Anna Schorer

Lupus anticoagulant induces a selective defect in thrombin‐mediated endothelial prostacyclin release and platelet aggregation

Summary A patient with microvascular thrombosis and thrombocytopenia was found to have a high‐titre lupus anticoagulant. The biological effects of the patients lupus anticoagulant were studied using whole patient serum and plasma, Staph Protein A eluate, and affinity‐purified lupus anticoagulant. The latter was isolated by immunoadsorption of serum onto cardiolipin/phosphatidylserine/cholesterol liposomes. Each source of lupus anticoagulant demonstrated‘anticoagulant’activity, defined as prolongation of a modified kaolin clotting time, and contained antibody which bound to endothelial monolayers. Each interfered with thrombin‐mediated prostacyclin release from endothelial cells, but had no effect on arachidonate‐induced prostacyclin release. In addition, the lupus anticoagulant selectively blocked platelet aggregation in response to thrombin, but not in response to arachidonate, ADP or epinephrine. Lupus anticoagulant also reduced thrombin‐stimulated shifts in cytosolic calcium. Thrombin‐mediated membrane inositol metabolism and total thrombin binding to endothelium were unaffected by lupus anticoagulant, and another endothelial anticoagulant function related thrombin binding, Protein C activation by thrombomodulin, was not altered. We conclude that the binding of lupus anticoagulant to endothelial cells and platelets does not prevent all thrombin signalling events, but does interrupt prostacyclin production.

Lupus anticoagulant inhibition of in vitro prostacyclin release is associated with a thrombosis-prone subset of patients.

PURPOSE The effect of lupus anticoagulant-containing sera on endothelial prostacyclin generation (both basal and after thrombin stimulation) was determined. Subsets of patients who had experienced arterial, venous, or no thrombosis were compared with respect to the quantitation of antiphospholipid antibody and effects on prostacyclin production. PATIENTS AND METHODS Serum antiphospholipid antibodies were detected in 26 patients by immunologic (enzyme-linked immunosorbent assay) and kinetic (anticoagulant) assays. Cultured human endothelial cells were exposed to patient or normal serum, and the release of prostacyclin was determined by radioimmunoassay of supernatants. Release was determined in the absence and presence of the secretagogue, thrombin (1 U/mL), corrected for interassay variation, and correlated with other clinical and laboratory variables. RESULTS The normal prostacyclin response was a 2.5-fold increase after thrombin (1 U/mL) compared to basal production. Patients with a history of arterial thrombosis (Group 1, n = 10) had the highest IgG anticardiolipin antibody titers (449 +/- 115 [OD x 1,000]), most prolonged kaolin clotting times (140 +/- 15 seconds), and the least prostacyclin response to thrombin (1.36-fold). Patients with venous thrombosis (Group 2, n = 6) had lower titers (329 +/- 120), intermediate clotting times (125 +/- 19 seconds), and slightly impaired prostacyclin responses (2.18-fold). Patients with no history of thrombosis (Group 3, n = 10) had low antibody titers (220 +/- 20), mildly prolonged clotting times (108 +/- 6 seconds), and normal prostacyclin responses (2.33-fold). Patient serum did not alter basal or arachidonate-induced prostacyclin production. Group 1 had significantly lower platelet counts (99 +/- 19) compared to Group 2 (167 +/- 35) or Group 3 (167 +/- 34), but were similar in age and associated diagnoses. CONCLUSIONS Inhibition of prostacyclin responses is commonly found in serum from patients with lupus anticoagulants, and is likely to be present in patients with high IgG anticardiolipin antibodies, strong lupus anticoagulants, low platelet counts, and a recent arterial thrombosis.

Endothelial Cell Heterogeneity: Antioxidant Profiles Determine Vulnerability to Oxidant Injury

Abstract Human umbilical vein endothelial cells were more sensitive to hydrogen peroxide lysis than cow pulmonary artery endothelial cells. Conversely, activated neutrophils which utilize hydrogen peroxide-mediated cell cytotoxicity cell mechanisms were more toxic to the cow pulmonary artery cells. This discordance was not related to neutrophil adhesion to either cell type or cell passage number. The antioxidant profiles of the endothelial cells revealed that cow pulmonary artery cells were rich in catalase to consume bolus hydrogen peroxide presented to them, while human umbilical vein endothelial cells utilize glutathione peroxidase-linked mechanisms to detoxify a slower more sustained release of hydrogen peroxide generated by neutrophils. Endothelial cells from different species and sites may utilize diversified antioxidant protective mechanisms.

Interleukin 1 enhances arterial thrombogenicity in vitro

An in vitro model of platelet adhesion, the annular perfusion chamber, was utilized to test the effects of Interleukin 1 on vascular thrombogenicity for platelets. De-endothelialized, everted human umbilical arteries were placed in cell culture media with or without Interleukin 1. The arteries were later perfused with citrated human blood and then fixed. Platelet adhesion and aggregate formation on artery segments was quantified by blinded morphometric analysis. A monolayer of contact platelets was seen on control artery segments, but arteries exposed to 100 Units/ml Interleukin 1 for 2-20 hours had increased numbers and size of platelet aggregates. Ultrastructurally, intact endothelial cells were not present on any segment. Both prostacyclin and thromboxane were released by vascular cells in the artery segments, but the quantity and ratio of these eicosanoids was not altered by artery exposure to Interleukin 1. Arterial thrombogenicity is modulated by non-endothelial vascular cells in response to Interleukin 1, and this does not appear to be mediated by changes in vascular production of thromboxane or prostacyclin.