Total parenteral nutrition induces a shift in the Firmicutes to Bacteroidetes ratio in association with Paneth cell activation in rats

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.

Revealing the effect of sea buckthorn oil, fish oil and structured lipid on intestinal microbiota, colonic short chain fatty acid composition and serum lipid profiles in vivo

In this study, the effects of sea buckthorn oil (SBO), fish oil (FO) and an enzymatically synthesized structured lipid (SL) on serum, short-chain fatty acids (SCFAs) and intestinal microbiota in Sprague-Dawley (SD) rats were investigated. The results demonstrated that FO, SBO, and SL effectively reduced the levels of high-density lipoprotein cholesterol and low-density lipoprotein cholesterol in the serum of SD rats. SBO increased serum triglyceride levels, while FO elevated total cholesterol levels. Furthermore, all three dietary lipids decreased short-chain fatty acid production and enhanced intestinal microbiota diversity. FO increased the abundance of intestinal microbiota including Romboutsia, Lactobacillus, Escherichia-Shigella, and Lachnospiraceae_NK4A136_group. Conversely, all three dietary lipids reduced the abundance of Klebsiella and Blautia. These findings provide a foundation for understanding the functionality of SBO and FO as well as their potential application in synthesizing novel SLs to regulate intestinal microbiota.

Microbiome changes under enteral deprivation are dynamic and dependent on intestinal location

BACKGROUND

The microbiome has a pivotal role in intestinal health, and nutrition has a major role shaping its structure. Enteral deprivation, in which no oral/enteral nutrition is administered, is common in hospitalized/gastrointestinal patients. The dynamics that enteral deprivation exerts on the microbial community, specifically in the small intestine, are not well understood.

METHODS

Enteral deprivation was modeled with exclusive parenteral nutrition (EPN) mice. Mice were allocated to receive either EPN or saline and chow (control) and euthanized after 0, 2, 4, or 6 days. DNA was extracted from jejunum, ileum, and colon content. 16S sequencing was used to compare changes in microbial communities between groups. Functional pathways were predicted using Phylogenetic Investigation of Communities by Reconstruction of Unobserved States.

RESULTS

EPN-treated mice showed community changes throughout the intestine. Beta diversity in colon showed clear separation between the groups (Bray-Curtis, P < 0.001). Time-dependent dynamics were seen in ileal but not jejunal samples. Alpha diversity was lower in the colon of EPN mice compared with control/baseline mice (Chao1, P < 0.01) but not in ileum/jejunum. Progressive loss of single-taxon domination was seen, most notably in the small intestine. This was accompanied by increases/decreases in specific taxa. A clear separation was seen in the functional capacity of the community between fed and enterally deprived mice at the ileum and colon, which was observed early on.

CONCLUSIONS

Enteral deprivation disturbs the microbial community in a spatial and dynamic manner. There should be further focus on studying the effect of these changes on the host.

Effects of Human Milk Fat Substitutes on Lipid Metabolism in First-Weaned Rats

Although numerous studies indicate that formula-fed infants are more prone to obesity than breastfed ones, the underlying reasons have not been fully elucidated. This study aimed to determine the impact of human milk fat substitutes (HMFS) on the lipid metabolism of first-weaned Sprague Dawley rats. The findings revealed that administering HMFS did not affect the body weight of the rats (control: 298.38 ± 26.73 g, OPO (1,3-dioleic acid-2-palmitoyl triglyceride): 287.82 ± 19.85 g and HMFS: 302.31 ± 19.21 g), but it significantly decreased their body fat content (control: 28.70 ± 1.17 cm3, OPO: 22.51 ± 1.10 cm3 and HMFS: 14.90 ± 0.95 cm3) (p < 0.05). Lipidome analysis revealed that glycerophospholipid was the primary differentiating lipid present in the liver of HMFS-fed rats. The abundance of Bacteroides significantly increased in the intestine of HMFS-fed rats (p < 0.05), and their short-chain fatty acid (SCFA) content significantly increased (p < 0.05). The multi-omics correlation analysis established the "Bacteroidetes-SCFAs-Glycerophospholipid pathway" as a potential mechanism by which administering HMFS affects body fat buildup in first-weaned rats. Additionally, it was found that HMFS administration significantly promoted lipid metabolism in the rat liver at both the gene and protein levels (p < 0.05). These findings serve to underscore the nutritional benefits of HMFS for infants.

Current Insights Regarding Intestinal Failure-Associated Liver Disease (IFALD): A Narrative Review

Intestinal failure-associated liver disease (IFALD) is a spectrum of liver disease including cholestasis, biliary cirrhosis, steatohepatitis, and gallbladder disease in patients with intestinal failure (IF). The prevalence of IFALD varies considerably, with ranges of 40-60% in the pediatric population, up to 85% in neonates, and between 15-40% in the adult population. IFALD has a complex and multifactorial etiology; the risk factors can be parenteral nutrition-related or patient-related. Because of this, the approach to managing IFALD is multidisciplinary and tailored to each patient based on the etiology. This review summarizes the current knowledge on the etiology and pathophysiology of IFALD and examines the latest evidence regarding preventative measures, diagnostic approaches, and treatment strategies for IFALD and its associated complications.

Dietary glutamate enhances intestinal immunity by modulating microbiota and Th17/Treg balance-related immune signaling in piglets after lipopolysaccharide challenge

The purpose of this study was to explore the effects of glutamate on piglet growth performance and intestinal immunity function, and to further elucidate its mechanism. In a 2 × 2 factorial design involving immunological challenge (lipopolysaccharide (LPS) or saline) and diet (with or without glutamate), twenty-four piglets were randomly assigned to four groups, each with 6 replicates. Piglets were fed with a basal or glutamate diet for 21 d before being injected intraperitoneally with LPS or saline. Piglet's intestinal samples were collected 4 h after injection. Results showed that glutamate increased daily feed intake, average daily gain, villus length, villus area, and villus length to crypt depth ratio (V/C), and decreased the crypt depth (P < 0.05). Furthermore, glutamate increased the mRNA expression of forkhead box P3 (FOXP3), a signal transducer and activator of transcription 5 (STAT5) and transforming growth factor beta, while decreasing the mRNA expression of RAR-related orphan receptor c and STAT3. Glutamate increased interleukin-10 (IL-10) mRNA expression while decreasing the mRNA expression of IL-1β, IL-6, IL-8, IL-17, IL-21, and tumor necrosis factor-α. At the phylum level, glutamate increased the Actinobacteriota abundance and Firmicutes-to-Bacteroidetes ratio while decreasing Firmicutes abundance. At the genus level, glutamate improved the abundance of beneficial bacteria (e.g., Lactobacillus, Prevotellaceae-NK3B31-group, and UCG-005). Furthermore, glutamate increased the concentrations of short-chain fatty acids (SCFAs). Correlation analysis revealed that the intestinal microbiota is closely related to Th17/Treg balance-related index and SCFAs. Collectively, glutamate can improve piglet growth performance and intestinal immunity by modulating gut microbiota and Th17/Treg balance-related signaling pathways.

Remodelling of the intestinal ecosystem during caloric restriction and fasting

Benefits of fasting and caloric restriction on host metabolic health are well established, but less is known about the effects on the gut microbiome and how this impacts renewal of the intestinal mucosa. What has been repeatedly shown during fasting, however, is that bacteria utilising host-derived substrates proliferate at the expense of those relying on dietary substrates. Considering the increased recognition of the gut microbiome's role in maintaining host (metabolic) health, disentangling host-microbe interactions and establishing their physiological relevance in the context of fasting and caloric restriction is crucial. Such insights could aid in moving away from associations of gut bacterial signatures with metabolic diseases consistently reported in observational studies to potentially establishing causality. Therefore, this review aims to summarise what is currently known or still controversial about the interplay between fasting and caloric restriction, the gut microbiome and intestinal tissue physiology.

Nutritional modulation of the gut microbiome in allogeneic hematopoietic stem cell transplantation recipients

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) represents a potentially curative strategy for many oncological and non-oncological diseases, but it is associated with marked morbidity and mortality. The disruption of gut microbiota (GM) eubiosis has been linked to major allo-HSCT complications, including infections and acute graft vs. host disease (aGvHD), and correlates with mortality. This increasing knowledge on the role of the GM in the allo-HSCT procedure has led to fascinating ideas for modulating the intestinal ecosystem in order to improve clinical outcomes. Nutritional strategies, either by changing the route of nutritional supplementation or by administering specific molecules, are increasingly being considered as cost- and risk-effective methods of modulating the GM. Nutritional support has also emerged in the past several years as a key feature in supportive care for allo-HSCT recipients, and deterioration of nutritional status is associated with decreased overall survival and higher complication rates during treatment. Herein we provide a complete overview focused on nutritional modulation of the GM in allo-HSCT recipients. We address how pre transplant diet could affect GM composition and its ability to withstand the upsetting events occurring during transplantation. We also provide a complete overview on the influence of the route of nutritional administration on the intestinal ecosystem, with a particular focus on the comparison between enteral and parenteral nutrition (PN). Moreover, as mounting evidence are showing how specific components of post-transplant diet, such as lactose, could drastically shape the GM, we will also summarize the role of prebiotic supplementation in the modulation of the intestinal flora and in allo-HSCT outcomes.

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.

Herbal Extract Mixture Modulates Intestinal Antioxidative Capacity and Microbiota in Weaning Piglets

Recently, herbal extracts have been applied in multiple aspects, such as medicine and animal feed. Different compositions of herbal extract mixture (HEM) have various components and diverse functions. This study aimed to evaluate the effects of HEM (Lonicera japonica, Astragalus membranaceus, Eucommia folium, and Codonopsis pilosula) on intestinal antioxidant capacity and colonic microbiota in weaned pigs. A total of 18 piglets [Duroc × (Landrace × Yorkshire)] with the initial body weight of 5.99 ± 0.13 kg (weaned at 21 days) were randomly divided into two groups (n = 9): the control group (CON, basal diet) and the HEM treatment group (HEM, 1,000 mg/kg HEM + basal diet). The experiment period lasted for 14 days. Our results showed that dietary supplementation with HEM modulated the antioxidant capacity through decreasing the activity of superoxide dismutase (SOD) in the ileum and glutathione peroxidase (GSH-PX) in the serum, and decreasing the mRNA expression of Kelch like-ECH-associated protein 1 (Keap1) in the jejunum and the protein level of Keap1 in the ileum. Moreover, the HEM group modified the composition of colonic microbiota with affecting relative abundances of the Firmicutes and Bacteroidetes at the phylum level. Taken together, supplementation of HEM can regulate the antioxidant capacity and modify the composition of colonic bacteria in weaning piglets. This study provides new insights into the combination effects of herbal extracts on weaning piglets.

Fish oil-based lipid emulsion alleviates parenteral nutrition-associated liver diseases and intestinal injury in piglets

BACKGROUND

Thisstudy aimed to investigate the impact of fish oil-based lipid emulsion (FO) on enterohepatic injuries and intestinal microbiota in piglets of parenteral nutrition (PN).

METHODS

Newborn piglets were divided into three groups, including enteral diet (the controls), PN with 100% FO and PN with medium-chain triglyceride/long-chain triglyceride-based lipid emulsion (MCT/LCT) for 14 days. Serum biochemical indicators, hepatic and intestinal histology, and expression of genes associated with inflammation, oxidative stress, and lipid metabolism were measured. The bile acid (BA) profiles in serum and the taxonomic composition of the gut microbiome in different intestinal segments were analyzed.

RESULTS

Compared with MCT/LCT-piglets, FO reduced inflammation, promoted fatty acid oxidation, and decreased oxidative stress in the liver. In the intestine, FO decreased intestinal inflammation and intestinal permeability, leading to reduced lipopolysaccharide entry into the blood circulation relative to MCT/LCT-piglets. PN groups have dominant contents of Proteobacteria and Bacteroides, whereas the control group have Firmicutes at the phylum level. FO altered the taxonomic compositions of the gut microbiome in different segments, increased the relative abundance of Bacteroidaceae in ileum, and Rikenellaceae and Ruminococcaceae in the colon. FO treatment shifted BA composition ratio in serum and had a lower ratio of secondary BAs to primary BAs.

CONCLUSION

FO alleviates PNLAD and intestinal injury by regulating the homeostasis of BAs' enterohepatic circulation and altering microbiota composition in different intestinal segments.

Starvation and Its Effects on the Gut

There is growing awareness that intestinal dysfunction determines the clinical outcomes of situations as diverse as undernourished children in urban tropical slums and undernourished surgical patients in intensive care units. As experimental starvation in humans has only rarely been studied, and largely not using current biomedical research tools, we must draw inference from disparate clinical and experimental observations as to the derangements present in the starved gut. There is good evidence of intestinal atrophy and achlorhydria in starvation and severe undernutrition. Historical reports from concentration camps and conflict settings consistently reported a noncontagious phenomenon called "hunger diarrhea," but in settings where starved individuals are isolated from others (prisoners on hunger strike, anorexia nervosa) diarrhea is not a feature. Changes in intestinal permeability and absorption have been infrequently studied in experimental starvation; available data suggest that short-term starvation reduces sugar absorption but not permeability. Severe acute malnutrition in children is associated with severe changes in the intestinal mucosa. Experimental animal models may help explain some observations in humans. Starved rats develop a hypersecretory state and intestinal barrier defects. Starved pigs demonstrate prolongation of rotavirus diarrhea and reproduce some of the absorptive and barrier defects observed in malnourished children. However, there remains much to be learned about the effects of starvation on the gut. Given the high prevalence of undernutrition in hospitals and disadvantaged communities, the lack of attention to the interaction between undernutrition and gastrointestinal damage is surprising and needs to be corrected. Current sophisticated cellular and molecular techniques now provide the opportunity to create fresh understanding of gastrointestinal changes in pure undernutrition, using volunteer studies and samples from anorexia nervosa.

Nutrition and the gut microbiome during critical illness: A new insight of nutritional therapy

Changes in the microbiome in response to environmental influences can affect the overall health. Critical illness is considered one of the major environmental factors that can potentially influence the normal gut homeostasis. It is associated with pathophysiological effects causing damage to the intestinal microbiome. Alteration of intestinal microbial composition during critical illness may subsequently compromise the integrity of the intestinal epithelial barrier and intestinal mucosa absorptive function. Many factors can impact the microbiome of critically ill patients including ischemia, hypoxia and hypotension along with the iatrogenic effects of therapeutic agents and the lack of enteral feeds. Factors related to disease state and medication are inevitable and they are part of the intensive care unit (ICU) exposure. However, a nutritional intervention targeting gut microbiota might have the potential to improve clinical outcomes in the critically ill population given the extensive vascular and lymphatic links between the intestines and other organs. Although nutrition is considered an integral part of the treatment plan of critically ill patients, still the role of nutritional intervention is restricted to improve nitrogen balance. What is dismissed is whether the nutrients we provide are adequate and how they are processed and utilised by the host and the microbiota. Therefore, the goal of nutrition therapy during critical illness should be extended to provide good quality feeds with balanced macronutrient content to feed up the entire body including the microbiota and host cells. The main aim of this review is to examine the current literature on the effect of critical illness on the gut microbiome and to highlight the role of nutrition as a factor affecting the intestinal microbiome-host relationship during critical illness.

Trichinella spiralis infection ameliorated diet-induced obesity model in mice

Obesity is an increasingly prevalent disease worldwide, and genetic and environmental factors are known to regulate the development of obesity and associated metabolic diseases. Emerging studies indicate that innate and adaptive immune cell responses in adipose tissue play critical roles in the regulation of metabolic homeostasis. Parasitic helminths are the strongest natural inducers of type 2 inflammatory responses, and several studies have revealed that helminth infections inversely correlate with metabolic syndrome. Hence, this study investigated whether helminth infections could have preventative effects on high fat diet-induced obesity. Female C57BL/6 mice were maintained on either a low fat diet (LFD, 10% fat) or a high fat diet (HFD, 60% fat) for 6 weeks after Trichinella spiralis infection. The mice were randomly divided into four groups and were fed a normal diet, LFD, LFD after T. spiralis infection (Inf + LFD), a high fat diet (HFD), or HFD after T. spiralis infection (HFD + inf). All groups were assayed for body weight, food efficiency ratio (FER), total body weight gain (g)/total food intake amount (g) fat weight, and blood biochemical parameters. Our data indicate that the HFD + inf group significantly reduced body weight gain, fat mass, total cholesterol, and FER. Analysis of immune cell composition by flow cytometry revealed that T. spiralis promoted strong decreases in proinflammatory adipose macrophages (F4/80⁺CD11c⁺) and T cells. The alterations in microbiota from fecal samples of mice were analyzed, which showed that T. spiralis infection decreased the ratio of Firmicutes to Bacteriodetes, thereby restoring the previously increased ratio of Firmicutes to Bacteriodetes in HFD-fed mice. Moreover, elimination of T. spiralis retained the protective effects in the HFD-fed obese mice whereas flubendazole (FLBZ) treatment increased levels of the families Lachnospiraceae and Ruminococcaceae. In summary, we provided novel data suggesting that helminth infection protects against obesity and the protection was closely related to M2 macrophage proliferation, an inhibiting proinflammatory response. In addition, it alters the microbiota in the gut.

Does an Apple a Day Also Keep the Microbes Away? The Interplay Between Diet, Microbiota, and Host Defense Peptides at the Intestinal Mucosal Barrier

A crucial mechanism of intestinal defense includes the production and secretion of host defense peptides (HDPs). HDPs control pathogens and commensals at the intestinal interface by direct killing, by sequestering vital ions, or by causing bacterial cells to aggregate in the mucus layer. Accordingly, the combined activity of various HDPs neutralizes gut bacteria before reaching the mucosa and thus helps to maintain the homeostatic balance between the host and its microbes at the mucosal barrier. Defects in the mucosal barrier have been associated with various diseases that are on the rise in the Western world. These include metabolic diseases, such as obesity and type 2 diabetes, and inflammatory intestinal disorders, including ulcerative colitis and Crohn's disease, the two major entities of inflammatory bowel disease. While the etiology of these diseases is multifactorial, highly processed Western-style diet (WSD) that is rich in carbohydrates and fat and low in dietary fiber content, is considered to be a contributing lifestyle factor. As such, WSD does not only profoundly affect the resident microbes in the intestine, but can also directly alter HDP function, thereby potentially contributing to intestinal mucosal barrier dysfunction. In this review we aim to decipher the complex interaction between diet, microbiota, and HDPs. We discuss how HDP expression can be modulated by specific microbes and their metabolites as well as by dietary factors, including fibers, lipids, polyphenols and vitamins. We identify several dietary compounds that lead to reduced HDP function, but also factors that stimulate HDP production in the intestine. Furthermore, we argue that the effect of HDPs against commensal bacteria has been understudied when compared to pathogens, and that local environmental conditions also need to be considered. In addition, we discuss the known molecular mechanisms behind HDP modulation. We believe that a better understanding of the diet-microbiota-HDP interdependence will provide insights into factors underlying modern diseases and will help to identify potential dietary interventions or probiotic supplementation that can promote HDP-mediated intestinal barrier function in the Western gut.

Exogenous Secretin Improves Parenteral Nutrition-associated Liver Disease in Rats

OBJECTIVES

Intestinal failure-associated liver disease (IFALD) is a feared and life-threatening complication in neonates with intestinal failure (IF) receiving long-term total parenteral nutrition (TPN). This study aims to investigate the effect of exogenous secretin on liver pathology and hepatic function in a rat model of PN-associated liver disease (PNALD).

METHODS

Male Sprague-Dawley rats underwent right jugular venous catheterization to receive 14-day continuous TPN therapy. All rats were allocated into 3 groups: the Control group (n = 8) did not have surgery or TPN and was fed standard rat chow ad libitum; the TPN group (n = 8) underwent catheter insertion and TPN treatment; and the TPN/S group (n = 8) also underwent catheter insertion, TPN treatment, and exogenous secretin treatment (2.5 nmol · kg · day) daily. Fourteen days after initial surgery, we collected the animals' liver and blood samples for further test.

RESULTS

The TPN/S group had diminished direct bilirubin (TPN, 2.1 ± 0.7 μmol/L; TPN/S, 1.5 ± 0.2 μmol/L) and liver total bile acid levels (TPN, 144.5 ± 21.2 μmol/L; TPN/S, 123.4 ± 10.4 μmol/L) and improved histological outcomes compared with those in the TPN group. Exogenous secretin also enhanced the canalicular transporter (BSEP, 0.5-fold, P = 0.011) and inhibited the basolateral transporter (OSTA, -0.48-fold, P = 0.002; OSTB, -0.6-fold, P = 0.013) of liver bile acid.

CONCLUSIONS

In this animal model of PNALD, secretin may improve cholestasis by enhancing canalicular transport, inhibiting the basolateral export of liver bile acid, and eventually decreasing the total bile acid level in the liver. Exogenous secretin treatment may potentially prevent and treat IFALD in IF patients relying on long-term TPN therapy.

Different dietary lipid consumption affects the serum lipid profiles, colonic short chain fatty acid composition and the gut health of Sprague Dawley rats

Palm oil (PO), leaf lard oil (LO), rapeseed oil (RO), sunflower oil (SO), and linseed oil (LINO) are the five of the most typical dietary lipids, while few studies have explored and compared their influences on the serum lipid profiles, colonic short chain fatty acids (SCFAs) composition and colon health of Sprague Dawley (SD) rats. Results from the present work showed that PO and LO groups showed significantly higher serum TG and TC level compared with Ctrl group, whereas, the LDL-C/HDL-C and TC/HDL-C ratio were significantly lower in the RO, SO and LINO groups. Different dietary lipid consumption (15% of the normal diet) decreased the colonic SCFAs concentration. The saturated fatty acid (SFA) was negatively correlated, while unsaturated fatty acid (UFA)/SFA ratio was positively correlated, with colonic isobutyric acid concentration. The C18:2ω6 and ω3 fatty acids were positively correlated with colonic butyric acid and isovaleric acid concentration, respectively. Results also demonstrated that PO and LO could decrease the colon villus length and crypt depth, and led to colon injury, which might be due to their high SFAs content. Moreover, results suggested that PO and LO could specifically up-regulate the colon inflammation related gene expression levels and down-regulate the Muc2 expression levels, thus, imposing negative impact on the mucus layers. The present study could provide some information for nutritional evaluation about these dietary lipids.

Early downregulation of P-glycoprotein facilitates bacterial attachment to intestinal epithelial cells and thereby triggers barrier dysfunction in a rodent model of total parenteral nutrition

Intestinal barrier dysfunction is a major complication of total parenteral nutrition (TPN). Our preliminary study revealed that intestinal P-glycoprotein (P-gp) was significantly downregulated under TPN treatment followed by disruption of barrier function, and thus the significance of early downregulation of P-gp needs to be addressed. Herein, we report a pivotal role of P-gp in the development of intestinal barrier dysfunction under TPN. Functional suppression of P-gp may facilitate bacterial attachment to intestinal epithelial cells (IECs) and thereby induce degradation of tight junctions to trigger barrier dysfunction. By using a rat model of TPN, we found early downregulation of P-gp function in ileum after 3-day TPN, followed by disruption of barrier function after 7-day TPN. By using Escherichia coli (E. coli) k88 and DH5α as type strains, we found significantly increased bacterial attachment to IECs in TPN group compared to sham. By using Caco-2 cells as an IEC model in vitro, we found that functional suppression of P-gp remarkably facilitated bacterial attachment to Caco-2 cells, leading to subsequent disruption of intestinal barrier function. Of note, Occludin was significantly downregulated by bacterial attachment when P-gp was functionally suppressed. Mechanistically, changes on Occludin were attributed to enhanced protein degradation instead of suppressed protein translation. Despite the half-life of Occludin protein being unchanged by DH5α treatment alone, it was decreased by about 40% when P-gp was simultaneously suppressed. Taken together, our findings revealed that early downregulation of intestinal P-gp under TPN may be a potential therapeutic target to prevent the development of barrier dysfunction.

Mechanisms of Parenteral Nutrition-Associated Liver and Gut Injury

Parenteral nutrition (PN) has revolutionized the care of patients with intestinal failure by providing nutrition intravenously. Worldwide, PN remains a standard tool of nutrition delivery in neonatal, pediatric, and adult patients. Though the benefits are evident, patients receiving PN can suffer serious cholestasis due to lack of enteral feeding and sometimes have fatal complications from liver injury and gut atrophy, including PN-associated liver disease or intestinal failure-associated liver disease. Recent studies into gut-systemic cross talk via the bile acid-regulated farnesoid X receptor (FXR)-fibroblast growth factor 19 (FGF19) axis, gut microbial control of the TGR5-glucagon-like peptide (GLP) axis, sepsis, and role of prematurity of hepatobiliary receptors are greatly broadening our understanding of PN-associated injury. It has also been shown that the composition of ω-6/ω-3 polyunsaturated fatty acids given parenterally as lipid emulsions can variably drive damage to hepatocytes and cell integrity. This manuscript reviews the mechanisms for the multifactorial pathogenesis of liver disease and gut injury with PN and discusses novel ameliorative strategies.

The effect of ω-3 polyunsaturated fatty acids on the liver lipidome, proteome and bile acid profile: parenteral versus enteral administration

Parenteral nutrition (PN) is often associated with the deterioration of liver functions (PNALD). Omega-3 polyunsaturated fatty acids (PUFA) were reported to alleviate PNALD but the underlying mechanisms have not been fully unraveled yet. Using omics´ approach, we determined serum and liver lipidome, liver proteome, and liver bile acid profile as well as markers of inflammation and oxidative stress in rats administered either ω-6 PUFA based lipid emulsion (Intralipid) or ω-6/ω-3 PUFA blend (Intralipid/Omegaven) via the enteral or parenteral route. In general, we found that enteral administration of both lipid emulsions has less impact on the liver than the parenteral route. Compared with parenterally administered Intralipid, PN administration of ω-3 PUFA was associated with 1. increased content of eicosapentaenoic (EPA)- and docosahexaenoic (DHA) acids-containing lipid species; 2. higher abundance of CYP4A isoenzymes capable of bioactive lipid synthesis and the increased content of their potential products (oxidized EPA and DHA); 3. downregulation of enzymes involved CYP450 drug metabolism what may represent an adaptive mechanism counteracting the potential negative effects (enhanced ROS production) of PUFA metabolism; 4. normalized anti-oxidative capacity and 5. physiological BAs spectrum. All these findings may contribute to the explanation of ω-3 PUFA protective effects in the context of PN.

Proceedings of the 2017 ASPEN Research Workshop-Gastric Bypass: Role of the Gut

The goal of the National Institutes of Health-funded American Society for Parenteral and Enteral Nutrition 2017 research workshop (RW) "Gastric Bypass: Role of the Gut" was to focus on the exciting research evaluating gut-derived signals in modulating outcomes after bariatric surgery. Although gastric bypass surgery has undoubted positive effects, the mechanistic basis of improved outcomes cannot be solely explained by caloric restriction. Emerging data suggest that bile acid metabolic pathways, luminal contents, energy balance, gut mucosal integrity, as well as the gut microbiota are significantly modulated after bariatric surgery and may be responsible for the variable outcomes, each of which was rigorously evaluated. The RW served as a timely and novel academic meeting that brought together clinicians and researchers across the scientific spectrum, fostering a unique venue for interdisciplinary collaboration among investigators. It promoted engaging discussion and evolution of new research hypotheses and ideas, driving the development of novel ameliorative, therapeutic, and nonsurgical interventions targeting obesity and its comorbidities. Importantly, a critical evaluation of the current knowledge regarding gut-modulated signaling after bariatric surgery, potential pitfalls, and lacunae were thoroughly addressed.

Arginine accelerates intestinal health through cytokines and intestinal microbiota

Arginine supplementation improves intestinal damage and intestinal immunity, but the underlying mechanism of the effects of arginine supplementation on intestinal SIgA secretion is largely unknown. Therefore, this study was conducted to investigate the underlying pathway on the effects of arginine supplementation in secretory IgA (SIgA) production in mice. The results showed that 0.4% arginine supplementation promoted (P < 0.05) SIgA production in intestinal lumina and IgA⁺ plasma cell numbers in the ileum of mouse. Arginine supplementation significantly increased (P < 0.05) cytokines expression in mouse ileal associated with T cell-dependent and T cell-independent pathways of SIgA induction, including IL-5, IL-6, IL-13, transforming growth factor (TGF-)β2, TGF-β3, TGF-βR2, a proliferation-inducing ligand (APRIL), B cell-activating factor (BAFF), vasoactive intestinal peptide (VIP) receptor, and retinal dehydrogenases. Further study showed that 0.4% arginine supplementation markly decreased (P < 0.05) bacterial loads in mouse mesenteric lymph nodes and increased bacterial invasion into the mouse ileal wall, while supplementation of antibiotic abrogated the influence of arginine supplementation on SIgA secretion. Therefore, these data suggest that arginine supplementation might promote SIgA secretion through cytokines and intestinal microbiota might play an important role in SIgA secretion by arginine supplementation in the mouse intestine.

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.

Chronic stress-induced gut dysfunction exacerbates Parkinson's disease phenotype and pathology in a rotenone-induced mouse model of Parkinson's disease

Recent evidence provides support for involvement of the microbiota-gut-brain axis in Parkinson's disease (PD) pathogenesis. We propose that a pro-inflammatory intestinal milieu, due to intestinal hyper-permeability and/or microbial dysbiosis, initiates or exacerbates PD pathogenesis. One factor that can cause intestinal hyper-permeability and dysbiosis is chronic stress which has been shown to accelerate neuronal degeneration and motor deficits in Parkinsonism rodent models. We hypothesized that stress-induced intestinal barrier dysfunction and microbial dysbiosis lead to a pro-inflammatory milieu that exacerbates the PD phenotype in the low-dose oral rotenone PD mice model. To test this hypothesis, mice received unpredictable restraint stress (RS) for 12 weeks, and during the last six weeks mice also received a daily administration of low-dose rotenone (10 mg/kg/day) orally. The initial six weeks of RS caused significantly higher urinary cortisol, intestinal hyperpermeability, and decreased abundance of putative "anti-inflammatory" bacteria (Lactobacillus) compared to non-stressed mice. Rotenone alone (i.e., without RS) disrupted the colonic expression of the tight junction protein ZO-1, increased oxidative stress (N-tyrosine), increased myenteric plexus enteric glial cell GFAP expression and increased α-synuclein (α-syn) protein levels in the colon compared to controls. Restraint stress exacerbated these rotenone-induced changes. Specifically, RS potentiated rotenone-induced effects in the colon including: 1) intestinal hyper-permeability, 2) disruption of tight junction proteins (ZO-1, Occludin, Claudin1), 3) oxidative stress (N-tyrosine), 4) inflammation in glial cells (GFAP + enteric glia cells), 5) α-syn, 6) increased relative abundance of fecal Akkermansia (mucin-degrading Gram-negative bacteria), and 7) endotoxemia. In addition, RS promoted a number of rotenone-induced effects in the brain including: 1) reduced number of resting microglia and a higher number of dystrophic/phagocytic microglia as well as (FJ-C+) dying cells in the substantia nigra (SN), 2) increased lipopolysaccharide (LPS) reactivity in the SN, and 3) reduced dopamine (DA) and DA metabolites (DOPAC, HVA) in the striatum compared to control mice. Our findings support a model in which chronic stress-induced, gut-derived, pro-inflammatory milieu exacerbates the PD phenotype via a dysfunctional microbiota-gut-brain axis.

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.

Effects of Psychological, Environmental and Physical Stressors on the Gut Microbiota

Stress, a ubiquitous part of daily human life, has varied biological effects which are increasingly recognized as including modulation of commensal microorganisms residing in the gastrointestinal tract, the gut microbiota. In turn, the gut microbiota influences the host stress response and associated sequelae, thereby implicating the gut microbiota as an important mediator of host health. This narrative review aims to summarize evidence concerning the impact of psychological, environmental, and physical stressors on gut microbiota composition and function. The stressors reviewed include psychological stress, circadian disruption, sleep deprivation, environmental extremes (high altitude, heat, and cold), environmental pathogens, toxicants, pollutants, and noise, physical activity, and diet (nutrient composition and food restriction). Stressors were selected for their direct relevance to military personnel, a population that is commonly exposed to these stressors, often at extremes, and in combination. However, the selected stressors are also common, alone or in combination, in some civilian populations. Evidence from preclinical studies collectively indicates that the reviewed stressors alter the composition, function and metabolic activity of the gut microbiota, but that effects vary across stressors, and can include effects that may be beneficial or detrimental to host health. Translation of these findings to humans is largely lacking at present. This gap precludes concluding with certainty that transient or cumulative exposures to psychological, environmental, and physical stressors have any consistent, meaningful impact on the human gut microbiota. However, provocative preclinical evidence highlights a need for translational research aiming to elucidate the impact of stressors on the human gut microbiota, and how the gut microbiota can be manipulated, for example by using nutrition, to mitigate adverse stress responses.

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.

The intestinal microenvironment in sepsis

The gastrointestinal tract has long been hypothesized to function as "the motor" of multiple organ dysfunction syndrome. The gastrointestinal microenvironment is comprised of a single cell layer epithelia, a local immune system, and the microbiome. These three components of the intestine together play a crucial role in maintaining homeostasis during times of health. However, the gastrointestinal microenvironment is perturbed during sepsis, resulting in pathologic changes that drive both local and distant injury. In this review, we seek to characterize the relationship between the epithelium, gastrointestinal lymphocytes, and commensal bacteria during basal and pathologic conditions and how the intestinal microenvironment may be targeted for therapeutic gain in septic patients.

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.

The effect of aspartate supplementation on the microbial composition and innate immunity on mice

The study was conducted to investigate the changes of intestinal microbiota composition and innate immunity with different dietary dosages of aspartate (Asp) supplementation. Thirty-six female ICR mice were divided randomly to four groups and thereafter fed the basal diets (controls) or those supplemented with additional 0.5, 1.0 and 2.0% aspartate. After 2 week feeding, microbial composition in ileum and feces, gene expression of pro-inflammatory cytokine, and innate immune factors in ileum were determined. The ratio of Firmicutes: Bacteroidetes in ileum and feces decreased in 0.5 and 1.0% Asp-supplemented groups, whereas this ratio increased in feces in 2.0% Asp-supplemented group. Meanwhile, the gene expression of IL-17 and IFN-γ in ileum decreased in 1.0% Asp-supplemented group; the gene expression in ileum of Muc2 decreased in 0.5 and 1.0% Asp-supplemented groups. Dietary supplementation with 2.0% Asp enhanced the expression of pIgR and Crp1 as compared to the other three groups. The results indicated that dietary 1.0% Asp supplementation lowers the ratio of Firmicutes:Bacteroidetes, which affects the innate immunity by decreasing the gene expression of IL-17, IFN-γ, and Muc2 in ileum.

High Fat Diet Alters Gut Microbiota and the Expression of Paneth Cell-Antimicrobial Peptides Preceding Changes of Circulating Inflammatory Cytokines

Obesity is an established risk factor for many diseases including intestinal cancer. One of the responsible mechanisms is the chronic inflammation driven by obesity. However, it remains to be defined whether diet-induced obesity exacerbates the intestinal inflammatory status by cytokines produced in adipose tissue or the high fat diet first alters the gut microbiota and then drives intestinal inflammation. To address this question, we fed C57BL/6 mice with a high fat diet (HF, 60%) and sacrificed them sequentially after 8, 12, and 16 weeks, and then compositions of gut microbiota and expressions of antimicrobial peptides were determined. The compositions of gut microbiota were altered at 8 wk HF feeding, followed with reduced Paneth antimicrobial peptides lysozyme and Reg IIIγ after 12 and 16 wk HF feeding (p < 0.05), whereas elevations of circulating inflammatory cytokines IFNγ and TNF-α were observed until feeding a HF diet for 16 weeks (p < 0.05). These results indicated that high fat diet may stimulate intestinal inflammation via altering gut microbiota, and it occurs prior to the potential influence by circulating inflammatory cytokines. These findings emphasized the importance of microbiota, in addition to adipose tissue per se, in driving intestinal inflammation, which may thereafter promote intestinal tumorigenesis.

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.

Preserved Gut Microbial Diversity Accompanies Upregulation of TGR5 and Hepatobiliary Transporters in Bile Acid-Treated Animals Receiving Parenteral Nutrition

BACKGROUND

Parenteral nutrition (PN) is a lifesaving therapy but is associated with gut atrophy and cholestasis. While bile acids (BAs) can modulate intestinal growth via gut receptors, the gut microbiome likely influences gut proliferation and inflammation. BAs also regulate the bile salt export pump (BSEP) involved in cholestasis. We hypothesized that the BA receptor agonist oleanolic acid (OA) regulates gut TGR5 receptor and modulates gut microbiota to prevent PN-associated injury.

MATERIALS AND METHODS

Neonatal piglets were randomized to approximately 2 weeks of isocaloric enteral nutrition (EN), PN, or PN + enteral OA. Serum alanine aminotransferase, bilirubin, BAs, hepatic BSEP, gut TGR5, gut, liver morphology, and fecal microbiome utilizing 16S rRNA sequencing were evaluated. Kruskal-Wallis test, pairwise Mann-Whitney U test, and multilevel logistic regression analysis were performed.

RESULTS

PN support resulted in gut atrophy substantially prevented by OA. The median (interquartile range) for villous/crypt ratio was as follows: EN, 3.37 (2.82-3.80); PN, 1.73 (1.54-2.27); and OA, 2.89 (2.17-3.34; P = .006). Pairwise comparisons yielded P = .002 (EN vs PN), P = .180 (EN vs OA), P = .026 (PN vs OA). OA upregulated TGR5 and BSEP without significant improvement in serum bilirubin ( P = .095). A decreased microbial diversity and shift toward proinflammatory phylum Bacteroidetes were seen with PN, which was prevented by OA.

CONCLUSIONS

OA prevented PN-associated gut mucosal injury, Bacterioides expansion, and the decreased microbial diversity noted with PN. This study demonstrates a novel relationship among PN-associated gut dysfunction, BA treatment, and gut microbial changes.

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.

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.

Controversies in the Mechanism of Total Parenteral Nutrition Induced Pathology

Over 30,000 patients are permanently dependent on Total Parenteral Nutrition (TPN) for survival with several folds higher requiring TPN for a prolonged duration. Unfortunately, it can cause potentially fatal complications. TPN infusion results in impairment of gut mucosal integrity, enhanced inflammation, increased cytokine expression and trans-mucosal bacterial permeation. It also causes endotoxin associated down regulation of bile acid transporters and Parenteral Nutrition Associated Liver Disease (PNALD), which includes steatosis, disrupted glucose metabolism, disrupted lipid metabolism, cholestasis and liver failure. Despite multiple theories, its etiology and pathophysiology remains elusive and is likely multifactorial. An important cause for TPN related pathologies appears to be a disruption in the normal enterohepatic circulation due to a lack of feeding during such therapy. This is further validated by the fact that in clinical settings, once cholestasis sets in, its reversal occurs when a patient is receiving a major portion of calories enterally. There are several other postulated mechanisms including gut bacterial permeation predisposing to endotoxin associated down regulation of bile acid transporters. An additional potential mechanism includes toxicity of the TPN solution itself, such as lipid mediated hepatic toxicity. Prematurity, leading to a poor development of bile acid regulating nuclear receptors and transporters has also been implicated as a causative factor. This review presents the current controversies and research into mechanisms of TPN associated injury.

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.

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.

Alterations of gut barrier and gut microbiota in food restriction, food deprivation and protein-energy wasting

Increasing evidence shows that gut microbiota composition is related to changes of gut barrier function including gut permeability and immune function. Gut microbiota is different in obese compared to lean subjects, suggesting that gut microbes are also involved in energy metabolism and subsequent nutritional state. While research on gut microbiota and gut barrier has presently mostly focused on intestinal inflammatory bowel diseases and more recently on obesity and type 2 diabetes, this review aims at summarizing the present knowledge regarding the impact, in vivo, of depleted nutritional states on structure and function of the gut epithelium, the gut-associated lymphoid tissue (GALT), the gut microbiota and the enteric nervous system. It highlights the complex interactions between the components of gut barrier in depleted states due to food deprivation, food restriction and protein energy wasting and shows that these interactions are multidirectional, implying the existence of feedbacks.

Dietary L-glutamine supplementation modulates microbial community and activates innate immunity in the mouse intestine

This study was conducted to determine effects of dietary supplementation with 1 % L-glutamine for 14 days on the abundance of intestinal bacteria and the activation of intestinal innate immunity in mice. The measured variables included (1) the abundance of Bacteroidetes, Firmicutes, Lactobacillus, Streptococcus and Bifidobacterium in the lumen of the small intestine; (2) the expression of toll-like receptors (TLRs), pro-inflammatory cytokines, and antibacterial substances secreted by Paneth cells and goblet cells in the jejunum, ileum and colon; and (3) the activation of TLR4-nuclear factor kappa B (NF-κB), mitogen-activated protein kinases (MAPK), and phosphoinositide-3-kinases (PI3K)/PI3K-protein kinase B (Akt) signaling pathways in the jejunum and ileum. In the jejunum, glutamine supplementation decreased the abundance of Firmicutes, while increased mRNA levels for antibacterial substances in association with the activation of NF-κB and PI3K-Akt pathways. In the ileum, glutamine supplementation induced a shift in the Firmicutes:Bacteroidetes ratio in favor of Bacteroidetes, and enhanced mRNA levels for Tlr4, pro-inflammatory cytokines, and antibacterial substances participating in NF-κB and JNK signaling pathways. These results indicate that the effects of glutamine on the intestine vary with its segments and compartments. Collectively, dietary glutamine supplementation of mice beneficially alters intestinal bacterial community and activates the innate immunity in the small intestine through NF-κB, MAPK and PI3K-Akt signaling pathways.

Dietary arginine supplementation of mice alters the microbial population and activates intestinal innate immunity

Currently, little is known about the function of arginine in the homeostasis of the intestinal immune system. This study was conducted to test the hypothesis that dietary arginine supplementation may alter intestinal microbiota and innate immunity in mice. Mice were fed a basal diet (containing 0.93% l-arginine; grams per gram) or the basal diet supplemented with 0.5% l-arginine for 14 d. We studied the composition of intestinal microbiota, the activation of innate immunity, and the expression of toll-like receptors (Tlrs), proinflammatory cytokines, and antimicrobials in the jejunum, ileum, or colon of mice. Signal transduction pathway activation in the jejunum and ileum, including TLR4-nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), mitogen-activated protein kinase (MAPK), and phosphoinositide-3 kinase (PI3K)/PI3K-protein kinase B (Akt), was analyzed by Western blotting. Quantitative polymerase chain reaction analysis revealed that arginine supplementation induced (P < 0.05) a shift in the Firmicutes-to-Bacteroidetes ratio to favor Bacteroidetes in the jejunum (0.33 ± 0.04 vs. 1.0 ± 0.22) and ileum (0.20 ± 0.08 vs. 1.0 ± 0.27) compared with the control group. This finding coincided with greater (P < 0.05) activation of the innate immune system, including TLR signaling, as well as expression of proinflammatory cytokines, ​secretory immunoglobulin A, mucins, and Paneth antimicrobials in the jejunum and ileum. Finally, arginine supplementation reduced (P < 0.05) expression of the proteins for NF-κB, MAPK, and PI3K-Akt signaling pathways but activated (P < 0.05) p38 and c-Jun N-terminal protein kinase in the jejunum and the ileum, respectively. Collectively, dietary arginine supplementation of mice changes the intestinal microbiota, contributing to the activation of intestinal innate immunity through NF-κB, MAPK, and PI3K-phosphorylated Akt signaling pathways.

Non-alcoholic fatty liver disease, diet and gut microbiota

Non-alcoholic fatty liver disease (NAFLD) is a severe liver disease that is increasing in prevalence with the worldwide epidemic of obesity and its related insulin-resistance state. Evidence for the role of the gut microbiota in energy storage and the subsequent development of obesity and some of its related diseases is now well established. More recently, a new role of gut microbiota has emerged in NAFLD. The gut microbiota is involved in gut permeability, low-grade inflammation and immune balance, it modulates dietary choline metabolism, regulates bile acid metabolism and produces endogenous ethanol. All of these factors are molecular mechanisms by which the microbiota can induce NAFLD or its progression toward overt non-alcoholic steatohepatitis. Modification of the gut microbiota composition and/or its biochemical capacity by specific dietary or pharmacological interventions may advantageously affect host metabolism. Large-scale intervention trials, investigating the potential benefit of prebiotics and probiotics in improving cardiometabolic health in high-risk populations, are fervently awaited.

The gut-liver axis

PURPOSE OF REVIEW

The liver adaptively responds to extra-intestinal and intestinal inflammation. In recent years, the role of the autonomic nervous system, intestinal failure and gut microbiota has been investigated in the development of hepatic, intestinal and extra-intestinal disease.

RECENT FINDINGS

The autonomic nervous system can be stimulated via enteral fat leading to cholecystokinin release, stimulating receptors in the gut and in the brain. This promotes bowel integrity, dampening the inflammatory response to food antigens. Consensus exists that intravenously administered long-chain fatty acids can cause liver damage but randomized-controlled trials are lacking. Disruption of the enterohepatic circulation of bile salts can give rise to cholestasis and nonalcoholic fatty liver disease, which may progress to fibrosis and cirrhosis. Reduced intestinal availability of bile salts reduces stimulation of the farnesoid X receptor. This may induce hepatic bile salt overload and associated hepatotoxicity through reduced action of intestinal fibroblast growth factor 19. Evidence is put forward to suggest that the intestinal microbiota is associated with liver abnormalities.

SUMMARY

Enteral lipids reduce inflammation and liver damage during stress or systemic inflammation, whereas parenteral lipid is associated with liver damage. Maintaining the enterohepatic circulation of bile salts limits hepatic cholestasis through an farnesoid X receptor feedback pathway. Changes in gut microbiota composition may induce liver disease.

Nonalcoholic fatty liver disease: for better or worse, blame the gut microbiota?

Nonalcoholic fatty liver disease (NAFLD) is a major clinical consequence for people with obesity and metabolic syndrome and is also associated with enteral and parenteral nutrition. Early studies suggested that altered gut microbiota might contribute to obesity by affecting energy harvest from the diet and energy storage in the host. Recent evidence in humans as well as in animal models has linked gut microbiota to the development of NAFLD through the gut-liver axis. With bacterial overgrowth and increased intestinal permeability observed in patients with NAFLD and in animal models, gut-derived bacterial products such as endotoxin (lipopolysaccharide) and bacterial DNA are being delivered to the liver through the portal vein and then activate Toll-like receptors (TLRs), mainly TLR4 and TLR9, and their downstream cytokines and chemokines, leading to the development and progression of NAFLD. Given the limited data in humans, the role of gut microbiota in the pathogenesis of NAFLD is still open to discussion. Prebiotics and probiotics have been attempted to modify the microbiota as preventive or therapeutic strategies on this pathological condition. Their beneficial effects on NALFD have been demonstrated in animal models and limited human studies. However, prospective, appropriately powered, randomized, controlled clinical trials are needed to determine whether prebiotics and probiotics and other integrated strategies to modify intestinal microbiota are efficacious therapeutic modalities to treat NALFD.