Synergistic effect of supplemental enteral nutrients and exogenous glucagon-like peptide 2 on intestinal adaptation in a rat model of short bowel syndrome

Digestive enzyme expression in the large intestine of children with short bowel syndrome in a late stage of adaptation

BACKGROUND AND AIMS

Intestinal adaptation in short bowel syndrome (SBS) includes morphologic processes and functional mechanisms. This study investigated whether digestive enzyme expression in the duodenum and colon is upregulated in SBS patients.

METHOD

Sucrase-isomaltase (SI), lactase-phlorizin hydrolase (LPH), and neutral Aminopeptidase N (ApN) were analyzed in duodenal and colonic biopsies from nine SBS patients in a late stage of adaptation as well as healthy and disease controls by immunoelectron microscopy (IEM), Western blots, and enzyme activities. Furthermore, proliferation rates and intestinal microbiota were analyzed in the mucosal specimen.

RESULTS

We found significantly increased amounts of SI, LPH, and ApN in colonocytes in most SBS patients with large variation and strongest effect for SI and ApN. Digestive enzyme expression was only partially elevated in duodenal enterocytes due to a low proliferation level measured by Ki-67 staining. Microbiome analysis revealed high amounts of Lactobacillus resp. low amounts of Proteobacteria in SBS patients with preservation of colon and ileocecal valve. Colonic expression was associated with a better clinical course in single cases.

CONCLUSION

In SBS patients disaccharidases and peptidases can be upregulated in the colon. Stimulation of this colonic intestinalization process by drugs, nutrients, and pre- or probiotics might offer better therapeutic approaches.

Effects of exogenous glucagon-like peptide-2 and distal bowel resection on intestinal and systemic adaptive responses in rats

OBJECTIVE

To determine the effects of exogenous glucagon-like peptide-2 (GLP-2), with or without massive distal bowel resection, on adaptation of jejunal mucosa, enteric neurons, gut hormones and tissue reserves in rats.

BACKGROUND

GLP-2 is a gut hormone known to be trophic for small bowel mucosa, and to mimic intestinal adaptation in short bowel syndrome (SBS). However, the effects of exogenous GLP-2 and SBS on enteric neurons are unclear.

METHODS

Sprague Dawley rats were randomized to four treatments: Transected Bowel (TB) (n = 8), TB + GLP-2 (2.5 nmol/kg/h, n = 8), SBS (n = 5), or SBS + GLP-2 (2.5 nmol/kg/h, n = 9). SBS groups underwent a 60% jejunoileal resection with cecectomy and jejunocolic anastomosis. All rats were maintained on parenteral nutrition for 7 d. Parameters measured included gut morphometry, qPCR for hexose transporter (SGLT-1, GLUT-2, GLUT-5) and GLP-2 receptor mRNA, whole mount immunohistochemistry for neurons (HuC/D, VIP, nNOS), plasma glucose, gut hormones, and body composition.

RESULTS

Resection increased the proportion of nNOS immunopositive myenteric neurons, intestinal muscularis propria thickness and crypt cell proliferation, which were not recapitulated by GLP-2 therapy. Exogenous GLP-2 increased jejunal mucosal surface area without affecting enteric VIP or nNOS neuronal immunopositivity, attenuated resection-induced reductions in jejunal hexose transporter abundance (SGLT-1, GLUT-2), increased plasma amylin and decreased peptide YY concentrations. Exogenous GLP-2 attenuated resection-induced increases in blood glucose and body fat loss.

CONCLUSIONS

Exogenous GLP-2 stimulates jejunal adaptation independent of enteric neuronal VIP or nNOS changes, and has divergent effects on plasma amylin and peptide YY concentrations. The novel ability of exogenous GLP-2 to modulate resection-induced changes in peripheral glucose and lipid reserves may be important in understanding the whole-body response following intestinal resection, and is worthy of further study.

Nutritional strategies to enhance adaptation in intestinal failure

PURPOSE OF REVIEW

This article summarizes the current and potential future nutritional approaches to stimulate adaptation in intestinal failure. Adaptation in this context usually refers to intestinal adaptation but also involves changes in whole body physiology as well as in eating/drinking behavior.

RECENT FINDINGS

Adaptation largely depends on residual functional anatomy. Luminal exposure to complex nutrients is the most important trigger for intestinal adaptation. Enteral fat as well as enteral or parenteral short chain fatty acids have a specific stimulatory effect. Zinc and vitamin A status need to be optimized for adaptation to proceed and be maintained. In the context of maintaining sodium and water homeostasis, flushing the remnant intestine because of uncontrolled thirst/drinking must be avoided. Complications of nutritional care such as malnutrition, intestinal failure-associated liver disease, and recurrent line sepsis also need optimal management.

SUMMARY

Stimulation by luminal nutrients as well as prophylaxis against and treatment of (nutritional) complications are the cornerstones of adaptation to the short bowel situation. Based on ample data from animal studies but only limited evidence in humans specific nutritional stimulators need to be studied more rigorously. As long as such data are missing they can be tried on an individual basis.

Glucagon-Like Peptide-2 Requires a Full Complement of Bmi-1 for Its Proliferative Effects in the Murine Small Intestine

The intestinal hormone, glucagon-like peptide-2 (GLP-2), stimulates growth, survival, and function of the intestinal epithelium through increased crypt cell proliferation, and a long-acting analog has recently been approved to enhance intestinal capacity in patients with short bowel syndrome. The goal of the present study was to determine whether GLP-2-induced crypt cell proliferation requires a full complement of B-cell lymphoma Moloney murine leukemia virus insertion region-1 homolog (Bmi-1), using the Bmi-1(eGFP/+) mouse model in comparison with age- and sex-matched Bmi-1(+/+) littermates. Bmi-1 is a member of the polycomb-repressive complex family that promotes stem cell proliferation and self-renewal and is expressed by both stem cells and transit-amplifying (TA) cells in the crypt. The acute (6 h) and chronic (11 d) proliferative responses to long-acting human (Gly(2))GLP-2 in the crypt TA zone, but not in the active or reserve stem cell zones, were both impaired by Bmi-1 haploinsufficiency. Similarly, GLP-2-induced crypt regeneration after 10-Gy irradiation was reduced in the Bmi-1(eGFP/+) animals. Despite these findings, chronic GLP-2 treatment enhanced overall intestinal growth in the Bmi-1(eGFP/+) mice, as demonstrated by increases in small intestinal weight per body weight and in the length of the crypt-villus axis, in association with decreased apoptosis and an adaptive increase in crypt epithelial cell migration rate. The results of these studies therefore demonstrate that a full complement of Bmi-1 is required for the intestinal proliferative effects of GLP-2 in both the physiological and pathological setting, and mediates, at least in part, the proliferation kinetics of cells in the TA zone.

The prolonged effect of glucagon-like peptide 2 pretreatment on growth performance and intestinal development of weaned piglets

BACKGROUND

Glucagon-like peptide 2 (GLP-2) is a potent epithelium-specific intestinal growth factor. The aim of this study was to demonstrate the prolonged effect of GLP-2 on the growth performance of weaned piglets. Forty piglets weaned at the age of 28 d with an average BW of 6.8 ± 0.4 kg were assigned to four treatments: (i) non-challenged control; (ii) LPS-challenged control; (iii) LPS + low GLP-2; and (iv) LPS + high GLP-2. Piglets in groups (i), (ii), and (iv) were s.c. injected with PBS supplemented with human [Gly2]GLP-21-34 at doses of 0, 2 and 10 nmol/kg BW per day for seven consecutive days. BW, gain:feed ratio (G:F), and plasma GLP-2 levels were determined on d 0, 7, and 14 after weaning. Piglets were challenged with i.p. administration of Escherichia coli lipopolysaccharide (LPS) at a dose of 100 μg/kg on d 14 to induce intestinal damage. Twenty-four hours later, intestinal tract samples were collected to assess intestinal morphology and quantify enzyme activity.

RESULTS

Plasma GLP-2 levels decreased after weaning, but in the high GLP-2 group, plasma GLP-2 was maintained on d 7 and even increased to a level higher than the preweaning level on d 14 (P < 0.05). High GLP-2 treatment significantly increased the duodenal, jejunal and ileal weight, as well as the gross weight of the small intestine (SI), and the SI weight index (P < 0.05). LPS caused villous atrophy and disrupted intestinal morphology in the duodenum, jejunum and ileum. GLP-2 also significantly increased the villus height and the villus height/crypt depth ratio (VCR) of the duodenum, jejunum, and ileum (P < 0.05). Histological examination revealed that in GLP-2-treated groups, the integrity of the villus was maintained, and the villus was protected against LPS-induced damage. GLP-2 significantly increased the activity of alkaline phosphatase (AKP), γ-glutamyltranspeptidase (γ-GT), and pancreatic lipase in the duodenum and jejunum (P < 0.05). GLP-2 treatment also significantly increased the average daily gain (ADG) and G:F of piglets at 0 to 7, 7 to 14, as well as 0 to14 d (P < 0.05), resulting in a significant increase of final BW in high GLP-2 pigs (P = 0.016).

CONCLUSIONS

Exogenous GLP-2 improved the growth of weaned piglets and protected them against LPS-induced intestinal damage. These effects may be due to the ability of GLP-2 to promote the secretion of endogenous GLP-2 to stimulate the small intestinal development.

Teduglutide-Stimulated Intestinal Adaptation Is Complemented and Synergistically Enhanced by Partial Enteral Nutrition in a Neonatal Piglet Model of Short Bowel Syndrome

BACKGROUND

Teduglutide, a glucagon-like peptide-2 (GLP-2) analogue, is available for long-term use by parenteral nutrition (PN)-dependent adults to promote intestinal adaptation but is not approved for use in pediatric patients. The objective of this study was to assess teduglutide-stimulated induced intestinal adaptation, potential synergies with partial enteral nutrition (PEN), and distinct temporal markers of adaptation in a neonatal piglet model of short bowel syndrome (SBS).

MATERIALS AND METHODS

Neonatal piglets (48 hours old; n = 72) underwent an 80% jejunoileal resection and were randomized to 1 of 4 treatment groups, in a 2 × 2 factorial design, with PN or PEN (80% standard PN/20% standard enteral nutrition) and teduglutide (0.1 mg/kg/d) or control. Piglets received nutrient infusions for 4 hours, 48 hours, or 7 days.

RESULTS

Teduglutide improved ( P < .05) mucosal surface area (villus height: duodenum, jejunum, ileum; crypt depth: ileum, colon; proliferation: duodenum, jejunum, ileum; colon; apoptosis: jejunum, ileum, colon) and acute nutrient processing capacity (glucose: duodenum, jejunum, ileum; glutamine: duodenum, jejunum). These effects were complemented and synergistically enhanced by PEN in both site and timing of action. Structural adaptations preceded functional adaptations, but crypt depth remained a strong indicator of adaptation, regardless of time.

CONCLUSIONS

The combination of teduglutide and PEN enhances intestinal adaptation beyond that of either therapy alone.

Animal models of gastrointestinal and liver diseases. Animal models of infant short bowel syndrome: translational relevance and challenges

Intestinal failure (IF), due to short bowel syndrome (SBS), results from surgical resection of a major portion of the intestine, leading to reduced nutrient absorption and need for parenteral nutrition (PN). The incidence is highest in infants and relates to preterm birth, necrotizing enterocolitis, atresia, gastroschisis, volvulus, and aganglionosis. Patient outcomes have improved, but there is a need to develop new therapies for SBS and to understand intestinal adaptation after different diseases, resection types, and nutritional and pharmacological interventions. Animal studies are needed to carefully evaluate the cellular mechanisms, safety, and translational relevance of new procedures. Distal intestinal resection, without a functioning colon, results in the most severe complications and adaptation may depend on the age at resection (preterm, term, young, adult). Clinically relevant therapies have recently been suggested from studies in preterm and term PN-dependent SBS piglets, with or without a functional colon. Studies in rats and mice have specifically addressed the fundamental physiological processes underlying adaptation at the cellular level, such as regulation of mucosal proliferation, apoptosis, transport, and digestive enzyme expression, and easily allow exogenous or genetic manipulation of growth factors and their receptors (e.g., glucagon-like peptide 2, growth hormone, insulin-like growth factor 1, epidermal growth factor, keratinocyte growth factor). The greater size of rats, and especially young pigs, is an advantage for testing surgical procedures and nutritional interventions (e.g., PN, milk diets, long-/short-chain lipids, pre- and probiotics). Conversely, newborn pigs (preterm or term) and weanling rats provide better insights into the developmental aspects of treatment for SBS in infants owing to their immature intestines. The review shows that a balance among practical, economical, experimental, and ethical constraints will determine the choice of SBS model for each clinical or basic research question.

Dipeptidyl peptidase IV inhibition prevents the formation and promotes the healing of indomethacin-induced intestinal ulcers in rats

BACKGROUNDS AND AIMS

We studied the intestinotrophic hormone glucagon-like peptide-2 (GLP-2) as a possible therapy for non-steroidal anti-inflammatory drug (NSAID)-induced intestinal ulcers. Luminal nutrients release endogenous GLP-2 from enteroendocrine L cells. Since GLP-2 is degraded by dipeptidyl peptidase IV (DPPIV), we hypothesized that DPPIV inhibition combined with luminal administration of nutrients potentiates the effects of endogenous GLP-2 on intestinal injury.

METHODS

Intestinal injury was induced by indomethacin (10 mg/kg, sc) in fed rats. The long-acting DPPIV inhibitor K579 was given intragastrically (ig) or intraperitoneally (ip) before or after indomethacin treatment. L-Alanine (L-Ala) and inosine 5'-monophosphate (IMP) were co-administered ig after the treatment.

RESULTS

Indomethacin treatment induced intestinal ulcers that gradually healed after treatment. Pretreatment with ig or ip K579 given at 1 mg/kg reduced total ulcer length, whereas K579 at 3 mg/kg had no effect. Exogenous GLP-2 also reduced intestinal ulcers. The preventive effect of K579 was dose-dependently inhibited by a GLP-2 receptor antagonist. Daily treatment with K579 (1 mg/kg), GLP-2, or L-Ala + IMP after indomethacin treatment reduced total ulcer length. Co-administration (ig) of K579 and L-Ala + IMP further accelerated intestinal ulcer healing.

CONCLUSION

DPPIV inhibition and exogenous GLP-2 prevented the formation and promoted the healing of indomethacin-induced intestinal ulcers, although high-dose DPPIV inhibition reversed the preventive effect. Umami receptor agonists also enhanced the healing effects of the DPPIV inhibitor. The combination of DPPIV inhibition and luminal nutrient-induced GLP-2 release may be a useful therapeutic tool for the treatment of NSAIDs-induced intestinal ulcers.

Glucagon-like peptide 2 treatment may improve intestinal adaptation during weaning

Transition from sow's milk to solid feed is associated with intestinal atrophy and diarrhea. We hypothesized that the intestinotrophic hormone glucagon-like peptide 2 (GLP-2) would induce a dose- and health status-dependent effect on gut adaptation. In Exp. 1, weaned pigs (average BW at weaning 4.98 ± 0.18 kg) were kept in a high-sanitary environment and injected with saline or short-acting GLP-2 (80 μg/(kg BW·12 h); n = 8). Under these conditions, there was no diarrhea and GLP-2 did not improve gastrointestinal structure or function. In Exp. 2, weaned pigs (average BW at weaning 6.68 ± 0.27 kg) were kept in a low-sanitary environment, leading to weaning diarrhea, and injected with saline or short-acting GLP-2 (200 µg/(kg BW·12 h); n = 11). Treatment with GLP-2 increased goblet cell density (P < 0.05) and reduced short chain fatty acid concentration in the colon (P < 0.01) but had limited effects on diarrhea. In Exp. 3, weaned pigs (average BW at weaning 6.90 ± 0.32 kg) were kept in a low-sanitary environment and injected with saline or a long-acting acylated GLP-2 analogue (25 µg/(kg BW·12 h); n = 8). In this experiment, GLP-2 increased intestinal weight (+22%; P < 0.01) and activity of brush border enzymes (+50-100%; P < 0.05). Circulating GLP-2 levels were in the pharmacological range in Exp. 3 (constant levels >20,000 pmol/L) and Exp. 2 (increases to 20,000 pmol/L for a few hours each day) while they were in the supraphysiological range in Exp. 1 (50-200 pmol/L). In conclusion, GLP-2 may improve gut structure and function in weanling pigs. However, the effects may be significant only under conditions of diarrhea and if GLP-2 exposure time is extended using long-acting analogues.

Glutamate prevents intestinal atrophy via luminal nutrient sensing in a mouse model of total parenteral nutrition

Small intestine luminal nutrient sensing may be crucial for modulating physiological functions. However, its mechanism of action is incompletely understood. We used a model of enteral nutrient deprivation, or total parenteral nutrition (TPN), resulting in intestinal mucosal atrophy and decreased epithelial barrier function (EBF). We examined how a single amino acid, glutamate (GLM), modulates intestinal epithelial cell (IEC) growth and EBF. Controls were chow-fed mice, T1 receptor-3 (T1R3)-knockout (KO) mice, and treatment with the metabotropic glutamate receptor (mGluR)-5 antagonist MTEP. TPN significantly changed the amount of T1Rs, GLM receptors, and transporters, and GLM prevented these changes. GLM significantly prevented TPN-associated intestinal atrophy (2.5-fold increase in IEC proliferation) and was dependent on up-regulation of the protein kinase pAkt, but independent of T1R3 and mGluR5 signaling. GLM led to a loss of EBF with TPN (60% increase in FITC-dextran permeability, 40% decline in transepithelial resistance); via T1R3, it protected EBF, whereas mGluR5 was associated with EBF loss. GLM led to a decline in circulating glucagon-like peptide 2 (GLP-2) during TPN. The decline was regulated by T1R3 and mGluR5, suggesting a novel negative regulator pathway for IEC proliferation not previously described. Loss of luminal nutrients with TPN administration may widely affect intestinal taste sensing. GLM has previously unrecognized actions on IEC growth and EBF. Restoring luminal sensing via GLM could be a strategy for patients on TPN.

Physiology and pharmacology of the enteroendocrine hormone glucagon-like peptide-2

Glucagon-like peptide-2 (GLP-2) is a 33-amino-acid proglucagon-derived peptide secreted from enteroendocrine L cells. GLP-2 circulates at low basal levels in the fasting period, and plasma levels rise rapidly after food ingestion. Renal clearance and enzymatic inactivation control the elimination of bioactive GLP-2. GLP-2 increases mesenteric blood flow and activates proabsorptive pathways in the gut, facilitating nutrient absorption. GLP-2 also enhances gut barrier function and induces proliferative and cytoprotective pathways in the small bowel. The actions of GLP-2 are transduced via a single G protein-coupled receptor (GLP-2R), expressed predominantly within the gastrointestinal tract. Disruption of GLP-2R signaling increases susceptibility to gut injury and impairs the adaptive mucosal response to refeeding. Sustained augmentation of GLP-2R signaling reduces the requirement for parenteral nutrition in human subjects with short-bowel syndrome. Hence GLP-2 integrates nutrient-derived signals to optimize mucosal integrity and energy absorption.

Review article: a comparison of glucagon-like peptides 1 and 2

BACKGROUND

Recent advancements in understanding the roles and functions of glucagon-like peptide 1 (GLP-1) and 2 (GLP-2) have provided a basis for targeting these peptides in therapeutic strategies.

AIM

To summarise the preclinical and clinical research supporting the discovery of new therapeutic molecules targeting GLP-1 and GLP-2.

METHODS

This review is based on a comprehensive PubMed search, representing literature published during the past 30 years related to GLP-1 and GLP-2.

RESULTS

Although produced and secreted together primarily from L cells of the intestine in response to ingestion of nutrients, GLP-1 and GLP-2 exhibit distinctive biological functions that are governed by the expression of their respective receptors, GLP-1R and GLP-2R. Through widespread expression in the pancreas, intestine, nervous tissue, et cetera, GLP-1Rs facilitates an incretin effect along with effects on appetite and satiety. GLP-1 analogues resistant to degradation by dipeptidyl peptidase-IV and inhibitors of dipeptidyl peptidase-IV have been developed to aid treatment of diabetes and obesity. The GLP-2R is expressed almost exclusively in the stomach and bowel. The most apparent role for GLP-2 is its promotion of growth and function of intestinal mucosa, which has been targeted for therapies that promote repair and adaptive growth. These are used as treatments for intestinal failure and related conditions.

CONCLUSIONS

Our growing understanding of the biology and function of GLP-1, GLP-2 and corresponding receptors has fostered further discovery of fundamental biological function as well as new categories of potent therapeutic medicines.

Enteroendocrine cells in terminal ileal Crohn's disease

BACKGROUND AND AIMS

Enteroendocrine cells sense gut luminal contents, and orchestrate digestive physiology whilst contributing to mucosal homeostasis and innate immunity. The terminal ileum is the key site of EEC expression but detailed assessment of their subtypes, lineage transcription factors and expression products has not been undertaken in terminal ileal Crohn's disease. Recent Crohn's disease gene wide association studies have linked the neuroendocrine transcription factor Phox2b; while autoantibodies to an enteroendocrine protein, ubiquitination protein 4a, have been identified as a disease behaviour biomarker.

METHODS

Terminal ileal tissue from small or large bowel Crohn's disease and normal controls was analysed for enteroendocrine marker expression by immunohistochemistry and quantitative polymerase chain reaction. Inflammation was graded by endoscopic, clinical, histological and biochemical scoring.

RESULTS

In small bowel disease, glucagon-like peptide 1 and chromogranin A cells were increased 2.5-fold (p=0.049) and 2-fold (p=0.031) respectively. Polypeptide YY cells were unchanged. Ileal enteroendocrine cell expression was unaffected in the presence of Crohn's colitis. Phox2b was co-localised to enteroendocrine cells and showed a 1.5-fold increase in ileal disease. Significant mRNA increases were noted for chromogranin A (3.3-fold; p=0.009), glucagon-like peptide 1 (3.1-fold; p=0.007) and ubiquitination protein 4a (2.2-fold; p=0.02). Neurogenin 3, an enteroendocrine transcription factor showed ~2 fold-upregulation (p=0.048).

CONCLUSIONS

Enhanced enteroendocrine cell activity is present in small bowel disease, and observed in restricted cell lineages. This may impact on the epithelial immune response, cellular homeostasis and nutrient handling and influence appetite via increased satiety signalling in the gut-brain axis.

Enteral nutrients potentiate glucagon-like peptide-2 action and reduce dependence on parenteral nutrition in a rat model of human intestinal failure

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent, proglucagon-derived gut hormone that shows promise for the treatment of short bowel syndrome (SBS). Our objective was to investigate how combination GLP-2 + enteral nutrients (EN) affects intestinal adaption in a rat model that mimics severe human SBS and requires parenteral nutrition (PN). Male Sprague-Dawley rats were assigned to one of five groups and maintained with PN for 18 days: total parenteral nutrition (TPN) alone, TPN + GLP-2 (100 μg·kg(-1)·day(-1)), PN + EN + GLP-2(7 days), PN + EN + GLP-2(18 days), and a nonsurgical oral reference group. Animals underwent massive distal bowel resection followed by jejunocolic anastomosis and placement of jugular catheters. Starting on postoperative day 4, rats in the EN groups were allowed ad libitum access to EN. Groups provided PN + EN + GLP-2 had their rate of PN reduced by 0.25 ml/day starting on postoperative day 6. Groups provided PN + EN + GLP-2 demonstrated significantly greater body weight gain with similar energy intake and a safe 80% reduction in PN compared with TPN ± GLP-2. Groups provided PN + EN + GLP-2 for 7 or 18 days showed similar body weight gain, residual jejunal length, and digestive capacity. Groups provided PN + EN + GLP-2 showed increased jejunal GLP-2 receptor (GLP-2R), insulin-like growth factor-I (IGF-I), and IGF-binding protein-5 (IGFBP-5) expression. Treatment with TPN + GLP-2 demonstrated increased jejunal expression of epidermal growth factor. Cessation of GLP-2 after 7 days with continued EN sustained the majority of intestinal adaption and significantly increased expression of colonic proglucagon compared with PN + EN + GLP-2 for 18 days, and increased plasma GLP-2 concentrations compared with TPN alone. In summary, EN potentiate the intestinotrophic actions of GLP-2 by improving body weight gain allowing for a safe 80% reduction in PN with increased jejunal expression of GLP-2R, IGF-I, and IGFBP-5 following distal bowel resection in the rat.

GLP-2 enhances barrier formation and attenuates TNFα-induced changes in a Caco-2 cell model of the intestinal barrier

INTRODUCTION

Tight junctions are intercellular permeability seals that regulate paracellular transport across epithelia. Tight junction function, expression and localisation of constituent proteins are significantly altered by cytokines such as TNFα. Glucagon-like peptide-2 (GLP-2) is an intestinotrophic enteroendocrine peptide. It is not known whether GLP-2 regulates the barrier or tight junctions. The aim of this study was to investigate whether GLP-2 has an effect on tight junction function or protein expression, alone or in response to TNFα exposure.

METHODS

Caco-2 cells were grown to confluence on filters in the presence or absence of GLP-2. The time course of transepithelial electrical resistance developing across the monolayer was measured; tight junction protein expression was quantified by immunoblotting. At day 20, TNFα in the presence or absence of GLP-2 was added. Changes in TEER and tight junction proteins expression were quantified. Both TNFα and GLP-2 were added on the basolateral side.

RESULTS

GLP-2 exposed Caco-2 cell monolayers showed a significant increase in transepithelial electrical resistance compared to that in untreated control cells. At the same time, expression of the tight junction proteins occludin and zona occludens-1 (ZO-1) was increased at day 17 post-seeding (1.6-fold; p=0.037 and 4.7 fold; p=0.039 respectively). Subsequent TNFα exposure induced a significant 9.3-fold (p<0.001) decrease in transepithelial electrical resistance and a corresponding reduction in the expression of ZO-1 (5.3 fold; p<0.01). However, the TNFα-induced reduction in transepithelial electrical resistance in GLP-2-exposed cells was highly attenuated to 1.8-fold (p<0.01). No change in tight junction protein expression was noted in GLP-2 exposed cells after cytokine exposure.

CONCLUSION

GLP-2 enhances formation of the epithelial barrier and its constituent proteins in Caco-2 cells, and diminishes the effects of TNFα. If these effects are replicated in vivo the GLP-2 receptor may present a therapeutic target in intestinal inflammation.

Dipeptidyl peptidase-4 expression is reduced in Crohn's disease

BACKGROUND

Dipeptidyl peptidase 4 (DP4) is a serine protease that preferentially cleaves N-terminal dipeptides from polypeptides containing proline or alanine as the penultimate amino acid. DP4 inactivates glucagon like peptide-2 (GLP-2), a trophic peptide with cytoprotective and reparative properties in the injured gut; therefore DP4 potentially inhibits repair processes. DP4 also modulates the activity of GLP-1 and polypeptide YY (PYY) which regulate appetite and motility. No data are yet available on the tissue and plasma expression of DP4 in inflammatory bowel disease (IBD).

METHODS

Tissue and plasma were studied from active CD and healthy controls for DP4 quantification. Experiments were also carried out in a reductionist Caco-2 cell line model of intestinal inflammation with TNFα incubation. DP4 expression was studied by tissue Western blotting and plasma enzymelinked immunosorbent assay (ELISA), in addition to quantitative polymerase chain reaction (qPCR).

RESULTS

There was a ~2.7-fold decrease in DP4 protein in CD tissue (p=0.05). Plasma DP4 in CD was also significantly lower than the control group. A negative correlation between plasma DP4 levels and inflammatory activity as measured by C-reactive protein was observed. In Caco-2 cells an ~18-fold increase (p<0.0001) in DP4 protein expression was seen after incubation with TNFα at a concentration of 25 ng/μl for 48 hours paralleled by a 2-fold increase in DP4 mRNA.

DISCUSSION

DP4 is reduced in tissue and plasma in active Crohn's disease. This is unlikely to represent simple downregulation induced by inflammation since the key proinflammatory cytokine strongly upregulated DP4 expression in Caco-2 cells. Clearly a more complex situation exists in vivo. We propose that reduced DP4 activity limits the cleavage of regulatory peptides, for example potentiating the trophic signal from GLP-2. Pharmacological DP4 inhibition may present an additional therapeutic target in IBD.

Intestinal adaptation is stimulated by partial enteral nutrition supplemented with the prebiotic short-chain fructooligosaccharide in a neonatal intestinal failure piglet model

BACKGROUND

Butyrate has been shown to stimulate intestinal adaptation when added to parenteral nutrition (PN) following small bowel resection but is not available in current PN formulations. The authors hypothesized that pre- and probiotic administration may be a clinically feasible method to administer butyrate and stimulate intestinal adaptation.

METHODS AND MATERIALS

Neonatal piglets (48 hours old, n = 87) underwent placement of a jugular catheter and an 80% jejunoileal resection and were randomized to one of the following treatment groups: control (20% standard enteral nutrition/80% standard PN), control plus prebiotic (10 g/L short-chain fructooligosaccharides [scFOS]), control plus probiotic (1 × 10(9) CFU Lactobacillus rhamnosus GG [LGG]), or control plus synbiotic (scFOS + LGG). Animals received infusions for 24 hours, 3 days, or 7 days, and markers of intestinal adaptation were assessed.

RESULTS

Prebiotic treatment increased ileal mucosa weight compared with all other treatments (P = .017) and ileal protein compared with control (P = .049), regardless of day. Ileal villus length increased in the prebiotic and synbiotic group (P = .011), regardless of day, specifically due to an increase in epithelial proliferation (P = .003). In the 7-day prebiotic group, peptide transport was upregulated in the jejunum (P = .026), whereas glutamine transport was increased in both the jejunum and colon (P = .001 and .003, respectively).

CONCLUSIONS

Prebiotic and/or synbiotic supplementation resulted in enhanced structure and function throughout the residual intestine. Identification of a synergistic prebiotic and probiotic combination may enhance the promising results obtained with prebiotic treatment alone.

Exogenous GLP-2 and IGF-I induce a differential intestinal response in IGF binding protein-3 and -5 double knockout mice

Glucagon-like peptide-2 (GLP-2) action is dependent on intestinal expression of IGF-I, and IGF-I action is modulated by IGF binding proteins (IGFBP). Our objective was to evaluate whether the intestinal response to GLP-2 or IGF-I is dependent on expression of IGFBP-3 and -5. Male, adult mice in six treatment groups, three wild-type (WT) and three double IGFBP-3/-5 knockout (KO), received twice daily intraperitoneal injections of GLP-2 (0.5 μg/g body wt), IGF-I (4 μg/g body wt), or PBS (vehicle) for 7 days. IGFBP-3/-5 KO mice showed a phenotype of lower plasma IGF-I concentration, but greater body weight and relative mass of visceral organs, compared with WT mice (P < 0.001). WT mice showed jejunal growth with either IGF-I or GLP-2 treatment. In KO mice, IGF-I did not stimulate jejunal growth, crypt mitosis, sucrase activity, and IGF-I receptor (IGF-IR) expression, suggesting that the intestinotrophic actions of IGF-I are dependent on expression of IGFBP-3 and -5. In KO mice, GLP-2 induced significant increases in jejunal mucosal cellularity, crypt mitosis, villus height, and crypt depth that was associated with increased expression of the ErbB ligand epiregulin and decreased expression of IGF-I and IGF-IR. This suggests that in KO mice, GLP-2 action in jejunal mucosa is independent of the IGF-I system and linked with ErbB ligands. In summary, the intestinotrophic actions of IGF-I, but not GLP-2, in mucosa are dependent on IGFBP-3 and -5. These findings support the role of multiple downstream mediators for the mucosal growth induced by GLP-2.

Enteroendocrine cells: neglected players in gastrointestinal disorders?

Enteroendocrine cells (EEC) form the basis of the largest endocrine system in the body. They secrete multiple regulatory molecules which control physiological and homeostatic functions, particularly postprandial secretion and motility. Their key purpose is to act as sensors of luminal contents, either in a classical endocrine fashion, or by a paracrine effect on proximate cells, notably vagal afferent fibres. They also play a pivotal role in the control of food intake, and emerging data add roles in mucosal immunity and repair. We propose that EEC are fundamental in several gastrointestinal pathologies, notably Post-infectious Irritable Bowel Syndrome, infectious enteritis, and possibly inflammatory bowel disease. Further work is needed to fully illustrate the importance, detailed biology and therapeutic potential of these frequently overlooked cells.

Sustained glucagon-like peptide-2 infusion is required for intestinal adaptation, and cessation reverses increased cellularity in rats with intestinal failure

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent, proglucagon-derived hormone that is a proposed treatment for human short bowel syndrome (SBS). The objective was to determine how the timing, duration, and cessation of GLP-2 administration affect intestinal adaptation and enterocyte kinetics in a rat model of human SBS that results in intestinal failure requiring total parenteral nutrition (TPN). Rats underwent 60% jejunoileal resection plus cecectomy and jugular vein cannulation and were maintained exclusively with TPN for 18 days in these treatments: TPN control (no GLP-2); sustained GLP-2 (1-18 days); early GLP-2 (1-7 days, killed at 7 or 18 days); and delayed GLP-2 (12-18 days). Body weight gain was similar across groups, and plasma bioactive GLP-2 was significantly increased with coinfusion of GLP-2 (100 μg·kg⁻¹·day⁻¹) with TPN. GLP-2-treated rats showed significant increases in duodenum and jejunum mucosal dry mass, protein, DNA, and sucrase activity compared with TPN control. The increased jejunum cellularity reflected significantly decreased apoptosis and increased crypt mitosis and crypt fission due to GLP-2. When GLP-2 infusion stopped at 7 days, these effects were reversed at 18 days. Sustained GLP-2 infusion significantly increased duodenum length and decreased 18-day mortality to 0% from 37.5% deaths in TPN control (P = 0.08). Colon proglucagon expression quantified by real-time RT-qPCR was increased in TPN controls and attenuated by GLP-2 infusion; jejunal expression of the GLP-2 receptor did not differ among groups. In summary, early, sustained GLP-2 infusion reduces mortality, induces crypt fission, and is required for intestinal adaptation, whereas cessation of GLP-2 reverses gains in mucosal cellularity in a rat model of intestinal failure.

The effect of glucagon-like peptide 2 injection on performance, small intestinal morphology, and nutrient transporter expression of stressed broiler chickens

An experiment was conducted to determine the effect of injecting glucagon-like peptide 2 (GLP-2) on the small intestinal weight, morphology, and nutrient transporter expression in pharmacologically stressed broiler chickens. A total of 144 seven-day-old birds were fed either a basal diet (CTRL) or a basal diet plus 30 mg of corticosterone (CORT)/kg of diet for a total of 14 d. Half of the birds from each group were injected daily with GLP-2 (6.7 nmol/kg of BW) or saline for 14 d. The average final BW, ADG, ADFI, and the ratio of feed intake to weight gain (F:G) was recorded over 21 d for the 4 groups of 36 birds, namely CTRL + saline, CTRL + GLP-2, CORT + saline, and CORT + GLP-2. In addition, the absolute and relative small intestinal weight, villus height (VH), and crypt depth (CD) of the duodenum and jejunum, as well as the abundance of sodium and glucose co-transporter 1 (SGLT-1), vitamin D-dependent calcium-binding protein-28,000 molecular weight (CaBP-D28k), and peptide transporter 1 (PepT-1) mRNA in the duodenum and of liver fatty acid-binding protein (L-FABP) mRNA in the jejunum. The total DNA, RNA, and protein content in small intestinal mucosa were also determined. The results showed that CORT administration significantly lowered average final BW, ADG, ADFI, absolute small intestinal weight, VH, and CD of duodenum and jejunum (P < 0.05) while increasing the relative small intestinal weight, F:G, relative abundance of SGLT-1, CaBP-D28k, PepT-1, and L-FABP mRNA (P < 0.05). Glucagon-like peptide 2 injection increased the average final BW, ADG, VH, and CD in duodenum and jejunum and relative abundance of SGLT-1, CaBP-28k, PepT1, and PepT1 mRNA of broiler chickens, respectively (P < 0.05), and decreased F:G (P < 0.05). In chickens fed basal diet plus CORT, injecting GLP-2 decreased F:G (P < 0.05); increased VH and CD of duodenum and CD of jejunum; and increased relative abundance of SGLT-1, CaBP-D28k, PepT-1, and L-FABP mRNA, RNA, and total protein content in small intestine compared with the injection of saline (P < 0.05). In birds fed the basal diet, GLP-2 injection decreased F:G (P < 0.05) and increased final BW, ADG, small bowel weight, CD of jejunum, and relative abundance of CaBP-D28k and PepT-1 mRNA compared with injecting saline (P < 0.05). In conclusion, GLP-2 injection reversed the negative effect of stress on the weight and morphology and the absorptive function of small bowel of broiler chickens. Glucagon-like peptide 2 injection also had a positive effect on the growth performance of healthy broiler chickens.

The assessment, and glucagon-like peptide-2 modulation, of intestinal absorption and function

The treatment of patients with short bowel syndrome is hampered by a lack of treatment and measurement methods. This article reviews our evolving understanding of the role of glucagon-like peptide 2 (GLP-2) in controlling the adaptive process. The ability of the remnant intestine to produce GLP-2 appears to be predictive of the adaptive process; exogenous GLP-2 may be a therapy to augment adaptation. Strategies for monitoring patients, including conventional means, such as anthropomorphic measurements, plasma levels of specific nutrients, and vitamins and radiological contrast studies are reviewed. Investigational methods, such as nutrient balance studies, plasma citrulline levels, and the absorption of inert sugars (3-0 methyl glucose, mannitol, and lactulose) are discussed with the evidence to support their use.

Whey protein potentiates the intestinotrophic action of glucagon-like peptide-2 in parenterally fed rats

Glucagon-like peptide-2 (GLP-2) is a nutrient-regulated intestinotrophic hormone derived from proglucagon in the distal intestine. Enteral nutrients (EN) potentiate the action of GLP-2 to reverse parenteral nutrition (PN)-induced mucosal hypoplasia. The objective was to determine what enteral protein component, casein, soy, or whey protein, potentiates the intestinal growth response to GLP-2 in rats with PN-induced mucosal hypoplasia. Rats received PN and continuous intravenous infusion of GLP-2 (100 microg/kg/day) for 7 days. Six EN groups received PN+GLP-2 for days 1-3 and partial PN+GLP-2 plus EN for days 4-7. EN was provided by ad libitum intake of a semielemental liquid diet with different protein sources: casein, hydrolyzed soy, whey protein concentrate (WPC), and hydrolyzed WPC+casein. Controls received PN+GLP-2 alone. EN induced significantly greater jejunal sucrase activity and gain of body weight, and improved feed efficiency compared with PN+GLP-2 alone. EN induced greater ileal proglucagon expression, increased plasma concentration of bioactive GLP-2 by 35%, and reduced plasma dipeptidyl peptidase IV (DPP-IV) activity compared with PN+GLP-2 alone, P < 0.05. However, only whey protein, and not casein or soy, potentiated the ability of GLP-2 to reverse PN-induced mucosal hypoplasia and further increase ileal villus height, crypt depth, and mucosa cellularity compared with PN+GLP-2 alone, P < 0.05. The ability of whey protein to induce greater mucosal surface area was associated with decreased DPP-IV activity in ileum and colon compared with casein, soy, or PN+GLP-2 alone, P < 0.05. In conclusion, whey protein potentiates the action of GLP-2 to reverse PN-induced mucosal hypoplasia in association with decreased intestinal DPP-IV activity.

Nutritional effects of the serial transverse enteroplasty procedure in experimental short bowel syndrome

BACKGROUND/PURPOSE

The serial transverse enteroplasty (STEP) procedure appears beneficial clinically, but the mechanism(s) underlying these effects remains unclear. The present study evaluated the nutritional, hormonal, and morphologic effects of the STEP procedure in a rodent model of short bowel syndrome.

METHODS

With institutional animal care ethics approval, Sprague-Dawley rats underwent an 80% distal bowel resection, anastomosing the 30 cm remnant of jejunum to the ascending colon; at day 14, animals were randomly assigned to control or a STEP procedure (n = 8/group). Animals were pair-fed with normal chow; after a further 3 weeks, intestinal transit, hormonal and metabolic balance studies were done, and intestinal tissues were taken for analysis.

RESULTS

The STEP group had increased weight gain (resected: -0.34% +/- 2.9% vs STEP: 2.5% +/- 1.5%), increased bowel length (34.1 +/- 1.5 vs 36.9 +/- 2.2 cm), increased jejunal villus height (555 +/- 59 vs 635 +/- 65 microm), decreased rates of crypt cell apoptosis, increased expression of mRNA for the GLP-2 receptor, and increased postprandial production of glucagon-like peptide 2 (45 +/- 14 vs 65 +/- 12 pmol/L) (P < .05 by Student t test). There were no differences in intestinal transit; absorption of total calories, protein, fat, or carbohydrate; crypt cell proliferation rates; or the expression of intestinal transporter proteins (SGLT-1, GLUT-2, and GLUT-5).

CONCLUSIONS

The STEP procedure improves weight gain and augments gross and microscopic intestinal morphology in severe experimental short bowel syndrome. Postprandial GLP-2 levels are increased, as is the expression of the GLP-2 receptor; these mechanisms may contribute to these metabolic effects and may be useful in guiding the use of the STEP procedure clinically.

Colonic GLP-2 is not sufficient to promote jejunal adaptation in a PN-dependent rat model of human short bowel syndrome

BACKGROUND

Bowel resection may lead to short bowel syndrome (SBS), which often requires parenteral nutrition (PN) due to inadequate intestinal adaptation. The objective of this study was to determine the time course of adaptation and proglucagon system responses after bowel resection in a PN-dependent rat model of SBS.

METHODS

Rats underwent jugular catheter placement and a 60% jejunoileal resection + cecectomy with jejunoileal anastomosis or transection control surgery. Rats were maintained exclusively with PN and killed at 4 hours to 12 days. A nonsurgical group served as baseline. Bowel growth and digestive capacity were assessed by mucosal mass, protein, DNA, histology, and sucrase activity. Plasma insulin-like growth factor I (IGF-I) and bioactive glucagon-like peptide 2 (GLP-2) were measured by radioimmunoassay.

RESULTS

Jejunum cellularity changed significantly over time with resection but not transection, peaking at days 3-4 and declining by day 12. Jejunum sucrase-specific activity decreased significantly with time after resection and transection. Colon crypt depth increased over time with resection but not transection, peaking at days 7-12. Plasma bioactive GLP-2 and colon proglucagon levels peaked from days 4-7 after resection and then approached baseline. Plasma IGF-I increased with resection through day 12. Jejunum and colon GLP-2 receptor RNAs peaked by day 1 and then declined below baseline.

CONCLUSIONS

After bowel resection resulting in SBS in the rat, peak proglucagon, plasma GLP-2, and GLP-2 receptor levels are insufficient to promote jejunal adaptation. The colon adapts with resection, expresses proglucagon, and should be preserved when possible in massive intestinal resection.

Enteral nutrients potentiate the intestinotrophic action of glucagon-like peptide-2 in association with increased insulin-like growth factor-I responses in rats

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent, intestinotrophic hormone derived from posttranslational processing of proglucagon in the distal bowel. GLP-2 is thought to act through indirect mediators, such as IGF-I. We investigated whether intestinal expression of GLP-2 and IGF-I system components are increased with the mucosal growth induced by enteral nutrient (EN) and/or a low dose of GLP-2 in parenterally fed rats. Rats were randomized to four treatment groups using a 2 x 2 design and maintained with parenteral nutrition (PN) for 7 days: PN alone, EN, GLP-2, and EN+GLP-2; n = 7-9. The two main treatment effects are +/-GLP-2 (100 microg.kg body wt(-1).day(-1)) and +/-EN (43% of energy needs, days 4-6). Combination treatment with EN+GLP-2 induced synergistic intestinal growth in ileum, resulting in greater mucosal cellularity, sucrase segmental activity, and gain of body weight (ENxGLP-2, P < 0.04). In addition, EN+GLP-2 induced a significant 28% increase in plasma concentration of bioactive GLP-2, a significant 102% increase in ileal proglucagon mRNA with no change in ileal dipeptidyl peptidase-IV (DPP-IV) specific activity, and significantly reduced plasma DPP-IV activity compared with GLP-2. This indicates that EN potentiates the intestinotrophic action of GLP-2. Proliferation of enterocytes due to GLP-2 infusion was associated with greater expression of ileal proglucagon, GLP-2 receptor, IGF-I, IGF binding protein-3 mRNAs, and greater IGF-I peptide concentration in ileum (P < 0.032). Ileal IGF-I mRNA was positively correlated with expression of proglucagon, GLP-2R, and IGFBP-5 mRNAs (R2 = 0.43-0.56, P < 0.0001). Our findings support the hypothesis that IGF-I is one of the downstream mediators of GLP-2 action in a physiological model of intestinal growth.

The effects of variations in dose and method of administration on glucagon like peptide-2 activity in the rat

Glucagon-like peptide-2 (GLP-2) is a potent, intestinal-specific trophic hormone. However, the relationship between the dose and timing of GLP-2 administration and these trophic effects is not clear. We investigated the effects of variations in the dose and timing of GLP-2 administration on its intestinal trophic activity. A rodent model of total parenteral nutrition (TPN) mucosal atrophy was used, examining intestinal morphology in the adult male rat after 5 days. Groups were: controls, maintained with TPN alone and GLP-2 treated groups (high dose; 240 microg/kg/day, low dose; 24 microg/kg/day) given by continuous or intermittent (over 1 h, twice daily) intravenous infusion. Body weight and total small bowel length were significantly increased in the high dose, continuous infusion group. Both high dose infusion methods increased total small bowel weight, villus height, crypt depth, and total mucosal surface area. Both high dose infusion and low dose intermittent infusion routes increased crypt cell proliferation (P<0.05 for all comparisons). Both high dose routes gave nearly equivalent exposures; low dose continuous infusion gave higher exposure but intermittent low dose infusion resulted in an increase in crypt proliferation; neither low dose method resulted in morphologic changes. There were no differences in transporter protein expression or apoptosis rates. High dose continuous infusion appears to maximally induce intestinal growth, and also increases weight gain, while high dose GLP-2 intermittent infusion results in similar morphologic effects. A threshold level for the induction of proliferative and morphologic effects was seen in the low dose groups. These observations may be relevant for planning therapeutic trials.

Exogenous glucagon-like peptide-2 (GLP-2) augments GLP-2 receptor mRNA and maintains proglucagon mRNA levels in resected rats

BACKGROUND

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent proglucagon-derived hormone that stimulates intestinal adaptive growth. Our aim was to determine whether exogenous GLP-2 increases resection-induced adaptation without diminishing endogenous proglucagon and GLP-2 receptor expression.

METHODS

Rats underwent transection or 70% jejunoileal resection +/- GLP-2 infusion (100 microg/kg body weight/d) and were fed a semipurified diet with continuous infusion of GLP-2 or saline by means of jugular catheter. After 7 days, body weight, mucosal cellularity (dry mass, protein and DNA), crypt-villus height, and crypt cell proliferation (by bromodeoxyuridine staining) were determined. Plasma bioactive GLP-2 (by radioimmunoassay), proglucagon and GLP-2 receptor mRNA expression (by Northern blot and real-time reverse transcriptase quantitative polymerase chain reaction) were measured. GLP-2 receptor was colocalized to neuroendocrine markers by immunohistochemistry.

RESULTS

Low-dose exogenous GLP-2 increased mucosal cellularity and crypt-villus height in the duodenum, jejunum, and ileum; enterocyte proliferation in the jejunal crypt; and duodenal and jejunal sucrase segmental activity. Plasma bioactive GLP-2 concentration increased 70% upon resection, with an additional 54% increase upon GLP-2 infusion in resected rats (P < .05). Ileal proglucagon mRNA expression increased with resection, and exogenous ileum GLP-2 failed to blunt this response. Exogenous GLP-2 increased ileum GLP-2 receptor expression 3-fold in resected animals and was colocalized to vasoactive intestinal peptide-positive and endothelial nitric oxide synthase-expressing enteric neurons and serotonin-containing enteroendocrine cells in the jejunum and ileum of resected rats.

CONCLUSIONS

Exogenous GLP-2 augments adaptive growth and digestive capacity of the residual small intestine in a rat model of mid-small bowel resection by increasing plasma GLP-2 concentrations and GLP-2 receptor expression without diminishing endogenous proglucagon expression.

Insulin-like growth factor I and glucagon-like peptide-2 responses to fasting followed by controlled or ad libitum refeeding in rats

Luminal nutrients stimulate structural and functional regeneration in the intestine through mechanisms thought to involve insulin-like growth factor I (IGF-I) and glucagon-like peptide-2 (GLP-2). We investigated the relationship between IGF-I and GLP-2 responses and mucosal growth in rats fasted for 48 h and then refed for 2 or 4 days by continuous intravenous or intragastric infusion or ad libitum feeding. Fasting induced significant decreases in body weight, plasma concentrations of IGF-I and bioactive GLP-2, jejunal mucosal cellularity (mass, protein, DNA, and villus height), IGF-I mRNA, and ileal proglucagon mRNA. Plasma IGF-I concentration was restored to fed levels with 2 days of ad libitum refeeding but not with 4 days of intravenous or intragastric refeeding. Administration of an inhibitor of endogenous GLP-2 (rat GLP-2 3-33) during ad libitum refeeding partially attenuated mucosal growth and prevented the increase in plasma IGF-I to fed levels; however, plasma GLP-2 and jejunal IGF-I mRNA were restored to fed levels. Intragastric refeeding restored intestinal cellularity and functional capacity (sucrase activity and sodium-glucose transporter-1 expression) to fed levels, whereas intravenous refeeding had no effect. Intestinal regeneration after 4 days of intragastric or 2 days of ad libitum refeeding was positively associated with increases in plasma concentrations of GLP-2 and jejunal IGF-I mRNA. These data suggest that luminal nutrients stimulate intestinal growth, in part, by increased expression of both GLP-2 and IGF-I.

Cell-specific effects of insulin receptor substrate-1 deficiency on normal and IGF-I-mediated colon growth

Insulin-like growth factor I (IGF-I) potently stimulates intestinal growth. Insulin receptor substrate-1 (IRS-1) mediates proliferative and antiapoptotic actions of IGF-I in cell lines, but its in vivo relevance in intestine is not defined. This study tested the hypothesis that there is cell type-specific dependence on IRS-1 as a mediator of IGF-I action. Length, mass, crypt cell proliferation, and apoptosis were measured in small intestine and colon of IRS-1-null mice and wild-type (WT) littermates and in colon of IRS-1-null or WT mice expressing IGF-I transgenes. Expression of IGF-I receptor and signaling intermediates was examined in intestine of WT and IRS-1-null mice, cultured intestinal epithelial cells, and myofibroblasts. Absolute IRS-1 deficiency reduced mucosal mass in jejunum and colon, but effects were more pronounced in colon. Muscularis mass was decreased in both segments. In IGF-I transgenics, IRS-1 deficiency significantly attenuated IGF-I-stimulated growth of colonic mucosa and abolished antiapoptotic but not mitogenic effects of IGF-I transgene on crypt cells. IGF-I-induced muscularis growth was unaffected by IRS-1 deficiency. In intestinal epithelial cells, IRS-1 was expressed at higher levels than IRS-2 and was preferentially activated by IGF-I. In contrast, IGF-I activated both IRS-1 and IRS-2 in intestinal myofibroblasts and IRS-2 activation was upregulated in IRS-1-null myofibroblasts. We conclude that the intestinal epithelium but not the muscularis requires IRS-1 for normal trophic actions of IGF-I and that IRS-1 is required for antiapoptotic but not mitogenic effects of IGF-I in the intestinal crypts in vivo.