Report of the IWGT working group on strategy/interpretation for regulatory in vivo tests II. Identification of in vivo-only positive compounds in the bone marrow micronucleus test

A survey conducted as part of an International Workshop on Genotoxicity Testing (IWGT) has identified a number of compounds that appear to be more readily detected in vivo than in vitro. The reasons for this property varies from compound to compound and includes metabolic differences; the influence of gut flora; higher exposures in vivo compared to in vitro; effects on pharmacology, in particular folate depletion or receptor kinase inhibition. It is possible that at least some of these compounds are detectable in vitro if a specific in vitro test is chosen as part of the test battery, but the 'correct' choice of test may not always be obvious when testing a compound of unknown genotoxicity. It is noted that many of the compounds identified in this study interfere with cell cycle kinetics and this can result in either aneugenicity or chromosome breakage. A decision tree is outlined as a guide for the evaluation of compounds that appear to be genotoxic agents in vivo but not in vitro. The regulatory implications of these findings are discussed.

Report of the IWGT working group on strategies and interpretation of regulatory in vivo tests I. Increases in micronucleated bone marrow cells in rodents that do not indicate genotoxic hazards

In vivo genotoxicity tests play a pivotal role in genotoxicity testing batteries. They are used both to determine if potential genotoxicity observed in vitro is realised in vivo and to detect any genotoxic carcinogens that are poorly detected in vitro. It is recognised that individual in vivo genotoxicity tests have limited sensitivity but good specificity. Thus, a positive result from the established in vivo assays is taken as strong evidence for genotoxic carcinogenicity of the compound tested. However, there is a growing body of evidence that compound-related disturbances in the physiology of the rodents used in these assays can result in increases in micronucleated cells in the bone marrow that are not related to the intrinsic genotoxicity of the compound under test. For rodent bone marrow or peripheral blood micronucleus tests, these disturbances include changes in core body temperature (hypothermia and hyperthermia) and increases in erythropoiesis following prior toxicity to erythroblasts or by direct stimulation of cell division in these cells. This paper reviews relevant data from the literature and also previously unpublished data obtained from a questionnaire devised by the IWGT working group. Regulatory implications of these findings are discussed and flow diagrams have been provided to aid in interpretation and decision-making when such changes in physiology are suspected.

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.

DNA damage induced by red food dyes orally administered to pregnant and male mice

We determined the genotoxicity of synthetic red tar dyes currently used as food color additives in many countries, including JAPAN: For the preliminary assessment, we treated groups of 4 pregnant mice (gestational day 11) once orally at the limit dose (2000 mg/kg) of amaranth (food red No. 2), allura red (food red No. 40), or acid red (food red No. 106), and we sampled brain, lung, liver, kidney, glandular stomach, colon, urinary bladder, and embryo 3, 6, and 24 h after treatment. We used the comet (alkaline single cell gel electrophoresis) assay to measure DNA damage. The assay was positive in the colon 3 h after the administration of amaranth and allura red and weakly positive in the lung 6 h after the administration of amaranth. Acid red did not induce DNA damage in any sample at any sampling time. None of the dyes damaged DNA in other organs or the embryo. We then tested male mice with amaranth, allura red, and a related color additive, new coccine (food red No. 18). The 3 dyes induced DNA damage in the colon starting at 10 mg/kg. Twenty ml/kg of soaking liquid from commercial red ginger pickles, which contained 6.5 mg/10 ml of new coccine, induced DNA damage in colon, glandular stomach, and bladder. The potencies were compared to those of other rodent carcinogens. The rodent hepatocarcinogen p-dimethylaminoazobenzene induced colon DNA damage at 1 mg/kg, whereas it damaged liver DNA only at 500 mg/kg. Although 1 mg/kg of N-nitrosodimethylamine induced DNA damage in liver and bladder, it did not induce colon DNA damage. N-nitrosodiethylamine at 14 mg/kg did not induce DNA damage in any organs examined. Because the 3 azo additives we examined induced colon DNA damage at a very low dose, more extensive assessment of azo additives is warranted.

Detection of dichromate (VI)-induced DNA strand breaks and formation of paramagnetic chromium in multiple mouse organs

DNA single-strand breaks (and/or alkali-labile sites) induced by Cr(VI) were evaluated with the alkaline single cell gel electrophoresis (SCG) (Comet) assay in five organs (liver, kidney, spleen, lung, and brain) of male mice dosed with K(2)Cr(2)O(7) (20 mg Cr/kg) by a single ip injection in vivo, and the formation of paramagnetic Cr(V) in these organs was investigated by electron spin resonance (ESR) spectrometry. Furthermore, the in vivo effects of deferoxamine (DFO), an iron chelator, and dimethylthiourea (DMTU), a hydroxyl radical scavenger, on the formation of Cr(V) and DNA strand breaks induced by the metal in the liver and kidney were examined. SCG assay detected DNA strand breaks were detected in the liver and kidney at 15 min and showed that they were being repaired at 3 h after Cr(VI) injection. The ESR spectra of paramagnetic Cr(V) were also observed in the liver and kidney for 15 min to 24 h after Cr(VI) injection. In contrast, there were no significant levels of DNA strand breaks and Cr(V) in the spleen, lung, or brain. The pretreatment of mice with DFO reduced the formation of Cr(VI)-induced DNA strand breaks and Cr(V) complexes as well as the total contents of Cr in the liver and kidney at 15 min after the metal injection. In the case of the pretreatment with DMTU, DNA strand breaks induced by Cr(VI) were suppressed in the liver and kidney at 15 min, without any influence on the levels of Cr(V) complexes and total Cr contents in the organs. The in vitro study showed that DFO decreased the levels of Cr(V)-GSH complexes and Cr(V)-mediated hydroxyl radicals, while DMTU reduced only the levels of Cr(V)-mediated hydroxyl radicals without affecting the formation of Cr(V)-GSH complexes. These results demonstrated that the SCG assay may be useful for detecting DNA strand breaks and/or alkali-labile sites caused by Cr(VI) in vivo. The results also indicated that the in vivo formation of hydroxyl radicals during the reduction of Cr(VI) may play an important role in the induction of the DNA strand breaks caused by this metal and implied that the levels of Cr(V) inside the cells may not always be related to the induction of DNA strand breaks.

The comet assay with multiple mouse organs: comparison of comet assay results and carcinogenicity with 208 chemicals selected from the IARC monographs and U.S. NTP Carcinogenicity Database

The comet assay is a microgel electrophoresis technique for detecting DNA damage at the level of the single cell. When this technique is applied to detect genotoxicity in experimental animals, the most important advantage is that DNA lesions can be measured in any organ, regardless of the extent of mitotic activity. The purpose of this article is to summarize the in vivo genotoxicity in eight organs of the mouse of 208 chemicals selected from International Agency for Research on Cancer (IARC) Groups 1, 2A, 2B, 3, and 4, and from the U.S. National Toxicology Program (NTP) Carcinogenicity Database, and to discuss the utility of the comet assay in genetic toxicology. Alkylating agents, amides, aromatic amines, azo compounds, cyclic nitro compounds, hydrazines, halides having reactive halogens, and polycyclic aromatic hydrocarbons were chemicals showing high positive effects in this assay. The responses detected reflected the ability of this assay to detect the fragmentation of DNA molecules produced by DNA single strand breaks induced chemically and those derived from alkali-labile sites developed from alkylated bases and bulky base adducts. The mouse or rat organs exhibiting increased levels of DNA damage were not necessarily the target organs for carcinogenicity. It was rare, in contrast, for the target organs not to show DNA damage. Therefore, organ-specific genotoxicity was necessary but not sufficient for the prediction of organ-specific carcinogenicity. It would be expected that DNA crosslinkers would be difficult to detect by this assay, because of the resulting inhibition of DNA unwinding. The proportion of 10 DNA crosslinkers that was positive, however, was high in the gastrointestinal mucosa, stomach, and colon, but less than 50% in the liver and lung. It was interesting that the genotoxicity of DNA crosslinkers could be detected in the gastrointestinal organs even though the agents were administered intraperitoneally. Chemical carcinogens can be classified as genotoxic (Ames test-positive) and putative nongenotoxic (Ames test-negative) carcinogens. The Ames test is generally used as a first screening method to assess chemical genotoxicity and has provided extensive information on DNA reactivity. Out of 208 chemicals studied, 117 are Ames test-positive rodent carcinogens, 43 are Ames test-negative rodent carcinogens, and 30 are rodent noncarcinogens (which include both Ames test-positive and negative noncarcinogens). High positive response ratio (110/117) for rodent genotoxic carcinogens and a high negative response ratio (6/30) for rodent noncarcinogens were shown in the comet assay. For Ames test-negative rodent carcinogens, less than 50% were positive in the comet assay, suggesting that the assay, which detects DNA lesions, is not suitable for identifying nongenotoxic carcinogens. In the safety evaluation of chemicals, it is important to demonstrate that Ames test-positive agents are not genotoxic in vivo. This assay had a high positive response ratio for rodent genotoxic carcinogens and a high negative response ratio for rodent genotoxic noncarcinogens, suggesting that the comet assay can be used to evaluate the in vivo genotoxicity of in vitro genotoxic chemicals. For chemicals whose in vivo genotoxicity has been tested in multiple organs by the comet assay, published data are summarized with unpublished data and compared with relevant genotoxicity and carcinogenicity data. Because it is clear that no single test is capable of detecting all relevant genotoxic agents, the usual approach should be to carry out a battery of in vitro and in vivo tests for genotoxicity. The conventional micronucleus test in the hematopoietic system is a simple method to assess in vivo clastogenicity of chemicals. Its performance is related to whether a chemical reaches the hematopoietic system. Among 208 chemicals studied (including 165 rodent carcinogens), 54 rodents carcinogens do not induce micronuclei in mouse hematopoietic system despite the positive finding with one or two in vitro tests. Forty-nine of 54 rodent carcinogens that do not induce micronuclei were positive in the comet assay, suggesting that the comet assay can be used as a further in vivo test apart from the cytogenetic assays in hematopoietic cells. In this review, we provide one recommendation for the in vivo comet assay protocol based on our own data.

The alkaline single cell electrophoresis assay with eight mouse organs: results with 22 mono-functional alkylating agents (including 9 dialkyl N-nitrosoamines) and 10 DNA crosslinkers

The genotoxicity of 22 mono-functional alkylating agents (including 9 dialkyl N-nitrosoamines) and 10 DNA crosslinkers selected from IARC (International Agency for Research on Cancer) groups 1, 2A, and 2B was evaluated in eight mouse organs with the alkaline single cell gel electrophoresis (SCGE) (comet) assay. Groups of four mice were treated once intraperitoneally at the dose at which micronucleus tests had been conducted, and the stomach, colon, liver, kidney, bladder, lung, brain, and bone marrow were sampled 3, 8, and/or 24 h later. All chemicals were positive in the SCGE assay in at least one organ. Of the 22 mono-functional alkylating agents, over 50% were positive in all organs except the brain and bone marrow. The two subsets of mono-functional alkylating agents differed in their bone marrow genotoxicity: only 1 of the 9 dialkyl N-nitrosoamines was positive in bone marrow as opposed to 8 of the 13 other alkylating agents, reflecting the fact that dialkyl N-nitrosoamines are poor micronucleus inducers in hematopoietic cells. The two groups of mono-functional alkylating agents also differ in hepatic carcinogenicity in spite of the fact that they are similar in hepatic genotoxicity. While dialkyl N-nitrosoamines produce tumors primarily in mouse liver, only one (styrene-7,8-oxide) out of 10 of the other type of mono-functional alkylating agents is a mouse hepatic carcinogen. Taking into consideration our previous results showing high concordance between hepatic genotoxicity and carcinogenicity for aromatic amines and azo compounds, a possible explanation for the discrepancy might be that chemicals that require metabolic activation show high concordance between genotoxicity and carcinogenicity in the liver. A high percent of the 10 DNA crosslinkers were positive in the SCGE assay in the gastrointestinal mucosa, but less than 50% were positive in the liver and lung. In this study, we allowed 10 min alkali-unwinding to obtain low and stable control values. Considering that DNA crosslinking lesions can be detected as lowering of not only positive but also negative control values, low control values by short alkali-treatment might make it difficult to detect DNA crosslinking lesions. In conclusion, although both mono-functional alkylating agents and DNA crosslinkers are genotoxic in mouse multiple organs, the genotoxicity of DNA crosslinkers can be detected in the gastrointestinal organs even though they were given intraperitoneally followed by the short alkali-treatment.

The influence of antioxidants on cigarette smoke-induced DNA single-strand breaks in mouse organs: a preliminary study with the alkaline single cell gel electrophoresis assay

According to published information, the lung is the only clear target organ for tumors when mice are exposed to cigarette smoke. Liver, skin, and upper digestive tract are target organs when orally or dermally exposed to cigarette smoke condensate, but not kidney, brain, or bone marrow. We tested the genotoxicity of cigarette smoke in the known target organ (lung), possible target organs (stomach and liver), and non-target organs (kidney, brain, and bone marrow) of the mouse using the alkaline single-cell gel electrophoresis (SCG, or comet) assay, as modified by us. We also tested the effect of free radical scavengers on the genotoxicity of the smoke. Male ICR mice were exposed to cigarette smoke. DNA single-strand breaks (SSB) were measured by the SCG assay 15, 30, 60, 120, and 240 min after the exposure. Fifteen min after the animals were exposed for 1 min to a 6-fold dilution of smoke, SSB appeared in the lungs, stomach, and liver; the damage in the lungs and liver returned to almost control levels by 60 min, and that of the stomach by 120 min. Kidney, brain, and bone marrow DNA were not damaged. Exposure to more dilute smoke (12- or 24-fold dilution) did not cause DNA damage. Single oral pretreatment (100 mg/kg) of either ascorbic acid (VC) or alpha-tocopherol acetate (VE) 1 h before smoke inhalation prevented SSB in the stomach and liver, while VE but not VC significantly reduced SSB in the lung. Five consecutive days of either VC or VE (100 mg/kg/day) pretreatment completely prevented SSB in the lung, stomach, and liver. Thus, the SCG assay detected DNA SSB, induced by cigarette smoke, in the known target organ, two possible target organs, and none of the non-target organs. Antioxidants could prevent those effects, suggesting that free radicals may have been a source of the damage. Our results suggest the importance of the SCG assay as a tool in the study of genotoxicity and carcinogenicity.

The comet assay in eight mouse organs: results with 24 azo compounds

The genotoxicity of 24 azo compounds selected from IARC (International Agency for Research on Cancer) groups 2A, 2B, and 3 were determined by the comet (alkaline single cell gel electrophoresis, SCG) assay in eight mouse organs. We treated groups of four mice once orally at the maximum tolerated dose (MTD) and sampled stomach, colon, liver, kidney, bladder, lung, brain, and bone marrow 3, 8, and 24 h after treatment. For the 17 azo compounds, the assay was positive in at least one organ; (1) 14 and 12 azo compounds induced DNA damage in the colon and liver, respectively, (2) the genotoxic effect of most of them was greatest in the colon, and (3) there were high positive responses in the gastrointestinal organs, but those organs are not targets for carcinogenesis. One possible explanation for this discrepancy is that the assay detects DNA damage induced shortly after administration of a relatively high dose, while carcinogenicity is detected after long treatment with relatively low doses. The metabolic enzymes may become saturated following high doses and the rates and pathways of metabolic activation and detoxification may differ following high single doses vs. low long-term doses. Furthermore, considering that spontaneous colon tumors are very rare in rats and mice, the ability to detect tumorigenic effects in the colon of those animals might be lower than the ability to detect genotoxic events in the comet assay. The in vivo comet assay, which has advantage of reflecting test chemical absorption, distribution, and excretion as well as metabolism, should be effective for estimating the risk posed by azo dyes to humans in spite of the difference in dosage regimen.

Single cell gel/comet assay: guidelines for in vitro and in vivo genetic toxicology testing

Atthe International Workshop on Genotoxicity Test Procedures (IWGTP) held in Washington, DC, March 25-26, 1999, an expert panel met to develop guidelines for the use of the single-cell gel (SCG)/Comet assay in genetic toxicology. The expert panel reached a consensus that the optimal version of the Comet assay for identifying agents with genotoxic activity was the alkaline (pH > 13) version of the assay developed by Singh et al. [1988]. The pH > 13 version is capable of detecting DNA single-strand breaks (SSB), alkali-labile sites (ALS), DNA-DNA/DNA-protein cross-linking, and SSB associated with incomplete excision repair sites. Relative to other genotoxicity tests, the advantages of the SCG assay include its demonstrated sensitivity for detecting low levels of DNA damage, the requirement for small numbers of cells per sample, its flexibility, its low costs, its ease of application, and the short time needed to complete a study. The expert panel decided that no single version of the alkaline (pH > 13) Comet assay was clearly superior. However, critical technical steps within the assay were discussed and guidelines developed for preparing slides with agarose gels, lysing cells to liberate DNA, exposing the liberated DNA to alkali to produce single-stranded DNA and to express ALS as SSB, electrophoresing the DNA using pH > 13 alkaline conditions, alkali neutralization, DNA staining, comet visualization, and data collection. Based on the current state of knowledge, the expert panel developed guidelines for conducting in vitro or in vivo Comet assays. The goal of the expert panel was to identify minimal standards for obtaining reproducible and reliable Comet data deemed suitable for regulatory submission. The expert panel used the current Organization for Economic Co-operation and Development (OECD) guidelines for in vitro and in vivo genetic toxicological studies as guides during the development of the corresponding in vitro and in vivo SCG assay guidelines. Guideline topics considered included initial considerations, principles of the test method, description of the test method, procedure, results, data analysis and reporting. Special consideration was given by the expert panel to the potential adverse effect of DNA degradation associated with cytotoxicity on the interpretation of Comet assay results. The expert panel also discussed related SCG methodologies that might be useful in the interpretation of positive Comet data. The related methodologies discussed included: (1) the use of different pH conditions during electrophoreses to discriminate between DNA strand breaks and ALS; (2) the use of repair enzymes or antibodies to detect specific classes of DNA damage; (3) the use of a neutral diffusion assay to identify apoptotic/necrotic cells; and (4) the use of the acellular SCG assay to evaluate the ability of a test substance to interact directly with DNA. The alkaline (pH > 13) Comet assay guidelines developed by the expert panel represent a work in progress. Additional information is needed before the assay can be critically evaluated for its utility in genetic toxicology. The information needed includes comprehensive data on the different sources of variability (e.g., cell to cell, gel to gel, run to run, culture to culture, animal to animal, experiment to experiment) intrinsic to the alkaline (pH > 3) SCG assay, the generation of a large database based on in vitro and in vivo testing using these guidelines, and the results of appropriately designed multilaboratory international validation studies.

Synchronized oscillatory discharges of mitral/tufted cells with different molecular receptive ranges in the rabbit olfactory bulb

Individual glomeruli in the mammalian olfactory bulb represent a single or a few type(s) of odorant receptors. Signals from different types of receptors are thus sorted out into different glomeruli. How does the neuronal circuit in the olfactory bulb contribute to the combination and integration of signals received by different glomeruli? Here we examined electrophysiologically whether there were functional interactions between mitral/tufted cells associated with different glomeruli in the rabbit olfactory bulb. First, we made simultaneous recordings of extracellular single-unit spike responses of mitral/tufted cells and oscillatory local field potentials in the dorsomedial fatty acid-responsive region of the olfactory bulb in urethan-anesthetized rabbits. Using periodic artificial inhalation, the olfactory epithelium was stimulated with a homologous series of n-fatty acids or n-aliphatic aldehydes. The odor-evoked spike discharges of mitral/tufted cells tended to phase-lock to the oscillatory local field potential, suggesting that spike discharges of many cells occur synchronously during odor stimulation. We then made simultaneous recordings of spike discharges from pairs of mitral/tufted cells located 300-500 microm apart and performed a cross-correlation analysis of their spike responses to odor stimulation. In approximately 27% of cell pairs examined, two cells with distinct molecular receptive ranges showed synchronized oscillatory discharges when olfactory epithelium was stimulated with one or a mixture of odorant(s) effective in activating both. The results suggest that the neuronal circuit in the olfactory bulb causes synchronized spike discharges of specific pairs of mitral/tufted cells associated with different glomeruli and the synchronization of odor-evoked spike discharges may contribute to the temporal binding of signals derived from different types of odorant receptor.

The alkaline single cell gel electrophoresis assay with mouse multiple organs: results with 30 aromatic amines evaluated by the IARC and U.S. NTP

The genotoxicity of 30 aromatic amines selected from IARC (International Agency for Research on Cancer) groups 1, 2A, 2B and 3 and from the U.S. NTP (National Toxicology Program) carcinogenicity database were evaluated using the alkaline single cell gel electrophoresis (SCG) (Comet) assay in mouse organs. We treated groups of four mice once orally at the maximum tolerated dose (MTD) and sampled stomach, colon, liver, kidney, bladder, lung, brain, and bone marrow 3, 8 and 24 h after treatment. For the 20 aromatic amines that are rodent carcinogens, the assay was positive in at least one organ, suggesting a high predictive ability for the assay. For most of the SCG-positive aromatic amines, the organs exhibiting increased levels of DNA damage were not necessarily the target organs for carcinogenicity. It was rare, in contrast, for the target organs not to show DNA damage. Organ-specific genotoxicity, therefore, is necessary but not sufficient for the prediction of organ-specific carcinogenicity. For the 10 non-carcinogenic aromatic amines (eight were Ames test-positive and two were Ames test-negative), the assay was negative in all organs studied. In the safety evaluation of chemicals, it is important to demonstrate that Ames test-positive agents are not genotoxic in vivo. Chemical carcinogens can be classified as genotoxic (Ames test-positive) and putative non-genotoxic (Ames test-negative) carcinogens. The alkaline SCG assay, which detects DNA lesions, is not suitable for identifying non-genotoxic carcinogens. The present SCG study revealed a high positive response ratio for rodent genotoxic carcinogens and a high negative response ratio for rodent genotoxic non-carcinogens. These results suggest that the alkaline SCG assay can be usefully used to evaluate the in vivo genotoxicity of chemicals in multiple organs, providing for a good assessment of potential carcinogenicity.

Detection of in vivo genotoxicity of haloalkanes and haloalkenes carcinogenic to rodents by the alkaline single cell gel electrophoresis (comet) assay in multiple mouse organs

The micronucleus test is widely used to assess in vivo clastogenicity because of its convenience, but it is not appropriate for some carcinogenic chemical classes. Halogenated compounds, for example, are inconsistent micronucleus inducers. We assessed the genotoxicity of 7 haloalkanes and haloalkenes carcinogenic to rodents in 7 mouse organs-stomach, liver, kidney, bladder, lung, brain, and bone marrow-using the alkaline single cell gel electrophoresis (SCG) assay. The carcinogens we studied were 1, 2-dibromo-3-chloropropane (DBCP), 1,3-dichloropropene (mixture of cis and trans) (DCP), 1,2-dibromoethane (EDB), 1,2-dichloroethane (EDC), vinyl bromide, dichloromethane, and carbon tetrachloride; only DBCP induces micronuclei in mouse bone marrow. Except for carbon tetrachloride, halocompounds studied are mutagenic to Salmonella typhimurium. Mice were sacrificed 3 or 24 h after carcinogen administration. DCP and EDC induced DNA damage in all of the organs studied. Vinyl bromide yielded DNA damage in all of the organs except for bone marrow. DBCP induced DNA damage in the stomach, liver, kidney, lung, and bone marrow; EDB in the stomach, liver, kidney, bladder, and lung; and dichloromethane in the liver and lung. Since no deaths, morbidity, clinical signs, organ pathology, or microscopic signs of necrosis were observed, the DNA damage was not attributable to cytotoxicity. On the other hand, the positive response in the liver induced by carbon tetrachloride, which was accompanied by necrosis, was considered to be a false positive response. We suggest that the alkaline SCG assay can be used in multiple organs to detect in vivo genotoxicity that is not expressed in bone marrow cells in mice given non-necrogenic doses of halocompounds.

Computation of molecular information in mammalian olfactory systems

The olfactory system is unique in that the sensory input is in the form of molecular information carried in odour molecules and that a huge variety of compounds can function as odour molecules. The mammalian olfactory system has neuronal networks that can process and integrate the molecular information for discrimination of odour molecules and for perception of olfactory images of objects. Recent rapid advances have begun to provide new insights into the functional logic employed by the main olfactory system for odour discrimination, for odour classification and for olfactory perception of objects. This review discusses how the odour molecule information is encoded, transmitted, processed and decoded at distinct anatomical structures (sensory epithelium, olfactory bulb and olfactory cortex) of the olfactory nervous system. We also discuss the functional network in the accessory olfactory system with regard to the processing of pheromonal information.

Evaluation of a tissue homogenization technique that isolates nuclei for the in vivo single cell gel electrophoresis (comet) assay: a collaborative study by five laboratories

We evaluated a tissue homogenization technique that isolates nuclei for use in the in vivo comet assay. Five laboratories independently tested the technique using the liver, kidney, lung, spleen, and bone marrow of untreated and mutagen-treated male CD-1 mice. The direct mutagen methylmethanesulfonate (MMS) or the promutagen diethylnitrosamine (DEN) were injected intraperitoneally at maximum tolerated doses. Three and twenty-four hours later, the organs were removed and, except for bone marrow, were minced and homogenized and a nuclear suspension was prepared. The nuclear suspensions and bone marrow cells were used in the comet assay. None of the nuclear suspensions from the non-treated mice induced a positive response. All nuclear suspensions derived from the MMS-treated mice and those of the liver, kidney, and lung from DEN-treated mice induced positive responses in all the laboratories similarly. Reproducibility was demonstrated by five replicate studies in one laboratory. Furthermore, the organ-specific responses to MMS and DEN reflected the characteristic genotoxicity of the chemicals. We concluded from these results that the homogenization technique is a valid one to be used for mouse organs in the in vivo comet assay.

Detection of nivalenol genotoxicity in cultured cells and multiple mouse organs by the alkaline single-cell gel electrophoresis assay

We tested the genotoxicity of nivalenol (NIV), a potent toxic trichothecene from Fusarium nivale, in cultured CHO cells and in several mouse organs and tissues (liver, kidney, thymus, bone marrow and mucosa of stomach, jejunum, and colon) using the alkaline single-cell gel electrophoresis (SCG, or Comet) assay. NIV at 50 and 100 micrograms/ml damaged the nuclear DNA of CHO cells in the absence of S9 mix, showing that NIV was a direct mutagen. In an in vivo study, mice were sacrificed 2, 4, and 8 h after either oral (20 mg/kg) or intraperitoneal (3.7 mg/kg) administration of NIV. DNA damage was measured by the SCG assay as modified by us. After oral dosing, DNA damage appeared in the kidney and bone marrow at 2 h (returning to almost control level within the following 2 h), and in the stomach, jejunum, and colon at 2, 4, and 8 h, respectively. Liver and thymus DNA were not damaged. After intraperitoneal injection, no DNA damage appeared in any of the organs or tissues tested except for the colon, where extensive DNA damage was observed, as in the oral study, at 8 h. For histopathological examination, mice were sacrificed 2, 4, and 8 h after oral (20 mg/kg) administration of NIV. No necrotic changes were detected in any of the organs where NIV yielded statistically significant DNA damage. To measure the effect of NIV on transport activity in mice, 10 ml/kg (same volume as NIV treatments) of 1% brilliant blue FCF (BB) was administered orally. Thirty minutes later, the BB reached the colon, and simultaneous oral administration of NIV (20 mg/kg, dissolved in 10 ml BB solution) did not affect the dye transport rate. Thus, the strong yet delayed damage to colon DNA may follow from a systemic absorption rather than a topical effect. As a direct mutagen, NIV showed organ specific genotoxicity in mice in time and intensity.

Detection of DNA lesions induced by chemical mutagens by the single cell electrophoresis (Comet) assay. 1. Relationship between the onset of DNA damage and the characteristics of mutagens

We evaluated the relationship between the onset of DNA damage and the characteristics of 5 model chemical mutagens with the single-cell gel electrophoresis (SCG) assay using L5178Y mouse lymphoma cells. We treated the cells with each chemical for 3 h and sampled them 0.21, and 45 h after treatment. DNA damage induced by UV mimetic mutagens MMS and MNU, and X-ray mimetic mutagen BLM was observed just after treatment, crosslinking agent MMC-induced DNA damage was detected 21 h after treatment, and 6-MP as an inhibitor of DNA synthesis did not induce DNA damage at any sampling time. These results suggest that the SCG assay detects DNA lesions just after treatment with UV and X-ray mimetic mutagens, but needs a waiting period after treatment with crosslinking agents.

Organ-specific genotoxicity of the potent rodent colon carcinogen 1,2-dimethylhydrazine and three hydrazine derivatives: difference between intraperitoneal and oral administration

We used a modification of the alkaline single cell gel electrophoresis (SCG) (Comet) assay to test the in vivo genotoxicity of four hydrazine derivatives--1,2-dimethylhydrazine (SDMH), 1,1-dimethylhydrazine (UDMH), hydrazine (HZ), and procarbazine (PCZ)--in mouse liver, lung, kidney, brain, and bone marrow, and in the mucosa of stomach, colon, and bladder. Mice were sacrificed 3 and 24 h after intra-peritoneal (i.p.) and oral (p.o.) administration. SDMH at 20 mg/kg i.p. yielded statistically significant DNA damage in all tested organs except for lung. In the gastrointestinal tract, SDMH was genotoxic in the stomach and the colon after i.p. treatment but only in the colon after 20 and 30 mg/kg p.o. treatment. UDMH at 50 mg/kg i.p. yielded DNA damage in the liver and lung at 3 h. PCZ at 200 mg/kg i.p. caused DNA damage in the liver, kidney, lung, brain, and bone marrow. UDMH and PCZ were positive in the stomach and colon p.o. but not by i.p. treatment. HZ at 100 mg/kg yielded DNA damage in the stomach, liver, and lung when given i.p. and in the brain when p.o. Thus, the administration route is important when evaluating organ-specific genotoxicity in multiple organs.

Detection of pyrimethamine-induced DNA damage in mouse embryo and maternal organs by the modified alkaline single cell gel electrophoresis assay

We studied the embryonic and maternal genotoxicity of pyrimethamine (PYR), a potent teratogen and folate antagonist, using alkaline single cell gel electrophoresis (SCG, or Comet) assay as modified by us (we used isolated nuclei instead of isolated cells). ICR mice were treated on the 13th day of pregnancy with a single oral dose of 50 mg PYR/kg. Six maternal organs (liver, kidney, lung, brain, spleen, bone marrow), maternal and fetal placentas, and two embryos were taken 6 and 16 h after treatment; the embryos were divided into head and body portions. Each sample was minced, homogenized gently, and centrifuged. The nuclei from the precipitates were used. PYR induced DNA damage in all maternal organs except spleen and bone marrow 6 h after administration. The DNA damage in all the affected organs was less at 16 h than at 6 h, and that of the kidney and brain returned to control level at 16 h. PYR also induced DNA damage in maternal and fetal placentas and embryos that was detected at 6 and 16 h, with greater damage at 6 h. Co-treatment of folinic acid calcium salt (FNA, 10 mg/kg ip), a reduced active folate form, prevented the PYR-induced DNA damage in all target tissues examined 6 h after treatment. These data indicate that the observed embryonic and maternal DNA damage caused by PYR may be related to folate deficiency, and that the modified alkaline SCG assay can be used to predict fetal/embryonic genotoxicity in vivo, in addition to the organ-specific maternal genotoxicity.

Increased NMDA current and spine density in mice lacking the NMDA receptor subunit NR3A

The NMDA (N-methyl-D-aspartate) subclass of glutamate receptor is essential for the synaptic plasticity thought to underlie learning and memory and for synaptic refinement during development. It is currently believed that the NMDA receptor (NMDAR) is a heteromultimeric channel comprising the ubiquitous NR1 subunit and at least one regionally localized NR2 subunit. Here we report the characterization of a regulatory NMDAR subunit, NR3A (formerly termed NMDAR-L or chi-1), which is expressed primarily during brain development. NR3A co-immunoprecipitates with receptor subunits NR1 and NR2 in cerebrocortical extracts. In single-channel recordings from Xenopus oocytes, addition of NR3A to NR1 and NR2 leads to the appearance of a smaller unitary conductance. Genetic knockout of NR3A in mice results in enhanced NMDA responses and increased dendritic spines in early postnatal cerebrocortical neurons. These data suggest that NR3A is involved in the development of synaptic elements by modulating NMDAR activity.

Colon-specific genotoxicity of heterocyclic amines detected by the modified alkaline single cell gel electrophoresis assay of multiple mouse organs

The in vivo genotoxicity of five heterocyclic amines-Trp-P-2 (13 mg/kg), IQ (13 mg/kg), MeIQ (13 mg/kg), MeIQx (13 mg/kg), and PhIP (40 mg/kg)-in the mucosa of gastrointestinal and urinary tract organs (stomach, duodenum, jejunum, ileum, colon, and bladder) was studied by the alkaline single cell gel electrophoresis (SCG) (Comet) assay. Male CD-1 mice were sacrificed 1, 3, and 8 h after intraperitoneal injection. All the heterocyclic amines studied yielded statistically significant DNA damage in the colon but not the small intestine (duodenum, jejunum, and ileum) or urinary bladder. In this study, five heterocyclic amines were injected intraperitoneally to avoid the consequences of ingestion. Thus, the extensive damage to colon DNA was concluded to be due, at least in part, to a systemic effect.

Development of genotoxicity assay systems that use aquatic organisms

Our aim is to develop and evaluate monitoring systems that use aquatic organisms to assess the genotoxicity of water in the field and in the laboratory. In a field study, we have shown that the micronucleus assay is applicable to freshwater and marine fishes and that gill cells are more sensitive than hematopoietic cells to micronucleus-inducing agents. Gill cells from Carassius sp. (Funa) and Zacco platypus (Oikawa) collected upstream on the Tomio River (Nara, Japan), tended to have lower micronucleus frequencies than gill cells from fish collected at the midstream of the river. Leiognathus nuchalis (Hiiragi) and Ditrema temmincki (Umitanago), small marine fishes collected periodically at Mochimune Harbor (Shizuoka, Japan), showed seasonal differences in the frequencies of micronucleated gill cells and erythrocytes; they were highest in summer. For laboratory studies, we developed a method for analyzing chromosomal aberrations and micronuclei using Rhodeus ocellatus ocellatus (rose bitterling) embryos. One day after artificial insemination (gastrula stage), we observed structural chromosomal aberrations and micronuclei in the cells of embryos grown in water containing trichloroethylene. Although more work is needed to fully assess their sensitivity, these assays show promise as a means of detecting environmental genotoxins.

Organ-specific genotoxicity of the potent rodent bladder carcinogens o-anisidine and p-cresidine

We used a modification of the alkaline single-cell gel electrophoresis (SCG) (Comet) assay to evaluate the in vivo genotoxicity of two potent rodent bladder carcinogens, o-anisidine and p-cresidine, in mouse liver, lung, kidney, brain, and bone marrow, and in the mucosa of stomach, colon, and bladder. Male CD-1 mice (8 weeks old) were sacrificed 3 and 24 h after oral administration of o-anisidine at 690 mg/kg or p-cresidine at 595 mg/kg. Both chemicals were dissolved in olive oil. Both chemicals yielded statistically significant DNA damage in bladder mucosa 3 and 24 h after treatment. o-Anisidine yielded DNA damage in the colon at 3 h, but not at 24 h. No significant effects were observed in any other organs. Our results suggest the importance of the urinary bladder as a sentinel organ for evaluating chemical genotoxicity in rodents.

Enhanced neuronal death from focal ischemia in AMPA-receptor transgenic mice

Excitatory amino acid (EAA) receptors play an important role in neuronal cell death in acute cerebral ischemia. Blocking the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) subtype of EAA receptor has been shown to reduce cell death in global cerebral ischemia. However their role in focal stroke, although suggestive, has remained more contentious. To clarify this issue, we generated transgenic mice overexpressing the AMPA receptor (AMPAR) subunit GluR2-flip which would increase AMPAR-mediated currents. Excitatory neurons in these transgenic mice are thus predicted to be more susceptible than wild-type neurons to EAA (glutamate)-induced excitotoxic damage. Consistent with this prediction, cultured neurons from transgenic mice had a lower LD50 for exposure to glutamate (10(-3)-10(-5) M for 5 min) compared to wild-type neurons. Moreover, transgenic mice subjected to permanent focal ischemia of the middle cerebral artery (MCA) using the intralumenal filament model sustained larger infarctions compared to wild-type controls. Hence we have developed a genetic mouse model that demonstrates the crucial role of AMPAR containing GluR2-flip in the pathogenesis of focal hypoxic-ischemic neuronal cell death. This model will be a valuable tool in elucidating molecular mechanisms of glutamate excitotoxicity and evaluating the efficacy of glutamate receptor antagonists in attenuating post-ischemic neuronal cell death.

In vivo genotoxicity of ortho-phenylphenol, biphenyl, and thiabendazole detected in multiple mouse organs by the alkaline single cell gel electrophoresis assay

In Japan, ortho-phenylphenol (OPP), biphenyl (BP), and thiabendazole (2-(4'-thiazolyl)benzimidazole, TBZ) are commonly used as a postharvest treatment to preserve imported citrus fruits during transport and storage. We used a modification of the alkaline single cell gel electrophoresis (SCG) (Comet) assay to test the in vivo genotoxicity of those agents in mouse stomach, liver, kidney, bladder, lung, brain, and bone marrow. CD-1 male mice were sacrificed 3, 8, and 24 h after oral administration of the test compounds. OPP (2000 mg/kg) induced DNA damage in the stomach, liver, kidney, bladder, and lung, BP (2000 mg/kg) and TBZ (200 mg/kg) induced DNA damage in all the organs studied. For OPP, increased DNA damage peaked at 3-8 h and tended to decrease at 24 h. For BP, on the contrary, increased DNA migration peaked at 24 h. That delay may have been due to the fact that OPP is metabolized by cytochrome 450 and prostaglandin H synthase to phenylbenzoquinone (PBQ), a DNA binding metabolite, and BP is metabolized to PBQ via OPP and m-phenylphenol. The positive response to TBZ, an aneugen, supports the in vivo DNA-damaging action of TBZ.

In vivo genotoxicity of heterocyclic amines detected by a modified alkaline single cell gel electrophoresis assay in a multiple organ study in the mouse

We used a modification of the alkaline single cell gel electrophoresis (SCG) (Comet) assay to test the in vivo genotoxicity of 6 heterocyclic amines, Trp-P-1 (25 mg/kg), Trp-P-2 (13 mg/kg), IQ (13 mg/kg), MeIQ (13 mg/kg), MeIQx (13 mg/kg) and PhIP (40 mg/kg), in mouse liver, lung, kidney, brain, spleen, bone marrow and stomach mucosa. Mice were sacrificed 1, 3, and 24 h after intraperitoneal injection. Trp-P-2, IQ, MeIQ, and MeIQx yielded statistically significant DNA damage in the stomach, liver, kidney, lung and brain; Trp-P-1 in the stomach, liver and lung; and PhIP in the liver, kidney and brain. None of the heterocyclic amines induced DNA damage in the spleen and bone marrow. Our results suggest that the alkaline SCG assay applied to multiple organs is a good way to detect organ-specific genotoxicity of heterocyclic amines in mammals.

Detection of DNA lesions induced by chemical mutagens using the single-cell gel electrophoresis (comet) assay. 2. Relationship between DNA migration and alkaline condition

The alkaline condition is an important factor for the alkaline single-cell gel electrophoresis (SCG) assay to detect the genotoxic effects of chemicals. In order to understand the relationship between DNA migration and alkaline condition, the effect of 13 model chemical mutagens with different modes of action was evaluated with the alkaline SCG assay under two different alkaline conditions (pH 12.1 and 12.6). CHO cells were sampled just after treatment for 1 h. The X-ray mimetic mutagen BLM increased DNA migration at pH 12.1 and 12.6 and the results were the same at both pH values. Six alkylating mutagens MNU, ENU, MNNG, ENNG, MMS, and EMS and one base adduct inducer 4-NQO induced a dose-dependent response only at pH 12.6. Two DNA crosslinking agents, MMC and DDP, and AMD had negative results. MMC and DDP, however, reduced the positive response of BLM, suggesting that DNA crosslinks could be detected. These results demonstrated that the alkaline condition was important factor for the alkaline SCG assay to detect the genotoxic effects of chemicals.

Detection of genotoxicity of polluted sea water using shellfish and the alkaline single-cell gel electrophoresis (SCE) assay: a preliminary study

We exposed two species of shellfish, Patunopecten yessoensis and Tapes japonica, for 4 h to artificial sea water in which N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), ethyl nitrosourea (EMS), 3-chloro-4-dichloromethyl-5-hydroxy-2(H)-furanone (MX), or benzo[a]pyrene (B[a]P) were dissolved. We then assessed the DNA damage in cells isolated from the gills using the alkaline single-cell gel electrophoresis (SCG) assay. A statistically significant increase in DNA damage was observed for all exposures. Therefore, the alkaline SCG assay detected DNA damage in gill cells produced by direct mutagens and promutagen dissolved in sea water. T. japonica was exposed to sea water sampled from two Pacific Ocean coasts of Japanese local cities--Hachinohe (Aomori Prefecture, Tohoku) and Nakatsu (Oita Prefecture, Kyushu)--and three bay coasts of the industrial megalopolises--Tokyo, Osaka, and Kobe. A significant increase in DNA damage was observed after the exposure to sea water from Tokyo, Osaka, and Kobe, but not from Hachinohe and Nakatsu. These results suggested the utility of the alkaline SCG assay with shellfish gill cells for monitoring sea water genotoxicity.

Detection of in vivo genotoxicity of 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX) by the alkaline single cell gel electrophoresis (Comet) assay in multiple mouse organs

We tested the genotoxicity of 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX) in the mouse in 6 organs (liver, lung, kidney, brain, spleen, and bone marrow) and in the mucosa of stomach, jejunum, ileum, colon, and bladder using the alkaline single-cell gel electrophoresis (SCG) (Comet) assay modified by us. Mice were sacrificed 1, 3, 6, and 24 h after oral administration of the mutagen at 100 mg/kg. MX yielded statistically significant DNA damage in the liver, kidney, lung, and brain and in all the mucosa samples. While DNA damage persisted in the gastrointestinal and urinary tract for 6-24 h after a single oral dosing, it peaked in the liver at 1 h and returned to almost the control level at 3 h. Our present results suggest that MX is genotoxic for various mouse organs, but not for the hematopoietic system, and that the alkaline SCG assay with a homogenization technique can be used to predict genotoxicity in the gastrointestinal and urinary tracts.

Detection of DNA lesions induced by chemical mutagens by the single cell gel electrophoresis (Comet) assay. 1. Relationship between the onset of DNA damage and the characteristics of mutagens

We evaluated the relationship between the onset of DNA damage and the characteristics of 5 model chemical mutagens with the single-cell gel electrophoresis (SCG) assay using L5178Y mouse lymphoma cells. We treated the cells with each chemical for 3 h and sampled them 0, 21, and 45 h after treatment. DNA damage induced by UV mimetic mutagens MMS and MNU, and X-ray mimetic mutagen BLM was observed just after treatment, crosslinking agent MMC-induced DNA damage was detected 21 h after treatment, and 6-MP as an inhibitor of DNA synthesis did not induce DNA damage at any sampling time. These results suggest that the SCG assay detects DNA lesions just after treatment with UV and X-ray mimetic mutagens, but needs a waiting period after treatment with crosslinking agents.

The genotoxicity of diaveridine and trimethoprim

We examined the genotoxicity of diaveridine and trimethoprim in the bacterial umu test, the bacterial reverse mutation test, the in vitro chromosome aberration test, the in vivo rodent bone marrow micronucleus test in two species, and the in vivo comet assay in five mouse organs. Both compounds were negative in the umu test (Salmonella typhimurium TA1535/pSK1002) and in the reverse mutation tests (S. typhimurium TA100, TA98, TA97, TA102, and Escherichia coli WP2 uvrA/pKM101) in the presence and absence of S9 mix. Diaveridine induced structural chromosome aberrations in cultured Chinese hamster CHL cells in the absence of a metabolic activation system, but not in the presence of a liver S9 fraction. No clastogenic activity in CHL cells was detected for trimethoprim. Bone marrow micronucleus tests in mice and rats conducted on diaveridine by single- and triple-oral dosing protocols were negative. The comet assay revealed that a single oral administration of diaveridine significantly induced DNA damage in liver, kidney, lung, and spleen cells, but not in bone marrow cells. The significant increase in migration values of DNA was reproducible with dose-response relationship. We suggest that the liver detoxifies the compound before it reaches the bone marrow, and that is why it is negative in the in vivo bone marrow micronucleus test. We concluded that diaveridine is genotoxic to mammalian cells in vitro and in vivo.

Simple detection of in vivo genotoxicity of pyrimethamine in rodents by the modified alkaline single-cell gel electrophoresis assay

We tested the genotoxicity of pyrimethamine in 5 mouse and rat organs (liver, lung, kidney, spleen, and bone marrow) using a modified alkaline single-cell gel electrophoresis (SCG) (Comet) assay. Mice and rats were sacrificed 1, 3, 6, and 24 h after oral administration of the drug at 50 and 120 mg/kg, respectively. Nuclei were isolated from each tissue and evaluated for DNA migration. Pyrimethamine induced DNA damage in cells of the liver, kidney, and lung in both species. For mice, DNA damage persisted in the liver for 24 h, while it peaked in the lung and kidney at 6 and 24 h, respectively. For rats, DNA damage in the liver peaked at 1 h and returned to almost control level at 24 h. Genotoxicity in the spleen was only observed in mice. Our results suggest that the SCG technique, using isolated nuclei can be applied to rats and mice and that the optimal sampling time is different for different organs and species.

Detection of rodent liver carcinogen genotoxicity by the alkaline single-cell gel electrophoresis (Comet) assay in multiple mouse organs (liver, lung, spleen, kidney, and bone marrow)

We have recently designed a simple method for applying the alkaline single-cell gel electrophoresis (SCG) assay to mouse organs. With this method, each organ is minced, suspended in chilled homogenizing buffer containing NaCl and Na2EDTA, gently homogenized using a Potter-type homogenizer set in ice, and then centrifuged nuclei are used for the alkaline SCG assay. In the present study, we used the method to assess the genotoxicity of 8 rodent hepatic carcinogens in 5 mouse organs (liver, lung, kidney, spleen, and bone marrow). The carcinogens we studied were p-aminoazobenzene, auramine, 2,4-diaminotoluene, p-dichlorobenzene, ethylene thiourea (ETU), styrene-7,8-oxide, phenobarbital sodium, and benzene-1,2,3,4,5,6-hexachloride (BHC); except for p-aminoazobenzene, they do not induce micronuclei in mouse bone marrow cells. Mice were sacrificed 3 and 24 h after the administration of each carcinogen. p-Aminoazobenzene, ETU, and styrene-7,8-oxide induced alkaline labile DNA lesions in all of the organs studied. Auramine, 2,4-diaminotoluene, p-dichlorobenzene, and phenobarbital sodium also produced lesions, but their effect was greatest in the liver. BHC, which is not genotoxic in in vitro tests, did not show any effects. We suggest that it may be possible to use the alkaline SCG assay to detect in vivo activity of chemicals whose genotoxicity is not expressed in bone marrow cells.

Simple detection of chemical mutagens by the alkaline single-cell gel electrophoresis (Comet) assay in multiple mouse organs (liver, lung, spleen, kidney, and bone marrow)

Recently, we designed a fast and simple method to obtain nuclei for the alkaline SCG assay and we tested it with mouse liver, lung, kidney, spleen, and bone marrow. Instead of isolating organ cells by trypsinization, we homogenized tissue and isolated the nuclei. Each organ was minced, and the mince was suspended in chilled homogenizing buffer containing NaCl and Na2EDTA, homogenized gently using a Potter-type homogenizer set in ice, and then centrifuged. The nuclei from the precipitate were used for the assay. To evaluate the validity of this method, we tested the genotoxicity in mouse organs of 11 chemical mutagens with different modes of action. Mice were sacrificed 3 and 24 h after administration of each mutagen. Treatment with three alkylating agents (MMS, EMS, and MNNG), a DNA crosslinking agent (MMC), two aromatic amines (2-AAF and phenacetin), a polycyclic aromatic hydrocarbon (B[a]P), and two inorganic chemicals (KBrO3 and K2CrO4) increased migration of the DNA from mouse organs. 5-FU (a base analog) and colchicine (a spindle poison) treatment produced negative results in all organ studied. Considering that the alkaline SCG assay detects genotoxicity as DNA fragments derived from DNA single-strand breaks and alkali-labile damage, our results showed that the SCG assay using our homogenization technique detected chemical mutagens as a function of their modes of action.

Species-specificity of pyrimethamine in the rodent bone marrow micronucleus test

An antiprotozoal agent pyrimethamine is a potent clastogen that induces structural chromosome aberrations and micronuclei in cultured Chinese hamster (CHL) cells in vitro. Our previous study on the compound, however, demonstrated no significant induction of micronuclei in the mouse bone marrow micronucleus test, even with dosings on 4 consecutive days. In the present study, we investigated the clastogenicity of pyrimethamine in the rat bone marrow micronucleus test. An obvious dose-dependent increase in the frequency of micronucleated polychromatic erythrocytes (MNPCEs) was observed when the compound was given 3 times by oral gavage at 20-120 mg/kg/day. The MNPCE frequency at the highest dose was 80 times that of the control group. Single dose of pyrimethamine at 80 and 160 mg/kg also significantly induced MNPCEs. Thus, pyrimethamine showed species-specific effects in rodent bone marrow micronucleus assays. Our finding implies that micronucleus tests using not only mouse, but also rat, may be necessary for the evaluation of clastogens detected in in vitro cytogenetic studies.

Evaluation of the rodent micronucleus assay in the screening of IARC carcinogens (groups 1, 2A and 2B) the summary report of the 6th collaborative study by CSGMT/JEMS MMS. Collaborative Study of the Micronucleus Group Test. Mammalian Mutagenicity Study Group

To assess the correlation between micronucleus induction and human carcinogenicity, the rodent micronucleus assay was performed on known and potential human carcinogens in the 6th MMS/CSGMT collaborative study. Approximately 100 commercially available chemicals and chemical groups on which there was little or no micronucleus assay data were selected from IARC (International Agency for Research on Cancer) Groups 1 (human carcinogen), 2A (probable human carcinogen) and 2B (possible human carcinogen). As minimum requirements for the collaborative study, 5 male mice were treated by intraperitoneal injection or oral gavage once or twice with each chemical at three dose levels, and bone marrow and/or peripheral blood was analyzed. Five positives and 2 inconclusives out of 13 Group 1 chemicals, 7 positives and 5 inconclusives of 23 Group 2A chemicals, and 26 positives and 6 inconclusives of 67 Group 2B chemicals were found. Such low positive rates were not surprising because of a test chemical selection bias, and we excluded well-known micronucleus inducers. The overall evaluation of the rodent micronucleus assay was based on the present data combined with published data on the IARC carcinogens. After merging, the positive rates for Groups 1, 2A and 2B were 68.6, 54.5 and 45.6%, respectively. Structure-activity relationship analysis suggested that the micronucleus assay is more sensitive to the genetic toxicity of some classes of chemicals. Those to which it is sensitive consist of (1) aziridines and bis(2-chloroethyl) compounds; (2) alkyl sulfonate and sulfates; (3) acyl-type N-nitroso compounds; (4) hydrazines; (5) aminobiphenyl and benzidine derivatives; and (6) azo compounds. Those to which it is less sensitive consist of (1) dialkyl type N-nitroso compounds; (2) silica and metals and their compounds; (3) aromatic amines without other functional groups; (4) halogenated compounds; and (5) steroids and other hormones. After incorporation of structure-activity relationship information, the positive rates of the rodent micronucleus assay became 90.5, 65.2 and 60.0% for IARC Groups 1, 2A and 2B, respectively. Noteworthy was the tendency of the test to be more sensitive to those carcinogens with stronger evidence human carcinogenicity.

Antimutagenicity of Tochu tea (an aqueous extract of Eucommia ulmoides leaves): 1. The clastogen-suppressing effects of Tochu tea in CHO cells and mice

The suppressing effect of crude extracts of Tochu tea, an aqueous extract of Eucommia ulmoides leaves and a popular beverage in Japan, on the induction of chromosome aberrations in CHO cells and mice was studied. When CHO cells were treated with Tochu tea crude extract after MMC treatment, the frequency of chromosome aberrations was reduced. Out of 17 Tochu tea components, 5 irridoids (geniposidic acid, geniposide, asperulosidic acid, deacetyl asperulosidic acid, and asperuloside) and 3 phenols (pyrogallol, protocatechuic acid, and p-trans-coumaric acid) were found to have anticlastogenic activity. Since the anticlastogenic irridoids had an alpha-unsaturated carbonyl group, this structure was considered to play an important role in the anticlastogenicity. The anticlastogenic effect of Tochu tea extracts was examined in mice using a micronucleus assay. When mice received 1.0 ml 4% Tochu tea extract by oral gavage 6 h before intraperitoneal injection of MMC, a decrease in the frequency of micronuclei was observed. This decrease was not due to a delay in the maturation of micronucleated reticulocytes.

Detection of chemically induced DNA lesions in multiple mouse organs (liver, lung, spleen, kidney, and bone marrow) using the alkaline single cell gel electrophoresis (Comet) assay

The effect of 2 model chemical mutagens on DNA was evaluated with the alkaline single cell gel electrophoresis (SCG) (Comet) assay in 5 mouse organs--liver, lung, kidney, spleen and bone marrow. Mice were sacrificed 3 and 24 h after the administration of the direct mutagen ethyl nitrosourea (ENU) or the liver-targeting promutagen p-dimethylaminoazobenzene (DAB). Each organ was minced, suspended at a concentration of 1 g/ml in chilled homogenizing buffer (pH 7.5) containing 0.075 M NaCl and 0.024 M Na2EDTA, homogenized gently using a Potter-type homogenizer at 500-800 rpm set in ice, and then centrifuged nuclei were used for the alkaline SCG assay. ENU induced DNA damage in cells all of the organs studied DAB, on the other hand, produced a positive response in the liver only. We suggest that it may be possible to use the alkaline SCG assay using a homogenization technique to detect the genotoxicity of chemicals in vivo in their target organs.

Antimutagenicity of Tochu tea (an aqueous extract of Eucommia ulmoides leaves): 2. Suppressing effect of Tochu tea on the urine mutagenicity after ingestion of raw fish and cooked beef

The effect of Tochu tea, which is an aqueous extract of Eucommia ulmoides leaves and a popular-beverage in Japan, on the urine mutagenicity before and after ingestion of raw fish and cooked beef was studied using Salmonella typhimurium YG1024. Urines were collected from seven healthy, non-smoking Japanese women before and after ingestion of raw fish and cooked beef. In experiment 1,3 were in a control group and 4 were in a Tochu tea-drinking group (2000 ml per day). The mutagenicity of urine from the Tochu tea-drinking group was much lower. In experiment 2 the 7 women switched groups; the tea-drinking group became the control group, and the control group became the Tochu tea-drinking group. Again, the mutagenicity of urine collected from the Tochu tea-drinking group was much lower. These results suggest that the decrease in the mutagenicity of the urine from the Tochu tea-drinking group was due to the intake of Tochu tea, but not to individual differences. Thus, the ingestion of Tochu tea may reduce human exposure to dietary mutagens.

Cyclin I: a new cyclin encoded by a gene isolated from human brain

A new member of the cyclin family has been isolated from an equalized cDNA library derived from human forebrain cortex. This putative cyclin, designated cyclin I, contains a typical cyclin box near the N-terminus and a PEST sequence near the C-terminus. Cyclin I shows the highest sequence similarity in the cyclin box to cyclins G and E, while the similarity between cyclins I and G also extends toward the C-terminus from the cyclin box. Cyclin I mRNA was expressed at high levels in postmitotic tissues, including skeletal muscle, heart, and brain, and was expressed constantly during cell cycle progression. The expression of cyclin I mRNA does not correlate directly to the cell cycle, and therefore cyclin I may be a novel cyclin member that functions independently of the cell cycle control.

Effect of aging on spontaneous micronucleus frequencies in peripheral blood of nine mouse strains: the results of the 7th collaborative study organized by CSGMT/JEMS.MMS. Collaborative Study Group for the Micronucleus Test. Environmental Mutagen Society of Japan. Mammalian Mutagenesis Study Group

The spontaneous frequencies of micronucleated reticulocytes (MNRETs) were examined monthly over the life spans of animals belonging to nine mouse strains for the 7th collaborative study organized by the CSGMT/JEMS.MMS. Both sexes of the BDF1 strain and females of the A/J strain showed a statistically significant increase in mean spontaneous MNRET frequency in their last month of life, suggesting the possibility of strain-specific, age-dependent chromosomal instability. SAMP6/Tan, an accelerated senescence-prone strain, showed the same tendency, although it was not statistically significant. The other strains studied, ddY, CD-1, B6C3F1, SAMR1, and MS/Ae, did not show significant age-related differences in mean of MNRET frequencies. More extensive statistical analyses are underway, and the outcomes will be reported separately.

Construction of a normalized cDNA library by introduction of a semi-solid mRNA-cDNA hybridization system

We report a novel procedure to construct a normalized (equalized) cDNA library. By introduction of the highly efficient self-hybridization system between a whole mRNA population and their corresponding cDNA immobilized on latex beads, which involves relatively simple manipulations, we were able to generate an mRNA population in which the copy number of abundant species was reduced while that of rare species was enriched. In a typical experiment, after several cycles of self-hybridization on the beads, the ratio of the most to the least abundant marker mRNA species dropped by a factor of 300 (from 10,000 to 30) while the complexity and length of mRNAs in the population remained unchanged. The procedure should provide a potent tool for the expression cloning of cDNA and also facilitate the construction of whole cDNA catalogs from specific tissues (or cell types) from higher organisms.

Bio-anticlastogenic effects of unsaturated fatty acids included in fish oil--docosahexaenoic acid, docosapentaenoic acid, and eicosapentaenoic acid--in cultured Chinese hamster cells

Bio-anticlastogenic effects of unsaturated fatty acids--cis-4,7,10,13,16,19-docosahexaenoic acid (DHA), cis-7,10,13,16,19-docosapentaenoic acid (DPA), and cis-5,8,11,14,17-eicosapentaenoic acid (EPA)--on chemically induced chromosome aberrations were studied in cultured Chinese hamster cells. The induction of chromosome aberrations by the crosslinking agents mitomycin C (MMC) and cisplatin (DDP), the SN-1 type alkylating agents N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG), methyl nitrosourea (MNU), and ethyl nitrosourea (ENU), and the SN-2 type alkylating agent ethyl methanesulfonate (EMS), but not by the SN-1 type alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and the SN-2 type alkylating agent methyl methanesulfonate (MMS), was suppressed by post-treatment with DHA, DPA, and EPA. Since there was no opportunity to inactivate mutagens by desmutagenic mechanisms under the post-treatment schedule used, the results demonstrate the bio-anticlastogenicity of unsaturated fatty acids. Suppression by the unsaturated fatty acids was observed when cells were treated during the G2 phase, suggesting that G2 events were responsible for the bio-anticlastogenic effects. Two saturated fatty acids with the same number of carbons as the studied unsaturated fatty acids--docosanoic acid and eicosanoic acid--did not affect chromosome aberration induction, suggesting the necessity of unsaturation for fatty acid bio-anticlastogenicity.

Construction of an equalized cDNA library from human brain by semi-solid self-hybridization system

A cDNA library enriched in clones for mRNA species (an equalized cDNA library) was constructed from human brain employing semi-solid self-hybridization system and cDNA amplification by in vitro transcription. Sequence analysis of the clones in the cDNA library indicated that (1) clones representing abundant species such as those of mitochondrial origin and expression sequence taq (EST) are drastically reduced in their proportion compared to the original library and (2) clones representing rare mRNA species or which do not have matched sequences in the database increased substantially in their proportion. cDNA libraries thus constructed, therefore, are a good source for cloning of cDNA for rare mRNA species from specific mammalian tissues and also for direct expression cloning since the inserts maintained their original molecular sizes after equalization.

Potentiating effects of organomercuries on clastogen-induced chromosome aberrations in cultured Chinese hamster cells

Mercury compounds are among the most serious environmental pollutants. In this communication, the potentiating effects of organic and inorganic mercuries on clastogen-induced chromosome aberrations were studied in Chinese hamster CHO K1 cells. Post-treatment with monoalkylated mercuries--methyl mercuric chloride (MeHgCl) and ethyl mercuric chloride (EtHgCl)--increased the number of breakage- and exchange-type aberrations induced by 4-nitroquinoline 1-oxide (4NQO) and methyl methanesulfonate. With the DNA crosslinking agents mitomycin C (MMC) and cisplatin, MeHgCl enhanced both types of aberrations while EtHgCl enhanced breakage-type aberrations only. Since these monoalkylated mercuries did not show clastogenic effects by themselves under the present experimental conditions, the increases in chromosome aberrations were not additive. Dialkylated mercuries (dimethyl mercury and diethyl mercury) and inorganic mercuries (HgCl and HgCl2) did not show any potentiating effects. When MMC- or 4NQO-treated cells were post-treated with MeHgCl during the G1 phase, both breakage- and exchange-type aberrations were enhanced. Treatment with EtHgCl during the G1 phase also enhanced both types of aberrations induced by 4NQO. With MMC, however, G1 treatment with EtHgCl did not show any potentiating effect. MeHgCl and EtHgCl treatments during the G2 phase enhanced breakage-type aberrations only. Based on these results, the following possible mechanisms for potentiation of clastogenicity by monoalkylated mercuries were suggested; (1) they interfere with repair of base lesions induced by 4NQO and MMS during the pre-replicational stage, thereby increasing unrepaired DNA lesions which convert into DNA double-strand breaks in S phase, (2) MeHgCl (but not EtHgCl) also inhibits repair of crosslinking lesions during the pre-replicational stage, and (3) their G2 effects enhance breakage-type aberrations only.

Inorganic cadmium increases the frequency of chemically induced chromosome aberrations in cultured mammalian cells

The co-clastogenic effect of cadmium ion (Cd2+) was studied in Chinese hamster CHO K1 cells and excision repair-deficient human XP20SSV cells. Cd2+ at < or = 28.0 microM did not show any clastogenic effects under the experimental conditions used. Cd2+ post-treatment at < or = 3.50 microM, however, increased the number of both breakage- and exchange-type chromatid aberrations induced by mitomycin C (MMC) and 4-nitroquinoline 1-oxide (4NQO) in CHO K1 cells. Enhancement of chromosome aberrations induced by MMC was observed when CHO K1 cells were treated with Cd2+ during the G1 phase. Cd2+ was also co-clastogenic with MMC in XP20SSV cells. Its co-clastogenic effect, however, was not observed in 4NQO-treated XP20SSV cells. These results suggest that Cd2+ inhibits DNA pre-replicational repair, perhaps DNA excision repair, thereby causing co-clastogenic effects.

Suppressing effects of S phase post-treatment with carbolines on sister-chromatid exchanges induced by mitomycin C in Chinese hamster cells

The effects of post-treatment with four types of carbolines-alpha-, beta-, gamma-, and delta-carbolines-and aminoimidazoazaarenes during S phase on the frequency of SCEs induced by MMC were studied in synchronized Chinese hamster CHO cells. Post-treatment with alpha-carbolines (A alpha C, MeA alpha C), beta-carbolines (harman, norharman, harmine, and harmaline), gamma-carbolines (Trp-P-1 and Trp-P-2) and delta-carbolines (Glu-P-1, and Glu-P-2) during S phase at non-clastogenic concentrations caused a statistically significant decrease in the frequency of SCEs induced by MMC. Aminoimidazoazaarenes (IQ, MeIQ, and diMeIQx) showed no effects on SCEs, suggesting that the SCE-suppressing activity resides in the carboline structure. The data suggest that the suppressing effect may be due to inhibition of DNA replication.

3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) inhibits the removal of both cyclobutane dimers and (6-4) photoproducts from the DNA of ultraviolet-irradiated E. coli

Heterocyclic amines have been isolated from cooked foods and found to be mutagens and carcinogens. Among them, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) were also found to enhance UV-induced mutation frequencies in Escherichia coli at the concentrations where they were neither toxic nor mutagenic by themselves. Using an immunological method recently developed to detect UV-induced DNA damage, we investigated the inhibitory effect of Trp-P-1 on the removal of both cyclobutane dimers and (6-4)photoproducts from the DNA of UV-irradiated E.coli. Cells repaired 60% of the initial cyclobutane dimers within 30 min and 75% at 120 min after UV-irradiation. Furthermore, the same cells repaired 90% of the initial (6-4)photoproducts within 30 min. On the other hand, Trp-P-1 clearly showed inhibition of repair of both photolesions in a concentration-dependent manner. The levels of repair inhibition by Trp-P-1 were almost the same between cyclobutane dimers and (6-4)photoproducts. These results suggested that the enhancing effect of Trp-P-1 on UV-induced mutagenesis in E.coli stemmed from the inhibition of the removal of photolesions from the DNA.

Increasing effect of tri-n-butyltins and triphenyltins on the frequency of chemically induced chromosome aberrations in cultured Chinese hamster cells

Organotins have been widely used as anti-fouling coatings for fishing nets and ship bottoms, and marine pollution by them has become a serious environmental problem. In this communication, the potentiating effects of three kinds of tri-n-butyltins and three thiphenyltins on chromosome aberrations were studied in Chinese hamster CHO K1 cells. None of the organotins studied showed any clastogenic activity under the experimental conditions without rat liver S9. Post-treatment with organotins, however, increased the number of breakage-type (but not exchange-type) chromatid aberrations induced by five kinds of S-phase-dependent clastogens: MMC, cisPt, 4NQO, MMS, and AMD). Enhancement of the induction of chromosome aberrations by MMC was observed when cells were treated with organotins during the G2 phase. These results suggest that organotin G2 effect causes potentiating effects. Organotins also enhanced the induction of breakage-type chromatid aberrations by clastogenic pollutants in chlorinated tap water, indicating their potential for a more realistic health risk.

The clastogen-suppressing effects of green tea, Po-lei tea and Rooibos tea in CHO cells and mice

The suppressing effects of crude extracts of three kinds of tea-green tea (GT) from Japan, Po-lei tea (PT) from China, and Rooibos tea (RT) from South Africa-on the induction of chromosome aberrations in cultured CHO cells and mice were studied. When CHO cells were exposed to each tea extract in the presence of rat liver microsomal enzymes (S9 mix) together with benzo[a]pyrene (B(a)P) or mitomycin C (MMC), a decrease in the frequency of chromosome aberrations was observed. PT and RT, but not GT, also suppressed the induction of chromosome aberrations by MMC in the absence of S9 mix. When cells were treated with tea extract after B(a)P or MMC treatment, RT suppressed the induction of chromosome aberrations in the presence and absence of S9 mix whereas GT and PT showed suppressing effects only in the presence of S9 mix. These data suggest that catechines, well-known antimutagens in tea samples, might account for the inhibitory effect in the case of GT and PT. Since RT contains few catechines, several unknown antimutagenic components could be responsible for its effect. The antimutagenic effects of tea extracts at concentration levels consumed by humans were examined in mice using micronucleus induction with B(a)P or MMC. When mice received oral gavage of 0.2% GT, 0.1% PT, and 0.1% RT at 1.0 ml/mouse 6 h before intraperitoneal injection of MMC, a decrease in the frequency of micronuclei was observed. The induction of micronuclei by B(a)P was suppressed by oral dosage of GT, PT and RT at 1.0 ml/mouse/day for 28 days. This was not due to a delay in the maturation of micronucleated reticulocytes. In conclusion, intake of tea might suppress the mutagenic activity of certain potent mutagens in human beings.