High levels of gut microbiome-generated TMAO associated with CV events and mortality

Gut microbe-generated metabolite trimethylamine-N-oxide as cardiovascular risk biomarker: a systematic review and dose-response meta-analysis

Literature - Schiattarella GG, Sannino A, Toscano E et al. - Eur Heart J ehx342. DOI: https://doi.org/10.1093/eurheartj/ehx342 Published: 11 July 2017


The interplay between dietary composition , gut microbiota and microbe-generated metabolite is receiving increasing attention. This is also interesting for CV risk management, as dietary habits are considered a modifiable risk factor. Trimethylamine N-oxide (TMAO) is a small, organic, gut

microbiome-generated compound. TMAO concentration is higher after ingesting dietary L-carnitine and phosphatidylcholine-rich foods like red meat, eggs and fish [1,2].

Preclinical studies suggest a mechanistic link between TMAO and CVD [2-4]. TMAO may promote atherosclerosis through increased expression of macrophage scavenger receptors and formation of foam cells in the artery wall [3]. Moreover, non-lethal inhibition of microbial production of TMAO in mice has been shown to diminish atherosclerotic lesions [5]. TMAO has also been associated with (reverse) cholesterol transport and bile acid composition [2, 6-9]. Moreover, high levels of TMAO have also been found to promote endothelial dysfunction, exacerbate platelet reactivity, and to enhance thrombosis, affect lipid metabolism and inflammatory response [4, 10-12].

The potential impact of TMAO as a novel biomarker for CVD and its prognostic role in disease progression has not yet been systematically addressed. Plus, a potential causal role is debated, for instance because fish as an important dietary source of TMAO is confusing, since fish consumption has been shown to be protective for CVD.

This is the first systematic review and dose-response meta-analysis of published studies to quantitatively assess the association between TMAO plasma levels and CV outcomes (mortality and MACCE: death, MI and stroke). 17 Studies with at least 100 included patients with CVD, with TMAO plasma levels reported as either categorical or continuous variable were included, with data on 26167 subjects. Mean follow-up was 4.3 ± 1.5 years.

Main results

  • Across 16 cohorts enrolling 15662 subjects, higher TMAO levels were associated with greater risk of all-cause mortality (HR: 1.91, 95%CI: 1.40-2.61, P<0.0001), vs ‘low’ TMAO (top vs. bottom tertile).
  • When stratified for the presence or absence of CKD, both groups showed a significant association between TMAO and mortality (non-CKD: HR: 1.79, 95%CI: 1.23-2.60, P=0.002, CEK: HR: 2.27, 95%CDI: 1.13-4.58, P=0.02).
  • The significant association with mortality also persisted after stratification for geographical location of enrollment (USA, Europe, rest).
  • The dose-response meta-analysis showed an RR for all-cause mortality of 7.6% higher risk per each 10 µmol/L increment of TMAO (summary RR: 1.07, 95%CI: 1.04-1.11, P<0.0001). There was evidence for a non-linear association (P non-linearity <0.00001).
  • The incidence of MACCE was significantly higher in those with high vs. low TMAO levels (HR: 1.67, 95%CI: 1.33-2.11, P<0.0001).
  • Various sensitivity analyses confirmed the observed associations.
  • Meta-regression analysis only revealed coronary artery disease as a potential effect modifier, in the sense that studies with a higher percentage of CAD patients showed an increase of the association between high TMAO levels and mortality.


This analysis in a large population shows that high-circulating concentrations of TMAO were associated with higher risk of all-cause mortality and MACCE. A dose-dependent, direct association was observed, and the observed association was consistent across subgroups and all study populations. The shape of the dose-response association requires further characterization.

Surprisingly, observations were consistent for patients with or without CKD, although high circulating TMAO levels have been described in CKD. Nor did geographical localization of populations affect the primary outcome, although dietary patterns may vary, although most studies were conducted in the USA and Europe.


1. Zeisel SH, Wishnok JS, Blusztajn JK. Formation of methylamines from ingested choline and lecithin. J Pharmacol Exp Ther 1983;225:320–324.

2. Koeth RA, Wang Z, Levison BS et al. Intestinal microbiota metabolism of l-carnitine, a nutrient in red meat, promotes atherosclerosis. Nature Med 2013;19:576–585.

3. Wang Z, Klipfell E, Bennett BJ et al. Gut flora metabolism of phosphatidylcholine promotes cardiovascular disease. Nature 2011;472:57–63.

4. Zhu W, Gregory JC, Org E et al. Gut microbial metabolite tmao enhances platelet hyperreactivity and thrombosis risk. Cell 2016;165:111–124.

5. Wang Z, Roberts AB, Buffa JA et al. Non-lethal inhibition of gut microbial trimethylamine production for the treatment of atherosclerosis. Cell 2015;163:1585–1595.

6. Warrier M, Shih DM, Burrows AC et al. The TMAO generating enzyme flavin monooxygenase 3 is a central regulator of cholesterol balance. Cell Rep 2015;10:326–338.

7. Bennett BJ, de Aguiar Vallim TQ, Wang Z et al. Trimethylamine-n-oxide, a metabolite associated with atherosclerosis, exhibits complex genetic and dietary regulation. Cell Metab 2013;17:49–60.

8. Shih DM, Wang Z, Lee R et al. Flavin containing monooxygenase 3 exerts broad effects on glucose and lipid metabolism and atherosclerosis. J Lipid Res 2015;56:22–37.

9. Miao J, Ling AV, Manthena PV et al. Flavin-containing monooxygenase 3 as a potential player in diabetes-associated atherosclerosis. Nat Commun 2015;6:6498.

10. Sun X, Jiao X, Ma Y et al. Trimethylamine N-oxide induces inflammation and endothelial dysfunction in human umbilical vein endothelial cells via activating ROS-TXNIP-NLRP3 inflammasome. Biochem Biophys Res Commun 2016;481:63–70.

11. Gao X, Liu X, Xu J et al. Dietary trimethylamine N-oxide exacerbates impaired glucose tolerance in mice fed a high fat diet. J Biosci Bioeng 2014;118:476–481.

12. Seldin MM, Meng Y, Qi H et al. Trimethylamine N-oxide promotes vascular inflammation through signaling of mitogen-activated protein kinase and nuclear factor-kappaB. J Am Heart Assoc 2016;5.

pii: e002767. doi: 10.1161/JAHA.115.002767.

Find this article online at Eur Heart J

Facebook Comments


We’re glad to see you’re enjoying PACE-CME…
but how about a more personalized experience?

Register for free