Abstract
The metabolism of radiolabelled benz(j)aceanthrylene (B(j)A) was studied in suspensions of isolated human peripheral mononuclear blood cells (lymphocytes), using high performance liquid chromatography (HPLC). The only known metabolite found after 24 h exposure to 30 μg/ml (120 μM) B(j)A, was B(j)A-1,2-dihydrodiol, representing approximately 35% of the total metabolites formed. B(j)A, benz(l)aceanthrylene (B(1)A) and benzo(a)pyrene (B(a)P) all caused DNA adducts in human lymphocytes, as well as in the human promyelocytic cell line HL-60 cells, as measured by the 32P-postlabelling technique (30 μg/ml, 24 h). The total DNA adduct levels in human lymphocytes exposed to B(j)A, B(1)A or B(a)P were 0.13±0.03, 1.10±0.62 and 0.37±0.10 fmol/ μg DNA, respectively, and similar levels were obtained in HL-60 cells (0.18±0.14, 0.97±0.35 and 0.29±0.17 fmol/ μg DNA, respectively). For each compound, the human lymphocytes and HL-60 cells in addition showed similar DNA adduct patterns. Cells exposed to B(j)A revealed only one DNA adduct, which, judged by its TLC properties, resulted from B(j)A-1,2-epoxide. As measured by the alkaline filter elution technique, only low levels of single strand DNA breaks (SSB) were observed in both human lymphocytes and HL-60 cells after exposure to B(j)A, B(l)A or B(a)P (24 h, 30 μg/ml). By adding cytosine-1- β- d-arabinofuranoside (Are C) and hydroxyurea (HU) 1 h prior to analysis to prevent strand break rejoining, some increase in SSB (2–3 times) was observed in the lymphocytes. Co-incubation of human lymphocytes with liver microsomes from PCB-treated rats for 1 h and exposure to B(j)A or B(l)A, increased the DNA adduct levels in the lymphocytes to 12.3 and 37.8 fmol/ μg DNA, respectively. A large increase in SSB was also observed, whereas no such increase was observed after co-incubation with human liver microsomes. In vivo exposure of rats to 30 mg/kg B(j)A (i.p.) for 24 h revealed one major DNA adduct in lymphocytes and lung tissue (only one of three rats showed an adduct in liver tissue), apparently resulting from B(j)A-1,2-epoxide. The total DNA adduct level in the lymphocytes was 0.09 fmol/ μg DNA, and in lung tissue between 0.10 and 0.62 fmol/ μg DNA. Overall, the present data suggests that oxidation at the cyclopenta-ring is an important activation pathway for B(j)A in rats as well as in humans.
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