1
|
Koschinsky ML, Stroes ESG, Kronenberg F. Daring to dream: Targeting lipoprotein(a) as a causal and risk-enhancing factor. Pharmacol Res 2023; 194:106843. [PMID: 37406784 DOI: 10.1016/j.phrs.2023.106843] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/07/2023] [Revised: 06/15/2023] [Accepted: 06/27/2023] [Indexed: 07/07/2023]
Abstract
Lipoprotein(a) [Lp(a)], a distinct lipoprotein class, has become a major focus for cardiovascular research. This review is written in light of the recent guideline and consensus statements on Lp(a) and focuses on 1) the causal association between Lp(a) and cardiovascular outcomes, 2) the potential mechanisms by which elevated Lp(a) contributes to cardiovascular diseases, 3) the metabolic insights on the production and clearance of Lp(a) and 4) the current and future therapeutic approaches to lower Lp(a) concentrations. The concentrations of Lp(a) are under strict genetic control. There exists a continuous relationship between the Lp(a) concentrations and risk for various endpoints of atherosclerotic cardiovascular disease (ASCVD). One in five people in the Caucasian population is considered to have increased Lp(a) concentrations; the prevalence of elevated Lp(a) is even higher in black populations. This makes Lp(a) a cardiovascular risk factor of major public health relevance. Besides the association between Lp(a) and myocardial infarction, the relationship with aortic valve stenosis has become a major focus of research during the last decade. Genetic studies provided strong support for a causal association between Lp(a) and cardiovascular outcomes: carriers of genetic variants associated with lifelong increased Lp(a) concentration are significantly more frequent in patients with ASCVD. This has triggered the development of drugs that can specifically lower Lp(a) concentrations: mRNA-targeting therapies such as anti-sense oligonucleotide (ASO) therapies and short interfering RNA (siRNA) therapies have opened new avenues to lower Lp(a) concentrations more than 95%. Ongoing Phase II and III clinical trials of these compounds are discussed in this review.
Collapse
Affiliation(s)
- Marlys L Koschinsky
- Robarts Research Institute, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada; Department of Physiology & Pharmacology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada
| | - Erik S G Stroes
- Department of Vascular Medicine, Amsterdam Cardiovascular Sciences, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands
| | - Florian Kronenberg
- Institute of Genetic Epidemiology, Medical University of Innsbruck, Innsbruck, Austria.
| |
Collapse
|
2
|
Boffa MB, Koschinsky ML. Understanding the ins and outs of lipoprotein (a) metabolism. Curr Opin Lipidol 2022; 33:185-192. [PMID: 35695615 DOI: 10.1097/mol.0000000000000823] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE OF REVIEW This review summarizes our current understanding of the processes of apolipoprotein(a) secretion, assembly of the Lp(a) particle and removal of Lp(a) from the circulation. We also identify existing knowledge gaps that need to be addressed in future studies. RECENT FINDINGS The Lp(a) particle is assembled in two steps: a noncovalent, lysine-dependent interaction of apo(a) with apoB-100 inside hepatocytes, followed by extracellular covalent association between these two molecules to form circulating apo(a).The production rate of Lp(a) is primarily responsible for the observed inverse correlation between apo(a) isoform size and Lp(a) levels, with a contribution of catabolism restricted to larger Lp(a) isoforms.Factors that affect apoB-100 secretion from hepatocytes also affect apo(a) secretion.The identification of key hepatic receptors involved in Lp(a) clearance in vivo remains unclear, with a role for the LDL receptor seemingly restricted to conditions wherein LDL concentrations are low, Lp(a) is highly elevated and LDL receptor number is maximally upregulated. SUMMARY The key role for production rate of Lp(a) [including secretion and assembly of the Lp(a) particle] rather than its catabolic rate suggests that the most fruitful therapies for Lp(a) reduction should focus on approaches that inhibit production of the particle rather than its removal from circulation.
Collapse
Affiliation(s)
| | - Marlys L Koschinsky
- Robarts Research Institute
- Department of Physiology & Pharmacology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Ontario, Canada
| |
Collapse
|
3
|
Mehta A, Jain V, Saeed A, Saseen JJ, Gulati M, Ballantyne CM, Virani SS. Lipoprotein(a) and ethnicities. Atherosclerosis 2022; 349:42-52. [DOI: 10.1016/j.atherosclerosis.2022.04.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 02/13/2022] [Accepted: 04/01/2022] [Indexed: 12/24/2022]
|
4
|
Clark JR, Gemin M, Youssef A, Marcovina SM, Prat A, Seidah NG, Hegele RA, Boffa MB, Koschinsky ML. Sortilin enhances secretion of apolipoprotein(a) through effects on apolipoprotein B secretion and promotes uptake of lipoprotein(a). J Lipid Res 2022; 63:100216. [PMID: 35469919 PMCID: PMC9131257 DOI: 10.1016/j.jlr.2022.100216] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Revised: 04/06/2022] [Accepted: 04/08/2022] [Indexed: 12/30/2022] Open
Abstract
Elevated plasma lipoprotein(a) (Lp(a)) is an independent, causal risk factor for atherosclerotic cardiovascular disease and calcific aortic valve stenosis. Lp(a) is formed in or on hepatocytes from successive noncovalent and covalent interactions between apo(a) and apoB, although the subcellular location of these interactions and the nature of the apoB-containing particle involved remain unclear. Sortilin, encoded by the SORT1 gene, modulates apoB secretion and LDL clearance. We used a HepG2 cell model to study the secretion kinetics of apo(a) and apoB. Overexpression of sortilin increased apo(a) secretion, while siRNA-mediated knockdown of sortilin expression correspondingly decreased apo(a) secretion. Sortilin binds LDL but not apo(a) or Lp(a), indicating that its effect on apo(a) secretion is likely indirect. Indeed, the effect was dependent on the ability of apo(a) to interact noncovalently with apoB. Overexpression of sortilin enhanced internalization of Lp(a), but not apo(a), by HepG2 cells, although neither sortilin knockdown in these cells or Sort1 deficiency in mice impacted Lp(a) uptake. We found several missense mutations in SORT1 in patients with extremely high Lp(a) levels; sortilin containing some of these mutations was more effective at promoting apo(a) secretion than WT sortilin, though no differences were found with respect to Lp(a) internalization. Our observations suggest that sortilin could play a role in determining plasma Lp(a) levels and corroborate in vivo human kinetic studies which imply that secretion of apo(a) and apoB are coupled, likely within the hepatocyte.
Collapse
Affiliation(s)
- Justin R Clark
- Department of Physiology & Pharmacology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON, Canada
| | - Matthew Gemin
- Department of Chemistry & Biochemistry, University of Windsor, Windsor, ON, Canada
| | - Amer Youssef
- Robarts Research Institute, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON, Canada
| | | | - Annik Prat
- Institut de Recherches Cliniques de Montreal, Montréal, QC, Canada
| | - Nabil G Seidah
- Institut de Recherches Cliniques de Montreal, Montréal, QC, Canada
| | - Robert A Hegele
- Robarts Research Institute, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON, Canada; Department of Biochemistry, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON, Canada; Department of Medicine, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON, Canada
| | - Michael B Boffa
- Robarts Research Institute, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON, Canada; Department of Biochemistry, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON, Canada
| | - Marlys L Koschinsky
- Department of Physiology & Pharmacology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON, Canada; Robarts Research Institute, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON, Canada.
| |
Collapse
|
5
|
Youssef A, Clark JR, Marcovina SM, Boffa MB, Koschinsky ML. Apo(a) and ApoB Interact Noncovalently Within Hepatocytes: Implications for Regulation of Lp(a) Levels by Modulation of ApoB Secretion. Arterioscler Thromb Vasc Biol 2022; 42:289-304. [PMID: 35045727 DOI: 10.1161/atvbaha.121.317335] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
BACKGROUND Elevated plasma Lp(a) (lipoprotein(a)) levels are associated with increased risk for atherosclerotic cardiovascular disease and aortic valve stenosis. However, the cell biology of Lp(a) biosynthesis remains poorly understood, with the locations of the noncovalent and covalent steps of Lp(a) assembly unclear and the nature of the apoB-containing particle destined for Lp(a) unknown. We, therefore, asked if apo(a) and apoB interact noncovalently within hepatocytes and if this impacts Lp(a) biosynthesis. METHODS Using human hepatocellular carcinoma cells expressing 17K (17 kringle) apo(a), or a 17KΔLBS7,8 variant with a reduced ability to bind noncovalently to apoB, we performed coimmunoprecipitation, coimmunofluorescence, and proximity ligation assays to document intracellular apo(a):apoB interactions. We used a pulse-chase metabolic labeling approach to measure apo(a) and apoB secretion rates. RESULTS Noncovalent complexes containing apo(a)/apoB are present in lysates from cells expressing 17K but not 17KΔLBS7,8, whereas covalent apo(a)/apoB complexes are absent from lysates. 17K and apoB colocalized intracellularly, overlapping with staining for markers of endoplasmic reticulum trans-Golgi, and early endosomes, and less so with lysosomes. The 17KΔLBS7,8 had lower colocalization with apoB. Proximity ligation assays directly documented intracellular 17K/apoB interactions, which were dramatically reduced for 17KΔLBS7,8. Treatment of cells with PCSK9 (proprotein convertase subtilisin/kexin type 9) enhanced, and lomitapide reduced, apo(a) secretion in a manner dependent on the noncovalent interaction between apo(a) and apoB. Apo(a) secretion was also reduced by siRNA-mediated knockdown of APOB. CONCLUSIONS Our findings explain the coupling of apo(a) and Lp(a)-apoB production observed in human metabolic studies using stable isotopes as well as the ability of agents that inhibit apoB biosynthesis to lower Lp(a) levels.
Collapse
Affiliation(s)
- Amer Youssef
- Robarts Research Institute (A.Y., M.B.B., M.L.K.), Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Canada
| | - Justin R Clark
- Department of Physiology & Pharmacology (J.R.C., M.L.K.), Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Canada
| | | | - Michael B Boffa
- Robarts Research Institute (A.Y., M.B.B., M.L.K.), Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Canada.,Department of Biochemistry (M.B.B.), Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Canada
| | - Marlys L Koschinsky
- Robarts Research Institute (A.Y., M.B.B., M.L.K.), Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Canada.,Department of Physiology & Pharmacology (J.R.C., M.L.K.), Schulich School of Medicine & Dentistry, The University of Western Ontario, London, Canada
| |
Collapse
|
6
|
Blanchard V, Chemello K, Hollstein T, Hong-Fong CC, Schumann F, Grenkowitz T, Nativel B, Coassin S, Croyal M, Kassner U, Lamina C, Steinhagen-Thiessen E, Lambert G. The size of apolipoprotein (a) is an independent determinant of the reduction in lipoprotein (a) induced by PCSK9 inhibitors. Cardiovasc Res 2021; 118:2103-2111. [PMID: 34314498 DOI: 10.1093/cvr/cvab247] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/28/2021] [Accepted: 07/24/2021] [Indexed: 12/14/2022] Open
Abstract
AIMS Lipoprotein (a) [Lp(a)] is a lipoprotein species causatively associated with atherosclerosis. Unlike statins, PCSK9 inhibitors (PCSK9i) reduce Lp(a), but this reduction is highly variable. Levels of Lp(a) are chiefly governed by the size of its signature protein, apolipoprotein (a) [apo(a)]. Whether this parameter determines some of the reduction in Lp(a) induced by PCSK9i remains unknown. We aimed to investigate if the Lp(a) lowering efficacy of PCSK9i is modulated by the size of apo(a), which is genetically determined by the variable number of KIV domains present on that protein. METHODS AND RESULTS The levels of Lp(a) and the size of apo(a) were assessed in plasma samples from 268 patients before and after treatment with PCSK9i. Patients were recruited at the Outpatient Lipid Clinic of the Charité Hospital (Berlin) between 2015 and 2020. They were hypercholesterolemic at very high CVD risk with LDL-cholesterol levels above therapeutic targets despite maximally tolerated lipid-lowering therapy. Patients received either Alirocumab (75 or 150 mg) or Evolocumab (140 mg) every 2 weeks. Apo(a), apoB100, and apoE concentrations as well as apoE major isoforms were determined by liquid chromatography high-resolution mass spectrometry. Apo(a) isoforms sizes were determined by Western Blot. PCSK9i sharply reduced LDL-cholesterol (-57%), apoB100 (-47%) and Lp(a) (-36%). There was a positive correlation between the size of apo(a) and the relative reduction in Lp(a) induced by PCSK9i (r = 0.363, p = 0.0001). The strength of this association remained unaltered after adjustment for baseline Lp(a) levels and all other potential confounding factors. In patients with two detectable apo(a) isoforms, there was also a positive correlation between the size of apo(a) and the reduction in Lp(a), separately for the smaller (r = 0.350, p = 0.0001) and larger (r = 0.324, p = 0.0003) isoforms. The relative contribution of the larger isoform to the total concentration of apo(a) was reduced from 29% to 15% (p < 0.0001). CONCLUSIONS The size of apo(a) is an independent determinant of the response to PCSK9i. Each additional kringle domain is associated with a 3% additional reduction in Lp(a). This explains in part the variable efficacy of PCSK9i and allows to identify patients who will benefit most from these therapies in terms of Lp(a) lowering. TRANSLATIONAL PERSPECTIVE Unlike statins, PCSK9 inhibitors reduce the circulating levels of the highly atherogenic Lipoprotein (a). The underlying mechanism remains a matter of considerable debate. The size of apo(a), the signature protein of Lp(a), is extremely variable (300 to more than 800 kDa) and depends on its number of kringle domains. We now show that each increase in apo(a) size by one kringle domain is associated with a 3% additional reduction in Lp(a) following PCSK9i treatment and that apo(a) size polymorphism is an independent predictor of the reduction in Lp(a) induced by these drugs. In an era of personalized medicine, this allows to identify patients who will benefit most from PCSK9i in terms of Lp(a) lowering.
Collapse
Affiliation(s)
- Valentin Blanchard
- Université de La Réunion, INSERM UMR 1188 DéTROI, Sainte-Clotilde, France.,Centre for Heart & Lung Innovation, St. Paul's Hospital, Vancouver, Canada; Department of Medicine, UBC, Vancouver, Canada
| | - Kévin Chemello
- Université de La Réunion, INSERM UMR 1188 DéTROI, Sainte-Clotilde, France
| | - Tim Hollstein
- Department of Endocrinology, Campus Virchow-Klinikum, Charité Universitätsmedizin, Berlin, Germany.,Division of Endocrinology, Diabetology and Clinical Nutrition, Department of Internal Medicine 1, University of Kiel, Kiel, Germany
| | | | - Friederike Schumann
- Department of Endocrinology, Campus Virchow-Klinikum, Charité Universitätsmedizin, Berlin, Germany
| | - Thomas Grenkowitz
- Department of Endocrinology, Campus Virchow-Klinikum, Charité Universitätsmedizin, Berlin, Germany
| | - Brice Nativel
- Université de La Réunion, INSERM UMR 1188 DéTROI, Sainte-Clotilde, France
| | - Stefan Coassin
- Institute of Genetic Epidemiology, Department of Genetics and Pharmacology, Medical University of Innsbrück, Innsbrück, Austria
| | - Mikaël Croyal
- NUN, INRA, CHU Nantes, UMR 1280, PhAN, IMAD, CRNH-O, Nantes, France
| | - Ursula Kassner
- Department of Endocrinology, Campus Virchow-Klinikum, Charité Universitätsmedizin, Berlin, Germany
| | - Claudia Lamina
- Institute of Genetic Epidemiology, Department of Genetics and Pharmacology, Medical University of Innsbrück, Innsbrück, Austria
| | | | - Gilles Lambert
- Université de La Réunion, INSERM UMR 1188 DéTROI, Sainte-Clotilde, France
| |
Collapse
|
7
|
Rhainds D, Brodeur MR, Tardif JC. Lipoprotein (a): When to Measure and How to Treat? Curr Atheroscler Rep 2021; 23:51. [PMID: 34235598 DOI: 10.1007/s11883-021-00951-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/03/2021] [Indexed: 12/11/2022]
Abstract
PURPOSE OF REVIEW The purpose of this article is to review current evidence for lipoprotein (a) (Lp(a)) as a risk factor for multiple cardiovascular (CV) disease phenotypes, provide a rationale for Lp(a) lowering to reduce CV risk, identify therapies that lower Lp(a) levels that are available clinically and under investigation, and discuss future directions. RECENT FINDINGS Mendelian randomization and epidemiological studies have shown that elevated Lp(a) is an independent and causal risk factor for atherosclerosis and major CV events. Lp(a) is also associated with non-atherosclerotic endpoints such as venous thromboembolism and calcific aortic valve disease. It contributes to residual CV risk in patients receiving standard-of-care LDL-lowering therapy. Plasma Lp(a) levels present a skewed distribution towards higher values and vary widely between individuals and according to ethnic background due to genetic variants in the LPA gene, but remain relatively constant throughout a person's life. Thus, elevated Lp(a) (≥50 mg/dL) is a prevalent condition affecting >20% of the population but is still underdiagnosed. Treatment guidelines have begun to advocate measurement of Lp(a) to identify patients with very high levels that have a family history of premature CVD or elevated Lp(a). Lipoprotein apheresis (LA) efficiently lowers Lp(a) and was recently associated with a reduction of incident CV events. Statins have neutral or detrimental effects on Lp(a), while PCSK9 inhibitors significantly reduce its level by up to 30%. Specific lowering of Lp(a) with antisense oligonucleotides (ASO) shows good safety and strong efficacy with up to 90% reductions. The ongoing CV outcomes study Lp(a)HORIZON will provide a first answer as to whether selective Lp(a) lowering with ASO reduces the risk of major CV events. Given the recently established association between Lp(a) level and CV risk, guidelines now recommend Lp(a) measurement in specific clinical conditions. Accordingly, Lp(a) is a current target for drug development to reduce CV risk in patients with elevated levels, and lowering Lp(a) with ASO represents a promising avenue.
Collapse
Affiliation(s)
- David Rhainds
- Montreal Heart Institute Research Center, 5000 Belanger Street, Montréal, Canada
| | - Mathieu R Brodeur
- Montreal Heart Institute Research Center, 5000 Belanger Street, Montréal, Canada
| | - Jean-Claude Tardif
- Montreal Heart Institute Research Center, 5000 Belanger Street, Montréal, Canada. .,Faculty of Medicine, Université de Montréal, Montréal, Canada.
| |
Collapse
|
8
|
Page MM, Watts GF. Contemporary perspectives on the genetics and clinical use of lipoprotein(a) in preventive cardiology. Curr Opin Cardiol 2021; 36:272-280. [PMID: 33741767 DOI: 10.1097/hco.0000000000000842] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
PURPOSE OF REVIEW The pathogenicity of lipoprotein(a) [Lp(a)] as a risk factor for atherosclerotic cardiovascular disease (ASCVD) is well evidenced and recognized by international consensus-based guidelines. However, the measurement of Lp(a) is not routine clinical practice. Therapeutic agents targeting Lp(a) are now progressing through randomised clinical trials, and it is timely for clinicians to familiarize themselves with this complex and enigmatic lipoprotein particle. RECENT FINDINGS Recent developments in the understanding of genetic influences on the structure, plasma concentration and atherogenicity of Lp(a) have contextualized its clinical relevance. Mendelian randomization studies have enabled estimation of the contribution of Lp(a) to ASCVD risk. Genotyping individual patients with respect to Lp(a)-raising single nucleotide polymorphisms predicts ASCVD, but has not yet been shown to add value beyond the measurement of Lp(a) plasma concentrations, which should be done by Lp(a) isoform-independent assays capable of reporting in molar concentrations. Contemporary gene-silencing technology underpins small interfering RNA and antisense oligonucleotides, which are emerging as the leading Lp(a)-lowering therapeutic agents. The degree of Lp(a)-lowering required to achieve meaningful reductions in ASCVD risk has been estimated by Mendelian randomization, providing conceptual support. SUMMARY Measurement of Lp(a) in the clinical setting contributes to the assessment of ASCVD risk, and will become more important with the advent of specific Lp(a)-lowering therapies. Knowledge of an individual patient's genetic predisposition to increased Lp(a) appears to impart little or not additional clinical value beyond Lp(a) particle concentration.
Collapse
Affiliation(s)
- Michael M Page
- School of Medicine, University of Western Australia, Crawley
- Western Diagnostic Pathology
| | - Gerald F Watts
- School of Medicine, University of Western Australia, Crawley
- Lipid Disorders Clinic, Cardiovascular Medicine, Royal Perth Hospital, Perth, Western Australia, Australia
| |
Collapse
|
9
|
Lipoprotein(a) the Insurgent: A New Insight into the Structure, Function, Metabolism, Pathogenicity, and Medications Affecting Lipoprotein(a) Molecule. J Lipids 2020; 2020:3491764. [PMID: 32099678 PMCID: PMC7016456 DOI: 10.1155/2020/3491764] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2019] [Accepted: 08/17/2019] [Indexed: 12/15/2022] Open
Abstract
Lipoprotein(a) [Lp(a)], aka “Lp little a”, was discovered in the 1960s in the lab of the Norwegian physician Kåre Berg. Since then, we have greatly improved our knowledge of lipids and cardiovascular disease (CVD). Lp(a) is an enigmatic class of lipoprotein that is exclusively formed in the liver and comprises two main components, a single copy of apolipoprotein (apo) B-100 (apo-B100) tethered to a single copy of a protein denoted as apolipoprotein(a) apo(a). Plasma levels of Lp(a) increase soon after birth to a steady concentration within a few months of life. In adults, Lp(a) levels range widely from <2 to 2500 mg/L. Evidence that elevated Lp(a) levels >300 mg/L contribute to CVD is significant. The improvement of isoform-independent assays, together with the insight from epidemiologic studies, meta-analyses, genome-wide association studies, and Mendelian randomization studies, has established Lp(a) as the single most common independent genetically inherited causal risk factor for CVD. This breakthrough elevated Lp(a) from a biomarker of atherosclerotic risk to a target of therapy. With the emergence of promising second-generation antisense therapy, we hope that we can answer the question of whether Lp(a) is ready for prime-time clinic use. In this review, we present an update on the metabolism, pathophysiology, and current/future medical interventions for high levels of Lp(a).
Collapse
|
10
|
Morgan BM, Brown AN, Deo N, Harrop TWR, Taiaroa G, Mace PD, Wilbanks SM, Merriman TR, Williams MJA, McCormick SPA. Nonsynonymous SNPs in LPA homologous to plasminogen deficiency mutants represent novel null apo(a) alleles. J Lipid Res 2019; 61:432-444. [PMID: 31806727 DOI: 10.1194/jlr.m094540] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2019] [Revised: 11/18/2019] [Indexed: 12/20/2022] Open
Abstract
Plasma lipoprotein (a) [Lp(a)] levels are largely determined by variation in the LPA gene, which codes for apo(a). Genome-wide association studies (GWASs) have identified nonsynonymous variants in LPA that associate with low Lp(a) levels, although their effect on apo(a) function is unknown. We investigated two such variants, R990Q and R1771C, which were present in four null Lp(a) individuals, for structural and functional effects. Sequence alignments showed the R990 and R1771 residues to be highly conserved and homologous to each other and to residues associated with plasminogen deficiency. Structural modeling showed both residues to make several polar contacts with neighboring residues that would be ablated on substitution. Recombinant expression of the WT and R1771C apo(a) in liver and kidney cells showed an abundance of an immature form for both apo(a) proteins. A mature form of apo(a) was only seen with the WT protein. Imaging of the recombinant apo(a) proteins in conjunction with markers of the secretory pathway indicated a poor transit of R1771C into the Golgi. Furthermore, the R1771C mutant displayed a glycosylation pattern consistent with ER, but not Golgi, glycosylation. We conclude that R1771 and the equivalent R990 residue facilitate correct folding of the apo(a) kringle structure and mutations at these positions prevent the proper folding required for full maturation and secretion. To our knowledge, this is the first example of nonsynonymous variants in LPA being causative of a null Lp(a) phenotype.
Collapse
Affiliation(s)
- Benjamin M Morgan
- Department of Biochemistry, School of Biomedical Sciences University of Otago, Dunedin, New Zealand
| | - Aimee N Brown
- Department of Biochemistry, School of Biomedical Sciences University of Otago, Dunedin, New Zealand
| | - Nikita Deo
- Department of Biochemistry, School of Biomedical Sciences University of Otago, Dunedin, New Zealand.,Maurice Wilkins Centre for Molecular Biodiscovery, Auckland, New Zealand
| | - Tom W R Harrop
- Department of Biochemistry, School of Biomedical Sciences University of Otago, Dunedin, New Zealand
| | - George Taiaroa
- Department of Biochemistry, School of Biomedical Sciences University of Otago, Dunedin, New Zealand
| | - Peter D Mace
- Department of Biochemistry, School of Biomedical Sciences University of Otago, Dunedin, New Zealand.,Maurice Wilkins Centre for Molecular Biodiscovery, Auckland, New Zealand
| | - Sigurd M Wilbanks
- Department of Biochemistry, School of Biomedical Sciences University of Otago, Dunedin, New Zealand
| | - Tony R Merriman
- Department of Biochemistry, School of Biomedical Sciences University of Otago, Dunedin, New Zealand.,Maurice Wilkins Centre for Molecular Biodiscovery, Auckland, New Zealand
| | - Michael J A Williams
- Department of Medicine, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand
| | - Sally P A McCormick
- Department of Biochemistry, School of Biomedical Sciences University of Otago, Dunedin, New Zealand .,Maurice Wilkins Centre for Molecular Biodiscovery, Auckland, New Zealand
| |
Collapse
|
11
|
Awad K, Mikhailidis DP, Katsiki N, Muntner P, Banach M. Effect of Ezetimibe Monotherapy on Plasma Lipoprotein(a) Concentrations in Patients with Primary Hypercholesterolemia: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Drugs 2019; 78:453-462. [PMID: 29396832 DOI: 10.1007/s40265-018-0870-1] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
BACKGROUND AND AIMS Ezetimibe reduces plasma low-density lipoprotein cholesterol (LDL-C) levels by up to 20%. However, its effect on plasma lipoprotein(a) [Lp(a)] concentrations in patients with primary hypercholesterolemia has not been defined. OBJECTIVE Therefore, we performed a systematic review and meta-analysis to assess this effect based on the available randomized controlled trials (RCTs). METHODS We searched the PubMed and SCOPUS databases from inception until 28 February 2017 to identify RCTs that investigated the effect of ezetimibe monotherapy on plasma Lp(a) concentrations in patients with primary hypercholesterolemia. We pooled mean percentage changes in plasma Lp(a) concentrations as a mean difference (MD) with a 95% confidence interval (CI). RESULTS Seven RCTs with 2337 patients met the selection criteria and were included in the analysis. Overall pooled analysis suggested that ezetimibe 10 mg significantly reduced plasma Lp(a) concentrations in patients with primary hypercholesterolemia by - 7.06% (95% CI - 11.95 to - 2.18; p = 0.005) compared with placebo. No significant heterogeneity was observed (χ2 = 5.34; p = 0.5). Excluding one study from the analysis resulted in insignificant differences between the two groups (p = 0.2). Meta-regression did not find a significant association between the mean percentage changes in Lp(a) and other potential moderator variables, which included the mean percentage changes of LDL-C concentrations (p = 0.06) and baseline Lp(a) mean values (p = 0.46). CONCLUSIONS Ezetimibe monotherapy (10 mg/day) showed a small (7.06%) but statistically significant reduction in the plasma levels of Lp(a) in patients with primary hypercholesterolemia. According to current literature, this magnitude of reduction seems to have no clinical relevance. However, further studies are warranted to clarify the mechanism mediating this effect of ezetimibe and to investigate its efficacy in combination with other drugs that have shown promise in lowering Lp(a) levels.
Collapse
Affiliation(s)
- Kamal Awad
- Faculty of Medicine, Zagazig University, Zagazig, 44519, El-Sharkia, Egypt.
| | - Dimitri P Mikhailidis
- Department of Clinical Biochemistry, University College London Medical School, University College London (UCL), Royal Free Campus, London, UK
| | - Niki Katsiki
- Second Propedeutic Department of Internal Medicine, Medical School, Aristotle University of Thessaloniki, Hippokration Hospital, Thessaloniki, Greece
| | - Paul Muntner
- Department of Epidemiology, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Maciej Banach
- Head Department of Hypertension, WAM University Hospital in Lodz, Medical University of Lodz (MUL), Lodz, Poland.,Polish Mother's Memorial Hospital Research Institute (PMMHRI), Lodz, Poland.,Cardiovascular Research Centre, University of Zielona Gora, Zielona Gora, Poland
| | | |
Collapse
|
12
|
Borrelli MJ, Youssef A, Boffa MB, Koschinsky ML. New Frontiers in Lp(a)-Targeted Therapies. Trends Pharmacol Sci 2019; 40:212-225. [PMID: 30732864 DOI: 10.1016/j.tips.2019.01.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2018] [Revised: 01/07/2019] [Accepted: 01/08/2019] [Indexed: 12/13/2022]
Abstract
Interest in lipoprotein (a) [Lp(a)] has exploded over the past decade with the emergence of genetic and epidemiological studies pinpointing elevated levels of this unique lipoprotein as a causal risk factor for atherosclerotic cardiovascular disease (ASCVD) and calcific aortic valve disease (CAVD). This review summarizes the most recent discoveries regarding therapeutic approaches to lower Lp(a) and presents these findings in the context of an emerging, although far from complete, understanding of the biosynthesis and catabolism of Lp(a). Application of Lp(a)-specific lowering agents to outcome trials will be the key to opening this new frontier in the battle against CVD.
Collapse
Affiliation(s)
- Matthew J Borrelli
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada
| | - Amer Youssef
- Robarts Research Institute, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada
| | - Michael B Boffa
- Robarts Research Institute, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada; Department of Biochemistry, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada
| | - Marlys L Koschinsky
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada; Robarts Research Institute, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada.
| |
Collapse
|
13
|
Boffa MB, Koschinsky ML. Oxidized phospholipids as a unifying theory for lipoprotein(a) and cardiovascular disease. Nat Rev Cardiol 2019; 16:305-318. [DOI: 10.1038/s41569-018-0153-2] [Citation(s) in RCA: 114] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
|
14
|
Boffa MB. Emerging Therapeutic Options for Lowering of Lipoprotein(a): Implications for Prevention of Cardiovascular Disease. Curr Atheroscler Rep 2017; 18:69. [PMID: 27761705 DOI: 10.1007/s11883-016-0622-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
PURPOSE OF REVIEW Elevated plasma concentrations of lipoprotein(a) (Lp(a)) are an independent and causal risk factor for cardiovascular diseases including coronary artery disease, ischemic stroke, and calcific aortic valve stenosis. This review summarizes the rationale for Lp(a) lowering and surveys relevant clinical trial data using a variety of agents capable of lowering Lp(a). RECENT FINDINGS Contemporary guidelines and recommendations outline populations of patients who should be screened for elevated Lp(a) and who might benefit from Lp(a) lowering. Therapies including drugs and apheresis have been described that lower Lp(a) levels modestly (∼20 %) to dramatically (∼80 %). Existing therapies that lower Lp(a) also have beneficial effects on other aspects of the lipid profile, with the exception of Lp(a)-specific apheresis and an antisense oligonucleotide that targets the mRNA encoding apolipoprotein(a). No clinical trials conducted to date have managed to answer the key question of whether Lp(a) lowering confers a benefit in terms of ameliorating cardiovascular risk, although additional outcome trials of therapies that lower Lp(a) are ongoing. It is more likely, however, that Lp(a)-specific agents will provide the most appropriate approach for addressing this question.
Collapse
Affiliation(s)
- Michael B Boffa
- Department of Biochemistry, Room 4245A Robarts Research Institute, University of Western Ontario, 1151 Richmond Street North, London, ON, Canada, N6A 5B7.
| |
Collapse
|
15
|
Roles of the low density lipoprotein receptor and related receptors in inhibition of lipoprotein(a) internalization by proprotein convertase subtilisin/kexin type 9. PLoS One 2017; 12:e0180869. [PMID: 28750079 PMCID: PMC5531514 DOI: 10.1371/journal.pone.0180869] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Accepted: 06/22/2017] [Indexed: 12/19/2022] Open
Abstract
Elevated plasma concentrations of lipoprotein(a) (Lp(a)) are a causal risk factor for cardiovascular disease. The mechanisms underlying Lp(a) clearance from plasma remain unclear, which is an obvious barrier to the development of therapies to specifically lower levels of this lipoprotein. Recently, it has been documented that monoclonal antibody inhibitors of proprotein convertase subtilisin/kexin type 9 (PCSK9) can lower plasma Lp(a) levels by 30%. Since PCSK9 acts primarily through the low density lipoprotein receptor (LDLR), this result is in conflict with the prevailing view that the LDLR does not participate in Lp(a) clearance. To support our recent findings in HepG2 cells that the LDLR can act as a bona fide receptor for Lp(a) whose effects are sensitive to PCSK9, we undertook a series of Lp(a) internalization experiments using different hepatic cells, with different variants of PCSK9, and with different members of the LDLR family. We found that PCSK9 decreased Lp(a) and/or apo(a) internalization by Huh7 human hepatoma cells and by primary mouse and human hepatocytes. Overexpression of human LDLR appeared to enhance apo(a)/Lp(a) internalization in both types of primary cells. Importantly, internalization of Lp(a) by LDLR-deficient mouse hepatocytes was not affected by PCSK9, but the effect of PCSK9 was restored upon overexpression of human LDLR. In HepG2 cells, Lp(a) internalization was decreased by gain-of-function mutants of PCSK9 more than by wild-type PCSK9, and a loss-of function variant had a reduced ability to influence Lp(a) internalization. Apo(a) internalization by HepG2 cells was not affected by apo(a) isoform size. Finally, we showed that very low density lipoprotein receptor (VLDLR), LDR-related protein (LRP)-8, and LRP-1 do not play a role in Lp(a) internalization or the effect of PCSK9 on Lp(a) internalization. Our findings are consistent with the idea that PCSK9 inhibits Lp(a) clearance through the LDLR, but do not exclude other effects of PCSK9 such as on Lp(a) biosynthesis.
Collapse
|
16
|
Schmidt K, Noureen A, Kronenberg F, Utermann G. Structure, function, and genetics of lipoprotein (a). J Lipid Res 2016; 57:1339-59. [PMID: 27074913 DOI: 10.1194/jlr.r067314] [Citation(s) in RCA: 281] [Impact Index Per Article: 35.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Indexed: 12/29/2022] Open
Abstract
Lipoprotein (a) [Lp(a)] has attracted the interest of researchers and physicians due to its intriguing properties, including an intragenic multiallelic copy number variation in the LPA gene and the strong association with coronary heart disease (CHD). This review summarizes present knowledge of the structure, function, and genetics of Lp(a) with emphasis on the molecular and population genetics of the Lp(a)/LPA trait, as well as aspects of genetic epidemiology. It highlights the role of genetics in establishing Lp(a) as a risk factor for CHD, but also discusses uncertainties, controversies, and lack of knowledge on several aspects of the genetic Lp(a) trait, not least its function.
Collapse
Affiliation(s)
- Konrad Schmidt
- Divisions of Human Genetics Medical University of Innsbruck, Innsbruck, Austria Genetic Epidemiology, Medical University of Innsbruck, Innsbruck, Austria
| | - Asma Noureen
- Genetic Epidemiology, Medical University of Innsbruck, Innsbruck, Austria
| | - Florian Kronenberg
- Genetic Epidemiology, Medical University of Innsbruck, Innsbruck, Austria
| | - Gerd Utermann
- Divisions of Human Genetics Medical University of Innsbruck, Innsbruck, Austria
| |
Collapse
|
17
|
Noureen A, Fresser F, Utermann G, Schmidt K. Sequence variation within the KIV-2 copy number polymorphism of the human LPA gene in African, Asian, and European populations. PLoS One 2015; 10:e0121582. [PMID: 25822457 PMCID: PMC4378929 DOI: 10.1371/journal.pone.0121582] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Accepted: 02/13/2015] [Indexed: 11/18/2022] Open
Abstract
Amazingly little sequence variation is reported for the kringle IV 2 copy number variation (KIV 2 CNV) in the human LPA gene. Apart from whole genome sequencing projects, this region has only been analyzed in some detail in samples of European populations. We have performed a systematic resequencing study of the exonic and flanking intron regions within the KIV 2 CNV in 90 alleles from Asian, European, and four different African populations. Alleles have been separated according to their CNV length by pulsed field gel electrophoresis prior to unbiased specific PCR amplification of the target regions. These amplicons covered all KIV 2 copies of an individual allele simultaneously. In addition, cloned amplicons from genomic DNA of an African individual were sequenced. Our data suggest that sequence variation in this genomic region may be higher than previously appreciated. Detection probability of variants appeared to depend on the KIV 2 copy number of the analyzed DNA and on the proportion of copies carrying the variant. Asians had a high frequency of so-called KIV 2 type B and type C (together 70% of alleles), which differ by three or two synonymous substitutions respectively from the reference type A. This is most likely explained by the strong bottleneck suggested to have occurred when modern humans migrated to East Asia. A higher frequency of variable sites was detected in the Africans. In particular, two previously unreported splice site variants were found. One was associated with non-detectable Lp(a). The other was observed at high population frequencies (10% to 40%). Like the KIV 2 type B and C variants, this latter variant was also found in a high proportion of KIV 2 repeats in the affected alleles and in alleles differing in copy numbers. Our findings may have implications for the interpretation of SNP analyses in other repetitive loci of the human genome.
Collapse
Affiliation(s)
- Asma Noureen
- Division of Genetic Epidemiology, Department of Medical Genetics, Molecular and Clinical Pharmacology, Innsbruck Medical University, Innsbruck, Austria
- Division of Human Genetics, Department of Medical Genetics, Molecular and Clinical Pharmacology, Innsbruck Medical University, Innsbruck, Austria
| | - Friedrich Fresser
- Division of Human Genetics, Department of Medical Genetics, Molecular and Clinical Pharmacology, Innsbruck Medical University, Innsbruck, Austria
- Division of Translational Cell Genetics, Department of Medical Genetics, Molecular and Clinical Pharmacology, Innsbruck Medical University, Innsbruck, Austria
| | - Gerd Utermann
- Division of Human Genetics, Department of Medical Genetics, Molecular and Clinical Pharmacology, Innsbruck Medical University, Innsbruck, Austria
| | - Konrad Schmidt
- Division of Genetic Epidemiology, Department of Medical Genetics, Molecular and Clinical Pharmacology, Innsbruck Medical University, Innsbruck, Austria
- Division of Human Genetics, Department of Medical Genetics, Molecular and Clinical Pharmacology, Innsbruck Medical University, Innsbruck, Austria
- Centre de Recherches Médicales de Lambaréné, Albert Schweitzer Hospital, Lambaréné, Gabon
- Department for Tropical Medicine, Eberhard-Karls-University Tübingen, Tübingen, Germany
- * E-mail:
| |
Collapse
|
18
|
Romagnuolo R, Scipione CA, Boffa MB, Marcovina SM, Seidah NG, Koschinsky ML. Lipoprotein(a) catabolism is regulated by proprotein convertase subtilisin/kexin type 9 through the low density lipoprotein receptor. J Biol Chem 2015; 290:11649-62. [PMID: 25778403 DOI: 10.1074/jbc.m114.611988] [Citation(s) in RCA: 154] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2014] [Indexed: 01/07/2023] Open
Abstract
Elevated levels of lipoprotein(a) (Lp(a)) have been identified as an independent risk factor for coronary heart disease. Plasma Lp(a) levels are reduced by monoclonal antibodies targeting proprotein convertase subtilisin/kexin type 9 (PCSK9). However, the mechanism of Lp(a) catabolism in vivo and the role of PCSK9 in this process are unknown. We report that Lp(a) internalization by hepatic HepG2 cells and primary human fibroblasts was effectively reduced by PCSK9. Overexpression of the low density lipoprotein (LDL) receptor (LDLR) in HepG2 cells dramatically increased the internalization of Lp(a). Internalization of Lp(a) was markedly reduced following treatment of HepG2 cells with a function-blocking monoclonal antibody against the LDLR or the use of primary human fibroblasts from an individual with familial hypercholesterolemia; in both cases, Lp(a) internalization was not affected by PCSK9. Optimal Lp(a) internalization in both hepatic and primary human fibroblasts was dependent on the LDL rather than the apolipoprotein(a) component of Lp(a). Lp(a) internalization was also dependent on clathrin-coated pits, and Lp(a) was targeted for lysosomal and not proteasomal degradation. Our data provide strong evidence that the LDLR plays a role in Lp(a) catabolism and that this process can be modulated by PCSK9. These results provide a direct mechanism underlying the therapeutic potential of PCSK9 in effectively lowering Lp(a) levels.
Collapse
Affiliation(s)
- Rocco Romagnuolo
- From the Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada
| | - Corey A Scipione
- From the Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada
| | - Michael B Boffa
- From the Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada
| | - Santica M Marcovina
- the Northwest Lipid Metabolism and Diabetes Research Laboratories, University of Washington, Seattle, Washington 98109, and
| | - Nabil G Seidah
- the Laboratory of Biochemical Neuroendocrinology, Institut de Recherches Cliniques de Montréal, Montréal, Québec H2W 1R7, Canada
| | - Marlys L Koschinsky
- From the Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario N9B 3P4, Canada,
| |
Collapse
|
19
|
|
20
|
Koschinsky ML, Boffa MB. Lipoprotein(a): an important cardiovascular risk factor and a clinical conundrum. Endocrinol Metab Clin North Am 2014; 43:949-62. [PMID: 25432390 DOI: 10.1016/j.ecl.2014.08.002] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Elevated plasma concentrations of lipoprotein(a) (Lp[a]) are an emerging risk factor for the development of coronary heart disease (CHD). Recent genetic and epidemiologic data have provided strong evidence for a causal role of Lp(a) in CHD. Despite these developments, which have attracted increasing interest from clinicians and basic scientists, many unanswered questions persist. The true pathogenic mechanism of Lp(a) remains a mystery. Significant uncertainty exists concerning the appropriate use of Lp(a) in the clinical setting. No therapeutic intervention remains that can specifically lower plasma Lp(a) concentrations, although the list of compounds that lower Lp(a) and LDL continues to expand.
Collapse
Affiliation(s)
- Marlys L Koschinsky
- Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ontario N9B 3P4, Canada.
| | - Michael B Boffa
- Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ontario N9B 3P4, Canada
| |
Collapse
|
21
|
Koschinsky M, Boffa M. Lipoprotein(a) as a therapeutic target in cardiovascular disease. Expert Opin Ther Targets 2014; 18:747-57. [PMID: 24848373 DOI: 10.1517/14728222.2014.920326] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
INTRODUCTION Recent advances in genetics and epidemiology have once again thrust lipoprotein(a) (Lp(a)) into the clinical spotlight. Elevated plasma concentrations of Lp(a) are an independent, causal risk factor for coronary heart disease. The mechanisms underlying the pathogenicity of Lp(a) remain obscure, and uncertainty continues to surround the appropriate use of Lp(a) in the clinic. AREAS COVERED We summarize the most recent findings on the biology and epidemiology of Lp(a), and use this as a platform to discuss strategies to lower plasma Lp(a) concentrations. The majority of the existing approaches are not Lp(a) specific since they also improve other aspects of the lipid profile. It is possible, however, that the unique characteristics of Lp(a) can be exploited to design therapeutics to specifically lower Lp(a). EXPERT OPINION Lp(a) should be measured in selected patients, including those with a family history of cardiovascular disease (CVD), those with several risk factors for CVD and those who exhibit resistance to statins. Lp(a) lowering should not be the primary driver of choice of therapy, as it has not yet been established through randomized controlled trials that Lp(a) lowering per se has clinical benefit. The development of agents that specifically lower Lp(a) will allow interrogation of this question.
Collapse
Affiliation(s)
- Marlys Koschinsky
- Chemistry and Biochemistry, University of Windsor , Room 242 Essex Hall, 401 Sunset Avenue, Windsor, Ontario, N9B 3P4 , Canada
| | | |
Collapse
|
22
|
Abstract
Plasma lipoprotein(a) [Lp(a)] is a quantitative genetic trait with a very broad and skewed distribution, which is largely controlled by genetic variants at the LPA locus on chromosome 6q27. Based on genetic evidence provided by studies conducted over the last two decades, Lp(a) is currently considered to be the strongest genetic risk factor for coronary heart disease (CHD). The copy number variation of kringle IV in the LPA gene has been strongly associated with both Lp(a) levels in plasma and risk of CHD, thereby fulfilling the main criterion for causality in a Mendelian randomization approach. Alleles with a low kringle IV copy number that together have a population frequency of 25-35% are associated with a doubling of the relative risk for outcomes, which is exceptional in the field of complex genetic phenotypes. The recently identified binding of oxidized phospholipids to Lp(a) is considered as one of the possible mechanisms that may explain the pathogenicity of Lp(a). Drugs that have been shown to lower Lp(a) have pleiotropic effects on other CHD risk factors, and an improvement of cardiovascular endpoints is up to now lacking. However, it has been established in a proof of principle study that lowering of very high Lp(a) by apheresis in high-risk patients with already maximally reduced low-density lipoprotein cholesterol levels can dramatically reduce major coronary events.
Collapse
Affiliation(s)
- F Kronenberg
- Division of Genetic Epidemiology, Innsbruck Medical University, Innsbruck, Austria
| | | |
Collapse
|
23
|
Qi Q, Qi L. Lipoprotein(a) and cardiovascular disease in diabetic patients. CLINICAL LIPIDOLOGY 2012; 7:397-407. [PMID: 23136583 PMCID: PMC3488449 DOI: 10.2217/clp.12.46] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Lipoprotein(a) (Lp[a]) is a LDL-like particle consisting of an ApoA moiety linked to one molecule of ApoB(100). Recent data from large-scale prospective studies and genetic association studies provide highly suggestive evidence for a potentially causal role of Lp(a) in affecting risk of cardiovascular disease (CVD) in general populations. Patients with Type 2 diabetes display clustered metabolic abnormalities and elevated risk of CVD. Lower plasma Lp(a) levels were observed in diabetic patients in several recent studies. Epidemiology studies of Lp(a) and CVD risk in diabetic patients generated inconsistent results. We recently found that Lp(a)-related genetic markers did not predict CVD in two diabetic cohorts. The current data suggest that Lp(a) may differentially affect cardiovascular risk in diabetic patients and in the general population. More prospective studies, Mendelian randomization analysis and functional studies are needed to clarify the causal relationship of Lp(a) and CVD in diabetic patients.
Collapse
Affiliation(s)
- Qibin Qi
- Department of Nutrition, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, USA
| | - Lu Qi
- Department of Nutrition, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, USA
- Channing Laboratory, Department of Medicine, Brigham & Women’s Hospital & Harvard Medical School, Boston, MA 02115, USA
| |
Collapse
|
24
|
Anuurad E, Enkhmaa B, Berglund L. Enigmatic role of lipoprotein(a) in cardiovascular disease. Clin Transl Sci 2011; 3:327-32. [PMID: 21167011 DOI: 10.1111/j.1752-8062.2010.00238.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Lipoprotein (a), [Lp(a)] has many properties in common with low-density lipoprotein, (LDL) but contains a unique protein apolipoprotein(a), linked to apolipoprotein B-100 by a single disulfide bond. There is a substantial size heterogeneity of apo(a), and generally smaller apo(a) sizes tend to correspond to higher plasma Lp(a) levels, but this relation is far from linear, underscoring the importance to assess allele-specific apo(a) levels. The presence of apo(a), a highly charged, carbohydrate-rich, hydrophilic protein may obscure key features of the LDL moiety and offer opportunities for binding to vessel wall elements. Recently, interest in Lp(a) has increased because studies over the past decade have confirmed and more robustly demonstrated a risk factor role of Lp(a) for cardiovascular disease. In particular, levels of Lp(a) carried in particles with smaller size apo(a) isoforms are associated with coronary artery disease (CAD). Other studies suggest that proinflammatory conditions may modulate risk factor properties of Lp(a). Further, Lp(a) may act as a preferential acceptor for proinflammatory oxidized phospholipids transferred from tissues or from other lipoproteins. However, at present only a limited number of agents (e.g., nicotinic acid and estrogen) has proven efficacy in lowering Lp(a) levels. Although Lp(a) has not been definitely established as a cardiovascular risk factor and no guidelines presently recommend intervention, Lp(a)-lowering therapy might offer benefits in subgroups of patients with high Lp(a) levels.
Collapse
|
25
|
Gaeta G, Lanero S, Barra S, Silvestri N, Cuomo V, Materazzi C, Vitagliano G. Sex hormones and lipoprotein(a) concentration. Expert Opin Investig Drugs 2011; 20:221-38. [DOI: 10.1517/13543784.2011.548804] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
|
26
|
|
27
|
Ober C, Nord AS, Thompson EE, Pan L, Tan Z, Cusanovich D, Sun Y, Nicolae R, Edelstein C, Schneider DH, Billstrand C, Pfaffinger D, Phillips N, Anderson RL, Philips B, Rajagopalan R, Hatsukami TS, Rieder MJ, Heagerty PJ, Nickerson DA, Abney M, Marcovina S, Jarvik GP, Scanu AM, Nicolae DL. Genome-wide association study of plasma lipoprotein(a) levels identifies multiple genes on chromosome 6q. J Lipid Res 2009; 50:798-806. [PMID: 19124843 DOI: 10.1194/jlr.m800515-jlr200] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Plasma lipoprotein(a) (Lp[a]) level is an independent risk factor of cardiovascular disease that is under strong genetic control. We conducted a genome-wide association study of plasma Lp(a) in 386 members of a founder population that adheres to a communal lifestyle, proscribes cigarette smoking, and prepares and eats meals communally. We identified associations with 77 single nucleotide polymorphisms (SNPs) spanning 12.5 Mb on chromosome 6q26-q27 that met criteria for genome-wide significance (P <or= 1.3 x 10(-7)) and were within or flanking nine genes, including LPA. We show that variation in at least six genes in addition to LPA are significantly associated with Lp(a) levels independent of each other and of the kringle IV repeat polymorphism in the LPA gene. One novel SNP in intron 37 of the LPA gene was also associated with Lp(a) levels and carotid artery disease number in unrelated Caucasians (P = 7.3 x 10(-12) and 0.024, respectively), also independent of kringle IV number. This study suggests a complex genetic architecture of Lp(a) levels that may involve multiple loci on chromosome 6q26-q27.
Collapse
Affiliation(s)
- Carole Ober
- Department of Human Genetics, University of Chicago, Chicago, IL, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
28
|
Lippi G, Franchini M, Salvagno GL, Guidi GC. Lipoprotein[a] and cancer: Anti-neoplastic effect besides its cardiovascular potency. Cancer Treat Rev 2007; 33:427-36. [PMID: 17442497 DOI: 10.1016/j.ctrv.2007.02.006] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2007] [Revised: 02/26/2007] [Accepted: 02/26/2007] [Indexed: 11/24/2022]
Abstract
While the death rate from cancer has substantially decreased over the past decade, the search for effective and tolerable therapies is a great challenge as yet. The evidence that malignant cells cannot grow to a clinically detectable tumor mass and spread in the absence of an adequate vascular support, has opened a new area of research towards the selective inhibition or even destruction of tumor vessels. Angiostatin and angiostatin-related proteins are a family of specific angiogenesis inhibitors produced by tumors from a family of naturally occurring proteins, which also includes plasminogen and lipoprotein[a]. The anti-angiogenic activity of these proteins resides in cryptic and highly-repetitive molecular domains hidden within the protein moiety, called kringles. Lipoprotein[a] is an intriguing molecule consisting of a low-density lipoprotein core in addition to the covalently bound apolipoprotein[a]. Apolipoprotein[a] is characterized by an inactive protease domain, a single copy of the plasminogen kringle V and multiple repeats of domains homologous to the plasminogen kringle IV. Reliable studies on animal models indicate that the proteolytic break-down products of apolipoprotein[a] would posses anti-angiogenic and anti-tumoral properties both in vitro and in vivo, a premise to develop novel therapeutic modalities which may efficiently suppress tumor growth and metastasis. This review is focused on the biochemical structure, metabolism and the anti-angiogenic activity of this unique and elusive kringle-containing lipoprotein.
Collapse
Affiliation(s)
- Giuseppe Lippi
- Sezione di Chimica e Microscopia Clinica, Dipartimento di Scienze Morfologico-Biomediche, Università degli Studi di Verona, Ospedale Policlinico G.B. Rossi, Piazzale Scuro 10, 37134 Verona, Italy.
| | | | | | | |
Collapse
|
29
|
Osibow K, Malli R, Kostner GM, Graier WF. A new type of non-Ca2+-buffering Apo(a)-based fluorescent indicator for intraluminal Ca2+ in the endoplasmic reticulum. J Biol Chem 2006; 281:5017-5025. [PMID: 16368693 PMCID: PMC4845882 DOI: 10.1074/jbc.m508583200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Genetically encoded Ca2+ indicators are outstanding tools for the assessment of intracellular/organelle Ca2+ dynamics. Basically, most indicators contain the Ca2+-binding site of a (mutated) cytosolic protein that interacts with its natural (mutated) interaction partner upon binding of Ca2+. Consequently, a change in the structure of the sensor occurs that, in turn, alters the fluorescent properties of the sensor. Herein, we present a new type of genetically encoded Ca2+ indicator for the endoplasmic reticulum (ER) (apoK1-er (W. F. Graier, K. Osibow, R. Malli, and G. M. Kostner, patent application number 05450006.1 at the European patent office)) that is based on a single kringle domain from apolipoprotein(a), which is flanked by yellow and cyan fluorescent protein at the 3'- and 5'-ends, respectively. Notably, apoK1-er does not interact with Ca2+ itself but serves as a substrate for calreticulin, the main constitutive Ca2+-binding protein in the ER. ApoK1-er assembles with calreticulin and the protein disulfide isomerase ERp57 and undergoes a conformational shift in a Ca2+-dependent manner that allows fluorescence resonance energy transfer between the two fluorophores. This construct primarily offers three major advantages compared with the already existing probes: (i) it resolves perfectly the physiological range of the free Ca2+ concentration in the ER, (ii) expression of apoK1-er does not affect the Ca2+ buffering capacity of the ER, and (iii) apoK1-er is not inactivated by binding of constitutive interaction partners that prevent Ca2+-dependent conformational changes. These unique characteristics of apoK1-er make this sensor particularly attractive for studies on ER Ca2+ signaling and dynamics in which alteration of Ca2+ fluctuations by expression of any additional Ca2+ buffer essentially has to be avoided.
Collapse
Affiliation(s)
- Karin Osibow
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University Graz, 8010 Graz, Austria
| | - Roland Malli
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University Graz, 8010 Graz, Austria
| | - Gerhard M. Kostner
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University Graz, 8010 Graz, Austria
| | - Wolfgang F. Graier
- Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University Graz, 8010 Graz, Austria
| |
Collapse
|
30
|
Huby T, Afzal V, Doucet C, Lawn RM, Gong EL, Chapman MJ, Thillet J, Rubin EM. Regulation of the expression of the apolipoprotein(a) gene: evidence for a regulatory role of the 5' distal apolipoprotein(a) transcription control region enhancer in yeast artificial chromosome transgenic mice. Arterioscler Thromb Vasc Biol 2003; 23:1633-9. [PMID: 12842837 DOI: 10.1161/01.atv.0000084637.01883.ca] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE The apolipoprotein(a) [apo(a)] gene locus is the major determinant of the circulating concentration of the atherothrombogenic lipoprotein Lp(a). In vitro analysis of the intergenic region between the apo(a) and plasminogen genes revealed the presence of a putative apo(a) transcription control region (ACR) approximately 20 kb upstream of the apo(a) gene that significantly increases the minimal promoter activity of the human apo(a) gene. METHODS AND RESULTS To examine the function of the ACR in its natural genomic context, we used the Cre-loxP recombination system to generate 2 nearly identical apo(a)-yeast artificial chromosome transgenic mouse lines that possess a single integration site for the human apo(a) transgene in the mouse genome but differ by the presence or absence of the ACR enhancer. Analysis of the 2 groups of animals revealed that the deletion of the ACR was associated with 30% reduction in plasma and mRNA apo(a) levels. Apo(a)-yeast artificial chromosome transgenic mice with and without the ACR sequence were similar in all other aspects of apo(a) regulation, including liver-specific apo(a) expression and alteration in expression levels in response to sexual maturation and a high-fat diet. CONCLUSIONS This study provides the first experimental in vivo evidence for a functional role of the ACR enhancer in determining levels of apo(a) expression.
Collapse
MESH Headings
- 5' Untranslated Regions/genetics
- 5' Untranslated Regions/physiology
- Animals
- Apolipoproteins A/genetics
- Blastocyst/chemistry
- Blastocyst/metabolism
- Chimera
- Chromosomes, Artificial, Yeast/genetics
- Diet, Atherogenic
- Dietary Fats/pharmacology
- Enhancer Elements, Genetic/drug effects
- Enhancer Elements, Genetic/physiology
- Female
- Gene Expression Regulation/drug effects
- Gene Expression Regulation/genetics
- Gene Expression Regulation/physiology
- Gene Transfer Techniques
- Humans
- Mice
- Mice, Inbred C57BL
- Mice, Transgenic/genetics
- Organ Specificity/genetics
- Promoter Regions, Genetic/genetics
- Transcription, Genetic/genetics
- Transcription, Genetic/physiology
- Transgenes/genetics
Collapse
Affiliation(s)
- Thierry Huby
- Institut National de la Santé et de la Recherche Médicale, INSERM Unit 551, Dyslipemias and Atherosclerosis: Genetics, Metabolism and Therapeutics, Hôpital de la Pitié, Paris, France.
| | | | | | | | | | | | | | | |
Collapse
|
31
|
Nassir F, Xie Y, Davidson NO. Apolipoprotein[a] secretion from hepatoma cells is regulated in a size-dependent manner by alterations in disulfide bond formation. J Lipid Res 2003; 44:816-27. [PMID: 12562843 DOI: 10.1194/jlr.m200451-jlr200] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Apolipoprotein[a] (apo[a]) is a large disulfide linked glycoprotein synthesized by hepatocytes. We have examined the role of disulfide bond formation in the processing of apo[a] using human and rat hepatoma cells expressing apo[a] isoforms containing varying numbers of kringle 4 (K4) domains, following treatment with DTT. Hepatoma cells expressing 6- or 9-K4 isoforms revealed approximately 90% inhibition of apo[a] secretion following DTT treatment, although larger isoforms containing 13- or 17-K4 domains demonstrated continued secretion (up to 30% of control values), suggesting that a fraction of the larger isoforms is at least partially DTT resistant. Wash-out experiments demonstrated that these effects were completely reversible for all isoforms studied, with no enhanced degradation associated with prolonged intracellular retention. DTT treatment was associated with enhanced binding of apo[a] with the endoplasmic reticulum-associated chaperone proteins calnexin, calreticulin, and BiP, which was reversible upon DTT removal. The chemical chaperone 6-aminohexanoic acid, previously demonstrated by others to rescue defective apo[a] secretion associated with alterations in glycosylation, failed to alter the secretion of apo[a] following DTT treatment. The demonstration that DTT modulates apo[a] secretion in a manner influenced by both the type and number of K4 repeats extends understanding of the mechanisms that regulate its exit from the endoplasmic reticulum.
Collapse
Affiliation(s)
- Fatiha Nassir
- Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA
| | | | | |
Collapse
|
32
|
Abstract
Lipoprotein(a) is a cholesterol-enriched lipoprotein, consisting of a covalent linkage joining the unique and highly polymorphic apolipoprotein(a) to apolipoprotein B100, the main protein moiety of low-density lipoproteins. Although the concentration of lipoprotein(a) in humans is mostly genetically determined, acquired disorders might influence synthesis and catabolism of the particle. Raised concentration of lipoprotein(a) has been acknowledged as a leading inherited risk factor for both premature and advanced atherosclerosis at different vascular sites. The strong structural homologies with plasminogen and low-density lipoproteins suggest that lipoprotein(a) might represent the ideal bridge between the fields of atherosclerosis and thrombosis in the pathogenesis of vascular occlusive disorders. Unfortunately, the exact mechanisms by which lipoprotein(a) promotes, accelerates, and complicates atherosclerosis are only partially understood. In some clinical settings, such as in patients at exceptionally low risk for cardiovascular disease, the potential regenerative and antineoplastic properties of lipoprotein(a) might paradoxically counterbalance its athero-thrombogenicity, as attested by the compatibility between raised plasma lipoprotein(a) levels and longevity.
Collapse
Affiliation(s)
- Giuseppe Lippi
- Istituto di Chimica e Microscopia Clinica, Dipartimento di Scienze Morfologiche e Biomediche, Università degli Studi di Verona, Verona, Italy
| | | |
Collapse
|
33
|
Catena C, Novello M, Dotto L, De Marchi S, Sechi LA. Serum lipoprotein(a) concentrations and alcohol consumption in hypertension: possible relevance for cardiovascular damage. J Hypertens 2003; 21:281-8. [PMID: 12569257 DOI: 10.1097/00004872-200302000-00018] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
OBJECTIVES To evaluate the relationships between alcohol intake and serum lipoprotein(a) [Lp(a)], a powerful predictor of organ damage, in patients with essential hypertension with a wide range of alcohol intake, and to investigate whether the association between alcohol intake and serum Lp(a) concentrations occurs over the entire spectrum of apo(a) phenotypes. DESIGN Cross-sectional study of a case series. SETTING University medical centre. PATIENTS Four hundred and two patients with untreated essential hypertension recruited at a hypertension clinic. MAIN OUTCOME MEASURES Serum Lp(a) concentrations, apo(a) isoforms, alcohol consumption, smoking habits and cardiovascular status. RESULTS No difference in Lp(a) concentrations was observed between teetotalers and occasional drinkers. Light drinkers (1-20 g/day ethanol), moderate drinkers (21-50 g/day), and heavy drinkers (> 50 g/day) had, respectively, 21, 26 and 57% lower median Lp(a) concentrations than teetotalers and occasional drinkers. Similar findings were obtained when male and female patients were analysed separately. Log Lp(a) concentrations were inversely and independently correlated with alcohol consumption in both men and women with hypertension. The frequency distributions of apo(a) isoforms and liver function parameters were comparable across the different alcohol intake groups. Patients with evidence of cardiovascular damage had greater concentrations of serum Lp(a) and higher frequency of low-molecular weight apo(a) isoforms as compared with patients without such evidence. CONCLUSIONS Serum Lp(a) is inversely and dose-dependently related with alcohol intake in patients with hypertension, and this relationship is independent of the size distribution of apo(a) isoforms. Reduction of Lp(a) concentrations by regular consumption of alcohol might favourably affect the atherosclerotic risk profile of patients with hypertension and thereby decrease cardiovascular morbidity.
Collapse
Affiliation(s)
- Cristiana Catena
- Department of Experimental and Clinical Pathology and Medicine, University of Udine School of Medicine, Italy
| | | | | | | | | |
Collapse
|
34
|
Lourenço A, Máximo P, Ferreira L, Pereira M. Indolizidine and quinolizidine alkaloids structure and bioactivity. ACTA ACUST UNITED AC 2002. [DOI: 10.1016/s1572-5995(02)80038-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/21/2023]
|
35
|
Abstract
GB viruses A and B (GBV-A and GBV-B) are members of the Flaviviridae family and are isolated from tamarins injected with serum from a human hepatitis patient. Along with a related human virus, GB virus C, or alternatively, hepatitis G virus (GBV-C/HGV), the three viruses represent the GB agents. Of the three viruses, GBV-B has been proposed as a potential surrogate model for the study of hepatitis C virus (HCV) infections of humans. GBV-B is phylogenetically most closely related to HCV and causes an acute, self-resolving hepatitis in tamarins as indicated by an increase in alanine aminotransferase and changes in liver histology. Similarities between GBV-B and HCV are found at the nucleotide sequence level with the two viruses sharing 28% amino acid homology over the lengths of their open reading frames. Short regions have even higher levels of homology that are functionally significant as shown by the ability of the GBV-B NS3 protease to cleave recombinant HCV polyprotein substrates. The shared protease substrate specificities suggest that GBV-B may be useful in testing antiviral compounds for activity against HCV. Although there are numerous similarities between GBV-B and HCV, there are important differences in that HCV frequently causes chronic infections in people, whereas GBV-B appears to cause only acute infections. The acute versus chronic course of infection may point to important differences between the two viruses that, along with the numerous similarities, will make GBV-B in tamarins a good surrogate model for HCV.
Collapse
Affiliation(s)
- B Beames
- Department of Virology and Immunology, Southwest Foundation for Biomedical Research and Southwest Regional Primate Research Center, San Antonio, Texas, USA
| | | | | |
Collapse
|
36
|
Huby T, Dachet C, Lawn RM, Wickings J, Chapman MJ, Thillet J. Functional analysis of the chimpanzee and human apo(a) promoter sequences: identification of sequence variations responsible for elevated transcriptional activity in chimpanzee. J Biol Chem 2001; 276:22209-14. [PMID: 11301336 DOI: 10.1074/jbc.m102204200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Lp(a) concentrations vary considerably among individuals and are primarily determined by the apo(a) gene locus. We have previously shown that mean plasma Lp(a) levels in the chimpanzee are significantly higher than those observed in humans (Doucet, C., Huby, T., Chapman, J., and Thillet, J. (1994) J. Lipid Res 35, 263-270). To evaluate the possibility that this difference may result from a high level of expression of chimpanzee apo(a), we cloned and sequenced 1.4 kilobase (kb) of the 5'-flanking region of the gene and compared promoter activity to that of its human counterpart. Sequence analysis revealed 98% homology between chimpanzee and human apo(a) 5' sequences; among the differences observed, two involved polymorphic sites associated with Lp(a) levels in humans. The TTTTA repeat located 1.3 kb 5' of the apo(a) gene, present in a variable number of copies (n = 5-12) in humans, is uniquely present as four copies in the chimpanzee sequence. The second position concerns the +93 C>T polymorphism that creates an additional ATG start codon in the human apo(a) gene, thereby impairing translation efficiency. In chimpanzee, this position did not appear polymorphic, and a base difference at position +94 precluded the presence of an additional ATG. In transient transfection assays, the chimpanzee apo(a) promoter exhibited a 5-fold elevation in transcriptional activity as compared with its human counterpart. This marked difference in activity was maintained with either 1.4 kb of 5' sequence or the minimal promoter region -98 to +141 of the human and chimpanzee apo(a) genes. Using point mutational analyses, nucleotides present at positions -3, -2, and +8 (relative to the start site of transcription) were found to be essential for the high transcription efficiency of the chimpanzee apo(a) promoter. High transcriptional activity of the chimpanzee apo(a) gene may therefore represent a key factor in the elevated plasma Lp(a) levels characteristic of this non-human primate.
Collapse
Affiliation(s)
- T Huby
- INSERM, Unité 551, Dyslipoprotéinémies, Athérosclérose: Génétique, Métabolisme et Thérapeutique, Hôpital de la Pitié, 83 Boulevard de l'Hôpital, Paris 75651 Cedex 13, France
| | | | | | | | | | | |
Collapse
|
37
|
Wang J, Boedeker J, Hobbs HH, White AL. Determinants of human apolipoprotein [a] secretion from mouse hepatocyte cultures. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)32336-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
|
38
|
Kraft HG, Lingenhel A, Raal FJ, Hohenegger M, Utermann G. Lipoprotein(a) in homozygous familial hypercholesterolemia. Arterioscler Thromb Vasc Biol 2000; 20:522-8. [PMID: 10669652 DOI: 10.1161/01.atv.20.2.522] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Lipoprotein(a) [Lp(a)] is a quantitative genetic trait that in the general population is largely controlled by 1 major locus-the locus for the apolipoprotein(a) [apo(a)] gene. Sibpair studies in families including familial defective apolipoprotein B or familial hypercholesterolemia (FH) heterozygotes have demonstrated that, in addition, mutations in apolipoprotein B and in the LDL receptor (LDL-R) gene may affect Lp(a) plasma concentrations, but this issue is controversial. Here, we have further investigated the influence of mutations in the LDL-R gene on Lp(a) levels by inclusion of FH homozygotes. Sixty-nine members of 22 families with FH were analyzed for mutations in the LDL-R as well as for apo(a) genotypes, apo(a) isoforms, and Lp(a) plasma levels. Twenty-six individuals were found to be homozygous for FH, and 43 were heterozygous for FH. As in our previous analysis, FH heterozygotes had significantly higher Lp(a) than did non-FH individuals from the same population. FH homozygotes with 2 nonfunctional LDL-R alleles had almost 2-fold higher Lp(a) levels than did FH heterozygotes. This increase was not explained by differences in apo(a) allele frequencies. Phenotyping of apo(a) and quantitative analysis of isoforms in family members allowed the assignment of Lp(a) levels to both isoforms in apo(a) heterozygous individuals. Thus, Lp(a) levels associated with apo(a) alleles that were identical by descent could be compared. In the resulting 40 allele pairs, significantly higher Lp(a) levels were detected in association with apo(a) alleles from individuals with 2 defective LDL-R alleles compared with those with only 1 defective allele. This difference of Lp(a) levels between allele pairs was present across the whole size range of apo(a) alleles. Hence, mutations in the LDL-R demonstrate a clear gene-dosage effect on Lp(a) plasma concentrations.
Collapse
Affiliation(s)
- H G Kraft
- Institute for Medical Biology and Human Genetics. University of Innsbruck, Innsbruck, Austria.
| | | | | | | | | |
Collapse
|
39
|
Valenti K, Aveynier E, Leauté S, Laporte F, Hadjian AJ. Contribution of apolipoprotein(a) size, pentanucleotide TTTTA repeat and C/T(+93) polymorphisms of the apo(a) gene to regulation of lipoprotein(a) plasma levels in a population of young European Caucasians. Atherosclerosis 1999; 147:17-24. [PMID: 10525120 DOI: 10.1016/s0021-9150(99)00137-9] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Several studies indicate that the inter-individual variation in plasma concentrations of lipoprotein(a) (Lp(a)) is mainly under genetic control. To define the effect of three DNA polymorphisms on apolipoprotein(a) (apo(a)) expression, we have determined plasma Lp(a) concentrations, apo(a) isoform size, KpnI allele size, the TTTTA pentanucleotide repeat number in the 5' control region of the apo(a) gene and the +93 C/T polymorphism in a European Caucasian population. The simultaneous determination of the kringle 4 (K4) number by genotyping and by phenotyping revealed that the size distribution of non-expressed apo(a) alleles was markedly skewed towards alleles with greater than 25 K4 repeats. This is consistent with the inverse relationship frequently described between the kringle 4 number and the plasma Lp(a) level. Apportioning the Lp(a) concentration from the surface of the peaks on apo(a) phenotyping blots, we have observed that the Lp(a) plasma concentration associated with alleles having more than 25 K4 units does not exceed 400 mg/l, whereas the range of Lp(a) concentrations associated with smaller alleles was broad, from 0 to more than 1000 mg/l. It can thus be concluded that the number of K4 repeats is the main determinant of Lp(a) concentration when this number is more than 25, whereas other polymorphisms may be involved in the alleles with fewer than 26 K4. Analyses of the TTTTA repeat number and of the +93 C/T polymorphism were performed in subjects with KpnI alleles of the same length: low Lp(a) concentrations were shown to be preferentially associated with the presence of apo(a) alleles with more than eight pentanucleotide repeats while no association was revealed between Lp(a) plasma levels and the C/T polymorphism. These results demonstrate that the (TTTTA)(n) polymorphism affects the Lp(a) expression independently of apo(a) size polymorphism.
Collapse
Affiliation(s)
- K Valenti
- Laboratoire de Biochimie A, CHU de Grenoble, 38043, Grenoble, France
| | | | | | | | | |
Collapse
|
40
|
Aridor M, Balch WE. Integration of endoplasmic reticulum signaling in health and disease. Nat Med 1999; 5:745-51. [PMID: 10395318 DOI: 10.1038/10466] [Citation(s) in RCA: 199] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- M Aridor
- Department of Cell and Molecular biology, La Jolla, California 92037, USA
| | | |
Collapse
|
41
|
|
42
|
Abstract
Lipoprotein(a) is an atherogenic, cholesterol ester-rich lipoprotein of unknown physiological function. The unusual species distribution of lipoprotein(a) and the extreme polymorphic nature of its distinguishing apolipoprotein component, apolipoprotein(a), have provided unique challenges for the investigation of its biochemistry, genetics, metabolism and atherogenicity. Some fundamental questions regarding this enigmatic lipoprotein have escaped elucidation, as will be highlighted in this review.
Collapse
Affiliation(s)
- H H Hobbs
- Department of Internal Medicine, University of Texas Southwestern Medical Center at Dallas 75235, USA.
| | | |
Collapse
|
43
|
Abstract
Our understanding of the genetics, metabolism and pathophysiology of the atherogenic plasma lipoprotein Lp(a) has considerably increased over past years. Nevertheless, the precise mechanisms regulating the biosynthesis and assembly of Lp(a) are poorly understood and controversially discussed. Lp(a) plasma concentrations are determined by synthesis and not by degradation. Transcriptional and post-translational mechanisms have been identified as regulating Lp(a) production in primary hepatocytes and transfected cell lines. Assembly of Lp(a) occurs extracellularly from newly synthesized apolipoprotein(a) and circulating LDL. This view has recently been challenged by in-vivo kinetic studies in humans which are compatible with an intracellular assembly event. Lp(a) assembly is a complex two-step process of multiple non-covalent interactions between apolipoprotein(a) and apolipoprotein B-100 of LDL followed by covalent disulfide linkage of two free cysteine residues on both proteins.
Collapse
Affiliation(s)
- H Dieplinger
- Institute of Medical Biology and Human Genetics, University of Innsbruck, Austria
| | | |
Collapse
|
44
|
Abstract
Apolipoprotein (a) (apo(a)) is a component of the atherogenic lipoprotein, Lp(a). The efficiency with which apo(a) escapes the endoplasmic reticulum (ER) and is secreted by the liver is a major determinant of plasma Lp(a) levels. Apo(a) contains a series of domains homologous to plasminogen kringle (K) 4, each of which possesses a potential lysine-binding site. By using primary mouse hepatocytes expressing a 17K4 human apo(a) protein, we found that high concentrations (25-200 mM) of the lysine analog, 6-aminohexanoic acid (6AHA), increased apo(a) secretion 8-14-fold. This was accompanied by a decrease in apo(a) presecretory degradation. 6AHA inhibited accumulation of apo(a) in the ER induced by the proteasome inhibitor, lactacystin. Thus, 6AHA appeared to inhibit degradation by increasing apo(a) export from the ER. Significantly, 6AHA overcame the block in apo(a) secretion induced by the ER glucosidase inhibitor, castanospermine. 6AHA may therefore circumvent the requirement for calnexin and calreticulin interaction in apo(a) secretion. Sucrose gradients and a gel-based folding assay were unable to detect any influence of 6AHA on apo(a) folding. However, non-covalent or small, disulfide-dependent changes in apo(a) conformation would not be detected in these assays. Proline also increased the efficiency of apo(a) secretion. We propose that 6AHA and proline can act as chemical chaperones for apo(a).
Collapse
Affiliation(s)
- J Wang
- Center for Human Nutrition, University of Texas Southwestern Medical Center, Dallas, Texas 75235-9052, USA
| | | |
Collapse
|
45
|
Abstract
Apolipoprotein(a) is coded by one of the most polymorphic genes known in humans. In white and Asian populations variation in this gene is the major determinant of the plasma concentrations of the atherogenic lipoprotein(a) which varies enormously between individuals and considerably across populations. Recent studies have shown that the genetic architecture of the quantitative Lp(a) trait differs among major human groups. In Africans there is evidence for a transacting factor. Three types of variation have been identified in the apo(a) gene: a size polymorphism in the coding region (K IV type 2 repeats), a pentanucleotide repeat polymorphism in the promoter (5'PNRP) and sequence variation in coding and non-coding regions of the gene including a C/T polymorphism at +93 which creates an additional ATG start codon but also affects transcription. The causal +93 C/T effect is masked by linkage disequilibrium in white populations. Analysis of apo(a) K IV 6-10 exons revealed the existence of population-specific spectra of polymorphism in this domain. However further sequence variation which may provide clues for the understanding of the regulation of apo(a) concentrations still needs to be identified. DNA sequencing and phylogenetic analysis have demonstrated that two types of apo(a) exist, in phylogenetically distant mammalian lineages a K IV derived primate form and a K III-derived hedgehog form which are products of convergent evolution.
Collapse
Affiliation(s)
- G Utermann
- Institute for Medical Biology and Human Genetics, Innsbruck, Austria.
| |
Collapse
|
46
|
Fontana P, Mooser V, Bovet P, Shamlaye C, Burnand B, Lenain V, Marcovina SM, Riesen W, Darioli R. Dose-dependent inverse relationship between alcohol consumption and serum Lp(a) levels in black African males. Arterioscler Thromb Vasc Biol 1999; 19:1075-82. [PMID: 10195938 DOI: 10.1161/01.atv.19.4.1075] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Serum or plasma levels of Lp(a) vary widely between individuals and are higher in Africans and their descendants compared with white persons. In whites, high serum levels of Lp(a) are associated with the premature development of atherosclerosis. In both ethnic groups, serum Lp(a) levels are highly genetically determined and only a few environmental or physiological factors, like testosterone or estrogen, have been shown to lower serum Lp(a) levels. In whites, alcohol consumption is associated with lower serum Lp(a) levels. However, the mechanism underlying this association and whether it holds true for blacks is not known. To address these questions, we analyzed serum Lp(a) levels in 333 middle-aged males of African descent from the Seychelles Islands (Indian Ocean). In addition, we analyzed the size of the apo(a) isoforms and the serum levels of albumin and sex hormones in a subset of 279 subjects. Serum Lp(a) levels were similar in teetotalers (median, 32.5 mg/dL; n=42) and occasional drinkers (median, 34.1 mg/dL; n=112). In contrast, individuals consuming 10 to 80 g of ethanol/d (n=83) and heavy drinkers (>80 g of ethanol/d, n=96) had a 9% and 32% lower median Lp(a) level than teetotalers, respectively (P=0.01). The size distribution of the apo(a) isoforms and the mean serum levels of albumin, estradiol, and luteinizing hormone were similar in teetotalers and occasional drinkers compared with moderate and heavy drinkers. These latter 2 groups had lower serum levels of testosterone and sex hormone-binding globulin. These data indicate that alcohol intake is associated in a dose-dependent manner with lower serum Lp(a) levels in males of African descent and that this association is not related to the size of the apo(a) isoforms, to the synthetic function of the liver, or to sex hormone biochemical status.
Collapse
Affiliation(s)
- P Fontana
- Medical Policlinic, Institute of Social and Preventive Medicine, University of Lausanne, Switzerland
| | | | | | | | | | | | | | | | | |
Collapse
|
47
|
White AL, Guerra B, Wang J, Lanford RE. Presecretory degradation of apolipoprotein[a] is mediated by the proteasome pathway. J Lipid Res 1999. [DOI: 10.1016/s0022-2275(20)33367-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|
48
|
Bonen DK, Nassir F, Hausman AM, Davidson NO. Inhibition of N-linked glycosylation results in retention of intracellular apo[a] in hepatoma cells, although nonglycosylated and immature forms of apolipoprotein[a] are competent to associate with apolipoprotein B-100 in vitro. J Lipid Res 1998. [DOI: 10.1016/s0022-2275(20)32192-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|
49
|
Nassir F, Bonen DK, Davidson NO. Apolipoprotein(a) synthesis and secretion from hepatoma cells is coupled to triglyceride synthesis and secretion. J Biol Chem 1998; 273:17793-800. [PMID: 9651381 DOI: 10.1074/jbc.273.28.17793] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Apolipoprotein(a) (apo(a)) is synthesized and secreted from liver cells and represents one of the two major protein components of the atherogenic lipoprotein, Lp(a). Little is known, however, of the factors that regulate the secretion of this protein. We have undertaken an analysis of the response to oleate supplementation in stable clones of HepG2 and McA-RH7777 cells expressing either a 6 K-IV or 17 K-IV isoform of apo(a). These cell lines were examined by pulse-chase analysis and each demonstrated an increase (range 2-6-fold) in apo(a) secretion following supplementation with 0.8 mM oleate. Microsomal membranes, prepared from HepG2 cells expressing a 6 K-IV apo(a) isoform, demonstrated that oleate supplementation increased the apparent protection of apo(a) from protease digestion, suggesting that alterations in the translocation efficiency of apo(a) may accompany the addition of oleate. Cells incubated with brefeldin A demonstrated increased recovery of the precursor form of apo(a) with oleate supplementation, suggesting that alterations in post-translational degradation may also contribute to the observed increase in apo(a) secretion following oleate addition. To further characterize the oleate-dependent increase in apo(a) secretion, cells were incubated with an inhibitor of the microsomal triglyceride transfer protein. These experiments demonstrated a dose-dependent decrease in apo(a) secretion from both cell lines. Furthermore, addition of either the microsomal triglyceride transfer protein inhibitor or triacsin C, an inhibitor of acyl-CoA synthase, completely abrogated the oleate-dependent increase in apo(a) secretion. Taken together, these data provide evidence that apo(a) secretion from hepatoma cells may be linked to elements of cellular triglyceride assembly and secretion.
Collapse
Affiliation(s)
- F Nassir
- Department of Medicine, University of Chicago, Chicago, Illinois 60637, USA
| | | | | |
Collapse
|
50
|
Molecular basis of an apolipoprotein[a] null allele: a splice sitemutation is associated with deletion of a single exon. J Lipid Res 1998. [DOI: 10.1016/s0022-2275(20)32512-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
|