Ultrastructure of liver tumors induced in F344 rats by methapyrilene.

Liver tumors induced in F344 rats by methapyrilene were studied by electron microscopy. The tumor cells constituting hepatocellular carcinomas showed a pronounced increase in the number of mitochondria and conformational changes of these organelles while the content of lipid, glycogen and smooth endoplasmic reticulum was greatly reduced. The cholangiocarcinomas consisted of bile duct epithelia at varying stages of squamous metaplasia.

Metabolic basis for the pulmonary Clara cell as a target for pulmonary carcinogenesis.

The furan compound, 4-ipomeanol, is activated in lung tissue by cytochrome P-450 dependent oxidation to a highly reactive, electrophilic product that binds covalently to tissue macromolecules. Although the reactive metabolite(s) of 4-ipomeanol have not yet been definitively identified, recent studies with 3-methylfuran have indicated that a highly reactive, unsaturated dialdehyde is formed from microsomal oxidation and ring-opening of the furan nucleus. Metabolic experiments with 4-ipomeanol in intact lungs, lung slices, lung cells, lung microsomes and purified lung cytochromes P-450, supported the conclusion that the Clara cell is an important locus of cytochrome P-450 monooxygenase activity in lung. In vivo, 4-ipomeanol was bound covalently and caused necrosis preferentially in the pulmonary Clara cells of laboratory animals. Similarly, N-nitrosamines require metabolic activation mediated by the cytochrome P-450 monooxygenase system in the host organism. A number of nitrosamines which are lung carcinogens in rats and hamsters have been shown to bind preferentially to bronchial and bronchiolar Clara cells in these species. Early pathological changes occurred specifically in Clara cells and lung tumors that developed under continuous nitrosamine treatment originated from such altered Clara cells. The well-differentiated counterparts of these tumors clearly retained their ability to bind the nitrosamine that had induced their formation. Thus, the studies on these two different classes of compounds together supported the view that metabolism may be a factor critical to the progenitor role of the Clara cell in chemically-induced bronchogenic lung cancer.

Sequential morphologic changes during methapyrilene-induced hepatocellular carcinogenesis in rats.

The pathogenesis of hepatocellular tumors induced in F344 rats by the antihistaminic methapyrilene was investigated by light and electron microscopy in a serial sacrifice study. Eosinophilic foci of altered hepatocytes were found in portal areas after 1 week of treatment, the eosinophilia being caused by proliferation of mitochondria. Eosinophilic neoplastic nodules developed from such lesions after 16 weeks of treatment. Hepatocellular carcinomas developed after 26 weeks of treatment. Mitochondrial proliferation, which had been found as a marker for hepatocytes altered by this compound at 1 week of treatment, was still present in the hepatocellular carcinomas, which therefore met the morphologic criteria of oncocytomas.

Pathogenesis of tumors induced with N-nitrosomethylpiperazine in the olfactory region of the rat nasal cavity.

Tumors in the olfactory region of the nasal cavity of the F344 rat were induced by chronic treatment with N-nitrosomethylpiperazine. The pathogenesis of the neoplasms was studied in a serial sacrifice study by light and electron microscopy. Proliferating basal cells of the olfactory epithelium differentiated into cells with morphologic features of neuroendocrine cells, which then progressed further to become invasive carcinomas. The tumors exhibited areas of neuroendocrine, adenoid, squamous, and neuroblastic morphologies. The variability of morphologic patterns found within the same tumor can be explained by the ability of neuroendocrine cells to differentiate into these different cell types.

Spindle cell carcinoma of the hamster trachea induced by N-methyl-N-nitrosourea.

The tracheas of 63 male Syrian golden hamsters were exposed once each week for 12 weeks to a flowing stream of 0.5% N-methyl-N-nitrosourea in phosphate-buffered saline (pH 4.5) with a specially designed intratracheal cannula. The animals were killed when moribund or 6 months after the final exposure, and the respiratory tracts were examined grossly, histologically, and ultrastructurally for tumor formation. A total of 13 neoplasms was found in the larynx or trachea. Six were papillomas, 3 were carcinomas, and 4 were diagnosed as spindle-cell carcinomas. The average time of observation of the various tumor types was 33, 31, and 21 weeks, respectively. The spindle cell carcinomas contained an exophytic portion protruding into the tracheal or laryngeal lumen and an infiltrating portion growing circumferentially between the intact mucosa and the cartilage rings or plates. They were composed of sheets of elongated and spindle-shaped cells. Ultrastructurally, the cells contained bundles of tonofilaments and keratohyalin, and were connected by numerous desmosomes. These findings are consistent with a squamous origin of the tumor cells and a diagnosis of spindle cell carcinoma.

Ultrastructure of nitrosoheptamethyleneimine-induced lung tumours in Fischer rats.

Male F344 rats were given N-nitrosoheptamethyleneimine (NHMI) twice a week by gavage for 20 weeks. They developed peripheral squamous cell carcinomas of the lungs. Electron microscopy revealed the presence of mature keratin in the tumor centers and the formation of keratohyalin granules in the more peripheral tumor cells. Basal cells were identified as the actively growing component of the neoplasms. In contrast to NHMI-induced lung carcinomas in European hamsters, neither Clara, nor APUD-type, cells were found in the rat tumors. These data indicate that the mode of development of NHMI-induced lung tumors is different in these two species.

Electron microscopic autoradiography of the trachea in fetal Syrian golden hamsters treated transplacentally with N-nitrosodiethylamine.

Tritiated N-nitrosodiethylamine (DENA) was administered to female Syrian golden hamsters on each of the last 4 days (days 12--15) of pregnancy. The intracellular distribution of bound radioactivity was monitored by electron microscopic autoradiography in the epithelium of the fetal tracheas, from which transplacentally induced tumors arise in this system. Most of the bound radioactivity was concentrated in the rough endoplasmic reticulum of undifferentiated stem cells and mucous cells. The level of binding on the various days of pregnancy appeared to reflect the degree of differentiation of the endoplasmic reticulum in these cells. Basal cells, which were identified as the origin of DENA-induced tracheal tumors in adult hamsters by one or our earlier studies, demonstrated only little bound radioactivity in the fetal tracheas. The pathogenesis of DENA-induced tracheal tumors in this transplacental system may hence be different from that in adult animals.

Contrasting carcinogenic effects of nitroso-2,6-dimethylmorpholine given by gavage to F344 rats and Syrian golden hamsters.

Nitroso-2,6-dimethylmorpholine (Me2NM) has been given by gavage to F344 rats of both sexes and to male Syrian hamsters at similar doses. The rats died more rapidly from the tumors induced than did the hamsters, the males being more susceptible than the females. The rats developed mainly carcinomas and papillomas of the esophagus, whereas the hamsters died with angiosarcomas of the liver, ductal adenocarcinomas of the pancreas, adenocarcinomas of the lung and olfactory adenocarcinomas of the nasal cavity. It was notable that, with the exception of a few lung tumors in the rat, none of the tumors found in the hamster were induced by Me2NM in the rat, and no esophageal tumors were seen in the hamsters.

Labeling in cells of the nasal cavity of hamsters treated with tritiated N-nitrosodiethylamine.

Syrian golden hamsters were given a single dose of N-[3H]nitrosodiethylamine ([3H]DEN) by gavage. One hour later the animals were killed and their nasal cavities processed for high resolution light microscopic autoradiography for detection of bound radioactivity. The atrioturbinals, which are lined by squamous epithelium, were unlabeled. In the respiratory portion of the nose (nasal septum, naso- and maxilloturbinals) most bound radioactivity was concentrated in the mucous cells of the respiratory epithelium and the secretory cells of submucous glands). In the olfactory region (ecto and endoturbinals) most bound radioactivity was restricted to the secretory cells of submucous glands, while in the olfactory epithelium only the sustentacular cells were slightly labeled.

Morphology of spontaneous and induced tumors in the bronchiolo-alveolar region of F344 rats.

The morphology of spontaneous and chemically-induced metastasizing carcinomas and adenomas in the bronchiolo-alveolar region of F-344 rats was studied. Histologically, the tumors were tubulo-papillary. Ultra-structurally, they consisted of cells which formed and secreted osmiophilic lamellated inclusion bodies, a marker of alveolar type II cells. Mitotic tumor cells also demonstrated such bodies. No cells of bronchial or bronchiolar origin were found in the tumors. We conclude that in F344 rats, lung tumors located in the bronchioloalveolar region consist of alveolar type II cells exclusively and are, therefore, alveolar cell adenomas and carcinomas, respectively.

Morphology of early changes in liver carcinogenesis induced by methapyrilene.

Two weeks of treatment with the liver carcinogen methapyrilene induced a significant increase in mitochondria of periportal hepatocytes in F344 rats. Administration of [3H]-methapyrilene hydrochloride resulted in a pronounced concentration of bound radioactivity in the periportal hepatocytes, with mitochondria being the principal site of intracellular binding. The nuclei of the liver cells were unlabeled.

Autoradiographic study of the distribution of bound radioactivity in the respiratory tract of Syrian hamsters given N-[3H]nitrosodiethylamine.

Adult Syrian golden hamsters received a single intragastric dose of N-[3H]nitrosodiethylamine. Their tracheas, extrapulmonary stem bronchi, and lungs were processed for high-resolution light-microscopic autoradiography to monitor the distribution of bound radioactivity. In the trachea and extrapulmonary stem bronchi, mucous cells contained the most bound radioactivity, while in the lobar and segmental bronchi and bronchioles, Clara cells were the major site of binding. In conjunction with earlier conducted studies on the pathogenesis of N-[3H]nitrosodiethylamine-induced respiratory tract tumors, these findings indicate that metabolic competence and a preexisting capacity for proliferation are important factors in determining the target cell types of this compound.

Autoradiography in fetal golden hamsters treated with tritiated diethylnitrosamine.

Tritiated diethylnitrosamine was administered to female Syrian golden hamsters on each of the last 4 days (days 12-15) of pregnancy. The distribution of bound radioactivity was monitored by light microscopic autoradiography of fetal tracheas and livers, the placentas, and the maternal livers. In the trachea, the fetal target organ, bound radioactivity was restricted to the respiratory epithelium, where diethylnitrosamine-induced tracheal tumors arise. Mucous cells and nonciliated stem cells were identified as the principal sites of binding; other cell types within the tracheal epithelium contained only small amounts of bound radioactivity. The level of binding observed in the fetal trachea increased steadily from day 12 to day 15, which correlated well with the levels of differentiation of this tissue during this period. This observation also agrees with the previously reported observation that tumor incidence increases from 40 to 95% in Syrian golden hamsters between days 12 and 15.

Morphology of nasal cavity neoplasms in F344 rats after chronic feeding of p-cresidine, and intermediate of dyes and pigments.

p-Cresidine was administered in the feed at either of two concentrations (0.5 and 1.0 percent) to groups of 50 male and 50 female F344 rats for 104 weeks. Fifty animals of each sex were placed on test as controls and fed only the basic laboratory diet. All animals were observed for up to 2 weeks after discontinuation of treatment. In treated rats of both sexes, statistically significant numbers of adenomas, adenocarcinomas and squamous cell carcinomas were diagnosed in the nasal cavity. Most of the neoplasms were seen in the high dose male and female rats. 22 male rats (49%) showed poorly differentiated adenocarcinomas infiltrating the skull and brain. Only two male rats (4%) had a squamous cell carcinoma, whereas 8 female rats (17%) had squamous cell carcinomas and 14 female rats (30%) were diagnosed as having adenocarcinomas of the nasal cavity. In the 4 neoplasms studied ultrastructurally, features characteristic of adenocarcinomas were identified. Cells were arranged around central lumina lined with microvilli. The luminal edges of cells were linked together by junctional complexes. Cytoplasmic differentiation was generally poor, with ribosomes and polyribosomes being the predominant organelles. Neurogenic features were rare and difficult to identify due to unsatisfactory fixation. In one of the tumors, areas of squamous differentiation were found. The cells constituting such areas contained prominent bundles of tonofilaments which are characteristic of early squamous metaplasia.

Ultrastructure of tumors induced in the rat urinary bladder by nitrosomethyldodecylamine.

N-Nitroso-N-methyl-n-dodecylamine (NMDA) is a powerful carcinogen in the rat and the Syrian golden hamster. In both species the urinary bladder is the main target organ. We studied the ultrastructure of these bladder tumors in the Fischer rat in some detail, since this compound provides an interesting model for carcinogenesis in the urinary bladder. We found that the proliferating basal layers of the transitional cell carcinomas were undergoing squamous metaplasia, which indicates that squamous carcinomas in the organ may arise from pre-existing transitional cell tumors.