Fish consumption and breast cancer risk: an ecological study

Dietary long-chain n-3 fatty acids for the prevention of cancer: a review of potential mechanisms

Increasing evidence from animal and in vitro studies indicates that n-3 fatty acids, especially the long-chain polyunsaturated fatty acids eicosapentaenoic acid and docosahexaenoic acid, present in fatty fish and fish oils inhibit carcinogenesis. The epidemiologic data on the association between fish consumption, as a surrogate marker for n-3 fatty acid intake, and cancer risk are, however, somewhat less consistent. This review highlights current knowledge of the potential mechanisms of the anticarcinogenic actions of n-3 fatty acids. Moreover, a possible explanation of why some epidemiologic studies failed to find an association between n-3 fatty acid intake and cancer risk is provided. Several molecular mechanisms whereby n-3 fatty acids may modify the carcinogenic process have been proposed. These include suppression of arachidonic acid-derived eicosanoid biosynthesis; influences on transcription factor activity, gene expression, and signal transduction pathways; alteration of estrogen metabolism; increased or decreased production of free radicals and reactive oxygen species; and mechanisms involving insulin sensitivity and membrane fluidity. Further studies are needed to evaluate and verify these mechanisms in humans to gain more understanding of the effects of n-3 fatty acid intake on cancer risk.

The traditional diet of Greece and cancer

The term 'Mediterranean diet', implying that all Mediterranean people have the same diet, is a misnomer. The countries around the Mediterranean basin have different diets, religions and cultures. Their diets differ in the amount of total fat, olive oil, type of meat, wine, milk, cheese, fruits and vegetables; and the rates of coronary heart disease and cancer, with the lower death rates and longer life expectancy occurring in Greece. The diet of Crete represents the traditional diet of Greece prior to 1960. Analyses of the dietary pattern of the diet of Crete shows a number of protective substances, such as selenium, glutathione, a balanced ratio of n-6/n-3 essential fatty acids (EFA), high amounts of fibre, antioxidants (especially resveratrol from wine and polyphenols from olive oil), vitamins E and C, some of which have been shown to be associated with lower risk of cancer, including cancer of the breast. Epidemiological studies and animal experiments indicate that n-3 fatty acids exert protective effects against some common cancers, especially cancers of the breast, colon and prostate. Many mechanisms are involved, including suppression of neoplastic transformation, cell growth inhibition, and enhanced apoptosis and anti-angiogenicity, through the inhibition of eicosanoid production from n-6 fatty acids; and suppression of cyclooxygenase 2 (COX-2), interleukin 1 (IL-1) and IL-6 gene expression by n-3 fatty acids. Recent intervention studies in breast cancer patients indicate that n-3 fatty acids, and docosahexaenoic acid (DHA) in particular, increase the response to chemopreventive agents. In patients with colorectal cancer, eicosapentaenoic acid (EPA) and DHA decrease cell proliferation, and modulate favourably the balance between colonic cell proliferation and apoptosis. These findings should serve as a strong incentive for the initiation of intervention trials that will test the effect of specific dietary patterns in the prevention and management of patients with cancer.

Conjugated docosahexaenoic acid suppresses KPL-1 human breast cancer cell growth in vitro and in vivo: potential mechanisms of action

Introduction

The present study was conducted to examine the effect of conjugated docosahexaenoic acid (CDHA) on cell growth, cell cycle progression, mode of cell death, and expression of cell cycle regulatory and/or apoptosis-related proteins in KPL-1 human breast cancer cell line. This effect of CDHA was compared with that of docosahexaenoic acid (DHA).

Methods

KPL-1 cell growth was assessed by colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay; cell cycle progression and mode of cell death were examined by flow cytometry; and levels of expression of p53, p21^Cip1/Waf1, cyclin D₁, Bax, and Bcl-2 proteins were examined by Western blotting analysis. In vivo tumor growth was examined by injecting KPL-1 cells subcutaneously into the area of the right thoracic mammary fat pad of female athymic mice fed a CDHA diet.

Results

CDHA inhibited KPL-1 cells more effectively than did DHA (50% inhibitory concentration for 72 hours: 97 μmol/l and 270 μmol/l, respectively). With both CDHA and DHA growth inhibition was due to apoptosis, as indicated by the appearance of a sub-G₁ fraction. The apoptosis cascade involved downregulation of Bcl-2 protein; Bax expression was unchanged. Cell cycle progression was due to G₀/G₁ arrest, which involved increased expression of p53 and p21^Cip1/Waf1, and decreased expression of cyclin D₁. CDHA modulated cell cycle regulatory proteins and apoptosis-related proteins in a manner similar to that of parent DHA. In the athymic mouse system 1.0% dietary CDHA, but not 0.2%, significantly suppressed growth of KPL-1 tumor cells; CDHA tended to decrease regional lymph node metastasis in a dose dependent manner.

Conclusion

CDHA inhibited growth of KPL-1 human breast cancer cells in vitro more effectively than did DHA. The mechanisms of action involved modulation of apoptosis cascade and cell cycle progression. Dietary CDHA at 1.0% suppressed KPL-1 cell growth in the athymic mouse system.

Dietary docosahexaenoic acid suppresses N-methyl-N-nitrosourea-induced mammary carcinogenesis in rats more effectively than eicosapentaenoic acid

We compared the effects of identical amounts but different proportions of dietary n-3 polyunsaturated fatty acids (PUFAs) on N-methyl-N-nitrosourea (MNU)-induced mammary cancer in a rat model. The ability of dietary docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) to suppress mammary cancer was evaluated. Female Sprague-Dawley rats were randomly assigned to three groups and maintained on diets containing 10% fatty acid consisting of EPA, a 1:1 mixture of EPA-plus-DHA, or DHA. The experimental diet was started after administration of MNU at 49 days of age, and the rats were maintained on the respective diets until the largest mammary tumor reached >1 cm in diameter or until the end of the study period (20 wk after MNU). All histologically detected mammary carcinomas were evaluated, irrespective of size. The DHA diet was associated with significant suppression of the carcinogenic effect of MNU compared with the EPA and EPA-plus-DHA diets: tumor incidence decreased to 23% (3/13) compared with 73% (11/15) and 65% (12/17) (P < 0.01 and P < 0.05, respectively); tumor multiplicity decreased to 0.23 compared with 1.67 and 1.59 (P < 0.01 and P < 0.05, respectively). There was no significant difference in tumor latency among the DHA, EPA, and EPA-plus-DHA groups (119, 105, and 117 days, respectively). Over 20 wk, the fatty acid composition of serum and mammary fat tissue reflected differences in the dietary n-3 PUFAs. Although DHA suppressed MNU-induced mammary carcinogenesis more effectively than EPA, generalized steatosis including mammary fat tissue appeared in all three groups.

The Role of Nutrition in the Prevention of Breast Cancer

Nutrition has been widely studied as a leading environmental factor in the prevention of breast cancer (BC). Despite the challenges in relating consumption of specific nutrients to BC risk, particularly in the context of a total diet, many investigators have contributed valuable information. Dietary fat has received the most attention and also created the most uncertainty. Specific types of fat, particularly monounsaturated fat and the ratio of omega-3 to omega-6 fatty acids, demonstrate more potential to influence BC risk. A wide variety of other dietary factors have been studied in relation to BC including total energy, dietary fiber, alcohol, micronutrients, phytochemicals, specific foods, and food constituents. Results of epidemiological studies relating consumption of these dietary factors to BC have increased the knowledge base that provides rationale for various nutritional strategies to contribute to BC prevention.

Dietary factors protective against breast cancer in Japanese premenopausal and postmenopausal women

Since components of the Japanese diet that might be responsible for the relatively low breast cancer incidence rates observed in Japan have not been clarified in detail, a case-referent study with reference to menopausal status was conducted using data from the hospital-based epidemiologic research program at Aichi Cancer Center (HERPACC). In total, 2,385 breast cancer cases were included, and 19,013 women, confirmed as free of cancer, were recruited as the reference group. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were determined by multiple logistic regression analysis. There were reductions in risk associated with high intake of milk and green-yellow vegetables (green leafy vegetables, carrots and pumpkins) among both pre- and postmenopausal women. The protective effects of the Japanese diet were more prominent among postmenopausal than premenopausal women. The adjusted OR of fish consumption (5 or more times per week vs. fewer than 3 times per month) was 0.75 (95% CI 0.57-0.98, p(trend) = 0.01) for postmenopausal breast cancer. A significant decrease in postmenopausal breast cancer risk was also observed for increasing intake of fruit (OR = 0.61, 95% CI 0.41-0.91). Thus, traditional Japanese dietary factors may protect against breast cancer development, especially among postmenopausal women.

Fish Intake Is Positively Associated with Breast Cancer Incidence Rate

Animal studies have, in general, been supportive of a protective effect of fish and fish (n-3) PUFA against breast cancer risk; but the epidemiologic evidence of such a relationship is limited. Case-control and cohort studies have rarely shown significant associations. The association between total fish intake and the effect of fat content and preparation method of the fish, in relation to the incidence rate ratios of breast cancer, were investigated among postmenopausal women. We also investigated the effect of fish intake with respect to estrogen receptor expression of breast cancer tumors. A total of 23,693 postmenopausal women from the prospective study "Diet, Cancer and Health" were included in the study. During follow-up, 424 women were diagnosed with breast cancer. The incidence rate ratio (IRR) and 95% CI per each additional 25 g of mean daily intake of fish were 1.13 (CI, 1.03-1.23). Analysis of fatty fish gave IRR of 1.11 (CI, 0.91-1.34), and the result for lean fish was 1.13 (CI, 0.99-1.29). When fish intake was stratified into three types of preparation methods, the IRR for fried fish was 1.09 (CI, 0.95-1.25), for boiled fish 1.09 (CI, 0.85-1.42), and for processed fish 1.12 (CI, 0.93-1.34). The IRR per additional 25 g of mean daily intake of fish was 1.14 (CI, 1.03-1.26) for estrogen receptor-positive (ER+) and 1.00 (CI, 0.81-1.24) for estrogen receptor-negative (ER-) breast cancer. In conclusion, this study showed that higher intakes of fish were significantly associated with higher incidence rates of breast cancer. The association was present only for development of ER+ breast cancer.

Dietary (n-3)/(n-6) fatty acid ratio: possible relationship to premenopausal but not postmenopausal breast cancer risk in U.S. women

Recent research has suggested that an increased (n-3) fatty acid intake and/or increased (n-3)/(n-6) polyunsaturated fatty acid (PUFA) ratio in the diet is associated with a lower breast cancer risk. This case-control study investigated the association between intake of (n-3) and other fatty acids and the (n-3)/(n-6) PUFA ratio and breast cancer risk. After combining data from two related case-control studies in Connecticut, we had information available on a total of 1119 women (565 cases and 554 controls). Cases were all histologically confirmed, incident breast carcinoma patients. Controls were hospital-based (Yale-New Haven Hospital study site) and population-based (Tolland County study site). Information on dietary intake was obtained through a validated food-frequency questionnaire. Standard multivariate methods were used to address the independent effects of specific fatty acids, fat classes and macronutrients on breast cancer risk. In the full study population, there were no significant trends for any macronutrient/fatty acid when comparing the highest to the lowest quartile of intake. When the analysis was restricted to premenopausal women, consumption of the highest compared with the lowest quartile of the (n-3)/(n-6) PUFA ratio was associated with a nonsignificant 41% lower risk of breast cancer [odds ratio (OR) = 0.59, 95% confidence interval (CI) 0.29, 1.19, P for trend = 0.09]. A higher (n-3)/(n-6) PUFA ratio was significantly associated with a lower risk of breast cancer when the data were restricted to the Tolland County (population-based) study site; OR = 0.50, 95% CI 0.27, 0.95, P for trend = 0.02. These results are consistent with the hypothesis that a higher (n-3)/(n-6) PUFA ratio may reduce the risk of breast cancer, especially in premenopausal women.

Meat, fish and egg intake and risk of breast cancer

Intakes of animal protein, meat, and eggs have been associated with breast cancer incidence and mortality in ecological studies, but data from long-term prospective studies are limited. We therefore examined these relationships in the Nurses' Health Study. We followed 88,647 women for 18 years, with 5 assessments of diet by food frequency questionnaire, cumulatively averaged and updated over time. We calculated the relative risks (RR) and 95% confidence intervals (95% CI) for risk of developing invasive breast cancer, over categories of nutrient and food intake. During follow-up, 4,107 women developed invasive breast cancer. Compared to the lowest quintile of intake, the RR and 95% CI for the highest quintile of intake were 1.02 (0.92-1.14) for animal protein, 0.93 (0.83-1.05) for red meat and 0.89 (0.79-1.00) for all meat. Results did not differ by menopausal status or family history of breast cancer. We found no evidence that intake of meat or fish during mid-life and later was associated with risk of breast cancer.

Intakes of fish and marine fatty acids and the risks of cancers of the breast and prostate and of other hormone-related cancers: a review of the epidemiologic evidence

Marine fatty acids, particularly the long-chain eicosapentaenoic and docosahexaenoic acids, have been consistently shown to inhibit the proliferation of breast and prostate cancer cell lines in vitro and to reduce the risk and progression of these tumors in animal experiments. However, whether a high consumption of marine fatty acids can reduce the risk of these cancers or other hormone-dependent cancers in human populations is unclear. Focusing primarily on the results of cohort and case-control studies, we reviewed the current epidemiologic literature on the intake of fish and marine fatty acids in relation to the major hormone-dependent cancers. Despite the many epidemiologic studies that have been published, the evidence from those studies remains unclear. Most of the studies did not show an association between fish consumption or marine fatty acid intake and the risk of hormone-related cancers. Future epidemiologic studies will probably benefit from the assessment of specific fatty acids in the diet, including eicosapentaenoic and docosahexaenoic acids, and of the ratio of these to n-6 fatty acids, dietary constituents that have not been examined individually very often.

Eicosapentaenoic acid-induced apoptosis depends on acyl CoA-synthetase

Marine n-3 FA are known to inhibit proliferation or induce cell death in several cancer cell lines. We have previously reported that EPA promotes apoptosis in the lymphoma cell line Ramos, whereas the U-698 cell line is insensitive to EPA. Furthermore, acyl-CoA synthetase (ACS) is expressed to a higher extent in Ramos cells compared to U-698 cells. To investigate the importance of ACS in EPA-induced apoptosis, we incubated Ramos cells with triacsin C, an inhibitor of ACS. This caused a 70% reduction in the amount of cell-associated EPA and diminished activation of EPA. In addition, triacsin C caused a 90% reduction in EPA-induced apoptosis. Several different approaches were tried to overexpress ACS4 in EPA-insensitive lymphoma cell lines, but we did not obtain viable cells with high expression of acyl-CoA activation. However, we show that overexpression of ACS4 in the more robust COS-1 cells caused up to a fivefold increase in activation of EPA and a 67% increase in the amount of cell-associated radiolabeled EPA. Furthermore, we observed 28% elevated cellular level of TAG in EPA-incubated COS-1 cells overexpressing ACS4. The present study provides new information about ACS as an important enzyme for EPA-induced apoptosis in Ramos cells. Our data offer a potential mechanism that may explain the effect of dietary marine n-3 PUFA on growth of certain malignant cells.

Influence of omega-3 fatty acids on the growth of human colon carcinoma in nude mice

The present study investigated the influence of dietary omega-3 fatty acid supplementation on the growth of human colon carcinoma xenograft in athymic nude mice. Four diets were fed to evaluate the effect of levels and types of fat on colon tumor growth. Animals were maintained on a standard diet modified by addition of fats containing omega-3 and omega-6 fatty acids to represent high and low fat intakes for 53 days. The final mean estimated tumor weight for the high fat corn oil (24%) fed group was 2,302 mg, whereas the low fat (8% corn oil) group was 1,681 mg. The final mean tumor weight of the high fat menhaden oil fed group was 782 mg representing a 66% decrease in growth compared to the high fat corn oil group and a decrease of 54% compared to the low corn oil fed group. The high fat golden algae oil fed group resulted in a mean final tumor weight of 223 mg representing a 90% inhibition of tumor growth relative to the high fat corn oil fed group and 87% inhibition of growth compared to the low fat corn oil fed group. These findings indicate that dietary omega-3 fatty acids possess significant tumor suppressing properties and that the primary tumor suppressing fatty acid is docosahexaenoic acid. Histopathologic examination of control and treated tumors and expression array analyses (human cytokine and apoptosis arrays) support the tumor growth inhibition data and provide evidence for discussion of possible mechanisms for the observed growth inhibition.

Conjugated linoleic acids (CLAs) regulate the expression of key apoptotic genes in human breast cancer cells

Conjugated linoleic acid (CLA) reduces mammary tumorigenesis in rodent models, induces apoptosis in rodent mammary tumor cell lines, and decreases expression of antiapoptotic bcl-2 in rat mammary tissue. This investigation focused on the cell mechanisms underlying the antitumor effects of CLA. Changes (mRNA, protein) in expression of major proapoptotic p53, p21WAF1/CIP1, bax, bcl-Xs genes, and the antiapoptotic bcl-2 gene were observed in malignant MCF-7 and MDA-MB-231 cells and in benign MCF-10a human mammary tumor cells in culture. CLA, but not linoleic acid (LA), inhibited proliferation in all cells; CLA mix was most effective. CLA increased DNA damage (apoptosis). CLA increased mRNA expression of p53 and p21WAF1/CIP1 (three- to fivefold and twofold, respectively) but either decreased bcl-2 by 20-30% or had no effect in MCF-7 and MCF-10a cells, respectively; protein expression reflected mRNA values. In MDA-MBA-231 (mutant p53) cells, mRNA for p53 was not changed, but p21WAF1/CIP1 and bcl-2 mRNA was increased. Protein expression largely reflected mRNA changes but, surprisingly, CLA completely suppressed mutant p53 protein in MDA-MB-231 cells. Apparent antiapoptotic effects of increased bcl-2 expression in MDA-MBA-231 cells were countered by increased proapoptotic p21WAF1/CIP1, Bax, and Bcl-Xs proteins. Findings indicate that CLA elicits mainly proapoptotic effects in human breast tumor cells through both p53-dependent and p53-independent pathways, according to cell type.

Cell signal mechanisms, conjugated linoleic acids (CLAs) and anti-tumorigenesis

Fats have been adversely implicated in the aetiology of many forms of cancer yet evidence is accumulating that certain types of fatty acids have anticancer properties. This is well documented for fish-oil fatty acids of the n-3 family. Recently, fatty acids found to occur naturally in ruminant-derived food products were found to have anticancer properties. These fatty acids were identified as conjugated linoleic acids (CLAs) derived from the parent linoleic acid by its partial hydrogenation by rumen bacteria. Studies with tumour-bearing animals have shown that consumption of CLAs particularly with regard to breast and prostate cancer is beneficial. Studies with cancer cells have also shown that these fatty acids can inhibit cell proliferation and induce cell death. However, little is known regarding the mechanisms of action of these CLAs. In particular, which cellular signal mechanisms are regulated by CLAs which can explain their anticancer properties. We have shown that CLAs specifically up-regulate cell signal systems at the level of gene expression (mRNA, protein) in human breast and prostate cancer cells which are responsible for the induction of apoptosis or programmed cell death. These findings support the anticancer effects of CLA found in animal models and indicate similar effects could occur in man.

Linkage between retinoid and fatty acid receptors: implications for breast cancer prevention

Certain dietary retinoids and polyunsaturated fatty acids (PUFAs) consistently inhibit progression of mammary carcinogenesis both in animal studies and cell culture, but clinically, their effect is inconsistent. New evidence of synergistic interaction between the nuclear receptors for the two groups of nutritional agents suggests that appropriate selective ligands from each group might be combined in breast cancer chemoprevention studies. Peroxisome proliferator-activated receptor (PPAR) gamma is a nuclear receptor that is activated by PUFAs, eicosanoids and antidiabetic agents such as troglitazone. Such activation can cause growth inhibition in human mammary cancer cells in culture and the effect is enhanced by ligands of retinoic acid receptor (RAR) and retinoid X receptor (RXR). In mouse mammary tissue in organ culture, an RXR-selective ligand has been shown to enhance the effect of troglitazone in suppressing carcinogen-induced pre-neoplastic changes. A PPAR/RXR heterodimer is involved in tumour growth inhibition and has been shown to bind directly to nuclear oestrogen response elements (ERE) independently of oestrogen receptor (ER) activity. A combination of an RXR-selective retinoid with either troglitazone or else a long-chain n-3 PUFA, is proposed for a short-term study in postmenopausal women after primary surgery for intraductal breast cancer. The resulting activation of PPAR/RXR expression may increase response to retinoid administration, especially in the presence of obesity and insulin resistance, because of the ability of PPAR gamma ligands to reduce insulin-like growth factor I (IGF-I) concentrations. Serial core biopsies of breast tissue over a short term are proposed to identify changes in phenotype, which may influence progression to invasiveness. In addition to cytomorphological criteria, expression of ER alpha and beta, RAR alpha and beta, and IGF-I receptor in the nucleus should be examined.

Eicosapentaenoic acid promotes apoptosis in Ramos cells via activation of caspase-3 and -9

Eicosapentaenoic acid (EPA; 20:5n-3) may reduce the cell number in cultured leukemia/lymphoma cells owing to reduced cell proliferation, induction of cell death, or a combination of these processes. EPA has been shown to promote apoptosis in Ramos cells, and our present study was focused on a possible cell cycle arrest and the pathways by which the apoptotic process is induced. Apoptosis may proceed along the intrinsic (mitochondrial) or the extrinsic (death receptor) pathway, which are mediated via different caspases. Caspases are a class of homologous cysteine proteases recognized as pivotal mediators of apoptosis. We investigated whether EPA affects progression of the cell cycle or promotes apoptosis directly. By incorporation of [3H]thymidine and [3H]valine, we showed that DNA, as well as protein synthesis, was reduced after incubation of Ramos cells with EPA for 6 h. We monitored cell cycle distribution by 5-bromo-2'-deoxyuridine staining and observed no cell cycle arrest in the EPA-incubated cells. Incubation of cells with EPA caused PS-flipping, as demonstrated by annexin V-binding (flow cytometry), and cleavage of poly(ADP-ribose) polymerase measured by Western blot analysis. Furthermore, we observed increased activity of caspase-3 and -9, but not of caspase-8. Whereas inhibitors of caspase-3 and -9 reduced EPA-induced apoptosis, inhibition of caspase-8 did not. This suggests that EPA may promote apoptosis via the intrinsic pathway in Ramos cells. Thus, the reduction in cell number can be explained by a direct apoptotic effect of EPA rather than via cell cycle arrest.

N-3 fatty acids and lipid peroxidation in breast cancer inhibition

Long-chain n-3 fatty acids (FA) consistently inhibit the growth of human breast cancer (BC) cells both in culture and in grafts in immunosuppressed mice. Large cohort studies have, however, failed to confirm a protective effect for fish oils rich in n-3 FA against BC risk. The present review examines new evidence on biological mechanisms which may be involved in the inhibition of mammary carcinogenesis by long-chain n-3 FA, focusing on an apoptotic effect by its lipid peroxidation products. Dietary intake of n-3 FA leads to their incorporation into cell membrane lipids. Increased apoptosis in human BC cells following exposure to long-chain n-3 FA such as eicosapentaenoic and docosahexaenoic acids is generally ascribed to their inhibition of cyclooxygenase 2 which promotes mammary carcinogenesis. In addition however, long-chain n-3 FA are particularly likely to activate peroxisome proliferator-activated receptor (PPAR)-gamma, a key regulator of lipid metabolism but also capable of modulating proliferative activity in a variety of cells including mammary cells. Expression of PPAR-gamma in the nucleus is activated by second messengers such as J series prostaglandins and the latter have been shown to cause apoptosis in vivo in explants of human BC cells in immunosuppressed mice. In mammary tumours, it is observed that long-chain FA not only increase apoptosis, but also increase lipid peroxidation, and the apoptotic effect can be reversed by antioxidants. The rationale for use of n-3 FA dietary supplements in counteracting BC progression needs to be tested clinically in a phase 2 pilot study, while at the same time, the effect on whole-body lipid peroxidation needs to be monitored. Dietary supplements of fish oil rich in n-3 FA are proposed for premenopausal women over the age of 40 years who are shown to be at increased BC risk. Biological markers in breast tissue of BC progression will be monitored, and observed changes related to serial plasma levels of isoprostanes as a measure of whole-body lipid peroxidation.

Dietary fat reduction to reduce prostate cancer risk: controlled enthusiasm, learning a lesson from breast or other cancers, and the big picture

Breast and prostate cancer share similar intrinsic and extrinsic risk factors. Based on laboratory, ecologic/international comparison, and case-control studies, the impact of dietary fat or other fat subtypes has been suggested as a potential route to reduce risk. Recent large-scale prospective studies have failed to find an association between fat and breast cancer risk. These studies may provide some insight for researchers examining the relation between fat and prostate cancer. Prospective studies to date have also failed to find a consistent association between prostate cancer and fat intake. Some fat subtypes (eg, saturated fat) or other lifestyle changes (eg, obesity, physical activity) may affect risk and progression of these cancers when examining the sum total of the research, but more precise and specific investigations in humans are needed to address these issues. Other concerns, such as the impact of excess energy or overall caloric consumption on carcinogenesis, still need to be addressed, as well as other methodologic limitations of past investigations. Large gaps exist in environmental (eg, diet, lifestyle) and heritable causes of these diseases. Regardless, until more extensive research is completed, lifestyle changes should be recommended based on reducing morbidity and mortality from cardiovascular disease-the number 1 cause of death in the United States. Additionally, cardiovascular disease remains the number 1 or 2 cause of death in patients diagnosed with breast or prostate cancer. Practical and simple dietary changes should be encouraged by health professionals because they could improve the overall longevity and quality of patients' lives. Numerous ongoing prospective studies of diet and cancer should provide researchers and the public with much-needed answers in this area.

An ecologic study of dietary and solar ultraviolet-B links to breast carcinoma mortality rates

BACKGROUND

The role of diet in the etiology of breast carcinoma has been debated for decades. The ecologic approach generally finds that dietary fat is highly associated with breast carcinoma mortality, with fish intake and solar ultraviolet-B (UV-B) radiation, a source of vitamin D, inversely associated. Case-control and cohort studies generally find a variety of chemical, nonfat dietary, environmental, genetic, lifestyle, and reproductive factors to be important.

METHODS

An ecologic study was conducted using breast carcinoma mortality rates (1989-1996), dietary supply data, and latitude (an index of solar UV-B radiation) from 35 countries.

RESULTS

The fraction of energy derived from animal products (risk) combined with that from vegetable products (risk reduction), followed by solar UV-B radiation and, to a lesser extent, energy derived from alcohol (risk) and fish intake (risk reduction), were found to explain 80% of the variance of breast carcinoma mortality rates. Dietary fat contributed insignificantly in regressions involving the other factors.

CONCLUSIONS

It is hypothesized that animal products are associated with risk for breast carcinoma because they are associated with greater amounts of insulin-like growth factor-1 and lifetime doses of estrogen. Vegetable products contain several risk reduction components including antioxidants and phytoestrogens. The association with latitude is very likely because of solar UV-B radiation and vitamin D. Alcohol modulates estrogen's effects on breasts. Fish intake is associated with risk reduction through vitamin D and n-3 oils. These results are consistent with those of many case-control and cohort studies but should be assessed in well designed cohort studies.

Is there a role for iodine in breast diseases?

It is hypothesized that dietary iodine deficiency is associated with the development of mammary pathology and cancer. A review of the literature on this correlation and of the author's own work on the antioxidant function of iodide in iodide-concentrating extrathyroidal cells is reported. Mammary gland is embryogenetically derived from primitive iodide-concentrating ectoderm, and alveolar and ductular cells of the breast specialize in uptake and secretion of iodine in milk in order to supply offsprings with this important trace-element. Breast and thyroid share an important iodide-concentrating ability and an efficient peroxidase activity, which transfers electrons from iodide to the oxygen of hydrogen peroxide, forming iodoproteins and iodolipids, and so protects the cells from peroxidative damage. The mammary gland has only a temporary ability to concentrate iodides, almost exclusively during pregnancy and lactation, which are considered protective conditions against breast cancer.

Effect of omega-3 fatty acid (docosahexanoic acid) on BRCA1 gene expression and growth in MCF-7 cell line

Recently, we have demonstrated that omega-6 fatty acid linoleic acid (LA) in presence of estradiol (E2) enhances proliferation and anchorage independent growth with down regulation of BRCA1 mRNA expression in MCF-7 cell line. Since omega-3 fatty acid (docosahexanoic acid, DHA) is known to block the promoting effect of omega-6 polyunsaturated fatty acid (LA), we wanted to see whether addition of DHA can inhibit the growth of MCF-7 cells which are exposed to LA + E2 and any alteration of BRCA1 mRNA expression could be seen in DHA treated culture. Experiments on MCF-7 cells with DHA revealed both decrease in proliferation and anchorage independency as compared to controls; while no change of BRCA1 mRNA expression was observed. Further, when DHA was administered to cells along with LA + E2, no change in BRCA1 expression was observed, however, a marked decrease in proliferation and soft agar colony formation was evident, indicating inhibition of MCF-7 cells following DHA treatment. Flow cytometric analysis showed that DHA treated cells either alone or in combination with LA + E2 induced marked G1/S and G2/M arrest of the cells, suggesting the inhibitory effect of DHA at this phase of cell cycle. However, neither typical DNA ladder nor fragmented nuclei or apoptotic bodies were observed, ruling out presence of apoptosis following DHA treatment.

Necrosis and apoptosis in lymphoma cell lines exposed to eicosapentaenoic acid and antioxidants

The present study is focused on the role of oxidative stress in the induction of either necrosis or apoptosis by eicosapentaenoic acid (EPA) in the lymphoma cell lines Raji and Ramos, respectively. To investigate the different death modes induced by EPA, we assessed the importance of some antioxidants and reactive oxygen species in the two cell lines. We observed that different antioxidants counteracted the necrotic effect of EPA on Raji cells to a different extent, and that vitamin E counteracted EPA-induced accumulation of superoxide anion in this cell line. On the contrary, no effects of antioxidants were observed on development of apoptosis induced by EPA in Ramos cells, and vitamin E did not counteract EPA-induced accumulation of superoxide anions in Ramos cells. Moreover, apoptosis was partly inhibited by transcription inhibitors (actinomycin D) and protein synthesis inhibitors (cycloheximide), suggesting dependency upon new protein synthesis prior to apoptosis. Kinase inhibitors (staurosporin and calphostin C) did not alter the EPA-induced apoptosis. The observed cellular accumulation of superoxide anion following EPA incubation may be important for induction of necrosis in Raji cells. In contrast, none of the other investigated parameters indicated a role of oxidative stress promoted by EPA in the induction of apoptosis in Ramos cells.

Polyunsaturated fatty acids and epidermal growth factor receptor/mitogen-activated protein kinase signaling in mammary cancer

Mammary cancer is the second leading cause of cancer death in women, the second most common neoplasm in dogs and the third leading neoplasm in cats. Mammary tumors are similar in morphology and progression in these species, so cats and dogs are good models for determining treatment or prevention modalities for the human population. Epidemiological, in vitro and rodent studies have demonstrated that polyunsaturated fatty acids (PUFA) can influence the growth, progression and metastasis of mammary cancer. Although a role of PUFA in modulating mammary cancer growth has been shown, the mechanisms by which this occurs remain unclear. Recent studies have demonstrated that PUFA may influence the activity of the epidermal growth factor receptor/mitogen-activated protein kinase pathway, which is involved in regulating several oncogenes (c-myc, c-fos, neu/c-erb-b2) involved in the progression of cancer. We review the potential mechanism by which PUFA may modulate the growth of mammary cancer through regulation of the epidermal growth factor receptor/mitogen-activated protein kinase signal transduction cascade.

Diet profiles in a population sample from Mediterranean southern France

OBJECTIVE

A Mediterranean diet quality index (MDQI) was devised to give an overall assessment of dietary habits and to identify groups at risk.

DESIGN

The MDQI was based on scores given for selected levels of consumption of selected nutrients and foods.

SETTING

Mediterranean southern France.

SUBJECTS

The sample included 473 men and 491 women in three age classes recruited at random.

RESULTS

Only 9.5% of men, 9.0% of women, 4.7% of 20-34 year old subjects, 6.6% of 35-54 year old subjects and 14.0% of 55-76 year old subjects were shown to have a healthy diet. However, 10.1% of men, 8.6% of women, 19.4% of 20-34 year old subjects, 10.2% of 35-54 year old subjects and 4.6% of 55-76 year old subjects were shown to have a poor diet. There were significantly fewer smokers among subjects with a good diet but the distribution of moderate wine drinkers was comparable between those with a good diet and those with a poor diet. Correspondence analysis associated a healthy diet with 55-76 year old men and women living in rural areas, who had received primary schooling only and who were manual workers. Both men and women with a poor MDQI score tended to be young and smokers. In addition, women with a poor MDQI tended to be heavy drinkers and obese.

CONCLUSIONS

This study showed that the Mediterranean model, which is generally recognized as a healthy diet, appears restricted to older people and to rural areas, whereas urbanized young people depart from it. A nutritional prevention policy targeted at young adults is required to encourage them to adhere to the Mediterranean model. Smoking and drinking showed different distribution patterns in the sample under study.

Docosahexaenoic acid induces apoptosis in Jurkat cells by a protein phosphatase-mediated process

Docosahexaenoic acid (DHA) is an omega-3 fatty acid under intense investigation for its ability to modulate cancer cell growth and survival. This research was performed to study the cellular and molecular effects of DHA. Our experiments indicated that the treatment of Jurkat cells with DHA inhibited their survival, whereas similar concentrations (60 and 90 microM) of arachidonic acid and oleic acid had little effect. To explore the mechanism of inhibition, we used several measures of apoptosis to determine whether this process was involved in DHA-induced cell death in Jurkat cells. Caspase-3, an important cytosolic downstream regulator of apoptosis, is activated by death signals through proteolytic cleavage. Incubation of Jurkat cells with 60 and 90 microM DHA caused proteolysis of caspase-3 within 48 and 24 h, respectively. DHA treatment also caused the degradation of poly-ADP-ribose polymerase and DNA fragmentation as assayed by flow cytometric TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) assay. These results indicate that DHA induces apoptosis in Jurkat leukemic cells. DHA-induced apoptosis was effectively inhibited by tautomycin and cypermethrin at concentrations that affect protein phosphatase 1 (PP1) and protein phosphatase 2B (PP2B) activities, respectively, implying a role for these phosphatases in the apoptotic pathway. Okadaic acid, an inhibitor of protein phosphatase 2A, had no effect on DHA-induced apoptosis. These results suggest that one mechanism through which DHA may control cancer cell growth is through apoptosis involving PP1/PP2B protein phosphatase activities.

Profiles of a healthful diet and its relationship to biomarkers in a population sample from Mediterranean southern France

OBJECTIVES

The failure of single-nutrient supplementation to prevent disease in intervention studies underlines the necessity to develop a holistic view of food intake. The objectives of this study were to devise a diet quality index (DQI) and identify biomarkers of multidimensional dietary behavior.

DESIGN

A nutrition survey was conducted in Mediterranean southern France by means of a food frequency questionnaire. The DQI was based on current dietary recommendations for prevention of diet-related diseases such as cardiovascular disease and some cancers. A second DQI included tobacco use.

STATISTICAL ANALYSES

performed Spearman rank correlations, cross-classifications and intraclass correlations were computed between the DQI and biomarkers.

RESULTS

Of the 146 subjects, 10 had a healthful diet and 18 had a poor diet. Erythrocyte omega-3 fatty acids-eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)-beta carotene, and vitamin E concentrations were lower and cholesterol concentrations were higher in the poor diet; the difference was significant for EPA and DHA and borderline significant for vitamin E. Significant correlation was found between the DQI and vitamin E (-0.12), EPA (-0.30), and DHA (-0.28), and beta carotene (-0.17) when tobacco use was considered, but not between the DQI and cholesterol. The correlation coefficient reached 0.58 (P0.01) for a composite index based on all biomarkers except cholesterol.

CONCLUSIONS

Subjects with a beta carotene levels greater thanl micromol/L, vitamin E greater than 30 micromol/L and EPA greater than 0.65% and DHA greater than 4% of fatty acids in erythrocytes were likely to have a healthful diet. Each biomarker indicated the quality of diet, but correlation was higher with a composite index.

The relation between fish consumption, death from all causes, and incidence of coronary heart disease. the NHANES I Epidemiologic Follow-up Study

1 time/week (adjusted relative risk 0.85, 95% CI 0.68-1.06). Similar but nonsignificant trends were seen in white and black women, but not black men. In white men, risk of noncardiovascular death but not cardiovascular death was also significantly reduced in those consuming fish once or more a week. No consistent association of fish consumption and coronary heart disease incidence or mortality was seen. White men consuming fish once a week had significantly lower risk of death over a 22-year follow-up than those never consuming fish. This was mostly attributable to reductions in death from noncardiovascular causes. Similar patterns, though not significant, were seen in women. Further studies are needed to confirm these findings and to elucidate mechanisms for the effect of fish consumption on noncardiovascular mortality.

The effect of increased intakes of polyunsaturated fatty acids and vitamin E on DNA damage in human lymphocytes

The effect of increasing dietary intakes of polyunsaturated fatty acids (PUFAs) and vitamin E on indices of oxidative DNA damage was investigated. Twenty-one healthy male, nonsmokers aged 28.9 +/- 1.3 years participated in a free-living, split plot/change over trial in which half the volunteers consumed diets containing 5% PUFA as food energy for 4 wk and, after a 10 wk washout period, consumed a 15% PUFA diet for another 4 wk. The other volunteers followed an identical protocol, except that they consumed the 15% PUFA diet first. The diets were provided to volunteers either with or without an additional 80 mg dalpha-tocopherol acetate/day; otherwise total fat, carbohydrates, protein, and basal vitamin E contents remained unchanged. DNA damage induced by 200 microM H(2)O(2) in lymphocytes from volunteers as well as endogenous DNA damage in the form of oxidized pyrimidines, measured by alkaline single-cell gel electrophoresis (the comet assay), significantly decreased after consumption of the 5% PUFA diet (P<0.001 and P=0.01, respectively), but significantly increased after consumption of the 15% PUFA diet when alpha-tocopherol levels were in the range of 5-7 mg/day (P=0. 008 and P=0.03, respectively). These changes were abolished by an additional 80 mg dalpha-tocopherol/day. This study indicates that increasing dietary levels of PUFA to 15% may adversely affect some indices of DNA stability. However, increasing the dietary intake of vitamin E by 80 mg/day ameliorates the damaging effects of PUFA. -Jenkinson, A. McE., Collins, A. R., Duthie, S. J., Wahle, K. W. J., Duthie, G. G. The effect of increased intakes of polyunsaturated fatty acids and vitamin E on DNA damage in human lymphocytes.

Induction of apoptosis in HL-60 cells by eicosapentaenoic acid (EPA) is associated with downregulation of bcl-2 expression

Dietary polyunsaturated fatty acids (PUFAs) have been reported as a potential group of natural products which modulate tumor cell growth. In present study, eicosapentaenoic acid (EPA) was found to inhibit proliferation of human leukemic HL-60 and K-562 cells in vitro. EPA arrested cell cycle progression at G0/G1 phase, and induced necrosis in both HL-60 and K-562 cells. However, EPA induced apoptosis only in HL-60 but not K-562 cells. Also, bcl-2 protein expression was downregulated in much greater extent than that of bax showing that depression of bcl-2 might be an important step during the EPA-induced apoptosis in HL-60 cells.

Dietary fat and carcinogenesis

Epidemiologic investigations have suggested a relationship between dietary fat intake and various types of cancer incidences. Furthermore, epidemiologic studies as well as studies with animal models have demonstrated that not only the amount but also the type of fat consumed is important. At present, the mechanism by which dietary fat modulates carcinogenesis has not been elucidated. The effects of dietary fat on the development of tumours have been summarized in the present review with emphasis on colorectal, pancreas, breast and prostate cancer. It is concluded that influence on synthesis of prostaglandins and leukotrienes may be the universal mechanism by which dietary fats modulate carcinogenesis.

Fish consumption and cancer risk

BACKGROUND

Although several studies have investigated the relation between fish consumption and the risk of cardiovascular diseases, less attention has been paid to the relation between fish consumption and cancer risk.

OBJECTIVE

The relation between frequency of consumption of fish and risk of selected neoplasms was analyzed by using data from an integrated series of case-control studies conducted in northern Italy between 1983 and 1996.

DESIGN

The overall data set included the following incident, histologically confirmed neoplasms: oral cavity and pharynx (n = 181), esophagus (n = 316), stomach (n = 745), colon (n = 828), rectum (n = 498), liver (n = 428), gallbladder (n = 60), pancreas (n = 362), larynx (n = 242), breast (n = 3412), endometrium (n = 750), ovary (n = 971), prostate (n = 127), bladder (n = 431), kidney (n = 190), thyroid (n = 208), Hodgkin disease (n = 80), non-Hodgkin lymphomas (n = 200), and multiple myelomas (n = 120). Control subjects were 7990 patients admitted for acute, nonneoplastic conditions unrelated to long-term modifications of diet. Odds ratios (ORs) were computed for subsequent levels of fish consumption compared with no or occasional consumption (<1 serving/wk) by using multiple logistic regression, including terms for several covariates.

RESULTS

There was a consistent pattern of protection against the risk of digestive tract cancers with fish consumption: oral cavity and pharynx, OR = 0.5 for the highest compared with the lowest level of consumption; esophagus, OR = 0.6; stomach, OR = 0.7; colon, OR = 0.6; rectum, OR = 0.5; and pancreas, OR = 0.7. There were inverse trends in risk of larynx (OR = 0.7), endometrial (OR = 0.8), and ovarian (OR = 0.7) cancers and multiple myeloma (OR = 0.5). No pattern of cancer risk in relation to fish consumption was observed for cancers of the liver, gallbladder, breast, bladder, kidney, or thyroid or for lymphomas.

CONCLUSION

This study suggests that the consumption of even relatively small amounts of fish is a favorable indicator of the risk of several cancers, especially of the digestive tract.

Synergistic action of apoptosis induced by eicosapentaenoic acid and TNP-470 on human breast cancer cells

The effects of eicosapentaenoic acid (EPA) and an angiogenesis inhibitor (TNP-470) on the suppression of breast cancer cell growth were examined in five human breast cancer cell lines (MDA-MB-231, T-47D, MCF-7, KPL-1, and MKL-F). In all five cell lines, EPA and TNP-470 alone both showed tumor growth inhibition in a time- and dose-dependent manner, and in combination, a synergistic effect was seen at high concentrations. EPA plus TNP-470 treatment evoked apoptosis as confirmed by the appearance of sub G1 populations, by DNA fragmentation, and by cell morphology. With the combination, the expression of Bax and Bcl-xS, the apoptosis-enhancing proteins, was more up-regulated and that of Bcl-2 and Bcl-xL, the apoptosis-suppressing proteins, was more down-regulated compared to the use of EPA or TNP-470 alone, suggesting that their synergistic effect was due to an acceleration of apoptosis.

Fish consumption and mortality from all causes, ischemic heart disease, and stroke: an ecological study

BACKGROUND

The present study examined the relation between fish consumption and mortality from all causes, ischemic heart disease, and stroke.

METHODS

The fish consumption data in 1961-1963, 1979-1981, and 1989-1991 and mortality data, age-standardized to 45-74 years, mean of the latest available 3 years, mostly around 1992-1993, in 36 countries, were obtained from the Food and Agriculture Organization and the World Health Organization, respectively.

RESULTS

There exists an inverse univariate correlation between log fish consumption in 1961-1963, 1979-1981, and 1989-1991 and log all-cause (P < 0.01 to < 0.001) and ischemic heart disease (P < 0.05 to < 0.01) mortality in both sexes. An inverse univariate correlation between log fish consumption and log stroke mortality was found only for the period 1961-1963 in both sexes (P < 0.05). Log fish consumption was independently, significantly, and inversely associated with log all-cause (all P < 0.001), ischemic heart disease (P < 0.01 to < 0.001), and stroke (P < 0.05 to < 0.001) mortality in all three time periods in both sexes, after adjusting for confounding factors. These associations remained significant even after exclusion of Iceland and Japan, countries with the highest amount of fish consumption and the lowest all-cause mortality rate.

CONCLUSIONS

Fish consumption is associated with a reduced risk from all-cause, ischemic heart disease, and stroke mortality at the population level.

Association between breast and colorectal cancers

BACKGROUND

The risk of breast and colorectal cancers in immigrants from non-industrialised countries is sharply increased when they adopt a Western lifestyle. In addition, epidemiological studies on Western populations show an association between the two tumours, both in the same individual and also in close relatives. Most studies agree that high energy intake, obesity and inadequate physical exercise are associated with an increased risk of both tumours.

METHODS

Risk markers for each cancer are examined in order to identify causative nutritional factors or metabolic-endocrine dysfunction. The role of steroid hormones and other possible carcinogenic mechanisms is discussed, concentrating on evidence of a role for insulin and insulin-like growth factors (IGFs) in the promotion of carcinogenesis in both organs.

RESULTS

Individuals with a genetic susceptibility to insulin resistance show triggering of hyperinsulinaemia following excessive weight gain or long-term diet high in saturated fat. Case-control studies show an association between hyperinsulinaemia and evidence of breast or colorectal carcinoma. Multiple laboratory studies show that increased activity of IGFs can stimulate the growth of human breast and colorectal cancer cells.

CONCLUSION

It is postulated that either insulin resistance and its concomitants promote the development of breast and colorectal cancers, or that they share common risk factors. Sex steroid metabolism and organ specificity may explain age and sex differences between the tumours in relation to the role of obesity. Recent research suggests that a diet high in n-3 polyunsaturated fatty acids may reduce the risk of developing insulin resistance. This observation may be applied to test the hypothesis that an effect on hyperinsulinaemia may modify the risk of developing breast or colorectal cancer.

Breast cancer and the western diet: role of fatty acids and antioxidant vitamins

Epidemiological reports are inconsistent on the association between breast cancer risk and the dietary intake of either individual fatty acids or of antioxidant vitamins. It is postulated here that the inconsistencies are in part due to interactions between the two classes of nutrients at the level of the cell membrane, affecting their potential role in mammary carcinogenesis. In this review, the effects of specific dietary fatty acids and antioxidant vitamins on experimental mammary cancer systems are compared with reported epidemiological associations of the same agents with breast cancer risk in humans. An increased ratio of n-3 to n-6 polyunsaturated fatty acids (PUFAs) in the diet inhibits the growth of the rat mammary cancer model. There is also evidence that members of the n-3 PUFA series can inhibit the growth of human breast cancer cells both in vitro and in explants. Clinical trials of supplementary n-3 PUFAs in conjunction with a reduced fat intake have been proposed for breast cancer prevention. It is postulated that further dietary supplementation with vitamin E and a retinoid is likely to increase the effectiveness of such a diet. A study of this type allows better control of specific dietary components than prospective trials of dietary fat reduction which are presently under evaluation. In particular, it is suggested that studies focusing on a single nutrient often fail to recognise interactions with other nutrients.

Essential fatty acids, insulin resistance, and breast cancer risk

This review compares the prevalence of hyperinsulinemic insulin resistance in Caucasian-American women with that in Japanese-American and Pima Indian minority groups in the United States. It also examines the differences in breast cancer risk between these ethnic groups and suggests that risk may be modulated by ethnic genetic susceptibility to the effect of the Western diet in precipitating insulin resistance. It is widely agreed that the Western diet with its high saturated fatty acid content and high n-6/n-3 ratio of polyunsaturated fatty acids (PUFAs) favors the manifestation of hyperinsulinemia in individuals who are genetically predisposed. A number of case-control studies have shown hyperinsulinemia to be a marker of increased breast cancer risk, particularly in obese postmenopausal women. Mechanisms that have been postulated include an increased sex steroid level associated with a decreased serum level of sex hormone-binding globulin and an increased bioactive level of insulin-like growth factor I, which may synergize with estrogen in promoting mammary carcinogenesis. Dietary supplements rich in n-3 PUFAs have been shown to inhibit the growth of human breast cancer implants in nude mice, and members of the n-3 PUFA series can inhibit the growth of human breast cancer cell lines in vitro. On the basis of this experimental evidence, some have proposed dietary supplements rich in n-3 PUFAs for breast cancer protection. However, increased consumption of PUFAs requires increased intake of antioxidants. Vitamin E may be the most suitable agent, especially because of its added advantage that in animal models it is reported to reduce the incidence of carcinogen-induced mammary tumors. Preliminary trials of the combination may best be planned as adjuvant treatment after primary surgery for breast cancer, and the insulin hypothesis could be tested in the trials by monitoring fasting insulin and sex steroid levels.

Effects of dietary n-3-to-n-6 polyunsaturated fatty acid ratio on mammary carcinogenesis in rats

We investigated the effects of the dietary n-3-to-n-6 polyunsaturated fatty acid (PUFA) ratio (n-3/n-6 ratio) on mammary carcinogenesis induced by 7,12-dimethylbenz[a]anthracene in rats by feeding them several types of dietary fat with a fixed PUFA-to-saturated fatty acid ratio. Dietary fat was fed to the rats as 10% of the total feed weight, starting two weeks before the initiation. An increase in the n-3/n-6 ratio did not suppress the incidence or reduce the latency of mammary tumor development. The number and weight of mammary tumors per tumor-bearing rat tended to be large in the group with an n-3/n-6 ratio of 7.84 compared with those in the other groups. As the n-3/n-6 ratios were elevated, the total number and weight of tumors increased gradually. The prostaglandin E2 (PGE2) concentration in mammary tumor tissue was markedly low in the group with an n-3/n-6 ratio of 1.03 compared with the group with an n-3/n-6 ratio of 0.01. In addition, PGE2 concentrations were almost constant when n-3/n-6 ratios were > 1.03. These results suggested that the increase in the n-3/n-6 ratio of dietary fat with the fixed PUFA-to-saturated fatty acid ratio cannot suppress the mammary carcinogenesis but can promote development of tumors, despite reduced PGE2 concentration in the tumor.

Oxidative DNA damage levels in blood from women at high risk for breast cancer are associated with dietary intakes of meats, vegetables, and fruits

OBJECTIVE

We examined the relationship between intakes of specific foods--namely, meats, vegetables, and fruits--with levels of oxidative DNA damage in women consuming their own usual diet or a diet low in fat.

DESIGN

Blood was obtained from women who had been assigned randomly to a low-fat or nonintervention diet for 3 to 24 months. Levels of 5-hydroxymethyluracil, a type of oxidative DNA damage, were determined. Diet data were obtained from 3-day food records.

SUBJECTS/SETTING

The 21 women were participating in an outpatient clinic. All the women were healthy but had a first-degree relative with breast cancer.

INTERVENTION

The intervention was a self-selected diet with a goal of 15% of energy from fat.

MAIN OUTCOME MEASURES

Existing data on oxidative DNA damage levels were evaluated for possible relationships to foods eaten. Intakes of raw and cooked vegetables were examined separately. Meat intake was examined by type of meat (pork, beef, fish, chicken) and by cooking temperature.

STATISTICAL ANALYSES

Initial univariate analyses relied on Spearman rank correlations of each food item with DNA damage. Further analyses of the data were performed with univariate and multivariate weighted least squares regression models.

RESULTS

The model that best explained DNA damage levels was a bivariate regression model that included the intake of cooked vegetables and the sum of beef and pork intake. This model accounted for 85% of the variation in DNA damage levels among women. Preliminary results are suggestive of a positive association of DNA damage with beef and pork intake and a negative association with cooked vegetable intake.

APPLICATION

These observations, if confirmed in larger studies, suggest specific dietary changes to reduce oxidative DNA damage levels and possibly cancer risk.

Breast cancer risk, meat consumption and N-acetyltransferase (NAT2) genetic polymorphisms

Although inconsistencies exist, some studies have shown that meat consumption is associated with breast cancer risk. Several heterocyclic amines (HAs), formed in the cooking of meats, are mammary carcinogens in laboratory models. HAs are activated by polymorphic N-acetyltransferase (NAT2) and rapid NAT2 activity may increase risk associated with HAs. We investigated whether ingestion of meat, chicken and fish, as well as particular concentrated sources of HAs, was associated with breast cancer risk, and if NAT2 genotype modified risk. Caucasian women with incident breast cancer (n = 740) and community controls (n = 810) were interviewed and administered a food frequency questionnaire. A subset of these women (n = 793) provided a blood sample. Polymerase chain reaction and restriction fragment length polymorphism analyses were used to determine NAT2 genotype. Consumption of red meats, as well as an index of concentrated sources of HAs, was not associated with increased breast cancer risk, nor did risk vary by NAT2 genotype. In post-menopausal women, higher fish consumption was inversely associated with risk (odds ratio = 0.7; 95% confidence interval, 0.4-1.0); among pre-menopausal women, there was the suggestion of inverse associations between risk and pork and chicken intake. Our results suggest that consumption of meats and other concentrated sources of HAs is not associated with increased breast cancer risk. However, due to the strong biologic plausibility for a role of some HAs in mammary carcinogenesis, and the likely measurement error in evaluation of sources of HAs in this study, further studies of these possible relationships are warranted.

Meta-analyses of dietary fats and mammary neoplasms in rodent experiments

We review two meta-analyses of experiments on dietary fat and mammary tumor incidence in rodents, emphasizing a recent meta-analysis on the effects of different types of dietary fatty acids. This analysis shows that n-6 polyunsaturated fatty acids most strongly enhance mammary tumors in rodents, and saturated fats also enhance these tumors but less strongly. Further, the analysis shows that energy restriction protects against mammary tumors. We show that these results agree qualitatively with estimates of effects on human breast cancer derived from international correlations.

Eicosapentaenoic acid and sulphur substituted fatty acid analogues inhibit the proliferation of human breast cancer cells in culture

Numerous studies have shown dietary fatty acids to influence the progression of several types of cancers. The purpose of the present investigation was to examine the influence of various types of fatty acids, including omega-3 fatty acids and a new class of hypolipidemic peroxisome proliferating fatty acid analogues, namely the 3-thia fatty acids, on MCF-7 human breast cancer cell growth. 3-thia fatty acids represent non-beta-oxidizable fatty acid analogues in which a sulphur atom substitutes for the beta-methylene group (3-position) in the saturated and unsaturated fatty acids. The effects of increasing concentrations of palmitic acid, tetradecylthioacetic acid (a 3-thia fatty acid), eicosapentaenoic acid, docosahexaenoic acid, and two 3-thia polyunsaturated fatty acids on the proliferation of MCF-7 cells, maintained in serum-free culture, were studied. At the highest concentration of fatty acid used (64 microM) tetradecylthioacetic acid was found to be the most effective of all fatty acids tested in inhibiting cell growth, whilst palmitic acid and docosahexaenoic acid had no significant effect on cell growth. Thus, of the two dietary polyunsaturated omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid, only eicosapentaenoic acid possesses an inhibitory effect on the proliferation of MCF-7 cells. In all cases the inhibitory effect of the fatty acid was found to be reversible. Tetradecylthioacetic acid has been shown to be a potent peroxisome proliferator. It was, therefore, hypothesized that tetradecylthioacetic acid may inhibit the human MCF-7 cell growth by increasing the level of oxidative stress within the cell. However, use of agents which modify the cell's protective apparatus against oxidative stress had no influence on the inhibitory effect of tetradecylthioacetic acid. These experiments indicate that tetradecylthioacetic acid inhibits cell growth by mechanisms which may be independent of oxidative status.

Dietary modulation of omega-3/omega-6 polyunsaturated fatty acid ratios in patients with breast cancer

BACKGROUND

Polyunsaturated fatty acids of the omega-6 (omega-6) class, as found in corn and safflower oils, can act as precursors for intermediates involved in the growth of mammary tumors when fed to animals, whereas polyunsaturated fatty acids of the omega-3 (omega-3) class, as found in fish oil, can inhibit these effects. The effects of dietary intervention on the ratios of these fatty acids in breast and other adipose tissues have not previously been prospectively studied.

PURPOSE

The present investigation was conducted to study the impact on the ratio of omega-3 and omega-6 polyunsaturated fatty acid in plasma and in adipose tissue of the breast and buttocks when women with breast cancer consume a low-fat diet and fish oil supplements.

METHODS

Twenty-five women with high-risk localized breast cancer were enrolled in a dietary intervention program that required them to eat a low-fat diet and take a daily fish oil supplement throughout a 3-month period. Breast and gluteal fat biopsy specimens were obtained from each woman before and after dietary intervention. The fatty acid compositions of specimens of plasma, breast fat, and gluteal fat were determined by gas-liquid chromatography. Statistical analysis involved use of a two-sided paired t test.

RESULTS

After dietary intervention, a reduction in the level of total omega-6 polyunsaturated fatty acids in the plasma was observed (P<.0003); moreover, total omega-3 polyunsaturated fatty acids increased approximately three-fold (P<.0001) and the omega-3/omega-6 polyunsaturated fatty acids ratio increased approximately fourfold (i.e., mean values increased from 0.09 to 0.41; P = .0001). An increase in total omega-3 polyunsaturated fatty acids in breast adipose tissue was observed following dietary intervention (P = .04); the omega-3/omega-6 polyunsaturated fatty acid ratio increased from a mean value of 0.05 to 0.07 (P = .0001). An increase in total omega-3 polyunsaturated fatty acids was observed in gluteal adipose tissue following the intervention (P = .05); however, the ratio of omega-3 to omega-6 polyunsaturated fatty acids (mean ratio values of 0.036-0.045; P = .06) was unchanged.

CONCLUSION

Short-term dietary intervention can lead to statistically significant increases in omega-3/omega-6 polyunsaturated fatty acid ratios in plasma and breast adipose tissue. Breast adipose tissue changed more rapidly than gluteal adipose tissue in response to the dietary modification tested in this study. Therefore, gluteal adipose tissue may not be a useful surrogate to study the effect of diet on breast adipose tissue.