16α-Hydroxycholic Acid: In Vivo Microbial Transformation Product of Cholic Acid

Aims: This study describes the transformation of cholic acid to hydroxylated cholic acid metabolites that could not be easily synthesized.
Study Design: The transformation was catalyzed by thermophilic Geobacillus stearothermophilus comb. nov., isolated from oil contaminated soil in Kuwait. Cholic acid, as the sole source of carbon, was added to G. stearothermophilus cells in phosphate buffer pH 7 and shaken at 65ºC for 5 days.
Methodology: The cholic acid transformation products were extracted with ethyl acetate, purified on preparative TLC plates and their molecular structures were established from their spectral data.
Results: The bacterium could selectively oxidize hydroxyl-groups at C3 and C7 while leaving the C12-hydroxyl-group unoxidized, in cholic acid. Five commonly found metabolites of cholic acid and a novel transformation product, 16α-hydroxycholic acid, were identified.
Conclusion: Our results indicate that G. stearothermophilus can hydroxylate/oxidize a steroid nucleus at various ring positions, and has a unique ability for hydroxylation at C16α in cholic acid.