The epidermal growth factor receptor (EGF-R) is present on the basolateral, but not the apical, surface of enterocytes in the human gastrointestinal tract

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.

EGFR plays a pivotal role in the regulation of polyamine-dependent apoptosis in intestinal epithelial cells

Intracellular polyamine synthesis is regulated by the enzyme ornithine decarboxylase (ODC), and its inhibition by alpha-difluromethylornithine (DFMO), confers resistance to apoptosis. We have previously shown that DFMO leads to the inhibition of de novo polyamine synthesis, which in turn rapidly activates Src, STAT3 and NF-kappaB via integrin beta3 in intestinal epithelial cells. One mechanism to explain these effects involves the activation of upstream growth factor receptors, such as the epidermal growth factor receptor (EGFR). We therefore hypothesized that EGFR phosphorylation regulates the early response to polyamine depletion. DFMO increased EGFR phosphorylation on tyrosine residues 1173 (pY1173) and 845 (pY845) within 5 min. Phosphorylation declined after 10 min and was prevented by the addition of exogenous putrescine to DFMO containing medium. Phosphorylation of EGFR was concomitant with the activation of ERK1/2. Pretreatment with either DFMO or EGF for 1 h protected cells from TNF-alpha/CHX-induced apoptosis. Exogenous addition of polyamines prevented the protective effect of DFMO. In addition, inhibition of integrin beta3 activity (with RGDS), Src activity (with PP2), or EGFR kinase activity (with AG1478), increased basal apoptosis and prevented protection conferred by either DFMO or EGF. Polyamine depletion failed to protect B82L fibroblasts lacking the EGFR (PRN) and PRN cells expressing either a kinase dead EGFR (K721A) or an EGFR (Y845F) mutant lacking the Src phosphorylation site. Conversely, expression of WT-EGFR (WT) restored the protective effect of polyamine depletion. Fibronectin activated the EGFR, Src, ERKs and protected cells from apoptosis. Taken together, our data indicate an essential role of EGFR kinase activity in MEK/ERK-mediated protection, which synergizes with integrin beta3 leading to Src-mediated protective responses in polyamine depleted cells.

Consequences of Direct Versus Indirect Activation of Epidermal Growth Factor Receptor in Intestinal Epithelial Cells Are Dictated by Protein-tyrosine Phosphatase 1B

The epidermal growth factor receptor (EGFR) is an integral regulator of many cellular functions. EGFR also acts as a central conduit for extracellular signals involving direct activation of the receptor by EGFR ligands or indirect activation by G protein-coupled receptor (GPCR)-stimulated transactivation of the EGFR. We have previously shown that EGFR negatively regulates epithelial chloride secretion as a result of transforming growth factor-alpha-mediated EGFR transactivation in response to muscarinic GPCR activation. Here we show that direct activation of the EGFR by EGFR ligands produces a different pattern of EGFR tyrosine phosphorylation and downstream phosphatidylinositol 3-kinase recruitment than GPCR-stimulated transactivation of the EGFR occurring via paracrine EGFR ligand release. Moreover, we demonstrate that this differential signaling and its consequences depend on protein-tyrosine phosphatase 1B activity. Thus protein-tyrosine phosphatase 1B governs differential recruitment of signaling pathways involved in EGFR regulation of epithelial ion transport. Our findings furthermore establish how divergent signaling outcomes can arise from the activation of a single receptor.

Ontogeny of salivary epidermal growth factor and necrotizing enterocolitis

OBJECTIVE

To examine the ontogeny of salivary epidermal growth factor (sEGF) in premature infants and to determine the relation of sEGF to the development of necrotizing enterocolitis (NEC).

STUDY DESIGN

Salivary EGF was prospectively measured in 327 infants with gestational ages from 23 weeks to term. Infants of < or = 32 weeks' gestation (n = 261) were followed with weekly sEGF measurements through 3 weeks of life. Multivariable regression analyses were used to determine variables significantly related to sEGF levels and to identify predictors of NEC.

RESULTS

Over the first 3 weeks of life, sEGF increased across gestational age and postnatal age categories. In multivariable models, gestational age was a significant predictor of sEGF levels (P < .009). In a cohort of 27 infants who had NEC, gestational age, race, and changes in sEGF levels between weeks of life 1 and 2 were predictive of the development of NEC. These infants had lower sEGF at week 1 and greater increases from week 1 to week 2 compared with infants without NEC.

CONCLUSIONS

There is a positive relation between sEGF levels and gestational age. Patterns of sEGF levels over the first 2 weeks of life were significantly related to development of NEC in very low birth weight infants.

Epidermal growth factor stimulates chloride transport in primary cultures of weanling and adult rabbit colonocytes

OBJECTIVES

We have shown that Ca2+-dependent regulation of Cl- secretion in the mammalian colon exhibits age dependence. Because epidermal growth factor (EGF) has a well-established role in growth and can increase intracellular calcium [Ca2+]i, it is conceivable that its developmental influence may extend to the regulation of intestinal ion transport. In this study, we examined the role of EGF in the regulation of Cl- transport in the developing rabbit distal colon.

MATERIALS AND METHODS

Because serum contains growth factors, which could have confounded our studies, we first established an optimal milieu for testing EGF in primary cultures of adult rabbit distal colonocytes by culturing them for 24 h in media containing 0%, 1%, 5%, and 20% serum. Chloride transport (millimoles per second) and [Ca2+]i were measured with use of the fluorescent indicator N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide (MQAE) and Fura-2AM, respectively.

RESULTS

Serum depletion had no effect on cell number, DNA content, or basal Cl- transport, but it significantly affected cell viability. In media with 0%, 1%, or 20% serum, bethanechol, 8BrcAMP, taurodeoxycholate, and EGF stimulated Cl- transport to a similar extent. EGF maximally stimulated Cl- transport at 16.3 nmol/L and 20 minutes. Bethanechol, but not EGF, increased [Ca2+]i. EGF did not alter bethanechol-stimulated Cl- transport or [Ca2+]i. EGF acts via an EGF-receptor and mitogen activated protein kinase (MAPK) signaling pathway, since stimulation of Cl- transport was abolished by genistein, AG1478, and PD98059. Weanling and adult colonocytes, cultured in 1% serum, showed similar basal and EGF-stimulated Cl- transport.

CONCLUSIONS

EGF stimulates rabbit colonic Cl- transport via a Ca2+-independent, tyrosine kinase- and MAPK-dependent pathway, and its effects are not age dependent.

Epidermal growth factor receptor signaling is required for microadenoma formation in the mouse azoxymethane model of colonic carcinogenesis

Colonic carcinogenesis involves the progressive dysregulation of homeostatic mechanisms that control growth. The epidermal growth factor (EGF) receptor (EGFR) regulates colonocyte growth and differentiation and is overexpressed in many human colon cancers. A requirement for EGFR in colonic premalignancy, however, has not been shown. In the current study, we used a specific EGFR antagonist, gefitinib, to investigate this role of the receptor in azoxymethane colonic premalignancy. The azoxymethane model shares many clinical, histologic, and molecular features of human colon cancer. Mice received azoxymethane i.p. (5 mg/kg/wk) or saline for 6 weeks. Animals were also gavaged with gefitinib (10 mg/kg body weight) or vehicle (DMSO) thrice weekly for 18 weeks, a dose schedule that inhibited normal receptor activation by exogenous EGF. Compared with control colonocytes [bromodeoxyuridine (BrdUrd), 2.2+/-1.2%], azoxymethane significantly increased proliferation (BrdUrd, 12.6+/-2.8%), whereas gefitinib inhibited this hyperproliferation (BrdUrd, 6.2+/-4.0%; <0.005). Azoxymethane significantly induced pro-transforming growth factor-alpha (6.4+/-1.3-fold) and increased phospho-(active) EGFR (5.9+/-1.1-fold), phospho-(active) ErbB2 (2.3+/-0.2-fold), and phospho-(active) extracellular signal-regulated kinase (3.3+/-0.4-fold) in premalignant colonocytes. Gefitinib inhibited activations of these kinases by >75% (P<0.05). Gefitinib also significantly reduced the number of large aberrant crypt foci and decreased the incidence of colonic microadenomas from 75% to 33% (P<0.05). Gefitinib concomitantly decreased cell cycle-regulating cyclin D1 and prostanoid biosynthetic enzyme cyclooxygenase-2 in microadenomas, suggesting that these regulators are key targets of EGFR in colonic carcinogenesis. These results show for the first time that EGFR signaling is required for early stages of colonic carcinogenesis. Our findings suggest, moreover, that inhibitors of EGFR might be useful in chemopreventive strategies in individuals at increased risk for colonic malignancies.

Blocking airway mucous cell metaplasia by inhibiting EGFR antiapoptosis and IL-13 transdifferentiation signals

Epithelial hyperplasia and metaplasia are common features of inflammatory and neoplastic disease, but the basis for the altered epithelial phenotype is often uncertain. Here we show that long-term ciliated cell hyperplasia coincides with mucous (goblet) cell metaplasia after respiratory viral clearance in mouse airways. This chronic switch in epithelial behavior exhibits genetic susceptibility and depends on persistent activation of EGFR signaling to PI3K that prevents apoptosis of ciliated cells and on IL-13 signaling that promotes transdifferentiation of ciliated to goblet cells. Thus, EGFR blockade (using an irreversible EGFR kinase inhibitor designated EKB-569) prevents virus-induced increases in ciliated and goblet cells whereas IL-13 blockade (using s-IL-13Ralpha2-Fc) exacerbates ciliated cell hyperplasia but still inhibits goblet cell metaplasia. The distinct effects of EGFR and IL-13 inhibitors after viral reprogramming suggest that these combined therapeutic strategies may also correct epithelial architecture in the setting of airway inflammatory disorders characterized by a similar pattern of chronic EGFR activation, IL-13 expression, and ciliated-to-goblet cell metaplasia.

Epidermal growth factor and/or growth hormone induce differential, side-specific signal transduction protein phosphorylation in enterocytes

BACKGROUND

Epidermal growth factor (EGF) plus growth hormone (GH) enhances luminal glutamine transport into rabbit and human intestinal cells. Our objective was to screen for activation status of signal proteins in C2(BBe)1 cells (enterocyte-like cell line) in response to side-specific EGF or GH treatment and to investigate the dependence of EGF receptor (EGFR) phosphorylation status on its tyrosine kinase.

METHODS

C2(BBe)1 cells on Transwells were treated for 15 minutes on either the basolateral or apical-side with EGF or GH. Lysates underwent Kinetworks phospho site-screen-2.1 analysis (duplicate experiments). In addition, lysates from cells treated as above with or without tyrphostin AG1478 (a specific EGFR tyrosine kinase inhibitor) underwent Western blot analysis for total EGFR and EGFR phosphorylated on tyrosine 1173, 1086 or 1068 (4-7 experiments).

RESULTS

Kinetworks phospho-screening demonstrated a broad range of interactions dependent on both side of exposure and protein studied. From this screen, it appears that ErbB2, Met, and insulin receptor (R)/insulin-like growth factor 1 R are not involved in the growth factors signals. For EGFR phosphorylation, basolateral, but not apical, EGF was a strong activator. Synergism was seen, but only with apical EGF plus basolateral GH. All EGFR phosphorylations were EGFR tyrosine kinase dependent. In contradistinction, apical EGF phosphorylated FAK and MAPKs.

CONCLUSIONS

Kinetworks phosphoprotein screens can suggest pathways involved in side-specific and synergistic interaction between EGF and GH. For EGFR, synergism by EGF + GH was noticed only with Ap EGF plus Bl GH and was EGFR tyrosine kinase dependent. Adaptive intestinal responses due to enterally administrated EGF might be accelerated by the availability of parenteral GH.

Role of epidermal growth factor in the pathogenesis of neonatal necrotizing enterocolitis

Neonatal necrotizing enterocolitis (NEC) is an increasingly frequent condition encountered in premature infants for which the etiology is not well understood. Epidermal growth factor (EGF) is abundant in many fluids bathing the fetal and neonatal gastrointestinal tract, including amniotic fluid, saliva, and breast milk. EGF is acknowledged to be important for normal intestinal development as well as repair following injury to the gastrointestinal mucosa. There appears to be mounting evidence to support a possible link between deficient EGF production and the development of NEC. The relevant evidence for the role of EGF in intestinal development and mucosal repair, as well as its potential involvement in the genesis of NEC will be reviewed.

A pilot study of the use of epidermal growth factor in pediatric short bowel syndrome

BACKGROUND

This study examined the effects of enterally administered epidermal growth factor (EGF) on nutrient absorption and tolerance of enteral feeds in pediatric patients with short bowel syndrome (SBS).

METHODS

Patients identified with severe SBS (<25% bowel length predicted for age) were prospectively enrolled in treatment using human recombinant EGF (1-53); 100 microg/kg per day given mixed with enteral feeds and patients were treated for 6 weeks. End points followed were patient weight, tolerance of enteral feeds, nutrient absorption, and intestinal permeability as determined using carbohydrate probes and hematologic values for liver function parameters.

RESULTS

Five patients were treated with EGF; all showed a significant improvement in carbohydrate absorption (3-0 methylglucose): absorption 24.7% +/- 9.7% pretreatment vs 34.1% +/- 13.8% posttreatment and improved tolerance of enteral feeds (enteral energy as % of total energy, 25% +/- 28% pretreatment vs 36% +/- 24% posttreatment; mean +/- SD; P < .05 by Wilcoxon's signed rank test). Epidermal growth factor treatment was not associated with significant changes in intestinal permeability, the rate of weight gain, or liver function tests. During the treatment phase, no patients developed episodes of sepsis; however, within 2 weeks of discontinuation of EGF treatment, 3 patients developed septic episodes. No adverse effects of EGF administration were noted.

CONCLUSIONS

These results suggest that enteral treatment with EGF in pediatric SBS improves nutrient absorption, increases tolerance with enteral feeds, and may improve the infection rate. Further studies exploring treatment strategies including the timing and duration of EGF administration are indicated.

Cytokines and growth factor modulators in intestinal inflammation and repair

Breakdown in gastrointestinal mucosal integrity may be due to increased aggressive factors, including an excessive inflammatory response, decreased mucosal defence or a combination of the two. Our understanding of the control processes underlying these changes has rapidly expanded over the last decade and it is becoming clear that rather than being distinct elements, inflammation and repair are interrelated processes mediated by common cytokines and growth factors, with the division of factors as being a cytokine or a growth factor being somewhat artificial. The use of biological therapies, such as antibodies that cause receptor blockade or administering recombinant growth factors, has now progressed from the laboratory to the clinical arena. This review summarizes current thoughts on the use of these factors in general, but with particular emphasis on inflammatory bowel disease.

MEK1 restores migration of polyamine-depleted cells by retention and activation of Rac1 in the cytoplasm

We previously showed that polyamines are required for proliferation and migration both in vivo and in a cultured intestinal epithelial cell (IEC-6) model. Wounding of the IEC-6 monolayer induced transient ERK activation, which was further enhanced by EGF. EGF stimulated migration in control and polyamine-depleted cells, but the degree of stimulation was significantly less in polyamine-depleted cells. Inhibition of MEK1 inhibited basal as well as EGF-induced ERK activation and migration. Expression of constitutively active (CA)-MEK and dominant-negative (DN)-MEK had significant effects on F-actin structure. CA-MEK increased stress fiber and lamellipodia formation, while DN-MEK showed loss of stress fibers and abnormal actin cytoskeletal structure. Unlike EGF, CA-MEK significantly increased migration of both control and polyamine-depleted cells. The most important and significant finding in this study was that polyamine depletion caused localization of Rac1 and RhoA to the nuclear as well as perinuclear regions. Interestingly, CA-MEK completely reversed the subcellular distribution of Rac1 and RhoA proteins in polyamine-depleted cells. Polyamine depletion increased Rac1 in the nuclear fraction and decreased it in the cytoplasmic and membrane fractions of vector-transfected cells. CA-MEK prevented accumulation of Rac1 in the nucleus. Polyamine depletion significantly decreased Rac1 activity during 6-h migration in vector-transfected cells. Cells transfected with CA-MEK had almost identical levels of activated Rac1 in all three groups. These results suggest that polyamine depletion prevents activation of Rac1 and RhoA by sequestering them to the nucleus and that expression of constitutively active MEK reverses this effect, creating the cellular localization required for activation.

Growth hormone and epidermal growth factor upregulate specific sodium-dependent glutamine uptake systems in human intestinal C2BBe1 cells

Glutamine (Gln) is one of the major oxidative fuels of the enterocyte and enters from the lumen via Na(+)-dependent transport mechanisms. When given parenterally, growth hormone (GH) + epidermal growth factor (EGF) increase apical Gln uptake after massive enterectomy in rabbits. Although both receptors are basolateral, GH and EGF are present in luminal contents. We hypothesized that short-term luminal growth factor exposure to enterocytes increases apical Gln uptake by selective upregulation of systems A, B(0,+), or ASC+B(0). A monolayer of C2(BBe)1 cells was exposed for 10 or 60 min to GH (500 microg/L), EGF (100 microg/L), both, or neither. Initial uptake of [(3)H]Gln (50 micromol/L) was measured in the presence of Na(+) or choline. The contributions of systems A, B(0,+), and ASC+B(0) were determined by competitive inhibition with arginine and/or alpha-(methylamino)butyric acid. Gln uptake was linear for up to 8 min. Na(+)-independent transport was negligible. Under control conditions the relative contributions of systems A, B(0,+), and ASC+B(0) were 0, 19 +/- 6, and 80 +/- 4%, respectively. GH alone had no effect on Gln transport. After 10 min of EGF exposure, Na(+)-dependent Gln uptake increased by 50% (P < 0.001) with no change in individual transport systems. Combined EGF and GH for 60 min increased Gln transport by system B(0,+) nearly 250% (P < 0.001) and system A from undetectable levels to 16% of total transport (P < 0.01). Thus, short-term luminal exposure to EGF+GH increases Na(+)-dependent Gln transport mainly by upregulating system B(0+).

Differential response to keratinocyte growth factor receptor and epidermal growth factor receptor ligands of proliferating and differentiating intestinal epithelial cells

The expression of the keratinocyte growth factor receptor (KGFR) has been analyzed on intestinal epithelial Caco-2 cells upon confluence-induced spontaneous differentiation. Western blot and immunofluorescence analysis showed that the expression of functional KGFRs, differently from that of epidermal growth factor receptor (EGFR), was up-modulated in post-confluent differentiated cultures compared with the pre-confluent cells. Confocal microscopy and immunoelectron microscopy revealed that the up-regulated KGFRs displayed a basolateral polarized distribution on the cell surfaces in the monolayer. In vivo immunohistochemical analysis on normal human colon tissue sections showed that KGFRs, differently from EGFRs, were mostly distributed on the more differentiated cells located on the upper portion of the intestinal crypt. Bromodeoxyuridine incorporation assay and Ki67 labeling indicated that the differentiated cells were able to proliferate in response to the two ligands of KGFR, KGF and FGF-10, whereas they were not stimulated by the EGFR ligands TGFalpha and EGF. Western blot and quantitative immunofluorescence analysis of the expression of carcinoembryonic antigen (CEA) in post-confluent cells revealed that incubation with KGF induced an increase of cell differentiation. Taken together these results indicate that up-modulation of KGFR may be required to promote proliferation and differentiation in differentiating cells and that, among the cells componing the intestinal epithelial monolayer, the target cells for KGFR ligands appear to be different during differentiation from those responsive to EGFR ligands.

Modulation of chloride secretory responses and barrier function of intestinal epithelial cells by the Salmonella effector protein SigD

The Salmonella effector protein SigD is an inositol phosphate phosphatase that inhibits phosphatidylinositol 3-kinase-dependent signaling. Because epidermal growth factor (EGF) inhibits chloride secretion via phosphatidylinositol 3-kinase, we explored whether Salmonella infection might modify the inhibitory effect of EGF. As expected, EGF inhibited chloride secretion induced by carbachol in T(84) epithelial cells. Infection with wild-type (WT) but not sigD(-) mutant S. typhimurium SL1344 decreased CCh-stimulated chloride secretion. Moreover, WT but not sigD(-) Salmonella reduced the inhibitory effect of EGF on carbachol-stimulated chloride secretion. Complementation of sigD restored the ability of mutant Salmonella to reverse the inhibitory effect of EGF. EGF-induced EGF receptor phosphorylation was similar in cells infected with either WT or mutant Salmonella, and neither WT nor sigD(-) Salmonella altered recruitment of the p85 subunit of phosphatidylinositol 3-kinase to EGF receptor, implying that SigD acts downstream of these signaling events. Furthermore, transepithelial resistance fell more rapidly in cells infected with WT vs. sigD(-) Salmonella, indicating an early role for SigD in reducing barrier function, perhaps via activation of protein kinase C. We conclude that the Salmonella bacterial effector protein SigD may play critical roles in the pathogenesis of disease caused by this microorganism.

Synergistic effects of systemic trefoil factor family 1 (TFF1) peptide and epidermal growth factor in a rat model of colitis

Novel therapies for the treatment of colitis are required. We therefore examined the potential value of the trefoil factor family 1 (TFF1) peptide and epidermal growth factor (EGF) alone and in combination. Effects of TFF1- Cys58 +/- EGF on an in vitro HT29 cell wounding model of restitution showed synergistic activity when used in combination. In addition, animals had colitis induced by adding 4% dextran sulphate sodium (DSS) to the drinking water for 7 days and they also received twice daily subcutaneous injections of test peptides. Treatment with TFF1-Cys58 alone (100 microg/kg) reduced histological colitis score by 22%, but the TFF1-Ser58 variant was ineffective. In a second study, TFF1-Cys58 reduced histological colitis score by 15%, EGF (600 microg/kg) by 26%, and an additive response (42% reduction) was demonstrated when used together (P < 0.01 versus either peptide given alone). Similar results were found using tissue myeloperoxidase (MPO) activity as a marker of inflammation. Where clinical risk/benefit seems justified, these initial studies suggest that combination therapy of systemic EGF and TFF peptides may prove useful for treatment of colitis in patients with disease extending beyond the reach of topical (enema) therapy.

Epidermal growth factor and necrotizing enterocolitis

As the number of extremely low-birth-weight infants increases,necrotizing enterocolitis remains a critical eminent problem. Supplementation of enteral feeds with biologically active substances normally present in breast milk, such as epidermal growth factor, seems to be a logical and safe way to reduce the incidence of intestinal inflammation and necrotizing enterocolitis. Continuing basic research and clinical studies are essential before epidermal growth factor can be introduced as an efficient therapeutic approach in the treatment of neonatal necrotizing enterocolitis.

Polarity and proliferation are controlled by distinct signaling pathways downstream of PI3-kinase in breast epithelial tumor cells

Loss of tissue polarity and increased proliferation are the characteristic alterations of the breast tumor phenotype. To investigate these processes, we used a three-dimensional (3D) culture system in which malignant human breast cells can be reverted to a normal phenotype by exposure to inhibitors of phosphatidylinositol 3-kinase (PI3K). Using this assay, we find that Akt and Rac1 act as downstream effectors of PI3K and function as control points of cellular proliferation and tissue polarity, respectively. Our results also demonstrate that the PI3K signaling pathway is an integral component of the overall signaling network induced by growth in 3D, as reversion affected by inhibition of PI3K signaling also down-modulates the endogenous levels of beta1 integrin and epidermal growth factor receptor, the upstream modulators of PI3K, and up-regulates PTEN, the antagonist of PI3K. These findings reveal key events of the PI3K pathway that play distinct roles to maintain tissue polarity and that when disrupted are instrumental in the malignant phenotype.

Increased butyrate formation in the pig colon by feeding raw potato starch leads to a reduction of colonocyte apoptosis and a shift to the stem cell compartment

Whereas butyrate is well known to induce apoptosis in transformed colon cells in vitro, evidence exists that it inhibits apoptosis of colon crypt cells in vivo. In this study, pigs were fed with resistant potato starch to increase microbial butyrate formation in the colon and to investigate its effects on mitosis and apoptosis. In addition, apoptosis regulating proteins were determined by immunocytochemistry, such as proapoptotic Bak, antiapoptotic Bcl-2, and the epidermal growth factor (EGF), which is synthesized by goblet cells and functions as a survival factor. Two groups of 6 barrows were both supplied with 381 g crude protein and 31 MJ metabolizable energy (ME) daily over a 19-day experimental period. The rations differed in the carbohydrate composition. The controls received gelatinized starch as the main carbohydrate, whereas the experimental group (butyrate group) received a ration with raw potato starch (low ileal digestibility). In the feces, butyrate concentration and pH were monitored daily. After killing the pigs, colon tissue was obtained for histologic and immunocytochemical evaluation, which was performed separately in the luminal, middle, and stem cell compartment of the crypts. In the butyrate group, the total number of apoptotic cells was reduced by 34% (P< or =.001) compared with controls, whereas the mitotic rate was not altered. The crypt depth was only moderately increased by 15%. Apoptosis in the luminal compartment of the butyrate group was reduced by 18.8%, but was increased by 21.7% in the stem cell compartment. The effect of butyrate on apoptosis was paralleled by an increased number of Bcl-2 positive cells mainly in the luminal compartment (butyrate: 2.6 cells; controls: 1.2 cells, P< or =.001), which was more pronounced compared with the number of Bak positive cells in the same compartment. Bak activity in the stem cell compartment was 3.4-fold increased compared with controls (P< or =.001). The size of EGF-positive stained mucus-droplets from the goblet cells was increased in the butyrate group (P< or =.001). We conclude that butyrate inhibits apoptosis of colonocytes in vivo. An excessive proliferation of crypts is counteracted by a shift of the remaining apoptosis towards the stem cell compartment.

Growth hormone and epidermal growth factor together enhance amino acid transport systems B0,+ and A in remnant small intestine after massive enterectomy

BACKGROUND

Sodium-dependent brush-border nutrient transport is decreased 2 weeks after massive enterectomy. This down-regulation is ameliorated by a 1-week infusion of parenteral growth hormone (GH) and epidermal growth factor (EGF) started 1 week after resection. We hypothesize that glutamine (GLN) transport will be enhanced by earlier and longer growth factor infusion, with differential effects on the Na(+)-dependent GLN transport systems A, B(0,+), and B(0)/ASCT2.

MATERIALS AND METHODS

New Zealand White rabbits underwent 70% small bowel resection then immediately received parenteral EGF, GH, both EGF and GH, or neither for 2 weeks. Na(+)-dependent 3H-GLN uptake by jejunal and ileal brush-border membrane vesicles was measured and the contribution of systems A, B(0,+), and B(0) was then determined by competitive inhibition. Data were analyzed using one-way analysis of variance.

RESULTS

In nonresected animals, the relative contribution of the systems was similar in jejunum (A 9%, B(0,+) 20%, and B(0) 71%) and ileum (A 13%, B(0,+) 27%, and B(0) 60%). Na(+)-dependent GLN uptake was reduced by one half in resected untreated controls, primarily because of decreased B(0) activity. EGF or GH alone did not affect Na(+)-dependent GLN transport, but, as a combination, there was increased uptake in the residual ileum and jejunum by 144% and 150%, respectively, over resected controls (P < 0.05). This was twice that achieved by delayed and shorter-duration combination treatment. This augmentation was a result of a 6.1-8.2-fold increase in system A as well as a 3.8-3.9-fold enhancement of system B(0,+) activity in remnant ileum and jejunum (P < 0.01).

CONCLUSIONS

Parenteral EGF and GH, given in combination for 2 weeks immediately after massive enterectomy, synergistically enhance GLN uptake by systems A and B(0,+).

Growth hormone and epidermal growth factor together enhance amino acid transport systems B(0,+) and A in remnant small intestine after massive enterectomy

BACKGROUND

Sodium-dependent brush border nutrient transport is decreased 2 weeks after massive enterectomy. This downregulation is ameliorated by a 1-week infusion of parenteral growth hormone (GH) and epidermal growth factor (EGF) started 1 week after resection. We hypothesized that glutamine (GLN) transport would be enhanced by earlier and longer growth factor infusion, with differential effects on the Na(+)-dependent GLN transport systems A, B(0,+), and B0/ASCT2.

MATERIALS AND METHODS

New Zealand White rabbits underwent 70% small bowel resection then immediately received parenteral EGF, GH, both, or neither for 2 weeks. Na(+)-dependent 3H-GLN uptake by jejunal and ileal brush-border membrane vesicles was measured and the contribution of systems A, B(0,+), and B0 then determined by competitive inhibition. Data were analyzed using one-way analysis of variance.

RESULTS

In nonresected animals, the relative contribution of the systems was similar in jejunum (A, 9%, B(0,+), 20%; and B0, 71%) and ileum (A, 13%; B(0,+), 27%; and B0, 60%). Na(+)-dependent GLN uptake was reduced by half in resected, untreated controls, primarily because of decreased B(0) activity. EGF or GH alone did not affect Na(+)-dependent GLN transport, but as a combination, increased uptake in the residual ileum and jejunum by 144% and 150%, respectively, over resected controls (P<0.05). This was twice that achieved by delayed and shorter-duration combination treatment. This augmentation was due to a 6.1- to 8.2-fold increase in system A as well as a 3.8- to 3.9-fold enhancement of system B(0,+) activity in remnant ileum and jejunum (P<0.01).

CONCLUSIONS

Parenteral EGF and GH, given in combination for 2 weeks immediately after massive enterectomy, synergistically enhance GLN uptake by systems A and B(0,+).

Epidermal growth factor enemas with oral mesalamine for mild-to-moderate left-sided ulcerative colitis or proctitis

BACKGROUND

Epidermal growth factor (EGF) is a potent mitogenic peptide produced by salivary glands. We examined whether EGF enemas are an effective treatment for active left-sided ulcerative colitis and ulceration limited to the rectum (proctitis).

METHODS

In a randomized, double-blind clinical trial conducted at Leicester Royal Infirmary, 12 patients with mild-to-moderate left-sided ulcerative colitis received daily enemas of 5 microg of EGF in 100 ml of an inert carrier and 12 received daily enemas with carrier alone for 14 days. All also began to receive 1.2 g of oral mesalamine per day or had their dose increased by 1.2 g per day. Patients were assessed clinically at 0, 2, 4, and 12 weeks and by sigmoidoscopy and biopsy at 0, 2, and 4 weeks. The primary end point was disease remission (defined by a St. Marks score of 4 or less without sigmoidoscopic evidence of inflammation) at two weeks. Secondary end points were clinically significant improvements in disease activity (defined by a decrease of more than 3 points in the St. Marks score or the ulcerative colitis disease-activity index) at two and four weeks. Analyses were performed according to the intention-to-treat principle.

RESULTS

After two weeks, 10 of the 12 patients given EGF enemas were in remission, as compared with 1 of 12 in the control group (83 percent vs. 8 percent, P<0.001). At the 2-week assessment, disease-activity scores, sigmoidoscopic score, and histologic scores were all significantly better in the EGF group than in the placebo group (P<0.01 for all comparisons), and this benefit was maintained at 4 weeks and at 12 weeks.

CONCLUSIONS

This study provides preliminary data suggesting that EGF enemas are an effective treatment for active left-sided ulcerative colitis.

Oxidant-stimulated chloride secretion in rat jejunum in vitro is mediated by eicosanoids

Specific effects of the cytotoxic secondary lipid oxidation product, 4-hydroxynonenal (10(-8)-10(-4) M), on intact sheets of rat jejunum were measured as changes in short circuit current (delta(I)sc) following cumulative addition to either the mucosal or serosal side, using the analogous aldehyde, nonenal, as reference. 4-Hydroxynonenal stimulated I(sc) from the serosal side (maximal delta(I)sc = 27.2 +/- 3.5 microA/cm2, mean +/- SEM, N = 32) while nonenal stimulated I(sc) primarily from the mucosal side (maximal delta(I)sc = 16.2 +/- 3.4 microA/cm2, N = 20). Inhibition by 100 microM bumetanide (4-hydroxynonenal: 88.9 +/- 3.0%, N = 6, p < 0.05, nonenal: 69.3 +/- 2.9%, N = 6, P < 0.05) indicated chloride secretion. Nonenal-induced delta(I)sc was inhibited (72.5 +/- 1.2%, N = 8, P < 0.05) by a combination of nordihydroguaiaretic acid (100 microM) and piroxicam (10 microM), while 4-hydroxynonenal-induced delta(I)sc, was abolished by piroxicam (N = 8, P < 0.001) and inhibited by 1 microM tetrodotoxin (69.8 +/- 9.7%, N = 6, P < 0.001). These data indicate that 4-hydroxynonenal stimulates chloride secretion mediated by prostaglandins and the enteric nervous system. The site of action (serosal) being opposite to the reference aldehyde.

Mechanisms of transforming growth factor-alpha (TGF-alpha) induced gastroprotection against ethanol in the rat: roles of sensory neurons, sensory neuropeptides, and prostaglandins

The mechanisms by which transforming growth factor-a (TGP-alpha) protects the stomach against mucosal injury are incompletely understood. The aim of this study was to examine the roles of sensory neurons, sensory neuropeptides and prostaglandins in TGFalpha gastroprotection against ethanol. Fasted rats received TGF-alpha (50 microg/kg, intraperitoneally) prior to orogastric ethanol (75% v/v, 1 ml). Gastric injury was quantitated 30 min after ethanol. Involvement of sensory neurons and the sensory neuropeptides, calcitonin gene-related peptide (CGRP) and substance P (SP), were examined by capsaicin deafferentation and specific receptor antagonist infusion, respectively. Indomethacin (10 mg, intragastrically) was used to determine the role of prostaglandins in TGF-alpha-mediated gastroprotection. TGF-alpha significantly diminished ethanol-induced gastric lesion area to 5.7 +/- 0.8 mm2 vs 41.1 +/- 5.2 mm2 (p < 0.001). Sensory denervation and CGRP-receptor blockade abolished the TGF-alpha protective effect. In contrast, SP antagonist and indomethacin did not alter TGF-alpha gastroprotection. In conclusion, TGF-alpha-mediated gastroprotection involves sensory neuron activation and CGRP release and this protective effect did not involve substance P or prostaglandin generation.

Experimentally induced gluten enteropathy and protective effect of epidermal growth factor in artificially fed neonatal rats

BACKGROUND

A protective effect of breast-feeding against the development of celiac disease has been described, but the nature and effects of the actual milk components have not been established. Epidermal growth factor (EGF), a milk cytokine affecting the proliferation and differentiation of mucosal epithelial cells, was studied as to its potential protective effect on the damage of intestinal mucosa by gliadin in a model system.

METHODS

Enteropathy was induced by gliadin in inbred AVN strain rat pups delivered by cesarean section, breast-fed, or hand-fed a milk formula. All experimental groups were treated with interferon-gamma (1,000 U per animal, administered intraperitoneally) after birth. Gliadin (0.5 and 3 mg) was intragastrically administered to the pups on days 0 and 3, and a 30-mg challenge dose was given on day 20 (24 hours before the termination of the experiment). One group of artificially fed pups received EGF (100 ng/ml) continuously in the diet.

RESULTS

Gliadin- and interferon-gamma-treated formula-fed rat pups showed villus atrophy, increase of inflammatory cells, including CD4+ T lymphocytes in the lamina propria, and damage to epithelial tight junctions and the enterocyte brush border. Morphometrically, the villus height was significantly less than in other groups. Recombinant EGF was markedly increased in the epithelial cells of injured jejunum. The intestinal mucosa of gliadin- and interferon-gamma-treated pups kept on a EGF-supplemented artificial diet resembled that of breast-fed pups.

CONCLUSION

Pathologic changes in jejunal mucosa (villus atrophy and inflammation) resembling gliadin-induced atrophy appeared on administration of interferon-gamma and gliadin to rat pups fed an artificial milk diet immediately after birth. Addition of EGF to the diet protected the rats against pathologic mucosal changes.

Human transforming growth factor alpha (TGF-alpha) is digested to a smaller (1-43), less biologically active, form in acidic gastric juice

BACKGROUND

Transforming growth factor alpha (TGF-alpha) is a 50 amino acid peptide with potent proliferative and cytoprotective activity present in gastric mucosa and juice.

AIMS

To determine the forms and biological activity of natural and recombinant TGF-alpha following incubation with acid pepsin.

PATIENTS

Human gastric juice was obtained under basal conditions from patients taking acid suppressants and from volunteers undergoing intragastric neutralisation.

METHODS

Samples were analysed using mass spectroscopy and/or high pressure liquid chromatography with radioimmunoassay. Biological activity was determined using thymidine incorporation into rat hepatocytes and an indomethacin/restraint induced gastric damage rat model.

RESULTS

TGF-alpha(1-50) is cleaved to TGF-alpha(1-43) by acid pepsin and this is the predominant form in normal gastric juice. However, intragastric neutralisation or taking acid suppressants caused the predominant form to be TGF-alpha(1-50). TGF-alpha(1-43) had only half of the ability to maximally stimulate [(3)H]thymidine incorporation into primary rat hepatocytes (28 177 (1130) DPM/well for 2.16 nM TGF-alpha(1-43) v 63 184 (3536) DPM/well for TGF-alpha(1-50); p<0.001). A similar reduced potency was seen when used in an indomethacin induced rat gastric damage model (0.18 micro mol/kg/h of TGF-alpha(1-43) reduced ulcer area by 19% whereas TGF-alpha(1-50) reduced area by 62%; p<0.001).

CONCLUSIONS

TGF-alpha(1-50) is cleaved to the TGF-alpha(1-43) form by acid pepsin, causing 2-5-fold loss of biological activity. Such changes may have relevance to the actions of acid suppressants and the importance of this peptide in both normal and abnormal growth.

Apical EGF receptors regulate epithelial barrier to gastric acid: endogenous TGF-alpha is an essential facilitator

In previous studies, we found that apical and basolateral EGF receptors (EGFR) on primary canine gastric monolayers decreased paracellular permeability, evident by increased transepithelial electrical resistance (TER) and decreased flux of [(3)H]mannitol (MF). After studying monolayers in Ussing chambers, we now report that treatment with apical, but not basolateral, EGF enhanced tolerance to apical H(+), evident by a slower decay in TER and an attenuated rise in MF. Enhanced tolerance to apical acid was evident within 10 min of treatment with apical EGF. Immunoneutralization of endogenous transforming growth factor (TGF)-alpha accelerated the drop in TER and the rise in MF in response to apical acidification; apical EGF reversed these effects. Study of monolayers cultured in Transwell inserts showed that immunoblockade of basolateral, but not apical, EGFR also impaired the resistance to apical acidification and enhanced MF. We conclude that apical EGFR regulates the barrier to apical acidification via effects on paracellular resistance. Although exogenous basolateral EGF has a less apparent effect on the barrier to acid, endogenous ligand active at basolateral EGFR plays an important role in maintaining the barrier to apical acid. Our data implicate a role for an apical EGFR ligand, which may be EGF or another member of the EGF family.

Cell type specific expression of secretory TFF peptides: colocalization with mucins and synthesis in the brain

The "TFF domain" is an ancient cysteine-rich shuffled module forming the basic unit for the family of secretory TFF peptides (formerly P-domain peptides and trefoil factors). It is also an integral component of mosaic proteins associated with mucous surfaces. Three mammalian TFF peptides are known (i.e., TFF1-TFF3); however, in Xenopus laevis the pattern is more complex (xP1, xP4.1, xP4.2, and xP2). TFF peptides are typical secretory products of a variety of mucin-producing epithelial cells (e.g., the conjunctiva, the salivary glands, the gastrointestinal tract, the respiratory tract, and the uterus). Each TFF peptide shows an unique expression pattern and different mucin-producing cells are characterized by their specific TFF peptide/secretory mucin combinations. TFF peptides have a pivotal role in maintaining the surface integrity of mucous epithelia in vivo. They are typical constituents of mucus gels, they modulate rapid mucosal repair ("restitution") by their motogenic and their cell scattering activity, they have antiapoptotic effects, and they probably modulate inflammatory processes. Pathological expression of TFF peptides occurs as a result of chronic inflammatory diseases or certain tumors. TFF peptides are also found in the central nervous system, at least in mammals. In particular, TFF3 is synthesized from oxytocinergic neurons of the hypothalamus and is released from the posterior pituitary into the bloodstream.

Epidermal growth factor improves nutritional outcome in a rat model of short bowel syndrome

BACKGROUND/PURPOSE

This study investigates the effect of epidermal growth factor (EGF) on nutrient absorption in a rat model of short bowel syndrome (SBS).

METHODS

Male juvenile rats underwent either transection (Sham) or ileocecal resection leaving a 20-cm jejunal remnant. Animals underwent follow-up for 10 days, and resected animals were treated with placebo or recombinant human EGF (1-53). Animals were pair fed; in vivo nutrient absorption, intestinal permeability, morphology, and total intestinal DNA and protein content were measured.

RESULTS

Resected EGF-treated animals lost significantly less weight than those in the placebo group (-4.2 +/- 3 v -13.7 +/- 6.9%), absorbed significantly more 3-0 methylglucose (76.8 +/- 6.6 v 64.9 +/- 10.1%), and had reduced permeability (lactulose/mannitol ratio, 0.35 +/- 0.19 v 0.60 +/- 0.20; P <.05 for all comparisons).

CONCLUSIONS

These findings show that treatment of short bowel syndrome animals with EGF reduced weight loss and improved carbohydrate absorption and intestinal permeability. These findings suggest that enteral EGF may be a useful therapy for short bowel syndrome; further studies are indicated.

EGF promotes gastric mucosal restitution by activating Na(+)/H(+) exchange of epithelial cells

This study was conducted to determine whether the contributions of epidermal growth factor (EGF) to gastric mucosal restitution after injury are mediated by stimulation of Na(+)/H(+) exchangers in surface mucous cells (SMC). Intact sheets of guinea pig gastric mucosae were incubated in vitro. Intracellular pH (pH(i)) in SMC was measured fluorometrically, using 2',7'- bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein. Restitution after Triton X-100-induced injury was evaluated by recovery of electrical resistance. At neutral luminal pH, exogenous EGF (ex-EGF) increased pH(i) and enhanced restitution in the absence but not in the presence of serosal HCO. During exposure to luminal acid, ex-EGF not only prevented intracellular acidosis but also promoted restitution. These effects of ex-EGF were blocked by serosal amiloride or anti-EGF-receptor antibody. In the absence of ex-EGF, restitution was inhibited by replacement of luminal and serosal solutions with fresh solutions and was blocked more completely by serosal anti-EGF-receptor antibody. These results suggest that both endogenous and ex-EGF contribute to restitution via basolateral EGF receptors, with effects mediated, at least in part, by stimulation of basolateral Na(+)/H(+) exchangers.

Growth factor regulation of enterocyte nutrient transport during intestinal adaptation

BACKGROUND

Intestinal adaptation occurs in response to injury or alteration in nutrient availability. It is both morphologic and physiologic in nature and can be mediated by growth factors and nutrients. Pathologic conditions such as short-bowel syndrome and inflammatory bowel disease lead to derangements in nutrient absorption that may exceed the body's regenerative and adaptive capacity. Failure to fully adapt often results in long-term dependence on parenteral nutrition, leading to decreased quality of life and excessive medical expenses. The therapeutic use of appropriate growth factors may increase the adaptive capabilities of the gut.

DATA SOURCE

Medline and current literature review.

CONCLUSIONS

The major known nutrient transporters present in the gut and the mechanisms by which growth factors alter transport activity during intestinal adaptation are summarized. Growth factors have the potential to improve nutrient absorption in some bowel diseases.

Lectins can reverse the distal intestinal atrophy associated with elemental diets in mice

BACKGROUND

Elemental diets cause intestinal atrophy and reduced intestinal integrity, which can lead to significant increases in intestinal permeability and bacterial translocation. Recently, several lectins have been shown to have trophic effects on the intestine.

AIMS

We examined the effects of concanavalin-A and phytohaemagglutinin on cell proliferation and crypt fission throughout the intestine of mice fed on elemental diets.

METHODS

Mice were randomized to chow fed, elemental diet, elemental diet plus concanavalin-A and elemental diet plus phytohaemagglutinin groups. Cell proliferation and crypt fission were estimated in microdissected crypts. Plasma gastrin and enteroglucagon levels were measured by radioimmunoassay.

RESULTS

Elemental diet feeding significantly decreased cell proliferation and crypt fission of the middle and distal small intestine and throughout the colon. Phytohaemagglutinin significantly increased the weight of the intestine, but concanavalin-A had little effect. Cell proliferation in the small intestine was significantly increased by both lectins. However, in the stomach and colon, only phytohaemagglutinin increased proliferation. Crypt fission in the colon was dramatically increased by phytohaemagglutinin. Phytohaemagglutinin increased the plasma gastrin level, but not the enteroglucagon level.

CONCLUSIONS

Lectins have significant trophic effects on the small intestine and colon of mice fed elemental diets, and these actions vary between different sites in the gastrointestinal tract.

Immunohistochemical expression of transforming growth factor alpha and epidermal growth factor receptor in pancreatic endocrine tumors

Coexpression of transforming growth factor alpha (TGF-alpha) and its receptor epidermal growth factor receptor (EGFR) is known to be associated with aggressive biologic behavior and adverse clinical outcome in a variety of tumors, including pancreatic adenocarcinomas. However, very little information is currently available as to whether this is true of pancreatic endocrine tumors (PETs) as well. Thirty-five PETs were retrospectively studied for immunohistochemical expression of TGF-alpha, the intracellular and extracellular domains of EGFR, and various hormonal secretory products. Proliferative activity was additionally studied (in 20 cases only) using the MIB-1 antibody. Thirty-one (89%) of 35 tumors were reactive for 1 or more of the peptide hormones tested; 22 (63%) tumors were positive for TGF-alpha; and 23 (65%) were positive for the intracellular and/or extracellular domain of EGFR. Based on their TGF-alpha and EGFR expression, these tumors could be classified into 4 groups. Of the 10 tumors in group I (positive for TGF-alpha and the complete EGFR molecule), 3 were malignant, 6 were >2 cm in diameter, 5 were functional, and 1 had a proliferative index of >40%. The 12 tumors in group II (positive for TGF-alpha but negative for the intracellular and/or extracellular domain of EGFR) included 4 malignant tumors, 4 PETs >2 cm in diameter, 8 functional, and 1 with a proliferative index of >40%. The 7 PETs in group III (positive for the intracellular/extracellular domain of EGFR alone) included 3 malignant tumors, 3 PETs >2 cm in diameter, and 3 functional tumors. The 6 tumors in group IV (completely negative for both TGF-alpha and EGFR) included 4 malignant tumors, 3 PETs >2 cm in diameter, and 4 functional lesions. Therefore, immunohistochemical expression of TGF-alpha and EGFR, either alone or in concert, shows no correlation with size, functional status, secretory profile, or biologic behavior and hence cannot be used as a marker of malignancy in this group of tumors.

Trefoil factor family-peptides promote migration of human bronchial epithelial cells: synergistic effect with epidermal growth factor

A process termed "restitution" enables rapid repair of the respiratory epithelium by migration of neighbouring cells. Mucin-associated TFF-peptides (formerly P-domain peptides or trefoil factors) are typical motogens enhancing migration of cells in various in vitro models mimicking restitution of the intestine. The human bronchial epithelial cell line BEAS-2B was used as a model system of airway restitution. The motogenic activities of recombinant human TFF2 as well as porcine TFF2 were demonstrated by in vitro wound healing assays of BEAS-2B cells. TFF2 did not induce phosphorylation of the epidermal growth factor (EGF) receptor. EGF was capable of enhancing the motogenic effect of human TFF2 at a concentration of 3 x 10(-10) M whereas EGF itself (i.e., in the absence of TFF2) did not stimulate migration at this low concentration. Furthermore, TFF2 as well as monomeric and dimeric forms of TFF3 enhanced migration of BEAS-2B cells in Boyden chambers. Motogenic activity of TFF2 was also shown for normal human bronchial epithelial (NHBE) cells in Boyden chambers. These results suggest that TFF-peptides act as motogens in the human respiratory epithelium triggering rapid repair of damaged mucosa in the course of airway diseases such as asthma.

Role of growth factors and their receptors in gastric ulcer healing

The repair of gastric ulcers requires the reconstitution of epithelial structures and the underlying connective tissue, including vessels and muscle layers. Several growth factors have been implicated in this process, since they are able to regulate important cell functions, such as cell proliferation, migration, differentiation, secretion, and degradation of extracellular matrix, all of which are essential during tissue healing. Epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), hepatocyte growth factor (HGF), and trefoil factors (TFFs) are mainly involved in the reconstitution of the epithelial structures. Platelet derived growth factor (PDGF), basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), and transforming growth factor-beta (TGF-beta) play a major role in the reconstitution of connective tissue, including vessels and smooth muscle cells, and provide the extracellular matrix substrate for cell migration and differentiation. The expression of these growth factors and their receptors is increased during ulcer healing and, in some cases, intracellular signaling related to receptor binding and transduction has been demonstrated. EGF, TGF-alpha and TFFs are normally present either in the gastric juice or in the mucosa, and may exert their effects immediately after damage, before newly synthesized EGF and TFFs are released from the ulcer margin. The inhibition of their effects by neutralizing antibodies may result in delayed ulcer healing, while the administration of recombinant or natural analogues may improve ulcer repair. In this review, we will summarize the basic molecular characteristics of some of these growth factors, and will discuss available evidence supporting their role in the ulcer repair process.

Comparison of the effects of concanavalin-A and epidermal growth factor on epithelial cell proliferation in the rat intestine

BACKGROUND

Concanavalin-A, the lectin present in Jack beans, binds to mannose- and glucose-containing residues and can interact with the epidermal growth factor receptor and moderate cell proliferation in vitro.

AIM

To compare the actions of concanavalin-A and epidermal growth factor on the gastrointestinal tract in vivo.

METHODS

Rats maintained on total parenteral nutrition were given intragastric concanavalin-A, intravenous epidermal growth factor or concanavalin-A and epidermal growth factor. Cell proliferation and crypt fission were assayed in 'micro-dissected' crypts.

RESULTS

Concanavalin-A and epidermal growth factor both significantly elevated proliferation in the small intestine and colon. No significant interaction between the effects of these two agents was seen, except in the mid small intestine where there was a synergistic interaction. Concanavalin-A had no effect on crypt branching. Epidermal growth factor significantly reduced branching in the distal small intestine and mid colon.

CONCLUSION

The effects of the two agents appeared to be separate, except in the mid small intestine where they were additive. This is in marked contrast with the actions reported in vitro, where concanavalin-A is a powerful inhibitor of epidermal growth factor-induced cell proliferation. Concanavalin-A thus has potential for enhancing the functions of the small intestine.

Epidermal growth factor inhibits glycylsarcosine transport and hPepT1 expression in a human intestinal cell line

The human intestinal cell line Caco-2 was used as a model system to study the effects of epidermal growth factor (EGF) on peptide transport. EGF decreased apical-to-basolateral fluxes of [(14)C]glycylsarcosine ([(14)C]Gly-Sar) up to 50.2 +/- 3.6% (n = 6) of control values. Kinetic analysis of the fluxes showed that maximal flux (V(max)) of transepithelial transport decreased from 3.00 +/- 0.17 nmol x cm(-2) x min(-1) in control cells to 0.50 +/- 0.07 nmol x cm(-2) x min(-1) in cells treated with 5 ng/ml EGF (n = 6, P < 0.01). The apparent Michaelis-Menten constant (K(m)) was 2.71 +/- 0.31 mM (n = 6) in control cells and 1.89 +/- 0.28 mM (n = 6, not significantly different from control) in EGF-treated cells. Similarly, apical uptake of [(14)C]Gly-Sar decreased in cells treated with EGF, with an ED(50) value of 0.36 +/- 0.06 ng/ml (n = 6) EGF and a maximal inhibition of 80 +/- 0.02% (n = 6). V(max) decreased from 2.61 +/- 0.4 to 1.06 +/- 0.1 nmol x cm(-2) x min(-1) (n = 3, P < 0.05), whereas K(m) remained constant. Basolateral Gly-Sar uptake showed no changes in V(max) or K(m) after EGF treatment (n = 3). RT-PCR showed a decrease in hPepT1 mRNA (using glucose-6-phosphate dehydrogenase mRNA as control) in cells treated with EGF. Western blotting indicated a decrease in hPepT1 protein in cell lysates. We conclude that EGF treatment decreases Gly-Sar transport in Caco-2 cells by decreasing the number of peptide transporter molecules in the apical membrane.

Effect of ectopic expression of rat trefoil factor family 3 (intestinal trefoil factor) in the jejunum of transgenic mice

To further examine the function of the trefoil factor family (TFF), the expression of which is up-regulated at sites of injury, we have produced transgenic mice that chronically express rat TFF3 within the jejunum (using a rat fatty acid-binding protein promoter). The expression of rat TFF3 was limited to the villi of the jejunum and had no effect on base-line morphology. Rat TFF3 expression did result, however, in a reduced sensitivity to indomethacin (85 mg/kg subcutaneously), which only caused a 29% reduction in villus height in transgenics versus 51% reduction in controls (p < 0.01). Indomethacin increased initial intestinal epithelial cell proliferation and migration, but the presence of rat TFF3 caused no additional change in proliferation (bromodeoxyuridine), cell migration ([(3)H]thymidine and bromodeoxyuridine), apoptosis (terminal deoxyuridine nucleotidyl nick end labeling), or E-cadherin immunostaining. In vitro studies following changes in resistance of intestinal strips in Ussing chambers (voltage-clamp technique) showed increased base-line resistance in the rat TFF3-expressing region (326 +/- 60 versus 195 +/- 48 ohm.cm(2) in controls, p < 0.05) and reduced the fall in resistance following HCl exposure by about 40% (p < 0.01). Overexpression of TFF3 stabilizes the mucosa against noxious agents, supporting its role in mucosal protection/repair. It may therefore provide a novel approach to the prevention and/or treatment of intestinal ulceration.

Increased tight junction permeability can result from protein kinase C activation/translocation and act as a tumor promotional event in epithelial cancers

Exposure of LLC-PK1 epithelial cell cultures to phorbol ester tumor promoters causes immediate translocation of protein kinase C-alpha (PKC-alpha) from cytosolic to membrane-associated compartments. With a very similar time course, a dramatic and sustained increase in tight junctional (paracellular) permeability occurs. This increased permeability extends not only to salts and sugars but macromolecules as well. Fortyfold increases of transepithelial fluxes of biologically active EGF and insulin occur. Recovery of tight junction barrier function coincides with proteasomal downregulation of PKC-alpha. The failure to downregulate activated membrane-associated PKC-alpha has correlated with the appearance of multilayered cell growth and persistent leakiness of tight junctions. Accelerated downregulation of PKC-alpha results in only a partial and transient increase in tight junction permeability. Transfection of a dominant/negative PKC-alpha results in a slower increase in tight junction permeability in response to phorbol esters. In a separate study using rat colon, dimethylhydrazine (DMH)-induced colon carcinogenesis has been preceded by linear increases in both the number of aberrant crypts and transepithelial permeability, as a function of weeks of DMH treatment. Adenocarcinomas of both rat and human colon have been found to have uniformly leaky tight junctions. Whereas most human colon hyperplastic and adenomatous polyps contain nonleaky tight junctions, adenomatous polyps with dysplastic changes did possess leaky tight junctions. Our overall hypothesis is that tight junctional leakiness is a late event in epithelial carcinogenesis but will allow for growth factors in luminal fluid compartments to enter the intercellular and interstitial fluid spaces for the first time, binding to receptors that are located on only the basal-lateral cell surface, and causing changes in epithelial cell kinetics. Tight junctional leakiness is therefore a promotional event that would be unique to epithelial cancers.

Potency and stability of C terminal truncated human epidermal growth factor

INTRODUCTION

Epidermal growth factor (EGF) is normally present as EGF(1-53). A variety of C terminal truncated forms have been used in preliminary trials for treating gastrointestinal injury but their relative potency and stability when used in a clinical setting are unclear. Therefore, we compared the biological activity of recombinant EGF(1-53), EGF(1-52), EGF(1-51), and the C terminal peptides EGF(44-53) and EGF(49-53).

METHODS

Purity of forms was confirmed by mass spectrometry. Bioactivity of the different EGF forms was determined using [methyl-(3)H] thymidine incorporation into primary rat hepatocytes and their ability to reduce indomethacin (20 mg/kg subcutaneously)/restraint induced gastric injury in rats. Stability of EGF peptides was determined by serial sampling from a syringe driver system containing EGF/4% albumin in saline.

RESULTS

Biological activity assays of EGF(1-53), EGF(1-52), and EGF(1-51) gave almost identical thymidine uptake dose-response curves (maximal responses increasing baseline uptake from 4400 (600) cpm (mean (SEM)) to about 22 000 (2000) cpm when EGF was added at 1. 6 nM). EGF(44-53) and EGF(49-53) did not stimulate (3)H thymidine uptake. Control rats had 47 (4) mm(2) damage/stomach, EGF(1-51), EGF(1-52), and EGF(1-53) at 0.16 and 0.80 nmol/kg/h each reduced gastric injury by about 50% and 80%, respectively (both doses p<0.01 compared with control but no significant difference between the different forms). EGF was stable at room temperature for seven days but biological activity decreased by 35% and 40% at two and three weeks, respectively (both p<0.01). Exposure to light did not affect bioactivity.

CONCLUSION

EGF(1-51) and EGF(1-52) are as biologically active as full length EGF(1-53) but the C terminal penta- and decapeptides are ineffective. Clinical trials of EGF can probably use infusion systems for at least 48 hours at room temperature and with exposure to light, without reducing biological efficacy.

A multicenter, randomized, double-blind clinical trial examining the effect of oral human recombinant epidermal growth factor on the healing of duodenal ulcers

BACKGROUND

Our aim was to study the efficacy of oral human recombinant epidermal growth factor (EGF) in the treatment of duodenal ulcers, on the basis of its repairing actions in the gastrointestinal tract.

METHODS

A placebo-controlled, multicenter, randomized, and double-blind study was conducted. Treatment groups were A) placebo solution, B) 10 microg/ml of human recombinant (hr)-EGF, and C) 50 microg/ml of hr-EGF, three times daily during 6 weeks. Patients, 15-65 years old, with a duodenal ulcer >4 mm, who gave their written informed consent to participate were eligible. Exclusion criteria were gastric ulcer and more than one duodenal ulcer, ulcer-related complications, and previous treatment with oral EGF or other specific anti-ulcer drugs in the previous 2 weeks. The main outcome variable was ulcer healing, evaluated by endoscopy after the 2nd, 4th, and 6th week.

RESULTS

One hundred and three patients were included. The groups were comparable with regard to age, sex, toxic habits, antecedents of ulcerous disease, initial size and depth or the ulcer, initial symptoms, and positivity for Helicobacter pylori. The ulcers were healed in a larger proportion of patients treated with hr-EGF at the highest dose (70.6% in group C versus 40.0% and 35.3% in placebo and low-dose groups, respectively (P = 0.007)). The difference was significant from week 4 on. Groups A and B did not differ. Eighty-eight percent of group C patients were cured or improved versus 57% and 56% in groups A and B, respectively. No adverse reactions were reported.

CONCLUSIONS

Oral hr-EGF was effective in the treatment of duodenal ulcer at a 50-microg/ml dose every 8 h but not at 10 microg/ml.

Chloride secretion by the intestinal epithelium: molecular basis and regulatory aspects

Chloride secretion is the major determinant of mucosal hydration throughout the gastrointestinal tract, and chloride transport is also pivotal in the regulation of fluid secretion by organs that drain into the intestine. Moreover, there are pathological consequences if chloride secretion is either reduced or increased such as in cystic fibrosis and secretory diarrhea, respectively. With the molecular cloning of many of the proteins and regulatory factors that make up the chloride secretory mechanism, there have been significant advances in our understanding of this process at the cellular level. Similarly, emerging data have clarified the intercellular relationships that govern the extent of chloride secretion. The goal of our article is to review this area of investigation, with an emphasis on recent developments and their implications for the physiology and pathophysiology of chloride transport.

Colostrum and milk-derived peptide growth factors for the treatment of gastrointestinal disorders

Colostrum is the specific first diet of mammalian neonates and is rich in immunoglobulins, antimicrobial peptides, and growth factors. In this article we review some of these constituents of human and bovine colostrum in comparison with those of mature milk. Recent studies suggest that colostral fractions, or individual peptides present in colostrum, might be useful for the treatment of a wide variety of gastrointestinal conditions, including inflammatory bowel disease, nonsteroidal antiinflammatory drug-induced gut injury, and chemotherapy-induced mucositis. We therefore discuss the therapeutic possibilities of using whole colostrum, or individual peptides present in colostrum, for the treatment of various gastrointestinal diseases and the relative merits of the 2 approaches.

Epidermal growth factor receptor is increased in rabbit intestinal brush border membrane after small bowel resection

A defective epidermal growth factor receptor (EGFR) abrogates adaptation, while overexpression of EGFR or exogenous epidermal growth factor (EGF) enhances adaptation following small bowel resection (SBR). EGFR is predominantly located on the enterocyte basolateral membrane, yet luminal EGF is increased in injured mucosa. We hypothesized that EGFR is both increased and redistributed to the enterocyte brush border membrane (BBM) after SBR and that parenteral EGF will reverse this redistribution. Rabbits (N = 20) were subjected to sham operation or SBR. EGF or vehicle were administrated one week postoperatively to SBR rabbits, and the gut was harvested one week later. EGFR levels in intestinal crude extracts and purified BBM were determined by Western blot analysis. No difference in EGFR level was detected in the crude extract among any of the groups. SBR more than doubled EGFR amount in BBM (P < 0.006). Parenteral EGF did not influence this redistribution. Thus, EGFR is partially redistributed to the BBM in the mucosa of SBR rabbits, and parenteral EGF does not reverse this redistribution.

Diminished epidermal growth factor levels in infants with necrotizing enterocolitis

BACKGROUND/PURPOSE

Because epidermal growth factor (EGF) is trophic to the intestinal mucosa, and neonatal necrotizing enterocolitis (NEC) is associated with a disrupted intestinal mucosal barrier, the authors sought to determine whether diminished levels of EGF were present in infants with NEC.

METHODS

Saliva, serum, and urine specimens were obtained from infants with NEC during a 3-year period (February 1995 to May 1998). Control patients without NEC were chosen based on similar postnatal age and birthweight. EGF levels were determined by enzyme-linked immunosorbent assay (ELISA). Differences between groups were compared using Mann-Whitney Rank sum test with P less than .05 considered significant. Results are presented as mean values +/-SEM.

RESULTS

Twenty-five infants with NEC were compared with 19 control patients. Birth weight (1,616+/-238 g control v. 1,271+/-124 g NEC) and postnatal age (23+/-6 days control v. 22+/-3 days NEC) were similar. Infants with NEC had significantly lower levels of EGF in both saliva (590+/-80 pg/mL control v. 239+/-41 pg/mL NEC; P<.001) and serum (35+/-8 pg/mL control v. 5.6+/-1.9 pg/mL NEC; P<.001). Urinary EGF was also lower in the NEC group, but was not statistically significant.

CONCLUSIONS

Premature infants with NEC have significantly diminished levels of salivary and serum EGF. Reduced levels of this growth factor may distinguish infants at risk for NEC and play a pivotal role in the pathogenesis of the perturbed intestinal mucosal barrier that is central to this condition.

Transforming growth factor-alpha and epidermal growth factor receptor in colonic mucosa in active and inactive inflammatory bowel disease

Transforming growth factor-alpha (TGF-alpha) is overexpressed in colonic carcinomas and promotes mucosal wound healing. It may be implicated in chronic inflammatory bowel disease (IBD). We analyzed the expression of TGF-alpha and its receptor, epidermal growth factor receptor (EGF-r), in the colonic mucosa of patients with Crohn's disease (CD) or ulcerative colitis (UC), in active or inactive stages, as compared with controls. Proteins and mRNA were detected in biopsies from the right and left colon and in surgical colonic specimens. Immunoblot analysis revealed TGF-alpha protein as a 29 kDa band. This band was normally expressed in uninvolved colonic mucosa of patients with CD or UC whether in active or inactive stages, but decreased or absent in involved mucosa of active IBD, even when TGF-alpha mRNA and EGF-r protein were detected. In the unaffected mucosa of CD, the intensity of TGF-alpha immunoreactivity was similar to that of controls in the right colon but stronger (P = 0.05) in the left colon. There was no TGF-alpha overexpression in dysplastic regions. In conclusion, in active IBD disease, the decreased TGF-alpha protein amount seems not only related to epithelial cell loss but reflects a down-regulation at least at the protein level. We speculate that TGF-alpha does not play a role within the active stage but may be implicated later in the repair process.