Clinical aspects of plasma platelet-activating factor-acetylhydrolase

Proteomic aptamer analysis reveals serum markers that characterize preclinical systemic sclerosis (SSc) patients at risk for progression toward definite SSc

BACKGROUND

The study of molecular mechanisms characterizing disease progression may be relevant to get insights into systemic sclerosis (SSc) pathogenesis and to intercept patients at very early stage. We aimed at investigating the proteomic profile of preclinical systemic sclerosis (PreSSc) via a discovery/validation two-step approach.

METHODS

SOMAcan aptamer-based analysis was performed on a serum sample of 13 PreSSc (discovery cohort) according to 2001 LeRoy and Medsger criteria (characterized solely by Raynaud phenomenon plus a positive nailfold capillaroscopy and SSc-specific antibodies without any other sign of definite disease) and 8 healthy controls (HCs) age, gender, and ethnicity matched. Prospective data were available up to 4±0.6 years to determine the progression to definite SSc according to the EULAR/ACR 2013 classification criteria. In proteins with relative fluorescence units (RFU) > |1.5|-fold vs HCs values, univariate analysis was conducted via bootstrap aggregating models to determine the predicting accuracy (progression vs non-progression) of categorized baseline protein values. Gene Ontologies (GO terms) and Reactome terms of significant proteins at the adjusted 0.05 threshold were explored. Significant proteins from the discovery cohort were finally validated via ELISAs in an independent validation cohort of 50 PreSSc with clinical prospective data up to 5 years. Time-to-event analysis for interval-censored data was used to evaluate disease progression.

RESULTS

In the discovery cohort, 286 out of 1306 proteins analyzed via SomaScan, were differentially expressed versus HCs. Ten proteins were significantly associated with disease progression; analysis through GO and Reactome showed differentially enriched pathways involving angiogenesis, endothelial cell chemotaxis, and endothelial cell chemotaxis to fibroblast growth factor (FGF). In the validation cohort, endostatin (HR=10.23, CI95=2.2-47.59, p=0.003) was strongly associated with disease progression, as well as bFGF (HR=0.84, CI95=0.709-0.996, p=0.045) and PAF-AHβ (HR=0.372, CI95=0.171-0.809, p=0.013) CONCLUSIONS: A distinct protein profile characterized PreSSc from HCs and proteins associated with hypoxia, vasculopathy, and fibrosis regulation are linked with the progression from preclinical to definite SSc. These proteins, in particular endostatin, can be regarded both as markers of severity and molecules with pathogenetic significance as well as therapeutic targets.

PLA2G7/PAF-AH as Potential Negative Regulator of the Wnt Signaling Pathway Mediates Protective Effects in BRCA1 Mutant Breast Cancer

Past studies have confirmed that aberrant activation of the Wnt/β-catenin signaling is associated with tumorigenesis and metastasis in breast cancer, while the role of platelet-activating factor acetylhydrolase (PLA2G7/PAF-AH) in this signaling pathway remains unclear. In this study, we analyze the functional impact of PAF-AH on BRCA1 mutant breast cancer and explore its relationship to the Wnt signaling pathway. By performing immunohistochemistry, PAF-AH expression and β-catenin expression were examined in both BRCA1 WT and BRCA1 mutant breast cancer specimens. The BRCA1 mutant breast cancer cell line HCC1937 was used for in vitro experiments to assess the impact of PAF-AH on cellular functions. The intracellular distribution of β-catenin depending on PLA2G7/PAF-AH expression was investigated by immunocytochemistry. Significantly higher nuclear expression levels of PAF-AH were found in BRCA1 mutant tissue specimens than in BRCA1 WT samples. Cell viability, proliferation, and the motility rate of HCC1937 were significantly enhanced after PLA2G7 silencing, which indicated a protective role of PAF-AH in breast cancer. Nuclear PAF-AH expressed correlatedly with membranous β-catenin. PLA2G7 silencing provoked the β-catenin translocation from the membrane to the nucleus and activated Wnt signaling downstream genes. Our data showed a protective effect of high PAF-AH expression in BRCA1 mutant breast cancer. PAF-AH may achieve its protective effect by negatively regulating the Wnt pathway. In conclusion, our research sheds new light on the regulatory pathways in BRCA1 mutant breast cancer.

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.

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.

HDL and Oxidation

In this chapter, we will focus on HDLs' activity of inhibiting LDL oxidation and neutralizing some other oxidants. ApoA-I was known as the main antioxidant component in HDLs. The regulation of antioxidant capacity of HDL is mainly exhibited in regulation of apoA-I and alterations at the level of the HDL lipidome and the modifications of the proteome, especially MPO and PON1. HDL oxidation will influence the processes of inflammation and cholesterol transport, which are important processes in atherosclerosis, metabolic diseases, and many other diseases. In a word, HDL oxidation might be an effective antioxidant target in treatment of many diseases.

Deficiency of Type I Platelet-Activating Factor-Acetylhydrolase Catalytic Subunits Causes an Increase in Body Weight

Type I platelet-activating factor-acetylhydrolase (PAF-AH) forms a complex consisting of two catalytic subunits (α1 and/or α2) with a regulatory subunit (β). Although this protein was discovered as an enzyme that degrades an acetyl ester linked at the sn-2 position of platelet-activating factor (PAF), its physiological function remains unknown. In this study, to examine whether knockout mice lacking the catalytic subunits of this enzyme showed a different phenotype from that of wild-type mice, we measured and compared the body weights of knockout mice and control mice. The body weights of knockout mice were significantly increased compared to those of the control mice during 6 to 20 weeks from birth. Food intake was also significantly increased in knockout mice compared with control mice during these periods. Since a decrease in testis weight was reported in the knockout mice, we expected a decrease in testosterone levels. We measured and compared the amounts of testosterone in the serum and testis of knockout and control mice using liquid chromatography-tandem mass spectrometry, and found that testosterone levels in both the serum and testis were significantly decreased in the knockout mice compared with the control mice. These results suggest that a deficiency of type I PAF-AH catalytic subunits causes an increase in body weight, in part, due to reduced testosterone levels in male mice.

Evaluation of maternal plasma platelet activating factor acetylhydrolase activity and mRNA expression in pre-eclampsia: a case control study

Preeclampsia (PE) remains a leading cause of maternal morbidity and mortality all over the world. However, its aetiology and pathophysiology remain elusive. Platelet activating factor (PAF) is produced in response to oxidative stress and is a potent hypotensive agent. PAF acetylhydrolase (PAF-AH) inactivates PAF and is seen to decrease in normotensive women. The role of PAF-AH in preeclampsia has been in investigational literature, so far. The few studies done have shown a positive association of elevated levels of PAF-AH with preeclampsia. However, this marker has not been studied in the Indian population to-date and such studies are needed to elucidate the pathogenesis of this condition. Our study aimed to determine the PAF-AH activity by spectrophotometric assay in maternal plasma of 73 PE patients versus 73 normotensive controls and plasma PAF-AH mRNA expression to know the aberration of PAF-AH activity at the genetic level. Relative mRNA expression was calculated by Δ DCT method and a fold change was calculated by 2^-ΔDCT. We found that the mean plasma PAF-AH activity levels among cases was significantly higher than the normotensive controls. However, the mRNA expression of the PAF-AH gene was similar between the cases and controls, as well as between severe and non-severe preeclampsia (true fold change =1). To conclude, PAF-AH appears to be increased in women with preeclampsia and hence may contribute to pathophysiology and severity. However, a larger sample size will be required to reiterate this association. Recently, PAF-AH inhibitors such as Darapladib has been tested as a therapeutic option in atherosclerosis. After studying the role of PAF-AH in the pathogenesis of PE, PAF-AH inhibitors may be used as a therapeutic tool in the future in PE.IMPACT STATEMENTWhat is already known on this subject? Platelet activating factor (PAF) is produced in response to oxidative stress and is a potent hypotensive agent. PAF acetylhydrolase (PAF-AH) hydrolyses and inactivates PAF and is seen to decrease in normotensive women. The role of platelet activating factor-acetylhydrolase (PAF-AH) in preeclampsia has been investigational so far. Few studies done have shown a positive association of elevated levels of PAF-AH in preeclamptic women.What do the results of this study add? Our study aimed to determine the activity of PAF-AH in maternal plasma of PE patients versus normal pregnancy and plasma PAF-AH mRNA expression to know the aberration of PAF-AH activity at the level of the gene. We found that plasma PAF-AH activity among preeclamptics was significantly higher than in the controls with a possible role in early-onset preeclampsia (<32 weeks), in the Indian population. This marker has never been studied in this population earlier. The results of our study re-emphasised its role in the pathogenesis of preeclampsia.What are the implications of these findings for clinical practice and/or further research? Such studies are important to not only give us a greater understanding of the various pathways involved in this multifactorial dreaded condition, but can also offer us a marker for early identification of women at risk. Recently, PAF-AH inhibitors like Darapladib has been tested as a therapeutic option in atherosclerosis. After studying the role of PAF-AH in the pathogenesis of PE, PAF-AH inhibitors may be used as a therapeutic tool in the future in PE.

New perspectives in bronchial asthma: pathological, immunological alterations, biological targets, and pharmacotherapy

Asthma is the most common, long-lasting inflammatory airway disease that affects more than 10% of the world population. It is characterized by bronchial narrowing, airway hyperresponsiveness, vasodilatation, airway edema, and stimulation of sensory nerve endings that lead to recurring events of breathlessness, wheezing, chest tightness, and coughing. It is the main reason for global morbidity and occurs as a result of the weakening of the immune system in response to exposure to allergens or environmental exposure. In asthma condition, it results in the activation of numerous inflammatory cells like the mast and dendritic cells along with the accumulation of activated eosinophils and lymphocytes at the inflammation site. The structural cells such as airway epithelial cells and smooth muscle cells release inflammatory mediators that promote the bronchial inflammation. Long-lasting bronchial inflammation can cause pathological alterations, viz. the improved thickness of the bronchial epithelium and friability of airway epithelial cells, epithelium fibrosis, hyperplasia, and hypertrophy of airway smooth muscle, angiogenesis, and mucus gland hyperplasia. The stimulation of bronchial epithelial cell would result in the release of inflammatory cytokines and chemokines that attract inflammatory cells into bronchial airways and plays an important role in asthma. Asthma patients who do not respond to marketed antiasthmatic drugs needed novel biological medications to regulate the asthmatic situation. The present review enumerates various types of asthma, etiological factors, and in vivo animal models for the induction of asthma. The underlying pathological, immunological mechanism of action, the role of inflammatory mediators, the effect of inflammation on the bronchial airways, newer treatment approaches, and novel biological targets of asthma have been discussed in this review.

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.

Energy Intake and Plasma Adiponectin as Potential Determinants of Lipoprotein-Associated Phospholipase A2 Activity: A Cross-Sectional Study

Lipoprotein-associated phospholipase A₂ (Lp-PLA₂ ) is associated with increased risk of cardiovascular diseases (CVD) and type 2 diabetes mellitus. Lp-PLA₂ activity is positively associated with male sex, Caucasian race, the presence of metabolic syndrome (MetS) and low-density lipoprotein (LDL)-cholesterol, but it is negatively associated with high-density lipoprotein (HDL)-cholesterol. Associations with other cardiometabolic risk factors, inflammation markers, and lifestyle factors are few or inconsistent. We investigated potential determinants of Lp-PLA₂ activity among both nonmodifiable and modifiable CVD risk factors in a middle-aged Greek cohort without overt CVD. Two hundred eighty four subjects (159 men, 53 ± 9 years and 125 women 52 ± 9 years) participated in a cross-sectional study carried out during 2011-2012 in Athens, Attica. Cardiometabolic risk factors, inflammation markers, lifestyle factors, and Lp-PLA₂ activity were evaluated with established methods. The American Heart Association/National Heart, Lung, and Blood Institute (AHA/NHLBI) criteria were used to define MetS. Lp-PLA₂ activity was not associated with MetS, but was associated with MetS components, markers of liver function, and macronutrient intake. Increased total energy intake was associated with increased Lp-PLA₂ activity (odds ratio, 95% confidence interval: 1.07, 1.01-1.14 and 1.10, 1.03-1.16 for the 4th and 3rd quartiles, respectively, compared to the 1st quartile) after adjustments for sex, pack-years of smoking, LDL-cholesterol, and statin treatment. Adiponectin tended to be inversely associated with Lp-PLA₂ activity (0.91, 0.82-1.00, and 4th versus 1st quartile). Our results suggested that total energy intake and adiponectin levels are potential determinants of Lp-PLA₂ activity.

Monocyte-derived factors including PLA2G7 induced by macrophage-nasopharyngeal carcinoma cell interaction promote tumor cell invasiveness

The non-keratinizing undifferentiated subtype of nasopharyngeal carcinoma (NPC) is a malignancy characterized by an intimate relationship between neoplastic cells and a non-neoplastic lymphoid component. Tumor-associated macrophages (TAMs) foster tumor progression through production of soluble mediators that support proliferation, angiogenesis, survival and invasion of malignant cells. However, the role of macrophages in the progression of NPC remains poorly understood. This study aims to investigate the functional and phenotypic changes that occur to macrophages in macrophage-NPC cell co-culture systems, and how these changes influence tumor cells. We found that monocytes, including THP-1 cells and primary human monocytes, co-cultured with C666-1 NPC cells upregulate expression of pro-inflammatory cytokines at the early stages, followed by the induction of metastasis-related genes and interferon-stimulated genes at the later stage of coculture, indicating that TAMs are “educated” by NPC cells for cancer progression. Importantly, the induction of these factors from the TAMs was also found to enhance the migratory capabilities of the NPC cells. We have also identified one of these macrophage-derived factor, phospholipase A2 Group 7 (PLA2G7), to be important in regulating tumor cell migration and a novel tumor-promoting factor in NPC. Further studies to characterize the role of PLA2G7 in tumor metastasis may help determine its potential as a therapeutic target in NPC.

[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.

Coenzyme-A-Independent Transacylation System; Possible Involvement of Phospholipase A2 in Transacylation

The coenzyme A (CoA)-independent transacylation system catalyzes fatty acid transfer from phospholipids to lysophospholipids in the absence of cofactors such as CoA. It prefers to use C20 and C22 polyunsaturated fatty acids such as arachidonic acid, which are esterified in the glycerophospholipid at the sn-2 position. This system can also acylate alkyl ether-linked lysophospholipids, is involved in the enrichment of arachidonic acid in alkyl ether-linked glycerophospholipids, and is critical for the metabolism of eicosanoids and platelet-activating factor. Despite their importance, the enzymes responsible for these reactions have yet to be identified. In this review, we describe the features of the Ca²⁺-independent, membrane-bound CoA-independent transacylation system and its selectivity for arachidonic acid. We also speculate on the involvement of phospholipase A2 in the CoA-independent transacylation reaction.

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.

Low acylation stimulating protein levels are associated with cardiometabolic disorders-secondary to autoimmune activation?

Objective:

We investigated the possible association of serum acylation stimulating protein (ASP) with cardiometabolic disorders and the evidence of autoimmune activation.

Methods:

Population-based randomly selected 1024 participants were cross-sectionally and prospectively analyzed. ASP concentrations were measured with a validated ELISA kit. Correlations were sought separately in subjects with no cardiometabolic disorders (n=427) designated as “healthy.”

Results:

ASP was positively correlated with total testosterone and inversely correlated with platelet activating factor (PAF), PAF-acetylhydrolase (AH), in each gender, and positively correlated in “healthy” men with lipoprotein [Lp](a) and apolipoprotein B. Correlations of ASP with PAF values ≥22 nmol/L were abolished, contrasted to a strongly inverse one in subjects with PAF <22 nmol/L. In linear regression analyses in the whole sample, ASP was inversely associated independently with PAF and PAF-AH and, in men, positively with Lp(a) and sex hormone-binding globulin. Prevalent and (at 2.0 years’ follow-up) incident metabolic syndrome (MetS, n=393), diabetes (n=154), and coronary heart disease (CHD, n=171) were analyzed by sex-, age-, and Lp(a)-adjusted logistic regression, using tertiles of ASP and PAF. The lower two (<42 nmol/L) ASP tertiles were a risk factor in combined sexes for MetS and diabetes. In women, incident CHD was predicted by either reduced or elevated ASP tertiles.

Conclusion:

Findings can be explained by the notion of operation of immune responses against both ASP and oxidized PAF-like lipids of Lp(a) to yield for “reduced” values and increased likelihood of cardiometabolic disorders.

Activity and distribution of plasma platelet-activating factor acetylhydrolase in women with gestational diabetes mellitus and their neonates

BACKGROUND

Abnormal activity and distribution of plasma platelet-activating factor acetylhydrolase (PAF-AH) are associated with chronic inflammatory status. In this study, we investigate the activity and distribution of plasma PAF-AH and their association with metabolic components in mothers with gestational diabetes mellitus (GDM) and in their neonates.

METHODS

Based on the International Association of Diabetes Pregnancy Study Group criteria, we performed a case-controlled study of 101 women with GDM, 98 women with uncomplicated pregnancies, 142 neonates of mothers with GDM and 121 neonates of mothers with uncomplicated pregnancies. 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.

RESULTS

The plasma PAF-AH and apoB-PAF-AH activities, triglyceride (TG) levels, atherogenic index and TG/HDL-C ratio were increased, and the H-PAF-AH proportions were decreased in the mothers with GDM compared with the control mothers (p < 0.05). Multivariate regression analyses demonstrated that the apoB and TG levels were significant predictors of plasma PAF-AH or apoB-PAF-AH activities, while the low-density lipoprotein-cholesterol levels, weight gain during pregnancy and age were associated with H-PAF-AH activities. The neonates of mothers with GDM had higher plasma insulin and glucose concentrations (p < 0.05) and tended to exhibit increased serum apoB levels (p = 0.062) compared with the neonates of mothers with uncomplicated pregnancies.

CONCLUSIONS

The mothers with GDM presented with a state of chronic inflammation, and these mothers and their neonates also exhibited unfavourable metabolic profiles in terms of glucose and lipids. Copyright © 2016 John Wiley & Sons, Ltd.

Structural and Thermodynamic Characterization of Protein-Ligand Interactions Formed between Lipoprotein-Associated Phospholipase A2 and Inhibitors

Lipoprotein-associated phospholipase A2 (Lp-PLA2) represents a promising therapeutic target for atherosclerosis and Alzheimer's disease. Here we reported the first crystal structures of Lp-PLA2 bound with reversible inhibitors and the thermodynamic characterization of complexes. High rigidity of Lp-PLA2 structure and similar binding modes of inhibitors with completely different scaffolds are revealed. It not only provides the molecular basis for inhibitory activity but also sheds light on the essential features of Lp-PLA2 recognition with reversible inhibitors.

Inflammation-associated changes in lipid composition and the organization of the erythrocyte membrane

Background

Reduced erythrocyte survival and deformability may contribute to the so-called anemia of inflammation observed in septic patients. Erythrocyte structure and function are affected by both the membrane lipid composition and the organization. We therefore aimed to determine whether these parameters are affected during systemic inflammation.

Methods

A sensitive matrix-assisted laser desorption and ionization time-of-flight mass spectrometric method was used to investigate the effect of plasma components of 10 patients with septic shock and of 10 healthy volunteers subjected to experimental endotoxemia on erythrocyte membrane lipid composition.

Results

Incubation of erythrocytes from healthy control donors with plasma from patients with septic shock resulted in membrane phosphatidylcholine hydrolysis into lysophosphatidylcholine (LPC). Plasma from volunteers undergoing experimental human endotoxemia did not induce LPC formation. The secretory phospholipase A₂ IIA concentration was enhanced up to 200-fold in plasma of septic patients and plasma from endotoxin-treated subjects, but did not correlate with the ability of these plasmas to generate LPC. Erythrocyte phosphatidylserine exposure increased up to two-fold during experimental endotoxemia.

Conclusions

Erythrocyte membrane lipid remodeling as reflected by LPC formation and/or PS exposure occurs during systemic inflammation in a secretory phospholipase A₂ IIA-independent manner.

General significance

Sepsis-associated inflammation induces a lipid remodeling of the erythrocyte membrane that is likely to affect erythrocyte function and survival, and that is not fully mimicked by experimental endotoxemia.

•

Erythrocyte membrane lipid remodeling occurs during systemic inflammation.

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Erythrocyte phosphatidylcholine hydrolysis during sepsis does not rely on SPLA₂ IIA.

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Experimental endotoxemia does not fully mimic the effects of sepsis on erythrocytes.

Biomarkers of anaphylaxis, beyond tryptase

PURPOSE OF REVIEW

The purpose of this study is to describe the current knowledge regarding mediators involved in anaphylactic reactions, with a special focus on key effector cells and mechanisms.

RECENT FINDINGS

New insight into the potential relevance of pathways other than mast cell degranulation has been unravelled, such as the role of cytokines, platelet activation factor, lipid mediators and their metabolism or the activation of the contact system.

SUMMARY

Gaining knowledge into these pathophysiologic mechanisms will allow researchers to pursue the identification of risk factors and new preventive and therapeutic strategies in anaphylaxis.

Evaluation of predictive effect of PAF-AH on the prognosis of intensive care unit patients / Yoğun bakım hastalarında PAF-AH’ın prognoz üzerindeki prediktif etkisinin değerlendirilmesi

Objective: Determination of the factors associated with the intensive care unit (ICU) prognosis and mortality has important role in the clinical follow-up of the patients. Definition of novel biomarkers, beside older biomarkers available for evaluation of the outcome of these patients has been proposed. Platelet-activating factor acetylhydrolase (PAF-AH) is an enzyme that inactivates the platelet-activating factor. A reduction in the level of the PAF-AH has been demonstrated during systemic inflammation and multiple organ failure. This research aims to determine whether measurement of PAF-AH enzyme activity in ICUs can be used as a prognostic indicator like conventional biomarkers.

Methods: Eighty five adult patients have been included. Following data have been recorded: preliminary C-reactive protein (CRP), lactate, albumin and PAF-AH values, APACHE II scores and discharge forms from ICU. Patients were divided in two groups with respect to APACHE II values: Group 1 (1-19) and Group 2 (≥20).

Results: Observed mortality was 51.2%. In the APACHE II Group 2 patients, the values of CRP (p=0.001) and lactate (p=0.040) were significanty high, and the values of PAF-AH (p=0.008) and albumin (p=0.001) were significantly low. A statistically significant difference was found between PAF-AH values of exitus and alive patients (p=0.001). According to ROC analysis, the sensitivity and specificity of predicting mortality was 70.5% and 70.7% for CRP, 63.6% and 70.7% for lactate, 90.2% and 61.4% for albumin and 63.6% and 70% PAF-AH, respectively.

Conclusion: Our study demonstrated that, in predicting the ICU mortality risk, sensitivity of the PAF-AH is similar to the sensitivity of the lactate, and specificity of the PAF-AH is better than that of the albumin. According to our results, PAF-AH can be included in the novel biomarkers.

Plasma phospholipase, γ-CEHC and antioxidant capacity in fibromyalgia

OBJECTIVE

Recent studies have suggested a possible role of high levels of plasma lysophosphocholines (lysoPCs) in fibromyalgia syndrome (FMS). The aim of this study was to evaluate the content of plasma phospholipases (e.g., Platelet Activating Factor Acetyl Hydrolase [PAF-AH], secretory Phospholipase A₂ [sPLA₂ ], Total Antioxidant Capacity [TAOC] and 2,7,8-trimethyl-2-(2-carboxyethyl)-6-hydroxy chroman [γ-CEHC]) in FMS patients and their association with clinical status and quality of life.

METHODS

Thirty-six females meeting the 2011 American College of Rheumatology criteria for the classification of FMS and thirty-four healthy females were enrolled for the study. Plasma enzyme levels were quantified using commercial enzyme-linked-immunosorbent-assay (ELISA). In order to assess the disease severity and the functional status of patients, the Fibromyalgia Impact Questionnarie (FIQ) was used.

RESULTS

Higher levels of sPLA₂ and lower PAF-AH and γ-CEHC were observed in the plasma of FMS patients compared to the controls. A decrease in PAF-AH and TAOC levels were found in severe FMS (S-FMS) compared to mild/slight (MS-FMS) forms.

CONCLUSION

The results of the study indicate a possible involvement of phospholipases and γ-CEHC in fibromyalgia syndrome.

New risk factors for adult-onset incident asthma. A nested case-control study of host antioxidant defense

RATIONALE

Host antioxidant defense, consisting of enzymatic antioxidant activity and nonenzymatic antioxidant micronutrients, is implicated in asthma pathogenesis. Studies of antioxidant defense and adult incident asthma have either used measures of antioxidants estimated from questionnaires or not considered enzymatic aspects of host defense.

OBJECTIVES

We conducted the first study designed and powered to investigate the association of antioxidant defenses on adult incident asthma.

METHODS

In a nested case-control study, we followed Shanghai women (aged 40-70 years) without prevalent asthma at baseline, over 8 years. Subjects with incident asthma were ascertained prospectively by gold standard testing of symptomatic women and matched to two asymptomatic control subjects.

MEASUREMENTS AND MAIN RESULTS

Baseline urinary F2-isoprostanes, plasma concentrations of antioxidant micronutrients (tocopherols, xanthines, carotenes, and lycopene), and antioxidant enzyme activity (platelet-activating factor acetylhydrolase [PAF-AH] and superoxide dismutase) were measured from samples collected before disease onset. Among 65,372 women, 150 (0.24%) developed asthma. F2-isoprostane levels before asthma onset were not different between cases and control subjects. Doubling of α-tocopherol concentrations and PAF-AH activity was associated with 50 and 37% decreased risk of incident asthma (α-tocopherol: adjusted odds ratio = 0.52; 95% confidence interval, 0.32-0.84; PAF-AH: adjusted odds ratio = 0.63; 95% confidence interval, 0.42-0.93).

CONCLUSIONS

In this prospective study, α-tocopherol, within normal reference ranges, and PAF-AH enzymatic activity were associated with decreased asthma development. These modifiable risk factors may be an effective strategy to test for primary asthma prevention.

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.

Biological role of Trichoderma harzianum-derived platelet-activating factor acetylhydrolase (PAF-AH) on stress response and antagonism

We investigated the properties of platelet-activating factor acetylhydrolase (PAF-AH) derived from Trichoderma harzianum. The enzyme, comprised of 572 amino acids, shares high homology with PAF-AH proteins from T. koningii and other microbial species. The optimum enzymatic activity of PAF-AH occurred at pH 6 in the absence of Ca²⁺ and it localized in the cytoplasm, and we observed the upregulation of PAF-AH expression in response to carbon starvation and strong heat shock. Furthermore, PAF-AH knockout transformant growth occurred more slowly than wild type cells and over-expression strains grown in SM medium at 37°C and 42°C. In addition, PAF-AH expression significantly increased under a series of maize root induction assay. Eicosanoic acid and ergosterol levels decreased in the PAF-AH knockouts compared to wild type cells, as revealed by GC/MS analysis. We also determined stress responses mediated by PAF-AH were related to proteins HEX1, Cu/Zn superoxide dismutase, and cytochrome c. Finally, PAF-AH exhibited antagonistic activity against Rhizoctonia solani in plate confrontation assays. Our results indicate PAF-AH may play an important role in T. harzianum stress response and antagonism under diverse environmental conditions.

Bacterial clearance is improved in septic mice by platelet-activating factor-acetylhydrolase (PAF-AH) administration

Current evidence indicates that dysregulation of the host inflammatory response to infectious agents is central to the mortality of patients with sepsis. Strategies to block inflammatory mediators such as PAF have been investigated as adjuvant therapies for sepsis. PAF-AH, the enzyme responsible for PAF degradation, showed positive results in pre-clinical studies and phase II clinical trials, but the results of a phase III study were disappointing. In this study, we investigated the potential protective mechanism of PAF-AH in sepsis using the murine model of cecal ligation and puncture (CLP). Treatment with rPAF-AH increased peritoneal fluid levels of the anti-inflammatory mediators MCP-1/CCL2 after CLP. The numbers of bacteria (CFU) in the peritoneal cavity were decreased in the rPAF-AH-treated group, indicating more efficient bacterial clearance after rPAF-AH treatment. Interestingly, we observed increased levels of nitric oxide (NO) after PAF-AH administration, and rPAF-AH treatment did not decrease CFU numbers either in iNOS-deficient mice or in CCR2-deficient mice. We concluded that administration of exogenous rPAF-AH reduced inflammatory injury, altered cytokine levels and favored bacterial clearance with a clear impact on mortality through modulation of MCP-1/CCL2 and NO levels in a clinically relevant sepsis model.

Plasma HDL reduces nonesterified fatty acid hydroperoxides originating from oxidized LDL: a mechanism for its antioxidant ability

The antioxidant property of plasma high-density lipoprotein (HDL) is thought to be involved in potential anti-atherogenic effects but the exact mechanism is not known. We aimed to reveal the contribution of HDL on the elimination of lipid hydroperoxides (LOOH) derived from oxidized low-density lipoprotein (LDL). Oxidized LDL prepared by copper ion-induced oxidation contained nonesterified fatty acid hydroperoxides (FFA-OOH) and lysophosphatidylcholine (lysoPtdCho), in addition to cholesteryl ester hydroperoxides (CE-OOH) and phosphatidylcholine hydroperoxides (PtdCho-OOH). A platelet-activating factor-acetylhydrolase (PAF-AH) inhibitor suppressed formation of FFA-OOH and lysoPtdCho in oxidized LDL. Among LOOH species, FFA-OOH was preferentially reduced by incubating oxidized LDL with HDL. HDL exhibited selective FFA-OOH reducing ability if it was mixed with a liposomal solution containing FFA-OOH, CE-OOH and PtdCho-OOH. Two-electron reduction of the hydroperoxy group to the hydroxy group was confirmed by the formation of 13-hydroxyoctadecadienoic acid from 13-hydroperoxyoctadecadienoic acid in HPLC analyses. This reducing effect was also found in apolipoprotein A-1 (apoA-1). FFA-OOH released from PtdCho-OOH due to PAF-AH activity in oxidized LDL undergo two-electron reduction by the reducing ability of apoA1 in HDL. This preferential reduction of FFA-OOH may participate in the mechanism of the antioxidant property of HDL.

Lentiviral-mediated RNA interference of lipoprotein-associated phospholipase A2 ameliorates inflammation and atherosclerosis in apolipoprotein E-deficient mice

Lipoprotein associated phospholipase A2 (Lp-PLA2) overexpression is implicated in athero-sclerosis. In the present study, we evaluated the effects of lentiviral-mediated RNA interference (RNAi) of Lp-PLA2 on inflammation and atherosclerosis in apolipoprotein E-deficient mice. Apolipoprotein E-deficient mice were randomly allocated to control and experimental groups, and constrictive collars were used to induce plaque formation. Eight weeks after surgery, the lentiviral-mediated RNAi construct was used to silence expression of Lp-PLA2. Control and experimental lentivirus was transfected directly into carotid plaques or administered systemically. Tissues were collected for analysis 7 weeks after transfection. Inflammatory gene expression in the plasma and atherosclerotic lesions was then determined at the mRNA and protein levels. We observed no differences in body weight and plasma lipid levels at the end of the investigation. However, the expression levels of Lp-PLA2 and pro-inflammatory cytokines were significantly reduced in the RNAi groups, compared to the controls, whereas the plasma concentration of anti-inflammatory cytokines was markedly increased. Moreover, our results demonstrated a significant reduction in plaque area and lipid content, as well as a rise in collagen content following RNAi treatment. Importantly, when comparing the two methods of viral delivery, we found that transluminal local transfection exhibited enhanced improvement of plaque stability as compared to systemic administration. Inhibition of Lp-PLA2 by lentiviral-mediated RNAi ameliorates inflammation and atherosclerosis in apolipoprotein E-deficient mice. In addition, transluminal local delivery of Lp-PLA2 shRNA is superior to systemic administration for stabilizing atherosclerotic plaques.

Maternal and fetal plasma platelet-activating factor acetylhydrolase activity and distribution in pre-eclampsia

BACKGROUND

Distribution of platelet-activating factor acetylhydrolase (PAF-AH) in lipoproteins plays important roles in the onset of inflammation and atherosclerosis. We hypothesized that women with pre-eclampsia (PE), showing signs of inflammation and oxidative stress, and their fetuses have aberrations of PAF-AH activity and distribution.

METHODS

Maternal and fetal plasma PAF-AH activity, high-density lipoprotein (HDL)-associated PAF-AH (H-PAF-AH) and low-density lipoprotein (LDL)-associated PAF-AH (L-PAF-AH) were examined in women with PE (n = 127) and in women with uncomplicated pregnancies (n = 88).

RESULTS

The neonates of women with severe PE (n = 42) had significantly higher plasma PAF-AH, L-PAF-AH activities, and ratio of L-PAF-AH to H-PAF-AH activities than the neonates of women with normal pregnancies (n = 83). The mothers with severe PE (n = 106) and their neonates presented a significantly higher atherogenic index (AI) and triglyceride (TG)/HDL cholesterol (C) ratio than the control mothers and their neonates. The ratio of L-PAF-AH to H-PAF-AH activities correlated positively with TG levels, TG/HDL(C) ratio, and AI and negatively with HDL(C) levels in the neonates of women with PE.

CONCLUSION

The neonates of women with severe PE presented with a chronic inflammation status, increased oxidative stress, and unfavorable lipid changes, which may potentially link to related complications responsible for oxidative stress and inflammation in later life.

Regression of atherosclerosis in apolipoprotein E-deficient mice by lentivirus-mediated gene silencing of lipoprotein-associated phospholipase A2

Overexpression of lipoprotein-associated phospholipase A(2) (Lp-PLA(2)) is implicated in atherosclerosis. We tested the hypothesis that lentivirus-mediated Lp-PLA(2) silencing could inhibit atherosclerosis in apolipoprotein E-deficient mice. Sixty eight apolipoprotein E-deficient mice were fed a high-fat diet and a constrictive collar was placed around the left carotid artery to induce plaque formation. The mice were randomly divided into control, negative control (NC) and RNA interference (RNAi) groups. Lp-PLA(2) RNAi or scrambled NC lentivirus viral suspensions were constructed and transfected into the carotid plaques 8 weeks after surgery; the control group was administered saline. The carotid plaques were assessed 7 weeks later using hematoxylin and eosin, Masson's trichrome and oil red O staining; plasma and lesion inflammatory gene expression were examined using ELISAs and real-time PCR. Seven weeks after transfection, the serum concentration and plaque mRNA expression of Lp-PLA(2) was significantly lower in the RNAi group, and lead to reduced local and systemic inflammatory gene expression. Lp-PLA(2) RNAi also ameliorated plaque progression, reduced the plaque lipid content and increased the plaque collagen content. The effects of Lp-PLA(2) RNAi were independent of serum lipoprotein levels, as the triglyceride and total cholesterol levels of the control, NC and RNAi groups were not significantly different. These findings support the hypothesis that lentivirus-mediated Lp-PLA(2) gene silencing has therapeutic potential to inhibit atherosclerosis and increase plaque stability, without altering the plasma lipoprotein profile.

Plasma platelet-activating factor-acetyl hydrolase activity and the levels of free forms of biomarker of lipid peroxidation in cerebrospinal fluid of patients with aneurysmal subarachnoid hemorrhage

BACKGROUND

Free radicals and lipid peroxidation are thought to be related to the vasospasm generation after subarachnoid hemorrhage (SAH). Plasma platelet-activating factor-acetyl hydrolase (PAF-AH) degrades phospholipids with an oxidatively modified fatty acyl chain.

OBJECTIVE

To compare plasma PAF-AH activity and free forms of biomarker of lipid peroxidation in cerebrospinal fluid (CSF) between patients with and without symptomatic vasospasm (SVS) after SAH.

METHODS

The identification of PAF-AH in CSF was performed by Western blotting. The genotype at position 279 of the plasma PAF-AH gene was determined. The activities of PAF-AH and the levels of free 8-iso-prostaglandin F2α (free isoPs), free hydroxyoctadecadienoic acid (free HODE), and free hydroxyeicosatetraenoic acid (free HETE) in CSF were measured.

RESULTS

The PAF-AH in CSF was confirmed to be only the plasma type. The genotype of the plasma PAF-AH was not different between patients with and without SVS. Free isoPs, free HODE, and free HETE showed higher values in patients without SVS in 0 to 4 days and 5 to 9 days after SAH. The PAF-AH activity also was higher in patients without SVS in 0 to 4 days and 5 to 9 days after SAH. The associations between PAF-AH activity and free isoPs, and between PAF-AH activity and free HODE were significant.

CONCLUSION

Oxidized lipids of lipoproteins and blood cell membranes produced by reactive oxygen species in CSF when SAH occurs may be the main source of lipid peroxidation. Plasma PAF-AH can hydrolyze oxidized phospholipids, and may attenuate the spreading of lipid peroxidation and participate in defense mechanisms against vasospasm after SAH.

Utility of Lp-PLA2 in lipid-lowering therapy

Lipoprotein-associated phospholipase A2 (Lp-PLA2) is a vascular-specific inflammatory marker. It is so named because of its association with low-density lipoprotein in plasma. Atherosclerosis is an inflammatory disease. Lp-PLA2 is recognized as a risk marker in primary or secondary prevention of atherosclerosis. Elevated Lp-PLA2 levels are associated with the increased risk for cardiovascular events, even after multivariable adjustment for traditional risk factors. Patients with dyslipidemia are shown to benefit largely from the modification of Lp-PLA2. The degree of coronary artery disease (0-, 1-, 2-, or 3-vessel disease) and plasma low-density lipoprotein cholesterol significantly correlated to Lp-PLA2 levels. The low biologic fluctuation and high vascular specificity of Lp-PLA2 make it possible to use a single measurement in clinical decision making, and it also permits clinicians to follow the Lp-PLA2 marker serially. Simvastatin significantly reduces macrophage content, lipid retention, and the intima to media ratio but increased the content of smooth muscle cells in atherosclerotic lesions. Statin treatment markedly reduced Lp-PLA2 in both plasma and atherosclerotic plaques with attenuation of the local inflammatory response and improved plaque stability due to reduced inflammation and decreased apoptosis of macrophages. Darapladib, an inhibitor of Lp-PLA2 when added to lipid-lowering therapy such as statins, offers great benefit in the reduction of plaque formation. This article explores the atherosclerotic process at molecular level, role of Lp-PLA2 in atherosclerosis, the effect of lipid-lowering drugs on Lp-PLA2, effect of direct Lp-PLA2 inhibitor darapladib in the atherosclerosis process, the therapeutic implications of Lp-PLA2 as risk marker, and finally the net effect on plaque stabilization.

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.

Lung endothelial cell platelet-activating factor production and inflammatory cell adherence are increased in response to cigarette smoke component exposure

An early event in the pathogenesis of emphysema is the development of inflammation associated with accumulation of polymorphonuclear leukocytes (PMN) in small airways, and inflammatory cell recruitment from the circulation involves migration across endothelial and epithelial cell barriers. Platelet-activating factor (PAF) promotes transendothelial migration in several vascular beds, and we postulated that increased PAF production in the airways of smokers might enhance inflammatory cell recruitment and exacerbate inflammation. To examine this possibility, we incubated human lung microvascular endothelial cells (HMVEC-L) with cigarette smoke extract (CSE) and found that CSE inhibits PAF-acetylhydrolase (PAF-AH) activity. This enhances HMVEC-L PAF production and PMN adherence, and adherence is blocked by PAF receptor antagonists (CV3988 or ginkgolide B). CSE also inhibited PAF-AH activity of lung endothelial cells isolated from wild-type (WT) and iPLA(2)β knockout mice, and with WT cells, CSE enhanced PAF production and RAW 264.7 cell adherence. In contrast, CSE did not affect PAF production or RAW 264.7 cell adherence to iPLA(2)β-null cells, suggesting that iPLA(2)β plays an important role in PAF production by lung endothelial cells. These findings suggest that inhibition of PAF-AH by components of cigarette smoke may initiate or exacerbate inflammatory lung disease by enhancing PAF production and promoting accumulation of inflammatory cells in small airways. In addition, iPLA(2)β is identified as a potential target for therapeutic interventions to reduce airway inflammation and the progression of chronic lung disease.

Females with angina pectoris have altered lipoprotein metabolism with elevated cholesteryl ester transfer protein activity and impaired high-density lipoproteins-associated antioxidant enzymes

In order to investigate non-invasive biomarkers for angina pectoris (AP), we analyzed the lipid and protein composition in individual lipoproteins from females with angina pectoris (n=22) and age- and gender-matched controls (n=20). In the low-density lipoprotein (LDL) fraction, the triglycerides (TG) and protein content increased in the AP group compared to the control group. The AP group had lower total cholesterol (TC) and elevated TG in the high-density lipoprotein (HDL) fraction. In the AP group, cholesteryl ester transfer protein (CETP) activity was enhanced in HDL and LDL, while lecithin:cholesterol acyltransferase (LCAT) activity in HDL₃ was almost depleted. Antioxidant activity was significantly decreased in the HDL₃ fraction, with a decrease in the HDL₂ particle size. In the HDL₃ fraction, paraoxonase and platelet activating factor-acetylhydrolase (PAF-AH) activity were much lower and the levels of CETP and apoC-III were elevated in the AP group. The LDL from the AP group was more sensitive to cupric ion-mediated oxidation with faster mobility. In conclusion, the lipoprotein fractions in the AP group had impaired antioxidant activity and increased TG and apoC-III with structural and functional changes.

Albuterol isomers modulate platelet-activating factor synthesis and receptor signaling in human bronchial smooth muscle cells

BACKGROUND

Racemic albuterol is a 50:50 mixture of the (R)- and (S)-enantiomers of albuterol. Its clinical efficacy resides in the (R)-enantiomer (levalbuterol). Studies have shown that (S)-albuterol induces human bronchial smooth muscle cell (HBSMC) proliferation via a pathway linked to platelet-activating factor (PAF), but the underlying mechanism by which (S)-albuterol augments PAF effects is not clear. In this study, we compared effect of levalbuterol and (S)-albuterol on PAF receptor (PAFr)-mediated signaling and PAF metabolism by HBSMCs after incubation with the albuterol isomers.

METHODS

PAF binding and inositol phosphate (IP(3)) release were studied on adherent cultured cells. PAFr protein expression was measured by Western blotting, PAF synthesis and catabolism were measured in membrane and cytosolic proteins of cells incubated with albuterol isomers.

RESULTS

Compared to control conditions, (S)-albuterol increased PAF binding by 70% after 30 min of preincubation and by 150% after 24 h of preincubation. Levalbuterol had no effect on PAF binding under both conditions. (S)-albuterol also augmented PAF stimulation of IP(3) release, while levalbuterol and the racemic mixture had no effect. WEB 2170, a PAFr antagonist, inhibited the ability of (S)-albuterol to increase PAF binding or stimulate IP(3) release. (S)-albuterol stimulated PAFr protein expression. With PAF metabolism, (S)-albuterol treatment augmented PAF synthesis, but significantly inhibited PAF catabolism.

CONCLUSIONS

Our data suggest that one mechanism by which (S)-albuterol stimulates HBSMC proliferation involves upregulation of PAFr-mediated effects including increased PAF synthesis and decreased PAF catabolism.

Clinical significance of circulating platelet-activating factor acetylhydrolase levels in systemic sclerosis

Platelet-activating factor acetylhydrolase (PAF-AH) has been demonstrated to be one of anti-inflammatory and anti-apoptotic factors, suggesting the potential to be involved in the development of systemic sclerosis (SSc). The aim of this study is to determine serum PAF-AH levels and their clinical associations in patients with SSc. Serum PAF-AH levels were examined by enzyme-linked immunosorbent assay in 57 patients with SSc and 24 healthy individuals. Serum PAF-AH levels were significantly elevated in SSc patients (130.4 ± 69.5 ng/ml) compared with healthy individuals (81.6 ± 34.8 ng/ml; P < 0.001). Among SSc patients, there were no differences in serum PAF-AH levels between those with diffuse cutaneous SSc (135.5 ± 79.3 ng/ml; n = 29) and those with limited cutaneous SSc (125.1 ± 58.6 ng/ml; n = 28). Patients with SSc who had raised PAF-AH levels less often had digital ulcers and arthritis/arthralgias than those with normal PAF-AH levels. The results show that serum PAF-AH levels were increased in patients with SSc and associated with a lower frequency of pitting scars/digital ulcers and arthritis/arthralgias. PAF-AH could be a protective factor against the development of digital ulcers and arthritis/arthralgia in this disease and as such would be a useful serological marker for disease severity.

Apolipoprotein E-containing HDL-associated platelet-activating factor acetylhydrolase activities and malondialdehyde concentrations in patients with PCOS

PAF and PAF-like oxidized phospholipids hydrolysed by platelet-activating factor (PAF) acetylhydrolase (AH) are potent lipid mediators involved in inflammation and atherosclerosis. Apolipoprotein (apo) E-containing high-density lipoprotein (HDL) has antioxidant, anti-inflammatory and anti-atherogenic properties. The study investigated apoE-containing HDL-associated PAF-AH (HDL-PAF-AH) and total (apoE-containing+apoE-poor) HDL-PAF-AH activities as well as malondialdehyde (MDA) concentration in 291 patients with polycystic ovary syndrome (PCOS) using the Rotterdam consensus criteria and 281 control women. Compared with the control women, patients with hyperandrogenism+oligo/anovulation+polycystic ovaries (PCO) or hyperandrogenism+PCO had lower total, apoE-containing and apoE-poor HDL-PAF-AH activities, while those with oligo/anovulation+PCO showed decreased total and apoE-poor HDL-PAF-AH activities. Other factors including insulin resistance and obesity in PCOS had the adverse effects associated with the HDL-PAF-AH activities. Serum MDA concentration was associated with PCOS, hyperandrogenism, insulin resistance and hypertriglyceridaemia in patients with PCOS. Decreased total and apoE-containing HDL-PAF-AH activities and increased serum MDA concentration may contribute to the pathogenesis of PCOS and potentially link to related complications responsible for oxidative stress and inflammation such as an increased risk for type 2 diabetes mellitus and/or future cardiovascular diseases in PCOS patients.

A novel platelet-activating factor acetylhydrolase discovered in a metagenome from the earthworm-associated microbial community

Metagenomics is an emerging field for mining the bioresources for new biomolecules for potential application in biotechnology and biomedicine. In the present study, a novel acetylhydrolase (Est13) was detected during the function-based screening of a metagenomic library established from the DNA extracted from the cellulose-depleting microbial community set up with an earthworm cast. Analysis showed that Est13 exhibited some similarities with a human and parasite platelet-activating factor acetylhydrolase (PAF-AH) belonging to the SGNH hydrolase superfamily. Biochemical characterization of the purified recombinant enzyme using substrates common for hydrolases of this superfamily demonstrated that Est13 hydrolysed p-nitrophenyl acetate quite efficiently, with a k(cat) /K(M) value of 3209 mM(-1) s(-1). The Est13 showed highest activity at pH 8.0 and 40°C, conditions in which it is relatively stable compared with known PAF-AHs. In vitro functional analysis of the platelet-activating factor hydrolysis showed a dose- and time-dependent inhibition of platelet aggregation in the range of 2-4 µM, making this enzyme a potential candidate for biomedical applications.

The role of low-grade inflammation in the polycystic ovary syndrome

PCOS is not only the most frequent cause of oligomenorrhea in young women, but also a metabolic disorder characterized by insulin resistance, glucose intolerance, dyslipidemia, and obesity, especially the visceral phenotype. PCOS represents a broad spectrum of endocrine and metabolic alterations which change with age and with increasing adiposity. In fact, during adolescence and youth the predominant clinical manifestations of PCOS are menstrual abnormalities, hirsutism and acne, whereas in peri-menopausal and post-menopausal periods metabolic disorders and an increased risk for cardiovascular diseases prevail. The pathogenetic links between PCOS and metabolic or cardiovascular complications are still debated. However, recent evidence has been focused on a condition of low-grade chronic inflammation as a potential cause of the long-term consequence of the syndrome. In this review we describe the state of low-grade inflammation observed in PCOS. In addition, we hypothesize the potential mechanisms responsible for the generation of this inflammatory state and the role played by low-grade inflammation in linking hyperandrogenism and insulin resistance with the metabolic and cardiovascular long-term complications of the syndrome.

Serum platelet-activating factor acetylhydrolase activity: relationship with metabolic syndrome in women with history of gestational diabetes mellitus

OBJECTIVE

The aim of this study was to evaluate plasma platelet-activating factor acetylhydrolase (PAF-AH) activity in euglycaemic women with history of gestational diabetes (GDM), and to explore whether this activity is associated with metabolic syndrome (MS) in this group of women.

METHODS

The cross-sectional study included 36 women with history of GDM and 40 women with history of normal glucose tolerance in pregnancy (control group).

RESULTS

Compared to the controls, the GDM group had significantly higher mean values for serum glucose, insulin, HOMA-IR, triglyceride, GGT and plasma PAF-AH activity, and a statistically higher prevalence of MS. Within the GDM group, women diagnosed with MS had significantly higher PAF-AH activity than those without MS (p=0.002).

CONCLUSION

This is the first study to have shown that plasma PAF-AH activity and GGT levels may be significant for evaluating atherosclerosis risk and metabolic hepatic damage in women with history of GDM.

Circulating platelet-activating factor is primarily cleared by transport, not intravascular hydrolysis by lipoprotein-associated phospholipase A2/ PAF acetylhydrolase

RATIONALE

The phospholipid platelet-activating factor (PAF) stimulates all cells of the innate immune system and numerous cardiovascular cells. A single enzyme (plasma PAF acetylhydrolase [PAF-AH] or lipoprotein-associated phospholipase [Lp-PL]A(2)) in plasma hydrolyzes PAF, but significant controversy exists whether its action is pro- or antiinflammatory and accordingly whether its inhibition will slow cardiovascular disease.

OBJECTIVE

We sought to define how PAF and related short-chain oxidized phospholipids turnover in vivo and the role of PAF acetylhydrolase/Lp-PLA(2) in this process.

METHODS AND RESULTS

[(3)H-acetyl]PAF was hydrolyzed by murine or human plasma (t(1/2), 3 and 7 minutes, respectively), but injected [(3)H-acetyl]PAF disappeared from murine circulation more quickly (t(1/2), <30 seconds). [(3)H]PAF clearance was unchanged in PAF receptor(-/-) animals, or over the first 2 half-lives in PAF-AH(-/-) animals. [(3)H]PAF turnover was reduced by coinjecting excess unlabeled PAF or an oxidatively truncated phospholipid, and [(3)H]PAF clearance was slowed in hyperlipidemic apolipoprotein (apo)E(-/-) mice with excess circulating oxidatively truncated phospholipids. [(3)H]PAF, fluorescent NBD-PAF, or fluorescent oxidatively truncated phospholipid were primarily accumulated by liver and lung, and were transported into endothelium as intact phospholipids through a common mechanism involving TMEM30a.

CONCLUSIONS

Circulating PAF and oxidized phospholipids are continually and rapidly cleared, and hence continually and rapidly produced. Saturable PAF receptor-independent transport, rather than just intravascular hydrolysis, controls circulating inflammatory and proapoptotic oxidized phospholipid mediators. Intravascular PAF has access to intracellular compartments. Inflammatory and proapoptotic phospholipids may accumulate in the circulation as transport is overwhelmed by substrates in hyperlipidemia.

Mouse plasminogen has oxidized phosphatidylcholine adducts that are not metabolized by lipoprotein-associated phospholipase A₂under basal conditions

We previously showed that plasminogen (Plg) isolated from the plasma of normal human subjects contains 1–2 moles of oxidized phosphatidylcholine (oxPtdPC) adducts/mole of protein. Moreover, we suggested that these species are generated at the hepatic site and speculated that they may play a role in the reported cardiovascular pathogenicity of Plg. We aimed to determine whether mouse Plg also harbors linked oxPtdPCs and whether these molecules are metabolized by lipoprotein-associated phospholipase A₂/PAF acetylhydrolase (Lp-PLA₂/PAF-AH), an enzyme specific for hydrolysis of oxPtdPCs. We determined the total concentration of Plg in plasma samples from control (WT) and Lp-PLA₂-deficient (KO) mice, we isolated Plg, and assessed its content of oxPtdPCs by immunoblot analyses. We also evaluated whether human recombinant Lp-PLA₂ metabolized Plg-linked oxPtdPCs in vivo and in vitro. WT and KO mice expressed comparable levels (14.4–15.8 mg/dL) of plasma Plg, as determined by ELISA. We observed no differences in the content of oxPtdPC in Plg isolated from the two mouse strains and in parallel no changes in oxPtdPC content in mouse Plg following incubation with pure recombinant Lp-PLA₂. Plg from mouse plasma contains oxPtdPC adducts that are not affected by the action of Lp-PLA₂, suggesting that linkage to Plg protects oxPtdPCs from metabolism during their transport in the plasma. This modification may have important physio-pathological implications related to the function of Plg, oxPtdPCs, or both.

Atherosclerosis regression study in rabbits upon olive pomace polar lipid extract administration

BACKGROUND AND AIMS

Virgin olive oil polar lipid extract (OOPL) and olive pomace polar lipid extract (PPL) have similar antiatherosclerotic effects in cholesterol-fed rabbits. Our aim was to compare the effect of PPL with that of simvastatin on the progression of atherogenesis.

METHODS AND RESULTS

Rabbits were fed an atherogenic diet for 6 weeks in order to develop dyslipidemia and atheromatous lesions. Following documentation of these events in random animals (group A, n=6), the remaining were fed for 3 weeks with: standard chow alone (group B, n=6), chow supplemented with PPL (group C, n=6), and chow supplemented with simvastatin (group D, n=6). Blood was collected at 0, 6 and 9 weeks, to determine plasma lipid levels, plasma PAF-AH activity, platelet aggregation (PAF-EC(50)), resistance of plasma to oxidation (RPO) and extent of atheromatous lesions in aortas. The atherogenic diet induced dyslipidemia and increased PAF-AH activity. Dyslipidemia and PAF-activity reduced more effectively in groups C and D. RPO decreased in group B only. PAF-EC(50) values decreased in group C only. Atherogenesis progression in group C was prevented to an extent indistinguishable from that in group D. PAF-AH activity was positively correlated, whereas RPO was negatively correlated with the extent of atheromatous lesions.

CONCLUSION

PPL, as a dietary supplement, is equipotent to simvastatin in preventing the progression of atherogenesis.