Role of gut microbiota in the pathogenesis and therapeutics of minimal hepatic encephalopathy via the gut-liver-brain axis

Minimal hepatic encephalopathy (MHE) is a frequent neurological and psychiatric complication of liver cirrhosis. The precise pathogenesis of MHE is complicated and has yet to be fully elucidated. Studies in cirrhotic patients and experimental animals with MHE have indicated that gut microbiota dysbiosis induces systemic inflammation, hyperammonemia, and endotoxemia, subsequently leading to neuroinflammation in the brain via the gut-liver-brain axis. Related mechanisms initiated by gut microbiota dysbiosis have significant roles in MHE pathogenesis. The currently available therapeutic strategies for MHE in clinical practice, including lactulose, rifaximin, probiotics, synbiotics, and fecal microbiota transplantation, exert their effects mainly by modulating gut microbiota dysbiosis. Microbiome therapies for MHE have shown promised efficacy and safety; however, several controversies and challenges regarding their clinical use deserve to be intensively discussed. We have summarized the latest research findings concerning the roles of gut microbiota dysbiosis in the pathogenesis of MHE via the gut-liver-brain axis as well as the potential mechanisms by which microbiome therapies regulate gut microbiota dysbiosis in MHE patients.     

非酒精性脂肪性肝病与肠道菌群失调新观点

非酒精性脂肪性肝病（NAFLD）在世界范围内患病率逐渐升高,“二次打击学说”发病机制已经被认可,但是具体的病理生理学发病机制还不完全清楚。近期,已有大量研究的新观点来解释肠道菌群在 NAFLD 发病机制中的作用,包括调节肠粘膜通透性、低水平炎症反应和免疫平衡,调节饮食胆碱代谢,调节胆汁酸代谢和增加细菌产生的内源性乙醇等。这些因素在分子水平上解释了肠道菌群如何促发 NAFLD 的发生,并进一步诱导其向非酒精性脂肪性肝炎（NASH）进展。     

Role of gut microbiota in cardiovascular diseases

The human gut is colonized by a community of microbiota, primarily bacteria,that exist in a symbiotic relationship with the host. Intestinal microbiota-host interactions play a critical role in the regulation of human physiology.Deleterious changes to the composition of gut microbiota, referred to as gut dysbiosis, has been linked to the development and progression of numerous diseases, including cardiovascular disease(CVD). Imbalances in host-microbial interaction impair homeostatic mechanisms that regulate health and can activate multiple pathways leading to CVD risk factor progression. Most CVD risk factors, including aging, obesity, dietary patterns, and a sedentary lifestyle, have been shown to induce gut dysbiosis. Dysbiosis is associated with intestinal inflammation and reduced integrity of the gut barrier, which in turn increases circulating levels of bacterial structural components and microbial metabolites,including trimethylamine-N-oxide and short-chain fatty acids, that may facilitate the development of CVD. This article reviews the normal function and composition of the gut microbiome, mechanisms leading to the leaky gut syndrome, its mechanistic link to CVD and potential novel therapeutic approaches aimed towards restoring gut microbiome and CVD prevention. As CVD is the leading cause of deaths globally, investigating the gut microbiota as a locus of intervention presents a novel and clinically relevant avenue for future research.     

The emerging role of gut microbiota in cardiovascular diseases

There is mounting evidence which suggests the involvement of gut microbiota dysbiosis in the pathogenesis of various cardiovascular diseases (CVD) and associated risk states such as hypertension, type 2 diabetes, obesity and dyslipidaemia, atherosclerosis, heart failure and atrial fibrillation. The current review comprehensively summarizes the various pathogenetic mechanisms of dysbiosis in these conditions and discusses the key therapeutic implications. Further deeper understanding of the pathogenetic links between CVD and gut microbiota dysbiosis can aid in the development of novel microbiota-based targets for the management of CVDs.     

肠道菌群与非消化系统疾病关系的研究进展

肠道菌群由数万亿个微生物组成,正常情况下它们与宿主保持着共生关系,在调节宿主新陈代谢中发挥着重要作用。近年来,肠道菌群在各系统疾病中的作用受到了大量科研工作者的关注,本文就肠道菌群与非消化系统疾病的关系作一概述,为相关疾病的诊治提供更多的理论支持。     

肠道微生物在非酒精性脂肪肝发生发展中的作用机制

非酒精性脂肪肝是代谢综合征的肝脏表现,可发展为肝硬化和肝癌。非酒精性脂肪肝的病因尚未明确,近年来宿主肠道微生物在非酒精性脂肪肝的发生、发展及治疗中的作用越来越受到重视。目前认为人类肠道是一个内在重要的代谢及免疫器官,肠道微生物的组成可影响宿主代谢,改变肠道通透性,引起炎症及一系列免疫反应。本文就肠道微生物在非酒精性脂肪肝的病理生理过程中的作用机制进行综述。     

An update on the role of gut microbiota in chronic inflammatory diseases,and potential therapeutic targets

ABSTRACT

Introduction: The human microbiome plays a critical role in human health, having metabolic, protective, and trophic functions, depending upon its’ exact composition. This composition is affected by a number of factors, including the genetic background of the individual, early life factors (including method of birth, length of breastfeeding) and nature of the diet and other environmental exposures (including cigarette smoking) and general life habits. It plays a key role in the control of inflammation, and in turn, its’ composition is significantly influenced by inflammation.

Areas covered: We consider metabolic, protective, and trophic functions of the microbiome and influences through the lifespan from post-partum effects, to diet later in life in healthy older adults, the effects of aging on both its’ composition, and influence on health and potential therapeutic targets that may have anti-inflammatory effects.

Expert commentary: The future will see the growth of more effective therapies targeting the microbiome particularly with respect to the use of specific nutrients and diets personalized to the individual.     

Role of gut microbiota in liver diseases

The liver constantly encounters food‐derived antigens and bacterial components such as lipopolysaccharide translocated from the gut into the portal vein. Bacterial components stimulate Toll‐like receptors (TLR), which are expressed on Kupffer cells, biliary epithelial cells, hepatocytes, hepatic stellate cells, endothelial cells and dendritic cells and recognize specific pathogen‐associated molecular patterns. The signaling of TLR to its main ligand triggers inflammation. Usually, in order to protect against hyperactivation of the immune system and to prevent organ failure by persistent inflammation, TLR tolerance to repeated stimuli is induced. In chronic liver diseases, a breakdown in TLR tolerance occurs. Furthermore, Kupffer cells, hepatic stellate cells and natural killer T cells are key components of innate immunity. Decreased numbers and impaired ability of these cells lead to failures in immune tolerance, resulting in persistent inflammation. Recently, the activation of inflammasome was revealed to control the secretion of pro‐inflammatory cytokines such as interleukin‐1β in response to bacterial pathogens. Innate immunity seems to be an important contributor to the pathogenesis of fatty liver disease and autoimmune liver disease. Recently, probiotics were reported to affect various liver diseases via shifts in gut microbiota and the stability of intestinal permeability. However, many unresolved questions remain. Further analysis will be needed to gain a more comprehensive understanding of the association of innate immunity with the pathogenesis of various liver diseases.     

Upper gastrointestinal microbiota and digestive diseases

Metagenomics which combines the power of genomics,bioinformatics,and systems biology,provide new access to the microbial world.Metagenomics permit the genetic analysis of complex microbial populations without requiring prior cultivation.Through the conceptual innovations in metagenomics and the improvements in DNA high-throughput sequencing and bioinformatics analysis technology,gastrointestinal microbiology has entered the metagenomics era and become a hot topic worldwide.Human microbiome research is underway,however,most studies in this area have focused on the composition and function of the intestinal microbiota and the relationship between intestinal microbiota and metabolic diseases(obesity,diabetes,metabolic syndrome,etc.) and intestinal disorders [inflammatory bowel disease,colorectal cancer,irritable bowel syndrome(IBS),etc.].Few investigations on microbiota have been conducted within the upper gastrointestinal tract(esophagus,stomach and duodenum).The upper gastrointestinal microbiota is essential for several gastrointestinal illnesses,including esophagitis,Barrett’s esophagus,and esophageal carcinoma,gastritis and gastric cancer,small intestinal bacterial overgrowth,IBS and celiac disease.However,the constitution and diversity of the microbiota in different sections of the upper gastrointestinal tract under health and various disease states,as well as the function of microbiota in the pathogenesis of various digestive diseases are still undefined.The current article provides an overview of the recent findings regarding the relationship between upper gastrointestinal microbiota and gastrointestinal diseases;and discusses the study limitations and future directions of upper gastrointestinal microbiota research.     

Improving healthspan via changes in gut microbiota and fermentation

Dietary resistant starch impact on intestinal microbiome and improving healthspan is the topic of this review. In the elderly population, dietary fiber intake is lower than recommended. Dietary resistant starch as a source of fiber produces a profound change in gut microbiota and fermentation in animal models of aging. Dietary resistant starch has the potential for improving healthspan in the elderly through multiple mechanisms as follows: (1) enhancing gut microbiota profile and production of short-chain fatty acids, (2) improving gut barrier function, (3) increasing gut peptides that are important in glucose homeostasis and lipid metabolism, and (4) mimicking many of the effects of caloric restriction including upregulation of genes involved in xenobiotic metabolism.     

中药蒲公英对消化系统疾病的作用进展

中药蒲公英具有清热解毒、消肿散结、退黄利胆等功效,现代药理研究证实蒲公英植物体中含有多糖类、黄酮类、植物甾醇类、色素类、三萜类、挥发油类等化学成分,具有抗炎、提高免疫力、保肝、促进胃肠动力、调节肠道菌群等多种生物效用,能够对消化系统疾病发挥广泛作用。     

Role of gut microbiota on intestinal barrier function in acute pancreatitis

Acute pancreatitis(AP) is a common gastrointestinal disorder. Approximately15%-20% of patients develop severe AP. Systemic inflammatory response syndrome and multiple organ dysfunction syndrome may be caused by the massive release of inflammatory cytokines in the early stage of severe AP,followed by intestinal dysfunction and pancreatic necrosis in the later stage. A study showed that 59% of AP patients had associated intestinal barrier injury,with increased intestinal mucosal permeability, leading to intestinal bacterial translocation, pancreatic tissue necrosis and infection, and the occurrence of multiple organ dysfunction syndrome. However, the real effect of the gut microbiota and its metabolites on intestinal barrier function in AP remains unclear. This review summarizes the alterations in the intestinal flora and its metabolites during AP development and progression to unveil the mechanism of gut failure in AP.     

Role of diet and gut microbiota on colorectal cancer immunomodulation

Colorectal cancer(CRC) is one of the most commonly diagnosed cancers, and it is characterized by genetic and epigenetic alterations, as well as by inflammatory cell infiltration among malignant and stromal cells. However, this dynamic infiltration can be influenced by the microenvironment to promote tumor proliferation, survival and metastasis or cancer inhibition. In particular, the cancer microenvironment metabolites can regulate the inflammatory cells to induce a chronic inflammatory response that can be a predisposing condition for CRC retention. In addition, some nutritional components might contribute to a chronic inflammatory condition by regulating various immune and inflammatory pathways. Besides that, diet strongly modulates the gut microbiota composition,which has a key role in maintaining gut homeostasis and is associated with the modulation of host inflammatory and immune responses. Therefore, diet has a fundamental role in CRC initiation, progression and prevention. In particular,functional foods such as probiotics, prebiotics and symbiotics can have a potentially positive effect on health beyond basic nutrition and have antiinflammatory effects. In this review, we discuss the influence of diet on gut microbiota composition, focusing on its role on gut inflammation and immunity.Finally, we describe the potential benefits of using probiotics and prebiotics to modulate the host inflammatory response, as well as its application in CRC prevention and treatment.     

Lingguizhugan decoction attenuates diet-induced obesity and hepatosteatosis via gut microbiota

BACKGROUND Obesity is a major risk factor for a variety of diseases such as diabetes,nonalcoholic fatty liver disease, and cardiovascular diseases. Restricting energy intake, or caloric restriction(CR), can reduce body weight and improve metabolic parameters in overweight or obese patients. We previously found that Lingguizhugan decoction(LZD) in combination with CR can effectively lower plasma lipid levels in patients with metabolic syndrome. However, the mechanism underlying CR and LZD treatment is still unclear.AIM To investigate whether CR and LZD improve metabolic parameters by modulating gut microbiota.METHODS We extracted the water-soluble components out of raw materials and dried as LZD extracts. Eight-week old male C57 BL/6 mice were treated with a 3-d treatment regime that included 24 h-fasting followed by gavage of LZD extracts for 2 consecutive days, followed by a normal diet(ND) ad libitum for 16 wk. To test the effects of gut microbiota on diet-induced obesity, 8-wk old male C57 BL/6 mice received fecal microbiota transplantation(FMT) from CR and LZD-treated mice every 3 d and were fed with high-fat diet(HFD) ad libitum for 16 wk.Control mice received either saline gavage or FMT from ND-fed mice receiving saline gavage as mentioned above. Body weight was monitored bi-weekly. Food consumption of each cage hosting five mice was recorded weekly. To monitor blood glucose, total cholesterol, and total triglycerides, blood samples were collected via submandibular bleeding after 6 h fasting. Oxygen consumption rate was monitored with metabolic cages. Feces were collected, and fecal DNA was extracted. Profiles of gut microbiota were mapped by metagenomic sequencing.RESULTS We found that CR and LZD treatment significantly reduced the body weight of mice fed with ND(28.71 ± 0.29 vs 28.05 ± 0.15, P 0.05), but did not affect plasma total cholesterol or total triglyceride levels. We then transplanted the fecal microbiota collected from CR and LZD-treated mice under ND feeding to HFDfed mice. Intriguingly, transplanting the mice with fecal microbiota from CR and LZD-treated mice potently reduced body weight(44.95 ± 1.02 vs 40.53 ± 0.97, P 0.001). FMT also reduced HFD-induced hepatosteatosis, in addition to improved glycemic control. Mechanistic studies found that FMT increased OCR of the mice and suppressed the expression and protein abundance of lipogenic genes in the liver. Metagenomic analysis revealed that HFD drastically altered the profile of gut microbiota, and FMT modified the profile of the gut microbiota.CONCLUSION Our study suggests that CR and LZD improve metabolic parameters by modulating gut microbiota.     

Role of the intestinal microbiota and fecal transplantation in inflammatory bowel diseases

Ulcerative colitis and Crohn's disease are the two major types of inflammatory bowel disease (IBD). Despite intensive study, it is still challenging because the precise etiology and pathogenesis remains unclear. Studies have shown that IBD is associated with changes in the composition of intestinal microbiota, as either a cause or a consequence of abnormal host immune response in genetic susceptible population. Two specific microorganisms (Mycobacterium avium subsp. paratuberculosis and Escherichia coli) get more widely studied, but till now no single microorganism has been identified as the only pathogen. Genetic susceptibility data also suggest impaired handling of bacteria as well as an improper immune response to potential pathogens. The microbiota provides new therapeutic methods, and fecal microbiota transplantation may restore the balance of intestinal flora to supplement or optimize the current therapies.     

Exercise has the guts: How physical activity may positively modulate gut microbiota in chronic and immune-based diseases

Limited animal and human research findings suggests that exercise might have a beneficial role for health gut. Cardiorespiratory fitness correlates with health-associated gut parameters such as taxonomic diversity and richness. Physical exercise may augment intestinal microbial diversity through several mechanisms including promotion of an anti-inflammatory state. Disease-associated microbial functions were linked to distinct taxa in previous studies of familial type 1 diabetes mellitus (T1D). An integrated multi-approach in the study of T1D, including physical exercise, is advocated. The present review explores how exercise might modulate gut microbiota and microbiome characteristics in chronic and immune-based diseases, given the demonstrated relationship between gut function and human health.