The intestinal barrier in multiple sclerosis: implications for pathophysiology and therapeutics

The Role of the Gastrointestinal Mucus System in Intestinal Homeostasis: Implications for Neurological Disorders

Mucus is integral to gut health and its properties may be affected in neurological disease. Mucus comprises a hydrated network of polymers including glycosylated mucin proteins. We propose that factors that influence the nervous system may also affect the volume, viscosity, porosity of mucus composition and subsequently, gastrointestinal (GI) microbial populations. The gut has its own intrinsic neuronal network, the enteric nervous system, which extends the length of the GI tract and innervates the mucosal epithelium. The ENS regulates gut function including mucus secretion and renewal. Both dysbiosis and gut dysfunction are commonly reported in several neurological disorders such as Parkinson's and Alzheimer's disease as well in patients with neurodevelopmental disorders including autism. Since some microbes use mucus as a prominent energy source, changes in mucus properties could alter, and even exacerbate, dysbiosis-related gut symptoms in neurological disorders. This review summarizes existing knowledge of the structure and function of the mucus of the GI tract and highlights areas to be addressed in future research to better understand how intestinal homeostasis is impacted in neurological disorders.

Microbiome in Multiple Sclerosis; Where Are We, What We Know and Do Not Know

An increase of multiple sclerosis (MS) incidence has been reported during the last decade, and this may be connected to environmental factors. This review article aims to encapsulate the current advances targeting the study of the gut-brain axis, which mediates the communication between the central nervous system and the gut microbiome. Clinical data arising from many research studies, which have assessed the effects of administered disease-modifying treatments in MS patients to the gut microbiome, are also recapitulated.

Smad7 in intestinal CD4+ T cells determines autoimmunity in a spontaneous model of multiple sclerosis

Environmental triggers acting at the intestinal barrier are thought to contribute to the initiation of autoimmune disorders. The transforming growth factor beta inhibitor Smad7 determines the phenotype of CD4+ T cells. We hypothesized that Smad7 in intestinal CD4+ T cells controls initiation of opticospinal encephalomyelitis (OSE), a murine model of multiple sclerosis (MS), depending on the presence of gut microbiota. Smad7 was overexpressed or deleted in OSE CD4+ T cells to determine the effect on clinical progression, T cell differentiation, and T cell migration from the intestine to the central nervous system (CNS). Smad7 overexpression worsened the clinical course of OSE and increased CNS inflammation and demyelination. It favored expansion of intestinal CD4+ T cells toward an inflammatory phenotype and migration of intestinal CD4+ T cells to the CNS. Intestinal biopsies from MS patients revealed decreased transforming growth factor beta signaling with a shift toward inflammatory T cell subtypes. Smad7 in intestinal T cells might represent a valuable therapeutic target for MS to achieve immunologic tolerance in the intestine and suppress CNS inflammation.

Roles of short-chain fatty acids in kidney diseases

OBJECTIVE

In kidney diseases, uncontrolled blood pressure, inflammation, oxidative stress, imbalanced immunity response, and metabolic dysfunction were associated with the progressive deterioration of renal function. Short-chain fatty acids (SCFAs), as a group of metabolites fermented by gut microbiota exerted regulatory effects on kidney diseases through their activation of trans-membrane G protein-coupled receptors and their inhibition of histone acetylation. In this review article, we updated recent research advances that provided an opportunity to explore our understanding in physiology and function of SCFAs in kidney disease.

DATA SOURCES

We performed a comprehensive search in both PubMed and Embase using "short-chain fatty acids" and "kidney" with no restrictions on publication date.

STUDY SELECTION

After reading through the title and abstract for early screening, the full text of relevant studies was identified and reviewed to summarize the roles of SCFAs in kidney diseases.

RESULTS

Though controversial, growing evidence suggested SCFAs appeared to have a complex but yet poorly understood communications with cellular and molecular processes that affected kidney function and responses to injury. From recent studies, SCFAs influenced multiple aspects of renal physiology including inflammation and immunity, fibrosis, blood pressure, and energy metabolism.

CONCLUSIONS

The roles of intestinal SCFAs in kidney diseases were exciting regions in recent years; however, clinical trials and animal experiments in kidney diseases were still lacked. Thus, more research would be needed to obtain better understanding of SCFAs' potential effects in kidney diseases.

Melatonin and Multiple Sclerosis: From Plausible Neuropharmacological Mechanisms of Action to Experimental and Clinical Evidence

Multiple sclerosis (MS) is a devastating chronic autoimmune demyelinating disease of the central nervous system (CNS), thought to affect more than 2.5 million people worldwide. Regulation of the sleep-wake cycle might influence disease activity and the frequency of relapses in patients. As melatonin (or sleep hormone) involves the regulation of circadian rhythms, much attention has been paid to the management of MS symptoms with melatonin. This review describes the pharmacological mechanisms underlying the neuroprotective effects of melatonin and recent clinical evidence from MS patients. Apparent risks and benefits of melatonin therapies are also discussed. Various in vivo and clinical data presented in this up-to-date review suggest that melatonin may possibly possess a protective role against the behavioral deficits and neuropathological characteristics of MS. Multiple mechanisms of the neuroprotective effects of melatonin such as mitochondrial protection and antioxidant, anti-inflammatory, and anti-apoptotic properties, as well as its anti-demyelinating function are also discussed. A large body of evidence shows that melatonin potently regulates the immune system, demyelination, free radical generation, and inflammatory responses in neural tissue, which are mediated by multiple signal transduction cascades. In the present article, we focus on different pathways that are targeted by melatonin to prevent the development and progression of MS.

Intestinal epithelial barrier functions in ageing

The intestinal epithelial barrier protects the mucosa of the gastrointestinal (GI)-tract and plays a key role in maintaining the host homeostasis. It encompasses several elements that include the intestinal epithelium and biochemical and immunological products, such as the mucus layer, antimicrobial peptides (AMPs) and secretory immunologlobulin A (sIgA). These components are interlinked with the large microbial community inhabiting the gut to form a highly sophisticated biological system that plays an important role on many aspects of human health both locally and systemically. Like any other organ and tissue, the intestinal epithelial barrier is affected by the ageing process. New insights have surfaced showing that critical functions, including intestinal stem cell regeneration and regulation of the intestinal crypt homeostasis, barrier integrity, production of regulatory cytokines, and epithelial innate immunity to pathogenic antigens change across life. Here we review the age-associated changes of the various components of the intestinal epithelial barrier and we highlight the necessity to elucidate further the mechanisms underlying these changes. Expanding our knowledge in this area is a goal of high medical relevance and it will help to define intervention strategies to ameliorate the quality of life of the ever-expanding elderly population.

The Contribution of Gut Barrier Changes to Multiple Sclerosis Pathophysiology

The gut barrier consists of several components, including the mucus layer, made of mucins and anti-bacterial molecule, the epithelial cells, connected by tight junction proteins, and a mixed population of cells involved in the interplay with microbes, such as M cells, elongations of “antigen presenting cells” dwelling the lamina propria, intraepithelial lymphocytes and Paneth cells secreting anti-bacterial peptides. Recently, the influence of intestinal permeability (IP) changes on organs far from gut has been investigated, and IP changes in multiple sclerosis (MS) have been described. A related topic is the microbiota dysfunction that underpins the development of neuroinflammation in animal models and human diseases, including MS. It becomes now of interest to better understand the mechanisms through which IP changes contribute to pathophysiology of neuroinflammation. The following aspects seem of relevance: studies on other biomarkers of IP alterations; the relationship with known risk factors for MS development, such as vitamin D deficiency; the link between blood brain barrier and gut barrier breakdown; the effects of IP increase on microbial translocation and microglial activation; the parallel patterns of IP and neuroimmune changes in MS and neuropsychiatric disorders, that afflict a sizable proportion of patients with MS. We will also discuss the therapeutic implications of IP changes, considering the impact of MS-modifying therapies on gut barrier, as well as potential approaches to enhance or protect IP homeostasis.

How the Interplay Between the Commensal Microbiota, Gut Barrier Integrity, and Mucosal Immunity Regulates Brain Autoimmunity

The intestinal barrier provides the host with a strong defense line against the external environment playing also a pivotal role in the crosstalk between the gut microbiota and the immune system. Notably, increasing lines of evidence concerning autoimmune disorders such as Multiple Sclerosis (MS) report an imbalance in both intestinal microbiota composition and mucosal immunity activation, along with an alteration of gut barrier permeability, suggesting this complex network plays a crucial role in modulating the course of autoimmune responses occurring in tissues outside the gut such as the central nervous system (CNS). Here, we review current knowledge on how gut inflammation and breakage of gut barrier integrity modulates the interplay between the commensal gut microbiota and the immune system and its role in shaping brain immunity.

Biomarkers of intestinal barrier function in multiple sclerosis are associated with disease activity

BACKGROUND

Recent evidence suggests a role for the gut-brain axis in the pathophysiology of multiple sclerosis (MS).

MATERIALS AND METHODS

We studied biomarkers of intestinal permeability in 126 people with MS (57 relapsing-remitting multiple sclerosis (RRMS) and 69 progressive MS) and in a group of healthy controls for comparison. Serum/plasma concentrations of zonulin (a regulator of enterocyte tight junctions), tight junction proteins (ZO-1 and occludin), intestinal fatty acid binding protein (IFABP)/ileal bile acid binding protein (IBABP), D-lactate, and lipopolysaccharide (LPS) binding protein were measured.

RESULTS

Zonulin concentrations were significantly higher when a concurrent magnetic resonance imaging (MRI) confirmed the presence of blood-brain barrier (BBB) disruption (Gad+ RRMS) and were correlated with tight junction proteins. IBABP and D-lactate were elevated in people with RRMS compared to controls, but did not discriminate between Gad+ and Gad- subgroups. Baseline zonulin concentrations were associated with 1-year disease progression in progressive MS.

CONCLUSIONS

People with MS have altered biomarkers of intestinal barrier integrity. Zonulin concentrations are associated with 1-year disease progression in progressive MS and closely mirror BBB breakdown in RRMS. Zonulin may mediate breakdown of both the intestinal barrier and the BBB in gut dysbiosis through the regulation of tight junctions. This could explain how the gut-brain axis modulates neuroinflammation in MS.

Polyphenols in the treatment of autoimmune diseases

In addition to protecting body from infections and diseases, the immune system produces auto-antibodies that can cause complex autoimmune disorders, such as Type I diabetes, primary biliary cirrhosis, rheumatoid arthritis, and multiple sclerosis, to name a few. In such cases, the immune system fails to recognize between foreign agents and its own body cells. Different factors, such as genetic factors (CD25, STAT4), epigenetic factors (DNA methylation, histone modifications) and environmental factors (xenobiotics, drugs, hormones) trigger autoimmunity. Glucocorticoids, non-steroidal anti-inflammatory drugs (NSAIDs), immunosuppressive and biological agents are currently used to manage autoimmune diseases of different origins. However, complete cure remains elusive. Many dietary and natural products including polyphenols have been widely studied as possible alternative treatment strategies for the management of autoimmune disorders. Polyphenols possess a wide-range of pharmacological and therapeutic properties, including antioxidant and anti-inflammatory activities. As immunomodulatory agents, polyphenols are emerging pharmaceutical tools for management of various autoimmune disorders including vitiligo, ulcerative colitis and multiple sclerosis (MS). Polyphenols activate intracellular pathways such as arachidonic acid dependent pathway, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway, mitogen-activated protein kinases (MAPKs) pathway, phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway and epigenetic modulation, which regulate the host's immune response. This timely review discusses putative points of action of polyphenols in autoimmune diseases, characterizing their efficacy and safety as therapeutic agents in managing autoimmune disorders.

Microbe-metabolite-host axis, two-way action in the pathogenesis and treatment of human autoimmunity

The role of microorganism in human diseases cannot be ignored. These microorganisms have evolved together with humans and worked together with body's mechanism to maintain immune and metabolic function. Emerging evidence shows that gut microbe and their metabolites open up new doors for the study of human response mechanism. The complexity and interdependence of these microbe-metabolite-host interactions are rapidly being elucidated. There are various changes of microbial levels in models or in patients of various autoimmune diseases (AIDs). In addition, the relevant metabolites involved in mechanism mainly include short-chain fatty acids (SCFAs), bile acids (BAs), and polysaccharide A (PSA). Meanwhile, the interaction between microbes and host genes is also a factor that must be considered. It has been demonstrated that human microbes are involved in the development of a variety of AIDs, including organ-specific AIDs and systemic AIDs. At the same time, microbes or related products can be used to remodel body's response to alleviate or cure diseases. This review summarizes the latest research of microbes and their related metabolites in AIDs. More importantly, it highlights novel and potential therapeutics, including fecal microbial transplantation, probiotics, prebiotics, and synbiotics. Nonetheless, exact mechanisms still remain elusive, and future research will focus on finding a specific strain that can act as a biomarker of an autoimmune disease.

Focus on the gut-brain axis: Multiple sclerosis, the intestinal barrier and the microbiome

The brain-gut axis serves as the bidirectional connection between the gut microbiome, the intestinal barrier and the immune system that might be relevant for the pathophysiology of inflammatory demyelinating diseases. People with multiple sclerosis have been shown to have an altered microbiome, increased intestinal permeability and changes in bile acid metabolism. Experimental evidence suggests that these changes can lead to profound alterations of peripheral and central nervous system immune regulation. Besides being of pathophysiological interest, the brain-gut axis could also open new avenues of therapeutic targets. Modification of the microbiome, the use of probiotics, fecal microbiota transplantation, supplementation with bile acids and intestinal barrier enhancers are all promising candidates. Hopefully, pre-clinical studies and clinical trials will soon yield significant results.

Anti-hypertensive peptides released from milk proteins by probiotics

The development of agricultural products as well as the industrialization of food production have led to dramatic lifestyle changes, particularly in dietary patterns, which in turn has increased the occurrence of chronic diseases and hypertension. In order to help overcome this, the food industry has developed functional milk products. Milk products, particularly fermented milk containing probiotics, are popular. Probiotics may promote gut health, reduce allergenicity, increase the bio-accessibility of fats/proteins in foods, and lower blood pressure because they contain poly-amines and bioactive peptides. Bioactive peptides have been shown to lower the risk of hypertension and cancer. Herein, we discuss the potential role of fermented milk as a functional drink acting against hypertension. However, longer-term research studies are necessary to evaluate the role of fermented milk drinks in supporting human health.