Low-methoxyl pectin stimulates small intestinal mucin secretion irrespective of goblet cell proliferation and is characterized by jejunum Muc2 upregulation in rats

Journey of dietary fiber along the gastrointestinal tract: role of physical interactions, mucus, and biochemical transformations

Dietary fiber-rich foods have been associated with numerous health benefits, including a reduced risk of cardiovascular and metabolic diseases. Harnessing the potential to deliver positive health outcomes rests on our understanding of the underlying mechanisms that drive these associations. This review addresses data and concepts concerning plant-based food functionality by dissecting the cascade of physical and chemical digestive processes and interactions that underpin these physiological benefits. Functional transformations of dietary fiber along the gastrointestinal tract from the stages of oral processing and gastric emptying to intestinal digestion and colonic fermentation influence its capacity to modulate digestion, transit, and commensal microbiome. This analysis highlights the significance, limitations, and challenges in decoding the complex web of interactions to establish a coherent framework connecting specific fiber components' molecular and macroscale interactions across multiple length scales within the gastrointestinal tract. One critical area that requires closer examination is the interaction between fiber, mucus barrier, and the commensal microbiome when considering food structure design and personalized nutritional strategies for beneficial physiologic effects. Understanding the response of specific fibers, particularly concerning an individual's physiology, will offer the opportunity to exploit these functional characteristics to elicit specific, symptom-targeting effects or use fiber types as adjunctive therapies.

Effects of dietary citrus pulp level on the growth and intestinal health of largemouth bass (Micropterus salmoides)

BACKGROUND

Citrus pulp (CP) is rich in pectin, and studies have shown that pectin possesses antioxidant, anti-inflammatory, and gut microbiota-regulating properties. However, the application of CP in aquafeed is limited. In this study, the effect of dietary inclusion of CP on the intestinal health of largemouth bass (Micropterus salmoides) was investigated. Juveniles of similar size (6.95 ± 0.07 g) were fed isonitrogenous and isoenergetic diets containing different levels of CP (0%, 3%, 6%, 9%, 12%, or 15%) for 58 days.

RESULTS

As the level of CP in the feed for largemouth bass increased, the fish's growth performance and intestinal health initially improved and then declined. Adding low doses of CP (≤9%) to the feed had no significant impact on the growth performance of large-mouth black bass, whereas high doses of CP (>9%) significantly reduced their growth performance. Adding 6%, 9%, or 12% of CP to that feed enhanced the expression of genes related to tight junctions, anti-inflammatory activity, anti-apoptotic activity, and antioxidant activity in the intestines of largemouth bass. It reduced intestinal inflammation and improved intestinal nutrient absorption, intestinal mucosal barrier function, and intestinal antioxidant capacity. Moreover, it improved the α-diversity, structure, and function of the intestinal flora. The addition of 6% CP had the most beneficial effect on the intestinal health of largemouth bass. On the other hand, the addition of 15% CP had adverse effects on the intestinal antioxidant capacity and intestinal mucosal barrier function of largemouth bass.

CONCLUSION

Adding 6-9% CP to the feed for largemouth bass can improve their intestinal health without having a significant impact on their growth performance. CP could serve as a novel prebiotic and immunostimulant ingredient in aquafeed. © 2023 Society of Chemical Industry.

A polysaccharide from Alhagi honey protects the intestinal barrier and regulates the Nrf2/HO-1-TLR4/MAPK signaling pathway to treat alcoholic liver disease in mice

ETHNOPHARMACOLOGICAL RELEVANCE

According to the theory of traditional Chinese medicine, the main factors related to alcoholic liver disease (ALD) are qi stagnation and blood stasis of the five viscera. Previously, we showed that the bioactive components of Alhagi honey have various pharmacological effects in treating liver diseases, but the influence of Alhagi honey on ALD (and its mechanism of action) is not known.

AIM OF THE STUDY

To determine the efficacy of the main active component of Alhagi honey, the polysaccharide AHPN80, in ALD and to explore the potential mechanism of action.

MATERIALS AND METHODS

AHPN80 was isolated from dried Alhagi honey and identified by transmission electron microscopy, Fourier-transform infrared spectroscopy, and gas chromatography. Venous blood, liver tissue, and colon tissue were collected in a mouse model of alcohol-induced acute liver injury. Histology, staining (Oil Red O, Alcian Blue-Periodic Acid Schiff) and measurement of reactive oxygen species (ROS) levels were used to detect histopathologic and lipid-accumulation changes in the liver and colon. Lipopolysaccharide (LPS) levels and the content of proinflammatory cytokines in serum were measured by enzyme-linked immunosorbent assays. Commercial kits were employed to detect biochemistry parameters in serum and the liver. A terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining kit was used to identify hepatocyte apoptosis. Expression of tight junction-associated proteins in colon tissues and nuclear factor erythroid 2-related factor 2/heme oxygenase-1/toll-like receptor-4/mitogen-activated protein kinase (Nrf2/HO-1/TLR4/MAPK) pathway-related proteins in liver tissues and HepG2 cells were analyzed by immunofluorescence or western blotting.

RESULTS

In a mouse model of alcohol-induced acute liver injury, AHPN80 therapy: significantly improved liver parameters (cytochrome P450 2E1, alcohol dehydrogenase, aldehyde dehydrogenase, superoxide dismutase, malondialdehyde, glutathione peroxidase, catalase, total cholesterol, triglycerides, alanine transaminase, aspartate transaminase); reduced serum levels of LPS, interleukin (IL)-1β, IL-6, and tumor necrosis faction-α; increased levels of IL-10 and interferon-gamma. AHPN80 reduced ALD-induced lipid accumulation and ROS production, improved alcohol-induced inflammatory damage to hepatocytes, and inhibited hepatocyte apoptosis. Immunofluorescence staining and western blotting suggested that AHPN80 might eliminate hepatic oxidative stress by activating the Nrf2/HO-1 signaling pathway, repair the intestinal barrier, inhibit the LPS/TLR4/MAPK signaling pathway, and reduce liver inflammation.

CONCLUSIONS

AHPN80 may activate the Nrf2/HO-1 pathway to eliminate oxidative stress, protect the intestinal barrier, and regulate the TLR4/MAPK pathway to treat ALD in mice. AHPN80 could be a functional food and natural medicine to prevent ALD and its complications.

Modulation of pectin on intestinal barrier function via changes in microbial functional potential and bile acid metabolism

Weaning is one of the major factors that cause stress and intestinal infection in infants and in young animals due to an immature intestine and not fully developed immune functions. Pectin (PEC), a prebiotic polysaccharide, has attracted considerable attention in intestinal epithelial signaling and function via modulation of the microbial community. A total of 16 weaned piglets (21-d-old) were randomly assigned into two groups: control group and PEC group. Supplementation of 5% pectin improved intestinal mucosal barrier function by modulating the composition of the bile acid pool in piglets. Specifically, piglets in PEC group had less serum D-lactate content and alkaline phosphatase activity. In the ileum, dietary pectin increased the number of crypt PAS/AB-positive goblet cells and the mRNA expressions of MUC2, ZO-1, and Occludin. Piglets in PEC group displayed a decreased abundance of Enterococcus (2.71 vs. 65.92%), but the abundances of Lactobacillus (30.80 vs. 7.93%), Streptococcus (21.41 vs. 14.81%), and Clostridium_sensu_stricto_1 (28.34 vs. 0.01%) were increased. Elevated concentrations of bile acids especially hyocholic acid species (HCAs) including HCA, HDCA, and THDCA were also observed. Besides, correlation analysis revealed that dietary pectin supplementation may have beneficial effects through stimulation of the crosstalk between gut microbes and bile acid synthesis within the enterohepatic circulation. Thus, dietary pectin supplementation exhibited a further positive effect on the healthy growth and development of weaned piglets. These findings suggest pectin supplementation as the prebiotic is beneficial for gut health and improvement of weaned stress via regulating microbiota and bile acid metabolism.

The Use of Fruit and Vegetable by-Products as Enhancers of Health Status of Piglets after Weaning: The Role of Bioactive Compounds from Apple and Carrot Industrial Wastes

At weaning, piglets are exposed to a large variety of stressors, from environmental/behavioral factors to nutritional stress. Weaning transition affects the gastrointestinal tract especially, resulting in specific disturbances at the level of intestinal morphology, barrier function and integrity, mucosal immunity and gut microbiota. All these alterations are associated with intestinal inflammation, oxidative stress and perturbation of intracellular signaling pathways. The nutritional management of the weaning period aims to achieve the reinforcement of intestinal integrity and functioning to positively modulate the intestinal immunity and that of the gut microbiota and to enhance the health status of piglets. That is why the current research is focused on the raw materials rich in phytochemicals which could positively modulate animal health. The composition analysis of fruit, vegetable and their by-products showed that identified phytochemicals could act as bioactive compounds, which can be used as modulators of weaning-induced disturbances in piglets. This review describes nutritional studies which investigated the effects of bioactive compounds derived from fruit (apple) and vegetables (carrot) or their by-products on the intestinal architecture and function, inflammatory processes and oxidative stress at the intestinal level. Data on the associated signaling pathways and on the microbiota modulation by bioactive compounds from these by-products are also presented.

Spectroscopic Analyses Highlight Plant Biostimulant Effects of Baker's Yeast Vinasse and Selenium on Cabbage through Foliar Fertilization

The main aim of this study is to find relevant analytic fingerprints for plants' structural characterization using spectroscopic techniques and thermogravimetric analyses (TGAs) as alternative methods, particularized on cabbage treated with selenium-baker's yeast vinasse formulation (Se-VF) included in a foliar fertilizer formula. The hypothesis investigated is that Se-VF will induce significant structural changes compared with the control, analytically confirming the biofortification of selenium-enriched cabbage as a nutritive vegetable, and particularly the plant biostimulant effects of the applied Se-VF formulation on cabbage grown in the field. The TGA evidenced a structural transformation of the molecular building blocks in the treated cabbage leaves. The ash residues increased after treatment, suggesting increased mineral accumulation in leaves. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) evidenced a pectin-Iα-cellulose structure of cabbage that correlated with each other in terms of leaf crystallinity. FTIR analysis suggested the accumulation of unesterified pectin and possibly (seleno) glucosinolates and an increased network of hydrogen bonds. The treatment with Se-VF formulation induced a significant increase in the soluble fibers of the inner leaves, accompanied by a decrease in the insoluble fibers. The ratio of soluble/insoluble fibers correlated with the crystallinity determined by XRD and with the FTIR data. The employed analytic techniques can find practical applications as fast methods in studies of the effects of new agrotechnical practices, while in our particular case study, they revealed effects specific to plant biostimulants of the Se-VF formulation treatment: enhanced mineral utilization and improved quality traits.

Pectin from sunflower by-products obtained by ultrasound: Chemical characterization and in vivo evaluation of properties in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a public health challenge and the use of pectin for symptom amelioration is a promising option. In this work, sunflower pectin has been extracted without (CHP) and with assistance of ultrasound (USP) using sodium citrate as a food-grade extracting agent. At optimal conditions (64 °C, 23 min) the highest yield was obtained with ultrasound application (15.5 vs. 8.1 %). Both pectins were structurally characterized by 1H NMR, HPSEC-ELSD, FT-IR and GC-FID. Unlike CHP, USP showed a lower molecular weight, higher galacturonic acid, lower degree of methyl-esterification and, overall, higher viscosity. These characteristics could affect the anti-inflammatory activity of pectins, evaluated using DSS-induced IBD model mice. So, USP promoted the defence (ICAM-1) and repair of the gastrointestinal mucosa (TFF3, ZO-1) more effectively than CHP. These results demonstrate the potential amelioration of acute colitis in IBD mice through USP supplementation. Taking into account the biomarkers analysed, these results demonstrate, for the first time, the positive impact of sunflower pectin extracted by ultrasound under very soft conditions on inflammatory bowel disease that might open up new possibilities in the treatment of this serious pathology.

Unveiling Plant-Based Pectins: Exploring the Interplay of Direct Effects, Fermentation, and Technological Applications in Clinical Research with a Focus on the Chemical Structure

Pectin, a plant-derived polysaccharide, possesses immense technological and biological application value. Several variables influence pectin's physicochemical aspects, resulting in different fermentations, interactions with receptors, and other functional properties. Some of those variables are molecular weight, degree of methylation and blockiness, and monosaccharide composition. Cancer cell cytotoxicity, important fermentation-related byproducts, immunomodulation, and technological application were found in cell culture, animal models, and preclinical and clinical assessments. One of the greater extents of recent pectin technological usage involves nanoencapsulation methods for many different compounds, ranging from chemotherapy and immunotherapy to natural extracts from fruits and other sources. Structural modification (modified pectin) is also utilized to enhance the use of dietary fiber. Although pectin is already recognized as a component of significant importance, there is still a need for a comprehensive review that delves into its intricate relationships with biological effects, which depend on the source and structure of pectin. This review covers all levels of clinical research, including cell culture, animal studies, and clinical trials, to understand how the plant source and pectin structures influence the biological effects in humans and some technological applications of pectin regarding human health.

Pectin in Metabolic Liver Disease

Alterations in the composition of the gut microbiota (dysbiosis) are observed in nutritional liver diseases, including non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) and have been shown to be associated with the severity of both. Editing the composition of the microbiota by fecal microbiota transfer or by application of probiotics or prebiotics/fiber in rodent models and human proof-of-concept trials of NAFLD and ALD have demonstrated its possible contribution to reducing the progression of liver damage. In this review, we address the role of a soluble fiber, pectin, in reducing the development of liver injury in NAFLD and ALD through its impact on gut bacteria.

Role of dietary fiber in promoting immune health-An EAACI position paper

Microbial metabolism of specific dietary components, such as fiber, contributes to the sophisticated inter-kingdom dialogue in the gut that maintains a stable environment with important beneficial physiological, metabolic, and immunological effects on the host. Historical changes in fiber intake may be contributing to the increase of allergic and hypersensitivity disorders as fiber-derived metabolites are evolutionarily hardwired into the molecular circuitry governing immune cell decision-making processes. In this review, we highlight the importance of fiber as a dietary ingredient, its effects on the microbiome, its effects on immune regulation, the importance of appropriate timing of intervention to target any potential window of opportunity, and potential mechanisms for dietary fibers in the prevention and management of allergic diseases. In addition, we review the human studies examining fiber or prebiotic interventions on asthma and respiratory outcomes, allergic rhinitis, atopic dermatitis, and overall risk of atopic disorders. While exposures, interventions, and outcomes were too heterogeneous for meta-analysis, there is significant potential for using fiber in targeted manipulations of the gut microbiome and its metabolic functions in promoting immune health.

Pectin supplementation ameliorates intestinal epithelial barrier function damage by modulating intestinal microbiota in lipopolysaccharide-challenged piglets

During weaning, infants and young animals are susceptible to severe enteric infections, thus inducing intestinal microbiota dysbiosis, intestinal inflammation, and impaired intestinal barrier function. Pectin (PEC), a prebiotic polysaccharide, enhances intestinal health with the potential for therapeutic effect on intestinal diseases. One 21-days study was conducted to investigate the protective effect of pectin against intestinal injury induced by intraperitoneal injection of Escherichia coli lipopolysaccharide (LPS) in a piglet model. A total of 24 piglets (6.77±0.92 kg BW; Duroc × Landrace × Large White; barrows; 21 d of age) were randomly assigned into three groups: control group, LPS-challenged group, and PEC + LPS group. Piglets were administrated with LPS or saline on d14 and d21 of the experiment. All piglets were slaughtered and intestinal samples were collected after 3 h administration on d21. Pectin supplementation ameliorated the LPS-induced inflammation response and damage to the ileal morphology. Meanwhile, pectin also improved intestinal mucin barrier function, increased the mRNA expression of MUC2, and improved intestinal mucus glycosylation. LPS challenge reduced the diversity of intestinal microbiota and enriched the relative abundance of Helicobacter. Pectin restored alpha diversity improved the structure of the gut microbiota by enriching anti-inflammatory bacteria and short-chain fatty acid (SCFA)-producing bacteria, and increased the concentrations of acetate. In addition, Spearman rank correlation analysis also revealed the potential relationship between intestinal microbiota and intestinal morphology, intestinal inflammation, and intestinal glycosylation in piglets. Taken together, these results indicate that pectin enhances intestinal integrity and barrier function by altering intestinal microbiota composition and their metabolites, which subsequently alleviates intestinal injury and finally improves the growth performance of piglets.

Dietary Fiber in Plant Cell Walls—The Healthy Carbohydrates

Dietary fiber (DF) is one of the major classes of nutrients for humans. It is widely distributed in the edible parts of natural plants, with the cell wall being the main DF-containing structure. The DF content varies significantly in different plant species and organs, and the processing procedure can have a dramatic effect on the DF composition of plant-based foods. Given the considerable nutritional value of DF, a deeper understanding of DF in food plants, including its composition and biosynthesis, is fundamental to the establishment of a daily intake reference of DF and is also critical to molecular breeding programs for modifying DF content. In the past decades, plant cell wall biology has seen dramatic progress, and such knowledge is of great potential to be translated into DF-related food science research and may provide future research directions for improving the health benefits of food crops. In this review, to spark interdisciplinary discussions between food science researchers and plant cell wall biologists, we focus on a specific category of DF—cell wall carbohydrates. We first summarize the content and composition of carbohydrate DF in various plant-based foods, and then discuss the structure and biosynthesis mechanism of each carbohydrate DF category, in particular the respective biosynthetic enzymes. Health impacts of DF are highlighted, and finally, future directions of DF research are also briefly outlined.

Strategies for circadian rhythm disturbances and related psychiatric disorders: A new cue based on plant polysaccharides and intestinal microbiota

Circadian rhythm is essential to human physiological homeostasis and health. The oscillation of host circadian rhythm affects the composition and function of intestinal microbiota, meanwhile, the normal operation of host...

Recent advances in utilization of pectins in biomedical applications: a review focusing on molecular structure-directing health-promoting properties

The numerous health benefits of pectins justify their inclusion in human diets and biomedical products. This review provides an overview of pectin extraction and modification methods, their physico-chemical characteristics, health-promoting properties, and pharmaceutical/biomedical applications. Pectins, as readily available and versatile biomolecules, can be tailored to possess specific functionalities for food, pharmaceutical and biomedical applications, through judicious selection of appropriate extraction and modification technologies/processes based on green chemistry principles. Pectin's structural and physicochemical characteristics dictate their effects on digestion and bioavailability of nutrients, as well as health-promoting properties including anticancer, immunomodulatory, anti-inflammatory, intestinal microflora-regulating, immune barrier-strengthening, hypercholesterolemia-/arteriosclerosis-preventing, anti-diabetic, anti-obesity, antitussive, analgesic, anticoagulant, and wound healing effects. HG, RG-I, RG-II, molecular weight, side chain pattern, and degrees of methylation, acetylation, amidation and branching are critical structural elements responsible for optimizing these health benefits. The physicochemical characteristics, health functionalities, biocompatibility and biodegradability of pectins enable the construction of pectin-based composites with distinct properties for targeted applications in bioactive/drug delivery, edible films/coatings, nano-/micro-encapsulation, wound dressings and biological tissue engineering. Achieving beneficial synergies among the green extraction and modification processes during pectin production, and between pectin and other composite components in biomedical products, should be key foci for future research.

Echinacea purpurea polysaccharide prepared by fractional precipitation prevents alcoholic liver injury in mice by protecting the intestinal barrier and regulating liver-related pathways

Oxidative damage and intestinal dysbiosis are regarded as crucial culprits in alcoholic liver disease (ALD). This study aimed to examine the protective effects of Echinacea purpurea polysaccharides (EPPs) against ALD and explore the underlying mechanisms based on hepatic oxidative stress, inflammation, and intestinal barrier function. Three polysaccharide fractions, namely, EPP40, EPP60, and EPP80, were obtained by stepwise ethanol precipitation, and their antioxidant activity in vitro was investigated. The results showed that EPP80 with Mw 11.82 kDa had the strongest radical-scavenging capacity against DPPH, ABTS, and •OH radicals. Besides, EPP80 comprised arabinose, galactose, glucose, mannose, galacturonic acid, and glucuronic acid in molar ratios of 13.42:25.12:10.92:8.59:2.07:0.82. The in vivo results showed that EPP80 increased the activities of antioxidant enzymes and reduced the levels of inflammatory cytokines both in mouse serum and liver. Moreover, EPP80 upregulated the expression of Occludin and ZO-1, revealing its protective effect against intestinal barrier dysfunction. Furthermore, EPP80 inhibited alcohol-induced oxidative damage by promoting the expression of Nrf2, HO-1, and NQO1 in the liver. In summary, EPP80 markedly scavenged free radicals in vitro and ameliorated alcohol-induced liver injury via Nrf2/HO-1 pathways in vivo. These findings suggested that EPP80 could provide effective supplementary support in preventing and treating ALD.

Challenges of pectic polysaccharides as a prebiotic from the perspective of fermentation characteristics and anti-colitis activity

Several studies are described that contribute to the systematic exploration of new aspects of digestion, fermentation, and biological activities of pectic polysaccharides (PPS) leading to a better understanding of prebiotics. Inflammatory bowel disease (IBD) is thought to be associated with the dysbacteriosis induced by different environmental agents in genetically susceptible persons. PPS are considered as an indispensable gut-microbiota-accessible carbohydrate that play a dominant role in maintaining gut microbiota balance and show a better effect in ameliorating IBD than some traditional prebiotics. The aim of this review is to summarize the fermentation characteristics of PPS, highlight its role in improving IBD, and propose a view that PPS may be a new and effective prebiotic.

Dietary pectic substances enhance gut health by its polycomponent: A review

Pectic substances, one of the cell wall polysaccharides, exist widespread in vegetables and fruits. A surge of recent research has revealed that pectic substances can inhibit gut inflammation and relieve inflammatory bowel disease symptoms. However, physiological functions of pectins are strongly structure dependent. Pectic substances are essentially heteropolysaccharides composed of homogalacturonan and rhamnogalacturonan backbones substituted by various neutral sugar sidechains. Subtle changes in the architecture of pectic substances may remarkably influence the nutritional function of gut microbiota and the host homeostasis of immune system. In this context, developing a structure-function understanding of how pectic substances have an impact on an inflammatory bowel is of primary importance for diet therapy and new drugs. Therefore, the present review has summarized the polycomponent nature of pectic substances, the activities of different pectic polymers, the effects of molecular characteristics and the underlying mechanisms of pectic substances. The immunomodulated property of pectic substances depends on not only the chemical composition but also the physical structure characteristics, such as molecular weight (M_w ) and chain conformation. The potential mechanisms by which pectic substances exert their protective effects are mainly reversing the disordered gut microbiota, regulating immune cells, enhancing barrier function, and inhibiting pathogen adhesion. The manipulation of pectic substances on gut health is sophisticated, and the link between structural specificity of pectins and selective regulation needs further exploration.

Regulation effects of indigestible dietary polysaccharides on intestinal microflora: An overview

The human intestinal contains rich and diverse microbiota that utilizes a variety of polysaccharides. The intestinal microflora extends the metabolic functions of the body, obtaining energy from indigestible dietary polysaccharides. It is not only a highly competitive environment but also a comprehensive collaboration for these polysaccharides, as the microbiota work to maximize the energy harvested from them through the intestine. Indigestible dietary polysaccharides help to manage colon health and host health by affecting the gut microbial population. These polysaccharides also influence the metabolic activity of the intestinal microbiota by stimulating the formation of SCFAs. Most of these metabolic activities affect host physiology because the epithelium absorbs secondary metabolites and end products or transports them to the liver, where they could exert other beneficial effects. This article reviews the carbohydrates existing in the human intestine, the regulating actions of indigestible polysaccharides on intestinal microflora, and the molecular basis of the degradation process of these polysaccharides. PRACTICAL APPLICATIONS: Large deals of researches have shown that indigestible polysaccharides possess an outstanding regulation effect on the intestinal microflora, which indicates that indigestible polysaccharides have the potential to be used as prebiotics in the functional food and pharmaceutical industries. However, it is not clear how gut microbiota metabolizes these dietary polysaccharides, and how the resulting gut metabolites may further affect the intestinal microflora population and metabolism. This paper reviews the indigestible dietary polysaccharides existing in the human intestine, the regulation of polysaccharides on gut microbiota, and the molecular basis of the degradation process of these polysaccharides. This review helps to better understand the relationship between indigestible dietary polysaccharides and intestinal microflora, which will provide powerful evidence for the potential use of these polysaccharides as functional foods.

The effects of different dietary fiber pectin structures on the gastrointestinal immune barrier: impact via gut microbiota and direct effects on immune cells

Pectins are dietary fibers with different structural characteristics. Specific pectin structures can influence the gastrointestinal immune barrier by directly interacting with immune cells or by impacting the intestinal microbiota. The impact of pectin strongly depends on the specific structural characteristics of pectin; for example, the degree of methyl-esterification, acetylation and rhamnogalacturonan I or rhamnogalacturonan II neutral side chains. Here, we review the interactions of specific pectin structures with the gastrointestinal immune barrier. The effects of pectin include strengthening the mucus layer, enhancing epithelial integrity, and activating or inhibiting dendritic cell and macrophage responses. The direct interaction of pectins with the gastrointestinal immune barrier may be governed through pattern recognition receptors, such as Toll-like receptors 2 and 4 or Galectin-3. In addition, specific pectins can stimulate the diversity and abundance of beneficial microbial communities. Furthermore, the gastrointestinal immune barrier may be enhanced by short-chain fatty acids. Moreover, pectins can enhance the intestinal immune barrier by favoring the adhesion of commensal bacteria and inhibiting the adhesion of pathogens to epithelial cells. Current data illustrate that pectin may be a powerful dietary fiber to manage and prevent several inflammatory conditions, but additional human studies with pectin molecules with well-defined structures are urgently needed.

Hairy Region Concentrate of Pectin Strongly Stimulates Mucin Secretion in HT29-MTX Cells, but to a Lessor Degree in Rat Small Intestine

Pectin enhances mucin secretion in the rat small intestine. However, what structural features of pectin to stimulate mucin secretion remain unclear. The study aimed to clarify active constituents of pectin using a human goblet cell line, HT29-MTX. Various pectins at 100 mg/L commonly stimulated MUC5AC secretion, irrespective of their differences in molecular size, plant origin and degree of methoxylation, whereas other dietary fiber materials at 100 mg/L did not show any effects, except fucoidan. Hairy region concentrate (HRC) and its further fractions (F1-F3) were prepared by polygalacturonase treatment of citrus pectin and successive anion exchange chromatography. Neutral sugars, such as galactose and arabinose were enriched in these fractions. HRC and F1-F3 at 30 mg/L significantly increased MUC5AC secretion, which were 3 times more potent compared with a starting material (citrus pectin). Further, a dose-dependent study showed that F1 significantly increased MUC5AC secretion from at 0.3 mg/L, much stronger than that of mucin-secretagogue lipopolysaccharides. Rats consumed 5% apple pectin diet showed significant increases of luminal mucin contents and Muc2 expression in the small intestine, while the luminal mucin contents in rats consumed 1.5% HRC diet were increased by 24% compared to those in rats consumed control diet, but the difference did not reach significant. Thus, HRC is supposed to be active constituents of mucin-secretory effect of pectin in vitro. At present, however, the effect of HRC has not been verified in vivo.

Modulation of Pectin on Mucosal Innate Immune Function in Pigs Mediated by Gut Microbiota

The use of prebiotics to regulate gut microbiota is a promising strategy to improve gut health. Pectin (PEC) is a prebiotic carbohydrate that enhances the health of the gut by promoting the growth of beneficial microbes. These microbes produce metabolites that are known to improve mucosal immune responses. This study was conducted to better understand effects of PEC on the microbiome and mucosal immunity in pigs. Pigs were fed two diets, with or without 5% apple PEC, for 72 days. Effects of PEC on the microbiota, cytokine expression, short-chain fatty acids (SCFAs) concentration and barrier function were examined in the ileum and cecum of the pigs. An integrative analysis was used to determine interactions of PEC consumption with bacterial metabolites and microbiome composition and host mucosal responses. Consumption of PEC reduced expression of pro-inflammatory cytokines such as IFN-γ, IL-6, IL-8, IL-12 and IL-18, and the activation of the pro-inflammatory NF-κB signaling cascade. Expression of MUC2 and TFF and the sIgA content was upregulated in the mucosa of PEC-fed pigs. Network analysis revealed that PEC induced significant interactions between microbiome composition in the ileum and cecum on mucosal immune pathways. PEC-induced changes in bacterial genera and fermentation metabolites, such as Akkermansia, Faecalibacterium, Oscillibacter, Lawsonia and butyrate, correlated with the differentially expressed genes and cytokines in the mucosa. In summary, the results demonstrate the anti-inflammatory properties of PEC on mucosal immune status in the ileum and cecum effected through modulation of the host microbiome.

Marine Microalgae, Spirulina maxima-Derived Modified Pectin and Modified Pectin Nanoparticles Modulate the Gut Microbiota and Trigger Immune Responses in Mice

This study evaluated the modulation of gut microbiota, immune responses, and gut morphometry in C57BL/6 mice, upon oral administration of S. maxima-derived modified pectin (SmP, 7.5 mg/mL) and pectin nanoparticles (SmPNPs; 7.5 mg/mL). Metagenomics analysis was conducted using fecal samples, and mice duodenum and jejunum were used for analyzing the immune response and gut morphometry, respectively. The results of metagenomics analysis revealed that the abundance of Bacteroidetes in the gut increased in response to both modified SmP and SmPNPs (75%) as compared with that in the control group (66%), while that of Firmicutes decreased in (20%) as compared with that in the control group (30%). The mRNA levels of mucin, antimicrobial peptide, and antiviral and gut permeability-related genes in the duodenum were significantly (p < 0.05) upregulated (> 2-fold) upon modified SmP and SmPNPs feeding. Protein level of intestinal alkaline phosphatase was increased (1.9-fold) in the duodenum of modified SmPNPs feeding, evidenced by significantly increased goblet cell density (0.5 ± 0.03 cells/1000 µm2) and villi height (352 ± 10 µm). Our results suggest that both modified SmP and SmPNPs have the potential to modulate gut microbial community, enhance the expression of immune related genes, and improve gut morphology.

Modulation of Gut Microbiota by Low Methoxyl Pectin Attenuates Type 1 Diabetes in Non-obese Diabetic Mice

Intestinal homeostasis underpins the development of type 1 diabetes (T1D), and dietary manipulations to enhance intestinal homeostasis have been proposed to prevent T1D. The current study aimed to investigate the efficacy of supplementing a novel specific low-methoxyl pectin (LMP) dietary fiber in preventing T1D development. Female NOD mice were weaned onto control or 5% (wt/wt) LMP supplemented diets for up to 40 weeks of age, overt diabetes incidence and blood glucose were monitored. Then broad-spectrum antibiotics (ABX) treatment per os for 7 days followed by gut microbiota transfer was performed to demonstrate gut microbiota-dependent effects. Next-generation sequencing was used for analyzing the composition of microbiota in caecum. Concentration of short chain fatty acids were determined by GC-MS. The barrier reinforcing tight junction proteins zonula occludens-2 (ZO-2), claudin-1 and NOD like receptor protein 3 (NLRP3) inflammasome activation were determined by Western blot. The proportion of CD25⁺Foxp3⁺CD4⁺ regulatory T cell (Foxp3⁺ Treg) in the pancreas, pancreatic and mesenteric lymph nodes was analyzed by flow cytometry. We found that LMP supplementation ameliorated T1D development in non-obese diabetic (NOD) mice, as evidenced by decreasing diabetes incidence and fasting glucose levels in LMP fed NOD mice. Further microbiota analysis revealed that LMP supplementation prevented T1D-associated caecal dysbiosis and selectively enriched caecal bacterial species to produce more SCFAs. The LMP-mediated microbial balance further enhanced caecal barrier function and shaped gut-pancreatic immune environment, as characterized by higher expression of tight junction proteins claudin-1, ZO-2 in caecum, increased Foxp3⁺ Treg population and decreased NLRP3 inflammasome activation in both caecum and pancreas. The microbiota-dependent beneficial effect of LMP on T1D was further proven by the fact that aberration of caecal microbiota by ABX treatment worsened T1D autoimmunity and could be restored with transfer of feces of LMP-fed NOD mice. These data demonstrate that this novel LMP limits T1D development by inducing caecal homeostasis to shape pancreatic immune environment. This finding opens a realistic option for gut microbiota manipulation and prevention of T1D in humans.

Goblet cells and mucus layer in the gut of young pigs: Response to dietary contents of threonine and non-essential amino acids

Mucins secreted by goblet cells (GC) are the major components of mucus layer coating and protecting gut epithelium. The study aimed at determining the effect of non-essential amino acids (NEAA) and threonine (Thr) levels on GC number and mucus layer thickness measured in different parts of the gut. A two-factorial experiment was conducted on 72 pigs (initial BW 12.5 kg) using as factors: Thr level (5.1, 5.7, 6.3 and 6.9 g standardized ileal digestible [SID] Thr/kg) and wheat gluten (WG) level used as a source of NEAA (20.4, 40.4 and 60.4 g WG protein in WG20, WG40 and WG60 diets respectively). All diets covered the requirement for essential AA, except for Thr, and they were fed to six pigs for 20 days. Thr level affected only the count of GC containing acidic mucins in the proximal colon, which was higher in pigs fed a diet with 5.1 g SID Thr/kg in comparison with diet containing 6.3 g SID Thr/kg. In the villi, WG40 and/or WG60 increased the GC number containing acidic mucins and lowered that with neutral mucins in the middle jejunum. In the crypts, higher WG levels decreased the GC number with acidic mucins in the duodenum, ileum and proximal colon and increased that with neutral and mixed mucins in the duodenum and ileum. The mucus layer was thicker in the proximal and middle jejunum in WG20 pigs, whereas in the proximal colon it was thicker in WG60 pigs. The lowest GC count was found in the middle jejunum and the highest in the duodenum and proximal colon. The mucus layer was the thinnest in the proximal and middle jejunum and the thickest in the ileum. The results did not show the negative effect of a moderate Thr deficiency and the positive effect of non-essential AA supplementation on GC functions.

Dietary fiber sources and non-starch polysaccharide-degrading enzymes modify mucin expression and the immune profile of the swine ileum

Due to their complex chemical and physical properties, the effects and mechanisms of action of natural sources of dietary fiber on the intestine are unclear. Pigs are commonly fed high-fiber diets to reduce production costs and non-starch polysaccharide (NSP)-degrading enzymes have been used to increase fiber digestibility. We evaluated the expression of mucin 2 (MUC2), presence of goblet cells, and ileal immune profile of pigs housed individually for 28 days and fed either a low fiber diet based on corn-soybean meal (CSB, n = 9), or two high fiber diets formulated adding 40% corn distillers' dried grains with solubles (DDGS, n = 9) or 30% wheat middlings (WM, n = 9) to CSB-based diet. Pigs were also fed those diets supplemented with a NSP enzymes mix (E) of xylanase, β-glucanase, mannanase, and galactosidase (n = 8, 10, and 9 for CSB+E, DDGS+E and WM+E, respectively). Feeding DDGS and WM diets increased ileal MUC2 expression compared with CSB diet, and this effect was reversed by the addition of enzymes. There were no differences in abundance of goblet cells among treatments. In general, enzyme supplementation increased gene expression and concentrations of IL-1β, and reduced the concentrations of IL-4, IL-17A and IL-11. The effects of diet-induced cytokines on modulating intestinal MUC2 were assessed in vitro by treating mouse and swine enteroids with 1 ng/ml of IL-4 and IL-1β. In accordance with previous studies, treatment with Il-4 induced Muc2 and expansion of goblet cells in mouse enteroids. However, swine enteroids did not change MUC2 expression or number of goblet cells when treated with IL-4 or IL-1β. Our results suggest that mucin and immune profile are regulated by diet in the swine intestine, but by mechanisms different to mouse, emphasizing the need for using appropriate models to study responses to dietary fiber in swine.

Investigation of mechanisms involved in postprandial glycemia and insulinemia attenuation with dietary fibre consumption

This work examines the mechanisms involved in the attenuation of postprandial glycemic and insulinemic responses associated with soluble dietary fibre (SDF) consumption. The effect of SDF, including yellow mustard mucilage, soluble flaxseed gum and fenugreek gum on in vitro amylolysis and maltose transport was studied. Furthermore, a human clinical trial was conducted to investigate the effect of SDF consumption on postprandial glycemic and insulinemic responses and gastric emptying, as estimated based on the absorption of paracetamol. Participants (n = 15) at risk for type II diabetes consumed maltose syrup- and starch-based pudding treatments supplemented with each SDF, each at a concentration to match three times the apparent viscosity (18.54 mPa s at 60 s^-1) equivalent to the European Food Safety Authority (2011) glycemia control health claim for cereal β-glucan, measured under simulated small intestinal conditions. The presence of each SDF delayed in vitro amylolysis to a similar extent, but had no effect on maltose transport. Generally, all SDF-containing treatments attenuated blood glucose and plasma insulin peak concentrations and plasma paracetamol 1 h incremental area under the curve values to a similar extent, relative to the controls, despite differences in the amounts at which each SDF was used (from 5.9 to 15.5 g). The postprandial attenuations were related to the ability of each SDF to modify digesta viscosity, perhaps through the delay of gastric emptying, as a delay of amylolysis and sugar transport under simulated upper intestinal conditions did not seem to have a substantial effect.

Low-methoxyl lemon pectin attenuates inflammatory responses and improves intestinal barrier integrity in caerulein-induced experimental acute pancreatitis

SCOPE

Acute pancreatitis (AP) is a common clinical acute abdominal disease. The intestinal injury associated with AP will aggravate the condition retroactively. This study investigates whether the low-methoxyl pectin (LMP) isolated from lemon could attenuate AP and associated intestinal injury.

METHODS AND RESULTS

Experimental AP was induced in BALB/c mice by caerulien (CAE) hyperstimulation. Nutritional prophylactic group was pre-fed with 5% LMP supplemented forage 3 days before AP induction. We found that LMP supplementation attenuated the severity of AP as evidenced by reduced serum amylase and lipase levels, pancreatic edema and myeloperoxidase activity. The protective effect was also confirmed by histological examination of pancreatic damage. LMP suppressed the production of pancreatic proinflammatory cytokines including TNF-α, IL-1β, and IL-6. Moreover, LMP supplementation restored AP-associated disruption of intestinal barrier integrity as evidenced by upregulation of tight junction modulatory proteins occludin, zonula occludens (ZO)-1, antimicrobial peptides β-defensin-1 (DEFB1) and CRAMP as well as increase in SCFAs production. LMP supplemented mice with AP exhibited suppressed intestinal inflammation as shown by decreased ileal and colon cytokine production compared with CAE group.

CONCLUSION

Our results support dietary LMP supplementation as an effective nutritional intervention for AP and associated intestinal injury.

Increasing dietary oat fibre decreases the permeability of intestinal mucus

This study investigates the influence of the dietary fibre β-glucan on nutrient composition and mucus permeability. Pigs were fed a standard diet or a diet containing twice the β-glucan content for 3 days (n = 5 per group), followed by the collection of small intestinal mucus and tissue samples. Samples of the consumed diets were subjected to in vitro digestion to determine β-glucan release, nutrient profile and assessment of mucus permeability. In vitro digestion of the diets indicated that 90% of the β-glucan was released in the proximal small intestine. Measurements of intestinal mucus showed a reduction in permeability to 100 nm latex beads and also lipid from the digested enhanced β-glucan diet. The data from this study show for the first time that reducing mass transfer of bile and lipid through the intestinal mucus layer may be one way in which this decrease in bile reabsorption by soluble fibre is enabled.

Soluble Dietary Fiber Can Protect the Gastrointestinal Mucosa Against Nonsteroidal Anti-Inflammatory Drugs in Mice

BACKGROUND

Nonsteroidal anti-inflammatory drug (NSAID)-induced small intestinal damage is a serious problem in patients, but effective therapy is not available at present.

AIMS

The effects of feeding conditions and dietary fiber (DF) on NSAID-induced gastrointestinal lesions were examined in mice.

METHODS

NSAIDs (indomethacin, diclofenac, loxoprofen, aspirin) were administered to male mice in various feeding conditions. Gastrointestinal lesions were examined 24 h after NSAID dosing. Regular diets, dietary-fiber-free diet (FFD), and diets supplemented with various types of DF were given to mice.

RESULTS

NSAIDs produced marked ulcers and perforations selectively in the gastric antrum when they were administered after feeding of regular diet for 2 h after a 22-h fast. When NSAIDs, except for aspirin, were administered in unfasted conditions, they caused marked lesions in the small intestine. When mice were given FFD, antral ulcers and intestinal lesions induced by indomethacin (30 mg/kg, s.c.) markedly decreased, but when cellulose, an insoluble DF, was added to FFD, the lesions appeared again. The addition of pectin, a soluble DF, to regular diet containing 4.1 % crude fiber significantly inhibited the formation of antral ulcers as well as intestinal lesions caused by indomethacin or diclofenac (100 mg/kg, s.c.).

CONCLUSIONS

The results indicated that NSAIDs given after feeding of diet produced ulcers selectively in the gastric antrum. The severity of the gastrointestinal lesions depended on the concentration of soluble or insoluble DF in food. Our results suggest that soluble DF such as pectin may be a safe means for protecting the gastrointestinal mucosa against NSAIDs.

Sodium alginate decreases the permeability of intestinal mucus

In the small intestine the nature of the environment leads to a highly heterogeneous mucus layer primarily composed of the MUC2 mucin. We set out to investigate whether the soluble dietary fibre sodium alginate could alter the permeability of the mucus layer. The alginate was shown to freely diffuse into the mucus and to have minimal effect on the bulk rheology when added at concentrations below 0.1%. Despite this lack of interaction between the mucin and alginate, the addition of alginate had a marked effect on the diffusion of 500 nm probe particles, which decreased as a function of increasing alginate concentration. Finally, we passed a protein stabilised emulsion through a simulation of oral, gastric and small intestinal digestion. We subsequently showed that the addition of 0.1% alginate to porcine intestinal mucus decreased the diffusion of fluorescently labelled lipid present in the emulsion digesta. This reduction may be sufficient to reduce problems associated with high rates of lipid absorption such as hyperlipidaemia.

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There are no specific interactions between alginate and intestinal mucus.

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Mucus rheology was hardly altered by small additions of alginate.

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Alginate freely diffused into mucus and reduced diffusion of 500 nm beads.

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Intestinal mucus permeability was decreased by a factor of two.

Saturated and Unsaturated Fatty Acids Differently Modulate Colonic Goblet Cells In Vitro and in Rat Pups

BACKGROUND

High-fat diets induce intestinal barrier alterations and promote intestinal diseases. Little is known about the effects of long-chain fatty acids (LCFAs) on mucin 2 (MUC2) production by goblet cells, which are crucial for intestinal protection.

OBJECTIVE

We investigated the effects of LCFAs on the differentiation of colonic goblet cells, MUC2 expression, and colonic barrier function.

METHODS

Upon reaching confluence, human colonic mucus-secreting HT29-MTX cells were stimulated (21 d) with a saturated LCFA (palmitic or stearic acid), a monounsaturated LCFA (oleic acid), or a polyunsaturated LCFA (linoleic, γ-linolenic, α-linolenic, or eicosapentaenoic acid). In addition, rat pups underwent oral administration of oil (palm, rapeseed, or sunflower oil) or water (10 μL/g body weight, postnatal days 10-15). Subsequently, colon goblet cells were studied by Western blotting, reverse transcriptase-quantitative polymerase chain reaction, and immunohistochemistry and colonic transmucosal electrical resistance was measured by using Ussing chambers.

RESULTS

In vitro, palmitic acid enhanced MUC2 production (140% of control) and hepatocyte nuclear factor 4α expression, whereas oleic, linoleic, γ-linolenic, α-linolenic, and eicosapentaenoic acids reduced MUC2 expression (at least -50% of control). All unsaturated LCFAs decreased the expression of human atonal homolog 1, a transcription factor controlling goblet cell differentiation (at least -31% vs. control). In vivo, rats fed palm oil had higher palmitic acid concentrations (3-fold) in their colonic contents and increased mucus granule surfaces in their goblet cells (>2-fold) than did all other groups. Palm oil also increased colonic transmucosal electrical resistance (245% of control), yet had no effect on occludin and zonula occludens-1 expression. In contrast, sunflower and rapeseed oils decreased goblet cell number when compared with control (at least -10%) and palm oil (at least -14%) groups.

CONCLUSIONS

Palm oil in rat pups and palmitic acid in HT29-MTX cells increase the production of MUC2 and strengthen the intestinal barrier. In contrast, unsaturated LCFAs decrease MUC2 expression. These data should be taken into account in the context of preventive or therapeutic nutritional programs.