phosphorus-radioisotopes and benzo(a)pyrene-4-5-epoxide

Bronchial epithelial cells are often exposed to airborne mutagens that have the potential to induce genetic changes involved in the development of lung cancer. Although lung tumors often display alterations in the expression of oncogenes and/or tumor suppressor genes, the role of specific chemicals and/or metabolites in causing these alterations is not well defined. The polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (B[a]P), a by-product of combustion, is a prevalent airborne environmental mutagen and a constituent of cigarette smoke. The primary objective of this study was to compare the effect of B[a]P and two of its reactive metabolites, benzo[a]pyrene diol epoxide (BPDE or bay region epoxide) and benzo[a]pyrene-4,5-dihydroepoxide (BPE or K-region epoxide), on expression of the proto-oncogene c-myc in normal human bronchial epithelial (NHBE) cells using a quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) method. Changes in c-myc gene expression were compared with DNA adduct formation, growth inhibition, and cell-cycle progression as determined by (32)P-postlabelling, neutral red (NR), and flow cytometric analyses, respectively. None of the three test compounds altered the levels of 18S ribosomal RNA or beta-actin at the concentrations evaluated for c-myc expression, indicating that nonspecific changes in gene expression induced by cytotoxicity, for example, were not present at the concentrations evaluated. Cells exposed to B[a]P exhibited a dose-dependent increase in c-myc expression; conversely, a dose-dependent decrease in c-myc expression was observed following BPDE exposure. A marginal but concentration-dependent increase in c-myc mRNA levels was observed following exposure to the K-region epoxide. Our results demonstrated that, although B[a]P and its metabolites alter c-myc expression, the parent compound and its metabolites produce unequal and contrasting effects on the expression of this gene.

Topics: 7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; Air Pollutants; Benzo(a)pyrene; Benzopyrenes; Bronchi; Cell Cycle; Cell Division; Cells, Cultured; Coloring Agents; DNA Adducts; Epithelial Cells; Gene Expression Regulation; Humans; Mutagens; Neutral Red; Phosphorus Radioisotopes; Polycyclic Aromatic Hydrocarbons; Proto-Oncogene Mas; Proto-Oncogene Proteins c-myc; Reference Values; Reverse Transcriptase Polymerase Chain Reaction

Human placenta readily catalyzes the biotransformation of polycyclic aromatic hydrocarbons (PAHs) and other carcinogens to reactive metabolites that can damage DNA through formation of covalent adducts. Placenta is widely available for epidemiologic studies and may be a useful dosimeter for carcinogen exposures in humans. However, previous studies of human placental DNA have yielded discrepant results with respect to PAH-DNA adducts. In order to resolve some of the issues surrounding these discrepancies, placental DNA samples known to contain benzo[a]pyrene diol epoxide adducts were also analyzed by 32P-postlabeling and immunoaffinity chromatography. Results indicate that previous discrepancies can be accounted for by methodologic factors affecting the specificities of adduct assays in biological samples and suggest that human placental DNA contains adducts derived from multiple PAHs.

Topics: Benzo(a)pyrene; Benzopyrenes; Chromatography, Affinity; DNA; DNA Adducts; DNA Damage; Female; Humans; Phosphorus Radioisotopes; Placenta; Spectrometry, Fluorescence