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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.
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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.
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Genovesi S, Giussani M, Lieti G, Orlando A, Patti I, Parati G. Evidence and Uncertainties on Lipoprotein(a) as a Marker of Cardiovascular Health Risk in Children and Adolescents. Biomedicines 2023; 11:1661. [PMID: 37371756 PMCID: PMC10295837 DOI: 10.3390/biomedicines11061661] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Revised: 06/05/2023] [Accepted: 06/06/2023] [Indexed: 06/29/2023] Open
Abstract
Lipoprotein(a) (Lp(a)) is made up of apoprotein(a) (apo(a)) and an LDL-like particle. The LPA gene encodes apo(a) and thus determines the characteristics and amount of apo(a) and Lp(a). The proportion of Lp(a) in each individual is genetically determined and is only minimally modifiable by the environment or diet. Lp(a) has important pro-atherosclerotic and pro-inflammatory effects. It has been hypothesized that Lp(a) also has pro-coagulant and antifibrinolytic actions. For these reasons, high Lp(a) values are an important independent risk factor for cardiovascular disease and calcific aortic valve stenosis. Numerous studies have been performed in adults about the pathophysiology and epidemiology of Lp(a) and research is under way for the development of drugs capable of reducing Lp(a) plasma values. Much less information is available regarding Lp(a) in children and adolescents. The present article reviews the evidence on this topic. The review addresses the issues of Lp(a) changes during growth, the correlation between Lp(a) values in children and those in their parents, and between Lp(a) levels in children, and the presence of cardiovascular disease in the family. Gaining information on these points is particularly important for deciding whether Lp(a) assay may be useful for defining the cardiovascular risk in children, in order to plan a prevention program early.
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Affiliation(s)
- Simonetta Genovesi
- School of Medicine and Surgery, Milano-Bicocca University, 20126 Milan, Italy; (G.L.); (I.P.); (G.P.)
- Istituto Auxologico Italiano, Istituto Ricovero Cura Carattere Scientifico (IRCCS), 20135 Milan, Italy; (M.G.); (A.O.)
| | - Marco Giussani
- Istituto Auxologico Italiano, Istituto Ricovero Cura Carattere Scientifico (IRCCS), 20135 Milan, Italy; (M.G.); (A.O.)
| | - Giulia Lieti
- School of Medicine and Surgery, Milano-Bicocca University, 20126 Milan, Italy; (G.L.); (I.P.); (G.P.)
| | - Antonina Orlando
- Istituto Auxologico Italiano, Istituto Ricovero Cura Carattere Scientifico (IRCCS), 20135 Milan, Italy; (M.G.); (A.O.)
| | - Ilenia Patti
- School of Medicine and Surgery, Milano-Bicocca University, 20126 Milan, Italy; (G.L.); (I.P.); (G.P.)
| | - Gianfranco Parati
- School of Medicine and Surgery, Milano-Bicocca University, 20126 Milan, Italy; (G.L.); (I.P.); (G.P.)
- Istituto Auxologico Italiano, Istituto Ricovero Cura Carattere Scientifico (IRCCS), 20135 Milan, Italy; (M.G.); (A.O.)
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Chemello K, Chan DC, Lambert G, Watts GF. Recent advances in demystifying the metabolism of lipoprotein(a). Atherosclerosis 2022; 349:82-91. [DOI: 10.1016/j.atherosclerosis.2022.04.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Revised: 03/29/2022] [Accepted: 04/01/2022] [Indexed: 12/24/2022]
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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.
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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
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Reyes-Soffer G, Ginsberg HN, Berglund L, Duell PB, Heffron SP, Kamstrup PR, Lloyd-Jones DM, Marcovina SM, Yeang C, Koschinsky ML. Lipoprotein(a): A Genetically Determined, Causal, and Prevalent Risk Factor for Atherosclerotic Cardiovascular Disease: A Scientific Statement From the American Heart Association. Arterioscler Thromb Vasc Biol 2022; 42:e48-e60. [PMID: 34647487 PMCID: PMC9989949 DOI: 10.1161/atv.0000000000000147] [Citation(s) in RCA: 191] [Impact Index Per Article: 95.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
High levels of lipoprotein(a) [Lp(a)], an apoB100-containing lipoprotein, are an independent and causal risk factor for atherosclerotic cardiovascular diseases through mechanisms associated with increased atherogenesis, inflammation, and thrombosis. Lp(a) is predominantly a monogenic cardiovascular risk determinant, with ≈70% to ≥90% of interindividual heterogeneity in levels being genetically determined. The 2 major protein components of Lp(a) particles are apoB100 and apolipoprotein(a). Lp(a) remains a risk factor for cardiovascular disease development even in the setting of effective reduction of plasma low-density lipoprotein cholesterol and apoB100. Despite its demonstrated contribution to atherosclerotic cardiovascular disease burden, we presently lack standardization and harmonization of assays, universal guidelines for diagnosing and providing risk assessment, and targeted treatments to lower Lp(a). There is a clinical need to understand the genetic and biological basis for variation in Lp(a) levels and its relationship to disease in different ancestry groups. This scientific statement capitalizes on the expertise of a diverse basic science and clinical workgroup to highlight the history, biology, pathophysiology, and emerging clinical evidence in the Lp(a) field. Herein, we address key knowledge gaps and future directions required to mitigate the atherosclerotic cardiovascular disease risk attributable to elevated Lp(a) levels.
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Handhle A, Viljoen A, Wierzbicki AS. Elevated Lipoprotein(a): Background, Current Insights and Future Potential Therapies. Vasc Health Risk Manag 2021; 17:527-542. [PMID: 34526771 PMCID: PMC8436116 DOI: 10.2147/vhrm.s266244] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2021] [Accepted: 08/13/2021] [Indexed: 12/13/2022] Open
Abstract
Lipoprotein(a) forms a subfraction of the lipid profile and is characterized by the addition of apolipprotein(a) (apo(a)) to apoB100 derived particles. Its levels are mostly genetically determined inversely related to the number of protein domain (kringle) repeats in apo(a). In epidemiological studies, it shows consistent association with cardiovascular disease (CVD) and most recently with extent of aortic stenosis. Issues with standardizing the measurement of Lp(a) are being resolved and consensus statements favor its measurement in patients at high risk of, or with family histories of CVD events. Major lipid-lowering therapies such as statin, fibrates, and ezetimibe have little effect on Lp(a) levels. Therapies such as niacin or cholesterol ester transfer protein (CETP) inhibitors lower Lp(a) as well as reducing other lipid-related risk factors but have failed to clearly reduce CVD events. Proprotein convertase subtilisin kexin-9 (PCSK9) inhibitors reduce cholesterol and Lp(a) as well as reducing CVD events. New antisense therapies specifically targeting apo(a) and hence Lp(a) have greater and more specific effects and will help clarify the extent to which intervention in Lp(a) levels will reduce CVD events.
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Affiliation(s)
- Ahmed Handhle
- Department of Metabolic Medicine/Chemical Pathology, Addenbrookes Hospital, Cambridge, UK
| | - Adie Viljoen
- Department of Metabolic Medicine/Chemical Pathology, North & East Hertfordshire Hospitals Trust, Lister Hospital, Hertfordshire, UK
| | - Anthony S Wierzbicki
- Department of Metabolic Medicine/Chemical Pathology, Guy's & St Thomas', Hospitals, London, SE1 7EH, UK
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McCormick SPA, Schneider WJ. Lipoprotein(a) catabolism: a case of multiple receptors. Pathology 2018; 51:155-164. [PMID: 30595508 DOI: 10.1016/j.pathol.2018.11.003] [Citation(s) in RCA: 64] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Revised: 10/31/2018] [Accepted: 11/01/2018] [Indexed: 01/09/2023]
Abstract
Lipoprotein(a) [Lp(a)] is an apolipoprotein B (apoB)-containing plasma lipoprotein similar in structure to low-density lipoprotein (LDL). Lp(a) is more complex than LDL due to the presence of apolipoprotein(a) [apo(a)], a large glycoprotein sharing extensive homology with plasminogen, which confers some unique properties onto Lp(a) particles. ApoB and apo(a) are essential for the assembly and catabolism of Lp(a); however, other proteins associated with the particle may modify its metabolism. Lp(a) specifically carries a cargo of oxidised phospholipids (OxPL) bound to apo(a) which stimulates many proinflammatory pathways in cells of the arterial wall, a key property underlying its pathogenicity and association with cardiovascular disease (CVD). While the liver and kidney are the major tissues implicated in Lp(a) clearance, the pathways for Lp(a) uptake appear to be complex and are still under investigation. Biochemical studies have revealed an exceptional array of receptors that associate with Lp(a) either via its apoB, apo(a), or OxPL components. These receptors fall into five main categories, namely 'classical' lipoprotein receptors, toll-like and scavenger receptors, lectins, and plasminogen receptors. The roles of these receptors have largely been dissected by genetic manipulation in cells or mice, although their relative physiological importance for removal of Lp(a) from the circulation remains unclear. The LPA gene encoding apo(a) has an overwhelming effect on Lp(a) levels which precludes any clear associations between potential Lp(a) receptor genes and Lp(a) levels in population studies. Targeted approaches and the selection of unique Lp(a) phenotypes within populations has nevertheless allowed for some associations to be made. Few of the proposed Lp(a) receptors can specifically be manipulated with current drugs and, as such, it is not currently clear whether any of these receptors could provide relevant targets for therapeutic manipulation of Lp(a) levels. This review summarises the current status of knowledge about receptor-mediated pathways for Lp(a) catabolism.
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Affiliation(s)
- Sally P A McCormick
- Department of Biochemistry, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand.
| | - Wolfgang J Schneider
- Department of Medical Biochemistry, Max F. Perutz Laboratories, Medical University of Vienna, Vienna, Austria
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Scipione CA, Koschinsky ML, Boffa MB. Lipoprotein(a) in clinical practice: New perspectives from basic and translational science. Crit Rev Clin Lab Sci 2017; 55:33-54. [PMID: 29262744 DOI: 10.1080/10408363.2017.1415866] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Elevated plasma concentrations of lipoprotein(a) (Lp(a)) are a causal risk factor for coronary heart disease (CHD) and calcific aortic valve stenosis (CAVS). Genetic, epidemiological and in vitro data provide strong evidence for a pathogenic role for Lp(a) in the progression of atherothrombotic disease. Despite these advancements and a race to develop new Lp(a) lowering therapies, there are still many unanswered and emerging questions about the metabolism and pathophysiology of Lp(a). New studies have drawn attention to Lp(a) as a contributor to novel pathogenic processes, yet the mechanisms underlying the contribution of Lp(a) to CVD remain enigmatic. New therapeutics show promise in lowering plasma Lp(a) levels, although the complete mechanisms of Lp(a) lowering are not fully understood. Specific agents targeted to apolipoprotein(a) (apo(a)), namely antisense oligonucleotide therapy, demonstrate potential to decrease Lp(a) to levels below the 30-50 mg/dL (75-150 nmol/L) CVD risk threshold. This therapeutic approach should aid in assessing the benefit of lowering Lp(a) in a clinical setting.
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Affiliation(s)
- Corey A Scipione
- a Department of Advanced Diagnostics , Toronto General Hospital Research Institute, UHN , Toronto , Canada
| | - Marlys L Koschinsky
- b Robarts Research Institute , Western University , London , Canada.,c Department of Physiology & Pharmacology , Schulich School of Medicine & Dentistry, Western University , London , Canada
| | - Michael B Boffa
- d Department of Biochemistry , Western University , London , Canada
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Ellis KL, Boffa MB, Sahebkar A, Koschinsky ML, Watts GF. The renaissance of lipoprotein(a): Brave new world for preventive cardiology? Prog Lipid Res 2017; 68:57-82. [DOI: 10.1016/j.plipres.2017.09.001] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2017] [Revised: 09/01/2017] [Accepted: 09/05/2017] [Indexed: 12/24/2022]
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Boffa MB, Koschinsky ML. Update on lipoprotein(a) as a cardiovascular risk factor and mediator. Curr Atheroscler Rep 2014; 15:360. [PMID: 23990263 DOI: 10.1007/s11883-013-0360-6] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Recent genetic studies have put the spotlight back onto lipoprotein(a) [Lp(a)] as a causal risk factor for coronary heart disease. However, there remain significant gaps in our knowledge with respect to how the Lp(a) particle is assembled, the route of its catabolism, and the mechanism(s) of Lp(a) pathogenicity. It has long been speculated that the effects of Lp(a) in the vasculature can be attributed to both its low-density lipoprotein moiety and the unique apolipoprotein(a) component, which is strikingly similar to the kringle-containing fibrinolytic zymogen plasminogen. However, the ability of Lp(a) to modulate either purely thrombotic or purely atherothrombotic processes in vivo remains unclear. The presence of oxidized phospholipid on Lp(a) may underlie many of the proatherosclerotic effects of Lp(a) that have been identified both in cell models and in animal models, and provides a possible avenue for identifying therapeutics aimed at mitigating the effects of Lp(a) in the vasculature. However, the beneficial effects of targeted Lp(a) therapeutics, designed to either lower Lp(a) concentrations or interfere with its effects, on cardiovascular outcomes remains to be determined.
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Affiliation(s)
- Michael B Boffa
- Department of Chemistry & Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, ON, Canada.
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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.
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Affiliation(s)
- F Kronenberg
- Division of Genetic Epidemiology, Innsbruck Medical University, Innsbruck, Austria
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Frischmann ME, Ikewaki K, Trenkwalder E, Lamina C, Dieplinger B, Soufi M, Schweer H, Schaefer JR, König P, Kronenberg F, Dieplinger H. In vivo stable-isotope kinetic study suggests intracellular assembly of lipoprotein(a). Atherosclerosis 2012; 225:322-7. [PMID: 23099120 DOI: 10.1016/j.atherosclerosis.2012.09.031] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/21/2012] [Revised: 08/17/2012] [Accepted: 09/26/2012] [Indexed: 11/29/2022]
Abstract
OBJECTIVE Lipoprotein(a) [Lp(a)] consists of apolipoprotein B-100 (apoB-100) as part of an LDL-like particle and the covalently linked glycoprotein apolipoprotein(a) [apo(a)]. Detailed mechanisms of its biosynthesis, assembly, secretion and catabolism are still poorly understood. To address the Lp(a) assembly mechanism, we studied the in vivo kinetics of apo(a) and apoB-100 from Lp(a) and LDL apoB-100 in nine healthy probands using stable-isotope methodology. METHODS The level of isotope enrichment was used to calculate the fractional synthesis rate (FSR), production rate (PR) and retention time (RT) using SAAMII software and multicompartmental modeling. RESULTS We observed a similar mean PR for apo(a) (1.15 nmol/kg/d) and apoB-100 (1.31 nmol/kg/d) from Lp(a), which differed significantly from the PR for apoB-100 from LDL (32.6 nmol/kg/d). Accordingly, mean FSR and RT values for Lp(a)-apo(a) were similar to those of Lp(a)-apoB and different from those for LDL-apoB. CONCLUSION Two different kinetic apoB pools within Lp(a) and LDL suggest intracellular Lp(a) assembly from apo(a) and newly synthesized LDL.
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Affiliation(s)
- Michael E Frischmann
- Division of Genetic Epidemiology, Department of Medical Genetics, Molecular and Clinical Pharmacology, Innsbruck Medical University, Austria
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Chennamsetty I, Kostner KM, Claudel T, Vinod M, Frank S, Weiss TS, Trauner M, Kostner GM. Nicotinic acid inhibits hepatic APOA gene expression: studies in humans and in transgenic mice. J Lipid Res 2012; 53:2405-12. [PMID: 22930813 DOI: 10.1194/jlr.m029769] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Elevated plasma lipoprotein(a) (LPA) levels are recognized as an independent risk factor for cardiovascular diseases. Our knowledge on LPA metabolism is incomplete, which makes it difficult to develop LPA-lowering medications. Nicotinic acid (NA) is the main drug recommended for the treatment of patients with increased plasma LPA concentrations. The mechanism of NA in lowering LPA is virtually unknown. To study this mechanism, we treated transgenic (tg) APOA mice with NA and measured plasma APOA and hepatic mRNA levels. In addition, mouse and human primary hepatocytes were incubated with NA, and the expression of APOA was followed. Feeding 1% NA reduced plasma APOA and hepatic expression of APOA in tg-APOA mice. Experiments with cultured human and mouse primary hepatocytes in addition to reporter assays performed in HepG2 cells revealed that NA suppresses APOA transcription. The region between -1446 and -857 of the human APOA promoter harboring several cAMP response element binding sites conferred the negative effect of NA. In accordance, cAMP stimulated APOA transcription, and NA reduced hepatic cAMP levels. It is suggested that cAMP signaling might be involved in reducing APOA transcription, which leads to the lowering of plasma LPA.
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Liu G, Niu X, Wu RS, Chudasama N, Yao Y, Jin X, Weinberg R, Zakharov SI, Motoike H, Marx SO, Karlin A. Location of modulatory beta subunits in BK potassium channels. ACTA ACUST UNITED AC 2010; 135:449-59. [PMID: 20385746 PMCID: PMC2860586 DOI: 10.1085/jgp.201010417] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Large-conductance voltage- and calcium-activated potassium (BK) channels contain four pore-forming α subunits and four modulatory β subunits. From the extents of disulfide cross-linking in channels on the cell surface between cysteine (Cys) substituted for residues in the first turns in the membrane of the S0 transmembrane (TM) helix, unique to BK α, and of the voltage-sensing domain TM helices S1–S4, we infer that S0 is next to S3 and S4, but not to S1 and S2. Furthermore, of the two β1 TM helices, TM2 is next to S0, and TM1 is next to TM2. Coexpression of α with two substituted Cys’s, one in S0 and one in S2, and β1 also with two substituted Cys’s, one in TM1 and one in TM2, resulted in two αs cross-linked by one β. Thus, each β lies between and can interact with the voltage-sensing domains of two adjacent α subunits.
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Affiliation(s)
- Guoxia Liu
- Division of Cardiology, Department of Medicine, LaGuardia Community College, Long Island City, NY 11101, USA
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Abstract
Large-conductance, voltage- and Ca(2+)-gated potassium (BK) channels control excitability in a number of cell types. BK channels are composed of alpha subunits, which contain the voltage-sensor domains and the Ca(2+)- sensor domains and form the pore, and often one of four types of beta subunits, which modulate the channel in a cell-specific manner. beta 4 is expressed in neurons throughout the brain. Deletion of beta 4 in mice causes temporal lobe epilepsy. Compared with channels composed of alpha alone, channels composed of alpha and beta 4 activate and deactivate more slowly. We inferred the locations of the two beta 4 transmembrane (TM) helices TM1 and TM2 relative to the seven alpha TM helices, S0-S6, from the extent of disulfide bond formation between cysteines substituted in the extracellular flanks of these TM helices. We found that beta 4 TM2 is close to alpha S0 and that beta 4 TM1 is close to both alpha S1 and S2. At least at their extracellular ends, TM1 and TM2 are not close to S3-S6. In six of eight of the most highly crosslinked cysteine pairs, four crosslinks from TM2 to S0 and one each from TM1 to S1 and S2 had small effects on the V(50) and on the rates of activation and deactivation. That disulfide crosslinking caused only small functional perturbations is consistent with the proximity of the extracellular ends of TM2 to S0 and of TM1 to S1 and to S2, in both the open and closed states.
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Locations of the beta1 transmembrane helices in the BK potassium channel. Proc Natl Acad Sci U S A 2008; 105:10727-32. [PMID: 18669652 DOI: 10.1073/pnas.0805212105] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
BK channels are composed of alpha-subunits, which form a voltage- and Ca(2+)-gated potassium channel, and of modulatory beta-subunits. The beta1-subunit is expressed in smooth muscle, where it renders the BK channel sensitive to [Ca(2+)](i) in a voltage range near the smooth-muscle resting potential and slows activation and deactivation. BK channel acts thereby as a damped feedback regulator of voltage-dependent Ca(2+) channels and of smooth muscle tone. We explored the contacts between alpha and beta1 by determining the extent of endogenous disulfide bond formation between cysteines substituted just extracellular to the two beta1 transmembrane (TM) helices, TM1 and TM2, and to the seven alpha TM helices, consisting of S1-S6, conserved in all voltage-dependent potassium channels, and the unique S0 helix, which we previously concluded was partly surrounded by S1-S4. We now find that the extracellular ends of beta1 TM2 and alpha S0 are in contact and that beta1 TM1 is close to both S1 and S2. The extracellular ends of TM1 and TM2 are not close to S3-S6. In almost all cases, cross-linking of TM2 to S0 or of TM1 to S1 or S2 shifted the conductance-voltage curves toward more positive potentials, slowed activation, and speeded deactivation, and in general favored the closed state. TM1 and TM2 are in position to contribute, in concert with the extracellular loop and the intracellular N- and C-terminal tails of beta1, to the modulation of BK channel function.
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Liu G, Zakharov SI, Yang L, Deng SX, Landry DW, Karlin A, Marx SO. Position and role of the BK channel alpha subunit S0 helix inferred from disulfide crosslinking. ACTA ACUST UNITED AC 2008; 131:537-48. [PMID: 18474637 PMCID: PMC2391248 DOI: 10.1085/jgp.200809968] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The position and role of the unique N-terminal transmembrane (TM) helix, S0, in large-conductance, voltage- and calcium-activated potassium (BK) channels are undetermined. From the extents of intra-subunit, endogenous disulfide bond formation between cysteines substituted for the residues just outside the membrane domain, we infer that the extracellular flank of S0 is surrounded on three sides by the extracellular flanks of TM helices S1 and S2 and the four-residue extracellular loop between S3 and S4. Eight different double cysteine-substituted alphas, each with one cysteine in the S0 flank and one in the S3-S4 loop, were at least 90% disulfide cross-linked. Two of these alphas formed channels in which 90% cross-linking had no effect on the V(50) or on the activation and deactivation rate constants. This implies that the extracellular ends of S0, S3, and S4 are close in the resting state and move in concert during voltage sensor activation. The association of S0 with the gating charge bearing S3 and S4 could contribute to the considerably larger electrostatic energy required to activate the BK channel compared with typical voltage-gated potassium channels with six TM helices.
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Affiliation(s)
- Guoxia Liu
- 1 Division of Cardiology, Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
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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.
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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.
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