Pilot study: alterations of intestinal microbiota in obese humans are not associated with colonic inflammation or disturbances of barrier function

Exploring the Dynamic Relationship between the Gut Microbiome and Body Composition across the Human Lifespan: A Systematic Review

This systematic review aimed to identify different gut microbiome profiles across the human lifespan and to correlate such profiles with the body composition. PubMed, Scopus, and Cochrane were searched from inception to March 2022. Sixty studies were included in this systematic review. Overall, the gut microbiome composition in overweight participants exhibited decreased α-diversity, decreased levels of the phylum Bacteroidetes and its taxa, and increased levels of the phylum Firmicutes, its taxa, and the Firmicutes/Bacteroidetes ratio, in comparison to normal-weight participants. Other body composition parameters showed similar correlations. Fat mass and waist circumference were found to correlate positively with the Firmicutes taxa and negatively with the Bacteroidetes taxa. In contrast, lean body mass and muscle mass demonstrated a positive correlation with the Bacteroidetes taxa. Notably, these correlations were more pronounced in athletes than in obese and normal-weight individuals. The composition of the gut microbiome is evidently different in overweight individuals or athletes of all age groups, with the former tending towards decreased Bacteroidetes taxa and increased Firmicutes taxa, while a reversed relationship is observed concerning athletes. Further studies are needed to explore the dynamic relationship between energy intake, body composition, and the gut microbiome across the human lifespan.

Oral Pathogenic Bacteria and the Oral-Gut-Liver Axis: A New Understanding of Chronic Liver Diseases

Liver diseases have long been a prevalent cause of morbidity and mortality, and their development and progression involve multiple vital organs throughout the body. Recent studies on the oral-gut-liver axis have revealed that the oral microbiota is associated with the pathophysiology of chronic liver diseases. Since interventions aimed at regulating oral biological disorders may delay the progress of liver disease, it is crucial to better comprehend this process. Oral bacteria with potential pathogenicity have been extensively studied and are closely related to several types of chronic liver diseases. Therefore, this review will systemically describe the emerging role of oral pathogenic bacteria in common liver diseases, including alcoholic liver disease (ALD), non-alcoholic steatohepatitis (NASH), non-alcoholic fatty liver disease (NAFLD), cirrhosis, autoimmune liver diseases (AILD), and liver cancer, and bring in new perspectives for future research.

Impact of Sleeve Gastrectomy on Fecal Microbiota in Individuals with Morbid Obesity

BACKGROUND

The intestinal microbiota plays an important role in the etiology of obesity. Sleeve gastrectomy (SG) is a frequently performed and effective therapy for morbid obesity.

OBJECTIVE

To investigate the effect of sleeve gastrectomy on the fecal microbiota of individuals with morbid obesity and to examine whether shifts in microbiota composition are associated with markers of inflammation and intestinal barrier function.

METHODS

Fecal and blood samples of healthy individuals (n = 27) and morbidly obese individuals pre-SG (n = 24), and at 2 months (n = 13) and 6 months post-SG (n = 9) were collected. The 16SrRNA gene was sequenced to assess microbiota composition. Fecal calprotectin, plasma inflammatory markers and intestinal permeability markers (multi-sugar test) were determined.

RESULTS

Fecal microbiota composition between morbidly obese and lean individuals was significantly different. The fecal microbiota composition changed significantly 2 and 6 months post-SG (p = 0.008) compared to pre-SG but not towards a more lean profile. The post-SG microbiota profile was characterized by an increase in facultative anaerobic bacteria, characteristic for the upper gastrointestinal tract. No correlations were found between inflammatory markers, intestinal permeability and microbial profile changes.

CONCLUSIONS

Fecal microbiota composition in morbidly obese individuals changed significantly following SG. This change might be explained by functional changes induced by the SG procedure.

Are gut dysbiosis, barrier disruption, and endotoxemia related to adipose tissue dysfunction in metabolic disorders? Overview of the mechanisms involved

Recently, compelling evidence points to dysbiosis and disruption of the epithelial intestinal barrier as major players in the pathophysiology of metabolic disorders, such as obesity. Upon the intestinal barrier disruption, components from bacterial metabolism and bacteria itself can reach peripheral tissues through circulation. This has been associated with the low-grade inflammation that characterizes obesity and other metabolic diseases. While circulating bacterial DNA has been postulated as a common feature of obesity and even type 2 diabetes, almost no focus has been given to the existence and effects of bacteria in peripheral tissues, namely the adipose tissue. As a symbiont population, it is expected that gut microbiota modulate the immunometabolism of the host, thus influencing energy balance mechanisms and inflammation. Gut inflammatory signals cause direct deleterious inflammatory responses in adipose tissue and may also affect key gut neuroendocrine mechanisms governing nutrient sensing and energy balance, like incretins and ghrelin, which play a role in the gut-brain-adipose tissue axis. Thus, it is of major importance to disclose how gut microbiota and derived signals modulate neuroendocrine and inflammatory pathways, which contribute to the dysfunction of adipose tissue and to the metabolic sequelae of obesity and related disorders. This review summarizes the current knowledge regarding these topics and identifies new perspectives in this field of research, highlighting new pathways toward the reduction of the inflammatory burden of metabolic diseases.

The Effects of a Very-Low-Calorie Ketogenic Diet on the Intestinal Barrier Integrity and Function in Patients with Obesity: A Pilot Study

The very-low-calorie ketogenic diet (VLCKD) is effective and safe for obese individuals, but limited information exists on its impact on the intestinal barrier. This study analyzed the effects of 8 weeks of VLCKD on 24 obese patients (11M/13F). Carbohydrate intake was fixed at 20-50 g/day, while protein and lipid intake varied from 1-1.4 g/kg of ideal body weight and 15-30 g per day, respectively. Daily calorie intake was below 800 kcal. The lactulose-mannitol absorption test assessed small intestinal permeability. Multiple markers, such as serum and fecal zonulin, fatty acid-binding protein, diamine oxidase concentrations, urinary dysbiosis markers (indican and skatole), and circulating lipopolysaccharide levels, were analyzed. Inflammation markers (serum interleukin 6, 8, 10, and tumor necrosis factor-α concentrations) were also evaluated. The results showed significant reductions in weight, BMI, and waist circumference post-diet. However, the lactulose-mannitol ratio increased by 76.5%, and a significant increase in dysbiosis markers at the end of the diet occurred. This trend was particularly evident in a subgroup of patients. Despite initial benefits, the VLCKD might negatively affect the intestinal barrier function in obese patients, potentially worsening their compromised intestinal balance.

Fecal and Urinary Adipokines as Disease Biomarkers

The use of biomarkers is of great clinical value for the diagnosis and prognosis of disease and the assessment of treatment efficacy. In this context, adipokines secreted from adipose tissue are of interest, as their elevated circulating levels are associated with a range of metabolic dysfunctions, inflammation, renal and hepatic diseases and cancers. In addition to serum, adipokines can also be detected in the urine and feces, and current experimental evidence on the analysis of fecal and urinary adipokine levels points to their potential as disease biomarkers. This includes increased urinary adiponectin, lipocalin-2, leptin and interleukin-6 (IL-6) levels in renal diseases and an association of elevated urinary chemerin as well as urinary and fecal lipocalin-2 levels with active inflammatory bowel diseases. Urinary IL-6 levels are also upregulated in rheumatoid arthritis and may become an early marker for kidney transplant rejection, while fecal IL-6 levels are increased in decompensated liver cirrhosis and acute gastroenteritis. In addition, galectin-3 levels in urine and stool may emerge as a biomarker for several cancers. With the analysis of urine and feces from patients being cost-efficient and non-invasive, the identification and utilization of adipokine levels as urinary and fecal biomarkers could become a great advantage for disease diagnosis and predicting treatment outcomes. This review article highlights data on the abundance of selected adipokines in urine and feces, underscoring their potential to serve as diagnostic and prognostic biomarkers.

Gut Microbiota and Time-Restricted Feeding/Eating: A Targeted Biomarker and Approach in Precision Nutrition

Each individual has a unique gut microbiota; therefore, the genes in our microbiome outnumber the genes in our genome by about 150 to 1. Perturbation in host nutritional status influences gut microbiome composition and vice versa. The gut microbiome can help in producing vitamins, hormones, and other active metabolites that support the immune system; harvest energy from food; aid in digestion; protect against pathogens; improve gut transit and function; send signals to the brain and other organs; oscillate the circadian rhythm; and coordinate with the host metabolism through multiple cellular pathways. Gut microbiota can be influenced by host genetics, medications, diet, and lifestyle factors from preterm to aging. Aligning with precision nutrition, identifying a personalized microbiome mandates the provision of the right nutrients at the right time to the right patient. Thus, before prescribing a personalized treatment, it is crucial to monitor and count the gut flora as a focused biomarker. Many nutritional approaches that have been developed help in maintaining and restoring an optimal microbiome such as specific diet therapy, nutrition interventions, and customized eating patterns. One of these approaches is time-restricted feeding/eating (TRF/E), a type of intermittent fasting (IF) in which a subject abstains from food intake for a specific time window. Such a dietary modification might alter and restore the gut microbiome for proper alignment of cellular and molecular pathways throughout the lifespan. In this review, we have highlighted that the gut microbiota would be a targeted biomarker and TRF/E would be a targeted approach for restoring the gut-microbiome-associated molecular pathways such as hormonal signaling, the circadian system, metabolic regulators, neural responses, and immune-inflammatory pathways. Consequently, modulation of the gut microbiota through TRF/E could contribute to proper utilization and availability of the nutrients and in this way confer protection against diseases for harnessing personalized nutrition approaches to improve human health.

Study protocol for cholera vaccination as a model to measure the inflammatory response in the gut: A case of modulation with a Lactobacillus plantarum K8 lysate

It is crucial for human health that the immune system of the gastrointestinal tract works effectively. Dietary modulation is one of the factors that regulate the immune response in the gut. This study aims to develop a safe human challenge model to study gastrointestinal inflammation and immune function. This study focuses on evaluating gut stimulation induced by the oral cholera vaccine in healthy people. In addition, this paper describes the study design for assessing the efficacy and safety of a probiotic lysate, identifying whether functional ingredients in food can modulate inflammatory response induced by oral cholera vaccine. Forty-six males aged 20 to 50 with healthy bowel habits will be randomly allocated to the placebo or intervention group. Participants will consume 1 capsule of probiotic lysate or placebo twice daily for 6 weeks, take oral cholera vaccines on visit 2 (day 15) and visit 5 (day 29). The level of fecal calprotectin, a marker of gut inflammation, will be the primary outcome. The changes of cholera toxin-specific antibody levels and local/systemic inflammatory responses will be evaluated in blood. The purpose of this study is to evaluate gut stimulation of the oral cholera vaccine and investigate the effect of a probiotic lysate on improving the mild inflammatory response induced by the vaccine or supporting the immune response in healthy subjects. Trial registration: * This trial is registered in the International Clinical Trials Registry Platform of WHO (ICTRP, registration number: KCT0002589).

Intestinal Barrier Permeability in Obese Individuals with or without Metabolic Syndrome: A Systematic Review

Altered intestinal barrier permeability has been associated with obesity and its metabolic and inflammatory complications in animal models. The purpose of this systematic review is to assess the evidence regarding the association between obesity with or without Metabolic Syndrome (MetS) and alteration of the intestinal barrier permeability in humans. A systematic search of the studies published up until April 2022 in Latin America & Caribbean Health Sciences Literature (LILACS), PubMed, Scopus, Embase, and ScienceDirect databases was conducted. The methodological quality of the studies was assessed using the Newcastle–Ottawa scale (NOS) and the Agency for Healthcare Research and Quality (AHRQ) checklist. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) framework was used to assess the quality of the evidence. Eight studies were included and classified as moderate to high quality. Alteration of intestinal barrier permeability was evaluated by zonulin, lactulose/mannitol, sucralose, sucrose, lactulose/L-rhamnose, and sucralose/erythritol. Impaired intestinal barrier permeability measured by serum and plasma zonulin concentration was positively associated with obesity with MetS. Nonetheless, the GRADE assessment indicated a very low to low level of evidence for the outcomes. Thus, clear evidence about the relationship between alteration of human intestinal barrier permeability, obesity, and MetS was not found.

Interesterified palm oil increases intestinal permeability, promotes bacterial translocation, alters inflammatory parameters and tight-junction protein genic expression in Swiss mice

High-fat diets seem to have a negative influence on the development of obesity and the processes associated with low-grade chronic systemic inflammation. In recent years, partial hydrogenated oil, rich in trans isomers, has been associated with deleterious health effects. It has been replaced by interesterified fat (IF). However, there is no evidence whether IF ingestion can exert adverse effects on the intestinal mucosa. Thus, this study aimed to evaluate the effect of IF on the intestinal mucosa of male Swiss mice fed a normal or high-fat diet, focusing on its effects on intestinal permeability and bacterial translocation and its possible damage to the intestinal epithelium. The animals were divided into 4 groups: Control (C) and Interesterified Control (IC) groups (10 En% lipids from unmodified fat or interesterified fat, respectively) and High Fat (HF) and Interesterified High Fat (IHF) groups (45 En% lipids from unmodified fat or interesterified fat, respectively). Compare to C, the IC, HF, and IHF groups presented flattened epithelium, a shorter villi length and a lower percentage of goblet cells, less mucin 2, an increased oxidative stress and more inflammatory cells, higher IL-1β, IL-17, and IL-23 levels. These groups also presented increased intestinal permeability and gene expression of the protein claudin 2, while JAM-A and claudin 1 gene expression was reduced. IC and IHF increased IL-6 levels while reducing occludin expression. In addition, the IC group also presented a mucosa with lesions of low intensity in the ileum, an increased mucin 5ac, TNF-α levels, and reduced occludin expression in the distal jejunum. Moreover, there was a significant increase in bacterial translocation in the IC group to blood, liver, and lungs, while HF and IHF groups presented bacterial translocation which was restricted to the mesenteric lymph nodes. In summary, our results supported the hypothesis that IF added to a normolipidic diet can be considered harmful or even worse when compared to a HF.

Molecular and Pathophysiological Links between Metabolic Disorders and Inflammatory Bowel Diseases

Despite considerable epidemiological evidence indicating comorbidity between metabolic disorders, such as obesity, type 2 diabetes, and non-alcoholic fatty liver disease, and inflammatory bowel diseases (IBD), such as Crohn’s disease and ulcerative colitis, as well as common pathophysiological features shared by these two categories of diseases, the relationship between their pathogenesis at molecular levels are not well described. Intestinal barrier dysfunction is a characteristic pathological feature of IBD, which also plays causal roles in the pathogenesis of chronic inflammatory metabolic disorders. Increased intestinal permeability is associated with a pro-inflammatory response of the intestinal immune system, possibly leading to the development of both diseases. In addition, dysregulated interactions between the gut microbiota and the host immunity have been found to contribute to immune-mediated disorders including the two diseases. In connection with disrupted gut microbial composition, alterations in gut microbiota-derived metabolites have also been shown to be closely related to the pathogeneses of both diseases. Focusing on these prominent pathophysiological features observed in both metabolic disorders and IBD, this review highlights and summarizes the molecular risk factors that may link between the pathogeneses of the two diseases, which is aimed at providing a comprehensive understanding of molecular mechanisms underlying their comorbidity.

The pathogenic oral-gut-liver axis: new understandings and clinical implications

INTRODUCTION

Oral health is closely related to extra-oral disease status, as may be represented by the manifestations of gastrointestinal and liver diseases.

AREAS COVERED

This review focuses on the roles that the oral-gut or the oral-gut-liver axis play in the pathogenesis of inflammatory bowel disease, colorectal cancer, metabolic fatty liver disease, and nonalcoholic steatohepatitis. The discussion will begin with clinical data, including data from preclinical animal models, to elucidate mechanisms. We will also discuss ways to target oral dysbiosis and oral inflammation to treat gastrointestinal and liver diseases.

EXPERT OPINION

Several studies have demonstrated that oral pathobionts can translocate to the gastrointestinal tract where they contribute to inflammation and tumorigenesis. Furthermore, oral bacteria that migrate to the gastrointestinal tract can disseminate to the liver and cause hepatic disease. Thus, oral bacteria that ectopically colonize the intestine may serve as biomarkers for gastrointestinal and liver diseases. Also, understanding the characteristics of the oral-gut and oral-gut-liver microbial and immune axes will provide new insights into the pathogenesis of these diseases.

Intestinal barrier function in obesity with or without metabolic syndrome: a systematic review protocol

INTRODUCTION

Intestinal barrier function is dependent on the structure and function of intestinal epithelial cells and paracellular pathway. The derangement of the intestinal barrier function can originate from conditions involving local and systemic chronic inflammation and metabolic diseases such as obesity and metabolic disorders. This study aims to describe a systematic review protocol investigating if obesity with or without metabolic syndrome is associated with an altered intestinal barrier function.

METHODS AND ANALYSIS

This protocol is guided by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols. The databases to be searched are PubMed, Embase, Scopus, Science Direct and Web of Science. The systematic review will include original articles with adults and the elderly, who present obesity with or without metabolic syndrome, that address the intestinal barrier function. Two independent reviewers will perform study selection, data extraction and methodological quality assessment. Key information will be tabulated and a narrative synthesis will be conducted. The Grading of Recommendation, Assessment, Development and Evaluation framework will be used to assess the quality of evidence concerning the associations between intestinal barrier function and obesity with or without metabolic syndrome. The present protocol will assist in producing a systematic review that addresses if obesity with or without metabolic syndrome alters intestinal barrier function.

ETHICS AND DISSEMINATION

No ethical statement will be required. The results will be disseminated through a peer-reviewed publication and conference presentations.

PROSPERO REGISTRATION NUMBER

CRD42020178658.

Association of clinical characteristics and lifestyle factors with fecal S100/calgranulin concentrations in healthy dogs

Background

Fecal S100/calgranulin (S100A12 and calprotectin) concentrations are useful markers of gastrointestinal inflammation in dogs. In people, fecal S100/calgranulin concentrations are affected by age, obesity, diet and other lifestyle factors. Knowledge about the effects of such factors on fecal S100/calgranulin concentrations in dogs is currently scarce.

Objective

To evaluate the association between several factors and fecal S100/calgranulin concentrations in a large cohort of healthy adult dogs.

Methods

Single‐spot fecal samples from 181 healthy pet dogs and data derived from a standard questionnaire served to evaluate the effect of age, sex, reproductive status, body weight and body condition, breed type and size, vaccination, endoparasite treatment, diet, environment and travel history on fecal S100/calgranulin concentrations and the fecal calgranulin ratio (fCalR).

Results

Univariate analysis showed a significant association of reproductive status (in female dogs) and breed size with fecal S100A12, fecal calprotectin and fCalR. Breed type was linked to fecal S100A12 concentrations and fCalR; recent vaccination (particularly with a vaccine against canine parvovirus) to fCalR. In multivariate models, breed size was linked to fecal S100A12 and calprotectin concentrations, and recent vaccination affected S100A12 concentrations.

Conclusions

Breed size, recent vaccination and reproductive status in female dogs can affect fecal S100/calgranulin concentrations, and these biomarkers should be interpreted in light of those confounding factors. The utility of reference intervals for fecal canine S100/calgranulin concentrations might be improved through stratification by sex/reproductive status and breed size. Fecal canine S100/calgranulin concentrations are not confounded by age, body condition, deworming, diet, environment or travel history.

Effect of the ingestion of vegetable oils associated with energy-restricted normofat diet on intestinal microbiota and permeability in overweight women

Previous studies suggest that the type of dietary fatty acid may modulate the intestinal bacterial ecosystem. However, this effect is still inconclusive. Thus, the aim of this study was to investigate the effect of the intake of vegetable oils rich in different types of fatty acids, associated with energy-restricted normofat diets, on the composition of intestinal microbiota and permeability, on LPS concentrations, and fecal short chain fatty acids and pH. This was a 9 consecutive weeks (±5 days), randomized, parallel, double-blind clinical trial. Overweight women received daily breakfast containing 25 mL of one of the test oils: soybean oil (n = 17), extra virgin olive oil (n = 19) or coconut oil (n = 16). Blood, fecal and urine samples were collected on the first and last day of the experiment for the analysis of the variables of interest. The consumption of the three oils did not affect the diversity and relative abundance of intestinal bacteria. We observed an increase in bacterial richness estimated by the Chao 1 index, and a reduction in the concentration of isovaleric fatty acid in the group that ingested soybean oil. Paracellular and transcellular permeability increased after the ingestion of extra virgin olive oil and coconut oil. However, LPS concentrations remained unchanged. The intake of different types of fatty acids associated with the energy-restricted normofat diet modestly affected the intestinal microbiota and permeability, without resulting in metabolic endotoxemia in overweight women.

Serum zonulin measured by enzyme-linked immunosorbent assay may not be a reliable marker of small intestinal permeability in healthy adults

The association between intestinal permeability (IP) and body composition remains unclear. The gold standard differential sugar-absorption test is arduous to complete, with zonulin being increasingly used as an independent biomarker of IP. This pilot study aimed to explore the association between small IP, zonulin concentrations, and body composition in healthy adults. The urinary lactulose-rhamnose ratio was used to measure small IP. Serum zonulin, lipopolysaccharide (LPS) and high-sensitivity C-reactive protein (hs-CRP) were analyzed in serum. Body composition was measured using dual-energy X-ray absorptiometry and anthropometric measurements were collected. In total, 34 participants were included (12 males, median age 28 years, body mass index 24 kg/m², waist circumference 77cm). No correlation was observed between the lactulose-rhamnose ratio and zonulin (r = -.016, P = .929). The lactulose-rhamnose ratio displayed a strong positive correlation with LPS (n 20, r = .536, P = .018) but did not correlate with body composition measures. Conversely, zonulin displayed a moderate positive correlation with waist circumference (r = .437, P = .042) in female participants and hs-CRP (r = .485, P = .004) in all participants. These findings raise important considerations for the measurement of small IP, warranting exploration in larger powered studies that address the limitations of the present study.

Impact of Laparoscopic Sleeve Gastrectomy on Gut Permeability in Morbidly Obese Subjects

BACKGROUND

Recent studies have suggested that obesity is associated with an increased intestinal permeability as well as an altered microbiota profile. These conditions can promote the translocation of lipopolysaccharide into the circulation and, subsequently, contribute to the observed systemic inflammation. Our aim was to assess gut permeability in patients with obesity compared to non-obese subjects as well as after excessive weight loss following laparoscopic sleeve gastrectomy (LSG).

METHODS

We analyzed the dietary intake, metabolic and inflammatory markers, gut permeability (four-probe sugar test), and microbiota composition in 17 morbidly obese patients before and after LSG as well as in 17 age- and gender-matched non-obese subjects. Additionally, we compared gut permeability and inflammatory markers in patients of different stages of obesity.

RESULTS

Patients with obesity showed elevated levels of C-reactive protein and lipopolysaccharide-binding protein as compared to non-obese subjects, but no differences were noted for gut permeability between these two groups. LSG led to improvements in metabolic and inflammatory parameters in the obese patients. Moreover, gastroduodenal as well as small intestinal permeability decreased, whereas colonic permeability increased after surgery. Regarding gut microbiota, differences were noted for main phyla and alpha-diversity between non-obese and obese subjects. After surgery, the composition of the microbiota showed a tendency toward the pattern of the non-obese group.

CONCLUSIONS

Gut permeability is not dependent on body mass index, whereas weight loss after LSG initiates distinct changes in gastroduodenal, intestinal, and colonic permeability. These changes do not seem to be associated with changes in the microbiota composition.

CLINICAL TRIAL REGISTRY NUMBER AND WEBSITE

The trials were registered at https://www.drks.de/drks_web/ with the number DRKS00009008 and DRKS00006210.

Intestinal plasticity in response to nutrition and gastrointestinal surgery

The plasticity of a material corresponds to its capacity to change its feature under the effect of an external action. Intestinal plasticity could be defined as the ability of the intestine to modify its size or thickness and intestinal cells to modulate their absorption and secretion functions in response to external or internal cues/signals. This review will focus on intestinal adaptation mechanisms in response to diet and nutritional status. These physiological mechanisms allow a fine and rapid adaptation of the gut to promote absorption of ingested food, but they can also lead to obesity in response to overnutrition. This plasticity could thus become a therapeutic target to treat not only undernutrition but also obesity. How the intestine adapts in response to 2 types of surgical remodeling of the digestive tract-extensive bowel resection leading to intestinal failure and surgical treatment of pathological obesity (ie, bariatric surgeries)-will also be reviewed.

Serum endotoxin, gut permeability and skeletal muscle metabolic adaptations following a short term high fat diet in humans

BACKGROUND

Our previous work demonstrated that a short-term high fat diet (HFD) increased fasting serum endotoxin, altered postprandial excursions of serum endotoxin, and led to metabolic and transcriptional responses in skeletal muscle in young, healthy male humans.

PURPOSE

The purpose of the present study was to determine if a short-term high fat diet: 1) increases intestinal permeability and, in turn, fasting endotoxin concentrations and 2) decreases postprandial skeletal muscle fat oxidation.

METHODS

Thirteen normal weight young adult males (BMI 23.1 ± 0.8 kg/m², age 22.2 ± 0.4 years) were fed a control diet (55% carbohydrate, 30% fat, 9% of which was saturated, 15% protein) for two weeks, followed by 5 days of an isocaloric HFD (30% carbohydrate, 55% fat, 25% of which was saturated, 15% protein, isocaloric to the control diet). Intestinal permeability (via four sugar probe test) was assessed in the fasting state. Both before and after the HFD, a high fat meal challenge (HFM, 820 kcal, 25% carbohydrate, 63% fat, 26% of which was saturated, and 12% protein) was administered. After an overnight fast, blood samples were collected before and every hour for 4 h after the HFM to assess endotoxin, and other serum blood measures. Muscle biopsies were obtained from the vastus lateralis before and 4 h after the HFM in order to assess substrate oxidation (glucose, fatty acid and pyruvate) using radiolabeled techniques. Insulin sensitivity was assessed via intravenous glucose tolerance test. Intestinal permeability, blood samples and muscle biopsies were assessed in the same manner before and following the HFD.

MAIN FINDINGS

Intestinal permeability was not affected by HFD (p > 0.05), but fasting endotoxin increased two fold following the HFD (p = 0.04). Glucose oxidation and fatty acid oxidation in skeletal muscle homogenates significantly increased after the HFM before the HFD (+97%, and +106% respectively) but declined after the HFM following 5 days of the HFD (-24% and +16% respectively). Fatty acid suppressibility of pyruvate oxidation increased significantly after the HFM (+32%) but this physiological effect was abolished following 5 days of the HFD (+7%). Insulin sensitivity did not change following the HFD.

CONCLUSION

These findings demonstrate that in healthy young men, consuming an isocaloric HFD for 5 days increases fasting endotoxin, independent of changes in gut permeability. These changes in endotoxin are accompanied by a broad effect on skeletal muscle substrate metabolism including increases in postprandial fat oxidation. Importantly, the latter occurs independent of changes in body weight and whole-body insulin sensitivity.

Intestinal barrier function in morbid obesity: results of a prospective study on the effect of sleeve gastrectomy

BACKGROUND

Obesity has been associated with impaired intestinal barrier function. It is not known whether bariatric surgery leads to changes in intestinal barrier function. We hypothesized that obesity is associated with disturbances in gastrointestinal barrier function, and that after bariatric surgery barrier function will improve.

METHODS

Prospective single center study in which we assessed segmental gut permeability by urinary recovery of a multisugar drink in 27 morbidly obese (BMI 43.3 ± 1.1 kg/m²) and 27 age and gender matched lean subjects (BMI 22.9 ± 0.43 kg/m²). Fecal calprotectin, SCFAs, plasma cytokines, and hsCRP were assessed as inflammatory and metabolic markers. Comparisons: (a) morbidly obese subjects vs. controls and (b) 2 and 6 months postsleeve vs. presleeve gastrectomy (n = 14). In another group of 10 morbidly obese and 11 matched lean subjects colonic and ileal biopsies were obtained in order to measure gene transcription of tight junction proteins.

RESULTS

Gastroduodenal permeability (urinary sucrose recovery) was significantly increased in obese vs. lean controls (p < 0.05). Small intestinal and colonic permeability (urinary recovery of lactulose/L-rhamnose and sucralose/erythritol, respectively) in obese subjects were not significantly different from controls. Morbidly obese subjects had a proinflammatory systemic and intestinal profile compared with lean subjects. After sleeve gastrectomy BMI decreased significantly (p < 0.001). Postsleeve gastroduodenal permeability normalized to values that do not differ from lean controls.

CONCLUSIONS

Gastroduodenal permeability, but not small intestinal or colonic permeability, is significantly increased in morbidly obese patients. After sleeve gastrectomy, gastroduodenal permeability normalized to values in the range of lean controls. Thus, the proximal gastrointestinal barrier is compromised in morbid obesity and is associated with a proinflammatory intestinal and systemic profile.

Role for diet in normal gut barrier function: developing guidance within the framework of food-labeling regulations

A reduction in intestinal barrier function is currently believed to play an important role in pathogenesis of many diseases, as it facilitates passage of injurious factors such as lipopolysaccharide, peptidoglycan, whole bacteria, and other toxins to traverse the barrier to damage the intestine or enter the portal circulation. Currently available evidence in animal models and in vitro systems has shown that certain dietary interventions can be used to reinforce the intestinal barrier to prevent the development of disease. The relevance of these studies to human health is unknown. Herein, we define the components of the intestinal barrier, review available modalities to assess its structure and function in humans, and review the available evidence in model systems or perturbations in humans that diet can be used to fortify intestinal barrier function. Acknowledging the technical challenges and the present gaps in knowledge, we provide a conceptual framework by which evidence could be developed to support the notion that diet can reinforce human intestinal barrier function to restore normal function and potentially reduce the risk for disease. Such evidence would provide information on the development of healthier diets and serve to provide a framework by which federal agencies such as the US Food and Drug Administration can evaluate evidence linking diet with normal human structure/function claims focused on reducing risk of disease in the general public.

Comparison of the microbiome, metabolome, and lipidome of obese and non-obese horses

Metabolic diseases such as obesity and type 2 diabetes in humans have been linked to alterations in the gastrointestinal microbiota and metabolome. Knowledge of these associations has improved our understanding of the pathophysiology of these diseases and guided development of diagnostic biomarkers and therapeutic interventions. The cellular and molecular pathophysiology of equine metabolic syndrome (EMS) and obesity in horses, however, remain ill-defined. Thus, the objectives of this study were to characterize the fecal microbiome, fecal metabolome, and circulating lipidome in obese and non-obese horses. The fecal microbiota, fecal metabolome, and serum lipidome were evaluated in obese (case) horses (n = 20) and non-obese (control) horses (n = 20) matched by farm of origin (n = 7). Significant differences in metabolites of the mitochondrial tricarboxylic acid cycle and circulating free fatty acids were identified in the obese horses compared to the non-obese horses. These results indicate that the host and bacterial metabolism should be considered important in obese horses. Further studies to determine whether these associations are causal and the mechanistic basis of the association are warranted because they might reveal diagnostic biomarkers and therapeutic interventions to mitigate obesity, EMS, and sequelae including laminitis.

Interleukin-17/interleukin-17 receptor axis elicits intestinal neutrophil migration, restrains gut dysbiosis and lipopolysaccharide translocation in high-fat diet-induced metabolic syndrome model

Sound evidence supports a role for interleukin-17 (IL-17) -producing γδ T cells and IL-17-producing helper T (Th17) cells in intestinal homeostasis, especially in intestinal barrier integrity. In the present study, we aimed to evaluate the role of IL-17 cytokine in the regulation of intestinal immunity and obesity-induced metabolic syndrome (MetS) in an experimental murine model. C57BL/6 wild-type (WT) mice and mice lacking the IL-17 cytokine receptor (IL-17RA^-/- ) were fed either a control diet (CD) or a high-fat diet (HFD) for 9 weeks. Our data demonstrate that IL-17RA^-/- mice are protected against obesity, but develop hyperglycemia, hyperinsulinemia and insulin resistance. In parallel, HFD-fed IL-17RA^-/- mice display intense inflammation in the ileum compared with WT mice on the HFD. IL-17RA^-/- mice fed the HFD exhibit impaired neutrophil migration to the intestinal mucosa and reduced gene expression of the CXCL-1 chemokine and CXCR-2 receptor in the ileum. Interestingly, the populations of neutrophils (CD11b⁺  Ly6G⁺ ) and anti-inflammatory macrophages (CD11b⁺  CX3CR1⁺ ) are increased in the mesenteric lymph nodes of these mice. IL-17RA^-/- mice on the HFD also display increased commensal bacterial translocation into the bloodstream and elevated lipopolysaccharide (LPS) levels in the visceral adipose tissue (VAT). Metagenomic analysis of bacterial 16S gene revealed increased Proteobacteria and Bacteroidetes phyla, the main representatives of Gram-negative bacteria, and reduced Akkermansia muciniphila in the fecal samples of IL-17RA^-/- mice fed the HFD. Together, these data indicate that the IL-17/IL-17R axis drives intestinal neutrophil migration, limits gut dysbiosis and attenuates LPS translocation to VAT, resulting in protection to MetS.

Role of gut microbiota in chronic low-grade inflammation as potential driver for atherosclerotic cardiovascular disease: a systematic review of human studies

A hallmark of obesity is chronic low-grade inflammation, which plays a major role in the process of atherosclerotic cardiovascular disease (ACVD). Gut microbiota is one of the factors influencing systemic immune responses, and profound changes have been found in its composition and metabolic function in individuals with obesity. This systematic review assesses the association between the gut microbiota and markers of low-grade inflammation in humans. We identified 14 studies which were mostly observational and relatively small (n = 10 to 471). The way in which the microbiome is analysed differed extensively between these studies. Lower gut microbial diversity was associated with higher white blood cell counts and high sensitivity C-reactive protein (hsCRP) levels. The abundance of Bifidobacterium, Faecalibacterium, Ruminococcus and Prevotella were inversely related to different markers of low-grade inflammation such as hsCRP and interleukin (IL)-6. In addition, this review speculates on possible mechanisms through which the gut microbiota can affect low-grade inflammation and thereby ACVD. We discuss the associations between the microbiome and the inflammasome, the innate immune system, bile acids, gut permeability, the endocannabinoid system and TMAO. These data reinforce the importance of human research into the gut microbiota as potential diagnostic and therapeutic strategy to prevent ACVD.

Efficacy of an Anthocyanin and Prebiotic Blend on Intestinal Environment in Obese Male and Female Subjects

Background

Anthocyanins and prebiotics impact overall health and wellness, likely through modulation of the microbiota and the intestinal ecosystem.

Objectives

An 8-week open-label study in male and female volunteers with uncomplicated obesity was designed to study the efficacy of an anthocyanin and prebiotic blend in modulating intestinal microbiota and intestinal inflammation.

Results

After 8 weeks of daily supplementation, participants had a significant decrease in Firmicutes (p < 0.001) and Actinobacteria (p < 0.001) and a significant increase in Bacteroidetes (p < 0.001). Bowel habits were improved as evidenced by reductions in the severity of bloating (p < 0.05), gas (p=0.035), and abdominal pain (p=0.015) as well as significant improvements in stool consistency (p < 0.05). Finally, a nonsignificant decrease in the inflammatory marker fecal calprotectin was seen (p=0.107). The supplement was safe and well tolerated.

Conclusions

The results suggest that regular consumption of the anthocyanin-prebiotic blend positively modulated the intestinal ecosystem and provided insights into the mechanisms of action and its impact on health benefits.

A Comparative Study of Serum Biochemistry, Metabolome and Microbiome Parameters of Clinically Healthy, Normal Weight, Overweight, and Obese Companion Dogs

The aim of this study was to compare fecal microbiome, plasma, fecal and urine metabolomes, and serum biochemistry of adult companion dogs according to body condition scores. Blood, serum/plasma, urine, and fecal samples were collected from 66 clinically healthy, adult companion dogs of either normal weight (NW), overweight (OW), or obese dogs (OB). analyses included fecal microbiome analyses via 16S ribosomal RNA gene amplicon; sequencing, nontargeted plasma, fecal, and urine metabolomics using liquid chromatography/gas chromatography-mass; spectrometry, and serum biochemistry for each dog. Few significant differences in serum biochemistry and fecal microbiome Operational Taxonomic Unit (OTU) were found between weight groups and there was high OTU variation between individual dogs. NW dogs had higher relative abundance of the genus Eubacterium (log-fold change 4.3, adjusted P value = .003) and lower relative abundance of the family Bifidobacteriaceae (log-fold change -3.6, adjusted P value = .02) compared to OB dogs. The microbiome of NW dogs had higher OTU richness compared with OB dogs. Metabolome analysis showed 185 plasma, 37 fecal, and 45 urine metabolites that significantly differed between NW and OW or OB dogs. There were notable significant differences in relative abundance of several plasma phospholipid moieties and fecal volatile fatty acids between weight phenotypes. The combinations of host and gut microbiota and metabolic shifts suggest a pattern that could help detection of early metabolic changes in overweight dogs before the development of obesity related disease. The results of this study support the need for continued investigation into sensitive measures of metabolic aberrancies in overweight dogs.

Epithelial Barrier Function in Gut-Bone Signaling

The intestinal epithelial barrier plays an essential role in maintaining host homeostasis. The barrier regulates nutrient absorption as well as prevents the invasion of pathogenic bacteria in the host. It is composed of epithelial cells, tight junctions, and a mucus layer. Several factors, such as cytokines, diet, and diseases, can affect this barrier. These factors have been shown to increase intestinal permeability, inflammation, and translocation of pathogenic bacteria. In addition, dysregulation of the epithelial barrier can result in inflammatory diseases such as inflammatory bowel disease. Our lab and others have also shown that barrier disruption can have systemic effects including bone loss. In this chapter, we will discuss the current literature to understand the link between intestinal barrier and bone. We will discuss how inflammation, aging, dysbiosis, and metabolic diseases can affect intestinal barrier-bone link. In addition, we will highlight the current suggested mechanism between intestinal barrier and bone.

Obesity and inflammatory bowel disease: diagnostic and therapeutic implications

PURPOSE OF REVIEW

The review summarizes our current understanding of how obesity impacts diagnostic studies and therapies used in inflammatory bowel disease (IBD) as well as the safety and efficacy of medical and surgical weight loss therapies in the obese IBD patient.

RECENT FINDINGS

Many of the diagnostic tools we rely on in the identification and monitoring of IBD can be altered by obesity. Obesity is associated with increased acute phase proteins and fecal calprotectin. It can be more difficult to obtain and interpret cross sectional imaging of obese patients. Recent studies have also shown that common therapies used to treat IBD may be less effective in the obese population and may impact comorbid disease. Our understanding of how best to measure obesity is evolving. In addition to BMI, studies now include measures of visceral adiposity and subcutaneous to visceral adiposity ratios. An emerging area of interest is the safety and efficacy of obesity treatment including bariatric surgery in patients with IBD. A remaining question is how weight loss may alter the course of IBD.

SUMMARY

The proportion of obese IBD patients is on the rise. Caring for this population requires a better understanding of how obesity impacts diagnostic testing and therapeutic strategies. The approach to weight loss in this population is complex and future studies are needed to determine the safety of medical or surgical weight loss and its impact on the course of disease.

Multiple gut-liver axis abnormalities in children with obesity with and without hepatic involvement

BACKGROUND

Gut-liver axis (GLA) dysfunction appears to play a role in obesity and obesity-related hepatic complications.

OBJECTIVES

This study sought to concurrently explore several GLA components in a paediatric obese population with/without liver disease.

METHODS

Thirty-two children (mean age 11.2 years) were enrolled: nine controls with normal weight and 23 patients with obesity (OB+). Of the 23 patients OB(+), 12 had not steatosis (ST-), and 11 had steatosis (ST+) (associated [n = 8] or not [n = 3] with hypertransaminasaemia [ALT +/-]). Subjects were characterized by using auxologic, ultrasonographic and laboratory parameters. A glucose hydrogen breath test was performed to test for small intestinal bacterial overgrowth, a urinary lactulose/mannitol ratio (LMR) was obtained to assess intestinal permeability, and tests for transaminases, blood endogenous ethanol, endotoxin and faecal calprotectin were also conducted.

RESULTS

Eleven out of 23 patients OB(+) (p < 0.05) exhibited pathological (>90th percentile of the control group values) LMR, with values paralleling the grade of liver involvement (normal weight < OB[+] < OB[+]ST[+]ALT[-] < OB[+)]ST[+]ALT[+] [p < 0.05]). LMR significantly correlated with ethanolaemia (r = 0.38, p = 0.05) and endotoxaemia (r = 0.48, p = 0.015) concentrations. Increased permeability was a risk factor for the development of steatosis (p < 0.002). SIBO was present only in patients with obesity. Faecal calprotectin concentrations were within normal limits in all subjects.

CONCLUSIONS

Increased permeability, endogenous ethanol and systemic endotoxin concentrations reflect some GLA dysfunction in obesity and its hepatic complications. Pending further results to establish their potential causative roles, the modulation of the GLA appears to represent a possible target for the prevention and treatment of these conditions.

Microbiota, cirrhosis, and the emerging oral-gut-liver axis

Cirrhosis is a prevalent cause of morbidity and mortality, especially for those at an advanced decompensated stage. Cirrhosis development and progression involves several important interorgan communications, and recently, the gut microbiome has been implicated in pathophysiology of the disease. Dysbiosis, defined as a pathological change in the microbiome, has a variable effect on the compensated versus decompensated stage of cirrhosis. Adverse microbial changes, both in composition and function, can act at several levels within the gut (stool and mucosal) and have also been described in the blood and oral cavity. While dysbiosis in the oral cavity could be a source of systemic inflammation, current cirrhosis treatment modalities are targeted toward the gut-liver axis and do not address the oral microbiome. As interventions designed to modulate oral dysbiosis may delay progression of cirrhosis, a better understanding of this process is of the utmost importance. The concept of oral microbiota dysbiosis in cirrhosis is relatively new; therefore, this review will highlight the emerging role of the oral-gut-liver axis and introduce perspectives for future research.

The human gut microbiome of Latin America populations: a landscape to be discovered

PURPOSE OF REVIEW

The gut microbiome is critical for human health, and its alteration is associated with intestinal, autoimmune and metabolic diseases. Numerous studies have focused on prevention or treatment of dysbiotic microbiome to reduce the risk or effect of these diseases. A key issue is to define the microbiome associated with the state of good health. The purpose of this review is to describe factors influencing the gut microbiome with special emphasis on contributions from Latin America. In addition, we will highlight opportunities for future studies on gut microbiome in Latin America.

RECENT FINDINGS

A relevant factor influencing gut microbiome composition is geographical location associated with specific genetic, dietary and lifestyle factors. Geographical specificities suggest that a universal 'healthy microbiome' is unlikely.

SUMMARY

Several research programs, mostly from Europe and North America, are extensively sequencing gut microbiome of healthy people, whereas data from Latin America remain scarce yet slowly increasing. Few studies have shown difference in the composition of gut microbiome between their local populations with that of other industrialized countries (North American populations). Latin America is composed of countries with a myriad of lifestyles, traditions, genetic backgrounds and socioeconomic conditions, which may determine differences in gut microbiome of individuals from different countries. This represents an opportunity to better understand the relationship between these factors and gut microbiome.

Prebiotic milk oligosaccharides prevent development of obese phenotype, impairment of gut permeability, and microbial dysbiosis in high fat-fed mice

Microbial dysbiosis and increased intestinal permeability are targets for prevention or reversal of weight gain in high-fat (HF) diet-induced obesity (DIO). Prebiotic milk oligosaccharides (MO) have been shown to benefit the host intestine but have not been used in DIO. We hypothesized that supplementation with bovine MO would prevent the deleterious effect of HF diet on the gut microbiota and intestinal permeability and attenuate development of the obese phenotype. C57BL/6 mice were fed a control diet, HF (40% fat/kcal), or HF + prebiotic [6%/kg bovine milk oligosaccharides (BMO) or inulin] for 1, 3, or 6 wk. Gut microbiota and intestinal permeability were assessed in the ileum, cecum, and colon. Addition of BMO to the HF diet significantly attenuated weight gain, decreased adiposity, and decreased caloric intake; inulin supplementation also lowered weight gain and adiposity, but this did not reach significance. BMO and inulin completely abolished the HF diet-induced increase in paracellular and transcellular permeability in the small and large intestine. Both BMO and inulin increased abundance of beneficial microbes Bifidobacterium and Lactobacillus in the ileum. However, inulin supplementation altered phylogenetic diversity and decreased species richness. We conclude that addition of BMO to the HF diet completely prevented increases in intestinal permeability and microbial dysbiosis and was partially effective to prevent weight gain in DIO.NEW & NOTEWORTHY This study provides the first report of the effects of prebiotic bovine milk oligosaccharides on the host phenotype of high-fat diet-induced obesity in mice.

Gut Microbiota and Complications of Liver Disease

Chronic liver disease, cirrhosis, and its complications are epidemic worldwide. Most complications are mediated through a dysfunctional gut-liver axis. New techniques have made culture-independent analysis of the gut microbiome widespread. With insight into an unfavorable microbiome (dysbiosis) and how it affects liver disease, investigators have discovered new targets to potentially improve outcomes. Dysbiosis is associated with endotoxemia and propagates liver injury due to nonalcoholic steatohepatitis and alcohol. The composition and functionality of the microbiome changes with the development of cirrhosis, decompensation, and with treatments for these conditions. Gut microbiota can be used to predict clinically relevant outcomes in cirrhosis.

Reinforcement of intestinal epithelial barrier by arabinoxylans in overweight and obese subjects: A randomized controlled trial: Arabinoxylans in gut barrier

BACKGROUND & AIMS

Obesity and metabolic diseases are associated with alterations in microbial composition and impaired gut barrier. Previous in vitro and animal studies have shown that arabinoxylans (AX) have the potential to modulate gut microbiota and gut barrier and therefore could have a protective role. Primary aim of the study was to investigate the effect of AX on intestinal permeability. Secondary aims included the effect of AX on gene transcription and protein expression of tight junctions (TJ), intestinal microbiota composition and activity, immune response and metabolic markers in overweight and obese individuals.

METHODS

In this randomized, double-blind, placebo-controlled trial, 47 overweight subjects were randomly assigned to groups receiving 7.5 g/d AX (n = 16), 15 g/d AX (n = 17) or 15 g/d placebo (n = 14) for 6 wks. Intestinal permeability was investigated using a multi-sugar test. Sigmoid colon tissue was obtained from a subgroup (n = 26) for analyzing gene transcription and mucosal expression of TJ proteins. Fecal samples were collected to assess microbial composition and activity. Furthermore, the production of cytokines by stimulated peripheral blood mononuclear cells (PBMCs) was examined. Blood was also sampled for measuring metabolic markers.

RESULTS

No significant changes in gastrointestinal permeability and TJ protein expression were observed after 6 wks AX supplementation compared to placebo. However, gene transcription of occludin was upregulated in the 7.5 g AX group, and transcription of claudin-3 and claudin-4 were upregulated in the 15 g AX group compared to placebo. Furthermore, fecal microbiota diversity was decreased after 6 wks 15 g AX treatment, but no change in relative abundance of dominant phyla was observed. AX intake significantly decreased fecal pH and increased fecal concentrations of total SCFAs, acetate, propionate and butyrate, compared to placebo. Additionally, a decreased TNFα production by stimulated PBMCs was observed after 15 g AX treatment. No changes in metabolic markers were detected.

CONCLUSIONS

Regular consumption of AX resulted in a more beneficial fermentation profile in overweight and obese individuals. Further studies are required to assess whether such fermentation profile will translate into improved gut barrier function and immune health. The trial has been registered at ClinicalTrials.gov with study ID number NCT01877044.

Gut permeability is related to body weight, fatty liver disease, and insulin resistance in obese individuals undergoing weight reduction

BACKGROUND

Obesity and associated metabolic disorders are related to impairments of the intestinal barrier.

OBJECTIVE

We examined lactulose:mannitol (Lac:Man) permeability in obese individuals with and without liver steatosis undergoing a weight-reduction program to test whether an effective weight-loss program improves gut barrier function and whether obese patients with or without liver steatosis differ in this function.

DESIGN

Twenty-seven adult, nondiabetic individuals [mean ± SD body mass index (BMI; in kg/m²): 43.7 ± 5.2; 78% with moderate or severe liver steatosis] were included in the follow-up intervention study (n = 13 by month 12). All patients reduced their weight to a mean ± SD BMI of 36.4 ± 5.1 within 12 mo. We assessed barrier functions by the oral Lac:Man and the fecal zonulin tests. Insulin resistance was assessed by the homeostatic model assessment index (HOMA), and liver steatosis by sonography and the fatty liver index (FLI).

RESULTS

The Lac:Man ratio and circulating interleukin (IL) 6 concentration decreased during intervention from 0.080 (95% CI: 0.073, 0.093) to 0.027 (95% CI: 0.024, 0.034; P < 0.001) and from 4.2 ± 1.4 to 2.8 ± 1.6 pg/mL (P < 0.01), respectively. At study start, the Lac:Man ratio was higher in patients with moderate or severe steatosis than in those without any steatosis (P < 0.001). The Lac:Man ratio tended to correlate with HOMA (ρ = 0.55, P = 0.052), which correlated with FLI (ρ = 0.75, P < 0.01). A multiple-regression analysis led to a final model explaining FLI best through BMI, waist circumference, and the Lac:Man ratio.

CONCLUSIONS

Intestinal permeability is increased in obese patients with steatosis compared with obese patients without. The increased permeability fell to within the previously reported normal range after weight reduction. The data suggest that a leaky gut barrier is linked with liver steatosis and could be a new target for future steatosis therapies. This trial was registered at clinicaltrials.gov as NCT01344525.

Human Intestinal Barrier Function in Health and Disease

The gastrointestinal tract consists of an enormous surface area that is optimized to efficiently absorb nutrients, water, and electrolytes from food. At the same time, it needs to provide a tight barrier against the ingress of harmful substances, and protect against a reaction to omnipresent harmless compounds. A dysfunctional intestinal barrier is associated with various diseases and disorders. In this review, the role of intestinal permeability in common disorders such as infections with intestinal pathogens, inflammatory bowel disease, irritable bowel syndrome, obesity, celiac disease, non-celiac gluten sensitivity, and food allergies will be discussed. In addition, the effect of the frequently prescribed drugs proton pump inhibitors and non-steroidal anti-inflammatory drugs on intestinal permeability, as well as commonly used methods to assess barrier function will be reviewed.

Faecal calprotectin: factors affecting levels and its potential role as a surrogate marker for risk of development of Crohn's Disease

Background

Faecal calprotectin (FC) is one of the most widely used non-invasive tests for the diagnosis and assessment of Crohn’s disease (CD) activity. Despite this, factors other than disease activity which affect levels have not been extensively reviewed. This is of importance when using FC in the diagnostic setting but also may be of utility in studying the aetiology of disease.

Objectives

Our review outlines environmental risk factors that affect FC levels influencing diagnostic accuracy and how these may be associated with risk of developing CD. FC as a surrogate marker could be used to validate risk factors established in case control studies where prospective studies are not feasible. Proof of this concept is provided by our identification of obesity as being associated with elevated FC, our subsequent confirmation of obesity as risk factor for CD and the subsequent verification in prospective studies, as well as associations of lack of physical activity and dietary fibre intake with elevated FC levels and their subsequent confirmation as risk factors in prospective studies.

Conclusion

We believe that FC is likely to prove a useful surrogate marker for risk of developing CD. This review has given a theoretical basis for considering the epidemiological determinants of CD which to date has been missing.

High Fat Diets Induce Colonic Epithelial Cell Stress and Inflammation that is Reversed by IL-22

Prolonged high fat diets (HFD) induce low-grade chronic intestinal inflammation in mice, and diets high in saturated fat are a risk factor for the development of human inflammatory bowel diseases. We hypothesized that HFD-induced endoplasmic reticulum (ER)/oxidative stress occur in intestinal secretory goblet cells, triggering inflammatory signaling and reducing synthesis/secretion of proteins that form the protective mucus barrier. In cultured intestinal cells non-esterified long-chain saturated fatty acids directly increased oxidative/ER stress leading to protein misfolding. A prolonged HFD elevated the intestinal inflammatory cytokine signature, alongside compromised mucosal barrier integrity with a decrease in goblet cell differentiation and Muc2, a loss in the tight junction protein, claudin-1 and increased serum endotoxin levels. In Winnie mice, that develop spontaneous colitis, HFD-feeding increased ER stress, further compromised the mucosal barrier and increased the severity of colitis. In obese mice IL-22 reduced ER/oxidative stress and improved the integrity of the mucosal barrier, and reversed microbial changes associated with obesity with an increase in Akkermansia muciniphila. Consistent with epidemiological studies, our experiments suggest that HFDs are likely to impair intestinal barrier function, particularly in early life, which partially involves direct effects of free-fatty acids on intestinal cells, and this can be reversed by IL-22 therapy.

[Alteration of intestinal permeability: the missing link between gut microbiota modifications and inflammation in obesity?]

The increasing incidence of obesity and associated metabolic complications is a worldwide public health issue. The role of the gut in the pathophysiology of obesity, with an important part for microbiota, is becoming obvious. In rodent models of diet-induced obesity, the modifications of gut microbiota are associated with an alteration of the intestinal permeability increasing the passage of food or bacterial antigens, which contribute to low-grade inflammation and insulin resistance. In human obesity, intestinal permeability modification, and its role in the crosstalk between gut microbiota changes and inflammation at systemic and tissular levels, are still poorly documented. Hence, further characterization of the triggering mechanisms of such inflammatory responses in obese subjects could enable the development of personalized intervention strategies that will help to reduce the risk of obesity-associated diseases.

Impact of Dietary Lipids on Colonic Function and Microbiota: An Experimental Approach Involving Orlistat-Induced Fat Malabsorption in Human Volunteers

OBJECTIVES:

High-fat diets alter gut microbiota and barrier function, inducing metabolic endotoxemia and low-grade inflammation. Whether these effects are due to the high dietary lipid content or to the concomitant decrease of carbohydrate intake is unclear. The aim of this study was to determine whether higher amounts of dietary fat reaching the colon (through orlistat administration) affect the colonic ecosystem in healthy volunteers and the effect of the prebiotic oligofructose (OF) in this model.

METHODS:

Forty-one healthy young subjects were distributed among four groups: Control (C), Prebiotic (P), Orlistat (O), and Orlistat/Prebiotic (OP). They consumed a fat-standardized diet (60 g/day) during Week-1 (baseline) and after 1 week of washout, Week-3. During Week-3, they also received their respective treatment (Orlistat: 2 × 120 mg/day, OF: 16 g/day, and maltodextrin as placebo). A 72-h stool collection was carried out at the end of Week-1 (T0) and Week-3 (T1). Fecal fat, calprotectin, and short-chain fatty acids (SCFAs) as well as the antioxidant activity of fecal waters (ferric-reducing antioxidant power), fecal microbiota composition (by deep sequencing), and gut permeability (Sucralose/Lactulose/Mannitol test) were determined at these times.

RESULTS:

Fecal fat excretion was higher in the O (P=0.0050) and OP (P=0.0069) groups. This event was accompanied, in the O group, by an increased calprotectin content (P=0.047) and a decreased fecal antioxidant activity (P=0.047). However, these alterations did not alter gut barrier function and the changes observed in the composition of the fecal microbiota only affected bacterial populations with low relative abundance (<0.01%); in consequences, fecal SCFA remained mainly unchanged. Part of the colonic alterations induced by orlistat were prevented by OF administration.

CONCLUSIONS:

In the context of an equilibrated diet, the acute exposition of the colonic ecosystem to high amounts of dietary lipids is associated with an incremented excretion of fecal calprotectin and pro-oxidant activity of the colonic content, in the absence of significant changes in the microbiota.

The Intestinal Immune System in Obesity and Insulin Resistance

Obesity and insulin resistance are associated with chronic inflammation in metabolic tissues such as adipose tissue and the liver. Recently, growing evidence has implicated the intestinal immune system as an important contributor to metabolic disease. Obesity predisposes to altered intestinal immunity and is associated with changes to the gut microbiota, intestinal barrier function, gut-residing innate and adaptive immune cells, and oral tolerance to luminal antigens. Accordingly, the gut immune system may represent a novel therapeutic target for systemic inflammation in insulin resistance. This review discusses the emerging field of intestinal immunity in obesity-related insulin resistance and how it affects metabolic disease.

Role of Gut Microbiota in the Aetiology of Obesity: Proposed Mechanisms and Review of the Literature

The aetiology of obesity has been attributed to several factors (environmental, dietary, lifestyle, host, and genetic factors); however none of these fully explain the increase in the prevalence of obesity worldwide. Gut microbiota located at the interface of host and environment in the gut are a new area of research being explored to explain the excess accumulation of energy in obese individuals and may be a potential target for therapeutic manipulation to reduce host energy storage. Several mechanisms have been suggested to explain the role of gut microbiota in the aetiology of obesity such as short chain fatty acid production, stimulation of hormones, chronic low-grade inflammation, lipoprotein and bile acid metabolism, and increased endocannabinoid receptor system tone. However, evidence from animal and human studies clearly indicates controversies in determining the cause or effect relationship between the gut microbiota and obesity. Metagenomics based studies indicate that functionality rather than the composition of gut microbiota may be important. Further mechanistic studies controlling for environmental and epigenetic factors are therefore required to help unravel obesity pathogenesis.

Gut permeability, its interaction with gut microflora and effects on metabolic health are mediated by the lymphatics system, liver and bile acid

There is evidence to link obesity (and metabolic syndrome) with alterations in gut permeability and microbiota. The underlying mechanisms have been questioned and have prompted this review. We propose that the gut barrier function is a primary driver in maintaining metabolic health with poor health being linked to ‘gut leakiness'. This review will highlight changes in intestinal permeability and how it may change gut microflora and subsequently affect metabolic health by influencing the functioning of major bodily organs/organ systems: the lymphatic system, liver and pancreas. We also discuss the likelihood that metabolic syndrome undergoes a cyclic worsening facilitated by an increase in intestinal permeability leading to gut dysbiosis, culminating in ongoing poor health leading to further exacerbated gut leakiness.

Changes in intestinal barrier function and gut microbiota in high-fat diet-fed rats are dynamic and region dependent

A causal relationship between the pathophysiological changes in the gut epithelium and altered gut microbiota with the onset of obesity have been suggested but not defined. The aim of this study was to determine the temporal relationship between impaired intestinal barrier function and microbial dysbiosis in the small and large intestine in rodent high-fat (HF) diet-induced obesity. Rats were fed HF diet (45% fat) or normal chow (C, 10% fat) for 1, 3, or 6 wk; food intake, body weight, and adiposity were measured. Barrier function ex vivo using FITC-labeled dextran (4,000 Da, FD-4) and horseradish peroxidase (HRP) probes in Ussing chambers, gene expression, and gut microbial communities was assessed. After 1 wk, there was an immediate but reversible increase in paracellular permeability, decrease in IL-10 expression, and decrease in abundance of genera within the class Clostridia in the ileum. In the large intestine, HRP flux and abundance of genera within the order Bacteroidales increased with time on the HF diet and correlated with the onset of increased body weight and adiposity. The data show immediate insults in the ileum in response to ingestion of a HF diet, which were rapidly restored and preceded increased passage of large molecules across the large intestinal epithelium. This study provides an understanding of microbiota dysbiosis and gut pathophysiology in diet-induced obesity and has identified IL-10 and Oscillospira in the ileum and transcellular flux in the large intestine as potential early impairments in the gut that might lead to obesity and metabolic disorders.

High fat diet causes depletion of intestinal eosinophils associated with intestinal permeability

The development of intestinal permeability and the penetration of microbial products are key factors associated with the onset of metabolic disease. However, the mechanisms underlying this remain unclear. Here we show that, unlike liver or adipose tissue, high fat diet (HFD)/obesity in mice does not cause monocyte/macrophage infiltration into the intestine or pro-inflammatory changes in gene expression. Rather HFD causes depletion of intestinal eosinophils associated with the onset of intestinal permeability. Intestinal eosinophil numbers were restored by returning HFD fed mice to normal chow and were unchanged in leptin-deficient (Ob/Ob) mice, indicating that eosinophil depletion is caused specifically by a high fat diet and not obesity per se. Analysis of different aspects of intestinal permeability in HFD fed and Ob/Ob mice shows an association between eosinophil depletion and ileal paracelullar permeability, as well as leakage of albumin into the feces, but not overall permeability to FITC dextran. These findings provide the first evidence that a high fat diet causes intestinal eosinophil depletion, rather than inflammation, which may contribute to defective barrier integrity and the onset of metabolic disease.