The anticoagulant function of coagulation factor V

Proteomics analysis of serum from thymoma patients

Thymoma is the most common malignant tumor in thymic epithelial tumors (TETS). This study aimed to identify the changes in serum proteomics in patients with thymoma. Proteins were extracted from twenty patients with thymoma serum and nine healthy controls and prepared for mass spectrometry (MS) analysis. Data independent acquisition (DIA) quantitative proteomics technique was used to examine the serum proteome. Differential proteins of abundance changes in the serum were identified. Bioinformatics was used to examine the differential proteins. Functional tagging and enrichment analysis were conducted using the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. The string database was used to assess the interaction of different proteins. In all, 486 proteins were found in all samples. There were differences in 58 serum proteins between patients and healthy blood donors, 35 up-regulated and 23 down-regulated. These proteins are primarily exocrine and serum membrane proteins involved in controlling immunological responses and antigen binding, according to GO functional annotation. KEGG functional annotation showed that these proteins play a significant role in the complement and coagulation cascade and the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signal pathway. Notably, the KEGG pathway (complement and coagulation cascade) is enriched, and three key activators were up-regulated: von willebrand factor (VWF), coagulation factor v (F5) and vitamin k-dependent protein c (PC). Protein-protein interaction (PPI) analysis showed that six proteins ((VWF, F5, thrombin reactive protein 1 (THBS1), mannose-binding lectin-associated serine protease 2 (MASP2), apolipoprotein B (APOB), and apolipoprotein (a) (LPA)) were up-regulated and two proteins (Metalloproteinase inhibitor 1(TIMP1), ferritin light chain (FTL)) were down-regulated. The results of this study showed that several proteins involved in complement and coagulation cascades were up-regulated in the serum of patients.

The Magic of Proteases: From a Procoagulant and Anticoagulant Factor V to an Equitable Treatment of Its Inherited Deficiency

Proteostasis, i.e., the homeostasis of proteins, responsible for ensuring protein turnover, is regulated by proteases, which also participate in the etiopathogenesis of multiple conditions. The magic of proteases is such that, in blood coagulation, one same molecule, such as coagulation factor V, for example, can perform both a procoagulant and an anticoagulant function as a result of the activity of proteases. However, this magic has an insidious side to it, as it may also prevent the completion of the clinical value chain of factor V deficiency. This value chain encompasses the discovery of knowledge, the transfer of this knowledge, and its translation to clinical practice. In the case of rare and ultra-rare diseases like factor V deficiency, this value chain has not been completed as the knowledge acquisition phase has dragged out over time, holding up the transfer of knowledge to clinical practice. The reason for this is related to the small number of patients afflicted with these conditions. As a result, new indications must be found to make the therapies cost-effective. In the case of factor V, significant research efforts have been directed at developing a recombinant factor V capable of resisting the action of the proteases capable of inactivating this factor. This is where bioethics and health equity considerations come into the equation.

Identification of Potential Biomarkers for Coronary Artery Disease Based on Cuproptosis

Identifying peripheral biomarkers is an important noninvasive diagnosis method for coronary artery disease (CAD) which has aroused the strong interest of researchers. Cuproptosis, a newly reported kind of programmed cell death, is closely related to mitochondrial respiration, adenosine triphosphate (ATP) production, and the TCA cycle. Currently, no studies have been published about the effects of cuproptosis-related genes (CRGs) on diagnosing CAD. To screen marker genes for CAD from CRGs, we downloaded the whole blood cell gene expression profile of CAD patients and normal samples, i.e., the GSE20680 dataset, from the GEO database. By differential expression analysis, we obtained 10 differentially expressed CRGs (DE-CRGs), which were associated with copper ion response, immune response, and material metabolism. Based on the 10 DE-CRGs, we furtherly performed LASSO analysis and SVM-RFE analysis and identified 5 DE-CRGs as marker genes, including F5, MT4, RNF7, S100A12, and SORD, which had an excellent diagnostic performance. Moreover, the expression of the marker genes was validated in the GSE20681 and GSE42148 datasets, and consistent results were obtained. In mechanism, we conducted gene set enrichment analyses (GSEA) based on the marker genes, and the results implied that they might participate in the regulation of immune response. Therefore, we calculated the relative contents of 22 kinds of immune cells in CAD and normal samples using the CIBERSORT algorithm, followed by differential analysis and correlation analysis of the immune microenvironment, and found that regulatory T cell (Treg) significantly decreased and was negatively correlated with marker gene S100A12. To further reveal the regulation mechanisms, a lncRNA-miRNA-mRNA ceRNA network based on the marker genes was established. Finally, 13 potential therapeutic drugs targeting 2 marker genes (S100A12 and F5) were identified using the Drug Gene Interaction Database (DGIdb). In summary, our findings indicated that some CRGs may be diagnostic biomarkers and treatment targets for CAD and provided new ideas for further scientific research.

Assessing the individual roles of FII, FV, and FX activity in the thrombin generation process

Thrombin generation (TG) is known as a physiological approach to assess the hemostatic function. Although it correlates well with thrombosis and bleeding, in the current setup it is not sensitive to the effects of fluctuations in single coagulation factors. We optimized the calibrated automated thrombinography (CAT) method to quantify FII, FV and FX activity within the coagulation system. The CAT assay was fine-tuned for the assessment of FII, FV and FX by diluting the samples in FII-, FV-, or FX-deficient plasma, respectively, and measuring TG. Plasma FII levels correlated linearly with the ETP up to a plasma concentration of 100% FII. FV and FX levels correlated linearly with the peak height up to a plasma level of 2.5% FV and 10% FX, respectively. Sensitized CAT protocols were designed by adding a fixed volume of a pre-diluted patient sample to FII, FV, and FX deficient plasma in TG experiments. This approach makes the TG measurement dependent on the activity of the respective coagulation factor. The ETP or peak height were quantified as readouts for the coagulation factor activity. The intra- and inter-assay variation coefficients varied from 5.0 to 8.6%, and from 3.5 to 5.9%, respectively. Reference values were determined in 120 healthy subjects and the assays were clinically validated in 60 patients undergoing coronary artery bypass grafting (CABG). The sensitized CAT assays revealed that the contribution of FII, FV, and FX to the TG process was reduced after CABG surgery, leading to reduced prothrombin conversion and subsequently, lower TG.

The Vascular Endothelium and Coagulation: Homeostasis, Disease, and Treatment, with a Focus on the Von Willebrand Factor and Factors VIII and V

The vascular endothelium has several important functions, including hemostasis. The homeostasis of hemostasis is based on a fine balance between procoagulant and anticoagulant proteins and between fibrinolytic and antifibrinolytic ones. Coagulopathies are characterized by a mutation-induced alteration of the function of certain coagulation factors or by a disturbed balance between the mechanisms responsible for regulating coagulation. Homeostatic therapies consist in replacement and nonreplacement treatments or in the administration of antifibrinolytic agents. Rebalancing products reestablish hemostasis by inhibiting natural anticoagulant pathways. These agents include monoclonal antibodies, such as concizumab and marstacimab, which target the tissue factor pathway inhibitor; interfering RNA therapies, such as fitusiran, which targets antithrombin III; and protease inhibitors, such as serpinPC, which targets active protein C. In cases of thrombophilia (deficiency of protein C, protein S, or factor V Leiden), treatment may consist in direct oral anticoagulants, replacement therapy (plasma or recombinant ADAMTS13) in cases of a congenital deficiency of ADAMTS13, or immunomodulators (prednisone) if the thrombophilia is autoimmune. Monoclonal-antibody-based anti-vWF immunotherapy (caplacizumab) is used in the context of severe thrombophilia, regardless of the cause of the disorder. In cases of disseminated intravascular coagulation, the treatment of choice consists in administration of antifibrinolytics, all-trans-retinoic acid, and recombinant soluble human thrombomodulin.

Characterization of Platelet Function-Related Gene Predicting Survival and Immunotherapy Efficacy in Gastric Cancer

Immunotherapy is widely used to treat various cancers, but patients with gastric cancer (GC), which has a high mortality rate, benefit relatively less from this therapy. Platelets are closely related to GC progression and metastasis. This study aimed to find novel potential biomarkers related to platelet function to predict GC and immunotherapy efficacy. First, based on platelet activation, signaling, and aggregation (abbreviation: function)-related genes (PFRGs), we used the least absolute shrinkage and selection operator (Lasso) regression method to construct a platelet-function-related genes prognostic score (PFRGPS). PRFGPS was verified in three independent external datasets (GSE26901, GSE15459, and GSE84437) for its robustness and strong prediction performance. Our results demonstrate that PRFGPS is an independent prognostic indicator for predicting overall survival in patients with GC. In addition, prognosis, potential pathogenesis mechanisms, and the response to immunotherapy were defined via gene set enrichment analysis, tumor mutational burden, tumor microenvironment, tumor immune dysfunction and exclusion (TIDE), microsatellite instability, and immune checkpoint inhibitors. We found that the high-PRFGPS subgroup had a cancer-friendly immune microenvironment, a high TIDE score, a low tumor mutational burden, and relatively low microsatellite instability. In the immunophenoscore model, the therapeutic effect on anti-PD-1 and anti-CTLA-4 in the high-PRFGPS subgroup was relatively low. In conclusion, PRFGPS could be used as a reference index for GC prognosis to develop more successful immunotherapy strategies.

Homozygous Factor V Leiden Complicated by Heparin-Induced Thrombocytopenia: A Case Report

Homozygous factor V Leiden (FVL) is a rare condition, occurring in 0.2% of the white population. This disease's rarity and aggressive pathophysiology can represent a challenge even to the most experienced clinicians. We report a case of a 35-year-old white man, who presented to the emergency department with a 1-week history of bilateral thigh swelling and pain. His past medical history included homozygous FVL mutation complicated by multiple venous thromboembolic events in the last decade, recent inferior vena cava (IVC) filter placement, diabetes mellitus type 2, and hypertension. Despite being trialed for different anticoagulation therapies over 10 years, including warfarin (international normalized ratio (INR) goal 2 - 3), rivaroxaban, and dalteparin, he continued to thrombose. On admission, while on a therapeutic dose of dalteparin, he was diagnosed with extensive acute deep vein thrombosis involving the bilateral femoral and iliac veins, extending proximally to his IVC filter to the renal veins, and pulmonary embolisms in the bilateral lower lobes and right middle lobe. A heparin drip was initiated, and he developed progressive thrombocytopenia over 96 h. Heparin was discontinued, and he was switched to argatroban. He was diagnosed with heparin-induced thrombocytopenia (HIT) with positive anti-platelet factor 4 (PF4)/heparin antibodies and a serotonin release assay. His platelets trended up to normal levels 5 days after heparin discontinuation. He underwent multiple thrombectomies, thrombolysis, and angioplasty of the abdominal and lower extremity veins. The IVC filter was removed. Secondary thrombophilia workup was remarkable for a positive lupus anticoagulant, which had been negative in the past. The patient was bridged to warfarin, discharged with a higher INR goal of 3 - 3.5, and continuously monitored factor II activity (goal 15-30%). This case illustrates a patient with recurrent episodes of thromboembolic events because of homozygous FVL. This condition's pathophysiology and therapeutic approach has been well studied in heterozygous carriers; however, homozygous individuals represent <1% of cases. Given the rareness of the disease, there are no well-established therapeutic guidelines, and long-term anticoagulation remains the therapeutic cornerstone. This case emphasizes the challenges in managing patients with homozygous FVL and complications that can occur due to this gap in the literature. We suggest further case reports and research studies to shed light on this serious condition and its lifetime complications.

Coagulation factor V is a T-cell inhibitor expressed by leukocytes in COVID-19

Clotting Factor V (FV) is primarily synthesized in the liver and when cleaved by thrombin forms pro-coagulant Factor Va (FVa). Using whole blood RNAseq and scRNAseq of peripheral blood mononuclear cells, we find that FV mRNA is expressed in leukocytes, and identify neutrophils, monocytes, and T regulatory cells as sources of increased FV in hospitalized patients with COVID-19. Proteomic analysis confirms increased FV in circulating neutrophils in severe COVID-19, and immunofluorescence microscopy identifies FV in lung-infiltrating leukocytes in COVID-19 lung disease. Increased leukocyte FV expression in severe disease correlates with T-cell lymphopenia. Both plasma-derived and a cleavage resistant recombinant FV, but not thrombin cleaved FVa, suppress T-cell proliferation in vitro. Anticoagulants that reduce FV conversion to FVa, including heparin, may have the unintended consequence of suppressing the adaptive immune system.

Coagulation factor 5 (F5) is an estrogen-responsive gene in breast cancer cells

Most breast cancers express estrogen receptor (ER) where estrogen signaling plays an important role. Cancer contributes to activation of the coagulation system leading to an imbalance in the hemostatic system, and Coagulation factor (F) V, which is a key regulator of blood coagulation, has been shown to be increased in breast tumors. Thus, the molecular association between estrogens and FV was explored. Stimulation with 17-β-estradiol (E2) or 17-β-ethinylestradiol (EE2) resulted in a time- and dose-dependent increase in F5 mRNA and FV protein in ERα positive MCF-7 cells. Pre-treatment with the ER antagonist fulvestrant or knockdown of ERα prior to stimulation with E2 counteracted this effect. Three ERα binding half-sites were identified in the promoter region of the F5 gene in silico. Reporter gene analysis showed that all three half-sites were involved in the estrogen-induced gene regulation in vitro, as the effect was abolished only when all half-sites were mutated. High F5 levels in ER positive breast tumors were associated with increased relapse-free survival of breast cancer patients.

Cryo-EM structures of human coagulation factors V and Va

Coagulation factor V (fV) is the precursor of fVa, which, together with fXa, Ca2+, and phospholipids, defines the prothrombinase complex and activates prothrombin in the penultimate step of the coagulation cascade. We solved the cryogenic electron microscopy (cryo-EM) structures of human fV and fVa at atomic (3.3 Å) and near-atomic (4.4 Å) resolution, respectively. The structure of fV reveals the entire A1-A2-B-A3-C1-C2 assembly, but with a surprisingly disordered B domain. The C1 and C2 domains provide a platform for interaction with phospholipid membranes and support the A1 and A3 domains, with the A2 domain sitting on top of them. The B domain is highly dynamic and visible only for short segments connecting to the A2 and A3 domains. The A2 domain reveals all sites of proteolytic processing by thrombin and activated protein C, a partially buried epitope for binding fXa, and fully exposed epitopes for binding activated protein C and prothrombin. Removal of the B domain and activation to fVa exposes the sites of cleavage by activated protein C at R306 and R506 and produces increased disorder in the A1-A2-A3-C1-C2 assembly, especially in the C-terminal acidic portion of the A2 domain that is responsible for prothrombin binding. Ordering of this region and full exposure of the fXa epitope emerge as necessary steps in the assembly of the prothrombin-prothrombinase complex. These structures offer molecular context for the function of fV and fVa and pioneer the analysis of coagulation factors by cryo-EM.

A Prognostic Nomogram Model Based on mRNA Expression of DNA Methylation-Driven Genes for Gastric Cancer

PURPOSE

The exploration and interpretation of DNA methylation-driven genes might contribute to molecular classification, prognostic prediction and therapeutic choice. In this study, we built a prognostic risk model via integrating analysis of the transcriptome and methylation profile for patients with gastric cancer (GC).

METHODS

The mRNA expression profiles, DNA methylation profiles and corresponding clinicopathological information of 415 GC patients were downloaded from The Cancer Genome Atlas (TCGA). Differential expression and correlation analysis were performed to identify DNA methylation-driven genes. The candidate genes were selected by univariate Cox regression analyses followed by the least absolute shrinkage and selection operator (LASSO) regression. A prognostic risk nomogram model was then built together with clinicopathological parameters.

RESULTS

5 DNA methylation-driven genes (CXCL3, F5, GNAI1, GAMT and GHR) were identified by integrated analyses and selected to construct the prognostic risk model with clinicopathological parameters. High expression and low DNA hypermethylation of F5, GNAI1, GAMT and GHR, as well as low expression and high DNA hypomethylation of CXCL3 were significantly associated with poor prognosis rates, respectively. The high-risk group showed a significantly shorter prognosis than the low-risk group in the TCGA dataset (HR = 0.212, 95% CI = 0.139-0.322, P = 2e-15). The final nomogram model showed high predictive efficiency and consistency in the training and validation group.

CONCLUSION

We construct and validate a prognostic nomogram model for GC based on five DNA methylation-driven genes with high performance and stability. This nomogram model might be a powerful tool for prognosis evaluation in the clinic and also provided novel insights into the epigenetics in GC.

Sclerosing Mesenteritis in a Patient Heterozygous for Factor V Leiden

Patient: Male, 33-year-old

Final Diagnosis: Sclerosing mesenteritis

Symptoms: Abdominal pain • diaphoresis • nausea • tachycardia

Medication:—

Clinical Procedure: Exploratory laparotomy

Specialty: Surgery

Identification of F5 as a Prognostic Biomarker in Patients with Gastric Cancer

Association of Coagulation factor V (F5) polymorphisms with the occurrence of many types of cancers has been widely reported, but whether it is of prognostic relevance in some cancers remain to be resolved. The RNA-sequencing dataset was downloaded from The Cancer Genome Atlas (TCGA). The potential of F5 genes to predict the survival time of gastric cancer (GC) patients was investigated using univariate and multivariate survival analysis whereas “Kaplan-Meier plotter” (KM-plotter) online tools were employed to validate the outcomes. TCGA data revealed that F5 mRNA levels were significantly upregulated in gastric cancer samples. Survival analysis confirmed that high levels of F5 mRNA correlated with short overall survival (OS) in gastric cancer patients, and the area under the curve (AUC) values of 1-, 2-, and 5-year OS rate were 0.554, 0.593, and 0.603, respectively. Survival analysis by KM-plotter indicated that the high expression of F5 mRNA was significantly associated with a shorter OS compared with the low expression level in all patients with GC, and this was also the case for patients in stage III (hazard ratio (HR) = 1.78, P = 0.017). These findings suggest that the F5 gene is significantly upregulated in GC tumour tissues, and may be a potential prognostic biomarker for GC.

The roles of factor Va and protein S in formation of the activated protein C/protein S/factor Va inactivation complex

BACKGROUND

Activated protein C (APC)-mediated inactivation of factor (F)Va is greatly enhanced by protein S. For inactivation to occur, a trimolecular complex among FVa, APC, and protein S must form on the phospholipid membrane. However, direct demonstration of complex formation has proven elusive.

OBJECTIVES

To elucidate the nature of the phospholipid-dependent interactions among APC, protein S, and FVa.

METHODS

We evaluated binding of active site blocked APC to phospholipid-coated magnetic beads in the presence and absence of protein S and/or FVa. The importance of protein S and FV residues were evaluated functionally.

RESULTS

Activated protein C alone bound weakly to phospholipids. Protein S mildly enhanced APC binding to phospholipid surfaces, whereas FVa did not. However, FVa together with protein S enhanced APC binding (>14-fold), demonstrating formation of an APC/protein S/FVa complex. C4b binding protein-bound protein S failed to enhance APC binding, agreeing with its reduced APC cofactor function. Protein S variants (E36A and D95A) with reduced APC cofactor function exhibited essentially normal augmentation of APC binding to phospholipids, but diminished APC/protein S/FVa complex formation, suggesting involvement in interactions dependent upon FVa. Similarly, FVaNara (W1920R), an APC-resistant FV variant, also did not efficiently incorporate into the trimolecular complex as efficiently as wild-type FVa. FVa inactivation assays suggested that the mutation impairs its affinity for phospholipid membranes and with protein S within the complex.

CONCLUSIONS

FVa plays a central role in the formation of its inactivation complex. Furthermore, membrane proximal interactions among FVa, APC, and protein S are essential for its cofactor function.

Subtype-specific clinical and prognostic relevance of tumor-expressed F5 and regulatory F5 variants in breast cancer: the CoCaV study

Essentials The role of coagulation factor V (encoded by F5) in cancer pathogenesis is unknown. The clinical significance of tumor-expressed F5 was evaluated in breast cancer patient cohorts. F5 was expressed in human breast tumors, and the expression was higher than in normal tissue. High F5 expression was associated with aggressive tumors, but also with survival in breast cancer.

SUMMARY

Background Tumor expression of certain coagulation factors has been linked to cancer progression. Single nucleotide polymorphisms (SNPs) in F5 (encoding the FV protein) have been found to be associated with breast cancer; however, the role of coagulation factor V (FV) in cancer pathogenesis remains undiscovered. Objectives We aimed to investigate the clinical significance of FV and the regulatory role of F5 gene variants in breast cancer. Patients/Methods A Scandinavian 503-sample breast cancer cohort and three public breast cancer datasets (GOBO, TCGA and KM plotter) were used to determine associations between F5 gene expression (tumor-specific), circulating FV, F5 SNPs, clinical characteristics and breast cancer survival. Immunohistochemistry (IHC) was used to detect FV antigen in tumors. Results F5 expression was 2-fold higher in breast tumors compared with normal tissue, and the presence of FV antigen in breast tumors was confirmed by IHC staining. F5 expression was increased in patients with hormone receptor negative tumors, triple negative tumors, HER2-enriched and basal-like tumors. In patients with basal tumors, high expression of F5 was associated with improved overall survival (hazard ratio, HR = 0.52, 95% confidence interval, 0.31-0.86). SNPs in F5 were associated with tumor size and luminal A tumors. The rs6427202-rs9332542 C-G haplotype, previously associated with breast cancer, displayed a cis-regulatory effect on F5 expression in tumors and plasma FV antigen levels. In silico mining supported this regulatory function. Conclusions FV was a possible marker of aggressive breast cancer, yet also a predictor of favorable outcome. Evaluation of FV expression may be clinically useful for prognosis and treatment decisions in aggressive breast cancer.

Laboratory assessment of Activated Protein C Resistance/Factor V-Leiden and performance characteristics of a new quantitative assay

Activated Protein C Resistance is mainly associated to a factor V mutation (RQ506), which induces a deficient inactivation of activated factor V by activated protein C, and is associated to an increased risk of venous and arterial thrombosis in affected individuals, caused by the prolonged activated factor V survival. Its prevalence is mainly in Caucasians (about 5%), and this mutation is absent in Africans and Asians. Presence of Factor V-Leiden is usually evidenced with clotting methods, using a two-step APTT assay performed without or with APC: prolongation of blood coagulation time is decreased if this factor is present. The R506Q Factor V-Leiden mutation is now usually characterized using molecular biology, and this technique tends to become the first intention assay for characterization of patients. Both techniques are qualitative, and allow classifying tested individuals as heterozygotes or homozygotes for the mutation, when present. A new quantitative assay for Factor V-Leiden, using a one-step clotting method, has been developed, and designed with highly purified human coagulation proteins. Clotting is triggered with human Factor Xa, in presence of calcium and phospholipids (mixture which favours APC action over clotting process). Diluted tested plasma, is supplemented with a clotting mixture containing human fibrinogen, prothrombin, and protein S at a constant concentration. APC is added, and clotting is initiated with calcium. Calibration is performed with a pool of plasmas from patients carrying the R506Q Factor V mutation, and its mixtures with normal plasma. Homozygous patients have clotting times of about <40sec; heterozygous patients have clotting times of about 40-60sec and normal individuals yield clotting times >70sec. Factor V-Leiden concentration is usually >75% in homozygous patients, 30-60% in heterozygous patients and below 5% in normal. The assay is insensitive to clotting factor deficiencies (II, VII, VIII: C, IX, X), dicoumarol or heparin therapies, and has no interference with lupus anticoagulant (LA). This new assay for Factor V-Leiden can be easily used in any coagulation laboratory, is performed as a single test, and is quantitative. This assay has a high robustness, is accurate and presents a good intra- (<3%) and inter-assay (<5%) variability. It contributes solving most of the laboratory issues faced when testing factor V-Leiden. Quantitation of Factor V-L could contribute to a better assessment of thrombotic risk in affected patients, as this complication is first associated to and caused by the presence of a defined amount of FVa.

Pneumococcal meningitis and endocarditis in an infant: possible improved survival with factor V Leiden mutation

Streptococcus pneumoniae infections continue to remain associated with high morbidity and mortality. Although the incidence of invasive meningeal and/or lung disease are not uncommon, Streptococcus pneumoniae endocarditis is rare especially in healthy pediatric population. New studies have suggested a strong association between factor V leiden (FVL) mutation and favorable outcomes in critically ill children. A healthy 10 month old presented with sepsis and meningeal signs, was later confirmed to have Streptococcus pneumoniae meningitis and endocarditis. She was found to have factor V leiden mutation and made a complete recovery despite initial complications.

CONCLUSION

Presence of factor V leiden mutation in critically ill children with severe septicaemia possibly contributes to better outcomes. What is known: • Mortality and morbidity remain high with invasive pneumococcal disease. • Pneumococcal endocarditis is rare in healthy pediatric population and results in significant morbidity and mortality What is new: • New studies have suggested a strong association between factor V leiden (FVL) mutation and favorable outcomes in critically ill children. • The presence of factor V mutation in children with extensive invasive pneumococcal disease possibly contributes to a better outcome.

Reaction mechanism of blood coagulation factors in shear flow field

Thrombus formation in blood pumps is a major problem. It has been reported that the shear rate is closely related to thrombus formation in blood pumps; however, the mechanism of blood coagulation in a shear flow field is not yet fully understood. The purpose of this study is to evaluate the effect of shear loading on the reaction of blood coagulation factors quantitatively. Human blood and porcine blood were used as test blood and sheared at 2,880 s-1 for 3 h using a rheometer. After shear loading to the test blood, the activated partial thromboplastin time (APTT) and prothrombin time (PT) of sample plasma were measured using an automated coagulation analyzer. The APTT and PT of mixed plasma containing human blood coagulation factor-deficient plasma and sample plasma were also measured. The APTT and PT of mixed plasma reflected the reaction of the particular blood coagulation factor. Results show that shear loading prolonged the APTT and PT of human sample plasma. Accordingly, the APTT and PT of mixed plasma containing human blood coagulation factor V-deficient plasma and human sample plasma were prolonged after shear loading. Thus, the reaction of human blood coagulation factors was inhibited by specific inhibition of the reaction of human blood coagulation factor V in the shear flow field. The reaction time of porcine blood coagulation factors after shear loading differed from that of human blood coagulation factors. The result suggest the evaluation difficulty of animal blood coagulation reaction, that is, porcine blood coagulation reaction did not fully proceed with clinical reagents due to species specificity.

Coagulation factor V mediates inhibition of tissue factor signaling by activated protein C in mice

The key effector molecule of the natural protein C pathway, activated protein C (aPC), exerts pleiotropic effects on coagulation, fibrinolysis, and inflammation. Coagulation-independent cell signaling by aPC appears to be the predominant mechanism underlying its highly reproducible therapeutic efficacy in most animal models of injury and infection. In this study, using a mouse model of Staphylococcus aureus sepsis, we demonstrate marked disease stage-specific effects of the anticoagulant and cell signaling functions of aPC. aPC resistance of factor (f)V due to the R506Q Leiden mutation protected against detrimental anticoagulant effects of aPC therapy but also abrogated the anti-inflammatory and mortality-reducing effects of the signaling-selective 5A-aPC variant that has minimal anticoagulant function. We found that procofactor V (cleaved by aPC at R506) and protein S were necessary cofactors for the aPC-mediated inhibition of inflammatory tissue-factor signaling. The anti-inflammatory cofactor function of fV involved the same structural features that govern its cofactor function for the anticoagulant effects of aPC, yet its anti-inflammatory activities did not involve proteolysis of activated coagulation factors Va and VIIIa. These findings reveal a novel biological function and mechanism of the protein C pathway in which protein S and the aPC-cleaved form of fV are cofactors for anti-inflammatory cell signaling by aPC in the context of endotoxemia and infection.

Survival advantage of heterozygous factor V Leiden carriers in murine sepsis

BACKGROUND

The high allelic frequency of the prothrombotic Leiden polymorphism in human blood coagulation factor V (FV) has been speculated to reflect positive selection during evolution. Heterozygous Leiden carriers enrolled in the placebo arm of the PROWESS sepsis trial and heterozygous Leiden mice challenged with endotoxin both showed reduced mortality, whereas homozygous Leiden mice were not protected from lethal endotoxemia. Follow-up analyses of clinical outcomes and of mouse models of infection with various pathogens remained inconclusive.

OBJECTIVE

To establish whether activated protein C resistance of FV Leiden modifies the outcome of bacterial infection in murine sepsis models.

METHODS

Homozygous and heterozygous FV Leiden mice were subjected to gram-positive (S. aureus) or gram-negative (Y. pestis; E. coli) septic peritonitis or polymicrobial, focal septic peritonitis induced by cecal ligation and puncture. The effect of FV Leiden on 7-day survival and bacterial dissemination was assessed. Outcomes were compared with the sepsis survival of mice with genetically impaired hemostasis (hemophilia A, thrombocytopenia, thrombin receptor PAR4 [protease activated receptor 4] deficiency, endothelial protein C receptor [ProcR/EPCR] deficiency).

RESULTS

Heterozygous, but not homozygous, Leiden mice were protected from lethal infection with highly virulent S. aureus and Y. pestis strains. FV Leiden did not affect the outcome of sepsis induced by cecal ligation and puncture, staphylokinase-deficient S. aureus, Pla-deficient Y. pestis, or E. coli. Thrombocytopenia, deficiency of PAR1 or PAR4 did not affect S. aureus sepsis survival, whereas hemophilia A increased mortality. ProcR deficiency selectively abolished the survival advantage of heterozygous Leiden mice.

CONCLUSIONS

In mice, heterozygous FV Leiden carriers are protected from sepsis mortality after infection with clinically relevant human bacterial pathogens.

Coagulation function and mechanisms in various clinical phenotypes of patients with acquired factor V inhibitors

BACKGROUND

The clinical phenotype of individuals with acquired factor V (A-FV) inhibitors varies from asymptomatic (non-B group) to life-threatening bleeding (B group), but the mechanism(s) underlying this variation in hemorrhagic phenotype are poorly understood.

OBJECTIVE

To investigate coagulation mechanistically in a range of patients with A-FV antibodies.

METHODS AND RESULTS

Ten cases of A-FV inhibitors in the non-B (n = 5) and B groups (n = 5) were studied. Thrombin generation assays in these plasmas revealed little thrombin generation, despite similar FV activity levels in both groups. However, prothrombin time-based clot waveform analysis revealed that the clot times were significantly prolonged and the maximum velocity and acceleration of coagulation were lower in the B group than in the non-B group, suggesting that this technique might be useful for predicting and monitoring hemorrhagic symptoms. A-FV inhibitors from the non-B group recognized predominantly the FV heavy chain, whereas those from the B group recognized the light chain. Purified anti-FV autoantibodies (autoAbs) from the B group inhibited FV binding to phospholipid by 60-90%, whereas there was little effect on this reaction in the non-B group. In addition, anti-FV autoAbs from the non-B group impaired the activated protein C (APC) cofactor activity of FV in FVIIIa inactivation mechanisms, and delayed APC-catalyzed cleavage of FVa at Arg306, but not at Arg506, indicating the presence of APC resistance in the non-B group.

CONCLUSIONS

The results suggest that the different hemorrhagic phenotypes in A-FV inhibitors depend on the specific epitope of anti-FV autoAbs, and appear to be associated with an imbalance of procoagulant and anticoagulant function.

Anticoagulant factor V: factors affecting the integration of novel scientific discoveries into the broader framework

Since its initial discovery in the 1940s, factor V has long been viewed as an important procoagulant protein in the coagulation cascade. However, in the later part of the 20th century, two different scientists proposed novel anticoagulant roles for factor V. Philip Majerus proposed the first anticoagulant function for factor V in 1983, yet ultimately it was not widely accepted by the broader scientific community. In contrast, Björn Dahlbäck proposed a different anticoagulant role for factor V in 1994. While this role was initially contested, it was ultimately accepted and integrated into the scientific framework. In this paper, I present a detailed historical account of these two anticoagulant discoveries and propose three key reasons why Dahlbäck's anticoagulant role for factor V was accepted whereas Majerus' proposed role was largely overlooked. Perhaps most importantly, Dahlbäck's proposed anticoagulant role was of great clinical interest because the discovery involved the study of an important subset of patients with thrombophilia. Soon after Dahlbäck's 1994 work, this patient population was shown to possess the factor V Leiden mutation. Also key in the ultimate acceptance of the second proposed anticoagulant role was the persistence of the scientist who made the discovery and the interest in and ability of others to replicate and reinforce this work. This analysis of two different yet similar discoveries sheds light on factors that play an important role in how new discoveries are incorporated into the existing scientific framework.

Protein S and factor V in regulation of coagulation on platelet microparticles by activated protein C

INTRODUCTION

Platelets are the main source of microparticles in plasma and the concentration of microparticles is increased in many diseases. As microparticles expose negatively charged phospholipids, they can bind and assemble the procoagulant enzyme-cofactor complexes. Our aim was to elucidate possible regulation of these complexes on microparticles by the anticoagulant protein C system.

MATERIALS AND METHODS

Platelets were activated with thrombin ± collagen or the calcium ionophore A23187 ± thrombin to generate microparticles. The microparticles were analyzed using flow cytometry and functional coagulation assays to characterize parameters with importance for the activated protein C system.

RESULTS

Activation with A23187+thrombin was most efficient, fully converting the platelets to microparticle-like vesicles, characterized by high lactadherin and protein S binding capacity. Suppression of thrombin generation by activated protein C in plasma spiked with these microparticles was dependent on the presence of plasma protein S. Experiments with purified components showed that activated protein C inhibited both factor Va and factor VIIIa on the microparticle surface. Inhibition of factor Va was stimulated by, but not fully dependent on, the presence of protein S. In the factor VIIIa-degradation, activated protein C was dependent on the addition of protein S, and exogenous factor V further increased the efficiency.

CONCLUSIONS

Protein S is crucial for activated protein C-mediated inhibition of thrombin generation on platelet-derived microparticles in plasma. Moreover, protein S and factor V are synergistic cofactors in the inhibition of factor VIIIa. The results demonstrate that the activated protein C system has the capacity to counterbalance the procoagulant ability of microparticles.

Activated protein C resistance associated with lupus anticoagulants is a high risk in acute mesenteric venous thrombosis

BACKGROUND

Acute mesenteric venous thrombosis (AMVT) is one of those diseases that cannot be diagnosed by specific symptoms and signs. A high misdiagnosis rate makes AMVT a final diagnosis established by exploratory laparotomy or forensic examinations earlier, during the period when computed tomography was not as efficient as it is now. The main motivation of our research was to improve the diagnosis and treatment by finding the relationship among activated protein C (APC) resistance, antiphospholipid antibodies, and AMVT in the Chinese Han population.

METHODS

APC resistance was tested by activated partial thromboplastin time method in 70 AMVT patients and 75 healthy adult volunteers that excluded hypercoagulable states. Factor V Leiden mutation was analyzed by polymerase chain reaction with restriction fragment length polymorphism. Anticardiolipin antibodies (aCLs) were tested by enzyme-linked immunosorbent assay. A sensitive activated partial thromboplastin time-lupus anticoagulant (LA) test was used according to the guidelines.

RESULTS

Only two samples had factor V Leiden mutation and were excluded. Twenty-one (30.9%) of the 68 AMVT patients had APC resistance. The rate of aCLs positive in AMVT group (13.2%) was significantly increased compared with control group (1.33%; P = .014). The LA-positive rate is significantly different between the AMVT and control group. Among LA-positive patients, the number of APC resistance was much higher than LA-negative patients (P = .000), but aCLs do not have an increased predisposition to APC resistance (P = .85).

CONCLUSIONS

APC resistance associated with LAs is a high risk in AMVT. The way aCL may affect the process of AMVT is not the same as with LA.

Microtrauma stimulates rat Achilles tendon healing via an early gene expression pattern similar to mechanical loading

Mechanical loading increases the strength of healing tendons, but also induces small localized bleedings. Therefore, it is unclear if increased strength after loading is a response to mechanotransduction or microtrauma. We have previously found only five genes to be up-regulated 15 min after a single loading episode, of them four were transcription factors. These genes are followed by hundreds of genes after 3 h, many of them involved in inflammation. We now compared healing in mechanically unloaded tendons with or without added microtrauma induced by needling of the healing tissue. Nineteen rats received Botox into the calf muscle to reduce loading, and the Achilles tendon was transected. Ten rats were randomized to needling days 2–5. Mechanical testing on day 8 showed increased strength by 45% in the needling group. Next, another 24 rats were similarly unloaded, and 16 randomized to needling on day 5 after transection. Nineteen characteristic genes, known to be regulated by loading in this model, were analyzed by qRT-PCR. Four of these genes were regulated 15 min after needling. Three of them (Egr1, c-Fos, Rgs1) were among the five regulated genes after loading in a previous study. Sixteen of the 19 genes were regulated after 3 h, in the same way as after loading. In conclusion, needling increased strength, and there was a striking similarity between the gene expression response to needling and mechanical loading. This suggests that the response to loading in early tendon healing can, at least in part, be a response to microtrauma.

Mechanistic phenotypes: an aggregative phenotyping strategy to identify disease mechanisms using GWAS data

A single mutation can alter cellular and global homeostatic mechanisms and give rise to multiple clinical diseases. We hypothesized that these disease mechanisms could be identified using low minor allele frequency (MAF<0.1) non-synonymous SNPs (nsSNPs) associated with “mechanistic phenotypes”, comprised of collections of related diagnoses. We studied two mechanistic phenotypes: (1) thrombosis, evaluated in a population of 1,655 African Americans; and (2) four groupings of cancer diagnoses, evaluated in 3,009 white European Americans. We tested associations between nsSNPs represented on GWAS platforms and mechanistic phenotypes ascertained from electronic medical records (EMRs), and sought enrichment in functional ontologies across the top-ranked associations. We used a two-step analytic approach whereby nsSNPs were first sorted by the strength of their association with a phenotype. We tested associations using two reverse genetic models and standard additive and recessive models. In the second step, we employed a hypothesis-free ontological enrichment analysis using the sorted nsSNPs to identify functional mechanisms underlying the diagnoses comprising the mechanistic phenotypes. The thrombosis phenotype was solely associated with ontologies related to blood coagulation (Fisher's p = 0.0001, FDR p = 0.03), driven by the F5, P2RY12 and F2RL2 genes. For the cancer phenotypes, the reverse genetics models were enriched in DNA repair functions (p = 2×10−5, FDR p = 0.03) (POLG/FANCI, SLX4/FANCP, XRCC1, BRCA1, FANCA, CHD1L) while the additive model showed enrichment related to chromatid segregation (p = 4×10−6, FDR p = 0.005) (KIF25, PINX1). We were able to replicate nsSNP associations for POLG/FANCI, BRCA1, FANCA and CHD1L in independent data sets. Mechanism-oriented phenotyping using collections of EMR-derived diagnoses can elucidate fundamental disease mechanisms.

Mechanisms of anticoagulant and cytoprotective actions of the protein C pathway

The protein C pathway provides multiple important functions to maintain a regulated balance between hemostasis and host defense systems in response to vascular and inflammatory injury. The anticoagulant protein C pathway is designed to regulate coagulation, maintain the fluidity of blood within the vasculature, and prevent thrombosis, whereas the cytoprotective protein C pathway prevents vascular damage and stress. The cytoprotective activities of activated protein C (APC) include anti-apoptotic activity, anti-inflammatory activity, beneficial alterations of gene expression profiles, and endothelial barrier stabilization. These cytoprotective activities of APC, which require the endothelial protein C receptor (EPCR) and protease-activated receptor-1 (PAR1), have been a major research focus. Recent insights, such as non-canonical activation of PAR1 at Arg46 by APC and biased PAR1 signaling, provided better understanding of the molecular mechanisms by which APC elicits cytoprotective signaling through cleavage of PAR1. The discovery and development of anticoagulant-selective and cytoprotective-selective APC mutants provided unique opportunities for preclinical research that has been and may continue to be translated to clinical research. New mechanisms for the regulation of EPCR functionality, such as modulation of EPCR-bound lipids that affect APC's cytoprotective activities, may provide new research directions to improve the efficacy of APC to convey its cytoprotective activities to cells. Moreover, emerging novel functions for EPCR expand the roles of EPCR beyond mediating protein C activation and APC-induced PAR1 cleavage. These discoveries increasingly develop our understanding of the protein C pathway, which will conceivably expand its physiological implications to many areas in the future.

Proteomic characterisation of toxins isolated from nematocysts of the South Atlantic jellyfish Olindias sambaquiensis

Surprisingly little is known of the toxic arsenal of cnidarian nematocysts compared to other venomous animals. Here we investigate the toxins of nematocysts isolated from the jellyfish Olindias sambaquiensis. A total of 29 unique ms/ms events were annotated as potential toxins homologous to the toxic proteins from diverse animal phyla, including cone-snails, snakes, spiders, scorpions, wasp, bee, parasitic worm and other Cnidaria. Biological activities of these potential toxins include cytolysins, neurotoxins, phospholipases and toxic peptidases. The presence of several toxic enzymes is intriguing, such as sphingomyelin phosphodiesterase B (SMase B) that has only been described in certain spider venoms, and a prepro-haystatin P-IIId snake venom metalloproteinase (SVMP) that activates coagulation factor X, which is very rare even in snake venoms. Our annotation reveals sequence orthologs to many representatives of the most important superfamilies of peptide venoms suggesting that their origins in higher organisms arise from deep eumetazoan innovations. Accordingly, cnidarian venoms may possess unique biological properties that might generate new leads in the discovery of novel pharmacologically active drugs.

A new regulatory function of activated factor V: inhibition of the activation by tissue factor/factor VII(a) of factor X

BACKGROUND

We observed that minute amounts of thrombin or the enzyme Russell's viper venom activating factor V (RVV-V) added to plasma strongly diminish the potential of that plasma to generate thrombin after being triggered by tissue factor.

OBJECTIVE

To find the mechanism behind this phenomenon.

METHODS AND RESULTS

Thrombin generation (TG) initiated by tissue factor (TF) is strongly and dose-dependently inhibited by addition of activated factor V (FVa) or by addition of a factor V activator (thrombin or RVV-V). No inhibition is seen when TG is triggered via the intrinsic pathway or by direct activation of factor X. The effect is independent of proteins C and S and tissue factor pathway inhibitor (TFPI). In factor VII-deficient plasma the effect is seen when it is spiked with recombinant factor VII (FVII) and to a much lesser extent when spiked with recombinant FVIIa. In a purified system, FVa also dose-dependently inhibits the activation of FX by TF/FVII(a). The inhibitory effect is neutralized by antibodies against the light chain of FVa but not by antibodies against the heavy chain.

CONCLUSIONS

Our observations can be explained by assuming that FVa, via its light chain, binds to the complex TF/FVII(a) and prevents it from activating FX. We assume that this mechanism reduces the possibility that thrombin and factor Xa escaping from a wound area into the circulation, together with blood-borne tissue factor, would trigger intravascular coagulation.

The effect of filtration on residual levels of coagulation factors in plasma

Leukoreduced blood components are commonly manufactured via filtration. There are specifications for the residual leukocyte content of any final cellular blood component but not for residual clotting factors. Leukoreduced and nonleukoreduced platelet-poor plasma products were manufactured from filtered vs unfiltered platelet-rich plasma, respectively, using platelet leukoreduction filters. The leukoreduced plasma showed lower levels of factor VIII (75% ± 16% vs 88% ± 18%, P ≤ .05), factor XI (86% ± 9% vs 96% ± 10%, P ≤ .01) and factor VII (87% ± 14% vs 98% ± 11%, P ≤ .01). No difference was seen with factor X, factor V, or fibrinogen. Plasma filtered through a whole blood filter showed a reduction in factor V (105% ± 12% vs 124% ± 10%, P ≤ .01) but a minimal reduction in factor VIII (80% ± 5% vs 82% ± 6%, P = .04). Filtration can alter the residual levels of clotting factors to a variable extent in manufactured plasma, most noticeably factors V, VII, VIII, and XI.