Circulating Trimethylamine N-Oxide and Growth Rate of Abdominal Aortic Aneurysms and Surgical Risk.
IMPORTANCE: Plasma levels of the gut microbiota-dependent metabolite trimethylamine N-oxide (TMAO) are associated with prevalent abdominal aortic aneurysms (AAA) in humans and fostering of AAA progression in animal models; therapeutic targeting of TMAO production blocks AAA progression and rupture in multiple mouse models. A blood biomarker that identifies individuals at risk for incident AAA development, accelerated AAA expansion, or recommendation for surgical AAA repair could be an asset for risk stratification. OBJECTIVE: To determine whether TMAO is associated with risk for AAA development, rapid AAA expansion, and risk for recommended surgical intervention. DESIGN, SETTING, AND PARTICIPANTS: This was a prospective cohort study using 2 independent clinical cohorts undergoing aorta imaging surveillance: a European cohort and a US cohort. Included in this study were patients undergoing serial imaging surveillance of the aorta and long-term outcome monitoring. Patients were recruited from single-center studies in Uppsala, Sweden, and Cleveland, Ohio. Study data were analyzed from October 2023 to May 2025. EXPOSURES: Plasma TMAO concentrations measured by stable isotope dilution liquid chromatography with tandem mass spectrometry. MAIN OUTCOMES AND MEASURES: The association of TMAO levels with AAA risk, fast-growing AAA (≥4.0 mm per year), and recommended surgical intervention (≥4.0 mm per year or ≥5.5 cm diameter). RESULTS: The European cohort included 237 individuals (median [IQR] age, 65 [65-73] years; 211 male [89.0%]), and the US cohort included 658 individuals (median [IQR] age, 63 [57-70] years; 523 male [79.5%]). In the European cohort, elevated circulating TMAO was significantly associated with AAA risk independent of traditional risk factors and kidney function. Moreover, elevated TMAO predicted both greater risk for fast-growing AAA (adjusted odds ratio [aOR], 2.75; 95% CI, 1.20-6.79) and recommended surgical intervention (aOR, 2.67; 95% CI, 1.24-6.09). Similar patterns were observed in the US cohort and the combined European and US cohort, with heightened circulating TMAO corresponding with significantly increased adjusted risk for fast-growing AAA (US cohort: aOR, 2.71; 95% CI, 1.53-4.80; combined cohort: aOR, 2.30; 95% CI, 1.47-3.62) and recommended surgical intervention (US cohort: aOR, 2.73; 95% CI, 1.56-4.80; combined cohort: aOR, 2.41; 95% CI, 1.55-3.74). Addition of TMAO to base models containing traditional cardiovascular risk factors resulted in significant improvement in both risk estimation for fast-growing AAA and predicting recommended surgical intervention. CONCLUSION AND RELEVANCE: Results of this cohort study suggest that elevated circulating TMAO levels were associated with increased risk of AAA and identified patients at heightened risk for fast-growing AAA and recommended surgical intervention. TMAO may help identify individuals who may benefit from more frequent surveillance imaging and early surgical intervention to prevent aortic dissection or rupture.