Kunitoshi Mitsumori

Mortality, Major Cause of Moribundity, and Spontaneous Tumors in CD-1 Mice

Mortality, major causes of moribundity, and spontaneous tumors in CD-1 mice were studied in 891 males and 890 females, which were used as controls in 11 different 2-year chronic and oncogenicity studies during the past 5 years. Average mortality of males and females at 83 weeks of age was 32.6% and 28.6%, respectively, and at 109 weeks of age was 66.4% and 63.3%, respectively. Mortality was significantly lowered in males and females born after 1980 in accordance with an abruptly decreased occurrence of systemic amyloidosis in these animals. The major cause of death or moribundity included systemic arteritis, systemic amyloidosis, auricular thrombosis, glomerulosclerosis, lymphoma, and pulmonary adenocarcinoma in both sexes. Dysuria and hepatocellular carcinoma in males and mammary adenocarcinoma in females were also critical lesions. The major tumors occurring at more than 3% incidence were systemic lymphoma, adenoma/adenocarcinoma of the lung, adenoma/carcinoma of the liver and adenoma/adenocarcinoma of the Harderian gland for males, and systemic lymphoma, adenoma/adenocarcinoma of the lung, adenoma/carcinoma of the liver, leiomyoma/leiomyosarcoma of the uterus, adenoma/adenocarcinoma of the pituitary (anterior), adenoma/adenocarcinoma of the mammary gland and adenoma/adenocarcinoma of the Harderian gland for females. Intra-laboratory heterogeneities in the incidence were recorded as follows: systemic lymphoma in 1 of 11 control groups (1/11) and adenoma/adenocarcinoma in 1/11 for males, and systemic lymphoma in 3/11, adenoma/adenocarcinoma of the lung in 2/11, adenoma/adenocarcinoma of the liver in 1/11, and adenoma/adenocarcinoma in 1/11 for females.

Prediction model of potential hepatocarcinogenicity of rat hepatocarcinogens using a large-scale toxicogenomics database.

The present study was performed to develop a robust gene-based prediction model for early assessment of potential hepatocarcinogenicity of chemicals in rats by using our toxicogenomics database, TG-GATEs (Genomics-Assisted Toxicity Evaluation System developed by the Toxicogenomics Project in Japan). The positive training set consisted of high- or middle-dose groups that received 6 different non-genotoxic hepatocarcinogens during a 28-day period. The negative training set consisted of high- or middle-dose groups of 54 non-carcinogens. Support vector machine combined with wrapper-type gene selection algorithms was used for modeling. Consequently, our best classifier yielded prediction accuracies for hepatocarcinogenicity of 99% sensitivity and 97% specificity in the training data set, and false positive prediction was almost completely eliminated. Pathway analysis of feature genes revealed that the mitogen-activated protein kinase p38- and phosphatidylinositol-3-kinase-centered interactome and the v-myc myelocytomatosis viral oncogene homolog-centered interactome were the 2 most significant networks. The usefulness and robustness of our predictor were further confirmed in an independent validation data set obtained from the public database. Interestingly, similar positive predictions were obtained in several genotoxic hepatocarcinogens as well as non-genotoxic hepatocarcinogens. These results indicate that the expression profiles of our newly selected candidate biomarker genes might be common characteristics in the early stage of carcinogenesis for both genotoxic and non-genotoxic carcinogens in the rat liver. Our toxicogenomic model might be useful for the prospective screening of hepatocarcinogenicity of compounds and prioritization of compounds for carcinogenicity testing.

Sphingosine-1-phosphate receptor-2 deficiency leads to inhibition of macrophage proinflammatory activities and atherosclerosis in apoE-deficient mice.

Sphingosine-1-phosphate (S1P) is a biologically active sphingolipid that has pleiotropic effects in a variety of cell types including ECs, SMCs, and macrophages, all of which are central to the development of atherosclerosis. It may therefore exert stimulatory and inhibitory effects on atherosclerosis. Here, we investigated the role of the S1P receptor S1PR2 in atherosclerosis by analyzing S1pr2-/- mice with an Apoe-/- background. S1PR2 was expressed in macrophages, ECs, and SMCs in atherosclerotic aortas. In S1pr2-/-Apoe-/- mice fed a high-cholesterol diet for 4 months, the area of the atherosclerotic plaque was markedly decreased, with reduced macrophage density, increased SMC density, increased eNOS phosphorylation, and downregulation of proinflammatory cytokines compared with S1pr2+/+Apoe-/- mice. Bone marrow chimera experiments indicated a major role for macrophage S1PR2 in atherogenesis. S1pr2-/-Apoe-/- macrophages showed diminished Rho/Rho kinase/NF-κB (ROCK/NF-κB) activity. Consequently, they also displayed reduced cytokine expression, reduced oxidized LDL uptake, and stimulated cholesterol efflux associated with decreased scavenger receptor expression and increased cholesterol efflux transporter expression. S1pr2-/-Apoe-/- ECs also showed reduced ROCK and NF-κB activities, with decreased MCP-1 expression and elevated eNOS phosphorylation. Pharmacologic S1PR2 blockade in S1pr2+/+Apoe-/- mice diminished the atherosclerotic plaque area in aortas and modified LDL accumulation in macrophages. We conclude therefore that S1PR2 plays a critical role in atherogenesis and may serve as a novel therapeutic target for atherosclerosis.

Doxorubicin induces male germ cell apoptosis in rats

Abstract To clarify whether apoptosis is involved in doxorubicin (DXR)-induced testicular toxicity and to identify the target germ cell type, adult Sprague-Dawley rats were treated with a single intravenous dose of DXR (8 or 12 mg/kg) and euthanized at 3, 6, 12, 24, and 48 h subsequently. Histologically, germ cell degeneration was first found 6 h after dosing in meiotically dividing spermatocytes and early round spermatids of seminiferous tubules at stage I, and subsequently observed in spermatogonia at stages I–VI showing ultrastructural characteristics of apoptosis. Coincident with the appearance of morphological changes, degenerating germ cells were shown to be undergoing apoptosis as revealed by in situ terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). The frequency of TUNEL-labeled germ cells increased in a stage- and cell type-specific manner, the peak of frequency gradually progressing from stage I of seminiferous tubules to later stages with time after dosing, suggesting that the damaged germ cells, especially spermatogonia, gradually underwent the processes leading to apoptosis. DNA laddering on gel electrophoresis was apparent 24 and 48 h after dosing. The results demonstrate that apoptosis plays an important role in the induction of testicular toxicity caused by DXR with meiotically dividing spermatocytes and type A and intermediate spermatogonia as highly vulnerable target cells.

Relationship between the development of hepato-renal toxicity and cadmium accumulation in rats given minimum to large amounts of cadmium chloride in the long-term: preliminary study.

Abstract We wished to clarify the relationship between the sensitivity to induce hepato-renal toxicity and the level of cadmium (Cd) in the organs of rats exposed to minimum to large amounts of cadmium chloride (CdCl2). For this purpose, groups of female Sprague-Dawley (SD) rats, each consisting of 24 animals, were fed diet containing CdCl2 at concentrations of 0, 8, 40, 200, and 600 ppm for 2, 4, and 8 months from 5 weeks of age. All surviving rats given 600 ppm Cd were killed at 4␣months because of deterioration of their general condition. Animals of this group showed anemia and decreased hematopoiesis in the bone marrow, in addition to reduction of cancellous bone in their femurs. Hepatotoxicity was observed after 2 months in the groups treated with 200 ppm. By 4 months, the rats in the 600 ppm group had developed periportal liver cell necrosis. Renal toxicity characterized by degeneration of proximal tubular epithelia was apparent in the groups treated with 200 ppm from 2 months, becoming more prominent in the high-dose rats at 4 months. Hepatic accumulation of Cd increased linearly with the duration of treatment. In contrast, the concentration of Cd in the renal cortex of rats treated with 600 ppm reached a plateau level of ∼250 μg/g within the first 2 months. The renal concentration of Cd in the 200 ppm group when renal toxic lesions were first detected at 2 months ranged from 104 to 244 μg/g. No renal lesions were observed in the 40 ppm group after 8 months, despite the presence of 91–183 μg/g of Cd in the kidneys. The results thus suggest that renal toxicity would not be induced by treatment with minimum amounts of CdCl2 for periods longer than 8 months, although accumulation of Cd might gradually progress. A further 2-year feeding study of CdCl2 and Cd-polluted rice is now in progress.

Live Tumor-Promoting Effect of β-Naphthoflavone, a Strong CYP 1A1/2 Inducer, and the Relationship between CYP 1A1/2 Induction and Cx32 Decrease in Its Hepatocarcinogenesis in the Rat

Interrelationships among induction of cytochrome P-450 (CYP) 1A1/2, decrease in connexin 32 (Cx32), and liver tumor-promoting activity by β-naphthoflavone (BNF) in the promotion stage were examined in a 2-stage liver carcinogenesis model. A total of 20 male Fischer 344 rats were initiated with a single intraperitoneal injection of 150 mg/kg of diethylnitrosamine (DEN) or were given the saline vehicle alone. Starting 2 weeks later, they were fed a diet containing 2%, 1%, or 0% BNF for 6 weeks. All animals were subjected to a two-thirds partial hepatectomy at week 3 and were sacrificed at week 8. Absolute and relative liver weights were significantly increased in the DEN+BNF groups as compared to the DEN-alone group. Diffuse hepatocellular hypertrophy with cytoplasmic eosinophilia, sometimes accompanied by development of adenoma-like hepatic foci, was observed in the BNF-treated rats. Remarkable induction of cytochrome CYP 1A1/2 and significant increase in CYP 2E1 were noted in the DEN+BNF groups, and positive immunohistochemical staining for both was observed diffusely. The areas of Cx32-positive spots per hepatocyte in the centrilobular areas of livers of the BNF-treated rats were significantly decreased, but no changes were observed in periportal areas. The numbers and areas of foci positive for glutathione S-transferase placental form were increased in the BNF-treated groups. These results suggest that BNF is a liver tumor promoter that, unlike phenobarbital, does not induce CYP 2B1/2 isozymes, and there seems to be no direct relationship between CYP 1A1/2 induction and Cx32 reduction in BNF hepatocarcinogenesis.

Susceptibility of transgenic mice carrying human prototype c-Ha-ras gene in a short-term carcinogenicity study of vinyl carbamate and ras gene analyses of the induced tumors

To determine if hemizygous transgenic mice carrying the human c‐Ha‐ras gene (CB6F1‐Tg Hras2 mice (Hras2 mice)) are susceptible to the carcinogenic potential of known murine carcinogens, male and female Hras2 mice and their non‐transgenic CB6F1 littermates (non‐Tg mice) were each given a single intraperitoneal injection of 60 mg of vinyl carbamate (VC)/kg body weight or saline (vehicle control) and monitored for 16 wk without further treatment. At necropsy, grossly visible tumors were fixed for histopathologic diagnosis and, when of sufficient size, portions were frozen for subsequent molecular analysis. Nine of 31 male and nine of 29 female Hras2 mice treated with VC died within 16 wk as a result of lung tumor burden. At the termination of the study, lung tumors (alveolar‐bronchiolar epithelial neoplasms and hemangiosarcomas) and focal alveolar‐bronchiolar hyperplasias were present in both sexes of Hras2 and non‐Tg mice treated with VC; there were significantly more proliferative lung lesions in Hras2 than non‐Tg mice. Splenic hemangiosarcomas and squamous cell tumors of the forestomach were induced in male and female VC‐treated Hras2 mice but not in VC‐treated non‐Tg mice. Polymerase chain reaction–single‐strand conformation polymorphism analysis and DNA sequencing of the induced lung tumors revealed point mutations at codon 61 of the transgene in two of 29 lung tumors (one of 16 in males and one of 13 in females) from VC‐treated Hras2 mice; no mutations in murine Ki‐ras were found in these tumors. Point mutations at codons 12 and 61 of the murine Ki‐ras gene were observed, however, in one of 10 and six of 10 lung tumors respectively, from VC‐treated non‐Tg mice. These findings indicate that Hras2 mice are highly sensitive to pulmonary neoplasms and splenic and lung hemangiosarcomas after treatment with VC. The molecular analyses suggest that point mutations of the transgene and the murine Ki‐ras gene do not play a major role in VC induction of pulmonary neoplasms in these transgenic mice. Mol. Carcinog. 20:298–307, 1997.

Effect of thyroid stimulating hormone on the development and progression of rat thyroid follicular cell tumors

Time course changes in cell proliferative activity of thyroid focal hyperplastic and tumorous lesions as well as blood thyroid-related hormones in male F344 rats initiated with N-bis(2-hydroxypropyl)nitrosamine (DHPN: 2800 mg/kg body weight, single s.c. injection) were examined following chronic administration of 0.1% sulfadimethoxine (SM) in the drinking water for 1, 4, 8, 12 and 16 weeks and at the end of a subsequent 4-week recovery period. Serum thyroid stimulating hormone (TSH) levels increased rapidly from week 1 of SM treatment, reaching a peak at week 8, and then decreased gradually with prolongation of treatment period, although remaining significantly elevated as compared with the corresponding controls at all time points up to week 16. Follicular cell hyperplasias and adenomas of the thyroid occurred from week 4 and carcinomas from week 8. All of these lesions showed high cell proliferative activities corresponding to high serum TSH levels during the early stage, but the levels in hyperplasias and adenomas decreased rapidly with prolongation of SM treatment. After the recovery period, serum TSH levels had returned to below the normal range and cell proliferation in follicular hyperplasias and adenomas had stopped or was very low. Some carcinomas demonstrating invasive growth also showed remarkable decreases in the cell proliferative activity. The results of our study strongly suggest that a high serum TSH level plays an important role in the early stage of thyroid tumorigenesis and that some tumors exhibiting invasive growth are still dependent on TSH stimulation.

Liver Tumor Promoting Effects of Fenbendazole in Rats

In order to examine whether fenbendazole has tumor-promoting activity, a total of 70 male Fischer 344 rats were initiated with a single intraperitoneal injection of 100 mg/kg of diethylnitrosamine (DEN) or were given the saline vehicle alone; beginning 1 wk later, rats were given a diet containing 3,600; 1,800; 600; 200; 70; or 0 ppm of fenbendazole for 8 wk. Subgroups of 5 rats each from the DEN+1,800; DEN+0; 1,800; and 0 ppm groups were euthanatized after 1 wk of fenbendazole treatment, and the remaining animals were euthanatized at 8 wk. After 1 wk, relative liver weights (ratios to body weights) were significantly increased in the DEN+1,800 and 1,800 ppm groups, and based on light microscopy, periportal hepatocellular hypertrophy was evident in these groups. After 8 wk, relative liver weights were significantly increased in the groups given ≥600 ppm with or without DEN initiation. Periportal hepatocellular hypertrophy, characterized by a marked increase in smooth endoplasmic reticulum, was observed in the groups given ≥600 ppm with or without DEN initiation. Induction of cytochrome P-450 (CYP) 1A2, 2B1, or 4A1 was noted in the fenbendazole-treated groups with or without DEN initiation; that associated with CYP 1A2 was most marked. Positive immunostaining for anti-CYP 1A1/2 or CYP 2B1/2 was observed diffusely in the livers of animals in the DEN+1,800 and DEN+3,600 ppm groups. The numbers and areas of connexin 32 (Cx32)-positive spots per square centimeter in centrilobular hepatocytes were significantly decreased in an almost dose-dependent manner with fenbendazole treatment after DEN initiation. In situ hybridization for Cx32 mRNA revealed a remarkable decrease in its expression in the centrilobular hepatocytes in the DEN+70 ppm group. The numbers of glutathione S-transferase placental-form positive single cells (plus mini foci) were significantly increased in the DEN+1,800 and DEN+3,600 ppm groups. Since those agents that induce CYP 2B1/2 isozymes and reduce Cx32 in centrilobular hepatocytes have been suggested to be liver tumor promoters, the present results indicate that fenbendazole may be a liver tumor promoter.

Chronic Toxicity and Carcinogenicity of Methylmercury Chloride in B6C3F1 Mice

A 2-year feeding study of methylmercury chloride (MMC: 0, 0.4, 2, or 10 ppm) was conducted in B6C3F1 mice (60 mice of each sex/group) to compare chronic toxicity and carcinogenicity results with those for ICR mice from our previous study in which males of the 10-ppm group showed an increased incidence of renal tumors without any abnormal in-life parameters. In B6C3F1 mice of the 10-ppm group, neurotoxic signs characterized by posterior paralysis were observed in 33 males after 59 weeks and in 3 females after 80 weeks. In males, a marked increase in mortality and a remarkable decrease in body weight gain were observed after 60 weeks. Toxic encephalopathy consisting of neuronal necrosis of the brain and toxic peripheral sensory neuropathy were induced in both sexes in this group. Chronic nephropathy, testicular atrophy, and glandular stomach ulcer increased in incidence in the males; chronic nephropathy also increased in incidence in females. In proliferative lesions, there were significant increases in the incidence of renal adenoma and/or carcinoma (16/60) and tubular cell hyperplasia (14/60) in males of the 10-ppm group, as compared to the control group. The incidence of chronic nephropathy also increased in males of the 2-ppm group. The results of this study indicate that the susceptibility of B6C3F1 mice to renal toxicity and renal carcinogenicity is comparable to that of ICR mice, and B6C3F1 mice are more sensitive to the chronic neurotoxic effects of MMC than are ICR mice.