Malignant Myoepithelioma of the Parotid Gland in a Rat.

Myoepitheliomas of the salivary glands have been described in laboratory mice, but not in rats. A 20-week-old Wistar (Han) female rat developed a white to grey firm mass at the left side of the neck. Histologically, the mass was unencapsulated and infiltrated the adjacent tissue. The tumour parenchyma was cell rich without acinar or tubular architecture. The tumour showed a palisading basal cell pattern adjacent to blood vessels. There were areas of necrosis filled with cellular debris. The tumour cells showed strong immunohistochemical labelling for pan-cytokeratin types I and II (AE1/AE3), pan-cytokeratin (cytokeratins 1, 5, 6 and 8), cytokeratin 5, cytokeratin 14, vimentin and podoplanin, and only very slight positivity for cytokeratin 8 in small areas. There was no expression of smooth muscle actin. Based on the histological appearance and the immunohistochemistry, the tumour was diagnosed as a malignant myoepithelioma of the parotid gland originating from the parotid duct.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Progress to Date and Future Plans.

The International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice proposal (INHAND) has been operational since 2005. A Global Editorial Steering Committee manages the overall objectives of the project, and the development of harmonized terminology for each organ system is the responsibility of the Organ Working Groups, drawing upon experts from North America, Europe, and Japan. Great progress has been made with 9 systems published to date--respiratory, hepatobiliary, urinary, central/peripheral nervous systems, male reproductive and mammary, zymbals, clitoral, and preputial glands in Toxicologic Pathology and the integument and soft tissue and female reproductive in the Journal of Toxicologic Pathology as supplements and on a Web site--www.goReni.org. INHAND nomenclature guides offer diagnostic criteria and guidelines for recording lesions observed in rodent toxicity and carcinogenicity studies. The guides provide representative photomicrographs of morphologic changes, information regarding pathogenesis, and key references. The purpose of this brief communication is to provide an update on the progress of INHAND.

A toxicological evaluation of inhaled solid lipid nanoparticles used as a potential drug delivery system for the lung.

Inhalation is a non-invasive approach for both local and systemic drug delivery. This study aimed to define the therapeutic window for solid lipid nanoparticles (SLNs) as a drug delivery system by inhalation from a toxicological point of view. To estimate the toxic dose of SLNs in vitro, A549 cells and murine precision-cut lung slices (PCLS) were exposed to increasing concentrations of SLNs. The cytotoxic effect of SLNs on A549 cells was evaluated by MTT and NRU assays. Viability of lung tissue was determined with WST assay and by life/dead staining using calcein AM/EthD-1 for confocal microscopy (CLSM) followed by quantitative analysis with IMARIS. Inflammation was assessed by measuring chemokine KC and TNF-alpha levels. The in vivo effects were determined in a 16-day repeated-dose inhalation toxicity study using female BALB/c mice, which were daily exposed to different concentrations of SLN30 aerosols (1-200 microg deposit dose). Local inflammatory effects in the respiratory tract were evaluated by determination of total protein content, LDH, chemokine KC, IL-6, and differential cell counts, performed on days 4, 8, 12, and 16 in bronchoalveolar lavage fluid. Additionally, a histopathological evaluation of toxicologically relevant organs was accomplished. The in vitro and ex vivo dose finding experiments showed toxic effects beginning at concentrations of about 500 microg/ml. Therefore, we used 1-200 microg deposit doses/animal for the in vivo experiments. Even after 16 days of challenge with a 200-microg deposit dose, SLNs induced no significant signs of inflammation. We observed no consistent increase in LDH release, protein levels, or other signs of inflammation such as chemokine KC, IL-6, or neutrophilia. In contrast, the particle control (carbon black) caused inflammatory and cytotoxic effects at corresponding concentrations. These results confirm that repeated inhalation exposure to SLN30 at concentrations lower than a 200-microg deposit dose is safe in a murine inhalation model.

Assessment of the morphology and significance of the lymph nodal and hepatic lesions produced in rats by the feeding of certain mineral oils and waxes. Proceedings of a pathology workshop held at the Fraunhofer Institute of Toxicology and Aerosol Research Hannover, Germany, May 7-9, 2001.

A Panel of medical and veterinary pathologists reviewed published and unpublished reports dealing with studies of various white mineral oils and waxes in F344 and Sprague-Dawley rats. They also had available and studied histologic slides from both subchronic and chronic studies of certain mineral hydrocarbons (90-day oral study of low melting point wax (LMPW) in female Fischer 344 and Sprague-Dawley rats; 90-day studies of P15H* and P70H white oil and high melting point wax (HMPW) in male and female F344 rats and 24 month study of P70H white oil in male and female F344 rats. The Panel also reviewed mineral oil-induced alterations in tissues of human patients (liver, hepatic lymph node and spleen). The Panel agreed that certain of the mineral hydrocarbons produced lesions in the mesenteric lymph nodes and liver of the F344 rat and these lesions were best described as microgranulomas/granulomas. The lesions were fundamentally similar in both organs, although varying in severity with dose and type of mineral hydrocarbons. The Panel agreed that hepatic lesions with inflammatory cell infiltration, necrosis, and fibrosis were produced only by feeding of LMPW and the lesions were confined to F344 rats and not found in Sprague-Dawley rats. The most severe granulomatous lesions in the mesenteric lymph nodes were found in high dose LMPW-fed F344 rats. The microgranulomas were similar in subchronic and chronic studies. Also, little difference existed between controls and treated F344 rats in the incidence and severity of the lesions after 2 years of feeding P70H white oil. The Panel agreed that some slight reversibility existed for these lesions, but also agreed that complete resolution was unlikely as regression of the lesions in the rat would likely be slow. The Panel agreed that a minimal severity infiltrate of mononuclear inflammatory cells occurred in the base of the mitral valve in a slightly increased incidence in F344 rats fed LMPW. The Panel concluded that these mitral valve alterations had little if any toxicologic significance as the focal infiltrate was minimal in severity, occurred in controls, occurred in association with murine cardiomyopathy, and were unlike the responses in the liver and mesenteric lymph nodes. The Panel agreed that the lesions observed in the liver and mesenteric lymph nodes of F344 rats exposed to MHCs, especially the LMPW, were different morphologically from changes observed in lymph node, liver, and spleen of humans that were mineral oil-users. These changes in humans are usually found incidentally in tissues taken at biopsy or autopsy. The MHC-induced lesions can be considered incidental and inconsequential in humans.

M-CSF transgenic mice: role of M-CSF in infection and autoimmunity.

In this study, transgenic CD2F1 mouse lines (C-1.1-C-1.11) bearing a transgene encoding the murine growth factor M-CSF under the control of the liver specific alpha-1-antitrypsin gene promoter were generated. Transgenic C-1.4 mice showed elevated expression of transgene-encoded M-CSF in the liver and displayed a 2-3-fold increase of M-CSF plasma levels and of macrophage numbers in the liver as compared with non-transgenic littermates. M-CSF transgenic mice showed increased resistance against sublethal i.v. infections with Listeria monocytogenes as compared with infected non-transgenic mice. To investigate the influence of M-CSF in murine systemic lupus erythematosus (SLE), the M-CSF transgenic mouse line C-1.4 was bred into the genetic background of SLE-prone MRL+/+ mice. The resulting C-1.4/MRL transgenic mice bearing increased endogenous M-CSF levels showed consistently lower levels of anti-ss-DNA autoantibodies as compared with non-transgenic MRL+/+ mice. The life span of the C- 1.4/MRL transgenic mice and the severity of the disease in these mice remained unchanged as compared with their non-transgenic littermates. It is concluded that in addition to M-CSF further factors must be involved in the acceleration of the autoimmune disease in SLE prone MRL/lpr mice.

Chronic pulmonary effects of respirable methylene diphenyl diisocyanate (MDI) aerosol in rats: combination of findings from two bioassays.

Two independent bioassays are available which have examined the potential carcinogenicity of monomeric and polymeric methylene diphenyl diisocyanate (MDI) following long-term inhalation exposure in rats. These studies are not directly comparable, however, due to differences in design and conduct of the in-life phase, and differences in nomenclature used for some of the histopathological findings. This paper presents a definitive overview ofthe pulmonary toxicity of MDI developed following a thorough review of both investigations. As part of this process, the test materials and the designs of the studies were compared, and an in-depth review of lung lesions was conducted by an independent reviewing pathologist. This included the re-examination of the original lung slides, supported by an analysis of the exposure regimens, the results of which were used to develop an accurate profile of the doses received by the animals in the two studies. Histopathological findings were then combined with this information to give an overall dose-response curve for both studies as a whole. The range of total inhalation exposures to MDI was calculated as 559, 1972, 2881, 6001, 17,575 and 17,728 mgh/m3. Major pulmonary effects included increased lung weights together with bronchiolo-alveolar adenomas and hyperplasia, and interstitial fibrosis which occurred consistently in both studies, indicating a very similar qualitative response of the lungs to polymeric and monomeric MDI. The quantitative response of the lung was clearly dose-related in each study, and when the studies were considered as a whole a reasonable overall dose-response relationship was apparent for major lung lesions. Lung tumours (in low incidences) only occurred at the highest dose level in both studies (17,575 and 17,728 mgh/m3). For inflammatory and other non-neoplastic pulmonary changes, the lowest dose examined (559 mgh/m3) was regarded as a no-observed-adverse-effect-level for both polymeric and monomeric MDI. It was concluded that the results of the two studies could be combined to serve as a basis for human risk assessment of MDI.

Spontaneous neoplastic lesions in Harlan Sprague-Dawley rats.

In a 24-months study, the spontaneous tumour spectrum of the Hsd:Sprague-Dawley stock was examined. Pituitary gland tumours were found in 20% of the males and 39% of the females. This relatively low incidence, compared to other SPRD stocks, had little effect on the survival of females (50%), due to the high incidence (76%) of mammary gland tumours (predominantly fibroadenomas) that resulted in unscheduled sacrifices of many females. Other common neoplasms in Hsd:Sprague-Dawley rats were benign medullary tumours (27% in males, 11% in females), C-cell adenomas (23% in males, 28% in females), and endometrial stromal polyps (22% in females).

Odontogenic fibroma in Sprague-Dawley rats: a report of 2 cases.

Two cases of odontogenic fibroma occurring in aged Sprague-Dawley rats are described. Both neoplasms were associated with a maxillary incisor and had identical histomorphological features. They were composed of solid proliferations of primitive, dental pulp-like mesenchyme separated by areas of collagenization. Small strands and islands of mainly undifferentiated odontogenic epithelium immunostaining for keratins were scattered throughout both tumours. As a further characteristic, the lesions contained small foci of mineralization which were either cementum-like or resembled dysplastic dentin. The odontogenic fibroma represents a further type of odontogenic tumour in rats, which due to its typical histomorphology, can easily be differentiated from other odontogenic tumours such as ameloblastic odontoma or ameloblastoma.

Spontaneous neoplasms of the nasal cavity in rats.

The histomorphological features of two adenocarcinomas and two adenomas of the nasal cavity observed in two female Wistar rats and a male Sprague-Dawley rat are described. In one of the Wistar rats, a second tumour, classified as an adenoma, occurred in the posterior part of the nasal cavity.

Spontaneous cystic keratinizing epithelioma in the lung of a Sprague-Dawley rat.

A spontaneous cystic keratinizing epithelioma in the lung of a 704-day-old female Hsd:Sprague-Dawley rat is described. The rat had a white subpleural discoloration on 1 diaphragmatic lobe at necropsy. Microscopically, a central keratin mass, surrounded by a multilayered squamous epithelium of varying thickness, was found. In the periphery of the tumor, epithelial nests projected multifocally into the adjacent alveolar spaces. Immunohistochemical labeling of nuclei by PCNA (proliferating cell nuclear antigen) revealed proliferative activity in 1 or 2 peripheral cell layers in most locations. To the best of the authors' knowledge, this is the first report dealing with the morphological and immunohistochemical features of a spontaneous cystic keratinizing epithelioma in a rat.

Cystic squamous cell carcinomas in the lungs of Syrian golden hamsters induced by coal oven flue exhaust mixed with pyrolized tar pitch in combination with benzo(a)pyrene.

Among a variety of induced pulmonary tumours, cystic squamous cell carcinomas were observed in five Syrian hamsters that inhaled a mixture of pyrolized tar pitch with coal oven flue exhaust (PCE) and additionally received intratracheal injections of benzo(a)pyrene. The histological appearance of these particular tumours is described, compared to similar tumour types in rats and the susceptibility of both species to inert particles is discussed.

Pulmonary cystic keratinizing squamous cell lesions of rats after inhalation/instillation of different particles.

Cystic keratinizing squamous cell lesions from three inhalation studies (Study A, B, C) and one intratracheal instillation study (Study D) in rats were reclassified and a certain number of lesions examined immunohistochemically for PCNA (proliferating cell nuclear antigen) as a marker of cellular proliferation. The following classification was used: squamous cell metaplasia with marked keratinization, keratinizing cyst, cystic keratinizing epithelioma, cystic keratinizing squamous cell carcinoma, keratinizing squamous cell carcinoma and non-keratinizing squamous cell carcinoma. In study A (inhalation of coal oven exhaust and subcutaneous injection of a high dose of DB (ah)A) 49.3% of rats developed cystic keratinizing squamous cell carcinomas. Inhalation of coal oven exhaust gas together with intratracheal instillation of crocidolite or subcutaneous injection of a low dose DB(ah)A (dibenz(ah)anthracene) resulted in cystic keratinizing squamous cell carcinomas in 23% to 24% of the rats. High incidences of cystic squamous cell carcinomas in the range of 31.9% to 76.4% were observed in rats of Study B1 after a 10-months exposure to tar/pitch condensation aerosol (different B(a)P (benzo(a)pyrene) concentrations) with added carbon black in some groups. After a 20-months exposure period to the same inhalation atmospheres (Study B2) the incidence of squamous cell carcinomas was increased up to 95.8%. Exposure of rats to various concentrations of unfiltered diesel exhaust (Study C) resulted in incidences of cystic keratinizing epitheliomas ranging from 2.5% (2.5 mg/m3) to 10.7% (7.5 mg/m3). Epitheliomas were also observed in 16.2% of carbon black and 16.0% of titanium dioxide exposed rats. Only a few cystic keratinizing squamous cell carcinomas occurred. In the intratrachel instillation study (Study D) increased incidences of cystic keratinizing epitheliomas occurred in rats exposed to native diesel exhaust particles (16.7%), high dose of extracted diesel exhaust particles (14.6%), extracted printex 90-carbon black particles (18.8%), and extracted printex 90-carbon black particles + B(a)P (18.8%). High indicences of cystic keratinizing squamous cell carcinomas were noted in rats that received 15 mg B(a)P (14.6%) or 30 mg B(a)P (72.7%) intratracheally. Immunohistochemical labeling of nuclei with PCNA demonstrated proliferative activity in one or two (and focally more than two) peripheral cell layers of cystic keratinizing epitheliomas and in more than three peripheral cell layers of cystic keratinizing squamous cell carcinomas and keratinizing squamous cell carcinomas. The wall of keratinizing cysts showed no or a weak reaction.

Incidence and spectrum of spontaneous neoplasms in Han:NMRI mice of both sexes.

Two hundred Han:NMRI mice of both sexes were kept for their natural life-span to obtain information about the spontaneous tumour spectrum of this strain. Neoplasms were seen in 72% of the males and 64% of the females. Lung tumours, Harderian gland tumours, liver and adrenal gland neoplasms were common in males, while ovary tumours and lung tumours were the most frequent neoplasms in females.

Spontaneous myelofibrosis in castrated and ovariectomized NMRI mice.

The histopathological appearance of myelofibrosis of the bone marrow is described in aged castrated males, ovariectomized females and in male and female control NMRI mice. The highest incidence of the lesion was observed in ovariectomized and female control mice where more than 90% of the animals were affected. The presence of myelofibrosis in the bone marrow of ovariectomized females and castrated males indicates that estrogens may not play a major role in the development of the lesion and other hormonal disturbances must also be considered.

RITA--registry of industrial toxicology animal-data--guides for organ sampling and trimming procedures in rats.

RITA (Registry of Industrial Toxicology Animal-data) is a pathology data base for the collection of validated histopathological data on tumours and potentially pre-neoplastic lesions observed in laboratory rodents. To enable a better comparison of information, standardized techniques for the preparation of histological slides have been established for all organs. The current paper describes the guidelines for organ sampling and trimming procedures applied in the RITA project, i.e. the number of sections to be taken, the direction in which an organ should be cut, the localization (anatomical site) from which a sample should be taken, and the size of an organ (or part of an organ) to be placed in cassettes for processing. Schematical illustrations and additional explanations are provided to support the proposed standardized procedures in histology laboratories.

Chemically induced pulmonary mucoepidermoid carcinoma in a female Wistar rat.

A case of a mucoepidermoid carcinoma, conventionally classified as an adenosquamous carcinoma, is described. The tumour bearing rat was exposed to a mixture of a pyrolized pitch condensate rich in polycyclic aromatic hydrocarbons and carbon black particles by inhalation for 10 months. The neoplasm was examined by conventional histopathologic procedures and by immunohistochemical detection of intermediate filaments. Morphologically, the tumour consisted of two components. The centre of the neoplasm was predominantly of adenocarcinomatous tissue and this was surrounded by keratinized squamous epithelium. The predominantly adenocarcinomatous component had a characteristic structural pattern consisting of one or a few layers of squamous epithelium covered by a continuous layer of mature goblet cells. The flattened cells were recognizable as squamous cells on the light microscopic level only after immunohistochemical staining with cytokeratin antibodies. Goblet cells and extracellular mucin were intensely positive for the PAS-reagent. This mucoepidermoid carcinoma in the rat was morphologically similar to those described in man. It is still unclear whether pulmonary mucoepidermoid carcinomas of humans originate from the bronchial epithelium or bronchial glands. It is most probable that the mucoepidermoid carcinoma of a rat described in this communication occurred by metaplasia in a carcinoma of bronchiolo-alveolar origin.

Morphological comparison between benign keratinizing cystic squamous cell tumours of the lung and squamous lesions of the skin in rats.

Approximately 700 cases of keratinizing cystic squamous lung lesions in rats were investigated by light microscopy in order to clarify the nomenclature and classification of these lesions. The structure of benign keratinizing cystic squamous cell tumours of the lung was compared to that of cystic squamous lesions in the skin of rats, with consideration of data from the literature. We conclude that the reviewed keratinizing cystic squamous cell lesions of the lung are true neoplasms and that the growth pattern of these cystic lesions is inconsistent with that of a simple cyst. In the development of squamous lung cancer, a continuum of proliferation from exaggerated metaplasia through benign cystic tumours to invasive squamous cell carcinomas can be observed.

Visual documentation of neoplasms as part of the REGISTRY Nomenclature Information System.

The REGISTRY Nomenclature Information system (RENI) is a program which runs on IBM-compatible personal computers. It includes internationally accepted diagnostic criteria for tumors and pre-neoplastic lesions in the rat to be used in toxicologic pathology. A video disk system, connected to the computer, provides colored pictures of histopathological reference slides, which are used for a visual documentation of the written criteria.

RITA--Registry of Industrial Toxicology Animal-data--progress of the working group.

A data base for the collection of histopathological diagnoses of neoplastic and pre-neoplastic lesions and related data from control animals involved in long-term carcinogenicity or toxicity studies has been operated since 1988. Factors which may have an influence on the spontaneous tumor rate are integrated in the data base. Systematized nomenclature and standardized diagnostic criteria have been established as well as the applied data acquisition and data validation procedure.