The combined effects of dietary protein and fat on 7,12-dimethylbenz(a)anthracene-induced breast cancer in rats

Pharmacometabolomic Pathway Response of Effective Anticancer Agents on Different Diets in Rats with Induced Mammary Tumors

Metabolomics is an effective approach to characterize the metabotype which can reflect the influence of genetics, physiological status, and environmental factors such as drug intakes, diet. Diet may change the chemopreventive efficacy of given agents due to the altered physiological status of the subject. Here, metabolomics response to a chemopreventive agent targretin or tamoxifen, in rats with methylnitrosourea-induced tumors on a standard diet (4% fat, CD) or a high fat diet (21% fat, HFD) was evaluated, and found that (1) the metabolome was substantially affected by diet and/or drug treatment; (2) multiple metabolites were identified as potential pharmacodynamic biomarkers related to targretin or tamoxifen regardless of diet and time; and (3) the primary bile acid pathway was significantly affected by targretin treatment in rats on both diets, and the lysolipid pathway was significantly affected by tamoxifen treatment in rats on the high fat diet.

Comparison of Effects of Diet on Mammary Cancer: Efficacy of Various Preventive Agents and Metabolomic Changes of Different Diets and Agents

To determine the effects of diet, rats were placed on a standard diet (4% fat) or on a modified Western (high-fat diet, HFD) diet (21% fat) at 43 days of age (DOA) and administered methylnitrosourea (MNU) at 50 DOA. Rats were administered effective (tamoxifen, vorozole, and Targretin) or ineffective (metformin and Lipitor) chemopreventive agents either by daily gavage or in the diet beginning at 57 DOA and continuing until sacrifice (190 DOA). Latency period of the tumors was determined by palpation, and multiplicity and cancer weights per rat were determined at final sacrifice. Rats on the HFD versus standard diet had: (i) a 6% increase in final body weights; (ii) significant decreases in tumor latency; and (iii) significant increases in final tumor multiplicity and average tumor weight. Tamoxifen, vorozole, and Targretin were highly effective preventive agents, whereas Lipitor and metformin were ineffective in rats on either diet. Serum was collected at 78 DOA and at sacrifice (190 DOA), and metabolomics were determined to identify the metabolite changes due to diets and effective agents. Rats given the HFD had increased levels of saturated free fatty acids (including myristate) and decreased levels of 2-aminooctanoate. Furthermore, rats on the HFD diet had increased levels of 2-aminobutyrate and decreases in glycine markers previously identified as indicators of prediabetes. Targretin increased long-chain glycophospholipids (e.g., oleyl-linoleoyl-glycerophosphocholine) and decreased primary bile acids (e.g., taurocholate). Tamoxifen increased palmitoyl-linoleoyl-glycophosphocholine and decreased stearoyl-arachidonyl glycophosphocholine. Finally, increased levels of methylated nucleotides (5-methylcytidine) and decreased levels of urea cycle metabolites (N-acetylcitrulline) were associated with the presence of mammary cancers.

Photodynamic therapy for the treatment of induced mammary tumor in rats

The objective of this work was to evaluate photodynamic therapy (PDT) by using a hematoporphyrin derivative as a photosensitizer and light-emitting diodes (LEDs) as light source in induced mammary tumors of Sprague-Dawley (SD) rats. Twenty SD rats with mammary tumors induced by DMBA were used. Animals were divided into four groups: control (G1), PDT only (G2), surgical removal of tumor (G3), and submitted to PDT immediately after surgical removal of tumor (G4). Tumors were measured over 6 weeks. Lesions and surgical were LEDs lighted up (200 J/cm(2) dose). The light distribution in vivo study used two additional animals without mammary tumors. In the control group, the average growth of tumor diameter was approximately 0.40 cm/week. While for PDT group, a growth of less than 0.15 cm/week was observed, suggesting significant delay in tumor growth. Therefore, only partial irradiation of the tumors occurred with a reduction in development, but without elimination. Animals in G4 had no tumor recurrence during the 12 weeks, after chemical induction, when compared with G3 animals that showed 60 % recurrence rate after 12 weeks of chemical induction. PDT used in the experimental model of mammary tumor as a single therapy was effective in reducing tumor development, so the surgery associated with PDT is a safe and efficient destruction of residual tumor, preventing recurrence of the tumor.

Diet in vitamin A research

A properly formulated diet is an essential underpinning for all in vivo research. This chapter focuses on the use of diet in retinoid research from two perspectives: human research, in which diet is usually variable and analysis of dietary intake is paramount to interpreting the study's results, and animal (rodent) research, in which diet is imposed as a factor in the experimental design, and the diet consumed is usually monotonous. Many standard rodent diets are nonpurified and the amount of vitamin A in the diet is unknown. Moreover, it is likely to be much higher than expected from the label. By using a well-formulated purified diet with an exact amount of vitamin A, retinoid status in rodents can be closely controlled to create specific physiological conditions that represent the wide range of vitamin A status present in human populations.

Diet, anthropometry and breast cancer: integration of experimental and epidemiologic approaches

The interrelation ships of dietary fat and energy, growth rates and anthropometry, and breast carcinogenesis have been examined by a diverse array of approaches throughout the last 50 y as new investigative tools have been developed by laboratory scientists and epidemiologists. A consensus among investigators has not emerged, however, and dietary recommendations for breast cancer prevention have not been clearly formulated or effectively communicated to the public. Indeed, the gap between those investigators utilizing laboratory-based approaches and those using epidemiologic models has expanded in recent years. Cancer epidemiologists have become increasingly skeptical that results derived form laboratory animal models of breast carcinogenesis and in vitro systems are directly applicable to human breast cancer risk. Concurrently, laboratory scientists have questioned the ability of epidemiological tools to accurately measure dietary intake and relevant biomarkers and to account for a diverse array of potentially confounding environmental and genetic factors characteristic of human populations under study. These polarized views are reinforced by a failure of investigators using diverse approaches to interact, integrate their skills and resources, develop novel hypotheses, and propose solutions using both laboratory and epidemiologic techniques. Therefore, the objectives of this symposium are to summarize experimental and epidemiologic knowledge, foster communication and collaboration, and attempt to identify appropriate studies to bridge the gaps in our knowledge concerning dietary lipid and energy, anthropometrics, and breast cancer risk.

Diet and breast cancer: studies in laboratory animals

Increasing dietary fat content increases mammary gland tumorigenesis in laboratory rodents. The effect can be attributed only in part to increasing energy intake, which itself increases tumorigenesis. Restriction of dietary or energy intake, sufficient to reduce body weight, reduces mammary gland tumorigenesis. Consideration of these effects has led to discussion of the possible need for changes in the feeding of laboratory rodents in carcinogenesis bioassays and other chronic studies. Studies of endocrine or other growth factors for the mammary gland have not identified specific effects of dietary fat or energy. In addition, tumorigenesis in other organs responds similarly to increased fat or decreased energy intake, indicating that the mechanisms are not, or not entirely, specific for the mammary gland. Extrapolations of results between species must always be made with caution, but the marked effects of dietary fat and energy in rodent tumorigenesis models must be considered in designing diet advice for humans.

Experimentally induced mammary tumors in rats

Among the multiple experimental animal models employed for analyzing the various aspects of mammary carcinogenesis, the induction of mammary tumors in rats by chemical carcinogens is one of the models most utilized. Experimentally-induced mammary tumors in rodents have proven to constitute useful tools for the study of the pathogenesis of cancer and of the molecular mechanisms involved in the initiation and progression of the neoplastic process. In vivo experimental animal models provide information not available in human populations; they are adequate for hazard identification, dose-response modeling, exposure assessment, and risk characterization, the four required steps for quantifying the estimated risk of cancer development associated with toxic chemical exposure. Using the DMBA rat mammary model, we have been able to demonstrate that the carcinogen acts on the intermediate cell of the terminal end bud (TEB), and that this structure is the one that evolves to intraductal proliferation, carcinoma in situ, and invasive carcinoma. There are several factors that regulate the susceptibility of the TEB; some of them are: a) topographic location of the mammary gland, b) age of the animal, and c) reproductive history. The understanding of the mechanisms that modulate tumorigenesis will further our knowledge and understanding in the prevention of the disease, as a result of the development of strategies for stopping the progression of the initiated cells.

Review of the effects of dietary fat on experimental mammary gland tumorigenesis: role of lipid peroxidation

The purpose of this communication is threefold, that is, (1) to review and critique the studies designed to examine the interrelationship between dietary fat and experimental rodent mammary gland tumorigenesis, (2) to assess the influence of dietary fat on growth of human breast carcinoma transplants in immunodeficient mice, and (3) to examine and discuss the role of products of lipid peroxidation in these tumorigenic processes. It is concluded from this review and critique that the amount and type of dietary fat can significantly influence the development and/or growth of rodent mammary gland tumors and growth of human breast carcinomas in immune deficient mice. Dietary fat can be either stimulatory or inhibitory to these tumorigenic processes, phenomena that could be a function, at least in part, of the generation of products of lipid peroxidation.

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)

Effects of food or nutrient restriction on milk vitamin A transfer and neonatal vitamin A stores in the rat

We have investigated the effects of maternal diets low in fat or protein, or restricted in total food intake on vitamin A transfer from the dam to her pups. When animals were fed on diets moderately restricted in fat or protein, minimal differences in milk, serum, and liver vitamin A concentrations were observed compared with animals fed on a control diet. In a second study, dams were fed on diets more severely restricted in protein, or fat, or both, or were fed on a control diet equal to 50% of the intake of control rats but containing an equal amount of vitamin A. The quantity of milk obtained from these more severely restricted dams' nipples or the pups' stomachs was greatly reduced; however, there were no differences in milk vitamin A concentration. Body-weight, liver weight, and total liver vitamin A stores of undernourished pups were just half those measured for control pups, although serum vitamin A and serum retinol-binding protein were nearly normal in concentration. We conclude that (a) moderate restrictions in fat or protein in the maternal diet are insufficient to affect transfer of vitamin A to the suckling pup; (b) further dietary restrictions could cause decreased milk production with little change in milk vitamin A concentration and, hence, (c) the neonates' hepatic retinol accumulation during the suckling period is markedly reduced when maternal diets are severely deficient in fat or protein or of normal composition but restricted in amount.

Effects of dietary fat and protein on DMH-induced tumor development and immune responses

Although in three different mouse tumor systems with corn oil as dietary fat we previously found that milk protein decreased tumor development compared with beef, the results were reversed in 1,2-dimethylhydrazine (DMH)-injected mice. The purpose of this study was to determine if the latter result was due to the protein source. BALB/c mice (n = 280) were divided into five diet groups and injected 10 times at weekly intervals with DMH (20 mg/kg wt) or saline. Four diets contained 11% protein (casein, milk, or beef) and 5% fat (corn oil or beef tallow), and the AIN-76A diet was used as a control diet. The source of fat was a significant modulator of tumor development. Corn oil markedly increased total tumor volume and the number of tumors per mouse compared with beef tallow. Its tumor-enhancing effects were evident when it was combined with milk but not with casein. In addition, significantly lower lymphoproliferation and T-cell cytotoxicity against colon tumor cell targets was associated with corn oil consumption, whereas nonfat milk as the protein source was related to normal oxidative burst capacity of phagocytes. These results demonstrate that the source of dietary fat, in addition to the protein source, has a profound effect on both tumor development and immune responsiveness in this animal tumor system.

Histopathologic and dietary prognostic factors for canine mammary carcinoma

Histologic and dietary prognostic factors for survival following naturally occurring breast cancer were studied for 145 pet dogs. Information was collected from the dog's owner and veterinarian regarding medical and reproductive history, nutritional status, treatment, tumor recurrence, and length of survival. The usual intake of all dog and table foods consumed 1 year prior to diagnosis was obtained using a validated quantitative food frequency questionnaire. A histologic malignancy score was derived based on 7 histopathologic criteria. The mean age of the dogs was 10.4 +/- 2.5 years; 37% had been ovariohysterectomized prior to diagnosis. Product-limit estimates of survival indicated that 6 factors, namely body conformation 1 year prior to diagnosis (p = 0.03), histologic tumor type (p = 0.004), histologic malignancy score (p = 0.02), histologic invasion (p = 0.002), tumor recurrence (p less than 0.0001), and completeness of surgery (p = 0.01) were of prognostic significance. In addition, when dogs were characterized by the percent of total calories they derived from fat and protein, the median survival time for dogs in the low fat group (less than 39%) with protein greater than 27%, 23-27%, and less than 23% was 3 years, 1.2 years, and 6 months, respectively (p = 0.008). For dogs in the high fat group (greater than or equal to 39%), there was no difference in survival for the different intake levels of dietary protein (p = 0.84). When these data were fitted to a proportional hazards model, recurrence, histologic score, tumor type, percent of calories derived from protein, fat group, and a protein-fat group interaction term were statistically significant. Predicted 1 year survival for dogs on a low fat diet with 15%, 25%, and 35% of total calories derived from protein was 17%, 69%, and 93%, respectively.

Diet and nutrition research

The interest in nutrition and cancer, which was high in the 1940s and 1950s, was rekindled in the 1970s and is now more intense than ever. There has been considerable experimental work on dietary fat, but delineation of the precise role(s) of the essential fatty acids is still lacking. There have been few studies on protein or carbohydrate effects and only Visek has adequately addressed the important area of nutrient interactions. More work is needed in the fiber field with regard to the influences of short chain fatty acids, and the standardization of protocols is needed to make the various findings comparable. Currently, fiber data have been accrued using rats of different strains and gender, commercial and semipurified diets, a variety of colon carcinogens, and different routes of administration. The effects of energy restriction (in the literature since 1909) have not been widely studied as to mechanism and influence of energy expenditure (i.e., exercise) and merit more attention.

Comparison between the effects of dietary fat level and of calorie intake on methylnitrosourea-induced mammary carcinogenesis in female SD rats

The aim of this study was to separate the effects of calorie intake on tumorigenesis from those of fat content and fat composition in an animal model. Our principal observations were the following. Decreasing the calorie level by 30% significantly inhibited tumor development in any observed parameter of tumorigenesis, independently of the level of fat. The fat content of semi-synthetic diets, although varying by 44.4%, did not significantly influence mammary tumorigenesis; in fact, carcinogenic expression was discontinuously related to the fat level. A plateau of tumor incidence was observed at the level of 35 energy percentage of fat. Fat composition did not influence tumorigenesis or body weight gain. The role of caloric restriction is thus stressed in relation to possible dietary prevention of cancer.

The influence of different levels of dietary fat on the incidence and growth of MNU-induced mammary carcinoma in rats

This study describes the influence of isocalorically fed diets (containing different amounts of fat) on tumor incidence and parameters of fat metabolism in female Sprague-Dawley rats. Comparisons are made between rats induced with methylnitrosourea (25 mg/kg body wt) and untreated controls (Group I). The animals received either control diets (3.9% fat by weight, Groups I and II) or fat-enriched diets (10.7%, Group III; 15.6%, Group IV; 21.4%, Group V) over a period of 180 days. At the termination of the experiment, intake of the diet containing 10.7% fat by weight (24% fat per total calories) was associated with the highest tumor incidence. Comparing the different diets, liver lipid concentrations in the individual groups increased with increasing dietary fat, whereas the total lipid in plasma decreased. During the feeding period, total lipid of the liver and plasma, and plasma cholesterol, increased in all groups, but triglycerides of plasma decreased. However, when plasma cholesterol and triglycerides were calculated as a relative amount of total lipid in plasma, cholesterol was found to be significantly decreased in Groups III and IV, and triglycerides were increased in Group III but decreased significantly in Groups I, II, and V at the end of the experiment.

Dietary protein and experimental carcinogenesis

This review summarizes selected information about the influence of proteins, protein-fat interactions, and calorie intake on carcinogenesis. Most of the definitive studies concerning protein and cancer have utilized protein underfeeding and feed restriction. Optimal or less than optimal protein intakes have generally inhibited spontaneous and chemically induced tumor growth as well as the growth of transplantable tumors. Studies have focused on the quantity of protein and its amino acid supply rather than its source. Raising protein intake increases carcinogen metabolizing capacity, and the incidence of tumors depends upon the biologic activity of the metabolites that are formed. The few published studies dealing with the effects of protein on chemically induced colon, mammary, and liver cancers show that the incidence varied with the carcinogen and the level of protein fed at the time of carcinogen administration. With 1,2-dimethylhydrazine, a colon cancer-inducing agent, the toxic and tumorigenic responses have varied with the route of administration, the level of protein fed, and the level and duration of exposure to the carcinogen. In some instances, high protein diets may have led to a lower incidence of tumors because of depressed feed intake, a known confounding factor. The existing data about the relation of protein to cancer make generalizations about mechanisms hazardous because experimental models and protocols have varied widely. Some early studies undoubtedly used diets that lacked nutrients now known to be essential. Unfortunately, some recent studies have overlooked established nutritional principles and the known nutritional requirements appropriate for the age and species of animals used as models.