Involvement of mouse mammary tumor virus in spontaneous and hormone-induced mammary tumors in low-mammary-tumor mouse strains.

The involvement of the mouse mammary tumor virus (MTV) in spontaneous and hormone-induced mammary tumors in low-mammary-tumor mouse strains was studied by comparing the amounts of MTV RNA and MTV DNA sequences in mammary tumors and other tissues of mice with an without hormonal treatments. The following results were obtained. (i) Mammary tumors which appeared in C3H mice as a result of an infection with MTV contained more MTV DNA compared with noninfected organs; these mammary tumors also contained more MTV RNA than was present in lactating mammary gland cells. (ii) Hormonal stimulation by administration of excessive amounts of prolactin via hypophyseal isografts in C3Hf and O20 mice resulted in an increased expression of MTV RNA in the mammary glands. This elevated level of MTV RNA expression was, however, not maintained in the hormone-induced mammary tumors. (iii) Spontaneous mammary tumors in BALB/c mice contained similar levels of MTV DNA and MTV RNA sequences as were found in other cells of these animals.     

Effects of the MHC on hormonal induction of mammary tumors and function of hypophyseal isografts in the mouse

While the role of the H-2 complex in the resistance to virally induced tumors has been extensively studied, little is known about its influence on the development of epithelial tumors of non-viral etiology, although such tumors are most prevalent in humans. Therefore, we analyzed the role of the H-2 complex in susceptibility to mammary tumors induced by hormonal stimulation from heterotopic hypophyseal isografts in H-2 congenic strains from C57BL/10, BALB/c, and 020/A backgrounds. This method of induction allows an assessment of the effect ofH-2 genes on the function of various organs involved in this process. We found that the tumor susceptibility genes map to two segments: PE-S, and to the right of S. The mechanisms by which the H-2 complex affects the induction of mammary tumors in C57BL/10 congenic strains seem to include an influence on several factors involved in the hormonal stimulation, because the susceptible B10 congenic strains have higher plasma levels of prolactin and the H-2 complex also affects the growth of hypophyseal isografts. Their size correlates with tumor development in individual mice in the resistant C57BL/10 congenic strains. We reported previously H-2-dependent differences in levels of the estrogen receptor in hypophysis. For this study, we measured the levels of estrogen receptors in uteri to assess the tissue specificity of this effect of H-2. However, no influence of the H-2 complex on estrogen receptor levels was observed in uteri. Strains from BALB/c and 020 backgrounds developed mammary tumors much earlier than the B10 congenic strains, indicating a strong influence of non-H-2 genes.     

The induction of adenomyosis in mice by intrauterine pituitary isografts

Implantation of a single anterior pituitary into the uterine lumen induced the high incidence of adenomyosis in SHN strain of mice. The subserous nodules of the advanced state of adenomyosis appeared in larger numbers in the right uterine horns bearing the pituitary isografts than in the left ones bearing no isografts. Ovariectomy after implantation completely eliminated the occurrence of adenomyosis. Meanwhile, continuous treatments with estrogen in combination with progesterone recovered such pathological state in the ovariectomized mice receiving the pituitary isografts. The circulating levels of prolactin were consistently higher in mice given pituitary isografts than in the controls given isografts of pieces of submaxillary glands. The results indicate that, in this system, prolactin plays an important role in the genesis of adenomyosis, although the effect of ovarian sex steroids cannot be excluded.     

Effects of 2.45-GHz microwave radiation and phorbol ester 12-O-tetradecanoylphorbol-13-acetate on dimethylhydrazine-induced colon cancer in mice

The purpose of this study was to investigate the effects of 2.45 GHz microwave (MW) radiation on dimethylhydrazine (DMH)-induced colon cancer in mice. The subjects were 115 Balb/c mice 4 weeks of age. The animals were divided into group A (control), group B (DMH), group C (DMH + MW), and group D [DMH + 12-O-tetradecanoylphorbol-13-acetate (TPA)]. Radiation (10 mW/cm²) was delivered dorsally with the E field parallel to the mouse's long body axis in an anechoic chamber. Radiations were administered 3 hr daily, 6 days per week, over a period of 5 months. The average SAR was estimated to be 10–12 W/kg. During the course of radiation treatments, DMH was injected once per week. The tumor promoter TPA was administered once per week for 10 weeks, from the third week on, after the initial treatment. The incidence of tumors did not significantly differ between the three test groups (groups B, C, and D; P > 0.25). However, the number of tumors, the size of the tumors, and the incidence of protuberant and infiltrative types in tumor-bearing animals were higher in group D compared to groups B and C (P < 0.05). No difference was found between groups B and C (P > 0.25). The study indicates that 2.45 GHz microwave radiation at 10 mW/cm² power density did not promote DMH-induced colon cancers in young mice. The study also showed that TPA could accelerate colon tumor production if a tumor was initiated. © 1994 Wiley-Liss, Inc.     

Suppression of the development of uterine adenomyosis by danazol treatment in mice.

Inhibitory effects of danazol, an isoxazol derivative of synthetic steroid 17 alpha-ethinyl-testosterone, on the development of uterine adenomyosis, a pathological disorder of endometrial tissue defined as the presence of endometrial glands and stroma in the myometrium, were investigated in mice of SHN strain. Mice treated with 0.5 microgram danazol for 5 weeks during 4-9 weeks of age and killed at 21 weeks of age showed significantly lower incidence of the spontaneous development of adenomyosis than the age-matched intact control mice. The inhibitory effects of danazol were also evident in mice bearing pituitary isografts which were effective in inducing an early and a high incidence of adenomyosis. Furthermore, the treatment with danazol resulted in the decrease of serum levels of luteinizing hormone (LH) and prolactin (PRL) associated with hypofunction of ovaries and persistent diestrus. These results support the usefulness of danazol for the clinical treatment of gynecological disorders except for hypofunction of ovaries.     

Apparent synergism between radiation and the carcinogen 1,2-dimethylhydrazine in the induction of colonic tumors in rats

We have evaluated the interaction of radiation and 1,2-dimethylhydrazine (DMH) with respect to colon carcinogenesis in the Fischer 344 rat and have demonstrated the utility of this model for future more detailed mechanistic studies. In initial experiments, single doses of abdomen-only radiation (9 Gy) or DMH (150 mg/kg) were employed alone or in combination. Radiation was administered 3.5 days prior to the DMH. At 8 months post-treatment, the incidence of DMH-induced colon tumors was doubled by prior radiation exposure. When the protocol was repeated employing a DMH dose of 135 mg/kg with a 6-month observation period, the incidence of tumors induced by DMH alone was reduced, but the combination of radiation plus DMH still resulted in an augmentation of tumor incidence. When the protocol of radiation plus DMH was repeated three times at monthly intervals, a 15-fold increase in tumor incidence (from 5 to 74%) was observed at 6 months post-treatment. This finding demonstrates an apparent synergy between the radiation and the chemical carcinogen. Throughout these studies, the appearance of carcinomas was associated with preexisting colonic lymphoid nodules. The reproducibility of tumor induction as well as range of tumor incidence generated by variations in this system may be adequately sensitive to examine the combination of much lower doses of radiation and/or chemical carcinogen. The relationship between existing lymphoid aggregates which alter local epithelial cell kinetics and which are associated with fenestrations in the basement membrane, and the development of colon cancer in congruent sites may assist in defining dose-response curves for combined agents as well as providing a system for evaluating the mechanisms underlying their interactions.     

Fenugreek seeds modulate 1,2-dimethylhydrazine-induced hepatic oxidative stress during colon carcinogenesis

1,2-dimethylhydrazine (DMH) is a colon carcinogen which undergoes oxidative metabolism in the liver. We have investigated the modulatory effect of fenugreek seeds (a spice) on colon tumor incidence as well as hepatic lipid peroxidation (LPO) and antioxidant status during DMH-induced colon carcinogenesis in male Wistar rats. In DMH treated rats, 100% colon tumor incidence was accompanied by enhanced LPO and a decrease in reduced glutathione (GSH) content as well as a fall in glutathione peroxidase (GPx), glutathione S-transferase (GST), superoxide dismutase (SOD) and catalase (CAT) activities. Inclusion of fenugreek seed powder in the diet of DMH treated rats reduced the colon tumor incidence to 16.6%, decreased the LPO and increased the activities of GPx, GST, SOD and CAT in the liver. We report that fenugreek modulates DMH-induced hepatic oxidative stressduring colon cancer     

Vanadium and 1, 25 (OH)2 vitamin D3 combination in inhibitions of 1,2, dimethylhydrazine-induced rat colon carcinogenesis

The current investigation demonstrates the antitumor effects of combined supplementations of vanadium (V) (4.27 micromol/L drinking water ad libitum) and 1alpha, 25-dihydroxy vitamin D(3) (Vitamin D(3)) (0.3 mug/100 muL propylene glycol per os twice a week) on 1, 2 dimethylhydrazine (DMH) (20 mg/kg body weight) induced rat colon carcinogenesis. There was a significant reduction in incidence (70%), multiplicity (P<0.0001) and volume (P<0.01) of colon tumors. HPLC-fluorescence assay detected the combinatorial actions of V and Vitamin D(3) against DMH-induced colonic O(6)-methylguanine DNA adducts formation (at four sequential time points; ANOVA, F=13.56, P<0.01). Simultaneous inhibition of DNA single strand breaks (P<0.001) indicates the potency of the combination regimen in limiting the initiation event of colon carcinogenesis. Immunohistochemical analysis revealed that the effect of V and vitamin D(3) occurred through suppression of cell proliferation (BrdU-LI: P<0.001) along with an induction of apoptosis (TUNEL-LI: P<0.01). The immunoexpression of tumor suppressor p53 and downregulation of antiapoptotic protein BCl-2 in subsequent immunofluorescence assay further provide strong evidence for the combinatorial inhibitory actions of vanadium and vitamin D(3) against DMH-induced rat colon carcinogenesis.     

Folic acid and sodium butyrate prevent tumorigenesis in a mouse model of colorectal cancer

Colorectal cancer is a leading cause of morbidity and mortality worldwide, and its incidence has been increasing in recent years. The role of epigenetic modifications, including DNA methylation and histone modifications, has only recently been investigated. In this study, the effects of epigenetic agents such as folic acid (FA) and sodium butyrate (NaBu) on the development of colorectal cancer induced by 1,2-dimethylhydrazine (DMH) using ICR mice was examined. Of the mice treated in a chemopreventive manner with epigenetic agents, FA and NaBu, 15–50% developed colorectal cancer at 24 weeks compared with a 95% incidence of colorectal cancer in DMH-treated control mice. Folate deficiency can alter cytosine methylation in DNA leading to inappropriate activation of the proto-oncogene c-myc. We detected lower levels of p21WAF1 gene expression in colorectal cancer samples, as well as significantly lower levels of acetylated histone H3, compared with samples from corresponding normal colorectal mucosa. In contrast, administration of NaBu increased levels of p21WAF1 mRNA and p21WAF1 protein, and was associated with an accumulation of histone acetylation. In summary, our results show that FA and NaBu reduce the incidence of colorectal cancer induced by DMH-induced in ICR mice, and therefore we hypothesize that targeting epigenetic targets should be further investigated for the prevention of colorectal cancer in humans.     

Hereditary hydronephrosis in C57BL/KsJ mice.

We sought to determine if the incidence of renal hydronephrosis in male C57BL/KsJ mice increased with age and if grossly normal kidneys would develop hydronephrosis over time. Spontaneous hydronephrosis was found incidentally in 32% of 234 male C57BL/KsJ mice killed as pancreas donors for islet transplantation experiments. The incidence of hydronephrosis increased with age; the incidence was 15% in 6- to 8-week-old mice, 52% in 8- to 10-week-old mice and 63% in 11- to 15-week-old mice (P less than 0.001). Additional mice received islet isografts beneath the renal capsule. Only mice with grossly normal kidneys received islet grafts. These same kidneys were then re-examined when the graft recipients were killed at the end of the experiment and the incidence of hydronephrosis was determined. The conversion of normal kidneys to hydronephrotic kidneys increased with the time since islet transplantation. Kidneys re-examined less than 4 weeks since transplantation had only 5.8% new hydronephrosis, while those re-examined later than 4 weeks after transplantation had a new hydronephrosis incidence rate of 40% (P less than 0.001). Our findings suggest that hydronephrosis is hereditary but not congenital, that it develops rapidly, and that it can complicate experiments using this strain. This may also represent a useful new animal model of progressive hydronephrosis.     

比格犬垂体囊肿的组织形态学研究

目的研究比格犬垂体囊肿自发性病变的发生情况,以建立适用于GLP的实验动物背景资料。方法采用常规组织学方法,对60只8～10月龄实验对照组比格犬垂体进行组织病理学检查,光学显微镜下描述垂体囊肿的组织形态学特点并统计其发生率。结果囊肿多出现在垂体的远侧部,囊壁由一层扁平或立方状上皮构成,囊腔内可见黏液状物;囊肿总体发生率为23.3%,其中雌性为13.3%,雄性为33.3%。结论应加强比格犬自发病变的病理监测,为药物安全性评价提供实验动物的背景资料。     

Increase of DNA synthesis in uterine adenomyosis in mice with ectopic pituitary isograft.

Ectopic pituitary isografts (EPI) have been found to induce a high incidence of uterine adenomyosis in SHN mice. All the SHN mice given EPI in the right uterus at 40 days of age developed uterine adenomyosis, and more than 80% of mice showed the genesis of subserosal nodules, an advanced state of adenomyosis, 65 days after EPI. Activities of both thymidylate synthetase and thymidine kinase, i.e. DNA-synthesizing enzymes in de novo and salvage pathways of pyrimidine metabolism, respectively, were significantly increased in EPI-induced uterine adenomyosis to approximately 2-fold those in normal control uteri. Bromodeoxyuridine-immunoreactive cells were regarded as the cells in S phase, and the number in the endometrial epithelium and stroma in EPI-induced uterine adenomyosis was more than 1.5-fold that in normal control uteri. EPI may affect the genesis of uterine adenomyosis generally, but not locally, because there were no differences between the right uterus with EPI and the left without EPI in the incidence of adenomyosis, histology or DNA-synthesizing enzyme activities.     

Effects of low copper intake on dimethylhydrazine-induced colon cancer in rats.

Rats fed low copper show a high incidence of dimethylhydrazine (DMH)-induced colon tumors compared with rats fed very high Cu. The difference could be due to Cu deficiency in the low group or to Cu toxicity in the high group. In the present study, rats fed low Cu (0.2 ppm) showed greater DMH-stimulated colon tumorigenesis than rats fed adequate Cu (8 ppm). Differences were seen in the number of rats developing tumors (5 of 11 vs 1 of 10), total tumors (7 vs 2), and average tumor mass (1.02 g vs 0.29 g). Low Cu intake did not cause any general DMH toxicity as assessed by body weight gain. To prevent Cu deficiency-induced mortality, low Cu feeding was begun in postweanling rats (weight, about 80 g) housed in groups of five to six, rather than individually. This limited the effects of low Cu feeding to only a moderate Cu deficiency based on several parameters, including three Cu antioxidant enzyme activities. Group-housed rats fed marginal Cu levels (2.5 ppm) showed normal Cu status, and DMH produced only one tumor in 10 rats. In conclusion, high DMH-induced colon tumorigenesis can be found in rats with low activities of Cu antioxidant enzymes.     

Effects of cholestyramine on 1,2-dimethylhydrazine-induced enteric carcinoma in germfree rats.

Oral administration of 1,2-dimethylhydrazine (DMH) induced intestinal neoplasms in germfree rats. A supplement of 2% cholestyramine resin in the diet increased the frequency of DMH-induced intestinal tumors and accelerated malignant transformation. Bile acids in the cecal content were determined with and without cholestyramine in order to obtain a correlation between the bile acid metabolism and the enteric carcinogenesis.     

The age-related tumor incidence in Wistar-Imamichi rat

The age-related incidences and types of spontaneous tumors were studied in 320 male and 354 female Wistar-Imamichi rats reared up to 130 weeks of age. The tumor incidence increased abruptly between 53 and 78 weeks of age, and 170 males and 269 females were shown to bear tumors during the observation period. Multiple tumors occurred in 62 males and 115 females. Most common were hypophyseal (male 69: female 224), mammary gland (29:99), testicular (74:0) and adrenal gland (26:21) tumors. The incidences of hypophyseal and testicular tumors increased with age. Tumors occurred in later stages of the observation period in the ovary, uterus and vagina (0:27), thyroid and parathyroid (13:12), skin (8:8), spleen and lymph nodes (8:7), pancreas (9:5), liver (3:7), lung (3:3), thymus (1:4), omentum and mesenterium (2:3), stomach and intestine (2:2), kidney and urinary bladder (1:2), right femur (0:1), and brain (0:1).     

Fate of 3H-thymidine labelled myogenic cells in regeneration of muscle isografts

Summary Intact and denervated extensor digitorum longus (EDL) muscles of 20-day-old inbred Lewis-Wistar rats were labelled with ³H-thymidine. Ninety minutes after the injection of the isotope 4.0% of the nuclei were labelled in the intact (i.e. innervated) and 9.6% in the muscles, denervated 3 days before administration of the isotope. The labelled EDL muscles were grafted into the bed of the previously removed EDL muscles of inbred animals and these isografts were studied 30 days later.In the EDL muscles, regenerated from innervated isografts only occasionally labelled endothelial cells were found whereas in the muscles regenerated from denervated isografts also parenchymal muscle nuclei were regularly labelled. The incidence of labelled nuclei in the regenerated EDL muscles was, however, about 20 times lower than in the donor EDL muscles. The present experiments provide a direct proof of utilization of donor satellite cell nuclei for regeneration in grafted muscle tissue. With respect to the low incidence of labelled nuclei in regenerated EDL muscles, other sources of cells apparently also contribute to the regeneration process.     

Effects of ovariectomy on microsatellite instability in rat colon tumors induced by 1,2-dimethylhydrazine

To study the effects of ovariectomy on tumorigenesis and microsatellite instability (MSI) in rat colon tumors induced by 1,2-dimethylhydrazine, to elucidate the association between postmenopausal ovarian hormones depletion and MSI pathway in colorectal tumorigenesis. Forty female Wistar rats were randomly divided into two groups: Ovariectomized (Ovx) group and Sham-ovariectomized (Sham-Ovx) group. All rats were injected intraperitoneally with 1,2-dimethylhydrazine (DMH) (20 mg/kg b.w) once a week for 20 weeks. Ten weeks after the final DMH injection, all the rats were sacrificed to collect tumors. Microsatellite instability of six microsatellite loci was detected using fluorescent PCR followed by fragment analysis on automatic DNA sequencer with GeneScan 3.7 software. The tumor multiplicity in the OVX group was significantly higher than that in the Sham-OVX group (3.6 ± 1.4 vs. 2.4 ± 1.6, P < 0.05). The incidence of MSI-positive tumors in OVX group was higher than that in Sham-OVX group (32.1 vs. 10.8%, P < 0.05).The incidence of tumors showing MSI at multiple loci in OVX group was also higher than that in Sham-OVX group (18.9 vs. 2.7%, P < 0.05). Ovariectomy increased tumor formation and the frequency of MSI in DMH-induced colon tumors. It implied that postmenopausal ovarian hormones depletion might influence colorectal tumorigenesis through MSI pathway.     

Spontaneous tumors in nude mice: effect of the viable yellow gene.

The incidence and type of spontaneous tumors in athymic nude (nu/nu) mice (partially inbred in CBA/H background) which were also carrying the viable yellow gene (Avy, derived from C57BL/6JAvy mice), were comparable to those observed in the phenotypically normal nu/+ and +/+ control crosses carrying the Avy gene. The Avy gene increases the incidence of spontaneous and induced tumors in most mouse strains. These results would argue against the thymus dependency of the putative immunological surveillance mechanisms.     

Effect of the mitochondria-targeted antioxidant SkQ1 on development of spontaneous tumors in BALB/c mice

The mitochondria-targeted antioxidant SkQ1 (10-(6′-plastoquinonyldecyl)triphenylphosphonium) is a new pharmaceutical substance with a wide spectrum of effects including increase in lifespan of laboratory animals (for example, of BALB/c mice males) and inhibition of development of some experimental tumors and also of tumor cell growth. In this work, the effects of SkQ1 on development of spontaneous tumors in female and male BALB/c mice housed in an SPF-class vivarium were studied. We found that the addition of SkQ1 to drinking water at the dose of 1 and 30 nmol/kg body weight per day throughout the lifespan modified the spectrum of spontaneous tumors in the female mice, decreasing the incidence of follicular lymphomas. SkQ1 at the dose of 1 nmol/kg per day also suppressed the dissemination of these neoplasms, but it did not significantly influence the overall incidence of benign and malignant tumors (including primary multiple tumors) or the lifespan of the tumor-bearing mice (both males and females). Hence, the previously described ability of SkQ1 to increase the lifespan of laboratory BALB/c mice is not related to its anticarcinogenic activity.     

Effect of simulated American,Bulgarian, and Japanese human diets and of selenium supplementation on the incidence of virally induced mammary tumors in female mice

In attempts to simulate the effects of diet on human breast cancer development groups of female C3H mice infected with mammary tumor virus (MMTV-) were maintained on diets formulated to resemble the typical American, Bulgarian, and Japanese human diets. The incidence of mammary tumors was the highest (84%) in group of mice receiving the simulated meat- and fat-rich American diet, which was also low in selenium (Se content: 0.15 ppm). The appearance of mammary tumors was delayed in the mice maintained on the simulated Bulgarian diet, and the final tumor incidence (27%) paralleled the correspondingly lower Bulgarian breast cancer incidence. The simulated Bulgarian diet contained more Se (0.25 ppm), and was lower in fat, meat, and sugar and higher in complex carbohydrates (cereals) than the simulated American diet. In the mice fed the simulated Japanese diet, the appearance of mammary tumors was also delayed, and the tumor incidence was diminished to 47%. In this diet, fish meal was a major source of Se, which is known to have low bioavailability. Additional supplementation of the Japanese-type diet with bioavailable Se (1 ppm) lowered the tumor incidence to 10%. Based on these studies, recommendations are made for breast cancer risk reduction by dietary means.