Plasma fibrin clot proteomics in patients with acute pulmonary embolism: Association with clot properties

Fibrinaloid Microclots and Atrial Fibrillation

Atrial fibrillation (AF) is a comorbidity of a variety of other chronic, inflammatory diseases for which fibrinaloid microclots are a known accompaniment (and in some cases, a cause, with a mechanistic basis). Clots are, of course, a well-known consequence of atrial fibrillation. We here ask the question whether the fibrinaloid microclots seen in plasma or serum may in fact also be a cause of (or contributor to) the development of AF. We consider known 'risk factors' for AF, and in particular, exogenous stimuli such as infection and air pollution by particulates, both of which are known to cause AF. The external accompaniments of both bacterial (lipopolysaccharide and lipoteichoic acids) and viral (SARS-CoV-2 spike protein) infections are known to stimulate fibrinaloid microclots when added in vitro, and fibrinaloid microclots, as with other amyloid proteins, can be cytotoxic, both by inducing hypoxia/reperfusion and by other means. Strokes and thromboembolisms are also common consequences of AF. Consequently, taking a systems approach, we review the considerable evidence in detail, which leads us to suggest that it is likely that microclots may well have an aetiological role in the development of AF. This has significant mechanistic and therapeutic implications.

Fibrin Clot Properties in Cancer: Impact on Cancer-Associated Thrombosis

Cancer is associated with a high risk of venous thromboembolism (VTE) and its recurrence. There is evidence that the prothrombotic fibrin clot phenotype, involving the formation of denser and stiffer clots relatively resistant to lysis, occurs in cancer patients, which is in part related to enhanced inflammation, oxidative stress, and coagulation activation, along with the release of neutrophil extracellular traps, indicating that fibrin-related mechanisms might contribute to cancer-associated thrombosis (CAT). Multiple myeloma and its therapy have been most widely explored in terms of altered fibrin characteristics, but prothrombotic fibrin clot features have also been reported in patients with active solid cancer, including lung cancer and gastrointestinal cancer. Patient-related factors such as advanced age, smoking, and comorbidities might also affect fibrin clot characteristics and the risk of CAT. Prothrombotic fibrin clot features have been shown to predict the detection of cancer in patients following VTE during follow-up. Cancer-specific therapies and anticoagulation can favorably modify the phenotype of a fibrin clot, which may alter the course of CAT. It is unclear whether the fibrin clot phenotype might help identify patients with CAT who are more likely to experience recurrent events. This narrative review summarizes the current knowledge on the role of fibrin clot structure and function in cancer patients in the context of CAT.

Cytoplasmic Shotgun Proteomic Points to Key Proteins and Pathways in Temozolomide-Resistant Glioblastoma Multiforme

Temozolomide (TMZ) is the first line of chemotherapy to treat primary brain tumors of the type glioblastoma multiforme (GBM). TMZ resistance (TMZR) is one of the main barriers to successful treatment and is a principal factor in relapse, resulting in a poor median survival of 15 months. The present paper focuses on proteomic analyses of cytosolic fractions from TMZ-resistant (TMZR) LN-18 cells. The experimental workflow includes an easy, cost-effective, and reproducible method to isolate subcellular fraction of cytosolic (CYTO) proteins, mitochondria, and plasma membrane proteins for proteomic studies. For this study, enriched cytoplasmic fractions were analyzed in replicates by nanoflow liquid chromatography tandem high-resolution mass spectrometry (nLC-MS/MS), and proteins identified were quantified using a label-free approach (LFQ). Statistical analysis of control (CTRL) and temozolomide-resistant (TMZR) proteomes revealed proteins that appear to be differentially controlled in the cytoplasm. The functions of these proteins are discussed as well as their roles in other cancers and TMZ resistance in GBM. Key proteins are also described through biological processes related to gene ontology (GO), molecular functions, and cellular components. For protein-protein interactions (PPI), network and pathway involvement analyses have been performed, highlighting the roles of key proteins in the TMZ resistance phenotypes. This study provides a detailed insight into methods of subcellular fractionation for proteomic analysis of TMZ-resistant GBM cells and the potential to apply this approach to future large-scale studies. Several key proteins, protein-protein interactions (PPI), and pathways have been identified, underlying the TMZ resistance phenotype and highlighting the proteins' biological functions.

Low-grade endotoxemia in acute pulmonary embolism: Links with prothrombotic plasma fibrin clot phenotype

BACKGROUND

Lipopolysaccharide (LPS) can traverse the intestinal barrier and enter bloodstream, causing endotoxemia and triggering inflammation. Increased circulating LPS was reported in arterial thromboembolism. We investigated whether increased LPS levels occur in acute pulmonary embolism (PE) and if it is associated with a prothrombotic state.

METHODS

We studied 120 normotensive PE patients (aged 59 [48-68] years) on admission, after 5-7 days, and after a 3-month anticoagulation. Serum LPS levels, along with zonulin, a marker of gut permeability, endogenous thrombin potential (ETP), fibrin clot permeability (Ks), clot lysis time (CLT), fibrinolysis proteins, and platelet markers were assessed.

RESULTS

Median LPS concentration on admission was 70.5 (61.5-82) pg/mL (min-max, 34-134 pg/mL), in association with C-reactive protein (r = 0.22, p = 0.018), but not with fibrinogen, D-dimer or platelet markers. Patients with more severe PE had higher LPS levels compared with the remainder. Median zonulin level was 3.26 (2.74-4.08) ng/mL and correlated with LPS (r = 0.66, p < 0.0001). Patients with baseline LPS levels in the top quartile (≥82 pg/mL; n = 29) compared to lower quartiles had 18.6 % increased ETP, 14.5 % reduced Ks, and 25.3 % prolonged CLT, related to higher plasminogen activator inhibitor type 1 (PAI-1) levels. LPS decreased by 23.4 % after 5-7 days and by 40.4 % after 3-month anticoagulation together with reduced zonulin by 18.4 % and 22.3 %, respectively, compared to baseline (all p < 0.001). LPS levels were not related with fibrin characteristics and other variables assessed at 3 months.

CONCLUSIONS

Low-grade endotoxemia is detectable in patients with acute PE and may contribute to increased thrombin generation and PAI-1-mediated hypofibrinolysis.

Fibrin clots from patients with acute-on-chronic liver failure are weaker than those from healthy individuals and patients with sepsis without underlying liver disease

BACKGROUND

Previous studies identified decreased clot permeability, without differences in fibrin fiber density in clots, from patients with cirrhosis compared with those from healthy controls (HCs). Fibrinogen hypersialylation could be the reason for this discrepancy.

OBJECTIVES

The aim of this work was to study mechanical properties of clots and reassess clot permeability in relation to hypersialylation in patients with stable cirrhosis, acute decompensation, and acute-on-chronic liver failure (ACLF). Sepsis patients without liver disease were included to distinguish between liver-specific and inflammation-driven phenotypes.

METHODS

Pooled plasma was used for rheology and permeability experiments. Permeability was assessed with compression using a rheometer and by liquid permeation. Purified fibrinogen treated with neuraminidase was used to study the effects of fibrinogen hypersialylation on liquid permeation.

RESULTS

Mechanical properties of clots from patients with stable cirrhosis and acute decompensation were similar to those of clots from HCs, but clots from patients with ACLF were softer and ruptured at lower shear stress. Clots from sepsis patients without liver disease were stiffer than those from the other groups, but this effect disappeared after adjusting for increased plasma fibrinogen concentrations. Permeability was similar between clots under compression from HCs and clots under compression from patients but decreased with increasing disease severity in liquid permeation. Removal of fibrinogen sialic acid residues increased permeability more in patients than in controls.

CONCLUSION

Clots from patients with ACLF have weak mechanical properties despite unaltered fibrin fiber density. Previous liquid permeation experiments may have erroneously concluded that clots from patients with ACLF are prothrombotic as fibrinogen hypersialylation leads to underestimation of clot permeability in this setting, presumably due to enhanced water retention.

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.

Therapy with high-dose statins reduces soluble P-selectin: The impact on plasma fibrin clot properties

OBJECTIVE

Studies on the effect of statins on platelets in patients with coronary artery disease (CAD) yielded inconsistent results. We sought to investigate whether high-dose statin therapy reduces plasma concentrations of soluble P-selectin (sP-selectin), a well-established platelet activation marker and if such changes can affect fibrin clot properties, which are unfavorably altered in CAD patients.

METHODS

We studied 130 consecutive patients with advanced CAD who did not achieve the target LDL cholesterol on statins. At baseline and after 6-12 months of treatment with atorvastatin 80 mg/day or rosuvastatin 40 mg/day, soluble plasma sP-selectin, along with plasma fibrin clot permeability (Ks), clot lysis time (CLT), thrombin generation and fibrinolysis proteins were determined.

RESULTS

Before high-intensity statin treatment, lower Ks and longer CLT values were associated with increased sP-selectin (β -0.27 [95% CI -0.44 to -0.10] and β 0.21 [95% CI 0.01 to 0.41]; both p < 0.05, respectively) also after adjustment for potential confounders. sP-selectin, alongside fibrin features and other variables at baseline showed no association with lipid profile. On high-dose statin therapy, there was 32% reduction in sP-selectin levels (p < 0.001). On-treatment change (Δ) in sP-selectin correlated with ΔKs and ΔCLT (r = -0.32, p < 0.001 and r = 0.22, p = 0.011, respectively), but not with cholesterol and C-reactive protein lowering. We did not observe any associations between post-treatment sP-selectin levels and lipids, fibrin clot properties or thrombin generation.

CONCLUSIONS

High-dose statin therapy reduces markedly sP-selectin levels in association with improved fibrin clot phenotype, which highlights the contribution of platelet-derived proteins to a prothrombotic state in hypercholesterolemia and statin-induced antithrombotic effects.

Fibrin clot properties and thrombus composition in cirrhosis

Patients with cirrhosis frequently acquire profound hemostatic alterations, which may affect thrombus quality and composition-factors that determine the susceptibility to embolization and fibrinolysis. In this narrative review, we describe in vitro studies on fibrin clot formation and quantitative and qualitative changes in fibrinogen in patients with cirrhosis, and describe recent findings on the composition of portal vein thrombi in patients with cirrhosis. Patients with mild cirrhosis have increased thrombin generation capacity and plasma fibrinogen levels, which may be balanced by delayed fibrin polymerization and decreased factor XIII levels. With progressing illness, plasma fibrinogen levels decrease, but thrombin generation capacity remains elevated. Fibrinogen is susceptible to posttranslational protein modifications and is, for example, hypersialylated and carbonylated in patients with cirrhosis. Despite changes in thrombin generation, factor XIII levels and the fibrinogen molecule, fibrin fiber thickness, and density are normal in patients with cirrhosis. Paradoxically, fibrin clot permeability in patients with cirrhosis is decreased, possibly because of posttranslational protein modifications. Most patients have normal fibrinolytic potential. We have recently demonstrated that portal vein thrombosis is likely a misnomer as the material that may obstruct the cirrhotic portal vein frequently consists of a thickened portal vein wall, rather than a true thrombus. Patients with cirrhosis often have thrombocytopenia and anemia, which may also affect clot stability and composition, but the role of cellular components in clot quality in cirrhosis has not been extensively studied. Finally, we summarize abstracts on fibrin formation and clot quality that were presented at the ISTH 2022 meeting in London.

Discovery of protein biomarkers for venous thromboembolism in non-small cell lung cancer patients through data-independent acquisition mass spectrometry

Objective

Non-small cell lung cancer (NSCLC) patients present a high incidence of venous thromboembolism (VTE) with poor prognosis. It is crucial to identify and diagnose VTE early. The study aimed to identify potential protein biomarkers and mechanism of VTE in NSCLC patients via proteomics research.

Methods

Proteomic analysis of the human plasma was performed through data-independent acquisition mass spectrometry for 20 NSCLC patients with VTE, and 15 NSCLC patients without VTE. Significantly differentially expressed proteins were analyzed by multiple bioinformatics method for further biomarker analysis.

Results

A total of 280 differentially expressed proteins were identified in VTE and non-VTE patients, where 42 were upregulated and 238 were downregulated. These proteins were involved in acute-phase response, cytokine production, neutrophil migration and other biological processes related to VTE and inflammation. Five proteins including SAA1, S100A8, LBP, HP and LDHB had significant change between VTE and non-VTE patients, with the area under the curve (AUC) were 0.8067, 0.8308, 0.7767, 0.8021, 0.8533, respectively.

Conclusions

SAA1, S100A8, LBP, HP and LDHB may serve as potential plasma biomarkers for diagnosis VTE in NSCLC patients.

Properties of Plasma Clots in Adult Patients Following Fontan Procedure: Relation to Clot Permeability and Lysis Time-Multicenter Study

Objectives: thromboembolic complications are a major cause of morbidity and mortality following Fontan (FO) surgery. It is also well established that altered FO circulation results in systemic complications, including liver and endothelium damage. We sought to evaluate whether dysfunctions of these sources of hemostatic factors may result in changes of fibrin clot properties. Methods: a permeation coefficient (K_s) and clot lysis time (CLT) were assessed in 66 FO patients, aged 23.0 years [IQR 19.3–27.0], and 59 controls, aged 24.0 years [IQR 19.0–29.0]. K_s was determined using a pressure-driven system. CLT value was measured according to assay described by Pieters et al. Endothelium and liver-derived hemostatic factors along with liver function parameters were evaluated. The median time between FO operation and investigation was 20.5 years [IQR 16.3–22.0]. Results: FO patients had lower K_s (p = 0.005) and prolonged CLT (p < 0.001) compared to that of controls. K_s correlated with CLT (r = −0.28), FVIII (r = −0.30), FIX (r = −0.38), fibrinogen (r = −0.41), ALT (r = −0.25), AST (r = −0.26), GGTP (r = −0.27) and vWF antigen (r = −0.30), (all p < 0.05). CLT correlated with the time between FO operation and investigation (r = 0.29) and FIX (r = 0.25), (all p < 0.05). After adjustment for potential cofounders, TAFI antigen and GGTP were independent predictors of reduced K_s (OR 1.041 per 1% increase, 95% CI 1.009–1.081, p = 0.011 and OR 1.025 per 1 U/L increase, 95% CI 1.005–1.053, p = 0.033, respectively). Protein C and LDL cholesterol predicted prolonged CLT (OR 1.078 per 1% increase, 95% CI 1.027–1.153, p = 0.001 and OR 6.360 per 1 μmol/L increase, 95% CI 1.492–39.894, p = 0.011, respectively). Whereas elevated tPA was associated with lower risk of prolonged CLT (OR 0.550 per 1 ng/mL, 95% CI 0.314–0.854, p = 0.004). GGTP correlated positively with time between FO surgery and investigation (r = 0.25, p = 0.045) and patients with abnormal elevated GGTP activity (n = 28, 42.4%) had decreased K_s, compared to that of the others (5.9 × 10⁻⁹ cm² vs. 6.8 × 10⁻⁹ cm², p = 0.042). Conclusion: our study shows that cellular liver damage and endothelial injury were associated with prothrombotic clot phenotype reflected by K_s and CLT.

Fracture mechanics analysis of fibrin fibers using mesoscale and continuum level methods

Computational models for simulating and predicting fibrin fiber fracture are important tools for studying bulk mechanical properties and mechanobiological response of fibrin networks in physiological conditions. In this work, we employed a new strategy to model the mechanical response of a single fibrin fiber using a collection of bundled protofibrils and modeled the time-dependent properties using discrete particle simulations. Using a systematic characterization of the parameters, this model can be used to mimic the elastic behavior of fibrin fibers accurately and also to simulate fibrin fiber fracture. In addition, a continuum model was modified and used to obtain the individual fibrin fiber fracture toughness properties. Using this model and the experimentally available fibrin mechanical properties, we predicted the range of fracture toughness (1 to k P a m ) values of a typical fibrin fiber of diameter 100 nm and its critical flaw size to rupture (~4 nm), both of which are not currently available in the literature. The models can be collectively used as a foundation for simulating the mechanical behavior of fibrin clots. Moreover, the tunable discrete mesoscopic model that was employed can be extended to simulate and estimate the mechanical properties of other biological or synthetic fibers.

Right ventricular echocardiographic parameters associated with prothrombotic abnormalities in normotensive patients with acute pulmonary embolism

BACKGROUND

In acute pulmonary embolism (PE) right ventricular (RV) pressure overload negatively affects prognosis. Recently we have shown that RV dilatation is associated with a prothrombotic state in PE. We investigated which RV echocardiographic parameters best indicate prothrombotic alterations in acute PE.

METHODS

In 121 normotensive, noncancer PE patients, markers of RV dilatation and dysfunction were evaluated on admission using transthoracic echocardiography, along with prothrombotic state markers, i.e. increased endogenous thrombin generation (ETP), low fibrin clot permeability (K_s, a measure of clot density), and prolonged clot lysis time (CLT).

RESULTS

RV parasternal long axis (RVOT PLAX) >30 mm was associated with ETP (OR 3.86; 95% CI 1.55-9.62; p = 0.004) and CLT (OR 4.08; 95% CI 1.58-10.54; p = 0.004) in the top quartiles, but not with K_s. RV short parasternal axis (RVOT PSAX) >27 mm showed similar associations with higher ETP (OR 3.54; 95% CI 1.50-8.37; p = 0.004) and prolonged CLT (OR 2.78; 95% CI 1.17-6.62; p = 0.021). RV basal diameter >41 mm solely predicted prolonged CLT (OR 2.93; 95% CI 1.23-6.99; p = 0.016). The right atrium area, pulmonary trunk diameter, and tricuspid regurgitation maximum velocity were not related to prothrombotic markers, except for tricuspid annular plane systolic excursion weakly associated with ETP. Multivariable analysis showed that RVOT PSAX is independently associated with prolonged CLT (OR 1.16; 95% CI 1.04-1.30; p = 0.007), low K_s (OR 1.21; 95% CI 1.02-1.44; p = 0.029), and higher ETP (OR 1.14; 95% CI 1.03-1.26; p = 0.009).

CONCLUSIONS

Among RV echocardiographic parameters, the RVOT dilatation measured in PSAX best predicts prothrombotic alterations in PE patients.

Factor XIII and Fibrin Clot Properties in Acute Venous Thromboembolism

Coagulation factor XIII (FXIII) is converted by thrombin into its active form, FXIIIa, which crosslinks fibrin fibers, rendering clots more stable and resistant to degradation. FXIII affects fibrin clot structure and function leading to a more prothrombotic phenotype with denser networks, characterizing patients at risk of venous thromboembolism (VTE). Mechanisms regulating FXIII activation and its impact on fibrin structure in patients with acute VTE encompassing pulmonary embolism (PE) or deep vein thrombosis (DVT) are poorly elucidated. Reduced circulating FXIII levels in acute PE were reported over 20 years ago. Similar observations indicating decreased FXIII plasma activity and antigen levels have been made in acute PE and DVT with their subsequent increase after several weeks since the index event. Plasma fibrin clot proteome analysis confirms that clot-bound FXIII amounts associated with plasma FXIII activity are decreased in acute VTE. Reduced FXIII activity has been associated with impaired clot permeability and hypofibrinolysis in acute PE. The current review presents available studies on the role of FXIII in the modulation of fibrin clot properties during acute PE or DVT and following these events. Better understanding of FXIII’s involvement in the pathophysiology of acute VTE might help to improve current therapeutic strategies in patients with acute VTE.