Specific differential expression of phospholipase A2 subtypes in rat cerebellum

Phospholipase A₂ (PLA₂) is a family of enzymes playing diverse roles in lipid signaling in neurons and glia cells. In this study, we examined the expression of subtypes of PLA₂ in the cerebellum using immunolabeling and in situ hybridization methods. Two Ca²⁺-dependent cytosolic subtypes (cPLA₂α and cPLA₂β), one Ca²⁺-independent cytosolic subtype (iPLA₂), and two secretory subtypes (sPLA₂IIA and sPLA₂V) were detected in the cerebellum. cPLA₂α is present in somata and dendrites of Purkinje cells, while sPLA₂IIA is associated with the endoplasmic reticulum in perinuclear regions of Purkinje cell somata. iPLA₂ is present in granule cells, stellate cells and also in the nucleus of Purkinje cells. In addition, cPLA₂β is localized in granule cells, and sPLA₂V in Bergmann glia cells. These results provide an important basis for identifying functional roles of PLA₂s in the cerebellum.     

The molecular mechanism of human group IIA phospholipase A2 inactivation by bolinaquinone

The molecular basis of the human group IIA secretory phospholipase A₂ inactivation by bolinaquinone (BLQ), a hydroxyquinone marine terpenoid, has been investigated for the comprehension of its relevant antiinflammatory properties, through the combination of spectroscopic techniques, biosensors analysis, mass spectrometry (MS) and molecular docking. Indeed, sPLA₂s are well known to be implicated in the pathogenesis of inflammation such as rheumatoid arthritis, septic shock, psoriasis and asthma. Our results suggest a mechanism of competitive inhibition guided by a non‐covalent molecular recognition event, disclosing the key role of the BLQ hydroxyl‐quinone moiety in the chelation of the catalytic Ca²⁺ ion inside the enzyme active site. The understanding of the sPLA₂‐IIA inactivation mechanism by BLQ could be useful for the development of a new chemical class of PLA₂ inhibitors, able to specifically target the enzyme active site. Copyright © 2009 John Wiley & Sons, Ltd.     

Suppression of murine endotoxic shock by sPLA2 inhibitor,indoxam, through group IIA sPLA2-independent mechanisms

Endotoxic shock is a systemic inflammatory process, involving a variety of proinflammatory mediators. Two types of secretory phospholipase A₂ (sPLA₂) have been implicated in this process. Group IB sPLA₂ (PLA₂-IB) binds to the PLA₂ receptor (PLA₂R), and PLA₂R-deficient mice exhibit resistance to endotoxin-induced lethality with reduced plasma levels of proinflammatory cytokines, such as TNF-α. Group IIA sPLA₂ (PLA₂-IIA) is found in many tissues and cell types, and local and systemic levels are elevated under numerous inflammatory conditions including sepsis. In this study, we investigated the effect of a specific sPLA₂ inhibitor, indoxam, on murine endotoxic shock. Indoxam suppressed the elevation of plasma TNF-α with a similar potency in PLA₂-IIA-expressing and PLA₂-IIA-deficient mice after LPS challenge. In PLA₂-IIA-deficient mice, indoxam also suppressed the elevation of plasma IL-1β, IL-6 and NO, and prolonged survival after LPS challenge. Indoxam was found to block the PLA₂-IB binding to murine PLA₂R with a high potency (K_i=30 nM). The inhibitory effects of indoxam on the LPS-induced elevation of plasma TNF-α levels could not be observed in mice deficient in PLA₂R. These findings suggest that indoxam blocks the production of proinflammatory cytokines during endotoxemia through PLA₂-IIA-independent mechanisms, possibly via blockade of the PLA₂R function.     

Isozymes inhibited by active site blocking: versatility of calcium indifferent hesperidin binding to phospholipase A2 and its significance

sPLA₂ is released under inflammatory conditions from neutrophils, basophils and T-cells. They cleave the cellular phospholipids leading to the release of arachidonic acid and there by provide intermediates for biosynthesis of inflammatory mediators. The focus of this study is on the interaction of hesperidin, a natural flavonoid with Group IB, IIA, and V and X isozymes of sPLA₂. Affinity of hesperidin towards PLA₂ isozymes was analyzed through enzymatic studies and molecular modeling. The experiments showed that hesperidin competitively inhibited PLA₂ with IC₅₀ of 5.1?µM. Molecular modeling studies revealed the association of hesperidin with the docking scores ?6.90, ?9.53, ?5.63 and ?8.29?kcal for isozymes Group IB, IIA, V and X of PLA₂ respectively. Their binding energy values were calculated as ?20.25, ?21.63, ?21.66 and ?33.43?kcal for the Group IB, IIA, V and X respectively. Structural model for Group V was made by homology modeling since no structural coordinates were available. Molecular dynamics studies were carried out to evaluate the structural stability of protein ligand complex. The analyses showed that hesperidin blocked the entry of the substrate to the active site of PLA₂ and it was indifferent to the differences of the isozymes. Hence, hesperidin might serve as lead for designing highly specific anti-inflammatory drugs directed to the PLA₂ isozyme specific to various diseases, with IC₅₀ value of therapeutic significance.     

Secretory phospholipase A2 promotes MMP‐9‐mediated cell death by degrading type I collagen via the ERK pathway at an early stage of chondrogenesis

Background information. sPLA₂ (secretory phospholipase A₂) has been implicated in a wide range of cellular responses, including cell proliferation and ECM (extracellular matrix) remodelling. Even though ECM remodelling is an essential step for chondrogenesis, the expression and functions of sPLA₂ during chondrogenesis have not been studied. Results. In the present study, for the first time, we detect the secretion of sPLA₂ during limb development and suggest that sPLA₂ influences the proliferation and/or survival of limb mesenchymal cells. Treatment of wing bud mesenchymal cells with exogenous sPLA₂ promoted cell death by activating MMP‐9 (matrix metalloproteinase‐9) and increasing type I collagen degradation. The additive chondro‐inhibitory actions were induced by co‐treatment of mp‐BSA (p‐aminophenyl‐mannopyranoside‐BSA), a known ligand of the mannose receptor. Chondro‐inhibitory actions by sPLA₂ were prevented by functional blocking of FcRY (chicken yolk sac IgY receptor), a mannose receptor family member that is the orthologue of the mammalian PLA₂ (phospholipase A₂) receptor and by inhibition of ERK (extracellular‐signal‐regulated kinase) activity. Conclusions. Taken together, our results suggest that elevated levels of sPLA₂ secreted by wing bud mesenchymal cells promote type I collagen degradation by MMP‐9 in a manner typical of receptor‐mediated signalling and that these events lead to cell death.     

Phosphoinositides kinases in brain aging and amyloid beta neurotoxicity

Brain platelet-activating factor (PAF) is a lipid mediator involved in neurotransmission and in LTP. It has been reported that the induction of LTP by high frequency stimulation increases the activity of the enzymes responsible for its synthesis by a still unknown mechanism ( 1 ). One of the two biosynthetic pathways is Ca²⁺-dependent and transforms a membrane ether phospholipid into PAF by a sequence of two reactions being the first one, catalyzed by a phospholipase A₂ (PLA₂), rate limiting. Overproduction of PAF, taking place in pathological conditions, contributes to brain damage. Various PLA₂s are present in brain tissue and, particularly, sPLA₂-IIA is very likely involved in the production of PAF as its expression increases in pathological conditions. Recently, we have found the release of sPLA₂-IIA from rat brain cortex mitochondria and its association with nuclear membranes, which might be an intracellular target for the enzyme.     

Activation of cytosolic phospholipase A2 in permeabilized human neutrophils

Neutrophils (PMN) contain two types of phospholipase A₂ (PLA₂), a 14 kDa ‘secretory’ Type II PLA₂ (sPLA₂) and an 85 kDa ‘cytosolic’ PLA₂ (cPLA₂), that differ in a number of key characteristics: (1) cPLA₂ prefers arachidonate (AA) as a substrate but hydrolyzes all phospholipids; sPLA₂ is not AA specific but prefers ethanolamine containing phosphoacylglycerols. (2) cPLA₂ is active at nM calcium (Ca²⁺) concentrations; sPLA₂ requires μM Ca²⁺ levels. (3) cPLA₂ activity is regulated by phosphorylation; sPLA₂ lacks phosphorylation sites. (4) cPLA₂ is insensitive to reduction; sPLA₂ is inactivated by agents that reduce disulfide bonds. We utilized PMN permeabilized with Staphylococcus aureus α-toxin to determine whether one or both forms of PLA₂ were activated in porated cells under conditions designed to differentiate between the two enzymes. PMN were labeled with [³H]AA to measure release from phosphatidylcholine and phosphatidylinositol; gas chromatography-mass spectrometry was utilized to determine total AA release (mainly from phosphatidylethanolamine) and to asses oleate and linoleate mass. A combination of 500 nM Ca²⁺, a guanine nucleotide, and stimulation with n-formyl-met-leu-phe (FMLP) were necessary to induce maximal AA release in permeabilized PMN measured by either method; AA was preferentially released. [³H]AA and AA mass release occurred in parallel over time. A hydrolyzable form of ATP was necessary for maximum AA release and staurosporin inhibited PLA₂ activation. Dithiothreitol treatment had little affect on [³H]AA release and metabolism but inhibited AA mass release. Assay of cell supernatants after cofactor addition did not detect sPLA₂ activity and the cytosolic buffer utilized did not support activity of recombinant sPLA₂. These results strongly suggested that cPLA₂ was the enzyme activated in the permeabilized cell model and this is the first report which unambiguously demonstrates AA release in response to activation of a specific type of PLA₂ in PMN.     

Phospholipase A2-like activity of human bocavirus VP1 unique region

Human bocavirus (HBoV) is a new parvovirus first discovered in 2005, which is associated with acute respiratory infection. Analysis of sequence homology has revealed that a putative phospholipase A₂ (PLA₂) motif exists in the VP1 unique region of HBoV. However, little is known about whether the VP1 unique region of HBoV has PLA₂ enzymatic activity and how these critical residues contribute to its PLA₂ activity. To address these issues, the VP1 unique region protein and four of its mutants, were expressed in Eschericha coli. The purified VP1 unique protein (VP1U) showed a typical Ca²⁺-dependent secreted PLA₂-like (sPLA₂) activity, which was inhibited by sPLA₂-specific inhibitors in a time-dependent manner. Mutation of one of the amino acids (21Pro, 41His, 42Asp or 63Asp) in VP1U almost eliminated the sPLA₂ activity of HBoV VP1U. These data indicate that VP1U of HBoV has sPLA₂-like enzymatic activity, and these residues are crucial for its sPLA₂-like activity. Potentially, VP1U may be a target for the development of anti-viral drugs for HBoV.     

Upregulation of Fas and FasL in Taiwan cobra phospholipase A2‐treated human neuroblastoma SK‐N‐SH cells through ROS‐ and Ca2+‐mediated p38 MAPK activation

The aim of the present study is to elucidate the signaling pathway involved in death of human neuroblastoma SK‐N‐SH cells induced by Naja naja atra phospholipase A₂ (PLA₂). Upon exposure to PLA₂, p38 MAPK activation, ERK inactivation, ROS generation, increase in intracellular Ca²⁺ concentration, and upregulation of Fas and FasL were found in SK‐N‐SH cells. SB202190 (p38MAPK inhibitor) suppressed upregulation of Fas and FasL. N‐Acetylcysteine (ROS scavenger) and BAPTA‐AM (Ca²⁺ chelator) abrogated p38 MAPK activation and upregulation of Fas and FasL expression, but restored phosphorylation of ERK. Activated ERK was found to attenuate p38 MAPK‐mediated upregulation of Fas and FasL. Deprivation of catalytic activity could not diminish PLA₂‐induced cell death and Fas/FasL upregulation. Moreover, the cytotoxicity of arachidonic acid and lysophosphatidylcholine was not related to the expression of Fas and FasL. Taken together, our results indicate that PLA₂‐induced cell death is, in part, elicited by upregulation of Fas and FasL, which is regulated by Ca²⁺‐ and ROS‐evoked p38 MAPK activation, and suggest that non‐catalytic PLA₂ plays a role for the signaling pathway. J. Cell. Biochem. 106: 93–102, 2009. © 2008 Wiley‐Liss, Inc.     

High Plasma Phospholipase A2 Activity,Inflammation Markers,and LDL Alterations in Obesity With or Without Type 2 Diabetes

Plasma phospholipases A₂ (PLA₂) hydrolyze phospholipids of circulating lipoproteins or deposited in arteries producing bioactive lipids believed to contribute to the atherosclerotic inflammatory response. PLA₂(s) are elevated in obesity and type 2 diabetes (T2D) but it is not clear which of these conditions is the cause since they frequently coexist. This study attempts to evaluate if high plasma PLA₂(s) activities and markers of their effects in lipoproteins are associated with obesity or T2D diabetes, or with both. Total PLA₂ and Ca²⁺‐dependent and ‐independent activities, lipids, lipoproteins, apoAI, and apoB apolipoproteins and affinity of apoB‐lipoproteins for arterial proteoglycans were measured, as well as Inflammation markers. These parameters were evaluated in plasma samples of four groups: (i) apparently healthy controls with normal BMI (nBMI), (ii) obese subjects with no T2D, (iii) patients with T2D but with nBMI, and (iv) obese patients with T2D. PLA₂ activities were measured in the presence and absence of Ca²⁺ and in the presence of specific inhibitors. Obese subjects, with or without T2D, had high activities of total PLA₂ and of Ca²⁺‐dependent and Ca²⁺‐independent enzymes. The activities were correlated with inflammation markers in obese subjects with and without diabetes and with alterations of low‐density lipoproteins (LDLs) that increased their affinity for arterial proteoglycans. Ca²⁺‐dependent secretory (sPLA₂) enzymes were the main responsible of the obesity‐associated high activity. We speculate that augmented PLA₂(s) activity that increases affinity of circulating LDL for arterial intima proteoglycans could be another atherogenic component of obesity.     

Simultaneous inhibition of anti‐coagulation and inflammation: crystal structure of phospholipase A2 complexed with indomethacin at 1.4 Å resolution reveals the presence of the new common ligand‐binding site

A novel ligand‐binding site with functional implications has been identified in phospholipase A₂ (PLA₂). The binding of non‐steroidal anti‐inflammatory agent indomethacin at this site blocks both catalytic and anti‐coagulant actions of PLA₂. A group IIA PLA₂ has been isolated from Daboia russelli pulchella (Russell's viper) which is enzymatically active as well as induces a strong anti‐coagulant action. The binding studies have shown that indomethacin reduces the effects of both anti‐coagulant and pro‐inflammatory actions of PLA₂. A group IIA PLA₂ was co‐crystallized with indomethacin and the structure of the complex has been determined at 1.4 Å resolution. The structure determination has revealed the presence of an indomethacin molecule in the structure of PLA₂ at a site which is distinct from the conventional substrate‐binding site. One of the carboxylic group oxygen atoms of indomethacin interacts with Asp 49 and His 48 through the catalytically important water molecule OW 18 while the second carboxylic oxygen atom forms an ionic interaction with the side chain of Lys 69. It is well known that the residues, His 48 and Asp 49 are essential for catalysis while Lys 69 is a part of the anti‐coagulant loop (residues, 54–77). Indomethacin binds in such a manner that it blocks the access to both, it works as a dual inhibitor for catalytic and anti‐coagulant actions of PLA₂. This new binding site in PLA₂ has been observed for the first time and indomethacin is the first compound that has been shown to bind at this novel site resulting in the prevention of anti‐coagulation and inflammation. Copyright © 2009 John Wiley & Sons, Ltd.     

Biochemical characteristics of immune-associated phospholipase A<Subscript>2</Subscript> and its inhibition by an entomopathogenic bacterium, <Emphasis Type="Italic">Xenorhabdus nematophila</Emphasis>

An entomopathogenic bacterium, Xenorhabdus nematophila, induces an immunosuppression of target insects by inhibiting phospholipase A₂ (PLA₂) activity. Recently, an immune-associated PLA₂ gene was identified from the red flour beetle, Tribolium castaneum. This study cloned this PLA₂ gene in a bacterial expression vector to produce a recombinant enzyme. The recombinant T. castaneum PLA₂ (TcPLA₂) exhibited its characteristic enzyme activity with substrate concentration, pH, and ambient temperature. Its biochemical characteristics matched to a secretory type of PLA₂ (sPLA₂) because its activity was inhibited by dithiothreitol (a reducing agent of disulfide bond) and bromophenacyl bromide (a specific sPLA₂ inhibitor) but not by methylarachidonyl fluorophosphonate (a specific cytosolic type of PLA₂). The X. nematophila culture broth contained PLA₂ inhibitory factor(s), which was most abundant in the media obtained at a stationary bacterial growth phase. The PLA₂ inhibitory factor(s) was heat-resistant and extracted in both aqueous and organic fractions. Effect of a PLA₂-inhibitory fraction on the immunosuppression of T. castaneum was equally comparable with that resulted from inhibition of the TcPLA₂ gene expression by RNA interference.     

In silico and in vitro characterization of phospholipase A2 isoforms from soybean (Glycine max)

At the present, no secreted phospholipase A₂ (sPLA₂) from soybean (Glycine max) was investigated in detail. In this work we identified five sequences of putative secreted sPLA₂ from soybean after a BLAST search in G. max database. Sequence analysis showed a conserved PA2c domain bearing the Ca²⁺ binding loop and the active site motif. All the five mature proteins contain 12 cysteine residues, which are commonly conserved in plant sPLA₂s. We propose a phylogenetic tree based on sequence alignment of reported plant sPLA₂s including the novel enzymes from G. max. According to PLA₂ superfamily, two of G. max sPLA₂s are grouped as XIA and the rest of sequences as XIB, on the basis of differences found in their molecular weights and deviating sequences especially in the N- and C-terminal regions of the isoenzymes. Furthermore, we report the cloning, expression and purification of one of the putative isoenzyme denoted as GmsPLA₂-XIA-1. We demonstrate that this mature sPLA₂ of 114 residues had PLA₂ activity on Triton:phospholipid mixed micelles and determine the kinetic parameters for this system. We generate a model based on the known crystal structure of sPLA₂ from rice (isoform II), giving first insights into the three-dimensional structure of folded GmsPLA₂-XIA-1. Besides describing the spatial arrangement of highly conserved pair HIS-49/ASP-50 and the Ca⁺² loop domains, we propose the putative amino acids involved in the interfacial recognition surface. Additionally, molecular dynamics simulations indicate that calcium ion, besides its key function in the catalytic cycle, plays an important role in the overall stability of GmsPLA₂-XIA-1 structure.     

Expression of phospholipases A2 in primary human lung macrophages: Role of cytosolic phospholipase A2-α in arachidonic acid release and platelet activating factor synthesis

Macrophages are a major source of lipid mediators in the human lung. Expression and contribution of cytosolic (cPLA₂) and secreted phospholipases A₂ (sPLA₂) to the generation of lipid mediators in human macrophages are unclear. We investigated the expression and role of different PLA₂s in the production of lipid mediators in primary human lung macrophages. Macrophages express the alpha, but not the zeta isoform of group IV and group VIA cPLA₂ (iPLA₂). Two structurally-divergent inhibitors of group IV cPLA₂ completely block arachidonic acid release by macrophages in response to non-physiological (Ca²⁺ ionophores and phorbol esters) and physiological agonists (lipopolysaccharide and Mycobacterium protein derivative). These inhibitors also reduce by 70% the synthesis of platelet-activating factor by activated macrophages. Among the full set of human sPLA₂s, macrophages express group IIA, IID, IIE, IIF, V, X and XIIA, but not group IB and III enzymes. Me-Indoxam, a potent and cell impermeable inhibitor of several sPLA₂s, has no effect on arachidonate release or platelet-activating factor production. Agonist-induced exocytosis is not influenced by cPLA₂ inhibitors at concentrations that block arachidonic acid release. Our results indicate that human macrophages express cPLA₂-alpha, iPLA₂ and several sPLA₂s. Cytosolic PLA₂-alpha is the major enzyme responsible for lipid mediator production in human macrophages.     

Involvement of phospholipase A<Subscript>2</Subscript> in the response of <Emphasis Type="Italic">Solanum</Emphasis> species to an elicitor from <Emphasis Type="Italic">Phytophthora infestans</Emphasis>

Changes in activity of phospholipase A₂ (PLA₂), a key enzyme in lipid metabolism and signal network in defence mechanisms, were investigated in Solanum species and Phytophthora infestans interaction. We have compared PLA₂ activity in response to an elicitor, a culture filtrate (CF) derived from P. infestans, in non-host resistant Solanum nigrum var. gigantea, field resistant S. tuberosum cv Bzura and susceptible S. tuberosum clone H-8105. To elucidate the contribution of specific forms of PLA₂ to plant defence mechanism reasonably selective PLA₂ inhibitors, haloenol lactone suicide substrate (HELSS) and p-bromophenacyl bromide (BPB), which discriminate between Ca⁺²-independent PLA₂ (iPLA₂) and Ca⁺²-dependent secretory PLA₂ (sPLA₂), were used. The in vivo and in vitro effects of the inhibitors on PLA₂ activity and on generation of reactive oxygen species (ROS) induced by CF in the studied plants were assayed. We found that PLA₂ activity increased in response to CF treatment, displaying various kinetics and intensity depending on the resistance status of a given genotype. Differences among the genotypes in the effects of each inhibitor on CF-induced PLA₂ activity and on ROS production may reflect the diversity of PLA₂ isoforms in plants. Contrary to BPB, the inhibitory effect of HELSS was observable mainly on CF-induced PLA₂ activity, which suggests that iPLA₂ participates in signal transduction in defence reactions. Various effects of the two inhibitors on PLA₂ activity and ROS production suggest different contribution of sPLA₂ and iPLA₂ to modulation of defence reactions in the interaction between Solanum genotypes and P. infestans.     

Emerging roles of secreted phospholipase A2 enzymes: An update

Phospholipase A₂ (PLA₂) enzymes catalyze the hydrolysis of the sn-2 position of glycerophospholipids to produce free fatty acids and lysophospholipids. More than one third of the mammalian PLA₂ enzymes belong to the secreted PLA₂ (sPLA₂) family, which consists of low molecular mass, Ca²⁺-requiring enzymes with a His–Asp catalytic dyad. Individual sPLA₂ enzymes exhibit unique tissue and cellular localizations and specific enzymatic properties, suggesting their distinct biological roles. The past decade has met a new era of the sPLA₂ research field toward deciphering their in vivo functions by developing several specific tools and methods. These include i) the production of transgenic and knockout mouse lines for several sPLA₂s, ii) the development of specific analytical tools including the production of large amounts of recombinant sPLA₂ proteins, and iii) applying mass spectrometry lipidomics to unveil their specific enzymatic properties occurring in vivo. It is now obvious that individual sPLA₂s are involved in diverse biological events through lipid mediator-dependent and -independent processes, act redundantly or non-redundantly in the context of physiology and pathophysiology, and may represent potential drug targets or novel bioactive molecules in certain situations. In this review, we will highlight the newest understanding of the biological roles of sPLA₂s in the past few years.     

Proteolysis of Apolipoprotein A-I by Secretory Phospholipase A2: A NEW LINK BETWEEN INFLAMMATION AND ATHEROSCLEROSIS*

In the acute phase of the inflammatory response, secretory phospholipase A₂ (sPLA₂) reaches its maximum levels in plasma, where it is mostly associated with high density lipoproteins (HDL). Overexpression of human sPLA₂ in transgenic mice reduces both HDL cholesterol and apolipoprotein A-I (apoA-I) plasma levels through increased HDL catabolism by an unknown mechanism. To identify unknown PLA₂-mediated activities on the molecular components of HDL, we characterized the protein and lipid products of the PLA₂ reaction with HDL. Consistent with previous studies, hydrolysis of HDL phospholipids by PLA₂ reduced the particle size without changing its protein composition. However, when HDL was destabilized in the presence of PLA₂ by the action of cholesteryl ester transfer protein or by guanidine hydrochloride treatment, a fraction of apoA-I, but no other proteins, dissociated from the particle and was rapidly cleaved. Incubation of PLA₂ with lipid-free apoA-I produced similar protein fragments in the range of 6–15 kDa, suggesting specific and direct reaction of PLA₂ with apoA-I. Mass spectrometry analysis of isolated proteolytic fragments indicated at least two major cleavage sites at the C-terminal and the central domain of apoA-I. ApoA-I proteolysis by PLA₂ was Ca²⁺-independent, implicating a different mechanism from the Ca²⁺-dependent PLA₂-mediated phospholipid hydrolysis. Inhibition of proteolysis by benzamidine suggests that the proteolytic and lipolytic activities of PLA₂ proceed through different mechanisms. Our study identifies a previously unknown proteolytic activity of PLA₂ that is specific to apoA-I and may contribute to the enhanced catabolism of apoA-I in inflammation and atherosclerosis.     

Phospholipase A2 subclasses in acute respiratory distress syndrome

Phospholipases A₂ (PLA₂) catalyse the cleavage of fatty acids esterified at the sn-2 position of glycerophospholipids. In acute lung injury-acute respiratory distress syndrome (ALI-ARDS) several distinct isoenzymes appear in lung cells and fluid. Some are capable to trigger molecular events leading to enhanced inflammation and lung damage and others have a role in lung surfactant recycling preserving lung function: Secreted forms (groups sPLA₂-IIA, -V, -X) can directly hydrolyze surfactant phospholipids. Cytosolic PLA₂ (cPLA₂-IVA) requiring Ca²⁺ has a preference for arachidonate, the precursor of eicosanoids which participate in the inflammatory response in the lung. Ca²⁺-independent intracellular PLA₂s (iPLA₂) take part in surfactant phospholipids turnover within alveolar cells. Acidic Ca²⁺-independent PLA₂ (aiPLA₂), of lysosomal origin, has additionally antioxidant properties, (peroxiredoxin VI activity), and participates in the formation of dipalmitoyl-phosphatidylcholine in lung surfactant. PAF-AH degrades PAF, a potent mediator of inflammation, and oxidatively fragmented phospholipids but also leads to toxic metabolites. Therefore, the regulation of PLA₂ isoforms could be a valuable approach for ARDS treatment.