1
|
Dias IH, Borah K, Amin B, Griffiths HR, Sassi K, Lizard G, Iriondo A, Martinez-Lage P. Localisation of oxysterols at the sub-cellular level and in biological fluids. J Steroid Biochem Mol Biol 2019; 193:105426. [PMID: 31301352 DOI: 10.1016/j.jsbmb.2019.105426] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/21/2019] [Revised: 06/25/2019] [Accepted: 07/09/2019] [Indexed: 12/16/2022]
Abstract
Oxysterols are oxidized derivatives of cholesterol that are formed enzymatically or via reactive oxygen species or both. Cholesterol or oxysterols ingested as food are absorbed and packed into lipoproteins that are taken up by hepatic cells. Within hepatic cells, excess cholesterol is metabolised to form bile acids. The endoplasmic reticulum acts as the main organelle in the bile acid synthesis pathway. Metabolised sterols originating from this pathway are distributed within other organelles and in the cell membrane. The alterations to membrane oxysterol:sterol ratio affects the integrity of the cell membrane. The presence of oxysterols changes membrane fluidity and receptor orientation. It is well documented that hydroxylase enzymes located in mitochondria facilitate oxysterol production via an acidic pathway. More recently, the presence of oxysterols was also reported in lysosomes. Peroxisomal deficiencies favour intracellular oxysterols accumulation. Despite the low abundance of oxysterols compared to cholesterol, the biological actions of oxysterols are numerous and important. Oxysterol levels are implicated in the pathogenesis of multiple diseases ranging from chronic inflammatory diseases (atherosclerosis, Alzheimer's disease and bowel disease), cancer and numerous neurodegenerative diseases. In this article, we review the distribution of oxysterols in sub-cellular organelles and in biological fluids.
Collapse
Affiliation(s)
- Irundika Hk Dias
- Aston Medical Research Institute, Aston Medical School, Aston University, Birmingham, B4 7ET, UK.
| | - Khushboo Borah
- Faculty of Health and Medical Sciences, University of Surrey, Stag Hill, Guildford, GU2 7XH, UK
| | - Berivan Amin
- Aston Medical Research Institute, Aston Medical School, Aston University, Birmingham, B4 7ET, UK
| | - Helen R Griffiths
- Aston Medical Research Institute, Aston Medical School, Aston University, Birmingham, B4 7ET, UK; Faculty of Health and Medical Sciences, University of Surrey, Stag Hill, Guildford, GU2 7XH, UK
| | - Khouloud Sassi
- Team Bio-PeroxIL, Biochemistry of the Peroxisome, Inflammation and Lipid Metabolism (EA7270)/University Bourgogne Franche-Comté/Inserm, 21000 Dijon, France; Univ. Tunis El Manar, Laboratory of Onco-Hematology (LR05ES05), Faculty of Medicine, Tunis, Tunisia
| | - Gérard Lizard
- Team Bio-PeroxIL, Biochemistry of the Peroxisome, Inflammation and Lipid Metabolism (EA7270)/University Bourgogne Franche-Comté/Inserm, 21000 Dijon, France
| | - Ane Iriondo
- Department of Neurology, Center for Research and Advanced Therapies, CITA-Alzheimer Foundation, San Sebastian, Spain
| | - Pablo Martinez-Lage
- Department of Neurology, Center for Research and Advanced Therapies, CITA-Alzheimer Foundation, San Sebastian, Spain
| |
Collapse
|
2
|
Emerging role of various signaling pathways in the pathogenesis and therapeutics of atherosclerosis. ACTA ACUST UNITED AC 2017. [DOI: 10.1016/j.rvm.2017.05.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
|
3
|
Lee WR, Ishikawa T, Umetani M. The interaction between metabolism, cancer and cardiovascular disease, connected by 27-hydroxycholesterol. ACTA ACUST UNITED AC 2014; 9:617-624. [PMID: 25632306 DOI: 10.2217/clp.14.53] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Oxysterols are metabolites of cholesterol that are produced in liver and other peripheral tissues as a means to eliminate cholesterol to bile acid. Recent studies have revealed that the most abundant circulating oxysterol 27-hydroxycholesterol (27HC) is the first identified endogenous selective estrogen receptor modulator. 27HC levels correlate well with that of cholesterol, and also rise progressively with age. 27HC affects estrogen receptor function by the antagonism of estrogen action and also by the direct modulation of the receptor function, and similar to estrogen/estrogen receptors, 27HC has many actions in various tissues. This review article introduces the recent progress in the understanding of the role of 27HC in breast cancer and cardiovascular dysfunction.
Collapse
Affiliation(s)
- Wan-Ru Lee
- Division of Pulmonary & Vascular Biology, Departments of Pediatrics & Pharmacology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390, USA
| | - Tomonori Ishikawa
- Division of Pulmonary & Vascular Biology, Departments of Pediatrics & Pharmacology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390, USA ; Comprehensive Reproductive Medicine, Graduate School of Medical & Dental Sciences, Tokyo Medical & Dental University, Tokyo, Japan
| | - Michihisa Umetani
- Division of Pulmonary & Vascular Biology, Departments of Pediatrics & Pharmacology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390, USA
| |
Collapse
|
4
|
Vurusaner B, Gamba P, Testa G, Gargiulo S, Biasi F, Zerbinati C, Iuliano L, Leonarduzzi G, Basaga H, Poli G. Survival signaling elicited by 27-hydroxycholesterol through the combined modulation of cellular redox state and ERK/Akt phosphorylation. Free Radic Biol Med 2014; 77:376-85. [PMID: 25110320 DOI: 10.1016/j.freeradbiomed.2014.07.026] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Revised: 07/08/2014] [Accepted: 07/21/2014] [Indexed: 01/16/2023]
Abstract
The oxysterol 27-hydroxycholesterol (27-OH) is increasingly considered to be involved in a variety of pathophysiological processes, having been shown to modulate cell proliferation and metabolism, and also to exert proinflammatory and proapoptotic effects. This study aimed to elucidate the molecular pathways whereby 27-OH may generate survival signals in cells of the macrophage lineage, and to clarify whether its known prooxidant effect is involved in that process. A net up-regulation of survival signaling, involving the extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3K)/Akt phosphorylation pathways, was observed in U937 promonocytic cells cultivated over time in the presence of a low micromolar concentration of the oxysterol. Interestingly, the up-regulation of both kinases was shown to be closely dependent on an early 27-OH-induced intracellular increase of reactive oxygen species (ROS). In turn, stimulation of ERK and PI3K/Akt both significantly quenched ROS steady state and markedly phosphorylated Bad, thereby determining a marked delay of the oxysterol׳s proapoptotic action. The 27-OH-induced survival pathways thus appear to be redox modulated and, if they occur within or nearby inflammatory cells during progression of chronic diseases such as cancer and atherosclerosis, they could significantly impact the growth and evolution of such diseases.
Collapse
Affiliation(s)
- Beyza Vurusaner
- Biological Sciences and Bioengineering Program, Faculty of Engineering and Natural Sciences, Sabanci University, Orhanli-Tuzla, 34956 Istanbul, Turkey.
| | - Paola Gamba
- Department of Clinical and Biological Sciences, University of Turin, Turin, Italy.
| | - Gabriella Testa
- Department of Clinical and Biological Sciences, University of Turin, Turin, Italy.
| | - Simona Gargiulo
- Department of Clinical and Biological Sciences, University of Turin, Turin, Italy.
| | - Fiorella Biasi
- Department of Clinical and Biological Sciences, University of Turin, Turin, Italy.
| | - Chiara Zerbinati
- Department of Medical-Surgical Sciences and Biotechnology, Vascular Biology and Mass Spectrometry Laboratory, Sapienza University of Rome, Latina, Italy.
| | - Luigi Iuliano
- Department of Medical-Surgical Sciences and Biotechnology, Vascular Biology and Mass Spectrometry Laboratory, Sapienza University of Rome, Latina, Italy.
| | | | - Huveyda Basaga
- Biological Sciences and Bioengineering Program, Faculty of Engineering and Natural Sciences, Sabanci University, Orhanli-Tuzla, 34956 Istanbul, Turkey.
| | - Giuseppe Poli
- Department of Clinical and Biological Sciences, University of Turin, Turin, Italy.
| |
Collapse
|
5
|
The Influence of an Obesogenic Diet on Oxysterol Metabolism in C57BL/6J Mice. CHOLESTEROL 2014; 2014:843468. [PMID: 24672716 PMCID: PMC3941159 DOI: 10.1155/2014/843468] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/26/2013] [Revised: 12/18/2013] [Accepted: 12/21/2013] [Indexed: 11/18/2022]
Abstract
Our current understanding of oxysterol metabolism during different disease states such as obesity and dyslipidemia is limited. Therefore, the aim of this study was to determine the effect of diet-induced obesity on the tissue distribution of various oxysterols and the mRNA expression of key enzymes involved in oxysterol metabolism. To induce obesity, male C57BL/6J mice were fed a high fat-cholesterol diet for 24 weeks. Following diet-induced obesity, plasma levels of 4β-hydroxycholesterol, 5,6α-epoxycholesterol, 5,6β-epoxycholesterol, 7α-hydroxycholesterol, 7β-hydroxycholesterol, and 27-hydroxycholesterol were significantly (P < 0.05) increased. In the liver and adipose tissue of the obese mice, 4β-hydroxycholesterol was significantly (P < 0.05) increased, whereas 27-hydroxycholesterol was increased only in the adipose tissue. No significant changes in either hepatic or adipose tissue mRNA expression were observed for oxysterol synthesizing enzymes 4β-hydroxylase, 27-hydroxylase, or 7α-hydroxylase. Hepatic mRNA expression of SULT2B1b, a key enzyme involved in oxysterol detoxification, was significantly (P < 0.05) elevated in the obese mice. Interestingly, the appearance of the large HDL1 lipoprotein was observed with increased oxysterol synthesis during obesity. In diet-induced obese mice, dietary intake and endogenous enzymatic synthesis of oxysterols could not account for the increased oxysterol levels, suggesting that nonenzymatic cholesterol oxidation pathways may be responsible for the changes in oxysterol metabolism.
Collapse
|
6
|
Bingham TC, Parathath S, Tian H, Reiss A, Chan E, Fisher EA, Cronstein BN. Cholesterol 27-hydroxylase but not apolipoprotein apoE contributes to A2A adenosine receptor stimulated reverse cholesterol transport. Inflammation 2012; 35:49-57. [PMID: 21258856 DOI: 10.1007/s10753-010-9288-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Movement of free cholesterol between the cellular compartment and acceptor is governed by cholesterol gradients that are determined by several enzymes and reverse cholesterol transport proteins. We have previously demonstrated that adenosine A(2A) receptors inhibit foam cell formation and stimulate production of cholesterol 27-hydroxylase (CYP27A1), an enzyme involved in the conversion of cholesterol to oxysterols. We therefore asked whether the effect of adenosine A(2A) receptors on foam cell formation in vitro is mediated by CYP27A1 or apoE, a carrier for cholesterol in the serum. We found that specific lentiviral siRNA infection markedly reduced apoE or 27-hydroxylase mRNA in THP-1 cells. Despite diminished apoE expression (p < 0.0002, interferon-gamma (IFNγ) CGS vs. IFNγ alone, n=4), CGS-21680, an adenosine A(2A) receptor agonist, inhibits foam cell formation. In contrast, CGS-21680 had no effect on reducing foam cell formation in CYP27A1 KD cells (4 ± 2%; p<0.5113, inhibition vs. IFNγ alone, n=4). Previously, we reported the A(2A) agonist CGS-21680 increases apoAI-mediated cholesterol efflux nearly twofold in wild-type macrophages. Adenosine receptor activation had no effect on cholesterol efflux in CYP27A1 KD cells but reduced efflux in apoE KD cells. These results demonstrate that adenosine A(2A) receptor occupancy diminishes foam cell formation by increasing expression and function of CYP27A1.
Collapse
Affiliation(s)
- Taiese Crystal Bingham
- Department of Medicine, New York University School of Medicine, 550 First Avenue, New York, NY 10016, USA.
| | | | | | | | | | | | | |
Collapse
|
7
|
Bielska AA, Schlesinger P, Covey DF, Ory DS. Oxysterols as non-genomic regulators of cholesterol homeostasis. Trends Endocrinol Metab 2012; 23:99-106. [PMID: 22244444 PMCID: PMC3294026 DOI: 10.1016/j.tem.2011.12.002] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/29/2011] [Revised: 11/21/2011] [Accepted: 12/05/2011] [Indexed: 12/31/2022]
Abstract
Tight regulation of cellular and plasma cholesterol is crucial to proper cellular functioning because excess free cholesterol is toxic to cells and is associated with atherosclerosis and heart disease. Cellular cholesterol homeostasis is regulated by enzymatically formed oxygenated cholesterol derivatives termed oxysterols. Although the effects of oxysterols on transcriptional pathways are well described, the non-transcriptional mechanisms through which oxysterols acutely modulate cellular cholesterol levels are less well understood. We present emerging evidence suggesting that the membrane biophysical properties of oxysterols underlie their acute cholesterol-regulatory functions and discuss the relevance of these acute effects to cholesterol overload in physiological and pathophysiological states.
Collapse
Affiliation(s)
- Agata A Bielska
- Diabetic Cardiovascular Disease Center, Washington University School of Medicine, St Louis, MO 63110, USA
| | | | | | | |
Collapse
|
8
|
|
9
|
Ning Y, Xu L, Ren S, Pandak WM, Chen S, Yin L. StAR overexpression decreases serum and tissue lipids in apolipoprotein E-deficient mice. Lipids 2009; 44:511-9. [PMID: 19373502 DOI: 10.1007/s11745-009-3299-1] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2009] [Accepted: 03/24/2009] [Indexed: 02/07/2023]
Abstract
Cholesterol metabolism as initiated by mitochondrial sterol 27-hydroxylase (CYP27A1) is a ubiquitous pathway capable of synthesizing multiple key regulatory oxysterols involved in lipid homeostasis. Previously we have shown that the regulation of its activities within hepatocytes is highly controlled by the rate of mitochondrial cholesterol delivery. In the present study, we hypothesized that increasing expression of the mitochondrial cholesterol delivery protein, steroidogenic acute regulatory protein (StAR), is able to lower lipid accumulation in liver, aortic wall, as well as in serum in a well-documented animal model, apolipoprotein E-deficient (apoE(-/-)) mice. ApoE(-/-) mice, characterized by increased serum, liver, and endothelial cholesterol and triglyceride levels by 3 months of age, were infected with recombinant cytomegalovirus (CMV)-StAR adenovirus to increase StAR protein expression. Six days following infection, serum total cholesterol and triglycerides had decreased 19 and 30% (P < 0.01), respectively, with a compensatory 40% (P < 0.01) increase in serum HDL-cholesterol in increased StAR expressing mice as compared to controls (no or control virus). Histologic and biochemical analysis of the liver demonstrated not only a dramatic decrease in cholesterol ( downward arrow25%; P < 0.01), but an even more marked decrease in triglyceride ( downward arrow56%; P < 0.01) content. En bloc Sudan IV staining of the aorta revealed a >80% (P < 0.01) decrease in neutral lipid staining. This study demonstrates for the first time a possible therapeutic role of the CYP27A1-initiated pathway in the treatment of dyslipidemias.
Collapse
Affiliation(s)
- Yanxia Ning
- Department of Physiology and Pathophysiology, Shanghai Medical College, Fudan University, PO Box 224, 138 Yixueyuan Road, 200032, Shanghai, People's Republic China
| | | | | | | | | | | |
Collapse
|
10
|
Abstract
This review summarizes the mechanisms of cellular cholesterol transport and monogenic human diseases caused by defects in intracellular cholesterol processing. In addition, selected mouse models of disturbed cholesterol trafficking are discussed. Current pharmacological strategies to prevent atherosclerosis are largely based on altering cellular cholesterol balance and are introduced in this context. Finally, because of the organizing potential of cholesterol in membranes, disturbances in cellular cholesterol transport have implications for a wide variety of human diseases, of which selected examples are given.
Collapse
Affiliation(s)
- Elina Ikonen
- Institute of Biomedicine/Anatomy, University of Helsinki, Helsinki, Finland.
| |
Collapse
|
11
|
Ning Y, Chen S, Li X, Ma Y, Zhao F, Yin L. Cholesterol, LDL, and 25-hydroxycholesterol regulate expression of the steroidogenic acute regulatory protein in microvascular endothelial cell line (bEnd.3). Biochem Biophys Res Commun 2006; 342:1249-56. [PMID: 16516145 DOI: 10.1016/j.bbrc.2006.02.093] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2006] [Accepted: 02/15/2006] [Indexed: 10/25/2022]
Abstract
The steroidogenic acute regulatory (StAR) protein promotes intramitochondrial delivery of cholesterol to the cholesterol side-chain cleavage system. In this experiment, we first demonstrated that StAR expressed in endothelial cells as well. Immunochemistry showed positive staining of StAR in endothelial cells. To investigate whether steroids and oxysterols regulate StAR expression in endothelial cells, mouse brain microvascular endothelial cell line (bEnd.3) was treated with various steroids and oxysterols, including free cholesterol (CHO), low density lipoprotein (LDL), and 25-hydroxycholesterol (25-OH). All these three compounds increased StAR mRNA and protein expression in a time- and dose-dependent manner. When treated with CHO and LDL, the StAR mRNA change was prior to the protein change, suggesting that transcription may be one of the mechanisms of CHO and LDL regulation. In contrast to CHO and LDL, 25-OH increased StAR protein levels independently of mRNA amount. It suggested that 25-OH might regulate StAR activity at post-transcriptional level.
Collapse
Affiliation(s)
- Yanxia Ning
- Department of Physiology and Pathophysiology, Shanghai Medical College, Fudan University, Shanghai 200032, PR China
| | | | | | | | | | | |
Collapse
|
12
|
Ota Y, Eto TA, Tanaka SI, Sueta H, Shiotsuki H, Maeda Y, Une M, Chijiiwa K. Assay method for mitochondrial sterol 27-hydroxylase with 7alpha-hydroxy-4-cholesten-3-one as a substrate in the rat liver. J Lipid Res 2003; 44:2400-5. [PMID: 12951370 DOI: 10.1194/jlr.d200045-jlr200] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mitochondrial sterol 27-hydroxylase (EC 1.14.13.15) is an important enzyme, not only in the formation of bile acids from cholesterol intermediates in the liver but also in the removal of cholesterol by side chain hydroxylation in extrahepatic tissues. The enzyme has been assayed by complicated methods using radiolabeled substrates or deuterium-labeled tracers. These methods may be inaccurate for measuring enzyme activity, because the amount of electron-transferring proteins may be insufficient for maximal velocity. To solve this problem, after solubilization of the enzyme from rat liver mitochondria with n-octyl-beta-d-glucopyranoside (OGP), we measured the enzyme activity by incubating the solubilized enzyme with saturated amounts of electron-transferring proteins. In our assay system, using 7alpha-hydroxy-4-cholesten-3-one (HCO) as a substrate, we could easily measure the product, 7alpha,27-dihydroxy-4-cholesten-3-one, with HPLC monitoring absorbance at 240 nm. The product formation was proportionate to the time up to 5 min and the protein concentration up to 0.5 mg of protein/ml. The maximal velocity of the enzyme was 1.1 nmol/min/mg of protein, which was 4- to 16-fold higher than previously reported values. A simple and accurate assay method for sterol 27-hydroxylase in rat liver mitochondria is herein described.
Collapse
Affiliation(s)
- Yoshikazu Ota
- Department of Surgery I, Miyazaki Medical College, 5200 Kihara, Kiyotake, Miyazaki 889-1692, Japan
| | | | | | | | | | | | | | | |
Collapse
|
13
|
Liu SM, Cogny A, Kockx M, Dean RT, Gaus K, Jessup W, Kritharides L. Cyclodextrins differentially mobilize free and esterified cholesterol from primary human foam cell macrophages. J Lipid Res 2003; 44:1156-66. [PMID: 12671029 DOI: 10.1194/jlr.m200464-jlr200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human monocyte-derived foam cell macrophages (HMFCs) are resistant to cholesterol efflux mediated by physiological acceptors. The role of the plasma membrane in regulating depletion of free cholesterol (FC) and of cholesteryl ester (CE) was investigated using cyclodextrins (CDs). HMFCs were incubated in media containing CDs (1.0 mg/ml, approximately 0.7 mM) with low [hydroxypropyl-beta-CD (HP-CD)] or high [trimethyl-beta-CD (TM-CD)] affinity for cholesterol in the presence or absence of phospholipid vesicles (PLVs). Low-affinity HP-CD caused minimal cholesterol efflux on its own, but HP-CD+ PLV depleted cell FC and CE to 54.5 +/- 6.7% of control by 24 h. TM-CD depleted FC at least as well as HP-CD+PLV but without depleting CE, even when combined with PLV. This was not explained by acceptor saturation, instability of PLV vesicles, de novo cholesterol synthesis, kinetically distinct cholesterol pools, or inhibition of CE hydrolysis. TM-CD did, however, deplete CE when lower concentrations of TM-CD were combined with PLV and when acetyl-CoA cholesteryl acyltransferase was inhibited. TM-CD caused much greater depletion of plasma membrane cholesterol than HP-CD without depleting plasma membrane sphingomyelin. It is concluded that differential depletion of plasma membrane cholesterol pools regulates cholesterol efflux and CE clearance in human macrophages.
Collapse
Affiliation(s)
- Sue M Liu
- Heart Research Institute, Camperdown, Sydney New South Wales, Australia
| | | | | | | | | | | | | |
Collapse
|
14
|
Escher G, Krozowski Z, Croft KD, Sviridov D. Expression of sterol 27-hydroxylase (CYP27A1) enhances cholesterol efflux. J Biol Chem 2003; 278:11015-9. [PMID: 12531903 DOI: 10.1074/jbc.m212780200] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cholesterol efflux from CHOP cells transfected with sterol 27-hydroxylase (CYP27A1) was compared with non-transfected and mock-transfected cells. Transfection caused expression of CYP27A1, formation of 27-hydroxycholesterol, and inhibition of cholesterol biosynthesis. Transfection enhanced cholesterol efflux to apolipoprotein A-I or human plasma by 2-3-fold but did not affect the efflux in the absence of acceptor. The analysis of released sterols revealed that 27-hydroxycholesterol represented only a small proportion of sterols, most of which was non-oxidized cholesterol. Time course and dose dependence studies showed that expression of CYP27A1 in CHOP cells mostly affected the efflux of the "fast" cholesterol pool, and relatively more cholesterol was released with low concentrations of an acceptor. Preincubation of non-transfected cells with exogenous 27-hydroxycholesterol (10(-9) and 10(-7) m) led to the stimulation of cholesterol efflux by 24-60%. Expression of CYP27A1 in CHOP cells did not affect ABCA1 expression and abundance of ABCA1 protein. Thus, introduction of CYP27A1 into cells stimulates cholesterol efflux and therefore may increase protection against atherosclerosis.
Collapse
Affiliation(s)
- Genevieve Escher
- Wynn Domain, Baker Medical Research Institute, Melbourne, Victoria 8008, Australia
| | | | | | | |
Collapse
|
15
|
Hansson M, Ellis E, Hunt MC, Schmitz G, Babiker A. Marked induction of sterol 27-hydroxylase activity and mRNA levels during differentiation of human cultured monocytes into macrophages. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1593:283-9. [PMID: 12581873 DOI: 10.1016/s0167-4889(02)00398-1] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Sterol 27-hydroxylase has been suggested to be involved in an alternative pathway for the elimination of cholesterol from macrophages and early atherosclerotic lesions. We have previously shown that human lung macrophages as well as monocyte-derived macrophages have a relatively high activity of sterol 27-hydroxylase (CYP27). This enzyme converts intracellular cholesterol into 27-hydroxycholesterol and cholestenoic acid that flux from cultured cells into the medium. It is shown here that human monocytes have very low CYP27 activity and CYP27 mRNA levels. During differentiation into macrophages, both CYP27 activity and CYP27 mRNA levels increase markedly after 4 days of culture in serum-free medium. Addition of macrophage-colony stimulating factor had no significant effect on the induction and addition of fetal calf serum had an inhibitory effect. Cholesterol synthesis was found to be a critical factor for the production of 27-oxygenated products by the macrophages cultured in serum-free medium. The increased capacity of the differentiated cells to eliminate intracellular cholesterol is of interest and supports the contention that CYP27 is an antiatherogenic factor.
Collapse
Affiliation(s)
- Magnus Hansson
- Department of Medical Laboratory Sciences and Technology, Division of Clinical Chemistry, Karolinska Institutet, Huddinge University Hospital, SE-141 86, Stockholm, Sweden
| | | | | | | | | |
Collapse
|
16
|
Sparrow CP, Baffic J, Lam MH, Lund EG, Adams AD, Fu X, Hayes N, Jones AB, Macnaul KL, Ondeyka J, Singh S, Wang J, Zhou G, Moller DE, Wright SD, Menke JG. A potent synthetic LXR agonist is more effective than cholesterol loading at inducing ABCA1 mRNA and stimulating cholesterol efflux. J Biol Chem 2002; 277:10021-7. [PMID: 11790770 DOI: 10.1074/jbc.m108225200] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The LXR nuclear receptors are intracellular sensors of cholesterol excess and are activated by various oxysterols. LXRs have been shown to regulate multiple genes of lipid metabolism, including ABCA1 (formerly known as ABC1). ABCA1 is a lipid pump that effluxes cholesterol and phospholipid out of cells. ABCA1 deficiency causes extremely low high density lipoprotein (HDL) levels, demonstrating the importance of ABCA1 in the formation of HDL. The present work shows that the acetyl-podocarpic dimer (APD) is a potent, selective agonist for both LXRalpha (NR1H3) and LXRbeta (NR1H2). In transient transactivation assays, APD was approximately 1000-fold more potent, and yielded approximately 6-fold greater maximal stimulation, than the widely used LXR agonist 22-(R)-hydroxycholesterol. APD induced ABCA1 mRNA levels, and increased efflux of both cholesterol and phospholipid, from multiple cell types. Gas chromatography-mass spectrometry measurements demonstrated that APD stimulated efflux of endogenous cholesterol, eliminating any possible artifacts of cholesterol labeling. For both mRNA induction and stimulation of cholesterol efflux, APD was found to be more effective than was cholesterol loading. Taken together, these data show that APD is a more effective LXR agonist than endogenous oxysterols. LXR agonists may therefore be useful for the prevention and treatment of atherosclerosis, especially in the context of low HDL levels.
Collapse
Affiliation(s)
- Carl P Sparrow
- Merck Research Laboratories, Rahway, New Jersey 07065, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
17
|
Vosper H, Patel L, Graham TL, Khoudoli GA, Hill A, Macphee CH, Pinto I, Smith SA, Suckling KE, Wolf CR, Palmer CN. The peroxisome proliferator-activated receptor delta promotes lipid accumulation in human macrophages. J Biol Chem 2001; 276:44258-65. [PMID: 11557774 DOI: 10.1074/jbc.m108482200] [Citation(s) in RCA: 218] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The peroxisome proliferator-activated receptors (PPARs) are a family of fatty acid-activated transcription factors which control lipid homeostasis and cellular differentiation. PPARalpha (NR1C1) controls lipid oxidation and clearance in hepatocytes and PPARgamma (NR1C3) promotes preadipocyte differentiation and lipogenesis. Drugs that activate PPARalpha are effective in lowering plasma levels of lipids and have been used in the management of hyperlipidemia. PPARgamma agonists increase insulin sensitivity and are used in the management of type 2 diabetes. In contrast, there are no marketed drugs that selectively target PPARdelta (NR1C2) and the physiological roles of PPARdelta are unclear. In this report we demonstrate that the expression of PPARdelta is increased during the differentiation of human macrophages in vitro. In addition, a highly selective agonist of PPARdelta (compound F) promotes lipid accumulation in primary human macrophages and in macrophages derived from the human monocytic cell line, THP-1. Compound F increases the expression of genes involved in lipid uptake and storage such as the class A and B scavenger receptors (SRA, CD36) and adipophilin. PPARdelta activation also represses key genes involved in lipid metabolism and efflux, i.e. cholesterol 27-hydroxylase and apolipoprotein E. We have generated THP-1 sublines that overexpress PPARdelta and have confirmed that PPARdelta is a powerful promoter of macrophage lipid accumulation. These data suggest that PPARdelta may play a role in the pathology of diseases associated with lipid-filled macrophages, such as atherosclerosis, arthritis, and neurodegeneration.
Collapse
Affiliation(s)
- H Vosper
- Biomedical Research Centre, Ninewells Hospital and Medical School, Dundee DD1 9SY, Scotland
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
18
|
Fu X, Menke JG, Chen Y, Zhou G, MacNaul KL, Wright SD, Sparrow CP, Lund EG. 27-hydroxycholesterol is an endogenous ligand for liver X receptor in cholesterol-loaded cells. J Biol Chem 2001; 276:38378-87. [PMID: 11504730 DOI: 10.1074/jbc.m105805200] [Citation(s) in RCA: 423] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The nuclear receptors liver X receptor alpha (LXRalpha) (NR1H3) and LXRbeta (NR1H2) are important regulators of genes involved in lipid metabolism, including ABCA1, ABCG1, and sterol regulatory element-binding protein-1c (SREBP-1c). Although it has been demonstrated that oxysterols are LXR ligands, little is known about the identity of the physiological activators of these receptors. Here we confirm earlier studies demonstrating a dose-dependent induction of ABCA1 and ABCG1 in human monocyte-derived macrophages by cholesterol loading. In addition, we show that formation of 27-hydroxycholesterol and cholestenoic acid, products of CYP27 action on cholesterol, is dependent on the dose of cholesterol used to load the cells. Other proposed LXR ligands, including 20(S)-hydroxycholesterol, 22(R)-hydroxycholesterol, and 24(S),25-epoxycholesterol, could not be detected under these conditions. A role for CYP27 in regulation of cholesterol-induced genes was demonstrated by the following findings. 1) Introduction of CYP27 into HEK-293 cells conferred an induction of ABCG1 and SREBP-1c; 2) upon cholesterol loading, CYP27-expressing cells induce these genes to a greater extent than in control cells; 3) in CYP27-deficient human skin fibroblasts, the induction of ABCA1 in response to cholesterol loading was ablated; and 4) in a coactivator association assay, 27-hydroxycholesterol functionally activated LXR. We conclude that 27-hydroxylation of cholesterol is an important pathway for LXR activation in response to cholesterol overload.
Collapse
MESH Headings
- ATP Binding Cassette Transporter 1
- ATP Binding Cassette Transporter, Subfamily G, Member 1
- ATP-Binding Cassette Transporters/metabolism
- CCAAT-Enhancer-Binding Proteins/metabolism
- Cells, Cultured
- Cholestenones/metabolism
- Cholesterol/metabolism
- Cholesterol, LDL/metabolism
- DNA, Complementary/metabolism
- DNA-Binding Proteins/metabolism
- Dose-Response Relationship, Drug
- Fibroblasts/metabolism
- Gas Chromatography-Mass Spectrometry
- Humans
- Hydroxycholesterols/metabolism
- Ligands
- Liver X Receptors
- Macrophages/metabolism
- Orphan Nuclear Receptors
- Receptors, Cytoplasmic and Nuclear/metabolism
- Receptors, Retinoic Acid/metabolism
- Receptors, Thyroid Hormone/metabolism
- Reverse Transcriptase Polymerase Chain Reaction
- Skin/metabolism
- Sterol Regulatory Element Binding Protein 1
- Time Factors
- Transcription Factors
- Transfection
- Xanthomatosis, Cerebrotendinous/metabolism
Collapse
Affiliation(s)
- X Fu
- Department of Atherosclerosis and Endocrinology, and Metabolic Research, Merck Research Laboratories, Rahway, New Jersey 07065, USA
| | | | | | | | | | | | | | | |
Collapse
|
19
|
Hall E, Hylemon P, Vlahcevic Z, Mallonee D, Valerie K, Avadhani N, Pandak W. Overexpression of CYP27 in hepatic and extrahepatic cells: role in the regulation of cholesterol homeostasis. Am J Physiol Gastrointest Liver Physiol 2001; 281:G293-301. [PMID: 11408283 DOI: 10.1152/ajpgi.2001.281.1.g293] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
In the liver, sterol 27-hydroxylase (CYP27) participates in the classic and alternative pathways of bile acid biosynthesis from cholesterol (Chol). In extrahepatic tissues, CYP27 converts intracellular Chol to 27-hydroxycholesterol (27OH-Chol), which may regulate the activity of 3-hydroxy-3-methylglutaryl CoA reductase (HMG-CoA-R). This study attempts to better define the role of CYP27 in the maintenance of Chol homeostasis in hepatic and extrahepatic cells by overexpressing CYP27 in Hep G2 cells and Chinese hamster ovary (CHO) cells through infection with a replication-defective recombinant adenovirus encoding for CMV-CYP27. After infection, CYP27 mRNA and protein levels increased dramatically. CYP27 specific activity also increased two- to fourfold in infected cells (P < or = 0.02), with a marked increase in conversion of [(14)C]Chol to [(14)C]27OH-Chol (approximately 150%; P < or = 0.01). Accumulation of 27OH-Chol in CHO cells was associated with a 50% decrease in HMG-CoA-R specific activity (P < or = 0.02). In infected Hep G2 cells, the significant increase in bile acid synthesis (46%; P < or = 0.006), which prevented the accumulation of intracellular 27OH-Chol, resulted in increased HMG-CoA-R activity (183%; P < or = 0.02). Overexpression of CYP27 in Hep G2 cells also increased acyl CoA-cholesterol acyltransferase (71%, P < or = 0.02) and decreased cholesteryl ester hydrolase (55%, P < or = 0.02). In conclusion, CYP27 generates different physiological responses depending on cell type and presence or absence of bile acid biosynthetic pathways.
Collapse
Affiliation(s)
- E Hall
- Department of Medicine, Medical College of Virginia, Virginia Commonwealth University and McGuire Veterans Affairs Medical Center, Richmond, Virginia 23249, USA
| | | | | | | | | | | | | |
Collapse
|
20
|
Drobnik W, Lindenthal B, Lieser B, Ritter M, Christiansen Weber T, Liebisch G, Giesa U, Igel M, Borsukova H, Büchler C, Fung-Leung WP, Von Bergmann K, Schmitz G. ATP-binding cassette transporter A1 (ABCA1) affects total body sterol metabolism. Gastroenterology 2001; 120:1203-11. [PMID: 11266384 DOI: 10.1053/gast.2001.23250] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
BACKGROUND AND AIMS Members of the family of ABC transporters are involved in different processes of sterol metabolism, and ABCA1 was recently identified as a key regulator of high-density lipoprotein (HDL) metabolism. Our aim was to further analyze the role of ABCA1 in cholesterol metabolism. METHODS ABCA1-deficient mice (ABCA1-/-) and wild-type mice were compared for different aspects of sterol metabolism. Intestinal cholesterol absorption was determined by a dual stable isotope technique, and analysis of fecal, plasma, and tissue sterols was performed by gas chromatography/mass spectrometry. Key regulators of sterol metabolism were investigated by Northern and Western blot analyses or enzyme activity assays. RESULTS ABCA1-disrupted sv129/C57BL/6 hybrid mice showed a significant reduction in intestinal cholesterol absorption. The decrease in cholesterol absorption was followed by an enhanced fecal loss of neutral sterols, whereas fecal bile acid excretion was not affected. Total body cholesterol synthesis was significantly increased, with enhanced 3-hydroxy-3-methyglutaryl-coenzyme A (HMG-CoA) reductase observed in adrenals and spleen. In addition, ABCA1-/- mice showed markedly increased concentrations of cholesterol precursors in the plasma, lung, intestine, and feces. Reduced HMG-CoA reductase messenger RNA and enzyme activity in the liver suggest that enhanced cholesterol synthesis in ABCA1-/- mice occurs in peripheral tissues rather than the liver. CONCLUSIONS The metabolism of cholesterol and cholesterol precursors is markedly affected by a lack of ABCA1 function.
Collapse
Affiliation(s)
- W Drobnik
- Institute for Clinical Chemistry and Laboratory Medicine, University of Regensburg, D-93042 Regensburg, Germany
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
21
|
Dass CR, Jessup W. Apolipoprotein A-I, cyclodextrins and liposomes as potential drugs for the reversal of atherosclerosis. A review. J Pharm Pharmacol 2000; 52:731-61. [PMID: 10933125 DOI: 10.1211/0022357001774606] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
Several studies have revealed that high-density lipoprotein (HDL) is the most reliable predictor for susceptibility to cardiovascular disease. Since apolipoprotein A-I (apoA-I) is the major protein of HDL, it is worthwhile evaluating the potential of this protein to reduce the lipid burden of lesions observed in the clinic. Indeed, apoA-I is used extensively in cell culture to induce cholesterol efflux. However, while there is a large body of data emanating from in-vitro and cell-culture studies with apoA-I, little animal data and scant clinical trials examining the potential of this apolipoprotein to induce cholesterol (and other lipid) efflux exists. Importantly, the effects of oxysterols, such as 7-ketocholesterol (7KC), on cholesterol and other lipid efflux by apoA-I needs to be investigated in any attempt to utilise apoA-I as an agent to stimulate efflux of lipids. Lessons may be learnt from studies with other lipid acceptors such as cyclodextrins and phospholipid vesicles (PLVs, liposomes), by combination with other effluxing agents, by remodelling the protein structure of the apolipoprotein, or by altering the composition of the lipoprotein intended for administration in-vivo. Akin to any other drug, the usage of this apolipoprotein in a therapeutic context has to follow the traditional sequence of events, namely an evaluation of the biodistribution, safety and dose-response of the protein in animal trials in advance of clinical trials. Mass production of the apolipoprotein is now a simple process due to the advent of recombinant DNA technology. This review also considers the potential of cyclodextrins and PLVs for use in inducing reverse cholesterol transport in-vivo. Finally, the potential of cyclodextrins as delivery agents for nucleic acid-based constructs such as oligonucleotides and plasmids is discussed.
Collapse
Affiliation(s)
- C R Dass
- Johnson and Johnson Research, Strawberry Hills, Australia.
| | | |
Collapse
|
22
|
Dass CR. Apolipoprotein A-I, phospholipid vesicles, and cyclodextrins as potential anti-atherosclerotic drugs: delivery, pharmacokinetics, and efficacy. Drug Deliv 2000; 7:161-82. [PMID: 10989917 DOI: 10.1080/10717540050120205] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
High-density lipoprotein (HDL) is a reliable predictor for susceptibility to cardiovascular disease. Since apolipoprotein A-I (apoA-I) is the major protein of HDL, it is worthwhile to evaluate the potential of this protein to reduce the lipid burden of lesions observed in the clinic. While a large body of data emanates from in vitro and cell culture studies with apoA-I, few animal and lesser clinical trials examining the potential of this apolipoprotein to induce cholesterol (and other lipid) efflux exist. Lessons may be learned from studies with other lipid acceptors such as phospholipid vesicles (PLVs, liposomes) and cyclodextrins (CDs). Additionally, the combination of apoA-I with other effluxing agents, alteration of the composition of the lipoprotein, or a remodeling of the protein structure of the apolipoprotein to be administered in vivo may result in increased efficacy. The usage of this apolipoprotein in a therapeutic context has to follow the conventional sequence of events: an evaluation of the biodistribution, safety, and dose-response of the protein in animal trials before clinical trials. The review also considers the potential of cyclodextrins and PLVs to induce reverse cholesterol transport in vivo and discusses the potential of CDs as delivery agents for genetic constructs, such as plasmids and oligonucleotides.
Collapse
Affiliation(s)
- C R Dass
- Johnson and Johnson Research, Strawberry Hills, Australia.
| |
Collapse
|
23
|
Abstract
Bile acids originate from the liver and are transported via bile to the intestines where they perform an important role in the absorption of lipids and lipid-soluble nutrients. Most of the bile acids are reclaimed from the terminal ileum and returned to the liver via portal blood for reuse. The transport of bile acids is vectorial in both liver and intestinal cells, originating and terminating at opposite poles. Bile acids enter through the basolateral pole in liver cells, and through the apical pole in intestinal cells. During the past decade, much has been learned about the mechanisms by which bile acids enter and exit liver and intestinal cells. By contrast, the mechanisms by which bile acids are transported across cells remain poorly understood. The current body of evidence suggests that bile acids do not traverse the cell by vesicular transport. Although a carrier-mediated mechanism is a likely alternative, only a handful of intracellular proteins capable of binding bile acids have been described. The significance of these proteins in the intracellular transport of bile acids remains to be tested.
Collapse
Affiliation(s)
- L B Agellon
- Department of Biochemistry, University of Alberta, Edmonton, Alta, Canada.
| | | |
Collapse
|
24
|
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.
Collapse
Affiliation(s)
- G J Schroepfer
- Departments of Biochemistry, Rice University, Houston, Texas, USA.
| |
Collapse
|
25
|
Abstract
Sterol 27-hydroxylase is an evolutionarily old cytochrome P450 species that is critical for oxidation of the side chain of cholesterol in connection with bile acid biosynthesis in the liver. The wide tissue and organ distribution of the enzyme suggests that it may also have other functions. It was recently shown that some cells (e.g. macrophages) have a high capacity to convert cholesterol into both 27-hydroxycholesterol and cholestenoic acid and that there is a significant flux of these steroids from extrahepatic sources to the liver where they are further oxidized into bile acids. The magnitude of this flux is such that it may be of importance for overall homeostasis of cholesterol. Very recently it was shown that the brain utilizes a similar mechanism for removal of cholesterol. A unique brain-specific 24S-hydroxylase converts cholesterol into 24S-hydroxycholesterol that is transported over the blood-brain barrier much more rapidly than unmetabolized cholestero. When 24S-hydroxycholesterol has reached the circulation it is taken up by the liver and further metabolized, most probably into bile acids. This flux is likely to be of importance for cholesterol homeostasis in the brain. This review summarizes our current knowledge regarding oxidative mechanisms for removal of extrahepatic cholesterol. It is evident that some cells utilize these mechanisms as alternatives or complements to the classical HDL-dependent reverse cholesterol transport.
Collapse
Affiliation(s)
- I Björkhem
- Division of Clinical Chemistry, Karolinska Institutet, Huddinge Hospital, Sweden
| | | | | |
Collapse
|