Can gut microbial beta-glucuronidase deconjugate biliary compounds and promote enterohepatic reabsorption?

Biliary glucuronidation is often viewed as a route of elimination, but gut microbes can partially reverse it. This has important, compound-specific consequences for drug exposure and intestinal toxicity.

Mechanistic and clinical evidence

• Gut microbial β-glucuronidases hydrolyze glucuronide conjugates delivered in bile, releasing the parent aglycone. Because intact glucuronides are generally poorly absorbed, regenerated aglycones may be absorbed, return through portal blood to the liver, and undergo enterohepatic recirculation.
• This mechanism is established for several clinically relevant substrates. Deconjugation of mycophenolic-acid glucuronide can materially contribute to systemic mycophenolic-acid exposure and prolonged exposure. Hydrolysis of diclofenac conjugates regenerates diclofenac and can promote recurrent intestinal mucosal exposure.
• For irinotecan, microbial reactivation of SN-38 glucuronide to active SN-38 contributes to delayed diarrhea and intestinal injury. In mice, selective microbial β-glucuronidase inhibition reduced NSAID enteropathy, illustrating that local intestinal reactivation can matter even when short-term plasma or liver concentrations do not measurably change over 96 hours.

Transit and other determinants

• Slower intestinal transit is a biologically credible contributor because it extends, particularly in the colon, the time available for microbial deconjugation before fecal elimination. If the regenerated compound is permeable, this can permit more reabsorption and potentially secondary concentration peaks or a longer apparent half-life.
• The magnitude is not predictable from transit alone. It depends on biliary delivery, the specific glucuronide and microbial enzyme isoforms, microbiome composition, intestinal pH and fiber exposure, permeability, transporters, intestinal metabolism, and fecal loss.

Bottom line

• The core claim is well supported: microbial β-glucuronidase can reactivate biliary glucuronides and enable enterohepatic recycling. Slower transit plausibly increases the opportunity for this process, but its practical effect on drug levels or toxicity is highly compound- and individual-specific.