ENDOTHELIUM-DERIVED MICROPARTICLES INDUCE ENDOTHELIAL DYSFUNCTION AND ACUTE LUNG INJURY

Received 13 Jan 2006; first review completed 2 Feb 2006; accepted in final form 15 May 2006ABSTRACT—Acute lung injury (ALI) carries a high mortality in critically ill patients. Recent reports correlate elevatedconcentrations of endothelium-derived microparticles (EMPs) with diseases of endothelial dysfunction. Many of these dis-eases have ALI sequelae. We hypothesize that EMPs contribute to endothelial cell (EC) dysfunction and development ofALI. To test this hypothesis, we treated isolated vessels with EMPs and examined changes in vasodilation. Endothelial cellcultures were incubated with EMPs and examined for changes in stimulated nitric oxide (&NO) production and nitric oxidesynthase(eNOS) activation. Finally, EMPs were injectedinto rats and mice and lungs examinedfor ALI. In both mouse andhuman ex vivo vessel preparations, we found a marked attenuation of endothelium-mediated vasodilation after EMP treat-ment (4 610 /mL). This dysfunction was not corrected by pretreatment of EMPs with free radical scavengers. Coincubationof EMPs with EC cultures yielded a three-fold reduction in A23187-stimulated &NO release. Western analysis of these cellsshowed a corresponding decrease in eNOS phosphorylation at Ser1179 and a decrease in hsp90 association. Mea-surements of lung permeability, myeloperoxidase activity, and histology of EMPs-treated Brown Norway rats demonstratedpulmonary edema, neutrophil recruitment, and compromise of the endothelial-alveolar barrier as a second hit phenome-non. In C57BL/6 mice, exogenous EMPs caused a significant rise in pulmonary capillary permeability both as a primaryand secondary injury. These findings demonstrate EMPs are capable of inducing significant lung injury at patho-physiologically relevant concentrations. Endothelium-derived microparticles inhibit endothelium-mediated vasodilation and&NO generation from eNOS. Once elucidated, EMP mechanisms of inducing ALI and endothelial dysfunction may presentnew therapeutic targets.KEYWORDS—Vasodilation, endothelial permeability, cell signaling, nitric oxide, NOS