Differences in visceral fat and fat bacterial colonization between ulcerative colitis and Crohn's disease. An in vivo and in vitro study

Visceral Adiposity Independently Predicts Time to Flare in Inflammatory Bowel Disease but Body Mass Index Does Not

BACKGROUND

Obesity is associated with progression of inflammatory bowel disease (IBD). Visceral adiposity may be a more meaningful measure of obesity compared with traditional measures such as body mass index (BMI). This study compared visceral adiposity vs BMI as predictors of time to IBD flare among patients with Crohn's disease and ulcerative colitis.

METHODS

This was a retrospective cohort study. IBD patients were included if they had a colonoscopy and computed tomography (CT) scan within a 30-day window of an IBD flare. They were followed for 6 months or until their next flare. The primary exposure was the ratio of visceral adipose tissue to subcutaneous adipose tissue (VAT:SAT) obtained from CT imaging. BMI was calculated at the time of index CT scan.

RESULTS

A total of 100 Crohn's disease and 100 ulcerative colitis patients were included. The median age was 43 (interquartile range, 31-58) years, 39% had disease duration of 10 years or more, and 14% had severe disease activity on endoscopic examination. Overall, 23% of the cohort flared with median time to flare 90 (interquartile range, 67-117) days. Higher VAT:SAT was associated with shorter time to IBD flare (hazard ratio of 4.8 for VAT:SAT ≥1.0 vs VAT:SAT ratio <1.0), whereas higher BMI was not associated with shorter time to flare (hazard ratio of 0.73 for BMI ≥25 kg/m2 vs BMI <25 kg/m2). The relationship between increased VAT:SAT and shorter time to flare appeared stronger for Crohn's than for ulcerative colitis.

CONCLUSIONS

Visceral adiposity was associated with decreased time to IBD flare, but BMI was not. Future studies could test whether interventions that decrease visceral adiposity will improve IBD disease activity.

Radiological biomarkers reflecting visceral fat distribution help distinguish inflammatory bowel disease subtypes: a multicenter cross-sectional study

OBJECTIVES

To achieve automated quantification of visceral adipose tissue (VAT) distribution in CT images and screen out parameters with discriminative value for inflammatory bowel disease (IBD) subtypes.

METHODS

This retrospective multicenter study included Crohn's disease (CD) and ulcerative colitis (UC) patients from three institutions between 2012 and 2021, with patients with acute appendicitis as controls. An automatic VAT segmentation algorithm was developed using abdominal CT scans. The VAT volume, as well as the coefficient of variation (CV) of areas within the lumbar region, was calculated. Binary logistic regression and receiver operating characteristic analysis was performed to evaluate the potential of indicators to distinguish between IBD subtypes.

RESULTS

The study included 772 patients (365 CDs, median age [inter-quartile range] = 31.0. (25.0, 42.0) years, 255 males; 241 UCs, 46.0 (34.0, 55.5) years, 138 males; 166 controls, 40.0 (29.0, 53.0) years, 80 males). CD patients had lower VAT volume (CD = 1584.95 ± 1128.31 cm3, UC = 1855.30 ± 1326.12 cm3, controls = 2470.91 ± 1646.42 cm3) but a higher CV (CD = 29.42 ± 15.54 %, p = 0.006 and p ˂ 0.001) compared to UC and controls (25.69 ± 12.61 % vs. 23.42 ± 15.62 %, p = 0.11). Multivariate analysis showed CV was a significant predictor for CD (odds ratio = 6.05 (1.17, 31.12), p = 0.03). The inclusion of CV improved diagnostic efficiency (AUC = 0.811 (0.774, 0.844) vs. 0.803 (0.766, 0.836), p = 0.08).

CONCLUSION

CT-based VAT distribution can serve as a potential biomarker for distinguishing IBD subtypes.

CRITICAL RELEVANCE STATEMENT

Visceral fat distribution features extracted from CT images using an automated segmentation algorithm (1.14 min) show differences between Crohn's disease and ulcerative colitis and are promising for practical radiological screening.

KEY POINTS

• Radiological parameters reflecting visceral fat distribution were extracted for the discrimination of Crohn's disease (CD) and ulcerative colitis (UC). • In CD, visceral fat was concentrated in the lower lumbar vertebrae, and the coefficient of variation was a significant predictor (OR = 6.05 (1.17, 31.12), p = 0.03). • The differences between CD, UC, and controls are promising for practical radiological screening.

Residual abnormalities on CTE predict adverse outcomes in Crohn's disease with endoscopic healing

BACKGROUND

Residual abnormalities on computed tomography enterography (CTE) in Crohn's disease (CD) with endoscopic healing (EH) may have prognostic implications and affect therapeutic strategy.

METHODS

CD patients with EH who underwent CTE between March 2015 and June 2022 were enrolled. CTE findings of the terminal ileum and the most severe segment of colon at the time of EH were assessed respectively for each patient. Cox regression analysis and Kaplan-Meier curves were used to evaluate the association between residual abnormalities and adverse outcomes.

RESULTS

A total of 140 patients (217 digestive segments) were included. Mesenteric edema (hazard ratio [HR] = 3.61, 95% CI = 1.81-7.20, P<0.001), fibrofatty proliferation (HR = 3.40, 95% CI = 1.97-5.85, P<0.001) and active small bowel inflammation (HR = 2.74, 95% CI = 1.59-4.71, P<0.001) were risk factors for clinical relapse. Furthermore, we built a scoring system using the three parameters. Radiologic score ≥ 1 was the best threshold to predict clinical relapse (HR = 4.56, 95% CI = 2.54-8.19, P<0.001) and it was validated in different outcomes.

CONCLUSION

The scoring system based on three residual abnormalities on CTE can predict adverse outcomes in CD patients with EH.

Metabolic Disorders, the Microbiome as an Endocrine Organ, and Their Relations with Obesity: A Literature Review

The etiology of metabolic disorders, such as obesity, has been predominantly associated with the gut microbiota, which is acknowledged as an endocrine organ that plays a crucial role in modulating energy homeostasis and host immune responses. The presence of dysbiosis has the potential to impact the functioning of the intestinal barrier and the gut-associated lymphoid tissues by allowing the transit of bacterial structural components, such as lipopolysaccharides. This, in turn, may trigger inflammatory pathways and potentially lead to the onset of insulin resistance. Moreover, intestinal dysbiosis has the potential to modify the production of gastrointestinal peptides that are linked to the feeling of fullness, hence potentially leading to an increase in food consumption. In this literature review, we discuss current developments, such as the impact of the microbiota on lipid metabolism as well as the processes by which its changes led to the development of metabolic disorders. Several methods have been developed that could be used to modify the gut microbiota and undo metabolic abnormalities.

METHODS

After researching different databases, we examined the PubMed collection of articles and conducted a literature review.

RESULTS

After applying our exclusion and inclusion criteria, the initial search yielded 1345 articles. We further used various filters to narrow down our titles analysis and, to be specific to our study, selected the final ten studies, the results of which are included in the Results section.

CONCLUSIONS

Through gut barrier integrity, insulin resistance, and other influencing factors, the gut microbiota impacts the host's metabolism and obesity. Although the area of the gut microbiota and its relationship to obesity is still in its initial stages of research, it offers great promise for developing new therapeutic targets that may help prevent and cure obesity by restoring the gut microbiota to a healthy condition.

Set up and validation of a sensitive method to quantify prostaglandins, prostaglandin-glycerol esters and prostaglandin-ethanolamides, as well as their respective precursors

Arachidonic acid-derived prostaglandins are widely studied for their role in inflammation. However, besides arachidonic acid, other arachidonic moiety-containing lipids can be metabolized by COX-2. Indeed, the endocannabinoids 2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine (anandamide, AEA) can follow the same biochemical pathways than arachidonic acid leading to the formation of prostaglandin-glycerol esters (PG-G) and prostaglandin-ethanolamides (or prostamides, PG-EA), respectively. The data reported so far support the interest of these bioactive lipids in inflammatory conditions. However, there is only a handful of methods described for their quantification in biological matrices. Moreover, given the shared biochemical pathways for arachidonic acid, 2-AG and AEA, a method allowing for the quantification of these precursors and the corresponding prostaglandin derivatives appears as largely needed. Thus, we report here the development and validation of a single run UPLC-MS/MS quantification method allowing the quantification of these endocannabinoids-derived mediators together with the classical prostaglandin. Moreover, we applied the method to the quantification of these lipids in vitro (using lipopolysaccharides-activated J774 macrophage cells) and in vivo in several tissues from DSS-induced colitis mice. This femtomole-range method should improve the understanding of the interaction between these lipid mediators and inflammation.

Volumetric visceral fat machine learning phenotype on CT for differential diagnosis of inflammatory bowel disease

OBJECTIVES

To investigate whether volumetric visceral adipose tissue (VAT) features extracted using radiomics and three-dimensional convolutional neural network (3D-CNN) approach are effective in differentiating Crohn's disease (CD) and ulcerative colitis (UC).

METHODS

This retrospective study enrolled 316 patients (mean age, 36.25 ± 13.58 [standard deviation]; 219 men) with confirmed diagnosis of CD and UC who underwent CT enterography between 2012 and 2021. Volumetric VAT was semi-automatically segmented on the arterial phase images. Radiomics analysis was performed using principal component analysis (PCA) and the least absolute shrinkage and selection operator (LASSO) logistic regression algorithm. We developed a 3D-CNN model using VAT imaging data from the training cohort. Clinical covariates including age, sex, modified body mass index, and disease duration that impact VAT were added to the machine learning model for adjustment. The model's performance was evaluated on the testing cohort separating from the model's development process by its discrimination and clinical utility.

RESULTS

Volumetric VAT radiomics analysis with LASSO had the highest AUC value of 0.717 (95% CI, 0.614-0.820), though difference of diagnostic performance among the 3D-CNN model (AUC = 0.693; 95% CI, 0.587-0.798) and radiomics analysis with PCA (AUC = 0.662; 95% CI, 0.548-0.776) and LASSO have not reached statistical significance (all p > 0.05). The radiomics score was higher in UC than in CD on the testing cohort (mean ± SD, UC 0.29 ± 1.05 versus CD -0.60 ± 1.25; p < 0.001). The LASSO model with adjustment of clinical covariates reached an AUC of 0.775 (95%CI, 0.683-0.868).

CONCLUSION

The developed volumetric VAT-based radiomics and 3D-CNN models provided comparable and effective performance for the characterization of CD from UC.

KEY POINTS

• High-output feature data extracted from volumetric visceral adipose tissue on CT enterography had an effective diagnostic performance for differentiating Crohn's disease from ulcerative colitis. • With adjustment of clinical covariates that cause difference in volumetric visceral adipose tissue, adjusted clinical machine learning model reached stronger performance when distinguishing Crohn's disease patients from ulcerative colitis patients.

Medical and Surgical Implications of Mesenteric Adipose Tissue in Crohn's Disease: A Review of the Literature

Mesenteric adipose tissue (MAT) has gained substantial attention as an active player in Crohn's disease (CD), but its clinical significance is poorly understood and likely reflects, in part, difficulties assessing MAT noninvasively. Recent radiologic studies have identified candidate surrogate markers that may reflect inflammatory alterations of MAT in CD and have found that certain features including visceral adipose tissue may inform risk of complicated disease behavior, risk for surgery, and postoperative outcomes. Additionally, emerging surgical data have suggested MAT may even be a therapeutic target to mitigate postoperative recurrence of CD. However, the current studies have variable results, reduced sample sizes, and methodological limitations that preclude incorporating the radiologic and surgical findings into clinical practice. Nonetheless, the results are promising and potentially have important implications for the medical and surgical management of CD, which merits that additional studies are warranted. Thus, we have reviewed the available literature on the medical and surgical implications of MAT in CD to summarize our current understanding and identify gaps in knowledge to inform future investigations.

Anti-TNF Therapies Suppress Adipose Tissue Inflammation in Crohn’s Disease

Anti-TNF biologics have been shown to markedly improve the quality of life for patients with Crohn’s disease (CD), yet one-third of patients fail to benefit from this treatment. Patients with CD develop a characteristic wrapping of visceral adipose tissue (VAT) in the inflamed intestinal area, termed creeping fat, and it is known that adipose tissue expansion influences the efficacy of anti-TNF drugs. We questioned whether anti-TNF therapies impact the creeping fat in CD, which might affect the outcome of the disease. Adipose tissue biopsies were obtained from a cohort of 14 patients with CD that received anti-TNF drugs and from 29 non-anti-TNF-treated patients (control group) matched by sex, age, and body mass index undergoing surgical interventions for symptomatic complications. We found that anti-TNF therapies restored adipose tissue morphology and suppressed immune cell infiltration in the creeping fat. Additionally, anti-TNF treatments appeared to markedly improve the pro-inflammatory phenotype of adipose-tissue macrophages and adipose-tissue-derived stem cells. Our study provides evidence that anti-TNF medications influence immune cells and progenitor cells in the creeping of patients with CD, suppressing inflammation. We propose that perilesional VAT should be considered when administering anti-TNF therapy in patients with CD.

Aspects Towards the Anastomotic Healing in Crohn’s Disease: Clinical Approach and Current Gaps in Research

Anastomotic leakage is a major complication in gastrointestinal and colorectal surgery and its occurrence increases morbidity and mortality. Its incidence is even higher in Crohn’s disease surgeries. Several authors have identified factors involved in the pathophysiology of anastomotic leak in the literature, aiming to reduce its occurrence and, therefore, improve its surgical treatment. Surgical technique is the most discussed topic in studies on guiding the performance of side-to-side stapled anastomosis. Preoperative nutritional therapy also has been shown to reduce the risk of anastomotic leakage. Other factors remain controversial – immunomodulator use and biologic therapy, antibiotics, and gut microbiota – with studies showing a reduction in the risk of complication while other studies show no correlation. Although mesenteric adipose tissue has been related to disease recurrence, there is no evidence in the literature that it is related to a higher risk of anastomotic leakage. Further exploration on this topic is necessary, including prospective research, to support the development of techniques to prevent anastomotic leakage, in this way benefiting the inflammatory bowel disease patients who have to undergo a surgical procedure.

Intestinal homeostasis and inflammation: gut microbiota at the crossroads of pancreas-intestinal barrier axis

The pancreas contains exocrine glands, which release enzymes (e.g., amylase, trypsin, and lipase) that are important for digestion and islets, which produce hormones. Digestive enzymes and hormones are secreted from the pancreas into the duodenum and bloodstream, respectively. Growing evidence suggests that the roles of the pancreas extend to not only the secretion of digestive enzymes and hormones but also to the regulation of intestinal homeostasis and inflammation (e.g., mucosal defense to pathogens and pathobionts). Organ crosstalk between the pancreas and intestine is linked to a range of physiological, immunological, and pathological activities, such as the regulation of the gut microbiota by the pancreatic proteins and lipids, the retroaction of the gut microbiota on the pancreas, the relationship between inflammatory bowel disease, and pancreatic diseases. We herein discuss the current understanding of the pancreas–intestinal barrier axis and the control of commensal bacteria in intestinal inflammation.

Fecal microbiota transplantation does not alter bacterial translocation and visceral adipose tissue inflammation in individuals with obesity

AIMS

Visceral adipose tissue inflammation is a fundamental mechanism of insulin resistance in obesity and type 2 diabetes. Translocation of intestinal bacteria has been suggested as a driving factor for the inflammation. However, although bacterial DNA was detected in visceral adipose tissue of humans with obesity, it is unclear to what extent this is contamination or whether the gut microbiota is causally involved. Effects of fecal microbiota transplantation (FMT) on bacterial translocation and visceral adipose tissue inflammation in individuals with obesity and insulin resistance were assessed.

MATERIAL AND METHODS

Eight individuals with clinically severe obesity (body mass index [BMI] >35 kg/m2) and metabolic syndrome received lean donor FMT 4 weeks prior to elective bariatric surgery. The participants were age-, sex-, and BMI-matched to 16 controls that underwent no fecal transplantation. Visceral adipose tissue was collected during surgery. Bacterial translocation was assessed by 16S rRNA gene sequencing of adipose tissue and feces. Pro-inflammatory cytokine expression and histopathological analyses of visceral adipose tissue were performed to assess inflammation.

RESULTS

Fecal microbiota transplantation significantly altered gut microbiota composition. Visceral adipose tissue contained a very low quantity of bacterial DNA in both groups. No difference in visceral bacterial DNA content between groups was observed. Also, visceral expression of pro-inflammatory cytokines and macrophage infiltration did not differ between groups. No correlation between inflammatory tone and bacterial translocation was observed.

CONCLUSIONS

Visceral bacterial DNA content and level of inflammation were not altered upon FMT. Thus, bacterial translocation may not be the main driver of visceral adipose tissue inflammation in obesity.

Microbiota in mesenteric adipose tissue from Crohn's disease promote colitis in mice

BACKGROUND

Mesenteric adipose tissue (mAT) hyperplasia, known as creeping fat is a pathologic characteristic of Crohn's disease (CD). The reserve of creeping fat in surgery is associated with poor prognosis of CD patients, but the mechanism remains unknown.

METHODS

Mesenteric microbiome, metabolome, and host transcriptome were characterized using a cohort of 48 patients with CD and 16 non-CD controls. Multidimensional data including 16S ribosomal RNA gene sequencing (16S rRNA), host RNA sequencing, and metabolome were integrated to reveal network interaction. Mesenteric resident bacteria were isolated from mAT and functionally investigated both in the dextran sulfate sodium (DSS) model and in the Il10 gene-deficient (Il10^-/-) mouse colitis model to validate their pro-inflammatory roles.

RESULTS

Mesenteric microbiota contributed to aberrant metabolites production and transcripts in mATs from patients with CD. The presence of mAT resident microbiota was associated with the development of CD. Achromobacter pulmonis (A. pulmonis) isolated from CD mAT could translocate to mAT and exacerbate both DSS-induced and Il10 gene-deficient (Il10^-/-) spontaneous colitis in mice. The levels of A. pulmonis in both mAT and mucous layer from CD patients were higher compared to those from the non-CD group.

CONCLUSIONS

This study suggests that the mesenteric microbiota from patients with CD sculpt a detrimental microenvironment and promote intestinal inflammation. Video abstract.

Role of Vitamin B12 and Folate in Metabolic Syndrome

Metabolic syndrome (MS) is a collection of pathological metabolic conditions that includes insulin resistance, central or abdominal obesity, dyslipidemia, and hypertension. It affects large populations worldwide, and its prevalence is rising exponentially. There is no specific mechanism that leads to the development of MS. Proposed hypotheses range from visceral adiposity being a key factor to an increase in very-low-density lipoprotein and fatty acid synthesis as the primary cause of MS. Numerous pharmaceutical therapies are widely available in the market for the treatment of the individual components of MS. The relationship between MS and vitamin B complex supplementation, specifically folic acid and vitamin B12, has been a subject of investigation worldwide, with several trials reporting a positive impact with vitamin supplementation on MS.

In this study, an all-language literature search was conducted on Medline, Cochrane, Embase, and Google Scholar till September 2021. The following search strings and Medical Subject Headings (MeSH) terms were used: “Vitamin B12,” “Folate,” “Metabolic Syndrome,” and “Insulin Resistance.” We explored the literature on MS for its epidemiology, pathophysiology, newer treatment options, with a special focus on the effectiveness of supplementation with vitamins B9 and B12.

According to the literature, vitamin B12 and folate supplementation, along with a host of novel therapies, has a considerable positive impact on MS. These findings must be kept in mind while designing newer treatment protocols in the future.

Recent advances and health implications of dietary fasting regimens on the gut microbiome

Calorie restriction is a primary dietary intervention demonstrated over many decades in cellular and animal models to modulate aging pathways, positively affect age-associated diseases and, in clinical studies, to promote beneficial health outcomes. Because long-term compliance with daily calorie restriction has proven problematic in humans several intermittent fasting regimens, including alternate day fasting and time-restricted feeding, have evolved revealing similar clinical benefits as calorie restriction. Despite significant research on the cellular and physiological mechanisms contributing to, and responsible for, these observed benefits, relatively little research has investigated the impact of these various fasting protocols on the gut microbiome (GM). Reduced external nutrient supply to the gut may beneficially alter the composition and function of a "fed" gut microflora. Indeed, the prevalent, obesogenic Western diet can promote deleterious changes in the GM, signaling intermediates involved in lipid and glucose metabolism, and immune responses in the gastrointestinal tract. This review describes recent preclinical and clinical effects of varying fasting regimens on GM composition and associated physiology. Although the number of preclinical and clinical interventions are limited, significant data thus far suggest fasting interventions impact GM composition and physiology. However, there are considerable heterogeneities of study design, methodological considerations, and practical implications. Ongoing research on the health impact of fasting regimens on GM modulation is warranted.

Role of Adipose Tissue in Inflammatory Bowel Disease

Inflammatory bowel diseases (IBDs), chronic inflammatory disorders affecting the gastrointestinal tract, include Crohn's disease and ulcerative colitis. There are increasing clinical and experimental data showing that obesity, especially visceral adiposity, plays a substantial role in the pathogenesis of IBD. Obesity seems to be an important risk factor also for IBD disease severity and clinical outcomes. Visceral adipose tissue is an active multifunctional metabolic organ involved in lipid storage and immunological and endocrine activity. Bowel inflammation penetrates the surrounding adipose tissue along the mesentery. Mesenteric fat serves as a barrier to inflammation and controls immune responses to the translocation of gut bacteria. At the same time, mesenteric adipose tissue may be the principal source of cytokines and adipokines responsible for inflammatory processes associated with IBD. This review is particularly focusing on the potential role of adipokines in IBD pathogenesis and their possible use as promising therapeutic targets.

Circulating Leptin Levels as a Potential Biomarker in Inflammatory Bowel Diseases: A Systematic Review and Meta-Analysis

BACKGROUND

The differential diagnosis of inflammatory bowel diseases (IBDs) between Crohn's disease (CD) and ulcerative colitis (UC) is important for designing an effective therapeutic regimen. However, without any adequate gold standard method for differential diagnosis currently, therapeutic design remains a major challenge in clinical practice. In this context, recent studies have showed that circulating leptin stands out as a potential biomarker for the categorization of IBDs. Thus, we aimed to summarize the current understanding of the prognostic and diagnostic value of serum leptin in patients with IBDs.

METHODS

A systematic search was performed in PubMed/MEDLINE, Scopus, Cochrane Library, and Web of Science databases. Articles that aimed to study the relationship between circulating levels of leptin and IBDs were included. Finally, the meta-analysis was performed with the mean serum leptin levels in patients with IBDs and healthy controls using RevMan 5.3 software, with I2 > 50% as a criterion for substantial heterogeneity.

RESULTS

Nineteen studies were included. Serum leptin levels among patients with IBDs and healthy controls did not show a significant difference (95% CI, -2.15 to 0.57; I2, 86%, P ≤ 0.00001). Similarly, there was no association of leptin levels with the activity of IBDs (95% CI, -0.24 to 0.06; I2, 50%; P = 0.13). However, serum leptin levels were significantly higher in patients with CD than those in patients with UC (95% CI, -2.09 to -0.37; I2, 7%; P ≤ 0.36).

CONCLUSION

This review suggested that serum leptin levels might be a promising biomarker to help in the differentiation between CD and UC.

BMI in the lower and upper quartiles at diagnosis and at 1-year follow-up is significantly associated with higher risk of disease exacerbation in pediatric inflammatory bowel disease

Inflammatory bowel disease (IBD) has been associated with underweight and malnutrition, but obesity may also serve as a negative prognostic factor. This study aimed to present the longitudinal course of height, weight, and body mass index (BMI) of children from IBD diagnosis to 18 months of follow-up, and to describe the impact of BMI on the clinical course of the disease. One hundred and fifty-two children were identified, of whom 85 had Crohn's disease (CD) and 67 had ulcerative colitis (UC). During a median (interquartile range) follow-up of 2.95 (1.73-4.5) years, weight and BMI Z-scores increased in the first 18 months since diagnosis in both the CD (P < 0.001) and UC (P < 0.028) groups. BMI in lower and upper quartiles at diagnosis was associated with higher risk of hospitalization (hazard ratio [HR] = 2.72, P = 0.021). In a multivariate analysis, BMI in the lower quartile at diagnosis and at 6, 12, and 18 months was associated with higher risk of disease exacerbation (HR = 2.36, 1.90, 1.98, and 2.43, respectively, P < 0.021), as was BMI in the upper quartile (HR = 2.59, 2.91, and 2.29, respectively, P < 0.013).Conclusion: BMI in the lower and upper quartiles at diagnosis and during follow-up was associated with a more severe disease course in children with IBD. What is Known: • Inflammatory bowel disease (IBD) has been associated with underweight and malnutrition. • The impacts of weight and body mass index (BMI) on the presentation and course of IBD have been mainly investigated in the adult population. What is New: • In the era of the obesity epidemic, this study identifies both low and high BMIs at diagnosis and at follow-up as a marker for poor outcome in pediatric IBD. • The results support using BMI as a predictor of IBD course and prognosis.

Translocation of Viable Gut Microbiota to Mesenteric Adipose Drives Formation of Creeping Fat in Humans

A mysterious feature of Crohn's disease (CD) is the extra-intestinal manifestation of "creeping fat" (CrF), defined as expansion of mesenteric adipose tissue around the inflamed and fibrotic intestine. In the current study, we explore whether microbial translocation in CD serves as a central cue for CrF development. We discovered a subset of mucosal-associated gut bacteria that consistently translocated and remained viable in CrF in CD ileal surgical resections, and identified Clostridium innocuum as a signature of this consortium with strain variation between mucosal and adipose isolates, suggesting preference for lipid-rich environments. Single-cell RNA sequencing characterized CrF as both pro-fibrotic and pro-adipogenic with a rich milieu of activated immune cells responding to microbial stimuli, which we confirm in gnotobiotic mice colonized with C. innocuum. Ex vivo validation of expression patterns suggests C. innocuum stimulates tissue remodeling via M2 macrophages, leading to an adipose tissue barrier that serves to prevent systemic dissemination of bacteria.

Microbial Signature in Adipose Tissue of Crohn's Disease Patients

Crohn’s disease (CD) is characterized by compromised immune tolerance to the intestinal commensal microbiota, intestinal barrier inflammation, and hyperplasia of creeping fat (CF) and mesenteric adipose tissue (AT), which seems to be directly related to disease activity. Gut microbiota dysbiosis might be a determining factor in CD etiology, manifesting as a low microbial diversity and a high abundance of potentially pathogenic bacteria. We tested the hypothesis that CF is a reservoir of bacteria through 16S-rRNA sequencing of several AT depots of patients with active and inactive disease and controls. We found a microbiome signature within CF and mesenteric AT from patients, but not in subcutaneous fat. We failed to detect bacterial DNA in any fat depot of controls. Proteobacteria was the most abundant phylum in both CF and mesenteric AT, and positively correlated with fecal calprotectin/C-reactive protein. Notably, the clinical status of patients seemed to be related to the microbiome signature, as those with the inactive disease showed a reduction in the abundance of pathogenic bacteria. Predictive functional profiling revealed many metabolic pathways including lipopolysaccharide biosynthesis and sulfur metabolism overrepresented in active CD relative to that in inactive CD. Our findings demonstrate that microbiota dysbiosis associated with CD pathophysiology is reflected in AT and might contribute to disease severity.

Intestinal Dysbiosis and Markers of Systemic Inflammation in Viscerally and Generally Obese Persons Living With HIV

BACKGROUND

The intestinal microbiota contributes to the pathogenesis of obesity and metabolic disorders. People living with HIV (PLWH) have a higher risk for the development of visceral adiposity with accompanying worsened cardiovascular risk.

SETTING

Convenience sample from an HIV clinic and research unit.

METHODS

To understand the relationship between adiposity and intestinal dysbiosis, we compared the gut microbiota and inflammatory markers in a cross-sectional study of viscerally obese, generally obese, and lean PLWH. Fecal intestinal microbiota was characterized by 16S ribosomal DNA sequencing. Abdominal CTs quantified subcutaneous adipose tissue and visceral adipose tissue (SAT; VAT). Serum high sensitivity C-reactive protein, adiponectin, leptin, IL-6, MCP-1, and sCD14 were assayed.

RESULTS

We studied 15, 9, and 11 participants with visceral obesity, general obesity, and lean body type, respectively. The generally obese group were all women and 2/3 African American, whereas the visceral obesity and lean groups were predominantly white and men who have sex with men. Markers of systemic inflammation and sCD14 were higher in general obesity compared with lean. sCD14 was positively correlated with VAT, but not SAT. Bacterial diversity was significantly reduced in participants with visceral and general obesity and composition of intestinal microbiota was significantly different from lean body types. Bacterial alpha diversity was negatively correlated with VAT area, waist/hip ratio, and sCD14, but not with SAT area.

CONCLUSIONS

In this exploratory study, obesity in general was associated with dysbiotic intestinal microbiota. The relationships of VAT to bacterial diversity and sCD14 suggest that dysbiosis in viscerally obese PLWH could be associated with heightened inflammatory state.

Infection History Determines Susceptibility to Unrelated Diseases

Epidemiological data suggest that previous infections can alter an individual's susceptibility to unrelated diseases. Nevertheless, the underlying mechanisms are not completely understood. Substantial research efforts have expanded the classical concept of immune memory to also include long-lasting changes in innate immunity and antigen-independent reactivation of adaptive immunity. Collectively, these processes provide possible explanations on how acute infections might induce long-term changes that also affect immunity to unrelated diseases. Here, we review lasting changes the immune compartment undergoes upon infection and how infection experience alters the responsiveness of immune cells towards universal signals. This heightened state of alert enhances the ability of the immune system to combat even unrelated infections but may also increase susceptibility to autoimmunity. At the same time, infection-induced changes in the regulatory compartment may dampen subsequent immune responses and promote pathogen persistence. The concepts presented here outline how infection-induced changes in the immune system may affect human health.

Role of Obesity, Mesenteric Adipose Tissue, and Adipokines in Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBDs) are a group of disorders which include ulcerative colitis and Crohn's disease. Obesity is becoming increasingly more common among patients with inflammatory bowel disease and plays a role in the development and course of the disease. This is especially true in the case of Crohn's disease. The recent results indicate a special role of visceral adipose tissue and particularly mesenteric adipose tissue, also known as "creeping fat", in pathomechanism, leading to intestinal inflammation. The involvement of altered adipocyte function and the deregulated production of adipokines, such as leptin and adiponectin, has been suggested in pathogenesis of IBD. In this review, we discuss the epidemiology and pathophysiology of obesity in IBD, the influence of a Western diet on the course of Crohn's disease and colitis in IBD patients and animal's models, and the potential role of adipokines in these disorders. Since altered body composition, decrease of skeletal muscle mass, and development of pathologically changed mesenteric white adipose tissue are well-known features of IBD and especially of Crohn's disease, we discuss the possible crosstalk between adipokines and myokines released from skeletal muscle during exercise with moderate or forced intensity. The emerging role of microbiota and the antioxidative and anti-inflammatory enzymes such as intestinal alkaline phosphatase is also discussed, in order to open new avenues for the therapy against intestinal perturbations associated with IBD.

Mechanisms and consequences of gut commensal translocation in chronic diseases

Humans and other mammalian hosts have evolved mechanisms to control the bacteria colonizing their mucosal barriers to prevent invasion. While the breach of barriers by bacteria typically leads to overt infection, increasing evidence supports a role for translocation of commensal bacteria across an impaired gut barrier to extraintestinal sites in the pathogenesis of autoimmune and other chronic, non-infectious diseases. Whether gut commensal translocation is a cause or consequence of the disease is incompletely defined. Here we discuss factors that lead to translocation of live bacteria across the gut barrier. We expand upon our recently published demonstration that translocation of the gut pathobiont Enterococcus gallinarum can induce autoimmunity in susceptible hosts and postulate on the role of Enterococcus species as instigators of chronic, non-infectious diseases.

The Role of Adipose Tissue in the Pathogenesis and Therapeutic Outcomes of Inflammatory Bowel Disease

Though historically regarded as an inert energy store, adipose tissue is a complex endocrine organ, which is increasingly implicated in the pathogenesis of inflammatory bowel disease (IBD). Accumulating evidence points to visceral adipose tissue and specifically to its mesenteric component, or “creeping fat” as impacting on the disease course through its immunomodulatory properties. On the one hand, mesenteric fat acts as a physical barrier to inflammation and is involved in controlling host immune response to translocation of gut bacteria. On the other hand, however, there exists a strong link between visceral fat and complicated course of the disease with unfavorable therapeutic outcomes. Furthermore, “creeping fat” appears to play different roles in different IBD phenotypes, with the greatest pathogenetic contribution probably to an ileal form of Crohn’s disease. In this review, we summarize and discuss the existing literature on the subject and identify high-priority areas for future research. It may be that a better understanding of the role of mesenteric fat in IBD will determine new therapeutic targets and translate into improved clinical outcomes.

HIV Persistence in Adipose Tissue Reservoirs

PURPOSE OF REVIEW

The purpose of this review is to examine the evidence describing adipose tissue as a reservoir for HIV-1 and how this often expansive anatomic compartment contributes to HIV persistence.

RECENT FINDINGS

Memory CD4 T cells and macrophages, the major host cells for HIV, accumulate in adipose tissue during HIV/SIV infection of humans and rhesus macaques. Whereas HIV and SIV proviral DNA is detectable in CD4 T cells of multiple fat depots in virtually all infected humans and monkeys examined, viral RNA is less frequently detected, and infected macrophages may be less prevalent in adipose tissue. However, based on viral outgrowth assays, adipose-resident CD4 T cells are latently infected with virus that is replication-competent and infectious. Additionally, adipocytes interact with CD4 T cells and macrophages to promote immune cell activation and inflammation which may be supportive for HIV persistence. Antiviral effector cells, such as CD8 T cells and NK/NKT cells, are abundant in adipose tissue during HIV/SIV infection and typically exceed CD4 T cells, whereas B cells are largely absent from adipose tissue of humans and monkeys. Additionally, CD8 T cells in adipose tissue of HIV patients are activated and have a late differentiated phenotype, with unique TCR clonotypes of less diversity relative to blood CD8 T cells. With respect to the distribution of antiretroviral drugs in adipose tissue, data is limited, but there may be class-specific penetration of fat depots. The trafficking of infected immune cells within adipose tissues is a common event during HIV/SIV infection of humans and monkeys, but the virus may be mostly transcriptionally dormant. Viral replication may occur less in adipose tissue compared to other major reservoirs, such as lymphoid tissue, but replication competence and infectiousness of adipose latent virus are comparable to other tissues. Due to the ubiquitous nature of adipose tissue, inflammatory interactions among adipocytes and CD4 T cells and macrophages, and selective distribution of antiretroviral drugs, the sequestration of infected immune cells within fat depots likely represents a major challenge for cure efforts.

An improved rat model for chronic inflammatory bowel disease

BACKGROUND

Inflammatory bowel disease (IBD) is an important cause of chronic disability in humans.

METHODS

We characterized a model of chronic IBD in young male Wistar rats by administering dextran sodium sulfate (DSS: 0%, 0.25%, 0.5%, or 1% in drinking water) for six weeks, with 0.5% DSS for twelve weeks, following DSS cessation or together with treatment with sulfasalazine for the last 6 weeks. We measured gastrointestinal characteristics including stool consistency, blood in stools, small intestine and colon length, intestinal transit and permeability, and gut microbiota, as well as extra-intestinal parameters including oral glucose tolerance, systolic blood pressure, fat and lean mass, and left ventricular stiffness.

RESULTS

At 6 weeks, 0.25-1% DSS produced gastrointestinal changes as diarrhea and blood in stools. At 12 weeks, 0.5% DSS produced chronic and sustained gastrointestinal changes, with marked infiltration of inflammatory cells throughout the gastrointestinal tract and crypt distortion. Firmicutes increased and Bacteroidetes and Actinobacteria decreased in DSS-treated rats. Changes were reversed by DSS cessation or sulfasalazine treatment. Gastrointestinal permeability and extra-intestinal parameters did not change, so DSS changes were limited to the gastrointestinal tract.

CONCLUSION

Chronic 0.5% DSS produces selective and reversible gastrointestinal changes, providing an improved chronic model in rats that mimics human IBD for testing new interventions.

Sarcopenia is a Novel Predictor of the Need for Rescue Therapy in Hospitalized Ulcerative Colitis Patients

BACKGROUND AND AIMS

Acute severe ulcerative colitis [ASUC] affects one in four patients with UC. Clinical parameters perform modestly in predicting the need for rescue therapy. Sarcopenia and visceral adiposity predict natural history in Crohn's disease, but the role of such metabolic factors on ASUC outcomes is unknown. The aim of this study was to define the effect of sarcopenia and visceral adiposity on outcomes in ASUC.

METHODS

We studied patients hospitalized for ASUC who underwent an abdominal CT scan during the hospitalization. Quantification of skeletal muscle mass and visceral adiposity was performed by radiologists blinded to the outcome. Sarcopenia was defined as a skeletal muscle index of <55 cm2/m2 for men and <39 cm2/m2 for women. The primary outcome of interest was need for medical or surgical rescue therapy.

RESULTS

Our study included 89 patients with ASUC, among whom 39 [43.8%] patients required medical rescue therapy or surgery. Two-thirds of the cohort [70%] met the definition of sarcopenia [81% men, 48% women]. Patients with sarcopenia had similar disease characteristics and laboratory parameters to those with a normal muscle mass. However, a larger proportion of patients with sarcopenia required rescue therapy compared with those without (56% vs 28%, multivariable odds ratio [OR] 3.98, 95% confidence interval [CI] 1.12-14.1). Neither visceral [p = 0.23] nor subcutaneous adiposity [p = 0.53] predicted the need for rescue therapy.

CONCLUSIONS

Sarcopenia as determined on abdominal CT was a novel predictor of need for rescue therapy in hospitalized UC patients.

High body mass index is associated with increased risk of treatment failure and surgery in biologic-treated patients with ulcerative colitis

BACKGROUND

Though pharmacokinetic studies suggest accelerated biologic drug clearance with increasing body weight, evidence of obesity's impact on clinical outcomes in biologic-treated patients with ulcerative colitis (UC) is inconsistent.

AIM

To evaluate the impact of obesity on real world response to biological therapy in patients with UC.

METHODS

In a single-centre retrospective cohort study between 2011-2016 of biologic-treated patients with UC, we evaluated treatment response by baseline body mass index (BMI). Primary outcome was treatment failure (composite outcome of IBD-related surgery/hospitalisation or treatment modification including dose escalation, treatment discontinuation or addition of corticosteroids); secondary outcomes were risk of IBD-related surgery/hospitalisation and endoscopic remission. We conducted multivariate Cox proportional hazard analyses to evaluate the independent impact of BMI on clinical outcomes. Stratified analysis by weight-based regimens (infliximab) or fixed-dose regimens (adalimumab, golimumab, vedolizumab, certolizumab pegol) was performed.

RESULTS

We included 160 biologic-treated UC patients (50% males, 55% on infliximab) with median (IQR) age 36 y (26-52) and BMI 24.3 kg/m² (21.4-28.7). On multivariate analysis, each 1 kg/m² increase in BMI was associated with 4% increase in the risk of treatment failure (adjusted hazard ratio [aHR], 1.04 [95% CI, 1.00-1.08]) and 8% increase in the risk of surgery/hospitalisation (aHR, 1.08 [1.02-1.14]). The effect on treatment failure was seen in patients on weight-based dosing regimens or fixed-dose therapies.

CONCLUSION

BMI is independently associated with increased risk of treatment failure in biologic-treated patients with UC, independent of dosing regimen.

Increase of Intra-abdominal Adipose Tissue in Pediatric Crohn Disease

BACKGROUND AND OBJECTIVE

Recent evidence points toward an active immunological role of intra-abdominal adipose tissue in Crohn disease (CD). We quantified the abdominal adipose tissue compartments using magnetic resonance imaging (MRI) in 27 pediatric patients with CD compared with 14 controls undergoing MRI examination for other reasons.

METHODS

Total (TAAT), subcutaneous (SCAT) and intra-abdominal (IAAT) adipose tissue areas were measured by semiautomatic segmentation on a transverse slice centered on the umbilicus (mean ± standard deviation in square centimeter) using standard T1-weighted sequences. IAAT/TAAT and IAAT/height ratios were calculated and analyzed for associations with disease duration, phenotype, or therapy.

RESULTS

Patients with CD (median age 15.0 years, range 7.7-17.9, 18/27 boys, median disease duration 29 months, range 0-136) compared to controls (median age 13.9 years, range 3.3-17.8, 4/14 boys) had higher IAAT area (42.3 ± 21.0 vs 28.7 ± 11.6, P = 0.0494) but similar SCAT and TAAT areas (104.6 ± 72.8 vs 96.5 ± 50.8, P = 0.8170 and 146.9 ± 87.3 vs 125.3 ± 61.5, P = 0.7417, respectively). IAAT/TAAT ratio was higher in patients with CD compared to controls (0.32 ± 0.10 vs 0.24 ± 0.04, P = 0.0081). Patients with disease duration >2 years (n = 14) had higher IAAT/TAAT ratio than those with shorter disease and controls (0.35 ± 0.10 vs 0.28 ± 0.08, P = 0.0288 and 0.24 ± 0.04, P = 0.0009, respectively). In these patients, increased IAAT/height ratio was associated with complicated disease (P = 0.043, r = 0.573). No association was found between IAAT/TAAT ratio and actual disease activity or therapy.

CONCLUSIONS

IAAT is increased in pediatric CD and correlates with disease duration. Assessment of IAAT accumulation may be considered in future MRI scores for inflammation and bowel damage in CD and during follow-up of different therapeutic interventions.

Crohn's Disease Disturbs the Immune Properties of Human Adipose-Derived Stem Cells Related to Inflammasome Activation

Crohn's disease (CD) is characterized by the expansion of mesenteric fat, also known as “creeping fat.” We explored the plasticity and immune properties of adipose-derived stem cells (ASCs) in the context of CD as potential key players in the development of creeping fat. Mesenteric CD-derived ASCs presented a more proliferative, inflammatory, invasive, and phagocytic phenotype than equivalent cells from healthy donors, irrespective of the clinical stage. Remarkably, ASCs from the subcutaneous depot of patients with CD also showed an activated immune response that was associated with a reduction in their immunosuppressive properties. The invasive phenotype of mesenteric CD ASCs was governed by an inflammasome-mediated inflammatory state since blocking inflammasome signaling, mainly the secretion of interleukin-1β, reversed this characteristic. Thus, CD alters the biological functions of ASCs as adipocyte precursors, but also their immune properties. Selection of ASCs with the best immunomodulatory properties is advocated for the success of cell-based therapies.

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ASCs isolated from CD patients are highly proliferative, invasive, and phagocytic

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Proliferative ASCs may be responsible for the development of creeping fat

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ASCs from CD patients have dampened immunosuppressive properties

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Selection of the best immunosuppressive ASCs for cell therapy is advocated

Fecal microbiota transplantation in metabolic syndrome: History, present and future

The history of fecal microbiota transplantation (FMT) dates back even to ancient China. Recently, scientific studies have been looking into FMT as a promising treatment of various diseases, while in the process teaching us about the interaction between the human host and its resident microbial communities. Current research focuses mainly on Clostridium difficile infections, however interest is rising in other areas such as inflammatory bowel disease (IBD) and the metabolic syndrome. With regard to the latter, the intestinal microbiota might be causally related to the progression of insulin resistance and diabetes. FMT in metabolic syndrome has proven to be an intriguing method to study the role of the gut microbiota and open the way to new therapies by dissecting in whom insulin resistance is driven by microbiota. In this article we review the history of FMT, the present evidence on its role in the pathophysiology of metabolic syndrome and its efficacy, limitations and future prospects.

Obesity in IBD: epidemiology, pathogenesis, disease course and treatment outcomes

Incidence of IBD is rising in parallel with overweight and obesity. Contrary to conventional belief, about 15-40% of patients with IBD are obese, which might contribute to the development of IBD. Findings from cross-sectional and retrospective cohort studies are conflicting on the effect of obesity on natural history and course of IBD. Most studies are limited by small sample size, low event rates, non-validated assessment of disease activity and lack robust longitudinal follow-up and have incomplete adjustment for confounding factors. The effect of obesity on the efficacy of IBD-related therapy remains to be studied, though data from other autoimmune diseases suggests that obesity results in suboptimal response to therapy, potentially by promoting rapid clearance of biologic agents leading to low trough concentrations. These data provide a rationale for using weight loss interventions as adjunctive therapy in patients with IBD who are obese. Obesity also makes colorectal surgery technically challenging and might increase the risk of perioperative complications. In this Review, we highlight the existing literature on the epidemiology of obesity in IBD, discuss its plausible role in disease pathogenesis and effect on disease course and treatment response, and identify high-priority areas of future research.

Obesity in IBD: epidemiology, pathogenesis, disease course and treatment outcomes

Incidence of IBD is rising in parallel with overweight and obesity. Contrary to conventional belief, about 15-40% of patients with IBD are obese, which might contribute to the development of IBD. Findings from cross-sectional and retrospective cohort studies are conflicting on the effect of obesity on natural history and course of IBD. Most studies are limited by small sample size, low event rates, non-validated assessment of disease activity and lack robust longitudinal follow-up and have incomplete adjustment for confounding factors. The effect of obesity on the efficacy of IBD-related therapy remains to be studied, though data from other autoimmune diseases suggests that obesity results in suboptimal response to therapy, potentially by promoting rapid clearance of biologic agents leading to low trough concentrations. These data provide a rationale for using weight loss interventions as adjunctive therapy in patients with IBD who are obese. Obesity also makes colorectal surgery technically challenging and might increase the risk of perioperative complications. In this Review, we highlight the existing literature on the epidemiology of obesity in IBD, discuss its plausible role in disease pathogenesis and effect on disease course and treatment response, and identify high-priority areas of future research.

Postoperative excessive gain in visceral adipose tissue as well as body mass index are associated with adverse outcomes of an ileal pouch

BACKGROUND

There are no published studies on the impact of visceral adipose tissue (VAT) change on outcomes of restorative proctocolectomy and ileal pouch-anal anastomosis (IPAA). The aim of this historic cohort study was to evaluate the impact of excessive VAT gain on the outcomes of inflammatory bowel disease (IBD) patients with IPAA.

METHODS

We evaluated all eligible patients with at least two sequential CT scans after pouch construction from our prospectively maintained Pouchitis Registry between 2002 and 2014. The visceral fat area (VFA) was measured on CT images. The study group comprised patients with a significant VAT gain (> 15%), and the control group was those without. The adverse outcomes of the pouch were defined as the new development of chronic pouch inflammation (chronic pouchitis, chronic cuffitis or Crohn's disease of the pouch), anastomotic sinus and the combination of above (the composite adverse outcome) or pouch failure, after the inception CT.

RESULTS

Of 1564 patients in the Registry, 59 (3.8%) with at least 2 CT scans after pouch surgery were included. Twenty-nine patients (49.2%) were in the study group, and 30 (50.8%) were in the control group. The median duration from the inception to the latest CT was 552 (range: 31-2598) days for the entire cohort. We compared the frequency of new chronic pouch inflammation (13.8% vs 3.3%, P = 0.195), new pouch sinus (10.3% vs 0%, P = 0.112), composite adverse pouch outcome (24.1% vs 3.3%, P = 0.026) or pouch failure (10.3% vs 6.7%, P = 0.671) between the two groups. Kaplan-Meier plot for time-to-pouch failure between the pouch patients with or without excessive body mass index (BMI) gain (> 10%) showed statistical difference (P = 0.011). Limited stepwise multivariate analysis showed that excessive VAT gain (odds ratio = 12.608, 95% confidence interval: 1.190-133.538, P = 0.035) was an independent risk factor for the adverse pouch comes.

CONCLUSIONS

In this cohort of ileal pouch patients, excessive VAT gain as well as gain in BMI after pouch construction was found to be associated with poor long-term outcomes.

Linking the Microbiota, Chronic Disease, and the Immune System

Chronic inflammatory diseases (CIDs) are the most important causes of mortality in the world today and are on the rise. We now know that immune-driven inflammation is critical in the etiology of these diseases, though the environmental triggers and cellular mechanisms that lead to their development are still mysterious. Many CIDs are associated with significant shifts in the microbiota toward inflammatory configurations, which can affect the host both by inducing local and systemic inflammation and by alterations in microbiota-derived metabolites. This review discusses recent findings suggesting that shifts in the microbiota may contribute to chronic disease via effects on the immune system.

Adipokines and the role of visceral adipose tissue in inflammatory bowel disease

Recently, adipocytes have been recognized as actively participating in local and systemic immune responses via the secretion of peptides detectable in relevant levels in the systemic circulation, the so-called "adipo(cyto)kines". Multiple studies appearing within the last 10-15 years have focused on the possible impact of adipose tissue depots on inflammatory bowel disease (IBD). Consequently, various hypotheses regarding the role of different adipokines in inflammatory diseases in general and in intestinal inflammatory processes in particular have been developed and have been further refined in recent years. After a focused summary of the data reported concerning the impact of visceral adipose tissue on IBD, such as Crohn's disease and ulcerative colitis, our review focuses on recent developments indicating that adipocytes as part of the innate immune system actively participate in antimicrobial host defenses in the context of intestinal bacterial translocation, which are of utmost importance for the homeostasis of the whole organism. Modulators of adipose tissue function and regulators of adipokine secretion, as well as modifiers of adipocytic pattern recognition molecules, might represent future potential drug targets in IBD.

The Role of the Microbiota in Shaping Infectious Immunity

Humans are meta-organisms that maintain a diverse population of microorganisms on their barrier surfaces, collectively named the microbiota. Since most pathogens either cross or inhabit barrier surfaces, the microbiota plays a critical and often protective role during infections, both by modulating immune system responses and by mediating colonization resistance. However, the microbiota can also act as a reservoir for opportunistic microorganisms that can 'bloom', significantly complicating diseases of barrier surfaces by contributing to inflammatory immune responses. This review discusses our current understanding of the complex interactions between the host, its microbiota, and pathogenic organisms, focusing in particular on the intestinal mucosa.

Adipose tissue microbiota in humans: an open issue

BACKGROUND

A specific 'adipose tissue' microbiota has been recently identified in mice and hypothesized in humans. The purpose of this study was to verify the presence of microbiota of human whole adipose tissue and isolated adipocytes by combining culture-dependent and independent methods.

METHODS

Standard microbiological cultural techniques and 16S ribosomal RNA (16S rRNA) gene sequencing (Illumina technology) on DNA and RNA were employed to study (a) whole abdominal subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) from 14 obese and five normal-weight subjects and (b) mature adipocytes isolated from SAT and VAT after collagenase digestion or mechanical separation. To optimize the 16S rRNA gene detection, we used different DNA extraction methods (lysis with proteinase K, proteinase K+lysozyme and microbeads) and amplification procedures (semi-quantitative standard PCR and real-time quantitative PCR).

RESULTS

Microbiological cultures were negative in all analyzed samples. In enzymatically isolated adipocytes, 90% of the sequenced bacterial DNA belonged to Clostridium histolyticum, the bacterium from which the collagenase enzyme was isolated. Bacterial 16S rRNA gene was not detected from DNA and RNA of whole SAT and VAT, as well as of mechanically isolated mature adipocytes, even after blocking with a specific primer the nonspecific amplification of human mitochondrial 12S rRNA.

CONCLUSIONS

Our results do not support the presence of a human adipose tissue microbiota. In addition, they emphasized the technical problems encountered when applying metagenomic studies to human tissues with very low or absent bacterial load.

The Role of the Mesentery in Crohn's Disease: The Contributions of Nerves, Vessels, Lymphatics, and Fat to the Pathogenesis and Disease Course

Crohn's disease (CD) is a complex gastrointestinal disorder involving multiple levels of cross talk between the immunological, neural, vascular, and endocrine systems. The current dominant theory in CD is based on the unidirectional axis of dysbiosis-innate immunity-adaptive immunity-mesentery-body system. Emerging clinical evidence strongly suggests that the axis be bidirectional. The morphologic and/or functional abnormalities in the mesenteric structures likely contribute to the disease progression of CD, to a less extent the disease initiation. In addition to adipocytes, mesentery contains nerves, blood vessels, lymphatics, stromal cells, and fibroblasts. By the secretion of adipokines that have endocrine functions, the mesenteric fat tissue exerts its activity in immunomodulation mainly through response to afferent signals, neuropeptides, and functional cytokines. Mesenteric nerves are involved in the pathogenesis and prognosis of CD mainly through neuropeptides. In addition to angiogenesis observed in CD, lymphatic obstruction, remodeling, and impaired contraction maybe a cause and consequence of CD. Lymphangiogenesis and angiogenesis play a concomitant role in the progress of chronic intestinal inflammation. Finally, the interaction between neuropeptides, adipokines, and vascular and lymphatic endothelia leads to adipose tissue remodeling, which makes the mesentery an active participator, not a bystander, in the disease initiation and precipitation CD. The identification of the role of mesentery, including the structure and function of mesenteric nerves, vessels, lymphatics, and fat, in the intestinal inflammation in CD has important implications in understanding its pathogenesis and clinical management.

Can exercise affect the course of inflammatory bowel disease? Experimental and clinical evidence

The inflammatory bowel disease (IBD) consisting of Crohn's disease (CD) and ulcerative colitis (UC) are defined as idiopathic, chronic and relapsing intestinal disorders occurring in genetically predisposed individuals exposed to environmental risk factors such as diet and microbiome changes. Since conventional drug therapy is expensive and not fully efficient, there is a need for alternative remedies that can improve the outcome in patients suffering from IBD. Whether exercise, which has been proposed as adjunct therapy in IBD, can be beneficial in patients with IBD remains an intriguing question. In this review, we provide an overview of the effects of exercise on human IBD and experimental colitis in animal models that mimic human disease, although the information on exercise in human IBD are sparse and poorly understood. Moderate exercise can exert a beneficial ameliorating effect on IBD and improve the healing of experimental animal colitis due to the activity of protective myokines such as irisin released from working skeletal muscles. CD patients with higher levels of exercise were significantly less likely to develop active disease at six months. Moreover, voluntary exercise has been shown to exert a positive effect on IBD patients' mood, weight maintenance and osteoporosis. On the other hand, depending on its intensity and duration, exercise can evoke transient mild systemic inflammation and enhances pro-inflammatory cytokine release, thereby exacerbating the gastrointestinal symptoms. We discuss recent advances in the mechanism of voluntary and strenuous exercise affecting the outcome of IBD in patients and experimental animal models.

Microbiota-Dependent Sequelae of Acute Infection Compromise Tissue-Specific Immunity

Infections have been proposed as initiating factors for inflammatory disorders; however, identifying associations between defined infectious agents and the initiation of chronic disease has remained elusive. Here, we report that a single acute infection can have dramatic and long-term consequences for tissue-specific immunity. Following clearance of Yersinia pseudotuberculosis, sustained inflammation and associated lymphatic leakage in the mesenteric adipose tissue deviates migratory dendritic cells to the adipose compartment, thereby preventing their accumulation in the mesenteric lymph node. As a consequence, canonical mucosal immune functions, including tolerance and protective immunity, are persistently compromised. Post-resolution of infection, signals derived from the microbiota maintain inflammatory mesentery remodeling and consequently, transient ablation of the microbiota restores mucosal immunity. Our results indicate that persistent disruption of communication between tissues and the immune system following clearance of an acute infection represents an inflection point beyond which tissue homeostasis and immunity is compromised for the long-term. VIDEO ABSTRACT.

Changing views on diverticular disease: impact of aging, obesity, diet, and microbiota

The development of colonic diverticulosis is a common aging change in industrialized nations. While most patients have asymptomatic diverticulosis, around one in five develops symptomatic diverticular disease. This is characterized by recurrent abdominal pain and disturbed bowel habit. Some of the pain episodes are prolonged and are due to acute diverticulitis, which itself may be complicated by abscess, perforation, fistulation, or stricture formation. Risk factors favouring the development of symptomatic diverticular disease include obesity, smoking and diets low in fiber but high in red meat and animal fat. What determines the transition from asymptomatic diverticulosis to symptomatic diverticular disease is unclear but neuromuscular changes following acute diverticulitis may be responsible in some cases. The severity of symptoms generated depends on cerebral pain processing which is influenced by psychosocial factors. These are important considerations in deciding optimal patient management. Prior theories of the cause of diverticulosis suggested that constipation was an important cause, but new data challenge this and has provoked new ideas. Underlying mechanisms causing diverticulosis include weakening of the colonic wall and/or degenerative changes in the enteric nerves. Dietary induced changes in microbiota and the host inflammatory response may underlie the subsequent development of acute/chronic diverticulitis and its sequela.

Metabolic inflammation in inflammatory bowel disease: crosstalk between adipose tissue and bowel

Epidemiological studies show that both the incidence of inflammatory bowel disease (IBD) and the proportion of people with obesity and/or obesity-associated metabolic syndrome increased markedly in developed countries during the past half century. Obesity is also associated with the development of more active IBD and requirement for hospitalization and with a decrease in the time span between diagnosis and surgery. Patients with IBD, especially Crohn's disease, present fat-wrapping or "creeping fat," which corresponds to ectopic adipose tissue extending from the mesenteric attachment and covering the majority of the small and large intestinal surface. Mesenteric adipose tissue in patients with IBD presents several morphological and functional alterations, e.g., it is more infiltrated with immune cells such as macrophages and T cells. All these lines of evidence clearly show an association between obesity, adipose tissue, and functional bowel disorders. In this review, we will show that the mesenteric adipose tissue and creeping fat are not innocent by standers but actively contribute to the intestinal and systemic inflammatory responses in patients with IBD. More specifically, we will review evidence showing that adipose tissue in IBD is associated with major alterations in the secretion of cytokines and adipokines involved in inflammatory process, in adipose tissue mesenchymal stem cells and adipogenesis, and in the interaction between adipose tissue and other intestinal components (immune, lymphatic, neuroendocrine, and intestinal epithelial systems). Collectively, these studies underline the importance of adipose tissue for the identification of novel therapeutic approaches for IBD.

Anatomical localization of commensal bacteria in immune cell homeostasis and disease

The mammalian gastrointestinal (GI) tract is colonized by trillions of beneficial commensal bacteria that are essential for promoting normal intestinal physiology. While the majority of commensal bacteria are found in the intestinal lumen, many species have also adapted to colonize different anatomical locations in the intestine, including the surface of intestinal epithelial cells (IECs) and the interior of gut-associated lymphoid tissues. These distinct tissue localization patterns permit unique interactions with the mammalian immune system and collectively influence intestinal immune cell homeostasis. Conversely, dysregulated localization of commensal bacteria can lead to inappropriate activation of the immune system and is associated with numerous chronic infectious, inflammatory, and metabolic diseases. Therefore, regulatory mechanisms that control proper anatomical containment of commensal bacteria are essential to maintain tissue homeostasis and limit pathology. In this review, we propose that commensal bacteria associated with the mammalian GI tract can be anatomically defined as (i) luminal, (ii) epithelial-associated, or (iii) lymphoid tissue-resident, and we discuss the role and regulation of these microbial populations in health and disease.

Role of fat and adipokines in intestinal inflammation

PURPOSE OF REVIEW

This review summarizes current knowledge on the contribution of mesenteric adipose tissue in intestinal inflammation. We will describe the cellular and humoral characteristics of creeping fat, their potential impact for Crohn's disease and propose a working model for the critical interplay between the creeping fat and the inflamed intestine.

RECENT FINDINGS

Creeping fat can be distinguished from healthy adipose tissue by its distinctively small adipocytes, by a specific microenvironment defined by high levels of adipokines and by a dominant immune cell infiltration. In Crohn's disease transmural inflammation facilitates increased bacterial translocation into the creeping fat. Translocalizing antigens can directly activate (pre)adipocytes via innate receptors. Adipocyte-derived mediators modulate phenotype and function of innate and adaptive immune cells. Activated (pre)adipocytes and adipokine-modulated immune cells might support a degree of inflammatory activation within the creeping fat that allows competent immune defense against exogenous factors while preventing systemic inflammation.

SUMMARY

Fat tissue as an active organ in health and disease has been ignored for too long. The last few years of research provided evidence for the complex metabolic and immunological functions of adipose tissue. On the basis of the available data, creeping fat in Crohn's disease exerts a protective function by a localized anti-inflammatory effect, thus preventing a systemic inflammatory response.

Adipose-tissue and intestinal inflammation - visceral obesity and creeping fat

Obesity has become one of the main threats to health worldwide and therefore gained increasing clinical and economic significance as well as scientific attention. General adipose-tissue accumulation in obesity is associated with systemically increased pro-inflammatory mediators and humoral and cellular changes within this compartment. These adipose-tissue changes and their systemic consequences led to the concept of obesity as a chronic inflammatory state. A pathognomonic feature of Crohn’s disease (CD) is creeping fat (CF), a locally restricted hyperplasia of the mesenteric fat adjacent to the inflamed segments of the intestine. The precise role of this adipose-tissue and its mediators remains controversial, and ongoing work will have to define whether this compartment is protecting from or contributing to disease activity. This review aims to outline specific cellular changes within the adipose-tissue, occurring in either obesity or CF. Hence the potential impact of adipocytes and resident immune cells from the innate and adaptive immune system will be discussed for both diseases. The second part focuses on the impact of generalized adipose-tissue accumulation in obesity, respectively on the locally restricted form in CD, on intestinal inflammation and on the closely related integrity of the mucosal barrier.