title: Human hepatoblastoma cells (HepG2) and rat hepatoma cells are defective in important enzyme activities in the oxidation of the C27 steroid side chain in bile acid formation.
abstract: We have examined the ability of HepG2 human hepatoblastoma cells and 7800 C1 Morris rat hepatoma cells to convert 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid (THCA) and 3 alpha, 7 alpha-dihydroxy-5 beta-cholestanoic acid (DHCA) to cholic acid and chenodeoxycholic acid, respectively. Cell extracts from both these cell lines could neither form cholic acid from THCA nor from the activated form, THCA-CoA. This suggests that both cell lines are defective in two enzyme activities involved in the pathway, the microsomal THCA-CoA ligase and the peroxisomal THCA-CoA oxidase. Furthermore, we show that the subsequent enzymes are active in the conversion to bile acids, because the product of the THCA-CoA oxidase, 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholest-24-enoyl-coenzyme A (delta 24-THCA-CoA) or delta 24-THCA in the presence of THCA-CoA ligase, are converted to cholic acid by both cell lines. HepG2 cells were able to slowly form chenodeoxycholic acid and cholic acid from 5 beta-cholestane-3 alpha, 7 alpha-diol and 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol, respectively, in 24- and 96-h incubations. The rate of cholic acid formation was lower than the rate for chenodeoxycholic acid and there was a clear accumulation of THCA. 7800 C1 Morris cells had no ability to form cholic acid or chenodeoxycholic acid after 96 h incubation. We conclude that these two cell lines have defects in two enzyme activities involved in the peroxisomal oxidation in bile acid formation, the microsomal THCA-CoA ligase and the peroxisomal THCA-CoA oxidase.
authors.affiliation: Institute for Nutrition Research, School of Medicine, University of Oslo, Norway.
authors.forename: A K
authors.initials: AK
authors.lastname: Farrants
authors.forename: A
authors.initials: A
authors.lastname: Nilsson
authors.forename: J I
authors.initials: JI
authors.lastname: Pedersen
mesh_terms: D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism*; D002635:Chenodeoxycholic Acid / Q000378:metabolism; D002777:Cholestanols / Q000378:metabolism / Q000494:pharmacology; D002790:Cholesterol 7-alpha-Hydroxylase / Q000378:metabolism; D019826:Cholic Acid; D002793:Cholic Acids / Q000378:metabolism; D002995:Clofibric Acid / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D005227:Fatty Acids / Q000494:pharmacology; D018197:Hepatoblastoma / Q000201:enzymology*; D006801:Humans; D008113:Liver Neoplasms / Q000201:enzymology*; D008114:Liver Neoplasms, Experimental / Q000201:enzymology*; D008297:Male; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar; D012176:Retinoids / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: C000986:3,7-dihydroxycholestan-26-oic acid; D001647:Bile Acids and Salts; D002777:Cholestanols; D002793:Cholic Acids; D005227:Fatty Acids; D012176:Retinoids; D002635:Chenodeoxycholic Acid; D002995:Clofibric Acid; C022069:3,7,12-trihydroxycholestan-26-oic acid; D003907:Dexamethasone; D002790:Cholesterol 7-alpha-Hydroxylase; D019826:Cholic Acid