The Fibrinolytic System: Mysteries and Opportunities

Thrombolytic efficacy and safety of recombinant scu-PA in a rabbit retinal vein occlusion model

Retinal vein occlusion (RVO) has become the second most common retinal vascular disease after diabetic retinopathy. Existing therapeutic approaches, including intravitreal injection of antivascular endothelial growth factors (anti-VEGFs) and/or glucocorticoids and laser therapy, primarily address secondary macular edema and neovascularisation. However, these strategies do not address the underlying cause of the disease and may have harmful side effects. There is an urgent need for therapies that have a better prognosis and include the administration of thrombolytics at an early stage. Therefore, in the present study, we investigated the thrombolytic effect of treatment with recombinant human Single-chain urokinase-type plasminogen activators (scu-PA)and the differences in its efficacy at different doses in a rabbit RVO model. In addition, through a series of ophthalmological examinations, such as optical coherence tomography (OCT) and electrophysiology, conducted to ascertain the effects of treatment with scu-PA on the ocular fibrinolytic system, we noted a definitive safety window for the vitreous administration of scu-PA. Therefore, this study is the first to confirm that an intravenous or vitreous cavity injection of scu-PA has definitive potential for treating RVO; however, additional clinical studies are needed for further validation.

Bioprinted Micro-Clots for Kinetic Analysis of Endothelial Cell-Mediated Fibrinolysis

Vascular hypo-fibrinolysis is a historically underappreciated and understudied aspect of venous thromboembolism (VTE). This paper describes the development of a micro-clot dissolution assay for quantifying the fibrinolytic capacity of endothelial cells - a key driver of VTE development. This assay is enabled using aqueous two-phase systems (ATPS) to bioprint microscale fibrin clots over human umbilical vein endothelial cells (HUVECs). Importantly, these micro-clots are orders of magnitude smaller than conventional fibrin constructs and allow HUVEC-produced plasminogen activators to mediate visually quantifiable fibrinolysis. Using live-cell time-lapse imaging, micro-clot dissolution by HUVECs is tracked, and fibrinolysis kinetics are quantified. The sensitivity of cell-driven fibrinolysis to various stimuli is rapidly tested. The physiological relevance of this convenient high-throughput assay is illustrated through treatments with lipopolysaccharide (LPS) and rosuvastatin that elicit anti- and pro-fibrinolytic responses, respectively. Furthermore, treatment with baricitinib, an anti-inflammatory therapeutic found to increase cardiovascular risks after market approval, provokes an anti-fibrinolytic response - which highlights the potential role of endothelial cells in increasing VTE risk for patients receiving this drug. This endothelial cell fibrinolysis assay provides a high-throughput and versatile drug testing platform - potentially allowing for early preclinical identification of therapeutics that may beneficially enhance or adversely impair endothelial fibrinolysis.

Calreticulin-From the Endoplasmic Reticulum to the Plasma Membrane-Adventures of a Wandering Protein

Calreticulin (CRT) is a 46 kDa highly conserved protein initially identified as calregulin, a prominent Ca2+-binding protein of the endoplasmic reticulum (ER). Subsequent studies have established that CRT functions in the ER's protein folding response and Ca2+ homeostatic mechanisms. An ER retention signal on the carboxyl terminus of CRT suggested that CRT was restricted to the ER. However, the identification of CRT in the nucleus and cytosol has established that CRT is a multi-compartmental, multifunctional protein. CRT also plays an important role in cancer progression. Most recently, CRT was identified on the cell surface and shown to be a potent 'eat-me' signal that plays a key role in the uptake of apoptotic and viable cancer cells by phagocytes. Elevated CRT exposure on the outer leaflet of cancer cells has been linked with anticancer immunity and superior therapeutic outcomes in patients with non-small cell lung carcinoma, colorectal carcinoma, acute myeloid leukemia, ovarian cancer, and high-grade serous carcinomas. Mutations in the CRT gene have been identified in a subset of patients with myeloproliferative neoplasms. The most recent studies from our laboratory have revealed a new and significant function for extracellular CRT as a plasminogen receptor. This discovery has profound implications for our understanding of the role of CRT in myeloproliferative neoplasms, specifically, essential thrombocythemia.

Mesenchymal stem/stromal cells alleviate early-stage pulmonary fibrosis in a uPAR-dependent manner

Pulmonary fibrosis, a debilitating lung disorder characterised by excessive fibrous tissue accumulation in lung parenchyma, compromises respiratory function leading to a life-threatening respiratory failure. While its origins are multifaceted and poorly understood, the urokinase system, including urokinase-type plasminogen activator (uPA) and its receptor (uPAR), plays a significant role in regulating fibrotic response, extracellular matrix remodelling, and tissue repair. Mesenchymal stem/stromal cells (MSCs) hold promise in regenerative medicine for treating pulmonary fibrosis. Our study aimed to investigate the potential of MSCs to inhibit pulmonary fibrosis as well as the contribution of uPAR expression to this effect. We found that intravenous MSC administration significantly reduced lung fibrosis in the bleomycin-induced pulmonary fibrosis model in mice as revealed by MRI and histological evaluations. Notably, administering the MSCs isolated from adipose tissue of uPAR knockout mice (Plaur-/- MSCs) attenuated lung fibrosis to a lesser extent as compared to WT MSCs. Collagen deposition, a hallmark of fibrosis, was markedly reduced in lungs treated with WT MSCs versus Plaur-/- MSCs. Along with that, endogenous uPA levels were affected differently; after Plaur-/- MSCs were administered, the uPA content was specifically decreased within the blood vessels. Our findings support the potential of MSC treatment in attenuating pulmonary fibrosis. We provide evidence that the observed anti-fibrotic effect depends on uPAR expression in MSCs, suggesting that uPAR might counteract the uPA accumulation in lungs.

The hemostatic activity and Mechanistic roles of glucosyloxybenzyl 2-isobutylmalate extract (BSCE) from Bletilla striata (Thunb.) Rchb.f. in Inhibiting pulmonary hemorrhage

Background

Hemorrhagic events cause numerous deaths annually worldwide, highlighting the urgent need for effective hemostatic drugs. The glucosyloxybenzyl 2-isobutylmalates Control Extract (BSCE) from the orchid plant Bletilla striata (Thunb.) Rchb.f. has demonstrated significant hemostatic activity in both in vitro and in vivo studies. However, the effect and mechanism of BSCE on non-traumatic bleeding remain unclear.

Methods

Pulmonary hemorrhage was induced in 40 Sprague-Dawley rats by administering Zingiber officinale Roscoe. for 14 days. These rats were then randomly divided into five groups: model (Mod), positive control (YNBY), and BSCE low, medium, and high-dose groups. An additional 8 rats served as the control group (Con). The BSCE groups received different doses of BSCE for 10 days, while the YNBY group received Yunnan Baiyao suspension. The effects on body weight, food and water intake, red blood cell count (RBC), hemoglobin concentration (HGB), lung tissue pathology, platelet count, coagulation parameters, and fibrinolytic system markers were evaluated. Network pharmacology and molecular docking analyses were also conducted to identify potential targets and pathways involved in BSCE's effects.

Results

BSCE treatment significantly improved body weight, food intake, and water consumption in rats with pulmonary hemorrhage. RBC and HGB levels increased significantly in the BSCE medium and high-dose groups compared to the Mod group (P < 0.05). Pathological examination revealed that BSCE reduced lung tissue hemorrhage and inflammation, with improvements in alveolar structure. BSCE also positively affected platelet count, thrombin time (TT), activated partial thromboplastin time (APTT), fibrinogen (FIB) levels, and fibrinolytic markers (D-dimer, PAI-1, and t-PA). Network pharmacology and molecular docking identified key targets such as MMPs, CASPs, and pathways including IL-17 and TNF signaling, suggesting BSCE's involvement in hemostasis and anti-inflammatory processes.

Conclusions

BSCE exhibits significant hemostatic and protective effects on Z.officinale-induced pulmonary hemorrhage in rats by improving hematological parameters, reducing lung tissue damage, and modulating the coagulation and fibrinolytic systems. The study provides evidence supporting the potential of BSCE as a therapeutic agent for hemorrhagic diseases, with its efficacy linked to multi-target and multi-pathway interactions.

The Significance of Endothelial Dysfunction in Long COVID-19 for the Possible Future Pandemic of Chronic Kidney Disease and Cardiovascular Disease

Various symptoms have been reported to persist beyond the acute phase of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, which is referred to as long coronavirus disease 19 (long COVID-19). Over 65 million individuals suffer from long COVID-19. However, the causes of long COVID-19 are largely unknown. Since long COVID-19 symptoms are observed throughout the body, vascular endothelial dysfunction is a strong candidate explaining the induction of long COVID-19. The angiotensin-converting enzyme 2 (ACE2), the entry receptor for SARS-CoV-2, is ubiquitously expressed in endothelial cells. We previously found that the risk factors for atherosclerotic cardiovascular disease (ASCVD) and a history of ASCVD raise the risk of severe COVID-19, suggesting a contribution of pre-existing endothelial dysfunction to severe COVID-19. Here, we show a significant association of endothelial dysfunction with the development of long COVID-19 and show that biomarkers for endothelial dysfunction in patients with long COVID-19 are also crucial players in the development of ASCVD. We consider the influence of long COVID-19 on the development of chronic kidney disease (CKD) and ASCVD. Future assessments of the outcomes of long COVID-19 in patients resulting from therapeutic interventions that improve endothelial function may imply the significance of endothelial dysfunction in the development of long COVID-19.

Plasminogen missense variants and their involvement in cardiovascular and inflammatory disease

Human plasminogen (PLG), the zymogen of the fibrinolytic protease, plasmin, is a polymorphic protein with two widely distributed codominant alleles, PLG/Asp453 and PLG/Asn453. About 15 other missense or non-synonymous single nucleotide polymorphisms (nsSNPs) of PLG show major, yet different, relative abundances in world populations. Although the existence of these relatively abundant allelic variants is generally acknowledged, they are often overlooked or assumed to be non-pathogenic. In fact, at least half of those major variants are classified as having conflicting pathogenicity, and it is unclear if they contribute to different molecular phenotypes. From those, PLG/K19E and PLG/A601T are examples of two relatively abundant PLG variants that have been associated with PLG deficiencies (PD), but their pathogenic mechanisms are unclear. On the other hand, approximately 50 rare and ultra-rare PLG missense variants have been reported to cause PD as homozygous or compound heterozygous variants, often leading to a debilitating disease known as ligneous conjunctivitis. The true abundance of PD-associated nsSNPs is unknown since they can remain undetected in heterozygous carriers. However, PD variants may also contribute to other diseases. Recently, the ultra-rare autosomal dominant PLG/K311E has been found to be causative of hereditary angioedema (HAE) with normal C1 inhibitor. Two other rare pathogenic PLG missense variants, PLG/R153G and PLG/V709E, appear to affect platelet function and lead to HAE, respectively. Herein, PLG missense variants that are abundant and/or clinically relevant due to association with disease are examined along with their world distribution. Proposed molecular mechanisms are discussed when known or can be reasonably assumed.

Diverse origins of fibrinolytic enzymes: A comprehensive review

Fibrinolytic enzymes cleave fibrin which plays a crucial role in thrombus formation which otherwise leads to cardiovascular diseases. While different fibrinolytic enzymes have been purified, only a few have been utilized as clinical and therapeutic agents; hence, the search continues for a fibrinolytic enzyme with high specificity, fewer side effects, and one that can be mass-produced at a lower cost with a higher yield. In this context, this review discusses the physiological mechanism of thrombus formation and fibrinolysis, and current thrombolytic drugs in use. Additionally, an overview of the optimization, production, and purification of fibrinolytic enzymes and the role of Artificial Intelligence (AI) in optimization and the patents granted is provided. This review classifies microbial as well as non-microbial fibrinolytic enzymes isolated from food sources, including fermented foods and non-food sources, highlighting their advantages and disadvantages. Despite holding immense potential for the discovery of novel fibrinolytic enzymes, only a few fermented food sources limited to Asian countries have been studied, necessitating the research on fibrinolytic enzymes from fermented foods of other regions. This review will aid researchers in selecting optimal sources for screening fibrinolytic enzymes and is the first one to provide insights and draw a link between the implication of source selection and in vivo application.

Mechanisms of endothelial activation, hypercoagulation and thrombosis in COVID-19: a link with diabetes mellitus

Early since the onset of the COVID-19 pandemic, the medical and scientific community were aware of extra respiratory actions of SARS-CoV-2 infection. Endothelitis, hypercoagulation, and hypofibrinolysis were identified in COVID-19 patients as subsequent responses of endothelial dysfunction. Activation of the endothelial barrier may increase the severity of the disease and contribute to long-COVID syndrome and post-COVID sequelae. Besides, it may cause alterations in primary, secondary, and tertiary hemostasis. Importantly, these responses have been highly decisive in the evolution of infected patients also diagnosed with diabetes mellitus (DM), who showed previous endothelial dysfunction. In this review, we provide an overview of the potential triggers of endothelial activation related to COVID-19 and COVID-19 under diabetic milieu. Several mechanisms are induced by both the viral particle itself and by the subsequent immune-defensive response (i.e., NF-κB/NLRP3 inflammasome pathway, vasoactive peptides, cytokine storm, NETosis, activation of the complement system). Alterations in coagulation mediators such as factor VIII, fibrin, tissue factor, the von Willebrand factor: ADAMST-13 ratio, and the kallikrein-kinin or plasminogen-plasmin systems have been reported. Moreover, an imbalance of thrombotic and thrombolytic (tPA, PAI-I, fibrinogen) factors favors hypercoagulation and hypofibrinolysis. In the context of DM, these mechanisms can be exacerbated leading to higher loss of hemostasis. However, a series of therapeutic strategies targeting the activated endothelium such as specific antibodies or inhibitors against thrombin, key cytokines, factor X, complement system, the kallikrein-kinin system or NETosis, might represent new opportunities to address this hypercoagulable state present in COVID-19 and DM. Antidiabetics may also ameliorate endothelial dysfunction, inflammation, and platelet aggregation. By improving the microvascular pathology in COVID-19 and post-COVID subjects, the associated comorbidities and the risk of mortality could be reduced.

Recent Advances in Molecular and Cellular Functions of S100A10

S100A10 (p11, annexin II light chain, calpactin light chain) is a multifunctional protein with a wide range of physiological activity. S100A10 is unique among the S100 family members of proteins since it does not bind to Ca2+, despite its sequence and structural similarity. This review focuses on studies highlighting the structure, regulation, and binding partners of S100A10. The binding partners of S100A10 were collated and summarized.

Tranexamic acid for haemostasis and beyond: does dose matter?

Tranexamic acid (TXA) is a widely used antifibrinolytic agent that has been used since the 1960's to reduce blood loss in various conditions. TXA is a lysine analogue that competes for the lysine binding sites in plasminogen and tissue-type plasminogen activator impairing its interaction with the exposed lysine residues on the fibrin surface. The presence of TXA therefore, impairs the plasminogen and tPA engagement and subsequent plasmin generation on the fibrin surface, protecting fibrin clot from proteolytic degradation. However, critical lysine binding sites for plasmin(ogen) also exist on other proteins and on various cell-surface receptors allowing plasmin to exert potent effects on other targets that are unrelated to classical fibrinolysis, notably in relation to immunity and inflammation. Indeed, TXA was reported to significantly reduce post-surgical infection rates in patients after cardiac surgery unrelated to its haemostatic effects. This has provided an impetus to consider TXA in other indications beyond inhibition of fibrinolysis. While there is extensive literature on the optimal dosage of TXA to reduce bleeding rates and transfusion needs, it remains to be determined if these dosages also apply to blocking the non-canonical effects of plasmin.

Trace Metals and The Hemostatic System

In this narrative review we report the main relationships between trace metals and the hemostatic system since this aspect has seldom attracted the attention of the scientific community. A basic aspect to be considered is the importance of maintaining the fine control of all trace metals' levels since they have an important impact on the pathophysiology of the hemostatic system. It is worth noting that poor diet habits are responsible for most trace metal deficiencies, while pollution is responsible for dangerous exposure to them with a consequent negative impact on the general population. This appears of paramount importance in planning the implementation of food and nutrient support to ameliorate the hidden hunger and the quality of life of people especially in developing countries and limiting poisons both in the air and food. As it often happens, when damage to certain mechanisms takes a very long time to appear, no attention is paid to the importance of a systematic prevention to avoid late negative outcomes.

Targeting NETs using dual-active DNase1 variants

Background

Neutrophil Extracellular Traps (NETs) are key mediators of immunothrombotic mechanisms and defective clearance of NETs from the circulation underlies an array of thrombotic, inflammatory, infectious, and autoimmune diseases. Efficient NET degradation depends on the combined activity of two distinct DNases, DNase1 and DNase1-like 3 (DNase1L3) that preferentially digest double-stranded DNA (dsDNA) and chromatin, respectively.

Methods

Here, we engineered a dual-active DNase with combined DNase1 and DNase1L3 activities and characterized the enzyme for its NET degrading potential in vitro. Furthermore, we produced a mouse model with transgenic expression of the dual-active DNase and analyzed body fluids of these animals for DNase1 and DNase 1L3 activities. We systematically substituted 20 amino acid stretches in DNase1 that were not conserved among DNase1 and DNase1L3 with homologous DNase1L3 sequences.

Results

We found that the ability of DNase1L3 to degrade chromatin is embedded into three discrete areas of the enzyme's core body, not the C-terminal domain as suggested by the state-of-the-art. Further, combined transfer of the aforementioned areas of DNase1L3 to DNase1 generated a dual-active DNase1 enzyme with additional chromatin degrading activity. The dual-active DNase1 mutant was superior to native DNase1 and DNase1L3 in degrading dsDNA and chromatin, respectively. Transgenic expression of the dual-active DNase1 mutant in hepatocytes of mice lacking endogenous DNases revealed that the engineered enzyme was stable in the circulation, released into serum and filtered to the bile but not into the urine.

Conclusion

Therefore, the dual-active DNase1 mutant is a promising tool for neutralization of DNA and NETs with potential therapeutic applications for interference with thromboinflammatory disease states.

Rare inherited coagulation and fibrinolytic defects that challenge diagnostic laboratories

BACKGROUND

Coagulation factors, anticoagulants, and fibrinolytic proteins are important for hemostasis, and mutations affecting these proteins causes some rare inherited bleeding disorders that are particularly challenging to diagnose.

AIMS

This review provides current information on rare inherited bleeding disorders that are difficult to diagnose.

MATERIAL & METHODS

A review of the literature was conducted for up to date information on rare and difficult to diagnose bleeding disorders.

RESULTS

Some rare bleeding disorders cause an inherited deficiency of multiple coagulation factors (F), such as combined FV and FVIII deficiency and familial vitamin K-dependent clotting factor deficiency. Additionally, congenital disorders of glycosylation can affect a variety of procoagulant and anticoagulant proteins and also platelets. Some bleeding disorders reflect mutations with unique impairments in the procoagulant/anticoagulant balance, including those caused by F5 mutations that secondarily increase the plasma levels of tissue factor pathway inhibitor as well as THBD mutations that increase functional thrombomodulin in plasma or cause a consumptive coagulopathy due to thrombomodulin deficiency. Some bleeding disorders accelerate fibrinolysis due to loss-of-function mutations in SERPINE1 and SERPINF2 or in the case of Quebec platelet disorder, a duplication mutation that rewires PLAU and selectively increases expression in megakaryocytes, resulting in a unique platelet-dependent gain-of-function defect in fibrinolysis.

DISCUSSION

Current information on rare and difficult to diagnose bleeding disorders indicates they have unique clinical and laboratory features, and pathogenic characteristics to consider for diagnostic evaluation.

CONCLUSION

Laboratories and clinicians should consider rare inherited disorders, and difficult to diagnose conditions, in their strategy for diagnosing bleeding disorders.

A review of hemostatic chemical components and their mechanisms in traditional Chinese medicine and ethnic medicine

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicine and ethnic medicine together play an important value in the modern medicine system that is different from that of chemical drugs. Chinese medicine and ethnic medicine with hemostatic effect have unique advantages and development potential in the prevention and treatment of clinical hemorrhagic diseases, reflecting multi-component, multi-target and multi-pathway effects.

AIM OF THE STUDY

In this paper, the active ingredients related to the hemostatic effect of traditional Chinese medicine and ethnic medicine are taken as the starting point, and the traditional Chinese medicine and ethnic medicine with traditional hemostatic purposes are reviewed, and the existing research progress on the active ingredients and their mechanism of action of these drugs is systematically expounded, aiming to provide theoretical reference for the development of traditional hemostatic drugs, the discovery of hemostatic active ingredients and the research of new hemostatic methods.

MATERIALS AND METHODS

Hemostatic chinese medicine and ethnic medicine were collected and summarized from the classic books of Materia Medica, public literature database and doctoral or master's thesis repositories. At the same time, we discussed the classification of various types of hemostatic active ingredients of traditional Chinese medicine and ethnic medicine according to the different mechanisms of hemostasis.

RESULTS

A total of 436 traditional Chinese medicine and ethnic medicine with hemostatic effects have been collected, and their hemostatic active ingredients include alkaloids, quinones, flavonoids, phenylpropanoids, organic acids, amino acids, terpenoids, steroids, phenols, tannins, esters, polysaccharides and herbal extracts, etc. These active ingredients accelerate the formation of hemostasis by improving endogenous and exogenous hemostatic pathways mainly through enhancing vascular wall contraction, increasing platelet aggregation, promoting coagulation system activation and inhibiting fibrinolysis.

CONCLUSIONS

This article reviews the previous data on various aspects of the hemostatic effect of traditional Chinese medicine and ethnomedicine. Many traditional hemostatic drugs have been discovered and many active ingredients and mechanisms have been reported. However, although there are a large number of drugs with traditional hemostatic effects, there are still few developed and applied. At the same time, the hemostatic components of many drugs still remain in the study of the activity of their total extracts, and the potential link between some drug components achieving hemostatic effects through different mechanisms remains to be elucidated.

Plasmin and plasminogen prevent sepsis severity by reducing neutrophil extracellular traps and systemic inflammation

Sepsis is a lethal syndrome characterized by systemic inflammation and abnormal coagulation. Despite therapeutic advances, sepsis mortality remains substantially high. Herein, we investigated the role of the plasminogen/plasmin (Plg/Pla) system during sepsis. Plasma levels of Plg were significantly lower in mice subjected to severe compared with nonsevere sepsis, whereas systemic levels of IL-6, a marker of sepsis severity, were higher in severe sepsis. Plg levels correlated negatively with IL-6 in both septic mice and patients, whereas plasminogen activator inhibitor-1 levels correlated positively with IL-6. Plg deficiency render mice susceptible to nonsevere sepsis induced by cecal ligation and puncture (CLP), resulting in greater numbers of neutrophils and M1 macrophages, liver fibrin(ogen) deposition, lower efferocytosis, and increased IL-6 and neutrophil extracellular trap (NET) release associated with organ damage. Conversely, inflammatory features, fibrin(ogen), and organ damage were substantially reduced, and efferocytosis was increased by exogenous Pla given during CLP- and LPS-induced endotoxemia. Plg or Pla protected mice from sepsis-induced lethality and enhanced the protective effect of antibiotics. Mechanistically, Plg/Pla-afforded protection was associated with regulation of NET release, requiring Pla-protease activity and lysine binding sites. Plg/Pla are important host-protective players during sepsis, controlling local and systemic inflammation and collateral organ damage.

Vascular Dysfunction in Alzheimer's Disease: Alterations in the Plasma Contact and Fibrinolytic Systems

Alzheimer's disease (AD) is the most common neurodegenerative disease, affecting millions of people worldwide. The classical hallmarks of AD include extracellular beta-amyloid (Aβ) plaques and neurofibrillary tau tangles, although they are often accompanied by various vascular defects. These changes include damage to the vasculature, a decrease in cerebral blood flow, and accumulation of Aβ along vessels, among others. Vascular dysfunction begins early in disease pathogenesis and may contribute to disease progression and cognitive dysfunction. In addition, patients with AD exhibit alterations in the plasma contact system and the fibrinolytic system, two pathways in the blood that regulate clotting and inflammation. Here, we explain the clinical manifestations of vascular deficits in AD. Further, we describe how changes in plasma contact activation and the fibrinolytic system may contribute to vascular dysfunction, inflammation, coagulation, and cognitive impairment in AD. Given this evidence, we propose novel therapies that may, alone or in combination, ameliorate AD progression in patients.

Plant-Derived Compounds and Extracts as Modulators of Plasmin Activity-A Review

Functionality of the fibrinolytic system is based on activity of its central enzyme, plasmin, responsible for the removal of fibrin clots. Besides the hemostasis, fibrinolytic proteins are also involved in many other physiological and pathological processes, including immune response, extracellular matrix degradation, cell migration, and tissue remodeling. Both the impaired and enhanced activity of fibrinolytic proteins may result in serious physiological consequences: prothrombotic state or excessive bleeding, respectively. However, current medicine offers very few options for treating fibrinolytic disorders, particularly in the case of plasmin inhibition. Although numerous attempts have been undertaken to identify natural or to develop engineered fibrinolytic system modulators, structural similarities within serine proteases of the hemostatic system and pleiotropic activity of fibrinolytic proteins constitute a serious problem in discovering anti- or profibrinolytic agents that could precisely affect the target molecules and reduce the risk of side effects. Therefore, this review aims to present a current knowledge of various classes of natural inhibitors and stimulators of the fibrinolytic system being well-defined low-molecular plant secondary metabolites or constituents of plant extracts as well as plant peptides. This work also discusses obstacles caused by low specificity of most of natural compounds and, hence, outlines recent trends in studies aimed at finding more efficient modulators of plasmin activity, including investigation of modifications of natural pharmacophore templates.

The Role of the Plasminogen/Plasmin System in Inflammation of the Oral Cavity

The oral cavity is a unique environment that consists of teeth surrounded by periodontal tissues, oral mucosae with minor salivary glands, and terminal parts of major salivary glands that open into the oral cavity. The cavity is constantly exposed to viral and microbial pathogens. Recent studies indicate that components of the plasminogen (Plg)/plasmin (Pm) system are expressed in tissues of the oral cavity, such as the salivary gland, and contribute to microbial infection and inflammation, such as periodontitis. The Plg/Pm system fulfills two major functions: (a) the destruction of fibrin deposits in the bloodstream or damaged tissues, a process called fibrinolysis, and (b) non-fibrinolytic actions that include the proteolytic modulation of proteins. One can observe both functions during inflammation. The virus that causes the coronavirus disease 2019 (COVID-19) exploits the fibrinolytic and non-fibrinolytic functions of the Plg/Pm system in the oral cavity. During COVID-19, well-established coagulopathy with the development of microthrombi requires constant activation of the fibrinolytic function. Furthermore, viral entry is modulated by receptors such as TMPRSS2, which is necessary in the oral cavity, leading to a derailed immune response that peaks in cytokine storm syndrome. This paper outlines the significance of the Plg/Pm system for infectious and inflammatory diseases that start in the oral cavity.

Antifibrinolytics in the treatment of traumatic brain injury

PURPOSE OF REVIEW

Traumatic brain injury (TBI) is a leading cause of trauma-related deaths, and pharmacologic interventions to limit intracranial bleeding should improve outcomes. Tranexamic acid reduces mortality in injured patients with major systemic bleeding, but the effects of antifibrinolytic drugs on outcomes after TBI are less clear. We therefore summarize recent evidence to guide clinicians on when (not) to use antifibrinolytic drugs in TBI patients.

RECENT FINDINGS

Tranexamic acid is the only antifibrinolytic drug that has been studied in patients with TBI. Several recent studies failed to conclusively demonstrate a benefit on survival or neurologic outcome. A large trial with more than 12 000 patients found no significant effect of tranexamic acid on head-injury related death, all-cause mortality or disability across the overall study population, but observed benefit in patients with mild to moderate TBI. Observational evidence signals potential harm in patients with isolated severe TBI.

SUMMARY

Given that the effect of tranexamic acid likely depends on a variety of factors, it is unlikely that a 'one size fits all' approach of administering antifibrinolytics to all patients will be helpful. Tranexamic acid should be strongly considered in patients with mild to moderate TBI and should be avoided in isolated severe TBI.

Factors Modulating COVID-19: A Mechanistic Understanding Based on the Adverse Outcome Pathway Framework

Addressing factors modulating COVID-19 is crucial since abundant clinical evidence shows that outcomes are markedly heterogeneous between patients. This requires identifying the factors and understanding how they mechanistically influence COVID-19. Here, we describe how eleven selected factors (age, sex, genetic factors, lipid disorders, heart failure, gut dysbiosis, diet, vitamin D deficiency, air pollution and exposure to chemicals) influence COVID-19 by applying the Adverse Outcome Pathway (AOP), which is well-established in regulatory toxicology. This framework aims to model the sequence of events leading to an adverse health outcome. Several linear AOPs depicting pathways from the binding of the virus to ACE2 up to clinical outcomes observed in COVID-19 have been developed and integrated into a network offering a unique overview of the mechanisms underlying the disease. As SARS-CoV-2 infectibility and ACE2 activity are the major starting points and inflammatory response is central in the development of COVID-19, we evaluated how those eleven intrinsic and extrinsic factors modulate those processes impacting clinical outcomes. Applying this AOP-aligned approach enables the identification of current knowledge gaps orientating for further research and allows to propose biomarkers to identify of high-risk patients. This approach also facilitates expertise synergy from different disciplines to address public health issues.

Platelet-targeted thrombolysis for treatment of acute ischemic stroke

Thrombolysis with tissue-type plasminogen activator (tPA) remains the main treatment for acute ischemic stroke. Nevertheless, tPA intervention is limited by a short therapeutic window, low recanalization rates, and a risk of intracranial hemorrhage (ICH), highlighting the clinical demand for improved thrombolytic drugs. We examined a novel thrombolytic agent termed "SCE5-scuPA," comprising a single-chain urokinase plasminogen activator (scuPA) fused with a single-chain antibody (SCE5) that targets the activated glycoprotein IIb/IIIa platelet receptor, for its effects in experimental stroke. SCE5-scuPA was first tested in a whole blood clot degradation assay to show the benefit of platelet-targeted thrombolysis. The tail bleeding time, blood clearance, and biodistribution were then determined to inform the use of SCE5-scuPA in mouse models of photothrombotic stroke and middle cerebral artery occlusion against tenecteplase. The impacts of SCE5-scuPA on motor function, ICH, blood-brain barrier (BBB) integrity, and immunosuppression were evaluated. Infarct size was measured by computed tomography imaging and magnetic resonance imaging. SCE5-scuPA enhanced clot degradation ex vivo compared with its nonplatelet-targeting control. The maximal SCE5-scuPA dose that maintained hemostasis and a rapid blood clearance was determined. SCE5-scuPA administration both before and 2 hours after photothrombotic stroke reduced the infarct volume. SCE5-scuPA also improved neurologic deficit, decreased intracerebral blood deposits, preserved the BBB, and alleviated immunosuppression poststroke. In middle cerebral artery occlusion, SCE5-scuPA did not worsen stroke outcomes or cause ICH, and it protected the BBB. Our findings support the ongoing development of platelet-targeted thrombolysis with SCE5-scuPA as a novel emergency treatment for acute ischemic stroke with a promising safety profile.

D-dimer: an analyte with increasing application in Covid-19 infection

INTRODUCTION

: D- Dimer levels from peripheral blood are increasingly used to assess various pathological conditions. Initially an area for haematologists, now this analyte is evaluated more extensively from many specialities of medicine. Covid-19 infection has not only added a new dimension to D-Dimer level assessment in this disease but has also shed newer lights to the underlying pathophysiological mechanisms for its elevation in this disease.

AREAS COVERED

Innate variability in measuring D- Dimer levels, Impact of various techniques in measuring D- Dimer, non availability of uniform controls and standards, molecular heterogeneity of the product, how it is produced. Reasons for raised D- Dimer in covid-19 infection. D- Dimer in other pathological states. Articles with relevant key words from 1990 searched in PubMed were utilized for review.

EXPERT OPINION

: D-Dimer has important application in diagnosis, prognosis, management and understanding various conditions. Its level can rise with increased coagulability of blood, sepsis, cytokine storm and snake bite etc. Renal function, age influences its reference ranges. Units of measurement, its expression varies in different reports needing international standardization. In Covid-19 infection its levels correlate with stage of the disease, pathology and complications.

The ANXA2/S100A10 Complex—Regulation of the Oncogenic Plasminogen Receptor

The generation of the serine protease plasmin is initiated by the binding of its zymogenic precursor, plasminogen, to cell surface receptors. The proteolytic activity of plasmin, generated at the cell surface, plays a crucial role in several physiological processes, including fibrinolysis, angiogenesis, wound healing, and the invasion of cells through both the basement membrane and extracellular matrix. The seminal observation by Albert Fischer that cancer cells, but not normal cells in culture, produce large amounts of plasmin formed the basis of current-day observations that plasmin generation can be hijacked by cancer cells to allow tumor development, progression, and metastasis. Thus, the cell surface plasminogen-binding receptor proteins are critical to generating plasmin proteolytic activity at the cell surface. This review focuses on one of the twelve well-described plasminogen receptors, S100A10, which, when in complex with its regulatory partner, annexin A2 (ANXA2), forms the ANXA2/S100A10 heterotetrameric complex referred to as AIIt. We present the theme that AIIt is the quintessential cellular plasminogen receptor since it regulates the formation and the destruction of plasmin. We also introduce the term oncogenic plasminogen receptor to define those plasminogen receptors directly activated during cancer progression. We then discuss the research establishing AIIt as an oncogenic plasminogen receptor-regulated during EMT and activated by oncogenes such as SRC, RAS, HIF1α, and PML-RAR and epigenetically by DNA methylation. We further discuss the evidence derived from animal models supporting the role of S100A10 in tumor progression and oncogenesis. Lastly, we describe the potential of S100A10 as a biomarker for cancer diagnosis and prognosis.