Parenteral nutrition decreases paneth cell function and intestinal bactericidal activity while increasing susceptibility to bacterial enteroinvasion

Parenteral Nutrition, Inflammatory Bowel Disease, and Gut Barrier: An Intricate Plot

Malnutrition poses a critical challenge in inflammatory bowel disease, with the potential to detrimentally impact medical treatment, surgical outcomes, and general well-being. Parenteral nutrition is crucial in certain clinical scenarios, such as with patients suffering from short bowel syndrome, intestinal insufficiency, high-yielding gastrointestinal fistula, or complete small bowel obstruction, to effectively manage malnutrition. Nevertheless, research over the years has attempted to define the potential effects of parenteral nutrition on the intestinal barrier and the composition of the gut microbiota. In this narrative review, we have gathered and analyzed findings from both preclinical and clinical studies on this topic. Based on existing evidence, there is a clear correlation between short- and long-term parenteral nutrition and negative effects on the intestinal system. These include mucosal atrophic damage and immunological and neuroendocrine dysregulation, as well as alterations in gut barrier permeability and microbiota composition. However, the mechanistic role of these changes in inflammatory bowel disease remains unclear. Therefore, further research is necessary to effectively address the numerous gaps and unanswered questions pertaining to these issues.

When can we start early enteral nutrition safely in patients with shock on vasopressors?

Shock is a common critical illness characterized by microcirculatory disorders and insufficient tissue perfusion. Patients with shock and hemodynamic instability generally require vasopressors to maintain the target mean arterial pressure. Enteral nutrition (EN) is an important therapeutic intervention in critically ill patients and has unique benefits for intestinal recovery. However, the initiation of early EN in patients with shock receiving vasopressors remains controversial. Current guidelines make conservative and vague recommendations regarding early EN support in patients with shock. Increasing studies demonstrates that early EN delivery is safe and feasible in patients with shock receiving vasopressors; however, this evidence is based on observational studies. Changes in gastrointestinal blood flow vary by vasopressor and inotrope and are complex. The risk of gastrointestinal complications, especially the life-threatening complications of non-occlusive mesenteric ischemia and non-occlusive bowel necrosis, cannot be ignored in patients with shock during early EN support. It remains a therapeutic challenge in critical care nutrition therapy to determine the initiation time of EN in patients with shock receiving vasopressors and the safe threshold region for initiating EN with vasopressors. Therefore, the current review aimed to summarize the evidence on the optimal and safe timing of early EN initiation in patients with shock receiving vasopressors to improve clinical practice.

Total parenteral nutrition impairs glucose metabolism by modifying the gut microbiome

Total parenteral nutrition (TPN) can lead to complications, such as glucose metabolism disorders. While TPN is associated with impairments in intestinal function, the gut barrier and mucosal immunity, the relationship between the gut microbiome and TPN-related glucose metabolism disorders remains to be explored. In a cohort of 256 participants with type 2 intestinal failure, we show that parenteral nutrition providing >80% of total energy induces insulin resistance and a higher risk of complications. Using various male mouse models, we demonstrate that changes in Lactobacillaceae and indole-3-acetic acid (IAA) levels underlie these complications. Lactobacillaceae and IAA levels decrease in TPN-treated mice and participants, while their abundances in the latter are negatively correlated with insulin resistance and serum lipopolysaccharide levels. Furthermore, IAA activates the aryl hydrocarbon receptor and increases glucagon-like peptide-1 secretion through upregulation of Gcg expression and increased stem cell differentiation towards L cells. Finally, liraglutide, a glucagon-like peptide-1 receptor agonist, completely prevents TPN-induced glucose metabolism disorders in mice. Thus, TPN induces glucose metabolism disorders by altering the gut microbiota and its metabolites.

Partially hydrolyzed guar gum alleviates hepatic steatosis and alters specific gut microbiota in a murine liver injury model

PURPOSE

The gut microbiota, via the gut-liver axis, plays an important role in the development of intestinal failure-associated liver disease. Here, we investigated whether partially hydrolyzed guar gum (PHGG), a dietary fiber could alleviate liver damage and modulate the gut microbiota in a murine liver injury (LI) model.

METHODS

Liver injury was induced in 6-week-old male C57BL/6 mice using an enteral liquid diet composed of parenteral nutrition (LI group) and treated with 5% PHGG (LI/PHGG group). Liver histopathology was examined using oil red O and a tumor necrosis factor-α (TNF-α) labeling. The gut microbiota was examined using 16S rRNA gene sequencing.

RESULTS

Lipid accumulation was significantly decreased in the LI /PHGG group when compared with that of the LI group. The area of TNF-α-positive cells was significantly higher in the LI group when compared with that of the control. The principal coordinate analysis (PCoA) revealed pronounced changes in the gut microbiota after PHGG treatment. Linear discriminant analysis of effect size showed that PHGG treatment significantly increased cecal abundance of Parabacteroides.

CONCLUSIONS

PHGG alleviated hepatic steatosis following liver injury in mice. The protective effect of PHGG treatment could be associated with increased abundance of Parabacteroides in the cecum.

Bermúdez M, Campoy C. Impact of Total Parenteral Nutrition on Gut Microbiota in Pediatric Population Suffering Intestinal Disorders

Parenteral nutrition (PN) is a life-saving therapy providing nutritional support in patients with digestive tract complications, particularly in preterm neonates due to their gut immaturity during the first postnatal weeks. Despite this, PN can also result in several gastrointestinal complications that are the cause or consequence of gut mucosal atrophy and gut microbiota dysbiosis, which may further aggravate gastrointestinal disorders. Consequently, the use of PN presents many unique challenges, notably in terms of the potential role of the gut microbiota on the functional and clinical outcomes associated with the long-term use of PN. In this review, we synthesize the current evidence on the effects of PN on gut microbiome in infants and children suffering from diverse gastrointestinal diseases, including necrotizing enterocolitis (NEC), short bowel syndrome (SBS) and subsequent intestinal failure, liver disease and inflammatory bowel disease (IBD). Moreover, we discuss the potential use of pre-, pro- and/or synbiotics as promising therapeutic strategies to reduce the risk of severe gastrointestinal disorders and mortality. The findings discussed here highlight the need for more well-designed studies, and harmonize the methods and its interpretation, which are critical to better understand the role of the gut microbiota in PN-related diseases and the development of efficient and personalized approaches based on pro- and/or prebiotics.

Gut microbiota alterations in critically ill older patients: a multicenter study

Background

Aging generates changes in the gut microbiota, affecting its functionality. Little is known about gut microbiota in critically ill older adults. The objective of this study was to describe the profile of gut microbiota in a cohort of critically ill older adults.

Methods

This observational study was conducted in five health institutions. Over a 6-month study period, critically ill patients over 18 years old who were admitted to the intensive care unit were enrolled. Fecal microbiota profiles were determined from 155 individuals, over 60 years old (n = 72) and under 60 years old (n = 83). Gut microbiota was analyzed by sequencing the V3-V4 region of the 16S rRNA gene. Alpha and beta diversity, operational taxonomic units and the interaction of gut microbiota with variables under study were analyzed. Amplicon sequence variants (ASVs) specifically associated with age were recovered by including gender, discharge condition, BMI, ICU stay and antibiotics as covariates in a linear mixed model.

Results

In older adults, sepsis, malnutrition, antibiotic prescription and severity (APACHE and SOFA scores) were higher than in the group under 60 years of age. Alpha diversity showed lower gut microbiota diversity in those over 60 years of age (p < 0.05); beta diversity evidenced significant differences between the groups (PERMANOVA = 1.19, p = 0.038). The microbiota of the adults under 60 years old showed greater abundance of Murdochiella, Megasphaera, Peptoniphilus and Ezakiella, whereas those over 60 years old Escherichia-Shigella and Hungatella were more abundant.

Conclusion

The gut microbial community was altered by different factors; however, age significantly explained the variability in critically ill patients. A lower presence of beneficial genera and a higher abundance of pathogens was observed in adults over 60 years old.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-022-02981-0.

The Pathology and Physiology of Ileostomy

An ileostomy is a surgery that is commonly performed to protect low pelvic anastomoses or prevent high-risk anastomotic leakages. However, various postoperative complications remain of major concern. After an ileostomy, the distal intestinal segment is left open for an extended period and is in a non-functional state. Consequently, the intestinal mucosa, smooth muscle, and microbiota undergo significant changes that are closely related to postoperative recovery and complications. A systematic description of these changes is necessary to understand the relationship among them and take more effective measures for postoperative intervention.

Role of the Gut Microbiota in Parenteral Nutrition-Associated Liver Disease: From Current Knowledge to Future Opportunities

Parenteral nutrition-associated liver disease (PNALD) refers to a spectrum of conditions that can develop cholestasis, steatosis, fibrosis, and cirrhosis in the setting of parenteral nutrition (PN) use. Patient risk factors include short bowel syndrome, bacterial overgrowth and translocation, disturbance of hepatobiliary circulation, and lack of enteral feeding. A growing body of evidence suggests an intricate linkage between the gut microbiota and the pathogenesis of PNALD. In this review, we highlight current knowledge on the taxonomic and functional changes in the gut microbiota that might serve as noninvasive biomarkers. We also discuss the function of microbial metabolites and associated signaling pathways in the pathogenesis of PNALD. By providing the perspectives of microbiota-host interactions in PNALD for basic and translational research and summarizing current limitations of microbiota-based approaches, this review paves the path for developing novel and precise microbiota-based therapies in PNALD.

Autonomic Nervous System Neuroanatomical Alterations Could Provoke and Maintain Gastrointestinal Dysbiosis in Autism Spectrum Disorder (ASD): A Novel Microbiome-Host Interaction Mechanistic Hypothesis

Dysbiosis secondary to environmental factors, including dietary patterns, antibiotics use, pollution exposure, and other lifestyle factors, has been associated to many non-infective chronic inflammatory diseases. Autism spectrum disorder (ASD) is related to maternal inflammation, although there is no conclusive evidence that affected individuals suffer from systemic low-grade inflammation as in many psychological and psychiatric diseases. However, neuro-inflammation and neuro-immune abnormalities are observed within ASD-affected individuals. Rebalancing human gut microbiota to treat disease has been widely investigated with inconclusive and contradictory findings. These observations strongly suggest that the forms of dysbiosis encountered in ASD-affected individuals could also originate from autonomic nervous system (ANS) functioning abnormalities, a common neuro-anatomical alteration underlying ASD. According to this hypothesis, overactivation of the sympathetic branch of the ANS, due to the fact of an ASD-specific parasympathetic activity deficit, induces deregulation of the gut-brain axis, attenuating intestinal immune and osmotic homeostasis. This sets-up a dysbiotic state, that gives rise to immune and osmotic dysregulation, maintaining dysbiosis in a vicious cycle. Here, we explore the mechanisms whereby ANS imbalances could lead to alterations in intestinal microbiome-host interactions that may contribute to the severity of ASD by maintaining the brain-gut axis pathways in a dysregulated state.

Immediate vs. gradual advancement to goal of enteral nutrition after elective abdominal surgery: A multicenter non-inferiority randomized trial

BACKGROUND & AIMS

The strategy of increasing the postoperative enteral nutrition dose to the target goal has not yet been clarified. This study aimed to determine whether an immediate goal-dose enteral nutrition (IGEN) strategy is non-inferior to a gradual goal-dose enteral nutrition (GGEN) strategy in reducing infections in patients undergoing abdominal surgery involving the organs of the digestive system.

METHODS

This randomized controlled trial enrolled postoperative patients with nutritional risk screening 2002 scores ≥3 from 11 Chinese hospitals. Energy targets were calculated as 25 kcal/kg and 30 kcal/kg of ideal body weight for women and men, respectively. Patients were randomly assigned 1:1 to IGEN or GGEN group after enteral tolerance was confirmed (30% of the target on day 2). The IGEN group immediately started receiving 100% of the caloric requirements on day 3, while the GGEN group received 40% progressing to 80% of target on day 7. The primary endpoint was the infection rate until discharge, based on the intention-to-treat population.

RESULTS

A total of 411 patients were enrolled and randomized to the IGEN and GGEN groups, and five patients did not receive the allocated intervention. A total of 406 patients were included in the primary analysis, with 199 and 207 in the IGEN and GGEN groups, respectively. Infection was observed in 17/199 (8.5%) in the IGEN group and 19/207 (9.2%) in the GGEN group, respectively (difference, -0.6%; [95% confidence interval (CI), -6.2%-4.9%]; P = 0.009 for non-inferiority test). There were significantly more gastrointestinal intolerance events with IGEN than with GGEN (58/199 [29.1%] vs. 32/207 [15.5%], P < 0.001). All other secondary endpoints were non-significant.

CONCLUSIONS

Among postoperative patients at nutritional risk, IGEN was non-inferior to GGEN in regards to infectious complications. IGEN was associated with more gastrointestinal intolerance events. It showed that IGEN cannot be considered to be clinically directive. ClinicalTrials.gov (#NCT03117348).

The effect of enteral stimulation on the immune response of the intestinal mucosa and its application in nutritional support

The intestine plays a fundamental role as a regulator of the mucosal immune response, mostly through the production and secretion of secretory Immunoglobulin A (sIgA) by the gut-associated lymphoid tissue (GALT). Enteral stimulation, a balance between the commensal microbiota and pathogenic microorganisms, in addition to an adequate nutritional status is required for the optimal immune function of the intestine. Fasting subjects or those supported only with parenteral nutrition, show a progressive anatomical and physiological deterioration of the GALT, triggering a series of alterations resulting in a decrease in the intestinal immune response, modification in the type of microbiota, and changes that lead to or aggravate malnutrition. Patients with malnutrition present an increase in the rate of nosocomial infections, hospital length of stay, and mortality. An adequate nutritional assessment at hospital admission and avoiding long periods of fasting are paramount to prevent these unfavorable outcomes. Herein, we present a mini-state of the art review on the role and importance of enteral stimulation by GALT-mediated immune response.

Glucagon-Like Peptide-2 Modulates Enteric Paneth Cells Immune Response and Alleviates Gut Inflammation During Intravenous Fluid Infusion in Mice With a Central Catheter

Background: Glucagon-like peptide-2 (GLP-2) has protective effects on gastrointestinal functions. Our previous study found that GLP-2 could significantly reduce intestinal permeability and bacterial translocation in total parenteral nutrition (TPN) animal model. However, the effects of GLP-2 on the impairment of the intestinal Paneth cells immune function and gut inflammation during intravenous fluid infusion mainly consisted of nutritional materials is currently scattered.

Objective: The current study was aimed to investigate the efficacy of the GLP-2 in alleviating gut inflammation and modulating enteric Paneth cells immune response in parenterally fed mice and its underlying mechanisms.

Methods: Thirty-six male ICR mice underwent venous catheterization were divided into 3 groups: Chow, TPN, and TPN+GLP-2 groups. GLP-2 was administered intravenously at 60 μg/day for 5 days. The small intestine tissue and serum samples were collected on the 7th day.

Results: Compared with the TPN group, the expression of tight junction proteins occludin and claudin-1 were significantly increased in the TPN+GLP-2 group. In addition, the expression of lysozyme, sPLA2, insulin-like growth factor-1, and epithelial protection and repair genes were improved in the TPN+GLP-2 group. The levels of IL-6 and TNF-α proteins and mRNAs in the ileum tissues were remarkably reduced in the TPN+GLP-2 group, while IL-10 protein and mRNA level were elevated in the TPN+GLP-2 group (all p < 0.05). Moreover, the TPN+GLP-2 group has higher levels of serum endotoxin, D-lactic acid, and MPO than those of the TPN group.

Conclusions: GLP-2 alleviated gut inflammation and improved enteric Paneth cells immune responses through intravenous fluid infusion, possibly by improving the functioning of epithelial protection and repair, and reducing mucosal inflammatory responses.

Alterations of gut microbiota and serum bile acids are associated with parenteral nutrition-associated liver disease

BACKGROUND

Parenteral nutrition-associated liver disease (PNALD) is a major complication of long-term parenteral nutrition (PN). The pathogenesis of PNALD remains unclear. We investigated the changes in taxonomic and functional composition of gut microbiota and serum bile acid levels in a rat model of PNALD.

METHODS

Male 4-week-old Sprague Dawley rats received either total parenteral nutrition or standard chow with 0.9% saline for 7 days. The taxonomic composition of cecal microbiota and its functional composition associated with bile acid metabolism were measured.

RESULTS

There were differences in taxonomic composition between the two groups. The abundance of the secondary bile acid biosynthesis pathway was higher in the TPN group (p < 0.05) with an increase in the percentage of bacteria expressing 7-alpha-hydroxysteroid dehydrogenase (p < 0.05). The abundance of enzymes associated with bile salt hydrolase was also higher (p < 0.05) in the TPN group. The TPN group showed a distinct bile acid profile characterized by a higher ratio of secondary bile acids to primary bile acids.

CONCLUSIONS

The alteration of bile acid-associated microbiota may lead to increased secondary bile acid production in a rat model of PNALD.

Gut microbiota profiles in critically ill patients, potential biomarkers and risk variables for sepsis

Critically ill patients are physiologically unstable and recent studies indicate that the intestinal microbiota could be involved in the health decline of such patients during ICU stays. This study aims to assess the intestinal microbiota in critically ill patients with and without sepsis and to determine its impact on outcome variables, such as medical complications, ICU stay time, and mortality. A multi-center study was conducted with a total of 250 peri-rectal swabs obtained from 155 patients upon admission and during ICU stays. Intestinal microbiota was assessed by sequencing the V3-V4 hypervariable regions of the 16S rRNA gene. Linear mixed models were used to integrate microbiota data with more than 40 clinical and demographic variables to detect covariates and minimize the effect of confounding factors. We found that the microbiota of ICU patients with sepsis has an increased abundance of microbes tightly associated with inflammation, such as Parabacteroides, Fusobacterium and Bilophila species. Female sex and aging would represent an increased risk for sepsis possibly because of some of their microbiota features. We also evidenced a remarkable loss of microbial diversity, during the ICU stay. Concomitantly, we detected that the abundance of pathogenic species, such as Enterococcus spp., was differentially increased in sepsis patients who died, indicating these species as potential biomarkers for monitoring during ICU stay. We concluded that particular intestinal microbiota signatures could predict sepsis development in ICU patients. We propose potential biomarkers for evaluation in the clinical management of ICU patients.

Intestinal plasticity in response to nutrition and gastrointestinal surgery

The plasticity of a material corresponds to its capacity to change its feature under the effect of an external action. Intestinal plasticity could be defined as the ability of the intestine to modify its size or thickness and intestinal cells to modulate their absorption and secretion functions in response to external or internal cues/signals. This review will focus on intestinal adaptation mechanisms in response to diet and nutritional status. These physiological mechanisms allow a fine and rapid adaptation of the gut to promote absorption of ingested food, but they can also lead to obesity in response to overnutrition. This plasticity could thus become a therapeutic target to treat not only undernutrition but also obesity. How the intestine adapts in response to 2 types of surgical remodeling of the digestive tract-extensive bowel resection leading to intestinal failure and surgical treatment of pathological obesity (ie, bariatric surgeries)-will also be reviewed.

TGR5 signaling mitigates parenteral nutrition-associated liver disease

Bile acid receptors regulate the metabolic and immune functions of circulating enterohepatic bile acids. This process is disrupted by administration of parenteral nutrition (PN), which may induce progressive hepatic injury for unclear reasons, especially in the newborn, leading to PN-associated liver disease. To explore the role of bile acid signaling on neonatal hepatic function, we initially observed that Takeda G protein receptor 5 (TGR5)-specific bile acids were negatively correlated with worsening clinical disease markers in the plasma of human newborns with prolonged PN exposure. To test our resulting hypothesis that TGR5 regulates critical liver functions to PN exposure, we used TGR5 receptor deficient mice (TGR5^-/-). We observed PN significantly increased liver weight, cholestasis, and serum hepatic stress enzymes in TGR5^-/- mice compared with controls. Mechanistically, PN reduced bile acid synthesis genes in TGR5^-/-. Serum bile acid composition revealed that PN increased unconjugated primary bile acids and secondary bile acids in TGR5^-/- mice, while increasing conjugated primary bile acid levels in TGR5-competent mice. Simultaneously, PN elevated hepatic IL-6 expression and infiltrating macrophages in TGR5^-/- mice. However, the gut microbiota of TGR5^-/- mice compared with WT mice following PN administration displayed highly elevated levels of Bacteroides and Parabacteroides, and possibly responsible for the elevated levels of secondary bile acids in TGR5^-/- animals. Intestinal bile acid transporters expression was unchanged. Collectively, this suggests TGR5 signaling specifically regulates fundamental aspects of liver bile acid homeostasis during exposure to PN. Loss of TGR5 is associated with biochemical evidence of cholestasis in both humans and mice on PN.NEW & NOTEWORTHY Parenteral nutrition is associated with deleterious metabolic outcomes in patients with prolonged exposure. Here, we demonstrate that accelerated cholestasis and parental nutrition-associated liver disease (PNALD) may be associated with deficiency of Takeda G protein receptor 5 (TGR5) signaling. The microbiome is responsible for production of secondary bile acids that signal through TGR5. Therefore, collectively, these data support the hypothesis that a lack of established microbiome in early life or under prolonged parenteral nutrition may underpin disease development and PNALD.

Butyric Acid and Leucine Induce α-Defensin Secretion from Small Intestinal Paneth Cells

The intestine not only plays a role in fundamental processes in digestion and nutrient absorption, but it also has a role in eliminating ingested pathogenic bacteria and viruses. Paneth cells, which reside at the base of small intestinal crypts, secrete α-defensins and contribute to enteric innate immunity through potent microbicidal activities. However, the relationship between food factors and the innate immune functions of Paneth cells remains unknown. Here, we examined whether short-chain fatty acids and amino acids induce α-defensin secretion from Paneth cells in the isolated crypts of small intestine. Butyric acid and leucine elicit α-defensin secretion by Paneth cells, which kills Salmonella typhimurium. We further measured Paneth cell secretion in response to butyric acid and leucine using enteroids, a three-dimensional ex vivo culture system of small intestinal epithelial cells. Paneth cells expressed short-chain fatty acid receptors, Gpr41, Gpr43, and Gpr109a mRNAs for butyric acid, and amino acid transporter Slc7a8 mRNA for leucine. Antagonists of Gpr41 and Slc7a8 inhibited granule secretion by Paneth cells, indicating that these receptor and transporter on Paneth cells induce granule secretion. Our findings suggest that Paneth cells may contribute to intestinal homeostasis by secreting α-defensins in response to certain nutrients or metabolites.

The Effect of Butyrate-Supplemented Parenteral Nutrition on Intestinal Defence Mechanisms and the Parenteral Nutrition-Induced Shift in the Gut Microbiota in the Rat Model

Butyrate produced by the intestinal microbiota is essential for proper functioning of the intestinal immune system. Total dependence on parenteral nutrition (PN) is associated with numerous adverse effects, including severe microbial dysbiosis and loss of important butyrate producers. We hypothesised that a lack of butyrate produced by the gut microbiota may be compensated by its supplementation in PN mixtures. We tested whether i.v. butyrate administration would (a) positively modulate intestinal defence mechanisms and (b) counteract PN-induced dysbiosis. Male Wistar rats were randomised to chow, PN, and PN supplemented with 9 mM butyrate (PN+But) for 12 days. Antimicrobial peptides, mucins, tight junction proteins, and cytokine expression were assessed by RT-qPCR. T-cell subpopulations in mesenteric lymph nodes (MLN) were analysed by flow cytometry. Microbiota composition was assessed in caecum content. Butyrate supplementation resulted in increased expression of tight junction proteins (ZO-1, claudin-7, E-cadherin), antimicrobial peptides (Defa 8, Rd5, RegIIIγ), and lysozyme in the ileal mucosa. Butyrate partially alleviated PN-induced intestinal barrier impairment and normalised IL-4, IL-10, and IgA mRNA expression. PN administration was associated with an increase in Tregs in MLN, which was normalised by butyrate. Butyrate increased the total number of CD4+ and decreased a relative amount of CD8+ memory T cells in MLN. Lack of enteral nutrition and PN administration led to a shift in caecal microbiota composition. Butyrate did not reverse the altered expression of most taxa but did influence the abundance of some potentially beneficial/pathogenic genera, which might contribute to its overall beneficial effect.

Gut Microbiota as a Modulator of Paneth Cells During Parenteral Nutrition in Mice

BACKGROUND

Parenteral nutrition (PN) leads to decreased production of Paneth cell-derived antimicrobial peptides and is accompanied by dysbiosis of the gut. The role of gut microbiota in regulating Paneth cell function during PN is unknown.

METHODS

Male C57BL/6 mice received either an antibiotic cocktail (Abx) or nothing (Normal) in their drinking water for 2 weeks before being fed either standard laboratory chow (Abx-Chow and Normal-Chow) or a continuous infusion of PN solution (Abx-PN and Normal-PN) for 7 days. In a separate experiment, the intestinal contents of mice having received 7 days of Chow or PN were transferred by gavage to germ-free (GF) mice.

RESULTS

Antibiotic treatment decreased the protein levels of lysozyme and RegIIIγ and the mRNA level of α-defensin 5, with no further effect by PN compared with chow. However, these measurements were higher in Abx-PN mice than in Normal-PN mice. When compared with Chow→GF, PN→GF mice demonstrated lower body weight, shorter intestinal length, severe atrophy of the ileum villus, and lower levels of lysozyme and RegIIIγ protein and α-defensin 5 mRNA. Interleukin (IL)-22 and IL-17 mRNA levels declined in the ileum. Principal component analysis revealed major differences between the metabolite compositions of the Chow and PN, as well as the Chow→GF and PN→GF groups that appears to indicate aberrant tryptophan metabolism.

CONCLUSIONS

Gut microbiota plays a vital role in PN-related Paneth cell dysfunction. Dysbiosis during PN might alter the production of microbial metabolites, thereby influencing the production of Paneth cell-derived antimicrobial peptides.

Role of the Gut⁻Liver Axis in Driving Parenteral Nutrition-Associated Injury

For decades, parenteral nutrition (PN) has been a successful method for intravenous delivery of nutrition and remains an essential therapy for individuals with intolerance of enteral feedings or impaired gut function. Although the benefits of PN are evident, its use does not come without a significant risk of complications. For instance, parenteral nutrition-associated liver disease (PNALD)—a well-described cholestatic liver injury—and atrophic changes in the gut have both been described in patients receiving PN. Although several mechanisms for these changes have been postulated, data have revealed that the introduction of enteral nutrition may mitigate this injury. This observation has led to the hypothesis that gut-derived signals, originating in response to the presence of luminal contents, may contribute to a decrease in damage to the liver and gut. This review seeks to present the current knowledge regarding the modulation of what is known as the “gut–liver axis” and the gut-derived signals which play a role in PN-associated injury.

The gut in trauma

PURPOSE OF REVIEW

The purpose of this review is to describe established and emerging mechanisms of gut injury and dysfunction in trauma, describe emerging strategies to improve gut dysfunction, detail the effect of trauma on the gut microbiome, and describe the gut-brain connection in traumatic brain injury.

RECENT FINDINGS

Newer data suggest intraluminal contents, pancreatic enzymes, and hepatobiliary factors disrupt the intestinal mucosal layer. These mechanisms serve to perpetuate the inflammatory response leading to multiple organ dysfunction syndrome (MODS). To date, therapies to mitigate acute gut dysfunction have included enteral nutrition and immunonutrition; emerging therapies aimed to intestinal mucosal layer disruption, however, include protease inhibitors such as tranexamic acid, parenteral nutrition-supplemented bombesin, and hypothermia. Clinical trials to demonstrate benefit in humans are needed before widespread applications can be recommended.

SUMMARY

Despite resuscitation, gut dysfunction promotes distant organ injury. In addition, postresuscitation nosocomial and iatrogenic 'hits' exaggerate the immune response, contributing to MODS. This was a provocative concept, suggesting infectious and noninfectious causes of inflammation may trigger, heighten, and perpetuate an inflammatory response culminating in MODS and death. Emerging evidence suggests posttraumatic injury mechanisms, such as intestinal mucosal disruption and shifting of the gut microbiome to a pathobiome. In addition, traumatic brain injury activates the gut-brain axis and increases intestinal permeability.

The potential of gut microbiota and fecal volatile organic compounds analysis as early diagnostic biomarker for necrotizing enterocolitis and sepsis in preterm infants

Although the exact pathophysiological mechanisms of both necrotizing enterocolitis (NEC) and late-onset sepsis (LOS) in preterm infants are yet to be elucidated, evidence is emerging that the gut microbiota plays a key role in their pathophysiology. Areas covered: In this review, initial microbial colonization and factors influencing microbiota composition are discussed. For both NEC and LOS, an overview of studies investigating preclinical alterations in gut microbiota composition and fecal volatile organic compounds (VOCs) is provided. Fecal VOCs are considered to reflect not only gut microbiota composition, but also their metabolic activity and concurrent interaction with the host. Expert review: Heterogeneity in study protocols and applied analytical techniques hampers reliable comparison between outcomes of different microbiota studies, limiting the ability to draw firm conclusions. This dilemma is illustrated by the finding that study results often cannot be reproduced, or even contradict each other. A NEC- and sepsis specific microbial or metabolic signature has not yet been discovered. Identification of 'disease-specific' VOCs and microbiota composition may increase understanding on pathophysiological mechanisms and may allow for development of an accurate screening tool, opening avenues towards timely identification and initiation of targeted treatment for preterm infants at increased risk for NEC and sepsis.

Hypermetabolism and Nutritional Support in Sepsis

BACKGROUND

Surgical metabolism has been a founding field of investigation in surgery without which the boundaries of critical care, trauma, and surgical oncology could not have advanced. Traditionally, understanding the shifts in electrolytes, carbohydrates, fats, and amino acids that could explain the rapidly evolving proteolysis after catabolic stress and tumor growth has been a major focus of research that led to our current approach to maintaining homeostasis over the course of major surgical intervention and injury.

METHOD

Review of the English-language literature.

RESULTS

With the emerging field of inflammation and the discovery of cytokines and chemokines, surgical metabolism has taken a second seat in the surgical research arena. Yet central to all patient management after injury is an understanding of how catabolic stress erodes vital organ function and how current approaches can support metabolism through the most physiologically stressful perturbations known to man, for which there is no evolutionary precedent. Although it is well accepted that unabated proteolysis is not a sustainable physiologic state, in the era of modern medicine, precisely how to manipulate the body nutritionally to drive a recovery-directed immune response remains highly debated. This review incorporates multiple lines of inquiry in surgical metabolism, with a particular focus on sepsis.

CONCLUSION

The changing landscape of previous paradigms in the field is discussed. Finally, how next-generation technology might spark renewed interest in this field among surgical investigators is considered.

Partial enteral nutrition increases intestinal sIgA levels in mice undergoing parenteral nutrition in a dose-dependent manner

BACKGROUND AND AIMS

Partial enteral nutrition (PEN) protects parenteral nutrition (PN) induced gut mucosal immunity impairment. However, the gastrointestinal function of most patients with PN is too poor to tolerate full dosage of PEN and no guidelines recommend PEN dose. We aimed to identify an optimal PEN dose and to understand the protective mechanism.

METHODS

Mice were assigned to groups with total parenteral nutrition (TPN), total enteral nutrition (TEN), or various degrees of PEN with PN. Additionally, AS1517499 was used to inhibit STAT6. Five days after treatment, secretory immunoglobulin A (sIgA) levels of luminal washing fluid and JAK1-STAT6 signalling in ileum tissue of different groups were assessed.

RESULTS

We found that TPN lowered luminal sIgA and down-regulated pIgR, phosphorylated JAK1 and STAT6, IL-4 and IL-13 as well relative to TEN. Moreover, 40% EN were lowest dose that reversed these detrimental consequences of PN to an equivalent level as TEN. The rescue of pIgR and luminal sIgA expression was decreased when the JAK1-STAT6 pathway was inhibited.

CONCLUSION

We conclude that 40% EN is the optimal PEN dose that reverses PN-induced impairment of gut mucosal immunity. Additionally, we hypothesise that this benefit involves activation of the JAK1-STAT6 pathway.

Parenteral Nutrition-Associated Liver Disease: The Role of the Gut Microbiota

Parenteral nutrition (PN) provides life-saving nutritional support in situations where caloric supply via the enteral route cannot cover the necessary needs of the organism. However, it does have serious adverse effects, including parenteral nutrition-associated liver disease (PNALD). The development of liver injury associated with PN is multifactorial, including non-specific intestine inflammation, compromised intestinal permeability, and barrier function associated with increased bacterial translocation, primary and secondary cholangitis, cholelithiasis, short bowel syndrome, disturbance of hepatobiliary circulation, lack of enteral nutrition, shortage of some nutrients (proteins, essential fatty acids, choline, glycine, taurine, carnitine, etc.), and toxicity of components within the nutrition mixture itself (glucose, phytosterols, manganese, aluminium, etc.). Recently, an increasing number of studies have provided evidence that some of these factors are directly or indirectly associated with microbial dysbiosis in the intestine. In this review, we focus on PN-induced changes in the taxonomic and functional composition of the microbiome. We also discuss immune cell and microbial crosstalk during parenteral nutrition, and the implications for the onset and progression of PNALD. Finally, we provide an overview of recent advances in the therapeutic utilisation of pro- and prebiotics for the mitigation of PN-associated liver complications.

N-3 polyunsaturated fatty acid-enriched lipid emulsion improves Paneth cell function via the IL-22/Stat3 pathway in a mouse model of total parenteral nutrition

Total parenteral nutrition (TPN) is a life-saving therapy for patients with gastrointestinal dysfunction or failure. Long-term TPN impairs gut barrier function and contributes to infections and poor clinical outcomes. However, the underlying mechanisms of TPN-related gut barrier damage have not been fully elucidated, and effective measures are still rare. Here, we compared the effects of a predominantly n-6 polyunsaturated fatty acids emulsion (PUFAs; Intralipid) and a lipid emulsion containing n-3 PUFAs (Intralipid plus Omegaven) on antimicrobial peptides produced by Paneth cells. Our results show for the first time that n-3 PUFAs markedly ameliorated intestine atrophy, and increased protein levels of lysozyme, RegIIIγ, and α-cryptdin 5, and their mRNA expression, compared to the n-6 PUFAs emulsion. Importantly, our study reveals that downregulation of IL-22 and phosphorylated Stat3 (p-Stat3) is associated with Paneth cell dysfunction, which may mediate TPN-related gut barrier damage. Lastly, n-3 PUFAs upregulated levels of IL-22 and increased the p-Stat3/Stat3 ratio in ileal tissue, suggesting that n-3 PUFAs improve Paneth cell function through activation of the IL-22/Stat3 pathway. Therefore, our study provides a cogent explanation for the beneficial effects of n-3 PUFAs, and indicates the IL-22/Stat3 pathway as a promising target in the treatment of TPN-related gut barrier damage.

Influence of nutrition therapy on the intestinal microbiome

PURPOSE OF REVIEW

This review describes the relationship between nutritional therapies and the intestinal microbiome of critically ill patients.

RECENT FINDINGS

The intestinal microbiome of the critically ill displays a near complete loss of health-promoting microbiota with overgrowth of virulent healthcare-associated pathogens. Early enteral nutrition within 24 h of admission to the ICU has been advocated in medical and surgical patients to avoid derangements of the intestinal epithelium and the microbiome associated with starvation. Contrary to previous dogma, permissive enteral underfeeding has recently been shown to have similar outcomes to full feeding in the critically ill, whereas overfeeding has been shown to be deleterious in those patients who are not malnourished at baseline. Randomized clinical trials suggest that peripheral nutrition can be used safely either as the sole or supplemental source of nutrition even during the early phases of critical care. The use of probiotics has been associated with a significant reduction in infectious complications in the critically ill without a notable mortality benefit.

SUMMARY

Focus of research is shifting toward strategies that augment the intestinal environment to facilitate growth of beneficial microorganisms, strengthen colonization resistance, and maintain immune homeostasis.

Gastrointestinal immune and microbiome changes during parenteral nutrition

Parenteral nutrition (PN) is a lifesaving therapy that provides intravenous nutrition support to patients who cannot, or should not, feed via the gastrointestinal (GI) tract. Unfortunately, PN also carries certain risks related to infection and metabolic complications compared with enteral nutrition. In this review, an overview of PN and GI immune and microbiome changes is provided. PN impacts the gut-associated lymphoid tissue functions, especially adaptive immune cells, changes the intestinal epithelium and chemical secretions, and significantly alters the intestinal microbiome. Collectively, these changes functionally result in increased susceptibility to infectious and injurious challenge. Since PN remains necessary in large numbers of patients, the search to improve outcomes by stimulating GI immune function during PN remains of interest. This review closes by describing recent advances in using enteric nervous system neuropeptides or microbially derived products during PN, which may improve GI parameters by maintaining immunity and physiology.

Bacterial nutrient foraging in a mouse model of enteral nutrient deprivation: insight into the gut origin of sepsis

Total parenteral nutrition (TPN) leads to a shift in small intestinal microbiota with a characteristic dominance of Proteobacteria This study examined how metabolomic changes within the small bowel support an altered microbial community in enterally deprived mice. C57BL/6 mice were given TPN or enteral chow. Metabolomic analysis of jejunal contents was performed by liquid chromatography/mass spectrometry (LC/MS). In some experiments, leucine in TPN was partly substituted with [¹³C]leucine. Additionally, jejunal contents from TPN-dependent and enterally fed mice were gavaged into germ-free mice to reveal whether the TPN phenotype was transferrable. Small bowel contents of TPN mice maintained an amino acid composition similar to that of the TPN solution. Mass spectrometry analysis of small bowel contents of TPN-dependent mice showed increased concentration of ¹³C compared with fed mice receiving saline enriched with [¹³C]leucine. [¹³C]leucine added to the serosal side of Ussing chambers showed rapid permeation across TPN-dependent jejunum, suggesting increased transmucosal passage. Single-cell analysis by fluorescence in situ hybridization (FISH)-NanoSIMS demonstrated uptake of [¹³C]leucine by TPN-associated bacteria, with preferential uptake by Enterobacteriaceae Gavage of small bowel effluent from TPN mice into germ-free, fed mice resulted in a trend toward the proinflammatory TPN phenotype with loss of epithelial barrier function. TPN dependence leads to increased permeation of TPN-derived nutrients into the small intestinal lumen, where they are predominately utilized by Enterobacteriaceae The altered metabolomic composition of the intestinal lumen during TPN promotes dysbiosis.

Lipid Emulsion Formulation of Parenteral Nutrition Affects Intestinal Microbiota and Host Responses in Neonatal Piglets

BACKGROUND

Total parenteral nutrition (TPN) is a cause of intestinal microbial dysbiosis and impaired gut barrier function. This may contribute to life-threatening parenteral nutrition-associated liver disease and sepsis in infants. We compared the effects of a lipid emulsion containing long-chain ω-3 polyunsaturated fatty acids (PUFAs; SMOFlipid) and a predominantly ω-6 PUFA emulsion (Intralipid) on microbial composition and host response at the mucosal surface.

MATERIALS AND METHODS

Neonatal piglets were provided isocaloric, isonitrogenous TPN for 14 days versus sow-fed (SF) controls. Equivalent lipid doses (10 g/kg/d) were given of either SMOFlipid (ML; n = 10) or Intralipid (SO; n = 9). Ileal segments and mucosal scrapings were used to characterize microbial composition by 16S rRNA gene sequencing and quantitative gene expression of tight junction proteins, mucins, antimicrobial peptides, and inflammatory cytokines.

RESULTS

The microbial composition of TPN piglets differed from SF, while ML and SO differed from each other (analysis of molecular variance; P < .05); ML piglets were more similar to SF, as indicated by UniFrac distance ( P < .05). SO piglets showed a specific and dramatic increase in Parabacteroides ( P < .05), while ML showed an increase in Enterobacteriaceae ( P < .05). Gene expression of mucin, claudin 1, β-defensin 2, and interleukin 8 were higher in TPN; overall increases were significantly less in ML versus SO ( P < .05).

CONCLUSION

The formulation of parenteral lipid is associated with differences in the gut microbiota and host response of TPN-fed neonatal piglets. Inclusion of ω-3 long-chain PUFAs appears to improve host-microbial interactions at the mucosal surface, although mechanisms are yet to be defined.

Cysteinyl-glycine reduces mucosal proinflammatory cytokine response to fMLP in a parenterally-fed piglet model

BACKGROUND

PepT1 transports dietary and bacterial peptides in the gut. We hypothesized that cysteinyl-glycine would ameliorate the inflammatory effect of a bacterial peptide, formyl-methionyl-leucyl-phenylalanine (fMLP), in both sow-fed and parenterally-fed piglets.

METHODS

An intestinal perfusion experiment was performed in piglets (N = 12) that were sow-reared or provided with parenteral nutrition (PN) for 4 d. In each piglet, five segments of isolated intestine were perfused with five treatments including cysteine and glycine, cysteinyl-glycine, fMLP, free cysteine and glycine with fMLP, or cysteinyl-glycine with fMLP. Mucosal cytokine responses and intestinal morphology was assessed in each gut segment.

RESULTS

PN piglets had lower mucosal IL-10 by approximately 20% (P < 0.01). Cysteinyl-glycine lowered TNF-α response to fMLP in PN-fed animals and IFN-γ response to fMLP in both groups (P < 0.05). The free cysteine and glycine treatment reduced TNF-α in sow-fed animals (P < 0.05). fMLP affected villus height in parenterally (P < 0.05), but not sow-fed animals.

CONCLUSION

Parenteral feeding conferred a susceptibility to mucosal damage by fMLP. The dipeptide was more effective at attenuating the inflammatory response to a bacterial peptide than free amino acids. This may be due to competitive inhibition of fMLP transport or a greater efficiency of transport of dipeptides.

Paneth cells in the developing gut: when do they arise and when are they immune competent?

BACKGROUND

Little is known about the perinatal development of Paneth cells (PCs) during gestation and the relation with necrotizing enterocolitis (NEC). We aimed to investigate when PCs arise and when they become immune competent during gestation.

METHODS

We included 57 samples of ileum tissue of fetuses/infants with a gestional age (GA) between 9 and 40 wk taken as part of a standard autopsy procedure. Hematoxylin-eosin staining and anti-human defensin 5 immunohistochemistry were performed. We performed a semi-quantitative assessment of (immune-competent) PC numbers per 10 crypts per tissue section per GA.

RESULTS

The number of PCs and the number of immune-competent PCs increased with increasing GA (Spearman's ρ = 0.41, P = 0.002 and ρ = 0.61, P < 0.001, respectively). Whereas significantly higher PC numbers were observed after 37 wk gestation (median 7, range 0-12) compared to preterm infants (median 0, range 0-15; P = 0.002), we counted higher numbers of immune-competent PCs already in infants with GA above 29 wk (median 6, range 0-18) compared to infants with GA under 29 wk (median 2, range 0-9; P < 0.001).

CONCLUSION

The significant increase of immune-competent PCs starting from a GA of 29 wk mimics the rise in incidence of NEC during a similar postmenstrual age in preterm infants.

Diet-dependent, microbiota-independent regulation of IL-10-producing lamina propria macrophages in the small intestine

Intestinal resident macrophages (Mϕs) regulate gastrointestinal homeostasis via production of an anti-inflammatory cytokine interleukin (IL)-10. Although a constant replenishment by circulating monocytes is required to maintain the pool of resident Mϕs in the colonic mucosa, the homeostatic regulation of Mϕ in the small intestine (SI) remains unclear. Here, we demonstrate that direct stimulation by dietary amino acids regulates the homeostasis of intestinal Mϕs in the SI. Mice that received total parenteral nutrition (TPN), which deprives the animals of enteral nutrients, displayed a significant decrease of IL-10-producing Mϕs in the SI, whereas the IL-10-producing CD4⁺ T cells remained intact. Likewise, enteral nutrient deprivation selectively affected the monocyte-derived F4/80⁺ Mϕ population, but not non-monocytic precursor-derived CD103⁺ dendritic cells. Notably, in contrast to colonic Mϕs, the replenishment of SI Mϕs and their IL-10 production were not regulated by the gut microbiota. Rather, SI Mϕs were directly regulated by dietary amino acids. Collectively, our study highlights the diet-dependent, microbiota-independent regulation of IL-10-producing resident Mϕs in the SI.

Homeostasis alteration within small intestinal mucosa after acute enteral refeeding in total parenteral nutrition mouse model

Feeding strategies to care for patients who transition from enteral nutrient deprivation while on total parenteral nutrition (TPN) to enteral feedings generally proceed to full enteral nutrition once the gastrointestinal tract recovers; however, an increasing body of literature suggests that a subgroup of patients may actually develop an increased incidence of adverse events, including death. To examine this further, we studied the effects of acute refeeding in a mouse model of TPN. Interestingly, refeeding led to some beneficial effects, including prevention in the decline in intestinal epithelial cell (IEC) proliferation. However, refeeding led to a significant increase in mucosal expression of proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), as well as an upregulation in Toll-like receptor 4 (TLR-4). Refeeding also failed to prevent TPN-associated increases in IEC apoptosis, loss of epithelial barrier function, and failure of the leucine-rich repeat-containing G protein-coupled receptor 5-positive stem cell expression. Transitioning from TPN to enteral feedings led to a partial restoration of the small bowel microbial population. In conclusion, while acute refeeding led to some restoration of normal gastrointestinal physiology, enteral refeeding led to a significant increase in mucosal inflammatory markers and may suggest alternative strategies to enteral refeeding should be considered.

ZnT2-Mediated Zinc Import Into Paneth Cell Granules Is Necessary for Coordinated Secretion and Paneth Cell Function in Mice

BACKGROUND & AIMS

Defects in Paneth cell (PC) function are associated with microbial dysbiosis and intestinal inflammation. PC granules contain antimicrobial peptides, cytokines, and substantial stores of zinc (Zn). We hypothesized that Zn, transported into the granule through the Zn transporter (ZnT)2, is critical for signature PC functions.

METHODS

ZnT2 was localized to PC granules using immunofluorescence and sucrose gradient fractionation in wild-type (wt) mice, and consequences of ZnT2 loss were characterized in ZnT2 knockout (ZnT2ko) mice. Terminal ilea were harvested for immunofluorescence, electron microscopy, and fluorescent imaging with the Zn reporter Zinpyr-1. Alterations in fecal microbiota were characterized using 16s ribosomal RNA sequencing. PC degranulation, bacterial translocation, cytokine response to Escherichia coli endotoxin lipopolysaccharide, crypt viability after exposure to the oxidant monochloramine (NH₂Cl), and bactericidal activity of luminal contents of terminal ilea against enteropathogenic E coli were assessed.

RESULTS

ZnT2 was localized to the membrane of PC granules. In ZnT2ko mice, spontaneous degranulation was observed more frequently than among wt mice. Secretory granules were hypodense with less active lysozyme, and there was evidence of autophagosome accumulation and granule degradation in PCs from ZnT2ko mice. Gut microbiota of ZnT2ko mice were enriched in Bacteroidales S24-7 and relatively depleted of species commonly found in wt mice. Evidence of PC dysfunction in ZnT2ko mice included impaired granule secretion and increased inflammatory response to lipopolysaccharide, less bactericidal activity, and greater susceptibility to cell death from NH₂Cl.

CONCLUSIONS

ZnT2 is critical for Zn import into PC granules, and the inability to import Zn leads to profound defects in PC function and uncoordinated granule secretion.

Changes to the Intestinal Microbiome With Parenteral Nutrition: Review of a Murine Model and Potential Clinical Implications

Parenteral nutrition (PN) dependence, while life sustaining, carries a significant risk of septic complications associated with epithelial barrier dysfunction and translocation of gut-derived microbiota. Increasing evidence suggests that PN-associated changes in the intestinal microbiota play a central role in the breakdown of the intestinal epithelial barrier. This review outlines the clinical and experimental evidence of epithelial barrier dysfunction with PN, the role of gut inflammatory dysregulation in driving this process, and the role of the intestinal microbiome in modulating inflammation in the gut and systemically. The article summarizes the most current work of our laboratory and others and describes many of the laboratory findings behind our current understanding of the PN enteral environment. Understanding the interaction between nutrient delivery, the intestinal microbiome, and PN-associated complications may lead to the development of novel therapies to enhance safety and quality of life for patients requiring PN.

Intestine, immunity, and parenteral nutrition in an era of preferred enteral feeding

PURPOSE OF REVIEW

To review the benefits of enteral nutrition in contrast to the inflammatory consequences of administration of parenteral nutrition and enteral deprivation. To present the most recent evidence for the mechanisms of these immunologic changes and discuss potential areas for modification to decrease infectious complications of its administration.

RECENT FINDINGS

There is significant data supporting the early initiation of enteral nutrition in both medical and surgical patients unable to meet their caloric goals via oral intake alone. Despite the preference for enteral nutrition, some patients are unable to utilize their gut for nutritious gain and therefore require parenteral nutrition administration, along with its infectious complications. The mechanisms behind these complications are multifactorial and have yet to be fully elucidated. Recent study utilizing both animal and human models has provided further information regarding parenteral nutrition's deleterious effect on intestinal epithelial barrier function along with the complications associated with enterocyte deprivation.

SUMMARY

Changes associated with parenteral nutrition administration and enteral deprivation are complex with multiple potential areas for modification to allow for safer administration. Recent discovery of the mechanisms behind these changes present exciting areas for future study as to make parenteral nutrition administration in the enterally deprived patient safer.

Partial Enteral Nutrition Preserves Elements of Gut Barrier Function, Including Innate Immunity, Intestinal Alkaline Phosphatase (IAP) Level, and Intestinal Microbiota in Mice

Lack of enteral nutrition (EN) during parenteral nutrition (PN) leads to higher incidence of infection because of gut barrier dysfunction. However, the effects of partial EN on intestina linnate immunity, intestinal alkaline phosphatase (IAP) and microbiota remain unclear. The mice were randomized into six groups to receive either standard chow or isocaloric and isonitrogenous nutritional support with variable partial EN to PN ratios. Five days later, the mice were sacrificed and tissue samples were collected. Bacterial translocation, the levels of lysozyme, mucin 2 (MUC2), and IAP were analyzed. The composition of intestinal microbiota was analyzed by 16S rRNA pyrosequencing. Compared with chow, total parenteral nutrition (TPN) resulted in a dysfunctional mucosal barrier, as evidenced by increased bacterial translocation (p < 0.05), loss of lysozyme, MUC2, and IAP, and changes in the gut microbiota (p < 0.001). Administration of 20% EN supplemented with PN significantly increased the concentrations of lysozyme, MUC2, IAP, and the mRNA levels of lysozyme and MUC2 (p < 0.001). The percentages of Bacteroidetes and Tenericutes were significantly lower in the 20% EN group than in the TPN group (p < 0.001). These changes were accompanied by maintained barrier function in bacterial culture (p < 0.05). Supplementation of PN with 20% EN preserves gut barrier function, by way of maintaining innate immunity, IAP and intestinal microbiota.

Introducing enteral feeding induces intestinal subclinical inflammation and respective chromatin changes in preterm pigs

Aim: To analyze how enteral food introduction affects intestinal gene regulation and chromatin structure in preterm pigs. Materials & methods: Preterm pigs were fed parenteral nutrition plus/minus slowly increasing volumes of enteral nutrition. Intestinal gene-expression and chromatin structure were analyzed 5 days after birth. Results: Enteral feeding led to differential upregulation of inflammatory and pattern recognition receptor genes, including IL8 (median: 5.8, 95% CI: 3.9–7.8 for formula; median: 2.2, 95% CI: 1.3–3.3 for colostrum) and TLR4 (median: 3.7, 95% CI: 2.6–4.8 for formula; no significant differences for colostrum) with corresponding decondensed chromatin configurations. On histology this correlated with mild mucosal lesions, particularly in formula-fed pigs. In CaCo-2 cells, histone hyperacetylation led to a marked increase in TLR4 mRNA and increased IL8 expression upon stimulation with lipopolysaccharide (median: 7.0; interquartile range: 5.63–8.85) compared with naive cells (median 4.2; interquartile range: 2.45–6.33; p = 0.03). Conclusion: Enteral feeding, particular with formula, induces subclinical inflammation in the premature intestine and more open chromatin structure in key inflammatory genes. This may increase the susceptibility for necrotizing enterocolitis.

Bombesin Preserves Goblet Cell Resistin-Like Molecule β During Parenteral Nutrition but Not Other Goblet Cell Products

INTRODUCTION

Parenteral nutrition (PN) increases the risk of infection in critically ill patients and is associated with defects in gastrointestinal innate immunity. Goblet cells produce mucosal defense compounds, including mucin (principally MUC2), trefoil factor 3 (TFF3), and resistin-like molecule β (RELMβ). Bombesin (BBS), a gastrin-releasing peptide analogue, experimentally reverses PN-induced defects in Paneth cell innate immunity. We hypothesized that PN reduces goblet cell product expression and PN+BBS would reverse these PN-induced defects.

METHODS

Two days after intravenous cannulation, male Institute of Cancer Research mice were randomized to chow (n = 15), PN (n = 13), or PN+BBS (15 µg tid) (n = 12) diets for 5 days. Defined segments of ileum and luminal fluid were analyzed for MUC2, TFF3, and RELMβ by quantitative reverse transcriptase polymerase chain reaction and Western blot. Th2 cytokines interleukin (IL)-4 and IL-13 were measured by enzyme-linked immunosorbent assay.

RESULTS

Compared with chow, PN significantly reduced MUC2 in ileum (P < .01) and luminal fluid (P = .01). BBS supplementation did not improve ileal or luminal MUC2 compared with PN (P > .3). Compared with chow, PN significantly reduced TFF3 in ileum (P < .02) and luminal fluid (P < .01). BBS addition did not improve ileal or luminal TFF3 compared with PN (P > .3). Compared with chow, PN significantly reduced ileal RELMβ (P < .01). BBS supplementation significantly increased ileal RELMβ to levels similar to chow (P < .03 vs PN; P > .6 vs chow). Th2 cytokines were decreased with PN and returned to chow levels with BBS.

CONCLUSION

PN significantly impairs the goblet cell component of innate mucosal immunity. BBS only preserves goblet cell RELMβ during PN but not other goblet cell products measured.

Should enteral nutrition be started in the first week of critical illness?

PURPOSE OF REVIEW

To review the mechanistic evidence for early enteral nutrition in critically ill patients within the first week of ICU admission.

RECENT FINDINGS

There is a lack of recent large randomized controlled trials showing clinically important outcome benefits related to early enteral nutrition. Most supporting studies are based on the animal models, and explore mechanisms of benefit related to gut immunity and oxidative stress. In addition, the impact of nutrient deprivation on the microbiome recently shown in a human trial is compelling. Large randomized controlled clinical trials have emerged in the last 2 years, however, comparing minimal enteral nutrition therapy and enteral nutrition versus parenteral nutrition. They call into question the low quality of clinical evidence and the widespread support for early enteral nutrition as a primary recommendation. As a result, the questions of whether or not enteral nutrition should be initiated in the first week versus standard of care or parenteral nutrition and how clinicians justify this recommendation are raised.

SUMMARY

Despite the wide range of quality in the current clinical outcomes evidence, early enteral nutrition within the first week of ICU admission, delivered to the appropriate patient, promotes gut-mediated immunity, lowers metabolic response to stress, maintains microbial diversity, and improves clinical outcomes versus standard of care or parenteral nutrition therapy.

The enteric nervous system neuropeptide, bombesin, reverses innate immune impairments during parenteral nutrition

BACKGROUND

Lack of enteral stimulation during parenteral nutrition (PN) impairs mucosal immunity. Bombesin (BBS), a gastrin-releasing peptide analogue, reverses PN-induced defects in acquired immunity. Paneth cells produce antimicrobial peptides (AMPs) of innate immunity for release after cholinergic stimulation.

OBJECTIVE

Determine if BBS restores AMPs and bactericidal function during PN.

METHODS

Intravenously cannulated male ICR mice were randomized to Chow, PN, or PN+BBS (15 μg 3 times daily, n = 7 per group) for 5 days. Ileum was analyzed for AMPs (Protein: sPLA2 by fluorescence, lysozyme and RegIII-γ by western andcryptdin-4 by ELISA; mRNA: all by RT-PCR). Cholinergic stimulated (100 μM bethanechol) ileal specimens assessed Pseudomonas bactericidal activity. Ileum (Chow: n = 7; PN: n = 9; PN+BBS: n = 8) was assessed for Escherichia coli invasion in ex-vivo culture.

RESULTS

PN significantly decreased most AMPs versus Chow while BBS maintained Chow levels (sPLA2: Chow: 107 + 14*, PN: 44.6 + 7.2, PN+BBS: 78.7 + 13.4* Fl/min/μL/total protein; Lysozyme: Chow: 63.9 + 11.9*, PN: 26.8 + 6.2; PN+BBS: 64.9 + 13.8* lysozyme/total protein; RegIII-γ: Chow: 51.5 + 10.0*, PN: 20.4 + 4.3, PN+BBS: 31.0 + 8.4 RegIII-γ/total protein; Cryptdin-4: Chow: 18.4 + 1.5*, PN: 12.7 + 1.6, PN+BBS: 26.1 + 2.4*† pg/mg [all *P < 0.05 vs PN and †P < 0.05 vs Chow]). Functionally, BBS prevented PN loss of bactericidal activity after cholinergic stimulation (Chow: 25.3 + 3.6*, PN: 13.0 + 3.2; PN+BBS: 27.0 + 4.7* percent bacterial killing, *P < 0.05 vs PN). BBS reduced bacterial invasion in unstimulated tissue barely missing significance (P = 0.06).

CONCLUSIONS

The enteric nervous system (ENS) controls AMP levels in Paneth cells during PN but mucosal protection by innate immunity requires both ENS and parasympathetic stimulation.

Glutamine Improves Innate Immunity and Prevents Bacterial Enteroinvasion During Parenteral Nutrition

BACKGROUND

Patients receiving parenteral nutrition (PN) are at increased risk of infectious complications compared with enteral feeding, which is in part explained by impaired mucosal immune function during PN. Adding glutamine (GLN) to PN has improved outcome in some clinical patient groups. Although GLN improves acquired mucosal immunity, its effect on innate mucosal immunity (defensins, mucus, lysozymes) has not been investigated.

METHODS

Forty-eight hours following venous cannulation, male Institute of Cancer Research mice were randomized to chow (n = 10), PN (n = 12), or PN + GLN (n = 13) for 5 days. Small intestine tissue and luminal fluid were collected for mucin 2 (MUC2), lysozyme, cryptdin 4 analysis, and luminal interleukin (IL)-4, IL-10, and IL-13 level measurement. Tissue was also harvested for ex vivo intestinal segment culture to assess tissue susceptibility to enteroinvasive Escherichia coli.

RESULTS

In both luminal and tissue samples, PN reduced MUC2 and lysozyme (P < .0001, respectively) compared with chow, whereas GLN addition increased MUC2 and lysozyme (luminal, P < .05; tissue, P < .0001, respectively) compared with PN alone. PN significantly suppressed cryptdin 4 expression, while GLN supplementation significantly enhanced expression. IL-4, IL-10, and IL-13 decreased significantly with PN compared with chow, whereas GLN significantly increased these cytokines compared with PN. Functionally, bacterial invasion increased with PN compared with chow (P < .05), while GLN significantly decreased enteroinvasion to chow levels (P < .05).

CONCLUSIONS

GLN-supplemented PN improves innate immunity and resistance to bacterial mucosal invasion lost with PN alone. This work confirms a clinical rationale for providing glutamine for the protection of the intestinal mucosa.

Intestinal epithelial cell apoptosis and loss of barrier function in the setting of altered microbiota with enteral nutrient deprivation

Total parenteral nutrition (TPN), a commonly used treatment for patients who cannot receive enteral nutrition, is associated with significant septic complications due in part to a loss of epithelial barrier function (EBF). While the underlying mechanisms of TPN-related epithelial changes are poorly understood, a mouse model of TPN-dependence has helped identify several contributing factors. Enteral deprivation leads to a shift in intestinal microbiota to predominantly Gram-negative Proteobacteria. This is associated with an increase in expression of proinflammatory cytokines within the mucosa, including interferon-γ and tumor necrosis factor-α. A concomitant loss of epithelial growth factors leads to a decrease in epithelial cell proliferation and increased apoptosis. The resulting loss of epithelial tight junction proteins contributes to EBF dysfunction. These mechanisms identify potential strategies of protecting against TPN-related complications, such as modification of luminal bacteria, blockade of proinflammatory cytokines, or growth factor replacement.