Release of Lipids Stored in the Intestine by Glucagon-Like Peptide-2 Involves a Gut-Brain Neural Pathway

BACKGROUND

The gut hormone GLP-2 (glucagon-like peptide-2) plays important roles in lipid handling in the intestine. During postabsorptive stage, it releases preformed chylomicrons stored in the intestine, the underlying mechanisms of which are not well understood. Previous studies implicate the involvement of neural pathways in GLP-2's actions on lipid absorption in the intestine, but the role of such mechanisms in releasing postabsorptive lipid storage has not been established.

METHODS

Here, in mesenteric lymph duct cannulated rats, we directly tested whether gut-brain neural communication mediates GLP-2's effects on postabsorptive lipid mobilization in the intestine. We performed total subdiaphragmatic vagotomy to disrupt the gut-brain neural communication and analyzed lipid output 5 hours after a lipid load in response to intraperitoneal GLP-2 or saline.

RESULTS

Peripheral GLP-2 administration led to increased lymph lipid output and activation of proopiomelanocortin neurons in the arcuate nucleus of hypothalamus. Disruption of gut-brain neural communication via vagotomy blunted GLP-2's effects on promoting lipid release in the intestine.

CONCLUSIONS

These results, for the first time, demonstrate a novel mechanism in which postabsorptive mobilization of intestinal lipid storage by GLP-2 enlists a gut-brain neural pathway.

Glucagon-Like Peptide-2 Ameliorates Age-Associated Bone Loss and Gut Barrier Dysfunction in Senescence-Accelerated Mouse Prone 6 Mice

<b><i>Introduction:</i></b> Senile osteoporosis is one of the most common age-related diseases worldwide. Glucagon like peptide-2 (GLP-2), a naturally occurring gastrointestinal peptide, possesses therapeutic effects on bone loss in postmenopausal women and ovariectomized rats. However, the role of GLP-2 in senile osteoporosis and underlying mechanisms has not been explored. <b><i>Methods:</i></b> GLP-2 was subcutaneously injected into the 6-month-old male senile osteoporosis model of senescence-accelerated mouse prone 6 (SAMP6) mice for 6 weeks. SAMP6 subjected to normal saline and senescence-accelerated mouse resistant 1 served as control groups. Micro-computed tomography was performed to evaluate the bone mass and microarchitecture of the mice. Osteoblastic and osteoclastic activities were determined by biochemical, quantitative real-time PCR, histological, and histomorphometric analyses combined with hematoxylin-eosin, toluidine blue, and tartrate-resistant acid phosphatase staining. We also examined the proteins and structure of intestinal tight junction using immunohistochemical assay as well as a transmission electron microscope. Serum inflammation marker levels were measured using ELISA. Additionally, anti-oxidative enzymes GPX-4 and SOD-2 and receptors of GLP-2 and vitamin D expression in the ileum and colon were detected under immunofluorescence staining. <b><i>Results:</i></b> Six-week GLP-2 treatment attenuated bone loss in SAMP6 mice, as evidenced by increased bone mineral density, improved microarchitecture in femora, and enhanced osteogenic activities. In contrast, the activity of osteoclastic activity was not obviously inhibited. Moreover, GLP-2 ameliorated tight junction structure and protein expression in the intestinal barrier, which was accompanied by the reduction of TNF-α level. The expression of receptors of intestinal GLP-2 and vitamin D in the ileum was elevated. Furthermore, the oxidative stress in the intestines was improved by increasing the GPX-4 and SOD-2 signaling. <b><i>Conclusion:</i></b> Our findings suggest that GLP-2 could ameliorate age-associated bone loss, tight junction structure, and improved antioxidant enzyme activity in the gut in SAMP6 mice. Amelioration of gut barrier dysfunction may potentially contribute to improving bone formation and provide evidence for targeting the entero-bone axis in the treatment of senile osteoporosis.

GLP-2 Regulation of Dietary Fat Absorption and Intestinal Chylomicron Production via Neuronal Nitric Oxide Synthase (nNOS) Signaling

Postprandial dyslipidemia is a metabolic condition commonly associated with insulin-resistant states, such as obesity and type 2 diabetes. It is characterized by the overproduction of intestinal chylomicron particles and excess atherogenic chylomicron remnants in circulation. We have previously shown that glucagon-like peptide 2 (GLP-2) augments dietary fat uptake and chylomicron production in insulin-resistant states; however, the underlying mechanisms remain unclear. Previous studies have implicated nitric oxide (NO) in the absorptive actions of GLP-2. In this study, we report a novel role for neuronal NO synthase (nNOS)-mediated NO generation in lipid uptake and chylomicron formation based on studies in C57BL/6J mice, nNOS-/- mice, and Syrian golden hamsters after intraduodenal and oral fat administration. GLP-2 treatment in wild-type (WT) mice significantly increased postprandial lipid accumulation and circulating apolipoprotein B48 protein levels, while these effects were abolished in nNOS-/- mice. nNOS inhibition in Syrian golden hamsters and protein kinase G (PKG) inhibition in WT mice also abrogated the effect of GLP-2 on postprandial lipid accumulation. These studies demonstrate a novel mechanism in which nNOS-generated NO is crucial for GLP-2-mediated lipid absorption and chylomicron production in both mouse and hamster models. Overall, our data implicate an nNOS-PKG-mediated pathway in GLP-2-mediated stimulation of dietary fat absorption and intestinal chylomicron production.

Enterohormone therapy for short bowel syndrome

PURPOSE OF REVIEW

Short bowel syndrome (SBS) patients are at risk to develop intestinal failure when the decreased absorption of macronutrients, water, and electrolytes necessitates parenteral support for survival. The adverse effects of SBS and parenteral support negatively affect the quality of life (QoL) of SBS-intestinal failure patients. However, spontaneous intestinal adaptation along with disease-modifying therapies allow reducing parenteral support, thereby improving QoL.

RECENT FINDINGS

During the first years following extensive surgery, spontaneous structural and functional intestinal changes take place which stimulate a more efficient nutrient and fluid absorption in the remaining bowel. Given their potential role in the ileal braking mechanism, enterohormones, such as glucagon-like peptide (GLP)-2, GLP-1, and peptide YY (PYY), promote an accelerated adaptation or hyperadaptation. While the exact role of GLP-1 and PYY in SBS is still being explored, GLP-2 analogs have clearly shown to be effective in improving outcome in SBS.

SUMMARY

Whereas spontaneous intestinal adaptation improves the nutritional status of SBS patients to a certain extent, GLP-2 analogs can further decrease parenteral support needs through hyperadaptation. There are, however, other promising candidates on the horizon that - alone or in combination - could possibly establish additional disease-modifying effects.

A Protective Role for Glucagon-like Peptide-2 in Heat-stable Enterotoxin b (STb)-Induced L-Cell Toxicity

Enterotoxigenic Escherichia coli (ETEC)-derived purified heat-stable enterotoxin b (STb) is responsible for secretory diarrhea in livestock and humans. STb disrupts intestinal fluid homeostasis, epithelial barrier function, and promotes cell death. Glucagon-like peptide-2 (GLP-2) is a potent intestinotrophic hormone secreted by enteroendocrine L cells. GLP-2 enhances crypt cell proliferation, epithelial barrier function, and inhibits enterocyte apoptosis. Whether STb can affect GLP-2 producing L cells remains to be elucidated. First, secreted-His-labeled STb from transformed E coli was collected and purified. When incubated with L-cell models (GLUTag, NCI-H716, and secretin tumor cell line [STC-1]), fluorescent immunocytochemistry revealed STb was internalized and was differentially localized in the cytoplasm and nucleus. Cell viability experiments with neutral red and resazurin revealed that STb was toxic in all but the GLUTag cells. STb stimulated 2-hour GLP-2 secretion in all cell models. Interestingly, GLUTag cells produced the highest amount of GLP-2 when treated with STb, demonstrating an inverse relationship in GLP-2 secretion and cell toxicity. To demonstrate a protective role for GLP-2, GLUTag-conditioned media (rich in GLP-2) blocked STb toxicity in STC-1 cells. Confirming a protective role of GLP-2, teduglutide was able to improve cell viability in cells treated with H2O2. In conclusion, STb interacts with the L cell, stimulates secretion, and may induce toxicity if GLP-2 is not produced at high levels. GLP-2 or receptor agonists have the ability to improve cell viability in response to toxins. These results suggest that GLP-2 secretion can play a protective role during STb intoxication. This work supports future investigation into the use of GLP-2 therapies in enterotoxigenic-related diseases.

GIP and GLP-2 together improve bone turnover in humans supporting GIPR-GLP-2R co-agonists as future osteoporosis treatment

The intestinal hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-2 (GLP-2) are key regulators of postprandial bone turnover in humans. We hypothesized that GIP and GLP-2 co-administration would provide stronger effect on bone turnover than administration of the hormones separately, and tested this using subcutaneous injections of GIP and GLP-2 alone or in combination in humans. Guided by these findings, we designed series of GIPR-GLP-2R co-agonists as template for new osteoporosis treatment. The clinical experiment was a randomized cross-over design including 10 healthy men administered subcutaneous injections of GIP and GLP-2 alone or in combination. The GIPR-GLP-2R co-agonists were characterized in terms of binding and activation profiles on human and rodent GIP and GLP-2 receptors, and their pharmacokinetic (PK) profiles were improved by dipeptidyl peptidase-4 protection and site-directed lipidation. Co-administration of GIP and GLP-2 in humans resulted in an additive reduction in bone resorption superior to each hormone individually. The GIPR-GLP-2R co-agonists, designed by combining regions of importance for cognate receptor activation, obtained similar efficacies as the two native hormones and nanomolar potencies on both human receptors. The PK-improved co-agonists maintained receptor activity along with their prolonged half-lives. Finally, we found that the GIPR-GLP-2R co-agonists optimized toward the human receptors for bone remodeling are not feasible for use in rodent models. The successful development of potent and efficacious GIPR-GLP-2R co-agonists, combined with the improved effect on bone metabolism in humans by co-administration, support these co-agonists as a future osteoporosis treatment.

Melanocortin receptor-4 mediates the anorectic effect induced by the nucleus tractus solitarius injection of glucagon-like Peptide-2 in fasted rats

Glucagon-like peptide-2 (GLP-2) is secreted from enteroendocrine L-type cells of the gut and also released from preproglucagonergic (PPG) neurons in the nucleus tractus solitarius (NTS) and adjacent medial reticular nucleus of the brain stem. The neurons in the NTS express GLP-2, and the neurons send extensive projections to the hypothalamus. Recent studies show that the intracerebroventricular administration of GLP-2 significantly suppresses food intake in animals and some evidence suggest that the melanocortin receptor-4 (MC4-R) signaling in the hypothalamus is required for intracerebroventricular GLP-2-mediated inhibition of feeding. There is proopiomelanocortin (POMC) positive neurons expressing MC4-R in the NTS. Suppression of MC4-R expressing neurons in the brain stem inhibits gastric emptying. In this study, we tested the effects of NTS GLP-2R activation and blockade on feeding behavior and evaluated the endogenous melanocortin system's role in the NTS in mediating effects of GLP-2 on feeding behavior in fed and fasted rats. Our results demonstrated that microinjection of GLP-2 into the NTS suppressed food intake in fasted-refeeding rats but did not affect food intake in free-feeding rats, and this inhibition was blocked by pretreatment of either Exendin _(9-39) or SHU 9119, suggesting the GLP-2 system in the NTS exerts an inhibitory action on food intake. MC4-R mediates this action in the NTS.

GLP-2 restores impairments in spatial working memory and hippocampal LTD via the MEK/ERK pathway in juvenile-onset diabetes rats

Type 1 diabetic animal models, generated by injecting streptozotocin (STZ), have been widely used in research. We previously reported that juvenile-onset diabetes mellitus (JDM) rats, which were prepared by administering STZ to 17-day-old rats, developed cognitive impairments and hippocampal synaptic plasticity deficiencies, which were restored by glucagon-like peptide-1 (GLP-1). GLP-1 and GLP-2 are simultaneously derived from proglucagon and act through their own specific receptors. The present study was performed to investigate the potential of GLP-2 in JDM rats. The results obtained demonstrated that GLP-2 restored impairments in spatial working memory and hippocampal long-term depression (LTD) in JDM rats, and that the MEK1/2 inhibitor, U0126, inhibited this recovery. Therefore, GLP-2 has potential in the treatment of cognitive deficits in childhood-onset diabetes.

[Gly²]-GLP-2, But Not Glucagon or [D-Ala²]-GLP-1, Controls Collagen Crosslinking in Murine Osteoblast Cultures

Bone tissue is organized at the molecular level to resist fracture with the minimum of bone material. This implies that several modifications of the extracellular matrix, including enzymatic collagen crosslinking, take place. We previously highlighted the role of several gut hormones in enhancing collagen maturity and bone strength. The present study investigated the effect of proglucagon-derived peptides on osteoblast-mediated collagen post-processing. Briefly, MC3T3-E1 murine osteoblasts were cultured in the presence of glucagon (GCG), [D-Ala²]-glucagon-like peptide-1 ([D-Ala²]-GLP-1), and [Gly²]-glucagon-like peptide-2 ([Gly²]-GLP-2). Gut hormone receptor expression at the mRNA and protein levels were investigated by qPCR and Western blot. Extent of collagen postprocessing was examined by Fourier transform infrared microspectroscopy. GCG and GLP-1 receptors were not evidenced in osteoblast cells at the mRNA and protein levels. However, it is not clear whether the known GLP-2 receptor is expressed. Nevertheless, administration of [Gly²]-GLP-2, but not GCG or [D-Ala²]-GLP-1, led to a dose-dependent increase in collagen maturity and an acceleration of collagen post-processing. This mechanism was dependent on adenylyl cyclase activation. In conclusion, the present study highlighted a direct effect of [Gly²]-GLP-2 to enhance collagen post-processing and crosslinking maturation in murine osteoblast cultures. Whether this effect is translatable to human osteoblasts remains to be elucidated.

GLP-2 and GIP exert separate effects on bone turnover: A randomized, placebo-controlled, crossover study in healthy young men

BACKGROUND

Glucagon-like peptide-2 (GLP-2) and glucose-dependent insulinotropic polypeptide (GIP) both inhibit bone resorption in humans but the underlying mechanisms are poorly understood. In vitro, GLP-2 activates the GIP-receptor (GIPR).

OBJECTIVE

Based on in vitro studies, we hypothesized that the antiresorptive effect of GLP-2 was mediated through the GIPR. This was tested using the selective GIPR-antagonist GIP(3-30)NH₂.

METHODS

The study was a randomized, single-blinded, placebo-controlled, crossover study conducted at Hvidovre University Hospital, Denmark. Eight healthy young men were included and studied on four study days: GIP (200 μg), GLP-2 (800 μg), GIP(3-30)NH₂ (800 pmol/kg/min) + GLP-2 (800 μg), and placebo. The main outcomes were bone resorption measured as collagen type 1 C-terminal telopeptide (CTX) and bone formation measured as procollagen type 1 N-terminal propeptide (P1NP).

RESULTS

CTX (mean ± SEM) significantly decreased after both GIP (to 55.3 ± 6.3% of baseline at t = 90 min) and GLP-2 (to 60.5 ± 5.0% of baseline at t = 180 min). The maximal reduction in CTX after GIP(3-30)NH₂ + GLP-2 (to 63.2 ± 3.1% of baseline) did not differ from GLP-2 alone (p = 0.95) nor did net AUC_0-240 (-6801 ± 879%*min vs -6027 ± 648%*min, p = 0.56). At t = 30 min, GIP significantly (p < 0.0001) increased P1NP to 115.1 ± 2.2% of baseline compared with 103.1 ± 1.5% after placebo. Both GLP-2 and GIP(3-30)NH₂ + GLP-2 significantly (p < 0.0001) decreased P1NP to 91.3 ± 1.1% and 88.1 ± 3.0% of baseline, respectively (at t = 45 min) compared with placebo.

CONCLUSIONS

GIPR antagonism did not inhibit the GLP-2-induced reduction in bone resorption (CTX) in healthy young men. In contrast to GLP-2, GIP increased P1NP despite decreasing CTX indicating an uncoupling of bone resorption from formation. Thus, GLP-2 and GIP seem to exert separate effects on bone turnover in humans.

CLINICAL TRIALS INFORMATION

ClinicalTrials.gov (NCT03159741).

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.

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 Improve Intestinal Mucosal Barrier Function in Aged Rats

Glucagon-like peptide-2 (GLP-2) plays a major role in repairing impaired intestinal mucosa, but its mechanism in the improvement of intestinal barrier function during the aging process remains unclear. In this study, 26-month-old male Sprague-Dawley rats were randomized to control group and GLP-2 group treated with a dose of 250 μg•kg-1•d-1 by intraperitoneal injection. After 14 days of treatment, intestinal mucosal morphometric changes were observed by light microscopy and transmission electron microscopy (TEM). Small intestinal permeability was evaluated by fluorescein isothiocyanate (FITC)-labeled dextran. The mRNA and protein expression of Zonula Occludens-1 (ZO-1), occludin, claudin-1 and the GLP-2 receptor (GLP-2R) were detected by Real-time PCR and Western blot. Our results showed that GLP-2 administration significantly improved the age-related atrophy of intestinal mucosa and villi and increased small intestinal permeability. The mRNA and protein expression of ZO-1and occludin in ileum were up regulated in the GLP-2-treated old rats. In addition, the serum GLP-2 levels were negatively correlated with small intestinal permeability measured by FITC-dextran levels (r=-0.610, P<0.01). Taking all these data together, it is concluded that GLP-2 improved small intestinal epithelial barrier function in aged rats mainly by facilitating intestinal mucosa growth, alleviating the increased small intestinal permeability and increasing ZO-1 and occludin expression. Our observations provide evidence for the clinical significance of GLP-2 in preventing the intestinal epithelial barrier dysfunction during aging.

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.

Influence of endogenous glucagon-like peptide-2 on lipid disorders in mice fed a high-fat diet

AIM

The purpose of the present study was to investigate the influence of endogenous glucagon-like peptide-2 (GLP-2) on lipid profile in mice fed a standard diet (STD) or a high-fat diet (HFD).

MATERIALS AND METHODS

HFD- and age-matched STD mice were injected once a day with GLP-2 (3-33), a GLP-2 receptor (GLP-2R) antagonist, or vehicle for 4 weeks.

RESULTS

HFD mice displayed increased intrahepatic lipid concentration and hepatic steatosis and higher plasma concentrations of cholesterol, LDL, AST, and ALT than STD mice. No difference was observed in lipid fecal elimination. In STD mice, the chronic treatment with GLP-2 (3-33) did not affect any parameter, while in HFD mice, it enhanced plasma triglycerides, cholesterol, ALT, and AST and reduced HDL, it increased intrahepatic lipid concentration, and it worsened the hepatic steatosis degree, without affecting lipid fecal elimination.

CONCLUSIONS

The present results suggest that GLP-2R antagonism worsens lipid disorders in HFD mice, and endogenous GLP-2 might even exert a defensive role against lipid imbalance.

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.

Glucagon-like peptide 2 and its beneficial effects on gut function and health in production animals

Numerous endocrine cell subtypes exist within the intestinal mucosa and produce peptides contributing to the regulation of critical physiological processes including appetite, energy metabolism, gut function, and gut health. The mechanisms of action and the extent of the physiological effects of these enteric peptides are only beginning to be uncovered. One peptide in particular, glucagon-like peptide 2 (GLP-2) produced by enteroendocrine L cells, has been fairly well characterized in rodent and swine models in terms of its ability to improve nutrient absorption and healing of the gut after injury. In fact, a long-acting form of GLP-2 recently has been approved for the management and treatment of human conditions like inflammatory bowel disease and short bowel syndrome. However, novel functions of GLP-2 within the gut continue to be demonstrated, including its beneficial effects on intestinal barrier function and reducing intestinal inflammation. As knowledge continues to grow about GLP-2's effects on the gut and its mechanisms of release, the potential to use GLP-2 to improve gut function and health of food animals becomes increasingly more apparent. Thus, the purpose of this review is to summarize: (1) the current understanding of GLP-2's functions and mechanisms of action within the gut; (2) novel applications of GLP-2 (or stimulators of its release) to improve general health and production performance of food animals; and (3) recent findings, using dairy calves as a model, that suggest the therapeutic potential of GLP-2 to reduce the pathogenesis of intestinal protozoan infections.

COMPARATIVE GUT PHYSIOLOGY SYMPOSIUM: Comparative physiology of glucagon-like peptide-2: Implications and applications for production and health of ruminants

Glucagon-like peptide-2 (GLP-2) is a 33-amino acid peptide derived from proteolytic cleavage of proglucagon by prohormone convertase 1/3 in enteroendocrine L cells. Studies conducted in humans, in rodent models, and in vitro indicate that GLP-2 is secreted in response to the presence of molecules in the intestinal lumen, including fatty acids, carbohydrates, amino acids, and bile acids, which are detected by luminal chemosensors. The physiological actions of GLP-2 are mediated by its G protein-coupled receptor expressed primarily in the intestinal tract on enteric neurons, enteroendocrine cells, and myofibroblasts. The biological activity of GLP-2 is further regulated by dipeptidyl peptidase IV, which rapidly cleaves the N-terminus of GLP-2 that is responsible for GLP-2 receptor activation. Within the gut, GLP-2 increases nutrient absorption, crypt cell proliferation, and mesenteric blood flow and decreases gut permeability and motility, epithelial cell apoptosis, and inflammation. Outside the gut, GLP-2 reduces bone resorption, can suppress appetite, and is cytoprotective in the lung. Thus, GLP-2 has been studied intensively as a therapeutic to improve intestinal function of humans during parenteral nutrition and following small bowel resection and, more recently, as a treatment for osteoporosis and obesity-related disorders and to reduce cellular damage associated with inflammation of the gut and lungs. Recent studies demonstrate that many biological actions and properties of GLP-2 in ruminants are similar to those in nonruminants, including the potential to reduce intestinal nitro-oxidative stress in calves caused by parasitic diseases such as coccidiosis. Because of its beneficial impacts on nutrient absorption, gut healing, and normal gut development, GLP-2 therapy offers significant opportunities to improve calf health and production efficiency. However, GLP-2 therapies require an extended time course to achieve desired physiological responses, as well as daily administration because of the hormone's short half-life. Thus, practical means of administration and alternative strategies to enhance basal GLP-2 secretion (e.g., through specific feed additives), which are more likely to achieve consumer acceptance, are needed. Opportunities to address these challenges are discussed.

GLP-2 Attenuates LPS-Induced Inflammation in BV-2 Cells by Inhibiting ERK1/2, JNK1/2 and NF-κB Signaling Pathways

The pathogenesis of Parkinson’s disease (PD) often involves the over-activation of microglia. Over-activated microglia could produce several inflammatory mediators, which trigger excessive inflammation and ultimately cause dopaminergic neuron damage. Anti-inflammatory effects of glucagon-like peptide-2 (GLP-2) in the periphery have been shown. Nonetheless, it has not been illustrated in the brain. Thus, in this study, we aimed to understand the role of GLP-2 in microglia activation and to elucidate the underlying mechanisms. BV-2 cells were pretreated with GLP-2 and then stimulated by lipopolysaccharide (LPS). Cells were assessed for the responses of pro-inflammatory enzymes (iNOS and COX-2) and pro-inflammatory cytokines (IL-1β, IL-6 and TNF-α); the related signaling pathways were evaluated by Western blotting. The rescue effect of GLP-2 on microglia-mediated neurotoxicity was also examined. The results showed that GLP-2 significantly reduced LPS-induced production of inducible nitric oxide synthase (iNOS), cyclooxygenase-s (COX-2), IL-1β, IL-6 and TNF-α. Blocking of Gα_s by NF449 resulted in a loss of this anti-inflammatory effect in BV-2 cells. Analyses in signaling pathways demonstrated that GLP-2 reduced LPS-induced phosphorylation of ERK1/2, JNK1/2 and p65, while no effect was observed on p38 phosphorylation. In addition, GLP-2 could suppress microglia-mediated neurotoxicity. All results imply that GLP-2 inhibits LPS-induced microglia activation by collectively regulating ERK1/2, JNK1/2 and p65.

Does Glp-2 have a protective effect on cerebral ischemia/reperfusion model?

BACKGROUND/AIM

To investigate the neuroprotective effects of glucagon-like peptide 2 (Glp-2), which increases cerebral blood flow, on the hippocampal complex after cerebral ischemia/reperfusion (I/R) injury in rats.

MATERIALS AND METHODS

Animals were randomized into 4 groups: sham, I/R + 0.9% NaCl, I/R + pre-Glp-2, and I/R + post-Glp-2. Cerebral ischemia was performed via the occlusion of the bilateral internal carotid artery for 40 min and continued with a reperfusion process. At the end of 6 h of reperfusion, animals were decapitated in all groups and brain tissues were removed. Malondialdehyde (MDA) and natural intracellular antioxidant glutathione (GSH) levels and myeloperoxidase (MPO) activities were measured in the left hippocampal tissue. The right hippocampal tissues of all group members were taken for histopathologic study.

RESULTS

MDA levels and MPO activities increased from Group I to Group II and decreased from Group II to Groups III and IV. On the other hand, GSH levels were not significantly different among the groups. The number of apoptotic hippocampal tissue cells increased from Group I to Group II and decreased from Group II to Groups III and IV.

CONCLUSION

Our preliminary study revealed that Glp-2 treatment may decrease oxidative damage from I/R in cerebral tissue.

Glucagon-like peptide-2 protects impaired intestinal mucosal barriers in obstructive jaundice rats

AIM: To observe the protective effect of glucagon-like peptide-2 (GLP-2) on the intestinal barrier of rats with obstructive jaundice and determine the possible mechanisms of action involved in the protective effect.

METHODS: Thirty-six Sprague-Dawley rats were randomly divided into a sham operation group, an obstructive jaundice group, and a GLP-2 group; each group consisted of 12 rats. The GLP-2 group was treated with GLP-2 after the day of surgery, whereas the other two groups were treated with the same concentration of normal saline. Alanine aminotransferase (ALT), total bilirubin, and endotoxin levels were recorded at 1, 3, 7, 10 and 14 d. Furthermore, on the 14^th day, body weight, the wet weight of the small intestine, pathological changes of the small intestine and the immunoglobulin A (IgA) expressed by plasma cells located in the small intestinal lamina propria were recorded for each group.

RESULTS: In the rat model, jaundice was obvious, and the rats’ activity decreased 4-6 d post bile duct ligation. Compared with the sham operation group, the obstructive jaundice group displayed increased yellow staining of abdominal visceral serosa, decreased small intestine wet weight, thinning of the intestinal muscle layer and villi, villous atrophy, uneven height, fusion, partial villous epithelial cell shedding, substantial inflammatory cell infiltration and significantly reduced IgA expression. However, no significant gross changes were noted between the GLP-2 and sham groups. With time, the levels of ALT, endotoxin and bilirubin in the GLP-2 group were significantly increased compared with the sham group (P < 0.01). The increasing levels of the aforementioned markers were more significant in the obstructive jaundice group than in the GLP-2 group (P < 0.01).

CONCLUSION: GLP-2 reduces intestinal mucosal injuries in obstructive jaundice rats, which might be attributed to increased intestinal IgA and reduced bilirubin and endotoxin.

Effects of PEGylated porcine glucagon-like peptide-2 therapy in weaning piglets challenged with lipopolysaccharide

This study aims to evaluate the therapeutic effect of polyethylene glycosylated porcine glucagon-like peptide-2 (pGLP-2), a long-acting form of pGLP-2, in lipopolysaccharide (LPS)-challenged piglets. Eighteen 21-day-old weaning piglets were randomly assigned into three groups: control (saline solution), LPS (100 μg/kg LPS), and PEG-pGLP-2 (10 nmol/kg PEG-pGLP-2+100 μg/kg LPS). All treatments were administered intraperitoneally. Compared with the control treatment, LPS treatment significantly decreased (P<0.05) the villus heights of the duodenum and jejunum, as well as the villus height/crypt depth ratio of the jejunum. However, PEG-pGLP-2 therapy reduced these effects (P>0.05). Specifically, PEG-pGLP-2 infusion significantly increased the villus height/crypt depth ratio of the duodenum (P<0.05) compared with LPS treatment. Compared with the control treatment, LPS treatment significantly increased (P<0.05) the mRNA expression levels of interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) in the jejunum. However, PEG-pGLP-2 therapy reduced these effects (P<0.05). Specifically, PEG-pGLP-2 infusion significantly decreased (P<0.05) the mRNA expression levels of interleukin (IL)-8 and TNF-α in the duodenum and jejunum, IL-10 in the duodenum, and IFN-γ in the jejunum compared with the LPS treatment. LPS treatment increased the caspase-3 activity of the ileum mucosal (P<0.05), and this effect was significantly reduced by PEG-pGLP-2 treatment. These results indicate that PEG-pGLP-2 infusion alleviates the severity of intestinal injury in weaning piglets by reducing the secretion of inflammatory cytokines and the caspase-3 activity, and increasing the villus height/crypt depth ratio.

Purified PEGylated porcine glucagon-like peptide-2 reduces the severity of colonic injury in a murine model of experimental colitis

The rapid degradation of porcine glucagon-like peptide-2 (pGLP-2) by the enzyme dipeptidyl peptidase-IV (DPP-IV) is the main impediment in the development of pGLP-2 as a potential therapeutic agent for intestinal dysfunction and damage. In this study, one mono-modified Lys(30)-polyethylene glycol (PEG)-pGLP-2 was prepared using mPEG-succinimidyl propionate. To determine the optimized condition for PEGylation, the reactions were monitored by RP-HPLC and MALDI-TOF-MS. Stability was tested in purified DPP-IV in vitro. In vivo, the protective effects for colonic injury were measured in dextran sulfate sodium (DSS)-induced colitis in mice. The monoPEGylated products reached the maximum yield at 4:1 ratio of mPEG5k-SPA to pGLP-2. An effective method of successfully separating PEGylated pGLP-2 from mPEG-SPA5kD using CM Sepharose Fast Flow resin was established. The half-life of Lys(30)-PEG-pGLP-2 was 16-fold longer than that of pGLP-2 in DPP-IV. The DSS mice exhibited marked weight loss), which was significantly reduced by Lys(30)-PEG-pGLP-2 therapy. DSS treatment significantly increased colonic damage score, which was significantly reduced by administration of Lys(30)-PEG-pGLP-2 in DSS-mice. DSS-induced colitis clearly induced Myeloperoxidase activity in the colon, which was significantly reduced by treatments with 3% DSS-pGLP-2 or 3% DSS-PEG-pGLP-2. These results showed that site-specific Lys(30)-PEG-GLP-2 was resistant to degradation and reduced the severity of colonic injury in murine colitis. The enhanced biological potency of this product highlighted its potential as a therapeutic agent for intestinal diseases.

The intestinal epithelial insulin-like growth factor-1 receptor links glucagon-like peptide-2 action to gut barrier function

Glucagon-like peptide-2 (GLP-2) is an intestinal growth-promoting hormone used to treat short bowel syndrome. GLP-2 promotes intestinal growth through a mechanism that involves both IGF-1 and the intestinal-epithelial IGF-1 receptor (IE-IGF-1R). GLP-2 also enhances intestinal barrier function, but through an unknown mechanism. We therefore hypothesized that GLP-2-enhanced barrier function requires the IE-IGF-1R and is mediated through alterations in expression and localization of tight junction proteins. Conditional IE-IGF-1R-null and control mice were treated with vehicle or degradation-resistant Gly(2)-GLP-2 for 10 days; some animals also received irinotecan to induce enteritis. Mice were then examined for gastrointestinal permeability to 4-kDa fluorescein isothiocyanate-dextran, jejunal resistance using Ussing chambers, tight junction structure by electron microscopy, and expression and localization of tight junction proteins by immunoblot and immunohistofluorescence, respectively. GLP-2 treatment decreased permeability to 4-kDa fluorescein isothiocyanate-dextran and increased jejunal resistance (P <.05-.01), effects that were lost in IE-IGF-1R-null mice. Electron microscopy did not reveal major structural changes in the tight junctions in any group of animals. However, the tight junctional proteins claudin-3 and -7 were upregulated by GLP-2 in control (P <.05-.01) but not null mice, whereas IE-IGF-1R deletion induced a shift in occludin localization from apical to intracellular domains; no changes were observed in expression or distribution of claudin-15 and zona occludins-1. Finally, in irinotecan-induced enteritis, GLP-2 normalized epithelial barrier function in control (P < .05) but not knockout animals. In conclusion, the effects of GLP-2 on intestinal barrier function are dependent on the IE-IGF-1R and involve modulation of key components of the tight junctional complex.

Neuronal Fos-like immunoreactivity associated with dexamethasone-induced hypertension in rats and effects of glucagon-like peptide-2

AIMS

Dexamethasone-induced hypertension models have been used to study the mechanisms of glucocorticoid induced hypertension, but the role of glucocorticoids in central cardiovascular regulation is not clearly understood. In the present study, we investigated the sites associated with dexamethasone-induced hypertension in the central nervous system in rats. We further investigated whether glucagon-like peptide-2 (GLP-2) was effective for dexamethasone-induced hypertension.

MAIN METHODS

Male Sprague–Dawley rats were treated with saline or dexamethasone (0.03mg/kg/day, s.c) for 10 days. GLP-2 (60 μg/kg, i.v.) was given to rats after dexamethasone treatment. We measured systolic blood pressure by a tail-cuff method in conscious rats, and arterial blood pressure in anesthetized rats. Immunohistochemical techniques were used to detection of the c-fos protein (Fos).

KEY FINDINGS

Fos-immunoreactivity (Fos-IR) in the dorsomedial hypothalamic nucleus (DMH) was higher in dexamethasone-treated rats than in saline-treated rats. However, Fos-IR in the infralimbic cortex, amygdala, and hippocampus was similar in saline-treated and dexamethasone-treated rats. Peripheral administration of GLP-2 reduced mean arterial blood pressure by 26%. After the peripheral administration of GLP-2, Fos-IR in the caudal ventrolateral medulla (CVLM) increased in dexamethasone-treated rats.

SIGNIFICANCE

Chronic dexamethasone treatment induced Fos-IR in the DMH. Peripheral administration of GLP-2 suppressed dexamethasone-induced hypertension in rats by enhancing inhibitory neuronal activity.

GLP-2 and mesenteric blood flow

The 33 amino acid peptide hormone GLP-2 is produced by enteroendocrine L-cells, the density of which is highest in the ileum and the colon, in response to the presence of nutrients in the lumen. The biological effect of GLP-2 is mediated by activation of a G-protein-coupled 7-transmembrane receptor. GLP-2 receptors are expressed in the brainstem, lungs, stomach, small intestine and colon, but not in the heart. It has been shown in several animal studies that GLP-2 infusion increases intestinal blood flow and that this increase is confined to the small intestine. The aim of the three studies, on which the thesis is based, was to investigate basic physiological effects of GLP-2, in healthy volunteers and in SBS patients, with focus on the effects on mesenteric blood flow, blood flow at other vascular sites and effects on cardiac parameters. These parameters have been evaluated after both meal stimulation and GLP-2 administration. The studies showed the following results: Blood flow: In all three studies, blood flow changes in the SMA after GLP-2 administration were similar regarding changes over time and degree of change. Blood flow changes were similar to changes seen after a standard meal. Only RI changes were registered in all three studies, but the TAMV changes in study 2 and 3 had similar characteristics. Cardiovascular parameters: In all three studies no significant changes in blood pressure were registered in relation to GLP-2 administration. In study two and three, where cardiac parameters also were registered by impedance cardiography, increases in CO and SV were seen. Plasma GLP-2: There were, as expected, supraphysiological GLP-2 plasma levels after SC administration. All three studies have shown rapid changes in mesenteric blood flow after administration GLP-2. The changes have been the same both in regards to time to maximum changes (increase) and relatively close in regards to maximum extent of change. The changes in the SBS patients were less than in the healthy test subjects. The findings leave no doubt about that GLP-2 is a potent regulator of upper splanchnic blood flow. The study findings also support the notion that the observed increased mesenteric blood flow, isolated to the SMA, is secondary to the metabolic responses to GLP-2, and that these are likely due to a paracrine action by GLP-2 acting on GLP-2R bearing cells such as enteric neurons, probably expressing NO. In conclusion GLP-2 increases mesenteric blood flow in healthy subjects and in SBS patients, the increase is equivalent to a standard meal and dose dependent. The blood flow is not increased at other arterial vascular sites. GLP-2 does not acutely alter blood pressure, but increases, probably as compensation, pulse rate and cardiac output. GLP-2 induced vascular response in the superior mesenteric artery is related with the length of remaining intestine in SBS patients. The effect is therefore likely to reflect the metabolic activity in the tissue rather than direct effect on the vascular system.

Glucagon-like peptide 2 induces vasoactive intestinal polypeptide expression in enteric neurons via phophatidylinositol 3-kinase-γ signaling

Glucagon-like peptide 2 (GLP-2) is an enteroendocrine hormone trophic for intestinal mucosa; it has been shown to increase enteric neuronal expression of vasoactive intestinal polypeptide (VIP) in vivo. We hypothesized that GLP-2 would regulate VIP expression in enteric neurons via a phosphatidylinositol-3 kinase-γ (PI3Kγ) pathway. The mechanism of action of GLP-2 was investigated using primary cultures derived from the submucosal plexus (SMP) of the rat and mouse colon. GLP-2 (10(-8) M) stimulation for 24 h increased the proportion of enteric neurons expressing VIP (GLP-2: 40 ± 6% vs. control: 22 ± 5%). GLP-2 receptor expression was identified by immunohistochemistry on neurons (HuC/D+) and glial cells (GFAP+) but not on smooth muscle or fibroblasts in culture. Over 1-4 h, GLP-2 stimulation of SMP increased phosphorylated Akt/Akt ratios 6.1-fold, phosphorylated ERK/ERK 2.5-fold, and p70S6K 2.2-fold but did not affect intracellular cAMP. PI3Kγ gene deletion or pharmacological blockade of PI3Kγ, mammalian target of rapamycin (mTOR), and MEK/ERK pathways blocked the increase in VIP expression by GLP-2. GLP-2 increased the expression of growth factors and their receptors in SMP cells in culture [IGF-1r (3.2-fold increase), EGFr (5-fold), and ErbB-2-4r (6- to 7-fold)] and ligands [IGF-I (1.5-fold), amphiregulin (2.5-fold), epiregulin (3.2-fold), EGF (7.5-fold), heparin-bound EGF (2.0-fold), β-cellulin (50-fold increase), and neuregulins 2-4 (300-fold increase) (by qRT-PCR)]. We conclude that GLP-2 acts on enteric neurons and glial cells in culture via a PI3Kγ/Akt pathway, stimulating neuronal differentiation via mTOR and ERK pathways, and expression of receptors and ligands for the IGF-I and ErbB pathways.

GLP-2 receptor in POMC neurons suppresses feeding behavior and gastric motility

Glucagon-like peptides (GLP-1/2) are cosecreted from endocrine L cells in the gut and preproglucagonergic neurons in the brain. Peripheral GLP-2 action is essential for maintaining intestinal homeostasis, improving absorption efficiency and blood flow, promoting immune defense, and producing efficacy in treatment of gastrointestinal diseases. However, it is unknown if CNS GLP-2 plays a physiological role in the control of energy homeostasis. Since GLP-1/2 are cotranslated from preproglucagongene and coproduced by prohormone convertase-1, it is challenging to knockout GLP-2 only. Instead, our laboratory has generated a Glp2r-floxed mouse line to dissect cell-specific GLP-2 receptor GLP-2R) action in the regulation of energy balance. Our objective was to determine if GLP-2R in the hypothalamus modulates feeding behavior and gastric emptying. We show that Glp2r mRNA and protein are highly expressed in the arcuate nucleus and dorsomedial nucleus of the mouse hypothalamus. Using the Cre-LoxP system, we generated mice that lack Glp2r expression in POMC neurons (KO; mainly in the hypothalamus). The KO mice showed hyperphagic behavior (such as increases in food intake and meal frequency), accelerated gastric emptying (assessed by [(13)C]octanoic acid breath test), and late-onset obesity, yet there was no decrease in basal metabolic rate. Infusion of GLP-2 (2.5 nmol into the 4th ventricle) suppressed food intake and gastric emptying, while GLP-2-mediated effects were abolished in the melanocortin receptor-4 (MC4R) KO mice. We conclude that Glp2r deletion in POMC neurons enhances feeding behavior and gastric motility, whereas icv GLP-2R activation suppresses food intake and gastric emptying through the MC4R signaling pathway. This study indicates that CNS GLP-2R plays a physiological role in the control of feeding behavior and gastric emptying and that this is mediated probably through the melanocortin system.

Glucagon-like peptide-2 (GLP-2) modulates the cGMP signalling pathway by regulating the expression of the soluble guanylyl cyclase receptor subunits in cultured rat astrocytes

The aim of this work was to study the effect of glucagon-like peptide-2 (GLP-2) on the cyclic guanosine monophosphate (cGMP) signalling pathway and whether insulin or epidermal growth factor (EGF) might modulate the effects of GLP-2. GLP-2 produced a dose-dependent decrease in intracellular sodium nitroprusside-induced cGMP production. However, insulin induced an increase in the levels of cGMP that was dose-dependently decreased by the addition of GLP-2. By contrast, EGF induced a decrease in cGMP production, which was further reduced by the addition of GLP-2. To assess whether variations in cGMP production might be related with changes in some component of soluble guanylyl cyclase (sGC), the expression of the α1, α2, and β1 subunits were determined by Western blot analysis. At 1 h, GLP-2 produced a decrease in the expression of both α1 and β1 in the cytosolic fraction, but at 24 h only β1was reduced. As expected, insulin induced an increase in the expression of both subunits after 1 h of incubation; this was decreased by the addition of GLP-2. Likewise, incubation with EGF for 24 h produced a decrease in the expression of both subunits that was maximal when GLP-2 was added. In addition, incubation with insulin for 1 h produced an increase in the expression of the α2 subunit, which was reduced by the addition of GLP-2. These results suggest that GLP-2 inhibits cGMP production by decreasing the cellular content of at least one subunit of the heterodimeric active form of the sGC, independently of the presence of insulin or EFG. This may open new insights into the actions of this neuropeptide.

Food intake in lean and obese mice after peripheral administration of glucagon-like peptide 2

We investigated the potential anorectic action of peripherally administered glucagon-like peptide 2 (GLP2) in lean and diet-induced obese (DIO) mice. Mice, fasted for 16 h, were injected i.p. with native GLP2 or [Gly2]GLP2, stable analog of GLP2, before or after GLP2 (3-33), a GLP2 receptor (GLP2R) antagonist, or exendin (9-39), a GLP1R antagonist. Food intake was measured at intervals 1, 2, 4, 8, and 24 h postinjection. In addition, we tested in lean mice the influence of [Gly2]GLP2 on gastric emptying and the effects of GLP1 alone or in combination with [Gly2]GLP2 on food intake. [Gly2]GLP2 dose dependently and significantly inhibited food intake in lean and DIO mice. The reduction of food intake occurred in the first hour postinjection and it was sustained until 4 h postinjection in lean mice while it was sustained until 2 h postinjection in DIO mice. GLP2 significantly inhibited food intake in both lean and DIO mice but only in the first hour postinjection. The efficiency of [Gly2]GLP2 or GLP2 in suppressing food intake was significantly weaker in DIO mice compared with lean animals. The [Gly2]GLP2 anorectic actions were blocked by the GLP2R antagonist GLP2 (3-33) or by the GLP1R antagonist exendin (9-39). The coadministration of [Gly2]GLP2 and GLP1 did not cause additive effects. [Gly2]GLP2 decreased the gastric emptying rate. Results suggest that GLP2 can reduce food intake in mice in the short term, likely acting at a peripheral level. DIO mice are less sensitive to the anorectic effect of the peptide.

Receptor identification and physiological characterisation of glucagon-like peptide-2 in the rat heart

BACKGROUND AND AIMS

The anorexigenic glucagon-like peptide (GLP)-2 is produced by intestinal L cells and released in response to food intake. It affects intestinal function involving G-protein-coupled receptors. To verify whether GLP-2 acts as a cardiac modulator in mammals, we analysed, in the rat heart, the expression of GLP-2 receptors and the myocardial and coronary responses to GLP-2.

METHODS AND RESULTS

GLP-2 receptors were detected on ventricular extracts by quantitative real-time polymerase chain reaction (Q-RT-PCR) and Western blotting. Cardiac GLP-2 effects were analysed on Langendorff perfused hearts. Intracellular GLP-2 signalling was investigated on Langendorff perfused hearts and by Western blotting and enzyme-linked immunosorbent assay (ELISA) on ventricular extracts. By immunoblotting and Q-RT-PCR, we revealed the expression of ventricular GLP-2 receptors. Perfusion analyses showed that GLP-2 induces positive inotropism at low concentration (10-12 mol l(-1)), and negative inotropism and lusitropism from 10 to 10 mol l(-1). It dose-dependently constricts coronaries. The negative effects of GLP-2 were independent from GLP-1 receptors, being unaffected by exendin-3 (9-39) amide. GLP-2-dependent negative action involves Gi/o proteins, associates with a reduction of intracellular cyclic adenosine monophosphate (cAMP), an increase in extracellular signal regulated kinases 1 and 2 (ERK1/2) and a decrease in phospholamban phosphorylation, but is independent from endothelial nitric oxide synthase (eNOS) and protein kinase G (PKG). Finally, GLP-2 competitively antagonised β-adrenergic stimulation.

CONCLUSIONS

For the first time, to our knowledge, we found that: (1) the rat heart expresses functional GLP-2 receptors; (2) GLP-2 acts on both myocardium and coronaries, negatively modulating both basal and β-adrenergic stimulated cardiac performance; and (3) GLP-2 effects are mediated by G-proteins and involve ERK1/2.

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 directly regulates hypothalamic neurons expressing neuropeptides linked to appetite control in vivo and in vitro

Glucagon-like peptide-2 (GLP-2), a proglucagon-derived peptide, has been postulated to affect appetite at the level of the hypothalamus. To gain better insight into this process, a degradation-resistant GLP-2 analog, human (Gly(2))GLP-2(1-33) [h(Gly(2))GLP-2] was intracerebroventricularly injected into mice to examine its action on food and water intake and also activation of hypothalamic anorexigenic α-melanocyte-stimulating hormone/proopiomelanocortin, neurotensin, and orexigenic neuropeptide Y, and ghrelin neurons. Central h(Gly(2))GLP-2 administration significantly suppressed food and water intake with acute weight loss at 2 h. Further, central h(Gly(2))GLP-2 robustly induced c-Fos activation in the hypothalamic arcuate, dorsomedial, ventromedial, paraventricular, and the lateral hypothalamic nuclei. We found differential colocalization of neuropeptides with c-Fos in specific regions of the hypothalamus. To assess whether hypothalamic neuropeptides are directly regulated by GLP-2 in vitro, we used an adult-derived clonal, immortalized hypothalamic cell line, mHypoA-2/30, that endogenously expresses functional GLP-2 receptors (GLP-2R) and two of the feeding-related neuropeptides linked to GLP-2R activation in vivo: neurotensin and ghrelin. Treatment with h(Gly(2))GLP-2 stimulated c-Fos expression and phosphorylation of cAMP response element-binding protein/activating transcription factor-1. In addition, treatment with h(Gly(2))GLP-2 significantly increased neurotensin and ghrelin mRNA transcript levels by 50 and 95%, respectively, at 24 h after treatment in protein kinase A-dependent manner. Taken together, these findings implicate the protein kinase A pathway as the means by which GLP-2 can up-regulate hypothalamic neuropeptide mRNA levels and provide evidence for a link between central GLP-2R activation and specific hypothalamic neuropeptides involved in appetite regulation.

The separate and combined impact of the intestinal hormones, GIP, GLP-1, and GLP-2, on glucagon secretion in type 2 diabetes

Type 2 diabetes mellitus (T2DM) is associated with reduced suppression of glucagon during oral glucose tolerance test (OGTT), whereas isoglycemic intravenous glucose infusion (IIGI) results in normal glucagon suppression in these patients. We examined the role of the intestinal hormones glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and glucagon-like peptide-2 (GLP-2) in this discrepancy. Glucagon responses were measured during a 3-h 50-g OGTT (day A) and an IIGI (day B) in 10 patients with T2DM [age (mean ± SE), 51 ± 3 yr; body mass index, 33 ± 2 kg/m(2); HbA(1c), 6.5 ± 0.2%]. During four additional IIGIs, GIP (day C), GLP-1 (day D), GLP-2 (day E) and a combination of the three (day F) were infused intravenously. Isoglycemia during all six study days was obtained. As expected, no suppression of glucagon occurred during the initial phase of the OGTT, whereas significantly (P < 0.05) lower plasma levels of glucagon during the first 30 min of the IIGI (day B) were observed. The glucagon response during the IIGI + GIP + GLP-1 + GLP-2 infusion (day F) equaled the inappropriate glucagon response to OGTT (P = not significant). The separate GIP infusion (day C) elicited significant hypersecretion of glucagon, whereas GLP-1 infusion (day D) resulted in enhancement of glucagon suppression during IIGI. IIGI + GLP-2 infusion (day E) resulted in a glucagon response in the midrange between the glucagon responses to OGTT and IIGI. Our results indicate that the intestinal hormones, GIP, GLP-1, and GLP-2, may play a role in the inappropriate glucagon response to orally ingested glucose in T2DM with, especially, GIP, acting to increase glucagon secretion.

Glucagon-like peptide-2-stimulated protein synthesis through the PI 3-kinase-dependent Akt-mTOR signaling pathway

Glucagon-like peptide-2 (GLP-2) is a nutrient-responsive neuropeptide that exerts diverse actions in the gastrointestinal tract, including enhancing mucosal cell survival and proliferation. GLP-2 stimulates mucosal growth in vivo with an increased rate of protein synthesis. However, it was unclear whether GLP-2 can directly stimulate protein synthesis. The objective was to test critically whether GLP-2 receptor (GLP-2R) activation directly stimulates protein synthesis through a PI 3-kinase-dependent Akt-mTOR signaling pathway. HEK 293 cells (transfected with human GLP-2R cDNA) were treated with human GLP-2 with/without pretreatment of PI 3-kinase inhibitor (LY-294002) or mTOR inhibitor (rapamycin). Results show that 1) GLP-2 specifically bound to GLP-2R overexpressed in the HEK cells with K(a) = 0.22 nM and B(max) = 321 fmol/μg protein; 2) GLP-2-stimulated protein synthesis was dependent on the amount of GLP-2R cDNA and the dosage of GLP-2 and reached the plateau among 0.2-2 nM GLP-2; 3) GLP-2-stimulated protein synthesis was abolished by the PI 3-kinase inhibitor and mTOR inhibitor; and 4) GLP-2-mediated stimulation of phosphorylation on Akt and mTOR was dependent on the amount of GLP-2R cDNA transfected and the dosage of GLP-2. In addition, GLP-2-mediated action and signaling in regulation of protein synthesis were confirmed in mouse hippocampal neurons (expressing native GLP-2R). GLP-2 directly stimulated protein synthesis of primary cultured neurons in dosage-dependent, PI 3-kinase-dependent, and rapamycin-sensitive manners, which linked with activation of Akt-mTOR signaling pathway as well. We conclude that GLP-2R activation directly stimulates protein synthesis by activating the PI 3-kinase-dependent Akt-mTOR signaling pathway. GLP-2-stimulated protein synthesis may be physiologically relevant to maintaining neuronal long-term potentiation and providing secondary mediators (namely neuropeptides or growth factors).

Mechanism of action of glucagon-like peptide-2 to increase IGF-I mRNA in intestinal subepithelial fibroblasts

IGF-I, a known secretory product of intestinal subepithelial myofibroblasts (ISEMFs), is essential for the intestinotropic effects of glucagon-like peptide-2 (GLP-2). Furthermore, GLP-2 increases IGF-I mRNA transcript levels in vitro in heterogeneous fetal rat intestinal cultures, as well as in vivo in the rodent small intestine. To determine the mechanism underlying the stimulatory effect of GLP-2 on intestinal IGF-I mRNA, murine ISEMF cells were placed into primary culture. Immunocytochemistry showed that the ISEMF cells appropriately expressed α-smooth muscle actin and vimentin but not desmin. The cells also expressed GLP-2 receptor and IGF-I mRNA transcripts. Treatment of ISEMF cells with (Gly2)GLP-2 induced IGF-I mRNA transcripts by up to 5-fold of basal levels after treatment with 10(-8) m GLP-2 for 2 h (P < 0.05) but did not increase transcript levels for other intestinal growth factors, such as ErbB family members. Immunoblot revealed a 1.6-fold increase in phospho (p)-Akt/total-(t)Akt with 10(-8) m GLP-2 treatment (P < 0.05) but no changes in cAMP, cAMP-dependent β-galactosidase expression, pcAMP response element-binding protein/tcAMP response element-binding protein, pErk1/2/tErk1/2, or intracellular calcium. Furthermore, pretreatment of ISEMF cells with the phosphatidylinositol 3 kinase (PI3K) inhibitors, LY294002 and wortmannin, abrogated the IGF-I mRNA response to GLP-2, as did overexpression of kinase-dead Akt. The role of PI3K/Akt in GLP-2-induced IGF-I mRNA levels in the murine jejunum was also confirmed in vivo. These findings implicate the PI3K/Akt pathway in the stimulatory effects of GLP-2 to enhance intestinal IGF-I mRNA transcript levels and provide further evidence in support of a role for IGF-I produced by the ISEMF cells in the intestinotropic effects of GLP-2.

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.

[Effect of glucagon-like peptide-2 (GLP-2) on intestinal barrier function in bile duct ligated rats]

OBJECTIVE

To investigate the effect of glucagon-like peptide-2 (GLP-2) on intestinal barrier function in bile duct ligated rats.

METHODS

Seventy-two SD rats were randomly divided into three groups: GLP-2 treated group (T), obstructive jaundice control group (C) and sham operation group (SO). Proliferating cell nuclear antigen (PCNA) and caspase-3 expression in the intestinal mucosa were measured by immunohistochemistry staining equiped image analyzing systems (Image proplus Version 4.5), and the height of the intestinal villi was observed and measured with light microscope, in the rats 1, 3 and 7 days after operation.

RESULTS

The expression of PCNA in the intestinal villi of rats in C group decreased significantly (P < 0.05), which was more serious than those in the SO and T groups especially on the third and seventh day after operation (P < 0.05). Compared with the SO and T groups, the expression of caspase-3 in the rats of C group increased significantly. The expression of caspase-3 increased with timeafter operation (P < 0.05). The height of the villi of the rats in C group was shorter than those of the rats in SO and T groups, and it became shorter and shorter day by day(P < 0.05). The height of the intestinal villi of the rats in SO group and T groups had no significant changes post operation.

CONCLUSION

GLP-2 may stimulate the growth of intestinal mucosa, increase the intestinal mucosa cell proliferation, diminish the number of the apoptosis cells, and protect the intestinal barrier function in obstructive jaundice rats.

Four-month treatment with GLP-2 significantly increases hip BMD: a randomized, placebo-controlled, dose-ranging study in postmenopausal women with low BMD

We have previously shown that repeated dosing of glucagon-like peptide-2 (GLP-2) at 10 p.m. in postmenopausal women for 14 days results in a dose-dependent decrease in the nocturnal bone resorption, as assessed by s-CTX. In contrast, bone formation, as assessed by serum osteocalcin, appeared to be unaffected by treatment with exogenous GLP-2, at least over 14 days. The present study extends the observation period to four months. The study was a double-blind placebo-controlled dose-ranging trial comparing three different doses of GLP-2 (0.4 mg, 1.6 mg and 3.2 mg GLP-2, administered nightly) against a saline control injection. We examined safety and tolerability, and the effects on biochemical markers of bone turnover and the effect on bone mineral density. Injection of 0.4 mg, 1.6 mg and 3.2 mg GLP-2 resulted in similar reduction in the nocturnal rise of s-CTX, at Treatment Day 120 the mean difference to placebo was approximately -150%*h at AUC(0-10H) (P<0.01). Osteocalcin levels were unaffected in the 10-hour period after injection indicating that injections of 0.4 mg, 1.6 mg and 3.2 mg GLP-2 do not exert any acute stimulatory or inhibitory effect on bone formation. Treatment with GLP-2 resulted in a significant dose-dependent increase in total hip BMD over the course of the study that for the 3.2 mg GLP-2 group reached 1.1% (P=0.007) from baseline. The overall rates of adverse events in the 4 treatment groups were similar and there were no signs of tachyphylaxis or antibodies against GLP-2. The results indicate that GLP-2 produces a substantial decrease in bone resorption without suppression of bone formation thereby changing the bone remodeling balance in favor of bone formation, particularly at the hip.

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.

Synergistic effect of glucagon-like peptide 2 (GLP-2) and of key growth factors on the proliferation of cultured rat astrocytes. Evidence for reciprocal upregulation of the mRNAs for GLP-2 and IGF-I receptors

The aim of this work was to determine whether the stimulating effect of glucagon-like peptide (GLP)-2 on astrocyte proliferation could be reinforced by proliferating substances, including growth factors such as EGF, platelet-derived growth factor, insulin-like growth factor type I (IGF-I) or a hormone such as insulin. Both DNA synthesis and astrocyte density, as well as the expression of c-Fos, Ki-67, proliferating cell nuclear antigen and glial fibrillary acidic proteins, were found to be higher in the presence of GLP-2 than in its absence. In an attempt to get a better understanding of this process, intracellular cyclic adenosine monophosphate (cAMP) production, extracellular signal-regulated kinase (ERK) 1/2 phosphorylation and the expression of GLP-2R and IGF-I receptor (IGF-IR) mRNAs were studied in response to growth factors. Our results indicate that, in the presence of different growth factors, GLP-2 does not increase cAMP production but raises ERK 1/2 phosphorylation. In addition, GLP-2R mRNA expression was increased by IGF-I, whilst mRNA expression of IGF-IR was higher in cells incubated with GLP-2 than in control cells. These results suggest for the first time that GLP-2 and several growth factors show synergistic effects on the proliferation of rat astrocytes, a process in which an enhanced expression of GLP-2R and IGF-IR may be involved, providing additional insights into the physiological role of this novel neuropeptide, specially during astroglial regeneration.

Early but not late administration of glucagon-like peptide-2 following ileo-cecal resection augments putative intestinal stem cell expansion

Expansion of intestinal progenitors and putative stem cells (pISC) occurs early and transiently following ileo-cecal resection (ICR). The mechanism controlling this process is not defined. We hypothesized that glucagon-like peptide-2 (GLP-2) would augment jejunal pISC expansion only when administered to mice immediately after ICR. Since recent reports demonstrated increases in intestinal insulin-like growth factor (IGF)-I following GLP-2 administration, we further hypothesized that increased intestinal IGF-I expression would correlate with pISC expansion following ICR. To assess this, GLP-2 or vehicle was administered to mice either immediately after resection (early) or before tissue harvest 6 wk following ICR (late). Histological analysis quantified proliferation and intestinal morphometrics. Serum levels of GLP-2 were measured by ELISA and jejunal IGF-I mRNA by qRT-PCR. Expansion of jejunal pISC was assessed by fluorescent-activated cell sorting of side population cells, immunohistochemistry for phosphorylated beta-catenin at serine 552 (a pISC marker), percent of crypt fission, and total numbers of crypts per jejunal circumference. We found that early but not late GLP-2 treatment after ICR significantly augmented pISC expansion. Increases in jejunal IGF-I mRNA correlated temporally with early pISC expansion and effects of GLP-2. Early GLP-2 increased crypt fission and accelerated adaptive increases in crypt number and intestinal caliber. GLP-2 increased proliferation and intestinal morphometrics in all groups. This study shows that, in mice, GLP-2 promotes jejunal pISC expansion only in the period immediately following ICR. This is associated with increased IGF-I and accelerated adaptive increases in mucosal mass. These data provide clinical rationale relevant to the optimal timing of GLP-2 in patients with intestinal failure.

Glucagon-like peptide-2 reduces intestinal permeability but does not modify the onset of type 1 diabetes in the nonobese diabetic mouse

The development of type 1 diabetes (T1D) has been linked to environmental factors and dietary components. Increasing evidence indicates that the integrity of the gut mucosa plays a role in the development of autoimmune diseases, and evidence from both preclinical and clinical studies demonstrates that increased leakiness of the intestinal epithelium precedes the development of type 1 diabetes. However, there is limited information on modulation of gut barrier function and its relationship to diabetes development. Here we show that the nonobese diabetic (NOD) mouse, a model of T1D, exhibits enhanced intestinal transcellular permeability before the development of autoimmune diabetes. Treatment of NOD mice with a glucagon-like peptide 2 (GLP-2) analog, synthetic human [Gly(2)] glucagon-like peptide-2 (h[Gly(2)]GLP-2, increased the length and weight of the small bowel and significantly improved jejunal transepithelial resistance. However, chronic administration of once daily h[Gly(2)]GLP-2 failed to delay or reverse the onset of T1D when treatment was initiated in young, normoglycemic female NOD mice. Furthermore, h[Gly(2)]GLP-2 administration had no significant effect on lymphocyte subpopulations in NOD mice. These findings demonstrate that h[Gly(2)]GLP-2-mediated enhancement of gut barrier function in normoglycemic NOD mice disease is not sufficient to prevent or delay the development of experimental T1D.

[Influence of glucagon-like peptide-2 on intestinal lymphocyte homing in mice with acute pancreatitis]

OBJECTIVE

To investigate the influence of glucagon-like peptide-2 (GLP-2) on intestinal lymphocyte homing receptor-integrin alpha 4 beta 7 and homing ligand-intestinal mucosal addressin cell adhesion molecule-1 (MAdCAM-1) in mice with acute pancreatitis (AP).

METHODS

A total of 96 mice were divided into three groups randomly (n=32 in each group): AP group, GLP-2 group and control group. Murine AP model was reproduced by intraperitoneal injection of caerulein and lipopolysaccharides (LPS). GLP-2 (250 microg/kg) was injected intraperitoneally at 15 minutes after the establishment of model, then it was injected twice a day for 3 days in GLP-2 group, while the mice in control group received normal saline instead. Mice were sacrificed at 6, 12, 24 and 48 hours after reproduction of AP, and tissue specimens were harvested. Integrin alpha 4 beta 7 positive peripheral blood lymphocytes were determined by flow cytometry. The expression of MAdCAM-1 in the terminal ileum mucosa and Peyer patch was measured by immunohistochemistry. Same observations were also done in the control and GLP-2 groups.

RESULTS

Compared with control group, integrin alpha 4 beta 7 positive lymphocyte in peripheral blood and the expression of MAdCAM-1 in the terminal ileum mucosa and Peyer patch were significantly reduced at 6, 12, 24 and 48 hours in AP mice (all P<0.05). Integrin alpha 4 beta 7 positive lymphocyte and the expression of MAdCAM-1 were markedly higher in GLP-2 group than those in AP group (all P<0.05), but were lower in GLP-2 group than those in control group (all P>0.05).

CONCLUSION

Administration of GLP-2 may restore expression of integrin alpha 4 beta 7 and MAdCAM-1, promote lymphocyte homing to intestine, thus improve the immunological function of intestine.

Glucagon-like peptide-2 activates beta-catenin signaling in the mouse intestinal crypt: role of insulin-like growth factor-I

Chronic administration of glucagon-like peptide-2 (GLP-2) induces intestinal growth and crypt cell proliferation through an indirect mechanism requiring IGF-I. However, the intracellular pathways through which IGF-I mediates GLP-2-induced epithelial tropic signaling remain undefined. Because beta-catenin and Akt are important regulators of crypt cell proliferation, we hypothesized that GLP-2 activates these signaling pathways through an IGF-I-dependent mechanism. In this study, fasted mice were administered Gly(2)-GLP-2 or LR(3)-IGF-I (positive control) for 0.5-4 h. Nuclear translocation of beta-catenin in non-Paneth crypt cells was assessed by immunohistochemistry and expression of its downstream proliferative markers, c-myc and Sox9, by quantitative RT-PCR. Akt phosphorylation and activation of its targets, glycogen synthase kinase-3beta and caspase-3, were determined by Western blot. IGF-I receptor (IGF-IR) and IGF-I signaling were blocked by preadministration of NVP-AEW541 and through the use of IGF-I knockout mice, respectively. We found that GLP-2 increased beta-catenin nuclear translocation in non-Paneth crypt cells by 72 +/- 17% (P < 0.05) and increased mucosal c-myc and Sox9 mRNA expression by 90 +/- 20 and 376 +/- 170%, respectively (P < 0.05-0.01), with similar results observed with IGF-I. This effect of GLP-2 was prevented by blocking the IGF-IR as well as ablation of IGF-I signaling. GLP-2 also produced a time- and dose-dependent activation of Akt in the intestinal mucosa (P < 0.01), most notably in the epithelium. This action was reduced by IGF-IR inhibition but not IGF-I knockout. We concluded that acute administration of GLP-2 activates beta-catenin and proliferative signaling in non-Paneth murine intestinal crypt cells as well as Akt signaling in the mucosa. However, IGF-I is required only for the GLP-2-induced alterations in beta-catenin.

The alpha cell expresses glucagon-like peptide-2 receptors and glucagon-like peptide-2 stimulates glucagon secretion from the rat pancreas

AIMS/HYPOTHESIS

Glucagon-like peptide-2 (GLP-2) is a gut hormone regulating intestinal growth and nutrient absorption. Recently, GLP-2 has been reported to stimulate glucagon secretion in healthy humans. We sought to clarify the mechanism and physiological significance of this endocrine effect.

MATERIALS AND METHODS

The expression of the GLP-2 receptor gene, Glpr2, and the localisation of the protein were evaluated by real-time PCR on cDNA from isolated rat islets and by immunohistochemistry in rat and human pancreas. The glucagon, insulin and somatostatin responses to 0.1, 1 and 10 nmol/l GLP-2 and to GLP-1 and GLP-2 given simultaneously were studied in the isolated perfused rat pancreas.

RESULTS

Expression of Glp2r transcript was confirmed by PCR. In both human and rat pancreas, GLP-2r immunoreactivity was colocalised with proglucagon. GLP-2 at 10 nmol/l increased glucagon secretion significantly from a pre-infusion level of 0.314 +/- 0.07 to 0.508 +/- 0.09 pmol/min (p < 0.0005), whereas lower GLP-2 concentrations were ineffective. Neither insulin nor somatostatin output was influenced. During simultaneous administration of GLP-1 and GLP-2, net glucagon release was no longer reduced by 0.1, 1 or 10 nmol/l GLP-1, which, when given alone, inhibited glucagon secretion by 25.0 +/- 9.9, 46.2 +/- 4.8, and 44.1 +/- 2.9%, respectively.

CONCLUSIONS/INTERPRETATION

Our results suggest that GLP-2 stimulates glucagon secretion through GLP-2r present on the alpha cell in rats. In the presence of GLP-2, the glucagonostatic effect of GLP-1, normally co-secreted with GLP-2, is markedly inhibited. Based on our analogous immunohistochemical findings in human pancreas, this mechanism also applies in all likelihood to humans. However, further in vivo studies are required to assess the physiological significance of the glucagonotropic action of GLP-2 in humans.

The intestinotrophic peptide, glp-2, counteracts intestinal atrophy in mice induced by the epidermal growth factor receptor inhibitor, gefitinib

PURPOSE

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors have been introduced as antitumor agents in the treatment of cancers overexpressing the receptor. The treatment has gastrointestinal side effects which may decrease patient compliance and limit the efficacy. Glucagon-like peptide-2 (GLP-2) is an intestinal hormone with potent intestinotrophic properties and therapeutic potential in disorders with compromised intestinal capacity. The growth stimulation is highly specific to the gastrointestinal tract, and no effects are observed elsewhere. The aim of this study was to examine whether the inhibition of the EGFR induces intestinal atrophy and if this can be counteracted by treatment with GLP-2.

EXPERIMENTAL DESIGN

Mice were treated for 10 days with either gefitinib orally, GLP-2 as injections, or a combination of both. After sacrifice, the weight and length of the segments of the gastrointestinal tract were determined, and histologic sections were analyzed by morphometric methods.

RESULTS

A significant atrophy of the small-intestinal wall was observed after treatment with gefitinib because both intestinal weight and morphometrically estimated villus height and cross-sectional area were decreased. The same parameters were increased by GLP-2 treatment alone, and when GLP-2 was combined with the gefitinib treatment, the parameters remained unchanged.

CONCLUSIONS

Treatment with an EGFR tyrosine kinase inhibitor in mice results in small-intestinal growth inhibition that can be completely prevented by simultaneous treatment with GLP-2. This suggests that the gastrointestinal side effects elicited by treatment with EGFR tyrosine kinase inhibitors can be circumvented by GLP-2 treatment.

Role of glial cell-line derived neurotropic factor family receptor alpha2 in the actions of the glucagon-like peptides on the murine intestine

The intestinal glucagon-like peptides GLP-1 and GLP-2 inhibit intestinal motility, whereas GLP-2 also stimulates growth of the intestinal mucosa. However, the mechanisms of action of these peptides in the intestine remain poorly characterized. To determine the role of the enteric nervous system in the actions of GLP-1 and GLP-2 on the intestine, the glial cell line-derived neurotropic factor family receptor alpha(2) (GFRalpha2) knockout (KO) mouse was employed. The mice exhibited decreased cholinergic staining, as well as reduced mRNA transcripts for substance P-ergic excitatory motoneurons in the enteric nervous system (ENS) (P < 0.05). Examination of parameters of intestinal growth (including small and large intestinal weight and small intestinal villus height, crypt depth, and crypt cell proliferation) demonstrated no differences between wild-type and KO mice in either basal or GLP-2-stimulated mucosal growth. Nonetheless, KO mice exhibited reduced numbers of synaptophysin-positive enteroendocrine cells (P < 0.05), as well as a markedly impaired basal gastrointestinal (GI) transit rate (P < 0.05). Furthermore, acute administration of GLP-1 and GLP-2 significantly inhibited transit rates in wild-type mice (P < 0.05-0.01) but had no effect in GFRalpha2 KO mice. Despite these changes, expression of mRNA transcripts for the GLP receptors was not reduced in the ENS of KO animals, suggesting that GLP-1 and -2 modulate intestinal transit through enhancement of inhibitory input to cholinergic/substance P-ergic excitatory motoneurons. Together, these findings demonstrate a role for GFRalpha2-expressing enteric neurons in the downstream signaling of the glucagon-like peptides to inhibit GI motility, but not in intestinal growth.