Oxidized phospholipids and lipoprotein-associated phospholipase A2 as important determinants of Lp(a) functionality and pathophysiological role.
ABSTRACT: Lipoprotein(a) [Lp(a)] is composed of a low density lipoprotein (LDL)-like particle to which apolipoprotein (a) [apo(a)] is linked by a single disulfide bridge. Lp(a) is considered a causal risk factor for ischemic cardiovascular disease (CVD) and calcific aortic valve stenosis (CAVS). The evidence for a causal role of Lp(a) in CVD and CAVS is based on data from large epidemiological databases, mendelian randomization studies, and genomewide association studies. Despite the well-established role of Lp(a) as a causal risk factor for CVD and CAVS, the underlying mechanisms are not well understood. A key role in the Lp(a) functionality may be played by its oxidized phospholipids (OxPL) content. Importantly, most of circulating OxPL are associated with Lp(a); however, the underlying mechanisms leading to this preferential sequestration of OxPL on Lp(a) over the other lipoproteins, are mostly unknown. Several studies support the hypothesis that the risk of Lp(a) is primarily driven by its OxPL content. An important role in Lp(a) functionality may be played by the lipoprotein-associated phospholipase A2 (Lp-PLA2), an enzyme that catalyzes the degradation of OxPL and is bound to plasma lipoproteins including Lp(a). The present review article discusses new data on the pathophysiological role of Lp(a) and particularly focuses on the functional role of OxPL and Lp-PLA2 associated with Lp(a).
Project description:Background:Lipoprotein(a) (Lp[a]) is the preferential lipoprotein carrier of oxidized phospholipids (OxPLs) and a well-established genetic risk factor for calcific aortic valve stenosis (CAVS). Whether Lp(a) predicts aortic valve microcalcification in individuals without CAVS is unknown. Our objective was to estimate the prevalence of elevated Lp(a) and OxPL levels in patients with CAVS and to determine if individuals with elevated Lp(a) but without CAVS have higher aortic valve microcalcification. Methods:We recruited 214 patients with CAVS from Montreal and 174 patients with CAVS and 108 controls from Québec City, Canada. In a second group of individuals with high (?75 nmol/L, n = 27) or low (<75 nmol/L, n = 28) Lp(a) levels, 18F-sodium fluoride positron emission tomography/computed tomography was performed to determine the difference in mean tissue-to-background ratio (TBR) of the aortic valve. Results:Patients with CAVS had 62.0% higher Lp(a) (median = 28.7, interquartile range [8.2-116.6] vs 10.9 [3.6-28.8] nmol/L, P < 0.0001), 50% higher OxPL-apolipoprotein-B (2.2 [1.3-6.0] vs 1.1 [0.7-2.6] nmol/L, P < 0.0001), and 69.9% higher OxPL-apolipoprotein(a) (7.3 [1.8-28.4] vs 2.2 [0.8-8.4] nmol/L, P < 0.0001) levels compared with individuals without CAVS (all P < 0.0001). Individuals without CAVS but elevated Lp(a) had 40% higher mean TBR compared with individuals with low Lp(a) levels (mean TBR = 1.25 ± 0.23 vs 1.15 ± 0.11, P = 0.02). Conclusions:Elevated Lp(a) and OxPL levels are associated with prevalent CAVS in patients studied in an echocardiography laboratory setting. In individuals with elevated Lp(a), evidence of aortic valve microcalcification by 18F-sodium fluoride positron emission tomography/computed tomography is present before the development of clinically manifested CAVS.
Project description:Epidemiological, genetic association, and Mendelian randomization studies have provided strong evidence that lipoprotein (a) [Lp(a)] is an independent causal risk factor for CVD, including myocardial infarction, stroke, peripheral arterial disease, and calcific aortic valve stenosis. Lp(a) levels >50 mg/dl are highly prevalent (20% of the general population) and are overrepresented in patients with CVD and aortic stenosis. These data support the notion that Lp(a) should be a target of therapy for CVD event reduction and to reduce progression of aortic stenosis. However, effective therapies to specifically reduce plasma Lp(a) levels are lacking. Recent animal and human studies have shown that Lp(a) can be specifically targeted with second generation antisense oligonucleotides (ASOs) that inhibit apo(a) mRNA translation. In apo(a) transgenic mice, an apo(a) ASO reduced plasma apo(a)/Lp(a) levels and their associated oxidized phospholipid (OxPL) levels by 86 and 93%, respectively. In cynomolgus monkeys, a second generation apo(a) ASO, ISIS-APO(a)Rx, significantly reduced hepatic apo(a) mRNA expression and plasma Lp(a) levels by >80%. Finally, in a phase I study in normal volunteers, ISIS-APO(a)Rx ASO reduced Lp(a) levels and their associated OxPL levels up to 89 and 93%, respectively, with minimal effects on other lipoproteins. ISIS-APO(a)Rx represents the first specific and potent drug in clinical development to lower Lp(a) levels and may be beneficial in reducing CVD events and progression of calcific aortic valve stenosis.
Project description:Importance:Several studies have reported an association of levels of lipoprotein(a) (Lp[a]) and the content of oxidized phospholipids on apolipoprotein B (OxPL-apoB) and apolipoprotein(a) (OxPL-apo[a]) with faster calcific aortic valve stenosis (CAVS) progression. However, whether this association is threshold or linear remains unclear. Objective:To determine whether the plasma levels of Lp(a), OxPL-apoB, and OxPL-apo(a) have a linear association with a faster rate of CAVS progression. Design, Setting, and Participants:This secondary analysis of a randomized clinical trial tested the association of baseline plasma levels of Lp(a), OxPL-apoB, and OxPL-apo(a) with the rate of CAVS progression. Participants were included from the ASTRONOMER (Effects of Rosuvastatin on Aortic Stenosis Progression) trial, a multicenter study conducted in 23 Canadian sites designed to test the effect of statin therapy (median follow-up, 3.5 years [interquartile range, 2.9-4.5 years]). Patients with mild to moderate CAVS defined by peak aortic jet velocity ranging from 2.5 to 4.0 m/s were recruited; those with peak aortic jet velocity of less than 2.5 m/s or with an indication for statin therapy were excluded. Data were collected from January 1, 2002, through December 31, 2005, and underwent ad hoc analysis from April 1 through September 1, 2018. Interventions:After the randomization process, patients were followed up by means of echocardiography for 3 to 5 years. Main Outcomes and Measures:Progression rate of CAVS as assessed by annualized progression of peak aortic jet velocity. Results:In this cohort of 220 patients (60.0% male; mean [SD] age, 58? years), a linear association was found between plasma levels of Lp(a) (odds ratio [OR] per 10-mg/dL increase, 1.10; 95% CI, 1.03-1.19; P?=?.006), OxPL-apoB (OR per 1-nM increase,?1.06; 95% CI, 1.01-1.12; P?=?.02), and OxPL-apo(a) (OR per 10-nM increase,?1.16; 95% CI, 1.05-1.27; P?=?.002) and faster CAVS progression, which is marked in younger patients (OR for Lp[a] level per 10-mg/dL increase, 1.19 [95% CI, 1.07-1.33; P = .002]; OR for OxPL-apoB level per 1-nM increase, 1.06 [95% CI, 1.02-1.17; P = .01]; and OR for OxPL-apo[a] level per 10-nM increase, 1.26 [95% CI, 1.10-1.45; P = .001]) and remained statistically significant after comprehensive multivariable adjustment (? coefficient, ? 0.25; SE, ? 0.004 [P ? .005]; OR, ?1.10 [P ? .007]). Conclusions and Relevance:This study demonstrates that the association of Lp(a) levels and its content in OxPL with faster CAVS progression is linear, reinforcing the concept that Lp(a) levels should be measured in patients with mild to moderate CAVS to enhance management and risk stratification. Trial Registration:ClinicalTrials.gov Identifier: NCT00800800.
Project description:To determine whether biomarkers of oxidized lipoproteins are genetically determined. Lipoprotein(a) (Lp[a]) is a heritable risk factor and carrier of oxidized phospholipids (OxPL).We measured oxidized phospholipids on apolipoprotein B-containing lipoproteins (OxPL-apoB), Lp(a), IgG, and IgM autoantibodies to malondialdehyde-modified low-density lipoprotein, copper oxidized low-density lipoprotein, and apoB-immune complexes in 386 monozygotic and dizygotic twins to estimate trait heritability (h(2)) and determine specific genetic effects among traits. A genome-wide linkage study followed by genetic association was performed. The h(2) (scale: 0-1) for Lp(a) was 0.91±0.01 and for OxPL-apoB 0.87±0.02, which were higher than physiological, inflammatory, or lipid traits. h(2) of IgM malondialdehyde-modified low-density lipoprotein, copper oxidized low-density lipoprotein, and apoB-immune complexes were 0.69±0.04, 0.67±0.05, and 0.80±0.03, respectively, and for IgG malondialdehyde-modified low-density lipoprotein, copper oxidized low-density lipoprotein, and apoB-immune complexes 0.62±0.05, 0.52±0.06, and 0.53±0.06, respectively. There was an inverse correlation between the major apo(a) isoform and OxPL-apoB (R=-0.49; P<0.001) and Lp(a) (R=-0.48; P<0.001) and OxPL-apoB was modestly correlated with Lp(a) (?=0.57; P<0.0001). The correlation in major apo(a) isoform size was concordant (R=1.0; P<0.001) among monozygotic twins but not dizygotic twins (R=0.40; P=0.055). Lp(a) and OxPL-apoB shared genetic codetermination (genetic covariance, ?G=0.774±0.032; P=1.09×10(-38)), although not environmental determination (environmental covariance, ?E=0.081±0.15; P=0.15). In contrast, Lp(a) shared environmental but not genetic codetermination with autoantibodies to malondialdehyde-modified low-density lipoprotein and copper oxidized low-density lipoprotein, and apoB-immune complexes. Sib-pair genetic linkage of the Lp(a) trait revealed that single nucleotide polymorphism rs10455872 was significantly associated with OxPL-apoB after adjusting for Lp(a).OxPL-apoB and other biomarkers of oxidized lipoproteins are highly heritable cardiovascular risk factors that suggest novel genetic origins of atherothrombosis.
Project description:The LPA gene is the only monogenetic risk factor for calcific aortic valve stenosis (CAVS). Oxidized phospholipids (OxPL) and lysophosphatidic acid generated by autotaxin (ATX) from OxPL are pro-inflammatory. Aortic valve leaflets were categorized pathologically from Both ATX-apoB and ATX-apo(a) were measureable in plasma. Lp(a), autotaxin, OxPL and MDA epitopes progressively increased in immunostaining (p<0.001 for all). Six species of OxPL and LysoPA were identified following extraction from valve leaflets. The presence of a constellation of pathologically-linked, Lp(a)-associated molecules in plasma and in aortic valve leaflets of patients with CAVS suggest that Lp(a) is a key etiological factor in CAVS.
Project description:This study sought to assess whether plasminogen, which is homologous to lipoprotein (a) [Lp(a)], contains proinflammatory oxidized phospholipids (OxPL) and whether this has clinical relevance.OxPL measured on apolipoprotein B-100 (OxPL/apoB), primarily reflecting OxPL on Lp(a), independently predict cardiovascular disease (CVD) events.The authors examined plasminogen from commercially available preparations and plasma from chimpanzees; gorillas; bonobos; cynomolgus monkeys; wild-type, apoE(-/-), LDLR(-/-), and Lp(a)-transgenic mice; healthy humans; and patients with familial hypercholesterolemia, stable CVD, and acute myocardial infarction (AMI). Phosphocholine (PC)-containing OxPL (OxPC) present on plasminogen were detected directly with liquid chromatography-mass spectrometry (LC-MS/MS) and immunologically with monoclonal antibody E06. In vitro clot lysis assays were performed to assess the effect of the OxPL on plasminogen on fibrinolysis.LC-MS/MS revealed that OxPC fragments were covalently bound to mouse plasminogen. Immunoblot, immunoprecipitation, density gradient ultracentrifugation, and enzyme-linked immunosorbent assay analyses demonstrated that all human and animal plasma samples tested contained OxPL covalently bound to plasminogen. In plasma samples subjected to density gradient fractionation, OxPL were present on plasminogen (OxPL/plasminogen) in non-lipoprotein fractions but on Lp(a) in lipoprotein fractions. Plasma levels of OxPL/apoB and OxPL/apo(a) varied significantly (>25×) among subjects and also strongly correlated with Lp(a) levels. In contrast, OxPL/plasminogen levels were distributed across a relatively narrow range and did not correlate with Lp(a). Enzymatic removal of OxPL from plasminogen resulted in a longer lysis time for fibrin clots (16.25 vs. 11.96 min, p = 0.007). In serial measurements over 7 months, OxPL/plasminogen levels did not vary in normal subjects or in patients with stable CVD, but increased acutely over the first month and then slowly decreased to baseline in patients following AMI.These data demonstrate that plasminogen contains covalently bound OxPL that influence fibrinolysis. OxPL/plasminogen represent a second major plasma pool of OxPL, in addition to those present on Lp(a). OxPL present on plasminogen may have pathophysiological implications in AMI and atherothrombosis.
Project description:The goal of this study was to examine the prospective association between oxidation-specific biomarkers, primarily oxidized phospholipids (OxPL) on apolipoprotein B-100-containing lipoproteins (OxPL/apoB) and lipoprotein (a) [Lp(a)], and risk of peripheral artery disease (PAD). We examined, as secondary analyses, indirect measures of oxidized lipoproteins, including autoantibodies to malondialdehyde-modified low-density lipoprotein (MDA-LDL) and apolipoprotein B-100 immune complexes (ApoB-IC).Biomarkers to predict the development of PAD are lacking. OxPL circulate in plasma, are transported by Lp(a), and deposit in the vascular wall and induce local inflammation.The study population included 2 parallel nested case-control studies of 143 men within the Health Professionals Follow-up Study (1994 to 2008) and 144 women within the Nurses' Health Study (1990 to 2010) with incident confirmed cases of clinically significant PAD, matched 1:3 to control subjects.Levels of OxPL/apoB were positively associated with risk of PAD in men and women: pooled relative risk: 1.37, 95% confidence interval: 1.19 to 1.58 for each 1-SD increase after adjusting age, smoking, fasting status, month of blood draw, lipids, body mass index, and other cardiovascular disease risk factors. Lp(a) was similarly associated with risk of PAD (pooled adjusted relative risk: 1.36; 95% confidence interval: 1.18 to 1.57 for each 1-SD increase). Autoantibodies to MDA-LDL and ApoB-IC were not consistently associated with risk of PAD.OxPL/apoB were positively associated with risk of PAD in men and women. The major lipoprotein carrier of OxPL, Lp(a), was also associated with risk of PAD, reinforcing the key role of OxPL in the pathophysiology of atherosclerosis mediated by Lp(a).
Project description:Paraoxonase-1 (PON1) and lipoprotein phospholipase A2 (Lp-PLA2) may exert an important protective role by preventing the oxidative transformation of high- and low-density lipoproteins (HDL and LDL, respectively). The activity of both enzymes is influenced by lipidome and proteome of the lipoprotein carriers. T2DM typically presents significant changes in the molecular composition of the lipoprotein subclasses. Thus, it becomes relevant to understand the interaction of PON1 and Lp-PLA2 with the subspecies of HDL, LDL, and other lipoproteins in T2DM. Serum levels of PON1-arylesterase and PON1-lactonase and Lp-PLA2 activities and lipoprotein subclasses were measured in 202 nondiabetic subjects (controls) and 92 T2DM outpatients. Arylesterase, but not lactonase or Lp-PLA2 activities, was inversely associated with TD2M after adjusting for potential confounding factors such as age, sex, smoking, body mass index, hypertension, and lipoprotein subclasses (odds ratio?=?3.389, 95% confidence interval 1.069-14.756). Marked difference between controls and T2DM subjects emerged from the analyses of the associations of the three enzyme activities and lipoprotein subclasses. Arylesterase was independently related with large HDL-C and small intermediate-density lipoprotein cholesterol (IDL-C) in controls while, along with lactonase, it was related with small low-density lipoprotein cholesterol LDL-C, all IDL-C subspecies, and very low-density lipoprotein cholesterol (VLDL-C) in T2DM (p < 0.05 for all). Concerning Lp-PLA2, there were significant relationships with small LDL-C, large IDL-C, and VLDL-C only among T2DM subjects. Our study showed that T2DM subjects have lower levels of PON1-arylesterase compared to controls and that T2DM occurrence may coincide with a shift of PON1 and Lp-PLA2 towards the more proatherogenic lipoprotein subclasses. The possibility of a link between the two observed phenomena requires further investigations.
Project description:BACKGROUND:Findings regarding the association of lipoprotein-associated phospholipase A? (Lp-PLA2) activity and mass with incident cardiovascular disease (CVD) have been inconsistent, and their role in risk prediction is uncertain. METHODS:A case-cohort sample from the Women's Health Initiative Observational Study (WHI-OS) comprised 1821 CVD cases and a reference subcohort of 1992 women. We used Cox regression models with inverse sampling weights to assess the association of Lp-PLA2 mass and activity with CVD (myocardial infarction, stroke, and CVD mortality). RESULTS:Subcohort means were 184.3 mmol/min/mL for Lp-PLA2 activity and 499.2 ?g/L for Lp-PLA2 mass, with 99% having mass above 200 ?g/L, the clinically recommended cut point. Both activity and mass were positively associated with incident CVD in age- and race/ethnicity-adjusted analyses. Following adjustment according to CVD risk factors, the association with activity became null (hazard ratio = 1.02 for top vs bottom quartile, 95% CI = 0.79-1.33, P for trend = 0.65), but the association with mass remained (hazard ratio = 1.84, 95% CI = 1.45-2.34, P for trend < 0.0001). In contrast to blood pressure, HDL, and hsCRP, reclassification statistics for Lp-PLA2 mass did not suggest improvement for overall CVD after full adjustment. CONCLUSIONS:In the WHI-OS Lp-PLA2 mass, but not activity, was independently associated with CVD. However, model fit did not significantly improve with Lp-PLA2 mass, and assay calibration remains a clinical concern.
Project description:Lipoprotein characteristics were analyzed in familial combined hyperlipidemia (FCH) patients before and after statin treatment. Twenty-six FCH patients were classified according to the presence (HTG group, n = 13) or absence (normotriglyceridemic (NTG) group, n = 13) of hypertriglyceridemia. Fifteen healthy subjects comprised the control group. Lipid profile, inflammation markers, and qualitative characteristics of lipoproteins were assessed. Both groups of FCH subjects showed high levels of plasma C-reactive protein (CRP), lipoprotein-associated phospholipase A2 (Lp-PLA2) activity and apolipoprotein J. Statins reverted the increased levels of Lp-PLA2 and CRP. Lipoprotein composition alterations detected in FCH subjects were much more frequent in the HTG group, leading to dysfunctional low-density lipoproteins (LDL) and high-density lipoproteins (HDL). In the HTG group, LDL was smaller, more susceptible to oxidation, and contained more electronegative LDL (LDL(-)) compared to the NTG and control groups. Regarding HDL, the HTG group had less Lp-PLA2 activity than the NTG and control groups. HDL from both FCH groups was less anti-inflammatory than HDL from the control group. Statins increased LDL size, decreased LDL(-), and lowered Lp-PLA2 in HDL from HTG. In summary, pro-atherogenic alterations were more frequent and severe in the HTG group. Statins improved some alterations, but many remained unchanged in HTG.