Can control of gut microbiota be a future therapeutic option for inflammatory bowel disease?

Inflammatory bowel disease (IBD) is a chronic inflammatory condition of the gastrointestinal tract encompassing two main clinical entities, Crohn’s disease and ulcerative colitis. Accumulated evidence indicates that an aberrant immune activation caused by the interplay of genetic susceptibility and environmental impact on the gut microbiota may be involved in the pathogenesis of IBD. Rapid advances in next-generation sequencing technology have enabled a number of studies to identify the alteration of the gut microbiota, termed dysbiosis, in IBD. Moreover, the alteration in the metabolites derived from the gut microbiota in IBD has also been described in many studies. Therefore, microbiota-based interventions such as fecal microbiota transplantation (FMT) have attracted attention as a novel therapeutic option in IBD. However, in clinical trials, the efficacy of FMT for IBD remains controversial. Additional basic and clinical studies are required to validate whether FMT can assume a complementary role in the treatment of IBD. The present review provides a synopsis on dysbiosis in IBD and on the association between the gut microbiota and the pathogenesis of IBD. In addition, we summarize the use of probiotics in IBD and the results of current clinical trials of FMT for IBD.     

Role of antibiotics for treatment of inflammatory bowel disease

Inflammatory bowel disease is thought to be caused by an aberrant immune response to gut bacteria in a genetically susceptible host. The gut microbiota plays an important role in the pathogenesis and complications of the two main inflammatory bowel diseases: Crohn's disease(CD) and ulcerative colitis. Alterations in gut microbiota, and specifically reduced intestinal microbial diversity, have been found to be associated with chronic gut inflammation in these disorders. Specific bacterial pathogens, such as virulent Escherichia coli strains, Bacteroides spp, and Mycobacterium avium subspecies paratuberculosis, have been linked to the pathogenesis of inflammatory bowel disease. Antibiotics may influence the course of these diseases by decreasing concentrations of bacteria in the gut lumen and altering the composition of intestinal microbiota. Different antibiotics, including ciprofloxacin, metronidazole, the combination of both, rifaximin, and anti-tuberculous regimens have been evaluated in clinical trials for the treatment of inflammatory bowel disease. For the treatment of active luminal CD, antibiotics may have a modest effect in decreasing disease activity and achieving remission, and are more effective in patients with disease involving the colon. Rifamixin, a non absorbable rifamycin has shown promising results. Treatment of suppurative complications of CD such as abscesses and fistulas, includes drainage and antibiotic therapy, most often ciprofloxacin, metronidazole, or a combination of both. Antibiotics might also play a role in maintenance of remission and prevention of post operative recurrence of CD. Data is more sparse for ulcerative colitis, and mostly consists of small trials evaluating ciprofloxacin, metronidazole and rifaximin. Most trials did not show a benefit for the treatment of active ulcerative colitis with antibiotics, though 2 meta-analyses concluded that antibiotic therapy is associated with a modest improvement in clinical symptoms. Antibiotics show a clinical benefit when used for the treatment of pouchitis. The downsides of antibiotic treatment, especially with recurrent or prolonged courses such as used in inflammatory bowel disease, are significant side effects that often cause intolerance to treatment, Clostridium dificile infection, and increasing antibiotic resistance. More studies are needed to define the exact role of antibiotics in inflammatory bowel diseases.     

Bacterial flora as a cause or treatment of chronic diarrhea

Intestinal microflora can be considered an organ of the body. It has several functions in the human gut, mostly metabolic and immunologic, and constantly interacts with the intestinal mucosa in a delicate equilibrium. Chronic diarrhea is associated with an alteration of gut microbiota when a pathogen invades the gut and also in several conditions associated with intestinal mucosal damage or bowel dysfunction, as in inflammatory bowel disease, irritable bowel syndrome, or small bowel bacterial overgrowth. This article discusses the basis of gut microbiota modulation. Evidence for the efficacy of gut microbiota modulation in chronic conditions is also discussed.     

Periodontal and inflammatory bowel diseases: Is there evidence of complex pathogenic interactions?

Periodontal disease and inflammatory bowel disease (IBD) are both chronic inflammatory diseases. Their pathogenesis is mediated by a complex interplay between a dysbiotic microbiota and the host immune-inflammatory response, and both are influenced by genetic and environmental factors. This review aimed to provide an overview of the evidence dealing with a possible pathogenic interaction between periodontal disease and IBD. There seems to be an increased prevalence of periodontal disease in patients with IBD when compared to healthy controls, probably due to changes in the oral microbiota and a higher inflammatory response. Moreover, the induction of periodontitis seems to result in gut dysbiosis and altered gut epithelial cell barrier function, which might contribute to the pathogenesis of IBD. Considering the complexity of both periodontal disease and IBD, it is very challenging to understand the possible pathways involved in their coexistence. In conclusion, this review points to a complex pathogenic interaction between periodontal disease and IBD, in which one disease might alter the composition of the microbiota and increase the inflammatory response related to the other. However, we still need more data derived from human studies to confirm results from murine models. Thus, mechanistic studies are definitely warranted to clarify this possible bidirectional association.     

Gut microbiota,inflammatory bowel disease and colorectal cancer

The gut microbiota is a complex community of microorganisms that inhabit the digestive tracts of humans, living in symbiosis with the host. Dysbiosis, characterized by an imbalance between the beneficial and opportunistic gut microbiota, is associated with several gastrointestinal disorders, such as irritable bowel syndrome (IBS); inflammatory bowel disease (IBD), represented by ulcerative colitis and Crohn’s disease; and colorectal cancer (CRC). Dysbiosis can disrupt the mucosal barrier, resulting in perpetuation of inflammation and carcinogenesis. The increase in some specific groups of harmful bacteria, such as Escherichia coli (E. coli) and enterotoxigenic Bacteroides fragilis (ETBF), has been associated with chronic tissue inflammation and the release of pro-inflammatory and carcinogenic mediators, increasing the chance of developing CRC, following the inflammation-dysplasia-cancer sequence in IBD patients. Therefore, the aim of the present review was to analyze the correlation between changes in the gut microbiota and the development and maintenance of IBD, CRC, and IBD-associated CRC. Patients with IBD and CRC have shown reduced bacterial diversity and abundance compared to healthy individuals, with enrichment of Firmicute sand Bacteroidetes. Specific bacteria are also associated with the onset and progression of CRC, such as Fusobacterium nucleatum, E. coli, Enterococcus faecalis, Streptococcus gallolyticus, and ETBF. Future research can evaluate the advantages of modulating the gut microbiota as preventive measures in CRC high-risk patients, directly affecting the prognosis of the disease and the quality of life of patients.     

Therapies to modulate gut microbiota:Past,present and future

The human gut microbiota comprises of a complex and diverse array of microorganisms,and over the years the interaction between human diseases and the gut microbiota has become a subject of growing interest.Disturbed microbial milieu in the gastrointestinal tract is central to the pathogenesis of several diseases including antibiotic-associated diarrhea and Clostridioides difficile infection(CDI).Manipulation of this microbial milieu to restore balance by microbial replacement therapies has proven to be a safe and effective treatment for recurrent CDI.There is considerable heterogeneity in various aspects of stool processing and administration for fecal microbiota transplantation(FMT)across different centers globally,and standardized microbioal replacement therapies offer an attractive alternative.The adverse effects associated with FMT are usually mild.However,there is paucity of data on long term safety of FMT and there is a need for further studies in this regard.With our increasing understanding of the host-microbiome interaction,there is immense potential for microbial replacement therapies to emerge as a treatment option for several diseases.The role of microbioal replacement therapies in diseases other than CDI is being extensively studied in ongoing clinical trials and it may be a potential treatment option for inflammatory bowel disease,irritable bowel syndrome,obesity,multidrug resistant infections,and neuropsychiatric illnesses.Fecal microbiota transplantation for non-CDI disease states should currently be limited only to research settings.     

Enteric microbiota leads to new therapeutic strategies for ulcerative colitis

Ulcerative colitis(UC) is a leading form of inflammatory bowel disease that involves chronic relapsing or progressive inflammation. As a significant proportion of UC patients treated with conventional therapies do not achieve remission, there is a pressing need for the development of more effective therapies. The human gut contains a large, diverse, and dynamic population of microorganisms, collectively referred to as the enteric microbiota. There is a symbiotic relationship between the human host and the enteric microbiota, which provides nutrition, protection against pathogenic organisms, and promotes immune homeostasis. An imbalance of the normal enteric microbiota composition(termed dysbiosis) underlies the pathogenesis of UC. A reduction of enteric microbiota diversity has been observed in UC patients, mainly affecting the butyrateproducing bacteria, such as Faecalibacterium prausnitzii, which can repress pro-inflammatory cytokines. Many studies have shown that enteric microbiota plays an important role in anti-inflammatory and immunoregulatory activities, which can benefit UC patients. Therefore, manipulation of the dysbiosis is an attractiveapproach for UC therapy.Various therapies targeting a restoration of the enteric microbiota have shown efficacy in treating patients with active and chronic forms of UC.Such therapies include fecal microbiota transplantation,probiotics,prebiotics,antibiotics,helminth therapy,and dietary polyphenols,all of which can alter the abundance and composition of the enteric microbiota.Although there have been many large,randomized controlled clinical trials assessing these treatments,the effectiveness and safety of these bacteria-driven therapies need further evaluation.This review focuses on the important role that the enteric microbiota plays in maintaining intestinal homeostasis and discusses new therapeutic strategies targeting the enteric microbiota for UC.     

Gastrointestinal dysbiosis and the use of fecal microbial transplantation in Clostridium difficile infection

The impact of antibiotics on the human gut microbiota is a significant concern. Antibiotic-associated diarrhea has been on the rise for the past few decades with the increasing usage of antibiotics. Clostridium difficile infections (CDI) have become one of the most prominent types of infectious diarrheal disease, with dramatically increased incidence in both the hospital and community setting worldwide. Studies show that variability in the innate host response may in part impact upon CDI severity in patients. That being said, CDI is a disease that shows the most prominent links to alterations to the gut microbiota, in both cause and treatment. With recurrence rates still relatively high, it is important to explore alternative therapies to CDI. Fecal microbiota transplantation (FMT) and other types of bacteriotherapy have become exciting avenues of treatment for CDI. Recent clinical trials have generated excitement for the use of FMT as a therapeutic option for CDI; however, the exact components of the human gut microbiota needed for protection against CDI have remained elusive. Additional investigations on the effects of antibiotics on the human gut microbiota and subsequent CDI will help reduce the socioeconomic burden of CDI and potentially lead to new therapeutic modalities.     

The normal intestinal microbiota

PURPOSE OF REVIEW: Long neglected and considered a difficult ecosystem to study, several developments have recently converged to renew interest in studying the normal gut microbiota. These include molecular methods of studying the microbiota, improved understanding of host-microbe interactions in health and disease, and the potential for therapeutic manipulation of the microbiota. This review focuses on the most recent work in these areas. RECENT FINDINGS: Host-microbe signaling in the gut is critical for normal development and homeostasis of the gastrointestinal mucosa. The molecular basis of these interactions promises new therapeutic strategies for various disorders. Particularly noteworthy has been the emergence of evidence for the role of enteric bacterial metabolism in the pathogenesis of disorders ranging from functional and inflammatory bowel diseases to human obesity. Metagenomic and metabolomic profiling of the microbiota, although at an early stage, has demonstrated the range and complexity of the gut ecosystem and cast insights into several diseases. The molecular basis of host-microbe dialogue and the mechanisms by which the host contains enteric bacteria within the lumen has immediate relevance to infectious and chronic inflammatory bowel disease. SUMMARY: Improved understanding of the normal gut microbiota has made the therapeutic manipulation of the gut ecosystem a valid and realistic future prospect.     

Fecal microbiota transplantation for severe enterocolonic fistulizing Crohn’s disease

The concept of fecal microbiota transplantation(FMT)has been used in traditional Chinese medicine at least since the 4thcentury.Evidence from recent human studies strongly supports the link between intestinal bacteria and inflammatory bowel disease.We proposed that standardized FMT might be a promising rescue therapy for refractory inflammatory bowel disease.However,there were no reports of FMT used in patients with severe Crohn’s disease(CD).Here,we report the successful treatment of standardized FMT as a rescue therapy for a case of refractory CD complicated with fistula,residual Barium sulfate and formation of intraperitoneal large inflammatory mass.As far as we know,this is the first case of severe CD treated using FMT through mid-gut.     

Characterisation and therapeutic manipulation of the gut microbiome in inflammatory bowel disease

Inflammatory bowel diseases are thought to develop as a result of dysregulation of the relationship that exists between the gut microbiota, host genetics and the immune system. The advent of culture‐independent techniques has revolutionised the ability to characterise the role of the gut microbiota in health and disease based on the microbiota's genetic make‐up. Inflammatory bowel diseases are characterised by dysbiosis which is an imbalance between pro‐ and anti‐inflammatory bacteria and a reduction in bacterial diversity. Emerging data suggest that it is not only the presence of the gut microbiota but the functional activity of the microbiota that appears to play an important role in health and disease. Current strategies to manipulate therapeutically the gut microbiota using dietary modification, prebiotics, probiotics, antibiotics and faecal microbiota transplantation aim to restore the balance to a state of normobiosis. However, the ability of such strategies to correct dysbiosis and thereby achieve therapeutic benefit is yet to be fully characterised.     

Gut microbiota in the pathogenesis of inflammatory bowel disease

Inflammatory bowel disease (IBD), including ulcerative colitis and Crohn’s disease, is a chronic and relapsing inflammatory disorder of the intestine. Although its incidence is increasing globally, the precise etiology remains unclear and a cure for IBD has yet to be discovered. The most accepted hypothesis of IBD pathogenesis is that complex interactions between genetics, environmental factors, and the host immune system lead to aberrant immune responses and chronic intestinal inflammation. The human gut harbors a complex and abundant aggregation of microbes, collectively referred to as the gut microbiota. The gut microbiota has physiological functions associated with nutrition, the immune system, and defense of the host. Recent advances in next-generation sequencing technology have identified alteration of the composition and function of the gut microbiota, which is referred to as dysbiosis, in IBD. Clinical and experimental data suggest dysbiosis may play a pivotal role in the pathogenesis of IBD. This review is focused on the physiological function of the gut microbiota and the association between the gut microbiota and pathogenesis in IBD. In addition, we review the therapeutic options for manipulating the altered gut microbiota, such as probiotics and fecal microbiota transplantation.     

Dysbiosis in gastrointestinal disorders

The recent development of advanced sequencing techniques has revealed the complexity and diverse functions of the gut microbiota. Furthermore, alterations in the composition or balance of the intestinal microbiota, or dysbiosis, are associated with many gastrointestinal diseases. The looming question is whether dysbiosis is a cause or effect of these diseases. In this review, we will evaluate the contribution of intestinal microbiota in obesity, fatty liver, inflammatory bowel disease, and irritable bowel syndrome. Promising results from microbiota or metabolite transfer experiments in animals suggest the microbiota may be sufficient to reproduce disease features in the appropriate host in certain disorders. Less compelling causal associations may reflect complex, multi-factorial disease pathogenesis, in which dysbiosis is a necessary condition. Understanding the contributions of the microbiota in GI diseases should offer novel insight into disease pathophysiology and deliver new treatment strategies such as therapeutic manipulation of the microbiota.     

Bacteria in the pathogenesis of inflammatory bowel disease

PURPOSE OF REVIEW: Inflammatory bowel disease is thought to result from an abnormal response to the gut microbiota. This review discusses advances in knowledge of the changes in gut microbiota and host response in inflammatory bowel disease. RECENT FINDINGS: Approximately 15% of Crohn's disease cases in western populations result from mutations in NOD2/CARD15. This disease leads to defective intestinal defensin production and defective monocyte interleukin-8 response to bacterial peptidoglycan. A similar defective interleukin-8 response and consequent delayed neutrophil recruitment have also been shown in patients with Crohn's disease who do not have the NOD2 mutation. A consequence seems to be the accumulation in tissue of macrophages containing various bacteria, perhaps particularly Escherichia coli. In keeping with this patients with Crohn's disease have circulating antibodies against bacterial flagellar proteins of enterobacteria and clostridia. In ulcerative colitis, there is less evidence for invasion by or immune response to bacteria but changes in gut microbiota include a relative deficiency of bifidobacteria. There is considerable interest in probiotic or prebiotic therapies although so far little evidence for their efficacy. SUMMARY: Molecular techniques are giving us better insight into the gut microbiota in inflammatory bowel disease that should translate into improved therapies.     

Role of commensal gut bacteria in inflammatory bowel diseases

Aberrant immune responses toward commensal gut bacteria can result in the onset and perpetuation of inflammatory bowel diseases (IBD). Reduced microbiota diversity in conjunction with lower proportion of Gram positive and higher proportion of Gram negative bacteria than in healthy subjects is frequently reported in IBD patients. In a subset of IBD patients, E. coli strains with specific features trigger disease. Important molecular mechanisms underlying this effect have been identified. However, in the majority of patients the exact nature of host-microbe interactions that contribute to IBD development has so far not been defined. The application of metagenomic techniques may help to identify bacterial functions that are involved in the aggravation or alleviation of IBD. Subsequently, the relevance for disease development of bacterial candidate genes may be tested taking advantage of reductionist animal models of chronic gut inflammation. This approach may help to identify bacterial functions that can be targeted in future concepts of IBD therapy.     

Gut bacteria signaling to mitochondria in intestinal inflammation and cancer

ABSTRACT

The gastrointestinal microbiome plays a pivotal role in physiological homeostasis of the intestine as well as in the pathophysiology of diseases including inflammatory bowel diseases (IBD) and colorectal cancer (CRC). Emerging evidence suggests that gut microbiota signal to the mitochondria of mucosal cells, including epithelial cells and immune cells. Gut microbiota signaling to mitochondria has been shown to alter mitochondrial metabolism, activate immune cells, induce inflammasome signaling, and alter epithelial barrier function. Both dysbiosis of the gut microbiota and mitochondrial dysfunction are associated with chronic intestinal inflammation and CRC. This review discusses mitochondrial metabolism of gut mucosal cells, mitochondrial dysfunction, and known gut microbiota-mediated mitochondrial alterations during IBD and CRC.     

Recent progress on the role of gut microbiota in the pathogenesis of inflammatory bowel disease

In recent years investigations of inflammatory bowel disease (IBD) have advanced rapidly with regard to the relationship between the host immune response and gut microbiota. Patients with IBD have been shown to have an abnormal composition of gut microbiota and host immune dysregulation. Abnormal components of gut microbiota, to which the host mounts aberrant immune responses in genetically vulnerable individuals, appear to play a critical role in the pathogenesis of IBD. Therefore, inappropriate innate and adaptive host immune responses to abnormal components of gut microbiota and their products form the basis of IBD pathogenesis. Modern molecular genetic methods should be utilized to help to illuminate the pathogenetic mechanism of IBD and to develop personalized therapeutic strategies for this disease.     

Human microbiome: From the bathroom to the bedside

The human gut contains trillions of bacteria, the major phylae of which include Bacteroidetes, Firmicutes, Actinobacteria and Proteobacteria. Fecal microbial transplantation(FMT) has been known of for manyyears but only recently has been subjected to rigorous examination. We review the evidence regarding FMT for recurrent Clostridium difficile infection which has resulted in it being an approved treatment. In addition there is some evidence for its use in both irritable bowel syndrome and inflammatory bowel disease. Further research is needed in order to define the indications for FMT and the most appropriate method of administration.     

Role of commensal gut bacteria in inflammatory bowel diseases

Aberrant immune responses toward commensal gut bacteria can result in the onset and perpetuation of inflammatory bowel diseases (IBD). Reduced microbiota diversity in conjunction with lower proportion of Gram positive and higher proportion of Gram negative bacteria than in healthy subjects is frequently reported in IBD patients. In a subset of IBD patients, E. coli strains with specific features trigger disease. Important molecular mechanisms underlying this effect have been identified. However, in the majority of patients the exact nature of host-microbe interactions that contribute to IBD development has so far not been defined. The application of metagenomic techniques may help to identify bacterial functions that are involved in the aggravation or alleviation of IBD. Subsequently, the relevance for disease development of bacterial candidate genes may be tested taking advantage of reductionist animal models of chronic gut inflammation. This approach may help to identify bacterial functions that can be targeted in future concepts of IBD therapy.