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Tsubakio-Yamamoto K, Nishida M, Nakagawa-Toyama Y, Masuda D, Ohama T, Yamashita S. Current therapy for patients with sitosterolemia--effect of ezetimibe on plant sterol metabolism. J Atheroscler Thromb 2010; 17:891-900. [PMID: 20543520 DOI: 10.5551/jat.4614] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Sitosterolemia is a rare, autosomal recessive inherited sterol storage disease associated with high tissue and serum plant sterol concentrations, caused by mutations in the adenosine triphosphate-bind-ing cassette (ABC) transporter ABCG5 or ABCG8 genes. Markedly increased serum concentration of plant sterols. such as sitosterol and campesterol, cause premature atherosclerosis and massive xanthomas. Hitherto known treatments for sitosterolemia, including a low-sterol diet, bile-salt binding resins, ileal bypass surgery and low density lipoprotein (LDL) apheresis have not yielded sufficient reduction of serum plant sterol levels and many patients show a sustained elevation of plant sterol levels, subsequently developing premature atherosclerotic cardiovascular diseases. Ezetimibe, an inhibitor of intestinal cholesterol absorption through its binding to Niemann-Pick C1-like 1 (NPC1L1), has been widely used for decreasing serum LDL-cholesterol levels in patients with hypercholesterolemia. Ezetimibe also reduces the gastrointestinal absorption of plant sterols, thereby also lowering the serum concentrations of plant sterols. This pharmacological property of ezetimibe shows its potential as a novel effective therapy for sitosterolemia. In the current review, we discuss the current therapy for patients with sitosterolemia and present two Japanese adolescent patients with this disease, one of whom underwent percutaneous coronary intervention for accelerated coronary atherosclerosis. Ezetimibe administration in addition to conventional drug therapy successfully reduced serum sitosterol levels by 51.3% and 48.9%, respectively, in the two patients, demonstrating ezetimibe as a novel and potent treatment agent for sitosterolemia that could work additively with conventional drug therapy.
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Affiliation(s)
- Kazumi Tsubakio-Yamamoto
- Department of Cardiovascular Medicine, Osaka University Graduate School of Medicine, Suita, Osaka, Japan
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Fitzgerald ML, Mujawar Z, Tamehiro N. ABC transporters, atherosclerosis and inflammation. Atherosclerosis 2010; 211:361-70. [PMID: 20138281 DOI: 10.1016/j.atherosclerosis.2010.01.011] [Citation(s) in RCA: 139] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2009] [Revised: 01/06/2010] [Accepted: 01/07/2010] [Indexed: 10/19/2022]
Abstract
Atherosclerosis, driven by inflamed lipid-laden lesions, can occlude the coronary arteries and lead to myocardial infarction. This chronic disease is a major and expensive health burden. However, the body is able to mobilize and excrete cholesterol and other lipids, thus preventing atherosclerosis by a process termed reverse cholesterol transport (RCT). Insight into the mechanism of RCT has been gained by the study of two rare syndromes caused by the mutation of ABC transporter loci. In Tangier disease, loss of ABCA1 prevents cells from exporting cholesterol and phospholipid, thus resulting in the build-up of cholesterol in the peripheral tissues and a loss of circulating HDL. Consistent with HDL being an athero-protective particle, Tangier patients are more prone to develop atherosclerosis. Likewise, sitosterolemia is another inherited syndrome associated with premature atherosclerosis. Here mutations in either the ABCG5 or G8 loci, prevents hepatocytes and enterocytes from excreting cholesterol and plant sterols, including sitosterol, into the bile and intestinal lumen. Thus, ABCG5 and G8, which from a heterodimer, constitute a transporter that excretes cholesterol and dietary sterols back into the gut, while ABCA1 functions to export excess cell cholesterol and phospholipid during the biogenesis of HDL. Interestingly, a third protein, ABCG1, that has been shown to have anti-atherosclerotic activity in mice, may also act to transfer cholesterol to mature HDL particles. Here we review the relationship between the lipid transport activities of these proteins and their anti-atherosclerotic effect, particularly how they may reduce inflammatory signaling pathways. Of particular interest are recent reports that indicate both ABCA1 and ABCG1 modulate cell surface cholesterol levels and inhibit its partitioning into lipid rafts. Given lipid rafts may provide platforms for innate immune receptors to respond to inflammatory signals, it follows that loss of ABCA1 and ABCG1 by increasing raft content will increase signaling through these receptors, as has been experimentally demonstrated. Moreover, additional reports indicate ABCA1, and possibly SR-BI, another HDL receptor, may directly act as anti-inflammatory receptors independent of their lipid transport activities. Finally, we give an update on the progress and pitfalls of therapeutic approaches that seek to stimulate the flux of lipids through the RCT pathway.
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Affiliation(s)
- Michael L Fitzgerald
- Lipid Metabolism Unit, Massachusetts General Hospital, Harvard Medical School, 185 Cambridge Street, Boston, MA 02114, USA.
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Abstract
Dysregulation of cholesterol balance contributes significantly to atherosclerotic cardiovascular disease (ASCVD), the leading cause of death in the United States. The intestine has the unique capability to act as a gatekeeper for entry of cholesterol into the body, and inhibition of intestinal cholesterol absorption is now widely regarded as an attractive non-statin therapeutic strategy for ASCVD prevention. In this chapter we discuss the current state of knowledge regarding sterol transport across the intestinal brush border membrane. The purpose of this work is to summarize substantial progress made in the last decade in regards to protein-mediated sterol trafficking, and to discuss this in the context of human disease.
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Affiliation(s)
| | - Liqing Yu
- Address correspondence to: Liqing Yu, M.D., Ph.D., Department of Pathology Section on Lipid Sciences, Wake Forest University School of Medicine, Medical Center Blvd, Winston-Salem, NC 27157-1040, Tel: 336-716-0920, Fax: 336-716-6279,
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54
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Transport of lipids by ABC proteins: interactions and implications for cellular toxicity, viability and function. Chem Biol Interact 2009; 180:327-39. [PMID: 19426719 DOI: 10.1016/j.cbi.2009.04.012] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2008] [Revised: 04/15/2009] [Accepted: 04/24/2009] [Indexed: 12/16/2022]
Abstract
Members of the ATP-binding cassette (ABC) family of membrane-bound transporters are involved in multiple aspects of transport and redistribution of various lipids and their conjugates. Most ABC transporters localize to the plasma membrane; some are associated with liquid-ordered cholesterol-/sphingolipid-rich microdomains, and to a lesser extent the membranes of the Golgi and endoplasmic reticulum. Hence, ABC transporters are well placed to regulate plasma membrane lipid composition and the efflux and redistribution of structural phospholipids and sphingolipids during periods of cellular stress and recovery. ABC transporters can also modulate cellular sensitivity to extrinsic pro-apoptotic signals through regulation of sphingomyelin-ceramide biosynthesis and metabolism. The functionality of ABC transporters is, in turn, modulated by the lipid content of the microdomains in which they reside. Cholesterol, a major membrane microdomain component, is not only a substrate of several ABC transporters, but also regulates ABC activity through its effects on microdomain structure. Several important bioactive lipid mediators and toxic lipid metabolites are also effluxed by ABC transporters. In this review, the complex interactions between ABC transporters and their lipid/sterol substrates will be discussed and analyzed in the context of their relevance to cellular function, toxicity and apoptosis.
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55
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Brown JM, Yu L. Opposing Gatekeepers of Apical Sterol Transport: Niemann-Pick C1-Like 1 (NPC1L1) and ATP-Binding Cassette Transporters G5 and G8 (ABCG5/ABCG8). IMMUNOLOGY, ENDOCRINE & METABOLIC AGENTS IN MEDICINAL CHEMISTRY 2009; 9:18-29. [PMID: 20174593 PMCID: PMC2824437 DOI: 10.2174/187152209788009797] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cholesterol is essential for the growth and function of all mammalian cells, but abnormally elevated levels of circulating low-density lipoprotein cholesterol (LDL-C) are a major risk factor for the development of atherosclerotic cardiovascular disease (ASCVD). For many years, statin drugs have been used to effectively lower LDL-C, but ASCVD still persists in most of the world. Hence, additional LDL-C lowering is now recommended, and the search for therapeutic strategies that work in synergy with statins has now begun. Intestinal absorption and biliary excretion of cholesterol represent two major pathways and continue to show promise as druggable processes. Importantly, both of these complex physiological pathways are tightly regulated by key proteins located at the apical surface of the small intestine and the liver. One of these proteins, the target of ezetimibe Niemann-Pick C1-Like 1 (NPC1L1), was recently identified to be essential for intestinal cholesterol absorption and protect against excessive biliary sterol loss. In direct opposition of NPC1L1, the heterodimer of ATP-binding cassette transporters G5 and G8 (ABCG5/ABCG8) has been shown to be critical for promoting biliary cholesterol secretion in the liver, and has also been proposed to play a direct role in intestinal disposal of sterols. The purpose of this review is to summarize the current state of knowledge regarding the function of these opposing apical cholesterol transporters, and provide a framework for future studies examining these proteins.
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Affiliation(s)
- J. Mark Brown
- Department of Pathology-Section on Lipid Sciences, Wake Forest University School of Medicine, Winston-Salem, North Carolina, USA
| | - Liqing Yu
- Department of Pathology-Section on Lipid Sciences, Wake Forest University School of Medicine, Winston-Salem, North Carolina, USA
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56
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Kidambi S, Patel SB. Cholesterol and non-cholesterol sterol transporters: ABCG5, ABCG8 and NPC1L1: a review. Xenobiotica 2008; 38:1119-39. [PMID: 18668442 DOI: 10.1080/00498250802007930] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
1. Whole-body sterol (cholesterol and xenosterol) balance is delicately regulated by the gastrointestinal tract and liver, which control sterol absorption and excretion, respectively, in addition to the contribution to the cholesterol pool by whole-body cholesterol synthesis. In the past ten years enormous strides have been made not only in establishing that specific transporters mediate the entry and exit of sterols and how these may regulate selective sterol access to the body pools, but also in how these pathways operate to integrate these physiological pathways. 2. The entry of sterols from the gastrointestinal and biliary canalicular lumen into the body is mediated by NPC1L1, which was discovered by a novel method, via a genomics-bioinformatics approach. 3. Identification of the genetic basis responsible for causing sitosterolaemia, characterized by plant sterol accumulation, led to the identification of two half-transporters (ABCG5 and ABCG8) that normally efflux plant sterols (and cholesterol) into the intestinal and biliary lumen for faecal excretion. 4. The objective of this review is to provide up-to-date knowledge on genomics, proteomics and function of these two transporter systems.
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Affiliation(s)
- S Kidambi
- Division of Endocrinology, Metabolism and Clinical Nutrition, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
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Lütjohann D, von Bergmann K, Sirah W, Macdonell G, Johnson-Levonas AO, Shah A, Lin J, Sapre A, Musliner T. Long-term efficacy and safety of ezetimibe 10 mg in patients with homozygous sitosterolemia: a 2-year, open-label extension study. Int J Clin Pract 2008; 62:1499-510. [PMID: 18822021 DOI: 10.1111/j.1742-1241.2008.01841.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
OBJECTIVE To assess the long-term efficacy and safety profile of ezetimibe 10 mg/day in patients with homozygous sitosterolemia. METHODS This was an extension of a multi-centre, randomised, double-blind, placebo-controlled base study in which patients with homozygous sitosterolemia and plasma sitosterol concentrations > 5 mg/dl were randomised 4 : 1 to ezetimibe 10 mg/day (n = 30) or placebo (n = 7) for 8 weeks. Patients who successfully completed the base study with > 80% compliance to study medication were eligible to enter two, successive, 1-year extension studies in which ezetimibe 10 mg/day was administered in an open-label manner. Patients remained on their current treatment regimen (e.g. bile salt-binding resins, statins and low-sterol diet) during the base and extension studies. Patients had to be off ezetimibe therapy for > or = 4 weeks prior to entering the first extension. Efficacy and safety/tolerability parameters were evaluated every 12 and 26 weeks in the first and second years respectively. The primary efficacy end-point was mean percentage change in plasma sitosterol from baseline to study end for the cohort of patients (n = 21) who successfully completed the second extension study. RESULTS Treatment with ezetimibe 10 mg/day led to significant mean percentage reductions from baseline in plasma concentrations of sitosterol (-43.9%; p < 0.001), campesterol (-50.8%; p < 0.001), low-density lipoprotein (LDL) sterols (-13.1%; p < 0.050), total sterols (-10.3%; p < 0.050) and apolipoprotein (apo) B (-10.1%; p < 0.050). No significant changes from baseline were observed for lathosterol, high-density lipoprotein sterol, triglycerides or apo A-1. Maximal reductions in sitosterol and campesterol occurred within the first 52 weeks of treatment and were sustained for the duration of the study. For LDL sterol, total sterols and apo B, maximal reductions were achieved early (by weeks 4 or 16) and waned slightly through the remainder of the study. Overall ezetimibe 10 mg was well tolerated. CONCLUSION In patients with homozygous sitoserolemia, long-term treatment with ezetimibe 10 mg/day for 2 years was effective in reducing plasma plant sterol concentrations with an overall favourable safety and tolerability profile.
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Affiliation(s)
- D Lütjohann
- Department of Clinical Pharmacology, University of Bonn, Bonn, Germany
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58
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Musliner T, Cselovszky D, Sirah W, McCrary Sisk C, Sapre A, Salen G, Lütjohann D, von Bergmann K. Efficacy and safety of ezetimibe 40 mg vs. ezetimibe 10 mg in the treatment of patients with homozygous sitosterolaemia. Int J Clin Pract 2008; 62:995-1000. [PMID: 18484971 DOI: 10.1111/j.1742-1241.2008.01786.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
OBJECTIVE To assess the effect of ezetimibe (EZE) 40 mg/day on non-cholesterol sterol plasma concentrations in patients with homozygous sitosterolaemia (HoS). METHODS This was a multi-centre, randomised, double-blind, placebo-controlled parallel group study. Twenty-seven patients (> or = 18 years) with HoS and plasma sitosterol levels > 5 mg/dl who had been taking EZE 10 mg/day for > or = 6 months prior to enrolment received open-label EZE 10 mg/day for the duration of the study and were randomised 1 : 1 to blinded EZE 30 mg/day (4 x EZE 10 mg tablets; n = 13) or placebo (1 x EZE 10 mg tablet and 3 x matching placebo tablets; n = 14) for 26 weeks. Patients were permitted to remain on other ongoing treatments (e.g. bile salt-binding resin, statin and/or low sterol diet). End-points included median per cent between-group changes from baseline in plasma sitosterol, campesterol, lathosterol, low-density lipoprotein (LDL) sterols, LDL cholesterol (LDL-C) measured by gas-liquid chromatography, and Achilles tendon thickness size measured radiographically. RESULTS Ezetimibe 40 mg/day resulted in median per cent changes from baseline in plasma sitosterol levels of 3.3% vs. -10% in the EZE 10 mg/day group, in plasma campesterol of -0.5% vs. -9.7% in the EZE 10 mg/day group, and in plasma lathosterol of 0.8% vs. 1.1% in the EZE 10 mg/day group (p = ns for all between-group differences). Median per cent changes in the EZE 40 mg/day and EZE 10 mg/day groups, respectively, were 1.3% and 0% for LDL sterols and 2.5% and 4.4% for LDL-C (p = ns for both between-group differences). At study end-point, Achilles tendon thickness remained unchanged in the EZE 40 mg/day group and increased slightly in the EZE 10 mg/day group (2.2%), yielding a non-significant between-group difference of -2.2%. EZE 40 mg/day was generally well tolerated. CONCLUSIONS In patients with HoS, treatment with EZE 40 mg/day for 26 weeks was no more effective at reducing plasma plant sterol concentrations vs. EZE 10 mg/day. EZE 40 mg/day had a safety and tolerability profile similar to EZE 10 mg/day.
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Affiliation(s)
- T Musliner
- Merck Research Laboratories, Rahway, NJ, USA.
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59
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Biros E, Karan M, Golledge J. Genetic variation and atherosclerosis. Curr Genomics 2008; 9:29-42. [PMID: 19424482 PMCID: PMC2674308 DOI: 10.2174/138920208783884856] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2008] [Revised: 02/22/2008] [Accepted: 02/22/2008] [Indexed: 01/06/2023] Open
Abstract
A family history of atherosclerosis is independently associated with an increased incidence of cardiovascular events. The genetic factors underlying the importance of inheritance in atherosclerosis are starting to be understood. Genetic variation, such as mutations or common polymorphisms has been shown to be involved in modulation of a range of risk factors, such as plasma lipoprotein levels, inflammation and vascular calcification. This review presents examples of present studies of the role of genetic polymorphism in atherosclerosis.
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Affiliation(s)
| | | | - Jonathan Golledge
- Vascular Biology Unit, School of Medicine, James Cook University, Townsville, QLD 4811, Australia
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60
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Safety assessment of common foods enriched with natural nonesterified plant sterols. Eur J Clin Nutr 2008; 63:684-91. [DOI: 10.1038/ejcn.2008.11] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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61
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Mannucci L, Guardamagna O, Bertucci P, Pisciotta L, Liberatoscioli L, Bertolini S, Irace C, Gnasso A, Federici G, Cortese C. Beta-sitosterolaemia: a new nonsense mutation in the ABCG5 gene. Eur J Clin Invest 2007; 37:997-1000. [PMID: 17976197 DOI: 10.1111/j.1365-2362.2007.01880.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
BACKGROUND Sitosterolaemia is a rare autosomal recessive disorder characterised by elevated plasma levels of plant sterols and cholesterol. Sitosterolaemia is caused by gene mutations in either of two ATP-binding cassette (ABC) half transporters, ABCG5 and ABCG8. The plasma sterol profile and genetic analysis of a 10-year-old girl who had tuberous xanthomas is the subject of this report. MATERIALS AND METHODS Genomic DNA was isolated from white blood cells from the proband, her family and a control group of healthy people. All exons of ABCG5 and ABCG8 were sequenced. Plasma cholesterol and triglycerides were measured by routine methods. All other plasma sterols were measured by Gas Chromatography coupled to Mass Spectrometry. RESULTS The proband was found to be homozygous for a single nucleotide mutation in exon 10 of the ABCG5 gene, consisting of a C to T transition at nucleotide 1336 of the coding sequence, which results in the premature termination of the ABCG5 protein at amino acid 446 (Arg446X). Her mother and brother were also homozygous for the same mutation and all had elevated plasma beta-sitosterol levels. The father was heterozygous and showed normal beta-sitosterol levels. This mutation was not found in healthy normolipidaemic subjects. CONCLUSIONS We describe a novel nonsense mutation in exon 10 of the ABCG5 gene in a 10-year-old girl showing clinical and biochemical features of sitosterolaemia. This family study broadens the spectrum of the ABCG5/ABCG8 mutations causing sitosterolaemia and helps highlight the correlations between such gene mutations, biochemical phenotype and the development of cardiovascular disease.
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Affiliation(s)
- L Mannucci
- Department of Internal Medicine, University of Tor Vergata, Rome, Italy.
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62
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Nagayama M, Uchida T, Gohara K. Temporal and spatial variations of lipid droplets during adipocyte division and differentiation. J Lipid Res 2007; 48:9-18. [PMID: 17057226 DOI: 10.1194/jlr.m600155-jlr200] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
By capturing time-lapse images of primary stromal-vascular cells (SVCs) derived from rat mesenteric adipose tissue, we revealed temporal and spatial variations of lipid droplets (LDs) in individual SVCs during adipocyte differentiation. Numerous small LDs (a few micrometers in diameter) appeared in the perinuclear region at an early stage of differentiation; subsequently, several LDs grew to more than 10 microm in diameter and occupied the cytoplasm. We have developed a method for the fluorescence staining of LDs in living adipocytes. Time-lapse observation of the stained cells at higher magnification showed that nascent LDs (several 100 nm in diameter) grew into small LDs while moving from lamellipodia to the perinuclear region. We also found that adipocytes are capable of division and that they evenly distribute the LDs between two daughter cells. Immunofluorescence observations of LD-associated proteins revealed that such cell divisions of SVCs occurred even after LDs were coated with perilipin, suggesting that the "final" cell division during adipocyte differentiation occurs considerably later than that characterized in 3T3-L1 cells. Our time-lapse observations have provided a detailed account of the morphological changes that SVCs undergo during adipocyte division and differentiation.
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Affiliation(s)
- Masafumi Nagayama
- Division of Applied Physics, Graduate School of Engineering, Hokkaido University, North 13, West 8, Sapporo 060-8628, Japan.
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63
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Abstract
Numerous epidemiological studies have identified high-density lipoprotein cholesterol (HDL) to be an independent risk factor for coronary heart disease (CHD). HDL is an emerging therapeutic target that could rival the impact of 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase inhibitors (statins) on LDL and CHD risk reduction. HDL metabolism, HDL kinetics, the concentration of various HDL subclasses, and other genetic factors affecting HDL functionality may all contribute to the anti-atherogenic properties of HDL; thus, standard plasma measurement may not capture the full range of HDL effects. Algorithms have been suggested to treat low HDL levels in subgroups of patients; however, no formal HDL target goals or treatment guidelines have been implemented as there is a lack of strong clinical evidence to support effective pharmacologic therapy for primary risk reduction. Available therapies have a modest impact on serum HDL levels; however, emerging therapies could have a more significant influence.
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Affiliation(s)
- Jeffrey J Link
- Department of Internal Medicine, Parkland Memorial Hospital affiliated with the University of Texas, Southwestern Medical Center, Dallas, Texas 75390-9047, USA
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64
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Wang HH, Patel SB, Carey MC, Wang DQH. Quantifying anomalous intestinal sterol uptake, lymphatic transport, and biliary secretion in Abcg8(-/-) mice. Hepatology 2007; 45:998-1006. [PMID: 17393508 PMCID: PMC1906848 DOI: 10.1002/hep.21579] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
UNLABELLED Sitosterolemia is caused by mutations in either ABCG5 or ABCG8, but simultaneous mutations of these genes have never been observed. To explore whether ABCG8, the sterol efflux (hemi-)transporter, plays a major role in determining intestinal absorption efficiency and hepatic secretion rates of cholesterol and sitostanol, we performed direct measurements of the absorption and lymphatic transport of these sterols in mice with chronic biliary and lymphatic fistulae, as well as the transport rates of radiolabeled cholesterol and sitostanol from plasma high-density lipoprotein (HDL) into bile in male Abcg8(-/-) and wild-type mice. We observed that the absorption and lymphatic transport rates of radiolabeled cholesterol and sitostanol were increased by approximately 40% and approximately 500%, respectively, in Abcg8(-/-) mice in the setting of constant intraduodenal infusion of micellar taurocholate and lecithin. Both strains displayed identical intestinal Npc1l1 expression levels and small intestinal transit rates. After 45 minutes of intraduodenal infusion, acute intestinal uptake rates of trace [(14)C]cholesterol and [(3)H]sitostanol were essentially similar in both groups of mice with intact biliary secretion. Furthermore, in wild-type mice, mass transport rate of [(3)H]sitostanol from plasma HDL into bile was significantly faster than that of [(14)C]cholesterol; however, no [(3)H]sitostanol and only traces of [(14)C]cholesterol were detected in bile of Abcg8(-/-) mice. CONCLUSION Deletion of the Abcg8 gene alone significantly increases the mass of intestinal cholesterol and sitostanol absorption and reduces but does not eliminate hepatic secretion of cholesterol. Moreover, the mutation has no influence on acute uptake of cholesterol and sitostanol by the enterocyte nor small intestinal transit time.
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Affiliation(s)
- Helen H. Wang
- Department of Medicine, Liver Center and Gastroenterology Division, Beth Israel Deaconess Medical Center, Harvard Medical School and Harvard Digestive Diseases Center, Boston, MA
| | - Shailendra B. Patel
- Division of Endocrinology, Metabolism, and Clinical Nutrition, Medical College of Wisconsin, Milwaukee, WI
- Clement J. Zablocki Veterans Medical Center, Milwaukee, WI
| | - Martin C. Carey
- Division of Gastroenterology, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School and Harvard Digestive Diseases Center, Boston, MA
| | - David Q.-H. Wang
- Department of Medicine, Liver Center and Gastroenterology Division, Beth Israel Deaconess Medical Center, Harvard Medical School and Harvard Digestive Diseases Center, Boston, MA
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65
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Abstract
The identification of defective structures in the ATP-binding cassette (ABC) transporters ABCG5 and ABCG8 in patients with sitosterolemia suggests that these two proteins are an apical sterol export pump promoting active efflux of cholesterol and plant sterols from enterocytes back into the intestinal lumen for excretion. The newly identified Niemann-Pick C1-like 1 (NPC1L1) protein is also expressed at the apical membrane of enterocytes and plays a crucial role in the ezetimibe-sensitive cholesterol absorption pathway. These findings indicate that cholesterol absorption is a multistep process that is regulated by multiple genes at the enterocyte level and that the efficiency of cholesterol absorption may be determined by the net effect between influx and efflux of intraluminal cholesterol molecules crossing the brush border membrane of the enterocyte. Combination therapy using cholesterol absorption (NPC1L1) inhibitor (ezetimibe) and 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase inhibitors (statins) provides a powerful novel strategy for the prevention and treatment of hypercholesterolemia.
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Affiliation(s)
- David Q-H Wang
- Department of Medicine, Liver Center and Gastroenterology Division, Beth Israel Deaconess Medical Center, Harvard Medical School and Harvard Digestive Diseases Center, Boston, Massachusetts 02115, USA.
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66
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Abstract
PURPOSE OF REVIEW Phytosterols and stanols are plant derivatives that compete with cholesterol for intestinal absorption and thereby lower serum cholesterol concentrations. They have been developed as food additives to help lower serum cholesterol but there is concern that these additives could inadvertently increase cardiovascular risk. This concern arises from the observation that patients with the rare genetic condition phytosterolemia overabsorb phytosterols and develop premature atherosclerosis. This review evaluates the relationship between phytosterol and stanol supplementation and cardiovascular risk. RECENT FINDINGS Plant sterol supplementation produces minimal increases in blood phytosterol concentrations in humans. Recent animal studies suggest that phytosterols reduce atherosclerosis in the Apo-E deficient mouse model. The evidence from human studies is mixed and does not prove or disprove an increase in atherosclerotic risk from serum phytosterol levels. An increase in risk seems unlikely, but additional studies should address this possibility. SUMMARY Phytosterols are effective in lowering low-density lipoprotein-cholesterol levels, and do not appear to increase atherosclerotic risk, but additional research on this topic is necessary.
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Affiliation(s)
- Saji John
- Section of Preventive Cardiology, Division of Cardiology, The Henry Low Heart Center, Hartford Hospital, Hartford, Connecticut 06102, USA
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67
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Hazard SE, Patel SB. Sterolins ABCG5 and ABCG8: regulators of whole body dietary sterols. Pflugers Arch 2007; 453:745-52. [PMID: 16440216 PMCID: PMC1785388 DOI: 10.1007/s00424-005-0040-7] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2005] [Revised: 12/13/2005] [Accepted: 12/23/2005] [Indexed: 12/12/2022]
Abstract
ABCG5 and ABCG8 are two ATP-binding cassette half-transporters that belong to the G family members. They were identified as proteins that are mutated in a rare human disorder, sitosterolemia, and their identification led to the completion of the physiological pathways by which dietary cholesterol, as well as noncholesterol sterols, traffics in the mammalian body. These proteins are likely to function as heterodimers, and current evidence suggests that these proteins are responsible for the majority of sterol secretions into bile, thus may define the long sought-after biliary sterol transporters. This review will focus on some of the backgrounds of this physiology, the genetics and regulation of these genes, as well as our current understanding of their functions. This review will also highlight the current limitations in our knowledge gap.
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Affiliation(s)
- Starr E Hazard
- Biomolecular Computing Resource, Medical University of South Carolina, Charleston, SC 29403, USA
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Guirado SSS, Conejo-Mir JS, Muñoz MA, Wite JB, Fernandez-Freire LR, Ortíz JV. Sitosterol xanthomatosis. J Eur Acad Dermatol Venereol 2007; 21:100-3. [PMID: 17207176 DOI: 10.1111/j.1468-3083.2006.01763.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
BACKGROUND Sitosterolaemia is a lipid disorder in which plasma plant sterol levels are extremely elevated. Sitosterolaemia is clinically characterized by tuberous and tendon xanthomas, premature vascular disease and arthritis. OBJECTIVE To report a case of sitosterolaemia diagnosed by cutaneous manifestations and to review this rare disease. METHODS We report the case of a 60-year-old woman who presented with cutaneous xanthomas, arterial hypertension and polyarthralgias. The patient had had hypercholesterolaemia for many years without reduction of serum cholesterol, despite treatment with fenofibrate. RESULTS Ezetimibe therapy was started, decreasing sitosterol plasmatic levels and tuberous xanthomas after 3 months of treatment. CONCLUSION It is important to detect levels of sitosterol in plasma in patients with premature vascular disease, presence of xanthomas, and uncontrolled hypercholesterolaemia. Ezetimibe therapy is effective.
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Affiliation(s)
- S S S Guirado
- Department of Dermatology, Hospital Universitario Virgen del Rocío, Seville, Spain
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69
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Pinedo S, Vissers MN, von Bergmann K, Elharchaoui K, Lütjohann D, Luben R, Wareham NJ, Kastelein JJP, Khaw KT, Boekholdt SM. Plasma levels of plant sterols and the risk of coronary artery disease: the prospective EPIC-Norfolk Population Study. J Lipid Res 2007; 48:139-44. [PMID: 17074925 DOI: 10.1194/jlr.m600371-jlr200] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Some studies have suggested that a modest increase of plant sterol levels is a risk factor for coronary artery disease (CAD). We studied the relationship between plant sterol levels and CAD risk in a prospective nested case-control study consisting of 373 cases and 758 controls. Sitosterol and campesterol concentrations did not differ between cases and controls [sitosterol, 0.21 vs. 0.21 mg/dl (P = 0.1); campesterol, 0.31 vs. 0.32 mg/dl (P = 0.5)]. The sitosterol-to-cholesterol ratio was significantly lower in cases than in controls (1.19 vs. 1.29 microg/mg; P = 0.008), whereas the campesterol-to-cholesterol ratio did not differ significantly (1.78 vs. 1.88 microg/mg; P = 0.1). Plant sterol concentrations correlated positively with cholesterol levels and inversely with body mass index and triglyceride and lathosterol concentrations. Among individuals in the highest tertile of the sitosterol concentration, the unadjusted odds ratio (OR) for future CAD was 0.75 [95% confidence interval (CI) = 0.56-1.01]. After adjustment for traditional risk factors, the OR was 0.79 (95% CI = 0.56-1.13). For the campesterol concentration, the unadjusted OR was 0.95 (95% CI = 0.71-1.29) and the adjusted OR was 0.97 (95% CI = 0.68-1.39). In this large prospective study, higher levels of plant sterols, at least in the physiological range, do not appear to be adversely related to CAD in apparently healthy individuals.
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Affiliation(s)
- Sabine Pinedo
- Department of Vascular Medicine, Academic Medical Center, Amsterdam, The Netherlands
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70
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Salen G, Starc T, Sisk CM, Patel SB. Intestinal cholesterol absorption inhibitor ezetimibe added to cholestyramine for sitosterolemia and xanthomatosis. Gastroenterology 2006; 130:1853-7. [PMID: 16697747 DOI: 10.1053/j.gastro.2006.02.027] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2005] [Accepted: 02/01/2006] [Indexed: 12/02/2022]
Abstract
Sitosterolemia is a rare, recessively inherited disorder characterized by increased absorption and delayed removal of noncholesterol sterols, which is associated with accelerated atherosclerosis, premature coronary artery disease, hemolysis, and xanthomatosis. Treatments include low-sterol diet and bile salt-binding resins; however, these often do not reduce the xanthomatosis. We examined the effects of the intestinal cholesterol/phytosterol transporter inhibitor ezetimibe added to cholestyramine in a young female patient with sitosterolemia and associated xanthomatosis. The patient was an 11-year-old female with sitosterolemia presenting with prominent xanthomas in the subcutaneous tissue of both elbows who was receiving treatment with cholestyramine 2 g once daily. Bilateral carotid bruits were audible, and a grade II/VI systolic murmur was detected at the left upper sternal border. She also had a low platelet count of 111,000/microL. Ezetimibe 10 mg once daily was added to the patient's ongoing cholestyramine regimen, and she was evaluated for 1 year. The patient followed an unrestricted diet during the 1-year treatment period. After 1 year of treatment with ezetimibe added to ongoing cholestyramine therapy, the patient's plasma sitosterol and campesterol levels decreased by approximately 50%. Her carotid bruits completely resolved, her systolic murmur diminished, and her platelet count rose to 268,000/microL. More remarkably, the tuberous xanthomas on her elbows had completely regressed. Ezetimibe added to ongoing low-dose cholestyramine therapy led to a marked improvement in plasma sterol concentrations, complete regression of xanthomatosis, resolution of carotid bruits, and improvement in cardiac murmur in a young female patient with sitosterolemia.
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Affiliation(s)
- Gerald Salen
- Department of Medicine, UMD-New Jersey Medical School, Newark, New Jersey; Veterans Affairs Medical Center, East Orange, New Jersey, USA.
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72
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Abstract
Phytosterols or plant sterols have long been known to lower serum cholesterol concentrations by competing with dietary and biliary cholesterol for intestinal absorption. Food products containing phytosterols and phytostanols are now available to assist in lowering blood cholesterol levels. In contrast to these possibly beneficial effects of plant sterols, a rare genetic condition called sitosterolemia, an autosomal recessive disorder also known as phytosterolemia, is characterized by over absorption of phytosterols and premature coronary artery and aortic valve disease. Phytosterols have also recently been identified in atheromatous plaque obtained from individuals with apparently normal absorption of plant sterols raising the possibility that phytosterols are a novel atherosclerotic risk factor. This article reviews phytosterols and their relationship to vascular disease.
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Affiliation(s)
- Manoj D Patel
- Section of Preventive Cardiology, Division of Cardiology, Henry Low Heart Center, Hartford Hospital, 80 Seymour Street, Hartford, CT 06102, USA
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73
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Pandit B, Ahn GS, Hazard SE, Gordon D, Patel SB. A detailed Hapmap of the Sitosterolemia locus spanning 69 kb; differences between Caucasians and African-Americans. BMC MEDICAL GENETICS 2006; 7:13. [PMID: 16507104 PMCID: PMC1413519 DOI: 10.1186/1471-2350-7-13] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/25/2005] [Accepted: 02/28/2006] [Indexed: 12/13/2022]
Abstract
Background Sitosterolemia is an autosomal recessive disorder that maps to the sitosterolemia locus, STSL, on human chromosome 2p21. Two genes, ABCG5 and ABCG8, comprise the STSL and mutations in either cause sitosterolemia. ABCG5 and ABCG8 are thought to have evolved by gene duplication event and are arranged in a head-to-head configuration. We report here a detailed characterization of the STSL in Caucasian and African-American cohorts. Methods Caucasian and African-American DNA samples were genotypes for polymorphisms at the STSL locus and haplotype structures determined for this locus Results In the Caucasian population, 13 variant single nucleotide polymorphisms (SNPs) were identified and resulting in 24 different haplotypes, compared to 11 SNPs in African-Americans resulting in 40 haplotypes. Three polymorphisms in ABCG8 were unique to the Caucasian population (E238L, INT10-50 and G575R), whereas one variant (A259V) was unique to the African-American population. Allele frequencies of SNPs varied also between these populations. Conclusion We confirmed that despite their close proximity to each other, significantly more variations are present in ABCG8 compared to ABCG5. Pairwise D' values showed wide ranges of variation, indicating some of the SNPs were in strong linkage disequilibrium (LD) and some were not. LD was more prevalent in Caucasians than in African-Americans, as would be expected. These data will be useful in analyzing the proposed role of STSL in processes ranging from responsiveness to cholesterol-lowering drugs to selective sterol absorption.
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Affiliation(s)
- Bhaswati Pandit
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, STR 541, 114 Doughty Street, Charleston, SC 29403, USA
- Department of Human Genetics, Mount Sinai School of Medicine, New York, NY 10029
| | - Gwang-Sook Ahn
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, STR 541, 114 Doughty Street, Charleston, SC 29403, USA
- Department of Biology, College of Natural Science, Daejeon University, Daejeon 300-716, South Korea
| | - Starr E Hazard
- Biomolecular Computing Resource, Medical University of South Carolina, STR 541, 114 Doughty Street, Charleston, SC 29403, USA
| | - Derek Gordon
- Lab of Statistical Genetics, Rockefeller University, 1230 York Avenue, NY 10021, USA
- Department of Genetics, Rutgers, The State University of New Jersey, 145 Bevier Road, Room 128, Piscataway, NJ 08854-8009
| | - Shailendra B Patel
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, STR 541, 114 Doughty Street, Charleston, SC 29403, USA
- Division of Endocrinology, Metabolism & Clinical Nutrition, Medical College of Wisconsin, 9200 West Wisconsin Avenue, E4950, Milwaukee, WI 53226, USA
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74
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Miettinen TA, Klett EL, Gylling H, Isoniemi H, Patel SB. Liver transplantation in a patient with sitosterolemia and cirrhosis. Gastroenterology 2006; 130:542-7. [PMID: 16472606 PMCID: PMC1391914 DOI: 10.1053/j.gastro.2005.10.022] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/12/2005] [Accepted: 10/12/2005] [Indexed: 12/18/2022]
Abstract
Sitosterolemia (MIM 210250) is a rare genetic disorder caused by disruption of the normal mechanisms that regulate dietary cholesterol absorption and prevent the accumulation of noncholesterol sterols. As a result of this defect, affected individuals accumulate high concentrations of plant sterols in plasma and tissues. They present clinically with tendon or tuberoeruptive xanthomas, premature coronary artery disease, and/or hemolytic anemia. Two genes, ABCG5 and ABCG8, compose the STSL locus, and complete mutation in either, but not both, results in disease. The expression of these genes is confined to the intestine and liver. They are thought to function as sterol efflux pumps. It is not clear which organ, liver or intestine, is of greater importance in maintaining sterol balance with respect to noncholesterol sterols. We report here a case of a patient who presented with "chronic active liver disease" and was found to have sitosterolemia by chance and subsequently underwent orthotopic liver transplantation. Following transplantation, the grossly elevated pretransplantation serum plant sterol levels decreased to values only slightly higher than those of the patient's heterozygous father. This case highlights 2 important features: (1) The liver functions as the predominant organ for maintaining noncholesterol sterol balance (because the intestinal defect was not altered), and (2) a new clinical feature of undiagnosed sitosterolemia may be "idiopathic" liver disease. Because the diagnosis of sitosterolemia is based on specialized plasma analyses, we would propose that some consideration to this diagnosis should be given in appropriate cases.
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75
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Solcà C, Stanga Z, Pandit B, Diem P, Greeve J, Patel SB. Sitosterolaemia in Switzerland: molecular genetics links the US Amish-Mennonites to their European roots. Clin Genet 2005; 68:174-8. [PMID: 15996216 PMCID: PMC1201539 DOI: 10.1111/j.1399-0004.2005.00472.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Sitosterolaemia is a rare autosomal recessive disease characterized by increased intestinal absorption of plant sterols, decreased hepatic excretion into bile and elevated concentrations in plasma phytosterols. Homozygous or compound heterozygous loss of function mutations in either of the ATP-binding cassette (ABC) proteins ABCG5 and ABCG8 explain the increased absorption of plant sterols. Here we report a Swiss index patient with sitosterolaemia, who presented with the classical symptoms of xanthomas, but also had mitral and aortic valvular heart disease. Her management over the last 20 years included a novel therapeutic approach of high-dose cholesterol feeding that was semi-effective. Mutational and extended haplotype analyses showed that our patient shared this haplotype with that of the Amish-Mennonite sitosterolaemia patients, indicating they are related ancestrally.
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Affiliation(s)
- C Solcà
- Division of Endocrinology, Diabetes and Medical Genetics STR 541, Medical University of South Carolina, Charleston, SC, USA
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76
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Chen J, Batta A, Zheng S, Fitzgibbon WR, Ullian ME, Yu H, Tso P, Salen G, Patel SB. The missense mutation in Abcg5 gene in spontaneously hypertensive rats (SHR) segregates with phytosterolemia but not hypertension. BMC Genet 2005; 6:40. [PMID: 16026620 PMCID: PMC1190168 DOI: 10.1186/1471-2156-6-40] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2005] [Accepted: 07/18/2005] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Sitosterolemia is a recessively inherited disorder in humans that is associated with premature atherosclerotic disease. Mutations in ABCG5 or ABCG8, comprising the sitosterolemia locus, STSL, are now known to cause this disease. Three in-bred strains of rats, WKY, SHR and SHRSP, are known to be sitosterolemic, hypertensive and they carry a missense 'mutation' in a conserved residue of Abcg5, Gly583Cys. Since these rat strains are also know to carry mutations at other genetic loci and the extent of phytosterolemia is only moderate, it is important to verify that the mutations in Abcg5 are causative for phytosterolemia and whether they contribute to hypertension. METHODS To investigate whether the missense change in Abcg5 is responsible for the sitosterolemia we performed a segregation analysis in 103 F2 rats from a SHR x SD cross. Additionally, we measured tail-cuff blood pressure and measured intestinal lipid transport to identify possible mechanisms whereby this mutation causes sitosterolemia. RESULTS Segregation analysis showed that the inheritance of the Gly583Cys mutation Abcg5 segregated with elevated plant sterols and this pattern was recessive, proving that this genetic change is responsible for the sitosterolemia in these rat strains. Tail-cuff monitoring of blood pressure in conscious animals showed no significant differences between wild-type, heterozygous and homozygous mutant F2 rats, suggesting that this alteration may not be a significant determinant of hypertension in these rats on a chow diet. CONCLUSION This study shows that the previously identified Gly583Cys change in Abcg5 in three hypertension-susceptible rats is responsible for the sitosterolemia, but may not be a major determinant of blood pressure in these rats.
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Affiliation(s)
- Jianliang Chen
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, STR 541, 114 Doughty Street, Charleston, SC 29403, USA
| | - Ashok Batta
- Research Service and Medical Service, Department of Veterans Affairs Medical Center, East Orange, NJ 07019, USA
| | - Shuqin Zheng
- Department of Pathology and laboratory Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267. USA
| | - Wayne R Fitzgibbon
- Division of Nephrology, Medical University of South Carolina, Charleston, SC 29403, USA
| | - Michael E Ullian
- Division of Nephrology, Medical University of South Carolina, Charleston, SC 29403, USA
| | - Hongwei Yu
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, STR 541, 114 Doughty Street, Charleston, SC 29403, USA
| | - Patrick Tso
- Department of Pathology and laboratory Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267. USA
| | - Gerald Salen
- Research Service and Medical Service, Department of Veterans Affairs Medical Center, East Orange, NJ 07019, USA
| | - Shailendra B Patel
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, STR 541, 114 Doughty Street, Charleston, SC 29403, USA
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77
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Abstract
The recent discovery of transporters in the intestinal mucosa and the canalicular membrane has given new insights into the regulation of intestinal absorption as well as the biliary output of cholesterol and plant sterols. The 2 adenosine triphosphate (ATP)-binding cassette (ABC) half-transporters ABCG5 and ABCG8 are expressed in the mucosa cells and the canalicular membrane, and they resecrete sterols, especially absorbed plant sterols, back into the intestinal lumen and from the liver into bile. Defects of either of these cotransporters lead to the rare inherited disease of phytosterolemia, which is clinically defined by hyperabsorption and diminished biliary excretion of plant sterols. Furthermore, it has been recently demonstrated that the Niemann-Pick C1-Like 1 (NPC1L1) transporter is most likely responsible for the transport of cholesterol and plant sterols from the brush border membrane into the intestinal mucosa. Ezetimibe interferes with NPC1L1, reducing the intestinal uptake of cholesterol and plant sterols. These new findings contribute to our understanding of cholesterol and plant sterol concentrations in serum, and the effect of dietary and drug intervention to reduce serum concentrations of sterols.
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78
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Hui DY, Howles PN. Molecular mechanisms of cholesterol absorption and transport in the intestine. Semin Cell Dev Biol 2005; 16:183-92. [PMID: 15797829 DOI: 10.1016/j.semcdb.2005.01.003] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Many enzymes and transport proteins participate in cholesterol absorption. This review summarizes recent results on several proteins that are important for each step of the cholesterol absorption pathway, including the important roles of: (i) pancreatic triglyceride lipase (PTL), carboxyl ester lipase (CEL), and ileal bile acid transporter in determining the rate of cholesterol absorption; (ii) ATP binding cassette (ABC) transporters and the Niemann-Pick C-1 like-1 (NPC1L1) protein as intestinal membrane gatekeepers for cholesterol efflux and influx; and (iii) intracellular membrane vesicles and transport proteins in lipid trafficking through intracellular compartments prior to lipoprotein assembly and secretion to plasma circulation.
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Affiliation(s)
- David Y Hui
- Department of Pathology, University of Cincinnati Genome Research Institute, Cincinnati, OH 45237-0507, USA.
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79
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Abstract
The expanding market of 'functional foods' containing plant sterols and stanols has focused interest on their cholesterol-lowering effects as well on possible adverse effects. Trials of cholesterol lowering demonstrate that intake of 2 g/day of plant sterols and stanols reduces serum low-density lipoprotein (LDL) cholesterol concentrations by approximately 10%. Safety concerns regarding elevations in serum plant sterol levels, or effects on fat-soluble vitamin absorption or hypothetical effects on serum sex hormone balance have received attention and been addressed in studies. Plant sterol (but not stanol) supplementation increased serum plant sterol concentrations but these levels remained much lower than those observed in homozygous sitosterolemia making an adverse health effect unlikely. Prolonged statin therapy also causes elevations in all cholesterol-adjusted plant sterol levels as well as small but significant elevations in serum unadjusted campesterol levels from baseline. This is probably caused by a statin-induced reduction in biliary cholesterol efflux resulting in a diminished intestinal cholesterol pool. The diminished competition with cholesterol molecules allows more plant sterol molecules to become incorporated in mixed micelles facilitating their uptake in enterocytes. With the exception of beta-carotene, reductions in serum concentrations of fat-soluble (pro)vitamins are usually abolished by adjustment for cholesterol suggesting that they reflect reductions in carrier lipoproteins, mainly LDL. The small reductions in serum beta-carotene are not regarded as a major concern, nor have any adverse effects on sex hormone metabolism been demonstrated apart from parenteral administration of large doses in experimental animals. However, as increasing consumer populations become exposed to a large variety of food products enriched with plant sterols and stanols the likelihood of rare adverse effects increases and surveillance is necessary.
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Affiliation(s)
- M J Tikkanen
- Department of Medicine, Division of Cardiology, Helsinki University Central Hospital, Finland.
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80
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Sudhop T, Lütjohann D, von Bergmann K. Sterol transporters: targets of natural sterols and new lipid lowering drugs. Pharmacol Ther 2004; 105:333-41. [PMID: 15737409 DOI: 10.1016/j.pharmthera.2004.10.011] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/28/2004] [Indexed: 12/18/2022]
Abstract
Recent insights in the role of ATP-binding cassette (ABC) transporters ABCG5 and ABCG8, the discovery of ezetimibe, the first approved direct cholesterol absorption inhibitor, as well as the identification of Niemann-Pick C1 Like 1 (NPC1L1) protein as sterol transporter in the gut, focused attention on sterol transport processes in the small intestine and the liver. The identification of defective structures in the ABCG5 or ABCG8 transporters in patients with the rare disease of sitosterolemia elucidated their role as sterol efflux pumps regulating at least in parts the intestinal sterol absorption and the hepatic sterol output. ABCG5 and ABCG8 themselves are regulated by cholesterol via liver X receptors (LXRs), which are also activated by oxysterols and some derivatives of plant sterols. NPC1L1 could recently be identified as a major sterol transporter for the intestinal uptake of cholesterol as well as plant sterols. Studies in NPC1L1 knockout mice indicate that this transporter is essential for the intestinal uptake of sterols and that NPC1L1 might also be involved in the mechanism of action of ezetimibe. However, studies with photoreactive cholesterol as well as with photoreactive ezetimibe analogues suggest that other processes might also be involved in the mechanism of action of ezetimibe.
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Affiliation(s)
- Thomas Sudhop
- Department of Clinical Pharmacology, University of Bonn, Sigmund-Freud-Str. 25, 53105 Bonn, Germany.
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81
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Abstract
Sitosterolemia is a rare autosomal recessive disorder of lipoprotein metabolism characterized by xanthomas and increased plasma concentrations of plant sterols, such as sitosterol. Causative mutations occur in either the ABCG5 or ABCG8 gene, each of which encodes a sterol half-transporter expressed in the intestine. We report five Canadian subjects with nonsense mutations in these half-transporters: four related Caucasian subjects were homozygous for the ABCG8 S107X mutation, and one unrelated Japanese-Canadian subject was homozygous for a complex insertion/deletion (I/D) mutation in ABCG5 exon 3. A female subject with each mutation was symptomatic with coronary atherosclerosis: a 5-year-old ABCG8 S107X homozygote and a 75-year-old ABCG5 exon 3 I/D homozygote; these represent the extreme ends of the spectrum of vascular involvement in sitosterolemia. The largest reductions in plasma concentrations of sitosterol and LDL-cholesterol were seen with ezetimibe or bile acid sequestrant treatment, and less dramatic reductions were seen with statin drug treatment. These findings extend the range of clinical phenotypes in sitosterolemia caused by nonsense mutations in either ABCG5 or ABCG8.
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Affiliation(s)
- Jian Wang
- Robarts Research Institute and University of Western Ontario, London, Ontario, Canada
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82
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Sudhop T, von Bergmann K. Sitosterolemia—a rare disease. ACTA ACUST UNITED AC 2004; 93:921-8. [PMID: 15599566 DOI: 10.1007/s00392-004-0165-2] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2004] [Accepted: 08/16/2004] [Indexed: 10/25/2022]
Abstract
Elevated plasma plant sterol concentrations, xanthomatosis, and accelerated-often fatal-atherosclerosis at young age are the major findings in patients with homozygous sitosterolemia. A defect in the ABCG5 or ABCG8 co-transporter gene locus (STSL) causes an increased intestinal absorption and a decreased biliary elimination of all sterols, plant sterols as well as cholesterol, leading to a 50 to 200-fold increase in plasma plant sterol concentrations. A few recent publications indicate that even moderately elevated plasma plant sterol levels might be associated with an increased risk of atherosclerosis. This raises the question whether plant sterols themselves might be atherogenic or whether elevated plasma levels are a marker for a decreased ABCG5/G8 transporter activity which itself causes an increased risk for atherosclerosis. However, current data are too few to conclude that elevated plant sterol concentrations in plasma are an additional risk factor for coronary heart disease. But especially young patients suffering from xanthomatosis and/or atherosclerotic diseases with only mildly or moderately elevated plasma cholesterol should be screened for sitosterolemia by measurement of plasma plant sterol levels.
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Affiliation(s)
- T Sudhop
- Universitätsklinikum Bonn, Abteilung für Klinische Pharmakologie, European Network for inherited Dyslipidaemias-Cerebrotendinous Xanthomatosis and Phytosterolemia, Sigmund-Freud-Str. 25, 53105 Bonn, Germany.
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83
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Pollin TI, Hsueh WC, Steinle NI, Snitker S, Shuldiner AR, Mitchell BD. A genome-wide scan of serum lipid levels in the Old Order Amish. Atherosclerosis 2004; 173:89-96. [PMID: 15177127 DOI: 10.1016/j.atherosclerosis.2003.11.012] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2003] [Accepted: 11/05/2003] [Indexed: 10/26/2022]
Abstract
Elevated serum low density lipoprotein cholesterol (LDL-C) and triglyceride (TG) and decreased high density lipoprotein cholesterol (HDL-C) levels are established risk factors for cardiovascular disease (CVD). To identify quantitative trait loci influencing lipid levels, we conducted genome-wide linkage analyses of total serum cholesterol (TSC), HDL-C, ln-transformed TG (LNTG) and LDL-C levels in 612 individuals from 28 families of the Amish Family Diabetes Study (AFDS). Subjects were genotyped for 373 microsatellite markers covering all 22 autosomes and the X chromosome at an average density of 9.7 centimorgans. All lipid traits exhibited moderate estimated heritability (h2 +/- S.E.): TSC, 0.63 +/- 0.11; HDL-C, 0.54 +/- 0.08; LNTG, 0.37 +/- 0.08; LDL-C, 0.62 +/- 0.10. The highest logarithm of the odds (LOD) score observed was 2.47 (P = 0.0003), at 3p25 for LDL-C. LOD scores exceeding 2.0 (P < 0.001) were also observed at 2p23 (LOD = 2.17) and 19p13 (LOD = 2.23) for LDL-C, and at 11q23 (LOD = 2.03) for LNTG. Three additional regions exhibited LOD scores greater than 1.5, corresponding to a P-value of <0.005. Many of the regions suggestively linked in this genome-wide scan contain genes encoding proteins with established roles in lipid metabolism, including apolipoproteins, peroxisome proliferater-activated receptor-gamma and the LDL receptor.
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Affiliation(s)
- Toni I Pollin
- Division of Endocrinology, Diabetes, and Nutrition, University of Maryland School of Medicine, 660 W Redwood Street, Room 492, Baltimore, MD 21201, USA
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84
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Berger A, Jones PJH, Abumweis SS. Plant sterols: factors affecting their efficacy and safety as functional food ingredients. Lipids Health Dis 2004; 3:5. [PMID: 15070410 PMCID: PMC419367 DOI: 10.1186/1476-511x-3-5] [Citation(s) in RCA: 160] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2004] [Accepted: 04/07/2004] [Indexed: 11/10/2022] Open
Abstract
Plant sterols are naturally occurring molecules that humanity has evolved with. Herein, we have critically evaluated recent literature pertaining to the myriad of factors affecting efficacy and safety of plant sterols in free and esterified forms. We conclude that properly solubilized 4-desmetyl plant sterols, in ester or free form, in reasonable doses (0.8-1.0 g of equivalents per day) and in various vehicles including natural sources, and as part of a healthy diet and lifestyle, are important dietary components for lowering low density lipoprotein (LDL) cholesterol and maintaining good heart health. In addition to their cholesterol lowering properties, plant sterols possess anti-cancer, anti-inflammatory, anti-atherogenicity, and anti-oxidation activities, and should thus be of clinical importance, even for those individuals without elevated LDL cholesterol. The carotenoid lowering effect of plant sterols should be corrected by increasing intake of food that is rich in carotenoids. In pregnant and lactating women and children, further study is needed to verify the dose required to decrease blood cholesterol without affecting fat-soluble vitamins and carotenoid status.
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Affiliation(s)
- Alvin Berger
- Head, Biochemical Profiling, Paradigm Genetics, P.O. Box 14528, Research Triangle Park, North Carolina, 27709-4528, USA
| | - Peter JH Jones
- School of Dietetics and Human Nutrition, McGill University, 21,111 Lakeshore Road, Ste-Anne-de-Bellevue, Quebec, H9X3V9, Canada
| | - Suhad S Abumweis
- School of Dietetics and Human Nutrition, McGill University, 21,111 Lakeshore Road, Ste-Anne-de-Bellevue, Quebec, H9X3V9, Canada
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85
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Klett EL, Lu K, Kosters A, Vink E, Lee MH, Altenburg M, Shefer S, Batta AK, Yu H, Chen J, Klein R, Looije N, Oude-Elferink R, Groen AK, Maeda N, Salen G, Patel SB. A mouse model of sitosterolemia: absence of Abcg8/sterolin-2 results in failure to secrete biliary cholesterol. BMC Med 2004; 2:5. [PMID: 15040800 PMCID: PMC394351 DOI: 10.1186/1741-7015-2-5] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/17/2003] [Accepted: 03/24/2004] [Indexed: 11/24/2022] Open
Abstract
BACKGROUND Mutations in either of two genes comprising the STSL locus, ATP-binding cassette (ABC)-transporters ABCG5 (encoding sterolin-1) and ABCG8 (encoding sterolin-2), result in sitosterolemia, a rare autosomal recessive disorder of sterol trafficking characterized by increased plasma plant sterol levels. Based upon the genetics of sitosterolemia, ABCG5/sterolin-1 and ABCG8/sterolin-2 are hypothesized to function as obligate heterodimers. No phenotypic difference has yet been described in humans with complete defects in either ABCG5 or ABCG8. These proteins, based upon the defects in humans, are responsible for regulating dietary sterol entry and biliary sterol secretion. METHODS In order to mimic the human disease, we created, by a targeted disruption, a mouse model of sitosterolemia resulting in Abcg8/sterolin-2 deficiency alone. Homozygous knockout mice are viable and exhibit sitosterolemia. RESULTS Mice deficient in Abcg8 have significantly increased plasma and tissue plant sterol levels (sitosterol and campesterol) consistent with sitosterolemia. Interestingly, Abcg5/sterolin-1 was expressed in both liver and intestine in Abcg8/sterolin-2 deficient mice and continued to show an apical expression. Remarkably, Abcg8 deficient mice had an impaired ability to secrete cholesterol into bile, but still maintained the ability to secrete sitosterol. We also report an intermediate phenotype in the heterozygous Abcg8+/- mice that are not sitosterolemic, but have a decreased level of biliary sterol secretion relative to wild-type mice. CONCLUSION These data indicate that Abcg8/sterolin-2 is necessary for biliary sterol secretion and that loss of Abcg8/sterolin-2 has a more profound effect upon biliary cholesterol secretion than sitosterol. Since biliary sitosterol secretion is preserved, although not elevated in the sitosterolemic mice, this observation suggests that mechanisms other than by Abcg8/sterolin-2 may be responsible for its secretion into bile.
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Affiliation(s)
- Eric L Klett
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, Charleston, SC 29403, USA
| | - Kangmo Lu
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, Charleston, SC 29403, USA
| | - Astrid Kosters
- Department of Experimental Hepatology, AMC Liver Center, Academic Medical Center, Amsterdam 1105 BK, The Netherlands
| | - Edwin Vink
- Department of Experimental Hepatology, AMC Liver Center, Academic Medical Center, Amsterdam 1105 BK, The Netherlands
| | - Mi-Hye Lee
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, Charleston, SC 29403, USA
| | - Michael Altenburg
- Department of Pathology, School of Medicine, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Sarah Shefer
- Department of Medicine, UMD-New Jersey Medical School, Newark, NJ 07013, USA
| | - Ashok K Batta
- Research Service and Medical Service, Department of Veterans Affairs Medical Center, East Orange, NJ 07019, USA
| | - Hongwei Yu
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, Charleston, SC 29403, USA
| | - Jianliang Chen
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, Charleston, SC 29403, USA
| | - Richard Klein
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, Charleston, SC 29403, USA
| | - Norbert Looije
- Department of Experimental Hepatology, AMC Liver Center, Academic Medical Center, Amsterdam 1105 BK, The Netherlands
| | - Ronald Oude-Elferink
- Department of Experimental Hepatology, AMC Liver Center, Academic Medical Center, Amsterdam 1105 BK, The Netherlands
| | - Albert K Groen
- Department of Experimental Hepatology, AMC Liver Center, Academic Medical Center, Amsterdam 1105 BK, The Netherlands
| | - Nobuyo Maeda
- Department of Pathology, School of Medicine, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Gerald Salen
- Department of Medicine, UMD-New Jersey Medical School, Newark, NJ 07013, USA
- Research Service and Medical Service, Department of Veterans Affairs Medical Center, East Orange, NJ 07019, USA
| | - Shailendra B Patel
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, Charleston, SC 29403, USA
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86
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Abstract
AIM Dietary cholesterol absorption, endogenous cholesterol synthesis and biliary cholesterol excretion regulate whole body cholesterol balance as a result of biotransformation into bile acids or direct cholesterol excretion. Recent studies have significantly advanced our understanding of intestinal sterol absorption at molecular level. This review concentrates on two major issues: the mechanisms of sterol absorption, and the currently available or experimental drugs that affect this pathway. DATA SYNTHESIS Nuclear hormone receptors, such as the liver X, farnesoid X and retinoid X receptors, regulate the absorption of dietary sterols by modulating the transcription of several genes involved in cholesterol metabolism, The ABC proteins transport dietary cholesterol from enterocytes back to the intestinal lumen, thus limiting the amount of absorbed cholesterol. By means of the same mechanism, ABC transporters also provide an efficient barrier against the absorption of plant sterols. Phytosterols, bile acid sequestrants, ezetimibe and ACAT inhibitors are possible means of affecting these pathways. CONCLUSION In addition to providing an insight into the molecular mechanisms of sterol absorption, these recent findings may lead to new therapeutic options for the treatment of hypercholesterolemia. This is particularly true in the case of patients at high risk of coronary artery disease requiring aggressive lipid-lowering therapy combining a statin with drugs affecting cholesterol absorption in order to ensure the optimal management of dyslipidemia.
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Affiliation(s)
- G D Norata
- Department of Pharmacological Sciences, University of Milano, Milano, Italy
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87
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Sehayek E. Genetic regulation of cholesterol absorption and plasma plant sterol levels: commonalities and differences. J Lipid Res 2003; 44:2030-8. [PMID: 12897193 DOI: 10.1194/jlr.r300008-jlr200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The molecular basis of the processes that control two closely related traits, the absorption of cholesterol from the intestines and plasma plant sterol levels, are only partially understood. The discovery that mutations in two novel hemitransporters, ATP binding cassette transporter G5 (ABCG5) and ABCG8, underlie a rare inborn error in plant sterol metabolism, beta-sitosterolemia, represents a major breakthrough in this field. More recently, genetic studies in the mouse that mapped loci in linkage with cholesterol absorption and plasma plant sterol levels and studies in humans that examined the relationship of plasma plant sterol levels to sequence variation in the ABCG5/ABCG8 locus suggested the involvement of other genes. Moreover, studies in beta-sitosterolemic patients, in ABCG5/ABCG8-targeted animals, and on a newly developed cholesterol absorption inhibitor, ezetimibe, suggest commonalities and differences in the regulation of the two traits. This review summarizes the evidence for genetic control of cholesterol absorption and plasma plant sterol levels, presents the evidence for commonalities and differences between the two traits, and discusses recent developments and future perspectives in this field.
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Affiliation(s)
- Ephraim Sehayek
- Laboratory of Biochemical Genetics and Metabolism, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
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88
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Hobbs HH, Graf GA, Yu L, Wilund KR, Cohen JC. Genetic defenses against hypercholesterolemia. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2003; 67:499-505. [PMID: 12858576 DOI: 10.1101/sqb.2002.67.499] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
MESH Headings
- ATP Binding Cassette Transporter, Subfamily G, Member 5
- ATP Binding Cassette Transporter, Subfamily G, Member 8
- ATP-Binding Cassette Transporters/genetics
- ATP-Binding Cassette Transporters/metabolism
- Adaptor Proteins, Signal Transducing
- Adaptor Proteins, Vesicular Transport/genetics
- Adaptor Proteins, Vesicular Transport/metabolism
- Bile/metabolism
- Chromosomes, Human, Pair 1/genetics
- Endocytosis
- Genes, Recessive
- Humans
- Hyperlipoproteinemia Type II/genetics
- Hyperlipoproteinemia Type II/metabolism
- Lipoproteins/genetics
- Lipoproteins/metabolism
- Mutation
- Receptors, LDL/metabolism
- Sitosterols/blood
- Sterols/metabolism
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Affiliation(s)
- H H Hobbs
- McDermott Center for Human Growth and Development, Department of Molecular Genetics and Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
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89
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Abstract
PURPOSE OF REVIEW This review discusses recent progress in the role of ATP-binding cassette proteins ABCG5 and G8 in dietary sterol absorption, excretion and pathogenesis of cardiovascular disease. RECENT FINDINGS Identification of the genetic defect(s) underlying sitosterolemia has led to a renewed interest in the mechanisms of sterol absorption and biliary excretion. Mutations in ABCG5 (encoding sterolin-1) or ABCG8 (encoding sterolin-2) cause this disease. These proteins are thought to function by preventing dietary noncholesterol sterols from being retained by the body and for cholesterol excretion into bile. SUMMARY Despite improvements in treatments for hypercholesterolemia with cholesterol lowering agents, cardiovascular disease still remains highly prevalent. This has prompted many to consider that molecules other than cholesterol may be better biomarkers for this disease and targeting these more directly may allow us to develop more effective therapies. Ideally, if such a biomarker were also the bioactive molecule that is key to initiating/propagating the atherosclerosis pathogenic pathway, this would allow us to develop an optimal predictor and monitor of the disease process. One source of such molecules could come from our diet, with potential candidates such as noncholesterol sterols, oxysterols, oxidized sterols or some as yet unidentified dietary bioactive molecule. Nature has evolved a protective mechanism by which such molecules are kept out of the body, thereby reducing the negative effects of these compounds. The newly identified sterolin proteins involved in the absorption and excretion of dietary sterols may fit this bill. If so, we would speculate that a better biomarker may be lurking within their substrate specificities.
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Affiliation(s)
- Eric L Klett
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, Charleston, South Carolina 29403, USA.
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90
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Abstract
Sitosterolemia was first described 28 years ago in two sisters. They had tendonxanthomas, normal plasma cholesterol levels, and elevated plant sterol levels. The high plant sterol levels were shown to be due to the increased absorption and delayed removal of plant sterols from the body. The increased absorption of plant sterols does not affect cholesterol absorption in these patients. However, cholesterol biosynthesis pathway is downregulated and turnover rates are reduced. Bile acid binding resins and ileal bypass surgery are effective treatments for sitosterolemic patients, whereas statins are ineffective. Sitosterolemia is inherited as a recessive trait. Recent studies have shown that mutations in ABCG5 and ABCG8 genes contribute to sitosterolemia. Most likely, ABCG5 and ABCG8 proteins function as obligate heterodimers and play a role in the absorption of plant sterol or control their rate of absorption.
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Affiliation(s)
- Gerald Salen
- VA Medical Center, 385 Tremont Avenue, East Orange, NJ 07081, USA.
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91
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Yu H, Pandit B, Klett E, Lee MH, Lu K, Helou K, Ikeda I, Egashira N, Sato M, Klein R, Batta A, Salen G, Patel SB. The rat STSL locus: characterization, chromosomal assignment, and genetic variations in sitosterolemic hypertensive rats. BMC Cardiovasc Disord 2003; 3:4. [PMID: 12783625 PMCID: PMC165443 DOI: 10.1186/1471-2261-3-4] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2003] [Accepted: 06/03/2003] [Indexed: 11/21/2022] Open
Abstract
BACKGROUND Elevated plant sterol accumulation has been reported in the spontaneously hypertensive rat (SHR), the stroke-prone spontaneously hypertensive rat (SHRSP) and the Wistar-Kyoto (WKY) rat. Additionally, a blood pressure quantitative trait locus (QTL) has been mapped to rat chromosome 6 in a New Zealand genetically hypertensive rat strain (GH rat). ABCG5 and ABCG8 (encoding sterolin-1 and sterolin-2 respectively) have been shown to be responsible for causing sitosterolemia in humans. These genes are organized in a head-to-head configuration at the STSL locus on human chromosome 2p21. METHODS To investigate whether mutations in Abcg5 or Abcg8 exist in SHR, SHRSP, WKY and GH rats, we initiated a systematic search for the genetic variation in coding and non-coding region of Abcg5 and Abcg8 genes in these strains. We isolated the rat cDNAs for these genes and characterized the genomic structure and tissue expression patterns, using standard molecular biology techniques and FISH for chromosomal assignments. RESULTS Both rat Abcg5 and Abcg8 genes map to chromosome band 6q12. These genes span ~40 kb and contain 13 exons and 12 introns each, in a pattern identical to that of the STSL loci in mouse and man. Both Abcg5 and Abcg8 were expressed only in liver and intestine. Analyses of DNA from SHR, SHRSP, GH, WKY, Wistar, Wistar King A (WKA) and Brown Norway (BN) rat strains revealed a homozygous G to T substitution at nucleotide 1754, resulting in the coding change Gly583Cys in sterolin-1 only in rats that are both sitosterolemic and hypertensive (SHR, SHRSP and WKY). CONCLUSIONS The rat STSL locus maps to chromosome 6q12. A non-synonymous mutation in Abcg5, Gly583Cys, results in sitosterolemia in rat strains that are also hypertensive (WKY, SHR and SHRSP). Those rat strains that are hypertensive, but not sitosterolemic (e.g. GH rat) do not have mutations in Abcg5 or Abcg8. This mutation allows for expression and apparent apical targeting of Abcg5 protein in the intestine. These rat strains may therefore allow us to study the pathophysiological mechanisms involved in the human disease of sitosterolemia.
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Affiliation(s)
- Hongwei Yu
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, STR 541, 114 Doughty Street, Charleston, SC 29403, USA
| | - Bhaswati Pandit
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, STR 541, 114 Doughty Street, Charleston, SC 29403, USA
| | - Eric Klett
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, STR 541, 114 Doughty Street, Charleston, SC 29403, USA
| | - Mi-Hye Lee
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, STR 541, 114 Doughty Street, Charleston, SC 29403, USA
| | - Kangmo Lu
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, STR 541, 114 Doughty Street, Charleston, SC 29403, USA
| | - Khalil Helou
- Genetics Branch, Center for Cancer Research, National Cancer, Institute/NIH, Bethesda, Maryland 20892, USA
- Department of Oncology, Institute of Selected Clinical Sciences, Goteborg University, SE 413 45, Gothenburg, Sweden
| | - Ikuo Ikeda
- Laboratory of Nutrition Chemistry, Department of Bioscience and Biotechnology, Faculty of Agriculture, Graduate School Kyushu University, Fukuoka, 812-8581, Japan
| | - Nami Egashira
- Laboratory of Nutrition Chemistry, Department of Bioscience and Biotechnology, Faculty of Agriculture, Graduate School Kyushu University, Fukuoka, 812-8581, Japan
| | - Masao Sato
- Laboratory of Nutrition Chemistry, Department of Bioscience and Biotechnology, Faculty of Agriculture, Graduate School Kyushu University, Fukuoka, 812-8581, Japan
| | - Richard Klein
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, STR 541, 114 Doughty Street, Charleston, SC 29403, USA
| | - Ashok Batta
- Research Service and Medical Service, Department of Veterans Affairs Medical Center, East Orange, NJ, USA
| | - Gerald Salen
- Research Service and Medical Service, Department of Veterans Affairs Medical Center, East Orange, NJ, USA
| | - Shailendra B Patel
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, STR 541, 114 Doughty Street, Charleston, SC 29403, USA
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92
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Miettinen TA, Gylling H, Lindbohm N, Miettinen TE, Rajaratnam RA, Relas H. Serum noncholesterol sterols during inhibition of cholesterol synthesis by statins. THE JOURNAL OF LABORATORY AND CLINICAL MEDICINE 2003; 141:131-7. [PMID: 12577049 DOI: 10.1067/mlc.2003.9] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We studied changes in serum cholestanol and plant sterols (indexes of cholesterol absorption) and cholesterol precursors (indexes of cholesterol synthesis) in response to cholesterol reduction by way of 1 year's treatment with atorvastatin (n = 102) and simvastatin (n = 105) treatments in patients with coronary heart disease. Serum cholesterol levels and ratios of the precursor sterols to cholesterol after 1 year of treatment were reduced in proportion to the pretreatment values (33% +/- 1% by simvastatin and 36% +/- 1% by atorvastatin; P <.01 for difference between groups) for cholesterol; the respective reductions in the precursor sterol:cholesterol ratios were also higher with atorvastatin (50% +/- 2% for lathosterol) than with simvastatin (42% +/- 1%; P <.01 between groups), but the ratio of squalene to cholesterol was increased (17% +/- 5%, P <.001) by atorvastatin. Plant sterol concentrations were gradually increased by atorvastatin but decreased initially by simvastatin. However, their ratios with respect to cholesterol were increased by as much as 82% with atorvastatin and by as much as 39% with simvastatin. In conclusion, effective inhibition of cholesterol synthesis and subsequent reduction in serum cholesterol levels by statins lead to increases in serum plant-sterol levels, probably as a result of reduced biliary secretion and enhanced absorption of these sterols. Because serum plant sterols have been claimed to be involved in the early development of atherosclerosis, the question arises whether continuously increasing serum plant sterols during long-term statin treatment should be prevented by cholesterol malabsorption (eg, by plant stanol ester consumption), especially in subjects with high baseline plant sterol values and effective sterol absorption.
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Affiliation(s)
- Tatu A Miettinen
- Division of Internal Medicine, Department of Medicine, University Central Hospital, University of Helsinki, HUS, Finland.
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93
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Albrecht C, Elliott JI, Sardini A, Litman T, Stieger B, Meier PJ, Higgins CF. Functional analysis of candidate ABC transporter proteins for sitosterol transport. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1567:133-42. [PMID: 12488046 DOI: 10.1016/s0005-2736(02)00608-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Two ATP-binding cassette (ABC) proteins, ABCG5 and ABCG8, have recently been associated with the accumulation of dietary cholesterol in the sterol storage disease sitosterolemia. These two 'half-transporters' are assumed to dimerize to form the complete sitosterol transporter which reduces the absorption of sitosterol and related molecules in the intestine by pumping them back into the lumen. Although mutations altering ABCG5 and ABCG8 are found in affected patients, no functional demonstration of sitosterol transport has been achieved. In this study, we investigated whether other ABC transporters implicated in lipid movement and expressed in tissues with a role in sterol synthesis and absorption, might also be involved in sitosterol transport. Transport by the multidrug resistance P-glycoprotein (P-gp; Abcb1), the multidrug resistance-associated protein (Mrp1; Abcc1), the breast cancer resistance protein (Bcrp; Abcg2) and the bile salt export pump (Bsep; Abcb11) was assessed using several assays. Unexpectedly, none of the candidate proteins mediated significant sitosterol transport. This has implications for the pathology of sitosterolemia. In addition, the data suggest that otherwise broad-specific ABC transporters have acquired specificity to exclude sitosterol and related sterols like cholesterol presumably because the abundance of cholesterol in the membrane would interfere with their action; in consequence, specific transporters have evolved to handle these sterols.
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Affiliation(s)
- C Albrecht
- MRC Clinical Sciences Centre, Faculty of Medicine, Imperial College, Hammersmith Hospital Campus, Du Cane Rd., London W12 ONN, UK.
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94
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Sehayek E, Duncan EM, Lutjohann D, Von Bergmann K, Ono JG, Batta AK, Salen G, Breslow JL. Loci on chromosomes 14 and 2, distinct from ABCG5/ABCG8, regulate plasma plant sterol levels in a C57BL/6J x CASA/Rk intercross. Proc Natl Acad Sci U S A 2002; 99:16215-9. [PMID: 12446833 PMCID: PMC138591 DOI: 10.1073/pnas.212640599] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/21/2002] [Indexed: 01/24/2023] Open
Abstract
Plasma plant sterol levels differ among humans due to genetic and dietary factors. A disease characterized by high plasma plant sterol levels, beta-sitosterolemia, was recently found to be due to mutations at the ABCG5ABCG8 locus. To detect variants at this and other loci, a genetic cross was carried out between two laboratory mouse strains. Parental C57BL6J had almost twice the campesterol and sitosterol levels compared with parental CASARk mice, and F(1) mice had levels halfway between the parentals. An intercross between F(1)s was performed and plasma plant sterol levels measured in 102 male and 99 female F(2) mice. Plasma plant sterols in F(2)s displayed a unimodal distribution, suggesting the effects of several rather a single major gene. In the F(2) mice, a full genome scan revealed significant linkages on chromosomes 14 and 2. With regard to chromosome 14, analysis showed a single peak for linkage at 17 cM with a logarithm of odds (LOD) score of 9.9, designated plasma plant sterol 14 (Plast14). With regard to chromosome 2, analysis showed two significant peaks for linkage at 18 and 65 cMs with LOD scores of 4.1 and 3.65, respectively, designated Plast2a and Plast2b, respectively. Four interactions between loci, predominantly of an additive nature, were also demonstrated, the most significant between Plast14 and Plast2b (LOD 16.44). No significant linkage or gene interaction was detected for the ABCG5ABCG8 locus on chromosome 17. Therefore, other genes besides ABCG5ABCG8 influence plasma plant sterol levels and now become candidates to explain differences in plasma plant sterol levels between humans.
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Affiliation(s)
- Ephraim Sehayek
- Laboratory of Biochemical Genetics and Metabolism, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
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95
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Lu K, Lee MH, Yu H, Zhou Y, Sandell SA, Salen G, Patel SB. Molecular cloning, genomic organization, genetic variations, and characterization of murine sterolin genes Abcg5 and Abcg8. J Lipid Res 2002. [DOI: 10.1016/s0022-2275(20)31486-3] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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96
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Lu K, Lee MH, Yu H, Zhou Y, Sandell SA, Salen G, Patel SB. Molecular cloning, genomic organization, genetic variations, and characterization of murine sterolin genes Abcg5 and Abcg8. J Lipid Res 2002; 43:565-78. [PMID: 11907139 PMCID: PMC1815568] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/24/2023] Open
Abstract
Mammalian physiological processes can distinguish between dietary cholesterol and non-cholesterol, retaining very little of the non-cholesterol in their bodies. We have recently identified two genes, ABCG5 and ABCG8, encoding sterolin-1 and -2 respectively, mutations of which cause the human disease sitosterolemia. We report here the mouse cDNAs and genomic organization of Abcg5 and Abcg8. Both genes are arranged in an unusual head-to-head configuration, and only 140 bases separate their two respective start-transcription sites. A single TATA motif was identified, with no canonical CCAT box present between the two genes. The genes are located on mouse chromosome 17 and this complex spans no more than 40 kb. Expression of both genes is confined to the liver and intestine. For both genes, two different sizes of transcripts were identified which differ in the lengths of their 3' UTRs. Additionally, alternatively spliced forms for Abcg8 were identified, resulting from a CAG repeat at the intron 1 splice-acceptor site, causing a deletion of a glutamine. We screened 20 different mouse strains for polymorphic variants. Although a large number of polymorphic variants were identified, strains reported to show significant differences in cholesterol absorption rates did not show significant genomic variations in Abcg5 or Abcg8.
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MESH Headings
- ATP Binding Cassette Transporter, Subfamily G, Member 5
- ATP Binding Cassette Transporter, Subfamily G, Member 8
- ATP-Binding Cassette Transporters/genetics
- Alternative Splicing/genetics
- Amino Acid Sequence
- Animals
- Base Sequence
- Chromosomes
- Cloning, Molecular
- DNA, Complementary
- Exons
- Gene Deletion
- Genetic Variation
- Glutamine/genetics
- Humans
- Introns
- Lipoproteins/genetics
- Mice
- Mice, Inbred Strains
- Molecular Sequence Data
- Polymorphism, Genetic
- Promoter Regions, Genetic
- RNA, Messenger/metabolism
- Tissue Distribution
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Affiliation(s)
- Kangmo Lu
- Division of Endocrinology, Diabetes, and Medical
Genetics, Medical University of South Carolina, Charleston, SC 29403; and
| | - Mi-Hye Lee
- Division of Endocrinology, Diabetes, and Medical
Genetics, Medical University of South Carolina, Charleston, SC 29403; and
| | - Hongwei Yu
- Division of Endocrinology, Diabetes, and Medical
Genetics, Medical University of South Carolina, Charleston, SC 29403; and
| | - Yuehua Zhou
- Division of Endocrinology, Diabetes, and Medical
Genetics, Medical University of South Carolina, Charleston, SC 29403; and
| | - Shelley A. Sandell
- Division of Endocrinology, Diabetes, and Medical
Genetics, Medical University of South Carolina, Charleston, SC 29403; and
| | - Gerald Salen
- Division of Gastroenterology, University of Medicine
and Dentistry New Jersey, Newark, NJ 07018
| | - Shailendra B. Patel
- Division of Endocrinology, Diabetes, and Medical
Genetics, Medical University of South Carolina, Charleston, SC 29403; and
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97
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Abstract
Bile formation, the exocrine function of the liver, represents a process that is unique to the hepatocyte as a polarized epithelial cell. The generation of bile flow is an osmotic process and largely depends on solute secretion by primary active transporters in the apical membrane of the hepatocyte. In recent years an impressive progress has been made in the discovery of these proteins, most of which belong to the family of ABC transporters. The number of identified ABC transporter genes has been exponentially increasing and the mammalian subfamily now counts at least 52. This development has been of crucial importance for the elucidation of the mechanism of bile formation, and it is therefore not surprising that the development in this field has run in parallel with the discovery of the ABC genes. With the identification of these transporter genes, the background of a number of inherited diseases, which are caused by mutations in these solute pumps, has now been elucidated. We now know that at least six primary active transporters are involved in canalicular secretion of biliary components (MDR1, MDR3, BSEP, MRP2, BCRP and FIC1). Four of these transporter genes are associated with inherited diseases. In this minireview we will shortly describe our present understanding of bile formation and the associated inherited defects.
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Affiliation(s)
- Ronald Oude Elferink
- Laboratory for Experimental Hepatology, Academic Medical Center Amsterdam F0-116, Meibergdreef 9, 1105 AZ, Netherlands.
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98
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Hegele RA. Monogenic dyslipidemias: window on determinants of plasma lipoprotein metabolism. Am J Hum Genet 2001; 69:1161-77. [PMID: 11704922 PMCID: PMC1235529 DOI: 10.1086/324647] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2001] [Accepted: 09/27/2001] [Indexed: 12/19/2022] Open
Affiliation(s)
- R A Hegele
- John P. Robarts Research Institute, London, Ontario, Canada.
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Wang DQH, Paigen B, Carey MC. Genetic factors at the enterocyte level account for variations inintestinal cholesterol absorption efficiency among inbred strains of mice. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)31508-x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Atkinson TP, Schäffer AA, Grimbacher B, Schroeder HW, Woellner C, Zerbe CS, Puck JM. An immune defect causing dominant chronic mucocutaneous candidiasis and thyroid disease maps to chromosome 2p in a single family. Am J Hum Genet 2001; 69:791-803. [PMID: 11517424 PMCID: PMC1226065 DOI: 10.1086/323611] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2001] [Accepted: 07/31/2001] [Indexed: 12/26/2022] Open
Abstract
We describe a large family in which a combination of chronic mucocutaneous candidiasis (fungal infections of the skin, nails, and mucous membranes) and thyroid disease segregate as an autosomal dominant trait with reduced penetrance. The family includes (a) four members with both candidiasis and thyroid disease, (b) five members, including one pair of phenotype-concordant MZ twins, with candidiasis only, and (c) three members with thyroid disease only. A whole-genome scan using DNA samples from 20 members of the family identified a candidate linkage region on chromosome 2p. By sampling additional individuals and genotyping supplementary markers, we established linkage to a region of approximately 15 cM bounded by D2S367 and D2S2240 and including seven adjacent markers consistent with linkage. With a penetrance estimate of.8, which was based on pedigree and affected status, the peak two-point LOD score was 3.70 with marker D2S2328, and the peak three-point LOD score was 3.82. This is the first linkage assignment of a dominant locus for mucocutaneous candidiasis.
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Affiliation(s)
- T P Atkinson
- Department of Pediatrics, University of Alabama at Birmingham, Birmingham, AL, USA
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