Selenium and cancer: effects of selenium and of the diet on the genesis of spontaneous mammary tumors in virgin inbred female C3H/St mice

Inbred female C3H/St mice exhibit the normal incidence of spontaneous mammary adenocarcinoma of 80--100% if they are maintained on a standard commercial laboratory diet containing 0.15 ppm of selenium with meat and dried skimmed milk as major sources of protein. The tumor incidence drops to 42% if animals of the same strain are kept on a diet containing 0.45 ppm of selenium, with fishmeal as the main source of protein. The tumor incidence declines further to 25, 19 and 10% if the animals in addition receive 0.1, 0.5, and 1.0 ppm of selenium in the drinking water. Selenium supplementation at these levels has no noticable adverse effects on weight-grains and survival of the mice. Selenium supplmented groups of animals also remained tumor-free for longer periods than the unsupplemented controls. The results of this study indicate that a diet rich in seafoods and cereals provides more selenium and may in turn lower the probability of cancer development. Reference is made to the average human diet in the U.S.A., which only contains 0.07--0.15 ppm of selenium due to the comparatively low consumption of cereals and seafoods. An equivalent mouse diet would not have any cancer-protecting effect in the C3H/St mice of our study. Australian workers have reported significantly lower tumor incidence in a different strain of C3H mice if it was kept in Australia rather than in the U.S.A. We have found that the Australian feed contained three times more selenium than that employed in the U.S.A. and propose that this difference in selenium content was primarily responsible for these previous observations.     

Inhibition of the genesis of spontaneous mammary tumors in C3H mice: effects of selenium and of selenium-antagonistic elements and their possible role in human breast cancer.

The inhibitory effect of selenium on the genesis of spontaneous mammary tumors in C3H mice is statistically significant even at toxic levels of selenium (5 and 15 ppm of Se in form of selenite added to the supply water), no evidence for stimulation of tumor growth by selenium has been obtained. Arsenite lowers the tumor incidence at higher dosage (80 ppm of As in supply water) as well, but animals developing tumors under these conditions demonstrate significantly enhanced tumor growth rates. The addition of subtoxic concentrations of zinc (200 ppm in form of ZnCl2) to supply water containing 5 ppm of Se abolishes the cancer-protecting effect of selenium. The latter result is of possible importance with respect to the human breast cancer mortality experience: The calculated dietary zinc intakes of average adults in 28 countries correlate with the female age-corrected mortalities from breast cancer directly, with P less than 0.005. The zinc concentrations in whole blood from donors in different parts of the U.S.A. are also directly correlated with the female breast cancer mortalities.     

Effect of dietary selenium and tumor status on the retention of75Se by tissues and mammary tumors of DMBA-treated rats

The effects of the presence of mammary tumors on 75Se retention was examined in DMBA-treated rats. Tumor bearing rats fed varying amounts of Se exhibited an inverse linear dose response between dietary Se intake and tissue retention of 75Se in whole body, heart, lungs, ovaries, adrenals, spleen, and muscle. Tumor 75Se retention, however, was independent of the dietary intake of Se. Tumor bearing rats excreted more 75 Se label in the urine compared to both control rats fed the same amount of Se and DMBA-treated animals that remained tumor free. In the short term, no significant differences were seen in tissue retention of 75Se. By 7 d, the increased urinary excretion of the label resulted in significantly decreased retention of 75Se in blood, spleen, liver, lungs, and kidneys of tumor-bearing rats compared to tumor-free animals. The presence of tumors, however, did not affect the liver distribution of the label among cytosolic proteins. These results suggest that tumor bearing animals have an accelerated urinary excretion of Se compared to animals without tumors and that tumors either have a very slow turnover of Se or a low priority for the element.     

Effects of amphetamine on the development of MTV-induced mammary tumors in female mice.

Female C3H/He mice carrying the mammary tumor virus (MTV) were monitored for mammary tumor incidence and latent periods while submitted to a daily subcutaneous injection with amphetamine (0,4 mg/kg/day). Results show that amphetamine caused an increase in incidence and a decrease in latency of tumors compared with placebo. There was also appreciated a correlation with the lethality of mice.     

Increased fluidity of serum lipids and development of spontaneous mammary tumors in C3H mice

Summary The degree of lipid fluidity (LFU) was quantitatively monitored by fluorescence polarization analysis of the hydrocarbon fluorescent probe diphenylhexatriene when embedded in artificial and biological lipid complexes. The results have shown a marked increase in LFU in serum lipids associated with the development of spontaneous mammary tumors in C3H mice. An increase in serum LFU was observed during the initiation of primary tumors. The serum LFU further increases as a function of increase in the tumor volume. This increase was not observed when animals were given transplants of syngeneic, spontaneously arising mammary tumors or following implants of antigenically inert glass beads. Since the serum LFU in C57BL/6, NZB and A/JAX non-tumor-bearing mice was found to be significantly lower than in C3H non-tumor-bearing mice, it is suggested that alterations in the dynamics of serum lipids in the C3H system may have a direct relation to the induction and/or growth of spontaneous tumors in these mice. Moreover, experiments carried out with an artificial membrane model system have shown that the dynamics of a lipid complex are directly determined by its lipid composition. The three major parameters that determine the LFU of a lipid domain are: (a) the relative amounts of different phospholipids; (b) the molar ratio of cholesterol to phospholipids; and (c) the degree of saturation of the fatty acids. It is therefore suggested that alterations of this kind may occur in serum lipids during spontaneous mammary tumor development in C3H mice.Abbreviations DPH diphenylhexatriene - P fluorescence polarization - LFU lipid fluidity units - PBS phosphate-buffered saline Recipient of NIH Fellowship (IF32CA 06293-02) awarded by NCI     

Effects of dietary fat on mammary development relative to age and hormones in BALB/c mice

Earlier studies reported that mammary ducts grew faster if the 10% fat in the diet was composed of oils containing polyunsaturated fatty acids (corn oil: CO) compared to hydrogenated cottonseed oil (HCTO), which is devoid of such fatty acids. These experiments were primarily carried out in immature mice and left unanswered questions regarding the effects of dietary fats on more differentiated stages of mammary development. The use of transplanted ducts permitted the study of mammary growth rates in adult mice. If the diet was started when the animals were adults, there was no difference in the growth rate of those fed HCTO diet compared to those fed CO diet. However, when the diets were fed to immature mice, the mammary gland grew slower in mice fed the HCTO diet, confirming our earlier observations. The HCTO and CO diets caused no difference in the growth rate or morphology of fine ducts and alveoli that developed during pregnancy. Furthermore, no differences were seen in female mice following 6 weeks of progesterone administration begun at 3 weeks of age. Experiments that used male mice to examine the initial stages of mammary duct growth also showed that the effect of dietary fat was not observed when estrogen (E) or E and progesterone (P) were injected. In addition, there was no effect of dietary fat in ovariectomized 3-week-old females when any dose of E was administered from 0.01 to 1 microgram/day. Examination of the ovaries from mice fed either HCTO or CO diets from 3 to 9 weeks or 3 to 13 weeks of age showed that mice fed HCTO diet did not develop corpora lutea, while those fed CO diet had normal appearing ovaries. The HCTO diet inhibits normal maturation of the follicle and corpus luteum formation. We conclude that the effect of the dietary fat on the developing mouse is on the maturation of the ovary and subsequently on mammary growth.     

Prolactin as a promoter of initial progression of spontaneous mammary tumors in mice and lack of relationship to age

In a high mammary tumor strain of SHN virgin mice, the percent increase in the number of palpable mammary tumors during 3 weeks after the 1st tumor appearance was significantly retarded by ovariectomy and this retardation was prevented by pituitary grafting associated with the decrease and the increase in the circulating prolactin levels, respectively. A low mammary tumor strain of SLN virgin mice grafted with a single pituitary each at 2 and 5 months of ages developed mammary tumors 4 and 2 months after grafting (6 and 7 months of ages), respectively. However, there was no difference between groups in mammary tumor incidence at any month after mice in each group developed tumors first. Mammary tumor incidences of both groups were significantly higher than that of the untreated control at all ages examined. These findings have demonstrated that prolactin plays a key role in the initial progression of spontaneous mammary tumors of mice besides its prerequisite role in tumor development. They also suggest that there is no intrinsically age-related difference in prolactin effect on mammary tumorigenesis.     

Effect of dietary selenium deficiency on the in vitro fertilizing ability of mice spermatozoa

Selenium is an essential micronutrient for mammals, being integral part of antioxidant system. The aim of the study was to evaluate the effect of selenium deficiency on in vitro fertilization (IVF) capacity of spermatozoa and on oxidative stress in these cells. Male C57BL/6N mice were maintained on selenium-deficient or selenium-sufficient diets (0.02 or 0.2 ppm of selenium as selenomethionine, respectively) for 4 months. Liver glutathione peroxidase activity measurements were used to confirm selenium deficiency. Sperm quality and IVF capability among both groups were evaluated. To assess oxidative damage, lipid peroxidation as malondialdehyde production was determined in spermatozoa as well as the testes. Ultrastructural analyses of spermatozoa nuclei using transmission electron microscopy were also performed. The percentage of eggs fertilized with sperm from selenium-deficient mice was significantly decreased by approximately 67%. This reduced fertilization capacity was accompanied by increased levels of lipid peroxidation in both the testes and sperm, indicating that selenium deficiency induced oxidative stress. Consistent with this finding, spermatozoa from selenium-deficient animals exhibited altered chromatin condensation. Deficiency in dietary selenium decreases the reproductive potential of male mice and is associated with oxidative damage in spermatozoa.     

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.