A gut-vascular barrier controls the systemic dissemination of bacteria

Myogenic tone contributes to the regulation of permeability in mesenteric microvessels

The microvascular endothelium plays a key role in regulating solute permeability in the gut, but the contribution of vascular smooth muscle to barrier function is unknown. We sought to determine the role of vascular smooth muscle and its myogenic tone in the vascular barrier to solutes in mesenteric microvessels. We determined vascular permeability to 4.4 kDa and 70 kDa dextrans in isolated mouse mesenteric arteries at increasing pressure increments. The myogenic response was simultaneously monitored using video edge-detection of vessel diameter and wall thickness. We expressed permeability as the apparent permeability coefficient, or the solute flux per second normalized to surface area and concentration gradient. We compared the effects of myogenic tone, L-type calcium channel blockade, calcium elimination, and endothelial removal on the permeability of each dextran. We found arteries resisted changes in 4.4 kDa and 70 kDa dextran permeability coefficients at intravascular pressures associated with myogenic tone. Manipulations that reduced or eliminated myogenic tone (L-type calcium channel blockade or calcium elimination) caused vasodilation and increased permeability coefficients. Thus, the maintenance of a reactive mesenteric vascular smooth muscle layer and its myogenic tone prevents increases in vascular permeability that would otherwise occur with increasing pressure. Conditions that impact vascular tone, such as trauma, stroke, or major surgery could diminish the gut-vascular barrier against dissemination of the microbiome.

The Influence of Maternal-Foetal Parameters on Concentrations of Zonulin and Calprotectin in the Blood and Stool of Healthy Newborns during the First Seven Days of Life. An Observational Prospective Cohort Study

Background: It can be hypothetically assumed that maternal and perinatal factors influence the intestinal barrier. Methods: The study was conducted with 100 healthy, full-term newborns breastfed in the first week of life, with similar analyses for their mothers. Zonulin and calprotectin levels were used as intestinal permeability markers. Results: The median (range) zonulin concentrations (ng/mL) were in mothers: serum, 21.39 (6.39–57.54); stool, 82.23 (42.52–225.74); and newborns: serum cord blood, 11.14 (5.82–52.34); meconium, 54.15 (1.36–700.65); and stool at age seven days, 114.41 (29.38–593.72). Calprotectin median (range) concentrations (µg/mL) in mothers were: stool, 74.79 (3.89–211.77); and newborns: meconium, 154.76 (6.93–8884.11); and stool at age seven days 139.12 (11.89–627.35). The use of antibiotics during pregnancy resulted in higher zonulin concentrations in umbilical-cord serum and calprotectin concentrations in newborn stool at seven days, while antibiotic therapy during labour resulted in higher zonulin concentrations in the stool of newborns at seven days. Zonulin concentrations in the stool of newborns (at seven days) who were born via caesarean section were higher compared to with vaginal birth. With further analyses, caesarean section was found to have a greater effect on zonulin concentrations than prophylactic administration of antibiotics in the perinatal period. Pregnancy mass gain >18 kg was associated with higher calprotectin concentrations in maternal stool. Body Mass Index (BMI) increase >5.7 during pregnancy was associated with decreased zonulin concentrations in maternal stool and increased calprotectin concentrations in stool of mothers and newborns at seven days. There was also a negative correlation between higher BMI increase in pregnancy and maternal zonulin stool concentrations and a positive correlation between BMI increase in pregnancy and maternal calprotectin stool concentrations. Conclusion: Maternal-foetal factors such as caesarean section, antibiotic therapy during pregnancy, as well as change in mother’s BMI during pregnancy may increase intestinal permeability in newborns. Changes in body mass during pregnancy can also affect intestinal permeability in mothers. However, health consequences associated with increased intestinal permeability during the first days of life are unknown. Additionally, before the zonulin and calprotectin tests can be adopted as universal diagnostic applications to assess increased intestinal permeability, validation of these tests is necessary.

Alcohol, liver disease and the gut microbiota

Alcoholic liver disease, which ranges from mild disease to alcoholic hepatitis and cirrhosis, is a leading cause of morbidity and mortality worldwide. Alcohol intake can lead to changes in gut microbiota composition, even before liver disease development. These alterations worsen with advancing disease and could be complicit in disease progression. Microbial function, especially related to bile acid metabolism, can modulate alcohol-associated injury even in the presence of cirrhosis and alcoholic hepatitis. Microbiota changes might also alter brain function, and the gut-brain axis might be a potential target to reduce alcoholic relapse risk. Gut microbiota manipulation including probiotics, faecal microbial transplant and antibiotics has been studied in alcoholic liver disease with varying success. Further investigation of the modulation of the gut-liver axis is relevant, as most of these patients are not candidates for liver transplantation. This Review focuses on clinical studies involving the gut microbiota in patients with alcoholic liver disease across the spectrum from alcoholic fatty liver to cirrhosis and alcoholic hepatitis. Specific alterations in the gut-liver-brain axis that are complicit in the interactions between the gut microbiota and alcohol addiction are also reviewed.

Gone with the Antibody

Bacterial metabolites can reach distant organs, and in this issue of Immunity, Uchimura et al. (2018) show a fast systemic distribution of microbiota metabolites. This distribution is controlled by antibodies that accelerate bacterial transit through the small intestine, resulting in reduced local and systemic metabolite penetration and attenuation of immune responses.

Talin-Dependent Integrin Activation Regulates VE-Cadherin Localization and Endothelial Cell Barrier Function

RATIONALE

Endothelial barrier function depends on the proper localization and function of the adherens junction protein VE (vascular endothelial)-cadherin. Previous studies have suggested a functional relationship between integrin-mediated adhesion complexes and VE-cadherin yet the underlying molecular links are unclear. Binding of the cytoskeletal adaptor protein talin to the β-integrin cytoplasmic domain is a key final step in regulating the affinity of integrins for extracellular ligands (activation) but the role of integrin activation in VE-cadherin mediated endothelial barrier function is unknown.

OBJECTIVE

To test the requirement of talin-dependent activation of β1 integrin in VE-cadherin organization and endothelial cell (EC) barrier function.

METHODS AND RESULTS

EC-specific deletion of talin in adult mice resulted in impaired stability of intestinal microvascular blood vessels, hemorrhage, and death. Talin-deficient endothelium showed altered VE-cadherin organization at EC junctions in vivo. shRNA (short hairpin RNA)-mediated knockdown of talin1 expression in cultured ECs led to increased radial actin stress fibers, increased adherens junction width and increased endothelial monolayer permeability measured by electrical cell-substrate impedance sensing. Restoring β1-integrin activation in talin-deficient cells with a β1-integrin activating antibody normalized both VE-cadherin organization and EC barrier function. In addition, VE-cadherin organization was normalized by reexpression of talin or integrin activating talin head domain but not a talin head domain mutant that is selectively deficient in activating integrins.

CONCLUSIONS

Talin-dependent activation of EC β1-integrin stabilizes VE-cadherin at endothelial junctions and promotes endothelial barrier function.

Alterations of the Gut Microbiome in Chronic Hepatitis B Virus Infection Associated with Alanine Aminotransferase Level

The changes in the gut microbiota of healthy hepatitis B virus (HBV) carriers, including asymptomatic and non-cirrhotic subjects, have been rarely scrutinized. From 1463 faecal samples in health examinees, in total 112 subjects, including 36 hepatitis B surface antigen (HBsAg)-positive and 76 control subjects, were included. Twenty-eight of 36 HBsAg-positive individuals (78%) showed normal alanine aminotransferase (ALT) levels (normal ALT group), whereas eight subjects exhibited elevated ALT levels (22%, high ALT group). By using 16S rRNA gene sequencing, the distance between normal and high ALT groups among HBsAg-positive subjects showed a significant separation after the pairwise comparison of weighted UniFrac distance (permutational analysis of variance q-value = 0.039), when compared with the distances to the control group. In comparison with the control group, the normal ALT group had Anaerostipes as a significant taxon that showed a positive association (Coefficient (Coef.) = 0.028, q = 0.039). Desulfovibrio (Coef. = 0.54, q = 0.014) and Megasphaera (Coef. = 1.41, q = 0.030) showed positive correlations, and Acidaminococcus (Coef. = -1.31, q = 4.15 × 10^-75) exhibited a negative correlation with high ALT level. Gut microbial composition was different according to HBV-induced serum ALT levels, indicative of a potential link between gut and liver metabolism.

ATP released by intestinal bacteria limits the generation of protective IgA against enteropathogens

T cell dependent secretory IgA (SIgA) generated in the Peyer's patches (PPs) of the small intestine shapes a broadly diverse microbiota that is crucial for host physiology. The mutualistic co-evolution of host and microbes led to the relative tolerance of host's immune system towards commensal microorganisms. The ATP-gated ionotropic P2X7 receptor limits T follicular helper (Tfh) cells expansion and germinal center (GC) reaction in the PPs. Here we show that transient depletion of intestinal ATP can dramatically improve high-affinity IgA response against both live and inactivated oral vaccines. Ectopic expression of Shigella flexneri periplasmic ATP-diphosphohydrolase (apyrase) abolishes ATP release by bacteria and improves the specific IgA response against live oral vaccines. Antibody responses primed in the absence of intestinal extracellular ATP (eATP) also provide superior protection from enteropathogenic infection. Thus, modulation of eATP in the small intestine can affect high-affinity IgA response against gut colonizing bacteria.

Gut pathobionts underlie intestinal barrier dysfunction and liver T helper 17 cell immune response in primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a chronic inflammatory liver disease and its frequent complication with ulcerative colitis highlights the pathogenic role of epithelial barrier dysfunction. Intestinal barrier dysfunction has been implicated in the pathogenesis of PSC, yet its underlying mechanism remains unknown. Here, we identify Klebsiella pneumonia in the microbiota of patients with PSC and demonstrate that K. pneumoniae disrupts the epithelial barrier to initiate bacterial translocation and liver inflammatory responses. Gnotobiotic mice inoculated with PSC-derived microbiota exhibited T helper 17 (T_H17) cell responses in the liver and increased susceptibility to hepatobiliary injuries. Bacterial culture of mesenteric lymph nodes in these mice isolated K. pneumoniae, Proteus mirabilis and Enterococcus gallinarum, which were prevalently detected in patients with PSC. A bacterial-organoid co-culture system visualized the epithelial-damaging effect of PSC-derived K. pneumoniae that was associated with bacterial translocation and susceptibility to T_H17-mediated hepatobiliary injuries. We also show that antibiotic treatment ameliorated the T_H17 immune response induced by PSC-derived microbiota. These results highlight the role of pathobionts in intestinal barrier dysfunction and liver inflammation, providing insights into therapeutic strategies for PSC.

Wound Healing: A Cellular Perspective

Wound healing is one of the most complex processes in the human body. It involves the spatial and temporal synchronization of a variety of cell types with distinct roles in the phases of hemostasis, inflammation, growth, re-epithelialization, and remodeling. With the evolution of single cell technologies, it has been possible to uncover phenotypic and functional heterogeneity within several of these cell types. There have also been discoveries of rare, stem cell subsets within the skin, which are unipotent in the uninjured state, but become multipotent following skin injury. Unraveling the roles of each of these cell types and their interactions with each other is important in understanding the mechanisms of normal wound closure. Changes in the microenvironment including alterations in mechanical forces, oxygen levels, chemokines, extracellular matrix and growth factor synthesis directly impact cellular recruitment and activation, leading to impaired states of wound healing. Single cell technologies can be used to decipher these cellular alterations in diseased states such as in chronic wounds and hypertrophic scarring so that effective therapeutic solutions for healing wounds can be developed.

A Systematic Review, Meta-Analysis, and Meta-Regression Evaluating the Efficacy and Mechanisms of Action of Probiotics and Synbiotics in the Prevention of Surgical Site Infections and Surgery-Related Complications

Intestinal microbiota play an important role in the pathogenesis of surgical site infections (SSIs) and other surgery-related complications (SRCs). Probiotics and synbiotics were found to lower the risk of surgical infections and other surgery-related adverse events. We systematically reviewed the approach based on the administration of probiotics and synbiotics to diminish SSIs/SRCs rates in patients undergoing various surgical treatments and to determine the mechanisms responsible for their effectiveness. A systematic literature search in PubMed/MEDLINE/Cochrane Central Register of Controlled Trials from the inception of databases to June 2018 for trials in patients undergoing surgery supplemented with pre/pro/synbiotics and randomized to the intervention versus placebo/no treatment and reporting on primarily: (i) putative mechanisms of probiotic/symbiotic action, and secondarily (ii) SSIs and SRCs outcomes. Random-effect model meta-analysis and meta-regression analysis of outcomes was done. Thirty-five trials comprising 3028 adult patients were included; interventions were probiotics (n = 16) and synbiotics (n = 19 trials). We found that C-reactive protein (CRP) and Interleukin-6 (IL-6) were significantly decreased (SMD: -0.40, 95% CI [-0.79, -0.02], p = 0.041; SMD: -0.41, 95% CI [-0.70, -0.02], p = 0.006, respectively) while concentration of acetic, butyric, and propionic acids were elevated in patients supplemented with probiotics (SMD: 1.78, 95% CI [0.80, 2.76], p = 0.0004; SMD: 0.67, 95% CI [0.37, -0.97], p = 0.00001; SMD: 0.46, 95% CI [0.18, 0.73], p = 0.001, respectively). Meta-analysis confirmed that pro- and synbiotics supplementation was associated with significant reduction in the incidence of SRCs including abdominal distention, diarrhea, pneumonia, sepsis, surgery site infection (including superficial incisional), and urinary tract infection, as well as the duration of antibiotic therapy, duration of postoperative pyrexia, time of fluid introduction, solid diet, and duration of hospital stay (p < 0.05). Probiotics and synbiotics administration counteract SSIs/SRCs via modulating gut-immune response and production of short chain fatty acids.

Microbiome-The Missing Link in the Gut-Brain Axis: Focus on Its Role in Gastrointestinal and Mental Health

The central nervous system (CNS) and the human gastrointestinal (GI) tract communicate through the gut-brain axis (GBA). Such communication is bi-directional and involves neuronal, endocrine, and immunological mechanisms. There is mounting data that gut microbiota is the source of a number of neuroactive and immunocompetent substances, which shape the structure and function of brain regions involved in the control of emotions, cognition, and physical activity. Most GI diseases are associated with altered transmission within the GBA that are influenced by both genetic and environmental factors. Current treatment protocols for GI and non-GI disorders may positively or adversely affect the composition of intestinal microbiota with a diverse impact on therapeutic outcome(s). Alterations of gut microbiota have been associated with mood and depressive disorders. Moreover, mental health is frequently affected in GI and non-GI diseases. Deregulation of the GBA may constitute a grip point for the development of diagnostic tools and personalized microbiota-based therapy. For example, next generation sequencing (NGS) offers detailed analysis of microbiome footprints in patients with mental and GI disorders. Elucidating the role of stem cell⁻host microbiome cross talks in tissues in GBA disorders might lead to the development of next generation diagnostics and therapeutics. Psychobiotics are a new class of beneficial bacteria with documented efficacy for the treatment of GBA disorders. Novel therapies interfering with small molecules involved in adult stem cell trafficking are on the horizon.

The microbiome and HLA-B27-associated acute anterior uveitis

Acute anterior uveitis (AAU) and the spondyloarthritis (SpA) subtypes ankylosing spondylitis, reactive arthritis and psoriatic arthritis are among the inflammatory diseases affected by the biology of the intestinal microbiome. In this Review, the relationship between AAU, SpA and the microbiome is discussed, with a focus on the major SpA risk gene HLA-B*27 and how it is associated with both intestinal tolerance and the loss of ocular immune privilege that can accompany AAU. We provide four potential mechanisms to account for how dysbiosis, barrier function and immune response contribute to the development of ocular inflammation and the pathogenesis of AAU. Finally, potential therapeutic avenues to target the microbiota for the clinical management of AAU and SpA are outlined.

Salmonella enterica Serovar Typhimurium Travels to Mesenteric Lymph Nodes Both with Host Cells and Autonomously

Salmonella infection is a globally important cause of gastroenteritis and systemic disease and is a useful tool to study immune responses in the intestine. Although mechanisms leading to immune responses against Salmonella have been extensively studied, questions remain about how bacteria travel from the intestinal mucosa to the mesenteric lymph nodes (MLN), a key site for Ag presentation. In this study, we used a mouse model of infection with Salmonella enterica serovar Typhimurium (STM) to identify changes in intestinal immune cells induced during early infection. We then used fluorescently labeled STM to identify interactions with immune cells from the site of infection through migration in lymph to the MLN. We show that viable STM can be carried in the lymph by any subset of migrating dendritic cells but not by macrophages. Moreover, approximately half of the STM in lymph are not associated with cells at all and travel autonomously. Within the MLN, STM associates with dendritic cells and B cells but predominantly with MLN-resident macrophages. In conclusion, we describe the routes used by STM to spread systemically in the period immediately postinfection. This deeper understanding of the infection process could open new avenues for controlling it.

Leaky Gut, Leaky Brain?

'Leaky gut' syndrome, long-associated with celiac disease, has attracted much attention in recent years and for decades, was widely known in complementary/alternative medicine circles. It is often described as an increase in the permeability of the intestinal mucosa, which could allow bacteria, toxic digestive metabolites, bacterial toxins, and small molecules to 'leak' into the bloodstream. Nervous system involvement with celiac disease is know to occur even at subclinical levels. Gluten and gluten sensitivity are considered to trigger this syndrome in individuals genetically predisposed to celiac disease. However, the incidence of celiac disease in the general population is quite low. Nevertheless, increased public interest in gluten sensitivity has contributed to expanded food labels stating 'gluten-free' and the proliferation of gluten-free products, which further drives gluten-free lifestyle changes by individuals without frank celiac disease. Moreover, systemic inflammation is associated with celiac disease, depression, and psychiatric comorbidities. This mini-review focuses on the possible neurophysiological basis of leaky gut; leaky brain disease; and the microbiota's contribution to inflammation, gastrointestinal, and blood-brain barrier integrity, in order to build a case for possible mechanisms that could foster further 'leaky' syndromes. We ask whether a gluten-free diet is important for anyone or only those with celiac disease.

Mesenteric ischemia as an unusual cause of Streptococcus bovis bacteremia in the absence of endocarditis or colorectal neoplasm

Streptococcus bovis bacteremia is nearly always pathological and has been associated with colorectal cancer and endocarditis. Here, we present the first published case of S. bovis bacteremia secondary to acute mesenteric ischemia. This case illustrates the typical presentation of acute mesenteric ischemia with an atypical consequence of S. bovis bacteremia, as well as the diagnostic evaluations and management options.

Rho kinase inhibition maintains intestinal and vascular barrier function by upregulation of occludin in experimental necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a deadly disease that occurs in 5-10% of neonates. Although NEC has been extensively studied, no single therapeutic target has been identified. Rho kinase (ROCK) is a serine/threonine kinase that affects multiple cellular processes, including tight junction (TJ) function, cellular permeability, and apoptosis. We hypothesized that ROCK inhibition would decrease cellular permeability, stabilize TJ proteins (occludin), and decrease the severity of NEC. To test this hypothesis, human colon epithelial cells (Caco-2) and human endothelial cells were studied. Cells were treated with lipopolysaccharide to simulate an in vitro model of NEC. The effect of ROCK inhibition was measured by transepithelial membrane resistance (TEER) and cellular permeability to FITC-dextran. The effects of ROCK inhibition in vivo were analyzed in the rat pup model of NEC. NEC was induced by feeding formula supplemented with Cronobacter sakazakii with or without gavaged ROCK inhibitor. Rat intestines were scored based on histological degree of injury. RNA and protein assays for occludin protein were performed for all models of NEC. Treatment with ROCK inhibitor significantly decreased cellular permeability in Caco-2 cells and increased TEER. Intestinal injury scoring revealed decreased scores in ROCK inhibitor-treated pups compared with NEC only. Both cell and rat pup models demonstrated an upregulation of occludin expression in the ROCK inhibitor-treated groups. Therefore, we conclude that ROCK inhibition protects against experimental NEC by strengthening barrier function via upregulation of occludin. These data suggest that ROCK may be a potential therapeutic target for patients with NEC. NEW & NOTEWORTHY These studies are the first to demonstrate an upregulation of occludin tight junction protein in response to Rho kinase (ROCK) inhibition. Furthermore, we have demonstrated that ROCK inhibition in experimental models of necrotizing enterocolitis (NEC) is protective against NEC in both in vitro and in vivo models of disease.

A Review: The Fate of Bacteriocins in the Human Gastro-Intestinal Tract: Do They Cross the Gut-Blood Barrier?

The intestinal barrier, consisting of the vascular endothelium, epithelial cell lining, and mucus layer, covers a surface of about 400 m2. The integrity of the gut wall is sustained by transcellular proteins forming tight junctions between the epithelial cells. Protected by three layers of mucin, the gut wall forms a non-permeable barrier, keeping digestive enzymes and microorganisms within the luminal space, separate from the blood stream. Microorganisms colonizing the gut may produce bacteriocins in an attempt to outcompete pathogens. Production of bacteriocins in a harsh and complex environment such as the gastro-intestinal tract (GIT) may be below minimal inhibitory concentration (MIC) levels. At such low levels, the stability of bacteriocins may be compromised. Despite this, most bacteria in the gut have the ability to produce bacteriocins, distributed throughout the GIT. With most antimicrobial studies being performed in vitro, we know little about the migration of bacteriocins across epithelial barriers. The behavior of bacteriocins in the GIT is studied ex vivo, using models, flow cells, or membranes resembling the gut wall. Furthermore, little is known about the effect bacteriocins have on the immune system. It is generally believed that the peptides will be destroyed by macrophages once they cross the gut wall. Studies done on the survival of neurotherapeutic peptides and their crossing of the brain-blood barrier, along with other studies on small peptides intravenously injected, may provide some answers. In this review, the stability of bacteriocins in the GIT, their effect on gut epithelial cells, and their ability to cross epithelial cells are discussed. These are important questions to address in the light of recent papers advocating the use of bacteriocins as possible alternatives to, or used in combination with, antibiotics.

Contribution of the commensal microbiota to atherosclerosis and arterial thrombosis

The commensal gut microbiota is an environmental factor that has been implicated in the development of cardiovascular disease. The development of atherosclerotic lesions is largely influenced not only by the microbial-associated molecular patterns of the gut microbiota but also by the meta-organismal trimethylamine N-oxide pathway. Recent studies have described a role for the gut microbiota in platelet activation and arterial thrombosis. This review summarizes the results from gnotobiotic mouse models and clinical data that linked microbiota-induced pattern recognition receptor signalling with atherogenesis. Based on recent insights, we here provide an overview of how the gut microbiota could affect endothelial cell function and platelet activation, to promote arterial thrombosis. LINKED ARTICLES: This article is part of a themed section on When Pharmacology Meets the Microbiome: New Targets for Therapeutics? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.24/issuetoc.

Pathogen interactions with endothelial cells and the induction of innate and adaptive immunity

There are over 10 trillion endothelial cells (EC) that line the vasculature of the human body. These cells not only have specialized functions in the maintenance of homeostasis within the circulation and various tissues but they also have a major role in immune function. EC also represent an important replicative niche for a subset of viral, bacterial, and parasitic organisms that are present in the blood or lymph; however, there are major gaps in our knowledge regarding how pathogens interact with EC and how this influences disease outcome. In this article, we review the literature on EC-pathogen interactions and their role in innate and adaptive mechanisms of resistance to infection and highlight opportunities to address prominent knowledge gaps.

Prevalence of Yersinia Species in the Ileum of Crohn's Disease Patients and Controls

Yersinia are common contaminants of food products, but their prevalence in the human gut is poorly documented. Yersinia have been implicated in Crohn's Disease (CD, an inflammatory bowel disease) however their role in CD is controversial. We performed highly sensitive PCR assays of specific sequences for the gyrB gene of Y. aldovae, Y. bercovieri, Y. enterocolitica, Y. intermedia, Y. mollaretii and the inv gene of Y. pseudotuberculosis. We analyzed a total of 470 ileal samples taken from 338 participants (262 CD patients and 76 controls) belonging to three independent cohorts. All patients and controls were phenotyped and genotyped for the main CD susceptibility variants: NOD2, ATG16L1, and IRGM. Yersinia were found in 7.7% of ileal samples (respectively 7.9 and 7.6% in controls and CD patients) corresponding to 10% of participants (respectively 11.8 and 9.5% in controls and CD patients). Y. enterocolitica, Y. pseudotuberculosis and Y. intermedia were the most frequently identified species. The bacteria were more frequent in resected specimens, lymph nodes and Peyer's patches. Yersinia were no more likely to be detected in CD tissues than tissues from inflammatory and non-inflammatory controls. CD patients treated with immunosuppressants were less likely to be Yersinia carriers. In conclusion, this work shows that Yersinia species are frequently found at low levels in the human ileum in health and disease. The role of Yersinia species in this ecosystem should now be explored.

Recurrent bacterial translocation from gut and sepsis in Head and neck cancer patients and its prevention by probiotics

Head and neck cancers are the 6th most common cancer type in human malignant tumors and treated with chemoradiotherapy and surgery. Chemotherapy during these treatment modalities leads to damage of intestinal epithelial barriers and results in translocation of intestinal bacteria in bloodstream through invasion in these damaged regions. In this report, we report two cases of hypopharyngeal cancer patients, both of whom received chemotherapy before surgery. The patients demonstrated repeated sepsis before and after surgery, supporting translocation of intestinal bacteria. Proper continuous probiotic use prevented proliferation and intestinal bacterial translocation. Hypothesis of bacterial translocation and prevention by probiotics are discussed.

Gut inflammation exacerbates hepatic injury in the high-fat diet induced NAFLD mouse: Attention to the gut-vascular barrier dysfunction

AIMS

Gut inflammation has been put forward to be associated with hepatic injury in the clinical practice. The dismantled intestinal barrier was highly concerned, however, largely unknown about the role of gut-vascular barrier (GVB) in this process. This study aimed to investigate if inflamed gut directly contributes to the progression of non-alcoholic steatohepatitis (NASH), especially attention to the GVB dysfunction.

MAIN METHODS

Male C57bl/6 mice were fed with a high-fat diet (HFD) and 1% DSS for 12 weeks. The colonic inflammatory injury as well as hepatic injury were evaluated. The GVB function was assessed via measuring the permeability to fluorescently-labeled dextran (70 kDa) and the expression of plasmalemma vesicle-associated protein-1 (PV1). Furthermore, the plasma endotoxin level and hepatic TLR4/TLR9 mRNA expression were detected.

KEY FINDINGS

There were evident colitis in DSS-exposed mice, which trend to be more apparent in HFD ones. The HFD + DSS mice exhibited more serious hepatic steatosis, inflammation and fibrosis than HFD groups. The downregulated tight junction protein in HFD + DSS mice indicated loss of epithelial barrier. The GVB disruption were also confirmed with increased permeability to macromolecules and high expression of endothelial PV1 in HFD + DSS mice. Accordingly, potentially elevated plasma endotoxin levels and markedly increased TLR4/TLR9 mRNA expression were demonstrated in HFD + DSS mice rather than HFD groups.

SIGNIFICANCE

Gut inflammation exacerbates liver injury and fibrosis in HFD mice, which may contribute to the development of NASH. Beyond the damaged intestinal epithelial barrier, GVB disruption with bacterial translocation into may play a key role in the pathogenesis of NASH.

Celiac Disease and Liver Disorders: From Putative Pathogenesis to Clinical Implications

Immunologically mediated liver diseases belong to the common extraintestinal manifestations of celiac disease. We have reviewed the current literature that addresses the association between celiac disease and liver disorders. We searched relevant articles on MEDLINE/PubMed up to 15 June 2018. The objective of the article is to provide a comprehensive and up-to-date review on the latest hypotheses explaining the pathogenetic relationship between celiac disease and liver injury. Besides the involvement of gut–liver axis, tissue transglutaminase antibodies, and impairment of intestinal barrier, we integrate the latest achievements made in elucidation of the role of gut microbiota in celiac disease and liver disorders, that has not yet been sufficiently discussed in the literature in this context. The further objective is to provide a complete clinical overview on the types of liver diseases frequently found in celiac disease. In conclusion, the review highlights the clinical implication, recommend a rational approach for managing elevated transaminases in celiac patients, and underscore the importance of screening for celiac disease in patients with associated liver disease.

Bacterial translocation in patients with liver cirrhosis: physiology, clinical consequences, and practical implications

The gut liver axis is an operative unit that works to protect the human body against potentially harmful substances and microorganisms, maintaining the homeostasis of the immune system. Liver cirrhosis profoundly alters this complex system. The intestine becomes more permeable allowing the translocation of bacteria, bacterial products and fragments into the portal circulation, triggering an abnormal local and systemic inflammatory response and a condition of perpetual immunologic alarm. This immune-inflammatory disorder related to dysbiosis is involved in the development of liver damage and liver cirrhosis complications and increases intestinal permeability in a vicious circle. Areas covered: The most relevant studies on bacterial translocation, the mechanism of intestinal barrier dysfunction and its consequences in patients with liver cirrhosis have been revised through a PubMed search. Data have been discussed with particular regard to their significance in clinical practice. Expert commentary: The assessment of bacterial translocation and intestinal permeability is not currently used in clinical practice but may be useful to stratify patients' prognosis.

Goblet cell associated antigen passages are inhibited during Salmonella typhimurium infection to prevent pathogen dissemination and limit responses to dietary antigens

Dietary antigen acquisition by lamina propria (LP) dendritic cells (DCs) is crucial to induce oral tolerance and maintain homeostasis. However, encountering innocuous antigens during infection can lead to inflammatory responses, suggesting processes may limit steady-state luminal antigen capture during infection. We observed that goblet cell (GC) associated antigen passages (GAPs), a steady-state pathway delivering luminal antigens to LP-DCs, are inhibited during Salmonella infection. GAP inhibition was mediated by IL-1β. Infection abrogated luminal antigen delivery and antigen-specific T cell proliferation in the mesenteric lymph node (MLN). Antigen-specific T cell proliferation to dietary antigen was restored by overriding GAP suppression; however, this did not restore regulatory T cell induction, but induced inflammatory T cell responses. Salmonella translocation to the MLN required GCs and correlated with GAPs. Genetic manipulations overriding GAP suppression, or antibiotics inducing colonic GAPs, but not antibiotics that do not, increased dissemination and worsened outcomes independent of luminal pathogen burden. Thus, steady-state sampling pathways are suppressed during infection to prevent responses to dietary antigens, limit pathogen entry, and lessen the disease. Moreover, antibiotics may worsen Salmonella infection by means beyond blunting gut microbiota colonization resistance, providing new insight into how precedent antibiotic use aggravates enteric infection.

Composition and richness of the serum microbiome differ by age and link to systemic inflammation

Advanced age has been associated with alterations to the microbiome within the intestinal tract as well as intestinal permeability (i.e., “leaky gut”). Prior studies suggest that intestinal permeability may contribute to increases in systemic inflammation—an aging hallmark—possibly via microorganisms entering the circulation. Yet, no studies exist describing the state of the circulating microbiome among older persons. To compare microbiota profiles in serum between healthy young (20–35 years, n = 24) and older adults (60–75 years, n = 24) as well as associations between differential microbial populations and prominent indices of age-related inflammation. Unweighted Unifrac analysis, a measure of β-diversity, revealed that microbial communities clustered differently between young and older adults. Several measures of α-diversity, including chao1 (p = 0.001), observed species (p = 0.001), and phylogenetic diversity (p = 0.002) differed between young and older adults. After correction for false discovery rate (FDR), age groups differed (all p values ≤ 0.016) in the relative abundance of the phyla Bacteroidetes, SR1, Spirochaetes, Bacteria_Other, TM7, and Tenericutes. Significant positive correlations (p values ≤ 0.017 after FDR correction) were observed between IGF1 and Bacteroidetes (ρ = 0.380), Spirochaetes (ρ = 0.528), SR1 (ρ = 0.410), and TM7 (ρ = 0.399). Significant inverse correlations were observed for IL6 with Bacteroidetes (ρ = − 0.398) and TM7 (ρ = − 0.423), as well as for TNFα with Bacteroidetes (ρ = − 0.344). Similar findings were observed at the class taxon. These data are the first to demonstrate that the richness and composition of the serum microbiome differ between young and older adults and that these factors are linked to indices of age-related inflammation.

Transcriptome analysis in whole blood reveals increased microbial diversity in schizophrenia

The role of the human microbiome in health and disease is increasingly appreciated. We studied the composition of microbial communities present in blood across 192 individuals, including healthy controls and patients with three disorders affecting the brain: schizophrenia, amyotrophic lateral sclerosis, and bipolar disorder. By using high-quality unmapped RNA sequencing reads as candidate microbial reads, we performed profiling of microbial transcripts detected in whole blood. We were able to detect a wide range of bacterial and archaeal phyla in blood. Interestingly, we observed an increased microbial diversity in schizophrenia patients compared to the three other groups. We replicated this finding in an independent schizophrenia case-control cohort. This increased diversity is inversely correlated with estimated cell abundance of a subpopulation of CD8+ memory T cells in healthy controls, supporting a link between microbial products found in blood, immunity and schizophrenia.

Injections of Lipopolysaccharide into Mice to Mimic Entrance of Microbial-derived Products After Intestinal Barrier Breach

The intestinal epithelial barrier separates the host from the microbiota that is normally tolerated or ignored. The breach of this barrier results in the entrance of bacteria or bacteria-derived products into the host, accessing the host circulation and inner organs leading to the uncontrolled inflammation as observed in patients with inflammatory bowel disease (IBD), that are characterized by an increased intestinal epithelial permeability. To mimic the entrance of bacterial-derived compounds into the host, an endotoxemia model has been adopted in which lipopolysaccharide (LPS), a component of the outer cell wall of Gram-negative bacteria, were injected into mice. In this study, a sublethal dose of LPS was intraperitoneally injected and the mice were subsequently monitored for 8 h using a disease score. Furthermore, the expression levels of the inflammatory cytokines Il6, Il1b, and Tnfa were analyzed in the spleen, liver and colon by qPCR at different time points post LPS injection. This model could be useful for the studies involving investigation of immune responses after the invasion of microorganisms or bacterial-derived products caused by a barrier breach of body surfaces.

Role of Subclinical Gut Inflammation in the Pathogenesis of Spondyloarthritis

Subclinical gut inflammation occurring in patients affected by spondyloarthritis (SpA) is correlated with the severity of spine inflammation. Several evidences indicate that dysbiosis occurs in SpA, and that may modulate intestinal permeability and intestinal immune responses. The presence of intestinal dysbiosis is accompanied in SpA patients with the presence of zonulin-dependent alterations of gut-epithelial and gut-vascular barriers. The leakage of epithelial and endothelial surface layers is followed by the translocation of bacterial products, such as lipopolysaccharide and intestinal fatty acid binding protein, in the systemic circulation. These bacterial products may downregulate the expression of CD14 on circulating monocytes leading to an “anergic” phenotype. In the gut, IL-23 may induce the expansion of innate immune cells such as mucosal-associated invariant T cells, γδ T cells, and innate lymphoid cells of group 3 that through the interaction with MAdCAM1 may recirculate form the gut to the sites of SpA active inflammation. On the basis of these findings, gut inflammation observed in SpA patient seems to be not only an epiphenomenon of the on going systemic inflammatory process but may also represent the base camp in which inflammatory cells are activated and from whom they shuttle.

The microbiome and autoimmunity: a paradigm from the gut-liver axis

Microbial cells significantly outnumber human cells in the body, and the microbial flora at mucosal sites are shaped by environmental factors and, less intuitively, act on host immune responses, as demonstrated by experimental data in germ-free and gnotobiotic studies. Our understanding of this link stems from the established connection between infectious bacteria and immune tolerance breakdown, as observed in rheumatic fever triggered by Streptococci via molecular mimicry, epitope spread and bystander effects. The availability of high-throughput techniques has significantly advanced our capacity to sequence the microbiome and demonstrated variable degrees of dysbiosis in numerous autoimmune diseases, including rheumatoid arthritis, type 1 diabetes, multiple sclerosis and autoimmune liver disease. It remains unknown whether the observed differences are related to the disease pathogenesis or follow the therapeutic and inflammatory changes and are thus mere epiphenomena. In fact, there are only limited data on the molecular mechanisms linking the microbiota to autoimmunity, and microbial therapeutics is being investigated to prevent or halt autoimmune diseases. As a putative mechanism, it is of particular interest that the apoptosis of intestinal epithelial cells in response to microbial stimuli enables the presentation of self-antigens, giving rise to the differentiation of autoreactive Th17 cells and other T helper cells. This comprehensive review will illustrate the data demonstrating the crosstalk between intestinal microbiome and host innate and adaptive immunity, with an emphasis on how dysbiosis may influence systemic autoimmunity. In particular, a gut–liver axis involving the intestinal microbiome and hepatic autoimmunity is elucidated as a paradigm, considering its anatomic and physiological connections.

Von Willebrand factor indicates bacterial translocation, inflammation, and procoagulant imbalance and predicts complications independently of portal hypertension severity

BACKGROUND

Elevated plasma von Willebrand factor antigen (vWF) has been shown to indicate the presence of clinically significant portal hypertension, and thus, predicts the development of clinical events in patients with cirrhosis.

AIM

To investigate the impact of bacterial translocation and inflammation on vWF, as well as the association between vWF and procoagulant imbalance. Moreover, we assessed whether vWF predicts complications of cirrhosis, independent of the severity of portal hypertension.

METHODS

Our study population comprised 225 patients with hepatic venous pressure gradient (HVPG) ≥ 10 mm Hg without active bacterial infections or hepatocellular carcinoma.

RESULTS

vWF correlated with markers of bacterial translocation (lipopolysaccharide-binding protein [LBP; ρ = 0.201; P = 0.021]), inflammation (interleukin 6 [IL-6; ρ = 0.426; P < 0.001] and C-reactive protein [CRP; ρ = 0.249; P < 0.001]), and procoagulant imbalance (factor VIII/protein C ratio; ρ = 0.507; P < 0.001). Importantly, the associations between vWF and these parameters were independent of HVPG. Moreover, vWF (per 10%) independently predicted variceal bleeding (hazard ratio [HR]: 1.08 [95% confidence interval (95% CI): 1.01-1.16]; P = 0.023), requirement of paracentesis (HR: 1.05 [95% CI: 1.01-1.1]; P = 0.023) and bacterial infections (HR: 1.04 [95% CI: 1-1.09]; P = 0.04) including spontaneous bacterial peritonitis (HR: 1.09 [95% CI: 0.999-1.18]; P = 0.053) on a trend-wise level. After backward elimination, vWF (HR: 1.05 [95% CI: 1.02-1.08]; P = 0.003) and CRP (per 10 mg/L; HR: 1.53 [95% CI: 1.14-2.05]; P = 0.005) remained in the final model for transplant-free mortality. Finally, the independent prognostic value of vWF/CRP groups for mortality was confirmed by competing risk analysis.

CONCLUSION

Our results demonstrate that vWF is not only a marker of portal hypertension but also independently linked to bacterial translocation, inflammation and procoagulant imbalance, which might explain its HVPG-independent association with most clinical events. Prognostic groups based on vWF/CRP efficiently discriminate between patients with a poor 5-year survival and patients with a favourable prognosis.

Translocation of a gut pathobiont drives autoimmunity in mice and humans

Despite multiple associations between the microbiota and immune diseases, their role in autoimmunity is poorly understood. We found that translocation of a gut pathobiont, Enterococcus gallinarum, to the liver and other systemic tissues triggers autoimmune responses in a genetic background predisposing to autoimmunity. Antibiotic treatment prevented mortality in this model, suppressed growth of E. gallinarum in tissues, and eliminated pathogenic autoantibodies and T cells. Hepatocyte-E. gallinarum cocultures induced autoimmune-promoting factors. Pathobiont translocation in monocolonized and autoimmune-prone mice induced autoantibodies and caused mortality, which could be prevented by an intramuscular vaccine targeting the pathobiont. E. gallinarum-specific DNA was recovered from liver biopsies of autoimmune patients, and cocultures with human hepatocytes replicated the murine findings; hence, similar processes apparently occur in susceptible humans. These discoveries show that a gut pathobiont can translocate and promote autoimmunity in genetically predisposed hosts.

Microbial interactions with the intestinal epithelium and beyond: Focusing on immune cell maturation and homeostasis

Microbial metabolites influence the function of epithelial, endothelial and immune cells in the intestinal mucosa. Microbial metabolites like SCFAs and B complex vitamins direct macrophage polarization whereas microbial derived biogenic amines modulate intestinal epithelium and immune response. Aberrant bacterial lipopolysaccharide-mediated signaling may be involved in the pathogenesis of chronic intestinal inflammation and colorectal carcinogenesis. Our perception of human microbes has changed from that of opportunistic pathogens to active participants maintaining intestinal and whole body homeostasis. This review attempts to explain the dynamic and enriched interactions between the intestinal epithelial mucosa and commensal bacteria in homeostasis maintenance.

Firewalls Prevent Systemic Dissemination of Vectors Derived from Human Adenovirus Type 5 and Suppress Production of Transgene-Encoded Antigen in a Murine Model of Oral Vaccination

To define the bottlenecks that restrict antigen expression after oral administration of viral-vectored vaccines, we tracked vectors derived from the human adenovirus type 5 at whole body, tissue, and cellular scales throughout the digestive tract in a murine model of oral delivery. After intragastric administration of vectors encoding firefly luciferase or a model antigen, detectable levels of transgene-encoded protein or mRNA were confined to the intestine, and restricted to delimited anatomical zones. Expression of luciferase in the form of multiple small bioluminescent foci in the distal ileum, cecum, and proximal colon suggested multiple crossing points. Many foci were unassociated with visible Peyer's patches, implying that transduced cells lay in proximity to villous rather than follicle-associated epithelium, as supported by detection of transgene-encoded antigen in villous epithelial cells. Transgene-encoded mRNA but not protein was readily detected in Peyer's patches, suggesting that post-transcriptional regulation of viral gene expression might limit expression of transgene-encoded antigen in this tissue. To characterize the pathways by which the vector crossed the intestinal epithelium and encountered sentinel cells, a fluorescent-labeled vector was administered to mice by the intragastric route or inoculated into ligated intestinal loops comprising a Peyer's patch. The vector adhered selectively to microfold cells in the follicle-associated epithelium, and, after translocation to the subepithelial dome region, was captured by phagocytes that expressed CD11c and lysozyme. In conclusion, although a large number of crossing events took place throughout the intestine within and without Peyer's patches, multiple firewalls prevented systemic dissemination of vector and suppressed production of transgene-encoded protein in Peyer's patches.

Co-administration of Antimicrobial Peptides Enhances Toll-like Receptor 4 Antagonist Activity of a Synthetic Glycolipid

This study examines the effect of co‐administration of antimicrobial peptides and the synthetic glycolipid FP7, which is active in inhibiting inflammatory cytokine production caused by TLR4 activation and signaling. The co‐administration of two lipopolysaccharide (LPS)‐neutralizing peptides (a cecropin A–melittin hybrid peptide and a human cathelicidin) enhances by an order of magnitude the potency of FP7 in blocking the TLR4 signal. Interestingly, this is not an additional effect of LPS neutralization by peptides, because it also occurs if cells are stimulated by the plant lectin phytohemagglutinin, a non‐LPS TLR4 agonist. Our data suggest a dual mechanism of action for the peptides, not exclusively based on LPS binding and neutralization, but also on a direct effect on the LPS‐binding proteins of the TLR4 receptor complex. NMR experiments in solution show that peptide addition changes the aggregation state of FP7, promoting the formation of larger micelles. These results suggest a relationship between the aggregation state of lipid A‐like ligands and the type and intensity of the TLR4 response.

Intestinal dysbiosis activates renal renin-angiotensin system contributing to incipient diabetic nephropathy

Considerable interest nowadays has focused on gut microbiota owing to their pleiotropic roles in human health and diseases. This intestinal community can arouse a variety of activities in the host and function as "a microbial organ" by generating bioactive metabolites and participating in a series of metabolism-dependent pathways. Alternations in the composition of gut microbiota, referred to as intestinal dysbiosis, are reportedly associated with several diseases, especially diabetes mellitus and its complications. Here we focus on the relationship between gut microbiota and diabetic nephropathy (DN), as the latter is one of the major causes of chronic kidney diseases. The activation of renin angiotensin system (RAS) is a critical factor to the onset of DN, and emerging data has demonstrated a provoking and mediating role of gut microbiota for this system in the context of metabolic diseases. The purpose of the current review is to highlight some research updates about the underlying interplay between gut microbiota, their metabolites, and the development and progression of DN, along with exploring innovative approaches to targeting this intestinal community as a therapeutic perspective in clinical management of DN patients.

Intestinal Permeability in Relapsing-Remitting Multiple Sclerosis

Changes of intestinal permeability (IP) have been extensively investigated in inflammatory bowel diseases (IBD) and celiac disease (CD), underpinned by a known unbalance between microbiota, IP and immune responses in the gut. Recently the influence of IP on brain function has greatly been appreciated. Previous works showed an increased IP that preceded experimental autoimmune encephalomyelitis development and worsened during disease with disruption of TJ. Moreover, studying co-morbidity between Crohn's disease and MS, a report described increased IP in a minority of cases with MS. In a recent work we found that an alteration of IP is a relatively frequent event in relapsing-remitting MS, with a possible genetic influence on the determinants of IP changes (as inferable from data on twins); IP changes included a deficit of the active mechanism of absorption from intestinal lumen. The results led us to hypothesize that gut may contribute to the development of MS, as suggested by another previous work of our group: a population of CD8+CD161high T cells, belonging to the mucosal-associated invariant T (MAIT) cells, a gut- and liver-homing subset, proved to be of relevance for MS pathogenesis. We eventually suggest future lines of research on IP in MS: studies on IP changes in patients under first-line oral drugs may result useful to improve their therapeutic index; correlating IP and microbiota changes, or IP and blood-brain barrier changes may help clarify disease pathogenesis; exploiting the IP data to disclose co-morbidities in MS, especially with CD and IBD, may be important for patient care.

Colon Ascendens Stent Peritonitis (CASP) Induces Excessive Inflammation and Systemic Metabolic Dysfunction in a Septic Rat Model

The colon ascendens stent peritonitis (CASP) surgery induces a leakage of gut contents, causing polymicrobial sepsis related to post-operative multiple organ failure and death in surgical patient. To evaluate the effects of CASP on multiple organs, we analyzed the systemic metabolic consequences in liver, kidney, lung, and heart of rats after CASP by employing a combination of metabolomics, clinical chemistry, and biological assays. We found that CASP surgery after 18 h resulted in striking elevations of lipid, amino acids, acetate, choline, PC, and GPC in rat liver together with significant depletion of glucose and glycogen. Marked elevations of organic acids including lactate, acetate, and creatine and amino acids accompanied by decline of glucose, betaine, TMAO, choline metabolites (PC and GPC) nucleotides, and a range of organic osmolytes such as myo-inositol are observed in the kidney of 18 h post-operative rat. Furthermore, 18 h post-operative rats exhibited accumulations of lipid, amino acids, and depletions of taurine, myo-inositol, choline, PC, and GPC and some nucleotides including uridine, inosine, and adenosine in the lung. In addition, significant elevations of some amino acids, uracil, betaine, and choline metabolites, together with depletion of inosine-5'-monophosphate, were only observed in the heart of 18 h post-operative rats. These results provide new insights into pathological consequences of CASP surgery, which are important for timely prognosis of sepsis.

Visceral Inflammation and Immune Activation Stress the Brain

Stress refers to a dynamic process in which the homeostasis of an organism is challenged, the outcome depending on the type, severity, and duration of stressors involved, the stress responses triggered, and the stress resilience of the organism. Importantly, the relationship between stress and the immune system is bidirectional, as not only stressors have an impact on immune function, but alterations in immune function themselves can elicit stress responses. Such bidirectional interactions have been prominently identified to occur in the gastrointestinal tract in which there is a close cross-talk between the gut microbiota and the local immune system, governed by the permeability of the intestinal mucosa. External stressors disturb the homeostasis between microbiota and gut, these disturbances being signaled to the brain via multiple communication pathways constituting the gut-brain axis, ultimately eliciting stress responses and perturbations of brain function. In view of these relationships, the present article sets out to highlight some of the interactions between peripheral immune activation, especially in the visceral system, and brain function, behavior, and stress coping. These issues are exemplified by the way through which the intestinal microbiota as well as microbe-associated molecular patterns including lipopolysaccharide communicate with the immune system and brain, and the mechanisms whereby overt inflammation in the GI tract impacts on emotional-affective behavior, pain sensitivity, and stress coping. The interactions between the peripheral immune system and the brain take place along the gut-brain axis, the major communication pathways of which comprise microbial metabolites, gut hormones, immune mediators, and sensory neurons. Through these signaling systems, several transmitter and neuropeptide systems within the brain are altered under conditions of peripheral immune stress, enabling adaptive processes related to stress coping and resilience to take place. These aspects of the impact of immune stress on molecular and behavioral processes in the brain have a bearing on several disturbances of mental health and highlight novel opportunities of therapeutic intervention.

Targeting the gut-liver axis in liver disease

The gut-liver axis is widely implicated in the pathogenesis of liver diseases, where it is increasingly the focus of clinical research. Recent studies trialling an array of therapeutic and preventative strategies have yielded promising results. Considering these strategies, the armamentarium for targeting the gut-liver axis will continue to expand. Further clinical trials, translated from our current knowledge of the gut-liver axis, promise an exciting future in liver treatment.

MFSD2A Promotes Endothelial Generation of Inflammation-Resolving Lipid Mediators and Reduces Colitis in Mice

BACKGROUND & AIMS

Alterations in signaling pathways that regulate resolution of inflammation (resolving pathways) contribute to pathogenesis of ulcerative colitis (UC). The resolution process is regulated by lipid mediators, such as those derived from the ω-3 docosahexaenoic acid (DHA), whose esterified form is transported by the major facilitator superfamily domain containing 2A (MFSD2A) through the endothelium of brain, retina, and placenta. We investigated if and how MFSD2A regulates lipid metabolism of gut endothelial cells to promote resolution of intestinal inflammation.

METHODS

We performed lipidomic and functional analyses of MFSD2A in mucosal biopsies and primary human intestinal microvascular endothelial cells (HIMECs) isolated from surgical specimens from patients with active, resolving UC and healthy individuals without UC (controls). MFSD2A was knocked down in HIMECs with small hairpin RNAs or overexpressed from a lentiviral vector. Human circulating endothelial progenitor cells that overexpress MFSD2A were transferred to CD1 nude mice with dextran sodium sulfate-induced colitis, with or without oral administration of DHA.

RESULTS

Colonic biopsies from patients with UC had reduced levels of inflammation-resolving DHA-derived epoxy metabolites compared to healthy colon tissues or tissues with resolution of inflammation. Production of these metabolites by HIMECs required MFSD2A, which is required for DHA retention and metabolism in the gut vasculature. In mice with colitis, transplanted endothelial progenitor cells that overexpressed MFSD2A not only localized to the inflamed mucosa but also restored the ability of the endothelium to resolve intestinal inflammation, compared with mice with colitis that did not receive MFSD2A-overexpressing endothelial progenitors.

CONCLUSIONS

Levels of DHA-derived epoxides are lower in colon tissues from patients with UC than healthy and resolving mucosa. Production of these metabolites by gut endothelium requires MFSD2A; endothelial progenitor cells that overexpress MFSD2A reduce colitis in mice. This pathway might be induced to resolve intestinal inflammation in patients with colitis.

Interplay of GTPases and Cytoskeleton in Cellular Barrier Defects during Gut Inflammation

An essential role of the intestine is to build and maintain a barrier preventing the luminal gut microbiota from invading the host. This involves two coordinated physical and immunological barriers formed by single layers of intestinal epithelial and endothelial cells, which avoid the activation of local immune responses or the systemic dissemination of microbial agents, and preserve tissue homeostasis. Accordingly, alterations of epithelial and endothelial barrier functions have been associated with gut inflammation, for example during inflammatory bowel disease (IBD). The discriminative control of nutriment uptake and sealing toward potentially pathological microorganisms requires a profound regulation of para- and transcellular permeability. On the subcellular level, the cytoskeleton exerts key regulatory functions in the maintenance of cellular barriers. Increased epithelial/endothelial permeability occurs primarily as a result of a reorganization of cytoskeletal–junctional complexes. Pro-inflammatory mediators such as cytokines can induce cytoskeletal rearrangements, causing inflammation-dependent defects in gut barrier function. In this context, small GTPases of the Rho family and large GTPases from the Dynamin superfamily appear as major cellular switches regulating the interaction between intercellular junctions and actomyosin complexes, and in turn cytoskeleton plasticity. Strikingly, some of these proteins, such as RhoA or guanylate-binding protein-1 (GBP-1) have been associated with gut inflammation and IBD. In this review, we will summarize the role of small and large GTPases for cytoskeleton plasticity and epithelial/endothelial barrier in the context of gut inflammation.

From clinical uncertainties to precision medicine: the emerging role of the gut barrier and microbiome in small bowel functional diseases

Over the last decade, remarkable progress has been made in the understanding of disease pathophysiology. Many new theories expound on the importance of emerging factors such as microbiome influences, genomics/omics, stem cells, innate intestinal immunity or mucosal barrier complexities. This has introduced a further dimension of uncertainty into clinical decision-making, but equally, may shed some light on less well-understood and difficult to manage conditions. Areas covered: Comprehensive review of the literature on gut barrier and microbiome relevant to small bowel pathology. A PubMed/Medline search from 1990 to April 2017 was undertaken and papers from this range were included. Expert commentary: The scenario of clinical uncertainty is well-illustrated by functional gastrointestinal disorders (FGIDs). The movement towards achieving a better understanding of FGIDs is expressed in the Rome IV guidelines. Novel diagnostic and therapeutic protocols focused on the GB and SB microbiome can facilitate diagnosis, management and improve our understanding of the underlying pathological mechanisms in FGIDs.

The Liver at the Nexus of Host-Microbial Interactions

The liver receives blood from the intestine, from the spleen, and directly from the heart and holds a vital position in vertebrate physiology. It plays a role in intermediary metabolism, bile secretion, maintaining blood sterility, serum homeostasis, xenobiotic detoxification, and immunological activity. This article provides our perspective on the liver as a nexus in establishing and maintaining host microbial mutualism. We discuss the role of the liver not only in sanitizing the blood stream from penetrant live microbes, but also in metabolizing xenobiotics that are synthesized or modified by intestinal microbes, and how microbiota modify the signaling potential of bile acids. The combination of bile acids as hormones and the metabolic control from pervasive effects of other absorbed microbial molecules powerfully shape hepatic metabolism. In addition, intestinal microbial metabolites can be sensed by liver-resident immune cells, which may disturb liver homeostasis, leading to fibrosis and liver cancer.

Organ-specific protection mediated by cooperation between vascular and epithelial barriers

Immune privilege is a complex process that protects organs from immune-mediated attack and damage. It is accomplished by a series of cellular barriers that both control immune cell entry and promote the development of tolerogenic immune cells. In this Review, we describe the vascular endothelial and epithelial barriers in organs that are commonly considered to be immune privileged, such as the brain and the eye. We compare these classical barriers with barriers in the intestine, which share features with barriers of immune-privileged organs, such as the capacity to induce tolerance and to protect from external insults. We suggest that when intestinal barriers break down, disruption of other barriers at distant sites can ensue, and this may underlie the development of various neurological, metabolic and intestinal disorders.