Higher levels of trimethylamine N-oxide (TMAO) are independently associated with a greater prevalence of atrial fibrillation (AF), according to a study published in The Journal of Clinical Investigation. Researchers found that TMAO, a metabolite produced by gut microbes from nutrients like choline, may trigger AF by inhibiting muscarinic receptor 2 signaling and disrupting autonomic regulation in the heart.
The Link Between Gut Microbiome and Atrial Fibrillation
A cohort of 5,090 individuals from the Cleveland Clinic GeneBank provided the data for this human analysis. Using liquid chromatography-electrospray ionization-tandem mass spectrometry, researchers quantified plasma levels of TMAO, betaine, and choline in patients undergoing elective cardiac catheterization.
The study found that plasma TMAO levels were significantly linked to AF prevalence. Specifically, the adjusted odds ratio for those in the highest concentration tertile compared to the lowest was 1.7. This association remained significant after accounting for age, sex, smoking, comorbidities, and kidney function (eGFR).
Did you know? TMAO is formed when gut bacteria convert choline into trimethylamine (TMA), which the liver then oxidizes into TMAO.
How TMAO Alters Heart Structure and Electrical Activity
To move beyond observation, researchers used genetically engineered mice expressing the human CREM-IbΔC-X gene variant. According to the study, mice fed TMAO or choline-supplemented diets developed AF earlier than those on standard chow. Those receiving TMAO supplementation showed an 11-fold increase in AF inducibility during transesophageal pacing studies.
The researchers observed structural changes in the heart of choline-fed mice, including a significant increase in left atrial size at five and eight weeks. Optical mapping further revealed a reduction in cardiac wavelength and a shortened action-potential duration at 80% repolarization.
The Role of Autonomic Dysfunction
The study proposes that TMAO promotes AF by interfering with autonomic regulation. In HEK293 cells engineered to express muscarinic receptor 2 (M2R), TMAO inhibited receptor signaling when the agonist carbachol was present. This inhibition supports a possible role for autonomic dysfunction in promoting AF.
Potential for TMAO-Lowering Interventions
The research explored whether blocking the microbial production of TMA could reverse these effects. The team used iodomethylcholine (IMC), a selective inhibitor of choline trimethylamine-lyase (CutC/D).
According to the findings, IMC treatment:
- Delayed the onset of both paroxysmal and persistent AF in mice.
- Reduced circulating TMAO levels by suppressing the microbial conversion of choline to TMA.
- Attenuated the enlargement of the left atrium at eight weeks.
- Reversed the loss of gut microbiome diversity associated with high-choline diets.
Expert Insight: While the study linked Parvibacter caecicola to the timing of AF onset in mice, the authors noted this association requires further investigation.
Comparing Mechanisms: TMAO vs. Inflammasomes
The researchers tested whether the NLRP3 inflammasome played a role in this process. They exposed cardiac cells to physiologically relevant TMAO levels and administered MCC950, a chemical compound that inhibits NLRP3.
The results showed that TMAO did not increase the expression of NLRP3 or interleukin-1β (IL-1β). Furthermore, MCC950 did not delay the development of AF in the mouse models. This indicates that NLRP3 inflammasome activation was not a major mechanism in this mouse model.
Frequently Asked Questions
What is TMAO and where does it come from?
Trimethylamine N-oxide (TMAO) is a metabolite produced when the liver oxidizes trimethylamine (TMA), which is created by gut bacteria breaking down nutrients like choline.
Does high TMAO definitely cause AF in humans?
The human analysis was observational and assessed existing rather than incident AF, while the mechanistic and therapeutic findings came from mice and cell experiments.
Can diet prevent atrial fibrillation?
The study suggests that diet, through its effects on the gut microbiome and TMAO production, may influence AF susceptibility, although dietary effects were tested only in mice, and the human findings came from a cardiovascular referral cohort.
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