Simultaneous determination of cellular mutagenesis and transformation by chemical carcinogens in Fischer rat embryo cells

ATSDR evaluation of health effects of chemicals. IV. Polycyclic aromatic hydrocarbons (PAHs): understanding a complex problem

Polycyclic Aromatic Hydrocarbons (PAHs) are a group of chemicals that are formed during the incomplete burning of coal, oil, gas, wood, garbage, or other organic substances, such as tobacco and charbroiled meat. There are more than 100 PAHs. PAHs generally occur as complex mixtures (for example, as part of products such as soot), not as single compounds. PAHs are found throughout the environment in the air, water, and soil. As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals, including PAHs (ATSDR, 1995), found at facilities on the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) and which pose the most significant potential threat to human health, as determined by ATSDR and the Environmental Protection Agency (EPA). These profiles include information on health effects of chemicals from different routes and durations of exposure, their potential for exposure, regulations and advisories, and the adequacy of the existing database. Assessing the health effects of PAHs is a major challenge because environmental exposures to these chemicals are usually to complex mixtures of PAHs with other chemicals. The biological consequences of human exposure to mixtures of PAHs depend on the toxicity, carcinogenic and noncarcinogenic, of the individual components of the mixture, the types of interactions among them, and confounding factors that are not thoroughly understood. Also identified are components of exposure and health effects research needed on PAHs that will allow estimation of realistic human health risks posed by exposures to PAHs. The exposure assessment component of research should focus on (1) development of reliable analytical methods for the determination of bioavailable PAHs following ingestion, (2) estimation of bioavailable PAHs from environmental media, particularly the determination of particle-bound PAHs, (3) data on ambient levels of PAHs metabolites in tissues/fluids of control populations, and (4) the need for a critical evaluation of current levels of PAHs found in environmental media including data from hazardous waste sites. The health effects component should focus on obtaining information on (1) the health effects of mixtures of PAHs particularly their noncarcinogenic effects in humans, and (2) their toxicokinetics. This report provides excerpts from the toxicological profile of PAHs (ATSDR, 1995) that contains more detailed information.

Cell transformation by chemical agents--a review and analysis of the literature. A report of the U.S. Environmental Protection Agency Gene-Tox Program

The literature on cell transformation by chemical carcinogens has been critically reviewed. This subject is highly relevant to carcinogenesis in vivo, because the phenotypic changes that are collectively referred to as cell transformation usually involve the acquisition of tumorigenicity on inoculation into suitable rodent hosts. The systems chosen for review fall into 3 categories: cell strains (cells with a limited lifespan); cell lines (cells with an unlimited lifespan); and oncogenic viral-chemical interactions involving cells (Fischer rat embryo cells expressing an endogenous retrovirus, mouse embryo cells expressing the AKR leukemia virus, chemical enhancement of a simian adenovirus, SA7 transformation of Syrian hamster or rat embryo cells). Of the entire literature reviewed, 117 papers have been accepted for data abstraction by pre-defined criteria; these include 41 references to cell strains, 40 in cell lines, and 38 in viral-chemical interactions including cells. Because different systems have been reviewed, it would be meaningless to group all the compounds. The overall summary of the systems is as follows (many compounds have been tested in more than one system and, hence, are duplicated in these totals). (Chart: see text) In general, there is a reasonably good correlation between the results of the cell transformation systems and in vivo carcinogenesis. However, the many deficiencies of the EPA Merged Carcinogen List preclude definitive comparisons. Moreover, a number of 'false negatives' were obtained in systems that did not employ external metabolic activation. Further validation of all systems is required, but it seems very probable that several cell transformation systems will become valuable in assaying (with reasonable time and cost) the carcinogenic potential of environmental chemicals.

Chemical carcinogenesis in vitro: an improved method for chemical transformation in Rauscher leukemia virus-infected rat embryo cells

In vitro assay for carcinogenesis, using mammalian cells, provide opportunity for rapid and inexpensive means, compared to in vivo assays, for studying carcinogenesis and for identifying potential carcinogens. These assays must, however, be shown to be reproducible, reliable and able to detect a variety of known carcinogens before they can be recommended for general use. We have, independently, reproduced a transformation assay which utilizes murine leukemia virus-infected rat embryo cells as targets. In the process a new culture, designated 2FR4(50), was generated to replace the F1706 line, of Freeman, which is no longer available. Through careful control of the assay parameters a readily reproducible test has been developed. In 2-4 culture passages after chemical treatment, morphologically transformed foci of cells are observed while no such foci are found in noncarcinogen treated or control cultures. Over 75 compounds have been tested in this assay; 20 of these are detailed here as representative of the chemically diverse types of carcinogens detected.

Metabolism of 2-acetylaminofluorene in primary rat hepatocyte cultures

Primary cultures of adult rat parenchymal hepatocytes were developed as an in vitro model to investigate the biochemical fate of 2-acetylaminofluorene (AAF), a potent hepatocarcinogen. More than 5 x 10(8) viable cells were routinely isolated by collagenase perfusion in rat liver; the cells were cultured 2-5 d on collagen-coated dishes in serum-free culture medium containing hormones and other factors to retard the decline of cytochrome P-450. All of 137 ng or 13.7 microgram AAF was metabolized in 21-24 h by 2 x 10(6) cultured hepatocytes in 4.0 ml defined medium. At the higher dose, water-soluble metabolites appeared at 70% of the rate of metabolism at the lower dose, which was 17 ng/h for the initial 4 h. As the parent compound was consumed, bound AAF residues were recovered with exhaustively extracted, trichloro-acetic acid-precipitated hepatocellular macromolecules, accounting for a maximum of 5% of the 137-ng dose. Addition of hormones to the culture medium stimulated the rate of appearance of water-soluble metabolites, AAF, correlating with the enhanced cytochrome P-450 levels of hormone-treated cells. Metabolism of AAF was diminished 50% during 3 h of incubation with 10(-4) M SKF 525A and 100% with 10(-3) M SKF 525A. At a dose of 40 microgram AAF per 2 X 10(6) cells, only 31% of the carcinogen was recovered from the culture medium as water-soluble products after 24 h; the cells were sown to be capable of metabolizing a subsequent 40-microgram dose at an undiminished rate, suggesting that saturation of metabolizing enzymes rather than toxicity occurred. These results support the validity of primary hepatocyte cultures as a model system for quantitative investigations of the biochemical fate of AAF in mammalian cells, and provide preliminary characterization of the cells' processes of detoxification and metabolic activation of a chemical carcinogen.

Mutagenicity and transformation by recycled water

Increased use of contaminated water and long-range plans for the direct use of recycled water necessitate a careful assessment of the potential health effect on the population. Selected in vitro assays were used to evaluate the mutagenic and carcinogenic potential of a concentrated, recycled water sample. It was found that the concentrated water induced mutagenicity in hamster lung cells and cellular transformation in human embryonic lung fibroblasts. The use of in vitro analyses in conjunction with epidemiologic studies in determining the human risks of environmental carcinogens is discussed.