Lipoprotein(a) in various conditions: To keep a sense of proportions

Consideration and Application of Lipoprotein(a) in the Risk Assessment of Atherosclerotic Cardiovascular Disease Risk in Adults

Lipoprotein(a) (Lp[a]) is an low-density lipoprotein (LDL)-like particle in which apolipoprotein (apo) B is covalently bound to a plasminogen-like molecule called apo(a). A High level of Lp(a) has been demonstrated to be an independent, causal, and prevalent risk factor for atherosclerotic cardiovascular disease (ASCVD), as well as aortic valve disease, through mechanisms that promote atherogenesis, inflammation, and thrombosis. With reliable and accessible assays, Lp(a) level has been established to be associated linearly with the risk for ASCVD. The 2021 Canadian Cardiovascular Society Dyslipidemia Guidelines recommend measuring an Lp(a) level once in a person's lifetime as part of the initial lipid screening. The aim of this review is to provide an update and overview of the utility and application of Lp(a) level in the assessment and treatment of adults at risk for ASCVD, consistent with this guideline recommendation.

Lipoprotein(a)

Lipoprotein(a) [Lp(a)] is an atherogenic lipoprotein with a strong genetic regulation. Up to 90% of the concentrations are explained by a single gene, the LPA gene. The concentrations show a several-hundred-fold interindividual variability ranging from less than 0.1 mg/dL to more than 300 mg/dL. Lp(a) plasma concentrations above 30 mg/dL and even more above 50 mg/dL are associated with an increased risk for cardiovascular disease including myocardial infarction, stroke, aortic valve stenosis, heart failure, peripheral arterial disease, and all-cause mortality. Since concentrations above 50 mg/dL are observed in roughly 20% of the Caucasian population and in an even higher frequency in African-American and Asian-Indian ethnicities, it can be assumed that Lp(a) is one of the most important genetically determined risk factors for cardiovascular disease.Carriers of genetic variants that are associated with high Lp(a) concentrations have a markedly increased risk for cardiovascular events. Studies that used these genetic variants as a genetic instrument to support a causal role for Lp(a) as a cardiovascular risk factor are called Mendelian randomization studies. The principle of this type of studies has been introduced and tested for the first time ever with Lp(a) and its genetic determinants.There are currently no approved pharmacologic therapies that specifically target Lp(a) concentrations. However, some therapies that target primarily LDL cholesterol have also an influence on Lp(a) concentrations. These are mainly PCSK9 inhibitors that lower LDL cholesterol by 60% and Lp(a) by 25-30%. Furthermore, lipoprotein apheresis lowers both, Lp(a) and LDL cholesterol, by about 60-70%. Some sophisticated study designs and statistical analyses provided support that lowering Lp(a) by these therapies also lowers cardiovascular events on top of the effect caused by lowering LDL cholesterol, although this was not the main target of the therapy. Currently, new therapies targeting RNA such as antisense oligonucleotides (ASO) or small interfering RNA (siRNA) against apolipoprotein(a), the main protein of the Lp(a) particle, are under examination and lower Lp(a) concentrations up to 90%. Since these therapies specifically lower Lp(a) concentrations without influencing other lipoproteins, they will serve the last piece of the puzzle whether a decrease of Lp(a) results also in a decrease of cardiovascular events.

Towards an SI-Traceable Reference Measurement System for Seven Serum Apolipoproteins Using Bottom-Up Quantitative Proteomics: Conceptual Approach Enabled by Cross-Disciplinary/Cross-Sector Collaboration

Current dyslipidemia management in patients with atherosclerotic cardiovascular disease (ASCVD) is based on traditional serum lipids. Yet, there is some indication from basic research that serum apolipoproteins A-I, (a), B, C-I, C-II, C-III, and E may give better pathophysiological insight into the root causes of dyslipidemia. To facilitate the future adoption of clinical serum apolipoprotein (apo) profiling for precision medicine, strategies for accurate testing should be developed in advance. Recent discoveries in basic science and translational medicine set the stage for the IFCC Working Group on Apolipoproteins by Mass Spectrometry. Main drivers were the convergence of unmet clinical needs in cardiovascular disease (CVD) patients with enabling technology and metrology. First, the residual cardiovascular risk after accounting for established risk factors demonstrates that the current lipid panel is too limited to capture the full complexity of lipid metabolism in patients. Second, there is a need for accurate test results in highly polymorphic and atherogenic apolipoproteins such as apo(a). Third, sufficient robustness of mass spectrometry technology allows reproducible protein quantification at the molecular level. Fourth, several calibration hierarchies in the revised ISO 17511:2020 guideline facilitate metrological traceability of test results, the highest achievable standard being traceability to SI. This article outlines the conceptual approach aimed at achieving a novel, multiplexed Reference Measurement System (RMS) for seven apolipoproteins based on isotope dilution mass spectrometry and peptide-based calibration. This RMS should enable standardization of existing and emerging apolipoprotein assays to SI, within allowable limits of measurement uncertainty, through a sustainable network of Reference Laboratories.

[Lipoprotein(а) Level, Apolipoprotein(а) Polymorphism аnd Autoаntibodies Against Lipoprotein(а) in Patients with Stenotic Cаrotid Atherosclerosis]

Аim. Comparative assessment of respiratory indicators according to multifunctional monitoring (PFM) with the recommended standard for a complete polysomnographic study and an assessment of the effect of blood pressure (BP) measurements in PFM on sleep quality. Triаls on the аssociаtion of Lp(а) and cаrotid аtherosclerosis аre limited. The аim of the study wаs to investigаte the аssociаtion of Lp(а), аpolipoprotein(а) [apo(а)] polymorphism аnd аutoаntibodies to Lp(а) with stenotic (≥50%) cаrotid аtherosclerosis in dependence on CHD presence. Materials and methods. The study included 785 pаtients аt the аge from 21 to 92 with dаtа of instrumentаl exаmination of coronаry, cаrotid аnd lower limbs аrteries. Stenotic cаrotid аtherosclerosis wаs diаgnosed in 447 pаtients who were divided into two groups depending on presence (n=344) or аbsence (n=103) of CHD. The control group comprised of 338 pаtients without stenotic аtherosclerosis of coronаry, cаrotid аnd lower limbs аrteries. In the blood serum of pаtients levels of Lp(а), аutoаntibodies to Lp(а) were determined аnd аlso аpo(а) phenotyping wаs conducted. Results. There were more mаles, higher аverаge аge аnd frequency of hypertension, type 2 diаbetes mellitus, smoking, Lp(а) concentrаtion (mediаn [interquаrtile rаnge]): 30 [11; 63] vs. 14 [5; 30] mg/dl, p<0.01) in the group with stenotic cаrotid аtherosclerosis in compаrison with control group. Besides, Lp(а) level wаs higher in CHD subgroup thаn in pаtients with stenotic cаrotid аtherosclerosis without CHD: 32 [12; 72] vs. 24 [8; 50] mg/dl, respectively, p=0.01. Elevаted (≥30 mg/dl) Lp(а) level, low moleculаr weight аpolipoprotein(а) [(LMW аpo(а)] phenotype were аssociаted with stenotic cаrotid аtherosclerosis (odds rаtio (OR) 2.9; 95% confidence intervаl (CI) 2.1-4.0, p<0.01 аnd OR 2.3; 95% CI 1.6-3.4, p<0.01, respectively). Logistic regression аnаlysis showed independent аssociаtion of elevаted Lp(а) level аnd LMW аpo(а) phenotype with stenotic cаrotid аtherosclerosis both in the presence аnd absence of CHD. The level of IgM аutoаntibodies to Lp(а) wаs higher in control group thаn in pаtients with stenotic cаrotid аtherosclerosis, p=0.02. Conclusion The level of Lp(a) ≥30 mg/dl and low molecular weight phenotype of aprotein(a) are predictors of stenotic atherosclerosis CA, regardless of the presence of coronary heart disease and other risk factors, while a reverse relationship was found between the level of autoantibodies of the IgM class against Lp(a) and the severity of atherosclerosis CA.

Prediction of cardiovascular risk by Lp(a) concentrations or genetic variants within the LPA gene region

In the middle of the 1990s the interest in Lp(a) vanished after a few badly performed studies almost erased Lp(a) from the map of biological targets. However, since roughly 10 years the interest has begun to grow again mainly for two reasons: first, genetic studies using easily accessible and high-throughput techniques for genotyping of single-nucleotide polymorphisms (SNPs) have allowed large studies in patients with cardiovascular disease and controls to be performed. This strengthened the earlier findings on a copy number variation in the LPA gene and its association with cardiovascular outcomes. Second, new therapies are on the horizon raising strong and justified hope that in a few years drugs will become available which tremendously lower Lp(a) concentrations. This review article should provide an introduction to the genetic determination of Lp(a) concentrations and considerations whether Lp(a) concentrations or genetic variants are important for the prediction of cardiovascular risk.

Human Genetics and the Causal Role of Lipoprotein(a) for Various Diseases

Lipoprotein(a) [Lp(a)] is a highly atherogenic lipoprotein that is under strong genetic control by the LPA gene locus. Genetic variants including a highly polymorphic copy number variation of the so called kringle IV repeats at this locus have a pronounced influence on Lp(a) concentrations. High concentrations of Lp(a) as well as genetic variants which are associated with high Lp(a) concentrations are both associated with cardiovascular disease which very strongly supports causality between Lp(a) concetrations and cardiovascular disease. This method of using a genetic variant that has a pronounced influence on a biomarker to support causality with an outcome is called Mendelian randomization approach and was applied for the first time two decades ago with data from Lp(a) and cardiovascular disease. This approach was also used to demonstrate a causal association between high Lp(a) concentrations and aortic valve stenosis, between low concentrations and type-2 diabetes mellitus and to exclude a causal association between Lp(a) concentrations and venous thrombosis. Considering the high frequency of these genetic variants in the population makes Lp(a) the strongest genetic risk factor for cardiovascular disease identified so far. Promising drugs that lower Lp(a) are on the horizon but their efficacy in terms of reducing clinical outcomes still has to be shown.

Double positivity of the IgG isotype of both anticardiolipin and anti-β2gpI antibodies is associated with the highest number of vascular impairment parameters in patients with primary antiphospholipid syndrome: preliminary data

Although numerous studies investigated the association between homocysteine (Hcy), tumor necrosis factor alpha (TNF-α), C-reactive protein (CRP) and apolipoproteins (apo_s) with thrombosis and/or recurrent pregnancy losses, studies that analyzed the abovementioned parameters and multiple positivity of antiphospholipid antibodies (aPL Abs) in patients with primary antiphospholipid syndrome (PAPS) are lacking. Therefore, the aim of this study was to analyze the presence of various combinations of the abovementioned parameters and their associations with clinical and/or serological features of PAPS. High-pressure liquid chromatography (HPLC) was used for determination of Hcy, while apoAI, apoB, and lipoprotein (Lp) (a) concentrations were estimated by immunonephelometry. High-sensitivity C-reactive protein (hsCRP) was measured by immunoturbidimetry. Apo (a), TNF-α, and aPL Abs were measured by ELISA. Various combinations of analyzed parameters (Hcy/CRP/TNF/apoAI/apoB/apo (a)/Lp (a)) were not associated with a single presence of either aPL Abs. Double positivity for both isotypes of anticardiolipin (aCL) Abs (IgG + IgM) was associated with the increased apoB levels. The presence of the IgG isotype of both aCL + anti-beta2 glycoprotein I (aβ2gpI) Abs was associated with the highest number of analyzed parameters (i.e., increased levels of hsCRP, Lp (a), and apo (a)). The presence of the IgG isotype of both aCL + aβ2gpI Abs was associated with the highest number of vascular impairment parameters in patients with PAPS, and this combination confers the highest risk for the recurrence of thrombotic episodes. This is the first report that analyzed the association between various combinations of vascular impairment parameters with multiple aPL Ab positivity. Our results provide a rationale for further investigations of therapeutic approaches for PAPS patients.

Effects of Lipoprotein apheresis on the Lipoprotein(a) levels in the long run

BACKGROUND

Lipoprotein(a) (Lp(a)) is a low density lipoprotein-like particle to which apolipoprotein(a) is bound. It is recognized as an atherosclerosis-inducing risk factor. Up to now a detailed description of the effect of Lipoprotein apheresis (LA) on Lp(a) levels in the long run is lacking.

METHODS

We studied 59 patients with elevated Lp(a) levels who were treated with LA at the Lipoprotein Apheresis Center at the University Hospital Dresden. We analyzed Lp(a) concentrations before the start of the LA treatment and during this extracorporeal therapy.

RESULTS

Comparing the Lp(a) levels before the start of LA therapy and pre-apheresis (measured before the LA sessions) Lp(a) levels, we observed a reduction of the Lp(a) levels of about 22.8% in all patients. Lp(a) levels were acutely (comparing post-apheresis with pre-apheresis concentrations) reduced by all 6 available LA methods (by about 70%). A linear regression analysis was performed to differentiate the long term course of pre-apheresis Lp(a) levels. In 30 patients we saw an increase of the pre-apheresis Lp(a) levels over the time, in 15 patients a constancy and in 14 patients a decrease. Patients with a decrease of pre-apheresis Lp(a) levels over the time had significantly higher initial (before the start of the extracorporeal treatment) and pre-apheresis values and they were significantly older. These patients had significantly more severe peripheral arterial disease as well as cardiac valve and carotid stenosis. The patients with the lowest initial Lp(a) levels and an increase of the pre-apheresis Lp(a) levels over the time had the highest percentage of intake of Tredaptive(®)/Niaspan(®) though after stopping the intake of these nicotinic acid preparations no clear increase of Lp(a) concentrations was observed. The applied LA systems did not seem to have a significant influence on the course of pre-apheresis Lp(a) levels. In all patients there was a high variability of Lp(a) concentrations between LA sessions which may in part be due to the inaccuracy of the method used to measure Lp(a) concentrations.

CONCLUSION

Pre-apheresis Lp(a) levels (before the LA sessions) are lower than those before the start of a LA treatment but they behave differently among patients during LA treatment.