Differential effect of dietary methionine on the biopotency of selenomethionine and selenite in cancer chemoprevention

The influence of a low methionine intake on the chemopreventive efficacy of selenomethionine versus selenite was compared in the 7,12-dimethylbenz[a]anthracene-induced mammary tumor model in rats. Animals were fed from weaning a purified 20% casein diet with or without 0.3% methionine supplementation. Selenomethionine or selenite, at a final concentration of 3 ppm of selenium (Se), was added to the diet starting 5 days after DMBA administration. Control rats continued to receive the basal diets which contained 0.1 ppm of Se. Results of the carcinogenesis experiment indicated that suboptimal dietary methionine significantly reduced the protective effect of selenomethionine in cancer prevention. In contrast, the efficacy of selenite was not affected. In rats given 3 ppm of selenomethionine, tissue Se was actually higher in those fed a diet with a suboptimal amount of methionine than in those with an adequate intake of methionine. On the other hand, dietary methionine did not influence the level of tissue Se in animals given selenite. An increase of dietary methionine to 0.6% did not enhance the efficacy of selenomethionine in cancer protection but would allow the use of a higher level of selenite without the accompanying adverse effects. The biological significance of Se utilization under suboptimal or adequate methionine intake was also assessed using the glutathione peroxidase assay in the liver of Se-deficient rats given graded levels of Se as either selenite or selenomethionine. The enzyme study demonstrated that low dietary methionine decreased the nutritional biopotency of selenomethionine in restoring glutathione peroxidase activity but not that of selenite. These experiments suggest that adequate methionine intake is required for the utilization of selenomethionine for nutritional and anticarcinogenic purposes.     

Dietary selenium supplementation modifies breast tumor growth and metastasis

The survival rate for breast cancer drops dramatically once the disease progresses to the metastatic stage. Selenium (Se) is an essential micronutrient credited with having high anticancer and chemopreventive properties. In our study, we investigated if dietary Se supplementation modified breast cancer development in vivo. Three diets supplemented with sodium selenite, methylseleninic acid (MSA) or selenomethionine (SeMet), as well as a Se‐deficient and a Se‐adequate diet were fed to mice before mammary gland inoculation of 4T1.2 cells. The primary tumor growth, the numbers of cancer cells present in lungs, hearts, livers, kidneys and femurs and several proinflammatory cytokines were measured. We found that inorganic selenite supplementation provided only short‐term delay of tumor growth, whereas the two organic SeMet and MSA supplements provided more potent growth inhibition. These diets also affected cancer metastasis differently. Mice fed selenite developed the most extensive metastasis and had an increased incidence of kidney and bone metastasis. On the other hand, mice fed the SeMet diet showed the least amount of cancer growth at metastatic sites. The MSA diet also provided some protection against breast cancer metastasis although the effects were less significant than those of SeMet. The cytokine profiles indicated that serum levels of interlukin‐2, interleukin‐6, interferon γ and vascular endothelial growth factor were elevated in SeMet‐supplemented mice. There was no significant difference in tumor growth and the patterns of metastasis between the Se‐deficient and Se‐adequate groups. Our data suggest that organic Se supplementation may reduce/delay breast cancer metastasis, while selenite may exacerbate it.     

Effects of dietary selenium on bis(2-oxopropyl)nitrosamine-induced carcinogenesis in Syrian golden hamsters

In studies designed to determine the influence of dietary Se on pancreatic carcinogenesis, Syrian golden hamsters were fed unsupplemented torula yeast diet or diet supplemented with 0.1 or 5.0 ppm Se, from sodium selenite, starting at 4 weeks of age until the termination of the study. In separate groups, hamsters were given the diet supplemented with 0.1 ppm Se until 5 days after carcinogen treatment. Then they were fed either the unsupplemented diet or the diet supplemented with 5.0 ppm Se until the end of the experiment. N-Nitrosobis(2-oxopropyl)amine (BOP; CAS; 60599-38-4) treatment was given as a single sc injection of 20 mg/kg (body wt) at 8 weeks of age, and surviving hamsters were killed 50 weeks later. As a measure of Se status, glutathione peroxidase (GSHPX) activities were determined in plasma, erythrocytes, and liver. Values were elevated in animals fed higher levels of dietary Se. BOP treatment depressed plasma GSHPX at 24 hours and elevated erythrocyte and liver values at 4 weeks. Pancreatic ductular adenoma yields were inhibited with each elevation of dietary Se in female hamsters fed the diets, both before and after BOP administration, and were further inhibited in females that were fed diets containing 0.1 ppm Se before BOP administration and that were changed to the unsupplemented or 5.0-ppm-supplemented diets after BOP was given. Pancreatic ductular adenoma yields were highest in all male groups given diets of 0.1 ppm Se before BOP administration, irrespective of the Se level after BOP was fed. Adenoma yields in males were lowest in hamsters fed unsupplemented diet, both before and after BOP treatment. Pancreatic carcinoma yields were low and not influenced by dietary Se. The incidence of hepatic necrosis was elevated in BOP-treated hamsters fed the unsupplemented diet, and that of biliary cystic adenomas was highest in the group fed 0.1 ppm Se before and after BOP treatment.     

Both dietary calorie and fat affect the growth of transplanted mammary-tumors in riii/sa mice - the effect of calorie is more profound than the effect of fat

The effects of dietary calories and/or fat on the growth of mammary tumor transplants, their expression of mouse mammary tumor virus (MMTV) and the incidence of lung metastasis were examined in RIII/Sa mice. Starting at 3-4 weeks of age, groups of female mice were fed either high isocaloric diets (16 kcal/day/mouse) containing 25% or 5% corn or fish oil or low isocaloric (10 kcal/day/mouse) diets containing 25% or 5% fish or corn oil. After one week, small pieces (2x2x2 mm) of tumor tissue, prepared from a transplantable mammary tumor, were inserted into the fourth pair of mammary glands of mice, and the mice maintained on their respective diets until sacrifice. All mice developed palpable tumors during a period of 3-4 weeks. After 12 weeks, all those mice that were assessed for tumor burden were sacrificed, tumor weight in each mouse determined, and the level of the expression of MMTV in the tumors evaluated by dot blot hybridization. Our results show that low isocalorie diets, regardless of the type or amount of fat, inhibited tumor growth by at least 60% in comparison to high isocalorie diets. However, mice fed low isocaloric diets containing fish oil were also found to produce smaller tumors (20-40%) as opposed to those mice fed similar, but corn oil containing diets. Fatty acid analyses of mammary tumors and liver tissue of mice fed corn oil and fish oil containing diets revealed that while normal and tumor tissues from both groups contained high levels of polyunsaturated fatty acids, the tissues of mice fed corn oil had the n-6, whereas the mice fed fish oil had the n-3 family of fatty acids. The levels of MMTV expression were found to be unaffected by either caloric or fat content in the diet. In a separate set of experiments, the effect of a low calorie diet on lung metastasis was determined, It was found that mice fed a low calorie diet produced significantly less metastatic lung nodules than those mice fed a high calorie diet: the mean survival time for the former group of mice was 106 days, as compared to only 71 days for the latter group of mice. In conclusion, we suggest that the amount of calories in a diet is more important than the amount or the type of fat in suppressing the growth of transplanted tumors and that a low calorie diet may also lower the incidence of lung metastasis.     

Different weekly changes in immune response in virus-transformed cell-injected mice fed two different diets

Changes in tumor development and in certain immune responses were investigated at 7-weekly intervals after subcutaneous injection of 5 X 10(5) herpes simplex virus Type 2-transformed cells (H238 cells) into male BALB/c mice fed 2 different diets. One diet contained 11% casein and 5% fat while the other had 11% supplemented wheat gluten and 30% fat. Weanling mice (140/group) were fed one or the other of the diets for 12 weeks before injection and subsequent testing of 15 injected and 5 non-injected mice from each diet group each week. In mice fed the low-fat diet containing casein both tumor incidence and tumor volume were significantly lower (P less than or equal to 0.05) than in the group fed the 30% fat diet containing supplemented wheat protein. The casein-fed mice also had less splenomegaly and a higher proportion of mature lymphocytes in the spleen during tumor growth. The proliferative capability of the spleen cells after phytohemagglutinin stimulation was enhanced 2 weeks after H238 cell injection only in the casein-fed mice.     

The effect of four chemical forms of selenium on mammary tumor incidence in BALB/c female mice treated with 7-12-dimethylbenz[a]anthracene

The study was conducted to determine the effect of four forms of selenium on inhibition of DMBA-induced mammary tumors. BALB/c virgin female mice were fed the AIN-76 diet containing 0.2 or 2.0 ppm Se as selenite, selenate, selenomethionine, or selenocystine prior to and for 6 months post DMBA-treatment. At necropsy, mammary glands were histologically treated for confirmation of adenocarcinomas and the livers were removed for analysis of glutathione-peroxidase (GSHPx) activity and selenium concentrations. Dietary levels or forms of selenium had no effect on body weights. Inorganic selenium fed at 2.0 ppm Se (selenite and selenate) decreased mammary tumor incidence, but organic selenium (selenomethionine and selenocystine) had no effect on mammary tumor incidence. Hepatic GSHPx activity was highest with the 2.0 ppm selenium as selenocystine diet, but hepatic selenium levels were highest with the 2.0 ppm selenium as selenite. This study showed that the dietary form of selenium affects inhibition of mammary tumorigenesis. Furthermore, the study suggested that the pathways for selenium incorporation into GSHPx and for tumor inhibition are different.     

Modulation of peroxidation in murine melanoma by dietary tyrosine-phenylalanine restriction, levodopa methylester chemotherapy, and sodium ascorbate supplementation

Treatment with the drug combination of levodopa methylester and benserazide, supplemental ascorbate, and dietary deficiencies of tyrosine and phenylalanine more than doubled the median survival time of female (C57BL/6 X DBA/2)F1 mice bearing B16 melanoma tumors. The mechanism for this antitumor effect was not well defined. This study was designed to test the hypothesis that the antitumor activity of levodopa methylester and ascorbate against B16 melanoma is related to the generation of free radicals of oxygen, which peroxidize lipid constituents of cell membranes leading to cell death. As an indication of lipid peroxidation, the individual and combined effects of drug treatment and ascorbate supplementation on host and tumor malondialdehyde levels were examined in mice fed one of three test diets (commercial, purified, or deficient) containing decreasing amounts of tyrosine and phenylalanine. Malondialdehyde levels were increased in the livers of all untreated tumor-bearing mice, which suggests that the tumor alters host antioxidant defenses. Drug treatment and ascorbate supplementation alone and in combination increased hepatic malondialdehyde levels inversely to the amounts of tyrosine and phenylalanine in the diet, and the effects of drug and ascorbate on malondialdehyde levels were additive. Plasma levels remained unchanged by drug treatment, ascorbate supplementation, or tumors in mice fed the commercial or purified diets. Higher levels were observed only in tumor-bearing mice fed the deficient diet and given both drug treatment and ascorbate supplementation. Changes in tumor malondialdehyde levels generally correlated with the effects of the drug and ascorbate on survival time of mice bearing B16 melanoma. Tumors from mice fed the commercial diet accumulated little malondialdehyde, and therapy was relatively ineffective in this dietary group. In mice fed purified or deficient diets, drug treatment and ascorbate supplementation alone increased survival and tumor malondialdehyde levels, but the level of peroxidation in mice receiving the ascorbate supplementation was low compared to its greater antitumor effect on B16 melanoma. Although ascorbate enhanced the peroxidative activity of the drug on B16 melanoma tumors, the effects of the drug and ascorbate on malondialdehyde levels were not additive. Ascorbate enhanced survival of tumor-bearing mice that were fed the deficient diet and that were treated with drug, which indicated that ascorbate supplementation acted via other mechanisms.(ABSTRACT TRUNCATED AT 400 WORDS)     

Dose-response studies of the effect of dietary butylated hydroxyanisole on colon carcinogenesis induced by methylazoxymethanol acetate in female CF1 mice

The effect of dietary butylated hydroxyanisole (BHA) on methylazoxymethanol acetate [(MAM AC) CAS: 592-62-1; methyl-ONN-azoxy)methanol acetate]-induced intestinal carcinogenesis was studied in female CF1 mice. BHA was added at levels of 0, 0.03, 0.1, 0.3, and 0.6% to the NIH-07 open-formula diet and at 0 and 0.6% to the AIN-76 semipurified diet and fed to mice, starting at 5 weeks of age until termination of the experiment. At 7 weeks of age, all animals except the vehicle-treated controls were given ip injections of MAM AC (15 mg/kg body wt for four times in 11 days for the low-dose group: total dose, 60 mg/kg body; 15 mg/kg body wt for eight times in 22 days for the high-dose group: total dose, 120 mg/kg body wt). With a low dose of carcinogen, the lung tumor incidence was inhibited in mice fed the NIH-07 diet containing 0.03-0.6% BHA and the AIN-76 diet containing 0.6% BHA compared to lung tumor incidence in those fed the diets without BHA; with a high dose of carcinogen, the inhibition was observed in mice fed the NIH-07 diet containing 0.1-0.6% BHA. Colon tumor incidence and colon tumor multiplicity (number of tumors per animal and number of tumors per tumor-bearing animal, respectively) were lower in mice fed the NIH-07 diets with 0.03-0.6% BHA or fed the AIN-76 diet with 0.6% BHA, as well as treated with a low dose of carcinogen, than in animals fed no BHA; with a high dose of carcinogen, colon tumor multiplicity and colon tumor incidence were inhibited in animals fed the NIH-07 diet containing 0.1-0.6% BHA. Consumption of the NIH-07 diets containing 0.03-0.6% BHA resulted in increased glutathione transferase activity of liver and small intestinal and colon mucosae in a dose-related manner.     

Effect of dietary fat on growth of MCF-7 and MDA-MB231 human breast carcinomas in athymic nude mice: relationship between carcinoma growth and lipid peroxidation product levels

Human breast carcinoma cell lines MCF-7 and MDA-MB231 were transplanted s.c. to female athymic nude mice at 3-4 weeks of age. At 7-10 days after transplantation, the mice were divided into groups and fed for 6-8 weeks one of the following semi-purified diets containing different amounts and types of fat, i.e. 5% corn oil, 20% corn oil, 20% butter, 19% beef tallow/1% corn oil and 19% fish (Menhaden) oil/1% corn oil. In addition experiments, the fish oil diets were supplemented with antioxidants (vitamin E, 8 g or 2000 IU/kg diet plus tertiary butyl hydroquinone, TBHQ, 4 g/kg diet) or ferric citrate (3 g/kg diet). Tumor peroxidation product levels were assessed by measuring 2-thiobarbituric acid reactants (TBA assay). At the termination of the studies (6-8 weeks of diet feeding) mean human breast carcinoma volume (MCF-7 and MDA-MB231) was the largest in mice fed the 20% corn oil diet, intermediate in mice fed the butter or beef tallow diets and the least in mice fed the fish oil diet. The difference in mean tumor volumes among mice fed the 20% corn oil diet and those fed the fish oil diet was significant (P less than 0.01). When comparing low (5% corn oil) and high (20% corn oil) fat diets, numerical increases in human breast carcinoma volume (MCF-7 and MDA-MB231) were consistently observed in the high-fat diet groups but these differences were not always significant. Tumor lipid peroxidation product levels were determined on the MDA-MB231 tumors; tumor lipid peroxidation levels were significantly (P less than 0.01) increased only in mice fed the fish oil diets. Supplementation of the fish oil diets with antioxidants (vitamin E + TBHQ) significantly reduced the level of tumor peroxidation products and significantly increased tumor volume (P less than 0.05). When tumor lipid peroxidation product levels in the fish oil plus antioxidant fed mice were reduced to the level of that observed in the tumors of the corn oil fed mice, no significant differences in tumor volumes were observed in these two groups. In contrast, supplementation of the fish oil diets with ferric citrate, significantly (P less than 0.05) increased tumor lipid peroxidation product levels and decreased tumor volume. Thus, the type of dietary fat can clearly affect the growth of human breast carcinomas (MCF-7 and MDA-MB231) maintained in athymic nude mice.(ABSTRACT TRUNCATED AT 400 WORDS)     

Inhibition by dietary organoselenium, p-methoxybenzene-selenol, of hepatocarcinogenesis induced by azoxymethane in rats

The effect of dietary p-methoxybenzeneselenol, a new organoselenium compound, on azoxymethane (AOM)-induced hepatocarcinogenesis was examined in female F344 rats. Semipurified diets containing 0 and 5 ppm p-methoxybenzeneselenol were fed to the rats, starting at 5 weeks of age until one week after the carcinogen treatment. At 7 weeks of age, all animals except the vehicle-treated controls were given weekly sc injections of AOM (15 mg/kg body weight, 3 times). At 34 weeks after the last AOM treatment, the liver neoplasm incidence and liver tumor multiplicity as well as the incidence of altered liver cell foci were significantly lower in AOM-treated rats fed the diet containing 50 ppm p-methoxybenzeneselenol (tumor incidence 19%, tumor multiplicity 0.45/rat, foci incidence 3.47/cm2) than in AOM-treated animals fed the diet without p-methoxybenzeneselenol (tumor incidence 66%, tumor multiplicity 2.24/rat, foci incidence 12.08/cm2). These results indicate that dietary p-methoxybenzeneselenol at a dose of 50 ppm inhibits AOM-induced hepatic tumorigenesis.