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Microbiome interface

Bile acids as signaling molecules — FXR and TGR5

Hypothesis Mechanism review
bile acids barrier mechanism microbiome marker intervention supplement
Editor's note
Bile acids signal through intestinal receptors to strengthen the epithelial barrier and resist infection—a mechanism that antibiotics unwittingly disrupt by eliminating the bacteria that produce them. This reframes recurrent C. difficile as partly a signaling deficiency, not just dysbiosis, and suggests measurable bile acid profiling could identify high-risk patients and guide targeted restoration strategies. Gastroenterologists, infectious disease specialists, and researchers studying barrier recovery after antibiotic exposure should take note.

Bile acids are not just fat emulsifiers. They are signaling molecules.

The intestinal epithelium prominently expresses two key bile acid receptors — farnesoid X receptor (FXR) and G-protein-coupled bile acid receptor 1 (TGR5) — which play indispensable roles in maintaining bile acid homeostasis and intestinal barrier function.

Bile acids can promote epithelial regeneration by activating TGR5 in intestinal stem cells. Chenodeoxycholic acid (CDCA) protects intestinal barrier function through the FXR-MLCK pathway. Bile acid-mediated activation of FXR/TGR5 increases tight junction protein expression, improving barrier integrity and limiting bacterial translocation.

Clinical implication: In patients with repeated antibiotic exposure, secondary bile acid production may be compromised. Secondary bile acids are produced by specific bacteria (Clostridium scindens, Clostridium hiranonis) that convert primary into secondary. Antibiotics easily eliminate these strains. Consequence: weakened FXR/TGR5 activation, weakened barrier, less MUC2 stimulation, lower colonization resistance against C. difficile.

Measurement: bile acid profile in stool (primary vs secondary, conjugated vs free). UDCA (ursodeoxycholic acid) is available as a pharmaceutical and has documented barrier-protective effects.

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Published 2026-05-24 · Last kit-update 2026-05-24