Lipoprotein(a) (Lp(a)) is a low-density lipoprotein (LDL)-like particle in which the apolipoprotein B component is covalently linked to apolipoprotein(a) (apo(a)). Lp(a) is a well-established independent risk factor for cardiovascular diseases. Plasma Lp(a) concentrations vary enormously between individuals and ethnic groups. Several nucleotide polymorphisms in the SLC22A3 gene associate with Lp(a) concentration in people of different ethnicities. We investigated the association of a Polynesian-specific (Māori and Pacific peoples) SLC22A3 gene coding variant p.Thr44Met) with the plasma concentration of Lp(a) in a cohort of 302 healthy Polynesian males. An apo(a)-size independent assay assessed plasma Lp(a) concentrations; all other lipid and apolipoprotein concentrations were measured using standard laboratory techniques. Quantitative real-time polymerase chain reaction was used to determine apo(a) isoforms. The range of metabolic (HbA1c, blood pressure, and blood lipids) and blood lipid variables were similar between the non-carriers and carriers in age, ethnicity and BMI adjusted models. However, rs8187715 SLC22A3 variant was significantly associated with lower Lp(a) concentrations. Median Lp(a) concentration was 10.60 nmol/L (IQR: 5.40-41.00) in non-carrier group, and was 7.60 nmol/L (IQR: 5.50-12.10) in variant carrier group (P<0.05). Lp(a) concentration inversely correlated with apo(a) isoform size. After correction for apo(a) isoform size, metabolic parameters and ethnicity, the association between the SLC22A3 variant and plasma Lp(a) concentration remained. The present study is the first to identify the association of this gene variant and low plasma Lp(a) concentrations. This provides evidence for better guidance on ethnic specific cut-offs when defining \'elevated\' and \'normal\' plasma Lp(a) concentrations in clinical applications.

Platelets are small anucleate cells that play a key role in thrombosis and hemostasis. Our group previously identified apolipoprotein A-IV (apoA-IV) as an endogenous inhibitor of thrombosis by competitive blockade of the αIIbβ3 integrin on platelets. ApoA-IV inhibition of platelets was dependent on the N-terminal D5/D13 residues, and enhanced with absence of the C-terminus, suggesting it sterically hinders its N-terminal platelet binding site. The C-terminus is also the site of common apoA-IV polymorphisms apoA-IV-1a (T347S) and apoA-IV-2 (Q360H). Interestingly, both are linked with an increased risk of cardiovascular disease, however, the underlying mechanism remains unclear. Here, we generated recombinant apoA-IV and found that the Q360H or T347S polymorphisms dampened its inhibition of platelet aggregation in human platelet-rich plasma and gel-filtered platelets, reduced its inhibition of platelet spreading, and its inhibition of P-selectin on activated platelets. Using an ex vivo thrombosis assay, we found that Q360H and T347S attenuated its inhibition of thrombosis at both high (1800s-1) and low (300s-1) shear rates. We then demonstrate a conserved monomer-dimer distribution among apoA-IV WT, Q360H, and T347S and use protein structure modelling software to show Q360H and T347S enhance C-terminal steric hindrance over the N-terminal platelet-binding site. These data provide critical insight into increased cardiovascular risk for individuals with Q360H or T347S polymorphisms.

Lipoprotein(a) [Lp(a)] consists of a low-density lipoprotein-like molecule and an apolipoprotein(a) [apo(a)] particle. Lp(a) has been suggested to be an independent risk factor of atherosclerotic cardiovascular disease (ASCVD). Lp(a) plasma levels are considered to be 70-90% genetically determined through the codominant expression of the LPA gene. Therefore, Lp(a) levels are almost stable during an individual\'s lifetime. This lifelong stability, together with the difficulties in measuring Lp(a) levels in a standardized manner, may account for the scarcity of available drugs targeting Lp(a). In this review, we synopsize the latest data regarding the structure, metabolism, and factors affecting circulating levels of Lp(a), as well as the laboratory determination measurement of Lp(a), its role in the pathogenesis of ASCVD and thrombosis, and the potential use of various therapeutic agents targeting Lp(a). In particular, we discuss novel agents, such as antisense oligonucleotides (ASOs) and small interfering RNAs (siRNAs) that are currently being developed and target Lp(a). The promising role of muvalaplin, an oral inhibitor of Lp(a) formation, is then further analyzed.

OBJECTIVE: High plasma lipoprotein (a) [Lp(a)] levels are associated with increased atherosclerotic cardiovascular disease (ASCVD), in part attributed to elevated inflammation. High plasma Lp(a) levels inversely correlate with apolipoprotein (a) [(APO(a)] isoform size. APO(a) isoform size is negatively associated with APO(a) production rate (PR) and positively associated with APO(a) fractional catabolic rate (FCR). We asked whether APO(a) PR and FCR (kinetics) are associated with plasma levels of interleukin (IL)-6 and IL-18, pro-inflammatory interleukins that promote ASCVD.
METHODS: We used samples from existing data of APO(a) kinetic studies from an ethnically diverse cohort (n = 25: 10 Black, 9 Hispanic, and 6 White subjects) and assessed IL-6 and IL-18 plasma levels. We performed multivariate linear regression analyses to examine the relationships between predictors APO(a) PR or APO(a) FCR, and outcome variables IL-6 or IL-18. In these analyses, we adjusted for parameters known to affect Lp(a) levels and APO(a) PR and FCR, including race/ethnicity and APO(a) isoform size.
RESULTS: APO(a) PR and FCR were positively associated with plasma IL-6, independent of isoform size, and dependent on race/ethnicity. APO(a) PR was positively associated with plasma IL-18, independent of isoform size and race/ethnicity. APO(a) FCR was not associated with plasma IL-18.
CONCLUSIONS: Our studies demonstrate a relationship between APO(a) PR and FCR and plasma IL-6 or IL-18, interleukins that promote ASCVD. These studies provide new insights into Lp(a) pro-inflammatory properties and are especially relevant in view of therapies targeting APO(a) to decrease cardiovascular risk.

Lipoprotein(a) [Lp(a)] is a well-established risk factor for cardiovascular disease, predisposing to major cardiovascular events, including coronary heart disease, stroke, aortic valve calcification and abdominal aortic aneurysm. Lp(a) is differentiated from other lipoprotein molecules through apolipoprotein(a), which possesses atherogenic and antithrombolytic properties attributed to its structure. Lp(a) levels are mostly genetically predetermined and influenced by the size of LPA gene variants, with smaller isoforms resulting in a greater synthesis rate of apo(a) and, ultimately, elevated Lp(a) levels. As a result, serum Lp(a) levels may highly vary from extremely low to extremely high. Hyperlipoproteinemia(a) is defined as Lp(a) levels > 30 mg/dL in the US and >50 mg/dL in Europe. Because of its association with CVD, Lp(a) levels should be measured at least once a lifetime in adults. The ultimate goal is to identify individuals with increased risk of CVD and intervene accordingly. Traditional pharmacological interventions like niacin, statins, ezetimibe, aspirin, PCSK-9 inhibitors, mipomersen, estrogens and CETP inhibitors have not yet yielded satisfactory results. The mean Lp(a) reduction, if any, is barely 50% for all agents, with statins increasing Lp(a) levels, whereas a reduction of 80-90% appears to be required to achieve a significant decrease in major cardiovascular events. Novel RNA-interfering agents that specifically target hepatocytes are aimed in this direction. Pelacarsen is an antisense oligonucleotide, while olpasiran, LY3819469 and SLN360 are small interfering RNAs, all conjugated with a N-acetylgalactosamine molecule. Their ultimate objective is to genetically silence LPA, reduce apo(a) production and lower serum Lp(a) levels. Evidence thus so far demonstrates that monthly subcutaneous administration of a single dose yields optimal results with persisting substantial reductions in Lp(a) levels, potentially enhancing CVD risk reduction. The Lp(a) reduction achieved with novel RNA agents may exceed 95%. The results of ongoing and future clinical trials are eagerly anticipated, and it is hoped that guidelines for the tailored management of Lp(a) levels with these novel agents may not be far off.

UNASSIGNED: Patients with COVID-19 have a higher risk of thrombosis and thromboembolism, but the underlying mechanism(s) remain to be fully elucidated. In patients with COVID-19, high lipoprotein(a) (Lp(a)) is positively associated with the risk of ischemic heart disease. Lp(a), composed of an apoB-containing particle and apolipoprotein(a) (apo(a)), inhibits the key fibrinolytic enzyme, tissue-type plasminogen activator (tPA). However, whether the higher Lp(a) associates with lower tPA activity, the longitudinal changes of these parameters in hospitalized patients with COVID-19, and their correlation with clinical outcomes are unknown.
UNASSIGNED: To assess if Lp(a) associates with lower tPA activity in COVID-19 patients, and how in COVID-19 populations Lp(a) and tPA change post infection.
UNASSIGNED: Endogenous tPA enzymatic activity, tPA or Lp(a) concentration were measured in plasma from hospitalized patients with and without COVID-19. The association between plasma tPA and adverse clinical outcomes was assessed.
UNASSIGNED: In hospitalized patients with COVID-19, we found lower tPA enzymatic activity and higher plasma Lp(a) than that in non-COVID-19 controls. During hospitalization, Lp(a) increased and tPA activity decreased, which associates with mortality. Among those who survived, Lp(a) decreased and tPA enzymatic activity increased during recovery. In patients with COVID-19, tPA activity is inversely correlated with tPA concentrations, thus, in another larger COVID-19 cohort, we utilized plasma tPA concentration as a surrogate to inversely reflect tPA activity. The tPA concentration was positively associated with death, disease severity, plasma inflammatory, and prothrombotic markers, and with length of hospitalization among those who were discharged.
UNASSIGNED: High Lp(a) concentration provides a possible explanation for low endogenous tPA enzymatic activity, and poor clinical outcomes in patients with COVID-19.

Lipoprotein(a) (Lp[a]) is associated with atherosclerotic disease and aortic stenosis. Lp(a) forms by bonding between apolipoprotein(a) (apo[a]) and apo B100. Muvalaplin is an orally administered small molecule that inhibits Lp(a) formation by blocking the apo(a)-apo B100 interaction while avoiding interaction with a homologous protein, plasminogen.
To determine the safety, tolerability, pharmacokinetics, and pharmacodynamic effects of muvalaplin.
This phase 1 randomized, double-blind, parallel-design study enrolled 114 participants (55 assigned to a single-ascending dose; 59 assigned to a multiple-ascending dose group) at 1 site in the Netherlands.
The single ascending dose treatment evaluated the effect of a single dose of muvalaplin ranging from 1 mg to 800 mg or placebo taken by healthy participants with any Lp(a) level. The multiple ascending dose treatment evaluated the effect of taking daily doses of muvalaplin (30 mg to 800 mg) or placebo for 14 days in patients with Lp(a) levels of 30 mg/dL or higher.
Outcomes included safety, tolerability, pharmacokinetics, and exploratory pharmacodynamic biomarkers.
Among 114 randomized (55 in the single ascending dose group: mean [SD] age, 29 [10] years, 35 females [64%], 2 American Indian or Alaska Native [4%], 50 White [91%], 3 multiracial [5%]; 59 in the multiple ascending dose group: mean [SD] age 32 [15] years; 34 females [58%]; 3 American Indian or Alaska Native [5%], 6 Black [10%], 47 White [80%], 3 multiracial [5%]), 105 completed the trial. Muvalaplin was not associated with tolerability concerns or clinically significant adverse effects. Oral doses of 30 mg to 800 mg for 14 days resulted in increasing muvalaplin plasma concentrations and half-life ranging from 70 to 414 hours. Muvalaplin lowered Lp(a) plasma levels within 24 hours after the first dose, with further Lp(a) reduction on repeated dosing. Maximum placebo-adjusted Lp(a) reduction was 63% to 65%, resulting in Lp(a) plasma levels less than 50 mg/dL in 93% of participants, with similar effects at daily doses of 100 mg or more. No clinically significant changes in plasminogen levels or activity were observed.
Muvalaplin, a selective small molecule inhibitor of Lp(a) formation, was not associated with tolerability concerns and lowered Lp(a) levels up to 65% following daily administration for 14 days. Longer and larger trials will be required to further evaluate safety, tolerability, and effect of muvalaplin on Lp(a) levels and cardiovascular outcomes.
ClinicalTrials.gov Identifier: NCT04472676.

High levels of Lp(a) (lipoprotein(a)) are associated with multiple forms of cardiovascular disease. Lp(a) consists of an apoB100-containing particle attached to the plasminogen homologue apo(a). The pathways for Lp(a) clearance are not well understood. We previously discovered that the plasminogen receptor PlgRKT (plasminogen receptor with a C-terminal lysine) promoted Lp(a) uptake in liver cells. Here, we aimed to further define the role of PlgRKT and to investigate the role of 2 other plasminogen receptors, annexin A2 and S100A10 (S100 calcium-binding protein A10) in the endocytosis of Lp(a).
Human hepatocellular carcinoma (HepG2) cells and haploid human fibroblast-like (HAP1) cells were used for overexpression and knockout of plasminogen receptors. The uptake of Lp(a), LDL (low-density lipoprotein), apo(a), and endocytic cargos was visualized and quantified by confocal microscopy and Western blotting.
The uptake of both Lp(a) and apo(a), but not LDL, was significantly increased in HepG2 and HAP1 cells overexpressing PlgRKT, annexin A2, or S100A10. Conversely, Lp(a) and apo(a), but not LDL, uptake was significantly reduced in HAP1 cells in which PlgRKT and S100A10 were knocked out. Surface binding studies in HepG2 cells showed that overexpression of PlgRKT, but not annexin A2 or S100A10, increased Lp(a) and apo(a) plasma membrane binding. Annexin A2 and S100A10, on the other hand, appeared to regulate macropinocytosis with both proteins significantly increasing the uptake of the macropinocytosis marker dextran when overexpressed in HepG2 and HAP1 cells and knockout of S100A10 significantly reducing dextran uptake. Bringing these observations together, we tested the effect of a PI3K (phosphoinositide-3-kinase) inhibitor, known to inhibit macropinocytosis, on Lp(a) uptake. Results showed a concentration-dependent reduction confirming that Lp(a) uptake was indeed mediated by macropinocytosis.
These findings uncover a novel pathway for Lp(a) endocytosis involving multiple plasminogen receptors that enhance surface binding and stimulate macropinocytosis of Lp(a). Although the findings were produced in cell culture models that have limitations, they could have clinical relevance since drugs that inhibit macropinocytosis are in clinical use, that is, the PI3K inhibitors for cancer therapy and some antidepressant compounds.

Lipoprotein(a) is a complex lipoprotein with unique characteristics distinguishing it from all the other apolipoprotein B-containing lipoprotein particles. Its lipid composition and the presence of a single molecule of apolipoprotein B per particle, render lipoprotein(a) similar to low-density lipoproteins. However, the presence of a unique, carbohydrate-rich protein termed apolipoprotein(a), linked by a covalent bond to apolipoprotein B imparts unique characteristics to lipoprotein(a) distinguishing it from all the other lipoproteins. Apolipoprotein(a) is highly polymorphic in size ranging in molecular weight from <300 KDa to >800 kDa. Both the size polymorphism and the concentration of lipoprotein(a) in plasma are genetically determined and unlike other lipoproteins, plasma concentration is minimally impacted by lifestyle modifications or lipid-lowering drugs. Many studies involving hundreds of thousands of individuals have provided strong evidence that elevated lipoprotein(a) is genetically determined and a causal risk factor for atherosclerotic cardiovascular disease. The concentration attained in adulthood is already present in children at around 5 years of age and therefore, those with elevated lipoprotein(a) are prematurely exposed to a high risk of cardiovascular disease. Despite the large number of guidelines and consensus statements on the management of lipoprotein(a) in atherosclerotic cardiovascular disease published in the last decade, lipoprotein(a) is still seldom measured in clinical settings. In this review, we provide an overview of the most important features that characterize lipoprotein(a), its role in cardiovascular disease, and the importance of adding the measurement of lipoprotein(a) for screening adults and youths to identify those at increased risk of atherosclerotic cardiovascular disease due to their elevated plasma concentration of lipoprotein(a).

Despite increased clinical interest in lipoprotein(a) (Lp(a)), many questions remain about the molecular mechanisms by which it contributes to atherosclerotic cardiovascular disease. Existing murine transgenic (Tg) Lp(a) models are limited by low plasma levels of Lp(a) and have not consistently shown a pro-atherosclerotic effect of Lp(a).
We generated Tg mice expressing both human apolipoprotein(a) (apo(a)) and human apoB-100, with pathogenic levels of plasma Lp(a) (range 87-250 mg/dL). Female and male Lp(a) Tg mice (Tg(LPA+/0;APOB+/0)) and human apoB-100-only controls (Tg(APOB+/0)) (n = 10-13/group) were fed a high-fat, high-cholesterol diet for 12 weeks, with Ldlr knocked down using an antisense oligonucleotide. FPLC was used to characterize plasma lipoprotein profiles. Plaque area and necrotic core size were quantified and immunohistochemical assessment of lesions using a variety of cellular and protein markers was performed.
Male and female Tg(LPA+/0;APOB+/0) and Tg(APOB+/0) mice exhibited proatherogenic lipoprotein profiles with increased cholesterol-rich VLDL and LDL-sized particles and no difference in plasma total cholesterol between genotypes. Complex lesions developed in the aortic sinus of all mice. Plaque area (+22%), necrotic core size (+25%), and calcified area (+65%) were all significantly increased in female Tg(LPA+/0;APOB+/0) mice compared to female Tg(APOB+/0) mice. Immunohistochemistry of lesions demonstrated that apo(a) deposited in a similar pattern as apoB-100 in Tg(LPA+/0;APOB+/0) mice. Furthermore, female Tg(LPA+/0;APOB+/0) mice exhibited less organized collagen deposition as well as 42% higher staining for oxidized phospholipids (OxPL) compared to female Tg(APOB+/0) mice. Tg(LPA+/0;APOB+/0) mice had dramatically higher levels of plasma OxPL-apo(a) and OxPL-apoB compared to Tg(APOB+/0) mice, and female Tg(LPA+/0;APOB+/0) mice had higher plasma levels of the proinflammatory cytokine MCP-1 (+3.1-fold) compared to female Tg(APOB+/0) mice.
These data suggest a pro-inflammatory phenotype exhibited by female Tg mice expressing Lp(a) that appears to contribute to the development of more severe lesions with greater vulnerable features.