Association of Mild to Moderate Aortic Valve Stenosis Progression With Higher Lipoprotein(a) and Oxidized Phospholipid Levels: Secondary Analysis of a Randomized Clinical Trial

ApoC-III is a novel inducer of calcification in human aortic valves

Calcific aortic valve disease (CAVD) occurs when subpopulations of valve cells undergo specific differentiation pathways, promoting tissue fibrosis and calcification. Lipoprotein particles carry oxidized lipids that promote valvular disease, but low-density lipoprotein-lowering therapies have failed in clinical trials, and there are currently no pharmacological interventions available for this disease. Apolipoproteins are known promoters of atherosclerosis, but whether they possess pathogenic properties in CAVD is less clear. To search for a possible link, we assessed 12 apolipoproteins in nonfibrotic/noncalcific and fibrotic/calcific aortic valve tissues by proteomics and immunohistochemistry to understand if they were enriched in calcified areas. Eight apolipoproteins (apoA-I, apoA-II, apoA-IV, apoB, apoC-III, apoD, apoL-I, and apoM) were enriched in the calcific versus nonfibrotic/noncalcific tissues. Apo(a), apoB, apoC-III, apoE, and apoJ localized within the disease-prone fibrosa and colocalized with calcific regions as detected by immunohistochemistry. Circulating apoC-III on lipoprotein(a) is a potential biomarker of aortic stenosis incidence and progression, but whether apoC-III also induces aortic valve calcification is unknown. We found that apoC-III was increased in fibrotic and calcific tissues and observed within the calcification-prone fibrosa layer as well as around calcification. In addition, we showed that apoC-III induced calcification in primary human valvular cell cultures via a mitochondrial dysfunction/inflammation-mediated pathway. This study provides a first assessment of a broad array of apolipoproteins in CAVD tissues, demonstrates that specific apolipoproteins associate with valvular calcification, and implicates apoC-III as an active and modifiable driver of CAVD beyond its potential role as a biomarker.

Current Evidence and Future Perspectives on Pharmacological Treatment of Calcific Aortic Valve Stenosis

Calcific aortic valve stenosis (CAVS), the most common heart valve disease, is characterized by the slow progressive fibro-calcific remodeling of the valve leaflets, leading to progressive obstruction to the blood flow. CAVS is an increasing health care burden and the development of an effective medical treatment is a major medical need. To date, no effective pharmacological therapies have proven to halt or delay its progression to the severe symptomatic stage and aortic valve replacement represents the only available option to improve clinical outcomes and to increase survival. In the present report, the current knowledge and latest advances in the medical management of patients with CAVS are summarized, placing emphasis on lipid-lowering agents, vasoactive drugs, and anti-calcific treatments. In addition, novel potential therapeutic targets recently identified and currently under investigation are reported.

The role of oxidized phospholipids in the development of disease

Oxidized phospholipids (OxPLs), complex mixtures of phospholipid oxidation products generated during normal or pathological processes, are increasingly recognized to show bioactive effects on many cellular signalling pathways. There is a growing body of evidence showing that OxPLs play an important role in many diseases, so it is essential to define the specific role of OxPLs in different diseases for the design of disease therapies. In vastly diverse pathological processes, OxPLs act as pro-inflammatory agents and contribute to the progression of many diseases; in addition, they play a role in anti-inflammatory processes, promoting the dissipation of inflammation and inhibiting the progression of some diseases. In addition to participating in the regulation of inflammatory responses, OxPLs affect the occurrence and development of diseases through other pathways, such as apoptosis promotion. In this review, the different and even opposite effects of different OxPL molecular species are discussed. Furthermore, the specific effects of OxPLs in various diseases, as well as the receptor and cellular mechanisms involved, are summarized.

Plasma lipoprotein(a) concentration as an independent predictor of hemodynamic progression of aortic valve stenosis

Calcific aortic valve disease (CAVD) is a common cardiovascular disorder of high social significance. This study aimed to identify independent predictors of hemodynamic progression of CAVD. The relationship between some risk factors, including the rs10455872 polymorphism in the intron 25 of the lipoprotein(a) [Lp(a)] coding region and the plasma Lp(a) concentration, and CAVD severity were prospectively examined in 114 patients. Age (p = 0.023), smoking (p = 0.038), lack of obesity (p = 0.005), triglyceride levels (p = 0.039), and plasma Lp(a) (p < 0.0001) levels were found to be significant determinants of stenosis progression. The rs10455872 polymorphism; however, was not found to be a significant factor for neither the stenosis severity (p = 0.773) nor for plasma Lp(a) levels (p = 0.617). We established a highly significant Lp(a) cut-off concentration (21.2 mg/dL) distinguishing the aortic valve calcification without stenosis from the significant stenosis. Plasma Lp(a) concentration was the only independent predictor of disease progression (p < 0.0001). Moreover, patients with plasma levels of Lp(a) ≥ 21.2 mg/dL were 55 times more likely to develop aortic valve stenosis. We conclude that Lp(a) concentration may prove valuable for more reliable identification of patients at risk of accelerated CAVD development. Future studies are desirable to determine whether plasma Lp(a) levels could be used as a potential biomarker for aortic stenosis progression.

Lipoprotein (a): An Update on a Marker of Residual Risk and Associated Clinical Manifestations

Lipoprotein (a) [Lp(a)] is a low-density, cholesterol-containing lipoprotein that differs from other low-density lipoproteins due to the presence of apolipoprotein(a) bound to its surface apolipoprotein B100. Multiple epidemiologic studies, including Mendelian Randomization studies, have demonstrated that increasing Lp(a) levels are associated with increased risk of heart disease, including atherosclerotic cardiovascular disease and calcific aortic stenosis. The risk associated with elevations in Lp(a) appears to be independent of other lipid markers. While the current treatment options for elevated Lp(a) are limited, promising new therapies are under development, leading to renewed interest in Lp(a). This review provides an overview of the biology and epidemiology of Lp(a), available outcome studies, and insights into future therapies.

Lipoprotein(a) and calcific aortic valve stenosis: A systematic review

Calcific aortic valve stenosis (AS) is the most common form of acquired valvular heart disease needing intervention and our understanding of this disease has evolved from one of degenerative calcification to that of an active process driven by the interplay of genetic factors and chronic inflammation modulated by risk factors such as smoking, hypertension and elevated cholesterol. Lipoprotein(a) [Lp (a)] is a cholesterol rich particle secreted by the liver which functions as the major lipoprotein carrier of phosphocholine-containing oxidized phospholipids. Lp(a) levels are largely genetically determined by polymorphisms in the LPA gene. While there is an extensive body of evidence linking Lp(a) to atherosclerotic cardiovascular disease, emerging evidence now suggests a similar association of Lp(a) to calcific AS. In this article, we performed a systematic review of all published literature to assess the association between Lp(a) and calcific aortic valve (AV) disease. In addition, we review the potential mechanisms by which Lp(a) influences the progression of valve disease. Our review identified a total of 21 studies, varying from case-control studies, prospective or retrospective observational cohort studies to Mendelian randomized studies that assessed the association between Lp(a) and calcific AS. All but one of the above studies demonstrated significant association between elevated Lp(a) and calcific AS. We conclude that there is convincing evidence supporting a causal association between elevated Lp(a) and calcific AS. In addition, elevated Lp(a) predicts a faster hemodynamic progression of AS, and increased risk of AV replacement, especially in younger patients. Further research into the clinical utility of Lp(a) as a marker for predicting the incidence, progression, and outcomes of sclerodegenerative AV disease is needed.

Association of serum lipoprotein(a) level with the severity and prognosis of calcific aortic valve stenosis: a Chinese cohort study

BACKGROUND

There was a causal relationship between elevated lipoprotein(a) [Lp(a)] levels and increased risk of calcific aortic valve stenosis (CAVS) in whites and blacks. The present study aimed to investigate whether Lp(a) levels were associated with aortic stenosis (AS) severity and clinical events in Chinese patients.

METHODS

Levels of serum Lp(a) were measured in 652 patients with CAVS, whom all underwent baseline echocardiographic examination. The clinical endpoint was defined as a composite of aortic valve replacement (AVR) and cardiac death.

RESULTS

Patients in the tertile 3 of Lp(a) had a higher percentage of severe AS compared with those in the tertile 1 and 2 of Lp(a) (46.2% vs. 33.9%, P = 0.005). Moreover, the top tertile of Lp(a) was an independent predictor of severe AS (OR = 1.78, 95% CI: 1.18-2.66, P = 0.006). However, there was no significant association between tertile 3 of Lp(a) and clinical events (hazard ratio: 0.73; 95% CI: 0.43-1.24; P = 0.239) in the multivariate Cox regression analysis during a mean follow-up time of 3.16 ± 2.74 years.

CONCLUSIONS

Elevated Lp(a) level was an independent predictor of severe AS by echocardiography in the Chinese population, but was not associated with the increased risk of AVR and cardiac death, suggesting that Lp(a) levels might be helpful in the risk stratification of patients with CAVS.

Durability of transcatheter aortic valve implantation: A translational review

Until recently, transcatheter aortic valve implantation was restricted to high-risk and inoperable patients. The updated 2017 European Society of Cardiology Guidelines has widened the indication to include intermediate-risk patients, based on two recently published trials (PARTNER 2 and SURTAVI). Moreover, two other recent trials (PARTNER 3 and EVOLUT LOW RISK) have demonstrated similar results with transcatheter aortic valve implantation in low-risk patients. Thus, extension of transcatheter aortic valve implantation to younger patients, who are currently treated by surgical aortic valve replacement, raises the crucial question of bioprosthesis durability. In this translational review, we propose to produce a state-of-the-art overview of the durability of transcatheter aortic valve implantation by integrating knowledge of the basic science of bioprosthesis degeneration (pathophysiology and biomarkers). After summarising the new definition of structural valve deterioration, we will present what is known about the pathophysiology of aortic stenosis and bioprosthesis degeneration. Next, we will consider how to identify a population at risk of early degeneration, and how basic science with the help of biomarkers could identify and predict structural valve deterioration. Finally, we will present data on the differences in durability of transcatheter aortic valve implantation compared with surgical aortic valve replacement.

ApoCIII-Lp(a) complexes in conjunction with Lp(a)-OxPL predict rapid progression of aortic stenosis

OBJECTIVE

This study assessed whether apolipoprotein CIII-lipoprotein(a) complexes (ApoCIII-Lp(a)) associate with progression of calcific aortic valve stenosis (AS).

METHODS

Immunostaining for ApoC-III was performed in explanted aortic valve leaflets in 68 patients with leaflet pathological grades of 1-4. Assays measuring circulating levels of ApoCIII-Lp(a) complexes were measured in 218 patients with mild-moderate AS from the AS Progression Observation: Measuring Effects of Rosuvastatin (ASTRONOMER) trial. The progression rate of AS, measured as annualised changes in peak aortic jet velocity (V_peak), and combined rates of aortic valve replacement (AVR) and cardiac death were determined. For further confirmation of the assay data, a proteomic analysis of purified Lp(a) was performed to confirm the presence of apoC-III on Lp(a).

RESULTS

Immunohistochemically detected ApoC-III was prominent in all grades of leaflet lesion severity. Significant interactions were present between ApoCIII-Lp(a) and Lp(a), oxidised phospholipids on apolipoprotein B-100 (OxPL-apoB) or on apolipoprotein (a) (OxPL-apo(a)) with annualised V_peak (all p<0.05). After multivariable adjustment, patients in the top tertile of both apoCIII-Lp(a) and Lp(a) had significantly higher annualised V_peak (p<0.001) and risk of AVR/cardiac death (p=0.03). Similar results were noted with OxPL-apoB and OxPL-apo(a). There was no association between autotaxin (ATX) on ApoB and ATX on Lp(a) with faster progression of AS. Proteomic analysis of purified Lp(a) showed that apoC-III was prominently present on Lp(a).

CONCLUSION

ApoC-III is present on Lp(a) and in aortic valve leaflets. Elevated levels of ApoCIII-Lp(a) complexes in conjunction with Lp(a), OxPL-apoB or OxPL-apo(a) identify patients with pre-existing mild-moderate AS who display rapid progression of AS and higher rates of AVR/cardiac death.

TRIAL REGISTRATION

NCT00800800.

Conceptualization of Heterogeneity of Chronic Diseases and Atherosclerosis as a Pathway to Precision Medicine: Endophenotype, Endotype, and Residual Cardiovascular Risk

The article discusses modern approaches to the conceptualization of pathogenetic heterogeneity in various branches of medical science. The concepts of endophenotype, endotype, and residual cardiovascular risk and the scope of their application in internal medicine and cardiology are considered. Based on the latest results of studies of the genetic architecture of atherosclerosis, five endotypes of atherosclerosis have been proposed. Each of the presented endotypes represents one or another pathophysiological mechanism of atherogenesis, having an established genetic substrate, a characteristic panel of biomarkers, and a number of clinical features. Clinical implications and perspectives for the study of endotypes of atherosclerosis are briefly reviewed.

Vascular and valvular calcification biomarkers

Vascular and valvular calcification constitutes a major health problem with serious clinical consequences. It is important for medical laboratorians to improve their knowledge on this topic and to know which biological markers may have a potential interest and might be useful for diagnosis and for management of ectopic calcifications. This review focuses on the pathophysiological mechanisms of vascular and valvular calcification, with emphasis on the mechanisms that are different for the two types of events, which underscore the need for differentiated healthcare, and explain different response to therapy. Available imaging and scoring tools used to assess both vascular and valvular calcification, together with the more studied and reliable biological markers emerging in this field (e.g., Fetuin A and matrix Gla protein), are discussed. Recently proposed functional assays, measuring the propensity of human serum to calcify, appear promising for vascular calcification assessment and are described. Further advancement through omic technologies and statistical tools is also reported. Clinical chemistry and laboratory medicine practitioners overlook this new era that will engage them in the near future, where a close cooperation of professionals with different competencies, including laboratorists, is required. This innovative approach may truly revolutionize practice of laboratory and of whole medicine attitude, making progression in knowledge of pathways relevant to health, as the complex calcification-related pathways, and adding value to patient care, through a precision medicine strategy.

Lipoprotein apheresis is an optimal therapeutic option to reduce increased Lp(a) levels

BACKGROUND

Lipoprotein(a) (Lp(a)) is a genetic risk factor for cardiovascular disease (CVD) and is associated with the induction and sustaining of atherosclerotic cardiovascular diseases (ASCVD). Since 2008 Lp(a) along with progressive CVD has been approved as an indication for regular lipoprotein apheresis (LA) in Germany. The German Lipoprotein Apheresis Registry (GLAR) has been initiated to provide statistical evidence for the assessment of extracorporeal procedures to treat dyslipidemia for both LDL-cholesterol (LDL-C) and Lp(a). The GLAR now allows prospective investigations over a 5-year period about annual incidence rates of cardiovascular events. Here Lp(a) patients (LDL-C < 100 mg/dl; Lp(a) > 60 mg/dl or >120 nmol/l) showed the same reduction of major coronary (83%) and non-coronary events (63%) as had been formerly shown in the Pro(a)LiFe study. However, Lp(a) is not only an apolipoprotein(a) (apo(a)) and LDL-C containing particle, which is covalently bound to a LDL-C core by a disulphide bridge. The composition of this particle, inter alia containing oxidized phospholipids, gives pro-atherosclerotic, pro-inflammatory, and pro-thrombotic properties, inducing atherosclerotic processes mainly in the arterial wall. However, recent investigations have shown that a reduction of inflammatory settings without LDL-C or Lp(a) reduction may reduce ASCVD events. Lipoprotein apheresis (LA) could not only reduce LDL-C and Lp(a) in parallel, but also different inflammatory and coagulation parameters. In summary lipoprotein apheresis is not only anti-atherosclerotic, but also anti-inflammatory and anti-thrombotic and therefore an ideal treatment option with respect to the shown reduction of major adverse coronary events (MACE) and major adverse non-coronary events (MANCE) by reducing Lp(a) levels.

Prediction of cardiovascular risk by Lp(a) concentrations or genetic variants within the LPA gene region

In the middle of the 1990s the interest in Lp(a) vanished after a few badly performed studies almost erased Lp(a) from the map of biological targets. However, since roughly 10 years the interest has begun to grow again mainly for two reasons: first, genetic studies using easily accessible and high-throughput techniques for genotyping of single-nucleotide polymorphisms (SNPs) have allowed large studies in patients with cardiovascular disease and controls to be performed. This strengthened the earlier findings on a copy number variation in the LPA gene and its association with cardiovascular outcomes. Second, new therapies are on the horizon raising strong and justified hope that in a few years drugs will become available which tremendously lower Lp(a) concentrations. This review article should provide an introduction to the genetic determination of Lp(a) concentrations and considerations whether Lp(a) concentrations or genetic variants are important for the prediction of cardiovascular risk.

Relation of Lipid-Lowering Therapy to Need for Aortic Valve Replacement in Patients With Asymptomatic Mild to Moderate Aortic Stenosis

In this study, we aimed to determine if pretreatment low-density lipoprotein (LDL) levels and aortic stenosis (AS) severity alter the efficacy of lipid-lowering therapy on reducing aortic valve replacement (AVR). We used 1,687 patients with asymptomatic mild-to-moderate AS, who were randomly assigned (1:1) to 40/10 mg simvastatin/ezetimibe combination versus. placebo in the simvastatin and ezetimibe in aortic stenosis (SEAS) trial. Pretreatment LDL levels (>4 mmol/L) and peak aortic jet velocity (3 m/s) were used to partition study participants into 4 groups, which were followed for a primary endpoint of AVR. Cox regression with tests for interaction was used to study the effect of randomized treatment in each subgroup. During a median follow-up of 4.3 years (IQR 4.2 to 4.7 years; total 7,396 patient-years of follow-up), 478 (28%) patients underwent AVR and 146 (9%) died. A significant risk dependency was detected between simvastatin/ezetimibe combination, LDL levels and mild versus moderate AS on rates of AVR (p = 0.01 for interaction). In stratified analyses, randomized treatment, therefore, reduced the rate of AVR in patients with LDL levels >4 mmol and mild AS at baseline (HR 0.4; 95% CI: 0.2 to 0.9). There was no detectable effect of randomized treatment on the need for AVR in the 3 other participants subgroups. We conclude, that in a secondary analysis from a prospective randomized clinical trial, treatment with simvastatin/ezetimibe combination reduced the need for AVR in a subset of patients with mild AS and high pretreatment LDL levels (Unique identifier on clinicaltrials.gov: NCT00092677).

Molecular, Population, and Clinical Aspects of Lipoprotein(a): A Bridge Too Far?

There is now significant evidence to support an independent causal role for lipoprotein(a) (Lp(a)) as a risk factor for atherosclerotic cardiovascular disease. Plasma Lp(a) concentrations are predominantly determined by genetic factors. However, research into Lp(a) has been hampered by incomplete understanding of its metabolism and proatherogeneic properties and by a lack of suitable animal models. Furthermore, a lack of standardized assays to measure Lp(a) and no universal consensus on optimal plasma levels remain significant obstacles. In addition, there are currently no approved specific therapies that target and lower elevated plasma Lp(a), although there are recent but limited clinical outcome data suggesting benefits of such reduction. Despite this, international guidelines now recognize elevated Lp(a) as a risk enhancing factor for risk reclassification. This review summarises the current literature on Lp(a), including its discovery and recognition as an atherosclerotic cardiovascular disease risk factor, attempts to standardise analytical measurement, interpopulation studies, and emerging therapies for lowering elevated Lp(a) levels.

An update on lipid oxidation and inflammation in cardiovascular diseases

Cardiovascular diseases (CVD), including ischemic heart diseases and cerebrovascular diseases, are the leading causes of morbidity and mortality worldwide. Atherosclerosis is the major underlying factor for most CVD. It is well-established that oxidative stress and inflammation are two major mechanisms leading to atherosclerosis. Under oxidative stress, polyunsaturated fatty acids (PUFA)-containing phospholipids and cholesterol esters in cellular membrane and lipoproteins can be readily oxidized through a free radical-induced lipid peroxidation (LPO) process to form a complex mixture of oxidation products. Overwhelming evidence demonstrates that these oxidized lipids are actively involved in the inflammatory responses in atherosclerosis by interacting with immune cells (such as macrophages) and endothelial cells. In addition to lipid lowering in the prevention and treatment of atherosclerotic CVD, targeting chronic inflammation has been entering the medical realm. Clinical trials are under way to lower the lipoprotein (a) (Lp(a)) and its associated oxidized phospholipids, which will provide clinical evidence that targeting inflammation caused by oxidized lipids is a viable approach for CVD. In this review, we aim to give an update on our understanding of the free radical oxidation of LPO, analytical technique to analyze the oxidation products, especially the oxidized phospholipids and cholesterol esters in low density lipoproteins (LDL), and focusing on the experimental and clinical evidence on the role of lipid oxidation in the inflammatory responses associated with CVD, including myocardial infarction and calcific aortic valve stenosis. The challenges and future directions in understanding the role of LPO in CVD will also be discussed.

Lipoprotein(a) in Patients Undergoing Transcatheter Aortic Valve Replacement

Lipoprotein(a) [Lp(a)] is a genetically determined risk factor for calcific aortic valve stenosis (CAVS) for which transcatheter aortic valve replacement (TAVR) is increasingly utilized as treatment. We evaluated the effect of a program to increase testing of and define the prevalence of elevated Lp(a) among patients undergoing TAVR. Educational efforts and incorporation of a “check-box” Lp(a) order to the preoperative TAVR order set were instituted. Retrospective chart review was performed in 229 patients requiring TAVR between May 2013 and September 2018. Of these patients, 57% had an Lp(a) level measured; testing rates increased from 0% in 2013 to 96% in 2018. Lipoprotein(a) testing occurred in 11% of patients before and in 80% of patients after the “check-box” order set ( P < .001). The prevalence of elevated Lp(a) (≥30 mg/dL) was 35%; these patients had a higher incidence of coronary artery disease requiring revascularization compared with patients with normal Lp(a) (65% vs 47%; P = .047). Patients with Lp(a) ≥30 mg/dL also had higher incidence of paravalvular leak compared with those with normal Lp(a) (13% vs 4%; P = .04). This study defines the prevalence of elevated Lp(a) in advanced stages of CAVS and provides a practice pathway to assess procedural complications and long-term outcomes of TAVR in patients with elevated Lp(a) levels.