Polyethylene glycol-conjugated superoxide dismutase protects rats against oxygen toxicity

Superoxide dismutase (SOD) has an important role in the protection against O2 toxicity. Conjugation of Cu,Zn-SOD to polyethylene glycol (PEG-SOD) prolongs its plasma half-life and facilitates its cellular uptake. However, prior studies have shown that intravenous injection of PEG-SOD does not protect animals against O2 toxicity. In this study, we demonstrated that tracheal insufflation of PEG-SOD resulted in a dose-dependent protection against O2 toxicity. Nine of 15 rats (60%) insufflated with 25,000 U PEG-SOD survived continuous 100% O2 exposure for more than 7 days compared with control rats (n = 45), all of which died within 3 days of O2 exposure (P < 0.025). In contrast, insufflation of 25,000 U SOD, 9.7 mg methoxy-PEG (equivalent to the amount of methoxy-PEG present in 25,000 U PEG-SOD), or a combination of SOD and methoxy-PEG had no protective effect. Furthermore, intravenous or intraperitoneal injection of PEG-SOD did not afford significant protection. Protection against O2 toxicity by PEG-SOD insufflation was associated with attenuated O2-induced pulmonary injury as evidenced by a reduced volume of pleural effusion. Insufflation of PEG-SOD markedly increased pulmonary SOD activity (to 300 and 370% of controls at 24 and 50 h, respectively) without affecting pulmonary catalase activity. We conclude that insufflation of PEG-SOD protects rats against O2 toxicity, possibly by enhancing pulmonary SOD activity.