Exogenous administration of heme oxygenase-1 by gene transfer provides protection against hyperoxia-induced lung injury

Heme oxygenase-l (HO-1) confers protection against a variety of oxidant-ind uced cell and tissue injury. In this study, we examined whether exogenous a dministration of HO-1 by gene transfer could also confer protection. We fir st demonstrated the feasibility of overexpressing HO-1 in the lung by gene transfer. A fragment of the rat HO-1 cDNA clone containing the entire codin g region was cloned into plasmid pAC-CMVpLpA, and recombinant adenoviruses containing the rat HO-1 cDNA fragment Ad5-HO-1 were generated by homologous recombination. Intratracheal administration of Ad5-HO-1 resulted in a time -dependent increase in expression of HB-l mRNA and protein in the rat lungs . Increased HO-1 protein expression was detected diffusely in the bronchiol ar epithelium of rats receiving Ad5-HO-1, as assessed by immunohistochemica l studies. We then examined whether ectopic expression of HO-l could confer protection against hyperoxia-induced lune injury. Rats receiving Ad5-HO-1, but not AdV-beta Gal, a recombinant adenovirus expressing Escherichia coli beta-galactosidase, before exposure to hyperoxia (>99% O-2) exhibited mark ed reduction in lung injury, as assessed by volume of pleural effusion and histological analyses (significant reduction of edema, hemorrhage, and infl ammation). In addition, rats receiving Ad5-HO-1 also exhibited increased su rvivability against hyperoxic stress when compared with rats receiving AdV- beta Gal. Expression of the antioxidant enzymes manganese superoxide dismut ase (Mn-SOD) and copper-zinc superoxide dismutase (CuZn-SOD) and of L-ferri tin and H-ferritin was not affected by Ad5-HO-1 administration. Furthermore , rats treated with Ad5-HO-1 exhibited attenuation of hyperoxia-induced neu trophil inflammation and apoptosis. Taken together, these data suggest the feasibility of high-level HO-1 expression in the rat lung by gene delivery. To our knowledge, we have demonstrated for the first time that HO-1 can pr ovide protection against hyperoxia-induced lung injury in vivo by modulatio n of neutrophil inflammation and lung apoptosis.