Fish oil, lipid peroxidation and mammary tumor growth

Sorafenib and docosahexaenoic acid act in synergy to suppress cancer cell viability: a role of heme oxygenase 1

Background

Docosahexaenoic acid (DHA) is a long chain n-3 polyunsaturated fatty acid that has anticancer activity. Heme oxygenase 1 (HO-1) is a potential therapeutic target due to its cytoprotective activity in cancer cells. We recently reported that DHA induces HO-1 gene transcription in human cancer cells by augmenting the degradation of Bach1 protein, which functions as a negative regulator of HO-1. Since the degradation of Bach1 protein relies on protein phosphorylation, we hypothesized that DHA-induced HO-1 gene transcription could be attenuated by kinase inhibitors, resulting in an enhanced cytotoxicity. Sorafenib, a tyrosine kinase inhibitor, was first applied to test our hypothesis.

Methods

Human cancer cell lines and a xenograft nude mouse model were applied to test our hypothesis. Gene expression was analyzed by western blot analysis and reporter gene assay. Cell viability was analyzed using a colorimetric assay. Isobologram was applied to analyze drug action.

Results

Pretreatment of cancer cells with Sorafenib significantly attenuated DHA-induced degradation of Bach1 protein. Consequently, DHA-induced HO-1 gene transcription was reversed by Sorafenib as evidenced by western blot and reporter gene analysis. Sorafenib acted synergistically with DHA to suppress cancer cell viability in various human cancer cell lines and suppressed tumor xenograft growth in mice fed a fish oil enriched diet (high n-3/DHA), as compared to mice fed a corn oil (high n-6) diet. Screening of the NCI-Oncology Drug Set IV identified a group of anticancer compounds, including Sorafenib, which enhanced DHA’s cytotoxicity, as well as a set of compounds that attenuated DHA’s cytotoxicity.

Conclusions

We demonstrate that sorafenib attenuates DHA-induced HO-1 expression and acts in synergy with DHA to suppress cancer cell viability and tumor growth. Considering the known health benefits of DHA and the clinical effectiveness of Sorafenib, their combination is an attractive therapeutic strategy against cancer.

Role of n-3 Polyunsaturated Fatty Acids and Exercise in Breast Cancer Prevention: Identifying Common Targets

Diet and exercise are recognized as important lifestyle factors that significantly influence breast cancer risk. In particular, dietary n-3 polyunsaturated fatty acids (PUFAs) have been shown to play an important role in breast cancer prevention. Growing evidence also demonstrates a role for exercise in cancer and chronic disease prevention. However, the potential synergistic effect of n-3 PUFA intake and exercise is yet to be determined. This review explores targets for breast cancer prevention that are common between n-3 PUFA intake and exercise and that may be important study outcomes for future research investigating the combined effect of n-3 PUFA intake and exercise. These lines of evidence highlight potential new avenues for research and strategies for breast cancer prevention.

Role of Omega-3 Fatty Acid Supplementation in Inflammation and Malignancy

Omega-3 fatty acids (FAs), which include eicosapentaenoic acid (EPA) and docosahexaenoic acid, are found in fish oils and have long been investigated as components of therapy for various disease states. Population studies initially revealed the cardioprotective and anti-inflammatory effects of omega-3 FAs and EPA, with subsequent clinical studies supporting the therapeutic role of omega-3 FAs in cardiovascular and chronic inflammatory conditions. Prospective randomized placebo-controlled trials have also demonstrated the utility of omega-3 FA supplementation in malignancy and cancer cachexia. In recent years, in vitro and animal studies have elucidated some of the mechanistic explanations underlying the wide range of biological effects produced by omega-3 FAs and EPA, including their antiproliferative and anticachectic actions in malignancy. In this review, the authors discuss the recent progress made with omega-3 FAs, focusing on the advances in mechanistic understanding and the results of clinical trials.

Orthomolecular Oncology Review: Ascorbic Acid and Cancer 25 Years Later

The effect of ascorbic acid on cancer has been a subject of great controversy. This is a follow-up review of the 1979 article by Cameron, Pauling, and Leibovitz published in Cancer Research. In this updated version, the authors address general aspects of ascorbic acid and cancer that have been presented before, while reviewing, analyzing, and updating new existing literature on the subject. In addition, they present and discuss their own mechanistic hypothesis on the effect of ascorbic acid on the cancer cell. The objective of this review is to provide an updated scientific basis for the use of ascorbic acid, especially intravenously as adjuvant treatment in pharmacological nutritional oncology.

Characterization of docosahexaenoic acid (DHA)-induced heme oxygenase-1 (HO-1) expression in human cancer cells: the importance of enhanced BTB and CNC homology 1 (Bach1) degradation

The effect of docosahexaenoic acid (DHA) on heme oxygenase-1 (HO-1) expression in cancer cells has never been characterized. This study examines DHA-induced HO-1 expression in human cancer cell model systems. DHA enhanced HO-1 gene expression in a time- and concentration-dependent manner, with maximal induction at 21 h of treatment. This induction of HO-1 expression was confirmed in vivo using a xenograft nude mouse model fed a fish-oil-enriched diet. The increase in HO-1 gene transcription induced by DHA was significantly attenuated by the antioxidant N-acetyl cysteine, suggesting the involvement of oxidative stress. This was supported by direct measurement of lipid peroxide levels after DHA treatment. Using a human HO-1 gene promoter reporter construct, we identified two antioxidant response elements (AREs) that mediate the DHA-induced increase in HO-1 gene transcription. Knockdown of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) expression compromised the DHA-induced increase in HO-1 gene transcription, indicating the importance of the Nrf2 pathway in this event. However, the nuclear protein levels of Nrf2 remained unchanged upon DHA treatment. Further studies demonstrated that DHA reduces nuclear Bach1 protein expression by promoting its degradation and attenuates Bach1 binding to the AREs in the HO-1 gene promoter. In contrast, DHA enhanced Nrf2 binding to the AREs without affecting nuclear Nrf2 expression levels, indicating a new cellular mechanism that mediates DHA's induction of HO-1 gene transcription. To our knowledge, this is the first characterization of DHA-induced HO-1 expression in human malignant cells.

Why docosahexaenoic acid and aspirin supplementation could be useful in women as a primary prevention therapy against Alzheimer's disease?

The assumption that disease specific risk factors are similar or the same in men and women may lead to incorrect primary prevention strategies. This study focused on the evaluation of gender-specific Alzheimer's disease (AD) risk factors. In AD, female gender appears to be an important risk factor associated with the aberrant production of beta amyloid (βA) peptides. Although decreased levels in plasma DHA concentration are associated with cognitive decline in healthy elderly and Alzheimer's patients, pre-treatment with DHA significantly reduced the survival of cortical neurons incubated with beta amyloid (βA). Hence, in the presence of an increasing amount of βA, paradoxically women - who have higher plasma levels of DHA - are more likely to develop AD. Aspirin (ASA) converts cyclooxygenase (COX)-2 into a form that generates new neuroprotective docosanoids from DHA; therefore, ASA might positively resolve the paradoxical effect of the concomitant presence of DHA and βA.

Role of dietary fatty acids in mammary gland development and breast cancer

Breast cancer is the most common cancer among women worldwide. Estimates suggest up to 35% of cases may be preventable through diet and lifestyle modification. Growing research on the role of fats in human health suggests that early exposure in life to specific fatty acids, when tissues are particularly sensitive to their environment, can have long-term health impacts. The present review examines the role of dietary fat in mammary gland development and breast cancer throughout the lifecycle. Overall, n-3 polyunsaturated fatty acids have promising cancer-preventive effects when introduced early in life, and warrant further research to elucidate the mechanisms of action.

Docosahexaenoic acid inhibits superoxide dismutase 1 gene transcription in human cancer cells: the involvement of peroxisome proliferator-activated receptor alpha and hypoxia-inducible factor-2alpha signaling

Docosahexaenoic acid (DHA; n-3, 22:6) is known to have anticancer activity, but its mechanisms of action remain to be further elucidated. We recently demonstrated that DHA down-regulates superoxide dismutase (SOD) 1 gene expression, thereby weakening cellular antioxidant forces and enhancing cytotoxicity in various human cancer cells. The objective of this study was to investigate the mechanism of the inhibitory effect of DHA on SOD-1 gene expression in human cancer cells. A reporter gene assay indicated that DHA suppresses SOD-1 gene transcription in a time- and concentration-dependent manner in human cancer cells. Pretreatment with vitamin E did not block the inhibitory effect of DHA, indicating that this suppression does not depend on lipid peroxidation. The suppressive effect of DHA on SOD-1 gene transcription could be mimicked by the peroxisome proliferator-activator receptor (PPAR) alpha ligand clofibrate but not the PPARgamma ligand troglitazone, suggesting the involvement of PPARalpha signaling. Deletion analysis of the key DNA binding elements in the SOD-1 gene promoter identified the distal hypoxia response element (HRE), but not the peroxisome proliferator response element or nuclear factor-kappaB element, as essential for the suppressive effects of DHA. Coimmunoprecipitation confirmed that PPARalpha, but not PPARgamma, forms a complex with hypoxia-inducible factor (HIF)-2alpha in cancer cells. Chromatin immunoprecipitation analysis indicated that both DHA and clofibrate reduce HIF-2alpha binding to the HRE. Thus, we have identified the distal HRE in the SOD-1 gene promoter that mediates the suppression on the transcription of this gene by DHA, and we have demonstrated the involvement of PPARalpha and HIF-2alpha signaling in this event.

Zinc-binding compounds induce cancer cell death via distinct modes of action

Metal-binding compounds have been shown to have anticancer activity and are being evaluated clinically as anticancer agents. We have recently found that a zinc-binding compound, 5-chloro-7-iodo-8-hydroxyquinoline (clioquinol), kills cancer cells by transporting zinc into the cells. We therefore compared the action of clioquinol with two other cytotoxic zinc-binding compounds, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) and pyrrolidine dithiocarbamate (PDTC). We demonstrate that metal-binding compounds can be subclassified based upon the reversibility of their cytotoxicity by metal supplementation and their modes of action. Understanding the mechanisms whereby metal-binding compounds affect cell behavior may aid in their optimization for clinical use.

Clioquinol and docosahexaenoic acid act synergistically to kill tumor cells

Clioquinol, an 8-hydroxyquinoline derivative (5-chloro-7-iodo-8-hydroxyquinoline) with antimicrobial properties, has recently been found to have cytotoxic activity towards human cancer cell lines at concentrations achieved by oral administration. This study was initiated to determine whether clioquinol could potentiate the antitumor effects of two drugs, doxorubicin and docosahexaenoic acid (DHA), believed to act in part via the generation of reactant oxidant species. At low micromolar concentrations, clioquinol had little effect upon cell viability and did not potentiate doxorubicin's cytotoxicity. Clioquinol significantly enhanced DHA's cytotoxic effects, an interaction that was shown to be synergistic by isobolographic analysis. Clioquinol exhibited a synergistic interaction with DHA in reducing nuclear factor-kappaB activity and inducing apoptosis, and the combination reduced the level of several molecules that promote cell survival, including Akt, p65, and Bcl-2. Interestingly, clioquinol neither induced lipid peroxidation itself nor increased peroxidation brought about by the addition of DHA. However, when cells were pretreated with antioxidant vitamin E, the synergism of clioquinol and DHA was blocked, indicating the essential role of lipid peroxidation for their action. These findings reveal a novel antitumor drug combination that synergistically targets major cell survival signaling pathways.

Long-chain (n-3) fatty acid intake and risk of cancers of the breast and the prostate: recent epidemiological studies, biological mechanisms, and directions for future research

The association between dietary (n-3) fatty acids and hormone-responsive cancers continues to attract considerable attention in epidemiological, clinical, and experimental studies. We previously reviewed the epidemiological literature on the association between hormone-responsive cancers and the long-chain fatty acids eicosapentaenoic acid and docosahexaenoic acid. We concluded that the compelling evidence from ecological studies, animal models, and mechanistic experiments in vitro was not supported clearly by the available epidemiological data. To various degrees, epidemiological studies published more recently attempted to address some of the methodological limitations plaguing earlier studies by using validated questionnaires, examining specific fatty acids and their interrelationships, and adjusting estimates for a wider range of potentially confounding factors than in previous studies. In this review, our aim was to update the previous review with the results of recent epidemiological studies and to discuss possible biological mechanisms and directions for future research.

Nutritional and botanical modulation of the inflammatory cascade--eicosanoids, cyclooxygenases, and lipoxygenases--as an adjunct in cancer therapy

Emerging on the horizon in cancer therapy is an expansion of the scope of treatment beyond cytotoxic approaches to include molecular management of cancer physiopathology. The goal in these integrative approaches, which extends beyond eradicating the affected cells, is to control the cancer phenotype. One key new approach appears to be modulation of the inflammatory cascade, as research is expanding that links cancer initiation, promotion, progression, angiogenesis, and metastasis to inflammatory events. This article presents a literature review of the emerging relationship between neoplasia and inflammatory eicosanoids (PGE2 and related prostaglandins), with a focus on how inhibition of their synthesizing oxidases, particularly cyclooxygenase (COX), offers anticancer actions in vitro and in vivo. Although a majority of this research emphasizes the pharmaceutical applications of nonsteroidal anti-inflammatory drugs and selective COX-2 inhibitors, these agents fail to address alternate pathways available for the synthesis of proinflammatory eicosanoids. Evidence is presented that suggests the inhibition of lipoxygenase and its by-products-LTB4, 5-HETE, and 12-HETE-represents an overlooked but crucial component in complementary cancer therapies. Based on the hypothesis that natural agents capable of modulating both lipoxygenase and COX may advance the efficacy of cancer therapy, an overview and discussion is presented of dietary modifications and selected nutritional and botanical agents (notably, omega-3 fatty acids, antioxidants, boswellia, bromelain, curcumin, and quercetin) that favorably influence eicosanoid production.

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.

Role of lipid peroxidation and antioxidant enzymes in omega 3 fatty acids induced suppression of breast cancer xenograft growth in mice

Background

Supplementing mice with high levels of dietary n-3 polyunsaturated fatty acids (PUFAs) increases the n-3 PUFAs in cell membranes, increases the susceptibility of the cells for lipid peroxidation (LPO) and decreases the growth rate of mammary and other tumors. However, the results of an earlier study indicated that a factor in addition to LPO was involved in the reduction in tumor growth in n-3 PUFAs fed mice. Athymic mice bearing MDA-MB-231 human breast carcinoma xenografts, were fed fish oil concentrate (FOC) or control diets, with and without supplemental Vitamin E (2000 IU /kg diet) and were sacrificed both before and after doxorubicin (DOX) treatment to evaluate factors involved in tumor growth suppression.

Results

Prior to DOX, basal LPO in the tumor of 3% FOC fed mice was slightly higher than in the control fed mice and was decreased in mice consuming FOC with vitamin E. Vitamin E suppressed the DOX induced increase in LPO in the tumors of control mice, however, vitamin E was not sufficient to suppress a DOX induced increase in LPO in the tumors of FOC fed mice. The mean growth rate of tumors of FOC fed mice was significantly less than the mean growth rate of the tumors of control mice. Multiple regression analyses indicated that suppression of glutathione peroxidase (GPX) activity by FOC prior to DOX therapy was more important than increased LPO as an explanation of tumor growth suppression. Tumor induced cachexia was decreased in mice consuming FOC.

Conclusions

It appears that the increased sensitivity to DOX was related to an FOC induced reduction in GPX activity. FOC reduced tumor induced cachexia.

The diet-induced proinflammatory state: a cause of chronic pain and other degenerative diseases?

BACKGROUND

It is the rare physician who includes diet therapy and nutritional supplements in patient care. Perhaps this is because chiropractic and medical schools devote very few classroom hours to nutrition. It is also possible that physicians are under the misconception that a detailed biochemical understanding of each individual disease is required before nutritional interventions can be used.

OBJECTIVE

The purpose of this article is two-fold: (1) to demonstrate that chronic pain and other degenerative conditions encountered in clinical practice have similar biochemical etiologies, such as a diet-induced proinflammatory state, and (2) to outline a basic nutritional program that can be used by all practitioners.

DATA SOURCES

The data were accumulated over a period of years by reviewing contemporary articles and books and subsequently by retrieving relevant articles. Articles were also selected through MEDLINE and manual library searches.

RESULTS

The typical American diet is deficient in fruits and vegetables and contains excessive amounts of meat, refined grain products, and dessert foods. Such a diet can have numerous adverse biochemical effects, all of which create a proinflammatory state and predispose the body to degenerative diseases. It appears that an inadequate intake of fruits and vegetables can result in a suboptimal intake of antioxidants and phytochemicals and an imbalanced intake of essential fatty acids. Through different mechanisms, each nutritional alteration can promote inflammation and disease.

CONCLUSION

We can no longer view different diseases as distinct biochemical entities. Nearly all degenerative diseases have the same underlying biochemical etiology, that is, a diet-induced proinflammatory state. Although specific diseases may require specific treatments, such as adjustments for hypomobile joints, beta-blockers for hypertension, and chemotherapy for cancer, the treatment program must also include nutritional protocols to reduce the proinflammatory state.

Effect of an alpha-linolenic acid-rich diet on rat mammary tumor growth depends on the dietary oxidative status

To investigate whether the oxidative status of an 18:3(n-3) polyunsaturated fatty acid (PUFA)-enriched diet could modulate the growth of chemically induced rat mammary tumors, three independent experiments were performed. Experiments I and II examined the variation of tumor growth by addition of antioxidant (vitamin E) or a prooxidant system (sodium ascorbate/2-methyl-1,4-naphthoquinone) to a 15% linseed oil diet rich in 18:3(n-3). Experiment III addressed the role of PUFA in the tumor growth modulation by vitamin E. For this purpose, we compared the effect of vitamin E in 15% fat diets containing a high level of 18:3(n-3) (linseed oil, high-PUFA diet) or devoid of 18:3(n-3) (hydrogenated palm/sunflower oil, low-PUFA diet). In Experiments I-III, tumor growth increased in the presence of vitamin E compared with control (without vitamin E). Furthermore, it decreased when prooxidant was added. In contrast, no difference was observed when the diet was low in PUFA, suggesting that sensitivity of PUFA to peroxidation may interfere with tumor growth. This observation was supported by growth kinetic parameter analysis, which indicated that tumor growth resulted from variations in cell loss but not from changes in cell proliferation. These data show that, in vivo, PUFA effects on tumor growth are highly dependent on diet oxidative status.

Effects of dietary fat on benz-a-pyrene-induced forestomach tumorigenesis in mice chronically exposed to arsenic

The modulating effect of As (As2O3) in drinking water plus dietary fatty acids on benzo-a-pyrene (BP) induced forestomach tumorigenesis was assayed in mice fed with corn oil (CO), Olein (O), palmstearin (PS) and cod liver oil (CLO) enriched formulae, and a mixed-fat (S-stock) diet during 28 weeks. Neither pre-or neoplastic lesions were recorded in esophagus or forestomach of mice treated with As alone. CLO diet showed a protective effect. Indeed, multiple epidermal hyperplasia were significantly reduced compared to S group and a reduction in papillomas multiplicity with respect to S, CO and O groups was also observed. Mice fed on PS formula showed minor papillomas per mouse with respect to CO and O. These results indicate that As plus BP did not exhibit any synergistic effect on the development of epidermoid tumor lesions, whereas CLO diet exerted antipromoting activity . In spite of their common essential fatty acid deficiency (EFAD) condition, PS and O lots showed contradictory results. Hence, the dietary enrichment in 18:1 n-9 (O diet) per se, and not the EFAD state, may play a deleterious role. Corn diet showed no promoting activity on the epidermoid tumor development in this model.

The influence of maternal diet on breast cancer risk among female offspring

The induction of breast cancer is a long process, containing a series of biological events that drive a normal mammary cell towards malignant growth. However, it is not known when the initiation of breast cancer occurs. One hypothesis is that a high estrogenic environment during the perinatal period increases subsequent breast cancer risk. There are many sources of extragonadal estrogens, particularly in the diet. The purpose of this paper is to review the evidence that a high maternal intake of dietary fats increases serum estrogens during pregnancy and increases breast cancer risk in daughters. Our animal studies show that a high maternal consumption of corn oil consisting mainly of linoleic acid (omega-6 polyunsaturated fatty acid, PUFA), increases both circulating estradiol (E2) levels during pregnancy and the risk of developing carcinogen-induced mammary tumors among the female rat offspring. A similar increase in breast cancer risk occurs in female offspring exposed to injections of E2 through their pregnant mother. Our data suggest that the mechanisms by which an early exposure to dietary fat and/or estrogens increases breast cancer risk is related to reduced differentiation of the mammary epithelial tree and increased number of mammary epithelial cell structures that are known to the sites of neoplastic transformation. These findings may reflect our data of the reduced estrogen receptor protein levels and protein kinase C activity in the developing mammary glands of female rats exposed to a high-fat diet in utero. In summary, a high dietary linoleic acid intake can elevate pregnancy estrogen levels and this, possibly by altering mammary gland morphology and expression of fat- and/or estrogen-regulated genes, can increase breast cancer risk in the offspring. If true for women, breast cancer prevention in daughters may include modulating the mother's pregnancy intake of some dietary fats.

Differential effects of dietary Oenothera, Zizyphus mistol, and corn oils, and essential fatty acid deficiency on the progression of a murine mammary gland adenocarcinoma

The modulating effect of dietary enrichment in mistol seed oil (MO) containing 25% of alpha-linolenic acid (ALA), evening primrose oil (EPO) enriched in gamma-linolenic acid (GLA) and corn oil (CO) as sources of omega-6 and omega-9 fatty acids on the growth parameters of one transplantable mammary tumor were compared. Mice fed on different lipid formulae were inoculated with a mammary gland adenocarcinoma and different growth development tumor parameters were recorded. Results showed that corn oil feeding slowed down most of the tumor growth parameters, as did the EPO diet. MO also showed antitumor activity. Olein feeding, which induces an essential fatty acid deficiency (EFAD), increased the incidence and the multiplicity of metastases when compared with the controls. It may be concluded that a diet enriched in omega-6 fatty acids did not behave as a tumor promoter in this mammary gland tumor model. The antitumor activities of EPO and MO are corroborated in present experiments, suggesting that both oils may be of value in nutritional approaches of mammary gland tumor therapies. In addition, present data add further experimental proof about the proposed protumorigenic proneness induced by the EFAD state.

Influence of docosahexaenoic acid on cerebral lipid peroxide level in aged rats with and without hypercholesterolemia

Female Wistar rats, 100 weeks old, were divided into four groups: one group was fed a high-cholesterol diet, one received a non-cholesterol diet, and the others were fed either a non- or a high-cholesterol diet plus docosahexaenoic acid. The level of lipid peroxide (LPO) in brain tissue was measured with a LPO assay kit. Fatty acid concentrations were analyzed by gas chromatography. Brain LPO in the aged and hypercholesterolemic rats fed docosahexaenoic acid decreased in the cerebrum but not in the brain stem or cerebellum. In the cerebrum, LPO showed a decrease, with an increase in the ratio of docosahexaenoic acid to arachidonic acid. The cerebrum, unlike the other areas of the brain, was more sensitive to docosahexaenoic acid as the concentrations of LPO decreased.

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

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

Mechanisms by which high maternal fat intake during pregnancy increases breast cancer risk in female rodent offspring

Emerging evidence indicates that a high in utero estrogenic environment increases breast cancer risk in women. We have proposed that a maternal intake of a high-fat diet is a source for high pregnancy estrogen levels and increases breast cancer risk among female offspring. In this review, the role of dietary fat in breast cancer, particularly during fetal life, is discussed. In addition, we provide possible mechanisms of action of the effects of a high-fat diet on the breast. These mechanisms include protein kinase C, estrogens and estrogen receptor, and alterations in mammary parenchymal structures.

Omega-3 and omega-6 fatty acids in the insulin resistance syndrome. Lipid and lipoprotein metabolism and atherosclerosis

Dietary fatty acids appear to be of significant importance for several of the most-common diseases in modern societies. To obtain more knowledge about the health consequences of dietary fatty acids, we depend upon a better understanding of the mechanisms of action of these fatty acids in vivo. With regard to the IRS, omega-3 PUFA may exert beneficial effects upon many of the associated pathophysiological metabolic changes. Omega-3 PUFA reduce fasting and postprandial TG, may improve insulin sensitivity (as shown in animal experiments), decrease platelet and leukocyte reactivity, alter immunological functions, and may slightly decrease blood pressure. Omega-3 PUFA may also beneficially influence vessel wall characteristics and blood rheology. Furthermore, both types of PUFA (omega-3 and omega-6) have been shown to inhibit cardiac arrhythmias in animals. The role of omega-3 PUFA in blood clotting and fibrinolysis still remains controversial, whereas omega-6 fatty acids may lead to increased oxidation of lipoproteins. Regardless of the effects on LDL oxidizability, both types of PUFA have shown beneficial effects on the development of atherosclerosis. As yet, little is known about the effect of specific omega-6 fatty acids with respect to the IRS. Potential adverse effects of dietary PUFA must not be neglected, but should be viewed in light of the beneficial effects of these agents.

The paradoxical role of lipid peroxidation on carcinogenesis and tumor growth: a commentary

Lipid peroxidation has been shown to both enhance carcinogenesis and to have an anticarcinogenic effect. This paradox is of great relevance to the fields of free radical biology, biochemistry, pathology, nutrition and oncology among others and needs to be addressed. A proper understanding of this issue can be a key to more effective treatment of malignant tumors in the near future.