Background: Systemic capillary leak syndrome (SCLS) is
a rare disorder of unknown etiology that is characterized by acute
recurrent attacks of hypovolemic shock commonly following an
inflammatory stimulus such as a viral illness. Prophylactic therapy is
generally ineffective, and the outcome is frequently fatal.
Methods: In order to investigate the cellular mechanisms
leading to SCLS, we examined the effects of sera from two patients with
active SCLS on microvascular endothelial cell apoptosis in
vitro. Apoptosis was determined by morphologic criteria, DNA
fragmentation, annexin V stain, and by a quantitative photometric
assay. The apoptotic pathway was investigated by Western blot of
endothelial cells lysate after exposure to SCLS sera.
Results: The sera from patients with active SCLS mediated
profound apoptosis of microvascular endothelial cells shortly after
exposure. The exposed microvascular endothelial cells underwent
immediate apoptosis as evidenced by morphologic changes, plasma
membrane phosphatidylserine exposure, and by DNA fragmentation.
Increased Bax/Bcl-2 ratio in endothelial cells exposed to SCLS sera was
observed and suggested an oxidation injury as the possible mechanism
for endothelial apoptosis. This potential mechanism was further
explored by measuring intracellular reactive oxygen species (ROS)
following SCLS 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 capillary leak syndrome in contrast to healthy subject
sera mediate early and extensive endothelial apoptosis in
vitro that is associated with oxidation injury. These data
represent compelling initial evidence for oxidation-induced apoptosis
as a likely mechanism for endothelial injury leading to