CHOLESTEROL 7-ALPHA-HYDROXYLASE IS UP-REGULATED BY THE COMPETITIVE INHIBITOR 7-OXOCHOLESTEROL IN RAT-LIVER

Title

CHOLESTEROL 7-ALPHA-HYDROXYLASE IS UP-REGULATED BY THE COMPETITIVE INHIBITOR 7-OXOCHOLESTEROL IN RAT-LIVER

Creator

Breuer O; Sudjanasugiaman E; Eggertsen G; Chiang J Y L; Bjorkhem I

Publisher

European Journal of Biochemistry

Date

1993
1993-08

Description

Rats of the Sprague-Dawley strain were infused intravenously with a fat emulsion (Intralipid, trademark of Kabi Pharmacia, Uppsala, Sweden) containing 7-oxocholesterol. This resulted in an increased cholesterol 7alpha-hydroxylase activity in liver microsomes as compared to controls and was accompanied by increased levels of cholesterol 7alpha-hydroxylase mRNA and microsomal cholesterol 7alpha-hydroxylase protein. Rats were also fed a cholestyramine-supplemented diet and infused with 7-oxocholesterol. These animals excreted about half as much bile acids in faeces as cholestyramine-fed controls. Addition of 7-oxocholesterol to liver microsomes from normal rats in amounts corresponding to those present in microsomes from 7-oxocholesterol-treated rats inhibited the cholesterol 7alpha-hydroxylase activity by about 75%. Cholesterol induced a type-I binding spectrum when added to a purified bacterial-expressed cholesterol 7alpha-hydroxylase (P-450c7DELTA2-24). 7-Oxocholesterol competitively inhibited the cholesterol binding spectrum, while 7beta-hydroxycholesterol did not interfere with binding of cholesterol to the enzyme. It is concluded that treatment with the competitive inhibitor 7-oxocholesterol leads to a reduced bile acid biosynthesis and, as a consequence of reduced bile acid inhibition, a compensatory increase in cholesterol 7alpha-hydroxylase synthesis. The high enzyme activity measured in microsomal preparations from 7-oxocholesterol-treated rats may be due to a continuous conversion of 7-oxocholesterol into less inhibitory metabolites, e.g. 7beta-hydroxycholesterol. The latter compound was found in high concentrations in liver microsomes from rats treated with 7-oxocholesterol. The physiological importance of these results is discussed in relation to the previous findings that 7-oxocholesterol is accumulated in liver after cholesterol feeding and that 7-oxocholesterol is formed from cholesterol during lipid peroxidation.

Subject

Biochemistry & Molecular Biology; expression; cloning; dietary-cholesterol; purification; messenger-rna; circadian-rhythm; reductase; microsomes; sequence; serum-cholesterol

Format

Journal Article or Conference Abstract Publication

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Rights

Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).

Pages

705-710

Issue

3

Volume

215

Citation

Breuer O; Sudjanasugiaman E; Eggertsen G; Chiang J Y L; Bjorkhem I, “CHOLESTEROL 7-ALPHA-HYDROXYLASE IS UP-REGULATED BY THE COMPETITIVE INHIBITOR 7-OXOCHOLESTEROL IN RAT-LIVER,” NEOMED Bibliography Database, accessed December 6, 2021, https://neomed.omeka.net/items/show/8727.

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