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

Authors, Journal, Affiliations, Type, DOI

• Stamatios Lampsas, Maria Xenou, Evangelos Oikonomou (corresponding), Pantelidis P, Lysandrou A, Sarantos S, Goliopoulou A, Kalogeras K, Tsigkou V, Kalpis A, Paschou SA, Theofilis P, Vavuranakis M, Tousoulis D, Siasos G
• Molecules 2023; 28(3):969 (MDPI, open access)
• 3rd Department of Cardiology, National and Kapodistrian University of Athens / Sotiria Chest Disease Hospital; 1st Department of Cardiology, NKUA / Hippokration General Hospital; Cardiovascular Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA
• Narrative review
• DOI: https://doi.org/10.3390/molecules28030969

Overview

This 30-page multi-author narrative review from Greek cardiology groups provides comprehensive coverage of Lp(a) molecular mechanisms across vascular inflammation, atherosclerosis, endothelial dysfunction, and thrombogenicity. The review's primary contribution relative to other Lp(a) reviews is detailed molecular mechanistic coverage: platelet GPIIb/IIIa interaction via the RGD epitope of apo(a), tissue factor upregulation via Mac-1/NF-κB, TFPI inhibition (lysine-dependent), PAI-1 upregulation, endothelial barrier disruption via Rho/Rho-kinase pathway, EPC impairment, and MMP-12-mediated Lp(a) fragmentation. The treatment section largely recapitulates data from Tsimikas 2017 and does not include data on pelacarsen, olpasiran, or zerlasiran (pre-publication). No primary data; published in a lower-impact MDPI journal by a non-specialist Lp(a) research group.

Keywords

Lipoprotein(a), Lp(a), genetic variations, atherosclerotic disease, cardiovascular disease, thrombosis, inflammation, treatment

Key Takeaways

Section 2: Structure, Genetics, and LPA Gene Variations

• Lp(a) = LDL-like lipid core + apoB-100 + apo(a) via single disulfide bond; assembly site uncertain (intracellular / cell surface / extracellular); exclusively hepatic synthesis (minor: testes, brain, lung, adrenals, pituitary)
• Apo(a) 400–700 kDa; KIV2 copy variable (1 to >40 copies); fewer KIV2 → smaller apo(a) → higher Lp(a) production rate; apo(a) size heterogeneity also driven by SNPs affecting RNA splicing and 5' UTR translation initiation
• Smaller apo(a) isoforms specifically: (1) increased capacity for bound OxPLs; (2) increased lysine-binding to fibrin and vessel walls; (3) greater inhibition of plasmin activity → greater thrombogenicity; (4) synergistic action with small-dense LDL and OxLDL
• LPA gene at chromosome 6q26–27, 70% homology with plasminogen gene; two key CVD-associated SNPs: rs3798220 and rs10455872 (both independently increase Lp(a) levels and CVD risk); LPA SNPs rs783147/rs3798220/rs10455872 also associated with increased CIMT and impaired endothelial function

Section 3: Measurement and Standardization

• Mass measurement (mg/dL) inherently more variable than molar (nmol/L) due to apo(a) size heterogeneity; two individuals with the same nmol/L concentration may have substantially different mg/dL values
• Cannot accurately convert mg/dL to nmol/L; a rough 2–2.5× conversion factor has been proposed but yields inaccurate results and should not be used for clinical decisions
• Commercial kits measuring mg/dL remain widely encountered despite limitations; clinical practice and published literature still use both units inconsistently
• ESC/EAS 2016: at least once-lifetime measurement recommended, especially in high-risk populations (ESC Class IIa C)

Section 4: Role of Lp(a) on Atherosclerosis

4.1. Arterial Wall Attachment

• Lp(a) accumulates in intima/subintima more than LDL (relative apo(a)/apoB amounts in early plaques confirm this)
• Decorin binding: 2-part interaction — (1) electrostatic bond between apoB-100 and glycosaminoglycan (GAG) chain of decorin; (2) hydrophobic bond between apo(a) and decorin's protein core — the second interaction explains greater arterial wall affinity of Lp(a) vs LDL
• Alpha-defensins (neutrophil-derived, present in atherosclerotic plaques) cluster with Lp(a) extracellularly — one mechanism preventing Lp(a) endothelial cell traversal and maintaining subendothelial retention
• KIV10 lysine-binding sites critical for arterial retention (transgenic mice with KIV10 mutation → decreased vessel wall Lp(a))
• Foam cell formation: fibronectin interaction (Lp(a)-fibronectin → macrophage internalization); calcium-dependent macrophage internalization (independent of LDL-R, scavenger, LRP, or plasminogen receptors); sphingomyelinase + lipoprotein lipase drive Lp(a)/LDL adhesion to SMCs and ECM

4.2. Adhesion Molecules and Cytokines

• VCAM-1 and E-selectin upregulated in human coronary endothelial cells by Lp(a)
• ICAM-1 upregulated in human umbilical vein endothelial cells; partly via TGF-β inhibition by Lp(a)
• Mac-1 (β2-integrin) + Lp(a) → monocyte attachment and infiltration via NF-κB activation
• MCP-1: Lp(a) binds OxPLs directly to MCP-1 AND induces MCP-1 production in endothelial cells; cGMP-driven chemotaxis independent of MCP-1 also demonstrated
• IL-8: released from THP-1 macrophages via C-terminal apo(a)/OxPL-KIV10 interaction; IL-8 subsequently promotes neutrophil infiltration AND downregulates TIMP → MMP-mediated ECM degradation
• IL-1β, TNF-α, IL-6 also induced by Lp(a) in macrophages; IL-6 feedback increases LPA gene expression; TGF-β and TNF-α feedback decreases LPA expression — dynamic regulation
• I-309 chemotactic factor production induced in HUVECs by Lp(a)

4.3. OxPL Effects — Dose-Dependent Bidirectionality

• At low Lp(a) levels: anti-inflammatory — removes OxPLs from plasma (OxPLs as DAMPs); Lp-PLA2 (PAF-acetylhydrolase) on Lp(a) converts OxPLs to oxidized fatty acids + lysoPC, reducing concentration
• At high Lp(a) levels: pro-inflammatory — excessive OxPL delivery to arterial wall; OxPLs on apo(a) compete for Lp-PLA2 catalytic site → autocrine loop amplifying OxPL accumulation
• This dose-dependent bidirectionality may partly explain why the relationship between Lp(a) and ASCVD risk is curvilinear

4.4. VSMC Effects

• Lp(a) promotes VSMC proliferation by blocking plasminogen → plasmin conversion → impairs plasmin-mediated TGF-β activation (TGF-β is an autocrine inhibitor of SMC growth)
• Apo(a) also induces concentration-dependent chemorepulsion in SMC via RhoA and integrin αVβ3 (TGF-β-independent)
• Calcifying extracellular vesicles from SMC and valvular interstitial cells: one study links high Lp(a) to partially mediating VIC/SMC calcification via EVs

4.5. Plaque Vulnerability

• MMP-12 cleaves Lp(a) into fragments F1 and F2; F2 (not F1) interacts with fibrinogen, fibronectin, and decorin — key molecules in atherogenesis
• IL-8 downregulates TIMPs → enhanced MMP activity → ECM degradation (amplified by Lp(a)-driven IL-8 release)
• OxPL-apo(a) → ER-stressed macrophage apoptosis → plaque necrosis (autophagy/apoptosis pathway)
• Lp(a) upregulates urokinase and urokinase receptors on monocytes → plasmin activation → ECM shrinkage

Section 5: Lp(a) in Inflammation

• Monocyte skewing to pro-inflammatory M1 phenotype; apo(a) (OxPL-binding site) facilitates adhesion to type I collagen + MMP-9 production → collagen degradation + macrophage infiltration
• M1 macrophages under Lp(a) release CXCL10 (IP10) → Th1 and NK cell activation
• Autotaxin mechanism for NF-κB: autotaxin converts lysophosphatidylcholine (OxPL component) → lysophosphatidic acid → NF-κB activation (distinct pathway from Mac-1-mediated NF-κB activation)
• In apo(a) transgenic mice: apo(a) paradoxically inhibits neutrophil recruitment (reduces CXCL1, CXCL2, MIP-2) — suggests complex differential effects on neutrophil vs monocyte chemotaxis

Section 6: Lp(a) on Endothelial Function

• ROS generation and senescence: Lp(a) accelerates endothelial cell senescence; generates ROS in human aortic endothelial cells; upregulates p53 and p21 (cell-cycle arrest mediators)
• Barrier disruption: ROS produced in Lp(a)'s presence increases endothelial monolayer permeability
• Rho/Rho-kinase pathway: apo(a) via Rho/ROCK → myosin light chain phosphorylation → actin cytoskeleton rearrangement → endothelial cell contraction → loss of cell contact (structural barrier breakdown)
• EPC impairment: apo(a) attenuates EPC adhesion and migration; reduces CD31+ capillary formation; inhibits ischemic limb perfusion improvement in vivo
• Anti-angiogenesis: full-length and urinary fragments of apo(a) halt capillary tube generation; apo(a) induces endothelial cell apoptosis; modifies nuclear factors via OxPLs
• FMD inverse correlation: Lp(a) inversely correlated with flow-mediated dilation (r = −0.33, p<0.005) in multiethnic study; small apo(a) isoforms ≤22 KIV repeats → significantly lower FMD independent of Lp(a) concentration — suggesting isoform size has endothelial effects beyond Lp(a) level

Section 7: Thrombogenicity

7.1. Platelet Activation and Aggregation

• Apo(a) contains an RGD (Arg-Gly-Asp) epitope that binds GPIIb/IIIa on platelets → platelet activation and aggregation via cAMP-dependent mechanism
• Additional dispute in literature: separate report suggests platelet interaction does not require lysine-binding sites of apo(a) — GPIIb/IIIa pathway dominant
• Correlation between arachidonic acid-induced aggregation rate and Lp(a) demonstrated in cross-sectional studies

7.2. Tissue Factor

• Lp(a) and r-apo(a) upregulate tissue factor (TF) on monocytes via αMβ2 (Mac-1)/NF-κB pathway
• Lp(a) binds and inhibits TFPI (tissue factor pathway inhibitor) in a lysine-dependent manner — dual TF upregulation + TFPI inhibition → amplified extrinsic coagulation cascade
• Case-control data (167 CAD patients): serum Lp(a) and total TFPI positively correlated in CAD (Lp(a)-TFPI complex formation); patients with higher Lp(a) had reduced TFPI antigen levels but similar TFPI activity

7.3. Fibrinolysis Inhibition

• Apo(a) competes with plasminogen for lysine-binding sites on fibrin surface → quaternary complex formation → reduced tPA turnover → impaired fibrinolysis
• Inverse relationship between plasma Lp(a) concentration and rate of plasmin formation (dose-dependent in purified system; LDL had no effect)
• PAI-1 upregulation (positive correlation between Lp(a) and PAI-1; correlation with CRP, IL-6, D-dimer, fibrinogen, vWF also demonstrated)
• Fibrin clot tightening: Lp(a) ≥30 mg/dL → lower fibrin clot permeability vs Lp(a) <30 mg/dL; haplotypes with ≤22 KIV repeats also had lower clot permeability
• VTE association: elevated Lp(a) (≥30 mg/dL) in 20% of VTE patients vs 7% controls; FV G1691A (Factor V Leiden) + elevated Lp(a) synergistically more prevalent in VTE cases — suggests Lp(a) thrombotic risk amplified when combined with underlying coagulation propensity; no independent VTE causal link established without coexisting prothrombotic factor

Section 8: Neointimal Hyperplasia

• Lp(a) is a predictor of vein graft stenosis and PTCA restenosis (neointimal hyperplasia)
• Mechanism: Mac-1-mediated monocyte infiltration (NF-κB) + direct SMC proliferation via TGF-β suppression (plasmin-dependent autocrine inhibition pathway)
• SMC proliferation effect concentration-dependent; consistent with VSMC section mechanisms

Section 9: Predictive Value

• Lp(a) levels stable from the 7th postnatal day onward — supports once-lifetime measurement approach
• ~20% of the general population has Lp(a) >42 mg/dL (Copenhagen City Heart Study data)
• ESC/EAS 2016: Class IIa Level C recommendation for at least once-lifetime Lp(a) measurement in selected high-risk cases
• HEART UK guideline: recommends Lp(a) screening specifically in CAVS patients
• Small apo(a) isoforms (≤22 KIV repeats) independently associated with greater CIMT progression and carotid stenosis (Kronenberg/Paultre data) — effect beyond Lp(a) mass level

Section 10: Treatment

• Statins: mean +11% Lp(a) increase confirmed (consistent with Tsimikas 2017); mechanism unknown; overall statin CV benefit maintained
• Ezetimibe: conflicting data — one meta-analysis showed −7% Lp(a) reduction (considered insufficient for CV event reduction); second large meta-analysis (10 RCTs) showed no effect; not established as Lp(a)-lowering therapy
• Niacin: 25–38% reduction depending on dose (2–4 g daily); mechanism: silencing of apo(a) gene expression in hepatocytes; identified as the only currently approved treatment for Lp(a) reduction as of 2023; no CV event benefit demonstrated despite significant Lp(a) lowering; large meta-analysis (14 RCTs): 23% Lp(a) reduction of uncertain prognostic relevance
• PCSK9i: 26.7% mean reduction (meta-analysis of 41 studies, n=64,107); mechanisms include LDLR upregulation → Lp(a) clearance + reduced apoB availability for Lp(a) assembly + reduced apo(a) synthesis; alirocumab: 0.6% MACE reduction per 1 mg/dL Lp(a) reduction independent of LDL-C (ODYSSEY); evolocumab (FOURIER): up to 27% Lp(a) reduction in high-baseline patients; PCSK9i CV event benefit confirmed in CAD but Lp(a)-specific benefit not primary endpoint; 7-trial meta-analysis shows ~18% mean reduction with 8–78 week follow-up
• ASO to apo(a) (ISIS-APO(a)Rx): subcutaneous; hepatocyte uptake; binds apo(a) mRNA → breakdown → inhibits apo(a) synthesis; up to 90% reduction dose-dependent; concurrent reduction in OxPL-apoB; further CVOTs needed to prove CV event benefit and CAVS benefit

Limitations of the Document

• Narrative review; no meta-analysis or systematic review; no primary data
• Multi-author group not specialised in Lp(a) research; significant overlap with existing Tsimikas reviews
• Published January 2023 in Molecules (MDPI open-access; lower impact factor); EAS 2022 consensus statement cited (ref 6) but treatment section does not incorporate its recommendations fully
• Treatment section pre-dates Phase 3 CVOT data for pelacarsen (Lp(a) HORIZON), olpasiran (OCEAN[a]-OUTCOMES), and zerlasiran — all trials underway at time of publication
• Mechanistic claims for several mechanisms (e.g., RGD-GPIIb/IIIa platelet interaction; VTE synergy with FV Leiden) based on relatively small studies or in vitro data
• No attempt to weigh evidence quality; all studies presented with similar weight regardless of design

Key Concepts Mentioned

• concepts/Lipoprotein-a — central subject; thrombogenicity, endothelial dysfunction, vascular inflammation, treatment
• concepts/ASCVD-Risk-Assessment — Lp(a) as independent residual CV risk factor

Key Entities Mentioned

• entities/Oxidized-Phospholipids — dose-dependent pro/anti-inflammatory role at high/low Lp(a) levels

Wiki Pages Updated

• Created wiki/sources/lpa-molecules-2023.md
• Updated wiki/concepts/Lipoprotein-a.md (new thrombogenicity mechanisms section; endothelial dysfunction detail; arterial wall interaction; isoform-specific thrombogenicity; neointimal hyperplasia)
• Updated wiki/sourceindex.md
• Updated wiki/wikiindex.md