Intestinal steroid profiles and microbiota composition in colitic mice

Reduced gut microbiota diversity in conjunction with a bloom of few bacterial species is a common feature in inflammatory bowel disease (IBD) patients. However, the environmental changes caused by inflammation and their possible impact on the microbiota are largely unknown. Since IBD is associated with an impaired intestinal steroid metabolism, we hypothesized that changes in intestinal steroid and particularly bile acid (BA) concentrations affect microbial communities. We used Interleukin-10 deficient (IL-10-/-) mice as a model for chronic gut inflammation. Healthy wild-type mice served as controls. In these animals, intestinal steroid concentrations and gut microbial diversity were analyzed at 24 weeks of age. The IL 10-/- mice developed moderate inflammation in cecum and colon and colorectal tumor formation was observed in 55 % of the animals. Compared to the healthy conditions, gut inflammation was associated with higher intestinal cholesterol and cholic acid concentrations and a reduced microbial diversity. The latter was accompanied by a proliferation of Robinsoniella peoriensis, Clostridium innocuum, Escherichia coli, and Enterococcus gallinarum. All these species proved to be highly bile acid resistant. We concluded that chronic colitis in IL-10-/- mice is associated with changes in intestinal steroid profiles. These changes may be due to alterations in gut microbiota composition or vice versa. Whether the bacterial sterol and bile acid metabolism is implicated in colitis and colorectal carcinoma etiology remains to be clarified.     

Intestinal steroid profiles and microbiota composition in colitic mice

Reduced gut microbiota diversity in conjunction with a bloom of few bacterial species is a common feature in inflammatory bowel disease (IBD) patients. However, the environmental changes caused by inflammation and their possible impact on the microbiota are largely unknown. Since IBD is associated with an impaired intestinal steroid metabolism, we hypothesized that changes in intestinal steroid and particularly bile acid (BA) concentrations affect microbial communities. We used Interleukin-10 deficient (IL-10-/-) mice as a model for chronic gut inflammation. Healthy wild-type mice served as controls. In these animals, intestinal steroid concentrations and gut microbial diversity were analyzed at 24 weeks of age. The IL 10-/- mice developed moderate inflammation in cecum and colon and colorectal tumor formation was observed in 55 % of the animals. Compared to the healthy conditions, gut inflammation was associated with higher intestinal cholesterol and cholic acid concentrations and a reduced microbial diversity. The latter was accompanied by a proliferation of Robinsoniella peoriensis, Clostridium innocuum, Escherichia coli, and Enterococcus gallinarum. All these species proved to be highly bile acid resistant. We concluded that chronic colitis in IL-10-/- mice is associated with changes in intestinal steroid profiles. These changes may be due to alterations in gut microbiota composition or vice versa. Whether the bacterial sterol and bile acid metabolism is implicated in colitis and colorectal carcinoma etiology remains to be clarified.     

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.     

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 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.     

MICROBIOTA INSIGHTS IN CLOSTRIDIUM DIFFICILE INFECTION AND INFLAMMATORY BOWEL DISEASE

ABSTRACT

Inflammatory bowel disease (IBD) is characterized by chronic intestinal inflammation that includes Crohn´s disease (CD) and ulcerative colitis (UC). Although the etiology is still unknown, some specific factors have been directly related to IBD, including genetic factors, abnormal intestinal immunity, and/or gut microbiota modifications. Recent findings highlight the primary role of the gut microbiota closely associated with a persistent inappropriate inflammatory response. This gut environment of dysbiosis in a susceptible IBD host can increasingly worsen and lead to colonization and infection with some opportunistic pathogens, especially Clostridium difficile. C. difficile is an intestinal pathogen considered the main cause of antibiotic-associated diarrhea and colitis and an important complication of IBD, which can trigger or worsen an IBD flare. Recent findings have highlighted the loss of bacterial cooperation in the gut ecosystem, as well as the pronounced intestinal dysbiosis, in patients suffering from IBD and concomitant C. difficile infection (CDI). The results of intestinal microbiota studies are still limited and often difficult to compare because of the variety of disease conditions. However, these data provide important clues regarding the main modifications and interrelations in the complicated gut ecosystem to better understand both diseases and to take advantage of the development of new therapeutic strategies. In this review, we analyze in depth the gut microbiota changes associated with both forms of IBD and CDI and their similarity with the dysbiosis that occurs in CDI. We also discuss the metabolic pathways that favor the proliferation or decrease in several important taxa directly related to the disease.     

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.     

Prebiotics in chronic intestinal inflammation

Prebiotics are nondigestible fermentable fibers that are reported to have health benefits for the host. Older as well as more recent studies show beneficial effects in experimental colitis and lately also in human inflammatory bowel diseases (IBD), such as Crohn's disease, ulcerative colitis, and chronic pouchitis. In this review we give an overview of the benefits of prebiotics in rodent IBD models and in IBD patients and discuss their possible protective mechanisms. Commensal intestinal bacteria induce and perpetuate chronic intestinal inflammation, whereas others are protective. However, most of the current medications are directed against the exaggerated proinflammatory immune response of the host, some of them toxic and costly. Feeding prebiotics changes the composition of the intestinal microflora toward more protective intestinal bacteria and alters systemic and mucosal immune responses of the host. Therapy for IBD targeting intestinal bacteria and their function is just emerging. Prebiotics have the promise to be relatively safe, inexpensive, and easy to administer. Unraveling their protective mechanisms will help to develop rational applications of prebiotics. However, the initial promising results with dietary prebiotics in preclinical trials as well as small studies in human IBD will need to be confirmed in large randomized controlled clinical trials.     

Tryptophan:A gut microbiota-derived metabolites regulating inflammation

Inflammatory bowel diseases(IBD), which comprise Crohn's disease and ulcerative colitis, are chronic intestinal disorders with an increased prevalence and incidence over the last decade in many different regions over the world. The etiology of IBD is still not well defined, but evidence suggest that it results from per-turbation of the homeostasis between the intestinal microbiota and the mucosal immune system, with the involvement of both genetic and environmental factors. Genome wide association studies, which involve large-scale genome-wide screening of potential polymorphism, have identified several mutations associated with IBD. Among them, Card9, a gene encoding an adapter molecule involved in innate immune response to fungi(via type C-lectin sensing) through the activation of IL-22 signaling pathway, has been identified as one IBD susceptible genes. Dietary compounds, which represent a source of energy and metabolites for gut bacteria, are also appreciated to be important actors in the etiology of IBD, for example by altering gut microbiota composition and by regulating the generation of short chain fatty acids. A noteworthy study published in the June 2016 issue of Nature Medicine by Lamas and colleagues investigates the interaction between Card9 and the gut microbiota in the generation of the microbiota-derived tryptophan metabolite. This study highlights the role of tryptophan in dampening intestinal inflammation in susceptible hosts.     

Intestinal IgA as a modulator of the gut microbiota

Accumulating evidence suggests that dysbiosis plays a role in the pathogenesis of intestinal diseases including inflammatory bowel disease (IBD) as well as extra-intestinal disorders. As a modulator of the intestinal microbiota, we isolated a mouse monoclonal IgA antibody (clone W27) with high affinities for multiple commensal bacteria, but not for beneficial bacteria such as Lactobacillus casei (L. casei). Via specific recognition of an epitope in serine hydroxymethyltransferase (SHMT), a bacterial metabolic enzyme, W27 IgA selectively inhibited the in vitro growth of bound bacteria, including Escherichia coli (E. coli), while having no effect on unbound beneficial bacteria such as L. casei. By modulating the gut microbiota in vivo, oral administration of W27 IgA effectively prevented development of colitis in several mouse models. Here we discuss how intestinal IgA modulates the gut microbiota through recognition of SHMT.     

Treatment of inflammatory bowel disease with antibiotics

Although antibiotics are clearly recognized as having a role in treating the infectious complications of inflammatory bowel diseases (IBD), their impact in the primary treatment of IBD has long been an area of speculation. Over the past decade there is increasing evidence that luminal gut bacteria play a role in the pathogenesis of IBD, particularly Crohn's disease. Compelling evidence that normal commensal bacteria induce chronic intestinal inflammation in susceptible rodents provides an excellent rationale for treatment of human IBD with antibiotics. This article summarizes published studies of antibiotics in IBD patients and reviews available data for the use of antibiotic therapy in Crohn's disease and ulcerative colitis.     

Bacterial load in animal models of acute and chronic 'reactivated' colitis

BACKGROUND: The involvement of enteropathogenic microorganisms in the pathogenesis of inflammatory bowel disease (IBD) and their importance in the different phases of inflammation are still unknown. AIM: To quantify the aerobic bacterial load in models of acute and chronic 'reactivated' colitis, and correlate this with damage. METHODS: Acute colitis was induced in rats by administration of trinitrobenzene sulfonic acid (TNBS) or dextran sulfate sodium (DSS). Colitis was 'reactivated' 6 weeks later by intravenous administration of TNBS. The distal colon was removed and scored macroscopically before inoculating samples. RESULTS: Bacterial load in rats with acute colitis (72 h) and chronic 'reactivated' colitis or their controls was significantly higher than untreated (p < 0.05); however, there were significantly more bacteria in acute colitis than in chronic 'reactivated' or their controls (p < 0.05). Both acute and chronic 'reactivated' colitis had significantly higher damage scores than untreated animals (p < 0.05). Bacterial load and damage score were significantly correlated only with acute colitis. CONCLUSIONS: The role of enteric microflora in the pathogenesis of IBD is greater during the acute phase of colitis. The correlation between bacterial load and tissue damage suggests that damage contributes to bacterial multiplication and exacerbation of colitis. Normal colonic flora may contribute to the relapse of the disease.     

Microbiota alterations in acute and chronic gastrointestinal inflammation of cats and dogs

The intestinal microbiota is the collection of the living microorganisms(bacteria, fungi, protozoa, and viruses) inhabiting the gastrointestinal tract. Novel bacterial identification approaches have revealed that the gastrointestinal microbiota of dogs and cats is, similarly to humans, a highly complex ecosystem. Studies in dogs and cats have demonstrated that acute and chronic gastrointestinal diseases, including inflammatory bowel disease(IBD), are associated with alterations in the small intestinal and fecal microbial communities. Of interest is that these alterations are generally similar to the dysbiosis observed in humans with IBD or animal models of intestinal inflammation, suggesting that microbial responses to inflammatory conditions of the gut are conserved across mammalian host types. Studies have also revealed possible underlying susceptibilities in the innate immune system of dogs and cats with IBD, which further demonstrate the intricate relationship between gut microbiota and host health. Commonly identified microbiome changes in IBD are decreases in bacterial groups within the phyla Firmicutes and Bacteroidetes, and increases within Proteobacteia. Furthermore, a reduction in the diversity of Clostridium clusters XIVa and IV(i.e., Lachnospiraceae and Clostridium coccoides subgroups) are associated with IBD, suggesting that these bacterial groups may play an important role in maintenance of gastrointestinal health. Future studies are warranted to evaluate the functional changes associated with intestinal dysbiosis in dogs and cats.     

Ulcerative colitis as a polymicrobial infection characterized by sustained broken mucus barrier

To reduce medication for patients with ulcerative colitis (UC), we need to establish the etiology of UC. The intestinal microbiota of patients with inflammatory bowel disease (IBD) has been shown to differ from that of healthy controls and abundant data indicate that it changes in both composition and localization. Small intestinal bacterial overgrowth is significantly higher in IBD patients compared with controls. Probiotics have been investigated for their capacity to reduce the severity of UC. The luminal surfaces of the gastrointestinal tract are covered by a mucus layer. This normally acts as a barrier that does not allow bacteria to reach the epithelial cells and thus limits the direct contact between the host and the bacteria. The mucus layer in the colon comprises an inner layer that is firmly adherent to the intestinal mucosa, and an outer layer that can be washed off with minimal rinsing. Some bacteria can dissolve the protective inner mucus layer. Defects in renewal and formation of the inner mucus layer allow bacteria to reach the epithelium and have implications for the causes of colitis. In this review, important elements of UC pathology are thought to be the intestinal bacteria, gut mucus, and the mucosa-associated immune system.     

Bacterial-induced inflammation in germ-free rabbit appendix

The intestinal ecosystem is defined by a series of interactions between the microbiota, the mucosal epithelium, and the gut-associated lymphoid tissue (GALT). Perturbations in the fine balance of the interactions between these components can result in gastrointestinal diseases such as inflammatory bowel disease (IBD). The pathophysiology of IBD is thought to develop as a result of dysregulated mucosal immune responses to normal luminal microflora. Several animal models for IBD have been developed and underscore the role of the immune system in development of disease. Most of the existing animal models studying IBD are based on the use of chemically induced IBD or of genetically modified and germ-free animals. It is, however, important to study inflammatory responses that can develop from interactions between bacteria, the mucosal epithelium, and GALT in animals that are not genetically modified or immunocompromised. In this report, we document the use of a germ-free ligated rabbit appendix model to induce inflammatory changes in response to specific bacteria. With the introduction of a Bacteroides vulgatus isolate from humans into the germ-free ligated appendix, we found chronic inflammatory changes, including glandular distortion, gland drop-out, decreased goblet cells, and crypt abscess formation. However, with the introduction of other experimental luminal contents, we observed no inflammation. These results show that specific microbial composition can induce inflammation. We suggest that this model may be useful to study the mechanism by which specific bacteria establish inflammatory responses in the gut.     

Rebooting the microbiome

Using a murine Salmonella model of colitis, we recently reported that mice receiving a community of defined gut microbiota (MET-1) lost less weight, had reduced systemic inflammation and splenic S. typhimurium infection, and decreased neutrophil infiltration in the cecum, compared to vehicle controls. In addition, animals receiving MET-1 exhibited preserved tight junction protein expression (Zonula occludens-1, claudin-1), suggesting important effects on barrier function. In this addendum, we describe additional in vitro experiments examining effects of MET-1, as well as in vivo experiments demonstrating that MET-1 is protective in a DSS model of colitis after administration of antibiotics. Placed in the context of our findings and those of others, we discuss differences in our findings between the Salmonella colitis and DSS colitis models, provide speculation as to which bacteria may be important in the protective effects of MET-1, and discuss potential implications for other GI diseases such as IBD.     

Therapeutic approaches targeting intestinal microflora in inflammatory bowel disease

Inflammatory bowel diseases, ulcerative colitis, and Crohn's disease, are chronic intestinal disorders of unknown etiology in which in genetically susceptible individuals, the mucosal immune system shows an aberrant response towards commensal bacteria. The gastrointestinal tract has developed ingenious mechanisms to coexist with its autologous microflora, but rapidly responds to invading pathogens and then returns to homeostasis with its commensal bacteria after the pathogenic infection is cleared. In case of disruption of this tightly-regulated homeostasis, chronic intestinal inflammation may be induced. Previous studies showed that some commensal bacteria are detrimental while others have either no influence or have a protective action. In addition, each host has a genetically determined response to detrimental and protective bacterial species. These suggest that therapeutic manipulation of imbalance of microflora can influence health and disease. This review focuses on new insights into the role of commensal bacteria in gut health and disease, and presents recent findings in innate and adaptive immune interactions. Therapeutic approaches to modulate balance of intestinal microflora and their potential mechanisms of action are also discussed.     

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.     

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.     

Nutritional and Probiotic Supplementation in Colitis Models

In vitro and animals models have long been used to study human diseases and identify novel therapeutic approaches that can be applied to combat these conditions. Ulcerative colitis and Crohn’s disease are the two main entities of inflammatory bowel disease (IBD). There is an intricate relationship between IBD features in human patients, in vitro and animal colitis models, mechanisms and possible therapeutic approaches in these models, and strategies that can be extrapolated and applied in humans. Malnutrition, particularly protein-energy malnutrition and vitamin and micronutrient deficiencies, as well as dysregulation of the intestinal microbiota, are common features of IBD. Based on these observations, dietary supplementation with essential nutrients known to be in short supply in the diet in IBD patients and with other molecules believed to provide beneficial anti-inflammatory effects, as well as with probiotic organisms that stimulate immune functions and resistance to infection has been tested in colitis models. Here we review current knowledge on nutritional and probiotic supplementation in in vitro and animal colitis models. While some of these strategies require further fine-tuning before they can be applied in human IBD patients, their intended purpose is to prevent, delay or treat disease symptoms in a non-pharmaceutical manner.