RECOVERY FROM OXIDANT-MEDIATED LUNG INJURY: Response of Metallothionein, MIP-2, and MCP-1 to Nitrogen Dioxide, Oxygen, and Ozone Exposures

Abstract

Oxidant-induced lung injury is believed to be mediated by reactive oxygen species. Recovery from oxidant exposure has been associated with pulmonary inflammation. Inflammatory cell accumulation involves the synthesis of chemokines, including neutrophil chemoattractants such as macrophage inflammatory protein-2 (MIP-2) and monocyte chemoattractants such as monocyte chemoattractant protein-1 (MCP-1). Antioxidants are the first line of defense of lung cells against inhaled oxidants. Metallothionein (MT) can act as an antioxidant and free-radical scavenger. To better understand the pulmonary response associated with recovery from oxidant-mediated injury, we exposed mice to either 15 ppm nitrogen dioxide for 24 h, >99% oxygen for 72 h, or 1 ppm ozone for 24 h. Mice were examined at the end of exposure or after recovering in room air for 4 or 24 h. Neutrophils were elevated at the end of exposure and remained elevated through the postexposure period, whereas macrophage numbers were decreased at the end of exposure and remained below control levels at 4 and 24 h postexposure. MT, MIP-2, and MCP-1 mRNA levels were elevated at 4 h postexposure; however, after 24 h of recovery only MCP-1 remained elevated. These results indicate that MT, MIP-2, and MCP-1 mRNA levels responded similarly to recovery from nitrogen dioxide, oxygen, and ozone exposure. Monocyte accumulation was delayed as compared to neutrophils and was consistent with the timing of MIP-2 and MCP-1 expression. Peak expression of MT and MIP-2 preceded peak neutrophil accumulation. Consequently, the timing of MT, MIP-2, and MCP-1 expression may be important biological markers in assessing the state of injury and recovery associated with oxidant-mediated injury.