Glucagon-like peptide-2 does not modify the growth or survival of murine or human intestinal tumor cells

A nanoparticle platform for combined mucosal healing and immunomodulation in inflammatory bowel disease treatment

Current treatments for inflammatory bowel disease (IBD) treatment consist of anti-inflammatory products. In this study, we sought to induce the physiological secretion of glucagon-like peptide 2, a peptide with intestinal growth-promoting activity, via nanoparticles while simultaneously providing with immunomodulation by tailoring the nanoparticle surface. To this end, we developed hybrid lipid hyaluronate-KPV conjugated nanoparticles loaded with teduglutide for combination therapy in IBD. The nanocarriers induced (or did not induce) immunosuppression depending on the presence (or absence) of a hyaluronan-KPV functionalization. This strategy holds promise as a nanoparticle platform for combined mucosal healing and immunomodulation in IBD treatment.

Distinct Identity of GLP-1R, GLP-2R, and GIPR Expressing Cells and Signaling Circuits Within the Gastrointestinal Tract

Enteroendocrine cells directly integrate signals of nutrient content within the gut lumen with distant hormonal responses and nutrient disposal via the production and secretion of peptides, including glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide 1 (GLP-1) and glucagon-like peptide 2 (GLP-2). Given their direct and indirect control of post-prandial nutrient uptake and demonstrated translational relevance for the treatment of type 2 diabetes, malabsorption and cardiometabolic disease, there is significant interest in the locally engaged circuits mediating these metabolic effects. Although several specific populations of cells in the intestine have been identified to express endocrine receptors, including intraepithelial lymphocytes (IELs) and αβ and γδ T-cells (Glp1r+) and smooth muscle cells (Glp2r+), the definitive cellular localization and co-expression, particularly in regards to the Gipr remain elusive. Here we review the current state of the literature and evaluate the identity of Glp1r, Glp2r, and Gipr expressing cells within preclinical and clinical models. Further elaboration of our understanding of the initiating G-protein coupled receptor (GPCR) circuits engaged locally within the intestine and how they become altered with high-fat diet feeding can offer insight into the dysregulation observed in obesity and diabetes.

Intestinal Growth in Glucagon Receptor Knockout Mice Is Not Associated With the Formation of AOM/DSS-Induced Tumors

Treatment with exogenous GLP-2 has been shown to accelerate the growth of intestinal adenomas and adenocarcinomas in experimental models of colonic neoplasia, however, the role of endogenous GLP-2 in tumor promotion is less well known. Mice with a global deletion of the glucagon receptor (Gcgr^-/-) display an increase in circulating GLP-1 and GLP-2. Due to the intestinotrophic nature of GLP-2, we hypothesized that Gcgr^-/- mice would be more susceptible to colonic dysplasia in a model of inflammation-induced colonic carcinogenesis. Female Gcgr^-/- mice were first characterized for GLP-2 secretion and in a subsequent study they were given a single injection with the carcinogen azoxymethane (7.5 mg/kg) and treated with dextran sodium sulfate (DSS) (3%) for six days (n=19 and 9). A cohort of animals (n=4) received a colonoscopy 12 days following DSS treatment and all animals were sacrificed after six weeks. Disruption of glucagon receptor signaling led to increased GLP-2 secretion (p<0.0001) and an increased concentration of GLP-2 in the pancreas of Gcgr^-/- mice, coinciding with an increase in small intestinal (p<0.0001) and colonic (p<0.05) weight. Increased villus height was recorded in the duodenum (p<0.001) and crypt depth was increased in the duodenum and jejunum (p<0.05 and p<0.05). Disruption of glucagon receptor signaling did not affect body weight during AOM/DSS treatment, neither did it affect the inflammatory score assessed during colonoscopy or the number of large and small adenomas present at the end of the study period. In conclusion, despite the increased endogenous GLP-2 secretion Gcgr^-/- mice were not more susceptible to AOM/DSS-induced tumors.

Identification of prognosis-associated immune genes and exploration of immune cell infiltration in colorectal cancer

Aim: To identify prognosis-related immune genes (PRIGs) and construct a prognosis model of colorectal cancer (CRC) patients for clinical use. Materials & methods: Expression profiles were obtained from The Cancer Genome Atlas database and identified differentially expressed PRIGs of CRC. Results: A prognostic model was conducted based on nine PRIGs. The risk score, based on prognosis model, was an independent prognostic predictor. Five PRIGs and risk score were significantly associated with the clinical stage of CRC and five immune cells related to the risk score. Conclusion: The risk score was an independent prognostic biomarker for CRC patients. The research excavated immune genes that were associated with survival and that could be potential biomarkers for prognosis and treatment for CRC patients.

Loss of Glp2r signaling activates hepatic stellate cells and exacerbates diet-induced steatohepatitis in mice

A glucagon-like peptide-2 (GLP-2) analog is used in individuals with intestinal failure who are at risk for liver disease, yet the hepatic actions of GLP-2 are not understood. Treatment of high-fat diet-fed (HFD-fed) mice with GLP-2 did not modify the development of hepatosteatosis or hepatic inflammation. In contrast, Glp2r-/- mice exhibited increased hepatic lipid accumulation, deterioration in glucose tolerance, and upregulation of biomarkers of hepatic inflammation. Both mouse and human liver expressed the canonical GLP-2 receptor (GLP-2R), and hepatic Glp2r expression was upregulated in mice with hepatosteatosis. Cell fractionation localized the Glp2r to hepatic stellate cells (HSCs), and markers of HSC activation and fibrosis were increased in livers of Glp2r-/- mice. Moreover, GLP-2 directly modulated gene expression in isolated HSCs ex vivo. Taken together, these findings define an essential role for the GLP-2R in hepatic adaptation to nutrient excess and unveil a gut hormone-HSC axis, linking GLP-2R signaling to control of HSC activation.

The Discovery of GLP-2 and Development of Teduglutide for Short Bowel Syndrome

The proglucagon gene encodes multiple structurally related peptides with overlapping actions promoting the absorption and assimilation of ingested energy. Notably, glucagon has been developed pharmaceutically to treat hypoglycemia, and glucagon-like peptide-1 (GLP-1) receptor agonists are used for the therapy of type 2 diabetes and obesity. Here I describe the discovery of glucagon-like peptide-2 (GLP-2), a 33 amino acid peptide cosecreted together with GLP-1 from gut endocrine cells. GLP-2 was found to exhibit robust intestinal growth-promoting activity, following serendipitous observations that proglucagon-producing tumors induced intestinal growth in mice. Key developments in the pharmaceutical development of GLP-2 included the cloning of the GLP-2 receptor, and the recognition of the importance of dipeptidyl peptidase-4 as a critical determinant of GLP-2 bioactivity. A therapeutic focus on short bowel syndrome, a serious medical disorder with compelling unmet medical need, enabled the pharmaceutical development of a simple GLP-2 analogue, teduglutide, suitable for once daily administration.

Novel peptide inhibitor of dipeptidyl peptidase IV (Tyr-Pro-D-Ala-NH2) with anti-inflammatory activity in the mouse models of colitis

Protease inhibition has become a new possible approach in the inflammatory bowel disease (IBD) therapy. A serine exopeptidase, dipeptidyl peptidase IV (DPP IV) is responsible for inactivation of incretin hormone, glucagon-like peptide 2 (GLP-2), a potent stimulator of intestinal epithelium regeneration and growth. Recently we showed that the novel peptide analog of endomorphin-2, EMDB-1 (Tyr-Pro-D-ClPhe-Phe-NH₂) is a potent blocker of DPP IV and exhibits an anti-inflammatory activity in vivo. The aim of this study was to design, synthesize and characterize the therapeutic activity and mechanism of action of a series of novel EMDB-1 analogs. The inhibitory potential of all peptides was evaluated using the fluorometric screening assay employing Gly-Pro-Aminomethylcoumarin (AMC) to measure DPP IV activity. Consequently, one compound, namely DI-1 was selected and its therapeutic activity evaluated using mouse models of experimental colitis (induced by TNBS and DSS). Macro- and microscopic score, ulcer score, colonic wall thickness as well as myeloperoxidase activity were measured. We showed that DI-1 blocks DPP IV in vitro (IC₅₀ = 0.76 ± 0.04 nM) and attenuates acute, semichronic and relapsing TNBS- as well as DSS-induced colitis in mice after topical administration. Its anti-inflammatory action is associated with the increase of colonic GLP-2 but not GLP2 receptor or DPP IV expression. Our results validate DPP IV as a pharmacological target for the anti-IBD drugs and its inhibitors, such as DI-1, have the potential to become valuable anti-inflammatory therapeutics.

GLP-2 Dysregulates Hepatic Lipoprotein Metabolism, Inducing Fatty Liver and VLDL Overproduction in Male Hamsters and Mice

Fundamental complications of insulin resistance and type 2 diabetes include the development of nonalcoholic fatty liver disease and an atherogenic fasting dyslipidemic profile, primarily due to increases in hepatic very-low-density lipoprotein (VLDL) production. Recently, central glucagon-like peptide-2 receptor (GLP2R) signaling has been implicated in regulating hepatic insulin sensitivity; however, its role in hepatic lipid and lipoprotein metabolism is unknown. We investigated the role of glucagon-like peptide-2 (GLP-2) in regulating hepatic lipid and lipoprotein metabolism in Syrian golden hamsters, C57BL/6J mice, and Glp2r-/- mice consuming either a normal chow or high-fat diet (HFD). In the chow-fed hamsters, IP GLP-2 administration significantly increased fasting dyslipidemia, hepatic VLDL production, and the expression of key genes involved in hepatic de novo lipogenesis. In HFD-fed hamsters and chow-fed mice, GLP-2 administration exacerbated or induced hepatic lipid accumulation. HFD-fed Glp2r-/- mice displayed reduced glucose tolerance, VLDL secretion, and microsomal transfer protein lipid transfer activity, as well as exacerbated fatty liver. Thus, we conclude that GLP-2 plays a lipogenic role in the liver by increasing lipogenic gene expression and inducing hepatic steatosis, fasting dyslipidemia, and VLDL overproduction. In contrast, the lack of Glp2r appears to interfere with VLDL secretion, resulting in enhanced hepatic lipid accumulation. These studies have uncovered a role for GLP-2 in maintaining hepatic lipid and lipoprotein homeostasis.

Advances in glucagon like peptide-2 therapy. physiology, current indications and future directions

The treatment paradigm for pediatric patients with short bowel syndrome (SBS) and intestinal failure (IF) has changed significantly over recent years; the development of dedicated IF teams, refinements in PN and surgical treatments have greatly improved survival. The majority of SBS patients undergo intestinal adaptation such that nutrient absorption from enteral feeds increases and the child can come off of PN. This "adaptation" or upregulation in nutrient absorptive capacity is still poorly understood; the enteric hormone Glucagon like peptide 2 (GLP-2) appears to be a key regulator in this process. The development of Teduglutide, a long acting GLP-2 ligand as a therapy to specifically enhance adaptation has been anticipated as a further shift in the paradigm. This article reviews the physiology of GLP-2 with an emphasis on the known or potential roles in infants and children with SBS and IF. The results and implications of the present studies and approved indications for GLP-2 and its ligands are discussed. Finally, the potential future uses of GLP-2 ligands in the pediatric population are considered.

The Intestinotrophic Effects of Glucagon-Like Peptide-2 in Relation to Intestinal Neoplasia

CONTEXT

Glucagon-like peptide-2 (GLP-2) is a gastrointestinal hormone with intestinotrophic and antiapoptotic effects. The hormone's therapeutic potential in intestinal diseases and relation to intestinal neoplasia has raised great interest among researchers. This article reviews and discusses published experimental and clinical studies concerning the growth-stimulating and antiapoptotic effects of GLP-2 in relation to intestinal neoplasia.

EVIDENCE ACQUISITION

The data used in this narrative review were collected through literature research in PubMed using English keywords. All studies to date examining GLP-2's relation to intestinal neoplasms have been reviewed in this article, as the studies on the matter are sparse.

EVIDENCE SYNTHESIS

GLP-2 has been found to stimulate intestinal growth through secondary mediators and through the involvement of Akt phosphorylation. Studies on rodents have shown that exogenously administered GLP-2 increases the growth and incidence of adenomas in the colon, suggesting that GLP-2 may play an important role in the progression of intestinal tumors. Clinical studies have found that exogenous GLP-2 treatment is well tolerated for up to 30 months, but the tolerability for even longer periods of treatment has not been examined.

CONCLUSION

Exogenous GLP-2 is currently available as teduglutide for the treatment of short bowel syndrome. However, the association between exogenous GLP-2 treatment and intestinal neoplasia in humans has not been fully identified. This leads to a cause for concern regarding the later risk of the development or progression of intestinal tumors with long-term GLP-2 treatment. Therefore, further research regarding GLP-2's potential relation to intestinal cancers is needed.

Glucagon like peptide-2 and neoplasia; a systematic review

Glucagon like peptide-2 is synthesized from enteroendocrine L cells primarily located in the ileum and large intestine. GLP-2 stimulates crypt cell proliferation, increases intestinal blood flow, enhances gut barrier function, induces mucosal healing, and exerts an anti-apoptotic effect. Due to these effects GLP-2 is used in the treatment of short bowel syndrome (SBS). Areas covered: The aim of this systematic review was to provide information on the potential risk of intestinal neoplasia in patients receiving treatment with GLP-2. The literature search was performed independently by two authors in the following databases; Pubmed, Embase, Scopus, Web of Science and Cochrane. Expert commentary: This systematic review indicated that treatment with GLP-2(1-33) up to 30 months in humans without any known pre-existing cancer did not confer an increased risk of intestinal neoplasia in patients or animals. However, due to the small amount of patients studied it is premature to reach any final conclusions about GLP-2 - induced neoplasia. GLP-2(1-33) treatment in animals with a pre-induced cancer showed that GLP-2(1-33) may promote growth of existing neoplasia.

New Peptide Inhibitor of Dipeptidyl Peptidase IV, EMDB-1 Extends the Half-Life of GLP-2 and Attenuates Colitis in Mice after Topical Administration

Protease inhibition has become a possible new approach in inflammatory bowel disease (IBD) therapy. A serine exopeptidase, dipeptidyl peptidase IV (DPP IV), is responsible for the inactivation of incretin hormone, glucagon-like peptide 2 (GLP-2), a potent stimulator of intestinal epithelium regeneration and growth. Recently, we showed that the novel peptide analog of endomorphin-2, Tyr-Pro-D-ClPhe-Phe-NH2 (EMDB-1) is a potent blocker of DPP IV and has an inhibitory effect on gastrointestinal (GI) smooth muscle contractility. The aim of this study was to characterize the anti-inflammatory effect and mechanism of action of EMDB-1 in the mouse GI tract. We used two models of experimental colitis (induced by TNBS and DSS). The anti-inflammatory effect of EMDB-1 was assessed by the determination of macroscopic score, ulcer score, colonic wall thickness, as well as myeloperoxidase activity. Additionally, we measured the expression of GLP-2, GLP2R, and DPP IV in the colon of control and colitic animals treated with the test compound. The expression of GLP-2 and GLP2R in the serum and colon of IBD patients and healthy control subjects has been assessed. We showed that EMDB-1 elevates the half-life of GLP-2 in vitro and attenuates acute, semichronic, and relapsing TNBS as well as DSS-induced colitis in mice after topical administration. The anti-inflammatory action of EMDB-1 is associated with changes in the level of colonic GLP-2 but not DPP IV expression. Our results validate DPP IV as a pharmacological target for the anti-IBD drugs, and its inhibitors based on natural substrates, such as EMDB-1, have the potential to become valuable anti-inflammatory therapeutic agents.

Glucagon-like petide-2 acts on colon cancer myofibroblasts to stimulate proliferation, migration and invasion of both myofibroblasts and cancer cells via the IGF pathway

Glucagon-like peptide (GLP)-2 stimulates intestinal epithelial proliferation by acting, in part, via IGF release from sub-epithelial myofibroblasts. The response of myofibroblasts to GLP-2 remains incompletely understood. We studied the action of GLP-2 on myofibroblasts from colon cancer and adjacent tissue, and the effects of conditioned medium from these cells on epithelial cell proliferation, migration and invasion. GLP-2 stimulated proliferation, migration and invasion of myofibroblasts and the proliferative and invasive responses of cancer-associated myofibroblasts were greater than those of myofibroblasts from adjacent tissue. The responses were inhibited by an IGF receptor inhibitor, AG1024. Conditioned medium from GLP-2 treated myofibroblasts increased proliferation, migration and invasion of SW480, HT29, LoVo epithelial cells and these responses were inhibited by AG1024; GLP-2 alone had no effect on these cells. In addition, when myofibroblasts and epithelial cells were co-cultured in Ibidi chambers there was mutual stimulation of migration in response to GLP-2. The latter increased both IGF-1 and IGF-2 transcript abundance in myofibroblasts. Moreover, a number of IGF binding proteins (IGFBP-4, -5, -7) were identified in myofibroblast medium; in the presence of GLP-2 there was increased abundance of the cleavage products of IGBBP-4 and IGFBP-5 suggesting activation of a degradation mechanism that might increase IGF bioavailability. The data suggest that GLP-2 stimulates cancer myofibroblast proliferation, migration and invasion; GLP-2 acts indirectly on epithelial cells partly via increased IGF expression in myofibroblasts and partly, perhaps, by increased bioavailability through degradation of IGFBPs.

Glucagon-Like Peptide-1 Receptor Expression in Normal and Neoplastic Human Pancreatic Tissues

OBJECTIVES

Studies have proposed pro-oncogenic effects of glucagon-like peptide-1 receptor (GLP-1R) agonists in the pancreas by promoting GLP-1R overactivation in pancreatic cells. However, the expression of GLP-1R in normal and neoplastic pancreatic cells remains poorly defined, and reliable methods for detecting GLP-1R in tissue specimens are needed.

METHODS

We used RNA in situ hybridization to quantify glp-1r RNA in surgically resected human pancreatic specimens, including pancreatic ductal adenocarcinoma (PDAC), preinvasive intraepithelial lesions (pancreatic intraepithelial neoplasia), and non-neoplastic ductal, acinar, and endocrine cells. A mixed-effect linear regression model was used to investigate the relationship between glp-1r signals and all cells, ordered by increasing grade of dysplasia.

RESULTS

All cell types had evidence of glp-1r transcripts, with the highest expression in endocrine cells and lowest in ductal cells. The slope of the fitted line was not significantly different from zero (0.07; 95% confidence interval, -0.0094 to 0.244; P = 0.39), suggesting that progression from normal cells to PDAC is not associated with a parallel increase in glp-1r RNA. A series of pairwise comparisons between all cell types with respect to their glp-1r expression showed no significant difference in glp-1r in cancer, pancreatic intraepithelial neoplasia, and acinar and ductal cells.

CONCLUSIONS

Our study supports the lack of evidence for GLP-1R overexpression in PDAC.

The Effects of Glucagon-like Peptide-2 on the Tight Junction and Barrier Function in IPEC-J2 Cells through Phosphatidylinositol 3-kinase-Protein Kinase B-Mammalian Target of Rapamycin Signaling Pathway

Glucagon-like peptide-2 (GLP-2) is important for intestinal barrier function and regulation of tight junction (TJ) proteins, but the intracellular mechanisms of action remain undefined. The purpose of this research was to determine the protective effect of GLP-2 mediated TJ and transepithelial electrical resistance (TER) in lipopolysaccharide (LPS) stressed IPEC-J2 cells and to test the hypothesis that GLP-2 regulate TJ and TER through the phosphatidylinositol 3-kinase (PI3K)-protein kinase B (Akt)-mammalian target of rapamycin (mTOR) signaling pathway in IPEC-J2 cells. Wortmannin and LY294002 are specific inhibitors of PI3K. The results showed that 100 μg/mL LPS stress decreased TER and TJ proteins occludin, claudin-1 and zonula occludens protein 1 (ZO-1) mRNA, proteins expressions (p<0.01) respectively. GLP-2 (100 nmol/L) promote TER and TJ proteins occludin, claudin-1, and zo-1 mRNA, proteins expressions in LPS stressed and normal IPEC-J2 cells (p<0.01) respectively. In normal cells, both wortmannin and LY294002, PI3K inhibitors, prevented the mRNA and protein expressions of Akt and mTOR increase induced by GLP-2 (p<0.01) following with the significant decreasing of occludin, claudin-1, ZO-1 mRNA and proteins expressions and TER (p<0.01). In conclusion, these results indicated that GLP-2 can promote TJ’s expression and TER in LPS stressed and normal IPEC-J2 cells and GLP-2 could regulate TJ and TER through the PI3K/Akt/mTOR pathway.

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.

Teduglutide enhances structural adaptation of the small intestinal mucosa in patients with short bowel syndrome

BACKGROUND

Intestinotrophic therapies, such as glucagon-like peptide-2 (GLP-2) analogs, may enhance intestinal adaptation and reduce dependence on parenteral nutrition (PN) in patients with intestinal failure associated with short bowel syndrome (SBS-IF). However, because GLP-2 enhances cellular growth, there is concern that GLP-2 analogs may also encourage growth of malignant cells.

AIMS

To histologically examine the effects of teduglutide, a recombinant human GLP-2 analog, on the mucosa of the small and large intestine for indications of dysplastic transformation.

METHODS

In a multicenter, prospective, randomized, placebo-controlled study, 83 PN-dependent patients with SBS-IF were monitored for several weeks to ensure optimal and stable PN. Patients were then randomized to receive 24 weeks of placebo (n=16), teduglutide (0.5 mg/kg/d; n=35), or teduglutide (0.10 mg/kg/d; n=32).

RESULTS

Biopsies were obtained from 77 patients to yield 390 individual histologic interpretations. After 6 months of treatment, no features of dysplasia were found in any biopsy from the large or small intestine of patients receiving placebo or either dose of teduglutide. New secondary diagnoses, such as eosinophilic colitis or Crohn's disease, were found at a low frequency overall: teduglutide (0.05 mg/kg/d; range, 3.1% to 6.3%); teduglutide (0.10 mg/kg/d, 3.3%); placebo (range, 6.7% to 13.3%).

CONCLUSIONS

Although this histologic substudy of biopsy samples was not powered to detect differences in occurrence of dysplasia between teduglutide-treated patients and those randomized to placebo, it demonstrated that no dysplasia or other pathologic processes were evident within the intestinal mucosa in the placebo group or the 2 teduglutide groups after 6 months of treatment.

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.

GLP-2 receptors in human disease: high expression in gastrointestinal stromal tumors and Crohn's disease

Peptide hormones of the glucagon-like peptide (GLP) family play an increasing clinical role, as reported for GLP-1 in diabetes therapy and insulinoma diagnostics. GLP-2, despite its known trophic and anti-inflammatory intestinal actions translated into preliminary clinical studies using the GLP-2 analogue teduglutide for treatment of short bowel syndrome and Crohn's disease, remains poorly characterized in terms of expression of its receptor in tissues of interest. Therefore, the GLP-2 receptor expression was assessed in 237 tumor and 148 non-neoplastic tissue samples with in vitro receptor autoradiography. A GLP-2 receptor expression was present in 68% of gastrointestinal stromal tumors (GIST). Furthermore, GLP-2 receptors were identified in the intestinal myenteric plexus, with significant up-regulation in active Crohn's disease. The GLP-2 receptors in GIST may be used for clinical applications like in vivo targeting with radiolabelled GLP-2 analogues for imaging and therapy. Moreover, the over-expressed GLP-2 receptor in the myenteric plexus may represent the morphological correlate of the clinical target of teduglutide in Crohn's disease.

GLP1 and cancer: friend or foe?

The new incretin-based therapies, dipeptidyl peptidase-4 (DPP4) inhibitors and glucagon like peptide 1 (GLP1) receptor agonists are widely used for the treatment of type 2 diabetes because of their glucose-lowering capacity with low risk of hypoglycemia. As they are weight neutral or induce weight loss in this mostly overweight population, they are popular among clinicians and patients alike. Nonetheless, concerns have been raised about GLP1's trophic effects. While increased β cell mass observed in rodents sounds appealing for treatment of diabetes, there was also an increased incidence of medullary thyroid cancer (MTC) in some species. We reviewed literature available in the Medline database until March 2012. Safety signals have emerged for MTC and pancreatic carcinoma from adverse event databases in the United States and Europe. Considering the relatively short duration of these studies, it is more likely that premalignant lesions are stimulated in presence of GLP1, rather than new neoplasms induced. Moreover, interpreting results of animal studies is difficult because of species-specific differences in presence and density of GLP1 receptors. Furthermore, data are emerging suggesting beneficial effects of GLP1 on colon and breast cancer. In conclusion, presently, the benefits of using DPP4 inhibitors or GLP1 receptor agonists for treatment of type 2 diabetes outweigh the risks. Nonetheless, their safety profile should be monitored and their indications should be widened cautiously. At present they remain contra-indicated in patients with a personal or family history of MTC or multiple endocrine neoplasia type 2.

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.

Reduced intestinal tumorigenesis in APCmin mice lacking melanin-concentrating hormone

BACKGROUND

Melanin-concentrating hormone (MCH) is an evolutionary conserved hypothalamic neuropeptide that in mammals primarily regulates appetite and energy balance. We have recently identified a novel role for MCH in intestinal inflammation by demonstrating attenuated experimental colitis in MCH deficient mice or wild type mice treated with an anti-MCH antibody. Therefore, targeting MCH has been proposed for the treatment of inflammatory bowel disease. Given the link between chronic intestinal inflammation and colorectal cancer, in the present study we sought to investigate whether blocking MCH might have effects on intestinal tumorigenesis that are independent of inflammation.

METHODOLOGY

Tumor development was evaluated in MCH-deficient mice crossed to the APCmin mice which develop spontaneously intestinal adenomas. A different cohort of MCH-/- and MCH+/+ mice in the APCmin background was treated with dextran sodium sulphate (DSS) to induce inflammation-dependent colorectal tumors. In Caco2 human colorectal adenocarcinoma cells, the role of MCH on cell survival, proliferation and apoptosis was investigated.

RESULTS

APCmin mice lacking MCH developed fewer, smaller and less dysplastic tumors in the intestine and colon which at the molecular level are characterized by attenuated activation of the wnt/beta-catenin signaling pathway and increased apoptotic indices. Form a mechanistic point of view, MCH increased the survival of colonic adenocarcinoma Caco2 cells via inhibiting apoptosis, consistent with the mouse studies.

CONCLUSION

In addition to modulating inflammation, MCH was found to promote intestinal tumorigenesis at least in part by inhibiting epithelial cell apoptosis. Thereby, blocking MCH as a therapeutic approach is expected to decrease the risk for colorectal cancer.

Intestinotrophic glucagon-like peptide-2 (GLP-2) activates intestinal gene expression and growth factor-dependent pathways independent of the vasoactive intestinal peptide gene in mice

The enteroendocrine and enteric nervous systems convey signals through an overlapping network of regulatory peptides that act either as circulating hormones or as localized neurotransmitters within the gastrointestinal tract. Because recent studies invoke an important role for vasoactive intestinal peptide (VIP) as a downstream mediator of glucagon-like peptide-2 (GLP-2) action in the gut, we examined the importance of the VIP-GLP-2 interaction through analysis of Vip(-/-) mice. Unexpectedly, we detected abnormal villous architecture, expansion of the crypt compartment, increased crypt cell proliferation, enhanced Igf1 and Kgf gene expression, and reduced expression of Paneth cell products in the Vip(-/-) small bowel. These abnormalities were not reproduced by antagonizing VIP action in wild-type mice, and VIP administration did not reverse the intestinal phenotype of Vip(-/-) mice. Exogenous administration of GLP-2 induced the expression of ErbB ligands and immediate-early genes to similar levels in Vip(+/+) vs. Vip(-/-) mice. Moreover, GLP-2 significantly increased crypt cell proliferation and small bowel growth to comparable levels in Vip(+/+) vs. Vip(-/-) mice. Unexpectedly, exogenous GLP-2 administration had no therapeutic effect in mice with dextran sulfate-induced colitis; the severity of colonic injury and weight loss was modestly reduced in female but not male Vip(-/-) mice. Taken together, these findings extend our understanding of the complex intestinal phenotype arising from loss of the Vip gene. Furthermore, although VIP action may be important for the antiinflammatory actions of GLP-2, the Vip gene is not required for induction of a gene expression program linked to small bowel growth after enhancement of GLP-2 receptor signaling.

Glucagon-like peptide-2 increases dysplasia in rodent models of colon cancer

The intestinal hormone, glucagon-like peptide-2 (GLP-2), enhances intestinal growth and reduces inflammation in rodent models. Hence, a degradation-resistant GLP-2 analog is under investigation for treatment of Crohn's disease. However, GLP-2 increases colonic dysplasia in murine azoxymethane (AOM)-induced colon cancer. Considering the increased colon cancer risk associated with chronic colitis, we have therefore examined the effects of long-acting hGly(2)GLP-2, as well as of endogenous GLP-2 using the antagonist hGLP-2(3-33) in two novel models of inflammation-associated colon cancer: rats fed the carcinogen 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and a high-fat diet (HFD) for one or three cycles, and mice with chronic dextran sodium-sulfate (DSS)-induced colitis administered AOM. hGly(2)GLP-2 treatment of one-cycle PhIP/HFD rats increased the number of colonic aberrant crypt foci by 72 ± 11% (P < 0.01). Fifty-one weeks after three PhIP/HFD cycles, hGly(2)GLP-2-treated rats had a 22% incidence of colon cancer, compared with 0% in vehicle-treated rats. AOM-DSS mice treated with vehicle or hGly(2)GLP-2 had high-grade dysplasia/colon cancer incidences of 56 and 64%, respectively, compared with 46% in hGLP-2(3-33)-treated AOM-DSS animals (P < 0.05). Unexpectedly, hGLP-2(3-33) also reduced the colitis damage score by 32.0 ± 8.4% (P < 0.05). All high-grade dysplastic/cancerous tumors had nuclear localization of β-catenin although β-catenin mRNA transcript and protein levels did not differ between treatment groups. GLP-2 receptor mRNA expression also was not different. However, hGLP-2(3-33)-treated mice had markedly reduced numbers of doublecortin-and-calmodulin-kinase-like-1-positive stem cells, by 73.7 ± 8.6% (P < 0.05). In conclusion, the results of this study indicate a role for hGly(2)GLP-2 and endogenous GLP-2 as potential cancer promoters in rodents.

Losing balance: Hardy-Weinberg disequilibrium as a marker for recurrent loss-of-heterozygosity in cancer

Identifying regions of loss-of-heterozygosity (LOH) in a tumor sample is a challenging problem. State-of-the-art computational approaches can infer LOH from single-nucleotide polymorphism (SNP) array data, but calling precise boundaries is complicated by normal-cell contamination and markers that are homozygous in the germline and therefore non-informative. More recently, the focus has shifted to pinpointing the loci recurrently affected by LOH events across multiple tumors. Recurrent LOH regions often harbor genes important for tumor suppression. Here, we propose a method that infers LOH rates across an entire sample set on an SNP-by-SNP basis. Our method achieves this by leveraging the straightforward principle that, by definition, LOH depletes heterozygotes, thereby disrupting Hardy-Weinberg equilibrium. We apply a statistical test for such LOH-influenced disruptions, and derive a maximum-likelihood estimator for the LOH rate based on the observed number of heterozygotes. This accounts for LOH in both its hemizygous deletion and copy-neutral forms, and does not make use of matched normal genotypes. Power simulations show high levels of sensitivity for the statistical test, and application to a control normal-tissue data set demonstrates a low false-discovery rate. We apply the method to three large publicly available tumor SNP array data sets, where it is able to localize tumor-suppressor gene targets of the LOH events. Inferred LOH rates are quite concordant across platforms/laboratories and between cell lines and tumors, but in a tumor type-dependent fashion. Finally, we produce rate estimates that are generally higher than previously published, and provide evidence that the latter are likely underestimates.

Teduglutide for the treatment of short bowel syndrome

Extensive resection of the intestine impairs its absorptive capacity and results in short bowel syndrome when the nutritional equilibrium is compromised. The remnant intestine adapts structurally to compensate, but nutritional autonomy cannot be achieved in patients with intestinal failure, requiring intravenous fluids and parenteral nutrition (PN) for sustenance of life. PN is expensive and associated with serious complications. Efforts to minimize or eliminate the need for PN heralded research focusing on the therapeutic utility of intrinsic gut factors involved in the postresection adaptation process. With the breakthrough recognition of the intestinotrophic properties of glucagon-like peptide-2, teduglutide, a recombinant analogue of glucagon-like peptide-2, is being investigated as a promising hope to mitigate the requirement of PN. Clinical studies to date have demonstrated a desirable benefit-to-risk profile in regards to its safety and efficacy. If approved for marketing, it will be the first of its class in short bowel syndrome management, offering an innovative therapeutic modality for this debilitating condition.

Emerging treatment options for short bowel syndrome: potential role of teduglutide

INTRODUCTION

Current medical management of short bowel syndrome (SBS) involves the use of lifelong parenteral nutrition (PN). Glucagon-like peptide-2 (GLP-2), an important intestinotrophic growth factor has been shown to increase intestinal absorption in SBS through augmentation of post-resection intestinal adaptation. This may lead to the reduction of PN dependence in patients with SBS.

AREAS COVERED IN REVIEW

Advancing research of GLP-2 physiology has spurred the growing understanding of the diverse effects of GLP-2. The development of the degradation resistant GLP-2 analog, teduglutide (Gattex(TM), NPS Pharmaceuticals, Bedminster, NJ), has allowed its exploration as a therapeutic agent in a variety of clinical settings. Recent multicenter, placebo-controlled studies of GLP-2 in SBS patients demonstrate meaningful reductions in PN requirements with good safety profiles. The reparative and immunomodulatory effects of teduglutide may also be beneficial in patients with inflammatory bowel disease (IBD). Safety concerns about possible carcinogenic properties during long-term use require ongoing evaluation.

SUMMARY

GLP-2 appears to offer a novel adjuvant treatment modality for SBS. Promise for its use in other clinical settings like IBD has been shown in small pilot studies.

The "cryptic" mechanism of action of glucagon-like peptide-2

Glucagon-like peptide-2 (GLP-2) is a peptide hormone with multiple beneficial effects on the intestine, including expansion of the mucosal surface area through stimulation of crypt cell proliferation, as well as enhancement of nutrient digestion and absorption. Recent advances in clinical trials involving GLP-2 necessitate elucidation of the exact signaling pathways by which GLP-2 acts. In particular, the GLP-2 receptor has been localized to several intestinal cell types that do not include the proliferating crypt cells, and the actions of GLP-2 have thus been linked to a complex network of indirect mediators that induce diverse signaling pathways. The intestinotropic actions of GLP-2 on the colon have been shown to be mediated through the actions of keratinocyte growth factor and insulin-like growth factor (IGF)-2, whereas small intestinal growth has been linked to IGF-1, IGF-2, and ErbB ligands, as well as the IGF-1 receptor and ErbB. The cellular source of these mediators remains unclear, but it likely includes the intestinal subepithelial myofibroblasts. Conversely, the anti-inflammatory and blood flow effects of GLP-2 are dependent on vasoactive intestinal polypeptide released from submucosal enteric neurons and nitric oxide, respectively. Finally, recent studies have suggested that GLP-2 not only modulates intestinal stem cell behavior but may also promote carcinogenesis in models of sporadic colon cancer. Further consideration of the molecular cross-talk and downstream signaling pathways mediating the intestinotropic effects of GLP-2 is clearly warranted.

The intestinotrophic peptide, GLP-2, counteracts the gastrointestinal atrophy in mice induced by the epidermal growth factor receptor inhibitor, erlotinib, and cisplatin

PURPOSE

Erlotinib, an epidermal-growth-factor receptor inhibitor, belongs to a new generation of targeted cancer therapeutics. Gastrointestinal side-effects are common and have been markedly aggravated when erlotinib is combined with cytostatics. We examined the effects of erlotinib alone and combined with the cytostatic, cisplatin, on the gastrointestinal tract and examined whether glucagon-like peptide-2 (GLP-2), an intestinal hormone with potent intestinotrophic properties, might counteract the possible damaging effects of the treatments.

EXPERIMENTAL DESIGN

Groups of ten mice were treated for 10 days with increasing doses of erlotinib alone or in combination with cisplatin and/or GLP-2. Weight and length of the gastrointestinal organs were determined and histological sections were analyzed with morphometric methods as well as BrdU- and ApopTag-staining to determine mitotic and apoptotic activity.

RESULTS

Erlotinib was found to induce small-intestinal and colonic growth inhibition through an increased apoptotic activity but had no effect on mitotic activity. The combined treatment with cisplatin synergistically aggravated the intestinal growth inhibition. Erlotinib, and especially the combination therapy, increased the weight of the stomach contents considerably. Concomitant treatment with GLP-2 counteracted the intestinal mucosal atrophy induced both by erlotinib alone and combined with cisplatin through a reduction of the apoptotic activity. There was no influence on the mitotic activity.

CONCLUSIONS

The findings demonstrate that the intestinal mucosal damage induced by erlotinib alone and in combination with cisplatin can be counteracted by GLP-2 treatment, which might suggest a role for GLP-2 in the treatment of the gastrointestinal side-effects caused by these cancer therapeutics.

Glucagon-like peptide-2 receptor modulates islet adaptation to metabolic stress in the ob/ob mouse

BACKGROUND & AIMS

Glucagon-like peptide-2 (GLP-2) is a gut hormone that increases gut growth, reduces mucosal cell death, and augments mesenteric blood flow and nutrient absorption. Exogenous GLP-2(1-33) also stimulates glucagon secretion and enhances gut barrier function with implications for susceptibility to systemic inflammation and subsequent metabolic dysregulation. We examined the importance of GLP-2 receptor (GLP-2R) signaling for glucose homeostasis in multiple models of metabolic stress, diabetes, and obesity.

METHODS

Body weight, islet function, glucose tolerance, and islet histology were studied in wild-type, high-fat fed, lean diabetic, Glp2r(-/-) and ob/ob:Glp2r(-/-) mice.

RESULTS

GLP-2 did not stimulate glucagon secretion from isolated pancreatic islets in vitro, and exogenous GLP-2 had no effect on the glucagon response to insulin-induced hypoglycemia in vivo. Glp2r(-/-) mice exhibit no change in glycemia, and plasma glucagon levels were similar in Glp2r(-/-) and Glp2r(+/+) mice after hypoglycemia or after oral or intraperitoneal glucose challenge. Moreover, glucose homeostasis was comparable in Glp2r(-/-) and Glp2r(+/+) mice fed a high-fat diet for 5 months or after induction of streptozotocin-induced diabetes. In contrast, loss of the GLP-2R leads to increased glucagon secretion and alpha-cell mass, impaired intraperitoneal glucose tolerance and hyperglycemia, reduced beta-cell mass, and decreased islet proliferation in ob/ob:Glp2r(-/-) mice.

CONCLUSIONS

Our results show that, although the GLP-2R is not critical for the stimulation or suppression of glucagon secretion or glucose homeostasis in normal or lean diabetic mice, elimination of GLP-2R signaling in obese mice impairs the normal islet adaptive response required to maintain glucose homeostasis.

Carcinogenic effects of exogenous and endogenous glucagon-like peptide-2 in azoxymethane-treated mice

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent intestinotropic hormone that promotes intestinal growth, via increased intestinal proliferation and decreased apoptosis, as well as increases in nutrient absorption and barrier function. The long-acting analog h(Gly(2))GLP-2[1-33] is currently being tested for treatment of short bowel syndrome and Crohn's disease. However, the role of GLP-2 in colon carcinogenesis is controversial. To assess the intestinotropic effects of exogenous and endogenous GLP-2, C57BL6/J mice were injected with 1 microg h(Gly(2))GLP-2[1-33]; 30 or 60 ng hGLP-2[3-33], a GLP-2 receptor antagonist; or PBS (4 wk, twice a day, sc). Chronic h(Gly(2))GLP-2[1-33] increased small intestinal weight/body weight (P < 0.001), villus height (P < 0.001), crypt depth (P < 0.001), and crypt cell proliferation, as measured by expression of the proliferative marker Ki67 (P < 0.05-0.01). In contrast, chronic hGLP-2[3-33] decreased small intestinal weight/body weight (P < 0.05) and colon weight/body weight (P < 0.05). To assess the carcinogenic effects of endogenous and exogenous GLP-2, separate mice were injected with azoxymethane (10 mg/kg, 4 wk, every 7 d, ip), followed by 1.5 microg h(Gly(2))GLP-2[1-33], 30 ng hGLP-2[3-33], or PBS (4 wk, twice a day, sc) 2 or 12 wk thereafter. At 10 or 46 wk after azoxymethane treatment, the numbers of aberrant crypt foci increased with h(Gly(2))GLP-2[1-33] (P < 0.001) and decreased with hGLP-2[3-33] (P < 0.01-0.05) treatment. Furthermore, mucin-depleted aberrant foci, consistent with progressive dysplasia, were almost exclusively present in h(Gly(2))GLP-2[1-33]-treated mice (P < 0.01-0.001). Additionally, adenocarcinomas developed in h(Gly(2))GLP-2[1-33]-treated mice but not in those receiving hGLP-2[3-33] or PBS. Taken together, these studies indicate that chronic treatment with GLP-2 enhances colon carcinogenesis, whereas antagonism of the GLP-2 receptor decreases dysplasia, with possible implications for human therapy.

ErbB signaling is required for the proliferative actions of GLP-2 in the murine gut

BACKGROUND & AIMS

Glucagon-like peptide-2 (GLP-2) is a 33-amino acid peptide hormone secreted by enteroendocrine cells in response to nutrient ingestion. GLP-2 stimulates crypt cell proliferation leading to expansion of the mucosal epithelium; however, the mechanisms transducing the trophic effects of GLP-2 are incompletely understood.

METHODS

We examined the gene expression profiles and growth-promoting actions of GLP-2 in normal mice in the presence or absence of an inhibitor of ErbB receptor signaling, in Glp2r(-/-) mice and in Egfr(wa2) mice harboring a hypomorphic point mutation in the epidermal growth factor receptor.

RESULTS

Exogenous GLP-2 administration rapidly induced the expression of a subset of ErbB ligands including amphiregulin, epiregulin, and heparin binding (HB)-epidermal growth factor, in association with induction of immediate early gene expression in the small and large bowel. These actions of GLP-2 required a functional GLP-2 receptor because they were eliminated in Glp2r(-/-) mice. In contrast, insulin-like growth factor-I and keratinocyte growth factor, previously identified mediators of GLP-2 action, had no effect on the expression of these ErbB ligands. The GLP-2-mediated induction of ErbB ligand expression was not metalloproteinase inhibitor sensitive but was significantly diminished in Egfr(wa2) mice and completed abrogated in wild-type mice treated with the pan-ErbB inhibitor CI-1033. Furthermore, the stimulatory actions of GLP-2 on crypt cell proliferation and bowel growth were eliminated in the presence of CI-1033.

CONCLUSIONS

These findings identify the ErbB signaling network as a target for GLP-2 action leading to stimulation of growth factor-dependent signal transduction and bowel growth in vivo.

Short bowel syndrome: the role of GLP-2 on improving outcome

PURPOSE OF REVIEW

The medical management of short bowel syndrome frequently requires lifelong parenteral nutrition. Methods of increasing intestinal absorption and reducing parenteral nutrition dependence, by improving postresection intestinal adaptation, are increasingly being explored. Glucagon-like peptide-2 (GLP-2) is an important intestinotrophic growth factor and mediator of intestinal adaptation. This review summarizes our current understanding of GLP-2 physiology and provides an update on clinical trials in short bowel syndrome and related conditions.

RECENT FINDINGS

There is growing understanding how the effects of GLP-2 are mediated by downstream effectors such as insulin-like growth factor-1. In the treatment of short bowel syndrome, GLP-2 and the long-acting GLP-2 analogue teduglutide (Gattex) are effective in improving fluid absorption. A recent multicentre, placebo-controlled study demonstrates that this can translate into meaningful reductions in parenteral nutrition requirements. Treatment dose and timing of treatment initiation might influence the mucosal growth response. Most of the small intestine has to be preserved to facilitate the previously documented benefits of GLP-2 on bone metabolism. Therapeutic uses of GLP-2 in other gastrointestinal conditions are being explored. GLP-2 treatment appears well tolerated, although concerns about the long-term use of this growth-promoting agent remain.

SUMMARY

GLP-2 therapy holds promise as an adjuvant treatment modality for short bowel syndrome and other gastrointestinal disorders.