Chemopreventive n-3 fatty acids activate RXRalpha in colonocytes

Dysregulation of cellular membrane homeostasis as a crucial modulator of cancer risk

Cellular membranes serve as an epicentre combining extracellular and cytosolic components with membranous effectors, which together support numerous fundamental cellular signalling pathways that mediate biological responses. To execute their functions, membrane proteins, lipids and carbohydrates arrange, in a highly coordinated manner, into well-defined assemblies displaying diverse biological and biophysical characteristics that modulate several signalling events. The loss of membrane homeostasis can trigger oncogenic signalling. More recently, it has been documented that select membrane active dietaries (MADs) can reshape biological membranes and subsequently decrease cancer risk. In this review, we emphasize the significance of membrane domain structure, organization and their signalling functionalities as well as how loss of membrane homeostasis can steer aberrant signalling. Moreover, we describe in detail the complexities associated with the examination of these membrane domains and their association with cancer. Finally, we summarize the current literature on MADs and their effects on cellular membranes, including various mechanisms of dietary chemoprevention/interception and the functional links between nutritional bioactives, membrane homeostasis and cancer biology.

Delineating the role of nuclear receptors in colorectal cancer, a focused review

Colorectal cancer (CRC) stands as one of the most prevalent form of cancer globally, causing a significant number of deaths, surpassing 0.9 million in the year 2020. According to GLOBOCAN 2020, CRC ranks third in incidence and second in mortality in both males and females. Despite extensive studies over the years, there is still a need to establish novel therapeutic targets to enhance the patients' survival rate in CRC. Nuclear receptors (NRs) are ligand-activated transcription factors (TFs) that regulate numerous essential biological processes such as differentiation, development, physiology, reproduction, and cellular metabolism. Dysregulation and anomalous expression of different NRs has led to multiple alterations, such as impaired signaling cascades, mutations, and epigenetic changes, leading to various diseases, including cancer. It has been observed that differential expression of various NRs might lead to the initiation and progression of CRC, and are correlated with poor survival outcomes in CRC patients. Despite numerous studies on the mechanism and role of NRs in this cancer, it remains of significant scientific interest primarily due to the diverse functions that various NRs exhibit in regulating key hallmarks of this cancer. Thus, modulating the expression of NRs with their agonists and antagonists, based on their expression levels, holds an immense prospect in the diagnosis, prognosis, and therapeutical modalities of CRC. In this review, we primarily focus on the role and mechanism of NRs in the pathogenesis of CRC and emphasized the significance of targeting these NRs using a variety of agents, which may represent a novel and effective strategy for the prevention and treatment of this cancer.

Omega-3 Fatty Acids in Arterial Hypertension: Is There Any Good News?

Omega-3 polyunsaturated fatty acids (ω-3 PUFAs), including alpha-linolenic acid (ALA) and its derivatives eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are "essential" fatty acids mainly obtained from diet sources comprising plant oils, marine blue fish, and commercially available fish oil supplements. Many epidemiological and retrospective studies suggested that ω-3 PUFA consumption decreases the risk of cardiovascular disease, but results of early intervention trials have not consistently confirmed this effect. In recent years, some large-scale randomized controlled trials have shed new light on the potential role of ω-3 PUFAs, particularly high-dose EPA-only formulations, in cardiovascular prevention, making them an attractive tool for the treatment of "residual" cardiovascular risk. ω-3 PUFAs' beneficial effects on cardiovascular outcomes go far beyond the reduction in triglyceride levels and are thought to be mediated by their broadly documented "pleiotropic" actions, most of which are directed to vascular protection. A considerable number of clinical studies and meta-analyses suggest the beneficial effects of ω-3 PUFAs in the regulation of blood pressure in hypertensive and normotensive subjects. These effects occur mostly through regulation of the vascular tone that could be mediated by both endothelium-dependent and independent mechanisms. In this narrative review, we summarize the results of both experimental and clinical studies that evaluated the effect of ω-3 PUFAs on blood pressure, highlighting the mechanisms of their action on the vascular system and their possible impact on hypertension, hypertension-related vascular damage, and, ultimately, cardiovascular outcomes.

Ileum Gene Expression in Response to Acute Systemic Inflammation in Mice Chronically Fed Ethanol: Beneficial Effects of Elevated Tissue n-3 PUFAs

Chronic alcohol consumption leads to disturbances in intestinal function which can be exacerbated by inflammation and modulated by different factors, e.g., polyunsaturated fatty acids (PUFAs). The mechanisms underlying these alterations are not well understood. In this study, RNA-seq analysis was performed on ileum tissue from WT and fat-1 transgenic mice (which have elevated endogenous n-3 PUFAs). Mice were chronically fed ethanol (EtOH) and challenged with a single lipopolysaccharide (LPS) dose to induce acute systemic inflammation. Both WT and fat-1 mice exhibited significant ileum transcriptome changes following EtOH + LPS treatment. Compared to WT, fat-1 mice had upregulated expression of genes associated with cell cycle and xenobiotic metabolism, while the expression of pro-inflammatory cytokines and pro-fibrotic genes was decreased. In response to EtOH + LPS, fat-1 mice had an increased expression of genes related to antibacterial B cells (APRIL and IgA), as well as an elevation in markers of pro-restorative macrophages and γδ T cells that was not observed in WT mice. Our study significantly expands the knowledge of regulatory mechanisms underlying intestinal alterations due to EtOH consumption and inflammation and identifies the beneficial transcriptional effects of n-3 PUFAs, which may serve as a viable nutritional intervention for intestinal damage resulting from excessive alcohol consumption.

Omega-3 polyunsaturated fatty acids: anti-inflammatory and anti-hypertriglyceridemia mechanisms in cardiovascular disease

Cardiovascular disease (CVD) is the world's most recognized and notorious cause of death. It is known that increased triglyceride-rich lipoproteins (TRLs) and remnants of triglyceride-rich lipoproteins (RLP) are the major risk factor for CVD. Furthermore, hypertriglyceridemia commonly leads to a reduction in HDL and an increase in atherogenic small dense low-density lipoprotein (sdLDL or LDL-III) levels. Thus, the evidence shows that Ω-3 fatty acids (eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have a beneficial effect on CVD through reprogramming of TRL metabolism, reducing inflammatory mediators (cytokines and leukotrienes), and modulation of cell adhesion molecules. Therefore, the purpose of this review is to provide the molecular mechanism related to the beneficial effect of Ω-3 PUFA on the lowering of plasma TAG levels and other atherogenic lipoproteins. Taking this into account, this study also provides the TRL lowering and anti-inflammatory mechanism of Ω-3 PUFA metabolites such as RvE1 and RvD2 as a cardioprotective function.

Natural and synthetic retinoids in preclinical colorectal cancer models

Colorectal cancer (CRC) remains a leading cause of cancer-related morbidity and mortality worldwide. Although targeted therapy in combination with chemotherapy in CRC prolongs the overall survival of patients with metastatic disease, acquired resistance and relapse hinder their clinical benefits. Moreover, patients with some specific genetic profile are unlikely to benefit from targeted therapy, suggesting the need for safe and effective treatment strategies. Retinoids, comprising of natural and synthetic analogs, are a class of chemical compounds that regulate cellular proliferation, differentiation, and cell death. Retinoids have been used in the clinic for several leukemias and solid tumors, either as single agents or in combination therapy. Furthermore, retinoids have shown potent chemotherapeutic and chemopreventive properties in different cancer models, including CRC. In this review, we summarize the major preclinical findings in CRC in which natural and synthetic retinoids showed promising antitumor activities and stress on the proposed mechanisms of action. Understanding of the retinoids' antitumor mechanisms would provide insights to support and warrant their development in the management of CRC.

Functional link between plasma membrane spatiotemporal dynamics, cancer biology, and dietary membrane-altering agents

The cell plasma membrane serves as a nexus integrating extra- and intracellular components, which together enable many of the fundamental cellular signaling processes that sustain life. In order to perform this key function, plasma membrane components assemble into well-defined domains exhibiting distinct biochemical and biophysical properties that modulate various signaling events. Dysregulation of these highly dynamic membrane domains can promote oncogenic signaling. Recently, it has been demonstrated that select membrane-targeted dietary bioactives (MTDBs) have the ability to remodel plasma membrane domains and subsequently reduce cancer risk. In this review, we focus on the importance of plasma membrane domain structural and signaling functionalities as well as how loss of membrane homeostasis can drive aberrant signaling. Additionally, we discuss the intricacies associated with the investigation of these membrane domain features and their associations with cancer biology. Lastly, we describe the current literature focusing on MTDBs, including mechanisms of chemoprevention and therapeutics in order to establish a functional link between these membrane-altering biomolecules, tuning of plasma membrane hierarchal organization, and their implications in cancer prevention.

The impact of polyunsaturated fatty acids on DNA methylation and expression of DNMTs in human colorectal cancer cells

Growing evidence suggests a role of polyunsaturated fatty acids (PUFA) in the prevention of various types of malignancy, including colorectal cancer (CRC). No published studies have yet examined the direct effect of PUFA treatment on DNA methylation in CRC cells. In this study, 5 human CRC cells were treated with 100 μM DHA, EPA, and LA for 6 days and changes in their global- and gene-specific DNA methylation status as well as expression of DNA methyl transferases (DNMT) were investigated. Cell-type specific differences in DNA methylation and expression of DNMTs were observed in PUFA-treated cells. DHA and EPA treatment induced global hypermethylation in HT29/219 and HCT116 cells, but reduced methylation in Caco2 cells (p < 0.05). Among 10 tumor related genes tested in 5 CRC cell lines, DHA and EPA induced promoter demethylation of Cox2 in HT29/219, p14 and PPARγ in HCT116, and ECAD in SW742 cells. Cell-type specific differences in expression of DNMT1, DNMT3a, and 3b genes were also observed between PUFA-treated and control cells (p < 0.05). Overall, treatment of PUFAs coordinately induced the expression of DNMTs in HT29/219, but suppressed in other 4 cell lines investigated in this study.

RA and ω-3 PUFA co-treatment activates autophagy in cancer cells

Retinoic acid (RA), is a promising therapeutic agent for the treatment of breast cancer. However, metabolic disorders and drug resistance reduce the efficacy of RA. In this study, we found that RA and ω-3 polyunsaturated fatty acids (ω-3 PUFAs) synergistically induced cell death in vitro and in vivo and autophagy activation. Moreover, RA-induced hypercholesterolemia was completely corrected by ω-3 PUFA supplementation. In addition, we demonstrated that the effects of this combination on the autophagic flux were independent of the two major canonic regulatory complexes controlling autophagic vesicle formation. The treatment activated Gαq-p38 MAPK signaling pathways, which resulted in autophagy of breast cancer cells. Knockdown of Gαq or P38 expression prevented RA and ω-3 PUFAs from inducing autophagy. Data indicated that Gαq-p38activation was mediated by the co-activation of GPR40 and RARα in lipid rafts, rather than by the activation of GPR120, RARβ, or RARγ. The results of this study suggest that hyperlipidemic drug side effects may be ameliorated by the administration of ω-3 PUFAs. Thus, the therapeutic indexes of the corresponding drugs may be increased.

Expression of chicken ovalbumin upstream promoter-transcription factor II and liver X receptor as prognostic indicators for human colorectal cancer

Cholesterol increases the risk of colorectal cancer. Liver X receptor (LXR), retinoid X receptor (RXR)α and sterol regulatory element binding protein (SREBP)-1c are transcriptional regulators of lipid metabolism. Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) serves an essential role in angiogenesis and development, but its role in cancer is controversial. The expression of COUP-TFII, LXR, RXRα and SREBP-1c in colorectal cancer, as well as their association with clinicopathologic features, was assessed, and their utility as prognostic indicators in colorectal cancer evaluated. Colorectal cancer samples (n=707 patients) were analyzed for COUP-TII, LXR, RXRα and SREBP-1c expression by immunohistochemistry. Overall survival curves of patients with tumors expressing different levels of these proteins were produced and risk factors were assessed. Of the 707 patients, 32.7, 50.9, 56.4, and 41.7% were positive for COUP-TFII, LXR, RXRα, and SREBP-1c, respectively. The lack of COUP-TFII or LXR expression was associated with lower overall survival rates (P=0.0154 for COUP-TFII, and 0.0113 for LXR). Following adjustment for other clinical risk factors (age, sex, tumor size, grade, vascular invasion, and Tumor-Node-Metastasis stage), the lack of COUP-TFII or LXR expression was a negative independent prognostic factor for survival. The expression of COUP-TFII and LXR alone or in combination may be biomarkers to indicate a positive prognosis in patients with colorectal cancer.

Fundamental studies of adrenal retinoid-X-receptor: Protein isoform, tissue expression, subcellular distribution, and ligand availability

Adrenal gland reportedly expresses many nuclear receptors that are known to heterodimerize with retinoid-X-receptor (RXR) for functions, but the information regarding the glandular RXR is not adequate. Studies of rat adrenal homogenate by Western blotting revealed three RXR proteins: RXRα (55kDa), RXRβ (47kDa) and RXR (56kDa). RXRγ was not detectable. After fractionation, RXRα was almost exclusively localized in the nuclear fraction. In comparison, substantial portions of RXRβ and RXR were found in both nuclear and post-nuclear particle fractions, suggesting genomic and non-genomic functions. Cells immunostained for RXRα were primarily localized in zona fasciculata (ZF) and medulla, although some stained cells were found in zona glomerulosa (ZG) and zona reticularis (ZR). In contrast, cells immunostained for RXRβ were concentrated principally in ZG, although some stained cells were seen in ZR, ZF, and medulla (in descending order, qualitatively). Analysis of adrenal lipid extracts by LC/MS did not detect 9-cis-retinoic acid (a potent RXR-ligand) but identified all-trans retinoic acid. Since C20 and C22 polyunsaturated fatty acids (PUFAs) can also activate RXR, subcellular availabilities of unesterified fatty acids were investigated by GC/MS. As results, arachidonic acid (C20:4), adrenic acid (C22:4), docosapentaenoic acid (C22:5), and cervonic acid (C22:6) were detected in the lipids extracted from each subcellular fraction. Thus, the RXR-agonizing PUFAs are available in all the main subcellular compartments considerably. The present findings not only shed light on the adrenal network of RXRs but also provide baseline information for further investigations of RXR heterodimers in the regulation of adrenal steroidogenesis.

G0S2: A small giant controller of lipolysis and adipose-liver fatty acid flux

The discovery of adipose triglyceride lipase (ATGL) and its coactivator comparative gene identification-58 (CGI-58) provided a major paradigm shift in the understanding of intracellular lipolysis in both adipocytes and nonadipocyte cells. The subsequent discovery of G0/G1 switch gene 2 (G0S2) as a potent endogenous inhibitor of ATGL revealed a unique mechanism governing lipolysis and fatty acid (FA) availability. G0S2 is highly conserved in vertebrates, and exhibits cyclical expression pattern between adipose tissue and liver that is critical to lipid flux and energy homeostasis in these two tissues. Biochemical and cell biological studies have demonstrated that a direct interaction with ATGL mediates G0S2's inhibitory effects on lipolysis and lipid droplet degradation. In this review we examine evidence obtained from recent in vitro and in vivo studies that lends support to the proof-of-principle concept that G0S2 functions as a master regulator of tissue-specific balance of TG storage vs. mobilization, partitioning of metabolic fuels between adipose and liver, and the whole-body adaptive energy response. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink.

Liver X receptor mediates hepatic triglyceride accumulation through upregulation of G0/G1 Switch Gene 2 expression

Liver X receptors (LXRs) are transcription factors essential for cholesterol homeostasis and lipogenesis. LXRα has been implicated in regulating hepatic triglyceride (TG) accumulation upon both influx of adipose-derived fatty acids (FAs) during fasting and stimulation of de novo FA synthesis by chemical agonism of LXR. However, whether or not a convergent mechanism is employed to drive deposition of FAs from these 2 different sources in TGs is undetermined. Here, we report that the G0/G1 Switch Gene 2 (G0S2), a selective inhibitor of intracellular TG hydrolysis/lipolysis, is a direct target gene of LXRα. Transcriptional activation is conferred by LXRα binding to a direct repeat 4 (DR4) motif in the G0S2 promoter. While LXRα^-/- mice exhibited decreased hepatic G0S2 expression, adenoviral expression of G0S2 was sufficient to restore fasting-induced TG storage and glycogen depletion in the liver of these mice. In response to LXR agonist T0901317, G0S2 ablation prevented hepatic steatosis and hypertriglyceridemia without affecting the beneficial effects on HDL. Thus, the LXRα-G0S2 axis plays a distinct role in regulating hepatic TG during both fasting and pharmacological activation of LXR.

The commonly used nonionic surfactant Span 80 has RXRα transactivation activity, which likely increases the obesogenic potential of oil dispersants and food emulsifiers

Obesity has reached pandemic proportions, and there is mounting evidence that environmental exposures to endocrine disrupting chemicals known as "obesogens" may contribute to obesity and associated medical conditions. The Deepwater Horizon (DWH) oil spill resulted in a massive environmental release of crude oil and remediation efforts applied large quantities of Corexit dispersants to the oil spill. The Corexit-enhanced Water Accommodated Fraction (CWAF) of DWH crude oil contains PPARγ transactivation activity, which is attributed to dioctyl sodium sulfosuccinate (DOSS), a probable obesogen. In addition to its use in oil dispersants, DOSS is commonly used as a stool softener and food additive. Because PPARγ functions as a heterodimer with RXRα to transcriptionally regulate adipogenesis we investigated the potential of CWAF to transactivate RXRα and herein demonstrated that the Corexit component Span 80 has RXRα transactivation activity. Span 80 bound to RXRα in the low micromolar range and promoted adipocyte differentiation of 3T3-L1 preadipocytes. Further, the combination of DOSS and Span 80 increased 3T3-L1 adipocyte differentiation substantially more than treatment with either chemical individually, likely increasing the obesogenic potential of Corexit dispersants. From a public health standpoint, the use of DOSS and Span 80 as food additives heightens concerns regarding their use and mandates further investigations.

Decreased Expression of Retinoid X Receptors During Human and Azoxymethane-induced Colorectal Carcinogenesis in the Rat

BACKGROUND/AIM

The family of retinoid X receptors (RXRs) including RXRα, β and γ, is involved in regulating cell proliferation, differentiation, apoptosis and development.

MATERIALS AND METHODS

In order to characterize the role of RXRs during colorectal carcinogenesis, the expression of RXRs in human and azoxymethane (AOM)-induced rat colorectal tumors was profiled by immunohistochemistry.

RESULTS

Both human and rat normal colorectal epithelia and hyperplasia exhibited strong nuclear, but weak cytoplasmic staining for all three proteins. Expression of RXRα, β and γ was significantly reduced in rat carcinomas compared to high-grade dysplasia whether in aberrant crypt foci or in adenomas. All three proteins displayed dramatically reduced nuclear expression in both human adenomas and carcinomas. Reduced expression of RXRα and RXRγ seems more significant than RXRβ in both human and rat carcinomas.

CONCLUSION

Reduced expression of RXRs is associated with colorectal carcinogenesis in both humans and AOM-treated rats.

9-cis-13,14-Dihydroretinoic Acid Is an Endogenous Retinoid Acting as RXR Ligand in Mice

The retinoid X receptors (RXRs) are ligand-activated transcription factors which heterodimerize with a number of nuclear hormone receptors, thereby controlling a variety of (patho)-physiological processes. Although synthetic RXR ligands are developed for the treatment of various diseases, endogenous ligand(s) for these receptors have not been conclusively identified. We show here that mice lacking cellular retinol binding protein (Rbp1-/-) display memory deficits reflecting compromised RXR signaling. Using HPLC-MS and chemical synthesis we identified in Rbp1-/- mice reduced levels of 9-cis-13,14-dihydroretinoic acid (9CDHRA), which acts as an RXR ligand since it binds and transactivates RXR in various assays. 9CDHRA rescues the Rbp1-/- phenotype similarly to a synthetic RXR ligand and displays similar transcriptional activity in cultured human dendritic cells. High endogenous levels of 9CDHRA in mice indicate physiological relevance of these data and that 9CDHRA acts as an endogenous RXR ligand.

Daily nutrition, in addition to being a source of energy, contains micronutrients, a class of nutrients including vitamins which are essential for life and which act by orchestrating a vast number of developmental and physiological processes. During metabolism, micronutrients are frequently transformed into their bioactive forms. Nuclear hormone receptors are a family of proteins functioning as ligand-regulated transcription factors which can sense such bioactive molecules and translate those signals into transcriptional, adaptive responses. Retinoid X receptors occupy a central place in this signaling as they directly interact, and thereby control, activities of several nuclear hormone receptors. We report here the identification of a novel bioactive form of vitamin A, which is the first endogenous form of this vitamin capable to bind and activate retinoid X receptors. Accordingly, we show that this single molecule displays biological activity similar to synthetic agonists of retinoid X receptors and coordinates transcriptional activities of several nuclear receptor signaling pathways. Those findings may have immediate biomedical implications, as retinoid X receptors are implicated in the control of a number of physiological functions and their pathology.

Chemoprotective epigenetic mechanisms in a colorectal cancer model: Modulation by n-3 PUFA in combination with fermentable fiber

Colorectal cancer is the third major cause of cancer-related mortality in both men and women worldwide. The beneficial role of n-3 polyunsaturated fatty acids (PUFA) in preventing colon cancer is substantiated by experimental, epidemiological, and clinical data. From a mechanistic perspective, n-3 PUFA are pleiotropic and multifaceted with respect to their molecular mechanisms of action. For example, this class of dietary lipid uniquely modulates membrane and nuclear receptors, sensors/ion channels, and membrane structure/cytoskeletal function, thereby regulating signaling processes that influence patterns of gene expression and cell phenotype. In addition, n-3 PUFA can synergize with other potential chemoprotective agents known to reprogram the chromatin landscape, such as the fermentable fiber product, butyrate. Nutri-epigenomics is an emerging field of research that is focused on the interaction between nutrition and epigenetics. Epigenetics refers to a group of heterogeneous processes that regulate transcription without changing the DNA coding sequence, ranging from DNA methylation, to histone tail modifications and transcription factor activity. One implication of the nutri-epigenome is that it may be possible to reprogram epigenetic marks that are associated with increased disease risk by nutritional or lifestyle interventions. This review will focus on the nutri-epigenomic role of n-3 PUFA, particularly DHA, as well as the combinatorial effects of n-3 PUFA and fermentable fiber in relation to colon cancer.

Regulation of the nongenomic actions of retinoid X receptor-α by targeting the coregulator-binding sites

Retinoid X receptor-α (RXRα), a unique member of the nuclear receptor superfamily, represents an intriguing and unusual target for pharmacologic interventions and therapeutic applications in cancer, metabolic disorders and neurodegenerative diseases. Despite the fact that the RXR-based drug Targretin (bexarotene) is currently used for treating human cutaneous T-cell lymphoma and the fact that RXRα ligands (rexinoids) show beneficial effects in the treatment of cancer and diseases, the therapeutic potential of RXRα remains unexplored. In addition to its conventional transcription regulation activity in the nucleus, RXRα can act in the cytoplasm to modulate important biological processes, such as mitochondria-dependent apoptosis, inflammation, and phosphatidylinositol 3-kinase (PI3K)/AKT-mediated cell survival. Recently, new small-molecule-binding sites on the surface of RXRα have been identified, which mediate the regulation of the nongenomic actions of RXRα by a class of small molecules derived from the nonsteroidal anti-inflammatory drug (NSAID) Sulindac. This review discusses the emerging roles of the nongenomic actions of RXRα in the RXRα signaling network, and their possible implications in cancer, metabolic and neurodegenerative disorders, as well as our current understanding of RXRα regulation by targeting alternate binding sites on its surface.

Fish consumption and risk of gastrointestinal cancers: A meta-analysis of cohort studies

AIM: To assess quantitatively the relationship between fish intake and the incidence of gastrointestinal cancers in a meta-analysis of cohort studies.

METHODS: We searched MEDLINE, Embase, Science Citation Index Expanded, and the bibliographies of retrieved articles. Prospective cohort studies were included if they reported relative risks (RRs) and corresponding 95% confidence intervals (CIs) of various cancers with respect to fish intake. When RRs were not available in the published article, they were computed from the exposure distributions. Two investigators extracted the data independently and discrepancies were resolved by discussion with a third investigator. We performed random-effect meta-analyses and meta-regressions of study-specific incremental estimates to determine the risk of cancer associated with a 20-g/d increment of fish consumption.

RESULTS: Forty-two studies, comprising 27 independent cohorts, met our inclusion criteria. The studies included 2325040 participants and 24115 incident cases of gastrointestinal cancer, with an average follow-up of 13.6 years. Compared with individuals who did not eat, or seldom ate, fish, the pooled RR of gastrointestinal cancers was 0.93 (95%CI: 0.88-0.98) for regular fish consumers, 0.94 (0.89-0.99) for low to moderate fish consumers, and 0.91 (0.84-0.97) for high fish consumers. Overall, a 20-g increase in fish consumption per day was associated with a 2% reduced risk of gastrointestinal cancers (RR = 0.98; 95%CI: 0.96-1.01). In subgroup analyses, we noted that fish consumption was associated with reduced risk of colorectal (RR = 0.93; 95%CI: 0.87-0.99; P < 0.01), esophageal (RR = 0.91; 95%CI: 0.83-0.99; P < 0.05) and hepatocellular cancers (RR = 0.71; 95%CI: 0.48-0.95; P < 0.01).

CONCLUSION: This meta-analysis suggested that fish consumption may reduce total gastrointestinal cancer incidence. Inverse relationships were also detected between fish consumption and specific types of cancers.

Marine omega-3 fatty acids and inflammatory processes: Effects, mechanisms and clinical relevance

Inflammation is a condition which contributes to a range of human diseases. It involves a multitude of cell types, chemical mediators, and interactions. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are omega-3 (n-3) fatty acids found in oily fish and fish oil supplements. These fatty acids are able to partly inhibit a number of aspects of inflammation including leukocyte chemotaxis, adhesion molecule expression and leukocyte-endothelial adhesive interactions, production of eicosanoids like prostaglandins and leukotrienes from the n-6 fatty acid arachidonic acid, production of inflammatory cytokines, and T-helper 1 lymphocyte reactivity. In addition, EPA gives rise to eicosanoids that often have lower biological potency than those produced from arachidonic acid and EPA and DHA give rise to anti-inflammatory and inflammation resolving mediators called resolvins, protectins and maresins. Mechanisms underlying the anti-inflammatory actions of marine n-3 fatty acids include altered cell membrane phospholipid fatty acid composition, disruption of lipid rafts, inhibition of activation of the pro-inflammatory transcription factor nuclear factor kappa B so reducing expression of inflammatory genes, activation of the anti-inflammatory transcription factor peroxisome proliferator activated receptor γ and binding to the G protein coupled receptor GPR120. These mechanisms are interlinked, although the full extent of this is not yet elucidated. Animal experiments demonstrate benefit from marine n-3 fatty acids in models of rheumatoid arthritis (RA), inflammatory bowel disease (IBD) and asthma. Clinical trials of fish oil in RA demonstrate benefit, but clinical trials of fish oil in IBD and asthma are inconsistent with no overall clear evidence of efficacy. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

The multifaceted effects of omega-3 polyunsaturated Fatty acids on the hallmarks of cancer

Omega-3 polyunsaturated fatty acids, in particular eicosapentaenoic acid, and docosahexaenoic acid have been shown to have multiple beneficial antitumour actions that affect the essential alterations that dictate malignant growth. In this review we explore the putative mechanisms of action of omega-3 polyunsaturated fatty acid in cancer protection in relation to self-sufficiency in growth signals, insensitivity to growth-inhibitory signals, apoptosis, limitless replicative potential, sustained angiogenesis, and tissue invasion, and how these will hopefully translate from bench to bedside.

Curcumin and docosahexaenoic acid block insulin-induced colon carcinoma cell proliferation

Diets high in fish and curcumin are associated with a decreased risk of CRC. Insulin resistance and obesity are associated with increased CRC risk and higher reoccurrence rates. We utilized cell culture to determine if dietary compounds could reduce insulin-induced cell proliferation comparing the response in normal and metastatic colon epithelial cells. We treated model normal murine colon epithelial cells (YAMC) and adenocarcinoma cells (MC38) with docosahexaenoic acid (DHA) or curcumin alone and then co-treatments of the diet-derived compound and insulin were combined. Cell proliferation was stimulated with insulin (1 ug/mL) to model insulin resistance in obesity. Despite the presence of insulin, proliferation was reduced in the MC38 cells treated with 10 μM curcumin (p<0.001) and 50 μM DHA (p<0.001). Insulin stimulated MAPK and MEK phosphorylation was inhibited by DHA and curcumin in MC38 cancer cells. Here we show that curcumin and DHA can block insulin-induced colon cancer cell proliferation in vitro via a MEK mediated mechanism.

N-3 PUFAs have antiproliferative and apoptotic effects on human colorectal cancer stem-like cells in vitro

The n-3 polyunsaturated fatty acids have been shown to inhibit the induction and progression of many kinds of tumor and to increase the therapeutic effects of numerous chemotherapeutics, but their anticancer effect on cancer stem cells from colorectal cancer has not been described previously. In the present study, we cultivated spheres from the SW620 cell line in serum-free medium and evaluated the features of the spheres by immunofluorescence, cell cycle distribution, resistance to chemotherapeutics and soft agar clone formation, and the spheres were shown to be cancer stem-like cells through tumorigenicity in athymic nude mice. Reverse transcriptase polymerase chain reaction analysis of pluripotency genes, such as Sox-2, Oct-4 and Bmi-1, showed that the spheres were generated by dedifferentiation of SW620 cells. The study explored the use of n-3 polyunsaturated fatty acids (PUFAs) in spheres, which were treated with two n-3 PUFAs [docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA)]. Treatment of the spheres with DHA and EPA alone or in combination for 72 h led to apoptosis and the progressive loss of viability and DNA fragmentation and an increase in annexin V expression. DHA and EPA can enhance the chemotherapeutic sensitivity effect of 5-Fu and mitomycin C, especially DHA combined with EPA. Taken together, these results provide evidence that n-3 PUFAs exert a direct anticancer action that may contribute to their antiproliferative and proapoptotic effect on the cancer stem-like cells.

Immunomodulatory action of dietary fish oil and targeted deletion of intestinal epithelial cell PPARδ in inflammation-induced colon carcinogenesis

The ligand-activated transcription factor peroxisome proliferator-activated receptor (PPAR)-δ is highly expressed in colonic epithelial cells; however, the role of PPARδ ligands, such as fatty acids, in mucosal inflammation and malignant transformation has not been clarified. Recent evidence suggests that the anti-inflammatory/chemoprotective properties of fish oil (FO)-derived n-3 polyunsaturated fatty acids (PUFAs) may be partly mediated by PPARδ. Therefore, we assessed the role of PPARδ in modulating the effects of dietary n-3 PUFAs by targeted deletion of intestinal epithelial cell PPARδ (PPARδ(ΔIEpC)). Subsequently, we documented changes in colon tumorigenesis and the inflammatory microenvironment, i.e., local [mesenteric lymph node (MLN)] and systemic (spleen) T cell activation. Animals were fed chemopromotive [corn oil (CO)] or chemoprotective (FO) diets during the induction of chronic inflammation/carcinogenesis. Tumor incidence was similar in control and PPARδ(ΔIEpC) mice. FO reduced mucosal injury, tumor incidence, colonic STAT3 activation, and inflammatory cytokine gene expression, independent of PPARδ genotype. CD8(+) T cell recruitment into MLNs was suppressed in PPARδ(ΔIEpC) mice. Similarly, FO reduced CD8(+) T cell numbers in the MLN. Dietary FO independently modulated MLN CD4(+) T cell activation status by decreasing CD44 expression. CD11a expression by MLN CD4(+) T cells was downregulated in PPARδ(ΔIEpC) mice. Lastly, splenic CD62L expression was downregulated in PPARδ(ΔIEpC) CD4(+) and CD8(+) T cells. These data demonstrate that expression of intestinal epithelial cell PPARδ does not influence azoxymethane/dextran sodium sulfate-induced colon tumor incidence. Moreover, we provide new evidence that dietary n-3 PUFAs attenuate intestinal inflammation in an intestinal epithelial cell PPARδ-independent manner.

Omega-3 fatty acids and cardiovascular disease: effects on risk factors, molecular pathways, and clinical events

We reviewed available evidence for cardiovascular effects of n-3 polyunsaturated fatty acid (PUFA) consumption, focusing on long chain (seafood) n-3 PUFA, including their principal dietary sources, effects on physiological risk factors, potential molecular pathways and bioactive metabolites, effects on specific clinical endpoints, and existing dietary guidelines. Major dietary sources include fatty fish and other seafood. n-3 PUFA consumption lowers plasma triglycerides, resting heart rate, and blood pressure and might also improve myocardial filling and efficiency, lower inflammation, and improve vascular function. Experimental studies demonstrate direct anti-arrhythmic effects, which have been challenging to document in humans. n-3 PUFA affect a myriad of molecular pathways, including alteration of physical and chemical properties of cellular membranes, direct interaction with and modulation of membrane channels and proteins, regulation of gene expression via nuclear receptors and transcription factors, changes in eicosanoid profiles, and conversion of n-3 PUFA to bioactive metabolites. In prospective observational studies and adequately powered randomized clinical trials, benefits of n-3 PUFA seem most consistent for coronary heart disease mortality and sudden cardiac death. Potential effects on other cardiovascular outcomes are less-well-established, including conflicting evidence from observational studies and/or randomized trials for effects on nonfatal myocardial infarction, ischemic stroke, atrial fibrillation, recurrent ventricular arrhythmias, and heart failure. Research gaps include the relative importance of different physiological and molecular mechanisms, precise dose-responses of physiological and clinical effects, whether fish oil provides all the benefits of fish consumption, and clinical effects of plant-derived n-3 PUFA. Overall, current data provide strong concordant evidence that n-3 PUFA are bioactive compounds that reduce risk of cardiac death. National and international guidelines have converged on consistent recommendations for the general population to consume at least 250 mg/day of long-chain n-3 PUFA or at least 2 servings/week of oily fish.

The retinoid X receptors and their ligands

This chapter presents an overview of the current status of studies on the structural and molecular biology of the retinoid X receptor subtypes α, β, and γ (RXRs, NR2B1-3), their nuclear and cytoplasmic functions, post-transcriptional processing, and recently reported ligands. Points of interest are the different changes in the ligand-binding pocket induced by variously shaped agonists, the communication of the ligand-bound pocket with the coactivator binding surface and the heterodimerization interface, and recently identified ligands that are natural products, those that function as environmental toxins or drugs that had been originally designed to interact with other targets, as well as those that were deliberately designed as RXR-selective transcriptional agonists, synergists, or antagonists. Of these synthetic ligands, the general trend in design appears to be away from fully aromatic rigid structures to those containing partial elements of the flexible tetraene side chain of 9-cis-retinoic acid. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).

A synergistic antiproliferation effect of curcumin and docosahexaenoic acid in SK-BR-3 breast cancer cells: unique signaling not explained by the effects of either compound alone

BACKGROUND

Breast cancer is a collection of diseases in which molecular phenotypes can act as both indicators and mediators of therapeutic strategy. Therefore, candidate therapeutics must be assessed in the context of multiple cell lines with known molecular phenotypes. Docosahexaenoic acid (DHA) and curcumin (CCM) are dietary compounds known to antagonize breast cancer cell proliferation. We report that these compounds in combination exert a variable antiproliferative effect across multiple breast cell lines, which is synergistic in SK-BR-3 cells and triggers cell signaling events not predicted by the activity of either compound alone.

METHODS

Dose response curves for CCM and DHA were generated for five breast cell lines. Effects of the DHA+ CCM combination on cell proliferation were evaluated using varying concentrations, at a fixed ratio, of CCM and DHA based on their individual ED₅₀. Detection of synergy was performed using nonlinear regression of a sigmoid dose response model and Combination Index approaches. Cell molecular network responses were investigated through whole genome microarray analysis of transcript level changes. Gene expression results were validated by RT-PCR, and western blot analysis was performed for potential signaling mediators. Cellular curcumin uptake, with and without DHA, was analyzed via flow cytometry and HPLC.

RESULTS

CCM+DHA had an antiproliferative effect in SK-BR-3, MDA-MB-231, MDA-MB-361, MCF7 and MCF10AT cells. The effect was synergistic for SK-BR-3 (ER⁻ PR⁻ Her2⁺) relative to the two compounds individually. A whole genome microarray approach was used to investigate changes in gene expression for the synergistic effects of CCM+DHA in SK-BR-3 cells lines. CCM+DHA triggered transcript-level responses, in disease-relevant functional categories, that were largely non-overlapping with changes caused by CCM or DHA individually. Genes involved in cell cycle arrest, apoptosis, inhibition of metastasis, and cell adhesion were upregulated, whereas genes involved in cancer development and progression, metastasis, and cell cycle progression were downregulated. Cellular pools of PPARγ and phospho-p53 were increased by CCM+DHA relative to either compound alone. DHA enhanced cellular uptake of CCM in SK-BR-3 cells without significantly enhancing CCM uptake in other cell lines.

CONCLUSIONS

The combination of DHA and CCM is potentially a dietary supplemental treatment for some breast cancers, likely dependent upon molecular phenotype. DHA enhancement of cellular curcumin uptake is one potential mechanism for observed synergy in SK-BR-3 cells; however, transcriptomic data show that the antiproliferation synergy accompanies many signaling events unique to the combined presence of the two compounds.

DHA alters expression of target proteins of cancer therapy in chemotherapy resistant SW620 colon cancer cells

Diets rich in n-3 polyunsaturated fatty acids (PUFAs) have been associated with a reduced risk of several types of cancer. Recent reports have suggested that these PUFAs enhance the cytotoxic effect of cancer chemoradiotherapy. The effect of docosahexaenoic acid (DHA) on key cell cycle regulators and target proteins of cancer therapy was investigated in the human malign colon cancer cell line SW620. Cell cycle check point proteins such as p21 and stratifin (14-3-3 sigma) increased at mRNA and protein level, whereas cell cycle progression proteins such as cell division cycle 25 homolog and cyclin-dependent kinase 1 decreased after DHA treatment. Protein levels of inhibitors of apoptosis family members associated with chemotherapy resistance and cancer malignancy, survivin and livin, decreased after the same treatment: likewise the expression of NF-kappaB. Levels of the proapoptotic proteins phosphorylated p38 MAPK and growth arrest-inducible and DNA damage-inducible gene 153/C/EBP-homologous protein (CHOP) increased. The results indicate that DHA treatment causes simultaneous cell cycle arrest in both the G1 and G2 phase. In conclusion, DHA affects several target proteins of chemotherapy in a favorable way. This may explain the observed enhanced chemosensitivity in cancer cells supplemented with n-3 PUFAs and encourage further studies investigating the role of n-3 PUFAs as adjuvant to chemotherapy and radiotherapy in vivo.

Genetic variation in the retinoid X receptor and calcium-sensing receptor and risk of colorectal cancer in the Colon Cancer Family Registry

Genetic variants in the calcium/vitamin D metabolic pathway may be related to risk for colorectal cancer. While several investigations of vitamin D receptor (VDR) polymorphisms and colorectal cancer have been conducted, no studies to date have evaluated the association of genetic variation in the heterodimer partner for VDR, the retinoid X receptor (RXR). Another important gene in this pathway is the calcium-sensing receptor (CASR). Employing a discordant-sibship case-control design, we examined the association between single nucleotide polymorphisms (SNPs) in RXRA and CASR and risk for colorectal cancer overall and by colorectal subsite and microsatellite instability (MSI) status using data from the Colon Cancer Family Registry. No gene-level relationships between RXRA or CASR and colorectal cancer overall were observed. However, for RXRA SNP rs7861779, a high-interest SNP selected for study a priori, there was a statistically significantly increased risk for proximal colorectal cancer among those with at least one A allele [odds ratio (OR) = 1.42; 95% confidence interval (CI) = 1.03-1.97]. Another selected RXRA SNP, rs12004589, was significantly associated with risk of MSI-high cancers (OR = 2.27; 95% CI = 1.13-4.56). Additionally, CASR SNP rs1801726 was significantly associated with a reduced risk for rectal cancer (OR = 0.53; 95% CI = 0.29-0.96). These results provide support that RXRA SNPs rs7861779 and rs12004589 and CASR SNP rs1801726 may be important markers for colorectal neoplasia. Further work is needed to elucidate their role in the carcinogenic pathway.

Association between polymorphic variation in VDR and RXRA and circulating levels of vitamin D metabolites

The vitamin D metabolite 1,25(OH)2D is the bioactive ligand of the vitamin D receptor (VDR). VDR forms a heterodimer with the retinoid X receptors (RXRs) that when bound to ligand influences the transcriptional control of genes that regulate circulating levels of vitamin D metabolites. Whether genetic variation in VDR or RXRA affects circulating levels of 1,25(OH)2D or 25(OH)D has not been established. We used a single nucleotide polymorphism (SNP) tagging approach to evaluate the association between SNPs in VDR and RXRA and serum levels of 1,25(OH)2D and 25(OH)D. A total of 42 tagSNPs in VDR and 32 in RXRA were analyzed in a sample of 415 participants. Principal components analyses revealed a gene-level association between RXRA and serum 1,25(OH)2D concentrations (P=0.01), but not 25(OH)D. No gene-level association was found for VDR with either serum biomarker. At the single-SNP level, a significant positive trend was observed for increasing 1,25(OH)2D levels with each additional copy of the A allele for RXRA SNP rs9409929 (P-trend=0.003). After a multiple comparisons adjustment, no individual SNP in VDR or RXRA was significantly associated with either outcome. These results demonstrate an association between genetic variation in RXRA and 1,25(OH)2D serum concentrations.

Incorporation of a dietary omega 3 fatty acid impairs murine macrophage responses to Mycobacterium tuberculosis

BACKGROUND

Beside their health benefits, dietary omega 3 polyunsaturated fatty acids (n-3 PUFA) might impair host resistance to Mycobacterium tuberculosis (Mtb) by creating an immunosuppressive environment. We hypothesized that incorporation of n-3 PUFA suppresses activation of macrophage antimycobacterial responses and favors bacterial growth, in part, by modulating the IFNgamma-mediated signaling pathway.

METHODOLOGY/PRINCIPAL FINDINGS

Murine macrophage-like J774A.1 cells were incubated with bovine serum albumin (BSA)-conjugated docosahexaenoic acid (DHA; 22:6n-3) or BSA alone, activated with recombinant IFNgamma, and infected with a virulent strain (H37Rv) of M. tuberculosis. The fatty acid composition of macrophage membranes was modified significantly by DHA treatment. DHA-treated macrophages were less effective in controlling intracellular mycobacteria and showed impaired oxidative metabolism and reduced phagolysosome maturation. Incorporation of DHA resulted in defective macrophage activation, as characterized by reduced production of pro-inflammatory cytokines (TNFalpha, IL-6 and MCP-1), and lower expression of co-stimulatory molecules (CD40 and CD86). DHA treatment impaired STAT1 phosphorylation and colocalization of the IFNgamma receptor with lipid rafts, without affecting surface expression of IFNgamma receptor.

CONCLUSIONS/SIGNIFICANCE

We conclude that DHA reduces the ability of J774A.1 cells to control M. tuberculosis in response to activation by IFNgamma, by modulation of IFNgamma receptor signaling and function, suggesting that n-3 PUFA-enriched diets may have a detrimental effect on host immunity to tuberculosis.

Fatty acids and signalling in endothelial cells

The endothelium is critical for the maintenance of a proper vessel function. Disturbances of endothelial function, called endothelial dysfunction, have serious implications, and lead to the development of atherosclerosis. It is well established that the risk for atherosclerosis development is influenced by nutritional factors such as the intake of certain fatty acids. Due to the fundamental role of the endothelium for atherosclerosis development, it is, therefore, likely that fatty acids directly influence the function of endothelial cells. The present review aims to explain the divergent effects of different types of fatty acids on cardiovascular disease risk by summarizing in vitro-data on the effects of fatty acids on (1) important signalling pathways involved in the modulation of endothelial cell function, and (2) endothelial cell functional properties, namely vasoactive mediator release and mononuclear cell recruitment, both of which are typically dysregulated during endothelial dysfunction.

Characterization of anticancer properties of 2,6-diisopropylphenol-docosahexaenoate and analogues in breast cancer cells

The present study describes the characterization and evaluation of novel anticancer conjugates, 2,6-diisopropylphenol-docosahexaenoate (PP-DHA), and its analogues including 2,4-diisopropylphenol-docosahexaenoate (DIPP-DHA), 2-isopropylphenol-docosahexaenoate (IPP-DHA), 2-cyclohexanephenol-docosahexaenoate (CHP-DHA) and phenol-docosahexaenoate (P-DHA) on breast cancer cell lines. Representative breast cancer cell lines, based on estrogen alpha receptor (ER) and oncogene Her-2 expression, were used and include MDA-MB-231 (ER-negative, Her-2-negative), MCF-7 (ER-positive, Her-2-negative) AU565 (ER-negative, Her-2-positive) and MDA-MB-361 (ER-positive, Her-2-positive). The PP-DHA conjugate significantly inhibited cell growth and induced cell loss in the breast cancer cell lines similarly; however, this conjugate was not effective against normal mammary epithelial cells. The effect of various conjugates were in PP-DHA>IPP-DHA>DIPP-DHA>CHP-DHA>>P-DHA order. PP-DHA and IPP-DHA conjugates were stable in human and mouse serum. Furthermore, the non-hydrolyzable amide-linked conjugate analogues affected breast cancer cells in a manner similar to that of the ester-linked conjugates. This suggests that ester-linked PP-DHA and IPP-DHA conjugates were stable during treatment to breast cancer cells due to structural hindrance. PP-DHA did not affect PPARalpha or PPARgamma activities but its anticancer effects appear to be mediated in part though the inhibition of histone deacetylase (HDAC) activity. Further experiments are needed to confirm their molecular target and to test the effectiveness of these compounds in an in vivo model for their anticancer properties. In conclusion, these results suggest that the novel PP-DHA and IPP-DHA conjugates and their amide derivatives may be useful for the treatment of breast cancer.

Therapeutic potential of n-3 polyunsaturated fatty acids in disease

PURPOSE

The potential therapeutic benefits of supplementation with n-3 polyunsaturated fatty acids (PUFAs) in various diseases are reviewed, and the antiinflammatory actions, activity, and potential drug interactions and adverse effects of n-3 PUFAs are discussed.

SUMMARY

Fish oils are an excellent source of long-chain n-3 PUFAs, such as eicosapentaenoic acid and docosahexaenoic acid. After consumption, n-3 PUFAs can be incorporated into cell membranes and reduce the amount of arachidonic acid available for the synthesis of proinflammatory eicosanoids (e.g., prostaglandins, leukotrienes). Likewise, n-3 PUFAs can also reduce the production of inflammatory cytokines, such as tumor necrosis factor alpha, interleukin-1, and interleukin-6. Considerable research has been conducted to evaluate the potential therapeutic effects of fish oils in numerous conditions, including arthritis, coronary artery disease, inflammatory bowel disease, asthma, and sepsis, all of which have inflammation as a key component of their pathology. Additional investigations into the use of supplementation with fish oils in patients with neural injury, cancer, ocular diseases, and critical illness have recently been conducted. The most commonly reported adverse effects of fish oil supplements are a fishy aftertaste and gastrointestinal upset. When recommending an n-3 PUFA, clinicians should be aware of any possible adverse effect or drug interaction that, although not necessarily clinically significant, may occur, especially for patients who may be susceptible to increased bleeding (e.g., patients taking warfarin).

CONCLUSION

The n-3 PUFAs have been shown to be efficacious in treating and preventing various diseases. The wide variation in dosages and formulations used in studies makes it difficult to recommend dosages for specific treatment goals.

Dietary docosahexaenoic and eicosapentaenoic acid: emerging mediators of inflammation

The inflammatory response is designed to help fight and clear infection, remove harmful chemicals, and repair damaged tissue and organ systems. Although this process, in general, is protective, the failure to resolve the inflammation and return the target tissue to homeostasis can result in disease, including the promotion of cancer. A plethora of published literature supports the contention that dietary n-3 polyunsaturated fatty acids (PUFA), and eicosapentaenoic (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) in particular, are important modulators of a host's inflammatory/immune responses. The following review describes a mechanistic model that may explain, in part, the pleiotropic anti-inflammatory and immunosuppressive properties of EPA and DHA. In this review, we focus on salient studies that address three overarching mechanisms of n-3 PUFA action: (i) modulation of nuclear receptor activation, i.e., nuclear factor-kappaB (NF-kappaB) suppression; (ii) suppression of arachidonic acid-cyclooxygenase-derived eicosanoids, primarily prostaglandin E(2)-dependent signaling; and (iii) alteration of the plasma membrane micro-organization (lipid rafts), particularly as it relates to the function of Toll-like receptors (TLRs), and T-lymphocyte signaling molecule recruitment to the immunological synapse (IS). We propose that lipid rafts may be targets for the development of n-3 PUFA-containing dietary bioactive agents to down-modulate inflammatory and immune responses and for the treatment of autoimmune and chronic inflammatory diseases.

3D-pharmacophore model for RXR(gamma) agonists

Three-dimensional pharmacophore models were generated for retinoid X receptor (RXR(gamma)) agonists using quantitative approach (CATALYST HypoRefine). One optimal pharmacophore model for selective RXR(gamma) agonists was determined through careful validation processes. The best quantitative model (Hypo-1) had five features and five excluded volumes: three hydrophobic aliphatic groups (HAL1, HAL2, and HAL3), one hydrophobic aromatic ring (HAR), and one hydrogen bond acceptor (HBA). The model was validated using a wide range of test molecules. It could predict agonist activity and identify highly potent molecules. The present results are valuable to discover and develop specific RXR(gamma) agonists with desired biological activities.

A comparison of the effects of soya isoflavonoids and fish oil on cell proliferation, apoptosis and the expression of oestrogen receptors alpha and beta in the mammary gland and colon of the rat

Isoflavonoids and fish oil may be protective against colorectal cancer, but the evidence in relation to breast cancer risk is ambiguous. In the present study, we have investigated the impact of soya-derived isoflavonoids and n-3 fatty acids from fish oil, both individually and in combination, on apoptosis, cell proliferation and oestrogen receptor (ER) expression in the colon and mammary gland of the rat. Female rats were fed diets high in n-3 fatty acids (80 g/kg diet) or soya protein (765 mg/kg diet isoflavones) for 2 weeks, and then killed before the removal of the colon and mammary glands. Cell proliferation and apoptosis were quantified morphologically in whole crypts and terminal end buds. The expressions of ERalpha and ERbeta were measured in colon tissue scrapes and the mammary gland. Fish oil significantly increased apoptosis and decreased mitosis in both tissues, an effect associated with a decrease in the expressions of ERalpha and ERbeta. Soya had no effect on apoptosis in either tissue, but reduced mitosis in the colon (P < 0.001) while increasing it in the mammary gland (P = 0.001). The changes in proliferation were associated with contrasting changes in the ER expression such that fish oil significantly decreased both ERbeta and ERalpha, while soya increased ERalpha and decreased ERbeta. The results may provide a novel mechanism by which n-3 fatty acids could reduce cancer risk, but the interpretation of the results in relation to soya consumption and breast cancer risk requires further investigation.

Bioactive dietary long-chain fatty acids: emerging mechanisms of action

The plasma membranes of all eukaryotic cells contain heterogeneous self-organising intrinsically unstable liquid ordered domains or lipid assemblies in which key signal transduction proteins are localised. These assemblies are classified as 'lipid rafts' (10-200 nm), which are composed mostly of cholesterol and sphingolipid microdomains and therefore do not integrate well into the fluid phospholipid bilayers. In addition, caveolae represent a subtype of lipid raft macrodomain that form flask-shaped membrane invaginations containing structural proteins, i.e. caveolins. With respect to the diverse biological effects of long-chain PUFA, increasing evidence suggests that n-3 PUFA and perhaps conjugated fatty acids uniquely alter the basic properties of cell membranes. Because of its polyunsaturation, DHA and possibly conjugated linoleic acid are sterically incompatible with sphingolipid and cholesterol and, therefore, appear to alter lipid raft behaviour and protein function. The present review examines the evidence indicating that dietary sources of n-3 PUFA can profoundly alter the biochemical make up of lipid rafts/caveolae microdomains, thereby influencing cell signalling, protein trafficking and cell cytokinetics.

The influence of feeding linoleic, gamma-linolenic and docosahexaenoic acid rich oils on rat brain tumor fatty acids composition and fatty acid binding protein 7 mRNA expression

Background

Experimental studies indicate that gamma linolenic acid (GLA) and docosahexaenoic acid (DHA) may inhibit glioma cells growth but effects of oral consumption of these fatty acids on brain tumor fatty acid composition have not been determined in vivo.

Methods

GLA oil (GLAO; 72% GLA), DHA oil (DHAO; 73% DHA) were fed to adult wistar rats (1 mL/rat/day) starting one week prior to C6 glioma cells implantation and continued for two weeks after implantation. Control group were fed same amount of high linoleic acid safflower oil (74–77% linoleic acid). Fatty acid composition of tumor samples was determined in a set of 8–12 animals in each group and serum fatty acid in 6 animals per each group. Gene expression of tumor fatty acid binding protein 7 (FABP7), epidermal growth factor receptor (EGFR), peroxisome proliferator activated receptor γ (PPAR-γ) and retinoid × receptor-α (RXR-α) were determined in a set of 18 animals per group.

Results

DHAO feeding increased EPA of brain tumors and decreased ratio of n-6/n-3 fatty acids. Serum levels of EPA were also increased in DHAO group. A similar trend in serum and tumor levels of DHA were observed in DHAO group but it did not achieve statistical significance. GLAO increased serum concentration of GLA but had no significant effect on tumor GLA or dihomo-gamma linolenic acid (DGLA) concentrations. Gene expression of FABP7 was up-regulated in tumors of DHAO group but no other significant effects were observed on EGFR, PPAR-γ or RXR-α expression, and expression of these genes in tumors of GLAO were not different from SFO group.

Conclusion

Dietary supplementation of DHA containing oil could be an effective way to increase levels of long chain n-3 fatty acids in brain tumors and this increase may be mediated partly by up-regulation of FABP7 expression.

Integrities of A/B and C domains of RXR are required for rexinoid-induced caspase activations and apoptosis

Here we have delineated regions of the retinoid X receptor alpha (RXRalpha) that are required for rexinoid (RXR agonist)-induced growth inhibition and apoptosis. Stable over-expression of RXRalpha in DT40 B lymphoma cells dramatically increased sensitivity to rexinoid-induced growth inhibition. By contrast, DT40 cells that over-expressed RXRalpha with a deletion of either the A/B or DNA binding domain (C domain) were resistant. We confirmed the importance of C domain integrity by point-mutating Cys(135) to Ser (C135S) to disrupt zinc-finger formation. Point mutating RXR Lys(201) to Thr and Arg(202) to Ala (KTRA) impairs RXR homodimer formation and does not affect RXR heterodimerization. When these mutated RXRs were over-expressed in DT40 cells, they failed to increase sensitivity to rexinoid. Over-expression did sensitize to growth inhibition by RAR and PPARgamma agonists. Over-expression of C135S mutated RXRalpha did not sensitize to RAR and PPARgamma agonists. Inhibitors of caspase-3 and/or caspase-9 blocked rexinoid-induced apoptosis, and activations of these caspases correlated with the ability of RXR mutants to induce cell death. These data show that the A/B and C domains of RXR and the ability of RXR to form homodimers are required for rexinoid-driven growth inhibition, caspase activation and subsequent apoptosis.

Multi-targeted therapy of cancer by omega-3 fatty acids

Omega-3 (n-3) and omega-6 (n-6) polyunsaturated fatty acids (PUFAs) are essential fatty acids necessary for human health. Currently, the Western diet contains a disproportionally high amount of n-6 PUFAs and low amount of n-3 PUFAs, and the resulting high n-6/n-3 ratio is thought to contribute to cardiovascular disease, inflammation, and cancer. Studies in human populations have linked high consumption of fish or fish oil to reduced risk of colon, prostate, and breast cancer, although other studies failed to find a significant association. Nonetheless, the available epidemiological evidence, combined with the demonstrated effects of n-3 PUFAs on cancer in animal and cell culture models, has motivated the development of clinical interventions using n-3 PUFAs in the prevention and treatment of cancer, as well as for nutritional support of cancer patients to reduce weight loss and modulate the immune system. In this review, we discuss the rationale for using long-chain n-3 PUFAs in cancer prevention and treatment and the challenges that such approaches pose in the design of clinical trials.

Effect of synthetic dietary triglycerides: a novel research paradigm for nutrigenomics

Background

The effect of dietary fats on human health and disease are likely mediated by changes in gene expression. Several transcription factors have been shown to respond to fatty acids, including SREBP-1c, NF-κB, RXRs, LXRs, FXR, HNF4α, and PPARs. However, it is unclear to what extent these transcription factors play a role in gene regulation by dietary fatty acids in vivo.

Methodology/Principal Findings

Here, we take advantage of a unique experimental design using synthetic triglycerides composed of one single fatty acid in combination with gene expression profiling to examine the effects of various individual dietary fatty acids on hepatic gene expression in mice. We observed that the number of significantly changed genes and the fold-induction of genes increased with increasing fatty acid chain length and degree of unsaturation. Importantly, almost every single gene regulated by dietary unsaturated fatty acids remained unaltered in mice lacking PPARα. In addition, the majority of genes regulated by unsaturated fatty acids, especially docosahexaenoic acid, were also regulated by the specific PPARα agonist WY14643. Excellent agreement was found between the effects of unsaturated fatty acids on mouse liver versus cultured rat hepatoma cells. Interestingly, using Nuclear Receptor PamChip® Arrays, fatty acid- and WY14643-induced interactions between PPARα and coregulators were found to be highly similar, although several PPARα-coactivator interactions specific for WY14643 were identified.

Conclusions/Significance

We conclude that the effects of dietary unsaturated fatty acids on hepatic gene expression are almost entirely mediated by PPARα and mimic those of synthetic PPARα agonists in terms of regulation of target genes and molecular mechanism. Use of synthetic dietary triglycerides may provide a novel paradigm for nutrigenomics research.

The expanding role for retinoid signaling in heart development

The importance of retinoid signaling during cardiac development has long been appreciated, but recently has become a rapidly expanding field of research. Experiments performed over 50 years ago showed that too much or too little maternal intake of vitamin A proved detrimental for embryos, resulting in a cadre of predictable cardiac developmental defects. Germline and conditional knockout mice have revealed which molecular players in the vitamin A signaling cascade are potentially responsible for regulating specific developmental events, and many of these molecules have been temporally and spatially characterized. It is evident that intact and controlled retinoid signaling is necessary for each stage of cardiac development to proceed normally, including cardiac lineage determination, heart tube formation, looping, epicardium formation, ventricular maturation, chamber and outflow tract septation, and coronary arteriogenesis. This review summarizes many of the significant milestones in this field and particular attention is given to recently uncovered cross-talk between retinoid signaling and other developmentally significant pathways. It is our hope that this review of the role of retinoid signaling during formation, remodeling, and maturation of the developing heart will serve as a tool for future discoveries.