Mucosal interleukin-6 secretion in ulcerative colitis. Effects of anti-inflammatory drugs and T-cell stimulation

Novel signal transduction pathways: analysis of STAT-3 and Rac-1 signaling in inflammatory bowel disease

Although the precise etiology of inflammatory bowel disease still remains unclear, considerable progress has been made in the identification of novel signal transduction pathways that elucidate the immunopathogenesis involved in the perpetuation of the inflammatory process. Augmented T cell resistance against apoptosis is regarded as a pivotal factor in the pathogenesis, as it impairs mucosal homeostasis and leads to unrestrained accumulation of activated T cells, which subsequently lead to the amplification of the inflammatory response. Therefore novel therapeutic strategies aim at restoring mucosal T cell susceptibility to apoptosis through targeting of signal transduction pathways that are elemental for augmented resistance of T lymphocytes against apoptosis. For example, a newly developed humanized anti-IL-6R monoclonal antibody that induces intestinal T cell apoptosis showed clinical efficacy in patients with active Crohn;s disease. Moreover, recent data that relate the immunosuppressive effects of azathioprine in inflammatory bowel disease to its apoptosis-inducing potential, have important implications for the design of a more specific therapeutic approach. The examination of these novel signal transduction pathways has elucidated the pathogenetic mechanisms involved in inflammatory bowel disease and gives hope for the development of new strategies that may result in a more effective and less toxic therapeutic procedure.

A form of circulating interleukin-6 receptor component soluble gp130 as a potential interleukin-6 inhibitor in inflammatory bowel disease

The presence and the role of soluble gp130, the soluble form of a component of the interleukin (IL)-6 receptor complex, were investigated in inflammatory bowel disease. The serum concentrations of soluble gp130 were increased in ulcerative colitis (active disease, median, 93.5 ng/ml; interquartile range, 26-125 ng/ml; inactive disease, 81 ng/ml, 24.8-137.3 ng/ml) and to a lesser extent in Crohn's disease (active disease, 66 ng/ml, 44.4-87.6 ng/ml; inactive disease, 63 ng/ml, 43.5-82.5 ng/ml) compared to normal controls (43 ng/ml, 27-59 ng/ml). Paired analysis of serum samples showed a decrease of IL-6 and soluble IL-6 receptor concentrations in both diseases and an increase of soluble gp130 concentrations, especially in ulcerative colitis, just after the resolution of disease exacerbation. Size fractionation of the serum revealed that a part of the IL-6 co-eluted with soluble gp130 and soluble IL-6 receptor. The IL-6-induced proliferation of murine B9 hybridoma was enhanced by recombinant soluble IL-6 receptor, whereas the proliferation was inhibited by recombinant soluble gp130. These results indicate that soluble gp130 may function as a natural inhibitor of the IL-6 actions in inflammatory bowel disease.

Involvement of IL-6 in the pathogenesis of inflammatory bowel disease and colon cancer

Inflammatory bowel disease (IBD), which consists of Crohn's disease and ulcerative colitis, is defined as a chronic inflammation of the gastrointestinal tract. The etiopathogenetic mechanisms underlying the development of IBD are still not completely understood, and the therapeutic strategies used thus far have been limited to mostly evidence-based principles. There is growing evidence that the pro-inflammatory cytokine interleukin (IL)-6 plays a crucial part in the uncontrolled intestinal inflammatory process, which is a main characteristic of IBD. There is elevated production of IL-6 and its soluble receptor (sIL-6R) by intestinal macrophages and CD4+T-cells. The increased formation of IL-6-sIL-6R complexes that interact with gp130 on the membrane of CD4+T-cells (trans-signaling) lead to an increased expression and nuclear translocation of STAT3, which causes the induction of anti-apoptotic genes, such as Bcl-xl. This leads to an augmented resistance of lamina propria T-cells to apoptosis. The ensuing T-cell expansion contributes to the perpetuation of chronic intestinal inflammation. This understanding concerning the predominant pathogenic role of an IL-6-dependent inflammatory cascade may lead to the development of new therapeutic strategies in the treatment of this disease. Recent studies have also suggested a potential role of IL-6-sIL-6R in the pathogenesis of colon cancer and, therefore, imply a possible novel therapeutic strategy targeting the sIL-6R and ensuing IL-6 trans-signaling.

Involvement of IL-6 in the pathogenesis of inflammatory bowel disease and colon cancer

Inflammatory bowel disease (IBD), which consists of Crohn's disease and ulcerative colitis, is defined as a chronic inflammation of the gastrointestinal tract. The etiopathogenetic mechanisms underlying the development of IBD are still not completely understood, and the therapeutic strategies used thus far have been limited to mostly evidence-based principles. There is growing evidence that the pro-inflammatory cytokine interleukin (IL)-6 plays a crucial part in the uncontrolled intestinal inflammatory process, which is a main characteristic of IBD. There is elevated production of IL-6 and its soluble receptor (sIL-6R) by intestinal macrophages and CD4+T-cells. The increased formation of IL-6-sIL-6R complexes that interact with gp130 on the membrane of CD4+T-cells (trans-signaling) lead to an increased expression and nuclear translocation of STAT3, which causes the induction of anti-apoptotic genes, such as Bcl-xl. This leads to an augmented resistance of lamina propria T-cells to apoptosis. The ensuing T-cell expansion contributes to the perpetuation of chronic intestinal inflammation. This understanding concerning the predominant pathogenic role of an IL-6-dependent inflammatory cascade may lead to the development of new therapeutic strategies in the treatment of this disease. Recent studies have also suggested a potential role of IL-6-sIL-6R in the pathogenesis of colon cancer and, therefore, imply a possible novel therapeutic strategy targeting the sIL-6R and ensuing IL-6 trans-signaling.

Quantitative measurement of cytokine mRNA in inflammatory bowel disease: relation to clinical and endoscopic activity and outcome

OBJECTIVE

The objective of this study was to quantitatively determine cytokine mRNA expression in inflammatory bowel disease under different clinical conditions including active disease, remission or an impaired response to a glucocorticoid (GC) therapy.

METHODS

Mucosal biopsies were taken from 33 patients with ulcerative colitis (UC), 21 patients with Crohn's disease (CD) and 11 controls. Peripheral blood mononuclear cells (PBMNC) were isolated from 24 CU patients, 18 CD patients and 11 controls. Cytokine-mRNA [interleukin (IL)-1beta, IL-2, IL-4, IL-6, IL-10, interferon gamma (IFN-gamma), tumour necrosis factor alpha (TNF-alpha)] expression was measured by quantitative reverse transcriptase-polymerase chain reaction in biopsies and PBMNC, and correlated to endoscopic findings, clinical activity and outcome after 6 months GC therapy.

RESULTS

IL-1beta, IL-6 and TNF-alpha were the largely dominating cytokines. In contrast to IL-1beta and TNF-alpha-, IL-6 expression was restricted to inflamed mucosa and correlated with the clinical activity and C-reactive protein levels in cases of pancolitis ulcerosa. TNF-alpha was elevated in CD even in endoscopic normal tissue. IL-2 and IFN-gamma were downregulated in PBMNC from CD and UC. No Th1 or Th2 specificity could be detected. Cytokine mRNA levels did not correlate with the response to a GC therapy.

CONCLUSION

IL-6 sharply distinguishes between inflamed and non-inflamed mucosa, and is therefore a suitable marker of intestinal inflammation. Its selective expression in the inflammatory site makes it an interesting target for future therapeutic strategies. TNF-alpha overexpression even in remission suggests a key role of this cytokine in CD pathogenesis and is possibly a feature that allows one to differentiate CD from UC.

Abnormal function of platelets and role of angelica sinensis in patients with ulcerative colitis

AIM: To explore the abnormal function of platelets and the role of angelica sinensis injection (ASI) in patients with ulcerative colitis (UC).

METHODS: In 39 patients with active UC, 25 patients with remissive UC and 30 healthy people, α-granule membrane protein (GMP-140) and thromboxane B₂ (TXB₂) were detected by means of ELISA, 6-keto-PGF_1a was detected by radioimmunoassay, platelet count (PC) and 1 min platelet aggregation rate (1 min PAR) were detected by blood automatic tester and platelet aggregation tester respectively, and von Willebrand factor related antigen (vWF:Ag) was detected by the means of monoclonal-ELISA. The 64 patients with UC were divided into two therapy groups. After routine treatment and angelica sinensis injection (ASI) + routine treatment respectively for 3 weeks, all these parameters were also detected.

RESULTS: The PC, 1 min PAR and levels of GMP-140, TXB₂, and vWF:Ag in active UC were significanrly higher than those in remissive UC and normal controls (P < 0.05-0.01).Meanwhile, 1 min PAR and levels of GMP-140, TXB₂, and vWF:Ag in remissive UC were still significantly higher than those in normal controls (P < 0.05). Furthermore, 6-keto-PGF_1a level in active and remissive UC was remarkably lower than that in normal control (P < 0.05-0.01). These parameters except 6-keto-PGF_1a were significantly improved after the treatment in ASI therapy group (P < 0.05-0.01), whereas they all were little changed in routine therapy group (P > 0.05).

CONCLUSION: Platelets can be significantly activated in UC, which might be related with vascular endothelium injury and imbalance between TXB₂ and 6-keto-PGF_1a in blood. ASI can significantly inhibit platelet activation, relieve vascular endothelial cell injury, and improve microcirculation in UC.

Human intestinal epithelial and smooth muscle cells are potent producers of IL-6

BACKGROUND

Interleukin-6 (IL-6), a pluripotent cytokine, has traditionally been considered the product of proinflammatory cells. However, many other cell types have been shown to produce IL-6. Since intestinal inflammation is commonly associated with a vigorous systemic inflammatory response, we hypothesized that intestinal epithelial and smooth muscle cells might contribute to that response by producing IL-6. We therefore studied the capacity of differentiated human intestinal epithelial and smooth muscle cell lines to produce IL-6 in response to various proinflammatory stimuli.

MATERIALS AND METHODS

CCL-241, a human intestinal epithelial cell line, and HISM, a human intestinal muscle cell line, were grown to confluency and then treated for 24 h with various concentrations of lipopolysaccharide, Clostridium difficile culture extract containing both toxin A and toxin B, recombinant human tumor necrosis factor-alpha (TNF-alpha), or recombinant human interleukin-1 beta (IL-1beta). Supernatants were then collected for IL-6 determination using an enzyme-linked immunosorbent assay. Cell numbers were determined using a Coulter counter. For comparison, parallel studies were performed using phorbol ester-primed U-937 and THP-1 human macrophage cell lines.

RESULTS

Both human intestinal epithelial and smooth muscle cells produced IL-6 under basal conditions. In HISM cells, but not in CCL-241 cells, IL-6 release was increased slightly by treatment with C. difficile culture extract containing both toxin A and toxin B and with lipopolysaccharide. In both cell lines, IL-6 production was profoundly stimulated by treatment with IL-1beta and less so with TNF-alpha. Combinations of high-dose TNF-alpha and IL-1beta may have a slightly additive, but not synergistic, effect on IL-6 release. The amount of IL-6 produced by IL-1-stimulated intestinal cell lines was 70-fold higher than that produced by stimulated macrophage cell lines. CONCLUSIONS; Both intestinal epithelial and smooth muscle cells demonstrate the ability to release significant amounts of IL-6. The profound response to IL-1beta and TNF-alpha stimulation by both cell lines suggests that human intestinal parenchymal cells, influenced by paracrine mediators liberated from proinflammatory cells, might significantly contribute to the overall systemic inflammatory response by producing IL-6.

Neutropenia, neutrophil dysfunction, and inflammatory bowel disease in glycogen storage disease type Ib: results of the European Study on Glycogen Storage Disease type I

OBJECTIVE

To investigate the incidence, the severity, and the course of neutropenia, neutrophil dysfunction, and inflammatory bowel disease (IBD) in glycogen storage disease (GSD) type Ib.

METHOD

As part of a collaborative European Study on GSD type I, a retrospective registry was established in 12 European countries that included all patients with GSD-I who were known at the centers and were born from 1960 to 1995. Of a total of 288 patients with GSD-I, 57 who had GSD-Ib form the basis of this study.

RESULTS

Neutropenia (defined as an absolute neutrophil count <1 x 10(9)/L) was found in 54 patients. In 64% of the patients neutropenia was documented before the age of 1 year, but in 18% of the patients neutropenia was first noted between the ages of 6 and 9 years. Neutropenia was persistent in 5 patients and intermittent without any clear cyclical course in 45. Neutrophil function was investigated in 18 patients with neutropenia and was abnormal in all. Perioral infections were reported in 37 patients, perianal infections in 27 patients, and protracted diarrhea in 23 patients. Findings on colonoscopy and radiologic studies in 10 of 20 patients suspected to have IBD were abnormal in all. All patients with IBD, perioral infections, and perianal infections had neutropenia.

CONCLUSIONS

Intermittent severe neutropenia is frequently found in patients with GSD-Ib. The study also indicates that IBD in GSD-Ib is underdiagnosed; up to 77% of the patients studied had evidence of IBD, all of whom had neutropenia. IBD was not detected in those with normal neutrophil counts. These findings support the notion that neutropenia and/or neutrophil dysfunction in GSD-Ib and IBD are causally related.

Local and systemic liberation of proinflammatory cytokines in ulcerative colitis

Determination of plasma and tissue cytokine levels in inflammatory bowel disease have frequently resulted in conflicting data. In the present study we determined in patients with ulcerative colitis (UC), the levels of the proinflammatory cytokines interleukin (IL)-1beta, IL-6, interferon (IFN)-gamma, and tumor-necrosis factor (TNF)-alpha liberated by peripheral blood mononuclear cells (PBMC) and lamina propria mononuclear cells (LPMC) after 48-hr culture with pokeweed mitogen (PWM). IL-1beta, IL-6, IFN-gamma and TNF-alpha in the supernatant were detected by ELISA. Results show low basal levels of IL-1beta secretion by PBMC and LPMC, and a considerable increase after mitogen stimulation. Basal IL-6 production by PBMC was higher in UC patients than in controls [2029 pg/ml, CI95(-165 to 4223) vs 572 pg/ml (-383 to 1527) respectively, P = 0.05] and also after PWM activation [14,995 pg/ml (7759-22,230) vs 6598 pg/ml (3240-9956), respectively, P = 0.05]. In LPMC, no differences in IL-6 secretion were observed. TNF-alpha in activated PBMC of patients with UC was not significantly increased in relation to control (P = 0.09). No constitutive secretion of IFN-gamma was observed in mononuclear cells. IFN-gamma levels secreted by activated LPMC were lower in patients with UC than in controls [1571 pg/ml (-108 to 3251) vs 7953 pg/ml (3851-12,055), respectively, P = 0.03]. These results suggest that IL-6, IL-1beta, and TNF-alpha participate as mediators in the inflammatory phenomena observed in UC. Further studies are necessary to evaluate the role of IFN-gamma in this condition.

Colonic explant production of IL-1and its receptor antagonist is imbalanced in inflammatory bowel disease (IBD)

IBD is associated with an increased activation of intestinal immune cells, which causes overproduction of proinflammatory cytokines such as IL-1beta. IL-1beta is implicated in mediating the sustained inflammatory response. IL-1 receptor antagonist (IL-1Ra), the naturally occurring inhibitor of IL-1, has been shown to have beneficial effects in experimental models of colitis. In this study we investigated the hypothesis that an imbalance between IL-1 and IL-1Ra exists in IBD by measuring their secretion by explant cultures of colonic biopsies. Freshly homogenized biopsies from involved tissue in IBD patients exhibited significantly lower IL-1Ra/IL-1beta ratios than control and uninvolved IBD mucosal tissue. Using explant cultures, in vitro production of IL-1beta and IL-1Ra increased progressively during the 4-18-h culture periods. IL-1beta secretion was higher in supernatants from involved Crohn's disease (CD) and ulcerative colitis tissue compared with control tissue, and IL-1beta levels increased with severity of inflammation. IL-1Ra secretion was not elevated in involved IBD samples, but significantly higher levels were released when moderate to severely involved tissue samples were compared with noninflammatory controls. Similar to freshly homogenized tissue, explant studies showed that the IL-1Ra/IL-1beta ratios were significantly decreased in involved IBD tissue, but not in uninvolved CD or inflammatory control specimens. These data support the hypothesis of an imbalance between IL-1beta and IL-1Ra in IBD.

Role of cytokines and platelet-activating factor in inflammatory bowel disease. Implications for therapy

BACKGROUND

Platelet-activating factor (PAF) and cytokines, such as interleukins, tumor necrosis factor, and others, are thought to play a role in the inflammatory process involving gastrointestinal disorders such as Crohn's disease, ulcerative colitis, ischemic colitis, or antibiotic-associated colitis.

PURPOSE

This study was undertaken to review the latest literature on the role of PAF and cytokines in the genesis of inflammatory bowel disease and implications for therapy and management.

RESULTS

PAF is an endogenous phospholipid involved in hypersensitivity and inflammatory reactions such as platelet and neutrophil aggregation, vasodilation, increased vascular permeability, and leukocyte adhesion, which have been associated with inflammatory processes. Cytokines are peptides that regulate and coordinate inflammatory and immunologic responses. Increased production of cytokines has been reported during Crohn's disease and ulcerative colitis and is correlated with disease activity.

CONCLUSIONS

Because PAF and cytokines may have an important role in the pathogenesis of inflammatory bowel disease, their inhibition by specific antagonists, mediators, or other agents such as steroids may have a potential therapeutic benefit in treatment and management of these inflammatory diseases in the near future.