Colonic leptin: source of a novel proinflammatory cytokine involved in IBD

Role of Adipose Tissue Hormones in Pathogenesis of Cryptoglandular Anal Fistula

The cryptoglandular perianal fistula is a common benign anorectal disorder that is managed mainly with surgery and in some cases may be an extremely challenging condition. Perianal fistulas are often characterized by significantly decreased patient quality of life. Lack of fully recognized pathogenesis of this disease makes it difficult to treat it properly. Recently, adipose tissue hormones have been proposed to play a role in the genesis of cryptoglandular anal fistulas. The expression of adipose tissue hormones and epithelial-to-mesenchymal transition (EMT) factors were characterized based on 30 samples from simple fistulas and 30 samples from complex cryptoglandular perianal fistulas harvested during surgery. Tissue levels of leptin, resistin, MMP2, and MMP9 were significantly elevated in patients who underwent operations due to complex cryptoglandular perianal fistulas compared to patients with simple fistulas. Adiponectin and E-cadherin were significantly lowered in samples from complex perianal fistulas in comparison to simple fistulas. A negative correlation between leptin and E-cadherin levels was observed. Resistin and MMP2 levels, as well as adiponectin and E-cadherin levels, were positively correlated. Complex perianal cryptoglandular fistulas have a reduced level of the anti-inflammatory adipokine adiponectin and have an increase in the levels of proinflammatory resistin and leptin. Abnormal secretion of these adipokines may affect the integrity of the EMT in the fistula tract. E-cadherin, MMP2, and MMP9 expression levels were shifted in patients with more advanced and complex perianal fistulas. Our results supporting the idea of using mesenchymal stem cells in the treatment of cryptoglandular perianal fistulas seem reasonable, but further studies are warranted.

Creeping Fat in the Pathogenesis of Crohn's Disease: An Orchestrator or a Silent Bystander?

Although the phenomenon of hypertrophied adipose tissue surrounding inflamed bowel segments in Crohn's disease has been described since 1932, the mechanisms mediating the creeping fat formation and its role in the pathogenesis of the disease have not been fully unraveled. Recent advances demonstrating the multiple actions of adipose tissue beyond energy storage have brought creeping fat to the forefront of scientific research. In Crohn's disease, dysbiosis and transmural injury compromise the integrity of the intestinal barrier, resulting in an excessive influx of intraluminal microbiota and xenobiotics. The gut and peri-intestinal fat are in close anatomic relationship, implying a direct reciprocal immunologic relationship, whereas adipocytes are equipped with an arsenal of innate immunity sensors that respond to invading stimuli. As a result, adipocytes and their progenitor cells undergo profound immunophenotypic changes, leading to adipose tissue remodeling and eventual formation of creeping fat. Indeed, creeping fat is an immunologically active organ that synthesizes various pro- and anti-inflammatory cytokines, profibrotic mediators, and adipokines that serve as paracrine/autocrine signals and regulate immune responses. Therefore, creeping fat appears to be involved in inflammatory signaling, which explains why it has been associated with a higher severity or complicated phenotype of Crohn's disease. Interestingly, there is growing evidence for an alternative immunomodulatory function of creeping fat as a second barrier that prevents an abnormal systemic inflammatory response at the expense of an increasingly proliferating profibrotic environment. Further studies are needed to clarify how this modified adipose tissue exerts its antithetic effect during the course of Crohn's disease.

Oxidative stress, hormones, and effects of natural antioxidants on intestinal inflammation in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic, relapsing gastrointestinal (GI) disorder characterized by intestinal inflammation. The etiology of IBD is multifactorial and results from a complex interplay between mucosal immunity, environmental factors, and host genetics. Future therapeutics for GI disorders, including IBD, that are driven by oxidative stress require a greater understanding of the cellular and molecular mechanisms mediated by reactive oxygen species (ROS). In the GI tract, oxidative stressors include infections and pro-inflammatory responses, which boost ROS generation by promoting the production of pro-inflammatory cytokines. Nuclear factor kappa B (NF-κB) and nuclear factor erythroid 2-related factor 2 (Nrf2) represent two important signaling pathways in intestinal immune cells that regulate numerous physiological processes, including anti-inflammatory and antioxidant activities. Natural antioxidant compounds exhibit ROS scavenging and increase antioxidant defense capacity to inhibit pro-oxidative enzymes, which may be useful in IBD treatment. In this review, we discuss various polyphenolic substances (such as resveratrol, curcumin, quercetin, green tea flavonoids, caffeic acid phenethyl ester, luteolin, xanthohumol, genistein, alpinetin, proanthocyanidins, anthocyanins, silymarin), phenolic compounds including thymol, alkaloids such as berberine, storage polysaccharides such as tamarind xyloglucan, and other phytochemicals represented by isothiocyanate sulforaphane and food/spices (such as ginger, flaxseed oil), as well as antioxidant hormones like melatonin that target cellular signaling pathways to reduce intestinal inflammation occurring with IBD.

A systematic review of the effect of structured exercise on inflammation and body composition in inflammatory bowel disease

PURPOSE

Given the substantial risk of treatment failure in inflammatory bowel disease (IBD), adjuvant therapies may play a role in disease management. We aim to carry out a systematic review to examine the effects of structured exercise on the inflammatory response in patients with IBD. Our secondary aim is to examine the effect of structured exercise programmes on body composition given both an increase in visceral obesity and the presence of sarcopenia have deleterious effects on outcomes in IBD.

METHODS

A systematic review was carried out following the Methodological Expectations of Cochrane Intervention Reviews (MECIR) manual and the Cochrane Handbook for Systematic Reviews of Interventions. Title/Abstract and MeSH Terms were used to search for relevant studies.

RESULTS

In total, 1516 records were screened for eligibility, and 148 records were reviewed for eligibility, of which 16 were included and a further 7 studies were identified from hand searching references. Four studies included body composition outcomes, and 14 studies reviewed the inflammatory response to exercise.

CONCLUSION

Further studies of adequate duration are required to include patients with more active disease to demonstrate an inflammatory response to exercise. Body composition measurements including muscle mass and visceral adiposity may play a key role in response to medical therapy in IBD and should be included as exploratory outcomes in future studies. A meta-analysis was not carried out due to the significant heterogeneity amongst studies.

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.

Paeoniflorin Ameliorates Colonic Fibrosis in Rats with Postinfectious Irritable Bowel Syndrome by Inhibiting the Leptin/LepRb Pathway

Postinfectious irritable bowel syndrome (PI-IBS) is a highly prevalent gastrointestinal disorder associated with immune dysregulation and depression- and anxiety-like behaviors. Through traditional medicine, the active ingredient of Paeoniae Radix called paeoniflorin (PF) was previously found to prevent the symptoms of PI-IBS. However, there is limited information on the effects of PF on intestinal function and depression- and anxiety-like symptoms in PI-IBS animal models. Here, we aimed to determine the effects of PF treatment on the symptoms of PI-IBS in a rat model. The PI-IBS rat model was established via early postnatal sibling deprivation (EPSD), trinitrobenzenesulfonic acid (TNBS), and chronic unpredictable mild stress (CUMS) stimulation and then treated with different dosages of PF (10, 20, and 40 mg/kg) and leptin (1 and 10 mg/kg). The fecal water content and body weight were measured to evaluate the intestinal function, while the two-bottle test for sucrose intake, open field test (OFT), and elevated plus maze test (EMT) were performed to assess behavioral changes. The serum leptin levels were also measured using an enzyme-linked immunosorbent assay. Furthermore, the expressions of leptin and its receptor, LepRb, were detected in colonic mucosal tissues through an immunohistochemical assay. The activation of the PI3K/AKT signaling pathway and the expression of brain-derived neurotrophic factor (BDNF) were also detected via western blotting. After the experimental period, the PI-IBS rats presented decreased body weight and increased fecal water content, which coincided with elevated leptin levels and heightened depression- and anxiety-like behaviors (e.g., low sucrose intake, less frequency in the center areas during OFT, and fewer activities in the open arms during EMT). However, the PF treatment ameliorated these observed symptoms. Furthermore, PF not only inhibited leptin/LepRb expression but also reduced the PI3K/AKT phosphorylation and BDNF expression in PI-IBS rats. Notably, cotreatment with leptin (10 mg/kg) reduced the effects of PF (20 mg/kg) on colonic fibrosis, leptin/LepRb expression, and PI3K/AKT activation. Therefore, our findings suggest that leptin is targeted by PF via the leptin/LepRb pathway, consequently ameliorating the symptoms of PI-IBS. Our study also contributes novel insights for elucidating the pharmacological action of PF on gastrointestinal disorders and may be used for the clinical treatment of PI-IBS in the future.

Circulating Levels of WISP-1 (Wnt1-Inducible Signaling Pathway Protein 1) and Other Selected Adipokines in Children With Inflammatory Bowel Disease

Wnt1 inducible protein-1 signaling pathway (WISP-1) is a relatively new adipokine involved in many cellular processes, including epithelial mucosa healing. The aim of the study was to compare circulating levels of WISP-1 and other selected adipokines [adiponectin, resistin and retinol-binding protein 4 (RBP-4)] in children with inflammatory bowel disease (IBD) with healthy controls and to investigate possible differences between Crohn's disease patients. (CD) or ulcerative colitis (UC). The study was performed as a case-control study. In addition to adipokines, anthropometric, lipid parameters, markers of inflammation or disease activity were evaluated in all participants. Compared to healthy controls (n=20), significantly lower levels of adiponectin and higher levels of resistin and WISP-1 were found in patients with IBD (n=58). Elevation of WISP-1 was detected only in the CD group (n=31). There were no differences in RBP-4 levels between the groups. Adiponectin, WISP-1 and RBP-4 were independently associated with body mass index only, resistin levels were associated with C-reactive protein levels and leukocyte counts. Adverse adipokines production reflects presence of dysfunctional fat tissue in IBD patients. Higher levels of WISP-1 in CD compared to patients with UC may indicate a specific role for mesenteric adipose tissue in WISP-1 production.

The Complex Relationship Between Microbiota, Immune Response and Creeping Fat in Crohn's Disease

In the last decade, there has been growing interest in the pathological involvement of hypertrophic mesenteric fat attached to the serosa of the inflamed intestinal segments involved in Crohn's disease [CD], known as creeping fat. In spite of its protective nature, creeping fat harbours an aberrant inflammatory activity which, in an already inflamed intestine, may explain why creeping fat is associated with a greater severity of CD. The transmural inflammation of CD facilitates the interaction of mesenteric fat with translocated intestinal microorganisms, contributing to activation of the immune response. This may be not the only way in which microorganisms alter the homeostasis of this fatty tissue: intestinal dysbiosis may also impair xenobiotic metabolism. All these CD-related alterations have a functional impact on nuclear receptors such as the farnesoid X receptor or the peroxisome proliferator-activated receptor γ, which are implicated in regulation of the immune response, adipogenesis and the maintenance of barrier function, as well as on creeping fat production of inflammatory-associated cells such as adipokines. The dysfunction of creeping fat worsens the inflammatory course of CD and may favour intestinal fibrosis and fistulizing complications. However, our current knowledge of the pathophysiology and pathogenic role of creeping fat is controversial and a better understanding might provide new therapeutic targets for CD. Here we aim to review and update the key cellular and molecular alterations involved in this inflammatory process that link the pathological components of CD with the development of creeping fat.

Visceral adiposity and inflammatory bowel disease

BACKGROUND

Rates of obesity are increasing worldwide, as is the incidence of inflammatory bowel disease (IBD). Obesity is now considered an inflammatory state. Visceral adiposity in particular may be associated with a more severe inflammatory phenotype in IBD.

AIM

The aim of this review article is to summarise the current literature on the association between visceral adiposity and outcomes in inflammatory bowel disease METHODS: To collect relevant articles, PubMed/MEDLINE and Embase searches were performed using Boolean search phrases. Grey literature and manual searches were also performed. Abstracts were selected by two independent reviewers based on pre-determined criteria. Full text articles were reviewed, and data extracted and assessed.

RESULTS

One hundred twenty-seven abstracts were obtained through the initial search, with 85 abstracts reviewed and 22 full text articles included. Characteristics are included in Table 1. Most of these were retrospective studies and of moderate or weak quality. Studies suggested visceral fat content is higher in Crohn's disease than in healthy controls. Visceral adiposity was associated with an increased risk of complex Crohn's disease phenotype (OR 26.1 95% CI 2-75.4; p = 0.02). Post-operative recurrence was higher in patients with higher visceral fat indices (RR 2.1; CI 1.5-3; p = 0.012). There were conflicting data regarding the effect of visceral adiposity on post-operative complications and the efficacy of medical therapy. Table 1 Study characteristics Author Year Country Study type Study numbers Control group Disease type Methodology e.g. CT Body composition measurements Results Argeny [24] 2018 Austria Retrospective cohort N = 95 N/A Crohn's disease CT; L3 level Visceral fat area (cm²) Visceral fat index (VFA/m²) No association between VFA or VFI and short-term post-operative outcomes Bryant [30] 2018 Australia Prospective cohort N = 110 N/A Crohn's disease and UC DXA Visceral adipose tissue (VAT) (cm³) Visceral adipose tissue (grams) VAT/height index (cm³/m²) VAT:subcutaneous adipose tissue ratio Fat mass index (kg/m²) VAT and VHI increased significantly over 24 months Bryant [13] 2018 Australia Prospective cohort N = 72 N/A Crohn's disease; female DXA Visceral adipose tissue (VAT) (cm³) Visceral adipose tissue (grams) VAT/height index (cm³/m²) VAT:subcutaneous adipose tissue ratio VAT:SAT positively associated with stricturing disease Adiposity not associated with fistulising disease phenotype VAT:SAT significantly associated with faecal calprotectin in L3 phenotype VAT:SAT significantly negatively associated with VHI and QoL over 24 months Buning [25] 2015 Germany Case control N = 50 N = 19 healthy controls Crohn's disease MRI US VAT Thickness of abdominal fat Distance to posterior wall of aorta Area of inferior part of perirenal fat VAT accumulation was higher in CD patients vs healthy controls VAT and VAT/fat mass ratio higher in patients in short-term remission vs long-term remission VAT/FM higher in stricturing/fistulising disease vs inflammatory subtype No association between VAT/FM and CDAI, HBI or anti-TNF treatment Connolly [26] 2014 US Retrospective cohort N = 143 N/A Crohn's disease CT (L1-L5 level) Visceral/intra-abdominal adiposity (VA) Subcutaneous adiposity (SA) VA not associated with post-operative morbidity Decreased SA and increased visceral/subcutaneous ratio were predictive of post-op complications. (p = 0.02; p < 0.001) Cravo [27] 2017 Portugal Retrospective cohort N = 71 N/A Crohn's disease CT (L3 level) Smooth muscle area (cm²) Visceral fat area (cm²) Subcutaneous fat area (cm²) Visceral fat index Muscle radiation attenuation L2 phenotype associated with lower muscle attenuation and higher visceral fat index (non-significant) B2/B3/surgery - significantly lower muscle attenuation. VFI associated with increased risk of complicated phenotype. (OR 26.1; 95% CI 1-75; p = 0.02) Ding [17] 2016 US Retrospective cohort N = 164 N/A Crohn's disease CT (L3 level) Visceral fat area (cm²) Subcutaneous fat area Total fat area Visceral obesity associated with longer duration of surgery, increased intra-operative blood loss and longer length of bowel resected Higher complication rates in patients with visceral obesity (p < 0.001) VFA independent risk factor of adverse post-op outcomes Ding [14] 2017 Retrospective cohort N = 106 N/A Crohn's disease CT (L3 level) Visceral fat area Subcutaneous fat area Skeletal muscle area Skeletal muscle index Visceral obesity and myopenic obesity not significantly associated with risk of primary non-response Body composition factors not associated with secondary loss of response Erhayiem [18] 2011 UK Retrospective cohort N = 50 N/A Crohn's disease CT (L4 level) Mesenteric fat index (visceral:subcutaneous area ratio)N = 50 Mesenteric fat index was significantly higher in complicated Crohn's disease. ROC analysis for MFI in identifying complicated Crohn's disease: AUC = 0.95 (95% CI 0.89-1.0) Feng [28] 2018 China Retrospective cohort N = 80 Non-IBD GI patients Crohn's disease CT-energy spectral Visceral fat area (cm²) Subcutaneous fat area (cm²) Mesenteric fat index No significant difference in VFA between Crohn's disease cohort and control group. (p = 0.669). ROC analysis: detection of disease based on VFA and MFI: AUC 0.776 Sensitivity 77.5% Specificity 67.5% Hafraoui [16] 1998 France/Belgium Prospective N = 43 Healthy volunteers n = 13 Intestinal resection n = 9 Crohn's disease MRI (umbilicus) Total abdominal fat (cm²) Intra-abdominal fat (cm²) Subcutaneous fat (cm²) Ratio of intra-abdominal:total fat area was significantly higher in patients with Crohn's vs controls. (p = 0.012) No correlation between abdominal fat tissue and disease activity, duration or steroid therapy Holt [29] 2017 Australia/New Zealand RCT N = 44 N = 11 placebo group Crohn's disease CT/MRI (L3, L4-5 levels) Visceral adipose tissue area Subcutaneous adipose tissue area Skeletal muscle area Visceral adipose tissue/height index VHI > 1.5 times gender mean was specific for endoscopic recurrence (100%) with sensitivity of 29%. PPV = 1 (0.59-1.00) There was no significant difference in disease activity at 18 months post-resection based on VHI > 1.5 gender mean Li [31] 2015 China Retrospective cohort N = 72 N/A Crohn's disease CT (umbilicus) Visceral fat area (cm²) Subcutaneous fat area (cm²) Mesenteric fat index Post-op recurrence was more frequent with high VFA values. (p = 0.019) VFA and MFI were independent risk factors for post-operative recurrence. (p = 0.013 and p = 0.028, respectively) High VFA and high MFI were significantly higher in patients with endoscopic activity (p = 0.023) Liu [32] 2016 Retrospective case-control N = 59 N = 30 (< 15% increase VFA) IBD with IPAA CT (L3) Visceral fat area Subcutaneous fat area No difference in pouchitis, pouch sinus formation and composite adverse pouch outcomes between the 2 groups with and without VFA increase > 15%. Excessive VAT gain was an independent risk factor for the composite adverse pouch outcomes. (OR 12.6 (95% CI 1.19-133.5) Magro [33] 2018 Brazil Cross-sectional study N = 78 N = 28 Health control Crohn's disease DEXA Fat and lean masses Visceral fat (kg) Visceral fat/BMI Visceral fat per %body fat VF was higher in Crohn's disease group (p = 0.004) compared to controls Parmentier-Decrucq [34] 2009 Prospective study N = 132 N/A Crohn's disease MRI Subcutaneous fat Visceral fat Total abdominal fat increased 18% in Crohn's disease patients treated with infliximab induction therapy Shen [35] 2018 China Retrospective N = 97 N/A Crohn's disease CT (umbilicus) Subcutaneous fat area Visceral fat area Mesenteric fat index VFA and MFI were significantly lower in patients with mucosal healing (post-infliximab). (p < 0.0001) SFA was not significantly different VFA correlated with CDAI (p < 0.001) and was an independent predictive factor for mucosal healing Stidham [15] 2015 Retrospective N = 269 N/A Crohn's disease CT(T10-L5) Subcutaneous fat volume Visceral fat volume No significant difference in visceral fat volume between patients with surgical complications Thiberge [36] 2018 France Retrospective N = 149 N/A Crohn's disease CT (L3 level) Skeletal muscle index Visceral adiposity index Subcutaneous adiposity index SAI and VAI were significantly lower in patients who underwent surgery or who died in 6 months post-CT(p = 0.009 and p < 0.001) VanDerSloot [37] 2017 Cohort study N/A Crohn's disease CT (T11-S5) Visceral adipose tissue volume Non-significant trend toward increased risk of surgery and penetrating disease with increasing VAT Wei [38] 2018 China Retrospective N = 86 N/A IBD post-resection CT (L3 level) Visceral adipose volume Subcutaneous adipose volume Increased visceral:subcutaneous fat ratio was associated with increased procalcitonin levels on post-op days 1, 3 and 5 Yadav [39] 2017 India Prospective N = 97 N/A IBD CT (L4 level) Visceral fat area Subcutaneous fat area No statistically significant correlation between visceral fat and disease behaviour in Crohn's disease N/A not applicable, VFA visceral fat area, VFI visceral fat index, VAT visceral adipose tissue, VHI visceral adipose tissue to height index, SAT subcutaneous adipose tissue, DXA dual-energy X-ray absorptiometry, CT computer tomography, MRI magnetic resonance imaging, US ultrasound, CDAI Crohn's disease activity index, HBI Harvey-Bradshaw Index, anti-TNF anti-tumour necrosis factor, SA subcutaneous adiposity, ROC receiver operating curve, AUC area under the curve, MFI mesenteric fat index, SAI subcutaneous adiposity index, PPV positive predictive value CONCLUSION: Visceral adiposity appears to be increased in Crohn's disease with some evidence that it is also associated with more complex disease phenotypes. There is also a signal that post-operative recurrence rates are affected by increasing mesenteric adiposity. There is a relative lack of data in UC patients and further high-quality studies are necessary to elucidate the relationship between visceral adiposity and IBD and the implications for patient outcomes.

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.

Role of Leptin in the Digestive System

Leptin is a pluripotent peptide hormone produced mainly by adipocytes, as well as by other tissues such as the stomach. Leptin primarily acts on the central nervous system, particularly the hypothalamus, where this hormone regulates energy homeostasis and neuroendocrine function. Owing to this, disruption of leptin signaling has been linked with numerous pathological conditions. Recent studies have also highlighted the diverse roles of leptin in the digestive system including immune regulation, cell proliferation, tissue healing, and glucose metabolism. Of note, leptin acts differently under physiological and pathological conditions. Here, we review the current knowledge on the functions of leptin and its downstream signaling in the gastrointestinal tract and accessory digestive organs, with an emphasis on its physiological and pathological implications. We also discuss the current therapeutic uses of recombinant leptin, as well as its limitations.

Intestinal Alkaline Phosphatase Combined with Voluntary Physical Activity Alleviates Experimental Colitis in Obese Mice. Involvement of Oxidative Stress, Myokines, Adipokines and Proinflammatory Biomarkers

Intestinal alkaline phosphatase (IAP) is an essential mucosal defense factor involved in the process of maintenance of gut homeostasis. We determined the effect of moderate exercise (voluntary wheel running) with or without treatment with IAP on the course of experimental murine 2,4,6-trinitrobenzenesulfonic acid (TNBS) colitis by assessing disease activity index (DAI), colonic blood flow (CBF), plasma myokine irisin levels and the colonic and adipose tissue expression of proinflammatory cytokines, markers of oxidative stress (SOD2, GPx) and adipokines in mice fed a standard diet (SD) or high-fat diet (HFD). Macroscopic and microscopic colitis in sedentary SD mice was accompanied by a significant decrease in CBF, and a significant increase in the colonic expression of tumor necrosis factor-alpha (TNF-α), IL-6, IL-1β and leptin mRNAs and decrease in the mRNA expression of adiponectin. These effects were aggravated in sedentary HFD mice but reduced in exercising animals, potentiated by concomitant treatment with IAP, especially in obese mice. Exercising HFD mice demonstrated a substantial increase in the mRNA for adiponectin and a decrease in mRNA leptin expression in intestinal mucosa and mesenteric fat as compared to sedentary animals. The expression of SOD2 and GPx mRNAs was significantly decreased in adipose tissue in HFD mice, but these effects were reversed in exercising mice with IAP administration. Our study shows for the first time that the combination of voluntary exercise and oral IAP treatment synergistically favored healing of intestinal inflammation, strengthened the antioxidant defense and ameliorated the course of experimental colitis; thus, IAP may represent a novel adjuvant therapy to alleviate inflammatory bowel disease (IBD) in humans.

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.

Adipokine-Modulated Immunological Homeostasis Shapes the Pathophysiology of Inflammatory Bowel Disease

Inflammatory colon diseases, which are a global health concern, include a variety of gastrointestinal tract disorders, such as inflammatory bowel disease and colon cancer. The pathogenesis of these colon disorders involves immune alterations with the pronounced infiltration of innate and adaptive immune cells into the intestines and the augmented expression of mucosal pro-inflammatory cytokines stimulated by commensal microbiota. Epidemiological studies during the past half century have shown that the proportion of obese people in a population is associated with the incidence and pathogenesis of gastrointestinal tract disorders. The advancement of understanding of the immunological basis of colon disease has shown that adipocyte-derived biologically active substances (adipokines) modulate the role of innate and adaptive immune cells in the progress of intestinal inflammation. The biomedical significance in immunological homeostasis of adipokines, including adiponectin, leptin, apelin and resistin, is clear. In this review, we highlight the existing literature on the effect and contribution of adipokines to the regulation of immunological homeostasis in inflammatory colon diseases and discuss their crucial roles in disease etiology and pathogenesis, as well as the implications of these results for new therapies in these disorders.

Immunolocalization of leptin and leptin receptor in colorectal mucosa of ulcerative colitis, Crohn's disease and control subjects with no inflammatory bowel disease

The expression of leptin and leptin receptor (Ob-R) has been partially elucidated in colon of patients with inflammatory bowel diseases (IBDs), even though leptin is involved in angiogenesis and inflammation. We previously reported overexpression of GLUT5 fructose transporter, in aberrant clusters of lymphatic vessels in lamina propria of IBD and controls. Here, we examine leptin and Ob-R expression in the same biopsies. Specimens were obtained from patients with ulcerative colitis (UC), Crohn’s disease (CD) and controls who underwent screening for colorectal cancer, follow-up after polypectomy or with a history of lower gastrointestinal symptoms. Immunohistochemistry revealed leptin in apical and basolateral membranes of short epithelial portions, Ob-R on the apical pole of epithelial cells. Leptin and Ob-R were also identified in structures and cells scattered in the lamina propria. In UC, a significant correlation between leptin and Ob-R in the lamina propria was found in all inflamed samples, beyond non-inflamed samples of the proximal tract, while in CD, it was found in inflamed distal samples. Most of the leptin and Ob-R positive areas in the lamina propria were also GLUT5 immunoreactive in inflamed and non-inflamed mucosa. A significant correlation of leptin or Ob-R expression with GLUT5 was observed in the inflamed distal samples from UC. Our findings suggest that there are different sites of leptin and Ob-R expression in large intestine and those in lamina propria do not reflect the status of mucosal inflammation. The co-localization of leptin and/or Ob-R with GLUT5 may indicate concomitance effects in colorectal lamina propria areas.

Leptin Downregulates Angulin-1 in Active Crohn's Disease via STAT3

Crohn’s disease (CD) has an altered intestinal barrier function, yet the underlying mechanisms remain to be disclosed. The tricellular tight junction protein tricellulin is involved in the maintenance of the paracellular macromolecule barrier and features an unchanged expression level in CD but a shifted localization. As angulins are known to regulate the localization of tricellulin, we hypothesized the involvement of angulins in CD. Using human biopsies, we found angulin-1 was downregulated in active CD compared with both controls and CD in remission. In T84 and Caco-2 monolayers, leptin, a cytokine secreted by fat tissue and affected in CD, decreased angulin-1 expression. This effect was completely blocked by STAT3 inhibitors, Stattic and WP1066, but only partially by JAK2 inhibitor AG490. The effect of leptin was also seen at a functional level as we observed in Caco-2 cells an increased permeability for FITC-dextran 4 kDa indicating an impaired barrier against macromolecule uptake. In conclusion, we were able to show that in active CD angulin-1 expression is downregulated, which leads to increased macromolecule permeability and is inducible by leptin via STAT3. This suggests that angulin-1 and leptin secretion are potential targets for intervention in CD to restore the impaired intestinal barrier.

Gut Microbiome, Intestinal Permeability, and Tissue Bacteria in Metabolic Disease: Perpetrators or Bystanders?

The emerging evidence on the interconnectedness between the gut microbiome and host metabolism has led to a paradigm shift in the study of metabolic diseases such as obesity and type 2 diabetes with implications on both underlying pathophysiology and potential treatment. Mounting preclinical and clinical evidence of gut microbiota shifts, increased intestinal permeability in metabolic disease, and the critical positioning of the intestinal barrier at the interface between environment and internal milieu have led to the rekindling of the "leaky gut" concept. Although increased circulation of surrogate markers and directly measurable intestinal permeability have been linked to increased systemic inflammation in metabolic disease, mechanistic models behind this phenomenon are underdeveloped. Given repeated observations of microorganisms in several tissues with congruent phylogenetic findings, we review current evidence on these unanticipated niches, focusing specifically on the interaction between gut permeability and intestinal as well as extra-intestinal bacteria and their joint contributions to systemic inflammation and metabolism. We further address limitations of current studies and suggest strategies drawing on standard techniques for permeability measurement, recent advancements in microbial culture independent techniques and computational methodologies to robustly develop these concepts, which may be of considerable value for the development of prevention and treatment strategies.

Leptin induces TNFα-dependent inflammation in acquired generalized lipodystrophy and combined Crohn's disease

Leptin has been shown to modulate intestinal inflammation in mice. However, clinical evidence regarding its immune-stimulatory potential in human Crohn’s disease remains sparse. We here describe a patient with the unique combination of acquired generalized lipodystrophy and Crohn’s disease (AGLCD) featuring a lack of adipose tissue, leptin deficiency and intestinal inflammation. Using mass and flow cytometry, immunohistochemistry and functional metabolic analyses, the AGLCD patient was compared to healthy individuals and Crohn’s disease patients regarding immune cell composition, function and metabolism and the effects of recombinant N-methionylleptin (rLeptin) were evaluated. We provide evidence that rLeptin exerts diverse pro-inflammatory effects on immune cell differentiation and function, including the metabolic reprogramming of immune cells and the induction of TNFα, ultimately aggravating Crohn’s disease in the AGLCD patient, which can be reversed by anti-TNFα therapy. Our results indicate that leptin is required for human immune homeostasis and contributes to autoimmunity in a TNFα-dependent manner.

The adipokine leptin modulates intestinal inflammation in mice. Here the authors describe a patient with inflammatory bowel disease and lipodystrophy, providing evidence that leptin aggravates intestinal inflammation with proinflammatory effects on leukocytes that are reversible by TNFα blockade.

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.

Adipose Tissue-Derived Biomarkers of Intestinal Barrier Functions for the Characterization of Diarrhoea-Predominant IBS

Background

Alterations of the small-intestinal permeability (s-IP) might play an essential role in a subgroup of diarrhoea-predominant IBS (D-IBS) patients.

Goals

(a) To analyse in D-IBS patients the symptom profile in relation to the altered (+) or not (−) s-IP using the Gastrointestinal Symptom Rating Scale (GSRS). (b) To assess the circulating levels of the adipokines IL-6, IL-8, TNF-α, leptin, and adiponectin, along with LPS, TLR-4, neurotensin, and brain-derived neurotrophic factor (BDNF). The frequency distribution of SNPs at the loci for the investigated molecules and leptin receptor was evaluated.

Study

The study included 34 D-IBS patients and 17 healthy controls (HC). s-IP permeability was assayed by high-performance liquid chromatography determination in the urine of the lactulose to mannitol ratio. Concentrations of IL-6, IL-8, TNF-α, LPS, TLR-4, leptin, adiponectin, neurotensin, and BDNF were assayed by ELISA. Screening of genetic variants was done employing the restriction fragment length polymorphism-polymerase chain reaction method.

Results

D-IBS(−) patients had a significantly higher GSRS cluster pain and diarrhoea profile than D-IBS(+) ones. Significant correlations were found between the symptoms clusters and immune activation and inflammation markers. The levels of adipo(cyto)kines in D-IBS(+) patients were higher than those of controls, and IL-6 levels correlated with those of LPS. Leptin and BDNF were significantly higher, and neurotensin levels were significantly lower in D-IBS(+) than in controls. No differences were found in the frequency distribution of genotypes among the study groups.

Conclusions

Results from this study could be of some help in the characterization of the D-IBS and highlight the contribution of an altered intestinal barrier in the pathogenesis of this syndrome. Besides, a role could be ascribed to molecules secreted by the visceral adipose tissue that can impact on barrier functions.

Adipokines and Their Role in Intestinal Inflammation

Fat tissue was initially described for its endocrine and metabolic function. Over the last two decades increasing evidence indicated a close interaction with the immune system. Partly responsible for this immune modulatory function are soluble factors released by the fat tissue, most prominently the so-called adipokines. These discoveries led to the question how adipokines influence inflammatory diseases. Linking inflammation and adipose tissue, Crohn's disease, a chronic inflammatory bowel disease, is of particular interest for studying the immune modulatory properties of adipokines since it is characterized by a hyperplasia of the mesenteric fat that subsequently is creeping around the inflamed segments of the small intestine. Thus, the role of several adipokines in the creeping fat as well as in intestinal inflammation was recently explored. The present review selected the four adipokines adiponectin, apelin, chemerin, and leptin and provides a working model based on the available literature how these factors participate in the maintenance of intestinal immune homeostasis.

The role of adipose tissue in the pathogenesis of Crohn's disease

Crohn's disease (CD) is a chronic, immune system-mediated inflammatory disease affecting gastrointestinal (GI) tract. The pathogenesis of the intestinal lesions is not entirely explained and understood: excessive activation of the immune system may come as a result of the interaction of environmental, genetic and infectious factors and the mediation of abnormal intestinal flora. The main objective of the current study is to further identify the role of adipose tissue in the pathogenesis of CD. Alterations in body fat distribution, accumulation of intra-abdominal white adipose tissue (WAT) and mesenteric obesity are well-known features of CD. Up to date, data concerning the role of WAT in the pathogenesis of CD is limited with only a few studies on the relationship between WAT and the course of the disease, as well as pro- and anti-inflammatory cytokine profile and general immune system functioning. In this review, we focus on the importance of physiological and pathophysiological WAT functions and secreted adipokines, which seem to have a vital role in the inflammatory and fibrotic processes in CD sufferers.

Function, Regulation, and Pathophysiological Relevance of the POT Superfamily, Specifically PepT1 in Inflammatory Bowel Disease

Mammalian members of the proton-coupled oligopeptide transporter family are integral membrane proteins that mediate the cellular uptake of di/tripeptides and peptide-like drugs and couple substrate translocation to the movement of H⁺ , with the transmembrane electrochemical proton gradient providing the driving force. Peptide transporters are responsible for the (re)absorption of dietary and/or bacterial di- and tripeptides in the intestine and kidney and maintaining homeostasis of neuropeptides in the brain. These proteins additionally contribute to absorption of a number of pharmacologically important compounds. In this overview article, we have provided updated information on the structure, function, expression, localization, and activities of PepT1 (SLC15A1), PepT2 (SLC15A2), PhT1 (SLC15A4), and PhT2 (SLC15A3). Peptide transporters, in particular, PepT1 are discussed as drug-delivery systems in addition to their implications in health and disease. Particular emphasis has been placed on the involvement of PepT1 in the physiopathology of the gastrointestinal tract, specifically, its role in inflammatory bowel diseases. © 2018 American Physiological Society. Compr Physiol 8:731-760, 2018.

Are adipocytokines inflammatory or metabolic mediators in patients with inflammatory bowel disease?

This study examined the adiponectin and leptin levels and insulin resistance (IR) in patients with inflammatory bowel disease (IBD) and the associations between these factors and IBD characteristics. Fasting serum leptin, adiponectin, glucose, and insulin levels, as well as inflammatory parameters, were measured in 105 patients with IBD (49 patients with Crohn’s disease [CD], 56 patients with ulcerative colitis [UC]) and 98 healthy controls [HC]. IR was evaluated using the Homeostatic Model Assessment of Insulin Resistance (HOMA-IR). Disease activity and severity in patients with UC were evaluated using the Truelove–Witts index, and patients with CD were evaluated using the Crohn’s Disease Activity Index. Serum adiponectin levels were found to be significantly lower in patients with CD and UC (p<0.001). Serum leptin levels were also found to be significantly higher in both the UC and CD groups (p<0.001). When HOMA-IR levels were compared, no significant difference was detected for either the CD or UC groups compared with the controls. In conclusion, it was shown that leptin levels increased and adiponectin levels decreased in patients with IBD, which is thought to be related to chronic inflammation. The effects of adipocytokines in patients with IBD with inflammatory and metabolic processes need to be investigated in further broader studies.

High-fat diet induced leptin and Wnt expression: RNA-sequencing and pathway analysis of mouse colonic tissue and tumors

Obesity, an immense epidemic affecting approximately half a billion adults, has doubled in prevalence in the last several decades. Epidemiological data support that obesity, due to intake of a high-fat, western diet, increases the risk of colon cancer; however, the mechanisms underlying this risk remain unclear. Here, utilizing next generation RNA sequencing, we aimed to determine the high-fat diet (HFD) mediated expression profile in mouse colon and the azoxymethane/dextran sulfate sodium model of colon cancer. Mice on HFD had significantly higher colonic inflammation, tumor burden, and a number of differentially expressed transcripts compared to mice on regular diet (RD). We identified 721 transcripts differentially expressed in mouse HFD colon that were in a shared pattern with colonic tumors (RD and HFD). Importantly, in mouse colon, HFD stimulated an expression signature strikingly similar to human colon cancer, especially those with inflammatory microsatellite instability. Furthermore, pathway analysis of these transcripts demonstrated their association with active inflammation and colon cancer signaling, with leptin and Wnt as the top two transcripts elevated in mouse HFD colon shared with tumors. Moreover, in mouse colon, HFD-stimulated tumorigenic Wnt pathway activation was further validated by upregulation of β-catenin transcriptional targets. Finally, in human colon cancer, upregulation of leptin pathway members was shown with a large network of dysregulated transcripts being linked with worse overall survival.

Transcriptional and Molecular Pathways Activated in Mesenteric Adipose Tissue and Intestinal Mucosa of Crohn's Disease Patients

Crohn's disease (CD) is a chronic inflammatory disorder, characterized by cytokine imbalance and transcription signaling pathways activation. In addition, the increase of mesenteric adipose tissue (MAT) near the affected intestinal area is a hallmark of CD. Therefore, we evaluated the transcription signaling pathways and cytokines expression in intestinal mucosa and MAT of active CD patients. Ten patients with ileocecal CD and eight with noninflammatory diseases were studied. The biopsies of intestinal mucosa and MAT were snap-frozen and protein expression was determined by immunoblotting. RNA levels were measured by qPCR. The pIkB/IkB ratio and TNFα level were significantly higher in intestinal mucosa of CD when compared to controls. However, STAT1 expression was similar between intestinal mucosa of CD and controls. Considering the MAT, the pIkB/IkB ratio was significantly lower and the anti-inflammatory cytokine IL10 was significantly higher in CD when compared to controls. Finally, the protein content of pSTAT1 was higher in MAT of CD compared to controls. These findings reinforce the predominance of the proinflammatory NF-kB pathway in CD intestinal mucosa. For the first time, we showed the activation of STAT1 pathway in MAT of CD patients, which may help to understand the physiopathology of this immune mediated disease.

Genome-wide analysis identifies colonic genes differentially associated with serum leptin and insulin concentrations in C57BL/6J mice fed a high-fat diet

Obesity-induced chronic inflammation is known to increase the risk of ulcerative colitis, Crohn's disease, and colorectal cancer. Accumulating evidence suggests that leptin and insulin are key molecules linking obesity with diseases of the lower intestine. Here, we identified serum phenotype-associated genes in the colon of diet-induced obese mice as early biomarkers of obesity-associated colonic diseases. C57BL/6J mice were fed with either normal diet (ND, 15% of fat calories) or high-fat diet (HFD, 45% of fat calories) for 8 weeks. Serum concentrations of insulin, insulin-like growth factor-1 (IGF-1), leptin, and adiponectin were measured as obesity-related phenotypic markers. Genome-wide gene expression profiles of colon tissue were determined, followed by statistical analyses to detect differentially expressed and serum phenotype-associated genes. HFD-fed mice showed higher serum concentrations of leptin (P < 0.001) and insulin (P < 0.01) than those in the ND group, whereas serum IGF-1 and adiponectin concentrations did not differ between the two dietary groups. Among differentially expressed genes affected by HFD, 135, 128, 110, and 341 genes were associated with serum levels of leptin, insulin, IGF-1, and adiponectin, respectively. We identified 17 leptin-associated genes and 4 insulin-associated genes that inversely responded to HFD and ND. Among these, leptin-associated Peli3 (Pellino E3 ubiquitin protein ligase family member 3), Creb1 (cAMP responsive element binding protein 1), and Enpp2 (ectonucleotide pyrophosphatase/phosphodiesterase 2, autotaxin) and insulin-associated Centg1 (AGAP2, ArfGAP with GTPase domain) are reported to play a role either in obesity or colonic diseases. mRNA expression of these genes was validated by RT-qPCR. Our data suggest Peli3, Creb1, Enpp2, and Centg1 as potential early biomarker candidates for obesity-induced pathophysiological changes in the colon. Future studies verifying the function of these candidates are needed for the prevention, early detection, and treatment of colon diseases.

Lifestyle and Horizontal Gene Transfer-Mediated Evolution of Mucispirillum schaedleri, a Core Member of the Murine Gut Microbiota

Shifts in gut microbiota composition have been associated with intestinal inflammation, but it remains unclear whether inflammation-associated bacteria are commensal or detrimental to their host. Here, we studied the lifestyle of the gut bacterium Mucispirillum schaedleri, which is associated with inflammation in widely used mouse models. We found that M. schaedleri has specialized systems to handle oxidative stress during inflammation. Additionally, it expresses secretion systems and effector proteins and can modify the mucosal gene expression of its host. This suggests that M. schaedleri undergoes intimate interactions with its host and may play a role in inflammation. The insights presented here aid our understanding of how commensal gut bacteria may be involved in altering susceptibility to disease.

Mucispirillum schaedleri is an abundant inhabitant of the intestinal mucus layer of rodents and other animals and has been suggested to be a pathobiont, a commensal that plays a role in disease. In order to gain insights into its lifestyle, we analyzed the genome and transcriptome of M. schaedleri ASF 457 and performed physiological experiments to test traits predicted by its genome. Although described as a mucus inhabitant, M. schaedleri has limited capacity for degrading host-derived mucosal glycans and other complex polysaccharides. Additionally, M. schaedleri reduces nitrate and expresses systems for scavenging oxygen and reactive oxygen species in vivo, which may account for its localization close to the mucosal tissue and expansion during inflammation. Also of note, M. schaedleri harbors a type VI secretion system and putative effector proteins and can modify gene expression in mucosal tissue, suggesting intimate interactions with its host and a possible role in inflammation. The M. schaedleri genome has been shaped by extensive horizontal gene transfer, primarily from intestinal Epsilon- and Deltaproteobacteria, indicating that horizontal gene transfer has played a key role in defining its niche in the gut ecosystem.

IMPORTANCE Shifts in gut microbiota composition have been associated with intestinal inflammation, but it remains unclear whether inflammation-associated bacteria are commensal or detrimental to their host. Here, we studied the lifestyle of the gut bacterium Mucispirillum schaedleri, which is associated with inflammation in widely used mouse models. We found that M. schaedleri has specialized systems to handle oxidative stress during inflammation. Additionally, it expresses secretion systems and effector proteins and can modify the mucosal gene expression of its host. This suggests that M. schaedleri undergoes intimate interactions with its host and may play a role in inflammation. The insights presented here aid our understanding of how commensal gut bacteria may be involved in altering susceptibility to disease.

Time-course microarray analysis for identifying candidate genes involved in obesity-associated pathological changes in the mouse colon

Background

Obesity is known to increase the risk of colorectal cancer. However, mechanisms underlying the pathogenesis of obesity-induced colorectal cancer are not completely understood. The purposes of this study were to identify differentially expressed genes in the colon of mice with diet-induced obesity and to select candidate genes as early markers of obesity-associated abnormal cell growth in the colon.

Methods

C57BL/6N mice were fed normal diet (11% fat energy) or high-fat diet (40% fat energy) and were euthanized at different time points. Genome-wide expression profiles of the colon were determined at 2, 4, 8, and 12 weeks. Cluster analysis was performed using expression data of genes showing log₂ fold change of ≥1 or ≤−1 (twofold change), based on time-dependent expression patterns, followed by virtual network analysis.

Results

High-fat diet-fed mice showed significant increase in body weight and total visceral fat weight over 12 weeks. Time-course microarray analysis showed that 50, 47, 36, and 411 genes were differentially expressed at 2, 4, 8, and 12 weeks, respectively. Ten cluster profiles representing distinguishable patterns of genes differentially expressed over time were determined. Cluster 4, which consisted of genes showing the most significant alterations in expression in response to high-fat diet over 12 weeks, included Apoa4 (apolipoprotein A-IV), Ppap2b (phosphatidic acid phosphatase type 2B), Cel (carboxyl ester lipase), and Clps (colipase, pancreatic), which interacted strongly with surrounding genes associated with colorectal cancer or obesity.

Conclusions

Our data indicate that Apoa4, Ppap2b, Cel, and Clps are candidate early marker genes associated with obesity-related pathological changes in the colon. Genome-wide analyses performed in the present study provide new insights on selecting novel genes that may be associated with the development of diseases of the colon.

Electronic supplementary material

The online version of this article (doi:10.1186/s12263-016-0547-x) contains supplementary material, which is available to authorized users.

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.

Hypertrophic Mesenteric Adipose Tissue May Play a Role in Atherogenesis in Inflammatory Bowel Diseases

BACKGROUND

Adipokines released by the adipose tissue are known to play a role in atherogenesis. The hypertrophic mesenteric fat in patients with inflammatory bowel diseases (IBD) also produces adipokines that are considered to play a role in intestinal inflammation. Whether they also contribute to accelerated atherosclerosis in IBD is unknown. The aim of this study was to assess the role of 2 adipokines, resistin and adiponectin, in IBD.

METHODS

We previously published data on 3 markers of cardiovascular risk, carotid intima-media thickness, carotid-femoral pulse wave velocity, and lipoprotein-associated phospholipase A2, in 44 patients with IBD and 44 controls matched for established cardiovascular risk factors. In this study, we measured resistin and adiponectin levels, and assessed their correlations with carotid intima-media thickness, pulse wave velocity, and lipoprotein-associated phospholipase A2.

RESULTS

Resistin levels were significantly higher in patients with IBD (13.7 versus 10 ng/mL; P = 0.022), but there was no difference in adiponectin levels. Resistin levels were significantly higher in patients with active disease compared with those in remission (18.9 versus 11.3 ng/mL; P = 0.014). Adiponectin levels were significantly lower in Crohn's disease compared with ulcerative colitis (6736.3 ± 3105 versus 10,476.1 ± 5575.7 ng/mL; P = 0.026). Adiponectin correlated inversely with pulse wave velocity (rho = -0.434; P < 0.0005) and carotid intima-media thickness (rho = -0.255; P = 0.021).

CONCLUSIONS

This is the first study to suggest that adipokines produced by the hypertrophic mesenteric fat in IBD may play a role not only in intestinal inflammation but also in atherogenesis. Resistin has mainly pro-inflammatory properties, whereas adiponectin likely exerts an angioprotective effect.

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.

Leptin in autoimmune diseases

The past twenty years of research on leptin has provided crucial information on the link between metabolic state and immune system function. Adipocytes influence not only the endocrine system but also the immune response, through several cytokine-like mediators known as adipokines, which include leptin. Initially described as an antiobesity hormone, leptin has subsequently been shown also to influence hematopoiesis, thermogenesis, reproduction, angiogenesis, and more importantly immune homeostasis. As a cytokine, leptin can affect thymic homeostasis and the secretion of acute-phase reactants such as interleukin-1 (IL-1) and tumor-necrosis factor-alpha (TNF-α). Leptin links nutritional status and proinflammatory T helper 1 (Th1) immune responses and the decrease in leptin plasma concentration during food deprivation leads to impaired immune function. Conversely, elevated circulating leptin levels in obesity appear to contribute to the low-grade inflammatory background which makes obese individuals more susceptible to increased risk of developing cardiovascular diseases, diabetes, or degenerative disease including autoimmunity and cancer. In this review, we provide an overview of recent advances on the role of leptin in the pathogenesis of several autoimmune disorders that may be of particular relevance in the modulation of the autoimmune attack through metabolic-based therapeutic approaches.

Leptin receptor mutation results in defective neutrophil recruitment to the colon during Entamoeba histolytica infection

Amebiasis is an enteric infection caused by Entamoeba histolytica, with symptoms ranging in severity from asymptomatic colonization to dysentery. Humans with the Q223R leptin receptor mutation have increased susceptibility to amebiasis, but the mechanism has been unclear. Using a mouse model expressing the mutation, we tested the impact of the Q223R mutation on the innate immune response to E. histolytica infection. The 223R mutation resulted in delayed clearance of amebae from the cecum, as had been previously observed. We found that neutrophil influx to the site of the infection was reduced 12 h after infection in 223R mice. Depletion of neutrophils with anti-Ly6G monoclonal antibody increased susceptibility of wild-type mice to infection, supporting the importance of neutrophils in innate defense. Leptin expression was increased in the cecum by E. histolytica infection, suggesting that leptin could serve as a homing signal for neutrophils to the gut. Interestingly, neutrophils from mice with the 223R mutation had diminished chemotaxis toward leptin. This impaired chemotaxis likely explained the reduced gut infiltration of neutrophils. The newly recognized effect of the leptin receptor Q223R mutation on neutrophil chemotaxis and the impact of this mutation on multiple infectious diseases suggest a broader impact of this mutation on susceptibility to disease.

The Q223R leptin receptor mutation results in increased susceptibility of children and adults to E. histolytica, one of the leading causes of diarrhea morbidity and mortality in children of the developing world. Here we show that the mutation results in reduced neutrophil infiltration to the site of infection. This decreased infiltration is likely due to the mutation’s impact on neutrophil chemotaxis toward leptin, an inflammatory agent upregulated in the cecum after infection. The significance of this work thus extends beyond understanding E. histolytica susceptibility by also providing insight into the potential impact of leptin on neutrophil function in other states of altered leptin signaling, which include both malnutrition and obesity.

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.

Connecting metabolism to intestinal barrier function: The role of leptin

Structure and function of the intestinal epithelial barrier (IEB) are dependent upon the integrity of junctional protein structures sealing the apical surface between epithelial cells. Tight junctions (TJ) and the surrounding apical F-actin cytoskeleton are involved in the regulation of paracellular permeability. The regulation of actin cytoskeleton organization by RhoA/Rho-kinase (ROCK) pathway plays an important role in TJ assembly and function. There is mounting evidence that the adipocyte-derived hormone leptin exerts pleiotropic effects on the intestinal epithelium including nutrient absorption, epithelial growth, inflammation and injury. Leptin activates multiple cell signaling pathways in intestinal epithelial cells (IEC) that can explain these pleiotropic effects. However, these pathways are also involved in the primary role of leptin that is the regulation of energy and glucose metabolism homeostasis. In this commentary, we examine how the interplay between leptin signaling pathways that regulate cell metabolism could impact upon IEB function.

Defective apoptosis in intestinal and mesenteric adipose tissue of Crohn's disease patients

BACKGROUND

Crohn's disease (CD) is associated with complex pathogenic pathways involving defects in apoptosis mechanisms. Recently, mesenteric adipose tissue (MAT) has been associated with CD ethiopathology, since adipose thickening is detected close to the affected intestinal area. However, the potential role of altered apoptosis in MAT of CD has not been addressed.

AIMS

To evaluate apoptosis in the intestinal mucosa and MAT of patients with CD.

METHODS

Samples of intestinal mucosa and MAT from patients with ileocecal CD and from non-inflammatory bowel diseases patients (controls) were studied. Apoptosis was assessed by TUNEL assay and correlated with the adipocytes histological morphometric analysis. The transcriptional and protein analysis of selected genes and proteins related to apoptosis were determined.

RESULTS

TUNEL assay showed fewer apoptotic cells in CD, when compared to the control groups, both in the intestinal mucosa and in MAT. In addition, the number of apoptotic cells (TUNEL) correlated significantly with the area and perimeter of the adipose cells in MAT. Transcriptomic and proteomic analysis reveal a significantly lower transcript and protein levels of Bax in the intestinal mucosa of CD, compared to the controls; low protein levels of Bax were found localized in the lamina propria and not in the epithelium of this tissue. Furthermore, higher level of Bcl-2 and low level of Caspase 3 were seen in the MAT of CD patients.

CONCLUSION

The defective apoptosis in MAT may explain the singular morphological characteristics of this tissue in CD, which may be implicated in the pathophysiology of the disease.

The emerging role of leptin antagonist as potential therapeutic option for inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic relapsing immune-mediated inflammatory disorder that affects millions of people around the world. Leptin is a satiety hormone produced primarily by adipose tissue and acts both centrally and peripherally. Leptin has been shown to play a major role in regulating metabolism, which increases during IBD progression. Leptin mediates several physiological functions including elevated blood pressure, tumorogenesis, cardiovascular pathologies and enhanced immune response in many autoimmune diseases. Recent development of a leptin mutant antagonist that blocks leptin activity raises great hope and opens up new possibilities for therapy in many autoimmune diseases including IBD. To this end, preliminary data from an ongoing study in our laboratory on pegylated leptin antagonist mutant L39A/D40A/F41A (PEG-MLA) treatment shows an inhibition of chronic colitis in IL-10-/- mice. PEG-MLA effectively attenuates the overall clinical scores, reverses colitis-associated pathogenesis including a decrease in body weight, and decreases systemic leptin level. PEG-MLA induces both central and peripheral leptin deficiency by mediating the cellular immune response. In summary, after blocking leptin activity, the correlative outcome between leptin-mediated cellular immune response, systemic leptin levels, and amount of adipose tissue together may provide new strategies for therapeutic intervention in autoimmune diseases, especially for intestinal inflammation.

Leptin antagonist ameliorates chronic colitis in IL-10⁻/⁻ mice

BACKGROUND

Although the etiology of two major forms of inflammatory bowel disease (IBD), Crohn's disease (CD) and ulcerative colitis (UC) are unknown and evidence suggests that chronic intestinal inflammation is caused by an excessive immune response to mucosal antigens. Previous studies support the role for TGF-β1 through 3 in the initiation and maintenance of tolerance via the induction of regulatory T cells (Tregs) to control intestinal inflammation. Leptin, a satiety hormone produced primarily by adipose tissue, has been shown to increase during colitis progression and is believed to contribute to disease genesis and/or progression.

AIM

We investigated the ability of a pegylated leptin antagonist (PG-MLA) to ameliorate the development of chronic experimental colitis.

RESULTS

Compared to vehicle control animals, PG-MLA treatment of mice resulted in an (1) attenuated clinical score; (2) reversed colitis-associated pathogenesis including a decrease in body weight; (3) reduced systemic and mucosal inflammatory cytokine expression; (4) increased insulin levels and (5) enhanced systemic and mucosal Tregs and CD39⁺ Tregs in mice with chronic colitis. The percentage of systemic and mucosal TGF-β1, -β2 and -β3 expressing CD4⁺ T cells were augmented after PG-MLA treatment. The activation of STAT1 and STAT3 and the expression of Smad7 were also reduced after PG-MLA treatment in the colitic mice. These findings clearly suggest that PG-MLA treatment reduces intestinal Smad7 expression, restores TGF-β1-3 signaling and reduces STAT1/STAT3 activation that may increase the number of Tregs to ameliorate chronic colitis.

CONCLUSION

This study clearly links inflammation with the metabolic hormone leptin suggesting that nutritional status influences immune tolerance through the induction of functional Tregs. Inhibiting leptin activity through PG-MLA might provide a new and novel therapeutic strategy for the treatment of IBD.