Abstract
The metabolism of radiolabelled benz(j)aceanthrylene (B(j)A) was studied by high performance liquid chromatography (HPLC) using suspensions of hepatocytes and liver microsomes from control- or Aroclor 1254 (PCB)-treated rats, or with human liver microsomes (five different donors) as activation systems. The major metabolites formed in hepatocytes were sulfate conjugates, indicating that sulfation is an important detoxication pathway for B(j)A. In incubations with B(j)A and rat or human liver microsomes, the major metabolite formed was B(j)A-1,2-diol. Studies with rat liver microsomes using antibodies (Ab) towards either P4501A1, 1A2 or 3A2, resulted in approximately 30% reduction in covalent binding with all Ab-using microsomes from control animals, whereas with microsomes from PCB-treated animals an 85% reduction was observed using Ab towards P4501A2, and only minor reductions were observed with 1A1 or 3A2. When compared to B(j)A and benzo(a)pyrene (B(a)P), benz(l)aceanthrylene (B(l)A) caused higher numbers of revertants in the Salmonella assay when plated with rat liver microsomes from control animals or human liver microsomes. The total DNA adduct levels in hepatocytes from control animals after 2 h exposure to 30 μg/ml (120 μM) B(j)A or B(l)A, as measured by the 32P-postlabelling technique, were 3.8±1.5 and 10.1±5.8 fmol/ μg DNA, respectively. PCB-treatment decreased the total level of B(j)A adducts slightly (1.8±0.5 fmol/ μg DNA), whereas in contrast the level of B(l)A adducts was increased (24.5±20.1 fmol/ μg DNA). The major DNA adduct formed in control hepatocytes exposed to B(j)A co-chromatographed with B(j)A-1,2-oxide, which also appeared to be the major adduct formed when rat or human liver microsomes were co-incubated with calf thymus DNA. The total DNA adduct levels in the modified calf thymus DNA after 30 min exposure to 30 μg/ml B(j)A, B(l)A or B(a)P using rat liver microsomes from control animals, were 3.6, 66.3 and 1.4 fmol/ μg DNA, respectively. These levels increased to 22.7, 93.3 and 7.4 fmol/ μg DNA, respectively, using microsomes from PCB-treated animals. With human liver microsomes, the total DNA adduct levels after exposure to B(j)A, B(l)A or B(a)P, ranged between 0.4–1.0, 0.3–4.3, and 0.1–0.3 fmol/ μg DNA, respectively. Overall, the present data supports the notion that oxidation at the cyclopenta-ring is an important activation pathway for B(j)A, and indicate that the activation mechanism for B(j)A is similar in rat and human liver tissue.
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