Elevated plasma factor VIII enhances venous thrombus formation in rabbits: contribution of factor XI, von Willebrand factor and tissue factor

Elevated plasma levels of factor VIII enhance arterial thrombus formation on erosive smooth muscle cell-rich neointima but not normal intima in rabbits

BACKGROUND

Plaque erosion, a type of coronary atherothrombosis, involves superficial injury to smooth muscle cell (SMC)-rich plaques. Elevated levels of coagulation factor VIII (FVIII) correlate with an increased ischemic heart disease risk. FVIII may contribute to thrombus formation on eroded plaques.

AIMS

We aimed to elucidate the role of elevated FVIII in arterial thrombus formation within SMC-rich neointima in rabbits.

METHODS AND RESULTS

We assessed the effect of recombinant human FVIII (rFVIII) on blood coagulation in vitro and platelet aggregation ex vivo. An SMC-rich neointima was induced through balloon injury to the unilateral femoral artery. Three weeks after the first balloon injury, superficial erosive injury and thrombus formation were initiated with a second balloon injury of the bilateral femoral arteries 45 min after the administration of rFVIII (100 IU/kg) or saline. The thrombus area and contents were histologically measured 15 min after the second balloon injury. rFVIII administration reduced the activated partial thromboplastin time and augmented botrocetin-induced, but not collagen- or adenosine 5'-diphosphate-induced, platelet aggregation. While rFVIII did not influence platelet-thrombus formation in normal intima, it increased thrombus formation on SMC-rich neointima post-superficial erosive injury. Enhanced immunopositivity for glycoprotein IIb/IIIa and fibrin was observed in rFVIII-administered SMC-rich neointima. Neutrophil count in the arterial thrombus on the SMC-rich neointima correlated positively with thrombus size in the control group, unlike the rFVIII group.

CONCLUSIONS

Increased FVIII contributes to thrombus propagation within erosive SMC-rich neointima, highlighting FVIII's potential role in plaque erosion-related atherothrombosis.

Construction and Validation of the Nomogram Based on von Willebrand Factor Predicting Mortality in Patients with Heatstroke

Heatstroke (HS), a severe condition, can develop multiple organ dysfunction syndrome and death. However, at present, no early reliable index exists for risk stratification and prognosis. von Willebrand factor (vWF), a marker of vascular endothelial injury, is a key regulatory target of inflammation and coagulation, which is closely associated with the pathogenesis of HS. vWF was reported as a prognostic marker in several infectious and noninfectious severe illness such as COVID-19, sepsis, and trauma. Although early increased level of vWF is seen in HS, the relationship between vWF and mortality is to be elucidated. Clinical data of patients with HS in a tertiary hospital were recorded and analyzed. It was shown that plasma vWF concentrations at admission were significantly increased in the nonsurvivors (351% ± 105%) compared with survivors (278% ± 104%, p = 0.021). After multivariate logistic regression analysis it was shown that vWF (odds ratio [OR] = 1.010; 95% confidence interval [CI], 1.002-1.18; p = 0.017), hemoglobin (Hb) (OR = 0.954; 95% CI, 0.931-0.979; p < 0.001), and hematocrit (HCT) in blood (OR = 0.859; 95% CI, 0.790-0.934; p < 0.001) were independent factors of in-hospital mortality in HS. The nomogram based on vWF and Hb was constructed in patients with HS. The area under curve under the receiver operating characteristic of this prediction model was 0.860 (95% CI, 0.773-0.923) and cutoff was 0.15, with Youden index 0.5840, which were not significantly different to sequential organ failure assessment (p = 0.0644), Acute Physiology and Chronic Health Evaluation II (APACHE II) (p = 0.7976), and systemic inflammatory response syndrome (SIRS) scores (p = 0.3274). The prediction model that integrated vWF and Hb showed a better predicting efficiency than single variable, and a higher specificity (81.48%) than APACHE II (72.84%) and SIRS (72.84%) scores. In summary, vWF, as an independent risk factor for in-hospital mortality, combined with Hb, could effectively prognosis the mortality in HS patients at early stage.

Combined effect of high factor VIII levels and high mean platelet volume on the risk of future incident venous thromboembolism

BACKGROUND

High factor VIII (FVIII) levels and large platelets, as reflected by a high mean platelet volume (MPV), are separately associated with increased risk of venous thromboembolism (VTE). Whether the combination of high FVIII levels and large platelets has a supra-additive effect on VTE risk is unknown.

OBJECTIVES

We aimed to investigate the joint effect of high FVIII levels and large platelets, as reflected by high MPV, on the risk of future incident VTE.

METHODS

A population-based nested case-control study with 365 incident VTE cases and 710 controls was derived from the Tromsø study. FVIII antigen levels and MPV were measured in blood samples drawn at baseline. Odds ratios with 95% CIs were estimated across FVIII tertiles (<85%, 85%-108%, and ≥108%) and within predefined MPV strata (<8.5, 8.5-9.5, and ≥9.5 fL).

RESULTS

VTE risk increased linearly across FVIII tertiles (Ptrend < .001) in models adjusted for age, sex, body mass index, and C-reactive protein. In the combined analysis, participants with FVIII levels in the highest tertile and an MPV of ≥9.5 fL (ie, joint exposure) had an odds ratio for VTE of 2.71 (95% CI, 1.44-5.11) compared with those with FVIII levels in the lowest tertile and an MPV of <8.5 fL (reference). In the joint exposure group, 52% (95% CI, 17%-88%) of VTEs were attributable to the biological interaction between FVIII and MPV.

CONCLUSION

Our results suggest that large platelets, as reflected by high MPV, might play a role in the mechanism by which high FVIII level increases the risk of incident VTE.

Factor VIII: A Dynamic Modulator of Hemostasis and Thrombosis in Trauma

A trace amount of thrombin cleaves factor VIII (FVIII) into an active form (FVIIIa), which catalyzes FIXa-mediated activation of FX on the activated platelet surface. FVIII rapidly binds to von Willebrand factor (VWF) after secretion and becomes highly concentrated via VWF-platelet interaction at a site of endothelial inflammation or injury. Circulating levels of FVIII and VWF are influenced by age, blood type (nontype O > type O), and metabolic syndromes. In the latter, hypercoagulability is associated with chronic inflammation (known as thrombo-inflammation). In acute stress including trauma, releasable pools of FVIII/VWF are secreted from the Weibel-Palade bodies in the endothelium and then augment local platelet accumulation, thrombin generation, and leukocyte recruitment. Early systemic increases of FVIII/VWF (>200% of normal) levels in trauma result in a lower sensitivity of contact-activated clotting time (activated partial thromboplastin time [aPTT] or viscoelastic coagulation test [VCT]). However, in severely injured patients, multiple serine proteases (FXa plasmin and activated protein C [APC]) are locally activated and may be systemically released. Severity of traumatic injury correlates with prolonged aPTT and elevated activation markers of FXa, plasmin, and APC, culminating in a poor prognosis. In a subset of acute trauma patients, cryoprecipitate that contains fibrinogen, FVIII/VWF, and FXIII is theoretically advantageous over purified fibrinogen concentrate to promote stable clot formation, but comparative efficacy data are lacking. In chronic inflammation or subacute phase of trauma, elevated FVIII/VWF contributes to the pathogenesis of venous thrombosis by enhancing not only thrombin generation but also augmenting inflammatory functions. Future developments in coagulation monitoring specific to trauma patients, and targeted to enhancement or inhibition of FVIII/VWF, are likely to help clinicians gain better control of hemostasis and thromboprophylaxis. The main goal of this narrative is to review the physiological functions and regulations of FVIII and implications of FVIII in coagulation monitoring and thromboembolic complications in major trauma patients.

Underlying mechanisms of thrombus formation/growth in atherothrombosis and deep vein thrombosis

Thrombosis remains a leading cause of death worldwide despite technological advances in prevention, diagnosis, and treatment. The traditional view of arterial thrombus formation is that it is a platelet-dependent process, whereas that of venous thrombus formation is a coagulation-dependent process. Current pathological and basic studies on atherothrombosis and venous thrombosis have revealed the diverse participation of platelet and coagulation activation mechanisms in both thrombus initiation and growth processes during clinical thrombotic events. Atherosclerotic plaque cell-derived tissue factor contributes to fibrin formation and platelet aggregation. The degree of plaque disruption and a blood flow alteration promote atherothrombotic occlusion. While blood stasis/turbulent flow due to luminal stenosis itself initiates venous thrombus formation. The coagulation factor XI-driven propagation phase of blood coagulation plays a major role in venous thrombus growth, but a minor role in hemostasis. These lines of evidence indicate that atherothrombosis onset is affected by the thrombogenic potential of atherosclerotic plaques, the plaque disruption size, and an alteration in blood flow. Upon onset of venous thrombosis, enhancement of the propagation phase of blood coagulation under blood stasis and a hypercoagulable state contribute to large thrombus formation.

Reduced ADAMTS13 Activity in Correlation with Pathophysiology, Severity, and Outcome of COVID-19: A Retrospective Observational Study

BACKGROUND

Low ADAMTS13 activity has been suggested to be an interplaying factor in the pathogenesis of COVID-19, considering that it is a thromboinflammatory disease with high risk of microthrombosis.

OBJECTIVES

The study aimed to explore the correlation between ADAMTS13 activity and the pathophysiological pathway of COVID-19.

METHODS

We carried out a retrospective observational study of 87 patients with COVID-19 in NMC Royal Hospital, Abu Dhabi, UAE. ADAMTS13 activity was measured and compared with patients' characteristics and clinical outcomes.

RESULTS

Low ADAMTS13 activity was associated with pneumonia (p = 0.007), severity of COVID-19 (p <0.001), and mechanical ventilation rates (p = 0.018). Death was more frequently observed among patients (5 patients) with low ADAMTS13 activity compared with normal activity (1 patient), as well as inflammatory markers. Decreased ADAMTS13 activity increased with the risk of pneumonia, severity of COVID-19, need for mechanical ventilation, and use of anticoagulants ([OR = 4.75, 95% CI 1.54-18.02, p = 0.011], [OR = 6.50, 95% CI 2.57-17.74; p <0.001], [OR = 4.10, 95% CI 1.29-15.82; p = 0.024], [OR = 8.00, 95% CI 3.13-22.16; p <0.001], respectively). The low ADAMTS13 activity group had a slightly longer time to viral clearance than the normal ADAMTS13 activity group, but it was not statistically significant (20 days, 95% CI 16-27 days vs 17 days, 95% CI 13-22 days; p = 0.08; Log rank = 3.1).

CONCLUSIONS

Low ADAMTS13 activity has been linked to pneumonia, COVID-19 severity, use of anticoagulants, and need for mechanical ventilation but not to mortality. We propose rADAMTS13 as a novel treatment for severe COVID-19.

Brazilian propolis (AF-08) inhibits collagen-induced platelet aggregation without affecting blood coagulation

Brazilian propolis (AF-08) is a dietary supplement containing a variety of flavonoids. It is used worldwide as a folk medicine. Flavonoids and a diet of fruits and vegetables containing them have been shown to reduce the risk of cardiovascular diseases (CVDs). Most of CVDs are caused by arterial thrombus formation. A thrombus is formed by the interaction between adhesion and aggregation of platelets to damaged blood vessels and blood coagulation consisting of extrisic and intrinsic pathways. Platelet aggregation and blood coagulation are closely linked to thrombosis. Therefore, we evaluated the effectiveness of AF-08 or its component flavonoids against thrombosis by examining their inhibition of platelet aggregation and blood coagulation. Human platelet-rich plasma was incubated with serial dilutions of AF-08 for 10 min to assess its inhibitory effect on platelet aggregation caused by collagen. The inhibitory effect of AF-08 on blood coagulation was evaluated by the prothrombin time (PT) and activated partial thromboplastin time (APTT), which reflect the coagulation function of extrinsic and intrinsic pathways, respectively. AF-08 significantly inhibited collagen-induced platelet aggregation but not PT and APTT, indicating that AF-08 inhibited platelet aggregation but not blood coagulation. Among three flavonoids contained in AF-08, apigenin and chrysin obviously inhibited platelet aggregation but the inhibitory effect of kaempferol was less effective. The three flavonoids did not affect PT and APTT. The inhibitory activity of AF-08 on human platelet aggregation without affecting blood coagulation was suggested to be partially due to apigenin and chrysin. AF-08 may be effective in suppressing platelet-based arterial thrombus formation and reducing the risk of CVDs.

Quantification of von Willebrand factor and ADAMTS-13 after traumatic injury: a pilot study

BACKGROUND

Von Willebrand factor (VWF) is an acute phase reactant synthesized in the megakaryocytes and endothelial cells. VWF forms ultra-large multimers (ULVWF) which are cleaved by the metalloprotease ADAMTS-13, preventing spontaneous VWF-platelet interaction. After trauma, ULVWF is released into circulation as part of the acute phase reaction. We hypothesized that trauma patients would have increased levels of VWF and decreased levels of ADAMTS-13 and that these patients would have accelerated thrombin generation.

METHODS

We assessed plasma concentrations of VWF antigen and ADAMTS-13 antigen, the Rapid Enzyme Assays for Autoimmune Diseases (REAADS) activity of VWF, which measure exposure of the platelet-binding A1 domain, and thrombin generation kinetics in 50 samples from 30 trauma patients and an additional 21 samples from volunteers. Samples were analyzed at 0 to 2 hours and at 6 hours from the time of injury. Data are presented as median (IQR) and Kruskal-Wallis test was performed between trauma patients and volunteers at both time points.

RESULTS

REAADS activity was greater in trauma patients than volunteers both at 0 to 2 hours (190.0 (132.0-264.0) vs. 92.0 (71.0-114.0), p<0.002) and at 6 hours (167.5 (108.0-312.5.0) vs. 92.0 (71.0-114.0), p<0.001). ADAMTS-13 antigen levels were also decreased in trauma patients both at 0 to 2 hours (0.84 (0.51-0.94) vs. 1.00 (0.89-1.09), p=0.010) and at 6 hours (0.653 (0.531-0.821) vs. 1.00 (0.89-1.09), p<0.001). Trauma patients had accelerated thrombin generation kinetics, with greater peak height and shorter time to peak than healthy volunteers at both time points.

DISCUSSION

Trauma patients have increased exposure of the VWF A1 domain and decreased levels of ADAMTS-13 compared with healthy volunteers. This suggests that the VWF burst after trauma may exceed the proteolytic capacity of ADAMTS-13, allowing circulating ULVWF multimers to bind platelets, potentially contributing to trauma-induced coagulopathy.

LEVEL OF EVIDENCE

Prospective case cohort study.

Pathophysiology of atherothrombosis: Mechanisms of thrombus formation on disrupted atherosclerotic plaques

Atherothrombosis is a leading cause of cardiovascular mortality and morbidity worldwide. The underlying mechanisms of atherothrombosis comprise plaque disruption and subsequent thrombus formation. Arterial thrombi are thought to mainly comprise aggregated platelets as a result of high blood velocity. However, thrombi that develop on disrupted plaques comprise not only aggregated platelets, but also large amounts of fibrin, because plaques contain large amount of tissue factor that activate the coagulation cascade. Since not all thrombi grow large enough to occlude the vascular lumen, the propagation of thrombi is also critical in the onset of adverse vascular events. Various factors such as vascular wall thrombogenicity, local hemorheology, systemic thrombogenicity and fibrinolytic activity modulate thrombus formation and propagation. Although the activation mechanisms of platelets and the coagulation cascade have been intensively investigated, the underlying mechanisms of occlusive thrombus formation on disrupted plaques remain obscure. Pathological findings derived from humans and animal models of human atherothrombosis have uncovered pathophysiological processes during thrombus formation and propagation after plaque disruption, and novel factors have been identified that modulate the activation of platelets and the coagulation cascade. These findings have also provided insights into the development of novel drugs for atherothrombosis.

Higher lactate and purine metabolite levels in erythrocyte-rich fresh venous thrombus: Potential markers for early deep vein thrombosis

BACKGROUND

Thrombolytic therapy is effective in fresh deep vein thrombosis (DVT) although the benefit may fall below the risk of bleeding in non-fresh thrombosis. Markers reflecting fresh DVT have not been established. The present study aims to identify metabolites reflecting fresh venous thrombus and their role in thrombus formation.

METHODS

Metabolites of rabbit venous blood and jugular venous thrombus 4 h after thrombus induction were analysed using electrophoresis-time of flight mass spectrometry. The effects of the altered metabolites on blood coagulation and platelet aggregation were assessed by using rotation thromboelastometry and platelet aggregometer. Cellular contents and glucose transporter (Glut)-1 expression in aspirated human DVT samples were pathologically analysed.

RESULTS

Metabolome analysis identified 226 metabolites (133 cationic and 93 anionic metabolites). Largely altered 18 metabolites (thrombus/blood ratio: >5 or <0.5) included glycolytic metabolites, redox-related metabolites, purine nucleotides and tryptophan metabolites. Among the metabolites with >5-fold increase, lactic acid was most abundant and guanine modestly enhanced whole blood clotting with thromboelastometry. Lactic acid and adenosine monophosphate inhibited collagen-induced platelet aggregation. Human DVTs were rich in erythrocytes expressing Glut-1. The erythrocyte content and Glut-1 expression were negatively correlated with the time after onset of DVT.

CONCLUSIONS

Glycolysis-, purine-, and redox-related metabolites may reflect fresh erythrocyte-rich venous thrombus, and altered metabolites may affect venous thrombus formation. An increased level of lactate may reflect active glycolysis of thrombus cellular components, predominantly erythrocytes.

Thrombus Formation and Propagation in the Onset of Cardiovascular Events

Ischemic cardiovascular disease is a major cause of morbidity and mortality worldwide and thrombus formation on disrupted atherosclerotic plaques is considered to trigger its onset. Although the activation of platelets and coagulation pathways has been investigated intensively, the mechanisms of thrombus formation on disrupted plaques have not been understood in detail. Platelets are thought to play a central role in the formation of arterial thrombus because of rapid flow conditions; however, thrombus that develops on disrupted plaques consistently includes large amounts of fibrin in addition to aggregated platelets. While, thrombus does not always become large enough to completely occlude the vascular lumen, indicating that the propagation of thrombus is also critical for the onset of cardiovascular events. Various factors, such as vascular wall thrombogenicity, altered blood flow and imbalanced blood hemostasis, modulate thrombus formation and propagation on disrupted plaques. Pathological findings derived from humans and experimental animal models of atherothrombosis have identified important factors that affect thrombus formation and propagation, namely platelets, extrinsic and intrinsic coagulation factors, proinflammatory factors, plaque hypoxia and blood flow alteration. These findings might provide insight into the mechanisms of thrombus formation and propagation on disrupted plaques that lead to the onset of cardiovascular events.

Regulation of VWF expression, and secretion in health and disease

PURPOSE OF REVIEW

Von Willebrand factor (VWF) is a large multidomain, multimeric glycoprotein that plays an essential role in regulating the balance between blood clotting and bleeding. Aberrant VWF regulation can lead to a spectrum of diseases extending from bleeding disorders [Von Willebrand disease (VWD)] to aberrant thrombotic thrombocytopenic purpura (TTP). Understanding the biology of VWF expression and secretion is essential for developing novel targeted therapies for VWF-related hemostasis disorders.

RECENT FINDINGS

A number of recent elegant in-vitro and in-vivo studies will be highlighted, including the discovery of intronic splicing in the VWF gene, microRNA-regulated VWF gene expression, and syntaxin binding protein and autophagy mediated VWF secretion. Compared with the already established critical role of VWF in VWD and TTP pathophysiology, additional clinical studies have clarified and reinforced the association of elevated plasma levels of VWF with an increased risk of stroke, myocardial infarction, venous thrombosis, and diabetic thrombotic complications. Moreover, experimental mouse models of ischemic stroke and myocardial infarction have further supported VWF as a potential therapeutic target.

SUMMARY

VWF biosynthesis, maturation, and secretion is a complex process, which mandates tight regulation. Significant progress has been made in our understandings of VWF expression and secretion and its association with thrombotic diseases, contributing to the development of novel targeting VWF drugs for prevention and treatment of deficient and enhanced hemostasis.