Subcutaneous but not intraluminal epidermal growth factor stimulates colonic growth in normal adult rats

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

BACKGROUND & AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Subcutaneous administration of epidermal growth factor: a true treatment option in case of postoperative liver failure?

Adequate hepatocyte regeneration is mandatory for successful recovery after liver resection. The role of epidermal growth factor (EGF), by subcutaneous injection as a simple route, has not been clearly elucidated yet. Wistar rats underwent 70 or 90% hepatectomy, respectively, and were treated with EGF at day 2 and 3 or served as non-EGF-treated controls. Postoperatively, proliferative parameters (weight of liver remnants, number of mitotic and Ki-67 positive cells, expression of cyclin D1 protein) were evaluated. After 90% hepatectomy, 5 day survival was recorded following EGF treatment using different dosages. A significant increase of hepatocellular proliferation was observed after 70% hepatectomy. However, survival following 90% hepatectomy was not as positively affected, irrespective of EGF dosage, with most animals dead before EGF application was completed. Subcutaneous EGF injection can augment postoperative liver regeneration, however, it might be used only as a prophylactic and not as a therapeutic drug in case of liver insufficiency.

Leptin reduces the development of the initial precancerous lesions induced by azoxymethane in the rat colonic mucosa

BACKGROUND & AIMS

Recent studies suggest that leptin, a hormone involved in food intake regulation, released into the circulation and gastrointestinal juice, may be a growth factor for intestine and may be involved in carcinogenesis; however, data are contradictory. This study investigates in rat colonic mucosa (1) the effects of hyperleptinemia on epithelial cell proliferation and development of aberrant crypts, earliest preneoplastic lesions, and (2) whether luminal leptin affects cell proliferation.

METHODS

Leptin (1 mg/kg/d) or vehicle was administered systemically by miniosmotic pump in Fischer 344 rats either for 7 days (BrdU-labeling indices study) or 23 days (azoxymethane-induced colonic lesions study). The effects of injections or continuous infusion of leptin into the colon were also studied.

RESULTS

In systemic leptin-treated rats, plasma leptin levels were 4- to 5-fold increased (P < 0.008 to P < 0.001); labeling indices were higher in proximal colon than in pair-fed control rats (P = 0.006) but unaffected in distal colon. Unexpectedly, in azoxymethane-treated rats, leptin significantly inhibited aberrant crypt foci formation in the middle and distal colon compared with controls (P = 0.006). Under these conditions, plasma insulin levels were reduced by 41%-58%, but gastrin levels were unchanged. In controls, luminal immunoreactive leptin reached the colon. A 3.6-fold increase in intraluminal leptin had no effect on epithelial cell proliferation.

CONCLUSIONS

This study provides the first evidence that leptin reduces the development of chemically induced precancerous lesions in colon, perhaps through decreased insulinemia, and thus does not support an important role for leptin in carcinogenesis promotion. Moreover, the study indicates that leptin is not a potent growth factor for normal intestine.

Structural-proliferative units and organ growth: effects of insulin-like growth factor 2 on the growth of colon and skin

Many epithelial renewal tissues in vertebrates are organised into structural-proliferative units. We have examined the effect of IGF2 dose on the structure of structural-proliferative units in skin and colon. The mouse strains used were the Igf2 knockout, wild type and K:Igf2, a transgenic in which Igf2 is overexpressed under control of a keratin promoter. For both skin and colon, the histological organisation of structural-proliferative units was unaltered with increasing IGF2 dose, although there was a higher fraction of dividing cells in the proliferative compartment. In the colon an increase in IGF2 dose increases the overall area of the epithelium. This is due to an increase in the number of crypts with no change of cell size or of crypt area. Growth stimulation appears to be due to a reduction in the duration of crypt fission. The conclusion is that the IGF2 pathway can stimulate the multiplication of colonic crypts independently of stimulating increased cell proliferation. The results for the skin are consistent with this. An increase of IGF2 dose increases the proportion of dividing cells in the basal layer, the thickness of the epidermis and the total area of the epidermis. By comparison with Drosophila, these results show no effects on cell size, but do show the possibility of inducing disproportionate growth. These differences may represent properties of the SPU organisation that is characteristic of vertebrate tissues.

Amniotic IGF-I supplements improve gut growth but reduce circulating IGF-I in growth-restricted fetal sheep

Insulin-like growth factor I (IGF-I) is an important regulator of fetal growth, and circulating concentrations are reduced in intrauterine growth-restricted (IUGR) fetuses. We investigated whether IGF-I administered into amniotic fluid could ameliorate IUGR in fetal sheep. Fetuses were assigned to control (n = 9), IUGR+saline (n = 12), or IUGR+IGF-I groups (daily intra-amniotic IGF-I injections of 20 microg, n = 13). IUGR was induced by placental embolization from 114 to 120 days. Treatment was from 120 to 130 days of gestation. Embolization produced asymmetrically IUGR fetuses with decreased body weight and lighter, thinner-walled guts. Fetal plasma and amniotic IGF-I levels were reduced. During treatment, fetal plasma, but not amniotic, IGF-I levels recovered in the saline group but remained depressed in the IGF-I-treated group. IGF-I treatment restored gut weight and wall thickness to control levels and increased the number of crypt mitoses. Fetal weight was similar to that of controls, but spleen, liver, and thymic weights were reduced by 30-37%, and placentome growth was altered. Amniotic fluid IGF-I supplementation may provide the basis of future therapeutic approaches to IUGR, but the systemic effects require further investigation.

Gut-trophic effects of keratinocyte growth factor in rat small intestine and colon during enteral refeeding

BACKGROUND

Keratinocyte growth factor (KGF) induces proliferation of gut epithelium in rat models, but KGF-nutrient interactions have not been studied. An experimental model of fasting-induced gut atrophy followed by different levels of enteral refeeding was used to investigate the influence of nutrient availability on the gut-trophic effects of exogenous KGF.

METHODS

After a 3-day fast, rats were enterally refed either ad libitum or at 25% of ad libitum intake for 3 subsequent days. Either intraperitoneal KGF (5 mg/kg/d) or saline was given in each dietary regimen. Wet weight, DNA, and protein content were measured as indices of full-thickness cellularity in duodenum, jejunum, ileum, and colon. Villus height in small bowel segments and crypt depth in all gut tissues were measured as specific indices of mucosal growth.

RESULTS

Refeeding at 25% of ad libitum intake significantly decreased full-thickness cellularity and mucosal growth indices in duodenum, jejunum, and ileum. In the colon, only protein content fell significantly and crypt depth was maintained. KGF administration during 25% refeeding did not alter full-thickness indices in any small bowel segment or affect jejunal mucosal growth. In contrast, KGF normalized duodenal villus height (p < .01) and duodenal and ileal crypt depth (p < .05) only in the 25%-refed model. KGF significantly increased ileal villus height in both ad libitum and 25%-refed rats (by 43% and 48%, respectively, p < .05) and markedly increased colonic cellularity and mucosal crypt depth with both levels of refeeding (p < .01).

CONCLUSIONS

Rat small bowel growth is more sensitive than colon to the level of enteral refeeding after a 3-day fast. KGF administration does not affect jejunal growth, but specifically prevents atrophy of duodenal and ileal mucosa during hypocaloric, hyponitrogenous refeeding. In ileum and colon, some KGF-mediated growth responses are independent of the level of enteral refeeding. Thus gut-trophic effects of KGF and KGF interactions with the level of nutrient intake are tissue-specific.

Effects of epidermal growth factor administration on repair of acetic acid-induced colonic ulcerations in rats

The effect of subcutaneous and luminal epidermal growth factor (EGF) administration on acetic acid-induced colonic ulceration was determined in adult rats. Application of acetic acid to the distal colonic lumen caused epithelial denudation, mucosal ulceration and inflammation in the exposed segment. Re-epithelialization was detectable 5 to 7 days later, with near-complete resolution of the lesion by 14 days post-injury. Luminal EGF (1.6 mg/kg bw/day) or subcutaneous EGF (200 micromilligrams/kg bw/day), administered for 4 or 6 days from the time of ulceration failed to enhance re-epithelialization of the acid-exposed segment. However, mucosal and submucosal thickening was attenuated 20-40% by subcutaneous EGF, reflecting a reduction in edema. Luminal EGF had a similar but less substantial effect in the submucosa, but was more effective at attenuating muscularis thickening adjacent to the lesion. In conclusion, administration of exogenous EGF for up to 6 days failed to enhance re-epithelialization of acetic acid-induced colonic ulcerations but did attenuate the associated edematous response.

Recombinant human epidermal growth factor1-48-induced structural changes in the digestive tract of cynomolgus monkeys (Macaca fascicularis)

To determine the cellular effects and potential toxicity of exogenously administered recombinant human epidermal growth factor1-48 (EGF1-48) in primates, intravenous bolus injections were given to 2 cynomolgus monkeys per sex at 0 (vehicle control). 10, 100, 500 (females only), and 1,000 micrograms/kg/day (males only) for up to 2 wk. Males given the suprapharmacologic dose of 1,000 micrograms/kg did not tolerate treatment and were necropsied after 5 days of dosing. All other monkeys completed the 2-wk study. Necropsy findings included enlarged, discolored, pale tan livers at 500 micrograms/kg and greater, firm, thickened pancreata in 500-micrograms/kg females, and enlarged salivary glands at all doses. Relative liver weights were increased at 500 and 1,000 micrograms/kg: mean salivary gland weights in all dose groups were greater than in controls. Histopathologic changes were primarily those of diffuse epithelial cell hypertrophy and hyperplasia in liver (hepatocytes and biliary tract), pancreas, salivary glands, tongue, esophagus, stomach, small and large intestine, and gallbladder. Alterations were dose-related in intensity and occurred in at last some tissues at the lowest dose. In gastric glands, colon crypts, pancreatic ducts, biliary tract, and salivary glands, differentiated epithelial cells were replaced by cells of less differentiated phenotype. These morphologic alterations were consistent with exuberant proliferation induced by this epithelial mitogen. The extent of the proliferative response in tissues of the digestive tract attests to the potency of this fragment of human EGF1-53 in primates. Furthermore, the epithelial proliferation was significantly greater than that reported previously in EGF-treated rodents.

Cellular hyperplasia in rats following continuous intravenous infusion of recombinant human epidermal growth factor

In this study, we determined in vivo morphologic effects of continuous intravenous infusion of recombinant human epidermal growth factor (EGF) in adult Wistar rats. The EGF used consisted of the amino acid residues 1-48 of the human 53-amino-acid EGF molecule, purified from transfected Escherichia coli. Doses of 25, 100, or 250 micrograms/kg body weight were administered using Harvard digital syringe infusion pumps for 4 weeks. At necropsy, the submandibular salivary glands, Harderian glands, liver, kidneys (females only), and ovaries were enlarged and urinary bladders were thickened in 100- and 250-micrograms/kg rats. Numerous tissues of the 100- and 250-micrograms/kg rats contained hyperplastic epithelial cells, and selected organs also had mesenchymal cell proliferation. Epithelial proliferation was most pronounced in the trachea, nasal cavity, nasolacrimal duct, tongue, stomach, small intestine, large intestine, urinary tract, salivary gland ducts, and Harderian gland. Periportal hepatocytes were hypertrophic, correlating with increased liver weight. In addition, mesenchymal cell proliferation was evident in the gastric mucosa lamina propria and in heart valves in 100- and 250-micrograms/kg rats. Increased ovarian weight correlated with increased number and size of corpora lutea and an increased incidence of luteal cysts. Continuous systemic exposure of adult Wistar rats to high doses of EGF resulted in generalized epithelial hyperplasia and tissue-selective mesenchymal proliferation.

Systemic treatment with epidermal growth factor in the rat. Biomechanical properties of the growing small intestine

Prolonged treatment with epidermal growth factor (EGF) in the rat provides an experimental model to growth of the gastrointestinal tract. We treated female Wistar rats for 0 (n = 15), 1 (n = 8), 2 (n = 8), and 4 (n = 8) weeks with subcutaneous EGF (i50 micrograms.kg-1.day-1). Segments were taken from locations at 10, 50 and 90% along the length of the small intestine, weighed, the wall thickness was measured and the luminal cross-sectional area and passive biomechanical properties were assessed using impedance planimetry. In addition, the wall composition was evaluated on histological sections. The weight of the total small intestine and of the three segments (measured in mg.cm-1) increased with the duration of the EGF treatment due to mucosal and muscular growth. After 1 week of treatment the wall thickness increased. After 2 weeks of treatment the cross-sectional area began to increase. The circumferential stress-strain distributions revealed translation of the curves to the right in the graphs implying reduced wall stiffness during EGF treatment. In conclusion EGF treatment for 1 to 4 weeks caused a time-dependent increase in intestinal weight. The growth was characterized by increased wall thickness, increased cross-sectional area and reduced wall stiffness.

Chronic systemic treatment with epidermal growth factor in the rat increases the mucosal surface of the small intestine

We examined the effects of treatment with human recombinant epidermal growth factor (EGF) on the functioning small intestine in the rat. Male Wistar rats, 7-8 weeks old, were treated with EGF administered subcutaneously in doses of 0 (n = 7) or 150 micrograms/kg/day (n = 8) for 4 weeks. The histological composition and mucosal surface area of the perfusion-fixed small intestine was quantified with stereological principles. The length of the gut remained unchanged. The amount of tissue and surface area per length of gut (median (ranges)) were increased from 117 (101-131) mg/cm and 2.6 (2.1-3.5) cm2/cm in the controls to 146 (138-152) mg/cm and 3.5 (2.5-3.8) cm2/cm for the complete small intestine (both comparisons P < 0.02). The weight increase was due to mucosal growth in all parts of the intestine, whereas the surface area was only increased in proximal and middle parts. It is concluded that EGF treatment in rats increases the mucosal weight and surface area of the functioning small intestine.