Ultrastructure and composition of thrombi in coronary and peripheral artery disease: correlations with clinical and laboratory findings

Fibrin to von Willebrand factor ratio in arterial thrombi is associated with plasma levels of inflammatory biomarkers and local abundance of extracellular DNA

INTRODUCTION

The composition of thrombi determines their structure, mechanical stability, susceptibility to lysis, and consequently, the clinical outcome in coronary artery disease (CAD), acute ischemic stroke (AIS), and peripheral artery disease (PAD). Fibrin forms the primary matrix of thrombi intertwined with DNA, derived from neutrophil extracellular traps (NETs), and von Willebrand factor (VWF) bridging DNA and platelets. Here we examined the relative content of fibrin, DNA and VWF in thrombi and analyzed their interrelations and quantitative associations with systemic biomarkers of inflammation and clinical characteristics of the patients.

PATIENTS, METHODS

Thrombi extracted from AIS (n = 17), CAD (n = 18) or PAD (n = 19) patients were processed for scanning electron microscopy, (immune)stained for fibrin, VWF and extracellular DNA. Fibrin fiber diameter, cellular components, fibrin/DNA and fibrin/VWF ratios were measured.

RESULTS

Patients' age presented as a strong explanatory factor for a linear decline trend of the VWF content relative to fibrin in thrombi from CAD (adjusted-R² = 0.43) and male AIS (adjusted-R² = 0.66) patients. In a subgroup of CAD and PAD patients with dyslipidemia and high (above 80%) prevalence of atherothrombosis a significant correlation was observed between the VWF and DNA content in thrombi (adjusted-R² = 0.40), whereas a 3.7-fold lower linear regression coefficient was seen in AIS patients, in whom the fraction of thrombi of atherosclerotic origin was 57%. Independently of anatomical location, in patients with atherosclerosis the VWF in thrombi correlated with the plasma C-reactive protein levels.

CONCLUSIONS

The observed interrelations between thrombus constituents and systemic inflammatory biomarkers suggest an intricate interplay along the VWF/NET/fibrin axis in arterial thrombosis.

Thrombus Structural Composition in Cardiovascular Disease

Thrombosis is a major complication of cardiovascular disease, leading to myocardial infarction, acute ischemic stroke, or venous thromboembolism. Thrombosis occurs when a thrombus forms inside blood vessels disrupting blood flow. Developments in thrombectomy to remove thrombi from vessels have provided new opportunities to study thrombus composition which may help to understand mechanisms of disease and underpin improvements in treatments. We aimed to review thrombus compositions, roles of components in thrombus formation and stability, and methods to investigate thrombi. Also, we summarize studies on thrombus structure obtained from cardiovascular patients and animal models. Thrombi are composed of fibrin, red blood cells, platelets, leukocytes, and neutrophil extracellular traps. These components have been analyzed by several techniques, including scanning electron microscopy, laser scanning confocal microscopy, histochemistry, and immunohistochemistry; however, each technique has advantages and limitations. Thrombi are heterogenous in composition, but overall, thrombi obtained from myocardial infarction are composed of mainly fibrin and other components, including platelets, red blood cells, leukocytes, and cholesterol crystals. Thrombi from patients with acute ischemic stroke are characterized by red blood cell- and platelet-rich regions. Thrombi from patients with venous thromboembolism contain mainly red blood cells and fibrin with some platelets and leukocytes. Thrombus composition from patients with myocardial infarction is influenced by ischemic time. Animal thrombosis models are crucial to gain further mechanistic information about thrombosis and thrombus structure, with thrombi being similar in composition compared with those from patients. Further studies on thrombus composition and function are key to improve treatment and clinical outcome of thrombosis.

Use of electron microscopy to study platelets and thrombi

Electron microscopy has been a valuable tool for the study of platelet biology and thrombosis for more than 70 years. Early studies using conventional transmission and scanning electron microscopy (EM) provided a foundation for our initial understanding of platelet structure and how it changes upon platelet activation. EM approaches have since been utilized to study platelets and thrombi in the context of basic, translational and clinical research, and they are instrumental in the diagnosis of multiple platelet function disorders. In this brief review, we provide a sampling of the many contributions EM based studies have made to the field, including both historical highlights and contemporary applications. We will also discuss exciting new imaging modalities based on EM and their utility for the study of platelets, hemostasis and thrombosis into the future.

The role of diabetes mellitus on the thrombus composition in patients with acute ischemic stroke

PURPOSE

Diabetes mellitus indicated poor clinical prognosis for patients with acute ischemic stroke. Furthermore, diabetes mellitus could also impact the hemostatic system, while its influence on the histological composition of thrombus is unclear.

METHODS

Consecutive patients with retrieved clots were included. Histologic staining for thrombus included hematoxylin and eosin, Martius Scarlet Blue, immunohistochemistry for von Willebrand factor. The differences in clot composition were compared according to diabetes mellitus history or hyperglycemia (≥7.8 mmol/L) on admission.

RESULTS

A total of 52 patients were included; half of them were diagnosed as diabetes mellitus previously. Diabetic patients showed higher serum glucose on admission (8.90 vs. 7.40, p = 0.012). The baseline characteristics (expect smoking history and thrombus location), procedural, and clinical outcomes were similar between diabetic patients and nondiabetic patients. As for histologic composition, thrombus in patients with diagnosed diabetes mellitus had more fibrin (44.2% vs. 28.3%, p = 0.004) and fewer red blood cells (26.0% vs. 42.9%, p = 0.013) and equivalent content of platelets (24.0% vs. 21.5%, p = 0.694) and von Willebrand factor (0.041 vs. 0.031, p = 0.234) than patients without diabetes mellitus. However, there was no statistical difference in the content of red blood cells (41.6% vs. 27.3%, p = 0.105), fibrin (37.6% vs. 34.3%, p = 0.627), platelets (21.2% vs. 24.2%, p = 0.498), and von Willebrand factor (0.038 vs. 0.034, p = 0.284) between patients with or without hyperglycemia on admission.

CONCLUSION

Clots in diabetic patients had more fibrin and fewer erythrocyte components compared with patients without diabetes mellitus, while hyperglycemia on admission did not show association with clot composition. Further studies are needed to confirm these results.

[Morphological and Immunohystochemical Characteristics of Aspirated Thrombi in Patients with ST-Elevation Myocardial Infarction]

The aim of study was to evaluate the morphological and immunohystochemical characteristics of aspirated thrombi in patients with ST-elevation myocardial infarction undergoing precutaneous coronary intervention to find the possible platelet activation and inflammatory cell involvement in coronary thrombi.

MATERIALS AND METHODS

Thrombi collected from 67 patients with ST-elevation myocardial infarction were studied. Macroscopic and immunohystochemical analyses were performed to reveal the cellular components of thrombi. The peroxidase - antiperoxidase immunohystochemical method was applied with monoclonal antibodies to CD4+, CD8+, CD15+, CD63+ and CD105+ using diaminobenzidine agent as a visualization agent to investigate the potential involvement of different cellular subpopulations.

RESULTS

The macroscopic examination revealed friable thrombi with apparent laminations (lines of Zahn). Microscopic analysis of thrombi revealed a loose meshwork of fibrin fibers with compact accumulation of activated platelets. The platelets were surrounded by neutrophilic granulocytes.The immunohystochemical analysis confirmed that cell aggregates are consisting of CD 63+ activated platelets and leucocytes. The granulocytes also tested positive for CD15 antigen. The immunohystochemical analysis revealed the presence of CD8+ cytotoxic T-lymphocytes and CD4+ helper T-lymphocytes. No expression of iNOS, CD105 and VEGF was found in the analyzed thrombi.

CONCLUSIONS

The hystopathological evaluation of thrombi in patients with acute ST-elevation myocardial infarction revealed the presence of activated CD63+ platelets and CD15+ neutrophilic granulocytes. Activated platelets and neutrophils may play a role in thromboinflammatory activation course leading to destabilization of atherosclerotic plaque and development of acute thrombosis in patients with ST-elevation acute myocardial infarction.

Atherosclerosis, myocardial infarction and primary hemostasis: Impact of platelets, von Willebrand factor and soluble glycoprotein VI

INTRODUCTION

Little is known about peril constellations in primary hemostasis contributing to an acute myocardial infarction (MI) in patients with already manifest atherosclerosis. The study aimed to establish a predicting model based on six biomarkers of primary hemostasis: platelet count, mean platelet volume, hematocrit, soluble glycoprotein VI, fibrinogen and von Willebrand factor ratio.

MATERIALS AND METHODS

The biomarkers were measured in 1.491 patients with manifest atherosclerosis of the Leipzig (LIFE) heart study. Three groups were divided: patients with coronary artery disease (900 patients) and patients with atherosclerosis and either ST-elevated MI (404 patients) or Non-ST-elevated MI (187 patients). Correlations were analyzed by non-linear analysis with Self Organizing Maps. Classification and discriminant analysis was performed using Learning Vector Quantization.

RESULTS AND CONCLUSIONS

The combination of hemostatic biomarkers is regarded as valuable tool for identifying patients with atherosclerosis at risk for MI. Nevertheless, our study contradicts this belief. The biomarkers did not allow to establish a predicting model usable in daily patient care. Good specificity and sensitivity for the detection of MI was only reached in models including acute phase parameters (specificity 0,9036, sensitivity 0,7937 in men; 0,8977 and 0,8133 in women). In detail, hematocrit and soluble glycoprotein VI were significantly different between the groups. Significant dissimilarities were also found for fibrinogen (in men) and von Willebrand factor ratio. In contrast, the most promising parameters mean platelet volume and platelet count showed no difference, which is an important contribution to the controversy concerning them as new risk and therapy targets for MI.

Neutrophil extracellular traps in thrombi retrieved during interventional treatment of ischemic arterial diseases

INTRODUCTION

The ultrastructure and cellular composition of thrombi has a profound effect on the outcome of acute ischemic stroke (AIS), coronary (CAD) and peripheral artery disease (PAD). Activated neutrophils release a web-like structure composed mainly of DNA and citrullinated histones, called neutrophil extracellular traps (NET) that modify the stability and lysability of fibrin. Here, we investigated the NET-related structural features of thrombi retrieved from different arterial localizations and their interrelations with routinely available clinical data.

PATIENTS AND METHODS

Thrombi extracted from AIS (n = 78), CAD (n = 66) or PAD (n = 64) patients were processed for scanning electron microscopy, (immune)stained for fibrin, citrullinated histone H3 (cH3) and extracellular DNA. Fibrin fiber diameter, cellular components, DNA and cH3 were measured and analyzed in relation to clinical parameters.

RESULTS

DNA was least present in AIS thrombi showing a 2.5-fold lower DNA/fibrin ratio than PAD, whereas cH3 antigen was unvaryingly present at all locations. The NET content of thrombi correlated parabolically with systemic inflammatory markers and positively with patients' age. The median platelet content was lower in PAD (2.2%) than in either AIS (3.9%) or CAD (3.1%) and thrombi from smokers contained less platelets than non-smokers. Fibrin fibers were significantly thicker in male patients with CAD (median fiber diameter 76.3 nm) compared to AIS (64.1 nm) or PAD (62.1 nm) and their diameter correlated parabolically with systemic inflammatory markers.

CONCLUSIONS

The observed NET-related variations in thrombus structure shed light on novel determinants of thrombus stability that eventually affect both the spontaneous progress and therapeutic outcome of ischemic arterial diseases.

Behçet's syndrome as a tool to dissect the mechanisms of thrombo-inflammation: clinical and pathogenetic aspects

Behçet's syndrome (BS) is a complex disease with different organ involvement. The vascular one is the most intriguing, considering the existence of a specific group of patients suffering from recurrent vascular events involving the venous and, more rarely, the arterial vessels. Several clinical clues suggest the inflammatory nature of thrombosis in BS, especially of the venous involvement, thus BS is considered a model of inflammation-induced thrombosis. Unique among other inflammatory conditions, venous involvement (together with the arterial one) is currently treated with immunosuppressants, rather than with anti-coagulants. Although many in-vitro studies have suggested the different roles of the multiple players involved in clot formation, in-vivo models are crucial to study this process in a physiological context. At present, no clear mechanisms describing the pathophysiology of thrombo-inflammation in BS exist. Recently, we focused our attention on BS patients as a human in-vivo model of inflammation-induced thrombosis to investigate a new mechanism of clot formation. Indeed, fibrinogen displays a critical role not only in inflammatory processes, but also in clot formation, both in the fibrin network and in platelet aggregation. Reactive oxygen species (ROS)-derived modifications represent the main post-translational fibrinogen alterations responsible for structural and functional changes. Recent data have revealed that neutrophils (pivotal in the pathogenetic mechanisms leading to BS damage) promote fibrinogen oxidation and thrombus formation in BS. Altogether, these new findings may help understand the pathogenetic bases of inflammation-induced thrombosis and, more importantly, may suggest potential targets for innovative therapeutic approaches.

Molecular and Physical Mechanisms of Fibrinolysis and Thrombolysis from Mathematical Modeling and Experiments

Despite the common use of thrombolytic drugs, especially in stroke treatment, there are many conflicting studies on factors affecting fibrinolysis. Because of the complexity of the fibrinolytic system, mathematical models closely tied with experiments can be used to understand relationships within the system. When tPA is introduced at the clot or thrombus edge, lysis proceeds as a front. We developed a multiscale model of fibrinolysis that includes the main chemical reactions: the microscale model represents a single fiber cross-section; the macroscale model represents a three-dimensional fibrin clot. The model successfully simulates the spatial and temporal locations of all components and elucidates how lysis rates are determined by the interplay between the number of tPA molecules in the system and clot structure. We used the model to identify kinetic conditions necessary for fibrinolysis to proceed as a front. We found that plasmin regulates the local concentration of tPA through forced unbinding via degradation of fibrin and tPA release. The mechanism of action of tPA is affected by the number of molecules present with respect to fibrin fibers. The physical mechanism of plasmin action (crawling) and avoidance of inhibition is defined. Many of these new findings have significant implications for thrombolytic treatment.

Antiplatelet Usage Impacts Clot Density in Acute Anterior Circulation Ischemic Stroke

We explored whether clot density in middle cerebral artery (MCA) occlusion is related to clinical variables, stroke etiology, blood constituents, and prestroke medication. We performed a retrospective chart review of patients with acute ischemic stroke of the anterior circulation admitted to two Central European stroke centers. The acquisition of non-contrast enhanced CT (NECT) and CT angiography (CTA) within 4.5 h of symptom onset was obligatory. We assessed the site of MCA occlusion as well as density, area, and length of the clot in 150 patients. The Hounsfield unit values for the clot were divided with contralateral MCA segment to yield relative Hounsfield Unit ratio (rHU). The site of the vessel occlusion (M1 vs. M2) and antiplatelet usage, but not stroke etiology, significantly influenced rHU. We found an inverse correlation of rHU with erythrocyte count (p < 0.001). The multivariate analysis revealed that a higher rHU (i.e., clot being more hyperdense) was more likely with the use of antiplatelets (OR 4.24, CI 1.10-16.31, p = 0.036). Erythrocyte (OR 0.18, CI 0.05-0.55, p = 0.003), and thrombocyte counts (OR 0.99, CI 0.98-0.99, p = 0.029) were associated with odds for more hypodense clots (lower rHU). Our study disclosed that antiplatelet therapy impacts the composition of intracranial clots of the anterior circulation.