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

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 20 mg/kg/day. Hepatocytes were collected approximately 24 h after the last TAA administration, and the incidence of micronuclei was assessed. In this study, bone marrow micronucleus assays were also conducted in the same animals. The 14- and 28-day RDLMN assays indicated that none of the TAA dosages significantly increased the proportion of micronucleated hepatocytes. Bone marrow micronucleus assays with TAA also provided negative results. It is known that TAA is a liver carcinogen in mice and rats. In the previous genotoxic studies, the Ames test and the chromosomal aberration test using CHL/IU cells have yielded negative results [1], [2], [3], [4]. The liver micronucleus assay using young adult rats singly dosed with TAA (75 and 150 mg/kg) also produced negative results [5]. TAA gave positive results only in the mouse bone marrow micronucleus assays [6], [7].