690. Angiopoietin-1 Reduces Lung Edema and Mortality Induced by Bacterial Endotoxin

Acute lung injury (ALI) is a frequent cause of morbidity and mortality in patients with bacterial sepsis. Capillary leakage together with interstitial and alveolar edema are the hallmarks of this condition. The loss of integrity in the endothelial barrier is a prerequisite for development of ALI. Angiopoietin-1 (Ang-1) binds to the Tie2 receptor. This interaction activates the phosphatidylinositol 3′-kinase/Akt survival pathway that promotes endothelial cell integrity and survival. Ang-1 has also been shown to reduce vascular permeability and vessel leakage induced by a variety of factors including VEGF and thrombin. We hypothesized that in an animal model of ALI, inducing Ang-1 expression would stabilize vessels and attenuate capillary leakage, thereby reducing lung edema formation. We therefore examined the effects of Ang-1 expression in a murine model of ALI. Ang-1 expression was induced by infection with a non-replicating adenoviral vector containing the Ang-1 cDNA (AdAng1). AdAng1 or a control E1a/E1b deleted adenovirus (Ad312) was injected by intraperitoneal injection (1×109 PFU) into C57BL/6 mice. Ang-1 was detectable in the serum by immunoblotting at day 4. Five days later, a single dose of endotoxin was given by intraperitoneal injection. At 24 hours following endotoxin administration, Evans blue was injected intravenously. Lung edema was evaluated by measuring the leakage of Evans blue into the lung. The concentration of Evans blue detected in the lung was increased in endotoxin treated mice compared to saline controls (0.72 se 0.11 vs. 0.37 se 0.01 OD units), suggesting capillary leakage. However, the level of Evans blue detected in the lung was lower in mice pretreated with AdAng1 than in mice pretreated with the control adenovirus (0.45 se 0.01 vs. 0.73 se 0.06 OD units). Furthermore, AdAng1 was effective in reducing the mortality associated with endotoxin administration. At 36 hours after endotoxin administration, all of the saline treated controls (n5) and all of the Ad312 treated controls (n5) had died. In contrast, all of the AdAng1 treated animals were alive at 36 hours, and 4 of 5 were still alive at 7 days. These data suggest that pre-treatment with Ang-1 protects against the development of lung edema and also decreases the mortality induced by endotoxin.