Autotaxin interacts with lipoprotein(a) and oxidized phospholipids in predicting the risk of calcific aortic valve stenosis in patients with coronary artery disease

Therapeutic Potential of Lipoprotein(a) Inhibitors

Increasing evidence has implicated lipoprotein(a) [Lp(a)] in the causality of atherosclerosis and calcific aortic stenosis. This has stimulated immense interest in developing novel approaches to integrating Lp(a) into the setting of cardiovascular prevention. Current guidelines advocate universal measurement of Lp(a) levels, with the potential to influence cardiovascular risk assessment and triage of higher-risk patients to use of more intensive preventive therapies. In parallel, considerable activity has been undertaken to develop novel therapeutics with the potential to achieve selective and substantial reductions in Lp(a) levels. Early studies of antisense oligonucleotides (e.g., mipomersen, pelacarsen), RNA interference (e.g., olpasiran, zerlasiran, lepodisiran) and small molecule inhibitors (e.g., muvalaplin) have demonstrated effective Lp(a) lowering and good tolerability. These agents are moving forward in clinical development, in order to determine whether Lp(a) lowering reduces cardiovascular risk. The results of these studies have the potential to transform our approach to the prevention of cardiovascular disease.

Lipoprotein(a): Emerging insights and therapeutics

The strong association between lipoprotein (a) [Lp(a)] and atherosclerotic cardiovascular disease has led to considerations of Lp(a) being a potential target for mitigating residual cardiovascular risk. While approximately 20 % of the population has an Lp(a) level greater than 50 mg/dL, there are no currently available pharmacological lipid-lowering therapies that have demonstrated substantial reduction in Lp(a). Novel therapies to lower Lp(a) include antisense oligonucleotides and small-interfering ribonucleic acid molecules and have shown promising results in phase 2 trials. Phase 3 trials are currently underway and will test the causal relationship between Lp(a) and ASCVD and whether lowering Lp(a) reduces cardiovascular outcomes. In this review, we summarize emerging insights related to Lp(a)'s role as a risk-enhancing factor for ASCVD, association with calcific aortic stenosis, effects of existing therapies on Lp(a) levels, and variations amongst patient populations. The evolving therapeutic landscape of emerging therapeutics is further discussed.

Autotaxin inhibition attenuates the aortic valve calcification by suppressing inflammation-driven fibro-calcific remodeling of valvular interstitial cells

BACKGROUND

Patients with fibro-calcific aortic valve disease (FCAVD) have lipid depositions in their aortic valve that engender a proinflammatory impetus toward fibrosis and calcification and ultimately valve leaflet stenosis. Although the lipoprotein(a)-autotaxin (ATX)-lysophosphatidic acid axis has been suggested as a potential therapeutic target to prevent the development of FCAVD, supportive evidence using ATX inhibitors is lacking. We here evaluated the therapeutic potency of an ATX inhibitor to attenuate valvular calcification in the FCAVD animal models.

METHODS

ATX level and activity in healthy participants and patients with FCAVD were analyzed using a bioinformatics approach using the Gene Expression Omnibus datasets, enzyme-linked immunosorbent assay (ELISA), immunohistochemistry, and western blotting. To evaluate the efficacy of ATX inhibitor, interleukin-1 receptor antagonist-deficient (Il1rn-/-) mice and cholesterol-enriched diet-induced rabbits were used as the FCAVD models, and primary human valvular interstitial cells (VICs) from patients with calcification were employed.

RESULTS

The global gene expression profiles of the aortic valve tissue of patients with severe FCAVD demonstrated that ATX gene expression was significantly upregulated and correlated with lipid retention (r = 0.96) or fibro-calcific remodeling-related genes (r = 0.77) in comparison to age-matched non-FCAVD controls. Orally available ATX inhibitor, BBT-877, markedly ameliorated the osteogenic differentiation and further mineralization of primary human VICs in vitro. Additionally, ATX inhibition significantly attenuated fibrosis-related factors' production, with a detectable reduction of osteogenesis-related factors, in human VICs. Mechanistically, ATX inhibitor prohibited fibrotic changes in human VICs via both canonical and non-canonical TGF-β signaling, and subsequent induction of CTGF, a key factor in tissue fibrosis. In the in vivo FCAVD model system, ATX inhibitor exposure markedly reduced calcific lesion formation in interleukin-1 receptor antagonist-deficient mice (Il1rn-/-, P = 0.0210). This inhibition ameliorated the rate of change in the aortic valve area (P = 0.0287) and mean pressure gradient (P = 0.0249) in the FCAVD rabbit model. Moreover, transaortic maximal velocity (Vmax) was diminished with ATX inhibitor administration (mean Vmax = 1.082) compared to vehicle control (mean Vmax = 1.508, P = 0.0221). Importantly, ATX inhibitor administration suppressed the effects of a high-cholesterol diet and vitamin D2-driven fibrosis, in association with a reduction in macrophage infiltration and calcific deposition, in the aortic valves of this rabbit model.

CONCLUSIONS

ATX inhibition attenuates the development of FCAVD while protecting against fibrosis and calcification in VICs, suggesting the potential of using ATX inhibitors to treat FCAVD.

Oxidized phospholipids in cardiovascular disease

Prolonged or excessive exposure to oxidized phospholipids (OxPLs) generates chronic inflammation. OxPLs are present in atherosclerotic lesions and can be detected in plasma on apolipoprotein B (apoB)-containing lipoproteins. When initially conceptualized, OxPL-apoB measurement in plasma was expected to reflect the concentration of minimally oxidized LDL, but, surprisingly, it correlated more strongly with plasma lipoprotein(a) (Lp(a)) levels. Indeed, experimental and clinical studies show that Lp(a) particles carry the largest fraction of OxPLs among apoB-containing lipoproteins. Plasma OxPL-apoB levels provide diagnostic information on the presence and extent of atherosclerosis and improve the prognostication of peripheral artery disease and first and recurrent myocardial infarction and stroke. The addition of OxPL-apoB measurements to traditional cardiovascular risk factors improves risk reclassification, particularly in patients in intermediate risk categories, for whom improving decision-making is most impactful. Moreover, plasma OxPL-apoB levels predict cardiovascular events with similar or greater accuracy than plasma Lp(a) levels, probably because this measurement reflects both the genetics of elevated Lp(a) levels and the generalized or localized oxidation that modifies apoB-containing lipoproteins and leads to inflammation. Plasma OxPL-apoB levels are reduced by Lp(a)-lowering therapy with antisense oligonucleotides and by lipoprotein apheresis, niacin therapy and bariatric surgery. In this Review, we discuss the role of role OxPLs in the pathophysiology of atherosclerosis and Lp(a) atherogenicity, and the use of OxPL-apoB measurement for improving prognosis, risk reclassification and therapeutic interventions.

Daring to dream: Targeting lipoprotein(a) as a causal and risk-enhancing factor

Lipoprotein(a) [Lp(a)], a distinct lipoprotein class, has become a major focus for cardiovascular research. This review is written in light of the recent guideline and consensus statements on Lp(a) and focuses on 1) the causal association between Lp(a) and cardiovascular outcomes, 2) the potential mechanisms by which elevated Lp(a) contributes to cardiovascular diseases, 3) the metabolic insights on the production and clearance of Lp(a) and 4) the current and future therapeutic approaches to lower Lp(a) concentrations. The concentrations of Lp(a) are under strict genetic control. There exists a continuous relationship between the Lp(a) concentrations and risk for various endpoints of atherosclerotic cardiovascular disease (ASCVD). One in five people in the Caucasian population is considered to have increased Lp(a) concentrations; the prevalence of elevated Lp(a) is even higher in black populations. This makes Lp(a) a cardiovascular risk factor of major public health relevance. Besides the association between Lp(a) and myocardial infarction, the relationship with aortic valve stenosis has become a major focus of research during the last decade. Genetic studies provided strong support for a causal association between Lp(a) and cardiovascular outcomes: carriers of genetic variants associated with lifelong increased Lp(a) concentration are significantly more frequent in patients with ASCVD. This has triggered the development of drugs that can specifically lower Lp(a) concentrations: mRNA-targeting therapies such as anti-sense oligonucleotide (ASO) therapies and short interfering RNA (siRNA) therapies have opened new avenues to lower Lp(a) concentrations more than 95%. Ongoing Phase II and III clinical trials of these compounds are discussed in this review.

Lipoprotein(a) and calcific aortic valve disease initiation and progression: a systematic review and meta-analysis

Although evidence indicates the association of lipoprotein(a) [Lp(a)] with atherosclerosis, the link with calcific aortic valve disease (CAVD) is unclear. This systematic review and meta-analysis explores the connection between Lp(a) and aortic valve calcification and stenosis (AVS). We included all relevant studies, indexed in eight databases, up to February 2023. A total of 44 studies (163 139 subjects) were included, with 16 of them being further meta-analysed. Despite considerable heterogeneity, most studies support the relationship between Lp(a) and CAVD, especially in younger populations, with evidence of early aortic valve micro-calcification in elevated-Lp(a) populations. The quantitative synthesis showed higher Lp(a) levels, by 22.63 nmol/L (95% CI: 9.98-35.27), for patients with AVS, while meta-regressing the data revealed smaller Lp(a) differences for older populations with a higher proportion of females. The meta-analysis of eight studies providing genetic data, revealed that the minor alleles of both rs10455872 and rs3798220 LPA gene loci were associated with higher risk for AVS (pooled odds ratio 1.42; 95% CI: 1.34-1.50 and 1.27; 95% CI: 1.09-1.48, respectively). Importantly, high-Lp(a) individuals displayed not only faster AVS progression, by a mean difference of 0.09 m/s/year (95% CI: 0.09-0.09), but also a higher risk of serious adverse outcomes, including death (pooled hazard ratio 1.39; 95% CI: 1.01-1.90). These summary findings highlight the effect of Lp(a) on CAVD initiation, progression and outcomes, and support the early onset of Lp(a)-related subclinical lesions before clinical evidence.

The Complex Relationship between Hypoxia Signaling, Mitochondrial Dysfunction and Inflammation in Calcific Aortic Valve Disease: Insights from the Molecular Mechanisms to Therapeutic Approaches

Calcific aortic valve stenosis (CAVS) is among the most common causes of cardiovascular mortality in an aging population worldwide. The pathomechanisms of CAVS are such a complex and multifactorial process that researchers are still making progress to understand its physiopathology as well as the complex players involved in CAVS pathogenesis. Currently, there is no successful and effective treatment to prevent or slow down the disease. Surgical and transcatheter valve replacement represents the only option available for treating CAVS. Insufficient oxygen availability (hypoxia) has a critical role in the pathogenesis of almost all CVDs. This process is orchestrated by the hallmark transcription factor, hypoxia-inducible factor 1 alpha subunit (HIF-1α), which plays a pivotal role in regulating various target hypoxic genes and metabolic adaptations. Recent studies have shown a great deal of interest in understanding the contribution of HIF-1α in the pathogenesis of CAVS. However, it is deeply intertwined with other major contributors, including sustained inflammation and mitochondrial impairments, which are attributed primarily to CAVS. The present review aims to cover the latest understanding of the complex interplay effect of hypoxia signaling pathways, mitochondrial dysfunction, and inflammation in CAVS. We propose further hypotheses and interconnections on the complexity of these impacts in a perspective of better understanding the pathophysiology. These interplays will be examined considering recent studies that shall help us better dissect the molecular mechanism to enable the design and development of potential future therapeutic approaches that can prevent or slow down CAVS processes.

Lipoprotein(a) As a Potential Predictive Factor for Earlier Aortic Valve Replacement in Patients with Bicuspid Aortic Valve

Bicuspid aortic valve (BAV) affects 0.5-2% of the general population and constitutes the major cause of severe aortic valve stenosis (AVS) in individuals ≤70 years. The aim of the present study was to evaluate the parameters that may provide information about the risk of AVS developing in BAV patients, with particular emphasis on lipoprotein(a) (Lp(a)), which is a well-recognized risk factor for stenosis in the general population. We also analyzed the impact of autotaxin (ATX) and interleukin-6 (IL-6) as parameters potentially related to the pathomechanism of Lp(a) action. We found that high Lp(a) levels (>50 mg/dL) occurred significantly more frequently in patients with AVS than in patients without AVS, both in the group below and above 45 years of age (p = 0.036 and p = 0.033, respectively). Elevated Lp(a) levels were also strictly associated with the need for aortic valve replacement (AVR) at a younger age (p = 0.016). However, the Lp(a) concentration did not differ significantly between patients with and without AVS. Similarly, we observed no differences in ATX between the analyzed patient groups, and both ATX activity and concentration correlated significantly with Lp(a) level (R = 0.465, p < 0.001 and R = 0.599, p < 0.001, respectively). We revealed a significantly higher concentration of IL-6 in young patients with AVS. However, this observation was not confirmed in the group of patients over 45 years of age. We also did not observe a significant correlation between IL-6 and Lp(a) or between CRP and Lp(a) in any of the analyzed groups of BAV patients. Our results demonstrate that a high level of Lp(a), greater than 50 mg/dL, may be a significant predictive factor for earlier AVR. Lp(a)-related parameters, such as ATX and IL-6, may be valuable in providing information about the additional cardiovascular risks associated with developing AVS.

Atherosclerosis Calcification: Focus on Lipoproteins

Atherosclerosis is a chronic inflammatory disease characterized by the accumulation of lipids in the vessel wall, leading to the formation of an atheroma and eventually to the development of vascular calcification (VC). Lipoproteins play a central role in the development of atherosclerosis and VC. Both low- and very low-density lipoproteins (LDL and VLDL) and lipoprotein (a) (Lp(a)) stimulate, while high-density lipoproteins (HDL) reduce VC. Apolipoproteins, the protein component of lipoproteins, influence the development of VC in multiple ways. Apolipoprotein AI (apoAI), the main protein component of HDL, has anti-calcific properties, while apoB and apoCIII, the main protein components of LDL and VLDL, respectively, promote VC. The role of lipoproteins in VC is also related to their metabolism and modifications. Oxidized LDL (OxLDL) are more pro-calcific than native LDL. Oxidation also converts HDL from anti- to pro-calcific. Additionally, enzymes such as autotaxin (ATX) and proprotein convertase subtilisin/kexin type 9 (PCSK9), involved in lipoprotein metabolism, have a stimulatory role in VC. In summary, a better understanding of the mechanisms by which lipoproteins and apolipoproteins contribute to VC will be crucial in the development of effective preventive and therapeutic strategies for VC and its associated cardiovascular disease.

Lipoprotein(a) and Atherosclerotic Cardiovascular Diseases: Evidence from Chinese Population

Cardiovascular disease (CVD) is the leading cause of mortality worldwide. Multiple factors are involved in CVD, and emerging data indicate that lipoprotein(a) (Lp(a)) may be associated with atherosclerotic cardiovascular disease (ASCVD) independent of other traditional risk factors. Lp(a) has been identified as a novel therapeutic target. Previous studies on the influence of Lp(a) in CVD have mainly used in western populations. In this review, the association of plasma Lp(a) concentration with ASCVD was summarized, with regards to epidemiological, population-based observational, and pathological studies in Chinese populations. Lp(a) mutations and copy number variations in Chinese populations are also explored. Finally, the impact of plasma Lp(a) levels on patients with type 2 diabetes mellitus, cancer, and familial hypercholesterolemia are discussed.

Calcific aortic valve disease: mechanisms, prevention and treatment

Calcific aortic valve disease (CAVD) is the most common disorder affecting heart valves and is characterized by thickening, fibrosis and mineralization of the aortic valve leaflets. Analyses of surgically explanted aortic valve leaflets have shown that dystrophic mineralization and osteogenic transition of valve interstitial cells co-occur with neovascularization, microhaemorrhage and abnormal production of extracellular matrix. Age and congenital bicuspid aortic valve morphology are important and unalterable risk factors for CAVD, whereas additional risk is conferred by elevated blood pressure and plasma lipoprotein(a) levels and the presence of obesity and diabetes mellitus, which are modifiable factors. Genetic and molecular studies have identified that the NOTCH, WNT-β-catenin and myocardin signalling pathways are involved in the control and commitment of valvular cells to a fibrocalcific lineage. Complex interactions between valve endothelial and interstitial cells and immune cells promote the remodelling of aortic valve leaflets and the development of CAVD. Although no medical therapy is effective for reducing or preventing the progression of CAVD, studies have started to identify actionable targets.

The mechanistic pathways of oxidative stress in aortic stenosis and clinical implications

Despite the elucidation of the pathways behind the development of aortic stenosis (AS), there remains no effective medical treatment to slow or reverse its progress. Instead, the gold standard of care in severe or symptomatic AS is replacement of the aortic valve. Oxidative stress is implicated, both directly as well as indirectly, in lipid infiltration, inflammation and fibro-calcification, all of which are key processes underlying the pathophysiology of degenerative AS. This culminates in the breakdown of the extracellular matrix, differentiation of the valvular interstitial cells into an osteogenic phenotype, and finally, calcium deposition as well as thickening of the aortic valve. Oxidative stress is thus a promising and potential therapeutic target for the treatment of AS. Several studies focusing on the mitigation of oxidative stress in the context of AS have shown some success in animal and in vitro models, however similar benefits have yet to be seen in clinical trials. Statin therapy, once thought to be the key to the treatment of AS, has yielded disappointing results, however newer lipid lowering therapies may hold some promise. Other potential therapies, such as manipulation of microRNAs, blockade of the renin-angiotensin-aldosterone system and the use of dipeptidylpeptidase-4 inhibitors will also be reviewed.

Implication of Lipids in Calcified Aortic Valve Pathogenesis: Why Did Statins Fail?

Calcific Aortic Valve Disease (CAVD) is a fibrocalcific disease. Lipoproteins and oxidized phospholipids play a substantial role in CAVD; the level of Lp(a) has been shown to accelerate the progression of valve calcification. Indeed, oxidized phospholipids carried by Lp(a) into the aortic valve stimulate endothelial dysfunction and promote inflammation. Inflammation and growth factors actively promote the synthesis of the extracellular matrix (ECM) and trigger an osteogenic program. The accumulation of ECM proteins promotes lipid adhesion to valve tissue, which could initiate the osteogenic program in interstitial valve cells. Statin treatment has been shown to have the ability to diminish the death rate in subjects with atherosclerotic impediments by decreasing the serum LDL cholesterol levels. However, the use of HMG-CoA inhibitors (statins) as cholesterol-lowering therapy did not significantly reduce the progression or the severity of aortic valve calcification. However, new clinical trials targeting Lp(a) or PCSK9 are showing promising results in reducing the severity of aortic stenosis. In this review, we discuss the implication of lipids in aortic valve calcification and the current findings on the effect of lipid-lowering therapy in aortic stenosis.

Association Between Lipoprotein(a) and Calcific Aortic Valve Disease: A Systematic Review and Meta-Analysis

Background

Preliminary studies indicated that enhanced plasma levels of lipoprotein(a) [lp(a)] might link with the risk of calcific aortic valve disease (CAVD), but the clinical association between them remained inconclusive. This systematic review and meta-analysis were aimed to determine this association.

Methods

We comprehensively searched PubMed, Embase, Web of Science, and Scopus databases for studies reporting the incidence of CAVD and their plasma lp(a) concentrations. Pooled risk ratio (RR) and 95% confidence interval (95% CI) were calculated to evaluate the effect of lp(a) on CAVD using the random-effects model. Subgroup analyses by study types, countries, and the level of adjustment were also conducted. Funnel plots, Egger's test and Begg's test were conducted to evaluate the publication bias.

Results

Eight eligible studies with 52,931 participants were included in this systematic review and meta-analysis. Of these, four were cohort studies and four were case-control studies. Five studies were rated as high quality, three as moderate quality. The pooled results showed that plasma lp(a) levels ≥50 mg/dL were associated with a 1.76-fold increased risk of CAVD (RR, 1.76; 95% CI, 1.47–2.11), but lp(a) levels ≥30 mg/dL were not observed to be significantly related with CAVD (RR, 1.28; 95% CI, 0.98–1.68). We performed subgroup analyses by study type, the RRs of cohort studies revealed lp(a) levels ≥50 mg/dL and lp(a) levels ≥30 mg/dL have positive association with CAVD (RR, 1.70; 95% CI, 1.39–2.07; RR 1.38; 95% CI, 1.19–1.61).

Conclusion

High plasma lp(a) levels (≥50 mg/dL) are significantly associated with increased risk of CAVD.

Lipoprotein(a) Levels at Birth and in Early Childhood: The COMPARE Study

BACKGROUND AND OBJECTIVE

High lipoprotein(a) is a genetically determined causal risk factor for cardiovascular disease, and 20% of the adult population has high levels (ie, >42 mg/dL, >88 nmol/L). We investigated whether early life lipoprotein(a) levels measured in cord blood may serve as a proxy for neonatal venous blood levels, whether lipoprotein(a) birth levels (ie, cord or venous) predict levels later in life, and whether early life and parental levels correlate.

METHODS

The Compare study is a prospective cohort study of newborns (N = 450) from Copenhagen, Denmark, including blood sampling of parents. Plasma lipoprotein(a) was measured in cord blood (N = 402), neonatal venous blood (N = 356), and at 2 (N = 320) and 15 months follow-up (N = 148) of infants, and in parents (N = 705).

RESULTS

Mean lipoprotein(a) levels were 2.2 (95% CI, 1.9-2.5), 2.4 (2.0-2.7), 4.1 (3.4-4.9), and 14.6 (11.4-17.9) mg/dL in cord, neonatal venous, and 2- and 15-month venous samples, respectively. Lipoprotein(a) levels in cord blood correlated strongly with neonatal venous blood levels (R2 = 0.95, P < 0.001) and neonatal levels correlated moderately with 2- and 15-month levels (R2 = 0.68 and 0.67, both P < 0.001). Birth levels ≥ 90th percentile predicted lipoprotein(a) > 42 mg/dL at 15 months with positive predictive values of 89% and 85% for neonatal venous and cord blood. Neonatal and infant levels correlated weakly with parental levels, most pronounced at 15 months (R2 = 0.22, P < 0.001).

CONCLUSIONS

Lipoprotein(a) levels are low in early life, cord blood may serve as a proxy for neonatal venous blood, and birth levels ≥ 90th percentile can identify newborns at risk of developing high levels.

Calcific aortic valve disease: from molecular and cellular mechanisms to medical therapy

Calcific aortic valve disease (CAVD) is a highly prevalent condition that comprises a disease continuum, ranging from microscopic changes to profound fibro-calcific leaflet remodelling, culminating in aortic stenosis, heart failure, and ultimately premature death. Traditional risk factors, such as hypercholesterolaemia and (systolic) hypertension, are shared among atherosclerotic cardiovascular disease and CAVD, yet the molecular and cellular mechanisms differ markedly. Statin-induced low-density lipoprotein cholesterol lowering, a remedy highly effective for secondary prevention of atherosclerotic cardiovascular disease, consistently failed to impact CAVD progression or to improve patient outcomes. However, recently completed phase II trials provide hope that pharmaceutical tactics directed at other targets implicated in CAVD pathogenesis offer an avenue to alter the course of the disease non-invasively. Herein, we delineate key players of CAVD pathobiology, outline mechanisms that entail compromised endothelial barrier function, and promote lipid homing, immune-cell infiltration, and deranged phospho-calcium metabolism that collectively perpetuate a pro-inflammatory/pro-osteogenic milieu in which valvular interstitial cells increasingly adopt myofibro-/osteoblast-like properties, thereby fostering fibro-calcific leaflet remodelling and eventually resulting in left ventricular outflow obstruction. We provide a glimpse into the most promising targets on the horizon, including lipoprotein(a), mineral-binding matrix Gla protein, soluble guanylate cyclase, dipeptidyl peptidase-4 as well as candidates involved in regulating phospho-calcium metabolism and valvular angiotensin II synthesis and ultimately discuss their potential for a future therapy of this insidious disease.

Lipoprotein Proteomics and Aortic Valve Transcriptomics Identify Biological Pathways Linking Lipoprotein(a) Levels to Aortic Stenosis

Lipoprotein(a) (Lp(a)) is one of the most important risk factors for the development of calcific aortic valve stenosis (CAVS). However, the mechanisms through which Lp(a) causes CAVS are currently unknown. Our objectives were to characterize the Lp(a) proteome and to identify proteins that may be differentially associated with Lp(a) in patients with versus without CAVS. Our second objective was to identify genes that may be differentially regulated by exposure to high versus low Lp(a) levels in explanted aortic valves from patients with CAVS. We isolated Lp(a) from the blood of 21 patients with CAVS and 22 volunteers and performed untargeted label-free analysis of the Lp(a) proteome. We also investigated the transcriptomic signature of calcified aortic valves from patients who underwent aortic valve replacement with high versus low Lp(a) levels (n = 118). Proteins involved in the protein activation cascade, platelet degranulation, leukocyte migration, and response to wounding may be associated with Lp(a) depending on CAVS status. The transcriptomic analysis identified genes involved in cardiac aging, chondrocyte development, and inflammation as potentially influenced by Lp(a). Our multi-omic analyses identified biological pathways through which Lp(a) may cause CAVS, as well as key molecular events that could be triggered by Lp(a) in CAVS development.

The Riskier Lipid: What Is on the HORIZON for Lipoprotein (a) and Should There Be Lp(a) Screening for All?

PURPOSE OF REVIEW

Despite widespread targeting of cardiovascular risk factors, many patients continue to experience clinical events. This residual risk has stimulated efforts to develop novel therapeutic approaches to target additional factors underscoring cardiovascular disease. This review aimed to summarize existing evidence supporting targeting of Lp(a) as a novel cardioprotective strategy.

RECENT FINDINGS

Increasing evidence has implicated lipoprotein (a) [Lp(a)] in the pathogenesis of both atherosclerotic and calcific aortic valve disease. Therapeutic advances have produced novel agents that selectively lower Lp(a) levels, which have now progressed to evaluate their impact on cardiovascular events in large clinical outcome trials. Evidence continues to accumulate suggesting that targeting Lp(a) may be effective in reducing cardiovascular risk. With advances in Lp(a) targeted therapeutics, clinical trials now have the opportunity to determine whether this strategy will be effective for high-risk patients.

Genetics of Lipoprotein(a): Cardiovascular Disease and Future Therapy

PURPOSE OF REVIEW

Lipoprotein(a) levels are determined 80-90% by genetics and differ by up to 1000-fold between individuals. This review discusses the most recent literature on lipoprotein(a) as a risk factor for cardiovascular disease, as well as future lipoprotein(a)lowering therapies.

RECENT FINDINGS

Over the past few decades, numerous studies have observed that high lipoprotein(a) levels are associated observationally and causally through human genetics with increased risk of cardiovascular disease. Also, the development of safe and effective therapies to lower lipoprotein(a) is ongoing, most importantly using antisense oligonucleotides to prevent production of lipoprotein(a). Finally, both observational and genetic studies have estimated the extent to which lowering of lipoprotein(a) is needed to obtain a clinically meaningful reduction in the risk of cardiovascular disease. Lipoprotein(a) is a causal risk factor for cardiovascular disease; however, currently no approved safe and effective therapy is available to lower lipoprotein(a) levels. That said, promising randomized studies using antisense oligonucleotides show up to 80% reductions in lipoprotein(a), reductions that hopefully will result in lowering the risk of cardiovascular disease as presently tested in the ongoing HORIZON phase 3 trial.

Correlations between lipoprotein(a) gene polymorphisms and calcific aortic valve disease and coronary heart disease in Han Chinese

Objective

To investigate the relationship between lipoprotein(a) gene (LPA) polymorphisms and calcific aortic valve disease (CAVD) and coronary heart disease (CHD) in Han Chinese.

Methods

A total of 148 patients were recruited (n = 71 with CAVD and n = 77 with CHD) based on a diagnosis achieved using color Doppler echocardiography, coronary angiography, or computed tomography angiography. Seventy-one control individuals without CAVD or CHD were also recruited. Biomarkers including levels of lipoprotein(a) [Lp(a)], low-density lipoprotein and high-density lipoprotein cholesterol, apolipoprotein A1, and apolipoprotein B were tested. LPA polymorphisms rs10455872, rs6415084, rs3798221, and rs7770628 were analyzed using SNaPshot SNP.

Results

Lp(a) levels were significantly higher in CAVD and CHD groups compared with controls. There was no significant difference in the allelic frequency distribution of rs3798221, rs7770628, or rs6415084 between CHD, CAVD, and control groups. Linear regression showed that rs3798221, rs7770628, and rs6415084 were associated with increased Lp(a) concentrations. Two CAVD patients among the 219 participants carried AG minor alleles at rs10455872, while the remainder carried AA minor alleles.

Conclusion

rs3798221, rs6415084, and rs7770628 polymorphisms within LPA are associated with higher Lp(a) plasma levels, which correlate with increased CAVD and CHD risks.

The Expression Regulation and Biological Function of Autotaxin

Autotaxin (ATX) is a secreted glycoprotein and functions as a key enzyme to produce extracellular lysophosphatidic acid (LPA). LPA interacts with at least six G protein-coupled receptors, LPAR1-6, on the cell membrane to activate various signal transduction pathways through distinct G proteins, such as Gi/0, G12/13, Gq/11, and Gs. The ATX-LPA axis plays an important role in physiological and pathological processes, including embryogenesis, obesity, and inflammation. ATX is one of the top 40 most unregulated genes in metastatic cancer, and the ATX-LPA axis is involved in the development of different types of cancers, such as colorectal cancer, ovarian cancer, breast cancer, and glioblastoma. ATX expression is under multifaceted controls at the transcription, post-transcription, and secretion levels. ATX and LPA in the tumor microenvironment not only promote cell proliferation, migration, and survival, but also increase the expression of inflammation-related circuits, which results in poor outcomes for patients with cancer. Currently, ATX is regarded as a potential cancer therapeutic target, and an increasing number of ATX inhibitors have been developed. In this review, we focus on the mechanism of ATX expression regulation and the functions of ATX in cancer development.

Role of inflammation, autotaxin and lipoprotein (a) in degenerative aortic valve stenosis in patients with coronary artery disease

Aim. To study the relationship between the concentration of lipoprotein (a) (Lp (a)) and autotaxin (ATX) in patients with and without degenerative aortic valve stenosis (AoS) in the presence of coronary artery disease (CAD).

Material and methods. The study included 461 patients (mean age, 66±11 years, men, 323), 354 of whom had CAD with stenosis ≥50% in at least one coronary artery according to angiography. Degenerative AoS was diagnosed with ultrasound. The control group consisted of 107 patients without CAD and degenerative AoS. Concentrations of Lp (a), ATX, lipids and blood cells were measured for all patients.

Results. CAD without degenerative AoS (group 1) was diagnosed in 307 patients, while 47 patients had CAD and degenerative AoS (group 2). Patients in both groups were older than patients in the control group (66±10, 74±8, and 61±13 years, respectively). The ATX level was lower in group 1 (median [25; 75%]: 495 [406; 583] ng/ml) than in the control group (545 [412; 654] ng/ml) or group 2 (545 [476; 605] ng/ml) (p<0,05 for all). Lp (a) was lower in the control group (14,5 [5,5; 36,0] mg/dl) than in group 1 (24,9 [9,7; 58,4] mg/dl) (p<0,005) and group 2 (23,8 [9,9; 75,7] mg/dL) (p<0,05). According to the logistic regression, an increased ATX level, regardless of age and other risk factors, was associated with degenerative AoS only in patients with CAD, while age and neutrophil to lymphocyte ratio were associated with the development of degenerative AoS both in patients with CAD and the general group.

Conclusion. An elevated Lp (a) level is associated with CAD regardless of the aortic valve involvement, while an increased concentration of ATX and neutrophil to lymphocyte ratio in patients with CAD were associated with degenerative AoS regardless of age and other risk factors.

A Comparative Analysis of the Lipoprotein(a) and Low-Density Lipoprotein Proteomic Profiles Combining Mass Spectrometry and Mendelian Randomization

Background

Lipoprotein(a) (Lp[a]), which consists of a low-density lipoprotein (LDL) bound to apolipoprotein(a), is one of the strongest genetic risk factors for atherosclerotic cardiovascular diseases. Few studies have performed hypothesis-free direct comparisons of the Lp(a) and the LDL proteomes. Our objectives were to compare the Lp(a) and the LDL proteomic profiles and to evaluate the effect of lifelong exposure to elevated Lp(a) or LDL cholesterol levels on the plasma proteomic profile.

Methods

We performed a label-free analysis of the Lp(a) and LDL proteomic profiles of healthy volunteers in a discovery (n = 6) and a replication (n = 9) phase. We performed inverse variance weighted Mendelian randomization to document the effect of lifelong exposure to elevated Lp(a) or LDL cholesterol levels on the plasma proteomic profile of participants of the INTERVAL study.

Results

We identified 15 proteins that were more abundant on Lp(a) compared with LDL (serping1, pi16, itih1, itih2, itih3, pon1, podxl, cd44, cp, ptprg, vtn, pcsk9, igfals, vcam1, and ttr). We found no proteins that were more abundant on LDL compared with Lp(a). After correction for multiple testing, lifelong exposure to elevated LDL cholesterol levels was associated with the variation of 18 plasma proteins whereas Lp(a) did not appear to influence the plasma proteome.

Conclusions

Results of this study highlight marked differences in the proteome of Lp(a) and LDL as well as in the effect of lifelong exposure to elevated LDL cholesterol or Lp(a) on the plasma proteomic profile.

Oxyphospholipids in Cardiovascular Calcification

Mineralization of cardiovascular structures including blood vessels and heart valves is a common feature. We postulate that ectopic mineralization is a response-to-injury in which signals delivered to cells trigger a chain of events to restore and repair tissues. Maladaptive response to external or internal signals promote the expression of danger-associated molecular patterns, which, in turn, promote, when expressed chronically, a procalcifying gene program. Growing evidence suggest that danger-associated molecular patterns such as oxyphospholipids and small lipid mediators, generated by enzyme activity, are involved in the transition of vascular smooth muscle cells and valve interstitial cells to an osteoblast-like phenotype. Understanding the regulation and the molecular processes underpinning the mineralization of atherosclerotic plaques and cardiac valves are providing valuable mechanistic insights, which could lead to the development of novel therapies. Herein, we provide a focus account on the role oxyphospholipids and their mediators in the development of mineralization in plaques and calcific aortic valve disease.

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.

Lipoprotein (a) and aortic valve calcium in South Asians compared to other race/ethnic groups

BACKGROUND AND AIMS

South Asians are at increased risk for cardiovascular disease (CVD). Aortic valve calcium (AVC) is associated with CVD risk and aortic stenosis. Elevated Lp(a) is a heritable risk factor for CVD and AVC. AVC prevalence and its association with Lp(a) have not been studied in South Asians.

METHODS

Among participants in the Mediators of Atherosclerosis in South Asians Living in America (MASALA) study (n = 695), AVC prevalence and extent were compared to four race/ethnic groups in the Multi-Ethnic Study of Atherosclerosis (MESA) (n = 4671). Multivariable regression was performed to evaluate associations between Lp(a) and AVC stratified by race/ethnic groups, adjusting for cardiovascular risk factors.

RESULTS

After age and sex adjustment, South Asians had higher median Lp(a) (17.0 mg/dL) compared to Whites (12.9 mg/dL), Hispanics (13.1 mg/dL) and Chinese Americans (12.9 mg/dL), and Blacks had highest Lp(a) levels (35.1 mg/dL). There were no differences in the odds of AVC in South Asians compared with Whites or Hispanics, after age and sex adjustment (p = 0.64 and 0.63, respectively). Odds of AVC was lower in Chinese (OR 0.35; 95%CI 0.23-0.54) and somewhat lower in Blacks compared with South Asians (OR 0.76; 0.56-1.04). There were no associations between Lp(a) and AVC presence or extent in South Asians. Lp(a) was associated with AVC only among Blacks and Whites.

CONCLUSIONS

Although present in Whites and Blacks, there were no associations between Lp(a) and AVC in South Asians. These differences may be due to statistic power or race specific modifying factors that influences the effect of Lp(a) particles on AVC pathogenesis.

Activated platelets promote an osteogenic programme and the progression of calcific aortic valve stenosis

AIMS

Calcific aortic valve stenosis (CAVS) is characterized by a fibrocalcific process. Studies have shown an association between CAVS and the activation of platelets. It is believed that shear stress associated with CAVS promotes the activation of platelets. However, whether platelets actively participate to the mineralization of the aortic valve (AV) and the progression of CAVS is presently unknown. To identify the role of platelets into the pathobiology of CAVS.

METHODS AND RESULTS

Explanted control non-mineralized and mineralized AVs were examined by scanning electron microscope (SEM) for the presence of activated platelets. In-depth functional assays were carried out with isolated human valve interstitial cells (VICs) and platelets as well as in LDLR-/- apoB100/100 IGFII (IGFII) mice. Scanning electron microscope and immunogold markings for glycoprotein IIb/IIIa (GPIIb/IIIa) revealed the presence of platelet aggregates with fibrin in endothelium-denuded areas of CAVS. In isolated VICs, collagen-activated platelets induced an osteogenic programme. Platelet-derived adenosine diphosphate induced the release of autotaxin (ATX) by VICs. The binding of ATX to GPIIb/IIIa of platelets generated lysophosphatidic acid (LysoPA) with pro-osteogenic properties. In IGFII mice with CAVS, platelet aggregates were found at the surface of AVs. Administration of activated platelets to IGFII mice accelerated the development of CAVS by 2.1-fold, whereas a treatment with Ki16425, an antagonist of LysoPA receptors, prevented platelet-induced mineralization of the AV and the progression of CAVS.

CONCLUSIONS

These findings suggest a novel role for platelets in the progression of CAVS.

Interaction of Autotaxin With Lipoprotein(a) in Patients With Calcific Aortic Valve Stenosis

Our objectives were to determine whether autotaxin (ATX) is transported by lipoprotein(a) [Lp(a)] in human plasma and if could be used as a biomarker of calcific aortic valve stenosis (CAVS). We first found that ATX activity was higher in Lp(a) compared to low-density lipoprotein fractions in isolated fractions of 10 healthy participants. We developed a specific assay to measure ATX-Lp(a) in 88 patients with CAVS and 144 controls without CAVS. In a multivariable model corrected for CAVS risk factors, ATX-Lp(a) was associated with CAVS (p = 0.003). We concluded that ATX is preferentially transported by Lp(a) and might represent a novel biomarker for CAVS.

Roles for lysophosphatidic acid signaling in vascular development and disease

The bioactive lipid lysophosphatidic acid (LPA) is emerging as an important mediator of inflammation in cardiovascular diseases. Produced in large part by the secreted lysophospholipase D autotaxin (ATX), LPA acts on a series of G protein-coupled receptors and may have action on atypical receptors such as RAGE to exert potent effects on vascular cells, including the promotion of foam cell formation and phenotypic modulation of smooth muscle cells. The signaling effects of LPA can be terminated by integral membrane lipid phosphate phosphatases (LPP) that hydrolyze the lipid to receptor inactive products. Human genetic variants in PLPP3, that predict lower levels of LPP3, associate with risk for premature coronary artery disease, and reductions of LPP3 expression in mice promote the development of experimental atherosclerosis and enhance inflammation in the atherosclerotic lesions. Recent evidence also supports a role for ATX, and potentially LPP3, in calcific aortic stenosis. In summary, LPA may be a relevant inflammatory mediator in atherosclerotic cardiovascular disease and heightened LPA signaling may explain the cardiovascular disease risk effect of PLPP3 variants.

Aortic Valve Stenosis and Mitochondrial Dysfunctions: Clinical and Molecular Perspectives

Calcific aortic stenosis is a disorder that impacts the physiology of heart valves. Fibrocalcific events progress in conjunction with thickening of the valve leaflets. Over the years, these events promote stenosis and obstruction of blood flow. Known and common risk factors are congenital defects, aging and metabolic syndromes linked to high plasma levels of lipoproteins. Inflammation and oxidative stress are the main molecular mediators of the evolution of aortic stenosis in patients and these mediators regulate both the degradation and remodeling processes. Mitochondrial dysfunction and dysregulation of autophagy also contribute to the disease. A better understanding of these cellular impairments might help to develop new ways to treat patients since, at the moment, there is no effective medical treatment to diminish neither the advancement of valve stenosis nor the left ventricular function impairments, and the current approaches are surgical treatment or transcatheter aortic valve replacement with prosthesis.

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.

Lipoprotein(a): Expanding our knowledge of aortic valve narrowing

Elevated levels of lipoprotein(a) [Lp(a)] have been identified as an independent and causal risk factor for atherosclerotic cardiovascular disease (ASCVD) and, more recently, calcific aortic valve disease (CAVD). CAVD is a slow, progressive disorder presenting as severe trileaflet calcification known as aortic valve stenosis (AS) that impairs valve motion and restricts ventricular outflow. AS afflicts 2% of the aging population (≥ 65 years) and tends to be quite advanced by the time it presents clinical symptoms of exertional angina, syncope, or heart failure. Currently, the only effective clinical therapy for AS patients is surgical or transcatheter aortic valve replacement. Evidence is accumulating that Lp(a) can exacerbate pathophysiological processes in CAVD, specifically, endothelial dysfunction, formation of foam cells, and promotion of a pro-inflammatory state. In the valve milieu, the pro-inflammatory effects of Lp(a) are manifested in valve thickening and mineralization through pro-osteogenic signaling and changes in gene expression in valve interstitial cells that is primarily facilitated by the oxidized phospholipid content of Lp(a). In AS pathogenesis, an incomplete understanding of the role of Lp(a) at the molecular level and the absence of appropriate animal models are barriers for the development of specific and effective clinical interventions designed to mitigate the role of Lp(a) in AS. However, the advent of effective therapies that dramatically lower Lp(a) provides the possibility of the first medical treatment to halt AS progression.

Lipoprotein(a) and Cardiovascular Diseases - Revisited

Two decades ago, it was recognized that lipoprotein(a) (Lp(a)) concentrations were elevated in patients with cardiovascular disease (CVD). However, the importance of Lp(a) was not strongly established due to a lack of both Lp(a)-lowering therapy and evidence that reducing Lp(a) levels improves CVD risk. Recent advances in clinical and genetic research have revealed the crucial role of Lp(a) in the pathogenesis of CVD. Mendelian randomization studies have shown that Lp(a) concentrations are causal for different CVDs, including coronary artery disease, calcified aortic valve disease, stroke, and heart failure, despite optimal low-density lipoprotein cholesterol (LDL-C) management. Lp(a) consists of apolipoprotein (apo) B100 covalently bound to apoA. Thus, Lp(a) has atherothrombotic traits of both apoB (from LDL) and apoA (thrombo-inflammatory aspects). Although conventional pharmacological therapies, such as statin, niacin, and cholesteryl ester transfer protein, have failed to significantly reduce Lp(a) levels, emerging new therapeutic strategies using proprotein convertase subtilisin-kexin type 9 inhibitors or antisesnse oligonucleotide technology have shown promising results in effectively lowering Lp(a). In this review we discuss the revisited important role of L(a) and strategies to overcome residual risk in the statin era.

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.

Biomarkers Associated with Aortic Stenosis and Structural Bioprosthesis Dysfunction

Prediction of patients at risk of aortic valve stenosis (AS), AS progression rate, and aortic bioprosthesis dysfunction are of major importance for clinical management and/or prevention. Many imaging modalities may be used; however, they may not be conclusive or available for all patients. Circulating biomarkers are easily available and may be related to a disease or process such as aortic valve calcification or associated with a risk factor of the disease. This article reviews current blood biomarkers associated with aortic valve stenosis/calcification and bioprosthesis dysfunction.

Potential Causality and Emerging Medical Therapies for Lipoprotein(a) and Its Associated Oxidized Phospholipids in Calcific Aortic Valve Stenosis

The prevalence of calcific aortic valve disease is increasing with aging of the population. Current treatment options for advanced or symptomatic aortic stenosis are limited to traditional surgical or percutaneous aortic valve replacement. Medical therapies that impact the progression of calcific aortic valve disease do not currently exist. New pathophysiological insights suggest that the processes leading to calcific aortic valve disease are metabolically active for many years before and during the clinical expression of disease. The identification of genetic and potentially causal mediators of calcific aortic valve disease allows opportunities for therapies that may slow progression to the point where aortic valve replacement can be avoided. Recent studies suggest that approximately one-third of aortic stenosis cases are associated with highly elevated lipoprotein(a) [Lp(a)] and pathways related to the metabolism of procalcifying oxidized phospholipids. Oxidized phospholipids can be carried by Lp(a) into valve leaflets but can also be formed in situ from cell membranes, lipoproteins, and apoptotic cells. This review will summarize the clinical data implicating the potential causality of Lp(a)/oxidized phospholipids, describe emerging therapeutic agents, and propose clinical trial designs to test the hypothesis that lowering Lp(a) will reduce progression aortic stenosis and the need for aortic valve replacement.

DNA methylation of a PLPP3 MIR transposon-based enhancer promotes an osteogenic programme in calcific aortic valve disease

Aims

Calcific aortic valve disease (CAVD) is characterized by the osteogenic transition of valve interstitial cells (VICs). In CAVD, lysophosphatidic acid (LysoPA), a lipid mediator with potent osteogenic activity, is produced in the aortic valve (AV) and is degraded by membrane-associated phospholipid phosphatases (PLPPs). We thus hypothesized that a dysregulation of PLPPs could participate to the osteogenic reprograming of VICs during CAVD.

Methods and results

The expression of PLPPs was examined in human control and mineralized AVs and comprehensive analyses were performed to document the gene regulation and impact of PLPPs on the osteogenic transition of VICs. We found that PLPP3 gene and enzymatic activity were downregulated in mineralized AVs. Multidimensional gene profiling in 21 human AVs showed that expression of PLPP3 was inversely correlated with the level of 5-methylcytosine (5meC) located in an intronic mammalian interspersed repeat (MIR) element. Bisulphite pyrosequencing in a larger series of 67 AVs confirmed that 5meC in intron 1 was increased by 2.2-fold in CAVD compared with control AVs. In isolated cells, epigenome editing with clustered regularly interspersed short palindromic repeats-Cas9 system containing a deficient Cas9 fused with DNA methyltransferase (dCas9-DNMT) was used to increase 5meC in the intronic enhancer and showed that it reduced significantly the expression of PLPP3. Knockdown experiments showed that lower expression of PLPP3 in VICs promotes an osteogenic programme.

Conclusions

DNA methylation of a MIR-based enhancer downregulates the expression of PLPP3 and promotes the mineralization of the AV.

NHLBI Working Group Recommendations to Reduce Lipoprotein(a)-Mediated Risk of Cardiovascular Disease and Aortic Stenosis

Pathophysiological, epidemiological, and genetic studies provide strong evidence that lipoprotein(a) [Lp(a)] is a causal mediator of cardiovascular disease (CVD) and calcific aortic valve disease (CAVD). Specific therapies to address Lp(a)-mediated CVD and CAVD are in clinical development. Due to knowledge gaps, the National Heart, Lung, and Blood Institute organized a working group that identified challenges in fully understanding the role of Lp(a) in CVD/CAVD. These included the lack of research funding, inadequate experimental models, lack of globally standardized Lp(a) assays, and inadequate understanding of the mechanisms underlying current drug therapies on Lp(a) levels. Specific recommendations were provided to facilitate basic, mechanistic, preclinical, and clinical research on Lp(a); foster collaborative research and resource sharing; leverage expertise of different groups and centers with complementary skills; and use existing National Heart, Lung, and Blood Institute resources. Concerted efforts to understand Lp(a) pathophysiology, together with diagnostic and therapeutic advances, are required to reduce Lp(a)-mediated risk of CVD and CAVD.

Lipoprotein(a), Oxidized Phospholipids, and Aortic Valve Microcalcification Assessed by 18F-Sodium Fluoride Positron Emission Tomography and Computed Tomography

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.

Targeting the autotaxin - Lysophosphatidic acid receptor axis in cardiovascular diseases

Lysophosphatidic acid (LPA) is a well-characterized bioactive lipid mediator, which is involved in development, physiology, and pathological processes of the cardiovascular system. LPA can be produced both inside cells and in biological fluids. The majority of extracellularLPAis produced locally by the secreted lysophospholipase D, autotaxin (ATX), through its binding to various β integrins or heparin sulfate on cell surface and hydrolyzing various lysophospholipids. LPA initiates cellular signalling pathways upon binding to and activation of its G protein-coupled receptors (LPA1-6). LPA has potent effects on various blood cells and vascular cells involved in the development of cardiovascular diseases such as atherosclerosis and aortic valve sclerosis. LPA signalling drives cell migration and proliferation, cytokine production, thrombosis, fibrosis, as well as angiogenesis. For instance, LPA promotes activation and aggregation of platelets through LPA5, increases expression of adhesion molecules in endothelial cells, and enhances expression of tissue factor in vascular smooth muscle cells. Furthermore, LPA induces differentiation of monocytes into macrophages and stimulates oxidized low-density lipoproteins (oxLDLs) uptake by macrophages to form foam cells during formation of atherosclerotic lesions through LPA1-3. This review summarizes recent findings of the roles played by ATX, LPA and LPA receptors (LPARs) in atherosclerosis and calcific aortic valve disease. Targeting the ATX-LPAR axis may have potential applications for treatment of patients suffering from various cardiovascular diseases.

Autotaxin and Lipoprotein Metabolism in Calcific Aortic Valve Disease

Calcific aortic valve disease (CAVD) is a complex trait disorder characterized by calcific remodeling of leaflets. Genome-wide association (GWA) study and Mendelian randomization (MR) have highlighted that LPA, which encodes for apolipoprotein(a) [apo(a)], is causally associated with CAVD. Apo(a) is the protein component of Lp(a), a LDL-like particle, which transports oxidized phospholipids (OxPLs). Autotaxin (ATX), which is encoded by ENPP2, is a member of the ecto-nucleotidase family of enzymes, which is, however, a lysophospholipase. As such, ATX converts phospholipids into lysophosphatidic acid (LysoPA), a metabolite with potent and diverse biological properties. Studies have recently underlined that ATX is enriched in the Lp(a) lipid fraction. Functional experiments and data obtained in mouse models suggest that ATX mediates inflammation and mineralization of the aortic valve. Recent findings also indicate that epigenetically-driven processes lower the expression of phospholipid phosphatase 3 (PLPP3) and increased LysoPA signaling and inflammation in the aortic valve during CAVD. These recent data thus provide novel insights about how lipoproteins mediate the development of CAVD. Herein, we review the implication of lipoproteins in CAVD and examine the role of ATX in promoting the osteogenic transition of valve interstitial cells (VICs).

Acute and chronic effect of bariatric surgery on circulating autotaxin levels

Autotaxin (ATX), an adipose tissue-derived lysophospholipase, has been involved in the pathophysiology of cardiometabolic diseases. The impact of bariatric surgery on circulating ATX levels is unknown. We examined the short- (24 h, 5 days) and longer-term (6 and 12 months) impact of bariatric surgery; as well as the short-term effect of caloric restriction (CR) on plasma ATX levels in patients with severe obesity. We measured ATX levels in 69 men and women (mean age: 41 ± 11 years, body mass index: 49.8 ± 7.1 kg/m2 ), before and after biliopancreatic diversion with duodenal switch surgery (BPD-DS) as well as in a control group (patients with severe obesity without surgery; n = 34). We also measured ATX levels in seven patients with severe obesity and type 2 diabetes who underwent a 3-day CR protocol before their BPD-DS. At baseline, ATX levels were positively associated with body mass index, fat mass, insulin resistance (HOMA-IR) as well as insulin and leptin levels and negatively with fat-free mass. ATX concentrations decreased 26.2% at 24 h after BPD-DS (342.9 ± 152.3 pg/mL to 253.2 ± 68.9 pg/mL, P < 0.0001) and by 16.4% at 12 months after BPD-DS (342.9 ± 152.3 pg/mL to 286.8 ± 182.6 pg/mL, P = 0.04). ATX concentrations were unchanged during follow-up in the control group (P = 0.4), and not influenced by short-term CR. In patients with severe obesity, bariatric surgery induced a rapid and sustained decrease in plasma ATX levels. Acute changes in ATX may not be explained by bariatric surgery-induced CR.

Lipoprotein(a) catabolism: a case of multiple receptors

Lipoprotein(a) [Lp(a)] is an apolipoprotein B (apoB)-containing plasma lipoprotein similar in structure to low-density lipoprotein (LDL). Lp(a) is more complex than LDL due to the presence of apolipoprotein(a) [apo(a)], a large glycoprotein sharing extensive homology with plasminogen, which confers some unique properties onto Lp(a) particles. ApoB and apo(a) are essential for the assembly and catabolism of Lp(a); however, other proteins associated with the particle may modify its metabolism. Lp(a) specifically carries a cargo of oxidised phospholipids (OxPL) bound to apo(a) which stimulates many proinflammatory pathways in cells of the arterial wall, a key property underlying its pathogenicity and association with cardiovascular disease (CVD). While the liver and kidney are the major tissues implicated in Lp(a) clearance, the pathways for Lp(a) uptake appear to be complex and are still under investigation. Biochemical studies have revealed an exceptional array of receptors that associate with Lp(a) either via its apoB, apo(a), or OxPL components. These receptors fall into five main categories, namely 'classical' lipoprotein receptors, toll-like and scavenger receptors, lectins, and plasminogen receptors. The roles of these receptors have largely been dissected by genetic manipulation in cells or mice, although their relative physiological importance for removal of Lp(a) from the circulation remains unclear. The LPA gene encoding apo(a) has an overwhelming effect on Lp(a) levels which precludes any clear associations between potential Lp(a) receptor genes and Lp(a) levels in population studies. Targeted approaches and the selection of unique Lp(a) phenotypes within populations has nevertheless allowed for some associations to be made. Few of the proposed Lp(a) receptors can specifically be manipulated with current drugs and, as such, it is not currently clear whether any of these receptors could provide relevant targets for therapeutic manipulation of Lp(a) levels. This review summarises the current status of knowledge about receptor-mediated pathways for Lp(a) catabolism.