Aerosolized Human Extracellular Superoxide Dismutase Prevents Hyperoxia-Induced Lung Injury

Chih-Ching Yen,Cheng-Wei Lai,Yu-Ping Kuan,Wei Chen,Chien-Yu Lin,Yi-Wen Lai,Hsiao-Ling Chen,Wu-Huei Hsu,Chuan-Mu Chen,Anil Kumar Tyagi

doi:10.1371/journal.pone.0026870

Abstract

An important issue in critical care medicine is the identification of ways to protect the lungs from oxygen toxicity and reduce systemic oxidative stress in conditions requiring mechanical ventilation and high levels of oxygen. One way to prevent oxygen toxicity is to augment antioxidant enzyme activity in the respiratory system. The current study investigated the ability of aerosolized extracellular superoxide dismutase (EC-SOD) to protect the lungs from hyperoxic injury. Recombinant human EC-SOD (rhEC-SOD) was produced from a synthetic cassette constructed in the methylotrophic yeast Pichia pastoris. Female CD-1 mice were exposed in hyperoxia (FiO2>95%) to induce lung injury. The therapeutic effects of EC-SOD and copper-zinc SOD (CuZn-SOD) via an aerosol delivery system for lung injury and systemic oxidative stress at 24, 48, 72 and 96 h of hyperoxia were measured by bronchoalveolar lavage, wet/dry ratio, lung histology, and 8-oxo-2′-deoxyguanosine (8-oxo-dG) in lung and liver tissues. After exposure to hyperoxia, the wet/dry weight ratio remained stable before day 2 but increased significantly after day 3. The levels of oxidative biomarker 8-oxo-dG in the lung and liver were significantly decreased on day 2 (P<0.01) but the marker in the liver increased abruptly after day 3 of hyperoxia when the mortality increased. Treatment with aerosolized rhEC-SOD increased the survival rate at day 3 under hyperoxia to 95.8%, which was significantly higher than that of the control group (57.1%), albumin treated group (33.3%), and CuZn-SOD treated group (75%). The protective effects of EC-SOD against hyperoxia were further confirmed by reduced lung edema and systemic oxidative stress. Aerosolized EC-SOD protected mice against oxygen toxicity and reduced mortality in a hyperoxic model. The results encourage the use of an aerosol therapy with EC-SOD in intensive care units to reduce oxidative injury in patients with severe hypoxemic respiratory failure, including acute respiratory distress syndrome (ARDS).

Highlights

Acute lung injury (ALI) and its severe form, acute respiratory distress syndrome (ARDS), are common causes of morbidity and mortality in intensive care units
Exposure to hyperoxia can result in lung injury and commonly produces pathological changes similar to those seen in ARDS
After purification with fast protein liquid chromatography (FPLC), the pure dimeric rhEC-superoxide dismutase (SOD) was collected from fraction No 10 (Figure 1D) with a specific activity of 251.72 U/mg

Summary

Introduction

Acute lung injury (ALI) and its severe form, acute respiratory distress syndrome (ARDS), are common causes of morbidity and mortality in intensive care units. The primary management of ALI includes treatment for underlying diseases, adequate hemodynamic support and mechanical ventilation with lung-protective strategies [1]. Exposure to hyperoxia can result in lung injury and commonly produces pathological changes similar to those seen in ARDS. Similar findings have not been reproduced in humans with healthy lungs, most clinicians suspect that oxygen may exacerbate and even cause ALI in critically ill patients [2]. A recent study revealed that even moderate hyperoxia (FiO2 = 50%) exacerbates ventilator-induced lung injury (VILI) in a rabbit model [3]. Clinical studies have supported the important role that oxidative stress plays an in the pathogenesis of ALI and other lung diseases, including pulmonary fibrosis, chronic obstructive pulmonary disease, and bronchopulmonary dysplasia [4,5,6]

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Results

Conclusion