Platelet function in Behçet's disease

Vascular Behçet syndrome: from pathogenesis to treatment

Behçet syndrome is a rare, chronic inflammatory disease of unknown aetiopathogenesis, most commonly presenting with mucocutaneous and ocular manifestations. Vascular involvement, most frequently superficial vein and deep vein thrombosis, can occur in up to 50% of patients with Behçet syndrome. Venous thrombosis at atypical sites (inferior and superior vena cava, suprahepatic veins with Budd-Chiari syndrome, portal vein, cerebral sinuses and right atrium and/or ventricle) and arterial involvement (mostly in situ thrombosis and aneurysms of the pulmonary arteries, as well as aneurysms of the abdominal aorta, and peripheral and visceral arteries) are also unique features of Behçet syndrome. Behçet syndrome is considered a natural model of inflammation-induced thrombosis in humans, with an impaired immune-inflammatory response rather than traditional cardiovascular risk factors contributing to thrombogenesis. Specifically, neutrophil hyperactivation and neutrophil-mediated mechanisms of damage directly promote endothelial dysfunction, platelet activation and thrombogenesis in Behçet syndrome. This unusual pathogenesis directly determines the treatment approach, which relies mostly on immunosuppressants rather than anticoagulants for treatment of thrombosis and for secondary prevention. This Review discusses the main histopathological, pathogenetic and clinical aspects of vascular Behçet syndrome, addressing their implications for therapeutic management. Future perspectives in terms of pathogenetic studies, disease monitoring and treatment strategies are also discussed.

Behçet's Disease as a Model of Venous Thrombosis

Behçet's disease (BD) is a chronic inflammatory disease of unknown aetiology characterized by recurrent oral, genital aphthous ulcerations, uveitis, skin lesions and other multisystem affections associated with vasculitis. Different types of vessels, predominantly veins, can be affected in BD. The frequency of vascular lesions in BD, such as superficial and deep venous thromboses, arterial aneurysms and occlusions, ranges between 7-29%. In this review, various factors of thrombogenesis in BD, particularly pro- and antithrombotic endothelial and non-endothelial factors, factors of coagulation, platelet activation and rheological changes are presented and discussed from positions of Virchow's triad of venous thrombosis. Despite advances in understanding of thrombogenesis in BD, still many issues of diagnosis and targeted preventive and therapeutic measures remain unresolved. Further studies are needed to clarify the pathobiology of BD-related thrombosis and to provide the clinicians with recommendations over the utility, safety and effectiveness of the antithrombotic therapy in BD.

Behçet’s Disease as a Model of Venous Thrombosis

Behçet’s disease (BD) is a chronic inflammatory disease of unknown aetiology characterized by recurrent oral, genital aphthous ulcerations, uveitis, skin lesions and other multisystem affections associated with vasculitis. Different types of vessels, predominantly veins, can be affected in BD. The frequency of vascular lesions in BD, such as superficial and deep venous thromboses, arterial aneurysms and occlusions, ranges between 7-29%.

In this review, various factors of thrombogenesis in BD, particularly pro- and antithrombotic endothelial and non-endothelial factors, factors of coagulation, platelet activation and rheological changes are presented and discussed from positions of Virchow’s triad of venous thrombosis.

Despite advances in understanding of thrombogenesis in BD, still many issues of diagnosis and targeted preventive and therapeutic measures remain unresolved. Further studies are needed to clarify the pathobiology of BD-related thrombosis and to provide the clinicians with recommendations over the utility, safety and effectiveness of the antithrombotic therapy in BD.

Circulated activated platelets and increased platelet reactivity in patients with Behçet's disease

Behçet's disease (BD) is a multisystem disorder. Venous as well as arterial thrombosis is a common complication of BD but exact pathogenetic mechanism of the thrombotic tendency is not well known. This study aimed to evaluate circulating activated platelets and platelet reactivity in Behçet's patients. Twenty-two Behçet's patients (4 female, 18 male; mean age 38.6 +/- 10.9 years) and 20 control subjects (8 female, 12 male; mean age 38.8 +/- 9.4 years) were included. Those patients who had hypertension, hyperlipidemia, peripheral or coronary artery disease, hepatic or renal function abnormality, and who were using aspirin and other platelet-active drugs were excluded. Platelet activity and reactivity to adenosine diphosphate (ADP) were measured by whole blood flow cytometry. We assessed markers of platelet degranulation (P-selectin; CD62P) and the activated glycoprotein IIb/IIIa receptor (PAC1 binding to fibrinogen binding site) before and after stimulation with ADP. Platelet P-selectin expression was not significantly different between patients and control subjects both at baseline (p=0.420) and after stimulation (p=0.56). Baseline (p=0.001) and ADP-stimulated (p=0.003) PAC1 binding was significantly higher in Behçet's patients than in the control group. Clinical activity has no effect on P-selectin expression and PAC1 binding. There is evidence of platelet activity and hyperreactivity in patients with BD and this may contribute to a prothrombotic state. In addition to aspirin, other antiplatelet drugs may be useful in the prevention and treatment of thrombosis in Behçet's patients.

Decreased prostacyclin sensitivity of platelets in patients with Behçet's syndrome

Patients with Behçet's syndrome have an increased risk of arterial and venous thrombosis, and abnormal platelet function has been implicated. Platelet function was studied in nine patients with Behçet's syndrome and in nine age- and sex-matched healthy volunteers. Platelet aggregation in response to ADP was measured, and the threshold concentration required to produce irreversible aggregation determined. Sensitivity of platelets to the inhibitory effect of prostacyclin was also determined. In addition, plasma levels of the platelet-specific proteins, beta-thromboglobulin and platelet factor 4, and stimulated platelet thromboxane B2 production, were measured. Platelets from patients with Behçet's syndrome showed normal aggregation in response to ADP, irrespective of disease activity. Platelet sensitivity to prostacyclin was, however, decreased compared with controls--with a mean prostacyclin ID50 of 5.5 +/- 1.3 ng ml-1 (mean +/- SEM) and 1.9 +/- 0.3 ng ml-1, respectively (P less than 0.01). This reduction in platelet sensitivity to prostacyclin was greatest in patients with the most active disease. These results suggest that Behçet's syndrome may be associated with altered platelet function, and this may have important consequences with regard to the increased risk of thrombosis associated with this condition.