comorbidities including diabetes, CVD and risk factors such as hypertension, elevated angiotensin II (Ang II) and obesity, levels of circulating EVs are raised. [3] [4] [5] [6] Increased EVs, especially from injured or TNF-α-stimulated endothelial cells (EC) carrying tissue factor (TF + ), or from platelets exposing phosphatidylserine (PS + ), are known to be procoagulant and to cause VTE. 7 Levels of EVs also correlate with von Willebrand Factor (vWF), a marker of EC damage and dysfunction, 8 that is released through Ang II-mediated superoxide damage and hypoxia-mediated oxidative stress and further still by severe acute respiratory syndrome coronavirus (SARS-CoV-2) binding to angiotensin-converting enzyme 2 (ACE2) on ECs and ensuant complement-mediated inflammation, 9 ( Figure [A and B] ). Previously, EC-mEV levels were found to be associated with stroke 10 and more recently CD31 + and CD144 + EC-derived mEVs, phenotypes reflecting apoptosis and structurally damaged endothelium, were found to relate to risk factors for CVD and thus increased risk of VTE, especially raised triglycerides, hypertension and metabolic syndrome. 4 Could it therefore be that changes in circulating EVs, raised and with modulated cargo in certain comorbidity groups, and possibly still further by infection with SARS-CoV-2, renders COVID-19 patients particularly susceptible to VTE? If so, EVs could be used as biomarkers in COVID-19. A TF + -EV procoagulant activity assay for example, based on fibrin formation, previously used in monitoring the risk of VTE in cancer patients, should be tried in COVID-19.
It was recently reported that higher rates of death from COVID-19 in the U.K. were found in BAME patients. 11 This study calculated the risk of death, adjusted for age and region, compared to the general population, the Standardized Mortality Ratio (SMR). The adjusted ethnic-specific If plasma EV levels are raised, and cargo modified in comorbidities associated with COVID-19, such as diabetes, and accounting for excess deaths in BAME patients, could EVs be playing a role and might there be a connection to ethnicity? In the United States, African Americans (AA) show a disproportionately high comborbidity-associated death rate from COVID-19, compared to White Americans (WA). 13 Interestingly, in work looking firstly at concentration and mean/modal sizes of circulating plasma EVs in AA and WA, regardless of gender, no ethnic difference was found. 14 However, assessing EV protein content involved in insulin signalling, the work found lower levels of phospho-AKT (pAKT) in AAs compared to WA which is associated with impaired insulin signalling, insulin resistance and an increased risk of VTE. Importantly, considering phosphorylated insulin signalling proteins, shown previously by the same group to be in EVs, and related to diabetes mellitus, 2, 3 the association of these EV proteins with clinical mortality risk markers, such as serum creatinine, lactate dehydrogenase (LDH), homeostatic model assessment of β-cell function (HOMA-B), serum alkaline phosphatase (ALP) and pulse pressure, did seem to depend on ethnicity.
The connection between EV cargo, mortality markers and race, may be of considerable importance, due to the current knowledge gap in susceptibility for COVID-19 amongst BAME patients. We know that EVs play roles in T2D 3 and CVD 4 and may thus constitute important risk factors leading to VTE in COVID-19. It is already known that proteins such as vWF contributing to VTE, show an association with ethnicity. 15 However, given that certain EV proteins and their relationship with clinical mortality markers may also vary according to ethnicity (summarized in
This article is protected by copyright. All rights reserved C5b-9 ). The resulting Ca 2+ influx through deposited C5b-9 and by the SARS-CoV-2 E-protein Ca 2+ channel from ERGIC/ER, leads to Ca 2+mediated EV release. Circulating EVs carrying phosphorylated insulin signalling proteins and related to diabetes mellitus, an important comorbidity in COVID-19, are associated with clinical mortality risk markers linked to ethnicity, A and B. In severe COVID-19, in particular in ethnicities with increased comorbidities such as diabetes, A, and associated circulating EV levels, EVs with their known role in coagulopathy could play an important role in COVID-19-related deaths through VTE. 