Biotransformation of bile acids by clostridia.

The metabolism of bile acids by nuclear dehydrogenating clostridia (NDC) was studied. NDC were able to desaturate the A-ring of 5 beta-cholan-3-oxo-24-oic acid, 12 alpha-hydroxy-5 beta-cholan-3-oxo-24-oic acid, 7 alpha-hydroxy-5 beta-cholan-3-oxo-24-oic acid, 6 alpha-hydroxy-5 beta-cholan-3-oxo-24-oic acid, 7 alpha, 12 alpha-dihydroxy-5 beta-cholan-3-oxo-24-oic acid, 3,12-dioxo-5 beta-cholan-24-oic acid but not 3,6-dioxo-5 beta-cholan-24-oic acid, 3,7-dioxo-5 beta-cholan-24-oic acid and 3,7,12-trioxo-5 beta-cholan-24-oic acid. In each case the sole product possessed a 4-ene-3-one structure. Desaturation of bile acids was more efficient than that of androstanes. NDC are, therefore, capable of introducing double bonds into the nucleus of bile acids as well as that of androstanes. The physiological significance of such reactions in relation to large bowel cancer has yet to be elucidated.