NF-kappaB activation precedes increases in mRNA encoding neurokinin-1 receptor, proinflammatory cytokines, and adhesion molecules in dextran sulfate sodium-induced colitis in rats

Mast cells and nerves tickle in the tummy: implications for inflammatory bowel disease and irritable bowel syndrome

Mast cells are well known as versatile cells capable of releasing and producing a variety of inflammatory mediators upon activation and are often found in close proximity of neurons. In addition, inflammation leads to local activation of neurons resulting in the release neuropeptides, which also play an important immune modulatory role by stimulation of immune cells. In intestinal disorders like inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), the number of mast cells is known to be much higher than in the normal intestine. Moreover, both these disorders are also reported to be associated with alterations in neuropeptide content and in neural innervation. Mutual association between mast cells and enteric nerves has been demonstrated to be increased in pathophysiological conditions and contribute to spreading and amplification of the response in IBD and IBS. In this review the focus lies on studies appointed to the direct interaction between mast cells and nerves in IBD, IBS, and animal models for these disorders so far.

Role of neuropeptides in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic, relapsing condition involving complex interactions between genes and the environment. The mechanisms triggering the initial attack and relapses, however, are not well understood. In the past several years the enteric nervous system (ENS) has been implicated in the pathophysiology of IBD. Both the ENS and the central nervous system (CNS) can amplify or modulate aspects of intestinal inflammation through secretion of neuropeptides that serve as a link between the ENS and CNS. Neuropeptides are defined as any peptide released from the nervous system that serves as an intercellular signaling molecule. Neuropeptides thought to play a potentially key role in IBD include substance P, corticotropin-releasing hormone, neurotensin, vasoactive intestinal peptide, mu-opioid receptor agonists, and galanin. This review focuses on the role of these neuropeptides in the pathophysiology of IBD and discusses the cell types and mechanisms involved in this process. The available evidence that neuropeptide blockade may be considered a therapeutic approach in both Crohn's disease and ulcerative colitis will also be discussed.

Immunomodulatory properties of substance P: the gastrointestinal system as a model

Communication between nerves and immune and inflammatory cells of the small and large intestine plays a major role in the modulation of several intestinal functions, including intestinal motility, ion transport, and mucosal permeability. Neuroimmune interactions at intestinal sites have been associated with the pathophysiology of infectious and enterotoxin-mediated diarrhea and intestinal inflammation, including inflammatory bowel disease (IBD). During the past 20 years the neuropeptide substance P (SP) has been identified as an important mediator in the development and progress of intestinal inflammation by binding to its high-affinity neurokinin-1 receptor (NK-1R). This peptide, released from enteric nerves, sensory neurons, and inflammatory cells of the lamina propria during intestinal inflammation, participates in gut inflammation by interacting, directly or indirectly, with NK-1R expressed on nerves, epithelial cells, and immune and inflammatory cells, such as mast cells, macrophages, and T cells. SP-dependent activation of these cells leads to the release of cytokines and chemokines as well as other neuropeptides that modulate diarrhea, inflammation, and motility associated with the pathophysiology of several intestinal disease states. The recent development of specific nonpeptide NK-1R antagonists and NK-1R-deficient mice helped us understand the functional importance of the SP-NK-1R system in mediating intestinal neuroimmune interactions and to identify the particular cells and signaling pathways involved in this response. This review summarizes our understanding on the immunomodulatory properties of SP and its receptor in the intestinal tract with particular focus on their involvement in intestinal physiology as well as in the pathophysiology of several intestinal disease states at the in vivo and cell signaling level.

Localized colonic inflammation increases cytokine levels in distant small intestinal segments in the rat

Local inflammation in the colon has been associated with nutrient malabsorption and altered motility in the small bowel. These remote effects suggest the release of mediators which can act (or alter) the function of intestinal segments located far from the primary area of inflammation. This study describes the changes in the expression of pro-inflammatory cytokines in the colon and in various segments of the small intestine in two rat models of experimental colitis. Colitis was induced by the intracolonic administration of 100 microL of 6% iodoacetamide or 250 microL of 2, 4, 6-trinitrobenzene sulfonic acid. Levels of interleukin one beta, interleukin 6, and tumor necrosis factor alpha were measured by ELISA in tissue homogenate sampled from duodenum, jejunum, ileum and colon at different time intervals. In homogenates of strips isolated from duodenum, jejunum and ileum, tumor necrosis alpha and interleukin-6, increased significantly 3-6 h after iodoacetamide or TNBS administration and remained elevated until the colonic inflammation subsided. Interleukin one beta showed comparable but delayed increase. Similar, but more pronounced increase of the three cytokines was noticed in areas of the colon adjacent to the ulcer. Histologic examinations revealed important inflammatory changes in the colon; however, examination of sections from the small intestines did not reveal significant differences between controls and rats with colitis. In conclusion, expression of pro-inflammatory cytokines is increased in remote segments of the small intestines during colitis. The findings may provide a partial explanation or a molecular substrate for the associated small bowel dysfunction.

A new transcription factor that regulates TNF-alpha gene expression, LITAF, is increased in intestinal tissues from patients with CD and UC

BACKGROUND

The proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) plays a key role in the pathogenesis of Crohn's disease (CD) and ulcerative colitis (UC). Recently, a new transcription factor termed LITAF (lipopolysaccharide-induced TNF-alpha factor) was shown to mediate TNF-alpha expression in human macrophages by direct binding to specific sequences in the promoter region of the TNF-alpha gene.

METHODS

In this report, we identified LITAF in resected ileal and colonic tissues from patients with CD and UC by immunohistochemistry, real-time polymerase chain reaction, and Western blot analysis. LITAF expression in inflamed and noninflamed areas of the tissues was compared.

RESULTS

This is the first demonstration of LITAF, a newly discovered transcription factor that regulates TNF-alpha gene transcription in ileal and colonic tissues from patients with either CD or UC. LITAF immunostaining was localized to lamina propria macrophages and was markedly increased relative to tissues from controls without inflammatory bowel disease. In patients with CD, a 5-fold increase in LITAF mRNA was measurable in noninflamed colonic tissues compared with controls without inflammatory bowel disease. LITAF mRNA in tissues from inflamed areas of the colon was increased by an additional 60% compared with noninflamed tissues. In patients with UC, LITAF mRNA levels in colonic tissues resected from noninflamed areas were elevated 15-fold above nondisease controls, but they were not different in tissues resected from inflamed areas. Western blot analysis showed that in patients with CD, there was a marked increase in LITAF protein in inflamed areas compared with noninflamed areas. LITAF protein levels were not different between noninflamed and inflamed tissues obtained from patients with UC. TNF-alpha mRNA and protein levels paralleled LITAF. Similarly, in inflamed ileal tissues from patients with CD, LITAF is also localized to lamina propria macrophages. LITAF mRNA and LITAF protein were significantly increased in inflamed ileal tissues compared with noninflamed areas.

CONCLUSIONS

LITAF is readily detectable in ileal and colonic tissues from patients with either CD or UC, is significantly elevated above controls, and is localized to macrophages, a major source of TNF-alpha. These data provide strong evidence of a role for LITAF in the pathophysiological regulation of the TNF-alpha gene and underscore the potential value of anti-LITAF strategies in the clinical management of these diseases.