Metabolism of unsaturated bile acids and androstanes by human faecal bacteria.

The metabolism of unsaturated bile acids and androstanes by mixed human faecal cultures has been studied. The reactions observed were mainly reductive. Unsaturated 4-ene-3-oxo and 1,4-diene-3-oxo bile acids were reduced in Ring A. 5 beta-3-Oxo bile acids were reduced to 5 beta-3-hydroxy bile acids. 4-Ene, 1,4-diene and 4,6-diene-3,17-dioxo-androstanes were reduced in Ring A with concomitant reduction of oxo groups to hydroxyl groups. The Gram-negative facultative anaerobic faecal bacteria are implicated in the reductive process, whilst the genus Clostridium does not appear to be important. Inclusion of menadione, a synthetic form of vitamin K, retards the reductive process.