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

AIMS: Gut microbiota-derived metabolite trimethylamine-N-oxide (TMAO) is emerging as a new potentially important cause of increased cardiovascular risk. The purpose of this meta-analysis was to systematically estimate and quantify the association between TMAO plasma levels, mortality, and major adverse cardio and cerebrovascular events (MACCE). METHODS AND RESULTS: MEDLINE, ISI Web of Science, and SCOPUS databases were searched for ad hoc studies published up to April 2017. Associations between TMAO plasma levels, all-cause mortality (primary outcome) and MACCE (secondary outcome) were systematically addressed. A total of 17 clinical studies were included in the analytic synthesis, enrolling 26 167 subjects. The mean follow-up in our study population was 4.3 ± 1.5 years. High TMAO plasma levels were associated with increased incidence of all-cause mortality 14 studies for 16 cohorts enrolling 15 662 subjects, hazard ratio (HR): 1.91; 95% confidence interval (CI): 1.40-2.61, P < 0.0001, I2 = 94% and MACCE (5 studies for 6 cohorts enrolling 13 944 subjects, HR: 1.67, 95% CI: 1.33-2.11, P < 0.00001, I2 = 46%,). Dose-response meta-analysis revealed that the relative risk (RR) for all-cause mortality increased by 7.6% per each 10 μmol/L increment of TMAO summary RR: 1.07, 95% CI (1.04-1.11), P < 0.0001; based on seven studies. Association of TMAO and mortality persisted in all examined subgroups and across all subject populations. CONCLUSIONS: This is the first systematic review and meta-analysis demonstrating the positive dose-dependent association between TMAO plasma levels and increased cardiovascular risk and mortality.