Affimer proteins as a tool to modulate fibrinolysis, stabilize the blood clot, and reduce bleeding complications.

Bleeding complications secondary to surgery, trauma, or coagulation disorders are important causes of morbidity and mortality. Although fibrin sealants are considered to minimize blood loss, this is not widely adopted because of its high cost and/or risk for infection. We present a novel methodology employing nonantibody fibrinogen-binding proteins, termed Affimers, to stabilize fibrin networks with the potential to control excessive bleeding. Two fibrinogen-specific Affimer proteins, F5 and G2, were identified and characterized for their effects on clot structure/fibrinolysis, using turbidimetric and permeation analyses and confocal and electron microscopy. Binding studies and molecular modeling identified interaction sites, whereas plasmin generation assays determined effects on plasminogen activation. In human plasma, F5 and G2 prolonged clot lysis time from 9.8 ± 1.1 minutes in the absence of Affimers to 172.6 ± 7.4 and more than 180 minutes (P < .0001), respectively, and from 7.6 ± 0.2 to 28.7 ± 5.8 (P < .05) and 149.3 ± 9.7 (P < .0001) minutes in clots made from purified fibrinogen. Prolongation in fibrinolysis was consistent across plasma samples from healthy control patients and individuals at high bleeding risk. F5 and G2 had a differential effect on clot structure and G2 profoundly altered fibrin fiber arrangement, whereas F5 maintained physiological clot structure. Affimer F5 reduced fibrin-dependent plasmin generation and was predicted to bind fibrinogen D fragment close to tissue plasminogen activator (tPA; residues γ312-324) and plasminogen (α148-160) binding sites, thus interfering with tPA-plasminogen interaction and representing 1 potential mechanism for modulation of fibrinolysis. Our Affimer proteins provide a novel methodology for stabilizing fibrin networks with potential future clinical implications to reduce bleeding risk.

Fibrinogen interaction with complement C3: a potential therapeutic target to reduce thrombosis risk.

Complement C3 binds fibrinogen and compromises fibrin clot lysis thereby enhancing thrombosis risk. We investigated the role of fibrinogen-C3 interaction as a novel therapeutic target to reduce thrombosis risk by analysing: i) consistency in the fibrinolytic properties of C3, ii) binding sites between fibrinogen and C3 and iii) modulation of fibrin clot lysis by manipulating fibrinogen-C3 interactions. Purified fibrinogen and C3 from the same individuals (n=24) were used to assess inter-individual variability in the anti-fibrinolytic effects of C3. Microarray screening and molecular modelling evaluated C3 and fibrinogen interaction sites. Novel synthetic conformational proteins, termed Affimers, were used to modulate C3-fibrinogen interaction and fibrinolysis. C3 purified from patients with type 1 diabetes showed enhanced prolongation of fibrinolysis compared with healthy control protein [195±105 and 522±166 seconds, respectively (p=0.04)], with consistent effects but a wider range (5-51% and 5-18% lysis prolongation, respectively). Peptide microarray screening identified 2 potential C3-fibrinogen interactions sites within fibrinogen ß chain (residues 424-433, 435-445). One fibrinogen-binding Affimer was isolated that displayed sequence identity with C3 in an exposed area of the protein. This Affimer abolished C3-induced prolongation of fibrinolysis (728±25.1 seconds to 632±23.7 seconds, p=0.005) and showed binding to fibrinogen in the same region that is involved in C3-fibrinogen interactions. Moreover, it shortened plasma clot lysis of patients with diabetes, cardiovascular disease or controls by 7-11%. C3 binds fibrinogen ß-chain and disruption of fibrinogen-C3 interaction using Affimer proteins enhances fibrinolysis, which represents a potential novel target tool to reduce thrombosis in high risk individuals.

Inhibition of complement C3 and fibrinogen interaction: a potential novel therapeutic target to reduce cardiovascular disease in diabetes.

BACKGROUND: Enhanced complement C3 incorporation into the fibrin network in diabetes is one mechanism for impaired fibrinolysis and increased thrombosis risk in this condition. Our aim was to develop new strategies to modulate fibrinolysis in diabetes by interfering with fibrin-C3 interaction. METHODS: To modulate interaction between fibrinogen and C3 we used a novel technique by screening fibrinogen with a phage display library of 3 billion random, conformational 9AA peptides (termed adhirons). The effect of high affinity fibrinogen binding adhirons, released by the addition of excess C3, on fibrin clot lysis and structure was assessed in turbidimetric assays. Fibrinogen-C3 interactions were further studied by peptide microarray techniques and modelled with the website PepSite2. FINDINGS: Ten high affinity fibrinogen binding adhirons, released by C3, were available for turbidimetric analysis. One adhiron (A6) was found to have a sequence homology with C3 and studied further. In the absence of C3, adhiron A6 failed to modulate fibrin clot lysis time (mean 644 s [SE 13] and 620 [14] without and with adhiron A6, respectively). However, adhiron A6 abolished C3-induced prolongation of clot lysis, reducing mean lysis time from 728 s (SE 25) to 632 (24) (p=0·01). The peptide microarray screening of C3 identified two peptide motifs within the ß chain of fibrinogen (residues 424-433, 435-445) that bound to C3. PepSite2 predicted that adhiron A6 binds to similar areas on the ß chain of fibrinogen. INTERPRETATION: Using a novel phage display system, we discovered an adhiron that shared sequence homology with C3 and abolished C3-induced prolongation of fibrin clot lysis by interfering with C3-fibrinogen interaction within the ß chain. This technique offers a unique method to identify new therapeutic targets for the reduction of diabetes-specific thrombosis risk. FUNDING: Sir Jules Thorn Charitable Trust.

Hypofibrinolysis in type 2 diabetes: the role of the inflammatory pathway and complement C3.

AIMS/HYPOTHESIS: Plasminogen activator inhibitor-1 (PAI-1) has been regarded as the main antifibrinolytic protein in diabetes, but recent work indicates that complement C3 (C3), an inflammatory protein, directly compromises fibrinolysis in type 1 diabetes. The aim of the current project was to investigate associations between C3 and fibrinolysis in a large cohort of individuals with type 2 diabetes. METHODS: Plasma levels of C3, C-reactive protein (CRP), PAI-1 and fibrinogen were analysed by ELISA in 837 patients enrolled in the Edinburgh Type 2 Diabetes Study. Fibrin clot lysis was analysed using a validated turbidimetric assay. RESULTS: Clot lysis time correlated with C3 and PAI-1 plasma levels (r = 0.24, p < 0.001 and r = 0.22, p < 0.001, respectively). In a multivariable regression model involving age, sex, BMI, C3, PAI-1, CRP and fibrinogen, and using log-transformed data as appropriate, C3 was associated with clot lysis time (regression coefficient 0.227 [95% CI 0.161, 0.292], p < 0.001), as was PAI-1 (regression coefficient 0.033 [95% CI 0.020, 0.064], p < 0.05) but not fibrinogen (regression coefficient 0.003 [95% CI -0.046, 0.051], p = 0.92) or CRP (regression coefficient 0.024 [95% CI -0.008, 0.056], p = 0.14). No correlation was demonstrated between plasma levels of C3 and PAI-1 (r = -0.03, p = 0.44), consistent with previous observations that the two proteins affect different pathways in the fibrinolytic system. CONCLUSIONS/INTERPRETATION: Similarly to PAI-1, C3 plasma levels are independently associated with fibrin clot lysis in individuals with type 2 diabetes. Therefore, future studies should analyse C3 plasma levels as a surrogate marker of fibrinolysis potential in this population.

Changes in fibrin clot properties in patients after Roux-en-Y gastric bypass surgery.

Background: Obesity is a complex condition associated with prothrombotic fibrin networks that are resistant to fibrinolysis. Altered fibrin clot properties enhance cardiovascular risk and associate with a poorer prognosis following acute ischemic events. Bariatric surgery is commonly employed to improve cardiometabolic outcomes in individuals with obesity. However, the effects of this surgical intervention on fibrin clot properties have not been comprehensively studied. Objectives: To examine fibrin clot and lysis parameters in Roux-en-Y gastric bypass (RYGB) patients before and after surgery. Methods: The fibrin clot properties of 32 individuals living with obesity before and 9 months after RYGB surgery were determined using turbidimetric analysis. Correlation and regression analyses were used to identify relationships between clot properties and anthropomorphic and clinical measures. Results: RYGB surgery resulted in a significant reduction in adiposity-associated anthropometric measures as well as improvements in glycemia and lipid profile. Clot maximum absorbance was reduced from 0.43 ± 0.11 at baseline to 0.29 ± 0.10 at 9 months postsurgery (P < .0001), while fibrin clot lysis time failed to show a difference. The change in maximum absorbance was not caused by alterations in fibrinogen levels, while plasminogen activator inhibitor-1 concentration was significantly increased after surgery from 10,560 ± 6681 pg/mL to 15,290 ± 6559 pg/mL (P = .009). Correlation and regression analyses indicated that maximum absorbance was influenced by markers of adiposity as well as glycated hemoglobin and high-sensitivity C-reactive protein concentrations. Conclusion: RYGB surgery led to a decrease in the maximum absorbance of the fibrin clot. Values of maximum absorbance were associated with measures of glycemic control and inflammation. In contrast to previous reports, fibrin clot lysis time was not affected after surgery.

Patients with morbid obesity should not be routinely screened for Cushing's syndrome: Results of retrospective study of patients attending a specialist weight management service.

Cushing's syndrome (CS) is a rare condition which results in multi-system involvement and can lead to significant morbidity and mortality. Screening for CS in patients with obesity has been suggested to identify undiagnosed or occult cases. This study was performed to determine whether CS screening is indicated in a tier 3 weight management centre in the UK. A retrospective review of all patients referred to the weight management service between 2013 and 2016 inclusive was undertaken. A final cohort of 569 patients was obtained. Clinic letters and laboratory databases were used to obtain demographic information, patient characteristics and biochemical results. A total of 387 patients were screened using the 1 mg overnight dexamethasone suppression test (ODST) and 182 patients were screened with two 24-hour urinary free cortisol (UFC) collections. A total of 27 patients had an initial abnormal result, of which 16 underwent further testing and had normal results. Six were reviewed and did not demonstrate any clinical features of CS. Five did not attend their clinic appointments but there were neither concerning features within their referrals, nor subsequent diagnoses of CS made. No patients from this cohort were diagnosed with CS. This study does not support routine CS screening of patients affected by severe obesity referred to a specialist tier 3 weight management service. Clinical assessment should be undertaken first and further investigations performed only if deemed necessary.

Vascular risk in obesity: Facts, misconceptions and the unknown.

Obesity is a major burden on healthcare systems worldwide due to the association with numerous complications, arguably the most important of which are the development of type 2 diabetes and cardiovascular disease. Both are thought to develop from similar origins and occur at variable rates in obese individuals, including those with similar body mass indices. This phenomenon is likely a result of an increased susceptibility for the storage of excess fat in the wrong place, namely, ectopic fat surrounding the liver, pancreas and muscles. This triggers a concatenation of events leading to insulin resistance and inflammation which culminate in an increased atherothrombotic potential due to the dysfunction of vascular endothelial cells causing accelerated atherosclerotic plaque formation and a pro-thrombotic phenotype. The degree of weight loss following different interventions is well documented but it is less widely known what effect weight loss by various means has on the deleterious process mentioned above, in particular their effects on cardiovascular events. This review summarises the processes leading to increased vascular risk in obesity and examines the effects of currently available weight loss strategies on reversing these processes and how this translates to cardiovascular disease.

Effects of dabigatran on the cellular and protein phase of coagulation in patients with coronary artery disease on dual antiplatelet therapy with aspirin and clopidogrel. Results from a prospective, randomised, double-blind, placebo-controlled study.

There is growing interest in understanding the effects of adding an oral anticoagulant in patients on dual antiplatelet therapy (DAPT). Vitamin K antagonists (VKAs) and clopidogrel represent the most broadly utilised oral anticoagulant and P2Y12 receptor inhibitor, respectively. However, VKAs can interfere with clopidogrel metabolism via the cytochrome P450 (CYP) system which in turn may result in an increase in platelet reactivity. Dabigatran is a direct acting (anti-II) oral anticoagulant which does not interfere with CYP and has favourable safety and efficacy profiles compared with VKAs. The pharmacodynamic (PD) effects on platelet reactivity and clot kinetic of adjunctive dabigatran therapy in patients on DAPT are poorly explored. In this prospective, randomised, double-blind, placebo-controlled PD study, patients (n=30) on maintenance DAPT with aspirin and clopidogrel were randomised to either dabigatran 150 mg bid or placebo for seven days. PD testing was performed before and after treatment using four different assays exploring multiple pathways of platelet aggregation and fibrin clot kinetics: light transmittance aggregometry (LTA), multiple electrode aggregometry (MEA), kaolin-activated thromboelastography (TEG) and turbidimetric assays. There were no differences in multiple measures of platelet reactivity investigating purinergic and non-purinergic signaling pathways assessed by LTA, MEA and TEG platelet mapping. Dabigatran significantly increased parameters related to thrombin activity and thrombus generation, and delayed fibrin clot formation, without affecting clot structure or fibrinolysis. In conclusion, in patients on DAPT with aspirin and clopidogrel, adjunctive dabigatran therapy is not associated with modulation of profiles of platelet reactivity as determined by several assays assessing multiple platelet signalling pathways. However, dabigatran significantly interferes with parameters related to thrombin activity and delays fibrin clot formation.

The fibrin network in diabetes: its role in thrombosis risk.

Despite advances in therapy, individuals with diabetes remain at high risk of cardiovascular disease and their clinical prognosis following vascular ischemia is worse than that of individuals with normal glucose metabolism. Current evidence suggests that the enhanced thrombotic environment in diabetes represents a key abnormality contributing to the adverse clinical outcome following vascular occlusion in this population. Thrombus formation occurs following a complex process that encompasses both the cellular (represented by platelets) and fluid phase of coagulation, involving a large number of plasma proteins. In the current review, we discuss some of the abnormalities encountered in coagulation factor levels or activity in diabetes. In particular, we focus on the pathological processes that lead to the formation of compact fibrin networks with increased resistance to lysis. We describe current knowledge on the mechanistic pathways responsible for the increased fibrin­related thrombosis risk in diabetes and explore alternative therapeutic targets. We also briefly cover various management strategies that may help control the enhanced thrombotic milieu in this population of patients at high cardiovascular risk.