Epidermal growth factor increases basal mucosal blood flow in the rat colon, a prostaglandin dependent effect.

OBJECTIVE/BACKGROUND: Non-mitogenic biological activity such as modulation of mucosal blood flow is suspected to convey the protective effects of epidermal growth factor (EGF) in vivo. The aims of our present study were to determine the effects of EGF on colonic mucosal blood flow and injury induced hyperaemia in rats. DESIGN/METHODS: Rats were pretreated with i.p. injections of vehicle, EGF, or indomethacin and EGF prior to mucosal injury. Basal mucosal blood flow and injury induced hyperaemia at the border of the damaged mucosa was determined by using reflectance spectrophotometry. RESULTS: EGF significantly increased basal mucosal blood flow but did not further enhance injury induced hyperaemia. The EGF induced increase in basal mucosal blood flow was completely abolished by indomethacin pretreatment. CONCLUSIONS: EGF induces an increase of basal mucosal blood flow through induction of prostaglandin synthesis. We hypothesize that the increase in mucosal blood flow contributes to the ability of EGF to protect the colonic mucosa against injury.

Keratinocyte growth factor ameliorates dextran sodium sulfate colitis in mice.

Keratinocyte growth factor (KGF) is emerging as an important mediator of mucosal defense and repair in the colon. The aim of the present study was to evaluate and further characterize the effects of exogenous KGF administration utilizing the dextran sodium sulfate (DSS) model of colitis in mice. Colitis was induced via oral administration of DSS (5 g/100 ml) to Balb/c mice for eight days. Intraperitoneal administration of KGF (5 mg/kg, once daily) or vehicle (VEH) was initiated 1 hr prior to the induction of the colitis (N = 10, each group). Mucosal injury of the entire colon was histologically assessed and graded. An approximately fourfold reduction in the crypt damage score was noted in the KGF group when compared to controls (VEH) (2.8 +/- 1.03 and 11.4 +/- 0.78, respectively). The significant reduction of mucosal injury in KGF treated mice confirms that KGF is a key mediator maintaining the integrity of the colonic mucosa.

Zinc metabolism in patients with exocrine pancreatic insufficiency.

OBJECTIVE: Metabolism of zinc was studied by administering radioactive zinc (Zn65), and by performing metabolic balance studies in eight patients with exocrine pancreatic insufficiency and eighteen control subjects. METHODS: Retention of radioactive zinc was measured by total body counter, and its urinary and fecal excretion by gamma scintillation counter. Metabolic balance studies were carried out by measuring dietary zinc intake as well as fecal and urinary excretion of zinc by atomic absorption spectrophotometry in this group of patients. RESULTS: These studies revealed a 50% reduction in intestinal absorption of Zn65 in patients with exocrine pancreatic insufficiency as compared to alcoholic and non-alcoholic control subjects. In addition, there was a 2 to 4 fold increase (p<0.05) in urinary excretion of zinc in subjects with pancreatic disease. In pancreatic insufficiency, reduced zinc absorption and increased urinary zinc excretion were balanced by lower (p<0.05) endogenous excretion of zinc as evidenced by reduced excretion of Zn65 in feces during the second 4-day period. The mean biological half-life of Zn65 tended to be lower in patients with pancreatic insufficiency as compared to alcoholic control subjects, however the difference did not reach statistical significance. CONCLUSION: These observations indicate marked alterations in zinc metabolism in patients with advanced chronic pancreatic disease and provide greater insight into development of zinc deficiency in this group of patients.

Reduced susceptibility of mice overexpressing transforming growth factor alpha to dextran sodium sulphate induced colitis.

BACKGROUND: Transforming growth factor alpha (TGF-alpha) knockout mice have increased susceptibility to dextran sodium sulphate (DSS) induced colitis. AIM: To substantiate the findings that TGF-alpha is a key mediator of colonic mucosal protection and/or repair mechanisms by evaluating the susceptibility of mice overexpressing TGF-alpha to DSS induced colitis. METHODS: TGF-alpha overexpression was induced in transgenic mice by ZnSO4 administration in drinking water (TG+). Three groups were used as controls: one transgenic group without ZnSO4 administration (TG-), and two non-transgenic littermate groups receiving ZnSO4 (Non-TG+) or only water (Non-TG-). Acute colitis was induced in all groups by administration of DSS (5%, w/v) in drinking water for six days and libitum. RESULTS: About 35-39% of the entire colonic mucosa was destroyed in Non-TG-, Non-TG+, and TG- animals compared with 9% in TG+ mice. the crypt damage score was 18.7 (0.9), 18.2 (1.0), 18.9 (0.8), and 6.8 (1.5) (means (SEM)) in Non-TG-, Non-TG+, TG-, and TG+ mice respectively. Mucin and bromodeoxyuridine staining were markedly enhanced in colons of TG+ mice compared with controls, indicating increased mucosal protection and regeneration. CONCLUSIONS: The significantly reduced susceptibility of mice overexpressing TGF-alpha to DSS further substantiates that endogenous TGF-alpha is a pivotal mediator of protection and/or healing mechanisms in the colon.

Keratinocyte growth factor promotes healing of left-sided colon anastomoses.

BACKGROUND: Inadequate healing and consequent leakage from bowel anastomoses are a significant cause of postoperative morbidity and mortality. Systemic application of keratinocyte growth factor (KGF) has been shown to promote mucosal healing in models of colitis in rats and mice. The aim of the present study was to evaluate the effect of systemic KGF administration on healing of colonic anastomoses in rats. METHODS: Rats underwent laparotomy, division of the left colon, and sigmoido-sigmoidostomy. KGF (5 mg/kg) or vehicle were administered intraperitoneally in two groups (n = 30 per group) 12 hours prior to surgery, and then once daily until sacrifice (6 animals per group; 2, 4, 7, 12, and 21 days after surgery). Bursting pressure measurements, histologic evaluation, morphometric analysis, mucin and collagen staining, and hydroxyproline measurements of the anastomotic site were performed. RESULTS: Administration of KGF significantly increased anastomotic bursting pressure on postoperative days 2, 4, and 7 by 34%, 49%, and 19%, respectively. Histology, mucin staining, and measurements of the colonic crypt depth showed markedly less extended inflammation with an increased acidic mucin content and a significantly thickened mucosal layer in the KGF treated group when compared with vehicle-treated animals. CONCLUSIONS: KGF promotes healing of colonic anastomoses in rats during a 1-week postoperative period following large bowel surgery. KGF may be acting to accelerate host reparative processes as well as to enhance protection of the anastomotic wound bed by increased colonic epithelium proliferation, increased mucus production, and reduction of the inflammatory activity at the anastomotic site.

Mice lacking transforming growth factor alpha have an increased susceptibility to dextran sulfate-induced colitis.

BACKGROUND & AIMS: There is indirect evidence that transforming growth factor alpha (TGF-alpha) is an important mediator of mucosal defense and repair. TGF-alpha knockout mice and TGF-alpha-deficient mice (wa-1) provide novel approaches to evaluate the role of TGF-alpha in preserving the integrity of the colon. METHODS: Colitis was induced by oral administration of dextran sodium sulfate (DSS, 5 g/dL) to knockout mice, their genetic controls (GC), wa-1 mice, and BALB/c mice. TGF-alpha was also administered intraperitoneally to wa-1 mice to evaluate the effect of exogenous TGF-alpha in DSS colitis. RESULTS: In response to DSS, nearly 60% of the entire colonic mucosa was destroyed in knockout and wa-1 mice, compared with 22% in GC mice and 16% in BALB/ c mice. Body weight loss was doubled in knockout (28%) and wa-1 mice (23%) compared with GC (11%) and Balb/c mice (12%). TGF-alpha application to wa-1 mice reduced the severity of mucosal injury by almost 70% compared with controls. CONCLUSIONS: The marked susceptibility of TGF-alpha knockout and wa-1 mice to DSS and the obvious amelioration of the colonic injury by exogenous TGF-alpha application in wa-1 mice suggest that TGF-alpha is a mediator of protection and/or healing mechanisms in the colon.

Increased expression of transforming growth factor alpha precursors in acute experimental colitis in rats.

BACKGROUND AND AIM: Epidermal growth factor (EGF) and transforming growth factor alpha (TGF-alpha), members of the EGF family of growth factors, protect rat gastric and colonic mucosa against injury. Having shown previously that exogenously applied EGF protects rat colonic mucosa against injury, the aim of the present study was to evaluate the endogenously expressed ligand mediating the protective effect of EGF/TGF-alpha in vivo. METHODS: In an experimental model of trinitrobenzene sulphonic acid (TNBS)/ethanol induced colitis in rats EGF and TGF-alpha expression was evaluated using a ribonuclease protection assay, northern blot analysis, western blot analysis, and immunohistochemistry. RESULTS: TGF-alpha mRNA increased 3-4 times at 4-8 hours after induction of colitis and returned to control levels within 24 hours. TGF-alpha immunoreactive protein with a molecular size of about 28 kDa representing TGF-alpha precursors increased markedly after induction of colitis with a peak at 8-12 hours. No fully processed 5.6 kDa TGF-alpha protein was detected in normal or inflamed colon tissue. Only a weak signal for EGF mRNA expression was detected in the rat colon and no EGF protein was observed by immunohistochemistry or western blot analysis. CONCLUSIONS: TGF-alpha precursors are the main ligands for the EGF receptor in acute colitis. It is hypothesised that TGF-alpha precursors convey the biological activity of endogenous TGF-alpha peptides during mucosal defence and repair.

Expression of insulin-like growth factor I receptors and binding proteins by colonic smooth muscle cells.

We recently demonstrated upregulation of insulin-like growth factor I (IGF-I) binding sites in the smooth muscle layer of inflamed rat colon. The increase in binding sites was due to increased expression of IGF binding proteins (IGFBPs), which modulate the effects of IGF. To further study the role of IGF in the colon, we investigated whether cultured colonic smooth muscle cells (SMC) express IGF-I receptors and IGFBPs. SMC were isolated by collagenase digestion from rat colonic smooth muscle and grown in primary culture. Equilibrium binding experiments using (125)I-labeled IGF-I showed the presence of an IGF-I receptor with a dissociation constant of 1.96 nM and a maximal binding constant of 53,000 receptors/cell. Competition binding studies with IGF-II and insulin, together with chemical cross-linking experiments, corroborated this conclusion. Western ligand blotting of conditioned medium and Northern analysis of total RNA demonstrated that the cells expressed and secreted IGFBP-4, -5, and -3 with molecular masses of 25, 31, and 45 kDa, respectively. These results, together with our in vivo studies in the rat, support a role for IGF in tissue fibrosis and stricture formation during chronic intestinal inflammation.

Neuropeptides in inflammatory bowel disease: an update.

SUMMARY: : Extrinsic and intrinsic neurons of the gut contain multiple neuropeptides, which through complex interactions modulate mucosal defense, inflammation, and repair in response to injury. Initial changes of the neurovascular peptidergic system may represent normal protective mechanisms against tissue injury, whereas subsequent alterations of neurovascular regulation may contribute to the pathogenesis and maintenance of the inflammatory state. Multiple interactions between sensory neurons, the immune system and growth factors appear to exist, and there is also a marked plasticity of the neurovascular peptidergic system with changes in the synthesis, release, binding, and degradation of peptides during inflammatory processes. A delicate and closely regulated balance between proinflammatory (e.g., SP, VIP, NPY) and antiinflammatory neuropeptides (e.g., CGRP, somatostatin, bombesin) seems to exist in the gastrointestinal tract. Disturbances of this balance might contribute to the pathophysiology of inflammatory bowel disease. In our overview, we will describe the results of studies in animal models of experimental inflammation and focus on the potential insight they provide in understanding the pathophysiology of inflammatory conditions of the bowel such as IBD. Knowledge with respect to these regulatory systems might provide novel insights into the inflammatory process and potentially expand the available therapeutic approaches in the management of IBD.

Keratinocyte growth factor ameliorates mucosal injury in an experimental model of colitis in rats.

BACKGROUND & AIMS: Keratinocyte growth factor (KGF) is known to enhance tissue repair in the skin; however, its role in the gastrointestinal tract is largely unknown. The aim of this study was to evaluate the effects of exogenous KGF in an experimental model of colitis in rats. METHODS: KGF was administered before or after induction of colitis with 2,4,6-trinitrobenzenesulfonic acid/ethanol. In the first two study groups, KGF (5 mg/kg) was administered intraperitoneally 24 hours and 1 hour before induction of colitis; animals were killed 8 hours (n=10) and 1 week (n=10) after injury. In subsequent study groups, KGF or vehicle treatment was begun 24 hours after the induction of colitis at doses of 5 (n=20), 1 (n=10), and 0.1 (n=10) mg/kg intraperitoneally and continued once daily for 1 week. Colonic tissue samples were evaluated macroscopically and microscopically for mucosal injury and assayed for myeloperoxidase activity. RESULTS: Administration of KGF after but not before induction of colitis significantly ameliorated tissue damage. Macroscopic necrosis and microscopic ulcerations were reduced by 40%-50% at KGF doses of 1 and 5 mg/kg. CONCLUSIONS: Exogenous KGF has a key role in mucosal healing in an experimental model of colitis in rats.

Protective effect of epidermal growth factor in an experimental model of colitis in rats.

BACKGROUND/AIMS: The role of epidermal growth factor (EGF) in the maintenance of mucosal integrity in the lower gastrointestinal tract is unknown. The aim of this study was to determine the effect of EGF in experimental colitis. METHODS: Colitis was induced with 2,4,6-trinitrobenzenesulfonic acid/ethanol enemas. Rats were pretreated with intraperitoneal administration of recombinant human EGF (600 micrograms/kg) or vehicle 1 hour before induction of colitis and daily thereafter until killed at 8 hours, 48 hours, and 1 week. A separate group received an identical dosage and administration of EGF or vehicle for 1 week with treatment initiated 24 hours after the induction of colitis. Colonic tissue was evaluated macroscopically, histologically, and for myeloperoxidase activity. RESULTS: Pretreatment with EGF reduced microscopic erosions at 8 and 48 hours by 74% and 54%, respectively (P < 0.05). At 1 week, microscopic ulcerations and myeloperoxidase activity were reduced by 65% in the EGF-pretreated group (P < 0.05). No significant difference in macroscopic injury, histological damage, or myeloperoxidase activity was noted when EGF treatment was initiated after the induction of colitis. CONCLUSIONS: Systemic EGF administration reduces mucosal damage and inflammation in a trinitrobenzenesulfonic acid/ethanol model of colitis in rats through a mechanism involving mucosal protection.