Effect of dietary polyunsaturated fat on the growth of a transplantable adenocarcinoma in C3HAvyfB mice

Effects of Lipids on Cancer Therapy

The fatty acid composition of cancer cell membranes can change substantially when the cells are exposed to different types of fat. Such change occurs when tumors are grown in animals fed high-fat diets that differ in degree of unsaturation or during culture in media supplemented with various fatty acids. Certain physical and functional properties of the membrane are modified when the polyunsaturated fatty acid content is increased, and the cells become more sensitive to hyperthermia or treatment with doxorubicin. These findings suggest a potential role for lipid nutrition in cancer therapy. By altering the properties of the membrane lipids, changes in the dietary fat intake may provide a new approach for enhancing the effectiveness of certain antineoplastic therapies.

Fatty acids and breast cancer cell proliferation

We and others have shown that fatty acids are important regulators of breast cancer cell proliferation. In particular individual fatty acids specifically alter EGF-induced cell proliferation in very different ways. This regulation is mediated by an EGFR/G-protein signaling pathway. Understanding the molecular mechanisms of how this signaling pathway functions and how fatty acids regulate it will provide important information on the cellular and molecular basis for the association of dietary fat and cancer. Furthermore these in vitro studies may explain data previously obtained from in vivo animal studies and identify "good" as well as "bad" fatty acids with respect to the development of cancer.

Omega-3 polyunsaturated fatty acids in rodent models of breast cancer

Quantitative increases in certain dietary fats promote mammary tumor growth, but the experimental data indicate that this tumor promoting capability is not equally expressed by all fatty acid families. There is a large body of evidence from experiments using either carcinogen-induced or transplanted animal mammary tumor models, as well as in vitro studies, which demonstrates that the omega-6 polyunsaturated fatty acids (PUFA) promote mammary tumor development more effectively than omega-3 PUFA. These data indicate that increases in the dietary levels of omega-6 PUFA enhance tumor development, while equivalent increases in dietary levels of omega-3 PUFA often delay or reduce tumor development. Several theoretical mechanisms have been proposed for these contrasting results, but as yet, no definitive explanation has been universally accepted.

Several nongenotoxic carcinogens uncouple mitochondrial oxidative phosphorylation

A number of plasticizers and lipid-lowering drugs induce peroxisomes and cause hepatocellular carcinoma in rodents by mechanisms which remain unknown. In this study, seven structurally dissimilar peroxisome proliferating agents were shown to uncouple oxidative phosphorylation in isolated rat liver mitochondria. For example, perfluorooctanoate (0.5 mM) increased succinate-induced (state 4) mitochondrial respiration by over 50% while stimulation of state 3 respiration with ADP was minimal (i.e., uncoupling occurred). Interestingly, compounds which are potent carcinogens in vivo (e.g., Wy-14,643 and perfluorooctanoate) were more powerful uncouplers of oxidative phosphorylation in vitro than weak tumor-causing agents (e.g., valproate). Uncoupling also occurred in vivo. Basal rates of oxygen uptake in perfused livers from chronically treated rats were increased from 137 +/- 7 mumol g-1/h in pair-fed controls to 153 +/- 5 mumol g-1/h after 2.5 months of feeding Wy-14,643 (0.1% w/v in diet). Concomitantly, rates of urea synthesis from ammonia, a process highly dependent on ATP supply, were reduced almost completely from 104 +/- 10 mumol g-1/h to 13 +/- 6 mumol g-1/h. Bile flow, another energy-dependent process, was also reduced significantly by treatment with Wy-14,643 in vivo for 24 h. Taken together, these data indicate that energy supply for cellular processes such as urea synthesis and bile flow was disrupted in vivo due to uncoupling of oxidative phosphorylation by Wy-14,643. It is proposed that peroxisomal proliferators accumulate in the liver where they uncouple mitochondrial oxidative phosphorylation and interfere with cellular energetics.

Dietary fat, calories, and mammary gland tumorigenesis

In this communication, a vast array of studies designed to examine the relationship between dietary fat and experimental mammary gland tumorigenesis was reviewed and critiqued. It is clear, as reported by many laboratories, that as the fat content of the diet is increased from a low or standard level to a high level, a consistent and substantial increase in the development of rodent mammary gland tumors is observed. The longer the duration the high-fat diet is fed, the greater the enhancing effect on tumorigenesis. Furthermore, the stimulatory effect of a high-fat diet is observed even when fed commencing late in an animal's life. A multitude of studies also have provided evidence that the type of fat can markedly influence the development of rodent mammary gland tumors. In general, high dietary levels of unsaturated fats (e.g., corn oil, sunflower-seed oil) stimulate this tumorigenic process more than high levels of saturated fats (e.g., beef tallow, coconut oil); diets rich in certain fish oils (e.g., Menhaden oil, Max EPA) are often the most inhibitory to this tumorigenic process. Importantly, however, supplementation of saturated fat or fish oil diets with modest amounts of unsaturated fats, e.g., corn oil, often negates the mammary tumor inhibitory activities of these fats. Thus, rather extreme differences in the types of fat are required for a differential in mammary gland tumorigenesis; common proportionate blends of different fats of animal, plant, and/or fish origin are often unable to differentially influence this tumorigenic process. Diets rich in monoenoic fatty acids, e.g., those containing high levels of olive oil, have been examined in a number of studies; results from these studies have been inconsistent. A number of reports suggest that the increase in development of mammary tumors in rodents fed a high-fat diet, compared with those fed a low-fat diet, is due to specific metabolic activities of the fat per se, activities independent of a caloric mechanism. Careful analysis of these reports suggest that such a conclusion may not be totally warranted. Indeed, persuasive evidence is accumulating indicating that the major mammary tumor development enhancing activities of a high-fat diet may be via a caloric (energy) mechanism. Caloric restriction, even in animals fed a high-fat diet, significantly suppresses mammary tumor development. Even mild caloric restriction (e.g., 12%) can significantly suppress development of mammary tumors in rodents.(ABSTRACT TRUNCATED AT 400 WORDS)

Adjuvant dietary fat intake reduction in postmenopausal breast cancer patient management. The Women's Intervention Nutrition Study (WINS)

Management of localized breast cancer now commonly involves a breast-sparing approach combined with systemic adjuvant therapy resulting in improved cosmetic results and patient survival. Reducing dietary fat intake represents a conceptually new approach to further improve outcome of patients with resected breast cancer. The rationale supporting evaluation of dietary fat reduction in the management of patients with localized breast cancer is based on: (1) epidemiologic observations (along with biochemical and hormonal correlates) of major differences in stage-by-stage survival of patients with localized breast cancer comparing outcome in countries with low fat (Japan) versus high fat (U.S.A.) dietary intakes; (2) relationships between dietary fat intake and factors prognostic of clinical outcome in patients with established breast cancer; (3) effects of weight gain (especially that associated with adjuvant chemotherapy) on breast cancer clinical outcome; (4) in vivo animal studies demonstrating adverse influence of increased dietary fat intake (especially linoleic acid) on growth and metastatic spread of mammary cancer; (5) direct adverse effects of increased linoleic acid on human breast cancer growth in vitro; (6) plausible mechanisms which could mediate the effects of dietary fat intake reduction on breast cancer growth and metastatic spread; (7) demonstration of adherence to dietary fat reduction regimens in ongoing clinical feasibility studies including those involving postmenopausal patients with resected breast cancer; and (8) favorable sample size requirements for definitive assessment of dietary fat intake reduction influence on breast cancer growth and metastases (using as endpoints relapse-free survival and overall survival) in postmenopausal breast cancer patients with localized disease.

Dietary fat and tumor metastasis

Evidence from several types of studies indicates a relationship between fat intake and occurrence of malignant tumors at specific sites. When rodents are fed high-fat diets, the incidence of mammary tumors sharply increases and latency of tumor appearance is greatly diminished, as compared with the same parameters in animals fed low levels of fat. Despite advances in surgical technique and the development of aggressive therapies for the treatment of primary cancers, most deaths in humans with cancer are caused by metastasis. Accordingly, we have reviewed the process of metastasis and have focused on the question of whether dietary fat can play a role. Metastasis is a complex, multistep, progressive process, and dietary fats may affect specific events such as implantation, survival, and proliferation of tumors. Finally, we discuss possible mechanisms by which dietary fat can modulate metastasis. Available data lead us to stress the importance of assessment of metastasis in studies of the effects of dietary fat on tumorigenesis.

Relationship between vitamin E and polyunsaturated fatty acids in breast cancer. Nutritional and metabolic aspects

Intake of vitamin E, total lipids, total cholesterol, and fatty acids were analyzed with the blood levels of vitamin E, total cholesterol, triglycerides, and the serum distribution of fatty acids in a hospital-based population of 120 patients and 109 controls. In regard to nutritional intake, the only significant differences involve saturated and monounsaturated fatty acid consumption, which is more elevated in postmenopausal patients than in postmenopausal controls. Vitamin E and total cholesterol blood levels are significantly higher in patients than in controls, where the difference is that vitamin E is independent from cholesterol level in premenopausal women only. Fatty acid serum distribution is comparable in both samples, with the exception of arachidonic acid, which is significantly lower in premenopausal patients than in premenopausal controls. Two multivariate regression analyses of the plasma vitamin E levels of patients and controls were done with menopausal status and nutrients as independent variables for the first analysis, and with menopausal status and all blood analytes for the second one. The regression coefficients for total cholesterol and triglycerides are statistically significant for both samples, whereas a positive association between vitamin E plasma level and sunflower oil consumption and between vitamin E plasma level and serum linoleic acid distribution is significant for patients only. Furthermore, the multiple regression shows that, when adjusted for analyte variables, plasma vitamin E levels are higher in premenopausal than in postmenopausal patients. In addition, plasma lipid peroxidation, evaluated by malondialdehyde measurement, is shown to be significantly lower in patients than in controls. Malondialdehyde level is associated with a significant lower odds ratio (OR) after multivariate tertile analysis (OR for the highest tertile: 0.51; 95% CI: 0.29-0.89). Together, these findings are consistent with a picture of lower lipid peroxidation in patients than in controls.

A role for dietary lipids and antioxidants in the activation of carcinogens

The ways in which dietary polyunsaturated fats and antioxidants affect the balance between activation and detoxification of environmental precarcinogens is discussed, with particular reference to the polycyclic aromatic hydrocarbon benzo(a)pyrene. The structure and composition of membranes and their susceptibility to peroxidation is dependent on the polyunsaturated fatty acid (PUFA) content of the cell and its antioxidant status, both of which are determined to a large degree by dietary intake of these compounds. An increase in the PUFA content of membranes stimulates the oxidation of precarcinogens to reactive intermediates by affecting the configuration and induction of membrane-bound enzymes (e.g., the mixed-function oxidase system and epoxide hydratase); providing increased availability of substrates (hydroperoxides) for peroxidases that cooxidise carcinogens (e.g., prostaglandin synthetase and P-450 peroxidase); and increasing the likelihood of direct activation reactions between peroxyl radicals and precarcinogens. Antioxidants, on the other hand, protect against lipid peroxidation, scavenge oxygen-derived free radicals and reactive carcinogenic species. In addition some synthetic antioxidants exert specific effects on enzymes, which results in increased detoxification and reduced rates of activation. The balance between dietary polyunsaturated fats, antioxidants and the initiation of carcinogenesis is discussed in relation to animal models of chemical carcinogenesis and the epidemiology of human cancer.

The influence of dietary medium chain triglycerides on rat mammary tumor development

The N-nitrosomethylurea rat mammary tumor model was used to compare the tumor-promoting effects of a high-fat (HF) diet containing a 3:1 mixture of medium chain triglycerides (MCT) and corn oil with that of a HF and a low-fat (LF) corn oil diet. The serum and tumor lipid content and fatty acid (FA) composition were also determined in the three dietary groups. It was found that the MCT-containing diet failed to promote tumor development compared with the HF corn oil group. Tumor incidence in the HF-MCT group was similar to that of the LF corn oil group (5% fat, w/w), but significantly decreased compared to the HF corn oil group. Total serum cholesterol levels were significantly depressed in the HF corn oil group compared to the HF-MCT and LF corn oil groups. Analysis of serum and tumor FA profiles indicated that the HF corn oil group exhibited approximately twice the amount of linoleic acid (LA) as the other two treatment groups. Differences among the three groups in the major FA metabolite of LA, arachidonic acid, were minimal. These results are consistent with the hypothesis that tumor promotion by dietary fat is more a function of the type than the amount of fat ingested. In addition, they indicate that MCT, due at least in part to their unique structural and physiological properties, exert markedly different effects on mammary tumor development than conventional long chain unsaturated fatty acids.

The dependence of the rate of BP metabolism in the rat small intestinal mucosa on the composition of the dietary fat

We studied the effects that dietary fat has on the capacity of preparations of rat small intestinal mucosal cells to metabolize benzo[a]pyrene (BP) in vitro and on the composition of fatty acids in the endoplasmic reticulum of the intestinal mucosa. When rats were fed diets containing different types of fat, there were significant changes in the incorporation of fatty acids into the endoplasmic reticulum of the mucosal cells of the small intestine: the proportions of polyunsaturated fatty acids in the endoplasmic reticulum reflected the amounts of these fatty acids in the dietary fat. The rate of BP oxidation in the intestinal mucosa was dependent on the amount and composition of the dietary fat, but the range and proportions of the metabolites produced were not affected. Dietary C18:2 was particularly important in elevating the rate of BP oxidation, but dietary C20:5 and C22:6 also effectively increased the rate of BP oxidation. The rate of BP oxidation in the small intestine of rats fed different diets was positively correlated with the proportion of polyunsaturated fatty acids in the endoplasmic reticulum of the mucosal cells.

Reversal of the promotional effect of high-fat diet on mammary tumorigenesis by subsequent lowering of dietary fat

Female Sprague-Dawley rats were given 7,12-dimethylbenz(a)anthracene at 50 days of age to induce mammary tumors, and beginning one week later were fed a high-fat, semipurified diet containing 20% sunflowerseed oil to promote tumor development. After another 7 weeks, when one third of the rats had palpable mammary tumors, the rats were randomly assigned to five groups of 31 animals each, with the same number of tumor-bearers in each group. One group was continued on the high-fat diet, another was given a fat-free diet, and the three remaining groups were fed diets containing 10% lard, butter, or coconut oil, respectively. During the next 29 weeks, rats fed the diets containing 0% or 10% fat developed significantly fewer tumors than those continued on the 20% fat diet. The diets containing 10% fat suppressed tumorigenesis at least as effectively as the fat-free diet. Rats fed the 10% butter and 10% lard diets had growth rates comparable to those fed the 20% sunflowerseed-oil diet throughout, and evidence of essential fatty acid deficiency was seen only in rats on the fat-free diet. These results provide additional evidence that high-fat diets promote development of mammary cancer and suggest that reducing the level of dietary fat might help to prevent the development and recurrence of breast cancer in humans.

Incidence of spontaneous tumors in laboratory rats

The Caw-Hoe-Wiga strain of the Sprague-Dawley rat was observed for a period of ten years (1974--1983). In toxicity studies, a gradual increase of food intake could be noted in 12- to 13-week-old rats. The food intake of males was 21 g in 1974 and 27 g in 1983; in females 16 g in 1974 and 19 g in 1984. Correspondingly, a gradual increase of body weight was measured. The body weight of males was 400 g in 1974 and 470 g in 1983; of females 240 g in 1974 and 285 g in 1983. The gradual increase of food intake and body weight was followed by a gradual increase in the incidence of spontaneous tumors, 1974: 5% and 1983: 13%. Our experiments support the opinion of a causal connection between food intake, body weight and incidence of spontaneous tumors. Tumors can appear in any age group, but tumors. occur more often in older animals. In our studies, the increase in the incidence of spontaneous tumors was proportional to the increase in age: At 15 months only 6%, at 32 months 86%. 32% of the tumors were located in the mammary glands, 27% in the hypophysis, 12% in skin and appendages, and 9% in other endocrine organs. The comparison of toxicity and carcinogenicity studies revealed no change in the tumor spectrum, but strain-related tumors appeared earlier in life, more frequently and more often multifocally towards the end of the 10-year observation period.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dietary stearic acid on the genesis of spontaneous mammary adenocarcinomas in strain A/ST mice

Strain A/ST female mice maintained on a high fat (15%) diet in which stearic acid was the major lipid component developed initial spontaneous mammary adenocarcinomas at an older age than mice fed a low fat (4.5%) stock diet. Mice placed on the SA diet at weaning developed tumors at 15.7 +/- 0.87 months compared to 12.7 +/- 0.43 months for those retained on the stock diet (p less than .05). Placing mice on the SA diet at 11.5 months resulted in a smaller but significant increase in the latency period (5.0 +/- 0.86 vs 3.0 +/- 0.57 months +/- 0.57 mo), (p less than .05). Fatty acid analyses of non-tumorous mammary tissue from mid-pregnant mice and of tumor tissues showed that feeding large amounts of 18:0 did not result in increases in the proportion of 18:0. Significant reductions in the percentages of polyunsaturated fatty acids (PUFA) was found in tissues on mice fed the SA diet. The percentage of 18:2 was reduced in both types of tissues; 20:3 and 20:4 was reduced in tumor tissues. Distribution of C18 fatty acids in plasma membranes of tumors of mice fed the two diets were similar; percentages 18:2 was higher in plasma membranes of non-tumorous tissues of mice fed the SA diet. These results suggest that dietary stearic acid interferes with the availability of certain PUFA required for tumor production.

The effect of dietary fat on tumor growth

Experiments in animals have shown that high-fat diets can enhance tumor growth. Animals receiving high-fat diets routinely ingest up to 5 times the level of fat (by weight) found in standard chow diets. Rats given oil by gavage can triple caloric intake from fat compared to untreated controls. In laboratory animals, high-fat diets appear to play a role during the postinitiation phase of tumorigenesis. The type, level, and nature of the dietary fat may also affect the outcome of bioassays. Fat does not initiate the tumorigenic process. Additional factors must be considered when studying and interpreting the effects of dietary fat. Animal diets and dietary fats should be protected against oxidation. Antioxidants protect against oxidation but may also modify the tumorigenic process. Adequate levels of essential fatty acids must be provided. Dietary fat level can alter nutrient density and palatability; each of these factors can affect nutrient intake which can in turn influence metabolic processes.

Effect of calorie restriction on the fate of hyperplastic liver nodules induced by concurrent administration of lasiocarpine and thioacetamide

1 Hyperplastic liver nodules were induced in F-344 rats by concurrent administration of lasiocarpine (50 ppm in diet) and thioacetamide (50 mg/kg body weight twice weekly) for 15 weeks. 2 The effect of carbohydrate calorie and total calorie restriction on the fate of hyperplastic liver nodules was examined. 3 The incidence of hepatocellular carcinoma was the same in all groups of rats irrespective of the magnitude of carbohydrate calorie restriction and 50% total calorie restriction. 4 These studies demonstrate that carbohydrate or total calorie restriction has no effect on the progression of hyperplastic nodules to hepatocellular carcinoma.

Vitamin E protection against tumor formation by transplanted murine sarcoma cells

Mice fed vitamin E at a level of 0.5 g DL-alpha-tocopheryl acetate/kg diet demonstrated decreased incidence and rate of appearance of tumors produced by transplanted sarcoma cells (K3T3), compared to control groups fed diets without the vitamin supplement. Protection was dependent on the degree of unsaturation of dietary fat and on the size of the tumor cell challenge. When vitamin E was increased 10-fold (to 5 g/kg diet), the protective effect was no longer observed. Protection may be mediated through the host immune system, because sublethal, whole-body X-irradiation abrogated differences in tumor development between the +E and the -E mice. Studies with in vitro immunization showed that treatment of the K3T3 cell with vitamin E enhanced its ability to induce a cytotoxic response. It appears that the direct effect of vitamin E is on the tumor cell rather than on the immune system, since spleen cells from mice fed diets with and without vitamin E supplementation were indistinguishable in their response to untreated K3T3 cells. K3T3 cells treated with excessive levels of vitamin E were unable to induce a cytotoxic response, a result that correlates with the loss of protection against tumor development when massive doses of vitamin E were fed.

Inhibitory effect of a fat-free diet on mammary carcinogenesis in rats

Young female Sprague-Dawley rats were administered 7,12-dimethylbenz(a)anthracene, and a week later the rats were transferred from commercial feed to a semipurified diet containing 20% corn oil. Eight weeks after receiving the carcinogen, half of the rats were changed to a fat-free diet to determine the effects on mammary tumor growth and development. After another 20 weeks, rats fed the fat-free diet had significantly fewer tumors per tumor-bearing rat and the tumors were smaller than those of rats that continued on the high-fat diet. Rats fed the fat-free diet weighed somewhat less, but showed no physical evidence of essential fatty acid deficiency. Tumors regressed in about half of the rats on the fat-free diet and in some cases became nonpalpable. After 28 weeks on this diet, the remaining rats were transferred back to the high-fat diet and subsequently showed a marked stimulation in tumor growth and development. This continued even after the rats were returned to the fat-free diet 8 weeks later, indicating that the tumors were no longer susceptible to the deprivation of dietary fat. The results of this study provide further evidence that dietary fat affects the promotional stage of mammary carcinogenesis.

Lack of effect of dietary fat on the growth and estrogen sensitivity of the MT-W9B transplantable mammary tumor

The growth rate and the estrogen responsiveness of the MT-W9B transplantable mammary tumor were examined in female Wistar-Furth rats which were fed diets containing either 0.5% or 20% fat for 50-60 days. Estrogen responsiveness was determined by changes in progesterone receptor concentration in response to estrogen deprivation and replacement. This parameter was also measured in the uterus as a normal tissue control. Progesterone receptor levels in tumor and uterus were reduced by ovariectomy to a similar extent in rats fed either low-or high-fat diets. In addition, estrogen induction of the progesterone receptor in ovariectomized rats was not altered by dietary fat intake. Growth of the MT-W9B tumor was not affected by either diet or endocrine manipulation. Uterine growth, as expected, was dependent on estrogen status, but both the growth and its sensitivity to estrogen manipulation were independent of the fat content of the diet. These data suggest that dietary fat does not influence the sensitivity of normal or neoplastic tissue to estrogen action.

Influence of diet on mammary cancer

Analysis of epidemiological data and experiments with animals have provided evidence that dietary fat has an important influence on mammary cancer. Further epidemiological studies should be carried out to examine this relationship more fully, and additional experimental work is required to determine the mechanisms by which dietary fat influences mammary cancer in animals. Dietary carbohydrate and minor dietary components, such as retinoids and certain trace elements, have also been shown to influence mammary cancer in animals. Decreasing the fat content of the diet may offer a practical means of reducing mortality from breast cancer, which continues to be a major cause of death in many parts of the world.

Dietary polyunsaturated fat versus saturated fat in relation to mammary carcinogenesis

High levels of dietary fat have been shown to promote the development of mammary tumors induced in rats by 7,12-dimethylbenz(alpha)anthracene, and polyunsaturated fats were found to be more effective than saturated fats. In further studies it was found that diets containing 3% sunflowerseed oil (polyunsaturated fat) and 17% beef tallow or coconut oil (saturated fats) enhance tumorigenesis as much as a diet containing 20% sunflowerseed oil. Rats on these diets developed at least twice as many tumors as those fed diets containing either 3% sunflowerseed oil or 20% of the saturated fats alone. These results are in accord with human epidemiological data which show that breast cancer mortality in different countries is positively correlated with total fat intake but not with intake of polyunsaturated fat. Total fat intake varies greatly in different countries, but most human diets probably contain levels of polyunsaturated fat at least equivalent to 3% sunflowerseed oil.