Adipokines from local fat cells shape the macrophage compartment of the creeping fat in Crohn's disease

Innate Immunity Activation in Newly Diagnosed Ileocolonic Crohn's Disease: A Cohort Study

BACKGROUND

Recent studies showed that early surgery for Crohn's disease leads to a lower recurrence rate. However, the underlying mechanism is unknown.

OBJECTIVE

The study aims to analyze the innate immunity microenvironment in ileal mucosa according to the duration of Crohn's disease.

DESIGN

A prospective cohort study.

SETTINGS

Tertiary referral center for IBD surgery.

PATIENTS

A total of 88 consecutive patients with Crohn's disease undergoing ileocolonic resection were prospectively enrolled. Mucosal samples were obtained from both healthy and inflamed ileum. Data from a public data set were analyzed as an external validation cohort.

MAIN OUTCOME MEASURES

Neutrophil infiltration was evaluated by histological asessment and macrophage subpopulation was assessed by immunohistochemistry. Expressions of TLR2 , TLR4 , TLR5 , DEFB1 , DEFB4A , DEFB103 , DEFA5 , and DEFA6 were quantified by real-time quantitative polymerase chain reaction. Concentrations of BDNF, CCL-11, ICAM-1, IL-1A, IL-1β, IL-1RN, IL-12p40, IL-12p70, IL-15, IL-17A, IL-23A, MMP-3, CCL-3, KITLG, and VEGFA were determined with an immunometric assay.

RESULTS

Neutrophil infiltration is inversely correlated with disease duration. DEFB4A mRNA expression tended to be higher in late-stage Crohn's disease ( p = 0.07). A higher number of macrophages expressed CD163 at low intensity in late-stage Crohn's disease ( p = 0.04). The concentration of IL-15 ( p = 0.02) and IL-23A ( p = 0.05) was higher in healthy ileal mucosa of early-stage patients. In the external cohort, expressions of DEFB1 ( p = 0.03), DEFB4A ( p = 0.01), IL-2 ( p = 0.04), and IL-3 ( p = 0.03) increased in patients with late-stage Crohn's disease.

LIMITATIONS

A relatively small number of patients, especially in the newly diagnosed group.

CONCLUSIONS

In newly diagnosed Crohn's disease, high levels of IL-15 and IL-23 in healthy mucosa suggest that innate immunity is the starter of acute inflammation. Moreover, M2 macrophages increase in the healthy mucosa of patients with late-stage Crohn's disease, suggesting that reparative and profibrotic processes are predominant in the long term, and in this phase, anti-inflammatory therapy may be less efficient. See Video Abstract .

ACTIVACIN DE LA INMUNIDAD INNATA EN LA RECIENTEMENTE DIAGNOSTICADA ENFERMEDAD DE CROHN ILEOCLICA UN ESTUDIO DE COHORTE

ANTECEDENTES:Estudios recientes demostraron que la cirugía temprana para la enfermedad de Crohn (EC) conduce a una menor tasa de recurrencia. Sin embargo, se desconoce el mecanismo subyacente.OBJETIVO:El estudio tiene como objetivo analizar el microambiente de la inmunidad innata en la mucosa ileal según la duración de la EC.DISEÑO:Un estudio de cohorte prospectivo.AJUSTES:Centro terciario de referencia para cirugía de EII.PACIENTES:Fueron registrados de manera prospectiva y consecutiva 88 pacientes con EC sometidos a resección ileocolónica. Se obtuvieron muestras de mucosa ileal, tanto del íleon sano como del íleon inflamado. Los datos se analizaron como una cohorte de validación externa.PRINCIPALES MEDIDAS DE RESULTADO:Fueron evaluados la infiltración de neutrófilos por histología y la subpoblación de macrófagos por inmunohistoquímica. La expresión de TLR2, TLR4, TLR5, DEFB1, DEFB4A, DEFB103, DEFA5 y DEFA6 fueron cuantificados mediante qPCR en tiempo real. Las concentraciones de BDNF, CCL-11, ICAM-1, IL-1A, IL-1B, IL-1RN, IL-12 p40, IL-12 p70, IL-15, IL-17A, IL-23A, MMP-3, CCL-3, KITLG, VEGFA se determinaron con ensayo inmunométrico.RESULTADOS:La infiltración de neutrófilos se correlaciona inversamente con la duración de la enfermedad. La expresión del ARNm de DEFB4A mostro una tendencia a ser mayor en la EC en etapa tardía ( p = 0,07). Un mayor número de macrófagos expresaron CD163 a baja intensidad en la etapa tardía ( p = 0,04). La concentración de IL15 ( p = 0,02) e IL23A ( p = 0,05) fue mayor en la mucosa ileal sana de pacientes en estadio temprano. En la cohorte externa, la expresión de DEFB1 ( p = 0,03) y DEFB4A ( p = 0,01), IL2 ( p = 0,04) e IL3 ( p = 0,03) aumentó en pacientes en etapa tardía.LIMITACIONES:Un número relativamente pequeño de pacientes, especialmente en el grupo recién diagnosticado.CONCLUSIONES:En la EC recién diagnosticada, los altos niveles de IL-15 e IL-23 en la mucosa sana sugieren que la inmunidad innata es el promotor de la inflamación aguda. Además, los macrófagos M2 aumentan en la mucosa sana de pacientes con EC en etapa tardía, lo que sugiere que los procesos reparadores y profibróticos son predominantes a largo plazo y en esta fase, la terapia antiinflamatoria puede ser menos eficiente. (Traducción-Dr. Osvaldo Gauto ).

Fibrosis in IBD: from pathogenesis to therapeutic targets

BACKGROUND

Intestinal fibrosis resulting in stricture formation and obstruction in Crohn's disease (CD) and increased wall stiffness leading to symptoms in ulcerative colitis (UC) is among the largest unmet needs in inflammatory bowel disease (IBD). Fibrosis is caused by a multifactorial and complex process involving immune and non-immune cells, their soluble mediators and exposure to luminal contents, such as microbiota and environmental factors. To date, no antifibrotic therapy is available. Some progress has been made in creating consensus definitions and measurements to quantify stricture morphology for clinical practice and trials, but approaches to determine the degree of fibrosis within a stricture are still lacking.

OBJECTIVE

We herein describe the current state of stricture pathogenesis, measuring tools and clinical trial endpoints development.

DESIGN

Data presented and discussed in this review derive from the past and recent literature and the authors' own research and experience.

RESULTS AND CONCLUSIONS

Significant progress has been made in better understanding the pathogenesis of fibrosis, but additional studies and preclinical developments are needed to define specific therapeutic targets.

Recent advances in intestinal fibrosis

Despite many progresses have been made in the treatment of inflammatory bowel disease, especially due to the increasing number of effective therapies, the development of tissue fibrosis is a very common occurrence along the natural history of this condition. To a certain extent, fibrogenesis is a physiological and necessary process in all those conditions characterised by chronic inflammation. However, the excessive deposition of extracellular matrix within the bowel wall will end up in the formation of strictures, with the consequent need for surgery. A number of mechanisms have been described in this process, but some of them are not yet clear. For sure, the main trigger is the presence of a persistent inflammatory status within the mucosa, which in turn favours the occurrence of a pro-fibrogenic environment. Among the main key players, myofibroblasts, fibroblasts, immune cells, growth factors and cytokines must be mentioned. Although there are no available therapies able to target fibrosis, the only way to prevent it is by controlling inflammation. In this review, we summarize the state of art of the mechanisms involved in gut fibrogenesis, how to diagnose it, and which potential targets could be druggable to tackle fibrosis.

Gut-bacteria derived membrane vesicles and host metabolic health: a narrative review

The intestinal microbiota, consisting of an estimated 10^10-10^11 organisms, regulate physiological processes involved in digestion, metabolism, and immunity. Surprisingly, these intestinal microorganisms have been found to influence tissues that are not directly in contact with the gut, such as adipose tissue, the liver, skeletal muscle, and the brain. This interaction takes place even when intestinal barrier function is uncompromised. An increasing body of evidence suggests that bacterial membrane vesicles (bMVs), in addition to bacterial metabolites such as short-chain fatty acids, are able to mediate effects of the microbiota on these host tissues. The ability of bMVs to dissipate from the intestinal lumen into systemic circulation hereby facilitates the transport and presentation of bacterial components and metabolites to host organs. Importantly, there are indications that the interaction between bMVs and tissues or immune cells may play a role in the etiology of (chronic metabolic) disease. For example, the gut-derived bMV-mediated induction of insulin resistance in skeletal muscle cells and pro-inflammatory signaling by adipocytes possibly underlies diseases such as type 2 diabetes and obesity. Here, we review the current knowledge on bMVs in the microbiota's effects on host energy/substrate metabolism with a focus on etiological roles in the onset and progression of metabolic disease. We furthermore illustrate that vesicle production by bacterial microbiota could potentially be modulated through lifestyle intervention to improve host metabolism.

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.

Adropin deficiency worsens TNBS-induced colitis

The aim of this study was to describe the effects of adropin deficiency on the distribution, phenotype and pathological phenotype of macrophages in colonic and mesenteric tissues of AdrKO (Enho-/-) mice, so as to explore the mechanism of adropin deficiency in spontaneous and experimental colitis. In this study, RNA-seq and metabonomics were used to screen the regulatory mechanism of adropin on the phenotypic transformation of macrophages. We found that adropin levels in active UC patients were significantly lower than those in normal subjects and remission UC patients, and at the same time, a large number of proinflammatory M1-type macrophages were infiltrated in the mesenteric tissue of colonic tissues from UC and CD patients. At the same time, spontaneous colitis occurred in Enho-/- (adropin-deficient)C57BL/6 mice, and there was an imbalance of M2 → M1 polarization of macrophages in colon and mesentery of Enho-/- mice. In vivo, it has showed that adropin deficiency could exacerbate the pathological phenotype of colitis induced by TNBS. In vitro, adropin was used to intervene RAW264.7 macrophages, and then combined analysis of RNA-seq and metabolomics demonstrated that adropin regulated lipid metabolism of macrophages through PPARγ, thus promoting the repolarization of macrophages from M1 to M2. Adropin deficiency led to an imbalance in the phenotypic distribution of macrophages infiltrating the colon and mesenteric tissues, namely, an increase in M1 type, which led to the occurrence and development of colitis.

Adiponectin Levels in Inflammatory Bowel Disease: A Systematic Review and Meta-Analysis

INTRODUCTION

Adipose tissue plays an important role in the pathogenesis of inflammatory conditions. The role of adipokines in inflammatory bowel disease (IBD) has been evaluated in the current literature with conflicting results. The aim of this study was to evaluate adiponectin levels in IBD patients, including Crohn's disease (CD) and ulcerative colitis (UC), compared to controls, as well as further subgroup analyses. Hence, assessing the potential role of adiponectin as a surrogate marker.

METHODS

We performed a systematic electronic search on PubMed, Embase, Scopus, and Cochrane Library, including observational or interventional studies evaluating serum or plasma adiponectin levels in IBD patients in humans. The primary summary outcome was the mean difference (MD) in serum or plasma adiponectin levels between IBD patients versus controls. Subgroup analyses were conducted involving adiponectin levels in CD and UC compared to controls, as well as CD compared to UC.

RESULTS

A total of 20 studies were included in our qualitative synthesis and 14 studies in our quantitative synthesis, with a total population sample of 2,085 subjects. No significant MD in serum adiponectin levels was observed between IBD patients versus controls {-1.331 (95% confidence interval [CI]: -3.135-0.472)}, UC patients versus controls (-0.213 [95% CI: -1.898-1.472]), and CD patients versus controls (-0.851 [95% CI: -2.263-0.561]). Nevertheless, a significant MD was found between UC patients versus CD patients (0.859 [95% CI: 0.097-1.622]).

CONCLUSIONS

Serum adiponectin levels were not able to differentiate between IBD, UC, and CD patients compared to controls. However, significantly higher serum adiponectin levels were observed in UC compared to CD patients.

How to Evaluate Fibrosis in IBD?

In this review, we will describe the importance of fibrosis in inflammatory bowel disease (IBD) by discussing its distinct impact on Crohn's disease (CD) and ulcerative colitis (UC) through their translation to histopathology. We will address the existing knowledge on the correlation between inflammation and fibrosis and the still not fully explained inflammation-independent fibrogenesis. Finally, we will compile and discuss the recent advances in the noninvasive assessment of intestinal fibrosis, including imaging and biomarkers. Based on the available data, none of the available cross-sectional imaging (CSI) techniques has proved to be capable of measuring CD fibrosis accurately, with MRE showing the most promising performance along with elastography. Very recent research with radiomics showed encouraging results, but further validation with reliable radiomic biomarkers is warranted. Despite the interesting results with micro-RNAs, further advances on the topic of fibrosis biomarkers depend on the development of robust clinical trials based on solid and validated endpoints. We conclude that it seems very likely that radiomics and AI will participate in the future non-invasive fibrosis assessment by CSI techniques in IBD. However, as of today, surgical pathology remains the gold standard for the diagnosis and quantification of intestinal fibrosis in IBD.

Crohn’s disease: Why the ileum?

Crohn’s disease (CD) is an inflammatory bowel disease characterized by immune-mediated flares affecting any region of the intestine alternating with remission periods. In CD, the ileum is frequently affected and about one third of patients presents with a pure ileal type. Moreover, the ileal type of CD presents epidemiological specificities like a younger age at onset and often a strong link with smoking and genetic susceptibility genes. Most of these genes are associated with Paneth cell dysfunction, a cell type found in the intestinal crypts of the ileum. Besides, a Western-type diet is associated in epidemiological studies with CD onset and increasing evidence shows that diet can modulate the composition of bile acids and gut microbiota, which in turn modulates the susceptibility of the ileum to inflammation. Thus, the interplay between environmental factors and the histological and anatomical features of the ileum is thought to explain the specific transcriptome profile observed in CD ileitis. Indeed, both immune response and cellular healing processes harbour differences between ileal and non-ileal CD. Taken together, these findings advocate for a dedicated therapeutic approach to managing ileal CD. Currently, interventional pharmacological studies have failed to clearly demonstrate distinct response profiles according to disease site. However, the high rate of stricturing disease in ileal CD requires the identification of new therapeutic targets to significantly change the natural history of this debilitating disease.

Adipocyte autophagy limits gut inflammation by controlling oxylipin and IL-10

Lipids play a major role in inflammatory diseases by altering inflammatory cell functions, either through their function as energy substrates or as lipid mediators such as oxylipins. Autophagy, a lysosomal degradation pathway that limits inflammation, is known to impact on lipid availability, however, whether this controls inflammation remains unexplored. We found that upon intestinal inflammation visceral adipocytes upregulate autophagy and that adipocyte-specific loss of the autophagy gene Atg7 exacerbates inflammation. While autophagy decreased lipolytic release of free fatty acids, loss of the major lipolytic enzyme Pnpla2/Atgl in adipocytes did not alter intestinal inflammation, ruling out free fatty acids as anti-inflammatory energy substrates. Instead, Atg7-deficient adipose tissues exhibited an oxylipin imbalance, driven through an NRF2-mediated upregulation of Ephx1. This shift reduced secretion of IL-10 from adipose tissues, which was dependent on the cytochrome P450-EPHX pathway, and lowered circulating levels of IL-10 to exacerbate intestinal inflammation. These results suggest an underappreciated fat-gut crosstalk through an autophagy-dependent regulation of anti-inflammatory oxylipins via the cytochrome P450-EPHX pathway, indicating a protective effect of adipose tissues for distant inflammation.

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.

Platelet-Rich stroma from Crohn's disease patients for treatment of perianal fistula shows a higher myeloid cell profile compared to non-IBD controls

BACKGROUND

New cell-based therapies are under investigation to improve perianal fistulizing Crohn's disease (pCD) healing. Autologous stromal vascular fraction combined with platelet-rich plasma (referred to as platelet-rich stroma [PRS]) is a new adipose-derived stromal therapy. The effect of Crohn's disease (CD) on adipose tissue, and adipose-derived therapies, is largely unknown. We characterized the cellular composition of subcutaneous lipoaspirate and PRS of pCD patients and non-Inflammatory Bowel Disease (IBD) controls.

METHODS

Consecutive pCD patients (≥18 years) and non-IBD controls, who underwent liposuction for the purpose of autologous PRS therapy, were included (October 2020 and March 2021). Mechanically fractionated lipoaspirate and the combined PRS product were analyzed for cell surface marker expression using fluorescence-activated cell sorting analysis.

RESULTS

Twenty-three patients (37.8 [IQR 30.7-45.0] years; 9 [39.1 %] male; 11CD patients) were included. Similar total number of cells were found in CD and non-IBD lipoaspirate (CD 8.23 ± 1.62*10⁵ cells/mL versus non-IBD 12.20 ± 3.39*10⁵). Presence of stromal cells, endothelial like cells, immune cells, T-cells, myeloid cells and M2/M1 macrophage ratio were similar in CD and non-IBD lipoaspirate. In PRS samples, more cells/mL were seen in CD patients (P = 0.030). Myeloid cells were more abundant in CD PRS samples (P = 0.007), and appeared to have a higher regulatory M2/M1 ratio. Interdonor variation was observed between lipoaspirate and PRS samples.

CONCLUSIONS

The composition of CD and non-IBD lipoaspirate were found to be similar and interdonor variation was observed. However, PRS from CD patients showed more myeloid cells with a regulatory phenotype. Crohn's disease does not appear to alter the immunological composition of adipose-derived products.

Adipokine C1q/Tumor Necrosis Factor- Related Protein 3 (CTRP3) Attenuates Intestinal Inflammation Via Sirtuin 1/NF-κB Signaling

BACKGROUND & AIMS

The adipokine CTRP3 has anti-inflammatory effects in several nonintestinal disorders. Although serum CTRP3 is reduced in patients with inflammatory bowel disease (IBD), its function in IBD has not been established. Here, we elucidate the function of CTRP3 in intestinal inflammation.

METHODS

CTRP3 knockout (KO) and overexpressing transgenic (Tg) mice, along with their corresponding wild-type littermates, were treated with dextran sulfate sodium for 6-10 days. Colitis phenotypes and histologic data were analyzed. CTRP3-mediated signaling was examined in murine and human intestinal mucosa and mouse intestinal organoids derived from CTRP3 KO and Tg mice.

RESULTS

CTRP3 KO mice developed more severe colitis, whereas CTRP3 Tg mice developed less severe colitis than wild-type littermates. The deletion of CTRP3 correlated with decreased levels of Sirtuin-1 (SIRT1), a histone deacetylase, and increased levels of phosphorylated/acetylated NF-κB subunit p65 and proinflammatory cytokines tumor necrosis factor-α and interleukin-6. Results from CTRP3 Tg mice were inverse to those from CTRP3 KO mice. The addition of SIRT1 activator resveratrol to KO intestinal organoids and SIRT1 inhibitor Ex-527 to Tg intestinal organoids suggest that SIRT1 is a downstream effector of CTRP3-related inflammatory changes. In patients with IBD, a similar CTRP3/SIRT1/NF-κB relationship was observed.

CONCLUSIONS

CTRP3 expression levels correlate negatively with intestinal inflammation in acute mouse colitis models and patients with IBD. CTRP3 may attenuate intestinal inflammation via SIRT1/NF-κB signaling. The manipulation of CTRP3 signaling, including through the use of SIRT1 activators, may offer translational potential in the treatment of IBD.

Aberrant Mesenteric Adipose Extracellular Matrix Remodelling is Involved in Adipocyte Dysfunction in Crohn's Disease: The Role of TLR-4-mediated Macrophages

BACKGROUND AND AIMS

Hypertrophic mesenteric adipose tissue [htMAT] is involved in the disease progression of Crohn's disease [CD] through expressing proinflammatory adipokines from dysfunctional adipocytes by unknown mechanism. Adipocyte function is affected by dynamic adipose tissue extracellular matrix [ECM] remodelling that is mainly mediated by macrophages, and our study aimed to reveal whether aberrant ECM remodelling was present in CD-htMAT and its effects on adipocyte dysfunction, as well as the mechanism.

METHODS

ECM remodelling was examined in MAT samples from CD patients and controls. Mice with dinitrobenzene sulphonic acid [DNBS]-induced colitis were used in vivo study, and lipopolysaccharide [LPS]-induced remodelling behaviour in macrophages was examined in vitro. Macrophages or TLR4 inhibition were used to analyse ECM remodelling mechanisms and their effects on adipocyte function.

RESULTS

Aberrant ECM remodelling: was observed in CD-htMAT, which was characterised by a widened and deformed ECM structure accompanied by dysregulated matrix synthesis and degradation; served as a reservoir for inflammatory factors/cells dominated by macrophages; and was involved in adipocyte dysfunction. In addition, macrophages were the main source of ECM remodelling regulatory factors with activation of Toll-like receptor 4 [TLR4] in htMAT. In vivo, macrophage depletion or TLR4 inhibition largely attenuated mesenteric ECM remodelling while improving mesenteric adipocyte dysfunction during chronic enteritis. In vitro, antagonizing TLR4 significantly inhibited LPS-induced macrophage ECM remodelling behavior.

CONCLUSIONS

The aberrant ECM remodelling in CD-htMAT contributed to mesenteric adipocyte dysfunction, which may be caused at least partly by TLR4-mediated macrophage remodelling behavior. Inhibiting ECM remodelling may be a potential therapeutic strategy for CD.

Macrophages-microenvironment crosstalk in fibrostenotic inflammatory bowel disease: from basic mechanisms to clinical applications

INTRODUCTION

Intestinal fibrosis is a common complication of Inflammatory Bowel Disease (IBD) with no available drugs. The current therapeutic principle is surgical intervention as the core. Intestinal macrophages contribute to both the progression of inflammation and fibrosis. Understanding the role of macrophages in the intestinal microenvironment could bring new hope for fibrosis prevention or even reversal.

AREAS COVERED

This article reviewed the most relevant reports on macrophage in the field of intestinal fibrosis. The authors discussed current opinions about how intestinal macrophages function and interact with surrounding mediators during inflammation resolution and fibrostenotic IBD. Based on biological mechanisms findings, authors summarized related clinical trial outcomes.

EXPERT OPINION

The plasticity of intestinal macrophages allows them to undergo dramatic alterations in their phenotypes or functions when exposed to gastrointestinal environmental stimuli. They exhibit distinct metabolic characteristics, secrete various cytokines, express unique surface markers, and transmit different signals. Nevertheless, the specific mechanism through which the intestinal macrophages contribute to intestinal fibrosis remains unclear. It should further elucidate a novel therapeutic approach by targeting macrophages, especially distinct mechanisms in specific subgroups of macrophages involved in the progression of fibrogenesis in IBD.

Macrophages in intestinal fibrosis and regression

Intestinal macrophages are heterogenous cell populations with different developmental ontogeny and tissue anatomy. The concerted actions of intestinal macrophage subsets are critical to maintaining tissue homeostasis. However, the dysregulation of macrophages following tissue injury or chronic inflammation could also lead to intestinal fibrosis, with few treatment options in the clinic. In this review, we will characterize the features of intestinal macrophages in light of the latest advances in lineage tracing and single-cell sequencing technology. The roles of macrophages in distinct stages of intestinal fibrosis would be also elaborated. Finally, based on the reciprocal interaction between macrophages and intestinal fibrosis, we will propose the potential macrophage targeting anti-intestinal fibrosis therapies.

Visceral adipose volume is correlated with surgical tissue fibrosis in Crohn's disease of the small bowel

Background

This study explored the diagnostic performance of visceral adiposity to predict the degree of intestinal inflammation and fibrosis.

Methods

The patients with Crohn’s disease (CD) who underwent surgical small bowel resection at the First Affiliated Hospital of Sun Yat-sen University (Guangzhou, China) between January 2007 and December 2017 were enrolled. We evaluated the intestinal imaging features of computed tomography enterography (CTE), including mesenteric inflammatory fat stranding, the target sign, mesenteric hypervascularity, bowel wall thickening, lymphadenopathy, stricture diameter, and maximal upstream diameter. We used A.K. software (Artificial Intelligence Kit, version 1.1) to calculate the visceral fat (VF) and subcutaneous fat (SF) volumes at the third lumbar vertebra level. Pathological tissue information was recorded. Diagnostic models were established based on the multivariate regression analysis results, and their effectiveness was evaluated by area under the curve (AUC) and decision curve analyses.

Results

Overall, 48 patients with CD were included in this study. The abdominal VF/SF volume ratio (odds ratio, 1.20; 95% confidence interval, 1.05–1.38; P = 0.009) and the stenosis diameter/upstream intestinal dilatation diameter (ND) ratio (odds ratio, 0.90; 95% confidence interval, 0.82–0.99; P = 0.034) were independent risk factors for the severe fibrosis of the small intestine. The AUC values of the VF/SF ratio, the ND ratio, and their combination were 0.760, 0.673, and 0.804, respectively. The combination of the VS/SF volume ratio and ND ratio achieved the highest net benefit on the decision curve.

Conclusion

The VF volume on CTE can reflect intestinal fibrosis. The combination of the VF/SF volume ratio and ND ratio of CD patients assessed using CTE can help predict severe fibrosis stenosis of the small intestine.

Fibrosis in fat: From other diseases to Crohn’s disease

Creeping fat is a specific feature of Crohn’s disease (CD) and is characterized by mesenteric fat wrapping around the intestine. It highly correlates with intestinal transmural inflammation, muscular hypertrophy, fibrosis, and stricture formation. However, the pathogenesis of creeping fat remains unclear. Molecular crosstalk exists between mesenteric fat and the intestine. Indeed, creeping fat contains different types of cells, including adipocytes and immune cells. These cell types can produce various cytokines, fatty acids, and growth factors, which affect the mesenteric fat function and modulate intestinal inflammation and immunity. Moreover, adipocyte progenitors can produce extracellular matrix to adapt to fat expansion. Previous studies have shown that fat fibrosis is an important feature of adipose tissue malfunction and exists in other diseases, including metabolic disorders, cancer, atrial fibrillation, and osteoarthritis. Furthermore, histological sections of CD showed fibrosis in the creeping fat. However, the role of fibrosis in the mesenteric fat of CD is not well understood. In this review, we summarized the possible mechanisms of fat fibrosis and its impact on other diseases. More specifically, we illustrated the role of various cells (adipocyte progenitors, macrophages, mast cells, and group 1 innate lymphoid cells) and molecules (including hypoxia-inducible factor 1-alpha, transforming growth factor-beta, platelet-derived growth factor, and peroxisome proliferator-activated receptor-gamma) in the pathogenesis of fat fibrosis in other diseases to understand the role of creeping fat fibrosis in CD pathogenesis. Future research will provide key information to decipher the role of fat fibrosis in creeping fat formation and intestinal damage, thereby helping us identify novel targets for the diagnosis and treatment of CD.

Reverse translation approach generates a signature of penetrating fibrosis in Crohn's disease that is associated with anti-TNF response

OBJECTIVE

Fibrosis is a common feature of Crohn's disease (CD) which can involve the mesenteric fat. However, the molecular signature of this process remains unclear. Our goal was to define the transcriptional signature of mesenteric fibrosis in CD subjects and to model mesenteric fibrosis in mice to improve our understanding of CD pathogenesis.

DESIGN

We performed histological and transcriptional analysis of fibrosis in CD samples. We modelled a CD-like fibrosis phenotype by performing repeated colonic biopsies in mice and analysed the model by histology, type I collagen-targeted positron emission tomography (PET) and global gene expression. We generated a gene set list of essential features of mesenteric fibrosis and compared it to mucosal biopsy datasets from inflammatory bowel disease patients to identify a refined gene set that correlated with clinical outcomes.

RESULTS

Mesenteric fibrosis in CD was interconnected to areas of fibrosis in all layers of the intestine, defined as penetrating fibrosis. We found a transcriptional signature of differentially expressed genes enriched in areas of the mesenteric fat of CD subjects with high levels of fibrosis. Mice subjected to repeated colonic biopsies showed penetrating fibrosis as shown by histology, PET imaging and transcriptional analysis. Finally, we composed a composite 24-gene set list that was linked to inflammatory fibroblasts and correlated with treatment response.

CONCLUSION

We linked histopathological and molecular features of CD penetrating fibrosis to a mouse model of repeated biopsy injuries. This experimental system provides an innovative approach for functional investigations of underlying profibrotic mechanisms and therapeutic concepts in CD.

The Role of Tissue-Resident Macrophages in the Development and Treatment of Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), comprising Crohn’s disease and ulcerative colitis, is a refractory disease with many immune abnormalities and pathologies in the gastrointestinal tract. Because macrophages can distinguish innocuous antigens from potential pathogens to maintain mucosa barrier functions, they are essential cells in the intestinal immune system. With numerous numbers in the intestinal tract, tissue-resident macrophages have a significant effect on the constant regeneration of intestinal epithelial cells and maintaining the immune homeostasis of the intestinal mucosa. They also have a significant influence on IBD through regulating pro-(M1) or anti-inflammatory (M2) phenotype polarization according to different environmental cues. The disequilibrium of the phenotypes and functions of macrophages, disturbed by intracellular or extracellular stimuli, influences the progression of disease. Further investigation of macrophages’ role in the progression of IBD will facilitate deciphering the pathogenesis of disease and exploring novel targets to develop novel medications. In this review, we shed light on the origin and maintenance of intestinal macrophages, as well as the role of macrophages in the occurrence and development of IBD. In addition, we summarize the interaction between gut microbiota and intestinal macrophages, and the role of the macrophage-derived exosome. Furthermore, we discuss the molecular and cellular mechanisms participating in the polarization and functions of gut macrophages, the potential targeted strategies, and current clinical trials for IBD.

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.

Characteristics of mesenteric adipose tissue attached to different intestinal segments and their roles in immune regulation

Mesenteric adipose tissue (MAT) plays a critical role in the intestinal physiological ecosystems. Small and large intestines have evidently intrinsic and distinct characteristics. However, whether there exist any mesenteric differences adjacent to the small and large intestines (SMAT and LMAT) has not been properly characterized. We studied the important facets of these differences, such as morphology, gene expression, cell components, and immune regulation of MATs, to characterize the mesenteric differences. The SMAT and LMAT of mice were used for comparison of tissue morphology. Paired mesenteric samples were analyzed by RNA-seq to clarify gene expression profiles. MAT partial excision models were constructed to illustrate the immune regulation roles of MATs, and 16S-seq was applied to detect the subsequent effect on microbiota. Our data show that different segments of mesenteries have different morphological structures. SMAT not only has smaller adipocytes but also contains more fat-associated lymphoid clusters than LMAT. The gene expression profile is also discrepant between these two MATs in mice. B-cell markers were abundantly expressed in SMAT, whereas development-related genes were highly expressed in LMAT. Adipose-derived stem cells of LMAT exhibited higher adipogenic potential and lower proliferation rates than those of SMAT. In addition, SMAT and LMAT play different roles in immune regulation and subsequently affect microbiota components. Finally, our data clarified the described differences between SMAT and LMAT in humans. There were significant differences in cell morphology, gene expression profiles, cell components, biological characteristics, and immune and microbiota regulation roles between regional MATs.NEW & NOTEWORTHY Our results change the paradigm of how we regard MAT as a contiguous and homogeneous tissue to an intensely heterogeneous tissue. Appreciation of the differences between regional MATs will guide future research to investigate the specialized roles of different MATs in intestinal health and disease.

Therapeutic Targeting of Intestinal Fibrosis in Crohn's Disease

Intestinal fibrosis is one of the most threatening complications of Crohn’s disease. It occurs in more than a third of patients with this condition, is associated with increased morbidity and mortality, and surgery often represents the only available therapeutic option. The mechanisms underlying intestinal fibrosis are partly known. Studies conducted so far have shown a relevant pathogenetic role played by mesenchymal cells (especially myofibroblasts), cytokines (e.g., transforming growth factor-β), growth factors, microRNAs, intestinal microbiome, matrix stiffness, and mesenteric adipocytes. Further studies are still necessary to elucidate all the mechanisms involved in intestinal fibrosis, so that targeted therapies can be developed. Although several pre-clinical studies have been conducted so far, no anti-fibrotic therapy is yet available to prevent or reverse intestinal fibrosis. The aim of this review is to provide an overview of the main therapeutic targets currently identified and the most promising anti-fibrotic therapies, which may be available in the near future.

Mesenteric SParIng versus extensive mesentereCtomY in primary ileocolic resection for ileocaecal Crohn's disease (SPICY): study protocol for randomized controlled trial

Background

There is emerging evidence to suggest that Crohn’s disease (CD) may be a disease of the mesentery, rather than of the bowel alone. A more extensive mesenteric resection, removing an increased volume of mesentery and lymph nodes to prevent recurrence of CD, may improve clinical outcomes. This study aims to analyse whether more extensive ‘oncological’ mesenteric resection reduces the recurrence rate of CD.

Methods

This is an international multicentre randomized controlled study, allocating patients to either group 1—mesenteric sparing ileocolic resection (ICR), the current standard procedure for CD, or group 2—extensive mesenteric ICR, up to the level of the ileocolic trunk. To detect a clinically relevant difference of 25 per cent in endoscopic recurrence at 6 months, a total of 138 patients is required (including 10 per cent dropout). Patients aged over 16 with CD undergoing primary ICR are eligible. Primary outcome is 6-month postoperative endoscopic recurrence rate (modified Rutgeerts score of greater than or equal to i2b). Secondary outcomes are postoperative morbidity, clinical recurrence, quality of life, and the need for (re)starting immunosuppressive medication. For long-term results, patients will be followed up for up to 5 years to determine the reoperation rate for recurrence of disease at the anastomotic site.

Conclusion

Analysing these two treatment strategies in a head-to-head comparison will allow an objective evaluation of the clinical relevance of extensive mesenteric resection in CD. If a clinical benefit can be demonstrated, this could result in changes to guidelines which currently recommend close bowel resection.

Registration number

NCT00287612 (http://www.clinicaltrials.gov)

Role of mesenteric component in Crohn’s disease: A friend or foe?

Crohn’s disease (CD) is a complex and relapsing gastrointestinal disease with mesenteric alterations. The mesenteric neural, vascular, and endocrine systems actively take part in the gut dysbiosis-adaptive immunity-mesentery-body axis, and this axis has been proven to be bidirectional. The abnormalities of morphology and function of the mesenteric component are associated with intestinal inflammation and disease progress of CD via responses to afferent signals, neuropeptides, lymphatic drainage, adipokines, and functional cytokines. The hypertrophy of mesenteric adipose tissue plays important roles in the pathogenesis of CD by secreting large amounts of adipokines and representing a rich source of proinflammatory or profibrotic cytokines. The vascular alteration, including angiogenesis and lymphangiogenesis, is concomitant in the disease course of CD. Of note, the enlarged and obstructed lymphatic vessels, which have been described in CD patients, are likely related to the early onset submucosa edema and being a cause of CD. The function of mesenteric lymphatics is influenced by endocrine of mesenteric nerves and adipocytes. Meanwhile, the structure of the mesenteric lymphatic vessels in hypertrophic mesenteric adipose tissue is mispatterned and ruptured, which can lead to lymph leakage. Leaky lymph factors can in turn stimulate adipose tissue to proliferate and effectively elicit an immune response. The identification of the role of mesentery and the crosstalk between mesenteric tissues in intestinal inflammation may shed light on understanding the underlying mechanism of CD and help explore new therapeutic targets.

The Clinical Significance of Mesenteric Lymphocytes in Human Colorectal Cancer

Objective

The mesentery is a potential site of residual tumor in patients with colorectal cancer (CRC). However, the mesenteric immune microenvironment remains unclear. In this study, we investigated the immune landscape of the mesentery, particularly the role of lymphocytes and its association with the clinicopathological characteristics of CRC.

Methods

Flow cytometry was used to detect lymphocytes in the paired mesenteric tissue specimens adjacent to the colorectal tumors and normal mesenteric tissue specimens 10 cm away from the colorectal tumor edge and preoperative peripheral blood samples obtained from patients with CRC who underwent surgery. T-distributed stochastic neighbor embedding was utilized to analyze multiparameter flow cytometry data. Multiplex immunohistochemistry was performed to evaluate T cells subsets in the paired mesentery adjacent to the colorectal tumors and normal mesentery. The Fisher’s exact test and non-parametric Wilcoxon’s matched-pairs tests were used for statistical analysis. The non-parametric Mann-Whitney U test was used to determine associations between percentage data and clinical parameters of patients with CRC.

Results

We found that immune cells in the normal mesentery were mainly of lymphoid lineage. Compared with peripheral blood, the normal mesentery showed decreased NK cells and the CD4/CD8 ratio and increased CD3⁺ CD56⁺, memory CD4⁺ T, memory CD8⁺ T, CD4⁺ tissue-resident memory T (TRM), and CD8⁺ TRM cells. Compared with the normal mesentery, the mesentery adjacent to the colorectal tumor showed increased B and regulatory T cells and decreased NK, CD3⁺ CD56⁺, CD4⁺ TRM, and CD8⁺ TRM cells. Moreover, memory CD8⁺ T cells and plasmablasts are negatively correlated with the depth of invasion of CRC. Increased memory CD4⁺ T cells are associated with distant metastasis of CRC and high preoperative serum carcinoembryonic antigen levels.

Conclusion

The mesentery shows a specific immune microenvironment, which differs from that observed in peripheral blood. CRC can alter the mesenteric immune response to promote tumor progression.

Diet in Intestinal Fibrosis: A Double-Edged Sword

The natural history of inflammatory bowel diseases, especially Crohn’s disease, is frequently complicated by intestinal fibrosis. Because of the lack of effective treatments for intestinal fibrosis, there is an urgent need to develop new therapies. Factors promoting intestinal fibrosis are currently unclear, but diet is a potential culprit. Diet may influence predisposition to develop intestinal fibrosis or alter its natural history by modification of both the host immune response and intestinal microbial composition. Few studies have documented the effects of dietary factors in modulating IBD-induced intestinal fibrosis. As the mechanisms behind fibrogenesis in the gut are believed to be broadly similar to those from extra-intestinal organs, it may be relevant to investigate which dietary components can inhibit or promote fibrosis factors such as myofibroblasts progenitor activation in other fibrotic diseases.

Review article: distinctions between ileal and colonic Crohn's disease: from physiology to pathology

BACKGROUND

Ileal and colonic Crohn's disease seem to be two separate entities.

AIMS

To describe the main physiological distinctions between the small and the large intestine and to analyse the differences between ileal and colonic Crohn's disease.

METHODS

The relevant literature was critically examined and synthesised.

RESULTS

The small and large intestine have fundamental distinctions (anatomy, cellular populations, immune defence, microbiota). The differences between ileal and colonic Crohn's disease are highlighted by a heterogeneous body of evidence including clinical features (natural history of the disease, efficacy of treatments, and monitoring), epidemiological data (smoking status, age, gender) and biological data (genetics, microbiota, immunity, mesenteric fat). However, the contribution of these factors to disease location remains poorly understood.

CONCLUSION

The classification of ileal and colonic Crohn's disease as distinct subphenotypes is well supported by the literature. Understanding of these differences could be exploited to develop more individualised patient care.

Location is important: differentiation between ileal and colonic Crohn's disease

Crohn's disease can affect any part of the gastrointestinal tract; however, current European and national guidelines worldwide do not differentiate between small-intestinal and colonic Crohn's disease for medical treatment. Data from the past decade provide evidence that ileal Crohn's disease is distinct from colonic Crohn's disease in several intestinal layers. Remarkably, colonic Crohn's disease shows an overlap with regard to disease behaviour with ulcerative colitis, underlining the fact that there is more to inflammatory bowel disease than just Crohn's disease and ulcerative colitis, and that subtypes, possibly defined by location and shared pathophysiology, are also important. This Review provides a structured overview of the differentiation between ileal and colonic Crohn's disease using data in the context of epidemiology, genetics, macroscopic differences such as creeping fat and histological findings, as well as differences in regard to the intestinal barrier including gut microbiota, mucus layer, epithelial cells and infiltrating immune cell populations. We also discuss the translation of these basic findings to the clinic, emphasizing the important role of treatment decisions. Thus, this Review provides a conceptual outlook on a new mechanism-driven classification of Crohn's disease.

Anatomical Variation in Mesenteric Macrophage Phenotypes in Crohn's Disease

INTRODUCTION:

Clinical trials are currently investigating whether an extended mesenteric resection for ileocecal resections could reduce postoperative recurrence in Crohn's disease. Resection of the mesorectum, which contains proinflammatory macrophages, during proct(ocol)ectomy, is associated with reduced recurrent inflammation and improved wound healing. We aimed to characterize the macrophages in the ileocecal mesentery, which were compared with those in the mesorectum, to provide a biological rationale for the ongoing trials.

METHODS:

In 13 patients with Crohn's disease and 4 control patients undergoing a proctectomy, tissue specimens were sampled at 3 locations from the mesorectum: distal (rectum), middle, and proximal (sigmoid). In 38 patients with Crohn's disease and 7 control patients undergoing ileocecal resections, tissue specimens also obtained from 3 locations: adjacent to the inflamed terminal ileum, adjacent to the noninflamed ileal resection margin, and centrally along the ileocolic artery. Immune cells from these tissue specimens were analyzed by flow cytometry for expression of CD206 to determine their inflammatory status.

RESULTS:

In the mesorectum, a gradient from proinflammatory to regulatory macrophages from distal to proximal was observed, corresponding to the adjacent inflammation of the intestine. By contrast, the ileocecal mesentery did not contain high amounts of proinflammatory macrophages adjacent to the inflamed tissue, and a gradient toward a more proinflammatory phenotype was seen in the central mesenteric area.

DISCUSSION:

Although the mesentery is a continuous structure, the mesorectum and the ileocecal mesentery show different immunological characteristics. Therefore, currently, there is no basis to perform an extended ileocecal resection in patients with Crohn's disease.

Intestinal stricture in Crohn's disease: A 2020 update

Crohn's disease (CD) is a chronic and relapsing-remitting inflammatory disorder of the gastrointestinal tract. Approximately 70% of patients inevitably develop fibrosis-associated intestinal stricture after 10 years of CD diagnosis, which seriously affects their quality of life. Current therapies play limited role in preventing or reversing the process of fibrosis and no specific anti-fibrotic therapy is yet available. Nearly half of patients thus have no alternative but to receive surgery. The potential mechanisms of intestinal fibrosis remain poorly understood; extracellular matrix remodeling, aberrant immune response, intestinal microbiome imbalance and creeping fat might exert fundamental influences on the multiple physiological and pathophysiological processes. Recently, the emerging new diagnostic techniques have markedly promoted an accurate assessment of intestinal stricture by distinguishing fibrosis from inflammation, which is crucial for guiding treatment and predicting prognosis. In this review, we concisely summarized the key studies published in the year 2020 covering pathogenesis, diagnostic modalities, and therapeutic strategy of intestinal stricture. A comprehensive and timely review of the updated researches in intestinal stricture could provide insight to further elucidate its pathogenesis and identify novel drug targets with anti-fibrotic potentiality.

Novel mechanisms and clinical trial endpoints in intestinal fibrosis

The incidence of inflammatory bowel diseases (IBD) worldwide has resulted in a global public health challenge. Intestinal fibrosis leading to stricture formation and bowel obstruction is a frequent complication in Crohn's disease (CD), and the lack of anti-fibrotic therapies makes elucidation of fibrosis mechanisms a priority. Progress has shown that mesenchymal cells, cytokines, microbial products, and mesenteric adipocytes are jointly implicated in the pathogenesis of intestinal fibrosis. This recent information puts prevention or reversal of intestinal strictures within reach through innovative therapies validated by reliable clinical trial endpoints. Here, we review the role of immune and non-immune components of the pathogenesis of intestinal fibrosis, including new cell clusters, cytokine networks, host-microbiome interactions, creeping fat, and their translation for endpoint development in anti-fibrotic clinical trials.

Chylomicrons-Simulating Sustained Drug Release in Mesenteric Lymphatics for the Treatment of Crohn's-Like Colitis

BACKGROUND AND AIMS

Alteration to both the structures and functions of mesenteric lymphatic vessels is a typical hallmark of Crohn's disease [CD]. Dysfunctional lymphatics was observed in patients with both CD and experimental colitis, suggesting mesenteric lymphatics could be potential therapeutic targets. This study aimed to develop a nano-delivery system which can enhance drug delivery in mesenteric lymphatic tissue [MLT] and evaluate the therapeutic effects in Crohn's colitis.

METHODS

We designed a mesoporous silica nanoparticle [MSN] conjugated with long-chain fatty acid [LMSN] and covered with enteric coating [ELMSN] which can be specifically transported via the mesenteric lymphatic system. The therapeutic efficacy of laquinimod-loaded nanoparticles [LAQ@ELMSN] was evaluated in the well-established interleukin [IL]-10-/- spontaneous experimental colitis.

RESULTS

ELMSNs induced sustainable drug release that markedly increased drug concentration in MLT. In experimental colitis, the lymphatics-targeting drug delivery system suppressed lymphangitis and promoted lymphatic drainage. The downregulation of pro-inflammatory cytokines and the downstream NF-κB-related proteins efficiently inhibited lymphangiogenesis and restored tight junctions of mesenteric lymphatic vessels [MLVs]. LAQ@ELMSN showed a superior therapeutic effect in ameliorating intestinal inflammation compared with free drug administration. Alteration of gut microbiota and metabolites in experimental colitis was also reversed by LAQ@ELMSN.

CONCLUSION

Our study demonstrates a convenient, orally administered drug delivery system which enhances drug release in MLT. The results confirm the contribution of the mesenteric lymphatic system to the pathogenesis of gut inflammation and shed light on the application of lymphatics-targeting drug delivery therapy as a potential therapeutic strategy for CD treatment.

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.

Disturbance of Fatty Acid Desaturation Mediated by FADS2 in Mesenteric Adipocytes Contributes to Chronic Inflammation of Crohn's Disease

BACKGROUND AND AIMS

The aim of this study was to investigate the metabolic profile of mesenteric adipocytes and the correlations between key metabolic changes and local inflammation in the context of Crohn's disease [CD].

METHODS

Metabolic dysfunction was shown to be regulated by fatty acid desaturase-2 [FADS2], through metabolomics and functional analyses of mesenteric adipose tissue biopsies and primary mesenteric adipocytes isolated from surgical specimens collected from CD patients and control subjects. FADS2 was overexpressed in vitro and in vivo using a lentiviral vector and an adeno-associated virus [AAV], respectively. The interaction between mesenteric adipocytes and inflammation responses was evaluated by establishing a cell coculture system and a FADS2-AAV treated animal model; 3T3-L1 cells were used to elucidate the mechanism underlying FADS2 deregulation.

RESULTS

We observed significant changes in the levels of metabolites involved in the multi-step synthesis of long-chain polyunsaturated fatty acids [PUFAs]. Gas chromatography analysis revealed impaired desaturation fluxes towards the n-6 and n-3 pathways, which are associated with reduced FADS2 activity in human mesentery tissue. Decreased FADS2 expression at both mRNA and protein levels was confirmed in surgical specimens. The restoration of FADS2 expression, which allows for the endogenous conversion of n-3 fatty acids into proresolving lipid mediators, resulted in a significant reduction in pro-inflammatory macrophage infiltration and attenuated expression of inflammatory cytokines or adipokines.

CONCLUSIONS

These findings indicate that impaired fatty acid desaturation and lipid mediator imbalance within mesenteric adipose tissue contributes to chronic inflammation in CD. The therapeutic role of FADS2 may lead to improved CD treatment.

Pathophysiology of Crohn's disease inflammation and recurrence

Chron’s Disease is a chronic inflammatory intestinal disease, first described at the beginning of the last century. The disease is characterized by the alternation of periods of flares and remissions influenced by a complex pathogenesis in which inflammation plays a key role. Crohn’s disease evolution is mediated by a complex alteration of the inflammatory response which is characterized by alterations of the innate immunity of the intestinal mucosa barrier together with a remodeling of the extracellular matrix through the expression of metalloproteins and increased adhesion molecules expression, such as MAcCAM-1. This reshaped microenvironment enhances leucocytes migration in the sites of inflammation, promoting a T_H1 response, through the production of cytokines such as IL-12 and TNF-α. IL-12 itself and IL-23 have been targeted for the medical treatment of CD. Giving the limited success of medical therapies, the treatment of the disease is invariably surgical. This review will highlight the role of inflammation in CD and describe the surgical approaches for the prevention of the almost inevitable recurrence.

Serum adipokines as non-invasive biomarkers in Crohn's disease

Adipose tissue secretes molecules that can promote activity in Crohn’s disease. We aimed to evaluate the role of serum adipokines as possible biomarkers in Crohn’s disease. Serum samples were obtained from 40 patients with endoscopically active or quiescent Crohn’s disease and 36 healthy controls. Serum leptin, ghrelin, resistin and adiponectin levels were analysed by Multiplex in a Luminex 200 system technology. Receiver Operating Characteristic curves were performed to evaluate the adipokines discriminatory capacity. A logistic regression adjusted by possible confounders (i.e. gender, age, BMI) was performed for those adipokines that showed an area under the curve > 0.7. No differences were found in age, gender or BMI among groups. Distribution for serum resistin was different among the three groups of study, and only this adipokine showed an area under the curve of 0.75 comparing actives patients and healthy control groups. Resistin median concentration was selected as a cut-off for a logistic regression analysis; odds ratio along its 95% confidence interval adjusted by gender, age, and BMI yielded a value of 5.46 (1.34–22.14) comparing actives patients and healthy controls. High concentration of serum resistin is probably associated to activity, being this association independent of gender, age or BMI.

Age-Dependent Changes of Adipokine and Cytokine Secretion From Rat Adipose Tissue by Endogenous and Exogenous Toll-Like Receptor Agonists

White adipose tissue but recently also brown adipose tissue have emerged as endocrine organs. Age-associated obesity is accompanied by prolonged and elevated lipopolysaccharide (LPS)-induced sickness symptoms and increased cytokine and adipokine levels in the circulation partially originating from adipose tissue. In the present study, ex vivo fat explants were used to investigate how the exogenous pathogen-associated molecular pattern (PAMP) LPS or the endogenous danger-associated molecular patterns (DAMPs) high mobility group box-1 protein (HMGB1) and biglycan modulate the release of cytokines and adipokines/batokines and, thus, could influence systemic and/or local inflammation. The response of adipose tissue (epididymal, retroperitoneal, subcutaneous, and brown) was compared between young lean and old obese rats (2 vs. 24 months old). LPS induced a strong interleukin (IL)-6 and tumor necrosis factor (TNF) alpha release into the supernatant of all adipose tissue types investigated. HMGB1 (subcutaneous) and biglycan (retroperitoneal) led to an increased release of IL-6 and TNFalpha (HMGB1) and decreased visfatin and adiponectin (biglycan) secretion from epididymal adipose tissue (young rats). Visfatin was also decreased by HMGB1 in retroperitoneal adipose tissue of old rats. We found significantly higher leptin (all fat pads) and adiponectin (subcutaneous) levels in supernatants of adipose tissue from old compared to young rats, whereas visfatin secretion showed the opposite. The expression of the biglycan receptor Toll-like receptor (TLR) 2 as well as the LPS and HMGB1 receptors TLR4 and receptor for advanced glycation end products (RAGE) were reduced with age (TLR4/RAGE) and by stimulation with their ligands (subcutaneous). Overall, we revealed that adipokines/adipose-tissue released cytokines show some modulation of their release caused by mediators of septic (batokines) and sterile inflammation with potential implication for acute and chronic disease. Moreover, aging may increase or decrease the release of fat-derived mediators. These data show that DAMPS and LPS locally modulate cytokine secretion while only DAMPS but not LPS can locally alter adipokine secretion during inflammation.

Crohn's versus Cancer: Comparison of Functional and Surgical Outcomes after Right-Sided Resections

BACKGROUND

The objective of this study was to compare functional and surgical outcomes of patients undergoing ileocecal resection for Crohn's disease (CD) to patients undergoing oncological right colectomy.

METHODS

Retrospective single-center cohort study including consecutive patients undergoing right colectomy for adenocarcinoma (oncological resection) or CD (mesentery-sparing resection) between July 2011 and November 2017. Outcome measures were pathological details (lymph node yield), postoperative recovery (pain levels, return to flatus and stool, intake of fluids, weight change, and mobilization), and early (30-day) outcomes (surgical/medical complications, hospital stay, readmissions).

RESULTS

A total of 195 patients (153 [78%] with cancer and 42 [22%] with CD) were included. Overall compliance with the institutional enhanced recovery protocol was comparable between the 2 groups (compliance ≥70%: 60% in CD patients vs. 62% in cancer, p = 0.458). The adenocarcinoma group had a larger lymph node yield than the CD group (26 ± 13 vs. 2.4 ± 5, respectively, p < 0.001). While the CD group experienced significantly more pain (3.7 ± 1.9/10 vs. 2.8 ± 2.5/10, p = 0.007, patients requiring opioids: 65 vs. 28%, p = 0.001), return of flatus (2.3 ± 1.2 days vs. 2.4 ± 2.8 days, p = 0.642) and stool (4.1 ± 6.0 vs. 3.0 ± 1.8 days, p = 0.292) was no different in both groups. No difference was observed regarding postoperative complications, length of stay, and readmission rate.

CONCLUSION

This study revealed no differences in both functional and surgical outcomes in CD and cancer patients undergoing mesentery-sparing or formal oncological right colectomy, respectively.

Fibrostenotic strictures in Crohn's disease

The use of biologic agents including anti-tumor necrosis factor monoclonal antibodies followed by anti-integrins and anti-interleukins has drastically changed the treatment paradigm of Crohn’s disease (CD) by improving clinical symptoms and mucosal healing. However, up to 70% of CD patients still eventually undergo surgery mainly due to fibrostenotic strictures. There are no specific anti-fibrotic drugs yet. This review comprehensively addresses the mechanism, prediction, diagnosis and treatment of the fibrostenotic strictures in CD. We also introduce promising anti-fibrotic agents which may be available in the near future and summarize challenges in developing novel therapies to treat fibrostenotic strictures in CD.

Bioactive Factors in Human Breast Milk Attenuate Intestinal Inflammation during Early Life

Human breast milk is well known as the ideal source of nutrition during early life, ensuring optimal growth during infancy and early childhood. Breast milk is also the source of many unique and dynamic bioactive components that play a key role in the development of the immune system. These bioactive components include essential microbes, human milk oligosaccharides (HMOs), immunoglobulins, lactoferrin and dietary polyunsaturated fatty acids. These factors all interact with intestinal commensal bacteria and/or immune cells, playing a critical role in establishment of the intestinal microbiome and ultimately influencing intestinal inflammation and gut health during early life. Exposure to breast milk has been associated with a decreased incidence and severity of necrotizing enterocolitis (NEC), a devastating disease characterized by overwhelming intestinal inflammation and high morbidity among preterm infants. For this reason, breast milk is considered a protective factor against NEC and aberrant intestinal inflammation common in preterm infants. In this review, we will describe the key microbial, immunological, and metabolic components of breast milk that have been shown to play a role in the mechanisms of intestinal inflammation and/or NEC prevention.

Whole transcriptional analysis identifies markers of B, T and plasma cell signaling pathways in the mesenteric adipose tissue associated with Crohn's disease

Background

Crohn’s disease (CD) is a multifactorial disease characterized by chronic intestinal inflammation. The increased visceral adiposity near the affected intestinal area, of which mesenteric adipose tissue (MAT) is the main component, is a feature of CD. Both protective and pathological roles have been attributed to this disease-associated tissue in CD. To understand the contribution of MAT to CD pathophysiology, a molecular and cellular signature of disease-associated MAT in CD patients was provided.

Methods

We performed an observational study with whole transcriptional analysis by RNA sequencing (RNA-seq) of MAT and ileal mucosa from CD patients with active disease and controls. qPCR and immunohistology were performed for validation analysis.

Results

RNA-seq identified 17 significantly regulated genes (|FC| > 1.5; FDR < 0.05) in CD-MAT compared to non-IBD controls, with a marked upregulation of plasma cell genes (i.e., IGLL5, MZB1, CD79A, POU2AF1, FCRL5, JCHAIN, DERL3, SDC1, PIM2). A less strict statistical cutoff value (|FC| > 1.5, nominal p ≤ 0.05) yielded a larger list of 651 genes in CD-MAT compared to controls. CD ileum showed the significant regulation compared to control ileum of 849 genes (|FC| > 1.5; FDR < 0.05) or 2654 genes (|FC| > 1.5, nominal p ≤ 0.05). Ingenuity Pathway Analysis revealed the significant regulation of pathways related to T- and B cell functionality in the MAT of CD patients. Despite the differences between the MAT and ileal signatures of CD patients, we identified a subset of 204 genes significantly modulated in both tissues compared to controls. This common signature included genes related to the plasma cell signature. Genes such as S100A8, S100A9 (calprotectin) and IL1B, which are associated with acute inflammatory response, were exclusively regulated in the ileal mucosa of CD disease. In contrast, some genes encoding for lymphocyte receptors such as MS4A1, CD3D and CD79A were exclusively regulated in CD-MAT, exhibiting a different pattern of immune cell activation compared to the ileal mucosa in CD patients. qPCR and immunohistology confirmed the presence of large infiltrates of CD3⁺ CD20⁺ lymphocytes and CD138⁺ plasma cells in CD-MAT.

Conclusion

Our data strongly supports the role of CD-associated MAT as a site for T-, B- and plasma cell activation, and suggests that it could also act as a reservoir of memory immune responses.

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.

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.

Celiac Disease Monocytes Induce a Barrier Defect in Intestinal Epithelial Cells

Intestinal epithelial barrier function in celiac disease (CeD) patients is altered. However, the mechanism underlying this effect is not fully understood. The aim of the current study was to evaluate the role of monocytes in eliciting the epithelial barrier defect in CeD. For this purpose, human monocytes were isolated from peripheral blood mononuclear cells (PBMCs) from active and inactive CeD patients and healthy controls. PBMCs were sorted for expression of CD14 and co-cultured with intestinal epithelial cells (IECs, Caco2BBe). Barrier function, as well as tight junctional alterations, were determined. Monocytes were characterized by profiling of cytokines and surface marker expression. Transepithelial resistance was found to be decreased only in IECs that had been exposed to celiac monocytes. In line with this, tight junctional alterations were found by confocal laser scanning microscopy and Western blotting of ZO-1, occludin, and claudin-5. Analysis of cytokine concentrations in monocyte supernatants revealed higher expression of interleukin-6 and MCP-1 in celiac monocytes. However, surface marker expression, as analyzed by FACS analysis after immunostaining, did not reveal significant alterations in celiac monocytes. In conclusion, CeD peripheral monocytes reveal an intrinsically elevated pro-inflammatory cytokine pattern that is associated with the potential of peripheral monocytes to affect barrier function by altering TJ composition.

dPGS Regulates the Phenotype of Macrophages via Metabolic Switching

The synthetic compound dendritic polyglycerol sulfate (dPGS) is a pleiotropic acting molecule but shows a high binding affinity to immunological active molecules as L-/P-selectin or complement proteins leading to well described anti-inflammatory properties in various mouse models. In order to make a comprehensive evaluation of the direct effect on the innate immune system, macrophage polarization is analyzed in the presence of dPGS on a phenotypic but also metabolic level. dPGS administered macrophages show a significant increase of MCP1 production paralleled by a reduction of IL-10 secretion. Metabolic analysis reveals that dPGS could potently enhance the glycolysis and mitochondrial respiration in M0 macrophages as well as decrease the mitochondrial respiration of M2 macrophages. In summary the data indicate that dPGS polarizes macrophages into a pro-inflammatory phenotype in a metabolic pathway-dependent manner.

Microbial Colonization in Adulthood Shapes the Intestinal Macrophage Compartment

BACKGROUND AND AIMS

Contact with distinct microbiota early in life has been shown to educate the mucosal immune system, hence providing protection against immune-mediated diseases. However, the impact of early versus late colonization with regard to the development of the intestinal macrophage compartment has not been studied so far.

METHODS

Germ-free mice were colonized with specific-pathogen-free [SPF] microbiota at the age of 5 weeks. The ileal and colonic macrophage compartment were analysed by immunohistochemistry, flow cytometry, and RNA sequencing 1 and 5 weeks after colonization and in age-matched SPF mice, which had had contact with microbiota since birth. To evaluate the functional differences, dextran sulfate sodium [DSS]-induced colitis was induced, and barrier function analyses were undertaken.

RESULTS

Germ-free mice were characterized by an atrophied intestinal wall and a profoundly reduced number of ileal macrophages. Strikingly, morphological restoration of the intestine occurred within the first week after colonization. In contrast, ileal macrophages required 5 weeks for complete restoration, whereas colonic macrophages were numerically unaffected. However, following DSS exposure, the presence of microbiota was a prerequisite for colonic macrophage infiltration. One week after colonization, mild colonic inflammation was observed, paralleled by a reduced inflammatory response after DSS treatment, in comparison with SPF mice. This attenuated inflammation was paralleled by a lack of TNFα production of LPS-stimulated colonic macrophages from SPF and colonized mice, suggesting desensitization of colonized mice by the colonization itself.

CONCLUSIONS

This study provides the first data indicating that after colonization of adult mice, the numeric, phenotypic, and functional restoration of the macrophage compartment requires the presence of intestinal microbiota and is time dependent.

The Adipokine Metrnl Ameliorates Chronic Colitis in Il-10-/- Mice by Attenuating Mesenteric Adipose Tissue Lesions During Spontaneous Colitis

BACKGROUND

Crosstalk between mesenteric adipose tissue [MAT] and the intestines affects the progression of Crohn's disease [CD]. The adipokine metrnl regulates adipocyte function and has anti-inflammatory activity. We aimed to explore metrnl expression in CD MAT, investigate the influence of metrnl on the experimental colitis disease course and determine the mechanism underlying this effect.

METHODS

Metrnl expression in MAT specimens obtained from patients with and without CD was tested by immunohistochemistry. Male Il-10-/- mice with spontaneous enteritis were divided into positive control and metrnl-treated [Metrnl-Fc, 10 mg/kg/d, intraperitoneally, 8 weeks] groups. Age-matched male wild-type [WT] mice were used as negative controls. The effects of metrnl on enteritis and mesenteric lesions and the potential controlling mechanisms were evaluated.

RESULTS

Metrnl expression was higher in human CD MAT than in control MAT. Systemic delivery of metrnl significantly ameliorated chronic colitis in Il-10-/- mice, as demonstrated by decreases in the disease activity index, inflammatory score and proinflammatory mediators. The protective effects of metrnl on MAT included reduced mesenteric hypertrophy, increased adipocyte size, improved adipocyte intrinsic function and ameliorated inflammation. Metrnl treatment activated STAT5/PPAR-γ signaling and promoted adipocyte differentiation in the MAT.

CONCLUSIONS

Metrnl expression was increased in the MAT of CD patients. Metrnl administration attenuated mesenteric lesions by promoting adipocyte function and differentiation partly through STAT5/PPAR-γ signaling pathway activation, thereby ameliorating CD-like colitis in mice.