Current and potentially novel antithrombotic treatment in acute ischemic stroke

Acute ischemic stroke (AIS) is the most common type of stroke and requires immediate reperfusion. Current acute reperfusion therapies comprise the administration of intravenous thrombolysis and/or endovascular thrombectomy. Although these acute reperfusion therapies are increasingly successful, optimized secondary antithrombotic treatment remains warranted, specifically to reduce the risk of major bleeding complications. In the development of AIS, coagulation and platelet activation play crucial roles by driving occlusive clot formation. Recent studies implicated that the intrinsic route of coagulation plays a more prominent role in this development, however, this is not fully understood yet. Next to the acute treatments, antithrombotic therapy, consisting of anticoagulants and/or antiplatelet therapy, is successfully used for primary and secondary prevention of AIS but at the cost of increased bleeding complications. Therefore, better understanding the interplay between the different pathways involved in the pathophysiology of AIS might provide new insights that could lead to novel treatment strategies. This narrative review focuses on the processes of platelet activation and coagulation in AIS, and the most common antithrombotic agents in primary and secondary prevention of AIS. Furthermore, we provide an overview of promising novel antithrombotic agents that could be used to improve in both acute treatment and stroke prevention.

The intrinsic coagulation pathway plays a dominant role in driving hypercoagulability in ANCA-associated vasculitis

ABSTRACT

The risk of a venous thrombotic event (VTE) is increased in patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV); however, a detailed understanding of the underlying mechanisms of hypercoagulability is limited. We assessed prospectively different coagulation parameters in 71 patients with active AAV at baseline and after 6 months of follow-up. D-dimers and fibrinogen were increased in most patients at presentation and remained elevated in half of the patients. Particularly, thrombin-antithrombin (T:AT) complex and activated coagulation factors in complex with their natural inhibitors of the intrinsic coagulation pathway (ie, activated FXII:C1 esterase inhibitor [FXIIa:C1Inh], FXIa:AT, and FXIa:alpha1-antitrypsin [FXIa:α1AT]) were profoundly elevated in patients at baseline. Thrombin formation was dominantly correlated with coagulation factors of the intrinsic pathway (ie, FXIIa:AT, FXIa:AT, FXIa:α1AT, and FXIa:C1Inh) compared to the extrinsic pathway (ie, FVIIa:AT). Hypercoagulability correlated with higher disease activity, ANCA levels, C-reactive protein, serum creatinine, and proteinuria. VTEs were observed in 5 out of 71 (7%) patients within 1 month (interquartile range, 1-5) after inclusion. Baseline T:AT levels were significantly higher in patients with VTE than in those without VTE (P = .044), but other clinical or laboratory markers were comparable between both groups. Hypercoagulability is dominantly characterized by activation of the intrinsic coagulation pathway and elevated D-dimers in active AAV. The driving factors of hypercoagulability are yet to be studied but are most likely related to an interplay of increased disease activity, vascular inflammation, and endothelial damage. Future targets for intervention could include inhibitors of the intrinsic coagulation pathway and compounds specifically reducing the hyperinflammatory state.

Platelet biology and function: plaque erosion vs. rupture

The leading cause of heart disease in developed countries is coronary atherosclerosis, which is not simply a result of ageing but a chronic inflammatory process that can lead to acute clinical events upon atherosclerotic plaque rupture or erosion and arterial thrombus formation. The composition and location of atherosclerotic plaques determine the phenotype of the lesion and whether it is more likely to rupture or to erode. Although plaque rupture and erosion both initiate platelet activation on the exposed vascular surface, the contribution of platelets to thrombus formation differs between the two phenotypes. In this review, plaque phenotype is discussed in relation to thrombus composition, and an overview of important mediators (haemodynamics, matrix components, and soluble factors) in plaque-induced platelet activation is given. As thrombus formation on disrupted plaques does not necessarily result in complete vessel occlusion, plaque healing can occur. Therefore, the latest findings on plaque healing and the potential role of platelets in this process are summarized. Finally, the clinical need for more effective antithrombotic agents is highlighted.

Higher levels of circulating desphospho-uncarboxylated matrix Gla protein over time are associated with worse survival: the prospective Maastricht Intensive Care COVID cohort

BACKGROUND

Extra-hepatic vitamin K-status, measured by dephosphorylated uncarboxylated matrix Gla protein (dp-ucMGP), maintains vascular health, with high levels reflecting poor vitamin K status. The occurrence of extra-hepatic vitamin K deficiency throughout the disease of COVID-19 and possible associations with pulmonary embolism (PE), and mortality in intensive care unit (ICU) patients has not been studied. The aim of this study was to investigated the association between dp-ucMGP, at endotracheal intubation (ETI) and both ICU and six months mortality. Furthermore, we studied the associations between serially measured dp-ucMGP and both PE and mortality.

METHODS

We included 112 ICU patients with confirmed COVID-19. Over the course of 4 weeks after ETI, dp-ucMGP was measured serially. All patients underwent computed tomography pulmonary angiography (CTPA) to rule out PE. Results were adjusted for patient characteristics, disease severity scores, inflammation, renal function, history of coumarin use, and coronary artery calcification (CAC) scores.

RESULTS

Per 100 pmol/L dp-ucMGP, at ETI, the odds ratio (OR) was 1.056 (95% CI: 0.977 to 1.141, p = 0.172) for ICU mortality and 1.059 (95% CI: 0.976 to 1.059, p = 0.170) for six months mortality. After adjustments for age, gender, and APACHE II score, the mean difference in plasma dp-ucMGP over time of ICU admission was 167 pmol/L (95% CI: 4 to 332, p = 0.047). After additional adjustments for c-reactive protein, creatinine, and history of coumarin use, the difference was 199 pmol/L (95% CI: 50 to 346, p = 0.010). After additional adjustment for CAC score the difference was 213 pmol/L (95% CI: 3 to 422, p = 0.051) higher in ICU non-survivors compared to the ICU survivors. The regression slope, indicating changes over time, did not differ. Moreover, dp-ucMGP was not associated with PE.

CONCLUSION

ICU mortality in COVID-19 patients was associated with higher dp-ucMGP levels over 4 weeks, independent of age, gender, and APACHE II score, and not explained by inflammation, renal function, history of coumarin use, and CAC score. No association with PE was observed. At ETI, higher levels of dp-ucMGP were associated with higher OR for both ICU and six month mortality in crude and adjusted modes, although not statistically significantly.

Biomarkers of sustained systemic inflammation and microvascular dysfunction associated with post-COVID-19 condition symptoms at 24 months after SARS-CoV-2-infection

Introduction

Comprehensive studies investigating sustained hypercoagulability, endothelial function, and/or inflammation in relation to post-COVID-19 (PCC) symptoms with a prolonged follow-up are currently lacking. Therefore, the aim of this single-centre cohort study was to investigate serum biomarkers of coagulation activation, microvascular dysfunction, and inflammation in relation to persisting symptoms two years after acute COVID-19.

Methods

Patients diagnosed with acute SARS-CoV-2 infection between February and June 2020 were recruited. Outcome measures included the CORona Follow-Up (CORFU) questionnaire, which is based on an internationally developed and partially validated basic questionnaire on persistent PCC symptoms. Additionally, plasma biomarkers reflecting coagulation activation, endothelial dysfunction and systemic inflammation were measured.

Results

167 individuals were approached of which 148 (89%) completed the CORFU questionnaire. At 24 months after acute infection, fatigue was the most prevalent PCC symptom (84.5%). Over 50% of the patients experienced symptoms related to breathing, cognition, sleep or mobility; 30.3% still experienced at least one severe or extreme (4 or 5 on a 5-point scale) PCC symptom. Multiple correlations were found between several PCC symptoms and markers of endothelial dysfunction (endothelin-1 and von Willebrand factor) and systemic inflammation (Interleukin-1 Receptor antagonist). No positive correlations were found between PCC symptoms and coagulation complexes.

Discussion

In conclusion, this study shows that at 24 months after acute COVID-19 infection patients experience a high prevalence of PCC symptoms which correlate with inflammatory cytokine IL-1Ra and markers of endothelial dysfunction, especially endothelin-1. Our data may provide a rationale for the selection of treatment strategies for further clinical studies.

Trial registration

This study was performed in collaboration with the CORona Follow-Up (CORFU) study (NCT05240742, https://clinicaltrials.gov/ct2/show/ NCT05240742).

Plasma protein signatures for high on-treatment platelet reactivity to aspirin and clopidogrel in peripheral artery disease

BACKGROUND

A significant proportion of patients with peripheral artery disease (PAD) displays a poor response to aspirin and/or the platelet P2Y12 receptor antagonist clopidogrel. This phenomenon is reflected by high on-treatment platelet reactivity (HTPR) in platelet function assays in vitro and is associated with an increased risk of adverse cardiovascular events.

OBJECTIVE

This study aimed to elucidate specific plasma protein signatures associated with HTPR to aspirin and clopidogrel in PAD patients.

METHODS AND RESULTS

Based on targeted plasma proteomics, 184 proteins from two cardiovascular Olink panels were measured in 105 PAD patients. VerifyNow ASPI- and P2Y12-test values were transformed to a continuous variable representing HTPR as a spectrum instead of cut-off level-defined HTPR. Using the Boruta random forest algorithm, the importance of 3 plasma proteins for HTPR in the aspirin, six in clopidogrel and 10 in the pooled group (clopidogrel or aspirin) was confirmed. Network analysis demonstrated clusters with CD84, SLAMF7, IL1RN and THBD for clopidogrel and with F2R, SELPLG, HAVCR1, THBD, PECAM1, TNFRSF10B, MERTK and ADM for the pooled group. F2R, TNFRSF10B and ADM were higher expressed in Fontaine III patients compared to Fontaine II, suggesting their relation with PAD severity.

CONCLUSIONS

A plasma protein signature, including eight targets involved in proatherogenic dysfunction of blood cell-vasculature interaction, coagulation and cell death, is associated with HTPR (aspirin and/or clopidogrel) in PAD. This may serve as important systems-based determinants of poor platelet responsiveness to aspirin and/or clopidogrel in PAD and other cardiovascular diseases and may contribute to identify novel treatment strategies.

Diabetes- versus smoking-related thrombo-inflammation in peripheral artery disease

Peripheral artery disease (PAD) is a major health problem with increased cardiovascular mortality, morbidity and disabling critical limb threatening ischemia (CLTI) and amputation. Diabetes mellitus (DM) and cigarette smoke are the main risk factors for the development of PAD. Although diabetes related PAD shows an accelerated course with worse outcome regarding complications, mortality and amputations compared with non-diabetic patients, current medical treatment does not make this distinction and includes standard antiplatelet and lipid lowering drugs for all patients with PAD. In this review we discuss the pathophysiologic mechanisms of PAD, with focus on differences in thrombo-inflammatory processes between diabetes-related and smoking-related PAD, and hypothesize on possible mechanisms for the progressive course of PAD in DM. Furthermore, we comment on current medical treatment and speculate on alternative medical drug options for patients with PAD and DM.

Tissue factor expression in monocyte subsets during human immunothrombosis, endotoxemia and sepsis

INTRODUCTION

Tissue factor expression on monocytes is implicated in the pathophysiology of sepsis-induced coagulopathy. How tissue factor is expressed by monocyte subsets (classical, intermediate and non-classical) is unknown.

METHODS

Monocytic tissue factor surface expression was investigated during three conditions. Primary human monocytes and microvascular endothelial cell co-cultures were used for in vitro studies. Volunteers received a bolus of lipopolysaccharide (2 ng/kg) to induce endotoxemia. Patients with sepsis, or controls with critical illness unrelated to sepsis, were recruited from four intensive care units.

RESULTS

Contact with endothelium and stimulation with lipopolysaccharide reduced the proportion of intermediate monocytes. Lipopolysaccharide increased tissue factor surface expression on classical and non-classical monocytes. Endotoxemia induced profound, transient monocytopenia, along with activation of coagulation pathways. In the remaining circulating monocytes, tissue factor was up-regulated in intermediate monocytes, though approximately 60 % of individuals (responders) up-regulated tissue factor across all monocyte subsets. In critically ill patients, tissue factor expression on intermediate and non-classical monocytes was significantly higher in patients with established sepsis than among non-septic patients. Upon recovery of sepsis, expression of tissue factor increased significantly in classical monocytes.

CONCLUSION

Tissue factor expression in monocyte subsets varies significantly during health, endotoxemia and sepsis.

Plasma Kallikrein as a Forgotten Clotting Factor

For decades, it was considered that plasma kallikrein's (PKa) sole function within the coagulation cascade is the activation of factor (F)XII. Until recently, the two key known activators of FIX within the coagulation cascade were activated FXI(a) and the tissue factor-FVII(a) complex. Simultaneously, and using independent experimental approaches, three groups identified a new branch of the coagulation cascade, whereby PKa can directly activate FIX. These key studies identified that (1) FIX or FIXa can bind with high affinity to either prekallikrein (PK) or PKa; (2) in human plasma, PKa can dose dependently trigger thrombin generation and clot formation independent of FXI; (3) in FXI knockout murine models treated with intrinsic pathway agonists, PKa activity results in increased formation of FIXa:AT complexes, indicating direct activation of FIX by PKa in vivo. These findings suggest that there is both a canonical (FXIa-dependent) and non-canonical (PKa-dependent) pathway of FIX activation. These three recent studies are described within this review, alongside historical data that hinted at the existence of this novel role of PKa as a coagulation clotting factor. The implications of direct PKa cleavage of FIX remain to be determined physiologically, pathophysiologically, and in the context of next-generation anticoagulants in development.

Predictive value for increased FXIa activity in acute venous thromboembolism

BACKGROUND

Venous thromboembolism (VTE) is associated with excessive coagulation activity, which in part can be attributed to activation of the contact system. However, the knowledge regarding the impact of contact activation in acute VTE is limited.

OBJECTIVE

To unravel the involvement of contact activation in acute VTE.

METHODS

Contact activation was investigated in acute VTE patients (n=321) and population controls without history of VTE (n=300). For comparison, FXI(a) levels, activity and plasma kallikrein (PKa) activity were determined in plasma samples with an aPTT- or thrombin generation-based assay (FXI:c and CAT:FXIa, respectively) and with enzyme-linked immunosorbent assay (ELISA) for enzyme-inhibitor complexes (FXIa:alpha-1-antitrypsin(a1AT), FXIa:antithrombin(AT), FXIa:C1-inhibitor(C1-inh), PKa:C1-inh).

RESULTS

In VTE patients, higher FXI:c levels (124±37% vs. 114±28%), but lower CAT:FXIa levels were apparent. This was accompanied by increased FXIa:a1AT, FXIa:AT and PKa:C1-inh levels in patients compared with controls (312pM[238-424] vs. 203pM[144-288]; 29pM[23-38] vs. 23pM[20-30]; 1.9nM[1.2-4.7] vs 1.4nM[0.7-3.5], respectively), whereas FXIa:C1-Inh levels did not differ. Logistic regression models showed good discriminatory value for FXI:c and FXIa:a1AT (AUC=0.64[0.6/0.69] and AUC=0.73[0.69/0.77], respectively). After 2-year follow-up, 81 recurrent VTE events or deaths occurred in the patient cohort, for which the baseline levels of FXIa:a1AT and FXIa:C1-Inh had a significant prognostic value (HR per SD[95%CI] 1.26[1.10-1.45], p=0.0012 and 1.19[1.05-1.36], p=0.0082, respectively).

CONCLUSIONS

Our study revealed elevated FXI(a) levels and activity in acute VTE which was also associated with recurrent VTE suggesting an important risk contribution of FXI activation to VTE. The evidence provided by this study supports the utility of FXI(a) inhibition in the setting of acute VTE.

Blood coagulation and beyond: Position paper from the Fourth Maastricht Consensus Conference on Thrombosis

The 4th Maastricht Consensus Conference on Thrombosis (MCCT), included the following themes: Theme 1: The "coagulome" as a critical driver of cardiovascular disease Blood coagulation proteins also play divergent roles in biology and pathophysiology, related to specific organs, including brain, heart, bone marrow and kidney. Four investigators shared their views on these organ-specific topics. Theme 2: Novel mechanisms of thrombosis Mechanisms linking factor XII to fibrin, including their structural and physical properties, contribute to thrombosis, which is also affected by variation in microbiome status. Virus infections associated-coagulopathies perturb the hemostatic balance resulting in thrombosis and/or bleeding. Theme 3: How to limit bleeding risks: insights from translational studies This theme included state of the art methodology for exploring the contribution of genetic determinants of a bleeding diathesis; determination of polymorphisms in genes that control the rate of metabolism by the liver of P2Y12 inhibitors, to improve safety of antithrombotic therapy. Novel reversal agents for direct oral anticoagulants are discussed. Theme 4: Hemostasis in extracorporeal systems: how to utilize ex vivo models? Perfusion flow chamber and nanotechnology developments are developed for studying bleeding and thrombosis tendencies. Vascularised organoids are utilized for disease modeling and drug development studies. Strategies for tackling extracorporeal membrane oxygenation (ECMO) associated coagulopathy are discussed. Theme 5: Clinical dilemmas in thrombosis and antithrombotic management Plenary presentations addressed controversial areas, ie thrombophilia testing, thrombosis risk assessment in hemophilia, novel antiplatelet strategies and clinically tested factor XI(a) inhibitors,both possibly with reduced bleeding risk. Finally, Covid-19 associated coagulopathy is revisited.

Clinical utility of the 4S-AF scheme in predicting progression of atrial fibrillation: data from the RACE V study

AIMS

The recent 4S-AF (scheme proposed by the 2020 ESC AF guidelines to address stroke risk, symptom severity, severity of AF burden and substrate of AF to provide a structured phenotyping of AF patients in clinical practice to guide therapy and assess prognosis) scheme has been proposed as a structured scheme to characterize patients with atrial fibrillation (AF). We aimed to assess whether the 4S-AF scheme predicts AF progression in patients with self-terminating AF.

METHODS AND RESULTS

We analysed 341 patients with self-terminating AF included in the well-phenotyped Reappraisal of Atrial Fibrillation: Interaction between HyperCoagulability, Electrical remodelling, and Vascular Destabilization in the Progression of AF (RACE V) study. Patients had continuous monitoring with implantable loop recorders or pacemakers. AF progression was defined as progression to persistent or permanent AF or progression of self-terminating AF with >3% burden increase. Progression of AF was observed in 42 patients (12.3%, 5.9% per year). Patients were given a score based on the components of the 4S-AF scheme. Mean age was 65 [interquartile range (IQR) 58-71] years, 149 (44%) were women, 103 (49%) had heart failure, 276 (81%) had hypertension, and 38 (11%) had coronary artery disease. Median CHA2DS2-VASc (the CHA2DS2-VASc score assesses thromboembolic risk. C, congestive heart failure/left ventricular dysfunction; H, hypertension; A2, age ≥ 75 years; D, diabetes mellitus; S2, stroke/transient ischaemic attack/systemic embolism; V, vascular disease; A, age 65-74 years; Sc, sex category (female sex)) score was 2 (IQR 2-3), and median follow-up was 2.1 (1.5-2.6) years. The average score of the 4S-AF scheme was 4.6 ± 1.4. The score points from the 4S-AF scheme did not predict the risk of AF progression [odds ratio (OR) 1.1 95% CI 0.88-1.41, C-statistic 0.53]. However, excluding the symptoms domain, resulting in the 3S-AF (4S-AF scheme without the domain symptom severity, only including stroke risk, severity of AF burden and substrate of AF) scheme, predicted the risk of progression (OR 1.59 95% CI 1.15-2.27, C-statistic 0.62) even after adjusting for sex and age.

CONCLUSIONS

In self-terminating AF patients, the 4S-AF scheme does not predict AF progression. The 3S-AF scheme, excluding the symptom domain, may be a more appropriate score to predict AF progression.

TRIAL REGISTRATION NUMBERS

Clinicaltrials.gov NCT02726698 for RACE V.

Translational insights into mechanisms underlying residual venous obstruction and the role of factor XI, P-selectin and GPVI in recurrent venous thromboembolism

BACKGROUND

Residual venous obstruction (RVO) after deep vein thrombosis (DVT) is considered a risk factor of recurrent venous thromboembolism (VTE), arterial events and post-thrombotic syndrome (PTS). We hypothesized thrombo-inflammatory markers might be associated with RVO and clinical outcomes.

MATERIALS AND METHODS

In a DVT cohort with routine RVO-assessment and 5-year follow-up, patients were invited for blood withdrawal after stopping anticoagulants. Thrombin generation potential, coagulation enzyme:inhibitor complexes, soluble platelet markers and clinical markers were measured in platelet-poor plasma. Associations were represented as odds ratio (OR) or hazard ratio (HR) per standard deviation.

RESULTS

Patients with RVO (102/306, 33 %) had higher rates of PTS (24 vs. 12 %, p = 0.008), but similar rates of recurrence (16 vs. 15 %, p = 0.91) and arterial events (7 vs. 4 %, p = 0.26). RVO was associated with thrombin peak height (OR 1.40 [1.04-1.88]), endogenous thrombin potential (ETP, OR 1.35 [1.02-1.79]), and CRP (OR 1.74 [1.10-2.75]). Recurrent VTE was associated with ETP (HR 1.36 [1.03-1.81]), FXIa:C₁-inhibitor (HR 1.34 [1.04-1.72]), thrombin:antithrombin (HR 1.36 [1.16-1.59]), soluble P-selectin (HR 2.30 [1.69-3.11]), soluble glycoprotein VI (sGPVI, HR 1.30 [1.01-1.69]), D-dimer (HR 1.56 [1.31-1.86]), and factor VIII (HR 1.44 [1.15-1.82]). Arterial events were associated with sGPVI (HR 1.80 [1.25-2.59]). PTS was not associated with any marker.

CONCLUSIONS

Our findings indicate RVO was associated with thrombo-inflammation, but this did not predict clinical outcomes in this setting. Importantly, we found recurrent VTE was associated with ongoing coagulation and platelet activation in patients well beyond the acute phase of DVT. Furthermore, sGPVI indicated an increased risk of arterial events, highlighting the role of platelets in arterial thrombosis following DVT.

Thrombin formation via the intrinsic coagulation pathway and von Willebrand factor reflect disease severity in COVID-19

Not available.

Integrating Mechanisms in Thrombotic Peripheral Arterial Disease

Peripheral arterial disease (PAD), a manifestation of systemic atherosclerosis, is underdiagnosed in the general population. Despite the extensive research performed to unravel its pathophysiology, inadequate knowledge exists, thus preventing the development of new treatments. This review aims to highlight the essential elements of atherosclerosis contributing to the pathophysiology of PAD. Furthermore, emphasis will be placed on the role of thrombo-inflammation, with particular focus on platelet and coagulation activation as well as cell-cell interactions. Additional insight will be then discussed to reveal the contribution of hypercoagulability to the development of vascular diseases such as PAD. Lastly, the current antithrombotic treatments will be discussed, and light will be shed on promising new targets aiming to aid the development of new treatments.

Dual pathway inhibition as compared to acetylsalicylic acid monotherapy in relation to endothelial function in peripheral artery disease, a phase IV clinical trial

Objective

Dual pathway inhibition (DPI) by combining acetylsalicylic acid (ASA) with low-dose rivaroxaban has been shown to reduce cardiovascular events in patients with peripheral arterial disease (PAD) when compared to ASA monotherapy. A potential explanation is that inhibition of factor Xa improves endothelial function through crosstalk between coagulation and inflammatory pathways, subsequently attenuating the occurrence of cardiovascular events. We hypothesize that the addition of rivaroxaban to ASA in PAD patients leads to improved endothelial function.

Design

An investigator-initiated, multicentre trial investigating the effect of DPI on endothelial function.

Methods

Patients, diagnosed with PAD, were enrolled in two cohorts: cohort A (Rutherford I-III) and cohort B (Rutherford IV-VI). Participants received ASA monotherapy for a 4-weeks run-in period, followed by 12 weeks of DPI. Macro- and microvascular endothelial dysfunction were studied by measuring carotid artery reactivity upon sympathetic stimulus and by measuring plasma endothelin-1 concentrations, respectively. All measurements were performed during the use of ASA (baseline) and after 12 weeks of DPI.

Results

159 PAD patients (111 cohort A, 48 cohort B) were enrolled. Twenty patients discontinued study drugs early. Carotid artery constriction upon sympathetic stimulation at baseline (ASA) and after 12 weeks of DPI was similar in the total group, 22.0 vs. 22.7% (p = 1.000), and in the subgroups (Cohort A 22.6 vs. 23.7%, p = 1.000; cohort B 20.5 vs. 20.5%, p = 1.000), respectively. The mean concentration of plasma endothelin-1 at baseline and after 12 weeks of DPI did not differ, 1.70 ± 0.5 vs. 1.66 ± 0.64 pmol/L (p = 0.440) in the total group, 1.69 ± 0.59 vs. 1.62 ± 0.55 pmol/L in cohort A (p = 0.202), and 1.73 ± 0.53 vs. 1.77 ± 0.82 pmol/L in cohort B (p = 0.682), respectively.

Conclusion

Macro- and microvascular endothelial dysfunction, as reflected by carotid artery reactivity and plasma endothelin-1 concentrations, are not influenced in PAD patients by addition of low-dose rivaroxaban to ASA monotherapy for 12 weeks.

Trial registration

https://clinicaltrials.gov/ct2/show/NCT04218656.

Serial thrombin generation and exploration of alternative anticoagulants in critically ill COVID-19 patients: Observations from Maastricht Intensive Care COVID Cohort

Background

COVID-19 associated coagulopathy (CAC) is associated with an increase in thromboembolic events. Current guidelines recommend prophylactic heparins in the management of CAC. However, the efficacy of this strategy in the intensive care population remains uncertain.

Objective

We aimed to measure thrombin generation (TG) to assess CAC in intensive care unit (ICU) patients receiving thromboprophylaxis with low molecular weight heparin (LMWH) or unfractionated heparin (UFH). In addition, we performed statistical modeling to link TG parameters to patient characteristics and clinical parameters. Lastly, we studied the potency of different anticoagulants as an alternative to LMWH treatment in ex vivo COVID-19 plasma.

Patients/Methods

We included 33 patients with confirmed COVID-19 admitted at the ICU. TG was measured at least twice over the course of 6 weeks after admission. Thrombin generation parameters peak height and endogenous thrombin potential (ETP) were compared to healthy controls. Results were subsequently correlated with a patient characteristics and laboratory measurements. In vitro spiking in TG with rivaroxaban, dabigatran, argatroban and orgaran was performed and compared to LMWH.

Results

Anti-Xa levels of all patients remained within the therapeutic range throughout follow-up. At baseline, the mean (SE) endogenous thrombin potential (ETP) was 1,727 (170) nM min and 1,620 (460) nM min for ellagic acid (EA) and tissue factor (TF), respectively. In line with this we found a mean (SE) peak height of 353 (45) nM and 264 (96) nM for EA and TF. Although fluctuating across the weeks of follow-up, TG parameters remained elevated despite thromboprophylaxis. In vitro comparison of LMWHs and direct thrombin inhibitors (e.g., agratroban, dabigatran) revealed a higher efficacy in reducing coagulation potential for direct thrombin inhibition in both ellagic acid (EA) and tissue factor (TF) triggered TG.

Conclusion

In a sub-group of mechanically ventilated, critically ill COVID-19 patients, despite apparent adequate anti-coagulation doses evaluated by anti-Xa levels, thrombin generation potential remained high during ICU admission independent of age, sex, body mass index, APACHE II score, cardiovascular disease, and smoking status. These observations could, only partially, be explained by (anti)coagulation and thrombosis, inflammation, and multi-organ failure. Our in vitro data suggested that direct thrombin inhibition compared with LMWH might offer an alternate, more effective anticoagulant strategy in COVID-19.

Lower levels of vWF are associated with lower risk of cardiovascular disease

Objective

The current study was undertaken to prospectively explore whether having low levels of von Willebrand factor (vWF) antigen and vWF activity reduce the risk for cardiovascular disease and death.

Methods

VWF antigen and vWF activity were measured by enzyme-linked immunosorbent assay and an immunological-based assay, respectively, in a subsample of 4857 individuals aged between 35 and 74 years old, enrolled between April 2007 and October 2008 in the population-based Gutenberg Health Study. VWF antigen and activity below the 20th percentile was set as a measure of "low vWF." Adjusted robust Poisson regression models were used to analyze the relation between low vWF and the incidence of cardiovascular disease (CVD). Consequent adjusted cox regression models as well as cumulative incidence plots were calculated to explore the relation between all-cause and cardiovascular mortality and low vWF.

Results

VWF activity levels <20th percentile (i.e., <76.2%) were associated with a decreased relative risk for CVD (RR: 0.59, 95% CI: 0.37-0.95), despite adjusting for age and sex. After adjusting for levels of F-VIII, the association persisted (RR: 0.60, 95% CI: 0.36-0.99). The cumulative incidence plots demonstrated that vWF antigen <20th percentile significantly correlated with decreased cardiovascular mortality. VWF antigen<20th percentile (i.e., <83%) was significantly associated with lower risk of all-cause mortality, despite adjusting for clinical factors (RR: 61, 95% CI: 0.41-0.91).

Conclusion

The study demonstrated that having low vWF activity levels were associated with a lower risk for CVD. Additionally, it revealed a decreased risk of cardiovascular and all-cause mortality in individuals with low levels of vWF antigen, shining new light on vWF as a potential target for novel therapies.

Relationships between coagulation factors and thrombin generation in a general population with arterial and venous disease background

Background

The current study aims to identify the relationships between coagulation factors and plasma thrombin generation in a large population-based study by comparing individuals with a history of arterial or venous thrombosis to cardiovascular healthy individuals.

Methods

This study comprised 502 individuals with a history of arterial disease, 195 with history of venous thrombosis and 1402 cardiovascular healthy individuals (reference group) from the population-based Gutenberg Health Study (GHS). Calibrated Automated Thrombography was assessed and coagulation factors were measured by means of BCS XP Systems. To assess the biochemical determinants of TG variables, a multiple linear regression analysis, adjusted for age, sex and antithrombotic therapy, was conducted.

Results

The lag time, the time to form the first thrombin, was mainly positively associated with the natural coagulant and anti-coagulant factors in the reference group, i.e. higher factors result in a longer lag time. The same determinants were negative for individuals with a history of arterial or venous thrombosis, with a 10 times higher effect size. Endogenous thrombin potential, or area under the curve, was predominantly positively determined by factor II, VIII, X and IX in all groups. However, the effect sizes of the reported associations were 4 times higher for the arterial and venous disease groups in comparison to the reference group.

Conclusion

This large-scale analysis demonstrated a stronger effect of the coagulant and natural anti-coagulant factors on the thrombin potential in individuals with a history of arterial or venous thrombosis as compared to healthy individuals, which implicates sustained alterations in the plasma coagulome in subjects with a history of thrombotic vascular disease, despite intake of antithrombotic therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12959-022-00392-0.

Atrial fibrillation and age synergistically increase clotting potential and promote atrial structural remodeling in goats

Funding Acknowledgements

Type of funding sources: Other. Main funding source(s): Netherlands Heart Foundation, European Union

Background

Age is a risk factor for atrial fibrillation (AF) as well as for stroke in patients with AF. However, the effect of ageing on AF mechanisms and on coagulation activity is not well understood.

Purpose

To evaluate the effect of age and AF on coagulation activity, AF characteristics, and atrial structural remodeling.

Methods

Four groups of female goats were investigated: Young sham (Y-Sh: sinus rhythm, &lt;3 years old, n=9), Young AF (Y-AF: 4 weeks of AF, &lt;3 years old, n=7), Old sham (O-Sh: sinus rhythm, &gt;8 years old, n=6), and Old AF (O-AF, 4 weeks of AF, &gt;8 years old, n=8). Groups were matched for body weight. AF was maintained using implantable pacemakers in both AF groups. Clotting potential, expressed as the ability of activated plasma to generate thrombin, was measured using tissue factor-induced thrombin generation assays at baseline and 4 weeks (final). A terminal experiment was performed with atrial contact mapping to study electrophysiological AF properties and to collect atrial tissue for histological analysis.

Results

Thrombin generation analysis showed that 4 weeks of AF induced a significant increase in clotting potential in old, but not in young goats. AF complexity and hemodynamics were not affected by age alone. AF, however, significantly increased the right atrial pressure in old (O-Sh: 6.4±1.9 vs. O-AF: 11.4±3.1 mmHg, p=0.02), but not in young goats. AF induced atrial myocyte hypertrophy and left atrial epicardial endomysial fibrosis in old goats, while this was not the case in young goats.

Conclusion

Four weeks of AF and advanced age synergistically enhanced coagulation potential and promoted atrial structural remodeling in goats. Complexity of atrial conduction was affected by AF, but not by age.

Thrombin in complex with dabigatran can still interact with PAR-1 via exosite-I and instigate loss of vascular integrity

BACKGROUND

Atrial fibrillation (AF) can lead to the loss of microvascular integrity thereby enhancing AF progression. Mechanistically, the pro-coagulant state that drives the risk of stroke in patients with AF may also play a causal role in microvascular loss. Direct oral anticoagulants (DOACs), the preferred anticoagulants for AF, can target factors upstream (factor Xa [FXa]) or downstream (thrombin) in the coagulation cascade and mediate differential vascular effects through interaction with protease-activated receptors (PARs).

OBJECTIVE

To investigate the potential effect of different DOACs on vascular integrity.

METHODS

To model the impact of DOACs on vascular integrity, we utilized platelet-free plasma in thrombin generation assays and endothelial barrier assays under identical experimental conditions. These multifactorial systems provide all coagulation factors and their respective natural inhibitors in physiological ratios in combination with the pro-coagulant endothelial surface on which coagulation is initiated. Furthermore, the system provides pro- and anti-barrier factors and monitoring both assays simultaneously permits coupling of thrombin kinetics to endothelial barrier dynamics.

RESULTS

We provide evidence that the anti-FXa DOAC rivaroxaban and the anti-thrombin DOAC dabigatran are efficient in blocking their target proteases. However, while rivaroxaban could preserve endothelial barrier function, dabigatran failed to protect endothelial integrity over time, which could be prevented in the presence of a custom-made peptide that blocks thrombin's exosite-I.

CONCLUSIONS

Proteolytically inactive thrombin in complex with dabigatran evokes loss of barrier function that can be prevented by a protease-activated receptor-1 mimicking peptide blocking thrombin's exosite-I.

Sustained inflammation, coagulation activation and elevated endothelin-1 levels without macrovascular dysfunction at 3 months after COVID-19

INTRODUCTION

Endothelial damage and thrombosis caused by COVID-19 may imperil cardiovascular health. More than a year since the WHO declared COVID-19 pandemic, information on its effects beyond the acute phase is lacking. We investigate endothelial dysfunction, coagulation and inflammation, 3 months post-COVID-19.

MATERIALS AND METHODS

A cohort study was conducted including 203 patients with prior COVID-19. Macrovascular dysfunction was assessed by measuring the carotid artery diameter in response to hand immersion in ice-water. A historic cohort of 312 subjects served as controls. Propensity score matching corrected for baseline differences. Plasma concentrations of endothelin-1 were measured in patients post-COVID-19, during the acute phase, and in matched controls. Coagulation enzyme:inhibitor complexes and inflammatory cytokines were studied.

RESULTS AND CONCLUSIONS

The prevalence of macrovascular dysfunction did not differ between the COVID-19 (18.6%) and the historic cohort (22.5%, RD -4%, 95%CI: -15-7, p = 0.49). Endothelin-1 levels were significantly higher in acute COVID-19 (1.67 ± 0.64 pg/mL) as compared to controls (1.24 ± 0.37, p < 0.001), and further elevated 3 months post-COVID-19 (2.74 ± 1.81, p < 0.001). Thrombin:antithrombin(AT) was high in 48.3%. Markers of contact activation were increased in 16-30%. FVIIa:AT (35%) and Von Willebrand Factor:antigen (80.8%) were elevated. Inflammatory cytokine levels were high in a majority: interleukin(IL)-18 (73.9%), IL-6 (47.7%), and IL-1ra (48.9%). At 3 months after acute COVID-19 there was no indication of macrovascular dysfunction; there was evidence, however, of sustained endothelial cell involvement, coagulation activity and inflammation. Our data highlight the importance of further studies on SARS-CoV-2 related vascular inflammation and thrombosis, as well as longer follow-up in recovered patients.

Thrombin generation by calibrated automated thrombography in goat plasma: Optimization of an assay

The goat model of atrial fibrillation (AF) allows investigation of the effect of AF on coagulation. However, assays for goat plasma are not available from commercial sources. Calibrated automated thrombography (CAT) provides a global view of the coagulation profile by assessing in vitro thrombin generation (TG). We describe the customization of the CAT assay in goat platelet-poor plasma (PPP) and in factor Xa (FXa)-inhibitor-anticoagulated PPP. TG was initiated in the presence of phospholipids and either (a) PPP reagent, reagent low, or reagent high; (b) goat brain protein extraction (GBP); or (c) Russell's viper venom-factor X activator (RVV-X). Contact activation was assessed by adding corn trypsin inhibitor. Different concentrations of prothrombin complex concentrate (PCC) were used to determine the sensitivity of both the GBP and RVV-X method. To obtain FXa-inhibitor anticoagulated plasma, rivaroxaban was added to plasma. TG settings with human reagents were not suitable for goat plasma. TG triggered with GBP increased peak height and ETP values. Similarly, the RVV-X method produced comparable TG curves and was more sensitive to PCC titration. Finally, both methods were able to detect the decrease in clotting potential induced by FXa inhibition. This is the first study that reports the customization of the CAT assay for goats. The GBP and RVV-X methods were comparable in triggering TG in goat plasma. The RVV-X method seemed to better discriminate changes in TG curves due to increases in clotting potential as well as to FXa inhibition by rivaroxaban in goat plasma.

ChAdOx1 vaccination, blood coagulation, and inflammation: No effect on coagulation but increased interleukin-6

BACKGROUND

Vaccination is the leading approach in combatting the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. ChAdOx1 nCoV-19 vaccination (ChAdOx1) has been linked to a higher frequency of rare thrombosis and thromboembolism. This study aimed to explore markers related to the blood coagulation system activation and inflammation, before and after ChAdOx1 vaccination.

PATIENTS AND METHODS

An observational cohort study including 40 health care workers. Whole blood samples were collected before, and either 1 or 2 days after vaccination. Activated coagulation factors in complex with their natural inhibitors were determined by custom ELISAs, including thrombin:antithrombin (T:AT), kallikrein:C1-esterase-inhibitor (PKa:C1Inh), factor(F)IXa:AT, FXa:AT, FXIaAT, FXIa:alpha-1-antitrypsin (α1AT), FXIa:C1inh, and FVIIa:AT. Plasma concentrations of interleukin (IL)-6 and IL-18 were quantified via ELISA. Analyses were performed using Wilcoxon signed-rank test.

RESULTS

Levels of FVIIa:AT decreased with a median (IQR) of 707 (549-1028) pg/ml versus 598 (471-996) pg/ml, p = 0.01; and levels of IL-6 increased, 4.0 (1.9-6.8) pg/ml versus 6.9 (3.6-12.2) pg/ml, p = 0.02, after vaccination. No changes were observed in T:AT, PKa:C1Inh, FIXa:AT, FXa:AT, FXIaAT, FXIa:α1AT, FXIa:C1inh, and IL-18.

CONCLUSION

ChAdOx1 leads to an inflammatory response with increased levels of IL-6. We did not observe activation of the blood coagulation system 1-2 days following vaccination.

Coagulation Factor Xa Induces Proinflammatory Responses in Cardiac Fibroblasts via Activation of Protease-Activated Receptor-1

Coagulation factor (F) Xa induces proinflammatory responses through activation of protease-activated receptors (PARs). However, the effect of FXa on cardiac fibroblasts (CFs) and the contribution of PARs in FXa-induced cellular signalling in CF has not been fully characterised. To answer these questions, human and rat CFs were incubated with FXa (or TRAP-14, PAR-1 agonist). Gene expression of pro-fibrotic and proinflammatory markers was determined by qRT-PCR after 4 and 24 h. Gene silencing of F2R (PAR-1) and F2RL1 (PAR-2) was achieved using siRNA. MCP-1 protein levels were measured by ELISA of FXa-conditioned media at 24 h. Cell proliferation was assessed after 24 h of incubation with FXa ± SCH79797 (PAR-1 antagonist). In rat CFs, FXa induced upregulation of Ccl2 (MCP-1; >30-fold at 4 h in atrial and ventricular CF) and Il6 (IL-6; ±7-fold at 4 h in ventricular CF). Increased MCP-1 protein levels were detected in FXa-conditioned media at 24 h. In human CF, FXa upregulated the gene expression of CCL2 (>3-fold) and IL6 (>4-fold) at 4 h. Silencing of F2R (PAR-1 gene), but not F2RL1 (PAR-2 gene), downregulated this effect. Selective activation of PAR-1 by TRAP-14 increased CCL2 and IL6 gene expression; this was prevented by F2R (PAR-1 gene) knockdown. Moreover, SCH79797 decreased FXa-induced proliferation after 24 h. In conclusion, our study shows that FXa induces overexpression of proinflammatory genes in human CFs via PAR-1, which was found to be the most abundant PARs isoform in this cell type.

Sustained endothelial, coagulation and inflammatory cytokine activation without macrovascular dysfunction at 3 months after COVID-19: a reflection on SARS-CoV-2 induced thrombo-inflammation

Background

Endothelial damage caused by COVID-19 may imperil the cardiovascular health of millions. More than a year since WHO declared the COVID-19 pandemic, information on the lasting effects of this infection on the cardiovascular system beyond the acute phase is still lacking.

Purpose

To study macrovascular endothelial dysfunction and activation, coagulation and inflammation, 3 months after resolution of acute COVID-19 symptoms.

Methods

A cross-sectional observational cohort study was conducted including 203 patients with PCR confirmed COVID-19 disease, 6–20 weeks after acute COVID-19. The primary endpoint was macrovascular endothelial function, assessed by the carotid artery reactivity (CAR) test. The CAR measures the carotid artery diameter in response to hand in ice-water immersion. A historic cohort of 313 subjects served as controls. Propensity score matching was used to correct for baseline differences. Plasma endothelin-1 (ET-1), interleukin (IL)-1ra, IL-6, IL-18 were measured by ELISA. ET-1 levels were also measured in a partially overlapping COVID-19 cohort of which plasma samples were available during the acute phase. Coagulation enzyme:inhibitor complexes for thrombin:antithrombin (TAT), factor (F) IXa:AT, FVIIa:AT, FXIa:AT, FXIa:alpha 1 antitrypsin (a1AT), FXIa:C1 esterase inhibitor (C1inh), kallikrein(PKa):C1inh and von Willebrand Factor:antigen (vWF:Ag), were assessed by in house developed ELISA.

Results

After propensity score matching, the prevalence of macrovascular dysfunction did not differ between the COVID-19 (22.5%) versus the historical control cohort (18.6%, RD −3.92%, 95%-CI −15 to 7.19, p=0.49). Plasma concentrations of markers for endothelial activation were elevated (>1 SD above normal); ET-1 (64.9%), and vWF:Ag (80.8%). In controls, ET-1 levels were significantly lower as compared to COVID-19 patients during the acute phase and after 3 months. ET-1 levels were significantly higher 3 months after COVID-19 as compared to the acute phase. Cytokines were high in a majority of patients: IL-18 (73.9%), IL-6 (51.2%), and IL-1ra (48.9%). TAT and FIXa:AT, reflecting a prothrombotic state, were high in 48.3% and 29.6% of the patients, respectively. FVIIa:AT, as marker of the extrinsic pathway, was elevated (35%). Markers of contact activation were also increased: PKa:C1inh (16.3%), FXIa:AT (16.3%), FXIa:a1AT (20.7%), and FXIa:C1inh (17.7%) (picture 1).

Conclusions

At 3 months after acute COVID-19 there was no indication of macrovascular dysfunction as compared to matched historic controls; there was evidence, however, of sustained thrombo-inflammation, indicated by high circulating concentrations of ET-1, vWF:Ag, proinflammatory cytokines, and markers of coagulation (picture 2). Elevated IL-18 levels could potentially induce arterial inflammation and subsequent atherogenesis. Our data highlight the importance of further studies on SARS-CoV-2 related thrombo-inflammation, as well as longer follow-ups in recovered patients.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): This study was supported by a grant from The Netherlands Organisation for Health Research and Development (ZonMw).

Calibrated automated thrombogram II: removing barriers for thrombin generation measurements

BACKGROUND

Thrombin generation (TG) assessed by Calibrated Automated Thrombogram (CAT-I) reflects the overall capacity of plasma to generate thrombin, thus evaluating the balance between the anti- and procoagulant processes. However, with this method the calibrator curve is usually not measured until completion which has a severe impact on the calculation of the TG parameters, especially under conditions where almost all substrate is consumed. In addition, direct thrombin inhibitor (DTI) cannot be present in the calibration sample due to inhibition of the calibrator. We have developed a modified TG assay (CAT-II) and performed head-to-head comparison with the CAT-I method using the same fluorometer. Furthermore, we have compared our CAT-II method to a new automated TG instrument (ST®-Genesia) using the same calibration method.

METHODS

TG was assessed with CAT-I and CAT-II using the same fulorometer and with ST®-Genesia in control plasma and plasma containing different anticoagulants (dabigatran, rivaroxaban, apixaban) and plasmas to which common interfering substances, bilirubin, hemoglobin and lipids were added. In CAT-I, calibration was against the same plasma containing calibrator in the presence of fluorogenic substrate (Z-GGR-AMC). In contrast, CAT-II method and ST®-Genesia used a standard concentration of thrombin in buffer and 7-amino-4-methylcoumarin (AMC) in a separate plasma sample for calibration.

RESULTS

TG obtained from CAT-I using anticoagulant-free plasmas was lower compared with TG from CAT-II but both methods demonstrated an intra-assay variation less than 5% on all measured parameters. When comparing the two different calibration methods in the presence of different anticoagulants, a high correlation was seen in the presence of rivaroxaban and apixaban (R² > 0.97), but not with dabigatran, a direct thrombin inhibitor. CAT-II method showed dose-dependent inhibition of TG in the presence of dabigatran, while CAT-I was not able to detect it. Both methods were able to correct for the interfering substances.

CONCLUSIONS

Our results showed high similarity between the results of CAT-I and CAT-II method when it is applied in control plasmas and plasmas not inhibited with a direct thrombin inhibitor. Furthermore, both the CAT-II method and ST-Genesia using the same calibration method were able to detect the effect of all oral anticoagulants. Taken together, applying a new calibration method is a significant improvement for monitoring patients on direct thrombin inhibitors while not introducing any bias to results obtained on other types of samples.

Serial markers of coagulation and inflammation and the occurrence of clinical pulmonary thromboembolism in mechanically ventilated patients with SARS-CoV-2 infection; the prospective Maastricht intensive care COVID cohort

Background

The incidence of pulmonary thromboembolism is high in SARS-CoV-2 patients admitted to the Intensive Care. Elevated biomarkers of coagulation (fibrinogen and D-dimer) and inflammation (c-reactive protein (CRP) and ferritin) are associated with poor outcome in SARS-CoV-2. Whether the time-course of fibrinogen, D-dimer, CRP and ferritin is associated with the occurrence of pulmonary thromboembolism in SARS-CoV-2 patients is unknown. We hypothesise that patients on mechanical ventilation with SARS-CoV-2 infection and clinical pulmonary thromboembolism have lower concentrations of fibrinogen and higher D-dimer, CRP, and ferritin concentrations over time compared to patients without a clinical pulmonary thromboembolism.

Methods

In a prospective study, fibrinogen, D-dimer, CRP and ferritin were measured daily. Clinical suspected pulmonary thromboembolism was either confirmed or excluded based on computed tomography pulmonary angiography (CTPA) or by transthoracic ultrasound (TTU) (i.e., right-sided cardiac thrombus). In addition, patients who received therapy with recombinant tissue plasminogen activator were included when clinical instability in suspected pulmonary thromboembolism did not allow CTPA. Serial data were analysed using a mixed-effects linear regression model, and models were adjusted for known risk factors (age, sex, APACHE-II score, body mass index), biomarkers of coagulation and inflammation, and anticoagulants.

Results

Thirty-one patients were considered to suffer from pulmonary thromboembolism ((positive CTPA (n = 27), TTU positive (n = 1), therapy with recombinant tissue plasminogen activator (n = 3)), and eight patients with negative CTPA were included. After adjustment for known risk factors and anticoagulants, patients with, compared to those without, clinical pulmonary thromboembolism had lower average fibrinogen concentration of − 0.9 g/L (95% CI: − 1.6 – − 0.1) and lower average ferritin concentration of − 1045 μg/L (95% CI: − 1983 – − 106) over time. D-dimer and CRP average concentration did not significantly differ, 561 μg/L (− 6212–7334) and 27 mg/L (− 32–86) respectively. Ferritin lost statistical significance, both in sensitivity analysis and after adjustment for fibrinogen and D-dimer.

Conclusion

Lower average concentrations of fibrinogen over time were associated with the presence of clinical pulmonary thromboembolism in patients at the Intensive Care, whereas D-dimer, CRP and ferritin were not. Lower concentrations over time may indicate the consumption of fibrinogen related to thrombus formation in the pulmonary vessels.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12959-021-00286-7.

Potent Cyclic Peptide Inhibitors of FXIIa Discovered by mRNA Display with Genetic Code Reprogramming

The contact system comprises a series of serine proteases that mediate procoagulant and proinflammatory activities via the intrinsic pathway of coagulation and the kallikrein-kinin system, respectively. Inhibition of Factor XIIa (FXIIa), an initiator of the contact system, has been demonstrated to lead to thrombo-protection and anti-inflammatory effects in animal models and serves as a potentially safer target for the development of antithrombotics. Herein, we describe the use of the Randomised Nonstandard Peptide Integrated Discovery (RaPID) mRNA display technology to identify a series of potent and selective cyclic peptide inhibitors of FXIIa. Cyclic peptides were evaluated in vitro, and three lead compounds exhibited significant prolongation of aPTT, a reduction in thrombin generation, and an inhibition of bradykinin formation. We also describe our efforts to identify the critical residues for binding FXIIa through alanine scanning, analogue generation, and via in silico methods to predict the binding mode of our lead cyclic peptide inhibitors.

Evaluation of the analytical performance of the PC100 platelet counter

Introduction

Platelet count can be altered in various diseases and treatments and measuring it may provide better insight into the expected outcome. So far, quantification of platelet count is done within laboratory conditions by using established hematology analyzers, whereas a point-of-care device could be used for this purpose outside of the clinical laboratories.

Aim

Our aim was to assess the closeness of agreement between a newly developed point-of-care PC100 platelet counter and two reference methods (Sysmex® XP-300, Sysmex® XN-9000) in measuring platelet counts in whole blood and platelet-rich-plasma (PRP).

Method

Whole blood was obtained from 119 individuals, of which 74 were used to prepare PRP samples. Whole blood platelet count was measured by the two reference methods and the PC100 platelet counter. PRP was prepared from the whole blood and platelet count was adjusted to the range of 250–3600 × 10³/μl and measured with the PC100 platelet counter and Sysmex® XP-300.

Results

A median difference of − 1.35% and − 2.98% occurred in whole blood platelet count between the PC100 platelet counter and the Sysmex® XP-300 and Sysmex® XN-9000, respectively. A strong linear correlation (r ≥ 0.98) was seen in both cases and regression equations indicated neither a constant nor a proportional bias between the methods. Direct comparison of the two reference methods revealed a median difference of − 1.15% and a strongly linear relationship (r = 0.99). Platelet count in PRP resulted in a median difference of 1.42% between the PC100 platelet counter and the reference method, Sysmex® XP-300. While the difference between two methods increased with concentration of platelets in PRP, a strong linear relationship remained throughout the whole measuring interval indicated by the high correlation coefficient (r = 0.99). Assessment of the predicted bias at predefined platelet counts showed that the bias in platelet counts falls within the acceptance criterion for both whole blood and PRP measurements.

Conclusions

Our results show that the PC100 platelet counter can be used interchangeably with the reference methods for determining platelet counts.

Off-target effects of oral anticoagulants - vascular effects of vitamin K antagonist and non-vitamin K antagonist oral anticoagulant dabigatran etexilate

INTRODUCTION

Vitamin K antagonists (VKA) and non-vitamin K oral antagonist anticoagulants (NOAC) are used in the clinic to reduce risk of thrombosis. However, they also exhibit vascular off-target effects. The aim of this study is to compare VKA and NOAC on atherosclerosis progression and calcification in an experimental setup.

MATERIAL AND METHODS

Female Apoe-/- mice (age 12 weeks) were fed Western-type diet as control or supplemented with dabigatran etexilate or warfarin for 6 or 18 weeks. Vascular calcification was measured in whole aortic arches using µCT and [18 F]-NaF. Atherosclerotic burden was assessed by (immuno)histochemistry. Additionally, in vitro effects of warfarin, thrombin, and dabigatran on primary vascular smooth muscle cells (VSMC) were assessed.

RESULTS

Short-term treatment with warfarin promoted formation of atherosclerotic lesions with a pro-inflammatory phenotype, and more rapid plaque progression compared with control and dabigatran. In contrast, dabigatran significantly reduced plaque progression compared with control. Long-term warfarin treatment significantly increased both presence and activity of plaque calcification compared with control and dabigatran. Calcification induced by warfarin treatment was accompanied by increased presence of uncarboxylated matrix Gla protein. In vitro, both warfarin and thrombin significantly increased VSMC oxidative stress and extracellular vesicle release, which was prevented by dabigatran.

CONCLUSION

Warfarin aggravates atherosclerotic disease activity, increasing plaque inflammation, active calcification, and plaque progression. Dabigatran lacks undesired vascular side effects and reveals beneficial effects on atherosclerosis progression and calcification. The choice of anticoagulation impacts atherosclerotic disease by differential off target effect. Future clinical studies should test whether this beneficial effect also applies to patients.

Serial EXTEM, FIBTEM, and tPA Rotational Thromboelastometry Observations in the Maastricht Intensive Care COVID Cohort-Persistence of Hypercoagulability and Hypofibrinolysis Despite Anticoagulation

Background: Coronavirus Disease 2019 (COVID-19) patients often present with thromboembolic events. In COVID-19 patients, routine hemostatic assays cannot correctly identify patients at risk for thromboembolic events. Viscoelastic testing with rotational thromboelastometry (ROTEM) might improve the characterization of COVID-19-associated coagulopathy.

Objective: To unravel underlying coagulopathy and fibrinolysis over time as measured by serial assessment heparin-independent (FIBTEM and EXTEM) and fibrinolysis illustrating (tissue plasminogen activator; tPA) ROTEM assays.

Patients/Methods: Between April 23 and June 12, consecutive adult patients enrolled within the Maastricht Intensive Care COVID (MaastrICCht) cohort were included, and a comprehensive set of clinical, physiological, pharmaceutical, and laboratory variables were collected daily. Twice per week, EXTEM, FIBTEM, and tPA ROTEM were performed. Clotting time (CT), clot formation time (CFT), maximum clot firmness (MCF), lysis onset time (LOT), and lysis time (LT) were determined to assess clot development and breakdown and were compared to routine hemostatic assays.

Results: In 36 patients, 96 EXTEM/FIBTEM and 87 tPA ROTEM tests were performed during a 6-week follow-up. CT prolongation was present in 54% of EXTEM measurements, which were not matched by prothrombin time (PT) in 37%. Respectively, 81 and 99% of all EXTEM and FIBTEM MCF values were above the reference range, and median MCF remained elevated during follow-up. The ROTEM fibrinolysis parameters remained prolonged with median LOT consequently >49 min and unmeasurable LT in 56% of measurements, suggesting a severe hypofibrinolytic phenotype.

Conclusion: ROTEM tests in COVID-19 ICU patients show hypercoagulability and severe hypofibrinolysis persisting over at least 6 weeks.

Thrombin-Fibrin(ogen) Interactions, Host Defense and Risk of Thrombosis

Fibrinogen is a well-known risk factor for arterial and venous thrombosis. Its function is not restricted to clot formation, however, as it partakes in a complex interplay between thrombin, soluble plasma fibrinogen, and deposited fibrin matrices. Fibrinogen, like thrombin, participates predominantly in hemostasis to maintain vascular integrity, but executes some important pleiotropic effects: firstly, as observed in thrombin generation experiments, fibrin removes thrombin from free solution by adsorption. The adsorbed thrombin is protected from antithrombins, notably α2-macroglobulin, and remains physiologically active as it can activate factors V, VIII, and platelets. Secondly, immobilized fibrinogen or fibrin matrices activate monocytes/macrophages and neutrophils via Mac-1 interactions. Immobilized fibrin(ogen) thereby elicits a pro-inflammatory response with a reciprocal stimulating effect of the immune system on coagulation. In contrast, soluble fibrinogen prohibits recruitment of these immune cells. Thus, while fibrin matrices elicit a procoagulant response, both directly by protecting thrombin and indirectly through the immune system, high soluble fibrinogen levels might protect patients due to its immune diminutive function. The in vivo influence of the 'protective' plasma fibrinogen versus the 'pro-thrombotic' fibrin matrices on thrombosis should be explored in future research.

No antiarrhythmic effect of direct oral anticoagulants versus vitamin K antagonists in paroxysmal atrial fibrillation patients undergoing catheter ablation

INTRODUCTION

Direct oral anticoagulants (DOACs) are superior to vitamin K antagonists (VKAs) for the prevention of stroke in atrial fibrillation (AF) patients with elevated stroke risk. Possible antiarrhythmic effects of DOACs have been discussed. We analyzed impact of DOAC treatment on recurrence-free survival after AF catheter ablation.

METHODS

Two-hundred and thirty-nine consecutive patients (median age 57 [IQR 48-64] years, 26.4% female) undergoing ablation for paroxysmal AF were included into this study. 68.6% of them received DOACs (DOAC group), 31.4% VKA (VKA group). The primary outcome was arrhythmia-free one-year survival.

RESULTS

DOAC patients had lower BMI, shorter history of AF, less arterial hypertension, less vascular disease, less use of antiarrhythmics and consequently lower CHA₂DS₂-VASc and HAS-BLED Scores. There was no difference in arrhythmia-free survival between DOAC and VKA groups (DOAC: 86.6%, VKA: 76.7%, p = 0.286).

CONCLUSIONS

Despite baseline characteristics favouring a better outcome of DOAC patients, arrhythmia-free survival was similar in both groups. Consequently, DOAC treatment did not have clinically relevant antiarrhythmic properties in these patients.

Pleiotropic actions of factor Xa inhibition in cardiovascular prevention: mechanistic insights and implications for anti-thrombotic treatment

Atherosclerosis is a chronic inflammatory disease in which atherothrombotic complications lead to cardiovascular morbidity and mortality. At advanced stages, myocardial infarction, ischaemic stroke, and peripheral artery disease, including major adverse limb events, are caused either by acute occlusive atherothrombosis or by thromboembolism. Endothelial dysfunction, vascular smooth muscle cell activation, and vascular inflammation are essential in the development of acute cardiovascular events. Effects of the coagulation system on vascular biology extend beyond thrombosis. Under physiological conditions, coagulation proteases in blood are pivotal in maintaining haemostasis and vascular integrity. Under pathological conditions, including atherosclerosis, the same coagulation proteases (including factor Xa, factor VIIa, and thrombin) become drivers of atherothrombosis, working in concert with platelets and vessel wall components. While initially atherothrombosis was attributed primarily to platelets, recent advances indicate the critical role of fibrin clot and plasma coagulation factors. Mechanisms of atherothrombosis and hypercoagulability vary depending on plaque erosion or plaque rupture. In addition to contributing to thrombus formation, factor Xa and thrombin can affect endothelial dysfunction, oxidative stress, vascular smooth muscle cell function as well as immune cell activation and vascular inflammation. By these mechanisms, they promote atherosclerosis and contribute to plaque instability. In this review, we first discuss the postulated vasoprotective mechanisms of protease-activated receptor signalling induced by coagulation enzymes under physiological conditions. Next, we discuss preclinical studies linking coagulation with endothelial cell dysfunction, thromboinflammation, and atherogenesis. Understanding these mechanisms is pivotal for the introduction of novel strategies in cardiovascular prevention and therapy. We therefore translate these findings to clinical studies of direct oral anticoagulant drugs and discuss the potential relevance of dual pathway inhibition for atherothrombosis prevention and vascular protection.

Relation between Tissue Factor Pathway Inhibitor Activity and Cardiovascular Risk Factors and Diseases in a Large Population Sample

OBJECTIVE

 Tissue factor pathway inhibitor (TFPI) is a potent anticoagulant protein in the extrinsic coagulation pathway. In the present study, we aim to identify the cardiovascular determinants for total TFPI activity and its association with cardiovascular disease (CVD) and total mortality.

METHODS

 Total TFPI activity was assessed in a selection of the population-based Gutenberg Health Study (n = 5,000). Statistical analysis was performed to identify the determinants for total TFPI activity as well as the associations with CVD and mortality.

RESULTS

 Multivariable linear regression analysis identified smoking (β 0.095 [0.054-0.136]) as a positive determinant for total TFPI activity, while diabetes (β -0.072 [-0.134 to -0.009]), obesity (β -0.063 [-0.101 to -0.024]), and history of coronary artery disease (CAD) were negatively associated with total TFPI activity, independent of age, sex, and the remaining cardiovascular risk factors. After adjustment for lipoprotein levels, the association between total TFPI activity levels and obesity and CAD was lost. The analysis additionally revealed a strong positive association between total TFPI activity levels and low-density lipoprotein (β 0.221 [0.204-0.237]). The Cox regression models revealed that a higher total TFPI activity, above 97.5th percentile of the reference group, was associated with an increased mortality risk (hazard ratio = 2.58 [95% confidence interval: 1.49-4.47]), independent of age, sex, and cardiovascular risk profile.

CONCLUSION

 In the Gutenberg Health Study population-based cohort, the highest percentage of total TFPI correlated with an increased mortality risk. While elevated TFPI may reflect endothelial cell activation, the associations between total TFPI activity and obesity and CAD, points to additional mechanistic interactions.

Thrombin generation in cardiovascular disease and mortality - results from the Gutenberg Health Study

Thrombin generation may be a potential tool to improve risk stratification for cardiovascular diseases. This study aims to explore the relation between thrombin generation and cardiovascular risk factors, cardiovascular diseases, and total mortality. For this study, N=5000 subjects from the population-based Gutenberg Health Study were analysed in a highly standardized setting. Thrombin generation was assessed by the Calibrated Automated Thrombogram method at 1 and 5 pM tissue factors trigger in platelet poor plasma. Lag time, endogenous thrombin potential, and peak height were derived from the thrombin generation curve. Sex-specific multivariable linear regression analysis adjusted for age, cardiovascular risk factors, cardiovascular diseases and therapy, was used to assess clinical determinants of thrombin generation. Cox regression models adjusted for age, sex, cardiovascular risk factors and vitamin K antagonists investigated the association between thrombin generation parameters and total mortality. Lag time was positively associated with obesity and dyslipidaemia for both sexes (p<0.0001). Obesity was also positively associated with endogenous thrombin potential in both sexes (p<0.0001) and peak height in males (1 pM tissue factor, p=0.0048) and females (p<0.0001). Cox regression models showed an increased mortality in individuals with lag time (1 pM tissue factor, hazard ratio=1.46, [95% CI: 1.07; 2.00], p=0.018) and endogenous thrombin potential (5 pM tissue factor, hazard ratio = 1.50, [1.06; 2.13], p=0.023) above the 95th percentile of the reference group, independent of the cardiovascular risk profile. This large-scale study demonstrates traditional cardiovascular risk factors, particularly obesity, as relevant determinants of thrombin generation. Lag time and endogenous thrombin potential were found as potentially relevant predictors of increased total mortality, which deserves further investigation.

Platelet-primed interactions of coagulation and anticoagulation pathways in flow-dependent thrombus formation

In haemostasis and thrombosis, platelet, coagulation and anticoagulation pathways act together to produce fibrin-containing thrombi. We developed a microspot-based technique, in which we assessed platelet adhesion, platelet activation, thrombus structure and fibrin clot formation in real time using flowing whole blood. Microspots were made from distinct platelet-adhesive surfaces in the absence or presence of tissue factor, thrombomodulin or activated protein C. Kinetics of platelet activation, thrombus structure and fibrin formation were assessed by fluorescence microscopy. This work revealed: (1) a priming role of platelet adhesion in thrombus contraction and subsequent fibrin formation; (2) a surface-independent role of tissue factor, independent of the shear rate; (3) a mechanism of tissue factor-enhanced activation of the intrinsic coagulation pathway; (4) a local, suppressive role of the anticoagulant thrombomodulin/protein C pathway under flow. Multiparameter analysis using blood samples from patients with (anti)coagulation disorders indicated characteristic defects in thrombus formation, in cases of factor V, XI or XII deficiency; and in contrast, thrombogenic effects in patients with factor V-Leiden. Taken together, this integrative phenotyping approach of platelet–fibrin thrombus formation has revealed interaction mechanisms of platelet-primed key haemostatic pathways with alterations in patients with (anti)coagulation defects. It can help as an important functional add-on whole-blood phenotyping.

Additive effect of erythropoietin use on exercise-induced endothelial activation and hypercoagulability in athletes

Purpose

Recombinant human erythropoietin (rHuEPO) is known to increase thrombotic risk in patients and might have similar effects in athletes abusing the drug. rHuEPO is prohibited by anti-doping legislation, but this risk has not been investigated thoroughly. This analysis was designed to evaluate whether rHuEPO impacts hemostatic profile and endothelial and platelet activation markers in trained subjects, and whether the combination with exercise affects exercise induced alterations.

Methods

This double-blind, randomized, placebo-controlled trial enrolled healthy, trained male cyclists aged 18–50 years. Participants were randomly allocated (1:1) to receive subcutaneous injections of rHuEPO (epoetin-β; mean dose 6000 IU per week) or placebo (0.9% NaCl) for 8 weeks. Subjects performed five maximal exercise tests and a road race, coagulation and endothelial/platelet markers were measured at rest and directly after each exercise effort.

Results

rHuEPO increased P-selectin (+ 7.8% (1.5–14.5), p = 0.02) and E-selectin (+ 8.6% (2.0–15.7), p = 0.01) levels at rest. Maximal exercise tests significantly influenced all measured coagulation and endothelial/platelet markers, and in the rHuEPO group maximal exercise tests led to 15.3% ((7.0–24.3%), p = 0.0004) higher E-selectin and 32.1% ((4.6–66.8%), p = 0.0207) higher Platelet factor 4 (PF4) levels compared to the placebo group.

Conclusion

In conclusion, rHuEPO treatment resulted in elevated E- and P-selectin levels in trained cyclists, indicating enhanced endothelial activation and/or platelet reactivity. Exercise itself induces hypercoagulability, and the combination of rHuEPO and exercise increased E-selectin and PF4 levels more than either intervention alone. Based on this, exercise potentially increases thrombotic risk, a risk that might be enhanced in combination with rHuEPO use.

Electronic supplementary material

The online version of this article (10.1007/s00421-020-04419-0) contains supplementary material, which is available to authorized users.

Role of Factor XIa and Plasma Kallikrein in Arterial and Venous Thrombosis

Cardiovascular disease, including stroke, myocardial infarction, and venous thromboembolism, is one of the leading causes of morbidity and mortality worldwide. Excessive coagulation may cause vascular occlusion in arteries and veins eventually leading to thrombotic diseases. Studies in recent years suggest that coagulation factors are involved in these pathological mechanisms. Factors XIa (FXIa), XIIa (FXIIa), and plasma kallikrein (PKa) of the contact system of coagulation appear to contribute to thrombosis while playing a limited role in hemostasis. Contact activation is initiated upon autoactivation of FXII on negatively charged surfaces. FXIIa activates plasma prekallikrein (PK) to PKa, which in turn activates FXII and initiates the kallikrein-kinin pathway. FXI is also activated by FXIIa, leading to activation of FIX and finally to thrombin formation, which in turn activates FXI in an amplification loop. Animal studies have shown that arterial and venous thrombosis can be reduced by the inhibition of FXI(a) or PKa. Furthermore, data from human studies suggest that these enzymes may be valuable targets to reduce thrombosis risk. In this review, we discuss the structure and function of FXI(a) and PK(a), their involvement in the development of venous and arterial thrombosis in animal models and human studies, and current therapeutic strategies.

Thrombo-Inflammation in Cardiovascular Disease: An Expert Consensus Document from the Third Maastricht Consensus Conference on Thrombosis

Thrombo-inflammation describes the complex interplay between blood coagulation and inflammation that plays a critical role in cardiovascular diseases. The third Maastricht Consensus Conference on Thrombosis assembled basic, translational, and clinical scientists to discuss the origin and potential consequences of thrombo-inflammation in the etiology, diagnostics, and management of patients with cardiovascular disease, including myocardial infarction, stroke, and peripheral artery disease. This article presents a state-of-the-art reflection of expert opinions and consensus recommendations regarding the following topics: (1) challenges of the endothelial cell barrier; (2) circulating cells and thrombo-inflammation, focused on platelets, neutrophils, and neutrophil extracellular traps; (3) procoagulant mechanisms; (4) arterial vascular changes in atherogenesis; attenuating atherosclerosis and ischemia/reperfusion injury; (5) management of patients with arterial vascular disease; and (6) pathogenesis of venous thrombosis and late consequences of venous thromboembolism.

Antithrombotic Therapy: Prevention and Treatment of Atherosclerosis and Atherothrombosis

Atherosclerosis is a multifactorial vascular disease that develops in the course of a lifetime. Numerous risk factors for atherosclerosis have been identified, mostly inflicting pro-inflammatory effects. Vessel injury, such as occurring during erosion or rupture of atherosclerotic lesions triggers blood coagulation, in attempt to maintain hemostasis (protect against bleeding). However, thrombo-inflammatory mechanisms may drive blood coagulation such that thrombosis develops, the key process underlying myocardial infarction and ischemic stroke (not due to embolization from the heart). In the blood coagulation system, platelets and coagulation proteins are both essential elements. Hyperreactivity of blood coagulation aggravates atherosclerosis in preclinical models. Pharmacologic inhibition of blood coagulation, either with platelet inhibitors, or better documented with anticoagulants, or both, limits the risk of thrombosis and may potentially reverse atherosclerosis burden, although the latter evidence is still based on animal experimentation.Patients at risk of atherothrombotic complications should receive a single antiplatelet agent (acetylsalicylic acid, ASA, or clopidogrel); those who survived an atherothrombotic event will be prescribed temporary dual antiplatelet therapy (ASA plus a P2Y12 inhibitor) in case of myocardial infarction (6-12 months), or stroke (<6 weeks), followed by a single antiplatelet agent indefinitely. High risk for thrombosis patients (such as those with peripheral artery disease) benefit from a combination of an anticoagulant and ASA. The price of gained efficacy is always increased risk of (major) bleeding; while tailoring therapy to individual needs may limit the risks to some extent, new generations of agents that target less critical elements of hemostasis and coagulation mechanisms are needed to maintain efficacy while reducing bleeding risks.

Searching for a Common Thrombo-Inflammatory Basis in Patients With Deep Vein Thrombosis or Peripheral Artery Disease

Background: Inflammation and hypercoagulability play a pivotal role in venous thromboembolism and atherothrombosis. Since venous thrombosis increases the risk of atherothrombotic events and vice versa, common mechanisms may be involved.

Objectives: To elucidate the role of neutrophils and coagulation in the occurrence of atherothrombotic events in patients with a history of deep vein thrombosis (DVT or peripheral artery disease (PAD).

Materials and Methods: We studied 115 patients from two cohorts (75 DVT, 40 PAD). From those with PAD, 20 patients had progressive disease; from those with DVT, 25 patients had a recurrent DVT and 25 suffered from post thrombotic syndrome (PTS); patients were age and sex matched to DVT and PAD patients without events. Markers of neutrophil recruitment (p-selectin) and activation [nucleosomes, human neutrophil elastase- α1anti-trypsin (HNE-AT)], an anti-inflammatory marker (Lipoxin A4) and a clotting activity marker (d-dimer), were measured with ELISA. Coagulation potential was analyzed by thrombin generation (CAT method).

Results: Higher nucleosome levels were found in DVT patients [11.3 U/mL (7.4–17.7)] compared to PAD patients [7.1 U/mL (5.1–13.8)], lower HNE-AT levels were found in DVT patients [33.4 ng/mL (23.5–40.5)] in comparison to PAD patients [158 ng/mL (88.1–283)]. No difference in nucleosome levels was found between DVT patients with cardiovascular (CV) events [12.6 U/mL (8.2–16.1)], and PAD patients with CV events [6.9 U/mL (4.9–11.2)]. Lipoxin A4 levels appeared to be significantly lower in DVT [2.4 ng/mL (1.7–4.8)] vs. PAD [35.6 ng/mL (16.6–80.1)], with similar results in DVT patients with CV events vs. PAD patients with CV events. Thrombin generation showed higher ETP [160.4% (141.1–215.4)], and peak height [292.1% (177.9–330)] values in DVT patients. D-dimer levels were significantly lower in the DVT cohort [330 ng/mL (220–550)] compared to the PAD cohort [550 ng/mL (369–959)].

Conclusion: In DVT patients, neutrophil activity does not appear to be an important driver of CV events. Although neutrophil activity is more pronounced in PAD, its effect is partly dampened by Lipoxin A4. Moreover, no associations were found between NET products and coagulation activity, suggesting that neutrophil activation does not play a pivotal role in the risk of thrombosis in either DVT or PAD.

Targeting Coagulation Factor Xa Promotes Regression of Advanced Atherosclerosis in Apolipoprotein-E Deficient Mice

Atherosclerosis is a progressive inflammatory vascular disorder, complicated by plaque rupture and subsequently atherothrombosis. In vitro studies indicate that key clotting proteases, such as factor Xa (FXa), can promote atherosclerosis, presumably mediated through protease activated receptors (PARs). Although experimental studies showed reduced onset of atherosclerosis upon FXa inhibition, the effect on pre-existing plaques has never been studied. Therefore, we investigated effects of FXa inhibition by rivaroxaban on both newly-formed and pre-existing atherosclerotic plaques in apolipoprotein-e deficient (ApoE^-/-) mice. Female ApoE^-/- mice (age: 8-9 weeks, n = 10/group) received western type diet (WTD) or WTD supplemented with rivaroxaban (1.2 mg/g) for 14 weeks. In a second arm, mice received a WTD for 14 weeks, followed by continuation with either WTD or WTD supplemented with rivaroxaban (1.2 mg/g) for 6 weeks (total 20 weeks). Atherosclerotic burden in aortic arch was assessed by haematoxilin & eosin immunohistochemistry (IHC); plaque vulnerability was examined by IHC against macrophages, collagen, vascular smooth muscle cells (VSMC) and matrix metalloproteinases (MMPs). In addition, PAR1 and -2 expressions and their main activators thrombin and FXa in the plaque were determined in the plaque. Administration of rivaroxaban at human therapeutic concentrations reduced the onset of atherosclerosis (-46%, p < 0.05), and promoted a regression of pre-existing plaques in the carotids (-24%, p < 0.001). In addition, the vulnerability of pre-existing plaques was reduced by FXa inhibition as reflected by reduced macrophages (-39.03%, p < 0.05), enhanced collagen deposition (+38.47%, p < 0.05) and diminished necrotic core (-31.39%, p < 0.05). These findings were accompanied with elevated vascular smooth muscle cells and reduced MMPs. Furthermore, expression of PARs and their activators, thrombin and FXa was diminished after rivaroxaban treatment. Pharmacological inhibition of FXa promotes regression of advanced atherosclerotic plaques and enhances plaque stability. These data suggest that inhibition of FXa may be beneficial in prevention and regression of atherosclerosis, possibly mediated through reduced activation of PARs.

Volume replacement strategies do not impair the binding of dabigatran to idarucizumab: Porcine model of hemodilution

Background

Idarucizumab is a humanized Fab fragment that specifically reverses dabigatran anticoagulation. In trauma, volume expanders are used for resuscitation to compensate for blood loss and hemorrhagic shock, but it is unknown whether volume expanders influence the binding of dabigatran to its antidote. Using a porcine dilutional coagulopathy model, this study investigated whether volume replacement strategies affect binding of dabigatran to idarucizumab.

Methods

Twenty-five male pigs were treated orally with dabigatran etexilate (30 mg/kg bid) for 3 days. The following day, animals were anesthetized, infused with dabigatran (total dose 0.645 mg/kg) to achieve supratherapeutic concentrations, and randomized 1:1:1:1:1 (n = 5 per group) to control (no hemodilution) or hemodilution where ~50% of blood volume was substituted with Ringer’s solution, 6% hydroxyethyl starch 130/0.4, 6% hydroxyethyl starch 200/0.5 or 4% gelatin. Idarucizumab was then administered intravenously (30 mg/kg) and serial blood samples were taken for up to 24 hours to measure diluted thrombin time (corresponding with dabigatran activity), total dabigatran (bound to antidote and free drug) and a panel of coagulation parameters.

Results

Mean plasma dabigatran levels were 617 ± 16 ng/mL after infusion and 600 ± 114 ng/mL after ~50% hemodilution with no significant differences between groups. Following treatment with idarucizumab, plasma concentrations of unbound dabigatran decreased markedly, with similar reductions in all groups. Dabigatran-induced prolongation of coagulation parameters was rapidly reversed in all groups.

Conclusion

This study indicates that several volume expanders used for resuscitation in trauma do not interfere with the binding of idarucizumab to dabigatran.

Pleiotropic effects of the hemostatic system

Atherothrombosis is characterized by the inflammatory process of atherosclerosis combined with a hypercoagulable state leading to superimposed thrombus formation. In atherosclerotic plaques, cell signaling can occur via protease-activated receptors (PARs), four of which have been identified so far (PAR1-PAR4). Proteases that are able to activate PARs can be produced systemically, but also at the sites of lesions, and they include thrombin and activated factor X. After PAR activation, downstream signaling can lead to both proinflammatory effects and a hypercoagulable state. Which specific effect occurs depends on the type of protease and activated PAR, and the site of activation. Hypercoagulable effects are mainly exerted through PAR1 and PAR4, whereas proinflammatory responses are mostly seen after PAR1 and PAR2 activation. PAR signaling pathways contribute to atherothrombosis, suggesting that inhibition of these pathways possibly prevents cardiovascular events based on this pathophysiological mechanism. In this review, we highlight the pathways by which PAR activation leads to proinflammatory responses and a hypercoagulable state. Furthermore, we give an overview of potential pharmacological treatment targets that promote vascular protection.