Plasma platelet-activating factor acetylhydrolase deficiency is associated with atherosclerotic occlusive disease in japan

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.

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.

Interface of Phospholipase Activity, Immune Cell Function, and Atherosclerosis

Phospholipases are a family of lipid-altering enzymes that can either reduce or increase bioactive lipid levels. Bioactive lipids elicit signaling responses, activate transcription factors, promote G-coupled-protein activity, and modulate membrane fluidity, which mediates cellular function. Phospholipases and the bioactive lipids they produce are important regulators of immune cell activity, dictating both pro-inflammatory and pro-resolving activity. During atherosclerosis, pro-inflammatory and pro-resolving activities govern atherosclerosis progression and regression, respectively. This review will look at the interface of phospholipase activity, immune cell function, and 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.

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.

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.

Collaborative meta-analysis of individual participant data from observational studies of Lp-PLA2 and cardiovascular diseases

BACKGROUND

A large number of observational epidemiological studies have reported generally positive associations between circulating mass and activity levels of lipoprotein-associated phospholipase A2 (Lp-PLA2) and the risk of cardiovascular diseases. Few studies have been large enough to provide reliable estimates in different circumstances, such as in different subgroups (e.g., by age group, sex, or smoking status) or at different Lp-PLA2 levels. Moreover, most published studies have related disease risk only to baseline values of Lp-PLA2 markers (which can lead to substantial underestimation of any risk relationships because of within-person variability over time) and have used different approaches to adjustment for possible confounding factors.

OBJECTIVES

By combination of data from individual participants from all relevant observational studies in a systematic 'meta-analysis', with correction for regression dilution (using available data on serial measurements of Lp-PLA2), the Lp-PLA2 Studies Collaboration will aim to characterize more precisely than has previously been possible the strength and shape of the age and sex-specific associations of plasma Lp-PLA2 with coronary heart disease (and, where data are sufficient, with other vascular diseases, such as ischaemic stroke). It will also help to determine to what extent such associations are independent of possible confounding factors and to explore potential sources of heterogeneity among studies, such as those related to assay methods and study design. It is anticipated that the present collaboration will serve as a framework to investigate related questions on Lp-PLA2 and cardiovascular outcomes.

METHODS

A central database is being established containing data on circulating Lp-PLA2 values, sex and other potential confounding factors, age at baseline Lp-PLA2 measurement, age at event or at last follow-up, major vascular morbidity and cause-specific mortality. Information about any repeat measurements of Lp-PLA2 and potential confounding factors has been sought to allow adjustment for possible confounding and correction for regression dilution. The analyses will involve age-specific regression models. Synthesis of the available observational studies of Lp-PLA2 will yield information on a total of about 15 000 cardiovascular disease endpoints.

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.

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.

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.

High Density Lipoprotein and it's Dysfunction

Plasma high-density lipoprotein cholesterol(HDL-C) levels do not predict functionality and composition of high-density lipoprotein(HDL). Traditionally, keeping levels of low-density lipoprotein cholesterol(LDL-C) down and HDL-C up have been the goal of patients to prevent atherosclerosis that can lead to coronary vascular disease(CVD). People think about the HDL present in their cholesterol test, but not about its functional capability. Up to 65% of cardiovascular death cannot be prevented by putative LDL-C lowering agents. It well explains the strong interest in HDL increasing strategies. However, recent studies have questioned the good in using drugs to increase level of HDL. While raising HDL is a theoretically attractive target, the optimal approach remains uncertain. The attention has turned to the quality, rather than the quantity, of HDL-C. An alternative to elevations in HDL involves strategies to enhance HDL functionality. The situation poses an opportunity for clinical chemists to take the lead in the development and validation of such biomarkers. The best known function of HDL is the capacity to promote cellular cholesterol efflux from peripheral cells and deliver cholesterol to the liver for excretion, thereby playing a key role in reverse cholesterol transport (RCT). The functions of HDL that have recently attracted attention include anti-inflammatory and anti-oxidant activities. High antioxidant and anti-inflammatory activities of HDL are associated with protection from CVD.This review addresses the current state of knowledge regarding assays of HDL functions and their relationship to CVD. HDL as a therapeutic target is the new frontier with huge potential for positive public health implications.

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.

Darapladib

IMPORTANCE OF THE FIELD

Atherosclerosis is an inflammatory-immune mediated disease process. Plaque rupture is responsible for the clinical events of ischemic death, myocardial infarction, acute coronary syndromes and ischemic strokes. Lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) seems to play a major role in the development of such high-risk lesions, in both the coronary and carotid arteries. Darapladib is a selective inhibitor of Lp-PLA(2).

AREAS COVERED IN THIS REVIEW

An overview of darapladib by reviewing the studies (1990 - 2009) that have provided the rationale for the development of darapladib; and a discussion of its potential merit as a new therapeutic drug to target high-risk atherosclerosis.

WHAT THE READER WILL GAIN

The reader should gain an understanding of the importance of inflammation during atherogenesis as well as of the biology of Lp-PLA(2) and its proatherogenic role. Additional insights will be gained into the role of selective inhibitors of Lp-PLA(2) as new therapeutic agents.

TAKE HOME MESSAGE

Darapladib is a selective inhibitor of Lp-PLA(2) and represents a new class of therapeutic agents that target inflammation to treat high-risk atherosclerosis.

Molecular Model of Plasma PAF Acetylhydrolase-Lipoprotein Association: Insights from the Structure

Plasma platelet-activating factor acetylhydrolase (PAF-AH), also called lipoprotein-associated phospholipase A₂ (Lp-PLA₂), is a group VIIA PLA₂ enzyme that catalyzes the hydrolysis of PAF and certain oxidized phospholipids. Although the role of PAF-AH as a pro- or anti-atherosclerotic enzyme is highly debated, several studies have shown it to be an independent marker of cardiovascular diseases. In humans the majority of plasma PAF-AH is bound to LDL and a smaller portion to HDL; the majority of the enzyme being associated with small dense LDL and VHDL-1 subclasses. Several studies suggest that the anti- or pro-atherosclerotic tendency of PAF-AH might be dependent on the type of lipoprotein it is associated with. Amino acid residues in PAF-AH necessary for binding to LDL and HDL have been identified. However our understanding of the interaction of PAF-AH with LDL and HDL is still incomplete. In this review we present an overview of what is already known about the interaction of PAF-AH with lipoprotein particles, and we pose questions that are yet to be answered. The recently solved crystal structure of PAF-AH, along with functional work done by others is used as a guide to develop a model of interaction of PAF-AH with lipoprotein particles.

Functional Consequences of Mutations and Polymorphisms in the Coding Region of the PAF Acetylhydrolase (PAF-AH) Gene

In the past several years a number of alterations in the PAF-AH/PLA₂G7/LpPLA₂ gene have been described. These include inactivating mutations, polymorphisms in the coding region, and other genetic changes located in promoter and intronic regions of the gene. The consequences associated with these genetic variations have been evaluated from different perspectives, including in vitro biochemical and molecular studies and clinical analyses in human subjects. This review highlights the current state of the field and suggests new approaches that can be used to evaluate functional consequences associated with mutations and polymorphisms in the PAF-AH gene.

Inter-individual variability of plasma PAF-acetylhydrolase activity in ARDS patients and PAFAH genotype

BACKGROUND

Platelet activating factor (PAF), a pro-inflammatory phospholipid, stimulates cytokine secretion from polymorphonuclear leukocytes expressing the transmembrane G-protein coupled PAF receptor. Elevated PAF levels are associated with acute respiratory distress syndrome (ARDS) and sepsis severity. The pro-inflammatory effects of PAF are terminated by PAF acetylhydrolase (PAF-AH).

OBJECTIVE

We sought to determine whether allelic variants in the human PAFAH gene (Arg92His, Ile198Thr, and Ala379Val) contribute to variability in PAF-AH activity in patient plasma obtained within 72 h of ARDS diagnosis.

RESULTS

Plasma PAF-AH activity (mean +/- SD) was higher in patients homozygous for the Arg92 allele compared to His92 allele carriers (2.21 +/- 0.77 vs. 1.64 +/- 0.68 U/min; P < 0.01; n = 31 and 21 respectively). Baseline plasma PAF-AH activity was higher among day 7 survivors vs. day 7 non-survivors (2.05 +/- 0.75 vs. 1.27 +/- 0.63, P = 0.05).

CONCLUSION

These data demonstrate an association between PAF-AH allelic variation, plasma activity, and outcome in ARDS.

Lipoprotein-associated phospholipase A2: a cardiovascular risk predictor and a potential therapeutic target

Lipoprotein-associated phospholipase A2 (Lp-PLA2), present in the circulation and in atherosclerotic plaque, is an inflammatory marker with potential use as a predictor of cardiovascular risk and as a therapeutic target. Although Lp-PLA2 is associated with both LDL and HDL, it is important to determine whether Lp-PLA2 has a predominantly pro- or anti-atherogenic effect. Increasing evidence suggests a proatherogenic role for Lp-PLA2. ©iEpidemiologic and clinical evidence suggests Lp-PLA2 is an independent predictor of risk and may be superior to other inflammatory markers owing to its specificity and minimal biovariation. Lp-PLA2 inhibitors currently being investigated in clinical trials are promising novel anti-inflammatory agents with a specificity for the vascular bed and a potential for decreasing plaque vulnerability.

Biology of platelet-activating factor acetylhydrolase (PAF-AH, lipoprotein associated phospholipase A2)

INTRODUCTION

This article is focused on platelet-activating factor acetylhydrolase (PAF-AH), a lipoprotein bound, calcium-independent phospholipase A(2) activity also referred to as lipoprotein-associated phospholipase A(2) or PLA(2)G7. 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.

DISCUSSION

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. This mechanism is likely responsible for the observed up-regulation of PAF-AH during atherosclerosis and suggests that increased expression of this enzyme is a physiological response to inflammatory stimuli. Administration of recombinant forms of PAF-AH attenuate inflammation in a variety of experimental models. Conversely, genetic deficiency of PAF-AH in defined human populations increases the severity of atherosclerosis and other syndromes. Recent advances pointing to an interplay among oxidized phospholipid substrates, Lp(a), and PAF-AH could hold the key to a number of unanswered questions.

Lipoprotein-associated phospholipase A2 and risk of venous thrombosis in older adults

Lipoprotein-associated phospholipase A2 (Lp-PLA2) is an enzyme involved in inflammation and platelet function. Inherited deficiency and elevated levels are associated with atherosclerosis. Given potential common etiologies of atherosclerosis and venous thrombosis (VT), we hypothesized that low and high Lp-PLA2 would be associated with VT risk. Lp-PLA(2) mass and activity were measured in baseline samples of Cardiovascular Health Study participants (5,888 men and women age > or =65), excluding 354 reporting pre-baseline VT. The study endpoint was VT unrelated to cancer after 11.6 years follow-up. Hazard ratios were estimated using Cox proportional hazard models, adjusting for age, race, sex, and body-mass index. With 129 cases of VT, there was no association of Lp-PLA2 activity with risk. Adjusted hazard ratios were 1.19 (CI 0.62, 2.29) and 0.87 (CI 0.43, 1.76) for the lowest and highest decile, respectively, compared to the 10-25th percentile. Corresponding hazard ratios for Lp-PLA2 mass were 1.63 (CI 0.79, 3.34) and 1.33 (CI 0.61, 2.87). Results were robust to several definitions of low or high Lp-PLA2. While the association of Lp-PLA(2) levels with arterial disease events implies a role for this enzyme in atherogenesis, our findings suggest that it is not prothrombotic.

Association of lipoprotein-associated phospholipase A2 with coronary calcification among American and Japanese men

BACKGROUND

We have previously reported that the prevalence of coronary artery calcification (CAC) was substantially lower among Japanese than American men despite a less favorable profile of many traditional risk factors in Japanese men. To determine whether lipoprotein-associated phospholipase A2 (Lp-PLA2) levels are related to the difference in the prevalence of CAC between the two populations.

METHODS

A total of 200 men aged 40-49 years were examined: 100 residents in Allegheny County, Pennsylvania, United States, and 100 residents in Kusatsu City, Shiga, Japan. Coronary calcium score (CCS) was evaluated by electron-beam tomography, Lp-PLA2 levels, nuclear magnetic resonance (NMR) lipoprotein subclasses, and other factors were assessed in 2001-2002.

RESULTS

Lp-PLA2 levels were higher among American than Japanese men (Mean ± standard deviation 301.7 ± 82.6 versus 275.9 ± 104.7 ng/mL, respectively, p=0.06). Among all Japanese men and those with low density lipoprotein (LDL) cholesterol >130 mg/dL, there was an inverse association of the prevalence of CCS>0 with the fertile groups of Lp-PLA2 levels (p=0.08 and p=0.03, respectively). American men did not have any association between CCS>0 with the fertile groups of Lp-PLA2 (p=0.62). Although Lp-PLA2 among both populations correlated positively with LDL and total cholesterol, American and Japanese men had different correlations with NMR lipoprotein subclasses. Reported high odds ratio for CCS>0 among American compared to Japanese men was not reduced after adjusting for Lp-PLA2 levels.

CONCLUSION

Lp-PLA2 may have different mechanisms of action among American and Japanese men. Lp-PLA2 levels can not explain the observed CAC differences between the two populations.

The role of lipoprotein-associated phospholipase A2 as a marker for atherosclerosis

Lipoprotein-associated phospholipase A2 (Lp-PLA2) is an enzyme that belongs to the superfamily of phospholipase A2 enzymes. Although initial studies showed that Lp-PLA2 might be protective against atherosclerosis, emerging data seem to suggest that Lp-PLA2 may be proatherogenic, which is an effect thought to be mediated by lysophosphatidylcholine and oxidized nonesterified fatty acids, two mediators generated by Lp-PLA2. This article reviews the potential mechanisms by which Lp-PLA2 may participate in the pathogenesis of atherosclerosis and its clinical manifestations, namely, coronary artery disease and stroke.

Clinical aspects of plasma platelet-activating factor-acetylhydrolase

Plasma platelet-activating factor (PAF)-acetylhydrolase (PAF-AH), which is characterized by tight association with plasma lipoproteins, degrades not only PAF but also phospholipids with oxidatively modified short fatty acyl chain esterified at the sn-2 position. Production and accumulation of these phospholipids are associated with the onset of inflammatory diseases and preventive role of this enzyme has been evidenced by many recent studies including prevalence of the genetic deficiency of the enzyme in the patients and therapeutic effects of treatment with recombinant protein or gene transfer. With respect to the atherosclerosis, however, it is not fully cleared whether this enzyme plays an anti-atherogenic role or pro-atherogenic role because plasma PAF-AH also might produce lysophosphatidylcholine (LysoPC) and oxidatively modified nonesterified fatty acids with potent pro-inflammatory and pro-atherogenic bioactivities. These dual roles of plasma PAF-AH might be regulated by the altered distribution of the enzyme between low density lipoprotein (LDL) and high density lipoprotein (HDL) particles because HDL-associated enzymes are considered to contribute to the protection of LDL from oxidative modification. This review focuses on the recent findings which address the role of this enzyme in the human diseases especially including asthma, septic shock and atherosclerosis.

Lipoprotein-associated phospholipase A2: Pathogenic mechanisms and clinical utility for predicting cardiovascular events

Lipoprotein-associated phospholipase A(2 )(Lp-PLA(2)), a member of the phospholipase superfamily, circulates primarily bound to low-density lipoprotein and has been associated with cardiovascular disease risk in epidemiologic studies. However, it has not been established whether Lp-PLA(2) is a risk marker or a risk factor. Identification of individuals with elevated Lp-PLA(2) may improve risk assessment, and Lp-PLA(2) may also provide an additional target of therapy. Statin therapy has been shown to reduce Lp-PLA(2), and selective inhibitors of Lp-PLA(2) are under development. Additional research is needed to further determine the role of Lp-PLA(2) in atherogenesis and atherothrombotic events.

A single nucleotide polymorphism in the plasma PAF acetylhydrolase gene and risk of atherosclerosis in Japanese patients with peripheral artery occlusive disease

BACKGROUND

Plasma PAF-acetylhydrolase (PAF-AH) gene polymorphisms (G994 --> T in exon 9) and the resulting deficiency of enzyme activity were identified in the Japanese population. The objective of this study was to assess the joint effect of the polymorphism and hypercholesterolemia on risk of atherosclerosis.

METHODS AND RESULTS

We performed a case-control study including 150 patients who underwent operation for peripheral arterial occlusive disease (PAOD) and 158 controls matched for age and sex. Genomic DNA was analyzed for the mutant allele by a specific polymerase-chain reaction. Plasma PAF-AH activity was measured in both groups. The patients with multiple atherosclerotic diseases showed higher levels of PAF-AH activities than the patients with only peripheral artery occlusive disease among normal genotypes. PAOD patients were assessed either with or without polymorphism or hypercholesterolemia in regard to accompanying coronary artery disease or stroke. The prevalence of the polymorphism was significantly more frequent in the patients with PAOD. The plasma PAF-AH activity was correlated with total cholesterol and LDL level, and inversely related with HDL in normal genotype (GG) PAOD patients. However, neither the correlation nor the inverse relation was found in patients with the polymorphism. Patients with both hypercholesterolemia and the polymorphisms revealed a relative risk for other atherosclerotic disease of 11.5 (6.0-40.3) compared with normal genotype and normal lipid level.

CONCLUSION

The plasma PAF-AH gene polymorphism and hypercholesterolemia may interact and increase the risk of atherosclerosis.

Platelet-activating factor-acetylhydrolase A379V (exon 11) gene polymorphism is an independent and functional risk factor for premature myocardial infarction

BACKGROUND

Oxidation of low density lipoproteins is an initial step of atherogenesis that generates pro-inflammatory phospholipids, including platelet-activating factor (PAF). PAF is degraded by PAF-acetylhydrolase (PAF-AH), which has been postulated to be a risk factor for myocardial infarction (MI). The role of PAF-AH for the onset of premature MI is unclear.

METHODS

Polymorphisms located in putatively functional regions were investigated in a cohort of patients having premature MI onset prior to 46 years of age (n = 200) and a sex-age-matched control group (n = 200). The activity of PAF-AH and coronary angiograms were evaluated for the severity of coronary atherosclerosis.

RESULTS

The V allele of A379V (exon 11) polymorphism on PAF-AH gene was more frequent in patients with premature MI (P = 0.001). This V allele polymorphism was also associated with a lower activity of plasma PAF-AH and a more complex coronary atherosclerosis (p Trends <0.05). Multiple logistic regression analysis showed that this polymorphism was an independent risk factor (Odds Ratio [OR] 1.66, 95% CI 1.14.1 to 5.80, P = 0.008) as well as smoking (OR 3.72, 95% CI 1.77 to 9.28, P = 0.001), diabetes mellitus (OR 2.25, 95% CI 1.40 to 5.32, P = 0.007) and hypertension (OR 1.88, 95% CI 1.25 to 5.36, P = 0.003) for the onset of premature MI.

CONCLUSION

We conclude that a functional and significant association between the A379V polymorphism on exon 11 of PAF-AH gene and premature MI exists in this Taiwanese population. This polymorphism is significantly associated with the PAF-AH activity and the severity of coronary atherosclerosis.

Lipoprotein-associated phospholipase A2: a novel marker of cardiovascular risk and potential therapeutic target

Although the clinical benefit of statins is well established, these agents reduce the risk of cardiovascular events by only 20 - 40%, and the residual risk for high-risk patients is considerable. The recognition of atherosclerosis as an inflammatory disease has opened the door to numerous complementary therapeutic approaches to further reduce risk and the overall burden of cardiovascular disease. Lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) is a novel inflammatory marker of cardiovascular risk that is being evaluated as a potential therapeutic target. The biological function of this enzyme in atherosclerosis has been controversial but recent evidence supports its pro-atherogenic role. The enzyme is predominantly bound to low-density lipoprotein cholesterol particles in humans, and its activity produces bioactive lipid mediators that promote inflammatory processes present at every stage of atherogenesis, from atheroma initiation to plaque destabilisation and rupture. Initial clinical studies suggest that the inhibitors of Lp-PLA(2) can block enzyme activity in plasma and within atherosclerotic plaques. However, more studies are needed to determine the potential clinical benefits of inhibiting Lp-PLA(2).

Regulating inflammation through the anti-inflammatory enzyme platelet-activating factor-acetylhydrolase

Platelet-activating factor (PAF) is one of the most potent lipid mediators involved in inflammatory events. The acetyl group at the sn-2 position of its glycerol backbone is essential for its biological activity. Deacetylation induces the formation of the inactive metabolite lyso-PAF. This deacetylation reaction is catalyzed by PAF-acetylhydrolase (PAF-AH), a calcium independent phospholipase A2 that also degrades a family of PAF-like oxidized phospholipids with short sn-2 residues. Biochemical and enzymological evaluations revealed that at least three types of PAF-AH exist in mammals, namely the intracellular types I and II and a plasma type. Many observations indicate that plasma PAF AH terminates signals by PAF and oxidized PAF-like lipids and thereby regulates inflammatory responses. In this review, we will focus on the potential of PAF-AH as a modulator of diseases of dysregulated inflammation.

Role of lipoprotein-associated phospholipase A2 in atherosclerosis: biology, epidemiology, and possible therapeutic target

The development of atherosclerotic vascular disease is invariably linked to the formation of bioactive lipid mediators and accompanying vascular inflammation. Lipoprotein-associated phospholipase A2 (Lp-PLA2) is an enzyme that is produced by inflammatory cells, co-travels with circulating low-density lipoprotein (LDL), and hydrolyzes oxidized phospholipids in LDL. Its biological role has been controversial with initial reports purporting atheroprotective effects of Lp-PLA2 thought to be a consequence of degrading platelet-activating factor and removing polar phospholipids in modified LDL. Recent studies, however, focused on pro-inflammatory role of Lp-PLA2 mediated by products of the Lp-PLA2 reaction (lysophosphatidylcholine and oxidized nonesterified fatty acids). These bioactive lipid mediators, which are generated in lesion-prone vasculature and to a lesser extent in the circulation (eg, in electronegative LDL), are known to elicit several inflammatory responses. The proinflammatory action of Lp-PLA2 is also supported by a number of epidemiology studies suggesting that the circulating level of the enzyme is an independent predictor of cardiovascular events, despite some attenuation of the effect by inclusion of LDL, the primary carrier of Lp-PLA2, in the analysis. These observations provide a rationale to explore whether inhibiting Lp-PLA2 activity and consequent interference with the formation of bioactive lipid mediators will abrogate inflammation associated with atherosclerosis, produce favorable changes in intermediate cardiovascular end points (eg, biomarkers, imaging, and endothelial function), and ultimately reduce cardiovascular events in high-risk patients.

Pioglitazone induces plasma platelet activating factor-acetylhydrolase and inhibits platelet activating factor-mediated cytoskeletal reorganization in macrophage

Platelet activating factor (PAF) is a key molecule for inflammation. To examine a role of peroxisome proliferator-activated receptor gamma (PPARgamma) in inflammatory reactions of atherosclerosis, we investigated the effects of 15-deoxy-(Delta12,14)-Prostaglandin J2 (15d-PGJ2) and pioglitazone, PPARgamma ligands, on plasma PAF-acetylhydrolase (PAF-AH) expression in THP-1 macrophages. PAF-AH mRNA and protein were up-regulated by the PPARgamma ligands. Prostaglandin F2alpha (PGF2alpha), a PARgamma inhibitor, abrogated the up-regulation of PAF-AH mRNA by pioglitazone, suggesting that PPARgamma activation is involved in the induction of PAF-AH by pioglitazone. As PAF promotes the cell motility with cytoskeletal reorganization, we investigated the effect of pioglitazone on PAF-mediated morphological changes in THP-1 macrophages. In the absence of pioglitazone, PAF promoted the elongation of actin cytoskeleton, which was inhibited by pretreatment with pioglitazone. In contrast, pioglitazone was not able to inhibit the morphological changes induced by C-PAF, a non-hydrolyzable PAF agonist. Thus, it is suggested that PAF-induced morphological changes could be inhibited by pioglitazone through PAF-AH, which rapidly hydrolyzed PAF. These data propose that PPARgamma/PAF-AH pathway is a clinical target for the prevention against atherosclerosis.

The significance of human platelet-activating factor-acetylhydrolase in patients with chronic stable angina

BACKGROUND: Inflammatory reactions within coronary atherosclerotic plaques are increasingly thought to be crucial determinants of the clinical course in patients with coronary artery disease (CAD). Platelet-activating factor-acetylhydrolase (PAF-AH) is considered to reflect the ongoing inflammatory process in patients with CAD. Our objective was to determine the activity of PAF-AH in patients with stable angina and its correlations to lipoprotein levels and the inflammatory status of the patient. METHODS: Forty-five patients with documented CAD and stable angina and 20 controls were investigated for PAF-AH activity, lipoprotein levels, and peripheral neutrophil (PMN) activity. RESULTS: Patients were divided into two groups according to the values of PAF-AH activity (group 1: </=250 IU/l and group 2: >250 IU/l). A correlation was observed between PAF-AH activity and LDL-C and HDL-C in controls and in all patients. The percentage of granulocytes generating intracellular O(2)(-) in unstimulated PMN was higher in group 2 patients than in group 1 patients and controls. The phagocytic activity of PMNs had an inverse correlation with PAF-AH in group 2. High intracellular O(2)(-) generation was coupled with low extracellular release of the anion and phagocytosis impairment in group 2. During the follow-up period, some of the patients in group 2 displayed a worsening of the clinical state and/or resting ECG changes. CONCLUSIONS: PAF-AH activity in patients with stable angina is correlated with hyperlipemia and a high PMN activation state, and it may be considered a potential predictor of vascular risk.

Platelet-activating factor, a pleiotrophic mediator of physiological and pathological processes

Platelet-activating factor (PAF) is a potent proinflammatory phospholipid with diverse pathological and physiological effects. This bioactive phospholipid mediates processes as diverse as wound healing, physiological inflammation, apoptosis, angiogenesis, reproduction and long-term potentiation. Recent progress has demonstrated the participation of MAP kinase signaling pathways as modulators of the two critical enzymes, phospholipase A2 and acetyltransferase, involved in the remodeling pathway of PAF biosynthesis. The unregulated production of structural analogs of PAF by non-specific oxidative reactions has expanded this superfamily of signaling molecules to include "PAF-like" lipids whose mode of action is identical to that of authentic PAF. The action of members of this family is mediated by the PAF receptor, a G protein-coupled membrane-spanning molecule that can engage multiple signaling pathways in various cell types. Inappropriate activation of this signaling pathway is associated with many diseases in which inflammation is thought to be one of the underlying features. Inactivation of all members of the PAF superfamily occurs by a unique class of enzymes, the PAF acetylhydrolases, that have been characterized at the molecular level and that terminate signals initiated by both regulated and unregulated PAF production.

Age-related increase of plasma platelet-activating factor concentrations in Chinese

BACKGROUND

Platelet-activating factor (PAF) is a potent bioactive phospholipid, which may be one of the determinants of atherogenesis. The purpose of this study was to investigate the relationship between the concentrations of plasma platelet-activating factor and age in a common Chinese population.

METHODS

Two-hundred seventy-nine Han nation subjects (male: n=162; female: n=117) who had visited two hospitals for overall health survey, as an annual medical check-up or for other reasons by clinical examinations were recruited and divided into six age groups (21-30, 31-40, 41-50, 51-60, 61-70, 71-80 years). PAF was extracted from their plasma and purified by thin-layer chromatography (TLC). The PAF concentrations were detected by radioimmunoassay.

RESULTS

The PAF concentrations (pg/ml) in plasma showed significantly age-related increase (r=0.3348, P<0.01, n=279). In the 21-30-year group, the PAF concentration was 338+/-96 pg/ml. Except for the 31-40-year group, the PAF concentrations in other four groups were all higher than that of the 21-30-year group (P<0.05, P<0.01, P<0.001 and P<0.001, respectively).

CONCLUSIONS

Considering PAF is one of the key factors relevant to progression of atherogenesis, and the high concentrations of plasma PAF may therefore serve as a marker for the risk of atherosclerosis. Adjustment of the concentrations of plasma PAF correlated with aging may be helpful to reducing the prevalence rate of multi-senile arteriosclerosis occlusive diseases.

Functional impairment of two novel mutations detected in lipoprotein-associated phospholipase A2 (Lp-PLA2) deficiency patients

Plasma lipoprotein-associated phospholipase A2 (Lp-PLA2), also known as platelet-activating factor (PAF) acetylhydrolase (PAF-AH), is a member of the serine-dependent class of A2 phospholipases that hydrolyze sn2-ester bonds of fragmented or oxidized phospholipids at sites where atherosclerotic plaques are forming. Most circulating Lp-PLA2 is bound to low-density lipoprotein (LDL) particles in plasma and the rest to high-density lipoprotein (HDL). Deficiency of Lp-PLA2 is a predisposing factor for cardiovascular diseases in the Japanese population. We describe here two novel mutations of the gene encoding Lp-PLA2, InsA191 and I317N in Japanese subjects. The first patient, with partial Lp-PLA2 deficiency, was heterozygous for the InsA191 mutation; macrophages from this patient secreted only half the normal amount of Lp-PLA2 in vitro. The other patient, who showed complete Lp-PLA2 deficiency, was a compound heterozygote for the novel I317N mutation and a common V279F mutation; macrophages from that patient failed to secrete any Lp-PLA2. Measurement of Lp-PLA2 mass, activity and Western blotting verified impaired production and secretion of the enzyme after transfection of mutant construct into COS-7 cells. These results indicated that both novel mutants, InsA191 and I317N, impair function of the Lp-PLA2 gene.

Association of gene polymorphisms with coronary artery disease in individuals with or without nonfamilial hypercholesterolemia

A substantial proportion of individuals with coronary artery disease (CAD) has concomitant hypercholesterolemia. A large-scale association study was performed to identify separately genes that confer susceptibility to CAD in the absence or presence of nonfamilial hypercholesterolemia. The study population comprised 5248 unrelated Japanese individuals, including 3085 subjects with CAD (2350 men, 735 women) and 2163 controls (1329 men, 834 women). Among all study subjects, 2541 individuals (1688 men, 853 women) had nonfamilial hypercholesterolemia, and 2707 individuals (1991 men, 716 women) did not have this condition. The genotypes for 33 polymorphisms of 27 candidate genes were determined with a fluorescence- or colorimetry-based allele-specific DNA primer-probe assay system. Multivariate logistic regression analysis with adjustment for age, body mass index, and the prevalence of smoking, hypertension, diabetes mellitus, and hyperuricemia revealed that three polymorphisms [994G --> T (Val279Phe) in the platelet-activating factor acetylhydrolase gene, 242C --> T (His72Tyr) in the NADH/NADPH oxidase p22 phox gene, and 1100C --> T in the apolipoprotein C-III gene] were significantly associated with CAD in men with hypercholesterolemia. Genotyping of these three polymorphisms may prove informative for prediction of the genetic risk for CAD in men with nonfamilial hypercholesterolemia.

Lipoprotein-associated phospholipase A2 (platelet-activating factor acetylhydrolase) and cardiovascular disease

PURPOSE OF REVIEW

Plasma lipoproteins carry a number of highly active enzymes in the circulation. One of these is lipoprotein-associated phospholipase A(2) (Lp-PLA(2)), also known as platelet-activating factor acetylhydrolase. This review addresses the molecular properties of Lp-PLA(2), the controversy surrounding its role in atherosclerosis and the regulation of its plasma levels in humans.

RECENT FINDINGS

Recent reports indicate that the enzyme Lp-PLA(2) found in both LDL and HDL may be independently regulated in these lipoprotein subclasses and have distinct roles in atherogenesis. Seminal findings establishing the response-to-retention hypothesis of atherosclerosis support further the potentially damaging role that in-situ release of LDL-associated oxidative products by Lp-PLA(2) may have in the formation of arterial wall lesions. In the mouse, where Lp-PLA(2) circulates mainly bound to HDL, overexpression leads to reduced atherosclerosis, raising the possibility that the enzyme in HDL may have a protective role. Further evidence for a potential protective role is seen in studies of partial or complete deficiency of the enzyme. In the more general setting of population studies, however, it is clear that Lp-PLA(2) is a positive risk factor for coronary disease and measurements of its mass may contribute to the prediction of coronary heart disease risk, especially in individuals with low LDL cholesterol levels.

SUMMARY

Lp-PLA(2) is an enzyme with potentially multiple risks in atherosclerosis. In humans the weight of evidence suggests that it is a positive risk factor for coronary heart disease - an observation commensurate with its position in the direct pathological sequence leading from formation of oxidized LDL in the artery wall to cellular dysfunction and formation of lesions.

Association between the Ala379Val variant of the lipoprotein associated phospholipase A2 and risk of myocardial infarction in the north and south of Europe

Lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) has been identified as a coronary heart disease (CHD) risk predictor. Both its anti-inflammatory role by hydrolysing platelet activating factor, and pro-inflammatory generation of atherogenic mediators may influence CHD risk. We investigated the association of the activity-reducing A379V variant with risk of myocardial infarction (MI) in a large European case-control study, which compared 527 post-MI men with 566 age-matched controls from north and south Europe. Overall, the frequency of the V379 allele was 0.24 (95%CI 0.21-0.26), with no evidence for differences between centres. Homozygosity for the V379 allele was associated with lower risk of MI, (Odds Ratio (OR) 0.56, 95%CI 0.32-0.98), maintained after adjustment for lifestyle factors and levels of inflammatory risk factors (C-reactive protein, fibrinogen, IL-6) (OR 0.46, 0.22-0.93). There was no evidence of heterogeneity of effect between the centres in the north and south of Europe (P-value for interaction=0.80). Since homozygosity for V379 occurs in only 5-6% of subjects, this genotype is not a major determinant of population genetic risk of CHD, but the association of this genotype with low levels of Lp-PLA(2), strongly support the pro-inflammatory causative, and not consequential, role of Lp-PLA(2) in CHD.

Plasma platelet activating factor-acetylhydrolase (PAF-AH)

The platelet-activating factor-acetylhydrolase (PAF-AH) is an enzyme which catalyzes the hydrolysis of acetyl ester at the sn-2 position of PAF. The family of PAF-AHs consists of two intracellular isoforms (Ib and II), and one secreted isoform (plasma). These PAF-AHs show different biochemical characteristics and molecular structures. Plasma PAF-AH and intracellular isoform, II degrade not only PAF but also oxidatively fragmented phospholipids with potent biological activities. Among these PAF-AHs, plasma PAF-AH has been the target of many clinical studies in inflammatory diseases, such as asthma, sepsis, and vascular diseases, because the plasma PAF-AH activity in the patients with these diseases is altered when compared with normal individuals. Finding a genetic deficiency in the plasma PAF-AH opened the gate in elucidating the protecting role of this enzyme in inflammatory diseases. The most common loss-of-function mutation, V279F, is found in more than 30% of Japanese subjects (4% homozygous, 27% heterozygous). This single nucleotide polymorphism in plasma PAF-AH and the resulting enzymatic deficiency is thought to be a genetic risk factor in various inflammatory diseases in Japanese subjects. Administration of recombinant plasma PAF-AH or transfer of the plasma PAF-AH gene improves pathology in animal models. Therefore, substitution of plasma PAF-AH would be an effective in the treatment of the patients with the inflammatory diseases and a novel clinical approach. In addition, the detection of polymorphisms in the plasma PAF-AH gene and abnormalities in enzyme activity would be beneficial in the diagnosis of the inflammatory diseases.

Association of plasma PAF acetylhydrolase gene polymorphism with IMT of carotid arteries in Japanese type 2 diabetic patients

The aim of this study was to investigate association of a missense mutation in plasma PAF acetylhydrolase (G994T) with intima media thickness (IMT) of the carotid arteries. One hundred and forty Japanese type 2 diabetic patients aged from 40 to 79 years without severe nephropathy were enrolled in this study. The genotype of the patients was determined by allele specific PCR. IMT of the carotid arteries of the subjects was recorded by B-mode ultrasound imaging. The patients were divided into two groups by genotyping, one carrying two wild alleles (wild group), and another carrying one or two mutant alleles (mutant group). Each group was further divided into two subgroups according to age; one subgroup consisted of 40s or 50s, and another consisted of 60s or 70s. The prevalence of the G994T mutation in the subjects was 28.6% (24.3% heterozygote, and 4.3% homozygote). IMT of the elderly patients of the mutant group was significantly greater (0.98 +/- 0.22 mm, n = 26) than of the elderly patients of the wild group (0.87 +/- 0.20 mm, n = 50, P = 0.0292). There was no significant difference in clinical characteristics between the two subgroups. The results of this study indicate that the missense mutation in plasma PAF acetylhydrolase is associated with development of atherosclerosis in the elderly.

Significance of platelet-activating factor acetylhydrolase in patients with non-insulin-dependent (type 2) diabetes mellitus

BACKGROUND

Non-insulin dependent diabetes mellitus (NIDDM) represents an independent risk factor for cardiovascular diseases (CVD), being characterized by a continuous low-grade inflammation and endothelial activation state. Plasma platelet - activating factor - acetylhydrolases (PAF-AHs) are a subgroup of Ca(2+)-independent phospholipase A(2) family (also known as lipoprotein-associated phospholipases A(2)) that hydrolyze and inactivate the lipid mediator platelet-activating factor (PAF) and/or oxidized phospholipids. This enzyme is considered to play an important role in inflammatory diseases and atherosclerosis. The present study aims to investigate the relations between the levels of PAF-AH activity and LDL-cholesterol / HDL-cholesterol (LDL-ch / HDL-ch) ratio in NIDDM patients as compared to controls.

METHODS

serum PAF-AH activity was measured in 50 patients with dyslipidemia, in 50 NIDDM patients and in 50 controls (normal lipid and glucose levels). Total cholesterol, LDL-ch, HDL-ch, triglyceride and blood glucose were determined in all subjects.

RESULTS

All NIDDM patients display hiperlipidemia, with increased LDL-ch and triglyceride levels. There is a significant correlation between LDL-ch levels (especially LDL-ch / HDL-ch ratio) and PAF-AH activity in dyslipidemic and NIDDM patients.

CONCLUSION

Diabetic and dyslipidemic patients have an increased plasma PAF-AH activity correlated with their LDL-ch levels and mainly with LDL-ch / HDL-ch ratio. Plasma PAF-AH high levels appear to be important as a risk marker for endothelial dysfunction in patients with NIDDM.

Reduction in the extent of atherosclerosis in apolipoprotein E-deficient mice induced by electroporation-mediated transfer of the human plasma platelet-activating factor acetylhydrolase gene into skeletal muscle

The effect of increasing the activity of plasma platelet-activating factor (PAF) acetylhydrolase (AH) (PAF-AH) on the progression of atherosclerosis in apolipoprotein E-deficient (apoE(-/-)) mice was examined by gene delivery to skeletal muscle. The expression vector pcDNA3.1 containing either human PAF-AH cDNA (pcDNA/PAF-AH) or green fluorescent protein cDNA (pcDNA/GFP) was introduced into the skeletal muscle of both hind legs of 6-week-old apoE(-/-) mice by electroporation. The activity of PAH-AH in plasma was significantly increased 4-16 weeks after electroporation of apoE(-/-) mice with 120 microg of pcDNA/PAF-AH; the maximal (2.5-fold) increase was apparent after 8 weeks. The mean thickness of the aortic wall, determined by 160 measurements in each mouse, was significantly reduced in apoE(-/-) mice 8-16 weeks after exposure to pcDNA/PAF-AH compared with that in corresponding control animals that received pcDNA/GFP. These results suggest that the electrotransfer of the plasma PAF-AH gene to skeletal muscle reduces the extent of atherosclerosis in apoE(-/-) mice.

Single nucleotide polymorphism (G994-->T) in the plasma platelet-activating factor-acetylhydrolase gene is associated with graft patency of femoropopliteal bypass

BACKGROUND

Plasma platelet-activating factor-acetylhydrolase (PAF-AH) is known to catalyze platelet-activating factor (PAF). The single nucleotide polymorphism (SNP) of plasma PAF-AH gene (G994 -->T in exon 9) is associated with a decreased level of plasma PAF-AH activity. This study analyzed the risk of the SNP on graft occlusion of femoropopliteal bypass in patients with atherosclerotic occlusive disease.

METHODS

We retrospectively assessed the patency of 50 above-knee femoropopliteal bypass grafting in 50 patients. Genomic DNA was analyzed for the mutant allele. Plasma PAF-AH activity was measured by radioimmunoassay.

RESULTS

The 10-year cumulative primary patency of the bypass was 78.5% in GG (normal genotype) and 50.0% in GT (heterozygous) or TT (homozygous deficient) (P <.05, Kaplan-Meier method). The relative risk of graft failure in GT or TT genotypes was 1.68 (P =.08, Cox proportional hazards model). PAF-AH activity (nmol/min/50 microL) was 1.92 +/- 0.82 in patients with patent grafts and 1.42 +/- 0.47 in those with occluded grafts (mean +/- standard deviation; P <.05, unpaired t test).

CONCLUSIONS

The SNP of plasma PAF-AH was associated with a decreased primary graft patency of above-knee femoropopliteal bypass. The risk of graft failure may increase when patients have the SNP. To confirm the independent risk of graft failure by the SNP, further study is necessary and prospective study should be performed.