Interactive effects of fatty acid and butyrate-induced mitochondrial Ca²⁺ loading and apoptosis in colonocytes

Dietary intake of α-ketoglutarate ameliorates α-synuclein pathology in mouse models of Parkinson's disease

Parkinson's disease (PD) is a progressive movement disorder characterized by dopaminergic (DA) neuron degeneration and the existence of Lewy bodies formed by misfolded α-synuclein. Emerging evidence supports the benefits of dietary interventions in PD due to their safety and practicality. Previously, dietary intake of α-ketoglutarate (AKG) was proved to extend the lifespan of various species and protect mice from frailty. However, the mechanism of dietary AKG's effects in PD remains undetermined. In the present study, we report that an AKG-based diet significantly ameliorated α-synuclein pathology, and rescued DA neuron degeneration and impaired DA synapses in adeno-associated virus (AAV)-loaded human α-synuclein mice and transgenic A53T α-synuclein (A53T α-Syn) mice. Moreover, AKG diet increased nigral docosahexaenoic acid (DHA) levels and DHA supplementation reproduced the anti-α-synuclein effects in the PD mouse model. Our study reveals that AKG and DHA induced microglia to phagocytose and degrade α-synuclein via promoting C1q and suppressed pro-inflammatory reactions. Furthermore, results indicate that modulating gut polyunsaturated fatty acid metabolism and microbiota Lachnospiraceae_NK4A136_group in the gut-brain axis may underlie AKG's benefits in treating α-synucleinopathy in mice. Together, our findings propose that dietary intake of AKG is a feasible and promising therapeutic approach for PD.

Intestinal Immune Homeostasis and Inflammatory Bowel Disease: A Perspective on Intracellular Response Mechanisms

The pathogenesis of inflammatory bowel disease (IBD) involves perturbation of intestinal immune homeostasis in genetically susceptible individuals. A mutual interplay between intestinal epithelial cells (IECs) and gut resident microbes maintains a homeostatic environment across the gut. An idiopathic gastrointestinal (GI) complication triggers aberrant physiological stress in the epithelium and peripheral myeloid cells, leading to a chronic inflammatory condition. Indeed, events in the endoplasmic reticulum (ER) and mitochondria contribute to orchestrating intracellular mechanisms such as the unfolded protein response (UPR) and oxidative stress, respectively, to resolve aberrant cellular stress. This review highlights the signaling cascades encrypted within ER and mitochondria in IECs and/or myeloid cells to dissipate chronic stress in maintaining intestinal homeostasis.

Faecalibacterium prausnitzii produces butyrate to decrease c-Myc-related metabolism and Th17 differentiation by inhibiting histone deacetylase 3

Decreased levels of Faecalibacterium prausnitzii (F. prausnitzii), whose supernatant plays an anti-inflammatory effect, are frequently found in inflammatory bowel disease (IBD) patients. However, the anti-inflammatory products in F. prausnitzii supernatant and the mechanism have not been fully investigated. Here we found that F. prausnitzii and F. prausnitzii-derived butyrate were decreased in the intestines of IBD patients. Supplementation with F. prausnitzii supernatant and butyrate could ameliorate colitis in an animal model. Butyrate, but not other substances produced by F. prausnitzii, exerted an anti-inflammatory effect by inhibiting the differentiation of T helper 17 (Th17) cells. The mechanism underlying the anti-inflammatory effects of the butyrate produced by F. prausnitzii involved the enhancement of the acetylation-promoted degradation of c-Myc through histone deacetylase 3 (HDAC3) inhibition. In conclusion, F. prausnitzii produced butyrate to decrease Th17 differentiation and attenuate colitis through inhibiting HDAC3 and c-Myc-related metabolism in T cells. The use of F. prausnitzii may be an effective new approach to decrease the level of Th17 cells in the treatment of inflammatory diseases.

Diet and Gut Microbes Act Coordinately to Enhance Programmed Cell Death and Reduce Colorectal Cancer Risk

Diet is an important risk factor for colorectal cancer (CRC), and several dietary constituents implicated in CRC are modified by gut microbial metabolism. Microbial fermentation of dietary fiber produces short-chain fatty acids, e.g., acetate, propionate, and butyrate. Dietary fiber has been shown to reduce colon tumors in animal models, and, in vitro, butyrate influences cellular pathways important to cancer risk. Furthermore, work from our group suggests that the combined effects of butyrate and omega-3 polyunsaturated fatty acids (n-3 PUFA) may enhance the chemopreventive potential of these dietary constituents. We postulate that the relatively low intakes of n-3 PUFA and fiber in Western populations and the failure to address interactions between these dietary components may explain why chemoprotective effects of n-3 PUFA and fermentable fibers have not been detected consistently in prospective cohort studies. In this review, we summarize the evidence outlining the effects of n-3 long-chain PUFA and highly fermentable fiber with respect to alterations in critical pathways important to CRC prevention, particularly intrinsic mitochondrial-mediated programmed cell death resulting from the accumulation of lipid reactive oxygen species (ferroptosis), and epigenetic programming related to lipid catabolism and beta-oxidation-associated genes.

Omega 3-DHA and Delta-Tocotrienol Modulate Lipid Droplet Biogenesis and Lipophagy in Breast Cancer Cells: the Impact in Cancer Aggressiveness

Omega 3-docosahexaenoic acid (DHA) and vitamin E Delta-tocotrienol (Delta-T3) are extensively studied as protective nutrients against cancer development. Little is known about the biological mechanisms targeted by these bioactive molecules on lipid droplet (LD) biogenesis, an important breast cancer aggressiveness marker, and the occurrence of lipophagy in breast cancer cells. The aim of this study was to investigate the effect of DHA, Delta-T3 and DHA plus Delta-T3 co-treatment in LD biogenesis and lipophagy process in triple negative breast cancer cell line MDA-MB-231. Cells were treated with 50 μM DHA and/or 5 μM Delta-T3. Our results demonstrated that DHA can trigger an increase in LD biogenesis and co-treatment with Delta-T3 was able to reduce this LD biogenesis. In addition, we showed that a higher cytoplasmic LD content is associated with a higher breast cancer cells malignance and proliferation. Reduction of cytoplasmic LD content by silencing ADRP (adipose differentiation-related protein), a structural LD protein, also decreased cell proliferation in MDA-MB-231 cells. Treatment with DHA and Delta-T3 alone or co-treatment did not reduce cell viability. Moreover, we showed here that DHA can trigger lipophagy in MDA-MB-231 cells and DHA plus Delta-T3 co-treatment was able to enhance this lipophagy process. Our findings demonstrated that co-treatment with DHA plus Delta-T3 in MDA-MB-231 cells could reduce LD biogenesis and potentiate lipophagy in these cells, possibly having a positive impact to inhibit breast cancer malignancy. Therefore, suitable doses of DHA and Delta-T3 vitamin E isoform supplementation can be a prominent tool in therapeutic treatments against breast cancer.

Inhibitory Effects of Short-Chain Fatty Acids and ω-3 Polyunsaturated Fatty Acids on Profibrotic Factors in Dermal Fibroblasts

Objective: Dermal fibroproliferative disorders impair patients' quality of life. Although several therapeutic approaches exist for treatment of dermal scars, the development of effective ointments with few adverse effects could improve these therapeutic methods. Short-chain and ω-3 polyunsaturated fatty acids are reported to be immunomodulators with anti-inflammatory properties. Our aim was to evaluate anti-inflammatory and antifibrogenic effects of these fatty acids in human dermal fibroblasts. Methods: Cells were incubated with short-chain fatty acids (butyrate or propionate; 0-16 mM) and/or ω-3 polyunsaturated fatty acids (docosahexaenoic acid or eicosapentaenoic acid; 0-100 μM) for 24 hours to evaluate antifibrogenic effects and for 3 or 48 hours to evaluate anti-inflammatory effects after stimulation with lipopolysaccharide or without stimulation. Expression levels of α-smooth muscle actin, collagen I, collagen III, and IL-6 were evaluated, as were cell proliferation, stress fiber formation, and histone acetylation. Results: In the lipopolysaccharide-unstimulated group, butyrate inhibited mRNA expression of α-smooth muscle actin and collagen III more effectively than propionate and increased histone acetylation. Docosahexaenoic acid inhibited mRNA expression of α-smooth muscle actin and collagen III, whereas eicosapentaenoic acid did not. Combining butyrate with docosahexaenoic acid had stronger effects, downregulating α-smooth muscle actin, collagen I, and collagen III mRNA. As for cell proliferation and stress fiber formation, butyrate acted as a stronger inhibitor than docosahexaenoic acid and the combined administration had stronger effects. In the lipopolysaccharide-stimulated group, butyrate and docosahexaenoic acid attenuated IL-6 mRNA upregulation by lipopolysaccharide. Conclusion: Butyrate and docosahexaenoic acid may be a novel therapeutic approach to treatment of dermal fibroproliferative disorders.

Faecalibacterium prausnitzii Produces Butyrate to Maintain Th17/Treg Balance and to Ameliorate Colorectal Colitis by Inhibiting Histone Deacetylase 1

BACKGROUND

Inflammatory bowel disease (IBD)-associated dysbiosis is characterized by a loss of Faecalibacterium prausnitzii, whose supernatant exerts an anti-inflammatory effect. However, the anti-inflammatory substances in F. prausnitzii supernatant and the mechanism in ameliorating colitis in IBD have not yet been fully investigated.

METHODS

Experimental colitis models were induced and evaluated by clinical examination and histopathology. Levels of cytokines and ratio of T cells were detected by enzyme-linked immunosorbent assay and flow cytometry analysis, respectively. F. prausnitzii supernatant was separated by macroporous resins. After extraction, the substances in supernatant were identified by gas chromatography-mass spectrometer. T-cell differentiation assay was conducted in vitro. Changes in signaling pathways were examined by immunoblot, immunohistochemistry, and immunofluorescent staining.

RESULTS

We found that the supernatant of F. prausnitzii could regulate T helper 17 cell (Th17)/regulatory T cell (Treg) differentiation. Then, we identified butyrate produced by F. prausnitzii that played the anti-inflammatory effects by inhibiting interleukin (IL)-6/signal transducer and the activator of transcription 3 (STAT3)/IL-17 pathway and promoting forkhead box protein P3 (Foxp3). Finally, we demonstrated that the target of butyrate was histone deacetylase 1 (HDAC1).

CONCLUSIONS

It is butyrate, instead of other substances produced by F. prausnitzii, that maintains Th17/Treg balance and exerts significant anti-inflammatory effects in colorectal colitis rodents, by inhibiting HDAC1 to promote Foxp3 and block the IL-6/STAT3/IL-17 downstream pathway. F. prausnitzii could be an option for further investigation for IBD treatment. Targeting the butyrate-HDAC1-T-cell axis offers an effective novel approach in the treatment of inflammatory disease.

Dietary fat and fiber interact to uniquely modify global histone post-translational epigenetic programming in a rat colon cancer progression model

Dietary fermentable fiber generates short-chain fatty acids (SCFA), for example, butyrate, in the colonic lumen which serves as a chemoprotective histone deacetylase inhibitor and/or as an acetylation substrate for histone acetylases. In addition, n-3 polyunsaturated fatty acids (n-3 PUFA) in fish oil can affect the chromatin landscape by acting as ligands for tumor suppressive nuclear receptors. In an effort to gain insight into the global dimension of post-translational modification of histones (including H3K4me3 and H3K9ac) and clarify the chemoprotective impact of dietary bioactive compounds on transcriptional control in a preclinical model of colon cancer, we generated high-resolution genome-wide RNA (RNA-Seq) and "chromatin-state" (H3K4me3-seq and H3K9ac-seq) maps for intestinal (epithelial colonocytes) crypts in rats treated with a colon carcinogen and fed diets containing bioactive (i) fish oil, (ii) fermentable fiber (a rich source of SCFA), (iii) a combination of fish oil plus pectin, or (iv) control, devoid of fish oil or pectin. In general, poor correlation was observed between differentially transcribed (DE) and enriched genes (DERs) at multiple epigenetic levels. The combinatorial diet (fish oil + pectin) uniquely affected transcriptional profiles in the intestinal epithelium, for example, upregulating lipid catabolism and beta-oxidation associated genes. These genes were linked to activated ligand-dependent nuclear receptors associated with n-3 PUFA and were also correlated with the mitochondrial L-carnitine shuttle and the inhibition of lipogenesis. These findings demonstrate that the chemoprotective fish oil + pectin combination diet uniquely induces global histone state modifications linked to the expression of chemoprotective genes.

Omega-3 fatty acids, membrane remodeling and cancer prevention

Proteins are often credited as the macromolecule responsible for performing critical cellular functions, however lipids have recently garnered more attention as our understanding of their role in cell function and human health becomes more apparent. Although cellular membranes are the lipid environment in which many proteins function, it is now apparent that protein and lipid assemblies can be organized to form distinct micro- or nanodomains that facilitate signaling events. Indeed, it is now appreciated that cellular function is partly regulated by the specific spatiotemporal lipid composition of the membrane, down to the nanosecond and nanometer scale. Furthermore, membrane composition is altered during human disease processes such as cancer and obesity. For example, an increased rate of lipid/cholesterol synthesis in cancerous tissues has long been recognized as an important aspect of the rewired metabolism of transformed cells. However, the contribution of lipids/cholesterol to cellular function in disease models is not yet fully understood. Furthermore, an important consideration in regard to human health is that diet is a major modulator of cell membrane composition. This can occur directly through incorporation of membrane substrates, such as fatty acids, e.g., n-3 polyunsaturated fatty acids (n-3 PUFA) and cholesterol. In this review, we describe scenarios in which changes in membrane composition impact human health. Particular focus is placed on the importance of intrinsic lipid/cholesterol biosynthesis and metabolism and extrinsic dietary modification in cancer and its effect on plasma membrane properties.

Detecting Multivariate Gene Interactions in RNA-Seq Data Using Optimal Bayesian Classification

Differential gene expression testing is an analysis commonly applied to RNA-Seq data. These statistical tests identify genes that are significantly different across phenotypes. We extend this testing paradigm to multivariate gene interactions from a classification perspective with the goal to detect novel gene interactions for the phenotypes of interest. This is achieved through our novel computational framework comprised of a hierarchical statistical model of the RNA-Seq processing pipeline and the corresponding optimal Bayesian classifier. Through Markov Chain Monte Carlo sampling and Monte Carlo integration, we compute quantities where no analytical formulation exists. The performance is then illustrated on an expression dataset from a dietary intervention study where we identify gene pairs that have low classification error yet were not identified as differentially expressed. Additionally, we have released the software package to perform OBC classification on RNA-Seq data under an open source license and is available at http://bit.ly/obc_package.

Emerging role of chemoprotective agents in the dynamic shaping of plasma membrane organization

In the context of an organism, epithelial cells by nature are designed to be the defining barrier between self and the outside world. This is especially true for the epithelial cells that form the lining of the digestive tract, which absorb nutrients and serve as a barrier against harmful substances. These cells are constantly bathed by a complex mixture of endogenous (bile acids, mucus, microbial metabolites) and exogenous (food, nutrients, drugs) bioactive compounds. From a cell biology perspective, this type of exposure would directly impact the plasma membrane, which consists of a myriad of complex lipids and proteins. The plasma membrane not only functions as a barrier but also as the medium in which cellular signaling complexes form and function. This property is mediated by the organization of the plasma membrane, which is exquisitely temporally (nanoseconds to minutes) and spatially (nanometers to micrometers) regulated. Since numerous bioactive compounds found in the intestinal lumen can directly interact with lipid membranes, we hypothesize that the dynamic reshaping of plasma membrane organization underlies the chemoprotective effect of select membrane targeted dietary bioactives (MTDBs). This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

Nutrient-Gene Interaction in Colon Cancer, from the Membrane to Cellular Physiology

The International Agency for Research on Cancer recently released an assessment classifying red and processed meat as "carcinogenic to humans" on the basis of the positive association between increased consumption and risk for colorectal cancer. Diet, however, can also decrease the risk for colorectal cancer and be used as a chemopreventive strategy. Bioactive dietary molecules, such as n-3 polyunsaturated fatty acids, curcumin, and fermentable fiber, have been proposed to exert chemoprotective effects, and their molecular mechanisms have been the focus of research in the dietary/chemoprevention field. Using these bioactives as examples, this review surveys the proposed mechanisms by which they exert their effects, from the nucleus to the cellular membrane. In addition, we discuss emerging technologies involving the culturing of colonic organoids to study the physiological effects of dietary bioactives. Finally, we address future challenges to the field regarding the identification of additional molecular mechanisms and other bioactive dietary molecules that can be utilized in our fight to reduce the incidence of colorectal cancer.

Target Intestinal Microbiota to Alleviate Disease Progression in Amyotrophic Lateral Sclerosis

PURPOSE

Emerging evidence has demonstrated that gut microbiome plays essential roles in the pathogenesis of human diseases in distal organs. Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive loss of motor neurons. Treatment with the only drug approved by the US Food and Drug Administration for use in ALS, riluzole, extends a patient׳s life span by only a few months. Thus, there is an urgent need to develop novel interventions that for alleviate disease progression and improve quality of life in patients with ALS. Here we present evidence that intestinal dysfunction and dysbiosis may actively contribute to ALS pathophysiology.

METHODS

We used G93A transgenic mice as a model of human ALS. The G93A mice show abnormal intestinal microbiome and damaged tight junctions before ALS disease onset. The mice were given 2% butyrate, a natural bacterial product, in the drinking water.

RESULTS

In mice fed with butyrate, intestinal microbial homeostasis was restored, gut integrity was improved, and life span was prolonged compared with those in control mice. At the cellular level, abnormal Paneth cells-specialized intestinal epithelial cells that regulate the host-bacterial interactions-were significantly decreased in the ALS mice treated with butyrate. In both ALS mice and intestinal epithelial cells cultured from humans, butyrate treatment was associated with decreased aggregation of the G93A superoxide dismutase 1 mutated protein.

IMPLICATIONS

The findings from this study highlight the complex role of the gut microbiome and intestinal epithelium in the progression of ALS and present butyrate as a potential therapeutic reagent for restoring ALS-related dysbiosis.

The Interaction between Dietary Fiber and Fat and Risk of Colorectal Cancer in the Women's Health Initiative

Combined intakes of specific dietary fiber and fat subtypes protect against colon cancer in animal models. We evaluated associations between self-reported individual and combinations of fiber (insoluble, soluble, and pectins, specifically) and fat (omega-6, omega-3, and docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), specifically) and colorectal cancer (CRC) risk in the Women's Health Initiative prospective cohort (n = 134,017). During a mean 11.7 years (1993-2010), 1952 incident CRC cases were identified. Cox regression models computed multivariate adjusted hazard ratios to estimate the association between dietary factors and CRC risk. Assessing fiber and fat individually, there was a modest trend for lower CRC risk with increasing intakes of total and insoluble fiber (p-trend 0.09 and 0.08). An interaction (p = 0.01) was observed between soluble fiber and DHA + EPA, with protective effects of DHA + EPA with lower intakes of soluble fiber and an attenuation at higher intakes, however this association was no longer significant after correction for multiple testing. These results suggest a modest protective effect of higher fiber intake on CRC risk, but not in combination with dietary fat subtypes. Given the robust results in preclinical models and mixed results in observational studies, controlled dietary interventions with standardized intakes are needed to better understand the interaction of specific fat and fiber subtypes on colon biology and ultimately CRC susceptibility in humans.

Role of Inflammatory Signaling in the Differential Effects of Saturated and Poly-unsaturated Fatty Acids on Peripheral Circadian Clocks

Inflammatory signaling may play a role in high-fat diet (HFD)-related circadian clock disturbances that contribute to systemic metabolic dysregulation. Therefore, palmitate, the prevalent proinflammatory saturated fatty acid (SFA) in HFD and the anti-inflammatory, poly-unsaturated fatty acid (PUFA), docosahexaenoic acid (DHA), were analyzed for effects on circadian timekeeping and inflammatory responses in peripheral clocks. Prolonged palmitate, but not DHA, exposure increased the period of fibroblast Bmal1-dLuc rhythms. Acute palmitate treatment produced phase shifts of the Bmal1-dLuc rhythm that were larger in amplitude as compared to DHA. These phase-shifting effects were time-dependent and contemporaneous with rhythmic changes in palmitate-induced inflammatory responses. Fibroblast and differentiated adipocyte clocks exhibited cell-specific differences in the time-dependent nature of palmitate-induced shifts and inflammation. DHA and other inhibitors of inflammatory signaling (AICAR, cardamonin) repressed palmitate-induced proinflammatory responses and phase shifts of the fibroblast clock, suggesting that SFA-mediated inflammatory signaling may feed back to modulate circadian timekeeping in peripheral clocks.

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The saturated fatty acid (SFA) palmitate differentially modulates the circadian timekeeping mechanism in peripheral clocks;

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Palmitate induces time-dependent phase shifts that coincide with its rhythmic induction of inflammatory signaling;

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Time-dependent nature of the palmitate-induced phase shifts and inflammatory signaling is cell specific;

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Inhibitors of inflammatory signaling repress the proinflammatory and phase shifting effects of palmitate;

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Inflammatory signaling plays a role in the mechanism by which palmitate alters circadian timekeeping in peripheral clocks.

Circadian or 24-hour clocks throughout the body mediate the local temporal coordination of tissue- or cell-specific processes necessary for normal inflammatory responses and metabolic homeostasis. Dysregulation of peripheral clocks and their timekeeping function contribute to obesity-related metabolic disorders (e.g., type 2 diabetes). Our data unveil a novel mechanism by which mutual interactions between peripheral clocks and inflammatory signaling pathways dysregulate circadian timekeeping, and exacerbate proinflammatory responses to saturated fatty acids. These studies will guide the development of chronotherapeutic drug and/or dietary omega-3 fatty acid treatments for managing and preventing metabolic disorders and other inflammation-related pathologies (e.g., cardiovascular disease, stroke, arthritis).

Mitochondrial dysfunction in inflammatory bowel disease

Inflammatory Bowel Disease (IBD) represents a group of idiopathic disorders characterized by chronic or recurring inflammation of the gastrointestinal tract. While the exact etiology of disease is unknown, IBD is recognized to be a complex, multifactorial disease that results from an intricate interplay of genetic predisposition, an altered immune response, changes in the intestinal microbiota, and environmental factors. Together, these contribute to a destruction of the intestinal epithelial barrier, increased gut permeability, and an influx of immune cells. Given that most cellular functions as well as maintenance of the epithelial barrier is energy-dependent, it is logical to assume that mitochondrial dysfunction may play a key role in both the onset and recurrence of disease. Indeed several studies have demonstrated evidence of mitochondrial stress and alterations in mitochondrial function within the intestinal epithelium of patients with IBD and mice undergoing experimental colitis. Although the hallmarks of mitochondrial dysfunction, including oxidative stress and impaired ATP production are known to be evident in the intestines of patients with IBD, it is as yet unclear whether these processes occur as a cause of consequence of disease. We provide a current review of mitochondrial function in the setting of intestinal inflammation during IBD.

Growth inhibitory effect of polyunsaturated fatty acids (PUFAs) on colon cancer cells via their growth inhibitory metabolites and fatty acid composition changes

Background

Colorectal cancer is common. Polyunsaturated fatty acids (PUFAs) exert growth-inhibitory and pro-apoptotic effects on colon cancer cells. Metabolites of PUFAs such as prostaglandins (PGs), leukotrienes (LTs) and lipoxins (LXs) play a significant role in colon cancer.

Methods

Human colon cancer LoVo and RKO cells were cultured with different concentration of PUFAs and 5-fluorouracil (5-FU) in vitro. Cell morphological changes, fatty acid composition, formation of PGE2, LTB4 and LXA4 and expression of COX-2, ALOX5, PGD synthase (PGDS), microsomal prostaglandin E synthase (mPGES) were assessed in LoVo and RKO cells when supplemented with PUFAs and 5-FU.

Results

PUFAs and 5-FU inhibited growth of LoVo and RKO cells to the same extent at the doses used and produced significant alterations in their shape. As expected, higher concentrations of supplemented PUFAs were noted in the cells compared to control. LA, GLA, AA, ALA and EPA supplementation to LoVo cells suppressed production of PGE₂, LTB₄,and ALOX5, mPGES expression, but enhanced that of LXA₄; whereas DHA enhanced PGE₂ and LXA₄ synthesis but decreased LTB₄ formation and COX-2, ALOX5, mPGES expression. In contrast, 5-FU enhanced formation of PGE₂, LTB₄ and mPGES expression, but suppressed LXA₄ synthesis and COX-2 expression. PGE₂, LTB₄ synthesis and ALOX5 expression was suppressed by LA, GLA, ALA and DHA; whereas AA, EPA and 5-FU enhanced PGE₂ but paradoxically AA decreased and EPA and 5-FU enhanced LTB4 synthesis in RKO cells. All the PUFAs tested enhanced, while 5-FU decreased LXA₄ formation in RKO cells; whereas GLA, AA, and 5-FU augmented while LA, ALA, EPA and DHA enhanced COX-2 expression in RKO cells.

Conclusions

Tumoricidal action of PUFAs on colorectal LoVo and RKO cancer cells in vitro was associated with increased formation of LXA₄, decreased synthesis of PGE₂ and LTB₄ and suppressed expression of COX-2, ALOX5, mPGES, whereas 5-FU produced contrasting actions on these indices.

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.

Chemoprevention in gastrointestinal physiology and disease. Natural products and microbiome

The human intestinal tract harbors a complex ecosystem of commensal bacteria that play a fundamental role in the well-being of their host. There is a general consensus that diet rich in plant-based foods has many advantages in relation to the health and well-being of an individual. In adults, diets that have a high proportion of fruit and vegetables and a low consumption of meat are associated with a highly diverse microbiota and are defined by a greater abundance of Prevotella compared with Bacteroides, whereas the reverse is associated with a diet that contains a low proportion of plant-based foods. In a philosophical term, our consumption of processed foods, widespread use of antibiotics and disinfectants, and our modern lifestyle may have forever altered our ancient gut microbiome. We may never be able to identify or restore our microbiomes to their ancestral state, but dietary modulation to manipulate specific gut microbial species or groups of species may offer new therapeutic approaches to conditions that are prevalent in modern society, such as functional gastrointestinal disorders, obesity, and age-related nutritional deficiency. We believe that this will become an increasingly important area of health research.

Dietary flaxseed intake exacerbates acute colonic mucosal injury and inflammation induced by dextran sodium sulfate

Flaxseed (FS), a dietary oilseed, contains a variety of anti-inflammatory bioactives, including fermentable fiber, phenolic compounds (lignans), and the n-3 polyunsaturated fatty acid (PUFA) α-linolenic acid. The objective of this study was to determine the effects of FS and its n-3 PUFA-rich kernel or lignan- and soluble fiber-rich hull on colitis severity in a mouse model of acute colonic inflammation. C57BL/6 male mice were fed a basal diet (negative control) or a basal diet supplemented with 10% FS, 6% kernel, or 4% hull for 3 wk prior to and during colitis induction via 5 days of 2% (wt/vol) dextran sodium sulfate (DSS) in their drinking water (n = 12/group). An increase in anti-inflammatory metabolites (hepatic n-3 PUFAs, serum mammalian lignans, and cecal short-chain fatty acids) was associated with consumption of all FS-based diets, but not with anti-inflammatory effects in DSS-exposed mice. Dietary FS exacerbated DSS-induced acute colitis, as indicated by a heightened disease activity index and an increase in colonic injury and inflammatory biomarkers [histological damage, apoptosis, myeloperoxidase, inflammatory cytokines (IL-6 and IL-1β), and NF-κB signaling-related genes (Nfkb1, Ccl5, Bcl2a1a, Egfr, Relb, Birc3, and Atf1)]. Additionally, the adverse effect of the FS diet was extended systemically, as serum cytokines (IL-6, IFNγ, and IL-1β) and hepatic cholesterol levels were increased. The adverse effects of FS were not associated with alterations in fecal microbial load or systemic bacterial translocation (endotoxemia). Collectively, this study demonstrates that although consumption of a 10% FS diet enhanced the levels of n-3 PUFAs, short-chain polyunsaturated fatty acids, and lignans in mice, it exacerbated DSS-induced colonic injury and inflammation.

The microbiome and colorectal neoplasia: environmental modifiers of dysbiosis

The etiology of colon cancer is complex, yet it is undoubtedly impacted by intestinal microbiota. Whether the contribution to colon carcinogenesis is generated through the presence of an overall dysbiosis or by specific pathogens is still a matter for debate. However, it is apparent that interactions between microbiota and the host are mediated by a variety of processes, including signaling cascades, the immune system, host metabolism, and regulation of gene transcription. To fully appreciate the role of microbiota in colon carcinogenesis, it will be necessary to expand efforts to define populations in niche environments, such as colonic crypts, explore cross talk between the host and the microbiota, and more completely define the metabolomic profile of the microbiota. These efforts must be pursued with appreciation that dietary substrates and other environmental modifiers mediate changes in the microbiota, as well as their metabolism and functional characteristics.

Colon cancer cell apoptosis is induced by combined exposure to the n-3 fatty acid docosahexaenoic acid and butyrate through promoter methylation

DNA methylation and histone acetylation contribute to the transcriptional regulation of genes involved in apoptosis. We have demonstrated that docosahexaenoic acid (DHA, 22:6 n-3) and butyrate enhance colonocyte apoptosis. To determine if DHA and/or butyrate elevate apoptosis through epigenetic mechanisms thereby restoring the transcription of apoptosis-related genes, we examined global methylation; gene-specific promoter methylation of 24 apoptosis-related genes; transcription levels of Cideb, Dapk1, and Tnfrsf25; and global histone acetylation in the HCT-116 colon cancer cell line. Cells were treated with combinations of (50 µM) DHA or linoleic acid (18:2 n-6), (5 mM) butyrate or an inhibitor of DNA methyltransferases, and 5-aza-2'-deoxycytidine (5-Aza-dC, 2 µM). Among highly methylated genes, the combination of DHA and butyrate significantly reduced methylation of the proapoptotic Bcl2l11, Cideb, Dapk1, Ltbr, and Tnfrsf25 genes compared to untreated control cells. DHA treatment reduced the methylation of Cideb, Dapk1, and Tnfrsf25. These data suggest that the induction of apoptosis by DHA and butyrate is mediated, in part, through changes in the methylation state of apoptosis-related genes.

Anti-cancer activities of pH- or heat-modified pectin

Despite enormous efforts that have been made in the search for novel drugs and treatments, cancer continues to be a major public health problem. Moreover, the emergence of resistance to cancer chemotherapy often prevents complete remission. Researchers have thus turned to natural products mainly from plant origin to circumvent resistance. Pectin and pH- or heat-modified pectin have demonstrated chemopreventive and antitumoral activities against some aggressive and recurrent cancers. The focus of this review is to describe how pectin and modified pectin display these activities and what are the possible underlying mechanisms. The failure of conventional chemotherapy to reduce mortality as well as serious side effects make natural products, such as pectin-derived products, ideal candidates for exerting synergism in combination with conventional anticancer drugs.

A chemoprotective fish oil/pectin diet enhances apoptosis via Bcl-2 promoter methylation in rat azoxymethane-induced carcinomas

We have demonstrated that diets containing fish oil and pectin (FO/P) reduce colon tumor incidence relative to control (corn oil and cellulose [CO/C]) in part by inducing apoptosis of DNA-damaged colon cells. Relative to FO/P, CO/C promotes colonocyte expression of the antiapoptotic modulator, Bcl-2, and Bcl-2 promoter methylation is altered in colon cancer. To determine if FO/P, compared with CO/C, limits Bcl-2 expression by enhancing promoter methylation in colon tumors, we examined Bcl-2 promoter methylation, mRNA levels, colonocyte apoptosis and colon tumor incidence in azoxymethane (AOM)-injected rats. Rats were provided diets containing FO/P or CO/C, and were terminated 16 and 34 weeks after AOM injection. DNA isolated from paraformaldehyde-fixed colon tumors and uninvolved tissue was bisulfite modified and amplified by quantitative reverese transcriptase-polymerase chain reaction to assess DNA methylation in Bcl-2 cytosine-guanosine islands. FO/P increased Bcl-2 promoter methylation (P = 0.009) in tumor tissues and colonocyte apoptosis (P = 0.020) relative to CO/C. An inverse correlation between Bcl-2 DNA methylation and Bcl-2 mRNA levels was observed in the tumors. We conclude that dietary FO/P promotes apoptosis in part by enhancing Bcl-2 promoter methylation. These Bcl-2 promoter methylation responses, measured in vivo, contribute to our understanding of the mechanisms involved in chemoprevention of colon cancer by diets containing FO/P.

Unfolded protein responses in the intestinal epithelium: sensors for the microbial and metabolic environment

In inflammatory bowel disease, the intestinal microbiota is a key driver of inflammation. Hence, efficient sensing of luminal antigens and subsequent initiation of adequate immune responses is crucial for maintaining homeostasis, particularly in intestinal epithelial cells. Pathways such as Toll-like receptor-mediated signaling and autophagy sense microbial products to activate inflammatory processes and, concomitantly, interact with cellular stress responses such as the unfolded protein response (UPR). Proteostasis is particularly sensitive toward environmental challenges and triggers, such as oxidative stress and metabolic alterations, and impact protein folding in different cellular compartments. In contrast, disturbances in energy supply including impaired mitochondrial function and epithelial β-oxidation have been suspected to contribute toward intestinal inflammation. Interestingly, the 2 main organelles linking metabolic pathways, inflammatory signaling and pathogen-sensing, endoplasmic reticulum (ER) and mitochondria (mt), can trigger distinct UPRs, and both ER UPR and mt UPR have been shown to be disease-relevant in inflammatory bowel disease. The ER is essential for the coordination of metabolic responses through controlling the synthetic and catabolic pathways of various nutrients and furthermore, ER UPR signaling directly intersects with inflammation-associated NF-κB and Toll-like receptor pathways. Consistently, next to their function in cellular energy supply, mitochondria are increasingly recognized as integrators of immune responses. For instance, mitochondria participate in innate immunity to viral infection through the pattern recognition receptor retinoic acid inducible gene-I and are involved in inflammasome activation. Thus, we hypothesize that a concerted UPR activation might represent an innate mechanism to sense potentially threatening changes of the mucosal metabolic environment and impacts host cellular functions and immune responses.

Butyrate suppresses colonic inflammation through HDAC1-dependent Fas upregulation and Fas-mediated apoptosis of T cells

Butyrate, an intestinal microbiota metabolite of dietary fiber, has been shown to exhibit protective effects toward inflammatory diseases such as ulcerative colitis (UC) and inflammation-mediated colorectal cancer. Recent studies have shown that chronic IFN-γ signaling plays an essential role in inflammation-mediated colorectal cancer development in vivo, whereas genome-wide association studies have linked human UC risk loci to IFNG, the gene that encodes IFN-γ. However, the molecular mechanisms underlying the butyrate-IFN-γ-colonic inflammation axis are not well defined. Here we showed that colonic mucosa from patients with UC exhibit increased signal transducer and activator of transcription 1 (STAT1) activation, and this STAT1 hyperactivation is correlated with increased T cell infiltration. Butyrate treatment-induced apoptosis of wild-type T cells but not Fas-deficient (Fas(lpr)) or FasL-deficient (Fas(gld)) T cells, revealing a potential role of Fas-mediated apoptosis of T cells as a mechanism of butyrate function. Histone deacetylase 1 (HDAC1) was found to bind to the Fas promoter in T cells, and butyrate inhibits HDAC1 activity to induce Fas promoter hyperacetylation and Fas upregulation in T cells. Knocking down gpr109a or slc5a8, the genes that encode for receptor and transporter of butyrate, respectively, resulted in altered expression of genes related to multiple inflammatory signaling pathways, including inducible nitric oxide synthase (iNOS), in mouse colonic epithelial cells in vivo. Butyrate effectively inhibited IFN-γ-induced STAT1 activation, resulting in inhibition of iNOS upregulation in human colon epithelial and carcinoma cells in vitro. Our data thus suggest that butyrate delivers a double-hit: induction of T cell apoptosis to eliminate the source of inflammation and suppression of IFN-γ-mediated inflammation in colonic epithelial cells, to suppress colonic inflammation.