As basic knowledge for evaluation of pancreatic toxicity, anatomical structures were compared among experimental animal species, including rats, dogs, monkeys, and minipigs. In terms of gross anatomy, the pancreases of dogs, monkeys, and minipigs are compact and similar to that of humans. The rat pancreas is relatively compact at the splenic segment, but the duodenal segment is dispersed within the mesentery. In terms of histology, the islet of each animal is characterized by a topographic distribution pattern of α- versus β-cells. β-cells occupy the large central part of the rat islet, and α-cells are located in the periphery and occasionally exhibit cuffing. In dog islets, β-cells are distributed in all parts and α-cells are scattered in the center or periphery of the islet (at body and left lobe); whereas β-cells occupy all parts of the islet and no α-cells are present in the islet (at right lobe). Monkey islets show two distinct patterns, that is, α-cell-rich or β-cell-rich islets, and the former represent peripheral β-cells forming an irregular ring. Minipig islets show an irregular outline, and both α- and β-cells are present in all parts of the islet, intermingling with each other. According to morphometry, the endocrine tissue accounts for <2% of the pancreas roughly in rats and minipigs, and that of monkeys accounts for >7% of the pancreas (at tail). The endocrine tissue proportion tends to increase as the position changes from right to left in the pancreas in each species.
Accurate analysis of female reproductive toxicity requires a thorough understanding the differences in and specifics of estrous or menstrual cycles between laboratory animals. There are some species differences such as the time of sex maturation, the length of the estrous or menstrual cycle, the length of the luteal phase, the number of dominant follicles or corpora lutea, the size of follicles, processes of luteinization, and hormonal changes during the estrous or menstrual cycle. Rodents have a short estrous cycle, and their ovarian cycling features are the same in both ovaries, which contain a large number of follicles and corpora lutea. The dog estrous cycle is much longer than those of other laboratory animals, and it includes a long anestrus phase. The duration of the menstrual cycle of monkeys is roughly 30 days, and their ovarian cycling features are different between the left and right ovaries. In both rodents and dogs, the theca cells invade the early luteum, mixing with granulosa cells during luteinization. However in monkeys, the theca layer dose not mix with the granulosa cells as it invaginates only slightly into the early luteum. In addition, we found that high progesterone levels after ovulation are sustained for a much shorter duration in rodents than in dogs and monkeys due to the comparatively rapid passage of the rodent luteal phase. Based on these species differences, animal species for use in ovarian toxicology studies need to be selected appropriately.
Histopathological and electrocardiographic features of myocardial lesions induced by combretastatin A4 disodium phosphate (CA4DP) were evaluated, and the relation between myocardial lesions and vascular changes and the direct toxic effect of CA4DP on cardiomyocytes were discussed. We induced myocardial lesions by administration of CA4DP to rats and evaluated myocardial damage by histopathologic examination and electrocardiography. We evaluated blood pressure (BP) of CA4DP-treated rats and effects of CA4DP on cellular impedance-based contractility of human induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs). The results revealed multifocal myocardial necrosis with a predilection for the interventricular septum and subendocardial regions of the apex of the left ventricular wall, injury of capillaries, morphological change of the ST junction, and QT interval prolongation. The histopathological profile of myocardial lesions suggested that CA4DP induced a lack of myocardial blood flow. CA4DP increased the diastolic BP and showed direct effects on hiPS-CMs. These results suggest that CA4DP induces dysfunction of small arteries and capillaries and has direct toxicity in cardiomyocytes. Therefore, it is thought that CA4DP induced capillary and myocardial injury due to collapse of the microcirculation in the myocardium. Moreover, the direct toxic effect of CA4DP on cardiomyocytes induced myocardial lesions in a coordinated manner.
Pregnant rats were treated intraperitoneally with a single dose of methotrexate (MTX) 90 mg/kg on gestation day (GD) 13, and fetal eyeballs were examined time-dependently from GD 13.5 to 15.5. Throughout the experimental period, the inner plate of the ocular cup in the MTX group was significantly thinner than that in the control group. In the inner plate of the ocular cup on GD 15 and 15.5, whereas a developed ganglion cell layer was observed in the control group, the ganglion cell layer in the MTX group was undeveloped and indistinguishable. Disturbance of the arrangement of lens fiber cells, narrowing of the hyaloid cavity of the optic cup, and hypoplasia of optic nerve fibers were observed in the MTX group on GD 15 and 15.5. Increase of pyknosis and decrease of mitosis were induced in the optic cup and the lens epithelium of the MTX group. In the inner plate of the optic cup and the lens epithelium of the MTX group, the cleaved caspase-3- and TUNEL-positive rates increased significantly throughout the experimental period. The phospho-histone H3-positive rate in the inner plate of the optic cup decreased significantly from GD 13.5 to 14.5, and it recovered on GD 15. On the other hand, the phospho-histone H3-positive rate in the lens epithelium decreased significantly throughout the experimental period. These results suggested that optic tissue on GD 13 in rats was sensitive to MTX.
Accumulation of macrophages containing brown pigments in the lungs is a well-known spontaneous lesion found in cynomolgus monkey. However, its pathogenesis has not been clearly described. In our survey, brown pigment-laden macrophages were found in the lungs of 4 out of 43 cases. Brown pigments were mostly found in the macrophages of the perivascular interstitium, which proved to be hemosiderin. Some small- to medium-sized vessels that exhibited prominent accumulation of brown pigment-laden macrophages showed degeneration and necrosis of the smooth muscle cells of tunica media. Furthermore, ruptures of the internal and external elastic laminae were seen in some of the vessels. These findings suggested that partial fragmentation of the vascular elastic lamina followed by degeneration and necrosis of the tunica media caused blood leakage leading to the accumulation of hemosiderin-laden macrophages in the perivascular interstitium of the lungs.
Carcinosarcoma is a rare neoplasm composed of malignant epithelial and stromal elements, and, for rats, carcinosarcomas in the kidney have not been reported. In a long-term study to gather background data, we encountered a spontaneous carcinosarcoma originating from the renal pelvis with metastasis to the lung. At necropsy, a mass was observed in the abdominal cavity, and white nodules were scattered in lung lobes. Microscopically, there was polypoid hyperplasia of the urothelium accompanied by hyperplasia of spindle stromal cells in the pelvis. The intra-abdominal tumor was composed of epithelial and stromal elements; in the lung, the tumor cells invaded along alveoli/bronchi and occasionally invaded the parenchyma from the blood vessels. Immunohistochemical and electron microscopic examinations revealed that the epithelial element consisted of transitional epithelial cells and that the stromal element consisted of lipoblasts. The tumor was diagnosed as a carcinosarcoma originating from the renal pelvis, and this is the first report of a carcinosarcoma originating from the renal pelvis in a rat.
A male cynomolgus monkey (Macaca fascicularis) of 5 years and 11 months of age from the vehicle control group of a 4-week repeated oral dose toxicity study had a spontaneously occurring mass lesion directly attached to the proximal part of the left trigeminal nerve. Histologically, the mass was characterized by a multifocal nodular appearance. Nodular zones showed low to moderate cellularity and were composed of small round cells exhibiting nuclear uniformity. On the other hand, inter-nodular zones were composed of nerve fiber containing septa and closely aggregated highly pleomorphic cells. Immunohistochemically, the small round cells were strongly immunopositive for synaptophysin, neuN, and class III beta-tubulin, while the highly pleomorphic cells were weakly immunopositive for neuN and occasionally immunopositive for class III beta-tubulin and doublecortin, suggesting that the tumor had originated from a neuronal lineage cell. Based on these findings, the mass was diagnosed as a neuroblastoma at the trigeminal nerve.
Craniopharyngiomas are extremely rare epithelial tumors of the sellar region in human beings and domestic and laboratory animals. A craniopharyngioma, 0.6 cm in diameter, was observed grossly in the sellar and parasellar regions of an untreated 23-month-old male Wistar-derived rat sacrificed moribund. The tumor was composed of cords, columns, and nests of neoplastic stratified squamous epithelium with marked hyperkeratosis and parakeratosis. Neoplastic cells formed solid or cystic areas, infiltrating the base of the skull, brain, and pituitary gland. Immunocytochemical evaluation revealed a strong cytoplasmic reaction for pan-cytokeratin in all tumor cells. Malignant craniopharyngioma should be considered a differential diagnosis in the rat when a tumor with stratified squamous epithelial features and a locally aggressive growth pattern is observed in the sellar or suprasellar region.
The incidence and range of spontaneous thyroid and parathyroid glands findings were determined in control Han-Wistar and Sprague-Dawley rats, and CD-1 mice from 104-week carcinogenicity studies carried out between 1998 and 2010 at Charles River Edinburgh. In both strains of rats and in CD-1 mice, non-proliferative lesions of the thyroid or parathyroid glands were generally uncommon apart from some findings in CD-1 mice such as ultimobranchial duct/cyst (5.72%), follicular distension/dilatation (3.84%), and cystic follicles (3.53%). In Han-Wistar rats, thyroid proliferative lesions were slightly more frequent in males than in females, but in Sprague-Dawley rats, they were of similar incidence in both sexes. The most common findings overall in Han-Wistar and Sprague-Dawley rats were C-cell hyperplasia (48.11% and 36.56%, respectively) and adenoma (10.87% and 9.52%, respectively), follicular cell hyperplasia (4.21% and 0.91%, respectively) and adenoma (4.32% and 1.36%, respectively). Secondary neoplastic lesions either in thyroid or parathyroid gland were poorly represented.
Fusarenon-X is a non-macrocyclic type B trichothecene mycotoxin. It occurs naturally in agricultural commodities, such as wheat and barley. We investigated fusarenon-X-induced apoptosis in the liver, kidney, and spleen of male and female mice after a single exposure. Thus, mice were orally administered fusarenon-X (4 mg/kg body weight) and were assessed at 0, 3, 9, 18, 24, and 48 hours after treatment. Apoptosis in the liver, kidney, and spleen was determined using hematoxylin and eosin staining, the terminal deoxynucleotidyl transferase dUTP nick end labeling method, immunohistochemistry for proliferating cell nuclear antigen, and electron microscopy. Fusarenon-X-induced apoptosis at 9 hours after treatment, particularly hepatocytes around the central lobular zone of the liver, in proximal tubular cells of the kidney, and in hematopoietic cells in the red pulp area of the spleen in both male and female mice. The results of this study should be very useful with regard to the toxicity of fusarenon-X in both humans and domestic animals, which has been attributed to the intake of food contaminated with mycotoxins, especially fusarenon-X.