Noriaki Ishigami

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.

Development of apoptosis and changes in lymphocyte subsetsin thymus, mesenteric lymph nodes and Peyer's patches of mice orally inoculated with T-2 toxin

Development of apoptosis and changes in lymphocyte subsets were examined mainly by flow cytometer in thymus, mesenteric lymph nodes and Peyers patches of mice up to 24 hours after oral inoculation with T-2 toxin (10 mg/kg). T-2 toxin attacked Peyers patches first, then mesenteric lymph nodes, and finally thymus in relation to the course of enteric absorption of orally inoculated T-2 toxin. The degree of lymphocyte apoptosis was prominent in the thymus, moderate in the Peyers patches, and somewhat mild in the mesenteric lymph nodes, suggesting the difference in lymphocyte population susceptible to T-2 toxin. As to the changes in lymphocyte subsets, CD4+ CD8+ T cells were most sensitive to T-2 toxin, and CD4+ CD8- T cells were more severely depressed than CD4- CD8+ T cells in the thymus. In the mesenteric lymph nodes, CD3+ cells was more clearly affected than CD19+ cells, and the numbers of CD4+ and CD8+ cells were similarly decreased. In the Peyers patches, the numbers of CD3+, CD 19+, CD4+ and CD8+ cells were unexceptionally decreased. In addition, among IgM+, IgG+ and IgA+ B cells, the number of IA+ B cells which are more important in the mucosal immunity was most severely affected.

Nivalenol-induced apoptosis in thymus, spleen and Peyer's patches of mice

ICR:CD-1 male mice were orally administered with Nivalenol(NIV) at the dose levels of 5, 10 and 15 mg/kg body weight, and examined at 12, 24 and 48 hours after inoculation (HAI), respectively, to elucidate the process of development of apoptosis in the thymus, spleen and Peyers patch. There were no signs of clinical disorders and no changes in body and organ weights until 48 HAI except for that the thymus weight significantly decreased at 48 HAI. Immunohistochemically, the number of apoptotic lymphocytes evaluated by in situ detection for fragmented DNA showed a dose-dependent increase at 12 HAI in both the thymus and the Peyers patch, while it became to increase at 24 HAI in the spleen. Dead lymphocytes in the thymus, spleen and Peyers patch showed ultrastructural characteristics of apoptosis. Moreover, the DNA ladder was first detected by agarose gel electrophoresis at 12 HAI in the thymus of 15 mg/kg-group. The results clearly indicate that NIV is able to induce apoptosis in the lymphoid tissues of mice.

Apoptosis in mouse fetuses from dams exposed to T-2 toxin at different days of gestation

T-2 toxin (2 mg/kg b.w.) was orally inoculated to pregnant mice at gestational day (GD) 8.5, 9.5, 10.5, 11.5, 12.5, 13.5, 14.5, 15.5 and GD 16.5, respectively, and the fetuses were examined 24 hours later. The number and region of pyknotic or karyorrhectic cells varied according to inoculation date. In the GD 13.5-subgroup, a moderate to high number of pyknotic or karyorrhectic neuronal cells were observed in the central nervous system, peri-ventricular zone to subventricular zone, and pyknosis or karyorrhexis were also observed in a small number of chondroblasts and chondrocytes. In the GD 16.5-subgroup, a moderate to high number of pyknotic or karyorrhectic cells were observed in the thymus and renal subcapsular parenchyma. The nuclei of these pyknotic or karyorrhectic cells were strongly stained by the terminal deoxy nucleotidyl transferase (TdT)-mediated dUTP-digoxigenin nick end labeling method widely used for the in situ detection of apoptotic nuclei. In addition, a few fetuses from dams which were given T-2 toxin at GD 13.5 or GD 14.5 and killed at GD 17.5 showed skeletal abnormalities such as wavy ribs and short scapula. From the present findings and the well known fact that T-2 toxin readily crosses the rat placenta, it seems that T-2 toxin-induced apoptosis in the developing mouse fetuses might be a direct effect of T-2 toxin on fetuses.

Intratubular Spermatocytic Seminomas in 2 Sprague-Dawley Rats

This report describes 2 cases of spontaneous intratubular spermatocytic seminomas in Sprague-Dawley rats. These rats were sacrificed at 10 weeks old (case 1) and 40 weeks old (case 2), respectively. Macroscopically, there were no remarkable changes in either case. Microscopically, tumor cells were observed within a single seminiferous tubule (case 1) or several seminiferous tubules (case 2). The proliferating tumor cells were a tripartite cell population comprising small lymphocyte-like, intermediate-sized or large-sized cells, with frequent mitoses, arranged in sheets or forming a basal layer around a tubule or tubules. Immunohistochemically, the tumor cells were strongly positive for proliferating cell nuclear antigen and weakly positive for c-kit, neuron specific enolase and VASA. Our cases provide valuable background control information for the occurrence of seminoma in rats.