Platelet-activating factor acetylhydrolase deficiency. A missense mutation near the active site of an anti-inflammatory phospholipase

Associations between healthy food groups and platelet-activating factor, lipoprotein-associated phospholipase A2 and C-reactive protein: a cross-sectional study

PURPOSE

To investigate the association between pro-inflammatory markers platelet-activating factor (PAF), lipoprotein-associated phospholipase A2 (Lp-PLA2), hsCRP, and intake of core food groups including fruit, cruciferous and other vegetables, grains, meat and poultry, fish and seafood, nuts and legumes, and dairy.

METHODS

A cross-sectional study was conducted. 100 adults (49 ± 13 years, 31% male) with variable cardiovascular disease risk were recruited. Data were collected in 2021 and 2022. Fasting PAF, Lp-PLA2 activity, hsCRP and usual dietary intake (via a validated food frequency questionnaire) were measured. Intake of foods were converted into serves and classified into food groups. Correlations and multiple regressions were performed with adjustment for confounders.

RESULTS

A one-serve increase in cruciferous vegetables per day was associated with 20-24% lower PAF levels. An increase of one serve per day of nuts and legumes was associated with 40% lower hsCRP levels. There were small correlations with PAF and Lp-PLA2 and cheese, however, these were not significant at the Bonferroni-adjusted P < 0.005 level.

CONCLUSION

The lack of associations between PAF and Lp-PLA2 and other healthy foods may be due to confounding by COVID-19 infection and vaccination programs which prevents any firm conclusion on the relationship between PAF, Lp-PLA2 and food groups. Future research should aim to examine the relationship with these novel markers and healthy food groups in a non-pandemic setting.

Genetic Polymorphism of Lipoprotein-Associated Phospholipase A2 Influences Susceptibility to Gestational Diabetes Mellitus in Chinese Population

Purpose

This paper aims to study the relationship between lipoprotein-associated phospholipase A2 (Lp-PLA2) and GDM (gestational diabetes mellitus) by detecting Lp-PLA2 level and its gene polymorphism.

Patients and Methods

From January to June 2022, 82 GDM patients treated in our hospital were included as an experimental group, and 89 healthy pregnant women during the same period were selected as the control group. Lp-PLA2 concentration and TG, TC, HDL-C, and LDL-C levels were tested with specialized instruments in clinical laboratories. The PLA2G7 gene polymorphisms (rs1805017, rs1805018, and rs76863441) were detected by fluorescent probe method and sequencing.

Results

Lp-PLA2 concentration was significantly higher in GDM group than control group (P<0.05). Among three polymorphism loci of PLA2G7 gene (rs1805017, rs1805018, and rs76863441) the significant associations were only found in GT genotype of rs76863441 loci (P<0.05).

Conclusion

Pregnant women with high levels of Lp-PLA2 concentration are more likely to develop GDM, especially those with PLA2G7 rs76863441 polymorphism. Lp-PLA2 concentration and PLA2G7 rs1805017 polymorphism may be a novel marker for GDM diagnosis and prediction.

Platelet Activating Factor (PAF): A Mediator of Inflammation

Platelet-activating factor (PAF) is a phospholipid-derived mediator with an established role in multiple inflammatory states. PAF is synthesized and secreted by multiple cell types and is then rapidly hydrolyzed and degraded to an inactive metabolite, lyso-PAF, by the enzyme PAF acetylhydrolase. In addition to its role in platelet aggregation and activation, PAF contributes to allergic and nonallergic inflammatory diseases such as anaphylaxis, sepsis, cardiovascular disease, neurological disease, and malignancy as demonstrated in multiple animal models and, increasingly, in human disease states. Recent research has demonstrated the importance of the PAF pathway in multiple conditions including the prediction of severe pediatric anaphylaxis, effects on blood-brain barrier permeability, effects on reproduction, ocular diseases, and further understanding of its role in cardiovascular risk. Investigation of PAF as both a biomarker and a therapeutic target continues because of the need for directed management of inflammation. Collectively, studies have shown that therapies focused on the PAF pathway have the potential to provide targeted and effective treatments for multiple inflammatory conditions.

Association Lp-PLA2 Gene Polymorphisms with Coronary Heart Disease

Objectives

The study evaluated the association between lipoprotein-associated phospholipase A2 (Lp-PLA2) gene polymorphisms and coronary heart disease (CHD), in order to explore the molecular genetics of CHD.

Methods

Groups of CHD patients (n = 283) and healthy controls (n = 261) were involved in this study. R92H, V279F, and A379V polymorphisms of LP-PLA2 gene were confirmed using polymerase chain reaction (PCR) and direct DNA sequencing. These polymorphisms and their interaction were also analyzed as potential risk factors of CHD.

Results

In this study population, the genotypes of R92H (GG, GA, and AA), V279F (CC, AC, and AA) and A379V (GG, GA, and AA) were studied. There was a significantly difference in frequencies of R92H between CHD patients and controls (P < 0.05). In contrast, no significant difference in frequencies of V279F and A379V existed between CHD patients and controls. Furthermore, R92H and A379V were in strong linkage disequilibrium.

Conclusions

These results suggested that R92H polymorphism might contribute to increased risk of CHD.

Predictive model based on gene and laboratory data for intravenous immunoglobulin resistance in Kawasaki disease in a Chinese population

BACKGROUND

Here, we investigated the predictive efficiency of a newly developed model based on single nucleotide polymorphisms (SNPs) and laboratory data for intravenous immunoglobulin (IVIG) resistance in Kawasaki disease (KD) in a Chinese population.

METHODS

Data relating to children with KD were acquired from a single center between December 2015 and August 2019 and used to screen target SNPs. We then developed a predictive model of IVIG resistance using previous laboratory parameters. We then validated our model using data acquired from children with KD attending a second center between January and December 2019.

RESULTS

Analysis showed that rs10056474 GG, rs746994GG, rs76863441GT, rs16944 (CT/TT), and rs1143627 (CT/CC), increased the risk of IVIG-resistance in KD patients (odds ratio, OR > 1). The new predictive model, which combined SNP data with a previous model derived from laboratory data, significantly increased the area under the receiver-operator-characteristic curves (AUC) (0.832, 95% CI: 0.776-0.878 vs 0.793, 95%CI:0.734-0.844, P < 0.05) in the development dataset, and (0.820, 95% CI: 0.730-0.889 vs 0.749, 95% CI: 0.652-0.830, P < 0.05) in the validation dataset. The sensitivity and specificity of the new assay were 65.33% (95% CI: 53.5-76.0%) and 86.67% (95% CI: 80.2-91.7%) in the development dataset and 77.14% (95% CI: 59.9-89.6%) and 86.15% (95% CI: 75.3-93.5%) in the validation dataset.

CONCLUSION

Analysis showed that rs10056474 and rs746994 in the SMAD5 gene, rs76863441 in the PLA2G7 gene, and rs16944 or rs1143627 in the interleukin (IL)-1B gene, were associated with IVIG resistant KD in a Chinese population. The new model combined SNPs with laboratory data and improved the predictve efficiency of IVIG-resistant KD.

Structural Modeling of Wild and Mutant Forms of Human Plasma Platelet Activating Factor-Acetyl Hydrolase Enzyme

PURPOSE

To investigate the structural features of wild and mutant forms of the pPAF-AH enzyme that are responsible for coronary artery disease.

METHODS

Mutant variants of human pPAF-AH having either V279F, Q281R, or both were modelled and evaluated for stereo chemical and structural correctness. The 3D coordinates of substrate PAF were retrieved from the PubChem database was solvated and minimized on Discovery Studio, and docked to the wild and mutant enzyme models. The top docked pose complex was refined by MD simulation.

RESULTS

pPAF-AH model comprises of 420 amino acids in a α/β-hydrolase fold that contains a substrate-binding hydrophobic channel with an active site pocket having a catalytic triad of Ser273, Asp296 and His351. Mutations at positions 279 and 281 are opposite one another on the middle of 12 residues long H5 helix that forms the hydrophobic core of the enzyme. V279F causes a tilt on the axis of the mutation bearing helix to avoid steric clashes with the hydrophobic residues on the β-sheets adjacent to it, inducing subtle conformational changes on the H5-β8 loop, β8 sheet, and the loop bearing Asp296. A cascade of conformational changes induces a change in the orientation of His351 resulting in loss of hydrogen bonded interaction with catalytic Ser273. Q281R causes a shortening of H5 and β8, which induces conformational changes of the loops bearing Ser273 and Asp296, respectively. Simultaneous conformational changes of secondary structural elements result in the flipping of His351 causing a break in the catalytic triad. Also, there is a compromise in the substrate-binding area and volume in the mutants resulting in loss of binding to its substrate.

CONCLUSION

Mutant enzymes show changes at the site of the mutation, secondary motif conformations and global structural conformations that adversely affect the active site, decrease substrate channel volume and decrease stability, thereby affecting enzymatic function.

A case report on concurrent occurrence of systemic mastocytosis and myeloid sarcoma presenting with extensive skin involvements and the results of genetic study

INTRODUCTION

Systemic mastocytosis is a rare disease due to mast cell accumulation in various extracutaneous sites. Systemic mastocytosis with an associated clonal hematologic non-MC lineage disease is the second most common subtype of systemic mastocytosis. The most common mutation associated with both systemic mastocytosis and myeloid sarcoma is mutation in Kit. Here, we identified the novel KIT D816V and ARID1A G1254S mutations co-occurring in systemic mastocytosis with myeloid sarcoma.

PATIENT CONCERNS

A 33-year old male patient presented multiple skin lesions for 10 years. Symptoms accelerated in 2017 with decreased body weight. Physical examination revealed enlarged lymph nodes in his neck, axilla and inguinal region; conjunctival hemorrhage; gingival hyperplasia. Skin biopsy showed mast cell infiltration. Flow cytometry detected CD2, CD25 and CD117 positive cells in lymph nodes. Codon 816 KIT mutation D816V and codon 1245 ARID1A mutation G1254S were found in peripheral blood. MPO, CD117, CD68 positive cells in lymph nodes indicated co-existing myeloid sarcoma.

DIAGNOSIS

Systemic mastocytosis with an associated clonal hematologic non-MC lineage disease of myeloid sarcoma INTERVENTIONS:: Cytarabine and daunorubicin for myeloid sarcoma and dasatinib for systemic mastocytosis were initiated. Anti-histamine and anti-leukotrienes therapy were used to prevent NSAIDs-induced shock. Platelets were infused to treat bone marrow suppression.

OUTCOMES

Patient was discharged after recovered from bone marrow suppression. Dasatinib continued on outpatient.

CONCLUSION

This is the first case of patient with systemic mastocytosis and myeloid sarcoma simultaneously presenting extensive skin involvements. Mutations of Kit and Arid1a emphasis the importance to notice possibility of various tumors occurring in patients with multiple mutations. In addition, cysteine-leukotrienes-receptor antagonists should always be used to prevent anaphylactic shock due to mast cell activation.

Effect of acyl and alkyl analogs of platelet-activating factor on inflammatory signaling

Platelet-activating factor (PAF), a bioactive ether phospholipid with significant pro-inflammatory properties, was identified almost half a century ago. Despite extensive study of this autocoid, therapeutic strategies for targeting its signaling components have not been successful, including the recent clinical trials with darapladib, a drug that targets plasma PAF-acetylhydrolase (PAF-AH). We recently provided experimental evidence that the previously unrecognized acyl analog of PAF, which is concomitantly produced along with PAF during biosynthesis, dampens PAF signaling by acting both as a sacrificial substrate for PAF-AH and probably as an endogenous PAF-receptor antagonist/partial agonist. If this is the scenario in vivo, PAF-AH needs to catalyze the selective hydrolysis of alkyl-PAF and not acyl-PAF. Accordingly, different approaches are needed for treating inflammatory diseases in which PAF signaling is implicated. The interplay between acyl-PAF, alkyl-PAF, PAF-AH, and PAF-R is complex, and the outcome of this interplay has not been previously appreciated. In this review, we discuss this interaction based on our recent findings. It is very likely that the relative abundance of acyl and alkyl-PAF and their interactions with PAF-R in the presence of their hydrolyzing enzyme PAF-AH may exert a modulatory effect on PAF signaling during inflammation.

Reinterpretation of common pathogenic variants in ClinVar revealed a high proportion of downgrades

High-frequency disease-causing alleles exist, but their number is rather small. This study aimed to interpret and reclassify common pathogenic (P) and likely pathogenic (LP) variants in ClinVar and to identify indicators linked with reclassification. We analyzed P/LP variants without conflicting interpretations in ClinVar. Only variants with an allele frequency exceeding 0.5% in at least one ancestry in gnomAD were included. Variants were manually interpreted according to the guidelines of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology. Of 326 variants retrieved, 217 variants in 173 genes were selected for curation. Overall, 87 (40%) variants were downgraded to benign, likely benign or variant of uncertain significance. Five variants (2%) were found to be more likely to be risk factors. Most of the reclassifications were of variants with a low rank, an older classification, a higher allele frequency, or which were collected through methods other than clinical testing. ClinVar provides a universal platform for users who intend to share the classification variants, resulting in the improved concordance of variant interpretation. P/LP variants with a high allele frequency should be used with caution. Ongoing improvements would further improve the practicability of ClinVar database.

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.

G994T polymorphism in exon 9 of plasma platelet-activating factor acetylhydrolase gene and lung ultrasound score as prognostic markers in evaluating the outcome of acute respiratory distress syndrome

The present study aimed to discover potential biomarkers for predicting the prognosis of acute respiratory distress syndrome (ARDS) in conjunction with lung ultrasound (LUS). Blood samples from 112 ARDS patients were collected to compare their partial oxygen pressure (PaO₂)/fraction of inspired oxygen (FiO₂), positive end-expiratory pressure (PEEP), lactic acid, sequential organ failure assessment (SOFA) score, clinical pulmonary infection score (CPIS) and APACHE II score. Kaplan-Meier plots and the log-rank test were performed to analyse the association between the platelet-activating factor acetylhydrolase (PAFAH) G994T polymorphism and the outcome of ARDS regarding mortality. A negative correlation between the LUS score and PaO₂/FiO₂, PEEP and lactic acid, as well as with the SOFA, CPIS and APACHE II score was confirmed with correlation coefficients of -0.493, -0.548, -0.642, -0.598, -0.566 and -0.567, respectively (all P<0.05). The activity of PAFAH and high-density lipoprotein-PAFAH in the serum collected from subjects of the GG genotype was similar to that in subjects of the GT genotype, but the low-density lipoprotein-PAFAH activity in the serum collected from GG subjects was significantly higher than that in GT subjects. An evident reduction in the PEEP, level of lactic acid, as well as the SOFA, CPIS and APACHE II score was observed in GG subjects, accompanied by a significantly increased PaO₂/FiO₂. Kaplan-Meier analysis indicated that subjects with a high LUS score had a significantly higher survival rate than those with a low LUS score, and the mortality risk for GG subjects was significantly lower than that for GT subjects. Finally, among all groups (genotype and LUS groups), GG subjects with a high LUS score had the lowest mortality risk, whereas GT subjects with a low LUS score had the highest mortality risk. In addition, the survival rate of GT subjects with a high LUS score was higher than that of GG subjects with a low LUS score. In conclusion, the combination of the LUS score and the G994T polymorphism in exon 9 of the PAFAH gene may be used as a potential prognostic marker for ARDS.

Platelet-activating factor acetylhydrolases: An overview and update

Platelet-activating factor acetylhydrolases (PAF-AHs) are unique members of the phospholipase A₂ family that can hydrolyze the acetyl group of PAF, a signaling phospholipid that has roles in diverse (patho)physiological processes. Three types of PAF-AH have been identified in mammals, one plasma type and two intracellular types [PAF-AH (I) and PAF-AH (II)]. Plasma PAF-AH and PAF-AH (II) are monomeric enzymes that are structurally similar, while PAF-AH (I) is a multimeric enzyme with no homology to other PAF-AHs. PAF-AH (I) shows a strong preference for an acetyl group, whereas plasma PAF-AH and PAF-AH (II) also hydrolyze phospholipids with oxidatively modified fatty acids. Plasma PAF-AH has been implicated in several diseases including cardiovascular disease. PAF-AH (I) is required for spermatogenesis and is increasingly recognized as an oncogenic factor. PAF-AH (II) was recently shown to act as a bioactive lipid-producing enzyme in mast cells and thus could be a drug target for allergic diseases. This article is part of a Special Issue entitled Novel functions of phospholipase A2 Guest Editors: Makoto Murakami and Gerard Lambeau.

Impact of a non-synonymous Q281R polymorphism on structure of human Lipoprotein-Associated Phospholipase A2 (Lp-PLA2 )

Non-synonymous single nucleotide polymorphisms (nsSNPs) are genetic variations at single base resulting in an amino acid change which have been associated with various complex human diseases. The human Lipoprotein-associated phospholipase A₂ (Lp-PLA₂ ) gene harbours a rare Q281R polymorphism which was previously reported to cause loss of enzymatic function. Lp-PLA₂ is an important enzyme which catalyzes the hydrolysis of polar phospholipids releasing pro-atherogenic and pro-inflammatory mediators involved in the pathogenesis of atherosclerosis. Our current study is aimed at elucidating the structural and functional consequences of Q281R polymorphism on Lp-PLA₂ . The Q281R mutation is classified as deleterious and causes protein instability as deduced from evolutionary, folding free energy changes and Support vector machine (SVM)-based methods. A Q281R mutant structure was deciphered using homology modelling approach and was validated using phi and psi dihedral angles distribution, ERRAT, Verify_3D scores, Protein Structure Analysis (ProSA) energ,y and Z-score. A decreased hydrophobic interactions and weaker substrate binding affinity was observed in the mutant compared to the wild- type (WT) using molecular docking. Further, the mutant displayed enhanced structural flexibility particularly in the low density lipoprotein (LDL) binding domain, decreased solvent accessibility of catalytic residues-Phe274 and Ser273 and increased Cɑ distance between Phe274 and Leu153 and large conformational entropy change as inferred from all-atom molecular dynamics (MD) simulation and essential dynamics (ED) studies. Our results corroborate well with previous experimental studies and thus these aberrations in the Q281R mutant structure may help explain the molecular basis of loss of enzyme activity.

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.

The associations of stroke, transient ischemic attack, and/or stroke-related recurrent vascular events with Lipoprotein-associated phospholipase A2: A systematic review and meta-analysis

BACKGROUND

Studies on stroke and lipoprotein-associated phospholipase A2 (Lp-PLA2) have produced conflicting results.

OBJECTIVE

The aim of the study was to assess the associations of Lp-PLA2 levels (mass and activity) with recurrent vascular events in patients with transient ischemic attack (TIA) and/or first ischemic stroke and with stroke in the general population.

METHODS

The MEDLINE, Embase, the Cochrane Library, Web of Science, Science Direct, China National Knowledge Infrastructure, China Biology Medical Disc (CBMdisc), and WanFang were searched for prospective observational studies reported until January 2017. Eligible studies reported Lp-PLA2 levels and adjusted risk estimates of recurrent vascular events and/or stroke. Risk ratio (RR) with corresponding 95% confidence intervals (CIs) were used to express the pooled data in a random-effects model.

RESULTS

A total of 11 studies that comprised 20,284 participants (4,045 were TIA and/or first ischemic stroke patients and 16,239 were residents in general population) were identified, which reported either Lp-PLA2 mass levels (4 studies) or Lp-PLA2 activity levels (10 studies). The pooled RR of recurrent vascular events (467 cases) in TIA and/or first ischemic group was 2.24 (95% CI, 1.33-3.78), whereas the pooled RR of stroke (1604 cases) in the general population was 1.47 (95% CI, 1.10-1.97). The pooled RRs of Lp-PLA2 mass and activity levels with the risk of stroke in the general population were 1.69 (95% CI, 1.03-2.79) and 1.28 (95% CI, 0.88-1.85), respectively.

CONCLUSIONS

In patients with TIA and first ischemic stroke, elevated Lp-PLA2 activity levels were associated with recurrent vascular events. And in the general population elevated Lp-PLA2 levels were associated with the risk of stroke, although the association between Lp-PLA2 activity levels and the risk of stroke was less profound compared with the corresponding association of stroke risk with the Lp-PLA2 mass levels.

The role of Lp-PLA2 and biochemistry parameters as potential biomarkers of coronary artery disease in Asian South-Indians: a case-control study

Background

Coronary artery disease (CAD) is the leading cause of death and disability worldwide. Lipoprotein associated phospholipase A₂ (Lp-PLA₂) is an emerging biomarker for inflammation that has shown association with CAD. Its significance in the Asian Indian population is not clearly known. We sought to compare the possible association of various biomarkers of atherosclerosis along with Lp-PLA₂, in symptomatic individuals with CAD vs. healthy controls in Asian South-Indians.

Methods

We conducted a cross-sectional case control study at three centers in a South Indian population. A total of 100 CAD patients with acute coronary syndrome (ACS), 100 age and gender matched healthy controls participated, of which, 166 subjects or 83 case-control pairs with complete data for both participants were identified for the statistical analysis. Lp-PLA₂ concentration and activity were measured using PLAC test and PLAC activity assay respectively (diaDexus Inc., San Francisco, CA, USA), while all other parameters were measured using standard commercially available kits.

Results

We enrolled a total of 200 subjects (mean age 50.7±9.6 years, 87.5% males). A total of 83 subjects completed the study in the CAD group (mean age 51 ±8.9 years, 85% males) and 83 subjects in the control group (mean age 50±8.9 years, 86.5% males). In the CAD group, Lp-PLA₂ concentration positively correlated with TC (ρ=0.19, P=0.02), non-HDL-C (ρ=0.20, P=0.02), Lp-PLA₂ activity (ρ=0.27, P=0.001) and Lp(a) (r=0.25, P=0.02). Lp-PLA₂ activity correlated positively with TC (ρ=0.28, P=0.001), LDL-C (ρ=0.30, P<0.001), non-HDL-C (ρ=0.35, P<0.001), ApoB (ρ=0.35, P<0.001) and negatively correlated to HDL-C (ρ=-0.24, P=0.004). Cox proportionality hazards model revealed Lp-PLA₂ concentration (β=0.006, SE =0.002, P=0.009) to have positive association with the event of CAD, while negative association was observed for ApoA1 (β=-0.06, SE =0.02, P=0.001). ROC analysis revealed that the highest quartile of Lp-PLA₂ concentration to have area under curve (AUC) of 0.80 (95% CI, 0.65-0.9; P<0.001) with cut off value of >427 ng/mL and ApoA1 with AUC of 0.78 (95% CI, 0.70-0.85; P<0.001) with cut off value of ≤129.6 mg/dL with the optimum balance of sensitivity and specificity.

Conclusions

In this study population, circulating plasma Lp-PLA₂ was found to be elevated in CAD group. ApoA1 showed negative association and Lp-PLA₂ concentration showed positive association with risk for CAD. In the highest quartile, Lp-PLA₂ concentration had the best diagnostic utility. Our results support the hypothesis that Lp-PLA₂ may be a potential risk marker for CAD in Asian Indians.

Maternal Gestational Diabetes Mellitus increases placental and foetal lipoprotein-associated Phospholipase A2 which might exert protective functions against oxidative stress

Increased Lipoprotein associated phospholipase A2 (LpPLA2) has been associated with inflammatory pathologies, including Type 2 Diabetes. Studies on LpPLA2 and Gestational Diabetes Mellitus (GDM) are rare, and have focused mostly on maternal outcome. In the present study, we investigated whether LpPLA2 activity on foetal lipoproteins is altered by maternal GDM and/or obesity (a major risk factor for GDM), thereby contributing to changes in lipoprotein functionality. We identified HDL as the major carrier of LpPLA2 activity in the foetus, which is in contrast to adults. We observed marked expression of LpPLA2 in placental macrophages (Hofbauer cells; HBCs) and found that LpPLA2 activity in these cells was increased by insulin, leptin, and pro-inflammatory cytokines. These regulators were also increased in plasma of children born from GDM pregnancies. Our results suggest that insulin, leptin, and pro-inflammatory cytokines are positive regulators of LpPLA2 activity in the foeto-placental unit. Of particular interest, functional assays using a specific LpPLA2 inhibitor suggest that high-density lipoprotein (HDL)-associated LpPLA2 exerts anti-oxidative, athero-protective functions on placental endothelium and foetus. Our results therefore raise the possibility that foetal HDL-associated LpPLA2 might act as an anti-inflammatory enzyme improving vascular barrier function.

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.

[Association between platelet-activating factor acetylhydrolase gene polymorphisms and gastrointestinal bleeding in children with Henoch-Schönlein purpura]

OBJECTIVE

To study the association between the single nucleotide polymorphisms (SNPs) of the ninth exon Val279Phe of platelet-activating factor acetylhydrolase (PAF-AH) gene and gastrointestinal bleeding in children with Henoch-Schönlein purpura (HSP).

METHODS

A total 516 children with HSP were enrolled, among whom 182 had gastrointestinal bleeding and 334 had no gastrointestinal bleeding. PCR was used to investigate the distribution of genotypes and alleles in the SNPs of Val97Phe. The plasma PAF-AH activity was measured, as well as the levels of platelet-activating factor (PAF), granular membrane protein-140 (GMP-140), β-thromboglobulin (β-TG), and platelet factor 4 (PF4).

RESULTS

The Val279Phe genotype and allele frequencies were in Hardy-Weinberg equilibrium, and the homozygous genotype TT and heterozygotes accounted for 0.97% and 6.05% respectively. The gastrointestinal bleeding group had a significantly higher allele frequency than the control group (5.22% vs 3.33%; P<0.01). The HSP patients with GG genotype in the gastrointestinal bleeding group had significantly higher levels of plasma PAF and GMP-140 than those in the non-gastrointestinal bleeding group (P<0.05), while the non-gastrointestinal bleeding group had a significantly higher PAF-AH activity than the gastrointestinal bleeding group (P<0.05). There were no significant differences in β-TG and PF4 between the two groups (P>0.05).

CONCLUSIONS

Val279Phe gene polymorphisms in PAF-AH are associated with PAF-AH activity and PAF and GMP-140 levels and may be a risk factor for HSP with gastrointestinal bleeding.

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.

Effect of the R92H and A379V genotypes of platelet-activating factor acetylhydrolase on its enzyme activity, oxidative stress and metabolic profile in Chinese women with polycystic ovary syndrome

Background

The G994T polymorphism in platelet-activating factor acetylhydrolase (PAF-AH) gene is associated with the risk of polycystic ovary syndrome (PCOS). The aim of this study was to investigate the relationship between R92H and A379V variants of the PAF-AH gene and the risk of PCOS and to evaluate the effects of the genotypes on PAF-AH activities and clinical, metabolic and oxidative stress indexes in Chinese women.

Methods

A total of 862 patients with PCOS based on the Rotterdam consensus criteria and 750 control women from a population of Chinese Han nationality in the Chengdu area were studied from 2006–2015. PAF-AH genotypes were determined by PCR and restriction fragment length polymorphism analysis. Plasma PAF-AH, high-density lipoprotein (HDL)-associated PAF-AH (H-PAF-AH) and apolipoprotein (apo) B-containing lipoprotein-associated PAF-AH (apoB-PAF-AH) activities were measured using the trichloroacetic acid precipitation procedure with PAF C-16 as a substrate. Circulating markers of oxidative stress, including serum total oxidant status, total antioxidant capacity, oxidative stress index and malondialdehyde levels, and clinical and metabolic parameters were also analyzed.

Results

No significant differences were observed in the frequencies of R92H and A379V genotypes and alleles of the PAF-AH gene between PCOS and control groups (P > 0.05). Compared with patients with the 92RR genotype, patients with H allele of R92H (RH + HH genotype) had significantly higher plasma PAF-AH and apoB-PAF-AH activities (P < 0.05) and tended to exhibit increased H-PAF-AH activity (P = 0.063) after adjusted for age and BMI. However, when serum LDL-C, HDL-C, TG and HOMA index were added as covariates, the comparisons no longer remained statistical significance (P > 0.05). There were no significant differences in clinical, hormonal, metabolic and circulating oxidative stress parameters and the frequencies of PAF-AH G449T genotype according to PAF-AH R92H or A379V genotyping in patients with PCOS and control women.

Conclusions

There were no significant associations between R92H and A379V variants of PAF-AH gene and risk of PCOS in Chinese women. The increased plasma PAF-AH and apoB-PAF-AH activities in patients with H allele of R92H are related to the R92 → H variation, changes in plasma lipoprotein levels, insulin resistance, aging, and gaining weight and thus may be involved in the pathogenesis of PCOS and the increased risks of future cardiovascular diseases.

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.

A previously unreported impact of a PLA2G7 gene polymorphism on the plasma levels of lipoprotein-associated phospholipase A2 activity and mass

Lipoprotein-associated phospholipase A2 (Lp-PLA₂) levels are associated with the development of atherosclerosis. We aimed to assess the genetic determinants of Lp-PLA₂ activity and mass by genotyping multiple polymorphisms in PLA2G7, the gene encoding Lp-PLA₂, among 1258 participants from the Chinese Multi-provincial Cohort Study-Beijing Project. The Sequenom MassARRAY system, Taqman assay and direct sequencing were adopted. For the first time, the rs13218408 polymorphism was found to be significantly associated with reduced Lp-PLA₂ levels. We also confirmed the significant association of previously validated polymorphisms (rs1421378, rs1805018, rs16874954 and rs2216465), even after adjusting for traditional cardiovascular risk factors and for Bonferroni correction. Percentages of variance attributable to rs13218408 were 7.2% for activity and 13.3% for mass, and were secondary to those of rs16874954 (8.1% for activity and 16.9% for mass). A significant joint effect of rs13218408 and rs16874954 was observed on Lp-PLA₂ activity (P = 0.058) and mass (P = 0.003), with their minor alleles together linking to the largest reduction in Lp-PLA₂ levels (37.8% reduction in activity and 41.6% reduction in mass). Taken together, our findings show a significant association of a PLA2G7 polymorphism with Lp-PLA₂ levels, which was previously unreported in any population. The functionality of this genetic variation deserves further investigations.

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.

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.

Phospholipase A2 as a Molecular Determinant of Store-Operated Calcium Entry

Activation of phospholipases A2 (PLA2) leads to the generation of biologically active lipid products that can affect numerous cellular events. Ca(2+)-independent PLA2 (iPLA2), also called group VI phospholipase A2, is one of the main types forming the superfamily of PLA2. Beside of its role in phospholipid remodeling, iPLA2 has been involved in intracellular Ca(2+) homeostasis regulation. Several studies proposed iPLA2 as an essential molecular player of store operated Ca(2+) entry (SOCE) in a large number of excitable and non-excitable cells. iPLA2 activation releases lysophosphatidyl products, which were suggested as agonists of store operated calcium channels (SOCC) and other TRP channels. Herein, we will review the important role of iPLA2 on the intracellular Ca(2+) handling focusing on its role in SOCE regulation and its implication in physiological and/or pathological processes.

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.

Lipoprotein-associated phospholipase A2 prognostic role in atherosclerotic complications

Atherosclerosis manifests itself clinically at advanced stages when plaques undergo hemorrhage and/or rupture with superimposed thrombosis, thus abruptly stopping blood supply. Identification of markers of plaque destabilization at a pre-clinical stage is, therefore, a major goal of cardiovascular research. Promising results along this line were provided by studies investigating the lipoprotein-associated phospholipase A2 (Lp-PLA2), a member of phospholipase A2 proteins family that plays a key role in the metabolism of pro-inflammatory phospholipids, as oxidized low-density lipoproteins, and in the generation of pro-atherogenic metabolites, including lysophosphatidylcholine and oxidized free fatty acids. We herein review the experimental and clinical studies supporting use of Lp-PLA2 activity for predicting cardiovascular events. To his end we considered not only Lp-PLA2 activity and mass, but also Lp-PLA2 gene variations and their association with incident coronary artery disease, stroke, and cardiovascular mortality. Based on these evidences the major scientific societies have included in their guidelines the measurement of Lp-PLA2 activity among the biomarkers that are useful in risk stratification of adult asymptomatic patients at intermediate cardiovascular risk. The results of two recently published major clinical trials with the Lp-PLA2 inhibitor darapladib, which seem to challenge the pathogenic role of Lp-PLA2, will also be discussed.

Plasma PAF-AH (PLA2G7): Biochemical Properties, Association with LDLs and HDLs, and Regulation of Expression

This chapter is focused on the plasma form of PAF-acetylhydrolase (PAF-AH), a lipoprotein-bound, calcium-independent phospholipase A2 activity also referred to as lipoprotein-associated phospholipase A2 and PLA2G7. PAF-AH catalyzes the removal of the acyl group at the sn-2 position of PAF and truncated phospholipids generated in settings of inflammation and oxidant stress. Here, I discuss current knowledge related to the structural features of this enzyme, including the molecular basis for association with lipoproteins and susceptibility to oxidative inactivation. The circulating form of PAF-AH is constitutively active and its expression is upregulated by mediators of inflammation at the transcriptional level. Several new mechanisms of regulation have been identified in recent years, including effects mediated by PPARs, VEGFR, and the state of cellular differentiation. Moreover, I discuss recent studies describing significant variations in the structure and regulation of PAF-AH from diverse species, which is likely to have important implications for the function of this enzyme in vivo.

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.

Naturally Occurring Missense Mutation in Plasma PAF-AH Among the Japanese Population

A single nucleotide polymorphism in the plasma PAF-AH enzyme, i.e., G994T, which causes the substitution of Val at amino acid 279 with Phe (V279F), has been found in the Japanese population. This enzyme preferentially degrades oxidatively modulated or truncated phospholipids; therefore, it has been suggested that this enzyme may prevent the accumulation of proinflammatory and proatherogenic oxidized phospholipids. This hypothesis is supported by the higher prevalence of the V279F mutation in patients with asthmatic and atherosclerotic diseases, as compared with healthy controls. This mutation is rare in the Caucasian population. The plasma PAF-AH mass and enzyme activity are distributed over a wide range in the plasma and they are positively correlated with low-density lipoprotein (LDL) cholesterol. However, several clinical studies in the Caucasian population have suggested that this enzyme has the opposite role. This enzyme plays an active role in the development and progression of atherosclerosis via proinflammatory and proatherogenic lysophosphatidylcholine and oxidized fatty acids produced through the oxidation of LDL by this enzyme. Thus, plasma PAF-AH is a unique enzyme with dual roles in human inflammatory diseases. In this chapter, on the basis of recent findings we describe the association between a naturally occurring missense mutation in plasma PAF-AH and human diseases especially including atherosclerosis and asthma.

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.

To hydrolyze or not to hydrolyze: the dilemma of platelet-activating factor acetylhydrolase

Mounting ambiguity persists around the functional role of the plasma form of platelet-activating factor acetylhydrolase (PAF-AH). Because PAF-AH hydrolyzes PAF and related oxidized phospholipids, it is widely accepted as an anti-inflammatory enzyme. On the other hand, its actions can also generate lysophosphatidylcholine (lysoPC), a component of bioactive atherogenic oxidized LDL, thus allowing the enzyme to have proinflammatory capabilities. Presence of a canonical lysoPC receptor has been seriously questioned for a multitude of reasons. Animal models of inflammation show that elevating PAF-AH levels is beneficial and not deleterious and overexpression of PAF receptor (PAF-R) also augments inflammatory responses. Further, many Asian populations have a catalytically inert PAF-AH that appears to be a severity factor in a range of inflammatory disorders. Correlation found with elevated levels of PAF-AH and CVDs has led to the design of a specific PAF-AH inhibitor, darapladib. However, in a recently concluded phase III STABILITY clinical trial, use of darapladib did not yield promising results. Presence of structurally related multiple ligands for PAF-R with varied potency, existence of multi-molecular forms of PAF-AH, broad substrate specificity of the enzyme and continuous PAF production by the so called bi-cycle of PAF makes PAF more enigmatic. This review seeks to address the above concerns.

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.

Platelet aggregation unchanged by lipoprotein-associated phospholipase A₂ inhibition: results from an in vitro study and two randomized phase I trials

BACKGROUND

We explored the theorized upregulation of platelet-activating factor (PAF)- mediated biologic responses following lipoprotein-associated phospholipase A2 (Lp-PLA2) inhibition using human platelet aggregation studies in an in vitro experiment and in 2 clinical trials.

METHODS AND RESULTS

Full platelet aggregation concentration response curves were generated in vitro to several platelet agonists in human plasma samples pretreated with rilapladib (selective Lp-PLA2 inhibitor) or vehicle. This was followed by a randomized, double-blind crossover study in healthy adult men (n = 26) employing a single-agonist dose assay of platelet aggregation, after treatment of subjects with 250 mg oral rilapladib or placebo once daily for 14 days. This study was followed by a second randomized, double-blind parallel-group trial in healthy adult men (n = 58) also treated with 250 mg oral rilapladib or placebo once daily for 14 days using a full range of 10 collagen concentrations (0-10 µg/ml) for characterizing EC50 values for platelet aggregation for each subject. Both clinical studies were conducted at the GlaxoSmithKline Medicines Research Unit in the Prince of Wales Hospital, Sydney, Australia. EC50 values derived from multiple agonist concentrations were compared and no pro-aggregant signals were observed during exposure to rilapladib in any of these platelet studies, despite Lp-PLA2 inhibition exceeding 90%. An increase in collagen-mediated aggregation was observed 3 weeks post drug termination in the crossover study (15.4% vs baseline; 95% confidence interval [CI], 3.9-27.0), which was not observed during the treatment phase and was not observed in the parallel-group study employing a more robust EC50 examination.

CONCLUSIONS

Lp-PLA2 inhibition does not enhance platelet aggregation.

TRIAL REGISTRATION

1) Study 1: ClinicalTrials.gov NCT01745458 2) Study 2: ClinicalTrials.gov NCT00387257.

Association of PLA2G7 gene polymorphisms with ischemic stroke in northern Chinese Han population

OBJECTIVE

Human lipoprotein-associated phospholipase A2 (Lp-PLA2), encoded by the PLA2G7 gene, plays an important role in the pathophysiology of inflammation. This study is aimed at evaluating the potential association of V279F and A379V in PLA2G7 gene with ischemic stroke where inflammatory process is involved.

DESIGN AND METHODS

A total of 386 patients with ischemic stroke and 386 healthy controls were included in the study. The single nucleotide polymorphisms, V279F and A379V, were analyzed by the polymerase chain reaction-ligation detection reaction method.

RESULTS

The frequencies of VV+AV genotype, AV genotype and V allele of A379V in the patients with ischemic stroke were significantly higher than those in the controls (P=0.02, P=0.03, P=0.02, respectively). These correlations still remained after adjusting for confounding risk factors of stroke. Furthermore, subgroup analysis showed that a significant association with A379V was found in large-artery atherosclerotic stroke subgroup. In addition, no significant association was observed between V279F and ischemic stroke.

CONCLUSION

The study indicated that the A379V variant in PLA2G7 gene might contribute to ischemic stroke susceptibility in northern Chinese Han population.

PLAC™ test for identification of individuals at increased risk for coronary heart disease

Recent advances in cardiovascular research point to a critical role of inflammatory processes in the etiology of cardiovascular disease. This has led to the discovery of novel inflammatory biomarkers, which may be useful as additional screening tools for the identification of individuals at increased risk of coronary heart disease. One such novel inflammatory biomarker is lipoprotein-associated phospholipase A(2). This review discusses the recent development of a US Food and Drug Administration-approved blood test for lipoprotein-associated phospholipase A(2) (PLAC test, diaDexus, Inc.) and its efficacy as a predictive biomarker of risk for cardiovascular disease. More specifically, the article addresses the potential target group most likely to benefit from this new screening test and provides a prospective scenario for its implementation.

The prevalence of platelet activating factor acetylhydrolase single nucleotide polymorphisms in relationship to necrotizing enterocolitis in Northwest Louisiana infants

PURPOSE

Studies documented that platelet activating factor (PAF) and the enzyme platelet activating factor acetylhydrolase (PAFAH) play a very important role in the pathogenesis of neonatal necrotizing enterocolitis (NEC). In this retrospective, case-controlled pilot study, the authors investigated the prevalence of single nucleotide polymorphisms (Ile198Thr and Ala379Val) of the PAFAH gene.

SUBJECTS AND METHODS

We screened 570 blood samples from both Caucasian and African-American preterm infants in the Northwest Louisiana population for the above mentioned PAFAH gene polymorphisms. Out of 570 infants, 36 had stage I or II NEC based on diagnostic coding, the International Classification of Diseases, 9th revision, Clinical Modification, 2009 (ICD-9-CM). The remaining infants without an ICD-9-CM diagnosis of NEC were recruited as control population. The DNA was isolated and restriction fragment length polymorphism microplate polymerase chain reaction assay was performed.

RESULTS

Variants of the PAFAH gene polymorphism (Ile198Thr and Ala379Val) frequencies were not significantly different between the infants with NEC and the control group (P value of 0.26 by either multiple logistic regression analysis or the Cochran-Mantel-Haenszel test).

CONCLUSIONS

This is the first study of its kind in exploring the relationship between NEC and single nucleotide polymorphisms in the coding genes of the enzyme PAFAH. Our preliminary data demonstrated that adjusted for the effect of race, PAFAH polymorphisms (Ile198Thr and Ala379Val) have no significant effect on NEC.

Determination of phospholipase activity of PAF acetylhydrolase

This article presents a radiometric assay to determine the enzymatic activity of platelet-activating factor (PAF) acetylhydrolase (PAF-AH), also known as lipoprotein-associated phospholipase A2 and phospholipase A2 group 7A. The method is based on the release of radioactively labeled acetate from sn-2-labeled PAF and separation of substrate and product using reversed-phase column chromatography on octadecyl silica gel cartridges. The assay is fast, convenient, reproducible, sensitive, and inexpensive. The instrumentation required includes standard laboratory equipment and a liquid scintillation counter. The assay is also useful to determine the activity of intracellular PAF-AH (PAF-AH II), provided that a few modifications are included. The enzymatic activity determined using PAF as the substrate is a direct indication of the ability of plasma samples, purified preparations, and cellular and tissue lysates to hydrolyze short- and medium-chain phospholipids that may or may not harbor oxidized functionalities. In addition, the assay can be used to test the suitability of other phospholipids, including species containing oxidized, long-chain sn-2 fatty acyl groups, as PAF-AH substrates. This versatile assay can be used to accurately determine PAF-AH activity in biological samples and preliminarily assess affinity and efficiency of the hydrolysis of potential substrates present in complex mixtures.