Platelets in COVID-19 disease: friend, foe, or both?

Protein disulfide isomerase 1 (PDIA1) regulates platelet-derived extracellular vesicle release

BACKGROUND

Protein disulfide isomerase 1 (PDIA1) and 3 (PDIA3) regulate platelet activation and thrombus formation. However, their role in the formation of platelet-derived extracellular vesicles (pEVs) remains unknown.

AIM

To characterise the effects of PDIA1 and PDIA3 inhibition on pEV formation in washed murine platelets in response to platelet glycoprotein VI (GPVI) receptor or intracellular calcium signal activation.

METHODS

Washed platelets were isolated from C57BL/6 mice and activated using convulxin or the calcium ionophore A23187. Then, the resulting pEVs were analysed using nano flow cytometry (FC), platelet aggregation was measured by FC and a 96-well plate-based assay, and intracellular free calcium concentration ([Ca2+]i) was measured by indicator fluorescence. Platelet PDIs were blocked by a classic selective PDIA1 inhibitor (bepristat 2a) and sulphonamides of aziridine-2-carboxylic acid derivatives, novel PDI inhibitors relatively selective for PDIA1 or PDIA3 (C-3389 and C-3399, respectively). Clinically relevant antiplatelet drugs were used for comparison.

RESULTS

Convulxin and A23187 concentration-dependently induced pEV formation. However, unlike convulxin, platelet activation by A23187 did not stimulate their aggregation. Bepristat 2a, C-3389 and C-3399 inhibited convulxin-induced pEV release accompanied by the reduction of [Ca2+]i. In contrast, only bepristat 2a inhibited A23187-induced pEV release, but without effect on [Ca2+]i. Cangrelor and tirofiban, but not acetylsalicylic acid (ASA), inhibited convulxin-induced pEV release, but neither of them inhibited A23187-induced pEV release.

CONCLUSION

The inhibition of PDIA1 represents a novel approach to inhibit pEV formation by a mechanism independent of platelet aggregation and calcium signaling.

Complex Pattern of Platelet Activation/Reactivity After SARS-CoV-2 Infection

COVID-19 and post-COVID (long COVID) are associated with thromboembolic complications; however, it is still not clear whether platelets play a leading role in this phenomenon. The platelet hyperreactivity could result from the direct interaction between platelets and viral elements or the response to inflammatory and prothrombotic factors released from blood and vessel cells following infection. The existing literature does not provide clear-cut answers, as the results determining platelet status vary according to methodology. Elevated levels of soluble markers of platelet activation (P selectin, PF4), increased platelet aggregates, and platelet-derived microparticles suggest the activation of platelets circulating in the bloodstream of COVID-19 patients. Similarly, platelets isolated from COVID-19 patients demonstrate increased reactivity in response to collagen, thrombin, and ADP. By contrast, an analysis of whole blood from COVID-19 patients indicates the reduced activation of the fibrinogen receptor. Similarly, some in vitro studies report potential targets for SARS-CoV-2 in platelets, whereas others do not indicate any direct effect of the virus on platelets. The aim of this work is to review and evaluate the reliability of the methodology for testing platelet function after contact with SARS-CoV-2. Despite the diversity of methods yielding varying results and the influence of plasma components or blood cells, it can be concluded that platelets play an important role in the development of thrombotic complications after exposure to SARS-CoV-2.

Distinct profile of antiviral drugs effects in aortic and pulmonary endothelial cells revealed by high-content microscopy and cell painting assays

Antiretroviral therapy have significantly improved the treatment of viral infections and reduced the associated mortality and morbidity rates. However, highly effective antiretroviral therapy (HAART) may lead to an increased risk of cardiovascular diseases, which could be related to endothelial toxicity. Here, seven antiviral drugs (remdesivir, PF-00835231, ritonavir, lopinavir, efavirenz, zidovudine and abacavir) were characterized against aortic (HAEC) and pulmonary (hLMVEC) endothelial cells, using high-content microscopy. The colourimetric study (MTS test) revealed similar toxicity profiles of all antiviral drugs tested in the concentration range of 1 nM-50 μM in aortic and pulmonary endothelial cells. Conversely, the drugs' effects on morphological parameters were more pronounced in HAECs as compared with hLMVECs. Based on the antiviral drugs' effects on the cytoplasmic and nuclei architecture (analyzed by multiple pre-defined parameters including SER texture and STAR morphology), the studied compounds were classified into five distinct morphological subgroups, each linked to a specific cellular response profile. In relation to morphological subgroup classification, antiviral drugs induced a loss of mitochondrial membrane potential, elevated ROS, changed lipid droplets/lysosomal content, decreased von Willebrand factor expression and micronuclei formation or dysregulated cellular autophagy. In conclusion, based on specific changes in endothelial cytoplasm, nuclei and subcellular morphology, the distinct endothelial response was identified for remdesivir, ritonavir, lopinavir, efavirenz, zidovudine and abacavir treatments. The effects detected in aortic endothelial cells were not detected in pulmonary endothelial cells. Taken together, high-content microscopy has proven to be a robust and informative method for endothelial drug profiling that may prove useful in predicting the organ-specific endothelial toxicity of various drugs.

The evolution of preexisting primary immune thrombocytopenia after COVID-19 onset: A nationally representative, prospective, multicentre, observational study

The symptoms in patients with primary immune thrombocytopenia (ITP) after COVID-19 onset remain largely unclear. The aim of this study was to describe the platelet count fluctuations in ITP patients following the diagnosis of COVID-19. A prospective multicentre observational study was conducted from December 15th, 2022, to January 31st, 2023 in 39 general hospitals across China. Patients with preexisting primary ITP who were newly diagnosed with COVID-19 were enrolled. A total of 1216 ITP patients with newly-diagnosed COVID-19 were enrolled. 375 (30.8%) patients experienced ITP exacerbation within eight weeks after the diagnosis of COVID-19, and most exacerbation (266/375, 70.9%) developed in the first two weeks. Immunosuppressive therapy for ITP and severe/critical COVID-19 infection were independent variables associated with ITP exacerbation. Overall the platelet count had a transient increasing trend, and the platelet peak value occurred at two weeks after COVID-19 infection. Then, the platelet count decreased to the baseline level in the following weeks. The platelet count had a transient increasing trend in ITP patients following the diagnosis of COVID-19. ITP exacerbation only occurred in less than one-third of ITP patients. Nonimmunosuppressive therapy may have an advantage to prevent ITP exacerbation during COVID-19.

COVID-19 and the Response to Antiplatelet Therapy

The coronavirus SARS-CoV2 disease (COVID-19) is connected with significant morbidity and mortality (3.4%), disorders in hemostasis, including coagulopathy, activation of platelets, vascular injury, and changes in fibrinolysis, which may be responsible for an increased risk of thromboembolism. Many studies demonstrated relatively high rates of venous and arterial thrombosis related to COVID-19. The incidence of arterial thrombosis in severe/critically ill intensive care unit-admitted COVID-19 patients appears to be around 1%. There are several ways for the activation of platelets and coagulation that may lead to the formation of thrombi, so it is challenging to make a decision about optimal antithrombotic strategy in patients with COVID-19. This article reviews the current knowledge about the role of antiplatelet therapy in patients with COVID-19.