Epidermal growth factor and the short bowel syndrome

Mechanisms of Epidermal Growth Factor Effect on Animal Intestinal Phosphate Absorption: A Review

Phosphorus is one of the essential mineral elements of animals that plays an important role in animal growth and development, bone formation, energy metabolism, nucleic acid synthesis, cell signal transduction, and blood acid–base balance. It has been established that the Type IIb sodium-dependent phosphate cotransporters (NaPi-IIb) protein is the major sodium-dependent phosphate (Pi) transporter, which plays an important role in Pi uptake across the apical membrane of epithelial cells in the small intestine. Previous studies have demonstrated that epidermal growth factor (EGF) is involved in regulating intestinal Pi absorption. Here we summarize the effects of EGF on active Pi transport of NaPi-IIb under different conditions. Under normal conditions, EGF inhibits the active transport of Pi by inhibiting the expression of NaPi-IIb, while, under intestinal injury condition, EGF promotes the active absorption of Pi through upregulating the expression of NaPi-IIb. This review provides a reference for information about EGF-regulatory functions in Pi absorption in the animal intestine.

Nutritional and pharmacological strategy in children with short bowel syndrome

Short bowel syndrome in neonates is a severe and life-threatening disease after a major loss of small bowel with or without large bowel. Intestinal adaptation, by which the organism tries to restore digestive and absorptive capacities, is entirely dependent on stimulation of the active enterocytes by enteral nutrition. This review summarizes recent knowledge about the pathophysiologic consequences after the loss of different intestinal parts and outlines the options for enteral nutrition and pharmacological therapies to support the adaptation process.

Enhancement of Colonic Absorptive Function after the Massive Resection of the Small Intestine Based on the Creation of an Artificial Colonic Valve

The colon can have an absorptive function similar to that of the small intestine after the massive resection of the small bowel. To improve colonic absorptive function, we created a valve in the colon (artificial colonic valve, ACV). ACVs were created in 20 rats that had 80 percent of their small intestine resected, with an observation time of 30 weeks. The ACV rats were compared with those in the non-operated control group, the short bowel syndrome (SBS) group and the colon interposition (CI) group. The ACV rats were much heavier than those in the control group, SBS group and CI group. In terms of histology and the levels of α-amylase and the Na⁺-dependent bile salt transporter, the absorptive function of the colons before the valves resembled that of the small intestine. The colonic absorptive function was more obvious in ACV rats than in CI rats. An ACV can enhance colonic absorptive function after the massive resection of the small intestine. The colonic absorptive function of ACV rats was better than that of the rats in the CI group.

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.

Novel therapies for the management of short bowel syndrome in children

Short bowel syndrome (SBS) is the most common cause of intestinal failure in children. It is defined as the inability to maintain adequate nutrition enterally as a result of a major loss of the small intestine. SBS is a life-threatening entity associated with potential significant morbidity and mortality. The etiology in the pediatric age group includes necrotizing enterocolitis (32%), atresia (20%), volvulus (18%), gastroschisis (17%), and aganglionosis (6%). It is characterized by substrate malabsorption, electrolyte imbalance, intestinal bacterial overgrowth, steatorrhea, and weight loss. Current medical management includes parenteral nutrition, progressive feeds as tolerated, various medications, and surgical manipulations. However, frequently this management is not successful in achieving the goal of attaining normal growth and development without parenteral nutrition. It has been known for decades that there is a normal physiologic response of the residual intestine to massive bowel resection referred to as intestinal adaptation. The mechanisms that control this process are unknown. Unfortunately, intestinal adaptation and the current management are not always successful. As a result of new knowledge regarding the pathophysiology of SBS over the past two decades, several novel strategies have been developed in experimental animal models as well as limited clinical trials in infants and children. They can be divided into several categories that potentially influence intestinal (1) absorption, (2) secretion, (3) motility, and (4) adaptation. More recently, newer modalities have been studied including small intestine transplantation, and the use of specific intestinal growth factors. Ultimately, tissue and organ engineering will become the treatment for infants and children with SBS.

Morphological, kinetic, membrane biochemical and genetic aspects of intestinal enteroplasticity

The process of intestinal adaptation (“enteroplasticity”) is complex and multifaceted. Although a number of trophic nutrients and non-nutritive factors have been identified in animal studies, successful, reproducible clinical trials in humans are awaited. Understanding mechanisms underlying this adaptive process may direct research toward strategies that maximize intestinal function and impart a true clinical benefit to patients with short bowel syndrome, or to persons in whom nutrient absorption needs to be maximized. In this review, we consider the morphological, kinetic and membrane biochemical aspects of enteroplasticity, focus on the importance of nutritional factors, provide an overview of the many hormones that may alter the adaptive process, and consider some of the possible molecular profiles. While most of the data is derived from rodent studies, wherever possible, the results of human studies of intestinal enteroplasticity are provided.

Gene expression in the adapting small bowel after massive small bowel resection

BACKGROUND

Intestinal adaptation occurs in the residual bowel following the loss or resection of a proportion of the small bowel. The purpose of the adaptive response is to return absorptive and digestive properties to near normal levels. This study employed a rat model of massive small bowel resection (MSBR) to study the adaptive response in the residual terminal ileum and the jejunum. The time points were chosen to reflect changes in gene expression early on in the response, because these are the genes that alter to initiate and maximize the response observed during adaptation.

METHODS

Sprague Dawley rats underwent an 80% resection. Differential display polymerase chain reaction (DD-PCR) analysis was performed on mRNA extracted from the remnant ileum and jejunum 0, 1, 2, 4, and 7 days post-MSBR.

RESULTS

DD-PCR identified 11 genes that were possibly regulated following MSBR. Genes confirmed to be regulated were 16S ribosomal RNA, lymphocyte antigen 6 (LY6)-like molecule, Krüppel-like factor-3 (KLF-3), G-protein-binding protein (CRFG), system A transporter 2 (SAT2), and an intestine-specific gene (similar to mKIAA0493).

CONCLUSIONS

DD-PCR analysis showed regulation of a number of genes not previously known to be involved in adaptation after MSBR or previously characterized in the intestine. These genes may be important in bringing about the complement of changes seen during the 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.

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.

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+).

Colostrum protein concentrate enhances intestinal adaptation after massive small bowel resection in juvenile pigs

OBJECTIVES

Short bowel syndrome (SBS) usually results from the surgical removal of a large segment of small intestine. Patient outcome depends on the extent of intestinal resection and adaptation of the remaining intestine. We evaluated the impact of colostrum protein concentrate (CPC) on intestinal adaptation after massive small bowel resection in a porcine model of infant SBS.

METHODS

Four-week-old piglets underwent an approximate 75% small bowel resection (R, n = 23) or a control transection operation (C, n = 14). Postoperatively, animals from both groups received either pig chow (R = 6, C = 5), polymeric infant formula (R = 6, C = 3) or polymeric infant formula supplemented with CPC (R = 11, C = 6) for 8 weeks until sacrifice. Clinical outcome measures included weight gain and stool consistency. Morphologic measures were intestinal villus height and crypt depth. Functional outcome measure was mucosal disaccharidase activity.

RESULTS

Resected animals fed polymeric infant formula alone had reduced weight gain compared with controls fed the same diet (P < 0.005). Despite massive small bowel resection, animals fed pig chow or polymeric infant formula supplemented with CPC grew at an equivalent rate to controls fed polymeric infant formula alone. Resected animals supplemented with CPC had increased villus length and crypt depth in the jejunum (P < 0.001) and ileum (P < 0.001) compared with resected animals fed either pig chow or polymeric infant formula alone.

CONCLUSION

In an animal model of SBS, CPC supplementation of polymeric infant formula resulted in normal weight gain and features of enhanced morphologic adaptation.

New and emerging therapies for short bowel syndrome in children

This review provides an overview of traditional as well as emerging therapies useful in the management of pediatric short bowel syndrome. Pediatric short bowel syndrome is relatively uncommon; however, when it does occur, it presents a unique challenge to medical care providers. The use of parenteral and enteral nutrition to maximize growth and enhance intestinal adaptation so as to increase absorptive surface area has been the primary focus of therapy. In recent years, the advent of pharmacologic advances, including the use of antibacterial drugs, anti-motility drugs and hormonal therapies, has had a significant impact on this condition. At times, surgery may be indicated for dealing with complications, or providing alternative therapy such as transplantation. With ongoing research, it is likely that improved pharmacologic therapy will be available for enhanced intestinal adaptation, control of gut motility, treatment of small bowel bacterial overgrowth, and treatment of rejection following small intestinal transplantation.

Transcriptional regulation of the human NaPi-IIb cotransporter by EGF in Caco-2 cells involves c-myb

The type IIb sodium-phosphate (NaP(i)-IIb) cotransporter mediates intestinal phosphate absorption. Previous work in our laboratory has shown that EGF inhibited NaP(i)-IIb cotransporter expression through transcriptional regulation. To understand this regulation, progressively shorter human NaP(i)-IIb promoter constructs were used to define the EGF response region, and gel mobility shift assays (GMSAs) were used to characterize DNA-protein interactions. Promoter analysis determined that the EGF response region was located between -784 and -729 base pair (bp) of the promoter. GMSAs and overexpression studies revealed an interaction between this promoter region and c-myb transcription factor. Inhibition of EGF receptor activation restored promoter function. Further studies suggested that MAPK, PKC, and/or PKA pathways are involved in this regulation. In conclusion, these studies suggest that EGF decreases human NaP(i)-IIb gene expression by modifying the c-myb protein such that it inhibits transcriptional activation. We further conclude that this downregulation of promoter function is mediated by EGF-activated PKC/PKA and MAPK pathways. This is the first study that demonstrates involvement of c-myb in the regulation of intestinal nutrient absorption.

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.

Key nutrients and growth factors for the neonatal gastrointestinal tract

The nutritional support of gastrointestinal growth and function is an important consideration in the clinical care of neonatal infants. In most health infants, the provision of either breast milk or formula seems to support normal intestinal mucosal growth, but the most significant advantages of breast milk may be for host defense or gut barrier-related functions that are involved in reducing infection. The specific effects of various milk-borne growth factors on key mucosal immune and barrier functions are likely to provide valuable new clues to the advantages of human milk. A substantial number of preterm, low-birth weight babies or those suffering from compromised intestinal function, however, often cannot tolerate oral feedings and instead receive TPN. The consequences of TPN on gastrointestinal function and how this contributes to morbidity of these infants warrants further study, with respect to both clinical and basic research questions. Although enteral nutrition seems to be a critical stimulus for intestinal function, the minimal amounts and composition of nutrients necessary to maintain specific intestinal functions remain to be established. The experimental tools exist to start defining the specific nutrient requirements for the infant gut and some of these nutrients are known (e.g., glutamate, glutamine, and threonine). Peptide growth factors and gut hormones clearly play a role in gut growth and in several ways mediate the trophic actions of enteral nutrition. Although a number of these growth factors are good candidates for therapeutic use, their clinical application in the management of gastrointestinal insufficiency and disease has been slow. The emergence of GLP-2 as a trophic peptide that seems to target the gut is a promising candidate on the horizon.

Small Intestinal Failure in Children

The treatment of children with intestinal failure should be predicated upon three overriding goals: 1) to keep the patient well nourished by parenteral nutrition (TPN), 2) to minimize the fecal loss of fluid, electrolytes, and nutrients, and 3) to enhance the natural process of intestinal adaptation whenever possible. The first goal is relatively easy to accomplish in the short- or intermediate-term, but difficult to accomplish for more than a few years because of recurrent septicemia, loss of venous access, and cholestatic liver disease. The risks of sepsis and loss of venous access can be minimized through meticulous central line care and the use of appropriate antibiotics when indicated. Cycling TPN and limiting parenteral protein intake sometimes ameliorates cholestasis. The second goal is only partially achievable regardless of the cause of intestinal failure. Fluid and electrolyte secretion often can be reduced but not normalized with antisecretory drugs. Bacterial overgrowth can be treated with the judicious use of antibiotics. The third goal generally can be accomplished only in a subpopulation of patients with surgically created short bowel. In these children, a satisfactory increase in surface area can occur only if nutrients are delivered directly into the bowel lumen. The trophic effects of glutamine, growth hormone, and other hormones remain to be universally accepted. Surgical bowel lengthening or bowel tapering can sometimes enhance intestinal function among patients with short bowel syndrome. If medical or nontransplantation surgical management of intestinal failure is unsuccessful, and the patient develops irreversible TPN-associated complications, transplantation of the intestine should be strongly considered.

Pharmacotherapy and growth factors in the treatment of short bowel syndrome

A review of the pharmacologic substances and growth factors that have been studied experimentally and administered clinically for the management of short bowel syndrome is presented. The medical management of short bowel syndrome is multifaceted. In the acute phase, efforts focus on fluid and electrolyte management and the reduction of gastric acid output. As enteral feeding is initiated, antimotility and antisecretory agents may be effective in reducing gastrointestinal losses. Additional modalities of management, including nutrients and growth factors, may be directed at maximizing absorptive function beyond that which occurs with intestinal adaptation. Continued research aimed at further elucidating the process of intestinal adaptation may allow us to use the various peptides and hormones that act as growth factors for the bowel mucosa. Knowledge gained from these studies combined with gene therapy techniques will result in the permanent enhancement of intestinal function beyond the normal adaptation process, eliminate the dependence on total parenteral nutrition, and avoid the need for intestine transplantation.

Regulation of the human sodium-phosphate cotransporter NaP(i)-IIb gene promoter by epidermal growth factor

The intestinal sodium-phosphate cotransporter (NaP(i)-IIb) plays a major role in intestinal P(i) absorption. Epidermal growth factor (EGF) is involved in the regulation of P(i) homeostasis. However, the role of EGF in intestinal NaP(i)-IIb regulation is not clear. The current studies showed that EGF decreased NaP(i)-IIb mRNA abundance by 40-50% in both rat intestine and Caco-2 cells. To understand the mechanism of this regulation, we cloned the human NaP(i)-IIb gene and promoter region and studied the effect of EGF on NaP(i)-IIb gene transcription. The human NaP(i)-IIb gene has 12 exons and 11 introns. Two transcription initiation sites were identified by primer extension. Additionally, 2.8 kb of the 5'-flanking region of the gene was characterized as a functional promoter in human intestinal (Caco-2) and human lung (A549) cells. Additional studies showed that EGF inhibited promoter activity by 40-50% in Caco-2 cells and that actinomycin D treatment abolished this inhibition. EGF had no effect on promoter activity in lung (A549) cells. We conclude that the human NaP(i)-IIb gene promoter is functional in Caco-2 and A549 cells and that the gene is responsive to EGF by a transcriptionally mediated mechanism in intestinal cells.

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.

Humoral factors in intestinal adaptation

The small bowel has a remarkable ability to adapt after injury, inflammation or resection. It has long been suggested that humoral factors, particularly enteroglucagon, epidermal growth factor, neurotensin and growth hormone/insulin-like growth factor I, might stimulate bowel growth. Of particular interest is the recent finding that glucagon-like peptide 2 (GLP-2), a product of the gene encoding proglucagon, exerts a trophic effect on the intestinal epithelium via a specific G-protein-coupled receptor. GLP-2 and/or these other trophic peptides might prove to have a role in the treatment of bowel diseases associated with structural or functional loss of the small bowel.

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.