Comparison of in vitro toxicity of mainstream cigarette smoke particulate matter from nano- to micro-size

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. PM_2.5 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 PM_2.5-induced cell injury, but the exact mechanisms are not well understood.

METHODS

The cytotoxic effects of PM_2.5 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 PM_2.5. The destabilized enhanced green fluorescent protein (d2EGFP) green fluorescent protein reporter system was used to determine the NF-κB activity induced by PM_2.5. The expression of pro-apoptotic Bcl-2-associated death promoter (BAD) proteins induced by PM_2.5 was determined by western blotting to explore the relationship between PM_2.5 and the NF-κB signaling pathway and to determine the toxicological mechanisms of PM_2.5.

RESULTS

PM_2.5 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 PM_2.5 and flow cytometry assays with 26.97% apoptosis rates at 200 μg/ml PM_2.5. PM_2.5 increases the activation levels of NF-κB, which have maintained for 24 h. 200 μg/ml PM_2.5 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 PM_2.5. In addition, PM_2.5 decreases the expression level of the pro-apoptotic protein BAD in a concentration-dependent manner.

CONCLUSIONS

PM_2.5 induces NF-κB activation, which persists for 24 h. The expression of pro-apoptotic protein BAD decreased with increased concentrations of PM_2.5. These findings suggest that PM_2.5 plays a major role in apoptosis by activating the NF-κB signaling pathway and reducing BAD protein expression.

Cytotoxicity and mutagenicity of sidestream cigarette smoke particulate matter of different particle sizes

Sidestream cigarette smoke, the major component of environmental tobacco smoke, is a complex and reactive aerosol. The particulate matter (PM) in sidestream smoke is one of the carriers of chemical constituents. However, particle size-dependent toxicological effects of PM are poorly understood. In this study, we evaluated the relationship between the PM size and in vitro cytotoxicity and mutagenicity of sidestream cigarette smoke. A NanoMoudi-II(™) 125A was used to collect PM samples ranging from 10 nm to 10 μm. The in vitro toxicity of PM was evaluated using a neutral red cytotoxicity assay and Salmonella mutagenicity assay. The results showed that the cytotoxicity and mutagenicity of PM larger than 1 μm was significantly lower than PM sized 10 nm-1 μm. Furthermore, there was a noticeable trend that the smaller the size of the PM of sidestream cigarette smoke, the greater the toxicity. This study suggests that the toxicity of PM in sidestream cigarette smoke is size-dependent.