Comparison of side chain oxidation of potential C27-bile acid intermediates between mitochondria and peroxisomes of the rat liver: presence of beta-oxidation activity for bile acid biosynthesis in mitochondria.

The oxidation of the side chains of two potential bile acid intermediates, 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid (THCA) and 3 alpha,7 alpha-dihydroxy-5 beta-cholestanoic acid (DHCA), were investigated in rat liver mitochondria and peroxisomes. Both THCA and DHCA were efficiently oxidized to yield cholic acid and chenodeoxycholic acid, along with 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholest-24-enoic acid and 3 alpha,7 alpha-dihydroxy-5 beta-cholest-24-enoic acid, respectively, in both the mitochondria and peroxisomes. However, the spectrum of the metabolites in the mitochondria differed greatly from those in the peroxisomes. The major products from THCA and DHCA in the mitochondria were 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-chol-22-enoic acid and 3 alpha,7 alpha-trihydroxy-5 beta-chol-22-enoic acid, respectively, which were tentatively identified from the mass spectral data. However, the formation of these C24-unsaturated bile acids was not observed in the peroxisomes. These results strongly suggest that the cleavage of the side chain of the C27-intermediates for bile acid biosynthesis also occurs independently in the mitochondria, not due to the contamination of peroxisomes.