MITIGATION OF OXIDANT INJURY TO LUNG MICROVASCULATURE BY INTRATRACHEAL INSTILLATION OF ANTIOXIDANT ENZYMES

We quantitated the ability of intratracheally administered liposome-en capsulated antioxidant enzymes to reduce reactive oxygen species injur y to the pulmonary microvasculature. Cationic liposomes containing 3,5 00 U of Cu,Zn superoxide dismutase (Cu,Zn SOD) and 3,124 U of catalase were instilled into rabbits. The animals were killed 2-72 h later and their lungs were removed and perfused with Krebs Ringer with 5% wt/vo l of fat-free bovine serum albumin. The pulmonary filtration coefficie nt (K(f,c)) was measured before and after adding 500 muM xanthine and 5 mU/ml xanthine oxidase (XO) into the lung perfusate. Two hours after a single intratracheal instillation of liposome-entrapped Cu,Zn SOD a nd catalase, lung antioxidant enzyme activities were 34 and 125% highe r than the corresponding control values, remained virtually unchanged for up to 8 h postinstillation, and then decreased, reaching baseline values between 24 and 72 h. Addition of xanthine and XO into the lung perfusate of uninstilled rabbits, or rabbits that received liposomes w ith inactivated enzymes, caused a 100% increase in K(f,c) (control val ue: 2 +/- 0.12 ml . min-1 . cmH2O-1 per 100 g1 dry lung weight). On th e other hand, K(f,c) values of rabbits lungs instilled with liposome-e ncapsulated active Cu,Zn SOD and catalase and challenged with xanthine and XO 8-24 h later remained at baseline levels. Instillation of lipo somes containing either enzyme was equally effective in preventing the increase in K(f,c) indicating that both superoxide anions and hydroge n peroxide were necessary for the initiation of injury. We concluded t hat intratracheal instillation of liposome-encapsulated antioxidant en zymes causes a transient increase of lung antioxidant enzyme levels wh ich protects the pulmonary microvasculature from free radical-initiate d injury.