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

Recently numerous attempts have been made to reduce the use of vertebrate animals in laboratory experiments to evaluate general and acute toxicity, mutagenesis and teratogenesis of new drugs or chemicals. One common approach is to use established, proliferating cell lines that preserve differentiated functions such as the competence to metabolize xenobiotics. To this end a continuous Chinese hamster epithelial liver cell line (CHEL cells) was established, cultured as used for mutagenesis studies. Structurally different promutagens, such as 7,12-dimethylbenz[a]anthracene (7,12-DMBA), benzo[a]pyrene (B(a)P), aflatoxin B1 (AB1) and cyclophosphamide (CP), were used in order to check and validate the test system. anti-Chrysene-1,2-diol 3,4-epoxide (CDE) and mitomycin C (MMC) were taken as representatives of direct mutagens. The genetic change induced by the mutagens was quantified by measuring mutation frequencies at the HGPRT locus. Several parameters, such as mutant expression time for each chemical, cell density for selection of mutants and enzymatic characterization for HGPRT phenotype, were examined to establish the optimal assay conditions. All promutagens analyzed significantly affected either the cloning efficiency and/or the mutant frequency of CHEL cells after 24 h of exposure. In addition, various enzyme activities involved in the metabolism of the promutagens were determined in CHEL cells, under the experimental conditions of chemical exposure used in the mutagenesis assay. The enzyme activities were compared with those found in uninduced Chinese hamster liver.     

The molecular nature of spontaneous and chemically induced mutations in the hypoxanthine-guanine phosphoribosyl transferase gene in rat liver epithelial cells

The molecular nature of mutations in 6-thioguanine-resistant hypoxanthine/guanine phosphoribosyl transferase (HGPRT)-deficient clones of an adult rat liver (ARL) epithelial cell line mutated by benzo[a]pyrene or aflatoxin B1 was studied. DNA from these clones or spontaneous HGPRT-deficient mutants was subjected to Southern blotting using an HGPRT probe following DNA digestion with the restriction enzymes BamH1, EcoR1, HindIII or XbaI. With either the chemically induced or spontaneous mutants, no difference in restriction fragment pattern was observed between any of the mutants and their wild-type parent. However, differences were found between two lines ARL 6 and ARL 14 and the lines ARL 18, ARL 19 and DNA from Fischer rat hepatocytes. Although the variants did not display loss of HGPRT activity. It is suggested that deletion or loss of a pseudogene sequence could be the basis for the alterations in restriction fragment patterns.     

An evaluation of the L5178Y TK+/− mouse lymophoma forward mutation assay using 42 chemicals

The L5178YTK^+/? mouse lymphoma assay (MLA) has been utilized in several laboratories as a short-term test for chemical-induced forward mutation in cultured mammalian cells. In order to evaluate several technical modifications to the MLA, 42 chemicals representing 9 chemical classes were tested and the results were compared with those published elsewhere as well as with findings in a genetic toxicology test battery currently used in this laboratory. A positive response for the induction of TK^+/? mutants was obtained for 26 chemicals. With the exception of p-aminophenol, all of these compounds were recognized mutagens or carcinogens and were represented of direct-acting and activation-dependent genotoxins. 16 compounds did not induce IK^?/? mutanants and among these were 5 compounds that were considered to be mutagens or carcinogens. A comparison of the results of this study with those published elsewhere revealed a strong agreement among findings for this test irrespective of minor technical variations. It was concluded that th MLA is a useful system for identifying chemical mutagens in mammalian cells and can serve as a valuabel component in a genetic toxicology test battery.     

Survival and mutagenesis of bacterial plasmids with localized carcinogen adducts

Induction of 6-thioguanine (TG) resistance by chemical mutagens was examined in a line of cells derived from a human epithelial teratocarcinoma cell clone. The cells, designated as P3 cells, have a stable diploid karyotype with 46(XX) chromosomes, including a translocation between chromosomes 15 and 20. Efficient recovery of TG-resistant mutants induced by the direct-acting mutagens: N-methyl-N'-nitro-N-nitrosoguanidine (MNNG); 7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10 -tetrahydrobenzo[a]pyrene (BPDE); and benzo[a]pyrene (B[a]P); activated in a cell-mediated assay, required an expression time of 7 days and a saturation density of 2 X 10(4) cells/60-mm petri dish. The TG-resistant mutant cells induced by MNNG and BPDE maintained their resistant phenotype 4-6 weeks after isolation. This mutant phenotype was associated with a more than 10-fold reduction in hypoxanthine-guanine phosphoribosyl transferase (HGPRT) activity relative to that of the parental P3 cell line, which was shown to catalyze the formation of 4.6 pmoles inosine-5'-monophosphate (IMP)/min/microgram protein. Induction of TG resistance was also observed in P3 cells cocultivated in a cell-mediated assay with human breast carcinoma cells, which are capable of polycyclic aromatic hydrocarbon (PAH) metabolism, after treatment with the carcinogenic PAHs: B[a]P, chrysene, 7,12-dimethylbenz[a]anthracene (DMBA), and 3-methylcholanthrene (MCA). The degree of mutant induction in this assay was related to the carcinogenic potency of these PAHs in experimental animals. The most potent mutagen was DMBA, followed in decreasing order by MCA, B[a]P, and chrysene. DMBA, at 0.4 microM, increased the frequency of mutants for TG resistance from 2 for the control to about 200 TG-resistant mutants/10(6) colony-forming cells (CFC). Benzo[e]pyrene (B[e]P) and pyrene, which are not carcinogenic, were not effective in the assay. None of the PAHs was mutagenic in the P3 cells cultivated in the absence of the PAH-metabolizing cells. These results indicate that the P3 cells can be useful for the study of mutagenesis at the HGPRT locus by direct-acting chemical mutagens, as well as by chemicals activated in a cell-mediated assay.     

Specific-locus mutations induced in eukaryotes (especially mammalian cells) by radiation and chemicals: a perspective

In the course of discovering the first mutagen (X-rays) just over 60 years ago, Herman J. Muller asked whether X-rays induced single-gene mutations and/or chromosomal (multiple-gene) mutations. To a large extent, his question has set the agenda for mutagenesis research ever since. We explore historically the answers to this question, with special emphasis on recent developments in the field of mammalian cell mutagenesis. Studies indicate that ionizing radiation and many chemical mutagens/carcinogens induce both gene and chromosomal mutations; however, only certain genetic systems permit the recovery and analysis of both classes of mutations. Few chemical mutagens induce only gene mutations in mammalian cells; instead, most mutagens appear to induce both classes of mutations, with chromosomal mutations (especially multilocus deletions) predominating at high doses. These results have implications regarding the mechanisms of mutagenesis, the role of chromosomal mutations in carcinogenesis and hereditary disease, and the type of data required for risk assessment of physical and chemical mutagens/carcinogens.     

An investigation on the antimutagenic properties of South African herbal teas

The antimutagenic properties of South African herbal teas were investigated using the Salmonella typhimurium mutagenicity assay. Aqueous extracts of fermented and unfermented rooibos tea (Aspalathus linearis) and honeybush tea (Cyclopia intermedia) both possess antimutagenic activity against 2-acetylaminofluorene (2-AAF) and aflatoxin B(1) (AFB(1))-induced mutagenesis using tester strains TA98 and TA100 in the presence of metabolic activation. A far less inhibitory effect was noticed against the direct acting mutagens, methyl methanesulfonate (MMS), cumolhydroperoxide (CHP), and hydrogen peroxide (H(2)O(2)) using TA102, a strain designed to detect oxidative mutagens and carcinogens. Depending on the mutagen used, the unfermented tea exhibited the highest protective effect. A similar response regarding the protection against mutagenesis was obtained when utilising different variations of the double layer Salmonella assay. The double layer technique proved to be more effective to detect the protective effect of the different tea preparations against the direct acting mutagens. With respect to indirect mutagens, the highest protection was noticed when the carcinogen was metabolically activated in the presence of the tea extract as compared with when the tea extract was incubated in a separate layer with the bacteria. The current data suggest that two mechanisms seem to be involved in the antimutagenicity of the tea extracts towards carcinogens that require metabolic activation: (i) the tea components may interfere with cytochrome P450-mediated metabolism of these mutagens and (ii) the direct interaction between the tea constituents, presumably the polyphenolic compounds, with the promutagens and/or the active mutagenic metabolites. However, the mild and/or lack of protection and in some cases even enhancement of mutagenesis induced by direct acting or oxidative mutagens, provide new perspectives regarding the role of the polyphenolic compounds known to exhibit antioxidant properties, in the protection against mutagenesis in the Salmonella assay. The present study provides the first evidence on the antimutagenic activity of honeybush tea and further evidence on the antimutagenicity of rooibos tea.     

A review and analysis of the Chinese hamster ovary/hypoxanthine guanine phosphoribosyl transferase assay to determine the mutagenicity of chemical agents. A report of phase III of the U.S. Environmental Protection Agency Gene-Tox Program

Published literature on the Chinese hamster ovary cell/hypoxanthine guanine phosphoribosyl transferase (CHO/HGPRT) assay from mid-1979 through June 1986 was reviewed and evaluated. Data from the papers considered acceptable include test results on 121 chemicals belonging to 25 chemical classes. A total of 87 chemicals were evaluated positive, 3 negative, and 31 inconclusive. Mutagenicity data on 49 of the 121 chemicals evaluated could also be compared with in vivo animal carcinogenicity data. 40 of the 43 reported animal carcinogens were considered mutagenic. Caprolactam, the only definitive noncarcinogen in the group of 49, was not mutagenic. The CHO/HGPRT assay was concluded to be an appropriate assay system for use in the screening of chemicals for genotoxicity.     

Mutagenicity of the oral carcinogen 4-nitroquinoline-1-oxide in cultured BigBlue rat tongue epithelial cells and fibroblasts

Environmental carcinogen exposures contribute to the development of oral cancer and improved test systems for the analysis of such carcinogens are needed. We have previously isolated and characterized an epithelial cell line from the tongue of a BigBlue rat. Now, we have established an immortalized fibroblast cell line from the same organ. We exposed these cells to 4-nitroquinoline-1-oxide (NQO), a well-known experimental oral carcinogen in the rat and other species, and measured its cytotoxic and genotoxic (cII transgene mutagenesis) effects. Both cell lines were very sensitive to NQO toxicity and showed dose-dependent mutant frequency responses. At the highest NQO dose tested, 70 ng/ml, the mutant frequency was elevated more than eight-fold above background for the epithelial cells and more than 25-fold for the fibroblast cells. We examined cellular parameters which could affect glutathione-dependent detoxication of mutagens. Glutathione (GSH) contents of the two cell lines were similar. Glutathione transferase (GST) activities were measured with several substrates and were generally higher in the epithelial cells. Although multiple biochemical and biological characteristics of individual cell lines are likely to determine responses to mutagens, the greater sensitivity of the fibroblast cells to NQO mutagenicity is in accord with the lower GST activity and the lower DNA content of these cells. These new cell lines are suitable for in vitro testing of chemicals as possible oral mutagens and for studies of their biochemical mechanisms of action.     

In vitro metabolic activation of ethidium bromide and other phenanthridinium compounds: mutagenic activity in Salmonella typhimurium.

The induction of mutation by a variety of mutagens has been measured utilizing the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) locus in Chinese hamster ovary (CHO) cells (CHO/HGPRT) system). These mutagens include physical agents such as UV light and X-rays, and chemicals such as alkylating agents, ICR-191, and metallic compounds. This system can also be modified for study of the mutagenicity of promutagens such as dimethylnitrosamine (DMN) which require biotransformation for mutagenic action, either through the addition of a rat liver microsomal activation preparation or through a host-mediated activation step using Balb/c athymic mice.     

Comparison of the AS52/XPRT and the CHO/HPRT assays: evaluation of 6 drug candidates

The purpose of this paper is to compare the result of testing a diverse group of chemicals in the CHO/HPRT and AS52/XPRT mutation assays. The AS52/XPRT system was as sensitive as the more widely used CHO/HPRT system in the case of the antitumor agents, and gave qualitatively similar results in all cases. On the basis of this and other experiments (Aaron et al., 1989) it appears that the AS52/XPRT system may be most useful in addressing mechanistic questions in mutagenesis. We recommend that the AS52/XPRT assay be used as the mammalian cell test system of choice in batteries used for identifying mutagens and genotoxic carcinogens.     

A comparison of the radiation-induced mutation at the HGPRT locus in V79 and BHK cells

Mutation response at the HGPRT locus has been compared in two differing cell lines: V79/4, an aneuploid Chinese-hamster fibroblast line with a complement of 20 chromosomes, and BHK21-C13, a diploid Syrian-hamster fibroblast line with a complement of 44 chromosomes. The data presented show that BHK is slightly more radiosensitive than V79/4; however, the toxicity curves and expression times are similar for both cell lines. If radiosensitivity is taken into account, a common line can be drawn for radiation mutagenesis. We conclude from the data that radiation-induced mutagenesis is broadly equivalent in the two cell lines examined, and is not dependent on the chromosome complement.     

Methods for analysis of the mutagenicity of indirect mutagens/carcinogens in eukaryotic cells

Summary The review discusses the variety of methods for activation of indirect mutagens/carcinogens and testing them in cell cultures, especially in mammalian cell cultures.After the necessity for including metabolizing components in mutagenicity tests has been pointed out, the enzymes that transform foreign compounds metabolically, and the factors influencing them, are described. In the main section the various methods of activating indirect mutagens/carcinogens are presented. The methods of including in vivo metabolism in mutagenicity tests are: Analysis of cells from organisms contaminated with a chemical (III.1.a); body fluid-mediated mutagenesis (III.1.b); host-mediated assay (III.1.c).The following activation systems are suitable for including in vitro metabolism of test compounds in mutagenicity tests: Liver and lung perfusion (III.2.a.); organ slices and homogenates (III.2.a.); subcellular fractions (III.2.a.); cultivated cells (cell-mediated mutagenesis) (III.2.b); nonenzymatic activation systems (III.2.c).Finally the main factors that influence the metabolism of test substances are summarized. Two figures illustrate the mutagenicity tests with regard to the metabolism of mammalian livers and the methods of performing mutagenicity tests in man.     

Induction of mutations by chemical agents at the hypoxanthine-guanine phosphoribosyl transferase locus in human epithelial teratoma cells

Induction of 6-thioguanine (TG) resistance by chemical mutagens was examined in a line of cells derived from a human epithelial teratocarcinoma cell clone. The cells, designated as P3 cells, have a stable diploid karyotype with 46(XX) chromosomes, including a translocation between chromosomes 15 and 20. Efficient recovery of TG-resistant mutants induced by the direct-acting mutagens: N-methyl-N′-nitro-N-nitrosoguanidine (MNNG); 7β,8α-dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE); and benzo[a]pyrene (B[a]P); activated in a cell-mediated assay, required an expression time of 7 days and a saturation density of 2 × 10⁴ cells/60-mm petri dish. The TG-resistant mutant cells induced by MNNG and BPDE maintained their resistant phenotype 4–6 weeks after isolation. This mutant phenotype was associated with a more than 10-fold reduction in hypoxanthine-guanine phosphoribosyl transferase (HGPRT) activity relative to that of the parental P3 cell line, which was shown to catalyze the formation of 4.6 pmoles inosine-5′-monophosphate (IMP)/min/μg protein. Induction of TG resistance was also observed in P3 cells cocultivated in a cell-mediated assay with human breast carcinoma cells, which are capable of polyclinic aromatic hydrocarbon (PAH) metabolism, after treatment with the carcinogenic PAHs: B[a]P, chrysene, 7,12-dimethylbenz[a]anthracene (DMBA), and 3-methylcholanthrene (MCA). The degree of mutant induction in this assay was related to the carcinogenic potency of these PAHs in experimental animals. The most potent mutagen was DMBA, followed in decreasing order by MCA, B[a]P, and chrysene. DMBA, at 0.4 μM, increased the frequency of mutants for TG resistance from 2 for the control to about 200 TG-resistant mutants/10⁶ colony-forming cells (CFC). Benzo[e]pyrene (B[e]P) and pyrene, which are not carcinogenic, were not effective in the assay. None of the PAHs was mutagenic in the P3 cells cultivated in the absence of the PAH-metabolizing cells. These results indicate that the P3 cells can be useful for the study of mutagenesis at the HGPRT locus by direct-acting chemical mutagens, as well as by chemicals activated in a cell-mediated assay.     

Establishment of epithelial cell lines from adult mouse regenerating liver

A simple technique for developing epithelial cell lines from regenerating mouse liver has been described. Twenty-one epithelial cell lines have been developed and can be divided into four groups according to their morphology. All these near diploid cell lines have the capacity to metabolize diverse classes of chemical carcinogens (3-methylcholanthrene, 2-acetylaminofluorene, dimethylnitrosamine and aflatoxin B1) to cytotoxic metabolites. It is not yet possible to determine which ones of these cell lines originated from hepatocytes. Studies are in progress to further characterize and to use these cell lines as lethally irradiated feeder layers for cell-mediated activation of various classes of chemical carcinogens and mutagens with C3H/10T1/2 mouse embryo fibroblasts as indicator cells.     

Induction of sister-chromatid exchanges by indirect mutagens/carcinogens in cultured rat hepatoma and esophageal tumor cells and in Chinese hamster Don cells co-cultivated with rat cells

2 rat cell lines originated from ascites hepatoma AH66-B and esophageal tumor R1 were examined for their inducibility of sister-chromatid exchanges (SCEs) after treatment with 14 kinds of indirect mutagens/carcinogens, including 6 amine derivatives, 4 azo compounds, 3 aromatic hydrocarbons and 1 steroid. Of the 14 chemicals tested, 2-acetylaminofluorene (AAF), butylbutanolnitrosamine (BBN), dimethylnitrosamine (DMN), cyclophosphamide (CP), urethane, 2-methyl-4-dimethylaminoazobenzene (2-MeDAB), 3′-methyl-4-dimethylaminoazobenzene (3′-MeDAB), 4-o-tolylazo-o-toluidine (4-TT), benzo[a]pyrene (BP), 7,12-dimethyl-benz[a]anthracene (DMBA) and diethylstilbestrol (DES) were estimated to be effective inducers of SCEs in AH66-B and/or R1 cells, without the use of exogenous activating systems. Cell-mediated SCE tests with 6 selected chemicals, CP, 2-MeDAB, 4-TT, BP, DMBA and DES, showed a significant increase of SCEs in Chinese hamster Don-6 cells co-cultivated with AH66-B or R1 cells, depending on the number and sensitivity of AH66-B or R1 cells, as well as on the dose of chemicals tested, whereas singly cultured Don-6 cells were much less sensitive or almost insensitive to these chemicals. The above findings suggest that AH66-B and R1 cells may retain metabolic activities to convert a wide range of indirect mutagens/carcinogens into their active forms to induce SCEs, and that these cell lines provide simple and reliable screening systems in vitro, including the cell-mediated SCE assay, for detection of genotoxic agents, without the use of exogenous activation systems.     

Mammalian cell transformation and cell-mediated mutagenesis by carcinogenic polycyclic hydrocarbons.

The introduction of a polycyclic hydrocarbon such as benzo(alpha)pyrene (BP) into normal golden hamster embryo cell cultures results, in addition to cytotoxicity, in malignant cell transformation. Studies on the effect of different doses of BP on the normal cells showed that the frequency of transformed colonies was directly related to the dose of the carcinogen. Analysis of this dose-response curve suggests a one-event ("one-hit") response for transformation by this carcinogen. The one-event response for transformation by carcinogenic polycyclic hydrocarbons and the fact that these carcinogens bind to DNA in susceptible cells suggests that transformation can involve a single alteration in the genetic constitution of the treated cells. Carcinogens may, therefore, produce somatic mutations, some of which may involve the genes that control malignancy. Recently, considerable progress has been made in developing models for the study of chemical mutagenesis in mammalian cells. Using resistance to 8-azaguanine as a marker, positive correlations between mutagenicity and transformation were obtained with chemically reactive carcinogens such as N-acetoxy-N-2-fluorenyl-acetamide, N-methyl-N'-nitro-N-nitrosoguanidine and K-region epoxides of polycyclic hydrocarbons. However, no such correlations were obtained with the carcinogenic polycyclic hydrocarbons themselves, since the cell lines used in chemical mutagenesis do not metabolize these carcinogens. In order to obtain better correlations, we have developed a cell-mediated mutagenic assay with carcinogenic hydrocarbons in which Chinese hamster cells, which are susceptible for mutagenesis, were co-cultivated with lethally irradiated rodent cells that can metabolize these compounds. Using this cell mediated assay, we obtained mutagenesis with the carcinogenic hydrocarbons 7,12-dimethylbenz(alpha)anthracene (DMBA), BP, 3-methylcholanthrene and 7-methylbenz(alpha)anthracene; the most potent carcinogen, DMBA, gave the highest frequency of mutations. The polycyclic hydrocarbons, pyrene and benz(alpha)anthracene, which are not carcinogenic were also not mutagenic. We have therefore demonstrated a relationship between the carcinogenecity of polycyclic hydrocarbons and their mutagenicity in mammalian cells, without having to isolate their reative metabolic intermediates. It should be possible to use in this system human cells from different organs and individuals to screen for environmental chemicals hazardous to humans which have to be metabolically activated.     

Rapid determination of hypoxanthine-guanine-phosphoribosyl transferase in human fibroblasts and amniotic cells.

A micromodification of the method of HGPRT and APRT assay is described, which measures the incorporation of 14C hypoxanthine and 14C adenine into cultured skin fibroblasts and amniotic cells grown on microtiter plates. Only about 10000 cells are needed per assay. By this method HGPRT deficient cells can be easily distinguished from normal cells. Investigations with respect to the effect of substrate concentrations and time of incubation have been carried out on some normal fibroblast cell lines, amniotic cell lines and 3 Lesch-Nyhan cell lines. Another modified method is described for quantitative determination of HGPRT activity by means of radio thin-layer chromatography.     

Immunological characterization of hypoxanthine-guanine phosphoribosyl transferase mutants of mouse L cells: Evidence for mutations at different loci in the HGPRT gene

A large collection (105) of mouse L cell mutants lacking hypoxanthine-guanine phosphoribosyl transferase activity (HGPRT; E. C. 2.4.2.8) were analyzed for the presence of serologically cross reacting material (CRM). Antibody directed against highly purified mouse liver HGPRT was used for detecting CRM activity by two methods: (1) the standard precipitation-inhibition assay; and (2) a radioimmune-precipitation assay. The latter assay proved to have far greater sensitivity for the detection of altered forms of HGPRT. Approximately 40% of the HGPRT⁻ cell lines contain CRM activity (i.e., were CRM⁺). This indicates that a minimum of 40% of the HGPRT⁻ clones arose as a result of mutations in the HGPRT structural gene. The CRM⁺ cell lines were shown to contain different levels of CRM activity. Measurements of the heat sensitivity of CRM in the different HGPRT⁻ cell lines showed a broad spectrum of CRM heat inactivation kinetics. These latter two observations provide strong evidence that the mutations giving rise to the HGPRT⁻CRM⁺ phenotype occurred at different sites in the HGPRT structural gene.     

Dietary inhibitors of mutagenesis and carcinogenesis

Dietary inhibitors of mutagenesis and carcinogenesis are of particular interest because they may be useful for human cancer prevention. Several mutagenesis inhibitors have been demonstrated to be carcinogenesis inhibitors also, e.g., ellagic acid, palmitoleic acid, and N-acetylcysteine. This means that the search for mutagenesis inhibitors may be useful for discovering anticarcinogenic agents. Many mutagenesis inhibitors have been discovered by the use of short-term assays, particularly the Ames Salmonella test. This simple in vitro system has provided opportunities to elucidate the mechanisms of inhibition. The elucidation of the mechanism may allow us to infer the possible anticarcinogenic activity of the reagent. In this chapter, inhibitors of mutagenesis and carcinogenesis that can arise as components of diet have been reviewed. Most of the inhibitors have been demonstrated to be effective against a specific class of mutagens or carcinogens. Therefore, it may be argued that these inhibitors are antagonistic only to those particular agents. Here again, understanding of the mechanisms of these inhibitions is necessary for the assessment. Dietary inhibitors reviewed in this article include: (1) as inhibitors of mutagenesis: porphyllins, fatty acids, vitamins, polyphenols, and sulfhydryl compounds, (2) as inhibitors of carcinogenesis: vitamins A, E and C, ellagic acid, sulfhydryl compounds, fats, selenium, calcium, and fiber. Further studies in this area of science appear to help establish the recipe of a healthy diet.     

Dietary fat modifies the in vivo mutagenicity of some food-borne carcinogens

Female BALB/c mice were fed a low fat diet (1% safflower oil, by weight) or one supplemented with 25% (by weight) of beef fat or olive oil. The abilities of these diets to modify the in vitro and in vivo hepatic conversion of the dietary carcinogens aflatoxin B1, 2-amino-3, 4-dimethylimidazo[4,5-f]quinoline (MeIQ) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) to bacterial mutagens was evaluated. Dietary olive oil appeared to increase the metabolism of both MeIQ and Trp-P-2 to bacterial mutagens in vivo using the intrasanguineous host-mediated assay. Feeding mice either of the high-fat diets increased hepatic conversion of these two compounds to bacterial mutagens in vitro. Dietary fat had no effect on the metabolism of aflatoxin B1. Subsequent experiments suggested that the in vivo effects of dietary olive oil on MeIQ and Trp-P-2 mutagenesis were due to the induction of hepatic enzyme activities rather than to increased rates of uptake of the carcinogen from the gut-lumen.