Carriage of the V279F null allele within the gene encoding Lp-PLA₂ is protective from coronary artery disease in South Korean males

Lp-PLA2 (Lipoprotein-Associated Phospholipase A2) Deficiency Lowers Cholesterol Levels and Protects Against Atherosclerosis in Rabbits

BACKGROUND

Elevated plasma Lp-PLA₂ (lipoprotein-associated phospholipase A₂) activity is closely associated with an increased risk of cardiovascular events. However, whether and how Lp-PLA₂ is directly involved in the pathogenesis of atherosclerosis is still unclear. To examine the hypothesis that Lp-PLA₂ could be a potential preventative target of atherosclerosis, we generated Lp-PLA₂ knockout rabbits and investigated the pathophysiological functions of Lp-PLA₂.

METHODS

Lp-PLA₂ knockout rabbits were generated using CRISPR/Cas9 system to assess the role of Lp-PLA₂ in plasma lipids regulation and identify its underlying molecular mechanisms. Homozygous knockout rabbits along with wild-type rabbits were fed a cholesterol-rich diet for up to 14 weeks and their atherosclerotic lesions were compared. Moreover, the effects of Lp-PLA₂ deficiency on the key cellular behaviors in atherosclerosis were assessed in vitro.

RESULTS

When rabbits were fed a standard diet, Lp-PLA₂ deficiency led to a significant reduction in plasma lipids. The decreased protein levels of SREBP2 (sterol regulatory element-binding protein 2) and HMGCR (3-hydroxy-3-methylglutaryl coenzyme A reductase) in livers of homozygous knockout rabbits indicated that the cholesterol biosynthetic pathway was impaired with Lp-PLA₂ deficiency. In vitro experiments further demonstrated that intracellular Lp-PLA₂ efficiently enhanced SREBP2-related cholesterol biosynthesis signaling independently of INSIGs (insulin-induced genes). When fed a cholesterol-rich diet, homozygous knockout rabbits exhibited consistently lower level of hypercholesterolemia, and their aortic atherosclerosis lesions were significantly reduced by 60.2% compared with those of wild-type rabbits. The lesions of homozygous knockout rabbits were characterized by reduced macrophages and the expression of inflammatory cytokines. Macrophages of homozygous knockout rabbits were insensitive to M1 polarization and showed reduced DiI-labeled lipoprotein uptake capacity compared with wild-type macrophages. Lp-PLA₂ deficiency also inhibited the adhesion between monocytes and endothelial cells.

CONCLUSIONS

These results demonstrate that Lp-PLA₂ plays a causal role in regulating blood lipid homeostasis and Lp-PLA₂ deficiency protects against dietary cholesterol-induced atherosclerosis in rabbits. Lp-PLA₂ could be a potential target for the prevention of atherosclerosis.

Human Secretary Phospholipase A2 Mutations and Their Clinical Implications

Phospholipases A2 (PLA₂s) belong to a superfamily of enzymes responsible for hydrolysis of the sn-2 fatty acids of membrane phospholipids to release arachidonic acid. PLA₂s are the rate limiting enzyme for the downstream synthesis of prostaglandins and leukotrienes that are the main mediators of inflammation. The extracellular forms of this enzyme are also called the secretary phospholipase A2 (sPLA₂) and are distributed extensively in most of the tissues in the human body. Their integral role in inflammatory pathways has been the primary reason for the extensive research on this molecule. The catalytic mechanism of sPLA₂ is initiated by a histidine/aspartic acid/calcium complex within the active site. Though they are known to have certain housekeeping functions, certain mutations of sPLA₂ are known to be implicated in causation of certain pathologies leading to diseases such as atherosclerosis, cardiovascular diseases, benign fleck retina, neurodegeneration, and asthma. We present an overview of human sPLA₂ and a comprehensive compilation of the mutations that result in various disease phenotypes. The study not only helps to have a holistic understanding of human sPLA₂ mutations and their clinical implications, but is also a useful platform to initiate research pertaining to structure–function relationship of the mutations to develop effective therapies for management of these diseases.

Phospholipase A2 is an Inflammatory Predictor in Cardiovascular Diseases: Is there any Spacious Room to Prove the Causation?

Lipoprotein-associated phospholipase A2 (Lp-PLA2) is an enzyme family of phospholipase A2 produced by the inflammatory cell in atherosclerotic plaque. It is transported in the circulation, attached mainly to low-density lipoprotein-cholesterol (LDL-C). It hydrolyzes glycerophospholipids particularly fatty acids at the sn-2 position and produces numerous bioactive lipids; and leads to endothelial dysfunction, atherosclerotic plaque inflammation, and development of the necrotic core in plaques. There are two kinds of phospholipase A2, namely: secretory phospholipase A2 (sPLA2) and Lp- PLA2. They are deemed as evolving predictors of cardiovascular disease (CVD) risk in hospitaland population-based studies, including healthy subjects, acute coronary syndromes (ACS) and patients with CVD. Unfortunately, Lp-PLA2 inhibitor (darapladib) and s-PLA2 inhibitor (varespladib methyl) failed to prove to lower the risk of composite CVD mortality, myocardial infarction and stroke in those with stable CVD and ACS. Herein, we describe the explanation based on the existing data why there is still a discrepancy among them. So, it highlights the opinion that phospholipase A2 is merely the inflammatory biomarkers of CVD and playing an important role in atherosclerosis. Further, there is more spacious room to prove the causation.

Lipoprotein-associated phospholipase A2: The story continues

Inflammation is thought to play an important role in the pathogenesis of vascular diseases. Lipoprotein-associated phospholipase A2 (Lp-PLA2) mediates vascular inflammation through the regulation of lipid metabolism in blood, thus, it has been extensively investigated to identify its role in vascular inflammation-related diseases, mainly atherosclerosis. Although darapladib, the most advanced Lp-PLA2 inhibitor, failed to meet the primary endpoints of two large phase III trials in atherosclerosis patients cotreated with standard medical care, the research on Lp-PLA2 has not been terminated. Novel pathogenic, epidemiologic, genetic, and crystallographic studies regarding Lp-PLA2 have been reported recently, while novel inhibitors were identified through a fragment-based lead discovery strategy. More strikingly, recent clinical and preclinical studies revealed that Lp-PLA2 inhibition showed promising therapeutic effects in diabetic macular edema and Alzheimer's disease. In this review, we not only summarized the knowledge of Lp-PLA2 established in the past decades but also emphasized new findings in recent years. We hope this review could be valuable for helping researchers acquire a much deeper insight into the nature of Lp-PLA2, identify more potent and selective Lp-PLA2 inhibitors, and discover the potential indications of Lp-PLA2 inhibitors.

Associations between four types of single-nucleotide polymorphisms in PLA2G7 gene and clinical atherosclerosis: a meta-analysis

BACKGROUND

Previous studies suggested that some types of single nucleotide polymorphisms (SNPs) in PLA2G7 genes, encoding Lp-PLA2 have been reported to yield an antiatherogenic effect, but other studies mentioned otherwise. Thus, a comprehensive study to explore the effect of SNPs in PLA2G7 genes (V279F, A379V, R92H, I198T) toward clinical atherosclerosis is needed.

METHODS

We searched eligible studies from PubMed, EBSCO, ProQuest, Science Direct, Springer, and Cochrane databases for case-control studies to assess the between four types of SNPs in PLA2G7 gene with risk of clinical atherosclerosis (CVD = cardiovascular disease, CAD = coronary artery disease, PAD = peripheral artery disease, ischemic stroke). All studies were assessed under Hardy-Weinberg Equilibrium, an additive model. This meta-analysis was performed by RevMan 5.3 to provide pooled estimate for odds ratio (ORs) with 95% confidence intervals (95% CIs).

RESULTS

Fourteen clinical studies met our inclusion criteria. Those included 12,432 patients with clinical atherosclerosis and 10,171 were controls. We found that ORs of two variants SNPs (V279F, R92H) were associated with clinical atherosclerosis {V279F, OR = 0.88 (95% CI, 0.81-0.95); p = 0.0007, I2 = 40%}, {R92H, OR = 1.29 (95% CI, 1.09-1.53); p = 0.003, I2 = 73%}. Meanwhile, there was no significant associations between the other two, A379V {OR = 1.08 (95% CI, 0.93-1.26); p = 0.31, I2 = 78%} and I198T {OR = 1.12 (95% CI = 0.79-1.59); p = 0.53, I2 = 81%}.

CONCLUSIONS

These results suggested that V279F polymorphism in PLA2G7 gene has a protective effect for clinical atherosclerosis, whereas R92H polymorphism might contribute toward increased risk of clinical atherosclerosis.

Failure to Launch: Targeting Inflammation in Acute Coronary Syndromes

The importance of inflammation and inflammatory pathways in atherosclerotic disease and acute coronary syndromes (ACS) is well established. The success of statin therapy rests not only on potently reducing levels of low-density lipoprotein cholesterol, but also on the many beneficial, pleiotropic effects statin therapy has on various inflammatory mechanisms in atherosclerotic disease, from reducing endothelial dysfunction to attenuating levels of serum C-reactive protein. Due to the growing awareness of the importance of inflammation in ACS, investigators have attempted to develop novel therapies against known markers of inflammation for several decades. Targeted pathways have ranged from inhibiting C5 cleavage with a high-affinity monoclonal antibody against C5 to inhibiting the activation of the p38 mitogen-activated protein kinase signaling cascades. In each of these instances, despite promising early preclinical and mechanistic studies and phase 2 trials suggesting a potential benefit in reducing post-MI complications or restenosis, these novel therapies have failed to show benefits during large, phase 3 clinical outcomes trials. This review discusses several examples of novel anti-inflammatory therapies that failed to show significant improvement on clinical outcomes when tested in large, randomized trials and highlights potential explanations for why targeted therapies against known markers of inflammation in ACS have failed to launch.

Pharmacogenetic meta-analysis of baseline risk factors, pharmacodynamic, efficacy and tolerability endpoints from two large global cardiovascular outcomes trials for darapladib

Darapladib, a lipoprotein-associated phospholipase A2 (Lp-PLA₂) inhibitor, failed to demonstrate efficacy for the primary endpoints in two large phase III cardiovascular outcomes trials, one in stable coronary heart disease patients (STABILITY) and one in acute coronary syndrome (SOLID-TIMI 52). No major safety signals were observed but tolerability issues of diarrhea and odor were common (up to 13%). We hypothesized that genetic variants associated with Lp-PLA₂ activity may influence efficacy and tolerability and therefore performed a comprehensive pharmacogenetic analysis of both trials. We genotyped patients within the STABILITY and SOLID-TIMI 52 trials who provided a DNA sample and consent (n = 13,577 and 10,404 respectively, representing 86% and 82% of the trial participants) using genome-wide arrays with exome content and performed imputation using a 1000 Genomes reference panel. We investigated baseline and change from baseline in Lp-PLA₂ activity, two efficacy endpoints (major coronary events and myocardial infarction) as well as tolerability parameters at genome-wide and candidate gene level using a meta-analytic approach. We replicated associations of published loci on baseline Lp-PLA₂ activity (APOE, CELSR2, LPA, PLA2G7, LDLR and SCARB1) and identified three novel loci (TOMM5, FRMD5 and LPL) using the GWAS-significance threshold P≤5E-08. Review of the PLA2G7 gene (encoding Lp-PLA₂) within these datasets identified V279F null allele carriers as well as three other rare exonic null alleles within various ethnic groups, however none of these variants nor any other loci associated with Lp-PLA₂ activity at baseline were associated with any of the drug response endpoints. The analysis of darapladib efficacy endpoints, despite low power, identified six low frequency loci with main genotype effect (though with borderline imputation scores) and one common locus (minor allele frequency 0.24) with genotype by treatment interaction effect passing the GWAS-significance threshold. This locus conferred risk in placebo subjects, hazard ratio (HR) 1.22 with 95% confidence interval (CI) 1.11–1.33, but was protective in darapladib subjects, HR 0.79 (95% CI 0.71–0.88). No major loci for tolerability were found. Thus, genetic analysis confirmed and extended the influence of lipoprotein loci on Lp-PLA₂ levels, identified some novel null alleles in the PLA2G7 gene, and only identified one potentially efficacious subgroup within these two large clinical trials.

Effects of overweight and the PLA2G7 V279F polymorphism on the association of age with systolic blood pressure

This prospective study aimed to determine the effects of the persistence of overweight for three years and the PLA2G7 V279F polymorphism, as well as the interaction between these factors, on the association of age with blood pressure (BP). Healthy middle-aged subjects with normotensive BP were divided into the normal-weight and overweight groups. The PLA2G7 V279F genotype, BP, lipoprotein-associated phospholipase A2 (Lp-PLA2) activity, and oxidized low-density lipoprotein (ox-LDL) were determined. Lp-PLA2 activity was lower in the F allele subjects (n = 111) than in those with the VV genotype (n = 389). The overweight individuals with the F allele had lower Lp-PLA2 activity and ox-LDL at both baseline and after three years and lower systolic and diastolic BP and LDL cholesterol after three years compared with those with the VV phenotype. After three years, the overweight subjects with the VV phenotype exhibited greater increases in Lp-PLA2 activity, systolic BP, and ox-LDL than those with the F allele and normal-weight subjects with the VV phenotype. A multivariate analysis revealed that the PLA2G7 V279F genotype, baseline BMI, changes in Lp-PLA2 activity and ox-LDL remained independently and positively associated with changes in systolic BP. The simultaneous presence of the PLA2G7 279VV genotype and persistence of overweight synergistically increases the risk for hypertension, whereas lower Lp-PLA2 activity in PLA2G7 279F allele carriers might offer certain protection against hypertension, even in individuals who have been overweight for over three years.

Genetic invalidation of Lp-PLA2 as a therapeutic target: Large-scale study of five functional Lp-PLA2-lowering alleles

Aims Darapladib, a potent inhibitor of lipoprotein-associated phospholipase A2 (Lp-PLA2), has not reduced risk of cardiovascular disease outcomes in recent randomized trials. We aimed to test whether Lp-PLA2 enzyme activity is causally relevant to coronary heart disease. Methods In 72,657 patients with coronary heart disease and 110,218 controls in 23 epidemiological studies, we genotyped five functional variants: four rare loss-of-function mutations (c.109+2T > C (rs142974898), Arg82His (rs144983904), Val279Phe (rs76863441), Gln287Ter (rs140020965)) and one common modest-impact variant (Val379Ala (rs1051931)) in PLA2G7, the gene encoding Lp-PLA2. We supplemented de-novo genotyping with information on a further 45,823 coronary heart disease patients and 88,680 controls in publicly available databases and other previous studies. We conducted a systematic review of randomized trials to compare effects of darapladib treatment on soluble Lp-PLA2 activity, conventional cardiovascular risk factors, and coronary heart disease risk with corresponding effects of Lp-PLA2-lowering alleles. Results Lp-PLA2 activity was decreased by 64% ( p = 2.4 × 10-25) with carriage of any of the four loss-of-function variants, by 45% ( p < 10-300) for every allele inherited at Val279Phe, and by 2.7% ( p = 1.9 × 10-12) for every allele inherited at Val379Ala. Darapladib 160 mg once-daily reduced Lp-PLA2 activity by 65% ( p < 10-300). Causal risk ratios for coronary heart disease per 65% lower Lp-PLA2 activity were: 0.95 (0.88-1.03) with Val279Phe; 0.92 (0.74-1.16) with carriage of any loss-of-function variant; 1.01 (0.68-1.51) with Val379Ala; and 0.95 (0.89-1.02) with darapladib treatment. Conclusions In a large-scale human genetic study, none of a series of Lp-PLA2-lowering alleles was related to coronary heart disease risk, suggesting that Lp-PLA2 is unlikely to be a causal risk factor.

Investigation of a Bicyclo[1.1.1]pentane as a Phenyl Replacement within an LpPLA2 Inhibitor

We describe the incorporation of a bicyclo[1.1.1]pentane moiety within two known LpPLA₂ inhibitors to act as bioisosteric phenyl replacements. An efficient synthesis to the target compounds was enabled with a dichlorocarbene insertion into a bicyclo[1.1.0]butane system being the key transformation. Potency, physicochemical, and X-ray crystallographic data were obtained to compare the known inhibitors to their bioisosteric counterparts, which showed the isostere was well tolerated and positively impacted on the physicochemical profile.

Val279Phe variant of Lp-PLA2 is a risk factor for a subpopulation of Indonesia patients with acute myocardial infarction

Lipoprotein-associated phospholipase A₂ (Lp-PLA₂), a member of the phospholipase A₂ superfamily, is an enzyme that hydrolyses phospholipids, is found in blood circulation as a sign of inflammation, and takes a role in atherogenesis. There is an epidemiologic relation between increased Lp-PLA₂ levels and coronary heart disease. Lp-PLA₂ is an enzyme that is produced by macrophages and takes a role as an independent predictor of a coronary event. A genetic variant of Val279Phe on the Lp-PLA₂ gene has been reported with various results in Japan, China, Korea, and Caucasian populations. This study aims to analyse the influence of the Val279Phe genetic variant on acute myocardial infarction (AMI) at Saiful Anwar Hospital, Indonesia. This study was conducted on 151 patients (111 AMI patients and 40 non-AMI patients). The genetic variant of Val279Phe was identified through a genotyping method. There were no significant differences in age, total cholesterol level, LDL-C (low-density lipoprotein cholesterol) level, and family history data between AMI and non-AMI patients. However, AMI patients had low HDL-C (high-density lipoprotein cholesterol), triglyceride levels, dyslipidaemia, and hypertension risk factors compared to non-AMI patients. The frequency of the GG genotype (279Val) was dominant in both AMI and non-AMI groups. Further analysis suggested that the GG genotype has a 2.9 times greater risk of AMI compared to the GT/TT genotype (279Phe). This study concluded that the Val279Phe genetic variant undoubtedly influenced AMI risk, which is a warrant for further development of early detection and improving strategy to prevent AMI in patients.

Lipoprotein-Associated Phospholipase A2 Activity Is a Marker of Risk But Not a Useful Target for Treatment in Patients With Stable Coronary Heart Disease

BACKGROUND

We evaluated lipoprotein-associated phospholipase A2 (Lp-PLA2) activity in patients with stable coronary heart disease before and during treatment with darapladib, a selective Lp-PLA2 inhibitor, in relation to outcomes and the effects of darapladib in the STABILITY trial.

METHODS AND RESULTS

Plasma Lp-PLA2 activity was determined at baseline (n=14 500); at 1 month (n=13 709); serially (n=100) at 3, 6, and 18 months; and at the end of treatment. Adjusted Cox regression models evaluated associations between Lp-PLA2 activity levels and outcomes. At baseline, the median Lp-PLA2 level was 172.4 μmol/min per liter (interquartile range 143.1-204.2 μmol/min per liter). Comparing the highest and lowest Lp-PLA2 quartile groups, the hazard ratios were 1.50 (95% CI 1.23-1.82) for the primary composite end point (cardiovascular death, myocardial infarction, or stroke), 1.95 (95% CI 1.29-2.93) for hospitalization for heart failure, 1.42 (1.07-1.89) for cardiovascular death, and 1.37 (1.03-1.81) for myocardial infarction after adjustment for baseline characteristics, standard laboratory variables, and other prognostic biomarkers. Treatment with darapladib led to a ≈65% persistent reduction in median Lp-PLA2 activity. There were no associations between on-treatment Lp-PLA2 activity or changes of Lp-PLA2 activity and outcomes, and there were no significant interactions between baseline and on-treatment Lp-PLA2 activity or changes in Lp-PLA2 activity levels and the effects of darapladib on outcomes.

CONCLUSIONS

Although high Lp-PLA2 activity was associated with increased risk of cardiovascular events, pharmacological lowering of Lp-PLA2 activity by ≈65% did not significantly reduce cardiovascular events in patients with stable coronary heart disease, regardless of the baseline level or the magnitude of change of Lp-PLA2 activity.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT00799903.

A phenome-wide association study of a lipoprotein-associated phospholipase A2 loss-of-function variant in 90 000 Chinese adults

Background: Lipoprotein-associated phospholipase A₂ (Lp-PLA₂) has been implicated in development of atherosclerosis; however, recent randomized trials of Lp-PLA₂ inhibition reported no beneficial effects on vascular diseases. In East Asians, a loss-of-function variant in the PLA2G7 gene can be used to assess the effects of genetically determined lower Lp-PLA₂.

Methods:PLA2G7 V279F (rs76863441) was genotyped in 91 428 individuals randomly selected from the China Kadoorie Biobank of 0.5 M participants recruited in 2004–08 from 10 regions of China, with 7 years’ follow-up. Linear regression was used to assess effects of V279F on baseline traits. Logistic regression was conducted for a range of vascular and non-vascular diseases, including 41 ICD-10 coded disease categories.

Results:PLA2G7 V279F frequency was 5% overall (range 3–7% by region), and 9691 (11%) participants had at least one loss-of-function variant. V279F was not associated with baseline blood pressure, adiposity, blood glucose or lung function. V279F was not associated with major vascular events [7141 events; odds ratio (OR) = 0.98 per F variant, 95% confidence interval (CI) 0.90-1.06] or other vascular outcomes, including major coronary events (922 events; 0.96, 0.79-1.18) and stroke (5967 events; 1.00, 0.92-1.09). Individuals with V279F had lower risks of diabetes (7031 events; 0.91, 0.84-0.98) and asthma (182 events; 0.53, 0.28-0.98), but there was no association after adjustment for multiple testing.

Conclusions: Lifelong lower Lp-PLA₂ activity was not associated with major risks of vascular or non-vascular diseases in Chinese adults. Using functional genetic variants in large-scale prospective studies with linkage to a range of health outcomes is a valuable approach to inform drug development and repositioning.

279(Val→Phe) Polymorphism of lipoprotein-associated phospholipase A(2) resulted in changes of folding kinetics and recognition to substrate

INTRODUCTION

PLA2G7 encodes Lp-PLA2 having role in the formation of atherosclerotic plaques by catalyzing its substrate, phosphatydilcholine (PC), to be pro-inflammatory substances. The increased risk for coronary artery disease (CAD) in Asian population has been related with this enzyme. 279(Val→Phe) variant was reported to have a protective role against CAD due to, in part, secretion defect or loss of enzymatic function. Therefore, We study folding kinetics and enzyme-substrate interaction in 279(Val→Phe) by using clinical and computational biology approach.

METHODS

Polymorphisms were detected by genotyping among 103 acute myocardial infarction patients and 37 controls. Folding Lp-PLA2 was simulated using GROMACS software by assessing helicity, hydrogen bond formation and stability. The interactions of Lp-PLA2 and its substrate were simulated using Pyrx software followed by molecular dynamics simulation using YASARA software.

RESULT

Polymorphism of 279(Val→Phe) was represented by the change of nucleotide from G to T of 994th PLA2G7 gene. The folding simulation suggested a decreased percentage of α-helix, hydrogen bond formation, hydrogen bond stability and hydrophobicity in 279(Val→Phe). The PC did not interact with active site of 279(Val→Phe) as paradoxically observed in 279 valine. 279(Val→Phe) polymorphism is likely to cause unstable binding to the substrate and decrease the enzymatic activity as observed in molecular dynamics simulations. The results of our computational biology study supported a protected effect of 279(Val→Phe) Polymorphism showed by the odd ratio for MI of 0.22 (CI 95% 0.035-1.37) in this study.

CONCLUSION

279(Val→Phe) Polymorphism of Lp-PLA2 may lead to decrease the enzymatic activity via changes of folding kinetics and recognition to its substrate.

[Lp-PLA2, a biomarker of vascular inflammation and vulnerability of atherosclerosis plaques]

A chronic inflammation is involved in various stages of development of the atherosclerotic plaques. Among the emerging biomarkers of atherogenesis, the lipoprotein-associated phospholipase A2 (Lp-PLA2), formerly known as PAF-acetylhydrolase (McIntyre et al., 2009), hydrolyses the oxidized short chain phospholipids of low-density lipoproteins (LDL), thereby releasing pro-inflammatory mediators (lysophospholipids and oxidized fatty acids). Lp-PLA2, produced by monocytes/macrophages and T-lymphocytes, and mainly associated with LDL (Gazi et al., 2005), is predominantly expressed in the necrotic center of the atherosclerotic plaques and in the macrophage-rich areas (Kolodgie et al., 2006). It would have a predictive role of cardiovascular (CV) events in relation to the vulnerability of atherosclerotic plaques. Determination of Lp-PLA2 has been proposed in the assessment of the CV risk, to ensure a better stratification of populations at intermediate risk for targeted therapy (Davidson et al., 2008). Its proatherogenic role suggested that inhibition of its activity could ensure a better vascular protection in combination with cholesterol-lowering agents. Nevertheless, Lp-PLA2 is not yet a fully validated marker for use in daily clinical practice, especially since the studies using an inhibitor of Lp-PLA2 (darapladib) (STABILITY Investigators et al., 2014; O'Donoghue et al., 2014) did not show any reduction in coronary events. Lp-PLA2 could have a site-specific role in plaque inflammation and development (Fenning et al., 2015). High Lp-PLA2 activity could reflect a response to pro-inflammatory stress characteristic of atherosclerosis (Marathe et al., 2014). This presentation aims at clarifying the involvement of Lp-PLA2 in the pathophysiology of atherosclerosis, and at assessing its interest both as a biomarker for the onset of CV events and as a therapeutic target.

Darapladib for the treatment of cardiovascular disease

Elevated levels of phospholipase A2 have been linked to atherosclerotic plaque progression, instability via promoting inflammation and subsequent acute coronary events. Epidemiological studies have demonstrated the correlation between elevated levels associated phospholipase A2 and cardiovascular events. Therefore, specific inhibition of lipoprotein-associated phospholipase A2 with darapladib has been tested as a therapeutic option for atherosclerosis. The aim of this profile is to review the physiologic aspects of lipoprotein-associated phospholipase A2 and to revisit the clinical evidence of darapladib as therapeutic option for atherosclerosis.

Deciphering the Causal Role of sPLA2s and Lp-PLA2 in Coronary Heart Disease

Over the last 10 to 15 years, animal and human observational studies have identified elevated levels of both proinflammatory secretory phospholipase A2-IIA and lipoprotein-associated phospholipase A2 as potential risk factors for coronary heart disease. However, Mendelian randomization, a genetic tool to test causality of a biomarker, and phase III randomized controlled trials of inhibitors of theses enzymes (varespladib and darapladib) converged to indicate that elevated levels are unlikely to be themselves causal of coronary heart disease and that inhibition had little or no clinical utility. The concordance of findings from Mendelian randomization and clinical trials suggests that for these 2 drugs, and for other novel biomarkers in future, validation of potential therapeutic targets by genetic studies (such as Mendelian randomization) before embarking on costly phase III randomized controlled trials could increase efficiency and offset the high risk of drug development, thereby facilitating discovery of new therapeutics and mitigating against the exuberant costs of drug development.

Lipoprotein-associated phospholipase A2 single-nucleotide polymorphisms and cardiovascular events in patients with coronary artery disease

AIMS

We tested the hypothesis that variations in the PLA2G7 gene encoding the lipoprotein-associated phospholipase A2 (Lp-PLA2), an enzyme deemed to have proatherogenic activity, affect the Lp-PLA2 levels and predicts cardiovascular events.

METHODS

Using a prospective cohort study design, we investigated incident cardiovascular events as a function of the PLA2G7 gene for rs1805017, rs1805018, and rs1051931 single-nucleotide polymorphisms (SNPs) in 643 randomly selected white patients from the GENICA Study, who at baseline underwent coronary angiography, measurement of Lp-PLA2 mass and activity. Cardiovascular event-free survival was compared across the genotypes by Cox regression, propensity score matching, and haplotype analysis.

RESULTS

The rs1805018 SNP did not follow the Hardy-Weinberg equilibrium and was not further explored. The rs1805017 GG genotype had a lower Lp-PLA2 mass and a higher Lp-PLA2 activity, thus suggesting that this SNP is functional. Long-term follow-up (median 7.8 years) was obtained in 75% of the cohort and allowed recording of incident cardiovascular events in 25.8% of the patients. On Cox regression analysis, the common rs1805017 GG genotype predicted acute myocardial infarction (AMI) [hazard ratio 1.75, 95% confidence interval (CI) 1.03-2.99, P = 0.041]; this finding was confirmed on propensity score matching (82.6% AMI-free survival in GG vs. 94.4% in GA + AA, P = 0.003). The rs1805017 and rs1051931 G/G haplotype was also associated with AMI (52.7 vs. 42.2%, P = 0.026) and cardiovascular event incidence (49.5 vs. 41.7%, P = 0.025).

CONCLUSION

In high-risk coronary artery disease patients of European ancestry, the PLA2G7 rs1805017 GG genotype is associated with increased Lp-PLA2 plasma activity and AMI.

Lipoprotein-associated phospholipase A2 and risk of incident cardiovascular disease in a multi-ethnic cohort: The multi ethnic study of atherosclerosis

OBJECTIVE

Prospective studies reporting a positive association of lipoprotein-associated phospholipase A2 (Lp-PLA2) mass and activity with incident cardiovascular disease (CVD) have included primarily white individuals. We evaluated associations of Lp-PLA2 and first-time cardiovascular events in a healthy multi-ethnic cohort characterized by presence or absence of baseline subclinical atherosclerosis.

METHODS

Lp-PLA2 mass and activity were measured at baseline in 5456 participants in the Multi-Ethnic Study of Atherosclerosis. Individuals were characterized for presence of baseline subclinical disease (coronary artery calcium score > 0 or carotid intima-media thickness value > 80th percentile) and followed prospectively for development of CVD events (coronary heart disease, ischemic stroke, and cardiovascular death).

RESULTS

516 incident CVD events occurred over median follow-up of 10.2 years. In adjusted Cox proportional hazards models, each higher standard deviation of both Lp-PLA2 activity and mass was associated with an increased risk of cardiovascular events; hazard ratios (HR; 95% confidence intervals (CI)) 1.12 (1.01-1.26) for Lp-PLA2 activity and 1.10 (1.01-1.21) for mass. Associations did not differ by subclinical disease status (p-value for interaction 0.99 for Lp-PLA2 activity and 0.32 for Lp-PLA2 mass) and there was no confounding by subclinical atherosclerosis measures. Associations of Lp-PLA2 activity but not mass were weaker in Chinese participants but there were relatively few events among Chinese in race-stratified analysis.

CONCLUSION

In this multi-ethnic cohort, Lp-PLA2 was positively associated with CVD risk, regardless of the presence of coronary artery calcium or a thickened carotid-intimal media.

Nonsynonymous polymorphisms in PLA2G7 gene are associated with the risk of coronary heart disease in a southern Chinese population

Lipoprotein-associated phospholipase A2 (Lp-PLA2) plays an important role in coronary heart disease (CHD). This study was aimed to investigate the associations of polymorphisms (R92H, V279F, I198T, and A379V) in PLA2G7 with CHD. A total of 322 patients with CHD and 414 CHD-free controls were included in the study. Polymorphisms in PLA2G7 were sequenced by DNA Sequencer and statistical analyses were performed to study the associations between polymorphisms and CHD. RH + HH genotype, RH genotype, and H allele of R92H were significantly associated with an increased risk of CHD (P = 0.005, P = 0.009, and P = 0.003, respectively), while no associations were observed between V279F and I198T and CHD (A379V was not analyzed because of deviation from Hardy-Weinberg equilibrium). Correlations between R92H and CHD still existed after adjustment for confounding risk factors of CHD (P = 0.001). Furthermore, stratified analyses showed subgroups of the senior, hypertension, non-smoking, non-diabetics, and male subjects brought a higher risk for CHD (P = 0.015, P = 0.001, P = 0.001, P = 0.002, and P = 0.004, respectively). We also observed a lower level of protective factor HDL-C in CHD patients carrying genotype RH + HH than patients with RR (P = 0.047). Furthermore, we conducted haplotype analysis and detected more harmful effects of haplotypes HVI and RVT as compared with other haplotypes (P = 2.538 × 10(-3) and P = 0.031). These findings indicated that R92H variant in PLA2G7 gene might contribute to CHD susceptibility in a southern Chinese population.

Carriage of the V279F homozygous genotype, a rare allele, within the gene encoding Lp-PLA2 leads to changes in circulating intermediate metabolites in individuals without metabolic syndrome

AIM

Identifying differences in plasma metabolic profiling between Lp-PLA2 279VV and 279FF in individuals without metabolic syndrome (MetS) can be used to elucidate the roles of novel Lp-PLA2 activities in normal physiological processes.

METHODS

Non-MetS individuals with 279FF (n=36) and age-, sex- and BMI-matched VV subjects (n=36) were included in this analysis.

RESULTS

The FF subjects exhibited no appreciable enzyme activity. No significant differences were observed between the VV and FF subjects in the serum lipid profiles or hs-CRP, plasma ox-LDL, MDA or urinary 8-epi-PGF2α levels. The FF subjects also showed lower activities of lyso-phosphatidylcholine (lysoPC) (16:0) (p=0.003) and oleamide (p＜0.001) and a higher activity of L-tryptophan (p=0.016) than the VV subjects. In addition, the Lp-PLA2 activity positively correlated with the lysoPC (16:0) and lysoPC (18:0) activities and negatively correlated with the PC (16:0/22:6) and L-tryptophan activities in the VV subjects. Furthermore, in the VV subjects, the lysoPC (16:0) and lysoPC (18:0) activities negatively correlated with the presence of PCs containing 14:0/20:2, 14:0/22:4 and 16:0/22:6, while the oleamide activity exhibited a strong positive correlation with lysoPCs and a negative correlation with PCs, whereas the relationship between oleamide and lysoPCs and PCs was weaker in the FF subjects.

CONCLUSIONS

The present results indicate that the natural absence of the plasma Lp-PLA2 activity due to carriage of the Lp-PLA2 279FF genotype may reduce the generation of lysoPC (16:0) and oleamide and thereby enhance the activity of plasma tryptophan in normal physiological processes.

Associations of platelet-activating factor acetylhydrolase (PAF-AH) gene polymorphisms with circulating PAF-AH levels and risk of coronary heart disease or blood stasis syndrome in the Chinese Han population

The circulating level of platelet-activating factor acetylhydrolase (PAF-AH) is a novel biomarker to predict the presence of coronary heart disease. PAF-AH gene polymorphisms may be responsible for the variance of circulating PAF-AH levels in individuals. However, the association of PAF-AH gene polymorphisms with circulating PAF-AH levels and the susceptibility to coronary heart disease (CHD) remains unsolved. Blood stasis syndrome (BSS) of CHD is the most common type of TCM syndromes, and a previous study discovered its relationship with the elevated circulating PAF-AH levels. However, the association of gene polymorphisms and CHD with BSS is unclear at present. In this study, four polymorphisms (R92H, I198T, A379V, V279F) of the PAF-AH gene were genotyped in 570 CHD patients, of which 299 had BSS. In addition, 317 unaffected individuals from the same hospitals served as controls. Plasma PAF-AH levels were measured in 155 controls and 271 CHD patients selected randomly, including 139 CHD patients with BSS. In the Chinese Han population, plasma PAF-AH levels in CHD patients with BSS or without BSS were significantly higher (12.9 ± 6.5 and 11.1 ± 5.0 μM, respectively) than in controls (9.3 ± 5.2 μM); this difference still remained significant after adjustment for traditional risk factors or the inflammatory factors. The R92H polymorphism was highly related to the plasma PAF-AH levels and the risk of CHD, especially among patients with BSS, even with the adjustment for the effects of traditional factors. The I198T polymorphism was highly associated with risk of CHD with BSS, but was associated with neither the risk of CHD with no BSS nor with elevated plasma PAF-AH levels.

Lipoprotein-associated phospholipase A2 regulates macrophage apoptosis via the Akt and caspase-7 pathways

AIM

Mutations in lipoprotein-associated phospholipase A2 (Lp-PLA2) are related to atherosclerosis. However, the molecular effects of Lp-PLA2 on atherosclerosis have not been fully investigated. Therefore, this study attempted to elucidate this issue.

METHODS

Monocytes were isolated from randomly selected healthy male volunteers according to each Lp-PLA2 genotype (wild-type Lp-PLA2 [Lp-PLA2 (V/V)], the heterozygous V279F mutation [LpPLA2 (V/F)] and the homozygous V279F mutation [Lp-PLA2 (F/F)]) and differentiated into macrophages. The level of apoptosis in the macrophages following incubation without serum was measured using the annexin V/propidium iodide double staining method, and the underlying mechanisms were further examined using a culture cell line.

RESULTS

The average plasma Lp-PLA2 concentration [Lp-PLA2 (V/V): 129.4 ng/mL, Lp-PLA2 (V/F): 70.7 ng/mL, Lp-PLA2 (F/F): 0.4 ng/mL] and activity [Lp-PLA2 (V/V): 164.3 nmol/min/mL, LpPLA2 (V/F): 100.9 nmol/min/mL, Lp-PLA2 (F/F): 11.6 nmol/min/mL] were significantly different between each genotype, although the basic clinical characteristics were similar. The percentage of apoptotic cells was significantly higher among the Lp-PLA2 (F/F) macrophages compared with that observed in the Lp-PLA2 (V/V) macrophages. This induction of apoptosis was independent of the actions of acetylated low-density lipoproteins. In addition, the transfection of the expression plasmid of V279F mutant Lp-PLA2 into Cos-7 cells or monocyte/macrophage-like U937 cells promoted apoptosis. The knockdown of Lp-PLA2 also increased the number of apoptotic cells. Among the cells expressing mutant Lp-PLA2, the caspase-7 activity was increased, while the activated Akt level was decreased.

CONCLUSIONS

The V279F mutation of Lp-PLA2 positively regulates the induction of apoptosis in macrophages and Cos-7 cells. An increase in the caspase-7 activity and a reduction in the activated Akt level are likely to be involved in this phenomenon.

Lp-PLA2 Inhibitors for the Reduction of Cardiovascular Events

Evidence suggests that inflammation plays a central role in the pathogenesis of atherosclerosis (Libby, Nature 420:868–874, 2002). Inflammation is a physiologic process with highly regulated and often redundant mechanisms to balance pro-inflammatory and anti-inflammatory responses. The complexity of these networks has made it challenging to identify those specific pathways or key enzymes that contribute directly to atherogenesis and could act as a valuable therapeutic target. Lipoprotein-associated phospholipase A₂ (Lp-PLA₂) is a member of the phospholipase A₂ family of enzymes and is believed to contribute to atherosclerotic plaque progression and instability by promoting inflammation. A large number of epidemiologic studies have demonstrated that elevated levels of Lp-PLA₂ are associated with an increased risk of cardiovascular events across diverse patient populations, independent of established risk factors including low-density lipoprotein cholesterol. Further, a growing number of preclinical and genetic studies support a causal role for Lp-PLA₂ in atherosclerosis. The development of a novel therapeutic agent that directly inhibits the Lp-PLA₂ enzyme has provided a unique opportunity to directly test the hypothesis that inhibition of this inflammatory enzyme will translate into improved clinical outcomes. In this article, we will review the evidence to support the notion that Lp-PLA₂ is causally implicated in the pathobiology of atherogenesis and discuss the potential utility of inhibiting this enzyme as a therapeutic target.

An association study between genetic polymorphisms related to lipoprotein-associated phospholipase A(2) and coronary heart disease

Previous genome-wide association studies (GWAS) have revealed seven single nucleotide polymorphisms (SNPs) that affect lipoprotein-associated phospholipase A₂ (Lp-PLA₂) activity or levels in American and European individuals. A total of 290 coronary heart disease (CHD) patients, 198 non-CHD patients and 331 unrelated healthy volunteers were recruited for the present case-control study of Han Chinese. Four SNPs (rs964184 of ZNF259, rs7528419 of CELSR2 and rs7756935 and rs1805017 of PLA2G7) were shown to be significantly associated with CHD. The rs964184-G allele of the ZNF259 gene was identified as a risk factor of CHD in females (odds ratio (OR) =1.49, 95% confidence interval (CI) =1.00–2.22, P=0.05). The rs7528419-G allele of the CELSR2 gene was protective against CHD in males (OR=0.48, 95% CI=0.25–0.93, P=0.04). The other two alleles (rs7756935-C and rs1805017-A) of the PLA2G7 gene acted as protective factors against CHD in females (rs7756935-C: OR=0.59, 95% CI=0.35–1.00, P=0.05; rs1805017-A: OR=0.51, 95% CI=0.28–0.93, P=0.03). Moreover, rs1805017 of the PLA2G7 gene was associated with the severity of CHD only in females (r²=0.02, P=0.04). We identified four Lp-PLA₂-associated SNPs significantly associated with CHD in a Han Chinese population. Specifically, rs7528419 was protective factor against CHD in males, while the other two SNPs (rs7756935 and rs1805017 of the PLA2G7 gene) were protective factors against CHD in females and rs964184 of the ZNF259 gene was regarded as a risk factor for CHD in females.

Selective inhibitors and tailored activity probes for lipoprotein-associated phospholipase A(2)

Lipoprotein-associated phospholipase A(2) (Lp-PLA(2) or PLA(2)G7) binds to low-density lipoprotein (LDL) particles, where it is thought to hydrolyze oxidatively truncated phospholipids. Lp-PLA(2) has also been implicated as a pro-tumorigenic enzyme in human prostate cancer. Several inhibitors of Lp-PLA(2) have been described, including darapladib, which is currently in phase 3 clinical development for the treatment of atherosclerosis. The selectivity that darapladib and other Lp-PLA(2) inhibitors display across the larger serine hydrolase family has not, however, been reported. Here, we describe the use of both general and tailored activity-based probes for profiling Lp-PLA(2) and inhibitors of this enzyme in native biological systems. We show that both darapladib and a novel class of structurally distinct carbamate inhibitors inactivate Lp-PLA(2) in mouse tissues and human cell lines with high selectivity. Our findings thus identify both inhibitors and chemoproteomic probes that are suitable for investigating Lp-PLA(2) function in biological systems.

Genome-Wide Association Study Evaluating Lipoprotein-Associated Phospholipase A 2 Mass and Activity at Baseline and After Rosuvastatin Therapy

Background—

Lipoprotein-associated phospholipase A 2 (Lp-PLA 2 ) is a proinflammatory enzyme bound to low-density lipoprotein cholesterol and other circulating lipoproteins. Two measures of Lp-PLA 2 , mass and activity, are associated with increased cardiovascular risk. Data are sparse regarding genetic determinants of Lp-PLA 2 mass and activity, and no prior data are available addressing genetic determinants of statin-induced changes for this proinflammatory biomarker.

Methods and Results —

We performed a genome-wide association study of Lp-PLA 2 mass and activity at baseline and after 12 months of rosuvastatin therapy (20 mg/d) among 6851 participants of European ancestry from the Justification for Use of Statins in Prevention: an Intervention Trial Evaluating Rosuvastatin (JUPITER) and performed replication in a meta-analysis of 13 664 participants from the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Consortium. Novel associations were identified and replicated at MS4A4E and TMEM49 for baseline Lp-PLA 2 activity with genome-wide significant joint P values ( P =2.0×10 −11 and P =2.9×10 −9 , respectively). In addition, genome-wide associations ( P <5×10 −8 ) were identified and replicated for baseline Lp-PLA 2 mass at CETP and for Lp-PLA 2 activity at the APOC1-APOE and PLA2G7 loci. Among 2673 statin-allocated participants, both Lp-PLA 2 mass and activity were reduced by >30% and low-density lipoprotein cholesterol by 50% after 12 months of statin therapy ( P <0.001 for both). Variants in ABCG2 and LPA were associated with change in statin-induced Lp-PLA 2 activity at genome-wide significance but were substantially attenuated after adjustment for statin-induced changes in lipid levels.

Conclusions—

Genome-wide significant associations at MS4A4E and TMEM49 may reflect novel influences on circulating levels of Lp-PLA 2 activity. In addition, genome-wide significant associations with rosuvastatin-induced change in Lp-PLA 2 activity were observed in ABCG2 and LPA , likely because of their impact on statin-induced low-density lipoprotein cholesterol lowering.

Variation of lipoprotein associated phospholipase A2 across demographic characteristics and cardiovascular risk factors: a systematic review of the literature

BACKGROUND

Lipoprotein association phospholipase A2 (Lp-PLA(2)), an enzyme which has been found in atherosclerotic plaque is currently under investigation in large Phase III clinical trials of vascular disease prevention. We assessed in a variety of different population settings variation of Lp-PLA(2) mass and activity across gender, ethnicity, diabetes, kidney disease and metabolic syndrome. We also assessed correlations with measures of circulating lipids, systemic inflammation and adiposity.

METHODS

Systematic review of studies measuring Lp-PLA(2) and at least one of the relevant characteristics in >50 participants.

RESULTS

We identified a total of 77 studies involving 102,499 participants meeting the inclusion criteria. Lp-PLA(2) mass and activity were consistently approximately 10% higher in males than females and 15% higher in Caucasians than African Americans or Hispanics. There were no clear associations of Lp-PLA(2) mass or activity with type II diabetes, markers of systemic inflammation (C-reactive protein, fibrinogen) or with body mass index. Correlations of Lp-PLA(2) mass or activity with low density lipoprotein cholesterol and apolipoprotein B were moderate and positive, whilst correlations with high density lipoprotein cholesterol were negative and moderate to weak. There was no clear differences in associations with any of the above characteristics in groups defined based upon prevalent cardiovascular disease or its risk factors.

CONCLUSIONS

Despite considerable variability in absolute levels of Lp-PLA(2) across studies, the variability of Lp-PLA(2) across gender, ethnicity, and levels of circulating lipids and markers of systemic inflammation are more consistent and appear not to vary importantly across categories defined by CVD or its risk factors.

Modulation of oxidative stress, inflammation, and atherosclerosis by lipoprotein-associated phospholipase A2

Lipoprotein-associated phospholipase A(2) (Lp-PLA(2)), also known as platelet-activating factor acetylhydrolase (PAF-AH), is a unique member of the phospholipase A(2) superfamily. This enzyme is characterized by its ability to specifically hydrolyze PAF as well as glycerophospholipids containing short, truncated, and/or oxidized fatty acyl groups at the sn-2 position of the glycerol backbone. In humans, Lp-PLA(2) circulates in active form as a complex with low- and high-density lipoproteins. Clinical studies have reported that plasma Lp-PLA(2) activity and mass are strongly associated with atherogenic lipids and vascular risk. These observations led to the hypothesis that Lp-PLA(2) activity and/or mass levels could be used as biomarkers of cardiovascular disease and that inhibition of the activity could offer an attractive therapeutic strategy. Darapladib, a compound that inhibits Lp-PLA(2) activity, is anti-atherogenic in mice and other animals, and it decreases atherosclerotic plaque expansion in humans. However, disagreement continues to exist regarding the validity of Lp-PLA(2) as an independent marker of atherosclerosis and a scientifically justified target for intervention. Circulating Lp-PLA(2) mass and activity are associated with vascular risk, but the strength of the association is reduced after adjustment for basal concentrations of the lipoprotein carriers with which the enzyme associates. Genetic studies in humans harboring an inactivating mutation at this locus indicate that loss of Lp-PLA(2) function is a risk factor for inflammatory and vascular conditions in Japanese cohorts. Consistently, overexpression of Lp-PLA(2) has anti-inflammatory and anti-atherogenic properties in animal models. This thematic review critically discusses results from laboratory and animal studies, analyzes genetic evidence, reviews clinical work demonstrating associations between Lp-PLA(2) and vascular disease, and summarizes results from animal and human clinical trials in which administration of darapladib was tested as a strategy for the management of atherosclerosis.

Translational studies of lipoprotein-associated phospholipase A₂ in inflammation and atherosclerosis

OBJECTIVES

This study sought to examine the role of lipoprotein-associated phospholipase A₂ (Lp-PLA₂/PLA2G7) in human inflammation and coronary atherosclerosis.

BACKGROUND

Lp-PLA₂ has emerged as a potential therapeutic target in coronary heart disease. Data supporting Lp-PLA₂ are indirect and confounded by species differences; whether Lp-PLA₂ is causal in coronary heart disease remains in question.

METHODS

We examined inflammatory regulation of Lp-PLA₂ during experimental endotoxemia in humans, probed the source of Lp-PLA₂ in human leukocytes under inflammatory conditions, and assessed the relationship of variation in PLA2G7, the gene encoding Lp-PLA₂, with coronary artery calcification.

RESULTS

In contrast to circulating tumor necrosis factor-alpha and C-reactive protein, blood and monocyte Lp-PLA₂ messenger ribonucleic acid decreased transiently, and plasma Lp-PLA₂ mass declined modestly during endotoxemia. In vitro, Lp-PLA₂ expression increased dramatically during human monocyte to macrophage differentiation and further in inflammatory macrophages and foamlike cells. Despite only a marginal association of single nucleotide polymorphisms in PLA2G7 with Lp-PLA₂ activity or mass, numerous PLA2G7 single nucleotide polymorphisms were associated with coronary artery calcification. In contrast, several single nucleotide polymorphisms in CRP were significantly associated with plasma C-reactive protein levels but had no relation with coronary artery calcification.

CONCLUSIONS

Circulating Lp-PLA₂ did not increase during acute phase response in humans, whereas inflammatory macrophages and foam cells, but not circulating monocytes, are major leukocyte sources of Lp-PLA₂. Common genetic variation in PLA2G7 is associated with subclinical coronary atherosclerosis. These data link Lp-PLA₂ to atherosclerosis in humans while highlighting the challenge in using circulating Lp-PLA₂ as a biomarker of Lp-PLA₂ actions in the vasculature.

Eight genetic loci associated with variation in lipoprotein-associated phospholipase A2 mass and activity and coronary heart disease: meta-analysis of genome-wide association studies from five community-based studies

AIMS

Lipoprotein-associated phospholipase A2 (Lp-PLA2) generates proinflammatory and proatherogenic compounds in the arterial vascular wall and is a potential therapeutic target in coronary heart disease (CHD). We searched for genetic loci related to Lp-PLA2 mass or activity by a genome-wide association study as part of the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Consortium.

METHODS AND RESULTS

In meta-analyses of findings from five population-based studies, comprising 13 664 subjects, variants at two loci (PLA2G7, CETP) were associated with Lp-PLA2 mass. The strongest signal was at rs1805017 in PLA2G7 [P = 2.4 × 10(-23), log Lp-PLA2 difference per allele (beta): 0.043]. Variants at six loci were associated with Lp-PLA2 activity (PLA2G7, APOC1, CELSR2, LDL, ZNF259, SCARB1), among which the strongest signals were at rs4420638, near the APOE-APOC1-APOC4-APOC2 cluster [P = 4.9 × 10(-30); log Lp-PLA2 difference per allele (beta): -0.054]. There were no significant gene-environment interactions between these eight polymorphisms associated with Lp-PLA2 mass or activity and age, sex, body mass index, or smoking status. Four of the polymorphisms (in APOC1, CELSR2, SCARB1, ZNF259), but not PLA2G7, were significantly associated with CHD in a second study.

CONCLUSION

Levels of Lp-PLA2 mass and activity were associated with PLA2G7, the gene coding for this protein. Lipoprotein-associated phospholipase A2 activity was also strongly associated with genetic variants related to low-density lipoprotein cholesterol levels.

Biallelic mutations in PLA2G5, encoding group V phospholipase A2, cause benign fleck retina

Flecked-retina syndromes, including fundus flavimaculatus, fundus albipunctatus, and benign fleck retina, comprise a group of disorders with widespread or limited distribution of yellow-white retinal lesions of various sizes and configurations. Three siblings who have benign fleck retina and were born to consanguineous parents are the basis of this report. A combination of homozygosity mapping and exome sequencing helped to identify a homozygous missense mutation, c.133G>T (p.Gly45Cys), in PLA2G5, a gene encoding a secreted phospholipase (group V phospholipase A(2)). A screen of a further four unrelated individuals with benign fleck retina detected biallelic variants in the same gene in three patients. In contrast, no loss of function or common (minor-allele frequency>0.05%) nonsynonymous PLA2G5 variants have been previously reported (EVS, dbSNP, 1000 Genomes Project) or were detected in an internal database of 224 exomes (from subjects with adult onset neurodegenerative disease and without a diagnosis of ophthalmic disease). All seven affected individuals had fundoscopic features compatible with those previously described in benign fleck retina and no visual or electrophysiological deficits. No medical history of major illness was reported. Levels of low-density lipoprotein were mildly elevated in two patients. Optical coherence tomography and fundus autofluorescence findings suggest that group V phospholipase A(2) plays a role in the phagocytosis of photoreceptor outer-segment discs by the retinal pigment epithelium. Surprisingly, immunohistochemical staining of human retinal tissue revealed localization of the protein predominantly in the inner and outer plexiform layers.

Study design and rationale for the Stabilization of pLaques usIng Darapladib-Thrombolysis in Myocardial Infarction (SOLID-TIMI 52) trial in patients after an acute coronary syndrome

BACKGROUND

Higher levels of lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) are associated with a higher risk of cardiovascular events and may play a causal role in atherogenesis. Darapladib inhibits Lp-PLA(2) activity in plasma and in arterial plaques and may confer clinical benefit in preventing cardiovascular events.

STUDY DESIGN

The SOLID-TIMI 52 trial is a randomized, double-blind, placebo-controlled, multicenter, event-driven trial. Approximately 13,000 subjects are being randomized to darapladib (160 mg enteric-coated tablet daily) or matching placebo within 30 days of hospitalization with an acute coronary syndrome. The primary end point is the composite of cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke. Secondary end points include major and total coronary events, individual components of the primary end point, and all-cause mortality. The study will continue until approximately 1,500 primary end point events have occurred to achieve 90% power to detect a 15.5% reduction in the primary end point. The median treatment duration is anticipated to be approximately 3 years, with a total study duration of approximately 4.1 years.

CONCLUSIONS

The SOLID-TIMI 52 trial will determine the clinical benefit of direct inhibition of Lp-PLA(2) activity with darapladib in patients after an acute coronary syndrome.