Clinical significance of the venous occlusion test on systemic lupus erythematosus patients with a focus on changes in blood levels of tissue plasminogen activator, von Willebrand factor antigen, and thrombomodulin

Changes to fibrinolysis in patients with systemic lupus erythematosus are associated with endothelial cell damage and inflammation, but not antiphospholipid antibodies

We investigated whether changes to fibrinolysis were associated with other manifestations of systemic lupus erythematosus (SLE), including antiphospholipid (APL) antibody status, endothelial damage, and inflammation. Ninety-four patients (36 SLE patients, 58 healthy controls) were recruited from Tasmania, Australia. Circulating levels of plasminogen, α2-antiplasmin, tissue-type plasminogen activator, plasminogen activator inhibitor-1, and thrombin-activatable fibrinolysis inhibitor (TAFI) were measured, as well as APL antibodies (including lupus anticoagulant, anticardiolipin, and antibeta-2 glycoprotein-1 antibodies), soluble E-selectin, and interleukin-6. Whereas there was a significant decrease in plasminogen (patient vs. control; median) (210 vs. 444 ng/ml; P < 0.0001) and increase in α2-antiplasmin (0.53 vs. 0.09 μg/ml; P = 0.0007), there was increased t-PA (0.65 vs. 0.40 ng/ml; P = 0.0001) and decreased TAFI (8.8 vs. 10.0 ng/ml; P = 0.002) in SLE patients compared to healthy controls. Plasminogen was significantly associated with α2-antiplasmin (rho = -0.563, P < 0.001); TAFI (rho = 0.410, P = 0.011); soluble E-selectin (rho = 0.531, P = 0.001); and interleukin-6 (rho = 0.489, P = 0.002) in SLE patients; however, APL antibody status was not associated with any of the markers measured. This study has demonstrated that fibrinolysis is significantly altered in patients with SLE compared to controls, and associated with endothelial cell damage and inflammation, but not APL antibody status.

Increased von Willebrand factor levels in patients with systemic lupus erythematosus reflect inflammation rather than increased propensity for platelet activation

Background

von Willebrand factor (VWF) is involved in platelet plug formation and protein transport. Increased VWF levels in systemic lupus erythematous (SLE) are considered risk factors for vascular events. VWF protein levels, however, do not accurately reflect its platelet-aggregating function, which has not been examined in SLE.

Methods

Cross-sectional study with clinical and laboratory data obtained in patients with SLE (n=92) from a regional lupus registry. VWF function was determined by ristocetin-induced platelet aggregation (VWF ristocetin cofactor, VWF:RCo) and VWF levels by turbidimetric assay (VWF antigen, VWF:Ag). The platelet-aggregating activity per VWF unit was estimated by the VWF RCo/Ag ratio. Healthy controls served as comparators and associations were evaluated by non-parametric methods.

Results

VWF:Ag (142% vs 107%, p=0.001) and VWF:RCo levels (123% vs 78%, p<0.041) were increased in patients with SLE, but VWF RCo/Ag ratio was similar as in controls (0.83 vs 0.82, p=0.8). VWF:Ag levels were higher in patients experiencing serositis but unrelated to other manifestations, thrombotic disease, Systemic Lupus Erythematous Disease Activity Index 2000 or Systemic Lupus International Collaborative Clinics-Damage Index. VWF:Ag levels correlated significantly with VWF:RCo levels (Rs 0.8, p<0.001), erythrocyte sedimentation rate (ESR) (Rs 0.32, p<0.01), anti-dsDNA Ab (Rs 0.27, p<0.01), total IgG (Rs 0.33 p<0.01), fibrinogen (Rs 0.28, p<0.01) and ceruloplasmin (Rs 0.367, p<0.01) levels. VWF:RCo levels were not related to clinical findings but were correlated with ESR, anti-dsDNA and transferrin levels. No serological associations existed for VWF RCo/Ag ratio (all p>0.2).

Conclusions

In this SLE cohort, VWF:Ag behaved similarly to acute-phase reactants, but VWF:Ag increases were not matched by increases in functional activity per unit of VWF. Thus, more VWF did not increase the propensity for platelet aggregation in SLE.

Antiendothelial cell antibodies in systemic lupus erythematosus

Sera from patients with systemic lupus erythematosus have been reported to contain IgM and/or IgG binding to endothelial cells (EC), i.e. anti-EC antibodies (AECA). Similar autoantibodies have been claimed to occur in a number of conditions associated with vasculitis. The original cyto-enzyme-linked immunosorbent assay (ELISA) remains the most widely used method for the detection of AECAs, although numerous pitfalls have been identified since then. These difficulties may explain why a consensus on the prevalence of AECAs has not been reached thus far. It is therefore desirable to confirm a positive result in the cyto-ELISA using other methods, such as flow cytometry, immunoprecipitation or Western blot. Yet, these methods appear to be difficult to use on a routine basis. With regard to the AECA effects, their binding induces activation of ECs, as substantiated by up-regulation of adhesion molecules, and synthesis of cytokines and chemokines, followed by their secretion. Some of these autoantibodies encourage the local production of tissue factor, and thereby favour coagulation. Other AECAs trigger apoptosis of ECs, although the Fas receptor does not seem to be involved in this process. In fact, since the target antigens are not well defined, the current challenge is to identify EC target molecules, and thus to gain further insights into the pathogenesis of diseases with vasculitis.

Thrombomodulin: an overview and potential implications in vascular disorders

Thrombomodulin (TM), a high affinity thrombin receptor present on endothelial cell membrane, plays an important role as a natural anticoagulant. It acts as a cofactor of thrombin-catalyzed activation of protein C, and inhibits the procoagulant functions of thrombin. TM is also located in other cells (keratinocytes, osteoblasts, macrophages,...) where it might be involved in cell differentiation or in inflammation. In the presence of cytokines, activated neutrophils and macrophages, endothelial TM is cleaved enzymatically, releasing soluble fragments which circulate in the blood and are eliminated in urine. Plasma TM level (pTM) can be measured using a two-site enzyme-linked immunosorbent assay (ELISA). pTM level is regarded as a molecular marker reflecting injury of endothelial cells. It is often increased in case of diffuse endothelial damage as in disseminated intravascular coagulation, diabetic microangiopathy, Plasmodium falciparum and rickettsial infections. pTM is also a predictive marker of hypertensive complications in pregnancy. In several systemic inflammatory diseases, pTM levels are correlated to the activity of the disease.

Fibrinolysis and coagulation abnormalities in systemic lupus erythematosus. Relationship with Raynaud's phenomenon, disease activity, inflammatory indices, anticardiolipin antibodies and corticosteroid therapy

Endothelial cell damage in systemic lupus erythematosus (SLE) was evaluated by measuring fibrinolytic activity and von Willebrand factor levels. Tissue-type plasminogen activator (t-PA) antigen, plasminogen activator inhibitor (PAI) activity, and von Willebrand factor antigen (vWF:Ag) and activity (vWF:RCof) were measured in 21 SLE patients (12 of whom were therapy free) and 22 controls. In addition, the relationship between such parameters and Raynaud's phenomenon, disease activity [according to personal criteria, Systemic Lupus Activity Measure (SLAM) and European Consensus Lupus Activity Measurement (ECLAM) scores] inflammatory indices [ESR, C-reactive protein (CRP), alpha 2-globulin], anticardiolipin antibodies and corticosteroid therapy was investigated. Lower levels of t-PA antigen (P = 0.003) and higher levels of vWF:Ag (P = 0.001) were found in SLE patients in comparison with controls. Moreover, t-PA antigen was lower (P = 0.02) in steroid-free patients in comparison with those taking steroids. No relationship was found between fibrinolysis and coagulation abnormalities and Raynaud's phenomenon, disease activity, inflammatory indices and anticardiolipin antibodies. Endothelial cell damage is probably a common feature in SLE patients; nevertheless, we were unable to clarify the nature of such abnormality. It is worth noting that low doses of steroids seem to be effective in improving endothelial cell function in SLE patients.