Purification of placental anemia inducing factor (PAIF) and its clinical application by radioimmunoassay

Intestinal Adaptation in Short Bowel Syndrome

Short bowel syndrome occurs when there is insufficient length of the small intestine to maintain adequate nutrition and/or hydration status without supplemental support. This syndrome most frequently occurs following extensive surgical resection of the intestine, and the extent of adaptation depends on the anatomy of the resected bowel and the amount of bowel remaining. Following resection, the intestinal tissue undergoes morphologic and functional changes to compensate for the lost function of the resected bowel. These changes are mediated by multiple interactive factors, including intraluminal and parenteral nutrients, gastrointestinal secretions, hormones, cytokines, and growth factors, many of which have been well characterized in animal models. The amount of small bowel remaining is the most important predictor of adaptive potential; neither structural nor functional adaptative changes have been demonstrated in humans or animal models with more extreme resections resulting in an end-jejunostomy. The current understanding of these processes has led to the recent use of supplemental hormones, such as growth hormone and glucagon-like peptide 2, in intestinal rehabilitation programs and may lead to the development of pharmacologic agents designed to augment the innate adaptive response.

Direct and indirect mechanisms regulating secretion of glucagon-like peptide-1 and glucagon-like peptide-2

The proglucagon-derived peptide family consists of three highly related peptides, glucagon and the glucagon-like peptides GLP-1 and GLP-2. Although the biological activity of glucagon as a counter-regulatory hormone has been known for almost a century, studies conducted over the past decade have now also elucidated important roles for GLP-1 as an antidiabetic hormone, and for GLP-2 as a stimulator of intestinal growth. In contrast to pancreatic glucagon, the GLPs are synthesized in the intestinal epithelial L cells, where they are subject to the influences of luminal nutrients, as well as to a variety of neuroendocrine inputs. In this review, we will focus on the complex integrative mechanisms that regulate the secretion of these peptides from L cells, including both direct and indirect regulation by ingested nutrients.

Circulating levels of glucagon-like peptide-2 in human subjects with inflammatory bowel disease

Glucagon-like peptide-2 (GLP-2) is a recently characterized intestine-derived peptide that exerts trophic activity in the small and large intestine. Whether circulating levels of GLP-2 are perturbed in the setting of human inflammatory bowel disease (IBD) remains unknown. The circulating levels of bioactive GLP-2-(1-33) compared with its degradation product GLP-2-(3-33) were assessed using a combination of RIA and HPLC in normal and immunocompromised control human subjects and patients hospitalized for IBD. The activity of the enzyme dipeptidyl peptidase IV (DP IV), a key determinant of GLP-2-(1-33) degradation was also assessed in the plasma of normal controls and subjects with IBD. The circulating levels of bioactive GLP-2-(1-33) were increased in patients with either ulcerative colitis (UC) or Crohn's Disease (CD; to 229 +/- 65 and 317 +/- 89%, P < 0.05, of normal, respectively). Furthermore, the proportion of total immunoreactivity represented by intact GLP-2-(1-33), compared with GLP-2-(3-33), was increased from 43 +/- 3% in normal healthy controls to 61 +/- 6% (P < 0.01) and 59 +/- 2% (P < 0.01) in patients with UC and CD, respectively. The relative activity of plasma DP IV was significantly reduced in subjects with IBD compared with normal subjects (1.4 +/- 0.3 vs. 5.0 +/- 1.1 mU/ml, respectively; P < 0.05). These results suggest that patients with active IBD may undergo an adaptive response to intestinal injury by increasing the circulating levels of bioactive GLP-2-(1-33), facilitating enhanced repair of the intestinal mucosal epithelium in vivo.

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

BACKGROUND

Glucagon-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.

METHODS

This review describes recent advances in our understanding of GLP-2 physiology from rodent experiments in vivo.

RESULTS

GLP-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.

CONCLUSIONS

GLP-2 is an intestine-derived peptide with intestinotrophic properties that may be therapeutically useful in diseases characterized by intestinal damage or insufficiency.

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

The pathology of Crohn's 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.

GLP-2 augments the adaptive response to massive intestinal resection in rat

To determine whether treatment with a potent protease-resistant analog of human glucagon-like peptide 2 (GLP-2) might augment the adaptive response to massive intestinal resection, rats were divided into resected, which had 75% of the midjejunoileum removed, sham-resected, and nonsurgical groups. Within each group, animals were assigned to 21 days of treatment with the drug (0.1 micrograms/g of the GLP-2 analog in phosphate-buffered saline) or vehicle alone subcutaneously twice daily. Food intake; weight gain; jejunal and ileal diameters, total and mucosal wet weights per centimeter, crypt depths, and villus heights; mucosal sucrase activity, milligrams of protein per centimeter, and micrograms of DNA per centimeter; and D-xylose absorption were measured. There was a significant increase in diameter, total and mucosal wet weights per centimeter, crypt-villus height, sucrase activity, milligrams of protein per centimeter and micrograms of DNA per centimeter in both the jejunum and ileum in response to resection and a significant additive response to the GLP-2 analog in the jejunum but not in the ileum. The ratio of milligrams of protein per centimeter to micrograms of DNA per centimeter of mucosa was not different among groups, consistent with hyperplasia. D-Xylose absorption was significantly reduced in response to resection; however, the GLP-2 analog enhanced the absorptive capacity in control animals and restored the absorptive capacity in resected animals. Thus the GLP-2 analog induces mucosal hyperplasia and enhances the rate and magnitude of the proximal intestinal adaptive response to massive resection.

Regulation of the biological activity of glucagon-like peptide 2 in vivo by dipeptidyl peptidase IV

Species-specific differences in the enzymatic inactivation of peptides is an important consideration in the evaluation of therapeutic efficacy. We demonstrate that glucagon-like peptide 2 (GLP-2), shown to be highly intestinotrophic in mice, promotes an increase in intestinal villus height but has no trophic effect on small bowel weight in rats. The reduced intestinotrophic activity of GLP-2 in rats is attributable to inactivation by the enzyme dipeptidyl peptidase IV (DPP-IV). GLP-2(1-33) was degraded to GLP-2(3-33) following incubation with human placental DPP-IV or rat serum but not by serum from DPP-IV-deficient rats. Administration of rat GLP-2 to DPP-IV-deficient rats was associated with markedly increased bioactivity of rat GLP-2 resulting in a significant increase in small bowel weight. A synthetic GLP-2 analog, r[Gly2]GLP-2, with an alanine to glycine substitution at position 2, was resistant to cleavage by both DPP-IV and rat serum in vitro. Treatment of wild-type rats with r[Gly2]GLP-2 produced a statistically significant increase in small bowel mass. DPP-IV-mediated inactivation of GLP-2 is a critical determinant of the growth factor-like properties of GLP-2.

Intestinal function in mice with small bowel growth induced by glucagon-like peptide-2

Glucagon-like peptide-2 (GLP-2) stimulates small intestinal growth through induction of intestinal epithelial proliferation. To examine the physiology of GLP-2-induced bowel, mice were treated with GLP-2 (2.5 micrograms) or vehicle for 10 days. Small intestinal weight increased to 136 +/- 2% of controls in GLP-2-treated mice, in parallel with 1.4 +/- 0.1- and 1.9 +/- 0.5-fold increments in duodenal RNA and protein content, respectively (P < 0.05-0.001). Similarly, the activities of duodenal maltase, sucrase, lactase, glutamyl transpeptidase, and dipeptidyl-peptidase IV (215 +/- 28% of controls; P < 0.001) were increased by GLP-2. Oral or duodenal administration of glucose or maltose did not reveal any differences in the ability of GLP-2-treated mice to absorb these nutrients, possibly because of decreases in expression of the glucose transporters sodium-dependent glucose transporter-1 (SGLT-1) and GLUT-2. In contrast, absorption of leucine plus triolein was increased after duodenal administration in GLP-2-treated mice (P < 0.01-0.001). Finally, GLP-2 did not alter other markers of intestinal or pancreatic gene expression, including levels of mRNA transcripts for ornithine decarboxylase, multidrug resistance gene, amylase, proglucagon, proinsulin, and prosomatostatin. Thus induction of intestinal growth by GLP-2 in wild-type mice results in a normal-to-increased capacity for nutrient digestion and absorption in vivo.

Adaptation of the small intestine to induced maldigestion in rats. Experimental pancreatic atrophy and acarbose feeding

Intestinal adaptation has been studied in rats with pancreatic atrophy induced by feeding a copper-deficient diet and penicillamine and in rats with carbohydrate maldigestion induced by feeding of an alpha-glucosidase inhibitor (acarbose). Pancreatic atrophy led to a significant increase of weight, protein, and DNA content as well as specific activities and total amounts of the enzymes sucrase and maltase in the distal but not in the proximal part of the small intestine. Plasma levels of CCK and GIP were significantly higher in rats with pancreatic atrophy, whereas plasma levels of gastrin and insulin were lower. Tissue concentrations of gastrin in the antrum and GIP in duodenum and jejunum were unchanged. Duodenal CCK and jejunal substance P, somatostatin, and VIP and ileal substance P and somatostatin were significantly decreased in rats with acinar atrophy. Glucosidase inhibition by acarbose feeding led to weight increase of the small intestine and cecum. This was more marked when acarbose was fed together with a fiber-free diet. Under these conditions the protein and DNA content also increased significantly in both gut segments and maltase and sucrase content predominantly in the distal part. Insulin plasma concentration decreased significantly in the acarbose-fed groups, whereas GIP, gastrin, and CCK plasma concentrations remained unchanged. After fiber-rich diet tissue concentrations of gastrin in the antrum and insulin in the pancreas were significantly higher and GIP concentrations in the duodenum and jejunum significantly lower than after fiber-free diet. Acarbose increased the pancreatic insulin concentration only in the fiber-free group and did not influence gastrin and GIP concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)