6-ketoprostaglandin-f1-alpha and Antiphospholipid-Syndrome

To investigate the ability of human anti-beta 2-glycoprotein I (anti-beta 2 GPI) antibodies to recognize the cofactor adherent on endothelial cells (EC) and to modulate endothelial functions.. Six human affinity-purified polyclonal anti-beta 2 GPI IgG and 2 IgM monoclonal antibodies (MAb) were obtained from patients with the antiphospholipid syndrome. The antibodies were tested for their ability to 1) bind to endothelial monolayers through the adherent beta 2 GPI and 2) modulate endothelial adhesion molecule expression and interleukin-6 (IL-6) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) secretion.. The affinity-purified IgG and the MAb with anti-beta 2 GPI activity, but not the respective controls, displayed EC binding, which declined on cells incubated in serum-free medium and was restored in a dose-dependent manner by exogenous human beta 2 GPI. After EC binding, both polyclonal and monoclonal antibodies up-regulated adhesion molecule expression. Anti-beta 2 GPI MAb also significantly increased IL-6 and 6-keto-PGF1 alpha secretion.. These findings support the hypothesis that anti-beta 2 GPI antibodies bind and activate EC through the adherent cofactor beta 2 GPI, likely leading to a procoagulant state.

Topics: 6-Ketoprostaglandin F1 alpha; Adult; Antibodies, Antiphospholipid; Antibodies, Monoclonal; Antiphospholipid Syndrome; Apolipoproteins; beta 2-Glycoprotein I; Cell Adhesion; Cell Adhesion Molecules; Cells, Cultured; Chromatography, Affinity; Endothelium, Vascular; Epitopes; Female; Glycoproteins; Humans; Immunoglobulin G; Interleukin-6; Male; Protein Binding; Umbilical Veins

Circulating antiphospholipids have been linked to recurrent pregnancy loss by a mechanism involving placental and decidual thrombosis. We hypothesized that platelet-activating factor, an autacoid synthesized by vascular endothelium, might mediate this phenomenon through its ability to promote platelet aggregation and fibrin deposition. Alternatively, antiphospholipid antibodies might exert a procoagulant effect by inhibiting the synthesis of prostacyclin. To evaluate these theories, endothelial cells (harvested from human umbilical veins) were grown to confluence and incubated for 48 hours with 20% concentrations of anticardiolipin antibody-positive and -negative human sera as well as fetal bovine serum. After incubation culture wells were stimulated with 10 mumol/ml calcium ionophore A23187 (an agonist of platelet-activating factor and prostacyclin synthesis). Intracellular platelet-activating factor was measured by tritiated acetate incorporation, phospholipid extraction, thin-layer chromatography, and scintillation spectrophotometry. Enhanced platelet-activating factor synthesis was identified in cultures incubated with anticardiolipin antibody-positive serum (25,544 +/- 2604 disintegrations per minute, mean +/- SD) when compared with anticardiolipin antibody-negative serum (18,600 +/- 3316 dpm) or fetal bovine serum (19,014 +/- 4233 dpm; analysis of variance, p = 0.033). In similar experiments, prostacyclin synthesis was determined by measuring its primary metabolite, 6-keto-prostaglandin F1 alpha, in culture supernatants. No differences between anticardiolipin antibody-positive and control cultures were observed (analysis of variance, p = 0.90). We conclude that in this endothelial cell model, anticardiolipin antibody-positive serum enhances ionophore-mediated platelet-activating factor synthesis but has no apparent effect on the production of prostacyclin. These findings suggest a potential role for platelet-activating factor in anticardiolipin antibody-mediated vascular thrombosis.

Topics: 6-Ketoprostaglandin F1 alpha; Antibodies; Antiphospholipid Syndrome; Calcimycin; Cardiolipins; Dose-Response Relationship, Drug; Endothelium, Vascular; Humans; Platelet Activating Factor; Umbilical Veins