Neurotoxicity caused by particulate matter (PM) has been highlighted as being a potential risk factor for neurodegenerative diseases. However, the effects of brain inflammation in response to traffic-related PM remain unclear. The objective of this study was to investigate the effects of traffic-related PM on microglial responses. We determined the cytotoxicity, oxidative stress, lipid peroxidation, inflammation, activation, autophagy, and apoptosis due to exposure to carbon black (CB) and diesel exhaust particles (DEPs) in Bv2 microglial cells. Additionally, cells were pretreated with corticosteroid to determine alterations in microglial activation and inflammation. For in vivo confirmation, Sprague Dawley (SD) rats were whole-body exposed to traffic-related PM1 (PM with an aerodynamic diameter of <1 μm) for 3 and 6 months. We observed that a decrease in cell viability and increases in dichlorodihydrofluorescein (DCFH), lactate dehydrogenase (LDH), and thiobarbituric acid-reactive substances (TBARSs) occurred due to CB and DEP. Production of interleukin (IL)-6 and soluble tumor necrosis factor (TNF)-α was significantly stimulated by CB and DEP, whereas production of cellular TNF-α was significantly stimulated by CB. Iba1 and prostaglandin E2 (PGE2) significantly increased due to CB and DEP. Consistently, we observed significant increases in Iba1 in the hippocampus of rats after 3 and 6 months of exposure to traffic-related PM1. We found that the light chain 3II (LC3II)/LC3I ratio and caspase-3 activity increased due to CB and DEP exposure. Subsequently, LDH, TBARS, LC3II/I, and caspase-3 activities did not clearly respond to corticosteroid pretreatment followed by DEP exposure in BV2 cells. Results of the present study suggested that traffic-related PM induced cytotoxicity, lipid peroxidation, microglial activation, and inflammation as well as autophagy and caspase-3 regulation in microglia. We demonstrated that microglial activation and inflammation may play important roles in the response of the brain to traffic-related PM.
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