Persistently High Levels of Coagulation Factor XI as a Risk Factor for Venous Thrombosis

Coagulation factor XI (FXI) promotes fibrin formation and inhibits fibrinolysis. Elevated plasma FXI levels, limited to a single measurement, are associated with a higher thrombotic risk. Our case-control study aimed to identify the effect of persistently increased plasma FXI levels on the risk of deep vein thrombosis (DVT). All patients evaluated between January 2016 and January 2018 for a first episode of proximal DVT of the lower extremity were considered for enrolment. Plasma FXI levels were measured at least 1 month after the discontinuation of anticoagulant treatment (T1). The patients with increased plasma FXI levels (>90th percentile of controls) were tested again 3 months later (T2). Among the 200 enrolled patients (M/F 114/86, age range 26-87 years), 47 patients had increased plasma FXI levels at T1 and16 patients had persistently increased plasma FXI levels at T2. The adjusted odds ratio for DVT was 2.4 (95% CI, 1.3 to 5.5, p < 0.001) for patients with increased FXI levels at T1 and 5.2 (95% CI, 2.3 to 13.2, p < 0.001) for patients with persistently high FXI levels at T2. Elevated FXI levels constitute a risk factor for deep vein thrombosis, and this risk nearly doubled in patients with persistently increased plasma FXI levels. Larger prospective studies are needed to confirm our findings.

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.

Global epidemiology of factor XI deficiency: A targeted review of the literature and foundation reports

INTRODUCTION

Hereditary factor XI (FXI) deficiency is a rare coagulation disorder that may result in excessive bleeding requiring intervention to restore haemostasis.

AIM

The aim of this review was to report the current knowledge of the worldwide incidence and prevalence of FXI deficiency.

METHODS

A targeted PubMed search using terms related to FXI deficiency was conducted to identify studies published from April 2002 through April 2022. A manual search supplemented the electronic search. Studies were eligible for data abstraction if they reported population-based incidence proportions/rates or prevalence proportions for FXI deficiency.

RESULTS

The electronic and manual searches returned 253 publications. After applying exclusion criteria, seven publications were included in the analysis, including a global report from the World Federation of Haemophilia (WFH). Six publications provided information on the prevalence of FXI deficiency that included 74 countries and regions. The estimated prevalence of FXI in the WFH report ranged from 0/100,000 in several countries to 55.85/100,000 individuals in the United Kingdom. Prevalence estimates in the PubMed findings ranged from .1 to 246.2/1,000,000 inhabitants with varying methods of case identification and time periods of analysis. One study estimated the incidence of FXI deficiency in Yecla, Spain at 2% of blood donors and .09% of hospital inpatients/outpatients with activated partial thromboplastin time (aPTT) tests.

CONCLUSION

FXI deficiency is rare across the world, but additional steps could be taken to improve incidence and prevalence estimation, for example, development of a consistent FXI deficiency definition and incorporating genetic testing into a clinical routine to better identify and characterise cases.

Revised model of the tissue factor pathway of thrombin generation: Role of the feedback activation of FXI

BACKGROUND

Biochemical reaction networks are self-regulated in part due to feedback activation mechanisms. The tissue factor (TF) pathway of blood coagulation is a complex reaction network controlled by multiple feedback loops that coalesce around the serine protease thrombin.

OBJECTIVES

Our goal was to evaluate the relative contribution of the feedback activation of coagulation factor XI (FXI) in TF-mediated thrombin generation using a comprehensive systems-based analysis.

MATERIALS AND METHODS

We developed a systems biology model that improves the existing Hockin-Mann (HM) model through an integrative approach of mathematical modeling and in vitro experiments. Thrombin generation measured using in vitro assays revealed that the feedback activation of FXI contributes to the propagation of thrombin generation based on the initial concentrations of TF or activated coagulation factor X (FXa). We utilized experimental data to improve the robustness of the HM model to capture thrombin generation kinetics without a role for FXI before including the feedback activation of FXI by thrombin to construct the extended (ext.) HM model.

RESULTS AND CONCLUSIONS

Using the ext.HM model, we predicted that the contribution of positive feedback of FXI activation by thrombin can be abolished by selectively eliminating the inhibitory function of tissue factor pathway inhibitor (TFPI), a serine protease inhibitor of FXa and TF-activated factor VII (FVIIa) complex. This prediction from the ext.HM model was experimentally validated using thrombin generation assays with function blocking antibodies against TFPI and plasmas depleted of FXI. Together, our results demonstrate the applications of combining experimental and modeling techniques in predicting complex biochemical reaction systems.

Associations of coagulation factor X and XI with incident acute coronary syndrome and stroke: A nested case-control study

BACKGROUND

Coagulation cascade contributes to thrombotic and hemorrhagic diseases, but it remains unclear whether coagulation factors X (FX) and XI (FXI) levels are associated with cardiovascular diseases.

OBJECTIVE

To evaluate prospective associations of FX and FXI levels with incident acute coronary syndrome (ACS), stroke, and their subtypes (acute myocardial infarction, unstable angina, ischemic stroke, and hemorrhagic stroke).

METHODS

We performed a nested case-control study (n = 1846) within the Dongfeng-Tongji cohort from 2013 to 2016 matched on age (within 1 year), sex, and sampling date (within 1 month) by incidence density sampling, and measured plasma FX and FXI levels by enzyme-linked immunosorbent assay. FX and FXI levels were categorized into three groups (low, <25th; middle, 25th to <75th; and high ≥75th percentiles) according to distributions, and conditional logistic regression models were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

After adjustment for traditional cardiovascular risk factors, compared with middle groups, the OR (95% CI) in high levels of FX and FXI were 1.11 (0.79-1.56) and 0.96 (0.68-1.36) for incident ACS, and 1.01 (0.63-1.62) and 1.72 (1.14-2.60) for incident stroke, respectively. As for subtypes of ACS and stroke, only high FXI levels were significantly associated with incident ischemic stroke (OR 1.66, 95% CI 1.05-2.65). Moreover, all associations remained steady after additional adjustment for platelet and leukocyte.

CONCLUSION

FXI levels were associated with a greater risk of incident ischemic stroke but not hemorrhagic stroke or ACS. FX levels were not associated with incident ACS or stroke.

Coagulation factor XI induces Ca2+ response and accelerates cell migration in vascular smooth muscle cells via proteinase-activated receptor 1

Activated coagulation factor XI (FXIa) is a serine proteinase that plays a key role in the intrinsic coagulation pathway. The analysis of FXI-knockout mice has indicated the contribution of FXI to the pathogenesis of atherosclerosis. However, the underlying mechanism remains unknown. We hypothesized that FXIa exerts vascular smooth muscle effects via proteinase-activated receptor 1 (PAR₁). Fura-2 fluorometry revealed that FXIa elicited intracellular Ca²⁺ signal in rat embryo aorta smooth muscle A7r5 cells. The influx of extracellular Ca²⁺ played a greater role in generating Ca²⁺ signal than the Ca²⁺ release from intracellular stores. The FXIa-induced Ca²⁺ signal was abolished by the pretreatment with atopaxar, an antagonist of PAR₁, or 4-amidinophenylmethanesulfonyl fluoride (p-APMSF), an inhibitor of proteinase, while it was also lost in embryonic fibroblasts derived from PAR₁^-/- mice. FXIa cleaved the recombinant protein containing the extracellular region of PAR₁ at the same site (R45/S46) as that of thrombin, a canonical PAR₁ agonist. The FXIa-induced Ca²⁺ influx was inhibited by diltiazem, an L-type Ca²⁺ channel blocker, and by siRNA targeted to Ca_V1.2. The FXIa-induced Ca²⁺ influx was also inhibited by GF109203X and rottlerin, inhibitors of protein kinase C. In a wound healing assay, FXIa increased the rate of cell migration by 2.46-fold of control, which was partly inhibited by atopaxar or diltiazem. In conclusion, FXIa mainly elicits the Ca²⁺ signal via the PAR₁/Ca_V1.2-mediated Ca²⁺ influx and accelerates the migration in vascular smooth muscle cells. The present study provides the first evidence that FXIa exerts a direct cellular effect on vascular smooth muscle.

Associations of coagulation factors IX and XI levels with incident coronary heart disease and ischemic stroke: the REGARDS study

Essentials Coagulation factors (F) IX and XI have been implicated in cardiovascular disease (CVD) risk. We studied associations of FIX and FXI with incident coronary heart disease (CHD) and stroke. Higher FIX antigen was associated with incident CHD risk in blacks but not whites. Higher levels of FIX antigen may be a CHD risk factor among blacks.

SUMMARY

Background Recent studies have suggested the importance of coagulation factor IX and FXI in cardiovascular disease (CVD) risk. Objectives To determine whether basal levels of FIX or FXI antigen were associated with the risk of incident coronary heart disease (CHD) or ischemic stroke. Patients/Methods The REasons for Geographic And Racial Differences in Stroke (REGARDS) study recruited 30 239 participants across the contiguous USA between 2003 and 2007. In a case-cohort study within REGARDS, FIX and FXI antigen were measured in participants with incident CHD (n = 609), in participants with incident ischemic stroke (n = 538), and in a cohort random sample (n = 1038). Hazard ratios (HRs) for CHD and ischemic stroke risk were estimated with Cox models per standard deviation higher FIX or FXI level, adjusted for CVD risk factors. Results In models adjusting for CHD risk factors, higher FIX levels were associated with incident CHD risk (HR 1.19; 95% confidence interval [CI] 1.01-1.40) and the relationship of higher FXI levels was slightly weaker (HR 1.15; 95% CI 0.97-1.36). When stratified by race, the HR of FIX was higher in blacks (HR 1.39; 95% CI 1.10-1.75) than in whites (HR 1.06; 95% CI 0.86-1.31). After adjustment for stroke risk factors, there was no longer an association of FIX levels with ischemic stroke, whereas the association of FXI levels with ischemic stroke was slightly attenuated. Conclusions Higher FIX antigen levels were associated with incident CHD in blacks but not in whites. FIX levels may increase CHD risk among blacks.

The hemostatic role of factor XI

Coagulation factor (F)XI has been described as a component of the early phase of the contact pathway of blood coagulation, acting downstream of factor XII. However, patients deficient in upstream members of the contact pathway, including FXII and prekallikrein, do not exhibit bleeding complications, while FXI-deficient patients sometimes experience mild bleeding, suggesting FXI plays a role in hemostasis independent of the contact pathway. Further complicating the picture, bleeding risk in FXI-deficient patients is difficult to predict because bleeding symptoms have not been found to correlate with FXI antigen levels or activity. However, recent studies have emerged to expand our understanding of FXI, demonstrating that activated FXI is able to activate coagulation factors FX, FV, and FVIII, and inhibit the anti-coagulant tissue factor pathway inhibitor (TFPI). Understanding these activities of FXI may help to better diagnose which FXI-deficient patients are at risk for bleeding. In contrast to its mild hemostatic activities, FXI is known to play a significant role in thrombosis, as it is a demonstrated independent risk factor for deep vein thrombosis, ischemic stroke, and myocardial infarction. Recent translational approaches have begun testing FXI as an antithrombotic, with one promising clinical study showing that an anti-sense oligonucleotide against FXI prevented venous thrombosis in elective knee surgery. A better understanding of the varied and complex role of FXI in both thrombosis and hemostasis will help to allow better prediction of bleeding risk in FXI-deficient patients and also informing the development of targeted agents to inhibit the thrombotic activities of FXI while preserving hemostasis.

Polyphosphate as modulator of hemostasis, thrombosis, and inflammation

Inorganic polyphosphate (polyP), a linear polymer of phosphates, is present in many infectious microorganisms and is secreted by mast cells and platelets. PolyP has recently been shown to accelerate blood clotting and slow fibrinolysis, in a manner that is highly dependent on polymer length. Very long-chain polyP (of the type present in microorganisms) is an especially potent trigger of the contact pathway, enhances the proinflammatory activity of histones, and may participate in host responses to pathogens. PolyP also inhibits complement, providing another link between polyP and inflammation/innate immunity. Platelet-size polyP (which is considerably shorter) accelerates factor V activation, opposes the anticoagulant action of tissue factor pathway inhibitor, modulates fibrin clot structure, and promotes factor XI activation. PolyP may have utility in treating bleeding. It is also a potential target for the development of antithrombotic drugs with a novel mechanism of action and potentially fewer bleeding side effects compared with conventional anticoagulants.