Estrogen dependence is generally accepted as a cue for mammary and uterine carcinogenesis, but recently estrogen metabolite or catechol-estrogen driven pathways have also come under consideration. Endometrial adenocarcinoma is a leading cause of cancer death in women. Although the cancer is rare in most strains of rodents, it develops spontaneously and can be readily induced in the Donryu rat strain, with many morphological, endocrinological and molecular similarities to the human case. The goal of this review is to weigh the hypothesis for a new pathway for endometrial carcinogenesis driven by modulation of estrogen metabolism through cytochrome P450 enzyme induction using data from the Donryu rat model. To test our hypothesis, indole-3-carbinol (I3C), an active ingredient of cruciferous vegetable, was selected, since it induces cytochrome P450 enzymes in the liver which impact on hydroxylation of estrogens. In uterotrophic assays using ovariectomized rats, neither 500 ppm nor 2000 ppm of I3C in the diet caused any estrogenic or anti-estrogenic activity. However, in our 2-stage rat uterine cancer model, dietary I3C and subcutaneous injection of 4-hydroxyestradiol (4HE), one of hydroxylation metabolites of 17β-estradiol (E2), elevated both incidences of uterine adenocarcinomas and multiplicities of uterine proliferative lesions. I3C treatment increased mRNAs for 1A1, 1A2 and 1B1 in the liver, reflecting the distribution of corresponding enzymes immunohistochemically demonstrated. In the uterus, only CYP 1A1 mRNA was increased by the treatment, without reflecting protein expression. In the liver, I3C consistently elevated estradiol 2 and 4 hydroxylation. These results indicate that modulation of estrogen metabolism, particularly to increase 4HE through induction of CYP 1 in the liver, plays a crucial role in promoting effects of dietary I3C on endometrial adenocarcinoma development, providing support for our hypothesis of a new pathway for endometrial carcinogenesis in the rat.

抄録全体を表示

Itai-itai disease (IID) is the most severe form of chronic cadmium (Cd) intoxication of human. The patients of IID suffer from renal anemia, tubular nephropathy and osteopenic osteomalacia, and 90% of the patients are post-menopausal women. Many efforts have been paid for reproducing the bone lesions using various animal species, but the pathogenesis of them is still controversial and conflicting among the reports. Two hypotheses have been proposed for the pathogenesis of the bone lesion: direct and indirect effects of Cd on bone. The former includes toxic effects of Cd on osteoblasts and impediment of calcification at the ossification front by Cd or Fe. The latter indicates nephrogenic osteopenia via hypocalcemia, hypophosphatemia and hyperparathyroidism. Each hypothesis secures solid scientific basis and may not be alternative. Our animal experiments using rats and monkeys demonstrated that hypoestrogenism induced by ovariectomy enhanced Cd toxicity, and osteopenic osteomalacia and tubular nephropathy distinctive to IID could be reproduced by Cd treatment without involvement of malnutrition such as hypovitaminosis D. Vitamin D has been prescribed to IID patients for bone lesions. However, the efficacy of the treatment is unpredictable depending on patients. Our experiments suggest concurrent administration of estradiol helps the vitamin D therapy for IID patients and the removal of Fe at the mineralization front of bone is important for the recovery to normal bone remodeling.

抄録全体を表示

The pathological and molecular biochemical analyses in the experimental animal models are important for the solutions of human disorders, including stomach cancer. Stomach cancers are induced experimentally by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and N-methyl-N-nitrosourea (MNU) in rats and mice. Helicobacter pylori (H. pylori) is one of the most important factor in the human stomach disorders, and the H. pylori infected and chemical carcinogen treated Mongolian gerbil (MG) has thus proved very useful for the analysis of human stomach carcinogenesis. Intestinal metaplasia is important not as a precancerous lesion but as a paracancerous cord from such studies of clonality of stomach cancers and of phenotypic expression of each intestinal metaplastic or stomach cancer cell, while the pepsinogen altered pyloric glands can be regarded as a common change in rodents, acting as a precursor for a variety of adenocarcinoma types. As the results of the analyses of the MG model, H. pylori is a strong promoter of gastric carcinogenesis rather than an initiator. The dose-dependent enhancing effects of salt on stomach carcinogenesis are demonstrated in the MGs treated with MNU and H. pylori, although high salt intake has a minor influence compared to H. pylori. Bile reflux is not an initiator, but rather an important promoter in the carcinogenesis of gastric stump after partial gastrectomy. Stomach cancers develop from single cells, based on data from clonality analysis in C3H/HeN⇔BALB/c chimeric mice. Intestinalization progresses from gastric, through gastric-and-intestinal mixed, to intestinal phenotypes in non-cancerous and cancerous tissue independently. The chemopreventive effects of H. pylori eradication and reduction of salt intake against stomach cancer are confirmed in the MG models.

抄録全体を表示

In the two-stage rat urinary bladder carcinogenesis model with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) as an initiator and sodium L-ascorbate (Na-AsA) as a promoter, we previously reported that F344/DuCrj (F344) and LEW/Crj (Lewis) rats were sensitive, whereas WS/Shi (WS) and ODS/Shi-od/od (ODS) rats were resistant. In the present study, for the development of a model useful to the QTL analysis of host genes, we examined the susceptibility to Na-AsA promotion in (F344 × WS)F₁, (F344 × ODS)F₁, (Lewis × WS)F₁, and (Lewis × ODS)F₁ hybrids of male rats. Rats were given 0.05% BBN in their drinking water for 4 weeks and then a basal diet with or without a 5% Na-AsA supplement for 32 weeks. In urine of all F₁ hybrids, Na-AsA elevated pH and concentrations of sodium ion and total ascorbic acid. There were not significant differences for susceptibilities to BBN alone among the four F₁ hybrids. In all F₁ hybrids, administration of Na-AsA increased urinary bladder carcinogenesis when compared to the matched control rats given BBN alone. Susceptibilities to Na-AsA promotion were high in (F344 × WS)F₁ and (F344 × ODS)F₁ hybrids, whereas they were mild in (Lewis × WS)F₁ and (Lewis × ODS)F₁ hybrids. The present results therefore indicate that F₁ hybrids among the F344, ODS, Lewis and WS strains may be a useful model for analyzing host genes susceptible to Na-AsA promotion in rat bladder carcinogenesis.

抄録全体を表示

Gap junctions, composed from molecules called connexins, play important roles in cell-to-cell communication and aberrant gap junctional intercellular communication (GJIC) has been reported in many types of cancers. We have established transgenic rats bearing a dominant negative mutant of the connexin 32 gene under control of the albumin promoter. In these rats, GJIC is markedly decreased in the liver, and is associated with increased induction of preneoplastic foci after a single treatment of diethylnitrosamine. In the present study, in order to explore whether organs other than the liver would demonstrate increased susceptibility to a carcinogen, we treated these transgenic rats (having disrupted GJIC of the liver) with diisopropanolnitrosamine (DHPN), a carcinogen targeting multiple organs, such as the liver, lung, kidney and thyroid gland. We found that increased susceptibility for the carcinogenicity was evident only in the liver, but not in the lung, kidney and thyroid gland. This result indicates that disrupted GJIC in the liver influences the liver carcinogenesis, but has no effect on carcinogenesis in other organs.

抄録全体を表示

The question of whether transforming growth factor-α (TGF-α) might be a useful marker of preneoplastic lesions during hepatocarcinogenesis was investigated using a medium-term liver carcinogenesis bioassay (Ito test) extended to 50 weeks. Male F344 rats, 6 weeks of age, received a single i.p. injection of 200 mg/kg diethylnitrosamine (DEN), then after 2 weeks, the animals were divided into four groups. Groups 1 and 2 were maintained on tap water supplemented with 10 ppm of N-nitrosomorpholine (NMOR), a genotoxic carcinogen, for 48 or 6 weeks, respectively. Animals in Group 3 were maintained on basal diet and tap water ad libitum as controls. Group 4 was included as the vehicle control and was maintained until experimental week 50. Two-thirds partial hepatectomy was performed on all rats at the end of week 3 of the experiment. Histopathology and immunohistochemical investigations of glutathione S-transferase placental form (GST-P) and TGF-α of the liver were performed sequentially at experimental weeks 8, 12, 20, 35 and 50. The numbers of TGF-α positive lesions were significantly lower than those of GST-P positive foci at all experimental time points. In contrast, the mean size values of TGF-α positive liver lesions in the continuous and 6-week treatments of DEN/NMOR, and the DEN alone protocol, were larger than those of their GST-P positive counterparts from week 35. Bromodeoxyuridine (BrdU) labeling indices for TGF-α positive foci and hepatocellular adenomas at week 20 were clearly higher than those for TGF-α negative lesions. In conclusion, the overexpression of TGF-α can be immunohistochemically detected in large hepatocellular lesions demonstrating increased levels of DNA synthesis. Therefore TGF-α may be a marker of a relatively late, progression stage of hepatocarcinogenesis.

抄録全体を表示

A novel method for intratracheal instillation of rats is described by which an operator can confidently administer a liquid sample into the tracheal lumen, with direct observation of the entrance to the trachea. To confirm its efficacy, indigo carmine was administered with or without air to investigate optimal conditions for exposure of the whole lung. After administration of 0.5 ml of indigo carmine and an equal volume of air simultaneously by intratracheal instillation, sections through the whole lung demonstrated positive staining with the dye. For histological examination, 0.5 ml of saline containing iron oxide followed by an equal volume of air was administered intratracheally. Iron particles were observed in the wall of bronchioles and alveolar macrophages of whole lung. The method allows reliable intratracheal administration to large numbers of rats within a short period and should, therefore, prove useful for assays of toxicity in the respiratory tract.

抄録全体を表示