肠上皮与肠道微生物相互作用研究进展

肠道不仅是消化和吸收的主要场所,也是机体重要的免疫器官。人类肠道中存在着超过百万亿的微生物,其在漫长的自然选择及共同进化中与宿主形成了紧密的共生关系。肠上皮是先天免疫的一个组成部分,通过各种黏膜保护屏障将肠腔内容物与机体内环境分隔开。各种肠上皮细胞相互协调维持肠道内稳态,并与肠道微生物、肠黏膜免疫系统共同形成抵御肠腔内有害抗原的第一道防线。肠上皮作为肠道微生物和肠黏膜免疫系统相互作用的枢纽,在黏膜免疫防御体系中具有重要作用,本文就肠上皮与肠道微生物之间的相互作用进行综述,旨在深入理解肠上皮,为探索肠道相关疾病的治疗提供新思路。     

肠黏膜屏障与病原细菌感染

人的肠道是一个非常复杂的环境,在这里存在有数量庞大的多种多样的微生物群落,它们的合集又通称为肠道菌群(gut microbiota)。通常情况下,人体与肠道菌群和平共处,互利互惠。肠道内环境与微生物的稳态主要依赖于肠黏膜的存在,它包括了上皮细胞层、固有层和黏膜肌层。肠黏膜协同其分泌的黏液层、黏膜免疫系统、以及其上依附的肠道菌群等一同组成了肠黏膜屏障,以抵御各种外界不利因素,尤其是病原细菌的侵袭。本文旨在概述肠道黏膜屏障与部分相关常见病原细菌感染机制的研究进展,并为科学研究和临床诊疗提供新思路。     

肠道黏膜受损及保护机制的研究进展

正常肠道屏障功能依赖于肠黏膜上皮屏障,肠道免疫系统以及肠道的正常微生物的平衡。一些常见肠道疾病是通过破坏肠道黏膜的正常结构和功能,导致其病理和生理的变化而发病。本文就肠道黏膜的受损及保护机制作一综述。     

痛泻要方对肝气乘脾泄泻小鼠肠道微生物活度的影响

目的探讨痛泻要方对肝气乘脾泄泻小鼠肠道微生物活度的影响,为痛泻要方通过调节肠道微生物治疗肝气乘脾泄泻提供实验基础和理论依据。方法将25只SPF级雄性昆明小鼠随机分为正常组10只和模型组15只,造模成功后,随机选取正常组和模型组动物各5只,在无菌环境下提取肠道内容物和肠黏膜,剩余模型动物随机分为自然恢复组和治疗组各5只,治疗成功后处死各组动物提取肠道内容物和肠黏膜。用荧光素二乙酸法测定各样品中微生物活度。结果肝气乘脾泄泻造模小鼠肠道内容物微生物活度高于正常组,与正常组相比差异有统计学意义(P=0.01),而模型组小鼠肠黏膜微生物活度降低,与正常组相比差异有统计学意义(P=0.01)。痛泻要方治疗组和自然恢复组小鼠肠道内容物微生物活度均降低,与正常组相比差异无统计学意义(P>0.05),治疗组和自然恢复组小鼠的肠黏膜前段和后段均与正常组差异有统计学意义(P=0.001),肠黏膜中段自然恢复组与正常组差异有统计学意义(P=0.043),而治疗组与正常组没有差异。结论肝气乘脾泄泻造模使肠道内容物微生物活度增加,而使肠黏膜微生物活度降低。痛泻要方能够使肝气乘脾泄泻小鼠肠道内容物中微生物活度降低,恢复至正常水平,增加肠黏膜中段微生物活度,对肠黏膜后段微生物活度增加作用更显著。     

肠道菌群调控黏膜免疫与脓毒症的发病机制

脓毒症和脓毒症休克是临床重症监护室患者的主要死亡原因之一。肠道菌群作为脓毒症过程中重要参与者,其紊乱能激活肠道黏膜免疫,进而影响全身免疫系统,诱发和加剧脓毒症。此外,肠道微生物还能通过"肠道-器官"轴参与脓毒症发生发展过程,针对肠道微生物的靶向治疗能防治脓毒症。本文深入探讨了肠道微生物、肠道黏膜免疫与脓毒症之间的相互作用,以期为临床开发新的疗法提供理论基础。     

肠道微生物与肠上皮细胞互作的免疫调节机制

人体肠道中寄居着数量众多、种类繁异的微生物,其在机体营养吸收、物质代谢以及免疫调节等方面发挥着积极作用,但肠道微生物(gut microbiota)群落结构失调或组织易位则与多种疾病的发生发展密切相关。肠上皮细胞(intestinal epithelial cells)作为机体直接接触众多肠道微生物的第一道屏障,在响应肠道微生物定植、调节肠道微生物群落结构以及维持肠黏膜屏障功能等方面发挥着至关重要的作用。本文将主要从肠黏膜免疫调控的角度,介绍肠道微生物与肠上皮细胞互作分子机制的最新研究进展。     

布拉酵母对炎症性肠病的治疗作用

炎症性肠病包括溃疡性结肠炎和克罗恩病, 其病因与发病机制尚未完全明确。大量研究表明, 肠道微生物在炎症性肠病的发生、发展中发挥重要作用。布拉酵母是一种有益于人体健康的肠道微生物, 研究发现能有效改善炎症性肠病症状, 可能与其抑制肠道致病菌、增强肠屏障功能、调节肠道黏膜免疫反应等有关。     

基于生物信息学的克罗恩病患者肠道炎症黏膜与非炎症黏膜来源的菌群差异研究CSCD

目的目前克罗恩病(CD)的具体病理机制仍不清楚,肠道菌群在CD的发生与进展过程中发挥了重要的作用。我们旨在通过比较CD患者肠道正常和炎症粘膜微生物群的组成来阐明肠道微生物群如何影响CD患者的粘膜愈合。方法使用“Crohn’s disease”作为关键词检索GEO与AE数据库并下载GSE162844与GSE198329数据集,使用R 4.2.3软件对两个数据集的微生物数据进行多样性分析和线性判别分析效应量以探讨不同肠道黏膜微生物的组成差异。结果CD患者肠道炎症部位黏膜菌群Shannon多样性指数和Simpson多样性指数较肠道正常部位有所下降,并且两个部位菌群组成有一定差异。在门水平上,变形菌门为肠道的主要优势菌群,软壁菌门在肠道炎症黏膜中的相对丰度升高(P<0.05);在属水平上,假单胞菌属为肠道的主要优势菌群,中间原体属和支原体属在肠道黏膜炎症部位中的相对丰度明显升高(P<0.05)。LEfSe分析结果进一步揭示了海洋芽孢杆菌属、嗜胨菌科等在CD患者肠道黏膜正常部位中富集,而假单胞菌属、Candidatus Saccharibacteria等在炎症部位出现富集。结论CD患者肠道黏膜炎症部位与正常部位菌群组成不同。     

肠道共生微生物脂质代谢物的黏膜免疫调节功能与机制

机体的肠道黏膜表面存在着大量与宿主免疫系统互作的共生微生物,其所编码的代谢通路可产生多种具有免疫调节活性的小分子物质。膳食脂肪可经脂解作用形成游离脂肪酸,并在肠道胆汁酸的协助下作为必需营养元素被机体所吸收利用。与此同时,肠道共生微生物既可将宿主来源的胆汁酸转化为多种脱结合胆汁酸或次级胆汁酸,也可将部分膳食来源的长链不饱和脂肪酸代谢为多种异构衍生物。目前,关于肠道共生微生物介导的脂质代谢网络调控宿主黏膜免疫系统发育、成熟与功能的研究方兴未艾。结合该实验室的相关研究,该文将对共生微生物脂质代谢物与肠道黏膜免疫互作机制的前沿进展进行综述与讨论。     

肠道微生物群落与炎症性肠病关系研究进展

目的炎症性肠病（IBD）包括克罗恩病（CD）和溃疡性结肠炎（UC）,以持续性肠道非特异性炎症为特征,通常反复发作、迁延不愈,临床上仍无特效性的治疗手段。IBD确切的发病机制尚不清楚,涉及免疫、环境及遗传等因素,这些因素共同诱导肠道炎症、黏膜损伤和修复。肠道微生物群落及其代谢产物、宿主基因易感性及肠道黏膜免疫三方面共同参与了IBD的发病机制。本文从消化道微生态角度出发,对目前IBD相关的肠道微生物群落研究现状、宿主-微生物间免疫应答及益生菌治疗等内容进行探讨。     

慢性肝病与肠道菌群的研究进展

肝脏与肠道微生态可谓息息相关,互为影响。慢性肝病患者均存在不同程度的菌群失调,而菌群失调与血内毒素水平升高相关,且可诱发肝性脑病、二重感染的发生。肠道菌群失调促进了慢性肝病并发症的发生、发展,增加了患者的死亡率,且菌群失调与肝功能损害程度成正比。微生态制剂可通过恢复肠道菌群平衡,维持肠道屏障的完整性,抑制产生内毒素的G-数量,减少肠氨的产生,辅助治疗慢性肝病。     

Studies on mammalian glucoamylases with special reference to monkey intestinal glucoamylase

1. Highly purified preparations of glucoamylase were obtained from liver, spleen and intestine of the monkey. The enrichment factor was lower for intestine (60-fold) compared with that of liver (1200-fold) and of spleen (2000-fold) but the final specific activities were of a similar magnitude. 2. The liver and spleen enzymes had maximum activity at pH4.8 whereas the intestinal enzyme showed an optimum at pH5.8. The K(m) values for both starch and maltose with spleen and liver enzymes were higher than for the intestinal enzyme. With the intestinal enzyme, the V(max.) values were higher for both starch and maltose than those of the spleen and liver enzymes. 3. Gel filtration on Sephadex G-200 under identical conditions revealed that liver and spleen enzymes emerge from the columns much later than the intestinal enzyme. 4. Evidence is presented that the glucoamylase activity of the intestinal mucosa is exhibited by the maltase II fraction. 5. Tris, pentaerythritol and turanose inhibited glucoamylase from all the three tissues, but turanose inhibited the spleen and liver enzymes to a higher degree than the intestinal enzyme.     

非酒精性脂肪性肝病与肠粘膜屏障关系的研究进展

近年来,非酒精性脂肪性肝病的发病率正呈逐年升高趋势,且可进一步发展为非酒精性肝炎、肝硬化甚至肝癌,但其具体的发病机制目前尚未完全阐明。迄今为止,关于非酒精性脂肪性肝病较为人们所接受的是"两次打击学说",即肝脏的脂肪变性及脂质的过氧化反应。自"肠-肝轴"被提出后,关于肠道粘膜屏障功能与非酒精性脂肪性肝病的发生和发展的关系备受研究人员的关注。近些年来,关于非酒精性脂肪性肝病与肠道粘膜的机械屏障、生物屏障、化学屏障、免疫屏障方面的研究越来越多,肠粘膜的四个屏障功能与非酒精性脂肪性肝病密切相关,相互影响共同促进疾病的发生发展。本文就非酒精性脂肪性肝病与肠粘膜屏障关系的研究进展进行了综述。     

HMG CoA reductase of intestinal mucosa and liver of the rat

Methods were developed for the determination of HMG CoA (3-hydroxy-3-methylglutaryl CoA) reductase activity in subcellular fractions of intestinal mucosa and liver of Wistar strain rats. In the liver, reductase activity was located exclusively in the microsomal fraction. In the intestinal mucosa, activity was found in both mitochondrial and microsomal fractions of crypt cells but not of villi. The microsomal HMG CoA reductases of liver and intestinal mucosa had similar kinetic characteristics and pH optima. However, the activity of the hepatic enzyme differed with age and sex of the experimental animals while that of the intestinal crypt cells did not. Cholestyramine treatment enhanced the activity of the microsomal HMG CoA reductase in both liver and intestinal mucosa. Reductase activity of the intestinal crypt cells was elevated in both jejunum and ileum. The greatest stimulation, both relatively and absolutely, was observed in the distal half of the jejunum.     

益生菌通过调整正常菌群缓解酒精性肝损伤的研究进展

许多临床试验表明慢性酒精性肝损伤会引起肠道菌群的失调,主要表现为双歧杆菌、乳杆菌数量减少,革兰氏阴性菌大量繁殖,破坏肠道屏障功能,增加肠道通透性,使细菌来源的内毒素大量释放出来,引起血液内毒素增加,并在肝脏中累积,超出肝脏的清除能力,导致肝损伤。本文主要综述益生菌通过调整正常菌群这一机制来缓解酒精性肝损伤的研究进展,进而深入了解酒精引起肠道菌群变化(酒精的摄入会导致肠道中拟杆菌、厚壁菌数量减少,革兰氏阴性变形菌、革兰氏阳性放线菌数量增加,同时肠道内细菌来源的内毒素水平增加)导致肝损伤的发病机制,以及益生菌如何通过调整肠道正常菌群改善酒精性肝损伤。     

Tissue-specific expression of genes encoding apolipoprotein E and apolipoprotein A-I in rabbits

We determined the site of synthesis of apolipoprotein (apo) E and apo-A-I in rabbit by measuring in vitro translational activity of their mRNAs from the liver and from the intestine. Poly(A+) RNA isolated from liver and intestinal epithelium of rabbits fed either a chow diet or a cholesterol-rich diet was translated in vitro in the rabbit reticulocyte lysate system using [35S] methionine as the labeled precursor. Newly synthesized apolipoproteins were immunoprecipitated with specific antisera and quantitated after electrophoresed on 10% polyacrylamide slab gels in the presence of 0.2% sodium dodecyl sulfate. The levels of liver apo-E and apo-A-I mRNAs from chow-fed rabbits are 0.41 and 0.002% of total translatable mRNA, respectively. The level of liver apo-A-I mRNA in the rabbit is approximately 500-fold lower than the reported level of apo-A-I mRNA in rat and human livers. Rabbit intestinal apo-E and apo-A-I mRNAs levels are 0.0036 and 0.67%, respectively. Our results indicate that in rabbits apo-E is synthesized primarily in the liver and that apo-A-I is synthesized primarily in the intestine. When rabbits are fed a cholesterol-rich diet, liver and intestinal apo-E in mRNA levels and intestinal apo-A-I mRNA levels are not changed. In contrast, the liver apo-A-I mRNA level increases 5-fold in response to the cholesterol-rich diet. However, because the intestinal liver apo-A-I mRNA level is so low, the 5-fold induction only increases liver mRNA levels to 2.7% of the corresponding intestinal apo-A-I mRNA level.     

Monoacylglycerol acyltransferase. Evidence that the activities from rat intestine and suckling liver are tissue-specific isoenzymes

The monoglycerol acyltransferase (EC 2.3.1.22) (recommended name acylglycerol palmitoltransferase) activities from rat intestinal mucosa and suckling liver microsomes were compared in order to determine why substrate specificities differed in the two tissues. Suckling liver monoacylglycerol acyltransferase activity was highly specific for sn-2-mono-C18:1 glycerol and acylated rac-1-mono-C18:1 glycerol and 1- and 2-mono-C18:1 glycerol ethers poorly. In contrast, the substrate specificity of intestinal monoacylglycerol acyltransferase activity was broad. 1-Acyl- and 1- and 2-alkylglycerols were acylated at rates that were 45-78% of the rate observed with the preferred substrate sn-2-mono-C18:1 glycerol. Partial heat inactivation did not alter these relative specific activities, making it unlikely that intestinal microsomes contained a second acyltransferase capable of acylating the alternate substrates. The hypothesis that intestine and liver contain non-identical monoacylglycerol acyltransferase activities was further tested. Intestinal mucosa monoacylglycerol acyltransferase was much more thermolabile than the liver activity. Incubation with 50 microM diethylpyrocarbonate inactivated liver monoacylglycerol acyltransferase activity 84% but had little effect on the intestinal activity. Hydroxylamine completely reversed diethylpyrocarbonate inactivation, suggesting that critical histidine residues were more accessible in liver monoacylglycerol acyltransferase. 2,4,6-Trinitrobenzene sulfonic acid inactivated hepatic monoacylglycerol acyltransferase more than the intestinal activity, suggesting that critical lysine residues were more accessible. The intestinal and liver activities were also differently affected by acetone, detergents, MgCl2, phospholipids, and bovine serum albumin. Taken as a whole, the data strongly suggest that rat intestinal mucosa and suckling liver contain tissue-specific monoacylglycerol acyltransferase isoenzymes.     

肝脏固有免疫系统对肠源性感染的免疫应答与免疫耐受机制

肝特殊的解剖结构及生理特征使其成为暴露肠源性抗原的主要器官。由于肝具有独特的固有免疫系统,在正常情况下,肝分布多种致耐受的抗原提呈细胞,对持续性表达或递呈于肝的肠源性抗原物质,诱发针对该抗原的系统性免疫耐受,避免肝受到不必要的免疫损伤。当炎症发生及肝脏固有免疫系统活化时,则通过免疫效应细胞及免疫效应因子对肠源性病原体发挥强烈地免疫应答以控制感染。该过程形成机制的研究对肝功能的理解及肝性疾病的预防与治疗至关重要。本文就肝固有免疫系统对肠源性感染的免疫应答与免疫耐受形成机制作一综述。     

Dietary betaine accumulates in the liver and intestinal tissue and stabilizes the intestinal epithelial structure in healthy and coccidia-infected broiler chicks

The aim of this experiment was to study the patterns of betaine accumulation into intestinal tissue, liver and plasma of broiler chicks with or without coccidial infection. The chicks were raised on a corn-based, low-betaine diet with or without 1000 ppm betaine supplementation and with or without intestinal microparasite (Eimeria maxima) challenge to the age of 21 days. Plasma, liver, intestinal tissue and digesta of non-challenged (NC) birds and plasma and intestinal tissue of coccidiosis challenged (CC) birds were analysed for betaine content. NC birds were also analyzed for homocysteine in plasma and S-adenosylmethionine (S-AM) in liver. The jejunal epithelium was histologically examined for the presence of coccidia and the crypt-villus ratio was measured. Dietary betaine supplementation decreased the plasma homocysteine concentration but had no effect on liver S-AM of NC birds. The data suggest that chicks on a low-betaine diet accumulate betaine into the intestinal tissue. When the diet was supplemented with betaine, betaine accumulated heavily into liver and to a lesser degree into intestinal tissue. The concentration of betaine in jejunal and ileal digesta was low suggesting that dietary betaine was mainly absorbed from the proximal small intestine. The coccidial challenge decreased the concentration of betaine in the liver, but greatly increased that in the intestinal tissue. The crypt-villus ratio was decreased by the dietary betaine supplementation in healthy and challenged chicks, suggesting that dietary betaine both protects the jejunal villi against coccidial infection and also stabilizes the mucosal structure in healthy broiler chicks. These results support our earlier findings suggesting that betaine is likely to act as an important intestinal osmolyte in broiler chicks.     

Inhibition of cyclooxygenase-2 enhanced intestinal epithelial homeostasis via suppressing β-catenin signalling pathway in experimental liver fibrosis

The intestinal barrier dysfunction is crucial for the development of liver fibrosis but can be disturbed by intestinal chronic inflammation characterized with cyclooxygenase-2 (COX-2) expression. This study focused on the unknown mechanism by which COX-2 regulates intestinal epithelial homeostasis in liver fibrosis. The animal models of liver fibrosis induced with TAA were established in rats and in intestinal epithelial–specific COX-2 knockout mice. The impacts of COX-2 on intestinal epithelial homeostasis via suppressing β-catenin signalling pathway were verified pharmacologically and genetically in vivo. A similar assumption was tested in Ls174T cells with goblet cell phenotype in vitro. Firstly, disruption of intestinal epithelial homeostasis in cirrhotic rats was ameliorated by celecoxib, a selective COX-2 inhibitor. Then, β-catenin signalling pathway in cirrhotic rats was associated with the activation of COX-2. Furthermore, intestinal epithelial–specific COX-2 knockout could suppress β-catenin signalling pathway and restore the disruption of ileal epithelial homeostasis in cirrhotic mice. Moreover, the effect of COX-2/PGE2 was dependent on the β-catenin signalling pathway in Ls174T cells. Therefore, inhibition of COX-2 may enhance intestinal epithelial homeostasis via suppression of the β-catenin signalling pathway in liver fibrosis.