Journal of Toxicologic Pathology最新文献

We examined the morphological effects of letrozole on placental development in pregnant rats. Letrozole was orally administered at a repeat dose to pregnant rats at 0 mg/kg (control group) and 0.04 mg/kg (letrozole group) from gestation day (GD) 6 to GD 20. In the letrozole group, fetal mortality and placental weight increased from GD 15 onwards and GD 13 onwards, respectively. Fetal weights increased on GDs 15 and 17 but decreased on GD 21. Histopathologically, letrozole treatment induced multiple cysts lined with undifferentiated syncytiotrophoblasts in the trophoblastic septa on GD 13. These cysts then develop into dilated maternal sinusoids with congestive hyperemia, resulting in an enlarged placenta. In the metrial gland, there was a dilated lumen of the spiral artery and interstitial edema throughout the experimental period, resulting in thickened metrial gland. These changes are considered to be due to maternal blood circulation stagnation in the metrial gland, which is associated with dilated maternal sinusoids in the labyrinth zone. Thus, although letrozole induces an enlarged placenta due to congestive hyperemia of the labyrinth zone and transient increases in fetal weight, these placentas are thought to decline in function as the pregnancy progresses, leading to intrauterine growth restriction at the end of pregnancy.

We have previously reported on thymomas in Wistar Hannover rats with medullary differentiation and revealed that two different cytokeratin (CK) immunohistochemical types of thymic epithelia (TE), CK18 and CK14, lead to the formation of cortical-medullary structures. In aged F344 rats, epithelial type thymoma rarely occurs, and thymic epithelial hyperplasia is common. However, CK expression in these F344 rat lesions is unknown. We investigated three hyperplasia and four thymomas in F344 for histopathological features and CK18 and CK14 expression. Hyperplasia was characterized by an increase in tubular structures in the medulla. Thymomas were nodular in shape, with tubular structures similar to those observed in hyperplasia, along with irregular structures such as cord, papillary, and spindloid. Immunohistochemical analysis revealed that the tubular structures consisted of two layers: inner cuboidal-to-columnar TE and outer round-to-oval TE, positive for CK18 and CK14, respectively. The two-layer pattern was maintained to some extent in the irregular structures.

In a past study, we proposed a modified Comparative Thyroid Assay (CTA) with additional examinations of brain thyroid hormone (TH) concentrations and brain histopathology but with smaller group sizes. The results showed that the modified CTA in Sprague Dawley rats detected 10 ppm 6-propylthiouracil (6-PTU)-induced significant suppressions of serum/brain TH concentrations in offspring. To confirm the reliability of qualitative brain histopathology and identify the optimal testing time for heterotopia (a cluster of ectopic neurons) in the modified CTA, brain histopathology together with serum/brain TH concentrations were assessed in GD20 fetuses and PND2, 4, 21, and 28 pups using a similar study protocol but with a smaller number of animals (N=3–6/group/time). Significant hypothyroidism was observed and brain histopathology revealed cerebral heterotopia formation in PND21 and PND28 pups, with likely precursor findings in PND2 and PND4 pups but not in GD20 fetuses. This study confirmed that the optimal testing time for cerebral heterotopia in rat CTA was PND21 and thereafter. These findings suggest that cerebral heterotopia assessment at appropriate times may be a useful alternative to the original CTA design.

B-cell lymphoma is generally observed in the spleen, mesenteric lymph nodes, and Peyer’s patches in aged mice and rarely appears in other organs. Herein, we report a case of spontaneous B-cell lymphoma originating from the cranial mediastinal lymph node in a male 75-week-old C57BL/6J mouse. Macroscopically, a white mass was found at the base of the heart with no connection to the thymus. Microscopic examination revealed a solid proliferation of tumor cells with large nuclei at the center of the mass. Some macrophages, normal-sized lymphocytes, and lymphatic sinuses were found in both central and peripheral areas. Immunohistochemical analysis showed positive staining for cluster of differentiation 19, paired box protein 5, immunoglobulin M, and Ki-67 but not for cytokeratin AE1/AE3. These findings were not completely consistent with the established mouse lymphoma classification, leading to a diagnosis of B-cell lymphoma originating from the cranial mediastinal lymph node. This case report is the first to document a B-cell lymphoma in the cranial mediastinal lymph nodes in an aged C57BL/6J mouse model.

Linalool oxide is frequently used as a flavoring agent, however, data on its toxicity is limited. In this study, we performed a 13-week subchronic toxicity study of linalool oxide (furanoid) in male and female Crl:CD(SD) rats. Doses of 0, 80, 250, and 800 mg/kg body weight (bw) per day were orally administered by gavage, using corn oil as the vehicle. Abnormal gait in both sexes and decreased locomotor activity in males were observed in the 800 mg/kg group. Reduced body weight gain was noted in both sexes at 800 mg/kg and at 250 mg/kg in males. In the 800 mg/kg group, serum biochemistry showed increased γ-glutamyl transpeptidase and decreased glucose in both sexes, increased total protein in males, and increased total cholesterol and phospholipids in females, suggesting that linalool oxide may have adverse effects on the liver. Increased relative and/or absolute liver weights, centrilobular hepatocellular hypertrophy in both sexes, and periportal microvesicular fatty changes in females were observed in the 800 mg/kg group. Increased relative liver weights and decreased serum glucose levels were observed in the 250 mg/kg male and female groups, respectively. Increased serum magnesium levels and relative kidney weights were observed in both sexes in the 800 mg/kg group, suggesting possible adverse effects of linalool oxide. Although histopathology showed accumulation of hyaline droplets in the male kidneys, immunohistochemistry revealed α_2u-globulin nephropathy, which was not considered toxicologically significant. These results indicate that the no-observed-adverse-effect level of linalool oxide was 80 mg/kg bw/day for both sexes.

Tuberculosis (TB) is a major health threat for humans and for non-human primates used for toxicology or research purposes. Emerging mycobacterial species represent a major challenge for diagnosis and surveillance programs. Here, we report a natural outbreak of Mycobacterium caprae in imported cynomolgus macaques (Macaca fascicularis) that occurred at AnaPath Research S.A.U. (APR). The macaques underwent repeated negative intradermal tuberculin tests (IDT) before importation and at the European quarantine station. Exhaustive TB screening was started at APR after confirmation of one positive case at another facility. The animal in question belonged to the same colony received at APR. Diagnostic approaches included clinical examination, PCR, culture, spoligotyping, IDT testing, interferon-γ release assay (IGRA), and thoracoabdominal ultrasound (US). Three regulatory toxicity studies and stock animals were affected. The macaques lacked clinical signs, except for one showing a fistulizing nodule in the right inguinal area, which tested positive for the Mycobacterium tuberculosis complex by PCR. All animals were necropsied and 10 macaques (n=114) showed gross and histologic findings compatible with TB confirmed by PCR and culture. M. caprae was identified as the etiological agent by Direct Variable Repeat spacer oligonucleotide typing (DVR spoligotyping). The infection was traced to Asia via the SB1622 spoligotype involved, confirming that the animals were infected prior to their import into Europe. Tuberculin skin test (TST), IGRA, and US were only sensitive in detecting advanced cases of M. caprae infection. One staff member showed a positive TST reaction, which was handled in accordance with the Spanish government’s health regulations. All the sanitary measures implemented were effective in eradicating the disease.

Gene therapy (GT) products created using adeno-associated virus (AAV) vectors tend to exhibit toxicity via immune reactions, but other mechanisms of toxicity remain incompletely understood. We examined the cardiotoxicity of an overexpressed transgenic protein. Male C57BL/6J mice were treated with a single intravenous dose of product X, an AAV-based GT product, at 2.6 × 10¹³ vg/kg. Necropsies were performed at 24 h, 7 days, and 14 days after dosing. Pathological examination and gene expression analysis were performed on the heart. Histopathologically, hypertrophy and vacuolar degeneration of cardiomyocytes and fibrosis were observed 14 days after dosing. Immunohistochemistry for endoplasmic reticulum (ER) stress-related proteins revealed increased positive reactions for glucose-regulated protein 78 and C/EBPR homologous protein in cardiomyocytes 7 days after dosing, without histopathological abnormalities. Fourteen days after dosing, some cardiomyocytes showed positivity for PKR-like endoplasmic reticulum kinase and activating transcription factor 4 expression. Ultrastructurally, increases in the ER and cytosol were observed in cardiomyocytes 7 days after dosing, along with an increase in the number of Golgi apparatus compartments 14 days after dosing. The tissue concentration of the transgene product protein increased 7 days after dosing. Gene expression analysis showed upregulation of ER stress-related genes 7 days after dosing, suggesting activation of the PKR-like ER kinase pathway of the unfolded protein reaction (UPR). Thus, the cardiotoxicity induced by product X was considered to involve cell damage caused by the overexpression of the product protein accompanied by UPR. Marked UPR activation may also cause toxicity of AAV-based GT products.

We report a histiocytic sarcoma originating from the epididymis observed in a 110-week-old male CD-1 mouse in a carcinogenicity study. At necropsy, no lesions were observed in the epididymis. Histologically, a neoplastic lesion was observed in the cauda of the epididymis that was well demarcated from the surrounding tissues. The lesion mainly consisted of spindle-shaped tumor cells with oval to elongated nuclei and abundant eosinophilic or foamy cytoplasm. The tumor cells were arranged in a fascicular pattern, interlacing bundles, or a whorl pattern. The nuclei showed mild atypia with irregular shapes and varied sizes, whereas few mitotic figures and no typical multinucleated cells were observed. The epididymal ducts remained within the neoplastic lesion, and the tumor cells invaded between the epithelium and the smooth muscle layer of the epididymal duct. Immunohistochemically, the tumor cells were positive for vimentin and macrophage markers (Iba1, CD204, F4/80, and Mac-2) but negative for cytokeratin and other mesenchymal cell (α-smooth muscle actin, desmin, CD31, and platelet-derived growth factor receptor-β), neural cell (S-100 and nestin), or Leydig cell markers (calretinin). Proliferating cell nuclear antigen-positive tumor cells were sporadically observed in the lesion. Based on these results, the tumor was diagnosed as a histiocytic sarcoma originating from the epididymis. This report provides additional histopathological evidence of spontaneous histiocytic sarcomas originating from the epididymis of aged mice.

The historical control database of a multinational laboratory services provider was queried for all histopathologic findings in New Zealand White rabbits which were used as control animals during a ten-year period (2011–2020). The query included all evaluated tissues, with or without microscopic findings, in studies conducted for safety testing for regulatory approval by the U.S. Food and Drug Agency (FDA) or the U.S. Environmental Protection Agency. A second query included studies conducted in the United Kingdom for control rabbits used in studies compliant with the Healthcare Products Regulatory Agency (MHRA) and/or the European Medicines Agency (EMA), which provide regulatory oversight in the United Kingdom and European Union, respectively. Infiltrates of inflammatory (mixed or mononuclear) cells were commonly noted in various organs including heart, digestive tract, muscle, thyroid, kidney, urinary bladder, eyelid, ocular structures, harderian gland, lacrimal gland, and lung. Mineralization was noted in aorta, kidney, urinary bladder, and ovary. Also noted were degeneration/necrosis in the myocardium, and intramuscular injection sites of the skin, degeneration/regeneration of muscle and diaphragm, ectopic tissue in the pancreas and thyroid, basophilic foci in salivary gland, increased/decreased vacuolation in adrenal gland, increased/decreased lymphocytic cellularity of lymph nodes, intrasinusoidal erythrocytes in lymph nodes, thymic atrophy, increased adipocytes in bone marrow, inflammatory cell foci in the liver and gall bladder, lacrimal gland atrophy, renal tubule basophilia, degeneration/regeneration, and dilatation; oviduct cyst; in the testis, degeneration/atrophy, cellular debris, dilatation, decreased sperm and segmental hypoplasia of seminiferous tubules; and squamous metaplasia of the testis and seminal vesicle.

Tissue cross-reactivity (TCR) studies for the development of therapeutic antibodies are conducted to estimate any possible binding sites within the human body that can be affected by the antibody when assessing safety in humans. Any possible binding sites include specific binding sites of the antibody to its target antigen and nonspecific or off-target binding sites. In TCR studies the therapeutic antibodies and immunohistochemistry (IHC) of frozen tissues must be applied in assays. However, there are technical issues with applying a therapeutic antibody or test article to IHC, such as human-on-human staining, difficulty in applying the test article to IHC, and retention of the target antigen in frozen sections. In the current review, we introduce three case studies in which these technical issues were addressed, and propose a practical scheme for points to consider when conducting a TCR study. Information on the target antigen distribution obtained through robust assays and case-by-case strategies were found to be useful for understanding and assessing the relevance of toxic effects between animals and humans. Thus, we anticipate that by considering the points discussed in the current review and combining the data with information on the biological features of the target antigens and therapeutic antibodies, it will be possible to predict safety risks in humans with higher accuracy.