Unraveling the PAF-AH/Lp-PLA2 controversy

Phospholipase PLA2G7 is complementary to GPX4 in mitigating punicic-acid-induced ferroptosis in prostate cancer cells

Ferroptosis is a cell death pathway that can be promoted by peroxidizable polyunsaturated fatty acids in cancer cells. Here, we investigated the mechanisms underlying the toxicity of punicic acid (PunA), an isomer of conjugated linolenic acids (CLnAs) bearing three conjugated double bonds highly prone to peroxidation, on prostate cancer (PCa) cells. PunA induced ferroptosis in PCa cells and triggered massive lipidome remodeling, more strongly in PC3 androgen-negative cells than in androgen-positive cells. The greater sensitivity of androgen-negative cells to PunA was associated with lower expression of glutathione peroxidase 4 (GPX4). We then identified the phospholipase PLA2G7 as a PunA-induced ferroptosis suppressor in PCa cells. Overexpressing PLA2G7 decreased lipid peroxidation levels, suggesting that PLA2G7 hydrolyzes hydroperoxide-containing phospholipids, thus preventing ferroptosis. Importantly, overexpressing both PLA2G7 and GPX4 strongly prevented PunA-induced ferroptosis in androgen-negative PCa cells. This study shows that PLA2G7 acts complementary to GPX4 to protect PCa cells from CLnA-induced ferroptosis.

Can Electronegative LDL Act as a Multienzymatic Complex?

Electronegative LDL (LDL(-)) is a minor form of LDL present in blood for which proportions are increased in pathologies with increased cardiovascular risk. In vitro studies have shown that LDL(-) presents pro-atherogenic properties, including a high susceptibility to aggregation, the ability to induce inflammation and apoptosis, and increased binding to arterial proteoglycans; however, it also shows some anti-atherogenic properties, which suggest a role in controlling the atherosclerotic process. One of the distinctive features of LDL(-) is that it has enzymatic activities with the ability to degrade different lipids. For example, LDL(-) transports platelet-activating factor acetylhydrolase (PAF-AH), which degrades oxidized phospholipids. In addition, two other enzymatic activities are exhibited by LDL(-). The first is type C phospholipase activity, which degrades both lysophosphatidylcholine (LysoPLC-like activity) and sphingomyelin (SMase-like activity). The second is ceramidase activity (CDase-like). Based on the complementarity of the products and substrates of these different activities, this review speculates on the possibility that LDL(-) may act as a sort of multienzymatic complex in which these enzymatic activities exert a concerted action. We hypothesize that LysoPLC/SMase and CDase activities could be generated by conformational changes in apoB-100 and that both activities occur in proximity to PAF-AH, making it feasible to discern a coordinated action among them.

A proteomic approach for investigating the pleiotropic effects of statins in the atherosclerosis risk in communities (ARIC) study

BACKGROUND

Statins are prescribed to reduce LDL-c and risk of CVD. Statins have pleiotropic effects, affecting pathophysiological functions beyond LDL-c reduction. We compared the proteome of statin users and nonusers (controls). We hypothesized that statin use is associated with proteins unrelated to lipid metabolism.

METHODS

Among 10,902 participants attending ARIC visit 3 (1993-95), plasma concentrations of 4955 proteins were determined using SOMAlogic's DNA aptamer-based capture array. 379 participants initiated statins within the 2 years prior. Propensity scores (PS) were calculated based on visit 2 (1990-92) LDL-c levels and visit 3 demographic/clinical characteristics. 360 statin users were PS matched to controls. Log2-transformed and standardized protein levels were compared using t-tests, with false discovery rate (FDR) adjustment for multiple comparisons. Analyses were replicated in visit 2.

RESULTS

Covariates were balanced after PS matching, except for higher visit 3 LDL-c levels among controls (125.70 vs 147.65 mg/dL; p < 0.0001). Statin users had 11 enriched and 11 depleted protein levels after FDR adjustment (q < 0.05). Proteins related and unrelated to lipid metabolism differed between groups. Results were largely replicated in visit 2.

CONCLUSION

Proteins unrelated to lipid metabolism differed by statin use. Pending external validation, exploring their biological functions could elucidate pleiotropic effects of statins.

SIGNIFICANCE

Statins are the primary pharmacotherapy for lowering low-density lipoprotein (LDL) cholesterol and preventing cardiovascular disease. Their primary mechanism of action is through inhibiting the protein 3hydroxy-3-methylglutaryl CoA reductase (HMGCR) in the mevalonate pathway of LDL cholesterol synthesis. However, statins have pleiotropic effects and may affect other biological processes directly or indirectly, with hypothesized negative and positive effects. The present study contributes to identifying these pathways by comparing the proteome of stain users and nonusers with propensity score matching. Our findings highlight potential biological mechanisms underlying statin pleiotropy, informing future efforts to identify statin users at risk of rare nonatherosclerotic outcomes and identify health benefits of statin use independent of LDL-C reduction.

Platelet Activating Factor (PAF): A Mediator of Inflammation

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

Association of circulating PLA2G7 levels with cancer cachexia and assessment of darapladib as a therapy

BACKGROUND

Cancer cachexia (CCx) is a multifactorial wasting disorder characterized by involuntary loss of body weight that affects many cancer patients and implies a poor prognosis, reducing both tolerance to and efficiency of anticancer therapies. Actual challenges in management of CCx remain in the identification of tumour-derived and host-derived mediators involved in systemic inflammation and tissue wasting and in the discovery of biomarkers that would allow for an earlier and personalized care of cancer patients. The aim of this study was to identify new markers of CCx across different species and tumour entities.

METHODS

Quantitative secretome analysis was performed to identify specific factors characteristic of cachexia-inducing cancer cell lines. To establish the subsequently identified phospholipase PLA2G7 as a marker of CCx, plasma PLA2G7 activity and/or protein levels were measured in well-established mouse models of CCx and in different cohorts of weight-stable and weight-losing cancer patients with different tumour entities. Genetic PLA2G7 knock-down in tumours and pharmacological treatment using the well-studied PLA2G7 inhibitor darapladib were performed to assess its implication in the pathogenesis of CCx in C26 tumour-bearing mice.

RESULTS

High expression and secretion of PLA2G7 were hallmarks of cachexia-inducing cancer cell lines. Circulating PLA2G7 activity was increased in different mouse models of CCx with various tumour entities and was associated with the severity of body wasting. Circulating PLA2G7 levels gradually rose during cachexia development. Genetic PLA2G7 knock-down in C26 tumours only partially reduced plasma PLA2G7 levels, suggesting that the host is also an important contributor. Chronic treatment with darapladib was not sufficient to counteract inflammation and tissue wasting despite a strong inhibition of the circulating PLA2G7 activity. Importantly, PLA2G7 levels were also increased in colorectal and pancreatic cancer patients with CCx.

CONCLUSIONS

Overall, our data show that despite no immediate pathogenic role, at least when targeted as a single entity, PLA2G7 is a consistent marker of CCx in both mice and humans. The early increase in circulating PLA2G7 levels in pre-cachectic mice supports future prospective studies to assess its potential as biomarker for cancer patients.

The lipid paradox in neuroprogressive disorders: Causes and consequences

Chronic systemic inflammation is associated with an increased risk of cardiovascular disease in an environment of low low-density lipoprotein (LDL) and low total cholesterol and with the pathophysiology of neuroprogressive disorders. The causes and consequences of this lipid paradox are explored. Circulating activated neutrophils can release inflammatory molecules such as myeloperoxidase and the pro-inflammatory cytokines interleukin-1 beta, interleukin-6 and tumour necrosis factor-alpha. Since activated neutrophils are associated with atherosclerosis and cardiovascular disease and with major depressive disorder, bipolar disorder and schizophrenia, it seems reasonable to hypothesise that the inflammatory molecules released by them may act as mediators of the link between systemic inflammation and the development of atherosclerosis in neuroprogressive disorders. This hypothesis is tested by considering the association at a molecular level of systemic inflammation with increased LDL oxidation; increased small dense LDL levels; increased lipoprotein (a) concentration; secretory phospholipase A₂ activation; cytosolic phospholipase A₂ activation; increased platelet activation; decreased apolipoprotein A1 levels and function; decreased paroxonase-1 activity; hyperhomocysteinaemia; and metabolic endotoxaemia. These molecular mechanisms suggest potential therapeutic targets.

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

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

Untargeted metabolomics predicts the functional outcome of ischemic stroke

BACKGROUND/PURPOSE

Metabolites in blood have been found associated with the occurrence of vascular diseases, but its role in the functional recovery of stroke is unclear. The aim of this study is to investigate whether the untargeted metabolomics at the acute stage of ischemic stroke is able to predict functional recovery.

METHODS

One hundred and fifty patients with acute ischemic stroke were recruited and followed up for 3 months. Fasting blood samples within 7 days of stroke were obtained, liquid chromatography and mass spectrometry were applied to identify outcome-associated metabolites. The patients' clinical characteristics and identified metabolites were included for constructing the outcome prediction model using machine learning approaches.

RESULTS

By using multivariate analysis, 220 differentially expressed metabolites (DEMs) were discovered between patients with favorable outcomes (modified Rankin Scale, mRS ≤ 2 at 3 months, n = 77) and unfavorable outcomes (mRS ≥ 3 at 3 months, n = 73). After feature selection, 63 DEMs were chosen for constructing the outcome prediction model. The predictive accuracy was below 0.65 when including patients' clinical characteristics, and could reach 0.80 when including patients' clinical characteristics and 63 selected DEMs. The functional enrichment analysis identified platelet activating factor (PAF) as the strongest outcome-associated metabolite, which involved in proinflammatory mediators release, arachidonic acid metabolism, eosinophil degranulation, and production of reactive oxygen species.

CONCLUSION

Metabolomics is a potential method to explore the blood biomarkers of acute ischemic stroke. The patients with unfavorable outcomes had a lower PAF level compared to those with favorable outcomes.

Metabolic Dysregulation of the Lysophospholipid/Autotaxin Axis in the Chromosome 9p21 Gene SNP rs10757274

BACKGROUND

Common chromosome 9p21 single nucleotide polymorphisms (SNPs) increase coronary heart disease risk, independent of traditional lipid risk factors. However, lipids comprise large numbers of structurally related molecules not measured in traditional risk measurements, and many have inflammatory bioactivities. Here, we applied lipidomic and genomic approaches to 3 model systems to characterize lipid metabolic changes in common Chr9p21 SNPs, which confer ≈30% elevated coronary heart disease risk associated with altered expression of ANRIL, a long ncRNA.

METHODS

Untargeted and targeted lipidomics was applied to plasma from NPHSII (Northwick Park Heart Study II) homozygotes for AA or GG in rs10757274, followed by correlation and network analysis. To identify candidate genes, transcriptomic data from shRNA downregulation of ANRIL in HEK-293 cells was mined. Transcriptional data from vascular smooth muscle cells differentiated from induced pluripotent stem cells of individuals with/without Chr9p21 risk, nonrisk alleles, and corresponding knockout isogenic lines were next examined. Last, an in-silico analysis of miRNAs was conducted to identify how ANRIL might control lysoPL (lysophosphospholipid)/lysoPA (lysophosphatidic acid) genes.

RESULTS

Elevated risk GG correlated with reduced lysoPLs, lysoPA, and ATX (autotaxin). Five other risk SNPs did not show this phenotype. LysoPL-lysoPA interconversion was uncoupled from ATX in GG plasma, suggesting metabolic dysregulation. Significantly altered expression of several lysoPL/lysoPA metabolizing enzymes was found in HEK cells lacking ANRIL. In the vascular smooth muscle cells data set, the presence of risk alleles associated with altered expression of several lysoPL/lysoPA enzymes. Deletion of the risk locus reversed the expression of several lysoPL/lysoPA genes to nonrisk haplotype levels. Genes that were altered across both cell data sets were DGKA, MBOAT2, PLPP1, and LPL. The in-silico analysis identified 4 ANRIL-regulated miRNAs that control lysoPL genes as miR-186-3p, miR-34a-3p, miR-122-5p, and miR-34a-5p.

CONCLUSIONS

A Chr9p21 risk SNP associates with complex alterations in immune-bioactive phospholipids and their metabolism. Lipid metabolites and genomic pathways associated with coronary heart disease pathogenesis in Chr9p21 and ANRIL-associated disease are demonstrated.

Forty Years Since the Structural Elucidation of Platelet-Activating Factor (PAF): Historical, Current, and Future Research Perspectives

In the late 1960s, Barbaro and Zvaifler described a substance that caused antigen induced histamine release from rabbit platelets producing antibodies in passive cutaneous anaphylaxis. Henson described a ‘soluble factor’ released from leukocytes that induced vasoactive amine release in platelets. Later observations by Siraganuan and Osler observed the existence of a diluted substance that had the capacity to cause platelet activation. In 1972, the term platelet-activating factor (PAF) was coined by Benveniste, Henson, and Cochrane. The structure of PAF was later elucidated by Demopoulos, Pinckard, and Hanahan in 1979. These studies introduced the research world to PAF, which is now recognised as a potent phospholipid mediator. Since its introduction to the literature, research on PAF has grown due to interest in its vital cell signalling functions and more sinisterly its role as a pro-inflammatory molecule in several chronic diseases including cardiovascular disease and cancer. As it is forty years since the structural elucidation of PAF, the aim of this review is to provide a historical account of the discovery of PAF and to provide a general overview of current and future perspectives on PAF research in physiology and pathophysiology.

Modulation of inflammatory platelet-activating factor (PAF) receptor by the acyl analogue of PAF

Platelet-activating factor (PAF) is a potent inflammatory mediator that exerts its actions via the single PAF receptor (PAF-R). Cells that biosynthesize alkyl-PAF also make abundant amounts of the less potent PAF analogue acyl-PAF, which competes for PAF-R. Both PAF species are degraded by the plasma form of PAF acetylhydrolase (PAF-AH). We examined whether cogenerated acyl-PAF protects alkyl-PAF from systemic degradation by acting as a sacrificial substrate to enhance inflammatory stimulation or as an inhibitor to dampen PAF-R signaling. In ex vivo experiments both PAF species are prothrombotic in isolation, but acyl-PAF reduced the alkyl-PAF-induced stimulation of human platelets that express canonical PAF-R. In Swiss albino mice, alkyl-PAF causes sudden death, but this effect can also be suppressed by simultaneously administering boluses of acyl-PAF. When PAF-AH levels were incrementally elevated, the protective effect of acyl-PAF on alkyl-PAF-induced death was serially decreased. We conclude that, although acyl-PAF in isolation is mildly proinflammatory, in a pathophysiological setting abundant acyl-PAF suppresses the action of alkyl-PAF. These studies provide evidence for a previously unrecognized role for acyl-PAF as an inflammatory set-point modulator that regulates both PAF-R signaling and hydrolysis.

Inflammation, not Cholesterol, Is a Cause of Chronic Disease

Since the Seven Countries Study, dietary cholesterol and the levels of serum cholesterol in relation to the development of chronic diseases have been somewhat demonised. However, the principles of the Mediterranean diet and relevant data linked to the examples of people living in the five blue zones demonstrate that the key to longevity and the prevention of chronic disease development is not the reduction of dietary or serum cholesterol but the control of systemic inflammation. In this review, we present all the relevant data that supports the view that it is inflammation induced by several factors, such as platelet-activating factor (PAF), that leads to the onset of cardiovascular diseases (CVD) rather than serum cholesterol. The key to reducing the incidence of CVD is to control the activities of PAF and other inflammatory mediators via diet, exercise, and healthy lifestyle choices. The relevant studies and data supporting these views are discussed in this review.

Phospholipid signaling in innate immune cells

Phospholipids comprise a large body of lipids that define cells and organelles by forming membrane structures. Importantly, their complex metabolism represents a highly controlled cellular signaling network that is essential for mounting an effective innate immune response. Phospholipids in innate cells are subject to dynamic regulation by enzymes, whose activities are highly responsive to activation status. Along with their metabolic products, they regulate multiple aspects of innate immune cell biology, including shape change, aggregation, blood clotting, and degranulation. Phospholipid hydrolysis provides substrates for cell-cell communication, enables regulation of hemostasis, immunity, thrombosis, and vascular inflammation, and is centrally important in cardiovascular disease and associated comorbidities. Phospholipids themselves are also recognized by innate-like T cells, which are considered essential for recognition of infection or cancer, as well as self-antigens. This Review describes the major phospholipid metabolic pathways present in innate immune cells and summarizes the formation and metabolism of phospholipids as well as their emerging roles in cell biology and disease.

SERUM LIPOPROTEIN-ASSOCIATED PHOSPHOLIPASE A2 IN MALES WITH METABOLIC SYNDROME AND OBSTRUCTIVE SLEEP APNEA

CONTEXT

Lipoprotein-associated phospholipase A2 (Lp-PLA2) is a novel biomarker for cardiovascular diseases (CVD) risk estimation with high specificity for vascular inflammation. Few studies have investigated Lp-PLA2 levels in patients with metabolic syndrome (MetS) and obstructive sleep apnea syndrome (OSAS).

OBJECTIVE

This study aimed to evaluate the role of Lp-PLA2 levels as a marker of vascular inflammation that contributes to cardiometabolic dysfunction in patients with MetS and OSAS.

DESIGN

This is a prospective case-control study.

SUBJECTS AND METHODS

83 men were enrolled. Following anthropometric measurements, laboratory analysis and overnight sleep study, patients were divided into three groups: MetS, OSAS with/without MetS. Serum Lp-PLA2 levels were determined by ELISA method.

RESULTS

Serum Lp-PLA2 levels were statistically significant among the three groups and were higher in OSAS with MetS group than those without MetS. A significant positive relationship between increased Lp-PLA2 level and CRP (C-reactive protein) and apnea-hypopnea index (AHI) was found. Average oxygen saturation (AvO2) and the lowest oxygen saturation were negatively correlated with Lp-PLA2. The number of desaturation events, oxygen desaturation index, AvO2, AHI and CRP were significant predictors of Lp-PLA2.

CONCLUSIONS

Lp-PLA2 levels are associated with OSAS severity and might play an important role in predicting CVD in OSAS with/without MetS.

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

Background

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

Methods

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

Results

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

Conclusions

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

Bioactive Carbohydrates and Peptides in Foods: An Overview of Sources, Downstream Processing Steps and Associated Bioactivities

Bioactive peptides and carbohydrates are sourced from a myriad of plant, animal and insects and have huge potential for use as food ingredients and pharmaceuticals. However, downstream processing bottlenecks hinder the potential use of these natural bioactive compounds and add cost to production processes. This review discusses the health benefits and bioactivities associated with peptides and carbohydrates of natural origin and downstream processing methodologies and novel processes which may be used to overcome these.

Phospholipase A2 regulation of lipid droplet formation

The classical regard of lipid droplets as mere static energy-storage organelles has evolved dramatically. Nowadays these organelles are known to participate in key processes of cell homeostasis, and their abnormal regulation is linked to several disorders including metabolic diseases (diabetes, obesity, atherosclerosis or hepatic steatosis), inflammatory responses in leukocytes, cancer development and neurodegenerative diseases. Hence, the importance of unraveling the cell mechanisms controlling lipid droplet biosynthesis, homeostasis and degradation seems evident Phospholipase A2s, a family of enzymes whose common feature is to hydrolyze the fatty acid present at the sn-2 position of phospholipids, play pivotal roles in cell signaling and inflammation. These enzymes have recently emerged as key regulators of lipid droplet homeostasis, regulating their formation at different levels. This review summarizes recent results on the roles that various phospholipase A2 forms play in the regulation of lipid droplet biogenesis under different conditions. These roles expand the already wide range of functions that these enzymes play in cell physiology and pathophysiology.