BENZO[A]PYRENE COATED FERRIC-OXIDE AND ALUMINUM-OXIDE PARTICLES - UPTAKE, METABOLISM AND DNA-BINDING IN HAMSTER PULMONARY ALVEOLAR MACROPHAGES AND TRACHEAL EPITHELIAL-CELLS IN-VITRO

Ferric oxide (Fe2O3) and aluminum oxide (Al2O3) particles are, widely encountered in occupational settings, Benzo[a] pyrene (B[a]P), a well- characterized environmental carcinogen, is frequently adsorbed onto pa rticles. It has been shown that B[a]P-coated Fe2O3 particles (B[a]P-Fe 2O3) significantly increased lung tumors in the hamster in contrast to B[a]P-coated Al2O3 (B[a]P-Al2O3) or B[a]P alone. In order to determin e the genotoxic effects of these particles on the metabolism of B[a]P, pulmonary alveolar macrophages (AM) from male Syrian golden hamsters were incubated with 5 mu g (19.8 nmol) B[a]P-coated respirable size (9 9% <5 mu m) Fe2O3 and Al2O3 particles with loads from 0.5 to 2.0 mg. I ntracellular uptake of B[a]P by AM at 24 h was higher with B[a]P-Fe2O3 than that of B[a]P alone (P < 0.05) or B[a]P-Al2O3 (P < 0.05). Total B[a]P metabolism was significantly greater in AM exposed to B[a]P-coat ed Fe2O3 at 1.0 and 1.5 mg than in the AM exposed to B[a]p-al(2)O(3) ( 0.5, 1.0 and 1.5 mg) (P < 0.05) or B[a]P alone (P < 0.05). Similar sig nificant differences for Fe2O3 relative to Al2O3 and B[a]P alone were also apparent for total dihydrodiols, quinones and phenolic metabolite s. Co-administration of 5 mu g alpha-naphthoflavone (alpha-NF, an inhi bitor of cytochrome P-4501A1 and P-4501A2) and 10(-3) M cyclohexene ox ide (CO, an inhibitor of epoxide hydrolase) significantly reduced B[a] P metabolism in B[a]P-Fe2O3 (P < 0.05) and B[a]P-Al2O3 (P < 0.05) trea ted groups relative to B[a]P alone. AM were co-cultured with hamster t racheal epithelial cells (HTE) and treated as described above for meta bolism studies to assess the DNA binding of B[a]P metabolites in the t arget cells, using P-32-postlabeling techniques. Two adducts were obse rved that had chromatographic behavior similar to 7R,8S,9S-trihydroxy- 10R-(N-2-deoxyguanosyl-3' -phosphate)-7,8,9,10-tetrahydrobenzo[a]pyren e [(+)-anti-BPDE-dG, adduct 1, major adduct representing 70-80% of tot al adducts] and yl-3'-phosphate)-7,8,9,10-tetrahydrobenzo[a]pyrene [(- )-anti-BPDE-dG, adduct 2, representing 20-30% of total adducts]. B[a]P -Fe2O3 treatment enhanced the levels of the two B[a]P-DNA adducts in t he HTE compared with B[a]P-Al2O3 (P < 0.05) or B[a]P alone. The inhibi tors alpha NF and CO significantly reduced total adduct levels in the HTE (P < 0.05) in the B[a]P and B[a]P-Fe2O3 treatments as well as addu ct 1 and adduct 2 levels. Our data suggest that the cocarcinogenic eff ect of B[a]P-Fe2O3 relative to B[a]P-coated Al2O3 can be due to: (i) t he enhancement of B[a]P metabolism in AM by Fe2O3 associated with the increased uptake of B[a]P; and (ii) augmentation of DNA adduct formati on in epithelial cells.