Prothrombotic State, Platelet Activation and Netosis in Systemic Lupus Erythematosus

Introduction: Systemic lupus erythematosus (SLE) is a chronic autoimmune disease of unknown origin characterized by a hypercoagulable state and a high mortality rate. Mechanisms that cause the accelerated deterioration of cardiovascular health in SLE are unknown.

Objectives: to characterize the prothrombotic state in SLE patients by global coagulation assays and the contribution of platelets, endothelial damage, microparticles and neutrophil extracellular traps (NETs) in their prothombotic profile.

Material and methods: 72 patients and 90 healthy controls were recruited. Patients were classified according to clinical characteristics in: 32 with lupus (SLE group), 29 with SLE and antiphospholipid antibodies (aFL, SLE+aFL group) and 12 who met the criteria for SLE and antiphospholipid syndrome (APS, SLE+APS group). Experimental protocol was approved by La Paz University Hospital Ethics Committee.

Venous blood collected in BD sodium citrate tubes (3.2%) was centrifuged at 150 g for 20 min at 23ºC to obtain platelet-rich plasma (PRP). PPP was obtained by centrifugation at 1500 g for 15 min at 23ºC.

To obtain neutrophils, whole blood was centrifuged to 1600 rpm 25 min using a Ficoll gradient and red cells were lysed.

Rotational thromboelastometry (ROTEM®) was performed in naTEM condition. Clotting time (CT, time from start of measurement until initiation of clotting [in seconds]); alpha angle (tangent to the curve at 2-mm amplitude [in degrees]), Ax (clot firmness at time x, [in mm]) and maximum clot firmness (MCF, [in mm]) were recorded.

Procoagulant activity associated to microparticle's content of tissue factor was determined in PPP by Calibrated Automated Thrombogram (CAT) using MP-reagent (4 mM phospholipids, Diagnostica Stago, Spain). We evaluated the endogenous thrombin potential (ETP, the total amount of thrombin generated over time); the lag time (the time to the beginning of the explosive burst of thrombin generation); the peak height of the curve (the maximum thrombin concentration produced) and the time to the peak.

Thrombin generation associated to NETs was also measured by CAT. Neutrophils from healthy controls or from LES patients were stimulated with 100 nM PMA in RPMI medium during 45 min at 37º and then cocultivated with PRP adjusted to 10⁵ platelets/µL. NETs formation was verified by fluorescent microscopy performed with DAPI and an anti-myeloperoxidase antibody.

Plasma levels of LDL-ox, E-Selectin and PAI-1 were determined by Elisa (R&D Systems, MN, USA and Affymetrix eBioscience, Vienna, Austria, respectively).

Platelet activation was analysed by flow cytometry (FCM, FACScan, BD Biosciences). Fibrinogen receptor activation was evaluated through PAC1-FITC binding and release of granule's content was assessed with monoclonal antibodies (mAbs) anti-CD63 and anti P-selectin in quiescent and 100 µM TRAP and 10 µM ADP stimulated platelets.

Data were analysed with Graphpad prism and p ≤0.05 was stablished as statistical significance.

Results: PAI-1 plasma level was increased in all patient's groups, whereas LDL-ox and E-selectin showed no differences with control cohort (Fig.1).

ROTEM demonstrated a procoagulant profile in SLE and SLE+aPL but not in SLE+APS group (Fig. 2). PAI-1 levels correlated with several ROTEM parameters (Table 1).

SLE patients and SLE+aFL showed a basal platelet activation. Moreover, SLE group exposed more P-selectin and CD63 than controls (Fig.3).

Regarding thrombin generation associated to tissue-factor content of microparticles, no differences were observed between SLE patients and healthy controls. On the other hand, SLE patients had an increased peak of thrombin generation related to NETs formation (control group: 170.3± 58.0, SLE patients: 230.6±39.3, p=0.019).

Conclusions: ROTEM^® detected a hypercoagulable state in SLE and SLE+aPL patients. The hypercoagulable state might be linked to increased PAI-1 plasma levels and basal platelet activation in SLE and SLE+aPL groups. Moreover, neutrophils from SLE patients seemed to present a basal activation that induced a NETs-related procoagulant state in these patients.

SLE+APS patients did not show a hypercoagulable state perhaps because of the presence of lupus anticoagulant and/or to therapeutic treatment of these patients.

This work was supported by grants from the FIS-FONDOS FEDER (PI15/01457, NB). NVB holds a Miguel Servet tenure track grant from FIS-FONDOS FEDER (CP14/00024).

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