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

Effect of antiplatelet therapy on the incidence, prognosis, and rebleeding of intracerebral hemorrhage

OBJECTIVE

Antiplatelet medications are increasingly being used for primary and secondary prevention of ischemic attacks owing to the increasing prevalence of ischemic stroke occurrences. Currently, many patients receive antiplatelet therapy (APT) to prevent thromboembolic events. However, long-term use of APT might also lead to an increased occurrence of intracerebral hemorrhage (ICH) and affect the prognosis of patients with ICH. Furthermore, some research suggest that restarting APT for patients who have previously experienced ICH may result in rebleeding events. The precise relationship between APT and ICH remains unknown.

METHODS

We searched PubMed for the most recent related literature and summarized the findings from various studies. The search terms included "antiplatelet," "intracerebral hemorrhage," "cerebral microbleeds," "hematoma expansion," "recurrent," and "reinitiate." Clinical studies involving human subjects were ultimately included and interpreted in this review, and animal studies were not discussed.

RESULTS

When individuals are administered APT, the risk of thrombotic events should be weighted against the risk of bleeding. In general, for some patients' concomitant with risk factors of thrombotic events, the advantages of antiplatelet medication may outweigh the inherent risk of rebleeding. However, the use of antiplatelet medications for other patients with a higher risk of bleeding should be carefully evaluated and closely monitored. In the future, a quantifiable system for assessing thrombotic risk and bleeding risk will be necessary. After evaluation, the appropriate time to restart APT for ICH patients should be determined to prevent underlying ischemic stroke events. According to the present study results and expert experience, most patients now restart APT at around 1 week following the onset of ICH. Nevertheless, the precise time to restart APT should be chosen on a case-by-case basis as per the patient's risk of embolic events and recurrent bleeding. More compelling evidence-based medicine evidence is needed in the future.

CONCLUSION

This review thoroughly discusses the relationship between APT and the development of ICH, the impact of APT on the course and prognosis of ICH patients, and the factors influencing the decision to restart APT after ICH. However, different studies' conclusions are inconsistent due to the differences in quality control. To support future clinical decisions, more large-scale randomized controlled trials are required.

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.

Increased procoagulant platelet levels are predictive of death in COVID-19

Prior research has identified abnormal platelet procoagulant responses in COVID-19. Coated-platelets, a form of procoagulant platelets, support thrombin formation and are elevated in ischemic stroke patients with increased risk for recurrent infarction. Our goal was to examine changes in coated-platelet levels over the course of COVID-19 infection and determine their association with disease severity, thrombosis, and death. Coated-platelet levels were assayed after admission and repeated weekly in COVID-19 patients, and in COVID-19 negative controls. Receiver operator characteristic (ROC) analysis was used to calculate area under the curve (AUC) values for a model including baseline coated-platelets to predict death. Kaplan–Meier and Cox proportional hazards analysis was used to predict risk for death at 90 days. We enrolled 33 patients (22 with moderate and 11 with severe infection) and 20 controls. Baseline coated-platelet levels were lower among moderate (mean ± SD; 21.3 ± 9.8%) and severe COVID-19 patients (28.5 ± 11.9%) compared to controls (38.1 ± 10.4%, p < 0.0001). Coated-platelet levels increased during follow-up in COVID-19 patients by 7% (relative) per day from symptom onset (95% CI 2–12%, p = 0.007). A cut-off of 33.9% for coated-platelet levels yielded 80% sensitivity and 96% specificity for death at 90 days, with resulting AUC of 0.880 (95% CI 0.680–1.0, p = 0.0002). The adjusted hazard ratio for death in patients with coated-platelet levels > 33.9% was 40.99 when compared to those with levels ≤ 33.9% (p < 0.0001). Platelet procoagulant potential is transiently decreased in most patients during COVID-19; however, increased baseline platelet procoagulant levels predict death. Defining the mechanisms involved and potential links with aging may yield novel treatment targets.

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.

Association between Coagulation Function and Cerebral Microbleeds in Ischemic Stroke Patients with Atrial Fibrillation and/or Rheumatic Heart Disease

Cerebral microbleeds (CMBs), which indicate hemorrhage-prone disease, may associate with hemostatic abnormalities, but the association between CMBs and coagulation function is uncertain. We aimed to examine this possible association. The following coagulation function indicators were evaluated in 85 consecutive ischemic stroke patients diagnosed with atrial fibrillation and/or rheumatic heart disease: prothrombintime (PT), activated partial thromboplastin time (APTT), and levels of D-dimer and fibrinogen. Indicators were assessed within 24 h after admission. CMBs were identified based on published criteria by two experienced stroke neurologists working independently. PT, APPT, and levels of D-dimer and fibrinogen were compared between patients with and without CMBs using univariate and multivariate analysis. CMBs were detected in 48 patients (56.5%), and fibrinogen levels in these patients were independently and significantly higher than in patients without CMBs after adjustment (OR 2.16, 95% CI 1.20-3.90, P=0.01), whereas the two types of patients did not differ significantly in PT, APPT, or D-dimer levels. The presence of CMBs in ischemic stroke patients with atrial fibrillation and/or rheumatic heart disease is associated with elevated levels of fibrinogen. Larger prospective studies are needed to verify this association and explore the mechanisms involved.

A cohort study of relationship between serum calcium levels and cerebral microbleeds (CMBs) in ischemic stroke patients with AF and/or RHD

Calcium is an essential element for life and has cerebroprotective property in stroke patients. Low serum calcium levels were found to be related to large hematoma volumes in intracerebral hemorrhagic patients and hemorrhagic transformation in ischemic stroke patients after thrombolysis. However, their impact on hemorrhage-prone small vessel disease represented by cerebral microbleeds (CMBs) is uncertain. We aim to investigate whether low serum calcium levels are associated with presence and location of CMBs.Ischemic stroke patients with atrial fibrillation (AF) and/or rheumatic heart disease admitted to our hospital were consecutively and prospectively enrolled. Demographic and clinical information were collected and analyzed according to the occurrence and location of CMBs, and levels of serum calcium. We used logistic regression analysis to estimate the multivariable adjusted relationship between serum calcium levels and the presence or location of CMBs.Among the 67 patients (28 males; mean age, 67.3 years) in the final analysis, 39 (58.2%) were found to have CMBs. After adjustment for age, sex, smoking habits, drinking habits, and renal impairment, the presence of CMBs and deep CMBs was, respectively, 4.96- and 4.83-fold higher in patients with lower serum calcium levels (≤2.15 mmol/L) than in patients with higher serum calcium levels.Lower serum calcium levels (≤2.15 mmol/L) are independently associated with the presence of CMBs and deep CMBs in ischemic stroke patients with AF and/or rheumatic heart disease, which should be verified and extended in large cohorts, with other types of stroke patients and the general population.

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.