Factor XII and prekallikrein promote microvascular inflammation and psoriasis in mice.

BACKGROUND AND PURPOSE: Psoriasis is an autoimmune inflammatory skin disease, featuring microvascular abnormalities and elevated levels of bradykinin. Contact activation of Factor XII can initiate the plasma kallikrein-kinin cascade, producing inflammation and angioedema. The role of Factor XII in psoriasis is unknown. EXPERIMENTAL APPROACH: The effects of deficiency of Factor XII or its enzymatic substrate, prekallikrein, were examined in the imiquimod-induced mouse model of psoriasis. Skin microcirculation was assessed using intravital confocal microscopy and laser Doppler flowmeter. A novel antibody blocking Factor XII activation was evaluated for psoriasis prevention. KEY RESULTS: Expression of Factor XII was markedly up-regulated in human and mouse psoriatic skin. Genetic deletion of Factor XII or prekallikrein, attenuated imiquimod-induced psoriatic lesions in mice. Psoriatic induction increased skin microvascular blood perfusion, causing vasodilation, hyperpermeability and angiogenesis. It also promoted neutrophil-vascular interaction, inflammatory cytokine release and enhanced Factor XII / prekallikrein enzymatic activity with elevated bradykinin. Factor XII or prekallikrein deficiency ameliorated these microvascular abnormalities and abolished bradykinin increase. Antagonism of bradykinin B2 receptors reproduced the microvascular protection of Factor XII / prekallikrein deficiency, attenuated psoriatic lesions, and prevented protection by Factor XII / prekallikrein deficiency against psoriasis. Furthermore, treatment of mice with Factor XII antibody alleviated experimentally induced psoriasis and suppressed microvascular inflammation. CONCLUSION AND IMPLICATIONS: Activation of Factor XII promoted psoriasis via prekallikrein-dependent formation of bradykinin, which critically mediated psoriatic microvascular inflammation. Inhibition of contact activation represents a novel therapeutic strategy for psoriasis.

Factor XII contact activation can be prevented by targeting 2 unique patches in its epidermal growth factor-like 1 domain with a nanobody.

BACKGROUND: Factor (F)XII triggers contact activation by binding to foreign surfaces, with the epidermal growth factor-like 1 (EGF-1) domain being the primary binding site. Blocking FXII surface-binding might hold therapeutic value to prevent medical device-induced thrombosis. OBJECTIVES: To unravel and prevent EGF-1-mediated FXII surface-binding with variable domains of a heavy chain-only antibody (VHH). METHODS: FXII variants with glutamine substitutions of 2 positively charged amino acid patches within the EGF-1 domain were created. Their role in FXII contact activation was assessed using kaolin pull-down experiments, amidolytic activity assays, and clotting assays. FXII EGF-1 domain-specific VHHs were raised to inhibit EGF-1-mediated FXII contact activation while preserving quiescence. RESULTS: Two unique, positively charged patches in the EGF-1 domain were identified (upstream, 73K74K76K78H81K82H; downstream, 87K113K). Neutralizing the charge of both patches led to a 99% reduction in FXII kaolin binding, subsequent decrease in autoactivation of 94%, and prolongation of clot formation in activated partial thromboplastin time assays from 36 (±2) to 223 (±13) seconds. Three FXII EGF-1-specific VHHs were developed that are capable of inhibiting kaolin binding and subsequent contact system activation in plasma. The most effective VHH "F2" binds the positively charged patches and thereby dose-dependently extends activated partial thromboplastin time clotting times from 29 (±2) to 43 (±3) seconds without disrupting FXII quiescence. CONCLUSION: The 2 unique, positively charged patches in FXII EGF-1 cooperatively mediate FXII surface-binding, making both patches crucial for contact activation. Targeting these with FXII EGF-1-specific VHHs can exclusively decrease FXII surface-binding and subsequent contact activation, while preserving zymogen quiescence. These patches thus have potential as druggable targets in preventing medical device-induced thrombosis.

[Pedigree Analysis of Hereditary Coagulation Factor XII Deficiency Caused by Compound Heterozygous Mutation p.Gly175Cys and p.Gly542Ser of F12 Gene].

OBJECTIVE: To analyze the clinical phenotype and gene mutation of a genetic coagulation factor XII (FXII) deficiency pedigree and explore the molecular pathogenesis. METHODS: The activated partial thromboplastin time (APTT) and FXII activity (FXII:C) were detected by clotting method. The FXII antigen (FXII:Ag) was tested with ELISA. All exons and flanks of F12 gene were determined by Sanger sequencing. ClustalX-2.1-win, PROVEAN and Swiss-Pdb Viewer software were used to analyze the conservatism of amino acids at the mutant site, forecast whether the mutant amino acids were harmful and confirm the influence of the mutation on protein structure. RESULTS: The APTT of the proband prolonged to 71.3 s. The FXII:C and FXII:Ag were decreased to 5% and 6%, respectively. There were two heterozygous missense mutations c.580G>T and c.1681G>A detected in exon 7 and exon 14 of F12 gene, resulting in p.Gly175Cys and p.Gly542Ser, severally. Proband's father carried the p.Gly175Cys heterozygous mutation, while mother, brother and daughter had the p.Gly542Ser heterozygous mutation. Software analysis showed that both Gly175 and Gly542 were conserved, the two mutations were harmful and when mutations had occurred, the corresponding sites affected the protein local structure. CONCLUSION: The p.Gly175Cys and p.Gly542Ser compound heterozygous mutations are the molecular pathogenesis of the hereditary coagulation FXII deficiency pedigree. The p.Gly175Cys mutation has been detected for the first time in the world.

Safety of Tonsillectomy and/or Adenoidectomy in Pediatric Patients with Prolonged Activated Partial Thromboplastin Time and Factor XII Deficiency.

Objective: To evaluate the safety and feasibility of tonsillectomy and/or adenoidectomy (T&A) in pediatric patients with prolonged activated partial thromboplastin time (APTT) and coagulation factor deficiency. Methods: A prospective study was admitted to the children undergoing T&A at our institution between October 2019 and January 2020, specifically focusing on preoperative coagulation function. Within this group, we identified 5 patients exhibiting prolonged APTT and coagulation factor deficiencies, constituting the experimental group, and 10 patients matched by gender and age with normal blood coagulation function were selected as the control group. Comparative analyses between the two groups were conducted, focusing on surgical duration, intraoperative bleeding volume, duration of hospital stay, and postoperative complications such as active bleeding across the groups. At the six-month postoperative mark, a reassessment of coagulation functions and factor assays was conducted within the experimental group. Results: No statistically significant differences were discovered in terms of surgical duration or bleeding volume when comparing the experimental subgroups with their respective control counterparts. Furthermore, there were no incidences of postoperative active bleeding observed in any of the groups. Notably, postoperative APTT values (32.7 ± 1.7s) exhibited a significant disparity compared to preoperative levels (43.7 ± 1.8s, p < 0.01). Coagulation factors demonstrated normalization, evidenced by a significant difference in postoperative Factor XII levels (40.2 ± 5.4%) compared to preoperative levels (63.1 ± 5.9%, p < 0.01). Conclusion: Prolonged APTT with FXII factor deficiency does not show a significant bleeding tendency and is not a contraindication for T&A surgery. Post T&A surgery, children with abnormal coagulation function and deficient clotting factors show significant improvement compared to pre-surgery. It is important to consider that chronic inflammation in adenoids and tonsils may contribute to the prolongation of APTT and the manifestation of Factor XII deficiency.

[Clinical development of anti-FXII therapeutics as a target in thrombo-inflammation]. / Développement clinique des thérapeutiques anti-facteur XII ciblant la thrombo-inflammation.

The history of anticoagulation has evolved considerably, from non-specific drugs to molecules that directly target specific coagulation factors, such as direct oral anticoagulants (DOACs). Since last decade, DOACs are widely used in clinical practice because of their ease to use with favorable pharmacological profile and not requiring monitoring. New therapeutics targeting the contact phase of coagulation are currently under development, and could make it possible to prevent thrombotic risk without altering hemostasis, thereby reducing the risk of bleeding. Factor XII, being at the crossroads between hemostasis and inflammation, appears to be an interesting target that could limit thrombo-inflammation without increasing bleeding risk. The aim of this article is to summarize the main information concerning FXII inhibitors and to review the results of various clinical trials available to date, focusing on applications beyond hemostasis, such as in the management of hereditary angioedema.

Histidine-Rich Glycoprotein Modulates the Toxic Effects of High-Dose Polyphosphate in Mice.

BACKGROUND: Polyphosphate (polyP), a procoagulant released from platelets, activates coagulation via the contact system and modulates cardiomyocyte viability. High-dose intravenous polyP is lethal in mice, presumably because of thrombosis. Previously, we showed that HRG (histidine-rich glycoprotein) binds polyP and attenuates its procoagulant effects. In this study, we investigated the mechanisms responsible for the lethality of intravenous polyP in mice and the impact of HRG on this process. METHODS: The survival of wild-type or HRG-deficient mice given intravenous synthetic or platelet-derived polyP in doses up to 50 mg/kg or saline was compared. To determine the contribution of thrombosis, the effect of FXII (factor XII) knockdown or enoxaparin on polyP-induced fibrin deposition in the lungs was examined. To assess cardiotoxicity, the ECG was continuously monitored, the levels of troponin I and the myocardial band of creatine kinase were quantified, and the viability of a cultured murine cardiomyocyte cell line exposed to polyP in the absence or presence of HRG was determined. RESULTS: In HRG-deficient mice, polyP was lethal at 30 mg/kg, whereas it was lethal in wild-type mice at 50 mg/kg. Although FXII knockdown or enoxaparin administration attenuated polyP-induced fibrin deposition in the lungs, neither affected mortality. PolyP induced dose-dependent ECG abnormalities, including heart block and ST-segment changes, and increased the levels of troponin and myocardial band of creatine kinase, effects that were more pronounced in HRG-deficient mice than in wild-type mice and were attenuated when HRG-deficient mice were given supplemental HRG. Consistent with its cardiotoxicity, polyP reduced the viability of cultured cardiomyocytes in a dose-dependent manner, an effect attenuated with supplemental HRG. CONCLUSIONS: High-dose intravenous polyP is cardiotoxic in mice, and HRG modulates this effect.

Recent advances in the discovery and development of drugs targeting the kallikrein-kinin system.

BACKGROUND: The kallikrein-kinin system is a key regulatory cascade involved in blood pressure maintenance, hemostasis, inflammation and renal function. Currently, approved drugs remain limited to the rare disease hereditary angioedema. However, growing interest in this system is indicated by an increasing number of promising drug candidates for further indications. METHODS: To provide an overview of current drug development, a two-stage literature search was conducted between March and December 2023 to identify drug candidates with targets in the kallikrein-kinin system. First, drug candidates were identified using PubMed and Clinicaltrials.gov. Second, the latest publications/results for these compounds were searched in PubMed, Clinicaltrials.gov and Google Scholar. The findings were categorized by target, stage of development, and intended indication. RESULTS: The search identified 68 drugs, of which 10 are approved, 25 are in clinical development, and 33 in preclinical development. The three most studied indications included diabetic retinopathy, thromboprophylaxis and hereditary angioedema. The latter is still an indication for most of the drug candidates close to regulatory approval (3 out of 4). For the emerging indications, promising new drug candidates in clinical development are ixodes ricinus-contact phase inhibitor for thromboprophylaxis and RZ402 and THR-149 for the treatment of diabetic macular edema (all phase 2). CONCLUSION: The therapeutic impact of targeting the kallikrein-kinin system is no longer limited to the treatment of hereditary angioedema. Ongoing research on other diseases demonstrates the potential of therapeutic interventions targeting the kallikrein-kinin system and will provide further treatment options for patients in the future.

Potential Pathways and Pathophysiological Implications of Viral Infection-Driven Activation of Kallikrein-Kinin System (KKS).

Microcirculatory and coagulation disturbances commonly occur as pathological manifestations of systemic viral infections. Research exploring the role of the kallikrein-kinin system (KKS) in flavivirus infections has recently linked microvascular dysfunctions to bradykinin (BK)-induced signaling of B2R, a G protein-coupled receptor (GPCR) constitutively expressed by endothelial cells. The relevance of KKS activation as an innate response to viral infections has gained increasing attention, particularly after the reports regarding thrombogenic events during COVID-19. BK receptor (B2R and B1R) signal transduction results in vascular permeability, edema formation, angiogenesis, and pain. Recent findings unveiling the role of KKS in viral pathogenesis include evidence of increased activation of KKS with elevated levels of BK and its metabolites in both intravascular and tissue milieu, as well as reports demonstrating that virus replication stimulates BKR expression. In this review, we will discuss the mechanisms triggered by virus replication and by virus-induced inflammatory responses that may stimulate KKS. We also explore how KKS activation and BK signaling may impact virus pathogenesis and further discuss the potential therapeutic application of BKR antagonists in the treatment of hemorrhagic and respiratory diseases.

High molecular weight kininogen interactions with the homologs prekallikrein and factor XI: importance to surface-induced coagulation.

BACKGROUND: In plasma, high molecular weight kininogen (HK) is either free or bound to prekallikrein (PK) or factor (F) XI (FXI). During contact activation, HK is thought to anchor PK and FXI to surfaces, facilitating their conversion to the proteases plasma kallikrein and FXIa. Mice lacking HK have normal hemostasis but are resistant to injury-induced arterial thrombosis. OBJECTIVES: To identify amino acids on the HK-D6 domain involved in PK and FXI binding and study the importance of the HK-PK and HK-FXI interactions to coagulation. METHODS: Twenty-four HK variants with alanine replacements spanning residues 542-613 were tested in PK/FXI binding and activated partial thromboplastin time clotting assays. Surface-induced FXI and PK activation in plasma were studied in the presence or absence of HK. Kng1-/- mice lacking HK were supplemented with human or murine HK and tested in an arterial thrombosis model. RESULTS: Overlapping binding sites for PK and FXI were identified in the HK-D6 domain. HK variants with defects only in FXI binding corrected the activated partial thromboplastin time of HK-deficient plasma poorly compared to a variant defective only in PK-binding. In plasma, HK deficiency appeared to have a greater deleterious effect on FXI activation than PK activation. Human HK corrected the defect in arterial thrombus formation in HK-deficient mice poorly due to a specific defect in binding to mouse FXI. CONCLUSION: Clinical observations indicate FXI is required for hemostasis, while HK is not. Yet, the HK-FXI interaction is required for contact activation-induced clotting in vitro and in vivo suggesting an important role in thrombosis and perhaps other FXI-related activities.

A clinical evaluation of patients with known mutations (plasminogen and factor XII) with a focus on prophylactic treatment.

BACKGROUND: Hereditary angioedema with normal C1-inhibitor (HAE-nC1-INH) is a rare genetic disease. The symptoms can resemble other forms of hereditary angioedema (HAE), but the specific laboratory values are inconspicuous. The knowledge about treatment strategies in HAE-nC1-INH remains insufficient; most of the drugs are only licensed and approved for other types of HAE. METHODS: An analysis of all patients with HAE-nC1-INH was carried out in a certified angioedema treatment center in southern Germany. Only patients with a confirmed HAE-nC1-INH mutation were included. The impact of disease was monitored with validated questionnaires. RESULTS: Eighteen patients were included: two families with a factor XII mutation and seven families with a plasminogen mutation. All individuals received icatibant for on-demand therapy-efficient treatment response was reported. Three patients were severely affected, and prophylaxis was initiated with lanadelumab. According to the questionnaires, the clinical course and symptoms improved significantly under this prophylactic regime. CONCLUSION: This is one of the first descriptions of the clinical outcomes as a response to prophylactic treatment with lanadelumab in HAE-nC1-INH patients with a known mutation. The therapeutic management of HAE-1 and HAE-2 should also be the basis of HAE-nC1-INH, including prophylaxis.

Inflammation and Coagulation are Two Interconnected Pathophysiological Pathways in Atrial Fibrillation Pathogenesis.

Introduction: Atrial fibrillation (AF) is associated with elevated levels of clotting factors such as tissue factor (TF) and factor XII (FXII). Various inflammation markers, such as interleukin-6 (IL-6), tumor necrosis factor-α (TNF- α), and high-sensitive C-reactive protein (hs-CRP), have also been associated with AF. This study explores the relationship between inflammation markers and coagulation activity, including their impact on heart structural changes in these patients. Methods: We observed 283 patients with nonvalvular AF who underwent a complete examination at admission, but only 183 patients have successful cardioversion. As a control group, similar patients without AF were examined. The markers of the coagulation and inflammation were studied by ELISA on the analyzer "Stat Fax 303 Plus". Studies were conducted using l statistical package SPSS 13.0. Results: It was revealed that patients with AF had significantly higher levels of hs-CRP, IL-6, and TNF-α and had elevated levels of TF and FXII compared with control group. The moderate correlations were observed between IL-6 and left atrial diameter (LAD), IL-6 and LA stiffness, hs-CRP and left atrial volume (LAV), TF and LAV. Conclusion: We have demonstrated that patients with AF have the relationship between elevated levels of inflammatory markers and coagulation activity, which contributes to structural atrial remodeling.

Elevated plasma FXII is associated with disease activity in ANCA-associated vasculitis: A Retrospective Cross-Sectional Study in Western China.

This study examined whether plasma FXII levels reflect disease activity in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Plasma FXII levels were detected by ELISA in 127 patients with AAV, and their associations with disease activity and plasma myeloperoxidase (MPO)-ANCA titre were examined. Immunofluorescent co-staining of FXII and neutrophils was performed on the renal tissues of patients with AAV. MPO expression in renal biopsy tissues was determined by immunohistochemical staining. The association between plasma FXII levels and histological activity was assessed in 82 patients who underwent kidney biopsy. Plasma FXII levels were considerably increased in patients with clinically active AAV compared to those in clinical remission and healthy individuals. Plasma FXII levels correlated positively with creatinine (r = 0.377), CRP (r = 0.222), urine red blood cell (r = 0.203), serum MPO-ANCA titer (r = 0.353), white blood cell (r = 0.194), percentage of glomeruli with crescents (P = 0.001), capillary breaks (P = 0.001), interstitial inflammation (P < 0.001) and fibrinoid necrosis (p < 0.001) on kidney biopsy. The plasma FXII optimal cut-off value for evaluating AAV activity was 24.5 µg/mL (sensitivity = 0.81, specificity = 0.82, P = 0.0001), which was superior to that achieved using conventional serologic biomarkers. Co-expression of FXII and neutrophils was higher, with increased MPO expression, in renal tissue with pathologically active AAV than that observed in pathologically inactive tissues. In conclusion, elevated plasma FXII levels reflect AAV clinical and histologic activity, and can serve as markers of active AAV.

"Familial Multiple Coagulation Factor Deficiencies of FXI and FXII in an Asymptomatic Saudi Woman".

Factor XI deficiency (FXI) is the third most common coagulation factor deficiency after hemophilia A and B, ie, in the hierarchy after factors VIII and IX, taking into account von Willebrand's factor deficiency, as bleeding disorders are higher than in hemophilia C. Factor XII deficiency (FXII) is a congenital condition, inherited in the vast majority of cases in an autosomal recessive manner, more often associated with thromboembolic complications. A combination of both factor deficiencies has been found very rarely, and it can be familial multiple coagulation factor deficiency (FMCFD). This study reports the case of a 39-year-old woman from Saudi Arabia who had the combination of FXI and FXII deficiencies, known to be on treatment for hypothyroidism and was referred to a hematology clinic with an incidental finding of prolonged activated partial thromboplastin time (aPTT). Although there was no history of bleeding tendency, her siblings had a family history of an unknown type of bleeding disorder. On physical examination, the patient did not show any bruising, petechiae, or ecchymosis. The aPTT was 69 seconds (27-38) with normal use of other hemostatic agents and was corrected after a 50:50 mixing study. Intrinsic coagulation factors were evaluated, and they revealed severe FXI and moderate FXII deficiencies. Due to a strong family history, the patient was diagnosed with FMCFD. In conclusion, familial combined multiple clotting factor deficiency (FCMFD) is a rare condition that requires attention and reporting. The management strategy in such cases has not been well studied, especially in the long-term symptomatic patient with severe but asymptomatic combined FXI and FXII deficiencies, which is an area for review and further study.

Factor XII promotes the thromboinflammatory response in a rat model of venoarterial extracorporeal membrane oxygenation.

BACKGROUND: Factor XII (FXII) is a multifunctional protease capable of activating thrombotic and inflammatory pathways. FXII has been linked to thrombosis in extracorporeal membrane oxygenation (ECMO), but the role of FXII in ECMO-induced inflammatory complications has not been studied. We used novel gene-targeted FXII- deficient rats to evaluate the role of FXII in ECMO-induced thromboinflammation. METHODS: FXII-deficient (FXII-/-) Sprague-Dawley rats were generated using CRISPR/Cas9. A minimally invasive venoarterial (VA) ECMO model was used to compare wild-type (WT) and FXII-/- rats in 2 separate experimental cohorts: rats placed on ECMO without pharmacologic anticoagulation and rats anticoagulated with argatroban. Rats were maintained on ECMO for 1 hour or until circuit failure occurred. Comparisons were made with unchallenged rats and rats that underwent a sham surgical procedure without ECMO. RESULTS: FXII-/- rats were maintained on ECMO without pharmacologic anticoagulation with low resistance throughout the 1-hour experiment. In contrast, WT rats placed on ECMO without anticoagulation developed thrombotic circuit failure within 10 minutes. Argatroban provided a means to maintain WT and FXII-/- rats on ECMO for the 1-hour time frame without thrombotic complications. Analyses of these rats demonstrated that ECMO resulted in increased neutrophil migration into the liver that was significantly blunted by FXII deficiency. ECMO also resulted in increases in high molecular weight kininogen cleavage and complement activation that were abrogated by genetic deletion of FXII. CONCLUSIONS: FXII initiates hemostatic system activation and key inflammatory sequelae in ECMO, suggesting that therapies targeting FXII could limit both thromboembolism and inopportune inflammatory complications in this setting.

An evolutionary history of F12 gene: Emergence, loss, and vulnerability with the environment as a driver.

In the context of macroevolutionary transitions, environmental changes prompted vertebrates already bearing genetic variations to undergo gradual adaptations resulting in profound anatomical, physiological, and behavioral adaptations. The emergence of new genes led to the genetic variation essential in metazoan evolution, just as was gene loss, both sources of genetic variation resulting in adaptive phenotypic diversity. In this context, F12-coding protein with defense and hemostatic roles emerged some 425 Mya, and it might have contributed in aquatic vertebrates to the transition from water-to-land. Conversely, the F12 loss in marine, air-breathing mammals like cetaceans has been associated with phenotypic adaptations in some terrestrial mammals in their transition to aquatic lifestyle. More recently, the advent of technological innovations in western lifestyle with blood-contacting devices and harmful environmental nanoparticles, has unfolded new roles of FXII. Environment operates as either a positive or a relaxed selective pressure on genes, and consequently genes are selected or lost. FXII, an old dog facing environmental novelties can learn new tricks and teach us new therapeutic avenues.

Is there a role for bradykinin in cerebral malaria pathogenesis?

Malaria is a parasitic disease of global health significance and a leading cause of death in children living in endemic regions. Although various Plasmodium species are responsible for the disease, Plasmodium falciparum infection accounts for most severe cases of the disease in humans. The mechanisms of cerebral malaria pathogenesis have been studied extensively in humans and animal malaria models; however, it is far from being fully understood. Recent discoveries indicate a potential role of bradykinin and the kallikrein kinin system in the pathogenesis of cerebral malaria. The aim of this review is to highlight how bradykinin is formed in cerebral malaria and how it may impact cerebral blood-brain barrier function. Areas of interest in this context include Plasmodium parasite enzymes that directly generate bradykinin from plasma protein precursors, cytoadhesion of P. falciparum infected red blood cells to brain endothelial cells, and endothelial cell blood-brain barrier disruption.

New Therapeutic Targets for the Prevention and Treatment of Venous Thromboembolism With a Focus on Factor XI Inhibitors.

FXI (factor XI) and FXII (factor XII) have emerged as targets for new anticoagulants that have the potential to be both more efficacious and safer than the currently available direct oral anticoagulants for the prevention and treatment of venous thromboembolism. In this review, we discuss the role of FXI and FXII in the pathogenesis of venous thromboembolism, explain why FXI is a better target, and explain why FXI inhibitors have potential advantages over currently available anticoagulants. Finally, we describe the FXI inhibitors under development and discuss their potential to address unmet needs in venous thromboembolism management.

Contact system and intrinsic pathway activation in patients with advanced pancreatic cancer: a prospective cohort study.

BACKGROUND: Despite high risk of venous thromboembolism (VTE) in patients with pancreatic cancer, there are little data on contact system activation in these patients. OBJECTIVES: To quantify contact system and intrinsic pathway activation and subsequent VTE risk in patients with pancreatic cancer. METHODS: Patients with advanced pancreatic cancer were compared with controls. Blood was drawn at baseline and patients were followed for 6 months. Complexes of proteases with their natural inhibitors, C1-esterase inhibitor (C1-INH), antithrombin (AT), or alpha-1 antitrypsin (α1at), were measured for complexes containing kallikrein (PKa:C1-INH), factor (F)XIIa (FXIIa:C1-INH), and FXIa (FXIa:C1-INH, FXIa:AT, FXIa:α1at). The association of cancer with complex levels was assessed in a linear regression model, adjusted for age, sex, and body mass index. In a competing risk regression model, we assessed associations between complex levels and VTE. RESULTS: One hundred nine patients with pancreatic cancer and 22 controls were included. The mean age was 66 years (SD, 8.4) in the cancer cohort and 52 years (SD, 10.1) in controls. In the cancer cohort, 18 (16.7%) patients developed VTE during follow-up. In the multivariable regression model, pancreatic cancer was associated with increased complexes of PKa:C1-INH (P < .001), FXIa:C1-INH (P < .001), and FXIa:AT (P < .001). High FXIa:α1at (subdistribution hazard ratio, 1.48 per log increase; 95% CI, 1.02-2.16) and FXIa:AT (subdistribution hazard ratio, 2.78 highest vs lower quartiles; 95% CI, 1.10-7.00) were associated with VTE. CONCLUSION: Complexes of proteases with their natural inhibitors were elevated in patients with cancer. These data suggest that the contact system and intrinsic pathway activation are increased in patients with pancreatic cancer.