Lipoprotein (a) in calcific aortic valve disease: from genomics to novel drug target for aortic stenosis

Calcific aortic valve stenosis: hard disease in the heart: A biomolecular approach towards diagnosis and treatment

Calcific aortic valve stenosis (CAVS) is common in the ageing population and set to become an increasing economic and health burden. Once present, it inevitably progresses and has a poor prognosis in symptomatic patients. No medical therapies are proven to be effective in holding or reducing disease progression. Therefore, aortic valve replacement remains the only available treatment option. Improved knowledge of the mechanisms underlying disease progression has provided us with insights that CAVS is not a passive disease. Rather, CAVS is regulated by numerous mechanisms with a key role for calcification. Aortic valve calcification (AVC) is actively regulated involving cellular and humoral factors that may offer targets for diagnosis and intervention. The discovery that the vitamin K-dependent proteins are involved in the inhibition of AVC has boosted our mechanistic understanding of this process and has opened up novel avenues in disease exploration. This review discusses processes involved in CAVS progression, with an emphasis on recent insights into calcification, methods for imaging calcification activity, and potential therapeutic options.

Calcification of the heart: mechanisms and therapeutic avenues

INTRODUCTION

Coronary artery calcification (CAC) is reflective of atherosclerotic disease and incrementally predictive of future cardiovascular events (CVE), independent of traditional risk factors. Extra coronary calcium such as aortic valve calcification, which can be identified and quantified by computed tomography (CT) imaging, has shown to predict future CVE in both asymptomatic and symptomatic (i.e. stable angina and acute coronary syndrome [ACS]) settings. It has hence been a vital tool in studies involving new therapies for cardiovascular disease. Areas covered: In this review, promising therapies on the horizon are reviewed, along with the role of cardiac CT and coronary calcification in these studies. A Medline search for peer-reviewed publications using keywords related to coronary calcium score, aortic valve calcium, and therapies targeting the same was carried out. Expert commentary: CT scanning provides a distinct means of detecting and quantifying coronary plaque as well as valvular calcification with excellent reproducibility. Based on voluminous data available, the absence of coronary calcium serves as a factor to de-risk patients for cardiovascular risk stratification and management algorithms. Newer therapies have shown to lower progression of coronary calcification, thus being beneficial in slowing progression of atherosclerotic disease. As British Epidemiologist Geoffrey Rose states, the best predictor of a life-threatening disease is the early manifestation of that disease. As CAC represents the early manifestation of atherosclerosis, it is the best-known stratifier of risk today, and its clinical use will continue to rise.

The journey towards understanding lipoprotein(a) and cardiovascular disease risk: are we there yet?

PURPOSE OF REVIEW

Evidence continues to mount for an important role for elevated plasma concentrations of lipoprotein(a) [Lp(a)] in mediating risk of atherothrombotic and calcific aortic valve diseases. However, there continues to be great uncertainty regarding some basic aspects of Lp(a) biology including its biosynthesis and catabolism, its mechanisms of action in health and disease, and the significance of its isoform size heterogeneity. Moreover, the precise utility of Lp(a) in the clinic remains undefined.

RECENT FINDINGS

The contribution of elevated Lp(a) to cardiovascular risk continues to be more precisely defined by larger studies. In particular, the emerging role of Lp(a) as a potent risk factor for calcific aortic valve disease has received much scrutiny. Mechanistic studies have identified commonalities underlying the impact of Lp(a) on atherosclerosis and aortic valve disease, most notably related to Lp(a)-associated oxidized phospholipids. The mechanisms governing Lp(a) concentrations remain a source of considerable dispute.

SUMMARY

This article highlights some key remaining challenges in understanding Lp(a) actions and clinical significance. Most important in this regard is demonstration of a beneficial effect of lowering Lp(a), a development that is on the horizon as effective Lp(a)-lowering therapies are being tested in the clinic.

Degenerative Aortic Stenosis, Dyslipidemia and Possibilities of Medical Treatment

Degenerative aortic stenosis (DAS) is the most frequently diagnosed heart valve disease in Europe and North America. DAS is a chronic progressive disease which resembles development of atherosclerosis. Endothelial dysfunction, lipid infiltration, calcification and ossification are evidenced in both diseases. The same risk factors such as older age, male sex, smoking, and elevated levels of lipids are identified. The effect of smoking, visceral obesity, metabolic syndrome, hypercholesterolemia, low-density lipoprotein, high-density lipoprotein, lipoprotein(a), adiponectin and apolipoprotein(a) on development of DAS are being studied. The search for genetic ties between disorders of lipid metabolism and DAS has been started. DAS is characterized by a long symptom-free period which can last for several decades. Aortic valve replacement surgery is necessary when the symptoms occur. The lipid-lowering therapy effect on stopping or at least slowing down the progression of DAS was studied. However, the results of the conducted clinical trials are controversial. In addition, calcium homeostasis, bone metabolism and calcinosis-reducing medication are being studied. Although prospective randomized clinical trials have not demonstrated any positive effect of statins used for slowing progression of the disease, statins are still recommended for patients with dyslipidemia. Recent study has suggested that a specific modification of treatment, based on severity of disease, may have a beneficial effect in patients with aortic sclerosis and mild DAS. New clinical studies analyzing new treatment possibilities which could correct the natural course of the disease and reduce the need for aortic valve replacement by surgery or transcatheter treatment interventions are needed.

The role of lipoprotein (a) in chronic kidney disease

Lipoprotein (a) [Lp(a)] and its measurement, structure and function, the impact of ethnicity and environmental factors, epidemiological and genetic associations with vascular disease, and new prospects in drug development have been extensively examined throughout this Thematic Review Series on Lp(a). Studies suggest that the kidney has a role in Lp(a) catabolism, and that Lp(a) levels are increased in association with kidney disease only for people with large apo(a) isoforms. By contrast, in those patients with large protein losses, as in the nephrotic syndrome and continuous ambulatory peritoneal dialysis, Lp(a) is increased irrespective of apo(a) isoform size. Such acquired abnormalities can be reversed by kidney transplantation or remission of nephrosis. In this Thematic Review, we focus on the relationship between Lp(a), chronic kidney disease, and risk of cardiovascular events.

Creation of disease-inspired biomaterial environments to mimic pathological events in early calcific aortic valve disease

An insufficient understanding of calcific aortic valve disease (CAVD) pathogenesis remains a major obstacle in developing treatment strategies for this disease. The aim of the present study was to create engineered environments that mimic the earliest known features of CAVD and apply this in vitro platform to decipher relationships relevant to early valve lesion pathobiology. Glycosaminoglycan (GAG) enrichment is a dominant hallmark of early CAVD, but culture of valvular interstitial cells (VICs) in biomaterial environments containing pathological amounts of hyaluronic acid (HA) or chondroitin sulfate (CS) did not directly increase indicators of disease progression such as VIC activation or inflammatory cytokine production. However, HA-enriched matrices increased production of vascular endothelial growth factor (VEGF), while matrices displaying pathological levels of CS were effective at retaining lipoproteins, whose deposition is also found in early CAVD. Retained oxidized low-density lipoprotein (oxLDL), in turn, stimulated myofibroblastic VIC differentiation and secretion of numerous inflammatory cytokines. OxLDL also increased VIC deposition of GAGs, thereby creating a positive feedback loop to further enrich GAG content and promote disease progression. Using this disease-inspired in vitro platform, we were able to model a complex, multistep pathological sequence, with our findings suggesting distinct roles for individual GAGs in outcomes related to valve lesion progression, as well as key differences in cell-lipoprotein interactions compared with atherosclerosis. We propose a pathogenesis cascade that may be relevant to understanding early CAVD and envision the extension of such models to investigate other tissue pathologies or test pharmacological treatments.

Lipoprotein(a) in clinical practice: New perspectives from basic and translational science

Elevated plasma concentrations of lipoprotein(a) (Lp(a)) are a causal risk factor for coronary heart disease (CHD) and calcific aortic valve stenosis (CAVS). Genetic, epidemiological and in vitro data provide strong evidence for a pathogenic role for Lp(a) in the progression of atherothrombotic disease. Despite these advancements and a race to develop new Lp(a) lowering therapies, there are still many unanswered and emerging questions about the metabolism and pathophysiology of Lp(a). New studies have drawn attention to Lp(a) as a contributor to novel pathogenic processes, yet the mechanisms underlying the contribution of Lp(a) to CVD remain enigmatic. New therapeutics show promise in lowering plasma Lp(a) levels, although the complete mechanisms of Lp(a) lowering are not fully understood. Specific agents targeted to apolipoprotein(a) (apo(a)), namely antisense oligonucleotide therapy, demonstrate potential to decrease Lp(a) to levels below the 30-50 mg/dL (75-150 nmol/L) CVD risk threshold. This therapeutic approach should aid in assessing the benefit of lowering Lp(a) in a clinical setting.

Medical Treatment of Aortic Stenosis

Untreated, severe, symptomatic aortic stenosis is associated with a dismal prognosis. The only treatment shown to improve survival is aortic valve replacement; however, before symptoms occur, aortic stenosis is preceded by a silent, latent phase characterized by a slow progression at the molecular, cellular, and tissue levels. In theory, specific medical therapy should halt aortic stenosis progression, reduce its hemodynamic repercussions on left ventricular function and remodeling, and improve clinical outcomes. In the present report, we performed a systematic review of studies focusing on the medical treatment of patients with aortic stenosis. Lipid-lowering therapy, antihypertensive drugs, and anticalcific therapy have been the main drug classes studied in this setting and are reviewed in depth. A critical appraisal of the preclinical and clinical evidence is provided, and future research avenues are presented.

Lipoprotein(a): new insights from modern genomics

PURPOSE OF REVIEW

Lipoprotein(a) [Lp(a)] is the strongest independent genetic risk factor for both myocardial infarction and aortic stenosis. It has also been associated with other forms of atherosclerotic cardiovascular disease (CVD) including ischemic stroke. Its levels are genetically determined and remain fairly stable throughout life. Elevated Lp(a), above 50 mg/dl, affects one in five individuals worldwide.

RECENT FINDINGS

Herein, we review the recent epidemiologic and genetic evidence supporting the causal role of Lp(a) in CVD, highlight recommendations made by European and Canadian guidelines regarding Lp(a) and summarize the rapidly evolving field of Lp(a)-lowering therapies including antisense therapies and Proprotein Convertase Subtilisin/Kexin Type 9 inhibitors.

SUMMARY

With novel therapies on the horizon, Lp(a) is poised to gain significant clinical relevance and its lowering could have a significant impact on the burden of CVD. VIDEO ABSTRACT.

The Prevalence of Lipoprotein(a) Measurement and Degree of Elevation Among 2710 Patients With Calcific Aortic Valve Stenosis in an Academic Echocardiography Laboratory Setting

Lipoprotein(a; Lp[a]) and its associated oxidized phospholipids are causal, genetic risk factors for calcific aortic valve stenosis (CAVS). We determined the prevalence of Lp(a) measurement among 2710 patients with CAVS and 1369 control patients (∼50% of study group) without CAVS with an echocardiogram between January 2010 and February 2016 in an academic echocardiography laboratory. Lipoprotein(a) measurements were performed at a referral laboratory using an isoform-independent assay. The prevalence of any Lp(a) measurement was 4.6% (124 of the 2710) in patients with CAVS and 3.1% (42 of the 1369) in the control group ( P = .021). In patients with CAVS, mean (standard deviation) Lp(a) levels were 38 (54) mg/dL and median (interquartile range) Lp(a) levels were 14 (6-48) mg/dL. Of the 124 patients with CAVS having Lp(a) measurements, 83 (66.9%) had Lp(a) <30 mg/dL and 41 (33.1%) had Lp(a) ≥30 mg/dL. This study reflects low physician testing of Lp(a) levels in CAVS. Given the role of Lp(a) as a causal risk factor for CAVS, and the ongoing development of therapies to normalize Lp(a) levels, our results suggest that Lp(a) measurements in CAVS should be more widely obtained in clinical practice.

Lipoprotein(a) Mass Levels Increase Significantly According to APOE Genotype: An Analysis of 431 239 Patients

OBJECTIVE

Lipoprotein(a) [Lp(a)] levels are genetically determined by hepatocyte apolipoprotein(a) synthesis, but catabolic pathways also influence circulating levels. APOE genotypes have different affinities for the low-density lipoprotein (LDL) receptor and LDL-related protein-1, with ε2 having the weakest binding to LDL receptor at <2% relative to ε3 and ε4. APPROACH AND RESULTS: APOE genotypes (ε2/ε2, ε2/ε3, ε2/ε4, ε3/ε3, ε3/ε4, and ε4/ε4), Lp(a) mass, directly measured Lp(a)-cholesterol levels, and a variety of apoB-related lipoproteins were measured in 431 239 patients. The prevalence of APOE traits were ε2: 7.35%, ε3: 77.56%, and ε4: 15.09%. Mean (SD) Lp(a) levels were 65% higher in ε4/ε4 compared with ε2/ε2 genotypes and increased significantly according to APOE genotype: ε2/ε2: 23.4 (29.2), ε2/ε3: 31.3 (38.0), ε2/ε4: 32.8 (38.5), ε3/ε3: 33.2 (39.1), ε3/ε4: 35.5 (41.6), and ε4/ε4: 38.5 (44.1) mg/dL (P<0.0001). LDL-cholesterol, apoB, Lp(a)-cholesterol, LDL-cholesterol corrected for Lp(a)-cholesterol content, LDL-particle number, and small, dense LDL also had similar patterns. Patients with LDL-cholesterol ≥250 mg/dL, who are more likely to have LDL receptor mutations and reduced affinity for apoB, had higher Lp(a) levels across all apoE isoforms, but particularly in patients with ε2 alleles, compared with LDL <250 mg/dL. The lowest Lp(a) mass levels were present in patients with ε2 isoforms and lowest LDL-cholesterol.

CONCLUSIONS

APOE genotypes strongly influence Lp(a) and apoB-related lipoprotein levels. This suggests that differences in affinity of apoE proteins for lipoprotein clearance receptors may affect Lp(a) catabolism, suggesting a competition between Lp(a) and apoE protein for similar receptors.

L-Carnitine/Simvastatin Reduces Lipoprotein (a) Levels Compared with Simvastatin Monotherapy: A Randomized Double-Blind Placebo-Controlled Study

Lipoprotein (a) [Lp(a)] is an independent risk factor for cardiovascular disease. There are currently limited therapeutic options to lower Lp(a) levels. L-Carnitine has been reported to reduce Lp(a) levels. The aim of this study was to compare the effect of L-carnitine/simvastatin co-administration with that of simvastatin monotherapy on Lp(a) levels in subjects with mixed hyperlipidemia and elevated Lp(a) concentration. Subjects with levels of low-density lipoprotein cholesterol (LDL-C) >160 mg/dL, triacylglycerol (TAG) >150 mg/dL and Lp(a) >20 mg/dL were included in this study. Subjects were randomly allocated to receive L-carnitine 2 g/day plus simvastatin 20 mg/day (N = 29) or placebo plus simvastatin 20 mg/day (N = 29) for a total of 12 weeks. Lp(a) was significantly reduced in the L-carnitine/simvastatin group [-19.4%, from 52 (20-171) to 42 (15-102) mg/dL; p = 0.01], but not in the placebo/simvastatin group [-6.7%, from 56 (26-108) to 52 (27-93) mg/dL, p = NS versus baseline and p = 0.016 for the comparison between groups]. Similar significant reductions in total cholesterol, LDL-C, apolipoprotein (apo) B and TAG were observed in both groups. Co-administration of L-carnitine with simvastatin was associated with a significant, albeit modest, reduction in Lp(a) compared with simvastatin monotherapy in subjects with mixed hyperlipidemia and elevated baseline Lp(a) levels.

LPA Gene, Ethnicity, and Cardiovascular Events

BACKGROUND

The relationship of LPA single nucleotide polymorphisms (SNPs), apolipoprotein(a) isoforms, and lipoprotein(a) [Lp(a)] levels with major adverse cardiovascular events (MACE) in different ethnic groups is not well known.

METHODS

LPA SNPs, apolipoprotein(a) isoforms, Lp(a), and oxidized phospholipids on apolipoprotein B-100 (OxPL-apoB) levels were measured in 1792 black, 1030 white, and 597 Hispanic subjects enrolled in the Dallas Heart Study. Their interdependent relationships and prospective association with MACE after median 9.5-year follow-up were determined.

RESULTS

LPA SNP rs3798220 was most prevalent in Hispanics (42.38%), rs10455872 in whites (14.27%), and rs9457951 in blacks (32.92%). The correlation of each of these SNPs with the major apolipoprotein(a) isoform size was highly variable and in different directions among ethnic groups. In the entire cohort, Cox regression analysis with multivariable adjustment revealed that quartiles 4 of Lp(a) and OxPL-apoB were associated with hazard ratios (95% confidence interval) for time to MACE of 2.35 (1.50-3.69, P<0.001) and 1.89 (1.26-2.84, P=0.003), respectively, versus quartile 1. Addition of the major apolipoprotein(a) isoform and the 3 LPA SNPs to these models attenuated the risk, but significance was maintained for both Lp(a) and OxPL-apoB. Evaluating time to MACE in specific ethnic groups, Lp(a) was a positive predictor and the size of the major apolipoprotein(a) isoform was an inverse predictor in blacks, the size of the major apolipoprotein(a) isoform was an inverse predictor in whites, and OxPL-apoB was a positive predictor in Hispanics.

CONCLUSIONS

The prevalence and association of LPA SNPs with size of apolipoprotein(a) isoforms, Lp(a), and OxPL-apoB levels are highly variable and ethnicity-specific. The relationship to MACE is best explained by elevated plasma Lp(a) or OxPL-apoB levels, despite significant ethnic differences in LPA genetic markers.

Antisense oligonucleotides targeting apolipoprotein(a) in people with raised lipoprotein(a): two randomised, double-blind, placebo-controlled, dose-ranging trials

BACKGROUND

Elevated lipoprotein(a) (Lp[a]) is a highly prevalent (around 20% of people) genetic risk factor for cardiovascular disease and calcific aortic valve stenosis, but no approved specific therapy exists to substantially lower Lp(a) concentrations. We aimed to assess the efficacy, safety, and tolerability of two unique antisense oligonucleotides designed to lower Lp(a) concentrations.

METHODS

We did two randomised, double-blind, placebo-controlled trials. In a phase 2 trial (done in 13 study centres in Canada, the Netherlands, Germany, Denmark, and the UK), we assessed the effect of IONIS-APO(a)_Rx, an oligonucleotide targeting apolipoprotein(a). Participants with elevated Lp(a) concentrations (125-437 nmol/L in cohort A; ≥438 nmol/L in cohort B) were randomly assigned (in a 1:1 ratio in cohort A and in a 4:1 ratio in cohort B) with an interactive response system to escalating-dose subcutaneous IONIS-APO(a)_Rx (100 mg, 200 mg, and then 300 mg, once a week for 4 weeks each) or injections of saline placebo, once a week, for 12 weeks. Primary endpoints were mean percentage change in fasting plasma Lp(a) concentration at day 85 or 99 in the per-protocol population (participants who received more than six doses of study drug) and safety and tolerability in the safety population. In a phase 1/2a first-in-man trial, we assessed the effect of IONIS-APO(a)-L_Rx, a ligand-conjugated antisense oligonucleotide designed to be highly and selectively taken up by hepatocytes, at the BioPharma Services phase 1 unit (Toronto, ON, Canada). Healthy volunteers (Lp[a] ≥75 nmol/L) were randomly assigned to receive a single dose of 10-120 mg IONIS-APO(a)L_Rx subcutaneously in an ascending-dose design or placebo (in a 3:1 ratio; single-ascending-dose phase), or multiple doses of 10 mg, 20 mg, or 40 mg IONIS-APO(a)L_Rx subcutaneously in an ascending-dose design or placebo (in an 8:2 ratio) at day 1, 3, 5, 8, 15, and 22 (multiple-ascending-dose phase). Primary endpoints were mean percentage change in fasting plasma Lp(a) concentration, safety, and tolerability at day 30 in the single-ascending-dose phase and day 36 in the multiple-ascending-dose phase in participants who were randomised and received at least one dose of study drug. In both trials, the randomised allocation sequence was generated by Ionis Biometrics or external vendor with a permuted-block randomisation method. Participants, investigators, sponsor personnel, and clinical research organisation staff who analysed the data were all masked to the treatment assignments. Both trials are registered with ClinicalTrials.gov, numbers NCT02160899 and NCT02414594.

FINDINGS

From June 25, 2014, to Nov 18, 2015, we enrolled 64 participants to the phase 2 trial (51 in cohort A and 13 in cohort B). 35 were randomly assigned to IONIS-APO(a)_Rx and 29 to placebo. At day 85/99, participants assigned to IONIS-APO(a)_Rx had mean Lp(a) reductions of 66·8% (SD 20·6) in cohort A and 71·6% (13·0) in cohort B (both p<0·0001 vs pooled placebo). From April 15, 2015, to Jan 11, 2016, we enrolled 58 healthy volunteers to the phase 1/2a trial of IONIS-APO(a)-L_Rx. Of 28 participants in the single-ascending-dose phase, three were randomly assigned to 10 mg, three to 20 mg, three to 40 mg, six to 80 mg, six to 120 mg, and seven to placebo. Of 30 participants in the multiple-ascending-dose phase, eight were randomly assigned to 10 mg, eight to 20 mg, eight to 40 mg, and six to placebo. Significant dose-dependent reductions in mean Lp(a) concentrations were noted in all single-dose IONIS-APO(a)-L_Rx groups at day 30. In the multidose groups, IONIS-APO(a)-L_Rx resulted in mean reductions in Lp(a) of 66% (SD 21·8) in the 10 mg group, 80% (SD 13·7%) in the 20 mg group, and 92% (6·5) in the 40 mg group (p=0·0007 for all vs placebo) at day 36. Both antisense oligonucleotides were safe. There were two serious adverse events (myocardial infarctions) in the IONIS-APO(a)_Rx phase 2 trial, one in the IONIS-APO(a)_Rx and one in the placebo group, but neither were thought to be treatment related. 12% of injections with IONIS-APO(a)_Rx were associated with injection-site reactions. IONIS-APO(a)-L_Rx was associated with no injection-site reactions.

INTERPRETATION

IONIS-APO(a)-L_Rx is a novel, tolerable, potent therapy to reduce Lp(a) concentrations. IONIS-APO(a)-L_Rx might mitigate Lp(a)-mediated cardiovascular risk and is being developed for patients with elevated Lp(a) concentrations with existing cardiovascular disease or calcific aortic valve stenosis.

FUNDING

Ionis Pharmaceuticals.

Lipoprotein (a) as a cause of cardiovascular disease: insights from epidemiology, genetics, and biology

Human epidemiologic and genetic evidence using the Mendelian randomization approach in large-scale studies now strongly supports that elevated lipoprotein (a) [Lp(a)] is a causal risk factor for cardiovascular disease, that is, for myocardial infarction, atherosclerotic stenosis, and aortic valve stenosis. The Mendelian randomization approach used to infer causality is generally not affected by confounding and reverse causation, the major problems of observational epidemiology. This approach is particularly valuable to study causality of Lp(a), as single genetic variants exist that explain 27-28% of all variation in plasma Lp(a). The most important genetic variant likely is the kringle IV type 2 (KIV-2) copy number variant, as the apo(a) product of this variant influences fibrinolysis and thereby thrombosis, as opposed to the Lp(a) particle per se. We speculate that the physiological role of KIV-2 in Lp(a) could be through wound healing during childbirth, infections, and injury, a role that, in addition, could lead to more blood clots promoting stenosis of arteries and the aortic valve, and myocardial infarction. Randomized placebo-controlled trials of Lp(a) reduction in individuals with very high concentrations to reduce cardiovascular disease are awaited. Recent genetic evidence documents elevated Lp(a) as a cause of myocardial infarction, atherosclerotic stenosis, and aortic valve stenosis.

Patients with calcific aortic stenosis exhibit systemic molecular evidence of ischemia, enhanced coagulation, oxidative stress and impaired cholesterol transport

BACKGROUND

The most common valve diseases are calcific aortic stenosis (AS) and aortic regurgitation (AR). The former is characterized by thickening of valve leaflets followed by progressive calcification, which produces progressive aortic valve (AV) narrowing, increased pressure afterload on the left ventricle (LV) and subsequent LV hypertrophy. On the other hand, AR is due to malcoaptation of the valve leaflets with resultant diastolic reflux of blood from aorta back to the LV producing volume and pressure overload and progressive LV dilatation. In order to isolate the molecular mechanisms taking place during AS, we have used an integrated "-omic" approach to compare plasma samples from AS and from AR patients used as controls. The final purpose of this work is to find molecular changes in response to the calcification of the AV, diminishing the effects of the AV dysfunction.

METHODS AND RESULTS

Using two-dimensional difference gel electrophoresis (2D-DIGE) and gas chromatography coupled to mass spectrometry (GC-MS) in a cohort of 6 subjects, we have found differences in 24 protein spots and 19 metabolites, respectively. Among them, 7 proteins and 3 metabolites have been verificated by orthogonal techniques (SRM or turbidimetry): fibrinogen beta and gamma chain, vitronectin, apolipoprotein C-II, antithrombin III, haptoglobin, succinic acid, pyroglutamic acid and alanine. Classification according to their main function showed alterations related to coagulation, inflammation, oxidative stress, response to ischemia and lipid metabolism, defining 4 different molecular panels that characterize AS with high specificity and sensitivity.

CONCLUSION

These results may facilitate management of these patients by making faster diagnostics of the disease and better understand these pathways for regulating its progression.

Oxidized Phospholipids on Lipoprotein(a) Elicit Arterial Wall Inflammation and an Inflammatory Monocyte Response in Humans

BACKGROUND

Elevated lipoprotein(a) [Lp(a)] is a prevalent, independent cardiovascular risk factor, but the underlying mechanisms responsible for its pathogenicity are poorly defined. Because Lp(a) is the prominent carrier of proinflammatory oxidized phospholipids (OxPLs), part of its atherothrombosis might be mediated through this pathway.

METHODS

In vivo imaging techniques including magnetic resonance imaging, (18)F-fluorodeoxyglucose uptake positron emission tomography/computed tomography and single-photon emission computed tomography/computed tomography were used to measure subsequently atherosclerotic burden, arterial wall inflammation, and monocyte trafficking to the arterial wall. Ex vivo analysis of monocytes was performed with fluorescence-activated cell sorter analysis, inflammatory stimulation assays, and transendothelial migration assays. In vitro studies of the pathophysiology of Lp(a) on monocytes were performed with an in vitro model for trained immunity.

RESULTS

We show that subjects with elevated Lp(a) (108 mg/dL [50-195 mg/dL]; n=30) have increased arterial inflammation and enhanced peripheral blood mononuclear cells trafficking to the arterial wall compared with subjects with normal Lp(a) (7 mg/dL [2-28 mg/dL]; n=30). In addition, monocytes isolated from subjects with elevated Lp(a) remain in a long-lasting primed state, as evidenced by an increased capacity to transmigrate and produce proinflammatory cytokines on stimulation (n=15). In vitro studies show that Lp(a) contains OxPL and augments the proinflammatory response in monocytes derived from healthy control subjects (n=6). This effect was markedly attenuated by inactivating OxPL on Lp(a) or removing OxPL on apolipoprotein(a).

CONCLUSIONS

These findings demonstrate that Lp(a) induces monocyte trafficking to the arterial wall and mediates proinflammatory responses through its OxPL content. These findings provide a novel mechanism by which Lp(a) mediates cardiovascular disease.

CLINICAL TRIAL REGISTRATION

URL: http://www.trialregister.nl. Unique identifier: NTR5006 (VIPER Study).