Oxidized phospholipids in cardiovascular disease

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

BACKGROUND

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Lipoprotein(a) in the Year 2024: A Look Back and a Look Ahead

In fitting with the American Heart Association’s 100th anniversary of its founding and Arteriosclerosis, Thrombosis and Vascular Biology organizing a Centennial Collection to celebrate this event, lipoprotein(a) [Lp(a)] celebrates its 61st birthday in November 2024. There has been substantial progress in understanding the biology and pathophysiology of Lp(a) in the last 6 decades, including its discovery as a unique β-lipoprotein containing the pathognomonic apolipoprotein(a) moiety covalently bound to apolipoprotein B-100, its independent monogenetic association with cardiovascular disease and calcific aortic valve disease, its increased content of pro-atherogenic and pro-inflammatory of oxidized phospholipids relative to other lipoproteins and the development of RNA therapeutics to lower plasma Lp(a) levels. The validation or refutation of the “Lp(a) hypothesis”, namely that lowering plasma Lp(a) will lead to clinical benefit, is ongoing in 3 clinical outcomes trials. This essay reviews the discovery of Lp(a), summarizes the seminal pathophysiological findings since its discovery, discusses ongoing clinical trials with novel drugs and approaches, and provides a look ahead to unanswered questions.

Associations between lipoprotein(a), oxidized phospholipids, and extracoronary vascular disease

The roles of lipoprotein(a) [Lp(a)] and related oxidized phospholipids (OxPLs) in the development and progression of coronary disease is known, but their influence on extracoronary vascular disease is not well-established. We sought to evaluate associations between Lp(a), OxPL apolipoprotein B (OxPL-apoB), and apolipoprotein(a) (OxPL-apo(a)) with angiographic extracoronary vascular disease and incident major adverse limb events (MALEs). Four hundred forty-six participants who underwent coronary and/or peripheral angiography were followed up for a median of 3.7 years. Lp(a) and OxPLs were measured before angiography. Elevated Lp(a) was defined as ≥150 nmol/L. Elevated OxPL-apoB and OxPL-apo(a) were defined as greater than or equal to the 75th percentile (OxPL-apoB ≥8.2 nmol/L and OxPL-apo(a) ≥35.8 nmol/L, respectively). Elevated Lp(a) had a stronger association with the presence of extracoronary vascular disease compared to OxPLs and was minimally improved with the addition of OxPLs in multivariable models. Compared to participants with normal Lp(a) and OxPL concentrations, participants with elevated Lp(a) levels were twice as likely to experience a MALE (odds ratio: 2.14, 95% confidence interval: 1.03, 4.44), and the strength of the association as well as the C statistic of 0.82 was largely unchanged with the addition of OxPL-apoB and OxPL-apo(a). Elevated Lp(a) and OxPLs are risk factors for progression and complications of extracoronary vascular disease. However, the addition of OxPLs to Lp(a) does not provide additional information about risk of extracoronary vascular disease. Therefore, Lp(a) alone captures the risk profile of Lp(a), OxPL-apoB, and OxPL-apo(a) in the development and progression of atherosclerotic plaque in peripheral arteries.

Lipoprotein(a), Oxidized Phospholipids, and Progression to Symptomatic Heart Failure: The CASABLANCA Study

BACKGROUND

Higher lipoprotein(a) and oxidized phospholipid concentrations are associated with increased risk for coronary artery disease and valvular heart disease. The role of lipoprotein(a) or oxidized phospholipid as a risk factor for incident heart failure (HF) or its complications remains uncertain.

METHODS AND RESULTS

A total of 1251 individuals referred for coronary angiography in the Catheter Sampled Blood Archive in Cardiovascular Diseases (CASABLANCA) study were stratified on the basis of universal definition of HF stage; those in stage A/B (N=714) were followed up for an average 3.7 years for incident stage C/D HF or the composite of HF/cardiovascular death. During follow-up, 105 (14.7%) study participants in stage A/B progressed to symptomatic HF and 57 (8.0%) had cardiovascular death. In models adjusted for multiple HF risk factors, including severe coronary artery disease and aortic stenosis, individuals with lipoprotein(a) ≥150 nmol/L were at higher risk for progression to symptomatic HF (hazard ratio [HR], 1.90 [95% CI, 1.15-3.13]; P=0.01) or the composite of HF/cardiovascular death (HR, 1.71 [95% CI, 1.10-2.67]; P=0.02). These results remained significant after further adjustment of the model to include prior myocardial infarction (HF: HR, 1.89, P=0.01; HF/cardiovascular death: HR, 1.68, P=0.02). Elevated oxidized phospholipid concentrations were similarly associated with risk, particularly when added to higher lipoprotein(a). In Kaplan-Meier analyses, individuals with stage A/B HF and elevated lipoprotein(a) had shorter time to progression to stage C/D HF or HF/cardiovascular death (both log-rank P<0.001).

CONCLUSIONS

Among individuals with stage A or B HF, higher lipoprotein(a) and oxidized phospholipid concentrations are independent risk factors for progression to symptomatic HF or cardiovascular death.

REGISTRATION

URL: https://wwwclinicaltrials.gov; Unique identifier: NCT00842868.

Apolipoprotein B Secretion Assay from Primary Hepatocytes

Apolipoprotein B (APOB) is the primary structural protein of atherogenic lipoproteins, which drive atherogenesis and thereby lead to deadly cardiovascular diseases (CVDs). Plasma levels of APOB-containing lipoproteins are tightly modulated by LDL receptor-mediated endocytic trafficking and cargo receptor-initiated exocytic route; the latter is much less well understood. This protocol aims to present an uncomplicated yet effective method for detecting APOB/lipoprotein secretion. We perform primary mouse hepatocyte isolation and culture coupled with well-established techniques such as immunoblotting for highly sensitive, specific, and semi-quantitative analysis of the lipoprotein secretion process. Its inherent simplicity facilitates ease of operation, rendering it a valuable tool widely utilized to explore the intricate landscape of cellular lipid metabolism and unravel the mechanistic complexities underlying lipoprotein-related diseases. Key features • A pipeline for the isolation and subsequent culture of mouse primary hepatocytes. • A procedure for tracking the secretion of APOB-containing lipoproteins. • A rapid and sensitive assay for detecting the APOB level based on immunoblotting.

Phosphatidylthreonine is a procoagulant lipid detected in human blood and elevated in coronary artery disease

Aminophospholipids (aPL) such as phosphatidylserine are essential for supporting the activity of coagulation factors, circulating platelets, and blood cells. Phosphatidylthreonine (PT) is an aminophospholipid previously reported in eukaryotic parasites and animal cell cultures, but not yet in human tissues. Here, we evaluated whether PT is present in blood cells and characterized its ability to support coagulation. Several PT molecular species were detected in human blood, washed platelets, extracellular vesicles, and isolated leukocytes from healthy volunteers using liquid chromatography-tandem mass spectrometry. The ability of PT to support coagulation was demonstrated in vitro using biochemical and biophysical assays. In liposomes, PT supported prothrombinase activity in the presence and absence of phosphatidylserine. PT nanodiscs strongly bound FVa and lactadherin (nM affinity) but poorly bound prothrombin and FX, suggesting that PT supports prothrombinase through recruitment of FVa. PT liposomes bearing tissue factor poorly generated thrombin in platelet poor plasma, indicating that PT poorly supports extrinsic tenase activity. On platelet activation, PT is externalized and partially metabolized. Last, PT was significantly higher in platelets and extracellular vesicle from patients with coronary artery disease than in healthy controls. In summary, PT is present in human blood, binds FVa and lactadherin, supports coagulation in vitro through FVa binding, and is elevated in atherosclerotic vascular disease. Our studies reveal a new phospholipid subclass, that contributes to the procoagulant membrane, and may support thrombosis in patients at elevated risk.