Stereospecific dehydrogenation of (25R)- and (25S)-3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acids by acyl-CoA oxidase in rat liver light mitochondrial fraction

Major biliary bile acids of the medaka (Oryzias latipes): 25R- and 25S-epimers of 3alpha,7alpha,12alpha-trihydroxy-5beta-cholestanoic acid

The biliary bile salts of the medaka, the Japanese rice fish (Oryzias latipes) were isolated and identified. Only bile acids were present, and all were N-acylamidated with taurine. Three bile acids, constituting 98% of total bile acids, were isolated by chromatography and their structure inferred from their properties compared to those of synthetic standards when analyzed by liquid chromatographytandem mass spectrometry. The dominant bile acid was the 25R-epimer (82%) of 3alpha,7alpha,12alpha-trihydroxy-5beta-cholestan-27-oic acid. The 25S-epimer was also present (11%), as was cholic acid (5%). Complete (1)H and (13)C NMR signal assignments of the C-25 epimers were made by using a combination of several 1D- and 2D-NMR techniques. The (1)H and (13)C NMR chemical shifts and spectral patterns of the hydrogen and carbon atoms, being close to the asymmetric centered at C-25, provided confirmatory evidence in that they distinguished the two epimeric diastereomers. The medaka is the first fish species identified as having C(27) biliary bile acids as dominant among its major bile salts.

A new, major C27 biliary bile acid in the red-winged tinamou (Rhynchotus rufescens):25R-1beta, 3alpha,7alpha-trihydroxy-5beta-cholestan-27-oic acid

The chemical structures of the three major bile acids present in the gallbladder bile of the Red-winged tinamou (Rhynchotus rufescens), an early evolving, ground-living bird related to ratites, were determined. Bile acids were isolated by preparative reversed-phase HPLC. Two of the compounds were identified as the taurine N-acylamidates of 25R-3alpha,7alpha-dihydroxy-5beta-cholestan-27-oic acid (constituting 22% of biliary bile acids) and 25R-3alpha,7alpha,12alpha-trihydroxy-5beta-cholestan-27-oic acid (constituting 51%). The remaining compound, constituting 21% of biliary bile acids, was an unknown C27 bile acid. Its structure was elucidated by LC/ESI-MS/MS and NMR and shown to be the taurine conjugate of 25R-1beta, 3alpha, 7alpha-trihydroxy-5beta-cholestan-27-oic acid, a C27 trihydroxy bile acid not previously reported. Although C27 bile acids with a 1beta-hydroxyl group have been identified as trace bile acids in the alligator, this is the first report of a major biliary C27 bile acid possessing a 1beta-hydroxyl group.

Substrate specificity of THCA-CoA oxidases from rat liver light mitochondrial fractions on dehydrogenation of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid CoA thioester

The substrate specificity of rat liver peroxisomal 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoyl-CoA (THCA-CoA) oxidases, which catalyze the dehydrogenation of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid (THCA) CoA thioester, having an asymmetric center at C-25, to form (24E)-3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholest-24-enoic acid (delta 24-THCA) CoA thioester, was studied. The stable isotope labeled substrates, [3,7,12-18O3]-(25R)- and (25S)-THCA CoA thioesters were synthesized by an exchange reaction of carbonyl oxygens on a steroid nucleus of 3,7,12-trioxo-5 beta-cholestanoic acid, followed by metal hydride reduction and condensation reaction with CoA. After incubation of a mixture of unlabeled (25R)- and 18O-labeled (25S)-THCA CoA thioester, or vice versa, with hepatic peroxisomal THCA-CoA oxidases, biotransformed delta 24-THCA was determined by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry. The delta 24-THCA was derived only from (25S)-THCA CoA thioester, indicating that the 25S epimer of THCA is a preferential substrate on dehydrogenation by THCA-CoA oxidases.