Epidermal growth factor augments adaptation following small bowel resection: optimal dosage, route, and timing of administration

Intestinal adaptation and rehabilitation

Massive intestinal resection is a regrettably necessary but life-saving intervention for progressive or fulminant necrotizing enterocolitis (NEC). However, the resultant short bowel syndrome (SBS) poses its own array of challenges and complications. Within hours of such an abrupt loss of intestinal length, the intestine begins to adapt. Our ability to understand this process of intestinal adaptation has proven critical in our ability to clinically treat the challenging problem of short bowel syndrome. This review first highlights key data relating to intestinal adaptation including structural and functional changes, biochemical regulation, and other factors affecting the magnitude of intestinal adaptation responses. We then focus on intestinal rehabilitation as it relates to strategies to enhance intestinal adaptation while meeting nutritional needs and preventing complications of parenteral nutrition.

Treatment of short bowel syndrome: Breaking the therapeutic ceiling?

Short bowel syndrome (SBS) is the most common cause of chronic intestinal failure, requiring home parenteral support (intravenous fluid, parenteral nutrition, or parenteral nutrition with intravenous fluid) to compensate for severe malabsorption. The loss of mucosal absorptive area after extensive intestinal resection is accompanied by an accelerated transit and hypersecretion. Changes in physiology and clinical outcomes differ between patients with SBS with or without the distal ileum and/or colon-in-continuity. This narrative review summarizes the treatments used in SBS, with a focus on novel approaches with intestinotrophic agents. During the early postoperative years, spontaneous adaptation occurs and can be induced or accelerated with conventional therapies, which include dietary and fluid modifications and antidiarrheal and antisecretory drugs. Based on the proadaptive role of enterohormones (eg, glucagon-like peptide [GLP]-2), analogues have been developed to allow enhanced or hyperadaptation after a period of stabilization. Teduglutide is the first GLP-2 analogue developed and commercialized with proadaptive effects resulting in reduced parenteral support needs; however, the potential for weaning of parenteral support is variable. Whether early treatment with enterohormones or accelerated hyperadaptation would further improve absorption and outcomes remains to be shown. Longer-acting GLP-2 analogues are currently being investigated. Encouraging reports with GLP-1 agonists require confirmation in randomized trials, and dual GLP-1 and GLP-2 analogues have yet to be clinically investigated. Future studies will prove whether the timing and/or combinations of different enterohormones will be able to break the ceiling of intestinal rehabilitation in SBS.

Structural studies of full-length receptor tyrosine kinases and their implications for drug design

Receptor tyrosine kinases (RTKs) are important drug targets for cancer and immunological disorders. Crystal structures of individual RTK domains have contributed greatly to the structure-based drug design of clinically used drugs. Low-resolution structures from electron microscopy are now available for the RTKs, EGFR, PDGFR, and Kit. However, there are still no high-resolution structures of full-length RTKs due to the technical challenges of working with these complex, membrane proteins. Here, we review what has been learned from structural studies of these three RTKs regarding their mechanisms of ligand binding, activation, oligomerization, and inhibition. We discuss the implications for drug design. More structural data on full-length RTKs may facilitate the discovery of druggable sites and drugs with improved specificity and effectiveness against resistant mutants.

Intestinal Failure: A Description of the Problem and Recent Therapeutic Advances

Pediatric intestinal failure occurs when gut function is insufficient to meet the nutrient and hydration needs of the growing child. The commonest cause is short bowel syndrome with maldigestion and malabsorption following massive bowel loss. The remnant bowel adapts during the process of intestinal rehabilitation. Management promotes the achievement of enteral autonomy while mitigating the risk of comorbid disease. The future of care is likely to see expansion of pharmacologic methods for augmenting bowel adaptation, tissue engineering techniques enabling immune suppression-free autologous bowel transplant, and the development of electronic health record tools for efficient, collaborative study and care improvement.

Host-Gut Microbiota Crosstalk in Intestinal Adaptation

Short-bowel syndrome represents the most common cause of intestinal failure and occurs when the remaining intestine cannot support fluid and nutrient needs to sustain adequate physiology and development without the use of supplemental parenteral nutrition. After intestinal loss or damage, the remnant bowel undergoes multifactorial compensatory processes, termed adaptation, which are largely driven by intraluminal nutrient exposure. Previous studies have provided insight into the biological processes and mediators after resection, however, there still remains a gap in the knowledge of more comprehensive mechanisms that drive the adaptive responses in these patients. Recent data support the microbiota as a key mediator of gut homeostasis and a potential driver of metabolism and immunomodulation after intestinal loss. In this review, we summarize the emerging ideas related to host-microbiota interactions in the intestinal adaptation processes.

Epithelial IGF1R is dispensable for IGF2 mediated enhanced intestinal adaptation in retinoblastoma-deficient mice

PURPOSE

Previously, we demonstrated enhanced adaptation after small bowel resection (SBR) in intestinal-specific retinoblastoma (Rb)-deficient mice along with elevated levels of insulin-like growth factor 2 (IGF2) expression within the villi. The purpose of this study was to verify that the insulin-like growth factor 1 receptor (IGF1R) plays a role in this phenomenon.

METHODS

Inducible and intestinal specific Rb and IGF1R double knockout mice (iRb/IGF1R-IKO) (n=4) and Rb single knockout mice (iRb-IKO) (n=5) underwent 50% mid SBR. On post-operative day 28, mice were harvested, and structural adaptation was measured as changes in crypt depth and villus height. Rates of enterocyte proliferation were recorded. IGF2 expression within the remnant villi was measured via RT-PCR.

RESULTS

Both iRb-IKO and iRb/IGF1R-IKO mice demonstrated enhanced adaptation with at least a 45% increase in both crypt depth and villus height in the proximal and distal remnant bowel. Both groups showed elevation of IGF2 expression in the remnant villi, but there were no differences between the two groups.

CONCLUSION

Epithelial IGF1R is dispensable for IGF2-mediated enhanced intestinal adaptation in retinoblastoma-deficient mice. Our findings suggest that IGF2 signals for enhanced adaptation in cells outside of the epithelium. Further investigation is needed to study the IGF2/IGF1R signaling interaction within the mesenchyme.

LEVEL OF EVIDENCE

Animal study - not clinical.

Synergy of glucagon-like peptide-2 and epidermal growth factor coadministration on intestinal adaptation in neonatal piglets with short bowel syndrome

Glucagon-like peptide-2 (GLP-2) and epidermal growth factor (EGF) treatment enhance intestinal adaptation. To determine whether these growth factors exert synergistic effects on intestinal growth and function, GLP-2 and EGF-containing media (EGF-cm) were administered, alone and in combination, in neonatal piglet models of short bowel syndrome (SBS). Neonatal Landrace-Large White piglets were block randomized to 75% midintestinal [jejunoileal (JI) group] or distal intestinal [jejunocolic (JC) group] resection or sham control, with 7-day infusion of saline (control), intravenous human GLP-2 (11 nmol·kg^-1·day^-1) alone, enteral EGF-cm (80 μg·kg^-1·day^-1) alone, or GLP-2 and EGF-cm in combination. Adaptation was assessed by intestinal length, histopathology, Üssing chamber analysis, and real-time quantitative PCR of intestinal growth factors. Combined EGF-cm and GLP-2 treatment increased intestinal length in all three surgical models (P < 0.01). EGF-cm alone selectively increased bowel weight per length and jejunal villus height in the JI group only. The JC group demonstrated increased intestinal weight and villus height (P < 0.01) when given either GLP-2 alone or in combination with EGF-cm, with no effect of EGF-cm alone. Jejunal permeability of mannitol and polyethylene glycol decreased with combination therapy in both SBS groups (P < 0.05). No difference was observed in fat absorption or body weight gain. IGF-1 mRNA was differentially expressed in JI vs. JC piglets with treatment. Combined treatment with GLP-2 and EGF-cm induced intestinal lengthening and decreased permeability, in addition to the trophic effects of GLP-2 alone. Our findings demonstrate the benefits of novel combination GLP-2 and EGF treatment for neonatal SBS, especially in the JC model representing most human infants with SBS.NEW & NOTEWORTHY Glucagon-like peptide-2 (GLP-2) and epidermal growth factor (EGF) are intestinotrophic, with demonstrated benefit in both animal models and human studies of short bowel syndrome (SBS). The current research shows that over and above known trophic effects, the combination of GLP-2 and EGF synergistically lengthens the bowel in neonatal piglet models of SBS. Most notable benefit occurred with resection of the terminal ileum, the common clinical anatomy seen in neonatal SBS and associated with least de novo lengthening postsurgery.

Transgenic Soybean Production of Bioactive Human Epidermal Growth Factor (EGF)

Necrotizing enterocolitis (NEC) is a devastating condition of premature infants that results from the gut microbiome invading immature intestinal tissues. This results in a life-threatening disease that is frequently treated with the surgical removal of diseased and dead tissues. Epidermal growth factor (EGF), typically found in bodily fluids, such as amniotic fluid, salvia and mother's breast milk, is an intestinotrophic growth factor and may reduce the onset of NEC in premature infants. We have produced human EGF in soybean seeds to levels biologically relevant and demonstrated its comparable activity to commercially available EGF. Transgenic soybean seeds expressing a seed-specific codon optimized gene encoding of the human EGF protein with an added ER signal tag at the N' terminal were produced. Seven independent lines were grown to homozygous and found to accumulate a range of 6.7 +/- 3.1 to 129.0 +/- 36.7 μg EGF/g of dry soybean seed. Proteomic and immunoblot analysis indicates that the inserted EGF is the same as the human EGF protein. Phosphorylation and immunohistochemical assays on the EGF receptor in HeLa cells indicate the EGF protein produced in soybean seed is bioactive and comparable to commercially available human EGF. This work demonstrates the feasibility of using soybean seeds as a biofactory to produce therapeutic agents in a soymilk delivery platform.

The Pathogenesis of Resection-Associated Intestinal Adaptation

After massive small-bowel resection, the remnant bowel compensates by a process termed adaptation. Adaptation is characterized by villus elongation and crypt deepening, which increases the capacity for absorption and digestion per unit length. The mechanisms/mediators of this important response are multiple. The purpose of this review is to highlight the major basic contributions in elucidating a more comprehensive understanding of this process.

Both epidermal growth factor and insulin-like growth factor receptors are dispensable for structural intestinal adaptation

PURPOSE

Intestinal adaptation structurally represents increases in crypt depth and villus height in response to small bowel resection (SBR). Previously, we found that neither epidermal growth factor receptor (EGFR) nor insulin-like growth factor 1 receptor (IGF1R) function was individually required for normal adaptation. In this study, we sought to determine the effect of disrupting both EGFR and IGF1R expression on resection-induced adaptation.

METHODS

Intestinal-specific EGFR and IGF1R double knockout mice (EGFR/IGF1R-IKO) (n=6) and wild-type (WT) control mice (n=7) underwent 50% proximal SBR. On postoperative day (POD) 7, structural adaptation was scored by measuring crypt depth and villus height. Rates of crypt cell proliferation, apoptosis, and submucosal capillary density were also compared.

RESULTS

After 50% SBR, normal adaptation occurred in both WT and EGFR/IGF1R-IKO. Rates of proliferation and apoptosis were no different between the two groups. The angiogenic response was less in the EGFR/IGF1R-IKO compared to WT mice.

CONCLUSION

Disrupted expression of EGFR and IGF1R in the intestinal epithelial cells does not affect resection-induced structural adaptation but attenuates angiogenesis after SBR. These findings suggest that villus growth is driven by receptors and pathways that occur outside the epithelial cell component, while angiogenic responses may be influenced by epithelial-endothelial crosstalk.

Pathogenesis of neonatal necrotizing enterocolitis

Although necrotizing enterocolitis (NEC) is the most lethal gastrointestinal disease in the neonatal population, its pathogenesis is poorly understood. Risk factors include prematurity, bacterial colonization, and formula feeding. This review examines how mucosal injury permits opportunistic pathogens to breach the gut barrier and incite an inflammatory response that leads to sustained overproduction of mediators such as nitric oxide and its potent adduct, peroxynitrite. These mediators not only exacerbate the initial mucosal injury, but they also suppress the intestinal repair mechanisms, which further compromises the gut barrier and culminates in bacterial translocation, sepsis, and full-blown NEC.

IGF-2 is necessary for retinoblastoma-mediated enhanced adaptation after small-bowel resection

Previously, we have demonstrated that genetically disrupting retinoblastoma protein (Rb) expression in enterocytes results in taller villi, mimicking resection-induced adaption responses. Rb deficiency also results in elevated insulin-like growth factor-2 (IGF-2) expression in villus enterocytes. We propose that postoperative disruption of Rb results in enhanced adaptation which is driven by IGF-2. Inducible, intestine-specific Rb-null mice (iRbIKO) and wild-type (WT) littermates underwent a 50% proximal small-bowel resection (SBR) at 7-9 weeks of age. They were then given tamoxifen on postoperative days (PODs) 4-6 and harvested on POD 28. The experiment was then repeated on double knockouts of both IGF-2 and Rb (IGF-2 null/iRbIKO). iRbIKO mice demonstrated enhanced resection-induced adaptive villus growth after SBR and increased IGF-2 messenger RNA (mRNA) in ileal villus enterocytes compared to their WT littermates. In the IGF-2 null/iRbIKO double-knockout mice, there was no additional villus growth beyond what was expected of normal resection-induced adaptation. Adult mice in which Rb is inducibly deleted from the intestinal epithelium following SBR have augmented adaptive growth. IGF-2 expression is necessary for enhanced adaptation associated with acute intestinal Rb deficiency.

Intestinal adaptation following resection

Intestinal adaptation is a natural compensatory process that occurs following extensive intestinal resection, whereby structural and functional changes in the intestine improve nutrient and fluid absorption in the remnant bowel. In animal studies, postresection structural adaptations include bowel lengthening and thickening and increases in villus height and crypt depth. Functional changes include increased nutrient transporter expression, accelerated crypt cell differentiation, and slowed transit time. In adult humans, data regarding adaptive changes are sparse, and the mechanisms underlying intestinal adaptation remain to be fully elucidated. Several factors influence the degree of intestinal adaptation that occurs post resection, including site and extent of resection, luminal stimulation with enteral nutrients, and intestinotrophic factors. Two intestinotrophic growth factors, the glucagon-like peptide 2 analog teduglutide and recombinant growth hormone (somatropin), are now approved for clinical use in patients with short bowel syndrome (SBS). Both agents enhance fluid absorption and decrease requirements for parenteral nutrition (PN) and/or intravenous fluid. Intestinal adaptation has been thought to be limited to the first 1-2 years following resection in humans. However, recent data suggest that a significant proportion of adult patients with SBS can achieve enteral autonomy, even after many years of PN dependence, particularly with trophic stimulation.

The role of growth factors in intestinal regeneration and repair in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating intestinal disease resulting in major neonatal morbidity and mortality. The pathology is poorly understood, and the means of preventing and treating NEC are limited. Several endogenous growth factors have been identified as having important roles in intestinal growth as well as aiding intestinal repair from injury or inflammation. In this review, we will discuss several growth factors as mediators of intestinal regeneration and repair as well as potential therapeutic agents for NEC.

Adaptation: paradigm for the gut and an academic career

Adaptation is an important compensatory response to environmental cues resulting in enhanced survival. In the gut, the abrupt loss of intestinal length is characterized by increased rates of enterocyte proliferation and apoptosis and culminates in adaptive villus and crypt growth. In the development of an academic pediatric surgical career, adaptation is also an important compensatory response to survive the ever changing research, clinical, and economic environment. The ability to adapt in both situations is critical for patients and a legacy of pediatric surgical contributions to advance our knowledge of multiple conditions and diseases.

Intestinal mucosal atrophy and adaptation

Mucosal adaptation is an essential process in gut homeostasis. The intestinal mucosa adapts to a range of pathological conditions including starvation, short-gut syndrome, obesity, and bariatric surgery. Broadly, these adaptive functions can be grouped into proliferation and differentiation. These are influenced by diverse interactions with hormonal, immune, dietary, nervous, and mechanical stimuli. It seems likely that clinical outcomes can be improved by manipulating the physiology of adaptation. This review will summarize current understanding of the basic science surrounding adaptation, delineate the wide range of potential targets for therapeutic intervention, and discuss how these might be incorporated into an overall treatment plan. Deeper insight into the physiologic basis of adaptation will identify further targets for intervention to improve clinical outcomes.

Enterocyte expression of epidermal growth factor receptor is not required for intestinal adaptation in response to massive small bowel resection

PURPOSE

Intestinal adaptation after massive small bowel resection (SBR) permits improved absorption of enteral nutrition despite significant loss of bowel length. Epidermal growth factor (EGF) and its receptor (EGFR) have previously been established to play major roles in the pathogenesis of adaptation. This study tested the hypothesis that EGFR signaling within the epithelial cell compartment (enterocytes) is required for intestinal adaptation.

METHODS

We developed a tamoxifen-inducible Villin-Cre/LoxP recombinant system for enterocyte-directed EGFR deletion using EGFR-floxed mice. Epidermal growth factor receptor-null mice and wild-type littermates underwent either 50% proximal SBR or sham operation. Ileal tissue was harvested on postoperative day 7. To assess for adaptation, villus height and crypt depth as well as rates of crypt cell proliferation and apoptosis were measured.

RESULTS

Adaptation after SBR occurred normally, as demonstrated by significant increases in villus height, crypt depth, and crypt proliferative and apoptotic index in both the wild-type and EGFR-null mice.

CONCLUSION

Enterocyte EGFR expression is not required for the adaptation response to massive SBR. This novel finding suggests that enterocyte proliferation during adaptation is regulated by EGFR signaling in cells other than enterocytes, perhaps within the mesenchymal cell compartment of the bowel wall via factor(s) that are presently unknown.

Amphiregulin promotes intestinal epithelial regeneration: roles of intestinal subepithelial myofibroblasts

Epidermal growth factor family plays critical roles in intestinal epithelial proliferation and differentiation. The precise function of amphiregulin (AREG), a member of the epidermal growth factor family, in intestinal biology is largely unknown. The present study attempted to address the functional roles of AREG in intestinal epithelial regeneration. Total body irradiation was performed, and intestinal regeneration was assessed in AREG knockout mice. Genetically disruption of AREG significantly impaired intestinal regeneration after radiation injury. It is known that prostaglandin E(2) (PGE(2)) exerts radio-protective and growth-stimulatory effects on intestinal epithelium. We found that PGE(2) radio-protective action did not involve AREG. However, PGE(2) growth-stimulatory effects required functional AREG. Localization of AREG expression was determined by immunohistochemistry in regenerative intestine. The immunoreactivity of AREG was predominantly localized in intestinal subepithelial myofibroblasts (ISEMF). Primary ISEMF cultures were established, and growth-stimulatory actions of ISEMF-generated AREG were demonstrated in cell coculture system. In addition, we found that the cAMP/protein kinase A pathway robustly induced AREG in cultured ISEMF. These studies suggest that AREG plays critical roles in intestinal epithelial growth. Modulation of levels of AREG by targeting ISEMF represents a novel strategy for treatment of certain intestinal disorders.

Growth factors: possible roles for clinical management of the short bowel syndrome

The structural and functional changes during intestinal adaptation are necessary to compensate for the sudden loss of digestive and absorptive capacity after massive intestinal resection. When the adaptive response is inadequate, short bowel syndrome (SBS) ensues and patients are left with the requirement for parenteral nutrition and its associated morbidities. Several hormones have been studied as potential enhancers of the adaptation process. The effects of growth hormone, insulin-like growth factor-1, epidermal growth factor, and glucagon-like peptide 2 on adaptation have been studied extensively in animal models. In addition, growth hormone and glucagon-like peptide 2 have shown promise for the treatment of SBS in clinical trials in human beings. Several lesser studied hormones, including leptin, corticosteroids, thyroxine, testosterone, and estradiol, are also discussed.

Generation of epidermal growth factor-expressing Lactococcus lactis and its enhancement on intestinal development and growth of early-weaned mice

BACKGROUND

Epidermal growth factor (EGF) plays an important role in intestinal proliferation and differentiation. Previous studies by others have shown that administration of EGF into the ileum lumen enhances intestinal development.

OBJECTIVE

The objective was to examine the feasibility of expressing and delivering EGF via Lactococcus lactis to early-weaned mice to enhance intestinal development at this critical transition stage.

DESIGN

EGF-expressing L. lactis (EGF-LL) was generated with a recombinant approach. Early-weaned mice were orally gavaged with the recombinant bacteria. Body weight, mean villous height, and crypt depth in the intestine were measured to examine the influence of EGF-LL on the intestinal development of early-weaned mice in vivo.

RESULTS

Populations of EGF-LL were shown to survive throughout the intestinal tract, and the recombinant EGF protein was also detected in intestinal contents. Weight gain was significantly greater in mice that received EGF-LL than in control mice fed phosphate-buffered saline or L. lactis transformed with the empty vector backbone but was comparable with that of the positive control mice that received recombinant human EGF. EGF-LL increased mean villous height and crypt depth in the intestine. Immunohistochemistry also confirmed that enterocyte proliferation was enhanced in mice that received EGF-LL, as evidenced by the greater number of cells stained with proliferative cell nuclear antigen in the intestine.

CONCLUSIONS

This study showed that EGF-LL had beneficial effects on the intestinal growth of newly weaned mice. The combination of growth factor delivery and a probiotic approach may offer possibilities for formulating dietary supplements for children during their weaning transition stage.

Epidermal growth factor treatment decreases mortality and is associated with improved gut integrity in sepsis

Epidermal growth factor (EGF) is a cytoprotective peptide that has healing effects on the intestinal mucosa. We sought to determine whether systemic administration of EGF after the onset of sepsis improved intestinal integrity and decreased mortality. FVB/N mice were subjected to either sham laparotomy or 2 x 23 cecal ligation and puncture (CLP). Septic mice were further randomized to receive injection of either 150 microg kg(-1) d(-1) (i.p.) EGF or 0.9% saline (i.p.). Circulating EGF levels were decreased after CLP compared with sham animals but were unaffected by giving exogenous EGF treatment. In contrast, intestinal EGF levels increased after CLP and were further augmented by exogenous EGF treatment. Intestinal EGF receptor was increased after CLP, whether assayed by immunohistochemistry, real-time polymerase chain reaction, or Western blot, and exogenous EGF treatment decreased intestinal EGF receptor. Villus length decreased 2-fold between sham and septic animals, and EGF treatment resulted in near total restitution of villus length. Sepsis decreased intestinal proliferation and increased intestinal apoptosis. This was accompanied by increased expression of the proapoptotic proteins Bid and Fas-associated death domain, as well as the cyclin-dependent kinase inhibitor p21 cip1/waf Epidermal growth factor treatment after the onset of sepsis restored both proliferation and apoptosis to levels seen in sham animals and normalized expression of Bid, Fas-associated death domain, and p21 cip1/waf . To determine whether improvements in gut homeostasis were associated with a decrease in sepsis-induced mortality, septic mice with or without EGF treatment after CLP were followed 7 days for survival. Mortality decreased from 60% to 30% in mice treated with EGF after the onset of sepsis (P < 0.05). Thus, EGF may be a potential therapeutic agent for the treatment of sepsis in part due to its ability to protect intestinal integrity.

Role of VEGF in small bowel adaptation after resection: the adaptive response is angiogenesis dependent

Previous work in our group has demonstrated that mouse salivary gland has the highest concentration of salivary-derived VEGF protein compared with other organs and is essential for normal palatal mucosal wound healing. We hypothesize that salivary VEGF plays an important role in maintaining the integrity of the gastrointestinal mucosa following small bowel resection (SBR). Thirty-five 8- to 10-wk-old C57BL/6 female mice were divided into seven treatment groups: 1) sham (transaction and anastomosis, n = 5); 2) SBR (n = 8); 3) sialoadenectomy and small bowel resection (SAL+SBR, n = 8); 4) sialoadenectomy and small bowel resection with EGF supplementation (SAL+SBR+EGF, n = 9); 5) sialoadenectomy and small bowel resection with VEGF supplementation (SAL+SBR+VEGF, n = 9); 6) sialoadenectomy and small bowel resection supplemented with EGF and VEGF (SAL+ SBR+VEGF+EGF, n = 6); 7) selective inhibition of VEGF in the submandibular gland by Ad-VEGF-Trap following small bowel resection (Ad-VEGF-Trap+SBR, n = 7). Adaptation was after 3 days by ileal villus height and crypt depth. The microvascular response was evaluated by CD31 immunostaining and for villus-vessel area ratio by FITC-labeled von Willebrand factor immunostaining. The adaptive response after SBR was significantly attenuated in the SAL group in terms of villus height (250.4 +/- 8.816 vs. 310 +/- 19.35, P = 0.01) and crypt depth (100.021 +/- 4.025 vs. 120.541 +/- 2.82, P = 0.01). This response was partially corrected by orogastric VEGF or EGF alone. The adaptive response was completely restored when both were administered together, suggesting that salivary VEGF and EGF both contribute to intestinal adaptation. VEGF increases the vascular density (6.4 +/- 0.29 vs. 6.1 +/- 0.29 vs. 5.96 +/- 0.20) and villus-vessel area ratio (0.713 +/- 0.01 vs. 0.73 +/- 0.01) in the adapting bowel. Supplementation of both EGF and VEGF fully rescues adaptation, suggesting that the adaptive response may be dependent on VEGF-driven angiogenesis. These results support a previously unrecognized role for VEGF in the small bowel adaptive response.

Gut hormones, and short bowel syndrome: The enigmatic role of glucagon-like peptide-2 in the regulation of intestinal adaptation

Short bowel syndrome (SBS) refers to the malabsorption of nutrients, water, and essential vitamins as a result of disease or surgical removal of parts of the small intestine. The most common reasons for removing part of the small intestine are due to surgical intervention for the treatment of either Crohn's disease or necrotizing enterocolitis. Intestinal adaptation following resection may take weeks to months to be achieved, thus nutritional support requires a variety of therapeutic measures, which include parenteral nutrition. Improper nutrition management can leave the SBS patient malnourished and/or dehydrated, which can be life threatening. The development of therapeutic strategies that reduce both the complications and medical costs associated with SBS/long-term parenteral nutrition while enhancing the intestinal adaptive response would be valuable.

Currently, therapeutic options available for the treatment of SBS are limited. There are many potential stimulators of intestinal adaptation including peptide hormones, growth factors, and neuronally-derived components. Glucagon-like peptide-2 (GLP-2) is one potential treatment for gastrointestinal disorders associated with insufficient mucosal function. A significant body of evidence demonstrates that GLP-2 is a trophic hormone that plays an important role in controlling intestinal adaptation. Recent data from clinical trials demonstrate that GLP-2 is safe, well-tolerated, and promotes intestinal growth in SBS patients. However, the mechanism of action and the localization of the glucagon-like peptide-2 receptor (GLP-2R) remains an enigma. This review summarizes the role of a number of mucosal-derived factors that might be involved with intestinal adaptation processes; however, this discussion primarily examines the physiology, mechanism of action, and utility of GLP-2 in the regulation of intestinal mucosal growth.

Critical roles for EGF receptor signaling during resection-induced intestinal adaptation

The adaptation response of the remnant gut to massive intestinal resection represents a mitogenic signal involving all bowel wall layers. In the mucosa, this response results in taller villi, deeper crypts, and enhanced enterocyte turnover as gauged by greater rates of both proliferation and apoptosis. Although the exact mechanisms and mediators of this important compensatory response remain incompletely understood, work from this laboratory over the past decade has illuminated a crucial role for intact receptor signaling for a robust response. Using a murine model for intestinal resection, transgenic, null and mutant mouse strains have provided unique experimental paradigms to dissect molecular mechanisms for epidermal growth factor (EGF) receptor-directed influence on adaptation. Stimulation of this receptor is linked with a magnified adaptation response, whereas attenuation of the activity of this receptor is associated with impaired adaptation. EGF receptor activation and expression are both elevated in enterocytes after resection, and salivary levels of EGF-the major ligand for the EGF receptor-are increased. In addition to stimulation of enterocyte proliferation, EGF receptor signaling prevents the typical increase in rates of enterocyte apoptosis, probably by affecting the ratio of expression of both pro- and anti-apoptotic Bcl-2 family members. The key to optimizing care for patients with short gut syndrome will necessarily follow a thorough understanding of intestinal adaptation responses.

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.

Intestinal adaptation after massive intestinal resection

Patients with short bowel syndrome require long term parenteral nutrition support. However, after massive intestinal resection the intestine undergoes adaptation and nutritional autonomy may be obtained. Given that the complications of parenteral nutrition may be life threatening or result in treatment failure and the need for intestinal transplantation, a more attractive option is to wean patients off nutrition support by optimising the adaptive process. The article examines the evidence that after extensive small bowel resection adaptation occurs in humans and focuses on the factors that influence adaptation and the strategies that have been used to optimise this process. The review is based on an English language Medline search with secondary references obtained from key articles. There is evidence that adaptation occurs in humans. Adaptation is a complex process that results in response to nutrient and non-nutrient stimuli. Successful and reproducible strategies to improve adaptation remain elusive despite an abundance of experimental data. Nevertheless given the low patient survival and quality of life associated with other treatments for irreversible intestinal failure it is imperative that clinical research continues into the optimisation of the adaptation.

Intestinal adaptation after massive intestinal resection

Patients with short bowel syndrome require long term parenteral nutrition support. However, after massive intestinal resection the intestine undergoes adaptation and nutritional autonomy may be obtained. Given that the complications of parenteral nutrition may be life threatening or result in treatment failure and the need for intestinal transplantation, a more attractive option is to wean patients off nutrition support by optimising the adaptive process. The article examines the evidence that after extensive small bowel resection adaptation occurs in humans and focuses on the factors that influence adaptation and the strategies that have been used to optimise this process. The review is based on an English language Medline search with secondary references obtained from key articles. There is evidence that adaptation occurs in humans. Adaptation is a complex process that results in response to nutrient and non-nutrient stimuli. Successful and reproducible strategies to improve adaptation remain elusive despite an abundance of experimental data. Nevertheless given the low patient survival and quality of life associated with other treatments for irreversible intestinal failure it is imperative that clinical research continues into the optimisation of the adaptation.

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.

Comparative effects of glucagon-like peptide-2 (GLP-2), growth hormone (GH), and keratinocyte growth factor (KGF) on markers of gut adaptation after massive small bowel resection in rats

BACKGROUND

Administration of specific growth factors exert gut-trophic effects in animal models of massive small bowel resection (SBR); however, little comparative data are available. Our aim was to compare effects of a human glucagon-like peptide-2 (GLP-2) analog, recombinant growth hormone (GH) and recombinant keratinocyte growth factor (KGF) on jejunal, ileal, and colonic growth and functional indices after 80% SBR in rats.

METHODS

Thirty-seven male rats underwent small bowel transection (sham operation) with s.c. saline administration (control; Tx-S; n = 7) or 80% midjejuno-ileal resection (Rx) and treatment with either s.c. saline (Rx-S, n = 7), GLP-2 at 0.2 mg/kg/d (Rx-GLP-2; n = 8), GH at 3.0 mg/kg/d (Rx-GH; n = 8), or KGF at 3.0 mg/kg/d (Rx-KGF; n = 7) for 7 days. All groups were pair-fed to intake of Rx-S rats. Gut mucosal cell growth indices (wet weight, DNA and protein content, villus height, crypt depth, and total mucosal height) were measured. Expression of the cytoprotective trefoil peptide TFF3 was determined by Western blot. Gut mucosal concentrations of the tripeptide glutathione (L-glutamyl-L-cysteinyl-glycine) and glutathione disulfide (GSSG) were measured by high-performance liquid chromatography and the glutathione/GSSG ratio calculated.

RESULTS

SBR increased adaptive growth indices in jejunal, ileal, and colonic mucosa. GLP-2 treatment increased jejunal villus height and jejunal total mucosal height compared with effects of resection alone or resection with GH or KGF treatment. Both GH and KGF modestly increased colonic crypt depth after SBR. SBR did not affect small bowel or colonic goblet cell number or TFF3 expression; however, goblet cell number and TFF3 expression in both small bowel and colon were markedly up-regulated by KGF treatment and unaffected by GLP-2 and GH. SBR oxidized the ileal and colonic mucosal glutathione/GSSG redox pools. GLP-2 treatment after SBR increased the glutathione/GSSG ratio in jejunum, whereas KGF had an intermediate effect. In addition, GLP-2 (but not GH or KGF) prevented the SBR-induced oxidation of the glutathione/GSSG pools in both ileum and colon.

CONCLUSIONS

GLP-2 exerts superior trophic effects on jejunal growth and also improves mucosal glutathione redox status throughout the bowel after massive SBR in rats. Both GH and KGF increase colonic mucosal growth in this model. KGF alone potently increases gut mucosal goblet cell number and expression of the cytoprotective trefoil peptide TFF3. The differential effects of GLP-2, GH and KGF administration in this model of short bowel syndrome suggest that individual therapy with these growth factors may not be an adequate strategy to maximally improve adaptive gut mucosal growth and cytoprotection after massive small intestinal resection. Future research should address the use of these agents in combination in short bowel syndrome.

Epidermal growth factor receptor signaling regulates goblet cell production after small bowel resection

BACKGROUND/PURPOSE

Intestinal adaptation is a compensatory response to massive small bowel loss in which there are increased numbers of absorptive enterocytes. However, the generation of secretory epithelial cell subtypes in this process has not been investigated. The purpose of this study was to examine the adaptive changes of several small intestinal cell lineage changes in response to massive small bowel resection (SBR).

METHODS

A 75% SBR or sham operation was performed on male Sprague-Dawley rats. On postoperative day 7, the remnant ileum was harvested and immunohistochemical staining for goblet, Paneth, and enteroendocrine cells was performed. Cell subtypes were evaluated as cells per micrometer of villus/crypt length and compared among operations.

RESULTS

A significant increase in goblet cell density occurred after SBR. Intestinal resection did not alter the number of Paneth and enteroendocrine cells. In additional experiments, inhibition of epidermal growth factor receptor signaling was associated with a diminished goblet cell density.

CONCLUSIONS

The adaptive response of the intestine to massive bowel loss results in an expansion of the goblet cell population in addition to greater numbers of absorptive enterocytes. Although the mechanism and purpose for selective expansion of these stem cell-derived lineages are not presently known, epidermal growth factor receptor signaling appears to be a common pathway.

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,+).

EGF receptor signaling affects bcl-2 family gene expression and apoptosis after massive small bowel resection

BACKGROUND

After massive small bowel resection (SBR), enterocyte apoptosis is elevated and inversely correlates with epidermal growth factor receptor (EGFR) signaling. The purpose of the current study was to determine whether EGFR manipulation affects the expression of specific bcl-2 family members.

METHODS

A 50% proximal SBR or sham operation was performed in 3 groups of mice control, after exogenous EGF, or mutant mice with defective EGFR signaling (waved-2). Apoptotic index (no. of apoptotic bodies per crypt), and bax (pro-apoptosis) and bcl-w (anti-apoptosis) protein expression was measured in the remnant ileum after 12, 24, and 72 hours.

RESULTS

Waved-2 mice with defective EGFR showed the greatest increase in apoptosis and altered the ratio of bax to bcl-w in favor of apoptosis after SBR. Conversely, EGF prevented the expected increase in apoptosis after SBR by shifting the ratio of bax to bcl-w in favor of cell survival.

CONCLUSIONS

After massive small bowel resection, inhibition of the EGFR accelerates the rate of apoptosis and modifies the expression of specific bcl-2 family members to favor apoptosis. These results further support a specific mechanistic pathway for the regulation of enterocyte apoptosis after SBR via EGFR signaling.

Localization of postresection EGF receptor expression using laser capture microdissection

BACKGROUND/PURPOSE

Epidermal growth factor (EGF) and its receptor (EGFR) are key components in the genesis of adaptation after small bowel resection (SBR). Within intestinal homogenates, EGFR expression is increased after SBR; however, the exact cells responsible for altered EGFR expression are unknown. In this study, laser capture microdissection (LCM) microscopy was used to elucidate the specific cellular compartment(s) responsible for postresection changes in EGFR expression.

METHODS

Male ICR mice underwent a 50% proximal SBR or sham operation. After 3 days, frozen sections were taken from the remnant ileum. Individual cells from villi, crypt, muscularis, and mesenchymal compartments were isolated by LCM. EGFR mRNA expression for each cell compartment was quantified using real-time polymerase chain reaction (PCR).

RESULTS

EGFR expression was increased after SBR within the crypt (2-fold) and muscularis compartments (3-fold). There were no changes detected after SBR in the villus tips or mesenchymal compartments.

CONCLUSIONS

Increased expression of EGFR in crypts directly correlates with the zone of cell proliferation and supports the hypothesis that EGFR signaling is crucial for the mitogenic stimulus for adaptation. The finding of increased EGFR expression in the muscular compartment is novel and may implicate a role for EGFR as a mediator of the muscular hyperplasia seen after massive SBR.

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.

The management of patients with the short bowel syndrome

The surgeon is invariably the primary specialist involved in managing patients with short bowel syndrome. Because of this they will play an important role in co-ordinating the management of these patients. The principal aims at the initial surgery are to preserve life, then to preserve gut length, and maintain its continuity. In the immediate postoperative period, there needs to be a balance between keeping the patient alive through the use of TPN and antisecretory agents and promoting gut adaptation with the use of oral nutrition. If the gut fails to adapt during this period, then the patient may require therapy with more specific agents to promote gut adaptation such as growth factors and glutamine. If following this, the patient still has a short gut syndrome, then the principal options remain either long term TPN, or intestinal transplantation which remains a difficult and challenging procedure with a high mortality and morbidity due to rejection.

Intestinal adaptation: structure, function, and regulation

After massive small bowel resection (SBR), the remnant intestine undergoes an adaptive process characterized by increases in wet weight, protein and DNA content, villus height and crypt depth, and absorptive surface area. These changes are the result of a proliferative stimulus that increases crypt cell mitosis and augments cellular progression along the villus axis. Functionally, there is upregulation of the Na(+)/glucose cotransporter, Na(+)/H(+) exchanger, and other enzymes involved in intestinal digestion and absorption. These physiologic events are a compensatory response to the sudden loss of digestive and absorptive capacity by the remnant intestine. A major consequence of inadequate intestinal adaptation is lifelong dependence on parenteral nutrition, which results ultimately in cholestatic liver dysfunction. Furthermore, adaptation may be associated with changes in intestinal permeability and an increased risk of bacterial translocation and sepsis. Several mediators thought to be integral to the postresection adaptive response have been proposed, including luminal nutrients, gastrointestinal secretions, and humoral factors. A thorough understanding of intestinal adaptation will be essential in the rational development of new and innovative therapies that amplify this complex but important process.

Serum from mice after small bowel resection enhances intestinal epithelial cell growth

BACKGROUND/PURPOSE

The adaptive response of the intestine to massive small bowel resection (SBR) is remarkably complex. An in vitro model of adaptation may facilitate the elucidation of signaling pathways involved in this process. In an effort to establish such a model, the effects of serum from resected mice on cultured intestinal epithelial cells were studied.

METHODS

Serum was collected and pooled from male ICR mice 3 days after either 50% SBR or sham operation. Rat intestinal epithelial cells (RIEC-6) were plated at equal density and grown in the presence of 1% fetal bovine serum (FBS), 10% FBS, 1% FBS plus 9% sham serum, or 1% FBS plus 9% SBR serum. Cell number, proliferation, and caspase-3 activity were determined.

RESULTS

RIEC-6 cell growth was reduced significantly in 1% FBS or sham serum. SBR serum markedly accelerated cell growth and proliferation when compared with all other groups and significantly suppressed caspase-3 activity.

CONCLUSIONS

Massive intestinal resection in mice results in a serum factor that induces intestinal cell growth in vitro. This in vitro model of trophic signaling will permit further detailed investigations into the mechanisms of intestinal adaptation.

Epidermal growth factor is critical for intestinal adaptation following small bowel resection

The loss of small intestinal mucosal surface area is a relatively common clinical situation seen in both the pediatric and adult population. The most frequent causes include mesenteric ischemia, trauma, inflammatory bowel disease, necrotizing enterocolitis, and volvulus. Following surgical resection, the remnant intestine compensates or adapts to the loss of native bowel by increasing its absorptive surface area and functional capacity. Unfortunately, many patients fail to adapt adequately, and are relegated to lifelong intravenous nutrition. Research into intestinal adaptation following small bowel resection (SBR) has evolved only recently from the gross and microscopic level to the biochemical and genetic level. As understanding of this process has increased, numerous therapeutic strategies to augment adaptation have been proposed. Epidermal growth factor (EGF) is an endogenous peptide that is secreted into the gastrointestinal tract and able to influence gut ontogeny, as well as mucosal healing. Early studies have demonstrated its ability to augment the adaptive process. Focusing on a murine model of massive intestinal loss, the morphological, structural, biochemical, and genetic changes that occur during the intestinal adaptive process will be reviewed. The role of EGF and its receptor as critical mediators of the adaptive process will be discussed. Additionally, the ability of EGF to augment intestinal proliferation and diminish programmed cell death (apoptosis) following SBR will be examined. Enhancing adaptation in a controlled manner may allow patients to transition off parenteral nutrition to enteral feeding and, thereby, normalize their lifestyle.

Epidermal growth factor is critical for intestinal adaptation following small bowel resection

The loss of small intestinal mucosal surface area is a relatively common clinical situation seen in both the pediatric and adult population. The most frequent causes include mesenteric ischemia, trauma, inflammatory bowel disease, necrotizing enterocolitis, and volvulus. Following surgical resection, the remnant intestine compensates or adapts to the loss of native bowel by increasing its absorptive surface area and functional capacity. Unfortunately, many patients fail to adapt adequately, and are relegated to lifelong intravenous nutrition. Research into intestinal adaptation following small bowel resection (SBR) has evolved only recently from the gross and microscopic level to the biochemical and genetic level. As understanding of this process has increased, numerous therapeutic strategies to augment adaptation have been proposed. Epidermal growth factor (EGF) is an endogenous peptide that is secreted into the gastrointestinal tract and able to influence gut ontogeny, as well as mucosal healing. Early studies have demonstrated its ability to augment the adaptive process. Focusing on a murine model of massive intestinal loss, the morphological, structural, biochemical, and genetic changes that occur during the intestinal adaptive process will be reviewed. The role of EGF and its receptor as critical mediators of the adaptive process will be discussed. Additionally, the ability of EGF to augment intestinal proliferation and diminish programmed cell death (apoptosis) following SBR will be examined. Enhancing adaptation in a controlled manner may allow patients to transition off parenteral nutrition to enteral feeding and, thereby, normalize their lifestyle.

Salivary epidermal growth factor and intestinal adaptation in male and female mice

Salivary epidermal growth factor (sEGF) levels are increased in male mice after small bowel resection (SBR) and may be important during intestinal adaptation. Since males have greater sEGF than females, the influence of sex on postresection adaptation was tested. Females had lower sEGF; however, sEGF substantially increased in both sexes after a massive (50%) SBR. Adaptive increases in DNA and protein content, villus height, and crypt depth, as well as crypt cell proliferation rates in the remnant ileum, were not different between males and females. Although significant postresection increases in sEGF were identified, EGF mRNA and protein did not change within the submandibular gland. Glandular kallikrein-13 and ileal EGF receptor expression were greater after SBR in female mice. Intestinal adaptation is equivalent in female and male mice after SBR. Despite lower sEGF, females demonstrated increased expression of a kallikrein responsible for sEGF precursor cleavage as well as amplified ileal EGF receptor expression. These results endorse an important differential response between sexes regarding sEGF mobilization and intestinal receptor availability during adaptation.

Epidermal growth factor alters the bax:bcl-w ratio following massive small bowel resection

BACKGROUND

Following massive small bowel resection (SBR), the expression of bax and bcl-w is associated with increased enterocyte apoptosis. Epidermal growth factor (EGF) has been shown to enhance enterocyte proliferation and retard apoptosis in the adapting bowel. This study examined the effect of EGF on the expression of these bcl-2 family members during adaptation.

MATERIALS AND METHODS

Mice (C57Bl/6; n = 38) underwent a 50% SBR or sham operation and then were randomized to receive twice-daily orogastric saline or EGF (50 microg/kg/day). After 3 days, the remnant ileum was removed, apoptotic index (No. apoptotic bodies/crypt) calculated, and expression of mRNA and protein for bax and bcl-w quantified.

RESULTS

EGF prevented the expected increase in the apoptotic index after SBR and altered the ratio of bax to bcl-w in favor of cell survival.

CONCLUSION

Following massive small bowel resection, EGF retards rates of enterocyte apoptosis and modifies the expression of bcl-2 family members. By decreasing bax and increasing bcl-w expression, the balance between pro- and anti-apoptotic genes is shifted in favor of cell survival. Alteration of bcl-2 family member expression may be an important mechanism by which EGF reduces the increased enterocyte apoptosis that occurs after massive small bowel resection.

Intestinal adaptation occurs independent of transforming growth factor-alpha

BACKGROUND/PURPOSE

Signal transduction via the epidermal growth factor receptor (EGFR) is critical for intestinal adaptation after massive small bowel resection (SBR). Although it has been assumed that the major ligand for the EGFR during adaptation is EGF, the role for transforming growth factor-alpha (TGF-alpha), another major ligand for the EGFR is unknown. The purpose of this study was to test the hypothesis that TGF-alpha is an important ligand for the EGFR during intestinal adaptation.

METHODS

Wild-type mice (C57BI/6) underwent a 50% proximal SBR or sham operation (bowel transection or reanastomosis) and were then assigned randomly to receive either intraperitoneal TGF-alpha or placebo. In a separate experiment, SBR or sham operations were performed in mice lacking TGF-alpha (Waved-1). After 3 days, adaptation was measured in the ileum.

RESULTS

Exogenous TGF-alpha enhanced intestinal adaptation in the wild-type mice after SBR as shown by increased ileal wet weight and DNA content. Normal adaptation occurred in the mice lacking TGF-alpha as shown by increased ileal wet weight, protein and DNA content, proliferation, villus height, and crypt depth.

CONCLUSIONS

Although exogenous TGF-alpha enhanced adaptation after massive SBR, adaptation was preserved in TGF-alpha-absent mice. These results refute TGF-alpha as an essential ligand for EGFR signaling during intestinal adaptation.

Differential expression of ileal Na(+)/H(+) exchanger isoforms after enterectomy

BACKGROUND

Na(+)/H(+) exchangers (NHE) are transporters involved in the absorption of NaCl along the gastrointestinal tract. The aim of this study was to determine the expression pattern of the intestinal brush border NHE isoforms 2 and 3 following massive small bowel resection (SBR). Additionally, the effect of epidermal growth factor (EGF) and salivarectomy (removal of the primary source of EGF) on the expression pattern was studied.

MATERIALS AND METHODS

ICR mice underwent a proximal SBR or sham surgery and then received either orogastric saline or EGF (50 microg/kg/day). In separate experiments mice underwent salivarectomy followed by SBR or sham. Postoperatively the remaining ileum was isolated and levels of NHE-2 and NHE-3 mRNA and protein were resolved.

RESULTS

Following SBR, the expression of both mRNA and protein for NHE-3 increased by approximately 2.5-fold. Treatment with EGF enhanced NHE-3 mRNA in sham animals with further elevation following SBR. The expression of NHE-2 mRNA demonstrated minimal change while protein marginally increased (40%) following SBR. EGF did not affect the expression of NHE-2 mRNA. Salivarectomy did not influence NHE-2 protein expression and inhibited the increased NHE-3 protein expression following SBR.

CONCLUSIONS

Following SBR, the expression pattern for brush border NHE isoforms is distinctive. Increased expression of NHE-3 secondary to SBR and/or EGF treatment with loss of this increase following salivarectomy implies a common mechanism to enhance enterocyte proliferation and luminal absorption of NaCl and water. These results suggest that NHE-3 is an important ileal exchanger following SBR.