Dietary Meat, Trimethylamine N-Oxide-Related Metabolites, and Incident Cardiovascular Disease Among Older Adults: The Cardiovascular Health Study

Abstract

Background: Effects of animal source foods (ASF) on atherosclerotic cardiovascular disease (ASCVD) and underlying mechanisms remain controversial. We investigated prospective associations of different ASF with incident ASCVD and potential mediation by gut microbiota-generated trimethylamine N-oxide, its L-carnitine-derived intermediates γ-butyrobetaine and crotonobetaine, and traditional ASCVD risk pathways.

Methods: Among 3931 participants from a community-based US cohort aged 65+ years, ASF intakes and trimethylamine N-oxide-related metabolites were measured serially over time. Incident ASCVD (myocardial infarction, fatal coronary heart disease, stroke, other atherosclerotic death) was adjudicated over 12.5 years median follow-up. Cox proportional hazards models with time-varying exposures and covariates examined ASF-ASCVD associations; and additive hazard models, mediation proportions by different risk pathways.

Results: After multivariable-adjustment, higher intakes of unprocessed red meat, total meat, and total ASF associated with higher ASCVD risk, with hazard ratios (95% CI) per interquintile range of 1.15 (1.01-1.30), 1.22 (1.07-1.39), and 1.18 (1.03-1.34), respectively. Trimethylamine N-oxide-related metabolites together significantly mediated these associations, with mediation proportions (95% CI) of 10.6% (1.0-114.5), 7.8% (1.0-32.7), and 9.2% (2.2-44.5), respectively. Processed meat intake associated with a nonsignificant trend toward higher ASCVD (1.11 [0.98-1.25]); intakes of fish, poultry, and eggs were not significantly associated. Among other risk pathways, blood glucose, insulin, and C-reactive protein, but not blood pressure or blood cholesterol, each significantly mediated the total meat-ASCVD association.

Conclusions: In this large, community-based cohort, higher meat intake associated with incident ASCVD, partly mediated by microbiota-derived metabolites of L-carnitine, abundant in red meat. These novel findings support biochemical links between dietary meat, gut microbiome pathways, and ASCVD.

Keywords: cardiovascular diseases; microbiome; myocardial infarction; red meat; stroke; trimethylamine N-oxide.

Figure 1.. Pathways for generation of trimethylamine N-oxide (TMAO) and its intermediates.

Arrows in black represent transformations performed by the host, and arrows in red represent transformations performed by gut microbes. The endogenous biosynthesis of carnitine involves multiple steps from lysine to γ-butyrobetaine, indicated by a chain of arrows. In healthy subjects, γ-butyrobetaine is also endogenously synthesized from lysine, independent of gut-microbiota (6,58). In contrast, production of TMAO and crotonobetaine are profoundly suppressed by antibiotic administration (58), supporting a dominant role of gut microbial metabolism in their generation.

Figure 2.. Conceptual diagram of dietary exposures, gut microbiota-generated TMAO-related metabolites (mediators), and ASCVD.

For mediation modeling, eight potential causal pathways were jointly assessed: 1) ASF (animal source food)→ASCVD through other pathways; and ASF to ASCVD via: 2) γ-butyrobetaine→ASCVD; 3) γ-butyrobetaine→ crotonobetaine→ASCVD; 4) γ-butyrobetaine→ crotonobetaine→TMAO→ASCVD; 5) γ-butyrobetaine→TMAO→ASCVD; 6) crotonobetaine→ASCVD; 7) crotonobetaine→TMAO→ASCVD; 8) TMAO→ASCVD. Confounders are not shown in the graph to focus on the main causal pathways and for better visualization.

Figure 3.. Multivariable adjusted relationships between intakes of each ASF and the risk of ASCVD, evaluated using restricted cubic splines.

Knots were evaluated at the 10^th, 50^th, and 90^th percentiles. Dotted vertical lines represent, from left to right, the 10^th, 25^th, 50^th, 75^th, and 90^th percentiles of dietary intake. Covariates are specified in Table 3. The top 1% of the exposure distribution was not shown for better visualization.