Shinya Sehata

The University of Tokyo, Edo, Tōkyō, Japan

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Publications (17)28.13 Total impact

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    Kunio Doi · Noriaki Ishigami · Shinya Sehata
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    ABSTRACT: 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.
    International Journal of Molecular Sciences 12/2008; 9(11):2146-58. DOI:10.3390/ijms9112146 · 2.86 Impact Factor
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    ABSTRACT: A pulmonary mass was observed in a 16-year-old beagle dog. In the histopathology, a well-circumscribed mass composed of cuboidal to low or tall columnar neoplastic cells proliferating in a papillary, acinar or solid pattern and abundant cholesterin deposition was observed. The tumor cells had eosinophilic to abundant clear or foamy cytoplasms. The cells were arranged around blood vessels with the nuclei at the periphery of the cells in a pseudo-rosette formation, especially in the tall columnar cells. In the immunohistochemistry, the neoplastic cells were positive for cytokeratin and surfactant apoprotein A, but not for vimentin and chromogranin A. In the electron microscopy, numerous vacuoles ranging from 0.5 to 2 mu m in diameter were observed in the basal part of the neoplastic cells and some of these vacuoles contained myelin-like materials. These findings indicate that these neoplastic cells were derived from alveolar type II cells. Therefore, the pulmonary mass was diagnosed as bronchioloalveolar carcinoma. (J Toxicol Pathol 2008; 21: 109-113)
    Journal of Toxicologic Pathology 01/2008; 21(2):109-113. DOI:10.1293/tox.21.109 · 0.94 Impact Factor
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    ABSTRACT: Connexin32 (Cx32), one of the components of gap junction intercellular communication, is commonly detected by the fluorescent antibody method, although this method has some defects when conducting detailed histopathological investigations. In order to develop a new method to improve the fluorescent antibody method, the optimal immunohistochemical procedure on formalin-fixed paraffin-embedded sections was examined. According to the results, the localization of Cx32 was observed on sections prepared with the Dako catalyzed signal amplification (CSA) method after 0.2% protease digestion for 30 minutes after a 3-day or 6-month fixation. As the CSA method is highly sensitive and based on signal amplification by biotinylated tyramide, the localization of Cx32 was clearly shown on the cell membranes of hepatocytes. In fact, by this CSA method, a decrease in the signals of Cx32 was shown in the liver of rats treated with phenobarbital or in hepatocellular adenoma, which were consistent with previous reports using cryosections. In conclusion, the CSA method is considered an appropriate method for the detection of Cx32 in formalin-fixed paraffin-embedded sections.
    Journal of Toxicologic Pathology 01/2006; 19(3):151-154. DOI:10.1293/tox.19.151 · 0.94 Impact Factor
  • Kunio Doi · Junko Shinozuka · Shinya Sehata
    Journal of Toxicologic Pathology 01/2006; 19(1):15-27. DOI:10.1293/tox.19.15 · 0.94 Impact Factor
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    ABSTRACT: Pregnant rats on day 13 of gestation were treated orally with 2 mg/kg of T-2 toxin and sacrificed at 1, 3, 6, 9 and 12 h after the treatment (HAT). Histopathologically, the number of apoptotic cells was increased in the liver, placenta and fetal liver (peaked at 6, 12 and 9-12 HAT, respectively). To examine the gene expression profiles, we performed microarray analysis of these tissues at two selected time points based on the results of the TdT-mediated dUTP nick end labeling (TUNEL) staining. Increased expression of oxidative stress- and apoptosis-related genes was detected in the liver of dams, placenta and fetal liver of pregnant rats treated with T-2 toxin at the peak time point of apoptosis. Decreased expression of lipid metabolism- and drug-metabolizing enzyme-related genes was also detected in these tissues. The results suggested that the mitogen-activated protein kinase (MAPK) pathway might be involved in the mechanism of T-2 toxin-induced apoptosis. In addition, increased expression of the c-jun gene was consistently observed in these tissues. Our results suggest that the mechanism of T-2 toxin-induced toxicity in pregnant rats is due to oxidative stress followed by the activation of the MAPK pathway, finally inducing apoptosis. The c-jun gene may play an important role in T-2 toxin-induced apoptosis.
    Experimental and Toxicologic Pathology 09/2005; 57(1):15-28. DOI:10.1016/j.etp.2005.02.005 · 2.01 Impact Factor
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    ABSTRACT: To examine morphological and gene expression changes induced by T-2 toxin in the fetal brain in detail, pregnant rats on day 13 of gestation were treated orally with a single dose of T-2 toxin (2 mg/kg) and sacrificed at 1, 3, 6, 9, 12 and 24 h after treatment (HAT). Histopathologically, the number of apoptotic neuroepithelial cells in the telencephalon increased from 1 HAT and peaked at 12 HAT. Based on the histopathological examinations, microarray analysis was performed at 6, 12 and 24 HAT. Microarray analysis showed that the expression of oxidative stress-related genes (heat shock protein 70 (HSP70) and heme oxygenase (HO)) was strongly induced by T-2 toxin at 12 HAT, the peak time point of apoptosis induction. The expression of mitogen-activated protein kinase (MAPK)-related genes (MEKK1 and c-jun) and other apoptosis-related genes (caspase-2 and insulin-like growth factor-binding protein-3 (IGF-BP3)) was also induced by the T-2 toxin treatment. The changes observed by microarray analysis were confirmed for four up-regulated genes (HSP70, HO, IGF-BP3 and VEGF-A) using real-time RT-PCR. Our results suggest that the T-2 toxin-induced apoptosis in the fetal brain is due to oxidative stress, and that the MAPK pathway may be involved in T-2 toxin-induced toxicity.
    Food and Chemical Toxicology 12/2004; 42(11):1727-36. DOI:10.1016/j.fct.2004.06.006 · 2.90 Impact Factor
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    ABSTRACT: 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.
    Experimental and Toxicologic Pathology 04/2004; 55(5):357-66. DOI:10.1078/0940-2993-00342 · 2.01 Impact Factor
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    ABSTRACT: 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-Tgmice 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.
    Toxicologic Pathology 03/2003; 31(2):191-9. DOI:10.1080/01926230309812 · 1.92 Impact Factor
  • Journal of Toxicologic Pathology 01/2003; 16(1):59-65. DOI:10.1293/tox.16.59 · 0.94 Impact Factor
  • Journal of Toxicologic Pathology 01/2003; 16(2):113-116. DOI:10.1293/tox.16.113 · 0.94 Impact Factor
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    ABSTRACT: 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 significant 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 nongenotoxic carcinogens. However, the sensitivity of rasH2-Tg mice to nongenotoxic carcinogens should be assessed with consideration of the results from the other ILSI-HESI project studies.
    Toxicologic Pathology 04/2002; 30(3):328-38. DOI:10.1080/01926230252929909 · 1.92 Impact Factor
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    ABSTRACT: Hepatic P450 monooxygenase activities, which strongly influence the efficacy and/or toxicity of drugs, are known to fluctuate daily. We also know that the P450 activities assessed by measurement of 7-alkoxycoumarin O-dealkylase (ACD) activities fluctuate daily, with apparently high values during the dark period in male rats. However, there is little knowledge about the factors that regulate daily fluctuation of P450 monooxygenase activities. In the present study using rats, we induced lesions in the suprachiasmatic nucleus (SCN) of the brain, the known site of the body's internal clock, and examined the effects on the daily fluctuation of the ACD activities to clarify the relationship between the SCN and the daily fluctuation of P450 monooxygenase activities. In addition, adrenalectomy was performed to re-evaluate the influence of adrenal hormones on the P450 activities. Our results indicated that daily fluctuations of the hepatic ACD activities were completely eliminated in the SCN-lesioned rats. However, the ACD activities in the adrenalectomized rats showed apparent daily fluctuations with high values during the dark period and low values during the light period. Therefore, this study demonstrated that the daily fluctuation of the hepatic P450 monooxygenase activities in male rats is controlled by the SCN but remains unaffected by the adrenal hormones.
    Archive für Toxikologie 09/1999; 73(7):367-372. DOI:10.1007/s002040050675 · 5.08 Impact Factor
  • Journal of Toxicologic Pathology 01/1999; 12(4):183-190. DOI:10.1293/tox.12.183 · 0.94 Impact Factor
  • Journal of Toxicologic Pathology 01/1999; 12(4):191-202. DOI:10.1293/tox.12.191 · 0.94 Impact Factor
  • Journal of Toxicologic Pathology 01/1999; 12(3):131-140. DOI:10.1293/tox.12.131 · 0.94 Impact Factor
  • Journal of Toxicologic Pathology 01/1999; 12(3):119-129. DOI:10.1293/tox.12.119 · 0.94 Impact Factor
  • Journal of Toxicologic Pathology 01/1998; 11(3):183-189. DOI:10.1293/tox.11.183 · 0.94 Impact Factor