In vivo mutagenesis by the hepatocarcinogen quinoline in the lacZ transgenic mouse: evidence for its in vivo genotoxicity

Genome-wide direct quantification of in vivo mutagenesis using high-accuracy paired-end and complementary consensus sequencing

Error-corrected next-generation sequencing (ecNGS) is an emerging technology for accurately measuring somatic mutations. Here, we report paired-end and complementary consensus sequencing (PECC-Seq), a high-accuracy ecNGS approach for genome-wide somatic mutation detection. We characterize a novel 2-aminoimidazolone lesion besides 7,8-dihydro-8-oxoguanine and the resulting end-repair artifacts originating from NGS library preparation that obscure the sequencing accuracy of NGS. We modify library preparation protocol for the enzymatic removal of end-repair artifacts and improve the accuracy of our previously developed duplex consensus sequencing method. Optimized PECC-Seq shows an error rate of <5 × 10-8 with consensus bases compressed from approximately 25 Gb of raw sequencing data, enabling the accurate detection of low-abundance somatic mutations. We apply PECC-Seq to the quantification of in vivo mutagenesis. Compared with the classic gpt gene mutation assay using gpt delta transgenic mice, PECC-Seq exhibits high sensitivity in quantitatively measuring dose-dependent mutagenesis induced by Aristolochic acid I (AAI). Moreover, PECC-Seq specifically characterizes the distinct genome-wide mutational signatures of AAI, Benzo[a]pyrene, N-Nitroso-N-ethylurea and N-nitrosodiethylamine and reveals the mutational signature of Quinoline in common mouse models. Overall, our findings demonstrate that high-accuracy PECC-Seq is a promising tool for genome-wide somatic mutagenesis quantification and for in vivo mutagenicity testing.

Probing the toxic effect of quinoline to catalase and superoxide dismutase by multispectral method

Quinoline is a common nitrogen heterocyclic aromatic hydrocarbon with high water solubility. Studies have shown that quinoline can be teratogenic, carcinogenic and mutagenic. And Hepatocytes are the target cell of quinoline, which contain a large number of mitochondria and are related to cell function and the balance of reactive oxygen species (ROS). However, the research on the effect of quinoline on hepatocyte damage and anti-oxidation system is still unclear. Through the means of multispectral experiments, it is concluded that quinoline can affect the catalase (CAT) and superoxide dismutase (SOD), change their structure and affect their activity. The binding mode and binding site of quinoline to CAT/SOD were analyzed by isothermal calorimetric titration (ITC) and Molecular Operating Environment (MOE). In molecular docking simulation, the binding site of quinoline-CAT system is close to the active site, and affect the microenvironment of Tyr 357. This may be the reason why quinoline affects CAT activity and synchronous fluorescence (Δλ = 15 nm). This study demonstrated that quinoline has a great effect on CAT, which may affect the intracellular ROS balance and become a potential way to cause hepatocyte damage.

Hepatocarcinogen 4-methylquinoline induced G:C to C:G transversions in the cII gene in the liver of lambda/lacZ transgenic mice (Muta™Mouse)

We have previously reported that quinoline increased the mutation frequency of the cII gene in the liver of lambda/lacZ transgenic mice (Muta™Mouse), and G:C to C:G transversions were the molecular signature of quinoline-induced mutations. 4-Methylquinoline (4-MeQ) has the highest mutagenicity among quinoline and isomeric methylquinolines according to the Ames test using Salmonella typhimurium TA 100, in the presence of rat liver microsomal enzymes. In this report, we examined the effect of 4-MeQ on mutagenesis in the lambda cII gene in the liver of the Muta™Mouse, and we analyzed the sequences of the mutated genes. The mutation frequency of the liver cII gene was seven times higher in 4-MeQ-treated mice than in control mice. Sequence analysis revealed that 4-MeQ primarily induced G:C to C:G transversions (37 of 45). The specificities of 4-MeQ for target organ and mutation pattern were very consistent with those of quinoline. Thus, we showed that 4-MeQ was also genotoxic in the liver of the Muta™Mouse, and as with quinoline, the G:C to C:G transversion was the molecular signature of the 4-MeQ-induced mutations.

Mutagenic properties of dimethylaniline isomers in mice as evaluated by comet, micronucleus and transgenic mutation assays

Background

The carcinogenic potential of dimethylaniline (DMA) isomers in rodents and humans has been previously reported, and there is sufficient evidence for the carcinogenicity of 2,6-DMA in experimental animals. The target organ of carcinogenesis of 2,6-DMA is the nasal cavity. In the current study, six DMA isomers, 2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-DMA, were evaluated for mutagenic properties.

Results

Male ddY mice (3/group) were treated intragastrically (i.g.) with 200 mg/kg of one of the six DMAs, and a comet assay was performed on samples of bone marrow, kidney, liver and lung at 3 and 24 h after the treatment. Positive responses were observed in the kidney, liver and lungs of mice from all of the DMA treatment groups after 3 h and in the bone marrow of mice treated with either 3,4- or 3,5-DMA after 3 h; however, these effects were diminished at the 24 h time point. The micronucleus induction in the bone marrow was analysed in the same mouse at 24 h after the treatment. No induction of micronucleated polychromatic erythrocytes was observed after treatment with any of the DMAs.Male transgenic Muta™ mice (five/group) were treated i.g. with 2,5-, 2,6- or 3,5-DMA at 100 mg/kg bw weekly for 4 weeks, and the lacZ and the cII mutation frequencies were examined in the nasal cavity, liver and bone marrow at 7 days after the last treatment. Statistically significant increases in the mutation frequencies of the lacZ and/or cII genes were observed in the nasal cavity of 2,5-DMA or 2,6-DMA treated mice. Sequence analysis showed increased incidences of AT to GC and GC to TA mutations in the nasal tissues.

Conclusions

These findings suggest that the carcinogenic activities of DMAs are associated with mutagenic events.

Carcinogenicity of quinoline by drinking-water administration in rats and mice

The carcinogenicity of quinoline was examined by administrating quinoline in the drinking water to groups of 50 F344/DuCrj rats and 50 Crj: BDF1 mice of each sex. In rats, the doses of quinoline were 0, 200, 400, and 800 ppm for males and 0, 150, 300, and 600 ppm for females. In male rats, administration of quinoline was terminated at week 96 due to high mortality caused by tumors. There were significant increases of hepatocellular adenomas, hepatocellular carcinomas, hepatocellular adenomas and/or carcinomas (combined), and liver hemangiomas, hemangiosarcomas, hemangiomas and/or hemangiosarcomas (combined) in both male and female rats, and nasal esthesioneuroepitheliomas and sarcoma NOS (not otherwise specified) in males. In mice, doses of quinoline were 0, 150, 300 and 600 ppm for both males and females. Administration of quinoline was terminated at week 65 in males and at week 50 in females due to high mortality caused by tumors. There were marked increases of hemangiomas, hemangiosarcomas, and hemangiomas and/or hemangiosarcomas (combined) in the retroperitoneum, mesenterium, and liver in males, and in the retroperitoneum, mesenterium, peritoneum, and subcutis in females. Additionally, histiocytic sarcomas were statistically increased in the livers of female mice. Thus the present studies provided clear evidence of carcinogenic activity of quinoline administered in the drinking water in both rats and mice.

Genotoxicity risk assessment of diversely substituted quinolines using the SOS chromotest

Quinolines are aromatic nitrogen compounds with wide therapeutic potential to treat parasitic and microbial diseases. In this study, the genotoxicity of quinoline, 4-methylquinoline, 4-nitroquinoline-1-oxide (4-NQO), and diversely functionalized quinoline derivatives and the influence of the substituents (functional groups and/or atoms) on their genotoxicity were tested using the SOS chromotest. Quinoline derivatives that induce genotoxicity by the formation of an enamine epoxide structure did not induce the SOS response in Escherichia coli PQ37 cells, with the exception of 4-methylquinoline that was weakly genotoxic. The chemical nature of the substitution (C-5 to C-8: hydroxyl, nitro, methyl, isopropyl, chlorine, fluorine, and iodine atoms; C-2: phenyl and 3,4-methylenedioxyphenyl rings) of quinoline skeleton did not significantly modify compound genotoxicities; however, C-2 substitution with α-, β-, or γ-pyridinyl groups removed 4-methylquinoline genotoxicity. On the other hand, 4-NQO derivatives whose genotoxic mechanism involves reduction of the C-4 nitro group were strong inducers of the SOS response. Methyl and nitrophenyl substituents at C-2 of 4-NQO core affected the genotoxic potency of this molecule. The relevance of these results is discussed in relation to the potential use of the substituted quinolines. The work showed the sensitivity of SOS chromotest for studying structure-genotoxicity relationships and bioassay-guided quinoline synthesis.

Discrimination of genotoxic and non-genotoxic hepatocarcinogens by statistical analysis based on gene expression profiling in the mouse liver as determined by quantitative real-time PCR

The general aim of the present study is to discriminate between mouse genotoxic and non-genotoxic hepatocarcinogens via selected gene expression patterns in the liver as analyzed by quantitative real-time PCR (qPCR) and statistical analysis. qPCR was conducted on liver samples from groups of 5 male, 9-week-old B6C3F(1) mice, at 4 and 48h following a single intraperitoneal administration of chemicals. We quantified 35 genes selected from our previous DNA microarray studies using 12 different chemicals: 8 genotoxic hepatocarcinogens (2-acetylaminofluorene, 2,4-diaminotoluene, diisopropanolnitrosamine, 4-dimethylaminoazobenzene, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, N-nitrosomorpholine, quinoline and urethane) and 4 non-genotoxic hepatocarcinogens (1,4-dichlorobenzene, dichlorodiphenyltrichloroethane, di(2-ethylhexyl)phthalate and furan). A considerable number of genes exhibited significant changes in their gene expression ratios (experimental group/control group) analyzed statistically by the Dunnett's test and Welch's t-test. Finally, we distinguished between the genotoxic and non-genotoxic hepatocarcinogens by statistical analysis using principal component analysis (PCA) of the gene expression profiles for 7 genes (Btg2, Ccnf, Ccng1, Lpr1, Mbd1, Phlda3 and Tubb2c) at 4h and for 12 genes (Aen, Bax, Btg2, Ccnf, Ccng1, Cdkn1a, Gdf15, Lrp1, Mbd1, Phlda3, Plk2 and Tubb2c) at 48h. Seven major biological processes were extracted from the gene ontology analysis: apoptosis, the cell cycle, cell proliferation, DNA damage, DNA repair, oncogenes and tumor suppression. The major, biologically relevant gene pathway suggested was the DNA damage response pathway, resulting from signal transduction by a p53-class mediator leading to the induction of apoptosis. Eight genes (Aen, Bax, Btg2, Ccng1, Cdkn1a, Gdf15, Phlda3 and Plk2) that are directly associated with Trp53 contributed to the PCA. The current findings demonstrate a successful discrimination between genotoxic and non-genotoxic hepatocarcinogens, using qPCR and PCA, on 12 genes associated with a Trp53-mediated signaling pathway for DNA damage response at 4 and 48 h after a single administration of chemicals.

A core in vitro genotoxicity battery comprising the Ames test plus the in vitro micronucleus test is sufficient to detect rodent carcinogens and in vivo genotoxins

In vitro genotoxicity testing needs to include tests in both bacterial and mammalian cells, and be able to detect gene mutations, chromosomal damage and aneuploidy. This may be achieved by a combination of the Ames test (detects gene mutations) and the in vitro micronucleus test (MNvit), since the latter detects both chromosomal aberrations and aneuploidy. In this paper we therefore present an analysis of an existing database of rodent carcinogens and a new database of in vivo genotoxins in terms of the in vitro genotoxicity tests needed to detect their in vivo activity. Published in vitro data from at least one test system (most were from the Ames test) were available for 557 carcinogens and 405 in vivo genotoxins. Because there are fewer publications on the MNvit than for other mammalian cell tests, and because the concordance between the MNvit and the in vitro chromosomal aberration (CAvit) test is so high for clastogenic activity, positive results in the CAvit test were taken as indicative of a positive result in the MNvit where there were no, or only inadequate data for the latter. Also, because Hprt and Tk loci both detect gene-mutation activity, a positive Hprt test was taken as indicative of a mouse-lymphoma Tk assay (MLA)-positive, where there were no data for the latter. Almost all of the 962 rodent carcinogens and in vivo genotoxins were detected by an in vitro battery comprising Ames+MNvit. An additional 11 carcinogens and six in vivo genotoxins would apparently be detected by the MLA, but many of these had not been tested in the MNvit or CAvit tests. Only four chemicals emerge as potentially being more readily detected in MLA than in Ames+MNvit--benzyl acetate, toluene, morphine and thiabendazole--and none of these are convincing cases to argue for the inclusion of the MLA in addition to Ames+MNvit. Thus, there is no convincing evidence that any genotoxic rodent carcinogens or in vivo genotoxins would remain undetected in an in vitro test battery consisting of Ames+MNvit.

Detailed review of transgenic rodent mutation assays

Induced chromosomal and gene mutations play a role in carcinogenesis and may be involved in the production of birth defects and other disease conditions. While it is widely accepted that in vivo mutation assays are more relevant to the human condition than are in vitro assays, our ability to evaluate mutagenesis in vivo in a broad range of tissues has historically been quite limited. The development of transgenic rodent (TGR) mutation models has given us the ability to detect, quantify, and sequence mutations in a range of somatic and germ cells. This document provides a comprehensive review of the TGR mutation assay literature and assesses the potential use of these assays in a regulatory context. The information is arranged as follows. (1) TGR mutagenicity models and their use for the analysis of gene and chromosomal mutation are fully described. (2) The principles underlying current OECD tests for the assessment of genotoxicity in vitro and in vivo, and also nontransgenic assays available for assessment of gene mutation, are described. (3) All available information pertaining to the conduct of TGR assays and important parameters of assay performance have been tabulated and analyzed. (4) The performance of TGR assays, both in isolation and as part of a battery of in vitro and in vivo short-term genotoxicity tests, in predicting carcinogenicity is described. (5) Recommendations are made regarding the experimental parameters for TGR assays, and the use of TGR assays in a regulatory context.

Nitrogen-substitution effect on in vivo mutagenicity of chrysene

We have previously reported the in vivo mutagenicity of aza-polycyclic aromatic hydrocarbons (azaPAHs), such as quinoline, benzo[f]quinoline, benzo[h]quinoline, 1,7-phenanthroline and 10-azabenzo[a]pyrene. The 1,10-diazachrysene (1,10-DAC) and 4,10-DAC, nitrogen-substituted analogs of chrysene, were shown to exhibit mutagenicity in Salmonella typhimurium TA100 in the presence of rat liver S9 and human liver microsomes in our previous report, although DACs could not be converted to a bay-region diol epoxide, the ultimate active form of chrysene, because of their nitrogen atoms. In the present study, we tested in vivo mutagenicity of DACs compared with chrysene using the lacZ transgenic mouse (Mutatrade markMouse) to evaluate the effect of the nitrogen substitution. DACs- and chrysene-induced mutation in all of the six organs examined (liver, spleen, lung, kidney, bone marrow and colon). The mutant frequencies obtained with chrysene showed only small differences between the organs examined and ranged from 1.5 to 3 times the spontaneous frequency. The 4,10-DAC was more mutagenic than chrysene in all the organs tested. The highest lacZ mutation frequency was observed in the lung of 4,10-DAC-treated mice and it was 19 and 6 times the spontaneous frequency and the frequency induced by chrysene, respectively. The 1,10-DAC induced lacZ mutation in the lung with a frequency 4.3- and 1.5-fold higher than in the control and chrysene-treated mice, respectively, although the mutant frequencies in the other organs of 1,10-DAC-treated mice were almost equivalent to those of chrysene-treated mice. Not only chrysene but also DACs depressed the G:C to A:T transition and increased the G:C to T:A transversion in the liver and lung. These results suggest that the two types of nitrogen substitutions in the chrysene structure may enhance mutagenicity in the mouse lung, although they showed no difference in the target-organ specificity and the mutation spectrum.

Evaluation of liver and peripheral blood micronucleus assays with 9 chemicals using young rats

We conducted simultaneous liver and peripheral blood micronucleus assays in young rats with seven rodent hepatocarcinogens-4,4'-methylenedianiline (MDA), quinoline, o-toluidine, 4-chloro-o-phenylenediamine (CPDA), dimethylnitrosamine (DMN), p-dimethylaminoazobenzene (DAB), and di(2-ethylhexyl)phthalate (DEHP)-and two mutagenic chemicals-kojic acid and methylmethanesulfonate (MMS). Quinoline, DMN, and DAB were positive in the liver assay, while o-toluidine, kojic acid, DAB, and MMS were positive in the peripheral blood assay. o-Toluidine, kojic acid, and DAB are reportedly negative in mouse bone marrow micronucleus assays, indicating a species difference. Our results revealed a correlation between micronucleus induction in hepatocytes and hepatocarcinogenicity. This technique can be useful for the detection of micronucleus-inducing chemicals that require metabolic activation, and it enables simultaneous comparison of the micronucleus-inducing potential of chemicals in the liver and peripheral blood in the same individual.

Mutagenicity testing with transgenic mice. Part I: Comparison with the mouse bone marrow micronucleus test

As part of a larger literature study on transgenic animals in mutagenicity testing, test results from the transgenic mutagenicity assays (lacI model; commercially available as the Big Blue(R) mouse, and the lacZ model; commercially available as the Mutatrade markMouse), were compared with the results on the same substances in the more traditional mouse bone marrow micronucleus test. 39 substances were found which had been tested in the micronucleus assay and in the above transgenic mouse systems. Although, the transgenic animal mutation assay is not directly comparable with the micronucleus test, because different genetic endpoints are examined: chromosome aberration versus gene mutation, the results for the majority of substances were in agreement. Both test systems, the transgenic mouse assay and the mouse bone marrow micronucleus test, have advantages and they complement each other. However, the transgenic animal assay has some distinct advantages over the micronucleus test: it is not restricted to one target organ and detects systemic as well as local mutagenic effects.

In vivo mutagenicity of benzo[f]quinoline, benzo[h]quinoline, and 1,7-phenanthroline using the lacZ transgenic mice

Phenanthrene, a simplest angular polycyclic aromatic hydrocarbon with a bay-region in its molecule, is reported to be non-mutagenic, although most angular (non-linear) polycyclic aromatic hydrocarbons, such as benzo[a]pyrene and chrysene, are known to show genotoxicity after metabolic transformation into a bay-region diol epoxide. On the other hand, benzo[f]quinoline (BfQ), benzo[h]quinoline (BhQ), and 1,7-phenanthroline (1,7-Phe), which are all aza-analogs of phenanthrene, are mutagenic in the Ames test using Salmonella typhimurium TA100 in the presence of a rat liver S9 fraction. In this report, we undertook to investigate the in vivo mutagenicity of BfQ, BhQ and 1,7-Phe by an in vivo mutation assay system using the lacZ transgenic mouse (Muta Mouse). BfQ and BhQ only slightly induced mutation in the liver and lung, respectively. BfQ- and BhQ-induced cII mutant spectra showed no characteristics compared with that of the control. These results suggest that the in vivo mutagenicities of BfQ and BhQ were equivocal. On the other hand, 1,7-Phe induced a potent mutation in the liver and a weak mutation in the lung. Furthermore 1,7-Phe depressed the G:C to A:T transition and increased the G:C to C:G transversion in the liver like quinoline, a hepatomutagen possessing the partial structure of 1,7-Phe, compared with the spontaneous mutation spectrum. These results suggest that the in vivo mutagenicity of 1,7-Phe might be caused by the same mechanism as that of quinoline, which induced the same mutational spectrum change (G:C to C:G transversion).

Effect of 10-aza-substitution on benzo[a]pyrene mutagenicity in vivo and in vitro

Benzo[a]pyrene (BaP), an environmental carcinogen, shows genotoxicity after metabolic transformation into the bay-region diol epoxide, BaP-7,8-diol 9,10-epoxide. 10-Azabenzo[a]pyrene (10-azaBaP), in which a ring nitrogen is located in the bay-region, is also a carcinogen and shows mutagenicity in the Ames test in the presence of the rat liver microsomal enzymes. In order to evaluate the effect of aza-substitution on in vivo genotoxicity, BaP and 10-azaBaP were assayed for their in vivo mutagenicity using the lacZ-transgenic mouse (MutaMouse). BaP was potently mutagenic in all of the organs examined (liver, lung, kidney, spleen, forestomach, stomach, colon, and bone marrow), as described in our previous report, whereas, 10-azaBaP was slightly mutagenic only in the liver and colon. The in vitro mutagenicities of BaP and 10-azaBaP were evaluated by the Ames test using liver homogenates prepared from several sources, i.e. CYP1A-inducer-treated rats, CYP1A-inducer-treated and non-treated mice, and humans. BaP showed greater mutagenicities than 10-azaBaP in the presence of a liver homogenate prepared from CYP1A-inducer-treated rodents. However, 10-azaBaP showed mutagenicities similar to or more potent than BaP in the presence of a liver homogenate or S9 from non-treated mice and humans. These results indicate that 10-aza-substitution markedly modifies the nature of mutagenicity of benzo[a]pyrene in both in vivo and in vitro mutagenesis assays.

Hepatocarcinogen quinoline induces G:C to C:G transversions in the cII gene in the liver of lambda/lacZ transgenic mice (MutaMouse)

Quinoline is carcinogenic to the liver in rodents, but it is not clear whether it acts by a genotoxic mechanism. We previously demonstrated that quinoline does induce gene mutation in the liver of lambda/lacZ transgenic mice. In the present report, we reveal the molecular nature of the mutations induced by quinoline in the lambda cII gene, which is also a phenotypically selectable marker in the lambda transgene. (The cII gene has 294bp, which enables much easier sequence analysis than the original lacZ gene (3kb)). The liver cII mutant frequency was nine times higher in quinoline-treated mice than in control mice. Sequence analysis revealed that quinoline induced primarily G:C to C:G transversions (25 of 34). Thus, we have confirmed that quinoline is genotoxic in its target organ, and the G:C to C:G transversion is the molecular signature of quinoline-induced mutations.

Recent advances in the protocols of transgenic mouse mutation assays

Transgenic mutation assays were developed to detect gene mutations in multiple organs of mice or rats. The assays permit (1) quantitative measurements of mutation frequencies in all tissues/organs including germ cells and (2) molecular analysis of induced and spontaneous mutations by DNA sequencing analysis. The protocols of recently developed selections in the lambda phage-based transgenic mutation assays, i.e. cII, Spi(-) and 6-thioguanine selections, are described, and a data set of transgenic mutation assays, including those using Big Blue and Muta Mouse, is presented.

Antimutagenic structural modification of quinoline assessed by an in vivo mutagenesis assay using lacZ-transgenic mice

Quinoline, a hepatocarcinogen, mutates the bacterial tester strains in the presence of the rat liver microsomal enzymes and induces GST-P (placental glutathione S-transferase)-positive foci in a medium-term bioassay system for hepatocarcinogenesis. On the other hand, 3-fluorinated quinoline was neither mutagenic nor carcinogenic in the same assay systems, whereas, 5-fluoroquinoline was mutagenic and carcinogenic. Quinoline was recently demonstrated to be mutagenic in an in vivo mutagenicity assay system using the lacZ-transgenic mouse (MutaMouse). The present study was undertaken to know whether 3-fluoroquinoline would be devoid of in vivo mutagenicity in MutaMouse. Quinoline and 5-fluoroquinoline were also tested in the same system. Mutagenicity was evaluated in the liver, the target organ of quinoline carcinogenesis, and also in the bone marrow and testis. The results strongly indicate that fluorine-substitution at the position-3 of quinoline could be an anti-genotoxic structural modification of quinoline in a wide range of its genotoxic end-points.