INVOLVEMENT OF OXIDATIVE STRESS IN MOTORCYCLE EXHAUST PARTICLE-INDUCED DNA-DAMAGE AND INHIBITION OF INTERCELLULAR COMMUNICATION

In this study, we investigated the involvement of reactive oxygen spec ies (ROS) in the motorcycle exhaust particle (MEP)-induced genotoxic a nd non-genotoxic activity in mammalian cell systems. Initially, the ca pability of MEP to induce ROS was evaluated by using 2',7'-dichloroflu orescin diacetate (DCFH-DA) to detect hydrogen peroxide (H2O2). A five -fold increase in H2O2 was observed in Chinese hamster lung V79 and hu man lung carcinoma Calu-l cells treated with 100 mu g/ml MEP for 2 h. Under the same experimental conditions, only a two-fold elevation in H 2O2 was detected in hepatic cell systems such as BNL.C1.2, HepG2, and Hep3B. Treatment of the V79 cells with varying concentrations of MEP c aused 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 oxi dized bases in the V79 cells after exposure to MEP. The result showed that 500 mu g/ml MEP induced a 3.7-fold increase in thymine glycol (TG ) and a seven-fold increase in 8-hydroxy-guanosine (8-OHGua) as compar ed to untreated cells. We subsequently examined whether MEP would affe ct gap junctional intercellular communication (GJIC), a tumor promotio n process, in V79 cells. We found that MEP inhibited GJIC in a dose-re sponse fashion. Maximal inhibition occurred at 500 mu g/ml. The concen tration that inhibited at 0.5 of the fraction of the control was 200 m u g/ml. Interestingly, when cells were pretreated with NAC or ascorbic acid, they could abolish the MEP-mediated inhibition of GJIC. In addi tion, 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, especiall y in lung cell systems. The MEP-induced oxidative stress was criticall y involved in both genotoxic and non-genotoxic activity. (C) 1998 Else vier Science B.V.