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Tempel W, Grabovec I, MacKenzie F, Dichenko YV, Usanov SA, Gilep AA, Park HW, Strushkevich N. Structural characterization of human cholesterol 7α-hydroxylase. J Lipid Res 2014; 55:1925-32. [PMID: 24927729 DOI: 10.1194/jlr.m050765] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Hepatic conversion to bile acids is a major elimination route for cholesterol in mammals. CYP7A1 catalyzes the first and rate-limiting step in classic bile acid biosynthesis, converting cholesterol to 7α-hydroxycholesterol. To identify the structural determinants that govern the stereospecific hydroxylation of cholesterol, we solved the crystal structure of CYP7A1 in the ligand-free state. The structure-based mutation T104L in the B' helix, corresponding to the nonpolar residue of CYP7B1, was used to obtain crystals of complexes with cholest-4-en-3-one and with cholesterol oxidation product 7-ketocholesterol (7KCh). The structures reveal a motif of residues that promote cholest-4-en-3-one binding parallel to the heme, thus positioning the C7 atom for hydroxylation. Additional regions of the binding cavity (most distant from the access channel) are involved to accommodate the elongated conformation of the aliphatic side chain. Structural complex with 7KCh shows an active site rigidity and provides an explanation for its inhibitory effect. Based on our previously published data, we proposed a model of cholesterol abstraction from the membrane by CYP7A1 for metabolism. CYP7A1 structural data provide a molecular basis for understanding of the diversity of 7α-hydroxylases, on the one hand, and cholesterol-metabolizing enzymes adapted for their specific activity, on the other hand.
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Affiliation(s)
- Wolfram Tempel
- Structural Genomics Consortium, University of Toronto, Toronto, Ontario, M5G 1L7, Canada
| | - Irina Grabovec
- Institute of Bioorganic Chemistry NAS of Belarus, Minsk, 220141 Belarus
| | - Farrell MacKenzie
- Structural Genomics Consortium, University of Toronto, Toronto, Ontario, M5G 1L7, Canada
| | | | - Sergey A Usanov
- Institute of Bioorganic Chemistry NAS of Belarus, Minsk, 220141 Belarus
| | - Andrei A Gilep
- Institute of Bioorganic Chemistry NAS of Belarus, Minsk, 220141 Belarus
| | - Hee-Won Park
- Department of Biochemistry and Molecular Biology, Tulane University School of Medicine, New Orleans, LA 70112
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Sohi G, Barry EJ, Velenosi TJ, Urquhart BL, Hardy DB. Protein Restoration in Low-Birth-Weight Rat Offspring Derived from Maternal Low-Protein Diet Leads to Elevated Hepatic CYP3A and CYP2C11 Activity in Adulthood. Drug Metab Dispos 2013; 42:221-8. [DOI: 10.1124/dmd.113.053538] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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3
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Zhou X, Han Y, Liu J, Gao L, Zhao J. Decreased protein and gene expression of hepatic cholesterol 7a-hydroxylase associated with dilated endoplasmic reticulum in chronic hypothyroid rats. Pathol Int 2009; 59:729-34. [DOI: 10.1111/j.1440-1827.2009.02435.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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4
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Xie Y, Blanc V, Kerr TA, Kennedy S, Luo J, Newberry EP, Davidson NO. Decreased expression of cholesterol 7alpha-hydroxylase and altered bile acid metabolism in Apobec-1-/- mice lead to increased gallstone susceptibility. J Biol Chem 2009; 284:16860-16871. [PMID: 19386592 PMCID: PMC2719322 DOI: 10.1074/jbc.m109.010173] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Quantitative trait mapping in mice identified a susceptibility locus for gallstones (Lith6) spanning the Apobec-1 locus, the structural gene encoding the RNA-specific cytidine deaminase responsible for production of apolipoprotein B48 in mammalian small intestine and rodent liver. This observation prompted us to compare dietary gallstone susceptibility in Apobec-1(-/-) mice and congenic C57BL/6 wild type controls. When fed a lithogenic diet (LD) for 2 weeks, 90% Apobec-1(-/-) mice developed solid gallstones in comparison with 16% wild type controls. LD-fed Apobec-1(-/-) mice demonstrated increased biliary cholesterol secretion as well as increased cholesterol saturation and bile acid hydrophobicity indices. These changes occurred despite a relative decrease in cholesterol absorption in LD-fed Apobec-1(-/-) mice. Among the possible mechanisms to account for this phenotype, expression of Cyp7a1 mRNA and protein were significantly decreased in chow-fed Apobec-1(-/-) mice, decreasing further in LD-fed animals. Cyp7a1 transcription in hepatocyte nuclei, however, was unchanged in Apobec-1(-/-) mice, excluding transcriptional repression as a potential mechanism for decreased Cyp7a1 expression. We demonstrated that APOBEC-1 binds to AU-rich regions of the 3'-untranslated region of the Cyp7a1 transcript, containing the UUUN(A/U)U consensus motif, using both UV cross-linking to recombinant APOBEC-1 and in vivo RNA co-immunoprecipitation. In vivo Apobec-1-dependent modulation of Cyp7a1 expression was further confirmed following adenovirus-Apobec-1 administration to chow-fed Apobec-1(-/-) mice, which rescued Cyp7a1 gene expression. Taken together, the findings suggest that the AU-rich RNA binding-protein Apobec-1 mediates post-transcriptional regulation of murine Cyp7a1 expression and influences susceptibility to diet-induced gallstone formation.
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Affiliation(s)
- Yan Xie
- From the Departments of Medicine, St. Louis, Missouri 63110
| | - Valerie Blanc
- From the Departments of Medicine, St. Louis, Missouri 63110
| | - Thomas A Kerr
- From the Departments of Medicine, St. Louis, Missouri 63110
| | - Susan Kennedy
- From the Departments of Medicine, St. Louis, Missouri 63110
| | - Jianyang Luo
- From the Departments of Medicine, St. Louis, Missouri 63110
| | | | - Nicholas O Davidson
- From the Departments of Medicine, St. Louis, Missouri 63110; Pharmacology and Developmental Biology, Washington University School of Medicine, St. Louis, Missouri 63110.
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5
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Antunez-Solis J, Hernández-Derramadero F, Aquino-Vega M, Ibarra-Ramírez S, Rodríguez-Páez L, Baeza I, Wong C. 2,4,5-trimethoxycinnamic acid: the major metabolite of α-asarone, retains most of the pharmacological properties of α-asarone. J Enzyme Inhib Med Chem 2008; 24:903-9. [DOI: 10.1080/14756360802318902] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Affiliation(s)
- Javier Antunez-Solis
- Departamento de Bioquímica, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Apartado Postal 4-129, Admon. 4, México City 06401, Mexico
| | - Fernando Hernández-Derramadero
- Departamento de Bioquímica, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Apartado Postal 4-129, Admon. 4, México City 06401, Mexico
| | - Mayda Aquino-Vega
- Departamento de Bioquímica, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Apartado Postal 4-129, Admon. 4, México City 06401, Mexico
| | - Selene Ibarra-Ramírez
- Departamento de Bioquímica, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Apartado Postal 4-129, Admon. 4, México City 06401, Mexico
| | - Lorena Rodríguez-Páez
- Departamento de Bioquímica, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Apartado Postal 4-129, Admon. 4, México City 06401, Mexico
| | - Isabel Baeza
- Departamento de Bioquímica, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Apartado Postal 4-129, Admon. 4, México City 06401, Mexico
| | - Carlos Wong
- Departamento de Bioquímica, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Apartado Postal 4-129, Admon. 4, México City 06401, Mexico
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6
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Sontag TJ, Parker RS. Influence of major structural features of tocopherols and tocotrienols on their omega-oxidation by tocopherol-omega-hydroxylase. J Lipid Res 2007; 48:1090-8. [PMID: 17284776 DOI: 10.1194/jlr.m600514-jlr200] [Citation(s) in RCA: 132] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Human cytochrome P450 4F2 (CYP4F2) catalyzes the initial omega-hydroxylation reaction in the metabolism of tocopherols and tocotrienols to carboxychromanols and is, to date, the only enzyme shown to metabolize vitamin E. The objective of this study was to characterize this activity, particularly the influence of key features of tocochromanol substrate structure. The influence of the number and positions of methyl groups on the chromanol ring, and of stereochemistry and saturation of the side chain, were explored using HepG2 cultures and microsomal reaction systems. Human liver microsomes and microsomes selectively expressing recombinant human CYP4F2 exhibited substrate activity patterns similar to those of HepG2 cells. Although activity was strongly associated with substrate accumulation by cells or microsomes, substantial differences in specific activities between substrates remained under conditions of similar microsomal membrane substrate concentration. Methylation at C5 of the chromanol ring was associated with markedly low activity. Tocotrienols exhibited much higher Vmax values than their tocopherol counterparts. Side chain stereochemistry had no effect on omega-hydroxylation of alpha-tocopherol (alpha-TOH) by any system. Kinetic analysis of microsomal CYP4F2 activity revealed Michaelis-Menten kinetics for alpha-TOH but allosteric cooperativity for other vitamers, especially tocotrienols. Additionally, alpha-TOH was a positive effector of omega-hydroxylation of other vitamers. These results indicate that CYP4F2-mediated tocopherol-omega-hydroxylation is a central feature underlying the different biological half-lives, and therefore biopotencies, of the tocopherols and tocotrienols.
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Affiliation(s)
- Timothy J Sontag
- Division of Nutritional Sciences, Cornell University, Ithaca, NY 14850, USA
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7
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Li X, Hylemon P, Pandak WM, Ren S. Enzyme activity assay for cholesterol 27-hydroxylase in mitochondria. J Lipid Res 2006; 47:1507-12. [PMID: 16585782 DOI: 10.1194/jlr.m600117-jlr200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mitochondrial cholesterol 27-hydroxylase (CYP27A1) plays an important role in the maintenance of intracellular cholesterol homeostasis. Cholesterol delivery to the mitochondrial inner membrane is believed to be a rate-limiting step for the "acidic" pathway of bile acid synthesis. This work reports that proteinase K treatment of mitochondria markedly increases CYP27A1 specific activity. With endogenous mitochondrial cholesterol, treatment with proteinase K increased CYP27A1 specific activity by 5-fold. Moreover, the addition of the exogenous cholesterol in beta-cyclodextrin plus proteinase K treatment increased the specific activity by 7-fold. Kinetic studies showed that the increased activity was time-, proteinase K-, and substrate concentration-dependent. Proteinase K treatment decreased the apparent K(m) of CYP27A1 for cholesterol from 400 to 150 microM. Using this new assay, we found that during rat hepatocyte preparation and cell culture, mitochondria gradually lose CYP27A1 activity compared with mitochondria freshly isolated from rat liver tissue.
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Affiliation(s)
- Xiaobo Li
- Department of Medicine, Division of Gastroenterology, Veterans Affairs Medical Center and Virginia Commonwealth University, Richmond, USA
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8
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Rodríguez-Páez L, Juárez-Sanchez M, Antúnez-Solís J, Baeza I, Wong C. Alpha-asarone inhibits HMG-CoA reductase, lowers serum LDL-cholesterol levels and reduces biliary CSI in hypercholesterolemic rats. PHYTOMEDICINE : INTERNATIONAL JOURNAL OF PHYTOTHERAPY AND PHYTOPHARMACOLOGY 2003; 10:397-404. [PMID: 12834005 DOI: 10.1078/0944-7113-00274] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Our results showed that alpha-asarone was an inhibitor of hepatic HMG-CoA reductase and that the administration of alpha-asarone at 80 mg/kg body wt. for 8 days decreased serum cholesterol by 38% (p < 0.001) in hypercholesterolemic rats. This alpha-asarone treatment affected mainly the serum LDL-cholesterol levels, leaving serum HDL-cholesterol lipoproteins unaffected, with a consequent decrease of 74% in the LDL/HDL ratio. In addition, alpha-asarone especially stimulated bile flow in hypercholesterolemic rats (60%), increasing the secretion of bile salts, phospholipids and bile cholesterol. The drug also reduced the cholesterol levels of gallbladder bile, whereas the concentration of phospholipids and bile salts increased only slightly, leading to a decrease in the cholesterol saturation index (CSI) of bile in the hypercholesterolemic rats. This CSI decrease and the increase in bile flow induced by alpha-asarone may account for the cholelitholytic effect of alpha-asarone. It seems that alpha-asarone induced clearance of cholesterol from the bloodstream and that the excess of hepatic cholesterol provided by LDL-cholesterol is diverted to bile sterol secretion via a bile choleresis process. The inhibition of HMG-CoA reductase and the increase in bile flow induced by alpha-asarone, as well as the decrease in the CSI, could then explain the hypocholesterolemic and cholelitholytic effects of alpha-asarone.
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Affiliation(s)
- L Rodríguez-Páez
- Departamento de Bioquímica, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, México City, México
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9
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Menke JG, Macnaul KL, Hayes NS, Baffic J, Chao YS, Elbrecht A, Kelly LJ, Lam MH, Schmidt A, Sahoo S, Wang J, Wright SD, Xin P, Zhou G, Moller DE, Sparrow CP. A novel liver X receptor agonist establishes species differences in the regulation of cholesterol 7alpha-hydroxylase (CYP7a). Endocrinology 2002; 143:2548-58. [PMID: 12072387 DOI: 10.1210/endo.143.7.8907] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The liver X receptors, LXRalpha and LXRbeta, are members of the nuclear receptor superfamily. Originally identified as orphans, both receptor subtypes have since been shown to be activated by naturally occurring oxysterols. LXRalpha knockout mice fail to regulate cyp7a mRNA levels upon cholesterol feeding, implicating the role of this receptor in cholesterol homeostasis. LXR activation also induces the expression of the lipid pump involved in cholesterol efflux, the gene encoding ATP binding cassette protein A1 (ABCA1). Therefore, LXR is believed to be a sensor of cholesterol levels and a potential therapeutic target for atherosclerosis. Here we describe a synthetic molecule named F(3)MethylAA [3-chloro-4-(3-(7-propyl-3-trifluoromethyl-6-(4,5)-isoxazolyl)propylthio)-phenyl acetic acid] that is more potent than 22(R)-hydroxycholesterol in LXR in vitro assays. F(3)MethylAA is capable not only of inducing ABCA1 mRNA levels, but also increasing cholesterol efflux from THP-1 macrophages. In rat hepatocytes, F(3)MethylAA induced cyp7a mRNA, confirming conclusions from the knockout mouse studies. Furthermore, in rat in vivo studies, F(3)MethylAA induced liver cyp7a mRNA and enzyme activity. A critical species difference is also reported in that neither F(3)MethylAA nor 22(R)-hydroxycholesterol induced cyp7a in human primary hepatocytes. However, other LXR target genes, ABCA1, ABCG1, and SREBP1, were regulated.
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Affiliation(s)
- John G Menke
- Molecular Endocrinology at Merck & Co., Rahway, New Jersey 07065, USA.
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10
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Moore GL, Davis RA. Expression of cholesterol-7α-hydroxylase in murine macrophages prevents cholesterol loading by acetyl-LDL. J Lipid Res 2002. [DOI: 10.1016/s0022-2275(20)31493-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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11
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Davis RA, Miyake JH, Hui TY, Spann NJ. Regulation of cholesterol-7α-hydroxylase: BAREly missing a SHP. J Lipid Res 2002. [DOI: 10.1016/s0022-2275(20)31482-6] [Citation(s) in RCA: 129] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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12
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Davis RA, Hui TY. 2000 George Lyman Duff Memorial Lecture: atherosclerosis is a liver disease of the heart. Arterioscler Thromb Vasc Biol 2001; 21:887-98. [PMID: 11397693 DOI: 10.1161/01.atv.21.6.887] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The production of apolipoprotein B (apoB)-containing lipoproteins by the liver is regulated by a complex series of processes involving apoB being cotranslationally translocated across the endoplasmic reticulum and assembled into a lipoprotein particle. The translocation of apoB across the endoplasmic reticulum is facilitated by the intraluminal chaperone, microsomal triglyceride transfer protein (MTP). MTP facilitates the translocation and folding of apoB, as well as the addition of lipid to lipid-binding domains (which consist of amphipathic beta sheets and alpha helices). In the absence of MTP or sufficient lipid, apoB exhibits translocation arrest. Thus, apoB translation, translocation, and assembly with lipids to form a core-containing lipoprotein particle occur as concerted processes. Abrogation of >/=1 of these processes diverts apoB into a degradation pathway that is dependent on conjugation with ubiquitin and proteolysis by the proteasome. The nascent core-containing lipoprotein particle that forms within the lumen of the endoplasmic reticulum can be "enlarged" to form a mature very low density lipoprotein particle. Additional studies show that the assembly and secretion of apoB-containing lipoproteins are linked to the cholesterol/bile acid synthetic pathway controlled by cholesterol 7alpha-hydroxylase. Studies in cultured cells and transgenic mice indicate that the expression of cholesterol 7alpha-hydroxylase indirectly regulates the expression of lipogenic enzymes through changes in the cellular content of mature sterol response element binding proteins. Oxysterols and bile acids may also act via the ligand-activated nuclear receptors LXR and FXR to link the metabolic pathways controlling energy balance and lipid metabolism to nutritional state.
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Affiliation(s)
- R A Davis
- Mammalian Cell and Molecular Biology Laboratory, San Diego State University, San Diego, CA 92182-4614, USA.
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13
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In nonhepatic cells, cholesterol 7α-hydroxylase induces the expression of genes regulating cholesterol biosynthesis, efflux, and homeostasis. J Lipid Res 2000. [DOI: 10.1016/s0022-2275(20)33443-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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14
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Abstract
Oxygenated derivatives of cholesterol (oxysterols) present a remarkably diverse profile of biological activities, including effects on sphingolipid metabolism, platelet aggregation, apoptosis, and protein prenylation. The most notable oxysterol activities center around the regulation of cholesterol homeostasis, which appears to be controlled in part by a complex series of interactions of oxysterol ligands with various receptors, such as the oxysterol binding protein, the cellular nucleic acid binding protein, the sterol regulatory element binding protein, the LXR nuclear orphan receptors, and the low-density lipoprotein receptor. Identification of the endogenous oxysterol ligands and elucidation of their enzymatic origins are topics of active investigation. Except for 24, 25-epoxysterols, most oxysterols arise from cholesterol by autoxidation or by specific microsomal or mitochondrial oxidations, usually involving cytochrome P-450 species. Oxysterols are variously metabolized to esters, bile acids, steroid hormones, cholesterol, or other sterols through pathways that may differ according to the type of cell and mode of experimentation (in vitro, in vivo, cell culture). Reliable measurements of oxysterol levels and activities are hampered by low physiological concentrations (approximately 0.01-0.1 microM plasma) relative to cholesterol (approximately 5,000 microM) and by the susceptibility of cholesterol to autoxidation, which produces artifactual oxysterols that may also have potent activities. Reports describing the occurrence and levels of oxysterols in plasma, low-density lipoproteins, various tissues, and food products include many unrealistic data resulting from inattention to autoxidation and to limitations of the analytical methodology. Because of the widespread lack of appreciation for the technical difficulties involved in oxysterol research, a rigorous evaluation of the chromatographic and spectroscopic methods used in the isolation, characterization, and quantitation of oxysterols has been included. This review comprises a detailed and critical assessment of current knowledge regarding the formation, occurrence, metabolism, regulatory properties, and other activities of oxysterols in mammalian systems.
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Affiliation(s)
- G J Schroepfer
- Departments of Biochemistry, Rice University, Houston, Texas, USA.
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15
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Björkhem I, Lund E, Rudling M. Coordinate regulation of cholesterol 7 alpha-hydroxylase and HMG-CoA reductase in the liver. Subcell Biochem 1997; 28:23-55. [PMID: 9090290 DOI: 10.1007/978-1-4615-5901-6_2] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- I Björkhem
- Department of Clinical Chemistry, Huddinge University Hospital, Karolinska Institute, Sweden
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16
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Spady DK, Cuthbert JA, Willard MN, Meidell RS. Feedback regulation of hepatic 7alpha-hydroxylase expression by bile salts in the hamster. J Biol Chem 1996; 271:18623-31. [PMID: 8702514 DOI: 10.1074/jbc.271.31.18623] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Hepatic 7alpha-hydroxylase activity appears to be regulated at the transcriptional level by the quantity of bile salts fluxing through the enterohepatic circulation. Whether bile salts directly suppress 7alpha-hydroxylase expression at the level of the hepatocyte or do so indirectly by promoting the release or absorption of an intestinal factor has not been resolved. We have investigated the ability of primary bile salts to suppress hepatic 7alpha-hydroxylase expression in bile-diverted hamsters. Biliary diversion was accompanied by derepression of both hepatic 7alpha-hydroxylase activity (4-5-fold) and bile salt secretion (approximately 3-fold). Derepression of hepatic 7alpha-hydroxylase expression could be prevented by several interventions that increase the availability of bile salts within the hepatocyte including 1) overexpression of an exogenous 7alpha-hydroxylase gene by adenovirus-mediated gene transfer, 2) obstruction of the common bile duct, and 3) intravenous infusions of taurocholate. In contrast, none of these interventions prevented derepression of hepatic cholesterol synthesis or significantly down-regulated hepatic low density lipoprotein receptor expression over the relatively short time course (24 h) of these studies. Together, these data indicate that primary bile salts contribute to the regulation of bile salt synthesis through feedback repression of 7alpha-hydroxylase expression at the level of the hepatocyte.
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Affiliation(s)
- D K Spady
- Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75235, USA
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17
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Abstract
Material dealing with the chemistry, biochemistry, and biological activities of oxysterols is reviewed for the period 1987-1995. Particular attention is paid to the presence of oxysterols in tissues and foods and to their physiological relevance.
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Affiliation(s)
- L L Smith
- University of Texas Medical Branch, Galveston 77555-0653, USA
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18
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Liang KH, Oveisi F, Vaziri ND. Gene expression of hepatic cholesterol 7 alpha-hydroxylase in the course of puromycin-induced nephrosis. Kidney Int 1996; 49:855-60. [PMID: 8648930 DOI: 10.1038/ki.1996.118] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Cholesterol conversion to and biliary excretion of bile acids represents the principal pathway of cholesterol catabolism in mammals. Cholesterol 7 alpha-hydroxylase (Ch-7 alpha-H) is the first and the rate limiting step in bile acid production. Recently, Ch-7 alpha-H enzymatic activity has been shown to be normal in rats with established puromycin aminonucleoside-induced nephrosis (NS). To our knowledge, the gene expression of Ch-7 alpha-H in NS has not been investigated. We measured hepatic Ch-7 alpha-H mRNA and protein (by Northern and Western blot analyses) in rats at baseline and longitudinally during the course of induction and chronic phase of puromycin (PAN) induced NS. Groups of placebo-treated (controls) and diet-induced hypercholesterolemic (DHC) rats were included for comparison. The NS and DHC animals exhibited severe hypercholesterolemia of similar magnitude. Hepatic Ch-7 alpha-H transcript and protein remained virtually unchanged throughout the study period in the NS group. In contrast, Ch-7 alpha-H gene expression was markedly up-regulated in the DHC group. These observations suggest that hepatic Ch-7 alpha-H gene expression may be inappropriately low for the degree of the associated hypercholesterolemia in the NS group. It should be noted, however, that hepatic tissue cholesterol concentration was normal in the NS group and greatly increased in the DHC group. This can account for the disparity in Ch-7 alpha-H mRNA levels between the two groups since intracellular rather than extracellular cholesterol modulates Ch-7 alpha-H gene expression. In conclusion, the present study revealed that hepatic Ch-7 alpha-H gene expression remains unchanged during the course of PAN-induced NS in rats. It thus appears that generation and maintenance of hypercholesterolemia in this model of NS does not involve significant alteration of Ch-7 alpha-H gene expression.
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Affiliation(s)
- K H Liang
- Department of Medicine, University of California, Irvine, USA
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19
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The Regulation of Cholesterol Conversion to Bile Acids. ACTA ACUST UNITED AC 1996. [DOI: 10.1016/s1569-2558(08)60347-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Honda A, Yoshida T, Tanaka N, Matsuzaki Y, He B, Shoda J, Osuga T. Accumulation of 7 alpha-hydroxycholesterol in liver tissue of patients with cholesterol gallstones. J Gastroenterol 1995; 30:651-6. [PMID: 8574339 DOI: 10.1007/bf02367793] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Patients with cholesterol gallstones have a reduced pool of bile acids. This study was undertaken to clarify the mechanism by which bile acid biosynthesis does not increase to supranormal levels to cause a reexpansion of the pool. We investigated the first two steps of the bile acid biosynthesis pathway by assaying the activities of cholesterol 7 alpha-hydroxylase, the rate-limiting enzyme in this pathway, and 3 beta-hydroxy-delta 5-C27-steroid dehydrogenase/isomerase, and by measuring the concentrations of 7 alpha-hydroxycholesterol and 7 alpha-hydroxy-4-cholesten-3-one in liver specimens from ten patients with cholesterol gallstones and ten gallstone-free controls. In the patients with gallstones, cholesterol 7 alpha-hydroxylase activity, 3 beta-hydroxy-delta 5-C27-steroid dehydrogenase/isomerase activity, and hepatic 7 alpha-hydroxy-4-cholesten-3-one concentration did not significantly different from levels in controls, but hepatic 7 alpha-hydroxycholesterol concentration was more than twofold that of controls (12.9 +/- 2.6 vs 5.3 +/- 1.2 nmol/g liver, P < 0.01). The concentration of 7 alpha-hydroxycholesterol positively correlated with the ratio of cholesterol 7 alpha-hydroxylase activity to 3 beta-hydroxy-delta 5-C27-steroid dehydrogenase/isomerase activity (r = 0.93; P < 0.005) in the gallstone-free controls. In contrast, this correlation disappeared in the patients with gallstones. These results suggest a derangement of the normal 7 alpha-hydroxycholesterol metabolism in the patients with gallstones. The reason for the accumulation of 7 alpha-hydroxycholesterol remains unclear; however, it is possible that, in patients with cholesterol gallstone, the accumulated 7 alpha-hydroxycholesterol causes inappropriate suppression of cholesterol 7 alpha-hydroxylase activity by product inhibition.
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Affiliation(s)
- A Honda
- Department of Gastroenterology, University of Tsukuba, Japan
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Payne DW, Shackleton C, Toms H, Ben-Shlomo I, Kol S, deMoura M, Strauss JF, Adashi EY. A novel nonhepatic hydroxycholesterol 7 alpha-hydroxylase that is markedly stimulated by interleukin-1 beta. Characterization in the immature rat ovary. J Biol Chem 1995; 270:18888-96. [PMID: 7642545 DOI: 10.1074/jbc.270.32.18888] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
During studies on the regulation of rat ovarian steroidogenic enzymes by interleukin-1 beta (IL-1 beta), we observed substantial metabolism of 25-hydroxycholesterol to two unusual polar products. This unexpected effect was observed both in isolated granulosa cells and in whole ovarian dispersates and was also induced by tumor necrosis factor alpha, but not by insulin-like growth factor I or follicle-stimulating hormone. The effect was dependent on time and the dose of IL-1 beta and was blocked by and IL-1 receptor antagonist. The formation of the polar metabolites was inhibited by ketoconazole and trilostane, but not by aminoglutethimide. Subsequent purification of these novel metabolites and analysis by gas chromatography/ mass spectrometry, NMR, and high performance liquid chromatography revealed them to be related 7 alpha-hydroxylated hydroxycholesterols (cholest-4-ene-7 alpha,25-diol-3-one and cholest-5-ene-3 beta,7 alpha,25-triol). IL-1 beta-stimulated ovarian 7 alpha-hydroxylase activity (3-10 pmol/min/mg of cellular protein) was nearly 4-fold that of control levels using 25-hydroxycholesterol as substrate. Activities at or below control levels were observed when IL-1 beta-treated cell sonicates were boiled or assayed in the presence of NADH (rather than NADPH), indicating that involvement of a nonenzymatic process was unlikely. IL-1 beta-stimulated 7 alpha-hydroxylase activity was inhibited to basal levels by a 10-fold excess of unlabeled 25- or 27-hydroxycholesterol, but not by cholesterol, pregnenolone, progesterone, testosterone, or dehydroepiandrosterone, suggesting that ovarian 7 alpha-hydroxylase is specific for hydroxycholesterols. Furthermore, when IL-1 beta-treated ovarian cultures were incubated with radiolabeled cholesterol or testosterone, no 7 alpha-hydroxylated products were observed. We were also unable to detect any mRNA transcripts for liver cholesterol 7 alpha-hydroxylase in IL-1 beta-stimulated ovarian cultures. This study describes an ovarian hydroxycholesterol 7 alpha-hydroxylase that differs from liver cholesterol 7 alpha-hydroxylase and from other nonhepatic progestin/ androgen 7 alpha-hydroxylases. The novel finding of the regulation of a 7 alpha-hydroxylase by IL-1 beta (and tumor necrosis factor alpha) suggests a unique role for cytokines in the regulation of cholesterol metabolism in the ovary and possibly other tissues.
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Affiliation(s)
- D W Payne
- Department of Obstetrics/Gynecology, University of Maryland Medical School, Baltimore 21201, USA
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22
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Bertolotti M, Spady DK, Dietschy JM. Regulation of hepatic cholesterol metabolism in the rat in vivo: effect of a synthetic fat-free diet on sterol synthesis and low-density lipoprotein transport. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1255:293-300. [PMID: 7734446 DOI: 10.1016/0005-2760(94)00245-t] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
A synthetic fat-free diet, previously shown to decrease hepatic cholesterol synthesis, was utilized to manipulate cholesterol balance in vivo in female Sprague-Dawley rats. A significant 65% decrease of hepatic cholesterol synthesis compared to controls was shown after 1 week of treatment, which remained constant during the following 3 weeks. The inhibitory effect of the diet was completely abolished by cholestyramine supplementation. At week 3 of the experimental diet, bile acid synthesis was reduced by 63%, this reduction being correlated with decreased recycling frequency of the bile acid pool. Hepatic clearance of low-density lipoprotein (LDL) was slightly decreased, with no changes in plasma cholesterol, hepatic LDL-cholesterol uptake and whole body LDL-cholesterol production. When cholesterol and saturated fatty acids were supplemented to the diets in the attempt to disclose alteration in LDL transport, LDL clearance was unaffected; plasma LDL-cholesterol and hepatic LDL-cholesterol uptake were increased, as a consequence of increased LDL-cholesterol production. On the other hand, hepatic cholesterol synthesis was further suppressed; bile acid synthesis was increased by cholesterol supplementation in the fat-free group, even if to subnormal levels. These findings suggest that: (1) bile acid synthesis is decreased by feeding a synthetic fat-free diet, probably due to slower recirculation of bile acids along the entero-hepatic axis in conditions of reduced functional need; (2) consequently, a significant reduction of hepatic cholesterol synthesis is observed with no changes in LDL-cholesterol uptake; (3) further supplementation of dietary cholesterol and saturated fats is compensated for by changes in the rates of cholesterol and bile acid synthesis, but not of LDL transport. The data confirm the existence of independent regulation for hepatic sterol synthesis and LDL transport in this species.
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Affiliation(s)
- M Bertolotti
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, USA
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23
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Chico Y, Fresnedo O, Lacort M, Ochoa B. Effect of estradiol and progesterone on cholesterol 7 alpha-hydroxylase activity in rats subjected to different feeding conditions. Steroids 1994; 59:528-35. [PMID: 7846735 DOI: 10.1016/0039-128x(94)90071-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The regulation of cholesterol 7 alpha-hydroxylase activity by estradiol and progesterone was investigated in liver microsomes isolated from rats fed standard diet, either ad libitum or fasted for 24 h, and diet containing the bile acid sequesterant cholestyramine. Differential effects were observed when the direct action of estradiol and progesterone on microsome preparations was examined. Cholesterol 7 alpha-hydroxylase activity was inhibited by progesterone in a dose-dependent way to almost complete abolition; similar patterns of declines were found in the three feeding groups under study. In contrast, the addition of 5 microM estradiol induced small and selective 7 alpha-hydroxylase increases in fasting and cholestryamine-fed animals, then activity declined to control values and consistent decreases were found from 20 microM. The administration of estradiol (50 micrograms) or progesterone (100 micrograms) for 21 days resulted in depressed cholesterol 7 alpha-hydroxylase activity in rats with high bile acid synthesis basal rate due to cholestyramine feeding. In rats receiving a standard diet, either ad libitum or after 24 h fasting, the hormonal effects did not reach significance. Declines in the content of free cholesterol were provoked by progesterone, not by estradiol, in liver microsomes prepared from all feeding groups. No changes in cholesterol 7 alpha-hydroxylase activity and microsomal free cholesterol were observed after administration of the sex hormones for 3 days. Rapid and transient inhibitions in 7 alpha-hydroxylase activity were found after the single injection of progesterone to fed animals. Estradiol, on the contrary, was unable to alter rapidly the hepatic 7 alpha-hydroxylase capacity.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- Y Chico
- Department of Physiology, University of the Basque Country Medical School, Bilbao, Spain
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25
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26
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Stedronsky ER. Interaction of bile acids and cholesterol with non-systemic agents having hypocholesterolemic properties. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1210:255-87. [PMID: 8305482 DOI: 10.1016/0005-2760(94)90230-5] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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27
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Effect of dietary cholesterol and taurocholate on cholesterol 7 alpha-hydroxylase and hepatic LDL receptors in inbred mice. J Lipid Res 1993. [DOI: 10.1016/s0022-2275(20)39679-6] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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28
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Jones MP, Pandak WM, Heuman DM, Chiang JY, Hylemon PB, Vlahcevic ZR. Cholesterol 7 alpha-hydroxylase: evidence for transcriptional regulation by cholesterol or metabolic products of cholesterol in the rat. J Lipid Res 1993. [DOI: 10.1016/s0022-2275(20)39675-9] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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29
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Petrack B, Latario BJ. Synthesis of 27-hydroxycholesterol in rat liver mitochondria: HPLC assay and marked activation by exogenous cholesterol. J Lipid Res 1993. [DOI: 10.1016/s0022-2275(20)39988-0] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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30
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Lakeev YV, Kosykh VA, Kosenkov EI, Novikov VL, Lebedev AV, Repin VS. Effect of natural and synthetic antioxidants (polyhydroxynaphthaquinones) on cholesterol metabolism in cultured rabbit hepatocytes. Bull Exp Biol Med 1992. [DOI: 10.1007/bf00837651] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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31
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Everson GT, Daggy BP, McKinley C, Story JA. Effects of psyllium hydrophilic mucilloid on LDL-cholesterol and bile acid synthesis in hypercholesterolemic men. J Lipid Res 1992. [DOI: 10.1016/s0022-2275(20)40770-9] [Citation(s) in RCA: 100] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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32
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Bile acid synthesis. VI. Regulation of cholesterol 7 alpha-hydroxylase by taurocholate and mevalonate. J Lipid Res 1992. [DOI: 10.1016/s0022-2275(20)41430-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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33
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Rudling M. Hepatic mRNA levels for the LDL receptor and HMG-CoA reductase show coordinate regulation in vivo. J Lipid Res 1992. [DOI: 10.1016/s0022-2275(20)41615-3] [Citation(s) in RCA: 94] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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34
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Regulation of hepatic sterol metabolism in the rat. Parallel regulation of activity and mRNA for 7 alpha-hydroxylase but not 3-hydroxy-3-methylglutaryl-coenzyme A reductase or low density lipoprotein receptor. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)42805-0] [Citation(s) in RCA: 93] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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35
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Grogan WM, Bailey ML, Heuman DM, Vlahcevic ZR. Effects of perturbations in hepatic free and esterified cholesterol pools on bile acid synthesis, cholesterol 7 alpha-hydroxylase, HMG-CoA reductase, acyl-CoA:cholesterol acyltransferase and cytosolic cholesteryl ester hydrolase. Lipids 1991; 26:907-14. [PMID: 1805095 DOI: 10.1007/bf02535976] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Effects of expansion of the hepatic free cholesterol pool on bile acid and cholesterol metabolism and homeostasis were examined in rats fed cholesterol in high-fat diets or treated with oleyl-p-(n-decyl)-benzenesulfonate (ODS) or progesterone. Cholesterol feeding for 10-16 days, which increased free (33%) and esterified (6-fold) cholesterol, had no effect on cholate synthesis, total bile acid synthesis, or cholate turnover, whereas these activities were increased 60-80% by ODS and progesterone, which produced only small increases (19%) in free cholesterol. Cholesterol feeding reduced beta-hydroxy-beta-methylglutaryl (HMG)-CoA reductase (72%) and cholesteryl ester hydrolase (48%) and increased acyl-CoA:cholesterol acyltransferase (184%), whereas ODS and progesterone reversed these compensatory responses in cholesterol-fed rats. Cholesterol 7 alpha-hydroxylase was changed no more than 22% by any treatment. A bolus of ODS elevated biliary cholesterol output 41% and shifted biliary bile acid synthesis and composition toward 12-deoxy bile acids. These effects were not seen in ODS-fed or progesterone-treated rats, in which cholesteryl ester stores were depleted. It is concluded that effects of free cholesterol on bile acid synthesis and biliary cholesterol are probably mediated by specific precursor or regulatory pools which can be independently regulated and which represent a relatively small fraction of hepatic free cholesterol.
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Affiliation(s)
- W M Grogan
- Department of Biochemistry and Molecular Biophysics, McGuire Veterans Administration Hospital, Richmond, Virginia
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36
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Kosykh VA, Novikov DK, Trakht IN, Podrez EA, Victorov AV, Repin VS, Smirnov VN. Effect of chylomicron remnants on cholesterol metabolism in cultured rabbit hepatocytes: very low density lipoprotein and bile acid production. Lipids 1991; 26:799-805. [PMID: 1795601 DOI: 10.1007/bf02536161] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The interrelationship between very low density lipoprotein (VLDL) secretion and bile acid production was studied in primary culture of rabbit hepatocytes. Chylomicron remnants (CR) were added to the cultures to study their effect on VLDL secretion and bile acid production. After 24 hr preincubation of cells with CR (10-50 micrograms protein/mL), intercellular neutral lipid content was increased 1.5-4-fold in a dose-dependent manner. Neutral lipid accumulation was accompanied by a 70-90% reduction of [14C]acetate incorporation into cholesterol, while no stimulation of [14C]oleate incorporation into cholesteryl esters was observed. Incubation of cells with CR increased secretion of free cholesterol, triacylglycerol and apoproteins B and E in VLDL. Stimulation of VLDL cholesterol secretion was accompanied by a reduction of taurocholic acid synthesis. These data demonstrate the existence of an inverse relationship between secretion of VLDL cholesterol and bile acid production under conditions of effective uptake of triacylglycerol-rich CR by hepatocytes.
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Affiliation(s)
- V A Kosykh
- USSR Cardiology Research Center, Academy of Medical Sciences, Moscow
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37
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Affiliation(s)
- F Kern
- Department of Medicine, University of Colorado School of Medicine, Denver 80262
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38
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39
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40
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Pandak WM, Li YC, Chiang JY, Studer EJ, Gurley EC, Heuman DM, Vlahcevic ZR, Hylemon PB. Regulation of cholesterol 7 alpha-hydroxylase mRNA and transcriptional activity by taurocholate and cholesterol in the chronic biliary diverted rat. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(19)67810-5] [Citation(s) in RCA: 149] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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