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Suppression of sterol 27-hydroxylase mRNA and transcriptional activity by bile acids in cultured rat hepatocytes

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Author: Twisk, J. · Wit, E.C.M. de · Princen, H.M.G.
Type:article
Date:1995
Institution: TNO Preventie en Gezondheid
Source:Biochemical Journal, 2, 305, 505-511
Identifier: 232889
Keywords: Biology · bile acid · chenodeoxycholic acid · cholesterol 7alpha monooxygenase · cholic acid · deoxycholic acid · lithocholic acid · messenger rna · oxygenase · sterol · taurocholic acid · animal cell · article · bile acid synthesis · cholesterol metabolism · controlled study · enzyme inhibition · gene repression · liver cell culture · nonhuman · priority journal · rat · transcription regulation · Adenosine Triphosphate · Animal · Bile Acids and Salts · Cells, Cultured · Cholesterol 7-alpha-Hydroxylase · Cytochrome P-450 Enzyme System · Dose-Response Relationship, Drug · Down-Regulation · Gene Expression Regulation, Enzymologic · Liver · Male · Mitochondria · Oxidoreductases · Rats · Rats, Wistar · RNA, Messenger · Steroid Hydroxylases · Support, Non-U.S. Gov't · Taurocholic Acid · Transcription, Genetic

Abstract

In previous work we have demonstrated suppression of cholesterol 7α-hydroxylase by bile acids at the level of mRNA and transcription, resulting in a similar decline in bile acid synthesis in cultured rat hepatocytes. In view of the substantial contribution of the 'alternative' or '27-hydroxylase' route to total bile acid synthesis, as demonstrated in cultured rat hepatocytes and in vivo in humans, we here evaluate the effects of various bile acids commonly found in bile of rats on the regulation of sterol 27-hydroxylase in cultured rat hepatocytes. Addition of taurocholic acid, the predominant bile acid in rat bile, to the culture medium of rat hepatocytes resulted in a 72% inhibition of sterol 27-hydroxylase activity. The effect was exerted at the level of sterol 27-hydroxylase mRNA, showing a time- and dose-dependent decline with a maximal suppression (-75%) at 50 μM taurocholic acid after 24 h of culture. The decline in mRNA followed first-order kinetics with an apparent half-life of 13 h. Under these conditions cholesterol 7α-hydroxylase mRNA (-91%) and bile acid synthesis (i.e. chenodeoxycholic and β-muricholic acid, -81%) were also maximally suppressed. In contrast, no change was found in the level of lithocholic acid 6β-hydroxylase mRNA. Assessment of the transcriptional activity of a number of genes involved in routing of cholesterol towards bile acids showed similar suppressive effects of taurocholate on expression of the sterol 27-hydroxylase and cholesterol 7α-hydroxylase genes (-43% and -42% respectively), whereas expression of the lithocholic 6β-hydroxylase gene was not affected. Taurocholic acid and unconjugated cholic acid were equally as effective in suppressing sterol 27-hydroxylase mRNA. The more hydrophobic bile acids, chenodeoxycholic acid and deoxycholic acid also produced a strong inhibition of 57% and 76% respectively whereas the hydrophilic β-muricholic acid was not active. We conclude that (1) a number of bile acids, at physiological concentrations, suppress sterol 27-hydroxylase by down-regulation of sterol 27-hydroxylase mRNA and transcriptional activity and (2) co-ordinated suppression of both sterol 27-hydroxylase and cholesterol 7α-hydroxylase results in inhibition of bile acid synthesis in cultured rat hepatocytes. Chemicals/CAS: chenodeoxycholic acid, 474-25-9; cholesterol 7alpha monooxygenase, 9037-53-0; cholic acid, 32500-01-9, 361-09-1, 81-25-4; deoxycholic acid, 83-44-3; lithocholic acid, 434-13-9; oxygenase, 9037-29-0, 9046-59-7; taurocholic acid, 145-42-6, 59005-70-8, 81-24-3; Adenosine Triphosphate, 56-65-5; Bile Acids and Salts; Cholesterol 7-alpha-Hydroxylase, EC 1.14.13.17; Cytochrome P-450 Enzyme System, 9035-51-2; cytochrome P-450C27/25, EC 1.14.-; Oxidoreductases, EC 1.; RNA, Messenger; Steroid Hydroxylases, EC 1.14.-; Taurocholic Acid, 81-24-3