Metabolism of Mono-and Dihydroxylated Bile Acids in Preparations of Human Liver

Abstract. The metabolism of tritium-labelled taurodeoxycholic acid, taurochenodeoxycholic acid, taurolithocholic acid and of 24-¹⁴C] lithocholic acid and 24-¹⁴C] 3-keto-5β-cholanoic acid was studied in fractions of human liver homogenates.—In the presence of microsomal fraction fortified with an NADPH-generating system a small conversion of taurodeoxycholic acid into taurocholic acid occurred. No significant hydroxylation of taurochenodeoxycholic acid, taurolithocholic acid or free lithocholic acid could be detected. In the presence of microsomal fraction fortified with NAD lithocholic acid was converted into 3-keto-5β-cholanoic acid. In the presence of microsomal fraction fortified with NADH, 3-keto-5β-cholanoic acid was reduced to isolithocholic acid and lithocholic acid (ratio 3:1). In the presence of 100000 × g supernatant fraction only lithocholic acid was formed from 3-keto-5β-cholanoic acid.—The physiological significance of the ability of human liver to convert lithocholic acid into isolithocholic acid is discussed.