Genotoxic effects of cyclopenta-fused polycyclic aromatic hydrocarbons in different types of isolated rat lung cells.

ABSTRACT

The genotoxic effects of the environmental contaminants benz[j]aceanthrylene (B[j]A), benz[l]aceanthrylene (B[l]A) and benzo[a]pyrene (B[a]P), and the metabolism of radiolabelled B[j]A, were studied using rat lung microsomes and various types of isolated rat lung cells from control and Aroclor 1254 (PCB) treated animals. All three compounds (10 or 20 microg/plate) resulted in low, but detectable, levels of His+ revertants in the Salmonella assay when plated with control lung microsomes. The two cyclopenta polycyclic aromatic hydrocarbons (CP-PAH) B[j]A and B[l]A, gave increased levels of revertants when plated with microsomes from PCB-treated animals. Clara cells, type 2 cells and alveolar macrophages isolated from control rats were exposed to B[j]A, B[l]A or B[a]P (30 microg/ml, 1 h), but neither of the cell types showed any DNA damage when measured by alkaline filter elution. However, both B[j]A and B[l]A (30 microg/ml, 2 h) caused DNA adducts in all three cell types, measured by the 32P-post-labelling technique, whereas no B[a]P adducts were detected (30 microg/ml, 2 h). The total DNA adduct levels in Clara cells, type 2 cells and macrophages exposed to B[j]A were 0.085 +/- 0.033, 0.053 +/- 0.001 and 0.170 +/- 0.030 fmol/microg DNA, respectively, whereas the total levels in cells exposed to B[l]A were 0.140 +/- 0.070, 0.140 +/- 0.030 and 0.220 +/- 0.080 fmol/microg DNA, respectively. Cells exposed to B[j]A revealed only one adduct which corresponds with the B[j]A-1,2-oxide DNA adduct. Judged from high performance liquid chromatography (HPLC) analysis using radiolabelled B[j]A (30 microg/ml, 30 min), the major metabolite formed in control microsomes was B[j]A-1,2-diol. Thus, oxidation at the cyclopenta ring appears to be the most important activation pathway for B[j]A with control rat lung cells. Exposure of lung cells to CP-PAH (30 microg/ml, 2 h) isolated from PCB pretreated rats resulted in slightly increased DNA adduct levels in Clara cells and macrophages when compared to cells isolated from control rats. Furthermore, the adduct pattern had shifted, and no apparent B[j]A-1,2-oxide adduct could be detected on the thin layer chromatography (TLC) plate. In contrast, the major metabolite formed with microsomes from PCB-treated animals was still the B[j]A-1,2-diol.