Bile salt biotransformations by human intestinal bacteria

Area of Science:

• Microbiology
• Biochemistry
• Gastroenterology

Background:

• Secondary bile acids, produced by gut bacteria, can reach high levels in the enterohepatic circulation.
• Elevated secondary bile acids are implicated in the pathogenesis of colon cancer, gallstones, and other gastrointestinal diseases.

Purpose of the Study:

• To investigate the role of microbial enzymes in bile acid metabolism.
• To explore the potential for therapeutic interventions targeting bile acid biotransformation pathways.

Main Methods:

• Studied bile salt hydrolysis, hydroxy group dehydrogenation, and bile acid 7-dehydroxylation by intestinal anaerobic bacteria.
• Utilized crystallization, site-directed mutagenesis, and protein secondary structure comparisons to understand enzyme mechanisms.
• Employed molecular cloning to identify genes encoding bile salt-modifying enzymes.

Main Results:

• Bile acid 7-dehydroxylation is performed by a limited subset of intestinal anaerobes.
• Microbial bile salt-modifying enzymes exhibit species-specific characteristics (pH optima, kinetics, substrate specificity).
• Molecular cloning provided insights into the genetic organization of bile acid modification pathways.

Conclusions:

• Understanding microbial bile acid metabolism is crucial for addressing associated GI diseases.
• Targeting key enzymes in the 7alpha/beta-dehydroxylation pathway via pharmaceuticals or probiotics could alter bile acid pools.
• This approach may lead to effective host removal of excess bile acids and disease prevention.