Up-regulation of insulinlike growth factor I binding sites in experimental colitis in rats

Insulin-Like Growth Factor-1 Contributes to Mucosal Repair by β-Arrestin2-Mediated Extracellular Signal-Related Kinase Signaling in Experimental Colitis

Insulin-like growth factor-1 (IGF-1) possesses the ability to attenuate intestinal damage and promote mucosal repair of colitis. β-Arrestins, as the scaffolding proteins of G protein-coupled receptors or non-G protein-coupled receptors signaling, can be involved in IGF-1-mediated signaling pathways. However, the interaction of IGF-1 and β-arrestin2 in the mucosal repair of experimental colitis remains unexplored. Ulcerative colitis was induced in β-arrestin2 wild-type mice and β-arrestin2 knockout littermates by using 3% dextran sulfate sodium for 5 days, followed by regular water consumption for 1, 2, 3, and 4 weeks to analyze the mucosal repair from experimental colitis. Disease activity index and histologic score analyses were performed. Apoptosis and proliferation were assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and Ki-67 staining, respectively. The expressions of β-arrestin2, phospho (p)-IGF-1R, and p-extracellular signal-regulated kinase (ERK)1/2 were examined. Furthermore, β-arrestin2 was overexpressed or altered in HCT116 cells by transfection before IGF-1 treatment in vitro. IGF-1 and β-arrestin2 expression was up-regulated in the repairing phase of experimental colitis. Targeted deletion of β-arrestin2 delayed the repair of colitis by inhibiting cell proliferation without affecting the levels of IGF-1 and p-IGF-1R. The β-arrestin2/ERK signaling pathway was involved in IGF-1-mediated mucosal repair through promoting epithelial cell and goblet cell regeneration from experimental colitis. These results indicate that IGF-1 contributes to the mucosal repair by β-arrestin2-mediated ERK signaling in experimental colitis.

Insulin-like growth factor binding proteins-3 and -5: central mediators of fibrosis and promising new therapeutic targets

Fibrosis involves an orchestrated cascade of events including activation of fibroblasts, increased production and deposition of extracellular matrix components, and differentiation of fibroblasts into myofibroblasts. Epithelial-mesenchymal cross-talk plays an important role in this process, and current hypotheses of organ fibrosis liken it to an aberrant wound healing response in which epithelial-mesenchymal transition (EMT) and cellular senescence may also contribute to disease pathogenesis. The fibrotic response is associated with altered expression of growth factors and cytokines, including increased levels of transforming growth factor-β1 (TGF-β1) and the more recent observation that increased levels of several insulin-like growth factor binding proteins (IGFBPs) are associated with a number of fibrotic conditions. IGFBPs have been implicated in virtually every cell type and process associated with the fibrotic response, making the IGFBPs attractive targets for the development of novel anti-fibrotic therapies. In this review, the current state of knowledge regarding the classical IGFBP family in organ fibrosis will be summarized and the clinical implications considered.

Amelioration of excess collagen IαI, fibrosis, and smooth muscle growth in TNBS-induced colitis in IGF-I(+/-) mice

BACKGROUND

Strictures occur in ≈ 30% of patients with Crohn's disease (CD) and are characterized by intestinal smooth muscle hyperplasia, hypertrophy, and fibrosis due to excess extracellular matrix production including collagen. Insulin-like growth factor-I (IGF-I) expression is increased in smooth muscle cells of the muscularis propria in CD and in animal models of CD, including trinitrobenzene sulfonic acid (TNBS)-induced colitis. While upregulated IGF-I is conjectured to cause smooth muscle cell growth and collagen production in the inflamed intestine, its role in the development of fibrosis has not been directly demonstrated.

METHODS

Colitis was induced in IGF-I(+/-) or wildtype C57BL/6J mice by rectal administration of TNBS or ethanol vehicle. After 7 days, colonic smooth muscle cells were isolated and used to prepare RNA or protein lysates. Transcript levels of IGF-IEa, IGF binding protein (IGFBP)-3, IGFBP-5, TGF-β1, and collagen IαI were measured by quantitative reverse-transcription polymerase chain reaction (RT-PCR). Corresponding protein levels were measured by Western blot or enzyme-linked immunosorbent assay (ELISA). Fibrosis was measured using digital image analysis of Masson's trichrome-stained histologic sections.

RESULTS

In IGF-I(+/-) mice, which express significantly lower levels of IGF-I than wildtype, the response to TNBS-induced colitis: upregulation of IGF-I, IGFBP-3, IGFBP-5 muscle growth, and collagen IαI expression, the resulting collagen deposition, and fibrosis are all significantly diminished compared to C57BL/6J wildtype controls. TGF-β1 expression and its increase following TNBS administration are not altered in IGF-I(+/-) mice compared to wildtype.

CONCLUSIONS

The findings indicate that IGF-I is a key regulator in intestinal smooth muscle hyperplasia and excess collagen production that leads to fibrosis and long term to stricture formation.

Endogenous IGF-I and alpha v beta3 integrin ligands regulate increased smooth muscle growth in TNBS-induced colitis

Endogenous insulin-like growth factor-I (IGF-I) regulates intestinal smooth muscle growth by concomitantly stimulating proliferation and inhibiting apoptosis. IGF-I-stimulated growth is augmented by the alpha(v)beta(3) integrin ligands vitronectin and fibronectin. IGF-I expression in smooth muscle is increased in both TNBS-induced colitis and Crohn's disease. We hypothesized that intestinal inflammation increased vitronectin and fibronectin expression by smooth muscle and, along with IGF-I upregulation, increased intestinal muscle growth. Intestinal smooth muscle cells were examined 7 days following the induction of TNBS-induced colitis. Although alpha(v)beta(3) integrin expression was not altered by TNBS-induced colitis, vitronectin and fibronectin levels were increased by 80 +/- 10% and 90 +/- 15%, above control levels, respectively. Basal IGF-I receptor phosphorylation in inflamed muscle from TNBS-treated rats was increased by 86 +/- 8% over vehicle-treated controls. Basal ERK1/2, p70S6 kinase, and GSK-3beta phosphorylation in muscle cells of TNBS-treated rats were also increased by 140-180%. TNBS treatment increased basal muscle cell proliferation by 130 +/- 15% and decreased apoptosis by 20 +/- 2% compared with that in vehicle-treated controls. The changes in proliferation and apoptosis were reversed by an IGF-I receptor tyrosine kinase inhibitor or an alpha(v)beta(3) integrin antagonist. The results suggest that smooth muscle hyperplasia in TNBS-induced colitis partly results from the upregulation of endogenous IGF-I and ligands of alpha(v)beta(3) integrin that mediate increased smooth muscle cell proliferation and decreased apoptosis. This paper has identified one mechanism regulating smooth muscle hyperplasia, a feature of stricture formation that occurs in the chronically inflamed intestine of TNBS-induced colitis and potentially Crohn's disease.

Colostrum supplementation restores insulin-like growth factor -1 levels and alters muscle morphology following massive small bowel resection

BACKGROUND

Colostrum protein concentrate (CPC) contains a high level of insulin-like growth factor-1 (IGF-1). IGF-1 and IGF binding protein (IGFBPs) may play an important role during the postresection adaptation response. As smooth muscle is an important site for IGF-1 action in the intestine, this study aims to (1) investigate the effect of CPC supplementation on circulating levels and tissue expression of IGF-1, IGF-1 receptor, and IGFBPs following massive small bowel resection (MSBR), and (2) characterize the effect of CPC on the muscular adaptation response following MSBR.

METHODS

Four-week-old piglets underwent either a 75% MSBR or sham operation. Piglets received either a polymeric infant formula (PIF) diet or PIF supplemented with CPC for 8 weeks. Serum was analyzed by enzyme-linked immunosorbent assay, and ileal tissue assessed by molecular and histological analysis.

RESULTS

There was no difference in IGF-1 or IGFBPs mRNA among groups. CPC treatment resulted in significant increases in circulating levels of IGF-1 and IGFBPs and a concurrent increase in muscle width and the number of muscle cells, but did not alter muscle cell size.

CONCLUSIONS

Strategies aimed at increasing muscular adaptation may decrease Gl transit and allow greater mucosal contact time for absorption. We have shown that CPC supplementation following resection results in increased levels of circulating IGF-1, IGFBP-2, and IGFBP-3 and muscular hypertrophy. Our results suggest that IGF-1 and its mediators may play a role in the muscular adaptation response and warrant further exploration as a treatment option for short bowel syndrome.

Contribution of insulin-like growth factor I to the healing of colonic anastomoses in rats

The aim of this experimental study was to investigate the contribution of insulin-like growth factor I (IGF)-I in the colonic healing process when injected intraperitoneally after colon resection. Forty male Wistar rats were used. Rats in the control group were injected with 3 mL of a solution of 0.9% NaCl intraperitoneally after the operation and on postoperative day 2, 4, and 6. Rats in the IGF-I group received recombinant human IGF-I in a dose of 2 mg/kg body weight intraperitoneally, immediately after the colonic anastomosis was performed and on postoperative day 2, 4, and 6. All rats were killed on postoperative day 7. The hydroxyproline tissue content was significantly higher in the IGF-1 group than in the control group. The bursting pressures were also significantly higher in IGF-1 group than in the control group. The weight change between the groups differed significantly; in the control group the average weight decreased about 5% postoperatively, while in the IGF-1 group the average weight increased about 6%. The average inflammatory cell infiltration score was significantly higher in the control group. Neoagiogenesis did not differ significantly between the two groups. The fibroblast activity differed significantly between the two groups, as the control group had significantly less fibroblasts compared to the IGF-1 group. In conclusion, IGF-I when given intraperitoneally stimulates the healing of colonic anastomoses in the rats. Further studies are required in order to determine whether this effect is dose related.

IGF-I increases IGFBP-5 and collagen alpha1(I) mRNAs by the MAPK pathway in rat intestinal smooth muscle cells

IGF-I is a potent fibrogenic growth factor that stimulates proliferation of intestinal smooth muscle cells and increases synthesis of collagen and IGF-I-binding proteins by the cells. These processes contribute to intestinal fibrosis that develops in patients with Crohn's disease and in Lewis-strain rats with experimental Crohn's disease. The aim of this study was to determine which early docking proteins are associated with IGF-I receptor signal transduction and which transduction pathway is involved in IGF-I-mediated gene regulation in intestinal smooth muscle cells. Primary cultures of smooth muscle cells isolated from the muscularis externa of the distal colon of Lewis rats were treated with IGF-I (100 ng/ml). Immunoprecipitation studies demonstrated that IGF-I stimulation resulted in tyrosine phosphorylation of IRS-1, IRS-2, and Shc. Coimmunoprecipitation demonstrated a close association between the IGF-I receptor and these three early docking proteins. Concurrent treatment with the MAPK inhibitor PD98059 (10 microM) resulted in an inhibition of the IGF-I-mediated increase in IGFBP-5 and collagen alpha(1)(I) mRNAs, while concurrent treatment with the phosphatidylinositol 3-kinase (PI3-K) inhibitor wortmannin (100 nM) had no effect. In additional experiments, cells were transiently transfected with adenoviral vectors dominantly expressing inactive mutant Akt or constitutively expressing wild-type Akt. In both cases, the IGF-I-mediated increase in collagen I protein did not differ from that observed in control cultures that had been transfected with an adenoviral vector carrying the LacZ reporter gene. These results suggest that the MAPK pathway is key to IGF-I-mediated gene regulation in intestinal smooth muscle cells, whereas data do not suggest a role for the Akt-dependent pathway in our system.

Transcriptome analysis of a human colorectal cancer cell line shows molecular targets of insulin-like growth factor-binding protein-4 overexpression

Insulin-like growth factor II (IGF-II) is expressed commonly in colorectal tumors. IGF-binding protein-4 (IGFBP-4) counteracts the tumor promoting activities of IGF-II by binding this growth factor. We have shown previously that in LS1034 cells, which highly express IGF-II, overexpression of IGFBP-4 led to a strong reduction in proliferation, colony formation and invasive capacity. To investigate the effects of IGFBP-4 at the molecular level we analyzed growth parameters of LS1034 human colon cancer cells vs. cells expressing the murine IGFBP-4 (mIGFBP-4) and used a subtractive cDNA library approach in combination with cDNA array hybridization to detect changes in the mRNA expression profiles. The mRNA levels for several proteins that are known to affect important biological properties of neoplastic cells, such as proteolysis, proliferation and differentiation were altered by overexpression of IGFBP-4. Transcript levels for tumor markers, like the carcinoembryonic antigen-related cell adhesion molecule (CEACAM), were reduced by elevated mIGFBP-4. Changes at the mRNA level were confirmed by Western blotting for CST1 (proteolysis or protease inhibitor), COX-2 (cell motility) and CEACAM5 (tumor marker). Furthermore, the effect of mIGFBP-4 on apoptosis was investigated and no increase of apoptosis could be detected in the IGFBP-4 overexpressing LS1034 cells. Our data indicate that IGFBP-4 is involved in the regulation of gene products that are known or supposed to be important for the pathogenesis of colon cancer cells.

Effects of weaning and rearing environment on intestinal gene expression of IGF-I, IGFBP (1-6), and the IGF receptor and on specific binding of IGF-I to mucosal membranes in the pig

The objective of this study was to investigate changes in gene expression of intestinal IGF-I, IGFBPs, and IGF-I receptor in pigs in response to weaning and different rearing environment. Pigs were weaned early at 12 days of age and either remained on-site in a separate facility (CON) or were moved to a segregated site with reduced infection pressure (segregated early weaning; SEW). Small intestinal samples were collected from a total of 15 pigs killed at 11 (pre-weaning), 15 (3 days post-weaning), and 34 days of age. Intestinal IGF-I mRNA levels were higher (P < 0.01) in SEW than in CON pigs at 3 days post-weaning, but not at 34 days of age. Weaning reduced (P < 0.05) both IGF-IR mRNA levels and specific binding of IGF-1 in the jejunum in both groups at day 34, but only in SEW pigs (P < 0.05) at day 3 post-weaning. Weaning resulted in a major reduction (P < 0.05) in intestinal IGFBP-2 mRNA, with no difference between SEW and CON. Intestinal IGFBP-3 mRNA levels were unaffected by weaning or post-weaning environment. Weaning did not affect intestinal IGFBP-4 mRNA levels, except for an increase (P < 0.05) in CON pigs compared to pre-weaning, and to SEW pigs at 3 days post-weaning. The abundance of IGFBP-5 mRNA in the gut was highly variable with no apparent treatment effect. Intestinal IGFBP-6 mRNA levels were reduced (P < 0.05) after weaning, with lower (P < 0.05) levels in SEW pigs than in CON pigs at 34 days of age. This study documents the changes in IGF-1, IGF-IR, and IGFBP mRNA abundance, and in IGF-1 binding during post-weaning adaptation of the intestine in early-weaned pigs. In addition, the relative differences observed in intestinal expression of IGF-1, IGF-IR, and in IGF-1 binding between the post-weaning environments are consistent with previous observations in a companion study indicating that segregated early weaning enhances post-weaning intestinal maturation in pigs.

Expression of insulin-like growth factor binding proteins and collagen in experimental colitis in rats

OBJECTIVES AND DESIGN

Crohn's disease is complicated by smooth muscle hyperplasia and stricture formation. Insulin-like growth factor (IGF)-1 and insulin-like growth factor binding proteins (IGFBPs) may be involved in stimulating intestinal smooth muscle growth and collagen synthesis. Therefore, we investigated the expression of IGFBPs, collagen and collagenase activity in rat colitis and the effects of IGF-1 on IGFBP and collagen expression in rat colonic smooth muscle cells.

METHODS

Animals were sacrificed during a 4-week time course of 2,4,6-trinitrobenzenesulphonic acid (TNBS)-induced colitis. RNA from the animals' colons was blotted and hybridized with collagen-1 and IGFBP mRNA probes. Tissue proteins were screened for IGFBPs by Western ligand blotting. Collagenase activity was measured by zymography. Rat colonic smooth muscle cells in primary culture were incubated with IGF-1 then collagen-1, and IGFBP mRNAs and proteins were measured.

RESULTS

In the rat tissue, IGFBP-3 mRNA and protein were increased 2 h after induction of colitis. IGFBP-4 mRNA was elevated after 2 h and IGFBP-4 protein after 4 h. IGFBP-5 mRNA was upregulated after 2 h with a peak at 12 h. IGFBP-5 protein was upregulated after 1 h and reached a peak at 3 days. Collagen-1 mRNA was increased after 5 days. Collagenase levels were decreased after 1 h and returned to normal by 28 days. In rat colonic smooth muscle cells, IGF-1 increased collagen-1 and IGFBP-5 expression.

CONCLUSION

We demonstrated an upregulation of IGFBP and collagen expression and a downregulation of collagenase in rat colitis. In colonic smooth muscle cells, we found an upregulation of collagen-1 and IGFBP-5 following IGF-1 incubation. These results suggest an important role of IGF-1 in the collagen synthesis in colitis, mediated by IGFBPs.

Insulin and IGF-I inhibit calcium-dependent chloride secretion by T84 human colonic epithelial cells

D-Myo-inositol (3,4,5,6) tetrakisphosphate [Ins(3,4,5,6)P(4)] or phosphatidylinositol 3-kinase (PI 3-kinase) activity acts to inhibit calcium-dependent chloride secretion in T84 colonic epithelial cells. To further distinguish between the contributions of these two signaling pathways to the inhibition of secretion, we studied effects of insulin, because the insulin receptor links to PI 3-kinase but not to pathways postulated to generate Ins(3,4,5,6)P(4). Chloride secretion across T84 cell monolayers was studied in Ussing chambers. Activation of PI 3-kinase was assessed by Western blotting. Basolateral, but not apical, addition of insulin inhibited carbachol- and thapsigargin-induced chloride secretion in a time- and concentration-dependent fashion. Insulin-like growth factor-I (IGF-I) had similar effects. Insulin had no effect on Ins(3,4,5,6)P(4) levels, and the inhibitory effects of insulin and IGF-I on chloride secretion were fully reversed by the PI 3-kinase inhibitors wortmannin and LY-294002. Western blot analysis showed that both insulin and IGF-I recruited the 85-kDa regulatory and 110-kDa catalytic subunits of PI 3-kinase to anti-phosphotyrosine immunoprecipitates. In conclusion, insulin and IGF-I act to inhibit calcium-dependent chloride secretion through a PI 3-kinase-dependent pathway. Because insulin is released in a pulsatile fashion postprandially and IGF-I levels are elevated in pathological settings, our findings may have physiological and/or pathophysiological significance.

Insulin-like growth factor I and insulin-like growth factor binding protein 5 in Crohn's disease

Insulin-like growth factor (IGF)-I and its binding protein IGF binding protein 5 (IGFBP-5) were highly expressed in inflamed and fibrotic intestine in experimental Crohn's disease. IGF-I induced proliferation and increased collagen synthesis by smooth muscle cells and fibroblasts/myofibroblasts in vitro. Here we studied IGF-I and IGFBP-5 in Crohn's disease tissue. Tissue was collected from patients undergoing intestinal resection for Crohn's disease. IGF-I and IGFBP-5 mRNAs were quantitated by RNase protection assay and Northern blot analysis, respectively. In situ hybridization was performed to localize mRNA expression, and Western immunoblot was performed to quantitate protein expression. IGF-I and IGFBP-5 mRNAs were increased in inflamed/fibrotic intestine compared with normal-appearing intestine. IGF-I mRNA was expressed in multiple cell types in the lamina propria and fibroblast-like cells of the submucosa and muscularis externa. IGFBP-5 mRNA was highly expressed in smooth muscle of the muscularis mucosae and muscularis externa as well as fibroblast-like cells throughout the bowel wall. Tissue IGFBP-5 protein correlated with collagen type I (r = 0.82). These findings are consistent with a mechanism whereby IGF-I acts on smooth muscle and fibroblasts/myofibroblasts to increase collagen synthesis and cellular proliferation; its effects may be modulated by locally expressed IGFBP-5.

Heparin therapy for ulcerative colitis? Effects and mechanisms

Despite intensive medical treatment with steroids and immunosuppressants, acute colitis is still associated with a colectomy rate of up to 15%. Following the observation that a patient with severe steroid-resistant colitis went into remission when treated with heparin for a deep vein thrombosis, there have been a number of reports on the use of heparin in acute ulcerative colitis. Although small and uncontrolled, these studies consistently demonstrate the beneficial effects of heparin, with surprisingly few side-effects in a disease characterized by mucosal haemorrhage. The mechanisms by which heparin may ameliorate ulcerative colitis remain unclear. A simple anticoagulant effect may be responsible, but similar effects are not seen with warfarin. As a result of their intense negative charge, the glycosaminoglycans that constitute heparin have diverse biological effects. These include potent anti-inflammatory actions, in vitro and in vivo, and the potentiation of the activity of the peptide growth factors necessary for mucosal regeneration and repair. This review summarizes the clinical reports on heparin treatment for ulcerative colitis and explores the mechanisms by which this novel form of treatment may exert its effects.

Insulin-like growth factor I and truncated keratinocyte growth factor accelerate healing of left-sided colonic anastomoses

BACKGROUND

Human full-length keratinocyte growth factor (KGF) promotes healing of colon anastomoses in rats through mechanisms other than enhancement of collagen synthesis. Since insulin-like growth factor (IGF) I increases matrix synthesis, the aim of this study was to evaluate the effect of systemic truncated KGF (tKGF), IGF-I and combined tKGF-IGF-I administration on the healing of colonic anastomoses in rats.

METHODS

Rats underwent laparotomy, division of the left colon, and sigmoidosigmoidostomy. tKGF (1 mg/kg), IGF-I (1 mg/kg), tKGF-IGF-I (both 1 mg/kg) or vehicle was administered intraperitoneally in four groups (n = 18 per group) 12 h before surgical intervention, and then once daily until killing (six animals per group; 2, 4 and 6 days after surgery). Bursting pressure measurements, histological evaluation, morphometric analysis, mucin and collagen staining, and 5-bromo-2'-deoxyuridine (BrdU) immunohistochemistry of the anastomotic site were undertaken.

RESULTS

Administration of tKGF, IGF-I and the combination of both growth factors significantly increased anastomotic bursting pressure at postoperative day 2 (63, 71 and 113 per cent respectively), day 4 (68, 83 and 80 per cent) and day 6 (48, 43 and 43 per cent) compared with the control group. No intergroup differences were found. Histological examination, mucin and BrdU staining, and measurement of colonic crypt depth indicated less inflammation, increased acidic mucin content, a higher crypt cell proliferation rate and thickened mucosal layer in the growth factor-treated animals than in controls. Enhanced collagen staining was observed only in IGF-treated animals.

CONCLUSION

tKGF and IGF-I markedly accelerate the healing of colonic anastomoses in rats. However, combined administration of the two growth factors does not show additional benefit. Both growth factors may be acting to accelerate host reparative processes as well as to enhance protection of the anastomotic wound bed.

Enterotrophic effect of insulin-like growth factor-I but not growth hormone and localized expression of insulin-like growth factor-I, insulin-like growth factor binding protein-3 and -5 mRNAs in jejunum of parenterally fed rats

BACKGROUND

Administration of insulin-like growth factor (IGF)-I, but not growth hormone (GH), stimulates mucosal hyperplasia in surgically stressed rats with intestinal atrophy induced by hypocaloric total parenteral nutrition (TPN). Our aim was to characterize the basis for this disparity in enterotrophic action by assessing the relationships between stimulation of intestinal growth, nutritional adequacy, and localization of expression of IGF-I, insulin-like growth factor binding protein (IGFBP)-3 and IGFBP-5 mRNAs in jejunum.

METHODS

Rats were maintained with TPN for 8 days and treated with IGF-I or GH and adequate nutrition for 5 days after recovery from surgery. Jejunal mass, morphology, and sucrase activity were assessed. Localization of expression of IGF-I, IGFBP-3, and IGFBP-5 mRNAs in jejunum was accomplished by in situ hybridization.

RESULTS

Serum IGF-I and body weight gain were significantly increased by IGF-I or GH. Jejunal mucosal dry mass, morphology, and sucrase activity were improved with IGF-I but not GH. There were no differences in IGF-I mRNA. IGFBP-3 mRNA was localized in the lamina propria of the villi. IGF-I or GH stimulated IGFBP-3 expression. IGF-I strongly stimulated IGFBP-5 expression in the lamina propria and the muscularis and induced a twofold increase in IGFBP-5 mRNA based on RNase protection assay of intact jejunum total RNA. GH induced a modest increase in IGFBP-5 expression in the muscularis with no effect on intact jejunum total RNA.

CONCLUSIONS

The GH resistance observed in the jejunal mucosa of TPN rats cannot be fully explained by inadequate nutrition. The expression of IGFBP-5 in the lamina propria suggests it may modulate the enterotrophic action of exogeneous IGF-I.

Ontogeny of intestinal nutrient transport

Children born prematurely lack the ability to digest and to absorb nutrients at rates compatible with their nutritional needs. As a result, total parenteral nutrition may need to be given. While this nutritional support may be life-saving, the baby who receives this therapy is exposed to the risks of possible sepsis, catheter dysfunction, and liver disease. The rodent model of postnatal development provides a useful framework to investigate some of the cellular features of human intestinal development. The up-regulation of intestinal gene expression and precocious development of intestinal nutrient absorption can be achieved by providing growth factor(s) or by modifying the composition of the maternal diet during pregnancy and nursing or the weaning diet of the infant. Accelerating the digestive and absorptive functions of the intestine would thereby allow for the maintenance of infant nutrition through oral food intake, and might possibly eliminate the need for, and risks of, total parenteral nutrition. Accordingly, this review was undertaken to focus on the adaptive processes available to the intestine, to identify what might be the signals for and mechanisms of the modified nutrient absorption, and to speculate on approaches that need to be studied as means to possibly accelerate the adaptive processes in ways which would be beneficial to the newborn young.Key words: absorption, adaptation, diet, peptides.

Endogenous IGF-I regulates IGF binding protein production in human intestinal smooth muscle cells

Human intestinal smooth muscle in culture produces insulin-like growth factor (IGF)-I and IGF binding protein (IGFBP)-3, IGFBP-4, and IGFBP-5, which modulate the effects of IGF-I. This study examined the regulation of IGFBP production by endogenous IGF-I. R3-IGF-I, an agonist unaffected by IGFBPs, elicited concentration-dependent increase in growth, measured by [(3)H]thymidine incorporation, and production of IGFBP-3, IGFBP-4, and IGFBP-5, measured by Western blot. Antagonists of the IGF-I receptor, IGF-I Analog or monoclonal antibody 1H7, elicited concentration-dependent inhibition of growth and decrease in IGFBP-3, IGFBP-4, and IGFBP-5 production, implying that endogenous IGF-I stimulated growth and IGFBP production. R3-IGF-I-induced increase in IGFBP-3, IGFBP-4, and IGFBP-5 production was partially inhibited by a mitogen-activated protein (MAP) kinase or a phosphatidylinositol-3-kinase (PI 3-kinase) inhibitor and abolished by the combination. We conclude that endogenous IGF-I stimulates growth and IGFBP-3, IGFBP-4, and IGFBP-5 production in human intestinal smooth muscle cells. Regulation of IGFBP production by IGF-I is mediated by activation of distinct MAP kinase and PI 3-kinase pathways, the same pathways through which IGF-I stimulates growth.

Growth factors in inflammatory bowel disease

The pathogenesis of both ulcerative colitis and Crohn's disease is unknown but these forms of inflammatory bowel disease (IBD) may be associated with an inability of the intestinal mucosa to protect itself from luminal challenges and/or inappropriate repair following intestinal injury. Numerous cell populations regulate these broad processes through the expression of a complex array of peptides and other agents. Growth factors can be distinguished by their actions regulating cell proliferation. These factors also mediate processes such as extracellular matrix formation, cell migration and differentiation, immune regulation, and tissue remodeling. Several families of growth factors may play an important role in IBD including: epidermal growth factor family (EGF) [transforming growth factor alpha (TGF alpha), EGF itself, and others], the transforming growth factor beta (TGF beta) super family, insulin-like growth factors (IGF), fibroblast growth factors (FGF), hepatocyte growth factor (HGF), trefoil factors, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and others. Collectively these families may determine susceptibility of IBD mucosa to injury and facilitate tissue repair.

Growth factors in inflammatory bowel disease

The pathogenesis of both ulcerative colitis and Crohn's disease is unknown but these forms of inflammatory bowel disease (IBD) may be associated with an inability of the intestinal mucosa to protect itself from luminal challenges and/or inappropriate repair following intestinal injury. Numerous cell populations regulate these broad processes through the expression of a complex array of peptides and other agents. Growth factors can be distinguished by their actions regulating cell proliferation. These factors also mediate processes such as extracellular matrix formation, cell migration and differentiation, immune regulation, and tissue remodeling. Several families of growth factors may play an important role in IBD including: epidermal growth factor family (EGF) [transforming growth factor alpha (TGF alpha), EGF itself, and others], the transforming growth factor beta (TGF beta) super family, insulin-like growth factors (IGF), fibroblast growth factors (FGF), hepatocyte growth factor (HGF), trefoil factors, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and others. Collectively these families may determine susceptibility of IBD mucosa to injury and facilitate tissue repair.

IGFBP-3 and IGFBP-5 production by human intestinal muscle: reciprocal regulation by endogenous TGF-beta1

Insulin-like growth factor-I (IGF-I)-mediated growth of cells can be modulated by specific IGF binding proteins (IGFBPs) that inhibit or augment IGF-I ligand-receptor interaction. IGFBP expression and production by human intestinal muscle cells in culture was characterized in rapidly growing cells (day 3 of culture), in confluent cells (day 7), and in postconfluent cells (day 14). RT-PCR analysis identified IGFBP-3, IGFBP-4, and IGFBP-5 mRNA during all three phases of growth. The production of IGFBP-3 and IGFBP-5 was regulated in reciprocal fashion. IGFBP-5 production was high on day 3 and decreased two- to fivefold by day 14, and IGFBP-3 production was low on day 3 and increased five- to eightfold by day 14. IGFBP-4 production remained constant. IGFBP-3 inhibited and IGFBP-5 augmented IGF-I-induced proliferation. IGFBP-3 and IGFBP-5 production was regulated in reciprocal fashion by transforming growth factor-beta1 (TGF-beta1). Immunoneutralization of endogenous TGF-beta1 decreased the production of IGFBP-3 and increased the production of IGFBP-5. Addition of exogenous recombinant human TGF-beta1 had the opposite effect. We conclude that the expression and time-dependent production of IGFBP-3, IGFBP-4, and IGFBP-5 and their regulation by endogenous TGF-beta1 represent mechanisms by which human intestinal muscle cells regulate autocrine IGF-I-mediated growth.

Insulin-like growth factor axis of gluten-sensitive dogs during a gluten challenge

Eight gluten-sensitive Irish setters underwent a gluten challenge to investigate changes in the insulin-like growth factor (IGF) axis. In the first study, they were challenged with an acute intraduodenal administration of tryptic-peptic gluten digest and then maintained on dietary gluten for three months. In the second study, the challenge came solely from dietary gluten fed for three months. After the acute intraduodenal administration of gluten, serum IGF-I levels decreased significantly by 21.8 per cent, (P = 0.01) on day 3 after challenge and then returned to normal. There was also a decrease (52.5 per cent, P < 0.03) in the levels of serum IGF-binding protein-3 (IGFBP-3) until day 14 after challenge but they had returned to normal by day 28. In two dogs IGFBP-3 levels decreased through specific serum protease activity. There were no changes in serum IGF-I or IGFBP levels during the second study after the dietary gluten challenge alone, or in four non-gluten-sensitive beagles studied as controls during the acute intraduodenal/dietary gluten challenge.

IGF-I stimulates intestinal muscle cell growth by activating distinct PI 3-kinase and MAP kinase pathways

Insulin-like growth factor I (IGF-I), acting via its cognate receptor, plays an autocrine role in the regulation of growth of intestinal muscle cells. In the present study the signaling pathways mediating the growth effects of IGF-I were characterized in cultured human intestinal smooth muscle cells. Growth induced by a maximally effective concentration of IGF-I (100 nM), measured as [3H]thymidine incorporation, was only partially inhibited by LY-294002 [phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor] or PD-98059 [mitogen-activated protein (MAP) kinase kinase (MEK) inhibitor] (86 +/- 7% and 35 +/- 6% inhibition, respectively) alone but was abolished by the two combined (114 +/- 18% inhibition), implying the participation of both pathways. IGF-I elicited time- and concentration-dependent increases in PI 3-kinase activity. This effect was inhibited only by LY-294002 (89 +/- 12%). IGF-I elicited time- and concentration-dependent phosphorylation of p44/p42 MAP kinase and increased MAP kinase activity. These effects were inhibited only by PD-98059 (78 +/- 9% and 98 +/- 7%, respectively). We conclude that in human intestinal muscle cells IGF-I activates distinct PI 3-kinase and MAP kinase signaling pathways, which act in conjunction to mediate growth.

Differential expression and localization of IGF-I and IGF binding proteins in inflamed rat colon

Recent studies indicate increased insulin-like growth factor I (IGF-I) expression and altered expression of IGF binding proteins (IGFBP) in the bowel during experimental colitis. This study analyzes the cellular sites of altered IGF-I and IGFBP-expression in large bowel of rats with experimental colitis. Colitis was induced by colonic instillation of 2, 4, 6-trinitrobenzenesulfonic (TNB) acid in ethanol. Animals were sacrificed at 7 days after induction of colitis. Cryostat sections of colon from TNB-treated and control rats were hybridized with 35S-labeled antisense probes for IGF-I, IGFBP-3, IGFBP-4 and IGFBP-5. IGF-I mRNA was up-regulated in lamina propria cells, submucosa and smooth muscle of inflamed colon. IGFBP-3 mRNA was localized to lamina propria and was down-regulated in inflamed colon. IGFBP-4 and IGFBP-5 mRNAs were both up-regulated in inflamed colon. IGFBP-4 mRNA was increased in lamina propria, submucosa and smooth muscle, whereas IGFBP-5 mRNA was increased in smooth muscle. Increased IGF-I expression in mesenchymal layers of colon during experimental colitis supports the hypothesis that IGF-I contributes to hyperplasia and fibrosis in response to inflammation. Altered expression of IGFBP-3, IGFBP-4 and IGFBP-5 in specific bowel layers during colitis suggests that they play a role in modulating IGF-I action.

Insulin-like growth factor-I partially attenuates colonic damage in rats with experimental colitis induced by oral dextran sulphate sodium

BACKGROUND

Administration of insulin-like growth factor-I (IGF-I) results in selective growth of the gastrointestinal tract. We investigated the effects of IGF-I on the colonic damage induced by oral dextran sulphate sodium (DSS) in the rat.

METHODS

Rats consumed 2% DSS in the drinking water for 10 days to induce colitis. Pumps were implanted on day 3 to deliver IGF-I for 7 days. Colonic histopathology and immunolocalization of transforming growth factor-beta1 (TGF-beta1) were assessed on day 10.

RESULTS

Compared with the colon of vehicle-treated rats consuming DSS, IGF-I increased the numbers of goblet cells by 76%, reduced the proportion of lamina propria cells expressing TGF-beta1, and reduced the thickness of submucosal and muscularis externa layers by 26% and 20%, respectively.

CONCLUSIONS

We conclude that the effects of IGF-I treatment on the colonic epithelium may be mediated directly, whereas the reduced inflammation in the mucosa and submucosa may be mediated by a mechanism other than up-regulation of TGF-beta1-mediated immunosuppression.

IGF-I induces collagen and IGFBP-5 mRNA in rat intestinal smooth muscle

Insulin-like growth factor (IGF) binding protein 5 (IGFBP-5) mRNA was studied in intestines of rats with peptidoglycan-polysaccharide enterocolitis by Northern analysis and in situ hybridization. IGFBP-5 mRNA was increased 2.4 +/- 0.5-fold in inflamed rat colon compared with controls and was highly expressed in smooth muscle. Cultured rat intestinal smooth muscle cells were used to study the regulation of IGFBP-5 and type I collagen synthesis. IGF-I (100 ng/ml) increased IGFBP-5 mRNA (1.9 +/- 0.1-fold) and collagen type alpha1(I) mRNA (1.6 +/- 0.2-fold) in cultured smooth muscle cells. IGF-I induced a dose- and time-dependent increase in IGFBP-5 in conditioned medium by Western ligand blot and by immunoblot. IGF-I did not affect the IGFBP-5 mRNA decay rate after transcriptional blockade. Cycloheximide abolished IGFBP-5 mRNA. In conclusion, IGFBP-5 mRNA is expressed by intestinal smooth muscle and is increased during chronic inflammation. IGF-I increases IGFBP-5 and collagen mRNAs in intestinal smooth muscle cells.

Protein-energy malnutrition delays small-intestinal recovery in neonatal pigs infected with rotavirus

Infectious diarrheal diseases and protein-energy malnutrition (PEM) are major causes of child morbidity and mortality worldwide. In the present study, PEM was superimposed on rotavirus infection in neonatal pigs to simulate chronic small intestinal stress in malnourished infants with viral gastroenteritis. Two-day-old cesarean-derived pigs (n = 39) were allotted to three treatment groups: 1) noninfected, full-fed; 2) infected, full-fed; and 3) infected, malnourished. Two days postinfection, severe diarrhea and weight loss (11%) were accompanied by reductions in villus height (60%) and lactase activity (78%) and increased crypt depth (32%) in infected full-fed compared with noninfected pigs (P < 0.05). Malnutrition blunted (P < 0.05) increases in crypt depth elicited by rotavirus. By 9 d postinfection, body weight was 59% less, villus height and lactase activity remained lower (50%), and crypt depth remained greater (62%) in infected full-fed compared with noninfected pigs (P < 0.05). However, diarrhea began to clear in infected full-fed, but not in infected malnourished pigs. Plasma insulin-like growth factor-I (IGF-I) was reduced 68% and crypt depth was reduced 19% in infected-malnourished compared with infected full-fed pigs (P < 0.05). Sixteen days postinfection, full-fed pigs had recovered from rotaviral infection; however, in infected-malnourished pigs, diarrhea and growth stasis persisted, and plasma IGF-I, villus height and alkaline phosphatase activity remained reduced compared with infected full-fed pigs (P < 0.05). Overall, PEM prolonged diarrhea and delayed small-intestinal recovery, indicating that nutritional status during diarrhea is essential for recovery from rotaviral enteritis.