Lipoprotein(a): intrigues and insights

Executive summary of the Hellenic Atherosclerosis Society guidelines for the diagnosis and treatment of dyslipidemias - 2023

Atherosclerotic cardiovascular disease (ASCVD) remains the main cause of death worldwide, and thus its prevention, early diagnosis and treatment is of paramount importance. Dyslipidemia represents a major ASCVD risk factor that should be adequately managed at different clinical settings. 2023 guidelines of the Hellenic Atherosclerosis Society focus on the assessment of ASCVD risk, laboratory evaluation of dyslipidemias, new and emerging lipid-lowering drugs, as well as diagnosis and treatment of lipid disorders in women, the elderly and in patients with familial hypercholesterolemia, acute coronary syndromes, heart failure, stroke, chronic kidney disease, diabetes, autoimmune diseases, and non-alcoholic fatty liver disease. Statin intolerance is also discussed.

Targeted proteomics using stable isotope labeled protein fragments enables precise and robust determination of total apolipoprotein(a) in human plasma

Lipoprotein(a), also known as Lp(a), is an LDL-like particle composed of apolipoprotein(a) (apo(a)) bound covalently to apolipoprotein B100. Plasma concentrations of Lp(a) are highly heritable and vary widely between individuals. Elevated plasma concentration of Lp(a) is considered as an independent, causal risk factor of cardiovascular disease (CVD). Targeted mass spectrometry (LC-SRM/MS) combined with stable isotope-labeled recombinant proteins provides robust and precise quantification of proteins in the blood, making LC-SRM/MS assays appealing for monitoring plasma proteins for clinical implications. This study presents a novel quantitative approach, based on proteotypic peptides, to determine the absolute concentration of apo(a) from two microliters of plasma and qualified according to guideline requirements for targeted proteomics assays. After optimization, assay parameters such as linearity, lower limits of quantification (LLOQ), intra-assay variability (CV: 4.7%) and inter-assay repeatability (CV: 7.8%) were determined and the LC-SRM/MS results were benchmarked against a commercially available immunoassay. In summary, the measurements of an apo(a) single copy specific peptide and a kringle 4 specific peptide allow for the determination of molar concentration and relative size of apo(a) in individuals.

Familial Hypercholesterolemia and Lipoprotein(a): A Gordian Knot in Cardiovascular Prevention

Familial hypercholesterolemia (FH) is the most frequent genetic disorder resulting in increased low-density lipoprotein cholesterol (LDL-C) levels from childhood, leading to premature atherosclerotic cardiovascular disease (ASCVD) if left untreated. FH diagnosis is based on clinical criteria and/or genetic testing and its prevalence is estimated as being up to 1:300,000−400,000 for the homozygous and ~1:200−300 for the heterozygous form. Apart from its late diagnosis, FH is also undertreated, despite the available lipid-lowering therapies. In addition, elevated lipoprotein(a) (Lp(a)) (>50 mg/dL; 120 nmol/L), mostly genetically determined, has been identified as an important cardiovascular risk factor with prevalence rate of ~20% in the general population. Novel Lp(a)-lowering therapies have been recently developed and their cardiovascular efficacy is currently investigated. Although a considerable proportion of FH patients is also diagnosed with high Lp(a) levels, there is a debate whether these two entities are associated. Nevertheless, Lp(a), particularly among patients with FH, has been established as a significant cardiovascular risk factor. In this narrative review, we present up-to-date evidence on the pathophysiology, diagnosis, and treatment of both FH and elevated Lp(a) with a special focus on their association and joint effect on ASCVD risk.

Association of lipoprotein(a) with aortic dissection

Background

Lipoprotein(a) [Lp(a)] is associated with coronary atherosclerotic heart disease, aortic stenosis, stroke, and heart failure. We aimed to determine the relationship between Lp(a) and aortic dissection (AD).

Methods

Two hundred patients with AD were included in our case group. The control group consisted of 200 non‐AD people who were age‐ (±5 years) and gender‐matched to the case group. Data were collected retrospectively, including hypertension, smoking, coronary artery disease, diabetes mellitus, Lp(a), total cholesterol, triglyceride, low‐density lipoprotein cholesterol, and high‐density lipoprotein cholesterol. The association between Lp(a) and AD was studied using univariate and multivariate logistic regression analysis.

Results

Patients with AD had greater median Lp(a) concentrations than non‐AD people (152.50 vs. 81.75 mg/L). Lp(a) was associated with AD in a multivariate logistic regression analysis (odds ratio, 8.03; 95% confidence interval, 2.85–22.62), comparing those with Lp(a) quartile 4 with those with Lp(a) quartile 1. Stratified analysis showed that this relationship was observed in both men and women, as well as in older and younger individuals.

Conclusions

High levels of Lp(a) are strongly associated with AD, independent of other cardiovascular risk factors.

Association of lipoprotein (a) with coronary artery disease in a South Asian population: A case-control study

Introduction

Coronary artery disease (CAD), the leading cause of mortality worldwide, is characterised by an earlier onset and more severe disease in South Asians as compared to Western populations.

Methods

This is an observational study on 928 individuals who attended three tertiary care centres in Kerala, India from 2014-to 2017. The demographic, anthropometric, behavioural factors and the lipoprotein (Lp(a)) and cholesterol values were compared between the two groups and across disease severity. The Chi-square test was used to compare the categorical variables and independent sample t-test for the continuous variables. Multivariable logistic regression was performed to investigate the association of demographic, clinical and behavioural factors with the disease. Odds ratios are presented with a 95% confidence interval. In individuals below 50 years, two logistic regression models were compared to investigate the improvement in modelling the association of the independent factors and Lp(a) with the occurrence of the disease.

Results

We included 682 patients in the diseased group and 246 patients treated for non-coronary conditions in the control group. Those in the control group were significantly younger than in the diseased group(p<0.002). Significantly more patients were diabetic, hypertensive, tobacco users and consumers of alcohol in the diseased group. Multivariable logistic regression on data from all age groups showed that age (OR = 2.55, 95% CI 1.51–4.33, p = 0.01), diabetes (OR = 3.71, 95% CI 2.42–5.70, p = 0.01), hypertension (OR = 3.03, 95% CI 2.12–4.34, p = 0.01) and tobacco use (OR = 5.44, 95% CI 3.39–8.75, p = 0.01) are significantly associated with the disease. Lp(a) (OR = 1.22, 95% CI 0.87–1.72) increased the odds of the disease by 22% but was not statistically significant. In individuals below 50 years, Lp(a) significantly increased the likelihood of CAD (OR = 3.52, 95% CI 1.63–7.57, p = 0.01). Those with diabetes were seven times more likely to be diseased (OR = 7.06, 95% CI 2.59–19.21, p = 0.01) and the tobacco users had six times the likelihood of disease occurrence (OR = 6.38, 95% CI 2.62–15.54, p = 0.01). The median Lp(a) values showed a statistically significant increasing trend with the extent/severity of the disease in those below 50 years.

Conclusion

Age, diabetes, hypertension and tobacco use appear to be associated more with the occurrence of coronary artery disease in adults of all ages. Lipoprotein(a), cholesterol and BMI categories do not seem to be related to disease status in all ages. However, in individuals below 50 years, diabetes, tobacco use and lipoprotein (a) are significantly associated with the occurrence of the disease.

Lipoprotein(a), a Lethal Player in Calcific Aortic Valve Disease

Calcified aortic valve disease (CAVD) is the most common valvular cardiovascular disease with increasing incidence and mortality. The primary treatment for CAVD is surgical or transcatheter aortic valve replacement and there remains a lack of effective drug treatment. Recently, lipoprotein (a) (Lp(a)) has been considered to play a crucial role in CAVD pathophysiology. Multiple studies have shown that Lp(a) represents an independent risk factor for CAVD. Moreover, Lp(a) mediates the occurrence and development of CAVD by affecting aortic valve endothelial dysfunction, indirectly promoting foam cell formation through oxidized phospholipids (OxPL), inflammation, oxidative stress, and directly promotes valve calcification. However, there is a lack of clinical trials with Lp(a) reduction as a primary endpoint. This review aims to explore the relationship and mechanism between Lp(a) and CAVD, and focuses on the current drugs that can be used as potential therapeutic targets for CAVD.

Diet and Lp(a): Does Dietary Change Modify Residual Cardiovascular Risk Conferred by Lp(a)?

Lipoprotein(a) [Lp(a)] is an independent, causal, genetically determined risk factor for cardiovascular disease (CVD). We provide an overview of current knowledge on Lp(a) and CVD risk, and the effect of pharmacological agents on Lp(a). Since evidence is accumulating that diet modulates Lp(a), the focus of this paper is on the effect of dietary intervention on Lp(a). We identified seven trials with 15 comparisons of the effect of saturated fat (SFA) replacement on Lp(a). While replacement of SFA with carbohydrate, monounsaturated fat (MUFA), or polyunsaturated fat (PUFA) consistently lowered low-density lipoprotein cholesterol (LDL-C), heterogeneity in the Lp(a) response was observed. In two trials, Lp(a) increased with carbohydrate replacement; one trial showed no effect and another showed Lp(a) lowering. MUFA replacement increased Lp(a) in three trials; three trials showed no effect and one showed lowering. PUFA or PUFA + MUFA inconsistently affected Lp(a) in four trials. Seven trials of diets with differing macronutrient compositions showed similar divergence in the effect on LDL-C and Lp(a). The identified clinical trials show diet modestly affects Lp(a) and often in the opposing direction to LDL-C. Further research is needed to understand how diet affects Lp(a) and its properties, and the lack of concordance between diet-induced LDL-C and Lp(a) changes.

Lipoprotein(a) the Insurgent: A New Insight into the Structure, Function, Metabolism, Pathogenicity, and Medications Affecting Lipoprotein(a) Molecule

Lipoprotein(a) [Lp(a)], aka "Lp little a", was discovered in the 1960s in the lab of the Norwegian physician Kåre Berg. Since then, we have greatly improved our knowledge of lipids and cardiovascular disease (CVD). Lp(a) is an enigmatic class of lipoprotein that is exclusively formed in the liver and comprises two main components, a single copy of apolipoprotein (apo) B-100 (apo-B100) tethered to a single copy of a protein denoted as apolipoprotein(a) apo(a). Plasma levels of Lp(a) increase soon after birth to a steady concentration within a few months of life. In adults, Lp(a) levels range widely from <2 to 2500 mg/L. Evidence that elevated Lp(a) levels >300 mg/L contribute to CVD is significant. The improvement of isoform-independent assays, together with the insight from epidemiologic studies, meta-analyses, genome-wide association studies, and Mendelian randomization studies, has established Lp(a) as the single most common independent genetically inherited causal risk factor for CVD. This breakthrough elevated Lp(a) from a biomarker of atherosclerotic risk to a target of therapy. With the emergence of promising second-generation antisense therapy, we hope that we can answer the question of whether Lp(a) is ready for prime-time clinic use. In this review, we present an update on the metabolism, pathophysiology, and current/future medical interventions for high levels of Lp(a).

Lipoprotein (a) and the Risk of Chronic Kidney Disease in Hospitalized Japanese Patients

Objective Lipoprotein (a), or Lp (a), has been shown to be associated with the development of chronic kidney disease (CKD) in populations of various ethnicities. This study aimed to investigate the association between serum Lp (a) and CKD in Japanese patients. Methods A total of 6,130 subjects who underwent a serum Lp (a) level assessment for any reason (e.g. any type of surgery requiring prolonged bed rest or risk factors for atherosclerosis, such as hypertension or diabetes) were retrospectively investigated at Kanazawa University Hospital from April 2004 to March 2014. Of these, 1,895 subjects were excluded because of the lack of clinical data. Subjects were assessed for Lp (a), low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides, hypertension, diabetes, smoking, body mass index (BMI), coronary artery disease (CAD), and CKD (stage ≥3). Results When the study subjects were divided into quartiles of Lp (a) levels, significant trends were observed with regard to the presence of CKD (p = 2.7×10^-13). A multiple regression analysis showed that Lp (a) was significantly associated with CKD [odds ratio (OR), 1.12; 95% confidence interval (CI), 1.08-1.17; p = 1.3×10^-7, per 10 mg/dL], independent of other classical risk factors, including age, gender, BMI, hypertension, diabetes, smoking, LDL cholesterol, and triglycerides. Under these conditions, Lp (a) was significantly associated with CAD (OR = 1.11, 95% CI = 1.06-1.16; p = 1.7×10^-6, per 10 mg/dL), independent of other risk factors. Conclusion Serum Lp (a) was associated with CKD, independent of other classical risk factors in a Japanese population.

Relationship between LPA SNPs and inflammatory burden in patients with preeclampsia to address future cardiovascular risk

OBJECTIVE

The study tested whether cardiovascular corresponding LPA risk genotypes improve pre-eclampsia and coronary heart disease (CHD) risk prediction beyond conventional risk factors.

BACKGROUND

Studies have shown that women specific risk factors for cardiovascular disease (CVD) have taken an attention recently. It might be possible to identify women who have the highest risk in developing CVD in their further lives. It is well-known that Lp(a) levels have an impact on increased risk of CVD which is affected by LPA gene. Further, LPA risk genotypes are not considered in cardiovascular risk prediction.

METHODS

We have included 200 pregnant Turkish women into the study. We stratified the preeclamptic (PE) group: early (EOP) (28.7 ± 3.0 weeks) and late onset (LOP) (36.0 ± 1.4 weeks). 14 LPA SNPs were evaluated in the study. Rs9355296 and rs3798220 were found as independent risk factors for preeclampsia by logistic regression analysis. A positive correlation was found between rs9355296 and the diagnostic criteria of preeclampsia. Further rs9355296 G/* carriers have higher vascular inflammation rather than AA carriers.

CONCLUSIONS

The findings reveal that LPA genetic variability with high inflammatory response might be an indication of future cardiovascular events.

A Meta-Analysis of the Effect of PCSK9-Monoclonal Antibodies on Circulating Lipoprotein (a) Levels

BACKGROUND

Lipoprotein (a) [Lp(a)] is an atherogenic lipoprotein. While no effective therapy for Lp(a) is currently available, recently, several pooled analyses with small sample sizes have suggested that proprotein convertase subtilisin/kexin type 9 monoclonal antibodies (PCSK9-mAbs) could reduce circulating Lp(a) levels. This meta-analysis was performed to comprehensively investigate the efficacy of PCSK9-mAbs with respect to serum Lp(a) concentrations.

METHODS

PubMed, MEDLINE, Embase, ClinicalTrials.gov, Cochrane CENTRAL, Web of Science and recent conferences up to July 2018 were searched. Randomized clinical trials evaluating the effect of PCSK9-mAbs and control treatment on plasma Lp(a) concentrations were included. Mean differences and odds ratios with 95% confidence intervals (CIs) were used.

RESULTS

Twenty-seven randomized clinical trials with a total of 11,864 participants were included. PCSK9-mAbs showed a significant efficacy in reducing Lp(a) (- 21.9%, 95% CI - 24.3 to - 19.5), irrespective of PCSK9-mAb types, treatment duration, participant characteristics, treatment methods, differences of control treatment, baseline Lp(a) levels, and test methods. The greatest reduction was achieved with 150 mg alirocumab biweekly (- 24.6%, 95% CI - 28.0 to - 21.2) and  140 mg evolocumab monthly (- 26.8%, 95% CI - 31.6 to - 21.9). Meta-regression analyses found that the more intense low-density lipoprotein cholesterol levels declined during PCSK9-mAb treatment, the greater the reduction in Lp(a) levels. Safety was in accordance with previous reports.

CONCLUSIONS

The results of this analysis suggested that PCSK9-mAbs could significantly reduce circulating Lp(a) levels. Long-term studies may be needed to confirm the effect of PCSK9-mAbs on Lp(a) in the future.

Is Lp(a) ready for prime time use in the clinic? A pros-and-cons debate

Lipoprotein (a) (Lp(a)) is a cholesterol-rich lipoprotein known since 1963. In spite of extensive research on Lp(a), there are still numerous gaps in our knowledge relating to its function, biosynthesis and catabolism. One reason for this might be that apo(a), the characteristic glycoprotein of Lp(a), is expressed only in primates. Results from experiments using transgenic animals therefore may need verification in humans. Studies on Lp(a) are also handicapped by the great number of isoforms of apo(a) and the heterogeneity of apo(a)-containing fractions in plasma. Quantification of Lp(a) in the clinical laboratory for a long time has not been standardized. Starting from its discovery, reports accumulated that Lp(a) contributed to the risk of cardiovascular disease (CVD), myocardial infarction (MI) and stroke. Early reports were based on case control studies but in the last decades a great deal of prospective studies have been published that highlight the increased risk for CVD and MI in patients with elevated Lp(a). Final answers to the question of whether Lp(a) is ready for wider clinical use will come from intervention studies with novel selective Lp(a) lowering medications that are currently underway. This article expounds arguments for and against this proposition from currently available data.

Oxidized phospholipids and lipoprotein-associated phospholipase A2 as important determinants of Lp(a) functionality and pathophysiological role

Lipoprotein(a) [Lp(a)] is composed of a low density lipoprotein (LDL)-like particle to which apolipoprotein (a) [apo(a)] is linked by a single disulfide bridge. Lp(a) is considered a causal risk factor for ischemic cardiovascular disease (CVD) and calcific aortic valve stenosis (CAVS). The evidence for a causal role of Lp(a) in CVD and CAVS is based on data from large epidemiological databases, mendelian randomization studies, and genome-wide association studies. Despite the well-established role of Lp(a) as a causal risk factor for CVD and CAVS, the underlying mechanisms are not well understood. A key role in the Lp(a) functionality may be played by its oxidized phospholipids (OxPL) content. Importantly, most of circulating OxPL are associated with Lp(a); however, the underlying mechanisms leading to this preferential sequestration of OxPL on Lp(a) over the other lipoproteins, are mostly unknown. Several studies support the hypothesis that the risk of Lp(a) is primarily driven by its OxPL content. An important role in Lp(a) functionality may be played by the lipoprotein-associated phospholipase A₂ (Lp-PLA₂), an enzyme that catalyzes the degradation of OxPL and is bound to plasma lipoproteins including Lp(a). The present review article discusses new data on the pathophysiological role of Lp(a) and particularly focuses on the functional role of OxPL and Lp-PLA₂ associated with Lp(a).

Lipoprotein(a) Induces Human Aortic Valve Interstitial Cell Calcification

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Lp(a) significantly increased alkaline phosphatase activity, phosphate and calcium content, and matrix vesicle formation and induced apoptosis and calcification of normal human aortic valve interstitial cells.

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The type of minerals induced by Lp(a) resembles that seen in calcified human aortic valves as shown by Raman spectroscopy.

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Lp(a)-induced calcification of human aortic valve interstitial cells is mediated by activation of MAPK38, GSK3β, and Wnt signaling.

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Inhibition of GSK3β and MAPK38 significantly reduced lipoprotein(a)-induced aortic valve interstitial cell calcification.

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Lp(a)is abundant in calcified aortic valves, and lipoprotein(a) immunoreactivity colocalized with that of oxidized phospholipids.

Lipoprotein(a), or Lp(a), significantly increased alkaline phosphatase activity, release of phosphate, calcium deposition, hydroxyapatite, cell apoptosis, matrix vesicle formation, and phosphorylation of signal transduction proteins; increased expression of chondro-osteogenic mediators; and decreased SOX9 and matrix Gla protein (p < 0.001). Inhibition of MAPK38 and GSK3β significantly reduced Lp(a)-induced calcification of human aortic valve interstitial cells (p < 0.001). There was abundant presence of Lp(a) and E06 immunoreactivity in diseased human aortic valves. The present study demonstrates a causal effect for Lp(a) in aortic valve calcification and suggests that interfering with the Lp(a)pathway could provide a novel therapeutic approach in the management of this debilitating disease.

Effect of Two Lipoprotein (a)-Associated Genetic Variants on Plasminogen Levels and Fibrinolysis

Two genetic variants (rs3798220 and rs10455872) in the apolipoprotein (a) gene (LPA) have been implicated in cardiovascular disease (CVD), presumably through their association with lipoprotein (a) [Lp(a)] levels. While Lp(a) is recognized as a lipoprotein with atherogenic and thrombogenic characteristics, it is unclear whether or not the two Lp(a)-associated genetic variants are also associated with markers of thrombosis (i.e., plasminogen levels and fibrinolysis). In the present study, we genotyped the two genetic variants in 2919 subjects of the Old Order Amish (OOA) and recruited 146 subjects according to the carrier and noncarrier status for rs3798220 and rs10455872, and also matched for gender and age. We measured plasma Lp(a) and plasminogen levels in these subjects, and found that the concentrations of plasma Lp(a) were 2.62- and 1.73-fold higher in minor allele carriers of rs3798220 and rs10455872, respectively, compared with noncarriers (P = 2.04 × 10⁻¹⁷ and P = 1.64 × 10⁻⁶, respectively). By contrast, there was no difference in plasminogen concentrations between carriers and noncarriers of rs3798220 and rs10455872. Furthermore, we observed no association between carrier status of rs3798220 or rs10455872 with clot lysis time. Finally, plasminogen mRNA expression in liver samples derived from 76 Caucasian subjects was not significantly different between carriers and noncarriers of these two genetic variants. Our results provide further insight into the mechanism of action behind two genetic variants previously implicated in CVD risk and show that these polymorphisms are not major modulating factors for plasma plasminogen levels and fibrinolysis.

Genetic markers: Potential candidates for cardiovascular disease

The effective prevention of cardiovascular disease depends upon the ability to recognize the high-risk individuals at an early stage of the disease or long before the development of adverse events. Evolving technologies in the fields of proteomics, metabolomics, and genomics have played a significant role in the discovery of cardiovascular biomarkers, but so far these methods have achieved the modest success. Hence, there is a crucial need for more reliable, suitable, and lasting diagnostic and therapeutic markers to screen the disease well in time to start the clinical aid to the patients. Gene polymorphisms associated with the cardiovascular disease play a decisive role in the disease onset. Therefore, the genetic marker evaluation to classify high-risk patients from low-risk patients trends an effective approach to patient management and care. Currently, there are no genetic markers available for extensive adoption as risk factors for coronary vascular disease, yet, there are numerous promising, biologically acceptable candidates. Many of these gene biomarkers, alone or in combination, can play an essential role in the prediction of cardiovascular risk. The present review highlights some putative emerging genetic biomarkers that could facilitate more authentic and fast diagnosis of CVD. This review also briefly describes few technological approaches employed in the biomarker search.

Lipoprotein apheresis for the treatment of elevated circulating levels of lipoprotein(a): a critical literature review

Lipoprotein(a), which consists of a low-density lipoprotein (LDL) particle linked to an apolipoprotein(a) moiety, is currently considered an independent risk factor for cardiovascular disease due to its atherogenic (LDL-like) and prothrombotic (plasminogen-like) properties. The aim of this review is to provide an overview of the current and newer therapies for lowering increased lipoprotein(a) levels, focusing on lipoprotein apheresis. After a systematic literature search, we identified ten studies which, overall, documented that lipoprotein apheresis is effective in reducing increased lipoprotein(a) levels and cardiovascular events.

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.

Genome-wide study for circulating metabolites identifies 62 loci and reveals novel systemic effects of LPA

Genome-wide association studies have identified numerous loci linked with complex diseases, for which the molecular mechanisms remain largely unclear. Comprehensive molecular profiling of circulating metabolites captures highly heritable traits, which can help to uncover metabolic pathophysiology underlying established disease variants. We conduct an extended genome-wide association study of genetic influences on 123 circulating metabolic traits quantified by nuclear magnetic resonance metabolomics from up to 24,925 individuals and identify eight novel loci for amino acids, pyruvate and fatty acids. The LPA locus link with cardiovascular risk exemplifies how detailed metabolic profiling may inform underlying aetiology via extensive associations with very-low-density lipoprotein and triglyceride metabolism. Genetic fine mapping and Mendelian randomization uncover wide-spread causal effects of lipoprotein(a) on overall lipoprotein metabolism and we assess potential pleiotropic consequences of genetically elevated lipoprotein(a) on diverse morbidities via electronic health-care records. Our findings strengthen the argument for safe LPA-targeted intervention to reduce cardiovascular risk.

Circulating metabolites reflect human health and disease. Here, Kettunen et al. perform a genome-wide association study on 123 circulating metabolic traits and identify novel genetic loci influencing systemic metabolism. They also link new molecular pathways with a known cardiovascular risk factor Lp(a).

Lipoprotein(a) in Familial Hypercholesterolemia With Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) Gain-of-Function Mutations

BACKGROUND

It has been shown that serum lipoprotein(a) [Lp(a)] is elevated in familial hypercholesterolemia (FH) with mutation(s) of the LDL receptor (LDLR) gene. However, few data exist regarding Lp(a) levels in FH with gain-of-function mutations of the PCSK9 gene.

METHODS AND RESULTS

We evaluated 42 mutation-determined heterozygous FH patients with aPCSK9gain-of-function mutation (FH-PCSK9, mean age 52, mean LDL-C 235 mg/dl), 198 mutation-determined heterozygous FH patients with aLDLRmutation (FH-LDLR, mean age 44, mean LDL-C 217 mg/dl), and 4,015 controls (CONTROL, mean age 56, mean LDL-C 109 mg/dl). We assessed their Lp(a), total cholesterol, triglycerides, HDL-C, LDL-C, use of statins, presence of hypertension, diabetes, chronic kidney disease, smoking, body mass index (BMI) and coronary artery disease (CAD). Multiple regression analysis showed that HDL-C, use of statins, presence of hypertension, smoking, BMI, and Lp(a) were independently associated with the presence of CAD. Under these conditions, the serum levels of Lp(a) in patients with FH were significantly higher than those of the CONTROL group regardless of their causative genes, among the groups propensity score-matched (median Lp(a) 12.6 mg/dl [IQR:9.4-33.9], 21.1 mg/dl [IQR:11.7-34.9], and 5.0 mg/dl [IQR:2.7-8.1] in the FH-LDLR, FH-PCSK9, and CONTROL groups, respectively, P=0.002 for FH-LDLR vs. CONTROL, P=0.002 for FH-PCSK9 vs. CONTROL).

CONCLUSIONS

These data demonstrate that serum Lp(a) is elevated in patients with FH caused by PCSK9 gain-of-function mutations to the same level as that in FH caused by LDLR mutations.

New and emerging biomarkers in cardiovascular disease

Cardiovascular disease (CVD) is the most common cause of death and disability worldwide. Therefore, great importance has been placed on the discovery of novel risk factors and metabolic pathways relevant in the prevention and management of CVD. Such research is ongoing and may continue to lead to better risk stratification of individuals and/or the development of new intervention targets and treatment options. This review highlights emerging biomarkers related to lipid metabolism, glycemia, inflammation, and cardiac damage, some of which show promising associations with CVD risk and provide further understanding of the underlying pathophysiology. However, their measurement methodology and assays will require validation and standardization, and it will take time to accumulate evidence of their role in CVD in various population settings in order to fully assess their clinical utility. Several of the novel biomarkers represent intriguing, potentially game-changing targets for therapy.

Lipoprotein (a) as a risk factor for ischemic stroke: a meta-analysis

OBJECTIVE

Lipoprotein (a) [Lp(a)] harbors atherogenic potential but its role as a risk factor for ischemic stroke remains controversial. We conducted a meta-analysis to determine the relative strength of the association between Lp(a) and ischemic stroke and identify potential subgroup-specific risk differences.

METHODS

A systematic search using the MeSH terms "lipoproteins" OR "lipoprotein a" AND "stroke" was performed in PubMed and ScienceDirect for case-control studies from June 2006 and prospective cohort studies from April 2009 until December 20th 2014. Data from eligible papers published before these dates were reviewed and extracted from previous meta-analyses. Studies that assessed the relationship between Lp(a) levels and ischemic stroke and reported generic data-i.e. odds ratio [OR], hazard ratio, or risk ratio [RR]-were eligible for inclusion. Studies that not distinguish between ischemic and hemorrhagic stroke and transient ischemic attack were excluded. Random effects meta-analyses with mixed-effects meta-regression were performed by pooling adjusted OR or RR.

RESULTS

A total of 20 articles comprising 90,904 subjects and 5029 stroke events were eligible for the meta-analysis. Comparing high with low Lp(a) levels, the pooled estimated OR was 1.41 (95% CI, 1.26-1.57) for case-control studies (n = 11) and the pooled estimated RR was 1.29 (95% CI, 1.06-1.58) for prospective studies (n = 9). Sex-specific differences in RR were inconsistent between case-control and prospective studies. Study populations with a mean age of ≤55 years had an increased RR compared to older study populations. Reported Lp(a) contrast levels and ischemic stroke subtype significantly contributed to the heterogeneity observed in the analyses.

CONCLUSION

Elevated Lp(a) is an independent risk factor for ischemic stroke and may be especially relevant for young stroke patients. Sex-specific risk differences remain conflicting. Further studies in these subgroups may be warranted.

Lipoprotein (a): a Unique Independent Risk Factor for Coronary Artery Disease

The current epidemic affecting Indians is coronary artery disease (CAD), and is currently one of the most common causes of mortality and morbidity in developed and developing countries. The higher rate of CAD in Indians, as compared to people of other ethnic origin, may indicate a possible genetic susceptibility. Hence, Lp(a), an independent genetic risk marker for atherosclerosis and cardiovascular disease assumes great importance. Lp(a), an atherogenic lipoprotein, contains a cholesterol rich LDL particle, one molecule of apolipoprotein B-100 and a unique protein, apolipoprotein (a) which distinguishes it from LDL. Apo(a) is highly polymorphic and an inverse relationship between Lp(a) concentration and apo(a) isoform size has been observed. This is genetically controlled suggesting a functional diversity among the apo(a) isoforms. The LPA gene codes for apo(a) whose genetic heterogeneity is due to variations in its number of kringles. The exact pathogenic mechanism of Lp(a) is still not completely elucidated, but the structural homology of Lp(a) with LDL and plasmin is possibly responsible for its acting as a link between atherosclerosis and thrombosis. Upper limits of normal Lp(a) levels have not been defined for the Indian population. A cut off limit of 20 mg/dL has been suggested while for the Caucasian population it is 30 mg/dL. Though a variety of assays are available for its measurement, standardization of the analytical method is highly complicated as a majority of the methods are affected by the heterogeneity in apo(a) size. No therapeutic drug selectively targets Lp(a) but recently, new modifiers of apo(a) synthesis are being considered.

Novel metabolic biomarkers of cardiovascular disease

Coronary heart disease (CHD) accounts for one in every six deaths in US individuals. Great advances have been made in identifying important risk factors for CHD, such as hypertension, diabetes mellitus, smoking and hypercholesterolaemia, which have led to major developments in therapy. In particular, statins represent one of the greatest successes in the prevention of CHD. While these standard risk factors are important, an obvious opportunity exists to take advantage of ongoing scientific research to better risk-stratify individuals and to identify new treatment targets. In this Review, we summarize ongoing scientific research in a number of metabolic molecules or features, including lipoproteins, homocysteine, calcium metabolism and glycaemic markers. We evaluate the current state of the research and the strength of evidence supporting each emerging biomarker. We also discuss whether the associations with CHD are strong and consistent enough to improve current risk stratification metrics, and whether these markers enhance our understanding of the underlying biology of CHD and thus point towards new treatment options.

New therapies targeting apoB metabolism for high-risk patients with inherited dyslipidaemias: what can the clinician expect?

Apolipoprotein B (apoB) has a key role in the assembly and secretion of very low-density lipoprotein (VLDL) from the liver. Plasma apoB concentration affects the number of circulating atherogenic particles, and serves as an independent predictor of the risk of atherosclerotic cardiovascular disease. While statins are the most potent apoB-lowering agents currently prescribed, their efficacy in achieving therapeutic targets for low-density lipoprotein cholesterol (LDL-C) in high-risk patients, such as those with familial hypercholesterolaemia (FH), is limited. Resistance and intolerance to statins also occurs in a significant number of patients, necessitating new types of lipid-lowering therapies. Monoclonal antibodies against proprotein convertase subtilisin/kexin type 9 (PCSK9; AMG 145 and REGN727), a sequence-specific antisense oligonucleotide against apoB mRNA (mipomersen) and a synthetic inhibitor of microsomal triglyceride transfer protein (MTTP; lomitapide) have been tested in phase III clinical trials, particularly in patients with FH. The trials demonstrated the efficacy of these agents in lowering apoB, LDL-C, non-high-density lipoprotein cholesterol and lipoprotein(a) by 32-55 %, 37-66 %, 38-61 % and 22-50 % (AMG 145), 21-68 %, 29-72 %, 16-60 % and 8-36 % (REGN727), 16-71 %, 15-71 %, 12-66 % and 23-49 % (mipomersen) and 24-55 %, 25-51 %, 27-50 % and 15-19 % (lomitapide), respectively. Monoclonal antibodies against PCSK9 have an excellent safety profile and may be indicated not only in heterozygous FH, but also in statin-intolerant patients and those with other inherited dyslipidemias, such as familial combined hyperlipidaemia and familial elevation in Lp(a). Mipomersen and lomitapide increase hepatic fat content and are at present indicated for treating adult patients with homozygous FH alone.

Relook at lipoprotein (A): independent risk factor of coronary artery disease in north Indian population

AIMS

Lipoprotein (a) [Lp(a)] levels have shown wide ethnic variations. Sparse data on mean Lp(a) levels, its link with clinical variables and severity of coronary artery disease (CAD) in North Indian population needed further studies.

METHODS

150 patients, each of single vessel disease (SVD), double vessel disease (DVD) and triple vessel disease (TVD) with 150 healthy controls were drawn for the study. Serum Lp(a) estimation was performed by immunoturbidimetric method.

RESULTS

Lp(a) had a skewed distribution. Median Lp(a) level was significantly raised in cases as compared to controls (median 30.30 vs. 20 mg/dl, p < 0.001). Cases with acute coronary syndrome (ACS, 55.8%) had significantly higher median Lp(a) levels as compared to those with chronic stable angina (35.4 mg/dl vs. 23 mg/dl, p < 0.001). Significant difference in median Lp(a) levels were observed in patients with DVD or TVD versus control (30, 39.05 vs 20 mg/dl, p < 0.008). Lp(a) level was found to be an independent risk factor for CAD (AOR{adjusted odds ratio} 1.018, 95% CI 1.010-1.027; p < 0.001). Analysis using Lp(a) as categorical variable showed that progressive increase in Lp(a) concentration was associated with increased risk of CAD [AOR from lowest to highest quartile (1, 1.04, 1.43 and 2.65, p value for trend = 0.00026)]. Multivariably AOR of CAD for subjects with Lp(a) in the highest quartile (above 40 mg/dl) compared to those with Lp(a) ≤40 mg/dl was 2.308 (95% CI 1.465-3.636, p < 0.001).

CONCLUSION

Lp(a) above 40 mg/dl (corresponding to 75th percentile)assessed by an isoform insensitive assay is an independent risk factor for CAD. Raised Lp(a) level is also associated with increased risk of ACS and multivessel CAD.

The association between the LPA gene polymorphism and coronary artery disease in Chinese Han population

Lp(a) has been well known as an independent risk factor for coronary artery disease (CAD). The LPA gene, as it encodes apo(a) of the Lp(a) lipoprotein particle, was associated with increased risk of CAD. The purpose of this study was to analyze the relationship between the polymorphisms of LPA gene and CAD in Chinese Han population. Five SNPs (rs1367211, rs3127596, rs6415085, rs9347438, and rs9364559) in the LPA gene were genotyped using Sequenom MassARRAY time-of-flight mass spectrometer (TOF) in 560 CAD patients as case group and 531 non-CAD subjects as control group. The numbers of these two groups were from Chinese Han ancestry. The results showed that allele (P = 0.046) and genotype (P = 0.026) of rs9364559 in the LPA gene was associated with CAD. The frequency of rs9364559 minor allele (G) in case group was obviously higher than that in control group. Results of haplotype analysis showed that 4 haplotypes which contained rs9364559-G were associated with increased risk of CAD in this population. This study explored rs9364559 in the LPA gene may be associated with the pathogenesis of CAD; and the risk of CAD might be higher in the population carrying 4 haplotypes of different blocks in the LPA gene.

Lower Incidence of M2/ANXA5 Carriage in Recurrent Pregnancy Loss Patients With Elevated Lipoprotein(a) Levels

This study compared the incidence of M2/ANXA5 haplotype carriage, a documented repeated miscarriage risk factor, in patient groups with normal and elevated lipoprotein(a) (Lp(a)) levels. A total of 138 women with ≥2 consecutive, idiopathic recurrent miscarriages, categorized in patients with elevated (≥30 mg/dL, n = 44) and normal Lp(a) level (<30 mg/dL, n = 94) were recruited at the recurrent pregnancy loss (RPL) clinic of Munich Großhadern University Hospital. A total of 500 fertile women served as controls. All patients were genotyped for ANXA5 promoter haplotypes, genetic frequencies were compared, and odds ratios (ORs) and relative risks of M2 carriers were calculated. Women with M2 haplotype had an almost 2 times higher relative risk of RPL (OR 2.6, 95% confidence interval 1.5-4.6, P = .001) than fertile controls. Furthermore, risk rises to 2.47 in patients having normal Lp(a) levels (OR 3.2, 95% confidence interval 1.7-5.9, P = .001), whereas women with high Lp(a) levels exhibit notably lower apparent RPL risk of 1.39 (OR 1.4, 95% confidence interval 0.5-4.1, P = .659).

Lipoprotein(a): a promising marker for residual cardiovascular risk assessment

Atherosclerotic cardiovascular diseases (CVD) are still the leading cause of morbidity and mortality worldwide, although optimal medical therapy has been prescribed for primary and secondary preventions. Residual cardiovascular risk for some population groups is still considerably high although target low density lipoprotein-cholesterol (LDL-C) level has been achieved. During the past few decades, compelling pieces of evidence from clinical trials and meta-analyses consistently illustrate that lipoprotein(a) (Lp(a)) is a significant risk factor for atherosclerosis and CVD due to its proatherogenic and prothrombotic features. However, the lack of effective medication for Lp(a) reduction significantly hampers randomized, prospective, and controlled trials conducting. Based on previous findings, for patients with LDL-C in normal range, Lp(a) may be a useful marker for identifying and evaluating the residual cardiovascular risk, and aggressively lowering LDL-C level than current guidelines' recommendation may be reasonable for patients with particularly high Lp(a) level.

Hyperlipoproteinemia(a): clinical significance and treatment options

Recent epidemiologic and Mendelian randomization studies together have provided evidence that lipoprotein(a) (Lp(a)) plays a causal role in the pathogenesis of atherosclerosis and cardiovascular disease (CVD). The risk association with CVD is weak but seems continuous in shape and without an obvious threshold for Lp(a) levels. A plasma concentration of 60 mg/dl compared to usual levels is associated with an odds ratio for coronary heart disease of about 1.5 after adjustment for other cardiovascular risk factors. Niacin (nicotinic acid) is the pharmacologic means of choice for decreasing elevated Lp(a) levels but the drug is often poorly tolerated due to adverse reactions. Dietary measures, exercise and other lipid-lowering drugs, especially statins, fibrates and ezetimibe, are without effect. In patients with severe progressive cardiovascular disease and very high Lp(a) levels, lipoprotein apheresis may be used to effectively decrease Lp(a) concentrations. The method is expensive and impractical for most patients and its feasibility depends by and large on the healthcare reimbursement system of the respective country. No established treatment, however, selectively reduces Lp(a) without influencing other lipoproteins. Moreover, despite the clear association of hyperlipoproteinemia(a) with cardiovascular risk, no rigorously designed study to date has demonstrated that lowering Lp(a) concentrations has beneficial effects on cardiovascular endpoints. Randomized trials to this effect are urgently needed.

Lipoprotein(a): resurrected by genetics

Plasma lipoprotein(a) [Lp(a)] is a quantitative genetic trait with a very broad and skewed distribution, which is largely controlled by genetic variants at the LPA locus on chromosome 6q27. Based on genetic evidence provided by studies conducted over the last two decades, Lp(a) is currently considered to be the strongest genetic risk factor for coronary heart disease (CHD). The copy number variation of kringle IV in the LPA gene has been strongly associated with both Lp(a) levels in plasma and risk of CHD, thereby fulfilling the main criterion for causality in a Mendelian randomization approach. Alleles with a low kringle IV copy number that together have a population frequency of 25-35% are associated with a doubling of the relative risk for outcomes, which is exceptional in the field of complex genetic phenotypes. The recently identified binding of oxidized phospholipids to Lp(a) is considered as one of the possible mechanisms that may explain the pathogenicity of Lp(a). Drugs that have been shown to lower Lp(a) have pleiotropic effects on other CHD risk factors, and an improvement of cardiovascular endpoints is up to now lacking. However, it has been established in a proof of principle study that lowering of very high Lp(a) by apheresis in high-risk patients with already maximally reduced low-density lipoprotein cholesterol levels can dramatically reduce major coronary events.

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).

Genetic variants, plasma lipoprotein(a) levels, and risk of cardiovascular morbidity and mortality among two prospective cohorts of type 2 diabetes

AIMS

To examine the relations between genetic loci, plasma lipoprotein(a) [Lp(a)] levels, and cardiovascular disease (CVD) risk among diabetic patients and compare with the observations in the general population.

METHODS AND RESULTS

In two prospective cohorts of patients with type 2 diabetes (n= 2308) from the Nurses' Health Study and the Health Professional Follow-Up Study, we performed (i) genome-wide association (GWA) scans for plasma Lp(a); (ii) prospective analysis of plasma Lp(a) for CVD risk and mortality; and (iii) genetic association analysis for CVD risk and mortality. Meta-analysis of the two GWA scans yielded 71 single-nucleotide polymorphisms (SNPs) on chromosome 6q associated with plasma Lp(a) levels at a genome-wide significance level (P< 5 × 10(-8)). The SNP rs10455872 in LPA was most strongly associated with Lp(a) (P= 4.60 × 10(-39)). Forward-selection analysis indicated that rs10455872 and other five SNPs in a region encompassing LPA, PLG, SLC22A3, and LPAL2 genes were independently associated with Lp(a) levels and jointly explained ∼20% of variation in diabetic patients. In prospective analysis, we did not find any significant association between plasma levels and CVD incidence; the relative risk for coronary heart disease (CHD), CVD, and CVD death was 1.05 [95% confidence interval (CI): 0.95-1.15], 1.05 (0.96-1.15), and 1.21 (0.99-1.47) per 1-SD higher log-transformed Lp(a) levels, respectively. Consistently, none of the Lp(a) SNPs were associated with CVD risk or mortality (all P> 0.09). For the best SNP rs10455872 for plasma Lp(a) levels, the OR for CHD, CVD, and CVD death was 0.94 (95% CI: 0.69-1.28), 0.97 (0.72-1.29), and 1.23 (0.79-1.92), respectively. The genetic effect on CHD risk showed a significant heterogeneity between the diabetic and the general populations (P= 0.006).

CONCLUSION

Our data indicate that the effect of Lp(a) on CVD risk among diabetic patients might be different from that in the general population. Diabetes status may attenuate the relation between Lp(a) and cardiovascular risk.

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) and family history of cardiovascular disease in children with familial dyslipidemias

OBJECTIVE

To investigate in children and adolescents with familial dyslipidemias the association between lipoprotein(a) [Lp(a)] level and family history of cardiovascular disease (CVD), and whether this association is independent of the disturbed lipid profile.

STUDY DESIGN

Lp(a) level, lipid profile, and a 2-generation genealogic tree to detect cardiovascular events were evaluated in 231 patients with familial dyslipidemias. Lp(a) levels were stratified according to presence, age of occurrence, and number and type of cardiovascular events in the patient's kindreds.

RESULTS

Lp(a) and other plasma lipid fractions did not differ between patients with and those without a family history of cardiovascular events. However, the percentage of patients with elevated Lp(a) level (≥85th percentile) was higher in those with a positive family history for early cardiovascular events (P = .01). Lp(a) level was a significant independent predictor of the number of premature cardiovascular events (β = 0.17; P = .01) and of cerebrovascular events in kindreds (OR, 2.5; 95% CI, 1.05-6.03; P = .039), independent of plasma lipid fractions and other cardiovascular risk factors.

CONCLUSIONS

In children and adolescents with familial dyslipidemias, the overall association between Lp(a) level and family history of early CVD may be due to a threshold effect in those with the highest Lp(a) levels. However, multiple cardiovascular events and cerebrovascular events are predicted by any increase in plasma Lp(a) level, independent of other cardiovascular risk factors.

Increased lipoprotein(a) is associated with polyvascular disease in patients undergoing coronary artery bypass graft

OBJECTIVE

We sought to identify clinical and biochemical predictors of disease in multiple vascular territories, in patients with established coronary heart disease.

METHODS

A total of 470 patients (329 men, 141 female) who had undergone coronary artery bypass grafting (CABG) were enrolled in this prospective study. Polyvascular disease was defined on the presence of existing symptomatic or asymptomatic carotid artery stenosis and/or peripheral artery disease, which is present in 32.1% of patients (n=151).

RESULTS

Clinical and laboratory features independently associated with the presence of polyvascular disease included age ≥65 years, male sex, hypertension, former or current smoker, low BMI, and high Lp(a). Lp(a) was the only biochemical marker that had an independent association with polyvascular disease (OR=1.01 per 1mg/dl increase; 95% CI, 1.00-1.01). The fourth quartile of Lp(a) has significant associations with the risk of two or more vascular territories involvement (OR=1.866; 95% CI, 1.056-3.297), and three vascular territories involvement (OR=4.240; 95% CI, 1.405-12.798). There was a significant trend towards patients with the highest quartile of Lp(a) that has association with more advanced polyvascular disease (test for trend: p=0.008 for involvement of three vascular territories).

CONCLUSION

High Lp(a) was independently associated with polyvascular disease in patients who undergo CABG, which is suggestive of an indirect evidence of the pathophysiologic function of Lp(a) in polyvascular disease.

Antisense oligonucleotide lowers plasma levels of apolipoprotein (a) and lipoprotein (a) in transgenic mice

OBJECTIVES

This study sought to assess whether an antisense oligonucleotide (ASO) directed to apolipoprotein (a) [apo(a)] reduces apo(a) and lipoprotein (a) [Lp(a)] levels in transgenic mouse models.

BACKGROUND

Elevated Lp(a) is a causal, independent, genetic risk factor for cardiovascular disease and myocardial infarction. Effective therapies to specifically lower plasma Lp(a) levels are lacking.

METHODS

Three transgenic mouse models were utilized: 8K-apo(a) mice expressing 8 kringle IV (KIV) repeats with a single copy of KIV-2; 8K-Lp(a) mice expressing both the 8K apo(a) plus human apolipoprotein B-100; and 12K-apo(a) mice expressing a 12K apo(a) with 3 KIV-2 repeats. The mice were treated intraperitoneally with saline, a control ASO, or ASO 144367 directed to KIV-2 for 4 to 6 weeks. Apo(a), Lp(a), and oxidized phospholipids present on human apoB (OxPL/h-apoB) or apo(a) [OxPL/apo(a)] were measured at baseline and on and off therapy.

RESULTS

ASO 144367 significantly reduced Lp(a) by 24.8% in 8K-Lp(a) mice, and reduced apo(a) levels by 19.2% in 8K-Lp(a) mice, 30.0% in 8K-apo(a) mice, and 86% in 12K-apo(a) mice; ASO 144367 also significantly reduced OxPL/apoB 22.4% in 8K-Lp(a) mice, and OxPL/apo(a) levels by 19.9% in 8K-Lp(a) mice, 22.1% in 8K-apo(a) mice, and 92.5% in 12K-apo(a) mice (p < 0.004, or less, for all). No significant changes occurred in Lp(a), apo(a), OxPL/apoB, or OxPL/apo(a) levels with control ASO or saline.

CONCLUSIONS

This study documents the first specific therapy, to our knowledge, for lowering apo(a)/Lp(a) levels and their associated OxPL. A more potent effect was documented in mice expressing apo(a) with multiple KIV-2 repeats. Targeting liver expression of apo(a) with ASOs directed to KIV-2 repeats may provide an effective approach to lower elevated Lp(a) levels in humans.

Enigmatic role of lipoprotein(a) in cardiovascular disease

Lipoprotein (a), [Lp(a)] has many properties in common with low-density lipoprotein, (LDL) but contains a unique protein apolipoprotein(a), linked to apolipoprotein B-100 by a single disulfide bond. There is a substantial size heterogeneity of apo(a), and generally smaller apo(a) sizes tend to correspond to higher plasma Lp(a) levels, but this relation is far from linear, underscoring the importance to assess allele-specific apo(a) levels. The presence of apo(a), a highly charged, carbohydrate-rich, hydrophilic protein may obscure key features of the LDL moiety and offer opportunities for binding to vessel wall elements. Recently, interest in Lp(a) has increased because studies over the past decade have confirmed and more robustly demonstrated a risk factor role of Lp(a) for cardiovascular disease. In particular, levels of Lp(a) carried in particles with smaller size apo(a) isoforms are associated with coronary artery disease (CAD). Other studies suggest that proinflammatory conditions may modulate risk factor properties of Lp(a). Further, Lp(a) may act as a preferential acceptor for proinflammatory oxidized phospholipids transferred from tissues or from other lipoproteins. However, at present only a limited number of agents (e.g., nicotinic acid and estrogen) has proven efficacy in lowering Lp(a) levels. Although Lp(a) has not been definitely established as a cardiovascular risk factor and no guidelines presently recommend intervention, Lp(a)-lowering therapy might offer benefits in subgroups of patients with high Lp(a) levels.

A novel peptide derived from human apolipoprotein E is an inhibitor of tumor growth and ocular angiogenesis

Angiogenesis is a hallmark of tumor development and metastasis and now a validated target for cancer treatment. We previously reported that a novel dimer peptide (apoEdp) derived from the receptor binding region of human apolipoprotein E (apoE) inhibits virus-induced angiogenesis. However, its role in tumor anti-angiogenesis is unknown. This study demonstrates that apoEdp has anti-angiogenic property in vivo through reduction of tumor growth in a mouse model and ocular angiogenesis in a rabbit eye model. Our in vitro studies show that apoEdp inhibits human umbilical vein endothelial cell proliferation, migration, invasion and capillary tube formation. We document that apoEdp inhibits vascular endothelial growth factor-induced Flk-1 activation as well as downstream signaling pathways that involve c-Src, Akt, eNOS, FAK, and ERK1/2. These in vitro data suggest potential sites of the apoE dipeptide inhibition that could occur in vivo.

This is the first evidence that a synthetic dimer peptide mimicking human apoE has anti-angiogenesis functions and could be an anti-tumor drug candidate.

Optimizing lipid-lowering therapy in the prevention of coronary heart disease

Optimized lipid-lowering therapy is laid out in guidelines from national and international bodies. Statins are first-line treatment and instituted early in secondary prevention. The challenge in primary prevention is identification of the person at risk. This can be achieved by using scoring systems that assess classical risk factors, and then by adding information from predictive panels of biomarkers related to atherogenic pathways and by noninvasive imaging of vascular beds. At present, outcome trials validate the widespread use of statins in the population but studies of other agents have not generated proof of efficacy. Levels of high-density lipoprotein are related inversely to coronary heart disease risk but, so far, it is unclear if increasing high-density lipoprotein leads to a reduction in risk. Clinical trials on the utility of high-density lipoprotein raising on a background of statin therapy are underway.