Coated-platelet levels are low in patients with spontaneous intracerebral hemorrhage

Platelet Subtypes in Inflammatory Settings

In addition to their essential role in hemostasis and thrombosis, platelets also modulate inflammatory reactions and immune responses. This is achieved by specialized surface receptors as well as secretory products including inflammatory mediators and cytokines. Platelets can support and facilitate the recruitment of leukocytes into inflamed tissue. The various properties of platelet function make it less surprising that circulating platelets are different within one individual. Platelets have different physical properties leading to distinct subtypes of platelets based either on their function (procoagulant, aggregatory, secretory) or their age (reticulated/immature, non-reticulated/mature). To understand the significance of platelet phenotypic variation, qualitatively distinguishable platelet phenotypes should be studied in a variety of physiological and pathological circumstances. The advancement in proteomics instrumentation and tools (such as mass spectrometry-driven approaches) improved the ability to perform studies beyond that of foundational work. Despite the wealth of knowledge around molecular processes in platelets, knowledge gaps in understanding platelet phenotypes in health and disease exist. In this review, we report an overview of the role of platelet subpopulations in inflammation and a selection of tools for investigating the role of platelet subpopulations in inflammation.

Antiplatelet Medications and Biomarkers of Hemostasis May Explain the Association of Hematoma Appearance and Subsequent Hematoma Expansion After Intracerebral Hemorrhage

BACKGROUND

To test the hypothesis that appearances of intracranial hematomas on diagnostic computed tomography (CT) are not idiosyncratic and reflect a biologically plausible mechanism, we evaluated the association between hematoma appearance on CT, biomarkers of platelet activity, and antiplatelet or anticoagulant medication use prior to admission.

METHODS

We studied 330 consecutively identified patients from 2006 to 2019. Biomarkers of platelet activity (platelet aspirin assay) and medication history (aspirin, clopidogrel) were prospectively recorded on admission. A blinded interpreter recorded the presence of hematoma appearances from the diagnostic scan. Associations were tested with parametric or nonparametric statistics, as appropriate.

RESULTS

The black hole sign (101, 30%) was most prevalent, followed by the island sign (57, 17%) and blend sign (32, 10%). There was reduced platelet activity in patients with a black hole sign (511 [430-610] vs. 562 [472-628] aspirin reaction units, P = 0.01) or island sign (505 [434-574] vs. 559 [462-629] aspirin reaction units, P = 0.004). Clopidogrel use prior to admission was associated with the black hole sign (odds ratio 2.25, 95% confidence interval 1.02-4.98, P = 0.04).

CONCLUSIONS

In patients with acute intracerebral hemorrhage, hematoma appearances on CT are associated with biomarkers of platelet activity and clopidogrel use prior to admission. Appearances of intracranial hematomas on CT may reflect reduced hemostasis from antiplatelet medication use.

Levels of procoagulant microparticles expressing phosphatidylserine contribute to bleeding phenotype in patients with inherited thrombocytopenia

Inherited thrombocytopenia is a heterogeneous group of hereditary disorders with varying bleeding tendencies, not simply related to platelet count. Platelets transform into different subpopulations upon stimulation, including procoagulant platelets and platelet microparticles (PMPs), which are considered critical for haemostasis. We aimed to investigate whether abnormalities in PMP and procoagulant platelet function were associated with the bleeding phenotype of inherited thrombocytopenia patients. We enrolled 53 inherited thrombocytopenia patients. High-throughput sequencing of 36 inherited thrombocytopenia related genes was performed in all patients and enabled a molecular diagnosis in 57%. Bleeding phenotype was evaluated using the ISTH bleeding assessment tool, dividing patients into bleeding (n = 27) vs. nonbleeding (n = 26). Unstimulated and ADP, TRAP or collagen-stimulated PMP and procoagulant platelet functions were analysed by flow cytometry using antibodies against granulophysin (CD63), P-selectin (CD62P), activated GPIIb/IIIa (PAC-1) and a marker for phosphatidylserine expression (lactadherin). Procoagulant platelets were measured in response to collagen stimulation. An in-house healthy reference level was available. Overall, higher levels of activated platelets, PMPs and procoagulant platelets were found in nonbleeding patients compared with the reference level. Nonbleeding patients had higher proportions of phosphatidylserine and PMPs compared with bleeding patients and the reference level, in response to different stimulations. Interestingly, this finding of high proportions of phosphatidylserine and PMPs was limited to PMPs, and not present in procoagulant platelets or platelets. Our findings indicate that nonbleeding inherited thrombocytopenia patients have compensatory mechanisms for improved platelet subpopulation activation and function, and that generation of phosphatidylserine expressing PMPs could be a factor determining bleeding phenotype in inherited thrombocytopenia.

Diagnostic utility of flow cytometry based coated-platelets assay as a biomarker to predict thrombotic or hemorrhagic phenotype in acute stroke

BACKGROUND

Coated-platelets are sub-population of platelets "coated" with highly procoagulant proteins and phosphatidylserine that sustains thrombin generation. They are produced upon dual agonist stimulation by collagen and thrombin. This study was conducted to assess if there was any difference in the levels of coated-platelets in patients with primary intracranial hemorrhage (PICH) and ischemic stroke due to large artery atherosclerosis (LAA) as compared to healthy controls, and to see if coated-platelet levels had any influence on the hemorrhagic transformation (HT) of ischemic stroke.

METHODS

Coated-platelet levels were determined by flow cytometry using fluorescently tagged Annexin V antibody to identify phosphatidylserine exposed on the surface of platelets activated by dual agonists (convulxin and thrombin) in cross-sectional cohort of 75 patients with stroke and 34 controls.

RESULTS

Patients with PICH (n = 35) had significantly lower coated-platelets than the controls (adjusted mean ± SE, 21.0 ± 1.9% vs. 36.1 ± 1.7%, p < 0.001), while patients with LAA (n = 30) had significantly higher coated-platelets than controls (adjusted mean ± SE, 51.9 ± 1.5% vs. 36.1 ± 1.7%, p < 0.001). Patients with subsequent HT of ischemic stroke (n = 10) had significantly lower coated-platelet levels at admission compared to those without HT (adjusted mean ± SE, 18.1 ± 2.6% vs. 51.9 ± 1.5%, p < 0.001).

CONCLUSIONS

Coated-platelet levels are significantly different in patients with hemorrhagic and ischemic stroke as compared with controls. Lower levels of coated-platelets measured by flow cytometry may be earliest predictor of subsequent HT in patients with ischemic stroke even before the radiological changes suggestive of HT are visualized.

Procoagulant Platelets: Mechanisms of Generation and Action

During the past decades, it has been increasingly recognized that the major function of accelerating membrane-dependent reactions of blood coagulation is predominantly implemented by a subset of activated platelets. These procoagulant platelets (also called collagen- and thrombin-activated or COAT, coated, necrotic, although there could be subtle differences between these definitions) are uniquely characterized by both procoagulant activity and, at the same time, inactivated integrins and profibrinolytic properties. The mechanisms of their generation both in vitro and in situ have been increasingly becoming clear, suggesting unique and multidirectional roles in hemostasis and thrombosis. In this mini-review, we shall highlight the existing concepts and challenges in this field.

High-Dose Epinephrine Enhances Platelet Aggregation at the Expense of Procoagulant Activity

Platelet activation is characterized by shape change, granule secretion, activation of fibrinogen receptor (glycoprotein IIb/IIIa) sustaining platelet aggregation, and externalization of negatively charged aminophospholipids contributing to platelet procoagulant activity. Epinephrine (EPI) alone is a weak platelet activator. However, it is able to potentiate platelet activation initiated by other agonists. In this work, we investigated the role of EPI in the generation of procoagulant platelets. Human platelets were activated with convulxin (CVX), thrombin (THR) or protease-activated receptor (PAR) agonists, EPI, and combination thereof. Platelet aggregation was assessed by light transmission aggregometry or with PAC-1 binding by flow cytometry. Procoagulant collagen-and-THR (COAT) platelets, induced by combined activation with CVX-and-THR, were visualized by flow cytometry as Annexin-V-positive and PAC-1-negative platelets. Cytosolic calcium fluxes were monitored by flow cytometry using Fluo-3 indicator. EPI increased platelet aggregation induced by all agonist combinations tested. On the other hand, EPI dose-dependently reduced the formation of procoagulant COAT platelets generated by combined CVX-and-THR activation. We observed a decreased Annexin-V-positivity and increased binding of PAC-1 with the triple activation (CVX + THR + EPI) compared with CVX + THR. Calcium mobilization with triple activation was decreased with the higher EPI dose (1,000 µM) compared with CVX + THR calcium kinetics. In conclusion, when platelets are activated with CVX-and-THR, the addition of increasing concentrations of EPI (triple stimulation) modulates platelet response reducing cytosolic calcium mobilization, decreasing procoagulant activity, and enhancing platelet aggregation.

Thrombocytopathies: Not Just Aggregation Defects-The Clinical Relevance of Procoagulant Platelets

Platelets are active key players in haemostasis. Qualitative platelet dysfunctions result in thrombocytopathies variously characterized by defects of their adhesive and procoagulant activation endpoints. In this review, we summarize the traditional platelet defects in adhesion, secretion, and aggregation. In addition, we review the current knowledge about procoagulant platelets, focusing on their role in bleeding or thrombotic pathologies and their pharmaceutical modulation. Procoagulant activity is an important feature of platelet activation, which should be specifically evaluated during the investigation of a suspected thrombocytopathy.

Characterization of Procoagulant COAT Platelets in Patients with Glanzmann Thrombasthenia

Patients affected by the rare Glanzmann thrombasthenia (GT) suffer from defective or low levels of the platelet-associated glycoprotein (GP) IIb/IIIa, which acts as a fibrinogen receptor, and have therefore an impaired ability to aggregate platelets. Because the procoagulant activity is a dichotomous facet of platelet activation, diverging from the aggregation endpoint, we were interested in characterizing the ability to generate procoagulant platelets in GT patients. Therefore, we investigated, by flow cytometry analysis, platelet functions in three GT patients as well as their ability to generate procoagulant collagen-and-thrombin (COAT) platelets upon combined activation with convulxin-plus-thrombin. In addition, we further characterized intracellular ion fluxes during the procoagulant response, using specific probes to monitor by flow cytometry kinetics of cytosolic calcium, sodium, and potassium ion fluxes. GT patients generated higher percentages of procoagulant COAT platelets compared to healthy donors. Moreover, they were able to mobilize higher levels of cytosolic calcium following convulxin-plus-thrombin activation, which is congruent with the greater procoagulant activity. Further investigations will dissect the role of GPIIb/IIIa outside-in signalling possibly implicated in the regulation of platelet procoagulant activity.

Effect of coagulation function on cerebral microbleeds in intracerebral hemorrhage

OBJECTIVE

Our study aimed to confirm whether coagulation function of patients presenting with intracerebral hemorrhage (ICH) was associated with onset of cerebral microbleeds (CMBs).

METHODS

A total of 174 patients with basal ganglia ICH were divided into CMBs and non-CMBs groups. Indicators of coagulation function and other clinical data that included fibrinogen (FBI), prothrombin time (PT), activated partial thromboplastin time (APTT), and the international normalized ratio (INR) were compared by univariate and multivariate analysis between the two groups. A receiver operating characteristic (ROC) curve was plotted to determine the predictive value of coagulation function indicators for CMBs.

RESULTS

Univariate analysis showed that APTT levels was significantly higher in the CMBs group than the non-CMBs group (30.20 ± 5.18 vs. 27.95 ± 4.19; p = .004), while there was no significant difference between PT, INR, and FBI. The proportion of male patients in the CMBs group was significantly higher than the non-CMBs group (76.58% vs. 52.38%, p = .001). Multifactor logistic regression analysis demonstrated that APTT and male gender were independent risk factors for CMBs in patients with ICH (OR 1.100, 95% CI: 1.026-1.180, p = .008; OR 2.957, 95% CI: 1.500-5.826, p = .002; respectively). ROC curve analysis indicated that the area under the curve of APTT and male gender for CMBs in patients with ICH was 0.641 and 0.621, respectively (p = .002 and .008; respectively).

CONCLUSION

APTT was an independent risk factor for CMBs in patients with ICH.

Clopidogrel use and smoking cessation result in lower coated-platelet levels after stroke

Coated-platelets are a subset of highly procoagulant platelets elevated in patients with non-lacunar ischemic stroke and associated with stroke recurrence. Cross-sectional studies in controls have shown that smoking is associated with higher coated-platelet levels while chronic use of serotonin reuptake inhibitors (SSRIs), statins or aspirin is associated with lower coated-platelet levels. We now investigate if initiation of treatment with SSRIs, statins, clopidogrel, aspirin or oral anticoagulants and smoking cessation impacts coated-platelet levels at 90 days after ischemic stroke. Coated-platelet levels, reported as percent of cells converted to coated-platelets, were measured in 87 consecutive patients with stroke at baseline and repeated at 90 days. Repeated-measure ANOVA was used to determine if initiation of treatment with individual medications or smoking cessation impacted coated-platelet levels. Decreased coated-platelets levels at 90 days as compared to baseline were observed after initiation of treatment with clopidogrel (p = .0001, partial η² = 0.17) and smoking cessation (p = .014, partial η² = 0.10). Initiation of treatment with SSRIs, statins, aspirin or oral anticoagulants did not result in significant changes in coated-platelet potential. These novel longitudinal data suggest that clopidogrel therapy and smoking cessation attenuate coated-platelet potential at 90 days after ischemic stroke.

Human platelets express endothelial protein C receptor, which can be utilized to enhance localization of factor VIIa activity

Essentials Factor VIIa binds activated platelets to promote hemostasis in hemophilia patients with inhibitors. The interactions and sites responsible for platelet-FVIIa binding are not fully understood. Endothelial cell protein C receptor (EPCR) is expressed on activated human platelets. EPCR binding enhances the efficacy of a FVIIa variant and could impact design of new therapeutics.

SUMMARY

Background High-dose factor VIIa (FVIIa) is routinely used as an effective bypassing agent to treat hemophilia patients with inhibitory antibodies that compromise factor replacement. However, the mechanism by which FVIIa binds activated platelets to promote hemostasis is not fully understood. FVIIa-DVQ is an analog of FVIIa with enhanced tissue factor (TF)-independent activity and hemostatic efficacy relative to FVIIa. Our previous studies have shown that FVIIa-DVQ exhibits greater platelet binding, thereby suggesting that features in addition to lipid composition contribute to platelet-FVIIa interactions. Objectives Endothelial cell protein C receptor (EPCR) also functions as a receptor for FVIIa on endothelial cells. We therefore hypothesized that an interaction with EPCR might play a role in platelet-FVIIa binding. Methods/results In the present study, we used flow cytometric analyses to show that platelet binding of both FVIIa and FVIIa-DVQ is partially inhibited in the presence of excess protein C or an anti-EPCR antibody. This decreased binding results in a corresponding decrease in the activity of both molecules in FXa and thrombin generation assays. Enhanced binding to EPCR was sufficient to account for the increased platelet binding of FVIIa-DVQ compared with wild-type FVIIa. As EPCR protein expression has not previously been shown in platelets, we confirmed the presence of EPCR in platelets using immunofluorescence, flow cytometry, immunoprecipitation, and mass spectrometry. Conclusions This work represents the first demonstration that human platelets express EPCR and suggests that modulation of EPCR binding could be utilized to enhance the hemostatic efficacy of rationally designed FVIIa analogs.

Procoagulant platelets: generation, function, and therapeutic targeting in thrombosis

Current understanding of how platelets localize coagulation to wound sites has come mainly from studies of a subpopulation of activated platelets. In this review, we summarize data from the last 4 decades that have described these platelets with a range of descriptive titles and attributes. We identify striking overlaps in the reported characteristics of these platelets, which imply a single subpopulation of versatile platelets and thus suggest that their commonality requires unification of their description. We therefore propose the term procoagulant platelet as the unifying terminology. We discuss the agonist requirements and molecular drivers for the dramatic morphological transformation platelets undergo when becoming procoagulant. Finally, we provide perspectives on the biomarker potential of procoagulant platelets for thrombotic events as well as on the possible clinical benefits of inhibitors of carbonic anhydrase enzymes and the water channel Aquaporin-1 for targeting this subpopulation of platelets as antiprocoagulant antithrombotics.

Coated-platelet levels are persistently elevated in patients with mild traumatic brain injury

OBJECTIVE

Coated-platelets are procoagulant platelets that are elevated in patients with large-vessel ischemic stroke and are associated with stroke recurrence. Because of recent reports showing an increased risk for stroke following traumatic brain injury (TBI), we undertook a pilot study to investigate coated-platelet synthesis in veterans with TBI.

DESIGN

Cross-sectional study.

PARTICIPANTS

Forty patients with a diagnosis of mild TBI (mTBI) and 40 controls without a history of TBI and matched for age, gender, and ethnicity/race were enrolled in the study.

MAIN MEASURE

Coated-platelet levels were determined in patients with mTBI and controls. The time period since most recent injury ranged from 6 months to 9 years.

RESULTS

Coated-platelet levels were significantly higher for mTBI patients than for controls (mean ± SD = 52.0% ± 14.0% vs 35.4% ± 13.0%; P < .0001). No relationship between these levels and the length of time since the last injury was found (P = .5).

CONCLUSIONS

Coated-platelet levels are markedly and persistently elevated in individuals with mTBI. These data suggest a link to previous findings of increased stroke risk and chronic inflammation among individuals who sustained a TBI.

Acute hemorrhagic complications are associated with lower coated-platelet levels in non-lacunar brain infarction

BACKGROUND

Coated platelets are procoagulant platelets observed upon dual agonist stimulation with collagen and thrombin. Coated-platelet levels are elevated in patients with non-lacunar ischemic stroke and decreased in patients with spontaneous intracerebral hemorrhage as compared with controls.

OBJECTIVE

To investigate whether acute hemorrhagic complications occurring during the initial hospital admission for non-lacunar ischemic stroke are associated with lower coated-platelet levels.

PATIENTS/METHODS

Coated-platelet levels were determined in 385 consecutive patients with non-lacunar stroke. Hemorrhagic complications were defined as either intracranial hemorrhage or significant extracranial bleeding (drop in hemoglobin of ≥ 2 g dL(-1) ). The rate of acute hemorrhagic complication was compared among subjects categorized into tertiles of coated-platelet levels using an exact Cochrane-Armitage trend test. Logistic regression was used to estimate the adjusted odds of hemorrhagic complication associated with coated-platelet levels.

RESULTS

Hemorrhagic complications were present in 15 (3.9%) cases. Of these, four had intracranial hemorrhage and 11 had extracranial hemorrhage. The occurrence of hemorrhagic complications differed among the coated-platelet tertiles: 10.2% for the first tertile (coated-platelet levels < 35.5%), 1.5% for the second tertile and 0% for the third tertile (coated-platelet levels ≥ 47.5%, trend test). Logistic regression showed that the odds of hemorrhagic complication in those with levels < 35.5% were 14.59 times the odds for patients with levels ≥ 35.5% (95% CI: 3.24-65.7).

CONCLUSIONS

Lower levels of procoagulant platelets are associated with acute hemorrhagic complications following non-lacunar ischemic stroke. These results suggest a role for coated-platelets in risk/benefit assessment in the early stages of stroke.

Coated-Platelet Levels Increase with Number of Injuries in Patients with Mild Traumatic Brain Injury

Coated-platelets are procoagulant platelets that are elevated in stroke and are associated with stroke recurrence. In a previous study, prompted by data showing an increased risk for stroke following traumatic brain injury (TBI), we found that coated-platelet levels are elevated in patients with combat-related mild TBI (mTBI) several years after the injury, compared with controls. We now investigate in an expanded patient population whether parameters commonly recorded in mTBI are related to increased coated-platelet potential. Coated-platelet levels were assayed in 120 mTBI patients at intervals ranging from 6 months to 10 years from the last injury. Correlations were calculated between coated-platelet levels and age, gender, race/ethnicity, loss of consciousness, alteration in consciousness, post-traumatic amnesia, number of injuries, mechanism of injury, time since first and last injury, smoking, medications that may influence coated-platelet levels, and pertinent comorbid conditions. Significant correlations were detected between coated-platelet levels and number of injuries (p = 0.026), gender (p = 0.01), and time since last injury (p = 0.04). A multi-variable linear model analysis, including these three parameters and an additional three parameters (race/ethnicity, smoking, and mechanism of injury) that reached a p value of <0.2, showed that the number of injuries were predictive of coated-platelet levels (p = 0.004). These results support a mechanistic link between increased coated-platelet levels and repeated injuries in mTBI. Long-term studies will be required to determine the impact of increased prothrombotic potential in mTBI patients.

Lower Coated-Platelet Levels Are Associated With Increased Mortality After Spontaneous Intracerebral Hemorrhage

BACKGROUND AND PURPOSE

Coated-platelets are highly procoagulant platelets observed on dual-agonist stimulation with collagen and thrombin. Coated-platelet levels are decreased in patients with spontaneous intracerebral hemorrhage when compared with controls and inversely correlated with bleed volume. We sought to investigate whether coated-platelets are associated with increased mortality at 30 days after spontaneous intracerebral hemorrhage.

METHODS

Coated-platelet levels were assayed in 95 consecutive patients with spontaneous intracerebral hemorrhage. The main outcome was mortality at 30 days according to coated-platelet levels at enrollment. Subjects were grouped into tertiles of the observed coated-platelet level distribution. Groups defined by tertile of coated-platelet level were compared using either ANOVA or a Kruskal-Wallis test for small group size for continuous measures and an exact Cochrane-Armitage trend test for categorical measures. Logistic regression was used to estimate the adjusted odds of death within 30 days associated with coated-platelet levels.

RESULTS

Cumulative mortality at 30 days was 23% (22 subjects). Mortality at 30 days differed among the coated-platelet tertiles: 44% for the first tertile (lowest coated-platelet levels), 19% for the second tertile, and 6% for the third tertile (trend test; P=0.0004). Logistic regression examining the association between mortality and coated-platelet levels showed that the odds of death at 30 days in those with levels <27% (n=47) were 6.83× the odds for patients with levels ≥27% (95% confidence interval, 2.10-22.23).

CONCLUSIONS

These results support a link between impaired coated-platelet potential and outcome in intracerebral hemorrhage.

Role of amyloid peptides in vascular dysfunction and platelet dysregulation in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative cause of dementia in the elderly. AD is accompanied by the accumulation of amyloid peptides in the brain parenchyma and in the cerebral vessels. The sporadic form of AD accounts for about 95% of all cases. It is characterized by a late onset, typically after the age of 65, with a complex and still poorly understood aetiology. Several observations point towards a central role of cerebrovascular dysfunction in the onset of sporadic AD (SAD). According to the "vascular hypothesis", AD may be initiated by vascular dysfunctions that precede and promote the neurodegenerative process. In accordance to this, AD patients show increased hemorrhagic or ischemic stroke risks. It is now clear that multiple bidirectional connections exist between AD and cerebrovascular disease, and in this new scenario, the effect of amyloid peptides on vascular cells and blood platelets appear to be central to AD. In this review, we analyze the effect of amyloid peptides on vascular function and platelet activation and its contribution to the cerebrovascular pathology associated with AD and the progression of this disease.

Cerebral microbleeds in nonlacunar brain infarction are associated with lower coated-platelet levels

BACKGROUND

Coated-platelets are a subset of platelets with high procoagulant potential observed on dual-agonist stimulation with collagen and thrombin. Coated-platelet levels are elevated in patients with nonlacunar ischemic stroke compared with controls, although the presence of early hemorrhagic transformation is associated with lower coated-platelet levels. In contrast to infarction, patients with spontaneous intracerebral hemorrhage have lower coated-platelet levels, and these levels inversely correlate with bleed size. Cerebral microbleeds (CMBs) represent previous small hemorrhagic occurrences. We undertook a pilot study to investigate coated-platelet production and the presence of CMBs in patients with nonlacunar ischemic stroke.

METHODS

Coated-platelet levels were determined in 110 consecutive patients with a diagnosis of nonlacunar stroke. Microbleeds were identified using the published criteria by an experienced stroke neurologist. Coated-platelet levels were compared statistically between patients with and without CMBs using the nonparametric Wilcoxon rank sum test.

RESULTS

Coated-platelet levels (median [interquartile range]) for all patients were 44.1% [34%-51.2%]. CMBs were detected in 22 patients (20%); these patients had significantly lower coated-platelet levels compared with those without CMBs (35.6% [22.6%-47.2%] versus 45.1% [36.1%-51.5%]; P = .025), whereas other demographic and clinical factors did not differ significantly.

CONCLUSIONS

The presence of CMBs in patients with nonlacunar ischemic stroke is associated with lower levels of coated-platelets. Larger prospective studies are needed to better establish the potential connection between altered coated-platelet synthesis, microbleeds, cerebral infarction, and possible hemorrhage-prone vascular changes.

Decreased generation of procoagulant platelets detected by flow cytometric analysis in patients with bleeding diathesis

BACKGROUND

A clinically relevant bleeding diathesis is a frequent diagnostic challenge, which sometimes remains unexplained despite extensive investigations. The aim of our work was to evaluate the diagnostic utility of functional platelet testing by flow cytometry in this context.

METHODS

In case of negative results after standard laboratory workup, flow cytometric analysis (FCA) of platelet function was done. We performed analysis of surface glycoproteins Ibα, IIb, IIIa; P-selectin expression and PAC-1 binding after graded doses of ADP, collagen, and thrombin; content/secretion of dense granules; and ability to generate procoagulant platelets.

RESULTS

Of 437 patients investigated with standard tests between January 2007 and December 2011, we identified 67 (15.3%) with high bleeding scores and nondiagnostic standard laboratory workup including platelet aggregation studies. Among these patients, FCA revealed some potentially causative platelet defects: decreased dense granule content/secretion (n = 13); decreased α-granule secretion induced by ADP (n = 10), convulxin (n = 4), or thrombin (n = 3); decreased fibrinogen receptor activation induced by ADP (n = 11), convulxin (n = 11), or thrombin (n = 8); and decreased generation of COAT platelets, that is, highly procoagulant platelets induced by simultaneous activation with collagen and thrombin (n = 16).

CONCLUSION

Our work confirms that storage pool defects are frequent in patients with a bleeding diathesis and normal coagulation and platelet aggregations studies. Additionally, FCA is able to identify discrete platelet activation defects. In particular, we show for the first time that a relevant proportion of these patients has an isolated impaired ability to generate COAT platelets--a conceptually new defect in platelet procoagulant activity, which is missed by conventional laboratory workup.

Higher levels of coated-platelets are observed in patients with subarachnoid hemorrhage but lower levels are associated with increased mortality at 30 days

BACKGROUND

Coated-platelets are procoagulant platelets observed upon dual agonist stimulation with collagen and thrombin. Coated-platelet levels are elevated in non-lacunar ischemic stroke compared to either lacunar stroke or controls. In contrast, coated-platelet levels are decreased in spontaneous intracerebral hemorrhage (ICH) and inversely correlated with bleed size. We now report the first investigation of coated-platelets in patients with subarachnoid hemorrhage (SAH).

METHODS

Coated-platelet levels were determined in 40 consecutive patients with spontaneous SAH and in 40 controls. Results are reported as percent of cells converted to coated-platelets. Mortality at one month was recorded for all patients.

RESULTS

Coated-platelet levels (mean ± SD) were significantly higher in SAH patients compared to controls (41.8 ± 11.4% vs. 30.7 ± 12.2%, p<0.0001). Among all patients, mortality at 1 month was 20% (8 deaths). Patients were analyzed according to tertiles of coated-platelet levels (split at <36.7%, 36.7-46.2%, >46.2%). The 1-month mortality differed significantly between the coated-platelet tertiles (p=0.01) with 46% mortality (6/13) among patients in the lowest tertile (lowest levels) compared to 14.3% (2/14) among those in the middle tertile and 0% in the highest tertile.

CONCLUSIONS

Coated-platelet levels are higher in SAH patients compared to controls. However, lower coated-platelet levels are associated with increased 1-month mortality in SAH patients, a finding compatible with prior observations of an inverse relationship between coated-platelet levels and bleed volume in ICH. The current data support the role played by these prothrombotic platelets in thrombosis or hemorrhage and suggest a potential place for coated-platelet levels in predicting prognosis after SAH.

Superactivated Platelets

Platelets contribute to hemostasis by forming the platelet plug and then contributing to coagulation by providing a catalytic surface where thrombin generation occurs efficiently. This catalytic activity, known as the platelet procoagulant response, is being recognized as a nuanced response. This review examines platelets’ response to strong stimuli, which results in the formation of a platelet subpopulation (superactivated platelets) with several unique properties, including enhanced procoagulant activity. These platelets contribute uniquely to thrombus architecture and seem to have thrombus regulatory activity. Superactivated platelets’ role in diseases of thrombosis and hemostasis, as either potentiating or mitigating factors, is not currently known, but may be an important pharmacological target.

Elevated coated-platelets in symptomatic large-artery stenosis patients are associated with early stroke recurrence

Coated-platelets are a subset of platelets with increased procoagulant potential observed upon dual agonist stimulation with collagen and thrombin. These prothrombotic platelets are elevated in patients with non-lacunar ischemic stroke and decreased in patients with spontaneous intracerebral hemorrhage compared to controls. We now investigated coated-platelet synthesis in patients with symptomatic large-artery stenosis and explored the association between coated-platelet levels and stroke recurrence at 3 months in this population. Coated-platelet levels were determined in 60 patients with either acute stroke or transient ischemic attack due to large-artery stenosis and 60 controls. Recurrent stroke incidence at 3 months was stratified by tertiles of coated-platelet levels and compared among groups using a log-rank test. Large-artery stenosis patients had significantly higher coated-platelet levels than controls (mean ± SD, 42.0 ± 15.5% vs. 29.4 ± 13.5%, p < 0.0001). The 3-month cumulative incidence of recurrent stroke was 41% for the highest, 6% for the middle, and 5% for the lowest tertile of coated-platelet levels (p = 0.0045). These results show that elevated coated-platelet levels in patients with symptomatic large-artery stenosis are associated with early stroke recurrence.

Higher coated-platelet levels are associated with stroke recurrence following nonlacunar brain infarction

Coated-platelets are procoagulant platelets observed upon dual-agonist stimulation with collagen and thrombin. Coated-platelet levels are elevated in patients with nonlacunar (large-vessel) ischemic stroke and decreased in patients with spontaneous intracerebral hemorrhage as compared with controls. The purpose of this study was to investigate a possible relationship between coated-platelet levels and stroke recurrence in patients with nonlacunar ischemic stroke. We assayed coated-platelet levels in 190 consecutive patients with nonlacunar stroke who were followed for up to 12 months; 20 subjects experienced recurrent stroke. Subjects were categorized into tertiles of coated-platelet levels. The distributions of time-to-recurrent stroke were estimated for each tertile using cumulative incidence curves and compared statistically using a log-rank test. The cumulative incidence of recurrent stroke at 12 months differed among the coated-platelet tertiles: 2% for the first tertile (lowest coated-platelet levels), 18% for the second tertile, and 17% for the third tertile (overall log-rank test, P=0.019). These data suggest that higher levels of coated-platelets, measured shortly after a nonlacunar stroke, are associated with an increased incidence of stroke recurrence. This observation offers an additional tool for identifying patients at highest risk for stroke recurrence following a nonlacunar (large-vessel) infarct.

Coated-platelet levels are elevated in patients with transient ischemic attack

Transient ischemic attack (TIA) presents a medical management dilemma because of the high frequency of subsequent ischemic strokes. The ABCD2 score is designed to stratify the short-term risk for stroke in TIA patients. Coated-platelets, which are a subset of procoagulant platelets observed after dual agonist stimulation with collagen and thrombin, are increased in cortical ischemic stroke and decreased in spontaneous intracerebral hemorrhage. Because TIA increases the risk of subsequent ischemic stroke, we conducted a pilot study to investigate whether coated-platelet production is increased in patients with TIA (n = 60) compared with controls (n = 60). Coated-platelet levels were higher in TIA patients versus controls [mean ± standard deviation (SD), 38.4 ± 15.1% vs 31.0 ± 13.2%, P = 0.005], and a significant linear correlation was detected between ABCD2 scores and coated-platelet levels in TIA patients (P = 0.0003, r = 0.45). These findings lend support to the hypothesis that TIA and ischemic stroke represent a spectrum of conditions dependent on similar prothrombotic processes.

Coated-platelet levels and progression from mild cognitive impairment to Alzheimer disease

OBJECTIVES

Coated-platelets are a subset of platelets produced by dual-agonist activation with collagen and thrombin. These platelets retain full-length amyloid precursor protein on their surface, are elevated in patients with amnestic as compared to nonamnestic mild cognitive impairment (MCI), and correlate with disease progression in Alzheimer disease (AD). Prompted by these findings, we investigated the association between coated-platelet production in amnestic MCI and rate of progression to AD.

METHODS

Coated-platelet levels were assayed in 74 patients with amnestic MCI who were subsequently followed longitudinally for up to 36 months in an outpatient dementia clinic. Levels are reported as percent of cells converted into coated-platelets. Subjects were categorized into tertiles of coated-platelet levels. The distributions of time to progression to AD were estimated for each tertile using cumulative incidence curves and compared statistically using a log-rank test. Cox proportional hazards regression was used to adjust for potential confounders.

RESULTS

The 24-month cumulative incidence of progression to AD was different among tertiles: 4% for the first tertile (lowest coated-platelet levels), 13% for the second tertile, and 37% for the third tertile (overall log-rank test, p = 0.02). The hazard rate of progression to AD for patients in the highest coated-platelet tertile was 5.1 times that for patients in the lowest tertile (p = 0.04), whereas the hazard rate for the middle tertile was similar to that for the lowest tertile (hazard rate ratio = 1.5, p = 0.7).

CONCLUSIONS

Elevated coated-platelet levels in patients with amnestic MCI are associated with increased risk for progression to AD.

Lower coated-platelet levels are associated with early hemorrhagic transformation in patients with non-lacunar brain infarction

BACKGROUND

Coated-platelets, representing a subset of platelets with procoagulant potential, are elevated in patients with non-lacunar ischemic stroke and decreased in patients with spontaneous intracerebral hemorrhage. However, within the non-lacunar patient population there are individuals with lower levels of coated-platelets, which raises the possibility that these individuals would be susceptible to early hemorrhagic transformation (HT) of ischemic stroke.

OBJECTIVE

Because extremes in coated-platelet potential may be associated with either thrombotic or hemorrhagic events, we undertook a pilot study to investigate whether there is an association between coated-platelet production and the presence of early HT in patients with non-lacunar ischemic stroke.

PATIENTS AND METHODS

Coated-platelet levels were determined in 115 consecutive eligible patients with a diagnosis of non-lacunar ischemic stroke. Early HT was determined on CT scan examination and confirmed by MRI studies. The distribution of coated-platelet levels was summarized using the median and interquartile range (25th-75th percentiles) and compared statistically between patients with and without early HT using the non-parametric Wilcoxon rank sum test.

RESULTS

The median coated-platelet level in all non-lacunar stroke patients was 38.0% (interquartile range 30.5-48.3%). Early HT was detected in 11 patients (9.6%), and these patients had significantly lower coated-platelet levels compared with those without early HT [median 25.1% (interquartile range 20.4-35.5%) vs. 39.2% (31.6-49.5%), P = 0.003].

CONCLUSIONS

Lower levels of coated-platelets are associated with the presence of early HT in patients with non-lacunar ischemic stroke.

Coated platelet levels correlate with bleed volume in patients with spontaneous intracerebral hemorrhage

BACKGROUND AND PURPOSE

Coated platelets are produced on dual agonist stimulation with collagen and thrombin. These highly procoagulant platelets are critical to normal hemostasis, and an earlier study demonstrated decreased coated platelet production in patients with spontaneous intracerebral hemorrhage. We have expanded this observation to investigate if coated platelet levels correlate with bleed volume in spontaneous intracerebral hemorrhage.

METHODS

Coated platelet levels and bleed volume were determined in 45 patients with a diagnosis of spontaneous intracerebral hemorrhage.

RESULTS

There was an inverse relationship between coated platelet levels and bleed volume (r=-0.38, P=0.01).

CONCLUSIONS

These data support a link between decreased coated platelet synthesis and the severity of spontaneous intracerebral hemorrhage.