Electrophoretic measurement of lipoprotein(a) cholesterol in plasma with and without ultracentrifugation: comparison with an immunoturbidimetric lipoprotein(a) method

Effect of Pelacarsen on Lipoprotein(a) Cholesterol and Corrected Low-Density Lipoprotein Cholesterol

BACKGROUND

Laboratory methods that report low-density lipoprotein cholesterol (LDL-C) include both LDL-C and lipoprotein(a) cholesterol [Lp(a)-C] content.

OBJECTIVES

The purpose of this study was to assess the effect of pelacarsen on directly measured Lp(a)-C and LDL-C corrected for its Lp(a)-C content.

METHODS

The authors evaluated subjects with a history of cardiovascular disease and elevated Lp(a) randomized to 5 groups of cumulative monthly doses of 20-80 mg pelacarsen vs placebo. Direct Lp(a)-C was measured on isolated Lp(a) using LPA4-magnetic beads directed to apolipoprotein(a). LDL-C was reported as: 1) LDL-C as reported by the clinical laboratory; 2) LDL-C_corr = laboratory-reported LDL-C - direct Lp(a)-C; and 3) LDL-C_corrDahlén = laboratory LDL-C - [Lp(a) mass × 0.30] estimated by the Dahlén formula.

RESULTS

The baseline median Lp(a)-C values in the groups ranged from 11.9 to 15.6 mg/dL. Compared with placebo, pelacarsen resulted in dose-dependent decreases in Lp(a)-C (2% vs -29% to -67%; P = 0.001-<0.0001). Baseline laboratory-reported mean LDL-C ranged from 68.5 to 89.5 mg/dL, whereas LDL-C_corr ranged from 55 to 74 mg/dL. Pelacarsen resulted in mean percent/absolute changes of -2% to -19%/-0.7 to -8.0 mg/dL (P = 0.95-0.05) in LDL-C_corr, -7% to -26%/-5.4 to -9.4 mg/dL (P = 0.44-<0.0001) in laboratory-reported LDL-C, and 3.1% to 28.3%/0.1 to 9.5 mg/dL (P = 0.006-0.50) increases in LDL-C_corrDahlén. Total apoB declined by 3%-16% (P = 0.40-<0.0001), but non-Lp(a) apoB was not significantly changed.

CONCLUSIONS

Pelacarsen significantly lowers direct Lp(a)-C and has neutral to mild lowering of LDL-C_corr. In patients with elevated Lp(a), LDL-C_corr provides a more accurate reflection of changes in LDL-C than either laboratory-reported LDL-C or the Dahlén formula.

Assessing the Accuracy of Estimated Lipoprotein(a) Cholesterol and Lipoprotein(a)-Free Low-Density Lipoprotein Cholesterol

Background

Accurate measurement of the cholesterol within lipoprotein(a) (Lp[a]‐C) and its contribution to low‐density lipoprotein cholesterol (LDL‐C) has important implications for risk assessment, diagnosis, and treatment of atherosclerotic cardiovascular disease, as well as in familial hypercholesterolemia. A method for estimating Lp(a)‐C from particle number using fixed conversion factors has been proposed (Lp[a]‐C from particle number divided by 2.4 for Lp(a) mass, multiplied by 30% for Lp[a]‐C). The accuracy of this method, which theoretically can isolate “Lp(a)‐free LDL‐C,” has not been validated.

Methods and Results

In 177 875 patients from the VLDbL (Very Large Database of Lipids), we compared estimated Lp(a)‐C and Lp(a)‐free LDL‐C with measured values and quantified absolute and percent error. We compared findings with an analogous data set from the Mayo Clinic Laboratory. Error in estimated Lp(a)‐C and Lp(a)‐free LDL‐C increased with higher Lp(a)‐C values. Median error for estimated Lp(a)‐C <10 mg/dL was −1.9 mg/dL (interquartile range, −4.0 to 0.2); this error increased linearly, overestimating by +30.8 mg/dL (interquartile range, 26.1–36.5) for estimated Lp(a)‐C ≥50 mg/dL. This error relationship persisted after stratification by overall high‐density lipoprotein cholesterol and high‐density lipoprotein cholesterol subtypes. Similar findings were observed in the Mayo cohort. Absolute error for Lp(a)‐free LDL‐C was +2.4 (interquartile range, −0.6 to 5.3) for Lp(a)‐C<10 mg/dL and −31.8 (interquartile range, −37.8 to −26.5) mg/dL for Lp(a)‐C≥50 mg/dL.

Conclusions

Lp(a)‐C estimations using fixed conversion factors overestimated Lp(a)‐C and subsequently underestimated Lp(a)‐free LDL‐C, especially at clinically relevant Lp(a) values. Application of inaccurate Lp(a)‐C estimations to correct LDL‐C may lead to undertreatment of high‐risk patients.

Performance evaluation of five lipoprotein(a) immunoassays on the Roche cobas c501 chemistry analyzer

Objectives

Measurement of lipoprotein(a) [Lp(a)] is used in risk assessment of atherosclerotic cardiovascular disease (ASCVD). The aim of the current study was to evaluate performance characteristic of five different Lp(a) assays using the cobas c501 (Roche Diagnostics) analyzer.

Design and methods

Lp(a) was measured using five Lp(a) assays (Diazyme, Kamiya, MedTest, Randox, and Roche) configured to mg/dL units. Assays from Diazyme and Kamiya were also configured using nmol/L units in separate experiments. Studies included sensitivity, imprecision, linearity, method comparison, and evaluation of healthy subjects. Imprecision (intra-day, 20 replicates; inter-day, duplicates twice daily for five days) and linearity were evaluated using patient pools. Linearity assessed a minimum of five patient splits spanning the analytical measurement range (AMR). Method comparison used 80 residual serum samples. Specimens from 120 self-reported healthy subjects (61 females / 59 males) were also tested. Method comparison for two assays in nmol/L units was conducted using 96 residual serum samples.

Results

Assay sensitivities met all manufacturer claims. Imprecision studies demonstrated %CVs ranging from 2.5 to 5.2% for the low pool (average concentration from 7.3 to 12.4 ​mg/dL); high pool %CVs ranged from 0.8 to 3.0% (average concentrations from 31.5–50.2 ​mg/dL). Linearity was confirmed for all assays. Variation in accuracy was observed when comparing results to an all method average. Lp(a) results were higher in females versus males in self-reported healthy subjects.

Conclusions

All assays performed according to manufacturer described performance characteristics, although differences were observed across Lp(a) assays tested when compared to an all method average.

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Five automated assays for Lp(a) measurement (mg/dL units) were compared.

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Differences in accuracy were observed across the methods investigated.

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Two assays were also compared using nmol/L units.

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More Lp(a) assay traceability to the international reference material is needed.

Novel method for quantification of lipoprotein(a)-cholesterol: implications for improving accuracy of LDL-C measurements

Current methods for determining “LDL-C” in clinical practice measure the cholesterol content of both LDL and lipoprotein(a) [Lp(a)-C]. We developed a high-throughput, sensitive, and rapid method to quantitate Lp(a)-C and improve the accuracy of LDL-C by subtracting for Lp(a)-C (LDL-C_corr). Lp(a)-C is determined following isolation of the Lp(a) on magnetic beads linked to monoclonal antibody LPA4 recognizing apolipoprotein(a). This Lp(a)-C assay does not detect cholesterol in plasma samples lacking Lp(a) and is linear up to 747 nM Lp(a). To validate this method clinically over a wide range of Lp(a) (9.0–822.8 nM), Lp(a)-C and LDL-C_corr were determined in 21 participants receiving an Lp(a)-specific lowering antisense oligonucleotide and in eight participants receiving placebo at baseline, at 13 weeks during peak drug effect, and off drug. In the groups combined, Lp(a)-C ranged from 0.6 to 35.0 mg/dl and correlated with Lp(a) molar concentration (r = 0.76; P < 0.001). However, the percent Lp(a)-C relative to Lp(a) mass varied from 5.8% to 57.3%. Baseline LDL-C_corr was lower than LDL-C [mean (SD), 102.2 (31.8) vs. 119.2 (32.4) mg/dl; P < 0.001] and did not correlate with Lp(a)-C. It was demonstrated that three commercially available “direct LDL-C” assays also include measures of Lp(a)-C. In conclusion, we have developed a novel and sensitive method to quantitate Lp(a)-C that provides insights into the Lp(a) mass/cholesterol relationship and may be used to more accurately report LDL-C and reassess its role in clinical medicine.

Study of lipoprotein(a) and its impact on atherosclerotic cardiovascular disease: Design and rationale of the Mass General Brigham Lp(a) Registry

Lipoprotein(a) [Lp(a)] is independently associated with atherosclerotic cardiovascular disease and calcific aortic valve stenosis. Elevated Lp(a) affects approximately one in five individuals and meaningfully contributes to the residual cardiovascular risk in individuals with otherwise well-controlled risk factors. With targeted therapies in the therapeutic pipeline, there is a need to further characterize the clinical phenotypes and outcomes of individuals with elevated levels of this unique biomarker. The Mass General Brigham Lp(a) Registry will be built from the longitudinal electronic health record of two large academic medical centers in Boston, Massachusetts, to develop a detailed cohort of patients who have had their Lp(a) measured. In combination with structured data sources, clinical documentation will be analyzed using natural language processing techniques to accurately characterize baseline characteristics. Important outcome measures including all-cause mortality, cardiovascular mortality, and cardiovascular events will be available for analysis. Approximately 30 000 patients who have had their Lp(a) tested within the Mass General Brigham system from January 2000 to July 2019 will be included in the registry. This large Lp(a) cohort will provide meaningful observational data regarding the differential risk associated with Lp(a) values and cardiovascular disease. With a new frontier of targeted Lp(a) therapies on the horizon, the Mass General Brigham Lp(a) Registry will help provide a deeper understanding of Lp(a)'s role in long term cardiovascular outcomes.

Measuring the contribution of Lp(a) cholesterol towards LDL-C interpretation

BACKGROUND

Lipoprotein(a) [Lp(a)] is a pro-atherogenic and pro-thrombotic LDL-like particle recognized as an independent risk factor for cardiovascular disease (CVD). The cholesterol within Lp(a) (Lp(a)-C) contributes to the reported LDL-cholesterol (LDL-C) concentration by nearly all available methods. Accurate LDL-C measurements are critical for identification of genetic dyslipidemias such as familial hypercholesterolemia (FH). FH diagnostic criteria, such as the Dutch Lipid Clinic Network (DLCN) criteria, utilize LDL-C concentration cut-offs to assess the likelihood of FH. Therefore, failure to adjust for Lp(a)-C can impact accurate FH diagnosis and classification, appropriate follow-up testing and treatments, and interpretation of cholesterol-lowering treatment efficacy.

OBJECTIVE

In this study, we use direct Lp(a)-C measurements to assess the potential misclassification of FH from contributions of Lp(a)-C to reported LDL-C in patient samples submitted for advanced lipoprotein profiling.

METHODS

A total of 31,215 samples submitted for lipoprotein profiling were included. LDL-C was measured by beta quantification or calculated by one of three equations. Lp(a)-C was measured by quantitative lipoprotein electrophoresis. DLCN LDL-C cut-offs were applied to LDL-C results before and after accounting for Lp(a)-C contribution.

RESULTS

Lp(a)-C was detected in 8665 (28%) samples. A total of 940 subjects were reclassified to a lower DLCN LDL-C categories; this represents 3% of the total patient series or 11% of subjects with measurable Lp(a)-C.

CONCLUSION

Lp(a)-C is present in a significant portion of samples submitted for advanced lipid testing and could cause patient misclassification when using FH diagnostic criteria. These misclassifications could trigger inappropriate follow-up, treatment, and cascade testing for suspected FH.

Current and future role of lipoprotein(a) in preventive cardiology

PURPOSE OF REVIEW

The purpose of this review is to highlight our emerging understanding of lipoprotein(a) [Lp(a)]'s role in atherosclerotic cardiovascular disease (ASCVD), its structure-function relationship, and promising developments within the therapeutic pipeline.

RECENT FINDINGS

Elevated levels of Lp(a) are strongly associated with an increased risk of coronary heart disease, calcific aortic valve stenosis, and ischemic stroke. With circulating levels almost exclusively genetically mediated, increased levels of Lp(a) contribute significantly to the residual cardiovascular disease risk in individuals with otherwise well controlled risk factors. The unique structure of Lp(a) - comprised of a genetically heterogeneous apolipoprotein(a) molecule bound to an LDL-like moiety - provides insight into its pathogenic role in cardiovascular disease and also complicates its accurate measurement. Emerging therapies targeting the apolipoprotein(a) component of Lp(a) have the potential to revolutionize the management of individuals with elevated Lp(a).

SUMMARY

With promising therapies on the horizon, there has been a renewed focus on the role of Lp(a) in ASCVD. Given Lp(a)'s strong and independent association with key cardiovascular outcomes, it is hopeful that these promising targeted therapies will add another therapeutic option for the prevention of cardiovascular disease.

Lipid Biomarkers for Risk Assessment in Acute Coronary Syndromes

PURPOSE OF REVIEW

The objective of this review was to summarize evidence gathered for the prognostic value of routine and novel blood lipids and lipoproteins measured in patients with acute coronary syndromes (ACS).

RECENT FINDINGS

Data supports clear association with risk and actionable value for non-high-density lipoprotein (Non-HDL) cholesterol and plasma ceramides in a setting of ACS. The prognostic value and clinical actionability of apolipoprotein B (apoB) and lipoprotein(a) [Lp(a)] in ACS have not been thoroughly tested, while the data for omega-3 fatty acids and oxidized low-density lipoprotein (Ox-LDL) are either untested or more varied. Measuring basic lipids, which should include Non-HDL cholesterol, at the time of presentation for ACS is guideline mandated. Plasma ceramides also provide useful information to guide both treatment decisions and follow-up. Additional studies targeting ACS patients are necessary for apoB, Lp(a), omega-3 fatty acids, and Ox-LDL.

Evaluation of Lipoprotein(a) Electrophoretic and Immunoassay Methods in Discriminating Risk of Calcific Aortic Valve Disease and Incident Coronary Heart Disease: The Multi-Ethnic Study of Atherosclerosis

BACKGROUND

A number of lipoprotein(a) [Lp(a)] analytical techniques are available that quantify distinct particle components, yet their clinical efficacy has not been comprehensively evaluated. This study determined whether Lp(a) mass [Lp(a)-M], Lp(a) cholesterol content [Lp(a)-C], and particle concentration [Lp(a)-P] differentially discriminated risk of calcific aortic valve disease (CAVD) or incident coronary heart disease (CHD) among 4679 participants of the Multi-Ethnic Study of Atherosclerosis (MESA).

METHODS

Lp(a)-M, Lp(a)-C, and Lp(a)-P were measured in individuals without clinical evidence of CHD at baseline. Relative risk regression and Cox proportional analysis determined associations between Lp(a) and the presence of CAVD or 12-year risk of CHD, respectively. To control for the relatively high lower limits of quantification for Lp(a)-C and Lp(a)-P assays, the upper 25th and 15th percentiles were selected as analytical cutoff points.

RESULTS

Regardless of method or analytical cutoff, high Lp(a) concentrations were significantly associated with CAVD and CHD in MESA participants following adjustment for typical cardiovascular risk factors. Stratifying by race/ethnicity rendered most associations nonsignificant after correction for multiple comparisons, but Lp(a) remained associated with CAVD in whites irrespective of method (all P &lt; 0.0001).

CONCLUSIONS

Associations of Lp(a)-C, Lp(a)-P, and Lp(a)-M with CAVD or incident CHD were similar in this entire MESA sample using a dichotomized statistical approach. However, the high lower limits of quantification and imprecision of the Lp(a)-C and Lp(a)-P assays limited their usefulness in our analyses and would likely do so in research and clinical settings.

Lipoprotein(a) Mass Levels Increase Significantly According to APOE Genotype: An Analysis of 431 239 Patients

OBJECTIVE

Lipoprotein(a) [Lp(a)] levels are genetically determined by hepatocyte apolipoprotein(a) synthesis, but catabolic pathways also influence circulating levels. APOE genotypes have different affinities for the low-density lipoprotein (LDL) receptor and LDL-related protein-1, with ε2 having the weakest binding to LDL receptor at <2% relative to ε3 and ε4. APPROACH AND RESULTS: APOE genotypes (ε2/ε2, ε2/ε3, ε2/ε4, ε3/ε3, ε3/ε4, and ε4/ε4), Lp(a) mass, directly measured Lp(a)-cholesterol levels, and a variety of apoB-related lipoproteins were measured in 431 239 patients. The prevalence of APOE traits were ε2: 7.35%, ε3: 77.56%, and ε4: 15.09%. Mean (SD) Lp(a) levels were 65% higher in ε4/ε4 compared with ε2/ε2 genotypes and increased significantly according to APOE genotype: ε2/ε2: 23.4 (29.2), ε2/ε3: 31.3 (38.0), ε2/ε4: 32.8 (38.5), ε3/ε3: 33.2 (39.1), ε3/ε4: 35.5 (41.6), and ε4/ε4: 38.5 (44.1) mg/dL (P<0.0001). LDL-cholesterol, apoB, Lp(a)-cholesterol, LDL-cholesterol corrected for Lp(a)-cholesterol content, LDL-particle number, and small, dense LDL also had similar patterns. Patients with LDL-cholesterol ≥250 mg/dL, who are more likely to have LDL receptor mutations and reduced affinity for apoB, had higher Lp(a) levels across all apoE isoforms, but particularly in patients with ε2 alleles, compared with LDL <250 mg/dL. The lowest Lp(a) mass levels were present in patients with ε2 isoforms and lowest LDL-cholesterol.

CONCLUSIONS

APOE genotypes strongly influence Lp(a) and apoB-related lipoprotein levels. This suggests that differences in affinity of apoE proteins for lipoprotein clearance receptors may affect Lp(a) catabolism, suggesting a competition between Lp(a) and apoE protein for similar receptors.

Lipoprotein(a) mass: a massively misunderstood metric

The importance of lipoprotein (a)-Lp(a)-as a cardiovascular (CV) risk marker has been underscored by recent findings that CV risk is directly related to baseline Lp(a) levels, even in well-treated patients. Although there is currently little that can be done pharmacologically to lower Lp(a) levels, knowledge of its serum concentration is important in overall risk assessment. This review focuses on 1 aspect of Lp(a) that is rarely discussed directly: how to express its levels in serum. There is considerable confusion on this point, and a fuller understanding of what the concentration units mean will help improve study-to-study comparisons and thereby advance our understanding of the pathobiology of this lipoprotein particle. As discussed here, the term Lp(a) mass refers to the entire mass of the particle: lipids, proteins, and carbohydrates combined. At present, there are no commercially available assays that are completely insensitive to the variability in particle mass, which arises not only from differences in apo(a) isoform mass but also from variations in lipid mass. Because lipoprotein "particle number" (molar concentration) has been found to be superior to component-based metrics (ie, low-density lipoprotein particle vs cholesterol concentrations) for CV disease risk prediction, the development of a mass-insensitive Lp(a) assay should be a high priority.

Lipoprotein(a) is strongly associated with coronary artery calcification in type-2 diabetic women

BACKGROUND

Lp(a), implicated in both atherogenesis and thrombosis pathways, varies significantly by demographic and metabolic factors, providing challenges for its use in Coronary Heart Disease (CHD) risk. The purpose of this study was to investigate whether type-2 diabetic subjects, relative to non-diabetics, might benefit more from Lp(a) measurement in the prediction of CHD risk, as measured by coronary artery calcium (CAC).

METHODS

We performed cross sectional analyses in two community-based studies: the Penn Diabetes Heart Study [N = 1299 with type-2 diabetes] and the Study of Inherited Risk of Coronary Atherosclerosis [N = 860 without diabetes].

RESULTS

Blacks had 2-3 fold higher Lp(a) levels than whites in diabetic and non-diabetic samples. There was significant difference by gender (interaction p<0.001), but not race, in the association of Lp(a) with CAC in type-2 diabetic subjects. In age and race adjusted analysis of diabetic women, Lp(a) was associated with CAC [Tobit regression ratio 2.76 (95% CI 1.73-4.40), p<0.001]. Adjustment for exercise, medications, Framingham risk score, metabolic syndrome, BMI, CRP and hemoglobin A1c attenuated this effect, but the association of Lp(a) with CAC remained significant [2.25, (1.34-3.79), p = 0.002]. This relationship was further maintained in women stratified by race, or by the use of HRT or lipid lowering drugs. In contrast, Lp(a) was not associated with CAC in diabetic men, nor in non-diabetic men and women.

CONCLUSIONS

Lp(a) is a strong independent predictor of CAC in type-2 diabetic women, regardless of race, but not in men. Lp(a) does not relate to CAC in men or women without type-2 diabetes.

Lipoprotein(a): A Unique Risk Factor for Cardiovascular Disease

Lipoprotein(a) (Lp(a)) is present in humans and primates. It has many properties in common with low-density lipoprotein, but contains a unique protein moiety designated apo(a), which is linked to apolipoprotein B-100 by a single disulfide bond. International standards for Lp(a) measurement and optimized Lp(a) assays insensitive to isoform size are not yet widely available. Lp(a) is a risk factor for coronary artery disease, and smaller size apo(a) is associated with coronary artery disease. The physiologic role of Lp(a) is unknown.