Platelet reticulated forms, size indexes, and functional activity. Interactions in healthy volunteers

Assessment of platelet functional activity in healthy individuals and patients receiving antiplatelet therapy. Possible inconsistencies between aggregation and flow cytometry tests

Platelet functional activity was assessed in healthy volunteers (HV, n=92), patients with stable angina pectoris (SA, n=42) and acute coronary syndrome (ACS, n=73), treated with acetylsalicylic acid (ASA) + clopidogrel and ASA + ticagrelor, respectively. In all HV and patients we have compared parameters of platelet aggregation (maximum light transmission and velocity, Tmax and Vmax) and parameters, characterizing exposure of platelet activation markers, evaluated by flow cytometry. HV platelets were activated by 10 μM, 1 μM TRAP, and 20 μM, 5 μM, 2.5 μM ADP; patient platelets were activated by 10 μM TRAP and by 20 μM and 5 μM ADP. Strong and significant correlations between the aggregation and flow cytometry parameters (the r correlation coefficient from 0.4 up to >0.6) most frequently were registered in HV platelet during activation by 1 μM TRAP and in SA patients during platelet activation by 20 μM and 5 μM ADP. However, in many other cases these correlations were rather weak (r < 0.3) and sometimes statistically insignificant. In HV the differences in PAC-1 binding parameters between platelets activated by 10 μM TRAP (the strongest agonist) and all ADP concentrations were negligible (≤ 10%), while CD62P binding (at all ADP concentrations) and LTA parameters for (5 μM and 2.5 μM ADP) were significantly lower (by 40-60%). Antiplatelet therapy in patients decreased all parameters as compared to HV, but to varying extents. For 10 μM TRAP the MFI index for PAC-1 binding (40-50% decrease) and for both ADP concentrations the Tmax values (60-85% decrease) appeared to be the most sensitive in comparison with the other parameters that decreased to a lesser extent. The data obtained indicate a possibility of inconsistency between different LTA and flow cytometry parameters in assessing platelet activity and efficacy of antiplatelet drugs.

Mean Platelet Volume and Its Association With In-Hospital Outcomes in Patients With Acute ST-Segment Elevation Myocardial Infarction Undergoing Primary Percutaneous Coronary Intervention

Background Mean platelet volume (MPV), reflecting platelet size and activation, has been associated with cardiovascular disease (CVD) risk and mortality. Yet, its prognostic significance in acute coronary syndrome (ACS) patients undergoing primary percutaneous coronary intervention (PCI) remains uncertain. This study investigates whether elevated MPV levels upon admission in ST-segment elevation myocardial infarction (STEMI) patients predict adverse in-hospital outcomes after primary PCI. Objectives The aim of this study was to measure MPV in patients with STEMI who underwent primary PCI and to evaluate its association with in-hospital outcomes such as death, recurrent myocardial infarction, heart failure, and bleeding. Methods We enrolled 400 consecutive patients with STEMI (mean age 56.20 years, 356 males, 44 females) who underwent primary PCI at our center. We obtained MPV values from complete blood count tests performed at admission. We divided the patients into two groups based on the normal MPV range of 7.40 to 12 fL. We compared the baseline characteristics and in-hospital outcomes of the two groups. We used Cox proportional hazards regression analysis to adjust for potential confounders and evaluate the impact of MPV on in-hospital outcomes. Results There was no significant difference in MPV values between the two groups (9.10 ± 1.20 fL vs. 9.00 ± 1.10 fL, p = 0.54). Patients who died exhibited higher age, male predominance, hypertension, diabetes, a lower left ventricular ejection fraction, lower levels of low-density lipoprotein cholesterol, and lower levels of hemoglobin and hematocrit compared to survivors. MPV was not associated with any of the in-hospital outcomes in the unadjusted or adjusted analyses. Conclusion In this cohort of patients with STEMI who underwent primary PCI, admission MPV was not a predictor of in-hospital outcomes. Further studies are needed to clarify the role of MPV in the pathophysiology and prognosis of ACS.

Apoptosis is one cause of thrombocytopenia in patients with high-altitude polycythemia

High-altitude polycythemia (HAPC) can occur in individuals who are intolerant to high-altitude hypoxia. In patients with HAPC, erythrocytosis is often accompanied by a decrease in platelet count. Chronic hypoxia can increase the incidence of arteriovenous thrombosis and the risk of bleeding during antithrombotic treatment due to thrombocytopenia; therefore, understanding the cause of thrombocytopenia can reduce the risk of treatment-related bleeding. In this study, we examined platelet production and apoptosis to understand the cause of thrombocytopenia in patients with HAPC. The classification of myeloid-derived megakaryocytes (MKs) in HAPC patients was mainly granular MKs rather than mature MKs, suggesting impaired differentiation and maturation. However, the total number of MKs and newly generated reticulated platelets in the peripheral blood increased, indicating sufficient platelet generation in HAPC thrombocytopenia. Increased platelet apoptosis may be one of the causes of thrombocytopenia. Platelet activation and GP1bα pathway activation induced by thrombin and von Willebrand factor can lead to platelet apoptosis. Platelet production was not reduced in patients with HAPC, whereas platelet apoptosis was associated with thrombocytopenia. These findings provide a rationale for considering the bleeding risk in HAPC patient while treating thrombotic diseases.

Interactions of platelets with obesity in relation to lung cancer risk in the UK Biobank cohort

BACKGROUND

Platelet count (PLT) is associated positively with lung cancer risk but has a more complex association with body mass index (BMI), positive only in women (mainly never smokers) and inverse in men (mainly ever smokers), raising the question whether platelets interact with obesity in relation to lung cancer risk. Prospective associations of platelet size (an index of platelet maturity and activity) with lung cancer risk are unclear.

METHODS

We examined the associations of PLT, mean platelet volume (MPV), and platelet distribution width (PDW) (each individually, per one standard deviation increase) with lung cancer risk in UK Biobank men and women using multivariable Cox proportional hazards models adjusted for BMI and covariates. We calculated Relative Excess Risk from Interaction (RERI) with obese (BMI ≥ 30 kg/m2), dichotomising platelet parameters at ≥ median (sex-specific), and multiplicative interactions with BMI (continuous scale). We examined heterogeneity according to smoking status (never, former, current smoker) and antiaggregant/anticoagulant use (no/yes).

RESULTS

During a mean follow-up of 10.4 years, 1620 lung cancers were ascertained in 192,355 men and 1495 lung cancers in 218,761 women. PLT was associated positively with lung cancer risk in men (hazard ratio HR = 1.14; 95% confidence interval (CI): 1.09-1.20) and women (HR = 1.09; 95%CI: 1.03-1.15) but interacted inversely with BMI only in men (RERI = - 0.53; 95%CI: - 0.80 to - 0.26 for high-PLT-obese; HR = 0.92; 95%CI = 0.88-0.96 for PLT*BMI). Only in men, MPV was associated inversely with lung cancer risk (HR = 0.95; 95%CI: 0.90-0.99) and interacted positively with BMI (RERI = 0.27; 95%CI = 0.09-0.45 for high-MPV-obese; HR = 1.08; 95%CI = 1.04-1.13 for MPV*BMI), while PDW was associated positively (HR = 1.05; 95%CI: 1.00-1.10), with no evidence for interactions. The associations with PLT were consistent by smoking status, but MPV was associated inversely only in current smokers and PDW positively only in never/former smokers. The interactions with BMI were retained for at least eight years of follow-up and were consistent by smoking status but were attenuated in antiaggregant/anticoagulant users.

CONCLUSIONS

In men, PLT was associated positively and MPV inversely with lung cancer risk and these associations appeared hindered by obesity. In women, only PLT was associated positively, with little evidence for interaction with obesity.

Laboratory Markers of Platelet Production and Turnover

Platelets are formed from bone marrow megakaryocytes, circulate in blood for 7-10 days, and then are destroyed in the spleen and/or liver. Platelet production depends on the megakaryocyte population state in the bone marrow: number and size of the cells. The platelet turnover, i.e., the number of platelets passing through the bloodstream in a certain time, is determined by both the rate of their production and the rate of their destruction. The review considers laboratory markers, which are used to assess platelet production and turnover in the patients with hematologic and cardiovascular pathologies. These markers include some characteristics of platelets themselves: (i) content of reticulated ("young") forms in the blood detected by their staining with RNA dyes; (ii) indicators of the platelet size determined in hematology analyzers (mean volume, percentage of large forms) and in flow cytometers (light scattering level). Alterations of platelet production and turnover lead to the changes in blood plasma concentrations of such molecules as thrombopoietin (TPO, main mediator of megakaryocyte maturation and platelet formation in the bone marrow) and glycocalicin (soluble fragment of the membrane glycoprotein Ib detached from the surface of platelets during their destruction). Specific changes in the markers of platelet production and turnover have been observed in: (i) hypoproductive thrombocytopenias caused by suppression of megakaryocytes in the bone marrow; (ii) immune thrombocytopenias caused by accelerated clearance of the autoantibody-sensitized platelets; and (iii) thrombocytosis (both primary and reactive). The paper presents the data indicating that in patients with cardiovascular diseases an increased platelet turnover and changes in the corresponding markers (platelet size indexes and content of reticulated forms) are associated with the decreased efficacy of antiplatelet drugs and increased risk of thrombotic events, myocardial infarction, and unstable angina (acute coronary syndrome).

Development and internal validation of a clinical prediction model for the diagnosis of immune thrombocytopenia

BACKGROUND

Immune thrombocytopenia (ITP) is a diagnosis of exclusion that can resemble other thrombocytopenic disorders.

OBJECTIVES

To develop a clinical prediction model (CPM) for the diagnosis of ITP to aid hematogists in investigating patients presenting with undifferentiated thrombocytopenia.

METHODS

We designed a CPM for ITP diagnosis at the time of the initial hematology consultation using penalized logistic regression based on data from patients with thrombocytopenia enrolled in the McMaster ITP registry (n = 523) called the Predict-ITP Tool. The case definition for ITP was a platelet count less than 100 × 109 /L and a platelet count response after high-dose corticosteroids or intravenous immune globulin, defined as the achievement of a platelet count above 50 × 109 /L and at least a doubling of baseline. Internal validation was done using bootstrap resampling. Model discrimination was assessed by the c-statistic, and calibration was assessed by the calibration slope, calibration-in-the-large, and calibration plot.

RESULTS

The final model included the following variables: (1) platelet count variability (based on three or more platelet count values), (2) lowest platelet count value, (3) maximum mean platelet volume, and (4) history of major bleeding (defined by the ITP bleeding scale). The optimism-corrected c-statistic was 0.83, the calibration slope was 0.88, and calibration-in-the-large for all performance measures was <0.001 with standard error <0.001, indicating good discrimination and excellent calibration.

CONCLUSIONS

The Predict-ITP Tool can estimate the likelihood of ITP for a given patient with thrombocytopenia at the time of the initial hematology consultation. The tool had high predictive accuracy for the diagnosis of ITP.

Association between mean platelet volume and obstructive sleep apnea-hypopnea syndrome in children

To evaluate the correlation between mean platelet volume (MPV) and obstructive sleep apnea-hypopnea syndrome (OSAHS) in children, and to explore the diagnostic value of MPV for OSAHS. Children with OSAHS diagnosed by polysomnography (PSG) at Fuyong People's Hospital of Bao'an District/Shenzhen Children's Hospital from January 2020 to January 2021 were enrolled in this study. MPV in peripheral venous blood of the enrolled children was detected. Based on the PSG results (apnea-hypopnea index [AHI] and lowest oxygen saturation [LSaO2]), illness severity was classified, and correlations between the 2 parameters were statistically analyzed. A total of 190 children (males = 135, females = 55) with OSAHS were enrolled in the study. There were no significant correlations between AHI, LSaO2, white blood cell count, red blood cell count, blood platelets, hemoglobin, and packed cell volume (P > .05), but there was a significant positive correlation between AHI and MPV (R > 0, P < .05). There was a significant negative correlation between the LSaO2 index and MPV (R > 0, P < .05). In addition, the receiver operating characteristic (ROC) curve indicated that the best cutoff value for MPV to diagnose mild and moderate-to-severe disease conditions was 9.35 fl, and the coincidence rates for these 2 disease conditions were 93% and 80%, respectively. The ROC curve was also optimal for the diagnosis of mild and moderate-to-severe hypoxia. The critical value was 8.85 fl, and the coincidence rates for these 2 conditions were 96.4% and 76.3%, respectively. In children with OSAHS, MPV is positively correlated with AHI and negatively correlated with the LSaO2 index of PSG. Based on the results of ROC curve analysis, MPV can be used as an auxiliary diagnostic index to judge the severity of OSAHS and the degree of hypoxia in children.

Role of Reticulated Platelets in Cardiovascular Disease

Human platelets differ considerably with regard to their size, RNA content and thrombogenicity. Reticulated platelets (RPs) are young, hyper-reactive platelets that are newly released from the bone marrow. They are larger and contain more RNA compared to older platelets. In comparison to more mature platelets, they exhibit a significantly higher thrombogenicity and are known to be elevated in patients with an increased platelet turnover such as, diabetics and after acute myocardial infarction. Several studies have shown that RPs correlate with an insufficient antiplatelet response to aspirin and specific P2Y₁₂ receptor inhibitors. In addition, RPs are promising novel biomarkers for the prediction of adverse cardiovascular events in cardiovascular disease. However, the reason for RPs intrinsic hyper-reactivity and their association with ischemic events is not completely understood and the biology of RPs is still under investigation. We here present a structured review of preclinical and clinical findings concerning the role of RPs in cardiovascular disease.

Use of Platelet Parameters in the Differential Diagnosis of Lung Adenocarcinoma-Associated Malignant Pleural Effusion and Tuberculous Pleural Effusion

Background

Both malignant pleural effusion (MPE) and tuberculous pleural effusion (TPE) are common etiologies of pleural effusion; the present study was conducted to establish the diagnostic value of platelet parameters in the differential diagnosis of MPE and TPE.

Methods

This retrospective study enrolled patients with lung adenocarcinoma-associated MPE and TPE. Platelet parameter data, including platelet count (PLT), mean platelet volume (MPV), plateletcrit (PCT), platelet distribution width (PDW), and platelet-larger cell ratio (P-LCR), were collected. Principal component analysis and multiple logistic regression modelling were carried out to assess the diagnostic value of these platelet parameters.

Results

The MPE group and the TPE group enrolled 270 and 433 patients, respectively. Demographic characteristics of patients were more female and higher age in the MPE group. MPV, PDW, and P-LCR were significantly higher in MPE patients, while PLT and PCT were significantly higher in TPE patients. Principal component analysis generated two principal components (PCs) based on above platelet parameters. After adjusting for confounding factors including gender and age, multiple logistic regression showed positive association between PC1 and MPE.

Conclusion

Platelet parameters were potential biomarkers in distinguishing lung adenocarcinoma-associated MPE from TPE. A patient with lower PLT and PCT and higher MPV, PDW, and P-LCR was more likely to be diagnosed as the former. Principal component analysis and multiple logistic regression performed well in improving multicollinearity, adjusting confounding factors, and identifying important risk factors for MPE.

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.