Clot Maximum Absorbance Research Articles

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

BackgroundObesity 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. ObjectivesTo examine fibrin clot and lysis parameters in Roux-en-Y gastric bypass (RYGB) patients before and after surgery. MethodsThe 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. ResultsRYGB 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. ConclusionRYGB 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.

Maturity onset diabetes of the young and fibrin-related thrombosis risk.

Background:Fibrin network characteristics determine predisposition to cardiovascular disease (CVD). Individuals with type 1 (T1DM) and type 2 diabetes mellitus (T2DM) have higher risk of CVD and display deranged fibrin network structure. Those with maturity onset diabetes of the young (MODY) may also be at increased risk but their fibrin clot properties have not been studied.Methods:Plasma clots properties from 13 individuals with HNF1A-MODY, 12 matched-individuals with T2DM and 12 with T1DM were studied using a validated turbidimetric assay and confocal microscopy. Plasma levels of fibrinogen, plasminogen activator inhibitor-1, complement C3 and C-reactive protein were also measured.Results:MODY clot maximum absorbance was 0.37 ± 0.03 AU, similar to T1DM (0.32 ± 0.03 AU; p = 0.26), but lower than T2DM (0.49 ± 0.03 AU; p = 0.02), with confocal microscopy confirming structural differences. Clot lysis time in MODY was similar to T1DM (456 ± 50 and 402 ± 20 s, respectively; p = 0.09) but shorter than T2DM (588 ± 58 s; p = 0.006). Comparing inflammatory/thrombotic proteins in HNF1A-MODY and T2DM, C3 levels were lower in MODY than T2DM (0.58 ± 0.09 and 0.80 ± 0.1 mg/ml, respectively; p < 0.01).Conclusions:HNF1A-MODY fibrin network alterations are at least as pronounced as in T1DM but less thrombotic than T2DM clots. Differences in fibrin clot characteristics comparing HNF1A-MODY and T2DM may, in part, relate to lower C3 levels.

Increased levels of histidine-rich glycoprotein are associated with the development of post-thrombotic syndrome

Denser fibrin networks which are relatively resistant to lysis can predispose to post-thrombotic syndrome (PTS). Histidine-rich glycoprotein (HRG), a blood protein displaying antifibrinolytic properties, is present in fibrin clots. We investigated whether HRG may affect the risk of PTS in relation to alterations to fibrin characteristics. In venous thromboembolism (VTE) patients, we evaluated plasma HRG levels, plasma clot permeability, maximum absorbance, clot lysis time and maximum rate of increase in D-dimer levels released from clots after 3 months of the index event. We excluded patients with cancer and severe comorbidities. After 2 years of follow-up, 48 patients who developed PTS had 18.6% higher HRG at baseline. Baseline HRG positively correlated with clot lysis time, maximum absorbance, and thrombin-activatable fibrinolysis inhibitor (TAFI) activity but was inversely correlated with plasma clot permeability and maximum rate of increase in D-dimer levels released from clots. On multivariate regression model adjusted for age, fibrinogen and glucose, independent predictors of PTS were recurrent VTE, baseline HRG level, and TAFI activity. VTE recurred in 45 patients, including 30 patients with PTS, and this event showed no association with elevated HRG. Our findings suggest that increased HRG levels might contribute to the development of PTS, in part through prothrombotic fibrin clot properties.

The ABO Locus is Associated with Increased Fibrin Network Formation in Patients with Stable Coronary Artery Disease.

The ABO locus has been associated with increased risk of myocardial infarction (MI) in patients with coronary artery disease (CAD), but the underlying mechanisms are unknown. As altered fibrin clot structure has been demonstrated to predict MI in CAD patients, we examined the association between the ABO risk variant and fibrin clot properties, and investigated the effects of other CAD-associated risk variants. We included 773 stable CAD patients. Patients were genotyped for 45 genome-wide CAD risk variants, including rs495828 at the ABO locus. We used a genetic risk score (GRS) for CAD calculated as the weighted sum of the number of risk alleles based on all 45 variants. Fibrin clot properties were evaluated using a turbidimetric assay. We studied clot maximum absorbance, a measure of clot density and fiber thickness, together with clot lysis time, an indicator of fibrinolysis potential. The rs495828 risk allele was present in 13.2% of patients and associated with higher clot maximum absorbance (adjusted effect size per risk allele: 1.05 [1.01 - 1.09], p = 0.01) but not with clot lysis time (p = 0.97). The rs12936587 (p = 0.04), rs4773144 (p = 0.02), and rs501120 (p = 0.04) were associated with clot lysis time; however, after Bonferroni correction, no significant associations were found between any of the remaining 44 CAD-associated variants and fibrin clot properties. The GRS was not associated with fibrin clot properties (p-values > 0.05). The ABO risk allele was associated with a more compact fibrin network in stable CAD patients, which may represent a mechanism for increased MI risk in ABO risk variant carriers.

Prothrombotic fibrin network characteristics in patients with acromegaly: a novel mechanism for vascular complications.

There remains increased cardiovascular mortality in patients with acromegaly. This study aims to evaluate whether GH/IGF-1 excess increases vascular disease by adversely affecting fibrin network characteristics. Cross-sectional study in 40 patients with acromegaly (21 males, age 53 ± 13 years) and 40 age/gender-matched controls. Clot structure was analysed using a validated turbidimetric assay and fibrin networks were visualised by laser scanning confocal microscopy (LSCM). Metabolic profile parameters, body composition, plasma fibrinogen and PAI-1 were also assessed. Twenty-two patients had active acromegaly and 18 were in remission. There was no difference in qualitative patient characteristics between the two groups. Both groups had less favourable body composition and cardiovascular risk profile compared with controls. Despite no difference in clot formation and lysis parameters between the two patient groups, active disease patients had higher fibrinogen and clot maximum absorbance compared with controls, after adjusting for BMI (3.8 ± 0.2 vs 2.6 ± 0.2 mg/mL, P < 0.001; and 0.39 ± 0.02 vs 0.33 ± 0.01 arbitrary units, P = 0.03, respectively). Patients in remission had higher fibrinogen compared with controls following adjustment for BMI (3.3 ± 0.2 vs 2.6 ± 0.2 mg/mL, P = 0.02) but not clot maximum absorbance (0.35 ± 0.03 vs 0.33 ± 0.02 arbitrary units, P = 0.6). LSCM showed increased fibrin network density only in active disease patients, consistent with turbidimetric analysis. In addition to active disease, BMI, fat mass and skinfold thickness were associated with higher clot density and longer lysis time. Patients with active acromegaly have more compact clots, thus conferring increased thrombosis risk. Prothrombotic fibrin networks may represent one mechanism for enhanced vascular risk in active acromegaly.

Reduced Plasma Magnesium Levels in Type-1 Diabetes Associate with Prothrombotic Changes in Fibrin Clotting and Fibrinolysis.

Individuals with type-1 diabetes mellitus (T1DM) have a higher risk of thrombosis and low plasma magnesium concentrations. As magnesium is a known regulator of fibrin network formation, we investigated potential associations between fibrin clot properties and plasma magnesium concentrations in 45 individuals with T1DM and 47 age- and sex-matched controls without diabetes. Fibrin clot characteristics were assessed using a validated turbidimetric assay and associations with plasma magnesium concentration were examined. Plasma concentrations of fibrinogen, plasminogen activator inhibitor-1 (PAI-1), and lipids were measured and fibrin fiber diameters assessed using scanning electron microscopy. Fibrin clot maximum absorbance was unchanged in subjects with T1DM compared with controls, while lysis time was prolonged ( p = 0.0273). No differences in fibrin fiber diameters or in lipid profile were observed between T1DM and controls. PAI-1 concentration was lower in the T1DM group compared with the controls ( p = 0.0232) and positively correlated with lysis time ( p = 0.0023). Plasma magnesium concentration was lower in the T1DM group compared with controls ( p < 0.0001). Magnesium concentration negatively correlated with clot maximum absorbance ( p = 0.0215) and lysis time ( p = 0.0464). A turbidimetric fibrin clot lysis assay performed in a purified system that included PAI-1 and 0 to 3.2 mM Mg 2+ showed a shortening of lysis time with increasing Mg 2+ concentrations ( p = 0.0004). Our findings reveal that plasma magnesium concentration is associated with changes in fibrin clot and lysis parameters.

Imbalance between Fibrin Clot Formation and Fibrinolysis Predicts Cardiovascular Events in Patients with Stable Coronary Artery Disease.

Despite long-term antiplatelet therapy with aspirin, recurrent cardiovascular events remain common in patients with coronary artery disease (CAD). We aimed to determine whether fibrin network characteristics are predictive of vascular events in patients with stable CAD treated with aspirin monotherapy. We included 786 patients with angiographically documented CAD and either prior myocardial infarction, type 2 diabetes mellitus, or both. Median follow-up time was 3 years. At inclusion, fibrin clot properties were evaluated using a turbidimetric assay and the following clot parameters were studied: (1) maximum absorbance, a measure of clot density and fiber thickness; (2) lysis time, assessing fibrinolysis potential; and (3) area under the curve (AUC), a measure of clot formation and lysis. The primary endpoint was the composite of nonfatal myocardial infarction, ischemic stroke, and cardiovascular death. Hazard ratios (HRs) were estimated using multivariable Cox proportional hazards regression. A total of 70 primary endpoints occurred. The primary endpoint occurred more frequently in CAD patients with increased clot AUC (crude HR for first vs. fourth quartile: 2.4 [95% confidence interval 1.2-4.6], p = 0.01). This finding remained significant after adjusting for potential confounders (adjusted HR: 2.4 [1.2-4.8], p = 0.01). Neither clot maximum absorbance nor lysis time showed significant association with future vascular events (adjusted HR for maximum absorbance 1.8 [0.9-3.7]; p = 0.09) and lysis time (1.6 [0.8-3.0]; p = 0.18). We demonstrate that increased clot AUC predicts future cardiovascular events in stable CAD patients receiving aspirin monotherapy.

SUN-075 Higher Fibrinogen and Clot Density in Patients with Acromegaly: The Role of Adverse Body Composition to the Increased Thrombotic Potential

Introduction: Patients with acromegaly have increased mortality rates compared with the general population, particularly due to cardiovascular and cerebrovascular disease. We hypothesized that one mechanism through which GH/IGF-1 excess increases vascular disease is via effects on hemostasis/fibrinolysis and subsequent clot formation. Patients and Methods: We conducted a case-control study in 40 patients with acromegaly and 40 age and sex-matched healthy controls. We measured parameters of metabolic profile, fibrinogen using the Clauss method and performed clot structure analysis using a validated turbidimetric assay. Results: Forty patients with acromegaly (21 males, mean age 53±13 years) were recruited. 30% had active disease (GH>1mcg/L and IGF-1 above the reference range), 27.5% had dichotomous GH/IGF-1 results and 42.5% were in remission. Compared with controls, patients had a less favorable metabolic profile with higher BMI (30±5.5 vs. 26.7±4.1 kg/m2, p=0.003), waist/hip ratio (0.91±0.08 vs. 0.87±0.08, p=0.045), total fat mass (29.8±10 vs. 23.4±10 kg, p=0.003) and triglycerides (1.5±0.9 vs. 1.1±0.5 mmol/L, p=0.02). Significantly higher fibrinogen levels were found in the patient group (3.59±1.56 vs. 2.58±0.37 mg/ml, p<0.001). Patients had raised clot maximum absorbance (a measure of clot density), compared with controls (0.38±0.13 vs. 0.32±0.08 arbitrary units, p=0.02). Regarding fibrinolysis, no statistical difference in clot lysis times was found between the two groups, however patients with acromegaly had numerically more prolonged lysis times compared with controls at all lysis stages (times from maximum clot optic density to 25%, 50% and 75% lysis were respectively: 15.5±16.6 vs. 10.4±5.4 min, p=0.067; 29±22.2 vs. 23.2±11.8 min, p=0.15; and 40.8±22.5 vs. 35.3±12.5 min, p=0.18). In the patient group smoking was associated with higher fibrinogen levels (coefficient 0.8, p=0.03), higher clot density (coefficient 0.07, p=0.035) and reduced lag time for clot formation (coefficient -39.3, p=0.02). Diagnosis of diabetes, higher BMI and total fat mass were associated with more prolonged lysis time (coefficients 13, p=0.04; 1.7, p=0.007; and 0.9, p=0.009 respectively). Total fat mass was also positively associated with higher clot density (coefficient 0.005, p=0.01). Additionally, a positive correlation was found between fibrinogen and clot density (coefficient 0.05, p<0.001). Conclusions: Patients with acromegaly demonstrate abnormalities in clot structure properties, particularly in clot formation, with higher fibrinogen and clot density, suggesting increased thrombotic potential with more compact clots. The adverse metabolic profile of these patients is a contributing factor to these clotting abnormalities. Prospective studies are required to assess whether hemostatic abnormalities in acromegaly are reversible after successful treatment.

Potential mechanism for increased risk of premature vascular disease in long-term survivors of primary brain tumours with established hormone deficits

BackgroundLong-term survivors of childhood-onset brain tumours have increased mortality rates, even after excluding deaths related to recurrence or regression of the original tumour. In particular, there is an increased risk of premature vascular disease by mechanisms that remain unclear. We tested our hypothesis that a thrombotic fibrin network profile is one mechanism for the increased vascular risk in this population. MethodsWe undertook a cross-sectional study in 33 patients (19 men, mean age 31·5 years [SD 14·2]) with previous history of primary brain tumours of either childhood or adulthood onset and 33 age-matched and sex-matched healthy controls. We performed clot structure analysis using a validated turbidimetric assay and also assessed plasma concentrations of thrombotic and inflammatory vascular markers including fibrinogen, C-reactive protein (CRP), and complement C3. The mean time from brain tumour diagnosis to the time of the study was 8·9 years (SD 6·2). FindingsAll patients had cranial radiotherapy, whereas 25 (76%) and 13 (39%) had additional surgery and chemotherapy, respectively. 31 patients (94%) had growth hormone deficiency, five (15%) had deficiences in luteinising hormone and follicle-stimulating hormone, four (12%) in adrenocorticotropic hormone, and two (6%) in thyroid-stimulating hormone. Patients had raised clot maximum absorbance (a measure of clot density) compared with controls (mean 0·412 arbritary units [SD 0·10] vs 0·277 [0·09], p<0·0001), increased clot lysis time (an indicator of fibrinolysis potential) (3695 s [731] vs 2720 [636], p<0·0001), and larger lysis area (a complex measure of clot formation time, clot density, and lysis potential) (1949 arbitrary units [1390] vs 906 [704], p<0·0001). Despite differences in fibrin network characteristics, fibrinogen concentrations were similar in patients and controls. Plasma CRP was higher in patients than in controls (3·08 mg/L [4·25] vs 0·78 [1·08], p=0·006) with similar findings for C3 (0·75 mg/mL [0·13] vs 0·67 [0·13], p=0·027). InterpretationWe demonstrate, for the first time to our knowledge, that survivors of brain tumours with hypopituitarism display a thrombotic fibrin network profile, providing one mechanism for the increased vascular risk in this population. These changes are not related to altered fibrinogen concentrations suggesting that other plasma proteins or qualitative changes in the proteins might contribute to the observed differences. Further longitudinal studies are required to clarify whether optimisation of the hormonal profile results in amelioration of the thrombotic environment in this population. FundingPfizer (investigator-initiated research grant).

203 Ticagrelor and Clopidogrel Attenuate the Prothrombotic State induced by Bacterial Endotoxaemia

Introduction In the PLATO study, the novel platelet P2Y 12 inhibitor ticagrelor was unexpectedly associated with fewer deaths following pulmonary infections and sepsis than clopidogrel. The risk of myocardial infarction or stroke is greatly increased following bacteremia, which can create an inflammatory environment associated with thrombotic changes in the fibrin network. We therefore aimed to determine whether greater P2Y 12 inhibition by ticagrelor compared to clopidogrel would result in greater reduction in platelet-leukocyte interactions, thereby reducing inflammatory responses and the prothrombotic state associated with inflammation. Methods Thirty healthy volunteers were randomised to ticagrelor 90 mg bd (n = 10), clopidogrel 75 mg od (n = 10) or no antiplatelet medications (controls; n = 10) for one week. E. coli endotoxin (LPS) 2 ng/kg was then administered intravenously. Plasma fibrin clot density was assessed ex vivo using a validated turbidimetric assay and D-dimer was measured using the INNOVANCE assay. Fibrin clot structure was investigated ex vivo using scanning electron microscopy. Fibrin network density and fibrin diameter were determined using imageJ software. Informed consent was obtained. The study was approved by a medical ethics committee and funded by the Medical Research Council (UK). Results In the control group, fibrin clot maximum absorbance (an indicator of fibrin clot density), increased by 109 ± 37% at 6 h after LPS administration compared to baseline (p Conclusion To our knowledge, this is the first study to show that ticagrelor reduces prothrombotic changes in fibrin clot structure induced by bacterial endotoxaemia in vivo . The greater potency of the effects of ticagrelor compared to clopidogrel provides a potential mechanism for the reduced mortality following sepsis observed in the PLATO study.

Abstract 16668: The Effects of Dabigatran on Fibrin Network Structure and Lysis: A Simple Technique to Monitor Efficacy of Treatment?

Background: Thrombus formation represent the final step in the atherothrombotic process and occurs secondary to a complex interaction between platelets and coagulation factors. Increased platelet reactivity and enhanced clot formation can both determine predisposition to vascular events. Direct platelet inhibition by modern antiplatelet therapy is now effective at controlling the cellular component of coagulation but the fibrin network is not generally targeted in arterial disease. Our aim was to investigate the effects of dabigatran on fibrin network characteristics in individuals dual antiplatelet therapy (DAPT). Methods: This was a prospective, randomized, double-blind study conducted in 30 patients on maintenance (at least 30 days) DAPT with aspirin (81mg/day) and clopidogrel (75mg/day). Patients were randomized to receive either dabigatran 150mg bid or matching placebo for 7 days. Fibrin clot properties were studied using a validated turbidimetric assay and the following parameters were recorded: lag phase and time to full clot formation, both of which measure clotting potential; clot maximum absorbance, representing fibrin network density and fibre thickness; clot lysis time to assess fibrinolytic efficiency. Results: Dabigatran treatment was associated with an increase in lag phase, compared with baseline, of 1013±167 sec , whereas no difference was detected in placebo treated patients (-17±14 sec, p&lt;0.001 for dabigatran vs placebo). Similar results were obtained for clot formation time with an increase of 240±37 sec in dabigatran treated patients with no change following placebo treatment (-24±18 sec; p&lt;0.001 comparing the two groups). The change in clot maximum absorbance after dabigatran and placebo treatment showed no differences (-0.02±0.01 and 0.00±0.01 au, respectively; p=0.2) and clot lysis time was similar. Conclusions: In patients on DAPT with aspirin and clopidogrel, additional treatment with dabigatran delays fibrin clot formation without affecting fibrinolysis. Therefore, triple therapy with dabigatran may be one option to reduce thrombosis potential in high risk individuals. Moreover, our assay, which can be conducted on stored samples, offers the opportunity to monitor response to dabigatran therapy.

The influence of type 2 diabetes on fibrin clot properties in patients with coronary artery disease.

Type 2 diabetes mellitus (T2DM) increases the risk of coronary thrombosis and both conditions are associated with altered fibrin clot properties. However, the influence of T2DM on fibrin clot properties in patients with coronary artery disease (CAD) remains unclear. We aimed to investigate the influence of T2DM on fibrin clot properties in patients with CAD. Fibrin clot structure and fibrinolysis were investigated in 581 CAD patients (148 with T2DM) using turbidimetric assays, confocal and scanning electron microscopy. Clots made from plasma and plasma-purified fibrinogen were studied, and plasma levels of inflammatory markers were analysed. T2DM patients had increased clot maximum absorbance compared with non-diabetic patients (0.36 ± 0.1 vs 0.33 ± 0.1 au; p=0.01), displayed longer lysis time (804 [618;1002] vs 750 [624;906] seconds; p=0.03) and showed more compact fibrin structure assessed by confocal and electron microscopy. Fibrinogen levels were elevated in T2DM (p< 0.001), but clots made from purified fibrinogen showed no differences in fibrin properties in the two populations. Adjusting for fibrinogen levels, T2DM was associated with C-reactive protein and complement C3 plasma levels, with the former correlating with clot maximum absorbance (r=0.24, p< 0.0001) and the latter with lysis time (r=0.30, p< 0.0001). Independent of fibrinogen levels, females had more compact clots with prolonged lysis time compared with males (all p-values< 0.001). In conclusion, T2DM is associated with prothrombotic changes in fibrin clot properties in patients with CAD. This is related to quantitative rather than qualitative changes in fibrinogen with a possible role for inflammatory proteins.

Fibrin Clot Structure and Platelet Aggregation in Patients with Aspirin Treatment Failure

BackgroundAspirin is a cornerstone in prevention of cardiovascular events and modulates both platelet aggregation and fibrin clot formation. Some patients experience cardiovascular events whilst on aspirin, often termed aspirin treatment failure (ATF). This study evaluated both platelet aggregation and fibrin clot structure in patients with ATF.MethodsWe included 177 stable coronary artery disease patients on aspirin monotherapy. Among these, 116 (66%) had ATF defined as myocardial infarction (MI) whilst on aspirin. Platelet aggregation was assessed by Multiplate® aggregometry and VerifyNow®, whereas turbidimetric assays and scanning electron microscopy were employed to study fibrin clot characteristics.ResultsEnhanced platelet aggregation was observed in patients with ATF compared with non-MI patients following stimulation with arachidonic acid 1.0 mM (median 161 (IQR 95; 222) vs. 97 (60; 1776) AU*min, p = 0.005) and collagen 1.0 µg/mL (293 (198; 427) vs. 220 (165; 370) AU*min, p = 0.03). Similarly, clot maximum absorbance, a measure of fibrin network density, was increased in patients with ATF (0.48 (0.41; 0.52) vs. 0.42 (0.38; 0.50), p = 0.02), and this was associated with thinner fibres (mean ± SD: 119.7±27.5 vs. 127.8±31.1 nm, p = 0.003) and prolonged lysis time (552 (498; 756) vs. 519 (468; 633) seconds; p = 0.02). Patients with ATF also had increased levels of C-reactive protein (CRP) (1.34 (0.48; 2.94) and 0.88 (0.32; 1.77) mg/L, p = 0.01) compared with the non-MI group. Clot maximum absorbance correlated with platelet aggregation (r = 0.31–0.35, p-values<0.001) and CRP levels (r = 0.60, p<0.001).ConclusionsPatients with aspirin treatment failure showed increased platelet aggregation and altered clot structure with impaired fibrinolysis compared with stable CAD patients without previous MI. These findings suggest that an increased risk of aspirin treatment failure may be identified by measuring both platelet function and fibrin clot structure.

Evidence that fibrinogen γ′ regulates plasma clot structure and lysis and relationship to cardiovascular risk factors in black Africans

AbstractFibrinogen γ′ is known to influence fibrin clot structure in purified experimental models, but little is known regarding its influence on clot structure in plasma. Furthermore, the environmental and biological factors that affect its concentration are poorly described. We analyzed fibrinogen γ′, total fibrinogen concentration, and fibrin clot structure in 2010 apparently healthy black South Africans and related them to traditional cardiovascular disease (CVD) risk factors. Fibrinogen γ′ generally increased with increasing fibrinogen concentration, but a decreased γ′/total fibrinogen ratio was found at the highest total fibrinogen concentrations. Clot maximum absorbance increased with total fibrinogen and fibrinogen γ′, but decreased with γ'/total fibrinogen ratio. Clot lysis time showed a stronger relationship with fibrinogen γ′ than with total fibrinogen, whereby increased fibrinogen γ′ delayed clot lysis. CVD risk factors (excluding fibrinogen) explained 20% and 3%, respectively, of the variance in fibrinogen γ′ and the γ′/total fibrinogen ratio, with C-reactive protein making the biggest contribution. More than 50% of the variance in fibrinogen γ′ and γ′/total fibrinogen ratio is explained by factors other than total fibrinogen or other traditional CVD risk factors. Our data show that fibrinogen γ′ modulates plasma clot structure and fibrinolysis and is also influenced by factors other than fibrinogen.

Thyroid Dysfunction and Fibrin Network Structure: A Mechanism for Increased Thrombotic Risk in Hyperthyroid Individuals

Hyperthyroidism is associated with increased thrombosis risk, and fibrin clot structure determines susceptibility to vascular thrombotic events. Our objective was to investigate clot formation and lysis in hyperthyroidism using observational and interventional studies. Ex vivo fibrin clot structure/fibrinolysis and plasma levels of thrombotic/inflammatory markers were investigated in hyperthyroid individuals (n = 24) and matched controls (n = 19), using turbidimetric assays, ELISA, and confocal and electron microscopy. The effects of normalizing thyroid function were analyzed (n = 19) and the role of short-term exogenous hyperthyroidism in healthy volunteers studied (n = 16). Hyperthyroid subjects displayed higher clot maximum absorbance compared with controls (0.41 ± 0.03 and 0.27 ± 0.01 arbitrary units, respectively; P < 0.01), and longer clot lysis time (518 ± 23 and 461 ± 18 sec, respectively; P < 0.05), which correlated with free T(4) levels. Plasma levels of fibrinogen and plasminogen activator inhibitor-1 were significantly higher in patients compared with controls. Normalizing thyroid function in 19 subjects was associated with lower maximum absorbance and shorter lysis time, accompanied by reduction in fibrinogen, plasminogen activator inhibitor-1, and D-dimer levels. Complement C3, but not C-reactive protein, levels were higher in hyperthyroid subjects compared with controls (0.92 ± 0.05 and 0.64 ± 0.03 g/liter, respectively; P < 0.01), correlated with clot structure parameters, and decreased after intervention. Confocal and electron microscopy confirmed more compact clots and impaired fibrinolysis during hyperthyroidism. Exogenous hyperthyroidism in healthy volunteers had no effect on any of the clot structure parameters. Endogenous hyperthyroidism is associated with more compact clots and resistance to fibrinolysis ex vivo, related to the degree of hyperthyroidism and C3 plasma levels, and these changes are modulated by achieving euthyroidism. Altered clot structure/lysis may be one mechanism for increased thrombotic risk in hyperthyroidism.