Chromosome breakage is primarily responsible for the micronuclei induced by 1,4-dioxane in the bone marrow and liver of young CD-1 mice.
1,4-Dioxane, a widely used industrial chemical and rodent hepatocarcinogen, has produced mixed, largely negative results in the mouse erythrocyte micronucleus assay. In contrast, a recent report has indicated that 1,4-dioxane induces micronuclei in mouse hepatocytes following in vivo treatment. The objective of this study was to confirm these earlier results and identify the origin of the induced micronuclei. Following an initial range-finding study, mice were administered 1,4-dioxane by gavage at doses ranging from 1500 to 3500 mg/kg. The test animals were also implanted with BrdU-releasing osmotic pumps to allow cell proliferation to be measured in the liver and to increase the sensitivity of the hepatocyte assay. Upon sacrifice, the frequency of micronuclei in the bone marrow erythrocytes and in the proliferating BrdU-labeled hepatocytes was determined. Significant dose-related increases in micronuclei were seen in both the liver and the bone-marrow with significant increases being detected at all the tested doses in the bone marrow and at the 2500 and 3500 mg/kg doses in the liver. Using CREST staining or pancentromeric FISH to determine the origin of the induced micronuclei, it was determined that 80-90% of the micronuclei in both tissues originated from chromosomal breakage. Small increases in centromere-containing micronuclei were also seen in the hepatocytes. Decreases in hepatocyte proliferation as well as in the ratio of bone marrow PCE:NCE were also observed. Based on these results, we conclude that at high doses: (i) dioxane exerts genotoxic effects in both the mouse bone marrow and liver; (ii) the induced micronuclei are formed primarily from chromosomal breakage; and (iii) dioxane can interfere with cell proliferation in both the liver and bone marrow.
Roy
S K
SK
Environmental Toxicology Graduate Program, 5429 Boyce Hall, University of California, Riverside, CA-92521, USA.
Thilagar
A K
AK
Eastmond
D A
DA
D000818:Animals; D001853:Bone Marrow / Q000187:drug effects*; D001973:Bromodeoxyuridine / Q000378:metabolism; D015197:Carcinogenicity Tests; D002273:Carcinogens / Q000633:toxicity*; D049109:Cell Proliferation / Q000187:drug effects; D002875:Chromosomes / Q000187:drug effects*; D004146:Dioxanes / Q000633:toxicity*; D004912:Erythrocytes / Q000166:cytology; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects; D017404:In Situ Hybridization, Fluorescence; D008099:Liver / Q000187:drug effects*; D008297:Male; D051379:Mice; D008817:Mice, Mutant Strains; D048629:Micronuclei, Chromosome-Defective / Q000139:chemically induced*
D002273:Carcinogens; D004146:Dioxanes; D001973:Bromodeoxyuridine; C025223:1,4-dioxane