LPS-induced epithelial barrier disruption via hyperactivation of CACC and ENaC

Gut Microbiome and Its Role in Valvular Heart Disease: Not a "Gutted" Relationship

The role of the gut microbiome (GM) and oral microbiome (OM) in cardiovascular disease (CVD) has been increasingly being understood in recent years. It is well known that GM is a risk factor for various CVD phenotypes, including hypertension, dyslipidemia, heart failure and atrial fibrillation. However, its role in valvular heart disease (VHD) is less well understood. Research shows that, direct, microbe-mediated and indirect, metabolite-mediated damage as a result of gut dysbiosis and environmental factors results in a subclinical, chronic, systemic inflammatory state, which promotes inflammatory cell infiltration in heart valves and subsequently, via pro-inflammatory molecules, initiates a cascade of reaction, resulting in valve calcification, fibrosis and dysfunction. This relationship between GM and VHD adds a pathophysiological link to the pathogenesis of VHD, which can be aimed therapeutically, in order to prevent or regress any risk for valvular pathologies. Therapeutic interventions include dietary modifications and lifestyle interventions, in order to influence environmental factors that can promote gut dysbiosis. Furthermore, the combination of probiotics and prebiotics, as well as fecal m transplantation and targeted treatment with inducers or inhibitors of microbial enzymes have showed promising results in animal and/or clinical studies, with the potential to reduce the inflammatory state and restore the normal gut flora in patients. This review, thus, is going to discuss the pathophysiological links behind the relationship of GM, CVD and VHD, as well as explore the recent data regarding the effect of GM-altering treatment in CVD, cardiac function and systemic inflammation.

Kv7 channel activation reduces brain endothelial cell permeability and prevents kainic acid-induced blood-brain barrier damage

Ion channels in the blood-brain barrier (BBB) play a main role in controlling the interstitial fluid composition and cerebral blood flow, and their dysfunction contributes to the disruption of the BBB occurring in many neurological diseases such as epilepsy. In this study, using morphological and functional approaches, we evaluated the expression and role in the BBB of Kv7 channels, a family of voltage-gated potassium channels including five members (Kv7.1-5) that play a major role in the regulation of cell excitability and transmembrane flux of potassium ions. Immunofluorescence experiments showed that Kv7.1, Kv7.4, and Kv7.5 were expressed in rat brain microvessels (BMVs), as well as brain primary- and clonal (BEND-3) endothelial cells (ECs). Kv7.5 localized at the cell-to-cell junction sites, whereas Kv7.4 was also found in pericytes. The Kv7 activator retigabine increased transendothelial electrical resistance (TEER) in both primary ECs and BEND-3 cells; moreover, retigabine reduced paracellular dextran flux in BEND-3 cells. These effects were prevented by the selective Kv7 blocker XE-991. Exposure to retigabine also hyperpolarized cell membrane and increased tight junctions (TJs) integrity in BEND-3 cells. BMVs from rats treated with kainic acid (KA) showed a disruption of TJs and a selective reduction of Kv7.5 expression. In BEND-3 cells, retigabine prevented the increase of cell permeability and the reduction of TJs integrity induced by KA. Overall, these findings demonstrate that Kv7 channels are expressed in the BBB, where they modulate barrier properties both in physiological and pathological conditions.NEW & NOTEWORTHY This study describes for the first time the expression and the functional role of Kv7 potassium channels in the blood-brain barrier. We show that the opening of Kv7 channels reduces endothelial cell permeability both in physiological and pathological conditions via the hyperpolarization of cell membrane and the sealing of tight junctions. Therefore, activation of endothelial Kv7 channels might be a useful strategy to treat epilepsy and other neurological disorders characterized by blood-brain barrier dysfunction.

Direct and indirect effects of pathogenic bacteria on the integrity of intestinal barrier

Bacterial translocation is a pathological process involving migration of pathogenic bacteria across the intestinal barrier to enter the systemic circulation and gain access to distant organs. This phenomenon has been linked to a diverse range of diseases including inflammatory bowel disease, pancreatitis, and cancer. The intestinal barrier is an innate structure that maintains intestinal homeostasis. Pathogenic infections and dysbiosis can disrupt the integrity of the intestinal barrier, increasing its permeability, and thereby facilitating pathogen translocation. As translocation represents an essential step in pathogenesis, a clear understanding of how barrier integrity is disrupted and how this disruption facilitates bacterial translocation could identify new routes to effective prophylaxis and therapy. In this comprehensive review, we provide an in-depth analysis of bacterial translocation and intestinal barrier function. We discuss currently understood mechanisms of bacterial-enterocyte interactions, with a focus on tight junctions and endocytosis. We also discuss the emerging concept of bidirectional communication between the intestinal microbiota and other body systems. The intestinal tract has established 'axes' with various organs. Among our regulatory systems, the nervous, immune, and endocrine systems have been shown to play pivotal roles in barrier regulation. A mechanistic understanding of intestinal barrier regulation is crucial for the development of personalized management strategies for patients with bacterial translocation-related disorders. Advancing our knowledge of barrier regulation will pave the way for future research in this field and novel clinical intervention strategies.

The Epithelial Sodium Channel-An Underestimated Drug Target

Epithelial sodium channels (ENaC) are part of a complex network of interacting biochemical pathways and as such are involved in several disease states. Dependent on site and type of mutation, gain- or loss-of-function generated symptoms occur which span from asymptomatic to life-threatening disorders such as Liddle syndrome, cystic fibrosis or generalized pseudohypoaldosteronism type 1. Variants of ENaC which are implicated in disease assist further understanding of their molecular mechanisms in order to create models for specific pharmacological targeting. Identification and characterization of ENaC modifiers not only furthers our basic understanding of how these regulatory processes interact, but also enables discovery of new therapeutic targets for the disease conditions caused by ENaC dysfunction. Numerous test compounds have revealed encouraging results in vitro and in animal models but less in clinical settings. The EMA- and FDA-designated orphan drug solnatide is currently being tested in phase 2 clinical trials in the setting of acute respiratory distress syndrome, and the NOX1/ NOX4 inhibitor setanaxib is undergoing clinical phase 2 and 3 trials for therapy of primary biliary cholangitis, liver stiffness, and carcinoma. The established ENaC blocker amiloride is mainly used as an add-on drug in the therapy of resistant hypertension and is being studied in ongoing clinical phase 3 and 4 trials for special applications. This review focuses on discussing some recent developments in the search for novel therapeutic agents.

Breaking the Gingival Barrier in Periodontitis

The break of the epithelial barrier of gingiva has been a subject of minor interest, albeit playing a key role in periodontal pathology, transitory bacteraemia, and subsequent systemic low-grade inflammation (LGI). The significance of mechanically induced bacterial translocation in gingiva (e.g., via mastication and teeth brushing) has been disregarded despite the accumulated knowledge of mechanical force effects on tight junctions (TJs) and subsequent pathology in other epithelial tissues. Transitory bacteraemia is observed as a rule in gingival inflammation, but is rarely observed in clinically healthy gingiva. This implies that TJs of inflamed gingiva deteriorate, e.g., via a surplus of lipopolysaccharide (LPS), bacterial proteases, toxins, Oncostatin M (OSM), and neutrophil proteases. The inflammation-deteriorated gingival TJs rupture when exposed to physiological mechanical forces. This rupture is characterised by bacteraemia during and briefly after mastication and teeth brushing, i.e., it appears to be a dynamic process of short duration, endowed with quick repair mechanisms. In this review, we consider the bacterial, immune, and mechanical factors responsible for the increased permeability and break of the epithelial barrier of inflamed gingiva and the subsequent translocation of both viable bacteria and bacterial LPS during physiological mechanical forces, such as mastication and teeth brushing.

Direct Action of Non-Digestible Oligosaccharides against a Leaky Gut

The epithelial monolayer is the primary determinant of mucosal barrier function, and tight junction (TJ) complexes seal the paracellular space between the adjacent epithelial cells and represent the main "gate-keepers" of the paracellular route. Impaired TJ functionality results in increased permeation of the "pro-inflammatory" luminal contents to the circulation that induces local and systemic inflammatory and immune responses, ultimately triggering and/or perpetuating (chronic) systemic inflammatory disorders. Increased gut leakiness is associated with intestinal and systemic disease states such as inflammatory bowel disease and neurodegenerative diseases such as Parkinson's disease. Modulation of TJ dynamics is an appealing strategy aiming at inflammatory conditions associated with compromised intestinal epithelial function. Recently there has been a growing interest in nutraceuticals, particularly in non-digestible oligosaccharides (NDOs). NDOs confer innumerable health benefits via microbiome-shaping and gut microbiota-related immune responses, including enhancement of epithelial barrier integrity. Emerging evidence supports that NDOs also exert health-beneficial effects on microbiota independently via direct interactions with intestinal epithelial and immune cells. Among these valuable features, NDOs promote barrier function by directly regulating TJs via AMPK-, PKC-, MAPK-, and TLR-associated pathways. This review provides a comprehensive overview of the epithelial barrier-protective effects of different NDOs with a special focus on their microbiota-independent modulation of TJs.