Trimethylamine N-Oxide and Cardiovascular Outcomes in Patients with ESKD Receiving Maintenance Hemodialysis

Spontaneously hypertensive rats exhibit increased liver flavin monooxygenase expression and elevated plasma TMAO levels compared to normotensive and Ang II-dependent hypertensive rats

Background: Flavin monooxygenases (FMOs) are enzymes responsible for the oxidation of a broad spectrum of exogenous and endogenous amines. There is increasing evidence that trimethylamine (TMA), a compound produced by gut bacteria and also recognized as an industrial pollutant, contributes to cardiovascular diseases. FMOs convert TMA into trimethylamine oxide (TMAO), which is an emerging marker of cardiovascular risk. This study hypothesized that blood pressure phenotypes in rats might be associated with variations in the expression of FMOs. Methods: The expression of FMO1, FMO3, and FMO5 was evaluated in the kidneys, liver, lungs, small intestine, and large intestine of normotensive male Wistar-Kyoto rats (WKY) and two distinct hypertensive rat models: spontaneously hypertensive rats (SHRs) and WKY rats with angiotensin II-induced hypertension (WKY-ANG). Plasma concentrations of TMA and TMAO were measured at baseline and after intravenous administration of TMA using liquid chromatography-mass spectrometry (LC-MS). Results: We found that the expression of FMOs in WKY, SHR, and WKY-ANG rats was in the descending order of FMO3 > FMO1 >> FMO5. The highest expression of FMOs was observed in the liver. Notably, SHRs exhibited a significantly elevated expression of FMO3 in the liver compared to WKY and WKY-ANG rats. Additionally, the plasma TMAO/TMA ratio was significantly higher in SHRs than in WKY rats. Conclusion: SHRs demonstrate enhanced expression of FMO3 and a higher plasma TMAO/TMA ratio. The variability in the expression of FMOs and the metabolism of amines might contribute to the hypertensive phenotype observed in SHRs.

Protein-rich foods, sea foods, and gut microbiota amplify immune responses in chronic diseases and cancers - Targeting PERK as a novel therapeutic strategy for chronic inflammatory diseases, neurodegenerative disorders, and cancer

The endoplasmic reticulum (ER) is a cellular organelle that is physiologically responsible for protein folding, calcium homeostasis, and lipid biosynthesis. Pathological stimuli such as oxidative stress, ischemia, disruptions in calcium homeostasis, and increased production of normal and/or folding-defective proteins all contribute to the accumulation of misfolded proteins in the ER, causing ER stress. The adaptive response to ER stress is the activation of unfolded protein response (UPR), which affect a wide variety of cellular functions to maintain ER homeostasis or lead to apoptosis. Three different ER transmembrane sensors, including PKR-like ER kinase (PERK), activating transcription factor 6 (ATF6), and inositol-requiring enzyme-1 (IRE1), are responsible for initiating UPR. The UPR involves a variety of signal transduction pathways that reduce unfolded protein accumulation by boosting ER-resident chaperones, limiting protein translation, and accelerating unfolded protein degradation. ER is now acknowledged as a critical organelle in sensing dangers and determining cell life and death. On the other hand, UPR plays a critical role in the development and progression of several diseases such as cardiovascular diseases (CVD), metabolic disorders, chronic kidney diseases, neurological disorders, and cancer. Here, we critically analyze the most current knowledge of the master regulatory roles of ER stress particularly the PERK pathway as a conditional danger receptor, an organelle crosstalk regulator, and a regulator of protein translation. We highlighted that PERK is not only ER stress regulator by sensing UPR and ER stress but also a frontier sensor and direct senses for gut microbiota-generated metabolites. Our work also further highlighted the function of PERK as a central hub that leads to metabolic reprogramming and epigenetic modification which further enhanced inflammatory response and promoted trained immunity. Moreover, we highlighted the contribution of ER stress and PERK in the pathogenesis of several diseases such as cancer, CVD, kidney diseases, and neurodegenerative disorders. Finally, we discuss the therapeutic target of ER stress and PERK for cancer treatment and the potential novel therapeutic targets for CVD, metabolic disorders, and neurodegenerative disorders. Inhibition of ER stress, by the development of small molecules that target the PERK and UPR, represents a promising therapeutic strategy.

Sweet, bloody consumption - what we eat and how it affects vascular ageing, the BBB and kidney health in CKD

In today's industrialized society food consumption has changed immensely toward heightened red meat intake and use of artificial sweeteners instead of grains and vegetables or sugar, respectively. These dietary changes affect public health in general through an increased incidence of metabolic diseases like diabetes and obesity, with a further elevated risk for cardiorenal complications. Research shows that high red meat intake and artificial sweeteners ingestion can alter the microbial composition and further intestinal wall barrier permeability allowing increased transmission of uremic toxins like p-cresyl sulfate, indoxyl sulfate, trimethylamine n-oxide and phenylacetylglutamine into the blood stream causing an array of pathophysiological effects especially as a strain on the kidneys, since they are responsible for clearing out the toxins. In this review, we address how the burden of the Western diet affects the gut microbiome in altering the microbial composition and increasing the gut permeability for uremic toxins and the detrimental effects thereof on early vascular aging, the kidney per se and the blood-brain barrier, in addition to the potential implications for dietary changes/interventions to preserve the health issues related to chronic diseases in future.

Serum Trimethylamine N-Oxide Level Is Positively Associated with Aortic Stiffness Measured by Carotid-Femoral Pulse Wave Velocity in Patients Undergoing Maintenance Hemodialysis

Trimethylamine N-oxide (TMAO) is a biomarker that is effective in predicting major adverse cardiovascular (CV) events. Age-related vascular problems are significantly affected by aortic stiffness (AS), which is independently linked to CV morbidity and mortality. This study aimed to determine the association between serum TMAO levels and carotid-femoral pulse wave velocity (cfPWV) in patients receiving hemodialysis (HD) therapy. In total, 115 patients with HD were enrolled in this study. The AS group included patients whose cfPWV was >10 m/s. Using high-performance liquid chromatography and mass spectrometry, the levels of serum TMAO were measured. The AS group included 42 (36.5%) patients, and compared with the non-AS group, the rates of diabetes, hypertension, older age, systolic blood pressure, serum glucose, and TMAO levels were high. In the multivariate logistic regression analysis, serum TMAO and age were independently linked with AS after correcting for the factors significantly associated with AS. Following multivariate stepwise linear regression analysis, serum TMAO in these individuals was found to be strongly correlated with cfPWV values (p < 0.001). In patients on chronic HD, serum TMAO level is an independent measure of AS and strongly correlated with cfPWV.

Significant correlation between the gut microbiota-derived metabolite trimethylamine-N-oxide and the risk of stroke: evidence based on 23 observational studies

The gut microbiota-derived metabolite trimethylamine-N-oxide (TMAO) is regarded as a major risk factor for cardiovascular events and diabetes. However, the association of TMAO with stroke has yet to be fully elucidated. The present meta-analysis was conducted to explore the association between TMAO and stroke. The present meta-analysis quantitatively summarized the results of studies that investigated the association between TMAO and stroke. The PubMed, Embase, Cochrane Library and Web of Science databases were systematically searched from January 1, 2001 to June 1, 2021. All studies that evaluated the association between TMAO and stroke were included in the present systematic review. The present meta-analysis included 30,808 participants and revealed that being in the higher TMAO category increased the odds of stroke by 68% (OR 1.83; 95% CI 1.02-3.29; P = 0.04), and that the mean TMAO concentration in stroke patients was 2.20 μmol/L higher than that of non-stroke controls (MD 2.20; 95% CI 1.23-3.16; P < 0.00001). In addition, TMAO plasma levels was associated with the risk of all-cause mortality, with a pooled HR of 1.89 (95% CI 1.15-3.08; P = 0.01). Both univariate analysis (UVA) and multivariate analysis (MVA) indicated that high TMAO levels significantly increased the risk of major adverse cardiovascular events (MACEs), with pooled RRs of 2.26 (95% CI 2.01-2.54; P < 0.00001) with UVA and 1.55 (95% CI 1.17-2.05; P = 0.002) with MVA respectively. In the current meta-analysis we revealed the positive association between circulating TMAO and stroke. Higher TMAO levels increased the risk of stroke and stroke patients experienced higher mean TMAO concentration. In addition, high TMAO plasma level was one of independent risk factors of MACEs and was associated with all-cause mortality.

Gut Microbiota-Targeted Interventions in the Management of Chronic Kidney Disease

Recent advances in microbiome research have informed the potential role of the gut microbiota in the regulation of metabolic, cardiovascular, and renal systems, and, when altered, in the pathogenesis of various cardiometabolic disorders, including chronic kidney disease (CKD). The improved understanding of gut dysbiosis in cardiometabolic pathologies in turn has led to a vigorous quest for developing therapeutic strategies. These therapeutic strategies aim to investigate whether interventions targeting gut dysbiosis can shift the microbiota toward eubiosis and if these shifts, in turn, translate into improvements in (or prevention of) CKD and its related complications, such as premature cardiovascular disease. Existing evidence suggests that multiple interventions (eg, plant-based diets; prebiotic, probiotic, and synbiotic supplementation; constipation treatment; fecal microbiota transplantation; and intestinal dialysis) might result in favorable modulation of the gut microbiota in patients with CKD, and thereby potentially contribute to improving clinical outcomes in these patients. In this review, we summarize the current understanding of the characteristics and roles of the gut microbiota in CKD and discuss the potential of emerging gut microbiota-targeted interventions in the management of CKD.

The role of gut-dependent molecule trimethylamine N-oxide as a novel target for the treatment of chronic kidney disease

Trimethylamine N-oxide (TMAO) is an intestinal uremic toxin molecule mainly excreted by the kidney. Therefore, the plasma TMAO concentration is significantly increased in chronic kidney disease (CKD) patients, and plasma TMAO can be cleared by dialysis. Furthermore, TMAO damage the kidney mainly through three mechanisms: oxidative stress, inflammation and endoplasmic reticulum stress. Clinical experiments have indicated that higher TMAO levels are strongly related to the elevated incidence and mortality of cardiovascular (CV) events in CKD patients. Moreover, experimental data have shown that high levels of TMAO directly aggravate atherosclerosis, thrombosis and enhance myocardial contractility, resulting in myocardial ischemia and stroke. Specially, there are currently four potential ways to reduce blood TMAO concentration or block the effect of TMAO, including reducing the intake of trimethylamine (TMA) precursors in the diet, regulating the intestinal flora to reduce TMA production, interrupting the role of flavin-dependent monooxygenase isoforms (FMOs) to reduce the generation of TMAO, and blocking the TMAO receptor protein kinase R-like endoplasmic reticulum kinase (PERK). We hope that more clinical studies and clinicians will focus on clinical treatment to reduce the concentration of TMAO and alleviate renal damage.

Neither Trimethylamine-N-Oxide nor Trimethyllysine Is Associated with Atherosclerosis: A Cross-Sectional Study in Older Japanese Adults

Recent evidence suggests that trimethylamine-N-oxide (TMAO), a metabolite of L-carnitine and choline, is linked to atherosclerosis and cardiovascular diseases. As TMAO content is very high in fish, we raised the following question: why do Japanese people, who consume lots of fish, show a low risk of atherosclerosis? To address this question, we investigated the effects of TMAO and other L-carnitine-related metabolites on carotid intima-media thickness (IMT). Participants were recruited from a small island and a mountainous region. Plasma L-carnitine, γ-butyrobetaine (γBB), TMAO, trimethyllysine (TML), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) levels were measured using liquid or gas chromatography-mass spectrometry. Plasma L-carnitine concentration was higher in men than in women. TMAO and TML were significantly higher in the residents of the island than in the mountainous people. In multiple linear regression analyses in all participants, TML showed a significant inverse association with max-IMT and plaque score (PS), whereas TMAO did not show any associations. In women, L-carnitine was positively associated with max-IMT and PS. TMAO was correlated with both EPA and DHA levels, implying that fish is a major dietary source of TMAO in Japanese people. Our study found that plasma TMAO was not an apparent risk factor for atherosclerosis in elderly Japanese people, whereas a low level of TML might be a potential risk. L-carnitine may be a marker for atherosclerosis in women.

Aorta- and liver-generated TMAO enhances trained immunity for increased inflammation via ER stress/mitochondrial ROS/glycolysis pathways

We determined whether gut microbiota-produced trimethylamine (TMA) is oxidized into trimethylamine N-oxide (TMAO) in nonliver tissues and whether TMAO promotes inflammation via trained immunity (TI). We found that endoplasmic reticulum (ER) stress genes were coupregulated with MitoCarta genes in chronic kidney diseases (CKD); TMAO upregulated 190 genes in human aortic endothelial cells (HAECs); TMAO synthesis enzyme flavin-containing monooxygenase 3 (FMO3) was expressed in human and mouse aortas; TMAO transdifferentiated HAECs into innate immune cells; TMAO phosphorylated 12 kinases in cytosol via its receptor PERK and CREB, and integrated with PERK pathways; and PERK inhibitors suppressed TMAO-induced ICAM-1. TMAO upregulated 3 mitochondrial genes, downregulated inflammation inhibitor DARS2, and induced mitoROS, and mitoTEMPO inhibited TMAO-induced ICAM-1. β-Glucan priming, followed by TMAO restimulation, upregulated TNF-α by inducing metabolic reprogramming, and glycolysis inhibitor suppressed TMAO-induced ICAM-1. Our results have provided potentially novel insights regarding TMAO roles in inducing EC activation and innate immune transdifferentiation and inducing metabolic reprogramming and TI for enhanced vascular inflammation, and they have provided new therapeutic targets for treating cardiovascular diseases (CVD), CKD-promoted CVD, inflammation, transplantation, aging, and cancer.

Associations of plasma TMAO and its precursors with stroke risk in the general population: A nested case-control study

BACKGROUND

Trimethylamine N-oxide (TMAO) is a gut-derived atherogenic metabolite. However, the role of TMAO and its precursors in the development of stroke remains unclear. We aimed to examine the associations between metabolites in TMAO biosynthesis and stroke risk.

METHODS

A nested case-control study was performed in a community-based cohort (2013-2018, n = 16,113). We included 412 identified stroke cases and 412 controls matched by age and sex. Plasma carnitine, choline, betaine, trimethyl lysine (TML), and TMAO were measured by ultrahigh performance liquid chromatography-tandem mass spectrometry. Conditional logistic regression analyses were used to calculate odds ratios (ORs) and their 95% confidence intervals (CIs) between these biomarkers and stroke risk.

RESULTS

After adjustment for body mass index, smoking, hypertension, educational attainment, and estimated glomerular filtration rate, the corresponding OR for the highest versus lowest quartile was 1.74 (95% CI: 1.16-2.61, P trend = 0.006) for total stroke and 1.81 (95% CI: 1.14-2.86, P trend = 0.020) for ischemic stroke in an essentially linear dose-response fashion. A significant association between TMAO and nonischemic stroke was shown as a J-shape with OR for the highest versus second quartile of 5.75 (95% CI: 1.73-19.1). No meaningful significant risk association was found among plasma carnitine, choline, betaine, and TML with stroke risk.

CONCLUSIONS

Increased TMAO was associated with higher stroke risk in the community-based population, whereas the TMAO precursors carnitine, choline, betaine, and TML were not associated. Further studies are warranted to confirm these findings and to further elucidate the role of TMAO in the development of stroke.

The association between TMAO, CMPF, and clinical outcomes in advanced chronic kidney disease: results from the European QUALity (EQUAL) Study

BACKGROUND

Trimethylamine N-oxide (TMAO), a metabolite from red meat and fish consumption, plays a role in promoting cardiovascular events. However, data regarding TMAO and its impact on clinical outcomes are inconclusive, possibly due to its undetermined dietary source.

OBJECTIVES

We hypothesized that circulating TMAO derived from fish intake might cause less harm compared with red meat sources by examining the concomitant level of 3-carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF), a known biomarker of fish intake, and investigated the association between TMAO, CMPF, and outcomes.

METHODS

Patients were recruited from the European QUALity (EQUAL) Study on treatment in advanced chronic kidney disease among individuals aged ≥65 y whose estimated glomerular filtration rate (eGFR) had dropped for the first time to ≤20 mL/min per 1.73 m2 during the last 6 mo. The association between TMAO, CMPF, and outcomes including all-cause mortality and kidney replacement therapy (KRT) was assessed among 737 patients. Patients were further stratified by median cutoffs of TMAO and CMPF, suggesting high/low red meat and fish intake.

RESULTS

During a median of 39 mo of follow-up, 232 patients died. Higher TMAO was independently associated with an increased risk of all-cause mortality (multivariable HR: 1.46; 95% CI: 1.17, 1.83). Higher CMPF was associated with a reduced risk of both all-cause mortality (HR: 0.79; 95% CI: 0.71, 0.89) and KRT (HR: 0.80; 95% CI: 0.71, 0.90), independently of TMAO and other clinically relevant confounders. In comparison to patients with low TMAO and CMPF, patients with low TMAO and high CMPF had reduced risk of all-cause mortality (adjusted HR: 0.49; 95% CI: 0.31, 0.73), whereas those with high TMAO and high CMPF showed no association across adjusted models.

CONCLUSIONS

High CMPF conferred an independent role in health benefits and might even counteract the unfavorable association between TMAO and outcomes. Whether higher circulating CMPF concentrations are due to fish consumption, and/or if CMPF is a protective factor, remains to be verified.

Circulating Trimethylamine-N-Oxide and Risk of All-Cause and Cardiovascular Mortality in Patients With Chronic Kidney Disease: A Systematic Review and Meta-Analysis

Background

Trimethylamine-N-oxide (TMAO) is expected to be a prognostic biomarker among patients suffering from chronic kidney disease (CKD). However, investigations on the association between TMAO and CKD prognosis are conflicting. In the present article, we aimed to assess the relationship of circulating TMAO with the risk of all-cause and cardiovascular mortality among CKD patients by a meta-analysis.

Methods

Data were collected from PubMed, EMBASE, and Web of Science for systematically searching related literature (last update: February 2022). The multivariable-adjusted hazard risks (HR) and their 95% confidence intervals (CI) were pooled using random effects models.

Results

Eleven prospective cohort studies covering 7,899 CKD patients were enrolled in this meta-analysis. When comparing individuals in the top and bottom baseline TMAO levels thirds, the multivariate adjusted pooled HR was 1.29 (95% CI 1.11–1.51, P = 0.001) for all-cause mortality, and 1.45 (95% CI 1.01–2.09, P = 0.043) for cardiovascular death. For continuous variables, per 1 unit increase of circulating TMAO levels was associated with a 3% higher all-cause mortality (HR 1.03, 95% CI 1.00–1.06, P = 0.032), but not significantly associated with cardiovascular death (HR 1.08, 95% CI 0.92–1.27, P = 0.346). Stratified analyses revealed that the positive relationship between TMAO and all-cause mortality remained significant after adjusting for diabetes, blood pressure, blood lipid, renal function, or inflammatory parameters.

Conclusion

Higher circulating TMAO was associated with an increased mortality risk among patients with CKD, and this relationship may be dependent on TMAO dose and independent of renal function, inflammation, diabetes, hypertension, and dyslipidemia.

Systematic Review Registration

[https://www.INPLASY.COM], identifier [INPLASY2021100049].

Gut microbiota-derived metabolite trimethylamine-N-oxide and multiple health outcomes: an umbrella review and updated meta-analysis

BACKGROUND

Trimethylamine-N-oxide (TMAO) is a gut microbiota-derived metabolite produced from dietary nutrients. Many studies have discovered that circulating TMAO concentrations are linked to a wide range of health outcomes.

OBJECTIVES

This study aimed to summarize health outcomes related to circulating TMAO concentrations.

METHODS

We searched the Embase, Medline, Web of Science, and Scopus databases from inception to 15 February, 2022 to identify and update meta-analyses examining the associations between TMAO and multiple health outcomes. For each health outcome, we estimated the summary effect size, 95% prediction CI, between-study heterogeneity, evidence of small-study effects, and evidence of excess-significance bias. These metrics were used to evaluate the evidence credibility of the identified associations.

RESULTS

This umbrella review identified 24 meta-analyses that investigated the association between circulating TMAO concentrations and health outcomes including all-cause mortality, cardiovascular diseases (CVDs), diabetes mellitus (DM), cancer, and renal function. We updated these meta-analyses by including a total of 82 individual studies on 18 unique health outcomes. Among them, 14 associations were nominally significant. After evidence credibility assessment, we found 6 (33%) associations (i.e., all-cause mortality, CVD mortality, major adverse cardiovascular events, hypertension, DM, and glomerular filtration rate) to present highly suggestive evidence.

CONCLUSIONS

TMAO might be a novel biomarker related to human health conditions including all-cause mortality, hypertension, CVD, DM, cancer, and kidney function. Further studies are needed to investigate whether circulating TMAO concentrations could be an intervention target for chronic disease.This review was registered at www.crd.york.ac.uk/prospero/ as CRD42021284730.

Higher dietary fibre intake is associated with lower CVD mortality risk among maintenance haemodialysis patients: a multicentre prospective cohort study

High fibre intake is associated with reduced mortality risk in both general and chronic kidney disease populations. However, in dialysis patients, such data are limited. Therefore, the association between dietary fibre intake (DFI) and the risk of all-cause and CVD mortality was examined in this study. A total of 1044 maintenance haemodialysis (MHD) patients from eight outpatient dialysis centres in China were included in this study. Data on DFI were collected using 24-h dietary recalls for 3 d in a week and were normalised to actual dry weight. The study outcomes included all-cause and CVD mortality. Over a median of 46 months of follow-up, 354 deaths were recorded, of which 210 (59 %) were due to CVD. On assessing DFI as tertiles, the CVD mortality risk was significantly lower in patients in tertiles 2-3 (≥0·13 g/kg per d; hazard ratio (HR) 0·71; 95 % CI 0·51, 0·97) compared with those in tertile 1 (<0·13 g/kg per d). A similar but non-significant trend was found for the association between DFI (tertiles 2-3 v. tertile 1; HR 0·83; 95 % CI 0·64, 1·07) and all-cause mortality. In summary, higher DFI was associated with lower CVD mortality risk among Chinese MHD patients. This study emphasises the significance of DFI in MHD patients and provides information that is critical for the improvement of dietary guidelines for dialysis patients.

Trimethylamine-N-oxide (TMAO) and clinical outcomes in patients with end-stage kidney disease receiving peritoneal dialysis

BACKGROUND

Trimethylamine-N-oxide (TMAO) is a gut bacteria-derived metabolite of l-carnitine and choline. A high concentration of TMAO has been proven to relate to cardiovascular disease (CVD), all-cause mortality and chronic kidney disease progression. We aimed to investigate the relation between the value of serum TMAO and outcomes for peritoneal dialysis (PD) patients.

METHODS

This is a prospective cohort study with data retrospectively analysed. All incident PD patients were enrolled and followed up. Log-rank test, competing risk survival analysis and COX regression were performed to test the effect of serum TMAO on developing first-episode peritonitis, all-cause and CVD mortality.

RESULTS

A wide distribution of serum TMAO concentration was observed in 513 PD patients, with a median level of 72.3 (43.7, 124.7) µmol/L. Patients with lower TMAO concentration were more likely to be without diabetes and hypertension. Patients with lower TMAO concentration showed better residual kidney function and solute clearance at baseline. Participants in the higher three TMAO quartiles showed an increased risk for first-episode peritonitis (p = 0.039). By competing risk survival analysis, after adjusting for age, sex, diabetes mellitus, CVD, body mass index, albumin, high-sensitive C-reactive protein, potassium, phosphorus, residual kidney function, normalised protein equivalent of total nitrogen appearance and calendar year of catheter implantation, patients in the higher three TMAO quartiles had a statistically or marginally higher risk for first-episode peritonitis compared with patients in the lowest quartile, with hazard ratio (HR) 1.65 (1.05, 2.58), 1.46 (0.92, 2.31) and 1.66 (1.05, 2.61), respectively. In the COX model, patients in the third quartile TMAO group had significantly higher CVD mortality risk compared with the lowest quartile group, as HR 2.27 (1.02, 5.05) after adjusting for various factors. As for all-cause mortality, TMAO did not show any associated effects.

CONCLUSIONS

Serum TMAO concentration is associated with the risk of first-episode peritonitis and CVD mortality in PD patients. No obvious association between serum TMAO and all-cause mortality was observed.

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.

Longitudinal Plasma Measures of Trimethylamine N-Oxide and Risk of Atherosclerotic Cardiovascular Disease Events in Community-Based Older Adults

Background

Trimethylamine N‐oxide (TMAO) is a gut microbiota‐dependent metabolite of dietary choline, L‐carnitine, and phosphatidylcholine‐rich foods. On the basis of experimental studies and patients with prevalent disease, elevated plasma TMAO may increase risk of atherosclerotic cardiovascular disease (ASCVD). TMAO is also renally cleared and may interact with and causally contribute to renal dysfunction. Yet, how serial TMAO levels relate to incident and recurrent ASCVD in community‐based populations and the potential mediating or modifying role of renal function are not established.

Methods and Results

We investigated associations of serial measures of plasma TMAO, assessed at baseline and 7 years, with incident and recurrent ASCVD in a community‐based cohort of 4131 (incident) and 1449 (recurrent) older US adults. TMAO was measured using stable isotope dilution liquid chromatography–tandem mass spectrometry (laboratory coefficient of variation, <6%). Incident ASCVD (myocardial infarction, fatal coronary heart disease, stroke, sudden cardiac death, or other atherosclerotic death) was centrally adjudicated using medical records. Risk was assessed by multivariable Cox proportional hazards regression, including time‐varying demographics, lifestyle factors, medical history, laboratory measures, and dietary habits. Potential mediating effects and interaction by estimated glomerular filtration rate (eGFR) were assessed. During prospective follow‐up, 1766 incident and 897 recurrent ASCVD events occurred. After multivariable adjustment, higher levels of TMAO were associated with a higher risk of incident ASCVD, with extreme quintile hazard ratio (HR) compared with the lowest quintile=1.21 (95% CI, 1.02–1.42; P‐trend=0.029). This relationship appeared mediated or confounded by eGFR (eGFR‐adjusted HR, 1.07; 95% CI, 0.90–1.27), as well as modified by eGFR (P‐interaction <0.001). High levels of TMAO were associated with higher incidence of ASCVD in the presence of impaired renal function (eGFR <60 mL/min per 1.73 m²: HR, 1.56 [95% CI, 1.13–2.14]; P‐trend=0.007), but not normal or mildly reduced renal function (eGFR ≥60 mL/min per 1.73 m²: HR, 1.03 [95% CI, 0.85–1.25]; P‐trend=0.668). Among individuals with prior ASCVD, TMAO associated with higher risk of recurrent ASCVD (HR, 1.25 [95% CI, 1.01–1.56]; P‐trend=0.009), without significant modification by eGFR.

Conclusions

In this large community‐based cohort of older US adults, serial measures of TMAO were associated with higher risk of incident ASCVD, with apparent modification by presence of impaired renal function and with higher risk of recurrent ASCVD.

Gut Microbiota-Derived Trimethylamine N-Oxide and Kidney Function: A Systematic Review and Meta-Analysis

Elevated circulating trimethylamine N-oxide (TMAO) concentrations have been observed in patients with chronic kidney disease (CKD). We aimed to systematically estimate and quantify the association between TMAO concentrations and kidney function. The PubMed, EMBASE, Cochrane Library, Scopus, and Web of Science databases were systematically searched from 1995 to 1 June, 2020, for clinical studies on circulating TMAO concentrations and kidney function indicators. We used R software to conduct meta-analyses of the extracted data. A cumulative meta-analysis was applied to test whether health status affected the pooled effect value. Meta-regression and subgroup analyses were performed to identify possible sources of heterogeneity. Ultimately, we included a total of 32 eligible clinical studies involving 42,062 participants. In meta-analyses of continuous-outcome variables, advanced CKD was associated with a 67.9 μmol/L (95% CI: 52.7, 83.2; P < 0.01) increase in TMAO concentration, and subjects with high concentrations of TMAO had a 12.9 mL/(min·1.73 m2) (95% CI: -16.6, -9.14; P < 0.01) decrease in glomerular filtration rate (GFR). In meta-analyses of the correlations, TMAO was strongly inversely correlated with GFR [Fisher's z-transformed correlation coefficient (ZCOR): -0.45; 95% CI: -0.58, -0.32; P < 0.01] and positively associated with the urine albumin-to-creatinine ratio (UACR; ZCOR: 0.26; 95% CI: 0.08, 0.43; P < 0.01), serum creatinine (sCr; ZCOR: 0.43; 95% CI: 0.28, 0.58; P < 0.01), urine albumin excretion rate (UAER; ZCOR: 0.06; 95% CI: 0.04, 0.09; P < 0.01), blood urea (ZCOR: 0.50; 95% CI: 0.29, 0.72; P < 0.01), blood uric acid (ZCOR: 0.32; 95% CI: 0.25, 0.38; P < 0.01), and serum cystatin C (CysC; ZCOR: 0.47, 95% CI: 0.44, 0.51; P < 0.01). This is the first systematic review and meta-analysis to reveal a negative association between circulating TMAO concentrations and kidney function.

Association of trimethylamine N-Oxide with cardiovascular and all-cause mortality in hemodialysis patients

Background

Trimethylamine-N-Oxide (TMAO) is a proatherogenic and prothrombotic metabolite. Our study examined the association of plasma TMAO level with cardiovascular and all-cause mortality in hemodialysis (HD) patients.

Methods

Patients who were at least 18 years-old and received HD for at least 6 months were enrolled within 6 months. Patients with coronary heart disease, congestive heart failure, arrhythmia, or stroke within 3 months before study onset were excluded. The primary endpoints were cardiovascular and all-cause death, and the secondary endpoint was cerebrovascular death.

Results

We recruited 252 patients and divided them into a high-TMAO group (>4.73 μg/mL) and a low-TMAO group (≤4.73 μg/mL). The median follow-up time was 73.4 months (interquartile range: 42.9, 108). A total of 123 patients died, 39 from cardiovascular disease, 19 from cerebrovascular disease, and 65 from other causes. Kaplan-Meier analysis indicated that the high-TMAO group had a greater incidence of cardiovascular death (Log-Rank: p = 0.006) and all-cause death (Log-Rank: p < 0.001). Cox regression analysis showed that high TMAO level was significantly associated with cardiovascular and all-cause mortality. After adjustment for confounding, this association remained significant for cardiovascular mortality (TMAO as a continuous variable: HR: 1.18, 95%CI: 1.07, 1.294, p < 0.001; TMAO as a dichotomous variable: HR: 3.44, 95%CI: 1.68, 7.08, p < 0.001) and all-cause mortality (TMAO as a continuous variable: HR: 1.14, 95%CI: 1.08, 1.21, p < 0.001; TMAO as a dichotomous variable: HR: 2.54, 95%CI: 1.71, 3.76, p < 0.001).

Conclusions

High plasma TMAO level is significantly and independently associated with cardiovascular and all-cause mortality in HD patients.

Total volatile basic nitrogen and trimethylamine in muscle foods: Potential formation pathways and effects on human health

The use of total volatile basic nitrogen (TVB-N) as a quality parameter for fish is rapidly growing to include other types of meat. Investigations of meat quality have recently focused on TVB-N as an index of freshness, but little is known on the biochemical pathways involved in its generation. Furthermore, TVB-N and methylated amines have been reported to exert deterimental health effects, but the relationship between these compounds and human health has not been critically reviewed. Here, literature on the formative pathways of TVB-N has been reviewed in depth. The association of methylated amines and human health has been critically evaluated. Interventions to mitigate the effects of TVB-N on human health are discussed. TVB-N levels in meat can be influenced by the diet of an animal, which calls for careful consideration when using TVB-N thresholds for regulatory purposes. Bacterial contamination and temperature abuse contribute to significant levels of post-mortem TVB-N increases. Therefore, controlling spoilage factors through a good level of hygiene during processing and preservation techniques may contribute to a substantial reduction of TVB-N. Trimethylamine (TMA) constitutes a significant part of TVB-N. TMA and trimethylamine oxide (TMA-N-O) have been related to the pathogenesis of noncommunicable diseases, including atherosclerosis, cancers, and diabetes. Proposed methods for mitigation of TMA and TMA-N-O accumulation are discussed, which include a reduction in their daily dietary intake, control of internal production pathways by targeting gut microbiota, and inhibition of flavin monooxygenase 3 enzymes. The levels of TMA and TMA-N-O have significant health effects, and this should, therefore, be considered when evaluating meat quality and acceptability. Agreed international values for TVB-N and TMA in meat products are required. The role of feed, gut microbiota, and translocation of methylated amines to muscles in farmed animals requires further investigation.

Contribution of Gut Microbiota-Derived Uremic Toxins to the Cardiovascular System Mineralization

Chronic kidney disease (CKD) affects more than 10% of the world population and leads to excess morbidity and mortality (with cardiovascular disease as a leading cause of death). Vascular calcification (VC) is a phenomenon of disseminated deposition of mineral content within the media layer of arteries preceded by phenotypic changes in vascular smooth muscle cells (VSMC) and/or accumulation of mineral content within the atherosclerotic lesions. Medial VC results in vascular stiffness and significantly contributes to increased cardio-vascular (CV) morbidity, whereas VC of plaques may rather increase their stability. Mineral and bone disorders of CKD (CKD-MBD) contribute to VC, which is further aggravated by accumulation of uremic toxins. Both CKD-MBD and uremic toxin accumulation affect not only patients with advanced CKD (glomerular filtration rate (GFR) less than 15 mL/min/1.72 m², end-stage kidney disease) but also those on earlier stages of a disease. The key uremic toxins that contribute to VC, i.e., p-cresyl sulphate (PCS), indoxyl sulphate (IS) and trimethylamine-N-oxide (TMAO) originate from bacterial metabolism of gut microbiota. All mentioned toxins promote VC by several mechanisms, including: Transdifferentiation and apoptosis of VSMC, dysfunction of endothelial cells, oxidative stress, interaction with local renin–angiotensin–aldosterone system or miRNA profile modification. Several attractive methods of gut microbiota manipulations have been proposed in order to modify their metabolism and to limit vascular damage (and VC) triggered by uremic toxins. Unfortunately, to date no such method was demonstrated to be effective at the level of “hard” patient-oriented or even clinically relevant surrogate endpoints.

Gut microbiota–associated trimethylamine N-oxide and increased cardiometabolic risk in adults: a systematic review and dose-response meta-analysis

Context

Several studies suggest a relationship between trimethylamine N-oxide (TMAO) concentrations and increased cardiometabolic risk, but findings are controversial.

Objective

The aim of this systematic review and meta-analysis was to summarize evidence of the relationship between circulating TMAO levels and risk of hypertension and increased serum lipids in a dose-response and 2-class meta-analysis of discrete and continuous variables.

Data Sources

PubMed, Scopus, Cochrane, and ProQuest databases were searched.

Study Selection

Observational studies that reported disease status of participants (≥ 18 years), type of sample in which TMAO was measured (serum or plasma), and results based on at least 2 categories of TMAO concentrations, including relative risks, hazard ratios, or odds ratios with 95%CIs for cardiometabolic risk factors in association with circulating TMAO levels were selected. Papers were reviewed independently by both authors. The Newcastle-Ottawa Scale was used to assess the quality of included studies.

Data Extraction

The following data were extracted: first author’s name, publication year, study design, study location, demographic information of participants, and concentrations of circulating TMAO.

Results

Eighteen studies were included in the meta-analysis. There was a dose-response relationship between circulating TMAO and increased odds of hypertension in cohort studies (P  for nonlinearity = 0.049), in plasma-derived TMAO samples (P  for nonlinearity = 0.043), in patients with cardiovascular disease (P  for nonlinearity = 0.048), and in apparently healthy individuals from community-based studies (P  for nonlinearity = 0.005). Moreover, the highest category of TMAO concentrations was associated with a 2.36 mmHg increase in systolic blood pressure when compared with the lowest category. The dose-response meta-analysis of continuous variables revealed that an increase in TMAO is associated with reduced high-density lipoprotein cholesterol in apparently healthy individuals and reduced high-density lipoprotein cholesterol and increased total cholesterol in patients with cardiovascular disease.

Conclusions

Circulating TMAO is positively associated with an increased risk of hypertension and other cardiometabolic disorders in adults.

Systematic Review Registration

PROSPERO identification number CRD42019138296.

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.

Plant-Based Diets, the Gut Microbiota, and Trimethylamine N-Oxide Production in Chronic Kidney Disease: Therapeutic Potential and Methodological Considerations

High circulating trimethylamine-N-oxide (TMAO) is associated with an increased risk of cardiovascular disease and mortality in people with chronic kidney disease (CKD). In individuals with CKD, reduced kidney function leads to decreased excretion of TMAO, which results in accumulation in the circulation. Higher circulating TMAO has been linked to higher intake of animal-based foods in omnivorous diets. Thus, plant-based diets have been suggested as an intervention to slow the progression of CKD and reduce cardiovascular risk, perhaps explained in part by reduced TMAO production. This article reviews the current evidence on plant-based diets as a dietary intervention to decrease gut-derived TMAO production in patients with CKD, while highlighting methodological issues that present challenges to advancing research and subsequent translation of this approach. Overall, we find that plant-based diets are promising for reducing gut-derived TMAO production in patients with CKD but that further interventional studies are warranted.

Trimethylamine-N-oxide is an independent risk factor for hospitalization events in patients receiving maintenance hemodialysis

Background

Hospitalization is a significant outcome measurement for maintenance hemodialysis pantients. Trimethylamine-N-oxide (TMAO), created by gut microflora from dietary l-carnitine and choline, cleared by the kidney, has been implicated in the causation of cardiovascular diseases in patients with chronic kidney disease. However, whether it associates with hospitalization risk for these patients is unclear.

Methods

In this study, 69 patients undergoing outpatient dialysis were enrolled. Enzyme-linked immunosorbent assay was used to quantitate the baseline plasma TMAO levels in patients. The patients were divided into a high TMAO level group (TMAO ≥ 15 μmol/L) and a low TMAO level group (TMAO < 15 μmol/L). During the 1-year follow-up, 1-year dialysis-related data and all-cause hospitalization events were recorded.

Results

The incidence of hospitalization events was significantly higher in the high TMAO level group than in the low TMAO level group (91 per 100 patient-year vs. 32 per 100 patient-year). The Kaplain–Meier survaial analysis showed that the incidence of hospitalization events in the high TMAO level group was significantly higher than that in the low TMAO level group (log-rank p = 0.0004). After adjustment age, sex, CK-MB and albumin, the results of multivariate Cox proportional hazard analysis showed that high TMAO level was an independent risk factor for hospitalization in maintenance hemodialysis patients.

Conclusion

TMAO is an independent risk factor for hospitalization events in patients receiving maintenance hemodialysis. It may be a new therapeutic target for improving the outcomes of these patients.

TMAO, a seafood-derived molecule, produces diuresis and reduces mortality in heart failure rats

Trimethylamine-oxide (TMAO) is present in seafood which is considered to be beneficial for health. Deep-water animals accumulate TMAO to protect proteins, such as lactate dehydrogenase (LDH), against hydrostatic pressure stress (HPS). We hypothesized that TMAO exerts beneficial effects on the circulatory system and protects cardiac LDH exposed to HPS produced by the contracting heart. Male, Sprague-Dawley and Spontaneously-Hypertensive-Heart-Failure (SHHF) rats were treated orally with either water (control) or TMAO. In vitro, LDH with or without TMAO was exposed to HPS and was evaluated using fluorescence correlation spectroscopy. TMAO-treated rats showed higher diuresis and natriuresis, lower arterial pressure and plasma NT-proBNP. Survival in SHHF-control was 66% vs 100% in SHHF-TMAO. In vitro, exposure of LDH to HPS with or without TMAO did not affect protein structure. In conclusion, TMAO reduced mortality in SHHF, which was associated with diuretic, natriuretic and hypotensive effects. HPS and TMAO did not affect LDH protein structure.

Heart failure is a common cause of death in industrialized countries with aging populations. Japan, however, has lower rates of heart failure and fewer deaths linked to this disease than the United States or Europe, despite having the highest proportion of elderly people in the world. Dietary differences between these regions may explain the lower rate of heart failure in Japan. The Japanese diet is rich in seafood, which contains nutrients that promote heart health, such as omega-3 fatty acids.

Seafood also contains other compounds, including trimethylamine oxide (TMAO). Fish that live in deep waters undergo high pressures, which can damage their proteins, but TMAO seems to protect the proteins from harm. In humans, eating seafood increases TMAO levels in the blood and urine, but it is unclear what effects this has on heart health. Increased levels of TMAO in the blood are associated with cardiovascular diseases, but scientists are not sure whether TMAO itself harms the heart. A toxic byproduct of gut bacteria called TMA is converted in TMAO in the body, so it is possible that TMA rather than TMAO is to blame.

To assess the effects of dietary TMAO on heart failure, Gawrys-Kopczynska et al. fed the compound to healthy rats and rats with heart failure for one year. TMAO had no effects on the healthy rats. Of the rats with heart failure that were fed TMAO, all of them survived the year, while one third of rats with heart failure that were not fed TMAO died. TMAO-treated rats with heart failure had lower blood pressure and urinated more than untreated rats with the condition.

The experiments suggest that dietary TMAO may mimic the effects of heart failure treatments, which remove excess water and salt and lower pressure on the heart. More studies are needed to confirm whether TMAO has this same effect on humans.

Gut microbiota-derived metabolite trimethylamine N-oxide (TMAO) potentially increases the risk of obesity in adults: An exploratory systematic review and dose-response meta- analysis

It has been suggested that trimethylamine N-oxide (TMAO) is associated with increased risk of diabetes and cardiovascular disease (CVD) morbidity and mortality. However, it is not known whether increased TMAO concentrations is associated with obesity. In the current study, we summarized the evidence related to the association of circulating TMAO with the risk of obesity measurements, including body mass index (BMI), waist circumference (WC), and waist-to-hip ratio (WHR) in a two-class and dose-response meta-analysis of observational studies. A systematic search carried out in PubMed, SCOPUS, Cochrane, and ProQuest through September 30, 2019 resulted in 12 eligible studies which were included in the current meta-synthesis. In these studies, BMI was reported but there were no reports of WC or WHR. Meta-analysis of two-class variables and dose-response meta-analysis of continuous variables were performed. Subgroup analysis and meta-regression were also performed to identify the source of heterogeneity. There was a dose-response association between circulating TMAO concentration and increased BMI in studies involving healthy individuals (P nonlinearity = .007), while no evidence of departure from linearity was observed according to study design or among patients with CVD. Results showed the highest category of TMAO was associated with 0.56 kg/m² increase in BMI (weighted mean difference [WMD], 0.563; CI, 0.026-1.100; P = .04). The results of the current meta-analysis revealed a positive association between circulating TMAO and obesity as presented by increased BMI. Moreover, a dose-dependent association between circulating TMAO and obesity was also identified in apparently healthy individuals. This is the first meta-analysis to reveal positive dose-dependent associations between circulating TMAO concentration and obesity.

Trimethylamine-N-oxide acutely increases cardiac muscle contractility

Cardiovascular disease is a major cause of morbidity and mortality among patients with chronic kidney disease (CKD). Trimethylamine-N-oxide (TMAO), a uremic metabolite that is elevated in the setting of CKD, has been implicated as a nontraditional risk factor for cardiovascular disease. While association studies have linked elevated plasma levels of TMAO to adverse cardiovascular outcomes, its direct effect on cardiac and smooth muscle function remains to be fully elucidated. We hypothesized that pathological concentrations of TMAO would acutely increase cardiac and smooth muscle contractility. These effects may ultimately contribute to cardiac dysfunction during CKD. High levels of TMAO significantly increased paced, ex vivo human cardiac muscle biopsy contractility (P < 0.05). Similarly, TMAO augmented contractility in isolated mouse hearts (P < 0.05). Reverse perfusion of TMAO through the coronary arteries via a Langendorff apparatus also enhanced cardiac contractility (P < 0.05). In contrast, the precursor molecule, trimethylamine (TMA), did not alter contractility (P > 0.05). Multiphoton microscopy, used to capture changes in intracellular calcium in paced, adult mouse hearts ex vivo, showed that TMAO significantly increased intracellular calcium fluorescence (P < 0.05). Interestingly, acute administration of TMAO did not have a statistically significant influence on isolated aortic ring contractility (P > 0.05). We conclude that TMAO directly increases the force of cardiac contractility, which corresponds with TMAO-induced increases in intracellular calcium but does not acutely affect vascular smooth muscle or endothelial function of the aorta. It remains to be determined if this acute inotropic action on cardiac muscle is ultimately beneficial or harmful in the setting of CKD.NEW & NOTEWORTHY We demonstrate for the first time that elevated concentrations of TMAO acutely augment myocardial contractile force ex vivo in both murine and human cardiac tissue. To gain mechanistic insight into the processes that led to this potentiation in cardiac contraction, we used two-photon microscopy to evaluate intracellular calcium in ex vivo whole hearts loaded with the calcium indicator dye Fluo-4. Acute treatment with TMAO resulted in increased Fluo-4 fluorescence, indicating that augmented cytosolic calcium plays a role in the effects of TMAO on force production. Lastly, TMAO did not show an effect on aortic smooth muscle contraction or relaxation properties. Our results demonstrate novel, acute, and direct actions of TMAO on cardiac function and help lay the groundwork for future translational studies investigating the complex multiorgan interplay involved in cardiovascular pathogenesis during CKD.

Targeted Inhibition of Gut Microbial Trimethylamine N-Oxide Production Reduces Renal Tubulointerstitial Fibrosis and Functional Impairment in a Murine Model of Chronic Kidney Disease

OBJECTIVE

Gut microbial metabolism of dietary choline, a nutrient abundant in a Western diet, produces trimethylamine (TMA) and the atherothrombosis- and fibrosis-promoting metabolite TMA-N-oxide (TMAO). Recent clinical and animal studies reveal that elevated TMAO levels are associated with heightened risks for both cardiovascular disease and incident chronic kidney disease development. Despite this, studies focusing on therapeutically targeting gut microbiota-dependent TMAO production and its impact on preserving renal function are limited. Approach and Results: Herein we examined the impact of pharmacological inhibition of choline diet-induced gut microbiota-dependent production of TMA, and consequently TMAO, on renal tubulointerstitial fibrosis and functional impairment in a model of chronic kidney disease. Initial studies with a gut microbial choline TMA-lyase mechanism-based inhibitor, iodomethylcholine, confirmed both marked suppression of TMA generation, and consequently TMAO levels, and selective targeting of the gut microbial compartment (ie, both accumulation of the drug in intestinal microbes and limited systemic exposure in the host). Dietary supplementation of either choline or TMAO significantly augmented multiple indices of renal functional impairment and fibrosis associated with chronic subcutaneous infusion of isoproterenol. However, the presence of the gut microbiota-targeting inhibitor iodomethylcholine blocked choline diet-induced elevation in TMAO, and both significantly improved decline in renal function, and significantly attenuated multiple indices of tubulointerstitial fibrosis. Iodomethylcholine treatment also reversed many choline diet-induced changes in cecal microbial community composition associated with TMAO and renal functional impairment.

CONCLUSIONS

Selective targeting of gut microbiota-dependent TMAO generation may prevent adverse renal structural and functional alterations in subjects at risk for chronic kidney disease.

Intestinal Microbiota in Cardiovascular Health and Disease: JACC State-of-the-Art Review

Despite major strides in reducing cardiovascular disease (CVD) burden with modification of classic CVD risk factors, significant residual risks remain. Recent discoveries that linked intestinal microbiota and CVD have broadened our understanding of how dietary nutrients may affect cardiovascular health and disease. Although next-generation sequencing techniques can identify gut microbial community participants and provide insights into microbial composition shifts in response to physiological responses and dietary exposures, provisions of prebiotics or probiotics have yet to show therapeutic benefit for CVD. Our evolving understanding of intestinal microbiota-derived physiological modulators (e.g., short-chain fatty acids) and pathogenic mediators (e.g., trimethylamine N-oxide) of host disease susceptibility have created novel potential therapeutic opportunities for improved cardiovascular health. This review discusses the roles of human intestinal microbiota in normal physiology, their associations with CVD susceptibilities, and the potential of modulating intestinal microbiota composition and metabolism as a novel therapeutic target for CVD.

Coexistence of micro-inflammatory and macrophage phenotype abnormalities in chronic kidney disease

The heterogeneity of macrophages promotes renal fibrosis and plays an important role in the repair of kidney damage. The "microinflammation state" is closely related to accelerated mortality in patients with chronic kidney disease (CKD). The aim of this study was to investigate the relationship between microinflammation and macrophage polarization in CKD. The levels of high-sensitivity C-reactive protein (hs-CRP), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in peripheral blood of 30 non-dialysis CKD-5 patients (CKD group) and 20 healthy subjects (Con group) were measured. Peripheral mononuclear cells (PBMC) of each group were obtained, induced to differentiate into mature macrophages, and the expression of CD206 on the surface of macrophage M2 was detected. The expression of IL-10, TGF-β1 and TNF-α in the supernatant of macrophage culture medium was detected by real time RCR and ELISA. We found that the levels of hs-CRP, IL-6 and TNF-α in peripheral blood of patients with CKD were significantly higher than those of the control group. The expression of CD206 in macrophages was significantly decreased in CKD patients. The anti-inflammatory cytokines IL-10 and TGF-β1 in the supernatant of CKD macrophages decreased significantly, while the pro-inflammatory factor TNF-α did not change significantly. Our results demonstrate that the expressions of macrophage phenotype and anti-inflammatory cytokine in CKD patients are abnormal, which may be related to the microinflammation state prevalent in CKD patients.

Short chain fatty acids and methylamines produced by gut microbiota as mediators and markers in the circulatory system

Ample evidence suggests that gut microbiota-derived products affect the circulatory system functions. For instance, short chain fatty acids, that are the products of dietary fiber bacterial fermentation, have been found to dilate blood vessels and lower blood pressure. Trimethylamine, a gut bacteria metabolite of carnitine and choline, has recently emerged as a potentially toxic molecule for the circulatory system. To enter the bloodstream, microbiota products cross the gut–blood barrier, a multilayer system of the intestinal wall. Notably, experimental and clinical studies show that cardiovascular diseases may compromise function of the gut–blood barrier and increase gut-to-blood penetration of microbiota-derived molecules. Hence, the bacteria products and the gut–blood barrier may be potential diagnostic and therapeutic targets in cardiovascular diseases. In this paper, we review research on the cardiovascular effects of microbiota-produced short chain fatty acids and methylamines.

The gut–kidney–heart axis in chronic kidney disease

The recent explosion of scientific interest in the gut microbiota has dramatically advanced our understanding of the complex pathophysiological interactions between the gut and multiple organs in health and disease. Emerging evidence has revealed that the gut microbiota is significantly altered in patients with chronic kidney disease (CKD), along with impaired intestinal barrier function. These alterations allow translocation of various gut-derived products into the systemic circulation, contributing to the development and progression of CKD and cardiovascular disease (CVD), partly mediated by chronic inflammation. Among potentially toxic gut-derived products identifiable in the systemic circulation, bacterial endotoxin and gut metabolites (e.g., p-cresyl sulfate and trimethylamine-N-oxide) have been extensively studied for their immunostimulatory and atherogenic properties. Recent studies have also suggested similar biological properties of bacterial DNA fragments circulating in the blood of patients with CKD, even in the absence of overt infections. Despite the accumulating evidence of the gut microbiota in CKD and its therapeutic potential for CVD, the precise mechanisms for multidirectional interactions between the gut, kidney, and heart remain poorly understood. This review aims to provide recent evidence on the associations between the gut microbiota, CKD, and CVD, and summarize current understanding of the potential pathophysiological mechanisms underlying the “gut–kidney–heart” axis in CKD.

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.

The path toward using microbial metabolites as therapies

Metabolites have emerged as the quintessential effectors mediating the impact of the commensal microbiome on human physiology, both locally at the sites of microbial colonization and systemically. The endocrine activity of the microbiome and its involvement in a multitude of complex diseases has made microbiome-modulated metabolites an attractive target for the development of new therapies. Several properties make metabolites uniquely suited for interventional strategies: natural occurrence in a broad range of concentrations, functional pleiotropy, ease of administration, and tissue bioavailability. Here, we provide an overview of recently discovered physiological effects of microbiome-associated small molecules that may serve as the first examples of metabolite-based therapies. We also highlight challenges and obstacles that the field needs to overcome on the path toward successful clinical trials of microbial metabolites for human disease.