Higher coated-platelet levels are associated with chronic hypertension in patients with transient ischemic attack

Advances in Platelet Subpopulation Research

Although lacking a nucleus, platelets are increasingly recognized not only for their complexity, but also for their diversity. Some 50 years ago platelet subpopulations were characterized by size and density, and these characteristics were thought to reflect platelet aging. Since, our knowledge of platelet heterogeneity has grown to recognize that differences in platelet biochemistry and function exist. This includes the identification of vanguard and follower platelets, platelets with differing procoagulant ability including "COAT-platelets" which enhance procoagulant protein retention on their surface, and most recently, the identification of platelet subpopulations with a differential ability to generate and respond to nitric oxide. Hence, in this mini-review, we summarize the current knowledge of platelet subpopulation diversity focusing on their physical, biochemical, and functional heterogeneity. In addition, we review how platelet subpopulations may change between health and disease and how differences among platelets may influence response to anti-platelet therapy. Finally, we look forward and discuss some of the future directions and challenges for this growing field of platelet research.

Coated-platelets predict stroke at 30 days following TIA

Objective:

To examine the potential for coated-platelets, a subset of highly procoagulant platelets observed on dual agonist stimulation with collagen and thrombin, for predicting stroke at 30 days in patients with TIA.

Methods:

Consecutive patients with TIA were enrolled and followed up prospectively. ABCD2 scores were obtained for each patient. Coated-platelet levels, reported as percent of cells converted to coated-platelets, were determined at baseline. The primary endpoint was the occurrence of stroke at 30 days. Receiver operator characteristic (ROC) analysis was used to calculate area under the curve (AUC) values for a model including coated-platelets to predict incident stroke at 30 days.

Results:

A total of 171 patients with TIA were enrolled, and 10 strokes were observed at 30 days. A cutoff of 51.1% for coated-platelet levels yielded a sensitivity of 0.80 (95% confidence interval [CI] 0.55–1.0), specificity of 0.73 (95% CI 0.66–0.80), positive predictive value of 0.16 (95% CI 0.06–0.26), and negative predictive value of 0.98 (95% CI 0.96–1.0). The adjusted hazard ratio of incident stroke in patients with coated-platelet levels ≥51.1% was 10.72 compared to those with levels <51.1%. ROC analysis showed significant improvement in the predictive ability of the coated-platelet model compared to ABCD2 score (AUC 0.78 ± 0.07 vs 0.54 ± 0.07, p = 0.01).

Conclusions:

These findings suggest a role for coated-platelets in risk stratification for stroke at 30 days after TIA.

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.

Metabolic syndrome, platelet activation and the development of transient ischemic attack or thromboembolic stroke

Stroke is the second most common cause of mortality in the world today, where transient ischemic attack (TIA) is a period of focal ischemia, the symptoms of which resemble a thromboembolic stroke. Contrary to stroke, TIA symptoms typically last less than one hour and necrosis is absent. Stroke is often preceded by TIA, making it an important predictor of future ischemic events. The causal role of atherosclerosis in the development of TIA is well established, however, research indicates that the atherosclerotic process begins years earlier with the development of metabolic syndrome, which affects approximately 45% of the adult population worldwide. Metabolic syndrome is present if three or more of the following is present: increased waist circumference, increased triglycerides, decreased HDL, increased fasting glucose and hypertension. This syndrome causes systemic inflammation that activates the coagulation system and may cause the formation of pathological thrombi. The role of platelets in stroke has been studied and platelet activation pathways identified. ADP and thromboxane A(2) are the most common activators of platelets in normal physiology. Several pharmacological treatments have been employed to prevent the activation of platelets, the most common of which include aspirin and P2Y(12)-inhibitors. Although treatment is administered strokes and subsequent TIAs are very common in individuals that suffered an initial event. This indicates that research needs to be done in order to elucidate new therapeutic targets, but also to better treat ischemic events to not only decrease the amount of recurring events but also decrease stroke mortality worldwide.

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.

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.

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.