PM2.5 obtained from urban areas in Beijing induces apoptosis by activating nuclear factor-kappa B

BACKGROUND Particulate matter (PM), which has adverse effects on citizen health, is a major air pollutant in Beijing city. PM2.5 is an indicator of PM in urban areas and can cause serious damage to human health. Many epidemiological studies have shown that nuclear factor-kappa B (NF-κB) is involved in PM2.5-induced cell injury, but the exact mechanisms are not well understood. METHODS The cytotoxic effects of PM2.5 at 25-1600 μg/ml for 24 h were determined by MTT assay in Chinese hamster ovary cells (CHO) cells. Flow cytometry was used to determine the apoptosis rate induced by PM2.5. The destabilized enhanced green fluorescent protein (d2EGFP) green fluorescent protein reporter system was used to determine the NF-κB activity induced by PM2.5. The expression of pro-apoptotic Bcl-2-associated death promoter (BAD) proteins induced by PM2.5 was determined by western blotting to explore the relationship between PM2.5 and the NF-κB signaling pathway and to determine the toxicological mechanisms of PM2.5. RESULTS PM2.5 collected in Beijing urban districts induces cytotoxic effects in CHO cells according to MTT assay with 72.28% cell viability rates even at 200 μg/ml PM2.5 and flow cytometry assays with 26.97% apoptosis rates at 200 μg/ml PM2.5. PM2.5 increases the activation levels of NF-κB, which have maintained for 24 h. 200 μg/ml PM2.5 cause activation of NF-κB after exposure for 4 h, the activation peak appears after 13.5 h with a peak value of 25.41%. The average percentage of NF-κB activation in whole 24 h is up to 12.9% by 200 μg/ml PM2.5. In addition, PM2.5 decreases the expression level of the pro-apoptotic protein BAD in a concentration-dependent manner. CONCLUSIONS PM2.5 induces NF-κB activation, which persists for 24 h. The expression of pro-apoptotic protein BAD decreased with increased concentrations of PM2.5. These findings suggest that PM2.5 plays a major role in apoptosis by activating the NF-κB signaling pathway and reducing BAD protein expression.