Comparative investigation of multiple organs of mice and rats in the comet assay

Mice and/or rats are usually used to detect chemical carcinogenicity and it has been known that there are species differences in carcinogenicity. To know whether there are species difference in genotoxicity, we conducted comparative investigation of multiple organs of mice and rats in the comet assay. Since the sensitivity to xenobiotics is different for different species, we queried species difference in the genotoxic sensitivity at one equitoxic level but not at one equidose. Therefore, groups of four mice or rats were treated once intraperitoneally or orally with a chemical at highest dose without death and distinct toxic manifestation. When the death was not observed at 2000 mg/kg of a chemical, 2000 mg/kg was used for the comet study. The stomach, colon, liver, kidney, bladder, lung, brain, and bone marrow were sampled 3, 8, and 24h after treatment. Among chemicals tested, benzyl acetate, chlorodibromomethane and p-chloro-o-toluidine are carcinogenic to mice but not rats, and aniline, azobenzene, o-phenylphenol Na, and D-limonene are carcinogenic to rats but not mice. Although the two species differed in genotoxicity target organs and migration values, the judgement of a positive or negative response was the same for all chemicals studied except for 2,4-dimethoxyaniline, 2,5-diaminotoluene, and p,p'-DDT when chemicals with positive responses in at least one organ are judged to be comet assay-positive. 2,4-Dimethoxyaniline and 2,5-diaminotoluene that are Ames test-positive non-carcinogens in both species were positive in one organ (urinary bladder for 2,4-dimethoxyaniline and stomach for 2,5-diaminotoluene) in rats, but negative in all mouse organs. p,p'-DDT, which is an Ames test-negative but in vitro cytogenetic test-positive hepatic carcinogen in mice and rats, was positive in multiple rat organs, but not in any mouse organ. These results suggest that species differences in genotoxicity at one equitoxic level are not consistent with species difference in carcinogenicity and that the use of both species is appropriate to indicate a carcinogenic potential in the comet assay with multiple organs, when chemicals being positive in at least one organ are judged to be comet assay-positive.     

Assessment of the potential germ cell mutagenicity of industrial and plant protection chemicals as part of an integrated study of genotoxicity in vitro and in vivo

An approach is described that enables the germ cell mutagenicity of chemicals to be assessed as part of an integrated assessment of genotoxic potential. It is recommended, first, that the genotoxicity of a chemical be defined by appropriate studies in vitro. This should involve use of the Salmonella mutation assay and an assay for the induction of chromosomal aberrations, but supplementary assays may be indicated in specific instances. If negative results are obtained from these 2 tests there is no need for the conduct of additional tests. Agents considered to be genotoxic in vitro should then be assessed for genotoxicity to rodents. This will usually involve the conduct of a bone marrow cytogenetic assay, and in the case of negative results, a genotoxicity test in an independent tissue. Agents found to be non-genotoxic in vivo are regarded as having no potential for germ cell mutagenicity. Agents found to be genotoxic in vivo may either be assumed to have potential as germ cell mutagens, or their status in this respect may be defined by appropriate germ cell mutagenicity studies. The basis of the approach, which is supported by the available experimental data, is that germ cell mutagens will be evident as somatic cell genotoxins in vivo, and that these will be detected as genotoxins in vitro given appropriate experimentation. The conduct of appropriate and adequate studies is suggested to be of more value than the conduct of a rigid set of prescribed tests.     

青蛙蝌蚪微核试验——一种水体诱变剂检测系统的建立

以青蛙蝌蚪为实验生物,利用甲基磺酸乙酯(EMS)和亚硝基胍(MNNG)探讨其化合物浓度、暴露时间和蝌蚪发育阶段等因素对诱发青蛙蝌蚪红细胞微核的影响,不同统计单位的特点和相互关系;提出了青蛙蝌蚪微核试验作为一种水体诱变剂检测系统的基本实验程序和一般原则。此外,还描述了“小体M”——一种特殊的细胞学现象,并初步讨论了微核代谢机制。     

Chemical structure, Salmonella mutagenicity and extent of carcinogenicity as indicators of genotoxic carcinogenesis among 222 chemicals tested in rodents by the U.S. NCI/NTP

A survey has been conducted of 222 chemicals evaluated for carcinogenicity in mice and rats by the United States NCI/NTP. The structure of each chemical has been assessed for potential electrophilic (DNA-reactive) sites, its mutagenicity to Salmonella recorded, and the level of its carcinogenicity to rodents tabulated. Correlations among these 3 parameters were then sought. A strong association exists among chemical structure (S/A), mutagenicity to Salmonella (Salm.) and the extent and sites of rodent tumorigenicity among the 222 compounds. Thus, a approximately 90% correlation exists between S/A and Salm. across the 115 carcinogens, the 24 equivocal carcinogens and the 83 non-carcinogens. This indicates the Salmonella assay to be a sensitive method of detecting intrinsic genotoxicity in a chemical. Concordance between S/A and Salm. have therefore been employed as an index of genotoxicity, and use of this index reveals two groups of carcinogens within the database, genotoxic and putatively non-genotoxic. These two broad groups are characterized by different overall carcinogenicity profiles. Thus, 16 tissues were subject to carcinogenesis only by genotoxins, chief among which were the stomach, Zymbal's glands, lung, subcutaneous tissue and circulatory system. Conclusions of carcinogenicity in these 16 tissues comprised 31% of the individual chemical/tissue reports of carcinogenicity. In contrast, both genotoxins and non-genotoxins were active in the remaining 13 tissues, chief among which was the mouse liver which accounted for 24% of all chemical/tissue reports of carcinogenicity. Further, the group of 70 carcinogens reported to be active in both species and/or in 2 or more tissues contained a higher proportion of Salmonella mutagens (70%) than observed for the group of 45 single-species/single-tissue carcinogens (39%). 30% of the 83 non-carcinogens were mutagenic to Salmonella. This confirms earlier observations that a significant proportion of in vitro genotoxins are non-carcinogenic, probably due to their non-absorption or preferential detoxification in vivo. Also, only 30% of the mouse liver-specific carcinogens were mutagenic to Salmonella. This is consistent with tumors being induced in this tissue (and to a lesser extent in other tissues of the mouse and rat) by mechanisms not dependent upon direct interaction of the test chemical with DNA. Detection of 103 of the 115 carcinogens could be achieved by use of only male rats and female mice.(ABSTRACT TRUNCATED AT 400 WORDS)     

In silico assessment of chemical mutagenesis in comparison with results of Salmonella microsome assay on 909 chemicals

Genotoxicity is one of the important endpoints for risk assessment of environmental chemicals. Many short-term assays to evaluate genotoxicity have been developed and some of them are being used routinely. Although these assays can generally be completed within a short period, their throughput is not sufficient to assess the huge number of chemicals, which exist in our living environment without information on their safety. We have evaluated three commercially available in silico systems, i.e., DEREK, MultiCASE, and ADMEWorks, to assess chemical genotoxicity. We applied these systems to the 703 chemicals that had been evaluated by the Salmonella/microsome assay from CGX database published by Kirkland et al. We also applied these systems to the 206 existing chemicals in Japan that were recently evaluated using the Salmonella/microsome assay under GLP compliance (ECJ database). Sensitivity (the proportion of the positive in Salmonella/microsome assay correctly identified by the in silico system), specificity (the proportion of the negative in Salmonella/microsome assay correctly identified) and concordance (the proportion of correct identifications of the positive and the negative in Salmonella/microsome assay) were increased when we combined the three in silico systems to make a final decision in mutagenicity, and accordingly we concluded that in silico evaluation could be optimized by combining the evaluations from different systems. We also investigated whether there was any correlation between the Salmonella/microsome assay result and the molecular weight of the chemicals: high molecular weight (>3000) chemicals tended to give negative results. We propose a decision tree to assess chemical genotoxicity using a combination of the three in silico systems after pre-selection according to their molecular weight.     

A comparison of intraperitoneal and oral gavage administration in comet assay in mouse eight organs

One of the important advantages of the comet assay is its ability to detect genotoxicity in many different organs. Since the exposure route of the test compounds is likely to influence the genotoxicity detected in a given organ, it is an important factor to consider when conducting the assay. In this study, we compared the effects of numerous model compounds on eight organs when administered to mice by intraperitoneal (i.p.) injection and oral (p.o.) gavage.Groups of four mice were treated once i.p. or p.o. at the identical proportion of LD50 for each route, and the stomach, colon, liver, kidney, bladder, lung, brain, and bone marrow were sampled 3, 8, and 24h after treatment. For 19 of the 20 tested mutagens with various modes of action, genotoxicity in some organs varied with treatment route; only the genotoxicity of methyl methane sulfonate was not affected. Treatment route, however, did not produce a qualitative difference in the genotoxicity of promutagens at the sites of conversion to ultimate mutagens, with aromatic hydrocarbons as the exception. When chemicals with positive responses in at least one organ were considered to be comet assay-positive, the administration route made no difference. Since azo reduction is mediated by azo reductase synthesized in the gastrointestinal wall and by gut microflora and i.p.-administered azo dyes bypass their activation site (colon), the administration route is expected to make a difference in their in vivo genotoxicity. Direct-acting mutagens are expected to affect the mucosa of the gastrointestinal tract when given p.o. For those mutagens, however, the administration route did not make a qualitative difference in gastrointestinal tract genotoxicity. Moreover, although the gastrointestinal mucosa is the first site to be exposed to p.o. administered agents, the peak times in the stomach tended to be the same as in most other organs. Based on those results, we concluded that the genotoxicity at high exposures was due to a systemic effect, and that both routes are acceptable for the comet assay when the liver and gastrointestinal organs are sampled, so long as appropriate dose levels for systemic exposure are selected for each route.     

Threshold effects in genetic toxicity: perspective of chemicals regulation in Germany

In the regulation of chemical substances, it is generally agreed that there are no thresholds for genotoxic effects of chemicals, i.e. , that there are no doses without genotoxic effects. When classifying and labelling chemicals, dangerous properties of chemicals are to be identified. In this context, in general, the mode of action (threshold or not) is not considered for genotoxic substances. In the process of quantitative risk assessment, however, determination of the type of dose-effect relationships is decisive for the outcome and the type of risk management. The presence of a threshold must be justified specifically in each individual case. Inter alia, the following aspects may be discussed in this respect: aneugenic activity, indirect modes of action, extremely steep dose-effect relationships in combination with strong toxicity, specific toxicokinetic conditions which may lead to 'metabolic protection' prior to an attack of DNA. In the practice of the regulation of chemical substances with respect to their genotoxic effects, the discussion of thresholds has played a minor role. For notified new substances, there are, in general, no data available that would allow a reasonable discussion. Concerning substances out of the European programme on existing substances, so far 29 have been assessed in our institute with respect to genetic toxicity. Eight out of these have shown considerable evidence for genotoxicity. For two of them, a possible threshold is discussed: one substance is an aneugen, the other one is metabolised to an endogenic compound with genotoxic potential. In the practice of risk assessment of genotoxic substances, the discussion of the mode of action for genotoxicity is frequently associated with the evaluation of potential carcinogenic effects. Here, tissue-specific genotoxic effects in target organs for carcinogenicity are to be discussed. Moreover, the contribution of genotoxicity to the multifactorial process of tumour development should be assessed.     

Mutagenicity of 80 chemicals in Escherichia coli tester strains IC203, deficient in OxyR, and its oxyR(+) parent WP2 uvrA/pKM101: detection of 31 oxidative mutagens

Strain IC203, deficient in OxyR, and its oxyR(+) parent WP2 uvrA/pKM101 (denoted IC188) are the basis of a new bacterial reversion assay, the WP2 Mutoxitest, which has been used in the evaluation of 80 chemicals for oxidative mutagenicity. The following 31 oxidative mutagens were recognized by their greater mutagenic response in IC203 than in IC188: (1) peroxides: hydrogen peroxide (HP), t-butyl hydroperoxide (BOOH) and cumene hydroperoxide (COOH); (2) benzoquinones (BQ): 2-methyl-1,4-BQ, 2,6-dimethyl-1,4-BQ and 2,3, 5,6-tetramethyl-1,4-BQ; (3) naphthoquinones (NQ): 1,4-NQ, 2-methyl-1, 4-NQ and 2-hydroxy-1,4-NQ; (4) phenol derivatives: catechol, hydroquinone, pyrogallol, 1,2,4-benzenetriol, t-butylhydroquinone, gallic acid and 4-aminophenol; (5) catecholamines: DL- and L-dopa, DL- and L-epinephrine, dopamine and L-norepinephrine; (6) thiols: L-cysteine methyl ester, L-cysteine ethyl ester, L-penicillamine and dithiothreitol; (7) diverse: 3,4-dihydroxyphenylacetic acid, hypoxanthine and xanthine, both in the presence of xanthine oxidase, L-ascorbic acid plus copper (II) and phenazine methosulfate. Among these oxidative mutagens, 25 were found to be uniquely positive in IC203. With the exception of BOOH and COOH, mutagenesis by all oxidative mutagens was inhibited by catalase present in rat liver S9, indicating that it is mediated by HP generation, probably in autoxidation reactions. These catalase-sensitive oxidative mutagens were poor inducers of mutations derived from 8-oxoguanine lesions, whereas such mutations were efficiently induced by organic hydroperoxides. The results support the usefulness of incorporating IC203 in the bacterial battery for testing of chemicals. The well-characterized oxidative mutagens available with the use of the WP2 Mutoxitest may serve as a reference in studies on the genotoxicity of oxidative stress.     

In silico assessment of chemical mutagenesis in comparison with results of Salmonella microsome assay on 909 chemicals

Genotoxicity is one of the important endpoints for risk assessment of environmental chemicals. Many short-term assays to evaluate genotoxicity have been developed and some of them are being used routinely. Although these assays can generally be completed within a short period, their throughput is not sufficient to assess the huge number of chemicals, which exist in our living environment without information on their safety. We have evaluated three commercially available in silico systems, i.e., DEREK, MultiCASE, and ADMEWorks, to assess chemical genotoxicity. We applied these systems to the 703 chemicals that had been evaluated by the Salmonella/microsome assay from CGX database published by Kirkland et al. [1]. We also applied these systems to the 206 existing chemicals in Japan that were recently evaluated using the Salmonella/microsome assay under GLP compliance (ECJ database). Sensitivity (the proportion of the positive in Salmonella/microsome assay correctly identified by the in silico system), specificity (the proportion of the negative in Salmonella/microsome assay correctly identified) and concordance (the proportion of correct identifications of the positive and the negative in Salmonella/microsome assay) were increased when we combined the three in silico systems to make a final decision in mutagenicity, and accordingly we concluded that in silico evaluation could be optimized by combining the evaluations from different systems. We also investigated whether there was any correlation between the Salmonella/microsome assay result and the molecular weight of the chemicals: high molecular weight (>3000) chemicals tended to give negative results. We propose a decision tree to assess chemical genotoxicity using a combination of the three in silico systems after pre-selection according to their molecular weight.     

Photomicronucleus assay of phototoxic and pseudophotoclastogenic chemicals in human keratinocyte NCTC2544 cells

Photochemical genotoxicity was evaluated in human keratinocyte NCTC2544 cells. The cells were pre-treated with photogenotoxic or pseudophotoclastogenic chemicals and irradiated with a solar-simulator for 50min at a total UV dose of 5J/cm(2) or placed in the dark for the same period. After washing, the cells were cultured for 1.5-2 cell cycles with fresh culture medium. At the end of culturing, slide specimens were prepared and examined for micronucleus formation. 8-Methoxypsoralen, a photogenotoxic chemical, strongly induced micronucleated cells with UV irradiation but not under non-irradiation conditions. Therefore, NCTC2544 cells were subjected to further investigation to evaluate the possible photogenotoxicity of other chemicals. 6-Methylcoumarin, 3,3',4',5-tetrachlorosalicylanilide and protoporphyrin IX disodium salt, which are all known phototoxic substances, induced micronucleated cells with irradiation but not in the non-irradiation state. These phototoxic substances were confirmed to be photogenotoxic. Tetrabenzoporphine and 5-aminolevulinic acid, which are used for photodynamic therapy, showed phototoxicity. However, these chemicals did not induce micronucleated cells in the irradiated or non-irradiated state, suggesting a lack of photogenotoxicity. Among 3 pseudophotoclastogenic chemicals having no light absorbance at 290-700nm, neither cycloheximide nor disulfoton induced micronucleated cells with or without irradiation; zinc oxide induced micronucleated cells with irradiation and, to a lesser extent, without irradiation. Based on the results of the photogenotoxicity assays of these 9 chemicals, NCTC2544 cells are considered to be a suitable test system to evaluate the photogenotoxic potential of chemicals.     

Chromosomal aberration tests on 29 chemicals combined with S9 mix in vitro.

A metabolic activation system with rat-liver microsome fraction plus cofactors (S9 mix) was applied to chromosomal aberration tests in vitro for the screening of chemical mutagens or carcinogens in the environment. Dialkylnitrosamines only induced chromosomal aberrations in Chinese hamster cells (CHL) when treated with S9 mix. The incidence of chromosomal aberrations in CHL varied with experimental conditions, e.g. incubation time, recovery time, components of S9 mic and inducers used for preparation of S9. For dimethylnitrosamine (DMN), the maximal incidence was obtained when the cells were incubated with S9 mix for 3 h and harvested 24 h after treatment. Therefore, this system (3 h incubation and 24 h recovery) was routinely applied to further screening of other chemicals with S9 prepared from PCB-pretreated rats. 10 carcinogens (e.g. 7,12-dimethylbenz[a]anthracene, benzo[a]pyrene, quinoline, etc.) out of 16 induced aberrations when they were treated with S9 mix, whereas the remaining 6 carcinogens (e.g., 3-methyl-cholanthrene, 4-o-tolylazo-o-toluidine, etc.) induced few or no aberrations even after activation. Two insecticides, allethrin and diazinon, were strongly positive at relatively low doses only when they were activated with the S9 mix. Medical drugs, such as ethenzamide, methyl p-hydroxybenzoate and nitrofurazone, and a food additive, sodium hypochlorite, were positive on activation. Chemicals used for industry, such as styrene monomer and tris-dichloropropylphosphate, were also positive in our activation system.     

Enhancing effect of tetrandrine on sister-chromatid exchanges induced by mitomycin C and cigarette-smoke condensate in mammalian cells

The enhancing effect of tetrandrine, an antisilicosis, antitumor and antiinflammatory drug, on the genotoxic activity of two known mutagens, mitomycin C (MMC) and cigarette-smoke condensate (CSC), has been studied using cultured Chinese hamster lung (V79) cells. The sister-chromatid exchange (SCE) was used as genetic endpoint to measure genotoxicity. One-day cultured cells were exposed to the test chemicals for 3 h with or without metabolic activation. The results show that the frequencies of SCE induced by MMC or CSC were enhanced by tetrandrine. The percent of enhancement was dependent on the concentration of tetrandrine.     

The structural basis of the mutagenicity of chemicals in Salmonella typhimurium: the Gene-Tox data base

The CASE structure-activity methodology has been applied to a Gene-Tox derived Salmonella mutagenicity data base consisting of 808 chemicals. Based upon qualitative structural features, CASE identified 29 activating and 3 inactivating structural determinants which correctly predicted the probability of carcinogenicity of 93.7% of the known mutagens and non-mutagens in the data base (sensitivity = 0.998, and specificity = 0.704). Additionally, based upon a qualitative structure-activity analysis, CASE's performance was even better, leading to a sensitivity of 0.981 and a specificity of 1.000. Using the structural determinants identified in this data base, CASE gave excellent predictions of the mutagenicity of chemicals not included in the data base. The identified biophores and biophobes can also be used to investigate the structural basis of the mutagenicity of various chemical classes.     

Glasshouse tests of chemicals for control of potato common scab

Quintozene is the only chemical used successfully in practice to control soil-borne Streptomyces scabies, the cause of potato common scab. However it may be carcinogenic, and the aim of this work was to find a substitute for it. About 100 chemicals, most of which had known fungitoxic action or were related to such chemicals, were tested in the glasshouse by growing potato plants in soil with which the chemicals had been mixed, usually at 50 ppm. Many of the chemicals failed to decrease the incidence of scab, or decreased the yield of tubers, or both. The most effective chemical was captafol, which was as effective as quintozene and, unlike quintozene, did not decrease yield. Captan and folpet, which are very closely related to captafol, were ineffective.     

Genotoxicity investigation of ELF-magnetic fields in Salmonella typhimurium with the sensitive SOS-based VITOTOX test

We performed a genotoxicity investigation of extremely low-frequency (ELF) magnetic fields (MFs, 50 Hz, 100 and 500 μT, 1 and 2 h exposure) alone and in combination with known chemical mutagens using the VITOTOX test. This test is a very sensitive reporter assay of Salmonella typhimurium bacteria based on the SOS response. Our study showed that ELF-MFs do not induce SOS-based mutagenicity in S. typhimurium bacteria and do not show any synergetic effect when combined with chemical mutagens.     

Chromosome damage induced by chemicals

During the past half century there has been a substantial increase in the number and extent of usage of drugs, food additives, pesticides and other environmental chemicals. As a result, mutation-induced susceptibility to disease, once largely self-eradicating, is now being conserved and even propagated. In addition, we have over the same time period, added to our internal and external environments, numerous synthetic chemicals, the cytogenetic properties of some of which have been reviewed, and to which man's metabolism has not necessarily been conditioned and adapted, and which may have the potential to augment the number of mutations of each succeeding generation.We need to know far more about what we are doing to ourselves and our planet, and the foetuses of our unborn children, and to the genetic heritage of these children, by the permissive use of the chemical wonders of our age. It would surely be impracticable that one should wait for time to reveal harmful mutations before we try to research out and eliminate the chemical mutagens.Chromosomal studies and evaluation of mutagenic potential of all new and established drugs, food additives and environmental chemicals should therefore be integral aspects of the current practices of safety evaluation of these materials, and the same stringent principles should be applied to the numerous chemicals met with as solvents and intermediates in industrial processes. Persons exposed to high risk, such as those working in chemical industries, or patients on continuous chemotherapy, should be offered routine chromosomal monitoring, and the appearance of adverse effects and abnormalities notified and correlated.     

Genetic toxicology testing of 41 industrial chemicals

41 compounds or mixtures of diverse structure and application have been tested for genotoxic activity. The materials were tested in bacterial mutation assays, in Saccharomyces cerevisiae JD1 for mitotic gene conversion and in a cultured rat-liver cell line for structural chromosome damage. 11 compounds were bacterial mutagens, 4 induced mitotic gene conversion in yeast and 5 were positive in the chromosome assay. 5 of the materials were positive in bacteria only and 2 compounds induced chromosome damage in cultured cells in the absence of mutation in bacteria or gene conversion in yeast. The materials were tested over a 5-year period and the performance and evolution of the 3 assays during this time is evaluated. The results are considered in relation to the structure of the chemicals and the genotoxicity of related compounds.     

Evaluation of a genotoxicity test measuring DNA-strand breaks in mouse lymphoma cells by alkaline unwinding and hydroxyapatite elution

A rapid genotoxicity test, based on the measurement of the proportion of single- to double-stranded DNA by alkaline unwinding and hydroxyapatite elution in mouse lymphoma cells treated in vitro with various chemicals, was evaluated. Seventy-eight compounds from diverse chemical groups, including commonly tested mutagens, toxic compounds not usually tested for genotoxicity and non-toxic compounds not thought to be genotoxic were tested. The results obtained were compared with those from the mouse lymphoma TK locus forward-mutation assay, providing a basis for assessing the relative sensitivity of the 2 assays using the same cells exposed to chemicals under similar conditions. Clear evidence of DNA-damaging activity was obtained with 43 of the compounds, while 4 gave equivocal results. Of the remaining 31 compounds, 14 were toxic without inducing DNA damage while the rest were non-toxic and did not induce any DNA damage. Results were available from both the alkaline unwinding assay and the mouse lymphoma assay for 61 compounds; they showed a concordance between the 2 assays of 77%. Of the 47 compounds that were positive or equivocal in the alkaline unwinding assay, only carbon tetrachloride and prednisolone were negative in the mouse lymphoma assay, while 12 of the 19 compounds that were negative in the alkaline unwinding assay were positive in the mouse lymphoma assay. These included 3 compounds that interfere with nucleic acid metabolism, and 3 crosslinking agents, which would be expected to produce mutations to a greater extent than strand breaks. The other 6 compounds were anthranilic acid, benzoquinone, p-chloroaniline, diethylmaleate, glucose and procarbazine HCl. Of these only the last is a known carcinogen. It is concluded from the present study that there was good overall agreement between the results of the DNA alkaline unwinding and mouse lymphoma TK locus assays, but that the sensitivity of the alkaline unwinding assay is lower for some classes of compounds. Bearing this in mind, the alkaline unwinding assay is considered suitable as a rapid screen for genotoxic activity in eukaryotic cells.     

A simple method for assessment of rat cytochrome P-448 isozymes responsible for the mutagenic activation of carcinogenic chemicals

Cytochrome P-448H/L-enriched and cytochrome P-448L-enriched microsomes were prepared from the livers of Sprague-Dawley rats treated with 3-methylcholanthrene (MC) and with a combination of MC and carbon tetrachloride, respectively, and their activities for mediating mutagenic activation of 9 carcinogenic aromatic amines and benzo[a]pyrene, which are found to be different from cyt. P-450 isozymes as to mutagenic activation, were compared on the basis of microsomal cytochrome P-450 content using Salmonella typhimurium TA98 as a tester bacterium. With regard to the substrate-specificity of cytochrome P-448 isozymes, the present results reflected the reported results with use of a cytochrome P-450-reconstituted system. These findings indicate that the mutation test with cytochrome P-448H/L-enriched and cytochrome P-448L-enriched microsomes could be used as a simple method for the determination of the cytochrome P-448 isozymes responsible for the mutagenic activation of carcinogens and mutagens without the use of a cytochrome P-450-reconstituted system.