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

Delayed episode of necrotising enterocolitis in an ex-preterm infant after intravitreal administration of low-dose ranibizumab for the treatment of retinopathy of prematurity

Retinopathy of prematurity (ROP) and necrotising enterocolitis (NEC) are complications of prematurity. Despite being quite different in terms of incidence, pathogenesis and consequences, both share a pathogenic role of aberrant vascularisation: increased in ROP, deficient for NEC. Current therapy for ROP includes the use of anti-vascular endothelial growth factor (anti-VEGF) agents, which are able to interrupt retinal hypervascularity. Despite being delivered intravitreously, anti-VEGF used in ROP can be absorbed into circulation and exert systemic effects. We present here a case of an ex-27 weeks gestational age infant, presenting multiple NEC risk factors, treated at 2 months of age with low-dose ranibizumab, who developed a large bowel NEC episode in the first week after treatment. We believe that this further report of an association between anti-VEGF agents and NEC could be interesting for the identification of children at risk of severe adverse events and stimulating further research on the topic.

Pediatric Intestinal Failure Associated Eating Disorder: An Overview of the Importance of Oral Feeding in a Population at Risk for Feeding Difficulties

Achieving feeding skills and food acceptance is a multi-layered process. In pediatric intestinal failure (PIF), oral feeding is important for feeding skills development, physiologic adaptation, quality of life and the prevention of eating disorders. In PIF, risk factors for feeding difficulties are common and early data suggests that feeding difficulties are prevalent. There is a unique paradigm for the feeding challenges in PIF. Conventional definitions of eating disorders have limited application in this context. A pediatric intestinal failure associated eating disorder (IFAED) definition that includes feeding/eating skills dysfunction, psychosocial dysfunction, and the influence on weaning nutrition support is proposed.

Nutrition and Intestinal Rehabilitation of Children With Short Bowel Syndrome: A Position Paper of the ESPGHAN Committee on Nutrition. Part 1: From Intestinal Resection to Home Discharge

Short bowel syndrome (SBS) is the leading cause of intestinal failure (IF) in children. The mainstay of treatment for IF is parenteral nutrition (PN). The aim of this position paper is to review the available evidence on managing SBS and to provide practical guidance to clinicians dealing with this condition. All members of the Nutrition Committee of the European Society for Paediatric Gastroenterology Hepatology and Nutrition (ESPGHAN) contributed to this position paper. Some renowned experts in the field joined the team to guide with their experience. A systematic literature search was performed from 2005 to May 2021 using PubMed, MEDLINE, and Cochrane Database of Systematic Reviews. In the absence of evidence, recommendations reflect the expert opinion of the authors. Literature on SBS mainly consists of retrospective single-center experience, thus most of the current papers and recommendations are based on expert opinion. All recommendations were voted on by the expert panel and reached >90% agreement. The first part of this position paper focuses on the physiological mechanism of intestinal adaptation after surgical resection. It subsequently provides some clinical practice recommendations for the primary management of children with SBS from surgical resection until discharged home on PN.

Colon cancer surgery in von Willebrand disease type 3 setting triggering vascular abnormalities on bowel anastomosis

Background

von Willebrand disease (VWD) is associated with vascular malformations in the gastrointestinal tract. This complication, more frequent in VWD types 2A and 3, may be due to abnormal angiogenesis, but the precise mechanism is still unclear. Angiogenesis and inflammation are closely linked and can potentiate each other.

Key Clinical Question

Can colon inflammation in the setting of cancer surgery potentiate angiogenesis in the VWD setting?

Clinical Approach

A woman with VWD type 3 underwent partial colectomy twice for an adenocarcinoma. After managing the first surgery with a plasma-derived von Willebrand factor (VWF) concentrate (Wilfactin; LFB), refractory gastrointestinal bleeding occurred from neovessels on bowel anastomosis. After a multidisciplinary discussion, a second surgery was undertaken with a recombinant VWF concentrate (Veyvondi; Takeda Pharmaceuticals). Pathologic neovessels were again observed on the new anastomosis.

Conclusion

Colectomy was complicated twice by pathologic neovessels on bowel anastomosis in 2 distinct procedures managed either with plasma-derived VWF or with recombinant VWF.

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.

The prevalence of feeding difficulties and potential risk factors in pediatric intestinal failure: Time to consider promoting oral feeds?

BACKGROUND & AIMS

Although nutritional care is a cornerstone in the management of pediatric intestinal failure (IF), little is known about feeding difficulty (FD) prevalence. The aim of this study was to determine the frequency of FD and associated factors and to characterize eating behaviours in two pediatric IF rehabilitation centres (Hôpital-Necker Enfants Malades (NEM), France and Alberta Children's Hospital (ACH), Canada).

METHODS

Parents of children (aged 1-18 years) on home parenteral nutrition (PN) for >3 months followed at NEM and ACH completed two validated tools: Montreal Children's Feeding scale for severity of FD, Child Eating Behaviour Questionnaire and a pediatric IF-specific questionnaire for FD associated risk factors.

RESULTS

In the entire cohort (n = 59, median 5.2 years), 15% had mild, 19% had moderate and 25% had severe FD. No FD was seen in 53% vs 11% and severe FD was seen in 20% vs. 39% of the NEM and ACH cohorts respectively (p = 0.003). Current ETF was less common at NEM vs. ACH (3% vs. 50%, p < 0.001). The FD score was associated with current enteral tube feed (ETF) use (p = 0.04). Compared to healthy reference children, the NEM cohort did not differ for the enjoyment of food, whereas the ACH cohort's enjoyment was lower (p < 0.0001). The ACH cohort scored higher for food avoidance behaviours: food fussiness (p < 0.02), satiety responsiveness (p < 0.0001), and slowness in eating (p < 0.0001) while the NEM cohort was not different from healthy reference children. In the entire cohort, according to parental recall, 60% were reported to be NPO for >12 weeks in the first 6 months of life, and late introduction of purees (>9 months) and lumpy textures (>1 year) were found in 40% and 58%, respectively. Parent-recalled ETF differed between NEM and ACH in the first 6 months of life (45% vs 76%, p = 0.03).

CONCLUSIONS

Feeding difficulty and associated risk factors, including early ETF, prolonged NPO and delays in achieving feeding milestones were frequently reported in pediatric IF. Feeding medicalization with the use of ETF may inadvertently contribute to FD and eating disorder behavioural characteristics. This study highlights the need for FD prevention and an increased focus on establishing healthy eating. Future prospective study of FD, associated risk factors and clinical outcomes are merited.

EGFR in enterocytes & endothelium and HIF1α in enterocytes are dispensable for massive small bowel resection induced angiogenesis

Background

Short bowel syndrome (SBS) results from significant loss of small intestinal length. In response to this loss, adaptation occurs, with Epidermal Growth Factor Receptor (EGFR) being a key driver. Besides enhanced enterocyte proliferation, we have revealed that adaptation is associated with angiogenesis. Further, we have found that small bowel resection (SBR) is associated with diminished oxygen delivery and elevated levels of hypoxia-inducible factor 1-alpha (HIF1α).

Methods

We ablated EGFR in the epithelium and endothelium as well as HIF1α in the epithelium, ostensibly the most hypoxic element. Using these mice, we determined the effects of these genetic manipulations on intestinal blood flow after SBR using photoacoustic microscopy (PAM), intestinal adaptation and angiogenic responses. Then, given that endothelial cells require a stromal support cell for efficient vascularization, we ablated EGFR expression in intestinal subepithelial myofibroblasts (ISEMFs) to determine its effects on angiogenesis in a microfluidic model of human small intestine.

Results

Despite immediate increased demand in oxygen extraction fraction measured by PAM in all mouse lines, were no differences in enterocyte and endothelial cell EGFR knockouts or enterocyte HIF1α knockouts by POD3. Submucosal capillary density was also unchanged by POD7 in all mouse lines. Additionally, EGFR silencing in ISEMFs did not impact vascular network development in a microfluidic device of human small intestine.

Conclusions

Overall, despite the importance of EGFR in facilitating intestinal adaptation after SBR, it had no impact on angiogenesis in three cell types–enterocytes, endothelial cells, and ISEMFs. Epithelial ablation of HIF1α also had no impact on angiogenesis in the setting of SBS.

Enteral Nutrition in Pediatric Short-Bowel Syndrome

Pediatric intestinal failure (IF) is the critical reduction of intestinal mass or function below the amount necessary for normal growth in children. Short-bowel syndrome (SBS) is the most common cause of IF in infants and children and is caused by intestinal resection. Enteral autonomy and freedom from parenteral nutrition is the mainstay of nutrition management in SBS. The goal is to achieve intestinal adaptation while maintaining proper growth and development. Treatment is variable, and there remains a paucity of evidence to draw well-informed conclusions for the care of individuals in this complex population. Physiological principles of enteral nutrition and practical recommendations for advancing the diet of patients with pediatric SBS are presented. Emerging trends in nutrition management, such as the growing interest in blending diets and the impact on SBS, are reviewed. Finally, the influence of the microbiome on enteral tolerance and small bowel bacterial overgrowth are considered.

Nutritional Feeding Strategies in Pediatric Intestinal Failure

Intestinal failure is defined as a critical reduction of the gut mass or function, below the minimum needed to absorb nutrients and fluids. The ultimate goal in intestinal failure is to promote bowel adaptation and reach enteral autonomy while a healthy growth and development is maintained. The condition is heterogeneous and complex. Therefore, recommendations for the type and duration of parenteral, enteral, and oral nutrition are variable, with the child's age as an additional key factor. The aim of this review is to provide an overview of nutritional feeding strategies in this heterogeneous population. Different perspectives on nutritional management, nutrition and adaptation, and microbiome and nutrition will be discussed.

Short Bowel Syndrome as the Leading Cause of Intestinal Failure in Early Life: Some Insights into the Management

Intestinal failure (IF) is the critical reduction of the gut mass or its function below the minimum needed to absorb nutrients and fluids required for adequate growth in children. Severe IF requires parenteral nutrition (PN). Pediatric IF is most commonly due to congenital or neonatal intestinal diseases or malformations divided into 3 groups: 1) reduced intestinal length and consequently reduced absorptive surface, such as in short bowel syndrome (SBS) or extensive aganglionosis; 2) abnormal development of the intestinal mucosa such as congenital diseases of enterocyte development; 3) extensive motility dysfunction such as chronic intestinal pseudo-obstruction syndromes. The leading cause of IF in childhood is the SBS. In clinical practice the degree of IF may be indirectly measured by the level of PN required for normal or catch up growth. Other indicators such as serum citrulline have not proven to be highly reliable prognostic factors in children. The last decades have allowed the development of highly sophisticated nutrient solutions consisting of optimal combinations of macronutrients and micronutrients as well as guidelines, promoting PN as a safe and efficient feeding technique. However, IF that requires long-term PN may be associated with various complications including infections, growth failure, metabolic disorders, and bone disease. IF Associated Liver Disease may be a limiting factor. However, changes in the global management of IF pediatric patients, especially since the setup of intestinal rehabilitation centres did change the prognosis thus limiting "nutritional failure" which is considered as a major indication for intestinal transplantation (ITx) or combined liver-ITx.

Prevention and Treatment of Intestinal Failure-Associated Liver Disease in Children

Intestinal failure-associated liver disease (IFALD) is a threatening complication for children on long-term parenteral nutrition because of intestinal failure. When progressive and intractable, it may jeopardize intestinal rehabilitation and lead to combined liver and intestinal transplantation. The institution of dedicated intestinal failure centers has dramatically decreased the incidence of such complication. IFALD may rapidly fade away if very early management aimed at preventing progression to end-stage liver disease is provided. In this review, we address the etiology and risk factors of IFALD in order to introduce pillars of prevention (nutritional management and catheter-related infections control). The latest evidence of therapeutic strategies, such as medical and surgical treatments, is also discussed.

Adhesions and Healing of Intestinal Anastomoses

Background. Postoperative adhesions are the result of aberrant peritoneal healing. As they are the leading cause of postoperative bowel obstruction, anti-adherence barriers are advocated for their prevention. This study looks into the effect of these biomaterials on the healing of intestinal anastomoses. Materials and Methods. Thirty-three New Zealand White rabbits underwent laparotomy, transection of the terminal ileum, and creation of an end-to-end anastomosis. Animals were randomized into 3 groups: the Control group (n = 11); the Icodextrin group, receiving icodextrin 4% intraperitonealy (n = 11); and the HA/CMC group, having the anastomosis wrapped with a hyaluronic acid/carboxymethylcellulose film (n = 11). All animals were sacrificed on the seventh postoperative day. Macroscopic adhesions were graded and anastomotic strength was tested by the burst pressure. Histological healing was assessed in a semiquantitative way for the presence of ulceration, reepithelization, granulation tissue, inflammation, eosinophilic infiltration, serosal inflammation, and microscopic adhesions. Univariate and multivariate analysis was used. Results are given as medians with interquartile range. Results. The median adhesion scores were the following: Control 1 (0-3), Icodextrin 0 (0-1), HA/CMC 0 (0-0), P = .017. The burst pressure did not differ between the groups; however, all except one bowel segments tested burst away from the anastomosis. The macroscopic and histological anastomotic healing was comparable in all 3 groups. A poor histological anastomotic healing score was associated with a higher adhesion grade (odds ratio = 1.92; 95% confidence interval = 1.06-3.47; P = .032). Conclusion. Adhesion formation was inhibited by the materials tested without direct detrimental effects on anastomotic healing. Poor anastomotic healing provokes adhesions even in the presence of anti-adhesion barriers.

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.

Angiogenesis and Vascular Endothelial Growth Factor-A Expression Associated with Inflammation in Pediatric Crohn's Disease

BACKGROUND AND AIMS

Angiogenesis is a component of chronic inflammatory diseases including inflammatory bowel disease. Some studies describe increased angiogenesis associated with acute disease in adult Crohn's disease and ulcerative colitis, while animal models aid investigations of mechanism and pathophysiology of angiogenesis. We aim to explore the role of angiogenesis and its pathways in pediatric Crohn's disease.

METHODS

Surgical specimens were obtained from pediatric Crohn's disease (both inflamed and non-inflamed regions of ileum) and control patients. Samples were examined for inflammation, microvessel density, and molecular expression of vascular endothelial growth factor-A, platelet-derived growth factor-β, angiopoietin-1, and angiopoietin-2.

RESULTS

Angiogenesis and inflammation were increased in parallel in Crohn's disease compared to controls. We also discovered increased angiogenesis in Crohn's disease tissue that was relatively free of inflammatory disease. Vascular endothelial growth factor-A gene expression (P = 0.034) was elevated in Crohn's disease over controls, while gene expression of platelet-derived growth factor-β (P = 0.069), angiopoietin-1 (P = 0.206), and angiopoietin-2 (P = 0.082) was not significantly elevated.

CONCLUSIONS

We confirm that inflammation-associated angiogenesis is upregulated in pediatric Crohn's disease. This population also exhibits elevated mucosal angiogenesis at the surgical margin with limited inflammation. This suggests that angiogenesis is an additional pathologic characteristic to potentially identify normal mucosa and margins of surgical resection that are uninvolved with disease and, furthermore, may have implications for monitoring complete disease remission. We further identify the vascular endothelial growth factor-A pathway involvement in the disease process, which may serve as a future molecular target for anti-angiogenic therapy in inflammatory bowel disease.

The effect of impaired angiogenesis on intestinal function following massive small bowel resection

PURPOSE

Intestinal adaptation involves villus lengthening, crypt deepening, and increased capillary density following small bowel resection (SBR). Mice lacking the proangiogenic chemokine CXCL5 have normal structural adaptation but impaired angiogenesis. This work evaluates the impact of incomplete adaptive angiogenesis on the functional capacity of the intestine after SBR.

METHODS

CXCL5 knockout (KO) and C57BL/6 wild-type (WT) mice underwent 50% SBR. Magnetic resonance imaging measured weekly body composition. Intestinal absorptive capacity was evaluated through fecal fat analysis. Gene expression profiles for select macronutrient transporters were measured via RT-PCR. Postoperative crypt and villus measurements were assessed for structural adaptation. Submucosal capillary density was measured through CD31 immunohistochemistry.

RESULTS

Comparable postoperative weight gain occurred initially. Diminished weight gain, impaired fat absorption, and elevated steatorrhea occurred in KO mice after instituting high-fat diet. Greater postoperative upregulation of ABCA1 fat transporter occurred in WT mice, while PEPT1 protein transporter was significantly downregulated in KO mice. KO mice had impaired angiogenesis but intact structural adaptation.

CONCLUSION

After SBR, KO mice display an inefficient intestinal absorption profile with perturbed macronutrient transporter expression, impaired fat absorption, and slower postoperative weight gain. In addition to longer villi and deeper crypts, an intact angiogenic response may be required to achieve functional adaptation to SBR.

CXCL5 is required for angiogenesis, but not structural adaptation after small bowel resection

PURPOSE

Intestinal adaptation is the compensatory response to massive small bowel resection (SBR) and characterized by lengthening of villi and deepening of crypts, resulting in increased mucosal surface area. Previous studies have demonstrated increased villus capillary blood vessel density after SBR, suggesting a role for angiogenesis in the development of resection-induced adaptation. Since we have previously shown enhanced expression of the proangiogenic chemokine CXCL5 after SBR, the purpose of this study was to determine the effect of disrupted CXCL5 expression on intestinal adaptation.

METHODS

CXCL5 knockout (KO) and C57BL/6 wild type (WT) mice were subjected to either a 50% proximal SBR or sham operation. Ileal tissue was harvested on postoperative day 7. To assess for adaptation, villus height and crypt depth were measured. Submucosal capillary density was measured by CD31 immunohistochemistry.

RESULTS

Both CXCL5-KO and WT mice demonstrated normal structural features of adaptation. Submucosal capillary density increased in the WT but not in the KO mice following SBR.

CONCLUSION

CXCL5 is required for increased intestinal angiogenesis during resection-induced adaptation. Since adaptive villus growth occurs despite impaired CXCL5 expression and enhanced angiogenesis, this suggests that the growth of new blood vessels is not needed for resection-induced mucosal surface area expansion following massive SBR.

Role of salivary vascular endothelial growth factor (VEGF) in palatal mucosal wound healing

The mucosa of alimentary tract heals more rapidly than cutaneous wounds. The underlying mechanisms of this enhanced healing have not been completely elucidated. Constant exposure to salivary growth factors has been shown to play a critical role in mucosal homeostasis and tissue repair. Angiogenesis also has an essential role in successful wound repair. One of the main angiogenic growth factors, vascular endothelial growth factor (VEGF), has a pleiotropic role in tissue repair via neovascularization, reepithelialization, and regulation of extracellular matrix. We have previously reported a critical role for salivary VEGF in bowel adaptation after small bowel resection. We hypothesize that salivary VEGF is an essential stimulus for oral mucosal tissue repair, and use the murine palatal wound model to test our hypothesis. In a loss-of-function experiment, we removed the primary source of VEGF production through selective submandibular gland (SMG) sialoadenectomy in a murine model and observed the effects on wound closure and neovascularization. We then performed a selective loss-of-function experiment using the protein VEGF-Trap to inhibit salivary VEGF. In a gain-of-function experiment, we supplemented oral VEGF following SMG sialoadenectomy. After SMG sialoadenectomy, there was significant reduction in salivary VEGF level, wound closure, and vessel density. Lower levels of salivary VEGF were correlated with impaired neovascularization and reepithelialization. The selective blockade of VEGF using VEGF-Trap resulted in a similar impairment in wound healing and neovascularization. The sole supplementation of oral VEGF after SMG sialoadenectomy rescued the impaired wound healing phenotype and restored neovascularization to normal levels. These data show a novel role for salivary-VEGF in mucosal wound healing, and provide a basis for the development of novel therapeutics aimed at augmenting wound repair of the oral mucosa, as well as wounds at other sites in the alimentary tract.

Up-regulation of hypoxia-inducible factor 1 alpha and hemodynamic responses following massive small bowel resection

PURPOSE

Massive small bowel resection (SBR) results in an adaptive response within the remnant bowel. We have previously shown an immediate reduction in intestinal blood flow and oxygen saturation (sO2) after SBR. We therefore sought to determine the duration of resection-induced intestinal hypoxia and expression of hypoxia-inducible factors (HIFs) following SBR.

METHODS

C57B6 mice were subjected to 50% proximal SBR or a sham procedure. Photoacoustic microscopy (PAM) was used to measure blood flow and sO2 on postoperative days (PODs) 1, 3, and 7. Ileal tissue was harvested 6h postoperatively and on PODs 1 and 2, and HIF1α, HIF2α, and VEGF mRNA expression were assessed via RT-PCR. A p value of less than 0.05 was considered significant.

RESULTS

Following SBR, reduction in intestinal blood flow persists for 24h and is followed with hyperemia by POD 3. The immediate reduction in venous sO2 and increased tissue oxygen utilization continued through POD 7. Enhanced expression of HIF1α was demonstrated 6h following SBR.

CONCLUSION

Massive SBR results in an immediate relative hypoxic state within the remnant bowel with early enhanced expression of HIF1α. On POD 7, increased tissue oxygen extraction and elevated blood flow persist in the adapting intestine.

Intestinal failure in children: the European view

Intestinal failure (IF) is a condition in which severe intestinal malabsorption mandates artificial nutrition through a parenteral route. Causes of severe protracted IF include short bowel syndrome, congenital diseases of enterocyte development, and severe motility disorders (total or subtotal aganglionosis or chronic intestinal pseudo-obstruction syndrome). IF can result in nutritional failure, defined as the long-term failure to nourish a child by natural or artificial means. Today, IF-associated liver disease is the most common cause of parenteral nutrition (PN) failure, but catheter-related sepsis and extensive vascular thrombosis may also jeopardize the health of those receiving PN. For a child with nutritional failure, intestinal transplantation, often in the form of a composite visceral graft, offers the only chance for long-term survival. The management of IF requires a multidisciplinary approach. There have been a number of recent advances in both medical and surgical treatments of IF. In particular, new intestinal lengthening techniques and the use of PN formulas rich in fish oil both have resulted in decreased rates of severe complications of IF and its treatments. In addition, better awareness of the risks and benefits of intestinal transplantation have resulted in better patient selection, and ultimately in improved patient survival, hence restricting the indication to transplantation only to patients with nutritional failure and no other chance to survive.

Neonatal short bowel syndrome as a model of intestinal failure: physiological background for enteral feeding

Intestinal failure (IF) is a well identified clinical condition, which is characterised by the reduction of functional gut capacity below the minimum needed for adequate digestion and absorption of nutrients for normal growth in children. Short bowel syndrome (SBS) is the leading cause of IF in neonates, infants and young children usually as a result of extensive intestinal resection during the neonatal period. Simultaneously maintaining optimal nutritional status and achieving intestinal adaptation is a clinical challenge in short bowel patients. Both growth and development of the child as well as gut adaptation should be considered synergistically as primary outcome parameters. Enteral nutrition (EN) can be introduced orally and/or by tube feeding (TF). Several controversies over nutritional treatment of children with SBS related intestinal failure remain. As reported from different centres around the world, most practices are more "experienced based" rather than "evidence based". This is partly due to the small number of patients with this condition. This review (based on a consensus) discusses the physiological principles and nutritional management, including the type of diet and route of delivery. Perspectives in optimizing intestinal adaptation and reducing the consequences of small intestinal bacterial overgrowth are also discussed.

Recent advances in small bowel diseases: Part II

As is the case in all areas of gastroenterology and hepatology, in 2009 and 2010 there were many advances in our knowledge and understanding of small intestinal diseases. Over 1000 publications were reviewed, and the important advances in basic science as well as clinical applications were considered. In Part II we review six topics: absorption, short bowel syndrome, smooth muscle function and intestinal motility, tumors, diagnostic imaging, and cystic fibrosis.

Immediate alterations in intestinal oxygen saturation and blood flow after massive small bowel resection as measured by photoacoustic microscopy

PURPOSE

Massive small bowel resection (SBR) results in villus angiogenesis and a critical adaptation response within the remnant bowel. Previous ex vivo studies of intestinal blood flow after SBR are conflicting. We sought to determine the effect of SBR on intestinal hemodynamics using photoacoustic microscopy, a noninvasive, label-free, high-resolution in vivo hybrid imaging modality.

METHODS

Photoacoustic microscopy was used to image the intestine microvascular system and measure blood flow and oxygen saturation (So(2)) of the terminal mesenteric arteriole and accompanying vein in C57BL6 mice (n = 7) before and immediately after a 50% proximal SBR. A P value of less than .05 was considered significant.

RESULTS

Before SBR, arterial and venous So(2) were similar. Immediately after SBR, the venous So(2) decreased with an increase in the oxygen extraction fraction. In addition, the arterial and venous blood flow significantly decreased.

CONCLUSION

Massive SBR results in an immediate reduction in intestinal blood flow and increase in tissue oxygen utilization. These physiologic changes are observed throughout the remnant small intestine. The contribution of these early hemodynamic alterations may contribute to the induction of villus angiogenesis and the pathogenesis of normal intestinal adaptation responses.

Ret heterozygous mice have enhanced intestinal adaptation after massive small bowel resection

Intestinal adaptation is an important compensatory response to massive small bowel resection (SBR) and occurs because of a proliferative stimulus to crypt enterocytes by poorly understood mechanisms. Recent studies suggest the enteric nervous system (ENS) influences enterocyte proliferation. We, therefore, sought to determine whether ENS dysfunction alters resection-induced adaptation responses. Ret+/- mice with abnormal ENS function and wild-type (WT) littermates underwent sham surgery or 50% SBR. After 7 days, ileal morphology, enterocyte proliferation, apoptosis, and selected signaling proteins were characterized. Crypt depth and villus height were equivalent at baseline in WT and Ret+/- mice. In contrast after SBR, Ret+/- mice had longer villi (Ret+/- 426.7 ± 46.0 μm vs. WT 306.5 ± 7.7 μm, P < 0.001) and deeper crypts (Ret+/- 119 ± 3.4 μm vs. WT 82.4 ± 3.1 μm, P < 0.001) than WT. Crypt enterocyte proliferation was higher in Ret+/- (48.8 ± 1.3%) than WT (39.9 ± 2.1%; P < 0.001) after resection, but apoptosis rates were similar. Remnant bowel of Ret+/- mice also had higher levels of glucagon-like peptide 2 (6.2-fold, P = 0.005) and amphiregulin (4.6-fold, P < 0.001) mRNA after SBR, but serum glucagon-like peptide 2 protein levels were equal in WT and Ret+/- mice, and there was no evidence of increased c-Fos nuclear localization in submucosal neurons. Western blot confirmed higher crypt epidermal growth factor receptor (EGFR) protein levels (1.44-fold; P < 0.001) and more phosphorylated EGFR (2-fold; P = 0.003) in Ret+/- than WT mice after SBR. These data suggest that Ret heterozygosity enhances intestinal adaptation after massive SBR, likely via enhanced EGFR signaling. Reducing Ret activity or altering ENS function may provide a novel strategy to enhance adaptation attenuating morbidity in patients with short bowel syndrome.

Potential benefits of pro- and prebiotics on intestinal mucosal immunity and intestinal barrier in short bowel syndrome

The mechanism of impaired gut barrier function in patients with short bowel syndrome (SBS) is poorly understood and includes decreased intestinal motility leading to bacterial overgrowth, a reduction in gut-associated lymphoid tissue following the loss of intestinal length, inhibition of mucosal immunity of the small intestine by intravenous total parental nutrition, and changes in intestinal permeability to macromolecules. Novel therapeutic strategies (i.e. nutritive and surgical) have been introduced in order to prevent the establishment or improve the outcome of this prevalent disease. Pre- and probiotics as a nutritive supplement are already known to be very active in the intestinal tract (mainly in the colon) by maintaining a healthy gut microflora and influencing metabolic, trophic and protective mechanisms, such as the production of SCFA which influence epithelial cell metabolism, turnover and apoptosis. Probiotics have been recommended for patients suffering from SBS in order to decrease bacterial overgrowth and prevent bacterial translocation, two major mechanisms in the pathogenesis of SBS. The present review discusses the research available in the international literature, clinical and experimental, regarding probiotic supplementation for this complicated group of patients based on the clinical spectrum and pathophysiological aspects of the syndrome. The clinical data that were collected for the purposes of the present review suggest that it is difficult to correctly characterise probiotics as a preventive or therapeutic measure. It is very challenging after all to examine the relationship of the bacterial flora, the intestinal barrier and the probiotics as, according to the latest knowledge, demonstrate an interesting interaction.

Intestinal adaptation following massive ileocecal resection in 20-day-old weanling rats

OBJECTIVE

Few infant animal models have been used to study infantile short bowel syndrome (SBS). Most SBS models involve removal of the proximal small bowel followed by jejunoileal anastomosis, which has unclear clinical relevance to human infantile SBS that often results from surgical treatment for necrotizing enterocolitis and involves removal of the ileum, ileocecal valve, and part of or the entire colon. Our objective was to develop a more appropriate SBS model in developing rats.

MATERIALS AND METHODS

Twenty-day-old weanling rats were divided into 2 surgery groups, ileocecal resection (ICR) and sham groups, and a control group that did not undergo surgery. All were fed a liquid diet ad libitum for 7 days after surgery or for 7 days in the controls, and body weight, food intake, and stool changes were recorded daily. The rats were then euthanized and intestinal lengths and weights were recorded. Samples of intestine from the distal jejunum and proximal colon were collected for histology. Mucosal samples from the middle, distal jejunum, and colon were collected for measurements of mucosal weights, DNA, RNA, and protein levels. Maltase activity was determined in the small intestine.

RESULTS

Eighty-five percent of rats survived the ICR with subsequent development of diarrhea, hyperphagia, and poor growth. Adaptive responses to ICR, as compared with sham, were evidenced by increased intestinal and mucosal weights, DNA, RNA, and protein levels, increased maltase activity and villous thickness in distal jejunum, and increased mucosal thickness in the colon.

CONCLUSIONS

This ICR model in weanling rats is appropriate for studying human infantile SBS.

Intestinal resection induces angiogenesis within adapting intestinal villi

PURPOSE

Adaptive growth of the intestinal mucosa in response to massive gut loss is fundamental for autonomy from parenteral nutrition. Although angiogenesis is essential for cellular proliferation in other tissues, its relevance to intestinal adaptation is unknown. We tested the hypothesis that resection-induced adaptation is associated with new blood vessel growth.

METHODS

Male C57Bl/6 mice underwent either a 50% small bowel resection or a sham (transection and reanastomosis) operation. After 1, 3, or 7 days, capillary density within the intestinal villi was measured using confocal microscopy. A messenger RNA reverse-transcriptase polymerase chain reaction (RT-PCR) array was used to determine angiogenic gene expression during adaptation.

RESULTS

Mice that underwent small bowel resection had a significantly increased capillary density compared to sham-operated mice at postoperative day 7. This morphological alteration was preceded by significant alterations in 5 candidate genes at postoperative day 3.

CONCLUSION

New vessel blood growth is observed in the adapting intestine after massive small bowel loss. This response appears to follow rather than initiate the adaptive alterations in mucosal morphology that are characteristic of adaptation. A better understanding of this progress and the signaling factors involved may improve therapeutic options for children with short gut syndrome.