Circulating Trimethylamine N-Oxide Is Associated with Increased Risk of Cardiovascular Mortality in Type-2 Diabetes: Results from a Dutch Diabetes Cohort (ZODIAC-59)

Duality of Branched-Chain Amino Acids in Chronic Cardiovascular Disease: Potential Biomarkers versus Active Pathophysiological Promoters

Branched-chain amino acids (BCAAs), comprising leucine (Leu), isoleucine (Ile), and valine (Val), are essential nutrients vital for protein synthesis and metabolic regulation via specialized signaling networks. Their association with cardiovascular diseases (CVDs) has become a focal point of scientific debate, with emerging evidence suggesting both beneficial and detrimental roles. This review aims to dissect the multifaceted relationship between BCAAs and cardiovascular health, exploring the molecular mechanisms and clinical implications. Elevated BCAA levels have also been linked to insulin resistance (IR), type 2 diabetes mellitus (T2DM), inflammation, and dyslipidemia, which are well-established risk factors for CVD. Central to these processes are key pathways such as mammalian target of rapamycin (mTOR) signaling, nuclear factor kappa-light-chain-enhancer of activate B cells (NF-κB)-mediated inflammation, and oxidative stress. Additionally, the interplay between BCAA metabolism and gut microbiota, particularly the production of metabolites like trimethylamine-N-oxide (TMAO), adds another layer of complexity. Contrarily, some studies propose that BCAAs may have cardioprotective effects under certain conditions, contributing to muscle maintenance and metabolic health. This review critically evaluates the evidence, addressing the biological basis and signal transduction mechanism, and also discusses the potential for BCAAs to act as biomarkers versus active mediators of cardiovascular pathology. By presenting a balanced analysis, this review seeks to clarify the contentious roles of BCAAs in CVD, providing a foundation for future research and therapeutic strategies required because of the rising prevalence, incidence, and total burden of CVDs.

Circulating Trimethylamine-N-Oxide Is Elevated in Liver Transplant Recipients

Liver transplant recipients (LTRs) have lower long-term survival rates compared with the general population. This underscores the necessity for developing biomarkers to assess post-transplantation mortality. Here we compared plasma trimethylamine-N-oxide (TMAO) levels with those in the general population, investigated its determinants, and interrogated its association with all-cause mortality in stable LTRs. Plasma TMAO was measured in 367 stable LTRs from the TransplantLines cohort (NCT03272841) and in 4837 participants from the population-based PREVEND cohort. TMAO levels were 35% higher in LTRs compared with PREVEND participants (4.3 vs. 3.2 µmol/L, p < 0.001). Specifically, TMAO was elevated in LTRs with metabolic dysfunction-associated steatotic liver disease, alcohol-associated liver disease, and polycystic liver disease as underlying etiology (p < 0.001 for each). Among LTRs, TMAO levels were independently associated with eGFR (std. β = -0.43, p < 0.001) and iron supplementation (std. β = 0.13, p = 0.008), and were associated with mortality (29 deaths during 8.6 years follow-up; log-rank test p = 0.017; hazard ratio of highest vs. lowest tertile 4.14, p = 0.007). In conclusion, plasma TMAO is likely elevated in stable LTRs, with impaired eGFR and iron supplementation as potential contributory factors. Our preliminary findings raise the possibility that plasma TMAO could contribute to increased mortality risk in such patients, but this need to be validated through a series of rigorous and methodical studies.

Metabolomics signature of cardiovascular disease in patients with diabetes, a narrative review

Objectives

The exact underlying mechanism of developing diabetes-related cardiovascular disease (CVD) among patients with type 2 diabetes (T2D) is not clear. Metabolomics can provide a platform enabling the prediction, diagnosis, and understanding of the risk of CVD in patients with diabetes mellitus. The aim of this review is to summarize the available evidence on the relationship between metabolomics and cardiovascular diseases in patients with diabetes.

Methods

The literature was searched to find out studies that have investigated the relationship between the alteration of specific metabolites and cardiovascular diseases in patients with diabetes.

Results

Evidence proposed that changes in the metabolism of certain amino acids, lipids, and carbohydrates, independent of traditional CVD risk factors, are associated with increased CVD risk.

Conclusions

Metabolomics can provide a platform to enable the prediction, diagnosis, and understanding of the risk of CVD in patients with diabetes mellitus. The association of the alteration in specific metabolites with CVD may be considered in the investigations for the development of new therapeutic targets for the prevention of CVD in patients with diabetes mellitus.

Plasma Citrate Levels Are Associated with an Increased Risk of Cardiovascular Mortality in Patients with Type 2 Diabetes (Zodiac-64)

Circulating citrate may represent a proxy of mitochondrial dysfunction which plays a role in the development of vascular complications in type 2 diabetes (T2D). Here, we determined the associations between plasma citrate levels and cardiovascular (CV) mortality in T2D patients. In this prospective cohort study, 601 patients were included who participated in the Zwolle Outpatient Diabetes project Integrating Available Care (ZODIAC). Plasma citrate levels were measured by nuclear magnetic resonance spectroscopy. Cox proportional hazards regression models were used to evaluate the associations between plasma citrate and the risk of CV mortality. Over a median follow-up of 11.4 years, 119 (19.8%) of the 601 patients died from a CV cause. In multivariable Cox proportional hazards regression models, adjusting for conventional risk factors, plasma citrate was associated with an increased risk of CV mortality (the hazard ratio (HR) per 1-SD increment was 1.19 (95%CI: 1.00-1.40), p = 0.048). This association was prominent in males (n = 49 with CV mortality) (HR 1.52 (95%CI: 1.14-2.03), p = 0.005), but not in females (n = 70 with CV mortality) (HR 1.11 (95%CI: 0.90-1.37), p = 0.319) (age-adjusted Pinteraction = 0.044). In conclusion, higher plasma citrate levels are associated with an increased risk of CV mortality in patients with established T2D. Future studies are warranted to unravel the potential role of citrate-related pathways in the pathogenesis of T2D-related vascular complications.

The Bittersweet Beat: Diabetes Complications

In this Editorial, we are focusing on a selection of articles recently published in the Journal of Clinical Medicine dealing with relevant aspects of cardiometabolic complications of diabetes mellitus [...].

High plasma levels of betaine, a trimethylamine N-Oxide-related metabolite, are associated with the severity of cirrhosis

BACKGROUND AND AIMS

The gut microbiome-related metabolites betaine and trimethylamine N-oxide (TMAO) affect major health issues. In cirrhosis, betaine metabolism may be diminished because of impaired hepatic betaine homocysteine methyltransferase activity, whereas TMAO generation from trimethylamine may be altered because of impaired hepatic flavin monooxygenase expression. Here, we determined plasma betaine and TMAO levels in patients with end-stage liver disease and assessed their relationships with liver disease severity.

METHODS

Plasma betaine and TMAO concentrations were measured by nuclear magnetic resonance spectroscopy in 129 cirrhotic patients (TransplantLines cohort study; NCT03272841) and compared with levels from 4837 participants of the PREVEND cohort study. Disease severity was assessed by Child-Pugh-Turcotte (CPT) classification and Model for End-stage Liver Disease (MELD) score.

RESULTS

Plasma betaine was on average 60% higher (p < .001), whereas TMAO was not significantly lower in cirrhotic patients vs. PREVEND population (p = .44). After liver transplantation (n = 13), betaine decreased (p = .017; p = .36 vs. PREVEND population), whereas TMAO levels tended to increase (p = .085) to higher levels than in the PREVEND population (p = .003). Betaine levels were positively associated with the CPT stage and MELD score (both p < .001). The association with the MELD score remained in the fully adjusted analysis (p < .001). The association of TMAO with the MELD score did not reach significance (p = .11). Neither betaine nor TMAO levels were associated with mortality on the waiting list for liver transplantation (adjusted p = .78 and p = .44, respectively).

CONCLUSION

Plasma betaine levels are elevated in cirrhotic patients in parallel with disease severity and decrease after liver transplantation.

Trimethylamine N-Oxide and Related Metabolites in the Serum and Risk of Type 2 Diabetes in the Chinese Population: A Case-Control Study

BACKGROUND

Trimethylamine N-oxide (TMAO) and its precursors have an association with type 2 diabetes mellitus (T2DM); however, the evidence is unclear. The current study examined the association of serial measures of serum TMAO and related metabolite concentrations with the risk of T2DM.

METHODS

Our study was designed as a community case-control study with 300 participants (150 T2DM and 150 non-T2DM). We examined the association of serum concentrations of TMAO and its related metabolites [trimethylamine, choline, betaine, and L-carnitine] using UPLC-MS/MS. The association between these metabolites and the risk of T2DM was analyzed using a restricted cubic spline and binary logistic regression.

RESULTS

A higher serum choline concentration was significantly associated with an increased risk of T2DM. Serum choline > 22.62 μmol/L was independently associated with an increased risk of T2DM, and the odds ratio was 3.615 [95% CI: (1.453,8.993), P = 0.006]. Similarly, serum betaine and L-carnitine concentrations had a markedly decreased risk of T2DM even after adjusting for the traditional risk factors for T2DM and betaine (0.978 [95% CI:0.964-0.992], P = 0.002) and L-carnitine (0.949 [95% CI: 0.9222-0.978], P = 0.001), respectively.

CONCLUSION

Choline, betaine, and L-carnitine are associated with the risk of T2DM and may be appropriate risk markers to protect high-risk individuals from T2DM.

Systematic analysis of relationships between plasma branched-chain amino acid concentrations and cardiometabolic parameters: an association and Mendelian randomization study

BACKGROUND

Branched-chain amino acids (BCAAs; valine, leucine, and isoleucine) are essential amino acids that are associated with an increased risk of cardiometabolic diseases (CMD). However, there are still only limited insights into potential direct associations between BCAAs and a wide range of CMD parameters, especially those remaining after correcting for covariates and underlying causal relationships.

METHODS

To shed light on these relationships, we systematically characterized the associations between plasma BCAA concentrations and a large panel of 537 CMD parameters (including atherosclerosis-related parameters, fat distribution, plasma cytokine concentrations and cell counts, circulating concentrations of cardiovascular-related proteins and plasma metabolites) in 1400 individuals from the Dutch population cohort LifeLines DEEP and 294 overweight individuals from the 300OB cohort. After correcting for age, sex, and BMI, we assessed associations between individual BCAAs and CMD parameters. We further assessed the underlying causality using Mendelian randomization.

RESULTS

A total of 838 significant associations were detected for 409 CMD parameters. BCAAs showed both common and specific associations, with the most specific associations being detected for isoleucine. Further, we found that obesity status substantially affected the strength and direction of associations for valine, which cannot be corrected for using BMI as a covariate. Subsequent univariable Mendelian randomization (UVMR), after removing BMI-associated SNPs, identified seven significant causal relationships from four CMD traits to BCAA levels, mostly for diabetes-related parameters. However, no causal effects of BCAAs on CMD parameters were supported.

CONCLUSIONS

Our cross-sectional association study reports a large number of associations between BCAAs and CMD parameters. Our results highlight some specific associations for isoleucine, as well as obesity-specific effects for valine. MR-based causality analysis suggests that altered BCAA levels can be a consequence of diabetes and alteration in lipid metabolism. We found no MR evidence to support a causal role for BCAAs in CMD. These findings provide evidence to (re)evaluate the clinical importance of individual BCAAs in CMD diagnosis, prevention, and treatment.

Association of Trimethylamine N-Oxide and Metabolites With Mortality in Older Adults

IMPORTANCE

Little is known about the association of trimethylamine N-oxide (TMAO), a novel plasma metabolite derived from L-carnitine and phosphatidylcholine, and related metabolites (ie, choline, betaine, carnitine, and butyrobetaine) with risk of death among older adults in the general population.

OBJECTIVE

To investigate the associations of serial measures of plasma TMAO and related metabolites with risk of total and cause-specific death (ie, deaths from cardiovascular diseases [CVDs] and non-CVDs) among older adults in the US.

DESIGN, SETTING, AND PARTICIPANTS

This prospective cohort study involved 5333 participants from the Cardiovascular Health Study-a community-based longitudinal cohort of adults aged 65 years or older-who were followed up from June 1, 1989, to December 31, 2015. Participants were from 4 communities in the US (Forsyth County, North Carolina; Sacramento County, California; Washington County, Maryland; and Allegheny County, Pennsylvania). Data were analyzed from March 17 to June 23, 2021.

EXPOSURES

Plasma TMAO, choline, betaine, carnitine, and butyrobetaine levels were measured using stored samples from baseline (June 1, 1989, to May 31, 1990, or November 1, 1992, to June 31, 1993) and follow-up examination (June 1, 1996, to May 31, 1997). Measurements were performed through stable-isotope dilution liquid chromatography with tandem mass spectrometry using high-performance liquid chromatography with online electrospray ionization tandem mass spectrometry.

MAIN OUTCOMES AND MEASURES

Deaths (total and cause specific) were adjudicated by a centralized Cardiovascular Health Study events committee based on information from medical records, laboratory and diagnostic reports, death certificates, and/or interviews with next of kin. The associations of each metabolite with mortality were assessed using Cox proportional hazards regression models.

RESULTS

Among 5333 participants in the analytic sample, the mean (SD) age was 73 (6) years; 2149 participants (40.3%) were male, 3184 (59.7%) were female, 848 (15.9%) were African American, 4450 (83.4%) were White, and 35 (0.01%) were of other races (12 were American Indian or Alaska Native, 4 were Asian or Pacific Islander, and 19 were of other races or ethnicities). During a median follow-up of 13.2 years (range, 0-26.9 years), 4791 deaths occurred. After adjustment for potential confounders, the hazard ratios for death from any cause (ie, total mortality) comparing extreme quintiles (fifth vs first) of plasma concentrations were 1.30 (95% CI, 1.17-1.44) for TMAO, 1.19 (95% CI, 1.08-1.32) for choline, 1.26 (95% CI, 1.15-1.40) for carnitine, and 1.26 (95% CI, 1.13-1.40) for butyrobetaine. Plasma betaine was not associated with risk of death. The extent of risk estimates was similar for CVD and non-CVD mortality.

CONCLUSIONS AND RELEVANCE

In this cohort study, plasma concentrations of TMAO and related metabolites were positively associated with risk of death. These findings suggest that circulating TMAO is an important novel risk factor associated with death among older adults.

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.

Temporal Course of Plasma Trimethylamine N-Oxide (TMAO) Levels in ST-Elevation Myocardial Infarction

The gut metabolite trimethylamine N-oxide (TMAO) at admission has a prognostic value in ST-elevation myocardial infarction (STEMI) patients. However, its sequential changes and relationship with long-term infarct-related outcomes after primary percutaneous coronary intervention (PCI) remain elusive. We delineated the temporal course of TMAO and its relationship with infarct size and left ventricular ejection fraction (LVEF) post-PCI, adjusting for the estimated glomerular filtration rate (eGFR). We measured TMAO levels at admission, 24 h and 4 months post-PCI in 379 STEMI patients. Infarct size and LVEF were determined by cardiac magnetic resonance 4 months after PCI. TMAO levels decreased from admission (4.13 ± 4.37 μM) to 24 h (3.41 ± 5.84 μM, p = 0.001) and increased from 24 h to 4 months (3.70 ± 3.86 μM, p = 0.026). Higher TMAO values at 24 h were correlated to smaller infarct sizes (rho = −0.16, p = 0.024). Larger declines between admission and 4 months suggestively correlated with smaller infarct size, and larger TMAO increases between 24 h and 4 months were associated with larger infarct size (rho = −0.19, p = 0.008 and rho = −0.18, p = 0.019, respectively). Upon eGFR stratification using 90 mL/min/1.73 m² as a cut-off, significant associations between TMAO and infarct size were only noted in subjects with impaired renal function. In conclusion, TMAO levels in post-PCI STEMI patients are prone to fluctuations, and these fluctuations could be prognostic for infarct size, particularly in patients with impaired renal function.