ABSTRACT
Background: Thrombotic events are frequent and life-threating complications of COVID-19, but are also observed in patients with bacterial sepsis. Disseminated thrombosis may occur despite strict anticoagulation, suggesting that platelets play a direct, but yet undefined role. Several studies demonstrate altered platelet function in COVID-19, but the impact of platelets in COVID-19 and sepsis remains poorly understood. Aim(s): Platelet phenotype and function were comprehensively assessed in over 100 patients with either COVID-19 (non-ECMO, all-ICU, n = 23), bacterial infection without sepsis (SOFA-score < 2;n = 29), or sepsis/septic shock (SOFA-score >=2;n = 49) at multiple time points during the disease. Method(s): Patients were recruited at the local University Hospital (Ethical vote 94/19). Platelet phenotype and function were studied using flow cytometry (lumino-) aggregometry and whole-mount transmission electron-microscopy. Thrombus formation was investigated using a collagen-and tissue factor-coated flow chamber model at arterial shear rate (1000s-1). Thrombi were imaged by confocal microscopy. Result(s): Upon stimulation with ADP or CRP-XL platelets of infection patients without sepsis showed reduced PAC-1 binding and CD62P exposition. In sepsis patients reactivity was even more impaired and highly associated with disease severity (mean normalized geo-MFI PAC-1 infection: 0.56 vs sepsis: 0.25, p < 0.01;ROC-AUC: 0.76, p < 0.001). Intriguingly, platelets of COVID-19 patients were more responsive towards stimulation compared to comparably-ill ICU patients with sepsis. This relative hyper-reactivity was reflected by increased clot-formation in the flow chamber, compared to sepsis patients (mean surface coverage: 36% vs. 19%, p < 0.05). Thrombi of COVID-19 patients were platelet-rich with little fibrin, in contrast to healthy donors or sepsis patients showing increased amount of fibrin and less platelets. Subtherapeutic doses of GPIIb/IIIa blockers eptifibatide or tirofiban, which had minor effect in control blood, sufficiently prevented thrombus formation in COVID-19 samples under arterial flow. Conclusion(s): Our findings provide evidence that low dose GPIIb/ IIIa blockade might act as a powerful therapeutic tool in COVID-19 patients.
ABSTRACT
Background : Infection with SARS-CoV-2 leads to an altered hemostatic system and Covid-19 associated coagulopathy (CAC). Platelet counts remain overall unaltered, but thromboembolic events are frequently reported. Studies on the contribution of platelets to CAC are emerging but still lacking precise cohort comparison and broad analyses of platelet markers. Aims : We aimed to analyze platelet receptor expression and function on platelets and biomarkers in platelet-poor plasma to investigate the role of platelets in the onset of critical progression of CAC. Methods : Extensive platelet function analyses were performed on 34 critically-ill patients with Covid-19 and data was compared to sepsis patients ( n = 24) and non-SARS-CoV-2 acute infection ( n = 18). Tests included PFA-200, aggregometry, flow cytometry and whole mount TEM. Plasma levels of TPO, sCD62P and sGPVI were determined by ELISA. For all patients, relatives, and for healthy controls ( n = 10) informed consent was obtained. Results : While platelet counts in patients of our Covid-19 cohort were expectably unaltered, platelet function was severely impaired in multiple assays. Platelets failed to aggregate in response to ADP or TRAP-6 and could not activate integrin response or release α-granules. The amount of platelet-leukocyte aggregates was markedly elevated, indicating previous platelet activation in line with higher levels of sCD62P and sGPVI. Remarkably, we observed platelet exhaustion in Covid-19 patients using whole mount TEM by means of a lack of dense granules corroborating with impaired uptake of mepacrine. Conclusions : Our data imply that SARS-CoV-2 infection leads to a sub-threshold activation of platelets in a way that they become activated already before critical disease progression, without being cleared from the circulation, which is in striking contrast to sepsis. The platelet pool appears to be exhausted with detrimental consequences for thrombus stability and the risk of thromboembolic events. The mere platelet count in Covid-19 does thus not reflect progression to CAC, whereas platelet function is of high prognostic relevance.