Lung barrier protection by Sphingosine-1
Phosphate (S1P) has been demonstrated experimentally, but recent evidence suggests barrier disruptive properties of high systemic S1P concentrations. The S1P analog
FTY720 recently gained an FDA approval for treatment of
multiple sclerosis. In case of
FTY720 treated patients experiencing
multiple organ dysfunction syndrome the drug may accumulate due to
liver failure, and the patients may receive
ventilator therapy. Whereas low doses of
FTY720 enhanced endothelial barrier function, data on effects of increased
FTY720 concentrations are lacking. We measured transcellular electrical resistance (TER) of human umbilical vein endothelial cell (HUVEC) monolayers, performed morphologic analysis and measured apoptosis by TUNEL staining and
procaspase-3 degradation in HUVECs stimulated with
FTY720 (0.01-100 μM). Healthy C57BL/6 mice and mice ventilated with 17 ml/kg tidal volume and 100%
oxygen for 2 h were treated with 0.1 or 2 mg/kg
FTY720 or
solvent, and lung permeability, oxygenation and leukocyte counts in BAL and blood were quantified. Further, electron microscopic analysis of lung tissue was performed. We observed barrier protective effects of
FTY720 on HUVEC cell layers at concentrations up to 1 μM while higher concentrations induced irreversible barrier breakdown accompanied by induction of apoptosis. Low
FTY720 concentrations (0.1 mg/kg) reduced lung permeability in mechanically ventilated mice, but 2 mg/kg
FTY720 increased pulmonary vascular permeability in ventilated mice accompanied by endothelial apoptosis, while not affecting permeability in non-ventilated mice. Moreover, hyperoxic
mechanical ventilation sensitized the pulmonary vasculature to a barrier disrupting effect of
FTY720, resulting in worsening of
ventilator induced lung injury. In conclusion, the current data suggest
FTY720 induced endothelial barrier dysfunction, which was probably caused by proapoptotic effects and enhanced by
mechanical ventilation.