Abstract 1830 Effects of Oxygen on Lung Oxidant/Antioxidant Balance Poster Sympos Sunday, 5/2

Bronchopulmonary dysplasia (BPD) is a chronic pneumopathy of preterm infants with significant associated mortality and morbidity, for which there is no effective preventive therapy. It is believed that pulmonary O2 toxicity, through the generation of reactive oxygen species (ROS) in excess of antioxidant defences, play a central role in the parenchymal injury of BPD. This has led to considerable interest in antioxidant therapy as an approach to prevention, including phase I clinical trials of superoxide dismutase. Unfortunately, current approaches have not been based on a solid understanding of which ROS actually mediate pulmonary oxygen toxicity, making the choice of a therapeutic antioxidant purely speculative. Nor have they considered the potential impact of antioxidant therapy on the physiological role of ROS as second messengers during normal lung growth.

A number of synthetic antioxidants have shown promise for prevention of oxygen toxicity, in particular the 21-aminosteroid, or lazaroid, U74389F. U74389F scavenges lipid hydroperoxides (L.OOH) and H2O2. In contrast, a subsequent product U74389G only scavenges L. OOH. The 21-aminosteroids are lipophilic and easily penetrate cell membranes reaching intracellular sites. They are potent iron-chelators and effective inhibitors of lipid peroxidation. A previous in vitro study (Luo et al. Free Rad Biol Med in press) showed that U74389G scavenges L.OOH and OH, but not H2O2 in cultured fetal rat distal lung epithelial cells, and provides no protection against O2 cytotoxicity. However the relative importance of specific ROS in the development of lung injury in vivo is still unknown. In this study, we tested the effect of U74389G, on 95% O2-induced free radical production, lipid peroxidation and inhibition of postnatal lung growth in a neonatal rat model. The results showed that the formation of hydroxyl radical and lipid peroxidation products in rat lungs and serum, as measured by total 8-isoprostane and aldehydes, were significantly increased after 95% O2 exposure. These changes could be completely or partially attenuated by U74389G. However U74389G did not improve the survival rate or lung wet/dry weight ratio. Expression of proliferating cell nuclear antigen (PCNA), a marker for DNA synthesis, was examined by immunohistochemistry. Four or seven day-old control rat lungs had active DNA synthesis, which was inhibited by 95% O2 exposure. U74389G had a protective effect against 95% O2-mediated inhibition of DNA synthesis, which could be due to scavenging L.OOH or limiting OH production. Air-exposed animals treated with U74389G also had a reduced lung DNA synthesis, suggesting a role for hydroxyl radical or lipid hydroperoxide as second messengers in the normal regulation of lung growth. This raise the concern that effective prophylactic antioxidant interventions designed to prevent BPD could also arrest signals essential for normal lung growth.

Funded by a Group grant from the Medical Research Council of Canada, and an equipment grant from the Ontario Thoracic Society.