title: Evaluation of the repeated-dose liver micronucleus assay using N-nitrosomorpholine in young adult rats: report on collaborative study by the Collaborative Study Group for the Micronucleus Test (CSGMT)/Japanese Environmental Mutagen Society (JEMS)-Mammalian Mutagenicity Study (MMS) Group.
abstract: The present study was conducted to evaluate the suitability of a repeated-dose liver micronucleus (LMN) assay in young adult rats as a collaborative study by the Mammalian mutagenicity study (MMS) group. All procedures were performed in accordance with the standard protocols of the MMS Group. Six-week-old male Crl:CD(SD) rats (5 animals/group) received oral doses of the hepatocarcinogen N-nitrosomorpholine (NMOR) at 0 (control), 5, 10, and 30mg/kg/day (10mL/kg) for 14 days. Control animals received vehicle (water). Hepatocytes were collected from the liver 24h after the last dose, and the number of micronucleated hepatocytes (MNHEPs) was determined by microscopy. The number of micronucleated immature erythrocytes (MNIMEs) in the femoral bone marrow was also determined. The liver was examined using histopathologic methods after formalin fixation. The results showed statistically significant and dose-dependent increases in the number of MNHEPs in the liver at doses of 10mg/kg and greater when compared with the vehicle control. However, no significant increase was noted in the number of MNIMEs in the bone marrow at doses of up to 30mg/kg. Histopathology of the liver revealed hypertrophy and single cell necrosis of hepatocytes at doses of 5mg/kg and above. These results showed that the induction of micronuclei by NMOR was detected by the repeated-dose LMN assay, but not by the repeated-dose bone marrow micronucleus assay.
authors.affiliation: Shin Nippon Biomedical Laboratories, Ltd., 2438 Miyanoura-cho, Kagoshima-shi 891-1394, Kagoshima, Japan. Electronic address: hayashi-aya@snbl.co.jp.
authors.forename: Aya
authors.initials: A
authors.lastname: Hayashi
authors.affiliation: Shin Nippon Biomedical Laboratories, Ltd., 2438 Miyanoura-cho, Kagoshima-shi 891-1394, Kagoshima, Japan.
authors.forename: Mizuki
authors.initials: M
authors.lastname: Kosaka
authors.affiliation: Shin Nippon Biomedical Laboratories, Ltd., 2438 Miyanoura-cho, Kagoshima-shi 891-1394, Kagoshima, Japan.
authors.forename: Aoi
authors.initials: A
authors.lastname: Kimura
authors.affiliation: LSI Medience Corporation, 14-1 Sunayama, Kamisu-shi 314-0255, Ibaraki, Japan.
authors.forename: Yumi
authors.initials: Y
authors.lastname: Wako
authors.affiliation: LSI Medience Corporation, 14-1 Sunayama, Kamisu-shi 314-0255, Ibaraki, Japan.
authors.forename: Kazufumi
authors.initials: K
authors.lastname: Kawasako
authors.affiliation: LSI Medience Corporation, 14-1 Sunayama, Kamisu-shi 314-0255, Ibaraki, Japan; National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku 158-0098, Tokyo, Japan; University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka-shi 422-8526, Shizuoka, Japan.
authors.forename: Shuichi
authors.initials: S
authors.lastname: Hamada
mesh_terms: D000284:Administration, Oral; D000367:Age Factors; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D001853:Bone Marrow / Q000187:drug effects; D002273:Carcinogens / Q000633:toxicity*; D002869:Chromosome Aberrations / Q000187:drug effects; D003299:Cooperative Behavior; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D022781:Hepatocytes / Q000187:drug effects* / Q000473:pathology; D006801:Humans; D007564:Japan; D008099:Liver / Q000187:drug effects* / Q000473:pathology; D008297:Male; D015162:Micronucleus Tests; D009602:Nitrosamines / Q000633:toxicity*; D009928:Organ Specificity; D051381:Rats; D017207:Rats, Sprague-Dawley; D012156:Reticulocytes / Q000187:drug effects; D012957:Societies, Pharmaceutical
chemical_list: D002273:Carcinogens; D009602:Nitrosamines; C002741:N-nitrosomorpholine
keywords: Bone marrow micronucleus assay; Liver micronucleus assay; N-nitrosomorpholine; Young adult rat