Human plasma lipoprotein [a]. Structural properties

Impact of Lipoprotein(a) Level on Low-Density Lipoprotein Cholesterol- or Apolipoprotein B-Related Risk of Coronary Heart Disease

BACKGROUND

Conventional low-density lipoprotein cholesterol (LDL-C) quantification includes cholesterol attributable to lipoprotein(a) (Lp(a)-C) due to their overlapping densities.

OBJECTIVES

The purposes of this study were to compare the association between LDL-C and LDL-C corrected for Lp(a)-C (LDLLp(a)corr) with incident coronary heart disease (CHD) in the general population and to investigate whether concomitant Lp(a) values influence the association of LDL-C or apolipoprotein B (apoB) with coronary events.

METHODS

Among 68,748 CHD-free subjects at baseline LDLLp(a)corr was calculated as "LDL-C-Lp(a)-C," where Lp(a)-C was 30% or 17.3% of total Lp(a) mass. Fine and Gray competing risk-adjusted models were applied for the association between the outcome incident CHD and: 1) LDL-C and LDLLp(a)corr in the total sample; and 2) LDL-C and apoB after stratification by Lp(a) mass (≥/<90th percentile).

RESULTS

Similar risk estimates for incident CHD were found for LDL-C and LDL-CLp(a)corr30 or LDL-CLp(a)corr17.3 (subdistribution HR with 95% CI) were 2.73 (95% CI: 2.34-3.20) vs 2.51 (95% CI: 2.15-2.93) vs 2.64 (95% CI: 2.26-3.10), respectively (top vs bottom fifth; fully adjusted models). Categorization by Lp(a) mass resulted in higher subdistribution HRs for uncorrected LDL-C and incident CHD at Lp(a) ≥90th percentile (4.38 [95% CI: 2.08-9.22]) vs 2.60 [95% CI: 2.21-3.07]) at Lp(a) <90th percentile (top vs bottom fifth; Pinteraction0.39). In contrast, apoB risk estimates were lower in subjects with higher Lp(a) mass (2.43 [95% CI: 1.34-4.40]) than in Lp(a) <90th percentile (3.34 [95% CI: 2.78-4.01]) (Pinteraction0.49).

CONCLUSIONS

Correction of LDL-C for its Lp(a)-C content provided no meaningful information on CHD-risk estimation at the population level. Simple categorization of Lp(a) mass (≥/<90th percentile) influenced the association between LDL-C or apoB with future CHD mostly at higher Lp(a) levels.

Lipoprotein(a) and Lung Function Are Associated in Older Adults: Longitudinal and Cross-Sectional Analyses

While numerous studies have confirmed a causal association between lipoprotein(a) [Lp(a)] and cardiovascular diseases, only a few studies have assessed the relationship between Lp(a) and pulmonary health, with inconsistent findings regarding this topic. This study's aim was to examine whether levels of serum Lp(a) are associated with lung function in a dataset of relatively healthy older adults. We used longitudinal data collected at two time points 7.4 ± 1.5 years apart from 679 participants (52% women, 68 [65-71] years old) from the Berlin Aging Study II (BASE-II). Multiple linear regression models adjusting for covariates were applied to examine the association between Lp(a) and lung function. The forced expiratory volume in one second (FEV1) and the forced vital capacity (FVC) were higher in both men and women with higher Lp(a) levels. However, since this association between lung function parameters and Lp(a) was not supported by Mendelian randomization analyses using recent genome-wide association study data, these relationships should be investigated in future work, as the observed differences are, in part, considerable and potentially clinically relevant.

Digital droplet PCR versus quantitative PCR for lipoprotein (a) kringle IV type 2 repeat polymorphism genetic characterization

BACKGROUND

Lipoprotein(a) [Lp(a)] level variability, related to atherothrombotic risk increase, is mainly attributed to LPA gene, encoding apolipoprotein(a), with kringle IV type 2 (KIV2) copy number variation (CNV) acting as the primary genetic determinant. Genetic characterization of Lp(a) is in continuous growth; nevertheless, the peculiar structural characteristics of this variant constitute a significant challenge to the development of effective detection methods. The aim of the study was to compare quantitative real-time PCR (qPCR) and digital droplet PCR (ddPCR) in the evaluation of KIV2 repeat polymorphism.

METHODS

We analysed 100 subjects tested for cardiovascular risk in which Lp(a) plasma levels were assessed.

RESULTS

Correlation analysis between CNV values obtained with the two methods was slightly significant (R = 0.413, p = 0.00002), because of the wider data dispersion in qPCR compared with ddPCR. Internal controls C1, C2 and C3 measurements throughout different experimental sessions revealed the superior stability of ddPCR, which was supported by a reduced intra/inter-assay coefficient of variation determined in this method compared to qPCR. A significant inverse correlation between Lp(a) levels and CNV values was confirmed for both techniques, but it was higher when evaluated by ddPCR than qPCR (R = -0.393, p = 0.000053 vs R = -0.220, p = 0.028, respectively). When dividing subjects into two groups according to 500 mg/L Lp(a) cut-off value, a significantly lower number of KIV2 repeats emerged among subjects with greater Lp(a) levels, with stronger evidence in ddPCR than in qPCR (p = 0.000013 and p = 0.001, respectively).

CONCLUSIONS

Data obtained support a better performance of ddPCR in the evaluation of KIV2 repeat polymorphism.

Quantification of LDL-Cholesterol Corrected for Molar Concentration of Lipoprotein(a)

PURPOSE

Cholesterol in lipoprotein(a) [Lp(a)-C] is commonly estimated as 30% of the measured Lp(a) mass. However, difficulties in the accurate measurement of Lp(a) mass, along with the inaccuracy of the 30% assumption, produce erroneous values when LDL-C is corrected for Lp(a) [LDL-CLp(a)corr]. Our aim was to develop a new formula for LDL-CLp(a)corr to reduce this error.

METHODS

We developed a new formula to calculate Lp(a)-C from the molar measurement of Lp(a), which is Lp(a) nmol/L × 0.077 = Lp(a)-C mg/dL. The calculated Lp(a)-C is subtracted from LDL-C to obtain LDL-CLp(a)corr. The results obtained with our novel formula versus the conventional formula were compared in 440 samples from 239 participants enrolled in the BANTING study.

RESULTS

With the conventional formula, approximately 7% of samples with low LDL-C resulted in negative LDL-CLp(a)corr values. With the new formula, no negative LDL-CLp(a)corr values occurred. Among groups with the highest Lp(a)/apoB ratio (p < 0.001) and smaller apolipoprotein(a) isoform size (p < 0.006), LDL-CLp(a)corr was significantly underestimated by the conventional formula, which may result in the undertreatment of some patients.

CONCLUSION

The new formula provides more reliable estimates of LDL-CLp(a)corr than the conventional formula.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02739984.

Lipoprotein(a): a Case for Universal Screening in Youth

PURPOSE OF REVIEW

Lipoprotein(a) has emerged as a strong independent risk factor for cardiovascular disease. Targeted screening recommendations for Lp(a) measurement exist for adults and youth known to be at high-risk. However, Lp(a) measurements are not included in universal screening guidelines in the US; hence, most families in the US with high Lp(a) levels who are at risk of future atherosclerotic heart disease, stroke, or aortic stenosis are not recognized. Lp(a) measurement included as part of routine universal lipid screening in youth would identify those children at risk of ASCVD and enable family cascade screening with identification and early intervention for affected family members.

RECENT FINDINGS

Lp(a) levels can be reliably measured in children as young as two years of age. Lp(a) levels are genetically determined. The Lp(a) gene is inherited in a co-dominant fashion. Serum Lp(a) attains adult levels by two years of age and is stable for the lifetime of the individual. Novel therapies that aim to specifically target Lp(a) are in the pipeline, including nucleic acid-based molecules such as antisense oligonucleotides and siRNAs. Inclusion of a single Lp(a) measurement performed as part of routine universal lipid screening in youth (ages 9-11; or at ages 17-21) is feasible and cost effective. Lp(a) screening would identify youth at-risk of ASCVD and enable family cascade screening with identification and early intervention for affected family members.

Identification of allele-specific KIV-2 repeats and impact on Lp(a) measurements for cardiovascular disease risk

The abundance of Lp(a) protein holds significant implications for the risk of cardiovascular disease (CVD), which is directly impacted by the copy number (CN) of KIV-2, a 5.5 kbp sub-region. KIV-2 is highly polymorphic in the population and accurate analysis is challenging. In this study, we present the DRAGEN KIV-2 CN caller, which utilizes short reads. Data across 166 WGS show that the caller has high accuracy, compared to optical mapping and can further phase ~50% of the samples. We compared KIV-2 CN numbers to 24 previously postulated KIV-2 relevant SNVs, revealing that many are ineffective predictors of KIV-2 copy number. Population studies, including USA-based cohorts, showed distinct KIV-2 CN, distributions for European-, African-, and Hispanic-American populations and further underscored the limitations of SNV predictors. We demonstrate that the CN estimates correlate significantly with the available Lp(a) protein levels and that phasing is highly important.

The effect of adjusting LDL-cholesterol for Lp(a)-cholesterol on the diagnosis of familial hypercholesterolaemia

BACKGROUND

Familial hypercholesterolaemia (FH) diagnostic tools help prioritise patients for genetic testing and include LDL-C estimates commonly calculated using the Friedewald equation. However, cholesterol contributions from lipoprotein(a) (Lp(a)) can overestimate 'true' LDL-C, leading to potentially inappropriate clinical FH diagnosis.

OBJECTIVE

To assess how adjusting LDL-C for Lp(a)-cholesterol affects FH diagnoses using Simon Broome (SB) and Dutch Lipid Clinic Network (DLCN) criteria.

METHODS

Adults referred to a tertiary lipid clinic in London, UK were included if they had undergone FH genetic testing based on SB or DLCN criteria. LDL-C was adjusted for Lp(a)-cholesterol using estimated cholesterol contents of 17.3%, 30% and 45%, and the effects of these adjustments on reclassification to 'unlikely' FH and diagnostic accuracy were determined.

RESULTS

Depending on the estimated cholesterol content applied, LDL-C adjustment reclassified 8-23% and 6-17% of patients to 'unlikely' FH using SB and DLCN criteria, respectively. The highest reclassification rates were observed following 45% adjustment in mutation-negative patients with higher Lp(a) levels. This led to an improvement in diagnostic accuracy (46% to 57% with SB, and 32% to 44% with DLCN following 45% adjustment) through increased specificity. However all adjustment factors led to erroneous reclassification of mutation-positive patients to 'unlikely' FH.

CONCLUSION

LDL-C adjustment for Lp(a)-cholesterol improves the accuracy of clinical FH diagnostic tools. Adopting this approach would reduce unnecessary genetic testing but also incorrectly reclassify mutation-positive patients. Health economic analysis is needed to balance the risks of over- and under-diagnosis before LDL-C adjustments for Lp(a) can be recommended.

Impact of lipoprotein(a) levels on primary patency after endovascular therapy for femoropopliteal lesions

Lipoprotein(a) [Lp(a)] is a risk factor for peripheral artery disease (PAD). However, the relationship between Lp(a) levels and clinical events after endovascular therapy (EVT) for the femoropopliteal artery in PAD patients remains unclear. Thus, this study aimed to assess the impact of Lp(a) levels on primary patency after EVT for de novo femoropopliteal lesions in PAD patients. A retrospective analysis was conducted on 109 patients who underwent EVT for de novo femoropopliteal lesions, and Lp(a) levels were measured before EVT between June 2016 and December 2019. Patients were divided into low Lp(a) [Lp(a) < 30 mg/dL; 78 patients] and high Lp(a) [Lp(a) ≥ 30 mg/dL; 31 patients] groups. The main outcome was primary patency following EVT. Loss of primary patency was defined as a peak systolic velocity ratio > 2.4 on a duplex scan or > 50% stenosis on angiography. Cox proportional hazards analysis was performed to determine whether high Lp(a) levels were independently associated with loss of primary patency. The mean follow-up duration was 28 months. The rates of primary patency were 83 and 76% at 1 year and 75 and 58% at 2 years in the low and high Lp(a) groups, respectively (P = 0.02). After multivariate analysis, High Lp(a)[Lp(a) ≥ 30 mg/dL] (hazard ratio 2.44; 95% CI 1.10-5.44; P = 0.03) and female sex (hazard ratio 2.65; 95% CI 1.27-5.51; P < 0.01) were independent predictors of loss of primary patency. Lp(a) levels might be associated with primary patency after EVT for de novo femoropopliteal lesions.

Elevated Lp(a) Levels Correlate with Severe and Multiple Coronary Artery Stenotic Lesions

Backgrounds and Aims

The role of Lipoprotein(a) (Lp(a)) in increasing the risk of cardiovascular diseases is reported in several populations. The aim of this study is to investigate the correlation of high Lp(a) levels with the degree of coronary artery stenosis.

Methods

Two hundred and sixty-eight patients were enrolled for this study. Patients who underwent coronary artery angiography and who had Lp(a) measurements available were included in this study. Binomial logistic regressions were applied to investigate the association between Lp(a) and stenosis in the four major coronary arteries. The effect of LDL and HDL Cholesterol on modulating the association of Lp(a) with coronary artery disease (CAD) was also evaluated. Multinomial regression analysis was applied to assess the association of Lp(a) with the different degrees of stenosis in the four major coronary arteries.

Results

Our analyses showed that Lp(a) is a risk factor for CAD and this risk is significantly apparent in patients with HDL-cholesterol ≥35 mg/dL and in non-obese patients. A large proportion of the study patients with elevated Lp(a) levels had CAD even when exhibiting high HDL serum levels. Increased HDL with low Lp(a) serum levels were the least correlated with stenosis. A significantly higher levels of Lp(a) were found in patients with >50% stenosis in at least two major coronary vessels arguing for pronounced and multiple stenotic lesions. Finally, the derived variant (rs1084651) of the LPA gene was significantly associated with CAD.

Conclusion

Our study highlights the importance of Lp(a) levels as an independent biological marker of severe and multiple coronary artery stenosis.

Lipoprotein(a) in Atherosclerotic Diseases: From Pathophysiology to Diagnosis and Treatment

Lipoprotein(a) (Lp(a)) is a low-density lipoprotein (LDL) cholesterol-like particle bound to apolipoprotein(a). Increased Lp(a) levels are an independent, heritable causal risk factor for atherosclerotic cardiovascular disease (ASCVD) as they are largely determined by variations in the Lp(a) gene (LPA) locus encoding apo(a). Lp(a) is the preferential lipoprotein carrier for oxidized phospholipids (OxPL), and its role adversely affects vascular inflammation, atherosclerotic lesions, endothelial function and thrombogenicity, which pathophysiologically leads to cardiovascular (CV) events. Despite this crucial role of Lp(a), its measurement lacks a globally unified method, and, between different laboratories, results need standardization. Standard antilipidemic therapies, such as statins, fibrates and ezetimibe, have a mediocre effect on Lp(a) levels, although it is not yet clear whether such treatments can affect CV events and prognosis. This narrative review aims to summarize knowledge regarding the mechanisms mediating the effect of Lp(a) on inflammation, atherosclerosis and thrombosis and discuss current diagnostic and therapeutic potentials.

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.

Serum concentrations of small dense low-density lipoprotein cholesterol and lipoprotein(a) are related to coronary arteriostenosis in Takayasu arteritis

Background

Serum small dense low‐density lipoprotein cholesterol (sdLDL‐C) and lipoprotein(a) [Lp(a)] levels are related to coronary disease, but their specific associations with coronary arteriostenosis in Takayasu arteritis (TA) have not been ascertained. This study explored the correlations between serum sdLDL‐C and Lp(a) levels and coronary arteriostenosis in TA patients as well as the degree of artery stenosis.

Methods

This retrospective study included 190 TA patients and 154 healthy subjects. TA patients were divided into three categories based on the degree of coronary stenosis: Group I, stenosis >50%; Group II, stenosis 1%–50%; and Group III, stenosis 0%. Independent risk factors for coronary arteriostenosis in TA were identified by logistic regression, followed by receiver operating characteristic curve analysis to determine the specificity and sensitivity of risk factors and Youden's Index score calculation to determine the cutoff points.

Results

Takayasu arteritis patients had significantly higher serum levels of sdLDL‐C and Lp(a) than healthy controls (p < 0.0001). The total cholesterol, triglyceride, LDL‐C, sdLDL‐C, and Lp(a) levels and the sdLDL‐C/LDL‐C ratio in Group I were significantly higher than those in Groups II and III (p < 0.05). An elevated serum sdLDL‐C level elevated the risk of coronary arteriostenosis by 5‐fold (cutoff value, 0.605 mmol/l). An increased serum Lp(a) level increased the risk of coronary arteriostenosis by 3.9‐fold (cutoff value, 0.045 g/l). An elevated sdLDL‐C/LDL‐C ratio increased the risk of coronary arteriostenosis by 2.1‐fold (cutoff value, 0.258).

Conclusions

Serum sdLDL‐C and Lp(a) levels and sdLDL‐C/LDL‐C ratio may be used as diagnostic factors for coronary arteriostenosis in TA patients.

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-Ccorr). 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-Ccorr 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-Ccorr 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.

High resolution structure of human apolipoprotein (a) kringle IV type 2: beyond the lysine binding site

Lipoprotein (a) [Lp(a)] is characterized by an LDL-like composition in terms of lipids and apoB100, and by one copy of a unique glycoprotein, apo(a). The apo(a) structure is mainly based on the repetition of tandem kringle domains with high homology to plasminogen kringles 4 and 5. Among them, kringle IV type 2 (KIV-2) is present in a highly variable number of genetically encoded repeats, whose length is inversely related to Lp(a) plasma concentration and cardiovascular risk. Despite it being the major component of apo(a), the actual function of KIV-2 is still unclear. Here, we describe the first high-resolution crystallographic structure of this domain. It shows a general fold very similar to other KIV domains with high and intermediate affinity for the lysine analog, ε-aminocaproic acid. Interestingly, KIV-2 presents a lysine binding site (LBS) with a unique shape and charge distribution. KIV-2 affinity for predicted small molecule binders was found to be negligible in surface plasmon resonance experiments; and with the LBS being nonfunctional, we propose to rename it "pseudo-LBS". Further investigation of the protein by computational small-molecule docking allowed us to identify a possible heparin-binding site away from the LBS, which was confirmed by specific reverse charge mutations abolishing heparin binding. This study opens new possibilities to define the pathogenesis of Lp(a)-related diseases and to facilitate the design of specific therapeutic drugs.

The role of Lipoprotein(a) in cardiovascular disease: Current concepts and future perspectives

High lipoprotein(a) [Lp(a)] levels are associated with the development of atherosclerotic cardiovascular disease (ASCVD) and with calcific aortic valve stenosis (CAVS) both observationally and causally from human genetic studies. The mechanisms are not well characterized but likely involve its role as a carrier of oxidized phospholipids (OxPLs), which are known to be increased in pro-inflammatory states, to induce pro-inflammatory changes in monocytes leading to plaque instability, and to impair vascular endothelial cell function, a driver of acute and recurrent ischemic events. In addition, Lp(a) itself has prothrombotic activity. Current lipid-lowering strategies do not sufficiently lower Lp(a) serum levels. Lp(a)-specific-lowering drugs, targeting apolipoprotein(a) synthesis, lower Lp(a) by up to 90% and are being evaluated in ongoing clinical outcome trials. This review summarizes the current knowledge on the associations of Lp(a) with ASCVD and CAVS, the current role of Lp(a) assessment in the clinical setting, and emerging Lp(a)-specific-lowering therapies.

Relationship Between Lipoprotein(a) and Angiographic Severity of Femoropopliteal Lesions

AIM

High levels of lipoprotein(a) [Lp(a)] are a risk factor for peripheral artery disease (PAD). However, the relationship between Lp(a) levels and the severity of femoropopliteal lesions in patients with PAD has not been systematically studied. This study aimed to assess the impact of Lp(a) levels on angiographic severity of femoropopliteal lesions in patients with PAD.

METHODS

We retrospectively analyzed a single-center database including 108 patients who underwent endovascular therapy for de novo femoropopliteal lesions and measured the Lp(a) levels before therapy between June 2016 and September 2019. Patients were divided into low Lp(a) [Lp(a) ＜30 mg/dL; 77 patients] and high Lp(a) [Lp(a) ≥ 30 mg/dL; 31 patients] groups. Trans-Atlantic Inter-Society Consensus (TASC) II classification, calcification [referring to the peripheral arterial calcium scoring system (PACSS) classification], and lesion length were compared between the groups.

RESULTS

The prevalence of TASC II class D (13% vs 38%, P＜0.01) and severe calcification (PACSS 4) (6% vs 23%, P=0.02) was significantly higher and the lesion length longer (123±88 mm vs 175±102 mm, P＜0.01) in the high Lp(a) group than in the low Lp(a) group. In multivariate analysis, Lp(a) ≥ 30 was an independent predictor for the prevalence of TASC II class D (HR=3.67, 95% CI 1.27-10.6, P=0.02) and PACSS 4 (HR=4.97, 95% CI 1.27-19.4, P=0.02).

CONCLUSION

The prevalence of TASC II class D and severe calcification of femoropopliteal lesions was higher in patients with high Lp(a) than those with low Lp(a).

Achieving low-density lipoprotein cholesterol targets as assessed by different methods in patients with familial hypercholesterolemia: an analysis from the HELLAS-FH registry

Background

Familial hypercholesterolemia (FH) is characterized by elevated low-density lipoprotein cholesterol (LDL-C) levels and increased cardiovascular disease (CVD) risk. FH patients often have increased lipoprotein(a) [Lp(a)] levels, which further increase CVD risk. Novel methods for accurately calculating LDL-C have been proposed.

Methods

Patients with FH were recruited by a network of Greek sites participating in the HELLAS-FH registry. LDL-C levels were calculated using the Friedewald (LDL-C_F) and the Martin/Hopkins (LDL-C_M/H) equations as well as after correcting LDL-C_M/H for Lp(a) levels [LDL-C_Lp(a)corM/H]. The objective was to compare LDL-C levels and target achievement as estimated by different methods in FH patients.

Results

This analysis included 1620 patients (1423 adults and 197 children). In adults at diagnosis, LDL-C_F and LDL-C_M/H levels were similar [235 ± 70 mg/dL (6.1 ± 1.8 mmol/L) vs 235 ± 69 mg/dL (6.1 ± 1.8 mmol/L), respectively; P = NS], while LDL-C_Lp(a)corM/H levels were non-significantly lower than LDL-C_F [211 ± 61 mg/dL (5.5 ± 1.6 mmol/L); P = 0.432]. In treated adults (n = 966) both LDL-C_F [150 ± 71 mg/dL (3.9 ± 1.8 mmol/L)] and LDL-C_M/H levels [151 ± 70 mg/dL (6.1 ± 1.8 mmol/L); P = 0.746] were similar, whereas LDL-C_Lp(a)corM/H levels were significantly lower than LDL-C_F [121 ± 62 mg/dL (3.1 ± 1.6 mmol/L); P < 0.001]. Target achievement as per latest guidelines in treated patients using the LDL-C_M/H (2.5%) and especially LDL-C_Lp(a)corM/H methods (10.7%) were significantly different than LDL-C_F (2.9%; P < 0.001).

In children, all 3 formulas resulted in similar LDL-C levels, both at diagnosis and in treated patients. However, target achievement by LDL-C_F was lower compared with LDL-C_M/H and LDL-C_Lp(a)corM/H methods (22.1 vs 24.8 vs 33.3%; P < 0.001 for both comparisons).

Conclusion

LDL-C_Lp(a)corM/H results in significantly lower values and higher target achievement rate in both treated adults and children. If validated in clinical trials, LDL-C_Lp(a)corM/H may become the method of choice to more accurately estimate ‘true’ LDL-C levels in FH patients.

Reviews and Original Articles Lipoprotein(A) and Apolipoprotein(A) Phenotypes in Patients with End-Stage Renal Disease

Objective

To evaluate the distribution pattern of apolipoprotein(a) [Apo(a)] phenotypes in Koreans and the effect of dialysis modality on serum lipoprotein(a) [Lp(a)] concentration according to apo(a) phenotype in patients with end-stage renal disease (ESRO).

Design

Cross-sectional study.

Setting

A university hospital. Participants: 153 normal controls, 99 hemodialysis (HO) patients and 82 continuous ambulatory peritoneal dialysis (CAPO) patients.

Main Outcome Measures

Fasting serum Lp(a), lipids, and apo(a) phenotypes were measured.

Results

The frequencies of the subjects with apo(a) phenotypes of high-molecular weight only, including S3, S4, or S5 or null type were 95.4% of control, 100% of HO patients, and 95.1% of CAPO patients. The frequent apo(a) phenotypes in Koreans consisted of S4, S4S5, S5, and S5S5 isoforms. Significant difference was found in serum Lp(a) concentration among controls and HO and CAPO patients [median (interquartile range): 0.05 g/L, (0.01 0.19); 0.19g/L, (0.10 0.35); 0.63g/L, (0.28 0.90), p< 0.001]. Lp(a) levels in CAPO patients were significantly higher than in HO patients for all four common apo(a) isoforms found in Korean subjects. CAPO patients had higher total and LOL cholesterol levels, and higher ApoB levels than H O patients. Significant differences were found in serum albumin levels between controls and HO and CAPO patients (44 ± 3 g/L, 40 ± 4 g/L, 32 ± 7 g/L, respectively, p < 0.05). There were significant inverse correlations between serum albumin and Lp(a) (r = -0.33, p < 0.01), total cholesterol (r = -0.31, p < 0.01), LOL (r = -0.39, p < 0.01) or ApoB (r = -0.35, p < 0.01) in ESRO patients. A significant positive correlation was found between serum albumin and ApoA1 (r = 0.24, p < 0.01).

Conclusion

These findings indicate that Koreans have mainly high -molecular weight apo(a) phenotypes and serum Lp(a) is elevated in CAPO patients compared to HO patients for common apo(a) phenotypes, which may contribute to the frequent cardiovascular mortality in CAPO patients.

Impact of Lipoprotein(a) on Long-Term (Mean 6.2 Years) Outcomes in Patients With Three-Vessel Coronary Artery Disease

The aim of the cohort study was to investigate the relation between plasma lipoprotein(a) (Lp[a]) and long-term clinical outcomes in patients with three-vessel disease (TVD) after the following treatment strategies, including medical therapy alone, percutaneous coronary intervention, and coronary artery bypass grafting. A total of 6,175 consecutive patients with angiographically confirmed TVD and available baseline Lp(a) data were included in this study. Based on the median level of Lp(a) at admission, the patient was divided into 2 subgroups. Primary endpoint was major adverse cardiovascular events (MACE), of which all-cause death, myocardial infarction, and unplanned revascularization were all included. In general, the median value of Lp(a) reached 13.76 mg/dl for all patients. The median follow-up time of all patients was 6.2 years. For MACE, a total of 1,433 cases were generated, accounting for 23.2%, including 804 (13.0%) all-cause death, 302 (4.9 %) myocardial infarction, and 494 (8.0%) unplanned revascularization. For the incidence of MACE, the high Lp (a) and low Lp (a) groups were 24.3% to 22.1% (p = 0.015), respectively. When the risk factors were adjusted, the multivariate analysis showed that high Lp(a) levels was an independent predictor of primary outcome (adjusted hazard ratio 1.169, 95% confidence interval 1.046 to 1.306, p = 0.006). Except for gender group, there is a relatively consistent correlation in the various subgroups. In conclusion, plasma Lp(a) is a potential biomarker for risk stratification and prognosis in patients diagnosed with TVD.

Lipoprotein(a) levels are associated with coronary severity but not with outcomes in Chinese patients underwent percutaneous coronary intervention

BACKGROUND AND AIMS

The association between lipoprotein(a) [Lp(a)] levels and the risk of cardiovascular disease is of great interest but still controversial. This study sought to investigate the impact of Lp(a) on coronary severity and long-term outcomes of patients who undergo percutaneous coronary intervention (PCI).

METHODS AND RESULTS

A total of 6714 consecutive patients who received PCI were enrolled to analyze the association between Lp(a) and coronary severity and major adverse cardiovascular and cerebrovascular events (MACCE). Patients were divided into tertiles according to Lp(a) levels on admission. Coronary severity was evaluated by SYNTAX scoring system. The MACCE included recurrent myocardial infarction, unplanned target vessel revascularization, stent thrombosis, ischemic stroke and all-cause mortality. Significantly, Lp(a) levels were positively associated with coronary severity (p < 0.001). Multivariate logistic regression analyses showed Lp(a) was an independent predictor of intermediate to high SYNTAX score. During an average of 874 days follow-up, 755 patients presented with MACCE (11.25%) were reported. The incidence rates of MACCE, all-cause mortality, cardiac death, target vessel revascularization, recurrent myocardial infarction, stent thrombosis, stroke and bleeding were not statistically different among the Lp(a) tertile groups. Furthermore, both Kaplan-Meier and Cox regression analyses found no relationship between Lp(a) and cardiovascular outcomes (p > 0.05).

CONCLUSION

Lp(a) is an independent predictor of the prevalence of more complex coronary artery lesions (SYNTAX score ≥ 23) in patients with PCI. In addition, our study has shown that Lp(a) has no relationship with long-term cardiovascular outcomes in Chinese patients with PCI.

Elevated Lipoprotein(a) Levels Lower ABCA1 Cholesterol Efflux Capacity

CONTEXT

Elevated serum lipoprotein(a) [Lp(a)] levels are associated with increased cardiovascular disease risk. ABCA1-mediated cholesterol efflux from macrophages may be an antiatherogenic process. Plasminogen (PLG) is a driver of ABCA1-mediated cholesterol efflux, and its action is inhibited by purified human Lp(a).

OBJECTIVE

To determine the effects of Lp(a) in human serum on ABCA1 cholesterol efflux.

METHODS

Cholesterol efflux capacity (CEC) was measured with two different cell-culture models using serum from 76 patients with either low (<50 mg/dL) or high (>50 mg/dL) Lp(a) levels.

RESULTS

Using cAMP-stimulated J774 macrophages or baby hamster kidney fibroblasts overexpressing human ABCA1, we show that CEC was lower in patients with high Lp(a) levels compared with patients with low levels (-30.6%, P = 0.002 vs -24.1%, P < 0.001, respectively). Total-serum CEC negatively correlated with Lp(a) levels (r = -0.433, P = 0.0007 vs r = -0.505, P = 0.0011, respectively). These negative associations persisted after adjusting for serum cholesterol, age, sex, and statin use in a multiple linear regression model (adjusted R2 = 0.413 or 0.405, respectively) and were strengthened when further adjusting for the interaction between Lp(a) and PLG levels (adjusted R2 = 0.465 and 0.409, respectively). Total-serum and isolated Lp(a) from patients with high Lp(a) inhibited PLG-mediated ABCA1 cholesterol efflux.

CONCLUSION

Total-serum CEC is reduced in patients with high Lp(a) levels. This is in part due to the inhibition of PLG-mediated ABCA1 cholesterol efflux by Lp(a). Our findings suggest an atherogenic role for Lp(a) through its ability to inhibit CEC.

Elevated lipoprotein(a) as a new risk factor of cerebral venous sinus thrombosis: association with fibrin clot properties

Elevated lipoprotein(a) [Lp(a)] has been reported to be associated with prothrombotic clot phenotype. We hypothesized that increased Lp(a) contributes to cerebral venous sinus thrombosis (CVST) and its recurrence in relation to clot features. In 80 consecutive patients (aged 39.36 ± 10.18 years, 61 women) following the first CVST after anticoagulation withdrawal, we assessed Lp(a) levels and plasma clot properties. Recurrence of CVST was recorded during follow-up (median 53, interquartile range 40-59 months). Lp(a) levels were inversely associated with clot permeability (K_s, r = - 0.58, P < 0.001) and the rate of D-dimer release from clots in the presence of tissue plasminogen activator (r = - 0.27, P = 0.017) along with increased maximum absorbance of fibrin gels (r = 0.42, P < 0.001) and maximum D-dimer levels achieved during lysis (D-D_max, r = 0.29, P = 0.01). Recurrence of CVST was observed in 12 patients (15%) after median follow-up of 26 months. Lp(a) concentrations were higher in patients with recurrence of CVST compared to the remainder (14.15 [8.85-25.25] vs. 28.3 [18.9-35.6] mg/dL; P = 0.001). The risk of recurrent CVST was fourfold higher among 17 (21.25%) patients with Lp(a) > 30 mg/dL compared to the remainder (adjusted hazard ratio, 3.9; 95% confidence interval [CI] 1.23-12.4). Recurrence of CVST was associated with 14% lower K_s (P = 0.001) and 10% higher D-D_max (P = 0.008), with no differences in other clot features. Multiple logistic regression model showed that CVST recurrence was independently associated with Lp(a) (odds ratio 1.09, 95% CI 1.02-1.16). Increased Lp(a) characterizes subjects at elevated risk of recurrent CVST after anticoagulation withdrawal, which could be partly explained by formation of denser fibrin clots.

Relationship between "LDL-C", estimated true LDL-C, apolipoprotein B-100, and PCSK9 levels following lipoprotein(a) lowering with an antisense oligonucleotide

BACKGROUND

The laboratory measurement of "low-density lipoprotein cholesterol (LDL-C)" includes the cholesterol content of lipoprotein(a) (Lp(a)-C).

OBJECTIVE

To estimate the "true" LDL-C in relation to changes in apolipoprotein B-100 (apoB-100) and assess changes in proprotein convertase subtilisin/kexin 9 (PCSK9) levels in patients with elevated Lp(a) treated with IONIS-APO(a)_Rx. METHODS: A pooled placebo group (n = 29), and cohort A (n = 24, baseline Lp(a) 50-175 mg/dL) and cohort B (n = 8, baseline Lp(a) > 175 mg/dL) treated with IONIS-APO(a)_Rx were studied. Lp(a) particle number, ultracentrifugation-measured "LDL-C", apoB-100, total PCSK9, and lipoprotein-associated PCSK9 (PCSK9-Lp(a), PCSK9-apoB, PCSK9-apoAI) were measured. Lp(a)-cholesterol (Lp(a)-C) and LDL-C corrected for Lp(a)-C (LDL-C_corr) were calculated.

RESULTS

Baseline mean (standard deviation) "LDL-C" was 120 (42), 128 (45), and 112 (39) mg/dL in placebo, cohorts A and B, respectively, whereas LDL-C_corr was 86 (48), 96 (43), and 57 (37) mg/dL (P < .001 compared with placebo), representing 28%, 25%, and 50% lower levels than "LDL-C". Following IONIS-APO(a)_Rx treatment at day 85/99, Lp(a) particle number and Lp(a)-C decreased -66.8% and -71.6%, apoB-100 -10.3% and -17.5%, "LDL-C" -11.8% and -22.7%, (P < .001 for all vs placebo), whereas LDL-C_corr increased +10.4% (P = .66) and +49.9% (P < .001) in cohorts A and B, respectively. Total PCSK9 did not change but PCSK9-Lp(a) decreased with IONIS-APO(a)_Rx vs placebo (-39.0% vs +8.4%, P < .001).

CONCLUSION

LDL-C_corr is lower than laboratory "LDL-C" in patients with elevated Lp(a). Following apolipoprotein(a) inhibition and decline in Lp(a) and Lp(a)-C, the decline in apoB-100 is consistent with the notion that LDL devoid of apo(a) is cleared faster than Lp(a). These types of analyses may provide insights into the mechanisms of drugs affecting Lp(a) levels in clinical trials.

Atherogenic postprandial remnant lipoproteins; VLDL remnants as a causal factor in atherosclerosis

Oxidized LDL (Ox-LDL) and chylomicron (CM) remnants have been suggested to be the most atherogenic lipoproteins that initiate and exacerbate coronary atherosclerosis. In this review, we propose a hypothesis of the causal lipoproteins in atherosclerosis based on our recent findings on postprandial remnant lipoproteins (RLP). Plasma RLP-C and RLP-TG increased significantly after food intake, especially a fat load. More than 80% of the TG increase after the fat load consisted of the TG in RLP, which contained significantly greater apoB100 than apoB48 particles as VLDL remnants. The majority of the LPL in non-heparin plasma was found in RLP as an RLP-LPL complex and released into the circulation after hydrolysis. Plasma LPL did not increase after food intake, which may have caused the partial hydrolysis of CM and VLDL as well as the significant increase of RLP-TG in the postprandial plasma. LPL was inversely correlated with the RLP particle size after food intake. We showed that VLDL remnants are the major atherogenic lipoproteins in the postprandial plasma associated with insufficient LPL activity and a causal factor in the initiation and progression of atherosclerosis. We also propose "LPL bound TG-rich lipoproteins" as a new definition of remnant lipoproteins based on the findings of the RLP-LPL complex in the non-heparin plasma.

Lipoprotein(a) and the risk of cardiovascular disease in the European population: results from the BiomarCaRE consortium

AIMS

As promising compounds to lower Lipoprotein(a) (Lp(a)) are emerging, the need for a precise characterization and comparability of the Lp(a)-associated cardiovascular risk is increasing. Therefore, we aimed to evaluate the distribution of Lp(a) concentrations across the European population, to characterize the association with cardiovascular outcomes and to provide high comparability of the Lp(a)-associated cardiovascular risk by use of centrally determined Lp(a) concentrations.

METHODS AND RESULTS

Based on the Biomarkers for Cardiovascular Risk Assessment in Europe (BiomarCaRE)-project, we analysed data of 56 804 participants from 7 prospective population-based cohorts across Europe with a maximum follow-up of 24 years. All Lp(a) measurements were performed in the central BiomarCaRE laboratory (Biokit Quantia Lp(a)-Test; Abbott Diagnostics). The three endpoints considered were incident major coronary events (MCE), incident cardiovascular disease (CVD) events, and total mortality. We found lower Lp(a) levels in Northern European cohorts (median 4.9 mg/dL) compared to central (median 7.9 mg/dL) and Southern European cohorts (10.9 mg/dL) (Jonckheere-Terpstra test P < 0.001). Kaplan-Meier curves showed the highest event rate of MCE and CVD events for Lp(a) levels ≥90th percentile (log-rank test: P < 0.001 for MCE and CVD). Cox regression models adjusted for age, sex, and cardiovascular risk factors revealed a significant association of Lp(a) levels with MCE and CVD with a hazard ratio (HR) of 1.30 for MCE [95% confidence interval (CI) 1.15‒1.46] and of 1.25 for CVD (95% CI 1.12‒1.39) for Lp(a) levels in the 67‒89th percentile and a HR of 1.49 for MCE (95% CI 1.29‒1.73) and of 1.44 for CVD (95% CI 1.25‒1.65) for Lp(a) levels ≥ 90th percentile vs. Lp(a) levels in the lowest third (P < 0.001 for all). There was no significant association between Lp(a) levels and total mortality. Subgroup analysis for a continuous version of cube root transformed Lp(a) identified the highest Lp(a)-associated risk in individuals with diabetes [HR for MCE 1.31 (95% CI 1.15‒1.50)] and for CVD 1.22 (95% CI 1.08‒1.38) compared to those without diabetes [HR for MCE 1.15 (95% CI 1.08‒1.21; HR for CVD 1.13 (1.07-1.19)] while no difference of the Lp(a)- associated risk were seen for other cardiovascular high risk states. The addition of Lp(a) levels to a prognostic model for MCE and CVD revealed only a marginal but significant C-index discrimination measure increase (0.001 for MCE and CVD; P < 0.05) and net reclassification improvement (0.010 for MCE and 0.011 for CVD).

CONCLUSION

In this large dataset on harmonized Lp(a) determination, we observed regional differences within the European population. Elevated Lp(a) was robustly associated with an increased risk for MCE and CVD in particular among individuals with diabetes. These results may lead to better identification of target populations who might benefit from future Lp(a)-lowering therapies.

Correlation of salivary neopterin and plasma fibrinogen levels in patients with chronic periodontitis and/or type 2 diabetes mellitus

Neopterin is a novel predictor for coronary events especially in diabetic patients and also an indicator for the effectiveness of the periodontal treatment. In this study, we assessed whether salivary neopterin can be used as a potential biomarker in evaluating the risk of cardiovascular disease in type 2 diabetic patients with chronic periodontitis. Forty subjects between 25 and 75 years of age and who matched the criteria were selected and divided into four groups. Their periodontal status was evaluated. Stimulated whole saliva and blood were collected for analysis of salivary neopterin and fibrinogen and HbA1c levels, respectively. Nonsurgical periodontal therapy was carried out. Patients were recalled after 3 months, and the same procedure was repeated. A reduction in all the parameters was seen after treatment in all the four groups. Salivary neopterin levels showed significant difference (p<0.001) in the values between the study groups and the control group before treatment. After 3 months of treatment, salivary neopterin levels showed a statistical significant reduction (p<0.001) in all the study groups. Neopterin could serve as an effective tool to assess the inflammatory process related to periodontitis and diabetes mellitus and also predict future cardiovascular events in diabetic patients.

Effects of nanoparticle chromium on chromium absorbability, growth performance, blood parameters and carcass traits of pigs

The aim of this study was to investigate the effect of dietary supplementation of nanoparticle trivalent chromium on chromium absorbability, growth performance, blood parameters and carcass characteristics of pigs. In Trial 1, five growing pigs (Landrace × Yorkshire × Duroc) (initial average weight was 31.3 ± 2.0 kg) were used in a 5 × 5 Latin square design as the Control group (without supplement of chromium), the chromium chloride group (CrCl3), the chromium picolinate group (CrPic), the nanoparticle chromium chloride group (NanoCrCl3), and the nanoparticle chromium picolinate group (NanoCrPic). The pigs were adapted for 7 days, followed by a 5-day test period and a collection period. The chromium was added at a 200 μg/kg level to the diet using different chromium sources for evaluating the chromium absorbability. The results of Trial 1 indicated that there were no differences in feed components digestibility among the groups, but the absorbability of chromium in the NanoCrPic (27.5%) group was the highest, whereas that in the CrCl3 group was the lowest (4.91%). Moreover, the chromium source, nanoparticle size and interaction effects were observed between these two factors (P < 0.001). In Trial 2, 60 Landrace × Yorkshire × Duroc growing pigs (average bodyweight was 76.7 ± 4.5 kg) were randomly allotted to five dietary treatment groups as used in Trial 1, each group with four pens (three pigs/pen). The study was conducted for 60 days. Their growth performance, carcass and meat traits were also evaluated. Trial 2 results indicated that feed intake in the chromium-added groups was greater (P < 0.007) than that in the Control group. The average daily bodyweight gain in the chromium-added groups was greater than that in the Control group (P = 0.046). The serum non-esterified fatty acids level was lower (P < 0.0001) in the NanoCr groups. Serum chromium concentration was increased by dietary chromium supplementation, and the chromium source, nanoparticle size and their interaction effects (P < 0.001) were observed. The average back fat thickness in the CrPic and NanoCrPic groups was lower (P < 0.05) than that of the Control group. Meat chromium content was elevated by dietary chromium supplementation, particularly in the CrPic and NanoCrPic groups (P < 0.05). The chromium source, nanoparticle size and interaction effects between these two factors were observed in serum non-esterified fatty acids and chromium content. The muscle chromium content also affected by chromium source and displayed interaction of source and nanoparticle size. In conclusion, chromium supplementation could increase feed intake and average daily gain, serum and longissimus muscle chromium content, as well as reduce back fat thickness of pigs. In addition, nanoparticle organic trivalent chromium could increase chromium absorbability and decrease serum non-esterified fatty acids concentrations. Organic form was better than inorganic form in chromium absorbability, serum and longissimus muscle chromium content and average back fat thickness.

A Case-Control Study of the Relationship Between SLC22A3-LPAL2-LPA Gene Cluster Polymorphism and Coronary Artery Disease in the Han Chinese Population

Background

Mutations in the solute carrier family 22 member 3 (SLC22A3), lipoprotein (a)-like 2 (LPAL2), and the lipoprotein (a) (LPA) gene cluster, which encodes apolipoprotein (a) [apo (a)] of the lipoprotein (a) [Lp (a)] lipoprotein particle, have been suggested to contribute to the risk of coronary artery disease (CAD), but the precise variants of this gene cluster have not yet been identified in Chinese populations.

Objectives

We sought to investigate the association between SLC22A3-LPAL2-LPA gene cluster polymorphisms and the risk of CAD in the Han Chinese population.

Patients and Methods

We recruited 551 CAD patients and 544 healthy controls for this case-control study. Four SNPs (rs9346816, rs2221750, rs3127596, and rs9364559) were genotyped in real time using the MassARRAY system (Sequenom; USA) in the SLC22A3-LPAL2-LPA gene cluster. All subjects were Chinese and of Han descent, and were recruited from the First Hospital of Jilin University based on convenience sampling from June 2009 to September 2012.

Results

The frequency of the minor allele G (34.8%) in rs9364559 was significantly higher in the CAD patients than in the healthy controls (29.4%) (P = 0.006). There was genotypic association between rs9364559 and CAD (P = 0.022), and these results still remained significant after adjustment for the conventional CAD risk factors through forward logistic regression analysis (P = 0.020, P = 0.019). Haplotype analyses from different blocks indicated that 11 haplotypes were associated with the risk of CAD. Seven haplotypes were associated with a reduced risk of CAD, whereas four haplotypes were associated with an increased risk of CAD.

Conclusions

Rs9364559 in the LPA gene may contribute to the risk of CAD in the Han Chinese population; haplotypes which contain rs9346816-G were all associated with an increased risk of CAD in this study.

Structure, function, and genetics of lipoprotein (a)

Lipoprotein (a) [Lp(a)] has attracted the interest of researchers and physicians due to its intriguing properties, including an intragenic multiallelic copy number variation in the LPA gene and the strong association with coronary heart disease (CHD). This review summarizes present knowledge of the structure, function, and genetics of Lp(a) with emphasis on the molecular and population genetics of the Lp(a)/LPA trait, as well as aspects of genetic epidemiology. It highlights the role of genetics in establishing Lp(a) as a risk factor for CHD, but also discusses uncertainties, controversies, and lack of knowledge on several aspects of the genetic Lp(a) trait, not least its function.

Distinct metabolism of apolipoproteins (a) and B-100 within plasma lipoprotein(a)

OBJECTIVES

Lipoprotein(a) [Lp(a)] is mainly similar in composition to LDL, but differs in having apolipoprotein (apo) (a) covalently linked to apoB-100. Our purpose was to examine the individual metabolism of apo(a) and apoB-100 within plasma Lp(a).

MATERIALS AND METHODS

The kinetics of apo(a) and apoB-100 in plasma Lp(a) were assessed in four men with dyslipidemia [Lp(a) concentration: 8.9-124.7nmol/L]. All subjects received a primed constant infusion of [5,5,5-(2)H3] L-leucine while in the constantly fed state. Lp(a) was immunoprecipitated directly from whole plasma; apo(a) and apoB-100 were separated by gel electrophoresis; and isotopic enrichment was determined by gas chromatography/mass spectrometry.

RESULTS

Multicompartmental modeling analysis indicated that the median fractional catabolic rates of apo(a) and apoB-100 within Lp(a) were significantly different at 0.104 and 0.263 pools/day, respectively (P=0.04). The median Lp(a) apo(a) production rate at 0.248nmol/kg·day(-1) was significantly lower than that of Lp(a) apoB-100 at 0.514nmol/kg·day(-1) (P=0.03).

CONCLUSION

Our data indicate that apo(a) has a plasma residence time (11days) that is more than twice as long as that of apoB-100 (4days) within Lp(a), supporting the concept that apo(a) and apoB-100 within plasma Lp(a) are not catabolized from the bloodstream as a unit in humans in the fed state.

Higher Lipoprotein (a) Levels Are Associated with Better Pulmonary Function in Community-Dwelling Older People - Data from the Berlin Aging Study II

Reduced pulmonary function and elevated serum cholesterol levels are recognized risk factors for cardiovascular disease. Currently, there is some controversy concerning relationships between cholesterol, LDL-cholesterol, HDL-cholesterol, serum triglycerides and lung function. However, most previous studies compared patients suffering from chronic obstructive pulmonary disease (COPD) with healthy controls, and only a small number examined this relationship in population-based cohorts. Moreover, lipoprotein a [Lp(a)], another lipid parameter independently associated with cardiovascular diseases, appears not to have been addressed at all in studies of lung function at the population level. Here, we determined relationships between lung function and several lipid parameters including Lp(a) in 606 older community-dwelling participants (55.1% women, 68±4 years old) from the Berlin Aging Study II (BASE-II). We found a significantly lower forced expiration volume in 1 second (FEV1) in men with low Lp(a) concentrations (t-test). This finding was further substantiated by linear regression models adjusting for known covariates, showing that these associations are statistically significant in both men and women. According to the highest adjusted model, men and women with Lp(a) levels below the 20^th percentile had 217.3ml and 124.2ml less FEV1 and 239.0ml and 135.2ml less FVC, respectively, compared to participants with higher Lp(a) levels. The adjusted models also suggest that the known strong correlation between pro-inflammatory parameters and lung function has only a marginal impact on the Lp(a)-pulmonary function association. Our results do not support the hypothesis that higher Lp(a) levels are responsible for the increased CVD risk in people with reduced lung function, at least not in the group of community-dwelling older people studied here.

Production of human apolipoprotein(a) transgenic NIBS miniature pigs by somatic cell nuclear transfer

Most cases of ischemic heart disease and stroke occur as a result of atherosclerosis. The purpose of this study was to produce a new Nippon Institute for Biological Science (NIBS) miniature pig model by somatic cell nuclear transfer (SCNT) for studying atherosclerosis. The human apolipoprotein(a) (apo(a)) genes were transfected into kidney epithelial cells derived from a male and a female piglet. Male cells were used as donors initially, and 275 embryos were transferred to surrogates. Three offspring were delivered, and the production efficiency was 1.1% (3/275). Serial female cells were injected into 937 enucleated oocytes. Eight offspring were delivered (production efficiency: 0.9%) from surrogates. One male and 2 female transgenic miniature pigs matured well. Lipoprotein(a) was found in the male and one of the female transgenic animals. These results demonstrate successful production of human apo(a) transgenic NIBS miniature pigs by SCNT. Our goal is to establish a human apo(a) transgenic NIBS miniature pig colony for studying atherosclerosis.

PCSK9 inhibition to reduce cardiovascular disease risk: recent findings from the biology of PCSK9

PURPOSE OF REVIEW

Review novel insights into the biology of proprotein convertase subtilisin/kexin 9 (PCSK9) that may explain the extreme efficiency of PCSK9 inhibition and the unexpected metabolic effects resulting from PCSK9 monoclonal antibody therapy, and may identify additional patients as target of therapy.

RECENT FINDINGS

For over 20 years, the practical knowledge of cholesterol metabolism has centered around cellular mechanisms, and around the idea that statin therapy is the essential step to control metabolic abnormalities for cardiovascular risk management. This view has been embraced by the recent AHA/ACC guidelines, but is being challenged by recent studies including nonstatin medications and by the development of a new class of cholesterol-lowering agents that seems destined to early US Food and Drug Administration approval. The discovery of PCSK9 - a circulating protein that regulates hepatic low-density lipoprotein (LDL) receptor and serum LDL cholesterol levels - has led to a race for its therapeutic inhibition. Recent findings on PCSK9 regulation and pleiotropic effects will help identify additional patient groups likely to benefit from the inhibitory therapy and unravel the full potential of PCSK9 inhibition therapy.

SUMMARY

Injectable human monoclonal antibodies to block the interaction between PCSK9 and LDL receptor are demonstrating extraordinary efficacy (LDL reductions of up to 70%) and almost the absence of any side-effects. A more moderate effect is seen on other lipoprotein parameters, with the exception of lipoprotein(a) levels. We describe mechanisms that can explain the effect on lipoprotein(a), predict a potential effect on postprandial triglyderides, and suggest a new category of patients for anti-PCSK9 therapy.

Lipoprotein(a) metabolism

PURPOSE OF REVIEW

Lipoprotein(a) [Lp(a)] is an atherogenic lipoprotein. The metabolism of this lipoprotein is still not well understood.

RECENT FINDINGS

It has long been known that the plasma concentration of Lp(a) is highly heritable, with its genetic determinants located in the apo(a) locus and regulating the rate of hepatic apo(a) production. Recent human intervention trials have convincingly established that, in addition to apo(a) production, hepatic apoB100 production plays an important role in Lp(a) levels. Although the major site and mode of Lp(a) clearance remain unidentified, a recent cell and animal study points to the involvement of the hepatic scavenger receptor class B type I in the uptake of both the lipid and protein constituents of Lp(a) from plasma.

SUMMARY

Progress in the understanding of Lp(a) metabolism has the potential to lead to the development of novel and specific treatments for the reduction of Lp(a) levels and the associated risk of cardiovascular disease.

Effect of Nicotinic acid/Laropiprant in the lipoprotein(a) concentration with regard to baseline lipoprotein(a) concentration and LPA genotype

BACKGROUND

Lipoprotein(a) [Lp(a)] is a lipoprotein in which apolipoproteinB-100 is linked to apolipoprotein(a) [apo(a)]. Significant variation in Lp(a) concentration is specific to LPA gene, which codes for apo(a). Nicotinic acid (NA) is used for treatment of dyslipidemias, and the lowering effect of NA on Lp(a) has been previously reported.

OBJECTIVE

To evaluate the Lp(a) lowering effect of 1g/20mg and 2g/40mgday of Nicotinic acid/Laropiprant in subjects with different baseline Lp(a) concentrations and depending on the LPA genotype.

METHODS

In an open-label, 10-week study, 1g/20mgday of NA/Laropiprant for 4weeks followed by 6weeks of 2g/40mgday conducted at 3 centers in Spain, 82 subjects were enrolled. Patients were studied at baseline and at the end of both treatment periods and were enrolled in three groups: normal Lp(a) (<50mg/dL), high Lp(a) (50-120mg/dL) and very high Lp(a) (>120mg/dL). The LPA genetic polymorphism was analyzed by a real-time PCR.

RESULTS

There was a significant difference in LPA genotypes among Lp(a) concentration groups and an inverse and significant correlation between baseline Lp(a) concentration and LPA genotype was found (R=-0.372, p<0.001). There were a significant decrease in total cholesterol, triglycerides, LDL cholesterol, apo B and Lp(a), and a significant increase in HDL cholesterol after NA/Laropiprant treatment, without changes in BMI. However, there were no statistical differences in percentage variation of analyzed variables depending on LPA genotype.

CONCLUSION

LPA genotype is a major determinant of Lp(a) baseline concentration. However, the lipid lowering effect of NA is not related to LPA genotype.

[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.

Lack of association between lipoprotein(a) genetic variants and subsequent cardiovascular events in Chinese Han patients with coronary artery disease after percutaneous coronary intervention

BACKGROUND

Elevated lipoprotein(a) [Lp(a)] levels predict cardiovascular events incidence in patients with coronary artery disease (CAD). Genetic variants in the rs3798220, rs10455872 and rs6415084 single-nucleotide polymorphisms (SNPs) in the Lp(a) gene (LPA) correlate with elevated Lp(a) levels, but whether these SNPs have prognostic value for CAD patients is unknown. The present study evaluated the association of LPA SNPs with incidence of subsequent cardiovascular events in CAD patients after percutaneous coronary intervention (PCI).

METHODS

TaqMan SNP genotyping assays were performed to detect the rs6415084, rs3798220 and rs10455872 genotypes in 517 Chinese Han patients with CAD after PCI. We later assessed whether there was an association of these SNPs with incidence of major adverse cardiovascular events (MACE: cardiac death, nonfatal myocardial infarction, ischemic stroke and coronary revascularization). Serum lipid profiles were also determined using biochemical methods.

RESULTS

Only the rs6415084 variant allele was associated with higher Lp(a) levels [41.3 (20.8, 74.6) vs. 18.6 (10.3, 40.9) mg/dl, p < 0.001]. During a 2-year follow-up period, 102 patients suffered MACE, and Cox regression analysis demonstrated that elevated Lp(a) (≥30 mg/dl) levels correlated with increased MACE (adjusted HR, 1.69; 95% CI 1.13-2.53), but there was no association between LPA genetic variants (rs6415084 and rs3798220) and MACE incidence (p > 0.05).

CONCLUSIONS

Our data did not support a relationship between genetic LPA variants (rs6415084 and rs3798220) and subsequent cardiovascular events after PCI in Chinese Han CAD patients.

Silent Brain Infarction – A Review of Recent Observations

Silent brain infarction is a cerebral ischaemic event evident on brain imaging without any clinical symptom. Silent brain infarction is often detected in apparently healthy, elderly people and in different selected patient groups as well. Lately, several studies were carried out in order to identify the clinical conditions leading to silent brain infarction. A large number of clinical and paraclinical parameters were found to increase silent brain infarction prevalence, and the continuously growing list of risk factors revealed that the majority of them are similar to those related to stroke. Accordingly, some consider silent brain infarction the preclinical stage of clinically overt stroke. This point of view emphasizes the early recognition and management of silent brain infarction-related risk factors, and a great need for comparative studies, which could elicit the most sensitive indicators of the increased silent brain infarction risk, especially the ones that could be cost-effectively screened in the large populations as well.

Anti-inflammatory and metabolic actions of FXR: insights into molecular mechanisms

The farnesoid X receptor (FXR) is a ligand-activated transcription factor belonging to the nuclear receptor (NR) superfamily. FXR plays an important role in positively regulating genes (transactivation) involved in bile acid homeostasis, fat and glucose metabolism. Recently, it has become clear that an additional important role for FXR consists of downregulating genes involved in inflammation. Because of this broad spectrum of regulated genes, therapeutically targeting FXR with full agonists will likely result in adverse side effects, in line with what is described for other NRs. It may therefore be necessary to develop selective FXR modulators. However, the molecular mechanisms that distinguish between FXR-mediated transactivation and transrepression are currently unknown. For other NRs, post-translational modifications such as SUMOylation and phosphorylation have been reported to be unique to either transactivation or transrepression. Here, we review current knowledge on post-translational regulation of FXR with respect to transactivation and transrepression. Ultimately, increased understanding of the different mechanisms of transactivation and transrepression of nuclear receptors will aid in the development of NR drugs with fewer side effects.

FGF19 signaling cascade suppresses APOA gene expression

OBJECTIVE

Lipoprotein(a) is a highly atherogenic lipoprotein, whose metabolism is poorly understood. Currently no safe drugs exists that lower elevated plasma lipoprotein(a) concentrations. We therefore focused on molecular mechanisms that influence apolipoprotein(a) (APOA) biosynthesis.

METHODS AND RESULTS

Transgenic human APOA mice (tg-APO mice) were injected with 1 mg/kg of recombinant human fibroblast growth factor 19 (FGF19). This led to a significant reduction of plasma APOA and hepatic expression of APOA. Incubation of primary hepatocytes of tg-APOA mice with FGF19 induced ERK1/2 phosphorylation and, in turn, downregulated APOA expression. Repression of APOA by FGF19 was abrogated by specific ERK1/2 phosphorylation inhibitors. The FGF19 effect on APOA was attenuated by transfection of primary hepatocytes with siRNA against the FGF19 receptor 4 (FGFR4). Using promoter reporter assays, mutation analysis, gel shift, and chromatin immune-precipitation assays, an Ets-1 binding element was identified at -1630/-1615bp region in the human APOA promoter. This element functions as an Elk-1 binding site that mediates repression of APOA transcription by FGF19.

CONCLUSIONS

These findings provide mechanistic insights into the transcriptional regulation of human APOA by FGF19. Further studies in the human system are required to substantiate our findings and to design therapeutics for hyper lipoprotein(a).

Farnesoid X receptor represses hepatic human APOA gene expression

High plasma concentrations of lipoprotein(a) [Lp(a), which is encoded by the APOA gene] increase an individual's risk of developing diseases, such as coronary artery diseases, restenosis, and stroke. Unfortunately, increased Lp(a) levels are minimally influenced by dietary changes or drug treatment. Further, the development of Lp(a)-specific medications has been hampered by limited knowledge of Lp(a) metabolism. In this study, we identified patients suffering from biliary obstructions with very low plasma Lp(a) concentrations that rise substantially after surgical intervention. Consistent with this, common bile duct ligation in mice transgenic for human APOA (tg-APOA mice) lowered plasma concentrations and hepatic expression of APOA. To test whether farnesoid X receptor (FXR), which is activated by bile acids, was responsible for the low plasma Lp(a) levels in cholestatic patients and mice, we treated tg-APOA and tg-APOA/Fxr-/- mice with cholic acid. FXR activation markedly reduced plasma concentrations and hepatic expression of human APOA in tg-APOA mice but not in tg-APOA/Fxr-/- mice. Incubation of primary hepatocytes from tg-APOA mice with bile acids dose dependently downregulated APOA expression. Further analysis determined that the direct repeat 1 element between nucleotides -826 and -814 of the APOA promoter functioned as a negative FXR response element. This motif is also bound by hepatocyte nuclear factor 4α (HNF4α), which promotes APOA transcription, and FXR was shown to compete with HNF4α for binding to this motif. These findings may have important implications in the development of Lp(a)-lowering medications.

Lipoprotein(a): genotype-phenotype relationship and impact on atherogenic risk

In 2010, more than 45 years after the initial discovery of lipoprotein(a) [Lp(a)] by Kare Berg, an European Atherosclerosis Society Consensus Panel recommended screening for elevated Lp(a) in people at moderate to high risk of atherosclerotic cardiovascular disease (CVD). This recommendation was based on extensive epidemiological findings demonstrating a significant association between elevated plasma Lp(a) levels and coronary heart disease, myocardial infarction, and stroke. In addition to those patients considered to be at moderate to high risk of heart disease, statin-treated patients with recurrent heart disease were also identified as targeted for screening of elevated Lp(a) levels. Taken together, recent findings have significantly strengthened the notion of Lp(a) as a causal risk factor for CVD. It is well established that Lp(a) levels are largely determined by the size of the apolipoprotein a [apo(a)] gene; however, recent studies have identified several other LPA gene polymorphisms that have significant associations with an elevated Lp(a) level and a reduced copy number of K4 repeats. In addition, the contribution of other genes in regulating Lp(a) levels has been described. Besides the strong genetic regulation, new evidence has emerged regarding the impact of inflammation as a modulator of Lp(a) risk factor properties. Thus, oxidized phospholipids that possess a strong proinflammatory potential are preferentially carried on Lp(a) particles. Collectively, these findings point to the importance of both phenotypic and genotypic factors in influencing apo(a) proatherogenic properties. Therefore, studies taking both of these factors into account determining the amount of Lp(a) associated with each individual apo(a) size allele are valuable tools when assessing a risk factor role of Lp(a).

Apolipoproteins in the brain: implications for neurological and psychiatric disorders

The brain is the most lipid-rich organ in the body and, owing to the impermeable nature of the blood-brain barrier, lipid and lipoprotein metabolism within this organ is distinct from the rest of the body. Apolipoproteins play a well-established role in the transport and metabolism of lipids within the CNS; however, evidence is emerging that they also fulfill a number of functions that extend beyond lipid transport and are critical for healthy brain function. The importance of apolipoproteins in brain physiology is highlighted by genetic studies, where apolipoprotein gene polymorphisms have been identified as risk factors for several neurological diseases. Furthermore, the expression of brain apolipoproteins is significantly altered in several brain disorders. The purpose of this article is to provide an up-to-date assessment of the major apolipoproteins found in the brain (ApoE, ApoJ, ApoD and ApoA-I), covering their proposed roles and the factors influencing their level of expression. Particular emphasis is placed on associations with neurological and psychiatric disorders.