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.     

Exposure to flaxseed or its purified lignan during suckling inhibits chemically induced rat mammary tumorigenesis

Previous studies have shown that feeding flaxseed (FS) or its lignan secoisolariciresinol diglucoside (SDG) to rat dams during lactation enhances the differentiation of rat mammary gland in the female offspring. This study determined whether exposure to a diet with 10% FS or SDG (equivalent to the amount in 10% FS) during suckling could protect against 9,10-dimethyl-1,2-benzanthracene (DMBA)-induced rat mammary tumorigenesis later in life. Dams were fed the AIN-93G basal diet (BD) throughout pregnancy. After delivery, dams were randomized to continue on BD or were fed BD supplemented with 10% FS or SDG during lactation. Three-day urine of dams was analyzed for mammalian lignans. After weaning, all offspring were fed BD. At postnatal Days 49 to 51, during proestrus phase, offspring were gavaged with 5 mg of DMBA. At Week 21 post-DMBA administration, compared with the BD group, the FS and SDG groups had significantly lower (P < 0.05) tumor incidence (31.3% and 42.0% lower, respectively), total tumor load (50.8% and 62.5% lower, respectively), mean tumor size (43.9% and 67.7% lower, respectively), and tumor number (46.9% and 44.8% lower, respectively) per rat. There was a significant decreasing trend (P < 0.05) in final tumor weights in rats fed FS or SDG. The high urinary lignan excretion in dams fed with FS or SDG corresponded with the reduced tumor development. The FS and SDG groups did not differ significantly in tumor indices, indicating that the effect of FS is primarily due to its SDG. There were no significant changes in selective reproductive indices measured among dams and offspring. In conclusion, exposure to FS or SDG during suckling suppressed DMBA-induced rat mammary tumorigenesis, suggesting that exposure to lignans at this early stage of mammary gland development reduces susceptibility to mammary carcinogenesis later in life without adverse effects on selective reproductive indices in dams or offspring.     

Influence of fatty acid‐free diet on mammary tumor development and growth rate in HER‐2/neu transgenic mice

Numerous investigations have found a relationship between higher risk of cancer and increased intake of fats, while results of clinical studies of fat reduction and breast cancer recurrence have been mixed. A diet completely free of fats cannot be easily administered to humans, but experimental studies in mice can be done to determine whether this extreme condition influences tumor development. Here, we examined the effects of a FA‐free diet on mammary tumor development and growth rate in female FVB‐neu proto‐oncogene transgenic mice that develop spontaneous multifocal mammary tumors after a long latency period. Mice were fed a fatty acid‐free diet beginning at 112, 35, and 30 days of age. In all these experiments, tumor appearance was delayed, tumor incidence was reduced and the mean number of palpable mammary tumors per mouse was lower, as compared to standard diet‐fed mice. By contrast, tumor growth rate was unaffected in mice fed the fatty acid‐free diet. Plasma of mice fed the fatty acid‐free diet revealed significantly higher contents of oleic, palmitoleic and 20:3ω9 acids and lower contents of linoleic and palmitic acids. In conclusion, these findings indicate that a FA‐free diet reduces tumor incidence and latency but not tumor growth rate, suggesting that a reduction in dietary FAs in humans may have a protective effect on tumorigenesis but not on tumors once they appear. J. Cell. Physiol. 228: 242–249, 2013. © 2012 Wiley Periodicals, Inc.     

Antitumor effects of atorvastatin in the chemoprevention of rat mammary carcinogenesis

Epidemiological studies indicate that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or statins, play a role in inhibition of several human neoplasia including breast cancer. In this study, chemopreventive effects of atorvastatin in N-methyl-N-nitrosourea-induced mammary carcinogenesis in female rats were evaluated. Atorvastatin was administered in the diet at two concentrations: 10 mg/kg (ATOR 10) and 100 mg/kg (ATOR 100). Atorvastatin treatment began 8 days prior to carcinogen administration and subsequently continued for 15 weeks till the end of the experiment. Atorvastatin at a higher dose suppressed tumor frequency by 80.5% (P = 0.0008) and tumor incidence by 49.5% (P = 0.015), and extended latency period by 14 days (P = 0.076) when compared to the control group. Atorvastatin at a lower dose did not significantly alter tumor parameters in comparison with the control group. In the specimens of mammary tumors, atorvastatin (in the ATOR 100 group) significantly decreased mRNA expression of Bcl-2 gene but non-significantly increased Bax mRNA expression compared to control group. Atorvastatin administration did not alter serum concentration of triacylglycerols, total cholesterol, and LDL cholesterol in comparison with controls. This study is the first report on tumor suppressive effect of atorvastatin in rat mammary carcinogenesis.     

Reduction of enhanced mammary carcinogenesis in LA/N-cp (corpulent) rats by energy restriction

Restriction of energy intake significantly reduces mammary tumorigenesis in normal rats exposed to carcinogens. Genetically obese LA/N-cp (corpulent) female rats were given 7,12-dimethylbenz[a]anthracene and fed purified diets ad libitum or restricted to 60% of the ad libitum caloric intake. Phenotypically lean littermates were also fed ad libitum. Obese animals developed large mammary tumors more rapidly than genetically normal rats so that 100% of the animals had tumors in less than 16 weeks. Only 21% of the lean animals developed tumors; the energy restricted obese animals had a tumor incidence of 27%. Although obese rats fed the restricted diet weighed significantly less than those fed ad libitum, percent body fat was not reduced, indicating that lean tissue was affected more. Obese animals were markedly hyperinsulinemic (1003 +/- 193 microunits/ml) and energy restriction reduced this to 328 +/- 41; the lean animals had insulin levels of 12 +/- 2. Tumor-bearing rats had higher insulin levels than rats without tumors. These data suggest that body fatness is not directly associated with risk of carcinogenesis. Lean body mass, adipose tissue mass, and their interaction with insulin in its capacity as a growth factor rather than body fatness per se may be determinants of tumor promotion.     

Effect of Siamese cassia leaves on the activities of chemical carcinogen metabolizing enzymes and on mammary gland carcinogenesis in the rat.

Male Wistar rats were fed AIN-76 semipurified diet or diet containing 5% ground lyophilized Siamese cassia leaves for 2 weeks before sacrifice. Hepatic S9 fractions were prepared and assayed for the level of cytochrome P450 (P450), the activities of monooxygenase, i.e., aniline hydroxylase (ANH), aminopyrine-N-demethylase (AMD) as well as the capacity to metabolically activate the mutagenicities of aflatoxin B(1) (AFB(1)) and benzo(a)pyrene (B(a)P). In addition, the activities of detoxificating enzymes such as glutathione-S-transferase (GST) and UDP-glucuronyltransferase (UGT) were also measured. It was found that feeding of Siamese cassia leaves significantly reduced the activities of hepatic ANH and AMD as well as the capacity to activate the mutagenicity of AFB(1) towards Salmonella typhimurium TA100, being 31, 73 and 41% of control group, respectively. It also slightly decreased, but not significantly, the capacity to activate the mutagenicity of B(a)P towards S. typhimurium YG1029. On the other hand, however, the activities of both GST and UGT were markedly increased in those animals, being 250 and 220% of control animals. The anticarcinogenic potential of Siamese cassia leaves was also investigated in female Sprague Dawley rats treated with 9,10-dimethyl-1,2-benzanthracene (DMBA). The animals were fed control diet or diet containing ground lyophilized Siamese cassia leaves 2 weeks prior to and 1 week after intragastrically administration of DMBA, and then they were placed on a pellet diet for additional 25 weeks. Interestingly, it was found that feeding of diet containing 2.5 and 4% Siamese cassia leaves resulted in a significant decrease in the multiplicity of mammary gland tumors as well as a slight delay of the onset of tumor development. The incidence of tumors in the group fed 4% Siamese cassia leaves, but not in the 2.5% group, was lowered, although not significantly, than that of control group. The results in the present study therefore demonstrated that Siamese cassia leaves possess phase II enzyme inducing property as well as the ability to reduce some phase I enzyme activities in rat liver. This Thai vegetable also exhibit cancer chemopreventive potential, at least against DMBA-induced mammary gland carcinogenesis which may be partly due to phase II inducing capacity as well as phase I inhibitory activity.     

Influence of caloric restriction and exercise on tumorigenesis in rats

Underfeeding or caloric restriction have been shown to inhibit the growth of spontaneous, transplanted, or chemically induced tumors in rats and mice. At 40% caloric restriction, growth of 7,12-dimethylbenz(a)anthracene-induced mammary and 1,2-dimethylhydrazine-induced colonic tumors is inhibited significantly even when the restricted diet contains twice as much fat as the control diet. Some inhibitory effects become evident even at 10% caloric restriction. In studies involving high fat diets, we find that rats receiving 20% fat ad libitum exhibit significantly higher 7,12-dimethylbenz(a)anthracene-induced mammary tumor incidence, multiplicity, and weight than rats ingesting the same amount of fat daily, but in a diet containing 25% fewer calories. In a study of intermittent ad libitum and restrictive feedings, chemically induced tumorigenicity varies inversely with feed efficiency. Exercise has also been shown to inhibit tumor growth. Sedentary rats fed ad libitum have a 108% higher incidence of 1,2-dimethylhydrazine-induced colon tumors than rats fed ad libitum but subjected to vigorous treadmill exercise. Caloric flux (either reduced intake or increased outflow) appears to reduce tumorigenicity in rodents.     

Effect of dietary zinc intake on N-methyl-N-nitrosourea-induced mammary tumorigenesis in rats

Numerous studies have shown that zinc nutrition influences the growth of several types of tumor. However, the influence of zinc nutrition on mammary tumorigenesis is not known. To study the effects of dietary zinc intake on N-methyl-N-nitrosourea (MNU)-induced mammary tumorigenesis, female Sprague-Dawley rats were fed an egg-white-based diet providing 3 (Z3), 12 (Z12), or 31 (Z31) mg zinc/kg diet ad libitum. In addition, two pair-fed controls, PFZ12 and PFZ31, were also included. Fourteen weeks after MNU injection, cumulative tumor incidence and total number of tumors were lower in Z3 rats than in Z12 and Z31 rats. Cumulative tumor incidence and total number of tumors were lower in Z3 rats than in PFZ12 rats, but were the same as in PFZ31 rats. Cumulative tumor incidence and total number of tumors were also lower in pair-fed controls than in their corresponding ad libitum controls, but were the same between the ad libitum controls. Overall, the results showed that the effect of marginal zinc deficiency on MNU-induced mammary tumorigenesis in rats was primarily the result of a reduced feed intake associated with marginal zinc deficiency rather than zinc per se.     

Influence of wheat bran on NMU-induced mammary tumor development, plasma estrogen levels and estrogen excretion in female rats.

In our animal experiments the hypothesis was tested that a high-fiber (HF) diet reduces tumor promotion by interruption of the enterohepatic circulation resulting in lowered estrogen exposure of the estrogen-sensitive tissue. In the first experiment the development of N-nitrosomethylurea (NMU) induced mammary tumors was investigated. One group of rats (HF) was fed a HF diet (11% fiber, based on wheat bran), the other group (LF) fed a low-fiber diet (0.5% fiber, based on white wheat flour). Tumor incidence (90 and 80%, respectively) and latency (121 and 128 days, respectively) were similar in the HF and LF groups. Compared to the LF group, HF rats had lower tumor weights (0.16 vs 0.55 g; P less than 0.01) and a slightly lower tumor multiplicity (1.8 vs 2.8 tumors per tumor-bearing rat). These differences were reduced after adjustment for body weight. In a second experiment rats, not treated with the carcinogen, were kept on the same HF and LF diets. From these rats 24-h urine and feces and orbital blood samples were collected for analysis of (un)conjugated estrogens. The excretion of both free and conjugated estrogens in fecal samples was about 3-fold higher in HF rats than in LF rats. During the basal period of the cycle urinary excretion of estrone was lower in HF rats (mean 9.7 ng/day) than in LF rats (mean 13.0 ng/day; P less than 0.05). It is concluded that wheat bran interrupts the enterohepatic circulation of estrogens, but plasma levels are not affected. Whether the development of mammary tumors is reduced by the introduction of specific components of wheat bran, or by a reduced body weight due to a lower (effective) energy intake remains to be determined.     

Effect of molybdenum supplementation onN-nitroso-N-methylurea-induced mammary carcinogenesis and molybdenum excretion in rats

Molybdenum (Mo) supplementation reduces the incidence of nitrosamine-induced tumors in the esophagus and forestomach of laboratory animals, and the incidence of mammary cancer in female rats induced byN-nitroso-N-methylurea (NMU). The present study was conducted to evaluate the effect of graded amounts of Mo on NMU-induced mammary carcinogenesis, and on the excretion of Mo and copper (Cu). Female Sprague-Dawley rats aged 5 wk were givenad libitum a low-Mo (0.026 mg/kg) diet and deionized water. After 15 d, a single SC injection of 50 mg NMU/kg body wt was administered to each of 30 rats in groups 2–5. Eight rats in group 1 served as untreated control. One week after the carcinogen treatment, 0.1, 1.0, or 10 mg Mo from sodium molybdate were added to each liter of drinking water for groups 3, 4, and 5, respectively. Groups 1 and 2 did not receive any Mo supplementation. After the rats had been Mosupplemented for 38, 67, and 85 d, 48-h urine and fecal samples were collected from the same 48 rats, and Mo and Cu were determined. Molybdenum seemed to have little effect on Cu excretion. At each time interval, animals fed 0 or 0.1 mg Mo/L excreted more Mo in feces than in urine, whereas rats fed 1 and 10 mg Mo/L water excreted more Mo in urine than in feces, which indicates that Mo absorption was not easily saturated as the amount of Mo increased. However, the liver became saturated with Mo when 0.1–1 mg Mo/L was fed. The total number of palpable tumors per group 101 d after NMU administration was 109, 115, 101, and 81, and the total carcinomas per group were 92, 96, 86, and 65 for the animals in groups 2–5, respectively. The results indicate that supplemental Mo in the amount of 10 mg/L of drinking water inhibited mammary carcinogenesis.     

Effects of dietary oyster extract on lipid metabolism, blood pressure, and blood glucose in SD rats, hypertensive rats, and diabetic rats

Oyster extract was prepared by hydrolysis of oyster protein with proteases, Aloase (a protease from Bacillus subtilis), and Pancitase (a protease from Aspergillus oryzae). Rats were fed a diet containing 20% casein (the control diet) or 15% casein and 5% oyster extract (the oyster extract diet) as the protein source. The oyster extract diet exerted a significant reduction in serum cholesterol and liver triglyceride concentrations as compared with the control diet in Sprague-Dawley (SD) rats fed cholesterol-supplemented diets for 4 weeks. The activities of cytosolic fatty acid synthase and glucose-6-phosphate dehydrogenase were significantly lower in the oyster extract group than in the control group in the liver of SD rats. Hepatic cholesterol and triglyceride concentrations were significantly lower in spontaneously hypertensive (SH) rats and Otsuka Long-Evans Tokushima Fatty (OLETF) rats, type 2 diabetic rats, fed the oyster extract diet, for 4 weeks and 4 months respectively, than in those fed the control diet in the cholesterol-free diet. Blood pressure was significantly lower in the oyster extract group than in the control group at the 2nd and 4th weeks after the beginning of feeding experimental diets in SH rats. These results suggest that oyster extract prepared by hydrolysis of oyster induces triglyceride-lowering activity in the liver through a decrease in hepatic lipogenesis in SD rats, and that it exerts the antihypertensive effect in SH rats.     

Exposure to lard-based high-fat diet during fetal and lactation periods modifies breast cancer susceptibility in adulthood in rats

The present study investigated whether early life exposure to high levels of animal fat increases breast cancer risk in adulthood in rats. Dams consumed a lard-based high-fat (HF) diet (60% fat-derived energy) or an AIN93G control diet (16% fat-derived energy) during gestation or gestation and lactation. Their 7-week-old female offspring were exposed to 7,12-dimethyl-benzo[a]anthracene to induce mammary tumors. Pregnant dams consuming an HF diet had higher circulating leptin levels than pregnant control dams. However, compared to the control offspring, significantly lower susceptibility to mammary cancer development was observed in the offspring of dams fed an HF diet during pregnancy (lower tumor incidence, multiplicity and weight), or pregnancy and lactation (lower tumor multiplicity only). Mammary epithelial elongation, cell proliferation (Ki67) and expression of NFκB p65 were significantly lower and p21 expression and global H3K9me3 levels were higher in the mammary glands of rats exposed to an HF lard diet in utero. They also tended to have lower Rank/Rankl ratios (P=.09) and serum progesterone levels (P=.07) than control offspring. In the mammary glands of offspring of dams consuming an HF diet during both pregnancy and lactation, the number of terminal end buds, epithelial elongation and the BCL-2/BAX ratio were significantly lower and serum leptin levels were higher than in the controls. Our data confirm that the breast cancer risk of offspring can be programmed by maternal dietary intake. However, contrary to our expectation, exposure to high levels of lard during early life decreased later susceptibility to breast cancer.     

Protection against ultraviolet B- and C-induced DNA damage and skin carcinogenesis by the flowers of Prunus persica extract

The ethanol extract of the flowers of Prunus persica (Ku-35) (50-200 microg/ml) was found to inhibit UVB- as well as UVC-induced DNA damage measured by the COMET assay in the skin fibroblast cell (NIH/3T3). In addition, Ku-35 inhibited UVB- or UVC-induced lipid peroxidation, especially against UVB-induced peroxidation at higher than 10 microg/ml. We also evaluated the protective effect of Ku-35 against UVB-induced non-melanoma skin cancer in mice. Ku-35 was applied topically before UVB exposure, and its effects on tumor incidence (% of mice with tumors) and tumor multiplicity (number of tumors per mouse) were evaluated. The application of Ku-35 clearly resulted in a delay of tumor development compared to the control. In tumor incidence, 100% mice in the control group and the low dose treatment of Ku-35 had tumors, whereas 94.1% of the mice had tumors after the high dose treatment of Ku-35 at the end of experiment (28 weeks). In tumor multiplicity, low and high treatments of Ku-35 resulted in 25.9 and 53.9% reduction at the end of the experiment (P<0.05, one-way analysis of variance (ANOVA)). The present data indicate that Ku-35 protects against photogenotoxicity in NIH/3T3 fibroblasts. The possible action mechanism of Ku-35 may be through its anti-oxidant activity without pro-oxidant effect. Ku-35 can also show a delay of tumor development against UVB-induced skin carcinogenesis. These results suggest that Ku-35 extract may be useful for protecting UV-induced DNA damage and carcinogenesis when topically applied.     

Antitumor activity of naltrexone and correlation with steroid hormone receptors.

We have evaluated the opiate peptide antagonist, naltrexone, for its effectiveness as an antitumor agent. For this evaluation, we tested the effect of naltrexone given daily in the diet on the growth of established 7,12-dimethylbenz(a)anthracene-induced mammary tumors. Tumors continued to grow actively in rats fed chow diet only (control group). In contrast, the naltrexone-supplemented diet (75 mg/kg diet) significantly decreased the size of the established mammary tumors in rats over the 25 day observation period, resulting in an average decrease in tumor volume by approximately 23% compared with their sizes at the beginning of the treatment. Tumor regression occurred in 70% of the rats. Tumors that respond to naltrexone showed appreciable amounts of estrogen and progesterone receptors while unresponsive tumors were negative for estrogen and progesterone receptors. For the first time, we report that naltrexone can regress established mammary tumors and that the inhibitory effect of naltrexone appears to be restricted to the hormonally responsive mammary tumors.     

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.     

Consumption of a buckwheat protein extract retards 7,12-dimethylbenz[alpha]anthracene-induced mammary carcinogenesis in rats

Female rats were examined for the effects of feeding buckwheat protein extract (BWPE) on the development of mammary tumor caused by administration of 7,12-dimethylbenz[alpha]anthracene. The percentage of rats with palpable mammary tumors and serum estradiol were lower in the BWPE-fed animals than the casein-fed ones, implying that BWPE intake retarded the mammary carcinogenesis by lowering serum estradiol.     

Dietary Supplementation with Methylseleninic Acid Inhibits Mammary Tumorigenesis and Metastasis in Male MMTV-PyMT Mice

Male breast cancer, which makes up approximately 1% of all breast cancers, is an aggressive disease with poor prognosis. We investigated the effects of dietary supplementation with selenium in the form of methylseleninic acid [(MSeA) 2.5 mg selenium/kg] on mammary tumorigenesis in male MMTV-PyMT mice. The mammary tumor latency was 14.6 weeks for the MSeA-fed group and 13.8 weeks for the controls fed the AIN93G diet (p < 0.05). Dietary supplementation with MSeA, versus the control, resulted in a 72% reduction in tumor progression, a 46% reduction in both final volume and weight of mammary tumors, and a 70% reduction in the number of lung metastases. Mammary tumorigenesis in MMTV-PyMT mice, versus non-tumor-bearing wild-type mice, resulted in significant increases in concentrations of plasminogen activator inhibitor-1, urokinase plasminogen activator, monocyte chemotactic protein-1, and vascular endothelial growth factor, but not aromatase and estrogen, in the plasma. Concentrations of all variables mentioned above in both plasma and mammary tumors were lower in MSeA-fed mice. Mammary tumorigenesis reduced plasma levels of adiponectin compared to non-tumor-bearing controls. Adiponectin concentrations in mammary tumors, but not in plasma, were higher in MSeA-fed mice than in controls. In summary, dietary supplementation with selenium in the form of MSeA inhibits mammary tumorigenesis and its pulmonary metastasis in male MMTV-PyMT mice.

     

Pubertally Initiated High-Fat Diet Promotes Mammary Tumorigenesis in Obesity-Prone FVB Mice Similarly to Obesity-Resistant BALB/c Mice

Premenopausal breast cancer is associated with increased animal fat consumption among normal-weight but not overweight women. Our previous findings in obesity-resistant BALB/c mice showed that a diet high in saturated animal fat (HFD) promotes mammary tumorigenesis in both DMBA carcinogenesis and Trp53-null transplant models. Having made these observations in BALB/c mice, which have very modest HFD weight gain, we determined the effects of HFD in FVB mice, which gain significant weight on HFD. Three-week-old FVB mice fed a low-fat diet or HFD were subjected to 7,12-dimethylbenz[a]anthracene-induced carcinogenesis. Like BALB/c mice, HFD promoted mammary tumorigenesis. Development of tumors largely occurred prior to mice becoming obese, indicating the role of animal-derived HFD rather than resulting obesity in tumor promotion. Also similar to BALB/c mice, early-occurring adenosquamous mammary tumors were abundant among HFD-fed FVB mice. Tumors from HFD mice also had increased intra-tumor M2 macrophages. Prior to tumor development, HFD accelerated normal mammary gland development and increased mammary M2 macrophages, similarly to BALB/c mice. The promotional effects of puberty-initiated HFD on carcinogen-induced mammary cancer are thus largely weight gain-independent. Like BALB/c mice, HFD promoted adenosquamous tumors, suggesting a role for early age HFD in promoting this subtype of triple negative mammary cancer. M2 macrophage recruitment was common to both mouse strains. We speculate that a similar effect of HFD on immune function may contribute to epidemiological findings of increased breast cancer risk in young, premenopausal, normal-weight women who consume a diet high in saturated animal fat.     

Dietary intervention of cow ghee and soybean oil on expression of cell cycle and apoptosis related genes in normal and carcinogen treated rat mammary gland

The present study investigated the effect of cow ghee (clarified butter fat) versus soybean oil on the expression of cyclins A and D1, and apoptosis regulating Bax, Bcl-2 and PKC-α genes in mammary gland of normal and 7,12-dimethylbenz(a)anthracene (DMBA) treated rats. Two groups of 21 days old female rats were fed for 44 weeks diet containing cow ghee or soybean oil (10%). The animals were given DMBA (30 mg/kg body weight) through oral intubation after 5 weeks feeding. Another two groups fed similarly but not given DMBA served as respective controls. In control groups, the expression of cyclin A was similar on both cow ghee and soybean oil, but that of cyclin D1 was more on soybean oil diet. However, in DMBA treated groups, the expression levels of cyclins A and D1 were significantly greater on soybean oil than on cow ghee. The expression levels of Bax, Bcl-2 and PKC-α were similar in two control groups. However, in tumor tissue expression levels of Bcl-2 and PKC-α were significantly lower in cow ghee fed rats than in soybean oil fed ones, but Bax was similarly expressed in both DMBA treated groups. The pro-apoptotic ratio Bax/Bcl-2 increased and the anti-apoptotic ratio PKC-α*(Bcl-2/Bax) decreased in cow ghee group compared to soybean oil group in DMBA treated rats. Hence, the decreased expressions of cyclins A and D1, Bcl-2 and PKC-α mediate the mechanism by which cow ghee protects from mammary carcinogenesis.     

Immunopotentiation of NKT cells by low-protein diet and the suppressive effect on tumor metastasis

Mice were fed with a 5% low-protein diet for two weeks, at which point tumor inoculation was conducted. Following this inoculation, the 5% low-protein diet was continued. On the other hand, control mice were fed with a normal diet (25% protein) and such diet was continued after tumor inoculation. In comparison with control mice, mice fed with the 5% low-protein diet showed a prominent prolongation of survival rate when injected with both EL4 and 3LL tumors. Interestingly, CD1d(-/-) mice, which primarily lack natural killer T (NKT) cells, did not show the prolongation of survival rate even when they received a 5% low-protein diet. The most striking phenomenon seen in tumor-bearing mice fed with the 5% low-protein diet was the suppression of tumor metastasis to the liver and lung. Such suppression was not seen in CD1d(-/-) mice who were fed with a 5% low-protein diet. Phenotypic study revealed that the proportion of NKT cells after tumor inoculation decreased in the mice fed with a normal diet. However, such decrease did not occur in mice fed with the 5% low-protein diet. Reflecting the activation of NKT cells by feeding, tumor cytotoxicity and cytokine production were also augmented by the 5% low-protein diet. These results suggest that a low-protein diet has the potential to augment the innate immunity against tumors, especially mediated by the activation of NKT cells.