An Insight into Recent Advances on Platelet Function in Health and Disease.

Platelets play a variety of roles in vascular biology and are best recognized as primary hemostasis and thrombosis mediators. Platelets have a large number of receptors and secretory molecules that are required for platelet functionality. Upon activation, platelets release multiple substances that have the ability to influence both physiological and pathophysiological processes including inflammation, tissue regeneration and repair, cancer progression, and spreading. The involvement of platelets in the progression and seriousness of a variety of disorders other than thrombosis is still being discovered, especially in the areas of inflammation and the immunological response. This review represents an integrated summary of recent advances on the function of platelets in pathophysiology that connects hemostasis, inflammation, and immunological response in health and disease and suggests that antiplatelet treatment might be used for more than only thrombosis.

Proteomics: A Tool to Study Platelet Function.

Platelets are components of the blood that are highly reactive, and they quickly respond to multiple physiological and pathophysiological processes. In the last decade, it became clear that platelets are the key components of circulation, linking hemostasis, innate, and acquired immunity. Protein composition, localization, and activity are crucial for platelet function and regulation. The current state of mass spectrometry-based proteomics has tremendous potential to identify and quantify thousands of proteins from a minimal amount of material, unravel multiple post-translational modifications, and monitor platelet activity during drug treatments. This review focuses on the role of proteomics in understanding the molecular basics of the classical and newly emerging functions of platelets. including the recently described role of platelets in immunology and the development of COVID-19.The state-of-the-art proteomic technologies and their application in studying platelet biogenesis, signaling, and storage are described, and the potential of newly appeared trapped ion mobility spectrometry (TIMS) is highlighted. Additionally, implementing proteomic methods in platelet transfusion medicine, and as a diagnostic and prognostic tool, is discussed.

COVID-19 induces a hyperactive phenotype in circulating platelets.

Coronavirus Disease 2019 (COVID-19), caused by the novel Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), has affected over 30 million globally to date. Although high rates of venous thromboembolism and evidence of COVID-19-induced endothelial dysfunction have been reported, the precise aetiology of the increased thrombotic risk associated with COVID-19 infection remains to be fully elucidated. Therefore, we assessed clinical platelet parameters and circulating platelet activity in patients with severe and nonsevere COVID-19. An assessment of clinical blood parameters in patients with severe COVID-19 disease (requiring intensive care), patients with nonsevere disease (not requiring intensive care), general medical in-patients without COVID-19, and healthy donors was undertaken. Platelet function and activity were also assessed by secretion and specific marker analysis. We demonstrated that routine clinical blood parameters including increased mean platelet volume (MPV) and decreased platelet:neutrophil ratio are associated with disease severity in COVID-19 upon hospitalisation and intensive care unit (ICU) admission. Strikingly, agonist-induced ADP release was 30- to 90-fold higher in COVID-19 patients compared with hospitalised controls and circulating levels of platelet factor 4 (PF4), soluble P-selectin (sP-selectin), and thrombopoietin (TPO) were also significantly elevated in COVID-19. This study shows that distinct differences exist in routine full blood count and other clinical laboratory parameters between patients with severe and nonsevere COVID-19. Moreover, we have determined all COVID-19 patients possess hyperactive circulating platelets. These data suggest abnormal platelet reactivity may contribute to hypercoagulability in COVID-19 and confirms the role that platelets/clotting has in determining the severity of the disease and the complexity of the recovery path.

Assessment of Platelet Thrombus Formation under Flow Conditions in Adult Patients with COVID-19: An Observational Study.

BACKGROUND: Coronavirus disease 2019 (COVID-19) is associated with systemic inflammation, which may dysregulate platelet function. Total Thrombus-Formation Analysis System (T-TAS) is a flow-chamber device that analyses platelet-mediated thrombus formation in capillary channels through the following parameters: (1) the area under the flow-pressure curve (AUC), (2) occlusion start time (OST), time needed to reach OST, and (3) occlusion time (OT), time needed to reach the occlusion pressure. METHODS AND FINDINGS: Sixty-one COVID-19 patients admitted to intensive, subintensive, and low intensive care were prospectively enrolled according to the time of admission: group A (up to 8 days) (n = 18); group B (from 9 to 21 days) (n = 19), and group C ( > 21 days) (n = 24). T-TAS measurements were performed at enrolment and after 7 days. Median OST was similar among groups. AUC was lower in group A compared to B (p = 0.001) and C (p = 0.033). OT was longer in group A compared to B (p = 0.001) and C (p = 0.028). Platelet count (PC) was higher in group B compared to A (p = 0.024). The linear regression showed that OT and AUC were independent from PC in group A (OT: 0.149 [95% confidence interval [CI]: -0.326 to 0.624], p = 0.513 and AUC: 0.005 [95% CI: -0.008 to 0.017], p = 0,447). In contrast, in group B, PC was associated with OT (-0.019 [-0.028 to 0.008], p = 0.023) and AUC (0.749 [0.358-1.139], p = 0,015), similarly to group C. Conversely, patients with different illness severity had similar T-TAS parameters. CONCLUSION: COVID-19 patients display an impaired platelet thrombus formation in the early phase of the disease compared to later stages and controls, independently from illness severity.

Coronavirus disease 2019 and coagulopathy: other prothrombotic coagulation factors.

There is an increasing evidence supporting the existence of coagulopathy in coronavirus disease 2019 (COVID-19) patients. Most of reports are mainly focused on d-dimer. Our objective is to describe coagulation parameters in these patients that could be involved in a hypercoagulate state and to test platelet function to see if there are short closure times. We analyzed coagulation samples from 80 patients admitted with COVID-19 in our hospital. We also tested platelet function by closure times in a small subgroup of patients. Most of samples had increased d-dimer (96.2%) (median of d-dimer: 1158 ng/ml FEU), increased fibrinogen (75.2%) (median: 5.23 g/l), increased factor VIII (86%) (median: 264.8 U/dl), decreased protein S (22.5% of women, 62.5% of men) (median: 62.8 and 68.5 U/dl, respectively), decreased protein C (7.6%) (median: 100 U/dl), decreased factor XII (25.3%) (median: 90.3 U/dl) and decreased antithrombin activity (21%) (median: 86 U/dl). International normalized ratio was higher than normal in 24 patients (30%) (median: 1.13). The activated partial thromboplastin time ratio was below the normal range in nine patients (11.2%) and above normal in three (3.75%) (median: 0.93). The closure times were short in the 20% and 40% of samples of collagen and ADP and collagen and epinephrine, respectively. Twelve of the 80 patients (15%) had a thrombotic event and all had several abnormal coagulation parameters related with increased thrombotic risk. The results of this study support a hypercoagulability state in COVID-19 patients and it may help to explain the microvascular thrombosis caused by the inflammatory response.

Von Willebrand factor with increased binding capacity is associated with reduced platelet aggregation but enhanced agglutination in COVID-19 patients: another COVID-19 paradox?

Patients with Coronavirus-associated disease-2019 (COVID-19) display alterations of the hemostatic system and the presence of a prothrombotic status frequently leading to vascular complications. However, the impact of COVID-19 on platelet activity, aggregation and agglutination still needs to be clarified. We measured total levels of von Willebrand factor (vWF) and vWF binding to the platelet glycoprotein (Gp) complex (GPIb-IX-V), in a cohort of COVID-19 patients admitted to the intensive care unit of our Institution. Moreover, we evaluated platelet aggregation in response to agonists (ADP, collagen, arachidonic acid) and platelet agglutination in response to ristocetin. We found that levels of vWF antigen and the active form of vWF binding to platelets (vWF:RCo), were markedly increased in these patients. These results were associated with higher agglutination rates induced by ristocetin, thereby indirectly indicating an increased capability of vWF to bind to platelets. Conversely, we found that platelet aggregation in response to both ADP and collagen was lower in COVID-19 patients compared to healthy volunteers. This study shows that COVID-19 is associated with increased vWF-induced platelet agglutination but reduced platelet responsivity to aggregation stimuli. Our findings have translational relevance since platelet adhesion to vWF may represent a marker to predict possible complications and better delineate therapeutic strategies in COVID-19 patients.

Coagulation profile of COVID-19 patients admitted to the ICU: An exploratory study.

BACKGROUND: Coagulation abnormalities in COVID-19 patients have not been addressed in depth. OBJECTIVE: To perform a longitudinal evaluation of coagulation profile of patients admitted to the ICU with COVID-19. METHODS: Conventional coagulation tests, rotational thromboelastometry (ROTEM), platelet function, fibrinolysis, antithrombin, protein C and S were measured at days 0, 1, 3, 7 and 14. Based on median total maximum SOFA score, patients were divided in two groups: SOFA ≤ 10 and SOFA > 10. RESULTS: Thirty patients were studied. Some conventional coagulation tests, as aPTT, PT and INR remained unchanged during the study period, while alterations on others coagulation laboratory tests were detected. Fibrinogen levels were increased in both groups. ROTEM maximum clot firmness increased in both groups from Day 0 to Day 14. Moreover, ROTEM-FIBTEM maximum clot firmness was high in both groups, with a slight decrease from day 0 to day 14 in group SOFA ≤ 10 and a slight increase during the same period in group SOFA > 10. Fibrinolysis was low and decreased over time in all groups, with the most pronounced decrease observed in INTEM maximum lysis in group SOFA > 10. Also, D-dimer plasma levels were higher than normal reference range in both groups and free protein S plasma levels were low in both groups at baseline and increased over time, Finally, patients in group SOFA > 10 had lower plasminogen levels and Protein C ​​than patients with SOFA <10, which may represent less fibrinolysis activity during a state of hypercoagulability. CONCLUSION: COVID-19 patients have a pronounced hypercoagulability state, characterized by impaired endogenous anticoagulation and decreased fibrinolysis. The magnitude of coagulation abnormalities seems to correlate with the severity of organ dysfunction. The hypercoagulability state of COVID-19 patients was not only detected by ROTEM but it much more complex, where changes were observed on the fibrinolytic and endogenous anticoagulation system.

Platelet functions and activities as potential hematologic parameters related to Coronavirus Disease 2019 (Covid-19).

Coronavirus disease 2019 (COVID-19) is a new infectious disease that currently lacks standardized and established laboratory markers to evaluate its severity. In COVID-19 patients, the number of platelets (PLTs) and dynamic changes of PLT-related parameters are currently a concern. The present paper discusses the potential link between PLT parameters and COVID-19. Several studies have identified a link between severe COVID-19 patients and specific coagulation index, in particular, high D-dimer level, prolonged prothrombin time, and low PLT count. These alterations reflect the hypercoagulable state present in severe COVID-19 patients, which could promote microthrombosis in the lungs, as well as in other organs. Further information and more advanced hematological parameters related to PLTs are needed to better estimate this link, also considering COVID-19 patients at different disease stages and stratified in different cohorts based on preexisting co-morbidity, age, and gender. Increasing the understanding of PLT functions in COVID-19 will undoubtedly improve our knowledge on disease pathogenesis, clinical management, and therapeutic options, but could also lead to the development of more precise therapeutic strategies for COVID-19 patients.