Application of an epithelial liver cell line, metabolically competent, for mutation studies of promutagens

Identification of genotoxic compounds in the airborne particulate matter endowed by small aerodynamic diameter in the city of Catania (Italy)

Airborne particulate matter (PM) is one of the most important polluting factors in the atmosphere containing solid particles generated during the combustion processes. PM, due to the particle size, is easily inhaled and constitutes a potential hazard for the human health. We previously documented, using in vitro cell culture systems, cytogenetic damages caused by exposure to a non-fractionated PM in two different areas from the city of Catania (Sicily, Italy). In the present work, the PM was fractionated in six different sub-fractions, and the relative extractable organic matters (EOM) were analyzed in order to quantify the presence of Polycyclic Aromatic Hydrocarbons (PHAs), a well known class of genotoxic agents. More than 70% of the total EOM was found in the PM with aerodynamic diameters less than 3.5 microm (PM35), and about 60% of the total EOM was detected between PM0.14 and PM1.2. Also the large amount of all the analyzed PAHs were found between the PM0.14 and PM1.2. The obtained data indicates that the genotoxic effect previously shown on mammalian cells (Chinese hamster epithelial liver cells) should be due, in the large part, to the PM with smaller particle size, namely less than PM1.2.

Cytogenetic evaluation of extractable agents from airborne particulate matter generated in the city of Catania (Italy)

In order to document cytogenetic damage associated with air pollution and, possibly, with health effects in the city of Catania, Sicily (Italy), we analyzed the induction of chromosomal aberrations by extractable agents from airborne particulate matter in a Chinese hamster epithelial liver (CHEL) cells. These cells retain their metabolic competence to activate different classes of promutagens/procarcinogens into biologically active metabolites. Airborne particulate matter was obtained from two stationary samplers (stations I and II) in two areas endowed by an elevated car transit in the centre of Catania. The results obtained clearly indicated that airborne particulate matter from both stations I and II proved to be clastogens in CHEL cells but not in Chinese hamster ovary (CHO) cells without metabolic activation, indicating that airborne particulate mixtures need to be metabolically converted before exerting their genotoxic potential. On the basis of these results we can assert that the test system employed to identify the cytogenetic potential of airborne particulate matter is useful and profitable for environmental control, and helpful to plan specific actions aimed at reducing the hazards derived from exposure to polluted air.

Phenolphthalein induces chromosome aberrations in human and Chinese hamster liver cells (CHEL) cultured in vitro

Phenolphthalein is a nonprescription laxative agent that has been widely used during this century. Recent studies in animal models have shown that phenolphthalein has carcinogenic activity. In order to assess cytogenetic effects on human cells in vitro, we tested phenolphthalein in a chromosome aberration assay in human embryo cells derived from amniotic fluid. Our results show that phenolphthalein induces a significant increase in the frequency of chromosome aberrations in human cells. The lowest dose level at which the clastogenic effect is evident is 23.2 microg/ml. Similar positive results were obtained in a Chinese hamster liver cell line, which is metabolically competent to activate different classes of promutagens and procarcinogens into biologically active metabolites. Instead, parallel experiments in Chinese hamster ovary cells did not show any clastogenic effect due to phenolphthalein. These latter data suggested that phenolphthalein acts as a promutagen and must be metabolically activated to exert its clastogenic effect. Teratogenesis Carcinog. Mutagen. 20:209-217, 2000.

6-thioguanine resistance in a human colon carcinoma cell line with unaltered levels of hypoxanthine guanine phosphoribosyltransferase activity

Cell populations resistant to high doses (30 microM) of 6-thioguanine (6-TG, 6-TG(r) cells) were selected from a human colon carcinoma cell line, LoVo. This cell line, which lacks hMSH2, a component of the human mismatch binding heterodimer hMutSalpha, is resistant to low doses of 6-TG. The level of activity of hypoxanthine-guanine phosphoribosyltransferase, the enzyme responsible for the phosphoribosylation of the thiopurine, was comparable to that expressed in the parental cells. No significant difference was found in the levels of enzyme activities involved in the conversion of 6-TG or its derivatives into non-toxic compounds. In contrast, a significant difference was found in the uptake kinetics of 6-TG in the 2 cell types. Net uptake of 6-TG ceased after 100-sec incubation in the 6-TG(r) cells, while it appeared to continue throughout the 10-min incubation in the wild-type cells. As a consequence, after 10-min incubation, the total amount of 6-TG taken up by the parental LoVo cells was approximately 3 times higher than that present in the 6-TG(r) cells.

DT-Diaphorase Affects the Mutagenic Activity of Pyrene 1,6-Quinone in Chinese Hamster Epithelial Liver (CHEL) Cells

The mutagenic potential of pyrene 1,6-quinone (P 1,6-Q) has been studied in a wide range of in vitro genetic assays including the use of mammalian cell lines. P 1,6-Q has been shown to induce gene mutations and micronuclei in V79 cells, whereas, in Chinese hamster epithelial liver (CHEL) cells, a cell line which retains activities of various xenobiotic-metabolising enzymes, a non-specific pattern of structural and numerical chromosomal aberrations has been observed. In this study, we have evaluated the mutagenic activity of P 1,6-Q on V79 and CHEL cells both with and without dicoumarol, a potent inhibitor of DT-diaphorase. In V79 cells, dicoumarol (100μM) did not affect the mutagenic response, whereas in CHEL cells, the mutation frequency significantly increased. This suggests that DT-diaphorase, which is expressed in liver cells at high levels, has a possible role in the detoxification of P 1,6-Q to redox-stable hydroquinone.

Development and validation of alternative metabolic systems for mutagenicity testing in short-term assays

We present here the results obtained within the framework of an EU funded project aimed to develop and validate alternative metabolic activating systems to be used in short-term mutagenicity assays, in order to reduce the use of laboratory animals for toxicology testing. The activating systems studied were established cell lines (Hep G2, CHEL), genetically engineered V79 cell lines expressing specific rat cytochromes P450, erythrocyte-derived systems, CYP-mimetic chemical systems and plant homogenates. The metabolically competent cell lines were used as indicator cells for genotoxic effects as well as for the preparation of external activating systems using other indicator cells. The following endpoints were used: micronuclei, chromosomal aberrations and sister chromatid exchanges, mutations at the hprt locus, gene mutations in bacteria (Ames test), unscheduled DNA synthesis and DNA breaks detected in the comet assay. All metabolic systems employed activated some promutagens. With some of them, promutagens belonging to many different classes of chemicals were activated to genotoxicants, including carcinogens negative in liver S9-mediated assays. In other cases, the use of the new activating systems allowed the detection of mutagens at much lower substrate concentrations than in liver S9-mediated assays. Therefore, the alternative metabolizing systems, which do not require the use of laboratory animals, have a substantial potential in in vitro toxicology, in the basic genotoxicity testing as well as in the elucidation of activation mechanisms. However, since the data basis is much smaller for the new systems than for the activating systems produced from subcellular liver preparations, the overlapping use of both systems is recommended for the present and near future. For example, liver S9 preparations may be used with some indicator systems (e.g., bacterial mutagenicity), and metabolically competent mammalian cell lines may be used with other indicator systems (e.g., a cytogenetic endpoint) in a battery of basic tests.

Metabolic activation of benzo[a]pyrene in two fetal mouse hepatocyte lines: induction of DNA adducts and micronuclei

We have studied the metabolic competence of two non-transformed epithelial-like cell lines derived from fetal mouse liver, C 6 and C 2.8, to activate the promutagen benzo[a]pyrene by measuring both the induction of DNA adducts through the nuclease P1-enhanced 32P-postlabeling assay and the formation of micronuclei. The pattern and level of DNA adducts detected in C 6 and C 2.8 cells treated with benzo[a]pyrene were compared with those obtained in human peripheral blood lymphocytes treated with the same compound and with [3H]anti-benzo[a]pyrene diolepoxide. In both the cell lines and in human lymphocytes we observed a consistent induction of distinct DNA adducts. In C 6 and C 2.8 cells, the most evident adduct showed a position similar to that of the main adduct induced by [3H]-anti-benzo[a]pyrene diolepoxide in human lymphocytes. In addition, benzo[a]pyrene caused a significant increase of micronucleated C 6 and C 2.8 cells, whereas the frequency of micronuclei did not increase in CHO cells treated, for comparison, in the same way.

Comparison of common gene mutation tests in mammalian cells in culture: a position paper of the GUM Commission for the Development of Guidelines for Genotoxicity Testing

In gene mutation tests a decision concerning mutations is made on the basis of hereditary functional changes. In terms of the large amount of data available, the most suitable tests for routine testing in mammalian cells in culture are the tests for acquisition of 6-thioguanine resistance in Chinese hamster cells (V79 and CHO) and for acquisition of alpha,alpha,alpha-trifluorothymidine resistance in the mouse lymphoma line L5178Y TK+/- 3.7.2C. The molecular bases, peculiarities, advantages and disadvantages of these systems will be presented. Which system is to be preferred in any particular case depends among other things on the purpose of the study and the extent to which a technically competent performance of these comparatively exacting tests can be guaranteed.

3-isobutyl-1-methylxanthine inhibits the mutagenic activity of 7,12-dimethylbenz[a]anthracene in epithelial liver cells in culture

The mutagenic activity of 7,12-dimethylbenz[a]anthracene in epithelial liver cells (CHEL) in culture was unaffected by the enhancement of intracellular cAMP induced to different extents and with different mechanisms by forskolin and 3-isobutyl-1-methylxanthine. However, the latter compound exerted antimutagenic effects (> 60%), which may be tentatively ascribed to inhibition of the inducible monooxygenase isoform(s) responsible for the specific biotransformation of 7,12-dimethylbenz[a]anthracene to highly mutagenic metabolites in CHEL cells.

Clastogenic effects of the dithiocarbamate fungicides thiram and ziram in Chinese hamster cell lines cultured in vitro

We report here the results obtained using the dithiocarbamate fungicides thiram and ziram to investigate the induction of chromosomal aberrations (CAs) in Chinese hamster ovary (CHO) cells both in the absence and presence of S9 metabolism, and in a Chinese hamster epithelial liver (CHEL) cells which retain metabolic competence to activate different classes of promutagens/procarcinogens. Both thiram and ziram proved to be strong chromosome breaking agents in the CHEL cells and CHO cells in the presence of S9 metabolism. These findings suggest that thiram and ziram require metabolic conversion to become genetically active, and corroborate the evidence that CHEL cells are suitable to activate and detect a broad spectrum of chemical procarcinogens including these two pesticides.