Human Milk Oligosaccharides Protect against Necrotizing Enterocolitis by Inhibiting Intestinal Damage via Increasing the Proliferation of Crypt Cells

Recent Progress in Human Milk Oligosaccharides and Its Antiviral Efficacy

Gastrointestinal (GI)-associated viruses, including rotavirus (RV), norovirus (NV), and enterovirus, usually invade host cells, transmit, and mutate their genetic information, resulting in influenza-like symptoms, acute gastroenteritis, encephalitis, or even death. The unique structures of human milk oligosaccharides (HMOs) enable them to shape the gut microbial diversity and endogenous immune system of human infants. Growing evidence suggests that HMOs can enhance host resistance to GI-associated viruses but without a systematic summary to review the mechanism. The present review examines the lactose- and neutral-core HMOs and their antiviral effects in the host. The potential negative impacts of enterovirus 71 (EV-A71) and other GI viruses on children are extensive and include neurological sequelae, neurodevelopmental retardation, and cognitive decline. However, the differences in the binding affinity of HMOs for GI viruses are vast. Hence, elucidating the mechanisms and positive effects of HMOs against different viruses may facilitate the development of novel HMO derived oligosaccharides.

More than nutrition: Therapeutic potential and mechanism of human milk oligosaccharides against necrotizing enterocolitis

Human milk is the most valuable source of nutrition for infants. The structure and function of human milk oligosaccharides (HMOs), which are key components of human milk, have long been attracting particular research interest. Several recent studies have found HMOs to be efficacious in the prevention and treatment of necrotizing enterocolitis (NEC). Additionally, they could be developed in the future as non-invasive predictive markers for NEC. Based on previous findings and the well-defined functions of HMOs, we summarize potential protective mechanisms of HMOs against neonatal NEC, which include: modulating signal receptor function, promoting intestinal epithelial cell proliferation, reducing apoptosis, restoring intestinal blood perfusion, regulating microbial prosperity, and alleviating intestinal inflammation. HMOs supplementation has been demonstrated to be protective against NEC in both animal studies and clinical observations. This calls for mass production and use of HMOs in infant formula, necessitating more research into the safety of industrially produced HMOs and the appropriate dosage in infant formula.

Effect of Human Milk Oligosaccharides on Learning and Memory in Mice with Alzheimer's Disease

Alzheimer's disease (AD) is distinguished by cognitive dysfunction and neuroinflammation in the brain. 2'-Fucosyllactose (2'-FL) is a major human milk oligosaccharide (HMO) that is abundantly present in breast milk and has been demonstrated to exhibit immunomodulatory effects. However, the role of 2'-FL and HMO in gut microbiota modulation in relation to AD remains insufficiently investigated. This study aimed to elucidate the preventive effect of the 2'-FL and HMO impact of AD and the relevant mechanism involved. Here, the behavioral results showed that 2'-FL and HMO intervention decreased the expression of Tau phosphorylation and amyloid-β (Aβ), inhibited neuroinflammation, and restored cognitive impairment in AD mice. The metagenomic analysis proved that 2'-FL and HMO intervention restored the dysbiosis of the gut microbiota in AD. Notably, 2'-FL and HMO intervention significantly enhanced the relative abundance of Clostridium and Akkermansia. The metabolomics results showed that 2'-FL and HMO enhanced the oleoyl-l-carnitine metabolism as potential drivers. More importantly, the levels of oleoyl-l-carnitine were positively correlated with the abundances of Clostridium and Akkermansia. These results indicated that 2'-FL and HMO had therapeutic potential to prevent AD-induced cognitive impairment, which is of great significance for the treatment of AD.

Human milk oligosaccharides promote intestinal epithelium regeneration independent of the microbiota during necrotizing enterocolitis

PURPOSE

Necrotizing enterocolitis (NEC) is a severe intestinal disease primarily affecting premature infants, marked by impaired epithelial regeneration. Breastfed infants are less susceptible to NEC than formula-fed ones, and human milk oligosaccharides (HMO) found in breast milk have prebiotic properties that can protect against NEC. However, it is unclear how HMOs influence intestinal epithelium regeneration in relation to the gut microbiota.

METHODS

Broad-spectrum antibiotics were administered to pregnant dams to reduce the microbiota in offspring. NEC was induced through administration of hyperosmolar formula, lipopolysaccharide, and hypoxia from postnatal days (p) 5-9. Intestinal epithelial organoids were derived from p9 mice. HMOs were isolated from human donor breast milk and then solubilized in the formula for each feed or culture media for organoids.

RESULTS

HMOs did not alter the microbiota profile in the presence of a normal or reduced microbiota. In the reduced microbiota, HMO treatment decreased NEC intestinal injury, and increased proliferation and stem cell activity. Additionally, in the complete absence of the microbiota, HMOs stimulated intestinal organoid growth.

CONCLUSION

This study demonstrates that HMOs promoted intestinal epithelial regeneration independent of the gut microbiota. These findings provide further insight into the various benefits HMOs may have in the protection against NEC.

Human Milk Oligosaccharides: A Critical Review on Structure, Preparation, Their Potential as a Food Bioactive Component, and Future Perspectives

Human milk is the gold standard for infant feeding. Human milk oligosaccharides (HMOs) are a unique group of oligosaccharides in human milk. Great interest in HMOs has grown in recent years due to their positive effects on various aspects of infant health. HMOs provide various physiologic functions, including establishing a balanced infant's gut microbiota, strengthening the gastrointestinal barrier, preventing infections, and potential support to the immune system. However, the clinical application of HMOs is challenging due to their specificity to human milk and the difficulties and high costs associated with their isolation and synthesis. Here, the differences in oligosaccharides in human and other mammalian milk are compared, and the synthetic strategies to access HMOs are summarized. Additionally, the potential use and molecular mechanisms of HMOs as a new food bioactive component in different diseases, such as infection, necrotizing enterocolitis, diabetes, and allergy, are critically reviewed. Finally, the current challenges and prospects of HMOs in basic research and application are discussed.

The Role of Intestinal Microbiota in Celiac Disease and Further Therapeutic Perspectives

Celiac disease (CD) is an immune-mediated enteropathy caused by exposure to gluten and related prolamins in genetically susceptible individuals. It is a complex genetic disorder with multiple contributing genes. Linkage studies have identified several genomic regions that probably contain CD susceptibility genes. The most important genetic factors are HLA-DQ2 and DQ8. Several known environmental triggers promote the onset of CD at any age after gluten introduction in individuals with a genetic background, such as viral infections and intestinal dysbiosis. Recent publications have described the interference of the intestinal microbiome in gluten metabolism, modulation of local immune reactions, and in maintaining normal gut permeability. These results have promoted further lines of research on the benefit of probiotic administration to prevent disease onset or alleviate clinical symptoms along with a gluten-free diet (GFD). The relationship between gut microbiome changes and the onset of CD is incompletely understood, still being the subject of current research. This narrative review analyzes the interplay between environmental factors, intestinal microbiome alterations, and the course of CD. Furthermore, this review sets out to discuss if modulation of intestinal microflora with pre- and probiotics along with a GFD could represent a reliable therapeutic target for celiac patients.

Intestinal organoids: A thriving and powerful tool for investigating dietary nutrients-intestinal homeostasis axis

Dietary nutrients regulate intestinal homeostasis through a variety of complex mechanisms, to affect the host health. Nowadays, various models have been used to investigate the dietary nutrients-intestinal homeostasis axis. Different from the limited flux in animal experiments, limited intestinal cell types and distorted simulation of intestinal environment of 2D cells, intestinal organoid (IO) is a 3D culture system of mini-gut with various intestinal epithelial cells (IECs) and producibility of intestinal biology. Therefore, IOs is a powerful tool to evaluate dietary nutrients-intestinal homeostasis interaction. This review summarized the application of IOs in the investigation of mechanisms for macronutrients (carbohydrates, proteins and fats) and micronutrients (vitamins and minerals) affecting intestinal homeostasis directly or indirectly (polysaccharides-intestinal bacteria, proteins-amino acids). In addition, new perspectives of IOs in combination with advanced biological techniques and their applications in precise nutrition were proposed.

Human breast milk: A promising treatment for necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a severe gastrointestinal disorder occurring in newborns, with a mortality rate ranging from 20 % to 30 %. The existing therapeutic approaches for NEC are limited in their effectiveness. Various factors contribute to the development of NEC, including disruption of barrier function, dysregulation of the intestinal immune system, and abnormal colonization of the intestinal microbiota. Researchers have shown considerable interest in exploring the therapeutic potential of the constituents present in human breast milk (HBM) for treating NEC. HBM contains numerous bioactive components, such as exosomes, growth factors, and oligosaccharides. However, the precise mechanisms by which HBM exerts its protective effects against NEC remain incompletely understood. In this study, our objective was to comprehensively review the bioactive substances present in HBM, aiming to facilitate the development of novel therapeutic strategies for NEC.

Necrotizing Enterocolitis following Onasemnogene Abeparvovec for Spinal Muscular Atrophy: A Case Series

Onasemnogene abeparvovec treats spinal muscular atrophy by delivering a functional SMN1 gene. Necrotizing enterocolitis typically occurs in preterm infants. We report 2 term infants diagnosed with spinal muscular atrophy who presented with necrotizing enterocolitis after onasemnogene abeparvovec infusion. We discuss potential etiologies and propose monitoring for necrotizing enterocolitis after onasemnogene abeparvovec therapy.

Response of the Glutathione (GSH) Antioxidant Defense System to Oxidative Injury in Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a neonatal intestinal disease associated with oxidative stress. The targets of peroxidation and the role of the innate intestinal epithelial antioxidant defense system are ill-defined. We hypothesized that oxidative stress in NEC correlates with oxidized GSH redox potentials, lipid peroxidation, and a dysfunctional antioxidant system. Methods: Intestinal samples from infants +/- NEC were generated into enteroids and incubated with lipopolysaccharide (LPS) and hypoxia to induce experimental NEC. HPLC assayed GSH redox potentials. Lipid peroxidation was measured by flow cytometry. Immunoblotting measured glutathione peroxidase 4 (Gpx4) expression. Results: GSH redox potentials were more oxidized in NEC intestinal tissue and enteroids as compared to controls. Lipid radicals in NEC-induced enteroids were significantly increased. Human intestinal tissue with active NEC and treated enteroid cultures revealed decreased levels of Gpx4. Conclusions: The ability of neonatal intestine to mitigate radical accumulation plays a role in its capacity to overcome oxidative stress. Accumulation of lipid radicals is confirmed after treatment of enteroids with NEC-triggering stimuli. Decreased Gpx4 diminishes a cell's ability to effectively neutralize lipid radicals. When lipid peroxidation overwhelms antioxidant machinery, cellular death ensues. Identification of the mechanisms behind GSH-dependent enzyme dysfunction in NEC may provide insights into strategies for reversing radical damage.

Human Milk Oligosaccharide Profile across Lactation Stages in Israeli Women-A Prospective Observational Study

Human milk oligosaccharides (HMOs) stimulate the growth of gut commensals, prevent the adhesion of enteropathogens and modulate host immunity. The major factors influencing variations in the HMO profile are polymorphisms in the secretor (Se) or Lewis (Le) gene, which affect the activity of the enzymes fucoslytransferase 2 and 3 (FUT2 and FUT3) that lead to the formation of four major fucosylated and non-fucosylated oligosaccharides (OS). This pilot study aimed to determine the HMO profile of Israeli breastfeeding mothers of 16 term and 4 preterm infants, from a single tertiary center in the Tel Aviv area. Fifty-two human milk samples were collected from 20 mothers at three-time points: colostrum, transitional milk and mature milk. The concentrations of nine HMOs were assessed using liquid chromatography coupled with mass spectra chromatograms. Fifty-five percent of the mothers were secretors and 45% were non-secretors. Infant sex affected HMO levels depending on the maternal secretor status. Secretor mothers to boys had higher levels of FUT2-dependent OS and higher levels of disialyllacto-N-tetraose in the milk of mothers to girls, whereas non-secretor mothers to girls had higher levels of 3'-sialyllactose. In addition, the season at which the human milk samples were obtained affected the levels of some HMOs, resulting in significantly lower levels in the summer. Our findings provide novel information on the irregularity in the HMO profile among Israeli lactating women and identify several factors contributing to this variability.

Necrotizing enterocolitis: recent advances in treatment with translational potential

Necrotizing enterocolitis (NEC) is one of the most prevalent and devastating gastrointestinal disorders in neonates. Despite advances in neonatal care, the incidence and mortality due to NEC remain high, highlighting the need to devise novel treatments for this disease. There have been a number of recent advancements in therapeutic approaches for the treatment of NEC; these involve remote ischemic conditioning (RIC), stem cell therapy, breast milk components (human milk oligosaccharides, exosomes, lactoferrin), fecal microbiota transplantation, and immunotherapy. This review summarizes the most recent advances in NEC treatment currently underway as well as their applicability and associated challenges and limitations, with the aim to provide new insight into the paradigm of care for NEC worldwide.

Development of the Neonatal Intestinal Barrier, Microbiome, and Susceptibility to NEC

The function of the intestinal barrier is partially dependent on host maturity and the colonization patterns of the microbiome to which it is exposed. Premature birth and stressors of neonatal intensive care unit (NICU)-related support (e.g., antibiotics, steroids, etc.) can alter the host internal environment resulting in changes in the intestinal barrier. Pathogenic microbial proliferation and breach of the immature intestinal barrier are proposed to be crucial steps in the development of neonatal diseases such as necrotizing enterocolitis. This article will review the current literature on the intestinal barrier in the neonatal gut, the consequences of microbiome development for this defense system, and how prematurity can influence neonatal susceptibility to gastrointestinal infection.

Exploitation of In Vivo-Emulated In Vitro System in Advanced Food Science

Reasonable model construction contributes to the accuracy of experimental results. Multiple in vivo models offer reliable choices for effective evaluation, whereas their applications are hampered due to adverse features including high time-consumption, high cost and ethical contradictions. In vivo-emulated in vitro systems (IVE systems) have experienced rapid development and have been brought into food science for about two decades. IVE systems' flexibly gathers the strengths of in vitro and in vivo models into one, reflecting the results in an efficient, systematic and interacted manner. In this review, we comprehensively reviewed the current research progress of IVE systems based on the literature published in the recent two decades. By categorizing the IVE systems into 2D coculture models, spheroids and organoids, their applications were systematically summarized and typically exemplified. The pros and cons of IVE systems were also thoroughly discussed, drawing attention to present challenges and inspiring potential orientation and future perspectives. The wide applicability and multiple possibilities suggest IVE systems as an effective and persuasive platform in the future of advanced food science.

Recent progress in health effects and biosynthesis of lacto-N-tetraose, the most dominant core structure of human milk oligosaccharide

Human milk oligosaccharides (HMOs), which are a group of complex carbohydrates highly abundant in human milk, have been recognized as critical functional biomolecules for infant health. Lacto-N-tetraose (LNT) is one of the most abundant HMO members and the most dominant core structure of HMO. The promising physiological effects of LNT have been well documented, including prebiotic property, antiadhesive antimicrobial activity, and antiviral effect. Its safety has been evaluated and it has been commercially added to infant formula as a functional ingredient. Because of great commercial importance of LNT, increasing attention has been paid to its highly efficient biological production. In particular, microbial synthesis based on metabolic engineering displays obvious advantages in large-scale production of LNT. This review contains important information about the recent progress in physiological effects, safety evaluation, and biosynthesis of LNT.

Necrotizing enterocolitis, gut microbes, and sepsis

Necrotizing enterocolitis (NEC) is a devastating disease in premature infants and the leading cause of death and disability from gastrointestinal disease in this vulnerable population. Although the pathophysiology of NEC remains incompletely understood, current thinking indicates that the disease develops in response to dietary and bacterial factors in the setting of a vulnerable host. As NEC progresses, intestinal perforation can result in serious infection with the development of overwhelming sepsis. In seeking to understand the mechanisms by which bacterial signaling on the intestinal epithelium can lead to NEC, we have shown that the gram-negative bacterial receptor toll-like receptor 4 is a critical regulator of NEC development, a finding that has been confirmed by many other groups. This review article provides recent findings on the interaction of microbial signaling, the immature immune system, intestinal ischemia, and systemic inflammation in the pathogenesis of NEC and the development of sepsis. We will also review promising therapeutic approaches that show efficacy in pre-clinical studies.

Oral Application of Mother's Own Milk for Reducing Necrotizing Enterocolitis in Preterm Infants: An Updated Meta-Analysis of RCTs

Background

Necrotizing enterocolitis (NEC) and late-onset sepsis (LOS) are the major contributors to mortality and morbidity in preterm infants. This updated meta-analysis was aimed to assess the effects of mother's milk on the incidence of NEC, LOS, and other clinical outcomes in preterm infants.

Methods

PubMed, Embase, and the Cochrane library were searched for papers published up to October 2022.

Results

A total of 13 RCTs with 1330 infants were included in the final analysis. Significant difference in NEC (stage 2 or 3) was found between the intervention group and the control group (RR = 0.508, 95% CI: 0.314-0.822, and P=0.008). The incidence of proven LOS (RR = 0.809, 95% CI: 0.610-1.071, and P=0.139) and death (RR = 0.800, 95% CI: 0.571-1.122, and P=0.196) was comparable between the two groups. Statistical differences in the incidence of proven or probable LOS (RR = 0.705, 95% CI: 0.577-0.862, and P=0.001) and length of hospitalization (WMD = -4.868, 95% CI: -6.608 to -3.128, and P < 0.001) between the intervention group and the control group were observed.

Conclusions

The results of this updated meta-analysis showed that compared to the placebo, mother's milk provides better effects in reducing the incidences of NEC, proven or probable LOS, and the length of stay, whereas no significant benefit of mother's milk was observed in reducing the incidence of proven LOS and death.

Lipopolysaccharide induced intestinal epithelial injury: a novel organoids-based model for sepsis in vitro

BACKGROUND

Advances in organoid culture technology have provided a greater understanding of disease pathogenesis, which has been rarely studied in sepsis before. We aim to establish a suitable organoids-based intestinal injury model for sepsis.

METHODS

Stable passaged organoids were constructed and pre-treated with lipopolysaccharide (LPS) to mimic sepsis-induced intestinal injury. The LPS-induced sepsis model was used as a reference. We used quantitative real-time polymerase chain reaction to evaluate the RNA levels of inflammatory factors and antimicrobial peptides. Enzyme-linked immunosorbent assay was used to evaluate the protein levels, hematoxylin and eosin staining was used to evaluate the pathology of the small intestine of mice, and immunohistochemistry and immunofluorescence were used to evaluate the intestinal epithelial barrier function. Perkin Elmer Operetta™ was used to obtain high-resolution images of three-dimensional organoids.

RESULTS

An LPS concentration >150 μg/mL after 24 h was identified to cause organoid growth restriction. The fluorescence intensity of zonula occludens-1 and occludins at LPS concentrations >100 μg/mL decreased significantly after 24 h. After LPS stimulation for 8 h, the RNA expression levels of interleukin (IL)-1α, tumor necrosis factor alpha, granulocyte-macrophage colony-stimulating factor, IL-6, and regenerating islet-derived protein 3 alpha, beta, and gamma increased. These results resembled those of intestinal epithelial layer alterations in a mouse sepsis model. For IL-10, the RNA expression level increased only when the LPS level >200 μg/mL for 24 h.

CONCLUSIONS

This study provides the primary intestinal in vitro model to study the effects of LPS-induced intestinal injury resembling sepsis. This model provides a platform for immune associated mechanism exploration and effective drug screening.

Clinical importance of immunonutrition in infants: a review of the recent literature

During the last decades, the role of nutrition has been well elucidated in medicine, especially among critically ill infants and children. Many nutrients have the potential to modulate the immune system. A healthy immune system is essential for the prevention and recovery of many pediatric illnesses. Intervention using specific nutrients for the immune system is called immunonutrition. Immunonutrient supplementation has been attempted to modulate inflammatory or immune responses, leading to an improved clinical course of critically ill patients with prolonged nutritional supplementation parenterally or enterally. This review discusses immunomodulatory nutrients for infants based on the recent literature.

Current Advances in Structure-Function Relationships and Dose-Dependent Effects of Human Milk Oligosaccharides

HMOs (human milk oligosaccharides) are the third most important nutrient in breast milk. As complex glycans, HMOs play an important role in regulating neonatal intestinal immunity, resisting viral and bacterial infections, displaying anti-inflammatory characteristics, and promoting brain development. Although there have been some previous reports of HMOs, a detailed literature review summarizing the structure-activity relationships and dose-dependent effects of HMOs is lacking. Hence, after introducing the structures and synthetic pathways of HMOs, this review summarizes and categorizes identified structure-function relationships of HMOs. Differential mechanisms of different structural HMOs utilization by microorganisms are summarized. This review also emphasizes the recent advances in the interactions between different health benefits and the variance of dosage effect based on in vitro cell tests, animal experiments, and human intervention studies. The potential relationships between the chemical structure, the dosage selection, and the physiological properties of HMOs as functional foods are vital for further understanding of HMOs and their future applications.

Role of milk carbohydrates in intestinal health of nursery pigs: a review

Intestinal health is essential for the resistance to enteric diseases and for nutrient digestion and absorption to support growth. The intestine of nursery pigs are immature and vulnerable to external challenges, which cause negative impacts on the structure and function of the intestine. Among nutritional interventions, the benefits of milk are significant for the intestinal health of pigs. Milk coproducts have traditionally been used in starter feeds to improve the growth of nursery pigs, but their use is somewhat limited due to the high costs and potential risks of excessive lactose on the intestine. Thus, understanding a proper feeding level of milk carbohydrates is an important start of the feeding strategy. For nursery pigs, lactose is considered a highly digestible energy source compared with plant-based starch, whereas milk oligosaccharides are considered bioactive compounds modulating intestinal immunity and microbiota. Therefore, milk carbohydrates, mainly composed of lactose and oligosaccharides, have essential roles in the intestinal development and functions of nursery pigs. The proper feeding levels of lactose in starter feeds could be variable by weaning age, body weight, or genetic lines. Effects of lactose and milk oligosaccharides have been broadly studied in human health and animal production. Therefore, this review focuses on the mechanisms of lactose and milk oligosaccharides affecting intestinal maturation and functions through modulation of enterocyte proliferation, intestinal immunity, and intestinal microbiota of nursery pigs.

Recent understanding of human milk oligosaccharides in establishing infant gut microbiome and roles in immune system

Human milk oligosaccharides (HMOs) are complex sugars with distinctive structural diversity present in breast milk. HMOs have various functional roles to play in infant development starting from establishing the gut microbiome and immune system to take it up to the mature phase. It has been a major energy source for human gut microbes that confer positive benefits on infant health by directly interacting through intestinal cells and generating short-chain fatty acids. It has recently become evident that each species of Bifidobacterium and other genera which are resident of the infant gut employ distinct molecular mechanisms to capture and digest diverse structural HMOs to avoid competition among themselves and successfully maintain gut homeostasis. HMOs also directly modulate gut immune responses and can decoy receptors of pathogenic bacteria and viruses, inhibiting their binding on intestinal cells, thus preventing the emergence of a disease. This review provides a critical understanding of how different gut bacteria capture and utilize selective sugars from the HMO pool and how different structural HMOs protect infants from infectious diseases.

Current therapy option for necrotizing enterocolitis: Practicalities and challenge

Necrotizing enterocolitis (NEC) is one of the most prevalent neonatal gastrointestinal disorders. Despite ongoing breakthroughs in its treatment and prevention, the incidence and mortality associated with NEC remain high. New therapeutic approaches, such as breast milk composition administration, stem cell therapy, immunotherapy, and fecal microbiota transplantation (FMT) have recently evolved the prevention and the treatment of NEC. This study investigated the most recent advances in NEC therapeutic approaches and discussed their applicability to bring new insight to NEC treatment.

Clinical implications of preterm infant gut microbiome development

Perturbations to the infant gut microbiome during the first weeks to months of life affect growth, development and health. In particular, assembly of an altered intestinal microbiota during infant development results in an increased risk of immune and metabolic diseases that can persist into childhood and potentially into adulthood. Most research into gut microbiome development has focused on full-term babies, but health-related outcomes are also important for preterm babies. The systemic physiological immaturity of very preterm gestation babies (born earlier than 32 weeks gestation) results in numerous other microbiome-organ interactions, the mechanisms of which have yet to be fully elucidated or in some cases even considered. In this Perspective, we compare assembly of the intestinal microbiome in preterm and term infants. We focus in particular on the clinical implications of preterm infant gut microbiome composition and discuss the prospects for microbiome diagnostics and interventions to improve the health of preterm babies.

Metabolome and microbiome of chronic periapical periodontitis in permanent anterior teeth: a pilot study

Background

Periapical periodontitis is a common oral inflammatory disease that affects periapical tissues and is caused by bacteria in the root canal system. The relationship among the local metabolome, the inflammatory grade, and the type and abundance of microorganisms associated with periapical periodontitis is discussed in this study.

Methods

The inflammatory grades of periapical samples from 47 patients with chronic periapical periodontitis in permanent anterior teeth were determined based on the immune cell densities in tissues subjected to haematoxylin and eosin staining. The metabolome was evaluated using ultrahigh-performance liquid chromatography-quadrupole time-of-flight mass spectrometry, followed by principal component analysis and orthogonal partial least squares discriminant analysis. The microbiome was accessed using 16 S rRNA high-throughput sequencing. The differences in the metabolomes and microbiomes of the periapical periodontitis samples were assessed using Spearman’s correlation analysis.

Result

N-acetyl-D-glucosamine, L-tryptophan, L-phenylalanine, and 15 other metabolites were identified by the comparison between samples with severe inflammation and mild or moderate inflammation. Four amino acid metabolism pathways and one sugar metabolism pathway were associated with the inflammatory grade of periapical periodontitis. The abundance of Actinomycetes was negatively correlated with the abundance of glucosamine (GlcN), while the abundance of Tannerella was positively correlated with the abundance of L-methionine.

Conclusions

The local metabolome of periapical periodontitis is correlated with the inflammatory grade. The abundance of the local metabolites GlcN and L-methionine is correlated with the abundance of the major microorganisms Actinomycetes and Tannerella, respectively.

Human Milk Oligosaccharides: A Comprehensive Review towards Metabolomics

Human milk oligosaccharides (HMOs) are the third most represented component in breast milk. They serve not only as prebiotics but they exert a protective role against some significant neonatal pathologies such as necrotizing enterocolitis. Furthermore, they can program the immune system and consequently reduce allergies and autoimmune diseases’ incidence. HMOs also play a crucial role in brain development and in the gut barrier’s maturation. Moreover, the maternal genetic factors influencing different HMO patterns and their modulation by the interaction and the competition between active enzymes have been widely investigated in the literature, but there are few studies concerning the role of other factors such as maternal health, nutrition, and environmental influence. In this context, metabolomics, one of the newest “omics” sciences that provides a snapshot of the metabolites present in bio-fluids, such as breast milk, could be useful to investigate the HMO content in human milk. The authors performed a review, from 2012 to the beginning of 2021, concerning the application of metabolomics to investigate the HMOs, by using Pubmed, Researchgate and Scopus as source databases. Through this technology, it is possible to know in real-time whether a mother produces a specific oligosaccharide, keeping into consideration that there are other modifiable and unmodifiable factors that influence HMO production from a qualitative and a quantitative point of view. Although further studies are needed to provide clinical substantiation, in the future, thanks to metabolomics, this could be possible by using a dipstick and adding the eventual missing oligosaccharide to the breast milk or formula in order to give the best and the most personalized nutritional regimen for each newborn, adjusting to different necessities.

Clinical Evaluation of 16-Week Supplementation with 5HMO-Mix in Healthy-Term Human Infants to Determine Tolerability, Safety, and Effect on Growth

Human milk oligosaccharides (HMOs) are complex sugars that occur naturally in human breast milk and provide many beneficial functions. Most formula products lack HMOs or contain only the most abundant HMO, 2′-fucosyllactose; however, benefits of HMOs come from multiple sugars. We therefore developed a mixture of five HMOs (5HMO-Mix) mimicking the natural concentrations of the top five HMOs (5.75 g/L total, comprising 52% 2′-fucosyllactose, 13% 3-fucosyllactose, 26% lacto-N-tetraose, 4% 3′-sialyllactose, and 5% 6′-sialyllactose) representing the groups of neutral, neutral-fucosylated, and sialylated HMOs. We conducted the first multicenter, randomized, controlled, parallel-group clinical study assessing the safety, tolerability, and effect on growth of formula containing the 5HMO-Mix in healthy infants. We enrolled 341 subjects aged ≤14 days; 225 were randomized into groups fed either with infant formula containing 5HMO-Mix (5HMO-Mix) or infant formula without HMOs (IF) for 4 months, with the others exclusively breastfed. There were no differences in weight, length, or head circumference gain between the two formula groups. The 5HMO-Mix was well tolerated, with 5HMO-Mix and breastfed infants producing softer stools at a higher stool frequency than the control formula group. Adverse events were equivalent in all groups. We conclude that the 5HMO-Mix at 5.75 g/L in infant formula is safe and well tolerated by healthy term infants during the first months of life.

The human milk oligosaccharide 2'-fucosyllactose attenuates β-lactoglobulin-induced food allergy through the miR-146a-mediated toll-like receptor 4/nuclear factor-κB signaling pathway

Our previous experiments have confirmed that human milk oligosaccharides (HMO) and its main component 2'-fucosyllactose (2'-FL), as prebiotics, could effectively alleviate cow milk allergy by regulating the intestinal microecology. This study intended to further explore the molecular mechanism of HMO regulating intestinal immunity. The results of the allergic mouse model showed that oral administration of 2'-FL or HMO reduced β-lactoglobulin (β-LG)-induced serum-specific IgE secretion and mast cell degranulation, while reducing the inflammatory cytokines, TNF-α, IL-4, and IL-6 production and promoting the miR-146a expression. In vitro results further confirmed that 2'-FL or HMO treatment reduced allergen-induced secretion of iNOS, NO, pro-inflammatory cytokines and reactive oxygen species in RAW264.7 cells. At the same time, in contrast to the β-LG group, 2'-FL dose-dependently inhibited the TLR4/NF-κB inflammatory pathway and upregulated miR-146a expression, and the effect of the 2'-FL mid-dose group was similar to that of the HMO intervention group. In particular, adding miR-146a inhibitors to macrophages attenuated the inhibitory effect of 2'-FL on the expression of TRAF6 and IRAKI in the TLR4 pathway, suggesting that miR-146a might be involved in the immune regulation of 2'-FL. The above results indicated that 2'-FL had a similar effect to HMOs, and its effect of reducing β-LG allergy might be related to the regulation of miR-146a to inhibit TLR4/NF-κB signaling pathway.

Breast milk nutrients driving intestinal epithelial layer maturation via Wnt and Notch signaling: Implications for necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is an often lethal, inflammatory disease of the preterm intestine. The underdeveloped immune system plays an important role; however, the initial trigger for NEC development is likely a damaged intestinal epithelial layer. We hypothesize that due to incomplete maturation of different epithelial cell lineages, nutrients and bacteria are able to damage the epithelial cells and cause the (immature) inflammatory response, food intolerance and malabsorption seen in NEC. Intestinal organoid research has shown that maturation of intestinal epithelial cell lineages is orchestrated by two key signaling pathways: Wnt and Notch. In NEC, these pathways are dysregulated by hyperactivation of Toll-like-receptor-4. Breastfeeding decreases the risk of developing NEC compared to formula milk. Here, we review the intricate link between breast milk components, Wnt and Notch signaling and intestinal epithelial maturation. We argue that (nutritional) interventions regulating these pathways may decrease the risk of NEC development in preterm infants.

Intestinal Microbiota in Common Chronic Inflammatory Disorders Affecting Children

The incidence and prevalence rate of chronic inflammatory disorders is on the rise in the pediatric population. Recent research indicates the crucial role of interactions between the altered intestinal microbiome and the immune system in the pathogenesis of several chronic inflammatory disorders in children, such as inflammatory bowel disease (IBD) and autoimmune diseases, such as type 1 diabetes mellitus (T1DM) and celiac disease (CeD). Here, we review recent knowledge concerning the pathogenic mechanisms underlying these disorders, and summarize the facts suggesting that the initiation and progression of IBD, T1DM, and CeD can be partially attributed to disturbances in the patterns of composition and abundance of the gut microbiota. The standard available therapies for chronic inflammatory disorders in children largely aim to treat symptoms. Although constant efforts are being made to maximize the quality of life for children in the long-term, sustained improvements are still difficult to achieve. Additional challenges are the changing physiology associated with growth and development of children, a population that is particularly susceptible to medication-related adverse effects. In this review, we explore new promising therapeutic approaches aimed at modulation of either gut microbiota or the activity of the immune system to induce a long-lasting remission of chronic inflammatory disorders. Recent preclinical studies and clinical trials have evaluated new approaches, for instance the adoptive transfer of immune cells, with genetically engineered regulatory T cells expressing antigen-specific chimeric antigen receptors. These approaches have revolutionized cancer treatments and have the potential for the protection of high-risk children from developing autoimmune diseases and effective management of inflammatory disorders. The review also focuses on the findings of studies that indicate that the responses to a variety of immunotherapies can be enhanced by strategic manipulation of gut microbiota, thus emphasizing on the importance of proper interaction between the gut microbiota and immune system for sustained health benefits and improvement of the quality of life of pediatric patients.

Enteral Feeding Interventions in the Prevention of Necrotizing Enterocolitis: A Systematic Review of Experimental and Clinical Studies

Necrotizing enterocolitis (NEC), which is characterized by severe intestinal inflammation and in advanced stages necrosis, is a gastrointestinal emergency in the neonate with high mortality and morbidity. Despite advancing medical care, effective prevention strategies remain sparse. Factors contributing to the complex pathogenesis of NEC include immaturity of the intestinal immune defense, barrier function, motility and local circulatory regulation and abnormal microbial colonization. Interestingly, enteral feeding is regarded as an important modifiable factor influencing NEC pathogenesis. Moreover, breast milk, which forms the currently most effective prevention strategy, contains many bioactive components that are known to support neonatal immune development and promote healthy gut colonization. This systematic review describes the effect of different enteral feeding interventions on the prevention of NEC incidence and severity and the effect on pathophysiological mechanisms of NEC, in both experimental NEC models and clinical NEC. Besides, pathophysiological mechanisms involved in human NEC development are briefly described to give context for the findings of altered pathophysiological mechanisms of NEC by enteral feeding interventions.

Maternal Microbiota, Early Life Colonization and Breast Milk Drive Immune Development in the Newborn

The innate immune system is the oldest protection strategy that is conserved across all organisms. Although having an unspecific action, it is the first and fastest defense mechanism against pathogens. Development of predominantly the adaptive immune system takes place after birth. However, some key components of the innate immune system evolve during the prenatal period of life, which endows the newborn with the ability to mount an immune response against pathogenic invaders directly after birth. Undoubtedly, the crosstalk between maternal immune cells, antibodies, dietary antigens, and microbial metabolites originating from the maternal microbiota are the key players in preparing the neonate’s immunity to the outer world. Birth represents the biggest substantial environmental change in life, where the newborn leaves the protective amniotic sac and is exposed for the first time to a countless variety of microbes. Colonization of all body surfaces commences, including skin, lung, and gastrointestinal tract, leading to the establishment of the commensal microbiota and the maturation of the newborn immune system, and hence lifelong health. Pregnancy, birth, and the consumption of breast milk shape the immune development in coordination with maternal and newborn microbiota. Discrepancies in these fine-tuned microbiota interactions during each developmental stage can have long-term effects on disease susceptibility, such as metabolic syndrome, childhood asthma, or autoimmune type 1 diabetes. In this review, we will give an overview of the recent studies by discussing the multifaceted emergence of the newborn innate immune development in line with the importance of maternal and early life microbiota exposure and breast milk intake.

Role of Human Milk Bioactives on Infants' Gut and Immune Health

Exclusive human milk feeding of the newborn is recommended during the first 6 months of life to promote optimal health outcomes during early life and beyond. Human milk contains a variety of bioactive factors such as hormones, cytokines, leukocytes, immunoglobulins, lactoferrin, lysozyme, stem cells, human milk oligosaccharides (HMOs), microbiota, and microRNAs. Recent findings highlighted the potential importance of adding HMOs into infant formula for their roles in enhancing host defense mechanisms in neonates. Therefore, understanding the roles of human milk bioactive factors on immune function is critical to build the scientific evidence base around breastfeeding recommendations, and to enhance positive health outcomes in formula fed infants through modifications to formulas. However, there are still knowledge gaps concerning the roles of different milk components, the interactions between the different components, and the mechanisms behind health outcomes are poorly understood. This review aims to show the current knowledge about HMOs, milk microbiota, immunoglobulins, lactoferrin, and milk microRNAs (miRNAs) and how these could have similar mechanisms of regulating gut and microbiota function. It will also highlight the knowledge gaps for future research.

Small RNA Sequencing Reveals Differentially Expressed miRNAs in Necrotizing Enterocolitis in Rats

Necrotizing enterocolitis (NEC) is the leading cause of death due to gastrointestinal disease in preterm infants. The role of miRNAs in NEC is still unknown. The objective of this study was to identify differentially expressed (DE) miRNAs in rats with NEC and analyze their possible roles. In this study, a NEC rat model was established using Sprague-Dawley rat pups. Small RNA sequencing was used to analyze the miRNA expression profiles in the NEC and control rats. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were carried out to identify target mRNAs for the DE miRNAs and to explore their potential roles. The DE miRNAs were verified by real-time quantitative PCR (RT-qPCR). The status of intestinal injury and the elevated levels of inflammatory cytokines in the NEC group confirmed that the NEC model was successfully established. The 16 miRNAs were found to be differentially expressed between the NEC group and the control group of rats. Bioinformatics analysis indicated that the parental genes of the DE miRNAs were predominantly implicated in the phosphorylation, cell migration, and protein phosphorylation processes. Moreover, the DE miRNAs were mainly found to be involved in the pathways of axon guidance, endocytosis, and focal adhesion, as well as in the Wnt signaling pathway, which is related to colitis. The expression patterns of the candidate miRNAs (rno-miR-27a-5p and rno-miR-187-3p), as assessed by RT-qPCR, were in accordance with the expression patterns obtained by miRNA-sequencing. The miRNA/mRNA/pathway network revealed that rno-miR-27a-5p and rno-miR-187-3p might be involved in NEC via the Wnt signaling pathway. We found an altered miRNA expression pattern in rats with NEC. We hypothesize that rno-miR-27a-5p and rno-miR-187-3p might mediate the NEC pathophysiological processes via the Wnt signaling pathway.

Prevention of Necrotizing Enterocolitis through Milk Polar Lipids Reducing Intestinal Epithelial Apoptosis

Neonatal necrotizing enterocolitis (NEC) is a common and devastating disease. The objective of this research was to investigate the protective mechanisms of milk polar lipids (MPLs) on the attenuation of lipopolysaccharides (LPS)-induced intestinal inflammation and apoptosis. MPLs were extracted from buttermilk and analyzed using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). A neonatal NEC rat model was used to investigate the effects of MPLs on NEC and its underlying mechanisms. Hematoxylin-eosin (H&E) staining and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) assay were used to observe intestinal morphological changes and intestinal epithelial cell apoptosis, which showed that MPLs could reduce NEC symptoms and intestinal apoptosis. The expressions of IL-6, IL-8, and TNF-α in the MPL group was significantly downregulated (P < 0.05), and the expression levels of IL-10 were significantly upregulated (P < 0.05). At the same time, MPLs also significantly reduced (P < 0.05) activation of the LPS-induced TLR4/NF-κB signaling pathway. Furthermore, MPLs inhibit apoptosis by reducing the expressions of Bax, caspase-9, and caspase-3 and by increasing the expression of Bcl-2. In conclusion, MPLs could reduce NEC symptoms in mice by inhibiting cell inflammation and protecting against intestinal apoptosis.

Precision-based modeling approaches for necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the leading cause of death from gastrointestinal disease in premature infants and remains stubbornly difficult to treat in many cases. Much of our understanding of NEC pathogenesis has been gained through the study of highly translational animal models. However, most models of NEC are limited by their overall complexity and by the fact that they do not incorporate human tissue. To address these limitations, investigators have recently developed precision-based ex vivo models of NEC, also termed ‘NEC-in-a-dish’ models, which provide the opportunity to increase our understanding of this disease and for drug discovery. These approaches involve exposing intestinal cells from either humans or animals with or without NEC to a combination of environmental and microbial factors associated with NEC pathogenesis. This Review highlights the current progress in the field of NEC model development, introduces NEC-in-a-dish models as a means to understand NEC pathogenesis and examines the fundamental questions that remain unanswered in NEC research. By answering these questions, and through a renewed focus on precision model development, the research community may finally achieve enduring success in improving the outcome of patients with this devastating disease.

Summary: Much of our understanding of necrotizing enterocolitis (NEC) pathogenesis has been achieved through animal models. Here, we discuss the development of advanced precision-based models to improve outcomes for patients with NEC.

Gut Microbiota in Celiac Disease: Is There Any Role for Probiotics?

Celiac disease (CD) is an immune-mediated disorder initiated by the ingestion of gluten in genetically predisposed individuals. Recent data shows that changes in the gut microbiome composition and function are linked with chronic inflammatory diseases; this might also be the case for CD. The main aim of this manuscript is to discuss our present knowledge of the relationships between gut microbiota alterations and CD and to understand if there is any role for probiotics in CD therapy. PubMed was used to search for all of the studies published from November 2009 to November 2019 using key words such as “Celiac Disease” and “Microbiota” (306 articles), “Celiac Disease” and “Gastrointestinal Microbiome” (139), and “Probiotics” and “Celiac Disease” (97 articles). The search was limited to articles published in English that provided evidence-based data. Literature analysis showed that the gut microbiota has a well-established role in gluten metabolism, in modulating the immune response and in regulating the permeability of the intestinal barrier. Promising studies suggest a possible role of probiotics in treating and/or preventing CD. Nevertheless, human trials on the subject are still scarce and lack homogeneity. A possible role was documented for probiotics in improving CD-related symptoms, modulating the peripheral immune response and altering the fecal microbiota, although the results were not consistent in all of the studies. No evidence was found that probiotic administration might prevent CD onset. Knowledge of the role of intestinal bacteria in the development of CD opens new possibilities for its treatment through probiotic administration, even though further studies are needed to better clarify whether probiotics can help treat or prevent the disease and to define which probiotics to use, at what dose and for how long.

More than sugar in the milk: human milk oligosaccharides as essential bioactive molecules in breast milk and current insight in beneficial effects

Human milk is the gold standard for newborn infants. Breast milk not only provides nutrients, it also contains bioactive components that guide the development of the infant's intestinal immune system, which can have a lifelong effect. The bioactive molecules in breast milk regulate microbiota development, immune maturation and gut barrier function. Human milk oligosaccharides (hMOs) are the most abundant bioactive molecules in human milk and have multiple beneficial functions such as support of growth of beneficial bacteria, anti-pathogenic effects, immune modulating effects, and stimulation of intestine barrier functions. Here we critically review the current insight into the benefits of bioactive molecules in mother milk that contribute to neonatal development and focus on current knowledge of hMO-functions on microbiota and the gastrointestinal immune barrier. hMOs produced via genetically engineered microorganisms are now applied in infant formulas to mimic the nutritional composition of breast milk as closely as possible, and their prospects and scientific challenges are discussed in depth.

Human Milk Oligosaccharides Activate Epidermal Growth Factor Receptor and Protect Against Hypoxia-Induced Injuries in the Mouse Intestinal Epithelium and Caco2 Cells

BACKGROUND

Hypoxia-induced intestinal barrier injuries lead to necrotizing enterocolitis (NEC). Although NEC in preterm neonates is preventable by human milk oligosaccharides (HMOs), the underlying mechanism remains unknown.

OBJECTIVE

To reveal the role and mechanism of HMOs in protecting against hypoxia-induced injuries in intestinal epithelium of neonatal mice and cultured Caco2 cells.

METHODS

NEC was induced by hypoxia and cold stress. Seventy C57BL/C pups (7-d-old) were divided into 5 groups and fed maternal breast milk (BM), formula alone (FF), or the formula added with HMOs at 5 (LHMO), 10 (MHMO), or 20 mg/mL (HHMO) for 3 d. Ileal hypoxia inducible factor 1α (HIF1α) and cleaved Caspase 3 were determined, along with staining for Ki-67 protein to labeled proliferative cells. In vitro, adherent Caco2 cells (undifferentiated, passage 14) were treated with HMOs, galacto-oligosaccharides, fructo-oligosaccharides, or mixed oligosaccharides at 10 mg/mL for 1 d exposed to 1% O2. Cell proliferation and apoptosis, along with phosphorylated epidermal growth factor receptor (P-EGFR) and 38KD MAPK (P-P38), were assayed in differentiated or undifferentiated Caco2 cells.

RESULTS

Compared with the FF-fed mice, those fed MHMO and HHMO had 52% lower (P < 0.05) NEC scores, 60-80% greater (P < 0.05) KI67-positive cell numbers, and 56-71% decreases (P < 0.05) in ileal HIF1α and cleaved Caspase 3 (56-71%). Compared with those untreated, the HMO-treated Caco2 cells displayed 60% greater (P < 0.05) proliferative activity and 19% lower (P < 0.05) apoptotic cells after the hypoxia exposure. The HMO treatment led to 58% or 10-fold increases (P < 0.05) of P-EGFR and 48-89% decreases (P < 0.05) of P-P38 in either differentiated or undifferentiated Caco2 cells compared with the controls.

CONCLUSION

Supplementing HMOs at 10-20 mg/mL into the formula for neonatal mice or media for Caco2 cells conferred protection against the hypoxia-induced injuries. The protection in the Caco2 cells was associated with an activation of EGFR.

Beyond Heat Stress: Intestinal Integrity Disruption and Mechanism-Based Intervention Strategies

The current climate changes have increased the prevalence and intensity of heat stress (HS) conditions. One of the initial consequences of HS is the impairment of the intestinal epithelial barrier integrity due to hyperthermia and hypoxia following blood repartition, which often results in a leaky gut followed by penetration and transfer of luminal antigens, endotoxins, and pathogenic bacteria. Under extreme conditions, HS may culminate in the onset of “heat stroke”, a potential lethal condition if remaining untreated. HS-induced alterations of the gastrointestinal epithelium, which is associated with a leaky gut, are due to cellular oxidative stress, disruption of intestinal integrity, and increased production of pro-inflammatory cytokines. This review summarizes the possible resilience mechanisms based on in vitro and in vivo data and the potential interventions with a group of nutritional supplements, which may increase the resilience to HS-induced intestinal integrity disruption and maintain intestinal homeostasis.

Effects of oropharyngeal administration of colostrum on the incidence of necrotizing enterocolitis, late-onset sepsis, and death in preterm infants: a meta-analysis of RCTs

Necrotizing enterocolitis (NEC) and late-onset sepsis (LOS) are two major contributors to death among preterm infants. Oropharyngeal administration of colostrum (OAC) has been proved as an easy, safe, and economically viable technique to help preterm neonates to build up their immunity. In this review, we assessed the effects of OAC on preterm infants. Several mainstream databases were searched including PubMed, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL), and a website of clinical trials. Randomized controlled trials (RCTs) comparing OAC vs. placebo or no intervention in preterm infants (gestation age <34 weeks or birth weight <1500 g) were eligible. Overall, nine RCTs (n = 689) were included in the review. Meta-analysis showed no statistical significance in terms of the incidence of NEC (RR = 0.59, 95% CI = 0.33-1.06, p = 0.08), LOS (RR = 0.78, 95% CI = 0.60-1.03, p = 0.08) and mortality rate (RR = 0.63, 95% CI = 0.38-1.05, p = 0.07). No significant difference was found in the subgroup analysis, apart from the group of the undeveloped region in NEC and mortality. In addition, time was significantly reduced in terms of achieving full enteral feeding (MD = -3.60, 95% CI = -6.55-0.64, p = 0.02) and hospital stay (MD = -10.38, 95% CI = -18.47-2.29, p = 0.01). The results show that OAC does not reduce the incidences of NEC, LOS, and death in preterm infants, but there is a trend toward a positive effect. It is therefore recommended as routine care for preterm infants in the NICU.

Celiac Disease and the Microbiome

Growing evidence supports the hypothesis that changes in both the composition and function of the intestinal microbiome are associated with a number of chronic inflammatory diseases including celiac disease (CD). One of the major advances in the field of microbiome studies over the last few decades has been the development of culture-independent approaches to identify and quantify the components of the human microbiota. The study of nucleic acids DNA and RNA found in feces or other biological samples bypasses the need for tissue cultures and also allows the characterization of non-cultivable microbes. Current evidence on the composition of the intestinal microbiome and its role as a causative trigger for CD is highly heterogeneous and sometimes contradictory. This review is aimed at summarizing both pre-clinical (basic science data) and clinical (cross-sectional and prospective studies) evidence addressing the relationship between the intestinal microbiome and CD.