Effect of the amount of dietary fat on the development of mammary tumors in BALB/c-MTV mice

A 3-D multicellular tumor spheroid on ultrathin matrix coated single cancer cells provides a tumor microenvironment model to study epithelial-to-mesenchymal transitions

We report a 3D tumor spheroid model to study epithelial-to-mesenchymal transitions (EMT) using ultra-thin matrix coated single cancer cells.

Energy balance modulates mouse skin tumor promotion through altered IGF-1R and EGFR crosstalk

Obesity, an established risk factor for epithelial cancers, remains prevalent in the United States and many other countries. In contrast to positive energy balance states (overweight, obesity), calorie restriction (CR) has been shown to act as a universal inhibitor of tumorigenesis in multiple animal models of human cancer. Unfortunately, the mechanisms underlying the enhancing effects of obesity or the inhibitory effects of CR on cancer etiology remain elusive. Here, we evaluated the impact of dietary energy balance manipulation on epithelial carcinogenesis and identified several potential mechanisms that may account for the differential effects of obesity and CR on cancer. Obesity enhanced tumor promotion during epithelial carcinogenesis, in part, due to altered insulin-like growth factor-1 receptor (IGF-1R)/EGF receptor (EGFR) crosstalk and downstream signaling to effectors such as Akt/mTOR. Obesity-induced changes in cellular signaling subsequently led to altered levels of cell-cycle proteins that favored enhanced epidermal proliferation during tumor promotion. In contrast, CR reduced susceptibility to tumor promotion, attenuated IGF-1R/EGFR crosstalk and downstream signaling, and altered levels of cell-cycle proteins that favored reduced epidermal proliferation during tumor promotion. Collectively, these findings suggest potential targets for the prevention of epithelial cancers, as well as for reversal of obesity-mediated cancer development and progression. Cancer Prev Res; 5(10); 1236-46. ©2012 AACR.

Effect of varying dietary fat levels on rat growth and oxidative DNA damage

Dietary fat has previously been shown to have somewhat complicated relationships to levels of oxidative stress in rats. In this study, we examined the effects of five different dietary fat intakes on levels of oxidative DNA damage in rats. Animals fed diets containing 3%, 5%, 10%, or 15% corn oil had body weights that were similar after 20 weeks. Animals fed a 20% fat diet, however, had significantly higher mean body weight than any other group. Levels of 5-hydroxymethyl-2'-deoxyuridine, one marker of oxidative DNA damage, had different relationships to dietary fat in blood and mammary gland. In blood, levels increased with dietary fat levels, and the highest levels were observed with the 20% fat diet (65% higher levels than with the 3% fat diet). In mammary gland, a plateau-type effect was observed, with maximal levels of oxidative DNA damage being obtained using 10% fat (representing a 68% increase relative to the 3% fat diet). This could be a result of induction of compensatory mechanisms in response to a high-fat diet in mammary gland but not in the short-lived nucleated blood cells. Oxidative DNA damage levels in blood thus appear to be a marker of dietary fat intake. In mammary gland, however, levels of DNA damage are consistent with previously observed promotional effects of dietary fat on mammary gland tumorigenesis at lower levels of fat intake with little or no incremental promoting effects at higher levels of fat intake.

Organosulfur compounds from Allium and the chemoprevention of cancer

Allium vegetables and their associated organosulfur constituents are extensively studied for their chemopreventive potential against cancer. This article overviews their anticarcinogenic and antigenotoxic properties. Epidemiological studies (mostly case-control studies) provide strong evidence that Allium vegetable consumption reduces the incidence of gastric and colon cancer while the association between Allium vegetable consumption and other cancers is less convincing. Furthermore, many experimental studies have demonstrated that organosulfur compounds and Allium extracts have inhibitory effects on carcinogenesis in animals. These inhibitory effects are supported by many diverse mechanisms, including inhibition of carcinogen formation, modulation of carcinogen metabolism, inhibition of mutagenesis and genotoxicity, inhibition of cell proliferation and increase of apoptosis, inhibition of angiogenesis, and immune system enhancement. Before such constituents or extracts can be used in chemopreventive trials, it is important to verify their lack of toxicity and to investigate further their precise mechanisms of action throughout the whole process of carcinogenesis.

Fat intake and breast cancer risk in an area where fat intake is low: a case-control study in Indonesia

BACKGROUND

Associations of fat and other macronutrients with breast cancer risk are not clear in areas where fat intake is low.

METHODS

We conducted a hospital-based case-control study from 1992 to 1995 in Jakarta, Indonesia.

RESULTS

The study, based on 226 cases and 452 age and socioeconomic status matched controls, provided the following findings. (a) In the pre-marriage period, the greater the fat or protein consumption, the larger the risk, whereas decreasing risk with increasing carbohydrate intake was detected. The odds ratio (OR) for the highest quartile of intake relative to the lowest was 8.47 (95% CI: 4.03-17.8) for fat, 2.19 (95% CI: 1.30-3.69) for protein, and 0.16 (95% CI: 0.08-0.31) for carbohydrate. A positive association with fat and a negative one with carbohydrate were also observed for the post-marriage period, but of weaker magnitude compared to the pre-marriage period. (b) The effects of macronutrient intakes were stronger among premenopausal than among postmenopausal women. (c) Most of the associations of protein and carbohydrate were insignificant after adjustment for fat intake.

CONCLUSIONS

These findings suggest that fat intake might be an important determinant of breast cancer among populations with a low fat diet in Indonesia.

Meta-analysis: dietary fat intake, serum estrogen levels, and the risk of breast cancer

BACKGROUND

There is compelling evidence that estrogens influence breast cancer risk. Since the mid-1980s, dietary fat intervention studies have been conducted to investigate the effect of fat intake on endogenous estrogen levels. To further our understanding of the possible relationship between dietary fat and breast cancer, we conducted a meta-analysis of dietary fat intervention studies that investigated serum estradiol levels, and we reviewed the nature of the evidence provided by prospective analytic studies of fat consumption and breast cancer risk.

METHODS

A computerized search of the English language literature on estrogen/estradiol and dietary fat intervention studies published from January 1966 through June 1998 was conducted using the MEDLINE database. Pooled estimates were derived from the change in estradiol levels associated with fat reduction from 13 studies. Analyses were conducted separately for premenopausal and postmenopausal women and in both groups combined.

RESULTS AND CONCLUSIONS

Statistically significant reductions in serum estradiol levels of -7.4% (95% confidence interval [CI] = -11.7% to -2.9%) among premenopausal women and -23.0% (95% CI = -27.7% to -18.1%) among postmenopausal women were observed, with an overall -13.4% (95% CI = -16.6% to -10.1%) reduction observed. The greatest reductions occurred in two studies in which dietary fat was reduced to 10%-12% of calories compared with 18%-25% of calories in the other studies. A statistically significant reduction in estradiol levels of -6.6% (95% CI = -10.3% to -2.7%) remained after exclusion of these two studies. Review of prospective analytic epidemiologic studies that allowed for dietary measurement error suggests that the possibility that reducing fat consumption below 20% of calories will reduce breast cancer risk cannot be excluded.

IMPLICATIONS

Dietary fat reduction can result in a lowering of serum estradiol levels and such dietary modification may still offer an approach to breast cancer prevention.

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.

The effect of dietary fat on the promotion of mammary and colon cancer in a dual-organ rat carcinogenesis model

Female Sprague-Dawley rats (n = 270) were randomly divided into nine subgroups (30 rats/group) and fed diets with fat contents ranging from 5% to 45% of total energy, in which fat was isocalorically substituted for carbohydrates. At Week 3, the rats were given a single injection of methylnitrosourea (MNU, 50 mg/kg body wt). At Weeks 4 and 5, rats were given an injection of azoxymethane (AOM, 15 mg/kg body wt sc). The rats were maintained on their respective experimental diets until they were sacrificed. Nine weeks after the injection of MNU, 10 rats from each group were killed and their mammary tissue was examined for tumors and their colons for aberrant crypt foci (ACF) formation. The results showed no significant increase in the number of colonic ACF or mammary tumors at 11 weeks among individual groups consuming 5-25% energy from fat or among groups consuming 30-45% energy from fat. Data analysis indicated that the effects of the two diets (5-25% energy from fat and 30-45% energy from fat) on ACF formation as well mammary tumor development were statistically different. Continuation of the diets for 32 weeks led to the development of colonic and mammary tumors. Analysis of the combined group tumor incidence data clearly showed that the colonic and mammary tumor incidence in groups fed 30-45% of energy from fat was significantly higher than that observed among groups fed 5-25% of energy from fat. Linear regression analysis of the colonic ACF at 11 weeks, colonic tumor incidence at 32 weeks, and mammary tumor incidence at 11 and 32 weeks showed good linear correlation, demonstrating the potential value of ACF and mammary tumors at 11 weeks for evaluating the carcinogenic risk associated with different diets. The main conclusion of the experiment is that the incidence of colon and mammary cancers increased rapidly when the dietary levels of fat were increased from 15% to 30% of calories and that there was no significant influence on the colon and mammary cancer risk beyond 30% of calories from fat.

Effects of two dietary fat levels and four dietary linoleic acid levels on mammary tumor development in Balb/c-MMTV mice under ad libitum feeding conditions

The relationship between dietary fat intake (level and type) and the development of breast cancer in humans is a matter of concern in Western society. A high fat intake is associated with a greater mammary cancer risk in humans and in animal models. Higher intake of polyunsaturated fatty acids in humans shows little or no association with mammary tumor development in epidemiologic surveys. From literature data, it appears that a higher intake of polyunsaturated fatty acids (linoleic acid) is related to an increase in mammary tumorigenesis in animal studies in which chemical carcinogens like dimethylbenz[a]anthracene are used as tumor initiator. Mostly the latency period of these chemically induced models in rather short. In this study, the Bald/c-MMTV (mouse mammary tumor virus) mouse strain was chosen as an animal model: MMTV leads to tumor initiation, and dietary factors influence tumor promotion over a relatively long latency period. The mice were fed diets with two fat concentrations: a high [36% of energy (en%)] or low (16 en%) fat level; fat was isocalorically replaced by carbohydrates (cornstarch). At both dietary fat levels, linoleic acid was given at four levels: 2, 3, 6, and 10 en%. Linoleic acid-rich fat was isocalorically replaced by oleic acid-rich fat. The diets were consumed ad libitum over a lifetime. Animals were euthanized as soon as mammary tumor diameter was > or = 1 cm or when the animals were in a poor clinical condition. The incidence of mammary tumors at 18 months was significantly higher in one group only: 36 en% fat and 2 en% linoleic acid. This group also showed the shortest mean latency period for mammary tumor development. Mean mammary tumor incidence was higher and mean onset time shorter in the four high-fat groups than in the low-fat groups. No (linear) dose-response relationship between dietary linoleic acid concentration and mammary tumor incidence and latency period was observed. This indicates that a higher dietary linoleic acid intake does not increase the incidence or shorten the latency period of breast cancer in the Balb/c-MMTV mouse strain at two different dietary fat levels.

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.

Interrelationship between dietary lipids and calories and experimental mammary gland tumorigenesis

The purpose of this communication was to review and critique the studies designed to examine the interrelationship between dietary fat and calories in experimental rodent mammary gland tumorigenesis. The results of these studies clearly show that hyperalimentation of fat, either saturated or unsaturated, significantly stimulates this tumorigenic process. This has been demonstrated in an impressive array of carcinogen-induced, transplantable, spontaneous, and metastatic experimental rodent mammary gland tumor systems. The stimulatory effect of high levels of dietary fat appears to act primarily at the promotional stage of this tumorigenic process. Whether the mammary tumor stimulatory effect of high levels of dietary fat is a result of the metabolic activity of the fat per se or is due to an excessive energy (caloric) intake has been examined. Data obtained from the experimental studies that address this issue support the viewpoint that the mammary tumorigenic-enhancing activities of a high fat diet is, at least in part, through a caloric mechanism.

Modulation of oxidative DNA damage levels by dietary fat and calories

Decreased dietary intake of fat and/or calories generally results in a lower incidence of mammary gland tumors in rodents. Feeding of either low-fat or calorie-restricted diets to rats also has been shown to result in decreased levels of oxidative DNA damage. Since oxidative DNA damage is suggested to have a role in carcinogenesis, this may be one mechanism by which dietary change can reduce cancer risk. The effects of calorie-restricted diets on both oxidative DNA damage levels and mammary gland tumor incidence are generally more pronounced than that of low-fat diets. There is, however, some difficulty in defining what amount of fat should be used to prepare 'low-fat' and 'high-fat' rodent diets as well as what a suitable fat intake for control diets should be in studies that examine the effects of dietary fat and/or calories on tumorigenesis. In particular, the promoting effects of dietary fat may be exerted only up to a certain level of fat, above which no further effect is observed. Another difficulty in the interpretation of the results is that there may be a time-dependent effect of high fat diets on oxidative damage, with increased damage resulting only when the diets are fed for longer periods of time. The appropriate experimental approach to model human dietary exposures therefore remains to be determined. Although the effects of caloric intake on mammary gland tumorigenesis appear to be more pronounced than that of fat intake, low-fat diets still may be useful as a preventive measure in human populations to reduce breast cancer risk for individuals who cannot safely reduce their caloric intake.

A rationale for dietary intervention in postmenopausal breast cancer patients: an update

In 1982, we proposed a large-scale randomized prospective trial to test the hypothesis that decreasing dietary fat intake from 38% to 20% of total calories would increase the disease-free interval and/or five-year survival rate for postmenopausal breast cancer patients. We now review new evidence from epidemiological studies, laboratory animal model studies, and preliminary feasibility trials that has accumulated over the past decade, in support of such a trial, and suggest that a more appropriate dietary goal is a reduction in fat intake to 15% of total calories.