Microbiology Meets Big Data: The Case of Gut Microbiota-Derived Trimethylamine

Electrophoretic Determination of Trimethylamine (TMA) in Biological Samples as a Novel Potential Biomarker of Cardiovascular Diseases Methodological Approach

In competitive athletes, the differential diagnosis between nonpathological changes in cardiac morphology associated with training (commonly referred to as “athlete’s heart”) and certain cardiac diseases with the potential for sudden death is an important and not uncommon clinical problem. The use of noninvasive, fast, and cheap analytical techniques can help in making diagnostic differentiation and planning subsequent clinical strategies. Recent studies have demonstrated the role of gut microbiota and their metabolites in the onset and the development of cardiovascular diseases. Trimethylamine (TMA), a gut bacteria metabolite consisting of carnitine and choline, has recently emerged as a potentially toxic molecule to the circulatory system. The present work aims to develop a simple and cost-effective capillary electrophoresis-based method for the determination of TMA in biological samples. Analytical characteristics of the proposed method were evaluated through the study of its linearity (R² > 0.9950) and the limit of detection and quantification (LOD = 1.2 µg/mL; LOQ = 3.6 µg/mL). The method shows great potential in high-throughput screening applications for TMA analysis in biological samples as a novel potential biomarker of cardiovascular diseases. The proposed electrophoretic method for the determination of TMA in biological samples from patients with cardiac disease is now in progress.

Fecal Microbiome Composition Does Not Predict Diet-Induced TMAO Production in Healthy Adults

Background Trimethylamine-N-oxide (TMAO) is a small molecule derived from the metabolism of dietary nutrients by gut microbes and contributes to cardiovascular disease. Plasma TMAO increases following consumption of red meat. This metabolic change is thought to be partly because of the expansion of gut microbes able to use nutrients abundant in red meat. Methods and Results We used data from a randomized crossover study to estimate the degree to which TMAO can be estimated from fecal microbial composition. Healthy participants received a series of 3 diets that differed in protein source (red meat, white meat, and non-meat), and fecal, plasma, and urine samples were collected following 4 weeks of exposure to each diet. TMAO was quantitated in plasma and urine, while shotgun metagenomic sequencing was performed on fecal DNA. While the cai gene cluster was weakly correlated with plasma TMAO (rho=0.17, P=0.0007), elastic net models of TMAO were not improved by abundances of bacterial genes known to contribute to TMAO synthesis. A global analysis of all taxonomic groups, genes, and gene families found no meaningful predictors of TMAO. We postulated that abundances of known genes related to TMAO production do not predict bacterial metabolism, and we measured choline- and carnitine-trimethylamine lyase activity during fecal culture. Trimethylamine lyase genes were only weakly correlated with the activity of the enzymes they encode. Conclusions Fecal microbiome composition does not predict systemic TMAO because, in this case, gene copy number does not predict bacterial metabolic activity. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT01427855.

Plasma TMAO increase after healthy diets: results from 2 randomized controlled trials with dietary fish, polyphenols, and whole-grain cereals

BACKGROUND

Plasma trimethylamine N-oxide (TMAO) has drawn much attention as a marker of several chronic diseases. Data on the relation between diet and TMAO are discordant and few human intervention studies have assessed causality for this association.

OBJECTIVES

We aimed to evaluate the effects on plasma TMAO of diets based on foods rich in polyphenols (PP) and/or long-chain n-3 fatty acids (LCn3) or whole-grain cereals (WGCs), in individuals at high cardiometabolic risk.

METHODS

An ancillary study was performed within 2 randomized controlled trials, aimed at evaluating the medium-term effects on cardiometabolic risk factors of diets naturally rich in PP and/or LCn3 (Etherpaths Project) or WGCs (HealthGrain Project).

RESULTS

In the Etherpaths study (n = 78), the changes in TMAO (8-wk minus baseline) were statistically significant for the diets rich in LCn3 (+1.15 ± 11.58 μmol/L) (P = 0.007), whereas they were not for the diets rich in PP (-0.14 ± 9.66 μmol/L) (P = 0.905) or their interaction (P = 0.655) (2-factor ANOVA). In the HealthGrain Study (n = 48), the TMAO change (12-wk minus baseline) in the WGC group (+0.94 ± 3.58 μmol/L) was significantly different from that in the Refined Cereal group (-1.29 ± 3.09 μmol/L) (P = 0.037). Considering the pooled baseline data of the participants in the 2 studies, TMAO concentrations directly correlated with LCn3, EPA (20:5n-3), and protein intake, but not SFAs, fiber, MUFAs, and PP intake. Among food groups, TMAO directly correlated with the intake of fish, vegetables, and whole-grain products, but not meat, processed meat, and dairy products.

CONCLUSIONS

Diets rich in LCn3 of marine origin or WGCs significantly increased plasma TMAO concentration. These changes mirrored the direct associations between TMAO concentrations and intakes of fish and WGCs, suggesting that TMAO reflects intakes of these healthy foods and, therefore, it is not a universally valid biomarker of cardiometabolic risk independent of the background diet.These trials were registered at clinicaltrials.gov as NCT01154478 and NCT00945854.

Pathobiological Relationship of Excessive Dietary Intake of Choline/L-Carnitine: A TMAO Precursor-Associated Aggravation in Heart Failure in Sarcopenic Patients

The microecological environment of the gastrointestinal tract is altered if there is an imbalance between the gut microbiota phylases, resulting in a variety of diseases. Moreover, progressive age not only slows down physical activity but also reduces the fat metabolism pathway, which may lead to a reduction in the variety of bacterial strains and bacteroidetes' abundance, promoting firmicutes and proteobacteria growth. As a result, dysbiosis reduces physiological adaptability, boosts inflammatory markers, generates ROS, and induces the destruction of free radical macromolecules, leading to sarcopenia in older patients. Research conducted at various levels indicates that the microbiota of the gut is involved in pathogenesis and can be considered as the causative agent of several cardiovascular diseases. Local and systematic inflammatory reactions are caused in patients with heart failure, as ischemia and edema are caused by splanchnic hypoperfusion and enable both bacterial metabolites and bacteria translocation to enter from an intestinal barrier, which is already weakened, to the blood circulation. Multiple diseases, such as HF, include healthy microbe-derived metabolites. These key findings demonstrate that the gut microbiota modulates the host's metabolism, either specifically or indirectly, by generating multiple metabolites. Currently, the real procedures that are an analogy to the symptoms in cardiac pathologies, such as cardiac mass dysfunctions and modifications, are investigated at a minimum level in older patients. Thus, the purpose of this review is to summarize the existing knowledge about a particular diet, including trimethylamine, which usually seems to be effective for the improvement of cardiac and skeletal muscle, such as choline and L-carnitine, which may aggravate the HF process in sarcopenic patients.

The Accumulation and Molecular Effects of Trimethylamine N-Oxide on Metabolic Tissues: It's Not All Bad

Since elevated serum levels of trimethylamine N-oxide (TMAO) were first associated with increased risk of cardiovascular disease (CVD), TMAO research among chronic diseases has grown exponentially. We now know that serum TMAO accumulation begins with dietary choline metabolism across the microbiome-liver-kidney axis, which is typically dysregulated during pathogenesis. While CVD research links TMAO to atherosclerotic mechanisms in vascular tissue, its molecular effects on metabolic tissues are unclear. Here we report the current standing of TMAO research in metabolic disease contexts across relevant tissues including the liver, kidney, brain, adipose, and muscle. Since poor blood glucose management is a hallmark of metabolic diseases, we also explore the variable TMAO effects on insulin resistance and insulin production. Among metabolic tissues, hepatic TMAO research is the most common, whereas its effects on other tissues including the insulin producing pancreatic β-cells are largely unexplored. Studies on diseases including obesity, diabetes, liver diseases, chronic kidney disease, and cognitive diseases reveal that TMAO effects are unique under pathologic conditions compared to healthy controls. We conclude that molecular TMAO effects are highly context-dependent and call for further research to clarify the deleterious and beneficial molecular effects observed in metabolic disease research.

Early modifications of the gut microbiome in children with hepatic sinusoidal obstruction syndrome after hematopoietic stem cell transplantation

Hepatic sinusoidal obstruction syndrome (SOS/VOD) represents a dramatic complication of hematopoietic stem cell transplantation (HSCT), particularly in children. Recent evidence has suggested a role for the gut microbiome (GM) in the context of HSCT and its related complications, but no data are available on the relationship between GM and SOS/VOD. Here, we conducted a retrospective case–control study in allo-HSCT pediatric patients developing or not SOS/VOD and profiled their GM over time, from before the transplant up to 72 days after. A rich and diverse GM before HSCT was found to be associated with a reduced likelihood of developing SOS/VOD. Furthermore, prior to transplant, patients not developing SOS/VOD showed an enrichment in some typically health-associated commensals, such as Bacteroides, Ruminococcaceae and Lachnospiraceae. Their levels remained overall higher until post-transplant. This high-diversity configuration resembles that described in other studies for other HSCT-related complications, including graft-versus-host disease, potentially representing a common protective GM feature against HSCT complications.

Ligustrum robustum Alleviates Atherosclerosis by Decreasing Serum TMAO, Modulating Gut Microbiota, and Decreasing Bile Acid and Cholesterol Absorption in Mice

SCOPE

Atherosclerosis (AS) is closely related to gut microbiota. Previous studies demonstrates that Ligustrum robustum (LR), a flavonoid-rich tea like plant, can mitigate several AS-related risk factors and modulate gut microbiota in animal models and human subjects. But its anti-AS effect and mechanisms remain unclear. Therefore, in this study, impacts of LR on AS development are investigated and the potential underlying mechanisms in C57BL/6J and Apoe^-/- mice are explored.

METHODS AND RESULTS

Female C57BL/6J and Apoe^{-/ -} mice are fed a chow diet or high-choline diet, supplemented with vehicle (water) or LR water extract (700 mg kg^-1 ) by gavage for 17 weeks. It is found that LR attenuates diet-induced AS by reducing serum trimethylamine and trimethylamine-N-oxide (TMAO) levels likely by modulating gut microbiota. Moreover, LR increases the abundance of the genus Bifidobacterium, which generates bile salt hydrolase, and thus presumably enhances bile acid (BA) deconjugation and increases fecal BA excretion. Meanwhile, LR increases fecal cholesterol excretion, decreases the levels of serum and hepatic cholesterol, but did not affect short-chain fatty acids in feces.

CONCLUSION

LR attenuates AS development presumably by decreasing serum TMAO levels and increasing fecal BA excretion likely via gut microbial modulation. These effects are accompanied by increases in fecal cholesterol excretion and decreases in serum and hepatic cholesterol.

Therapeutic and Improving Function of Lactobacilli in the Prevention and Treatment of Cardiovascular-Related Diseases: A Novel Perspective From Gut Microbiota

The occurrence and development of cardiovascular-related diseases are associated with structural and functional changes in gut microbiota (GM). The accumulation of beneficial gut commensals contributes to the improvement of cardiovascular-related diseases. The cardiovascular-related diseases that can be relieved by Lactobacillus supplementation, including hypercholesterolemia, atherosclerosis, myocardial infarction, heart failure, type 2 diabetes mellitus, and obesity, have expanded. As probiotics, lactobacilli occupy a substantial part of the GM and play important functional roles through various GM-derived metabolites. Lactobacilli ultimately have a beneficial impact on lipid metabolism, inflammatory factors, and oxidative stress to relieve the symptoms of cardiovascular-related diseases. However, the axis and cellular process of gut commensal Lactobacillus in improving cardiovascular-related diseases have not been fully elucidated. Additionally, Lactobacillus strains produce diverse antimicrobial peptides, which help maintain intestinal homeostasis and ameliorate cardiovascular-related diseases. These strains are a field that needs to be further investigated immediately. Thus, this review demonstrated the mechanisms and summarized the evidence of the benefit of Lactobacillus strain supplementation from animal studies and human clinical trials. We also highlighted a broad range of lactobacilli candidates with therapeutic capability by mining their metabolites. Our study provides instruction in the development of lactobacilli as a functional food to improve cardiovascular-related diseases.

Roles of Gut Microbial Metabolites in Diabetic Kidney Disease

Diabetes is a highly prevalent metabolic disease that has emerged as a global challenge due to its increasing prevalence and lack of sustainable treatment. Diabetic kidney disease (DKD), which is one of the most frequent and severe microvascular complications of diabetes, is difficult to treat with contemporary glucose-lowering medications. The gut microbiota plays an important role in human health and disease, and its metabolites have both beneficial and harmful effects on vital physiological processes. In this review, we summarize the current findings regarding the role of gut microbial metabolites in the development and progression of DKD, which will help us better understand the possible mechanisms of DKD and explore potential therapeutic approaches for DKD.

Dietary Strategies for Management of Metabolic Syndrome: Role of Gut Microbiota Metabolites

Metabolic syndrome (MetS) is a complex pathophysiological state with incidence similar to that of a global epidemic and represents a risk factor for the onset of chronic non-communicable degenerative diseases (NCDDs), including cardiovascular disease (CVD), type 2 diabetes mellitus, chronic kidney disease, and some types of cancer. A plethora of literature data suggest the potential role of gut microbiota in interfering with the host metabolism, thus influencing several MetS risk factors. Perturbation of the gut microbiota’s composition and activity, a condition known as dysbiosis, is involved in the etiopathogenesis of multiple chronic diseases. Recent studies have shown that some micro-organism-derived metabolites (including trimethylamine N-oxide (TMAO), lipopolysaccharide (LPS) of Gram-negative bacteria, indoxyl sulfate and p-cresol sulfate) induce subclinical inflammatory processes involved in MetS. Gut microbiota’s taxonomic species or abundance are modified by many factors, including diet, lifestyle and medications. The main purpose of this review is to highlight the correlation between different dietary strategies and changes in gut microbiota metabolites. We mainly focus on the validity/inadequacy of specific dietary patterns to reduce inflammatory processes, including leaky gut and subsequent endotoxemia. We also describe the chance of probiotic supplementation to interact with the immune system and limit negative consequences associated with MetS.

Personalized nutrition for colorectal cancer

The substantial burden of colorectal cancer and its increasing trend in young adults highlight the importance of dietary and lifestyle modifications for improved cancer prevention and survivorship. In this chapter, we review the cutting-edge evidence for the interplay between diet/lifestyle and the gut microbiota in the incidence and prognosis of colorectal cancer. We focus on factors for which there are data supporting their importance for the gut microbiota and colorectal cancer, including excess body weight, fiber, red and processed meat, and coffee. We discuss the potential precision nutrition approaches for modifying and exploiting the gut microbiota for improved cancer prevention and survivorship.

Effect of DLT-SML on Chronic Stable Angina Through Ameliorating Inflammation, Correcting Dyslipidemia, and Regulating Gut Microbiota

ABSTRACT

Chronic stable angina (CSA) is caused by coronary atherosclerosis. The gut microbiota (GM) and their metabolite trimethylamine-N-oxide (TMAO) levels are associated with atherosclerosis. Danlou tablet (DLT) combined with Salvia miltiorrhiza ligustrazine (SML) injection has been used to treat CSA. This study aims to investigate how DLT combined with SML (DLT-SML) regulates serum lipids, inflammatory cytokines, GM community, and microbial metabolite in patients with CSA. In this study, 30 patients with CSA were enrolled in the DLT-SML group, and 10 healthy volunteers were included in the healthy control group. The patients in the DLT-SML group were subdivided as the normal total cholesterol (TC) group and high-TC group according to their serum TC level before treatment. Blood samples were collected to investigate the (1) lipid content, including triglyceride (TG), TC, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol, (2) fasting blood glucose (Glu), (3) inflammatory cytokines, including interleukin-1 beta (IL-1β), interleukin-6 (IL-6), interleukin-10 (IL-10), and tumor necrosis factor-α (TNF-α), and (4) gut-derived metabolite, including lipopolysaccharides and TMAO level. GM composition was analyzed by sequencing 16S rRNA of fecal samples. Results showed that DLT-SML significantly decreased serum TG, TC, low-density lipoprotein cholesterol, IL-1β, TNF-α, and TMAO levels of patients with CSA. DLT-SML increased the abundance of Firmicutes and decreased Proteobacteria, which were significantly lower or higher in patients with CSA, respectively, compared with the healthy control group. In particular, DLT-SML increased the microbial diversity and decreased Firmicutes/Bacteroidetes ratio of patients with high-TC. The abundance of Sarcina, Anaerostipes, Streptococcus, Weissella, and Erysipelatoclostridium was decreased, whereas Romboutsia, Faecalibacterium, and Subdoligranulum were increased by DLT-SML treatment in patients with CSA. These findings indicated that DLT-SML improved patients with CSA by ameliorating dyslipidemia profile, decreasing the circulating inflammatory cytokines, and regulating the GM composition and their metabolites.

Use of dietary phytochemicals for inhibition of trimethylamine N-oxide formation

Trimethylamine-N-oxide (TMAO) has been reported as a risk factor for atherosclerosis development, as well as for other cardiovascular disease (CVD) pathologies. The objective of this review is to provide a useful summary on the use of phytochemicals as TMAO-reducing agents. This review discusses the main mechanisms by which TMAO promotes CVD, including the modulation of lipid and bile acid metabolism, and the promotion of endothelial dysfunction and oxidative stress. Current knowledge on the available strategies to reduce TMAO formation are discussed, highlighting the effect and potential of phytochemicals. Overall, phytochemicals (i.e., phenolic compounds or glucosinolates) reduce TMAO formation by modulating gut microbiota composition and/or function, inhibiting host's capacity to metabolize TMA to TMAO, or a combination of both. Perspectives for design of future studies involving phytochemicals as TMAO-reducing agents are discussed. Overall, the information provided by this review outlines the current state of the art of the role of phytochemicals as TMAO reducing agents, providing valuable insight to further advance in this field of study.

Act Locally, Act Globally-Microbiota, Barriers, and Cytokines in Atherosclerosis

Atherosclerosis is a lipid-driven chronic inflammatory disease that is characterized by the formation and progressive growth of atherosclerotic plaques in the wall of arteries. Atherosclerosis is a major predisposing factor for stroke and heart attack. Various immune-mediated mechanisms are implicated in the disease initiation and progression. Cytokines are key mediators of the crosstalk between innate and adaptive immune cells as well as non-hematopoietic cells in the aortic wall and are emerging players in the regulation of atherosclerosis. Progression of atherosclerosis is always associated with increased local and systemic levels of pro-inflammatory cytokines. The role of cytokines within atherosclerotic plaque has been extensively investigated; however, the cell-specific role of cytokine signaling, particularly the role of cytokines in the regulation of barrier tissues tightly associated with microbiota in the context of cardiovascular diseases has only recently come to light. Here, we summarize the knowledge about the function of cytokines at mucosal barriers and the interplay between cytokines, barriers, and microbiota and discuss their known and potential implications for atherosclerosis development.

Biomarkers of human gut microbiota diversity and dysbiosis

The association of gut microbiota dysbiosis with various human diseases is being substantiated with increasing evidence. Metabolites derived from both, microbiota and the human host play a central role in disease susceptibility and disease progression by extensively modulating host physiology and metabolism. Several of these metabolites have the potential to serve as diagnostic biomarkers for monitoring disease states in conjunction with intestinal microbiota dysbiosis. In this narrative review we evaluate the potential of trimethylamine-N-oxide, short-chain fatty acids, 3-indoxyl sulfate, p-cresyl sulfate, secondary bile acids, hippurate, human β-defensin-2, chromogranin A, secreted immunoglobulins and zonulin to serve as biomarkers for metabolite profiling and diagnostic suitability for dysbiosis and disease.

Metabolic networks of the human gut microbiota

The human gut microbiota controls factors that relate to human metabolism with a reach far greater than originally expected. Microbial communities and human (or animal) hosts entertain reciprocal exchanges between various inputs that are largely controlled by the host via its genetic make-up, nutrition and lifestyle. The composition of these microbial communities is fundamental to supply metabolic capabilities beyond those encoded in the host genome, and contributes to hormone and cellular signalling that support the dynamic adaptation to changes in food availability, environment and organismal development. Poor functional exchange between the microbial communities and their human host is associated with dysbiosis, metabolic dysfunction and disease. This review examines the biology of the dynamic relationship between the reciprocal metabolic state of the microbiota-host entity in balance with its environment (i.e. in healthy states), the enzymatic and metabolic changes associated with its imbalance in three well-studied diseases states such as obesity, diabetes and atherosclerosis, and the effects of bariatric surgery and exercise.

Therapeutic potential of natural products against atherosclerosis: Targeting on gut microbiota

Gut microbiota (GM) has emerged as an essential and integral factor for maintaining human health and affecting pathological outcomes. Metagenomics and metabolomics characterization have furthered gut metagenome's understanding and unveiled that deviation of specific GM community members and GM-dependent metabolites imbalance orchestrate metabolic or cardiovascular diseases (CVDs). Restoring GM ecosystem with nutraceutical supplements keenly prebiotics and probiotics relatively decreases CVDs incidence and overall mortality. In Atherosclerosis, commensal and pathogenic gut microbes correlate with atherogenesis events. GM-dependent metabolites-trimethylamine N-oxide and short-chain fatty acids regulate atherosclerosis-related metabolic processes in opposite patterns to affect atherosclerosis outcomes. Therefore, GM might be a potential therapeutic target for atherosclerosis. In atherogenic animal models, natural products with cardioprotective properties could modulate the GM ecosystem by revitalizing healthier GM phylotypes and abrogating proatherogenic metabolites, paving future research paths for clinical therapeutics.

An Expanded Genetic Code Enables Trimethylamine Metabolism in Human Gut Bacteria

Cardiovascular disease (CVD) has been linked to animal-based diets, which are a major source of trimethylamine (TMA), a precursor of the proatherogenic compound trimethylamine-N-oxide (TMAO). Human gut bacteria in the genus Bilophila have genomic signatures for genetic code expansion that could enable them to metabolize both TMA and its precursors without production of TMAO. We uncovered evidence that the Bilophila demethylation pathway is actively transcribed in gut microbiomes and that animal-based diets cause Bilophila to rapidly increase in abundance. CVD occurrence and Bilophila abundance in humans were significantly negatively correlated. These data lead us to propose that Bilophila, which is commonly regarded as a pathobiont, may play a role in mitigating cardiovascular disease. Human gut microbiomes have been shown to affect the development of a myriad of disease states, but mechanistic connections between diet, health, and microbiota have been challenging to establish. The hypothesis that Bilophila reduces cardiovascular disease by circumventing TMAO production offers a clearly defined mechanism with a potential human health impact, but investigations of Bilophila cell biology and ecology will be needed to fully evaluate these ideas.IMPORTANCE Links between trimethylamine-N-oxide (TMAO) and cardiovascular disease (CVD) have focused attention on mechanisms by which animal-based diets have negative health consequences. In a meta-analysis of data from foundational gut microbiome studies, we found evidence that specialized bacteria have and express a metabolic pathway that circumvents TMAO production and is often misannotated because it relies on genetic code expansion. This naturally occurring mechanism for TMAO attenuation is negatively correlated with CVD. Ultimately, these findings point to new avenues of research that could increase microbiome-informed understanding of human health and hint at potential biomedical applications in which specialized bacteria are used to curtail CVD development.

Vitamin D Decreases Plasma Trimethylamine-N-oxide Level in Mice by Regulating Gut Microbiota

As a metabolite generated by gut microbiota, trimethylamine-N-oxide (TMAO) has been proven to promote atherosclerosis and is a novel potential risk factor for cardiovascular disease (CVD). The objective of this study was to examine whether regulating gut microbiota by vitamin D supplementation could reduce the plasma TMAO level in mice. For 16 weeks, C57BL/6J mice were fed a chow (C) or high-choline diet (HC) without or with supplementation of vitamin D₃ (CD3 and HCD3) or a high-choline diet with vitamin D₃ supplementation and antibiotics (HCD3A). The results indicate that the HC group exhibited higher plasma trimethylamine (TMA) and TMAO levels, lower richness of gut microbiota, and significantly increased Firmicutes and decreased Bacteroidetes as compared with group C. Vitamin D supplementation significantly reduced plasma TMA and TMAO levels in mice fed a high-choline diet. Furthermore, gut microbiota composition was regulated, and the Firmicutes/Bacteroidetes ratio was reduced by vitamin D. Spearman correlation analysis indicated that Bacteroides and Akkermansia were negatively correlated with plasma TMAO in the HC and HCD3 groups. Our study provides a novel avenue for the prevention and treatment of CVD with vitamin D.

The Relationship between Choline Bioavailability from Diet, Intestinal Microbiota Composition, and Its Modulation of Human Diseases

Choline is a water-soluble nutrient essential for human life. Gut microbial metabolism of choline results in the production of trimethylamine (TMA), which, upon absorption by the host is converted into trimethylamine-N-oxide (TMAO) in the liver. A high accumulation of both components is related to cardiovascular disease, inflammatory bowel disease, non-alcoholic fatty liver disease, and chronic kidney disease. However, the relationship between the microbiota production of these components and its impact on these diseases still remains unknown. In this review, we will address which microbes contribute to TMA production in the human gut, the extent to which host factors (e.g., the genotype) and diet affect TMA production, and the colonization of these microbes and the reversal of dysbiosis as a therapy for these diseases.

Trimethylamine N-oxide: heart of the microbiota-CVD nexus?

We critically review potential involvement of trimethylamine N-oxide (TMAO) as a link between diet, the gut microbiota and CVD. Generated primarily from dietary choline and carnitine by gut bacteria and hepatic flavin-containing mono-oxygenase (FMO) activity, TMAO could promote cardiometabolic disease when chronically elevated. However, control of circulating TMAO is poorly understood, and diet, age, body mass, sex hormones, renal clearance, FMO3 expression and genetic background may explain as little as 25 % of TMAO variance. The basis of elevations with obesity, diabetes, atherosclerosis or CHD is similarly ill-defined, although gut microbiota profiles/remodelling appear critical. Elevated TMAO could promote CVD via inflammation, oxidative stress, scavenger receptor up-regulation, reverse cholesterol transport (RCT) inhibition, and cardiovascular dysfunction. However, concentrations influencing inflammation, scavenger receptors and RCT (≥100 µm) are only achieved in advanced heart failure or chronic kidney disease (CKD), and greatly exceed pathogenicity of <1-5 µm levels implied in some TMAO-CVD associations. There is also evidence that CVD risk is insensitive to TMAO variance beyond these levels in omnivores and vegetarians, and that major TMAO sources are cardioprotective. Assessing available evidence suggests that modest elevations in TMAO (≤10 µm) are a non-pathogenic consequence of diverse risk factors (ageing, obesity, dyslipidaemia, insulin resistance/diabetes, renal dysfunction), indirectly reflecting CVD risk without participating mechanistically. Nonetheless, TMAO may surpass a pathogenic threshold as a consequence of CVD/CKD, secondarily promoting disease progression. TMAO might thus reflect early CVD risk while providing a prognostic biomarker or secondary target in established disease, although mechanistic contributions to CVD await confirmation.

Carnitine metabolism in the human gut: characterization of the two-component carnitine monooxygenase CntAB from Acinetobacter baumannii

Bacterial formation of trimethylamine (TMA) from carnitine in the gut microbiome has been linked to cardiovascular disease. During this process, the two-component carnitine monooxygenase (CntAB) catalyzes the oxygen-dependent cleavage of carnitine to TMA and malic semialdehyde. Individual redox states of the reductase CntB and the catalytic component CntA were investigated based on mutagenesis and electron paramagnetic resonance (EPR) spectroscopic approaches. Protein ligands of the flavin mononucleotide (FMN) and the plant-type [2Fe-2S] cluster of CntB and also of the Rieske-type [2Fe-2S] cluster and the mononuclear [Fe] center of CntA were identified. EPR spectroscopy of variant CntA proteins suggested a hierarchical metallocenter maturation, Rieske [2Fe-2S] followed by the mononuclear [Fe] center. NADH-dependent electron transfer via the redox components of CntB and within the trimeric CntA complex for the activation of molecular oxygen was investigated. EPR experiments indicated that the two electrons from NADH were allocated to the plant-type [2Fe-2S] cluster and to FMN in the form of a flavin semiquinone radical. Single-turnover experiments of this reduced CntB species indicated the translocation of the first electron onto the [Fe] center and the second electron onto the Rieske-type [2Fe-2S] cluster of CntA to finally allow for oxygen activation as a basis for carnitine cleavage. EPR spectroscopic investigation of CntA variants indicated an unusual intermolecular electron transfer between the subunits of the CntA trimer via the "bridging" residue Glu-205. On the basis of these data, a redox catalytic cycle for carnitine monooxygenase was proposed.

Dietary bioactive ingredients to modulate the gut microbiota-derived metabolite TMAO. New opportunities for functional food development

There is a growing body of clinical evidence that supports a strong association between elevated circulating trimethylamine N-oxide (TMAO) levels with increased risk of developing adverse cardiovascular outcomes such as atherosclerosis and thrombosis. TMAO is synthesized through a meta-organismal stepwise process that involves (i) the microbial production of TMA in the gut from dietary precursors and (ii) its subsequent oxidation to TMAO by flavin-containing monooxygenases in the liver. Choline, l-carnitine, betaine, and other TMA-containing compounds are the major dietary precursors of TMA. TMAO can also be absorbed directly from the gastrointestinal tract after the intake of TMAO-rich foods such as fish and shellfish. Thus, diet is an important factor as it provides the nutritional precursors to eventually produce TMAO. A number of studies have attempted to associate circulating TMAO levels with the consumption of diets rich in these foods. On the other hand, there is growing interest for the development of novel food ingredients that reduce either the TMAO-induced damage or the endogenous TMAO levels through the interference with microbiota and host metabolic processes involved in TMAO pathway. Such novel functional food ingredients would offer great opportunities to control circulating TMAO levels or its effects, and potentially contribute to decrease cardiovascular risk. In this review we summarize and discuss current data regarding the effects of TMA precursors-enriched foods or diets on circulating TMAO levels, and recent findings regarding the circulating TMAO-lowering effects of specific foods, food constituents and phytochemicals found in herbs, individually or in extracts, and their potential beneficial effect for cardiovascular health.

Characteristic Metabolic Changes of the Crust from Dry-Aged Beef Using 2D NMR Spectroscopy

Two-dimensional quantitative nuclear magnetic resonance (2D qNMR)-based metabolomics was performed to understand characteristic metabolic profiles in different aging regimes (crust from dry-aged beef, inner edible flesh of dry-aged beef, and wet-aged beef striploin) over 4 weeks. Samples were extracted using 0.6 M perchlorate to acquire polar metabolites. Partial least squares-discriminant analysis showed a good cumulative explained variation (R² = 0.967) and predictive ability (Q² = 0.935). Metabolites of crust and aged beef (dry- and wet-aged beef) were separated in the first week and showed a completely different aspect in the second week via NMR-based multivariable analyses. Moreover, NMR-based multivariable analyses could be used to distinguish the method, degree, and doneness of beef aging. Among them, the crust showed more unique metabolic changes that accelerated proteolysis (total free amino acids and biogenic amines) and inosine 5′-monophosphate depletion than dry-aged beef and generated specific microbial catabolites (3-indoxyl sulfate) and γ-aminobutyric acid (GABA), while asparagine, glutamine, tryptophan, and glucose in the crust were maintained or decreased. Compared to the crust, dry-aged beef showed similar patterns of biogenic amines, as well as bioactive compounds and GABA, without a decrease in free amino acids and glucose. Based on these results, the crust allows the inner dry-aged beef to be aged similarly to wet-aged beef without microbial effects. Thus, 2D qNMR-based metabolomic techniques could provide complementary information about biochemical factors for beef aging.

Effects of dietary choline, betaine, and L-carnitine on the generation of trimethylamine-N-oxide in healthy mice

Trimethylamine-N-oxide (TMAO) is considered to have negative effect on human health. Different precursors of TMAO, such as choline, betaine, and L-carnitine, are commonly found in daily foods. The aim of the present study was to compare the ability of different precursors to be metabolized into TMAO, as well as the possible effect of chronic administration with TMAO precursors on TMAO production. The rate of TMAO generation after single gavage with different precursors was L-carnitine > choline >betaine. Moreover, the serum TMAO level of mice increased more than twofold after administration with choline for 3 weeks compared with L-carnitine and betaine groups, which was accompanied by the change of intestinal flora. After the gavage of choline chloride, the production for TMAO was 2.8 and 1.6 times higher in chronic choline-treated group compared with L-carnitine and betaine groups, respectively. In addition, administration with choline increased the lowest TMAO level after intraperitoneal injection of trimethylamine (TMA) hydrochloride among the three treated groups. These findings indicated that different TMAO precursors had different ability to form TMAO in vivo, and long-term dietary intervention would affect the metabolism of precursors to generate TMA and the TMA oxidation to form TMAO, suggesting that TMAO levels in vivo could be regulated by dietary intervention. PRACTICAL APPLICATION: Diverse TMAO precursors exhibited different ability to be converted into TMAO in vivo. The ability of choline to produce TMAO was stronger than that of betaine and L-carnitine. Long-term dietary intervention would affect the metabolism of precursors to generate TMA and the TMA oxidation to form TMAO, suggesting that TMAO levels in vivo could be regulated by adjustment of dietary structure.

Statin therapy is associated with lower prevalence of gut microbiota dysbiosis

Microbiome community typing analyses have recently identified the Bacteroides2 (Bact2) enterotype, an intestinal microbiota configuration that is associated with systemic inflammation and has a high prevalence in loose stools in humans^1,2. Bact2 is characterized by a high proportion of Bacteroides, a low proportion of Faecalibacterium and low microbial cell densities^1,2, and its prevalence varies from 13% in a general population cohort to as high as 78% in patients with inflammatory bowel disease². Reported changes in stool consistency³ and inflammation status⁴ during the progression towards obesity and metabolic comorbidities led us to propose that these developments might similarly correlate with an increased prevalence of the potentially dysbiotic Bact2 enterotype. Here, by exploring obesity-associated microbiota alterations in the quantitative faecal metagenomes of the cross-sectional MetaCardis Body Mass Index Spectrum cohort (n = 888), we identify statin therapy as a key covariate of microbiome diversification. By focusing on a subcohort of participants that are not medicated with statins, we find that the prevalence of Bact2 correlates with body mass index, increasing from 3.90% in lean or overweight participants to 17.73% in obese participants. Systemic inflammation levels in Bact2-enterotyped individuals are higher than predicted on the basis of their obesity status, indicative of Bact2 as a dysbiotic microbiome constellation. We also observe that obesity-associated microbiota dysbiosis is negatively associated with statin treatment, resulting in a lower Bact2 prevalence of 5.88% in statin-medicated obese participants. This finding is validated in both the accompanying MetaCardis cardiovascular disease dataset (n = 282) and the independent Flemish Gut Flora Project population cohort (n = 2,345). The potential benefits of statins in this context will require further evaluation in a prospective clinical trial to ascertain whether the effect is reproducible in a randomized population and before considering their application as microbiota-modulating therapeutics.

Gut microbiota and cardiovascular disease: opportunities and challenges

Coronary artery disease (CAD) is the most common health problem worldwide and remains the leading cause of morbidity and mortality. Over the past decade, it has become clear that the inhabitants of our gut, the gut microbiota, play a vital role in human metabolism, immunity, and reactions to diseases, including CAD. Although correlations have been shown between CAD and the gut microbiota, demonstration of potential causal relationships is much more complex and challenging. In this review, we will discuss the potential direct and indirect causal roots between gut microbiota and CAD development via microbial metabolites and interaction with the immune system. Uncovering the causal relationship of gut microbiota and CAD development can lead to novel microbiome-based preventative and therapeutic interventions. However, an interdisciplinary approach is required to shed light on gut bacterial-mediated mechanisms (e.g., using advanced nanomedicine technologies and incorporation of demographic factors such as age, sex, and ethnicity) to enable efficacious and high-precision preventative and therapeutic strategies for CAD.

The gut microbiome and thromboembolism

The gut microbiome plays a critical role in various inflammatory conditions, and its modulation is a potential treatment option for these conditions. The role of the gut microbiome in the pathogenesis of thromboembolism has not been fully elucidated. In this review, we summarize the evidence linking the gut microbiome to the pathogenesis of arterial and venous thrombosis. In a human host, potentially pathogenic bacteria are normal residents of the human gut microbiome, but significantly outnumbered by commensal anaerobic bacteria. Several disease states with an increased risk of venous thromboembolism (VTE) are associated with an imbalance in the gut microbiome characterized by a decrease in commensal anaerobic bacteria and an increase in the abundance of pathogenic bacteria of which the most common is the gram-negative Enterobacteriaceae (ENTERO) family. Bacterial lipopolysaccharides (LPS), the glycolipids found on the outer membrane of gram-negative bacteria, is one of the links between the microbiome and hypercoagulability. LPS binds to toll-like receptors to activate endothelial cells and platelets, leading to activation of the coagulation cascade. Bacteria in the microbiome can also metabolite compounds in the diet to produce important metabolites like trimethylamine-N-oxide (TMAO). TMAO causes platelet hyperreactivity, promotes thrombus formation and is associated with cardiovascular disease. Modulating the gut microbiome to target LPS and TMAO levels may be an innovative approach for decreasing the risk of thrombosis.

Dietary metabolism, the gut microbiome, and heart failure

Advances in our understanding of how the gut microbiota contributes to human health and diseases have expanded our insight into how microbial composition and function affect the human host. Heart failure is associated with splanchnic circulation congestion, leading to bowel wall oedema and impaired intestinal barrier function. This situation is thought to heighten the overall inflammatory state via increased bacterial translocation and the presence of bacterial products in the systemic blood circulation. Several metabolites produced by gut microorganisms from dietary metabolism have been linked to pathologies such as atherosclerosis, hypertension, heart failure, chronic kidney disease, obesity, and type 2 diabetes mellitus. These findings suggest that the gut microbiome functions like an endocrine organ by generating bioactive metabolites that can directly or indirectly affect host physiology. In this Review, we discuss several newly discovered gut microbial metabolic pathways, including the production of trimethylamine and trimethylamine N-oxide, short-chain fatty acids, and secondary bile acids, that seem to participate in the development and progression of cardiovascular diseases, including heart failure. We also discuss the gut microbiome as a novel therapeutic target for the treatment of cardiovascular disease, and potential strategies for targeting intestinal microbial processes.

Metagenomic analysis of gut microbiota modulatory effects of jujube (Ziziphus jujuba Mill.) polysaccharides in a colorectal cancer mouse model

Accumulating evidence has reported that the gut microbiota could play important roles in the occurrence and progression of colorectal cancer.

Urinary TMAO Levels Are Associated with the Taxonomic Composition of the Gut Microbiota and with the Choline TMA-Lyase Gene (cutC) Harbored by Enterobacteriaceae

Gut microbiota metabolization of dietary choline may promote atherosclerosis through trimethylamine (TMA), which is rapidly absorbed and converted in the liver to proatherogenic trimethylamine-N-oxide (TMAO). The aim of this study was to verify whether TMAO urinary levels may be associated with the fecal relative abundance of specific bacterial taxa and the bacterial choline TMA-lyase gene cutC. The analysis of sequences available in GenBank grouped the cutC gene into two main clusters, cut-Dd and cut-Kp. A quantitative real-time polymerase chain reaction (qPCR) protocol was developed to quantify cutC and was used with DNA isolated from three fecal samples collected weekly over the course of three consecutive weeks from 16 healthy adults. The same DNA was used for 16S rRNA gene profiling. Concomitantly, urine was used to quantify TMAO by ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). All samples were positive for cutC and TMAO. Correlation analysis showed that the cut-Kp gene cluster was significantly associated with Enterobacteriaceae. Linear mixed models revealed that urinary TMAO levels may be predicted by fecal cut-Kp and by 23 operational taxonomic units (OTUs). Most of the OTUs significantly associated with TMAO were also significantly associated with cut-Kp, confirming the possible relationship between these two factors. In conclusion, this preliminary method-development study suggests the existence of a relationship between TMAO excreted in urine, specific fecal bacterial OTUs, and a cutC subgroup ascribable to the choline-TMA conversion enzymes of Enterobacteriaceae.

Associations of dietary choline intake with risk of incident dementia and with cognitive performance: the Kuopio Ischaemic Heart Disease Risk Factor Study

BACKGROUND

Moderate egg intake has been associated with better cognitive performance in observational studies. This association may be due to the rich content of choline, especially phosphatidylcholine, in eggs because choline has been suggested to have a role in the prevention of cognitive decline.

OBJECTIVES

We investigated the associations of dietary choline intake with the risk of incident dementia and with cognitive performance in middle-aged and older men in the prospective, population-based Kuopio Ischaemic Heart Disease Risk Factor Study.

METHODS

A population-based sample of 2497 dementia-free men aged 42-60 y was examined in 1984-1989. A subset of 482 men completed 5 different cognitive performance tests 4 y later. Dementia and Alzheimer disease diagnoses were retrieved from Finnish health registers. Dietary intakes were assessed with the use of 4-d food records at baseline. Cox regression and ANCOVA were used for the analyses. All analyses were also stratified by the apolipoprotein E phenotype (APOE-ε4 compared with other phenotypes). These data were available for 1259 men.

RESULTS

The mean ± SD total choline intake was 431 ± 88 mg/d, of which 188 ± 63 mg/d was phosphatidylcholine. During a 21.9-y follow-up, 337 men were diagnosed with dementia. Those in the highest compared with the lowest phosphatidylcholine intake quartile had 28% (95% CI: 1%, 48%; P-trend = 0.02 across quartiles) lower multivariable-adjusted risk of incident dementia. Total choline intake had no association with the risk of incident dementia. However, both total choline and phosphatidylcholine intakes were associated with better performance in cognitive tests assessing frontal and temporal lobe functioning. For example, higher intakes were associated with better performance in verbal fluency and memory functions. The APOE phenotype had little or no impact on the associations.

CONCLUSION

Higher phosphatidylcholine intake was associated with lower risk of incident dementia and better cognitive performance in men in eastern Finland. This trial was registered at clinicaltrials.gov as NCT03221127.

Fecal metabonomics combined with 16S rRNA gene sequencing to analyze the changes of gut microbiota in rats with kidney-yang deficiency syndrome and the intervention effect of You-gui pill

ETHNOPHARMACOLOGICAL RELEVANCE

A myriad of evidence have shown that kidney-yang deficiency syndrome (KYDS) is associated with metabolic disorders of the intestinal microbiota, while TCMs can treat KYDS by regulating gut microbiota metabolism. However, the specific interplay between KYDS and intestinal microbiota, and the intrinsic regulation mechanism of You-gui pill (YGP) on KYDS' gut microbiota remains largely unknown so far.

MATERIALS AND METHODS

In the present study, fecal metabonomics combined with 16S rRNA gene sequencing analysis were used to explore the mutual effect between KYDS and intestinal flora, and the intrinsic regulation mechanism of YGP on KYDS's gut microbiota. Rats' feces from control (CON) group, KYDS group and YGP group were collected, and metabolomic analysis was performed using ¹H NMR technique combined with multivariate statistical analysis to obtain differential metabolites. Simultaneously, 16S rRNA gene sequencing analysis based on the Illumina HiSeq sequencing platform and ANOVA analysis were used to analyze the composition of the intestinal microbiota in the stool samples and to screen for the significant altered microbiota at the genus level. After that, MetaboAnalyst database and PICRUSt software were apply to conduct metabolic pathway analysis and functional prediction analysis of the screened differential metabolites and intestinal microbiota, respectively. What's more, Pearson correlation analysis was performed on these differential metabolites and gut microbiota.

RESULTS

Using fecal metabonomics, KYDS was found to be associated with 21 differential metabolites and seven potential metabolic pathways. These metabolites and metabolic pathways were mainly involved in amino acid metabolism, energy metabolism, methylamine metabolism, bile acid metabolism and urea cycle, and short-chain fatty acid metabolism. Through 16S rRNA gene sequencing analysis, we found that KYDS was related to eleven different intestinal microbiotas. These gut microbiota were mostly involved in amino acid metabolism, energy metabolism, nervous, endocrine, immune and digestive system, lipid metabolism, and carbohydrate metabolism. Combined fecal metabonomics and 16S rRNA gene sequencing analysis, we further discovered that KYDS was primarily linked to three gut microbiotas (i.e. Bacteroides, Desulfovibrio and [Eubacterium]_coprostanoligenes_group) and eleven related metabolites (i.e. deoxycholate, n-butyrate, valine, isoleucine, acetate, taurine, glycine, α-gluconse, β-glucose, glycerol and tryptophan) mediated various metabolic disorders (amino acid metabolism, energy metabolism, especially methylamine metabolism, bile acid metabolism and urea cycle, short-chain fatty acid metabolism. nervous, endocrine, immune and digestive system, lipid metabolism, and carbohydrate metabolism). YGP, however, had the ability to mediate four kinds of microbes (i.e. Ruminiclostridium_9, Ruminococcaceae_UCG-007, Ruminococcaceae_UCG-010, and uncultured_bacterium_f_Bacteroidales_S24-7_group) and ten related metabolites (i.e. deoxycholate, valine, isoleucine, alanine, citrulline, acetate, DMA, TMA, phenylalanine and tryptophan) mediated amino acid metabolism, especially methylamine metabolism, bile acid metabolism and urea cycle, short-chain fatty acid metabolism, endocrine, immune and digestive system, and lipid metabolism, thereby exerting a therapeutic effect on KYDS rats.

CONCLUSION

Overall, our findings have preliminary confirmed that KYDS is closely related to metabolic and microbial dysbiosis, whereas YGP can improve the metabolic disorder of KYDS by acting on intestinal microbiota. Meanwhile, this will lay the foundation for the further KYDS's metagenomic research and the use of intestinal microbiotas as drug targets to treat KYDS.

Biliopancreatic Diversion Induces Greater Metabolic Improvement Than Roux-en-Y Gastric Bypass

Diabetes remission is greater after biliopancreatic diversion (BPD) than Roux-en-Y gastric bypass (RYGB) surgery. We used a mixed-meal test with ingested and infused glucose tracers and the hyperinsulinemic-euglycemic clamp procedure with glucose tracer infusion to assess the effect of 20% weight loss induced by either RYGB or BPD on glucoregulation in people with obesity (ClinicalTrials.gov number: NCT03111953). The rate of appearance of ingested glucose into the circulation was much slower, and the postprandial increases in plasma glucose and insulin concentrations were markedly blunted after BPD compared to after RYGB. Insulin sensitivity, assessed as glucose disposal rate during insulin infusion, was ∼45% greater after BPD than RYGB, whereas β cell function was not different between groups. These results demonstrate that compared with matched-percentage weight loss induced by RYGB, BPD has unique beneficial effects on glycemic control, manifested by slower postprandial glucose absorption, blunted postprandial plasma glucose and insulin excursions, and greater improvement in insulin sensitivity.

The Effect of Maternal Postpartum Practices on Infant Gut Microbiota: A Chinese Cohort Study

(1) Background: The human gut microbiota at early life is shaped by numerous factors, especially factors from mothers, which have huge influence on infants' gut microbiotas. The aim of this study was to investigate the effect of maternal adherence to Chinese traditional postpartum practices of "doing the month" on the development of infant gut microbiota at 6-month postpartum. (2) Methods: A cohort of 62 Chinese women at late pregnancy was recruited from a tertiary general hospital in a central region of China. The participants and their babies were followed up to 6 months postpartum. Finally, 50 mother-infant dyads were enrolled in the study. Women's adherence to the traditional postpartum practices was measured by adherence to doing the month practices (ADP). Infant fecal samples were collected at six months of age and were analyzed using 16S rRNA V3 and V4 gene region sequences. (3) Results: Ruminococcus gnavus was significantly less abundant in infants whose mothers had a better adherence to the traditional postpartum practices of "doing the month." Infants receiving Clostridium-butyricum during the first month after delivery had a significant dominance of Escherichia/Shigella. (4) Conclusions: Adherence to the traditional postpartum practices of "doing the month" can impact an infant's gut microbiota at 6 months of age. Infants receiving probiotics during the first month after delivery had a significant dominance of opportunistic pathogens.

Trimethylamine-N-oxide as One Hypothetical Link for the Relationship between Intestinal Microbiota and Cancer - Where We Are and Where Shall We Go?

Previous epidemiological studies had provided evidence for a link between the microbial dysbiosis and cancer, particularly colorectal cancer (CRC), yet the molecular basis of this link remains elusive. Recently, the association between plasma levels of trimethylamine-N-oxide (TMAO), an oxidised form of trimethylamine (TMA), and risks of various cancers was demonstrated. The discovery could potentially provide an alternative explanation for the aforementioned link, as TMA production is attributed to intestinal bacteria. Current evidence suggests that inflammation could be a potential molecular mechanism to explain the link between TMAO and cancer, although other mechanisms such as oxidative stress, DNA damage and disruption in protein folding might also play a role. This mini-review article first provides an overview of the current evidence for the association between TMAO and certain cancer types, and the potential mechanisms that could explain their association. Thereafter, the direction of further research on the connection between the intestinal microbiota, TMAO and cancer is suggested.

Analysis of Nitrogen-containing Compounds in Mouth-exhaled Breath by Electrospray Ionization Quadrupole Time-of-Flight Mass Spectrometry

Nitrogen-containing compounds are important components in human breath. However, their origins have not yet been clearly understood. In this study, a modified electrospray ionization (ESI) source coupling with quadrupole time-of-flight mass spectrometry has been used for breath analysis. Fourteen nitrogen-containing compounds were identified in mouth-exhaled breath, and 10 of them were from the oral cavity and oropharynx. Moreover, 8 of these nitrogen-containing compounds were recognized as endogenous metabolites. This result provides important clues for exploring the biological origins of these nitrogen-containing compounds. Observation of the ion suppression phenomenon also indicates that breath analysis should be carried out after clearing of the oral cavity and oropharynx, or directly through nose-breathing to eliminate the influence of those nitrogen-containing compounds from the oral cavity.

Serum Metabolite Markers of Dementia Through Quantitative NMR Analysis: The Importance of Threonine-Linked Metabolic Pathways

There is a great need for diagnostic biomarkers of impending dementia. Metabolite markers in blood have been investigated in several studies, but inconclusive findings encourage further investigation, particularly in the pre-diagnostic phase. In the present study, the serum metabolomes of 110 dementia or pre-diagnostic dementia individuals and 201 healthy individuals matched for age, gender, and education were analyzed by nuclear magnetic resonance spectroscopy in combination with multivariate data analysis. 58 metabolites were quantified in each of the 311 samples. Individuals with dementia were discriminated from controls using a panel of seven metabolites, while the pre-diagnostic dementia subjects were distinguished from controls using a separate set of seven metabolites, where threonine was a common significant metabolite in both panels. Metabolite and pathway alterations specific for dementia and pre-diagnostic dementia were identified, in particular a disturbed threonine catabolism at the pre-diagnostic stage that extends to several threonine-linked pathways at the dementia stage.

Gut microbiota signatures and lipids metabolism profiles by exposure to polyene phosphatidylcholine

The aim of the study was to address the causality links and identify specific features of the gut microbiota signatures contributing to host lipids metabolism in the presence or absence of polyene phosphatidylcholine (PPC) administration, and evaluate potential risk of PPC consumption. About 20 C57BL/6J mice were randomly allocated into two groups, normal diet group (CK) and PPC administration group (205.2 mg/kg). Compared with CK group, the contents of unsaturated fatty acids were increased and the saturated fatty acids were decreased in PPC group. The content of free fatty acids (FFA) and lipopolysaccharides (LPS) were significantly decreased (P < 0.05), and expression of carnitine palmitoyltransferase 1A (CPT1A), cluster of differentiation 36 (CD36), liver fatty acid binding protein (L-FABP), fatty acid transport protein 5 (FATP5), and fatty acid synthase (FASN) were significantly decreased in the mRNA and protein levels after treated by PPC (P < 0.05, P < 0.01). Also, we found that acetic acid in feces was significantly increased after consumption of PPC (P < 0.05). After PPC administration the relative abundances of Firmicutes and Clostridia were increased within the phylum level and the class level, respectively. Microbial abundances in genus level were dominated by Lachnospiraceae and Lachnospiraceae_NK4A136_group, whereas the proportion of sequences assigned to Bacteroidetes within the phylum level, class Bacteroidias and Mollicutes, order Anaeroplasmatalesl, genus Bacteroidales_S24-7_group were decreased in metagenomes of treated group with PPC and did not significantly influence on the accumulation of trimethylamine-N-oxide (TMAO). This study revealed that intake of PPC could regulate the gut microbiota signatures and lipids metabolism in mice without TMAO accumulations. © 2019 BioFactors, 45(3):439-449, 2019.

The human microbiome in health and disease: hype or hope

OBJECTIVES

The prognostic, diagnostic, and therapeutic potential of the human gut microbiota is widely recognised. However, translation of microbiome findings to clinical practice is challenging. Here, we discuss current knowledge and applications in the field.

METHODS

We revisit some recent advances in the field of faecal microbiome analyses with a focus on covariate analyses and ecological interpretation.

RESULTS

Population-level characterization of gut microbiota variation among healthy volunteers has allowed identifying microbiome covariates required for clinical studies. Currently, microbiome research is moving from relative to quantitative approaches that will shed a new light on microbiota-host interactions in health and disease.

CONCLUSIONS

Covariate characterization and technical advances increase reproducibility of microbiome research. Targeted in vitro/in vivo intervention studies will accelerate clinical implementation of microbiota findings.

Lactobacillus plantarum ZDY04 exhibits a strain-specific property of lowering TMAO via the modulation of gut microbiota in mice

Trimethylamine N-oxide (TMAO), which is oxidized from trimethylamine (TMA) by hepatic flavin-containing monooxygenases (FMOs), promotes the development of atherosclerosis and is a new target for the prevention and treatment of cardiovascular disease from the perspective of intestinal flora. TMA is transformed by intestinal flora from TMA-containing nutrients, such as choline. Some small molecular agents lower serum TMAO and/or cecal TMA levels. However, probiotics that can effectively reduce serum TMAO levels are currently lacking. In this work, five potentially probiotic strains were administered to mice supplemented with 1.3% choline. Only Lactobacillus plantarum ZDY04 significantly reduced serum TMAO and cecal TMA levels by modulating the relative abundance of the families Lachnospiraceae, Erysipelotrichaceae and Bacteroidaceae and the genus Mucispirillum in mice and not by influencing the expression levels of hepatic FMO3 and metabolizing choline, TMA, and TMAO. In addition, L. plantarum ZDY04 can significantly inhibit the development of TMAO-induced atherosclerosis in ApoE-/- 1.3% choline-fed mice as compared with the untreated PBS group. In conclusion, the use of L. plantarum ZDY04 may be an alternative approach to reduce serum TMAO levels and TMAO-induced atherosclerosis in mice.

Microbial impact on cholesterol and bile acid metabolism: current status and future prospects

Recently, the gut microbiota has emerged as a crucial factor that influences cholesterol metabolism. Ever since, significant interest has been shown in investigating these host-microbiome interactions to uncover microbiome-mediated functions on cholesterol and bile acid (BA) metabolism. Indeed, changes in gut microbiota composition and, hence, its derived metabolites have been previously reported to subsequently impact the metabolic processes and have been linked to several diseases. In this context, associations between a disrupted gut microbiome, impaired BA metabolism, and cholesterol dysregulation have been highlighted. Extensive advances in metagenomic and metabolomic studies in this field have allowed us to further our understanding of the role of intestinal bacteria in metabolic health and disease. However, only a few have provided mechanistic insights into their impact on cholesterol metabolism. Identifying the myriad functions and interactions of these bacteria to maintain cholesterol homeostasis remain an important challenge in such a field of research. In this review, we discuss the impact of gut microbiota on cholesterol metabolism, its association with disease settings, and the potential of modulating gut microbiota as a promising therapeutic target to lower hypercholesterolemia.

Choline: The Underconsumed and Underappreciated Essential Nutrient

Choline has been recognized as an essential nutrient by the Food and Nutrition Board of the National Academies of Medicine since 1998. Its metabolites have structural, metabolic, and regulatory roles within the body. Humans can endogenously produce small amounts of choline via the hepatic phosphatidylethanolamine N-methyltransferase pathway. However, the nutrient must be consumed exogenously to prevent signs of deficiency. The Adequate Intake (AI) for choline was calculated at a time when dietary intakes across the population were unknown for the nutrient. Unlike the traditional National Academy of Medicine approach of calculating an AI based on observed or experimentally determined approximations or estimates of intake by a group (or groups) of healthy individuals, calculation of the AI for choline was informed in part by a depletion-repletion study in adult men who, upon becoming deficient, developed signs of liver damage. The AI for other gender and life-stage groups was calculated based on standard reference weights, except for infants 0 to 6 months, whose AI reflects the observed mean intake from consuming human breast milk. Recent analyses indicate that large portions of the population (ie, approximately 90% of Americans), including most pregnant and lactating women, are well below the AI for choline. Moreover, the food patterns recommended by the 2015-2020 Dietary Guidelines for Americans are currently insufficient to meet the AI for choline in most age-sex groups. An individual's requirement for choline is dependent on common genetic variants in genes required for choline, folate, and 1-carbon metabolism, potentially increasing more than one-third of the population's susceptibly to organ dysfunction. The American Medical Association and American Academy of Pediatrics have both recently reaffirmed the importance of choline during pregnancy and lactation. New and emerging evidence suggests that maternal choline intake during pregnancy, and possibly lactation, has lasting beneficial neurocognitive effects on the offspring. Because choline is found predominantly in animal-derived foods, vegetarians and vegans may have a greater risk for inadequacy. With the 2020-2025 Dietary Guidelines for Americans recommending expansion of dietary information for pregnant women, and the inclusion of recommendations for infants and toddlers 0 to 2 years, better communication of the role that choline plays, particularly in the area of neurocognitive development, is critical. This narrative review summarizes the peer-reviewed literature and discussions from the 2018 Choline Science Summit, held in Washington, DC, in February 2018.

Methodological considerations for the identification of choline and carnitine-degrading bacteria in the gut

The bacterial formation of trimethylamine (TMA) has been linked to cardiovascular disease. This review focuses on the methods employed to investigate the identity of the bacteria responsible for the formation of TMA from dietary choline and carnitine in the human gut. Recent studies have revealed the metabolic pathways responsible for bacterial TMA production, primarily the anaerobic glycyl radical-containing, choline-TMA lyase, CutC and the aerobic carnitine monooxygenase, CntA. Identification of these enzymes has enabled bioinformatics approaches to screen both human-associated bacterial isolate genomes and whole gut metagenomes to determine which bacteria are responsible for TMA formation in the human gut. We centre on several key methodological aspects for identifying the TMA-producing bacteria and report how these pathways can be identified in human gut microbiota through bioinformatics analysis of available bacterial genomes and gut metagenomes.

Pathogenic functions of host microbiota

BACKGROUND

It is becoming evident that certain features of human microbiota, encoded by distinct autochthonous taxa, promote disease. As a result, borders between the so-called opportunistic pathogens, pathobionts, and commensals are increasingly blurred, and specific targets for manipulating microbiota to improve host health are becoming elusive.

RESULTS

In this study, we focus on the functions of host bacterial communities that have the potential to cause disease, proposing the term "pathogenic function (pathofunction)". The concept is presented via three distinct examples, namely, the formation of (i) trimethylamine, (ii) secondary bile acids, and (iii) hydrogen sulfide, which represent metabolites of the gut microbiota linked to the development of non-communicable diseases. Using publicly available metagenomic and metatranscriptomic data (n = 2975), we quantified those pathofunctions in health and disease and exposed the key players. Pathofunctions were ubiquitously present with increased abundances in patient groups. Overall, the three pathofunctions were detected at low mean concentrations (< 1% of total bacteria carried respective genes) and encompassed various taxa, including uncultured members.

CONCLUSIONS

We outline how this function-centric approach, where all members of a community exhibiting a particular pathofunction are redundant, can contribute to risk assessment and the development of precision treatment directing gut microbiota to increase host health.