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Gonoi W, Akahane M, Watanabe Y, Isono S, Maeda E, Hagiwara K, Ohtomo K. Visualization of Bile Movement Using MRI Spin-Labeling Technique: Preliminary Results. AJR Am J Roentgenol 2013; 201:133-141. [PMID: 23789667 DOI: 10.2214/ajr.12.8928] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/29/2023]
Affiliation(s)
- Wataru Gonoi
- Department of Radiology, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan
| | - Masaaki Akahane
- Department of Radiology, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan
| | - Yasushi Watanabe
- Department of Radiology, The University of Tokyo Hospital, Tokyo, Japan
| | - Sachiko Isono
- MRI Applications, Toshiba Medical Systems, Tochigi, Japan
| | - Eriko Maeda
- Department of Computational Diagnostic Radiology and Preventive Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Kazuchika Hagiwara
- Department of Radiology, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan
| | - Kuni Ohtomo
- Department of Radiology, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan
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Bertolotti M, Crosignani A, Del Puppo M. The use of stable and radioactive sterol tracers as a tool to investigate cholesterol degradation to bile acids in humans in vivo. Molecules 2012; 17:1939-68. [PMID: 22343367 PMCID: PMC6268360 DOI: 10.3390/molecules17021939] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2012] [Revised: 02/03/2012] [Accepted: 02/08/2012] [Indexed: 12/17/2022] Open
Abstract
Alterations of cholesterol homeostasis represent important risk factors for atherosclerosis and cardiovascular disease. Different clinical-experimental approaches have been devised to study the metabolism of cholesterol and particularly the synthesis of bile acids, its main catabolic products. Most evidence in humans has derived from studies utilizing the administration of labeled sterols; these have several advantages over in vitro assay of enzyme activity and expression, requiring an invasive procedure such as a liver biopsy, or the determination of fecal sterols, which is cumbersome and not commonly available. Pioneering evidence with administration of radioactive sterol derivatives has allowed to characterize the alterations of cholesterol metabolism and degradation in different situations, including spontaneous disease conditions, aging, and drug treatment. Along with the classical isotope dilution methodology, other approaches were proposed, among which isotope release following radioactive substrate administration. More recently, stable isotope studies have allowed to overcome radioactivity exposure. Isotope enrichment studies during tracer infusion has allowed to characterize changes in the degradation of cholesterol via the "classical" and the "alternative" pathways of bile acid synthesis. Evidence brought by tracer studies in vivo, summarized here, provides an exceptional tool for the investigation of sterol metabolism, and integrate the studies in vitro on human tissue.
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Affiliation(s)
- Marco Bertolotti
- Divisone di Geriatria, Dipartimento di Medicina, Endocrinologia, Metabolismo e Geriatria, Università degli Studi di Modena e Reggio Emilia, Nuovo Ospedale Civile, Via Giardini 1355, Modena 41126, Italy.
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Stellaard F, Brufau G, Boverhof R, Jonkers EZ, Boer T, Kuipers F. Developments in bile acid kinetic measurements using (13)C and (2)H: 10(5) times improved sensitivity during the last 40 years. ISOTOPES IN ENVIRONMENTAL AND HEALTH STUDIES 2009; 45:275-288. [PMID: 20183239 DOI: 10.1080/10256010903356888] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Bile acid kinetics involve the measurement of pool sizes and turnover rates of individual bile acids. The technique is based on isotope dilution and was first described in the 1950s using radioactive (14)C-labelled cholic acid (CA). It took until the 1970s before stable isotopes were introduced for this purpose ((13)C, (2)H) and isotope analysis methods were developed for CA and chenodeoxycholic acid (CDCA) applying gas chromatography/electron impact mass spectrometry. Until the 1980s, the isotope enrichment measurements were performed in bile samples aspirated from the duodenum. Thereafter, methodology became available allowing measurements to be performed in blood requiring at least 2 ml serum samples. Simultaneous measurement of kinetics of metabolically dependent CA and deoxycholic acid using (13)C and (2)H labels was introduced. Until the 1990s, this technique was only possible in adult humans due to the large sample sizes. Introduction of pentafluorobenzyl bromide derivatisation and electron capture negative ion mass spectrometry (GC/ECN-MS) reduced the sample volume to 50 microl serum. This allowed isotope abundance measurement of CA in rats and in mice. However, repetitive collection of 100 microl blood samples in mice is too invasive (collection via the orbita) and exhaustive. Therefore, the method development is now focussing on enhanced sensitivity and reduction of blank effects originating from the sample preparation. The final goal is to determine CA isotope enrichments in 20 microl mouse blood obtained from the tail vein. This paper shows the feasibility of reaching this goal.
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Affiliation(s)
- Frans Stellaard
- Department of Laboratory Medicine, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
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Lefebvre P, Cariou B, Lien F, Kuipers F, Staels B. Role of bile acids and bile acid receptors in metabolic regulation. Physiol Rev 2009; 89:147-91. [PMID: 19126757 DOI: 10.1152/physrev.00010.2008] [Citation(s) in RCA: 1160] [Impact Index Per Article: 77.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The incidence of the metabolic syndrome has taken epidemic proportions in the past decades, contributing to an increased risk of cardiovascular disease and diabetes. The metabolic syndrome can be defined as a cluster of cardiovascular disease risk factors including visceral obesity, insulin resistance, dyslipidemia, increased blood pressure, and hypercoagulability. The farnesoid X receptor (FXR) belongs to the superfamily of ligand-activated nuclear receptor transcription factors. FXR is activated by bile acids, and FXR-deficient (FXR(-/-)) mice display elevated serum levels of triglycerides and high-density lipoprotein cholesterol, demonstrating a critical role of FXR in lipid metabolism. In an opposite manner, activation of FXR by bile acids (BAs) or nonsteroidal synthetic FXR agonists lowers plasma triglycerides by a mechanism that may involve the repression of hepatic SREBP-1c expression and/or the modulation of glucose-induced lipogenic genes. A cross-talk between BA and glucose metabolism was recently identified, implicating both FXR-dependent and FXR-independent pathways. The first indication for a potential role of FXR in diabetes came from the observation that hepatic FXR expression is reduced in animal models of diabetes. While FXR(-/-) mice display both impaired glucose tolerance and decreased insulin sensitivity, activation of FXR improves hyperglycemia and dyslipidemia in vivo in diabetic mice. Finally, a recent report also indicates that BA may regulate energy expenditure in a FXR-independent manner in mice, via activation of the G protein-coupled receptor TGR5. Taken together, these findings suggest that modulation of FXR activity and BA metabolism may open new attractive pharmacological approaches for the treatment of the metabolic syndrome and type 2 diabetes.
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Affiliation(s)
- Philippe Lefebvre
- Institut National de la Sante et de la Recherche Medicale, Lille, France
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Meija J, Mester Z. Paradigms in isotope dilution mass spectrometry for elemental speciation analysis. Anal Chim Acta 2008; 607:115-25. [DOI: 10.1016/j.aca.2007.11.050] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2007] [Revised: 11/23/2007] [Accepted: 11/26/2007] [Indexed: 10/22/2022]
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Bisschop PH, Bandsma RHJ, Stellaard F, ter Harmsel A, Meijer AJ, Sauerwein HP, Kuipers F, Romijn JA. Low-fat, high-carbohydrate and high-fat, low-carbohydrate diets decrease primary bile acid synthesis in humans. Am J Clin Nutr 2004; 79:570-6. [PMID: 15051599 DOI: 10.1093/ajcn/79.4.570] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Dietary fat content influences bile salt metabolism, but quantitative data from controlled studies in humans are scarce. OBJECTIVE The objective of the study was to establish the effect of dietary fat content on the metabolism of primary bile salts. DESIGN The effects of eucaloric extremely low-fat (0%), intermediate-fat (41%; control diet), and extremely high-fat (83%) diets on kinetic values of cholate and chenodeoxycholate metabolism were determined after 11 d by using stable isotope dilution in 6 healthy men. All diets contained identical amounts of cholesterol. RESULTS The total primary bile salt pool size was not significantly affected by dietary fat content, although the chenodeoxycholate pool was significantly higher during the low-fat diet. Fractional turnover rates of both primary bile salts were 30-50% lower during the low- and high-fat diets than during the control diet. Total hepatic bile salt synthesis was approximately 30% lower during both the high- and low-fat diets, but synthesis rates of the 2 primary bile salts were differentially affected. The molar ratio of cholate to total bile salt synthesis increased from 0.50 +/- 0.05 ( +/- SD) to 0.59 +/- 0.05 and 0.66 +/- 0.04 with increasing fat intake, whereas the molar ratio of chenodeoxycholate to total bile salt synthesis decreased from 0.50 +/- 0.05 to 0.41 +/- 0.05 and 0.34 +/- 0.04. The relative concentration of deoxycholate in plasma increased during the low-fat period, which indicated increased absorption from the colon. CONCLUSIONS Both low- and high-fat diets reduce the synthesis and turnover rates of primary bile salts in humans, although probably through different mechanisms, and consequently they affect the removal of cholesterol from the body.
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Affiliation(s)
- Peter H Bisschop
- Department of Endocrinology & Metabolism, Academic Medical Center, University of Amsterdam, Netherlands.
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vanBerge-Henegouwen GP, Venneman NG, Portincasa P, Kosters A, van Erpecum KJ, Groen AK. Relevance of hereditary defects in lipid transport proteins for the pathogenesis of cholesterol gallstone disease. SCANDINAVIAN JOURNAL OF GASTROENTEROLOGY. SUPPLEMENT 2004:60-9. [PMID: 15696852 DOI: 10.1080/00855920410011022] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
In the formation of cholesterol gallstones, cholesterol hypersecretion into bile causing cholesterol supersaturation and crystallization appears to be the primary factor, with disturbed gallbladder and intestinal motility as secondary factors. Although intestinal uptake mechanisms have not yet been fully elucidated, the HDL receptor scavenger receptor B1 (SRB1) may be involved. Since HDL-cholesterol, both from the intestine and peripheral sources, is the preferred type of cholesterol for biliary secretion, increased HDL transport to the liver can also cause cholesterol hypersecretion in bile. In the hepatocyte, bile formation is regulated by several transmembrane proteins, all belonging to the ABC family. A change in the activity in one of these proteins can have a profound impact on biliary lipid secretion. The bile salt export pump (BSEP or ABCB11) regulates the excretion of bile salts into bile and mutations cause severe cholestasis. The second ABC transporter, ABCB4 (MDR3) regulates the secretion in bile of phosphatidylcholine (PC), while ABCG5/G8 is active in the excretion of cholesterol and sterols into bile. These transporters also facilitate transport of sterols back into the intestinal lumen. Mutations in either of these genes cause sitosterolaemia with increased absorption of plant sterols and cholesterol. Until now, evidence for a genetic background of human gallstone disease is mostly indirect and based on ethnic differences. Only two single gene defects are associated with gallstones. One is an ABCB4 mutation which causes a deficiency in biliary PC secretion and the other is a CYP7A1 mutation, the rate-limiting enzyme in the synthesis of bile salts from cholesterol in the liver. Recently, several common DNA polymorphisms in the ABCG8 gene were discovered that are associated with variations in plasma sterols, which could also influence biliary cholesterol secretion, but there is still a paucity of human studies.
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Kosters A, Jirsa M, Groen AK. Genetic background of cholesterol gallstone disease. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1637:1-19. [PMID: 12527402 DOI: 10.1016/s0925-4439(02)00173-4] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Cholesterol gallstone formation is a multifactorial process involving a multitude of metabolic pathways. The primary pathogenic factor is hypersecretion of free cholesterol into bile. For people living in the Western Hemisphere, this is almost a normal condition, certainly in the elderly, which explains the very high incidence of gallstone disease. It is probably because the multifactorial background genes responsible for the high incidence have not yet been identified, despite the fact that genetic factors clearly play a role. Analysis of the many pathways involved in biliary cholesterol secretion reveals many potential candidates and considering the progress in unraveling the regulatory mechanisms of the responsible genes, identification of the primary gallstone genes will be successful in the near future.
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Affiliation(s)
- Astrid Kosters
- Department of Experimental Hepatology, AMC Liver Center S1-172, Academic Medical Center, Meibergdreef 69-71, 1105 BK, Amsterdam, The Netherlands.
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Love MW, Craddock AL, Angelin B, Brunzell JD, Duane WC, Dawson PA. Analysis of the ileal bile acid transporter gene, SLC10A2, in subjects with familial hypertriglyceridemia. Arterioscler Thromb Vasc Biol 2001; 21:2039-45. [PMID: 11742882 DOI: 10.1161/hq1201.100262] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Familial hypertriglyceridemia (FHTG), a disease characterized by elevated plasma very low density lipoprotein triglyceride levels, has been associated with impaired intestinal absorption of bile acids. The aim of this study was to test the hypothesis that defects in the active ileal absorption of bile acids are a primary cause of FHTG. Single-stranded conformation polymorphism analysis was used to screen the ileal Na(+)/bile acid cotransporter gene (SLC10A2) for FHTG-associated mutations. Analysis of 20 hypertriglyceridemic patients with abnormal bile acid metabolism revealed 3 missense mutations (V98I, V159I, and A171S), a frame-shift mutation (646insG) at codon 216, and 4 polymorphisms in the 5' flanking sequence of SLC10A2. The SLC10A2 missense mutations and 5' flanking sequence polymorphisms were not correlated with bile acid production or turnover in the hypertriglyceridemic patients and were equally prevalent in the unaffected control subjects. In transfected COS cells, the V98I, V159I, and A171S isoforms all transported bile acids similar to the wild-type SLC10A2. The 646insG frame-shift mutation abolished bile acid transport activity in transfected COS cells but was found in only a single FHTG patient. These findings indicate that the decreased intestinal bile acid absorption in FHTG patients is not commonly associated with inherited defects in SLC10A2.
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Affiliation(s)
- M W Love
- Department of Internal Medicine, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA
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Hulzebos CV, Renfurm L, Bandsma RH, Verkade HJ, Boer T, Boverhof R, Tanaka H, Mierau I, Sauer PJ, Kuipers F, Stellaard F. Measurement of parameters of cholic acid kinetics in plasma using a microscale stable isotope dilution technique: application to rodents and humans. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)31519-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Miyake JH, Doung XD, Strauss W, Moore GL, Castellani LW, Curtiss LK, Taylor JM, Davis RA. Increased production of apolipoprotein B-containing lipoproteins in the absence of hyperlipidemia in transgenic mice expressing cholesterol 7alpha-hydroxylase. J Biol Chem 2001; 276:23304-11. [PMID: 11323427 DOI: 10.1074/jbc.m101853200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The finding that expression of a cholesterol 7alpha-hydroxylase (CYP7A1) transgene in cultured rat hepatoma cells caused a coordinate increase in lipogenesis and secretion of apoB-containing lipoproteins led to the hypothesis that hepatic production of apoB-containing lipoproteins may be linked to the expression of CYP7A1 (Wang, S.-L., Du, E., Martin, T. D., and Davis, R. A. (1997) J. Biol. Chem. 272, 19351-19358). To examine this hypothesis in vivo, a transgene encoding CYP7A1 driven by the constitutive liver-specific enhancer of the human apoE gene was expressed in C56BL/6 mice. The expression of CYP7A1 mRNA (20-fold), protein ( approximately 10-fold), and enzyme activity (5-fold) was markedly increased in transgenic mice compared with non-transgenic littermates. The bile acid pool of CYP7A1 transgenic mice was doubled mainly due to increased hydrophobic dihydroxy bile acids. In CYP7A1 transgenic mice, livers contained approximately 3-fold more sterol response element-binding protein-2 mRNA. Hepatic expression of mRNAs encoding lipogenic enzymes (i.e. fatty-acid synthase, acetyl-CoA carboxylase, stearoyl-CoA desaturase, squalene synthase, farnesyl-pyrophosphate synthase, 3-hydroxy-3-methylglutaryl-CoA reductase, and low density lipoprotein receptor) as well as microsomal triglyceride transfer protein were elevated approximately 3-5-fold in transgenic mice. CYP7A1 transgenic mice also displayed a >2-fold increase in hepatic production and secretion of triglyceride-rich apoB-containing lipoproteins. Despite the increased hepatic secretion of apoB-containing lipoproteins in CYP7A1 mice, plasma levels of triglycerides and cholesterol were not significantly increased. These data suggest that the 5-fold increased expression of the low density lipoprotein receptor displayed by the livers of CYP7A1 transgenic mice was sufficient to compensate for the 2-fold increase production of apoB-containing lipoproteins. These findings emphasize the important homeostatic role that CYP7A1 plays in balancing the anabolic lipoprotein assembly/secretion pathway with the cholesterol catabolic bile acid synthetic pathway.
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Affiliation(s)
- J H Miyake
- Mammalian Cell and Molecular Biology Laboratory, San Diego State University, San Diego, California 92182-4614, USA
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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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Davis RA. Cell and molecular biology of the assembly and secretion of apolipoprotein B-containing lipoproteins by the liver. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1440:1-31. [PMID: 10477822 DOI: 10.1016/s1388-1981(99)00083-9] [Citation(s) in RCA: 145] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Triglycerides are one of the most efficient storage forms of free energy. Because of their insolubility in biological fluids, their transport between cells and tissues requires that they be assembled into lipoprotein particles. Genetic disruption of the lipoprotein assembly/secretion pathway leads to several human disorders associated with malnutrition and developmental abnormalities. In contrast, patients displaying inappropriately high rates of lipoprotein production display increased risk for the development of atherosclerotic cardiovascular disease. Insights provided by diverse experimental approaches describe an elegant biological adaptation of basic chemical interactions required to overcome the thermodynamic dilemma of producing a stable emulsion vehicle for the transport and tissue targeting of triglycerides. The mammalian lipoprotein assembly/secretion pathway shows an absolute requirement for: (1) the unique amphipathic protein: apolipoprotein B, in a form that is sufficiently large to assemble a lipoprotein particle containing a neutral lipid core; and, (2) a lipid transfer protein (microsomal triglyceride transfer protein-MTP). In the endoplasmic reticulum apolipoprotein B has two distinct metabolic fates: (1) entrance into the lipoprotein assembly pathway within the lumen of the endoplasmic reticulum; or, (2) degradation in the cytoplasm by the ubiquitin-dependent proteasome. The destiny of apolipoprotein B is determined by the relative availability of individual lipids and level of expression of MTP. The dynamically varied expression of cholesterol-7alpha-hydroxylase indirectly influences the rate of lipid biosynthesis and the assembly and secretion lipoprotein particles by the liver.
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Affiliation(s)
- R A Davis
- Mammalian Cell and Molecular Biology Laboratory, Department of Biology, The Molecular Biology Institute, San Diego State University, San Diego, CA 92182-0057, USA.
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Du EZ, Fleming JF, Wang SL, Spitsen GM, Davis RA. Translocation-arrested apolipoprotein B evades proteasome degradation via a sterol-sensitive block in ubiquitin conjugation. J Biol Chem 1999; 274:1856-62. [PMID: 9880570 DOI: 10.1074/jbc.274.3.1856] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In this study, we explored how sterol metabolism altered by the expression of cholesterol-7alpha-hydroxylase NADPH:oxygen oxidoreductase (7alpha-hydroxylase) affects the ubiquitin-dependent proteasome degradation of translocation-arrested apoB53 in Chinese hamster ovary cells. Stable expression of two different plasmids that encode either rat or human 7alpha-hydroxylase inhibited the ubiquitin conjugation of apoB and its subsequent degradation by the proteasome. Oxysterols (25-hydroxycholesterol and 7-ketocholesterol) reversed the inhibition of apoB degradation caused by 7alpha-hydroxylase. The combined results suggest that the normally rapid proteasome degradation of translocation-arrested apoB can be regulated by a sterol-sensitive polyubiquitin conjugation step in the endoplasmic reticulum. Blocked ubiquitin-dependent proteasome degradation caused translocation-arrested apoB to become sequestered in segregated membrane domains. Our results described for the first time a novel mechanism through which the "quality control" proteasome endoplasmic reticulum degradative pathway of translocation-arrested apoB is linked to sterol metabolism. Sterol-sensitive blocked ubiquitin conjugation appears to selectively inhibit the proteasome degradation of apoB, but not 7alpha-hydroxylase protein, with no impairment of cell vitality or function. Our findings may help to explain why the hepatic production of lipoproteins is increased when familial hypertriglyceridemic patients are treated with drugs that activate 7alpha-hydroxylase (e.g. bile acid-binding resins).
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Affiliation(s)
- E Z Du
- Mammalian Cell and Molecular Biology Laboratory, Department of Biology and Molecular Biology Institute, San Diego State University, San Diego, California 92182-0057, USA
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Abstract
The enterohepatic circulation of bile acids is maintained by a series of membrane transport proteins. Recent studies of the cloned sodium bile acid cotransporters have provided new insights into their tissue expression, regulation, and their relationship to cholesterol homeostasis and human diseases such as primary bile acid malabsorption.
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Affiliation(s)
- M W Love
- Department of Internal Medicine, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA
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Tonelli D, Gattavecchia E, Mazzella G, Roda A. Bile acid kinetics in man studied by radio thin-layer chromatography and densitometry coupling. JOURNAL OF CHROMATOGRAPHY. B, BIOMEDICAL SCIENCES AND APPLICATIONS 1997; 700:59-66. [PMID: 9390714 DOI: 10.1016/s0378-4347(97)00312-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
A method based on coupling of the techniques of radioscanning a TLC plate and densitometry has been developed for the determination of pool sizes and fractional turnover rate of bile acids in man after intraduodenal administration of 14C-labelled acid. The validity of the method has been checked by comparison of the results obtained with those of an enzymatic spectrophotometric analysis, and a measurement of the radioactivity by liquid scintillation counting, after elution of the separated bile acid from a TLC plate. Advantages of the proposed method over the previous one include a reduced number of manipulations, the possibility of automation, a better reproducibility, and the possibility of elaborating the radiometric data obtained for the primary bile acid for better characterising its metabolism inside the enterohepatic circulation.
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Affiliation(s)
- D Tonelli
- Dipartimento di Chimica Fisica ed Inorganica, Università di Bologna, Italy
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