Effect of gamma-linolenic acid or docosahexaenoic acid on tight junction permeability in intestinal monolayer cells and their mechanism by protein kinase C activation and/or eicosanoid formation

High-fat diet impairs gut barrier through intestinal microbiota-derived reactive oxygen species

Gut barrier disruption is a key event in bridging gut microbiota dysbiosis and high-fat diet (HFD)-associated metabolic disorders. However, the underlying mechanism remains elusive. In the present study, by comparing HFD- and normal diet (ND)-treated mice, we found that the HFD instantly altered the composition of the gut microbiota and subsequently damaged the integrity of the gut barrier. Metagenomic sequencing revealed that the HFD upregulates gut microbial functions related to redox reactions, as confirmed by the increased reactive oxygen species (ROS) levels in fecal microbiota incubation in vitro and in the lumen, which were detected using in vivo fluorescence imaging. This microbial ROS-producing capability induced by HFD can be transferred through fecal microbiota transplantation (FMT) into germ-free (GF) mice, downregulating the gut barrier tight junctions. Similarly, mono-colonizing GF mice with an Enterococcus strain excelled in ROS production, damaged the gut barrier, induced mitochondrial malfunction and apoptosis of the intestinal epithelial cells, and exacerbated fatty liver, compared with other low-ROS-producing Enterococcus strains. Oral administration of recombinant high-stability-superoxide dismutase (SOD) significantly reduced intestinal ROS, protected the gut barrier, and improved fatty liver against the HFD. In conclusion, our study suggests that extracellular ROS derived from gut microbiota play a pivotal role in HFD-induced gut barrier disruption and is a potential therapeutic target for HFD-associated metabolic diseases.

Effect of Lifelong Exposure to Dietary Plant and Marine Sources of n-3 Polyunsaturated Fatty Acids on Morphologic and Gene Expression Biomarkers of Intestinal Health in Early Life

Altered intestinal health is also associated with the incidence and severity of many chronic inflammatory conditions, which could be attenuated via dietary n-3 PUFA interventions. However, little is known about the effect of lifelong exposure to n-3 PUFA from plant and marine sources (beginning in utero via the maternal diet) on early life biomarkers of intestinal health. Harems of C57Bl/6 mice were randomly assigned to one of three isocaloric AIN-93G modified diets differing in their fat sources consisting of the following: (i) 10% safflower oil (SO, enriched in n-6 PUFA), (ii) 3% flaxseed oil + 7% safflower oil (FX, plant-based n-3 PUFA-enriched diet), or (iii) 3% menhaden fish oil + 7% safflower oil (MO, marine-based n-3 PUFA-enriched diet). Mothers remained on these diets throughout pregnancy and offspring (n = 14/diet) continued on the same parental diet until termination at 3 weeks of age. In ileum, villi:crypt length ratios were increased in both the FX and MO dietary groups compared to SO (p < 0.05). Ileum mRNA expression of critical intestinal health biomarkers was increased by both n-3 PUFA-enriched diets including Relmβ and REG3γ compared to SO (p < 0.05), whereas only the FX diet increased mRNA expression of TFF3 and Muc2 (p < 0.05) and only the MO diet increased mRNA expression of ZO-1 (p < 0.05). In the proximal colon, both the FX and MO diets increased crypt lengths compared to SO (p < 0.05), whereas only the MO diet increased goblet cell numbers compared to SO (p < 0.05). Further, the MO diet increased proximal colon mRNA expression of Relmβ and REG3γ (p < 0.05) and both MO and FX increased mRNA expression of Muc2 compared to SO (p < 0.05). Collectively, these results demonstrate that lifelong exposure to dietary n-3 PUFA, beginning in utero, from both plant and marine sources, can support intestinal health development in early life. The differential effects between plant and marine sources warrants further investigation for optimizing health.

Omega-3 polyunsaturated fatty acids improve intestinal barrier integrity-albeit to a lesser degree than short-chain fatty acids: an exploratory analysis of the randomized controlled LIBRE trial

PURPOSE

Adherence to the Mediterranean diet is associated with beneficial health effects, including gastrointestinal disorders. Preclinical studies suggest that omega-3 polyunsaturated fatty acids (n-3 PUFAs), found in Mediterranean foods like nuts and fish, improve intestinal barrier integrity. Here, we assessed possible effects of n-3 PUFAs on barrier integrity in a randomized controlled trial.

METHODS

We studied 68 women from the open-label LIBRE trial (clinicaltrials.gov: NCT02087592) who followed either a Mediterranean diet (intervention group, IG) or a standard diet (control group, CG). Study visits comprised baseline, month 3, and month 12. Barrier integrity was assessed by plasma lipopolysaccharide binding protein (LBP) and fecal zonulin; fatty acids by gas chromatography with mass spectrometry. Median and interquartile ranges are shown.

RESULTS

Adherence to the Mediterranean diet increased the proportion of the n-3 docosahexaenoic acid (DHA) (IG + 1.5% [0.9;2.5, p < 0.001]/ + 0.3% [- 0.1;0.9, p < 0.050] after 3/12 months; CG + 0.9% [0.5;1.6, p < 0.001]/ ± 0%) and decreased plasma LBP (IG - 0.3 µg/ml [- 0.6;0.1, p < 0.010]/ - 0.3 µg/ml [- 1.1; - 0.1, p < 0.001]; CG - 0.2 µg/ml [- 0.8; - 0.1, p < 0.001]/ ± 0 µg/ml) and fecal zonulin levels (IG - 76 ng/mg [- 164; - 12, p < 0.010]/ - 74 ng/mg [- 197;15, p < 0.001]; CG - 59 ng/mg [- 186;15, p < 0.050]/ + 10 ng/mg [- 117;24, p > 0.050]). Plasma DHA and LBP (R2: 0.14-0.42; all p < 0.070), as well as plasma DHA and fecal zonulin (R2: 0.18-0.48; all p < 0.050) were found to be inversely associated in bi- and multivariate analyses. Further multivariate analyses showed that the effect of DHA on barrier integrity was less pronounced than the effect of fecal short-chain fatty acids on barrier integrity.

CONCLUSIONS

Our data show that n-3 PUFAs can improve intestinal barrier integrity.

TRIAL REGISTRATION NUMBER

The trial was registered prospectively at ClinicalTrials.gov (reference: NCT02087592).

Research progress of gut microbiota and obesity caused by high-fat diet

Obesity, a chronic metabolic disorder caused by an energy imbalance, has been increasingly prevalent and poses a global health concern. The multifactorial etiology of obesity includes genetics factors, high-fat diet, gut microbiota, and other factors. Among these factors, the implication of gut microbiota in the pathogenesis of obesity has been prominently acknowledged. This study endeavors to investigate the potential contribution of gut microbiota to the development of high-fat diet induced obesity, as well as the current state of probiotic intervention therapy research, in order to provide novel insights for the prevention and management of obesity.

New hope for Parkinson's disease treatment: Targeting gut microbiota

There might be more than 10 million confirmed cases of Parkinson's disease (PD) worldwide by 2040. However, the pathogenesis of PD is still unclear. Host health is closely related to gut microbiota, which are affected by factors such as age, diet, and exercise. Recent studies have found that gut microbiota may play key roles in the progression of a wide range of diseases, including PD. Changes in the abundance of gut bacteria, such as Helicobacter pylori, Enterococcus faecalis, and Desulfovibrio, might be involved in PD pathogenesis or interfere with PD therapy. Gut microbiota and the distal brain achieve action on each other through a gut‐brain axis composed of the nervous system, endocrine system, and immune system. Here, this review focused on the current understanding of the connection between Parkinson's disease and gut microbiota, to provide potential therapeutic targets for PD.

Low Omega-3 Levels in the Diet Disturbs Intestinal Barrier and Transporting Functions of Atlantic Salmon Freshwater and Seawater Smolts

Due to a limited access to marine raw materials from capture fisheries, Atlantic salmon feeds are currently based on mainly plant ingredients (75%) while only 25% come from traditional marine ingredients including marine fish meal and fish oil. Thus, current feeds contain less of the essential omega-3 fatty acids. The aim of the study was to assess the impact of different omega-3 levels in fish feed on intestinal barrier and transporting functions of Atlantic salmon freshwater and seawater smolts. Atlantic salmon were fed three levels of omega-3 (2, 1 and 0.5%) and fish performance was followed through smoltification and the subsequent seawater acclimation. Intestinal barrier and transporting functions were assessed using Ussing chamber methodology and combined with transcript analysis of tight junction related proteins and ion transporters. A linear decrease in growth was observed with decreasing omega-3 levels. Low (0.5%) inclusion of omega-3 impaired the barrier function of the proximal intestine compared to 2% inclusion. Further, low levels of omega-3 decrease the transepithelial electrical potential across the epithelium indicating disturbed ion transport. It can be concluded that low dietary levels of omega-3 impair somatic growth and intestinal function of Atlantic salmon.

Blood-Brain Barrier Disruption Mediated by FFA1 Receptor-Evidence Using Miniscope

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), obtained from diet and dietary supplements, have been tested in clinical trials for the prevention or treatment of several diseases. n-3 PUFAs exert their effects by activation of free fatty acid (FFA) receptors. FFA1 receptor, expressed in the pancreas and brain, is activated by medium- to long-chain fatty acids. Despite some beneficial effects on cognition, the effects of n-3 PUFAs on the blood-brain barrier (BBB) are not clearly understood. We examined the effects of FFA1 activation on BBB permeability in vitro, using rat brain microvascular endothelial cells (RBMVEC), and in vivo, by assessing Evans Blue extravasation and by performing live imaging of brain microcirculation in adult rats. AMG837, a synthetic FFA1 agonist, produced a dose-dependent decrease in RBMVEC monolayer resistance assessed with Electric Cell-Substrate Impedance Sensing (ECIS); the effect was attenuated by the FFA1 antagonist, GW1100. Immunofluorescence studies revealed that AMG837 produced a disruption in tight and adherens junction proteins. AMG837 increased Evans Blue content in the rat brain in a dose-dependent manner. Live imaging studies of rat brain microcirculation with miniaturized fluorescence microscopy (miniscope) showed that AMG837 increased extravasation of sodium fluorescein. Taken together, our results demonstrate that FFA1 receptor activation reduced RBMVEC barrier function and produced a transient increase in BBB permeability.

Intestinal Barrier and Permeability in Health, Obesity and NAFLD

The largest surface of the human body exposed to the external environment is the gut. At this level, the intestinal barrier includes luminal microbes, the mucin layer, gastrointestinal motility and secretion, enterocytes, immune cells, gut vascular barrier, and liver barrier. A healthy intestinal barrier is characterized by the selective permeability of nutrients, metabolites, water, and bacterial products, and processes are governed by cellular, neural, immune, and hormonal factors. Disrupted gut permeability (leaky gut syndrome) can represent a predisposing or aggravating condition in obesity and the metabolically associated liver steatosis (nonalcoholic fatty liver disease, NAFLD). In what follows, we describe the morphological-functional features of the intestinal barrier, the role of major modifiers of the intestinal barrier, and discuss the recent evidence pointing to the key role of intestinal permeability in obesity/NAFLD.

The Role of Dietary Fats in the Development and Prevention of Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a significant cause of mortality and morbidity in preterm infants. The pathogenesis of NEC is not completely understood; however, intestinal immaturity and excessive immunoreactivity of intestinal mucosa to intraluminal microbes and nutrients appear to have critical roles. Dietary fats are not only the main source of energy for preterm infants, but also exert potent effects on intestinal development, intestinal microbial colonization, immune function, and inflammatory response. Preterm infants have a relatively low capacity to digest and absorb triglyceride fat. Fat may thereby accumulate in the ileum and contribute to the development of NEC by inducing oxidative stress and inflammation. Some fat components, such as long-chain polyunsaturated fatty acids (LC-PUFAs), also exert immunomodulatory roles during the early postnatal period when the immune system is rapidly developing. LC-PUFAs may have the ability to modulate the inflammatory process of NEC, particularly when the balance between n3 and n6 LC-PUFAs derivatives is maintained. Supplementation with n3 LC-PUFAs alone may have limited effect on NEC prevention. In this review, we describe how various fatty acids play different roles in the pathogenesis of NEC in preterm infants.

The assessment of plasma fatty acid profiles in newly diagnosed treatment-naive paediatric Crohn's disease

Fatty acid (FA) profiles as potentially relevant components of Crohn's disease (CD) have been insufficiently analysed. We sought to explore the plasma profiles of n-3 and n-6 polyunsa-turated fatty acids (PUFAs) in newly diagnosed untreated active CD. We included 26 consecutive CD pediatric patients (<19 years) and 14 healthy controls (HCs). Disease characteristics, including inflammatory markers, dietary histories, and the Pediatric Crohn's Disease Activity Index (PCDAI), were obtained. The profiles of plasma FAs in plasma lipid classes were analysed by gas chromatography with FID detection of methyl esters. The erythrocyte sedimentation rate, C-reactive protein level and fecal calprotectin level (all p<0.001) were significantly higher in CD patients than in HCs. Most changes were observed in plasma phospholipids (PLs), such as a higher content of n-3 and changes in n-6 long-chain PUFAs in the CD group. The CD group had a lower ratio of n-6/n-3 PUFAs in PLs (p<0.001) and triacylglycerols (TAGs) (p<0.01). Correlations of the FA content in plasma PLs with disease activity scores of CD were also observed, which were positive for the sum of monounsaturated fatty acids (MUFAs) as well as oleic acid (18:1n-9) (both p<0.05). The metabolism of PUFAs is significantly altered even in treatment-naive newly diagnosed active pediatric CD, and the content of major FAs in PLs correlates with disease activity and inflammatory markers, thus probably contributing to the still unclear early disease pathogenesis.

Leaky Gut: Effect of Dietary Fiber and Fats on Microbiome and Intestinal Barrier

Intestinal tract is the boundary that prevents harmful molecules from invading into the mucosal tissue, followed by systemic circulation. Intestinal permeability is an index for intestinal barrier integrity. Intestinal permeability has been shown to increase in various diseases-not only intestinal inflammatory diseases, but also systemic diseases, including diabetes, chronic kidney dysfunction, cancer, and cardiovascular diseases. Chronic increase of intestinal permeability is termed 'leaky gut' which is observed in the patients and animal models of these diseases. This state often correlates with the disease state. In addition, recent studies have revealed that gut microbiota affects intestinal and systemic heath conditions via their metabolite, especially short-chain fatty acids and lipopolysaccharides, which can trigger leaky gut. The etiology of leaky gut is still unknown; however, recent studies have uncovered exogenous factors that can modulate intestinal permeability. Nutrients are closely related to intestinal health and permeability that are actively investigated as a hot topic of scientific research. Here, we will review the effect of nutrients on intestinal permeability and microbiome for a better understanding of leaky gut and a possible mechanism of increase in intestinal permeability.

Omega-3 Polyunsaturated Fatty Acids and the Intestinal Epithelium-A Review

Epithelial cells (enterocytes) form part of the intestinal barrier, the largest human interface between the internal and external environments, and responsible for maintaining regulated intestinal absorption and immunological control. Under inflammatory conditions, the intestinal barrier and its component enterocytes become inflamed, leading to changes in barrier histology, permeability, and chemical mediator production. Omega-3 (ω-3) polyunsaturated fatty acids (PUFAs) can influence the inflammatory state of a range of cell types, including endothelial cells, monocytes, and macrophages. This review aims to assess the current literature detailing the effects of ω-3 PUFAs on epithelial cells. Marine-derived ω-3 PUFAs, eicosapentaenoic acid and docosahexaenoic acid, as well as plant-derived alpha-linolenic acid, are incorporated into intestinal epithelial cell membranes, prevent changes to epithelial permeability, inhibit the production of pro-inflammatory cytokines and eicosanoids and induce the production of anti-inflammatory eicosanoids and docosanoids. Altered inflammatory markers have been attributed to changes in activity and/or expression of proteins involved in inflammatory signalling including nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), peroxisome proliferator activated receptor (PPAR) α and γ, G-protein coupled receptor (GPR) 120 and cyclooxygenase (COX)-2. Effective doses for each ω-3 PUFA are difficult to determine due to inconsistencies in dose and time of exposure between different in vitro models and between in vivo and in vitro models. Further research is needed to determine the anti-inflammatory potential of less-studied ω-3 PUFAs, including docosapentaenoic acid and stearidonic acid.

Diet as a Modulator of Intestinal Microbiota in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic immune-driven inflammatory disease characterised by synovial inflammation, leading to progressive cartilage and bone destruction, impacting patients' functional capacity and quality of life. Patients with RA have significant differences in gut microbiota composition when compared to controls. Intestinal dysbiosis influences the intestinal barrier strength, integrity and function, and diet is considered the main environmental factor impacting gut microbiota. Over the last few years, researchers have focused on the influence of single components of the diet in the modulation of intestinal microbiota in RA rather than whole dietary patterns. In this review, we focus on how the Mediterranean diet (MD), a whole dietary pattern, could possibly act as an adjuvant therapeutic approach, modulating intestinal microbiota and intestinal barrier function in order to improve RA-related outcomes. We also review the potential effects of particular components of the MD, such as n-3 polyunsaturated fatty acids (PUFAs), polyphenols and fibre.

Dietary Carbohydrates and Lipids in the Pathogenesis of Leaky Gut Syndrome: An Overview

This review summarizes the recent knowledge on the effects of dietary carbohydrates and lipids on the pathophysiology of leaky gut syndrome (LGS). Alterations in intestinal barrier permeability may lead to serious gastrointestinal (GI) disorders. LGS is caused by intestinal hyperpermeability due to changes in the expression levels and functioning of tight junctions. The influence of dietary habits on intestinal physiology is clearly visible in incidence rates of intestinal diseases in industrial and developing countries. Diseases which are linked to intestinal hyperpermeability tend to localize to Westernized countries, where a diet rich in fats and refined carbohydrates predominates. Several studies suggest that fructose is one of the key carbohydrates involved in the regulation of the intestinal permeability and its overuse may cause harmful effects, such as tight junction protein dysfunction. On the other hand, short chain fatty acids (mainly butyrate) at appropriate concentrations may lead to the reduction of intestinal permeability, which is beneficial in LGS. However, long chain fatty acids, including n-3 and n-6 polyunsaturated fatty acids have unclear properties. Some of those behave as components untightening and tightening the intestinal membrane.

Lipid Composition of Liposomal Membrane Largely Affects Its Transport and Uptake through Small Intestinal Epithelial Cell Models

Lipid composition of liposomal bilayer should alter the cell response for permeability, transport, and uptake in small intestine. This work was done to investigate the transport and uptake of liposomes composed of docosahexaenoic acid-enriched phosphatidylcholine (PtdCho), phosphatidylserine (PtdSer), and sulfoquinovosyl diacylglycerol (SQDG) derived from marine products on multilamellar vesicles (MLV) in small intestinal epithelial cell models. The results showed that addition of PtdSer and SQDG as liposomal bilayer could improve the efficiency entrapment of liposomes. The liposomes containing PtdSer showed higher transport and uptake through both Caco-2 cell and M cell monolayers as compared to PtdCho-MLV. SQDG-containing liposomes exhibited only higher transport through M cell monolayer, while its uptake effect was higher both in Caco-2 cell and M cell monolayers. The results of experiments done with endocytosis inhibitors indicated that PtdCho-MLV must be transported via macropinocytosis and uptaken by phagocytosis in M cell monolayer model. PtdCho/PtdSer-MLV and PtdCho/SQDG-MLV might be transported and uptaken through M cell monolayer by phagocytosis. The result also indicated that PtdCho/SQDG-MLV could open the tight junction of small intestinal epithelial cell monolayers. Furthermore, our findings demonstrated that the surface status of cholesterol-containing liposomes were smooth, but they did not affect their transport and uptake through Caco-2 cell and M cell monolayers.

Regulation of the intestinal barrier by nutrients: The role of tight junctions

Tight junctions (TJs) play an important role in intestinal barrier function. TJs in intestinal epithelial cells are composed of different junctional molecules, such as claudin and occludin, and regulate the paracellular permeability of water, ions, and macromolecules in adjacent cells. One of the most important roles of the TJ structure is to provide a physical barrier to luminal inflammatory molecules. Impaired integrity and structure of the TJ barrier result in a forcible activation of immune cells and chronic inflammation in different tissues. According to recent studies, the intestinal TJ barrier could be regulated, as a potential target, by dietary factors to prevent and reduce different inflammatory disorders, although the precise mechanisms underlying the dietary regulation remain unclear. This review summarizes currently available information on the regulation of the intestinal TJ barrier by food components.

New Insights into Inflammatory Bowel Diseases from Proteomic and Lipidomic Studies

Ulcerative colitis (UC) and Crohn's disease (CD) represent the two main forms of chronic inflammatory bowel diseases (IBD). The exact IBD etiology is not yet revealed but CD and UC are likely induced by an excessive immune response against normal constituents of the intestinal microbial flora. IBD diagnosis is based on clinical symptoms often combined with invasive and costly procedures. Thus, the need for more non-invasive markers is urgent. Several routine laboratory investigations have been explored as indicators of intestinal inflammation in IBD, including blood testing for C-reactive protein, erythrocyte sedimentation rate, and specific antibodies, in addition to stool testing for calprotectin and lactoferrin. However, none has been universally adopted, some have been well-characterized, and others hold great promise. In recent years, the technological developments within the field of mass spectrometry (MS) and bioinformatics have greatly enhanced the ability to retrieve, characterize, and analyze large amounts of data. High-throughput research allowed enhancing the understanding of the biology of IBD permitting a more accurate biomarker discovery than ever before. In this review, we summarize currently used IBD serological and stool biomarkers and how proteomics and lipidomics are contributing to the identification of IBD biomarkers.

Dietary walnut as food factor to rescue from NSAID-induced gastrointestinal mucosal damages

Nuclear factor erythroid-derived 2-like 2 (Nrf-2) is transcription factor implicated in the antioxidant response element-mediated induction of endogenous antioxidant enzyme such as heme oxygenase-1 (HO-1), glutamate-cysteine ligase, and NAD(P)H quinone dehydrogenase 1, among which HO-1 is an enzyme catalyzing the degradation of heme.producing biliverdin, ferrous iron, and carbon monoxide. In the stomach, as much as regulating gastric acid secretions, well-coordinated establishment of defense system stands for maintaining gastric integrity. In previous study, author et al. for the first time discovered HO-1 induction was critical in affording faithful gastric defense against various irritants including Helicobacter pylori infection, stress, alcohol, non-steroidal anti-inflammatory drugs (NSAIDs), aspirin, and toxic bile acids. In this review article, we can add the novel evidence that dietary walnut intake can be reliable way to rescue from NSAIDs-induced gastrointestinal damages via the induction of HO-1 transcribed with Nrf-2 through specific inactivation of Keap-1. From molecular exploration to translational animal model of indomethacin-induced gastrointestinal damages, significant induction of HO-1 contributed to rescuing from damages. In addition to HO-1 induction action relevant to walnut, we added the description the general actions of walnut extracts or dietary intake of walnut regarding cytoprotection and why we have focused on to NSAID damages.

Effect of dietary L-glutamate levels on growth, digestive and absorptive capability, and intestinal physical barrier function in Jian carp (Cyprinus carpio var. Jian)

The present study explored effects of L-glutamate (Glu) levels on growth, digestive and absorptive capability, and intestinal physical barrier functions of Jian carp (Cyprinus carpio). A total of 600 Jian carp (126.40 ± 0.21 g) were randomly distributed into 5 groups with 3 replicates each, fed diets containing graded levels of Glu (53.4 [control], 57.2, 60.6, 68.4, and 83.4 g/kg) for 63 d. Results showed compared with control diet, feed intake and percent weight gain (PWG) in fish fed 83.4 g of Glu/kg diet were increased and feed conversion ratio in fish fed 68.4 g of Glu/kg diet was decreased (P < 0.05). Similarly, body crude protein and lipid contents in fish fed 68.4 g of Glu/kg diet were higher (P < 0.05). The activities of trypsin and chymotrypsin in the hepatopancreas and intestine, and amylase, alkaline phosphatase (AKP), Na⁺, K⁺-ATPase (NKA), and creatine kinase (CK) in intestine were higher in fish fed 68.4 g of Glu/kg diet (P < 0.05). Dietary Glu (57.2 to 83.4 g/kg diet) decreased malondialdehyde (MDA) and protein carbonyl (PCO) contents in the intestine (P < 0.05). The activities of catalase (CAT), glutathione peroxidase (GPx), and glutathione S-transferase (GST) in the hepatopancreas and intestine were higher in fish fed 60.6 and 68.4 g of Glu/kg diets (P < 0.05). Intestinal the glutathione reductase (GR) activity and glutathione (GSH) content in fish fed 60.6, 68.4, and 83.4 g of Glu/kg diet were increased (P < 0.05). The GPx1a, GST, and nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA expressions in the intestine were up-regulated in fish fed 60.6 and 68.4 g of Glu/kg diet (P < 0.05). The zonula occludens protein-1 (ZO-1), occludin1, and claudin3 mRNA expressions were also up-regulated in fish fed 83.4 g of Glu/kg diet (P < 0.05). Fish fed 68.4 g of Glu/kg diet had higher levels of claudin 2, claudin7, and protein kinase C (PKC) mRNA (P < 0.05). These results indicated that Glu improved fish growth, digestive and absorptive ability, and intestinal physical barrier functions. Based on the quadratic regression analysis of PWG, and MDA of the hepatopancreas and intestine, the optimal dietary Glu levels were estimated to be 81.97, 71.06, and 71.36 g/kg diet, respectively.

Acute regulation of intestinal ion transport and permeability in response to luminal nutrients: the role of the enteric nervous system

The small intestine regulates barrier function to absorb nutrients while avoiding the entry of potentially harmful substances or bacteria. Barrier function is dynamically regulated in part by the enteric nervous system (ENS). The role of the ENS in regulating barrier function in response to luminal nutrients is not well understood. We hypothesize that the ENS regulates intestinal permeability and ion flux in the small intestine in response to luminal nutrients. Segments of jejunum and ileum from mice were mounted in Ussing chambers. Transepithelial electrical resistance (TER), short-circuit current (I_sc), and permeability to 4-kDa FITC-dextran (FD4) were recorded after mucosal stimulation with either glucose, fructose, glutamine (10 mM), or 5% Intralipid. Mucosal lipopolysaccharide (1 mg/mL) was also studied. Enteric neurons were inhibited with tetrodotoxin (TTX; 0.5 μM) or activated with veratridine (10 μM). Enteric glia were inhibited with the connexin-43 blocker Gap26 (20 μM). Glucose, glutamine, Intralipid, and veratridine acutely modified I_sc in the jejunum and ileum, but the effect of nutrients on I_sc was insensitive to TTX. TTX, Gap26, and veratridine treatment did not affect baseline TER or permeability. Intralipid acutely decreased permeability to FD4, while LPS increased it. TTX pretreatment abolished the effect of Intralipid and exacerbated the LPS-induced increase in permeability. Luminal nutrients and enteric nerve activity both affect ion flux in the mouse small intestine acutely but independently of each other. Neither neuronal nor glial activity is required for the maintenance of baseline intestinal permeability; however, neuronal activity is essential for the acute regulation of intestinal permeability in response to luminal lipids and lipopolysaccharide.NEW & NOTEWORTHY Luminal nutrients and enteric nerve activity both affect ion transport in the mouse small intestine acutely, but independently of each other. Activation or inhibition of the enteric neurons does not affect intestinal permeability, but enteric neural activity is essential for the acute regulation of intestinal permeability in response to luminal lipids and lipopolysaccharide. The enteric nervous system regulates epithelial homeostasis in the small intestine in a time-dependent, region- and stimulus-specific manner.

Negative Effects of a High-Fat Diet on Intestinal Permeability: A Review

The intestinal tract is the largest barrier between a person and the environment. In this role, the intestinal tract is responsible not only for absorbing essential dietary nutrients, but also for protecting the host from a variety of ingested toxins and microbes. The intestinal barrier system is composed of a mucus layer, intestinal epithelial cells (IECs), tight junctions (TJs), immune cells, and a gut microbiota, which are all susceptible to external factors such as dietary fats. When components of this barrier system are disrupted, intestinal permeability to luminal contents increases, which is implicated in intestinal pathologies such as inflammatory bowel disease, necrotizing enterocolitis, and celiac disease. Currently, there is mounting evidence that consumption of excess dietary fats can enhance intestinal permeability differentially. For example, dietary fat modulates the expression and distribution of TJs, stimulates a shift to barrier-disrupting hydrophobic bile acids, and even induces IEC oxidative stress and apoptosis. In addition, a high-fat diet (HFD) enhances intestinal permeability directly by stimulating proinflammatory signaling cascades and indirectly via increasing barrier-disrupting cytokines [TNFα, interleukin (IL) 1B, IL6, and interferon γ (IFNγ)] and decreasing barrier-forming cytokines (IL10, IL17, and IL22). Finally, an HFD negatively modulates the intestinal mucus composition and enriches the gut microflora with barrier-disrupting species. Although further research is necessary to understand the precise role HFDs play in intestinal permeability, current data suggest a stronger link between diet and intestinal disease than was first thought to exist. Therefore, this review seeks to highlight the various ways an HFD disrupts the gut barrier system and its many implications in human health.

Regulatory Functions of Fatty Acids with Different Chain Lengths on the Intestinal Health in Pigs and Relative Signaling Pathways

Intestines are not only major organs for nutrient digestion and absorption, but are also the largest immune organ in pigs. They are essential for maintaining the health and growth of piglets. Fatty acids, including short-chain fatty acids, medium-chain fatty acids, and long-chain polyunsaturated fatty acids, are important nutrients; they are a major energy source, important components of the cell membrane, metabolic substrates in many biochemical pathways, cell-signaling molecules, and play role as immune modulators. Research has shown that fatty acids exert beneficial effects on intestinal health in animal models and clinical trials. The objective of this review is to give a clear understanding of the regulatory effects of fatty acids of different chain lengths on intestinal health in pigs and their signaling pathways, providing scientific reference for developing a feeding technique to apply fatty acids to piglet diets.

Gut Permeability Might be Improved by Dietary Fiber in Individuals with Nonalcoholic Fatty Liver Disease (NAFLD) Undergoing Weight Reduction

(1) Introduction: Zonulin (ZO) has been proposed as a marker of intestinal permeability. Only a few studies have analyzed to date how diet influences the serum concentration of ZO among patients with non-alcoholic fatty liver disease (NAFLD). We performed a six-month dietetic intervention to evaluate the association between fiber intake and ZO concentration in 32 individuals with NAFLD. (2) Methods: Fiber content in the diet was estimated by Food Frequency Questionnaire (FFQ) and by analyzing 72-h nutritional diaries. ZO concentrations in serum were measured before and after the intervention by immunoenzymatic assay (ELISA). Fatty liver was quantified using the Hamaguchi score before and after the dietetic intervention. (3) Results: During the intervention, the dietary fiber intake increased from 19 g/day to the 29 g/day concomitant with an increase in the frequency of fiber consumption. All patients experienced significant (all p < 0.05) improvements in serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) and gamma-glutamyltransferase (GGTP) activities. We also detected decreased serum triglycerides (p = 0.036), homeostatic model assessment insulin resistance (HOMA-IR (p = 0.041) and insulin content (p = 0.34), and improvement of fatty liver status according to the Hamaguchi score (p = 0.009). ZO concentration in serum decreased by nearly 90% (7.335 ± 13.492 vs. 0.507 ± 0.762 ng/mL, p = 0.001) and correlated with the amount of dietary fiber intake (p = 0.043) as well as the degree of fatty liver (p = 0.037). (4) Conclusion: Increasing nutritional fiber results in reduced serum ZO levels, reduced liver enzymes and improved hepatic steatosis in patients with NAFLD, possibly by altering intestinal permeability. Increased dietary fiber intake should be recommended in patients with NAFLD.

GPR40 receptor activation promotes tight junction assembly in airway epithelial cells via AMPK-dependent mechanisms

Tight junctions play key roles in the regulation of airway epithelial barrier function and promotion of tight junction integrity is beneficial to lung health. G-protein coupled receptor (GPR) 40 has been identified as a receptor of polyunsaturated fatty acids. This study aimed to investigate the function of GPR40 in regulating tight junction assembly in human airway epithelial cells (Calu-3 cells) using GW9508, a GPR40 agonist. Immunoblotting and immunofluorescence analyses showed that Calu-3 cells expressed both types of polyunsaturated fatty acid receptors including GPR40 and GPR120. Intracellular Ca²⁺ measurements confirmed that GW9508 stimulated GPR40, but not GPR120. In Ca²⁺ switch assays, GW9508 promoted the recovery of transepithelial electrical resistance and re-localization of zonula occludens (ZO)-1 to intercellular areas. These effects were suppressed by inhibitors of GPR40 and phospholipase C (PLC). Interestingly, GW9508 enhanced tight junction assembly in an AMP-activated protein kinase (AMPK)-dependent manner. The effect of GW9508 on inducing tight junction assembly was also confirmed in 16HBE14o- cells. Our results indicate that GPR40 stimulation by GW9508 leads to AMPK activation via calcium/calmodulin-dependent protein kinase kinase β (CaMKKβ). Collectively, this study reveals an unprecedented role of GPR40 in facilitating airway epithelial tight junction assembly via PLC-CaMKKβ-AMPK pathways. GPR40 represents a novel regulator of airway epithelial integrity and its stimulation may be beneficial in the treatment of airway diseases.

Self-renewing Monolayer of Primary Colonic or Rectal Epithelial Cells

BACKGROUND & AIMS

Three-dimensional organoid culture has fundamentally changed the in vitro study of intestinal biology enabling novel assays; however, its use is limited because of an inaccessible luminal compartment and challenges to data gathering in a three-dimensional hydrogel matrix. Long-lived, self-renewing 2-dimensional (2-D) tissue cultured from primary colon cells has not been accomplished.

METHODS

The surface matrix and chemical factors that sustain 2-D mouse colonic and human rectal epithelial cell monolayers with cell repertoires comparable to that in vivo were identified.

RESULTS

The monolayers formed organoids or colonoids when placed in standard Matrigel culture. As with the colonoids, the monolayers exhibited compartmentalization of proliferative and differentiated cells, with proliferative cells located near the peripheral edges of growing monolayers and differentiated cells predominated in the central regions. Screening of 77 dietary compounds and metabolites revealed altered proliferation or differentiation of the murine colonic epithelium. When exposed to a subset of the compound library, murine organoids exhibited similar responses to that of the monolayer but with differences that were likely attributable to the inaccessible organoid lumen. The response of the human primary epithelium to a compound subset was distinct from that of both the murine primary epithelium and human tumor cells.

CONCLUSIONS

This study demonstrates that a self-renewing 2-D murine and human monolayer derived from primary cells can serve as a physiologically relevant assay system for study of stem cell renewal and differentiation and for compound screening. The platform holds transformative potential for personalized and precision medicine and can be applied to emerging areas of disease modeling and microbiome studies.

Nutritional Keys for Intestinal Barrier Modulation

The intestinal tract represents the largest interface between the external environment and the human body. Nutrient uptake mostly happens in the intestinal tract, where the epithelial surface is constantly exposed to dietary antigens. Since inflammatory response toward these antigens may be deleterious for the host, a plethora of protective mechanisms take place to avoid or attenuate local damage. For instance, the intestinal barrier is able to elicit a dynamic response that either promotes or impairs luminal antigens adhesion and crossing. Regulation of intestinal barrier is crucial to control intestinal permeability whose increase is associated with chronic inflammatory conditions. The cross talk among bacteria, immune, and dietary factors is able to modulate the mucosal barrier function, as well as the intestinal permeability. Several nutritional products have recently been proposed as regulators of the epithelial barrier, even if their effects are in part contradictory. At the same time, the metabolic function of the microbiota generates new products with different effects based on the dietary content. Besides conventional treatments, novel therapies based on complementary nutrients are now growing. Fecal therapy has been recently used for the clinical treatment of refractory Clostridium difficile infection instead of the classical antibiotic therapy. In the present review, we will outline the epithelial response to nutritional components derived from dietary intake and microbial fermentation focusing on the consequent effects on the integrity of the epithelial barrier.

Intranasal microemulsion for targeted nose to brain delivery in neurocysticercosis: Role of docosahexaenoic acid

Intranasal Microemulsions (MEs) for nose to brain delivery of a novel combination of Albendazole sulfoxide (ABZ-SO) and Curcumin (CUR) for Neurocysticercosis (NCC), a brain infection are reported. MEs prepared by simple solution exhibited a globule size <20nm, negative zeta potential and good stability. The docosahexaenoic acid (DHA) ME revealed high and rapid ex vivo permeation of drugs through sheep nasal mucosa. Intranasal DHA ME resulted in high brain concentrations and 10.76 (ABZ-SO) and 3.24 (CUR) fold enhancement in brain area-under-the-curve (AUC) compared to intravenous DHA MEs at the same dose. Direct nose to brain transport (DTP) of >95% was seen for both drugs. High drug targeting efficiency (DTE) to the brain compared to Capmul ME and drug solution (P<0.05) suggested the role of DHA in aiding nose to brain delivery. Histopathology study confirmed no significant changes. High efficacy of ABZ-SO: CUR (100:10ng/mL) DHA ME in vitro on Taenia solium cysts was confirmed by complete ALP inhibition and disintegration of cysts at 96h. Considering that the brain concentration at 24h was 1400±160.1ng/g (ABZ-SO) and 120±35.2ng/g (CUR), the in vitro efficacy seen at a 10 fold lower concentration of the drugs strongly supports the assumption of clinical efficacy. The intranasal DHA ME is a promising delivery system for targeted nose to brain delivery.

Maternal 18:3n-3 favors piglet intestinal passage of LPS and promotes intestinal anti-inflammatory response to this bacterial ligand

We recently observed that maternal 18:3n-3 increases piglet jejunal permeability. We hypothesized that this would favor intestinal lipopolysaccharide (LPS) passage and alter gut immune system education toward this bacterial ligand. Sows were fed 18:3n-3 or 18:2n-6 diets throughout gestation and lactation. In each litter, two piglets were given oral Gram-negative spectrum antibiotic from post-natal day (PND) 14 to 28. All piglets were weaned on a regular diet at PND28. 18:3n-3 piglets exhibited greater jejunal permeability to FITC-LPS at PND28. Levels of 18:3n-3 but neither 20:5n-3 nor 20:4n-6 were greater in mesenteric lymph nodes (MLN) of 18:3n-3 piglets. Jejunal explant or MLN cell cytokine responses to LPS were not influenced by the maternal diet. Antibiotic increased jejunal permeability to FITC-LPS and lowered the level of 20:5n-3 in MLN, irrespective of the maternal diet. At PND52, no long-lasting effect of the maternal diet or antibiotic treatment on jejunal permeability was noticed. 18:3n-3 and 20:4n-6 levels were greater and lower, respectively, in MLN of 18:3n-3 compared to 18:2n-6 piglets. IL-10 production by MLN cells in response to LPS was greater in the 18:3n-3 group, irrespective of the neonatal antibiotic treatment. IL-8 secretion by jejunal explants in response to LPS was lower in antibiotic-treated 18:3n-3 compared to 18:2n-6 piglets. Finally, proportion of MHC class II(+) antigen-presenting cells was greater in 18:3n-3 than 18:2n-6 MLN cells. In conclusion, maternal 18:3n-3 directs the intestinal immune response to LPS toward an anti-inflammatory profile beyond the breastfeeding period; microbiota involvement seems dependent of the immune cells considered.

Central role of the gut epithelial barrier in the pathogenesis of chronic intestinal inflammation: lessons learned from animal models and human genetics

The gut mucosa is constantly challenged by a bombardment of foreign antigens and environmental microorganisms. As such, the precise regulation of the intestinal barrier allows the maintenance of mucosal immune homeostasis and prevents the onset of uncontrolled inflammation. In support of this concept, emerging evidence points to defects in components of the epithelial barrier as etiologic factors in the pathogenesis of inflammatory bowel diseases (IBDs). In fact, the integrity of the intestinal barrier relies on different elements, including robust innate immune responses, epithelial paracellular permeability, epithelial cell integrity, as well as the production of mucus. The purpose of this review is to systematically evaluate how alterations in the aforementioned epithelial components can lead to the disruption of intestinal immune homeostasis, and subsequent inflammation. In this regard, the wealth of data from mouse models of intestinal inflammation and human genetics are pivotal in understanding pathogenic pathways, for example, that are initiated from the specific loss of function of a single protein leading to the onset of intestinal disease. On the other hand, several recently proposed therapeutic approaches to treat human IBD are targeted at enhancing different elements of gut barrier function, further supporting a primary role of the epithelium in the pathogenesis of chronic intestinal inflammation and emphasizing the importance of maintaining a healthy and effective intestinal barrier.

Eicosapentaenoic acid enhances heat stress-impaired intestinal epithelial barrier function in Caco-2 cells

Objective

Dysfunction of the intestinal epithelial tight junction (TJ) barrier is known to have an important etiologic role in the pathophysiology of heat stroke. N-3 polyunsaturated fatty acids (PUFAs), including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), play a role in maintaining and protecting the TJ structure and function. This study is aimed at investigating whether n-3 PUFAs could alleviate heat stress-induced dysfunction of intestinal tight junction.

Methods

Human intestinal epithelial Caco-2 cells were pre-incubated with EPA, DHA or arachidonic acid (AA) and then exposed to heat stress. Transepithelial electrical resistance (TEER) and Horseradish Peroxidase (HRP) permeability were measured to analyze barrier integrity. Levels of TJ proteins, including occludin, ZO-1 and claudin-2, were analyzed by Western blot and localized by immunofluorescence microscopy. Messenger RNA levels were determined by quantitative real time polymerase chain reaction (Q-PCR). TJ morphology was observed by transmission electron microscopy.

Results

EPA effectively attenuated the decrease in TEER and impairment of intestinal permeability in HRP flux induced by heat exposure. EPA significantly elevated the expression of occludin and ZO-1, while DHA was less effective and AA was not at all effective. The distortion and redistribution of TJ proteins, and disruption of morphology were also effectively prevented by pretreatment with EPA.

Conclusion

This study indicates for the first time that EPA is more potent than DHA in protecting against heat-induced permeability dysfunction and epithelial barrier damage of tight junction.

Effect of polyunsaturated fatty acids on tight junctions in a model of the human intestinal epithelium under normal and inflammatory conditions

Owing to their immune-modulatory action on the intestinal mucosa immune cells, the n-3 and n-6 polyunsaturated fatty acids (PUFA) have been suggested to modulate the risk and development of inflammatory bowel diseases. Failure in the intestinal barrier is an important hallmark of inflammatory bowel diseases. This study aimed at evaluating the impact of dietary PUFA on tight junction protein localisation and on the modulation of epithelial permeability under physiological conditions or under an inflammatory stress. For this purpose, we first confirmed the accumulation of PUFA in phospholipid fractions of Caco-2 cells upon 7 days of incubation with specific PUFA. Thereafter, Caco-2 cells were cultured in inserts, which provide a model of the human intestinal barrier. Accumulation of dietary n-3 PUFA in phospholipids did not affect the presence of occludin in tight junction complexes, while that of dietary n-6 PUFA decreased it. Whatever the PUFA, at 30 μM, no distortion of the Caco-2 barrier function was observed. Otherwise, 150 μM of docosahexaenoic acid (DHA) affected ZO-1 intensity under normal conditions, but not occludin or the barrier function parameters. Finally, to simulate an inflammatory state, cells were exposed for 24 h to interleukin-1β, tumor necrosis factor-α, interferon-γ at their basolateral side and to lypopolysaccharides at both sides. DHA limited the effect of inflammatory stimulus on occludin, ZO-1 and barrier function. In conclusion, this study has evidenced the specific effect of individual PUFA to modulate occludin and ZO-1 localization, according to the inflammatory status of this in vitro model of the intestinal barrier.

Effect of eicosapentaenoic acid-derived prostaglandin E3 on intestinal epithelial barrier function

Prostaglandins (PG) are inflammatory mediators derived from arachidonic or eicosapentaenoic acid giving rise to the 2-series or the 3-series prostanoids, respectively. Previously, we have observed that PGE2 disrupts epithelial barrier function. Considering the beneficial effect of fish oil consumption in intestinal inflammatory processes, the aim of this study was to assess the role of PGE3 on epithelial barrier function assessed from transepithelial electrical resistance and dextran fluxes in Caco-2 cells. The results indicate that PGE3 increased paracellular permeability (PP) to the same extent as PGE2, through the interaction with EP1 and EP4 receptors and with intracellular Ca(2+) and cAMP as the downstream targets. Moreover, we observed a redistribution of tight junction proteins, occludin and claudin-4. In conclusion, PGE3 is able to increase PP thus leading to reconsider the role of PGE2/PGE3 ratio in the beneficial effects of dietary fish oil supplementation in the disruption of barrier function.

Regulation of intestinal epithelial permeability by tight junctions

The gastrointestinal epithelium forms the boundary between the body and external environment. It effectively provides a selective permeable barrier that limits the permeation of luminal noxious molecules, such as pathogens, toxins, and antigens, while allowing the appropriate absorption of nutrients and water. This selective permeable barrier is achieved by intercellular tight junction (TJ) structures, which regulate paracellular permeability. Disruption of the intestinal TJ barrier, followed by permeation of luminal noxious molecules, induces a perturbation of the mucosal immune system and inflammation, and can act as a trigger for the development of intestinal and systemic diseases. In this context, much effort has been taken to understand the roles of extracellular factors, including cytokines, pathogens, and food factors, for the regulation of the intestinal TJ barrier. Here, I discuss the regulation of the intestinal TJ barrier together with its implications for the pathogenesis of diseases.

Dietary long-chain PUFA enhance acute repair of ischemia-injured intestine of suckling pigs

Infant formula companies have been fortifying formulas with long-chain PUFA for 10 y. Long-chain PUFA are precursors of prostanoids, which stimulate recovery of intestinal barrier function. Supplementation of milk with PUFA increases the content of arachidonic acid (ARA) in enterocyte membranes; however, the effect of this enrichment on intestinal repair is not known. The objective of these experiments was to investigate the effect of supplemental ARA on intestinal barrier repair in ischemia-injured porcine ileum. One-day-old pigs (n = 24) were fed a milk-based formula for 10 d. Diets contained no PUFA (0% ARA), 0.5% ARA, 5% ARA, or 5% EPA of total fatty acids. Following dietary enrichment, ilea were subjected to in vivo ischemic injury by clamping the local mesenteric blood supply for 45 min. Following the ischemic period, control (nonischemic) and ischemic loops were mounted on Ussing chambers. Transepithelial electrical resistance (TER) was measured over a 240-min recovery period. Ischemia-injured ileum from piglets fed 5% ARA (61.0 ± 14%) exhibited enhanced recovery compared with 0% ARA (16 ± 14) and 0.5% ARA (22.1 ± 14)-fed pigs. Additionally, ischemia-injured ileum from 5% EPA (51.3 ± 14)-fed pigs had enhanced recovery compared with 0% ARA-fed pigs (P < 0.05). The enhanced TER recovery response observed with ischemia-injured 5% ARA supplementation was supported by a significant reduction in mucosal-to-serosal flux of (3)H-mannitol and (14)C-inulin compared with all other ischemia-injured dietary groups (P < 0.05). A histological evaluation of ischemic ilea from piglets fed the 5% ARA showed reduced histological lesions after ischemia compared with the other dietary groups (P < 0.05). These data demonstrate that feeding elevated levels of long-chain PUFA enhances acute recovery of ischemia-injured porcine ileum.

Ingestion of (n-3) fatty acids augments basal and platelet activating factor-induced permeability to dextran in the rat mesenteric vascular bed

Loss of intestinal barrier function and subsequent edema formation remains a serious clinical problem leading to hypoperfusion, anastomotic leakage, bacterial translocation, and inflammatory mediator liberation. The inflammatory mediator platelet activating factor (PAF) promotes eicosanoid-mediated edema formation and vasoconstriction. Fish oil-derived (n-3) fatty acids (FA) favor the production of less injurious eicosanoids but may also increase intestinal paracellular permeability. We hypothesized that dietary (n-3) FA would ameliorate PAF-induced vasoconstriction and enhance vascular leakage of dextran tracers. Rats were fed either an (n-3) FA-rich diet (EPA-rich diet; 4.0 g/kg EPA, 2.8 g/kg DHA) or a control diet (CON diet; 0.0 g/kg EPA and DHA) for 3 wk. Subsequently, isolated and perfused small intestines were stimulated with PAF and arterial pressure and the translocation of fluid and macromolecules from the vasculature to lumen and lymphatics were analyzed. In intestines of rats fed the EPA-rich diet, intestinal phospholipids contained up to 470% more EPA and DHA at the expense of arachidonic acid (AA). The PAF-induced increase in arterial pressure was not affected by the EPA-rich diet. However, PAF-induced fluid loss from the vascular perfusate was higher in intestines of rats fed the EPA-rich diet. This was accompanied by a greater basal loss of dextran from the vascular perfusate and a higher PAF-induced transfer of dextran from the vasculature to the lumen (P = 0.058) and lymphatics. Our data suggest that augmented intestinal barrier permeability to fluid and macromolecules is a possible side effect of (n-3) FA-rich diet supplementation.

n-3 polyunsaturated fatty acids in the maternal diet modify the postnatal development of nervous regulation of intestinal permeability in piglets

The intestinal epithelial barrier (IEB) plays a key role in the maintenance of gut homeostasis and the development of the immune system in newborns. The enteric nervous system (ENS), a key regulator of gastrointestinal functions, has been shown to be modulated by nutritional factors. However, it remains currently unknown whether maternal diet, in particular n-3 polyunsaturated fatty acids (n-3PUFAs), can impact upon the IEB in newborn piglets and whether the ENS is involved in this effect. Sows received either a control diet (lard based) or an n-3PUFA diet (linseed oil based) during gestation and lactation. Intestinal paracellular permeability was assessed in Ussing chambers on piglets at birth, 3, 7, 14, 21 and 28 postnatal days (PND). Basal jejunal permeability increased significantly and similarly in both groups until PND14 and decreased thereafter. However, at PND28, permeability was higher in n-3PUFA animals as compared to controls. In addition, a vasoactive intestinal peptide (VIP) receptor antagonist increased paracellular permeability in controls but not in n-3PUFA piglets. Conversely, atropine and hexamethonium decreased paracellular permeability in the n-3PUFA group but not in the control group. Moreover, the n-3PUFA diet increased the proportion of choline acetyltransferase (ChAT)-immunoreactive (IR) neurons and decreased the proportion of VIP-IR neurons in the submucosal plexus of piglet jejunum compared to controls. In addition, in primary culture of rat ENS, we showed that 20:5n-3 but not 18:3n-3 increased the proportion of ChAT-IR neurons and decreased the proportion of VIP-IR neurons. In conclusion, supplementation of the maternal diet with n-3PUFAs modified intestinal permeability probably via diet-induced neuroplastic changes in the ENS of newborn piglets.

Regulation of tight junction permeability by intestinal bacteria and dietary components

The human intestinal epithelium is formed by a single layer of epithelial cells that separates the intestinal lumen from the underlying lamina propria. The space between these cells is sealed by tight junctions (TJ), which regulate the permeability of the intestinal barrier. TJ are complex protein structures comprised of transmembrane proteins, which interact with the actin cytoskeleton via plaque proteins. Signaling pathways involved in the assembly, disassembly, and maintenance of TJ are controlled by a number of signaling molecules, such as protein kinase C, mitogen-activated protein kinases, myosin light chain kinase, and Rho GTPases. The intestinal barrier is a complex environment exposed to many dietary components and many commensal bacteria. Studies have shown that the intestinal bacteria target various intracellular pathways, change the expression and distribution of TJ proteins, and thereby regulate intestinal barrier function. The presence of some commensal and probiotic strains leads to an increase in TJ proteins at the cell boundaries and in some cases prevents or reverses the adverse effects of pathogens. Various dietary components are also known to regulate epithelial permeability by modifying expression and localization of TJ proteins.

Role of flavonoids in intestinal tight junction regulation

The gastrointestinal tract provides a physical barrier to the diffusion of foreign materials from the lumen into the circulatory system. Impairment of the intercellular tight junction (TJ) shield, which is the major determinant of intestinal barrier function, is associated with various diseases. Dietary flavonoids demonstrate various beneficial effects on our health; however, the information regarding their effects on TJ function is quite limited. To date, four flavonoids - epigallocatechin gallate (EGCG), genistein, myricetin and quercetin - have been reported to exhibit promotive and protective effects on intestinal TJ barrier functions. Genistein, a major soybean isoflavone, protects TJ barrier function against oxidative stress, acetaldehyde, enteric bacteria and inflammatory cytokines. Genistein blocks the tyrosine phosphorylation of the TJ proteins induced by oxidative stress and acetaldehyde, which results in the disassembly of the proteins from the junctional complex. Quercetin, a flavonol, enhances intestinal TJ barrier function through the assembly and expression of TJ proteins. The change in phosphorylation status is responsible for the quercetin-mediated assembly of TJ proteins. TJ protein induction has an additional role in this effect. This review presents the recent advances in our understanding of the flavonoid-mediated promotive and protective effects on intestinal TJ barrier function with a particular focus on intracellular molecular mechanisms.

Intracellular mechanisms involved in docosahexaenoic acid-induced increases in tight junction permeability in Caco-2 cell monolayers

We recently showed that enrichment of Caco-2 cells with docosahexaenoic acid (DHA) increases lipid peroxidation and the formation of hydrogen peroxide and peroxynitrite, which disrupt the epithelial barrier function. Studies were designed to test whether the participation of phospholipase C (PLC)/Ca(2+)/protein kinase C (PKC), cyclooxygenase (COX), and 5-lipooxygenase pathways are involved in mediating the effects of DHA. Paracellular permeability was assessed from D-mannitol flux and transepithelial electrical resistance (TER) in differentiated Caco-2 cell monolayers incubated in control or DHA-enriched conditions (100 micromol/L). The effect of DHA was prevented by U73122 (PLC inhibitor), chelerytrine (PKC inhibitor), and 1-[5-iodonaphtalene-1-sulfonyl]-1H-hexahydro-1,4-diazepine hydrochloride (myosin light chain kinase inhibitor). In contrast, the effect of DHA was enhanced by A23187 (Ca(2+) ionophore) and BAPTA-AM (Ca(2+) chelator). Indomethacin (COX inhibitor) and AA961 (5-lipooxygenase inhibitor) also prevented the changes in D-mannitol flux induced by DHA, but no effect was detected for TER. Moreover, occludin and ZO-1 immunogold staining microscopy showed that the increase in paracellular permeability was accompanied by the redistribution of both tight junction proteins. We conclude that the disruption of epithelial barrier function by DHA is partly mediated by the PLC/Ca(2+)/PKC pathway and by the formation of eicosanoids.

Dietary fat and bile juice, but not obesity, are responsible for the increase in small intestinal permeability induced through the suppression of tight junction protein expression in LETO and OLETF rats

Background

An increase in the intestinal permeability is considered to be associated with the inflammatory tone and development in the obesity and diabetes, however, the pathogenesis of the increase in the intestinal permeability is poorly understood. The present study was performed to determine the influence of obesity itself as well as dietary fat on the increase in intestinal permeability.

Methods

An obese rat strain, Otsuka Long Evans Tokushima Fatty (OLETF), and the lean counter strain, Long Evans Tokushima Otsuka (LETO), were fed standard or high fat diets for 16 weeks. Glucose tolerance, intestinal permeability, intestinal tight junction (TJ) proteins expression, plasma bile acids concentration were evaluated. In addition, the effects of rat bile juice and dietary fat, possible mediators of the increase in the intestinal permeability in the obesity, on TJ permeability were explored in human intestinal Caco-2 cells.

Results

The OLETF rats showed higher glucose intolerance than did the LETO rats, which became more marked with the prolonged feeding of the high fat diet. Intestinal permeability in the OLETF rats evaluated by the urinary excretion of intestinal permeability markers (Cr-EDTA and phenolsulfonphthalein) was comparable to that in the LETO rats. Feeding the high fat diet increased intestinal permeability in both the OLETF and LETO rats, and the increases correlated with decreases in TJ proteins (claudin-1, claudin-3, occludin and junctional adhesion molecule-1) expression in the small, but not in the large intestine (cecum or colon). The plasma bile acids concentration was higher in rats fed the high fat diet. Exposure to bile juice and the fat emulsion increased TJ permeability with concomitant reductions in TJ protein expression (claudin-1, claudin-3, and junctional adhesion molecule-1) in the Caco-2 cell monolayers.

Conclusion

Excessive dietary fat and/or increased levels of luminal bile juice, but not genetic obesity, are responsible for the increase in small intestinal permeability resulting from the suppression of TJ protein expression.

Barrier effects of nutritional factors

High dietary intake of fruits and vegetables is associated with a reduced disease risk. Therefore, clinical interest is growing in therapies based on dietary supplements and effects of food components. Immune-modulatory and barrier-protective effects have been described for the amino acid glutamine and the trace element zinc. In Caco-2-cells, zinc is necessary to maintain the expression of proteins like ZO-1 and occludin, and experimental evidence exists that glutamine has enterocyte-protective effects and modulates intestinal barrier function in stressed animals and humans. Polyunsaturated fatty acids (PUFA) improve paracellular permeability after IL-4 incubation. Enhancement of barrier properties by long-chain PUFA is discussed controversially, but a beneficial role preventing the redistribution of occludin and ZO-1 and reduction of epithelial resistance by IFN-gamma and TNF-alpha exists. In addition, a group of secondary plant compounds, the polyphenols, are supposed to be important in this respect. The flavonoid quercetin and its metabolite DHBA increased epithelial resistance of Caco-2-cells to 157 +/- 4% of control values, and DHBA up to 119 +/- 4% of control values, respectively. This is due to a 2.3 +/- 0.1-fold expression rate of the tight junction protein claudin-4.

Plasma lipids and inflammation in active inflammatory bowel diseases

BACKGROUND

Ulcerative colitis (UC) and Crohn's disease (CD) can cause metabolic and inflammatory alterations.

AIM

To evaluate the relationships between inflammatory parameters, plasma lipids and phospholipid fatty acid (FA) composition in patients with active UC and CD.

METHODS

Diet, the Harvey-Bradshaw Activity Index (HBAI), inflammatory parameters, lipoproteins and FA composition were assessed in 60 CD and 34 UC.

RESULTS

No differences in clinical parameters were observed in the two groups. Total cholesterol correlated inversely with the number of bowel movements in both groups and directly with BMI in UC. Arachidonic acid correlated inversely with HBAI in UC and total and HDL cholesterol were inversely related to C-reactive protein (CRP) in CD while HDL correlated with CRP in UC. Docosapentaenoic acid was the only polyunsaturated n-3 FA that was correlated to CRP in both groups. Total cholesterol was independently associated in the multiple regression analysis with the number of bowel movements and systemic inflammation.

CONCLUSIONS

Total and LDL cholesterol were lower in the active UC and CD than in the healthy subjects and were correlated with the systemic inflammatory status. Phospholipid FA composition was correlated to the systemic inflammatory status, but was unrelated to dietary intake and intestinal disease activity.

Molecular mechanism of intestinal permeability: interaction at tight junctions

The intestinal barrier plays a critical role in humans in the transport of nutrients and macromolecules. At the same time, it has to provide an effective barrier to harmful macromolecules and microorganisms. The tight junction (TJ) is an essential component of this barrier. The junctional complexes of the plasma membrane are not simply epithelial barriers in paracellular transport or barriers preventing diffusion in the plasma membrane, but also contain proteins involved in signal transduction and the maintenance of the physiological epithelial cell state. Occludin, claudin, junctional adhesion molecules, and the coxsackie virus and adenovirus receptor are the major components of TJs. This article highlights the structure and function of TJs as well as the molecular interactions occurring during permeation through TJs.

Polyunsaturated fatty acids support epithelial barrier integrity and reduce IL-4 mediated permeability in vitro

BACKGROUND

The intestinal mucosa functions as a barrier against harmful dietary and microbial antigens. An intact gut barrier forms a prerequisite for protection against infection and allergy. Both allergic and inflammatory mediators (e.g. IL-4, IFN-gamma) are known to compromise the epithelial barrier integrity by enhancing permeability. Breast milk provides protection against infection and allergy and contains polyunsaturated fatty acids (PUFA).

AIM OF THE STUDY

Although PUFA are commonly used in infant formulas their effect on intestinal barrier is still poorly understood. Therefore the effects of distinct PUFA (n-6: LA, GLA, DGLA, AA; n-3: ALA, EPA, DHA) and a fat blend with PUFA composition similar to that of the human breast milk fat fraction, on barrier integrity were investigated.

METHODS

Human intestinal epithelial cells (T84) were pre-incubated with individual PUFA or a lipase treated fat blend, with or without subsequent IL-4 exposure. Barrier integrity was evaluated by measuring transepithelial resistance and permeability. Membrane phospholipid composition was determined by capillary gas chromatography.

RESULTS

DGLA, AA, EPA, DHA and to a lesser extend GLA enhanced basal TER and strongly reduced IL-4 mediated permeability, while LA and ALA were ineffective. Furthermore, the lipase treated fat blend effectively supported barrier function. PUFA were incorporated in the membrane phospholipid fraction of T84 cells.

CONCLUSIONS

Long chain PUFA DGLA, AA, EPA and DHA were particularly effective in supporting barrier integrity by improving resistance and reducing IL-4 mediated permeability. Fat blends that release specific PUFA upon digestion in the gastrointestinal tract may support natural resistance.