Particulate Matter Exposure History Affects Antioxidant Defense Response of Mouse Lung to Haze Episodes.

Few studies have focused on the association between previous particulate matter (PM) exposure and antioxidant defense response to a haze challenge. In this study, a combined exposure model was used to investigate whether and how PM exposure history affected the antioxidant defense response to haze episodes. At first, C57BL/6 male mice were randomly assigned to three groups and exposed for 5 weeks to whole ambient air, ambient air containing a low (≤75 μg/m3) PM concentration, and filtered air, which simulated different exposure history of high, relatively low, and almost zero PM concentrations. Thereafter, all mice underwent a 3-day haze exposure followed by a 7-day exposure to filtered air. The indexes involved in the primary and secondary antioxidant defense response were determined after pre-exposure and haze exposure, as well as 1 day, 3 days, and 7 days after haze exposure. Our research demonstrated repeated exposure to a high PM concentration compromised the antioxidant defense response and was accompanied by an increased susceptibility to a haze challenge. Conversely, mice with a lower PM exposure developed an oxidative stress adaption that protected them against haze challenge more efficiently and in a more timely manner than was the case in mice without PM exposure history.