Seasonal variations in PM composition from Beijing, China drive liver oxidative stress

Air pollution can cause oxidative stress, inflammation and adverse health effects, but the underlying biological mechanisms are not completely understood. In order to understand how seasonal and chemical variations drive health impacts, we investigated the oxidative stress and inflammation in mice exposed to extracts (water and DCM) from urban PM collected in Beijing (China). Higher levels of pollution components were detected in the heating season (HS, winter) than in the non-heating season (NHS, summer). Higher concentrations of PM were measured in the heating season, mostly from coal and wood burning used for domestic heating. This was accompanied by increased levels of polyaromatic hydrocarbons (PAHs) in the DCM extracts. An increased inflammatory response was detected in the lung and liver with DCM extracts compared to the water extracts, and mostly in the winter aerosol. Reduced antioxidant response was observed in the lung, whereas it was activated in the liver. Gene expression of the Nrf2 transcription factor (A master regulator of stress response that controls the basal oxidative capacity and induces the expression of antioxidant response) and its related genes were induced. In the liver, higher levels of lipid peroxidation adducts were measured, correlated with histologic analysis that revealed morphologic features of damage/proliferation in the liver, indicating oxidative and toxic damage. Altogether, our study suggests that the acute effects of PM can vary by the season with the largest effect observed in winter than summer in Beijing, and that some secondary organs may be susceptible for exposure damage. This suggests that the liver is a potential organ to be influenced from PM especially by PAHs