Lipoprotein(a) particle concentration and lipoprotein(a) cholesterol assays yield discordant classification of patients into four physiologically discrete groups

Elevated Lipoprotein(a): Background, Current Insights and Future Potential Therapies

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.

Lipoprotein(a): An independent, genetic, and causal factor for cardiovascular disease and acute myocardial infarction

Lipoprotein(a) [Lp(a)] is a circulating lipoprotein, and its level is largely determined by variation in the Lp(a) gene (LPA) locus encoding apo(a). Genetic variation in the LPA gene that increases Lp(a) level also increases coronary artery disease (CAD) risk, suggesting that Lp(a) is a causal factor for CAD risk. Lp(a) is the preferential lipoprotein carrier for oxidized phospholipids (OxPL), a proatherogenic and proinflammatory biomarker. Lp(a) adversely affects endothelial function, inflammation, oxidative stress, fibrinolysis, and plaque stability, leading to accelerated atherothrombosis and premature CAD. The INTER-HEART Study has established the usefulness of Lp(a) in assessing the risk of acute myocardial infarction in ethnically diverse populations with South Asians having the highest risk and population attributable risk. The 2018 Cholesterol Clinical Practice Guideline have recognized elevated Lp(a) as an atherosclerotic cardiovascular disease risk enhancer for initiating or intensifying statin therapy.

Low LPA gene kringle IV-2 repeat copy number association with elevated lipoprotein (a) concentration as an independent risk factor of coronary atherosclerotic heart disease in the Chinese Han population

Background

Lipoprotein (a) [Lp(a)], which is genetically determined by the LPA gene kringle IV type 2 (KIV-2) repeat copy number, has previously been reported in different populations. However, it is uncertain if the same occurs in the Chinese Han population. This study explored the correlation of Lp(a) mass or particle concentration with KIV-2 repeat copy number and application for coronary atherosclerotic heart disease (CAHD) risk assessment.

Methods

A cross-sectional study including 884 subjects was conducted. The Lp(a) level and routine risk factors of CAHD were compared. The KIV-2 copy number distribution, relationship with Lp(a), and assessment for CAHD risk were explored.

Results

The mean of Lp(a) mass or particle concentration in the CAHD group was higher than that in the non-CAHD group, while the KIV-2 copy number in the CAHD group was lower. Lp(a) had auxiliary values in gauging the type of plaque and was significantly higher in the soft-plaque group than that in the other two groups (200 mg/L [21.5 nmol/L], 166 mg/L [18.6 nmol/L], 149 mg/L [17.1 nmol/L], respectively, P < 0.05). Kappa test indicated divergence for the same individual using two Lp(a) concentrations (kappa value was 0.536 [< 0.75]). Elevated Lp(a) was an independent CAHD risk factor, whatever mass or particle concentration, and large KIV-2 copy number was a protective factor.

Conclusion

Lp(a) level and small KIV-2 copy number are risk factors for CAHD in the Chinese Han population; furthermore, elevated Lp(a) may gauge the type of coronary plaque.

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)-cholesterol levels estimated by vertical auto profile correlate poorly with Lp(a) mass in hyperlipidemic subjects: Implications for clinical practice interpretation of Lp(a)-mediated risk

BACKGROUND

Lipoprotein(a) [Lp(a)] is generally measured as total mass of the entire particle or as apolipoprotein(a) particle number.

OBJECTIVE

The cholesterol content of Lp(a) [Lp(a)-C)] can be estimated by the vertical auto profile (VAP) method. We assessed whether this is an accurate surrogate measurement of Lp(a) mass.

METHODS

VAP-Lp(a)-C and VAP-high density lipoprotein cholesterol (HDL-C) estimated by the VAP technique, Lp(a) mass, oxidized phospholipids on apolipoprotein B-100 (OxPL-apoB) that primarily reflect OxPL on Lp(a), and HDL-C measured by enzymatic methods were measured in 552 hypercholesterolemic patients at baseline and 24 weeks after therapy with niacin monotherapy (N = 118), ezetimibe/simvastatin monotherapy (n = 155), or ezetimibe/simvastatin (10/20 mg) + niacin (to 2 g) (N = 279) in a randomized, double-blind trial.

RESULTS

VAP-Lp(a)-C correlated only modestly with Lp(a) mass at baseline (r = 0.56, P < .001) and 24 weeks (r = 0.56, P < .001), explaining only 31% of the association. VAP-Lp(a)-C correlated with HDL-C at baseline (r = 0.34, P < .001) and 24 weeks (r = 0.30, P < .001) and with VAP-HDL-C at baseline (r = 39, P < .001) and 24 weeks (r = 0.33, P < .001). In contrast, Lp(a) mass did not correlate with HDL-C at baseline (r = 0.06, P = .12) and 24 weeks (r = -0.01 P = .91). Lp(a) mass correlated strongly with oxidized phospholipids on apolipoprotein B-100 at baseline (r = 0.81, P < .001) and 24 weeks (r = 0.79, P < .001). VAP-Lp(a)-C levels increased linearly with HDL-C and VAP-HDL-C quartiles (P < .001 for both) but Lp(a) mass did not. Quantitating the percent of cholesterol present on Lp(a) by dividing VAP-Lp(a)-C by Lp(a) mass revealed that 25% of patients had a percentage >100, which is not possible.

CONCLUSIONS

VAP-Lp(a)-C is a poor estimate for Lp(a) mass and likely reflects the content of HDL-C in the overlapping density spectrum of Lp(a) and HDL. These data suggest that patients with prior VAP-Lp(a)-C measurements may have misclassification of Lp(a)-related risk.

Effect of dietary modification by calorie restriction on cholesterol levels in lipoprotein(a) and other lipoprotein classes

Background Dietary habits are associated with obesity which is a risk factor for coronary heart disease. The objective is to estimate the change of lipoprotein(a) and other lipoprotein classes by calorie restriction with obesity index and Framingham risk score. Methods Sixty females (56 ± 9 years) were recruited. Their caloric intakes were reduced during the six-month period, and the calorie from fat was not more than 30%. Lipoprotein profiles were estimated at baseline and after the six-month period of calorie restriction. Cholesterol levels in six lipoprotein classes (HDL, LDL, IDL, VLDL, chylomicron and lipoprotein(a)) were analysed by anion-exchange liquid chromatography. The other tests were analysed by general methods. Additionally, Framingham risk score for predicting 10-year coronary heart disease risk was calculated. Results Body mass index, waist circumference, insulin resistance, Framingham risk score, total cholesterol, LDL-cholesterol and IDL-cholesterol were significantly decreased by the calorie restriction, and the protein and cholesterol levels of lipoprotein(a) were significantly increased. The change of body mass index was significantly correlated with those of TC, VLDL-cholesterol and chylomicron-cholesterol, and that of waist circumference was significantly correlated with that of chylomicron-cholesterol. The change of Framingham risk score was significantly correlated with the change of IDL-C. Conclusion Obesity indexes and Framingham risk score were reduced by the dietary modification. Lipoprotein profile was improved with the reduction of obesity indexes, but lipoprotein(a) was increased. The changes of obesity indexes and Framingham risk score were related with those of triglyceride-rich lipoproteins, e.g. IDL, VLDL and CM.

Lipoprotein(a): Its relevance to the pediatric population

Lipoprotein(a) (Lp(a)) is a highly atherogenic and heterogeneous lipoprotein that is inherited in an autosomal codominant trait. A unique aspect of this lipoprotein is that it is fully expressed by the first or second year of life in children, a pattern that is distinctly different from other lipoproteins, which typically only reach adult levels after adolescence. Despite decades of research, Lp(a) metabolism is still poorly understood but what is abundantly clear is that it is an independent risk factor for atherosclerotic cardiovascular disease (ASCVD). The Expert Panel on Integrated Guidelines for Cardiovascular Health and Risk Reduction in Children and Adolescents does not recommend measuring Lp(a) levels as part of routine screening except in youth with an ischemic or hemorrhagic stroke or youth with a parental history of ASCVD not explained by classical risk factors. One of the reasons that both the pediatric and adult guidelines fail to include this lipoprotein as part of routine lipid screening is the absence of data to show that lowering Lp(a) will reduce current or future ASCVD risk independently of low-density lipoprotein cholesterol (LDL-C) lowering. The cholesterol carried by Lp(a) is included in the low-density lipoprotein cholesterol measurement, but a separate test is used to measure the lipoprotein mass and/or cholesterol carried only by Lp(a). Because levels seem to be largely under genetic control, studies of lifestyle modification have been inconclusive although one study in obese children showed a decrease in the Lp(a) level comparable with the favorable effect on other lipids. The most compelling data regarding the importance of Lp(a) in the pediatric population are the increased risk associated with arterial ischemic stroke, a risk that is comparable with that associated with antiphospholipid antibodies or protein C deficiency. Although no specific pharmaceutical treatments are recommended to lower Lp(a) levels in youth, it is vitally important to educate youth and their parents about the excessive risk associated with this lipoprotein and the need to avoid the acquisition of other lifestyle-related risk factors such as smoking, excess weight, and physical inactivity to preserve more ideal cardiovascular health in adulthood.

'LDL-C' = LDL-C + Lp(a)-C: implications of achieved ultra-low LDL-C levels in the proprotein convertase subtilisin/kexin type 9 era of potent LDL-C lowering

PURPOSE OF REVIEW

The measurement that is termed 'LDL-cholesterol' (LDL-C) includes the cholesterol content of lipoprotein(a) [Lp(a)-C], which can contribute approximately 30-45% to measured LDL-C levels as a percentage of its mass. We review the implications of achieved very low LDL-C levels in patients treated with potent LDL-C-lowering agents in the context of varying Lp(a) levels.

RECENT FINDINGS

Combination therapy with statins, ezetimibe, and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors can lower LDL-C to unprecedentedly low levels. Recent PCSK9 trials have shown that routine achievement of mean LDL-C less than 50 mg/dl is feasible, along with the modest reductions in Lp(a). Many patients will achieve LDL-C less than 25 mg/dl with concomitantly elevated Lp(a) levels that contribute substantially to the measured 'LDL-C'. Therefore, it is possible that some of these patients may have little to no circulating LDL-C.

SUMMARY

As the new era of ultralow LDL-C levels ensues, it is imperative to understand the contribution of Lp(a)-C to measured LDL-C and the consequences of achieving ultralow or potentially absent LDL-C in the setting of elevated Lp(a) levels and possibly free apo(a). We review this concept and suggest avenues of research, including analyses of existing datasets in current clinical trials and new research studies, to understand its pathophysiological and clinical significance.

Lipoprotein(a): an important cardiovascular risk factor and a clinical conundrum

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.

[Lipoprotein(a) is associated to atherosclerosis in primary hypercholesterolemia]

INTRODUCTION

Several studies have suggested that Lp(a) could be a risk factor mainly in hypercholesterolemic patients.

METHODS

A total of 909 individuals were selected for this study. 307 were diagnosed of familiar hypercholesterolemia with a pathogenic mutation in LDLR or APOB genes (FH+), 291 of familiar combined hyperlipidemia (FCH) and 311 of familial hypercholesterolemia without a pathogenic mutation in LDLR nor APOB genes (FH-). Main risk factor were studied, included statin treatment. Plasma lipids, Lp(a), HbA1c and C-reactive protein. Intima-media thickness (IMT) of common and bulb carotid in both sides were measured in all subjects.

RESULTS

Lp(a) values (median, interquartile range) were 21.9mg/dL (9.24-50.5) in FH+, 22.4mg/dL (6.56-51.6) in FCH and 32.7 (14.6-71.5) in FH- (P<.001). Regression analysis including age, gender, HDL cholesterol, LDL cholesterol corrected for Lp(a), Lp(a), C-reactive protein, packs of cigarettes/day per year, systolic blood pressure and glucose as independent variables, demonstrate that Lp(a) was associated with carotid IMT in FH- subjects. Cardiovascular disease was more frequent in subjects with Lp(a) >50mg/dL (17.9%) than in subjects with Lp(a) <15mg/dL (9.6%), and between 15-50mg/dL (10.1%), and it was concentrated mostly in FH-group (6.7, 11.3, and 23.4% for the groups of Lp(a) <15mg/dL 15-50mg/dL, and >50mg/dL, respectively).

CONCLUSIONS

Our results indicate that Lp(a) is associated with atherosclerosis burden especially in subjects with FH- and concentrations of Lp(a)>50mg/dL.

Lipoprotein(a), cardiovascular disease, and contemporary management

Elevated lipoprotein(a) (Lp[a]) is a causal genetic risk factor for cardiovascular disease. To determine if current evidence supports both screening and treatment for elevated Lp(a) in high-risk patients, an English-language search of PubMed and MEDLINE was conducted. In population studies, there is a continuous association between Lp(a) concentrations and cardiovascular risk, with synergistic effects when low-density lipoprotein (LDL) is also elevated. Candidates for Lp(a) screening include patients with a personal or family history of premature cardiovascular disease, familial hypercholesterolemia, recurrent cardiovascular events, or inadequate LDL cholesterol (LDL-C) responses to statins. Given the comparative strength of clinical evidence, reducing LDL-C to the lowest attainable value with a high-potency statin should be the primary focus of lipid-modifying therapies. If the Lp(a) level is 30 mg/dL or higher in a patient who has the aforementioned characteristics plus residual LDL-C elevations (≥70-100 mg/dL) despite maximum-potency statins or combination statin therapy, the clinician may consider adding niacin (up to 2 g/d). If, after these interventions, the patient has progressive coronary heart disease (CHD) or LDL-C levels of 160-200 mg/dL or higher, LDL apheresis should be contemplated. Although Lp(a) is a major causal risk factor for CHD, no currently available controlled studies have suggested that lowering it through either pharmacotherapy or LDL apheresis specifically and significantly reduces coronary risk. Further research is needed to (1) optimize management in order to reduce CHD risk associated with elevated Lp(a) and (2) determine what other intermediate- or high-risk groups might benefit from Lp(a) screening.

Severe coronary disease in an adult considered at low cardiovascular disease risk with a healthy lifestyle

Lipoprotein(a) [Lp(a)] is a lipoprotein subclass well-known among the lipid community to accelerate atherosclerosis and promote thrombosis through incompletely understood mechanism. We report a case of a young man with a healthy lifestyle and no major coronary or vascular risk factors who presented to the emergency department with an acute coronary syndrome and was ultimately found to have severe coronary artery disease. A diagnostic workup revealed elevated Lp(a). He was treated with consequent reduction in Lp(a) concentration. This case highlights the need to better understand atypical lipoproteins, how they relate to cardiovascular disease, the implications for screening family members, and the need to standardize patient management guidelines for the purpose of mortality risk reduction.