Robin P. Boushey

Human [Gly2]GLP-2 reduces the severity of colonic injury in a murine model of experimental colitis

The pathology of Crohns disease and ulcerative colitis is characterized by chronic inflammation and destruction of the gastrointestinal epithelium. Although suppression of inflammatory mediators remains the principle component of current disease therapeutics, strategies for enhancing repair and regeneration of the compromised intestinal epithelium have not been widely explored. The demonstration that a peptide hormone secreted by the intestinal epithelium, glucagon-like peptide-2 (GLP-2), is a potent endogenous stimulator of intestinal epithelial proliferation in the small bowel prompted studies of the therapeutic efficacy of GLP-2 in CD1 and BALB/c mice with dextran sulfate (DS)-induced colitis. We report here that a human GLP-2 analog (h[Gly2]GLP-2) significantly reverses weight loss, reduces interleukin-1 expression, and increases colon length, crypt depth, and both mucosal area and integrity in the colon of mice with acute DS colitis. The effects of h[Gly2]GLP-2 in the colon are mediated in part via enhanced stimulation of mucosal epithelial cell proliferation. These observations suggest that exploitation of the normal mechanisms used to regulate intestinal proliferation may be a useful adjunct for healing mucosal epithelium in the presence of active intestinal inflammation.The pathology of Crohns disease and ulcerative colitis is characterized by chronic inflammation and destruction of the gastrointestinal epithelium. Although suppression of inflammatory mediators remains the principle component of current disease therapeutics, strategies for enhancing repair and regeneration of the compromised intestinal epithelium have not been widely explored. The demonstration that a peptide hormone secreted by the intestinal epithelium, glucagon-like peptide-2 (GLP-2), is a potent endogenous stimulator of intestinal epithelial proliferation in the small bowel prompted studies of the therapeutic efficacy of GLP-2 in CD1 and BALB/c mice with dextran sulfate (DS)-induced colitis. We report here that a human GLP-2 analog (h[Gly2]GLP-2) significantly reverses weight loss, reduces interleukin-1 expression, and increases colon length, crypt depth, and both mucosal area and integrity in the colon of mice with acute DS colitis. The effects of h[Gly2]GLP-2 in the colon are mediated in part via enhanced stimulation of mucosal epithelial cell proliferation. These observations suggest that exploitation of the normal mechanisms used to regulate intestinal proliferation may be a useful adjunct for healing mucosal epithelium in the presence of active intestinal inflammation.

Glucagon-like peptide 2 decreases mortality and reduces the severity of indomethacin-induced murine enteritis.

Glucagon-like peptides (GLPs) are secreted from enteroendocrine cells in the gastrointestinal tract. GLP-1 actions regulate blood glucose, whereas GLP-2 exerts trophic effects on intestinal mucosal epithelium. Although GLP-1 actions are preserved in diseases such as diabetes, GLP-2 action has not been extensively studied in the setting of intestinal disease. We have now evaluated the biological effects of a human GLP-2 analog in the setting of experimental murine nonsteroidal antiinflammatory drug-induced enteritis. Human (h)[Gly2]GLP-2 significantly improved survival whether administered before, concomitant with, or after indomethacin. h[Gly2]GLP-2-treated mice exhibited reduced histological evidence of disease activity, fewer intestinal ulcerations, and decreased myeloperoxidase activity in the small bowel ( P < 0.05, h[Gly2]GLP-2- vs. saline-treated controls). h[Gly2]GLP-2 significantly reduced cytokine induction, bacteremia, and the percentage of positive splenic and hepatic bacterial cultures ( P < 0.05). h[Gly2]GLP-2 enhanced epithelial proliferation ( P < 0.05 for increased crypt cell proliferation in h[Gly2]GLP-2- vs. saline-treated mice after indomethacin) and reduced apoptosis in the crypt compartment ( P < 0.02). These observations demonstrate that a human GLP-2 analog exerts multiple complementary actions that serve to preserve the integrity of the mucosal epithelium in experimental gastrointestinal injury in vivo.

The Glucagon-like Peptide-2 Receptor Mediates Direct Inhibition of Cellular Apoptosis via a cAMP-dependent Protein Kinase-independent Pathway

Glucagon and the glucagon-like peptides regulate metabolic functions via signaling through a glucagon receptor subfamily of G protein-coupled receptors. Activation of glucagon-like peptide-2 receptor (GLP-2R) signaling maintains the integrity of the intestinal epithelial mucosa via regulation of crypt cell proliferation. Because GLP-2 decreases mortality and reduces intestinal apoptosis in rodents after experimental injury, we examined whether GLP-2R signaling directly modifies the cellular response to external injury. We show here that activation of GLP-2R signaling inhibits cycloheximide-induced apoptosis in baby hamster kidney fibroblasts expressing a transfected GLP-2 receptor. GLP-2 reduced DNA fragmentation and improved cell survival, in association with reduced activation of caspase-3 and decreased poly(ADP-ribose) polymerase cleavage and reduced caspase-8 and caspase-9-like activities. Both GLP-2 and forskolin reduced mitochondrial cytochrome crelease and decreased the cycloheximide-induced cleavage of caspase-3 in the presence or absence of the PKA inhibitor H-89. Similarly, GLP-2 increased cell survival following cycloheximide in the presence of the kinase inhibitors PD98054 and LY294002. These findings provide evidence that signaling through G protein-coupled receptors of the glucagon superfamily is directly linked to regulation of apoptosis and suggest the existence of a cAMP-dependent protein kinase-, phosphatidylinositol 3-kinase-, and mitogen-activated protein kinase-independent pathway coupling GLP-2R signaling to caspase inhibition and cell survival.

New developments in the biology of the glucagon-like peptides GLP-1 and GLP-2.

Abstract: Glucagon‐like peptides 1 and 2 (GLP‐1 and GLP‐2) are coencoded within a single mammalian proglucagon precursor, and are liberated in the intestine and brain. GLP‐1 exerts well known actions on islet hormone secretion, gastric emptying, and food intake. Recent studies suggest GLP‐1 plays a central role in the development and organization of islet cells. GLP‐1 receptor signaling appears essential for β cell signal transduction as exemplified by studies of GLP‐1R−/− mice. GLP‐2 promotes energy assimilation via trophic effects on the intestinal mucosa of the small and large bowel epithelium via a recently cloned GLP‐2 receptor. The actions of GLP‐2 are preserved in the setting of small and large bowel injury and inflammation. The biological actions of the glucagon‐like peptides suggest they may have therapeutic efficacy in diabetes (GLP‐1) or intestinal disorders (GLP‐2).

Biologic properties and therapeutic potential of glucagon-like peptide-2.

BACKGROUNDnGlucagon-like peptide-2 (GLP-2), a 33 amino acid, proglucagon-derived peptide with intestinotrophic activity, is secreted from enteroendocrine cells in the small and large intestine.nnnMETHODSnThis review describes recent advances in our understanding of GLP-2 physiology from rodent experiments in vivo.nnnRESULTSnGLP-2 administration induces mucosal epithelial proliferation in small and large bowel and stomach. GLP-2 is rapidly degraded by the enzyme dipeptidyl peptidase IV (DPP-IV) to produce the biologically inactive form GLP-2(3-33), however, GLP-2 analogs that confer resistance to DPP-IV exhibit enhanced biologic activity in vivo. GLP-2-treated bowel retains normal to enhanced functional absorptive capacity. Furthermore, GLP-2 infusion prevents total parenteral nutrition (TPN)-associated intestinal hypoplasia, and enhances bowel adaptation and nutrient absorption in rats following small bowel resection. GLP-2 also reverses weight loss and improves histologic and biochemical parameters of disease activity in mice with experimental colitis.nnnCONCLUSIONSnGLP-2 is an intestine-derived peptide with intestinotrophic properties that may be therapeutically useful in diseases characterized by intestinal damage or insufficiency.

Middle mediastinal parathyroid: diagnosis and surgical approach

We report two cases of middle mediastinal parathyroid ectopia associated with chronic renal disease. In both patients the diagnosis was delayed and prolonged due to the unusual location of the ectopic parathyroid tissue. The surgical approach was in error in 1 patient and corrected during the second procedure. We describe the surgical technique for exposing and excising parathyroid tissue from this area.

GI Hormones as Growth Factors

Gut hormones play important roles in the growth of the gastrointestinal tract. These peptides mediate their trophic effects by acting either directly or indirectly on pluripotent stem cells located in the crypts of the small and large intestine. A total of four to six stem cells are thought to reside in each crypt and are capable of regenerating the entire crypt and villus compartment under both steady-state and injury-associated conditions. This process requires the stem cell to undergo mitosis and results in the generation of two daughter stem cells, one that will remain a stem cell and another that will continue to divide and differentiate into an enterocyte, colonocyte, Paneth cell, goblet cell, or enteroendocrine cell as it migrates along the crypt–villus axis. Excess but otherwise healthy daughter stem cells are removed by a process of spontaneous apoptosis, as are mature enterocytes at the villus tip, in an attempt to maintain intestinal epithelial homeostasis. The enteroendocrine cell population, which constitutes less than 1% of all intestinal epithelial cells, along with the enteric nervous system (ENS) is responsible for producing and secreting the majority of gut peptide hormones. These peptides exert trophic effects via stimulation of cellular proliferation or by inhibiting apoptosis in the intestine and related organs, such as the pancreas. Perturbation of the temporal or spatial expression of these trophic factors during fetal development can lead to structural or functional abnormalities. This article discusses (1) the development of the gut endocrine and enteric nervous system and (2) the growth-promoting effects of peptides produced by enteroendocrine cells and the ENS during fetal enteropancreatic development and in the adult. The enteroendocrine cell-derived peptides discussed include gastrin, cholecystokinin, glucagon-like peptide-1, glucagon-like peptide-2, neurotensin, peptide YY, and thyrotropin-releasing hormone, as well as the neuropeptides vasoactive intestinal peptide and bombesin.

Hypoglycemia, defective islet glucagon secretion, but normal islet mass in mice with a disruption of the gastrin gene1 1The authors thank Emmy De Blay and Luc Bouwens for generous assistance with islet immunohistochemistry.

BACKGROUND AND AIMSnBoth cholecystokinin (CCK)-A and CCK-B receptors are expressed in the pancreas, and exogenous gastrin administration stimulates glucagon secretion from human islets. Although gastrin action has been linked to islet neogenesis, transdifferentiation, and beta-cell regeneration, an essential physiologic role(s) for gastrin in the pancreas has not been established.nnnMETHODSnWe examined glucose homeostasis, glucagon gene expression, glucagon secretion, and islet mass in mice with a targeted gastrin gene disruption.nnnRESULTSnGastrin -/- mice exhibit fasting hypoglycemia and significantly reduced glycemic excursion following glucose challenge. Insulin sensitivity was normal and levels of circulating insulin and insulin messenger RNA transcripts were appropriately reduced in gastrin -/- mice. In contrast, levels of circulating glucagon and pancreatic glucagon messenger RNA transcripts were not up-regulated in hypoglycemic gastrin -/- mice. Furthermore, the glucagon response to epinephrine in isolated perifused islets was moderately impaired in gastrin -/- versus gastrin +/+ islets (40% reduction; P < 0.01, gastrin +/+ vs. gastrin -/- mice). Moreover, the glucagon response but not the epinephrine response to hypoglycemia was significantly attenuated in gastrin -/- compared with gastrin +/+ mice (P < 0.05). Despite gastrin expression in the developing fetal pancreas, beta-cell area, islet topography, and the islet proliferative response to experimental injury were normal in gastrin -/- mice.nnnCONCLUSIONSnThese findings show an essential physiologic role for gastrin in glucose homeostasis; however, the gastrin gene is not essential for murine islet development or the adaptive islet proliferative response to beta-cell injury.