Enhanced platelet force development despite drug-induced inhibition of platelet aggregation in patients with thromboangiitis obliterans--two case reports

Early Diagnosis and Intervention Are Needed for a Reasonable Prognosis of Thromboangiitis Obliterans

Background

Thromboangiitis obliterans (TAO) poses a higher risk of amputation than atherosclerosis obliterans. It is characterized by onset at a relatively young age. There are currently no clear treatment guidelines for TAO other than smoking cessation. In this study, we aimed to identify factors that could influence a favorable prognosis of TAO.

Methods

From January 2009 to December 2019, we retrospectively reviewed the initial symptoms, characteristics, treatments, and disease course of 37 patients (45 limbs) with TAO. Logistic regression analysis was performed to investigate factors affecting the course of symptoms that persisted or worsened despite treatment.

Results

Patients' mean age was 37.2±11.4 years, and all patients were men. The mortality rate was 0% during the follow-up period (76.9±51.1 months). All patients were smokers at the time of diagnosis, and 19 patients (51.4%) successfully quit smoking during treatment. When comparing the Rutherford categories before and after treatment, 23 limbs (51.1%) showed improvement, the category was maintained in 11 limbs (24.4%), and 11 limbs (24.4%) worsened. Symptom persistence or exacerbation despite treatment was associated with a higher initial Rutherford category (odds ratio [OR], 1.59; 95% confidence interval [CI], 1.04-2.42; p=0.03) and a higher score of the involved below-knee artery at the time of diagnosis (OR, 2.26; 95% CI, 1.10-4.67; p=0.03).

Conclusion

The degree of disease progression at the time of diagnosis significantly affected patients' prognosis. Therefore, early diagnosis and intervention are important to improve the course of TAO.

Why platelet mechanotransduction matters for hemostasis and thrombosis

Mechanotransduction is the ability of cells to "feel" or sense their mechanical microenvironment and integrate and convert these physical stimuli into adaptive biochemical cellular responses. This phenomenon is vital for the physiology of numerous nucleated cell types to affect their various cellular processes. As the main drivers of hemostasis and clot retraction, platelets also possess this ability to sense the dynamic mechanical microenvironments of circulation and convert those signals into biological responses integral to clot formation. Like other cell types, platelets leverage their "hands" or receptors/integrins to mechanotransduce important signals in responding to vascular injury to achieve hemostasis. The clinical relevance of cellular mechanics and mechanotransduction is imperative as pathologic alterations or aberrant mechanotransduction in platelets has been shown to lead to bleeding and thrombosis. As such, the aim of this review is to provide an overview of the most recent research related to platelet mechanotransduction, from platelet generation to platelet activation, within the hemodynamic environment and clot contraction at the site of vascular injury, thereby covering the entire "life cycle" of platelets. Additionally, we describe the key mechanoreceptors in platelets and discuss the new biophysical techniques that have enabled the field to understand how platelets sense and respond to their mechanical microenvironment via those receptors. Finally, the clinical significance and importance of continued exploration of platelet mechanotransduction have been discussed as the key to better understanding of both thrombotic and bleeding disorders lies in a more complete mechanistic understanding of platelet function by way of mechanotransduction.

Quantification and optimization of clot retraction in washed human platelets by Sonoclot coagulation analysis

INTRODUCTION

Clot retraction is a pivotal process for haemostasis, where platelets develop a contractile force in fibrin meshwork and lead to the increased rigidity of clot. The pathophysiological alteration in contractile forces generated by the platelet-fibrin meshwork can lead to haemostatic disorders. Regardless of its utter significance, clot retraction remains a limited understood process owing to lack of quantification methodology. Sonoclot analysis is a point-of-care technique used in clinical laboratories for whole blood analysis that provides in vitro qualitative as well as quantitative assessment of coagulation process from initial fibrin formation to clot retraction.

METHODS

Human washed platelets were isolated by differential centrifugation method and analysed via optical imaging, microscopy and Sonoclot analysis using 1-2 × 10⁸ /mL of washed platelets, 1 U/mL of thrombin, 1 mg/mL of fibrinogen and 1 mM of calcium chloride.

RESULTS

In this study, we demonstrate the novelty of this instrument in the quantitative evaluation of clot retraction in washed platelets and attempted to optimize the reference range of Sonoclot parameters including ACT - 87.3 ± 20.997, CR - 16.23 ± 3.538 and PF - 3.57 ± 0.629, (n = 10).

DISCUSSION

Sonoclot analysis provides a simple and quantitative method to better understand in vitro clot retraction and its modulation by retraction components including platelet count, fibrinogen and platelet-fibrin interaction compared with existing conventional methods. Sonoclot may prove to be a valuable tool in thrombus biology research to understand fundamental basis of blood clot retraction.

The biophysics and mechanics of blood from a materials perspective

Cells actively interact with their microenvironment, constantly sensing and modulating biochemical and biophysical signals. Blood comprises a variety of non-adherent cells that interact with each other and with endothelial and vascular smooth muscle cells of the blood vessel walls. Blood cells are further experiencing a range of external forces by the hemodynamic environment and they also exert forces to remodel their local environment. Therefore, the biophysics and material properties of blood cells and blood play an important role in determining blood behaviour in health and disease. In this Review, we discuss blood cells and tissues from a materials perspective, considering the mechanical properties and biophysics of individual blood cells and endothelial cells as well as blood cell collectives. We highlight how blood vessels provide a mechanosensitive barrier between blood and tissues and how changes in vessel stiffness and flow shear stress can be correlated to plaque formation and exploited for the design of vascular grafts. We discuss the effect of the properties of fibrin on blood clotting, and investigate how forces exerted by platelets are correlated to disease. Finally, we hypothesize that blood and vascular cells are constantly establishing a mechanical homeostasis, which, when imbalanced, can lead to hematologic and vascular diseases.

Feeling the Force: Measurements of Platelet Contraction and Their Diagnostic Implications

In addition to the classical biological and biochemical framework, blood clots can also be considered as active biomaterials composed of dynamically contracting platelets, nascent polymeric fibrin that functions as a matrix scaffold, and entrapped blood cells. As platelets sense, rearrange, and apply forces to the surrounding microenvironment, they dramatically change the material properties of the nascent clot, increasing its stiffness by an order of magnitude. Hence, the mechanical properties of blood clots are intricately tied to the forces applied by individual platelets. Research has also shown that the pathophysiological changes in clot mechanical properties are associated with bleeding and clotting disorders, cancer, stroke, ischemic heart disease, and more. By approaching the study of hemostasis and thrombosis from a biophysical and mechanical perspective, important insights have been made into how the mechanics of clotting and the forces applied by platelets are linked to various diseases. This review will familiarize the reader with a mechanics framework that is contextualized with relevant biology. The review also includes a discussion of relevant tools used to study platelet forces either directly or indirectly, and finally, concludes with a summary of potential links between clotting forces and disease.

Allosterism-based simultaneous, dual anticoagulant and antiplatelet action: allosteric inhibitor targeting the glycoprotein Ibα-binding and heparin-binding site of thrombin

BACKGROUND

Allosteric inhibition is a promising approach for developing a new group of anticoagulants with potentially reduced bleeding consequences. Recently, we designed sulfated β-O4 lignin (SbO4L) as an allosteric inhibitor that targets exosite 2 of thrombin to reduce fibrinogen cleavage through allostery and compete with glycoprotein Ibα to reduce platelet activation.

OBJECTIVE

To assess: (i) the antithrombotic potential of a novel approach of simultaneous exosite 2-dependent allosteric inhibition of thrombin and competitive inhibition of platelet activation; and (ii) the promise of SbO4L as the first-in-class antithrombotic agent.

METHODS

A combination of whole blood thromboelastography, hemostasis analysis, mouse arterial thrombosis models and mouse tail bleeding studies were used to assess antithrombotic potential.

RESULTS AND CONCLUSIONS

SbO4L extended the clot initiation time, and reduced maximal clot strength, platelet contractile force, and the clot elastic modulus, suggesting dual anticoagulant and antiplatelet effects. These effects were comparable to those observed with enoxaparin. A dose of 1 mg of SbO4L per mouse prevented occlusion in 100% of arteries, and lower doses resulted in a proportionally reduced response. Likewise, the time to occlusion increased by ~ 70% with a 0.5-mg dose in the mouse Rose Bengal thrombosis model. Finally, tail bleeding studies demonstrated that SbO4L does not increase bleeding propensity. In comparison, a 0.3-mg dose of enoxaparin increased the bleeding time and blood volume loss. Overall, this study highlights the promise of the allosteric inhibition approach, and presents SbO4L as a novel anticoagulant with potentially reduced bleeding side effects.

Buerger’s disease in the northeast of Iran: Epidemiology and clinical features

Background

The aim of this study is to present our long-term clinical experience in describing a clinical picture of Buerger's disease in our region.

Materials and methods

In a retrospective study, files of 225 patients who were admitted to the hospital with diagnosis of thromboangiitis obliterans in a 10 year period from 2000 to 2010 were reviewed. All data including demographic, signs and symptoms, history of previous illness, history of smoking, medications, laboratory tests, angiography, and details of surgical operation were obtained.

Results

A total of 222 (98.7%) and 3 (1.3%) of patients were male and female, respectively. Average age of hospitalized patients was 40.7 ± 8.5 (20–62) years. A total of 200 patients (88.9%) were active cigarette smokers while 168 (74.7%) of them were opium addicts. The most prevalent symptoms were chronic ulcers (80%) and claudication (63.6%). Minor and major amputation was required in 113 (50.2%) and 41 (18.4%) patients, respectively. Amputation was carried out on the lower limb (80%), upper limb (4.1%), or on both (15.1%). Also, four patients underwent revascularization through surgical bypass procedures.

Conclusions

The diagnosis and treatment of Buerger’s Disease is still a challenge in those communities where the disease is endemic. Therefore, identifying the natural course of the disease can play a pivotal role in the diagnosis and treatment of these patients.

Diagnostic accuracy of mean platelet volume in thromboangiitis obliterans

Thromboangiitis obliterans (TAO) affects small- and medium-sized vessels of the extremities via a non-atherosclerotic inflammatory process in the elderly. Although diagnostic criteria have been determined, only a few studies have been described in the laboratory features. Diagnostic biomarkers are important for reducing disruptions caused by TAO. The diagnostic importance of mean platelet volume (MPV) was investigated in TAO patients. Forty-four patients diagnosed with TAO (study group) and 45 healthy individuals (control group) were included in the study. The age, gender and complete blood parameters obtained via peripheral venous blood samples were compared between the two groups. A receiver operating characteristic (ROC) curve was used for determining the diagnostic accuracy of the MPV variable. All the variables were statistically similar in each group except MPV and platelet counts. MPV was significantly higher and platelet count was significantly lower in the TAO group ( P < 0.05). In addition, diagnostic accuracy was measured by the area under the ROC curve (Figure  1 ), and MPV differs significantly ( P < 0.001), with a value of 0.783 (95% CI: 0.711–0.854). This study indicates that MPV is probably an important diagnostic predictor in TAO patients. Detection of blood parameters such as platelet properties is important for meticulous care of these patients. [Figure: see text]

Mechanobiology of platelets: techniques to study the role of fluid flow and platelet retraction forces at the micro- and nano-scale

Coagulation involves a complex set of events that are important in maintaining hemostasis. Biochemical interactions are classically known to regulate the hemostatic process, but recent evidence has revealed that mechanical interactions between platelets and their surroundings can also play a substantial role. Investigations into platelet mechanobiology have been challenging however, due to the small dimensions of platelets and their glycoprotein receptors. Platelet researchers have recently turned to microfabricated devices to control these physical, nanometer-scale interactions with a higher degree of precision. These approaches have enabled exciting, new insights into the molecular and biomechanical factors that affect platelets in clot formation. In this review, we highlight the new tools used to understand platelet mechanobiology and the roles of adhesion, shear flow, and retraction forces in clot formation.

The association of Raynaud syndrome with thromboangiitis obliterans--a meta-analysis

Thromboangiitis obliterans (TAO) has traditionally been included among the diseases associated with Raynaud syndrome (RS). The prevalence of RS in patients with TAO is not well defined. The objective of this meta-analysis is to assess the prevalence of RS in patients with TAO. A literature search was performed for the studies dealing with RS and TAO. The studies provided sufficient data to estimate the prevalence of RS in patients with TAO. A total of 8 eligible studies, contributing data on 851 patients, were included in this meta-analysis. For TAO, a pooled prevalence of 28.1% and 95% confidence interval ([CI] = 0.158, 0.423) were obtained. Statistically publication bias was not present (P = .232). Despite some heterogeneity, there is a possible indication of an association between RS and patients with TAO.

Platelet retraction force measurements using flexible post force sensors

Platelets play an important role in hemostasis by forming a thrombotic plug that seals the vessel wall and promotes vascular healing. After platelets adhere and aggregate at the wound site, their next step is to generate contractile forces through the coordination of physicochemical interactions between actin, myosin, and alpha(IIb)beta(3) integrin receptors that retract the thrombus' size and strengthen its adhesion to the exposed matrix. Although platelet contractile forces (PCF) are a definitive feature of hemostasis and thrombosis, there are few approaches that can directly measure them. In this study, we describe the development of an approach to measure PCF in microthrombi using a microscopic flexible post force sensor array. Quasi-static measurements and live microscopic imaging of thrombin-activated platelets on the posts were conducted to assay the development of PCF to various hemostatic conditions. Microthrombi were observed to produce forces that monotonically increased with thrombin concentration and activation time, but forces subsided when thrombin was removed. PCF results were statistically similar on arrays of posts printed with fibronectin or fibrinogen. PCF measurements were combined with clot volume measurements to determine that the average force per platelet was 2.1 +/- 0.1 nN after 60 min, which is significantly higher than what has been measured with previous approaches. Overall, the flexible post arrays for PCF measurements are a promising approach for evaluating platelet functionality, platelet physiology and pathology, the impacts of different matrices or agonists on hemostatic responses, and in providing critical information regarding platelet activity that can guide new hemostatic or thrombotic strategies.

Thromboangiitis obliterans (Buerger's disease): searching for a therapeutic strategy

Treatment of thromboangiitis obliterans (Buerger's disease) includes both surgical and nonsurgical approaches, or a combination of both. A definite therapeutic approach has not yet been set. This article reviews the proposed therapeutic strategies and considers the advantages and disadvantages of each treatment. Cessation of smoking seems to be the only globally accepted therapeutic measure to prevent disease progression. A number of promising novel therapeutic strategies may prove useful for the treatment of this physically and socially mutilating disease.

Aprotinin counteracts heparin-induced inhibition of platelet contractile force

BACKGROUND

Aprotinin interferes with heparin binding to platelets and decreases blood loss during cardiopulmonary bypass (CPB). Heparin abolishes platelet force during CPB, and the extent of platelet force recovery after protamine administration appears to correlate with blood loss. This study assessed the effect of aprotinin on heparin suppression of platelet force.

METHODS

Platelet force was measured using the Hemodyne Hemostasis Analyzer. Clots were formed from platelet-rich plasma (PRP) by the addition of batroxobin and 10 mM CaCl(2). Clotting conditions included pH 7.4, ionic strength 0.15 M, fibrinogen level 1 mg/ml and 75,000 platelets/microl.

RESULTS

After 1200 s of clotting, force was reduced from 7110+/-1190 to 450+/-450 dyn by 0.2 U/ml of heparin. Platelet force in aprotinin [20 microg/ml (140 KIU/ml)] containing PRP was not suppressed by heparin addition (7480+/-2410 dyn). Aprotinin [40 microg/ml (280 KIU/ml)] addition to previously heparinized plasma counteracted heparin force suppression. Aprotinin (40 microg/ml) increased platelet force from 5630 to 11,138+/-562 in PRP devoid of heparin. Aprotinin did not affect thrombin activity, fibrin structure, platelet aggregation or secretion.

CONCLUSIONS

Aprotinin counteracts heparin suppression of platelet force and enhances platelet force in the absence of heparin. Aprotinin-heparin-platelet interactions may help explain aprotinin's ability to reduce blood loss during CPB.

Platelet contractile force (PCF) and clot elastic modulus (CEM) are elevated in diabetic patients with chest pain

AIMS

Platelet function and clot structure may be altered in diabetes. We have noted increased platelet contractile force (PCF) and clot elastic modulus (CEM) in patients presenting to the emergency department with chest pain. Twenty-six of the chest pain patients were diabetic. Here, we compare the PCF, CEM and platelet aggregation in diabetic chest pain patients, non-diabetic patients with chest pain and asymptomatic controls.

PATIENTS AND METHODS

PCF, CEM and collagen whole blood aggregations were measured in 100 chest pain patients and 25 asymptomatic controls.

RESULTS

Platelet concentrations for diabetic patients, non-diabetic patients and controls were identical. PCF was significantly (P < 0.05) elevated in diabetic chest pain patients (9.42 +/- 0.59 kdynes) vs. controls (7.40 +/- 0.32 kdynes). CEM in diabetic patients (29.96 +/- 2.19 kdynes/cm2) was significantly elevated relative to that in non-diabetic chest pain patients (25.22 +/- 0.84 kdynes/cm2) and normal controls (23.18 +/- 0.74 kdynes/cm2). Collagen-induced whole blood aggregation was decreased (P < 0.05) in diabetic chest pain patients vs. controls. PCF values (10.23 +/- 0.76 kdynes) in diabetic patients with haemoglobin A1c > 7% were higher than in any other group.

CONCLUSION

PCF and CEM are elevated in diabetic chest pain patients. The significance of these laboratory findings awaits additional clinical studies.