Detection of hepatocarcinogens by combination of liver micronucleus assay and histopathological examination in 2-week or 4-week repeated dose studies.

Background: Currently, revisions to the ICH S1 guidance on rodent carcinogenicity testing are being proposed. Application of this approach would reduce the use of animals in accordance with the 3Rs principles (reduce/refine/replace). The method would also shift resources to focus on more scientific mechanism-based carcinogenicity assessments and promote safe and ethical development of new small molecule pharmaceuticals.

Relationship between osteoid formation and iron deposition induced by chronic cadmium exposure in ovariectomized rats.

Itai-itai (Japanese, "It hurts! It hurts!") disease (IID), a form of osteomalacia, can be induced in ovariectomized rats by long-term administration of cadmium (Cd). This IID rat model shows severe anemia, severe nephropathy, and osteomalacia accompanied by iron (Fe) deposition at the mineralization front. We characterized the pathogenesis of Cd-induced bone lesions by investigating the relationship between Fe deposition and osteoid tissue formation in ovariectomized rats.

A spontaneous middle ear adenocarcinoma characterized by abundant eosinophilic matrix in a young male Crl:CD(SD) rat.

A mass was detected in the right tympanic cavity of a 15-week-old male Crl:CD(SD) rat. Histological examination revealed papillary or tubular proliferations of epithelial cells including ciliated cells that produce mucus and have an abundant eosinophilic matrix. The malignancy of this tumor was revealed by its destructive proliferation, cellular polymorphism, and high proliferative activity.

Thymomas and Associated Hyperplastic Lesions in Wistar Hannover Rats.

Thymomas occur prevalently in aged Wistar Hannover (WH) rats, along with hyperplastic lesions that cannot be categorized as thymomas. We compared the histological features of hyperplastic lesions and thymomas in WH rats, the incidences of these lesions, and the relationship of these lesions to the degree of thymic involution and also compared these lesions with those of Sprague Dawley (SD) rats in 4-, 13-, 26-, and 104-week studies. There were no morphological differences between hyperplastic cells and benign tumor cells in thymomas.

Morphological and immunohistochemical diversity of endometrial stromal sarcoma in rats.

To clarify the histopathological characteristics of rat endometrial stromal sarcoma (ESS), we morphologically reviewed 12 malignant uterine tumors protruding into the lumen in previous rat carcinogenicity studies. The 12 cases were classified into the following 6 types based on their morphological features: spindle cell and collagen rich type, pleomorphic/spindle cell and compact type, decidual alteration type, histiocytic and multinucleated giant cell mixture type, Antoni A-type schwannoma type, and Antoni B-type schwannoma type. Immunohistochemically, tumor cells in all cases exhibited focal or diffuse positive reactions for vimentin, and 11 of the 12 cases were positive for S-100.

Evaluation of the repeated dose liver micronucleus assay using young adult rats with cyclophosphamide monohydrate: a report of a collaborative study by CSGMT/JEMS.MMS.

The repeated dose liver micronucleus (RDLMN) assay using young adult rats has the potential to detect liver carcinogens, and this assay could be integrated into general toxicological studies. In this study, in order to assess the performance of the assay, cyclophosphamide monohydrate (CP) was tested in a 14-day RDLMN assay. Based on the results of the 4-day repeated dose-finding study, 10 mg/kg/day of CP was selected as the highest dose and the lower doses were set at 5, 2.

Repeated-dose liver micronucleus test of 4,4'-methylenedianiline using young adult rats.

Liver micronucleus (MN) tests using partial hepatectomized rats or juvenile rats have been shown to be useful for the detection of hepatic carcinogens. Moreover, Narumi et al. established the repeated-dose liver MN test using young adult rats for integration into general toxicity.

Evaluation of repeated dose micronucleus assays of the liver using N-nitrosopyrrolidine: a report of the collaborative study by CSGMT/JEMS.MMS.

The repeated dose liver micronucleus (RDLMN) assay has the potential to detect liver carcinogens, and can be integrated into a general toxicological study. To assess the performance of the assay, N-nitrosopyrrolidine (NPYR), a genotoxic hepatocarcinogen, was tested in 14- or 28-day RDLMN assays. NPYR was orally administered to rats at a daily dose of 25, 50 or 100 mg/kg.

Spontaneous and bilateral necrosis of the femoral head in a young experimental beagle dog.

This report describes the pathological characterizations of a rare case of necrosis of the femoral head that was spontaneous, bilateral, avascular and nontraumatic. A 14-month-old beagle dog was presented with pain in the hind limbs. At necropsy, the articular surface in the bilateral femoral head was markedly irregular.

Arrhythmogenic right ventricular cardiomyopathy coincided with the cardiac fibrosis in the inner muscle layer of the left ventricular wall in a boxer dog.

A 7-year-old female boxer dog died suddenly without any clinical signs. It was suspected that the dog had arrhythmogenic right ventricular cardiomyopathy (ARVC) due to ventricular premature complexes and ventricular tachycardia at 3 years of age. The final diagnosis of ARVC was confirmed by histological characteristics, such as loss of cardiocytes and fibrofatty replacement, occurring in the right and left ventricular walls.

Repeated dose liver micronucleus assay using clofibrate in young adult rats.

The repeated-dose liver micronucleus (MN) assay is a newly established in vivo genotoxicity test for evaluation of liver carcinogens. It may be integrated into general toxicity studies, thereby reducing the numbers of animals required for assessment of chemical safety. A collaborative study by the Mammalian Mutagenicity Study (MMS) Group further evaluated this assay using a wide range of chemicals, including carcinogens and non-carcinogens in young adult rats.

Evaluation of the repeated-dose liver, bone marrow and peripheral blood micronucleus and comet assays using kojic acid.

The repeated-dose liver micronucleus assay has the potential to detect liver carcinogens and could be integrated into general toxicological studies. To assess the performance of this assay, kojic acid was tested in 14-day and 28-day liver micronucleus assays. We evaluated the incidence of micronucleated cells in liver, bone marrow and peripheral blood and performed comet assays in both the liver and peripheral blood (comet assay was performed only for 14-days).

Assessment of methyl methanesulfonate using the repeated-dose liver micronucleus assay in young adult rats.

A repeated-dose liver micronucleus assay using young adult rats was conducted with methyl methanesulfonate (MMS) as a part of a collaborative study supported by the Collaborative Study Group for the Micronucleus Test/the Japanese Environmental Mutagen Society-Mammalian Mutagenicity Study Group. MMS is a classical DNA-reactive carcinogen, but it is not a liver carcinogen. In the first experiment (14-day study), MMS was administered per os to 6-week-old male Crl:CD (SD) rats every day for 14 days at a dose of 12.

Repeated dose liver and gastrointestinal tract micronucleus assays using N-methyl-N'-nitro-N-nitrosoguanidine in young adult rats.

N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG) is a direct-acting mutagen that induces tumors in the glandular stomach, but not in the liver or colon, of rats after oral administration. To evaluate the performance of repeated dose liver and gastrointestinal tract micronucleus (MN) assays in young adult rats, MNNG was administered by oral gavage to male CD (SD) rats aged 6 weeks at doses of 0 (vehicle; 2.5% DMSO aqueous solution), 3.

Evaluation of in vivo genotoxicity by thioacetamide in a 28-day repeated-dose liver micronucleus assay using male young adult rats.

The repeated-dose liver micronucleus (RDLMN) assay has the potential to detect liver carcinogens and can be integrated into general toxicological studies. In this study, thioacetamide (TAA) was tested in 14- and 28-day RDLMN assays to assess the performance of the assay. The test substance, TAA, was administered orally to 6-week-old male Crl:CD (SD) rats once daily for 14 or 28 days at a dosage of 5, 10 or 20mg/kg/day.

Repeated-dose liver and gastrointestinal tract micronucleus assays with CI Solvent Yellow 14 (Sudan I) using young adult rats.

The in vivo genotoxicity of CI Solvent Yellow 14 (Sudan I) was examined using repeated-dose liver and gastrointestinal tract micronucleus (MN) assays in young adult rats. Sudan I is a mono-azo dye based on aniline and 1-amino-2-hydroxynaphthalene. This dye was demonstrated as a rat liver carcinogen in a National Toxicology Program (NTP) bioassay, and genotoxicity was noted in a rat bone marrow micronucleus (BMMN) assay.

Micronucleus induction in rat liver and bone marrow by acute vs. repeat doses of the genotoxic hepatocarcinogen monocrotaline.

The liver micronucleus (MN) assay is useful for predicting genotoxic rodent hepatocarcinogenicity. We have recently established the repeated-dose liver MN (RDLMN) assay in rats for integration into general toxicity studies. To investigate the effectiveness of the RDLMN assay, the genotoxic rodent hepatocarcinogen, monocrotaline (MCT), was administered by oral gavage to 6-week old male rats once daily for 14 days at 0.

Repeated-dose liver micronucleus assay: an investigation with 2-nitropropane, a hepatocarcinogen.

The utility of the repeated-dose liver micronucleus (RDLMN) assay in the detection of a genotoxic hepatocarcinogen was evaluated. In this paper, a rat hepatocarcinogen, 2-nitropropane (2-NP), was administered orally to young adult rats for 14 and 28 days without a partial hepatectomy or a mitogen, and the micronucleus induction in liver was examined using a simple method to isolate hepatocytes. In addition, a bone marrow micronucleus assay was conducted concomitantly.

Evaluation of the repeated-dose liver micronucleus assay with p-dimethylaminoazobenzene.

The micronucleus induction by p-dimethylaminoazobenzene (DAB), a genotoxic rat liver carcinogen, was assessed in the liver and bone marrow of young adult rats after the repeated administration of DAB for 14 (Lab. 1) and 28 (Lab. 2) days.

Repeated-dose liver and gastrointestinal tract micronucleus assays for quinoline in rats.

Repeated-dose liver, bone marrow, and gastrointestinal tract micronucleus assays that use young adult rats were evaluated in a collaborative study that was organized by the Japanese Environmental Mutagen Society-Mammalian Mutagenicity Study Group. A genotoxic hepatocarcinogen quinoline was orally administered to independent groups of five Crl:CD (SD) male rats at doses of 30, 60 and 120mg/kg for 14 days and at doses of 15, 30 and 60mg/kg for 28 days. After treatment, the livers were harvested and hepatocytes were isolated by collagenase treatment.

Evaluation of a repeated-dose liver micronucleus assay with 2,6-dinitrotoluene using young adult rats.

As part of a collaborative study by the Mammalian Mutagenicity Study Group of the Environmental Mutagen Society of Japan, we examined micronucleus induction in hepatocytes following oral administration of 2,6-dinitrotoluene (2,6-DNT) at 30, 40, and 50mg/kg/day for 14 days or at 20, 30, and 40mg/kg/day for 28 days to young adult male rats. This compound is known to be a rat liver carcinogen. The formation of micronucleated hepatocytes was confirmed to be dose-dependent with statistically significant increases observed in both treatments.

Evaluation of a repeated dose liver micronucleus assay in rats treated with two genotoxic hepatocarcinogens, dimethylnitrosamine and 2-acetylaminofluorene: the possibility of integrating micronucleus tests with multiple tissues into a repeated dose general toxicity study.

As part of a collaborative study by the Collaborative Study Group for Micronucleus Test (CSGMT) of the Mammalian Mutagenicity Study Group (MMS) in the Japanese Environmental Mutagen Society (JEMS), the present study evaluated the effectiveness of the repeated dose liver micronucleus (RDLMN) assay. Two genotoxic hepatocarcinogens, dimethylnitrosamine (DMN) and 2-acetylaminofluorene (2-AAF), were administered orally to male rats (6 weeks old at the initial dosing) once daily for 14 and 28 days to evaluate the micronucleus (MN) inducibility in the liver. In addition, these chemicals were evaluated for MN inducibility in the bone marrow (BM) and gastrointestinal (GI) tract, i.

Evaluation of the repeated-dose liver and gastrointestinal tract micronucleus assays with 22 chemicals using young adult rats: summary of the collaborative study by the Collaborative Study Group for the Micronucleus Test (CSGMT)/The Japanese Environmental Mutagen Society (JEMS) - Mammalian Mutagenicity Study Group (MMS).

The repeated-dose liver micronucleus (RDLMN) assay using young adult rats has the potential to detect hepatocarcinogens. We conducted a collaborative study to assess the performance of this assay and to evaluate the possibility of integrating it into general toxicological studies. Twenty-four testing laboratories belonging to the Mammalian Mutagenicity Study Group, a subgroup of the Japanese Environmental Mutagen Society, participated in this trial.

Follicular thyroid carcinoma characterized by abundant stromal components with chondroid and osseous metaplasia in a dog.

A dog developed a cervical mass, and computed tomography verified a mass surrounding the trachea with some pulmonary masses. Histopathologically, the cervical mass was composed of malignant neoplastic cells showing follicular appearance which reacted positive for thyroglobulin on immunohistochemistry. A characteristic feature of the tumor was abundant and metaplastic stromal components.

The 14-day repeated dose liver micronucleus test with methapyrilene hydrochloride using young adult rats.

The repeated dose liver micronucleus (RDLMN) assay using young adult rats has the potential to detect genotoxic hepatocarcinogens that can be integrated into a general toxicity study. The assay methods were thoroughly validated by 19 Japanese facilities. Methapyrilene hydrochloride (MP), known to be a non-genotoxic hepatocarcinogen, was examined in the present study.