Understanding the apothecaries within: the necessity of a systematic approach for defining the chemical output of the human microbiome

Bioactive small molecules produced by the human gut microbiome modulate Vibrio cholerae sessile and planktonic lifestyles

Humans live in symbiosis with a diverse community of microorganisms, which has evolved to carry out many specific tasks that benefit the host, including protection against invading pathogens. Within the chemical diversity of the gastrointestinal tract, small molecules likely constitute chemical cues for the communication between the microbiota and pathogens. Therefore, we sought to investigate if molecules produced by the human gut microbiota show biological activity against the human pathogen Vibrio cholerae. To probe the effects of the gut metabolome on V. cholerae, we investigated its response to small-molecule extracts from human feces, from a complex bacterial community cultivated in vitro, and from culture supernatants of Enterocloster citroniae, Bacteroides thetaiotaomicron, and Bacteroides vulgatus. Using RNA sequencing, we determined the impact of the human gut metabolome on V. cholerae global gene expression. Among the genes downregulated in the presence of the fecal extract, the most overrepresented functional category was cell motility, which accounted for 39% of repressed genes. Repression of V. cholerae motility by the fecal extract was confirmed phenotypically, and E. citroniae extracts reproduced this phenotype. A complex in vitro microbial community led to increased motility, as did extracts from B. vulgatus, a species present in this community. Accordingly, mucin penetration was also repressed by fecal and E. citroniae extracts, suggesting that the phenotypes observed may have implications for host colonization. Together with previous studies, this work shows that small molecules from the gut metabolome may have a widespread, significant impact on microbe-microbe interactions established in the gut environment.

Metabolomics in the clinic: A review of the shared and unique features of untargeted metabolomics for clinical research and clinical testing

Metabolomics is the untargeted measurement of the metabolome, which is composed of the complement of small molecules detected in a biological sample. As such, metabolomic analysis produces a global biochemical phenotype. It is a technology that has been utilized in the research setting for over a decade. The metabolome is directly linked to and is influenced by genetics, epigenetics, environmental factors, and the microbiome-all of which affect health. Metabolomics can be applied to human clinical diagnostics and to other fields such as veterinary medicine, nutrition, exercise, physiology, agriculture/plant biochemistry, and toxicology. Applications of metabolomics in clinical testing are emerging, but several aspects of its use as a clinical test differ from applications focused on research or biomarker discovery and need to be considered for metabolomics clinical test data to have optimum impact, be meaningful, and be used responsibly. In this review, we deconstruct aspects and challenges of metabolomics for clinical testing by illustrating the significance of test design, accurate and precise data acquisition, quality control, data processing, n-of-1 comparison to a reference population, and biochemical pathway analysis. We describe how metabolomics technology is integral to defining individual biochemical phenotypes, elaborates on human health and disease, and fits within the precision medicine landscape. Finally, we conclude by outlining some future steps needed to bring metabolomics into the clinical space and to be recognized by the broader medical and regulatory fields.

Losing weight for a better health: Role for the gut microbiota

In recent years, there have been several reviews on gut microbiota, obesity and cardiometabolism summarizing interventions that may impact the gut microbiota and have beneficial effects on the host (some examples include [1–3]). In this review we discuss how the gut microbiota changes with weight loss (WL) interventions in relation to clinical and dietary parameters. We also evaluate available evidence on the heterogeneity of response to these interventions. Two important questions were generated in this regard: 1) Can response to an intervention be predicted? 2) Could pre-intervention modifications to the gut microbiota optimize WL and metabolic improvement? Finally, we have delineated some recommendations for future research, such as the importance of assessment of diet and other environmental exposures in WL intervention studies, and the need to shift to more integrative approaches of data analysis.

Human microbial metabolites as a source of new drugs

Crosstalk between the microbiome and the human host is mediated by specific ligand-receptor interactions involving microbially generated metabolites that can be either agonists or antagonists of human proteins. The evolved co-compatibility of gut microbiota with human systems points to a potentially rich area for discovering new drug-like molecules that are both highly specific modulators of human pathways and derisked for adverse effects. In this review, we discuss the rapidly growing research into the role of microbial metabolites in human health and suggest potential strategies for developing these molecules into therapeutic agents.

Sharpening Precision Medicine by a Thorough Interrogation of Metabolic Individuality

Precision medicine is an active component of medical practice today, but aspirations are to both broaden its reach to a greater diversity of individuals and improve its “precision” by enhancing the ability to define even more disease states in combination with associated treatments. Given complexity of human phenotypes, much work is required. In this review, we deconstruct this challenge at a high level to define what is needed to move closer toward these aspirations. In the context of the variables that influence the diverse array of phenotypes across human health and disease – genetics, epigenetics, environmental influences, and the microbiome – we detail the factors behind why an individual's biochemical (metabolite) composition is increasingly regarded as a key element to precisely defining phenotypes. Although an individual's biochemical (metabolite) composition is generally regarded, and frequently shown, to be a surrogate to the phenotypic state, we review how metabolites (and therefore an individual's metabolic profile) are also functionally related to the myriad of phenotypic influencers like genetics and the microbiota. We describe how using the technology to comprehensively measure an individual's biochemical profile – metabolomics – is integrative to defining individual phenotypes and how it is currently being deployed in efforts to continue to elaborate on human health and disease in large population studies. Finally, we summarize instances where metabolomics is being used to assess individual health in instances where signatures (i.e. biomarkers) have been defined.

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Untargeted biochemical profiling has the potential to phenotype individuals where genetic associations do not seem to show penetrance

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Metabolomics can be leveraged with other ‘omics data to discern phenotype information that is driven by environmental, microbiota, or epigenetic factors.

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Tracking the biochemical profile of individuals may help discern effectiveness or response to treatment or disease progression.

Chemical communication in the gut: Effects of microbiota-generated metabolites on gastrointestinal bacterial pathogens

Gastrointestinal pathogens must overcome many obstacles in order to successfully colonize a host, not the least of which is the presence of the gut microbiota, the trillions of commensal microorganisms inhabiting mammals' digestive tracts, and their products. It is well established that a healthy gut microbiota provides its host with protection from numerous pathogens, including Salmonella species, Clostridium difficile, diarrheagenic Escherichia coli, and Vibrio cholerae. Conversely, pathogenic bacteria have evolved mechanisms to establish an infection and thrive in the face of fierce competition from the microbiota for space and nutrients. Here, we review the evidence that gut microbiota-generated metabolites play a key role in determining the outcome of infection by bacterial pathogens. By consuming and transforming dietary and host-produced metabolites, as well as secreting primary and secondary metabolites of their own, the microbiota define the chemical environment of the gut and often determine specific host responses. Although most gut microbiota-produced metabolites are currently uncharacterized, several well-studied molecules made or modified by the microbiota are known to affect the growth and virulence of pathogens, including short-chain fatty acids, succinate, mucin O-glycans, molecular hydrogen, secondary bile acids, and the AI-2 quorum sensing autoinducer. We also discuss challenges and possible approaches to further study of the chemical interplay between microbiota and gastrointestinal pathogens.

Insights on the human microbiome and its xenobiotic metabolism: what is known about its effects on human physiology?

INTRODUCTION

Our microbiome harbours a metabolic capacity far beyond our own. Moreover, its gene pool is highly adaptable and subject to selective pressure, including host exposure to xenobiotics. Yet, the resulting adaptations do not necessarily follow host well-being and can therefore contribute to disease or unfavourable metabolite production.

AREAS COVERED

This review provides an overview of our host-microbiome relationship in light of bacterial (xenobiotic) metabolism, community dynamics, entero-endocrine crosstalk, dysbiosis and potential therapeutic targets. In addition, it will highlight the need for a systematic analysis of the microbiome's potential for substance toxification.

EXPERT OPINION

The influence of our microbiota reaches from primary metabolites to secondary effects such as substrate competition or the activation of eukaryotic Phase I and Phase II enzymes. Further on it plays a hitherto underestimated role in drug metabolism, toxicity and pathogenesis. These effects are partly caused by entero-endocrine crosstalk and interference with eukaryotic regulatory networks. On first sight, the resulting concept of a metabolically competent microbiome adds enormous complexity to human physiology. Yet, the potential specificity of microbial targets harbours therapeutic promise for diseases such as diabetes, cancer and psychiatric disorders. A better physiological and biochemical understanding of the microbiome is thus of high priority for academia and biomedical research.

The microbiome in early life: self-completion and microbiota protection as health priorities

This minireview considers the benefits of refocusing attention away from treating the patient as a mammalian human to managing the complete patient: a majority microbial superorganism. Under the "completed self" model for formation of the human-microbial superorganism, the single, most pivotal sign in distinguishing a life course of health versus that filled with disease is self-completion (i.e., seeding of the minority mammalian human by the majority microbial portion of the symbiont). From a disease prevention perspective, microbial seeding at birth and subsequent nurturing of the microbiota are significant steps to reduce the risk of both noncommunicable diseases (e.g., type 1 diabetes) and certain infectious diseases. Management of the microbiome during pregnancy, birth, and shortly thereafter appears to be the most significant critical window for healthy superorganism formation. However, the bolus for microbiota seeding at birth and the nurturing process are subject to environmental influences and disruption, such as exposure to toxic chemicals and drugs, infections, and other physical and psychological stressors. Additionally, childhood and adult corrective measures, such as fecal transplantation and administration of prebiotics and probiotics, while potentially useful, may have limitations that are yet to be fully defined. This minireview considers (1) basic features of management of the microbiome to facilitate self-completion, (2) protection of the microbiota from environmental hazards, and (3) the benefits of using a superorganism focus for health management beginning with pregnancy and extending throughout childhood and adult life.