Pulmonary health effects of wintertime particulate matter from California and China following repeated exposure and cessation.

Epidemiological studies show strong associations between fine particulate matter (PM) air pollution and adverse pulmonary effects. In the present study, wintertime PM samples were collected from three geographically similar regions-Sacramento, California, USA; Jinan, Shandong, China; and Taiyuan, Shanxi, China-and extracted to form PM, PM, and PM, respectively, for comparison in a BALB/c mouse model. Each of four groups was oropharyngeally administered Milli-Q water vehicle control (50 μL) or one type of PM extract (20 μg/50 μL) five times over two weeks. Mice were necropsied on post-exposure days 1, 2, and 4 and examined using bronchoalveolar lavage (BAL), histopathology, and assessments of cytokine/chemokine mRNA and protein expression. Chemical analysis demonstrated all three extracts contained black carbon, but PM contained more sulfates and polycyclic aromatic hydrocarbons (PAHs) associated with significantly greater neutrophil numbers and greater alveolar/bronchiolar inflammation on post-exposure days 1 and 4. On day 4, PM-exposed mice also exhibited significant increases in interleukin-1 beta, tumor necrosis factor-alpha, and chemokine C-X-C motif ligands-3 and -5 mRNA, and monocyte chemoattractant protein-1 protein. These combined findings suggest greater sulfate and PAH content contributed to a more intense and progressive inflammatory response with repeated PM compared to PM or PM exposure.