phosphorus-radioisotopes and benz(j)aceanthrylene

Polycyclic aromatic hydrocarbons (PAHs) undergo metabolic activation reactions to yield intermediates that react with DNA to form covalent adducts. PAH administration leads to the formation of various types of DNA adducts that may differ between species, strains and tissues due to differences in metabolic activation and repair. The structures of PAH-DNA adducts can be identified by three approaches: co-chromatography with synthetic mononucleotide adduct standards; examining the adducts resulting from metabolism of pathway intermediates; or chemically blocking metabolic activation at specific sites on the PAH. Administration of putative metabolic intermediates of a PAH leads to enhanced formation of DNA adducts resulting from further activation along that pathway. Conversely, chemically blocking a bond or position on a PAH prevents adducts arising from activation at that site. By comparing the DNA adduct spectra generated by metabolites, blocked forms, and parent PAH administration, the pathways important in the metabolic activation of the PAH in each tissue may be deduced. Partial identification of these adducts may also be made by co-chromatography with the products of reactions between synthetic reactive intermediates and defined polydeoxynucleotides, and more thorough identification by using synthetic DNA adduct standards. These approaches have all been successfully applied to studies of PAH activation, and are reviewed here.

Topics: Animals; Benz(a)Anthracenes; Benzo(a)pyrene; Biotransformation; DNA; DNA Damage; Environmental Pollutants; Male; Methylcholanthrene; Mice; Phosphorus Radioisotopes; Polycyclic Compounds; Rats

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 microg/ml (120 microM) 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(l)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 microg/ml, 24 h). The total DNA adduct levels in human lymphocytes exposed to B(j)A, B(l)A or B(a)P were 0.13 +/- 0.03, 1.10 +/- 0.62 and 0.37 +/- 0.10 fmol/microg 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/microg 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 microg/ml). By adding cytosine-1-beta-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/microg 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/microg DNA, and in lung tissue between 0.10 and 0.62 fmol/microg 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.

Topics: Animals; Benz(a)Anthracenes; Benzo(a)pyrene; Biotransformation; Cyclopentanes; DNA Adducts; DNA Damage; DNA, Single-Stranded; HL-60 Cells; Humans; Lung; Lymphocytes; Male; Methylcholanthrene; Microsomes, Liver; Mutagens; Phosphorus Radioisotopes; Polycyclic Aromatic Hydrocarbons; Rats; Rats, Inbred WKY