Effect of bile acid oxazoline derivatives on microorganisms participating in 7 alpha-hydroxyl epimerization of primary bile acids.

We tested bile acid oxazoline derivatives of chenodeoxycholic (CDC-OX), 7-ketolithocholic (7-KLC-OX), ursodeoxycholic (UDC-OX), and deoxycholic (DC-OX) as inhibitors of the 7-epimerization of the primary bile acids cholic acid (CA) and CDC in cultures of four species of bacteria and the human fecal flora. The organisms tested elaborate a 7 alpha- and/or 7 beta-hydroxysteroid dehydrogenase (HSDH); they were Escherichia coli (7 alpha-HSDH), Bacteroides fragilis (7 alpha-HSDH), Clostridium absonum (7 alpha- and 7 beta-HSDH) and Eubacterium aerofaciens (7 beta-HSDH). None of the oxazolines affected 7 alpha-OH oxidation of CA or CDC by E. coli or the growth of the organism. All the oxazolines (except UDC-OX) inhibited the growth of B. fragilis and its 7 alpha-HSDH. In contrast, only DC-OX blocked 7 alpha-OH epimerization of CA by C. absonum. Surprisingly, the other three oxazolines enhanced 7 alpha-OH epimerization of CA, but not that of CDC, which was inhibited (CDC-OX greater than 7-KLC-OX much greater than UDC-OX). Enzymic data suggest that CDC-OX in the presence of CA can induce a greater level of both 7 alpha- and 7 beta-HSDH than CA or CDC-OX alone, CDC-OX being more toxic in the presence of CDC. Formation of urso-bile acid from 7-keto substrates by E. aerofaciens is totally blocked by the oxazolines (except UDC-OX). Similarly, suppression of urso-bile acid formation from primary bile acids by the human fecal flora was evident with DC-OX greater than 7-KLC-OX greater than CDC-OX much greater than UDC-OX, the last being ineffective. The inhibitory activity of the oxazolines on the 7-dehydroxylation of primary bile acids by human fecal flora followed the same order.