Journal of Toxicologic Pathology
Online ISSN : 1881-915X
Print ISSN : 0914-9198
ISSN-L : 0914-9198
Advance online publication
Displaying 1-5 of 5 articles from this issue
  • Manabu IKEDA, Toshihisa FUJIWARA, Junko FUJISHIMA, Airo YUKAWA, Kinji ...
    Article ID: 2022-0047
    Published: 2022
    Advance online publication: June 30, 2022

    In a 26-week carcinogenicity study in rasH2-Tg mice, squamous cell carcinoma on the epididymis was observed in a male mouse in the positive control group treated with N-methyl-N-nitrosourea. A 29-week-old male rasH2-Tg mouse that was euthanized 21 weeks after the administration of N-methyl-N-nitrosourea had a white-grayish mass on the left caput epididymis. The mass was nodular and consisted of pleomorphic tumor cells forming alveolar, sheeted, and trabecular structures suggesting epithelial tumor growth. These cells presented a cobblestone-like arrangement and formed intercellular bridges. Keratinization was infrequently observed. Periodic acid-methenamine-silver staining revealed argyrophilic fibrous structures around the alveolar structure of the tumor cells. Immunohistochemically, the tumor cells were positive for cytokeratin AE1/AE3 and cytokeratin 14 and negative for cytokeratin 5, p63, uroplakin III, vimentin, desmin, and αSMA. These immunohistochemical results suggested the tumor cells originated from the epididymal ducts. Metastatic lesions were observed in the mesenteric, inguinal, and pancreaticoduodenal lymph nodes. Based on these results, this tumor was diagnosed to be a primary squamous cell carcinoma of the epididymis. This is the first report of primary squamous cell carcinoma of the epididymis in a rasH2-Tg mouse.

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  • Teruaki HAGIWARA, Takamasa NUMANO, Tomomi HARA, Taiki SUGIYAMA, Yukino ...
    Article ID: 2022-0040
    Published: 2022
    Advance online publication: June 26, 2022

    In subcutaneous tumor models, changes in the tumor microenvironment can lead to differences in therapeutic treatment responses between the subcutaneous and parent tumors. Accordingly, we generated a lung carcinogenesis model that combines genetically modified mice (Tg-rasH2 mice) with two-stage chemical carcinogenesis as an alternative to the subcutaneous tumor model. In this model, Tg-rasH2 mice were treated with 1-ethyl-1-nitrosourea, followed by butylhydroxytoluene. Mice developed lung adenomas five weeks after treatment initiation. Subsequently, anti-mouse PD-1 antibody (α-mPD-1) or isotype control was administered intraperitoneally twice a week for 4 weeks. Tumor growth was examined by measuring the relative tumor area in serially sliced lung histopathological specimens. No statistically significant differences were observed in the relative lung tumor areas between treated and control groups. A second experiment then examined the antitumor efficacy of α-mPD-1 combined with gemcitabine in a mouse model. Mice were treated identically as in Experiment 1, except that the treated group received once-weekly intraperitoneal injections of 10 mg/kg gemcitabine. In contrast to Experiment 1, the combined treatment significantly reduced the relative tumor areas in the lungs. This result also resembles that of a phase III clinical trial (ORIENT-12), showing that patients with non-small-cell lung carcinoma benefited from combination treatment with gemcitabine and the anti-human PD-1 antibody sintilimab. Thus, this mouse model could be a feasible means to preclinically evaluate the antitumor efficacy of different immunotherapy and chemotherapy drug combinations.

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  • Kyohei YASUNO, Masako IMAOKA, Tetsuya OHSAWA, Keiko OKADO, Kiyonori KA ...
    Article ID: 2022-0022
    Published: 2022
    Advance online publication: June 11, 2022

    Inflammation of the cardiac coronary artery in ICR mice is occasionally observed in toxicity studies; however, this has not been well explored histologically. Herein, we investigated the detailed histology of the associated lesions in 6–8-week-old ICR mice. Coronary artery inflammation in the right ventricular wall was observed in 10 of 142 mice (7.0%). Histopathological examination revealed hypertrophy of the vascular smooth muscle cells and perivascular infiltration of macrophages in mild cases. In moderate to marked cases, single-cell necrosis of vascular smooth muscle cells, hemorrhage of the tunica media, and fibrinoid necrosis of the vessel wall were observed, in addition to the changes seen in mild cases. Electron microscopic examination of moderate cases revealed a discontinuous internal elastic lamina suggestive of rupture, and vascular smooth muscle cells beneath the elastic lamina showed degeneration and necrosis. These findings suggest that the lesions developed as a rupture of the internal elastic lamina and necrosis of vascular smooth muscle cells, while leaked plasma components caused vascular and perivascular inflammation. In ICR mice, dystrophic calcinosis (DCC) is known to occur rarely in the right ventricle. DCC is defined as focal calcification in necrotic myocardial fibers, the pathogenesis of which is considered to involve ectopic calcification. Since calcification was not observed in any part of the heart, including the inflammation region, the pathophysiology of cardiac arterial inflammation seen in our ICR mice was considered to differ from that of DCC.

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  • Yuichi TAKAI, Stephanie POWLIN, Yasuyuki AWASAKI, Toshiaki YAMAUCHI, T ...
    Article ID: 2022-0035
    Published: 2022
    Advance online publication: June 10, 2022

    To develop safe subcutaneous formulations and minimize the risk of local irritation, it is essential to optimize the composition of active pharmaceutical ingredients and excipients. Depending on the physicochemical properties of the active pharmaceutical ingredient, additional excipients may be required to improve the stability and solubility of the active pharmaceutical ingredient. However, some of these excipients may not have been previously used in injectable drugs. Owing to the lack of safety data for such excipients, especially those used in subcutaneous dosing, it is important to evaluate their potential for local irritation during the early stages of formulation development. We evaluated the tolerability of 44 formulations with 24 candidate novel excipients, such as surfactants, polymers, and lipids, in a single subcutaneous dose in rats. Excipient formulations were administered as single bolus subcutaneous injections with an injection volume of 1 mL. The injection sites were observed for 2 days, and macroscopic and microscopic examinations were conducted. Local tolerability was evaluated on the basis of severity, incidence, and pathophysiology of each finding. Formulations that caused tissue degeneration or necrosis, which is indicative of tissue injury, were determined to be irritative and poorly tolerated. A single-dose subcutaneous screening study in rats was considered effective in ranking the safety of candidate excipients during the formulation optimization phase.

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  • Yuko YAMAGUCHI, Tsubasa SAITO, Mizuho TAKAGI, Tomomi NAKAZAWA, Kazutos ...
    Article ID: 2022-0003
    Published: 2022
    Advance online publication: May 30, 2022

    5-Fluorouracil (5-FU) is widely used as a chemotherapeutic agent that blocks DNA synthesis and replication by inhibiting thymidylate synthetase. This study aimed to elucidate 5-FU-induced changes in the external granular cells (EGCs) in the cerebellum of infant rats and the possible underlying mechanism. Six-day-old infant rats were injected subcutaneously with 40 mg/kg of 5-FU, and their cerebellums were examined at 6, 9, 12, and 24 h after treatment (HAT), and 2, 4, and 10 d after treatment (DAT). The width of the external granular layer (EGL) decreased from 24 HAT to 4 DAT in the 5-FU group compared to that in the control group. However, the width in the 5-FU group was comparable to that of the control group at 10 DAT. The number of apoptotic cells, cleaved caspase 3-labeling index (LI%), p21 cip1-LI%, and expression levels of p53, p21 cip1, and Fas mRNAs increased at 24 HAT. However, no changes were detected in the expression levels of Puma and Bax mRNAs at any time point. BrdU-LI% increased at 6 and 12 HAT but decreased at 24 HAT. The phospho-histone H3-LI% decreased from 6 HAT to 2 DAT. The width of the molecular layer decreased compared to that of the control group at 10 DAT. No differences were observed in Purkinje cell development. These results indicate that 5-FU inhibited cell proliferation by inducing apoptosis of EGCs via activation of Fas and caspase-3 without the involvement of the mitochondrial pathway and induced p53-dependent G1-S and G2-M phase arrest.

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