Interplay between microbial-derived GABA and host GABA receptor signaling collectively influence the tumorigenic function of GABA in colon cancer.

Although classically recognized as a neurotransmitter, gamma aminobutyric acid (GABA) has also been identified in colonic tumors. Moreover, the gut microbiome represents another potential source of GABA. Both GABAA and GABAB receptors have been implicated in contributing to the effects of GABA in colorectal cancer, with both pro- and anti-tumorigenic functions identified. However, their subunit composition is often overlooked. Studies to date have not addressed whether the GABA-producing potential of the microbiome changes over the course of colon tumor development or whether receptor subunit expression patterns are altered in colon cancer. Therefore, we investigated the clusters of orthologous group frequencies of glutamate decarboxylase (GAD) in feces from two murine models of colon cancer and found that the frequency of microbial GAD was significantly decreased early in the tumorigenic process. We also determined that microbial-derived GABA inhibited proliferation of colon cancer cells in vitro and that this effect of GABA on SW480 cells involved both GABAA and GABAB receptors. GABA also inhibited prostaglandin E2 (PGE2)-induced proliferation and interleukin-6 (IL-6) expression in these cells. Gene expression correlations were assessed using the "Cancer Exploration" suite of the TIMER2.0 web tool and identified that GABA receptor subunits were differentially expressed in human colon cancer. Moreover, GABAA receptor subunits were predominantly positively associated with PGE2 synthase, cyclooxygenase-2 and IL-6. Collectively, these data demonstrate decreased potential of the microbiome to produce GABA during tumorigenesis, a novel anti-tumorigenic pathway for GABA, and that GABA receptor subunit expression adds a further layer of complexity to GABAergic signaling in colon cancer.

Microbial metabolites as modulators of host physiology.

The gut microbiota is increasingly recognised as a key player in influencing human health and changes in the gut microbiota have been strongly linked with many non-communicable conditions in humans such as type 2 diabetes, obesity and cardiovascular disease. However, characterising the molecular mechanisms that underpin these associations remains an important challenge for researchers. The gut microbiota is a complex microbial community that acts as a metabolic interface to transform ingested food (and other xenobiotics) into metabolites that are detected in the host faeces, urine and blood. Many of these metabolites are only produced by microbes and there is accumulating evidence to suggest that these microbe-specific metabolites do act as effectors to influence human physiology. For example, the gut microbiota can digest dietary complex polysaccharides (such as fibre) into short-chain fatty acids (SCFA) such as acetate, propionate and butyrate that have a pervasive role in host physiology from nutrition to immune function. In this review we will outline our current understanding of the role of some key microbial metabolites, such as SCFA, indole and bile acids, in human health. Whilst many studies linking microbial metabolites with human health are correlative we will try to highlight examples where genetic evidence is available to support a specific role for a microbial metabolite in host health and well-being.

Ultra-Endurance triathlon competition shifts fecal metabolome independent of changes to microbiome composition.

Understanding changes to gut microbiota composition and metabolic output in response to acute exercise may be necessary for understanding the mechanisms mediating the long-term health and performance benefits of exercise. Our primary objective was to characterize acute changes in the fecal microbiome and metabolome following participation in an ultra-endurance (3.9 km swim, 180.2 km bike, 42.2 km run) triathlon. An exploratory aim was to determine associations between athlete-specific factors [race performance (i.e., completion time) and lifetime years of endurance training] with pre-race gut microbiota and metabolite profiles. Stool samples from 12 triathletes (9 males/3 females; 43 ± 14 yr, 23 ± 2 kg/m2) were collected ≤48 h before and the first bowel movement following race completion. Intra- and inter-individual diversity of bacterial species and individual bacterial taxa were unaltered following race completion (P > 0.05). However, significant reductions (P < 0.05) in free and secondary bile acids [deoxycholic acid (DCA), 12-keto-lithocholic acid (12-ketoLCA)] and short-chain fatty acids (butyric and pivalic acids), and significant increases (P < 0.05) in long-chain fatty acids (oleic and palmitoleic acids) were observed. Exploratory analyses revealed several associations between pre-race bacterial taxa and fecal metabolites with race performance and lifetime history of endurance training (P < 0.05). These findings suggest that 1) acute ultra-endurance exercise shifts microbial metabolism independent of changes to community composition and 2) athlete performance level and training history relate to resting-state gut microbial ecology.NEW & NOTEWORTHY This is the first study to characterize acute changes in gut microbial ecology and metabolism following an ultra-endurance triathlon. We demonstrate changes in gut microbial community function, but not structure, as well as several associations between gut microbiome and fecal metabolome characteristics with race completion time and lifetime history of endurance training. These data add to a small but growing body of literature seeking to characterize the acute and chronic effects of exercise on the gut microbial ecosystem.

Lipidomic Analysis Reveals Differences in Bacteroides Species Driven Largely by Plasmalogens, Glycerophosphoinositols and Certain Sphingolipids.

There has been increasing interest in bacterial lipids in recent years due, in part, to their emerging role as molecular signalling molecules. Bacteroides thetaiotaomicron is an important member of the mammalian gut microbiota that has been shown to produce sphingolipids (SP) that pass through the gut epithelial barrier to impact host SP metabolism and signal into host inflammation pathways. B. thetaiotaomicron also produces a novel family of N-acyl amines (called glycine lipids) that are potent ligands of host Toll-like receptor 2 (TLR2). Here, we specifically examine the lipid signatures of four species of gut-associated Bacteroides. In total we identify 170 different lipids, and we report that the range and diversity of Bacteroides lipids is species specific. Multivariate analysis reveals that the differences in the lipid signatures are largely driven by the presence and absence of plasmalogens, glycerophosphoinositols and certain SP. Moreover, we show that, in B. thetaiotaomicron, mutations altering either SP or glycine lipid biosynthesis result in significant changes in the levels of other lipids, suggesting the existence of a compensatory mechanisms required to maintain the functionality of the bacterial membrane.

Characterization of the mechanism of bile salt hydrolase substrate specificity by experimental and computational analyses.

Bile salt hydrolases (BSHs) are currently being investigated as target enzymes for metabolic regulators in humans and as growth promoters in farm animals. Understanding structural features underlying substrate specificity is necessary for inhibitor design. Here, we used a multidisciplinary workflow including mass spectrometry, mutagenesis, molecular dynamic simulations, machine learning, and crystallography to demonstrate substrate specificity in Lactobacillus salivarius BSH, the most abundant enzyme in human and farm animal intestines. We show the preference of substrates with a taurine head and a dehydroxylated sterol ring for hydrolysis. A regression model that correlates the relative rates of hydrolysis of various substrates in various enzyme mutants with the residue-substrate interaction energies guided the identification of structural determinants of substrate binding and specificity. In addition, we found T208 from another BSH protomer regulating the hydrolysis. The designed workflow can be used for fast and comprehensive characterization of enzymes with a broad range of substrates.

Membrane lipids from gut microbiome-associated bacteria as structural and signalling molecules.

Bacteria produce an array of diverse, dynamic and often complex lipid structures, some of which function beyond their typical role in membrane structure. The model organism, E. coli, has three major membrane lipids, which are glycerophosphoglycerol (phosphatidylglycerol), glycerophosphoethanolamine (phosphatidylethanolamine) and cardiolipin. However, it is now appreciated that some bacteria have the capacity to synthesize a range of lipids, including glycerophosphocholines, glycerophosphoinositols, 'phosphorous-free' N-acyl amines, sphingolipids and plasmalogens. In recent years, some of these bacterial lipids have emerged as influential contributors to the microbe-host molecular dialogue. This review outlines our current knowledge of bacterial lipid diversity, with a focus on the membrane lipids of microbiome-associated bacteria that have documented roles as signalling molecules.

Chronic consumption of probiotics, oats, and apples has differential effects on postprandial bile acid profile and cardiometabolic disease risk markers compared with an isocaloric control (cornflakes): a randomized trial.

BACKGROUND: Dietary components that impact the gut microbiota may beneficially affect cardiometabolic health, possibly by altered bile acid metabolism. However, impacts of these foods on postprandial bile acids, gut microbiota, and cardiometabolic risk markers are unclear. OBJECTIVES: The aim of this study was to determine the chronic effects of probiotics, oats, and apples on postprandial bile acids, gut microbiota, and cardiometabolic health biomarkers. METHODS: Using an acute within chronic parallel design, 61 volunteers (mean ± SD: age 52 ± 12 y; BMI 24.8 ± 3.4 kg/m2) were randomly assigned to consume 40 g cornflakes (control), 40 g oats or 2 Renetta Canada apples each with 2 placebo capsules per day or 40 g cornflakes with 2 Lactobacillus reuteri capsules (>5 × 109 CFU) per day, for 8 wk. Fasting and postprandial serum/plasma bile acids and cardiometabolic health biomarkers, fecal bile acids, and gut microbiota composition were determined. RESULTS: At week 0, oats and apples significantly decreased postprandial serum insulin [area under the curve (AUC): 25.6 (17.4, 33.8) and 23.4 (15.4, 31.4) vs. 42.0 (33.7, 50.2) pmol/L × min and incremental AUC (iAUC): 17.8 (11.6, 24.0) and 13.7 (7.7, 19.8) vs. 29.6 (23.3, 35.8) pmol/L × min] and C-peptide responses [AUC: 599 (514, 684) and 550 (467, 632) vs. 750 (665, 835) ng/mL × min], whereas non-esterified fatty acids were increased [AUC 135 (117, 153) vs. 86.3 (67.9, 105) and iAUC 96.2 (78.8, 114) vs. 60 (42.1, 77.9) mmol/L × min] after the apples vs. control (P ≤ 0.05). Postprandial unconjugated [AUC: predicted means (95% CI) 1469 (1101, 1837) vs. 363 (-28, 754) µmol/L × min and iAUC: 923 (682, 1165) vs. 22.0 (-235, 279) µmol/L × min)] and hydrophobic [iAUC: 1210 (911, 1510) vs. 487 (168, 806) µmol/L × min] bile acid responses were increased after 8 wk probiotic intervention vs. control (P ≤ 0.049). None of the interventions modulated the gut microbiota. CONCLUSIONS: These results support beneficial effects of apples and oats on postprandial glycemia and the ability of the probiotic Lactobacillus reuteri to modulate postprandial plasma bile acid profiles compared with control (cornflakes), with no relationship evident between circulating bile acids and cardiometabolic health biomarkers.

Dietary-Induced Bacterial Metabolites Reduce Inflammation and Inflammation-Associated Cancer via Vitamin D Pathway.

Environmental factors, including westernised diets and alterations to the gut microbiota, are considered risk factors for inflammatory bowel diseases (IBD). The mechanisms underpinning diet-microbiota-host interactions are poorly understood in IBD. We present evidence that feeding a lard-based high-fat (HF) diet can protect mice from developing DSS-induced acute and chronic colitis and colitis-associated cancer (CAC) by significantly reducing tumour burden/incidence, immune cell infiltration, cytokine profile, and cell proliferation. We show that HF protection was associated with increased gut microbial diversity and a significant reduction in Proteobacteria and an increase in Firmicutes and Clostridium cluster XIVa abundance. Microbial functionality was modulated in terms of signalling fatty acids and bile acids (BA). Faecal secondary BAs were significantly induced to include moieties that can activate the vitamin D receptor (VDR), a nuclear receptor richly represented in the intestine and colon. Indeed, colonic VDR downstream target genes were upregulated in HF-fed mice and in combinatorial lipid-BAs-treated intestinal HT29 epithelial cells. Collectively, our data indicate that HF diet protects against colitis and CAC risk through gut microbiota and BA metabolites modulating vitamin D targeting pathways. Our data highlights the complex relationship between dietary fat-induced alterations of microbiota-host interactions in IBD/CAC pathophysiology.

Heterosubstituted Derivatives of PtPFPP for O2 Sensing and Cell Analysis: Structure-Activity Relationships.

Biological applications of phosphorescent probes for sensing molecular oxygen (O2) and bioimaging have gained popularity, but their choice is rather limited. We describe a family of new heterosubstituted phosphorescent bioprobes based on the Pt(II)-tetrakis(pentafluorophenyl)porphyrin (PtPFPP) dye. The probes are produced by simple click modification of its para-fluorine atoms with thiols, such as 1/2-thio-glucose, thio-poly(ethylene glycol) (PEG), or cysteamine. The probes were designed to have one cell-targeting moiety and three polar moieties forming a hydrophilic shell. Their chemical synthesis and purification were optimized to produce high reaction yields and easy scale-up. The ability to perform as cell-permeable or -impermeable probes was tuned by the polarity and molecular charge of the bioconjugate. The new PtPFPP derivatives were characterized for their spectral properties and cell-penetrating ability in the experiments with mammalian cell cultures, using a time-resolved fluorescence reader and PLIM imaging detection. Structure-activity relationships were established. Thus, the tri- and tetra-PEGylated structures showed low cell internalization allowing their use as extracellular probes, while cysteamine derivatives performed as efficient intracellular probes. No significant cytotoxicity was observed for all of the probes under the experimental conditions used.

Bile acids, bioactive signalling molecules in interoceptive gut-to-brain communication.

Aside from facilitating solubilisation and absorption of dietary lipids and lipid-soluble vitamins, amphipathic bile acids (BAs) also act as bioactive signalling molecules. A plethora of conjugated or unconjugated primary and bacterially modified secondary BA moieties have been identified, with significant divergence between species. These molecules are excreted into the external environment of the intestinal lumen, yet nuclear and membrane receptors that are sensitive to BAs are expressed internally in the liver, intestinal and neural tissues, amongst others. The diversity of BAs and receptors underpins the multitude of distinct bioactive functions attributed to BAs, but also hampers elucidation of the physiological mechanisms underpinning these actions. In this Topical Review, we have considered the potential of BAs as cross-barrier signalling molecules that contribute to interoceptive pathways informing the central nervous system of environmental changes in the gut lumen. Activation of BAs on FGF19 -secreting enterocytes, enteroendocrine cells coupled to sensory nerves or intestinal immune cells would facilitate indirect signalling, whereas direct activation of BA receptors in the brain is likely to occur primarily under pathophysiological conditions when concentrations of BAs are elevated.

Concentrations of Fecal Bile Acids in Participants with Functional Gut Disorders and Healthy Controls.

Bile acids are metabolites involved in nutrient absorption and signaling with levels influenced by dietary intake, metabolic processes, and the gut microbiome. We aimed to quantify 23 bile acids in fecal samples to ascertain if concentrations differed between healthy participants and those with functional gut disorders. Fecal bile acids were measured using liquid chromatography-mass spectrometry (LC-MS) in the COMFORT (The Christchurch IBS cohort to investigate mechanisms for gut relief and improved transit) cohort of 250 participants with Rome IV IBS (IBS-constipation (C), IBS-diarrhea (D), IBS-mixed (M)), functional gut disorders (functional constipation (FC), functional diarrhea (FD)) and healthy controls (FC n = 35, FD n = 13, IBS-C n = 24, IBS-D n = 52, IBS-M n = 29, and control n = 97). Dietary information was recorded to ascertain three-day dietary intake before fecal samples were collected. Fecal bile acid concentrations, predominantly primary bile acids, were significantly different between all functional gut disorder participants and healthy controls (CDCA p = 0.011, CA p = 0.003) and between constipation (FC + IBS-C) and diarrhea (FD + IBS-D) groups (CDCA p = 0.001, CA p = 0.0002). Comparison of bile acids between all functional groups showed four metabolites were significantly different, although analysis of combined groups (FC + IBS-C vs. FD + IBS-D) showed that 10 metabolites were significantly different. The bile acid profiles of FD individuals were similar to those with IBS-D, and likewise, those with FC were similar to IBS-C. Individuals with a diarrhea phenotype (FD + IBS-D) had higher concentrations of bile acids compared to those with constipation (FC + IBS-C). Bile acid metabolites distinguish between individuals with functional gut disorders and healthy controls but are similar in constipation (or diarrhea) whether classified as IBS or not.

Dietary Fibre Modulates the Gut Microbiota.

Dietary fibre has long been established as a nutritionally important, health-promoting food ingredient. Modern dietary practices have seen a significant reduction in fibre consumption compared with ancestral habits. This is related to the emergence of low-fibre "Western diets" associated with industrialised nations, and is linked to an increased prevalence of gut diseases such as inflammatory bowel disease, obesity, type II diabetes mellitus and metabolic syndrome. The characteristic metabolic parameters of these individuals include insulin resistance, high fasting and postprandial glucose, as well as high plasma cholesterol, low-density lipoprotein (LDL) and high-density lipoprotein (HDL). Gut microbial signatures are also altered significantly in these cohorts, suggesting a causative link between diet, microbes and disease. Dietary fibre consumption has been hypothesised to reverse these changes through microbial fermentation and the subsequent production of short-chain fatty acids (SCFA), which improves glucose and lipid parameters in individuals who harbour diseases associated with dysfunctional metabolism. This review article examines how different types of dietary fibre can differentially alter glucose and lipid metabolism through changes in gut microbiota composition and function.

In vitro-in vivo Validation of Stimulatory Effect of Oat Ingredients on Lactobacilli.

The prebiotic activity of a commercially available oat product and a novel oat ingredient, at similar ß-glucan loads, was tested using a validated in vitro gut model (M-SHIME®). The novel oat ingredient was tested further at lower ß-glucan loads in vitro, while the commercially available oat product was assessed in a randomised, single-blind, placebo-controlled, and cross-over human study. Both approaches focused on healthy individuals with mild hypercholesterolemia. In vitro analysis revealed that both oat products strongly stimulated Lactobacillaceae and Bifidobacteriaceae in the intestinal lumen and the simulated mucus layer, and corresponded with enhanced levels of acetate and lactate with cross-feeding interactions leading to an associated increase in propionate and butyrate production. The in vitro prebiotic activity of the novel oat ingredient remained at lower ß-glucan levels, indicating the prebiotic potential of the novel oat product. Finally, the stimulation of Lactobacillus spp. was confirmed during the in vivo trial, where lactobacilli abundance significantly increased in the overall population at the end of the intervention period with the commercially available oat product relative to the control product, indicating the power of in vitro gut models in predicting in vivo response of the microbial community to dietary modulation.

Genotypic and phenotypic characterization of food-associated Lactobacillus plantarum isolates for potential probiotic activities.

Lactic acid bacterium, Lactobacillus plantarum, has been applied, for centuries, for food and drink fermentations. Given the benefits associated with fermented products, Lb. plantarum strains have captured considerable industrial and scientific interest, so that they are included as fundamental components of functional foods. Indeed, some strains are marketed as probiotics. In the present study, food- and gut-associated Lb. plantarum isolates were genetically characterized by multilocus sequence typing (MLST) and phenotypically characterized for properties that could influence their probiotic potential. MLST and phylogenetic analysis stratified 22 Lb. plantarum isolates into six lineages. The isolates were further phenotypically characterized by an in vitro assay to assess their potential gut community influence via a limited number of assays including acidification activity, strain displacement activity and their intrinsic range of antibiotic resistance. Given growing recognition of the benefits of fermented foods, and the prevalence of Lb. plantarum in these applications, this study highlights analysis of a subset of preliminary important strain-specific features. These features are of interest to all stakeholders, to inform isolate comparison and selection for current functional food associations, and that can serve as a basis for future strain and food-microbe fermentation product development.

Impact of phospholipid digests and bile acid pool variations on the crystallization of atazanavir from supersaturated solutions.

Oral delivery of poorly water-soluble drugs (PWSDs), which predominate the development pipeline, poses significant challenges. Weakly basic compounds, such as atazanavir, represent a critical class of PWSDs as even the administration of the crystalline solid may invoke supersaturation during gastric-intestinal transfer. The absorption advantage afforded by this supersaturated state can be offset by inherent metastability and a tendency to revert to the lower energy crystalline state. Therefore, it is important to understand the physiological factors that can affect crystallization to improve in vitro-in vivo predictiveness and to regulate inter-individual responses. The first aim of this study was to elucidate the influence of lyso-phosphatidylcholine (lyso-PC) and sodium oleate on crystallization, as the products of phosphatidylcholine (PC) hydrolysis and the major lipid components of human intestinal fluid (HIF) and updated fasted state simulated intestinal fluid version 3 (FaSSIF-V3). Secondly, as an individual's bile acid pool is unique, dynamic and related to gut microbiome community structure, it was of interest to investigate the impact of bile acid pool variations on crystallization from supersaturated solutions. To study the effect of PC hydrolysis, media with 2.8 mM sodium glycocholate (GCA) and sodium taurocholate (TCA) (1:1) but varying concentrations of PC, lyso-PC or sodium oleate were prepared. To investigate the influence of inter-individual variations in intestinal bile acid pool size and composition, media simulating the profiles of six healthy Western volunteers were prepared based on previously published data. The crystalline and amorphous solubility of atazanavir, a weakly basic antiretroviral drug, was firstly determined in these media. Nucleation-induction time experiments were then performed at an equivalent extent of supersaturation in each medium (corresponding to the amorphous solubility). At a constant level of GCA/TCA, increasing concentrations of both PC and lyso-PC accelerated crystallization onset; however, this was at least 2-fold more pronounced with lyso-PC at a given molar concentration. The addition of sodium oleate was also observed to induce crystallization. Interestingly, substituting GCA/TCA with the bile salt fraction of other biorelevant media partially circumvented the crystallization-inducing effect of phospholipids and their digests. The presence of dihydroxy bile salts was found to be particularly significant in decelerating the crystallization process. Nucleation-induction times in simulated volunteer pools were found to be dependent upon bile salt concentration, with higher bile salt levels generally prolonging supersaturation. Differences of up to 6-fold were observed. This study demonstrates that the choice of biorelevant medium used to evaluate supersaturating formulations can influence the observed crystallization kinetics. While the presence of lyso-PC and sodium oleate in FaSSIF-V3 medium is more physiologically relevant, further attention should be paid to the bile salt fraction when designing a biorelevant medium for supersaturating formulations. In vivo, inter-individual differences in the amount and types of bile acids and phospholipids present may influence the behaviour of supersaturating formulations.

Evaluation of bile salt hydrolase inhibitor efficacy for modulating host bile profile and physiology using a chicken model system.

Gut microbial enzymes, bile salt hydrolases (BSHs) are the gateway enzymes for bile acid (BA) modification in the gut. This activity is a promising target for developing innovative non-antibiotic growth promoters to enhance animal production and health. Compelling evidence has shown that inhibition of BSH activity should enhance weight gain by altering the BA pool, host signalling and lipid metabolism. We recently identified a panel of promising BSH inhibitors. Here, we address the potential of them as alternative, effective, non-antibiotic feed additives, for commercial application, to promote animal growth using a chicken model. In this study, the in vivo efficacy of three BSH inhibitors (caffeic acid phenethylester, riboflavin, carnosic acid) were evaluated. 7-day old chicks (10 birds/group) were either untreated or they received one of the specific BSH inhibitors (25 mg/kg body weight) via oral gavage for 17 days. The chicks in treatment groups consistently displayed higher body weight gain than the untreated chicks. Metabolomic analysis demonstrated that BSH inhibitor treatment led to significant changes in both circulating and intestinal BA signatures in support of blunted intestinal BSH activity. Consistent with this finding, liver and intestinal tissue RNA-Seq analysis showed that carnosic acid treatment significantly altered expression of genes involved in lipid and bile acid metabolism. Taken together, this study validates microbial BSH activity inhibition as an alternative target and strategy to antibiotic treatment for animal growth promotion.

Beneficial bile acid metabolism from Lactobacillus plantarum of food origin.

Bile acid (BA) signatures are altered in many disease states. BA metabolism is an important microbial function to assist gut colonization and persistence, as well as microbial survival during gastro intestinal (GI) transit and it is an important criteria for potential probiotic bacteria. Microbes that express bile salt hydrolase (BSH), gateway BA modifying enzymes, are considered to have an advantage in the gut. This property is reported as selectively limited to gut-associated microbes. Food-associated microbes have the potential to confer health benefits to the human consumer. Here, we report that food associated Lactobacillus plantarum strains are capable of BA metabolism, they can withstand BA associated stress and propagate, a recognised important characteristic for GIT survival. Furthermore, we report that these food associated Lactobacillus plantarum strains have the selective ability to alter BA signatures in favour of receptor activation that would be beneficial to humans. Indeed, all of the strains examined showed a clear preference to alter human glycol-conjugated BAs, although clear strain-dependent modifications were also evident. This study demonstrates that BA metabolism by food-borne non-pathogenic bacteria is beneficial to both microbe and man and it identifies an evolutionary-conserved characteristic, previously considered unique to gut residents, among food-associated non-pathogenic isolates.

Nigral overexpression of α-synuclein in a rat Parkinson's disease model indicates alterations in the enteric nervous system and the gut microbiome.

BACKGROUND: A hallmark feature of Parkinson's disease (PD) is the build-up of α-synuclein protein aggregates throughout the brain; however α-synuclein is also expressed in enteric neurons. Gastrointestinal (GI) symptoms and pathology are frequently reported in PD, including constipation, increased intestinal permeability, glial pathology, and alterations to gut microbiota composition. α-synuclein can propagate through neuronal systems but the site of origin of α-synuclein pathology, whether it be the gut or the brain, is still unknown. Physical exercise is associated with alleviating symptoms of PD and with altering the composition of the gut microbiota. METHODS: This study investigated the effects of bilateral nigral injection of adeno-associated virus (AAV)-α-synuclein on enteric neurons, glia and neurochemistry, the gut microbiome, and bile acid metabolism in rats, some of whom were exposed to voluntary exercise. KEY RESULTS: Nigral overexpression of α-synuclein resulted in significant neuronal loss in the ileal submucosal plexus with no change in enteric glia. In contrast, the myenteric plexus showed a significant increase in glial expression, while neuronal numbers were maintained. Concomitant alterations were observed in the gut microbiome and related bile acid metabolism. Voluntary running protected against neuronal loss, increased enteric glial expression, and modified gut microbiome composition in the brain-injected AAV-α-synuclein PD model. CONCLUSIONS AND INFERENCES: These results show that developing nigral α-synuclein pathology in this PD model exerts significant alterations on the enteric nervous system (ENS) and gut microbiome that are receptive to modification by exercise. This highlights brain to gut communication as an important mechanism in PD pathology.

The Cholesterol-Lowering Effect of Oats and Oat Beta Glucan: Modes of Action and Potential Role of Bile Acids and the Microbiome.

Consumption of sufficient quantities of oat products has been shown to reduce host cholesterol and thereby modulate cardiovascular disease risk. The effects are proposed to be mediated by the gel-forming properties of oat ß-glucan which modulates host bile acid and cholesterol metabolism and potentially removes intestinal cholesterol for excretion. However, the gut microbiota has emerged as a major factor regulating cholesterol metabolism in the host. Oat ß-glucan has been shown to modulate the gut microbiota, particularly those bacterial species that influence host bile acid metabolism and production of short chain fatty acids, factors which are regulators of host cholesterol homeostasis. Given a significant role for the gut microbiota in cholesterol metabolism it is likely that the effects of oat ß-glucan on the host are multifaceted and involve regulation of microbe-host interactions at the gut interface. Here we consider the potential for oat ß-glucan to influence microbial populations in the gut with potential consequences for bile acid metabolism, reverse cholesterol transport (RCT), short-chain fatty acid (SCFA) production, bacterial metabolism of cholesterol and microbe-host signaling.

Microbial bile salt hydrolases mediate the efficacy of faecal microbiota transplant in the treatment of recurrent Clostridioides difficile infection.

OBJECTIVE: Faecal microbiota transplant (FMT) effectively treats recurrent Clostridioides difficile infection (rCDI), but its mechanisms of action remain poorly defined. Certain bile acids affect C. difficile germination or vegetative growth. We hypothesised that loss of gut microbiota-derived bile salt hydrolases (BSHs) predisposes to CDI by perturbing gut bile metabolism, and that BSH restitution is a key mediator of FMT's efficacy in treating the condition. DESIGN: Using stool collected from patients and donors pre-FMT/post-FMT for rCDI, we performed 16S rRNA gene sequencing, ultra performance liquid chromatography mass spectrometry (UPLC-MS) bile acid profiling, BSH activity measurement, and qPCR of bsh/baiCD genes involved in bile metabolism. Human data were validated in C. difficile batch cultures and a C57BL/6 mouse model of rCDI. RESULTS: From metataxonomics, pre-FMT stool demonstrated a reduced proportion of BSH-producing bacterial species compared with donors/post-FMT. Pre-FMT stool was enriched in taurocholic acid (TCA, a potent C. difficile germinant); TCA levels negatively correlated with key bacterial genera containing BSH-producing organisms. Post-FMT samples demonstrated recovered BSH activity and bsh/baiCD gene copy number compared with pretreatment (p<0.05). In batch cultures, supernatant from engineered bsh-expressing E. coli and naturally BSH-producing organisms (Bacteroides ovatus, Collinsella aerofaciens, Bacteroides vulgatus and Blautia obeum) reduced TCA-mediated C. difficile germination relative to culture supernatant of wild-type (BSH-negative) E. coli. C. difficile total viable counts were ~70% reduced in an rCDI mouse model after administration of E. coli expressing highly active BSH relative to mice administered BSH-negative E. coli (p<0.05). CONCLUSION: Restoration of gut BSH functionality contributes to the efficacy of FMT in treating rCDI.