title: Recommended protocols for the liver micronucleus test: Report of the IWGT working group.
abstract: At the 6th International Workshop on Genotoxicity Testing (IWGT), the liver micronucleus test working group discussed practical aspects of the in vivo rodent liver micronucleus test (LMNT). The group members focused on the three methodologies currently used, i.e., a partial hepatectomy (PH) method, a juvenile/young rat (JR) method, and a repeated-dose (RD) method in adult rodents. Since the liver is the main organ that metabolizes chemicals, the LMNT is expected to detect clastogens, especially those that need metabolic activation in the liver, and aneugens. Based on current data the three methods seem to have a high sensitivity and specificity, but more data, especially on non-genotoxic but toxic substances, would be needed to fully evaluate the test performance. The three methods can be combined with the micronucleus test (MNT) using bone marrow (BM) and/or peripheral blood (PB). The ability of the PH method to detect both clastogens and aneugens has already been established, but the methodology is technically challenging. The JR method is relatively straightforward, but animal metabolism might not be fully comparable to adult animals, and data on aneugens are limited. These two methods also have the advantage of a short testing period. The RD method is also straightforward and can be integrated into repeated-dose (e.g. 2 or 4 weeks) toxicity studies, but again data on aneugens are limited. The working group concluded that the LMNT could be used as a second in vivo test when a relevant positive result in in vitro mammalian cell genotoxicity tests is noted (especially under the condition of metabolic activation), and a negative result is observed in the in vivo BM/PB-MNT. The group members discussed LMNT protocols and reached consensus about many aspects of test procedures. However, data gaps as mentioned above remain, and further data are needed to fully establish the LMNT protocol.
authors.affiliation: Mitsubishi Tanabe Pharma Co., Chiba, Japan. Electronic address: Uno.Yoshifumi@ma.mt-pharma.co.jp.
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Uno
authors.affiliation: National Institute of Health Sciences, Tokyo, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Morita
authors.affiliation: Centre for Health Protection, National Institute for Public Health and the Environment, (RIVM), Bilthoven, The Netherlands.
authors.forename: Mirjam
authors.initials: M
authors.lastname: Luijten
authors.affiliation: Covance Laboratories Ltd., Harrogate, UK.
authors.forename: Carol
authors.initials: C
authors.lastname: Beevers
authors.affiliation: LSI Medience (formerly Mitsubishi Chemical Medience Co.), Ibaraki, Japan.
authors.forename: Shuichi
authors.initials: S
authors.lastname: Hamada
authors.affiliation: Daiichi Sankyo Co., Ltd., Tokyo, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Itoh
authors.affiliation: Yakult Honsha Co., Ltd., Tokyo, Japan.
authors.forename: Wakako
authors.initials: W
authors.lastname: Ohyama
authors.affiliation: LSI Medience (formerly Mitsubishi Chemical Medience Co.), Ibaraki, Japan.
authors.forename: Hironao
authors.initials: H
authors.lastname: Takasawa
mesh_terms: D024422:Aneugens / Q000032:analysis* / Q000633:toxicity*; D000818:Animals; D001773:Blood Cells / Q000378:metabolism / Q000473:pathology; D001854:Bone Marrow Cells / Q000378:metabolism / Q000473:pathology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008099:Liver / Q000378:metabolism* / Q000473:pathology; D048629:Micronuclei, Chromosome-Defective / Q000139:chemically induced*; D015162:Micronucleus Tests / Q000379:methods / Q000592:standards; D051381:Rats; D012680:Sensitivity and Specificity
chemical_list: D024422:Aneugens
keywords: IWGT; Liver; Micronucleus test; Protocol; Rodent