Effects of Extended-Release Nicotinic Acid on Apolipoprotein (a) Kinetics in Hypertriglyceridemic Patients

Effects of niacin on apo A1 and B levels: a systematic review and meta-analysis of randomised controlled trials

Niacin has been investigated for its potential impact on lipid metabolism and cardiovascular health. This meta-analysis aims to systematically evaluate the effects of niacin interventions on apo A1 and apo B levels, key regulators of lipoprotein metabolism and markers of cardiovascular risk. A comprehensive search of the literature was performed on five databases of PubMed, Scopus, Web of Science, Embase and Cochrane library, from inception up to 15 July 2023. This search identified 1452 publications, from which twelve randomised controlled trials met the inclusion criteria. The intervention dosages ranged from 500 to 3000 mg/d, and the study durations spanned from 6 to 102·8 weeks. The niacin intervention demonstrated a significant reduction in apo B levels (weighted mean differences (WMD): -24·37 mg/dl, P = 0·01). Subgroup analyses indicated that intervention duration played a role, with trials of ≤ 16 weeks showing a greater reduction in apo B. Regarding apo A1, niacin significantly increased its levels (WMD: 8·23 mg/dl, P < 0·001). Subgroup analyses revealed that the beneficial effects of niacin on apo A1 were observed at a dosage of > 1500 mg/d (P < 0·001), and extended-release niacin was more effective compared with other forms (P < 0·001). According to the Begg's regression test, no publication bias was observed in this systematic review and meta-analysis. This meta-analysis highlights niacin's potential role in improving lipid profiles and cardiovascular health. Further well-designed clinical trials are needed to elucidate and confirm optimal dosages and durations of niacin interventions for influencing apo A1 and B.

Consensus on lipoprotein(a) of the Spanish Society of Arteriosclerosis. Literature review and recommendations for clinical practice

The irruption of lipoprotein(a) (Lp(a)) in the study of cardiovascular risk factors is perhaps, together with the discovery and use of proprotein convertase subtilisin/kexin type 9 (iPCSK9) inhibitor drugs, the greatest novelty in the field for decades. Lp(a) concentration (especially very high levels) has an undeniable association with certain cardiovascular complications, such as atherosclerotic vascular disease (AVD) and aortic stenosis. However, there are several current limitations to both establishing epidemiological associations and specific pharmacological treatment. Firstly, the measurement of Lp(a) is highly dependent on the test used, mainly because of the characteristics of the molecule. Secondly, Lp(a) concentration is more than 80% genetically determined, so that, unlike other cardiovascular risk factors, it cannot be regulated by lifestyle changes. Finally, although there are many promising clinical trials with specific drugs to reduce Lp(a), currently only iPCSK9 (limited for use because of its cost) significantly reduces Lp(a). However, and in line with other scientific societies, the SEA considers that, with the aim of increasing knowledge about the contribution of Lp(a) to cardiovascular risk, it is relevant to produce a document containing the current status of the subject, recommendations for the control of global cardiovascular risk in people with elevated Lp(a) and recommendations on the therapeutic approach to patients with elevated Lp(a).

Lipoprotein(a): Just an Innocent Bystander in Arterial Hypertension?

Elevated plasma lipoprotein(a) [Lp(a)] is a relatively common and highly heritable trait conferring individuals time-dependent risk of developing atherosclerotic cardiovascular disease (CVD). Following its first description, Lp(a) triggered enormous scientific interest in the late 1980s, subsequently dampened in the mid-1990s by controversial findings of some prospective studies. It was only in the last decade that a large body of evidence has provided strong arguments for a causal and independent association between elevated Lp(a) levels and CVD, causing renewed interest in this lipoprotein as an emerging risk factor with a likely contribution to cardiovascular residual risk. Accordingly, the 2022 consensus statement of the European Atherosclerosis Society has suggested inclusion of Lp(a) measurement in global risk estimation. The development of highly effective Lp(a)-lowering drugs (e.g., antisense oligonucleotides and small interfering RNA, both blocking LPA gene expression) which are still under assessment in phase 3 trials, will provide a unique opportunity to reduce "residual cardiovascular risk" in high-risk populations, including patients with arterial hypertension. The current evidence in support of a specific role of Lp(a) in hypertension is somehow controversial and this narrative review aims to overview the general mechanisms relating Lp(a) to blood pressure regulation and hypertension-related cardiovascular and renal damage.

Relationship of apolipoprotein(a) isoform size with clearance and production of lipoprotein(a) in a diverse cohort

Lipoprotein(a) [Lp(a)] has two main proteins, apoB100 and apo(a). High levels of Lp(a) confer an increased risk for atherosclerotic cardiovascular disease. Most people have two circulating isoforms of apo(a) differing in their molecular mass, determined by the number of Kringle IV Type 2 repeats. Previous studies report a strong inverse relationship between Lp(a) levels and apo(a) isoform sizes. The roles of Lp(a) production and fractional clearance and how ancestry affects this relationship remain incompletely defined. We therefore examined the relationships of apo(a) size with Lp(a) levels and both apo(a) fractional clearance rates (FCR) and production rates (PR) in 32 individuals not on lipid-lowering treatment. We determined plasma Lp(a) levels and apo(a) isoform sizes, and used the relative expression of the two isoforms to calculate a "weighted isoform size" (wIS). Stable isotope studies were performed, using D3-leucine, to determine the apo(a) FCR and PR. As expected, plasma Lp(a) concentrations were inversely correlated with wIS (R2 = 0.27; P = 0.002). The wIS had a modest positive correlation with apo(a) FCR (R2 = 0.10, P = 0.08), and a negative correlation with apo(a) PR (R2 = 0.11; P = 0.06). The relationship between wIS and PR became significant when we controlled for self-reported race and ethnicity (SRRE) (R2 = 0.24, P = 0.03); controlling for SRRE did not affect the relationship between wIS and FCR. Apo(a) wIS plays a role in both FCR and PR; however, adjusting for SRRE strengthens the correlation between wIS and PR, suggesting an effect of ancestry.

Recent lipoprotein(a) trials

PURPOSE OF REVIEW

Lipoprotein(a) (Lp(a)) is a genetically determined independent risk factor for cardiovascular disease and calcific aortic stenosis; thus, serum levels are minimally affected by conventional treatments for hypercholesterolemia and hypertriglyceridemia. New RNA therapies directly targeting Lp(a) have demonstrated efficacy in decreasing serum levels. Several recent trials have demonstrated efficacy and safety of these RNA therapeutics.

RECENT FINDINGS

Single-stranded antisense oligonucleotides (ASOs) and small interfering RNA (siRNA) are two classes of RNA-targeted therapeutics that specifically target the LPA gene, which encodes for apolipoprotein(a), a dominant and rate-limiting component in the hepatic synthesis of Lp(a) particle. Pelacarsen (ASO), olpasiran (siRNA) and SLN360 (siRNA) are novel drugs that have demonstrated efficacy in lowering Lp(a) levels and excellent safety profiles.

SUMMARY

Lp(a) is an independent risk factor for cardiovascular disease. RNA-directed therapies, pelacarsen, olpasiran and SLN360, have shown efficacy in dramatically lowering serum Lp(a) levels. Outcomes data will be the next frontier of Lp(a) trials.

Pharmacotherapy for children with elevated levels of lipoprotein(a): future directions

INTRODUCTION

Elevated lipoprotein(a) [Lp(a)] is an independent risk factor for atherosclerotic cardiovascular disease (ASCVD). With the advent of the antisense oligonucleotides (ASOs) and small interfering RNAs (siRNAs) targeted at LPA, the gene encoding apolipoprotein(a), that are highly effective for lowering Lp(a) levels, this risk factor might be managed in the near future. Given that Lp(a) levels are mostly genetically determined and once elevated, present from early age, we have evaluated future directions for the treatment of children with high Lp(a) levels.

AREAS COVERED

In the current review, we discuss different pharmacological treatments in clinical development and provide an in-depth overview of the effects of ASOs and siRNAs targeted at LPA.

EXPERT OPINION

Since high Lp(a) is an important risk factor for ASCVD and given the promising effects of both ASOs and siRNAs targeted at apo(a), there is an urgent need for well-designed prospective studies to assess the impact of elevated Lp(a) in childhood. If the Lp(a)-hypothesis is confirmed in adults, and also in children, the rationale might arise for treating children with high Lp(a) levels. However, we feel that this should be limited to children with the highest cardiovascular risk including familial hypercholesterolemia and potentially pediatric stroke.

Unravelling lipoprotein metabolism with stable isotopes: tracing the flow

Dysregulated lipoprotein metabolism is a major cause of atherosclerotic cardiovascular disease (ASCVD). Use of stable isotope tracers and compartmental modelling have provided deeper understanding of the mechanisms underlying lipid disorders in patients at high risk of ASCVD, including familial hypercholesterolemia (FH), elevated lipoprotein(a) [Lp(a)] and metabolic syndrome (MetS). In patients with FH, deficiency in low-density lipoprotein (LDL) receptor activity not only impairs the catabolism of LDL, but also induces hepatic overproduction and decreases catabolism of triglyceride-rich lipoproteins (TRLs). Patients with elevated Lp(a) are characterized by increased hepatic secretion of Lp(a) particles. Atherogenic dyslipidemia in MetS patients relates to a combination of overproduction of very-low density lipoprotein-apolipoprotein (apo) B-100, decreased catabolism of apoB-100-containing particles, and increased catabolism of high-density lipoprotein-apoA-I particles, as well as to impaired clearance of TRLs in the postprandial state. Kinetic studies show that weight loss, fish oils, statins and fibrates have complementary modes of action that correct atherogenic dyslipidemia. Defining the kinetic mechanisms of action of proprotein convertase subtilisin/kexin type 9 and angiopoietin-like 3 inhibitors on lipid and lipoprotein mechanism in dyslipidemic subjects will further our understanding of these therapies in decreasing the development of ASCVD. "Everything changes but change itself. Everything flows and nothing remains the same... You cannot step twice into the same river, for other waters and yet others go flowing ever on." Heraclitus (c.535- c. 475 BCE).

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

Lipoprotein(a) forms a subfraction of the lipid profile and is characterized by the addition of apolipprotein(a) (apo(a)) to apoB100 derived particles. Its levels are mostly genetically determined inversely related to the number of protein domain (kringle) repeats in apo(a). In epidemiological studies, it shows consistent association with cardiovascular disease (CVD) and most recently with extent of aortic stenosis. Issues with standardizing the measurement of Lp(a) are being resolved and consensus statements favor its measurement in patients at high risk of, or with family histories of CVD events. Major lipid-lowering therapies such as statin, fibrates, and ezetimibe have little effect on Lp(a) levels. Therapies such as niacin or cholesterol ester transfer protein (CETP) inhibitors lower Lp(a) as well as reducing other lipid-related risk factors but have failed to clearly reduce CVD events. Proprotein convertase subtilisin kexin-9 (PCSK9) inhibitors reduce cholesterol and Lp(a) as well as reducing CVD events. New antisense therapies specifically targeting apo(a) and hence Lp(a) have greater and more specific effects and will help clarify the extent to which intervention in Lp(a) levels will reduce CVD events.

Plasma concentrations of lipoproteins and risk of lower-limb peripheral artery disease in people with type 2 diabetes: the SURDIAGENE study

AIMS/HYPOTHESIS

The lipid profile has not been fully investigated in individuals with peripheral artery disease (PAD). We aimed to evaluate the relationship between plasma concentrations of lipoproteins and the prevalence of lower-limb PAD at baseline and its incidence during follow-up in people with type 2 diabetes.

METHODS

Plasma concentrations of total cholesterol, HDL-cholesterol, triacylglycerol and apolipoprotein (Apo) A-I, ApoA-II, ApoB-100 and Apo(a) were measured at baseline using colorimetric or MS methods in the SURDIAGENE cohort. Total cholesterol/HDL-cholesterol ratio, non-HDL-cholesterol and LDL-cholesterol were estimated using computation formulas. Logistic and Cox proportional hazard regression models were fitted to estimate OR or HR, with related 95% CI, for baseline prevalence or incidence of major PAD (lower-limb amputation or requirement of revascularisation) during follow-up by increasing lipoprotein tertiles, after adjustment for key confounders.

RESULTS

Among 1468 participants (women 42%, mean ± SD age 65 ± 11 years, duration of diabetes 14 ± 10 years at baseline), 129 (8.8%) had a baseline history of major PAD. Major PAD was less prevalent at baseline in the highest (vs lowest) tertile of HDL-cholesterol (OR 0.42 [95% CI 0.26, 0.71], p = 0.001) and ApoA-I (OR 0.39 [95% CI 0.23, 0.67], p = 0.0007), and more frequent in the highest tertile of total cholesterol/HDL-cholesterol ratio (OR 1.95 [95% CI 1.18, 3.24], p = 0.01). Among 1339 participants without a history of PAD at baseline, incident PAD occurred in 97 (7.2%) during a median (25th-75th percentile) duration of follow-up of 7.1 (4.4-10.7) years, corresponding to 9685 person-years and an incidence rate of 9.8 (95% CI 8.0, 12.0) per 1000 person-years. The risk of incident PAD was lower in the top (vs bottom) tertile of HDL-cholesterol (HR 0.54 [95% CI 0.30, 0.95], p = 0.03) or ApoA-I (HR 0.50 [95% CI 0.28, 0.86], p = 0.01) and higher in the top tertile of total cholesterol/HDL-cholesterol ratio (HR 2.81 [95% CI 1.61, 5.04], p = 0.0002) and non-HDL-cholesterol (HR 1.80 [95% CI 1.06, 3.12], p = 0.03).

CONCLUSIONS/INTERPRETATION

We reported independent associations between HDL-cholesterol, ApoA-I, total cholesterol/HDL-cholesterol ratio or non-HDL-cholesterol and the prevalence or the incidence of major PAD in people with type 2 diabetes. Our findings provide a picture of lipoprotein profile in people with type 2 diabetes. Graphical abstract.

Bioactive Compounds for the Management of Hypertriglyceridemia: Evidence From Clinical Trials and Putative Action Targets

Hypertriglyceridemia refers to the presence of elevated concentrations of triglycerides (TG) in the bloodstream (TG >200 mg/dL). This lipid alteration is known to be associated with an increased risk of atherosclerosis, contributing overall to the onset of atherosclerotic cardiovascular disease (CVD). Guidelines for the management of hypertriglyceridemia are based on both lifestyle intervention and pharmacological treatment, but poor adherence, medication-related costs and side effects can limit the success of these interventions. For this reason, the search for natural alternative approaches to reduce plasma TG levels currently represents a hot research field. This review article summarizes the most relevant clinical trials reporting the TG-reducing effect of different food-derived bioactive compounds. Furthermore, based on the evidence obtained from in vitro studies, we provide a description and classification of putative targets of action through which several bioactive compounds can exert a TG-lowering effect. Future research may lead to investigations of the efficacy of novel nutraceutical formulations consisting in a combination of bioactive compounds which contribute to the management of plasma TG levels through different action targets.

Increased cardiovascular risk associated with hyperlipoproteinemia (a) and the challenges of current and future therapeutic possibilities

Population, genetic, and clinical studies demonstrated a causative and continuous, from other plasma lipoproteins independent relationship between elevated plasma lipoprotein (a) [Lp(a)] concentration and the development of cardiovascular disease (CVD), mainly those related to athe-rosclerotic CVD, and calcific aortic stenosis. Currently, a strong international consensus is still lacking regarding the single value which would be commonly used to define hyperlipoproteinemia (a). Its prevalence in the general population is estimated to be in the range of 10%–35% in accordance with the most commonly used threshold levels (>30 or >50 mg/dL). Since elevated Lp(a) can be of special importance in patients with some genetic disorders, as well as in individuals with otherwise controlled major risk factors, the identification and establishment of the proper therapeutic interventions that would lower Lp(a) levels and lead to CVD risk reduction could be very important. The majority of the classical lipid-lowering agents (statins, ezetimibe, and fibrates), as well as nutraceuticals (CoQ10 and garlic), appear to have no significant effect on its plasma levels, whereas for the drugs with the demonstrated Lp(a)-lowering effects (aspirin, niacin, and estrogens), their clinical efficacy in reducing cardiovascular (CV) events has not been unequivocally proven yet. Both Lp(a) apheresis and proprotein convertase subtilisin/kexin type 9 inhibitors can reduce the plasma Lp(a) by approximately 20%–30% on average, in parallel with much larger reduction of low-density lipoprotein cholesterol (up to 70%), what puts us in a difficulty to conclude about the true contribution of lowered Lp(a) to the reduction of CV events. The most recent advancement in the field is the introduction of the novel apolipoprotein (a) [apo(a)] antisense oligonucleotide therapy targeting apo(a), which has already proven itself as being very effective in decreasing plasma Lp(a) (by even >90%), but should be further tested in clinical trials. The aim of this review was to present some of the most important accessible scientific data, as well as dilemmas related to the currently and potentially in the near future more widely available therapeutic options for the management of hyperlipoproteinemia (a).

Lipoproteins and lipids in cardiovascular disease: from mechanistic insights to therapeutic targeting

With cardiovascular disease being the leading cause of morbidity and mortality worldwide, effective and cost-efficient therapies to reduce cardiovascular risk are highly needed. Lipids and lipoprotein particles crucially contribute to atherosclerosis as underlying pathology of cardiovascular disease and influence inflammatory processes as well as function of leukocytes, vascular and cardiac cells, thereby impacting on vessels and heart. Statins form the first-line therapy with the aim to block cholesterol synthesis, but additional lipid-lowering drugs are sometimes needed to achieve low-density lipoprotein (LDL) cholesterol target values. Furthermore, beyond LDL cholesterol, also other lipid mediators contribute to cardiovascular risk. This review comprehensively discusses low- and high-density lipoprotein cholesterol, lipoprotein (a), triglycerides as well as fatty acids and derivatives in the context of cardiovascular disease, providing mechanistic insights into their role in pathological processes impacting on cardiovascular disease. Also, an overview of applied as well as emerging therapeutic strategies to reduce lipid-induced cardiovascular burden is provided.

PCSK9 Inhibition with alirocumab increases the catabolism of lipoprotein(a) particles in statin-treated patients with elevated lipoprotein(a)

BACKGROUND

Lipoprotein(a) (Lp(a)) is a low-density lipoprotein (LDL) particle containing apolipoprotein(a) (apo(a)) covalently linked to apolipoprotein B-100 (apoB). Statin-treated patients with elevated Lp(a) have an increased risk of atherosclerotic cardiovascular disease (ASCVD). Recent trials show that proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibition decreases Lp(a) and cardiovascular events, particularly in high risk patients with elevated Lp(a). We investigated the kinetic mechanism whereby alirocumab, a PCSK9 inhibitor, lowers Lp(a) in statin-treated patients with high Lp(a) and ASCVD.

METHODS

The effects of 12-week alirocumab treatment (150 mg every 2 weeks) on apo(a) kinetics were studied in 21 patients with elevated Lp(a) concentration (>0.5 g/L). Apo(a) fractional catabolic rate (FCR) and production rate (PR) were determined using intravenous D3-leucine administration, mass spectrometry and compartmental modelling. All patients were on long-term statin treatment.

RESULTS

Alirocumab significantly decreased plasma concentrations of total cholesterol (-39%), LDL-cholesterol (-67%), apoB (-56%), apo(a) (-25%) and Lp(a) (-22%) (P< 0.001 for all). Alirocumab also significantly lowered plasma apo(a) pool size (-26%, P <0.001) and increased the FCR of apo(a) (+28%, P< 0.001), but did not alter apo(a) PR, which remained significantly higher relative to a reference group of patients on statins with normal Lp(a) (P< 0.001).

CONCLUSIONS

In statin-treated patients, alirocumab lowers elevated plasma Lp(a) concentrations by accelerating the catabolism of Lp(a) particles. This may be consequent on marked upregulation of hepatic receptors (principally for LDL) and/or reduced competition between Lp(a) and LDL particles for these receptors; the mechanism could contribute to the benefit of PCSK9 inhibition with alirocumab on cardiovascular outcomes.

A high-throughput mass spectrometry-based assay for large-scale profiling of circulating human apolipoproteins

Apolipoproteins govern lipoprotein metabolism and are promising biomarkers of metabolic and cardiovascular diseases. Unlike immunoassays, MS enables the quantification and phenotyping of multiple apolipoproteins. Hence, here, we aimed to develop a LC-MS/MS assay that can simultaneously quantitate 18 human apolipoproteins [A-I, A-II, A-IV, A-V, B48, B100, C-I, C-II, C-III, C-IV, D, E, F, H, J, L1, M, and (a)] and determined apoE, apoL1, and apo(a) phenotypes in human plasma and serum samples. The plasma and serum apolipoproteins were trypsin digested through an optimized procedure and peptides were extracted and analyzed by LC-MS/MS. The method was validated according to standard guidelines in samples spiked with known peptide amounts. The LC-MS/MS results were compared with those obtained with other techniques, and reproducibility, dilution effects, and stabilities were also assessed. Peptide markers were successfully selected for targeted apolipoprotein quantification and phenotyping. After optimization, the assay was validated for linearity, lower limits of quantification, accuracy (biases: -14.8% to 12.1%), intra-assay variability [coefficients of variation (CVs): 1.5-14.2%], and inter-assay repeatability (CVs: 4.1-14.3%). Bland-Altman plots indicated no major statistically significant differences between LC-MS/MS and other techniques. The LC-MS/MS results were reproducible over five repeated experiments (CVs: 1.8-13.7%), and we identified marked differences among the plasma and serum samples. The LC-MS/MS assay developed here is rapid, requires only small sampling volumes, and incurs reasonable costs, thus making it amenable for a wide range of studies of apolipoprotein metabolism. We also highlight how this assay can be implemented in laboratories.

VLDL (Very-Low-Density Lipoprotein)-Apo E (Apolipoprotein E) May Influence Lp(a) (Lipoprotein [a]) Synthesis or Assembly

Objective:

To clarify the association between PCSK9 (proprotein convertase subtilisin/kexin type 9) and Lp(a) (lipoprotein [a]), we studied Lp(a) kinetics in patients with loss-of-function and gain-of-function PCSK9 mutations and in patients in whom extended-release niacin reduced Lp(a) and PCSK9 concentrations.

Approach and Results:

Six healthy controls, 9 heterozygous patients with familial hypercholesterolemia (5 with low-density lipoprotein receptor [ LDLR ] mutations and 4 with PCSK9 gain-of-function mutations) and 3 patients with heterozygous dominant-negative PCSK9 loss-of-function mutations were included in the preliminary study. Eight patients were enrolled in a second study assessing the effects of 2 g/day extended-release niacin. Apolipoprotein kinetics in VLDL (very-low-density lipoprotein), LDL (low-density lipoprotein), and Lp(a) were studied using stable isotope techniques. Plasma Lp(a) concentrations were increased in PCSK9 -gain-of-function and familial hypercholesterolemia- LDLR groups compared with controls and PCSK9 -loss-of-function groups (14±12 versus 5±4 mg/dL; P =0.04), but no change was observed in Lp(a) fractional catabolic rate. Subjects with PCSK9 -loss-of-function mutations displayed reduced apoE (apolipoprotein E) concentrations associated with a VLDL-apoE absolute production rate reduction. Lp(a) and VLDL-apoE absolute production rates were correlated ( r =0.50; P <0.05). ApoE-to-apolipoprotein (a) molar ratios in Lp(a) increased with plasma Lp(a) ( r =0.96; P <0.001) but not with PCSK9 levels. Extended-release niacin-induced reductions in Lp(a) and VLDL-apoE absolute production rate were correlated ( r =0.83; P =0.015). In contrast, PCSK9 reduction (−35%; P =0.008) was only correlated with that of VLDL-apoE absolute production rate ( r =0.79; P =0.028).

Conclusions:

VLDL-apoE production could determine Lp(a) production and/or assembly. As PCSK9 inhibitors reduce plasma apoE and Lp(a) concentrations, apoE could be the link between PCSK9 and Lp(a).

Proprotein convertase subtilisin/kexin type 9 inhibitors and lipoprotein(a)-mediated risk of atherosclerotic cardiovascular disease: more than meets the eye?

PURPOSE OF REVIEW

Evidence continues to mount for elevated lipoprotein(a) [Lp(a)] as a prevalent, independent, and causal risk factor for atherosclerotic cardiovascular disease. However, the effects of existing lipid-lowering therapies on Lp(a) are comparatively modest and are not specific to Lp(a). Consequently, evidence that Lp(a)-lowering confers a cardiovascular benefit is lacking. Large-scale cardiovascular outcome trials (CVOTs) of inhibitory mAbs targeting proprotein convertase subtilisin/kexin type 9 inhibitors (PCSK9i) may address this issue.

RECENT FINDINGS

Although the ability of PCSK9i to lower Lp(a) by 15-30% is now clear, the mechanisms involved continue to be debated, with in-vitro and in-vivo studies showing effects on Lp(a) clearance (through the LDL receptor or other receptors) and Lp(a)/apolipoprotein(a) biosynthesis in hepatocytes. The FOURIER CVOT showed that patients with higher baseline levels of Lp(a) derived greater benefit from evolocumab and those with the lowest combined achieved Lp(a) and LDL-cholesterol (LDL-C) had the lowest event rate. Meta-analysis of ten phase 3 trials of alirocumab came to qualitatively similar conclusions concerning achieved Lp(a) levels, although an effect independent of LDL-C lowering could not be demonstrated.

SUMMARY

Although it is not possible to conclude that PCSK9i specifically lower Lp(a)-attributable risk, patients with elevated Lp(a) could derive incremental benefit from PCSK9i therapy.

Therapeutic management of hyperlipoproteinemia (a)

Cardiovascular disease (CVD) has consistently been the leading cause of death worldwide. Several clinical and epidemiological studies have demonstrated that an elevated plasma concentration of lipoprotein (a) [Lp(a)] is a causative and independent major risk factor for the development of CVD, as well as calcific aortic valve stenosis. Thus, the therapeutic management of hyperlipoproteinemia (a) has received much attention, as significant reductions in Lp(a) levels may, potentially, favorably affect cardiovascular risk. Aspirin, niacin, estrogens, and statins, which act on different molecular pathways, may be prescribed to patients with mild or modest elevations of Lp(a) levels. Other therapeutic interventions, such as proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors, Lp(a) apheresis, and the novel antisense oligonucleotides APO(a)-Rx and APO(a)-LRx, which are being evaluated in ongoing clinical trials, have provided some promising results and can potentially be used in severe cases of hyperlipoproteinemia (a). This review aims to present and discuss the current clinical and scientific data pertaining to the therapeutic options for the management of hyperlipoproteinemia (a).

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.

PCSK9 inhibition with alirocumab reduces lipoprotein(a) levels in nonhuman primates by lowering apolipoprotein(a) production rate

Therapeutic antibodies targeting proprotein convertase subtilisin kexin type 9 (PCSK9) (e.g. alirocumab) lower low-density lipoprotein cholesterol (LDL-C) and lipoprotein (a) [Lp(a)] levels in clinical trials. We recently showed that PCSK9 enhances apolipoprotein(a) [apo(a)] secretion from primary human hepatocytes but does not affect Lp(a) cellular uptake. Here, we aimed to determine how PCSK9 neutralization modulates Lp(a) levels in vivo.

Six nonhuman primates (NHP) were treated with alirocumab or a control antibody (IgG1) in a crossover protocol. After the lowering of lipids reached steady state, NHP received an intravenous injection of [2H3]-leucine, and blood samples were collected sequentially over 48 h. Enrichment of apolipoproteins in [2H3]-leucine was assessed by liquid chromatography–tandem mass spectrometry (LC–MS/MS). Kinetic parameters were calculated using numerical models with the SAAMII software. Compared with IgG1, alirocumab significantly reduced total cholesterol (TC) (−28%), LDL-C (−67%), Lp(a) (−56%), apolipoprotein B100 (apoB100) (−53%), and apo(a) (−53%). Alirocumab significantly increased the fractional catabolic rate of apoB100 (+29%) but not that of apo(a). Conversely, alirocumab sharply and significantly reduced the production rate (PR) of apo(a) (−42%), but not significantly that of apoB100, compared with IgG1, respectively.

In line with the observations made in human hepatocytes, the present kinetic study establishes that PCSK9 neutralization with alirocumab efficiently reduces circulating apoB100 and apo(a) levels by distinct mechanisms: apoB primarily by enhancing its catabolism and apo(a) primarily by lowering its production.

Kinetics of plasma apolipoprotein E isoforms by LC-MS/MS: a pilot study

Human apoE exhibits three major isoforms (apoE2, apoE3, and apoE4) corresponding to polymorphism in the APOE gene. Total plasma apoE concentrations are closely related to these isoforms, but the underlying mechanisms are unknown. We aimed to describe the kinetics of apoE individual isoforms to explore the mechanisms for variable total apoE plasma concentrations. We used LC-MS/MS to discriminate between isoforms by identifying specific peptide sequences in subjects (three E2/E3, three E3/E3, and three E3/E4 phenotypes) who received a primed constant infusion of ²H₃-leucine for 14 h. apoE concentrations and leucine enrichments were measured hourly in plasma. Concentrations of apoE2 were higher than apoE3, and concentrations of apoE4 were lower than apoE3. There was no difference between apoE3 and apoE4 catabolic rates and between apoE2 and apoE3 production rates (PRs), but apoE2 catabolic rates and apoE4 PRs were lower. The mechanisms leading to the difference in total plasma apoE concentrations are therefore related to contrasted kinetics of the isoforms. Production or catabolic rates are differently affected according to the specific isoforms. On these grounds, studies on the regulation of the involved biochemical pathways and the impact of pathological environments are now warranted.

IRES-dependent translation of the long non coding RNA meloe in melanoma cells produces the most immunogenic MELOE antigens

MELOE-1 and MELOE-2, two highly specific melanoma antigens involved in T cell immunosurveillance are produced by IRES-dependent translation of the long « non coding » and polycistronic RNA, meloe. In the present study, we document the expression of an additional ORF, MELOE-3, located in the 5' region of meloe. Data from in vitro translation experiments and transfection of melanoma cells with bicistronic vectors documented that MELOE-3 is exclusively translated by the classical cap-dependent pathway. Using a sensitive tandem mass spectrometry technique, we detected the presence of MELOE-3 in total lysates of both melanoma cells and normal melanocytes. This contrasts with our previous observation of the melanoma-restricted expression of MELOE-1 and MELOE-2. Furthermore, in vitro stimulation of PBMC from 6 healthy donors with overlapping peptides from MELOE-1 or MELOE-3 revealed a very scarce MELOE-3 specific T cell repertoire as compared to the abundant repertoire observed against MELOE-1. The poor immunogenicity of MELOE-3 and its expression in melanocytes is consistent with an immune tolerance towards a physiologically expressed protein. In contrast, melanoma-restricted expression of IRES-dependent MELOE-1 may explain its high immunogenicity. In conclusion, within the MELOE family, IRES-dependent antigens represent the best T cell targets for immunotherapy of melanoma.

Effect of cilostazol on plasma levels of proprotein convertase subtilisin/kexin type 9

The protein complex proprotein convertase subtilisin/kexin type 9 (PCSK9) serves as an important target for the prevention and treatment of atherosclerosis and lipid homeostasis. This study investigated the effect of cilostazol on plasma PCSK9 concentrations. We performed a post hoc analysis of two prospective, double-blind, randomized controlled trials including 115 patients of whom 61 received cilostazol 200 mg/day and 54 received placebo for 12 weeks. Linear regression analysis was performed to determine the associations between several parameters and changes in PCSK9 levels. Use of cilostazol, but not placebo, significantly increased plasma PCSK9 concentrations, high-density lipoprotein cholesterol levels, and number of circulating endothelial progenitor cells (EPCs), and decreased triglyceride levels with a trend toward an increase in total cholesterol (TC) levels. A reduction in hemoglobin A1C and an increase in plasma vascular endothelial growth factor and adiponectin levels with cilostazol treatment were also found. Changes in the number of circulating EPCs were positively correlated and the TC concentrations were inversely correlated with changes in the PCSK9 levels. After adjusting for changes in levels of TC and numbers of circulating EPCs and history of metabolic syndrome, use of cilostazol remained independently associated with changes in plasma PCSK9 levels. In conclusion, cilostazol treatment was significantly and independently associated with an increase in plasma PCSK9 levels in patients with peripheral artery disease or at a high risk of cardiovascular disease regardless of background statin use and caused an improvement in some metabolic disorders and levels of vasculo-angiogenic biomarkers.

Emerging Therapeutic Options for Lowering of Lipoprotein(a): Implications for Prevention of Cardiovascular Disease

PURPOSE OF REVIEW

Elevated plasma concentrations of lipoprotein(a) (Lp(a)) are an independent and causal risk factor for cardiovascular diseases including coronary artery disease, ischemic stroke, and calcific aortic valve stenosis. This review summarizes the rationale for Lp(a) lowering and surveys relevant clinical trial data using a variety of agents capable of lowering Lp(a).

RECENT FINDINGS

Contemporary guidelines and recommendations outline populations of patients who should be screened for elevated Lp(a) and who might benefit from Lp(a) lowering. Therapies including drugs and apheresis have been described that lower Lp(a) levels modestly (∼20 %) to dramatically (∼80 %). Existing therapies that lower Lp(a) also have beneficial effects on other aspects of the lipid profile, with the exception of Lp(a)-specific apheresis and an antisense oligonucleotide that targets the mRNA encoding apolipoprotein(a). No clinical trials conducted to date have managed to answer the key question of whether Lp(a) lowering confers a benefit in terms of ameliorating cardiovascular risk, although additional outcome trials of therapies that lower Lp(a) are ongoing. It is more likely, however, that Lp(a)-specific agents will provide the most appropriate approach for addressing this question.

Roles of the low density lipoprotein receptor and related receptors in inhibition of lipoprotein(a) internalization by proprotein convertase subtilisin/kexin type 9

Elevated plasma concentrations of lipoprotein(a) (Lp(a)) are a causal risk factor for cardiovascular disease. The mechanisms underlying Lp(a) clearance from plasma remain unclear, which is an obvious barrier to the development of therapies to specifically lower levels of this lipoprotein. Recently, it has been documented that monoclonal antibody inhibitors of proprotein convertase subtilisin/kexin type 9 (PCSK9) can lower plasma Lp(a) levels by 30%. Since PCSK9 acts primarily through the low density lipoprotein receptor (LDLR), this result is in conflict with the prevailing view that the LDLR does not participate in Lp(a) clearance. To support our recent findings in HepG2 cells that the LDLR can act as a bona fide receptor for Lp(a) whose effects are sensitive to PCSK9, we undertook a series of Lp(a) internalization experiments using different hepatic cells, with different variants of PCSK9, and with different members of the LDLR family. We found that PCSK9 decreased Lp(a) and/or apo(a) internalization by Huh7 human hepatoma cells and by primary mouse and human hepatocytes. Overexpression of human LDLR appeared to enhance apo(a)/Lp(a) internalization in both types of primary cells. Importantly, internalization of Lp(a) by LDLR-deficient mouse hepatocytes was not affected by PCSK9, but the effect of PCSK9 was restored upon overexpression of human LDLR. In HepG2 cells, Lp(a) internalization was decreased by gain-of-function mutants of PCSK9 more than by wild-type PCSK9, and a loss-of function variant had a reduced ability to influence Lp(a) internalization. Apo(a) internalization by HepG2 cells was not affected by apo(a) isoform size. Finally, we showed that very low density lipoprotein receptor (VLDLR), LDR-related protein (LRP)-8, and LRP-1 do not play a role in Lp(a) internalization or the effect of PCSK9 on Lp(a) internalization. Our findings are consistent with the idea that PCSK9 inhibits Lp(a) clearance through the LDLR, but do not exclude other effects of PCSK9 such as on Lp(a) biosynthesis.

CETP (Cholesteryl Ester Transfer Protein) Inhibition With Anacetrapib Decreases Production of Lipoprotein(a) in Mildly Hypercholesterolemic Subjects

OBJECTIVE

Lp(a) [lipoprotein (a)] is composed of apoB (apolipoprotein B) and apo(a) [apolipoprotein (a)] and is an independent risk factor for cardiovascular disease and aortic stenosis. In clinical trials, anacetrapib, a CETP (cholesteryl ester transfer protein) inhibitor, causes significant reductions in plasma Lp(a) levels. We conducted an exploratory study to examine the mechanism for Lp(a) lowering by anacetrapib.

APPROACH AND RESULTS

We enrolled 39 participants in a fixed-sequence, double-blind study of the effects of anacetrapib on the metabolism of apoB and high-density lipoproteins. Twenty-nine patients were randomized to atorvastatin 20 mg/d, plus placebo for 4 weeks, and then atorvastatin plus anacetrapib (100 mg/d) for 8 weeks. The other 10 subjects were randomized to double placebo for 4 weeks followed by placebo plus anacetrapib for 8 weeks. We examined the mechanisms of Lp(a) lowering in a subset of 12 subjects having both Lp(a) levels >20 nmol/L and more than a 15% reduction in Lp(a) by the end of anacetrapib treatment. We performed stable isotope kinetic studies using ²H₃-leucine at the end of each treatment to measure apo(a) fractional catabolic rate and production rate. Median baseline Lp(a) levels were 21.5 nmol/L (interquartile range, 9.9-108.1 nmol/L) in the complete cohort (39 subjects) and 52.9 nmol/L (interquartile range, 38.4-121.3 nmol/L) in the subset selected for kinetic studies. Anacetrapib treatment lowered Lp(a) by 34.1% (P≤0.001) and 39.6% in the complete and subset cohort, respectively. The decreases in Lp(a) levels were because of a 41% reduction in the apo(a) production rate, with no effects on apo(a) fractional catabolic rate.

CONCLUSIONS

Anacetrapib reduces Lp(a) levels by decreasing its production.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00990808.

Plasma PCSK9 measurement by liquid chromatography-Tandem mass spectrometry and comparison with conventional ELISA

The combination of liquid chromatography-tandem mass spectrometry (LC-MS/MS) and trypsin proteolysis is an effective tool for accurate quantitation of multiple proteins in a single run. However, expensive samples pre-treatment as immunoenrichment are often required to analyze low abundant proteins. Plasma proprotein convertase subtilisin/kexin type 9 (PCSK9), a circulating regulator of low-density lipoprotein metabolism, was studied as an example of a low abundant plasma protein. We investigated post-proteolysis solid-phase extraction (SPE) as an alternative strategy to improve its detection. After optimization of pretreatment, including denaturation, reduction, alkylation, tryptic digestion and selective SPE concentration, 91±7% of PCSK9 was recovered from human plasma samples and coefficients of variation were less than 13.2% with a lower limit of quantification of 37.5ng/ml. This LC-MS/MS method was compared with standard enzyme-linked immunosorbent assay in 30 human plasma samples with a broad range of PCSK9 concentrations. Both methods were significantly correlated (r=0.936, p<0.001) with less than 7% of the values out of the 95% confidence interval and similar concentrations were measured using either LC-MS/MS or ELISA methods (514.2±217.2 vs. 504.2±231.0ng/ml, respectively- p=NS). This method involving SPE is an effective measurement tool for low abundant plasma protein analysis that could be easily included in multiplexed assays.

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

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

Recent explanatory trials of the mode of action of drug therapies on lipoprotein metabolism

PURPOSE OF REVIEW

Dysregulated lipoprotein metabolism leads to increased plasma concentrations of atherogenic lipoproteins. We highlight the findings from recent studies of the effect of lipid-regulating therapies on apolipoprotein metabolism in humans employing endogenous labelling with stable isotopically labelled isotopomers.

RECENT FINDINGS

Fish oil supplementation and niacin treatment both reduce fasting and postprandial triglyceride levels by decreasing the hepatic secretion of VLDL-apoB-100 (apoB) and apoB-48-containing chylomicron particles in obese and/or type 2 diabetes. Niacin also lowers plasma LDL-apoB and Lp(a) levels by increasing catabolism of LDL-apoB and decreasing secretion of Lp(a), respectively. In subjects with hypercholesterolaemia, inhibition of cholesteryl ester transfer protein raises apoA-I and lowers apoB by decreasing and increasing the catabolism of HDL-apoA-I and LDL-apoB, respectively. Antisense oligonucleotides directed at apoB mRNA lowers plasma LDL-cholesterol and apoB chiefly by increasing the catabolism and decreasing the secretion of LDL-apoB in healthy subjects. That apoB ASO treatment does not lower hepatic secretion in humans is unexpected and merits further investigation.

SUMMARY

Kinetic studies provide mechanistic insight into the mode of action of lipid lowering therapies and lipoprotein disorders. Understanding the mode of action of new drugs in vivo is important to establish their effective use in clinical practice.

Lipoprotein(a) in postmenopausal women: assessment of cardiovascular risk and therapeutic options

INTRODUCTION

Lipoprotein(a) [Lp(a)], a low-density lipoprotein (LDL)-like particle, has been independently associated with increased cardiovascular disease (CVD) risk in various populations, such as postmenopausal women. The purpose of this narrative review is to present current data on the role of Lp(a) in augmenting CVD risk in postmenopausal women and focus on the available therapeutic strategies.

METHODS

PubMed was searched for English language publications until November 2015 under the following terms: "therapy" OR "treatment" AND ["lipoprotein (a)" OR "Lp(a)"] AND ("postmenopausal women" OR "menopausal women" OR "menopause").

RESULTS

Only hormone replacement therapy (mainly oral estrogens) and tibolone have been specifically studied in postmenopausal women and can reduce Lp(a) concentrations by up to 44%, although evidence indicating a concomitant reduction in CVD risk associated with Lp(a) is lacking. As alternative treatments for women who cannot, or will not, take hormonal therapies, niacin and the upcoming proprotein convertase subtilisin / kexin type 9 (PCSK-9) inhibitors are effective in reducing Lp(a) concentrations by up to 30%. Statins have minimal or no effect on Lp(a). However, data for these and other promising Lp(a)-lowering therapies including mipomersen, lomitapide, cholesterol-ester-transfer protein inhibitors and eprotirome are derived from studies in the general, mainly high CVD risk, population, and include only subpopulations of postmenopausal women.

CONCLUSIONS

Past, present and emerging therapies can reduce Lp(a) concentrations to a varying extent. Overall, it remains to be proven whether the aforementioned reductions in Lp(a) by these therapeutic options are translated into CVD risk reduction in postmenopausal women.

PCSK9 Modulates the Secretion But Not the Cellular Uptake of Lipoprotein(a) Ex Vivo: An Effect Blunted by Alirocumab

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Unlike LDL uptake, Lp(a) uptake is not altered by PCSK9 or PCSK9 inhibition in primary human hepatocytes and in primary dermal fibroblasts isolated from familial hypercholesterolemic and non–familial hypercholesterolemic patients.

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Lp(a) uptake is occurring in the absence of a functional LDL receptor and is not affected by LDL receptor blockade with monoclonal antibodies.

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Lp(a) cellular binding and whole particle uptake are not altered by PCSK9.

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The secretion of Lp(a) from primary human hepatocytes is enhanced by PCSK9, an effect that is blunted by PCSK9 inhibition with alirocumab.

To elucidate how the proprotein convertase subtilisin kexin type 9 (PCSK9) inhibitor alirocumab modulates lipoprotein(a) [Lp(a)] plasma levels, the authors performed a series of Lp(a) uptake studies in primary human hepatocytes and dermal fibroblasts and measured Lp(a) secretion from human hepatocytes. They found that Lp(a) cellular uptake occurred in a low-density lipoprotein receptor–independent manner. Neither PCSK9 nor alirocumab altered Lp(a) internalization. By contrast, the secretion of apolipoprotein (a) from human hepatocytes was sharply increased by PCSK9, an effect that was reversed by alirocumab. They propose that PCSK9 does not significantly modulate Lp(a) catabolism, but rather enhances the secretion of Lp(a) from liver cells.

PCSK9 and lipoprotein (a) levels are two predictors of coronary artery calcification in asymptomatic patients with familial hypercholesterolemia

BACKGROUND AND AIMS

We aimed to assess whether elevated PCSK9 and lipoprotein (a) [Lp(a)] levels associate with coronary artery calcification (CAC), a good marker of atherosclerosis burden, in asymptomatic familial hypercholesterolemia.

METHODS

We selected 161 molecularly defined FH patients treated with stable doses of statins for more than a year. CAC was measured using the Agatston method and quantified as categorical variable. Fasting plasma samples were collected and analyzed for lipids and lipoproteins. PCSK9 was measured by ELISA, Lp(a) and apolipoprotein (a) concentrations by inmunoturbidimetry and LC-MS/MS, respectively.

RESULTS

Circulating PCSK9 levels were significantly reduced in patients without CAC (n = 63), compared to those with CAC (n = 99). Patients with the highest CAC scores (above 100) had the highest levels of circulating PCSK9 and Lp(a). In multivariable regression analyses, the main predictors for a positive CAC score was age and sex followed by circulating PCSK9 and Lp(a) levels.

CONCLUSIONS

In statin treated asymptomatic FH patients, elevated PCSK9 and Lp(a) levels are independently associated with the presence and severity of CAC, a good predictor of coronary artery disease.

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.

Multiplexed peptide analysis for kinetic measurements of major human apolipoproteins by LC/MS/MS

A multiplexed assay was developed by MS to analyze, in a single run, six major human Apos involved in lipoprotein metabolism: ApoA-I, ApoA-II, ApoB100, ApoC-II, ApoC-III, and ApoE. This method was validated in vivo in six subjects who received a 14 h constant infusion of [5,5,5-(2)H3]L-leucine at 10 μM/kg/h. Plasma lipoprotein fractions were isolated from collected blood samples and were digested with trypsin. Proteotypic peptides were subsequently analyzed by LC/MS/MS. Enrichment measurement data were compared with those obtained by the standard method using GC/MS. The required time to obtain the LC/MS/MS data was less than that needed for GC/MS. The enrichments from both methods were correlated for ApoA-I (r = 0.994; P < 0.0001) and ApoB100 (r = 0.999; P < 0.0001), and the Bland-Altman plot confirmed the similarity of the two methods. Intra- and inter-assay variability calculated for the six Apos of interest did not exceed 10.7 and 12.5%, respectively, and kinetic parameters were similar and/or in agreement with previously reported data. Therefore, LC/MS/MS can be considered as a useful tool for human Apo kinetic studies using stable isotopes.

Current therapies for lowering lipoprotein (a)

Lipoprotein (a) [Lp(a)] is a human plasma lipoprotein with unique structural and functional characteristics. Lp(a) is an assembly of two components: a central core with apoB and an additional glycoprotein, called apo(a). Ever since the strong association between elevated levels of Lp(a) and an increased risk for CVD was recognized, interest in the therapeutic modulation of Lp(a) levels has increased. Here, the past and present therapies aiming to lower Lp(a) levels will be reviewed, demonstrating that these agents have had varying degrees of success. The next challenge will be to prove that Lp(a) lowering also leads to cardiovascular benefit in patients with elevated Lp(a) levels. Therefore, highly specific and potent Lp(a)-lowering strategies are awaited urgently.

Effects of extended-release niacin on the postprandial metabolism of Lp(a) and ApoB-100-containing lipoproteins in statin-treated men with type 2 diabetes mellitus

OBJECTIVE

The effects of extended-release niacin (ERN; 1-2 g/d) on the metabolism of lipoprotein(a) (Lp(a)) and apolipoprotein (apo) B-100-containing lipoproteins were investigated in 11 statin-treated white men with type 2 diabetes mellitus in a randomized, crossover trial of 12-weeks duration.

APPROACH AND RESULTS

The kinetics of Lp(a) and very low-density lipoprotein (VLDL), intermediate-density lipoprotein, and low-density lipoprotein (LDL) apoB-100 were determined following a standardized oral fat load (87% fat) using intravenous administration of D3-leucine, gas chromatography-mass spectrometry, and compartmental modeling. ERN significantly decreased fasting plasma total cholesterol, LDL cholesterol, and triglyceride concentrations. These effects were achieved without significant changes in body weight or insulin resistance. ERN significantly decreased plasma Lp(a) concentration (-26.5%) and the production rates of apo(a) (-41.5%) and Lp(a)-apoB-100 (-32.1%); the effect was greater in individuals with elevated Lp(a) concentration. ERN significantly decreased VLDL (-58.7%), intermediate-density lipoprotein (-33.6%), and LDL (-18.3%) apoB-100 concentrations and the corresponding production rates (VLDL, -49.8%; intermediate-density lipoprotein, -44.7%; LDL, -46.1%). The number of VLDL apoB-100 particles secreted increased in response to the oral fat load. Despite this, total VLDL apoB-100 production over the 10-hour postprandial period was significantly decreased with ERN (-21.9%).

CONCLUSIONS

In statin-treated men with type 2 diabetes mellitus, ERN decreased plasma Lp(a) concentrations by decreasing the production of apo(a) and Lp(a)-apoB-100. ERN also decreased the concentrations of apoB-100-containing lipoproteins by decreasing VLDL production and the transport of these particles down the VLDL to LDL cascade. Our study provides further mechanistic insights into the lipid-regulating effects of ERN.