Benzo(a)pyrene (BaP) modulates vascular smooth muscle cells (vSMCs) from a quiescent to proliferative phenotype, a shift associated with activation of L1Md retrotransposon [K.P. Lu, K.S. Ramos, Biochem. Biophys. Res. Commun. 253 (1998) 828-833]. The present studies were conducted to evaluate L1Md activation profiles in murine vSMCs treated with BaP or its oxidative metabolites, and to screen for possible insertional mutations into p53 and retinoblastoma (RB) genes. We also sought to examine the profile of DNA damage and repair in BaP-treated vSMCs. Northern analysis revealed that BaP (0. 03-3microM), and its major reactive 7,8-diol metabolite (0. 03-3microM), activate L1Md gene in a concentration-dependent manner. Two other metabolites, 3-OH BaP and 3,6-BaP quinone (0.03-3microM), as well as hydrogen peroxide (25-75microM) also activated L1Md. No insertional mutations into either p53 or RB genes were observed in vSMCs treated with BaP in vitro, although a slight elevation of p53 mRNA was observed as early as 4h after chemical challenge. Treatment of vSMCs with 3 or 30microM BaP for 4h increased unscheduled DNA synthesis (UDS) 1.4- and 2.5-fold, respectively. Challenge with 0. 3microM BaP for 24h inhibited DNA repair capacity in vSMCs for up to 48h. These results demonstrate that BaP and its oxidative metabolites activate L1Md retrotransposon in vSMCs, which coupled to DNA damage and inhibition of DNA repair are part of the atherogenic response elicited by BaP and related hydrocarbons.