Regulation of Intestinal Epithelial Cells Properties and Functions by Amino Acids

Hepatoprotective Effects of Ixeris chinensis on Nonalcoholic Fatty Liver Disease Induced by High-Fat Diet in Mice: An Integrated Gut Microbiota and Metabolomic Analysis

Ixeris chinensis (Thunb.) Nakai (IC) is a folk medicinal herb used in Mongolian medical clinics for the treatment of hepatitis and fatty liver diseases even though its pharmacological mechanism has not been well characterized. This study investigated the hepatoprotective mechanism of IC on mice with nonalcoholic fatty liver disease (NAFLD) by integrating gut microbiota and metabolomic analysis. A high-fat diet (HFD) was used to develop nonalcoholic fatty liver disease, after which the mice were treated with oral IC (0.5, 1.5 and 3.0 g/kg) for 10 weeks. HFD induced NAFLD and the therapeutic effects were characterized by pathological and histological evaluations, and the serum indicators were analyzed by ELISA. The gut microbial and metabolite profiles were studied by 16S rRNA sequencing and untargeted metabolomic analysis, respectively. The results showed that the administration of IC resulted in significant decreases in body weight; liver index; serum biomarkers such as ALT, TG, and LDL-C; and the liver inflammatory factors IL-1β, IL-6, and TNF-α. The 16S rRNA sequencing results showed that administration of IC extract altered both the composition and abundance of the gut microbiota. Untargeted metabolomic analysis of liver samples detected a total of 212 metabolites, of which 128 were differentially expressed between the HFD and IC group. IC was found to significantly alter the levels of metabolites such as L-glutamic acid, pyridoxal, ornithine, L-aspartic acid, D-proline, and N4-acetylaminobutanal, which are involved in the regulation of glutamine and glutamate, Vitamin B6 metabolism, and arginine and proline metabolic pathways. Correlation analysis indicated that the effects of the IC extract on metabolites were associated with alterations in the abundance of Akkermansiaceae, Lachnospiraceae, and Muribaculaceae. Our study revealed that IC has a potential hepatoprotective effect in NAFLD and that its function might be linked to improvements in the composition of gut microbiota and their metabolites.

Targeting Scavenger Receptors in Inflammatory Disorders and Oxidative Stress

Oxidative stress and inflammation cannot be considered as diseases themselves; however, they are major risk factors for the development and progression of the pathogenesis underlying many illnesses, such as cancer, neurological disorders (including Alzheimer's disease and Parkinson's disease), autoimmune and metabolic disorders, etc. According to the results obtained from extensive studies, oxidative stress-induced biomolecules, such as advanced oxidation protein products, advanced glycation end products, and advanced lipoxidation end products, are critical for an accelerated level of inflammation and oxidative stress-induced cellular damage, as reflected in their strong affinity to a wide range of scavenger receptors. Based on the limitations of antioxidative and anti-inflammatory molecules in practical applications, targeting such interactions between harmful molecules and their cellular receptors/signaling with advances in gene engineering technology, such as CRISPR or TALEN, may prove to be a safe and effective alternative. In this review, we summarize the findings of recent studies focused on the deletion of scavenger receptors under oxidative stress as a development in the therapeutic approaches against the diseases linked to inflammation and the contribution of advanced glycation end products (AGEs), advanced lipid peroxidation products (ALEs), and advanced oxidation protein products (AOPPs).

Integrity of the Intestinal Barrier: The Involvement of Epithelial Cells and Microbiota-A Mutual Relationship

Simple Summary

The gastrointestinal tract is a complex organization of various types of epithelial cells forming a single layer of the mucosal barrier, the host mucosal immune system, and microorganisms termed as gut microbiota inhabiting this area. The mucosal barrier, including physical and chemical factors, spatially segregates gut microbiota and the host immune system preventing the development of immune response directed towards non-pathogenic commensals and dietary antigens. However, for the maintenance of the integrity of the mucosal surfaces, cross-talk between epithelial cells and microbiota is required. The microbiome and the intestinal epithelium developed a complex dependence necessary for sustaining intestinal homeostasis. In this review, we highlight the role of specific epithelial cell subtypes and their role in barrier arrangement, the mechanisms employed by them to control intestinal microbiota as well as the mechanisms utilized by the microbiome to regulate intestinal epithelial function. This review will provide information regarding the development of inflammatory disorders dependent on the loss of intestinal barrier function and composition of the intestinal microbiota.

Abstract

The gastrointestinal tract, which is constantly exposed to a multitude of stimuli, is considered responsible for maintaining the homeostasis of the host. It is inhabited by billions of microorganisms, the gut microbiota, which form a mutualistic relationship with the host. Although the microbiota is generally recognized as beneficial, at the same time, together with pathogens, they are a permanent threat to the host. Various populations of epithelial cells provide the first line of chemical and physical defense against external factors acting as the interface between luminal microorganisms and immunocompetent cells in lamina propria. In this review, we focus on some essential, innate mechanisms protecting mucosal integrity, thus responsible for maintaining intestine homeostasis. The characteristics of decisive cell populations involved in maintaining the barrier arrangement, based on mucus secretion, formation of intercellular junctions as well as production of antimicrobial peptides, responsible for shaping the gut microbiota, are presented. We emphasize the importance of cross-talk between gut microbiota and epithelial cells as a factor vital for the maintenance of the homeostasis of the GI tract. Finally, we discuss how the imbalance of these regulations leads to the compromised barrier integrity and dysbiosis considered to contribute to inflammatory disorders and metabolic diseases.

Metabolomics changes in brain-gut axis after unpredictable chronic mild stress

BACKGROUND

Major depressive disorder is a leading cause of disability worldwide, affecting up to 17 % of the general population. The neural mechanisms of depression, however, are yet to be uncovered. Recently, attention has been drawn to the effects of dysfunctional brain-gut axis on depression, and many substances have been suggested to be involved in the communication between the gut and brain, such as ghrelin.

METHODS

We herein systematically examined the changes of metabolomics after unpredictable chronic mild stress (UCMS)-induced depression-like behaviors in rats and compared the altered metabolites in the hippocampus and jejunum samples.

RESULTS

Our results show that many metabolites significantly changed with UCMS both in the hippocampus and jejunum, such as L-glutamine, L-tyrosine, hydroxylamine, and 3-phosphoglyceric acid. Further studies suggested that these changes are the reasons for anxiety-like behaviors and depression-like behaviors in UCMS rats and also are the reasons for hippocampal neural plasticity.

CONCLUSIONS

Coexistence of brain and gut metabolic changes in UCMS-induced depressive behavior in rats suggests a possible role of brain-gut axis in depression. This study provides insights into the neurobiology of depression.

LKB1 in Intestinal Epithelial Cells Regulates Bile Acid Metabolism by Modulating FGF15/19 Production

BACKGROUND & AIMS

Liver kinase B1 (LKB1) is a master upstream protein kinase involved in nutrient sensing and glucose and lipid metabolism in many tissues; however, its metabolic role in intestinal epithelial cells (IEC) remains unclear. In this study, we investigated the regulatory role of LKB1 on bile acid (BA) homeostasis.

METHODS

We generated mice with IEC-specific deletion of LKB1 (LKB1^ΔIEC) and analyzed the characteristics of IEC development and BA level. In vitro assays with small interfering RNA, liquid chromatography/mass spectrometry, metagenomics, and RNA-sequencing were used to elucidate the regulatory mechanisms underlying perturbed BA homeostasis.

RESULTS

LKB1 deletion resulted in abnormal differentiation of secretory cell lineages. Unexpectedly, BA pool size increased substantially in LKB1^ΔIEC mice. A significant reduction of the farnesoid X receptor (FXR) target genes, including fibroblast growth factor 15/19 (FGF15/19), known to inhibit BA synthesis, was found in the small intestine (SI) ileum of LKB1^ΔIEC mice. We observed that LKB1 depletion reduced FGF15/19 protein level in human IECs in vitro. Additionally, a lower abundance of bile salt hydrolase-producing bacteria and elevated levels of FXR antagonist (ie, T-βMCA) were observed in the SI of LKB1^ΔIEC mice. Moreover, LKB1^ΔIEC mice showed impaired conversion of retinol to retinoic acids in the SI ileum. Subsequently, vitamin A treatment failed to induce FGF15 production. Thus, LKB1^ΔIEC mice fed with a high-fat diet showed improved glucose tolerance and increased energy expenditure.

CONCLUSIONS

LKB1 in IECs manages BA homeostasis by controlling FGF15/19 production.

Nanoencapsulation for Probiotic Delivery

Gut microbiota dynamically participate in diverse physiological activities with direct impact on the host's health. A range of factors associated with the highly complex intestinal flora ecosystem poses challenges in regulating the homeostasis of microbiota. The consumption of live probiotic bacteria, in principle, can address these challenges and confer health benefits. In this context, one of the major problems is ensuring the survival of probiotic cells when faced with physical and chemical assaults during their intake and subsequent gastrointestinal passage to the gut. Advances in the field have focused on improving conventional encapsulation techniques in the microscale to achieve high cell viability, gastric and temperature resistance, and longer shelf lives. However, these microencapsulation approaches are known to have limitations with possible difficulties in clinical translation. In this Perspective, we present a brief overview of the current progress of different probiotic encapsulation methods and highlight the contemporary and emerging single-cell encapsulation strategies using nanocoatings for individual probiotic cells. Finally, we discuss the relative advantages of various nanoencapsulation approaches and the future trend toward developing coated probiotics with advanced features and health benefits.

Lactoferrin Alleviated AFM1-Induced Apoptosis in Intestinal NCM 460 Cells through the Autophagy Pathway

Aflatoxin M1 (AFM1) is the only mycotoxin with maximum residue limit in milk, which may result in serious human diseases. On the contrary, lactoferrin (Lf) is an active protein with multiple functions. Studies have confirmed that Lf has a powerful potential to protect the intestines, but the influence of Lf on mycotoxins is not clear. This study aims to explore whether Lf can protect the cytotoxicity induced by AFM1, and determine the underlying mechanisms in human normal colonic epithelial NCM460 cells. The results indicated that AFM1 decreased the cell viability, and increased the levels of apoptosis and autophagy of NCM460 cells. Lf can alleviate the cytotoxicity induced by AFM1 through enhancing cell viability, significantly down-regulated the expression of apoptotic genes and proteins (BAX, caspase3, caspase9, caspase3, and caspase9), and regulated the gene and protein expression of autophagy factors (Atg5, Atg7, Atg12, Beclin1, ULK1, ULK2, LC3, and p62). Furthermore, interference of the key gene Atg5 of autophagy can reduce AFM1-induced apoptosis, which is consistent with the role of Lf, implying that Lf may protect AFM1-induced intestinal injury by inhibiting excessive autophagy-mediated apoptosis. Taken together, our data indicated that Lf has a mitigating effect on apoptosis induced by AFM1 through the autophagy pathway.

From the intestinal mucosal barrier to the enteric neuromuscular compartment: an integrated overview on the morphological changes in Parkinson's disease

Gastrointestinal dysfunctions represent the most common non-motor symptoms in Parkinson’s disease (PD). Of note, changes in gut microbiota, impairments of intestinal epithelial barrier (IEB), bowel inflammation and neuroplastic rearrangements of the enteric nervous system (ENS) could be involved in the pathophysiology of the intestinal disturbances in PD. In this context, although several review articles have pooled together evidence on the alterations of enteric bacteria-neuro-immune network in PD, a revision of the literature on the specific morphological changes occurring in the intestinal mucosal barrier, the ENS and enteric muscular layers in PD, is lacking. The present review provides a complete appraisal of the available knowledge on the morphological alterations of intestinal mucosal barrier, with particular focus on IEB, ENS and enteric muscular layers in PD. In particular, our intent was to critically discuss whether, based on evidence from translational studies and preclinical models, morphological changes in the intestinal barrier and enteric neuromuscular compartment contribute to the pathophysiology of intestinal dysfunctions occurring in PD.

Targeting the Gut Mucosal Immune System Using Nanomaterials

The gastrointestinal (GI) tract is one the biggest mucosal surface in the body and one of the primary targets for the delivery of therapeutics, including immunotherapies. GI diseases, including, e.g., inflammatory bowel disease and intestinal infections such as cholera, pose a significant public health burden and are on the rise. Many of these diseases involve inflammatory processes that can be targeted by immune modulatory therapeutics. However, nonspecific targeting of inflammation systemically can lead to significant side effects. This can be avoided by locally targeting therapeutics to the GI tract and its mucosal immune system. In this review, we discuss nanomaterial-based strategies targeting the GI mucosal immune system, including gut-associated lymphoid tissues, tissue resident immune cells, as well as GI lymph nodes, to modulate GI inflammation and disease outcomes, as well as take advantage of some of the primary mechanisms of GI immunity such as oral tolerance.

Capsaicin Attenuates Lipopolysaccharide-Induced Inflammation and Barrier Dysfunction in Intestinal Porcine Epithelial Cell Line-J2

Capsaicin is a spicy, highly pungent, colorless, vanilloid compound found in chili peppers with anti-inflammatory, antioxidant, anti-cancer, and analgesic properties. However, the protective effects of capsaicin on the pig intestine during inflammation are yet to be explored. This study investigated the effects of capsaicin on the gut inflammatory response, intestinal epithelial integrity, and gene expression level of nutrient transporters in a model of lipopolysaccharide (LPS)-induced inflammation in non-differentiated intestinal porcine epithelial cell line-J2 (IPEC-J2). The results showed that the pre-treatment of cells with capsaicin (100 μM) significantly decreased the gene expression and secretion of proinflammatory cytokines induced by LPS through Toll-like receptor 4 (TLR4)/NF-κB signaling pathway. In addition, pre-treatment of cells with capsaicin also increased both gene and protein abundance of tight junction proteins. Furthermore, pre-treatment cells with capsaicin significantly increased trans-epithelial electrical resistance (TEER) and decreased permeability of fluorescein isothiocyanate-dextran (FD4) from the apical side to the basolateral side compared with the control (P < 0.05). Additionally, pre-treatment of cells with capsaicin upregulated the mRNA abundance of nutrients transporters such as Na⁺/glucose cotransporter 1 (SGLT1). These results suggested that capsaicin could attenuate LPS-induced inflammation response through TLR4/NF-κB pathway and improve barrier integrity and glucose absorption.

A Co-Culture Model of IPEC-J2 and Swine PBMC to Study the Responsiveness of Intestinal Epithelial Cells: The Regulatory Effect of Arginine Deprivation

Simple Summary

The interest in amino acids comes from their involvement in research on alternative strategies for the utilization of antibiotics on farms. Among several substances used to replace antibiotics, there is arginine, an essential amino acid in newborns and piglets. This amino acid has a protective role in intestinal immune cells and improves intestinal immunity. The purpose of this research was to define a co-culture model, in which intestinal epithelial cells can communicate with peripheral blood mononuclear cells (PBMC) to deepen the effects of arginine deprivation on intestinal epithelial cells over time. The main finding was that the lack of arginine highly impacts on intestinal and immune cells by way of immuno-regulation mediated by the expression of pro- and anti-inflammatory cytokines. The use of this experimental model could allow us to investigate the impact of and interactions between specific nutrients and the complex intestinal environment and, in addition, to assess feed additives to improve health and animal production.

Abstract

Arginine is a semi-essential amino acid, supplementation with which induces a reduction of intestinal damage and an improvement of intestinal immunity in weaned piglets, but the mechanism is not yet entirely clear. The aim of this study was to characterise a co-culture model by measuring changes in gene expression over time (24 and 48 h) in intestinal IPEC-J2 cells in the presence of immune cells activated with phytohemagglutinin and, consequently, to assess the effectiveness of arginine deprivation or supplementation in modulating the expression of certain cytokines related to the regulation of intestinal cells’ function. The main results show the crucial role of arginine in the viability/proliferation of intestinal cells evaluated by an MTT assay, and in the positive regulation of the expression of pro-inflammatory (TNF-α, IL-1α, IL-6, IL-8) and anti-inflammatory (TGF-β) cytokines. This experimental model could be important for analysing and clarifying the role of nutritional conditions in intestinal immune cells’ functionality and reactivity in pigs as well as the mechanisms of the intestinal defence system. Among the potential applications of our in vitro model of interaction between IEC and the immune system there is the possibility of studying the effect of feed additives to improve animal health and production.

Robust Three-Dimensional (3D) Expansion of Bovine Intestinal Organoids: An In Vitro Model as a Potential Alternative to an In Vivo System

Intestinal organoids offer great promise for disease-modelling-based host-pathogen interactions and nutritional research for feed efficiency measurement in livestock and regenerative medicine for therapeutic purposes. However, very limited studies are available on the functional characterisation and three-dimensional (3D) expansion of adult stem cells in livestock species compared to other species. Intestinal crypts derived from intestinal organoids under a 3D culture system from the small intestine in adult bovine were successfully established and characterised for functionality testing, including the cellular potentials and genetic properties based on immunohistochemistry, immunocytochemistry, epithelial barrier permeability assay, QuantSeq 3' mRNA-Seq. data and quantitative reverse transcription-polymerase chain reaction. Intestinal organoids were long-term cultivated over several passages of culture without loss of the recapitulating capacity of crypts, and they had the specific expression of several specific markers involved in intestinal stem cells, intestinal epithelium, and nutrient absorption. In addition, they showed the key functionality with regard to a high permeability for compounds of up to FITC-dextran 4 kDa, while FITC-dextran 40 kDa failed to enter the organoid lumen and revealed that the genetic properties of bovine intestinal organoids were highly similar to those of in vivo. Collectively, these results provide a reliable method for efficient isolation of intestinal crypts from the small intestine and robust 3D expansion of intestinal organoids in adult bovine and demonstrate the in vitro 3D organoids mimics the in vivo tissue topology and functionality. Finally, intestinal organoids are potential alternatives to in vivo systems and will be facilitated as the practical model to replace animal experiments for various purposes in the fields of animal biotechnology.

The Intestinal Microbiota: Impacts of Antibiotics Therapy, Colonization Resistance, and Diseases

Trillions of microbes exist in the human body, particularly the gastrointestinal tract, coevolved with the host in a mutually beneficial relationship. The main role of the intestinal microbiome is the fermentation of non-digestible substrates and increased growth of beneficial microbes that produce key antimicrobial metabolites such as short-chain fatty acids, etc., to inhibit the growth of pathogenic microbes besides other functions. Intestinal microbiota can prevent pathogen colonization through the mechanism of colonization resistance. A wide range of resistomes are present in both beneficial and pathogenic microbes. Giving antibiotic exposure to the intestinal microbiome (both beneficial and hostile) can trigger a resistome response, affecting colonization resistance. The following review provides a mechanistic overview of the intestinal microbiome and the impacts of antibiotic therapy on pathogen colonization and diseases. Further, we also discuss the epidemiology of immunocompromised patients who are at high risk for nosocomial infections, colonization and decolonization of multi-drug resistant organisms in the intestine, and the direct and indirect mechanisms that govern colonization resistance to the pathogens.

The role of mucosal barriers in human gut health

The intestinal mucosa is continuously exposed to a large number of commensal or pathogenic microbiota and foreign food antigens. The intestinal epithelium forms a dynamic physicochemical barrier to maintain immune homeostasis. To efficiently absorb nutrients from food, the epithelium in the small intestine has thin, permeable layers spread over a vast surface area. Epithelial cells are renewed from the crypt toward the villi, accompanying epithelial cell death and shedding, to control bacterial colonization. Tight junction and adherens junction proteins provide epithelial cell-cell integrity. Microbial signals are recognized by epithelial cells via toll-like receptors. Environmental signals from short-chain fatty acids derived from commensal microbiota metabolites, aryl hydrocarbon receptors, and hypoxia-induced factors fortify gut barrier function. Here we summarize recent findings regarding various environmental factors for gut barrier function. Further, we discuss the role of gut barriers in the pathogenesis of human intestinal disease and the challenges of therapeutic strategies targeting gut barrier restoration.

Protein Isolates from Raw and Cooked Foxtail Millet Attenuate Development of Type 2 Diabetes in Streptozotocin-Induced Diabetic Mice

SCOPE

Millet protein has received much attention due to its beneficial role in alleviating metabolic disease symptoms. This study aims to investigate the role and molecular mechanism of foxtail millet protein isolates, including protein isolates from raw and cooked foxtail millet in alleviating diabetes, including gut microbiota and intracellular signal pathways.

METHODS AND RESULTS

Protein isolates from raw and cooked foxtail millet are orally administered to streptozotocin (STZ)-induced diabetic mice for 5 weeks before hypoglycemic effect evaluation. The results show that foxtail millet protein isolates improve glucose intolerance and insulin resistance in diabetic mice. However, only the protein isolate from cooked foxtail millet reverse the weight loss trend and alleviate lipid disorders in diabetic mice. Besides, 16S rRNA sequencing show that both raw and cooked foxtail millet protein isolates altered diabetes-induced gut dysbiosis. In addition, western blotting analysis indicated that the protein isolate from cooked foxtail millet increases the expression levels of glucagon-like peptide-1 receptor (GLP-1R), phosphoinositide 3-kinase (PI3K), and phosphoinositide-protein kinase B (p-AKT)/AKT while the protein isolate from raw foxtail millet downregulates stearoyl-coenzyme A desaturase 1 (SCD1) level.

CONCLUSION

Both raw and cooked foxtail millet protein isolates can exert hypoglycemic effects in diabetic mice through rewiring glucose homeostasis, mitigating diabetes-induced gut dysbiosis, and affecting the GLP-1R/PI3K/AKT pathway.

Characterization of a bovine intestinal myofibroblast cell line and stimulation using phytoglycogen-based nanoparticles bound to inosine monophosphate

The goal of the present study was to characterize a novel bovine intestinal myofibroblast (BT-IMF) cell line isolated from a fetal bovine intestine. This cell type is of importance as intestinal myofibroblasts play a key role in controlling intestinal epithelial cell proliferation, intestinal regulation, wound healing, epithelial cell turnover, and structural support. The present work demonstrates that BT-IMF cells could be successfully cryopreserved and thawed and cultured past 25 passages. Immunocytochemical staining of the BT-IMF cell line was positive for vimentin and smooth muscle actin (α-SMA) and negative for pancytokeratin, suggesting that the cells are myofibroblastic in type. Growth kinetic experiments demonstrate that hydrocortisone negatively impacts BT-IMF growth and non-essential amino acids enhance its proliferation. Inosine monophosphate (IMP) is a dietary nucleotide and is essential for supporting animal health. Stimulation with IMP bound to a novel phytoglycogen-based nanocarrier (IMP-NP) showed enhanced cell proliferation. BT-IMF provides a new tool for studying bovine cells in vitro and may be of particular interest for cultured meat manufacturing in the future.

Effect of fumonisin B1 on oxidative stress and gene expression alteration of nutrient transporters in porcine intestinal cells

Fumonisin B₁ (FB₁ ) is a common environmental mycotoxin produced by molds such as Fusarium verticillioides. The toxin poses health risks to domestic animals, including pigs, through FB₁ -contaminanted feed. However, the cytotoxicity of FB₁ to porcine intestines has not been fully analyzed. In the present study, the effects of FB₁ on oxidative stress and nutrient transporter-associated genes of the porcine intestinal IPEC-J2 cells were explored. FB₁ decreased IPEC-J2 proliferation but did not trigger reactive oxygen species (ROS) overproduction. Meanwhile, FB₁ reduced the expression levels of the transporters l-type amino acid transporter-1 (y⁺ LAT1), solute carrier family 7 member 1 (SLC7A1), solute carrier family 1 member 5 (ASCT2), and excitatory amino acid carrier 1 (EAAC1); in addition, FB₁ reduced the levels of the fatty acid transporters long-chain fatty acid transport protein 1 (FATP1) and long-chain fatty acid transport protein 4 (FATP4) as well as glucose transporters Na⁺ /glucose cotransporter 1 (SGLT1) and glucose transporter 2 (GLUT2). FB₁ stimulation increased the expression levels of peptide transporter peptide transporter 1 (PepT1) and metal ion transport-related gene zinc transporter 1 (ZNT1). Moreover, metal ion transporter divalent metal transporter 1 (DMT1) expression was depressed by a higher dosage of FB₁ . The data indicate that FB₁ results in aberrant expression of nutrient transporters in IPEC-J2 cells, thereby exerting its toxicity even though it fails to exert ROS-dependent oxidative stress.

Analysis of Human Faecal Host Proteins: Responsiveness to 10-Week Dietary Intervention Modifying Dietary Protein Intake in Elderly Males

Faecal proteomics targeting biomarkers of immunity and inflammation have demonstrated clinical application for the identification of changes in gastrointestinal function. However, there are limited comprehensive analyses of the host faecal proteome and how it may be influenced by dietary factors. To examine this, the Homo sapiens post-diet proteome of older males was analysed at the completion of a 10-week dietary intervention, either meeting the minimum dietary protein recommendations (RDA; n = 9) or twice the recommended dietary allowance (2RDA, n = 10). The host faecal proteome differed markedly between individuals, with only a small subset of proteins present in ≥ 60% of subjects (14 and 44 proteins, RDA and 2RDA, respectively, with only 7 common to both groups). No differences were observed between the diet groups on the profiles of host faecal proteins. Faecal proteins were detected from a wide range of protein classes, with high inter-individual variation and absence of obvious impact in response to diets with markedly different protein intake. This suggests that well-matched whole food diets with two-fold variation in protein intake maintained for 10 weeks have minimal impact on human faecal host proteins.

Endoplasmic Reticulum Stress and Intestinal Inflammation: A Perilous Union

The intestinal tract encompasses the largest mucosal surface fortified with a fine layer of intestinal epithelial cells along with highly sophisticated network of the lamina propria immune cells that are indispensable to sustain gut homeostasis. However, it can be challenging to uphold homeostasis when these cells in the intestine are perpetually exposed to insults of both endogenous and exogenous origin. The complex networking and dynamic microenvironment in the intestine demand highly functional cells ultimately burdening the endoplasmic reticulum (ER) leading to ER stress. Unresolved ER stress is one of the primary contributors to the pathogenesis of inflammatory bowel diseases (IBD). Studies also suggest that ER stress can be the primary cause of inflammation and/or the consequence of inflammation. Therefore, understanding the patterns of expression of ER stress regulators and deciphering the intricate interplay between ER stress and inflammatory pathways in intestinal epithelial cells in association with lamina propria immune cells contribute toward the development of novel therapies to tackle IBD. This review provides imperative insights into the molecular markers involved in the pathogenesis of IBD by potentiating ER stress and inflammation and briefly describes the potential pharmacological intervention strategies to mitigate ER stress and IBD. In addition, genetic mutations in the biomarkers contributing to abnormalities in the ER stress signaling pathways further emphasizes the relevance of biomarkers in potential treatment for IBD.

Alcohol stimulates the proliferation of mouse small intestinal epithelial cells via Wnt signaling

The intestinal epithelium is one of the fastest renewing tissues in mammals and is a barrier against toxic substances such as alcohol. Excessive alcohol can induce intestinal damage leading to intestinal bowel diseases. Thus, the control of small intestinal epithelial cell (IEC) regeneration is thought to be important for homeostasis in response to epithelium damage. However, reports on how epithelial cells respond to small intestinal damage are scarce. We investigated the effects of alcohol consumption on small intestinal epithelial cells of mice. To verify that alcohol altered the small intestinal epithelium, we used 8-10 weeks old male C57BL/6J mice for models of chronic and binge alcohol consumption (the NIAAA model) in addition to an organoid model. Alcohol promoted the proliferative activity of IECs and intestinal stem cells (ISCs) in intestinal crypts. Alcohol consumption increased expression of the proliferation marker cyclin D1 and activated the p44/42 MAPK (Erk1/2) signaling pathway in small intestinal epithelial cells. The Wnt target genes were markedly increased in IECs from alcohol-treated mice. In the small intestinal organoid model exposed to alcohol, the organoid area and numbers of buds increased with alcohol concentrations up to 0.5% similar to in vivo observations. These results suggest that alcohol consumption stimulates the proliferation of small intestinal epithelial cells via Wnt signaling.

Gallic acid affects intestinal-epithelial-cell integrity and selected amino-acid uptake in porcine in vitro and ex vivo permeability models

Gallic acid (GA) is widely used as a dietary supplement due to several health-promoting effects, although its effects on intestinal-epithelial-cell integrity and transport remain mostly unknown. The present study aims to clarify the effects of GA on tight junctions and intestinal nutrient uptake through in vitro and ex vivo models. Both intestinal porcine enterocyte cell line-J2 cells and porcine middle-jejunum segments were treated with 5 (T5), 25 (T25) and 50 (T50) µm GA and mounted in Ussing chambers to determine transepithelial resistance (TEER), claudin-1 (CLDN1), occludin (OCLN), zonula occludens-1 (ZO-1) protein (in tissues and cells) and mRNA (in cells) expression. In addition, uptake of l-glutamate (l-Glut), l-arginine (l-Arg), l-lysine (l-Lys) and l-methionine (l-Meth) together with cationic-amino-acid transporter-1 (CAT-1) and excitatory-amino-acid transporter-3 (EAAT3) expression was evaluated. No apoptosis was observed in GA-treated cells, but TEER and CLDN1 protein abundance was lower with T50 compared with untreated cells. l-Arg and l-Lys uptake was greater with T5 than with T25 and T50. Ex vivo, T50 decreased the TEER values and the protein levels of CLDN1, OCLN and ZO-1, whereas T5 and T25 only decreased CLDN1 protein expression compared with untreated tissues. Moreover, T25 increased l-Glut and l-Arg uptake, the latter confirmed by an increased protein expression of CAT-1. GA influences intestinal uptake of the tested cationic amino acids at low concentrations and decreases the intestinal-cell barrier function at high concentrations. Similarities were observed between in vitro and ex vivo, but different treatment times and structures must be considered.

Comparative Transcriptomics of Shiga Toxin-Producing and Commensal Escherichia coli and Cytokine Responses in Colonic Epithelial Cell Culture Infections

Ingestion of Shiga toxin-producing Escherichia coli (STEC) can result in a range of illness severity from asymptomatic to hemorrhagic colitis and death; thus risk assessment of STEC strains for human pathogenicity is important in the area of food safety. Illness severity depends in part on the combination of virulence genes carried in the genome, which can vary between strains even of identical serotype. To better understand how core genes are regulated differently among strains and to identify possible novel STEC virulence gene candidates that could be added to the risk assessment repertoire, we used comparative transcriptomics to investigate global gene expression differences between two STEC strains associated with severe illness and a commensal E. coli strain during in vitro intestinal epithelial cell (IEC) infections. Additionally, we compared a wide array of concomitant cytokine levels produced by the IECs. The cytokine expression levels were examined for a pattern representing STEC pathogenicity; however, while one STEC strain appeared to elicit a proinflammatory response, infection by the other strain produced a pattern comparable to the commensal E. coli. This result may be explained by the significant differences in gene content and expression observed between the STEC strains. RNA-Seq analysis revealed considerable disparity in expression of genes in the arginine and tryptophan biosynthesis/import pathways between the STEC strains and the commensal E. coli strain, highlighting the important role some amino acids play in STEC colonization and survival. Contrasting differential expression patterns were observed for genes involved in respiration among the three strains suggesting that metabolic diversity is a strategy utilized to compete with resident microflora for successful colonization. Similar temporal expression results for known and putative virulence genes were observed in the STEC strains, revealing strategies used for survival prior to and after initial adherence to IECs. Additionally, three genes encoding hypothetical proteins located in mobile genetic elements were, after interrogation of a large set of E. coli genomes, determined to likely represent novel STEC virulence factors.

Current Evidence on the Bioavailability of Food Bioactive Peptides

Food protein-derived bioactive peptides are recognized as valuable ingredients of functional foods and/or nutraceuticals to promote health and reduce the risk of chronic diseases. However, although peptides have been demonstrated to exert multiple benefits by biochemical assays, cell culture, and animal models, the ability to translate the new findings into practical or commercial uses remains delayed. This fact is mainly due to the lack of correlation of in vitro findings with in vivo functions of peptides because of their low bioavailability. Once ingested, peptides need to resist the action of digestive enzymes during their transit through the gastrointestinal tract and cross the intestinal epithelial barrier to reach the target organs in an intact and active form to exert their health-promoting properties. Thus, for a better understanding of the in vivo physiological effects of food bioactive peptides, extensive research studies on their gastrointestinal stability and transport are needed. This review summarizes the most current evidence on those factors affecting the digestive and absorptive processes of food bioactive peptides, the recently designed models mimicking the gastrointestinal environment, as well as the novel strategies developed and currently applied to enhance the absorption and bioavailability of peptides.

Effects of a microencapsulated formula of organic acids and essential oils on nutrient absorption, immunity, gut barrier function, and abundance of enterotoxigenic Escherichia coli F4 in weaned piglets challenged with E. coli F4

The objective was to study the effects of microencapsulated organic acids (OA) and essential oils (EO) on growth performance, immune system, gut barrier function, nutrient digestion and absorption, and abundance of enterotoxigenic Escherichia coli F4 (ETEC F4) in the weaned piglets challenged with ETEC F4. Twenty-four ETEC F4 susceptible weaned piglets were randomly distributed to 4 treatments including (1) sham-challenged control (SSC; piglets fed a control diet and challenged with phosphate-buffered saline (PBS)); (2) challenged control (CC; piglets fed a control diet and challenged with ETEC F4); (3) antibiotic growth promoters (AGP; CC + 55 mg·kg-1 of Aureomycin); and (4) microencapsulated OA and EO [P(OA+EO); (CC + 2 g·kg-1 of microencapsulated OA and EO]. The ETEC F4 infection significantly induced diarrhea at 8, 28, 34, and 40 hr postinoculation (hpi) (P < 0.05) in the CC piglets. At 28 d postinoculation (dpi), piglets fed P(OA+EO) had a lower (P < 0.05) diarrhea score compared with those fed CC, but the P(OA+EO) piglets had a lower (P < 0.05) diarrhea score compared with those fed the AGP diets at 40 dpi. The ETEC F4 infection tended to increase in vivo gut permeability measured by the oral gavaging fluorescein isothiocyanate-dextran 70 kDa (FITC-D70) assay in the CC piglets compared with the SCC piglets (P = 0.09). The AGP piglets had higher FITC-D70 flux than P(OA+EO) piglets (P < 0.05). The ETEC F4 infection decreased mid-jejunal VH in the CC piglets compared with the SCC piglets (P < 0.05). The P(OA+EO) piglets had higher (P < 0.05) VH in the mid-jejunum than the CC piglets. The relative mRNA abundance of Na+-glucose cotransporter and B0AT1 was reduced (P < 0.05) by ETEC F4 inoculation when compared with the SCC piglets. The AGP piglets had a greater relative mRNA abundance of B0AT1 than the CC piglets (P < 0.05). The ETEC F4 inoculation increased the protein abundance of OCLN (P < 0.05), and the AGP piglets had the lowest relative protein abundance of OCLN among the challenged groups (P < 0.05). The supplementation of microencapsulated OA and EO enhanced intestinal morphology and showed anti-diarrhea effects in weaned piglets challenged with ETEC F4. Even if more future studies can be required for further validation, this study brings evidence that microencapsulated OA and EO combination can be useful within the tools to be implemented in strategies for alternatives to antibiotics in swine production.

Influence of Resveratrol on the Cardiovascular Health Effects of Chronic Kidney Disease

Cardiovascular disease (CVD) is closely related to chronic kidney disease (CKD), and patients with CKD have a high risk of CVD-related mortality. Traditional CVD risk factors cannot account for the higher cardiovascular risk of patients with CKD, and standard CVD interventions cannot reduce the mortality rates among patients with CKD. Nontraditional factors related to mineral and vitamin-D metabolic disorders provide some explanation for the increased CVD risk. Non-dialyzable toxins, indoxyl sulfate (IS) and p-cresol sulfate (PCS)-produced in the liver by colonic microorganisms-cause kidney and vascular dysfunction. Plasma trimethylamine-N-oxide (TMAO)-a gut microbe-dependent metabolite of dietary L-carnitine and choline-is elevated in CKD and related to vascular disease, resulting in poorer long-term survival. Therefore, the modulation of colonic flora can improve prospects for patients with CKD. Managing metabolic syndrome, anemia, and abnormal mineral metabolism is recommended for the prevention of CVD in patients with CKD. Considering nontraditional risk factors, the use of resveratrol (RSV), a nutraceutical, can be helpful for patients with CVD and CKD. This paper discusses the beneficial effects of RSV on biologic, pathophysiological and clinical responses, including improvements in intestinal epithelial integrity, modulation of the intestinal microbiota and reduction in hepatic synthesis of IS, PCS and TMAO in patients with CVD and CKD.

Eugenol attenuates inflammatory response and enhances barrier function during lipopolysaccharide-induced inflammation in the porcine intestinal epithelial cells

Eugenol (4-allyl-2-methoxyphenol) is an essential oil component, possessing antimicrobial, anti-inflammatory, and antioxidative properties; however, the effect of eugenol on porcine gut inflammation has not yet been investigated. In this study, an in vitro lipopolysaccharide (LPS)-induced inflammation model in porcine intestinal epithelial cells (IPEC-J2) has been set up. Cells were pretreated with 100 μM (16.42 mg/L) eugenol for 2 h followed by 10 μg/mL LPS stimulation for 6 h. Proinflammatory cytokine secretion; reactive oxygen species; gene expression of proinflammatory cytokines, tight junction proteins, and nutrient transporters; the expression and distribution of zonula occludens-1 (ZO-1); transepithelial electrical resistance (TEER); and cell permeability were measured to investigate the effect of eugenol on inflammatory responses and gut barrier function. The results showed that eugenol pretreatment significantly suppressed the LPS-stimulated interleukin-8 level and the mRNA abundance of tumor necrosis factor-α and restored the LPS-stimulated decrease of the mRNA abundance of tight junction proteins, such as ZO-1 and occludin, and the mRNA abundance of nutrient transporters, such as B0 1 system ASC sodium-dependent neutral amino acid exchanger 2, sodium-dependent glucose transporter 1, excitatory amino acid transporter 1, and peptide transporter 1. In addition, eugenol improved the expression and even redistribution of ZO-1 and tended to increase TEER value and maintained the barrier integrity. In conclusion, a low dose of eugenol attenuated inflammatory responses and enhanced selectively permeable barrier function during LPS-induced inflammation in the IPEC-J2 cell line.

Production and characterization of avian crypt-villus enteroids and the effect of chemicals

BACKGROUND

Three-dimensional models of cell culture such as organoids and mini organs accord better advantage over regular cell culture because of their ability to simulate organ functions hence, used for disease modeling, metabolic research, and the development of therapeutics strategies. However, most advances in this area are limited to mammalian species with little progress in others such as poultry where it can be deployed to study problems of agricultural importance. In the course of enterocyte culture in chicken, we observed that intestinal mucosal villus-crypts self-repair and form spheroid-like structures which appear to be useful as ex vivo models to study enteric physiology and diseases.

RESULTS

The villus-crypts harvested from chicken intestinal mucosa were cultured to generate enteroids, purified by filtration then re cultured with different chemicals and growth factors to assess their response based on their morphological dispositions. Histochemical analyses using marker antibodies and probes showed the enteroids consisting different cell types such as epithelial, goblet, and enteroendocrine cells typical to villi and retain functional characteristics of intestinal mucosa.

CONCLUSIONS

We present a simple procedure to generate avian crypt-villous enteroids containing different cell types. Because the absorptive cells are functionally positioned outwards, similar to the luminal enterocytes, the cells have better advantages to interact with the factors present in the culture medium. Thus, the enteroids have the potential to study the physiology, metabolism, and pathology of the intestinal villi and can be useful for preliminary screenings of the factors that may affect gut health in a cost-effective manner and reduce the use of live animals.

Free Amino Acids in Human Milk: A Potential Role for Glutamine and Glutamate in the Protection Against Neonatal Allergies and Infections

Breastfeeding is indicated to support neonatal immune development and to protect against neonatal infections and allergies. Human milk composition is widely studied in relation to these unique abilities, which has led to the identification of various immunomodulating components in human milk, including various bioactive proteins. In addition to proteins, human milk contains free amino acids (FAAs), which have not been well-studied. Of those, the FAAs glutamate and glutamine are by far the most abundant. Levels of these FAAs in human milk sharply increase during the first months of lactation, in contrast to most other FAAs. These unique dynamics are globally consistent, suggesting that their levels in human milk are tightly regulated throughout lactation and, consequently, that they might have specific roles in the developing neonate. Interestingly, free glutamine and glutamate are reported to exhibit immunomodulating capacities, indicating that these FAAs could contribute to neonatal immune development and to the unique protective effects of breastfeeding. This review describes the current understanding of the FAA composition in human milk. Moreover, it provides an overview of the effects of free glutamine and glutamate on immune parameters relevant for allergic sensitization and infections in early life. The data reviewed provide rationale to study the role of free glutamine and glutamate in human milk in the protection against neonatal allergies and infections.

Utilizing Organoid and Air-Liquid Interface Models as a Screening Method in the Development of New Host Defense Peptides

Host defense peptides (HDPs), also known as antimicrobial peptides, are naturally occurring polypeptides (~12–50 residues) composed of cationic and hydrophobic amino acids that adopt an amphipathic conformation upon folding usually after contact with membranes. HDPs have a variety of biological activities including immunomodulatory, anti-inflammatory, anti-bacterial, and anti-biofilm functions. Although HDPs have the potential to address the global threat of antibiotic resistance and to treat immune and inflammatory disorders, they have yet to achieve this promise. Indeed, there are several challenges associated with bringing peptide-based drug candidates from the lab bench to clinical practice, including identifying appropriate indications, stability, toxicity, and cost. These challenges can be addressed in part by the development of innate defense regulator (IDR) peptides and peptidomimetics, which are synthetic derivatives of HDPs with similar or better efficacy, increased stability, and reduced toxicity and cost of the original HDP. However, one of the largest gaps between basic research and clinical application is the validity and translatability of conventional model systems, such as cell lines and animal models, for screening HDPs and their derivatives as potential drug therapies. Indeed, such translation has often relied on animal models, which have only limited validity. Here we discuss the recent development of human organoids for disease modeling and drug screening, assisted by the use of omics analyses. Organoids, developed from primary cells, cell lines, or human pluripotent stem cells, are three-dimensional, self-organizing structures that closely resemble their corresponding in vivo organs with regards to immune responses, tissue organization, and physiological properties; thus, organoids represent a reliable method for studying efficacy, formulation, toxicity and to some extent drug stability and pharmacodynamics. The use of patient-derived organoids enables the study of patient-specific efficacy, toxicogenomics and drug response predictions. We outline how organoids and omics data analysis can be leveraged to aid in the clinical translation of IDR peptides.

Ulcerative colitis: understanding its cellular pathology could provide insights into novel therapies

Dynamic interactions between the gastrointestinal epithelium and the mucosal immune system normally contribute to ensuring intestinal homeostasis and optimal immunosurveillance, but destabilisation of these interactions in genetically predisposed individuals can lead to the development of chronic inflammatory diseases. Ulcerative colitis is one of the main types of inflammatory diseases that affect the bowel, but its pathogenesis has yet to be completely defined. Several genetic factors and other inflammation-related genes are implicated in mediating the inflammation and development of the disease. Some susceptibility loci associated with increased risk of ulcerative colitis are found to be implicated in mucosal barrier function. Different biomarkers that cause damage to the colonic mucosa can be detected in patients, including perinuclear ANCA, which is also useful in distinguishing ulcerative colitis from other colitides. The choice of treatment for ulcerative colitis depends on disease severity. Therapeutic strategies include anti-tumour necrosis factor alpha (TNF-α) monoclonal antibodies used to block the production of TNF-α that mediates intestinal tract inflammation, an anti-adhesion drug that prevents lymphocyte infiltration from the blood into the inflamed gut, inhibitors of JAK1 and JAK3 that suppress the innate immune cell signalling and interferons α/β which stimulate the production of anti-inflammatory cytokines, as well as faecal microbiota transplantation. Although further research is still required to fully dissect the pathophysiology of ulcerative colitis, understanding its cellular pathology and molecular mechanisms has already proven beneficial and it has got the potential to identify further novel, effective targets for therapy and reduce the burden of this chronic disease.

Relaxation of Extracellular Matrix Forces Directs Crypt Formation and Architecture in Intestinal Organoids

Intestinal organoid protocols rely on the use of extracellular scaffolds, typically Matrigel, and upon switching from growth to differentiation promoting media, a symmetry breaking event takes place. During this stage, the first bud like structures analogous to crypts protrude from the central body and differentiation ensues. While organoids provide unparalleled architectural and functional complexity, this sophistication is also responsible for the high variability and lack of reproducibility of uniform crypt-villus structures. If function follows form in organoids, such structural variability carries potential limitations for translational applications (e.g., drug screening). Consequently, there is interest in developing synthetic biomaterials to direct organoid growth and differentiation. It has been hypothesized that synthetic scaffold softening is necessary for crypt development, and these mechanical requirements raise the question, what compressive forces and subsequent relaxation are necessary for organoid maturation? To that end, allyl sulfide hydrogels are employed as a synthetic extracellular matrix mimic, but with photocleavable bonds that temporally regulate the material's bulk modulus. By varying the extent of matrix softening, it is demonstrated that crypt formation, size, and number per colony are functions of matrix softening. An understanding of the mechanical dependence of crypt architecture is necessary to instruct homogenous, reproducible organoids for clinical applications.

Mechanisms of Regulation of Transporters of Amino Acid Absorption in Inflammatory Bowel Diseases

Intestinal absorption of dietary amino acids/peptides is essential for protein homeostasis, which in turn is crucial for maintaining health as well as restoration of health from significant diseases. Dietary amino acids/peptides are absorbed by unique transporter processes present in the brush border membrane of absorptive villus cells, which line the entire length of the intestine. To date, the only nutrient absorptive system described in the secretory crypt cells in the mammalian intestine is the one that absorbs the amino acid glutamine. Majority of the amino acid transporters are sodium dependent and therefore require basolateral membrane Na-K-ATPase to maintain an efficient transcellular Na gradient for their activity. These transport processes are tightly regulated by various cellular and molecular mechanisms that facilitate their optimal activity during normal physiological processes. Malabsorption of amino acids, recently described in pathophysiological states such as in inflammatory bowel disease (IBD), is undoubtedly responsible for the debilitating symptoms of IBD such as malnutrition, weight loss and ultimately a failure to thrive. Also recently, in vivo models of IBD and in vitro studies have demonstrated that specific immune-inflammatory mediators/pathways regulate specific amino acid transporters. This provides possibilities to derive novel nutrition and immune-based treatment options for conditions such as IBD. © 2020 American Physiological Society. Compr Physiol 10:673-686, 2020.

Beneficial effect of immunobiotic strains on attenuation of Salmonella induced inflammatory response in human intestinal epithelial cells

Probiotic bacteria have the ability to modulate host immune responses and have potent therapeutic functional effects against several diseases, including inflammatory diseases. However, beneficial effects of probiotics are strain specific and their interactions with host immune cells to modulate inflammatory response are largely unknown. Intestinal epithelial cells (IECs), which are the first line of defense against invading pathogens, and connects between commensals/probiotics and immune system; therefore, in this study, we used human IECs to assess the probiotic effects of three selected Lactobacillus strains in vitro. An HT-29 colonic epithelial cell and HT-29/blood mononuclear cells co-culture system were stimulated with Lactobacillus followed by Salmonella for different hours, after which the mRNA level of cytokines, β-defensin-2 and negative regulators for TLR signaling and protein levels of ZO-1 and IκB-α were analyzed by real-time polymerase chain reaction and western blot analysis. L. brevis decreased Salmonella induced IL-6, IL-8, MCP-1 and IL-1β levels, whereas L. pentosus suppressed IL-6 and MCP-1 in HT-29 cells. Moreover, L. brevis was able to increase the mRNA levels of A20, Tollip, SIGIRR and IRAKM, while L. pentosus reduced the levels of A20, and IRAKM in response to Salmonella. In addition, decrease in protein level of TNF-α and increase in mRNA level of IL-10 was observed in L. brevis and L. pentosus treated HT-29 cells. Lactobacillus strains were differentially modulated ZO-1 and p-IκB-α in HT-29 cells treated with Salmonella. Overall, the results of this study indicate that Lactobacillus strains attenuate Salmonella induced inflammatory responses through beneficial modulation of TLR negative regulators and the NF-κB pathway.

Insights into the Role of Human Gut Microbiota in Clostridioides difficile Infection

Clostridioides difficile infection (CDI) has emerged as a major health problem worldwide. A major risk factor for disease development is prior antibiotic use, which disrupts the normal gut microbiota by altering its composition and the gut’s metabolic functions, leading to the loss of colonization resistance and subsequent CDI. Data from human studies have shown that the presence of C. difficile, either as a colonizer or as a pathogen, is associated with a decreased level of gut microbiota diversity. The investigation of the gut’s microbial communities, in both healthy subjects and patients with CDI, elucidate the role of microbiota and improve the current biotherapeutics for patients with CDI. Fecal microbiota transplantation has a major role in managing CDI, aiming at re-establishing colonization resistance in the host gastrointestinal tract by replenishing the gut microbiota. New techniques, such as post-genomics, proteomics and metabolomics analyses, can possibly determine in the future the way in which C. difficile eradicates colonization resistance, paving the way for the development of new, more successful treatments and prevention. The aim of the present review is to present recent data concerning the human gut microbiota with a focus on its important role in health and disease.

A biotechnological approach for the production of branched chain amino acid containing bioactive peptides to improve human health: A review

Improper nutrition provokes many types of chronic diseases and health problems, which consequently are associated with particularly high costs of treatments. Nowadays, consumer's interest in healthy eating is shifting towards specific foods or food ingredients. As a consequence, bioactive peptides as a promising source of health promoting food additives are currently an intensely debated topic in research. Process design is still on its early stages and is significantly influenced by important preliminary decisions. Thus, parameters like peptide bioactivity within the product, selection of the protein source, enzyme selection for hydrolysis, peptide enrichment method, as well as stability of the peptides within the food matrix and bioavailability are sensitive decision points, which have to be purposefully coordinated, as they are directly linked to amino acid content and structure properties of the peptides. Branched chain amino acids (BCAA) are essential components for humans, possessing various important physiologic functions within the body. Incorporated within peptide sequences, they may induce dual functions, when used as nutraceuticals in functional food, thus preserving the foodstuff and prevent several widespread diseases. Furthermore, there is evidence that consuming this peptide-class can be a nutritional support for elderly people or improve human health to prevent diseases caused by incorrect nutrition. Based on the knowledge about the role of BCAA within various peptide functions, discussed in the review, special attention is given to different approaches for systematic selection of the protein source and enzymes used in hydrolysis, as well as suitable peptide enrichment methods, thereby showing current trends in research.

SIRT2 Contributes to the Regulation of Intestinal Cell Proliferation and Differentiation

BACKGROUND AND AIMS

Intestinal mucosa undergoes a continual process of proliferation, differentiation, and apoptosis. Disruption of this homeostasis is associated with disorders such as inflammatory bowel disease (IBD). We investigated the role of Sirtuin 2 (SIRT2), a NAD-dependent protein deacetylase, in intestinal epithelial cell (IEC) proliferation and differentiation and the mechanism by which SIRT2 contributes to maintenance of intestinal cell homeostasis.

METHODS

IECs were collected from SIRT2-deficient mice and patients with IBD. Expression of SIRT2, differentiation markers (mucin2, intestinal alkaline phosphatase, villin, Na,K-ATPase, and lysozyme) and Wnt target genes (EPHB2, AXIN2, and cyclin D1) was determined by western blot, real-time RT-PCR, or immunohistochemical (IHC) staining. IECs were treated with TNF or transfected with siRNA targeting SIRT2. Proliferation was determined by villus height and crypt depth, and Ki67 and cyclin D1 IHC staining. For studies using organoids, intestinal crypts were isolated.

RESULTS

Increased SIRT2 expression was localized to the more differentiated region of the intestine. In contrast, SIRT2 deficiency impaired proliferation and differentiation and altered stemness in the small intestinal epithelium ex vivo and in vivo. SIRT2-deficient mice showed decreased intestinal enterocyte and goblet cell differentiation but increased the Paneth cell lineage and increased proliferation of IECs. Moreover, we found that SIRT2 inhibits Wnt/β-catenin signaling, which critically regulates IEC proliferation and differentiation. Consistent with a distinct role for SIRT2 in maintenance of gut homeostasis, intestinal mucosa from IBD patients exhibited decreased SIRT2 expression.

CONCLUSION

We demonstrate that SIRT2, which is decreased in intestinal tissues from IBD patients, regulates Wnt-β-catenin signaling and is important for maintenance of IEC proliferation and differentiation.

In Vitro Intestinal Uptake And Permeability Of Fluorescently-Labelled Hyaluronic Acid Nanogels

Background

Oral administration remains the most common mode of drug delivery. However, orally administered bioactive compounds must first survive digestion and then be absorbed at the intestine in order to reach other tissues or organs. The efficiency of both processes can be improved by encapsulation or conjugation with polymeric nanoparticles. Here we report the synthesis of amphiphilic hyaluronic acid (HyA) nanogels as nanocarriers for drug delivery.

Methods

HyA nanogels were prepared by self-assembly from amphiphilic HyA conjugates produced by grafting hydrophobic alkyl chains to the HyA backbone. The dye Cy5.5 was covalently bonded and used for tracking. The nanogels were characterised according to their structure, size and zeta potential, as well as biocompatibility towards an intestinal epithelial cell line. The uptake and intestinal permeability of the nanogels were assessed using in vitro models, which physiological relevance was verified regarding the morphology of the epithelium, the production of mucus, the expression of occludin and the transepithelial electrical resistance.

Results

The covalent binding of Cy5.5 did not affect significantly the size and surface charge of the nanogels at 125.1 ± 3.2 nm and -57.6 ± 6.2 mV respectively after labelling. Studies of biocompatibility showed that the nanogels were non-toxic to Caco-2 cells up to the concentration of 0.1 mg∙mL^-1. The presence of mucus affected the nanogel uptake and highlighted the importance of considering mucus-producing cells in in vitro intestinal models. The uptake or adsorption to a Caco-2/HT29-MTX co-culture (8.1%) was higher than with single Caco-2 cell cultures (4.3%). Interestingly, both models led to minute (<0.5%) permeation of the nanogels across the intestinal barrier.

Conclusion

The HyA nanogels demonstrated to be mucoadhesive and effectively uptaken by intestinal cells. Both are determinant features for sustained release, but if systemic delivery is envisaged further modification with targeting moieties could be important to improve the nanogel permeability.

L-Arginine alleviates heat stress-induced intestinal epithelial barrier damage by promoting expression of tight junction proteins via the AMPK pathway

Heat stress (HS) and secondary restricted blood flow to the intestines cause dysfunction of the intestinal epithelial barrier. Tight junctions (TJs) are essential to maintain intestinal integrity. L-Arginine has beneficial effects on gut functions. However, the underlying mechanisms remain largely unknown. This study tested the hypothesis that L-arginine regulates the TJ network by activating AMP-activated protein kinase (AMPK) signaling, which in turn improves intestinal barrier functions under HS. IEC-6 cells and rat small intestines were used as experiment models of heat stress. AICAR and dorsomorphin were used to activate and inhibit the AMPK pathway, respectively. Cell proliferation, apoptosis, differential gene expression and KEGG pathway analysis, intestinal paracellular permeability, intestinal morphology, and expression of HSP and TJ proteins, and p-AMPK were determined. L-Arginine promoted cell proliferation and reduced apoptosis after heat exposure at an optimal concentration of 5 mmol. Transcriptome sequencing analysis revealed that differentially expressed genes associated with the HSP family and TJs were elevated by L-arginine. According to KEGG pathway analysis, L-arginine activated the AMPK signaling pathway. In vivo, intestinal damage resulted in obvious morphological changes as well as apoptosis with TUNEL and caspase-3 staining under HS and dorsomorphin treatments. Furthermore, HS and dorsomorphin increased the serum D-lactate concentration, diamine oxidase activity, and mRNA expression level of MLCK (P < 0.05). In contrast, L-arginine and AICAR treatments reduced intestinal injury, maintained intestinal permeability, and increased the villus/crypt ratio under hyperthermia. L-Arginine had the same effect as AICAR both in vitro and in vivo, namely increasing p-AMPK protein expression. L-Arginine and AICAR also upregulated the mRNA expression level of HSP70 and HSP90, and downregulated mRNA expression of MLCK (P < 0.05). The protein expression levels of TJ proteins ZO-1 and claudin-1 were suppressed by heat stroke and dorsomorphin, but enhanced by L-arginine and AICAR. Our findings indicate that activation of AMPK signaling by L-arginine is associated with improved intestinal mucosal barrier functions by enhancing the expression of TJs in rat small intestines and IEC-6 cells during HS.

Response of Human Small Intestinal Epithelium to Fractionated Irradiation: Dynamical Modeling Approach

A biologically motivated mathematical model of the dynamics of the small intestinal epithelium in humans treated with fractionated radiotherapy has been developed and is further investigated here. This model, originating from our previous work, is implemented as a system of nonlinear ordinary differential equations, in which the variables and parameters have a clear biological meaning. The model also includes, as input, the key parameters of fractionated irradiation. The modeling results on the dynamical response of the human normal small intestinal epithelium to fractionated radiation therapy regimens were in agreement with the corresponding empirical data, which, in turn, demonstrates the capability of the developed model for predicting the dynamics of this vital body system in humans receiving fractionated radiotherapy. It is also revealed that the cumulative damage effects of hypofractionated radiation therapy regimens on the human normal small intestinal epithelium are somewhat less pronounced than those of conventional fractionated radiation therapy regimens with the same total doses.

Gingival epithelial barrier: regulation by beneficial and harmful microbes

The gingival epithelium acts as a physical barrier to separate the biofilm from the gingival tissue, providing the first line of defense against bacterial invasion in periodontal disease. Disruption of the gingival epithelial barrier, and the subsequent penetration of exogenous pathogens into the host tissues, triggers an inflammatory response, establishing chronic infection. Currently, more than 700 different bacterial species have been identified in the oral cavity, some of which are known to be periodontopathic. These bacteria contribute to epithelial barrier dysfunction in the gingiva by producing several virulence factors. However, some bacteria in the oral cavity appear to be beneficial, helping gingival epithelial cells maintain their integrity and barrier function. This review aims to discuss current findings regarding microorganism interactions and epithelial barrier function in the oral cavity, with reference to investigations in the gut, where this interaction has been extensively studied.

Interactions Between the Gut Microbiota and the Host Innate Immune Response Against Pathogens

The mammalian intestine is colonized by over a trillion microbes that comprise the "gut microbiota," a microbial community which has co-evolved with the host to form a mutually beneficial relationship. Accumulating evidence indicates that the gut microbiota participates in immune system maturation and also plays a central role in host defense against pathogens. Here we review some of the mechanisms employed by the gut microbiota to boost the innate immune response against pathogens present on epithelial mucosal surfaces. Antimicrobial peptide secretion, inflammasome activation and induction of host IL-22, IL-17, and IL-10 production are the most commonly observed strategies employed by the gut microbiota for host anti-pathogen defense. Taken together, the body of evidence suggests that the host gut microbiota can elicit innate immunity against pathogens.

Different Temperature Treatments of Millet Grains Affect the Biological Activity of Protein Hydrolyzates and Peptide Fractions

The objective of this study was to analyze millet protein hydrolyzates and peptide fractions with molecular mass under 3.0 kDa obtained from grains treated with different temperature values as inhibitors of angiotensin-converting enzyme (ACE), α-amylase, and α-glucosidase activity. The protein fractions were hydrolyzed in vitro in gastrointestinal conditions and the highest degree of hydrolysis was noted for globulin 7S obtained from control grains (98.33%). All samples were characterized by a high peptide bioaccessibility index, which was 23.89 for peptides obtained from globulin 11S after treatment with 100 °C. The highest peptide bioavailability index was noted for peptides obtained from globulin 11S after the treatment with 65 °C (2.12). The highest potential metabolic syndrome inhibitory effect was determined for peptide fractions obtained from the prolamin control (IC50 for ACE and α-amylase was 0.42 and 0.11 mg/mL, respectively) and after the 100 °C treatment (IC50 for ACE and α-glucosidase was 0.33 and 0.12 mg/mL, respectively) and from globulin 11S after the 65 °C treatment (IC50 0.38 and 0.05 for ACE and α-glucosidase, respectively). The effect of these samples on endothelial cell HECa10 was determined. The sequences of potential inhibitory peptides were identified as GEHGGAGMGGGQFQPV, EQGFLPGPEESGR, RLARAGLAQ, YGNPVGGVGH, and GNPVGGVGHGTTGT.

Intestinal Microbiota as a Host Defense Mechanism to Infectious Threats

The intestinal microbiota is a complex microbial community, with diverse and stable populations hosted by the gastrointestinal tract since birth. This ecosystem holds multiple anti-infectious, anti-inflammatory, and immune modulating roles decisive for intestinal homeostasis. Among these, colonization resistance refers to the dynamic antagonistic interactions between commensals and pathogenic flora. Hence, gut bacteria compete for the same intestinal niches and substrates, while also releasing antimicrobial substances such as bacteriocines and changing the environmental conditions. Short chain fatty acids (SCFAs) generated in anaerobic conditions prompt epigenetic regulatory mechanisms that favor a tolerogenic immune response. In addition, the commensal flora is involved in the synthesis of bactericidal products, namely secondary biliary acids or antimicrobial peptides (AMPs) such as cathellicidin-LL37, an immunomodulatory, antimicrobial, and wound healing peptide. Gut microbiota is protected through symbiotic relations with the hosting organism and by quorum sensing, a specific cell-to-cell communication system. Any alterations of these relationships favor the uncontrollable multiplication of the resident pathobionts or external entero-pathogens, prompting systemic translocations, inflammatory reactions, or exacerbations of bacterial virulence mechanisms (T6SS, T3SS) and ultimately lead to gastrointestinal or systemic infections. The article describes the metabolic and immunological mechanisms through which the intestinal microbiota is both an ally of the organism against enteric pathogens and an enemy that favors the development of infections.