The mucosal barrier at a glance

Recent advances in cell-based in vitro models for predicting drug permeability across brain, intestinal, and pulmonary barriers

INTRODUCTION

Recent years have witnessed remarkable progress in the development of cell-based in vitro models aimed at predicting drug permeability, particularly focusing on replicating the barrier properties of the blood-brain barrier (BBB), intestinal epithelium, and lung epithelium.

AREA COVERED

This review provides an overview of 2D in vitro platforms, including monocultures and co-culture systems, highlighting their respective advantages and limitations. Additionally, it discusses tools and techniques utilized to overcome these limitations, paving the way for more accurate predictions of drug permeability. Furthermore, this review delves into emerging technologies, particularly microphysiological systems (MPS), encompassing static platforms such as organoids and dynamic platforms like microfluidic devices. Literature searches were performed using PubMed and Google Scholar. We focus on key terms such as in vitro permeability models, MPS, organoids, intestine, BBB, and lungs.

EXPERT OPINION

The potential of these MPS to mimic physiological conditions more closely offers promising avenues for drug permeability assessment. However, transitioning these advanced models from bench to industry requires rigorous validation against regulatory standards. Thus, there is a pressing need to validate MPS to industry and regulatory agency standards to exploit their potential in drug permeability prediction fully. This review underscores the importance of such validation processes to facilitate the translation of these innovative technologies into routine pharmaceutical practice.

Intestinal health of squab pigeons responded to parental dietary protein levels during breeding period

The objective of this study was to determine the effects of dietary crude protein (CP) levels on intestinal antioxidant status, tight junction proteins expression, and amino acids transporters levels in squabs. A total of 180 pairs of White King parent pigeons approximately 10 mo old were randomly assigned to 5 groups with 6 replications of 6 pairs of parental pigeons each, and were fed with 14, 15, 16, 17, and 18% CP diets for 46 d, respectively. Dietary increasing CP levels increased final body weight (linear and quadratic, P < 0.05), serum urea nitrogen (linear, P<0.05) and triglyceride levels (quadratic, P < 0.05), and reduced kidney relative weight (quadratic, P < 0.05) in squabs. Final body weight of squabs in the 18% CP diet group was higher than that of the 14, 15, and 16% CP diet groups (P < 0.05) but was similar to that of the 17% CP diet group (P > 0.05). Increasing dietary CP levels reduced intestinal malondialdehyde contents (linear and quadratic, P < 0.05) and jejunal total superoxide dismutase (T-SOD) activity (linear, P < 0.05), and enhanced (linear and quadratic, P<0.05) ileal catalase and T-SOD activities in squabs, and these effects were more prominent in the 17% CP diet group. Graded CP levels up-regulated the mRNA expression of intestinal zonula occludens 1 (linear, P < 0.05), solute carrier family 7 members 9 (linear, P < 0.05) and claudin 1 (CLDN1, linear and quadratic, P < 0.05), ileal CLDN3 and solute carrier family 6 members 14 (linear, P < 0.05) but lowered jejunal solute carrier family 6 member 14 (quadratic, P<0.05) mRNA expression in squabs. The effects of dietary CP levels on intestinal tight junction proteins expression were more apparent when its supplemental levels were 18%. These results suggested that increasing parental dietary CP levels ranged from 14 to 18% during breeding period improved growth and intestinal function of squabs, with its recommended level being 17%.

A short guide to the tight junction

Tight junctions (TJs) are specialized regions of contact between cells of epithelial and endothelial tissues that form selective semipermeable paracellular barriers that establish and maintain body compartments with different fluid compositions. As such, the formation of TJs represents a critical step in metazoan evolution, allowing the formation of multicompartmental organisms and true, barrier-forming epithelia and endothelia. In the six decades that have passed since the first observations of TJs by transmission electron microscopy, much progress has been made in understanding the structure, function, molecular composition and regulation of TJs. The goal of this Perspective is to highlight the key concepts that have emerged through this research and the future challenges that lie ahead for the field.

Alteration of Plasma Indoles in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is one of the most common endocrinopathies in reproductive-aged women. The occurrence of PCOS was reported to be associated with the alteration of gut microbiota. Microbiota-derived indoles may possibly play a key role in glycemic control. The purpose of this work is to reveal the alteration of plasma indoles in PCOS patients and to investigate the correlation between indoles levels and glucose metabolism. Sixty-five patients with PCOS and twenty-eight age-matched women were enrolled in this work. The concentrations of plasma indoles, including indoxyl sulfate (IS), indole-3-acetic acid (IAA), indole-3-propionate (IPA), indole (IND), and 3-methylindole (3-MI), were measured by HPLC with the fluorescence detection. The plasma levels of IS, IAA, and IND were significantly elevated in patients with PCOS compared to those in the control group (p < 0.05). Furthermore, the plasma levels of IS, IAA, and IND were positively correlated with fasting glucose, fasting insulin, and the homeostatic model of insulin resistance index (HOMA-IR) (p < 0.05). Besides, the 3-MI level in the plasma was positively correlated with the fasting glucose level, whereas plasma levels of IS, IAA, IND, and 3-MI were negatively correlated with glucagon-like peptide 1 (p < 0.05). Moreover, IS and IND were considered to be risk factors for PCOS after age, BMI, T, LH, and HOMA-IR adjustment. The area under the receiver-operating characteristic curve of the combined index of five indoles was 0.867 for PCOS diagnosis. Additionally, plasma indoles altered in PCOS, which was closely associated with the glucose metabolism.

PI3K/Akt signaling pathway mediates the effect of low-dose boron on barrier function, proliferation and apoptosis in rat intestinal epithelial cells

Boron is an essential trace element with roles in growth, development, and physiological functions; however, its mechanism of action is still unclear. In this study, the regulatory roles of the PI3K/Akt signaling pathway on boron-induced changes in barrier function, proliferation, and apoptosis in rat intestinal epithelial cells were evaluated. Occludin levels, the proportion of cells in the G2/M phase, cell proliferation rate, and mRNA and protein expression levels of PCNA were higher, while the proportions of cells in the G0/G1 and S phases, apoptosis rate, and caspase-3 mRNA and protein expression levels were lower in cells treated with 0.8 mmol/L boron than in control IEC-6 cells (P < 0.01 or P < 0.05). However, 40 mmol/L boron decreased ZO-1 and Occludin levels, the proportion of cells in the G2/M phase, cell proliferation rate, and mRNA and protein levels of PCNA and increased the apoptosis rate and caspase-3 mRNA expression (P < 0.01 or P < 0.05). After specifically blocking PI3K and Akt signals (using LY294002 and MK-2206 2HCL), 0.8 mmol/L boron had no effects on Occludin, PCNA level, apoptosis rates, and caspase-3 levels (P < 0.05); however, the proliferation rate and PCNA levels decreased significantly (P < 0.01 or P < 0.05). The addition of 40 mmol/L boron did not affect ZO-1 and Occludin levels and did not affect the apoptosis rate or PCNA and caspase-3 levels. These results suggested that the PI3K/Akt signaling pathway mediates the effects of low-dose boron on IEC-6 cells.

Surface layer proteins from Lactobacillus helveticus ATCC® 15009™ affect the gut barrier morphology and function

Paraprobiotics and postbiotics represent a valid alternative to probiotic strains for ameliorating and preserving a healthy intestinal epithelial barrier (IEB). The present study investigated the effects of surface layer proteins (S-layer) of the dairy strain Lactobacillus helveticus ATCC® 15009™ (Lb ATCC® 15009™), as paraprobiotic, on the morpho-functional modulation of IEB in comparison to live or heat-inactivated Lb ATCC® 15009™ in an in vitro co-culture of Caco-2/HT-29 70/30 cells. Live or heat-inactivated Lb ATCC® 15009™ negatively affected transepithelial electrical resistance (TEER) and paracellular permeability, and impaired the distribution of Claudin-1, a tight junction (TJ) transmembrane protein, as detected by immunofluorescence (IF). Conversely, the addition of the S-layer improved TEER and decreased permeability in physiological conditions in co-cultures with basal TEER lower than 50 ohmcm2, indicative of a more permeable physiological IEB known as leaky gut. Transmission electron microscopy (TEM) and IF analyses suggested that the S-layer induces a structural TJ rearrangement and desmosomes' formation. S-layer also restored TEER and permeability in the presence of LPS, but not of a mixture of pro-inflammatory cytokines (TNF-α plus IFN-γ). IF analyses showed an increase in Claudin-1 staining when LPS and S-layer were co-administered with respect to LPS alone; in addition, the S-layer counteracted the reduction of alkaline phosphatase detoxification activity and the enhancement of pro-inflammatory interleukin-8 release both induced by LPS. Altogether, these data corroborate a paraprobiotic role of S-layer from Lb ATCC® 15009™ as a possible candidate for therapeutic and prophylactic uses in conditions related to gastrointestinal health and correlated with extra-intestinal disorders.

Spontaneous episodic inflammation in the intestines of mice lacking HNF4A is driven by microbiota and associated with early life microbiota alterations

The inflammatory bowel diseases (IBD) occur in genetically susceptible individuals who mount inappropriate immune responses to their microbiota leading to chronic intestinal inflammation. Whereas IBD clinical presentation is well described, how interactions between microbiota and host genotype impact early subclinical stages of the disease remains unclear. The transcription factor hepatocyte nuclear factor 4 alpha (HNF4A) has been associated with human IBD, and deletion of Hnf4a in intestinal epithelial cells (IECs) in mice (Hnf4aΔIEC) leads to spontaneous colonic inflammation by 6-12 mo of age. Here, we tested if pathology in Hnf4aΔIEC mice begins earlier in life and if microbiota contribute to that process. Longitudinal analysis revealed that Hnf4aΔIEC mice reared in specific pathogen-free (SPF) conditions develop episodic elevated fecal lipocalin 2 (Lcn2) and loose stools beginning by 4-5 wk of age. Lifetime cumulative Lcn2 levels correlated with histopathological features of colitis at 12 mo. Antibiotic and gnotobiotic tests showed that these phenotypes in Hnf4aΔIEC mice were dependent on microbiota. Fecal 16S rRNA gene sequencing in SPF Hnf4aΔIEC and control mice disclosed that genotype significantly contributed to differences in microbiota composition by 12 mo, and longitudinal analysis of the Hnf4aΔIEC mice with the highest lifetime cumulative Lcn2 revealed that microbial community differences emerged early in life when elevated fecal Lcn2 was first detected. These microbiota differences included enrichment of a novel phylogroup of Akkermansia muciniphila in Hnf4aΔIEC mice. We conclude that HNF4A functions in IEC to shape composition of the gut microbiota and protect against episodic inflammation induced by microbiota throughout the lifespan. IMPORTANCE The inflammatory bowel diseases (IBD), characterized by chronic inflammation of the intestine, affect millions of people around the world. Although significant advances have been made in the clinical management of IBD, the early subclinical stages of IBD are not well defined and are difficult to study in humans. This work explores the subclinical stages of disease in mice lacking the IBD-associated transcription factor HNF4A in the intestinal epithelium. Whereas these mice do not develop overt disease until late in adulthood, we find that they display episodic intestinal inflammation, loose stools, and microbiota changes beginning in very early life stages. Using germ-free and antibiotic-treatment experiments, we reveal that intestinal inflammation in these mice was dependent on the presence of microbiota. These results suggest that interactions between host genotype and microbiota can drive early subclinical pathologies that precede the overt onset of IBD and describe a mouse model to explore those important processes.

Building better barriers: how nutrition and undernutrition impact pediatric intestinal health

Chronic undernutrition is a major cause of death for children under five, leaving survivors at risk for adverse long-term consequences. This review focuses on the role of nutrients in normal intestinal development and function, from the intestinal epithelium, to the closely-associated mucosal immune system and intestinal microbiota. We examine what is known about the impacts of undernutrition on intestinal physiology, with focus again on the same systems. We provide a discussion of existing animal models of undernutrition, and review the evidence demonstrating that correcting undernutrition alone does not fully ameliorate effects on intestinal function, the microbiome, or growth. We review efforts to treat undernutrition that incorporate data indicating that improved recovery is possible with interventions focused not only on delivery of sufficient energy, macronutrients, and micronutrients, but also on efforts to correct the abnormal intestinal microbiome that is a consequence of undernutrition. Understanding of the role of the intestinal microbiome in the undernourished state and correction of the phenotype is both complex and a subject that holds great potential to improve recovery. We conclude with critical unanswered questions in the field, including the need for greater mechanistic research, improved models for the impacts of undernourishment, and new interventions that incorporate recent research gains. This review highlights the importance of understanding the mechanistic effects of undernutrition on the intestinal ecosystem to better treat and improve long-term outcomes for survivors.

The Effects of Wildfire Smoke on Asthma and Allergy

PURPOSE OF REVIEW

To review the recent literature on the effects of wildfire smoke (WFS) exposure on asthma and allergic disease, and on potential mechanisms of disease.

RECENT FINDINGS

Spatiotemporal modeling and increased ground-level monitoring data are allowing a more detailed picture of the health effects of WFS exposure to emerge, especially with regard to asthma. There is also epidemiologic and some experimental evidence to suggest that WFS exposure increases allergic predisposition and upper airway or sinonasal disease, though much of the literature in this area is focused more generally on PM2.5 and is not specific for WFS. Experimental evidence for mechanisms includes disruption of epithelial integrity with downstream effects on inflammatory or immune pathways, but experimental models to date have not consistently reflected human disease in this area. Exposure to WFS has an acute detrimental effect on asthma. Potential mechanisms are suggested by in vitro and animal studies.

The immune role of the intestinal microbiome in knee osteoarthritis: a review of the possible mechanisms and therapies

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by cartilage damage and synovial inflammation and carries an enormous public health and economic burden. It is crucial to uncover the potential mechanisms of OA pathogenesis to develop new targets for OA treatment. In recent years, the pathogenic role of the gut microbiota in OA has been well recognized. Gut microbiota dysbiosis can break host-gut microbe equilibrium, trigger host immune responses and activate the "gut-joint axis", which aggravates OA. However, although the role of the gut microbiota in OA is well known, the mechanisms modulating the interactions between the gut microbiota and host immunity remain unclear. This review summarizes research on the gut microbiota and the involved immune cells in OA and interprets the potential mechanisms for the interactions between the gut microbiota and host immune responses from four aspects: gut barrier, innate immunity, adaptive immunity and gut microbiota modulation. Future research should focus on the specific pathogen or the specific changes in the gut microbiota composition to identify the related signaling pathways involved in the pathogenesis of OA. In addition, future studies should include more novel interventions on immune cell modifications and gene regulation of specific gut microbiota related to OA to validate the application of gut microbiota modulation in the onset of OA.

Sex difference in prebiotics on gut and blood-brain barrier dysfunction underlying stress-induced anxiety and depression

BACKGROUND

Most of the previous studies have demonstrated the potential antidepressive and anxiolytic role of prebiotic supplement in male subjects, yet few have females enrolled. Herein, we explored whether prebiotics administration during chronic stress prevented depression-like and anxiety-like behavior in a sex-specific manner and the mechanism of behavioral differences caused by sex.

METHODS

Female and male C57 BL/J mice on normal diet were supplemented with or without a combination of fructo-oligosaccharides (FOS) and galacto-oligosaccharides (GOS) during 3- and 4-week chronic restraint stress (CRS) treatment, respectively. C57 BL/J mice on normal diet without CRS were used as controls. Behavior consequences, gut microbiota, dysfunction of gut and brain-blood barriers, and inflammatory profiles were measured.

RESULTS

In the 3rd week, FOS + GOS administration attenuated stress-induced anxiety-like behavior in female, but not in male mice, and the anxiolytic effects in males were observed until the 4th week. However, protective effects of prebiotics on CRS-induced depression were not observed. Changes in the gene expression of tight junction proteins in the distal colon and hippocampus, and decreased number of colon goblet cells following CRS were restored by prebiotics only in females. In both female and male mice, prebiotics alleviated stress-induced BBB dysfunction and elevation in pro-inflammatory cytokines levels, and modulated gut microbiota caused by stress. Furthermore, correlation analysis revealed that anxiety-like behaviors were significantly correlated with levels of pro-inflammatory cytokines and gene expression of tight junction proteins in the hippocampus of female mice, and the abundance of specific gut microbes was also correlated with anxiety-like behaviors, pro-inflammatory cytokines, and gene expression of tight junction proteins in the hippocampus of female mice.

CONCLUSION

Female mice were more vulnerable to stress and prebiotics than males. The gut microbiota, gut and blood-brain barrier, and inflammatory response may mediate the protective effects of prebiotics on anxiety-like behaviors in female mice.

HMGB1 acts as an agent of host defense at the gut mucosal barrier

Mucosal barriers provide the first line of defense between internal body surfaces and microbial threats from the outside world. ¹ In the colon, the barrier consists of two layers of mucus and a single layer of tightly interconnected epithelial cells supported by connective tissue and immune cells. ² Microbes colonize the loose, outer layer of colonic mucus, but are essentially excluded from the tight, epithelial-associated layer by host defenses. ³ The amount and composition of the mucus is calibrated based on microbial signals and loss of even a single component of this mixture can destabilize microbial biogeography and increase the risk of disease. ^4-7 However, the specific components of mucus, their molecular microbial targets, and how they work to contain the gut microbiota are still largely unknown. Here we show that high mobility group box 1 (HMGB1), the prototypical damage-associated molecular pattern molecule (DAMP), acts as an agent of host mucosal defense in the colon. HMGB1 in colonic mucus targets an evolutionarily conserved amino acid sequence found in bacterial adhesins, including the well-characterized Enterobacteriaceae adhesin FimH. HMGB1 aggregates bacteria and blocks adhesin-carbohydrate interactions, inhibiting invasion through colonic mucus and adhesion to host cells. Exposure to HMGB1 also suppresses bacterial expression of FimH. In ulcerative colitis, HMGB1 mucosal defense is compromised, leading to tissue-adherent bacteria expressing FimH. Our results demonstrate a new, physiologic role for extracellular HMGB1 that refines its functions as a DAMP to include direct, virulence limiting effects on bacteria. The amino acid sequence targeted by HMGB1 appears to be broadly utilized by bacterial adhesins, critical for virulence, and differentially expressed by bacteria in commensal versus pathogenic states. These characteristics suggest that this amino acid sequence is a novel microbial virulence determinant and could be used to develop new approaches to diagnosis and treatment of bacterial disease that precisely identify and target virulent microbes.

Intestinal barrier dysfunction: an evolutionarily conserved hallmark of aging

A major challenge in the biology of aging is to understand how specific age-onset pathologies relate to the overall health of the organism. The integrity of the intestinal epithelium is essential for the wellbeing of the organism throughout life. In recent years, intestinal barrier dysfunction has emerged as an evolutionarily conserved feature of aged organisms, as reported in worms, flies, fish, rodents and primates. Moreover, age-onset intestinal barrier dysfunction has been linked to microbial alterations, elevated immune responses, metabolic alterations, systemic health decline and mortality. Here, we provide an overview of these findings. We discuss early work in the Drosophila model that sets the stage for examining the relationship between intestinal barrier integrity and systemic aging, then delve into research in other organisms. An emerging concept, supported by studies in both Drosophila and mice, is that directly targeting intestinal barrier integrity is sufficient to promote longevity. A better understanding of the causes and consequences of age-onset intestinal barrier dysfunction has significant relevance to the development of interventions to promote healthy aging.

[Latest Findings on the Interaction Mechanism Between Depressive Disorder and Intestinal Permeability]

The intestinal barrier, a complex structure consisting of multiple layers of defense barriers, blocks the transfer of intestinal and foreign bacteria and their metabolites into the internal environment of the human body. Intestinal permeability can be used to evaluate the integrity of the intestinal barrier. Increased intestinal permeability has been observed in patients with depressive disorder. Some studies have reported an interaction between depressive disorder and intestinal barrier. Herein, we reviewed reported findings on the mechanisms of how systematic low-grade inflammation, vagal nerve dysfunction, and hypothalamic-pituitary-adrenal axis dysfunction cause changes in intestinal permeability in patients with depressive disorder and the pathogenic mechanism of how bacterial translocation caused by damaged intestinal barrier leads to depressive disorder. In addition, the potential mechanisms of how antidepressants improve intestinal permeability and how probiotics improve depressive disorder have been discussed.

Progress of polymer-based strategies in fungal disease management: Designed for different roles

Fungal diseases have posed a great challenge to global health, but have fewer solutions compared to bacterial and viral infections. Development and application of new treatment modalities for fungi are limited by their inherent essential properties as eukaryotes. The microorganism identification and drug sensitivity analyze are limited by their proliferation rates. Moreover, there are currently no vaccines for prevention. Polymer science and related interdisciplinary technologies have revolutionized the field of fungal disease management. To date, numerous advanced polymer-based systems have been developed for management of fungal diseases, including prevention, diagnosis, treatment and monitoring. In this review, we provide an overview of current needs and advances in polymer-based strategies against fungal diseases. We high light various treatment modalities. Delivery systems of antifungal drugs, systems based on polymers' innate antifungal activities, and photodynamic therapies each follow their own mechanisms and unique design clues. We also discuss various prevention strategies including immunization and antifungal medical devices, and further describe point-of-care testing platforms as futuristic diagnostic and monitoring tools. The broad application of polymer-based strategies for both public and personal health management is prospected and integrated systems have become a promising direction. However, there is a gap between experimental studies and clinical translation. In future, well-designed in vivo trials should be conducted to reveal the underlying mechanisms and explore the efficacy as well as biosafety of polymer-based products.

Effects of short-chain fatty acids on intestinal function in an enteroid model of hypoxia

The healthy GI tract is physiologically hypoxic, but this may be perturbed by certain acute and chronic stressors that reduce oxygen availability systemically. Short-chain fatty acids have been shown to have beneficial effects on intestinal barrier function and inflammation. Therefore, our objective was to see whether short-chain fatty acids (SCFA) would improve GI barrier function, reduce production of pro-inflammatory cytokines, and increase the expression of genes regulating GI barrier function in enteroids exposed to hypoxia. Human duodenal enteroid monolayers were placed under hypoxia (1.0% O₂) for 72 h with either 24, or 48 h pre-treatment with a high acetate ratio of SCFA's or high butyrate ratio or placed under hypoxia concurrently. Transepithelial electrical resistance (TEER) increased with SCFA pre-treatment, especially 48 h of pre-treatment and this was maintained through the first 48 h of hypoxia while cells saw barrier function dramatically decrease by 72 h of hypoxia exposure. Inflammatory protein secretion largely decreased with exposure to hypoxia, regardless of SCFA pre-treatment. Gene expression of several genes related to barrier function were decreased with exposure to hypoxia, and with concurrent and 24 h SCFA pre-treatment. However, 48 h SCFA pre-treatment with a high butyrate ratio increased expression of several metabolic and differentiation related genes. Overall, pre-treatment or concurrent treatment with SCFA mixtures were not able to overcome the negative impacts of hypoxia on intestinal function and cells ultimately still cannot be sustained under hypoxia for 72 h. However, 48 h pre-treatment maintains TEER for up to 48 h of hypoxia while upregulating several metabolic genes.

Investigating on the influence mechanism of sausage of sea bass on calcium absorption and transport based on Caco-2 cell monolayer model

A monolayer Caco-2 cell model was established to explore the effects of sea bass sausage digestive juice containing phosphate on calcium ion transport. Differential proteins of Caco-2 cells treated with fish sausage juice were detected and analyzed by gene ontology (GO) functional annotation and kyoto encyclopedia of genes and genomes (KEGG) pathway analyses. Results revealed that after treatment with 0.23 mg/mL digestive juice of perch sausage in vitro, Caco-2 cell viability was the highest at 72 h (99.84%). Additionally, 0.23 mg/mL digestive juice of perch sausage in vitro significantly increased calcium ion transport. The transfer volume was 1.396 μg/well. Fish sausages containing phosphate significantly affected the protein expression levels of Caco-2 cells. Two hundred one differential proteins were detected, including 114 up-regulated and 87 down-regulated proteins. The main differential proteins included P02795, Q9P0W0, Q96PU5, Q9GZT9 and Q5EBL8. The adjustment ratios of the fish sausage group were 0.7485, 1.373, 1.2535, 0.6775, and 0.809, respectively. The pathway analysis showed that phosphate affected calcium ion absorption and transport through the P02795 enrichment pathway. The fish sausage group showed that the immune-related functions of cells were affected. This study expounds the effects of water-retaining agents on the nutritional quality of aquatic products and provides theoretical support for the research and application of surimi products.

Kefir microbiota and metabolites stimulate intestinal mucosal immunity and its early development

Kefir consists of a large number of probiotics, which can regulate or shape the balance of intestinal microbiota, and enhance the host's immune response. Kefir microbiota can shape the mucosal immunity of the body through SCFAs, EPS, polypeptides, lactic acid, and other metabolites and microbial antigens themselves, and this shaping may have time windows and specific pathways. Kefir can regulate antibody SIgA and IL-10 levels to maintain intestinal homeostasis, and its secreted SIgA can shape the stable microbiota system by wrapping and binding different classes of microorganisms. The incidence of intestinal inflammation is closely linked to the development and maturation of intestinal mucosal immunity. Based on summarizing the existing research results on Kefir, its metabolites, and immune system development, this paper proposes to use Kefir, traditional fermented food with natural immune-enhancing components and stable functional microbiota, as an intervention method. Early intervention in the immune system may seize the critical window period of mucosal immunity and stimulate the development and maturation of intestinal mucosal immunity in time.

Wumei pills attenuates 5-fluorouracil-induced intestinal mucositis through Toll-like receptor 4/myeloid differentiation factor 88/nuclear factor-κB pathway and microbiota regulation

BACKGROUND

Radiotherapy and chemotherapy can kill tumor cells and improve the survival rate of cancer patients. However, they can also damage normal cells and cause serious intestinal toxicity, leading to gastrointestinal mucositis[1]. Traditional Chinese medicine is effective in improving the side effects of chemotherapy. Wumei pills (WMP) was originally documented in the Treatise on Exogenous Febrile Diseases. It has a significant effect on chronic diarrhea and other gastrointestinal diseases, but it is not clear whether it affects chemotherapy-induced intestinal mucositis (CIM).

AIM

To explore the potential mechanism of WMP in the treatment of CIM through experimental research.

METHODS

We used an intraperitoneal injection of 5-fluorouracil (5-Fu) to establish a CIM mouse model and an oral gavage of WMP decoction (11325 and 22650 mg/kg) to evaluate the efficacy of WMP in CIM. We evaluated the effect of WMP on CIM by observing the general conditions of the mice (body weight, food intake, spleen weight, diarrhea score, and hematoxylin and eosin stained tissues). The expression of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), IL-1β, and myeloperoxidase (MPO), as well as the Toll-like receptor 4/myeloid differentiation factor 88/nuclear factor-κB (TLR4/MyD88/NF-κB) signaling pathway proteins and tight junction proteins (zonula occludens-1, claudin-1, E-cadherin, and mucin-2) was determined. Furthermore, intestinal permeability, intestinal flora, and the levels of short-chain fatty acids (SCFA) were also assessed.

RESULTS

WMP effectively improved the body weight, spleen weight, food intake, diarrhea score, and inflammatory status of the mice with intestinal mucositis, which preliminarily confirmed the efficacy of WMP in CIM. Further experiments showed that in addition to reducing the levels of TNF-α, IL-1β, IL-6, and MPO and inhibiting the expression of the TLR4/MyD88/NF-κB pathway proteins, WMP also repaired the integrity of the mucosal barrier of mice, regulated the intestinal flora, and increased the levels of SCFA (such as butyric acid).

CONCLUSION

WMP can play a therapeutic role in CIM by alleviating inflammation, restoring the mucosal barrier, and regulating gut microbiota.

A review of heat stress in chickens. Part I: Insights into physiology and gut health

Heat stress (HS) compromises the yield and quality of poultry products and endangers the sustainability of the poultry industry. Despite being homeothermic, chickens, especially fast-growing broiler lines, are particularly sensitive to HS due to the phylogenetic absence of sweat glands, along with the artificial selection-caused increase in metabolic rates and limited development of cardiovascular and respiratory systems. Clinical signs and consequences of HS are multifaceted and include alterations in behavior (e.g., lethargy, decreased feed intake, and panting), metabolism (e.g., catabolic state, fat accumulation, and reduced skeletal muscle accretion), general homeostasis (e.g., alkalosis, hormonal imbalance, immunodeficiency, inflammation, and oxidative stress), and gastrointestinal tract function (e.g., digestive and absorptive disorders, enteritis, paracellular barrier failure, and dysbiosis). Poultry scientists and companies have made great efforts to develop effective solutions to counteract the detrimental effects of HS on health and performance of chickens. Feeding and nutrition have been shown to play a key role in combating HS in chicken husbandry. Nutritional strategies that enhance protein and energy utilization as well as dietary interventions intended to restore intestinal eubiosis are of increasing interest because of the marked effects of HS on feed intake, nutrient metabolism, and gut health. Hence, the present review series, divided into Part I and Part II, seeks to synthesize information on the effects of HS on physiology, gut health, and performance of chickens, with emphasis on potential solutions adopted in broiler chicken nutrition to alleviate these effects. Part I provides introductory knowledge on HS physiology to make good use of the nutritional themes covered by Part II.

Junctional adhesion molecule-A deletion increases phagocytosis and improves survival in a murine model of sepsis

Expression of the tight junction–associated protein junctional adhesion molecule-A (JAM-A) is increased in sepsis, although the significance of this is unknown. Here, we show that septic JAM-A ^–/– mice have increased gut permeability, yet paradoxically have decreased bacteremia and systemic TNF and IL-1β expression. Survival is improved in JAM-A^–/– mice. However, intestine-specific JAM-A^–/– deletion does not alter mortality, suggesting that the mortality benefit conferred in mice lacking JAM-A is independent of the intestine. Septic JAM-A^–/– mice have increased numbers of splenic CD44^hiCD4⁺ T cells, decreased frequency of TNF⁺CD4⁺ cells, and elevated frequency of IL-2⁺CD4⁺ cells. Septic JAM-A^–/– mice have increased numbers of B cells in mesenteric lymph nodes with elevated serum IgA and intraepithelial lymphocyte IgA production. JAM-A^–/– × RAG^–/– mice have improved survival compared with RAG^–/– mice and identical mortality as WT mice. Gut neutrophil infiltration and neutrophil phagocytosis are increased in JAM-A^–/– mice, while septic JAM-A^–/– mice depleted of neutrophils lose their survival advantage. Therefore, increased bacterial clearance via neutrophils and an altered systemic inflammatory response with increased opsonizing IgA produced through the adaptive immune system results in improved survival in septic JAM-A^–/– mice. JAM-A may be a therapeutic target in sepsis via immune mechanisms not related to its role in permeability.

Dietary Crude Protein Levels Alter Diarrhea Incidence, Immunity, and Intestinal Barrier Function of Huanjiang Mini-Pigs During Different Growth Stages

Huanjiang mini-pig is an indigenous pig breed in China; however, the optimal dietary crude protein (CP) levels for this pig breed during different growth stages has not been standardized yet. This study investigated the effects of different CP levels on diarrhea incidence, immunity, and intestinal barrier function in pigs. A total of 360 Huanjiang mini-pigs were assigned to three independent trials and fed the following CP diets: 5−10 kg stage, 14, 16, 18, 20, and 22%; 10−20 kg stage, 12, 14, 16, 18, and 20% and 20−30 kg stage, 10, 12, 14, 16, and 18%. In the 5−10 kg stage, the 22%; diet increased the plasma IL-1β, IL-6, IL-8, and TNF-α concentrations compared to the 14−20% diets and decreased IL-10 and TGF-β; however, these results were fluctuated in the later stages, including the decrease of IL-1β and IL-8 in the 20% group, TNF-α in the 18−20% groups, and the increase of IFN-γ in the 20% group at the 10−20 kg stage and the decrease of TNF-α in the 16% group at the 20−30 kg stage. The 20% diet increased the jejunal and ileal IL-10 concentration compared to the 14% diet at the 5−10 kg stage, as well as in the 16% diet compared to the 12% diet at the 10−20 kg stage. In addition, ileal IL-10 concentration was increased in the 16% diet compared to the 10, 12, and 18% diets at the 20−30 kg stage. Furthermore, the 18% diet at the 5−10 kg stage and the 16% diet at the 10−20 kg stage decreased jejunal IL-6 expression, whereas the 20% diet increased the TNF-α and IFN-γ at the 5−10 kg stage. The 20% diet increased the Claudin, Occludin, ZO-1, ZO-2, Mucin-1, and Mucin-20 expressions at the 5−10 kg stage, as well as TLR-2, TLR-4, and NF-κB in the 22 and 20% diets at the 5−10 and 10−20 kg stages, respectively. Collectively, these findings suggest optimal dietary CP levels of 16, 14, and 12% for Huanjiang mini-pigs during the 5−10, 10−20, and 20−30 kg growth stages, respectively; and provide the guiding significance of dietary CP levels for Huanjiang mini-pigs during different growth stages.

Beta-Hydroxybutyrate: A Dual Function Molecular and Immunological Barrier Function Regulator

Ketone bodies are crucial intermediate metabolites widely associated with treating metabolic diseases. Accumulating evidence suggests that ketone bodies may act as immunoregulators in humans and animals to attenuate pathological inflammation through multiple strategies. Although the clues are scattered and untrimmed, the elevation of these ketone bodies in the circulation system and tissues induced by ketogenic diets was reported to affect the immunological barriers, an important part of innate immunity. Therefore, beta-hydroxybutyrate, a key ketone body, might also play a vital role in regulating the barrier immune systems. In this review, we retrospected the endogenous ketogenesis in animals and the dual roles of ketone bodies as energy carriers and signal molecules focusing on beta-hydroxybutyrate. In addition, the research regarding the effects of beta-hydroxybutyrate on the function of the immunological barrier, mainly on the microbiota, chemical, and physical barriers of the mucosa, were outlined and discussed. As an inducible endogenous metabolic small molecule, beta-hydroxybutyrate deserves delicate investigations focusing on its immunometabolic efficacy. Comprehending the connection between ketone bodies and the barrier immunological function and its underlining mechanisms may help exploit individualised approaches to treat various mucosa or skin-related diseases.

A Therapeutically Active Minibody Exhibits an Antiviral Activity in Oseltamivir-Resistant Influenza-Infected Mice via Direct Hydrolysis of Viral RNAs

Emerging Oseltamivir-resistant influenza strains pose a critical public health threat due to antigenic shifts and drifts. We report an innovative strategy for controlling influenza A infections by use of a novel minibody of the 3D8 single chain variable fragment (scFv) showing intrinsic viral RNA hydrolyzing activity, cell penetration activity, and epidermal cell penetration ability. In this study, we examined 3D8 scFv’s antiviral activity in vitro on three different H1N1 influenza strains, one Oseltamivir-resistant (A/Korea/2785/2009pdm) strain, and two Oseltamivir-sensitive (A/PuertoRico/8/1934 and A/X-31) strains. Interestingly, the 3D8 scFv directly digested viral RNAs in the ribonucleoprotein complex. scFv’s reduction of influenza viral RNA including viral genomic RNA, complementary RNA, and messenger RNA during influenza A infection cycles indicated that this minibody targets all types of viral RNAs during the early, intermediate, and late stages of the virus’s life cycle. Moreover, we further addressed the antiviral effects of 3D8 scFv to investigate in vivo clinical outcomes of influenza-infected mice. Using both prophylactic and therapeutic treatments of intranasal administered 3D8 scFv, we found that Oseltamivir-resistant H1N1-infected mice showed 90% (prophylactic effects) and 40% (therapeutic effects) increased survival rates, respectively, compared to the control group. The pathological signs of influenza A in the lung tissues, and quantitative analyses of the virus proliferations supported the antiviral activity of the 3D8 single chain variable fragment. Taken together, these results demonstrate that 3D8 scFv has antiviral therapeutic potentials against a wide range of influenza A viruses via the direct viral RNA hydrolyzing activity.

An Antioxidant Supplement Function Exploration: Rescue of Intestinal Structure Injury by Mannan Oligosaccharides after Aeromonas hydrophila Infection in Grass Carp (Ctenopharyngodon idella)

Mannan oligosaccharides (MOS) are a type of functional oligosaccharide which have received increased attention because of their beneficial effects on fish intestinal health. However, intestinal structural integrity is a necessary prerequisite for intestinal health. This study focused on exploring the protective effects of dietary MOS supplementation on the grass carp’s (Ctenopharyngodon idella) intestinal structural integrity (including tight junction (TJ) and adherent junction (AJ)) and its related signalling molecule mechanism. A total of 540 grass carp (215.85 ± 0.30 g) were fed six diets containing graded levels of dietary MOS supplementation (0, 200, 400, 600, 800 and 1000 mg/kg) for 60 days. Subsequently, a challenge test was conducted by injection of Aeromonas hydrophila for 14 days. We used ELISA, spectrophotometry, transmission electron microscope, immunohistochemistry, qRT-PCR and Western blotting to determine the effect of dietary MOS supplementation on intestinal structural integrity and antioxidant capacity. The results revealed that dietary MOS supplementation protected the microvillus of the intestine; reduced serum diamine oxidase and d-lactate levels (p < 0.05); enhanced intestinal total antioxidant capacity (p < 0.01); up-regulated most intestinal TJ and AJ mRNA levels; and decreased GTP-RhoA protein levels (p < 0.01). In addition, we also found several interesting results suggesting that MOS supplementation has no effects on ZO-2 and Claudin-15b. Overall, these findings suggested that dietary MOS supplementation could protect intestinal ultrastructure, reduce intestinal mucosal permeability and maintain intestinal structural integrity via inhibiting MLCK and RhoA/ROCK signalling pathways.

Urolithin A attenuates arsenic-induced gut barrier dysfunction

Environmental chemicals such as inorganic arsenic (iAs) significantly contribute to redox toxicity in the human body by enhancing oxidative stress. Imbalanced oxidative stress rapidly interferes with gut homeostasis and affects variety of cellular processes such as proliferation, apoptosis, and maintenance of intestinal barrier integrity. It has been shown that gut microbiota are essential to protect against iAs3+-induced toxicity. However, the effect of microbial metabolites on iAs3+-induced toxicity and loss of gut barrier integrity has not been investigated. The objectives of the study are to investigate impact of iAs on gut barrier function and determine benefits of gut microbial metabolite, urolithin A (UroA) against iAs3+-induced adversaries on gut epithelium. We have utilized both colon epithelial cells and in a human intestinal 3D organoid model system to investigate iAs3+-induced cell toxicity, oxidative stress, and gut barrier dysfunction in the presence or absence of UroA. Here, we report that treatment with UroA attenuated iAs3+-induced cell toxicity, apoptosis, and oxidative stress in colon epithelial cells. Moreover, our data suggest that UroA significantly reduces iAs3+-induced gut barrier permeability and inflammatory markers in both colon epithelial cells and in a human intestinal 3D organoid model system. Mechanistically, UroA protected against iAs3+-induced disruption of tight junctional proteins in intestinal epithelial cells through blockade of oxidative stress and markers of inflammation. Taken together, our studies for the first time suggest that microbial metabolites such as UroA can potentially be used to protect against environmental hazards by reducing intestinal oxidative stress and by enhancing gut barrier function.

Diosmetin has therapeutic efficacy in colitis regulating gut microbiota, inflammation, and oxidative stress via the circ-Sirt1/Sirt1 axis

Diosmetin (3',5,7 -trihydroxy-4'-methoxy flavone) is a natural flavonoid compound in the citrus species, it exhibits a variety of pharmacological activities, but little is known of its effects on colitis. In this study we evaluated the therapeutic effects of diosmetin on mouse models of chronic and acute colitis. Chronic colitis was induced in mice by drinking water containing 3% dextran sulfate sodium (DSS) from D0 to D8, followed by administration of diosmetin (25, 50 mg · kg^-1 · d^-1) for another 8 days. Acute colitis was induced by drinking water containing 5% DSS from D0 to D7, the mice concomitantly received diosmetin (25, 50 mg · kg^-1 · d^-1) from D1 to D7. During the experiments, body weight and disease activity index (DAI) were assessed daily. After the mice were sacrificed, colon tissue and feces samples were collected, and colon length was measured. We showed that in both models, diosmetin administration significantly decreased DAI score and ameliorated microscopic colon tissue damage; increased the expression of tight junction proteins (occludin, claudin-1, and zonula occludens-1), and reduced the secretion of proinflammatory cytokines IL-1β, IL-6, TNF-α, and Cox-2 in colon tissue. We found that diosmetin administration remarkably inhibited colon oxidative damage by adjusting the levels of intracellular and mitochondrial reactive oxygen species, GSH-Px, SOD, MDA and GSH in colon tissue. The protection of diosmetin against intestinal epithelial barrier damage and oxidative stress were also observed in LPS-treated Caco-2 and IEC-6 cells in vitro. Furthermore, we demonstrated that diosmetin markedly increased the expression of Nrf2 and HO-1 and reduced the ratio of acetylated NF-κB and NF-κB by activating the circ-Sirt1/Sirt1 axis, which inhibited oxidative stress and inflammation in vivo and in vitro. Diosmetin reversed the effects of si-circSirt1 and si-Sirt1 in LPS-treated Caco-2 and IEC-6 cells. When the gut microbiota was analyzed in the mouse model of colitis, we found that diosmetin administration modulated the abundance of Bacteroidetes, Actinobacteria, Cyanobacteria and Firmicutes, which were crucial for inflammatory bowel disease. Our results have linked colitis to the circ-Sirt1/Sirt1 signaling pathway, which is activated by diosmetin. The results imply that diosmetin may be a novel candidate to alleviate DSS-induced colitis and can be a lead compound for future optimization and modification.

γδ Intraepithelial Lymphocytes Facilitate Pathological Epithelial Cell Shedding Via CD103-Mediated Granzyme Release

BACKGROUND & AIMS

Excessive shedding of apoptotic enterocytes into the intestinal lumen is observed in inflammatory bowel disease and is correlated with disease relapse. Based on their cytolytic capacity and surveillance behavior, we investigated whether intraepithelial lymphocytes expressing the γδ T cell receptor (γδ IELs) are actively involved in the shedding of enterocytes into the lumen.

METHODS

Intravital microscopy was performed on GFP γδ T cell reporter mice treated with intraperitoneal lipopolysaccharide (10 mg/kg) for 90 minutes to induce tumor necrosis factor-mediated apoptosis. Cell shedding in various knockout or transgenic mice in the presence or absence of blocking antibody was quantified by immunostaining for ZO-1 funnels and cleaved caspase-3 (CC3). Granzyme A and granzyme B release from ex vivo-stimulated γδ IELs was quantified by enzyme-linked immunosorbent assay. Immunostaining for γδ T cell receptor and CC3 was performed on duodenal and ileal biopsies from controls and patients with Crohn's disease.

RESULTS

Intravital microscopy of lipopolysaccharide-treated mice revealed that γδ IELs make extended contact with shedding enterocytes. These prolonged interactions require CD103 engagement by E-cadherin, and CD103 knockout or blockade significantly reduced lipopolysaccharide-induced shedding. Furthermore, we found that granzymes A and B, but not perforin, are required for cell shedding. These extracellular granzymes are released by γδ IELs both constitutively and after CD103/E-cadherin ligation. Moreover, we found that the frequency of γδ IEL localization to CC3-positive enterocytes is increased in Crohn's disease biopsies compared with healthy controls.

CONCLUSIONS

Our results uncover a previously unrecognized role for γδ IELs in facilitating tumor necrosis factor-mediated shedding of apoptotic enterocytes via CD103-mediated extracellular granzyme release.

The Role of Vasoactive Intestinal Peptide and Mast Cells in the Regulatory Effect of Lactobacillus casei ATCC 393 on Intestinal Mucosal Immune Barrier

Vasoactive intestinal peptide (VIP) plays an important role in the neuro-endocrine-immune system. Mast cells (MCs) are important immune effector cells. This study was conducted to investigate the protective effect of L. casei ATCC 393 on Enterotoxigenic Escherichia coli (ETEC) K88-induced intestinal mucosal immune barrier injury and its association with VIP/MC signaling by in vitro experiments in cultures of porcine mucosal mast cells (PMMCs) and in vivo experiments using VIP receptor antagonist (aVIP) drug. The results showed that compared with the ETEC K88 and lipopolysaccharides (LPS)-induced model groups, VIP pretreatment significantly inhibited the activation of MCs and the release of β-hexosaminidase (β-hex), histamine and tryptase. Pretreatment with aVIP abolished the protective effect of L. casei ATCC 393 on ETEC K88-induced intestinal mucosal immune barrier dysfunction in C57BL/6 mice. Also, with the blocking of VIP signal transduction, the ETEC K88 infection increased serum inflammatory cytokines, and the numbers of degranulated MCs in ileum, which were decreased by administration of L. casei ATCC 393. In addition, VIP mediated the regulatory effect of L. casei ATCC 393 on intestinal microbiota in mice. These findings suggested that VIP may mediate the protective effect of L.casei ATCC 393 on intestinal mucosal immune barrier dysfunction via MCs.

Calcitriol ameliorates damage in high-salt diet-induced hypertension: Evidence of communication with the gut-kidney axis

Several studies have established a link between high-salt diet, inflammation, and hypertension. Vitamin D supplementation has shown anti-inflammatory effects in many diseases; gut microbiota is also associated with a wide variety of cardiovascular diseases, but potential role of vitamin D and gut microbiota in high-salt diet-induced hypertension remains unclear. Therefore, we used rats with hypertension induced by a high-salt diet as the research object and analyzed the transcriptome of their tissues (kidney and colon) and gut microbiome to conduct an overall analysis of the gut-kidney axis. We aimed to confirm the effects of high salt and calcitriol on the gut-kidney immune system and the composition of the intestinal flora. We demonstrate that consumption of a high-salt diet results in hypertension and inflammation in the colon and kidney and alteration of gut microbiota composition and function. High-salt diet-induced hypertension was found to be associated with seven microbial taxa and mainly associated with reduced production of the protective short-chain fatty acid butyrate. Calcitriol can reduce colon and kidney inflammation, and there are gene expression changes consistent with restored intestinal barrier function. The protective effect of calcitriol may be mediated indirectly by immunological properties. Additionally, the molecular pathways of the gut microbiota-mediated blood pressure regulation may be related to circadian rhythm signals, which needs to be further investigated. An innovative association analysis of the microbiota may be a key strategy to understanding the association between gene patterns and host.

Gossip in the gut: Quorum sensing, a new player in the host-microbiota interactions

Bacteria are known to communicate with each other and regulate their activities in social networks by secreting and sensing signaling molecules called autoinducers, a process known as quorum sensing (QS). This is a growing area of research in which we are expanding our understanding of how bacteria collectively modify their behavior but are also involved in the crosstalk between the host and gut microbiome. This is particularly relevant in the case of pathologies associated with dysbiosis or disorders of the intestinal ecosystem. This review will examine the different QS systems and the evidence for their presence in the intestinal ecosystem. We will also provide clues on the role of QS molecules that may exert, directly or indirectly through their bacterial gossip, an influence on intestinal epithelial barrier function, intestinal inflammation, and intestinal carcinogenesis. This review aims to provide evidence on the role of QS molecules in gut physiology and the potential shared by this new player. Better understanding the impact of intestinal bacterial social networks and ultimately developing new therapeutic strategies to control intestinal disorders remains a challenge that needs to be addressed in the future.

IL-1β and the Intestinal Epithelial Tight Junction Barrier

The intestinal epithelial tight junction (TJ) barrier controls the paracellular permeation of contents from the intestinal lumen into the intestinal tissue and systemic circulation. A defective intestinal TJ barrier has been implicated as an important pathogenic factor in inflammatory diseases of the gut including Crohn's disease, ulcerative colitis, necrotizing enterocolitis, and celiac disease. Previous studies have shown that pro-inflammatory cytokines, which are produced during intestinal inflammation, including interleukin-1β (IL-1β), tumor necrosis factor-α, and interferon-γ, have important intestinal TJ barrier-modulating actions. Recent studies have shown that the IL-1β-induced increase in intestinal TJ permeability is an important contributing factor of intestinal inflammation. The IL-1β-induced increase in intestinal TJ permeability is mediated by regulatory signaling pathways and activation of nuclear transcription factor nuclear factor-κB, myosin light chain kinase gene activation, and post-transcriptional occludin gene modulation by microRNA and contributes to the intestinal inflammatory process. In this review, the regulatory role of IL-1β on intestinal TJ barrier, the intracellular mechanisms that mediate the IL-1β modulation of intestinal TJ permeability, and the potential therapeutic targeting of the TJ barrier are discussed.

CRISPR/Cas9 genome editing reveals an essential role for basigin in maintaining a nonkeratinized squamous epithelium in cornea

One of the primary functions of nonkeratinized stratified squamous epithelia is to protect underlying tissues against chemical, microbial, and mechanical insult. Basigin is a transmembrane matrix metalloproteinase inducer commonly overexpressed during epithelial wound repair and cancer but whose physiological significance in normal epithelial tissue has not been fully explored. Here we used a CRISPR/Cas9 system to study the effect of basigin loss in a human cornea model of squamous epithelial differentiation. We find that epithelial cell cultures lacking basigin change shape and fail to produce a flattened squamous layer on the apical surface. This process is associated with the abnormal expression of the transcription factor SPDEF and the decreased biosynthesis of MUC16 and involucrin necessary for maintaining apical barrier function and structural integrity, respectively. Expression analysis of genes encoding tight junction proteins identified a role for basigin in promoting physiological expression of occludin and members of the claudin family. Functionally, disruption of basigin expression led to increased epithelial cell permeability as evidenced by the decrease in transepithelial electrical resistance and increase in rose bengal flux. Overall, these results suggest that basigin plays a distinct role in maintaining the normal differentiation of stratified squamous human corneal epithelium and could have potential implications to therapies targeting basigin function.

Research progress on diarrhoea and its mechanism in weaned piglets fed a high-protein diet

In order to pursue faster growth and development of weaned piglets, increased dietary protein (CP) levels were favoured by the pig industry and the feed industry. The digestive organs of piglets were not fully developed at weaning, and the digestive absorption capacity of protein was limited. High-protein diets can cause allergic reactions in piglets, destroy intestinal structural integrity, reduce immunity, and cause intestinal flora imbalance. Undigested proteins were prone to produce toxic substances, such as ammonia and biogenic amines, after fermentation in the hindgut, which negatively affects the health of the intestine and eventually causes reduced growth performance and diarrhoea in piglets. This review revealed the mechanism of diarrhoea caused by high-protein diets in weaned piglets and provided ideas for preventing diarrhoea in weaned piglets.

Ammonia impairs tight junction barriers by inducing mitochondrial dysfunction in Caco-2 cells

Ammonia is one of the major metabolites produced by intestinal microorganisms; however, its role in intestinal homeostasis is poorly understood. The present study investigated the regulation of intestinal tight junction (TJ) proteins by ammonia and the underlying mechanisms in human intestinal Caco-2 cells. Ammonia (15, 30, and 60 mM) increased the permeability of the cells in a dose-dependent manner, as indicated by reduced transepithelial electrical resistance and increased dextran flux. Immunoblot and immunofluorescence analyses revealed that the ammonia-induced increase in TJ permeability reduced the membrane localization of TJ proteins such as zonula occludens (ZO)1, ZO2, occludin, claudin-1, and claudin-3. DNA microarray analysis identified a biological pathway "response to reactive oxygen species" enriched by ammonia treatment, indicating the induction of oxidative stress in the cells. Ammonia treatment also increased the malondialdehyde content and decreased the ratio of reduced to oxidized glutathione. Meanwhile, ammonia treatment-induced mitochondrial dysfunction, as indicated by the downregulation of genes associated with the electron transport chain, reduction of the cellular ATP, NADH, and tricarboxylic acid cycle intermediate content, and suppression of the mitochondrial membrane potential. In contrast, N-acetyl cysteine reversed the ammonia-induced impairment of TJ permeability and structure without affecting the mitochondrial parameters. Collectively, ammonia impaired the TJ barrier by increasing oxidative stress in Caco-2 cells. A mitochondrial dysfunction is possibly an event preceding ammonia-induced oxidative stress. The findings of this study could potentially improve our understanding of the interplay between intestinal microorganisms and their hosts.

Colonic epithelial cathelicidin (LL-37) expression intensity is associated with progression of colorectal cancer and presence of CD8+ T cell infiltrate

Colorectal cancer (CRC) remains a leading cause of cancer mortality. Here, we define the colonic epithelial expression of cathelicidin (LL-37) in CRC. Cathelicidin exerts pleotropic effects including anti-microbial and immunoregulatory functions. Genetic knockout of cathelicidin led to increased size and number of colorectal tumours in the azoxymethane-induced murine model of CRC. We aimed to translate this to human disease. The expression of LL-37 in a large (n = 650) fully characterised cohort of treatment-naïve primary human colorectal tumours and 50 matched normal mucosa samples with associated clinical and pathological data (patient age, gender, tumour site, tumour stage [UICC], presence or absence of extra-mural vascular invasion, tumour differentiation, mismatch repair protein status, and survival to 18 years) was assessed by immunohistochemistry. The biological consequences of LL-37 expression on the epithelial barrier and immune cell phenotype were assessed using targeted quantitative PCR gene expression of epithelial permeability (CLDN2, CLDN4, OCLN, CDH1, and TJP1) and cytokine (IL-1β, IL-18, IL-33, IL-10, IL-22, and IL-27) genes in a human colon organoid model, and CD3+ , CD4+ , and CD8+ lymphocyte phenotyping by immunohistochemistry, respectively. Our data reveal that loss of cathelicidin is associated with human CRC progression, with a switch in expression intensity an early feature of CRC. LL-37 expression intensity is associated with CD8+ T cell infiltrate, influenced by tumour characteristics including mismatch repair protein status. There was no effect on epithelial barrier gene expression. These data offer novel insights into the contribution of LL-37 to the pathogenesis of CRC and as a therapeutic molecule.

Transglutaminase-Mediated Caseinate Oligochitosan Glycation Enhances the Effect of Caseinate Hydrolysate to Ameliorate the LPS-Induced Damage on the Intestinal Barrier Function in IEC-6 Cells

Some food components can regulate the intestinal barrier function. Herein, the effect of transglutaminase-type oligochitosan glycation on caseinate hydrolysate for its ability to maintain intestinal epithelial integrity and the tight junction (TJ) structure was investigated by assessing and comparing the bioactivities of glycated caseinate hydrolysate and caseinate hydrolysate against the lipopolysaccharide-induced barrier damage in the model cells (rat intestinal epithelial IEC-6 cells). The results from liquid chromatography with tandem mass spectrometry (LC-MS/MS) analysis demonstrated that oligochitosan glycation occurred at the Gln residues of α-S1-casein and α-S2-casein. The two hydrolysates retarded the lipopolysaccharide cytotoxicity toward IEC-6 cells and enhanced the barrier integrity by increasing the transepithelial electrical resistance or decreasing the paracellular permeability. In addition, these two hydrolysates could upregulate both mRNA and protein expression of three TJ proteins in IEC-6 cells. More importantly, the glycated caseinate hydrolysate had higher potential than caseinate hydrolysate to protect IEC-6 cells against the lipopolysaccharide-induced barrier damage, suggesting that the transglutaminase-mediated oligochitosan glycation of proteins is a useful approach to enforce protein biofunctions in the intestine.

An Experimental Workflow for Studying Barrier Integrity, Permeability, and Tight Junction Composition and Localization in a Single Endothelial Cell Monolayer: Proof of Concept

Endothelial and epithelial barrier function is crucial for the maintenance of physiological processes. The barrier paracellular permeability depends on the composition and spatial distribution of the cell-to-cell tight junctions (TJ). Here, we provide an experimental workflow that yields several layers of physiological data in the setting of a single endothelial cell monolayer. Human umbilical vein endothelial cells were grown on Transwell filters. Transendothelial electrical resistance (TER) and 10 kDa FITC dextran flux were measured using Alanyl-Glutamine (AlaGln) as a paracellular barrier modulator. Single monolayers were immunolabelled for Zonula Occludens-1 (ZO-1) and Claudin-5 (CLDN5) and used for automated immunofluorescence imaging. Finally, the same monolayers were used for single molecule localization microscopy (SMLM) of ZO-1 and CLDN5 at the nanoscale for spatial clustering analysis. The TER increased and the paracellular dextran flux decreased after the application of AlaGln and these functional changes of the monolayer were mediated by an increase in the ZO-1 and CLDN5 abundance in the cell–cell interface. At the nanoscale level, the functional and protein abundance data were accompanied by non-random increased clustering of CLDN5. Our experimental workflow provides multiple data from a single monolayer and has wide applicability in the setting of paracellular studies in endothelia and epithelia.

High Red Meat Intake Exacerbates Dextran Sulfate-Induced Colitis by Altering Gut Microbiota in Mice

Inflammatory bowel disease (IBD) is a serious hazard to public health, but the precise etiology of the disease is unclear. High intake of red meat diet is closely related to the occurrence of IBD. In this study, we investigated whether the high intake of red meat can increase the sensitivity of colitis and the underlying mechanism. Mice were fed with different levels of red meat for 8 weeks and then the colonic contents were analyzed by 16S rRNA sequencing. Then 3% dextran sulfate sodium was used to induce colitis in mice. We observed the severity of colitis and inflammatory cytokines. We found that high-dose red meat caused intestinal microbiota disorder, reduced the relative abundance of Lachnospiraceae_NK4A136_group, Faecalibaculum, Blautia and Dubosiella, and increased the relative abundance of Bacteroides and Alistipes. This in turn leads to an increase in colitis and inflammatory cytokine secretion. Moreover, we found that high red meat intake impaired the colon barrier integrity and decreased the expression of ZO-1, claudin, and occludin. We also found high red meat intake induced the production of more inflammatory cytokines such as IL-1β, TNF-α, IL-17, and IL-6 and inflammatory inducible enzymes such as COX-2 and iNOS in dextran sulfate sodium-induced colitis. These results suggest that we should optimize the diet and reduce the intake of red meat to prevent the occurrence of IBD.

Gastrointestinal Digestion of a Grape Pomace Extract: Impact on Intestinal Barrier Permeability and Interaction with Gut Microbiome

Grape pomace (GP) is a winemaking by-product rich in polyphenols and fibre. Supplementation with GP extracts has shown potential benefits against oxidative stress- and inflammation-related pathologies. As a new nutritional target, this paper explores the impact of the ingestion of a grape pomace extract on intestinal barrier functionality. A GP extract was sequentially subjected to gastrointestinal and colonic digestion using the dynamic gastrointestinal simulator (simgi^®). This generated two simulated fluids: intestinal-digested extract (IDE) and colonic-digested extract (CDE). The effects of these two fluids on paracellular permeability and the expression of tight junction (TJ) proteins (i.e., zonula occludens-1 (ZO-1) and occludin) were assessed in Caco-2-cell monolayers grown in Transwell^® inserts. The IDE fluid significantly (p < 0.001) reduced the paracellular transport of FITC-dextran with respect to the control, whereas no significant differences (p > 0.05) were found for CDE, which could be due, at least partially, to the pro-leaky effect of the colonic digestion medium. Accordant slight increases in the mRNA levels of both ZO-1 and occludin were observed for IDE, but without statistical significance. Additionally, the colonic fermentation of the GP extract promoted the production of short-chain fatty acids (SCFA) and phenolic metabolites and led to changes in the relative abundance of some bacteria that might affect paracellular permeability. Overall, this paper reports first trends about the effects of grape pomace extracts on intestinal permeability that would require further confirmation in future experiments.

The Epithelial Cell Leak Pathway

The epithelial cell tight junction structure is the site of the transepithelial movement of solutes and water between epithelial cells (paracellular permeability). Paracellular permeability can be divided into two distinct pathways, the Pore Pathway mediating the movement of small ions and solutes and the Leak Pathway mediating the movement of large solutes. Claudin proteins form the basic paracellular permeability barrier and mediate the movement of small ions and solutes via the Pore Pathway. The Leak Pathway remains less understood. Several proteins have been implicated in mediating the Leak Pathway, including occludin, ZO proteins, tricellulin, and actin filaments, but the proteins comprising the Leak Pathway remain unresolved. Many aspects of the Leak Pathway, such as its molecular mechanism, its properties, and its regulation, remain controversial. In this review, we provide a historical background to the evolution of the Leak Pathway concept from the initial examinations of paracellular permeability. We then discuss current information about the properties of the Leak Pathway and present current theories for the Leak Pathway. Finally, we discuss some recent research suggesting a possible molecular basis for the Leak Pathway.

An engineered human albumin enhances half-life and transmucosal delivery when fused to protein-based biologics

Needle-free uptake across mucosal barriers is a preferred route for delivery of biologics, but the efficiency of unassisted transmucosal transport is poor. To make administration and therapy efficient and convenient, strategies for the delivery of biologics must enhance both transcellular delivery and plasma half-life. We found that human albumin was transcytosed efficiently across polarized human epithelial cells by a mechanism that depends on the neonatal Fc receptor (FcRn). FcRn also transported immunoglobulin G, but twofold less than albumin. We therefore designed a human albumin variant, E505Q/T527M/K573P (QMP), with improved FcRn binding, resulting in enhanced transcellular transport upon intranasal delivery and extended plasma half-life of albumin in transgenic mice expressing human FcRn. When QMP was fused to recombinant activated coagulation factor VII, the half-life of the fusion molecule increased 3.6-fold compared with the wild-type human albumin fusion, without compromising the therapeutic properties of activated factor VII. Our findings highlight QMP as a suitable carrier of protein-based biologics that may enhance plasma half-life and delivery across mucosal barriers.

Challenges in Oral Drug Delivery and Applications of Lipid Nanoparticles as Potent Oral Drug Carriers for Managing Cardiovascular Risk Factors

BACKGROUND

The oral application of drugs is the most popular route through which the systemic effect can be achieved. Nevertheless, oral administration is limited by difficulties related to the physicochemical properties of the drug molecule, including low aqueous solubility, instability, low permeability, and rapid metabolism, all of which result in low and irregular oral bioavailability.

OBJECTIVE

The enhancement of oral bioavailability of drug molecules with such properties could lead to extreme complications in drug preparations. Oral lipid-based nanoparticles seem to possess extensive advantages due to their ability to increase the solubility, simplifying intestinal absorption and decrease or eradicate the effect of food on the absorption of low soluble, lipophilic drugs and therefore improving the oral bioavailability.

METHODS

The present review provides a summary of the general theory of lipid-based nanoparticles, their preparation methods, as well as their oral applications. Moreover, oral drug delivery challenges are discussed.

RESULTS

According to this review, the most frequent types of lipid-based nanoparticle, the solid lipid nanoparticles and nanostructured lipid carriers are potent oral carriers due to their ability to penetrate the oral drug adsorption barriers. Moreover, such lipid nanoparticles can be beneficial drug carriers against cardiovascular risk disorders as diabetes, hypertension, etc. Conclusion: In this review, the most current and promising studies involving Solid Lipid Nanoparticles and Nanostructured Lipid Carriers as oral drug carriers are reported aiming to assist researchers who focus their research on lipid-based nanoparticles.

Disorders of the enteric nervous system - a holistic view

The enteric nervous system (ENS) is the largest division of the peripheral nervous system and closely resembles components and functions of the central nervous system. Although the central role of the ENS in congenital enteric neuropathic disorders, including Hirschsprung disease and inflammatory and functional bowel diseases, is well acknowledged, its role in systemic diseases is less understood. Evidence of a disordered ENS has accumulated in neurodegenerative diseases ranging from amyotrophic lateral sclerosis, Alzheimer disease and multiple sclerosis to Parkinson disease as well as neurodevelopmental disorders such as autism. The ENS is a key modulator of gut barrier function and a regulator of enteric homeostasis. A 'leaky gut' represents the gateway for bacterial and toxin translocation that might initiate downstream processes. Data indicate that changes in the gut microbiome acting in concert with the individual genetic background can modify the ENS, central nervous system and the immune system, impair barrier function, and contribute to various disorders such as irritable bowel syndrome, inflammatory bowel disease or neurodegeneration. Here, we summarize the current knowledge on the role of the ENS in gastrointestinal and systemic diseases, highlighting its interaction with various key players involved in shaping the phenotypes. Finally, current flaws and pitfalls related to ENS research in addition to future perspectives are also addressed.

Colon epithelial cell TGFβ signaling modulates the expression of tight junction proteins and barrier function in mice

Defective barrier function is a predisposing factor in inflammatory bowel disease (IBD) and colitis-associated cancer (CAC). Although TGFβ signaling defects have been associated with IBD and CAC, few studies have examined the relationship between TGFβ and intestinal barrier function. Here, we examine the role of TGFβ signaling via SMAD4 in modulation of colon barrier function. The Smad4 gene was conditionally deleted in the intestines of adult mice and intestinal permeability assessed using an in vivo 4 kDa FITC-Dextran (FD4) permeability assay. Mouse colon was isolated for gene expression (RNA-sequencing), Western blot, and immunofluorescence analysis. In vitro colon organoid culture was utilized to assess junction-related gene expression by qPCR and transepithelial resistance (TER). In silico analyses of human IBD and colon cancer databases were performed. Mice lacking intestinal expression of Smad4 demonstrate increased colonic permeability to FD4 without gross mucosal damage. mRNA/protein expression analyses demonstrate significant increases in Cldn2/Claudin 2 and Cldn8/Claudin 8, and decreases in Cldn3, Cldn4, and Cldn7/Claudin 7 with intestinal SMAD4 loss in vivo without changes in Claudin protein localization. TGFβ1/BMP2 treatment of polarized SMAD4+ colonoids increases TER. Cldn2, Cldn4, Cldn7, and Cldn8 are regulated by canonical TGFβ signaling, and TGFβ-dependent regulation of these genes is dependent on nascent RNA transcription (Cldn2, Cldn4, Cldn8) but not nascent protein translation (Cldn4, Cldn8). Human IBD/colon cancer specimens demonstrate decreased SMAD4, CLDN4, CLDN7, and CLDN8 and increased CLDN2 compared with healthy controls. Canonical TGFβ signaling modulates the expression of tight junction proteins and barrier function in mouse colon.NEW & NOTEWORTHY We demonstrate that canonical TGFβ family signaling modulates the expression of critical tight junction proteins in colon epithelial cells, and that expression of these tight junction proteins is associated with maintenance of colon epithelial barrier function in mice.

The Immunomodulatory Effect of the Gut Microbiota in Kidney Disease

The human gut microbiota is a complex cluster composed of 100 trillion microorganisms, which holds a symbiotic relationship with the host under normal circumstances. Intestinal flora can facilitate the treatment of human metabolic dysfunctions and interact with the intestinal tract, which could influence intestinal tolerance, immunity, and sensitivity to inflammation. In recent years, significant interests have evolved on the association of intestinal microbiota and kidney diseases within the academic circle. Abnormal changes in intestinal microbiota, known as dysbiosis, can affect the integrity of the intestinal barrier, resulting in the bacterial translocation, production, and accumulation of dysbiotic gut-derived metabolites, such as urea, indoxyl sulfate (IS), and p-cresyl sulfate (PCS). These processes lead to the abnormal activation of immune cells; overproduction of antibodies, immune complexes, and inflammatory factors; and inflammatory cell infiltration that can directly or indirectly cause damage to the renal parenchyma. The aim of this review is to summarize the role of intestinal flora in the development and progression of several renal diseases, such as lupus nephritis, chronic kidney disease, diabetic nephropathy, and renal ischemia-reperfusion injury. Further research on these mechanisms should provide insights into the therapeutic potential of regulating intestinal flora and intervening related molecular targets for the abovementioned nephropathy.

Cryptosporidium parvum infection induces autophagy in intestinal epithelial cells

Autophagy, a process of degradation and recycling of macromolecules and organelles to maintain cellular homeostasis, has also been shown to help eliminate invading pathogens. Conversely, various pathogens including parasites have been shown to modulate/exploit host autophagy facilitating their intracellular infectious cycle. In this regard, Cryptosporidium parvum (CP), a protozoan parasite of small intestine is emerging as a major global health challenge. However, the pathophysiology of cryptosporidiosis is mostly unknown. We have recently demonstrated CP-induced epithelial barrier disruption via decreasing the expression of specific tight junction (TJ) and adherens junction (AJ) proteins such as occludin, claudin-4 and E-cadherin. Therefore, we utilised confluent Caco-2 cell monolayers as in vitro model of intestinal epithelial cells (IECs) to investigate the potential role of autophagy in the pathophysiology of cryptosporidiosis. Autophagy was assessed by increase in the ratio of LC3II (microtubule associated protein 1 light chain 3) to LC3I protein and decrease in p62/SQSTM1 protein levels. CP treatment of Caco-2 cells for 24 hr induced autophagy with a maximum effect observed with 0.5 × 106 oocyst/well. CP decreased mTOR (mammalian target of rapamycin, a suppressor of autophagy) phosphorylation, suggesting autophagy induction via mTOR inactivation. Measurement of autophagic flux utilizing the lysosomal inhibitor chloroquine (CQ) showed more pronounced increase in LC3II level in cells co-treated with CP + CQ as compared to CP or CQ alone, suggesting that CP-induced increase in LC3II was due to enhanced autophagosome formation rather than impaired lysosomal clearance. CP infection did not alter ATG7, a key autophagy protein. However, the decrease in occludin, claudin-4 and E-cadherin by CP was partially blocked following siRNA silencing of ATG7, suggesting the role of autophagy in CP-induced decrease in these TJ/AJ proteins. Our results provide novel evidence of autophagy induction by CP in host IECs that could alter important host cell processes contributing to the pathophysiology of cryptosporidiosis.

Carbapenem-Resistant Enterobacteriaceae-Implications for Treating Acute Leukemias, a Subgroup of Hematological Malignancies

Acute leukemias (AL) are a group of aggressive malignant diseases associated with a high degree of morbidity and mortality. Patients with AL are highly susceptible to infectious diseases due to the disease itself, factors attributed to treatment, and specific individual risk factors. Enterobacteriaceae presence (e.g., Klebsiella pneumonia and Escherichia coli) is a frequent cause of bloodstream infections in AL patients. Carbapenem-resistant Enterobacteriaceae (CRE) is an emerging health problem worldwide; however, the incidence of CRE varies greatly between different regions. Carbapenem resistance in Enterobacteriaceae is caused by different mechanisms, and CRE may display various resistance profiles. Bacterial co-expression of genes conferring resistance to both broad-spectrum β-lactam antibiotics (including carbapenems) and other classes of antibiotics may give rise to multidrug-resistant organisms (MDROs). The spread of CRE represents a major treatment challenge for clinicians due to lack of randomized clinical trials (RCTs), a limited number of antibiotics available, and the side-effects associated with them. Most research concerning CRE infections in AL patients are limited to case reports and retrospective reviews. Current research recommends treatment with older antibiotics, such as polymyxins, fosfomycin, older aminoglycosides, and in some cases carbapenems. To prevent the spread of resistant microbes, it is of pivotal interest to implement antibiotic stewardship to reduce broad-spectrum antibiotic treatment, but without giving too narrow a treatment to neutropenic infected patients.

Disruption of Epithelial Barrier of Caco-2 Cell Monolayers by Excretory Secretory Products of Trichinella spiralis Might Be Related to Serine Protease

The physical barrier is composed of epithelial cells which are joined together through intercellular connections. It serves to prevent pathogenic microorganisms from departing the intestinal lumen to invade the host. The excretory secretory (ES) products of Trichinella spiralis are critical for invasion. However, whether ES products of T. spiralis can act on the intestinal barrier is still unknown. In this study, the role of ES products of T. spiralis muscle larvae (Ts-ML-ES) in host invasion was studied by establishing an in vitro cell monolayers model. Barrier integrity analysis by a transmembrane resistance test and a paracellular permeability assay revealed that the Ts-ML-ES was able to destroy barrier function. It occurred via a reduction in the expression of tight junction (TJ) proteins, which was induced by serine protease. Furthermore, Western bolt analysis indicated that Ts-ML-ES reduced the expression of TJ proteins via the MAPK signaling pathway. Based on these data, we conclude that serine protease are likely the main factors from Ts-ML-ES that affect host intestinal barrier integrity by reducing the expression of TJs via the P38-MAPK signaling pathway. Serine protease in Ts-ML-ES might be a key invasion factor in T. spiralis.

Diarrheal Mechanisms and the Role of Intestinal Barrier Dysfunction in Campylobacter Infections

Campylobacter enteritis is the most common cause of foodborne bacterial diarrhea in humans. Although various studies have been performed to clarify the pathomechanism in Campylobacter infection, the mechanism itself and bacterial virulence factors are yet not completely understood. The purpose of this chapter is to (i) give an overview on Campylobacter-induced diarrheal mechanisms, (ii) illustrate underlying barrier defects, (iii) explain the role of the mucosal immune response and (iv) weigh preventive and therapeutic approaches. Our present knowledge of pathogenetic and diarrheal mechanisms of Campylobacter jejuni is explained in the first part of this chapter. In the second part, the molecular basis for the Campylobacter-induced barrier dysfunction is compared with that of other species in the Campylobacter genus. The bacteria are capable of overcoming the intestinal epithelial barrier. The invasion into the intestinal mucosa is the initial step of the infection, followed by a second step, the epithelial barrier impairment. The extent of the impairment depends on various factors, including tight junction dysregulation and epithelial apoptosis. The disturbed intestinal epithelium leads to a loss of water and solutes, the leak flux type of diarrhea, and facilitates the uptake of harmful antigens, the leaky gut phenomenon. The barrier dysfunction is accompanied by increased pro-inflammatory cytokine secretion, which is partially responsible for the dysfunction. Moreover, cytokines also mediate ion channel dysregulation (e.g., epithelial sodium channel, ENaC), leading to another diarrheal mechanism, which is sodium malabsorption. Future perspectives of Campylobacter research are the clarification of molecular pathomechanisms and the characterization of therapeutic and preventive compounds to combat and prevent Campylobacter infections.