Extracellular phospholipases in atherosclerosis

Mechanism of oxidized phospholipid-related inflammatory response in vascular ageing

Vascular ageing is an important factor in the morbidity and mortality of the elderly. Atherosclerosis is a characteristic disease of vascular ageing, which is closely related to the enhancement of vascular inflammation. Phospholipid oxidation products are important factors in inducing cellular inflammation. Through interactions with vascular cells and immune cells, they regulate intracellular signaling pathways, activate the expression of various cytokines, and affect cell behavior, such as metabolic level, proliferation, apoptosis, etc. Intervention in lipid metabolism and anti-inflammation are the two key pathways of drugs for the treatment of atherosclerosis. This review aims to sort out the signaling pathway of oxidized phospholipids-induced inflammatory factors in vascular cells and immune cells and the mechanism leading to changes in cell behavior, and summarize the therapeutic targets in the inflammatory signaling pathway for the development of atherosclerosis drugs.

Biotechnologically potential genes in a polysaccharide-degrading epibiont of the Indonesian brown algae Hydroclathrus sp

BACKGROUND

Marine bacteria have recently attracted increasing attention to be harnessed for the production of valuable enzymes, vitamins, and bioactive compounds. Bacteria associated with the surfaces of marine macroalgae, called epibionts, are particularly interesting from ecological and biotechnological points of view, as they often exhibit antimicrobial activities to compete with pathogenic bacteria for nutrients and spaces. In search for biotechnologically potential genes from marine bacteria, we sequenced and analysed the genome of the epibiont HI03-3b, a polysaccharide-degrading bacterium associated with the surface of the Indonesian brown algae Hydroclathrus sp.

RESULTS

The algal epibiont HI03-3b has a genome of approximately 4,860,704 bp in size with 42.02 mol% G + C content, consisting of 5655 open reading frames (ORFs), 4409 genes coding for proteins (CDSs), 94 genes for tRNAs, and 32 genes for rRNAs. The genome sequence of HI03-3b was most closely related to that of Cytobacillus firmus NCTC10335 with the average amino acid identity (AAI) of 95.0 %, average nucleotide identity (ANI) of 94.1 %, and a recommended DNA-DNA hybridization (DDH) of 57.60 %. These scores are lower than the most frequently used standard for species demarcation (95% ANI cutoff) and the new species threshold (DDH > 70.0% for the same bacterial species). Some differences in genome features and gene composition were observed between HI03-3b and NCTC10335, such as genes encoding carbohydrate active enzymes. These suggest that HI03-3b is unique and likely a novel species within Cytobacillus genus, and we therefore proposed its name as Cytobacillus wakatobiense HI03-3b. Genome sequence analyses indicated the presence of genes involved not only in polysaccharide and protein degradation but also in vitamin and secondary metabolite biosynthesis. Some of them encode enzymes and compounds with biotechnological interest, such as protease, chitinase, subtilisin, pullulanase, and bacillolysin, which are often associated with antimicrobial or antibiofilm activities. This antimicrobial potential is supported by our finding that the extracellular protein fraction of this epibiont inhibited the growth of the bacterial pathogen Staphylococcus aureus.

CONCLUSION

The epibiont Cytobacillus HI03-3b harbours genes for polysaccharide and protein degradation as well as for natural product biosynthesis, suggesting its potential ecological roles in outcompeting other bacteria during biofilm formation as well as in protecting its algal host from predation. Due to the presence of genes for vitamin biosynthesis, it might also provide the algal host with vitamins for growth and development. Some of these metabolic genes are biotechnologically important, as they could become a platform for bioengineering to generate various seaweed-derived substances sustainably, such as antibiofilm agents and vitamins, which are beneficial for human health.

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.

Combined Proteome and Toxicology Approach Reveals the Lethality of Venom Toxins from Jellyfish Cyanea nozakii

Jellyfish are a type of poisonous cnidarian invertebrate that secrete lethal venom for predation or defense. Human beings often become victims of jellyfish stings accidentally while swimming or fishing and suffer severe pain, itching, swelling, inflammation, shock, and even death. Jellyfish venom is composed of various toxins, and the lethal toxin is the most toxic and hazardous component of the venom, which is responsible for deaths caused by jellyfish stings and envenomation. Our previous study revealed many toxins in jellyfish venom, including phospholipase A2, metalloproteinase, and protease inhibitors. However, it is still unknown which type of toxin is lethal and how it works. Herein a combined toxicology analysis, proteome strategy, and purification approach was employed to investigate the lethality of the venom of the jellyfish Cyanea nozakii. Toxicity analysis revealed that cardiotoxicity including acute myocardial infarction and a significant decrease in both heart rate and blood pressure is the primary cause of death. Purified lethal toxin containing a fraction of jellyfish venom was subsequently subjected to proteome analysis and bioinformation analysis. A total of 316 and 374 homologous proteins were identified, including phospholipase A2-like toxins and metalloprotease-like toxins. Furthermore, we confirmed that the lethality of the jellyfish venom is related to metalloproteinase activity but without any phospholipase A2 activity or hemolytic activity. Altogether, this study not only provides a comprehensive understanding of the lethal mechanism of jellyfish venom but also provides very useful information for the therapeutic or rescue strategy for severe jellyfish stings.

Elevated serum levels of lipoprotein‑associated phospholipase A2 predict mortality rates in patients with sepsis

Sepsis remains one of the leading contributors to mortality rates in the intensive care unit (ICU) and emergency intensive care unit (EICU). Therefore, any treatments against the agents which produce sepsis in a medical emergency, are welcome. Elevated serum levels of lipoprotein‑associated phospholipase A2 (Lp‑PLA2) have been reported in a small cohort of patients with inflammation. The present study evaluated serum levels of Lp‑PLA2 in patients with sepsis and investigated the role of Lp‑PLA2 in sepsis. The investigation involved the selection of 151 patients with sepsis admitted to the emergency department of the Affiliated Hospital of Nantong University (Nantong, China) and 30 healthy controls. All patients (39 with sepsis, 55 with severe sepsis and 57 with septic shock) were examined on admission to the EICU. A complete blood count was performed, and serum levels of Lp‑PLA2, C‑reactive protein, procalcitonin, and interleukin 6, sequential organ failure (SOFA) scores and Acute Physiology and Chronic Health Evaluation II (APACHE II) scores were determined on hospital admission. The EICU and overall mortality rates were evaluated at baseline. The present study also assessed various laboratory parameters, clinical data and inflammatory cytokines. The patient follow up duration was 90 days. The data suggested that the serum levels of Lp‑PLA2 on admission to the EICU in patients with sepsis were elevated, compared with those in healthy controls. The concentrations of Lp‑PLA2 were correlated with the severity of disease, and were significantly associated with experimental markers of inflammation and established prognostic scores. In the total cohort, persistently elevated levels of Lp‑PLA2 on admission for EICU treatment was a predictor of poor prognosis, and provided superior diagnostic use, compared with the prognostic scoring systems, including SOFA or APACHE II scores. Taken together, the results suggested that Lp‑PLA2, with respect to other markers of inflammation, may have a role as a prognostic marker in sepsis, and provide background evidence for further trials to evaluate the clinical and pathophysiologic roles of Lp‑PLA2 in sepsis. Persistently elevated serum concentrations of Lp‑PLA2 indicated an unfavorable outcome in patients with sepsis. In addition, the results indicated the potential role of Lp‑PLA2 as a prognostic biomarker in patients with sepsis during the early course of EICU treatment.

Screening of phospholipase A activity and its production by new actinomycete strains cultivated by solid-state fermentation

Novel microbial phospholipases A (PLAs) can be found in actinomycetes which have been poorly explored as producers of this activity. To investigate microbial PLA production, efficient methods are necessary such as high-throughput screening (HTS) assays for direct search of PLAs in microbial cultures and cultivation conditions to promote this activity. About 200 strains isolated with selected media for actinomycetes and mostly belonging to Streptomyces (73%) and Micromonospora (10%) genus were first screened on agar-plates containing the fluorophore rhodamine 6G and egg yolk phosphatidylcholine (PC) to detect strains producing phospholipase activity. Then, a colorimetric HTS assay for general PLA activity detection (cHTS-PLA) using enriched PC (≈60%) as substrate and cresol red as indicator was developed and applied; this cHTS-PLA assay was validated with known PLAs. For the first time, actinomycete strains were cultivated by solid-state fermentation (SSF) using PC as inductor and sugar-cane bagasse as support to produce high PLA activity (from 207 to 2,591 mU/g of support). Phospholipase activity of the enzymatic extracts from SSF was determined using the implemented cHTS-PLA assay and the PC hydrolysis products obtained, were analyzed by TLC showing the presence of lyso-PC. Three actinomycete strains of the Streptomyces genus that stood out for high accumulation of lyso-PC, were selected and analyzed with the specific substrate 1,2-α-eleostearoyl-sn-glycero-3-phosphocholine (EEPC) in order to confirm the presence of PLA activity in their enzymatic extracts. Overall, the results obtained pave the way toward the HTS of PLA activity in crude microbial enzymatic extracts at a larger scale. The cHTS-PLA assay developed here can be also proposed as a routine assay for PLA activity determination during enzyme purification,directed evolution or mutagenesis approaches. In addition, the production of PLA activity by actinomycetes using SSF allow find and produce novel PLAs with potential applications in biotechnology.

Lipoprotein-associated phospholipase A2, and subsequent cardiovascular events and mortality among patients with coronary heart disease

OBJECTIVE

The objective of this study is to evaluate the relevance of Lp-PLA₂ to risk prediction among coronary heart disease (CHD) patients.

METHODS

Lp-PLA₂ activity was measured in 2538 CHD patients included in the Bezafibrate Infarction Prevention (BIP) study.

RESULTS

Adjusting for patient characteristics and traditional risk factors, 1 standard deviation of Lp-PLA₂ was associated with a hazard ratio (HR) of 1.12 (95% confidence interval (CI): 1.00-1.25) for mortality and 1.03 (0.93-1.14) for cardiovascular events. Lp-PLA₂ did not significantly improve model discrimination, or calibration nor result in noteworthy reclassification.

CONCLUSIONS

Our results do not support added value of Lp-PLA₂ for predicting cardiovascular events or mortality among CHD patients beyond traditional risk factor.

Circulating Lp-PLA2 is associated with high valvuloarterial impedance and low arterial compliance in patients with aortic valve bioprostheses

BACKGROUND

We previously reported that plasma Lp-PLA2 was associated with aortic valve disease progression and degeneration of bioprostheses. Low systemic arterial compliance and high valvuloarterial impedance (Z(va)) are predictors of poor survival in patients with aortic valve disease. However, the prevalence of high Z(va) after AVR is largely unknown and whether Lp-PLA2 could predict Z(va) has not been documented. We investigated the relationships between plasma lipoprotein-associated phospholipase A2 (Lp-PLA2) mass and activity and valvuloarterial impedance (Z(va)), an index of global LV hemodynamic load, in patients that underwent aortic valve replacement (AVR).

METHODS

A total of 195 patients with aortic bioprostheses underwent echocardiographic assessment of the prosthetic aortic valve function 8±3.4 years after AVR. Lp-PLA2 mass and activity were measured.

RESULTS

In this group of patients, the mean Z(va) was elevated (5.73±1.21 mm Hg·ml(-1)·m(2)). In univariate analyses, Lp-PLA2 mass (p=0.003) and Lp-PLA2 activity (p=0.046) were associated with Z(va). After adjustment for covariates including age, gender, clinical risk factors, anti-hypertensive medications, body mass index and prosthesis size, Lp-PLA2 mass was associated with high Z(va) (≥4.5 mm Hg·ml(-1)·m(2)) (OR: 1.29, 95%CI: 1.10-1.53; p=0.005) and was inversely related with the systemic arterial compliance (β=-0.01, SEM=0.003; p=0.003).

CONCLUSIONS

An increased Z(va), an index of excessive hemodynamic load, was highly prevalent 8-year post-AVR and was independently related to circulating Lp-PLA2.

Membrane and inhibitor interactions of intracellular phospholipases A2

Studying phospholipases A2 (PLA2s) is a challenging task since they act on membrane-like aggregated substrates and not on monomeric phospholipids. Multidisciplinary approaches that include hydrogen/deuterium exchange mass spectrometry (DXMS) and computational techniques have been employed with great success in order to address important questions about the mode of interactions of PLA2 enzymes with membranes, phospholipid substrates and inhibitors. Understanding the interactions of PLA2s is crucial since these enzymes are the upstream regulators of the eicosanoid pathway liberating free arachidonic acid (AA) and other polyunsaturated fatty acids (PUFA). The liberation of AA by PLA2 enzymes sets off a cascade of molecular events that involves downstream regulators such as cyclooxygenase (COX) and lipoxygenase (LOX) metabolites leading to inflammation. Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) work by inhibiting COX, while Zileuton inhibits LOX and both rely on PLA2 enzymes to provide them with AA. That means PLA2 enzymes can potentially also be targeted to diminish inflammation at an earlier point in the process. In this review we describe extensive efforts reported in the past to define the interactions of PLA2 enzymes with membranes, substrate phospholipids and inhibitors using DXMS, molecular docking, and molecular dynamics (MD) simulations.

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.

Critical role of TLR2 and MyD88 for functional response of macrophages to a group IIA-secreted phospholipase A2 from snake venom

The snake venom MT-III is a group IIA secreted phospholipase A₂ (sPLA₂) enzyme with functional and structural similarities with mammalian pro-inflammatory sPLA₂s of the same group. Previously, we demonstrated that MT-III directly activates the innate inflammatory response of macrophages, including release of inflammatory mediators and formation of lipid droplets (LDs). However, the mechanisms coordinating these processes remain unclear. In the present study, by using TLR2^−/− or MyD88^−/− or C57BL/6 (WT) male mice, we report that TLR2 and MyD88 signaling have a critical role in MT-III-induced inflammatory response in macrophages. MT-III caused a marked release of PGE₂, PGD₂, PGJ₂, IL-1β and IL-10 and increased the number of LDs in WT macrophages. In MT-III-stimulated TLR2^−/− macrophages, formation of LDs and release of eicosanoids and cytokines were abrogated. In MyD88^−/− macrophages, MT-III-induced release of PGE₂, IL-1β and IL-10 was abrogated, but release of PGD₂ and PGJ₂ was maintained. In addition, COX-2 protein expression seen in MT-III-stimulated WT macrophages was abolished in both TLR2^−/− and MyD88^−/− cells, while perilipin 2 expression was abolished only in MyD88^−/− cells. We further demonstrated a reduction of saturated, monounsaturated and polyunsaturated fatty acids and a release of the TLR2 agonists palmitic and oleic acid from MT-III-stimulated WT macrophages compared with WT control cells, thus suggesting these fatty acids as major messengers for MT-III-induced engagement of TLR2/MyD88 signaling. Collectively, our findings identify for the first time a TLR2 and MyD88-dependent mechanism that underlies group IIA sPLA₂-induced inflammatory response in macrophages.

Influence of platelet-activating factor, lyso-platelet-activating factor and edelfosine on Langmuir monolayers imitating plasma membranes of cell lines differing in susceptibility to anti-cancer treatment: the effect of plasmalogen level

Three structurally related but differing in biological activities single-chained ether phospholipids (PAF (platelet-activating factor) and lyso-PAF) and an anti-cancer drug (edelfosine (ED)) were investigated in Langmuir monolayers imitating natural membranes. The aim of the undertaken experiments was to study the influence of these lipids on monolayers mimicking plasma membranes of cell lines differing in susceptibility to the anti-cancer activity of ED, i.e. promyelocytic leukaemia cells (HL-60) and promyeloblastic leukaemia cells (K-562). As these cells differ essentially in the cholesterol/phospholipid ratio and plasmalogen concentration in the membrane, we have carried out systematic investigations in artificial systems of various compositions. The results for model leukaemia cell membrane were compared with data acquired for systems imitating normal leucocytes. Our results show that the level of plasmalogens significantly modulates the influence of the single-chained phospholipids on the investigated systems. The experiments confirmed also that the interactions of ether lipids with a model membrane of HL-60 cells (in biological tests sensitive to ED) have opposite character when compared with K-562, being resistant to ED. Moreover, the values of the parameters characterizing monolayers serving as membrane models (strength of interactions, monolayers fluidity and morphology) proved both sensitivity of these cells to ED and lack of their susceptibility towards PAF. Interestingly, it has been found that lyso-PAF, which is usually described as an inactive precursor of PAF, displays a stronger effect on HL-60 model membranes than ED.

Lp-PLA2 is associated with structural valve degeneration of bioprostheses

OBJECTIVES

In this study, we sought to determine the metabolic markers associated with structural valve degeneration (SVD).

BACKGROUND

Structural valve degeneration (SVD) is the major cause of bioprosthetic valve failure leading to bioprostheses (BPs) stenosis or regurgitation. We hypothesized that lipoprotein-associated phospholipase A2 (Lp-PLA2) is involved in the SVD of BPs.

METHODS

We included 197 patients who underwent aortic valve replacement with a bioprosthetic valve and had echocardiographic follow-up to evaluate valve function. Moreover, explanted BPs (n = 39) were analysed by immunohistochemistry for the expression of Lp-PLA2.

RESULTS

After a mean follow-up of 7·9 ±0·2 years, forty-one patients (21%) were identified as developing SVD. Patients with SVD had significantly higher plasma level of Lp-PLA2 mass (151·8 ± 9·2 ng/mL vs. 133·2 ± 3·4 ng/mL, P = 0·03) and activity (27·6 ± 0·9 nmol/min/mL vs. 25·0 ± 0·4 nmol/min/mL, P = 0·005). Multivariate analysis revealed that Lp-PLA2 activity (OR: 1·09, 95% CI: 1·01-1·18; P = 0·03) was the strongest independent predictor of SVD. Immunohistochemistry studies of explanted BP showed that 77% of explanted BPs had the expression of Lp-PLA2, which correlated with the density of macrophages (CD68), and ox-LDL levels in bioprosthetic tissues.

CONCLUSIONS

Increased blood plasma activity of Lp-PLA2 is associated with higher prevalence of SVD. These findings open new avenues for the identification of patients at risk for SVD and for the development of pharmacotherapy aiming at the prevention of SVD.

Chemical modulation of glycerolipid signaling and metabolic pathways

Thirty years ago, glycerolipids captured the attention of biochemical researchers as novel cellular signaling entities. We now recognize that these biomolecules occupy signaling nodes critical to a number of physiological and pathological processes. Thus, glycerolipid-metabolizing enzymes present attractive targets for new therapies. A number of fields-ranging from neuroscience and cancer to diabetes and obesity-have elucidated the signaling properties of glycerolipids. The biochemical literature teems with newly emerging small molecule inhibitors capable of manipulating glycerolipid metabolism and signaling. This ever-expanding pool of chemical modulators appears daunting to those interested in exploiting glycerolipid-signaling pathways in their model system of choice. This review distills the current body of literature surrounding glycerolipid metabolism into a more approachable format, facilitating the application of small molecule inhibitors to novel systems. This article is part of a Special Issue entitled Tools to study lipid functions.

Gender-dependent correlations of carotid intima-media thickness with gene expression in blood

The mechanisms underlying gender differences in stroke incidence, risk, and outcome are uncertain. We sought to determine whether transcriptional profiles of circulating blood cells of men and women differentially correlated with carotid artery intima-media thickness (CIMT), a predictor of atherosclerosis and stroke risk. Gene expression in whole blood was measured using Affymetrix expression arrays in men (n=17) and women (n=35), aged 45-64 years, with at least one risk factor for stroke. Mean average CIMT was measured using B-mode ultrasound. Expression levels of 746 genes positively and 292 genes negatively correlated with CIMT only in women (p<0.05); 881 genes positively and 597 genes negatively correlated with CIMT only in men (p<0.05). Forty-one genes correlated with CIMT in men and women, but in opposite directions. These genes were associated with estrogen, cholesterol and lipid metabolism, inflammation, coagulation, and vasoreactivity. This pilot study provides the first proof of principle that gene expression in blood cells correlates with CIMT. These results point to potential pathophysiological mechanisms underlying sex differences in stroke risk. Since the sample size is small, the findings are preliminary and need to be confirmed in independent, larger studies.

Using hydrogen/deuterium exchange mass spectrometry to define the specific interactions of the phospholipase A2 superfamily with lipid substrates, inhibitors, and membranes

The phospholipase A(2) (PLA(2)) superfamily consists of 16 groups and many subgroups and constitutes a diverse set of enzymes that have a common catalytic activity due to convergent evolution. However, different PLA(2) types have unique three-dimensional structures and catalytic residues as well as specific tissue localization and distinct biological functions. Understanding how the different PLA(2) enzymes associate with phospholipid membranes, specific phospholipid substrate molecules, and inhibitors on a molecular basis has advanced in recent years due to the introduction of hydrogen/deuterium exchange mass spectrometry. Its theory, practical considerations, and application to understanding PLA(2)/membrane interactions are addressed.

Modified lipoproteins provide lipids that modulate dendritic cell immune function

Both physiological and pathological situations can result in biochemical changes of low-density lipoproteins (LDL). Because they can deliver signals to dendritic cells (DC), these modified lipoproteins now appear as regulators of the immune response. Among these modified lipoproteins, oxidized LDL (oxLDL) that accumulate during inflammatory conditions have been extensively studied. Numerous studies have shown that oxLDL induce the maturation of DC, enhancing their ability to activate IFNγ secretion by T cells. LDL treated by secreted phospholipase A(2) also promote DC maturation. Among the bioactive lipids generated by oxidation or phospholipase treatment of LDL, lysophosphatidylcholine (LPC) and some saturated fatty acids induce DC maturation whereas some unsaturated fatty acids or oxidized derivatives have opposite effects. Among other factors, the nuclear receptor peroxisome-proliferator activated receptor γ (PPARγ) plays a crucial role in this regulation. Non-modified lipoproteins also contribute to the regulation of DC function, suggesting that the balance between native and modified lipoproteins, as well as the biochemical nature of the LDL modifications, can regulate the activation threshold of DC. Here we discuss two pathological situations in which the impact of LDL modifications on inflammation and immunity could play an important role. During atherosclerosis, modified LDL accumulating in the arterial intima may interfere with DC maturation and function, promoting a Th1 immune response and a local inflammation favoring the development of the pathology. In patients chronically infected, the hepatitis C virus (HCV) interferes with lipoprotein metabolism resulting in the production of infectious modified lipoproteins. These lipo-viral-particles (LVP) are modified low-density lipoproteins containing viral material that can alter DC maturation and affect specific toll-like receptor signaling. In conclusion, lipoprotein modifications play an important role in the regulation of immunity by delivering signals of danger to DC and modulating their function.

Circulating levels of secretory- and lipoprotein-associated phospholipase A2 activities: relation to atherosclerotic plaques and future all-cause mortality

AIMS

Secretory- and lipoprotein-associated phospholipases A2 (sPLA2 and Lp-PLA2) are enzymes both suggested to be of importance for atherosclerosis. We investigated relationships between the activities of these enzymes in the circulation and atherosclerosis as well as future clinical events.

METHODS AND RESULTS

The population-based Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study included 1016 randomly selected subjects, all aged 70. The prevalence of carotid artery plaques was recorded by ultrasound (n= 954), and arterial stenosis was assessed by whole-body magnetic resonance angiography (WBMRA, n= 302). Secretory-associated phospholipase A2 [odds ratio 1.23 for 1 SD increase, 95% confidence interval (CI): 1.05-1.44, P= 0.007], but not Lp-PLA2 (P= 0.26), activity was significantly related to carotid atherosclerosis and to the amount of stenosis at WBMRA (P= 0.006) following adjustment for multiple risk factors (waist circumference, serum triglycerides, body mass index, C-reactive protein, high density lipoprotein-C, low density lipoprotein-C, triglycerides, GFR, fasting glucose, blood pressure, statin use, and exercise habits). Secretory-associated phospholipase A2 [hazard ratio (HR) 1.45 for 1 SD increase, 95% CI: 1.15-1.84, P= 0.001], but not Lp-PLA2 (HR 0.95, P= 0.55), activity was a significant risk factor for all-cause mortality (114 had died) during 7.0 years follow-up after adjustment for the risk factors described above. In a sample of 1029 post-myocardial infarction (MI) patients (French registry of Acute ST-elevation and non-ST-elevation Myocardial Infarction), sPLA2 (adjusted HR 1.32 for 1 unit increase, 95% CI: 1.02-1.71, P= 0.036), but not Lp-PLA2 (HR 1.03, P= 0.90), activity predicted death or recurrent MI during 1-year follow-up (n= 136 cases).

CONCLUSION

sPLA2 activity was related to atherosclerosis and predicted all-cause mortality in a sample of elderly subjects, as well as death or MI in post-MI patients.

Phospholipase A(2) enzymes in metabolic and cardiovascular diseases

PURPOSE OF REVIEW

The phospholipase A2 (PLA2) family of proteins includes lipolytic enzymes that liberate the sn-2 fatty acyl chains from phospholipids to yield nonesterified fatty acids and lysophospholipids. The purpose of this review is to discuss recent findings showing distinct roles of several of these PLA2 enzymes in inflammatory metabolic diseases such as diabetes and atherosclerosis.

RECENT FINDINGS

The group 1B PLA2 digestion of phospholipids in the intestinal lumen facilitates postprandial lysophospholipid absorption, which suppresses hepatic fatty acid oxidation leading to increased VLDL synthesis, decreased glucose tolerance, and promotion of tissue lipid deposition to accentuate diet-induced hyperlipidemia, diabetes, and obesity. Other secretory PLA2s promote inflammatory metabolic diseases by generating bioactive lipid metabolites to induce inflammatory cytokine production, whereas the major intracellular PLA2s, cPLA2α, and iPLA2, generate arachidonic acid and lysophosphatic acid in response to extracellular stimuli to activate leukocyte chemotactic response.

SUMMARY

Each member of the PLA2 family of enzymes serves a distinct role in generating active lipid metabolites that promote inflammatory metabolic diseases including atherosclerosis, hyperlipidemia, obesity, and diabetes. The development of specific drugs that target one or more of these PLA2 enzymes may be novel strategies for treatment of these chronic inflammatory metabolic disorders.