Inflamed intestinal mucosa features a specific epithelial expression pattern of indoleamine 2,3-dioxygenase

Indoleamine 2,3-dioxygenase (IDO) catalyzes the first step in the degradation of tryptophan, an essential amino acid. During inflammation IDO can be induced in different cell types resulting in local tryptophan depletion. This inhibits T cell proliferation and may induce apoptosis. High expression of IDO was previously found in inflammatory bowel disease and is thought to represent a mechanism for downregulation of the local immune response. Our aim is to investigate the expression pattern of IDO in normal and inflamed murine and human intestinal mucosa. Immunohistochemical staining for IDO was performed on paraffin sections of colon of two mouse models for colitis and their controls and on paraffin sections of human ileum and colon in normal and two different inflammatory conditions, namely inflammatory bowel disease and diverticulitis. IDO immunohistochemistry showed similar results in murine and human tissue. In normal, as well as in inflamed mucosa, some mononuclear cells, fibroblasts and endothelial cells were positive for IDO. In inflamed mucosa a specific expression pattern of epithelial IDO was found where epithelial cells flanking ulcers or bordering crypt abscesses showed high IDO expression. Moreover, in human intestinal inflammation, IDO was expressed in ulcer associated cell lineage. Since bacterial invasion is more pronounced in erosions and in crypt abscesses and since IDO activity and the resulting local tryptophan depletion can cause growth arrest of several tryptophan-dependent microorganisms, IDO expression in the vicinity of interruptions of the epithelial barrier may point to a role for IDO as a local anti-infectious agent. Furthermore, expression of IDO at the margin of ulcerations and in the reparative ulcer-associated cell lineage suggests involvement of IDO in repair processes.     

中药对肠黏膜屏障的作用机制研究进展

肠黏膜屏障能够有效阻止肠内的有害物质穿过肠黏膜进入血液及其他组织,在维持机体与外环境的稳态上发挥着非常重要的作用。但机体在遭受严重应激后,易导致肠黏膜屏障功能下降。近年来,中医药的介入为肠黏膜屏障的保护开辟了一条新道路。中药可通过调控肠上皮细胞间紧密连接、调节肠道微生态平衡及激发肠道免疫应答等作用修复受损的肠黏膜屏障。本文对中药在受损肠黏膜保护及修复中的作用机制进行综述,旨在阐明中药在肠黏膜屏障保护中的重要作用。     

Effect of bile salts on nasal permeability in vitro

Nasal mucosa excised from dogs or rabbits was mounted as a flat sheet in an in vitro chamber. The permeability was assessed by measuring the unidirectional flux of the radiolabeled tracer compounds, water, sucrose, polyethylene glycol, and cholecystokinin octapeptide. The permeability coefficients calculated from the fluxes indicate that the nasal mucosa is moderately permeable to water-soluble compounds and compares with ileum or gallbladder. The addition of 0.5% sodium deoxycholate to the mucosal bathing solution caused a rapid, four- to fivefold increase in permeability to sucrose or cholecystokinin octapeptide. The increase in permeability was bidirectional, was not reversed by washing, and was accompanied by histological evidence of extensive loss of the surface epithelial layer. These results indicate that bile salts enhance nasal permeability by removing the epithelial cells, which constitute a major permeability barrier, rather than causing a chemical modification of the mucosal cells. This argues against the use of bile salts to enhance nasal drug absorption in patients.     

Glycan recognition at the interface of the intestinal immune system: target for immune modulation via dietary components

The intestinal mucosa is constantly exposed to the luminal content, which includes micro-organisms and dietary components. Prebiotic non-digestible oligosaccharides may be supplemented to the diet to exert modulation of immune responses in the intestine. Short chain galacto- and long chain fructo-oligosaccharides (scGOS/lcFOS), functionally mimicking oligosaccharides present in human milk, have been reported to reduce the development of allergy through modulation of the intestinal microbiota and immune system. Nonetheless, the underlying working mechanisms of scGOS/lcFOS are unclear. Intestinal epithelial cells lining the mucosa are known to express carbohydrate (glycan)-binding receptors that may be involved in modulation of the mucosal immune response. This review aims to provide an overview of glycan-binding receptors, in particular galectins, which are expressed by intestinal epithelial cells and immune cells. In addition, their involvement in health and disease will be addressed, especially in food allergy and inflammatory bowel disease, diseases originating from the gastro-intestinal tract. Insight in the recognition of glycans in the intestinal tract may open new avenues for the treatment of intestinal inflammatory diseases by either nutritional concepts or pharmacological intervention.     

TGF-β信号转导通路与遗传性脑小血管病

转化生长因子-β（transforming growth factor β,TGF-β）是一类具有生物活性的调节因子,广泛表达于内皮细胞、神经细胞、成纤维细胞、上皮细胞等。TGF-β可通过介导Smad依赖通路和非Smad依赖通路参与多种遗传性脑小血管病（cerebral small vessel disease,CSVD）,如CADASIL、CARASIL、HTRA1基因突变相关CSVD（症状携带者）、Fabry病等的发生发展。TGF-β信号通路可能通过影响内皮细胞功能、血管壁结构改变、血脑屏障通透性增加等导致CSVD。但此通路的调节异常不能作为一元论来解释CSVD的发生。本文将对TGF-β蛋白家族及其受体,TGF-β信号转导通路及其转导机制,TGF-β信号通路与遗传性CSVD等方面进行综述。     

Characterization of immunologically active drugs in a novel organotypic co-culture model of the human gut and whole blood

The human immune system represents a highly complex multicellular network that protects the organism against the environment and pathogens. Within this system, different immune cells communicate with each other, as well as with adjacent organs and tissues, using an impressive network of regulatory signals. This inherent complexity makes it rather difficult to mimic these processes in vitro. Unpredictable drug-induced side effects can be the consequence when moving from preclinical animal models into clinical phase. Therefore, there is a demand for more elaborate in vivo like human cell culture models. In this study, an in vitro co-culture model consisting of Caco-2 human gut epithelial cells and human whole blood representing the immune system is applied to investigate the intestinal absorption of anti-inflammatory drugs and the subsequent modulation of the immunoregulatory signaling processes. By using blood of different donors, the individuality of the immune system is integrated into the overall analysis. The anti-inflammatory drugs prednisolone and ibuprofen were applied on top of the Caco-2 epithelial cells and alterations in the extracellular communication via cytokines and chemokines were visualized using miniaturized multiplexed sandwich immunoassays. Optionally, pretreatment of the Caco-2 epithelial cells with pro-inflammatory mediators can be used to modulate the epithelial barrier function similar to the situation observed during inflammatory conditions of the gut. The presented translational test system, consisting of differentiated Caco-2 intestinal epithelial cells and whole blood substantially improves preclinical screening of immunologically active drugs with respect to an approximation of the human “in vivo” conditions.     

免疫细胞对肠干细胞命运调控的最新研究进展

肠道上皮作为机体防御外界病原体进入的“第一道防线”，其持续的自我更新是维持肠道物理屏障及肠道稳态的重要前提。而此过程依赖于隐窝底部的肠干细胞，并受到肠干细胞生态位内复杂信号网络的调控。然而，环境信号的来源及调控肠干细胞命运的方式仍有待研究。最新研究表明免疫细胞如T细胞、先天性淋巴细胞、树突状细胞和巨噬细胞在调控肠干细胞命运中起关键作用。本文综述了免疫细胞调控肠干细胞的最新进展，以期更好的理解肠道生理，为肠上皮屏障疾病的治疗提供参考。     

Chemosense for luminal environment in the large intestine

Gut lumen is continually exposed to many agents, including noxious compounds. The intestinal epithelia form a barrier between the internal and luminal (external) environments. Chemical receptors that detect the luminal environment are thought to play an important role as sensors and as modulators of epithelial cell functions. The Molecular analysis of various epithelial cell membrane receptor proteins has elucidated the sensory role of these cells in the gut chemosensing system. Nutrient sensing systems by these receptors in the small intestinal epithelia are thought to influence nutrient metabolism and local physiological function. Much less is known, however, about the physiological roles of chemosensing in the large intestine. We have investigated the contractile and secretory effects of short-chain fatty acids (SCFAs), the primary products of commensal bacteria, and the expression of SCFA receptors in the large intestine. The findings indicate that the epithelia in the large intestine also detect and respond to luminal contents, particularly bacterial metabolites, for host defense. We recently reported that luminal bitter tastants and odorants affect transepithelial ion transport in human and rat colon, and that putative receptors are expressed in colonic mucosa. In this review, we describe the secretory effects of chemical stimuli on lumen associated with the expression pattern of sensory receptors, focusing on the large intestine.     

Protective effects of lactoferrin against intestinal mucosal damage induced by lipopolysaccharide in human intestinal Caco-2 cells

Indirect evidence suggests that lactoferrin (Lf), a major iron-binding protein in human milk, induces enterocyte growth and proliferation, depending on its concentration and affects the function and permeability of the intestinal mucosa. The bacterial endotoxin (lipopolysaccharide, LPS) is known to cause mucosal hyperpermeability in vivo. However, protective effects of Lf against LPS-mediated intestinal mucosal damage and barrier function in epithelial cells are not yet fully clarified. The aim of this study was to investigate whether Lf can reduce the cellular injury and alter epithelial hyperpermeability caused by LPS in human intestinal Caco-2 cells. When cell viability was measured by a WST-1 assay (tetrazolium salt-based assay), the protective effects against LPS-induced damage to Caco-2 cells were observed at doses of 800 and 1000 microg/ml Lf. The barrier function of Caco-2 monolayer tight junctions was assessed by measuring transepithelial electrical resistance (TEER) and permeability of FITC-labeled dextran 4000 (FD-4). The treatment of Caco-2 cells with Lf at doses of 400 and 1000 microg/ml significantly increased TEER as compared to treatment with LPS alone for 2 h (p<0.05). Further, at doses of 400 and 1000 microg/ml, Lf inhibited the enhancement of LPS-mediated permeability in Caco-2 cell monolayer. The results of this study suggest that Lf may have protective effects against LPS-mediated intestinal mucosal damage and impairment of barrier function in intestinal epithelial cells.     

Effect of Deoxynivalenol and Other Type B Trichothecenes on the Intestine: A Review

The natural food contaminants, mycotoxins, are regarded as an important risk factor for human and animal health, as up to 25% of the world’s crop production may be contaminated. The Fusarium genus produces large quantities of fusariotoxins, among which the trichothecenes are considered as a ubiquitous problem worldwide. The gastrointestinal tract is the first physiological barrier against food contaminants, as well as the first target for these toxicants. An increasing number of studies suggest that intestinal epithelial cells are targets for deoxynivalenol (DON) and other Type B trichothecenes (TCTB). In humans, various adverse digestive symptoms are observed on acute exposure, and in animals, these toxins induce pathological lesions, including necrosis of the intestinal epithelium. They affect the integrity of the intestinal epithelium through alterations in cell morphology and differentiation and in the barrier function. Moreover, DON and TCTB modulate the activity of intestinal epithelium in its role in immune responsiveness. TCTB affect cytokine production by intestinal or immune cells and are supposed to interfere with the cross-talk between epithelial cells and other intestinal immune cells. This review summarizes our current knowledge of the effects of DON and other TCTB on the intestine.     

Histological and physiological studies on the intestine of the rat exposed to solutions of Myrj 52 and PEG 2000

The closed gut segment technique was used to investigate the effects of various concentrations of polyoxyethylene (40) stearate (Myrj 52) and Polyethylene glycol 2000 (PEG 2000) solutions on the histology of the intestinal mucosa and on fluid movements across the intestinal barrier. The results show that the higher concentrations of Myrj 52 and PEG 2000 induced cell loss and epithelial damage, and in addition solutions of PEG 2000 caused an unequal loss of enterocytes and goblet cells. Cell loss is likely to be a transient phenomena, with normal cell proliferation in the intestinal crypt being responsible for the restoration of villus architecture. Solutions of Myrj 52 caused little movement of fluid across the intestinal barrier but PEG 2000 at similar concentrations induced a considerable fluid loss from the mucosa to the lumen. The mechanism of this effect appears to be related to the anomalous osmotic behaviour of the PEG 2000 solutions, which dramatically changes the normal osmotic gradient across the intestinal barrier.     

The blood-central nervous system barriers actively control immune cell entry into the central nervous system

Before entering the central nervous system (CNS) immune cells have to penetrate any one of its barriers, namely either the endothelial blood-brain barrier, the epithelial blood-cerebrospinal fluid barrier or the tanycytic barrier around the circumventricular organs, all of which maintain homeostasis within the CNS. The presence of these barriers in combination with the lack of lymphatic vessels and the absence of classical MHC-positive antigen presenting cells characterizes the CNS as an immunologically privileged site. In multiple sclerosis a large number of inflammatory cells gains access to the CNS parenchyma. Studies performed in experimental autoimmune encephalomyelitis (EAE), a rodent model for multiple sclerosis, have enabled us to understand some of the molecular mechanisms involved in immune cell entry into the CNS. In particular, the realization that /alpha4-integrins play a predominant role in leukocyte trafficking to the CNS has led to the development of a novel drug for the treatment of relapsing-remitting multiple sclerosis, which targets /alpha4-integrin mediated immune cell migration to the CNS. At the same time, the involvement of other adhesion and signalling molecules in this process remains to be investigated and novel molecules contributing to immune cell entry into the CNS are still being identified. The entire process of immune cell trafficking into the CNS is strictly controlled by the brain barriers not only under physiological conditions but also during neuroinflammation, when some barrier properties are lost. Thus, immune cell entry into the CNS critically depends on the unique characteristics of the brain barriers maintaining CNS homeostasis.     

Toll-like receptors and NOD/CARD proteins: pattern recognition receptors are key elements in the regulation of immune response

The magnitude of the response to a specific immunogen such as an infectious agent is the result of a complex interaction between genetic and environmental factors. For example, in intestinal inflammation, the inflammatory response appears to be regulated by the indigenous microflora of the gut, by receptors in epithelial cells and antigen-presenting cells in the intestinal mucosa, and by immunologic factors. Recent evidence suggests that genetic variants of human immunomodulating genes influence the susceptibility to and severity of infectious diseases and the subsequent clinical outcome of disease. This review will focus on recently identified pattern recognition receptors which are located on innate immune and epithelial cells, and recognize pathogen-associated molecular patterns. The binding of specific pathogen-associated molecular patterns to these receptors results in the activation of a signal transduction pathway through nuclear factor (NF)-kappaB which leads to either enhanced or inhibited immune responses that modify the production of inflammatory effectors, such as cytokines. This article reports on the identification and functional characterization including the discovery of mutants which completely abolish NF-kappaB signal transduction of pattern recognition receptors, such as the extracellular Toll-like receptors and the intracellular nucleotide oligomerization domain/caspase recruitment domain (NOD/CARD) receptors, as well as their role in clinical disease. Knowledge of pattern recognition receptors such as Toll-like receptors and NOD/CARD intracytoplasmic proteins, including their functions and their downstream signaling pathways, may provide a new molecular basis for preventing or blocking inflammation associated with pathogenic microorganisms. This could direct a new focus for better and more specific therapeutic treatments based on immuno-intervention that can promise a better quality of life for those suffering from chronic disturbances of the immune response.     

Adenosine in the inflamed gut: a Janus faced compound

The purine ribonucleoside adenosine (Ado) has been recognized for its regulatory functions in situations of cellular stress like ischemia, hypoxia and inflammation. The importance of extracellular Ado as a modulator in the immune system is a theme of great appreciation and the focus of recent increasing interest in the field of gastrointestinal inflammation. In this review, the different aspects of Ado signaling during inflammatory responses in the gut are discussed, considering the contribution of the four known Ado receptors (ARs; A(1), A(2A), A(2B), and A(3)), their mechanisms and expression patterns. Activation of these receptors in epithelial cells as well as in immune cells recruited to the inflamed intestinal mucosa determines the overall effect, ranging from a protective, anti-inflammatory modulation to a strong pro-inflammatory induction. Here we present the current advances in agonists and antagonists development and their potential therapeutic application studied in animal models of intestinal inflammation. In addition, alternative complementary approaches to manipulate such a complex signaling system are discussed, for example, the use of AR allosteric modulators or interference with Ado metabolism. Special features of the gut environment are taken into account: the contribution of diet components; the involvement of Ado in intestinal infections; the interactions with the gut microbiome, particularly, the recent exciting finding that an intestinal bacterium can directly produce extracellular Ado in response to host defense mechanisms in an inflammation scenario. Understanding each component of this dynamic system will broaden the possibilities for applying Ado signaling as a therapeutic target in gut inflammation.     

Protective role of berberine on ulcerative colitis through modulating enteric glial cells–intestinal epithelial cells–immune cells interactions

Ulcerative colitis (UC) manifests as an etiologically complicated and relapsing gastrointestinal disease. The enteric nervous system (ENS) plays a pivotal role in rectifying and orchestrating the inflammatory responses in gut tract. Berberine, an isoquinoline alkaloid, is known as its anti-inflammatory and therapeutic effects in experimental colitis. However, little research focused on its regulatory function on ENS. Therefore, we set out to explore the pathological role of neurogenic inflammation in UC and the modulating effects of berberine on neuro–immune interactions. Functional defects of enteric glial cells (EGCs), with decreased glial fibrillary acidic protein (GFAP) and increased substance P expression, were observed in DSS-induced murine UC. Administration of berberine can obviously ameliorate the disease severity and restore the mucosal barrier homeostasis of UC, closely accompanying by maintaining the residence of EGCs and attenuating inflammatory infiltrations and immune cells overactivation. In vitro, berberine showed direct protective effects on monoculture of EGCs, bone marrow-derived dendritic cells (BMDCs), T cells, and intestinal epithelial cells (IECs) in the simulated inflammatory conditions. Furthermore, berberine could modulate gut EGCs–IECs–immune cell interactions in the co-culture systems. In summary, our study indicated the EGCs–IECs–immune cell interactions might function as a crucial paradigm in mucosal inflammation and provided an infusive mechanism of berberine in regulating enteric neurogenic inflammation.     

Neuro-immune interactions in inflammatory bowel disease and irritable bowel syndrome: future therapeutic targets

The gastro-intestinal tract is well known for its largest neural network outside the central nervous system and for the most extensive immune system in the body. Research in neurogastroenterology implicates the involvement of both enteric nervous system and immune system in symptoms of inflammatory bowel disease and irritable bowel syndrome. Since both disorders are associated with increased immune cell numbers, nerve growth and activation of both immune cells and nerves, we focus in this review on the involvement of immune cell–nerve interactions in inflammatory bowel disease and irritable bowel syndrome. Firstly, the possible effects of enteric nerves, especially of the nonadrenergic and noncholinergic nerves, on the intestinal immune system and their possible role in the pathogenesis of chronic intestinal inflammatory diseases are described. Secondly, the possible effects of immunological factors, from the innate (chemokines and Toll-like receptors) as well as the adaptive (cytokines and immunoglobulins) immune system, on gastro-intestinal nerves and its potential role in the development of inflammatory bowel disease and irritable bowel syndrome are reviewed. Investigations of receptor-mediated and intracellular signal pathways in neuro-immune interactions might help to develop more effective therapeutic approaches for chronic inflammatory intestinal diseases.     

Expression of defensins in gingiva and their role in periodontal health and disease

Oral epithelium is a stratified squamous epithelium that functions as the barrier between the outside environment and the host. In the oral cavity, epithelial tissues are constantly exposed to a variety of bacteria, but most individuals maintain healthy homeostasis. Epithelial cells contribute to the innate host response, and antimicrobial peptide expression in all human epithelia, including oral epithelia, is an important part of this epithelial function. These antimicrobial peptides have a broad spectrum of activity against both Gram-negative and Gram-positive bacteria as well as against yeast and viruses. In humans these antimicrobial peptides include defensins and a cathelicidin family member LL-37 in skin and oral mucosa and other epithelia. The human defensins include the alpha-defensins of intestinal and neutrophil origin, and the beta-defensins of skin and oral mucosa and other epithelia. Present studies have identified specific signaling routes that pathogens and commensals take in stimulating these innate immune responses, and this may open the way for development of new therapeutic agents for periodontal diseases.