Factor XIII, clot structure, thrombosis

Discovery of Heparin Mimetic, Potent, and Selective Inhibitors of Human Clotting Factor XIIIa

Factor XIIIa (FXIIIa) is a cysteine transglutaminase that catalyzes the last step in the coagulation process. An anion-binding site inhibition of FXIIIa is a paradigm-shifting strategy that may offer key advantages of controlled inhibition. Such an approach is likely to lead to novel FXIIIa inhibitors that do not carry bleeding risks. We previously reported a flavonoid trimer-based allosteric inhibitor of FXIIIa with moderate potency and selectivity. To further advance this approach, we evaluated a series of 27 variably sulfonated heparin mimetics against human FXIIIa. Only 13 molecules exhibited inhibitory activity at the highest concentration tested with IC50 values of 2-286 μM. Specifically, inhibitor 16 demonstrated an IC50 value of 2.4 ± 0.5 μM in a bisubstrate, fluorescence-based trans-glutamination assay. It also demonstrated a significant selectivity over other clotting factors including thrombin, factor Xa, and factor XIa as well as other cysteine enzymes including papain and tissue transglutaminase 2. Inhibitor 16 did not affect the viability of three human cell lines at a concentration that is 5-fold its FXIIIa-IC50. The molecule had a very weak effect on the activated partial thromboplastin time of human plasma at a concentration of >700 μM, further supporting its functional selectivity. Importantly, molecule 16 inhibited FXIIIa-mediated polymerization of fibrin(ogen) in a concentration-dependent manner as shown by the gel electrophoresis experiment. Michaelis-Menten kinetics revealed that the molecule competes with the Gln-donor protein substrate, i.e., dimethylcasein, but not with the Lys-donor small substrate, i.e., dansylcadaverine. Molecular modeling studies revealed that this type of molecule likely binds to an anion-binding site comprising the basic amino acids of Lys54, Lys61, Lys73, Lys156, and Arg244 among others. Overall, our work puts forward a new anion-binding site, selective, nontoxic, sulfonated heparin mimetic FXIIIa inhibitor 16 for further development as an effective and safer anticoagulant.

Haemostatic Gene Expression in Cancer-Related Immunothrombosis: Contribution for Venous Thromboembolism and Ovarian Tumour Behaviour

Ovarian cancer (OC) is the deadliest gynaecological malignancy. Identifying new prognostic biomarkers is an important research field. Haemostatic components together with leukocytes can drive cancer progression while increasing the susceptibility to venous thromboembolism (VTE) through immunothrombosis. Unravelling the underlying complex interactions offers the prospect of uncovering relevant OC prognostic biomarkers, predictors of cancer-associated thrombosis (CAT), and even potential targets for cancer therapy. Thus, this study evaluated the expression of F3, F5, F8, F13A1, TFPI1, and THBD in peripheral blood cells (PBCs) of 52 OC patients. Those with VTE after tumour diagnosis had a worse overall survival (OS) compared to their counterparts (mean OS of 13.8 ± 4.1 months and 47.9 ± 5.7 months, respectively; log-rank test, p = 0.001). Low pre-chemotherapy F3 and F8 expression levels were associated with a higher susceptibility for OC-related VTE after tumour diagnosis (χ2, p < 0.05). Regardless of thrombogenesis, patients with low baseline F8 expression had a shorter progression-free survival (PFS) than their counterparts (adjusted hazard ratio (aHR) = 2.54; p = 0.021). Among those who were not under platelet anti-aggregation therapy, low F8 levels were also associated with a shorter OS (aHR = 6.16; p = 0.006). Moving forward, efforts should focus on external validation in larger cohorts.

Discovery of plasma proteins associated with ventricular fibrillation during first ST-elevation myocardial infarction via proteomics

AIMS

The underlying biological mechanisms of ventricular fibrillation (VF) during acute myocardial infarction are largely unknown. To our knowledge, this is the first proteomic study for this trait, with the aim to identify and characterize proteins that are associated with VF during first ST-elevation myocardial infarction (STEMI).

METHODS AND RESULTS

We included 230 participants from a Danish ongoing case-control study on patients with first STEMI with VF (case, n = 110) and without VF (control, n = 120) before guided catheter insertion for primary percutaneous coronary intervention. The plasma proteome was investigated using mass spectrometry-based proteomics on plasma samples collected within 24 h of symptom onset, and one patient was excluded in quality control. In 229 STEMI patients {72% men, median age 62 years [interquartile range (IQR): 54-70]}, a median of 257 proteins (IQR: 244-281) were quantified per patient. A total of 26 proteins were associated with VF; these proteins were involved in several biological processes including blood coagulation, haemostasis, and immunity. After correcting for multiple testing, two up-regulated proteins remained significantly associated with VF, actin beta-like 2 [ACTBL2, fold change (FC) 2.25, P < 0.001, q = 0.023], and coagulation factor XIII-A (F13A1, FC 1.48, P < 0.001, q = 0.023). None of the proteins were correlated with anterior infarct location.

CONCLUSION

Ventricular fibrillation due to first STEMI was significantly associated with two up-regulated proteins (ACTBL2 and F13A1), suggesting that they may represent novel underlying molecular VF mechanisms. Further research is needed to determine whether these proteins are predictive biomarkers or acute phase response proteins to VF during acute ischaemia.

Novel Insights into Heterozygous Factor XIII Deficiency

The prevalence and clinical significance of heterozygous factor XIII (FXIII) deficiency has long been debated, with controversial reports emerging since 1988. In the absence of large epidemiologic studies, but based on a few studies, a prevalence of 1 per 1,000 to 5,000 is estimated. In southeastern Iran, a hotspot area for the disorder, a study of more than 3,500 individuals found an incidence of 3.5%. Between 1988 and 2023, a total of 308 individuals were found with heterozygous FXIII deficiency, of which molecular, laboratory, and clinical presentations were available for 207 individuals. A total of 49 variants were found in the F13A gene, most of which were missense (61.2%), followed by nonsense (12.2%) and small deletions (12.2%), most occurring in the catalytic domain (52.1%) of the FXIII-A protein and most frequently in exon 4 (17%) of the F13A gene. This pattern is relatively similar to homozygous (severe) FXIII deficiency. In general, heterozygous FXIII deficiency is an asymptomatic condition without spontaneous bleeding tendency, but it can lead to hemorrhagic complications in hemostatic challenges such as trauma, surgery, childbirth, and pregnancy. Postoperative bleeding, postpartum hemorrhage, and miscarriage are the most common clinical manifestations, while impaired wound healing has been rarely reported. Although some of these clinical manifestations can also be observed in the general population, they are more common in heterozygous FXIII deficiency. While studies of heterozygous FXIII deficiency conducted over the past 35 years have shed light on some of the ambiguities of this condition, further studies on a large number of heterozygotes are needed to answer the major questions related to heterozygous FXIII deficiency.

Research into New Molecular Mechanisms in Thrombotic Diseases Paves the Way for Innovative Therapeutic Approaches

Thrombosis is a multifaceted process involving various molecular components, including the coagulation cascade, platelet activation, platelet-endothelial interaction, anticoagulant signaling pathways, inflammatory mediators, genetic factors and the involvement of various cells such as endothelial cells, platelets and leukocytes. A comprehensive understanding of the molecular signaling pathways and cell interactions that play a role in thrombosis is essential for the development of precise therapeutic strategies for the treatment and prevention of thrombotic diseases. Ongoing research in this field is constantly uncovering new molecular players and pathways that offer opportunities for more precise interventions in the clinical setting. These molecular insights into thrombosis form the basis for the development of targeted therapeutic approaches for the treatment and prevention of thrombotic disease. The aim of this review is to provide an overview of the pathogenesis of thrombosis and to explore new therapeutic options.

Low factor XIII levels and altered fibrinolysis in patients with multiple myeloma

BACKGROUND

Acquired factor FXIII (FXIII) deficiency can be immune- or non-immune mediated and may cause severe bleeding symptoms. The incidence of acquired FXIII deficiency and its etiology in patients with multiple myeloma (MM) are poorly understood.

OBJECTIVES

To assess FXIII levels and the balance of fibrinolysis in newly diagnosed, untreated MM and monoclonal gammopathy of undetermined significance (MGUS) patients.

METHODS

FXIII activity, mixing studies, FXIII-A2B2 antigen, total FXIII-B antigen were measured in platelet-poor plasma from 17 untreated MM patients, 33 untreated MGUS patients, and 30 age and sex-matched healthy controls. Besides routine laboratory measurements, the balance of coagulation and fibrinolysis was evaluated using quantitative fibrin monomer (FM) test, thrombin-antithrombin assay, α2-antiplasmin activity, plasmin-α2-antiplasmin (PAP) complex, D-dimer, plasmin generation assay, clot lysis assay, and ClotPro-TPA test.

RESULTS

FXIII-A2B2 levels were significantly lower in MM patients compared to controls [median (IQR):14.6 (11.2-19.4) vs. 21.8 (17.1-26.4) mg/L, p = 0.0015], whereas total FXIII-B did not differ between groups. Decrease in FXIII activity was parallel to the decrease in FXIII-A2B2. An immune-mediated inhibitory mechanism was ruled out. Free/total FXIII-B was significantly higher in MM patients compared to MGUS and healthy controls, suggesting an etiology of FXIII-A consumption. In MM and MGUS patients, FM, D-dimer, and PAP complex were significantly elevated compared to controls, indicating hypercoagulability and ongoing fibrinolysis.

CONCLUSIONS

Low FXIII levels due to consumption were observed in MM patients at diagnosis. Hypercoagulability and ongoing fibrinolysis were detected in MM and MGUS, indicating that a disturbed hemostasis balance is already present in the latter benign condition.

Advances of Blood Coagulation Factor XIII in Bone Healing

The biologic process of bone healing is complicated, involving a variety of cells, cytokines, and growth factors. As a result of bone damage, the activation of a clotting cascade leads to hematoma with a high osteogenic potential in the initial stages of healing. A major factor involved in this course of events is clotting factor XIII (FXIII), which can regulate bone defect repair in different ways during various stages of healing. Autografts and allografts often have defects in clinical practice, making the development of advanced materials that support bone regeneration a critical requirement. Few studies, however, have examined the promotion of bone healing by FXIII in combination with biomaterials, in particular, its effect on blood coagulation and osteogenesis. Therefore, we mainly summarized the role of FXIII in promoting bone regeneration by regulating the extracellular matrix and type I collagen, bone-related cells, angiogenesis, and platelets, and described the research progress of FXIII = related biomaterials on osteogenesis. This review provides a reference for investigators to explore the mechanism by which FXIII promotes bone healing and the combination of FXIII with biomaterials to achieve targeted bone tissue repair.

Fibrin and Fibrinolytic Enzyme Cascade in Thrombosis: Unravelling the Role

Blood clot formation in blood vessels (thrombosis) is a major cause of life-threatening cardiovascular diseases. These clots are formed by αA-, βB-, and ϒ-peptide chains of fibrinogen joined together by isopeptide bonds with the help of blood coagulation factor XIIIa. These clot structures are altered by various factors such as thrombin, platelets, transglutaminase, DNA, histones, and red blood cells. Various factors are used to dissolve the blood clot, such as anticoagulant agents, antiplatelets drugs, fibrinolytic enzymes, and surgical operations. Fibrinolytic enzymes are produced by microorganisms (bacteria, fungi, etc.): streptokinase of Streptococcus hemolyticus, nattokinase of Bacillus subtilis YF 38, bafibrinase of Bacillus sp. AS-S20-I, longolytin of Arthrobotrys longa, versiase of Aspergillus versicolor ZLH-1, etc. They act as a thrombolytic agent by either enhancing the production of plasminogen activators (tissue or urokinase types), which convert inactive plasminogen to active plasmin, or acting as plasmin-like proteins themselves, forming fibrin degradation products which cause normal blood flow again in blood vessels. Fibrinolytic enzymes may be classified in two groups, as serine proteases and metalloproteases, based on their catalytic properties, consisting of a catalytic triad responsible for their fibrinolytic activity having different physiochemical properties (such as molecular weight, pH, and temperature). The analysis of fibrinolysis helps to detect hyperfibrinolysis (menorrhagia, renal failure, etc.) and hypofibrinolysis (diabetes, obesity, etc.) with the help of various fibrinolytic assays such as a fibrin plate assay, fibrin microplate assay, the viscoelastic method, etc. These fibrinolytic activities serve as a key aspect in the recognition of numerous cardiovascular diseases and can be easily produced on a large scale with a short generation time by microbes and are less expensive.

High prevalence of thrombophilic risk factors in patients with central retinal artery occlusion

INTRODUCTION

Central retinal artery occlusion (CRAO) is a common cause of blindness and visual morbidity. In the majority of cases, it is related to thrombotic embolism. Nevertheless, the role of inherited or acquired thrombophilic risk factors in CRAO pathogenesis has not been comprehensively studied.

METHODS

In 126 CRAO patients (66 [52.4%] men, median age 55 [range: 18-80] years) and 107 matched controls (56 [52.3%] men, median age 53 [range: 34-78] years) we evaluated classical atherosclerotic risk factors, including serum lipid profile and glucose level, analyzed intima-media complex thickness (IMT) of external carotid arteries, and performed transthoracic echocardiography. Furthermore, we established the prevalence of inherited and acquired thrombophilic risk factors, such as factor V Leiden (FVL) and prothrombin 20210 G/A genetic variants, plasma activity of factor (F) VIII, protein C and antithrombin activity, and free protein S levels. We also assessed the presence of antiphospholipid antibodies (APLA) and evaluated blood homocysteine in all enrolled subjects. Additionally, we estimated the occurrence of Val34Leu polymorphism of the A subunit of coagulation factor XIII (FXIII-A) in both groups as a potential thrombosis-protecting factor.

RESULTS

Among traditional atherosclerotic risk components, obesity/overweight and hypercholesterolemia were the most common in the CRAO group and occurred in 103 (81.7%) and 85 (67.5%) patients, respectively. CRAO patients also had elevated IMT and altered echocardiographic parameters, indicating diastolic cardiac dysfunction. In thrombophilia investigations, at least one laboratory risk factor occurred in 72.2% (n = 91) of CRAO patients, with APLA as the most frequent, detected in 38.1% (n = 48) of them (almost seven times more frequent than in controls, p < 0.001). Deficiencies in protein C activity and free protein S levels were also common in the CRAO group, reported in 17.5% (n = 22) and 19.8% (n = 25) of patients, respectively. Interestingly, among two analyzed prothrombotic genetic variants, only the FVL was related to CRAO, with the allelic frequency 2.4 times more prevalent than in controls (p = 0.044). Finally, the CRAO group was characterized by hyperhomocysteinemia, almost twice as common as in controls (p = 0.026). Antithrombin deficiency, elevated FVIII, and FXIII-A Val34Leu polymorphism were not associated with CRAO.

CONCLUSIONS

Our findings suggest that thrombophilia plays a vital role in the pathogenesis of CRAO. Thus, proper laboratory screening should be considered in the primary and secondary prevention of those episodes, with implementing appropriate therapy as needed.

Coagulation biomarkers for ischemic stroke

A State of the Art lecture titled "coagulation biomarkers for ischemic stroke" was presented at the International Society on Thrombosis and Haemostasis (ISTH) Congress in 2022. Ischemic stroke (IS) is a common disease with major morbidity and mortality. It is a challenge to determine which patients are at risk for IS or have poor clinical outcome after IS. An imbalance of coagulation markers may contribute to the progression and prognosis of IS. Therefore, we now discuss studies on the association of selected coagulation biomarkers from the hemostasis, inflammation, and immunothrombosis systems with the risk of IS, stroke severity at the acute phase, and clinical outcome after treatment. We report on coagulation biomarker-induced risk of IS, stroke severity, and outcomes following IS derived from prospective population studies, case-control studies, and acute-phase IS studies. We found indications that many coagulation and inflammation biomarkers are associated with IS, but it is early to conclude that any of these biomarkers can be applied in a therapeutic setting to predict patients at risk of IS, stroke severity at the acute phase, and clinical outcome after treatment. The strongest evidence for a role in IS was found for beta-thromboglobulin, von Willebrand factor, factor VIII, fibrinogen, thrombin-activatable fibrinolysis inhibitor, D-dimer, and neutrophil extracellular traps, and therefore, they are promising candidates. Further research and validation in large-size populations using well-defined study designs are warranted. Finally, we provide a selection of recent data relevant to this subject that was presented at the 2022 ISTH Congress.

Macrophages-derived Factor XIII links coagulation to inflammation in COPD

Background

The local, extravascular, activation of the coagulation system in response to injury is a key factor mediating the resulting inflammatory response. Coagulation Factor XIIIA (FXIIIA) found in alveolar macrophages (AM) and dendritic cells (DC), by influencing fibrin stability, might be an inflammatory modifier in COPD.

Aims

To study the expression of FXIIIA in AM and Langerin+DC (DC-1) and their relation to the inflammatory response and disease progression in COPD.

Methods

In 47 surgical lungs, 36 from smokers (22 COPD and 14 no-COPD) and 11 from non-smokers we quantified by immunohistochemistry FXIIIA expression in AM and DC-1 along with numbers of CD8+Tcells and CXCR3 expression in lung parenchyma and airways. Lung function was measured prior to surgery.

Results

The percentage of AM expressing FXIII (%FXIII+AM) was higher in COPD than no-COPD and non-smokers. DC-1 expressed FXIIIA and their numbers were higher in COPD than no-COPD and non-smokers. DC-1 positively correlated with %FXIII+AM (r=0.43; p<0.018). CD8+Tcells, which were higher in COPD than in no-COPD, were correlated with DC-1 (p<0.01) and %FXIII+AM. CXCR3+ cells were increased in COPD and correlated with %FXIII+AM (p<0.05). Both %FXIII+AM (r=-0.6; p=0.001) and DC-1 (r=-0.7; p=0.001) correlated inversely with FEV1.

Conclusion

FXIIIA, an important link between the extravascular coagulation cascade and inflammatory response, is significantly expressed in alveolar macrophages and dendritic cells of smokers with COPD, suggesting that it could play an important role in the adaptive inflammatory reaction characteristic of the disease.

Synergistic role of circulating CD14++CD16+ monocytes and fibrinogen in predicting the cardiovascular events after myocardial infarction

BACKGROUND

Monocytes and fibrinogen (FIB) play important roles in driving acute and reparative inflammatory pathways after myocardial infarction (MI). In humans, there are three subsets of monocytes, namely, CD14++CD16- (Mon1), CD14++CD16+ (Mon2), and CD14+CD16++ (Mon3). During the inflammatory response, monocyte subsets express high levels of integrin α_M β₂ and protease-activated receptors 1 and 3 to interact with FIB.

HYPOTHESIS

However, whether there is a synergistic role of FIB combined with Mon2 counts in prioritizing patients at high risk of future major adverse cardiovascular events (MACEs) after MI remains unknown.

METHODS

The MI patients who treated with primary percutaneous coronary intervention were enrolled. MI patients were categorized into four groups, that is, low FIB/low Mon2, low FIB/high Mon2, high FIB/low Mon2, and high FIB/high Mon2, according to cutoff values of 3.28 g/L for FIB and 32.20 cells/μL for Mon2. Kaplan-Meier survival analysis and Cox proportional hazards models were used to estimate the risk of MACEs of MI patients during a median follow-up of 2.7 years. Mediating effects of high FIB levels and MACEs associated with high monocyte subsets were calculated by mediation analysis.

RESULTS

High FIB/high Mon2 group had the highest risk of MACEs during a median follow-up of 2.7 years. Moreover, mediation analysis showed that a high FIB level could explain 24.9% (p < .05) of the increased risk of MACEs associated with Mon2.

CONCLUSION

This work provides evidence indicating the translational potential of a synergistic role of FIB combined with Mon2 in prioritizing patients at high risk of future MACEs after MI.

Fibrin clot properties in cardiovascular disease: from basic mechanisms to clinical practice

Fibrinogen conversion into insoluble fibrin and the formation of a stable clot is the final step of the coagulation cascade. Fibrin clot porosity and its susceptibility to plasmin-mediated lysis are the key fibrin measures, describing the properties of clots prepared ex vivo from citrated plasma. Cardiovascular disease (CVD), referring to coronary heart disease, heart failure, stroke, and hypertension, has been shown to be associated with the formation of dense fibrin networks that are relatively resistant to lysis. Denser fibrin mesh characterized acute patients at the onset of myocardial infarction or ischaemic stroke, while hypofibrinolysis has been identified as a persistent fibrin feature in patients following thrombotic events or in those with stable coronary artery disease. Traditional cardiovascular risk factors, such as smoking, diabetes mellitus, hyperlipidaemia, obesity, and hypertension, have also been linked with unfavourably altered fibrin clot properties, while some lifestyle modifications and pharmacological treatment, in particular statins and anticoagulants, may improve fibrin structure and function. Prospective studies have suggested that prothrombotic fibrin clot phenotype can predict cardiovascular events in short- and long-term follow-ups. Mutations and splice variants of the fibrinogen molecule that have been proved to be associated with thrombophilia or increased cardiovascular risk, along with fibrinogen post-translational modifications, prothrombotic state, inflammation, platelet activation, and neutrophil extracellular traps formation, contribute also to prothrombotic fibrin clot phenotype. Moreover, about 500 clot-bound proteins have been identified within plasma fibrin clots, including fibronectin, α2-antiplasmin, factor XIII, complement component C3, and histidine-rich glycoprotein. This review summarizes the current knowledge on the mechanisms underlying unfavourable fibrin clot properties and their implications in CVD and its thrombo-embolic manifestations.

Fibrin-Targeted Nanoparticles for Finding, Visualizing and Characterizing Blood Clots in Acute Ischemic Stroke

Recanalization of the occluded artery is the gold standard treatment for acute ischemic stroke, which includes enzymatic fibrinolytic treatment with the use of recombinant tissue plasminogen activators (rtPAs) to disrupt the occluding clot, the use of mechanical thrombectomy to physically remove the clot, or a combination of both. Fibrin is one of the main components of blood clots causing ischemic stroke and is the target of rtPA upon activation of plasminogen in the clot. In addition, fibrin content also influences the efficacy of mechanical thrombectomy. Current imaging methods can successfully identify occlusions in large vessels; however, there is still a need for contrast agents capable of visualizing small thrombi in ischemic stroke patients. In this work, we describe the synthesis and the in vitro characterization of a new diagnostic nanoparticle, as well as the in vivo evaluation in an animal model of thromboembolic stroke. Gd-labeled KCREKA peptides were synthesized and attached onto the surface of PEGylated superparamagnetic nanoparticles. Magnetic resonance imaging (MRI) of blood clots was performed in vitro and in vivo in animal models of thromboembolic stroke. KCREKA-NPs were synthesized by attaching the peptide to the amino (N) termini of the PEG-NPs. The sizes of the nanoparticles, measured via DLS, were similar for both KCREKA-NPs and PEG-NPs (23 ± 4 nm, PDI = 0.11 and 25 ± 8 nm, PDI = 0.24, respectively). In the same line, r2 relaxivities were also similar for the nanoparticles (149 ± 2 mM Fe s−1 and 151 ± 5 mM Fe s−1), whereas the r1 relaxivity was higher for KCREKA-NPs (1.68 ± 0.29 mM Fe s−1 vs. 0.69 ± 0.3 mM Fe s−1). In vitro studies showed that blood clots with low coagulation times were disrupted by rtPA, whereas aged clots were almost insensitive to the presence of rtPA. MRI in vitro studies showed a sharp decrease in the T1 × T2 signals measured for aged clots incubated with KCREKA-NPs compared with fresh clots (47% [22, 80] to 26% [15, 51]). Furthermore, the control blood showed a higher value of the T1 × T2 signal (39% [20, 61]), being the blood clots with low coagulation times the samples with the lowest values measured by MRI. In vivo studies showed a significant T1 × T2 signal loss in the clot region of 24% after i.v. injection of KCREKA-NPs. The thrombus age (2.5% ± 6.1% vs. 81.3% ± 19.8%, p < 0.01) confirmed our ability to identify in vivo fresh blood clots. In this study, we developed and tested a dual MRI nanoparticle, acting as T1 and T2 contrast agents in MRI analyses. The developed KCREKA-NPs showed affinity for the fibrin content of blood clots, and the MRI signals provided by the nanoparticles showed significant differences depending on the clot age. The developed KCREKA-NPs could be used as a tool to predict the efficacy of a recanalization treatment and improve the triage of ischemic stroke patients.

Association of factor V Leiden R506Q, FXIIIVal34Leu, and MTHFR C677T polymorphisms with acute myocardial infarction

Background

Acute myocardial infarction (AMI) is a leading cause of death and morbidity around the world. Although the association between thrombophilia and AMI is well-established, controversial data are present on the association between thrombophilic polymorphisms and AMI. The aim of this study was to investigate the association of three thrombophilic polymorphisms including factor V Leiden (FVL), MTHFRC677T (methylenetetrahydrofolate reductase), and Coagulation factor XIIIVal34Leu with AMI in East of Iran.

Result

There were no statistically significant differences between the patients and control groups in terms of the distributions of allelic and genotypic frequencies of FVL and FXIIIVal34Leu polymorphisms (P-value > 0.05). Subjects who carried CT genotype of MTHFR C677T polymorphism were at a 2.03-fold higher risk for AMI (P-value: 0.02, OR 1.76, 95% CI 1.07–2.75). Furthermore, patients with MTHFR 677CT (P-value < 0.001, β = - 0.90, 95% CI − 1.33, − 047) or 677CC (P-value < 0.001, β = - 1.04, 95% CI − 1.47, − 0.61) genotypes showed significantly Lower creatinine levels compared with patients having the MTHFR 677TT. No association was observed between the other remaining polymorphisms and AMI (P-value > 0.05).

Conclusion

Our findings showed that MTHFRC677T polymorphism could contribute to AMI susceptibility and increase creatinine levels in east Iran population. This was the first study to examine the association of these three polymorphisms with AMI in east Iran.

Diabetes mellitus and diabetic nephropathy: a review of the literature on hemostatic changes in coagulation and thrombosis

Vascular complications lead to morbidity and mortality in patients with diabetes. Diabetic nephropathy (DN) is one of the main life-threatening problems for these patients, as it is the main cause of end-stage renal disease. This study aimed to measure the clinical effects of diabetes in patients with diabetes and in patients with diabetic nephropathy. Improved hypoglycemic control in patients with diabetes could impressively reduce platelet hyperreactivity, and oxidative stress alters the levels of many coagulation and thrombosis factors, resulting in an abnormal hemostasis and impaired levels of numerous serum markers. Most studies have revealed that coagulation factor levels are high in patients with diabetes and nephrodiabetes. Serum inflammatory factors, and coagulation and endothelial functions are good predictors of diabetic nephropathy. This literature review was conducted with access to scholarly databases and Google Scholar through Qassim University, and it analyzes studies from early 2010 until November 2020. Many studies have inferred that diabetes severely affects hemostasis and increases the risk of cardiovascular disease.

Potential Biomarkers of Acute Ischemic Stroke Etiology Revealed by Mass Spectrometry-Based Proteomic Characterization of Formalin-Fixed Paraffin-Embedded Blood Clots

Background and Aims

Besides the crucial role in the treatment of acute ischemic stroke (AIS), mechanical thrombectomy represents a unique opportunity for researchers to study the retrieved clots, with the possibility of unveiling biological patterns linked to stroke pathophysiology and etiology. We aimed to develop a shotgun proteomic approach to study and compare the proteome of formalin-fixed paraffin-embedded (FFPE) cardioembolic and large artery atherosclerotic (LAA) clots.

Methods

We used 16 cardioembolic and 15 LAA FFPE thrombi from 31 AIS patients. The thrombus proteome was analyzed by label-free quantitative liquid chromatography-tandem mass spectrometry (LC-MS/MS). MaxQuant v1.5.2.8 and Perseus v.1.6.15.0 were used for bioinformatics analysis. Protein classes were identified using the PANTHER database and the STRING database was used to predict protein interactions.

Results

We identified 1,581 protein groups as part of the AIS thrombus proteome. Fourteen significantly differentially abundant proteins across the two etiologies were identified. Four proteins involved in the ubiquitin-proteasome pathway, blood coagulation or plasminogen activating cascade were identified as significantly abundant in LAA clots. Ten proteins involved in the ubiquitin proteasome-pathway, cytoskeletal remodeling of platelets, platelet adhesion or blood coagulation were identified as significantly abundant in cardioembolic clots.

Conclusion

Our results outlined a set of 14 proteins for a proof-of-principle characterization of cardioembolic and LAA FFPE clots, advancing the proteome profile of AIS human thrombi and understanding the pathophysiology of ischemic stroke.

Engineered Molecular Therapeutics Targeting Fibrin and the Coagulation System: a Biophysical Perspective

The coagulation cascade represents a sophisticated and highly choreographed series of molecular events taking place in the blood with important clinical implications. One key player in coagulation is fibrinogen, a highly abundant soluble blood protein that is processed by thrombin proteases at wound sites, triggering self-assembly of an insoluble protein hydrogel known as a fibrin clot. By forming the key protein component of blood clots, fibrin acts as a structural biomaterial with biophysical properties well suited to its role inhibiting fluid flow and maintaining hemostasis. Based on its clinical importance, fibrin is being investigated as a potentially valuable molecular target in the development of coagulation therapies. In this topical review, we summarize our current understanding of the coagulation cascade from a molecular, structural and biophysical perspective. We highlight single-molecule studies on proteins involved in blood coagulation and report on the current state of the art in directed evolution and molecular engineering of fibrin-targeted proteins and polymers for modulating coagulation. This biophysical overview will help acclimatize newcomers to the field and catalyze interdisciplinary work in biomolecular engineering toward the development of new therapies targeting fibrin and the coagulation system.

Recent Advances of Pyridinone in Medicinal Chemistry

Pyridinones have been adopted as an important block in medicinal chemistry that could serve as hydrogen bond donors and acceptors. With the help of feasible synthesis routes via established condensation reactions, the physicochemical properties of such a scaffold could be manipulated by adjustment of polarity, lipophilicity, and hydrogen bonding, and eventually lead to its wide application in fragment-based drug design, biomolecular mimetics, and kinase hinge-binding motifs. In addition, most pyridinone derivatives exhibit various biological activities ranging from antitumor, antimicrobial, anti-inflammatory, and anticoagulant to cardiotonic effects. This review focuses on recent contributions of pyridinone cores to medicinal chemistry, and addresses the structural features and structure–activity relationships (SARs) of each drug-like molecule. These advancements contribute to an in-depth understanding of the potential of this biologically enriched scaffold and expedite the development of its new applications in drug discovery.

A fibrin targeted molecular imaging evaluation of microvascular no-reflow in acute ischemic stroke

OBJECTIVE

To investigate the relationship between fibrin deposition and "no-reflow" within microcirculation after thrombolysis in acute ischemic stroke (AIS).

MATERIALS AND METHODS

Experiments were approved by the institutional animal care and use committee. An experimental AIS model was induced in C57BL/6 mice by middle cerebral artery occlusion (MCAO) via the photothrombotic method. Mice were randomly assigned to non-thrombolytic or thrombolytic treated groups (n = 12 per group). The modified Neurological Severity Score and Fast Beam Balance Test were performed by a researcher blinded to the treatment method. MRI was utilized to evaluate all of the mice. An FXIIIa-targeted probe was applied to detect fibrin deposition in acute ischemic brain regions by fluorescence imaging. Necrosis and pathological changes of brain tissue were estimated via Hematoxylin and eosin staining while fibrin deposition was observed by immunohistochemistry.

RESULTS

Thrombolytic therapy improved AIS clinical symptoms. The infarct area of non-thrombolytic treated mice was significantly greater than that of the thrombolytic treated mice (p < .0001). Fluorescent imaging indicated fibrin deposition in ischemic brain tissue in both groups, with less fibrin in non-thrombolytic treated mice than thrombolytic treated mice, though the difference was not significant. Brain cells with abnormal morphology, necrosis, and liquefication were observed in the infarcted area for both groups. Clotted red blood cells (RBCs) and fibrin build-up in capillaries were found near the ischemic area in both non-thrombolytic and thrombolytic treated groups of mice.

CONCLUSION

Fibrin deposition and stacked RBCs contribute to microcirculation no-reflow in AIS after thrombolytic therapy.

Patient-centered approach to managing factor XIII deficiency

Factor XIII (FXIII) is a thrombin-activated protransglutaminase that plays a key role in blood clot formation. Congenital FXIII A-subunit deficiency represents a rare bleeding disorder that affects one in 2-3 million individuals worldwide and is treated with recombinant FXIII (rFXIII). However, due to the rarity of the disease, clinicians are often left to weigh individual variation in FXIII activity and/or symptoms to optimally guide dosing. Cases often become further complicated when patients experience refractory bleeding, which can be difficult to treat. This report describes an approach to rFXIII dosing in two patients who required deviation from standard protocols to maintain therapeutic FXIII troughs. We highlight limitations in our understanding of FXIII deficiency management, while also providing an example of the application of pharmacokinetic data to individualise therapy for improved outcomes. Finally, the case reminds us of the importance of patient-centered, cost-conscious care and multidisplinary teamwork in complex cases.

Decreased clot burden is associated with factor XIII Val34Leu polymorphism and better functional outcomes in acute ischemic stroke patients treated with intravenous thrombolysis

BACKGROUND

Intravenous thrombolysis using recombinant tissue plasminogen activator remains the mainstay treatment of acute ischemic stroke (AIS), although endovascular treatment is becoming standard of care in case of large vessel occlusions (LVO). To quantify the thrombus burden in LVO, a semiquantitative CT angiography (CTA) grading system, the clot burden score (CBS) can be used. Here we aimed to study the association between CBS and various hemostasis parameters, and to evaluate which parameters are major determinants of thrombolysis outcome.

METHODS

In this single-centered prospective observational case-control study, 200 anterior circulation AIS patients receiving intravenous thrombolysis treatment without thrombectomy were enrolled: 100 AIS patients with LVO (CBS 0-9) and 100 age- and sex-matched AIS patients without LVO (CBS 10). Fibrinogen, α2-plasmin inhibitor, plasminogen, factor XIII and D-dimer were assessed from blood samples taken before and 24 h after thrombolysis, and FXIII-A Val34Leu was genotyped. CBS was calculated using admission CTA. Short-term outcomes were defined based on the change in NIHSS by day 7, long-term outcomes were assessed according to the modified Rankin scale at 3 months post-event.

RESULTS

Poor outcomes were significantly more frequent in the CBS 0-9 group. Plasminogen activity on admission was significantly higher in the CBS 0-9 group. In a univariate analysis, significant protective effect of the Leu34 allele against developing larger clots (CBS 0-9) could be demonstrated (OR:0.519; 95%CI:0.298-0.922, p = 0.0227). Multivariate regression analysis revealed that CBS is an independent predictor of short- and long-term functional outcomes, while such effect of the studied hemostasis parameters could not be demonstrated.

CONCLUSIONS

CBS was found to be a significant independent predictor of thrombolysis outcomes. FXIII-A Leu34 carrier status was associated with smaller thrombus burden, which is consistent with the in vitro described whole blood clot mass reducing effects of the allele, but the polymorphism had no effect on thrombolysis outcomes.

Factor XIII-A: An Indispensable "Factor" in Haemostasis and Wound Healing

Factor XIII (FXIII) is a transglutaminase enzyme that catalyses the formation of ε-(γ-glutamyl)lysyl isopeptide bonds into protein substrates. The plasma form, FXIIIA₂B₂, has an established function in haemostasis, with fibrin being its principal substrate. A deficiency in FXIII manifests as a severe bleeding diathesis emphasising its crucial role in this pathway. The FXIII-A gene (F13A1) is expressed in cells of bone marrow and mesenchymal lineage. The cellular form, a homodimer of the A subunits denoted FXIII-A, was perceived to remain intracellular, due to the lack of a classical signal peptide for its release. It is now apparent that FXIII-A can be externalised from cells, by an as yet unknown mechanism. Thus, three pools of FXIII-A exist within the circulation: plasma where it circulates in complex with the inhibitory FXIII-B subunits, and the cellular form encased within platelets and monocytes/macrophages. The abundance of this transglutaminase in different forms and locations in the vasculature reflect the complex and crucial roles of this enzyme in physiological processes. Herein, we examine the significance of these pools of FXIII-A in different settings and the evidence to date to support their function in haemostasis and wound healing.

A Clot Twist: Extreme Variation in Coagulotoxicity Mechanisms in Mexican Neotropical Rattlesnake Venoms

Rattlesnakes are a diverse clade of pit vipers (snake family Viperidae, subfamily Crotalinae) that consists of numerous medically significant species. We used validated in vitro assays measuring venom-induced clotting time and strength of any clots formed in human plasma and fibrinogen to assess the coagulotoxic activity of the four medically relevant Mexican rattlesnake species Crotalus culminatus, C. mictlantecuhtli, C. molossus, and C. tzabcan. We report the first evidence of true procoagulant activity by Neotropical rattlesnake venom in Crotalus culminatus. This species presented a strong ontogenetic coagulotoxicity dichotomy: neonates were strongly procoagulant via Factor X activation, whereas adults were pseudo-procoagulant in that they converted fibrinogen into weak, unstable fibrin clots that rapidly broke down, thereby likely contributing to net anticoagulation through fibrinogen depletion. The other species did not activate clotting factors or display an ontogenetic dichotomy, but depleted fibrinogen levels by cleaving fibrinogen either in a destructive (non-clotting) manner or via a pseudo-procoagulant mechanism. We also assessed the neutralization of these venoms by available antivenom and enzyme-inhibitors to provide knowledge for the design of evidence-based treatment strategies for envenomated patients. One of the most frequently used Mexican antivenoms (Bioclon Antivipmyn®) failed to neutralize the potent procoagulant toxic action of neonate C. culminatus venom, highlighting limitations in snakebite treatment for this species. However, the metalloprotease inhibitor Prinomastat substantially thwarted the procoagulant venom activity, while 2,3-dimercapto-1-propanesulfonic acid (DMPS) was much less effective. These results confirm that venom-induced Factor X activation (a procoagulant action) is driven by metalloproteases, while also suggesting Prinomastat as a more promising potential adjunct treatment than DMPS for this species (with the caveat that in vivo studies are necessary to confirm this potential clinical use). Conversely, the serine protease inhibitor 4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride (AEBSF) inhibited the direct fibrinogen cleaving actions of C. mictlantecuhtli venom, thereby revealing that the pseudo-procoagulant action is driven by kallikrein-type serine proteases. Thus, this differential ontogenetic variation in coagulotoxicity patterns poses intriguing questions. Our results underscore the need for further research into Mexican rattlesnake venom activity, and also highlights potential limitations of current antivenom treatments.

Incorporation of α2-Plasmin Inhibitor into Fibrin Clots and Its Association with the Clinical Outcome of Acute Ischemic Stroke Patients

Cross-linking of α2-plasmin inhibitor (α2-PI) to fibrin by activated factor XIII (FXIIIa) is essential for the inhibition of fibrinolysis. Little is known about the factors modifying α2-PI incorporation into the fibrin clot and whether the extent of incorporation has clinical consequences. Herein we calculated the extent of α2-PI incorporation by measuring α2-PI antigen levels from plasma and serum obtained after clotting the plasma by thrombin and Ca²⁺. The modifying effect of FXIII was studied by spiking of FXIII-A-deficient plasma with purified plasma FXIII. Fibrinogen, FXIII, α2-PI incorporation, in vitro clot-lysis, soluble fibroblast activation protein and α2-PI p.Arg6Trp polymorphism were measured from samples of 57 acute ischemic stroke patients obtained before thrombolysis and of 26 healthy controls. Increasing FXIII levels even at levels above the upper limit of normal increased α2-PI incorporation into the fibrin clot. α2-PI incorporation of controls and patients with good outcomes did not differ significantly (49.4 ± 4.6% vs. 47.4 ± 6.7%, p = 1.000), however it was significantly lower in patients suffering post-lysis intracranial hemorrhage (37.3 ± 14.0%, p = 0.004). In conclusion, increased FXIII levels resulted in elevated incorporation of α2-PI into fibrin clots. In stroke patients undergoing intravenous thrombolysis treatment, α2-PI incorporation shows an association with the outcome of therapy, particularly with thrombolysis-associated intracranial hemorrhage.

Role, Laboratory Assessment and Clinical Relevance of Fibrin, Factor XIII and Endogenous Fibrinolysis in Arterial and Venous Thrombosis

Diseases such as myocardial infarction, ischaemic stroke, peripheral vascular disease and venous thromboembolism are major contributors to morbidity and mortality. Procoagulant, anticoagulant and fibrinolytic pathways are finely regulated in healthy individuals and dysregulated procoagulant, anticoagulant and fibrinolytic pathways lead to arterial and venous thrombosis. In this review article, we discuss the (patho)physiological role and laboratory assessment of fibrin, factor XIII and endogenous fibrinolysis, which are key players in the terminal phase of the coagulation cascade and fibrinolysis. Finally, we present the most up-to-date evidence for their involvement in various disease states and assessment of cardiovascular risk.

Factor XIII-A in Diseases: Role Beyond Blood Coagulation

Multidisciplinary research from the last few decades has revealed that Factor XIII subunit A (FXIII-A) is not only involved in blood coagulation, but may have roles in various diseases. Here, we aim to summarize data from studies involving patients with mutations in the F13A1 gene, performed in FXIII-A knock-out mice models, clinical and histological studies assessing correlations between diseases severity and FXIII-A levels, as well as from in vitro experiments. By providing a complex overview on its possible role in wound healing, chronic inflammatory bowel diseases, athe-rosclerosis, rheumatoid arthritis, chronic inflammatory lung diseases, chronic rhinosinusitis, solid tumors, hematological malignancies, and obesity, we also demonstrate how the field evolved from using FXIII-A as a marker to accept and understand its active role in inflammatory and malignant diseases.

Valproic acid influences the expression of genes implicated with hyperglycaemia-induced complement and coagulation pathways

Because the liver plays a major role in metabolic homeostasis and secretion of clotting factors and inflammatory innate immune proteins, there is interest in understanding the mechanisms of hepatic cell activation under hyperglycaemia and whether this can be attenuated pharmacologically. We have previously shown that hyperglycaemia stimulates major changes in chromatin organization and metabolism in hepatocytes, and that the histone deacetylase inhibitor valproic acid (VPA) is able to reverse some of these metabolic changes. In this study, we have used RNA-sequencing (RNA-seq) to investigate how VPA influences gene expression in hepatocytes. Interesting, we observed that VPA attenuates hyperglycaemia-induced activation of complement and coagulation cascade genes. We also observe that many of the gene activation events coincide with changes to histone acetylation at the promoter of these genes indicating that epigenetic regulation is involved in VPA action.

Sustained depletion of FXIII-A by inducing acquired FXIII-B deficiency

The activated form of coagulation factor XIII (FXIII-A2B2), FXIII-A*, is a hemostatic enzyme essential for inhibiting fibrinolysis by irreversibly crosslinking fibrin and antifibrinolytic proteins. Despite its importance, there are no modulatory therapeutics. Guided by the observation that humans deficient in FXIII-B have reduced FXIII-A without severe bleeding, we hypothesized that a suitable small interfering RNA (siRNA) targeting hepatic FXIII-B could safely decrease FXIII-A. Here we show that knockdown of FXIII-B with siRNA in mice and rabbits using lipid nanoparticles resulted in a sustained and controlled decrease in FXIII-A. The concentration of FXIII-A in plasma was reduced by 90% for weeks after a single injection and for more than 5 months with repeated injections, whereas the concentration of FXIII-A in platelets was unchanged. Ex vivo, crosslinking of α2-antiplasmin and fibrin was impaired and fibrinolysis was enhanced. In vivo, reperfusion of carotid artery thrombotic occlusion was also enhanced. Re-bleeding events were increased after challenge, but blood loss was not significantly increased. This approach, which mimics congenital FXIII-B deficiency, provides a potential pharmacologic and experimental tool to modulate FXIII-A2B2 activity.

Genetic Factors in Antiphospholipid Syndrome: Preliminary Experience with Whole Exome Sequencing

As in many autoimmune diseases, the pathogenesis of the antiphospholipid syndrome (APS) is the result of a complex interplay between predisposing genes and triggering environmental factors, leading to a loss of self-tolerance and immune-mediated tissue damage. While the first genetic studies in APS focused primarily on the human leukocytes antigen system (HLA) region, more recent data highlighted the role of other genes in APS susceptibility, including those involved in the immune response and in the hemostatic process. In order to join this intriguing debate, we analyzed the single-nucleotide polymorphisms (SNPs) derived from the whole exome sequencing (WES) of two siblings affected by APS and compared our findings with the available literature. We identified genes encoding proteins involved in the hemostatic process, the immune response, and the phospholipid metabolism (PLA2G6, HSPG2, BCL3, ZFAT, ATP2B2, CRTC3, and ADCY3) of potential interest when debating the pathogenesis of the syndrome. The study of the selected SNPs in a larger cohort of APS patients and the integration of WES results with the network-based approaches will help decipher the genetic risk factors involved in the diverse clinical features of APS.

Machine Learning Analysis of the Cerebrovascular Thrombi Proteome in Human Ischemic Stroke: An Exploratory Study

Objective: Mechanical retrieval of thrombotic material from acute ischemic stroke patients provides a unique entry point for translational research investigations. Here, we resolved the proteomes of cardioembolic and atherothrombotic cerebrovascular human thrombi and applied an artificial intelligence routine to examine protein signatures between the two selected groups.

Methods: We specifically used n = 32 cardioembolic and n = 28 atherothrombotic diagnosed thrombi from patients suffering from acute stroke and treated by mechanical thrombectomy. Thrombi proteins were successfully separated by gel-electrophoresis. For each thrombi, peptide samples were analyzed by nano-flow liquid chromatography coupled to tandem mass spectrometry (nano-LC-MS/MS) to obtain specific proteomes. Relative protein quantification was performed using a label-free LFQ algorithm and all dataset were analyzed using a support-vector-machine (SVM) learning method. Data are available via ProteomeXchange with identifier PXD020398. Clinical data were also analyzed using SVM, alone or in combination with the proteomes.

Results: A total of 2,455 proteins were identified by nano-LC-MS/MS in the samples analyzed, with 438 proteins constantly detected in all samples. SVM analysis of LFQ proteomic data delivered combinations of three proteins achieving a maximum of 88.3% for correct classification of the cardioembolic and atherothrombotic samples in our cohort. The coagulation factor XIII appeared in all of the SVM protein trios, associating with cardioembolic thrombi. A combined SVM analysis of the LFQ proteome and clinical data did not deliver a better discriminatory score as compared to the proteome only.

Conclusion: Our results advance the portrayal of the human cerebrovascular thrombi proteome. The exploratory SVM analysis outlined sets of proteins for a proof-of-principle characterization of our cohort cardioembolic and atherothrombotic samples. The integrated analysis proposed herein could be further developed and retested on a larger patients population to better understand stroke origin and the associated cerebrovascular pathophysiology.

Proteomic Study of Aqueous Humor and Its Application in the Treatment of Neovascular Glaucoma

Aqueous humor (AH) proteins are involved in many physiological and pathological processes of the eye. The proteome analysis of AH is important to understand its physiological and pathophysiological functions. In the present study, AH samples obtained from 21 cataract volunteers were pooled together. After high-pH RPLC offline separation, the pooled sample was analyzed by LC-MS/MS to provide a comprehensive profile of AH proteome. The function analysis was provided by the GO and IPA annotation. In order to determine whether the AH proteome can reflect the pathophysiological changes of the disease, DIA technology was used to analyze the AH samples obtained from three neovascular glaucoma (NVG) patients (six samples) before and after drug treatment. The differential proteins were validated by PRM technology in an independent group (14 samples). In the AH proteome database, 802 proteins were identified, and 318 proteins were identified for the first time. Furthermore, 480 proteins were quantified based on the peak intensity-based semiquantification (iBAQ), which ranged by approximately 7 orders of magnitude. These proteins are primarily involved in immunity- and inflammation-related pathways. The differential AH proteomic analysis in NVG treatment revealed that the AH proteome can reflect the pathophysiological changes of drug treatment. Angiogenesis and thrombus coagulation progression are deeply involved in NVG treatment. The present experiment provided a comprehensive AH proteome analysis and expanded the profile of human AH proteome. The differential AH proteomic analysis of NVG treatment indicated that AH proteome can reflect the pathophysiological changes in drug intervention.

Terminal Phase Components of the Clotting Cascade in Patients with End-Stage Renal Disease Undergoing Hemodiafiltration or Hemodialysis Treatment

Hemostasis disorder in patients with end-stage renal disease (ESRD) is frequently associated with bleeding diathesis but it may also manifest in thrombotic complications. Analysis of individual coagulation and fibrinolytic factors may shed light on the background of this paradox situation. Here we explored components essential for fibrin formation/stabilization in ESRD patients being on maintenance hemodiafiltration (HDF) or hemodialysis (HD). Pre-dialysis fibrinogen, factor XIII (FXIII) antigen concentrations and FXIII activity were elevated, while α₂-plasmin inhibitor (α₂PI) activity decreased. The inflammatory status, as characterized by C-reactive protein (CRP) was a key determinant of fibrinogen concentration, but not of FXIII and α₂PI levels. During a 4-h course of HDF or HD, fibrinogen concentration and FXIII levels gradually elevated. When compensated for the change in plasma water, i.e., normalized for plasma albumin concentration, only FXIII elevation remained significant. There was no difference between HDF and HD treatments. Individual HDF treatment did not influence α₂PI activity, however after normalization it decreased significantly. HD treatment had a different effect, α₂PI activities became elevated but the elevation disappeared after normalization. Elevated fibrinogen and FXIII levels in ESRD patients might contribute to the increased thrombosis risk, while decreased α₂PI activity might be associated with elevated fibrinolytic potential.

Standing wave-assisted acoustic droplet vaporization for single and dual payload release in acoustically-responsive scaffolds

An ultrasound standing wave field (SWF) has been utilized in many biomedical applications. Here, we demonstrate how a SWF can enhance drug release using acoustic droplet vaporization (ADV) in an acoustically-responsive scaffold (ARS). ARSs are composite fibrin hydrogels containing payload-carrying, monodispersed perfluorocarbon (PFC) emulsions and have been used to stimulate regenerative processes such as angiogenesis. Elevated amplitudes in the SWF significantly enhanced payload release from ARSs containing dextran-loaded emulsions (nominal diameter: 6 μm) compared to the -SWF condition, both at sub- and suprathreshold excitation pressures. At 2.5 MHz and 4 MPa peak rarefactional pressure, the cumulative percentage of payload released from ARSs reached 84.1 ± 5.4% and 66.1 ± 4.4% under + SWF and -SWF conditions, respectively, on day 10. A strategy for generating a SWF for an in situ ARS is also presented. For dual-payload release studies, bi-layer ARSs containing a different payload within each layer were exposed to temporally staggered ADV at 3.25 MHz (day 0) and 8.6 MHz (day 4). Sequential payload release was demonstrated using dextran payloads as well as two growth factors relevant to angiogenesis: basic fibroblast growth factor (bFGF) and platelet-derived growth factor BB (PDGF-BB). In addition, bubble growth and fibrin degradation were characterized in the ARSs under +SWF and -SWF conditions. These results highlight the utility of a SWF for modulating single and dual payload release from an ARS and can be used in future therapeutic studies.

Factor XIIIa inhibitors as potential novel drugs for venous thromboembolism

Human factor XIIIa (FXIIIa) is a multifunctional transglutaminase with a significant role in hemostasis. FXIIIa catalyzes the last step in the coagulation process. It stabilizes the blood clot by cross-linking the α- and γ-chains of fibrin. It also protects the newly formed clot from plasmin-mediated fibrinolysis, primarily by cross-linking α2-antiplasmin to fibrin. Furthermore, FXIIIa is a major determinant of clot size and clot's red blood cells content. Therefore, inhibitors targeting FXIIIa have been considered to develop a new generation of anticoagulants to prevent and/or treat venous thromboembolism. Several inhibitors of FXIIIa have been discovered or designed including active site and allosteric site small molecule inhibitors as well as natural and modified polypeptides. This work reviews the structural, biochemical, and pharmacological aspects of FXIIIa inhibitors so as to advance their molecular design to become more clinically relevant.

Coagulation factor XIII activity predicts left ventricular remodelling after acute myocardial infarction

AIMS

Acute myocardial infarction (MI) is the major cause of chronic heart failure. The activity of blood coagulation factor XIII (FXIIIa) plays an important role in rodents as a healing factor after MI, whereas its role in healing and remodelling processes in humans remains unclear. We prospectively evaluated the relevance of FXIIIa after acute MI as a potential early prognostic marker for adequate healing.

METHODS AND RESULTS

This monocentric prospective cohort study investigated cardiac remodelling in patients with ST-elevation MI and followed them up for 1 year. Serum FXIIIa was serially assessed during the first 9 days after MI and after 2, 6, and 12 months. Cardiac magnetic resonance imaging was performed within 4 days after MI (Scan 1), after 7 to 9 days (Scan 2), and after 12 months (Scan 3). The FXIII valine-to-leucine (V34L) single-nucleotide polymorphism rs5985 was genotyped. One hundred forty-six patients were investigated (mean age 58 ± 11 years, 13% women). Median FXIIIa was 118% (quartiles, 102-132%) and dropped to a trough on the second day after MI: 109% (98-109%; P < 0.001). FXIIIa recovered slowly over time, reaching the baseline level after 2 to 6 months and surpassed baseline levels only after 12 months: 124% (110-142%). The development of FXIIIa after MI was independent of the genotype. FXIIIa on Day 2 was strongly and inversely associated with the relative size of MI in Scan 1 (Spearman's ρ = -0.31; P = 0.01) and Scan 3 (ρ = -0.39; P < 0.01) and positively associated with left ventricular ejection fraction: ρ = 0.32 (P < 0.01) and ρ = 0.24 (P = 0.04), respectively.

CONCLUSIONS

FXIII activity after MI is highly dynamic, exhibiting a significant decline in the early healing period, with reconstitution 6 months later. Depressed FXIIIa early after MI predicted a greater size of MI and lower left ventricular ejection fraction after 1 year. The clinical relevance of these findings awaits to be tested in a randomized trial.

N-glycosylation of blood coagulation factor XIII subunit B and its functional consequence

BACKGROUND

The protective/inhibitory B subunits of coagulation factor XIII (FXIII-B) is a ~80 kDa glycoprotein containing two N-glycosylation sites. Neither the structure nor the functional role of the glycans on FXIII-B has been explored.

OBJECTIVE

To reveal the glycan structures linked to FXIII-B, to design a method for deglycosylating the native protein, to find out if deglycosylation influences the dimeric structure of FXIII-B and its clearance from the circulation.

METHODS

Asparagine-linked carbohydrates were released from human FXIIII-B by PNGase F digestion. The released N-linked oligosaccharides were fluorophore labeled and analyzed by capillary electrophoresis. Structural identification utilized glycan database search and exoglycosidase digestion based sequencing. The structure of deglycosylated FXIII-B was investigated by gel filtration. The clearance of deglycosylated and native FXIII-B from plasma was compared in FXIII-B knock out mice.

RESULTS

PNGase F completely removed N-glycans from the denatured protein. Deglycosylation of the native protein was achieved by repeated digestion at elevated PNGase F concentration. The total N-glycan profile of FXIII-B featured nine individual structures; three were fucosylated and each structure contained at least one sialic acid. Deglycosylation did not change the native dimeric structure of FXIII-B, but accelerated its clearance from the circulation of FXIII-B knock out mice.

CONCLUSION

Characterization of the glycan moieties attached to FXIII-B is reported for the first time. Complete deglycosylation of the native protein was achieved by a deglycosylation workflow. The associated glycan structure is not required for FXIII-B dimer formation, but it very likely prolongs the half-life of FXIII-B in the plasma.

Plasma Fibrin Clot Properties Are Unfavorably Altered in Women following Venous Thromboembolism Associated with Combined Hormonal Contraception

The use of hormonal contraception is associated with an increased risk of venous thromboembolism (VTE). Unfavorably altered fibrin clot phenotype has been reported in patients following unprovoked VTE who are at risk of recurrences. It remains unknown whether fibrin clot characteristics in women with contraception-related VTE differ from those in unprovoked VTE. We studied three age-matched groups of women: (1) after contraception-related VTE, (n = 48) (2) after unprovoked VTE (n = 48), and (3) controls (n = 48). Plasma fibrin clot permeability (K _s), turbidity of clot formation, efficiency of fibrinolysis using clot lysis time (CLT), and rate of increase in D-dimer during lytic clot degradation (D-D_rate), along with thrombin generation and fibrinolysis proteins were determined. Compared with the controls, patients following contraception-related and unprovoked VTE formed faster (lag phase, -8.8% and -20.4%, respectively) fibrin clots of increased density (K _{s ,} -8.6% and -13.4%, respectively) displaying impaired fibrinolysis as evidenced by prolonged CLT (+11.5% and +14.5%, respectively) and lower D-D_rate (-7.1% and -5.6%, respectively), accompanied with higher plasminogen activator inhibitor-1 (PAI-1, +14.9% and +17.8%, respectively) and elevated peak thrombin generation (+63.8% and +36.7%, respectively). The only differences between women with unprovoked and contraception-related VTE were lower fibrin mass in plasma clots (D-D_max, -8.6%), along with higher peak thrombin generation (+19.8%) and shorter lag phase (-6.8%) in the latter group. This study suggests that women after contraception-related VTE, similar to those following unprovoked VTE, have denser fibrin clot formation and impaired clot lysis. These findings might imply higher risk of VTE recurrence in women with the prothrombotic clot phenotype.

Markers of Coagulation and Fibrinolysis Predicting the Outcome of Acute Ischemic Stroke Thrombolysis Treatment: A Review of the Literature

Intravenous administration of recombinant tissue plasminogen activator (rt-PA) has been proven to be safe and effective in the treatment of acute ischemic stroke. Little is known, however, why this treatment is less effective in some patients while in others life-threatening side-effects, e.g., symptomatic intracerebral hemorrhage might occur. Clinical failure of thrombolysis related to absent or partial recanalization or reocclusion as well as hemorrhagic complications of thrombolysis are possibly related to hemostatic events. Data on markers of coagulation and/or fibrinolysis in acute stroke patients are numerous and may provide indications regarding therapy outcomes. Better understanding of the hemostatic and fibrinolytic system during rt-PA therapy might be clinically useful and ultimately might lead to an improvement in the efficacy or safety of this treatment. Studies on thrombus composition retrieved from cerebral arteries may also advance our knowledge and provide a key to improve acute stroke therapy. Here we provide a comprehensive review on a wide range of factors and markers of coagulation and fibrinolysis that have been studied in the context of thrombolysis outcome in ischemic stroke patients. Moreover, a brief summary is given on the most recent research on thrombus composition having a potential influence on outcomes.

Evaluating the Effects of Fibrinogen αC Mutations on the Ability of Factor XIII to Crosslink the Reactive αC Glutamines (Q237, Q328, Q366)

Fibrinogen (Fbg) levels and extent of fibrin polymerization have been associated with various pathological conditions such as cardiovascular disease, arteriosclerosis, and coagulation disorders. Activated factor XIII (FXIIIa) introduces γ-glutamyl-ε-lysinyl isopeptide bonds between reactive glutamines and lysines in the fibrin network to form a blood clot resistant to fibrinolysis. FXIIIa crosslinks the γ-chains and at multiple sites in the αC region of Fbg. Fbg αC contains a FXIII binding site involving αC (389-402) that is located near three glutamines whose reactivities rank Q237 >> Q366 ≈ Q328. Mass spectrometry and two-dimensional heteronuclear single-quantum correlation nuclear magnetic resonance assays were used to probe the anchoring role that αC E396 may play in controlling FXIII function and characterize the effects of Q237 on the reactivities of Q328 and Q366. Studies with αC (233-425) revealed that the E396A mutation does not prevent the transglutaminase function of FXIII A₂ or A₂B₂. Other residues must play a compensatory role in targeting FXIII to αC. Unlike full Fbg, Fbg αC (233-425) did not promote thrombin cleavage of FXIII, an event contributing to activation. With the αC (233-425) E396A mutant, Q237 exhibited slower reactivities compared with αC wild-type (WT) consistent with difficulties in directing this N-terminal segment toward an anchored FXIII interacting at a weaker binding region. Q328 and Q366 became less reactive when Q237 was replaced with inactive N237. Q237 crosslinking is proposed to promote targeting of Q328 and Q366 to the FXIII active site. FXIII thus uses Fbg αC anchoring sites and distinct Q environments to regulate substrate specificity.

The multifaceted role of fibrinogen in tissue injury and inflammation

The canonical role of the hemostatic and fibrinolytic systems is to maintain vascular integrity. Perturbations in either system can prompt primary pathological end points of hemorrhage or thrombosis with vessel occlusion. However, fibrin(ogen) and proteases controlling its deposition and clearance, including (pro)thrombin and plasmin(ogen), have powerful roles in driving acute and reparative inflammatory pathways that affect the spectrum of tissue injury, remodeling, and repair. Indeed, fibrin(ogen) deposits are a near-universal feature of tissue injury, regardless of the nature of the inciting event, including injuries driven by mechanical insult, infection, or immunological derangements. Fibrin can modify multiple aspects of inflammatory cell function by engaging leukocytes through a variety of cellular receptors and mechanisms. Studies on the role of coagulation system activation and fibrin(ogen) deposition in models of inflammatory disease and tissue injury have revealed points of commonality, as well as context-dependent contributions of coagulation and fibrinolytic factors. However, there remains a critical need to define the precise temporal and spatial mechanisms by which fibrinogen-directed inflammatory events may dictate the severity of tissue injury and coordinate the remodeling and repair events essential to restore normal organ function. Current research trends suggest that future studies will give way to the identification of novel hemostatic factor-targeted therapies for a range of tissue injuries and disease.

Habu coagulotoxicity: Clinical implications of the functional diversification of Protobothrops snake venoms upon blood clotting factors

Venom can affect any part of the body reachable via the bloodstream. Toxins which specifically act upon the coagulation cascade do so either by anticoagulant or procoagulant mechanisms. Here we investigated the coagulotoxic effects of six species within the medically important pit viper genus Protobothrops (Habu) from the Chinese mainland and Japanese islands, a genus known to produce hemorrhagic shock in envenomed patients. Differential coagulotoxicity was revealed: P. jerdonii and P. mangshanensis produced an overall net anticoagulant effect through the pseudo-procoagulant clotting of fibrinogen; P. flavoviridis and P. tokarensis exhibit a strong anticoagulant activity through the destructive cleavage of fibrinogen; and while P. elegans and P. mucrosquamatus both cleaved the A-alpha and B-beta chains of fibrinogen they did not exhibit strong anticoagulant activity. These variations in coagulant properties were congruent with phylogeny, with the closest relatives exhibiting similar venom effects in their action upon fibrinogen. Ancestral state reconstruction indicated that anticoagulation mediated by pseudo-procoagulant cleavage of fibrinogen is the basal state, while anticoagulation produced by destructive cleavage of fibrinogen is the derived state within this genus. This is the first in depth study of its kind highlighting extreme enzymatic variability, functional diversification and clotting diversification within one genus surrounding one target site, governed by variability in co-factor dependency. The documentation that the same net overall function, anticoagulation, is mediated by differential underlying mechanics suggests limited antivenom cross-reactivity, although this must be tested in future work. These results add to the body of knowledge necessary to inform clinical management of the envenomed patient.

Low factor XIII levels after intravenous thrombolysis predict short-term mortality in ischemic stroke patients

In this observational study we investigated whether levels of factor XIII (FXIII) and its major polymorphisms affect the outcome of thrombolysis by recombinant tissue plasminogen activator (rtPA) in acute ischemic stroke (AIS) patients. Study cohort included 132 consecutive AIS patients undergoing i.v. thrombolysis within 4.5 h of symptom onset. Blood samples taken on admission, immediately after and 24 h after therapy were analyzed for FXIII activity and antigen levels. FXIII-A p.Val34Leu, p.Tyr204Phe, FXIII-B p.His95Arg and intron K(IVS11 + 144) polymorphisms were genotyped. Neurological deficit was assessed using the National Institutes of Health Stroke Scale. Intracranial hemorrhage was classified according to ECASSII criteria. Long-term functional outcome was defined at 3 months post-event by the modified Rankin scale. FXIII levels showed a gradual decrease immediately after thrombolysis and 24 h later, which was not related to therapy-associated bleeding. In a multiple logistic regression model, a FXIII level in the lowest quartile 24 h post-lysis proved to be an independent predictor of mortality by 14 days post-event (OR:4.95, 95% CI:1.31-18.68, p < 0.05). No association was found between the investigated FXIII polymorphisms and therapeutic outcomes. In conclusion, our findings indicate that FXIII levels 24 h after thrombolysis might help to identify patients at increased risk for short-term mortality.

Oxidation-induced modifications of the catalytic subunits of plasma fibrin-stabilizing factor at the different stages of its activation identified by mass spectrometry

Plasma fibrin-stabilizing factor (pFXIII) is a heterotetrameric proenzyme composed of two catalytic A subunits (FXIII-A₂) and two inhibitory/carrier B subunits (FXIII-B₂). The main function of the protein is the formation of cross-links between the polypeptide chains of the fibrin clot. The conversion of pFXIII into the enzymatic form FXIII-A₂* is a multistage process. Like many other blood plasma proteins, pFXIII is an oxidant-susceptible target. The influence of distinct sites susceptible to oxidation-mediated modifications on the changes in the structural-functional characteristics of the protein remains fully unexplored. For the first time, a set of the oxidation sites within FXIII-A₂ under ozone-induced oxidation of pFXIII at different stages of its activation have been identified by mass spectrometry, and the extent as well as the chemical nature of these modifications have been explored. It was shown that the set of amino acid residues susceptible to oxidative attack and the degree of oxidation of these residues in FXIII-A₂ of non-activated pFXIII, pFXIII activated by Ca²⁺ and fully activated pFXIII treated with thrombin and Ca²⁺ significantly differ. The obtained data enable one to postulate that in the process of the proenzyme conversion into FXIII-A₂*, new earlier-unexposed amino acid residues become available for the oxidizer while some of the initially surface-exhibited residues are buried within the protein globule.

Atherothrombosis and Thromboembolism: Position Paper from the Second Maastricht Consensus Conference on Thrombosis

Atherothrombosis is a leading cause of cardiovascular mortality and long-term morbidity. Platelets and coagulation proteases, interacting with circulating cells and in different vascular beds, modify several complex pathologies including atherosclerosis. In the second Maastricht Consensus Conference on Thrombosis, this theme was addressed by diverse scientists from bench to bedside. All presentations were discussed with audience members and the results of these discussions were incorporated in the final document that presents a state-of-the-art reflection of expert opinions and consensus recommendations regarding the following five topics: 1. Risk factors, biomarkers and plaque instability: In atherothrombosis research, more focus on the contribution of specific risk factors like ectopic fat needs to be considered; definitions of atherothrombosis are important distinguishing different phases of disease, including plaque (in)stability; proteomic and metabolomics data are to be added to genetic information. 2. Circulating cells including platelets and atherothrombosis: Mechanisms of leukocyte and macrophage plasticity, migration, and transformation in murine atherosclerosis need to be considered; disease mechanism-based biomarkers need to be identified; experimental systems are needed that incorporate whole-blood flow to understand how red blood cells influence thrombus formation and stability; knowledge on platelet heterogeneity and priming conditions needs to be translated toward the in vivo situation. 3. Coagulation proteases, fibrin(ogen) and thrombus formation: The role of factor (F) XI in thrombosis including the lower margins of this factor related to safe and effective antithrombotic therapy needs to be established; FXI is a key regulator in linking platelets, thrombin generation, and inflammatory mechanisms in a renin-angiotensin dependent manner; however, the impact on thrombin-dependent PAR signaling needs further study; the fundamental mechanisms in FXIII biology and biochemistry and its impact on thrombus biophysical characteristics need to be explored; the interactions of red cells and fibrin formation and its consequences for thrombus formation and lysis need to be addressed. Platelet-fibrin interactions are pivotal determinants of clot formation and stability with potential therapeutic consequences. 4. Preventive and acute treatment of atherothrombosis and arterial embolism; novel ways and tailoring? The role of protease-activated receptor (PAR)-4 vis à vis PAR-1 as target for antithrombotic therapy merits study; ongoing trials on platelet function test-based antiplatelet therapy adjustment support development of practically feasible tests; risk scores for patients with atrial fibrillation need refinement, taking new biomarkers including coagulation into account; risk scores that consider organ system differences in bleeding may have added value; all forms of oral anticoagulant treatment require better organization, including education and emergency access; laboratory testing still needs rapidly available sensitive tests with short turnaround time. 5. Pleiotropy of coagulation proteases, thrombus resolution and ischaemia-reperfusion: Biobanks specifically for thrombus storage and analysis are needed; further studies on novel modified activated protein C-based agents are required including its cytoprotective properties; new avenues for optimizing treatment of patients with ischaemic stroke are needed, also including novel agents that modify fibrinolytic activity (aimed at plasminogen activator inhibitor-1 and thrombin activatable fibrinolysis inhibitor.