Neutrophil extracellular traps and thrombosis in COVID-19

Characterization of Neutrophil Functional Responses to SARS-CoV-2 Infection in a Translational Feline Model for COVID-19

There is a complex interplay between viral infection and host innate immune response regarding disease severity and outcomes. Neutrophil hyperactivation, including excessive release of neutrophil extracellular traps (NETs), is linked to exacerbated disease in acute COVID-19, notably in hospitalized patients. Delineating protective versus detrimental neutrophil responses is essential to developing targeted COVID-19 therapies and relies on high-quality translational animal models. In this study, we utilize a previously established feline model for COVID-19 to investigate neutrophil dysfunction in which experimentally infected cats develop clinical disease that mimics acute COVID-19. Specific pathogen-free cats were inoculated with SARS-CoV-2 (B.1.617.2; Delta variant) (n = 24) or vehicle (n = 6). Plasma, bronchoalveolar lavage fluid, and lung tissues were collected at various time points over 12 days post-inoculation. Systematic and temporal evaluation of the kinetics of neutrophil activation was conducted by measuring markers of activation including myeloperoxidase (MPO), neutrophil elastase (NE), and citrullinated histone H3 (citH3) in SARS-CoV-2-infected cats at 4 and 12 days post-inoculation (dpi) and compared to vehicle-inoculated controls. Cytokine profiling supported elevated innate inflammatory responses with specific upregulation of neutrophil activation and NET formation-related markers, namely IL-8, IL-18, CXCL1, and SDF-1, in infected cats. An increase in MPO-DNA complexes and cell-free dsDNA in infected cats compared to vehicle-inoculated was noted and supported by histopathologic severity in respiratory tissues. Immunofluorescence analyses further supported correlation of NET markers with tissue damage, especially 4 dpi. Differential gene expression analyses indicated an upregulation of genes associated with innate immune and neutrophil activation pathways. Transcripts involved in activation and NETosis pathways were upregulated by 4 dpi and downregulated by 12 dpi, suggesting peak activation of neutrophils and NET-associated markers in the early acute stages of infection. Correlation analyses conducted between NET-specific markers and clinical scores as well as histopathologic scores support association between neutrophil activation and disease severity during SARS-CoV-2 infection in this model. Overall, this study emphasizes the effect of neutrophil activation and NET release in SARS-CoV-2 infection in a feline model, prompting further investigation into therapeutic strategies aimed at mitigating excessive innate inflammatory responses in COVID-19.

Immunologic mediators profile in COVID-19 convalescence

SARS-CoV-2 caused the pandemic situation experienced since the beginning of 2020, and many countries faced the rapid spread and severe form of the disease. Mechanisms of interaction between the virus and the host were observed during acute phase, but few data are available when related to immunity dynamics in convalescents. We conducted a longitudinal study, with 51 healthy donors and 62 COVID-19 convalescent patients, which these had a 2-month follow-up after symptoms recovery. Venous blood sample was obtained from all participants to measure blood count, subpopulations of monocytes, lymphocytes, natural killer cells and dendritic cells. Serum was used to measure cytokines, chemokines, growth factors, anti-N IgG and anti-S IgG/IgM antibodies. Statistic was performed by Kruskal-Wallis test, and linear regression with days post symptoms and antibody titers. All analysis had confidence interval of 95%. Less than 35% of convalescents were anti-S IgM+, while more than 80% were IgG+ in D30. Anti-N IgG decreased along time, with loss of seroreactivity of 13%. Eosinophil count played a distinct role on both antibodies during all study, and the convalescence was orchestrated by higher neutrophil-to-lymphocyte ratio and IL-15, but initial stages were marked by increase in myeloid DCs, B1 lymphocytes, inflammatory and patrolling monocytes, G-CSF and IL-2. Later convalescence seemed to change to cytotoxicity mediated by T lymphocytes, plasmacytoid DCs, VEGF, IL-9 and CXCL10. Anti-S IgG antibodies showed the longest perseverance and may be a better option for diagnosis. The inflammatory pattern is yet present on initial stage of convalescence, but quickly shifts to a reparative dynamic. Meanwhile eosinophils seem to play a role on anti-N levels in convalescence, although may not be the major causative agent. We must highlight the importance of immunological markers on acute clinical outcomes, but their comprehension to potentialize adaptive system must be explored to improve immunizations and further preventive policies.

Extracellular histones: a unifying mechanism driving platelet-dependent extracellular vesicle release and thrombus formation in COVID-19

BACKGROUND

COVID-19 can cause profound inflammation and coagulopathy, and while many mechanisms have been proposed, there is no known common pathway leading to a prothrombotic state.

OBJECTIVES

From the beginning of the COVID-19 pandemic, elevated levels of extracellular histones have been found in plasma of patients infected with SARS-CoV-2. We hypothesized that platelet activation triggered by extracellular histones might represent a unifying mechanism leading to increased thrombin generation and thrombosis.

METHODS

We utilized blood samples collected from an early clinical trial of hospitalized COVID-19 patients (NCT04360824) and recruited healthy subjects as controls. Using plasma samples, we measured the procoagulant and prothrombotic potential of circulating extracellular histones and extracellular vesicles (EVs). Platelet prothrombotic activity was assessed via thrombin generation potential and platelet thrombus growth. Circulating EVs were assessed for thrombin generation potential in vitro in plasma and enhancement of thrombotic susceptibility in vivo in mice.

RESULTS

Compared with controls, COVID-19 patients had elevated plasma levels of citrullinated histone H3, cell-free DNA, nucleosomes, and EVs. Plasma from COVID-19 patients promoted platelet activation, platelet-dependent thrombin generation, thrombus growth under venous shear stress, and release of platelet-derived EVs. These prothrombotic effects of COVID-19 plasma were inhibited by an RNA aptamer that neutralizes both free and DNA-bound histones. EVs isolated from COVID-19 plasma enhanced thrombin generation in vitro and potentiated venous thrombosis in mice in vivo.

CONCLUSION

We conclude that extracellular histones and procoagulant EVs drive the prothrombotic state in COVID-19 and that histone-targeted therapy may prove beneficial.

The effect of pre-hospital use of RAS inhibitors on COVID-19 mortality

The effect of pre-hospital use of renin-angiotensin system (RAS) inhibitors (angiotensin-converting enzyme inhibitors (ACEis)/angiotensin receptor blockers (ARBs)) on clinical outcomes of hypertensive patients with COVID-19 has been questioned due to conflicting reports on this issue. After applying exclusion criteria, 175 COVID-19 hospitalized patients admitted to the Tishreen Hospital from January 1 to July 31, 2021 were retrospectively enrolled in this study. Baseline characteristics and in-hospital mortality rate were assessed between hypertensive (N = 91, 52%) and non-hypertensive (N = 84, 48%) patients, as well as between patients taking ACEis/ARBs and non-ACEis/ARBs within the hypertensive group. A lower mortality rate (51.2 versus 31.9%, p = 0.009) was observed in the hypertensive group (mean age 64.6 years, 64.8% males) compared to the non-hypertensive (mean age 62.6 years, 66.7% males). Patients' mortality in the non-hypertensive group was associated with lower blood oxygen saturation (SPO2 = 75 versus 86%, p = 0.002), increased levels of inflammatory (CRP, white blood cell and neutrophils count), and tissue/renal injury markers (LDH, urea, and creatinine). In the hypertensive group, a lower mortality rate was noted in the ACEis/ARBs group compared to the non-ACEis/ARBs (24.1 versus 45.5%, p = 0.036), and this was associated with a decrease in D-DIMER levels, although not significant (1723 versus 2683 ng/mL, p > 0.05). Death in the non-ACEis/ARBs group was associated with decreased SPO2 and tissue/renal injury markers (LDH, CK, AST, urea, and creatinine). We concluded that hypertension is not a direct cause of poor prognosis in COVID-19 patients and that multi-organ damage is a significant indicator of death from COVID-19. RAS inhibitors could improve the survival of hypertensive COVID-19 patients.

NETs: Important players in cancer progression and therapeutic resistance

Neutrophil extracellular traps (NETs) are web-like structures composed of cytoplasmic contents, DNA chromatin and various granular proteins released by neutrophils in response to viruses, bacteria, immune complexes and cytokines. Studies have shown that NETs can promote the occurrence, development and metastasis of tumors. In this paper, the mechanism underlying the formation and degradation of NETs and the malignant biological behaviors of NETs, such as the promotion of tumor cell proliferation, epithelial mesenchymal transition, extracellular matrix remodeling, angiogenesis, immune evasion and tumor-related thrombosis, are described in detail. NETs are being increasingly studied as therapeutic targets for tumors. We have summarized strategies for targeting NETs or interfering with NET-cancer cell interactions and explored the potential application value of NETs as biomarkers in cancer diagnosis and treatment, as well as the relationship between NETs and therapeutic resistance.

Describing Elephants: An Update on the Immunopathology of Multisystem Inflammatory Syndrome in Children

First described in 2020, multi-system inflammatory syndrome in children (MIS-C) is an, initially life-threatening, disease characterised by severe inflammation and following exposure to SARS-CoV-2. The immunopathology of MIS-C involves a hyperinflammation characterised by a cytokine storm and activation of both the innate and adaptive immune system, eventually leading to multi-organ failure. Several etiological theories are described in literature. Firstly, it is suggested that the gut plays an important role in the translocation of microbial products to the systemic circulation. Additionally, the production of autoantibodies that develop after the initial infection with SARS-CoV-2 might lead to many of its broad clinical symptoms. Finally, the superantigen theory where non-specific binding of the SARS-CoV-2 spike glycoprotein to the T-cell receptor leads to a subsequent activation of T cells, generating a powerful immune response. Despite the sudden outbreak of MIS-C and alarming messages, as of 2024, cases have declined drastically and subsequently show a less severe clinical spectrum. However, subacute cases not meeting current diagnostic criteria might be overlooked even though they represent a valuable research population. In the future, research should focus on adjusting these criteria to better understand the broad pathophysiology of MIS-C, aiding early detection, therapy, and prediction.

Inflammation-, immunothrombosis,- and autoimmune-feedback loops may lead to persistent neutrophil self-stimulation in long COVID

Understanding the pathophysiology of long COVID is one of the most intriguing challenges confronting contemporary medicine. Despite observations recently made in the relevant molecular, cellular, and physiological domains, it is still difficult to say whether the post-acute sequelae of COVID-19 directly correspond to the consequences of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. This work hypothesizes that neutrophils and neutrophil extracellular traps (NETs) production are at the interconnection of three positive feedback loops which are initiated in the acute phase of SARS-CoV-2 infection, and which involve inflammation, immunothrombosis, and autoimmunity. This phenomenon could be favored by the fact that SARS-CoV-2 may directly bind and penetrate neutrophils. The ensuing strong neutrophil stimulation leads to a progressive amplification of an exacerbated and uncontrolled NETs production, potentially persisting for months beyond the acute phase of infection. This continuous self-stimulation of neutrophils leads, in turn, to systemic inflammation, micro-thromboses, and the production of autoantibodies, whose significant consequences include the persistence of endothelial and multiorgan damage, and vascular complications.

Interplay between Comorbidities and Long COVID: Challenges and Multidisciplinary Approaches

Long COVID, a name often given to the persistent symptoms following acute SARS-CoV-2 infection, poses a multifaceted challenge for health. This review explores the intrinsic relationship between comorbidities and autoimmune responses in shaping the trajectory of long COVID. Autoantibodies have emerged as significant players in COVID-19 pathophysiology, with implications for disease severity and progression. Studies show immune dysregulation persisting months after infection, marked by activated innate immune cells and high cytokine levels. The presence of autoantibodies against various autoantigens suggests their potential as comorbid factors in long COVID. Additionally, the formation of immune complexes may lead to severe disease progression, highlighting the urgency for early detection and intervention. Furthermore, long COVID is highly linked to cardiovascular complications and neurological symptoms, posing challenges in diagnosis and management. Multidisciplinary approaches, including vaccination, tailored rehabilitation, and pharmacological interventions, are used for mitigating long COVID's burden. However, numerous challenges persist, from evolving diagnostic criteria to addressing the psychosocial impact and predicting disease outcomes. Leveraging AI-based applications holds promise in enhancing patient management and improving our understanding of long COVID. As research continues to unfold, unravelling the complexities of long COVID remains paramount for effective intervention and patient care.

X-ray Attenuating Vesicles with Neutrophil Extracellular Trap (NET) Specificity: Synthesis and Testing in a Model System

X-ray attenuating contrast agents for imaging thrombi directly during endovascular thrombectomy (EVT) are urgently needed for shortening the wait time for treatment and for reducing the chances of blood clot fragmentation. Neutrophil extracellular traps (NETs) are a product of an innate immune system response by which neutrophils release decondensed chromatin strands decorated with granule and cytosolic proteins, including neutrophil elastase and citrullinated histone H3 (CitH3). NETs are frequently found within fibrous thrombi in pathology and represent a promising target for thrombi-specific imaging agents due to their common occurrence in human cerebrovascular thrombi. We designed and tested 200 nm lipid vesicles (LV) formulated in the presence of a combination of hydrophilic and hydrophobic computed tomography (CT) contrast agents with resultant efficacy of X-ray attenuation corresponding to 312 ± 54 mg/mL iodine. The LV incorporated trans-cyclooctene-terminated pegylated distearoylphosphatidylethanolamine (TCO-PEG-DSPE) for rapid conjugation of methyltetrazine(mTz)-modified monoclonal immunoglobulin G (IgG) with anti-citH3 binding specificity. By using differential fluorescent labeling of the antibody and lipid components, we determined that 80 ± 3% of mTz-linked IgG coprecipitated with the LV after conjugation in contrast to 0.1-0.2% of control IgG. The engineered NET-specific LV were tested in vitro using differentiated human HL60 promyeloblasts (dHL60) as a standard model of NETing neutrophils. Using fibrin meshwork-incorporated dHL60 as well as monolayer cell cultures, we determined that anti-citH3 LV showed specific and high-affinity binding to dHL60 cells, which were stimulated to undergo NETosis. This work suggests the high promise of NET-specific agents in providing thrombus-specific imaging contrast during EVT.

Proteomics of the heart

Mass spectrometry-based proteomics is a sophisticated identification tool specializing in portraying protein dynamics at a molecular level. Proteomics provides biologists with a snapshot of context-dependent protein and proteoform expression, structural conformations, dynamic turnover, and protein-protein interactions. Cardiac proteomics can offer a broader and deeper understanding of the molecular mechanisms that underscore cardiovascular disease, and it is foundational to the development of future therapeutic interventions. This review encapsulates the evolution, current technologies, and future perspectives of proteomic-based mass spectrometry as it applies to the study of the heart. Key technological advancements have allowed researchers to study proteomes at a single-cell level and employ robot-assisted automation systems for enhanced sample preparation techniques, and the increase in fidelity of the mass spectrometers has allowed for the unambiguous identification of numerous dynamic posttranslational modifications. Animal models of cardiovascular disease, ranging from early animal experiments to current sophisticated models of heart failure with preserved ejection fraction, have provided the tools to study a challenging organ in the laboratory. Further technological development will pave the way for the implementation of proteomics even closer within the clinical setting, allowing not only scientists but also patients to benefit from an understanding of protein interplay as it relates to cardiac disease physiology.

Between good and evil: Complexation of the human cathelicidin LL-37 with nucleic acids

The innate immune system provides a crucial first line of defense against invading pathogens attacking the body. As the only member of the human cathelicidin family, the antimicrobial peptide LL-37 has been shown to have antiviral, antifungal, and antibacterial properties. In complexation with nucleic acids, LL-37 is suggested to maintain its beneficial health effects while also acting as a condensation agent for the nucleic acid. Complexes formed by LL-37 and nucleic acids have been shown to be immunostimulatory with a positive impact on the human innate immune system. However, some studies also suggest that in some circumstances, LL-37/nucleic acid complexes may be a contributing factor to autoimmune disorders such as psoriasis and systemic lupus erythematosus. This review provides a comprehensive discussion of research highlighting the beneficial health effects of LL-37/nucleic acid complexes, as well as discussing observed detrimental effects. We will emphasize why it is important to investigate and elucidate structural characteristics, such as condensation patterns of nucleic acids within complexation, and their mechanisms of action, to shed light on the intricate physiological effects of LL-37 and the seemingly contradictory role of LL-37/nucleic acid complexes in the innate immune response.

Association of vascular netosis with COVID-19 severity in asymptomatic and symptomatic patients

We examined from a large exploratory study cohort of COVID-19 patients (N = 549) a validated panel of neutrophil extracellular traps (NETs) markers in different categories of disease severity. Neutrophil elastase (NE), myeloperoxidase (MPO), and circulating nuclear DNA (cir-nDNA) levels in plasma were seen to gradually and significantly (p < 0.0001) increase with the disease severity: mild (3.7, 48.9, and 15.8 ng/mL, respectively); moderate (9.8, 77.5, and 27.7 ng/mL, respectively); severe (11.7, 99.5, and 29.0 ng/mL, respectively); and critical (13.1, 110.2, and 46.0 ng/mL, respectively); and are also statistically different with healthy individuals (N = 140; p < 0.0001). All observations made in relation to the Delta variant-infected patients are in line with Omicron-infected patients. We unexpectedly observed significantly higher levels of NETs in asymptomatic individuals as compared to healthy subjects (p < 0.0001). Moreover, the balance of cir-nDNA and circulating mitochondrial DNA level was affected in COVID-19 infected patients attesting to mitochondrial dysfunction.

Mapping the vast landscape of multisystem complications of COVID-19: Bibliometric analysis

Background

With the rapid global spread of COVID-19, it has become evident that the virus can lead to multisystem complications, leading to a significant increase in related publications. Bibliometrics serves as a valuable tool for identifying highly cited literature and research hotspots within specific areas.

Objective

The aim of this study is to identify current research hotspots and future trends in COVID-19 complications.

Methods

The dataset was obtained from the Web of Science Core Collection, covering COVID-19 complications from December 8, 2019, to October 31, 2022. Various aspects, including publication general information, authors, journals, co-cited authors, co-cited references, research hotspots, and future trends, were subjected to analysis. Visual analysis was conducted using VOSviewer, The Online Analysis Platform of Literature Metrology, and Charticulator.

Results

There were 4597 articles in the study. The top three countries with the most published articles are the USA (n = 1350, 29.4 %), China (n = 765, 16.6 %), and Italy (n = 623, 13.6 %). USA and China have the closest collaborative relationship. The institute with the largest number of publications is Huazhong University of Science and Technology, followed by Harvard Medical School. Nevertheless, half of the top 10 institutes belong to the USA. "Rezaei, Nima" published 13 articles and ranked first, followed by "Yaghi, Shadi" with 12 articles and "Frontera, Jennifer" with 12 articles. The journal with the largest number of publications is "Journal of Clinical Medicine". The top 3 co-cited authors are "Zhou, Fei", "Guan, Wei-Jie", "Huang, Chaolin". The top 3 co-cited references addressed COVID-19's clinical features in China and noticed that COVID-19 patients had a wide range of complications. We also list four research hotspots.

Conclusions

This study conducted a bibliometric visual analysis of the literature on COVID-19 complications and summarized the current research hotspots. This study may provide valuable insights into the complications of COVID-19.

S100A9: The Unusual Suspect Connecting Viral Infection and Inflammation

The study of S100A9 in viral infections has seen increased interest since the COVID-19 pandemic. S100A8/A9 levels were found to be correlated with the severity of COVID-19 disease, cytokine storm, and changes in myeloid cell subsets. These data led to the hypothesis that S100A8/A9 proteins might play an active role in COVID-19 pathogenesis. This review explores the structures and functions of S100A8/9 and the current knowledge on the involvement of S100A8/A9 and its constituents in viral infections. The potential roles of S100A9 in SARS-CoV-2 infections are also discussed.

Elevated NET, Calprotectin, and Neopterin Levels Discriminate between Disease Activity in COVID-19, as Evidenced by Need for Hospitalization among Patients in Northern Italy

Coronavirus disease 2019 (COVID-19) displays clinical heterogeneity, but little information is available for patients with mild or very early disease. We aimed to characterize biomarkers that are useful for discriminating the hospitalization risk in a COVID-19 cohort from Northern Italy during the first pandemic wave. We enrolled and followed for four weeks 76 symptomatic SARS-CoV-2 positive patients and age/sex-matched healthy controls. Patients with mild disease were discharged (n.42), and the remaining patients were hospitalized (n.34). Blood was collected before any anti-inflammatory/immunosuppressive therapy and assessed for soluble C5b-9/C5a, H3-neutrophil extracellular traps (NETs), calprotectin, and DNase plasma levels via ELISA and a panel of proinflammatory cytokines via ELLA. Calprotectin and NET levels discriminate between hospitalized and non-hospitalized patients, while DNase negatively correlates with NET levels; there are positive correlations between calprotectin and both NET and neopterin levels. Neopterin levels increase in patients at the beginning of the disease and do so more in hospitalized than non-hospitalized patients. C5a and sC5b-9, and other acute phase proteins, correlate with neopterin, calprotectin, and DNase. Both NET and neopterin levels negatively correlate with platelet count. We show that calprotectin, NETs, and neopterin are important proinflammatory parameters potentially useful for discriminating between COVID-19 patients at risk of hospitalization.

When Our Best Friend Becomes Our Worst Enemy: The Mitochondrion in Trauma, Surgery, and Critical Illness

Common for major surgery, multitrauma, sepsis, and critical illness, is a whole-body inflammation. Tissue injury is able to trigger a generalized inflammatory reaction. Cell death causes release of endogenous structures termed damage associated molecular patterns (DAMPs) that initiate a sterile inflammation. Mitochondria are evolutionary endosymbionts originating from bacteria, containing molecular patterns similar to bacteria. These molecular patterns are termed mitochondrial DAMPs (mDAMPs). Mitochondrial debris released into the extracellular space or into the circulation is immunogenic and damaging secondary to activation of the innate immune system. In the circulation, released mDAMPS are either free or exist in extracellular vesicles, being able to act on every organ and cell in the body. However, the role of mDAMPs in trauma and critical care is not fully clarified. There is a complete lack of knowledge how they may be counteracted in patients. Among mDAMPs are mitochondrial DNA, cardiolipin, N-formyl peptides, cytochrome C, adenosine triphosphate, reactive oxygen species, succinate, and mitochondrial transcription factor A. In this overview, we present the different mDAMPs, their function, release, targets, and inflammatory potential. In light of present knowledge, the role of mDAMPs in the pathophysiology of major surgery and trauma as well as sepsis, and critical care is discussed.

Circulating nucleosomes as potential biomarkers for cancer diagnosis and treatment monitoring

Nucleosomes play a crucial role in regulating gene expression through their composition and post-translational modifications. When cells die, intracellular endonucleases are activated and cleave chromatin into oligo- and mono-nucleosomes, which are then released into the body fluids. Studies have shown that the levels of nucleosomes are increased in serum and plasma in various cancer types, suggesting that analysis of circulating nucleosomes can provide an initial assessment of carcinogenesis. However, it should be noted that elevated serum nucleosome levels may not accurately diagnose certain tumor types, as increased cell death may occur in different pathological conditions. Nevertheless, detection of circulating nucleosomes and their histone modifications, along with specific tumor markers, can help diagnose certain types of cancer. Furthermore, monitoring changes in circulating nucleosome levels during chemotherapy or radiotherapy in patients with malignancies can provide valuable insights into clinical outcomes and therapeutic efficacy. The utilization of circulating nucleosomes as biomarkers is an exciting and emerging area of research, with the potential for early detection of various diseases and monitoring of treatment response. Integrating nucleosome-based biomarkers with existing ones may improve the specificity and sensitivity of current assays, offering the possibility of personalized precision medical treatment for patients.

Neutrophil Activity and Extracellular Matrix Degradation: Drivers of Lung Tissue Destruction in Fatal COVID-19 Cases and Implications for Long COVID

Pulmonary fibrosis, severe alveolitis, and the inability to restore alveolar epithelial architecture are primary causes of respiratory failure in fatal COVID-19 cases. However, the factors contributing to abnormal fibrosis in critically ill COVID-19 patients remain unclear. This study analyzed the histopathology of lung specimens from eight COVID-19 and six non-COVID-19 postmortems. We assessed the distribution and changes in extracellular matrix (ECM) proteins, including elastin and collagen, in lung alveoli through morphometric analyses. Our findings reveal the significant degradation of elastin fibers along the thin alveolar walls of the lung parenchyma, a process that precedes the onset of interstitial collagen deposition and widespread intra-alveolar fibrosis. Lungs with collapsed alveoli and organized fibrotic regions showed extensive fragmentation of elastin fibers, accompanied by alveolar epithelial cell death. Immunoblotting of lung autopsy tissue extracts confirmed elastin degradation. Importantly, we found that the loss of elastin was strongly correlated with the induction of neutrophil elastase (NE), a potent protease that degrades ECM. This study affirms the critical role of neutrophils and neutrophil enzymes in the pathogenesis of COVID-19. Consistently, we observed increased staining for peptidyl arginine deiminase, a marker for neutrophil extracellular trap release, and myeloperoxidase, an enzyme-generating reactive oxygen radical, indicating active neutrophil involvement in lung pathology. These findings place neutrophils and elastin degradation at the center of impaired alveolar function and argue that elastolysis and alveolitis trigger abnormal ECM repair and fibrosis in fatal COVID-19 cases. Importantly, this study has implications for severe COVID-19 complications, including long COVID and other chronic inflammatory and fibrotic disorders.

Viewpoint: The value of non-criteria antiphospholipid antibodies

In 2006, at a meeting in Sydney, Australia, consensus was reached by an international group of specialists to establish a number of serological criteria that identify patients with a history of thrombosis or pregnancy complications as having antiphospholipid syndrome (APS). These criteria were originally formulated for research purposes and to compare clinical trials in different centres. However, these same criteria are now generally used and accepted for the diagnosis and treatment of patients. The practice of using these criteria for direct patient care requires that these criteria are based on sound scientific evidence. Indeed, for all the autoantibodies that are officially included in the serological criteria, it has been shown that they induce thrombosis and fetal loss when infused into mice. There are also a number of additional autoantibodies that have been identified in these patients but for these antibodies there was not enough evidence to meet the official APS criteria in 2006. Seventeen years have now passed since the consensus meeting, therefore, this review examines whether additional studies performed with these 'non-criteria' autoantibodies have provided sufficient results to suggest the inclusion of these autoantibodies in the official serological criteria of APS.

Outcomes of COVID-19 patients undergoing extracorporeal membrane oxygenation: A systematic review and meta-Analysis

BACKGROUND

The Coronavirus Disease 2019 (COVID-19) pandemic has been ongoing for over 3 years, during which numerous clinical and experimental studies have been conducted. The objective of this systematic review and meta-analysis was to assess the survival probability and complications of COVID-19 patients receiving extracorporeal membrane oxygenation (ECMO).

METHODS

We searched the databases by using Population-Intervention-Comparison-Outcome-Study Design (PICOS). We conducted a search of the PubMed, Web of Science, and EMBASE databases to retrieve studies published until December 10, 2022. A random-effects meta-analysis, subgroup analysis, and assessed the studies using the Newcastle-Ottawa Scale score. The results were presented as pooled morbidity with 95% confidence intervals.

RESULTS

The study was conducted on 19 studies that enrolled a total of 1494 patients, and the results showed a pooled survival probability of 66.0%. The pooled morbidity for intracranial hemorrhage was 8.7%, intracranial thrombosis 7.0%, pneumothorax 9.0%, pulmonary embolism 11.0%, pulmonary hemorrhage 9.0%, heart failure 14.0%, liver failure 13.0%, renal injury 44.0%, gastrointestinal hemorrhage 6.0%, gastrointestinal ischemia 6.0% and venous thrombosis 31.0%.

CONCLUSION

This systematic review and meta-analysis of observational studies focused on the survival probability and complications of COVID-19 patients undergoing ECMO, which are significant in evaluating the use of ECMO in COVID-19 patients and provide a basis for further research.

TRIAL REGISTRATION

Our study was registered on PROSPERO with registration number CRD42022382555.

Baseline and early changes in laboratory parameters predict disease severity and fatal outcomes in COVID-19 patients

Introduction

Coronavirus disease 2019 (COVID-19) has become the worst catastrophe of the twenty-first century and has led to the death of more than 6.9 million individuals across the globe. Despite the growing knowledge of the clinicopathological features of COVID-19, the correlation between baseline and early changes in the laboratory parameters and the clinical outcomes of patients is not entirely understood.

Methods

Here, we conducted a time series cross-sectional study aimed at assessing different measured parameters and socio-demographic factors that are associated with disease severity and the outcome of the disease in 268 PCR-confirmed COVID-19 Patients.

Results

We found COVID-19 patients who died had a median age of 61 years (IQR, 50 y - 70 y), which is significantly higher (p < 0.05) compared to those who survived and had a median age of 54 years (IQR, 42y - 65y). The median RBC count of COVID-19 survivors was 4.9 × 106/μL (IQR 4.3 × 106/μL - 5.2 × 106/μL) which is higher (p < 0.05) compared to those who died 4.4 × 106/μL (3.82 × 106/μL - 5.02 × 106/μL). Similarly, COVID-19 survivors had significantly (p < 0.05) higher lymphocyte and monocyte percentages compared to those who died. One important result we found was that COVID-19 patients who presented with severe/critical cases at the time of first admission but managed to survive had a lower percentage of neutrophil, neutrophil to lymphocyte ratio, higher lymphocyte and monocyte percentages, and RBC count compared to those who died.

Conclusion

To conclude here, we showed that simple laboratory parameters can be used to predict severity and outcome in COVID-19 patients. As these parameters are simple, inexpensive, and radially available in most resource-limited countries, they can be extrapolated to future viral epidemics or pandemics to allocate resources to particular patients.

Serum Calprotectin as a Potential Predictor of Microvascular Manifestations in Patients with Antiphospholipid Syndrome

INTRODUCTION

Microvascular manifestations constitute a subtype of antiphospholipid syndrome, and those patients have relatively poor prognoses, so it is important to find markers for microvascular manifestations. This study was conducted to explore whether serum calprotectin could be a predictor of microvascular manifestations in antiphospholipid antibody (aPL)-positive patients.

METHODS

Consecutive patients with persistent aPL positivity referred to Peking Union Medical College Hospital and age- and sex-matched health controls (HCs) were included. Microvascular manifestations included antiphospholipid syndrome (APS) nephropathy, livedo reticularis, valvular lesions, non-stroke central nervous system manifestations, myocarditis, catastrophic APS, and other microvascular manifestations confirmed by pathology, imaging, or clinical diagnosis. Calprotectin was measured by an enzyme-linked immunosorbent assay (ELISA). The cutoff value was defined as mean + 2 standard deviations of HCs. Multivariable logistic regression analysis was used to analyze risk factors. Pearson correlation analysis was used to detect the correlation between calprotectin and other laboratory data.

RESULTS

Of the 466 patients included in the study, 281 (60.3%) patients met the 2006 Sydney Revised Classification Criteria; among the latter, 77.2% were patients with primary APS. The mean age was 39.10 ± 13.05 years old, and 77.0% were female. Thirty-eight age- and sex-matched HCs were included in the study. Serum calprotectin levels were increased in aPL-positive patients compared with HCs (649.66 ± 240.79 vs 484.62 ± 149.37 ng/ml, p < 0.001), and were increased in patients with microvascular manifestations compared with patients without (693.03 ± 271.90 vs 639.43 ± 232.06 ng/ml, p = 0.044). The cutoff value was 783.36 ng/ml. Ninety-three patients (20.0%) were positive for calprotectin. Calprotectin positivity was independently associated with microvascular manifestations (odds ratio [OR] 1.90, 95% confidence interval [CI] 1.07-3.36) and platelet count (PLT) < 100 (OR 2.04, 95% CI 1.08-3.88). Age (OR 0.98, 95% CI 0.96-1.00), systemic lupus erythematosus (OR 2.08, 95% CI 1.15-3.75), calprotectin positivity (OR 1.83, 95% CI 1.02-3.26), hypertension (OR 2.73, 95% CI 1.36-5.45), hemolytic anemia (OR 2.66, 95% CI 1.13-6.23), and anti-β2GPI antibodies (OR 2.06, 95% CI 1.11-3.83) could independently predict microvascular manifestations in aPL-positive patients. Serum calprotectin negatively correlated with PLT (R = - 0.101, p = 0.031).

CONCLUSION

Serum calprotectin levels are increased in aPL-positive patients and could be a potential predictor of microvascular manifestations.

Mitochondrial N-formyl methionine peptides contribute to exaggerated neutrophil activation in patients with COVID-19

Neutrophil dysregulation is well established in COVID-19. However, factors contributing to neutrophil activation in COVID-19 are not clear. We assessed if N-formyl methionine (fMet) contributes to neutrophil activation in COVID-19. Elevated levels of calprotectin, neutrophil extracellular traps (NETs) and fMet were observed in COVID-19 patients (n = 68), particularly in critically ill patients, as compared to HC (n = 19, p < 0.0001). Of note, the levels of NETs were higher in ICU patients with COVID-19 than in ICU patients without COVID-19 (p < 0.05), suggesting a prominent contribution of NETs in COVID-19. Additionally, plasma from COVID-19 patients with mild and moderate/severe symptoms induced in vitro neutrophil activation through fMet/FPR1 (formyl peptide receptor-1) dependent mechanisms (p < 0.0001). fMet levels correlated with calprotectin levels validating fMet-mediated neutrophil activation in COVID-19 patients (r = 0.60, p = 0.0007). Our data indicate that fMet is an important factor contributing to neutrophil activation in COVID-19 disease and may represent a potential target for therapeutic intervention.

COVID-19-associated liver injury: Adding fuel to the flame

COVID-19 is mainly characterized by respiratory disorders and progresses to multiple organ involvement in severe cases. With expansion of COVID-19 and SARS-CoV-2 research, correlative liver injury has been revealed. It is speculated that COVID-19 patients exhibited abnormal liver function, as previously observed in the SARS and MERS pandemics. Furthermore, patients with underlying diseases such as chronic liver disease are more susceptible to SARS-CoV-2 and indicate a poor prognosis accompanied by respiratory symptoms, systemic inflammation, or metabolic diseases. Therefore, COVID-19 has the potential to impair liver function, while individuals with preexisting liver disease suffer from much worse infected conditions. COVID-19 related liver injury may be owing to direct cytopathic effect, immune dysfunction, gut-liver axis interaction, and inappropriate medication use. However, discussions on these issues are infancy. Expanding research have revealed that angiotensin converting enzyme 2 (ACE2) expression mediated the combination of virus and target cells, iron metabolism participated in the virus life cycle and the fate of target cells, and amino acid metabolism regulated immune response in the host cells, which are all closely related to liver health. Further exploration holds great significance in elucidating the pathogenesis, facilitating drug development, and advancing clinical treatment of COVID-19-related liver injury. This article provides a review of the clinical and laboratory hepatic characteristics in COVID-19 patients, describes the etiology and impact of liver injury, and discusses potential pathophysiological mechanisms.

NLRP3-Induced NETosis: A Potential Therapeutic Target for Ischemic Thrombotic Diseases?

Ischemic thrombotic disease, characterized by the formation of obstructive blood clots within arteries or veins, is a condition associated with life-threatening events, such as stroke, myocardial infarction, deep vein thrombosis, and pulmonary embolism. The conventional therapeutic strategy relies on treatments with anticoagulants that unfortunately pose an inherent risk of bleeding complications. These anticoagulants primarily target clotting factors, often overlooking upstream events, including the release of neutrophil extracellular traps (NETs). Neutrophils are integral components of the innate immune system, traditionally known for their role in combating pathogens through NET formation. Emerging evidence has now revealed that NETs contribute to a prothrombotic milieu by promoting platelet activation, increasing thrombin generation, and providing a scaffold for clot formation. Additionally, NET components enhance clot stability and resistance to fibrinolysis. Clinical and preclinical studies have underscored the mechanistic involvement of NETs in the pathogenesis of thrombotic complications, since the clots obtained from patients and experimental models consistently exhibit the presence of NETs. Given these insights, the inhibition of NETs or NET formation is emerging as a promising therapeutic approach for ischemic thrombotic diseases. Recent investigations also implicate a role for the nucleotide-binding oligomerization domain (NOD)-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome as a mediator of NETosis and thrombosis, suggesting that NLRP3 inhibition may also hold potential for mitigating thrombotic events. Therefore, future preclinical and clinical studies aimed at identifying and validating NLRP3 inhibition as a novel therapeutic intervention for thrombotic disorders are imperative.

Inflammation and Venous Thromboembolism in Hospitalized Patients with COVID-19

BACKGROUND

A link between inflammation and venous thromboembolism (VTE) in COVID-19 disease has been suggested pathophysiologically and clinically. The aim of this study was to investigate the association between inflammation and disease outcomes in adult hospitalized COVID-19 patients with VTE.

METHODS

This was a retrospective observational study, including quantitative and qualitative data collected from COVID-19 patients hospitalized at the Infectious Diseases Unit (IDU) of the University Hospital of Ioannina, from 1 March 2020 to 31 May 2022. Venous thromboembolism was defined as a diagnosis of pulmonary embolism (PE) and/or vascular tree-in-bud in the lungs. The burden of disease, assessed by computed tomography of the lungs (CTBoD), was quantified as the percentage (%) of the affected lung parenchyma. The study outcomes were defined as death, intubation, and length of hospital stay (LoS). A chi-squared test and univariate logistic regression analyses were performed in IBM SPSS 28.0.

RESULTS

After propensity score matching, the final study cohort included 532 patients. VTE was found in 11.2% of the total population. In patients with VTE, we found that lymphocytopenia and a high neutrophil/lymphocyte ratio were associated with an increased risk of intubation and death, respectively. Similarly, CTBoD > 50% was associated with a higher risk of intubation and death in this group of patients. The triglyceride-glucose (TyG) index was also linked to worse outcomes.

CONCLUSIONS

Inflammatory indices were associated with VTE. Lymphocytopenia and an increased neutrophil-to-lymphocyte ratio negatively impacted the disease's prognosis and outcomes. Whether these indices unfavorably affect outcomes in COVID-19-associated VTE must be further evaluated.

Immunothrombosis and Complement Activation Contribute to Disease Severity and Adverse Outcome in COVID-19

Severe COVID-19 is characterized by systemic inflammation and multiple organ dysfunction syndrome (MODS). Arterial and venous thrombosis are involved in the pathogenesis of MODS and fatality in COVID-19. There is evidence that complement and neutrophil activation in the form of neutrophil extracellular traps are main drivers for development of microvascular complications in COVID-19. Plasma and serum samples were collected from 83 patients infected by SARS-CoV-2 during the two first waves of COVID-19, before the availability of SARS-CoV-2 vaccination. Samples were collected at enrollment, day 11, and day 28; and patients had differing severity of disease. In this comprehensive study, we measured cell-free DNA, neutrophil activation, deoxyribonuclease I activity, complement activation, and D-dimers in longitudinal samples of COVID-19 patients. We show that all the above markers, except deoxyribonuclease I activity, increased with disease severity. Moreover, we provide evidence that in severe disease there is continued neutrophil and complement activation, as well as D-dimer formation and nucleosome release, whereas in mild and moderate disease all these markers decrease over time. These findings suggest that neutrophil and complement activation are important drivers of microvascular complications and that they reflect immunothrombosis in these patients. Neutrophil activation, complement activation, cell-free DNA, and D-dimer levels have the potential to serve as reliable biomarkers for disease severity and fatality in COVID-19. They might also serve as suitable markers with which to monitor the efficacy of therapeutic interventions in COVID-19.

Cell-free DNA reveals distinct pathology of multisystem inflammatory syndrome in children

Multisystem inflammatory syndrome in children (MIS-C) is a rare but life-threatening hyperinflammatory condition induced by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes pediatric COVID-19 (pCOVID-19). The relationship of the systemic tissue injury to the pathophysiology of MIS-C is poorly defined. We leveraged the high sensitivity of epigenomics analyses of plasma cell-free DNA (cfDNA) and plasma cytokine measurements to identify the spectrum of tissue injury and glean mechanistic insights. Compared with pediatric healthy controls (pHCs) and patients with pCOVID-19, patients with MIS-C had higher levels of cfDNA primarily derived from innate immune cells, megakaryocyte-erythroid precursor cells, and nonhematopoietic tissues such as hepatocytes, cardiac myocytes, and kidney cells. Nonhematopoietic tissue cfDNA levels demonstrated significant interindividual variability, consistent with the heterogenous clinical presentation of MIS-C. In contrast, adaptive immune cell-derived cfDNA levels were comparable in MIS-C and pCOVID-19 patients. Indeed, the cfDNA of innate immune cells in patients with MIS-C correlated with the levels of innate immune inflammatory cytokines and nonhematopoietic tissue-derived cfDNA, suggesting a primarily innate immunity-mediated response to account for the multisystem pathology. These data provide insight into the pathogenesis of MIS-C and support the value of cfDNA as a sensitive biomarker to map tissue injury in MIS-C and likely other multiorgan inflammatory conditions.

Inhibition of neutrophil extracellular trap formation alleviates vascular dysfunction in type 1 diabetic mice

While neutrophil extracellular traps (NETs) have previously been linked to some diabetes-associated complications, such as dysfunctional wound healing, their potential role in diabetic vascular dysfunction has not been studied. Diabetic Akita mice were crossed with either Elane-/- or Pad4-/- mice to generate NET-deficient diabetic mice. By 24 weeks of age, Akita aortae showed markedly impaired relaxation in response to acetylcholine, indicative of vascular dysfunction. Both Akita-Elane-/- mice and Akita-Pad4-/- mice had reduced levels of circulating NETs and improved acetylcholine-mediated aortic relaxation. Compared with wild-type aortae, the thromboxane metabolite TXB2 was roughly 10-fold higher in both intact and endothelium-denuded aortae of Akita mice. In contrast, Akita-Elane-/- and Akita-Pad4-/- aortae had TXB2 levels similar to wild type. In summary, inhibition of NETosis by two independent strategies prevented the development of vascular dysfunction in diabetic Akita mice. Thromboxane was up-regulated in the vessel walls of NETosis-competent diabetic mice, suggesting a role for neutrophils in driving the production of this vasoconstrictive and atherogenic prostanoid.

Effects of inflammation on thrombosis and outcomes in COVID-19: secondary analysis of the ATTACC/ACTIV-4a trial

Background

Patients hospitalized for COVID-19 are at high risk of thrombotic complications and organ failure, and often exhibit severe inflammation, which may contribute to hypercoagulability.

Objectives

To determine whether patients hospitalized for COVID-19 experience differing frequencies of thrombotic and organ failure complications and derive variable benefits from therapeutic-dose heparin dependent on the extent of systemic inflammation and whether observed benefit from therapeutic-dose anticoagulation varies depending on the degree of systemic inflammation.

Methods

We analyzed data from 1346 patients hospitalized for COVID-19 enrolled in the ATTACC and ACTIV-4a platforms who were randomized to therapeutic-dose heparin or usual care for whom levels of C-reactive protein (CRP) were reported at baseline.

Results

Increased CRP was associated with worse patient outcomes, including a >98% posterior probability of increased organ support requirement, hospital length of stay, risk of 28-day mortality, and incidence of major thrombotic events or death (patients with CRP 40-100 mg/L or ≥100 mg/L compared to patients with CRP <40 mg/L). Patients with CRP 40 to 100 mg/L experienced the greatest degree of benefit from treatment with therapeutic doses of unfractionated or low molecular weight heparin compared with usual-care prophylactic doses. This was most significant for an increase in organ support-free days (odds ratio: 1.63; 95% confidence interval, 1.09-2.40; 97.9% posterior probability of beneficial effect), with trends toward benefit for other evaluated outcomes.

Conclusion

Moderately ill patients hospitalized for COVID-19 with CRP between 40 mg/L and 100 mg/L derived the greatest benefit from treatment with therapeutic-dose heparin.

Endotheliitis and cytokine storm as a mechanism of clot formation in COVID-19 ischemic stroke patients: A histopathologic study of retrieved clots

BACKGROUND

Studies during the COVID-19 pandemic have demonstrated an association between COVID-19 virus infection and the development of acute ischemic stroke, particularly large vessel occlusion (LVO). Studying the characteristics and immunohistochemistry of retrieved stroke emboli during mechanical thrombectomy for LVO may offer insights into the pathogenesis of LVO in COVID-19 patients. We examined retrieved COVID-19 emboli from the STRIP, EXCELLENT, and RESTORE registries and compared their characteristics to a control group.

METHODS

We identified COVID-positive LVO patients from the STRIP, RESTORE, and EXCELLENT studies who underwent mechanical thrombectomy. These patients were matched to a control group controlling for stroke etiology based on Trial of Org 10172 in Acute Stroke Treatment criteria. All clots were stained with Martius Scarlet Blue (MSB) along with immunohistochemistry for interleukin-6 (IL-6), C-reactive protein (CRP), von Willebrand factor (vWF), CD66b, fibrinogen, and citrullinated Histone H3. Clot composition was compared between groups.

RESULTS

Nineteen COVID-19-positive patients and 38 controls were included. COVID-19-positive patients had a significantly higher percentage of CRP and vWF. There was no difference in IL-6, fibrin, CD66b, or citrullinated Histone H3 between groups. Based on MSB staining, there was no statistically significant difference regarding the percentage of red blood cells, white blood cells, fibrin, and platelets.

CONCLUSIONS

Our study found higher concentrations of CRP and vWF in retrieved clots of COVID-19-positive stroke patients compared to COVID-19-negative controls. These findings support the potential role of systemic inflammation as indicated by elevated CRP and endothelial injury as indicated by elevated vWF as precipitating factors in thrombus development in these patients.

Ginger intake suppresses neutrophil extracellular trap formation in autoimmune mice and healthy humans

We previously reported that treatment of mice with 6-gingerol, the most abundant phytochemical in ginger root, leads to phosphodiesterase inhibition that counteracts neutrophil hyperactivity in models of antiphospholipid syndrome (APS) and lupus. Here, we explored the extent to which oral intake of a whole-ginger extract would similarly impact neutrophils in both autoimmune mice and healthy humans. In vitro, a solubilized ginger extract was able to attenuate neutrophil extracellular trap formation (NETosis) by human neutrophils through a mechanism that was dependent upon the cyclic AMP-dependent kinase, protein kinase A. When mice with features of either APS or lupus were administered a ginger extract orally, they demonstrated reduced circulating NETs, as well as the tempering of other disease outcomes, such as large-vein thrombosis (APS) and autoantibody production (lupus). In a pilot clinical trial, which was validated in a second cohort, daily intake of a ginger supplement for 7 days by healthy volunteers boosted neutrophil cAMP, inhibited NETosis in response to disease-relevant stimuli, and reduced circulating plasma NET levels. In summary, this work demonstrates that ginger intake restrains neutrophil hyperactivity in autoimmune mouse models and that ginger consumption by healthy individuals makes their neutrophils more resistant to NETosis.

The Diagnostic, Prognostic, and Therapeutic Potential of Cell-Free DNA with a Special Focus on COVID-19 and Other Viral Infections

Cell-free DNA (cfDNA) in human blood serum, urine, and other body fluids recently became a commonly used diagnostic marker associated with various pathologies. This is because cfDNA enables a much higher sensitivity than standard biochemical parameters. The presence of and/or increased level of cfDNA has been reported for various diseases, including viral infections, including COVID-19. Here, we review cfDNA in general, how it has been identified, where it can derive from, its molecular features, and mechanisms of release and clearance. General suitability of cfDNA for diagnostic questions, possible shortcomings and future directions are discussed, with a special focus on coronavirus infection.

NLRP3 inflammasome and interleukin-1 contributions to COVID-19-associated coagulopathy and immunothrombosis

Immunothrombosis-immune-mediated activation of coagulation-is protective against pathogens, but excessive immunothrombosis can result in pathological thrombosis and multiorgan damage, as in severe coronavirus disease 2019 (COVID-19). The NACHT-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome produces major proinflammatory cytokines of the interleukin (IL)-1 family, IL-1β and IL-18, and induces pyroptotic cell death. Activation of the NLRP3 inflammasome pathway also promotes immunothrombotic programs including release of neutrophil extracellular traps and tissue factor by leukocytes, and prothrombotic responses by platelets and the vascular endothelium. NLRP3 inflammasome activation occurs in patients with COVID-19 pneumonia. In preclinical models, NLRP3 inflammasome pathway blockade restrains COVID-19-like hyperinflammation and pathology. Anakinra, recombinant human IL-1 receptor antagonist, showed safety and efficacy and is approved for the treatment of hypoxaemic COVID-19 patients with early signs of hyperinflammation. The non-selective NLRP3 inhibitor colchicine reduced hospitalization and death in a subgroup of COVID-19 outpatients but is not approved for the treatment of COVID-19. Additional COVID-19 trials testing NLRP3 inflammasome pathway blockers are inconclusive or ongoing. We herein outline the contribution of immunothrombosis to COVID-19-associated coagulopathy, and review preclinical and clinical evidence suggesting an engagement of the NLRP3 inflammasome pathway in the immunothrombotic pathogenesis of COVID-19. We also summarize current efforts to target the NLRP3 inflammasome pathway in COVID-19, and discuss challenges, unmet gaps, and the therapeutic potential that inflammasome-targeted strategies may provide for inflammation-driven thrombotic disorders including COVID-19.

NETosis induction reflects COVID-19 severity and long COVID: insights from a 2-center patient cohort study in Israel

BACKGROUND

COVID-19 severity and its late complications continue to be poorly understood. Neutrophil extracellular traps (NETs) form in acute COVID-19, likely contributing to morbidity and mortality.

OBJECTIVES

This study evaluated immunothrombosis markers in a comprehensive cohort of acute and recovered COVID-19 patients, including the association of NETs with long COVID.

METHODS

One-hundred-seventy-seven patients were recruited from clinical cohorts at 2 Israeli centers: acute COVID-19 (mild/moderate, severe/critical), convalescent COVID-19 (recovered and long COVID), along with 54 non-COVID controls. Plasma was examined for markers of platelet activation, coagulation, and NETs. Ex vivo NETosis induction capability was evaluated after neutrophil incubation with patient plasma.

RESULTS

Soluble P-selectin, factor VIII, von Willebrand factor, and platelet factor 4 were significantly elevated in patients with COVID-19 versus controls. Myeloperoxidase (MPO)-DNA complex levels were increased only in severe COVID-19 and did not differentiate between COVID-19 severities or correlate with thrombotic markers. NETosis induction levels strongly correlated with illness severity/duration, platelet activation markers, and coagulation factors, and were significantly reduced upon dexamethasone treatment and recovery. Patients with long COVID maintained higher NETosis induction, but not NET fragments, compared to recovered convalescent patients.

CONCLUSIONS

Increased NETosis induction can be detected in patients with long COVID. NETosis induction appears to be a more sensitive NET measurement than MPO-DNA levels in COVID-19, differentiating between disease severity and patients with long COVID. Ongoing NETosis induction capability in long COVID may provide insights into pathogenesis and serve as a surrogate marker for persistent pathology. This study emphasizes the need to explore neutrophil-targeted therapies in acute and chronic COVID-19.

Neutrophil extracellular traps mediate deep vein thrombosis: from mechanism to therapy

Deep venous thrombosis (DVT) is a part of venous thromboembolism (VTE) that clinically manifests as swelling and pain in the lower limbs. The most serious clinical complication of DVT is pulmonary embolism (PE), which has a high mortality rate. To date, its underlying mechanisms are not fully understood, and patients usually present with clinical symptoms only after the formation of the thrombus. Thus, it is essential to understand the underlying mechanisms of deep vein thrombosis for an early diagnosis and treatment of DVT. In recent years, many studies have concluded that Neutrophil Extracellular Traps (NETs) are closely associated with DVT. These are released by neutrophils and, in addition to trapping pathogens, can mediate the formation of deep vein thrombi, thereby blocking blood vessels and leading to the development of disease. Therefore, this paper describes the occurrence and development of NETs and discusses the mechanism of action of NETs on deep vein thrombosis. It aims to provide a direction for improved diagnosis and treatment of deep vein thrombosis in the near future.

SARS-CoV-2 Spike Proteins and Cell-Cell Communication Induce P-Selectin and Markers of Endothelial Injury, NETosis, and Inflammation in Human Lung Microvascular Endothelial Cells and Neutrophils: Implications for the Pathogenesis of COVID-19 Coagulopathy

COVID-19 progression often involves severe lung injury, inflammation, coagulopathy, and leukocyte infiltration into pulmonary tissues. The pathogenesis of these complications is unknown. Because vascular endothelium and neutrophils express angiotensin-converting enzyme-2 and spike (S)-proteins, which are present in bodily fluids and tissues of SARS-CoV-2-infected patients, we investigated the effect of S-proteins and cell-cell communication on human lung microvascular endothelial cells and neutrophils expression of P-selectin, markers of coagulopathy, NETosis, and inflammation. Exposure of endothelial cells or neutrophils to S-proteins and endothelial-neutrophils co-culture induced P-selectin transcription and expression, significantly increased expression/secretion of IL-6, von Willebrand factor (vWF, pro-coagulant), and citrullinated histone H3 (cit-H3, NETosis marker). Compared to the SARS-CoV-2 Wuhan variant, Delta variant S-proteins induced 1.4-15-fold higher P-selectin and higher IL-6 and vWF. Recombinant tissue factor pathway inhibitor (rTFPI), 5,5'-dithio-bis-(2-nitrobenzoic acid) (thiol blocker), and thrombomodulin (anticoagulant) blocked S-protein-induced vWF, IL-6, and cit-H3. This suggests that following SARS-CoV-2 contact with the pulmonary endothelium or neutrophils and endothelial-neutrophil interactions, S-proteins increase adhesion molecules, induce endothelial injury, inflammation, NETosis and coagulopathy via the tissue factor pathway, mechanisms involving functional thiol groups, and/or the fibrinolysis system. Using rTFPI, effectors of the fibrinolysis system and/or thiol-based drugs could be viable therapeutic strategies against SARS-CoV-2-induced endothelial injury, inflammation, NETosis, and coagulopathy.

Neutrophil extracellular traps contributing to atherosclerosis: From pathophysiology to clinical implications

Neutrophil extracellular traps (NETs) are network-like structures of chromatin filaments decorated by histones, granules, and cytoplasmic-derived proteins expelled by activated neutrophils under multiple pathogenic conditions. NETs not only capture pathogens in innate immunity but also respond to sterile inflammatory stimuli in atherosclerosis, such as lipoproteins and inflammatory cytokines. Atherosclerosis is a lipid-driven chronic inflammatory disease characterized by the accumulation and transformation of inflammatory cells, and smooth muscle cells in the intimal space. NETs-derived extracellular components possess toxic and proinflammatory properties leading to cellular dysfunction and tissue damage, which may establish a link among lipid metabolism, inflammatory immunity, and atherosclerosis. In this review, we discuss recent advances regarding the role of NETs engaged in the pathogenesis of atherosclerosis, particularly focusing on the interaction with lipids and inflammasomes, crosstalk with smooth muscle cells and inflammatory cells, and the association with aging. We also evaluate the current knowledge on the potential of NETs as biomarkers and therapeutic targets for atherosclerosis and its related diseases in clinical practice.

Post-acute sequelae of COVID-19: understanding and addressing the burden of multisystem manifestations

Individuals with SARS-CoV-2 infection can develop symptoms that persist well beyond the acute phase of COVID-19 or emerge after the acute phase, lasting for weeks or months after the initial acute illness. The post-acute sequelae of COVID-19, which include physical, cognitive, and mental health impairments, are known collectively as long COVID or post-COVID-19 condition. The substantial burden of this multisystem condition is felt at individual, health-care system, and socioeconomic levels, on an unprecedented scale. Survivors of COVID-19-related critical illness are at risk of the well known sequelae of acute respiratory distress syndrome, sepsis, and chronic critical illness, and these multidimensional morbidities might be difficult to differentiate from the specific effects of SARS-CoV-2 and COVID-19. We provide an overview of the manifestations of post-COVID-19 condition after critical illness in adults. We explore the effects on various organ systems, describe potential pathophysiological mechanisms, and consider the challenges of providing clinical care and support for survivors of critical illness with multisystem manifestations. Research is needed to reduce the incidence of post-acute sequelae of COVID-19-related critical illness and to optimise therapeutic and rehabilitative care and support for patients.

Extracellular histone proteins activate P2XR7 channel current

Extracellular histone proteins are elevated in circulation after injury or activation of the innate immune response. In resistance-size arteries, extracellular histone proteins increased endothelial cell (EC) Ca2+ influx and propidium iodide (PI) labeling, but paradoxically decreased vasodilation. These observations could be explained by the activation of an EC resident non-selective cation channel. We tested the hypothesis that the ionotropic purinergic receptor 7 (P2XR7), a non-selective cation channel associated with cationic dye uptake, is activated by histone proteins. We expressed mouse P2XR7 (C57BL/6J variant 451L) in heterologous cells and measured inward cation current using two-electrode voltage clamp (TEVC). Cells expressing mouse P2XR7 had robust ATP- and histone-evoked inward cation currents. ATP- and histone-evoked currents reversed approximately at the same potential. Current decay with agonist removal was slower for histone-evoked than ATP- or BzATP-evoked currents. As with ATP-evoked P2XR7 currents, histone-evoked currents were inhibited by non-selective P2XR7 antagonists (Suramin, PPADS, and TNP-ATP). Selective P2XR7 antagonists, AZ10606120, A438079, GW791343, and AZ11645373, inhibited ATP-evoked P2XR7 currents but did not inhibit histone-evoked P2XR7 currents. As previously reported with ATP-evoked currents, histone-evoked P2XR7 currents were also increased in conditions of low extracellular Ca2+. These data demonstrate that P2XR7 is necessary and sufficient for histone-evoked inward cation currents in a heterologous expression system. These results provide insight into a new allosteric mechanism of P2XR7 activation by histone proteins.

DNase analysed by a novel competitive assay in patients with complications after ChAdOx1 nCoV-19 vaccination and in normal unvaccinated blood donors

Increased levels of neutrophil extracellular traps (NETs) have been detected in individuals with vaccine complications after the ChAdOx1 nCov vaccine with a correlation between the severity of vaccine side effects and the level of NETosis. DNases may disrupt NETs by degrading their content of DNA, and a balance has been reported between NETs and DNases. Because of this and since the inflammatory marker NETs may be used as a confirmatory test in diagnosing VITT, it is of interest to monitor levels of DNase in patients with increased NETs levels. The current novel rapid DNase ELISA was tested in blood samples of patients with known increased levels of NETs with or without VITT after ChAdOx1 nCoV-19 vaccination. DNase levels in VITT patients were significantly increased compared with normal unvaccinated blood donors and compared with patients with post-vaccination symptoms but not VITT. However, since EDTA was found to inhibit DNase, serum and not EDTA-plasma samples should be applied for DNase testing. The novel DNase assay may serve as a supplementary test to the NETs test when analysing samples from patients with suspected increased NETs levels.

Alpha-1-antitrypsin antagonizes COVID-19: a review of the epidemiology, molecular mechanisms, and clinical evidence

Alpha-1-antitrypsin (AAT), a serine protease inhibitor (serpin), is increasingly recognized to inhibit SARS-CoV-2 infection and counter many of the pathogenic mechanisms of COVID-19. Herein, we reviewed the epidemiologic evidence, the molecular mechanisms, and the clinical evidence that support this paradigm. As background to our discussion, we first examined the basic mechanism of SARS-CoV-2 infection and contend that despite the availability of vaccines and anti-viral agents, COVID-19 remains problematic due to viral evolution. We next underscored that measures to prevent severe COVID-19 currently exists but teeters on a balance and that current treatment for severe COVID-19 remains grossly suboptimal. We then reviewed the epidemiologic and clinical evidence that AAT deficiency increases risk of COVID-19 infection and of more severe disease, and the experimental evidence that AAT inhibits cell surface transmembrane protease 2 (TMPRSS2) - a host serine protease required for SARS-CoV-2 entry into cells - and that this inhibition may be augmented by heparin. We also elaborated on the panoply of other activities of AAT (and heparin) that could mitigate severity of COVID-19. Finally, we evaluated the available clinical evidence for AAT treatment of COVID-19.

Coagulopathy and thromboembolic events a pathogenic mechanism of COVID-19 associated with mortality: An updated review

During 2019, the SARS-CoV-2 emerged from China, and during months, COVID-19 spread in many countries around the world. The expanding data about pathogenesis of this virus could elucidate the exact mechanism by which COVID-19 caused death in humans. One of the pathogenic mechanisms of this disease is coagulation. Coagulation disorders that affect both venous and arterial systems occur in patients with COVID-19. The possible mechanism involved in the coagulation could be excessive inflammation induced by SARS-CoV-2. However, it is not yet clear well how SARS-CoV-2 promotes coagulopathy. However, some factors, such as pulmonary endothelial cell damage and some anticoagulant system disorders, are assumed to have an important role. In this study, we assessed conducted studies about COVID-19-induced coagulopathy to obtain clearer vision of the wide range of manifestations and possible pathogenesis mechanisms.

Clinicopathologic Analysis of COVID‐19 Associated Thrombi in the Setting of Large Vessel Occlusion: A Prospective Case–Control Study

BACKGROUND

Acute ischemic stroke secondary to large vessel occlusion is among the most serious complications associated with COVID‐19 infection resulting in worse morbidity and mortality. We sought to study the association between COVID‐19 infection and large vessel occlusion thrombus pathology to better define the etiopathogenesis of this atypical cause of stroke.

METHODS

Thrombi were collected during mechanical thrombectomy and stained using hematoxylin and eosin. Blinded analysis of pathology was prospectively performed by a board‐certified neuropathologist. Red blood cell, fibrin, and white blood cell predominance was ascertained. Concomitant peripheral blood counts and clinical and imaging data were collected and analyzed. All samples underwent performance of reverse transcription polymerase chain reaction for SARS‐CoV2.

RESULTS

Between January 2020 and February 2022, a total of 952 acute ischemic stroke admissions were seen at the University Medical Center of El Paso, TX. Of these, 195 patients (20.5%) had large vessel occlusions and underwent mechanical thrombectomy and 53 patients had thrombus collected and analyzed. Seven patients (3.6%) tested positive for SARS‐CoV2. COVID‐19 positive patients were more likely to be younger (mean 57.4 years; P =0.07), male (85.7%; P =0.03), and have red blood cell predominant thrombi (85.7%; P =0.03). There was a statistically significant association between peripheral neutrophil count and white blood cell lysis in the overall cohort ( P =0.015), who did not differ according to COVID‐19 status.

CONCLUSION

Thrombi retrieved from patients who were COVID‐19 positive and had stroke demonstrated red blood cell predominance. This finding requires further investigation using appropriate immunohistochemical techniques in a larger cohort of patients.

Immune mechanisms underlying COVID-19 pathology and post-acute sequelae of SARS-CoV-2 infection (PASC)

With a global tally of more than 500 million cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections to date, there are growing concerns about the post-acute sequelae of SARS-CoV-2 infection (PASC), also known as long COVID. Recent studies suggest that exaggerated immune responses are key determinants of the severity and outcomes of the initial SARS-CoV-2 infection as well as subsequent PASC. The complexity of the innate and adaptive immune responses in the acute and post-acute period requires in-depth mechanistic analyses to identify specific molecular signals as well as specific immune cell populations which promote PASC pathogenesis. In this review, we examine the current literature on mechanisms of immune dysregulation in severe COVID-19 and the limited emerging data on the immunopathology of PASC. While the acute and post-acute phases may share some parallel mechanisms of immunopathology, it is likely that PASC immunopathology is quite distinct and heterogeneous, thus requiring large-scale longitudinal analyses in patients with and without PASC after an acute SARS-CoV-2 infection. By outlining the knowledge gaps in the immunopathology of PASC, we hope to provide avenues for novel research directions that will ultimately lead to precision therapies which restore healthy immune function in PASC patients.

A Post-Pandemic Enigma: The Cardiovascular Impact of Post-Acute Sequelae of SARS-CoV-2

COVID-19 has become the first modern-day pandemic of historic proportion, affecting >600 million individuals worldwide and causing >6.5 million deaths. While acute infection has had devastating consequences, postacute sequelae of SARS-CoV-2 infection appears to be a pandemic of its own, impacting up to one-third of survivors and often causing symptoms suggestive of cardiovascular phenomena. This review will highlight the suspected pathophysiology of postacute sequelae of SARS-CoV-2, its influence on the cardiovascular system, and potential treatment strategies.

Mesenchymal stromal cells and alpha-1 antitrypsin have a strong synergy in modulating inflammation and its resolution

Rationale: Trauma, surgery, and infection can cause severe inflammation. Both dysregulated inflammation intensity and duration can lead to significant tissue injuries, organ dysfunction, mortality, and morbidity. Anti-inflammatory drugs such as steroids and immunosuppressants can dampen inflammation intensity, but they derail inflammation resolution, compromise normal immunity, and have significant adverse effects. The natural inflammation regulator mesenchymal stromal cells (MSCs) have high therapeutic potential because of their unique capabilities to mitigate inflammation intensity, enhance normal immunity, and accelerate inflammation resolution and tissue healing. Furthermore, clinical studies have shown that MSCs are safe and effective. However, they are not potent enough, alone, to completely resolve severe inflammation and injuries. One approach to boost the potency of MSCs is to combine them with synergistic agents. We hypothesized that alpha-1 antitrypsin (A1AT), a plasma protein used clinically and has an excellent safety profile, was a promising candidate for synergism. Methods: This investigation examined the efficacy and synergy of MSCs and A1AT to mitigate inflammation and promote resolution, using in vitro inflammatory assay and in vivo mouse acute lung injury model. The in vitro assay measured cytokine releases, inflammatory pathways, reactive oxygen species (ROS), and neutrophil extracellular traps (NETs) production by neutrophils and phagocytosis in different immune cell lines. The in vivo model monitored inflammation resolution, tissue healing, and animal survival. Results: We found that the combination of MSCs and A1AT was much more effective than each component alone in i) modulating cytokine releases and inflammatory pathways, ii) inhibiting ROS and NETs production by neutrophils, iii) enhancing phagocytosis and, iv) promoting inflammation resolution, tissue healing, and animal survival. Conclusion: These results support the combined use of MSCs, and A1AT is a promising approach for managing severe, acute inflammation.

Xuanfei Baidu Decoction regulates NETs formation via CXCL2/CXCR2 signaling pathway that is involved in acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are life-threatening symptoms in Coronavirus Disease 2019 (COVID-19) patients. Xuanfei Baidu Decoction (XFBD) is a recommend first-line traditional Chinese medicine (TCM) formula therapeutic strategy for COVID-19 patients. Prior studies demonstrated the pharmacological roles and mechanisms of XFBD and its derived effective components against inflammation and infections through multiple model systems, which provided the biological explanations for its clinical use. Our previous work revealed that XFBD inhibited macrophages and neutrophils infiltration via PD-1/IL17A signaling pathway. However, the subsequent biological processes are not well elucidated. Here, we proposed a hypothesis that XFBD can regulate the neutrophils-mediated immune responses, including neutrophil extracellular traps (NETs) formation and the generation of platelet-neutrophil aggregates (PNAs) after XFBD administration in lipopolysaccharide (LPS)-induced ALI mice. The mechanism behind it was also firstly explained, that is XFBD regulated NETs formation via CXCL2/CXCR2 axis. Altogether, our findings demonstrated the sequential immune responses of XFBD after inhibiting neutrophils infiltration, as well as shedding light on exploiting the therapy of XFBD targeting neutrophils to ameliorate ALI during the clinical course.

Heparin, Low Molecular Weight Heparin, and Non-Anticoagulant Derivatives for the Treatment of Inflammatory Lung Disease

Unfractionated heparin has multiple pharmacological activities beyond anticoagulation. These anti-inflammatory, anti-microbial, and mucoactive activities are shared in part by low molecular weight and non-anticoagulant heparin derivatives. Anti-inflammatory activities include inhibition of chemokine activity and cytokine synthesis, inhibitory effects on the mechanisms of adhesion and diapedesis involved in neutrophil recruitment, inhibition of heparanase activity, inhibition of the proteases of the coagulation and complement cascades, inhibition of neutrophil elastase activity, neutralisation of toxic basic histones, and inhibition of HMGB1 activity. This review considers the potential for heparin and its derivatives to treat inflammatory lung disease, including COVID-19, ALI, ARDS, cystic fibrosis, asthma, and COPD via the inhaled route.