The importance of gut microbiota in gastrointestinal (GI) physiology was well described, but our ability to study gut microbial ecosystems in their entirety was limited by culture-based methods prior ...to the sequencing revolution. The advent of high-throughput sequencing opened new avenues, allowing us to study gut microbial communities as an aggregate, independent of our ability to culture individual microbes. Early studies focused on association of changes in gut microbiota with different disease states, which was necessary to identify a potential role for microbes and generate novel hypotheses. Over the past few years the field has moved beyond associations to better understand the mechanistic implications of the microbiome in the pathophysiology of complex diseases. This movement also has resulted in a shift in our focus toward therapeutic strategies, which rely on better understanding the mediators of gut microbiota-host cross-talk. It is not surprising the gut microbiome has been implicated in the pathogenesis of functional gastrointestinal disorders given its role in modulating physiological processes such as immune development, GI motility and secretion, epithelial barrier integrity, and brain-gut communication. In this review, we focus on the current state of knowledge and future directions in microbiome research as it pertains to functional gastrointestinal disorders. We summarize the factors that help shape the gut microbiome in human beings. We discuss data from animal models and human studies to highlight existing paradigms regarding the mechanisms underlying microbiota-mediated alterations in physiological processes and their relevance in human interventions. While translation of microbiome science is still in its infancy, the outlook is optimistic and we are advancing in the right direction toward precise mechanism-based microbiota therapies.
The genomic revolution promises to transform our approach to treat patients by individualizing treatments, reducing adverse events, and decreasing health care costs. The early advances using this ...have been realized primarily by optimizing preventive and therapeutic approaches in cancer using human genome sequencing. The ability to characterize the microbiome, which includes all the microbes that reside within and upon us and all their genetic elements, using next-generation sequencing allows us to now incorporate this important contributor to human disease into developing new preventive and therapeutic strategies. In this review we highlight the importance of the microbiome in all aspects of human disease, including pathogenesis, phenotype, prognosis, and response to treatment, as well as their role as diagnostic and therapeutic biomarkers. We provide a role for next-generation sequencing in both precise microbial identification of infectious diseases and characterization of microbial communities and their function. Taken together, the microbiome is emerging as an integral part of precision medicine approach as it not only contributes to interindividual variability in all aspects of a disease but also represents a potentially modifiable factor that is amenable to targeting by therapeutics.
Irritable bowel syndrome: a gut microbiota-related disorder? Bhattarai, Yogesh; Muniz Pedrogo, David A; Kashyap, Purna C
American journal of physiology: Gastrointestinal and liver physiology,
01/2017, Letnik:
312, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Irritable bowel syndrome (IBS) is one of the most common gastrointestinal (GI) disorders. Despite its prevalence, the pathophysiology of IBS is not well understood although multiple peripheral and ...central factors are implicated. Recent studies suggest a role for alterations in gut microbiota in IBS. Significant advances in next-generation sequencing technology and bioinformatics and the declining cost have now allowed us to better investigate the role of gut microbiota in IBS. In the following review, we propose gut microbiota as a unifying factor in the pathophysiology of IBS. We first describe how gut microbiota can be influenced by factors predisposing individuals to IBS such as host genetics, stress, diet, antibiotics, and early life experiences. We then highlight the known effects of gut microbiota on mechanisms implicated in the pathophysiology of IBS including disrupted gut brain axis (GBA), visceral hypersensitivity (VH), altered GI motility, epithelial barrier dysfunction, and immune activation. While there are several gaps in the field that preclude us from connecting the dots to establish causation, we hope this overview will allow us to identify and fill in the voids.
Several recent studies describe the influence of the gut microbiota on host brain and behavior. However, the mechanisms responsible for microbiota-nervous system interactions are largely unknown. ...Using a combination of genetics, biochemistry, and crystallography, we identify and characterize two phylogenetically distinct enzymes found in the human microbiome that decarboxylate tryptophan to form the β-arylamine neurotransmitter tryptamine. Although this enzymatic activity is exceedingly rare among bacteria more broadly, analysis of the Human Microbiome Project data demonstrate that at least 10% of the human population harbors at least one bacterium encoding a tryptophan decarboxylase in their gut community. Our results uncover a previously unrecognized enzymatic activity that can give rise to host-modulatory compounds and suggests a potential direct mechanism by which gut microbiota can influence host physiology, including behavior.
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•Gut microbiota produce tryptamine via tryptophan (Trp) decarboxylation•Two bacterial Trp decarboxylases from gut Firmicutes were identified and characterized•Structure of one of the tryptophan decarboxylase suggests catalytic mechanism•>10% of healthy humans harbor a Trp decarboxylase in their gut microbiome
Williams et al. describe tryptophan decarboxylases from human microbiota that produce the neurotransmitter tryptamine. Although rare among bacteria more broadly, at least 10% of the human population harbors this activity in their gut community. These results uncover a previously unrecognized enzymatic activity that can give rise to host-modulatory compounds.
Gut microbiota alterations have been described in several diseases with altered gastrointestinal (GI) motility, and awareness is increasing regarding the role of the gut microbiome in modulating GI ...function. Serotonin 5‐hydroxytryptamine (5‐HT) is a key regulator of GI motility and secretion. To determine the relationship among gut microbes, colonic contractility, and host serotonergic gene expression, we evaluated mice that were germ‐free (GF) or humanized (HM; ex‐GF colonized with human gut microbiota). 5‐HT reduced contractile duration in both GF and HM colons. Microbiota from HM and conventionally raised (CR) mice significantly increased colonic mRNAs Tph1 (tryptophan hydroxylase) 1, rate limiting for mucosal 5‐HT synthesis; P < 0.01 and chromogranin A (neuroendocrine secretion; P < 0.01), with no effect on monoamine oxidase A (serotonin catabolism), serotonin receptor 5‐HT4, or mouse serotonin transporter. HM and CR mice also had increased colonic Tph1 protein (P < 0.05) and 5‐HT concentrations (GF, 17 ± 3 ng/mg; HM, 25 ± 2 ng/mg; and CR, 35 ± 3 ng/mg; P < 0.05). Enterochromaffin (EC) cell numbers (cells producing 5‐HT) were unchanged. Short‐chain fatty acids (SCFAs) promoted TPH1 transcription in BON cells (human EC cell model). Thus, gut microbiota acting through SCFAs are important determinants of enteric 5‐HT production and homeostasis.—Reigstad, C. S., Salmonson, C. E., Rainey, III, J. F., Szurszewski, J. H., Linden, D. R., Sonnenburg, J. L., Farrugia, G., Kashyap, P. C. Gut microbes promote colonic serotonin production through an effect of short‐chain fatty acids on enterochromaffin cells. FASEB J. 29, 1395‐1403 (2015). www.fasebj.org
The gut microbiome has been implicated in multiple human chronic gastrointestinal (GI) disorders. Determining its mechanistic role in disease has been difficult due to apparent disconnects between ...animal and human studies and lack of an integrated multi-omics view of disease-specific physiological changes. We integrated longitudinal multi-omics data from the gut microbiome, metabolome, host epigenome, and transcriptome in the context of irritable bowel syndrome (IBS) host physiology. We identified IBS subtype-specific and symptom-related variation in microbial composition and function. A subset of identified changes in microbial metabolites correspond to host physiological mechanisms that are relevant to IBS. By integrating multiple data layers, we identified purine metabolism as a novel host-microbial metabolic pathway in IBS with translational potential. Our study highlights the importance of longitudinal sampling and integrating complementary multi-omics data to identify functional mechanisms that can serve as therapeutic targets in a comprehensive treatment strategy for chronic GI diseases.
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•Longitudinal sampling limits heterogeneity seen in cross-sectional microbiome studies•Alteration in the gut microbiome and microbial metabolites underlie IBS and symptom flares•Data integration reveals effect of microbial metabolites on gastrointestinal function•Purine starvation is identified as a possible therapeutic target in IBS
Integrated and longitudinal multiomic analyses of patients with irritable bowel syndrome reveals a role for the gut microbiota in modulating purine metabolism and influencing host gastrointestinal function.
Tryptamine, a tryptophan-derived monoamine similar to 5-hydroxytryptamine (5-HT), is produced by gut bacteria and is abundant in human and rodent feces. However, the physiologic effect of tryptamine ...in the gastrointestinal (GI) tract remains unknown. Here, we show that the biological effects of tryptamine are mediated through the 5-HT4 receptor (5-HT4R), a G-protein-coupled receptor (GPCR) uniquely expressed in the colonic epithelium. Tryptamine increases both ionic flux across the colonic epithelium and fluid secretion in colonoids from germ-free (GF) and humanized (ex-GF colonized with human stool) mice, consistent with increased intestinal secretion. The secretory effect of tryptamine is dependent on 5-HT4R activation and is blocked by 5-HT4R antagonist and absent in 5-HT4R−/− mice. GF mice colonized by Bacteroides thetaiotaomicron engineered to produce tryptamine exhibit accelerated GI transit. Our study demonstrates an aspect of host physiology under control of a bacterial metabolite that can be exploited as a therapeutic modality.
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•Tryptamine increases anion and fluid secretion in the proximal colon•Tryptamine-induced effect is mediated by the GPCR serotonin receptor-4 (5-HT4R)•Tryptamine activates epithelial 5-HT4R to increase cAMP level and drive fluid secretion•In vivo tryptamine production by an engineered microbe accelerates whole-gut transit
Bhattarai et al. uncovered the mechanism by which a bacteria-derived small molecule can alter host gastrointestinal function. Tryptamine produced by bacterial decarboxylation of dietary tryptophan accelerates gastrointestinal transit by activating the epithelial G-protein-coupled receptor (GPCR) serotonin receptor-4 (5-HT4R) and increasing anion-dependent fluid secretion in the proximal colon.
The community of microorganisms within the human gut (or microbiota) is critical to health and functions with a level of complexity comparable to that of an organ system. Alterations of this ecology ...(or dysbiosis) have been implicated in a number of disease states, and the prototypical example is Clostridium difficile infection (CDI). Fecal microbiota transplantation (FMT) has been demonstrated to durably alter the gut microbiota of the recipient and has shown efficacy in the treatment of patients with recurrent CDI. There is hope that FMT may eventually prove beneficial for the treatment of other diseases associated with alterations in gut microbiota, such as inflammatory bowel disease, irritable bowel syndrome, and metabolic syndrome, to name a few. Although the basic principles that underlie the mechanisms by which FMT shows therapeutic efficacy in CDI are becoming apparent, further research is needed to understand the possible role of FMT in these other conditions. Although relatively simple to perform, questions regarding both short-term and long-term safety as well as the complex and rapidly evolving regulatory landscape has limited widespread use. Future work will focus on establishing best practices and more robust safety data than exist currently, as well as refining FMT beyond current “whole-stool” transplants to increase safety and tolerability. Encapsulated formulations, full-spectrum stool-based products, and defined microbial consortia are all in the immediate future.
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