Stereoisomeric bio-inversion of (25R)- and (25S)-3α, 7α, 12α-trihydroxy-5β-cholestanoic acid CoA thioesters in rat liver peroxisome

The stereoisomeric inversion of (25R)- and (25S)-3α, 7 α, 12α-trihydroxy-5β-cholestanoic acid CoA thioester (THCA-CoA) and substrate specificity for the dehydrogenation catalyzed by acyl-CoA oxidase in rat liver peroxisomes was studied. After incubation of C-25 isomeric THCA-CoAs individually with a hepatic peroxisomal fraction, remaining 5β-cholestanoic acid C-25 stereoisomers were extracted and determined by liquid chromatography/atomic pressure ionization (APCI)-mass spectrometry. The biotransformed (24E)-3α, 7α, 12α-trihydroxy-5β-cholest-24-enoic acid (Δ²⁴-THCA) in the incubation mixture was also analyzed by gas chromatography/ negative-ion chemical ionization-mass spectrometry. The rapid enzymatic epimerizations from either direction were observed prior to biotransformation into (24E)-Δ²⁴-THCA and were inhibited by addition of CoA thioester of ibuprofen, a 2-arylpropionic acid derivative. In the presence of excess amounts of (R)- or (S)-ibuprofenyl-CoA in incubation mixture, suppressive conversion of (25R)-THCA-CoA into (24E)-Δ²⁴-THCA was observed, suggesting that (25S)-THCA-CoA thioester is a preferential substrate for acyl-CoA oxidase in hepatic peroxisome.