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Exposure of esophageal mucosa to hydrochloric acid (HCl) is a crucial factor in the pathogenesis of reflux disease. We examined supernatant of HCl-exposed rabbit mucosa for inflammatory mediators enhancing migration of leukocytes and production of H2O2as an indicator of leukocyte activation. A tubular segment of rabbit esophageal mucosa was tied at both ends to form a sac, which was filled with HCl-acidified Krebs buffer at pH 5 (or plain Krebs buffer as control) and kept oxygenated at 37°C. The medium around the sac (supernatant) was collected after 3 h. Rabbit peripheral blood leukocytes (PBL) were isolated, and sac supernatant was used to investigate PBL migration and H2O2production. HCl-exposed esophageal mucosa released substance P (SP), CGRP, platelet-activating factor (PAF), and IL-8 into the supernatant. PBL migration increased in response to IL-8 or to supernatant of the HCl-filled mucosal sac. Supernatant-induced PBL migration was inhibited by IL-8 antibodies and by antagonists for PAF (CV3988) or neurokinin 1 (i.e., SP), but not by a CGRP antagonist. Supernatant of the HCl-filled mucosal sac increased H2O2release by PBL that was significantly reduced by CV3988 and by a SP antagonist but was not affected by IL-8 antibodies or by a CGRP antagonist. We conclude that IL-8, PAF, and SP are important inflammatory mediators released by esophageal mucosa in response to acid that promote PBL migration. In addition, PAF and SP induce production of H2O2by PBL. These findings provide a direct link between acid exposure and recruitment and activation of immune cells in esophageal mucosa.

We have previously shown that sigmoid circular muscle cells from patients with ulcerative colitis (UC) exhibit reduced contraction and Ca2+signaling in response to the neurotransmitter neurokinin A (NKA) and that IL-1β and H2O2may contribute to these reduced responses in UC. In addition, we have found that nitric oxide (NO) levels were significantly increased in UC circular muscle. To establish the site of origin for IL-1β, H2O2, and NO, we assembled an in vitro system in which normal or UC mucosa were sealed between two chambers filled with oxygenated Krebs solution. Because the mucosa consists of full-thickness mucosa and submucosa, it is expected that whatever is released into the undernatant from the submucosal side may diffuse to the circular muscle layer in the intact colon. Treatment of normal sigmoid circular muscle cells for 2 h with undernatants collected from the UC submucosal side (UCS) significantly decreased contraction induced by NKA and thapsigargin and the NKA- and caffeine-induced Ca2+signal in Ca2+-free medium. In addition, UC mucosa released into the undernatant on its submucosal side significantly more H2O2, IL-1β, and NO than normal mucosa. The reduction in contraction and Ca2+signal induced by UCS was partially reversed by pretreatment with an IL-1β antibody or with catalase. The NO scavenger hemoglobin partially prevented UCS-induced reduction in contraction and Ca2+signaling in response to NKA but not the reduced response to thapsigargin or caffeine. Sodium nitroprusside inhibited NKA but not the caffeine-induced Ca2+signal. We conclude that in UC the mucosa releases IL-1β, H2O2, and NO, which may contribute to the impaired Ca2+release and altered sigmoid muscle contractility.

ACh is a neurotransmitter in cat esophageal circular muscle, as atropine nearly abolishes contraction of in vitro circular muscle strips in response to electric field stimulation (EFS) ( 5 , 12 ). Experimental esophagitis reduced EFS- but not ACh-induced contraction of esophageal circular muscle, suggesting that esophagitis impairs neurotransmitter release. Because IL-1β and IL-6 are produced in esophagitis and reproduce these changes in normal esophageal muscle ( 12 ), we examined the role of IL-1β and IL-6 in this motor dysfunction. IL-1β, IL-6 ( 12 ), H2O2, PGE2, and platelet-activating factor (PAF) were elevated in esophagitis specimens. Normal muscle incubated (2 h) in IL-1β and IL-6 had increases in H2O2, PGE2, and PAF levels. H2O2contributed to increased PGE2and PAF, as the increase was partially (60–80%) reversed by the H2O2scavenger catalase. EFS-induced [3H]ACh release from muscle strips significantly (42%) decreased in esophagitis and after 2 h incubation in PGE2and in PAF C-16. Similarly, EFS-induced but not ACh-induced muscle contraction decreased in esophagitis and after incubation in PGE2and PAF C-16. Finally, in normal muscle strips treated with IL-1β electrical field stimulation (EFS)-induced contraction was partially restored by indomethacin or by the PAF antagonist CV3988 and was completely restored by the combination of CV3988 and indomethacin, whereas in strips treated with IL-6, EFS-induced contraction was partially restored by the PAF antagonist CV3988 and not affected by indomethacin. We conclude that IL-1β-induced production of H2O2causes formation of PGE2and PAF that inhibit ACh release from esophageal cholinergic neurons without affecting ACh-induced contraction of esophageal circular muscle. IL-6 causes production of H2O2, PAF, and other unidentified inflammatory mediators.

Ulcerative colitis (UC) affects colonic motor function, but the mechanism responsible for this motor dysfunction is not well understood. We have shown that neurokinin A (NKA) may be an endogenous neurotransmitter mediating contraction of human sigmoid colonic circular muscle (HSCCM). To elucidate factors responsible for UC motor dysfunction, we examined the role of hydrogen peroxide (H2O2) in the decrease of NKA-induced response of HSCCM. As previously demonstrated, NKA-induced contraction or Ca2+increase of normal muscle cells is mediated by release of Ca2+from intracellular stores, because it was not affected by incubation in Ca2+-free medium (CFM) containing 200 μM BAPTA. In UC, however, CFM reduced both cell contraction and NKA-induced Ca2+increase, suggesting reduced Ca2+release from intracellular stores. In normal Ca2+medium, NKA and KCl caused normal Ca2+signal in UC cells but reduced cell shortening. The decreased Ca2+signal and contraction in response to NKA or thapsigargin were partly recovered in the presence of H2O2scavenger catalase, suggesting involvement of H2O2in UC-induced dysmotility. H2O2levels were higher in UC than in normal HSCCM, and enzymatically isolated UC muscle cells contained much higher levels of H2O2than normal cells, which were significantly reduced by catalase. H2O2treatment of normal cells in CFM reproduced the reduction of NKA-induced Ca2+release observed in UC cells. In addition, H2O2caused a measurable, direct release of Ca2+from intracellular stores. We conclude that H2O2may contribute to reduction of NKA-induced Ca2+release from intracellular Ca2+stores in UC and contribute to the observed colonic motor dysfunction.

Wound healing is an appropriate response to inflammation and tissue injury in the gastrointestinal tract. If wound healing responses are excessive, perpetuated, or prolonged, they lead to fibrosis, distortion of tissue architecture, and loss of function. This introductory editorial and the minireviews or reviews in this themes series highlight the diversity in severity and location of fibrosis in response to gastrointestinal inflammation. The multiplicity of cellular and molecular mediators and new players, including stem cells or extracellular matrix-producing cells derived from nonmesenchymal cell types, is reviewed. Comparisons of inflammation-induced fibrosis across organ systems and the need for integrated and systems-based molecular approaches, new imaging modalities, well-characterized animal models, cell culture models, and improved diagnostic or predictive markers are reviewed. To date, intestinal fibrosis has received much less attention than inflammation in terms of defining mechanisms and underlying causes. This themes series aims to illustrate the importance of research in this area in gastrointestinal health and disease.