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

The expanding incretin universe: from basic biology to clinical translation

Incretin hormones, principally glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1(GLP-1), potentiate meal-stimulated insulin secretion through direct (GIP + GLP-1) and indirect (GLP-1) actions on islet β-cells. GIP and GLP-1 also regulate glucagon secretion, through direct and indirect pathways. The incretin hormone receptors (GIPR and GLP-1R) are widely distributed beyond the pancreas, principally in the brain, cardiovascular and immune systems, gut and kidney, consistent with a broad array of extrapancreatic incretin actions. Notably, the glucoregulatory and anorectic activities of GIP and GLP-1 have supported development of incretin-based therapies for the treatment of type 2 diabetes and obesity. Here we review evolving concepts of incretin action, focusing predominantly on GLP-1, from discovery, to clinical proof of concept, to therapeutic outcomes. We identify established vs uncertain mechanisms of action, highlighting biology conserved across species, while illuminating areas of active investigation and uncertainty that require additional clarification.

NEUROENDOCRINE PEPTIDES IN THE PATHOGENESIS OF COLORECTAL CARCINOMA

Colorectal carcinoma (CRC) is the third most frequent neoplasm worldwide and the second leading cause of mortality. Neuroendocrine peptides such as glucagon, bombesin, somatostatin, cholecystokinin, and gastrin as well as growth factors such as platelet-derived growth factor, epidermal growth factor, insulin-like growth factor, and fibroblast growth factor have been postulated as being involved in carcinogenesis. The fact that these neuroendocrine peptides are involved in the development of CRC through the activation of growth factors that stimulate a series of molecular pathways that activate oncogenic signaling mechanisms is emphasized in this review. Peptides such as CCK1, serotonin, and bombesin have been found to be over-expressed in human tumor tissues. Meanwhile, the expression of peptides such as GLP2 has been seen mainly in murine models. The information contained in this review provides a better understanding of the role these peptides play in the pathogenesis of CRC for basic and clinical science studies.

GLP2-GLP2R signal affects the viability and EGFR-TKIs sensitivity of PC9 and HCC827 cells

Background

The resistance to epidermal growth factor receptor (EGFR)- tyrosine kinase inhibitors (TKIs) therapy is currently the major clinical challenge in the treatment of lung cancer. This study aims to reveal the role of glucagon-like peptide (GLP) 2 and GLP-2 receptor (GLP2R) signaling on the EGFR-TKIs and cisplatin resistance of lung cancer cells.

Methods

The common differentially expressed genes in PC9 and HCC827 cells that were individually resistant to one of the three EGFR-TKIs (dacomitinib, osimertinib and afatinib) were screened. The data were from GSE168043 and GSE163913. The expression of GLP2R in drug-resistant cells was detected by western blot. The effect of GLP2R expression down- or up-regulation on resistance to dacomitinib, osimertinib, afatinib or cisplatin was measured by CCK-8 and flow cytometry assays. The long-acting analog of GLP-2, teduglutide, treated the parental cells.

Results

A total of 143 common differentially expressed genes were identified. Compared with the parent cells, the GLP2R expression in drug-resistant cell lines was significantly up-regulated. The exogenous expression of GLP2R in parental cells enhanced cell viability, while knockdown of GLP2R levels in drug-resistant cell lines inhibited cell viability. In addition, teduglutide treatment also enhanced the viability of lung cancer cells.

Conclusion

GLP2-GLP2R signal may change the sensitivity of cells to EGFR-TKIs and cisplatin. The development of GLP-2 or GLP2R inhibitors may be beneficial to the clinical treatment of lung cancer.

Abnormal post-prandial glucagon-like peptide release in patients with Crohn's disease

BACKGROUND AND AIMS

Glucagon-like peptide GLP-1 and -2 have been shown to regulate immune responses in immune-mediated disorders, including Crohn's disease (CD). Our aim was to investigate post-prandial GLP release and its potential link to chronic inflammation, insulin secretion/sensitivity and body composition changes in CD patients.

METHODS

Fifteen patients with CD, 15 healthy controls (HC) and 15 patients with metabolic syndrome (MS) were recruited. All patients underwent assessment of body composition by means of bio-impedance followed by a meal tolerance test (MTT). Only one CD patient did not tolerate the MTT and was excluded.

RESULTS

Basal GLP-1 levels were up-regulated in CD, however, as compared to HC, stimulated GLP-1 secretion was significantly reduced in CD (-31 %, p < 0.05) as in MS (-52 %, p < 0.003). Similarly, basal GLP-2 levels were comparable to that of HC, while response to MTT in CD was virtually absent (p < 0.05). Similar fasting insulin sensitivity, estimated 1^st and 2^nd phase insulin secretion and insulinogenic index were found in CD and in HC. Post-prandial GLP secretion was positively correlated to insulin secretion indices, both in CD and MS. In CD, high-sensitive C reactive protein levels (hsCRP) and extra-cellular to intra-cellular water ratio (ECW/ICW), an index of cellular inflammation, were inversely correlated with stimulated GLP-1 (p < 0.05 and p < 0.01, respectively) levels.

CONCLUSION

CD is characterized by abnormal fasting and post-prandial GLP levels. Circulating GLP influences subclinical inflammation and glucose metabolism in CD patients, but not their body composition parameters.

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.

The endogenous preproglucagon system is not essential for gut growth homeostasis in mice

OBJECTIVE

The prevalence of obesity and related co-morbidities is reaching pandemic proportions. Today, the most effective obesity treatments are glucagon-like peptide 1 (GLP-1) analogs and bariatric surgery. Interestingly, both intervention paradigms have been associated with adaptive growth responses in the gut; however, intestinotrophic mechanisms associated with or secondary to medical or surgical obesity therapies are poorly understood. Therefore, the objective of this study was to assess the local basal endogenous and pharmacological intestinotrophic effects of glucagon-like peptides and bariatric surgery in mice.

METHODS

We used in situ hybridization to provide a detailed and comparative anatomical map of the local distribution of GLP-1 receptor (Glp1r), GLP-2 receptor (Glp2r), and preproglucagon (Gcg) mRNA expression throughout the mouse gastrointestinal tract. Gut development in GLP-1R-, GLP-2R-, or GCG-deficient mice was compared to their corresponding wild-type controls, and intestinotrophic effects of GLP-1 and GLP-2 analogs were assessed in wild-type mice. Lastly, gut volume was determined in a mouse model of vertical sleeve gastrectomy (VSG).

RESULTS

Comparison of Glp1r, Glp2r, and Gcg mRNA expression indicated a widespread, but distinct, distribution of these three transcripts throughout all compartments of the mouse gastrointestinal tract. While mice null for Glp1r or Gcg showed normal intestinal morphology, Glp2r-/- mice exhibited a slight reduction in small intestinal mucosa volume. Pharmacological treatment with GLP-1 and GLP-2 analogs significantly increased gut volume. In contrast, VSG surgery had no effect on intestinal morphology.

CONCLUSION

The present study indicates that the endogenous preproglucagon system, exemplified by the entire GCG gene and the receptors for GLP-1 and GLP-2, does not play a major role in normal gut development in the mouse. Furthermore, elevation in local intestinal and circulating levels of GLP-1 and GLP-2 achieved after VSG has limited impact on intestinal morphometry. Hence, although exogenous treatment with GLP-1 and GLP-2 analogs enhances gut growth, the contributions of endogenously-secreted GLP-1 and GLP-2 to gut growth may be more modest and highly context-dependent.

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.

Gonadotropin-Releasing Hormone Stimulate Aldosterone Production in a Subset of Aldosterone-Producing Adenoma

We aimed to detect novel genes associated with G protein-coupled receptors (GPCRs) in aldosterone-producing adenoma (APA) and elucidate the mechanisms underlying aldosterone production.Microarray analysis targeting GPCR-associated genes was conducted using APA without known mutations (APA-WT) samples (n = 3) and APA with the KCNJ5 mutation (APA-KCNJ5; n = 3). Since gonadotropin-releasing hormone receptor (GNRHR) was the highest expression in APA-WT by microarray analysis, we investigated the effect of gonadotropin-releasing hormone (GnRH) stimulation on aldosterone production.The quantitative polymerase chain reaction assay results revealed higher GNRHR expression levels in APA-WT samples those in APA-KCNJ5 samples (P < 0.05). LHCGR levels were also significantly elevated in APA-WT samples, and there was a significant and positive correlation between GNRHR and LHCGR expression in all APA samples (r = 0.476, P < 0.05). Patients with APA-WT (n = 9), which showed higher GNRHR and LHCGR levels, had significantly higher GnRH-stimulated aldosterone response than those with APA-KCNJ5 (n = 13) (P < 0.05). Multiple regression analysis revealed that the presence of the KCNJ5 mutation was linked to GNRHR mRNA expression (β = 0.94 and P < 0.01). HAC15 cells with KCNJ5 gene carrying T158A mutation exhibited a significantly lower GNRHR expression than that in control cells (P < 0.05).We clarified increased expression of GNRHR and LHCGR in APA-WT, and the molecular analysis including the receptor expression associated with clinical findings of GnRH stimulation.

Alveolar Rhabdomyosarcoma in a 69-Year-Old Woman Receiving Glucagon-Like Peptide-2 Therapy

A 69-year-old woman was diagnosed with alveolar rhabdomyosarcoma (ARMS) of the nasopharynx. She has a history of catastrophic thromboembolic event in the abdomen that caused short-gut syndrome and dependence on total parenteral nutrition (TPN) twelve hours per day. She was treated for short-gut syndrome with teduglutide, a glucagon-like peptide-2 (GLP-2) analog, which led to reduction of TPN requirements. However, a few months later, she developed metastatic alveolar rhabdomyosarcoma. Though a causative relationship is unlikely between the peptide and ARMS due to the brief time course between teduglutide therapy and sarcoma diagnosis, neoplastic growth may have been accelerated by the GLP-2 analog, causing release of IGF-1. The transmembrane receptor for IGF-1 is frequently overexpressed in ARMS and is implicated in cell proliferation and metastatic behavior. This case describes a rare incidence of metastatic alveolar rhabdomyosarcoma in a sexagenarian and possibly the first case reported associated with the use of teduglutide. Teduglutide was discontinued due to a potential theoretical risk of acceleration of sarcoma growth, and the patient's rhabdomyosarcoma is in remission following sarcoma chemotherapy.

The glucagon-like peptide 2 receptor is expressed in enteric neurons and not in the epithelium of the intestine

Glucagon-like peptide 2 (GLP-2) is a potent intestinotrophic growth factor with therapeutic potential in the treatment of intestinal deficiencies. It has recently been approved for the treatment of short bowel syndrome. The effects of GLP-2 are mediated by specific binding of the hormone to the GLP-2 receptor (GLP-2R) which was cloned in 1999. However, consensus about the exact receptor localization in the intestine has never been established. By physical, chemical and enzymatic tissue fragmentation, we were able to divide rat jejunum into different compartments consisting of: (1) epithelium alone, (2) mucosa with lamina propria and epithelium, (3) the external muscle coat including myenteric plexus, (4) a compartment enriched for the myenteric plexus and (5) intestine without epithelium. Expression of Glp2r; chromogranin A; tubulin, beta 3; actin, gamma 2, smooth muscle, enteric and glial fibrillary acidic protein in these isolated tissue fractions was quantified with qRT-PCR. Expression of the Glp2r was confined to compartments containing enteric neurons and receptor expression was absent in the epithelium. Our findings provide evidence for the expression of the GLP-2R in intestinal compartments rich in enteric neurons and, importantly they exclude significant expression in the epithelium of rat jejunal mucosa.

Glugacon-like peptide-2: broad receptor expression, limited therapeutic effect on intestinal inflammation and novel role in liver regeneration

The glucagon-like peptide 2 (GLP-2) is an intestinotrophic hormone with growth promoting and anti-inflammatory actions. However, the full biological functions of GLP-2 and the localization of its receptor (GLP-2R) remain controversial. Among cell lines tested, the expression of GLP-2R transcript was detected in human colonic myofibroblasts (CCD-18Co) and in primary culture of rat enteric nervous system but not in intestinal epithelial cell lines, lymphocytes, monocytes, or endothelial cells. Surprisingly, GLP-2R was expressed in murine (GLUTag), but not human (NCI-H716) enteroendocrine cells. The screening of GLP-2R mRNA in mice organs revealed an increasing gradient of GLP-2R toward the distal gut. An unexpected expression was detected in the mesenteric fat, mesenteric lymph nodes, bladder, spleen, and liver, particularly in hepatocytes. In two mice models of trinitrobenzene sulfonic acid (TNBS)- and dextran sulfate sodium (DSS)-induced colitis, the colonic expression of GLP-2R mRNA was decreased by 60% compared with control mice. Also, GLP-2R mRNA was significantly downregulated in intestinal tissues of inflammatory bowel disease patients. Therapeutically, GLP-2 showed a weak restorative effect on intestinal inflammation during TNBS-induced colitis as assessed by macroscopic score and inflammatory markers. Finally, GLP-2 treatment accelerated mouse liver regeneration following partial hepatectomy as assessed by histological and molecular analyses. In conclusion, the limited therapeutic effect of GLP-2 on colonic inflammation dampens its utility in the management of severe inflammatory intestinal disorders. However, the role of GLP-2 in liver regeneration is a novelty that might introduce GLP-2 into the management of liver diseases and emphasizes on the importance of elucidating other extraintestinal functions of GLP-2.

Dipeptidyl peptidase-4 inhibitors: multitarget drugs, not only antidiabetes drugs

Dipeptidyl peptidase (DPP)-4 inhibitors are a new class of antidiabetic agents that reduce blood glucose by preventing the degradation of the endogenous incretin hormones glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide. Protection by DPP-4 inhibitors of β-cell function has been demonstrated in patients with type 2 diabetes. Because DPP-4 is an enzyme widely expressed in humans, DPP-4 inhibitors are speculated to be multitarget agents. However, other potential therapeutic benefits of DPP-4 inhibitors remain unknown. Recently, some therapeutic effects of DPP-4 inhibitors, such as immune regulation, cardiovascular protection, and anti-inflammatory effects, have been observed. This article provides a systematic and comprehensive review of current research into the newly found effects and mechanism of action of DPP-4 inhibitors in a therapeutic context.

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.