Trimethylamine N-Oxide: A Link among Diet, Gut Microbiota, Gene Regulation of Liver and Intestine Cholesterol Homeostasis and HDL Function

A Novel Insight at Atherogenesis: The Role of Microbiome

There is an important task of current medicine to identify mechanisms and new markers of subclinical atherosclerosis in order to develop early targets for the diagnosis and treatment of this disease, since it causes such widespread diseases as myocardial infarction, stroke, sudden death, and other common reasons of disability and mortality in developed countries. In recent years, studies of the human microbiome in different fields of medicine have become increasingly popular; there is evidence from numerous studies of the significant contribution of microbiome in different steps of atherogenesis. This review attempted to determine the current status of the databases PubMed and Scopus (until May, 2020) to highlight current ideas on the potential role of microbiome and its metabolites in atherosclerosis development, its mechanisms of action in lipids metabolism, endothelial dysfunction, inflammatory pathways, and mitochondrial dysfunction. Results of clinical studies elucidating the relationship of microbiome with subclinical atherosclerosis and cardiovascular disease considered in this article demonstrate strong association of microbiome composition and its metabolites with atherosclerosis and cardiovascular disease. Data on microbiome impact in atherogenesis open a wide perspective to develop new diagnostic and therapeutic approaches, but further comprehensive studies are necessary.

Enzyme annotation in UniProtKB using Rhea

Motivation

To provide high quality computationally tractable enzyme annotation in UniProtKB using Rhea, a comprehensive expert-curated knowledgebase of biochemical reactions which describes reaction participants using the ChEBI (Chemical Entities of Biological Interest) ontology.

Results

We replaced existing textual descriptions of biochemical reactions in UniProtKB with their equivalents from Rhea, which is now the standard for annotation of enzymatic reactions in UniProtKB. We developed improved search and query facilities for the UniProt website, REST API and SPARQL endpoint that leverage the chemical structure data, nomenclature and classification that Rhea and ChEBI provide.

Availability and implementation

UniProtKB at https://www.uniprot.org; UniProt REST API at https://www.uniprot.org/help/api; UniProt SPARQL endpoint at https://sparql.uniprot.org/; Rhea at https://www.rhea-db.org.

Effects of gut microbial metabolite trimethylamine N-oxide (TMAO) on platelets and endothelial cells

Thrombotic events result from different pathologies and are the underlying causes of severe diseases like stroke or myocardial infarction. Recent basic research now revealed a link between food uptake, food conversion and gut metabolism. Gut microbial production of trimethylamine N-oxide (TMAO) from dietary nutrients like choline, lecithin and L-carnitine was associated with the development of cardiovascular diseases. Within this review we give a systematic overview about the influence of TMAO on blood components like platelets and endothelial cells which both are involved as key players in thrombotic processes. In summary, a mechanistic correlation between the gut microbiome, TMAO and cardiovascular diseases becomes obvious and emphasizes to the significance of the intestinal microbiome.

Role of gut microbiota in identification of novel TCM-derived active metabolites

Traditional Chinese Medicine (TCM) has been extensively used to ameliorate diseases in Asia for over thousands of years. However, owing to a lack of formal scientific validation, the absence of information regarding the mechanisms underlying TCMs restricts their application. After oral administration, TCM herbal ingredients frequently are not directly absorbed by the host, but rather enter the intestine to be transformed by gut microbiota. The gut microbiota is a microbial community living in animal intestines, and functions to maintain host homeostasis and health. Increasing evidences indicate that TCM herbs closely affect gut microbiota composition, which is associated with the conversion of herbal components into active metabolites. These may significantly affect the therapeutic activity of TCMs. Microbiota analyses, in conjunction with modern multiomics platforms, can together identify novel functional metabolites and form the basis of future TCM research.

Plasma trimethylamine n-oxide is associated with renal function in patients with heart failure with preserved ejection fraction

Background

Heart failure with preserved ejection fraction (HFpEF) is an emerging global health problem with less awareness. Renal dysfunction in HFpEF is associated with worse outcome. However, there is lack of rapid, noninvasive and accurate method for risk stratification in HFpEF and renal dysfunction. This study aimed to explore the utility of plasma trimethylamine n-oxide (TMAO) for evaluation of HFpEF and renal function.

Methods

Plasma TMAO levels were measured in total 324 subjects comprising 228 HFpEF patients and 96 healthy controls.

Results

TMAO levels were significantly elevated in patients with HFpEF compared with controls (12.65(9.32–18.66) μg/l vs 10.85(6.35–15.58) μg/l, p <  0.01). Subjects in higher TMAO tertile group had more incidences of HFpEF ((78.5%) in tertile 3 vs (73.39%) in tertile 2 vs (59.26%) in tertile 1, p <  0.01). TMAO concentrations were inversely correlated with estimated glomerular filtration rate (eGFR) and HFpEF patients with impaired renal function (eGFR < 60 ml/min/1.73 m²) had higher TMAO than those with normal eGFR (≥ 60 ml/min/1.73 m²) (14.18(10.4–23.06) μg/l vs 10.9(7.48–15.47) μg/l, p < 0.01). Increased TMAO levels were independently associated with higher risk of HFpEF (OR = 3.49, 95% CI: 1.23–9.86, p = 0.02) and renal dysfunction (OR = 9.57, 95% CI: 2.11–43.34, p < 0.01) after adjustment for multiple traditional risk factors. Furthermore, TMAO had good performance at distinguishing HFpEF from controls (AUC = 0.63, p < 0.01), and renal dysfunction from normal renal function in HFpEF (AUC = 0.67, p < 0.01).

Conclusion

In this cross-sectional study, HFpEF and renal function were closely related with plasma TMAO levels and TMAO may serve as a diagnostic biomarker for HFpEF and renal function.

Trimethylamine N-oxide levels are associated with NASH in obese subjects with type 2 diabetes

AIMS

Trimethylamine N-oxide (TMAO), choline and betaine serum levels have been associated with metabolic diseases including type 2 diabetes (T2D) and non-alcoholic fatty liver disease (NAFLD). These associations could be mediated by insulin resistance. However, the relationships among these metabolites, insulin resistance and NAFLD have not been thoroughly investigated. Moreover, it has recently been suggested that TMAO could play a role in NAFLD by altering bile acid metabolism. We examined the association between circulating TMAO, choline and betaine levels and NAFLD in obese subjects.

METHODS

Serum TMAO, choline, betaine and bile acid levels were measured in 357 Mexican obese patients with different grades of NAFLD as determined by liver histology. Associations of NAFLD with TMAO, choline and betaine levels were tested. Moreover, association of TMAO levels with non-alcoholic steatohepatitis (NASH) was tested separately in patients with and without T2D.

RESULTS

TMAO and choline levels were significantly associated with NAFLD histologic features and NASH risk. While increased serum TMAO levels were significantly associated with NASH in patients with T2D, in non-T2D subjects this association lost significance after adjusting for sex, BMI and HOMA2-IR. Moreover, circulating secondary bile acids were associated both with increased TMAO levels and NASH.

CONCLUSIONS

In obese patients, circulating TMAO levels were associated with NASH mainly in the presence of T2D. Functional studies are required to evaluate the role of insulin resistance and T2D in this association, both highly prevalent in NASH patients.

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.

Genoprotective Properties and Metabolites of β-Glucan-Rich Edible Mushrooms Following Their In Vitro Fermentation by Human Faecal Microbiota

A variety of bioactive compounds, constituents of edible mushrooms, in particular β-glucans, i.e., a group of β-d-glucose polysaccharides abundant in the fungal cell walls, have been linked to immunomodulating, anticancer and prebiotic activities. The aim of the study was the investigation of the genoprotective effects of edible mushrooms produced by Pleurotus eryngii, Pleurotus ostreatus and Cyclocybe cylindracea (Basidiomycota). Mushrooms from selected strains of the species mentioned above were fermented in vitro using faecal inocula from healthy volunteers. The cytotoxic and anti-genotoxic properties of the fermentation supernatants (FSs) were investigated in Caco-2 human colon adenocarcinoma cells. The FSs were cytotoxic in a dose-dependent manner. Non-cytotoxic concentrations were used for the genotoxicity studies, which revealed that mushrooms’ FSs have the ability to protect Caco-2 cells against tert-butyl hydroperoxide (t-BOOH), a known genotoxic agent. Their global metabolic profiling was assessed by ¹H-NMR spectroscopy. A total of 37 metabolites were identified with the use of two-dimensional (2D) homo- and hetero-nuclear NMR experiments. Multivariate data analysis monitored the metabolic variability of gut microbiota and probed to biomarkers potentially associated with the health-promoting effects of edible mushrooms.

Effects of choline supplementation on liver biology, gut microbiota, and inflammation in Helicobacter pylori-infected mice

AIMS

Diet is one of the factors affecting the pathogenicity of Helicobacter pylori (H. pylori) infection. Choline is a dietary component that is crucial for normal cellular function. However, choline intake imbalance can lead to liver injury, inflammation, and changes of the gut microbiota composition. The study aimed to explore the effects of choline supplementation on liver biology, gut microbiota, and inflammation in H. pylori-infected mice.

MAIN METHODS

Liver function was detected by biochemical and histopathological analysis. Serum inflammatory markers were measured using ELISA. Fecal microbial profiles were determined via 16S rRNA sequencing.

KEY FINDINGS

The results showed that choline supplementation decreased serum LDL level, while increased the activities of serum AST and ALT in normal BALB/c mice. Besides, choline also reduced hepatic SOD and GSH-Px activities, and elevated hepatic MDA level of H. pylori-infected mice. Moreover, choline markedly enhanced the concentrations of inflammatory factors including LPS, CRP, IL-6, TNF-α, and CXCL1 in H. pylori-infected mice. Meanwhile, choline and H. pylori cotreatment altered the richness and diversity of the mice gut microbiota, and increased the relative abundance of Escherichia_Shigella, which had a significant positive correlation with the levels of LPS, CRP, IL-6, TNF-α and CXCL1.

SIGNIFICANCE

Our data suggest, for the first time, that choline can aggravate H. pylori-induced inflammation, which may be associated with the alterations of gut microbiota. This study may provide novel insights into the possible effects of food-derived choline on H. pylori infection-related diseases.

Gut microbiota-associated metabolite trimethylamine N-Oxide and the risk of stroke: a systematic review and dose-response meta-analysis

AIMS

Several epidemiological studies have examined the association between trimethylamine N-Oxide (TMAO) and stroke risk; however, the results are still inconclusive. The purpose of this meta-analysis was to evaluate the relationship between TMAO concentrations and stroke risk.

METHODS

PubMed, Scopus, Cochrane and ProQuest search engines were systematically searched up to 18 June 2019. All of the studies that evaluated the relationship between TMAO and stroke were included in the systematic review and eligible studies were included into the meta-analysis. Meta-regression and subgroup analysis were also employed to find the source of heterogeneity.

RESULTS

Eight studies (two cross-sectional studies, two cohort studies, three case-control studies and one nested case-control study) with a total of 6150 participants were included in the meta-analysis. The overall result showed that being in the highest category of TMAO increased the odds of stroke by 68% (OR: 1.675; CI: 0.866-3.243; P = 0.047) and mean TMAO concentrations was 2.201 μmol/L higher in patients with stroke rather than non-stroke controls (weighted mean difference (WMD): 2.20; CI: 1.213-3.188; P < 0.001). Furthermore, we observed revealed a non-linear association between increased TMAO levels and increased odds of stroke (P- for nonlinearity < 0.001). In addition, visual inspection of the funnel plot revealed a significant asymmetry among studies examining the differences in TMAO in patients with stroke versus control group.

CONCLUSION

This is the first meta-analysis to show positive dose-dependent relations between circulating TMAO concentration and stroke risk. However, further interventional studies and long-term studies are needed to better explain causality.

Modulation of the Gut Microbiota by Olive Oil Phenolic Compounds: Implications for Lipid Metabolism, Immune System, and Obesity

There is extensive information of the beneficial effects of virgin olive oil (VOO), especially on cardiovascular diseases. Some VOO healthy properties have been attributed to their phenolic-compounds (PCs). The aim of this review is to present updated data on the effects of olive oil (OO) PCs on the gut microbiota, lipid metabolism, immune system, and obesity, as well as on the crosstalk among them. We summarize experiments and clinical trials which assessed the specific effects of the olive oil phenolic-compounds (OOPCs) without the synergy with OO-fats. Several studies have demonstrated that OOPC consumption increases Bacteroidetes and/or reduces the Firmicutes/Bacteroidetes ratio, which have both been related to atheroprotection. OOPCs also increase certain beneficial bacteria and gut-bacteria diversity which can be therapeutic for lipid-immune disorders and obesity. Furthermore, some of the mechanisms implicated in the crosstalk between OOPCs and these disorders include antimicrobial-activity, cholesterol microbial metabolism, and metabolites produced by bacteria. Specifically, OOPCs modulate short-chain fatty-acids produced by gut-microbiota, which can affect cholesterol metabolism and the immune system, and may play a role in weight gain through promoting satiety. Since data in humans are scarce, there is a necessity for more clinical trials designed to assess the specific role of the OOPCs in this crosstalk.

Calcific Aortic Valve Disease-Natural History and Future Therapeutic Strategies

Calcific aortic valve disease (CAVD) is the most frequent heart valve disorder. It is characterized by an active remodeling process accompanied with valve mineralization, that results in a progressive aortic valve narrowing, significant restriction of the valvular area, and impairment of blood flow.The pathophysiology of CAVD is a multifaceted process, involving genetic factors, chronic inflammation, lipid deposition, and valve mineralization. Mineralization is strictly related to the inflammatory process in which both, innate, and adaptive immunity are involved. The underlying pathophysiological pathways that go from inflammation to calcification and, finally lead to severe stenosis, remain, however, incompletely understood. Histopathological studies are limited to patients with severe CAVD and no samples are available for longitudinal studies of disease progression. Therefore, alternative routes should be explored to investigate the pathogenesis and progression of CAVD.Recently, increasing evidence suggests that epigenetic markers such as non-coding RNAs are implicated in the landscape of phenotypical changes occurring in CAVD. Furthermore, the microbiome, an essential player in several diseases, including the cardiovascular ones, has recently been linked to the inflammation process occurring in CAVD. In the present review, we analyze and discuss the CAVD pathophysiology and future therapeutic strategies, focusing on the real and putative role of inflammation, calcification, and microbiome.

A Role for Gut Microbiome Fermentative Pathways in Fatty Liver Disease Progression

Non-alcoholic fatty liver disease (NAFLD) is a multifactorial disease in which environmental and genetic factors are involved. Although the molecular mechanisms involved in NAFLD onset and progression are not completely understood, the gut microbiome (GM) is thought to play a key role in the process, influencing multiple physiological functions. GM alterations in diversity and composition directly impact disease states with an inflammatory course, such as non-alcoholic steatohepatitis (NASH). However, how the GM influences liver disease susceptibility is largely unknown. Similarly, the impact of strategies targeting the GM for the treatment of NASH remains to be evaluated. This review provides a broad insight into the role of gut microbiota in NASH pathogenesis, as a diagnostic tool, and as a therapeutic target in this liver disease. We highlight the idea that the balance in metabolic fermentations can be key in maintaining liver homeostasis. We propose that an overabundance of alcohol-fermentation pathways in the GM may outcompete healthier, acid-producing members of the microbiota. In this way, GM ecology may precipitate a self-sustaining vicious cycle, boosting liver disease progression.

The Molecular and Mechanistic Insights Based on Gut-Liver Axis: Nutritional Target for Non-Alcoholic Fatty Liver Disease (NAFLD) Improvement

Non-alcoholic fatty liver disease (NAFLD) is recognized as the most frequent classification of liver disease around the globe. Along with the sequencing technologies, gut microbiota has been regarded as a vital factor for the maintenance of human and animal health and the mediation of multiple diseases. The modulation of gut microbiota as a mechanism affecting the pathogenesis of NAFLD is becoming a growing area of concern. Recent advances in the communication between gut and hepatic tissue pave novel ways to better explain the molecular mechanisms regarding the pathological physiology of NAFLD. In this review, we recapitulate the current knowledge of the mechanisms correlated with the development and progression of NAFLD regulated by the gut microbiome and gut-liver axis, which may provide crucial therapeutic strategies for NAFLD. These mechanisms predominantly involve: (1) the alteration in gut microbiome profile; (2) the effects of components and metabolites from gut bacteria (e.g., lipopolysaccharides (LPS), trimethylamine-N-oxide (TMAO), and N,N,N-trimethyl-5-aminovaleric acid (TMAVA)); and (3) the impairment of intestinal barrier function and bile acid homeostasis. In particular, the prevention and therapy of NAFLD assisted by nutritional strategies are highlighted, including probiotics, functional oligosaccharides, dietary fibers, ω-3 polyunsaturated fatty acids, functional amino acids (L-tryptophan and L-glutamine), carotenoids, and polyphenols, based on the targets excavated from the gut-liver axis.

Gut metagenomic and short chain fatty acids signature in hypertension: a cross-sectional study

Hypertension is an independent and preventable risk factor for the development of cardiovascular diseases, however, little is known about the impact of gut microbiota composition in its development. We carried out comprehensive gut microbiota analysis and targeted metabolomics in a cross-sectional study of 29 non-treated hypertensive (HT) and 32 normotensive (NT) subjects. We determined fecal microbiota composition by 16S rRNA gene sequencing and bacterial functions by metagenomic analysis. The microbial metabolites analysed were short chain fatty acids (SCFA) both in plasma and feces, and trimethylamine N-oxide (TMAO) in plasma. The overall bacterial composition and diversity of bacterial community in the two groups were not significantly different. However, Ruminococcaceae NK4A214, Ruminococcaceae_UCG-010, Christensenellaceae_R-7, Faecalibacterium prausnitzii and Roseburia hominis were found to be significantly enriched in NT group, whereas, Bacteroides coprocola, Bacteroides plebeius and genera of Lachnospiraceae were increased in HT patients. We found a positive correlation between the HT-associated species and systolic and diastolic blood pressure after adjusted for measured confounders. SCFA showed antagonistic results in plasma and feces, detecting in HT subjects significant higher levels in feces and lower levels in plasma, which could indicate a less efficient SCFA absorption. Overall, our results present a disease classifier based on microbiota and bacterial metabolites to discriminate HT individuals from NT controls in a first disease grade prior to drug treatment.

Role of Gut Microbiota in Neuroendocrine Regulation of Carbohydrate and Lipid Metabolism via the Microbiota-Gut-Brain-Liver Axis

Gut microbiota play an important role in maintaining intestinal health and are involved in the metabolism of carbohydrates, lipids, and amino acids. Recent studies have shown that the central nervous system (CNS) and enteric nervous system (ENS) can interact with gut microbiota to regulate nutrient metabolism. The vagal nerve system communicates between the CNS and ENS to control gastrointestinal tract functions and feeding behavior. Vagal afferent neurons also express receptors for gut peptides that are secreted from enteroendocrine cells (EECs), such as cholecystokinin (CCK), ghrelin, leptin, peptide tyrosine tyrosine (PYY), glucagon-like peptide-1 (GLP-1), and 5-hydroxytryptamine (5-HT; serotonin). Gut microbiota can regulate levels of these gut peptides to influence the vagal afferent pathway and thus regulate intestinal metabolism via the microbiota-gut-brain axis. In addition, bile acids, short-chain fatty acids (SCFAs), trimethylamine-N-oxide (TMAO), and Immunoglobulin A (IgA) can also exert metabolic control through the microbiota-gut-liver axis. This review is mainly focused on the role of gut microbiota in neuroendocrine regulation of nutrient metabolism via the microbiota-gut-brain-liver axis.

The Presence of High Levels of Circulating Trimethylamine N-Oxide Exacerbates Central and Peripheral Inflammation and Inflammatory Hyperalgesia in Rats Following Carrageenan Injection

Gut microbiota-derived metabolite trimethylamine N-oxide (TMAO) has recently been shown to promote inflammation in peripheral tissues and the central nervous system (CNS), contributing to the pathogenesis of various human diseases. Here, we examined whether the presence of high levels of circulating TMAO would influence central and peripheral inflammation and inflammatory hyperalgesia in a carrageenan (CG)-induced rat model of inflammation. Rats were treated with vehicle or TMAO in drinking water. After 2 weeks of treatment, rats received intraplantar injection of saline or CG into the hind paw. Acute nociception was unaltered in TMAO-treated rats that had elevated plasma TMAO. Following CG injection, TMAO-treated rats were significantly more sensitive to thermal and mechanical stimulation of the inflamed paw and displayed greater paw edema. Molecular studies revealed that CG injection induced increases in recruitment of neutrophils/macrophages in the paw and activation of microglia in the spinal cord, along with increased activation of nuclear factor (NF)-kB and production of proinflammatory mediators in both vehicle-treated rats and TMAO-treated rats. However, the increases in the above parameters were more pronounced in TMAO-treated rats. Moreover, TMAO treatment decreased protein levels of anti-inflammatory mediator regulator of G protein signaling (RGS)-10 in both saline-injected rats and CG-injected rats. These findings suggest that the presence of high levels of circulating TMAO downregulates anti-inflammatory mediator RGS10 in both peripheral tissues and the CNS, which may increase the susceptibility to inflammatory challenge-induced NF-kB activity, leading to greater increase in production of inflammatory mediators and consequent exacerbation of peripheral inflammation and inflammatory hyperalgesia.

The “Green” FMOs: Diversity, Functionality and Application of Plant Flavoproteins

Flavin-dependent monooxygenases (FMOs) are ancient enzymes present in all kingdoms of life. FMOs typically catalyze the incorporation of an oxygen atom from molecular oxygen into small molecules. To date, the majority of functional characterization studies have been performed on mammalian, fungal and bacterial FMOs, showing that they play fundamental roles in drug and xenobiotic metabolism. By contrast, our understanding of FMOs across the plant kingdom is very limited, despite plants possessing far greater FMO diversity compared to both bacteria and other multicellular organisms. Here, we review the progress of plant FMO research, with a focus on FMO diversity and functionality. Significantly, of the FMOs characterized to date, they all perform oxygenation reactions that are crucial steps within hormone metabolism, pathogen resistance, signaling and chemical defense. This demonstrates the fundamental role FMOs have within plant metabolism, and presents significant opportunities for future research pursuits and downstream applications.

A Pilot Study on the Effects of l-Carnitine and Trimethylamine-N-Oxide on Platelet Mitochondrial DNA Methylation and CVD Biomarkers in Aged Women

l-carnitine supplementation has been used for cardiovascular health protection for a long time. Recently, trimethylamine-N-oxide (TMAO), which is an end product of l-carnitine metabolism via the activity of microbiota, has been identified as a cardiovascular disease (CVD) biomarker. The aim of this study was to assess the effect of 6 months of l-carnitine supplementation in a group of aged women engaged in a regular physical training. Platelet mitochondrial DNA methylation, an emerging and innovative biomarker, lipid profile and TMAO levels have been measured. TMAO increased after l-carnitine supplementation (before 344.3 ± 129.8 ng/mL vs. after 2216.8 ± 1869.0 ng/mL; n = 9; paired t-test, p = 0.02). No significant effects on TMAO were exerted by training alone (n = 9) or by l-leucine supplementation (n = 12). TMAO levels after 6 months of l-carnitine supplementation were associated with higher low-density lipoprotein-cholesterol (LDL-c) (Spearman Rho = 0.518, p = 0.003) and total cholesterol (TC) (Spearman Rho = 0.407, p = 0.026) levels. l-carnitine supplementation increased D-loop methylation in platelets (+6.63%; paired t-test, p = 0.005). D-loop methylation was not directly correlated to the TMAO augmentation observed in the supplemented group, but its increase inversely correlated with TC (Pearson coefficient = −0.529, p = 0.029) and LDL-c (Pearson coefficient = −0.439, p = 0.048). This evidence supports the hypothesis that the correlation between l-carnitine, TMAO and atherosclerosis might be more complex than already postulated, and the alteration of mitochondrial DNA (mtDNA) methylation in platelets could be involved in the pathogenesis of this multifactorial disease.

Adipokines and Adipose Tissue-Related Metabolites, Nuts and Cardiovascular Disease

Adipose tissue is a complex structure responsible for fat storage and releasing polypeptides (adipokines) and metabolites, with systemic actions including body weight balance, appetite regulation, glucose homeostasis, and blood pressure control. Signals sent from different tissues are generated and integrated in adipose tissue; thus, there is a close connection between this endocrine organ and different organs and systems such as the gut and the cardiovascular system. It is known that functional foods, especially different nuts, may be related to a net of molecular mechanisms contributing to cardiometabolic health. Despite being energy-dense foods, nut consumption has been associated with no weight gain, weight loss, and lower risk of becoming overweight or obese. Several studies have reported beneficial effects after nut consumption on glucose control, appetite suppression, metabolites related to adipose tissue and gut microbiota, and on adipokines due to their fatty acid profile, vegetable proteins, l-arginine, dietary fibers, vitamins, minerals, and phytosterols. The aim of this review is to briefly describe possible mechanisms implicated in weight homeostasis related to different nuts, as well as studies that have evaluated the effects of nut consumption on adipokines and metabolites related to adipose tissue and gut microbiota in animal models, healthy individuals, and primary and secondary cardiovascular prevention.

Amoxicillin Modulates ApoA-I Transcription and Secretion, Predominantly via PPARα Transactivation Inhibition

In a recent human study, we observed that amoxicillin treatment decreased HDL-C concentration. We hypothesize that antibiotics lower the transcription and secretion of ApoA-I, the responsible protein for HDL production. HepG2 and Caco-2 cells were exposed to increasing dose of amoxicillin, penicillin, and streptomycin. Secreted ApoA-I protein and mRNA transcripts were analyzed using ELISA and qPCR, respectively. To unravel underlying mechanisms, KEAP1, CPT1, and CHOP mRNA expressions were determined as well as PPARα transactivation. In HepG2 and Caco-2, amoxicillin decreased ApoA-I transcription and secretion. Effects on ApoA-I expression were clearly there for amoxicillin while no effects were observed for penicillin or streptomycin. KEAP1, CPT1, and CHOP mRNA expressions were reduced by amoxicillin treatments. Moreover, a significant correlation between ApoA-I and CPT1 mRNA expressions was found. Furthermore, amoxicillin lowered PPARα transactivation. All together, these data suggest that inhibited PPARα transactivation is involved in the effects of amoxicillin on ApoA-I. In conclusion, the direct effect of amoxicillin in treated HepG2 and Caco-2 cells was a lower ApoA-I secretion and transcription. Based on evaluating alterations in KEAP1, CPT1, and CHOP mRNA expressions plus PPARα transactivation, we suggest that a reduced PPARα activation is a potential mechanism behind the observed amoxicillin effects on ApoA-I expression.

Trimethylamine N-Oxide Metabolites in Early Pregnancy and Risk of Gestational Diabetes: A Nested Case-Control Study

OBJECTIVES

This study aimed to investigate the associations between trimethylamine N-oxide (TMAO) and related metabolites in early pregnancy and the risk of gestational diabetes mellitus (GDM).

DESIGN

A prospective cohort of 22,302 pregnant women from 2010 to 2012 in Tianjin, China, was used to perform a nested case-control study. A total of 243 women with GDM and 243 women without GDM matched by maternal age (±1 year) were used as cases and controls, respectively. Conditional logistic regression and restricted cubic spline were used to examine the full-range risk associations between individual TMAOs metabolites at the first antenatal care visit with GDM. Trimethylamine conversion ratio (TMAR) was defined as trimethylamine (TMA)/its precursors, and trimethylamine N-oxide conversion ratio (TMAOR) was defined as TMAO/TMA. An additive interaction between high TMAR and low TMAOR indicates a state of TMA accumulation, and a mathematical interaction between high TMAR and high TMAOR indicates accumulation of TMAO.

RESULTS

TMA was linearly associated with GDM, whereas TMA precursors and TMAO were inversely associated with GDM with clear threshold effects, i.e., 16 nmol/mL for TMAO, 200 nmol/mL for betaine, 112 nmol/mL for l-carnitine, and 110 and 270 nmol/mL for cholinechloride (a U-shaped relationship). Copresence of TMAR >0.35 and TMAOR ≤0.15 was associated with a markedly higher OR (11.16; 95% CI, 5.45 to 22.8), compared with TMAR >0.35 only (OR = 1.71; 95% CI, 0.42 to 6.95) or TMAOR ≤0.15 only (OR = 2.06; 95% CI, 1.09 to 3.90), with a significant additive interaction. However, the mathematical interaction was nonsignificant.

CONCLUSIONS

TMAO metabolites in the early pregnancy were associated with the risk of GDM, whereas TMA was more likely to play a causal role in GDM.

Decreased levels of circulating trimethylamine N-oxide alleviate cognitive and pathological deterioration in transgenic mice: a potential therapeutic approach for Alzheimer's disease

Trimethylamine-N-oxide (TMAO), a metabolite of gut microbiota, has been implicated in the pathogenesis of Alzheimer’s disease (AD). However, the mechanisms by which TMAO influence cognitive and pathological processes in the AD have not been investigated. In this study, we found that the circulating TMAO levels displayed an age-related increase in both WT and APP/PS1 mice and association with AD-like behavioral and pathological profile. Reduced TMAO by 3,3-Dimethyl-1-butanol (DMB) treatment ameliorated the cognitive deterioration and long-term potentiation (LTP) in APP/PS1 mice. Moreover, DMB treatment also induced a decrease in the Amyloid-β (Aβ)_1-42, β-secretase, and β-secretase-cleaved C-terminal fragment (βCTF) levels in the hippocampus. Finally, the effects obtained after treatment with DMB were accompanied by a reduction in circulating clusterin levels and hippocampal neuroinflammatory status in APP/PS1 mice. These findings demonstrate that elevated circulating TMAO during the aging process might deteriorate cognitive function and pathology in APP/PS1 mice.

A Crucial Role for Diet in the Relationship Between Gut Microbiota and Cardiometabolic Disease

Cardiometabolic disease (CMD), such as type 2 diabetes mellitus and cardiovascular disease, contributes significantly to morbidity and mortality on a global scale. The gut microbiota has emerged as a potential target to beneficially modulate CMD risk, possibly via dietary interventions. Dietary interventions have been shown to considerably alter gut microbiota composition and function. Moreover, several diet-derived microbial metabolites are able to modulate human metabolism and thereby alter CMD risk. Dietary interventions that affect gut microbiota composition and function are therefore a promising, novel, and cost-efficient method to reduce CMD risk. Studies suggest that fermentable carbohydrates can beneficially alter gut microbiota composition and function, whereas high animal protein and high fat intake negatively impact gut microbiota function and composition. This review focuses on the role of macronutrients (i.e., carbohydrate, protein, and fat) and dietary patterns (e.g., vegetarian/vegan and Mediterranean diet) in gut microbiota composition and function in the context of CMD.

Higher Circulating Trimethylamine N-oxide Sensitizes Sevoflurane-Induced Cognitive Dysfunction in Aged Rats Probably by Downregulating Hippocampal Methionine Sulfoxide Reductase A

Gut microbiota-derived metabolite trimethylamine N-oxide (TMAO) has recently been shown to promote oxidative stress and inflammation in the peripheral tissues, contributing to the pathogenesis of many diseases. Here we examined whether pre-existing higher circulating TMAO would influence cognitive function in aged rats after anesthetic sevoflurane exposure. Aged rats received vehicle or TMAO treatment for 3 weeks. After 2 weeks of treatment, these animals were exposed to either control or 2.6% sevoflurane for 4 h. One week after exposure, freezing as measured by fear conditioning test, microglia activity, proinflammatory cytokine expression and NADPH oxidase-dependent reactive oxygen species (ROS) production in the hippocampus (a key brain structure involved in learning and memory) were comparable between vehicle-treated rats exposed to control and vehicle-treated rats exposed to sevoflurane. TMAO treatment, which increased plasma TMAO before and 1 week after control or sevoflurane exposure, significantly reduced freezing to contextual fear conditioning, which was associated with increases in microglia activity, proinflammatory cytokine expression and NADPH oxidase-dependent ROS production in the hippocampus in rats exposed to sevoflurane but not in rats exposed to control. Moreover, hippocampal expression of antioxidant enzyme methionine sulfoxide reductase A (MsrA) was reduced by TMAO treatment in both groups, and TMAO-induced reduction in MsrA expression was negatively correlated with increased proinflammatory cytokine expression in rats exposed to SEV. These findings suggest that pre-existing higher circulating TMAO downregulates antioxidant enzyme MsrA in the hippocampus, which may sensitize the hippocampus to oxidative stress, resulting in microglia-mediated neuroinflammation and cognitive impairment in aged rats after sevoflurane exposure.

Microbiota-derived Trimethylamine N-oxide Predicts Cardiovascular Risk After STEMI

Trimethylamine N-oxide (TMAO), a metabolite derived from the gut microbiota, is proatherogenic and associated with cardiovascular events. However, the change in TMAO with secondary prevention therapies for ST-segment elevation acute myocardial infarction (STEMI) remains unclear. The purpose of this study was to investigate the sequential change in TMAO levels in response to the current secondary prevention therapies in patients with STEMI and the clinical impact of TMAO levels on cardiovascular events We included 112 STEMI patients and measured plasma TMAO levels at the onset of STEMI and 10 months later (chronic phase). After the chronic-phase assessment, patients were followed up for cardiovascular events. Plasma TMAO levels significantly increased from the acute phase to the chronic phase of STEMI (median: 5.63 to 6.76 μM, P = 0.048). During a median period of 5.4 years, 17 patients experienced events. The chronic-phase TMAO level independently predicted future cardiovascular events (adjusted hazard ratio for 0.1 increase in log chronic-phase TMAO level: 1.343, 95% confidence interval 1.122–1.636, P = 0.001), but the acute-phase TMAO level did not. This study demonstrated the clinical importance of the chronic-phase TMAO levels on future cardiovascular events in patients after STEMI.

The Microbial Metabolite Trimethylamine N-Oxide Links Vascular Dysfunctions and the Autoimmune Disease Rheumatoid Arthritis

Diet and microbiota each have a direct impact on many chronic, inflammatory, and metabolic diseases. As the field develops, a new perspective is emerging. The effects of diet may depend on the microbiota composition of the intestine. A diet that is rich in choline, red meat, dairy, or egg may promote the growth, or change the composition, of microbial species. The microbiota, in turn, may produce metabolites that increase the risk of cardiovascular disease. This article reviews our current understanding of the effects of the molecule trimethylamine-N-oxide (TMAO) obtained from food or produced by the microbiota. We review the mechanisms of actions of TMAO, and studies that associate it with cardiovascular and chronic kidney diseases. We introduce a novel concept: TMAO is one among a group of selective uremic toxins that may rise to high levels in the circulation or accumulate in various organs. Based on this information, we evaluate how TMAO may harm, by exacerbating inflammation, or may protect, by attenuating amyloid formation, in autoimmune diseases such as rheumatoid arthritis.

A New Light on Vitamin D in Obesity: A Novel Association with Trimethylamine-N-Oxide (TMAO)

Vitamin D deficiency and obesity are two public health problems extensively exacerbated over the last years. Among the several mechanisms proposed to account for the complex interplay between vitamin D and obesity, one that has gained particular attention is related to the emerging role of obesity-related changes in gut microbiota and gut-derived metabolites, such as Trimethylamine-N-oxide (TMAO). Vitamin D deficiency and high circulating TMAO levels are associated with body weight and the severity of non-alcoholic fatty liver disease (NAFLD). Considering the link of obesity with vitamin D on the one hand and obesity with TMAO on the other hand, and the central role of the liver in both the vitamin D and TMAO metabolism, the aim of this cross-sectional observational study was first, to confirm the possible inverse association between vitamin D and TMAO across different body mass index (BMI) classes and second, to investigate if this association could be influenced by the presence of NAFLD. One hundred and four adult subjects (50 males and 54 females; 35.38 ± 7.49 years) were enrolled. The fatty liver index (FLI) was used as a proxy for the diagnosis of NAFLD. Vitamin D deficiency was found in 65 participants (62.5%), while 33 subjects (31.7%) had insufficient levels, and the remaining subjects had sufficient levels of vitamin D. Subjects with both vitamin D deficiency and FLI-NAFLD had the highest TMAO levels (p < 0.001). By stratifying the sample population according to the BMI classes, vitamin D levels decreased significantly along with the increase of plasma TMAO concentrations, with the lowest vitamin D levels and highest TMAO, respectively, in class III obesity. Vitamin D levels showed significant opposite associations with circulating levels of TMAO (r = −0.588, p < 0.001), but this association was no longer significant after the adjustment for FLI values. The highest values of TMAO were significantly associated with the severity of obesity (OR 7.92; p < 0.001), deficiency of vitamin D (OR 1.62; p < 0.001), and FLI-NAFLD (OR 3.79; p < 0.001). The most sensitive and specific cut-off for vitamin D to predict the circulating levels of TMAO was ≤19.83 ng/mL (p < 0.001). In conclusion, our study suggests that high TMAO levels are associated with vitamin D deficiency and NAFLD. Further studies are required to investigate if there is a causality link or whether all of them are simply the consequence of obesity.

Differential effect of short-term popular diets on TMAO and other cardio-metabolic risk markers

BACKGROUND

Dietary nutrient intake and its metabolism by the gut microbiome have recently been implicated in cardiovascular disease (CVD) risk. In particular, trimethylamine N-oxide (TMAO), a metabolite of the gut microbiota, has been shown to be a predictor of incident CVD events. Elevated levels of branched-chain amino acids (BCAA) have also been associated with an increased propensity for insulin resistance.

METHODS

To study the association of dietary intake with systemic TMAO, its nutrient precursors, and BCAA levels on fasting plasma levels of TMAO and its nutrient precursors and BCAA, we conducted an exploratory post-hoc analysis of 3 popular diets - high fat (Atkins), Mediterranean (South Beach), and very low fat (Ornish) - using plasma samples from a prior randomized, crossover study, with each isocaloric dietary phase lasting 4 weeks. Metabolites were quantified using stable isotope dilution HPLC with on-line tandem mass spectrometry.

RESULTS

Compared to the low fat Ornish phase, the high fat Atkins dietary phase was characterized by increased levels of TMAO (3.3 vs. 1.8 μM, p = 0.01), and the BCAA valine (272.8 vs. 235.8 μM, p = 0.005) and leucine (105.9 vs. 96.4 μM, p = 0.01). The high fat Atkins dietary phase was also associated with higher levels of TMAO (3.3 vs 1.6 μM, p = 0.04), valine (272.8 vs. 240.7 μM, p = 0.004), and leucine (105.9 vs. 96.4 μM, p = 0.01) compared to baseline.

CONCLUSIONS

These data suggest that over a 4-week interval, a saturated fat diet that is predominantly animal-based, compared to an isocaloric, low fat, predominantly plant-based diet, is associated with heightened risk for cardiometabolic derangements, as monitored by a higher plasma levels of both TMAO and BCAA.

Cholesterol cholelithiasis: part of a systemic metabolic disease, prone to primary prevention

Cholesterol gallstone disease have relationships with various conditions linked with insulin resistance, but also with heart disease, atherosclerosis, and cancer. These associations derive from mechanisms active at a local (i.e. gallbladder, bile) and a systemic level and are involved in inflammation, hormones, nuclear receptors, signaling molecules, epigenetic modulation of gene expression, and gut microbiota. Despite advanced knowledge of these pathways, the available therapeutic options for symptomatic gallstone patients remain limited. Therapy includes oral litholysis by the bile acid ursodeoxycholic acid (UDCA) in a small subgroup of patients at high risk of postdissolution recurrence, or laparoscopic cholecystectomy, which is the therapeutic radical gold standard treatment. Cholecystectomy, however, may not be a neutral event, and potentially generates health problems, including the metabolic syndrome. Areas covered: Several studies on risk factors and pathogenesis of cholesterol gallstone disease, acting at a systemic level have been reviewed through a PubMed search. Authors have focused on primary prevention and novel potential therapeutic strategies. Expert commentary: The ultimate goal appears to target the manageable systemic mechanisms responsible for gallstone occurrence, pointing to primary prevention measures. Changes must target lifestyles, as well as experimenting innovative pharmacological tools in subgroups of patients at high risk of developing gallstones.

Extending PTR based breath analysis to real-time monitoring of reactive volatile organic compounds

Direct time resolved mass spectrometric monitoring of reactive exhaled nitrogen- and sulfur-containing volatile organic compounds (VOCs) related to metabolic processes, diseases and bacterial activity.