As human pharmaceuticals are physiologically active substances, it is essential to assess their potential risk to ecosystems after being released into the environment. In Japan, the "Guidance on the Environmental Risk Assessment in New Pharmaceutical Development" (hereafter referred to as "the guidance") was issued in 2016. The guidance includes the environmental risk assessment (ERA) workflow, in which novel pharmaceuticals subjected to ecotoxicity testing are selected based on n-octanol/water partition coefficient (log Kow), action limit (0.01 µg/L), and predicted environmental concentration (PEC). However, for the ERA workflow, neither the action limit has been completely validated nor a method to calculate PEC has been sufficiently established. The objective of this study was to demonstrate the effectiveness and issues of the ERA workflow in the guidance. Using data accumulated from ecotoxicity studies and measured environmental concentration (MEC) data of human pharmaceuticals, we evaluated the validity of the action limit and PEC values. The action limit was found to be sufficiently on the safe side, and the PEC values (to median or 95th percentile MEC values) were generally on the safe side for the evaluated pharmaceuticals. Conversely, issues were also identified, which included a need to establish exemption rules for some specific pharmaceuticals with toxicological concerns at a concentration below the action limit and to refine the PEC calculation method based on the consideration of drug metabolism and environmental fate. The endeavor to address these issues will increase the reliability and effectiveness of the workflow.

DNA polymerase κ (Polk), a member of Y-family DNA polymerases, plays an important role in translesion DNA synthesis (TLS), allowing DNA replication forks to bypass DNA damage or DNA adducts to continue daughter strand synthesis. Polk is also believed to contribute to the replication-independent repair of DNA lesions such as cross-links. TLS circumvents stalls of DNA replication and promotes gap filling in DNA repair which would otherwise result in DNA double-strand breaks (DSBs) and cell death. Mitomycin C (MMC) is a widely used chemotherapeutic drug which generates DNA cross-links and induces DSBs. To clarify how Polk contributes to the prevention of MMC-induced DSB in various organs or tissues, immunohistochemical staining of γH2AX was conducted in catalytically inactivated Polk knock-in (Polk KI) mice and Polk wild-type (Polk+) mice treated with MMC or saline. The γH2AX induction by MMC was enhanced by inactivation of Polk across many organs or tissues to varying degrees. Obvious enhancement was observed in liver, bladder, adrenal cortex, thyroid, and spermatids, whereas less enhancement was shown in brain and retina. The results suggest that Polk plays a role in preventing DSBs caused by MMC in most organs or tissues. Elevated DSB frequencies were observed in both proliferative cells, such as bladder epithelium cells, and less or slowly proliferative cells, such as hepatocytes. Increased DSB levels in inactivated Polk KI mice relative to Polk+ mice were also observed in saline-treated mice in the adrenal cortex and other tissues. Polk plays a systemic role in mitigating MMC-induced DSBs, likely through both DNA replication-dependent and -independent mechanisms. Furthermore, Polk appears to protect against DSBs caused by endogenous mutagens in some organs such as the adrenal cortex, prostate, and retina.

Zirconium(IV) butoxide (ZB; CAS 1071-76-7) is widely used in industrial applications as a catalyst, stabilizer, and precursor for ceramic materials utilized in medical devices such as artificial bones and teeth. Metal alkoxide compounds, including ZB, are easily hydrolyzed, polymerized, and precipitated in aqueous environments. Although a no-observed-adverse-effect level (NOAEL) for ZB has been estimated by extrapolating its hydrolysis product, 1-butanol, ZB toxicological profile remains unclear, leaving data gaps for risk evaluation. In this study, we developed a method for ZB preparation and administration using corn oil as vehicle, in which ZB was retained its polymerizable form. A 13-week repeated-dose oral toxicity study was conducted in 6-week-old Crl:CD(SD) rats. Groups of ten males and females were orally administered ZB at doses of 0 (vehicle: corn oil), 100, 300, and 1000 mg/kg body weight (bw)/day, or 1-butanol at 116 mg/kg bw/day, which was equivalent to its level after dosing ZB at 1000 mg/kg bw/day. No toxicologically significant effects were observed after ZB administration. The NOAEL for ZB was estimated to be 1000 mg/kg bw/day in both sexes. These results provide essential toxicological data for safety assessment and regulatory evaluation of ZB.

Toluene diisocyanates (TDIs) are high-production-volume chemicals widely used in polyurethane manufacturing. A typical commercial-grade TDI (TDI; 2,4-toluene diisocyanate: 2,6-toluene diisocyanate; 80:20), CAS: 26471-62-5, is mutagenic in Salmonella typhimurium with an S9 metabolic activation mix and induces chromosomal aberrations in Chinese hamster lung cells without S9 mix. While oral administration of TDI has been reported to be carcinogenic in female mice and rats of both sexes, its in vivo mutagenicity remains poorly understood. This study aimed to clarify the in vivo mutagenicity of orally administered TDI. In vivo mutagenicity was evaluated following the Organisation for Economic Co-operation and Development Test Guideline 488 (OECD TG488). MutaMouse females were orally dosed with TDI at 0 (corn oil; vehicle control), 250, 500, or 1,000 mg/kg/day for 28 days. Mutant frequencies (MFs) in the liver and glandular stomach were analyzed three days post-final dosing. Positive controls received intraperitoneal injections of N-ethyl-N-nitrosourea (ENU) at 100 mg/kg/day for two days, with MFs assessed ten days after the final dose. Significant increases in lacZ MFs were observed in the liver at 1,000 mg/kg/day, while MFs in the glandular stomach remained unchanged. Positive controls demonstrated significantly elevated MFs in both the liver and glandular stomach. These findings indicate that orally administered TDI is mutagenic in mice, supporting its classification as a mutagenic carcinogen.

Error-corrected next-generation sequencing (ecNGS) enables the sensitive detection of chemically induced mutations. Matsumura et al. reported Hawk-Seq™, an ecNGS method, demonstrating its utility in clarifying mutagenicity both qualitatively and quantitatively. To further promote the adoption of ecNGS-based assays, it is important to evaluate their inter-laboratory transferability and reproducibility. Therefore, we evaluated the inter-laboratory reproducibility of Hawk-Seq™ and its concordance with the transgenic rodent mutation (TGR) assay. The Hawk-Seq™ protocol was successfully transferred from the developer’s laboratory (lab A) to two additional laboratories (labs B, C). Whole genomic mutations were analyzed independently using the same genomic DNA samples from the livers of gpt delta mice exposed to benzo[a]pyrene (BP), N-ethyl-N-nitrosourea (ENU), and N-methyl-N-nitrosourea (MNU). In all laboratories, clear dose-dependent increases in base substitution (BS) frequencies were observed, specific to each mutagen (e.g. G:C to T:A for BP). Statistically significant increases in overall mutation frequencies (OMFs) were identified at the same doses across all laboratories, suggesting high reproducibility in mutagenicity assessment. The correlation coefficient (r2) of the six types of BS frequencies exceeded 0.97 among the three laboratories for BP- or ENU-exposed samples. Thus, Hawk-Seq™ provides qualitatively and quantitatively reproducible results across laboratories. The OMFs in the Hawk-Seq™ analysis positively correlated (r2 = 0.64) with gpt mutant frequencies (MFs). The fold induction of OMFs in the Hawk-Seq™ analysis of ENU- and MNU-exposed samples was at least 14.2 and 4.5, respectively, compared to 6.1 and 2.5 for gpt MFs. Meanwhile, the fold induction of OMFs in BP-exposed samples was ≤ 4.6, compared to 8.2 for gpt MFs. These observations suggest that Hawk-Seq™ demonstrates good concordance with the transgenic rodent (TGR) gene mutation assay, whereas the induction of mutation frequency by each mutagen might not directly correspond. Hawk-Seq™-based whole-genome mutagenicity evaluation demonstrated high inter-laboratory reproducibility and concordance with gpt assay results. Our results contribute to the growing evidence that ecNGS assays provide a suitable, or improved, alternative to the TGR assay.

Prediction of cytochrome P450 (CYP)-mediated metabolism is crucial for assessing the safety of chemicals. An in silico system to reproduce CYP1B1-mediated reactions has been developed by the reverse construction of ligand-accessible spaces from ligand assemblies as a fused grid Template* system. There are close similarities between Templates of CYP1B1 and previously established CYP1A1 (Genes Environ 2023) in the distribution area, Site of oxidation, and the available Width, except for the use of Position 52’ (Pier-sitting) and the lack of use of the bottom in the middle region (Rings F and Ea) on CYP1B1-Template. Experiments using various substrates of both enzymes further suggested the distinct localization of Bay-2 residues on Templates of CYP1A1 and CYP1B1. More than 260 reactions of CYP1A1/1B1 ligands were examined on the present CYP1A1- and CYP1B1-Template systems. From their placements on the Templates and rules for interaction modes, verifications of good and poor substrates, regio/stereo-selectivity, and inhibition became faithfully available for these ligands. To understand the structural basis of the inhibitory interaction, various inhibitors were applied to the Templates and verified modes of the steric interactions. Both the hangings at Position 32 of CYP1A1 ligands and the adherence at Positions 24–52 of CYP1B1 ligands are suggested to retard the dissociation of Bay-2 residues from ligand molecules. Dissociation interference of ligands with Bay-2 residue is thus possible to be a mechanism of ligand-mediated inhibition on CYP1A1 and CYP1B1.

Carbendazim is registered on the Japanese positive list (PL) for food contact materials (food utensils, containers, and packaging; UCP). However, to ensure food safety, a dietary risk assessment of carbendazim is necessary. The safety of carbendazim has been evaluated by several risk assessment bodies, from which health-based guidance values (HBGVs) have been established, mainly based on the no observed adverse effect level (NOAEL) approach. However, as most of the reviewed studies were not conducted in accordance with Good Laboratory Practice (GLP) or OECD test guidelines (TGs), they may not have fully met quality standards. Following the results of periodic re-evaluations, some HBGVs have been withdrawn owing to insufficient toxicological information. Therefore, we verified the HBGVs of carbendazim from the perspective of genotoxicity. The point of departure (PoD) for aneugenicity was calculated based on a dose-response analysis from in vivo micronucleus tests using the benchmark dose (BMD) approach. Overall, the HBGV based on the PoD of aneugenicity was comparable with the existing HBGV based on developmental toxicity tests in rats and rabbits using the NOAEL approach.

8-Hydroxydeoxyguanosine (8-OHdG) is well known not only as an effective biomarker of oxidative stress but also as a mutagenic DNA modification. Incorporation of dAMP at the opposite site of 8-OHdG induces G>T or A>C transversions. However, in vivo analyses of gene mutations caused by potassium bromate (KBrO3), which can induce 8-OHdG at carcinogenic target sites, showed that G>T was prominent in the small intestines of mice, but not in the kidneys of rats. Because KBrO3 was a much clearer carcinogen in the kidneys of rats, detailed analyses of gene mutations in the kidney DNA of rats treated with KBrO3 could improve our understanding of oxidative stress-mediated carcinogenesis. In the current study, site-specific reporter gene mutation assays were performed in the kidneys of gpt delta rats treated with KBrO3. Groups of 5 gpt delta rats were treated with KBrO3 at concentrations of 0, 125, 250, or 500 ppm in the drinking water for 9 weeks. At necropsy, the kidneys were macroscopically divided into the cortex and medulla. 8-OHdG levels in DNA extracted from the cortex were dramatically elevated at concentrations of 250 ppm and higher compared with those from the medulla. Cortex-specific increases in mutant frequencies in gpt and red/gam genes were found at 500 ppm. Mutation spectrum and sequence analyses of their mutants demonstrated significant elevations in A>T transversions in the gpt gene and single base deletions at guanine or adenine in the gpt or red/gam genes. While A>T transversions and single base deletions of adenine may result from the oxidized modification of adenine, the contribution of 8-OHdG to gene mutations was limited despite possible participation of the 8-OHdG repair process in guanine deletion.

Abstract Background Error-corrected next-generation sequencing (ecNGS) technologies have enabled the direct evaluation of genome-wide mutations after exposure to mutagens. Previously, we reported an ecNGS methodology, Hawk-Seq™, and demonstrated its utility in evaluating mutagenicity. The evaluation of technical transferability is essential to further evaluate the reliability of ecNGS-based assays. However, cutting-edge sequencing platforms are continually evolving, which can affect the sensitivity of ecNGS. Therefore, the effect of differences in sequencing instruments on mutation data quality should be evaluated. Results We assessed the performance of four sequencing platforms (HiSeq2500, NovaSeq6000, NextSeq2000, and DNBSEQ-G400) with the Hawk-Seq™ protocol for mutagenicity evaluation using DNA samples from mouse bone marrow exposed to benzo[a]pyrene (BP). The overall mutation (OM) frequencies per 106 bp in vehicle-treated samples were 0.22, 0.36, 0.46, and 0.26 for HiSeq2500, NovaSeq6000, NextSeq2000, and DNBSEQ-G400, respectively. The OM frequency of NextSeq2000 was significantly higher than that of HiSeq2500, suggesting the difference to be based on the platform. The relatively higher value in NextSeq2000 was a consequence of the G:C to C:G mutations in NextSeq2000 data (0.67 per 106 G:C bp), which was higher than the mean of the four platforms by a ca. of 0.25 per 106 G:C bp. A clear dose-dependent increase in G:C to T:A mutation frequencies was observed in all four sequencing platforms after BP exposure. The cosine similarity values of the 96-dimensional trinucleotide mutation patterns between HiSeq and the three other platforms were 0.93, 0.95, and 0.92 for NovaSeq, NextSeq, and DNBSeq, respectively. These results suggest that all platforms can provide equivalent data that reflect the characteristics of the mutagens. Conclusions All platforms sensitively detected mutagen-induced mutations using the Hawk-Seq™ analysis. The substitution types and frequencies of the background errors differed depending on the platform. The effects of sequencing platforms on mutagenicity evaluation should be assessed before experimentation.

Background Carbendazim (methyl 2-benzimidazolecarbamate, CASRN: 10605-21-7) exhibits spindle poisoning effects and is widely used as a fungicide. With respect to genotoxicity, carbendazim is deemed to be non-mutagenic in vitro, but it causes indicative DNA damage in vivo and chromosome aberrations in vitro and in vivo. In this study, we examined the mutagenicity of carbendazim in vivo. Results MutaMice were treated with carbendazim orally at doses of 0 (corn oil), 250, 500, and 1,000 mg/kg/day once a day for 28 days. A lacZ assay was used to determine the mutant frequency (MF) in the liver and glandular stomach of mice. MutaMice were administered up to the maximum dose recommended by the Organization for Economic Co-operation and Development Test Guidelines for Chemicals No. 488 (OECD TG488). The lacZ MFs in the liver and glandular stomach of carbendazim-treated animals were not significantly different from those in the negative control animals. In contrast, positive control animals exhibited a significant increase in MFs in both the liver and glandular stomach. Conclusions Carbendazim is non-mutagenic in the liver and glandular stomach of MutaMice following oral treatment.

1,2-Dichloroethane, a priority assessment chemical substance under the Japan Chemical Substances Control Law (CSCL), required a detailed human health hazard assessment under Assessment II. We evaluated its general, reproductive, and developmental toxicities, genotoxicity, and carcinogenicity, based on the hazard information provided by domestic and international risk assessment organizations, and the hazard assessment values (HAVs) for oral and inhalation exposure were proposed. For oral exposure, a 78-week gavage carcinogenicity study (US NCI, 1978) with incidence data of hemangiosarcoma in male rats was selected as a significant toxicological endpoint and the lower confidence limit of benchmark dose (BMD) at 10% benchmark response (BMDL10) of 9.3 mg/kg/day was obtained as a point of departure (POD). A slope factor of 1.07 × 10−2 (mg/kg/day)−1 from which a carcinogenic 10−5 risk of 0.93 µg/kg/day was derived as an oral HAV. For inhalation exposure, a 104-week inhalation exposure carcinogenicity study (Nagano et al., 2006) with a BMDL10 of 11.5 ppm based on the incidence data of mammary gland tumors (adenocarcinoma + adenoma + fibroadenoma, combined) in female rats was obtained, and the human equivalent BMDL10 of 15.7 mg/m3 was calculated. Therefore, a unit risk of 6.40 × 10−6 (µg/m3)−1 from which a carcinogenic 10−5 risk of 1.6 µg/m3 (0.00039 ppm) was derived as an inhalation HAV.

Abstract 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.

Abstract Background Styrene (CAS 100-42-5) is widely used as polystyrene and acrylonitrile–butadiene–styrene resin such as plastic, rubber, and paint. One of the primary uses of styrene is food utensils and containers, but a small amount of styrene transferred into food can be ingested by eating. Styrene is metabolized into styrene 7,8-oxide (SO). SO is mutagenic in bacteria and mouse lymphoma assays. It is clastogenic in cultured mammalian cells. However, styrene and SO are not clastogenic/aneugenic in rodents, and no rodent in vivo gene mutation studies were identified. Methods To investigate the mutagenicity of orally administered styrene, we used the transgenic rodent gene mutation assay to perform an in vivo mutagenicity test (OECD TG488). The transgenic MutaMouse was given styrene orally at doses of 0 (corn oil; negative control), 75, 150, and 300 mg/kg/day for 28 days, and mutant frequencies (MFs) were determined using the lacZ assay in the liver and lung (five male mice/group). Results There were no significant differences in the MFs of the liver and lung up to 300 mg/kg/day (close to maximum tolerable dose (MTD)), when one animal with extremely high MFs that were attributed to an incidental clonal mutation was omitted. Positive and negative controls produced the expected results. Conclusions These findings show that styrene is not mutagenic in the liver and lung of MutaMouse under this experimental condition.

The in vivo working group (WG) considered three topics: acceptable maximum doses for negative erythrocyte micronucleus (MN) tests, validation status of MN assays in non-hematopoietic tissues, and nuisance factors in the comet assay. The WG reached agreement on many issues, including: negative erythrocyte MN studies should be acceptable if dosing is conducted to Organisation for Economic Co-operation and Development (OECD) test guideline (TG) 474 recommendations and if sufficient bone marrow exposure is demonstrated; consensus on the evidence required to demonstrate "sufficient" exposure was not reached. The liver MN test using six-week-old rats is sufficiently validated to develop an OECD TG, but the impact of animal age warrants additional study. Ki-67 is a reliable marker for cellular proliferation in hepatocytes. The gastrointestinal tract MN test is useful for detecting poorly absorbed or rapidly degraded aneugens, and for genotoxic metabolites formed in the colon. Although current validation data are insufficient to support the development of an OECD TG, the methodologies are sufficient to consider as an appendix to OECD TG474. Comparison of comet assay results to laboratory historical control data (HCD) should not be used in data evaluation, unless the HCD distribution is demonstrated to be stable and the predominant source of HCD variation is due to animal, not study, factors. No universally acceptable negative control limit for any tissue was identified. Methodological differences in comet studies can result in variable data interpretations; more data are required before best practice recommendations can be made. Hedgehogs alone are unreliable indicators of cytotoxicity and additional investigations into cytotoxicity markers are required.

Supplementary Table 2 from Enhanced Spontaneous and Benzo(a)pyrene-Induced Mutations in the Lung of Nrf2-Deficient gpt Delta Mice

Background tert -Butyl hydroperoxide (TBHP; CAS 75–91-2), a hydroperoxide, is mainly used as a polymerization initiator to produce polyethylene, polyvinyl chloride, and unsaturated polyester. It is a high-production chemical, widely used in industrial countries, including Japan. TBHP is also used as an additive for the manufacturing of food utensils, containers, and packaging (UCP). Therefore, there could be consumer exposure through oral intake of TBHP eluted from UCPs. TBHP was investigated in various in vitro and in vivo genotoxicity assays. In Ames tests, some positive results were reported with and/or without metabolic activation. As for the mouse lymphoma assay, the positive result was reported, regardless of the presence or absence of metabolic activation enzymes. The results of some chromosomal aberrations test and comet assay in vitro also demonstrated the genotoxic positive results. On the other hand, in in vivo tests, there are negative results in the bone marrow micronucleus test of TBHP-administered mice by single intravenous injection and the bone marrow chromosomal aberration test using rats exposed to TBHP for 5 days by inhalation. Also, about dominant lethal tests, the genotoxic positive results appeared. In contrast, there is little information about in vivo mutagenicity and no information about carcinogenicity by oral exposure. Results We conducted in vivo gene mutation assay using MutaMice according to the OECD Guidelines for the Testing of Chemicals No. 488 to investigate in vivo mutagenicity of TBHP through oral exposure. After repeated dosing for 28 days, there were no significant differences in the mutant frequencies (MFs) of the liver and glandular stomach up to 300 mg/kg/day (close to the maximum tolerable dose (MTD)). The positive and negative controls produced the expected responses. Conclusions These findings show that orally administrated TBHP is not mutagenic in the mouse liver and glandular stomach under these experimental conditions.