Microvascular thrombosis: experimental and clinical implications

Coronary artery bypass grafting (CABG) induces pro-inflammatory and immunomodulatory phenotype of platelets in the absence of a pro-aggregatory state

BACKGROUND

Coronary artery bypass grafting (CABG) is considered the choice treatment for patients suffering from coronary artery disease (CAD). In the inflammatory milieu of cardiopulmonary bypass (CPB), systemic inflammatory response syndrome (SIRS) can induce a platelet pro-inflammatory state which could exacerbate post-CABG inflammatory status while affecting hemostatic function in patients. Therefore, focusing on platelets, the study presented here attempted to evaluate the pro-inflammatory and immunomodulatory profile of platelets as well as pro-aggregatory status during CABG.

METHODS

Platelets from patients undergoing CABG were subjected to flowcytometry analysis to evaluate P-selectin and CD40L expressions and PAC-1 binding in five intervals of 24 h before surgery, immediately, 2 h, 24 h, and one week after surgery. Moreover, intra-platelet TGF-β1 was also examined with western blotting.

RESULTS

Data showed increases of P-selectin and CD40L expressions in patients, with the meaningful loss of platelet contents of TGF-β1 after CABG (p < 0.001), where the changes tended to recover by day 7 of surgery while remaining above baseline (p < 0.001). Meanwhile, no significant change in PAC-1 binding capacity was shown.

CONCLUSION

The study presented here suggests that although the release of pro-inflammatory substances from platelets during CABG supports the post-operative inflammatory state, platelets are not pro-aggregatory enough to enhance thrombotic events after surgery. Whilst these observations could be due to successful medical interventions to optimize hemostasis during and after surgery, post-CABG reversal of anticoagulant by protamine is considered as another factor that may also have contributed to preventing pro-aggregatory but not pro-inflammatory and immunomodulatory functions of platelets.

Trauma diagnostic-related target proteins and their detection techniques

Trauma is a significant health issue that not only leads to immediate death in many cases but also causes severe complications, such as sepsis, thrombosis, haemorrhage, acute respiratory distress syndrome and traumatic brain injury, among trauma patients. Target protein identification technology is a vital technique in the field of biomedical research, enabling the study of biomolecular interactions, drug discovery and disease treatment. It plays a crucial role in identifying key protein targets associated with specific diseases or biological processes, facilitating further research, drug design and the development of treatment strategies. The application of target protein technology in biomarker detection enables the timely identification of newly emerging infections and complications in trauma patients, facilitating expeditious medical interventions and leading to reduced post-trauma mortality rates and improved patient prognoses. This review provides an overview of the current applications of target protein identification technology in trauma-related complications and provides a brief overview of the current target protein identification technology, with the aim of reducing post-trauma mortality, improving diagnostic efficiency and prognostic outcomes for patients.

Fundamental considerations for designing endothelialized in vitro models of thrombosis

Endothelialized in vitro models for cardiovascular disease have contributed greatly to our current understanding of the complex molecular mechanisms underlying thrombosis. To further elucidate these mechanisms, it is important to consider which fundamental aspects to incorporate into an in vitro model. In this review, we will focus on the design of in vitro endothelialized models of thrombosis. Expanding our understanding of the relation and interplay between the different pathways involved will rely in part on complex models that incorporate endothelial cells, blood, the extracellular matrix, and flow. Importantly, the use of tissue-specific endothelial cells will help in understanding the heterogeneity in thrombotic responses between different vascular beds. The dynamic and complex responses of endothelial cells to different shear rates underlines the importance of incorporating appropriate shear in in vitro models. Alterations in vascular extracellular matrix composition, availability of bioactive molecules, and gradients in concentration and composition of these molecules can all regulate the function of both endothelial cells and perivascular cells. Factors modulating these elements in in vitro models should therefore be considered carefully depending on the research question at hand. As the complexity of in vitro models increases, so can the variability. A bottom-up approach to designing such models will remain an important tool for researchers studying thrombosis. As new techniques are continuously being developed and new pathways are brought to light, research question-dependent considerations will have to be made regarding what aspects of thrombosis to include in in vitro models.

Severe ischaemic colitis secondary to microvenular thrombosis in a hypercoagulable patient

A young patient with multifactorial prothrombotic risk factors presented with signs and symptoms of ischaemic colitis, without evidence of bowel hypoperfusion on imaging. She deteriorated with trial of conservative management and required operative management. Intraoperative findings demonstrated severe, confluent large bowel necrosis, sparing the rectum. A total colectomy was performed, with return to intensive care unit due to intraoperative hemodynamic instability. A return to theatre the following day allowed for formation of ileostomy and definitive closure. Histopathological findings of microvenular thrombosis were confirmed. Venous causes of ischaemic colitis present diagnostic challenges due to variable presentation and imaging findings. Microvascular venous thrombosis is likely secondary to multifactorial prothrombotic risk factors including positive autoantibodies and variable compliance with warfarin therapy for aortic value replacement. We present this case of ischemic colitis secondary to an unusual aetiology to emphasize the need to remain clinically suspicious of severe abdominal pain despite relatively benign imaging findings.

Piezoelectric and Triboelectric Nanogenerators for Enhanced Wound Healing

Wound healing is a highly orchestrated biological process characterized by sequential phases involving inflammation, proliferation, and tissue remodeling, and the role of endogenous electrical signals in regulating these phases has been highlighted. Recently, external electrostimulation has been shown to enhance these processes by promoting cell migration, extracellular matrix formation, and growth factor release while suppressing pro-inflammatory signals and reducing the risk of infection. Among the innovative approaches, piezoelectric and triboelectric nanogenerators have emerged as the next generation of flexible and wireless electronics designed for energy harvesting and efficiently converting mechanical energy into electrical power. In this review, we discuss recent advances in the emerging field of nanogenerators for harnessing electrical stimulation to accelerate wound healing. We elucidate the fundamental mechanisms of wound healing and relevant bioelectric physiology, as well as the principles underlying each nanogenerator technology, and review their preclinical applications. In addition, we address the prominent challenges and outline the future prospects for this emerging era of electrical wound-healing devices.

Postoperative Bloodstream Infection Is Associated with Early Vascular Complications in Pediatric Liver Transplant Recipients with Biliary Atresia

Bloodstream infection (BSI) after pediatric liver transplantation (PLT) is a common and severe complication that affects patient survival. Children with biliary atresia (BA) are at an increased risk for clinically significant infections. This study evaluated the impact of post-PLT BSI on clinical outcomes in children with BA. A total of 67 patients with BA aged <18 years who underwent PLT between April 2006 and September 2020 were analyzed and divided into two groups according to the occurrence of post-PLT BSI within 1 month (BSI vs. no BSI = 13 [19.4%] vs. 54 [80.6%]). The BSI group was significantly younger at the time of PLT and had a higher frequency of BSI at the time of PLT than the no BSI group. Early vascular complications within 3 months and reoperations were significantly more frequent in the BSI group. Univariate and multivariate analyses revealed that bacteremia within 1 month of PLT and graft-to-recipient weight ratio >4% were significantly associated with vascular complications. In conclusion, BSI after PLT is associated with increased vascular complications and reoperations. Proper control of bacterial infections and early liver transplantation before uncontrolled BSI may reduce vascular complications and unexpected reoperations in children with BA.

Citrulline, Intestinal Fatty Acid-Binding Protein and the Acute Gastrointestinal Injury Score as Predictors of Gastrointestinal Failure in Patients with Sepsis and Septic Shock

Gastrointestinal (GI) failure can be both a cause of sepsis and a consequence of the systemic pro-inflammatory response in sepsis. Changes in biomarkers of enterocyte damage, citrulline and I-FABP (intestinal fatty acid binding protein), may indicate altered intestinal permeability and damage. The study group consisted of patients with sepsis (N = 28) and septic shock (N = 30); the control group included patients without infection (N = 10). Blood samples were collected for citrulline and I-FABP and a 4-point AGI score (acute GI injury score) was calculated to monitor GI function on days 1, 3, 5, 7, and 10. Citrulline concentrations in the study group were lower than in the control. Lower values were also noted in septic patients with shock when compared to the non-shock group throughout the study period. I-FABP was higher in the septic shock group than in the sepsis group only on days 1 and 3. Citrulline was lower in patients with GI failure (AGI III) when compared to AGI I/II, reaching significance on days 7 (p = 0.034) and 10 (p = 0.015); moreover, a higher AGI score was associated with an increased 28 day mortality (p = 0.038). The results indicate that citrulline measurements, along with the AGI assessment, have clinical potential in monitoring GI function and integrity in sepsis.

Role of antimicrobial peptide cathelicidin in thrombosis and thromboinflammation

Thrombosis is a frequent cause of cardiovascular mortality and hospitalization. Current antithrombotic strategies, however, target both thrombosis and physiological hemostasis and thereby increase bleeding risk. In recent years the pathophysiological understanding of thrombus formation has significantly advanced and inflammation has become a crucial element. Neutrophils as most frequent immune cells in the blood and their released mediators play a key role herein. Neutrophil-derived cathelicidin next to its strong antimicrobial properties has also shown to modulates thrombosis and thus presents a potential therapeutic target. In this article we review direct and indirect (immune- and endothelial cell-mediated) effects of cathelicidin on platelets and the coagulation system. Further we discuss its implications for large vessel thrombosis and consecutive thromboinflammation as well as immunothrombosis in sepsis and COVID-19 and give an outlook for potential therapeutic prospects.

Dual-modal molecular imaging and therapeutic evaluation of coronary microvascular dysfunction using indocyanine green-doped targeted microbubbles

Coronary microvascular dysfunction (CMD), which causes a series of cardiovascular diseases, seriously endangers human health. However, precision diagnosis of CMD is still challenging due to the lack of sensitive probes and complementary imaging technologies. Herein, we demonstrate indocyanine green-doped targeted microbubbles (named T-MBs-ICG) as dual-modal probes for highly sensitive near-infrared (NIR) fluorescence imaging and high-resolution ultrasound imaging of CMD in mouse models. In vitro results show that T-MBs-ICG can specifically target fibrin, a specific CMD biomarker, via the cysteine-arginine-glutamate-lysine-alanine (CREKA) peptide modified on the surface of microbubbles. We further employ T-MBs-ICG to achieve NIR fluorescence imaging of injured myocardial tissue in a CMD mouse model, leading to a signal-to-background ratio (SBR) of up to 50, which is 20 fold higher than that of the non-targeted group. Furthermore, ultrasound molecular imaging of T-MBs-ICG is obtained within 60 s after intravenous injection, providing molecular information on ventricular and myocardial structures and fibrin with a resolution of 1.033 mm × 0.466 mm. More importantly, we utilize comprehensive dual-modal imaging of T-MBs-ICG to evaluate the therapeutic efficacy of rosuvastatin, a cardiovascular drug for the clinical treatment of CMD. Overall, the developed T-MBs-ICG probes with good biocompatibility exhibit great potential in the clinical diagnosis of CMD.

Acute Microbleeds and Microinfarcts Within the Perihematomal Area After Intracerebral Hemorrhage

BACKGROUND

To further our understanding of the pathophysiology of spontaneous intracerebral hemorrhage (ICH) and related injury, we provided a postmortem neuropathological examination of acute microvascular lesions (microbleeds and microinfarcts) within the perihematomal area.

METHODS

We included all consecutive cases (2005-2019) from the Lille University Hospital brain bank of ICH patients who died within the first month. Paraffin-embedded tissue sections from the perihematomal area were processed for several stainings and immunolabelings to investigate the presence of acute microbleeds and microinfarcts in the perihematomal area and to characterize surrounding neuronal and systemic inflammatory reaction (macrophages and neutrophils).

RESULTS

We included 14 ICH cases (median age, 78 years; 10 females). Acute microbleeds were observed in the perihematomal area in 12/14 patients (86%, ranging from 1 through >10) and microinfarcts in 5/14 (36%, ranging from 1 through 4). Microbleeds were observed whatever the delay from ICH onset to death was, while most cases with acute microinfarcts were observed between day 3 and day 7 (n=3/5). Both lesions were characterized by an abundant accumulation of systemic inflammatory cells and necrotic areas.

CONCLUSIONS

Acute microbleeds and microinfarcts might contribute to the propagation of secondary brain tissue damages after ICH. Our examinations also question the potential role of massive systemic inflammatory cells recruitment in the genesis of these microvascular injuries.

Vitronectin promotes immunothrombotic dysregulation in the venular microvasculature

Microvascular immunothrombotic dysregulation is a critical process in the pathogenesis of severe systemic inflammatory diseases. The mechanisms controlling immunothrombosis in inflamed microvessels, however, remain poorly understood. Here, we report that under systemic inflammatory conditions the matricellular glycoproteinvitronectin (VN) establishes an intravascular scaffold, supporting interactions of aggregating platelets with immune cells and the venular endothelium. Blockade of the VN receptor glycoprotein (GP)IIb/IIIa interfered with this multicellular interplay and effectively prevented microvascular clot formation. In line with these experimental data, particularly VN was found to be enriched in the pulmonary microvasculature of patients with non-infectious (pancreatitis-associated) or infectious (coronavirus disease 2019 (COVID-19)-associated) severe systemic inflammatory responses. Targeting the VN-GPIIb/IIIa axis hence appears as a promising, already feasible strategy to counteract microvascular immunothrombotic dysregulation in systemic inflammatory pathologies.

Clinical and laboratory differences between pediatric hospitalized patients with sickle cell disease infected or not by SARS-CoV-2

OBJECTIVE

The aim of this study was to identify clinical and complete blood count differences between pediatric hospitalized patients with sickle cell disease infected or not by SARS-CoV-2 and compare the complete blood count of patients with sickle cell disease infected by SARS-CoV-2 before hospitalization and on admission.

METHODS

This study was a single-center prospective cohort. Data were collected from medical records of pediatric inpatients with sickle cell disease under 18 years old infected or not with SARS-CoV-2 from the first visit to the hospital until discharge and from the last medical appointment. All patients were tested for SARS-CoV-2 by the real-time reverse transcription polymerase chain reaction.

RESULTS

Among 57 pediatric patients with sickle cell disease hospitalized from March to November 2020 in a Brazilian academic hospital, 11 (19.3%) had a positive result for SARS-CoV-2. Patients infected by SARS-CoV-2 had a higher prevalence of comorbidities than the ones who were not infected (63.6 vs. 30.4%; p=0.046). During hospital stay, no clinical or complete blood count differences between groups were found. There was a decrease in eosinophil count on hospital admission in patients with sickle cell disease infected by SARS-CoV-2 (p=0.008).

CONCLUSIONS

Pediatric hospitalized patients with sickle cell disease infected by SARS-CoV-2 had more comorbidities and had a decrease in eosinophil count between hospital admission and the last medical appointment.

A novel interaction between extracellular vimentin and fibrinogen in fibrin formation

INTRODUCTION

Thrombosis is frequently manifested in critically ill patients with systemic inflammation, including sepsis and COVID-19. The coagulopathy in systemic inflammation is often associated with increased levels of fibrinogen and D-dimer. Because elevated levels of vimentin have been detected in sepsis, we sought to investigate the relationship between vimentin and the increased fibrin formation potential observed in these patients.

MATERIALS AND METHODS

This hypothesis was examined by using recombinant human vimentin, anti-vimentin antibodies, plasma derived from healthy and critically ill patients, confocal microscopy, co-immunoprecipitation assays, and size exclusion chromatography.

RESULTS

The level of vimentin in plasma derived from critically ill subjects with systemic inflammation was on average two-fold higher than that of healthy volunteers. We determined that vimentin directly interacts with fibrinogen and enhances fibrin formation. Anti-vimentin antibody effectively blocked fibrin formation ex vivo and caused changes in the fibrin structure in plasma. Additionally, confocal imaging demonstrated plasma vimentin enmeshed in the fibrin fibrils. Size exclusion chromatography column and co-immunoprecipitation assays demonstrated a direct interaction between extracellular vimentin and fibrinogen in plasma from critically ill patients but not in healthy plasma.

CONCLUSIONS

The results describe that extracellular vimentin engages fibrinogen in fibrin formation. In addition, the data suggest that elevated levels of an apparent aberrant extracellular vimentin potentiate fibrin clot formation in critically ill patients with systemic inflammation; consistent with the notion that plasma vimentin contributes to the pathogenesis of thrombosis.

The coming of age of neutrophil extracellular traps in thrombosis: Where are we now and where are we headed?

Thrombosis remains a major problem in our society, manifesting across multiple demographic groups and with high associated morbidity and mortality. Thrombus development is the result of a complex mechanism in which multiple cell types and soluble factors play a crucial role. One cell that has gained the most attention in recent years is the neutrophil. This key member of the innate immune system can form neutrophil extracellular traps (NETs) in response to activating stimuli in circulation. NETs form a scaffold for thrombus formation, both initiating the process and stabilizing the final product. As the first responders of the host immune system, neutrophils have the flexibility to recognize a variety of molecules and can quickly interact with a range of different cell types. This trait makes them sensitive to exogenous stimuli. NET formation in response to pathogens is well established, leading to immune-mediated thrombus formation or immunothrombosis. NETs can also be formed during sterile inflammation through the activation of neutrophils by fellow immune cells including platelets, or activated endothelium. In chronic inflammatory settings, NETs can ultimately promote the development of tissue fibrosis, with organ failure as an end-stage outcome. In this review, we discuss the different pathways through which neutrophils can be activated toward NET formation and how these processes can result in a shared outcome: thrombus formation. Finally, we evaluate these different interactions and mechanisms for their potential as therapeutic targets, with neutrophil-targeted therapies providing a future approach to treating thrombosis. In contrast to current practices, such treatment could result in reduced pathogenic blood clot formation without increasing the risk of bleeding.

Evaluating cell viability, capillary perfusion, and collateral tortuosity in an ex vivo mouse intestine fluidics model

Numerous disease conditions involve the sudden or progressive loss of blood flow. Perfusion restoration is vital for returning affected organs to full health. While a range of clinical interventions can successfully restore flow to downstream tissues, the microvascular responses after a loss-of-flow event can vary over time and may involve substantial microvessel instability. Increased insight into perfusion-mediated capillary stability and access-to-flow is therefore essential for advancing therapeutic reperfusion strategies and improving patient outcomes. To that end, we developed a tissue-based microvascular fluidics model to better understand (i) microvascular stability and access-to-flow over an acute time course post-ischemia, and (ii) collateral flow in vessels neighboring an occlusion site. We utilized murine intestinal tissue regions by catheterizing a feeder artery and introducing perfusate at physiologically comparable flow-rates. The cannulated vessel as well as a portion of the downstream vessels and associated intestinal tissue were cultured while constant perfusion conditions were maintained. An occlusion was introduced in a selected arterial segment, and changes in perfusion within areas receiving varying degrees of collateral flow were observed over time. To observe the microvascular response to perfusion changes, we incorporated (i) tissues harboring cell-reporter constructs, specifically Ng2-DsRed labeling of intestinal pericytes, and (ii) different types of fluorescent perfusates to quantify capillary access-to-flow at discrete time points. In our model, we found that perfusion tracers could enter capillaries within regions downstream of an occlusion upon the initial introduction of perfusion, but at 24 h tissue perfusion was severely decreased. However, live/dead cell discrimination revealed that the tissue overall did not experience significant cell death, including that of microvascular pericytes, even after 48 h. Our findings suggest that altered flow conditions may rapidly initiate cellular responses that reduce capillary access-to-flow, even in the absence of cellular deterioration or hypoxia. Overall, this ex vivo tissue-based microfluidics model may serve as a platform upon which a variety of follow-on studies may be conducted. It will thus enhance our understanding of microvessel stability and access-to-flow during an occlusive event and the role of collateral flow during normal and disrupted perfusion.

Relationships between indicators of prothrombotic activity and coronary microvascular dysfunction in patients with myocardial infarction with obstructive and non-obstructive coronary artery disease

The relationship between prothrombotic activity and coronary microvascular dysfunction (MVD) is limited. This study aimed to perform a comparative analysis of the relationship between prothrombotic activity and MVD in patients with myocardial infarction without obstructive coronary artery disease (MINOCA) and myocardial infarction with obstructive coronary artery disease (MI-CAD).

MATERIAL AND METHODS

A total of 37 patients were enrolled in the study; the main group included 16 MINOCA patients, and 21 MI-CAD patients were included in the control group. Blood samples for protein C, antithrombin, WF, plasminogen, and homocysteine were performed on the 4th ± 1 day of admission. CZT-SPECT data were used to determine the standard indices of myocardial perfusion dis-orders (SSS, SRS, and SDS), as well as stress and rest myocardial blood flow (MBF), myocardial flow reserve (MFR), and difference flows (DF). MVD was defined as MFR (≤ 1.91 ml/min); coronary slow flow (CSF) was defined as corrected TIMI frame count (21 ± 3).

RESULTS

We performed a step-by-step analysis of prothrombotic activity of the hemostasis system in binary logistic regression for MINOCA patients to identify factors associated with MVD (MFR ≤ 1.91 ml/min). A predictive model was developed to estimate the probability of reduced MFR. A low MFR is related to only plasminogen in MINOCA patients, whereas only wall motion score index (WMSI) in MI-CAD group was associated with a low MFR.

CONCLUSION

This small-scale study revealed the relationship between indicators of prothrombotic activity and MVD. The key factors that affect MVD in MINOCA patients was plasminogen, whereas, in patients with MI-CAD, WMSI was the key factor. Measurements of MVD may enhance the risk stratification and facilitate future targeting of adjunctive antithrombotic therapies in MINOCA and MI-CAD patients.

Novel Classification of Thrombotic Disorders Based on Molecular Hemostasis and Thrombogenesis Producing Primary and Secondary Phenotypes of Thrombosis

Thrombosis, the common and deadliest disorder among human diseases, develops as a result of the intravascular hemostasis following an intravascular injury, which can be caused by a variety of trauma, non-traumatic insults or clinical illnesses. Thrombosis can occur at any location of the vascular system supplied by blood from the heart to large and smallest arterial and venous systems and may affect the function and anatomy of the organ and tissue. It more commonly occurs in the smaller circulatory system of the vascular tree such as arterioles and capillaries, and venules of the organs, especially in the brain, lungs, heart, pancreas, muscle and kidneys, and sinusoids of the liver. Thrombosis has been referred as the disease of "blood clots", which concept is incompletely defined, but represents many different hemostatic diseases from microthrombosis to fibrin clot disease, macrothrombosis, and combined micro-macrothrombosis. Thrombosis is produced following an intravascular injury via one or more combination of four different mechanisms of thrombogenesis: microthrombogenesis, fibrinogenesis, macrothrombogenesis and micro-macrothrombogenesis initiated by normal physiological hemostasis in vivo. The clinical phenotype expression of thrombosis is determined by: (1) depth of the intravascular wall injury, (2) extent of the injury affecting the vascular tree system, (3) physiological character of the involved vascular system, (4) locality of the vascular injury, and (5) underlying non-hemostatic conditions interacting with hemostasis. Recent acquisition of "two-path unifying theory" of hemostasis and "two-activation theory of the endothelium" has opened a new frontier in science of medicine by identifying the pathophysiological mechanism of different thrombotic disorders and also contributing to the better understanding of many poorly defined human diseases, including different phenotypes of stroke and cardiovascular disease, trauma, sepsis and septic shock, multiorgan dysfunction syndrome, and autoimmune disease, and others. Reviewed are the fundamentals in hemostasis, thrombogenesis and thrombosis based on hemostatic theories, and proposed is a novel classification of thrombotic disorders.

Thrombosis and thromboembolism: Brighton collaboration case definition and guidelines for data collection, analysis, and presentation of immunization safety data

This is a Brighton Collaboration case definition of thrombosis and thromboembolism to be used in the evaluation of adverse events following immunization, and for epidemiologic studies for the assessment of background incidence or hypothesis testing. The case definition was developed by a group of experts convened by the Coalition for Epidemic Preparedness Innovations (CEPI) in the context of active development of SARS-CoV-2 vaccines. The case definition format of the Brighton Collaboration was followed to develop a consensus definition and defined levels of certainty, after an exhaustive review of the literature and expert consultation. The document underwent peer review by the Brighton Collaboration Network and by selected expert reviewers prior to submission.

Antithrombin as Therapeutic Intervention against Sepsis-Induced Coagulopathy and Disseminated Intravascular Coagulation: Lessons Learned from COVID-19-Associated Coagulopathy

Recent research has contributed significantly to our understanding of the pathogenesis of acute disseminated intravascular coagulation. COVID-19 can be considered as a new underlying condition of disseminated intravascular coagulation. In this narrative review, current evidence is presented regarding biomarker differences between sepsis-induced and COVID-19-associated coagulopathies, supporting the importance of acquired antithrombin deficiency in the early differential diagnosis of septic coagulopathy and its potential impact on treatment with endogenous anticoagulants. Establishing new scoring systems for septic coagulopathy in combination with endogenous anticoagulant biomarker activities may allow for the identification of those in the heterogeneous population of sepsis patients who are more likely to benefit from targeted specific treatment interventions.

The potential role of ischaemia-reperfusion injury in chronic, relapsing diseases such as rheumatoid arthritis, Long COVID, and ME/CFS: evidence, mechanisms, and therapeutic implications

Ischaemia–reperfusion (I–R) injury, initiated via bursts of reactive oxygen species produced during the reoxygenation phase following hypoxia, is well known in a variety of acute circumstances. We argue here that I–R injury also underpins elements of the pathology of a variety of chronic, inflammatory diseases, including rheumatoid arthritis, ME/CFS and, our chief focus and most proximally, Long COVID. Ischaemia may be initiated via fibrin amyloid microclot blockage of capillaries, for instance as exercise is started; reperfusion is a necessary corollary when it finishes. We rehearse the mechanistic evidence for these occurrences here, in terms of their manifestation as oxidative stress, hyperinflammation, mast cell activation, the production of marker metabolites and related activities. Such microclot-based phenomena can explain both the breathlessness/fatigue and the post-exertional malaise that may be observed in these conditions, as well as many other observables. The recognition of these processes implies, mechanistically, that therapeutic benefit is potentially to be had from antioxidants, from anti-inflammatories, from iron chelators, and via suitable, safe fibrinolytics, and/or anti-clotting agents. We review the considerable existing evidence that is consistent with this, and with the biochemical mechanisms involved.

The association of Curcuma and Scutellaria plant extracts improves laying hen thermal tolerance and egg oxidative stability and quality under heat stress conditions

Chronic exposure to high ambient temperatures is detrimental to laying hen performance and egg quality. Plant secondary metabolites may alleviate effects, partly due to their antioxidant activities. Herein, we investigated the effects of dietary supplementation with a phytonutrient solution (PHYTO) consisting of a plant extract combination of Scutellaria baicalensis and Curcuma longa on young layers (25–32 wk of age) raised under naturally elevated temperature conditions. Four hundred, 24-wk-old Lohmann hens were allocated in 50 cages and, after a week of adaptation, were offered a diet either containing 2 g/kg of PHYTO or not, for 8 wk. Hen BW was measured at the beginning and end of the trial, and egg production and feed intake were recorded weekly. At week 32, four eggs per cage were collected to determine egg quality characteristics as well as the rate of lipid and albumen oxidation in fresh eggs. At the end of the trial, two hens per cage were blood sampled for assessment of biochemical markers, one of which was euthanized for histopathological evaluation of the liver and intestine and assessment of intestinal histomorphometry. The herbal mixture supplementation significantly increased egg production rate at weeks 28 and 29 and for the overall production period, and feed efficiency at weeks 26–29. In addition, the degree of liver necrosis and microvascular thrombosis was lower (P < 0.05) whereas intestinal villosity was greater in duodenal and jejunal segments (P < 0.05) in the PHYTO compared to the control group. Supplementation also reduced (P < 0.05) blood concentrations of corticosterone, alanine aminotransferase activity, and TBARS, and a reduction in catalase activity was observed. Egg quality characteristics were not affected, except for eggshell thickness, egg diameter, and eggshell breaking strength that were superior in the PHYTO group (P < 0.05). PHYTO supplementation significantly improved egg lipid oxidation status of fresh eggs. In conclusion, supplementation with PHYTO improved laying hen productivity and egg quality, which was associated with an improvement in laying hen thermotolerance.

Panax Notoginseng Saponins Combined with Dual Antiplatelet Drugs Potentiates Anti-Thrombotic Effect with Alleviated Gastric Injury in A Carotid Artery Thrombosis Rat Model

OBJECTIVE

To observe the combination effects of Panax notoginseng saponins (PNS)and dual antiplatelet drugs (DAPT), and to explore the mechanism via cyclooxygenase /prostaglandin pathway.

METHODS

Right carotid artery thrombosis was induced in Wistar rats by infiltration with 70% FeCl₃, and the animals were randomly divided into sham group, model group, DAPT group and PNS + DAPT group, intragastrically treated for 4 weeks. The cerebral pia mater microcirculation was observed in vivo after anesthetizing by anatomical microscope. The wet weight of carotid artery thrombosis was measured. Gastric mucosal injury was observed by hematoxylin and eosin staining. Platelet aggregation rate was detected with adenosine diphosphate -induced turbidimetry. Platelet CD62p expression was detected by flow cytometry. Concentrations of 6-Ketoprostaglandin F1 alpha, prostaglandin E₂ in gastric mucosa and thromboxane B₂, 6-Ketoprostaglandin F1 alpha, tissue plasminogen activator, plasminogen activator inhibitor, and fibrin fragment D in the plasma were measured by radioimmunoassay.

RESULTS

PNS and DAPT increased the blood flow volume of cerebral pia mater and decreased erythrocyte aggregation and leukocyte adhesion of model rats. Compared to DAPT, PNS and DAPT further reduced the weight of carotid artery thrombosis with enhanced inhibition of platelet aggregation, increased tissue plasminogen activator levels and decreased fibrin fragment D levels. PNS and DAPT alleviated gastric injury induced by dual antiplatelet drugs and upregulated the expression of 6-Ketoprostaglandin F1 alpha in the gastric mucosa compared with DAPT.

CONCLUSIONS

PNS combined with DAPT increased anti-thrombosis effects of DAPT and mitigated DAPT-related gastric injury. The underlying mechanisms may be associated with enhanced antiplatelet aggregation and activation of the fibrinolytic system and up-regulation of 6-Ketoprostaglandin F1 alpha expression in gastric mucosa.

Fibrin Strands Will Grow from Soluble Fibrin and Hang Up in an In Vitro Microcirculatory Viscoelastic Model: Is This a Major Cause of COVID-19 Associated Coagulopathy?

Viscoelastic testing (VET) by both TEG and ROTEM has demonstrated hypercoagulability early in corona virus disease 2019 (COVID-19) associated coagulopathy (CAC). Additional VET studies demonstrated fibrinolytic shutdown late in a majority of severely ill COVID-19 patients with an associated elevation of d-dimer. Elevated d-dimer confirms that coagulation, followed by fibrinolysis, has occurred. These findings imply that, during CAC, three enzymes—thrombin, Factor XIIIa and plasmin—must have acted in sequence. However, limitations in standard VET analyses preclude exploration of the earliest phases of clot induction, as well as clot formation and clot dissolution in flowing blood. Herein, we describe a novel method illuminating aspects of this unexplored area. In addition, we created an in vitro blood flow model in which the interactions of thrombin, Factor XIII and plasmin with fibrinogen can be studied, allowing the determination of soluble fibrin (SF), the highly unstable form of fibrin that precedes the appearance of a visible clot. This model allows the determination of the SF level at which fibrin microclots begin to form.

Elucidating the Correlation of D-Dimer Levels with COVID-19 Severity: A Scoping Review

Aims. The review explores the findings of previous studies to elucidate the association between levels of D-dimer and COVID-19 severity and prognosis. In addition, we assessed the efficiency of anticoagulant therapies in reducing COVID-19 severity and improving the prognosis of the patients. Materials and Methods. A comprehensive literature review was conducted using MEDLINE/PubMed databases, Scopus, and Web of Science with the help of keywords “COVID-19,” “D-Dimer,” “Thrombosis,” “Fibrin network,” “Anticoagulant therapy,” “Inflammation,” and “disease severity.” Based on all these articles and clinical experience, a scoping review was constructed and the full texts of the articles that were retrieved were accessed. Results. A D-dimer is a complex protein molecule that is formed during plasmin-mediated degradation of the fibrin network. Thus, it serves as a marker of thrombotic activity. On the other hand, in addition to severe respiratory distress and reduction in pulmonary gas exchange, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) also triggers prothrombotic changes in the infected individuals. The levels of D-dimer have been postulated to be positively associated with the degree of disease severity among COVID-19 patients. Conclusions. It has been postulated that D-dimer could potentially be used as a biomarker to predict the prognosis and outcome of COVID-19 patients at the time of admission to hospitals and facilitate more personalized and efficient clinical management that could significantly reduce the mortality rate of such patients and allow more rapid recovery.

A central role for amyloid fibrin microclots in long COVID/PASC: origins and therapeutic implications

Post-acute sequelae of COVID (PASC), usually referred to as 'Long COVID' (a phenotype of COVID-19), is a relatively frequent consequence of SARS-CoV-2 infection, in which symptoms such as breathlessness, fatigue, 'brain fog', tissue damage, inflammation, and coagulopathies (dysfunctions of the blood coagulation system) persist long after the initial infection. It bears similarities to other post-viral syndromes, and to myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Many regulatory health bodies still do not recognize this syndrome as a separate disease entity, and refer to it under the broad terminology of 'COVID', although its demographics are quite different from those of acute COVID-19. A few years ago, we discovered that fibrinogen in blood can clot into an anomalous 'amyloid' form of fibrin that (like other β-rich amyloids and prions) is relatively resistant to proteolysis (fibrinolysis). The result, as is strongly manifested in platelet-poor plasma (PPP) of individuals with Long COVID, is extensive fibrin amyloid microclots that can persist, can entrap other proteins, and that may lead to the production of various autoantibodies. These microclots are more-or-less easily measured in PPP with the stain thioflavin T and a simple fluorescence microscope. Although the symptoms of Long COVID are multifarious, we here argue that the ability of these fibrin amyloid microclots (fibrinaloids) to block up capillaries, and thus to limit the passage of red blood cells and hence O2 exchange, can actually underpin the majority of these symptoms. Consistent with this, in a preliminary report, it has been shown that suitable and closely monitored 'triple' anticoagulant therapy that leads to the removal of the microclots also removes the other symptoms. Fibrin amyloid microclots represent a novel and potentially important target for both the understanding and treatment of Long COVID and related disorders.

Potential clinical applications of phytopharmaceuticals for the in-patient management of coagulopathies in COVID-19

Thrombotic complications occur in many cardiovascular pathologies and have been demonstrated in COVID‐19. The currently used antithrombotic drugs are not free of adverse reactions, and COVID‐19 patients in particular, when treated with a therapeutic dose of an anticoagulant do not receive mortality benefits. The clinical management of COVID‐19 is one of the most difficult tasks for clinicians, and the search for safe, potent, and effective antithrombotic drugs may benefit from exploring naturally bioactive molecules from plant sources. This review describes recent advances in understanding the antithrombotic potential of herbal drug prototypes and points to their future clinical use as potent antithrombotic drugs. Although natural products are perceived to be safe, their clinical and therapeutic applications are not always apparent or accepted. More in‐depth studies are necessary to demonstrate the clinical usefulness of plant‐derived, bioactive compounds. In addition, holistic approaches in systematic investigations and the identification of antithrombotic mechanisms of the herbal bioactive molecule(s) need to be conducted in pre‐clinical studies. Moreover, rigorous studies are needed to compare the potency of herbal drugs to that of competitor chemical antithrombotic drugs, and to examine their interactions with Western antithrombotic medicines. We have also proposed a road map to improve the commercialization of phytopharmaceuticals.

Circulating Microparticles in the Pathogenesis and Early Anticoagulation of Thrombosis in COVID-19 With Kidney Injury

As more is learned about the pathophysiological mechanisms of COVID-19, systemic thrombosis has been recognized as being associated with more severe clinical manifestations, mortality and sequelae. As many as 40% of patients admitted to the hospital due to COVID-19 have acute kidney injury, with coagulation abnormalities the main cause of impaired function. However, the mechanism of renal thrombosis and the process leading to kidney injury are unclear. Microparticles (MPs) are membrane bubbles released in response to activation, injury or apoptosis of cells. The phosphatidylserine (PS) exposed on the surface of MPs provides binding sites for endogenous and exogenous FXase complexes and prothrombin complexes, thus providing a platform for the coagulation cascade reaction and facilitating clot formation. In the context of COVID-19 infection, viral attack leads immune cells to release cytokines that damage circulating blood cells and vascular endothelial cells, resulting in increased MPs levels. Therefore, MPs can be used as a risk factor to predict renal microthrombosis and kidney injury. In this paper, we have summarized the latest data on the pathophysiological mechanism and treatment of renal thrombosis caused by MPs in COVID-19, revealing that the coagulation abnormality caused by MP and PS storms is a universal progression that aggravates the mortality and sequelae of COVID-19 and potentially other pandemic diseases. This paper also describes the risk factors affecting renal thrombosis in COVID-19 from the perspective of the Virchow’s triad: blood hypercoagulability, vascular endothelial injury, and decreased blood flow velocity. In summary, given the serious consequences of thrombosis, current guidelines and clinical studies suggest that early prophylactic anticoagulant therapy reduces mortality and improves clinical outcomes. Early anticoagulation, through inhibition of PS-mediated coagulopathy, allows maintenance of unobstructed blood circulation and oxygen delivery thereby facilitating the removal of inflammatory factors, viruses, MPs, and dead or damaged cells, and expediting patient rehabilitation.

Microfluidic post method for 3-dimensional modeling of platelet–leukocyte interactions

These studies demonstrate the versatility and relevance of a novel ‘platelet post’ model to examine the adhesive interactions between platelets and neutrophils under 3D disturbed flow conditions relevant to thromboinflammation.

Purification and characterization of fibrinolytic protease from Streptomyces parvulus by polyethylene glycol-phosphate aqueous two-phase system

Fibrinolytic proteases are a promising alternative in the pharmaceutical industry, they are used in the treatment of cardiovascular diseases, especially thrombosis. Microorganisms are the most interesting source of fibrinolytic proteases. The aim of this study was the production of fibrinolytic protease from Streptomyces parvulus DPUA 1573, the recovery of the protease by aqueous two-phase system and partial biochemical characterization of the enzyme. The aqueous two-phase system was performed according to a 24-full factorial design using polyethylene glycol molar mass, polyethylene glycol concentration, citrate concentration and pH as independent variables. It was analyzed the effect of different ions, surfactants, inhibitors, pH and temperature on enzyme activity. The best conditions for purifying the enzyme were 17.5% polyethylene glycol 8,000, 15% Phosphate and pH 8.0, it was obtained a partition coefficient of 7.33, a yield of 57.49% and a purification factor of 2.10-fold. There was an increase in enzyme activity in the presence of Fe2+ and a decrease in the presence of $\beta$-Mercaptoethanol, phenylmethylsulfonyl fluoride and Iodoacetic acid. The optimum pH was 7.0 and the optimum temperature was 40 ºC. The purified protease exhibited a molecular mass of 41 kDa. The fibrinolytic protease from Streptomyces parvulus proved to be a viable option for the development of a possible drug with fibrinolytic action.

Emerging Microfluidic Approaches for Platelet Mechanobiology and Interplay With Circulatory Systems

Understanding how platelets can sense and respond to hemodynamic forces in disturbed blood flow and complexed vasculature is crucial to the development of more effective and safer antithrombotic therapeutics. By incorporating diverse structural and functional designs, microfluidic technologies have emerged to mimic microvascular anatomies and hemodynamic microenvironments, which open the floodgates for fascinating platelet mechanobiology investigations. The latest endothelialized microfluidics can even recapitulate the crosstalk between platelets and the circulatory system, including the vessel walls and plasma proteins such as von Willebrand factor. Hereby, we highlight these exciting microfluidic applications to platelet mechanobiology and platelet–circulatory system interplay as implicated in thrombosis. Last but not least, we discuss the need for microfluidic standardization and summarize the commercially available microfluidic platforms for researchers to obtain reproducible and consistent results in the field.

Virchow's Triad and the Role of Thrombosis in COVID-Related Stroke

In December 2019, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was identified as a virally transmitted disease. Three months later, SARS-CoV-2 became one of the largest pandemics in recent times, causing more than 235 million cases globally, and accounting for at least 4.8 million deaths to date. SARS-COV-2 infection was initially classified as a respiratory tract infection, but later was recognized as a multisystemic disease compromising gastrointestinal, hematological, cardiac, and neurological systems. With this Review, we aim to describe the epidemiology, risk factors, mechanisms, and management of cerebrovascular events in patients infected with COVID-19. Neurological manifestations related to thromboembolic cerebrovascular events in patients infected with COVID-19 have been frequent and associated with poor prognosis in the majority of cases. A better understanding of the mechanisms of thrombosis and etiologies of this new disease process are necessary to determine how to prevent and treat patients to reduce their length of stay, morbidity, and mortality.

Age-Associated Increase in Thrombogenicity and Its Correlation with von Willebrand Factor

Endothelial cells that cover the lumen of all blood vessels have the inherent capacity to express both pro and anticoagulant molecules. However, under normal physiological condition, they generally function to maintain a non-thrombogenic surface for unobstructed blood flow. In response to injury, certain stimuli, or as a result of dysfunction, endothelial cells release a highly adhesive procoagulant protein, von Willebrand factor (VWF), which plays a central role in formation of platelet aggregates and thrombus generation. Since VWF expression is highly restricted to endothelial cells, regulation of its levels is among the most important functions of endothelial cells for maintaining hemostasis. However, with aging, there is a significant increase in VWF levels, which is concomitant with a significant rise in thrombotic events. It is not yet clear why and how aging results in increased VWF levels. In this review, we have aimed to discuss the age-related increase in VWF, its potential mechanisms, and associated coagulopathies as probable consequences.

Cardiovascular Disease Complicating COVID-19 in the Elderly

SARS-CoV-2, a single-stranded RNA coronavirus, causes an illness known as coronavirus disease 2019 (COVID-19). The highly transmissible virus gains entry into human cells primarily by the binding of its spike protein to the angiotensin-converting enzyme 2 receptor, which is expressed not only in lung tissue but also in cardiac myocytes and the vascular endothelium. Cardiovascular complications are frequent in patients with COVID-19 and may be a result of viral-associated systemic and cardiac inflammation or may arise from a virus-induced hypercoagulable state. This prothrombotic state is marked by endothelial dysfunction and platelet activation in both macrovasculature and microvasculature. In patients with subclinical atherosclerosis, COVID-19 may incite atherosclerotic plaque disruption and coronary thrombosis. Hypertension and obesity are common comorbidities in COVID-19 patients that may significantly raise the risk of mortality. Sedentary behaviors, poor diet, and increased use of tobacco and alcohol, associated with prolonged stay-at-home restrictions, may promote thrombosis, while depressed mood due to social isolation can exacerbate poor self-care. Telehealth interventions via smartphone applications and other technologies that document nutrition and offer exercise programs and social connections can be used to mitigate some of the potential damage to heart health.

A macrophage attack culminating in microthromboses characterizes COVID 19 pneumonia

Introduction

A neutrophilic infiltrate characterizes bacterial pneumonia. Macrophage infiltration is similarly characteristic of the viral pneumonia caused by SARS‐CoV‐2. These infiltrating macrophages, while phagocytic and capable of engulfing virus laden alveolar cells, are also rich in tissue factor—a thromboplastin. This prothrombotic aspect likely explains how a respiratory virus whose malign effects should be confined to the oropharynx, bronchi and lungs, can cause a panoply of extra‐pulmonary organ disorders. Elevated ferritin levels in ICU Covid 19 patients, and elevated acute phase proteins suggest immune overreaction. Elevated d‐dimers implicate clotting as well. This evidence links hyperactive innate immunity (macrophage lung infiltrates) with the elevated levels of oligomeric fibrin present in the bloodstream of these patients.

Methods

An in‐house assay measuring oligomeric (soluble) fibrin (also referred to as soluble fibrin monomer complexes or SFMC) in whole blood, previously developed for monitoring incipient disseminated intravascular coagulation (DIC) during liver transplantation, was made available to COVID ICU attendings. Since SFMC constitutes the input to intravascular fibrin clots and d‐dimer reflects fibrin clot dissolution, it was thought that the two tests, run in tandem along with assays of immune activation, might clarify the frequency and possibly the cause of DIC in patients with severe COVID‐19 pneumonia.

Results

Classical DIC with intravascular clotting and thrombocytopenia was documented only rarely. However, early in the pandemic shortly after the assay was made available, it identified three patients undergoing acute defibrination. In each patient virtually all of the body's fibrinogen was transformed into SFMC over 3–4 days and deposited somewhere in the vasculature without any gross clots being detected.

Conclusions

Three COVID‐19 patients with evidence of a hyperactive immune response (elevated ferritin and acute phase proteins) defibrinated while blood levels of SFMC were being monitored. SFMC levels that were five times higher than normal appeared in the circulation during the defibrination process. SFMC at these levels may precipitate as showers of microclots, damaging heart, kidney, brain, and so forth.

ACE2 Down-Regulation May Act as a Transient Molecular Disease Causing RAAS Dysregulation and Tissue Damage in the Microcirculatory Environment Among COVID-19 Patients

Severe acute respiratory syndrome coronavirus 2, the etiologic agent of coronavirus disease 2019 (COVID-19) and the cause of the current pandemic, produces multiform manifestations throughout the body, causing indiscriminate damage to multiple organ systems, particularly the lungs, heart, brain, kidney, and vasculature. The aim of this review is to provide a new assessment of the data already available for COVID-19, exploring it as a transient molecular disease that causes negative regulation of angiotensin-converting enzyme 2, and consequently, deregulates the renin-angiotensin-aldosterone system, promoting important changes in the microcirculatory environment. Another goal of the article is to show how these microcirculatory changes may be responsible for the wide variety of injury mechanisms observed in different organs in this disease. The new concept of COVID-19 provides a unifying pathophysiological picture of this infection and offers fresh insights for a rational treatment strategy to combat this ongoing pandemic.

Venous Thromboembolic Disease in Chronic Inflammatory Lung Diseases: Knowns and Unknowns

Persistent inflammation within the respiratory tract underlies the pathogenesis of numerous chronic pulmonary diseases. There is evidence supporting that chronic lung diseases are associated with a higher risk of venous thromboembolism (VTE). However, the relationship between lung diseases and/or lung function with VTE is unclear. Understanding the role of chronic lung inflammation as a predisposing factor for VTE may help determine the optimal management and aid in the development of future preventative strategies. We aimed to provide an overview of the relationship between the most common chronic inflammatory lung diseases and VTE. Asthma, chronic obstructive pulmonary disease, interstitial lung diseases, or tuberculosis increase the VTE risk, especially pulmonary embolism (PE), compared to the general population. However, high suspicion is needed to diagnose a thrombotic event early as the clinical presentation inevitably overlaps with respiratory disorders. PE risk increases with disease severity and exacerbations. Hence, hospitalized patients should be considered for thromboprophylaxis administration. Conversely, all VTE patients should be asked for lung comorbidities before determining anticoagulant therapy duration, as those patients are at increased risk of recurrent PE episodes rather than DVT. Further research is needed to understand the underlying pathophysiology of in-situ thrombosis in those patients.

Cerebral venous thrombosis in COVID-19

BACKGROUND AND AIMS

Initially, novel severe acute respiratory syndrome coronavirus (SARS-CoV-2) was considered primarily a respiratory pathogen. However, with time it has behaved as a virus with the potential to cause multi-system involvement, including neurological manifestations. Cerebral venous sinus thrombosis (CVT) has increasingly been reported in association with coronavirus infectious disease of 2019 (COVID-19). Here, we have shed light upon CVT and its possible mechanisms in the backdrop of the ongoing COVID-19 pandemic.

METHODS

In this review, data were collected from PubMed, EMBASE and Web of Science, until March 30, 2021, using pre-specified searching strategies. The search strategy consisted of a variation of keywords of relevant medical subject headings and keywords, including "COVID-19", "SARS-CoV-2", "coronavirus", and "cerebral venous sinus thrombosis".

RESULTS

COVID-19 has a causal association with a plethora of neurological, neuropsychiatric and psychological effects. CVT has gained particular importance in this regard. The known hypercoagulable state in SARS-CoV-2 infection is thought to be the main mechanism in COVID-19 related CVT. Other plausible mechanisms may include vascular endothelial dysfunction and altered flow dynamics.

CONCLUSIONS

Although there are no specific clinical characteristics, insidious or acute onset headache, seizures, stroke-like, or encephalopathy symptoms in a patient with, or who has suffered COVID-19, should prompt the attending physician to investigate for CVT. The treatment of COVID-19 associated CVT does not differ radically from the therapy of CVT without the infection, i.e. urgent initiation of parenteral unfractionated heparin or low molecular weight heparin followed by conventional or mostly newer oral anticoagulants.

Thromboembolic Complications in Covid-19: From Clinical Scenario to Laboratory Evidence

SARS-Cov-2 infection, a pandemic disease since March 2020, is associated with a high percentage of cardiovascular complications mainly of a thromboembolic (TE) nature. Although clinical patterns have been described for the assessment of patients with increased risk, many TE complications occur in patients with apparently moderate risk. Notably, a recent statement from the European Society of Cardiology (ESC) atherosclerosis and vascular biology working group pointed out the key role of vascular endothelium for the recruitment of inflammatory and thrombotic pathways responsible for both disseminated intravascular coagulation and cardiovascular complications. Therefore, a better understanding of the pathophysiological process linking infection to increased TE risk is needed in order to understand the pathways of this dangerous liaison and possibly interrupt it with appropriate treatment. In this review, we describe the histological lesions and the related blood coagulation mechanisms involved in COVID-19, we define the laboratory parameters and clinical risk factors associated with TE events, and propose a prophylactic anticoagulation treatment in relation to the risk category. Finally, we highlight the concept that a solid risk assessment based on prospective multi-center data would be the challenge for a more precise risk stratification and more appropriate treatment.

Understanding the Pathophysiology of Thrombotic APS through Animal Models

Antiphospholipid syndrome (APS) is a leading acquired cause of thrombotic events, with a notable tendency to promote thrombosis in vascular beds of all sizes, including both arterial and venous circuits. While pathogenic antiphospholipid antibodies circulate at relatively stable levels in blood, thrombosis tends to manifest as discrete and acute events, suggesting the requirement for a “second hit.” While this two-hit model is generally accepted, much remains to be learned about exactly how antiphospholipid antibodies predispose to thrombosis in vivo and exactly how this predisposition interacts with the second hit. To this end, investigators have turned to animal models. Numerous approaches for modeling APS in animals have been described to date, each with potential advantages and disadvantages. This review will attempt to describe the most common APS models employed so far while discussing some pros and cons of each. Mechanisms of thrombotic APS that have thus far been explored in animal models will also be briefly addressed.

The Relevance of a Physical Active Lifestyle and Physical Fitness on Immune Defense: Mitigating Disease Burden, With Focus on COVID-19 Consequences

The Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a fast spreading virus leading to the development of Coronavirus Disease-2019 (COVID-19). Severe and critical cases are characterized by damage to the respiratory system, endothelial inflammation, and multiple organ failure triggered by an excessive production of proinflammatory cytokines, culminating in the high number of deaths all over the world. Sedentarism induces worse, continuous, and progressive consequences to health. On the other hand, physical activity provides benefits to health and improves low-grade systemic inflammation. The aim of this review is to elucidate the effects of physical activity in physical fitness, immune defense, and its contribution to mitigate the severe inflammatory response mediated by SARS-CoV-2. Physical exercise is an effective therapeutic strategy to mitigate the consequences of SARS-CoV-2 infection. In this sense, studies have shown that acute physical exercise induces the production of myokines that are secreted in tissues and into the bloodstream, supporting its systemic modulatory effect. Therefore, maintaining physical activity influence balance the immune system and increases immune vigilance, and also might promote potent effects against the consequences of infectious diseases and chronic diseases associated with the development of severe forms of COVID-19. Protocols to maintain exercise practice are suggested and have been strongly established, such as home-based exercise (HBE) and outdoor-based exercise (OBE). In this regard, HBE might help to reduce levels of physical inactivity, bed rest, and sitting time, impacting on adherence to physical activity, promoting all the benefits related to exercise, and attracting patients in different stages of treatment for COVID-19. In parallel, OBE must improve health, but also prevent and mitigate COVID-19 severe outcomes in all populations. In conclusion, HBE or OBE models can be a potent strategy to mitigate the progress of infection, and a coadjutant therapy for COVID-19 at all ages and different chronic conditions.

Role of Tissue Factor in the Pathogenesis of COVID-19 and the Possible Ways to Inhibit It

COVID-19 (Coronavirus Disease 2019) is a highly contagious infection and associated with high mortality rates, primarily in elderly; patients with heart failure; high blood pressure; diabetes mellitus; and those who are smokers. These conditions are associated to increase in the level of the pulmonary epithelium expression of angiotensin-converting enzyme 2 (ACE-2), which is a recognized receptor of the S protein of the causative agent SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2). Severe cases are manifested by parenchymal lung involvement with a significant inflammatory response and the development of microvascular thrombosis. Several factors have been involved in developing this prothrombotic state, including the inflammatory reaction itself with the participation of proinflammatory cytokines, endothelial dysfunction/endotheliitis, the presence of antiphospholipid antibodies, and possibly the tissue factor (TF) overexpression. ARS-Cov-19 ACE-2 down-regulation has been associated with an increase in angiotensin 2 (AT2). The action of proinflammatory cytokines, the increase in AT2 and the presence of antiphospholipid antibodies are known factors for TF activation and overexpression. It is very likely that the overexpression of TF in COVID-19 may be related to the pathogenesis of the disease, hence the importance of knowing the aspects related to this protein and the therapeutic strategies that can be derived. Different therapeutic strategies are being built to curb the expression of TF as a therapeutic target for various prothrombotic events; therefore, analyzing this treatment strategy for COVID-19-associated coagulopathy is rational. Medications such as celecoxib, cyclosporine or colchicine can impact on COVID-19, in addition to its anti-inflammatory effect, through inhibition of TF.

The Novel Coronavirus and Haemostatic Abnormalities: Pathophysiology, Clinical Manifestations, and Treatment Recommendations

The COVID-19 pandemic, caused by the SARS-C0V-2 virus, was initially considered and managed in a similar manner to the previous SARS epidemic as they are both caused by coronaviruses. What has now become apparent is that a major cause of morbidity and mortality in COVID-19 is abnormal thrombosis. This thrombosis occurs on a macro- and microvascular level and is unique to this disease. The virus has been demonstrated in the endothelium of the pulmonary alveoli and as such is thought to contribute to the devastating respiratory complications encountered. D-dimer concentrations are frequently raised in COVID to levels not frequently seen previously. The optimal anticoagulation treatment in COVID remains to be determined, and the myriad of pathophysiologic effects caused by this virus in the human host have also yet to be fully elucidated.

Hemoglobinopathy and pediatrics in the time of COVID-19

INTRODUCTION

It is important to know if patients with hemoglobinopathy could be more susceptible to COVID-19.

OBJECTIVE

Analyze SARS-CoV-2 infection in pediatric patients with hemoglobinopathy.

METHODS

Using the online platforms LILACS, PUBMED and EMBASE, on 17- JUL-2020 a search was made for the terms COVID-19 and SARS-CoV-2 associated with "sickle cell", "thalassemia" and "hemoglobinopathy".

RESULTS

There were 623 pediatric and adult patients with sickle cell disease (SCD) or beta thalassemia (BT) and COVID-19. Total mortality rate was 6.42%. No pediatric patient with BT has been described. So, our analysis focused on children and adolescents with SCD: there were 121 pediatric patients, one adolescent died, prophylactic anticoagulation was prescribed to six patients, 11.76% needed intensive care unit, blood transfusion was prescribed in 29.70%. Vaso-occlusive crisis (VOC) and acute chest syndrome (ACS) were the main clinical manifestations in SCD.

DISCUSSION

Pediatric patients with SCD and COVID-19 have a low mortality rate when compared to adults, although is higher than the global pediatric population with COVID-19 (0-0.67%). The comorbidities associated with age and the long-term complications inherent to hemoglobinopathies may contribute to the increased mortality outside the pediatric age group. In SCD the clinical manifestations, both in children and adults, are VOC and ACS, and there was increase in blood requirement. Pediatric SCD patients with COVID-19 need more intensive care unit than the global pediatric population (3.30%).

CONCLUSION

Despite pediatric population with SCD needs more intensive care, the outcome after infection by COVID-19 is favorable.

Red Blood Cell Contribution to Hemostasis

Red Blood Cells (RBCs) have been increasingly recognized to play important roles in hemostasis and the mechanisms by which they do so continue to be elucidated. First and foremost, RBC biomechanics are the principal determinant of viscosity and flow dynamics of blood, which strongly influence all features of hemostasis. Of note, morphologic pathology, such as that found in sickle cell disease, leads to increased risk of thrombotic disease. RBC surface interactions govern signaling between platelets and RBCs and also aid in the conversion of prothrombin to thrombin. Additionally, RBCs generate microparticles which have been shown to reduce clotting time. Finally, blood clot structure and maturation are dependent on the inclusion of RBCs in forming thrombi. Here, we review the above mechanisms of RBC contribution to hemostasis.

Microcirculation alterations in severe COVID-19 pneumonia

Purpose

To assess the presence of sublingual microcirculatory and skin perfusion alterations in COVID-19 pneumonia.

Materials and methods

This is a preliminary report of a prospective observational study performed in four teaching intensive care units. We studied 27 mechanically ventilated patients with acute respiratory distress syndrome secondary to COVID-19. Sublingual microcirculation was assessed by hand-held videomicroscopy. A software-assisted analysis of videos was performed. We also measured capillary refill time.

Results

Patients were hemodynamically stable with normal lactate (1.8 [1.6–2.5] mmol/L) and high D-dimer (1.30 [0.58–2.93] μg/mL). Capillary refill time was prolonged (3.5 [3.0–5.0] s). Compared to previously reported normal values, total and perfused vascular density (21.9 ± 3.9 and 21.0 ± 3.5 mm/mm²) and heterogeneity flow index (0.91 ± 0.24) were high; and the proportion of perfused vessels (0.96 ± 0.03), microvascular flow index (2.79 ± 0.10), and red blood cell velocity (1124 ± 161 μm/s) were reduced. The proportion of perfused vessels was inversely correlated with total vascular density (Pearson r = −0.41, P = 0.03).

Conclusions

COVID-19 patients showed an altered tissue perfusion. Sublingual microcirculation was characterized by decreases in the proportion of perfused vessel and flow velocity along with high vascular densities. This last finding might be related to enhanced angiogenesis or hypoxia-induced capillary recruitment.

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Patients with COVID-19 show alterations in sublingual microcirculation and skin perfusion.

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Perfused vessels proportion and flow velocity decreases, and heterogeneity increases.

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The most striking result was the increase in vascular densities.

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High densities might result from angiogenesis or hypoxia-induced recruitment.