[Show abstract][Hide abstract] 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
[Show abstract][Hide abstract] 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)
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: T-2 toxin is a cytotoxic fungal secondary metabolite produced by various species of Fusarium. This paper reviews the reported data about the development and/or mechanisms of T-2 toxin-induced apoptosis in the hematopoietic, lymphoid and gastrointestinal tissues, dorsal skin and fetal tissues of mice and rats. Apoptosis occurs earlier in hematopoietic tissues than in lymphoid tissues, and moreover there is a difference among lymphocyte populations in the susceptibility to T-2 toxin. C-fos plays an important role in the early phase of T-2 toxin-induced apoptosis in hematopoietic and lymphoid tissues through mobilization of [Ca 2+] i and the PKC-dependent pathway, but not through Fas/Fasligand or p53-related pathways. In the gastrointestinal tract, apoptosis develops earlier in the small intestine than in the stomach, and is more prominent in the small intestine than in the large intestine. In the dorsal skin topically treated with T-2 toxin, epidermal basal cell proliferating activity is first suppressed due to the elevated TGFB-β 1 expression, and then basal cell apoptosis develops concomitantly with the elevation of c-fos, c-jun and TNF-α mRNAs expression. In the fetuses, T-2 toxin-induced apoptosis is mainly observed in the central nervous and skeletal systems. In the fetal brain, T-2 toxin induces oxidative stress, followed by activation of the MAPK-JNK-c-Jun pathway, finally resulting in apoptosis. The TNF receptor pathway may also be involved in T-2 toxin-induced apoptosis in the fetal brain. Thus, the development and mechanisms of T-2 toxin-induced apoptosis differ somewhat depending on the tissues affected.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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 · 5.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Growth hormone (GH) plays an important role in longitudinal bone growth, and hypophysectomized rats or mutant rats exhibiting dwarfism have generally been used as a GH-deficient model for humans. There also has been a GH deficient model produced by subcutaneous administration to neonatal rats with monosodium glutamate (MSG), followed by destroying GH releasing hormone (GHRH) neurons in the hypothalamic arcuate nucleus, leading to a reduction of GHRH release and a resultant reduction of GH. Recently, Mini rats, a Wistar-derived transgenic rat strain harboring a rat GH antisense gene and showing 40% lower plasma GH levels than Wistar rats, have been developed. In a previous study, Mini rats showed a smaller femur size with lower mineral density and a reduction of the metaphyseal and diaphyseal bone mass. In the present study, neonates of Wistar rats were treated subcutaneously with MSG to obtain GH-deficient rats (MSG rats), and their bones were examined and compared with age-matched MSG-untreated Wistar rats and Mini rats. Compared with the Wistar rats, body weights of the MSG rats were comparable, whereas those of the Mini rats were significantly lower. Bone size, bone mineral content and mineral density were significantly lower in the MSG rats and Mini rats than those in the Wistar rats. Histologically, the amounts of the metaphyseal cancellous bone mass and diaphyseal cortical bone mass were less in the MSG rats and much less in the Mini rats. Compared with the Wistar rats, the growth plate width and longitudinal growth rate were similarly lower. However, there were no differences in bone surface-referent parameters in the secondary spongiosa for histomorphometry among the MSG rats, Wistar rats, and Mini rats, indicating that GH may not influence bone remodeling. Thus, Mini rats are considered to be a useful model for clarifying features of GH-deficiency and examining the effects of various treatments on the bone without any specific surgery or drug administration.
[Show abstract][Hide abstract] ABSTRACT: Mini rats have been reported to be a Wistar-derived strain of transgenic rats that harbors a rat growth hormone (GH) antisense gene and shows lower plasma GH levels than Wistar rats. Our previous study has revealed that : 1) Mini rats show smaller hind limbs with lower metaphyseal and diaphyseal bone mass than Wistar rats; 2) that the differences of the diaphyseal cortical bone mass and metaphyseal bone mass between Mini rats and Wistar rats are due largely to the differences in the periosteal bone formation and longitudinal growth rate, respectively, and; 3) that the bone turnover in the secondary spongiosa, an area where bone remodeling may occur, does not differ between the two strains. In the present study, 8-week-old male Mini rats were treated intraperitoneally with GH at doses of 0, 2, 6 or 20 IU/kg/time twice daily for 14 days. After the dosage period, we measured the size, bone mineral content, and mineral density of the femur and tibia in each group, and we performed cancellous and cortical bone histomorphometry on the tibia to examine the effects of GH on the bone modeling and remodeling. In the GH-treated groups there were increases in the metaphyseal cancellous bone mass, growth plate width, longitudinal growth rate, and periosteal bone formation accompanied by increases in bone size, mineral content, and mineral density in a dose-related fashion. However, bone histomorphometric parameters related to bone turnover in the secondary spongiosa of the metaphysis, where lamellar bone formation took place, did not differ between the control and GH-treated groups. These findings indicated that GH may not influence bone remodeling in the latter groups, and that GH replacement may not influence the number of osteoclasts involved in bone resorption in Mini rats as a whole.
[Show abstract][Hide abstract] ABSTRACT: Mini rats, a Wistar-derived transgenic rat strain harboring a rat growth hormone (GH) antisense gene, show lower plasma GH levels than Wistar rats. In our previous study, Mini rats showed a smaller femur size with lower mineral density and a reduction of the metaphyseal and diaphyseal bone mass at 8 and 22 weeks of age. In the present study, we examined the femur and tibia from Mini rats and Wistar rats at 10 to 60 weeks of age, and we performed cancellous and cortical bone histomorphometry on the tibia to examine the status of bone turnover. We found that the bone size, mineral content, and mineral density of the femur and tibia were significantly lower in Mini rats and tended to increase in both strains until 38 or 60 weeks of age. The longitudinal growth rate was significantly higher in Wistar rats until 26 weeks of age, and at 38 weeks of age that in Wistar rats is comparable to that in Mini rats. The periosteal bone formation rate tended to be higher in Wistar rats until 60 weeks of age. The longitudinal growth rate in both strains and the periosteal bone formation rate in Wistar rats tended to decrease with age. In contrast, bone turnover in the secondary spongiosa of the proximal tibial metaphysis showed no apparent difference between the two strains and seemed to remain unchanged until 60 weeks of age. Therefore, it is suggested that the reductions of bone mass in the metaphysis and diaphysis in Mini rats may be attributable to the lower longitudinal growth rate and periosteal bone formation rate, and that GH may influence bone modeling but not bone remodeling.
[Show abstract][Hide abstract] ABSTRACT: Growth hormone (GH) plays an important role in longitudinal bone growth, and hypophysectomized rats have generally been used as a model for GH deficiency in humans. Recently, researchers have bred Mini rats, a Wistar-derived transgenic rat strain harboring a rat GH antisense gene and showing lower plasma GH levels than Wistar rats. In a previous study, Mini rats showed a smaller femur size with lower mineral density and a reduction of the metaphyseal and diaphyseal bone mass. In the present study, Wistar rats were hypophysectomized (HX) and treated with GH, and then their bones were examined and compared with vehicle-treated intact age-matched Wistar rats and Mini rats. GH-treated (HX + GH) rats exhibited an increase in the mineral density of the tibia and increases in the length and mineral content of the femur and tibia. These changes in the HX + GH rats were attributable to an increase in the longitudinal growth and periostea! bone formation of the femur and tibia. When Mini rats and HX rats were compared with Wistar rats, both animals showed similar reductions in the bone length, mineral content, and mineral density of the femur, but the Mini rats showed a greater longitudinal growth rate, cancellous bone mass, and mineralizing surface than the HX rats, as well as less remarkable changes in body weight, relative organ weights, and hematological and blood chemical parameters. Therefore, Mini rats are considered to be a useful model for clarifying features of GH deficiency and examining effects of various treatments on the bone without any specific surgery or drug-administration.
[Show abstract][Hide abstract] ABSTRACT: tert-Butylated hydroxyanisole (BHA) and 1, 2-bis(2-pyridyl)ethylene (2PY-e) are known to induce phase II drug metabolizing enzymes without inducing phase I enzymes. In this study, male F344 rats were treated with BHA, 2PY-e, or phenobarbital (PB) that is known to induce both phase I and phase II enzymes, for 7 or 28 days, and the effects of these agents on livers, in particular morphological changes, were compared. An increase in relative liver weight was observed in all treated groups. The BHA- and 2PY-e-treated groups showed significant increases in glutathione 5-transferase (GST) and UDP-glucuronosyltransferase activities, while cytochrome P450 (P450) contents or 7-alkoxycoumarin O-dealkylase activities showed no change. The PB-treated group showed significant increases in both phase I and phase II enzyme activities. Electron microscopic examination revealed that BHA and 2PY-e did not induce apparent SER proliferation which was observed in the PB treated liver. Immunohistochemical examination revealed that BHA and 2PY-e induced GST Yp in hepatocytes of the periportal and the centrilobular area, respectively. PB did not induce GST Yp in hepatocytes. The proliferating activities of the hepatocytes treated with these agents were also evaluated using the BrdU labeling index. In the PB-and 2PY-e-treated groups, significant increases in labeling indices were found and the index was higher in the centrilobular area than in the periportal area. The labeling index of the BHA-treated group was comparable to that of the control group. The present study clarified that there were different responses in SER proliferation, inducing pattern of GST Yp and proliferating activities of hepatocytes between the PB-, 2PY-e-, and BHA-treated groups. However, mechanisms which underlie the differences found in the present study remain to be determined.