UC Davis

Epidemiological studies show strong associations between fine particulate matter (PM_2.5) air pollution and adverse pulmonary effects. In the present study, wintertime PM_2.5 samples were collected from three geographically similar regions-Sacramento, California, USA; Jinan, Shandong, China; and Taiyuan, Shanxi, China-and extracted to form PM_CA, PM_SD, and PM_SX, 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_SX 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_SX-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_SX compared to PM_CA or PM_SD exposure.