Effect of milk formula protein content on intestinal barrier function in a porcine model of LBW neonates

Dopamine regulates colonic glial cell-derived neurotrophic factor secretion through cholinergic dependent and independent pathways

BACKGROUND AND PURPOSE

Glial cell-derived neurotrophic factor (GDNF) maintains gut homeostasis. Dopamine promotes GDNF release in astrocytes. We investigated the regulation by dopamine of colonic GDNF secretion.

EXPERIMENTAL APPROACH

D1 receptor knockout (D1 R-/- ) mice, adeno-associated viral 9-short hairpin RNA carrying D2 receptor (AAV9-shD2 R)-treated mice, 6-hydroxydopamine treated (6-OHDA) rats and primary enteric glial cells (EGCs) culture were used. Incubation fluid from colonic submucosal plexus and longitudinal muscle myenteric plexus were collected for GDNF and ACh measurements.

KEY RESULTS

D2 receptor-immunoreactivity (IR), but not D1 receptor-IR, was observed on EGCs. Both D1 receptor-IR and D2 receptor-IR were co-localized on cholinergic neurons. Low concentrations of dopamine induced colonic GDNF secretion in a concentration-dependent manner, which was mimicked by the D1 receptor agonist SKF38393, inhibited by TTX and atropine and eliminated in D1 R-/- mice. SKF38393-induced colonic ACh release was absent in D1 R-/- mice. High concentrations of dopamine suppressed colonic GDNF secretion, which was mimicked by the D2 receptor agonist quinpirole, and absent in AAV-shD2 R-treated mice. Quinpirole decreased GDNF secretion by reducing intracellular Ca2+ levels in primary cultured EGCs. Carbachol ( ACh analogue) promoted the release of GDNF. Quinpirole inhibited colonic ACh release, which was eliminated in the AAV9-shD2 R-treated mice. 6-OHDA treated rats with low ACh and high dopamine content showed decreased GDNF content and increased mucosal permeability in the colon.

CONCLUSION AND IMPLICATIONS

Low concentrations of dopamine promote colonic GDNF secretion via D1 receptors on cholinergic neurons, whereas high concentrations of dopamine inhibit GDNF secretion via D2 receptors on EGCs and/or cholinergic neurons.

The enteric nervous system

Of all the organ systems in the body, the gastrointestinal tract is the most complicated in terms of the numbers of structures involved, each with different functions, and the numbers and types of signaling molecules utilized. The digestion of food and absorption of nutrients, electrolytes, and water occurs in a hostile luminal environment that contains a large and diverse microbiota. At the core of regulatory control of the digestive and defensive functions of the gastrointestinal tract is the enteric nervous system (ENS), a complex system of neurons and glia in the gut wall. In this review, we discuss 1) the intrinsic neural control of gut functions involved in digestion and 2) how the ENS interacts with the immune system, gut microbiota, and epithelium to maintain mucosal defense and barrier function. We highlight developments that have revolutionized our understanding of the physiology and pathophysiology of enteric neural control. These include a new understanding of the molecular architecture of the ENS, the organization and function of enteric motor circuits, and the roles of enteric glia. We explore the transduction of luminal stimuli by enteroendocrine cells, the regulation of intestinal barrier function by enteric neurons and glia, local immune control by the ENS, and the role of the gut microbiota in regulating the structure and function of the ENS. Multifunctional enteric neurons work together with enteric glial cells, macrophages, interstitial cells, and enteroendocrine cells integrating an array of signals to initiate outputs that are precisely regulated in space and time to control digestion and intestinal homeostasis.

Distinct Gut Microbiome Induced by Different Feeding Regimes in Weaned Piglets

It is well accepted that the gut microbiota of breast-fed (BF) and formula-fed (FF) infants are significantly different. However, there is still a limited number of studies comparing the gut microbiota of BF and FF piglets, despite increasing numbers of FF piglets in the modern pig industry. The present study identified the differences in gut microbiota composition between BF- and FF-weaned Rongchang piglets at 30 days old, using pair-end sequencing on the Illumina HiSeq 2500 platform. The BF piglets had lower microbiota diversities than FF piglets (p < 0.05), and the community structures were well clustered as a result of each feeding pattern. Firmicutes and Bacteroidetes represented the most dominant phyla, and Ruminococcus, Prevotella, and Gemmiger were prominent genera in all piglets. Ruminococcus, Prevotella, Oscillospira, Eubacterium, Gemmiger, Dorea, and Lactobacillus populations were significantly higher, while Treponema and Coprococcus were significantly lower in BF piglets compared to FF piglets (p < 0.05). The metabolism pathways in the BF piglets were significantly different from FF piglets, which included carbohydrate and amino acid metabolism (p < 0.05). In addition, the top 10 abundance of microbiota were more or less significantly associated with the two phenotypes (p < 0.05). Collectively, these findings provide probable explanations for the importance of BF in neonates and support a theoretical basis for feeding regimes in indigenous Chinese piglets.

Feeding mode influences dynamic gut microbiota signatures and affects susceptibility to anti-CD3 mAb-induced intestinal injury in neonatal mice

Feeding modes influence the gut microbiome, immune system, and intestinal barrier homeostasis in neonates; how feeding modes impact susceptibility to neonatal gastrointestinal (GI) diseases is still uncertain. Here, we investigated the impact of dam feeding (DF) and formula feeding (FF) on features of the gut microbiome and physiological inflammation during the first 2 days of postnatal development and on the susceptibility to intestinal injury related to the inflammatory state in neonatal mouse pups. 16S rRNA sequencing data revealed microbiome changes, lower α-diversity, and a distinct pattern of β-diversity including expansion of f_Enterobacteriaceae and f_Enterococcaceae in the ileum of FF pups compared with DF pups by postnatal day (P)2. Together with gut dysbiosis, the FF cohort also had greater ileal mucosa physiological inflammatory activity compared with DF pups by P2 but maintained normal histological features. Interestingly, FF but not DF mouse pups developed necrotizing enterocolitis (NEC)-like intestinal injury within 24 h after anti-CD3 mAb treatment, suggesting that FF influences the susceptibility to intestinal injury in neonates. We further found that NEC-like incidence in anti-CD3 mAb-treated FF neonatal pups was attenuated by antibiotic treatment. Collectively, our data suggest that FF predisposes mouse pups to anti-CD3 mAb-induced intestinal injury due to abnormal f_Enterobacteriaceae and f_Enterococcaceae colonization. These findings advance our understanding of FF-associated microbial colonization and intestinal inflammation, which may help inform the development of new therapeutic approaches to GI diseases like NEC in infants.NEW & NOTEWORTHY This report shows that a feeding mode profoundly affects gut colonization in neonatal mice. Furthermore, our results demonstrate that formula feeding predisposes mouse pups to anti-CD3 mAb-induced necrotizing enterocolitis (NEC)-like intestinal injury upon inadequate microbial colonization. The study suggests the role of the combined presence of formula feeding-associated dysbiosis and mucosal inflammation in the pathogenesis of NEC and provides a new mouse model to study this disease.

Neonatal Diet Impacts the Large Intestine Luminal Metabolome at Weaning and Post-Weaning in Piglets Fed Formula or Human Milk

The impact of human milk (HM) or dairy milk-based formula (MF) on the large intestine’s metabolome was not investigated. Two-day old male piglets were randomly assigned to HM or MF diet (n = 26/group), from postnatal day (PND) 2 through 21 and weaned to a solid diet until PND 51. Piglets were euthanized at PND 21 and PND 51, luminal contents of the cecum, proximal (PC) and distal colons (DC), and rectum were collected and subjected to metabolomics analysis. Data analyses were performed using Metaboanalyst. In comparison to MF, the HM diet resulted in higher levels of fatty acids in the lumen of the cecum, PC, DC, and rectum at PND 21. Glutamic acid was greater in the lumen of cecum, PC, and DC relative to the MF group at PND 21. Also, spermidine was higher in the DC and rectal contents of HM relative to MF at PND 21. MF diet resulted in greater abundances of amino acids in the cecal lumen relative to HM diet at PND 21. Additionally, several sugar metabolites were higher in various regions of the distal gut of MF fed piglets relative to HM group at PND 21. In contrast, at PND 51, in various regions there were higher levels of erythritol, maltotriose, isomaltose in HM versus MF fed piglets. This suggests a post weaning shift in sugar metabolism that is impacted by neonatal diet. The data also suggest that infant diet type and host-microbiota interactions likely influence the lower gut metabolome.

Changes of the glutathione redox system during the weaning transition in piglets, in relation to small intestinal morphology and barrier function

Background

Weaning is known to result in barrier dysfunction and villus atrophy in the immediate post-weaning phase, and the magnitude of these responses is hypothesized to correlate with changes in the glutathione (GSH) redox system. Therefore, these parameters were simultaneously measured throughout the weaning phase, in piglets differing in birth weight category and weaning age, as these pre-weaning factors are important determinants for the weaning transition. Low birth weight (LBW) and normal birth weight (NBW) littermates were assigned to one of three weaning treatments; i.e. weaning at 3 weeks of age (3w), weaning at 4 weeks of age (4w) and removal from the sow at 3 d of age and fed a milk replacer until weaning at 3 weeks of age (3d3w). For each of these treatments, six LBW and six NBW piglets were euthanized at 0, 2, 5, 12 or 28 d post-weaning piglets, adding up 180 piglets.

Results

Weaning increased the glutathione peroxidase activity on d 5 post-weaning in plasma, and duodenal and jejunal mucosa. Small intestinal glutathione-S-transferase activity gradually increased until d 12 post-weaning, and this was combined with a progressive rise of mucosal GSH up till d 12 post-weaning. Oxidation of the GSH redox status (GSH/GSSG E_h) was only observed in the small intestinal mucosa of 3d3w weaned piglets at d 5 post-weaning. These piglets also demonstrated increased fluorescein isothiocyanate dextran (FD4) and horseradish peroxidase fluxes in the duodenum and distal jejunum during the experiment, and specifically demonstrated increased FD4 fluxes at d 2 to d 5 post-weaning. On the other hand, profound villus atrophy was observed during the weaning transition for all weaning treatments. Finally, LBW and NBW piglets did not demonstrate notable differences in GSH redox status, small intestinal barrier function and histo-morphology throughout the experiment.

Conclusion

Although moderate changes in the GSH redox system were observed upon weaning, the GSH redox status remained at a steady state level in 3w and 4w weaned piglets and was therefore not associated with weaning induced villus atrophy. Conversely, 3d3w weaned piglets demonstrated GSH redox imbalance in the small intestinal mucosa, and this co-occurred with a temporal malfunction of their intestinal barrier function.

Bovine dairy complex lipids improve in vitro measures of small intestinal epithelial barrier integrity

Appropriate intestinal barrier maturation is essential for absorbing nutrients and preventing pathogens and toxins from entering the body. Compared to breast-fed infants, formula-fed infants are more susceptible to barrier dysfunction-associated illnesses. In infant formula dairy lipids are usually replaced with plant lipids. We hypothesised that dairy complex lipids improve in vitro intestinal epithelial barrier integrity. We tested milkfat high in conjugated linoleic acid, beta serum (SureStart™Lipid100), beta serum concentrate (BSC) and a ganglioside-rich fraction (G600). Using Caco-2 cells as a model of the human small intestinal epithelium, we analysed the effects of the ingredients on trans-epithelial electrical resistance (TEER), mannitol flux, and tight junction protein co-localisation. BSC induced a dose-dependent improvement in TEER across unchallenged cell layers, maintained the co-localisation of tight junction proteins in TNFα-challenged cells with increased permeability, and mitigated the TEER-reducing effects of lipopolysaccharide (LPS). G600 also increased TEER across healthy and LPS-challenged cells, but it did not alter the co-location of tight junction proteins in TNFα-challenged cells. SureStart™Lipid100 had similar TEER-increasing effects to BSC when added at twice the concentration (similar lipid concentration). Ultimately, this research aims to contribute to the development of infant formulas supplemented with dairy complex lipids that support infant intestinal barrier maturation.

Personalizing protein nourishment

Proteins are not equally digestible-their proteolytic susceptibility varies by their source and processing method. Incomplete digestion increases colonic microbial protein fermentation (putrefaction), which produces toxic metabolites that can induce inflammation in vitro and have been associated with inflammation in vivo. Individual humans differ in protein digestive capacity based on phenotypes, particularly disease states. To avoid putrefaction-induced intestinal inflammation, protein sources, and processing methods must be tailored to the consumer's digestive capacity. This review explores how food processing techniques alter protein digestibility and examines how physiological conditions alter digestive capacity. Possible solutions to improving digestive function or matching low digestive capacity with more digestible protein sources are explored. Beyond the ileal digestibility measurements of protein digestibility, less invasive, quicker and cheaper techniques for monitoring the extent of protein digestion and fermentation are needed to personalize protein nourishment. Biomarkers of protein digestive capacity and efficiency can be identified with the toolsets of peptidomics, metabolomics, microbial sequencing and multiplexed protein analysis of fecal and urine samples. By monitoring individual protein digestive function, the protein component of diets can be tailored via protein source and processing selection to match individual needs to minimize colonic putrefaction and, thus, optimize gut health.

Milk Fat Globule Membrane Supplementation in Formula Modulates the Neonatal Gut Microbiome and Normalizes Intestinal Development

Breast milk has many beneficial properties and unusual characteristics including a unique fat component, termed milk fat globule membrane (MFGM). While breast milk yields important developmental benefits, there are situations where it is unavailable resulting in a need for formula feeding. Most formulas do not contain MFGM, but derive their lipids from vegetable sources, which differ greatly in size and composition. Here we tested the effects of MFGM supplementation on intestinal development and the microbiome as well as its potential to protect against Clostridium difficile induced colitis. The pup-in-a-cup model was used to deliver either control or MFGM supplemented formula to rats from 5 to 15 days of age; with mother’s milk (MM) reared animals used as controls. While CTL formula yielded significant deficits in intestinal development as compared to MM littermates, addition of MFGM to formula restored intestinal growth, Paneth and goblet cell numbers, and tight junction protein patterns to that of MM pups. Moreover, the gut microbiota of MFGM and MM pups displayed greater similarities than CTL, and proved protective against C. difficile toxin induced inflammation. Our study thus demonstrates that addition of MFGM to formula promotes development of the intestinal epithelium and microbiome and protects against inflammation.

A mixture of milk and vegetable lipids in infant formula changes gut digestion, mucosal immunity and microbiota composition in neonatal piglets

PURPOSE

Although composition of infant formula has been significantly improved during the last decade, major differences with the composition and structure of breast milk still remain and might affect nutrient digestion and gut biology. We hypothesized that the incorporation of dairy fat in infant formulas could modify their physiological impacts by making their composition closer to that of human milk. The effect of milk fat and milk fat globule membrane (MFGM) fragments in infant formulas on gut digestion, mucosal immunity and microbiota composition was evaluated.

METHODS

Three formulas containing either (1) vegetable lipids stabilized only by proteins (V-P), (2) vegetable lipids stabilized by a mixture of proteins and MFGM fragments (V-M) and (3) a mixture of milk and vegetable lipids stabilized by a mixture of proteins and MFGM fragments (M-M) were automatically distributed to 42 newborn piglets until slaughter at postnatal day (PND) 7 or 28, and compared to a fourth group of sow's suckling piglets (SM) used as a breast-fed reference.

RESULTS

At both PND, casein and β-lactoglobulin digestion was reduced in M-M proximal jejunum and ileum contents compared to V-P and V-M ones leading to more numerous β-Cn peptides in M-M contents. The IFNγ cytokine secretion of ConA-stimulated MLN cells from M-M piglets tended to be higher than in V-P ones at PND 7 and PND 28 and was closer to that of SM piglets. No dietary treatment effect was observed on IL-10 MLN cell secretion. Changes in faecal microbiota in M-M piglets resulted in an increase in Proteobacteria and Bacteroidetes and a decrease in Firmicutes phyla compared to V-P ones. M-M piglets showed higher abundances of Parabacteroides, Escherichia/Shigella and Klebsiella genus.

CONCLUSIONS

The incorporation of both milk fat and MFGM fragments in infant formula modifies protein digestion, the dynamic of the immune system maturation and the faecal microbiota composition.

Critical review evaluating the pig as a model for human nutritional physiology

The present review examines the pig as a model for physiological studies in human subjects related to nutrient sensing, appetite regulation, gut barrier function, intestinal microbiota and nutritional neuroscience. The nutrient-sensing mechanisms regarding acids (sour), carbohydrates (sweet), glutamic acid (umami) and fatty acids are conserved between humans and pigs. In contrast, pigs show limited perception of high-intensity sweeteners and NaCl and sense a wider array of amino acids than humans. Differences on bitter taste may reflect the adaptation to ecosystems. In relation to appetite regulation, plasma concentrations of cholecystokinin and glucagon-like peptide-1 are similar in pigs and humans, while peptide YY in pigs is ten to twenty times higher and ghrelin two to five times lower than in humans. Pigs are an excellent model for human studies for vagal nerve function related to the hormonal regulation of food intake. Similarly, the study of gut barrier functions reveals conserved defence mechanisms between the two species particularly in functional permeability. However, human data are scant for some of the defence systems and nutritional programming. The pig model has been valuable for studying the changes in human microbiota following nutritional interventions. In particular, the use of human flora-associated pigs is a useful model for infants, but the long-term stability of the implanted human microbiota in pigs remains to be investigated. The similarity of the pig and human brain anatomy and development is paradigmatic. Brain explorations and therapies described in pig, when compared with available human data, highlight their value in nutritional neuroscience, particularly regarding functional neuroimaging techniques.

Developmental Origins of Health and Disease in swine: implications for animal production and biomedical research

The concept of Developmental Origins of Health and Disease (DOHaD) addresses, from a large set of epidemiological evidences in human beings and translational studies in animal models, both the importance of genetic predisposition and the determinant role of maternal nutrition during pregnancy on adult morphomics and homeostasis. Compelling evidences suggest that both overnutrition and undernutrition may modify the intrauterine environment of the conceptus and may alter the expression of its genome and therefore its phenotype during prenatal and postnatal life. In fact, the DOHaD concept is an extreme shift in the vision of the factors conditioning adult phenotype and supposes a drastic change from a gene-centric perspective, only modified by lifestyle and nutritional strategies during juvenile development and adulthood, to a more holistic approach in which environmental, parental, and prenatal conditions are strongly determining postnatal development and homeostasis. The implications of DOHaD are profound in all the mammalian species and the present review summarizes current knowledge on causes and consequences of DOHaD in pigs, both for meat production and as a well-recognized model for biomedicine research.

Stress and the commensal microbiota: importance in parturition and infant neurodevelopment

The body is colonized by an enormous array of microbes that are collectively called the microbiota. During quiescent periods, microbial communities within the gut are relatively resistant to change. However, several factors that disrupt homeostasis can also significantly change gut microbial community structure. One factor that has been shown to change the composition of the gut microbiota is exposure to psychological stressors. Studies demonstrate that the commensal microbiota are involved in stressor-induced immunomodulation, but other biological effects are not yet known. This review discusses emerging evidence that the microbiota can impact the brain and behavior and indicates that stressor-induced alterations in the composition of gut microbial communities contribute to stressor-induced behavioral changes. This review will also discuss the evidence that such effects are most evident early in life, where both stress and the microbiota have been linked to birth outcomes, such as prematurity, and neurodevelopment. When considered together, a paradigm emerges in which stressor-induced alterations in commensal microbial populations significantly impact parturition and infant neurodevelopment.

The anti-inflammatory potential of a moderately hydrolysed casein and its 5 kDa fraction in in vitro and ex vivo models of the gastrointestinal tract

Bioactive peptides from milk can impart a wide range of physiological benefits without the allergies and intolerance associated with the consumption of whole milk.

Early maternal separation induces alterations of colonic epithelial permeability and morphology

BACKGROUND

Early maternal separation could lead to significant intestinal barrier and epithelial dysfunction. However, the exact mechanism remains to be elucidated and need to be investigated.

METHODS

Neonatal C57BL/6 mice were subjected to maternal separation: Maternal separation (MS) daily 3 h between postnatal day (PND) 5-9, single separation (SS) 3 h on PND 9 and no separation (NS). Colon and ileum permeability was measured by Ussing chamber. Severity of morphological changes in the colon was evaluated by blinded grading of histological stained sections.

RESULTS

Trans-epithelial resistance of colon and ileum did not change indicating that the tissues remained intact during the course of the experiment. Permeability of trans-cellular tracer Horseradish peroxidase (HRP) was significantly increased in the colon of MS compared to SS and NS (p < 0.05 for SS and p < 0.001 for NS), but there was no difference in para-cellular permeability of fluorescein isothiocyanate-conjugated dextran (FD4). However, there was no change in permeability of both HRP and FD4 in the ileum. MS and SS groups had marked intestinal epithelium morphology changes in comparison to controls (p < 0.05).

CONCLUSION

These preliminary observations indicate that neonatal maternal separation increases colonic trans-cellular permeability. This increase may be caused by the change of the transmural colonic morphology. The underlying mechanism is unknown and further investigation is necessary as it is of relevance to the development of early intestinal diseases such as necrotizing enterocolitis.

A high-protein formula increases colonic peptide transporter 1 activity during neonatal life in low-birth-weight piglets and disturbs barrier function later in life

Dietary peptides are absorbed along the intestine through peptide transporter 1 (PepT-1) which is highly responsive to dietary protein level. PepT-1 is also involved in gut homeostasis, both initiating and resolving inflammation. Low-birth-weight (LBW) neonates are routinely fed a high-protein (HP) formula to enhance growth. However, the influence of this nutritional practice on PepT-1 activity is unknown. Intestinal PepT-1 activity was compared in normal-birth-weight (NBW) and LBW piglets. The effect of HP v. normal-protein (NP) formula feeding on PepT-1 activity and gut homeostasis in LBW piglets was evaluated, during the neonatal period and in adulthood. Flux of cephalexin (CFX) across the tissue mounted in Ussing chambers was used as an indicator of PepT-1 activity. CFX flux was greater in the ileum, but not jejunum or colon, of LBW than NBW piglets during the neonatal period. When LBW piglets were formula-fed, the HP formula increased colonic CFX during the 1st week of life. Later in life, intestinal CFX fluxes and barrier function were similar whether LBW pigs had been fed NP or HP formula. However, colonic permeability of HP- but not NP-fed pigs increased when luminal pH was brought to 6·0. The formyl peptide N-formyl methionyl-leucyl-phenylalanine conferred colonic barrier protection in HP-fed piglets. Heat shock protein 27 levels in the colonic mucosa of HP-fed LBW pigs correlated with the magnitude of response to the acidic challenge. In conclusion, feeding a HP formula enhanced colonic PepT-1 activity in LBW pig neonates and increased sensitivity of the colon to luminal stress in adulthood.

Increased gut permeability and bacterial translocation after chronic chlorpyrifos exposure in rats

The epithelium's barrier function is crucial for maintaining homeostasis and preventing the passage of food antigens and luminal bacteria. This function is essentially subserved by tight junctions (TJs), multiprotein complexes located in the most apical part of the lateral membrane. Some gastrointestinal disease states are associated with elevated intestinal permeability to macromolecules. In a study on rats, we determined the influence of chronic, daily ingestion of chlorpyrifos (CPF, a pesticide that crosses the placental barrier) during pre- and postnatal periods on intestinal permeability and TJ characteristics in the pups. Fluorescein isothiocyanate (FITC)-dextran was used as a marker of paracellular transport and mucosal barrier dysfunction. Pups were gavaged with FITC-dextran solution and blood samples were collected every 30 min for 400 min and analyzed spectrofluorimetrically. At sacrifice, different intestinal segments were resected and prepared for analysis of the transcripts (qPCR) and localization (using immunofluorescence) of ZO-1, occludin and claudins (scaffolding proteins that have a role in the constitution of TJs). In rats that had been exposed to CPF in utero and after birth, we observed a progressive increase in FITC-dextran passage across the epithelial barrier from 210 to 325 min at day 21 after birth (weaning) but not at day 60 (adulthood). At both ages, there were significant changes in intestinal TJ gene expression, with downregulation of ZO-1 and occludin and upregulation of claudins 1 and 4. In some intestinal segments, there were changes in the cellular localization of ZO-1 and claudin 4 immunostaining. Lastly, bacterial translocation to the spleen was also observed. The presence of CPF residues in food may disturb epithelial homeostasis in rats. Changes in TJ protein expression and localization may be involved in gut barrier dysfunction in this model. Uncontrolled passage of macromolecules and bacteria across the intestinal epithelium may be a risk factor for digestive inflammatory diseases.

Supplementing formula-fed piglets with a low molecular weight fraction of bovine colostrum whey results in an improved intestinal barrier

To test the hypothesis that a low molecular weight fraction of colostral whey could affect the morphology and barrier function of the small intestine, 30 3-d-old piglets (normal or low birth weight) were suckled (n = 5), artificially fed with milk formula (n = 5), or artificially fed with milk formula with a low molecular weight fraction of colostral whey (n = 5) until 10 d of age. The small intestine was sampled for histology (haematoxylin and eosin stain; anti-KI67 immunohistochemistry) and enzyme activities (aminopeptidase A, aminopeptidase N, dipeptidylpeptidase IV, lactase, maltase, and sucrase). In addition, intestinal permeability was evaluated via a dual sugar absorption test and via the measurement of occludin abundance. Artificially feeding of piglets reduced final BW (P < 0.001), villus height (P < 0.001), lactase (P < 0.001), and dipeptidylpeptidase IV activities (P < 0.07), whereas crypt depth (P < 0.001) was increased. No difference was observed with regard to the permeability measurements when comparing artificially fed with naturally suckling piglets. Supplementing piglets with the colostral whey fraction did not affect BW, enzyme activities, or the outcome of the dual sugar absorption test. On the contrary, the small intestines of supplemented piglets had even shorter villi (P = 0.001) than unsupplemented piglets and contained more occludin (P = 0.002). In conclusion, at 10 d of age, no differences regarding intestinal morphology and permeability measurements were observed between the 2 BW categories. In both weight categories, the colostral whey fraction affected the morphology of the small intestine but did not improve the growth performances or the in vivo permeability. These findings should be acknowledged when developing formulated milk for neonatal animals with the aim of improving the performance of low birth weight piglets.

Reprint of: Role of enteric neurotransmission in host defense and protection of the gastrointestinal tract

Host defense is a vital role played by the gastrointestinal tract. As host to an enormous and diverse microbiome, the gut has evolved an elaborate array of chemical and physicals barriers that allow the digestion and absorption of nutrients without compromising the mammalian host. The control of such barrier functions requires the integration of neural, humoral, paracrine and immune signaling, involving redundant and overlapping mechanisms to ensure, under most circumstances, the integrity of the gastrointestinal epithelial barrier. Here we focus on selected recent developments in the autonomic neural control of host defense functions used in the protection of the gut from luminal agents, and discuss how the microbiota may potentially play a role in enteric neurotransmission. Key recent findings include: the important role played by subepithelial enteric glia in modulating intestinal barrier function, identification of stress-induced mechanisms evoking barrier breakdown, neural regulation of epithelial cell proliferation, the role of afferent and efferent vagal pathways in regulating barrier function, direct evidence for bacterial communication to the enteric nervous system, and microbial sources of enteric neurotransmitters. We discuss these new and interesting developments in our understanding of the role of the autonomic nervous system in gastrointestinal host defense.

Role of enteric neurotransmission in host defense and protection of the gastrointestinal tract

Host defense is a vital role played by the gastrointestinal tract. As host to an enormous and diverse microbiome, the gut has evolved an elaborate array of chemical and physicals barriers that allow the digestion and absorption of nutrients without compromising the mammalian host. The control of such barrier functions requires the integration of neural, humoral, paracrine and immune signaling, involving redundant and overlapping mechanisms to ensure, under most circumstances, the integrity of the gastrointestinal epithelial barrier. Here we focus on selected recent developments in the autonomic neural control of host defense functions used in the protection of the gut from luminal agents, and discuss how the microbiota may potentially play a role in enteric neurotransmission. Key recent findings include: the important role played by subepithelial enteric glia in modulating intestinal barrier function, identification of stress-induced mechanisms evoking barrier breakdown, neural regulation of epithelial cell proliferation, the role of afferent and efferent vagal pathways in regulating barrier function, direct evidence for bacterial communication to the enteric nervous system, and microbial sources of enteric neurotransmitters. We discuss these new and interesting developments in our understanding of the role of the autonomic nervous system in gastrointestinal host defense.

Long term effects of pre- and early postnatal nutrition and environment on the gut

The Developmental Origins of Health and Disease hypothesis formulated in the early 1990 s has stimulated research on long-term effects of early nutrition and environment over the last decades. Long-term is understood in this review as physiologically relevant periods such as after weaning, around sexual maturity, and in adulthood, as opposed to early developmental periods. The small and large intestines as targets for the study of long-term effects have received little attention until recent years and the stomach has been considered very rarely. Data have accumulated for laboratory animal models but they are still scarce in the swine species. Following the epidemics of metabolic diseases and obesity in western countries, experimental evidence has been published showing that nutritional factors, including energy, fat and fatty acids, protein, and micronutrients impact various facets of gut function. These include alterations in intestinal digestive, absorptive, secretory, barrier, and defense systems, often in a way potentially detrimental to the host. Environmental factors with long-term influence include stress (e.g., maternal deprivation, neonatal gut irritation), chemical pollutants (e.g., bisphenol A), and gut microbiota disturbances (e.g., by antibiotics). Examples of such long-term effects on the gut are provided in both laboratory animals and pigs together with underlying physiological mechanisms whenever available. Experimental evidence for the involvement of underlying epigenetic modifications (e.g., genomic DNA methylation) in long-term studies has just started to emerge with regard to the gastrointestinal tract. Also, interactions between the microbiota and the host are being considered pivotal in the early programming of gut functions. Finally, suggestions for future research are provided in order to better understand and then control early programming as an attempt to optimize vital functions of the gastrointestinal tract throughout adult life.

The digestive neuronal-glial-epithelial unit: a new actor in gut health and disease

The monolayer of columnar epithelial cells lining the gastrointestinal tract--the intestinal epithelial barrier (IEB)--is the largest exchange surface between the body and the external environment. The permeability of the IEB has a central role in the regulation of fluid and nutrient intake as well as in the control of the passage of pathogens. The functions of the IEB are highly regulated by luminal as well as internal components, such as bacteria or immune cells, respectively. Evidence indicates that two cell types of the enteric nervous system (ENS), namely enteric neurons and enteric glial cells, are potent modulators of IEB functions, giving rise to the novel concept of a digestive 'neuronal-glial-epithelial unit' akin to the neuronal-glial-endothelial unit in the brain. In this Review, we summarize findings demonstrating that the ENS is a key regulator of IEB function and is actively involved in pathologies associated with altered barrier function.

n-3 polyunsaturated fatty acids in the maternal diet modify the postnatal development of nervous regulation of intestinal permeability in piglets

The intestinal epithelial barrier (IEB) plays a key role in the maintenance of gut homeostasis and the development of the immune system in newborns. The enteric nervous system (ENS), a key regulator of gastrointestinal functions, has been shown to be modulated by nutritional factors. However, it remains currently unknown whether maternal diet, in particular n-3 polyunsaturated fatty acids (n-3PUFAs), can impact upon the IEB in newborn piglets and whether the ENS is involved in this effect. Sows received either a control diet (lard based) or an n-3PUFA diet (linseed oil based) during gestation and lactation. Intestinal paracellular permeability was assessed in Ussing chambers on piglets at birth, 3, 7, 14, 21 and 28 postnatal days (PND). Basal jejunal permeability increased significantly and similarly in both groups until PND14 and decreased thereafter. However, at PND28, permeability was higher in n-3PUFA animals as compared to controls. In addition, a vasoactive intestinal peptide (VIP) receptor antagonist increased paracellular permeability in controls but not in n-3PUFA piglets. Conversely, atropine and hexamethonium decreased paracellular permeability in the n-3PUFA group but not in the control group. Moreover, the n-3PUFA diet increased the proportion of choline acetyltransferase (ChAT)-immunoreactive (IR) neurons and decreased the proportion of VIP-IR neurons in the submucosal plexus of piglet jejunum compared to controls. In addition, in primary culture of rat ENS, we showed that 20:5n-3 but not 18:3n-3 increased the proportion of ChAT-IR neurons and decreased the proportion of VIP-IR neurons. In conclusion, supplementation of the maternal diet with n-3PUFAs modified intestinal permeability probably via diet-induced neuroplastic changes in the ENS of newborn piglets.

The level of protein in milk formula modifies ileal sensitivity to LPS later in life in a piglet model

Background

Milk formulas have higher protein contents than human milk. This high protein level could modify the development of intestinal microbiota, epithelial barrier and immune functions and have long-term consequences.

Methodology/Principal findings

We investigated the effect of a high protein formula on ileal microbiota and physiology during the neonatal period and later in life. Piglets were fed from 2 to 28 days of age either a normoprotein (NP, equivalent to sow milk) or a high protein formula (HP, +40% protein). Then, they received the same solid diet until 160 days. During the formula feeding period ileal microbiota implantation was accelerated in HP piglets with greater concentrations of ileal bacteria at d7 in HP than NP piglets. Epithelial barrier function was altered with a higher permeability to small and large probes in Ussing chambers in HP compared to NP piglets without difference in bacterial translocation. Infiltration of T cells was increased in HP piglets at d28. IL-1β and NF-κB sub-units mRNA levels were reduced in HP piglets at d7 and d28 respectively; plasma haptoglobin also tended to be reduced at d7. Later in life, pro-inflammatory cytokines secretion in response to high doses of LPS in explants culture was reduced in HP compared to NP piglets. Levels of mRNA coding the NF-κB pathway sub-units were increased by the challenge with LPS in NP piglets, but not HP ones.

Conclusions/Significance

A high protein level in formula affects the postnatal development of ileal microbiota, epithelial barrier and immune function in piglets and alters ileal response to inflammatory mediators later in life.