Characterizing "Adversity" of Pathology Findings in Nonclinical Toxicity Studies: Results from the 4th ESTP International Expert Workshop.

The identification of adverse health effects has a central role in the development and risk/safety assessment of chemical entities and pharmaceuticals. There is currently a need for better alignment regarding how nonclinical adversity is determined and characterized. The European Society of Toxicologic Pathology (ESTP) therefore coordinated a workshop to review available definitions of adversity, weigh determining and qualifying factors of adversity based on case examples, and recommend a practical approach to define and characterize adversity in toxicology reports, to serve as a valuable prerequisite for future organ- or lesion-specific workshops planned by the ESTP.

Malignant peritoneal mesothelioma with a sarcomatoid growth pattern and signet-ring-like structure in a female f344 rat.

We report a biphasic malignant mesothelioma in an aged female F344/DuCrlCrlj rat. Macroscopically, multiple pale brown nodules were observed in the abdominal cavity with retention of bloody ascites. Histopathologically, the tumor cells spread over the peritoneum and formed masses on the surface and underlying adipose tissues. The tumor cells dominantly proliferated in a solid, nodular or nest-like pattern with modest amount of fibrillar connective tissues, which contained hyaluronan. The tumor consisted of ovoid, polygonal or spindle-shaped cells that possessed eosinophilic cytoplasms including glycogen; some tumor cells showed a signet-ring-like structure. Multinucleated cells and mitosis were found frequently, and direct invasion to intra-abdominal organs and intravascular metastasis to the liver were observed. Immunohistochemically, keratin and mesothelin were strongly positive in most of tumor cells, while vimentin was mainly positive in spindle-shaped cells. Podoplanin was also positive, particularly in the cell membrane of tumor cells. Electron microscopically, tumor cells showed an intercellular desmosome-like structure, basement membrane and microvillus. We diagnosed the case as a malignant peritoneal mesothelioma with a sarcomatoid growth pattern and signet-ring-like structure.

Hypodectes propus (Acarina: Hypoderatidae) in a rufous turtle dove, Streptopelia orientalis (Aves: Columbiformes), in Japan.

An adult male rufous turtle dove, Streptopelia (S.) orientalis (Aves: Columbiformes), was found dead in Yorii-machi Town, Osato District 369-1217, Saitama Prefecture, Japan, and subjected to necropsy. A large number of immobile hypopi (deutonymphs) of the hypoderatid mite, Hypodectes (H.) propus (Acarina: Hypoderatidae), were found individually encapsulated subcutaneously primarily in the adipose tissue. The mites were 1.43 mm in length and 0.44 mm in width on average, and had provoked mild inflammatory reactions that predominantly manifested as foamy macrophages and lymphoplasmocytes. PCR analysis using ribosomal DNA extracted from paraffin-blocked tissues produced a 240 bp band specific for hypoderatids. Based on the morphological features (distinct coxal apodemes, especially in the anterior portion) and PCR-based findings, the hypopi were identified as H. propus. To the best of our knowledge, this is the first case describing the subcutaneous mite H. propus in a rufous turtle dove, S. orientalis, in Japan. This study also highlights the use of paraffin blocks as a source of tissue DNA for molecular evaluation.

Occurrence of the subcutaneous mite, Hypodectes propus (Acarina: Hypoderatidae), in the grey heron, Ardea cinerea (Aves: Ciconiiformes) a new host record in Japan.

An adult male grey heron, Ardea cinerea (Aves: Ciconiiformes), was rescued in Mikunigaoka 590-0021, Sakai, Osaka, Japan, and euthanized because of severe injury to both legs. At necropsy, a large number of deutonymphs (hypopi) of the hypoderatid mite, Hypodectes propus (Acarina: Hypoderatidae), were found in the subcutis and in the fasciae of the adipose tissue in the pectoral muscle and abdominal regions. The mites were 1.26 mm in length and 0.35 mm in width on average. The present hypopi were identified as H. propus, based on the dimensions of the mite, together with the distinct typical coxal apodemes in the anterior part. The present case reported the subcutaneous mite, H. propus, in the grey heron, A. cinerea, as a new host record in Japan.

Extraskeletal osteosarcoma with pulmonary metastasis in a female f344 rat.

A subcutaneous mass in the right femoral region of a female F344 Slc/N rat was examined histopathologically. At 83 weeks of age, the animal showed symptoms of severe anemia and nasal bleeding. Necropsy revealed that the mass had invaded the skeletal muscles but did not affect the bones. Multicentric nodules were also observed in the lung. Histopathology revealed a sheet-like growth pattern of polygonal tumor cells with round or comma-shaped nuclei and pale eosinophilic cytoplasm. Osteoid tissue was observed in not only the original lesion but also the metastatic foci in the lung. Each tumor cell was surrounded by argentophil fibers and few collagen fibers. Immunohistochemically, the tumor cells were positive for proliferating cell nuclear antigen (PCNA), vimentin, osterix and osteocalcin, but negative for keratin, S-100, von Willebrand factor, CD-31, CD-34, desmin, α-smooth muscle actin, lysozyme, α1-antitrypsin and rat malignant fibrous histiocytoma (MFH) antigen. CD-68-positive cells were considered to be infiltrated macrophages because they were negative for PCNA. On the basis of these findings, we diagnosed the present case as extraskeletal osteosarcoma.

Identification of the toxic trigger in mushroom poisoning.

We have isolated the small, highly strained carboxylic acid cycloprop-2-ene carboxylic acid from the Asian toxic mushroom Russula subnigricans. This compound is responsible for fatal rhabdomyolysis, a new type of mushroom poisoning that is indicated by an increase in serum creatine phosphokinase activity in mice. We found that polymerization of the compound at high concentrations via ene reaction abolishes its toxicity.

Spontaneous rhabdomyosarcoma in a young Sprague-Dawley rat.

An eight-week-old male Sprague-Dawley (SD) rat showed signs of emaciation, and masses were found in the subcutis around the cervical and thoracic regions. At necropsy, a multilobular mass, 2.2 x 1.8 x 2.0 cm in size, had grown from the left neck into the thoracic cavity. On a cutting surface, masses were firm and whitish to tan, with necrotic and hemorrhagic plaques. Microscopically, masses were composed of multiple nodules of tumor cells that were incompletely encapsulated with fibrous connective tissue. The tumor cells exhibited varied forms, from spindle to globoid shapes with minimal to abundant eosinophilic cytoplasm, and appeared as large, multinucleated cells; many of the tumor cells were vacuolated. Histochemistry results revealed that tumor cells exhibited some cross-striation in the cytoplasm using PTAH staining. There were some multinuclear tumor cells with vacuoles located around the nuclei, and these vacuoles showed reddish staining by the periodic acid Schiff (PAS) method. Immunohistochemical staining also expressed intense granular cytoplasmic staining for desmin and myoglobin, with highly positive staining for PCNA, whereas alpha-smooth muscle actin (alpha-SMA) was negative. Based on the pathology results, a spontaneous rhabdomyosarcoma with pleomorphic type was diagnosed in a young SD rat.

The effect of testosterone propionate supplement on testicular toxicity with thiamphenicol in male Sprague-Dawley rats.

Testosterone propionate (TP) was supplemented to male rats for assessment of its ameliorating effect on testicular toxicity with thiamphenicol (TAP). A total of 20 male Sprague-Dawley rats were treated orally with TAP at 200 mg/kg/day for up to 4 weeks. In addition, 5 male rats were allotted to the control group receiving vehicle only. Ten of the 20 treated rats had a Silastic capsule (containing about 80 mg of TP) implanted in the dorsal skin at Week 2 and assigned to the TAP-TP group, while the other 10 treated rats were in the TAP group. After Weeks 3 and 4, five of both treated groups were examined for weight and histology of the testis and accessory genital glands, and for staging analysis of the seminiferous tubules. The same parameters were also assessed in the control group after Week 4. Weights and morphology of the seminal vesicle and prostate recovered remarkably from the TAP toxicity after TP supplement. However, no ameliorating effects of TP were obtained for the testis in either weight, morphology, or staging analysis of the seminiferous tubules.