Extract of motorcycle exhaust particles induced macrophages apoptosis by calcium-dependent manner

Large survey and experiments have reported that environment pollutants from fossil fuel combustion would cause immune system deleterious by enhancement of allergic reaction and damage to respiratory tract. In this study, we reported that the extract of motorcycle exhaust particles (MEP) might affect the immune system by inducing cell apoptosis on macrophages. The motorcycle exhaust particles were collected from a two-stoke engine and their cytotoxic effect on macrophages was investigated. We found MEP is cytotoxic and induced apoptosis in RAW 264.7 cells, murine peritoneal macrophage, and rat alveolar macrophage. Pretreatment with mitochondria permeability transition inhibitor (cyclosporin A), intracellular (BAPTAAM) and extracellular (EGTA) Ca²⁺ chelator, and antioxidants (NAC, GSH, catalase, SOD) attenuated the MEP-induced cell apoptosis, and BAPTA-AM was the most effective one. Utilized Fura-2/AM loaded RAW 264.7 cells to directly detect the change of intracellular Ca²⁺ concentration ([Ca²⁺]_i), we found that MEP could induce a sustained increase of [Ca²⁺]_i. The raise of [Ca²⁺]_i induced by MEP could be completely blocked by the intracellular Ca²⁺ chelator, BAPTA-AM, however, only partially inhibited by the extracellular Ca²⁺ chelator, EGTA. These results suggested that both influx of extracellular Ca²⁺ and release of Ca²⁺ from the internal storage were involved. We also found that MEP caused a decrease of mitochondria membrane potential and an increase of oxidative stress in RAW 264.7 cells. In conclusion, we found that the particles, collected from the motorcycle exhaust, contain chemicals that will induce apoptosis of macrophage in calcium-dependent manner.