Initial evidence of endothelial cell apoptosis as a mechanism of systemic capillary leak syndrome

Background: Systemic capillary leak syndrome (SCLS) is a rare disorder of u nknown etiology that is characterized by acute recurrent attacks of hypovol emic shock commonly following an inflammatory stimulus such as a viral illn ess. Prophylactic therapy is generally, ineffective, and the outcome is fre quently fatal. Methods: In order to investigate the cellular mechanisms leading to SCLS, w e examined the effects of sera from two patients with active SCLS on microv ascular endothelial cell apoptosis in vitro. Apoptosis was determined by mo rphologic criteria, DNA fragmentation, annexin V stain, and by a quantitati ve photometric assay. The apoptotic pathway was investigated by Western blo t of endothelial cells lysate after exposure to SCLS sera. Results: The sera from patients with active SCLS mediated profound apoptosi s of microvascular endothelial cells shortly after exposure. The exposed mi crovascular endothelial cells underwent immediate apoptosis as evidenced by morphologic changes, plasma membrane phosphatidylserine exposure, and by D NA fragmentation. Increased Bax/Bcl-2 ratio in endothelial cells exposed to SCLS sera was observed and suggested an oxidation injury as the possible m echanism for endothelial apoptosis. This potential mechanism was further ex plored by measuring intracellular reactive oxygen species (ROS) following S CLS serum exposure. Sera from both patients caused marked increases in ROS, initially detectable at 1 h and persisted for at least 12 h, with control serum from healthy subjects showing no effect on basal endothelial cell ROS concentrations. Conclusion: Components from the sera of patients with active systemic capil lary leak syndrome in contrast to healthy subject sera mediate early, and e xtensive endothelial apoptosis in vitro that is associated with oxidation i njury. These data represent compelling initial evidence for oxidation-induc ed apoptosis as a likely mechanism for endothelial injury, leading to SCLS.