Involvement of oxidative stress in motorcycle exhaust particle-induced DNA damage and inhibition of intercellular communication

Abstract

In this study, we investigated the involvement of reactive oxygen species (ROS) in the motorcycle exhaust particle (MEP)-induced genotoxic and non-genotoxic activity in mammalian cell systems. Initially, the capability of MEP to induce ROS was evaluated by using 2′,7′-dichlorofluorescin diacetate (DCFH-DA) to detect hydrogen peroxide (H 2O 2). A five-fold increase in H 2O 2 was observed in Chinese hamster lung V79 and human lung carcinoma Calu-1 cells treated with 100 μg/ml MEP for 2 h. Under the same experimental conditions, only a two-fold elevation in H 2O 2 was detected in hepatic cell systems such as BNL.Cl.2, HepG2, and Hep3B. Treatment of the V79 cells with varying concentrations of MEP caused a dose-dependent increase in sister chromatid exchanges (SCEs), which are effectively inhibited by addition of antioxidants, N-acetyl- l-cysteine (NAC) and ascorbic acid. Furthermore, we determined the oxidized bases in the V79 cells after exposure to MEP. The result showed that 500 μg/ml MEP induced a 3.7-fold increase in thymine glycol (TG) and a seven-fold increase in 8-hydroxy-guanosine (8-OHGua) as compared to untreated cells. We subsequently examined whether MEP would affect gap junctional intercellular communication (GJIC), a tumor promotion process, in V79 cells. We found that MEP inhibited GJIC in a dose–response fashion. Maximal inhibition occurred at 500 μg/ml. The concentration that inhibited at 0.5 of the fraction of the control was 200 μg/ml. Interestingly, when cells were pretreated with NAC or ascorbic acid, they could abolish the MEP-mediated inhibition of GJIC. In addition, a moderate decrease of glutathione was observed in the V79 cells during exposure to MEP. Taken together, our findings suggest that MEP can induce oxidative stress in a broad range of cell lines, especially in lung cell systems. The MEP-induced oxidative stress was critically involved in both genotoxic and non-genotoxic activity.