Martin H. Holtmann

Blockade of interleukin 6 trans signaling suppresses T-cell resistance against apoptosis in chronic intestinal inflammation: evidence in crohn disease and experimental colitis in vivo.

The pro-inflammatory cytokine interleukin (IL)-6 (refs. 1–5) can bind to cells lacking the IL-6 receptor (IL-6R) when it forms a complex with the soluble IL-6R (sIL-6R) (trans signaling). Here, we have assessed the contribution of this system to the increased resistance of mucosal T cells against apoptosis in Crohn disease (CD), a chronic inflammatory disease of the gastrointestinal tract. A neutralizing antibody against IL-6R suppressed established experimental colitis in various animal models of CD mediated by type 1 T-helper cells, by inducing apoptosis of lamina propria T cells. Similarly, specific neutralization of sIL-6R in vivo by a newly designed gp130–Fc fusion protein caused suppression of colitis activity and induction of apoptosis, indicating that sIL-6R prevents mucosal T-cell apoptosis. In patients with CD, mucosal T cells showed strong evidence for IL-6 trans signaling, with activation of signal transducer and activator of transcription 3, bcl-2 and bcl-xl. Blockade of IL-6 trans signaling caused T-cell apoptosis, indicating that the IL-6–sIL-6R system mediates the resistance of T cells to apoptosis in CD. These data indicate that a pathway of T-cell activation driven by IL-6–sIL-6R contributes to the perpetuation of chronic intestinal inflammation. Specific targeting of this pathway may be a promising new approach for the treatment of CD.

CD28-dependent Rac1 activation is the molecular target of azathioprine in primary human CD4+ T lymphocytes

Azathioprine and its metabolite 6-mercaptopurine (6-MP) are immunosuppressive drugs that are used in organ transplantation and autoimmune and chronic inflammatory diseases such as Crohn disease. However, their molecular mechanism of action is unknown. In the present study, we have identified a unique and unexpected role for azathioprine and its metabolites in the control of T cell apoptosis by modulation of Rac1 activation upon CD28 costimulation. We found that azathioprine and its metabolites induced apoptosis of T cells from patients with Crohn disease and control patients. Apoptosis induction required costimulation with CD28 and was mediated by specific blockade of Rac1 activation through binding of azathioprine-generated 6-thioguanine triphosphate (6-Thio-GTP) to Rac1 instead of GTP. The activation of Rac1 target genes such as mitogen-activated protein kinase kinase (MEK), NF-kappaB, and bcl-x(L) was suppressed by azathioprine, leading to a mitochondrial pathway of apoptosis. Azathioprine thus converts a costimulatory signal into an apoptotic signal by modulating Rac1 activity. These findings explain the immunosuppressive effects of azathioprine and suggest that 6-Thio-GTP derivates may be useful as potent immunosuppressive agents in autoimmune diseases and organ transplantation.

Secretin and vasoactive intestinal peptide receptors: Members of a unique family of G protein-coupled receptors

The superfamily of guanine nucleotide–binding protein (G protein)-coupled receptors represents the largest group of receptor molecules yet identified. They bind ligands as structurally diverse as photons, odorants, biogenic amines, peptides, and large glycoproteins. This entire spectrum of natural agonists is accommodated by members of the largest, most extensively studied, and best understood family of such receptors, the rhodopsin/ b-adrenergic receptor family. Recently, another distinct family within this superfamily was identified.1 Known as the secretin receptor family, this family shares few of the specific sequence motifs of the rhodopsin/b-adrenergic receptor family and has less than 12% sequence homology with it, but still possesses the same predicted molecular architecture with seven transmembrane helices and appears to signal via a similar sequence of molecular events (Figure 1).1 Among the members of this family are receptors for two extremely important regulators of pancreatic, biliary, and gastrointestinal physiology: secretin and vasoactive intestinal polypeptide (VIP). Because of their clear physiological relevance to gastroenterology, they are the focus of this review. Also included in the secretin receptor family are receptors for pituitary adenylate cyclase–activating polypeptide (PACAP),2 gastric inhibitory polypeptide (GIP),3 glucagon,4 glucagon-like peptide 1,5 calcitonin,6 calcitonin gene-related peptide,7 parathyroid hormone,8 growth hormone–releasing factor (GHRF),9 corticotropin-releasing factor,10 insect diuretic hormone,11 and a few orphan receptors or more distantly related molecules. These receptors share substantial homology with each other, and all bind moderately large peptides possessing diffuse pharmacophoric domains. Some of these receptors are probably important in digestive physiology, but our current understanding of them does not suggest the presence of unique themes distinct from those that are developed in the following discussion. Biochemical and Molecular Characterization of Gastrointestinal Hormone Receptors

Noninvasive assessment of Crohn's disease activity: a comparison of 18F-fluorodeoxyglucose positron emission tomography, hydromagnetic resonance imaging, and granulocyte scintigraphy with labeled antibodies.

OBJECTIVES:Detection of disease activity in Crohns disease (CD) is of crucial importance for diagnosis and management of the disease. Noninvasive methods for monitoring are desirable and comprise hydromagnetic resonance imaging (hydro-MRI) and leukocyte scintigraphy. In addition, a recent case report indicated the potential of 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) to assess CD activity. However, comparative prospective studies are lacking.METHODS:Between February, 1999 and August, 2000, 59 patients with CD were enrolled in a prospective study to assess disease activity by FDG-PET, hydro-MRI, and immunoscintigraphy with anti-nonspecific cross-reacting antigen 95 antigranulocyte antibodies. In 28 of these patients, colonoscopy could be performed. Twelve patients with irritable bowel syndrome and 20 tumor patients without gut inflammation served as controls. Results were compared by statistical analysis.RESULTS:FDG-PET detected 127 pathological findings (average maximum standardized uptake value = 4.4 ± 1.1) in the terminal/neoterminal ileum (37), small bowel (24), and colon (66) of 54 patients with CD, whereas no pathological findings were seen in five patients with CD, the control patients with irritable bowel syndrome, and the tumor patients without gut inflammation. In contrast, examination with hydro-MRI or granulocyte antibodies detected less pathological findings in CD patients. Forty-five of the detected foci were accessible to endoscopic verification. The correlation of the foci with endoscopic findings showed a high specificity (>89%) of all three methods to detect inflamed areas in the terminal ileum and colon of patients with CD, although analyses by hydro-MRI and granulocyte antibody scan had strikingly lower sensitivities (40.9% and 66.7%) than FDG-PET analysis (85.4%).CONCLUSIONS:FDG-PET appears to be a reliable noninvasive tool for simultaneous detection of inflamed areas in the small and large bowel of patients with CD. FDG-PET can be used to detect disease activity in the terminal ileum and colon of CD patients with high sensitivity and specificity.

Differential TNF-signaling in chronic inflammatory disorders.

TNF-alpha is a pleiotropic cytokine with strong proinflammatory and immunomodulatory properties. TNF-alpha plays a critical role in many acute or chronic inflammatory diseases and anti-TNF-strategies have proven to be clinically effective. Two TNF-specific cell surface receptors TNF-R1 and TNF-R2 have been identified and the function of these receptors and the downstream intracellular signal transduction pathways have been extensively studied in vitro. For a long time TNF-R1 was considered to be the predominant mediator of TNF-signaling, whereas TNF-R2 was ascribed only auxilliary function. However, there is increasing clinical and experimental evidence for an important independent role of p80 signaling in chronic inflammatory conditions. It is conceivable that the multiple TNF-mediated chronic inflammatory disorders differ in terms of the ligand form (soluble TNF-alpha versus membrane bound TNF-alpha), the receptor (TNF-R1 versus TNF-R2) and the downstream signaling cascades utilized. The elucidation of the specific characteristics of TNF-signaling in distinct inflammatory disorders will lead to a better understanding ot the pathogenesis of these diseases and will be the basis for the development of more specific and more efficient therapeutic approaches.

Long-Term Effectiveness of Azathioprine in IBD Beyond 4 Years: A European Multicenter Study in 1176 Patients

In Crohn’s disease the optimal duration of azathioprine treatment is still controversial and for ulcerative colitis only limited data are available to support its efficacy. Charts of 1176 patients with IBD from 16 European centers were analyzed. Flare incidences and steroid dosages were assessed for the time before and during treatment and after discontinuation. Within the first 4 years, azathioprine suppressed flare incidence and steroid consumption in both diseases (P < 0.001). While in CD discontinuation after 3–4 years did not lead to reactivation, this was the case in UC. However, continuation beyond 4 years further improved clinical activity in CD and steroid requirement in both diseases (P < 0.001). Discontinuation of azathioprine may thus be considered after 3–4 years in CD patients in complete remission without steroid requirement. In all other CD patients and for UC patients in general, continuation seems beneficial. These results support a novel differential algorithm for long-term azathioprine therapy in IBD.

Tumor necrosis factor-receptor 2 is up-regulated on lamina propria T cells in Crohn's disease and promotes experimental colitis in vivo

Tumor necrosis factor (TNF) plays a pivotal role in the pathogenesis of Crohns disease (CD). However, little is known about the role of TNF receptors (TNF‐R) in this disease. Here, we found that TNF‐R2 (in contrast to TNF‐R1) was significantly up‐regulated on lamina propria and peripheral blood T cells in CD compared to control patients. To directly test the functional role of TNF‐R2 in Th1‐mediated experimental colitis in vivo, we took advantage of transgenic animals overexpressing TNF‐R2 in T cells. Reconstitution of SCID mice with CD4+ CD62L+ T cells from TNF‐R2 transgenic mice led to an earlier wasting syndrome, a more severe colitis and augmented Th1 cytokine production than reconstitution with cells from wild‐type littermates. In addition, TUNEL staining revealed a significantly decreased apoptosis rate of lamina propria mononuclear cells in mice reconstituted with TNF‐R2 transgenic T cells compared to mice reconstituted with wild‐type T cells. In summary, our data suggest a critical regulatory role of TNF‐R2 signaling for disease exacerbation in Th1‐mediated chronic colitis. Taken together with the increased expression of TNF‐R2 inCD, selective targeting of TNF‐R2 signaling thus emerges as a potentially novel approach to the treatment of CD.

Anti-TNF strategies in stenosing and fistulizing Crohn’s disease

BackgroundStenoses and fistulas are frequent complications in patients with Crohn’s disease (CD). They represent a major diagnostic and therapeutic challenge and surgical intervention is often required. The availability of novel, anti-TNF strategies for therapy has raised the question as to what extent these new treatment options have impact on the clinical decision-making process regarding the necessity for surgery.DiscussionA short overview of the current pathophysiological understanding of CD, focusing on the immunology of the intestinal mucosa, is given. Then the problems of proper clinical management of stenoses and fistulas are addressed. With regard to symptomatic stenoses, attention will be given to novel diagnostic tools for the distinction between inflammatory and fibrotic stenoses, and our clinical experience with the treatment of symptomatic inflammatory stenoses with infliximab will be discussed. With regard to fistulizing CD, the data that are currently available for medical therapy are summarized with special reference to the studies on the efficacy of anti-TNF treatment.ConclusionWith regard to moderately and severe inflammatory stenoses, medical treatment with infliximab may be an option after careful assessment of the inflammatory nature of the stenosis and exclusion of a septic focus. With regard to fistulas, anti-TNF treatment is a valuable option that is likely to improve the clinical outcome. Based on the available data, however, anti-TNF treatment cannot yet replace surgical intervention when necessary. Prospective trials of medical therapy and a combination of medical and surgical therapy for complex fistulas and internal fistulas are needed to define the potential and the limitations of these novel therapeutic approaches.

Treatment of patients with Crohn's disease and concomitant chronic hepatitis C with a chimeric monoclonal antibody to TNF.

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Current concept of pathophysiological understanding and natural course of ulcerative colitis

IntroductionAccording to the current paradigm both ulcerative colitis (UC) and Crohn’s disease (CD) result from a complex interplay of genetic susceptibility factors, environmental factors, alterations of the physiological intestinal flora and a defective regulation of the intestinal immune system.DiscussionThe objective of this review is to give an overview of these factors and mechanisms, including genetic, environmental and microbial factors, with special alterations of relevant cellular components of the intestinal immune system such as T cells, macrophages and epithelial cells will then be addressed. In addition, the most relevant animal model systems that have contributed to our current pathogenetic understanding will be introduced. Clinically, the natural course of UC with special reference to the risk of colorectal cancer will be addressed.ConclusionThe elucidation of pathomechanisms at the level of the intestinal immune system provides the potential for novel, effective treatment strategies. Best surgical management of patients with UC, however, still remains a challenge.