Historical data are presented for neoplastic and non-neoplastic lesions in B6C3F₁ (C57BL/6×C3H) mice that served as controls for short-term toxicity, long-term toxicity and carcinogenicity studies conducted at the Biosafety Research Center, Foods, Drugs, and Pesticides, (An-Pyo Center) during a 12-yr period (1980-1992). Patterns consistent with spontaneouslly-occurring tumors in specific organs were found in male and female mice and were similar to those reported in the literature. The incidence of most of the neoplastic and non-neoplastic lesions increased with age, suggesting that these pathological alterations are age-associated processes. However, some were believed to be caused by latent viral infections, nutritional or hormone-dependent factors.
The wide variety and a high incidence of these lesions seen in long-term studies may greatly complicate histopathological evaluations and the elucidation of treatment-related effects. Consequently, both quantitative and qualitative interpretations are needed for meaningful evaluations.

View full abstract

Many epidemiological and clinical studies have been conducted on the role of vitamin E in human cancers. Although the beneficial effects in many cases have not been conclusive, vitamin E exerted an inhibitory effect on cancer of the stomach ^{24, 37}, Colon ^{40, 48, 49} lung^{21, 39, 42, 43} and uterine cervix⁴⁴. These cancers have been demonstrated to require multiple gene-matations for their development ^114-118.
Many experimental studies have also been conducted on the role of vitamin E in chemical carcinogenesis. The inhibitory Effect of vitamin E has been shown on skin, alimentary tract, liver, pancreas, mammary, lung, and prostate carcinogenesis. The involvement of the antioxidative action of vitamin E for the inhibition of carcinogensis was strongly suggested in the skin⁹⁰, stomach^{88, 89}, mammary gland^73-75, and some cell lines^94-97. In spite of this inhibitory effect of vitamin E on chemical carcinogenesis, the direct carcinogenic potential of vitamin E has been demonstrated in the forestomach¹⁸, liver¹⁷, and soft tissues^{19, 20}. However, the ultimate carcinogenic structure of the vitamin E in this direct carcinogenesis remains to be elucidated.

View full abstract

To study the membrane changes in the myocardium, the sarcolemmal permeability of 16-week-old SHR and age-matched WKY myocardium was examined morphologically using horseradish peroxidase (HRP) on the first and fourth day after doxorubicin administration. No HRP was seen in either saline-treated controls or doxorubicin-treated WKY on the first day. On the fourth day, the doxorubicin-treated WKY showed, HRP around the myocytes due to an increase in the vascular permeability, whereas, the HRP-reactant product was not seen within the sarcoplasm. Electron micros-copy revealed osmiophilic, fine granular HRP-reactant products in the extracellular space of the WKY myocardium on the fourth day. On the other hand, in doxorubicin-treated SHR myocardium, HRP was seen in a portion of the papillary muscle or myocardial cells in the anterior wall on the first day and HRP-positive myocytes were scattered in the anterio-lateral wall at the fourth day. Cross striations were still visible within some HRP-positive myocytes of SHR. Electron microscopy also showed HRP-reactant products, not only in sarcotubules of normal-appearance myocytes, but also in myofibrils and/or mitochondria of highly degenerated myocytes. These results demonstrate the increase in the mem-brane permeability in the SHR myocardium, probably due to genetical disadvantage of the defense system and a proneness for membrane lipid peroxidation.

View full abstract

The effect of adriamycin-oxidized dextran (ADM-OXD) on hepatic macrophage (Kupffer cell) was studied using male Wistar rats. Kupffer cell function was measured using as an index the clearance rate from circulating blood of extrinsic carbon particles (phagocytic index). This index fell markedly from soon after a single intravenous injection of ADM-OXD at a dose of 30 or 60 mg/kg in terms of ADM content. Carbon uptake in periportal Kupffer cells, evaluated using HE stained liver sections, was markedly lower in ADM-OXD treated animals than in control animals. The relationship between damage to parenchymal cells and to sinusoidal lining cells, especially Kupffer cells, was monitored morphologically and biochemically for 48 hours after a single injection at a dose of 60 mg/kg. Serum biochemical changes showing parenchymal cell dysfunction and morphologically regressive changes such as diffuse centrilobular necrosis were observed in pronounced form at 48 hours. Kupffer cells, in contrast, were found to be degenerative or necrotic ultrastructurally as early as at 8 hours. Immunohistochemically, the number of ED2-positive Kupffer cells in the periportal area decreased from 8 hours. Activity of serum cathepsin D, thought to be leaked from Kupffer cell lysosomes, was elevated from an early stage. It was judged that Kupffer cell damage preceded parenchymal cell damage. Pretreatment with estrogen, which has a proliferative action on hepatic macrophages, mitigated ADM-OXD-induced hepatotoxicity. Damage to sinusoidal lining cells (Kupffer cells) would therefore seem to participate closely in the onset of parenchymal cell damage.

View full abstract

Treatment with 150mg/kg of spironolactone (SPL) and 100mg/kg of phenobarbital (PB) for 13 weeks increased thyroid weight, numbers of apical vesicles and colloid droplets in thyroid follicular cells, and thyroid follicular hypertrophy. The patterns of elevated serum thyrotropin (TSH) and transiently decreased serum thyroxine (T₄) and triiodothyronine (T₃) suggest that thyroid follicular hypertrophy is a compensatory reaction to lowered thyroid hormone levels. Treatment with PB or SPL induced increased liver weight, hepatocellular hypertrophy, and smooth endoplasmic reticulum proliferation in hepatocytes. PB-treatment increased Uridine diphosphate glucuronosyl transferase (UDP-GT) activity toward p-nitrophenol and P-450 content but SPL-treatment had no such effect on hepatic microsomal enzymes. PB and SPL have been shown not to directly affect thyroid hormone synthesis. It is concluded that the effect of PB on thyroid function in male rats is secondary to increased hepatic UDP-GT and P-450 and that in SPL-treated male rats a distinct spectrum of isozymes of cytochrome P-450 and UDP-GT and/or other enzymes may play an important role for induction of thyroid hypertrophy.

View full abstract

Nucleolar organizer regions, stainable with the one-step silver colloid method (AgNORs), were evaluated for estimation of proliferative activity of pancreatic lesions, including ductal hyperplasias, dysplasias, adenomas, and adenocarcinomas induced by N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) in dogs and compared with values for proliferating cell nuclear antigen (PCNA) positive cells. The mean numbers of AgNORs per nucleus of cells in adenocarcinoma, dysplasia and hyperplasia cases were 2.37 (p<0.01), 2.03, and 1.48, respectively, the first two being clearly increased as compared to normal pancreatic duct cells (1.46). The PCNA labeling indices of adenocarcinoma, dysplasia and hyperplasia, at 38.9% (P<0.01), 13.1% (p<0.01), and 2.4%, respectively, were similarly and even more pronouncedly elevated over the normal pancreatic duct cell value (1.3%).
The present results suggest that numbers of AgNORs, like PCNA positivity, well reflect cell kinetics of lesions involved in dog pancreatic ductal tumorigenesis.

View full abstract

Two hairless dogs and 2 Beagles were sensitized by intradermal inoculation of 2, 4-dinitroch-lorobenzene (DNCB). Three weeks later, they were challenged topically by applying a patch containing 0.01, 0.05, 0.1, 0.5 or 1.0% DNCB. Delayed-type hypersensitivity reaction occurred in both hairless dogs and Beagles. Twenty-four later, erythema developed macroscopically, and epidermal thickening and degeneration and intradermal infiltration of inflammatory cells and vasodilatation were observed microscopically. The total intensity of these changes was dose-dependent and generally weaker in hairless dogs than in Beagles. The present data suggest an existence of slightly depressed cellular immunity in hairless dogs. In addition, such an interesting finding as pigmentation due to deposition of melanin granules was observed in the sites treated with 0.01-0.1% DNCB in hairless dogs.

View full abstract

The monoterpenes are a new class of anticancer drugs having efficacy in both cancer prevention and treatment. We have shown that the monocyclic monoterpenes limonene and perillyl alcohol can prevent chemically-induced rat mammary carcinomas if fed either during the initiation stage or the promotion/progression stage of carcinogenesis. In addition, these terpenes can induce the complete regression of the majority of advanced mammary carcinomas without toxicity. The activities associated with tumor regression include the inhibition of the prenylation of small G proteins and the synthesis of ubiquinone. In addition, regressing tumors have elevated levels of TGFβ and its activating receptor. Both rodents and humans metabolize limonene to similar compounds. Based on these findings limonene is currently undergoing clinical testing in cancer patients.

View full abstract

A litter of ACI rat strain, foster bred by a female colon cancer-prone WF-Osaka rat, developed colon carcinoma in the ascending colon at the age of 4 months. We assumed that some microbial infection during their suckling might cause colon carcinoma of WF-Osaka rats, and that the high incidence of spontaneous regression of the colon carcinoma might be an immunologic reaction against microbial agent in the cancer cells. In this report, we showed that new born rats of ACI, LE and W/Shi strain developed colon carcinoma by the intraperitoneal injection of the serum from cancer carrying WF-Osaka rat within 2 months after birth, and that this microbial agent was transmissible among rats regardless the strain.
The etiology of colon carcinoma of WF-Osaka rat was considered to be virus-like infection as we found FITC positive granular materials in the cytoplasm of tissue culture cells of colon carcinoma (C2) and tissue specimen of transplantable gastric carcinoma (S3). Supernatant of tissue culture medium of colon carcinoma (C2) also induced colon carcinoma. Solid-phase immune electronmicroscopy study revealed round to oval particles, measuring approximately 40-50 nm in diameter, in the sediment of tissue culture medium of the transplantable gastric carcinoma (S3), which explain that oncogenic viral agent is substantially related to the induction of colon carcinoma in WF-Osaka rat strain.

View full abstract

Spontaneous hemangioendothelial cell tumor of the heart was found in five of 4, 160 male and 3, 910 female B6C3F₁ (C57BL/6CrSIc×C₃H/HeSlc) mice which were used in chronic toxicology and carcinogenicity studies at the An-Pyo Center. Two cases were diagnosed histologically as benign hemangioma and the other three cases were diagnosed as hemangiosarcoma. Hemangioendothelioma of the bone marrow, liver, and spleen were also observed in two out of three cases with hemangiosarcoma of the heart, and these cases were recognized as systemic, multiple vescular cell tumor of B6C3F₁ mice. The tumor cells were identified as hemangioendothelial cells by immunohistochemical techniques and lectin binding patterns. The finding of five cases of spontaneous hemangioendothelial cell tumor of the heart in this report is considered to be extremely rare.

View full abstract

This communication describes 2 cases of choroidal coloboma in untreated Sprague-Dawley rats. On ophthalmoscopical examination, a 4 weeks old female and 11 weeks old male rats had a focal pale area which in both cases were located inferonasal to the optic disc. These pale foci were oval and well-delineated from the surrounding fundus. Subsequent examination revealed that the foci were non-progressive or non-regressive. Histologically, the lesions were characterized by lack of choroid, atrophic and indistinct retinal pigment epithelium, lack of retinal photoreceptor and external granular layers, retinal fold, retinal herniation into the sclera, and unaffected inner retinal layers.

View full abstract

Following the induction of diabetes by streptozotocin (SZ) (50mg/kg/day for 5 consecutive days), cytomegalic hepatocytes (0/7 at 4 weeks after the last SZ-injection (4WAI), 2/7 at 8WAI and 3/7 at 12WAI) and bile duct hyperplasia (0/7 at 4WAI, 2/7 at 8WAI and 2/7 at 12WAI) developed in some mice. Cytomegalic hepatocytes showed a prominent increase in number of mitochondria and were frequently accompanied with invagination of cytoplasm into nuclei. Prominent bile duct hyperplasia was found in 4 out of 5 mice bearing cytomegalic hepatocytes. Hyperplastic bile ducts were lined with epithelia of various types and accompanied no apparent connective tissue proliferation around them.

View full abstract