Luminally polarized mural and vascular remodeling in ileal strictures of Crohn's disease

Creeping Fat in Crohn's Disease-Surgical, Histological, and Radiological Approaches

During the course of Crohn's disease, the response of mesenteric adipose tissue to the production of inflammatory mediators and bacterial invasion through the intestinal mucosa results in the formation of creeping fat. Creeping fat describes the arresting finger-like projections that surround the inflamed bowel. In this review, the microscopic and macroscopic features of creeping fat and histological evidence for the importance of this tissue are discussed. Moreover, the most recent insights into the radiological assessment of creeping fat in patients with Crohn's disease are reported. Advances in imaging techniques have revolutionized the possibility of visualization and quantification of adipose tissue depots with excellent accuracy. Visceral fat has been significantly correlated with various Crohn's-disease-related outcomes. Despite the difficulties in distinguishing physiologic perienteric fat from creeping fat, the growing interest in fat-wrapping in Crohn's disease has rejuvenated radiologic research. With regard to the noninvasive fat-wrapping assessment, a novel CT enterography-based mesenteric creeping fat index has been developed for the mitigation of the confounding effect of normal retroperitoneal and perienteric adipose tissue. Research on machine learning algorithms and computational radiomics in conjunction with mechanistic studies may be the key for the elucidation of the complex role of creeping fat in Crohn's disease.

Constrictive and Hypertrophic Strictures in Ileal Crohn's Disease

BACKGROUND & AIMS

Strictures in Crohn's disease (CD) are classically attributed to fibromuscular hypertrophy of the intestinal wall. We have identified and characterized CD-related ileal strictures that result instead from mural constriction (ie, reduced external circumference).

METHODS

Twenty-four strictures and internal controls from 17 adults with obstructive CD were analyzed by cross-sectional morphometry.

RESULTS

The stricture-to-control circumference ratios (CRs) ranged from 0.53 to 1.7. Six strictures with CR ≥1.0, designated hypertrophic, had concentrically thickened walls, mean 3-fold increases in cross-sectional area and stainable fibromucular tissue, and high transmural inflammation scores. In contrast, 18 strictures with CR <1.0, designated constrictive, had thin, pliant walls, cross-sectional areas and stainable fibromuscular tissue comparable with control values, and low transmural inflammation scores. Eight mildly constrictive strictures also showed mild fibromuscular mural expansion that fell short of statistical significance. Twelve of 18 constrictive strictures (67%) occurred multiply (2-4 strictures per specimen) in contrast with hypertrophic strictures, all of which occurred singly (P = .01). Constriction correlated quantitatively with circumferential serosal fat wrapping (P = .003) and was associated with myenteric lymphocytic plexitis (P = .02). Disease duration was shortest among subjects with constrictive strictures and correlated with increasing circumference (CR ≤0.8, 6.3 ± 6.2 years; CR >0.8, 8.7 ± 6.4 years; and CR ≥1.00, 13.7 ± 5.0 years, respectively; P = .03).

CONCLUSIONS

Constrictive ileal strictures in CD differ pathologically and clinically from hypertrophic strictures, featuring little or no fibromuscular mural expansion, frequent multiplicity, and earlier onset. Mesenteric fat wrapping and myenteric plexitis may contribute to their pathogenesis. Pathologic manifestations of constriction and hypertrophy can coexist, suggesting that stricture heterogeneity may be shaped in part by the dynamics of constrictive and hypertrophic processes.

International consensus to standardise histopathological scoring for small bowel strictures in Crohn's disease

OBJECTIVE

Effective medical therapy and validated trial outcomes are lacking for small bowel Crohn's disease (CD) strictures. Histopathology of surgically resected specimens is the gold standard for correlation with imaging techniques. However, no validated histopathological scoring systems are currently available for small bowel stricturing disease. We convened an expert panel to evaluate the appropriateness of histopathology scoring systems and items generated based on panel opinion.

DESIGN

Modified RAND/University of California Los Angeles methodology was used to determine the appropriateness of 313 candidate items related to assessment of CD small bowel strictures.

RESULTS

In this exercise, diagnosis of naïve and anastomotic strictures required increased bowel wall thickness, decreased luminal diameter or internal circumference, and fibrosis of the submucosa. Specific definitions for stricture features and technical sampling parameters were also identified. Histopathologically, a stricture was defined as increased thickness of all layers of the bowel wall, fibrosis of the submucosa and bowel wall, and muscularisation of the submucosa. Active mucosal inflammatory disease was defined as neutrophilic inflammation in the lamina propria and any crypt or intact surface epithelium, erosion, ulcer and fistula. Chronic mucosal inflammatory disease was defined as crypt architectural distortion and loss, pyloric gland metaplasia, Paneth cell hyperplasia, basal lymphoplasmacytosis, plasmacytosis and fibrosis, or prominent lymphoid aggregates at the mucosa/submucosa interface. None of the scoring systems used to assess CD strictures were considered appropriate for clinical trials.

CONCLUSION

Standardised assessment of gross pathology and histopathology of CD small bowel strictures will improve clinical trial efficiency and aid drug development.

Paediatric Ulcerative Colitis Is a Fibrotic Disease and Is Linked with Chronicity of Inflammation

BACKGROUND AND AIMS

Intestinal fibrosis has recently been characterised in adult ulcerative colitis and may affect motility, diarrhoea, and the symptom of urgency. We aimed to charactersze the presence of fibrosis in paediatric patients with ulcerative colitis, and its link to severity and chronicity of mucosal inflammation, as well as clinical factors of severity.

METHODS

We performed a single-centre cross-sectional study in children ages 1-18 years with ulcerative colitis, undergoing colectomy or proctocolectomy. Tissue cross-sections were derived from proximal, mid, and distal colon and rectum, and inflammation and fibrosis were graded based on previously developed scores. Clinical data were collected prospectively.

RESULTS

From 62 patients, 205 intestinal sections were evaluated. Median age at diagnosis was 13 years, 100% had extensive colitis, and all resections were done for refractory disease. The presence, chronicity, and degree of inflammation were linked with the presence of fibrosis. Thickness of the muscularis mucosa was also linked with presence and chronicity of inflammation. The overall submucosal fibrosis burden was associated with prior anti-tumour necrosis factor use.

CONCLUSIONS

Paediatric patients with ulcerative colitis exhibit colorectal submucosal fibrosis and muscularis mucosa thickening, which correlate with the presence, chronicity, and degree of mucosal inflammation. Fibrosis should be recognised as a complication of paediatric ulcerative colitis, and ulcerative colitis should be considered a progressive disease.

The Pathogenesis and Clinical Management of Stricturing Crohn Disease

Stricturing of the gastrointestinal tract is a common complication in Crohn disease and is a significant cause of morbidity and mortality among this population. The inflammatory process initiates fibrosis, leading to aberrant wound healing and excess deposition of extracellular matrix proteins. Our understanding of this process has grown and encompasses cellular mechanisms, epigenetic modifications, and inherent genetic predisposition toward fibrosis. Although medications can improve inflammation, there is still no drug to attenuate scar formation. As such, management of stricturing disease requires a multidisciplinary and individualized approach including medical management, therapeutic endoscopy, and surgery. This review details the current understanding regarding the pathogenesis, detection, and management of stricturing Crohn disease.

Ileal Crohn's Disease Exhibits Similar Transmural Fibrosis Irrespective of Phenotype

INTRODUCTION

In Crohn's disease (CD), the assessment of transmural inflammation and fibrosis is of utmost importance. This study aimed to quantify these parameters in CD ileal specimens and correlate them with disease progression.

METHODS

This is a retrospective unicentric study based on the analysis of archived specimens (n = 103) of primary ileal resection. Data were retrieved from a prospective national inflammatory bowel disease registry. Two pathologists, blinded for CD phenotype and clinical indications for surgery, examined 3 sections per patient and graded inflammation and fibrosis, based on a histopathological score.

RESULTS

Penetrating (B3, n = 74) CD exhibited significantly higher inflammation in diseased areas, compared with stricturing (B2, n = 29) disease (score 3: 96% vs 76%, P = 0.005 in inflamed areas; 78% vs 55%, P = 0.019 in most affected areas). This was also observed for the comparison of B2 CD with B3 CD with (B3s, n = 54) and without associated stricture (B3o, n = 20): B3s vs B2: 81% vs 55%, P = 0.033 in most affected areas; B3o vs B2: 100% vs 76%, P = 0.006 in inflamed areas; 70% vs 55%, P = 0.039 in most affected areas. We could not show differences in fibrosis scores between the subphenotypes. Postoperative new penetrating events occurred only in B3s (n = 6, 11%, P = 0.043) patients. The changing of biologic therapy after surgery correlated with severe inflammation at the proximal ileal margin (55% changed vs 25% not changed, P = 0.035).

DISCUSSION

In our cohort, fibrosis scores and fibromuscular changes were comparable, irrespective of CD phenotype. Inflammation severity was the major differentiator between penetrating and stricturing disease.JOURNAL/cltg/04.03/01720094-202104000-00012/inline-graphic1/v/2021-04-13T161901Z/r/image-tiff.

A myeloid-stromal niche and gp130 rescue in NOD2-driven Crohn's disease

Crohn's disease is a chronic inflammatory intestinal disease that is frequently accompanied by aberrant healing and stricturing complications. Crosstalk between activated myeloid and stromal cells is critical in the pathogenicity of Crohn's disease^1,2, and increases in intravasating monocytes are correlated with a lack of response to anti-TNF treatment³. The risk alleles with the highest effect on Crohn's disease are loss-of-function mutations in NOD2^4,5, which increase the risk of stricturing⁶. However, the mechanisms that underlie pathogenicity driven by NOD2 mutations and the pathways that might rescue a lack of response to anti-TNF treatment remain largely uncharacterized. Here we use direct ex vivo analyses of patients who carry risk alleles of NOD2 to show that loss of NOD2 leads to dysregulated homeostasis of activated fibroblasts and macrophages. CD14⁺ peripheral blood mononuclear cells from carriers of NOD2 risk alleles produce cells that express high levels of collagen, and elevation of conserved signatures is observed in nod2-deficient zebrafish models of intestinal injury. The enrichment of STAT3 regulation and gp130 ligands in activated fibroblasts and macrophages suggested that gp130 blockade might rescue the activated program in NOD2-deficient cells. We show that post-treatment induction of the STAT3 pathway is correlated with a lack of response to anti-TNF treatment in patients, and demonstrate in vivo in zebrafish the amelioration of the activated myeloid-stromal niche using the specific gp130 inhibitor bazedoxifene. Our results provide insights into NOD2-driven fibrosis in Crohn's disease, and suggest that gp130 blockade may benefit some patients with Crohn's disease-potentially as a complement to anti-TNF therapy.

Degree of Creeping Fat Assessed by Computed Tomography Enterography is Associated with Intestinal Fibrotic Stricture in Patients with Crohn's Disease: A Potentially Novel Mesenteric Creeping Fat Index

BACKGROUND AND AIMS

Emerging evidence points to a link between creeping fat and the pathogenesis of Crohn's disease [CD]. Non-invasive assessment of the severity of creeping fat on cross-sectional imaging modality has seldom been investigated. This study aimed to develop and characterize a novel mesenteric creeping fat index [MCFI] based on computed tomography [CT] in CD patients.

METHODS

MCFI was developed based on vascular findings on CT in a retrospective cohort [n = 91] and validated in a prospective cohort [n = 30]. The severity of creeping fat was graded based on the extent to which mesenteric fat extended around the intestinal circumference using the vessels in the fat as a marker. The accuracy of MCFI was assessed by comparing it with the degree of creeping fat observed in surgical specimens. The relationship between MCFI and fibrostenosis was characterized by determining if these correlated. The accuracy of MCFI was compared with other radiographic indices [i.e. visceral to subcutaneous fat area ratio and fibrofatty proliferation score].

RESULTS

In the retrospective cohort, MCFI had moderate accuracy in differentiating moderate-severe from mild fibrostenosis (area under the receiver operating characteristic [ROC] curve [AUC] = 0.799; p = 0.000). ROC analysis in the retrospective cohort identified a threshold MCFI of > 3 which accurately differentiated fibrostenosis severity in the prospective cohort [AUC = 0.756; p = 0.018]. An excellent correlation was shown between MCFI and the extent of fat wrapping in specimens in the prospective cohort [r = 0.840, p = 0.000]. Neither visceral to subcutaneous fat area ratio nor fibrofatty proliferation score correlated well with the degree of intestinal fibrosis.

CONCLUSIONS

MCFI can accurately characterize the extent of mesenteric fat wrapping in surgical specimens. It may become another non-invasive measure of CD fibrostenosis.

Mechanism of fibrosis and stricture formation in Crohn's disease

Crohn's disease (CD) is a chronic inflammatory disease of the gastrointestinal tract that leads to substantial suffering for millions of patients. In some patients, the chronic inflammation leads to remodelling of the extracellular matrix and fibrosis. Fibrosis, in combination with expansion of smooth muscle layers, leaves the bowel segment narrowed and stiff resulting in strictures, which often require urgent medical intervention. Although stricture development is associated with inflammation in the affected segment, anti‐inflammatory therapies fall far short of treating strictures. At best, current therapies might allow some patients to avoid surgery in a shorter perspective and no anti‐fibrotic therapy is yet available. This likely relates to our poor understanding of the mechanism underlying stricture development. Chronic inflammation is a prerequisite, but progression to strictures involves changes in fibroblasts, myofibroblasts and smooth muscle cells in a poorly understood interplay with immune cells and environmental cues. Much of the experimental evidence available is from animal models, cell lines or non‐strictured patient tissue. Accordingly, these limitations create the basis for many previously published reviews covering the topic. Although this information has contributed to the understanding of fibrotic mechanisms in general, in the end, data must be validated in strictured tissue from patients. As stricture formation is a serious complication of CD, we endeavoured to summarize findings exclusively performed using strictured tissue from patients. Here, we give an update of the mechanism driving this serious complication in patients, and how the strictured tissue differs from adjacent unaffected tissue and controls.

Mucosal Inflammatory and Wound Healing Gene Programs Reveal Targets for Stricturing Behavior in Pediatric Crohn's Disease

BACKGROUND AND AIMS

Ileal strictures are the major indication for resective surgery in Crohn's disease (CD). We aimed to define ileal gene programs present at diagnosis linked with future stricturing behavior during five year follow-up, and to identify potential small molecules to reverse these gene signatures.

METHODS

Antimicrobial serologies and pre-treatment ileal gene expression were assessed in a representative subset of 249 CD patients within the RISK multicenter pediatric CD inception cohort study, including 113 that are unique to this report. These data were used to define genes associated with stricturing behavior and for model testing to predict stricturing behavior. A bioinformatics approach to define small molecules which may reverse the stricturing gene signature was applied.

RESULTS

19 of the 249 patients developed isolated B2 stricturing behavior during follow-up, while 218 remained B1 inflammatory. Using deeper RNA sequencing than in our prior report, we have now defined an inflammatory gene signature including an oncostatin M co-expression signature, tightly associated with extra-cellular matrix (ECM) gene expression in those who developed stricturing complications. We further computationally prioritize small molecules targeting macrophage and fibroblast activation and angiogenesis which may reverse the stricturing gene signature. A model containing ASCA and CBir1 serologies and a refined eight ECM gene set was significantly associated with stricturing development by year five after diagnosis (AUC (95th CI) = 0.82 (0.7-0.94)).

CONCLUSION

An ileal gene program for macrophage and fibroblast activation is linked to stricturing complications in treatment naïve pediatric CD, and may inform novel small molecule therapeutic approaches.

M2 Macrophages and Phenotypic Modulation of Intestinal Smooth Muscle Cells Characterize Inflammatory Stricture Formation in Rats

The progression of Crohn disease to intestinal stricture formation is poorly controlled, and the pathogenesis is unclear, although increased smooth muscle mass is present. A previously described rat model of trinitrobenzenesulfonic acid-induced colitis is re-examined here. Although inflammation of the mid-descending colon typically resolved, a subset showed characteristic stricturing by day 16, with an inflammatory infiltrate in the neuromuscular layers including eosinophils, CD3-positive T cells, and CD68-positive macrophages. Closer study identified CD163-positive, CD206-positive, and arginase-positive cells, indicating a M2 macrophage phenotype. Stricturing involved ongoing proliferation of intestinal smooth muscle cells (ISMC) with expression of platelet-derived growth factor receptor beta and progressive loss of phenotypic markers, and stable expression of hypoxia inducible factor 1 subunit alpha. In parallel, collagen I and III showed a selective and progressive increase over time. A culture model of the stricture phenotype of ISMC showed stable hypoxia inducible factor 1 subunit alpha expression that promoted growth and improved both survival and growth in models of experimental ischemia. This phenotype was hyperproliferative to serum and platelet-derived growth factor BB, and unresponsive to transforming growth factor beta, a prominent cytokine of M2 macrophages, compared with control ISMC. We identified a hyperplastic phenotype of ISMC, uniquely adapted to an ischemic environment to drive smooth muscle layer expansion, which may reveal new targets for treating intestinal fibrosis.

Histopathology Scoring Systems of Stenosis Associated With Small Bowel Crohn's Disease: A Systematic Review

BACKGROUND & AIMS

Stenosis is a common complication of Crohn's disease (CD) that has no effective medical therapy. Development of antifibrotic agents will require testing in randomized controlled trials. Computed tomography enterography- and magnetic resonance enterography-based technologies might be used to measure outcomes in these trials. These approaches have been validated in studies of patients with symptomatic strictures who underwent imaging evaluations followed by resection with histopathologic grading of the intestinal tissue for inflammation and/or fibrosis (the reference standard). Imaging findings have correlated with findings from quantitative or semiquantitative histologic evaluation of the degree of fibromuscular stenosis and/or inflammation on the resection specimen. However, it is not clear whether histologic findings are an accurate reference standard. We performed a systematic review of all published histologic scoring systems used to assess stenosing CD.

METHODS

We performed a comprehensive search of Embase and MEDLINE of studies through March 13, 2019, that used a histologic scoring system to characterize small bowel CD and assessed inflammatory and fibrotic alterations within the same adult individual. All scores fitting the criteria were included in our analysis, independent of the presence of stricturing disease, as long as inflammation and fibrosis were evaluated separately but in the same scoring system.

RESULTS

We observed substantial heterogeneity among the scoring systems, which were not derived from modern principles for evaluative index development. None had undergone formal validity or reliability testing. None of the existing indices had been constructed according to accepted methods for the development of evaluative indices. Basic knowledge regarding their operating properties were lacking. Specific indices for evaluating the important pathologic component of myofibroblast hypertrophy or hyperplasia have not been proposed.

CONCLUSIONS

In a systematic review of publications, we found a lack of validated histopathologic scoring systems for assessment of fibromuscular stenosis. Data that describe the operating properties of existing cross-sectional imaging techniques for stenosing CD should be questioned. Development and validation of a histopathology index is an important research priority.

Correlation between the macroscopic severity of Crohn's disease in resected intestine and bowel wall thickness evaluated by water-immersion ultrasonography

Objectives: Transabdominal ultrasonography is a common and accurate tool for managing Crohn's disease (CD); however, the significance of the resulting data is poorly understood. This study was performed to determine the association between bowel wall thickness evaluated by water-immersion ultrasonography and macroscopic severity, namely, refractory inflammation and subsequent fibrosis in CD surgical specimens.Materials and methods: We retrospectively evaluated 100 segments of colon and small intestine from 27 patients with CD. The resected specimens were placed in saline postoperatively, and bowel wall thickness was measured by water-immersion ultrasonography and compared with macroscopic findings. Correlations between bowel wall thickness and macroscopic findings were assessed using analysis of variance and receiver operating characteristic curves.Results: According to the progression of macroscopic severity, the mean bowel wall thickness was increased as follows: macroscopically intact: 4.1 mm, longitudinal ulcer scars: 5.4 mm, longitudinal open ulcers: 6.0 mm, large ulcers: 6.4 mm, cobblestone-like lesions: 7.1 mm, and fibrotic strictures: 7.4 mm. For all lesions except longitudinal ulcer scars, the bowel wall thickness was significantly thicker than that of macroscopically-intact areas (p < .001). According to receiver operating characteristic curves, bowel wall thickness >4.5 mm was associated with CD lesions, and thickness >5.5 mm was associated with more severe lesions.Conclusions: The bowel wall thickness of CD lesions was evaluated by water-immersion ultrasonography correlated with macroscopic disease severity.