Increase in circulating ACE-positive endothelial microparticles during acute lung injury

Circulating endothelial microparticles (EMPs) are considered to be markers of endothelial injury, and lung microvascular endothelial cells express higher levels of angiotensin-converting enzyme (ACE). The aim of this study is to examine whether the number of ACE⁺ microvascular EMPs could be a prognostic marker for the development of acute respiratory distress syndrome (ARDS) in septic patients. The numbers of EMPs and ACE⁺ EMPs in the culture supernatant from human microvascular endothelial cells, as well as in the blood of mouse lung injury models and septic patients (n=82), were examined using flow cytometry. ACE⁺ EMPs in the culture supernatant from pulmonary microvascular endothelial cells increased after exposure to an inflammatory stimulus. In the mouse lung injury models, the circulating ACE⁺ EMPs and ACE⁺ EMP/EMP ratio were higher than in the controls (p<0.001). The ACE⁺ EMP/EMP ratio was correlated with the wet/dry lung ratio (r_s=0.775, p<0.001). The circulating ACE⁺ EMPs and ACE⁺ EMP/ EMP ratio on admission were significantly increased in septic patients who developed ARDS compared with septic patients who did not (p<0.001). Therefore, circulating ACE⁺ EMPs may be a prognostic marker for the development of ARDS in the septic patients.