Fibrin monomer antigen: a novel marker of mortality in acute myocardial infarction

Biomarkers of coagulation and fibrinolysis in acute myocardial infarction: a joint position paper of the Association for Acute CardioVascular Care and the European Society of Cardiology Working Group on Thrombosis

The formation of a thrombus in an epicardial artery may result in an acute myocardial infarction (AMI). Despite major advances in acute treatment using network approaches to allocate patients to timely reperfusion and optimal antithrombotic treatment, patients remain at high risk for thrombotic complications. Ongoing activation of the coagulation system as well as thrombin-mediated platelet activation may both play a crucial role in this context. Whether measurement of circulating biomarkers of coagulation and fibrinolysis could be useful for risk stratification in secondary prevention is currently not fully understood. In addition, measurement of such biomarkers could be helpful to identify thrombus formation as the leading mechanism for AMI. The introduction of biomarkers of myocardial injury such as high-sensitivity cardiac troponins made rule-out of AMI even more precise. However, elevated markers of myocardial injury cannot provide proof of a type 1 AMI, let alone thrombus formation. The combined measurement of markers of myocardial injury with biomarkers reflecting ongoing thrombus formation might be helpful for the fast and correct diagnosis of an atherothrombotic type 1 AMI. This position paper gives an overview of the current knowledge and possible role of biomarkers of coagulation and fibrinolysis for the diagnosis of AMI, risk stratification, and individualized treatment strategies in patients with AMI.

Fibrin monomers and association with significant hemorrhage or mortality in severely injured trauma patients

BACKGROUND

Post-traumatic hemorrhage is still the leading cause of potentially preventable death in patients with severe trauma. Traumatic-induced coagulopathy has been described as a risk factor for significant hemorrhage and mortality in this population. Fibrin monomers (FMs) are a direct marker of thrombin action, and thus reflect coagulation activation. This study sought to determine the association of FMs levels at admission with significant hemorrhage and 28-day mortality after a severe trauma.

METHODS

We conducted a retrospective, observational study including all severe trauma patients admitted in a level-1 trauma center between January 2012 and December 2017. Patients with severe traumatic brain injury or previous anticoagulant / antiaggregant therapies were excluded. FMs measurements and standard coagulation test were taken at admission. Significant hemorrhage was defined as a hemorrhage requiring the transfusion of ≥ 4 Red Blood Cells units during the first 6 h. Multivariable analysis was applied to identify predictors of significant hemorrhage and a simple logistic regression analysis was applied to identify an association between FMs and 28-day mortality.

RESULTS

Overall, 299 patients were included. A total of 47 (16%) experienced a significant hemorrhage. The ROC curve demonstrated that FMs had a poor accuracy to predict the occurrence of significant hemorrhage with an AUC of 0.65 (0.57-0.74). The best threshold at 92.45 µg/ml had excellent sensitivity (87%) and negative predictive value (95%), but was not independently associated with significant hemorrhage (OR = 1.5; 95%CI (0.5-4.2)). The 28-day mortality rate was 5%. In simple logistic regression analysis, FMs values ≥109.5 µg/ml were significantly associated with 28-day mortality (unadjusted OR = 13.2; 95%CI (1.7-102)).

CONCLUSIONS

FMs levels at admission are not associated with the occurrence of a significant hemorrhage in patients with severe trauma. However, the excellent sensitivity and NPV of FMs could help to identify patients with a low risk of severe bleeding during hospital care. In addition, FMs levels ≥109.5 µg/ml might be predictive of 28-day mortality.

Focal adhesion kinase and Src mediate microvascular hyperpermeability caused by fibrinogen- γC- terminal fragments

Objectives

We previously reported microvascular leakage resulting from fibrinogen-γ chain C-terminal products (γC) occurred via a RhoA-dependent mechanism. The objective of this study was to further elucidate the signaling mechanism by which γC induces endothelial hyperpermeability. Since it is known that γC binds and activates endothelial αvβ3, a transmembrane integrin receptor involved in intracellular signaling mediated by the tyrosine kinases FAK and Src, we hypothesized that γC alters endothelial barrier function by activating the FAK-Src pathway leading to junction dissociation and RhoA driven cytoskeletal stress-fiber formation.

Methods and results

Using intravital microscopy of rat mesenteric microvessels, we show increased extravasation of plasma protein (albumin) resulting from γC administration. In addition, capillary fluid filtration coefficient (K_fc) indicated γC-induced elevated lung vascular permeability. Furthermore, γC decreased transendothelial barrier resistance in a time-dependent and dose-related fashion in cultured rat lung microvascular endothelial cells (RLMVECs), accompanied by increased FAK/Src phosphorylation detection by western blot. Experiments with pharmacological inhibition or gene silencing of FAK showed significantly reduced γC-induced albumin and fluid leakage across microvessels, stress-fiber formation, VE-cadherin tyrosine phosphorylation, and improved γC-induced endothelial barrier dysfunction, indicating the involvement of FAK in γC mediated hyperpermeability. Comparable results were found when Src was targeted in a similar manner, however inhibition of FAK prevented Src activation, suggesting that FAK is upstream of Src in γC-mediated hyperpermeability. In addition, γC-induced cytoskeletal stress-fiber formation was attenuated during inhibition or silencing of these tyrosine kinases, concomitantly with RhoA inhibition.

Conclusion

The FAK-Src pathway contributes to γC-induced microvascular barrier dysfunction, junction protein phosphorylation and disorganization in a manner that involves RhoA and stress-fiber formation.

Fibrin(ogen) and its fragments in the pathophysiology and treatment of myocardial infarction

The occlusion of a coronary artery leads to ischemia of the myocardium, while permanent occlusion results in cell death and myocardial dysfunction. Early restoration of blood flow is the only means to reduce or prevent myocardial necrosis, but-paradoxically-reperfusion itself contributes to injury of the heart. In animal models, this phenomenon is well described, and there are many different unrelated approaches to reduce reperfusion injury. In humans, however, pharmacological interventions have so far failed to reduce myocardial reperfusion injury. We summarize the pathogenesis of reperfusion injury, detailing the role of fibrin(ogen) and its derivatives. Moreover, we introduce a new concept for fibrin derivatives as potential targets for reperfusion therapy.

Comparability of serum and plasma concentrations of haemostasis activation markers

Since serum and plasma D-dimer concentrations correlate very well, we evaluated the comparability of other haemostasis activation markers in plasma and serum. Prothrombin fragment F1+2, fibrin monomer and D-dimer concentrations were measured with commercially available immunoassays in serum and plasma. Serum to plasma ratios were evaluated to determine the direct (prothrombin fragment F1+2) and indirect (fibrin monomer, D-dimer) downstream influence of prothrombinase on the serum to plasma comparability. Prothrombin fragment F1+2 serum and plasma concentrations did not correlate (R2 = 0.09, ns), while an unexpected high degree of correlation was found for fibrin monomer (R2 = 0.66, p < 0.001), and, as expected, a very good correlation was found for D-dimer (R2 = 0.94, p < 0.001). Median serum to plasma ratios decreased from prothrombin fragment F1+2 (16.26) to fibrin monomer (2.24, p < 0.001) and D-dimer (1.00, p < 0.001), following a highly linear relationship (R2 = 0.93) Plasma and serum concentrations of the evaluated markers correlate the better the farther from prothrombinase activity the respective marker is generated. Serum is not suitable for prothrombin fragment F1+2 measurements, whereas fibrin monomer serum concentrations seem of value for research applications. With the used assay, serum seems an appropriate matrix for clinical D-dimer measurements. This would considerably simplify testing strategies. Validation in further clinical trials is needed.