Effectiveness of the liver micronucleus assay using juvenile mice

J Vet Med Sci. 2017 Jul 28;79(7):1310-1317. doi: 10.1292/jvms.17-0116. Epub 2017 Jul 11.


This study investigated the effectiveness of the liver micronucleus (MN) assay using juvenile mice. Therefore, we analyzed various hepatic cytochrome P450 (CYP)- mediated activities of ethoxyresorufin O-deethylation, pentoxyresorufin O-dealkylation, tolbutamide hydroxylation, bufuralol 1'-hydroxylation, aniline hydroxylation and midazolam 4-hydroxylation by CYP1A, CYP2B, CYP2C, CYP2D, CYP2E and CYP3A, respectively, in non-treated male ICR mice aged between 3 and 8 weeks. The enzyme efficiency levels in 3- and 4-week-old mice were approximately similar to or higher than those in 8-week-old mice, except for CYP1A and CYP2E in 3- and 4-week-old mice, respectively. Since these results suggest that juvenile mice have sufficient activities for most CYP enzymes, we also conducted a liver MN assay using diethylnitrosamine (DEN), a rodent hepatocarcinogen, on male ICR mice aged between 3 and 6 weeks. A peripheral blood (PB) MN assay was performed simultaneously in 4-week-old mice. Assays incorporating DEN produced positive results in 3- and 4-week-old mice and showed a dose-dependent increase in the micronucleated hepatocyte frequencies at 4 weeks. Both the liver MN assay in 5- and 6-week-old mice and the PB MN assay had negative results when using DEN. These results suggest that 3- and 4-week-old mice have micronuclei-inducing potential in the liver to detect genotoxic compounds using the liver MN assay.

Keywords: CYP; genotoxicity assay; juvenile mouse; liver micronucleus assay.

MeSH terms

  • Age Factors
  • Animals
  • Cytochrome P-450 Enzyme System / drug effects
  • Dose-Response Relationship, Drug
  • Male
  • Mice, Inbred ICR
  • Micronucleus Tests / methods*
  • Micronucleus Tests / standards
  • Microsomes, Liver / drug effects
  • Microsomes, Liver / enzymology


  • Cytochrome P-450 Enzyme System