Intestinal barrier: an interface between health and disease

Lower Neighborhood Socioeconomic Status Associated with Reduced Diversity of the Colonic Microbiota in Healthy Adults

In the United States, there are persistent and widening socioeconomic gaps in morbidity and mortality from chronic diseases. Although most disparities research focuses on person-level socioeconomic-status, mounting evidence suggest that chronic diseases also pattern by the demographic characteristics of neighborhoods. Yet the biological mechanisms underlying these associations are poorly understood. There is increasing recognition that chronic diseases share common pathogenic features, some of which involve alterations in the composition, diversity, and functioning of the gut microbiota. This study examined whether socioeconomic-status was associated with alpha-diversity of the colonic microbiota. Forty-four healthy adults underwent un-prepped sigmoidoscopy, during which mucosal biopsies and fecal samples were collected. Subjects’ zip codes were geocoded, and census data was used to form a composite indicator of neighborhood socioeconomic-status, reflecting household income, educational attainment, employment status, and home value. In unadjusted analyses, neighborhood socioeconomic-status explained 12–18 percent of the variability in alpha-diversity of colonic microbiota. The direction of these associations was positive, meaning that as neighborhood socioeconomic-status increased, so did alpha-diversity of both the colonic sigmoid mucosa and fecal microbiota. The strength of these associations persisted when models were expanded to include covariates reflecting potential demographic (age, gender, race/ethnicity) and lifestyle (adiposity, alcohol use, smoking) confounds. In these models neighborhood socioeconomic-status continued to explain 11–22 percent of the variability in diversity indicators. Further analyses suggested these patterns reflected socioeconomic variations in evenness, but not richness, of microbial communities residing in the sigmoid. We also found indications that residence in neighborhoods of higher socioeconomic-status was associated with a greater abundance of Bacteroides and a lower abundance of Prevotella, suggesting that diet potentially underlies differences in microbiota composition. These findings suggest the presence of socioeconomic variations in colonic microbiota diversity. Future research should explore whether these variations contribute to disparities in chronic disease outcomes.

Protective effects of β-casofensin, a bioactive peptide from bovine β-casein, against indomethacin-induced intestinal lesions in rats

SCOPE

β-casofensin, also known as peptide β-CN(94-123), is a milk bioactive peptide that modulates the intestinal barrier through its action on goblet cells. Here, we evaluated whether oral administration of β-casofensin can prevent indomethacin-induced injury of the jejunum in rats.

METHODS AND RESULTS

Rats received β-casofensin (0.01-100 μM) or tap water by daily gavage (4 μL/g) for eight days, then two subcutaneous injections of indomethacin (10 mg/kg, days 9 and 10) and were euthanized on day 12. In vitro, we investigated the effects of β-casofensin on the restitution of a wounded monolayer. Preventive administration of β-casofensin (100 μM) reduced intestinal macroscopic and microscopic damage induced by indomethacin. β-casofensin also prevented the depletion of goblet cells and increased myeloperoxidase activity, as well as tumor necrosis factor-ɑ (TNF-ɑ) expression and immunostaining of active caspase-3 in the jejunum of rats treated with indomethacin. In wound healing experiments, β-casofensin promoted epithelial restitution with no effect on cell proliferation. This effect was inhibited by pre-incubation with an anti-CC chemokine receptor 6 (CCR6) neutralizing antibody.

CONCLUSIONS

β-casofensin exerts protective effects in indomethacin-induced enteritis through preservation of goblet cells and improvement in wound healing. β-casofensin could therefore become vital in nutritional programs for the prevention of intestinal diseases.

Gut Microbiota Dysbiosis as Risk and Premorbid Factors of IBD and IBS Along the Childhood-Adulthood Transition

Gastrointestinal disorders, although clinically heterogeneous, share pathogenic mechanisms, including genetic susceptibility, impaired gut barrier function, altered microbiota, and environmental triggers (infections, social and behavioral factors, epigenetic control, and diet). Gut microbiota has been studied for inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) in either children or adults, while modifiable gut microbiota features, acting as risk and premorbid factors along the childhood-adulthood transition, have not been thoroughly investigated so far. Indeed, the relationship between variations of the entire host/microbiota/environmental scenario and clinical phenotypes is still not fully understood. In this respect, tracking gut dysbiosis grading may help deciphering host phenotype-genotype associations and microbiota shifts in an integrated top-down omics-based approach within large-scale pediatric and adult case-control cohorts. Large-scale gut microbiota signatures and host inflammation patterns may be integrated with dietary habits, under genetic and epigenetic constraints, providing gut dysbiosis profiles acting as risk predictors of IBD or IBS in preclinical cases. Tracking dysbiosis supports new personalized/stratified IBD and IBS prevention programmes, generating Decision Support System tools. They include (1) high risk or flare-up recurrence -omics-based dysbiosis profiles; (2) microbial and molecular biomarkers of health and disease; (3) -omics-based pipelines for laboratory medicine diagnostics; (4) health apps for self-management of score-based dietary profiles, which can be shared with clinicians for nutritional habit and lifestyle amendment; (5) -omics profiling data warehousing and public repositories for IBD and IBS profile consultation. Dysbiosis-related indexes can represent novel laboratory and clinical medicine tools preventing or postponing the disease, finally interfering with its natural history.

Screening of celiac disease in children with Henoch-Schoenlein purpura

Prevalence of celiac disease (CD) is 2.42 % in healthy Turkish children. The frequency of IgA-associated disorders is increased in CD. Henoch-Schoenlein purpura (HSP) is an IgA-associated vasculitis. Association of HSP with CD has not been evaluated. We aimed to evaluate whether CD prevalence is increased in children with HSP. Children with HSP were evaluated for demographic, anthropometric, clinical, and laboratory data including urinalysis, complete blood count, albumin, creatinine, and IgA levels. In addition, tTG-IgA, EMA-IgA, anti-DGP-IgA, and IgG antibody levels were measured. Seropositive patients were evaluated by endoscopic small bowel biopsy. The rate of CD seropositivity and confirmed CD in HSP patients was compared to the rate in healthy Turkish children. There were 42 children (25 male) with HSP. No patient had classical CD symptoms, but two patients had growth failure. None of them had IgA deficiency, anemia or hypoalbuminemia. Celiac serology was positive in five (12 %) children. Endoscopic evaluation was performed in four patients, and two (5 %) of them were confirmed to have CD. Prevalence of both CD seropositivity and histologically confirmed CD in children with HSP was significantly higher compared to healthy Turkish children (p < 0.001 and p = 0.019, respectively). CD seropositivity rate in children with HSP (12 %) is significantly higher than the rate in healthy children. Although the number of children with HSP is small in this preliminary study, this result suggests that celiac screening may be considered in children with HSP.

Mechanisms of action of vitamin D in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a complex chronic inflammatory disorder caused by the interaction of environmental, hereditary and immune factors. The etiology and pathogenesis of IBD remain unveiled. In recent years, growing attention has been paid to the role of vitamin D in immune-related diseases like IBD from traditional bone metabolism. Vitamin D not only participates in calcium and phosphorus metabolism but also alleviates IBD via regulating the immune cell factors, inducing antimicrobial peptide expression and maintaining the integrity of intestinal mucosal barrier. In view of anti-inflammatory and immunomodulatory activities of vitamin D, this article discusses its role in IBD.

Circulating Biomarkers of Gut Barrier Function: Correlates and Nonresponse to Calcium Supplementation among Colon Adenoma Patients

BACKGROUND

Gut barrier dysfunction contributes to several gastrointestinal disorders, including colorectal cancer, but factors associated with intestinal hyperpermeability have been minimally studied in humans.

METHODS

We tested the effects of two doses of calcium (1.0 or 2.0 g/d) on circulating biomarkers of gut permeability [anti-flagellin and anti-lipopolysaccharide (LPS) Ig, measured via ELISA] over a 4-month treatment period among colorectal adenoma patients in a randomized, double-blinded, placebo-controlled clinical trial (n = 193), and evaluated the factors associated with baseline levels of these biomarkers.

RESULTS

Baseline concentrations of anti-flagellin IgA and anti-LPS IgA were, respectively, statistically significantly proportionately higher by 11.8% and 14.1% among men, 31.3% and 39.8% among those with a body mass index ≥ 35 kg/m(2), and 19.9% and 22.0% among those in the upper relative to the lowest sex-specific tertile of waist circumference. A combined permeability score (the summed optical densities of all four biomarkers) was 24.3% higher among women in the upper tertile of plasma C-reactive protein (Ptrend < 0.01). We found no appreciable effects of supplemental calcium on anti-flagellin or anti-LPS Igs.

CONCLUSIONS

Our results suggest that (i) men and those with higher adiposity may have greater gut permeability, (ii) gut permeability and systemic inflammation may be directly associated with one another, and (iii) supplemental calcium may not modify circulating levels of gut permeability biomarkers within 4 months.

IMPACT

Our findings may improve the understanding of the factors that influence gut permeability to inform development of treatable biomarkers of risk for colorectal cancer and other health outcomes.

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.

A New, Discontinuous 2 Phases of Aging Model: Lessons from Drosophila melanogaster

Aging is commonly described as being a continuous process affecting progressively organisms as time passes. This process results in a progressive decrease in individuals fitness through a wide range of both organismal-decreased motor activity, fertility, resistance to stress-and molecular phenotypes-decreased protein and energy homeostasis, impairment of insulin signaling. In the past 20 years, numerous genes have been identified as playing a major role in the aging process, yet little is known about the events leading to that loss of fitness. We recently described an event characterized by a dramatic increase of intestinal permeability to a blue food dye in aging flies committed to die within a few days. Importantly, flies showing this so called 'Smurf' phenotype are the only ones, among a population, to show various age-related changes and exhibit a high-risk of impending death whatever their chronological age. Thus, these observations suggest that instead of being one continuous phenomenon, aging may be a discontinuous process well described by at least two distinguishable phases. In this paper we addressed this hypothesis by implementing a new 2 Phases of Aging mathematiCal model (2PAC model) to simulate longevity curves based on the simple hypothesis of two consecutive phases of lifetime presenting different properties. We first present a unique equation for each phase and discuss the biological significance of the 3 associated parameters. Then we evaluate the influence of each parameter on the shape of survival curves. Overall, this new mathematical model, based on simple biological observations, is able to reproduce many experimental longevity curves, supporting the existence of 2 phases of aging exhibiting specific properties and separated by a dramatic transition that remains to be characterized. Moreover, it indicates that Smurf survival can be approximated by one single constant parameter for a broad range of genotypes that we have tested under our environmental conditions.

Modulation of Intestinal Barrier and Bacterial Endotoxin Production Contributes to the Beneficial Effect of Nicotinic Acid on Alcohol-Induced Endotoxemia and Hepatic Inflammation in Rats

Alcohol consumption causes nicotinic acid deficiency. The present study was undertaken to determine whether dietary nicotinic acid supplementation provides beneficial effects on alcohol-induced endotoxin signaling and the possible mechanisms at the gut-liver axis. Male Sprague-Dawley rats were pair-fed the Lieber-DeCarli liquid diets containing ethanol or isocaloric maltose dextrin for eight weeks, with or without dietary supplementation with 750 mg/liter nicotinic acid. Chronic alcohol feeding elevated the plasma endotoxin level and activated hepatic endotoxin signaling cascade, which were attenuated by nicotinic acid supplementation. Alcohol consumption remarkably decreased the mRNA levels of claudin-1, claudin-5, and ZO-1 in the distal intestine, whereas nicotinic acid significantly up-regulated these genes. The concentrations of endotoxin, ethanol, and acetaldehyde in the intestinal contents were increased by alcohol exposure, and niacin supplementation reduced the intestinal endotoxin and acetaldehyde levels. Nicotinic acid supplementation upregulated the intestinal genes involved in aldehyde detoxification via transcriptional regulation. These results demonstrate that modulation of the intestinal barrier function and bacterial endotoxin production accounts for the inhibitory effects of nicotinic acid on alcohol-induced endotoxemia and hepatic inflammation.

Alcohol and the Intestine

Alcohol abuse is a significant contributor to the global burden of disease and can lead to tissue damage and organ dysfunction in a subset of alcoholics. However, a subset of alcoholics without any of these predisposing factors can develop alcohol-mediated organ injury. The gastrointestinal tract (GI) could be an important source of inflammation in alcohol-mediated organ damage. The purpose of review was to evaluate mechanisms of alcohol-induced endotoxemia (including dysbiosis and gut leakiness), and highlight the predisposing factors for alcohol-induced dysbiosis and gut leakiness to endotoxins. Barriers, including immunologic, physical, and biochemical can regulate the passage of toxins into the portal and systemic circulation. In addition, a host of environmental interactions including those influenced by circadian rhythms can impact alcohol-induced organ pathology. There appears to be a role for therapeutic measures to mitigate alcohol-induced organ damage by normalizing intestinal dysbiosis and/or improving intestinal barrier integrity. Ultimately, the inflammatory process that drives progression into organ damage from alcohol appears to be multifactorial. Understanding the role of the intestine in the pathogenesis of alcoholic liver disease can pose further avenues for pathogenic and treatment approaches.

Breaking down the barriers: the gut microbiome, intestinal permeability and stress-related psychiatric disorders

The emerging links between our gut microbiome and the central nervous system (CNS) are regarded as a paradigm shift in neuroscience with possible implications for not only understanding the pathophysiology of stress-related psychiatric disorders, but also their treatment. Thus the gut microbiome and its influence on host barrier function is positioned to be a critical node within the brain-gut axis. Mounting preclinical evidence broadly suggests that the gut microbiota can modulate brain development, function and behavior by immune, endocrine and neural pathways of the brain-gut-microbiota axis. Detailed mechanistic insights explaining these specific interactions are currently underdeveloped. However, the concept that a "leaky gut" may facilitate communication between the microbiota and these key signaling pathways has gained traction. Deficits in intestinal permeability may underpin the chronic low-grade inflammation observed in disorders such as depression and the gut microbiome plays a critical role in regulating intestinal permeability. In this review we will discuss the possible role played by the gut microbiota in maintaining intestinal barrier function and the CNS consequences when it becomes disrupted. We will draw on both clinical and preclinical evidence to support this concept as well as the key features of the gut microbiota which are necessary for normal intestinal barrier function.

A TEM protocol for quality assurance of in vitro cellular barrier models and its application to the assessment of nanoparticle transport mechanisms across barriers

We report here a protocol to characterise and monitor the quality of in vitro human cellular barrier models using Transmission Electron Microscopy (TEM), which can be applied for transport assays, mechanistic studies and screening of drug/compound (including nanoparticle) penetration across such biological barriers. Data from two examples of biological barriers are given, namely the hCMEC/D3 endothelial blood-brain barrier model, and the Caco-2 intestinal epithelial barrier model, to show the general applicability of the method. Several aspects of this method are applicable to the quality assurance of in vitro barrier models, e.g., assessment of the multi or mono-layer structure of the endothelial cells; identification of any potential "holes" in the barrier that could confound transport assay results; validation of tight junction expression; and determination of the types and amounts of key cellular organelles present in the barrier to account for any significant changes in phenotype that may occur compared to the in vivo situation. The method described here provides a key advantage in that it prevents loss of the filter membrane during monolayer sectioning, thereby preserving critical details associated with the basal cell membrane. Applicability of the protocol for other in vitro biological barriers, such as the blood-foetus, blood-testes, blood-cerebrospinal fluid (CSF) and lung alveolar-capillary barriers is also discussed. Additionally, we demonstrate the use of the method for assessment of nanoparticle transport across cellular barriers and elucidation of transcytosis mechanisms. Sequential events of cellular endocytosis, localisation and transcytosis can be described in detail by TEM imaging, revealing useful sub-cellular details that provide evidence for the mechanism of nanoparticle transport in the hCMEC/D3 blood-brain barrier model and the Caco-2 intestinal epithelial cell model. Potential artefacts resulting from the nanoparticles interacting with the Transwell membranes can also be assessed.

Overexpression of Hsp70 confers cytoprotection during gliadin exposure in Caco-2 cells

BACKGROUND

In Celiac disease (CD), cytoskeletal integrity of intestinal cells is disrupted by gliadin exposure. This study investigates the role of heat shock protein (Hsp)70 during cytoskeletal recovery in CD by assessing its induction and effects on junctional proteins.

METHODS

Using an in-vitro model of CD, cytoskeletal injury and recovery was assessed in gliadin-exposed Caco-2 cells by measuring cellular distribution of ezrin, E-cadherin, and Hsp70 by differential centrifugation. Effects of Hsp70 were tested by an in-vitro repair assay, based on the incubation of injured or recovered cytoskeletal cellular fractions in noncytoskeletal supernatants containing low or high levels of Hsp70, or by transient transfection of Caco-2 cells with Hsp70.

RESULTS

Cytoskeletal disruption of ezrin and E-cadherin was demonstrated in gliadin-exposed Caco-2 cells by their significant shift from the cytoskeletal pellet into the noncytoskeletal supernatant fraction. Recovery from gliadin exposure was associated with induction and cytoskeletal redistribution of Hsp70. The in-vitro repair assay delineated direct evidence for HSP-mediated repair by stabilization of junctional proteins by Hsp70. Overexpression of Hsp70 resulted in significantly increased cytoskeletal integrity.

CONCLUSION

Our results establish an essential role of HSP-mediated cytoskeletal repair in Caco-2 cells during recovery from in-vitro gliadin exposure.

Nutritional Impact of Dietary Plasma Proteins in Animals Undergoing Experimental Challenge and Implications for Patients with Inflammatory Bowel Disorders: A Meta-analysis

Studies administering plasma protein isolates (PPIs) to experimentally challenged animals have reported improvements in growth, food intake, and overall condition when compared with animals fed control diets, due in part to improvements in gut barrier function, normalization of cytokine signals, and support of enteric immune function. These and early clinical studies suggest that nutritional therapy with PPIs may similarly assist in restoring homeostasis to gut barrier function in humans experiencing mild or more acute enteropathic symptomatology such as irritable bowel syndrome and inflammatory bowel disease. This meta-analysis evaluated the ability of PPIs to promote weight gain and food intake in weanling animals, primarily piglets, after oral challenge with various enteric pathogens or bacterial toxins. MEDLINE, EMBASE, and PubMed were searched from 1980 through August 2012 for specified terms and keywords. Twenty-nine articles retrieved through this process were evaluated; 11 studies including 13 experiments were selected for inclusion in the analysis. The meta-analysis included descriptive analyses and methods for combining P values for the primary endpoint, average daily growth (ADG) at week 1, and secondary endpoints including ADG, average daily feed intake (ADFI), and gain to feed ratio (G:F) at weeks 1 and 2 and at the end of study. Primary and secondary endpoint analyses of growth (ADG, ADFI, and G:F) were significant (P < 0.01). The proinflammatory cytokines interleukin (IL) 1β, IL-6, and tumor necrosis factor α were significantly lower in animals fed dietary PPIs. Additional research in patients experiencing symptoms of enteropathy will further characterize the benefits of PPIs in clinical populations.

Dietary Leucine Supplementation Improves the Mucin Production in the Jejunal Mucosa of the Weaned Pigs Challenged by Porcine Rotavirus

The present study was mainly conducted to determine whether dietary leucine supplementation could attenuate the decrease of the mucin production in the jejunal mucosa of weaned pigs infected by porcine rotavirus (PRV). A total of 24 crossbred barrows weaned at 21 d of age were assigned randomly to 1 of 2 diets supplemented with 1.00% L-leucine or 0.68% L-alanine (isonitrogenous control) for 17 d. On day 11, all pigs were orally infused PRV or the sterile essential medium. During the first 10 d of trial, dietary leucine supplementation could improve the feed efficiency (P = 0.09). The ADG and feed efficiency were impaired by PRV infusion (P<0.05). PRV infusion also increased mean cumulative score of diarrhea, serum rotavirus antibody concentration and crypt depth of the jejunal mucosa (P<0.05), and decreased villus height: crypt depth (P = 0.07), goblet cell numbers (P<0.05), mucin 1 and 2 concentrations (P<0.05) and phosphorylated mTOR level (P<0.05) of the jejunal mucosa in weaned pigs. Dietary leucine supplementation could attenuate the effects of PRV infusion on feed efficiency (P = 0.09) and mean cumulative score of diarrhea (P = 0.09), and improve the effects of PRV infusion on villus height: crypt depth (P = 0.06), goblet cell numbers (P<0.05), mucin 1 (P = 0.08) and 2 (P = 0.07) concentrations and phosphorylated mTOR level (P = 0.08) of the jejunal mucosa in weaned pigs. These results suggest that dietary 1% leucine supplementation alleviated the decrease of mucin production and goblet cell numbers in the jejunal mucosa of weaned pigs challenged by PRV possibly via activation of the mTOR signaling.

Tight junction CLDN2 gene is a direct target of the vitamin D receptor

The breakdown of the intestinal barrier is a common manifestation of many diseases. Recent evidence suggests that vitamin D and its receptor VDR may regulate intestinal barrier function. Claudin-2 is a tight junction protein that mediates paracellular water transport in intestinal epithelia, rendering them “leaky”. Using whole body VDR^-/- mice, intestinal epithelial VDR conditional knockout (VDR^ΔIEC) mice, and cultured human intestinal epithelial cells, we demonstrate here that the CLDN2 gene is a direct target of the transcription factor VDR. The Caudal-Related Homeobox (Cdx) protein family is a group of the transcription factor proteins which bind to DNA to regulate the expression of genes. Our data showed that VDR-enhances Claudin-2 promoter activity in a Cdx1 binding site-dependent manner. We further identify a functional vitamin D response element (VDRE) 5΄-AGATAACAAAGGTCA-3΄ in the Cdx1 site of the Claudin-2 promoter. It is a VDRE required for the regulation of Claudin-2 by vitamin D. Absence of VDR decreased Claudin-2 expression by abolishing VDR/promoter binding. In vivo, VDR deletion in intestinal epithelial cells led to significant decreased Claudin-2 in VDR^-/- and VDR^ΔIEC mice. The current study reveals an important and novel mechanism for VDR by regulation of epithelial barriers.

IGF-1 decreases portal vein endotoxin via regulating intestinal tight junctions and plays a role in attenuating portal hypertension of cirrhotic rats

Background

Intestinal barrier dysfunction is not only the consequence of liver cirrhosis, but also an active participant in the development of liver cirrhosis. Previous studies showed that external administration of insulin-like growth factor 1 (IGF-1) improved intestinal barrier function in liver cirrhosis. However, the mechanism of IGF-1 on intestinal barrier in liver cirrhosis is not fully elucidated. The present study aims to investigate the mechanisms of IGF-1 improving intestinal barrier function via regulating tight junctions in intestines.

Methods

We used carbon tetrachloride induced liver cirrhotic rats to investigate the effect of IGF-1 on intestinal claudin-1 and occludin expressions, serum alanine transaminase (ALT) and aspartate transaminase (AST) levels, severity of liver fibrosis, portal pressures, enterocytic apoptosis and lipopolysaccharides (LPS) levels in portal vein. The changes of IGF-1 in serum during the development of rat liver cirrhosis were also evaluated. Additionally, we assessed the effect of IGF-1 on claudin-1 and occludin expressions, changes of transepithelial electrical resistance (TEER) and apoptosis in Caco-2 cells to confirm in vivo findings.

Results

Serum IGF-1 levels were decreased in the development of rat liver cirrhosis, and external administration of IGF-1 restored serum IGF-1 levels. External administration of IGF-1 reduced serum ALT and AST levels, severity of liver fibrosis, LPS levels in portal vein, enterocytic apoptosis and portal pressure in cirrhotic rats. External administration of IGF-1 increased the expressions of claudin-1 and occludin in enterocytes, and attenuated tight junction dysfunction in intestines of cirrhotic rats. LPS decreased TEER in Caco-2 cell monolayer. LPS also decreased claudin-1 and occludin expressions and increased apoptosis in Caco-2 cells. Furthermore, IGF-1 attenuated the effect of LPS on TEER, claudin-1 expression, occludin expression and apoptosis in Caco-2 cells.

Conclusions

Tight junction dysfunction develops during the development of liver cirrhosis, and endotoxemia will develop subsequently. Correspondingly, increased endotoxin in portal system worsens tight junction dysfunction via decreasing intestinal occludin and claudin-1 expressions and increasing enterocytic apoptosis. Endotoxemia and intestinal barrier dysfunction form a vicious circle. External administration of IGF-1 breaks this vicious circle. Improvement of tight junctions might be one possible mechanism of the restoration of intestinal barrier function mediated by IGF-1.

Short-term effects of Poly(I:C) on gut permeability

The intestinal barrier function depends on an adequate response to pathogens by the epithelium. Toll-like receptor 3 (TLR-3) recognizes double-stranded RNA, a virus-associated molecular pattern. Activation of TLR-3 with Poly(I:C), a synthetic agonist, modulates tissue repair and permeability in other epithelia; however, the effects of local luminal TLR-3 agonists on gut barrier function are unknown. The aim of this investigation was to evaluate short-term effects of Poly(I:C) on rat ileal and colonic permeability ex vivo. We also studied the acute effects of intrarectal administration of Poly(I:C) on colonic barrier function. Ileum tissues displayed decreased transepithelial electrical resistance (TEER) 1h after incubation with 200μg/mL Poly(I:C); however, the mucosa-to-serosa transit of macromolecules (4.4 and 40kDa dextrans - TD4.4 and FD40, respectively) remained unchanged. Conversely, colon tissue preparations stimulated with 200μg/mL Poly(I:C) showed a decreased thinning of the mucosal layer after 2h and a decreased transit of FD40 after 3h, in comparison to controls. There was no change in colonic TEER after 3h of treatment. In addition, colon tissue taken from rats 6h after an intrarectal administration of 100μg Poly(I:C) also showed decreased permeability to FD40 in the everted gut sac assay at 3h post-extraction. Tissue morphology remained unchanged. Our results suggest that an acute exposure to Poly(I:C) reduces colon permeability to macromolecules but increases ileum permeability to electrolytes/small molecules ex vivo. Although the mechanism associated to these effects needs further investigation, to our knowledge this is the first report of a direct effect of a TLR-3 ligand in intestinal barrier function and may be of significance to understand region-specific interactions between gut mucosa and microbiota.

Circadian rhythms, alcohol and gut interactions

The circadian clock establishes rhythms throughout the body with an approximately 24 hour period that affect expression of hundreds of genes. Epidemiological data reveal chronic circadian misalignment, common in our society, significantly increases the risk for a myriad of diseases, including cardiovascular disease, diabetes, cancer, infertility and gastrointestinal disease. Disruption of intestinal barrier function, also known as gut leakiness, is especially important in alcoholic liver disease (ALD). Several studies have shown that alcohol causes ALD in only a 20-30% subset of alcoholics. Thus, a better understanding is needed of why only a subset of alcoholics develops ALD. Compelling evidence shows that increased gut leakiness to microbial products and especially LPS play a critical role in the pathogenesis of ALD. Clock and other circadian clock genes have been shown to regulate lipid transport, motility and other gut functions. We hypothesized that one possible mechanism for alcohol-induced intestinal hyperpermeability is through disruption of central or peripheral (intestinal) circadian regulation. In support of this hypothesis, our recent data shows that disruption of circadian rhythms makes the gut more susceptible to injury. Our in vitro data show that alcohol stimulates increased Clock and Per2 circadian clock proteins and that siRNA knockdown of these proteins prevents alcohol-induced permeability. We also show that intestinal Cyp2e1-mediated oxidative stress is required for alcohol-induced upregulation of Clock and Per2 and intestinal hyperpermeability. Our mouse model of chronic alcohol feeding shows that circadian disruption through genetics (in Clock(▵19) mice) or environmental disruption by weekly 12h phase shifting results in gut leakiness alone and exacerbates alcohol-induced gut leakiness and liver pathology. Our data in human alcoholics show they exhibit abnormal melatonin profiles characteristic of circadian disruption. Taken together our data support circadian mechanisms for alcohol-induced gut leakiness that could provide new therapeutic targets for ALD.

Elevation of HO-1 Expression Mitigates Intestinal Ischemia-Reperfusion Injury and Restores Tight Junction Function in a Rat Liver Transplantation Model

Aims. This study was aimed at investigating whether elevation of heme oxygenase-1 (HO-1) expression could lead to restoring intestinal tight junction (TJ) function in a rat liver transplantation model. Methods. Intestinal mucosa injury was induced by orthotopic autologous liver transplantation (OALT) on male Sprague-Dawley rats. Hemin (a potent HO-1 activator) and zinc-protoporphyrin (ZnPP, a HO-1 competitive inhibitor), were separately administered in selected groups before OALT. The serum and intestinal mucosa samples were collected at 8 hours after the operation for analysis. Results. Hemin pretreatment significantly reduced the inflammation and oxidative stress in the mucosal tissue after OALT by elevating HO-1 protein expression, while ZnPP pretreatment aggravated the OALT mucosa injury. Meanwhile, the restriction on the expression of tight junction proteins zonula occludens-1 and occludin was removed after hemin pretreatment. These molecular events led to significant improvement on intestinal barrier function, which was proved to be through increasing nuclear translocation of nuclear factor-E2-related factor 2 (Nrf2) and reducing nuclear translocation of nuclear factor kappa-B (NF-κB) in intestinal injured mucosa. Summary. Our study demonstrated that elevation of HO-1 expression reduced the OALT-induced intestinal mucosa injury and TJ dysfunction. The HO-1 protective function was likely mediated through its effects of anti-inflammation and antioxidative stress.

Immunomodulating properties of protein hydrolysates for application in cow's milk allergy

Cow's milk proteins cause allergic symptoms in 2-3% of all infants. In these individuals, the tolerogenic state of the intestinal immune system is broken, which can lead to sensitization against antigens and eventually to allergic responses. Although a true treatment for food allergy is not available, symptoms can be avoided by providing the infants with hydrolyzed proteins. Hydrolyzed proteins are proteins that are enzymatically degraded. They lack typical allergenic IgE-binding epitopes but are also thought to play a pertinent role in other mechanisms inducing hypoallergenic effects. This review discusses the mechanisms and evidence for immunomodulating properties of cow's milk hydrolysates. Hydrolysates are found to strengthen the epithelial barrier, modulate T-cell differentiation, and decrease inflammation. Some studies suggest a role for hydrolysates in manipulating pathogen recognition receptors signaling as underlying mechanism. Peptides from hydrolysates have been shown to bind to TLR2 and TLR4 and influence cytokine production in epithelial cells and macrophages. Current insight suggests that hydrolysates may actively participate in modulating the immune responses in subjects with cow's milk allergy and those at risk to develop cow's milk allergy. However, more research is required to design effective and reproducible means to develop targeting strategies to modulate the immune response.

Leaky intestine and impaired microbiome in an amyotrophic lateral sclerosis mouse model

Emerging evidence has demonstrated that intestinal homeostasis and the microbiome play essential roles in neurological diseases, such as Parkinson's disease. Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by a progressive loss of motor neurons and muscle atrophy. Currently, there is no effective treatment. Most patients die within 3–5 years due to respiratory paralysis. Although the death of motor neurons is a hallmark of ALS, other organs may also contribute to the disease progression. We examined the gut of an ALS mouse model, G93A, which expresses mutant superoxide dismutase (SOD1^G93A), and discovered a damaged tight junction structure and increased permeability with a significant reduction in the expression levels of tight junction protein ZO-1 and the adherens junction protein E-cadherin. Furthermore, our data demonstrated increased numbers of abnormal Paneth cells in the intestine of G93A mice. Paneth cells are specialized intestinal epithelial cells that can sense microbes and secrete antimicrobial peptides, thus playing key roles in host innate immune responses and shaping the gut microbiome. A decreased level of the antimicrobial peptides defensin 5 alpha was indeed found in the ALS intestine. These changes were associated with a shifted profile of the intestinal microbiome, including reduced levels of Butyrivibrio Fibrisolvens, Escherichia coli, and Fermicus, in G93A mice. The relative abundance of bacteria was shifted in G93A mice compared to wild-type mice. Principal coordinate analysis indicated a difference in fecal microbial communities between ALS and wild-type mice. Taken together, our study suggests a potential novel role of the intestinal epithelium and microbiome in the progression of ALS.

Modulation of intestinal afferent nerve sensitivity to inflammatory mediators following systemic endotoxin in mice

BACKGROUND

Endotoxin exposure may be followed by visceral hypersensitvity but potential mechanisms are not fully explored. We aimed to test the hypothesis that mast cells and the cyclooxygenase pathway (COX) mediate modulation of afferent nerve sensitivity following systemic endotoxin.

METHODS

C57Bl6 mice received endotoxin injection i.p. to induce systemic inflammation. Control animals received normal saline. Extracellular multi-unit afferent nerve discharge was recorded from jejunal mesenteric nerves in vitro. Afferent nerve response to 5-hydroxytryptamine (5-HT, 250 μmol/L), bradykinin (BK, 0.5 μmol/L), and to mechanical ramp distension of the intestinal lumen from 0 to 60 cmH2O were recorded 2 h following endotoxin administration.

KEY RESULTS

Following endotoxin administration peak afferent discharge to 5-HT and BK was increased compared to controls (p < 0.05). Pre-perfusion with the mast cell stabilizer Doxantrazole (10(-4) M), or the cyclooxygenase inhibitor Naproxen inhibited the increased response to 5-HT and BK (p < 0.05 vs endotoxin pretreatment). Mechanosensitivity during luminal ramp distension from 10 to 60 cmH2O was increased following endotoxin pretreatment compared to controls (p < 0.05). This increase in sensitivity following endotoxin was no longer observed after Doxantrazole or Naproxen administration for pressures from 10 to 30 cmH2O (p < 0.05). Selective COX-2 inhibition by NS398 (10 μM) but not COX-1 inhibition by SC560 (300 μM) reduced increased afferent discharge in endotoxin pretreated animals to 5-HT, BK and mechanical ramp distension from 10 to 40 cmH2O (all p < 0.05).

CONCLUSIONS & INFERENCES

Systemic endotoxin sensitizes mesenteric afferent nerve fibers to 5-HT, BK and mechanical stimuli. The underlying mechanism responsible for this sensitization seems to involve mast cells and the COX-2 pathway.

Ascorbic Acid may Exacerbate Aspirin-Induced Increase in Intestinal Permeability

Ascorbic acid in combination with aspirin has been used to prevent aspirin-induced oxidative GI damage. We aimed to determine whether ascorbic acid reduces or prevents aspirin-induced changes in intestinal permeability over a 6-hr period using saccharidic probes mannitol and lactulose. The effects of administration of 600 mg aspirin alone, 500 mg ascorbic acid alone and simultaneous dosage of both agents were compared in a cross-over study in 28 healthy female volunteers. These effects were also compared with that of a placebo. The ability of ascorbic acid to mitigate the effects of aspirin when administered either half an hour before or after dosage with aspirin was also assessed in 19 healthy female volunteers. The excretion of lactulose over the 6-hr period was augmented after consumption of either aspirin or ascorbic acid compared with that after consumption of placebo. Dosage with ascorbic acid alone augmented the excretion of lactulose more than did aspirin alone. Simultaneous dosage with both agents augmented the excretion of lactulose in an additive manner. The timing of dosage with ascorbic acid in relation to that with aspirin had no significant effect on the excretion of the two sugars. These findings indicate that ascorbic acid does not prevent aspirin-induced increase in gut permeability rather that both agents augment it to a similar extent. The additive effect on simultaneous dosage with both agents in augmenting the absorption of lactulose suggests that each influences paracellular permeability by different pathways.

Antimicrobial peptide Cathelicidin-BF prevents intestinal barrier dysfunction in a mouse model of endotoxemia

Intestinal barrier functions are altered during the development of sepsis. Cathelicidin antimicrobial peptides, such as LL-37 and mCRAMP, can protect animals against intestinal barrier dysfunction. Cathelicidin-BF (C-BF), a new cathelicidin peptide purified from the venom of the snake Bungarus fasciatus, has been shown to have both antimicrobial and anti-inflammatory properties. This study investigated whether C-BF pretreatment could protect the intestinal barrier against dysfunction in a mouse model of endotoxemia, induced by intraperitoneal injection of LPS (10mg/kg). Mice were treated with low or high dose C-BF before treatment with LPS, and samples were collected 5h after LPS treatment. C-BF reduced LPS induced intestinal histological damage and gut permeability to 4 KD Fluorescein-isothiocyanate-conjugated dextran. Pretreatment with C-BF prevented LPS induced intestinal tight junction disruption and epithelial cell apoptosis. Moreover, C-BF down regulated the expression and secretion of TNF-α, a process involving the NF-κB signaling pathway. C-BF also reduced LPS induced TNF-α expression through the NF-κB signaling pathway in mouse RAW 264.7 macrophages. These findings indicate that C-BF can prevent gut barrier dysfunction induced by LPS, suggesting that C-BF may be used to develop a prophylactic agent for intestinal injury in endotoxemia.

Intestinal permeability regulation by tight junction: implication on inflammatory bowel diseases

Epithelial tight junctions (TJs) are the key structures regulating paracellular trafficking of macromolecules. The TJ is multi-protein complex that forms a selective permeable seal between adjacent epithelial cells and demarcates the boundary between apical and basolateral membrane domains. Disruption of the intestinal TJ barrier, followed by permeation of luminal noxious molecules, induces a perturbation of the mucosal immune system and inflammation, which can act as a trigger for the development of intestinal and systemic diseases. Inflammatory bowel disease (IBD) patients demonstrate increased intestinal paracellular permeability. Although it remains unclear whether barrier dysfunction precedes disease or results from active inflammation, increased intestinal TJ disruption is observed in IBD patients suggest that dysregulation of TJ barrier integrity may predispose or enhance IBD progression. Therefore, therapeutic target to restore the TJ barrier integrity may provide effective therapeutic and preventive approaches against IBD. This review discusses the molecular structure and regulation of intestinal TJs and the involvement of intestinal TJs in IBD pathogenesis.

Simultaneous gas-chromatographic urinary measurement of sugar probes to assess intestinal permeability: use of time course analysis to optimize its use to assess regional gut permeability

BACKGROUND

Measurement of intestinal permeability is important in several diseases but currently several methods are employed. We sought to: (1) develop a new GC based method to measure urinary mannitol, lactulose and sucralose to assess regional and total gut permeability; (2) analyze the kinetics of these sugars in the urine to determine which ratio is useful to represent intestinal permeability; and (3) determine whether age, gender, race and BMI impact these values.

METHODS

Subjects drank a cocktail of sucrose, lactulose, mannitol and sucralose and these sugars were measured in the urine at 5, 12 and 24h with gas chromatography.

RESULTS

Urinary mannitol exhibited significantly different kinetics than lactulose and sucralose which were similar to each other and varied little over the 24h. No permeability differences were observed for renal function, age, race, sex, or BMI.

CONCLUSIONS

Our data do not support the use of the widely used L/M ratio as an accurate estimate of intestinal permeability. Our data support the use of: the sucralose/lactulose (S/M) ratio to measure: small intestine permeability (first 5h); small and large intestine (first 12h), and total gut permeability (24h). This was also found to be true in a Parkinson's disease model.

Role of Corticotropin-releasing Factor in Gastrointestinal Permeability

The interface between the intestinal lumen and the mucosa is the location where the majority of ingested immunogenic particles face the scrutiny of the vast gastrointestinal immune system. Upon regular physiological conditions, the intestinal micro-flora and the epithelial barrier are well prepared to process daily a huge amount of food-derived antigens and non-immunogenic particles. Similarly, they are ready to prevent environmental toxins and microbial antigens to penetrate further and interact with the mucosal-associated immune system. These functions promote the development of proper immune responses and oral tolerance and prevent disease and inflammation. Brain-gut axis structures participate in the processing and execution of response signals to external and internal stimuli. The brain-gut axis integrates local and distant regulatory networks and super-systems that serve key housekeeping physiological functions including the balanced functioning of the intestinal barrier. Disturbance of the brain-gut axis may induce intestinal barrier dysfunction, increasing the risk of uncontrolled immunological reactions, which may indeed trigger transient mucosal inflammation and gut disease. There is a large body of evidence indicating that stress, through the brain-gut axis, may cause intestinal barrier dysfunction, mainly via the systemic and peripheral release of corticotropin-releasing factor. In this review, we describe the role of stress and corticotropin-releasing factor in the regulation of gastrointestinal permeability, and discuss the link to both health and pathological conditions.

Glutamine enhances tight junction protein expression and modulates corticotropin-releasing factor signaling in the jejunum of weanling piglets

BACKGROUND

Dysfunction of tight junction integrity is associated with decreased nutrient absorption and numerous gastrointestinal diseases in humans and piglets. Although l-glutamine has been reported to enhance intestinal-mucosal mass and barrier function under stressful conditions, in vivo data to support a functional role for l-glutamine on intestinal tight junction protein (TJP) expression in weanling mammals are limited.

OBJECTIVE

This study tested the hypothesis that glutamine regulates expression of TJPs and stress-related corticotropin-releasing factor (CRF) signaling in the jejunum of weanling piglets.

METHODS

Piglets were reared by sows or weaned at 21 d of age to a corn and soybean meal-based diet that was or was not supplemented with 1% l-glutamine for 7 d. Growth performance, intestinal permeability, TJP abundance, and CRF expression were examined.

RESULTS

Weaning caused increases (P < 0.05) in intestinal permeability by 40% and in CRF concentrations by 4.7 times in association with villus atrophy (P < 0.05). Western blot analysis showed reductions (P < 0.05) in jejunal expression of occludin, claudin-1, zonula occludens (ZO) 2, and ZO-3, but no changes in the abundance of claudin-3, claudin-4, or ZO-1 in weanling piglets compared with age-matched suckling controls. Glutamine supplementation improved (P < 0.05) intestinal permeability and villus height, while reducing (P < 0.05) jejunal mRNA and protein levels for CRF and attenuating (P < 0.05) weanling-induced decreases in occludin, claudin-1, ZO-2, and ZO-3 protein abundances.

CONCLUSION

Collectively, our results support an important role for l-glutamine in regulating expression of TJPs and CRF in the jejunum of weanling piglets.

Dietary requirement for serum-derived bovine immunoglobulins in the clinical management of patients with enteropathy

A variety of human disease conditions are associated with chronic intestinal disorders or enteropathies that are characterized by intestinal inflammation, increased gut permeability, and reduced capacity to absorb nutrients. Such disruptions in the homeostasis of the gastrointestinal (GI) tract can lead to symptoms of abdominal pain and discomfort, bloating, abnormal bowel function, and malabsorption of nutrients. While significant advances have been made in understanding the factors that influence the complex and fragile balance between the gut microbiota, intestinal epithelial cell integrity, and the underlying immune system, effective therapies for restoring intestinal balance during enteropathy are still not available. Numerous studies have demonstrated the ability of oral immunoglobulins to improve weight gain, support gut barrier function, and reduce the severity of enteropathy in animals. More recently, studies in humans provide evidence that serum-derived bovine immunoglobulin/protein isolate is safe and improves nutritional status and GI symptoms in patients with enteropathy associated with irritable bowel syndrome or infection with the human immunodeficiency virus. This review summarizes studies showing the impact of enteropathy on nutritional status and how specially formulated bovine immunoglobulins may help restore intestinal homeostasis and nutritional status in patients with specific enteropathies. Such protein preparations may provide distinct nutritional support required for the dietary management of patients who, because of therapeutic or chronic medical needs, have limited or impaired capacity to digest, absorb, or metabolize ordinary foodstuffs or certain nutrients, or other special medically determined nutrient requirements that cannot be satisfied by changes to the normal diet alone.

Exploring the physiology and pathology of aging in the intestine of Drosophila melanogaster

The gastrointestinal tract, due to its role as a digestive organ and as a barrier between the exterior and interior milieus, is critically impacted by dietary, environmental, and inflammatory conditions that influence health and lifespan. Work in flies is now uncovering the multifaceted molecular mechanisms that control homeostasis in this tissue, and establishing its central role in health and lifespan of metazoans. The Drosophila intestine has thus emerged as a productive, genetically accessible model to study various aspects of the pathophysiology of aging. Studies in flies have characterized the maintenance of regenerative homeostasis, the development of immune senescence, the loss of epithelial barrier function, the decline in metabolic homeostasis, as well as the maintenance of epithelial diversity in this tissue. Due to its fundamental similarity to vertebrate intestines, it can be anticipated that findings obtained in this system will have important implications for our understanding of age-related changes in the human intestine. Here, I review recent studies exploring age-related changes in the fly intestine, and their insight into the regulation of health and lifespan of the animal.

Coating with luminal gut-constituents alters adherence of nanoparticles to intestinal epithelial cells

BACKGROUND

Anthropogenic nanoparticles (NPs) have found their way into many goods of everyday life. Inhalation, ingestion and skin contact are potential routes for NPs to enter the body. In particular the digestive tract with its huge absorptive surface area provides a prime gateway for NP uptake. Considering that NPs are covered by luminal gut-constituents en route through the gastrointestinal tract, we wanted to know if such modifications have an influence on the interaction between NPs and enterocytes.

RESULTS

We investigated the consequences of a treatment with various luminal gut-constituents on the adherence of nanoparticles to intestinal epithelial cells. Carboxylated polystyrene particles 20, 100 and 200 nm in size represented our anthropogenic NPs, and differentiated Caco-2 cells served as model for mature enterocytes of the small intestine. Pretreatment with the proteins BSA and casein consistently reduced the adherence of all NPs to the cultured enterocytes, while incubation of NPs with meat extract had no obvious effect on particle adherence. In contrast, contact with intestinal fluid appeared to increase the particle-cell interaction of 20 and 100 nm NPs.

CONCLUSION

Luminal gut-constituents may both attenuate and augment the adherence of NPs to cell surfaces. These effects appear to be dependent on the particle size as well as on the type of interacting protein. While some proteins will rather passivate particles towards cell attachment, possibly by increasing colloid stability or camouflaging attachment sites, certain components of intestinal fluid are capable to modify particle surfaces in such a way that interactions with cellular surface structures result in an increased binding.

Migraine associated with gastrointestinal disorders: review of the literature and clinical implications

Recent studies suggest that migraine may be associated with gastrointestinal (GI) disorders, including irritable bowel syndrome (IBS), inflammatory bowel syndrome, and celiac disease. Here, an overview of the associations between migraine and GI disorders is presented, as well as possible mechanistic links and clinical implications. People who regularly experience GI symptoms have a higher prevalence of headaches, with a stronger association with increasing headache frequency. Children with a mother with a history of migraine are more likely to have infantile colic. Children with migraine are more likely to have experienced infantile colic compared to controls. Several studies demonstrated significant associations between migraine and celiac disease, inflammatory bowel disease, and IBS. Possible underlying mechanisms of migraine and GI diseases could be increased gut permeability and inflammation. Therefore, it would be worthwhile to investigate these mechanisms further in migraine patients. These mechanisms also give a rationale to investigate the effects of the use of pre- and probiotics in migraine patients.

Intestinal barrier function and the brain-gut axis

The luminal-mucosal interface of the intestinal tract is the first relevant location where microorganism-derived antigens and all other potentially immunogenic particles face the scrutiny of the powerful mammalian immune system. Upon regular functioning conditions, the intestinal barrier is able to effectively prevent most environmental and external antigens to interact openly with the numerous and versatile elements that compose the mucosal-associated immune system. This evolutionary super system is capable of processing an astonishing amount of antigens and non-immunogenic particles, approximately 100 tons in one individual lifetime, only considering food-derived components. Most important, to develop oral tolerance and proper active immune responses needed to prevent disease and inflammation, this giant immunogenic load has to be managed in a way that physiological inflammatory balance is constantly preserved. Adequate functioning of the intestinal barrier involves local and distant regulatory networks integrating the so-called brain-gut axis. Along this complex axis both brain and gut structures participate in the processing and execution of response signals to external and internal changes coming from the digestive tract, using multidirectional pathways to communicate. Dysfunction of brain-gut axis facilitates malfunctioning of the intestinal barrier, and vice versa, increasing the risk of uncontrolled immunological reactions that may trigger mucosal and brain low-grade inflammation, a putative first step to the initiation of more permanent gut disorders. In this chapter, we describe the structure, function and interactions of intestinal barrier, microbiota and brain-gut axis in both healthy and pathological conditions.

Review article: intestinal barrier dysfunction and central nervous system disorders--a controversial association

BACKGROUND

Central nervous system (CNS) development and physiopathology are greatly affected by environmental stimuli. The intestinal barrier restricts the entrance of toxins, pathogens, and antigens while modulating the expression of various neuroactive compounds. The existence of a rich gut-to-brain communication raises the possibility that intestinal barrier alterations may take part in the pathophysiology of CNS disorders.

AIM

To review evidence associating intestinal barrier dysfunction with the development of CNS disorders.

METHODS

Literature search was conducted on PubMed using the following terms: intestinal barrier, intestinal permeability, central nervous system, mental disorders, schizophrenia, autism, stress, anxiety, depression, and neurodegeneration.

RESULTS

Clinical and animal model studies of the association between intestinal barrier and schizophrenia, autism spectrum disorders, neurodegenerative diseases or depression were reviewed. The majority of reports concentrated on schizophrenia and autism spectrum disorders. About half of these described increased intestinal permeability/mucosal damage in patients compared with healthy controls, with up to 43% of children with autism spectrum disorders and up to 35% of schizophrenia patients displaying abnormally high urinary excretion of the sugars used as permeability markers. However, another substantial group of studies did not find such differences. In autism spectrum disorders, some reports show that the use of diets such as the gluten-free casein-free diet may contribute to the normalisation of lactulose/mannitol ratio, but to date there is no adequately controlled study showing improvement in behavioural symptoms following these dietary interventions.

CONCLUSIONS

Evidence of altered intestinal permeability in individuals suffering from CNS disorders is limited and cannot be regarded as proven. Moreover the efficacy of targeting gut barrier in the management of neurological and behavioural aspects of CNS disorders has not yet been established, and needs further investigation.

Gastrointestinal dysfunction in liver cirrhosis

Patients with liver cirrhosis exhibit several features of gut dysfunction which may contribute to the development of cirrhosis complications as well as have an impact on nutritional status and health-related quality of life. Gastrointestinal symptoms are common in cirrhosis and their pathophysiology probably involves factors related to liver disease severity, psychological distress, and gut dysfunction (e.g., increased gastric sensitivity to distension and delayed gut transit). They may lead to reduced food intake and, thus, may contribute to the nutritional status deterioration in cirrhotic patients. Although tense ascites appears to have a negative impact on meal-induced accommodation of the stomach, published data on gastric accommodation in cirrhotics without significant ascites are not unanimous. Gastric emptying and small bowel transit have generally been shown to be prolonged. This may be related to disturbances in postprandial glucose, insulin, and ghrelin levels, which, in turn, appear to be associated to insulin resistance, a common finding in cirrhosis. Furthermore, small bowel manometry disturbances and delayed gut transit may be associated with the development of small bowel bacterial overgrowth. Finally, several studies have reported intestinal barrier dysfunction in patients with cirrhosis (especially those with portal hypertension), which is related to bacterial translocation and permeation of intestinal bacterial products, e.g., endotoxin and bacterial DNA, thus potentially being involved in the pathogenesis of complications of liver cirrhosis.

5-Fluorouracil-induced changes of intestinal integrity biomarkers in BALB/c mice

Background:

Intestinal mucositis is a most frequently occurring toxicity in cancer chemotherapy, and consequent malnutrition reduces tolerance to cancer therapies. Therefore it is important to lessen the severity of mucotitis and to develop complementary agents capable of reducing mucotitis-related symptoms. This study was conducted to determine 5-fluorouracil (5-FU) induced intestinal damage to understand intestinal damages due to chemotherapy and to provide information on biomarkers which can be used to screen complementary agents in future studies.

Methods:

BALB/c mice were divided into three experimental groups and subjected to the intraperitoneal injection of either 100 mg/kg or 200 mg/kg of 5-FU. The third group was used as PBS controls. Body weights and the consistency of the stools were recorded every day, and the animals were sacrificed on the 7th day post 5-FU administration. The expressions of intestinal tight junction proteins and mRNAs of tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) were determined.

Results:

The body weight of the animals treated with 5-FU was significantly decreased in a dose-dependent manner. However, mice given 100 mg/kg 5-FU rapidly recovered the original body weight. Symptom of diarrhea was also more severe in 200 mg/kg 5-FU treated group than that of the 100 mg/kg 5-FU treated animals. The expressions of occludin and claudin-1, not ZO-1 protein expressions in 200 mg/kg 5-FU treated animals were significantly reduced compared to those of the control group or 100 mg/kg 5-FU group. The expression of Nuclear factor-kappa B p65 (NF-κB p65) protein and TNF-α mRNA were significantly higher in 5-FU treated group compared to those of control group. No difference was observed with IL-1β expression.

Conclusions:

These results suggested that selected tight junction proteins and inflammatory cytokines are related to 5-FU induced mucositis, and thereby can be used as targets of developing complementary agents.

Intestinal CYP2E1: A mediator of alcohol-induced gut leakiness

Chronic alcohol use can result in many pathological effects including alcoholic liver disease (ALD). While alcohol is necessary for the development of ALD, only 20-30% of alcoholics develop alcoholic steatohepatitis (ASH) with progressive liver disease leading to cirrhosis and liver failure (ALD). This suggests that while chronic alcohol consumption is necessary it is not sufficient to induce clinically relevant liver damage in the absence of a secondary risk factor. Studies in rodent models and alcoholic patients show that increased intestinal permeability to microbial products like endotoxin play a critical role in promoting liver inflammation in ALD pathogenesis. Therefore identifying mechanisms of alcohol-induced intestinal permeability is important in identifying mechanisms of ALD and for designing new avenues for therapy. Cyp2e1 is a cytochrome P450 enzyme that metabolizes alcohol has been shown to be upregulated by chronic alcohol use and to be a major source of oxidative stress and liver injury in alcoholics and in animal and in vitro models of chronic alcohol use. Because Cyp2e1 is also expressed in the intestine and is upregulated by chronic alcohol use, we hypothesized it could play a role in alcohol-induced intestinal hyperpermeability. Our in vitro studies with intestinal Caco-2 cells and in mice fed alcohol showed that circadian clock proteins CLOCK and PER2 are required for alcohol-induced permeability. We also showed that alcohol increases Cyp2e1 protein and activity but not mRNA in Caco-2 cells and that an inhibitor of oxidative stress or siRNA knockdown of Cyp2e1 prevents the increase in CLOCK or PER2 proteins and prevents alcohol-induced hyperpermeability. With our collaborators we have also shown that Cyp2e1 knockout mice are resistant to alcohol-induced gut leakiness and liver inflammation. Taken together our data support a novel Cyp2e1-circadian clock protein mechanism for alcohol-induced gut leakiness that could provide new avenues for therapy of ALD.

Bovine immunoglobulin protein isolates for the nutritional management of enteropathy

The gastrointestinal tract is responsible for a multitude of digestive and immune functions which depend upon the balanced interaction of the intestinal microbiota, diet, gut barrier function, and mucosal immune response. Disruptions in one or more of these factors can lead to intestinal disorders or enteropathies which are characterized by intestinal inflammation, increased gut permeability, and reduced capacity to absorb nutrients. Enteropathy is frequently associated with human immunodeficiency virus (HIV) infection, inflammatory bowel disease, autoimmune enteropathy, radiation enteritis, and irritable bowel syndrome (IBS), where pathologic changes in the intestinal tract lead to abdominal discomfort, bloating, abnormal bowel function (e.g., diarrhea, urgency, constipation and malabsorption). Unfortunately, effective therapies for the management of enteropathy and restoring intestinal health are still not available. An accumulating body of preclinical studies has demonstrated that oral administration of plasma- or serum-derived protein concentrates containing high levels of immunoglobulins can improve weight, normalize gut barrier function, and reduce the severity of enteropathy in animal models. Recent studies in humans, using serum-derived bovine immunoglobulin/protein isolate, demonstrate that such protein preparations are safe and improve symptoms, nutritional status, and various biomarkers associated with enteropathy. Benefits have been shown in patients with HIV infection or diarrhea-predominant IBS. This review summarizes preclinical and clinical studies with plasma/serum protein concentrates and describes the effects on host nutrition, intestinal function, and markers of intestinal inflammation. It supports the concept that immunoglobulin-containing protein preparations may offer a new strategy for restoring functional homeostasis in the intestinal tract of patients with enteropathy.

The protective effects of Rhodiola crenulata extracts on Drosophila melanogaster gut immunity induced by bacteria and SDS toxicity

The aim of this study was to observe the effect of the Rhodiola crenulata extracts on gut immunity of Drosophila melanogaster. Wild-type flies fed standard cornmeal-yeast medium were used as controls. Experimental groups were supplemented with 2.5% R. crenulata aqueous extracts in standard medium. Survival rate was determined by feeding pathogenic microorganisms and toxic compounds. The levels of reactive oxygen species and dead cells were detected by dihydroethidium and 7-amino-actinomycin D staining, respectively. The expression of antimicrobial peptides was evaluated by quantitative polymerase chain reaction, and morphological change of the intestine was imaged by an Axioskop 2 plus microscope. The results demonstrate that R. crenulata increased the survival rates of adult flies and expression of antimicrobial peptide genes after pathogen or toxic compound ingestion. Moreover, decreased levels of reactive oxygen species and epithelial cell death were associated with results in improved intestinal morphology. The pharmacological action of R. crenulata from Tibet was greater than that from Sichuan. These results indicate that the R. crenulata extracts from Tibet had better pharmacological effect on D. melanogaster gut immunity after ingestion of pathogens and toxic compounds. These results may provide the pharmacological basis for prevention of inflammatory diseases of the intestine.

Gut barrier dysfunction and microbial translocation in cancer cachexia: a new therapeutic target

Purpose of Review

Cachexia is a complex metabolic syndrome characterized by skeletal muscle and adipose tissue loss and is frequently associated with emaciation, anorexia, systemic inflammation, and metabolic dysfunction. Lack of a clear understanding of the cause of cancer cachexia has impeded progress in identifying effective therapeutic agents. This review summarizes recent publications on the role of gut barrier function, intestinal microbiota, and inflammation in the etiology of cancer cachexia and new therapeutic interventions that may benefit treatment strategies.

Recent Findings

Significant advances have been made in understanding the composition and metabolic capabilities of the intestinal microbiota and its impact on gut barrier function with implications for certain inflammatory-based diseases. Recent studies reported associations between intestinal permeability and endotoxemia with development of cancer cachexia and other metabolic disorders. Improvements in intestinal function and weight gain along with decreased inflammation have been reported for potential therapeutic agents such as eicosapentaenoic acid, immunoglobulin isolates, and probiotics.

Summary

Continued progress in the scientific understanding of the complex interplay between the intestinal microbiota, gut barrier function, and host inflammatory responses will uncover new therapeutic targets to help avoid the serious metabolic alterations associated with cachexia.