Trimethylamine N-oxide: a meta-organismal axis linking the gut and fibrosis
- Jae Woong Jang, Emma Capaldi, Tracy Smith, et al.
- 2024
Why this matters for your gut health
TMAO — a compound produced when gut bacteria break down nutrients from red meat, eggs, and fish (choline, L-carnitine, phosphatidylcholine) — is now directly linked to scarring (fibrosis) in the kidney, heart, and liver. The pathway begins entirely in the gut: gut microbes convert dietary nutrients → TMA → liver converts it → TMAO in blood. Chronically elevated TMAO doesn’t just signal disease — it actively drives organ damage through multiple molecular mechanisms.
Summary
Tissue fibrosis — the excessive buildup of scar tissue (extracellular matrix) in organs — is responsible for up to 45% of all deaths in industrialized nations. It’s the final common pathway in diseases like chronic kidney disease, heart failure, fatty liver disease, and systemic sclerosis. Despite its prevalence, the root causes are poorly understood.
This review paper reveals that the gut microbiome plays a central and previously underappreciated role in driving fibrosis. Gut bacteria metabolize dietary precursors into TMA, which the liver enzyme FMO3 converts into TMAO. Chronically elevated TMAO then activates pro-fibrotic signaling cascades — TGF-β/SMAD3, NLRP3 inflammasome, PERK/Akt/mTOR — across multiple organ systems simultaneously.
Crucially, the paper also reviews therapeutic strategies: dietary changes, probiotics, and especially small-molecule TMA lyase inhibitors (DMB and IMC) that can reduce TMAO without killing gut bacteria — a gentler, more targeted approach than antibiotics.
Key findings
Kidney
- In a prospective cohort study of 1,434 people with initially normal kidney function, those who later developed CKD had 33% higher plasma TMAO levels than those who did not.
- In a separate CKD cohort of 521 patients, higher TMAO was associated with a 2.8-fold dose-dependent increase in 5-year all-cause mortality.
- In animal models, dietary choline/TMAO supplementation led to kidney fibrosis and functional impairment.
- TMAO drives renal fibrosis via SMAD3 phosphorylation, NLRP3 inflammasome activation, and the PERK/Akt/mTOR signaling cascade.
Heart
- A meta-analysis of nearly 7,000 heart failure patients found increasing TMAO independently associated with higher all-cause death, repeat heart attacks, and rehospitalizations.
- Cardioprotective benefits of voluntary exercise were abolished by TMAO supplementation in mice.
Liver
- High circulating TMAO was associated with greater severity of MASLD in multiple human cohort studies.
- TMAO suppresses bile acid production, aggravating liver fat accumulation.
Systemic Sclerosis
- FMO3 is significantly upregulated in skin fibroblasts from SSc patients.
- TMAO reprograms skin cells into myofibroblasts via PERK activation.
Therapeutic Strategies
- Avoiding red meat reduced plasma TMAO within 4 weeks.
- DMB & IMC inhibitors reduce TMAO without killing gut bacteria.
Read the full paper
Citation
Jang JW, Capaldi E, Smith T, Verma P, Varga J, Ho KJ. Trimethylamine N-oxide: a meta-organismal axis linking the gut and fibrosis. Molecular Medicine. 2024;30:128.