Mechanisms of COVID-19 Associated Pulmonary Thrombosis: A Narrative Review (preprint)

COVID-19, the infectious disease caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), is frequently associated with pulmonary thrombotic events, especially in hospitalised patients. Severe SARS-CoV-2 infection is characterized by a proinflammatory state and an associated disbalance in hemostasis. Immune pathology analysis supports the inflammatory nature of pulmonary arterial thrombi composed by white blood cells, especially neutrophils, CD3+ and CD20+ lymphocytes, fibrin, red blood cells and platelets. Immune cells, cytokines, chemokines and the complement system are key drivers of immunothrombosis, as they induce the damage of endothelial cells and initiate pro-inflammatory and pro-coagulant positive feedback loops. Neutrophil extracellular traps induced by COVID-19-associated “cytokine storm”, platelets, red blood cells, and coagulation pathways close the inflammation-endotheliopathy-thrombosis axis, contributing to SARS-CoV-2 associated pulmonary thrombotic events. The hypothesis of immunothrombosis is also supported by the minor role of venous thromboembolism, chest CT imaging data showing peripheral blood clots associated with inflammatory lesions and the high incidence of thrombotic events despite routine thromboprophylaxis. Understanding the complex mechanisms behind COVID-19-induced pulmonary thrombosis will lead to future combination therapies for hospitalised patients with severe disease, that would target the crossroads of inflammatory and coagulation pathways.

A role for Toll-like receptor 3 in lung vascular remodeling associated with SARS-CoV-2 infection (preprint)

Cardiovascular sequelae of severe acute respiratory syndrome (SARS) coronavirus-2 (CoV-2) disease 2019 (COVID-19) contribute to the complications of the disease. One potential complication is lung vascular remodeling, but the exact cause is still unknown. We hypothesized that endothelial TLR3 insufficiency contributes to lung vascular remodeling induced by SARS-CoV-2. In the lungs of COVID-19 patients and SARS-CoV-2 infected Syrian hamsters, we discovered thickening of the pulmonary artery media and microvascular rarefaction, which were associated with decreased TLR3 expression in lung tissue and pulmonary artery endothelial cells (ECs). In vitro, SARS-CoV-2 infection reduced endothelial TLR3 expression. Following infection with mouse-adapted (MA) SARS-CoV-2, TLR3 knockout mice displayed heightened pulmonary artery remodeling and endothelial apoptosis. Treatment with the TLR3 agonist polyinosinic:polycytidylic acid reduced lung tissue damage, lung vascular remodeling, and endothelial apoptosis associated with MA SARS-CoV-2 infection. In conclusion, repression of endothelial TLR3 is a potential mechanism of SARS-CoV-2 infection associated lung vascular remodeling and enhancing TLR3 signaling is a potential strategy for treatment.

Placental vascular remodeling in pregnant women with COVID-19.

Severe acute respiratory syndrome coronavirus 2 has been causing the pandemic of coronavirus disease 2019 (COVID-19) that has so far resulted in over 450 million infections and six million deaths. This respiratory virus uses angiotensin-converting enzyme 2 as a receptor to enter host cells and affects various tissues in addition to the lungs. The present study reports that the placental arteries of women who gave birth to live full-term newborns while developing COVID-19 during pregnancy exhibit severe vascular wall thickening and the occlusion of the vascular lumen. A morphometric analysis of the placental arteries stained with hematoxylin and eosin suggests a 2-fold increase in wall thickness and a 5-fold decrease in the lumen area. Placental vascular remodeling was found to occur in all of SARS-CoV-2-positive mothers as defined by RT-PCR. Immunohistochemistry with α-smooth muscle actin and the Kv11.1 channel as well as Masson's trichrome staining showed that such placental vascular remodeling in COVID-19 is associated with smooth muscle proliferation and fibrosis. Placental vascular remodeling may represent a response mechanism to the clinical problems associated with childbirth in COVID-19 patients.

Angiogenic Role of Mesothelium-Derived Chemokine CXCL1 During Unfavorable Peritoneal Tissue Remodeling in Patients Receiving Peritoneal Dialysis as Renal Replacement Therapy.

Peritoneal dialysis (PD) is a valuable 'home treatment' option, even more so during the ongoing Coronavirus pandemic. However, the long-term use of PD is limited by unfavourable tissue remodelling in the peritoneal membrane, which is associated with inflammation-induced angiogenesis. This appears to be driven primarily through vascular endothelial growth factor (VEGF), while the involvement of other angiogenic signaling pathways is still poorly understood. Here, we have identified the crucial contribution of mesothelial cell-derived angiogenic CXC chemokine ligand 1 (CXCL1) to peritoneal angiogenesis in PD. CXCL1 expression and peritoneal microvessel density were analysed in biopsies obtained by the International Peritoneal Biobank (NCT01893710 at www.clinicaltrials.gov), comparing 13 children with end-stage kidney disease before initiating PD to 43 children on chronic PD. The angiogenic potential of mesothelial cell-derived CXCL1 was assessed in vitro by measuring endothelial tube formation of human microvascular endothelial cells (HMECs) treated with conditioned medium from human peritoneal mesothelial cells (HPMCs) stimulated to release CXCL1 by treatment with either recombinant IL-17 or PD effluent. We found that the capillary density in the human peritoneum correlated with local CXCL1 expression. Both CXCL1 expression and microvessel density were higher in PD patients than in the age-matched patients prior to initiation of PD. Exposure of HMECs to recombinant CXCL1 or conditioned medium from IL-17-stimulated HPMCs resulted in increased endothelial tube formation, while selective inhibition of mesothelial CXCL1 production by specific antibodies or through silencing of relevant transcription factors abolished the proangiogenic effect of HPMC-conditioned medium. In conclusion, peritoneal mesothelium-derived CXCL1 promotes endothelial tube formation in vitro and associates with peritoneal microvessel density in uremic patients undergoing PD, thus providing novel targets for therapeutic intervention to prolong PD therapy.

COVID-19 and dys-regulation of pulmonary endothelium: implications for vascular remodeling.

Coronavirus disease-2019 (COVID-19), the disease caused by severe acute respiratory syndrome-coronavirus-2, has claimed more than 4.4 million lives worldwide (as of 20 August 2021). Severe cases of the disease often result in respiratory distress due to cytokine storm, and mechanical ventilation is required. Although, the lungs are the primary organs affected by the disease, more evidence on damage to the heart, kidney, and liver is emerging. A common link in these connections is the cardiovascular network. Inner lining of the blood vessels, called endothelium, is formed by a single layer of endothelial cells. Several clinical manifestations involving the endothelium have been reported, such as its activation via immunomodulation, endotheliitis, thrombosis, vasoconstriction, and distinct intussusceptive angiogenesis (IA), a unique and rapid process of blood-vessel formation by splitting a vessel into two lumens. In fact, the virus directly infects the endothelium via TMPRSS2 spike glycoprotein priming to facilitate ACE-2-mediated viral entry. Recent studies have indicated a significant increase in remodeling of the pulmonary vascular bed via intussusception in patients with COVID-19. However, the lack of circulatory biomarkers for IA limits its detection in COVID-19 pathogenesis. In this review, we describe the implications of angiogenesis in COVID-19, unique features of the pulmonary vascular bed and its remodeling, and a rapid and non-invasive assessment of IA to overcome the technical limitations in patients with COVID-19.

Bilateral Chilblain-like Lesions of the Toes Characterized by Microvascular Remodeling in Adolescents During the COVID-19 Pandemic.

Importance: Chilblain-like lesions have been one of the most frequently described cutaneous manifestations during the COVID-19 pandemic. Their etiopathogenesis, including the role of SARS-CoV-2, remains elusive. Objective: To examine the association of chilblain-like lesions with SARS-CoV-2 infection. Design, Setting, and Participants: This prospective case series enrolled 17 adolescents who presented with chilblain-like lesions from April 1 to June 30, 2020, at a tertiary referral academic hospital in Italy. Main Outcomes and Measures: Macroscopic (clinical and dermoscopic) and microscopic (histopathologic) analysis contributed to a thorough understanding of the lesions. Nasopharyngeal swab, serologic testing, and in situ hybridization of the skin biopsy specimens were performed to test for SARS-CoV-2 infection. Laboratory tests explored signs of systemic inflammation or thrombophilia. Structural changes in peripheral microcirculation were investigated by capillaroscopy. Results: Of the 17 adolescents (9 [52.9%] male; median [interquartile range] age, 13.2 [12.5-14.3] years) enrolled during the first wave of the COVID-19 pandemic, 16 (94.1%) had bilaterally localized distal erythematous or cyanotic lesions. A triad of red dots (16 [100%]), white rosettes (11 [68.8%]), and white streaks (10 [62.5%]) characterized the dermoscopic picture. Histologic analysis revealed a remodeling of the dermal blood vessels with a lobular arrangement, wall thickening, and a mild perivascular lymphocytic infiltrate. SARS-CoV-2 infection was excluded by molecular and serologic testing. In situ hybridization did not highlight the viral genome in the lesions. Conclusions and Relevance: This study delineated the clinical, histologic, and laboratory features of chilblain-like lesions that emerged during the COVID-19 pandemic, and its findings do not support their association with SARS-CoV-2 infection. The lesions occurred in otherwise healthy adolescents, had a long but benign course to self-resolution, and were characterized by a microvascular remodeling with perivascular lymphocytic infiltrate but no other signs of vasculitis. These results suggest that chilblain-like lesions do not imply a concomitant SARS-CoV-2 infection. Ongoing studies will help clarify the etiopathogenic mechanisms.

Increased RV:LV Ratio on Chest CT-Angiogram in COVID-19 is a Marker of Adverse Outcomes (preprint)

PurposeOur study aimed to use chest CT-angiogram (CTA) to assess if right ventricular (RV) dilation, quantified as an increased RV:LV (left ventricle) ratio, is associated with adverse outcomes in the novel coronavirus (COVID-19) infection.MethodsWe reviewed clinical, laboratory, and chest CTA findings in COVID-19 patients (n=100), and two control groups: normal subjects (n=10) and subjects with organizing pneumonia (n=10). On a chest CTA, we measured basal dimensions of the RV and LV in a focused 4-chamber view; and dimensions of pulmonary artery (PA) and aorta (AO) at the PA bifurcation level. ResultsAmong the COVID-19 cohort, the mean age (±SD) was 55.1±14.9 years and 55% were female. A higher RV:LV ratio was correlated with adverse outcomes, defined as ICU admission, intubation, or death. In patients with adverse outcomes, the RV:LV ratio was 1.06±0.10, vs 0.95±0.15 in patients without adverse outcomes. Among the adverse outcomes group, compared to the control subjects with organizing pneumonia, the lung parenchymal damage was lower (22.6±9.0 vs 32.7±6.6), yet the RV:LV ratio was higher (1.06±0.14 vs 0.89±0.07). In ROC analysis, RV:LV ratio had an AUC= 0.707 with an optimal cut-off of RV:LV 1.1 as a predictor of adverse outcomes. In a validation cohort (n=25), an RV:LV ≥1.1 as a cut-off predicted adverse outcomes with an odds ratio of 76:1.ConclusionIn COVID-19 patients, RV:LV ratio ≥1.1 on CTA-chest is correlated with adverse outcomes. RV dilation in COVID-19 is out of proportion to parenchymal lung damage, pointing towards a vascular and/or thrombotic injury in the lungs.

Role of pulmonary circulation assessment in CT imaging in evaluating the severity and tendency of severe and critical COVID-19 pneumonia (preprint)

Objective: To investigate the value of changes of pulmonary circulation in CT imaging in evaluating the severity and tendency of 2019 novel coronavirus disease (COVID-19) pneumonia.Methods: This retrospective study analyzed 99 severe and critical COVID-19 pneumonia patients including the 47 improved cases and 52 dead cases. Demographic data, laboratory findings, comorbidities, and CT imaging features including the diameters of pulmonary vein (PV), pulmonary artery (PA) and ascending aorta were collected and assessed.Results: The PV diameters of the deceased patients were larger than recovered patients in the severe phase. Compared with the severe phase in the improvement group, the diameters of the pulmonary veins during the improved phase were smaller, and the total CT scores were significantly decreased (p < 0.001). Instead, there was no significant difference in the ratio of main PA to aorta diameter between the recovered group and the deceased group, nor did the self control of the recovered group and the deceased group (p > 0.05). Construction of a ROC curve yielded an optimal cut-off value of the PV diameters for prediction of survival (p < 0.05).Conclusion: The changes of the PV diameters might indirectly reflect the activity of pulmonary inflammation and cardiac insufficiency. Pulmonary manifestations of severe and critical COVID-19 pneumonia might be related to myocardial injury and cardiac insufficiency, expecially accompanied by dilated PVs. Evaluation of changes in pulmonary circulation by chest CT images may be considered as a useful tool for determining the severity, fatal outcome and tendency of COVID-19.Key words: COVID-19, pneumonia, pulmonary circulation, Computed Tomography