protein C, an anticoagulant protein, and fibrinopeptide A were measured in 37 patients with acute hemispheric stroke and in age-matched controls with nonvascular neurologic diseases. In 11 stroke patients who died within 15 days after the onset (nonsurvivors) protein C antigen concentration on admission was lower than in the control group (p less than 0.005), with a mean value of 63% of the concentrations found in the 26 survivors (p less than 0.001). The difference in protein C concentrations was not associated with different prothrombin time ratios and serum albumin concentration in survivors and nonsurvivors of stroke and was independent of the size of the cerebral lesion. Increased fibrinopeptide A concentration on admission was found in all stroke patients (p less than 0.001), but it was higher in nonsurvivors than in survivors (p less than 0.01), suggesting that lower protein C concentrations in nonsurvivors might be due to increased thrombin-dependent protein C activation. In survivors, protein C concentration was slightly but significantly higher than in controls (p less than 0.05) and was unchanged 2 months after stroke, a time when fibrinopeptide A concentrations had returned to normal. These results show that protein C is involved in the hemostatic derangement caused by stroke and provide a rationale for clinical trials evaluating the therapeutic supplementation with protein C of patients with acute ischemic stroke.

Beta-thromboglobulin in cerebral infarction

Plasma beta-thromboglobulin (BTG) was significantly elevated in the acute phase of 116 atherosclerotic thrombotic (p less than 0.0001) and 36 cardioembolic (p less than 0.005) infarcts but normal for 96 lacunes compared with controls. This elevation persisted into the 6th week after the acute event. Among atherosclerotic thrombotic infarcts, the acute beta-thromboglobulin level showed a tendency to correlate with infarct size on CT and predicted mortality at 6 weeks. These results suggest that platelet aggregation plays a primary role in the pathogenesis of atherothrombosis.

Platelet function and thrombin activity in patients with recent cerebral transient ischemic attacks

Platelet function and thrombin activity were investigated in 12 hospitalized patients (7 men and 5 women, mean age 53 years) who had had transient cerebral ischemic attacks in the previous 2-12 weeks. Each patient was given an extensive clinical and instrumental evaluation, including Doppler sonography of the cervical and lower limb vessels, cerebral angiography, and head computed tomography scan, after which relevant atherosclerotic disease was excluded. The controls consisted of 12 subjects hospitalized for nonvascular neurologic problems and matched for age, sex, and risk factors to the transient ischemic attack patients. Collagen-induced platelet thromboxane B2 production, plasma beta-thromboglobulin, and fibrinopeptide A were significantly higher in the patients than the controls. Platelet aggregability by collagen was the same in the 2 groups. Platelet hyperfunction and enhanced thrombin activity are present in patients some weeks after the acute episode, suggesting that the hemostatic system has a primary pathogenetic role.

Eicosenoid biosynthesis and platelet function with advancing age

The pathogenesis of atherosclerosis, a major cause of age-related mortality, remains poorly understood. Although platelets and their products, including thromboxane A2, may be of importance in this process, little is known about eicosenoid biosynthesis and platelet function with increasing age. In order to address the hypothesis that platelet activation increases with age, we measured various indices of platelet function in a group of apparently healthy individuals over the age of 50 years. The circulating platelet aggregate ratio, plasma beta-thromboglobulin and threshold aggregating concentration of arachidonic acid were similar to those in healthy subjects aged less than 40 years. Although the bleeding time (168 +/- 24 vs 300 +/- 24 seconds) was significantly (p less than 0.001) shorter in the older volunteers this may be unrelated to platelet function and merely reflect age related changes in skin and/or vascular function. To further assess platelet and vascular function in vivo, we measured excretion of the major thromboxane and prostacyclin metabolites in urine, 2,3-donor-thromboxane B2 (Tx-M) and 2,3-dinor-6-keto-PGF1 alpha (PGI-M). Both Tx-M (223 +/- 22 vs 152 +/- 19 pg/mg creatinine; p less than 0.005) and PGI-M (198 +/- 21 vs 121 +/- 13 pg/mg creatinine; p less than 0.005) excretion were significantly higher in the older volunteers. These subtle but significant changes in eicosenoid biosynthesis are consistent with the presence of platelet activation in vivo increasing with age in apparently healthy individuals.

Enhanced in vivo platelet activation in subtypes of ischemic stroke

It remains uncertain whether platelet activation in ischemic stroke is contributory or secondary to brain ischemia. The efficacy of aspirin (ASA) in stroke prevention suggests that platelet activation contributes to the occurrence of stroke. On the other hand, platelet activation may be simply a generalized consequence of cerebral ischemic damage. To examine this issue, plasma levels of the platelet specific proteins beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4) were measured in fifty-eight patients with various defined types of acute ischemic strokes. beta-TG was a broader indicator of platelet activation than PF4. Compared with an age-matched control group, thromboembolic and cardioembolic stroke patients had significantly elevated beta-TG levels (p less than 0.001). Also, beta-TG levels in these stroke categories were significantly higher in samples drawn within the first week after the event than in those drawn later (p less than 0.001). In contrast, beta-TG levels in lacunar stroke patients and in most TIA patients were normal. beta-TG levels did not correlate with the volume of cerebral infarction as measured by planimetry from CT scans. Moreover, beta-TG levels in patients on chronic ASA therapy at the time of stroke did not differ from those in patients of the same diagnostic categories not taking aspirin. These data indicate that platelet activation may be important in some, but not all, subtypes of ischemic stroke and that platelet activation can occur in stroke even though the platelet cyclooxygenase pathway is suppressed.

Hemostatic Balance Index in TIA patients: sex-related changes

In order to evaluate the occurrence of hemostatic disorders, 37 patients with transient ischemic attacks (TIAs) and 50 control subjects were studied by means of the Hemostatic Balance Index (H.B.I.) derived from Raby's Thrombodynamic Potential Index (T.P.I.) and Fearnley's Whole Blood Diluted Lysis Time (W.B.D.L.T.). Results showed a significant increase in T.P.I. and a tendency to a decrease in fibrinolytic activity in the TIA group: H.B.I. was shown to be significantly increased, thus indicating a pro-thrombotic imbalance in these patients. The occurrence of similar changes in TIA females when compared to male patients marks the importance of plasmatic factors in the mechanism of thrombotic disorders in females with cerebrovascular disease.

Drugs and platelet activation in migraine and transient ischemic attacks

In order to study the role of platelets in migraine and cerebrovascular disease, beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4) plasma levels, indices of in vivo platelet activation, were assayed in two groups of patients suffering from migraine (common/classic and classic/complicated migraine, respectively) and in one group suffering from transitory ischemic attacks (TIAs). Plasma determinations were carried out in the absence of treatment and during the administration of aspirin (50 mg/daily) and flunarizine (10 mg/daily). Platelet activation was found in patients suffering from TIA; patients affected by classic and complicated migraine showed a high incidence of activation, in comparison with common migraine sufferers, also in headache-free periods. Administration of aspirin (ASA) was more effective than flunarizine in inducing a decrease in beta-TG and PF4 plasma levels in migraineurs. Aspirin, however, did not affect platelet activation in subjects suffering from ischemic attack even though we did not observe any relapse after one year of treatment. The different effect of ASA in TIAs and migraine indicates that the platelet activation in TIA patients is due not only to cyclo-oxygenase pathway but also to other in vivo pathways.