Objective  To observe lung oxidative stress injury induced by particulate matter ≤ 2.5 μm in aerodynamic diameter (PM_2.5) and the effect of different dose alpha lipoic acid (ALA) against the injury in rats.

  Methods  Totally 48 male specific pathogen free Sprague-Dawley rats were randomly assigned into a PM_2.5 group with intratracheal instillation of suspension (2 ml/kg) of PM_2.5 sampled from ambient air in Weifang city once a day for three days, and three groups of PM_2.5 plus low, moderate and high dose ALA (intraperitoneal injection at dosages of 20, 40, 80 μg/kg 24 hours before the PM_2.5 treatment), and a control group with intratracheal instillation and intraperitoneal injection of saline. By the end of the treatments, all the rats were sacrificed after 8 hours of fasting; then, bronchoalveolar lavage fluid (BALF) and lung tissue specimens were collected for detections of superoxide dismutase (SOD), glutathione (GSH), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA) using kit assays.

  Results  The body weight gain of PM_2.5 group was significantly lower than that of control group (63.5 ± 3.69 g vs. 96.35 ± 4.32 g); while the body weight gain (93.56 ± 4.31 g) of PM_2.5 plus high-dose ALA pretreatment group was significantly higher than that of PM_2.5 group. Compared to those of the control group, the serum SOD and GSH of PM_2.5 group decreased significantly (both P < 0.05) and compared to those of the PM_2.5 group, the serum SOD, GSH-Px, and GSH of the PM_2.5 plus moderate and high ALA pretreatment group increased significantly (P < 0.05 for all). The GSH-Px and GSH decreased significantly but the MDA and glutathione disulfide (GSSG)/GSH ratio increased significantly in BALF of the PM_2.5 group in comparison to those of the control group (P < 0.05 for all); while, the GSH-Px and GSH increased but the GSSG/GSH ratio in BALF of the PM_2.5 plus moderate and high ALA pretreatment group decreased significantly in contrast to those of the PM_2.5 group (P < 0.05 for all). Significantly decreased SOD, GSH-Px, and GSH and increased MDA and GSSG/GSH ratio were observed in lung tissues of the PM_2.5 group compared to those of the control group (P < 0.05 for all); whereas, the PM_2.5 plus high ALA pretreatment group demonstrated significantly increased SOD and GSH and decreased GSSG/GSH ratio compared to the PM_2.5 group (P < 0.05 for all).

  Conclusion  PM_2.5 at certain dosages could induce lung oxidative damage and pretreatment with different dose of alpha lipoic acid is of protective effect against the injury in rats.