Ability of the gut microbiota to produce PUFA-derived bacterial metabolites: Proof of concept in germ-free versus conventionalized mice

Gut microbiota-derived metabolites tune host homeostasis fate

The gut microbiota, housing trillions of microorganisms within the gastrointestinal tract, has emerged as a critical regulator of host health and homeostasis. Through complex metabolic interactions, these microorganisms produce a diverse range of metabolites that substantially impact various physiological processes within the host. This review aims to delve into the intricate relationships of gut microbiota-derived metabolites and their influence on the host homeostasis. We will explore how these metabolites affect crucial aspects of host physiology, including metabolism, mucosal integrity, and communication among gut tissues. Moreover, we will spotlight the potential therapeutic applications of targeting these metabolites to restore and sustain host equilibrium. Understanding the intricate interplay between gut microbiota and their metabolites is crucial for developing innovative strategies to promote wellbeing and improve outcomes of chronic diseases.

The use of an in vitro fecal fermentation model to uncover the beneficial role of omega-3 and punicic acid in gut microbiota alterations induced by a Western diet

The influence of gut microbiota in the onset and development of several metabolic diseases has gained attention over the last few years. Diet plays an essential role in gut microbiota modulation. Western diet (WD), characterized by high-sugar and high-fat consumption, alters gut microbiome composition, diversity index, microbial relative levels, and functional pathways. Despite the promising health effects demonstrated by polyunsaturated fatty acids, their impact on gut microbiota is still overlooked. The effect of Fish oil (omega-3 source) and Pomegranate oil (punicic acid source), and a mixture of both oils in gut microbiota modulation were determined by subjecting the oil samples to in vitro fecal fermentations. Cecal samples from rats from two different dietary groups: a control diet (CD) and a high-fat high-sugar diet (WD), were used as fecal inoculum. 16S amplicon metagenomics sequencing showed that Fish oil + Pomegranate oil from the WD group increased α-diversity. This sample can also increase the relative abundance of the Firmicutes and Bacteroidetes phylum as well as Akkermansia and Blautia, which were affected by the WD consumption. All samples were able to increase butyrate and acetate concentration in the WD group. Moreover, tyrosine concentrations, a precursor for dopamine and norepinephrine, increase in the Fish oil + Pomegranate oil WD sample. GABA, an important neurotransmitter, was also increased in WD samples. These results suggest a potential positive impact of these oils' mixture on gut-brain axis modulation. It was demonstrated, for the first time, the great potential of using a mixture of both Fish and Pomegranate oil to restore the gut microbiota changes associated with WD consumption.

Human gut microbiota and their production of endocannabinoid-like mediators are directly affected by a dietary oil

Dietary omega-3 polyunsaturated fatty acids (n-3 PUFAs) and the gut microbiome affect each other. We investigated the impact of supplementation with Buglossoides arvensis oil (BO), rich in stearidonic acid (SDA), on the human gut microbiome. Employing the Mucosal Simulator of the Human Intestinal Microbial Ecosystem (M-SHIME), we simulated the ileal and ascending colon microbiomes of four donors. Our results reveal two distinct microbiota clusters influenced by BO, exhibiting shared and contrasting shifts. Notably, Bacteroides and Clostridia abundance underwent similar changes in both clusters, accompanied by increased propionate production in the colon. However, in the ileum, cluster 2 displayed a higher metabolic activity in terms of BO-induced propionate levels. Accordingly, a triad of bacterial members involved in propionate production through the succinate pathway, namely Bacteroides, Parabacteroides, and Phascolarctobacterium, was identified particularly in this cluster, which also showed a surge of second-generation probiotics, such as Akkermansia, in the colon. Finally, we describe for the first time the capability of gut bacteria to produce N-acyl-ethanolamines, and particularly the SDA-derived N-stearidonoyl-ethanolamine, following BO supplementation, which also stimulated the production of another bioactive endocannabinoid-like molecule, commendamide, in both cases with variations across individuals. Spearman correlations enabled the identification of bacterial genera potentially involved in endocannabinoid-like molecule production, such as, in agreement with previous reports, Bacteroides in the case of commendamide. This study suggests that the potential health benefits on the human microbiome of certain dietary oils may be amenable to stratified nutrition strategies and extend beyond n-3 PUFAs to include microbiota-derived endocannabinoid-like mediators.

High fat diet reveals sex-specific fecal and liver metabolic alterations in C57BL/6J obese mice

Obesity is a major health concern that poses significant risks for many other diseases, including diabetes, cardiovascular disease, and cancer. Prevalence of these diseases varies by biological sex. This study utilizes a mouse (C57BL/6J) model of obesity to analyze liver and fecal metabolic profiles at various time points of dietary exposure: 5, 9, and 12 months in control or high fat diet (HFD)-exposed mice. Our study discovered that the female HFD group has a more discernable perturbation and set of significant changes in metabolic profiles than the male HFD group. In the female mice, HFD fecal metabolites including pyruvate, aspartate, and glutamate were lower than control diet-exposed mice after both 9th and 12th month exposure time points, while lactate and alanine were significantly downregulated only at the 12th month. Perturbations of liver metabolic profiles were observed in both male and female HFD groups, compared to controls at the 12th month. Overall, the female HFD group showed higher lactate and glutathione levels compared to controls, while the male HFD group showed higher levels of glutamine and taurine compared to controls. These metabolite-based findings in both fecal and liver samples for a diet-induced effect of obesity may help guide future pioneering discoveries relating to the analysis and prevention of obesity in people, especially for females.

The gut-derived metabolites as mediators of the effect of healthy nutrition on the brain

Nutrition is now well recognized to be an environmental factor which positively or negatively influences the risk to develop neurological and psychiatric disorders. The gut microbiota has recently been shown to be an important actor mediating the relationship between environmental factors, including nutrition, and brain function. While its composition has been widely studied and associated with the risk of brain diseases, the mechanisms underlying the relationship between the gut and brain diseases remain to be explored. The wide range of bioactive molecules produced by the gut microbiota, called gut-derived metabolites (GDM), represent new players in the gut to brain interactions and become interesting target to promote brain health. The aim of this narrative review is to highlight some GDMs of interest that are produced in response to healthy food consumption and to summarize what is known about their potential effects on brain function. Overall, GDMs represent future useful biomarkers for the development of personalized nutrition. Indeed, their quantification after nutritional interventions is a useful tool to determine individuals' ability to produce microbiota-derived bioactive compounds upon consumption of specific food or nutrients. Moreover, GDMs represent also a new therapeutic approach to counteract the lack of response to conventional nutritional interventions.

The Chelating Ability of Plant Polyphenols Can Affect Iron Homeostasis and Gut Microbiota

In the past decades, many studies have widely examined the effects of dietary polyphenols on human health. Polyphenols are well known for their antioxidant properties and for their chelating abilities, by which they can be potentially employed in cases of pathological conditions, such as iron overload. In this review, we have highlighted the chelating abilities of polyphenols, which are due to their structural specific sites, and the differences for each class of polyphenols. We have also explored how the dietary polyphenols and their iron-binding abilities can be important in inflammatory/immunomodulatory responses, with a special focus on the involvement of macrophages and dendritic cells, and how they might contribute to reshape the gut microbiota into a healthy profile. This review also provides evidence that the axes “polyphenol–iron metabolism–inflammatory responses” and “polyphenol–iron availability–gut microbiota” have not been very well explored so far, and the need for further investigation to exploit such a potential to prevent or counteract pathological conditions.

Gut microbiome lipid metabolism and its impact on host physiology

Metabolites produced by commensal gut microbes impact host health through their recognition by the immune system and their influence on numerous metabolic pathways. Notably, the gut microbiota can both transform and synthesize lipids as well as break down dietary lipids to generate secondary metabolites with host modulatory properties. Although lipids have largely been consigned to structural roles, particularly in cell membranes, recent research has led to an increased appreciation of their signaling activities, with potential impacts on host health and physiology. This review focuses on studies that highlight the functions of bioactive lipids in mammalian physiology, with a special emphasis on immunity and metabolism.

Food and Gut Microbiota-Derived Metabolites in Nonalcoholic Fatty Liver Disease

Diet and lifestyle are crucial factors that influence the susceptibility of humans to nonalcoholic fatty liver disease (NAFLD). Personalized diet patterns chronically affect the composition and activity of microbiota in the human gut; consequently, nutrition-related dysbiosis exacerbates NAFLD via the gut–liver axis. Recent advances in diagnostic technology for gut microbes and microbiota-derived metabolites have led to advances in the diagnosis, treatment, and prognosis of NAFLD. Microbiota-derived metabolites, including tryptophan, short-chain fatty acid, fat, fructose, or bile acid, regulate the pathophysiology of NAFLD. The microbiota metabolize nutrients, and metabolites are closely related to the development of NAFLD. In this review, we discuss the influence of nutrients, gut microbes, their corresponding metabolites, and metabolism in the pathogenesis of NAFLD.

Chitin-glucan supplementation improved postprandial metabolism and altered gut microbiota in subjects at cardiometabolic risk in a randomized trial

Chitin-glucan (CG), an insoluble dietary fiber, has been shown to improve cardiometabolic disorders associated with obesity in mice. Its effects in healthy subjects has recently been studied, revealing its interaction with the gut microbiota. In this double-blind, randomized, cross-over, twice 3-week exploratory study, we investigated the impacts of CG on the cardiometabolic profile and gut microbiota composition and functions in 15 subjects at cardiometabolic risk. They consumed as a supplement 4.5 g of CG daily or maltodextrin as control. Before and after interventions, fasting and postprandial metabolic parameters and exhaled gases (hydrogen [H2] and methane [CH4]) were evaluated. Gut microbiota composition (16S rRNA gene sequencing analysis), fecal concentrations of bile acids, long- and short-chain fatty acids (LCFA, SCFA), zonulin, calprotectin and lipopolysaccharide binding protein (LBP) were analyzed. Compared to control, CG supplementation increased exhaled H2 following an enriched-fiber breakfast ingestion and decreased postprandial glycemia and triglyceridemia response to a standardized test meal challenge served at lunch. Of note, the decrease in postprandial glycemia was only observed in subjects with higher exhaled H2, assessed upon lactulose breath test performed at inclusion. CG decreased a family belonging to Actinobacteria phylum and increased 3 bacterial taxa: Erysipelotrichaceae UCG.003, Ruminococcaceae UCG.005 and Eubacterium ventriosum group. Fecal metabolites, inflammatory and intestinal permeability markers did not differ between groups. In conclusion, we showed that CG supplementation modified the gut microbiota composition and improved postprandial glycemic response, an early determinant of cardiometabolic risk. Our results also suggest breath H2 production as a non-invasive parameter of interest for predicting the effectiveness of dietary fiber intervention.

Lipidomics for the Prediction of Progressive Liver Disease in Patients with Alcohol Use Disorder

Alcohol-related liver disease is a public health care burden globally. Only 10-20% of patients with alcohol use disorder have progressive liver disease. This study aimed to identify lipid biomarkers for the early identification of progressive alcohol-related liver disease, which is a key step for early intervention. We performed untargeted lipidomics analysis in serum and fecal samples for a cohort of 49 subjects, including 17 non-alcoholic controls, 16 patients with non-progressive alcohol-related liver disease, and 16 patients with progressive alcohol-related liver disease. The serum and fecal lipidome profiles in the two patient groups were different from that in the controls. Nine lipid biomarkers were identified that were significantly different between patients with progressive liver disease and patients with non-progressive liver disease in both serum and fecal samples. We further built a random forest model to predict progressive alcohol-related liver disease using nine lipid biomarkers. Fecal lipids performed better (Area Under the Curve, AUC = 0.90) than serum lipids (AUC = 0.79). The lipid biomarkers identified are promising candidates for the early identification of progressive alcohol-related liver disease.

Leveraging the Microbiome for Obesity: Moving From Form to Function

Treatment of obesity, an ongoing global epidemic, is challenging, as weight-loss efforts require a multidisciplinary approach addressing both behavioral and biologic needs that are not completely understood. Recent studies of the gut microbiome may provide better insight into the condition, and ultimately serve to advance more effective therapies. Research in this field has shifted from analyzing microbiome compositional differences to investigating functional changes that affect disease pathophysiology and outcome. Bacteria-derived metabolites are a way to bridge compositional changes to functional consequences. Through the production of metabolites, such as short chain fatty acids, tryptophan derivatives and bile acids, and interactions with peripheral and central signaling pathways, the gut microbiome may alter the body's metabolic and behavioral responses to food. Here, we summarize these mechanisms driven by gut-derived metabolites, through which the microbiome is thought to contribute to obesity, as well as review recent investigations of interventions related to these metabolites. Limitations of existing research, primarily due to paucity of causal studies in humans, are also discussed in this review.

Impact of gut microbiota on plasma oxylipins profile under healthy and obesogenic conditions

BACKGROUND & AIMS

Oxylipins (OXLs) are bioactive lipid metabolites derived from polyunsaturated fatty acids (PUFAs) which act as signaling molecules and are involved in inflammatory processes such as those that occur in obesity. On the other hand, gut microbiota plays an essential role in regulating inflammatory responses. However, little is known about the potential impact of gut bacteria on OXLs metabolism. Thus, the objective of this study was to investigate the effect of gut microbiota dysbiosis on plasma oxylipins profile in healthy and diet-induced obese animals.

METHODS

Eight-week-old male Wistar rats were fed with either a standard or cafeteria diet (CAF) for 5 weeks and administered an antibiotic cocktail (ABX) in the drinking water (Ampicillin: 1 g/ml, Vancomycin: 0.5 g/ml, Imipenem: 0.25 g/ml) for the last 2 weeks in order to induce gut microbiota dysbiosis. Metabolomics analysis of OXLs in plasma was performed by HPLC-MS analysis. No antibiotic treated animals were included as controls.

RESULTS

Plasma OXLs profile was significantly altered due to both CAF feeding and ABX administration. ABX effect was more pronounced under obesogenic conditions. Several significant correlations between different bacteria taxa and these lipid mediators were observed. Among these, the positive correlation of Proteobacteria with LTB4, a proinflammatory OXL involved in obesity-related disorders, was especially remarkable.

CONCLUSIONS

Gut microbiota plays a key role in regulating these lipid metabolites and, therefore, affecting oxylipins-mediated inflammatory processes. These results are the first evidence to our knowledge of gut microbiota impact on OXLs metabolism. Moreover, this can set the basis for developing new obesity markers based on OXLs and gut microbiota profiles.

Nutritional Components in Western Diet Versus Mediterranean Diet at the Gut Microbiota-Immune System Interplay. Implications for Health and Disease

The most prevalent diseases of our time, non-communicable diseases (NCDs) (including obesity, type 2 diabetes, cardiovascular diseases and some types of cancer) are rising worldwide. All of them share the condition of an "inflammatory disorder", with impaired immune functions frequently caused or accompanied by alterations in gut microbiota. These multifactorial maladies also have in common malnutrition related to physiopathology. In this context, diet is the greatest modulator of immune system-microbiota crosstalk, and much interest, and new challenges, are arising in the area of precision nutrition as a way towards treatment and prevention. It is a fact that the westernized diet (WD) is partly responsible for the increased prevalence of NCDs, negatively affecting both gut microbiota and the immune system. Conversely, other nutritional approaches, such as Mediterranean diet (MD), positively influence immune system and gut microbiota, and is proposed not only as a potential tool in the clinical management of different disease conditions, but also for prevention and health promotion globally. Thus, the purpose of this review is to determine the regulatory role of nutritional components of WD and MD in the gut microbiota and immune system interplay, in order to understand, and create awareness of, the influence of diet over both key components.

Serum Acylcarnitines Associated with High Short-Term Mortality in Patients with Alcoholic Hepatitis

Alcohol-related liver disease is one of the most prevalent liver diseases in the United States. Early stages of alcohol-related liver disease are characterized by accumulation of triglycerides in hepatocytes. Alcoholic hepatitis is a severe form of alcohol-related liver disease associated with significant morbidity and mortality. We sought to identify patients who are at greatest risk of death using serum lipids. First, we performed lipidomics analysis on serum samples collected from 118 patients with alcoholic hepatitis to identify lipid markers that are associated with high risk of death. Next, we performed gene set enrichment analysis on liver transcriptomics data to identify dysregulated lipid metabolism in patients who received liver transplantation. Finally, we built a random forest model to predict 30-day mortality using serum lipids. A total of 277 lipids were annotated in the serum of patients with alcoholic hepatitis, among which 25 were significantly different between patients in the deceased and alive groups. Five chemical clusters were significantly altered between the two groups. In particular, acylcarnitine cluster was enriched in the deceased group. Several hepatic lipid metabolism pathways were dysregulated in patients with alcoholic hepatitis who received liver transplantation. The mRNA expression of genes involved in the fatty acid transport into mitochondria and β-oxidation were also dysregulated. When predicting 30-day mortality in alcoholic hepatitis patients using serum lipids, we found that the area under the curve achieved 0.95. Serum lipids such as acylcarnitines may serve as biomarkers to identify alcoholic hepatitis patients at the greatest risk of death.

Prebiotic dietary fibre intervention improves fecal markers related to inflammation in obese patients: results from the Food4Gut randomized placebo-controlled trial

Purpose

Inulin-type fructans (ITF) are prebiotic dietary fibre (DF) that may confer beneficial health effects, by interacting with the gut microbiota. We have tested the hypothesis that a dietary intervention promoting inulin intake versus placebo influences fecal microbial-derived metabolites and markers related to gut integrity and inflammation in obese patients.

Methods

Microbiota (16S rRNA sequencing), long- and short-chain fatty acids (LCFA, SCFA), bile acids, zonulin, and calprotectin were analyzed in fecal samples obtained from obese patients included in a randomized, placebo-controlled trial. Participants received either 16 g/d native inulin (prebiotic n = 12) versus maltodextrin (placebo n = 12), coupled to dietary advice to consume inulin-rich versus inulin-poor vegetables for 3 months, in addition to dietary caloric restriction.

Results

Both placebo and prebiotic interventions lowered energy and protein intake. A substantial increase in Bifidobacterium was detected after ITF treatment (q = 0.049) supporting our recent data obtained in a larger cohort. Interestingly, fecal calprotectin, a marker of gut inflammation, was reduced upon ITF treatment. Both prebiotic and placebo interventions increased the ratio of tauro-conjugated/free bile acids in feces. Prebiotic treatment did not significantly modify fecal SCFA content but it increased fecal rumenic acid, a conjugated linoleic acid (cis-9, trans-11 CLA) with immunomodulatory properties, that correlated notably to the expansion of Bifidobacterium (p = 0.031; r = 0.052).

Conclusions

Our study demonstrates that ITF-prebiotic intake during 3 months decreases a fecal marker of intestinal inflammation in obese patients. Our data point to a potential contribution of microbial lipid-derived metabolites in gastro-intestinal dysfunction related to obesity.

ClinicalTrials.gov Identifier

NCT03852069 (February 22, 2019 retrospectively, registered).

Supplementary Information

The online version contains supplementary material available at 10.1007/s00394-021-02484-5.

Linking Gut Microbiome and Lipid Metabolism: Moving beyond Associations

Various studies aiming to elucidate the role of the gut microbiome-metabolome co-axis in health and disease have primarily focused on water-soluble polar metabolites, whilst non-polar microbial lipids have received less attention. The concept of microbiota-dependent lipid biotransformation is over a century old. However, only recently, several studies have shown how microbial lipids alter intestinal and circulating lipid concentrations in the host, thus impacting human lipid homeostasis. There is emerging evidence that gut microbial communities play a particularly significant role in the regulation of host cholesterol and sphingolipid homeostasis. Here, we review and discuss recent research focusing on microbe-host-lipid co-metabolism. We also discuss the interplay of human gut microbiota and molecular lipids entering host systemic circulation, and its role in health and disease.

Associations among Dietary Omega-3 Polyunsaturated Fatty Acids, the Gut Microbiota, and Intestinal Immunity

Omega-3 polyunsaturated fatty acids (omega-3 PUFAs), which are essential fatty acids that humans should obtain from diet, have potential benefits for human health. In addition to altering the structure and function of cell membranes, omega-3 PUFAs (docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), alpha-linolenic acid (ALA), and docosapentaenoic acid (DPA)) exert different effects on intestinal immune tolerance and gut microbiota maintenance. Firstly, we review the effect of omega-3 PUFAs on gut microbiota. And the effects of omega-3 PUFAs on intestinal immunity and inflammation were described. Furthermore, the important roles of omega-3 PUFAs in maintaining the balance between gut immunity and the gut microbiota were discussed. Additional factors, such as obesity and diseases (NAFLD, gastrointestinal malignancies or cancer, bacterial and viral infections), which are associated with variability in omega-3 PUFA metabolism, can influence omega-3 PUFAs–microbiome–immune system interactions in the intestinal tract and also play roles in regulating gut immunity. This review identifies several pathways by which the microbiota modulates the gut immune system through omega-3 PUFAs. Omega-3 supplementation can be targeted to specific pathways to prevent and alleviate intestinal diseases, which may help researchers identify innovative diagnostic methods.

Towards Tailored Gut Microbiome-Based and Dietary Interventions for Promoting the Development and Maintenance of a Healthy Brain

Mental health is determined by a complex interplay between the Neurological Exposome and the Human Genome. Multiple genetic and non-genetic (exposome) factors interact early in life, modulating the risk of developing the most common complex neurodevelopmental disorders (NDDs), with potential long-term consequences on health. To date, the understating of the precise etiology underpinning these neurological alterations, and their clinical management pose a challenge. The crucial role played by diet and gut microbiota in brain development and functioning would indicate that modulating the gut-brain axis may help protect against the onset and progression of mental-health disorders. Some nutritional deficiencies and gut microbiota alterations have been linked to NDDs, suggesting their potential pathogenic implications. In addition, certain dietary interventions have emerged as promising alternatives or adjuvant strategies for improving the management of particular NDDs, at least in particular subsets of subjects. The gut microbiota can be a key to mediating the effects of other exposome factors such as diet on mental health, and ongoing research in Psychiatry and Neuropediatrics is developing Precision Nutrition Models to classify subjects according to a diet response prediction based on specific individual features, including microbiome signatures. Here, we review current scientific evidence for the impact of early life environmental factors, including diet, on gut microbiota and neuro-development, emphasizing the potential long-term consequences on health; and also summarize the state of the art regarding the mechanisms underlying diet and gut microbiota influence on the brain-gut axis. Furthermore, we describe the evidence supporting the key role played by gut microbiota, diet and nutrition in neurodevelopment, as well as the effectiveness of certain dietary and microbiome-based interventions aimed at preventing or treating NDDs. Finally, we emphasize the need for further research to gain greater insight into the complex interplay between diet, gut microbiome and brain development. Such knowledge would help towards achieving tailored integrative treatments, including personalized nutrition.

Bacterial Metabolites of Human Gut Microbiota Correlating with Depression

Depression is a global threat to mental health that affects around 264 million people worldwide. Despite the considerable evolution in our understanding of the pathophysiology of depression, no reliable biomarkers that have contributed to objective diagnoses and clinical therapy currently exist. The discovery of the microbiota-gut-brain axis induced scientists to study the role of gut microbiota (GM) in the pathogenesis of depression. Over the last decade, many of studies were conducted in this field. The productions of metabolites and compounds with neuroactive and immunomodulatory properties among mechanisms such as the mediating effects of the GM on the brain, have been identified. This comprehensive review was focused on low molecular weight compounds implicated in depression as potential products of the GM. The other possible mechanisms of GM involvement in depression were presented, as well as changes in the composition of the microbiota of patients with depression. In conclusion, the therapeutic potential of functional foods and psychobiotics in relieving depression were considered. The described biomarkers associated with GM could potentially enhance the diagnostic criteria for depressive disorders in clinical practice and represent a potential future diagnostic tool based on metagenomic technologies for assessing the development of depressive disorders.

The role of the microbiota in human genetic adaptation

As human populations spread across the world, they adapted genetically to local conditions. So too did the resident microorganism communities that everyone carries with them. However, the collective influence of the diverse and dynamic community of resident microbes on host evolution is poorly understood. The taxonomic composition of the microbiota varies among individuals and displays a range of sometimes redundant functions that modify the physicochemical environment of the host and may alter selection pressures. Here we review known human traits and genes for which the microbiota may have contributed or responded to changes in host diet, climate, or pathogen exposure. Integrating host–microbiota interactions in human adaptation could offer new approaches to improve our understanding of human health and evolution.

Metabolite profiling reveals the interaction of chitin-glucan with the gut microbiota

Dietary fibers are considered beneficial nutrients for health. Current data suggest that their interaction with the gut microbiota largely contributes to their physiological effects. In this context, chitin-glucan (CG) improves metabolic disorders associated with obesity in mice, but its effect on gut microbiota has never been evaluated in humans. This study explores the effect of a 3-week intervention with CG supplementation in healthy individuals on gut microbiota composition and bacterial metabolites. CG was given to healthy volunteers (n = 15) for three weeks as a supplement (4.5 g/day). Food diary, visual analog and Bristol stool form scales and a "quality of life" survey were analyzed. Among gut microbiota-derived metabolites, bile acids (BA), long- and short-chain fatty acids (LCFA, SCFA) profiling were assessed in stool samples. The gut microbiota (primary outcome) was analyzed by Illumina sequencing. A 3-week supplementation with CG is well tolerated in healthy humans. CG induces specific changes in the gut microbiota composition, with Eubacterium, Dorea and Roseburia genera showing the strongest regulation. In addition, CG increased bacterial metabolites in feces including butyric, iso-valeric, caproic and vaccenic acids. No major changes were observed for the fecal BA profile following CG intervention. In summary, our work reveals new potential bacterial genera and gut microbiota-derived metabolites characterizing the interaction between an insoluble dietary fiber -CG- and the gut microbiota.

Nuclear Receptor Chemical Reporter Enables Domain-Specific Analysis of Ligands in Mammalian Cells

The characterization of specific metabolite-protein interactions is important in chemical biology and drug discovery. For example, nuclear receptors (NRs) are a family of ligand-activated transcription factors that regulate diverse physiological processes in animals and are key targets for therapeutic development. However, the identification and characterization of physiological ligands for many NRs remains challenging, because of limitations in domain-specific analysis of ligand binding in cells. To address these limitations, we developed a domain-specific covalent chemical reporter for peroxisome proliferator-activated receptors (PPARs) and demonstrated its utility to screen and characterize the potency of candidate NR ligands in live cells. These studies demonstrate targeted and domain-specific chemical reporters provide excellent tools to evaluate endogenous and exogenous (diet, microbiota, therapeutics) ligands of PPARs in mammalian cells, as well as additional protein targets for further investigation.

Digestion of human milk fat in healthy infants

Lipid digestion is critical for infant development, and yet, the interconnection between lipid digestion and the microbiota is largely understudied. This review focuses on digestion of the human milk fat globule and summarizes the current understanding of the mechanisms underlying this process in infants. We first discuss the partial hydrolysis of milk fat in the stomach, which leads to rearrangement of lipid droplets, creating a lipid-water interface necessary for duodenal lipolysis. In the first few months of life, secretion of pancreatic triglyceride lipase, phospholipase A₂, and bile salts is immature. The dominant lipases aiding fat digestion in the newborn small intestine are therefore pancreatic lipase-related protein 2 and bile salt-stimulated lipase from both the exocrine pancreas and milk. We summarize the interaction between ionic fatty acids and cations to form insoluble fatty acid soaps and how it is influenced by various factors, including cation availability, pH, and bile salt concentration, as well as saturation and chain length of fatty acids. We further argue that the formation of the soap complex does not contribute to lipid bioavailability. Next, the possible roles that the gut microbiota plays in lipid digestion and absorption are discussed. Finally, we provide a perspective on how the manufacturing process of infant formula and dairy products may alter the physical properties and structure of lipid droplets, thereby altering the rate of lipolysis.

Fatty Acid Diets: Regulation of Gut Microbiota Composition and Obesity and Its Related Metabolic Dysbiosis

Long-term high-fat dietary intake plays a crucial role in the composition of gut microbiota in animal models and human subjects, which affect directly short-chain fatty acid (SCFA) production and host health. This review aims to highlight the interplay of fatty acid (FA) intake and gut microbiota composition and its interaction with hosts in health promotion and obesity prevention and its related metabolic dysbiosis. The abundance of the Bacteroidetes/Firmicutes ratio, as Actinobacteria and Proteobacteria species are associated with increased SCFA production, reported high-fat diet rich in medium-chain fatty acids (MCFAs), monounsaturated fatty acids (MUFAs), and n-3 polyunsaturated fatty acids (PUFAs) as well as low-fat diets rich in long-chain fatty acids (LCFAs). SCFAs play a key role in health promotion and prevention and, reduction and reversion of metabolic syndromes in the host. Furthermore, in this review, we discussed the type of fatty acids and their amount, including the administration time and their interplay with gut microbiota and its results about health or several metabolic dysbioses undergone by hosts.

Effectiveness of probiotics, prebiotics, and prebiotic-like components in common functional foods

The bioactive ingredients in commonly consumed foods include, but are not limited to, prebiotics, prebiotic-like components, probiotics, and postbiotics. The bioactive ingredients in functional foods have also been associated with beneficial effects on human health. For example, they aid in shaping of gut microflora and promotion of immunity. These functional components also contribute in preventing serious diseases such as cardiovascular malfunction and tumorigenesis. However, the specific mechanisms of these positive influences on human health are still under investigation. In this review, we aim to emphasize the major contents of probiotics, prebiotics, and prebiotic-like components commonly found in consumable functional foods, and we present an overview of direct and indirect benefits they provide on human health. The major contributors are certain families of metabolites, specifically short-chain fatty acids and polyunsaturated fatty acids produced by probiotics, and prebiotics, or prebiotic-like components such as flavonoids, polyphenols, and vitamins that are found in functional foods. These functional ingredients in foods influence the gut microbiota by stimulating the growth of beneficial microbes and the production of beneficial metabolites that, in turn, have direct benefits to the host, while also providing protection from pathogens and maintaining a balanced gut ecosystem. The complex interactions that arise among functional food ingredients, human physiology, the gut microbiota, and their respective metabolic pathways have been found to minimize several factors that contribute to the incidence of chronic disease, such as inflammation oxidative stress.

α-Linolenic Acid-Rich Diet Influences Microbiota Composition and Villus Morphology of the Mouse Small Intestine

α-Linolenic acid (ALA) is well-known for its anti-inflammatory activity. In contrast, the influence of an ALA-rich diet on intestinal microbiota composition and its impact on small intestine morphology are not fully understood. In the current study, we kept adult C57BL/6J mice for 4 weeks on an ALA-rich or control diet. Characterization of the microbial composition of the small intestine revealed that the ALA diet was associated with an enrichment in Prevotella and Parabacteroides. In contrast, taxa belonging to the Firmicutes phylum, including Lactobacillus, Clostridium cluster XIVa, Lachnospiraceae and Streptococcus, had significantly lower abundance compared to control diet. Metagenome prediction indicated an enrichment in functional pathways such as bacterial secretion system in the ALA group, whereas the two-component system and ALA metabolism pathways were downregulated. We also observed increased levels of ALA and its metabolites eicosapentanoic and docosahexanoic acid, but reduced levels of arachidonic acid in the intestinal tissue of ALA-fed mice. Furthermore, intestinal morphology in the ALA group was characterized by elongated villus structures with increased counts of epithelial cells and reduced epithelial proliferation rate. Interestingly, the ALA diet reduced relative goblet and Paneth cell counts. Of note, high-fat Western-type diet feeding resulted in a comparable adaptation of the small intestine. Collectively, our study demonstrates the impact of ALA on the gut microbiome and reveals the nutritional regulation of gut morphology.

The FiberTAG project: Tagging dietary fibre intake by measuring biomarkers related to the gut microbiota and their interest for health

The scientific rationale for dietary fibre intake recommendations comes from the recognition of their benefits for health based on studies first published many years ago. It remains unclear which are the key physiological effects generated by dietary fibre in view of the diversity of the food components considered as dietary fibre, of the relevance of their classification (soluble and insoluble) and from the recent discoveries putting forward their interactions with the gut microbiota. The project FiberTAG (Joint Programming Initiative 'A Healthy Diet for a Healthy Life' 2017-2020 https://www.fibertag.eu/) aims to establish a set of biomarkers (markers of gut barrier function and bacterial co-metabolites including volatile compounds and lipid derivatives), measured in different biological compartments (faeces, blood or breath) linking dietary fibre intake and gut microbiota-related health effects. The FiberTAG consortium brings together academic and industrial partners from Belgium, France, Germany and Canada to share data and samples obtained from existing as well as new intervention studies in order to evaluate the relevance of such biomarkers. The FiberTAG consortium is currently working on five existing cohorts (prospective observational or nutritional interventions in healthy or obese patients), and a number of new intervention studies to analyse the effect of insoluble dietary fibre (wheat bran and chitin-glucan, provided by the industrial partners) in healthy individuals or in obese patients at high cardiometabolic risk.

Pregnancy and diet-related changes in the maternal gut microbiota following exposure to an elevated linoleic acid diet

Dietary intakes of linoleic acid (LA) have increased, including in women of reproductive age. Changes in maternal gut microbiome have been implicated in the metabolic adaptions that occur during pregnancy. We aimed to investigate whether consumption of a diet with elevated LA altered fecal microbiome diversity before and during pregnancy. Female Wistar-Kyoto rats consumed a high-LA diet (HLA: 6.21% of energy) or a low-LA diet (LLA: 1.44% of energy) for 10 wk before mating and during pregnancy. DNA was isolated from fecal samples before pregnancy [embryonic day 0 (E0)], or during pregnancy at E10 and E20. The microbiome composition was assessed with 16S rRNA sequencing. At E0, the beta-diversity of LLA and HLA groups differed with HLA rats having significantly lower abundance of the genera Akkermansia, Peptococcus, Sutterella, and Xo2d06 but higher abundance of Butyricimonas and Coprococcus. Over gestation, in LLA but not HLA rats, there was a reduction in alpha-diversity and an increase in beta-diversity. In the LLA group, the abundance of Akkermansia, Blautia, rc4.4, and Streptococcus decreased over gestation, whereas Coprococcus increased. In the HLA group; only the abundance of Butyricimonas decreased. At E20, there were no differences in alpha- and beta-diversity, and the abundance of Roseburia was significantly increased in the HLA group. In conclusion, consumption of a HLA diet alters gut microbiota composition, as does pregnancy in rats consuming a LLA diet. In pregnancy, consumption of a HLA diet does not alter gut microbiota composition.

Improvement on metabolic syndrome in high fat diet-induced obese mice through modulation of gut microbiota by sangguayin decoction

ETHNOPHARMACOLOGICAL RELEVANCE

Our previous research found that Sangguayin (SGY) deccoction made by four dietary and medicinal plant components (Leaf of Morus alba L., Root of Pueraria lobata (Willd.) Ohwi., Root of Dioscorea opposita Thunb. and Fruit of Momordica charantia L.) showed significant anti-diabetic effects on db/db mice and high fat diet induced obese mice. Nevertheless, it remained unclear what the role of gut microbiota in the hypoglycaemia effects of SGY.

AIMS OF THE STUDY

This study aimed to examine the beneficial effects of Sangguayin Deccoction against metabolic syndrome and and its regulating role in gut microbiota and hepatic metabolome.

MATERIALS AND METHODS

C57BL/6J mice were divided to a normal chow diet (NCD), high-fat diet (HFD), and high-fat diet with Sangguayin Decoction (HFD-SGY, oral dose of 250 mg/kg/d) for 16 weeks. Next generation sequencing was applied for analyzing the gut microbial community of colonic contents. Further, untargeted metabolomic analysis based on LC-MS was used for determining the changes of hepatic metabolites. Hepatic genes expression were measured by quantitative PCR.

RESULTS

SGY supplement decreased blood glucose level and glucose intolerance. Illumina MiSeq sequencing revealed that SGY increased Verrucomicrobia phylum, resulting in a bloom of Akkermansia, and eventually upregulated the contents of Lachoclostridium and Roseburia. Additionally, dietary SGY decreased bacteria including Faecalibaculum, and Blautia. Moreover, the hepatic lipid metabolism was notably altered by SGY treatment. The oxidation of glutamione metabolism idecreasees, production of poly-unsaturated fatty acid (PUFA) got significant increase in liver tissue. The reversion of PUFA metabolism by SGY may act through PPARα mediated Fads1 and Fads2 gene expression. The altered metabolites in liver showed intimate correlatship with modified genera.

CONCLUSION

Data indicated that SGY reshaped gut microbial structure and improved PUFA metabolism. These functions of SGY may alter hepatic lipid metabolism, conferring preventative effects against high-fat diet induced metabolic syndrome.

Effects of Linoleic Acid on Gut-Derived Bifidobacterium breve DSM 20213: A Transcriptomic Approach

Bacterial production of conjugated linoleic acid (CLA) has recently received great attention because of the potential health benefits of this fatty acid. Linoleic acid (LA) can be converted to CLA by several microorganisms, including bifidobacteria, possibly as a detoxification mechanism to avoid the growth inhibition effect of LA. In the present in vitro study, we investigated the gene expression landscape of the intestinal strain Bifidobacterium breve DSM 20213 when exposed to LA. Transcriptomic analysis using RNA-seq revealed that LA induced a multifactorial stress response in the test strain, including upregulation of genes involved in iron uptake and downregulation of genes involved in sugar and oligopeptide transport. We also observed reduced transcription of genes involved in membrane and pili biosynthesis. The upregulation of iron uptake was not related to any putative ability of LA to chelate Fe²⁺, but was somewhat linked to stress response. Furthermore, we demonstrated that LA increased reactive oxygen species (ROS) production in bacterial cells, activating an oxidative stress response. This response was proved by thioredoxin reductase transcription, and was primarily evident among bacteria cultured in the absence of cysteine. This is the first report of the potential mechanisms involved in bacterial LA transport and stress response in B. breve.

Targeting strategies for chemotherapy-induced peripheral neuropathy: does gut microbiota play a role?

Chemotherapy-induced peripheral neuropathy (CIPN) is a progressive, often irreversible condition that produces severe neurological deficits. Emerging data suggest that chemotherapy also exerts detrimental effects on gut microbiota composition and intestinal permeability, contributing to dysbiosis and inflammation. Compared with other complications associated with chemotherapy, such as diarrhoea and mucositis, CIPN is of particular concern because it is the most common reason for terminating or suspending treatment. However, specific and effective curative treatment strategies are lacking. In this review, we provide an update on current preclinical and clinical understandings about the role of gut microbiota in CIPN. The gut microbiota serves as an intersection between the microbiome-gut-brain and the neuroimmune-endocrine axis, forming a complex network that can directly or indirectly affect key components involved in the manifestations of CIPN. Herein, we discuss several potential mechanisms within the context of the networks and summarize alterations in gut microbiome induced by chemotherapeutic drugs, providing great potential for researchers to target pathways associated with the gut microbiome and overcome CIPN.

Targeting gut microbiota with dietary components on cancer: Effects and potential mechanisms of action

Cancers are common chronic diseases worldwide and cause severe health burdens. There have been ongoing debates on the role of gut microbiota in the prevention and management of cancers, thus, it is worthwhile to pay high attention to the impacts of gut microbiota on several cancers, such as colon, liver, and breast cancers. In addition, it has been reported that gut microbiota may also affect the efficacy of cancer chemotherapy and immunotherapy. Among all the factors that influence gut microbiota, diet is the most influential and modifiable. The prebiotics, dietary fibers, short-chain fatty acids, and other bioactive compounds are all important dietary components to assist the growth of beneficial microbiota in the gut, which can protect against cancers and promote human health. Their beneficial effects can be due to the fermentation of dietary fibers, the metabolism of phytochemicals, the synthesis of estrogens, and interactions with chemotherapies and immunotherapies. In order to provide updated information of the relationships among dietary components, gut microbiota, and cancer, in this review, we summarize the reciprocal interactions between dietary components and gut microbiota, and highlight the impacts of dietary components on several common cancers by targeting gut microbiota, with the potential mechanisms of actions also intensively discussed. As a result, this review can be very helpful for healthy people as well as cancer patients to prevent or manage cancers via dietary factor-mediated regulation of gut microbiota.

Environmental Factors, Gut Microbiota, and Colorectal Cancer Prevention

The substantial burden of colorectal cancer and increasing trend in young adults highlight the importance of lifestyle modification as a complement to screening for colorectal cancer prevention. Several dietary and lifestyle factors have been implicated in the development of colorectal cancer, possibly through the intricate metabolic and inflammatory mechanisms. Likewise, as a key metabolic and immune regulator, the gut microbiota has been recognized to play an important role in colorectal tumorigenesis. Increasing data support that environmental factors are crucial determinants for the gut microbial composition and function, whose alterations induce changes in the host gene expression, metabolic regulation, and local and systemic immune response, thereby influencing cancer development. Here, we review the epidemiologic and mechanistic evidence regarding the links between diet and lifestyle and the gut microbiota in the development of colorectal cancer. We focus on factors for which substantial data support their importance for colorectal cancer and their potential role in the gut microbiota, including overweight and obesity, physical activity, dietary patterns, fiber, red and processed meat, marine omega-3 fatty acid, alcohol, and smoking. We also briefly describe other colorectal cancer-preventive factors for which the links with the gut microbiota have been suggested but remain to be mechanistically characterized, including vitamin D status, dairy consumption, and metformin use. Given limitations in available evidence, we highlight the need for further investigations in the relationship between environmental factors, gut microbiota, and colorectal cancer, which may lead to development and clinical translation of potential microbiota-based strategies for cancer prevention.

In a pilot study, reduced fatty acid desaturase 1 function was associated with nonalcoholic fatty liver disease and response to treatment in children

BACKGROUND

FADS1 gene encodes delta 5 desaturase, a rate-limiting enzyme in the metabolism of n-3 and n-6 polyunsaturated fatty acids (PUFAs). Minor alleles of FADS1 locus polymorphisms are associated with reduced FADS1 expression and intra-hepatic fat accumulation. However, the relationship between FADS1 expression and pediatric nonalcoholic fatty liver disease (NAFLD) risk remains to be explored.

METHODS

We analyzed FADS1 transcription levels and their association with intra-hepatic fat and histology in children, and we performed pathway enrichment analysis on transcriptomic profiles associated with FADS1 polymorphisms. We also evaluated the weight of FADS1 alleles on the response to combined docosahexaenoic acid, choline, and vitamin E (DHA-CHO-VE) treatment.

RESULTS

FADS1 mRNA level was significantly and inversely associated with intra-hepatic fat (p = 0.004), degree of steatosis (p = 0.03), fibrosis (p = 0.05), and NASH (p = 0.008) among pediatric livers. Transcriptomics demonstrated a significant enrichment of a number of pathways strongly related to NAFLD (e.g., liver damage, fibrosis, and hepatic stellate cell activation). Compared to children who are common allele homozygotes, children with FADS1 minor alleles had a greater reduction in steatosis, fibrosis, and NAFLD activity score after DHA-CHO-VE.

CONCLUSION

This study suggests that decreased FADS1 expression may be associated with NAFLD in children but an increased response to DHA-CHO-VE.

Conversion of dietary trans-vaccenic acid to trans11,cis13-conjugated linoleic acid in the rat lactating mammary gland by Fatty Acid Desaturase 3-catalyzed methyl-end Δ13-desaturation

In vitro, the rat Fatty Acid Desaturase 3 (FADS3) gene was shown to code for an enzyme able to catalyze the unexpected Δ13-desaturation of trans-vaccenic acid, producing the trans11,cis13-conjugated linoleic acid (CLA) isomer. FADS3 may therefore be the first methyl-end trans-vaccenate Δ13-desaturase functionally characterized in mammals, but the proof of this concept is so far lacking in vivo. The present study therefore aimed at investigating further the putative in vivo synthesis of trans11,cis13-CLA from dietary trans-vaccenic acid in rodents. During one week of pregnancy and two weeks post-partum, Sprague-Dawley female rats were fed two diets either high (10.0% of fatty acids and 3.8% of energy intake) or low (0.4% of fatty acids and 0.2% of energy intake) in trans-vaccenic acid. The trans11,cis13-CLA was specifically detected, formally identified and reproducibly quantified (0.06% of total fatty acids) in the mammary gland phospholipids of lactating female rats fed the high trans-vaccenic acid-enriched diet. This result was consistent with FADS3 mRNA expression being significantly higher in the lactating mammary gland than in the liver. Although the apparent metabolic conversion is low, this physiological evidence demonstrates the existence of this new pathway described in the lactating mammary gland and establishes the FADS3 enzyme as a reliable mammalian trans-vaccenate Δ13-desaturase in vivo.

Targeting the gut microbiota to influence brain development and function in early life

In the first 2-3 years of life, the gut microbiota of infants quickly becomes diverse and rich. Disruptions in the evolving gut microbiota during this critical developmental period can impact brain development. Communication between the microbiota, gut and brain is driven by hormonal and neural regulation, as well as immune and metabolic pathways, however, our understanding of how the parallel developments that may underlie this communication are limited. In this paper, we review the known associations between the gut microbiota and brain development and brain function in early life, speculate on the potential mechanisms involved in this complex relationship and describe how nutritional intervention can further modulate the microbiota and, ultimately, brain development and function.

Implication of trans-11,trans-13 conjugated linoleic acid in the development of hepatic steatosis

SCOPE

Conjugated linoleic acids are linoleic acid isomers found in the diet that can also be produced through bacterial metabolism of polyunsaturated fatty acids. Our objective was to evaluate the contribution of fatty acid metabolites produced from polyunsaturated fatty acids by the gut microbiota in vivo to regulation of hepatic lipid metabolism and steatosis.

METHODS AND RESULTS

In mice with depleted n-3 polyunsaturated fatty acids, we observed an accumulation of trans-11,trans-13 CLA and cis-9,cis-11 conjugated linoleic acids in the liver tissue that were associated with an increased triglyceride content and expression of lipogenic genes. We used an in vitro model to evaluate the impact of these two conjugated linoleic acids on hepatic lipid metabolism. In HepG2 cells, we observed that only trans-11,trans-13 conjugated linoleic acids recapitulated triglyceride accumulation and increased lipogenic gene expression, which is a phenomenon that may implicate the nuclear factors sterol regulatory element binding protein 1c (SREBP-1c) and carbohydrate-responsive element-binding protein (ChREBP).

CONCLUSION

The trans-11,trans-13 conjugated linoleic acids can stimulate hepatic lipogenesis, which supports the conclusion that gut microbiota and related metabolites should be considered in the treatment of non-alcoholic liver disease.

Diet and microbiota linked in health and disease

Diet has shaped microbiota profiles through human evolution.

Marine ω-3 polyunsaturated fatty acid intake and survival after colorectal cancer diagnosis

OBJECTIVE

Experimental evidence supports an antineoplastic activity of marine ω-3 polyunsaturated fatty acids (ω-3 PUFAs; including eicosapentaenoic acid, docosahexaenoic acid and docosapentaenoic acid). However, the influence of ω-3 PUFAs on colorectal cancer (CRC) survival is unknown.

DESIGN

Within the Nurses' Health Study and Health Professionals Follow-up Study, we prospectively studied CRC-specific and overall mortality in a cohort of 1659 patients with CRC according to intake of marine ω-3 PUFAs and its change after diagnosis.

RESULTS

Higher intake of marine ω-3 PUFAs after CRC diagnosis was associated with lower risk of CRC-specific mortality (p for trend=0.03). Compared with patients who consumed <0.10 g/day of marine ω-3 PUFAs, those consuming at least 0.30 g/day had an adjusted HR for CRC-specific mortality of 0.59 (95% CI 0.35 to 1.01). Patients who increased their marine ω-3 PUFA intake by at least 0.15 g/day after diagnosis had an HR of 0.30 (95% CI 0.14 to 0.64, p for trend <0.001) for CRC deaths, compared with those who did not change or changed their intake by <0.02 g/day. No association was found between postdiagnostic marine ω-3 PUFA intake and all-cause mortality (p for trend=0.47).

CONCLUSIONS

High marine ω-3 PUFA intake after CRC diagnosis is associated with lower risk of CRC-specific mortality. Increasing consumption of marine ω-3 PUFAs after diagnosis may confer additional benefits to patients with CRC.

Diet, Gut Microbiota, and Colorectal Cancer Prevention: A Review of Potential Mechanisms and Promising Targets for Future Research

Diet plays an important role in the development of colorectal cancer. Emerging data have implicated the gut microbiota in colorectal cancer. Diet is a major determinant for the gut microbial structure and function. Therefore, it has been hypothesized that alterations in gut microbes and their metabolites may contribute to the influence of diet on the development of colorectal cancer. We review several major dietary factors that have been linked to gut microbiota and colorectal cancer, including major dietary patterns, fiber, red meat and sulfur, and obesity. Most of the epidemiologic evidence derives from cross-sectional or short-term, highly controlled feeding studies that are limited in size. Therefore, high-quality large-scale prospective studies with dietary data collected over the life course and comprehensive gut microbial composition and function assessed well prior to neoplastic occurrence are critically needed to identify microbiome-based interventions that may complement or optimize current diet-based strategies for colorectal cancer prevention and management.

Probiotics: a proactive approach to health. A symposium report

This report summarises talks given at the 8th International Yakult Symposium, held on 23-24 April 2015 in Berlin. Two presentations explored different aspects of probiotic intervention: the small intestine as a probiotic target and inclusion of probiotics into integrative approaches to gastroenterology. Probiotic recommendations in gastroenterology guidelines and current data on probiotic efficacy in paediatric patients were reviewed. Updates were given on probiotic and gut microbiota research in obesity and obesity-related diseases, the gut-brain axis and development of psychobiotics, and the protective effects of equol-producing strains for prostate cancer. Recent studies were presented on probiotic benefit for antibiotic-associated diarrhoea and people with HIV, as well as protection against the adverse effects of a short-term high-fat diet. Aspects of probiotic mechanisms of activity were discussed, including immunomodulatory mechanisms and metabolite effects, the anti-inflammatory properties of Faecalibacterium prausnitzii, the relationship between periodontitis, microbial production of butyrate in the oral cavity and ageing, and the pathogenic mechanisms of Campylobacter. Finally, an insight was given on a recent expert meeting, which re-examined the probiotic definition, advised on the appropriate use and scope of the term and outlined different probiotic categories and the prevalence of different mechanisms of activity.

Pathways and functions of gut microbiota metabolism impacting host physiology

The bacterial populations in the human intestine impact host physiological functions through their metabolic activity. In addition to performing essential catabolic and biotransformation functions, the gut microbiota produces bioactive small molecules that mediate interactions with the host and contribute to the neurohumoral axes connecting the intestine with other parts of the body. This review discusses recent progress in characterizing the metabolic products of the gut microbiota and their biological functions, focusing on studies that investigate the responsible bacterial pathways and cognate host receptors. Several key areas are highlighted for future development: context-based analysis targeting pathways; integration of analytical approaches; metabolic modeling; and synthetic systems for in vivo manipulation of microbiota functions. Prospectively, these developments could further our mechanistic understanding of host-microbiota interactions.