Shinya Sehata

T-2 toxin-induced toxicity in pregnant mice and rats.

T-2 toxin is a cytotoxic secondary fungal metabolite that belongs to the trichothecene mycotoxin family. This mycotoxin is a well known inhibitor of protein synthesis through its high binding affinity to peptidyl transferase, which is an integral part of the ribosomal 60s subunit, and it also inhibits the synthesis of DNA and RNA, probably secondary to the inhibition of protein synthesis. In addition, T-2 toxin is said to induce apoptosis in many types of cells bearing high proliferating activity. T-2 toxin readily passes the placenta and is distributed to embryo/fetal tissues, which include many component cells bearing high proliferating activity. This paper reviews the reported data related to T-2 toxin-induced maternal and fetal toxicities in pregnant mice and rats. The mechanisms of T-2 toxin-induced apoptosis in maternal and fetal tissues are also discussed in this paper.

Interlaboratory Comparison of Short-Term Carcinogenicity Studies Using CB6F1-rasH2 Transgenic Mice

In order to evaluate a short-term carcinogenicity testing system using CB6F1-Tg rasH2 ( rasH2-Tg) mice carrying a human prototype c-Ha-ras gene, 26-week studies were conducted in 12 different facilities as a part of an International Life Science Institute Health and Environmental Science Institute (ILSI HESI) international collaborative project. In each study N-methyl-N-nitrosourea (MNU) was administered to a separate group of rasH2-Tg mice by single intraperitoneal injection (75 mg/kg) as a positive control. We herein have summarized the mortality, body weight change, and neoplastic and nonneoplastic lesions detected in these positive control groups as representative historical positive control data. Also, we performed an interlaboratory comparison of the response of rasH2-Tg mice to MNU based on the data of 11 positive control groups from these studies. Although the body weight of rasH2-Tg mice showed lower values than that of non-Tg mice during the experimental period, body weight gain in the rasH2-Tg mice was similar to that in non-Tg mice. The mortality of rasH2-Tg mice during the study period was very low, the same as for the non-Tg mice. Incidences of spontaneous alveolar/bronchiolar adenomas and splenic hemangiomas/hemangiosarcomas were also low in the rasH2-Tg mice. Nonneoplastic lesions detected in the rasH2-Tg mice were similar to those in non-Tg mice, excluding the incidence of myopathy. There were interlaboratory differences in mortality and incidence of some lesions in the MNU-treated groups. However, the causes of death were common among the 11 laboratories and almost all the MNU-treated rasH2-Tg mice developed forestomach squamous cell papillomas/carcinomas or malignant lymphomas. This suggests that there is no appreciable difference in the response of the rasH2-Tg mouse to MNU used as a positive control. Therefore, it is concluded that MNU would be an adequate positive control compound in this testing system.

Gene expression profiles in pregnant rats treated with T-2 toxin

Pregnant rats on day 13 of gestation were treated orally with T-2 toxin at a single dose of 2 mg/kg and sacrificed at 24 hours after treatment. Histopathologically, apoptosis was increased in the liver, placenta and fetal liver. Microarray analysis was performed to examine the gene expression in the liver, placenta, and fetal liver. The results of microarray analysis showed that the changes in the expression of apoptosis genes, metabolic enzymes and oxidative stress-related genes were detected in these tissues. Suppression of phase I and II enzymes-related genes expression in the liver, and suppression of phase II enzymes-related genes expression in the placenta and fetal liver were observed. Semiquantitive RT-PCR analysis also showed the same results as those of microarray analysis. From the results of microarray analysis and histopathological examination, T-2 toxin seems to induce oxidative stress in these tissues, following the changes in metabolism-related genes expression. These changes may alter the intracellular environments resulting in the induction of apoptosis. Further studies on the gene expression profiles at the earlier time point are necessary to clarify the detailed mechanisms of T-2 toxin-induced toxicity in pregnant rats.

Twenty-six-Week carcinogenicity study of chloroform in CB6F1 rasH2-transgenic mice.

The carcinogenic potential of chloroform was evaluated in a short-term carcinogenicity testing system using CB6F1 rasH2-Tg (rasH2-Tg) mice. Chloroform was administered to rasH2-Tg males at doses of 28, 90, or 140 mg/kg and rasH2-Tg females at 24, 90, or 240 mg/kg by oral gavage for 26 weeks. Wild-type (non-Tg) male and female mice received doses of 140 mg/kg and 240 mg/kg, respectively. N-methyl-N-nitrosourea was administered to rasH2-Tg mice by single intraperitoneal injection (75 mg/kg) as a positive control. In both the rasH2-Tg and non-Tg mice, there was no signifi cant increase in the incidence of neoplastic lesions by chloroform treatment. The incidence of hepatocellular foci in the rasH2- and non-Tg females receiving 240 mg/kg was increased. Forestomach tumors and malignant tumors occurred in most of the rasH2-mice in the positive control group. Swelling or vacuolation of hepatocytes, a toxic change induced by chloroform, occurred in both the rasH2-Tg and non-Tg mice. It is concluded that chloroform, a putative human noncarcinogen, did not show evidence of carcinogenic potential in the present study using rasH2-Tg mice. This study suggests that the rasH2-Tg mouse model may not be appropriate for detecting nongenotoxi c carcinogens. However, the sensitivity of rasH2-Tg mice to nongenotoxi c carcinogens should be assessed with consideration of the results from the other ILSI-HESI project studies.