Impact of Developmental Age, Necrotizing Enterocolitis Associated Stress, and Oral Therapeutic Intervention on Mucus Barrier Properties

Maternal circadian rhythm disruption affects neonatal inflammation via metabolic reprograming of myeloid cells

Disruption of circadian rhythm during pregnancy produces adverse health outcomes in offspring; however, the role of maternal circadian rhythms in the immune system of infants and their susceptibility to inflammation remains poorly understood. Here we show that disruption of circadian rhythms in pregnant mice profoundly aggravates the severity of neonatal inflammatory disorders in both male and female offspring, such as necrotizing enterocolitis and sepsis. The diminished maternal production of docosahexaenoic acid (DHA) and the impaired immunosuppressive function of neonatal myeloid-derived suppressor cells (MDSCs) contribute to this phenomenon. Mechanistically, DHA enhances the immunosuppressive function of MDSCs via PPARγ-mediated mitochondrial oxidative phosphorylation. Transfer of MDSCs or perinatal supplementation of DHA relieves neonatal inflammation induced by maternal rhythm disruption. These observations collectively demonstrate a previously unrecognized role of maternal circadian rhythms in the control of neonatal inflammation via metabolic reprograming of myeloid cells.

Neonatal intestinal mucus barrier changes in response to maturity, inflammation, and sodium decanoate supplementation

The integrity of the intestinal mucus barrier is crucial for human health, as it serves as the body's first line of defense against pathogens. However, postnatal development of the mucus barrier and interactions between maturity and its ability to adapt to external challenges in neonatal infants remain unclear. In this study, we unveil a distinct developmental trajectory of the mucus barrier in preterm piglets, leading to enhanced mucus microstructure and reduced mucus diffusivity compared to term piglets. Notably, we found that necrotizing enterocolitis (NEC) is associated with increased mucus diffusivity of our large pathogen model compound, establishing a direct link between the NEC condition and the mucus barrier. Furthermore, we observed that addition of sodium decanoate had varying effects on mucus diffusivity depending on maturity and health state of the piglets. These findings demonstrate that regulatory mechanisms governing the neonatal mucosal barrier are highly complex and are influenced by age, maturity, and health conditions. Therefore, our results highlight the need for specific therapeutic strategies tailored to each neonatal period to ensure optimal gut health.

Effect of Lifelong Exposure to Dietary Plant and Marine Sources of n-3 Polyunsaturated Fatty Acids on Morphologic and Gene Expression Biomarkers of Intestinal Health in Early Life

Altered intestinal health is also associated with the incidence and severity of many chronic inflammatory conditions, which could be attenuated via dietary n-3 PUFA interventions. However, little is known about the effect of lifelong exposure to n-3 PUFA from plant and marine sources (beginning in utero via the maternal diet) on early life biomarkers of intestinal health. Harems of C57Bl/6 mice were randomly assigned to one of three isocaloric AIN-93G modified diets differing in their fat sources consisting of the following: (i) 10% safflower oil (SO, enriched in n-6 PUFA), (ii) 3% flaxseed oil + 7% safflower oil (FX, plant-based n-3 PUFA-enriched diet), or (iii) 3% menhaden fish oil + 7% safflower oil (MO, marine-based n-3 PUFA-enriched diet). Mothers remained on these diets throughout pregnancy and offspring (n = 14/diet) continued on the same parental diet until termination at 3 weeks of age. In ileum, villi:crypt length ratios were increased in both the FX and MO dietary groups compared to SO (p < 0.05). Ileum mRNA expression of critical intestinal health biomarkers was increased by both n-3 PUFA-enriched diets including Relmβ and REG3γ compared to SO (p < 0.05), whereas only the FX diet increased mRNA expression of TFF3 and Muc2 (p < 0.05) and only the MO diet increased mRNA expression of ZO-1 (p < 0.05). In the proximal colon, both the FX and MO diets increased crypt lengths compared to SO (p < 0.05), whereas only the MO diet increased goblet cell numbers compared to SO (p < 0.05). Further, the MO diet increased proximal colon mRNA expression of Relmβ and REG3γ (p < 0.05) and both MO and FX increased mRNA expression of Muc2 compared to SO (p < 0.05). Collectively, these results demonstrate that lifelong exposure to dietary n-3 PUFA, beginning in utero, from both plant and marine sources, can support intestinal health development in early life. The differential effects between plant and marine sources warrants further investigation for optimizing health.

Native gastrointestinal mucus: Critical features and techniques for studying interactions with drugs, drug carriers, and bacteria

Gastrointestinal mucus plays essential roles in modulating interactions between intestinal lumen contents, including orally delivered drug carriers and the gut microbiome, and underlying epithelial and immune tissues and cells. This review is focused on the properties of and methods for studying native gastrointestinal mucus and its interactions with intestinal lumen contents, including drug delivery systems, drugs, and bacteria. The properties of gastrointestinal mucus important to consider in its analysis are first presented, followed by a discussion of different experimental setups used to study gastrointestinal mucus. Applications of native intestinal mucus are then described, including experimental methods used to study mucus as a barrier to drug delivery and interactions with intestinal lumen contents that impact barrier properties. Given the significance of the microbiota in health and disease, its impact on drug delivery and drug metabolism, and the use of probiotics and microbe-based delivery systems, analysis of interactions of bacteria with native intestinal mucus is then reviewed. Specifically, bacteria adhesion to, motility within, and degradation of mucus is discussed. Literature noted is focused largely on applications of native intestinal mucus models as opposed to isolated mucins or reconstituted mucin gels.

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.

Effects of prophylactic antibiotics administration on barrier properties of intestinal mucosa and mucus from preterm born piglets

Early intervention and short-duration treatments with antibiotics in premature infants are reported to reduce the incidence of necrotizing enterocolitis (NEC), a terrible disease with severe inflammation and impaired intestinal barrier properties. Yet, it is unclear how antibiotics exposure, as well as route of administration used for dosing, can minimize the risk of NEC. With this study, we aimed to investigate if and how administration of antibiotics may affect the barrier properties of intestinal mucosa and mucus. We compared how parenteral (PAR) and a combination of enteral and parenteral (ENT+PAR) ampicillin and gentamicin given to preterm born piglets within 48 h after birth affected both barrier and physical properties of ex vivo small intestinal mucosa and mucus. Permeation of the markers mannitol, metoprolol, and fluorescein-isothiocyanate dextran of 4 kDa (FD4) and 70 kDa (FD70) through the mucosa and mucus was evaluated. For all markers, permeation through the mucosa and mucus collected from PAR piglets tended to be reduced when compared to that observed using untreated piglets. In contrast, permeation through the mucosa and mucus collected from ENT+PAR piglets tended to be similar to that observed for untreated piglets. Additionally, rheological measurements on the mucus from PAR piglets and ENT+PAR piglets displayed a decreased G' and G'/G" ratio and decreased viscosity at 0.4 s^-1 as well as lower stress stability compared to the mucus from untreated piglets.

Increased expression of OLFM4 and lysozyme during necrotizing enterocolitis in neonates: an observational research study

Background

In neonatal patients with necrotizing enterocolitis (NEC) the inflammatory response is mediated by a plurality of different proteins. The proteins olfactomedin 4 (OLFM4) and lysozyme (LYZ) are part of the intestinal mucosal defense and especially OLFM4 has rarely been evaluated in neonatal gastrointestinal diseases. The aim of this study was to analyze whether expression levels of both proteins of innate immunity, OLFM4 and lysozyme, were increased during NEC in neonates.

Methods

Intestinal tissues of patients with NEC were examined with immunohistochemical staining of formalin-fixed and paraffin-embedded sections of resected tissue using antibodies against OLFM4 and lysozyme. Staining-positive tissues were semi-quantitatively scored from 0 (no staining), 1 (weak staining), 2 (moderate staining) to 3 (highly intense staining) by two individual investigators. Intestinal tissue of infants with volvulus was used as a control as other intestinal tissue without major inflammation was not available.

Results

Both applied antibodies against OLFM4 showed different staining patterns with higher staining intensity of the antibody OLFM4 (D1E4M). OLFM4 (median score of the antibody OLFM4 (D1E4M): 3.0) and lysozyme (median score: 3.0) are highly expressed in intestinal and immune cells during NEC. Expression of OLFM4 and lysozyme in the control samples with volvulus was observable but significantly lower (median score of the antibody OLFM4 (D1E4M): 1.25; median score of the antibody against LYZ: 2.0; p = 0.033 and p = 0.037, respectively).

Conclusions

Both proteins, OLFM4 and lysozyme, may play a role in the pathogenesis of NEC in neonatal patients, but the exact mechanisms of OLFM4 and lysozyme function and their role in immunological responses have not yet been resolved in detail. These observations add new insights as basis for further large-scale population research.

Early Antibiotic Exposure Alters Intestinal Development and Increases Susceptibility to Necrotizing Enterocolitis: A Mechanistic Study

Increasing evidence suggests that prolonged antibiotic therapy in preterm infants is associated with increased mortality and morbidities, such as necrotizing enterocolitis (NEC), a devastating gastrointestinal pathology characterized by intestinal inflammation and necrosis. While a clinical correlation exists between antibiotic use and the development of NEC, the potential causality of antibiotics in NEC development has not yet been demonstrated. Here, we tested the effects of systemic standard-of-care antibiotic therapy for ten days on intestinal development in neonatal mice. Systemic antibiotic treatment impaired the intestinal development by reducing intestinal cell proliferation, villi height, crypt depth, and goblet and Paneth cell numbers. Oral bacterial challenge in pups who received antibiotics resulted in NEC-like intestinal injury in more than half the pups, likely due to a reduction in mucous-producing cells affecting microbial–epithelial interactions. These data support a novel mechanism that could explain why preterm infants exposed to prolonged antibiotics after birth have a higher incidence of NEC and other gastrointestinal disorders.

Reactive oxygen species limit intestinal mucosa-bacteria homeostasis in vitro

Interactions between epithelial and immune cells with the gut microbiota have wide-ranging effects on many aspects of human health. Therefore, there is value in developing in vitro models capable of performing highly controlled studies of such interactions. However, several critical factors that enable long term homeostasis between bacterial and mammalian cultures have yet to be established. In this study, we explored a model consisting of epithelial and immune cells, as well as four different bacterial species (Bacteroides fragilis KLE1958, Escherichia coli MG1655, Lactobacillus rhamnosus KLE2101, or Ruminococcus gnavus KLE1940), over a 50 hour culture period. Interestingly, both obligate and facultative anaerobes grew to similar extents in aerobic culture environments during the co-culture period, likely due to measured microaerobic oxygen levels near the apical surface of the epithelia. It was demonstrated that bacteria elicited reactive oxygen species (ROS) production, and that the resulting oxidative damage heavily contributed to observed epithelial barrier damage in these static cultures. Introduction of a ROS scavenger significantly mitigated oxidative damage, improving cell monolayer integrity and reducing lipid peroxidation, although not to control (bacteria-free culture) levels. These results indicate that monitoring and mitigating ROS accumulation and oxidative damage can enable longer term bacteria-intestinal epithelial cultures, while also highlighting the significance of additional factors that impact homeostasis in mammalian cell-bacteria systems.

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.

Colloidal transport of lipid digesta in human and porcine small intestinal mucus

Small intestinal mucus transport of food-derived particulates has not been extensively studied, despite mucus being a barrier nutrients need to cross before absorption. We used complex dispersions of digesta obtained from simulated, dynamic gastrointestinal digestion of yogurt to examine the penetrability of human and porcine mucus to the particles formed of lipolysis products. Quantitative, time-lapse confocal microscopy revealed a sieve-like behaviour of the pig jejunal and ileal mucus. The digesta diffusivity decreased significantly over the first 30 min of mucus penetration, and then remained constant at ca. 5 × 10^-12 m² s^-1 (approx. 70% decrease from initial values). A non-significantly different penetrability was recorded for the ileal mucus of adult humans. The digesta diffusion rates in neonatal, jejunal mucus of 2 week old piglets were 5-8 times higher than in the three different types of adult mucus. This is the first report that validates the mucus of fully-grown pigs as a human-relevant substitute for mucus permeation studies of nutrients/bio-actives and/or complex colloidal dispersions (e.g., post-digestion food particulates, orally-administrated delivery systems).

Comparing the permeability of human and porcine small intestinal mucus for particle transport studies

The gastrointestinal mucus layer represents the last barrier between ingested food or orally administered pharmaceuticals and the mucosal epithelium. This complex gel structure plays an important role in the process of small intestinal absorption. It provides protection against hazardous particles such as bacteria but allows the passage of nutrients and drug molecules towards the intestinal epithelium. In scientific research, mucus from animal sources is usually used to simulate difficult-to-obtain human small intestinal mucus for investigating the intramucus transport of drug delivery systems or food nanoparticles. However, there is a lack of evidence the human mucus can be reliably substituted by animal counterparts for human-relevant transport models. In this report, a procedure for collecting human mucus has been described. More importantly, the permeability characteristics of human and porcine small intestinal mucus secretions to sub-micron sized particles have been compared under simulated intestinal conditions. Negatively charged, 500 nm latex beads were used in multiple-particle tracking experiments to examine the heterogeneity and penetrability of mucus from different sources. Diffusion of the probe particles in adult human ileal mucus and adult pig jejunal and ileal mucus revealed no significant differences in microstructural organisation or microviscosity between the three mucus types (P > 0.05). In contrast to this interspecies similarity, the intraspecies comparison of particle diffusivity in the mucus obtained from adult pigs vs. 2-week old piglets showed better penetrability of the piglet mucus. The mean Stokes–Einstein viscosity of the piglet jejunal mucus was approx. two times lower than the viscosity of the pig jejunal mucus (P < 0.05). All mucus structures were also visualised by scanning electron microscopy. This work validates the use of porcine small intestinal mucus collected from fully-grown pigs for studying colloidal transport of sub-micron sized particles in mucus under conditions mimicking the adult human small intestinal environment.