Emerging roles of secreted phospholipase A2 enzymes: the 3rd edition

The receptor binding mechanism of mouse sPLA2 group IIE

Secreted phospholipase A2s (sPLA2s) participate in physiological function by their enzyme and receptor binding activity. Muscle-type phospholipase A2 receptor (M-type PLA2R) is the sPLA2 binding protein with the highest affinity so far, and also inhibits the enzyme activity of sPLA2. There is species specificity and pH dependence for the binding of M-type PLA2R to sPLA2. Mouse sPLA2 Group IIE (mGIIE) has been verified to have a high affinity for mouse M-type PLA2R (M-type mPLA2R) at the nanomolar scale. For further exploration of the receptor binding mechanism of GIIE, in this study, we use Alphafold Multimer to generate complex models of mGIIE with the M-type mPLA2R ectodomain, wild-type CTLD5 domain of mPLA2R, and three CTLD5 mutants, respectively. mPLA2R-mGIIE models exhibit heterogeneous extended mPLA2R conformations with uncovered sPLA2-binding surface of CTLD5 domain. Complexed models of mGIIE with wild-type and mutated mCTLD5 further confirm that helix α1 of mCTLD5, especially essential residues F838 and W842, interact with the substrate pocket of mGIIE and thus inhibit its enzyme activity. Peptides from helix α1 of mCTLD5 are verified to inhibit the enzymatic activity of mGIIE. This AI-guided research would substantially accelerate our understanding of the functional study of GIIE, and provide the lead-peptide for the further inhibitor design of sPLA2.

Secreted Phospholipases A2: Drivers of Inflammation and Cancer

Secreted phospholipase 2 (sPLA2) is the largest family of phospholipase A2 (PLA2) enzymes with 11 mammalian isoforms. Each sPLA2 exhibits different localizations and specific properties, being involved in a very wide spectrum of biological processes. The enzymatic activity of sPLA2 has been well described; however, recent findings have shown that they could regulate different signaling pathways by acting directly as ligands. Arachidonic acid (AA) and its derivatives are produced by sPLA2 in collaboration with other molecules in the extracellular space, making important impacts on the cellular environment, being especially relevant in the contexts of immunity and cancer. For these reasons, this review focuses on sPLA2 functions in processes such as the promotion of EMT, angiogenesis, and immunomodulation in the context of tumor initiation and progression. Finally, we will also describe how this knowledge has been applied in the search for new sPLA2 inhibitory compounds that can be used for cancer treatment.

Phospholipase A2 expression in prostate cancer as a biomarker of good prognosis: A comprehensive study in patients with long follow-up

BACKGROUND

Phospholipase A2 (PLA2) is a large family of enzymes involved in the inflammatory process that catalyzes the hydrolysis of membrane phospholipids, leading to the production of free fatty acids and lysophospholipids, starting the arachidonic acid cascade. Their expression has been related to the behavior of several cancers. Our objective is to search for PLA2 expression in prostate cancer (PCa) tissue that correlates with prognosis and survival.

METHODS

Using qRT-PCR, we analyzed the expression levels of PLA2G1B, PLA2G2A, PLA2G2D, PLA2G4A, PLA2G4B, PLA2G4C, PLA2G4D, PLA2G4E, PLA2G4F, PLA2G6, PLA2G7, PLA2G16, PNPLA1, and PNPLA2 in PCa tissue from 108 patients submitted to radical prostatectomy, followed by a mean time of 163 months.

RESULTS

All PLA2 was overexpressed in PCa compared to normal tissue. Interestingly, higher expression of some PLA2 was related to favorable prognostic factors: lower levels of PSA (PLA2G2A, PLA2G4D), lower rates of lymph node metastasis (PLA2G16 and PLA2G1B), and organ-confined disease (PLA2G4A). Most importantly, PLAG4B was independently related to longer disease-free survival.

CONCLUSION

This is the first study exploring comprehensively the expression levels of PLA2 in PCa, showing that the higher expression of some PLA2 should be used as biomarkers of good prognosis and longer disease-free survival.

Multicentric investigations of the role in the disease severity of accelerated phospholipid changes in COVID-19 patient airway

CONTEXT

The changes in host membrane phospholipids are crucial in airway infection pathogenesis. Phospholipase A2 hydrolyzes host cell membranes, producing lyso-phospholipids and free fatty acids, including arachidonic acid (AA), which contributes significantly to lung inflammation.

AIM

Follow these changes and their evolution from day 1, day 3 to day 7 in airway aspirates of 89 patients with COVID-19-associated acute respiratory distress syndrome and examine whether they correlate with the severity of the disease. The patients were recruited in three French intensive care units. The analysis was conducted from admission to the intensive care unit until the end of the first week of mechanical ventilation.

RESULTS

In the airway aspirates, we found significant increases in the levels of host cell phospholipids, including phosphatidyl-serine and phosphatidyl-ethanolamine, and their corresponding lyso-phospholipids. This was accompanied by increased levels of AA and its inflammatory metabolite prostaglandin E2 (PGE2). Additionally, enhanced levels of ceramides, sphingomyelin, and free cholesterol were observed in these aspirates. These lipids are known to be involved in cell death and/or apoptosis, whereas free cholesterol plays a role in virus entry and replication in host cells. However, there were no significant changes in the levels of dipalmitoyl-phosphatidylcholine, the major surfactant phospholipid. A correlation analysis revealed an association between mortality risk and levels of AA and PGE2, as well as host cell phospholipids.

CONCLUSION

Our findings indicate a correlation between heightened cellular phospholipid modifications and variations in AA and PGE2 with the severity of the disease in patients. Nevertheless, there is no indication of surfactant alteration in the initial phases of the illness.

Pla2g12b drives expansion of triglyceride-rich lipoproteins

Vertebrates transport hydrophobic triglycerides through the circulatory system by packaging them within amphipathic particles called Triglyceride-Rich Lipoproteins. Yet, it remains largely unknown how triglycerides are loaded onto these particles. Mutations in Phospholipase A2 group 12B (PLA2G12B) are known to disrupt lipoprotein homeostasis, but its mechanistic role in this process remains unclear. Here we report that PLA2G12B channels lipids within the lumen of the endoplasmic reticulum into nascent lipoproteins. This activity promotes efficient lipid secretion while preventing excess accumulation of intracellular lipids. We characterize the functional domains, subcellular localization, and interacting partners of PLA2G12B, demonstrating that PLA2G12B is calcium-dependent and tightly associated with the membrane of the endoplasmic reticulum. We also detect profound resistance to atherosclerosis in PLA2G12B mutant mice, suggesting an evolutionary tradeoff between triglyceride transport and cardiovascular disease risk. Here we identify PLA2G12B as a key driver of triglyceride incorporation into vertebrate lipoproteins.

Structure Activity Relationship and Molecular Docking of Some Quinazolines Bearing Sulfamerazine Moiety as New 3CLpro, cPLA2, sPLA2 Inhibitors

The current work was conducted to synthesize several novel anti-inflammatory quinazolines having sulfamerazine moieties as new 3CLpro, cPLA2, and sPLA2 inhibitors. The thioureido derivative 3 was formed when compound 2 was treated with sulfamerazine. Also, compound 3 was reacted with NH2-NH2 in ethanol to produce the N-aminoquinazoline derivative. Additionally, derivative 4 was reacted with 4-hydroxy-3-methoxybenzaldehyde, ethyl chloroacetate, and/or diethyl oxalate to produce quinazoline derivatives 5, 6, and 12, respectively. The results of the pharmacological study indicated that the synthesized 4-6 and 12 derivatives showed good 3CLpro, cPLA2, and sPLA2 inhibitory activity. The IC50 values of the target compounds 4-6, and 12 against the SARS-CoV-2 main protease were 2.012, 3.68, 1.18, and 5.47 µM, respectively, whereas those of baicalein and ivermectin were 1.72 and 42.39 µM, respectively. The IC50 values of the target compounds 4-6, and 12 against sPLA2 were 2.84, 2.73, 1.016, and 4.45 µM, respectively, whereas those of baicalein and ivermectin were 0.89 and 109.6 µM, respectively. The IC50 values of the target compounds 4-6, and 12 against cPLA2 were 1.44, 2.08, 0.5, and 2.39 µM, respectively, whereas those of baicalein and ivermectin were 3.88 and 138.0 µM, respectively. Also, incubation of lung cells with LPS plus derivatives 4-6, and 12 caused a significant decrease in levels of sPLA2, cPLA2, IL-8, TNF-α, and NO. The inhibitory activity of the synthesized compounds was more pronounced compared to baicalein and ivermectin. In contrast to ivermectin and baicalein, bioinformatics investigations were carried out to establish the possible binding interactions between the newly synthesized compounds 2-6 and 12 and the active site of 3CLpro. Docking simulations were utilized to identify the binding affinity and binding mode of compounds 2-6 and 12 with the active sites of 3CLpro, sPLA2, and cPLA2 enzymes. Our findings demonstrated that all compounds had outstanding binding affinities, especially with the key amino acids of the target enzymes. These findings imply that compound 6 is a potential lead for the development of more effective SARS-CoV-2 Mpro inhibitors and anti-COVID-19 quinazoline derivative-based drugs. Compound 6 was shown to have more antiviral activity than baicalein and against 3CLpro. Furthermore, the IC50 value of ivermectin against the SARS-CoV-2 main protease was revealed to be 42.39 µM, indicating that it has low effectiveness.

PLA2G12A as a Novel Biomarker for Colorectal Cancer with Prognostic Relevance

Metastasis is the leading cause of colorectal cancer (CRC)-related deaths. Therefore, the identification of accurate biomarkers predictive of metastasis is needed to better stratify high-risk patients to provide preferred management and reduce mortality. In this study, we identified 13 new genes that modified circulating tumor cell numbers using a genome-wide genetic screen in a whole animal CRC model. Candidate genes were subsequently evaluated at the gene expression level in both an internal human CRC cohort of 153 patients and an independent cohort from the TCGA including 592 patients. Interestingly, the expression of one candidate, PLA2G12A, significantly correlated with both the time to recurrence and overall survival in our CRC cohort, with its low expression being an indicator of a poor clinical outcome. By examining the TCGA cohort, we also found that low expression of PLA2G12A was significantly enriched in epithelial-mesenchymal transition signatures. Finally, the candidate functionality was validated in vitro using three different colon cancer cell lines, revealing that PLA2G12A deficiency increases cell proliferation, migration, and invasion. Overall, our study identifies PLA2G12A as a prognostic biomarker of early-stage CRC, providing evidence that its deficiency promotes tumor growth and dissemination.

Alternative Targets for sPLA2 Activity: Role of Membrane-Enzyme Interactions

The secreted phospholipases A2 (sPLA2s) play important roles both physiologically and pathologically, with their expression increasing significantly in diseases such as sepsis, inflammation, different cancers, glaucoma, obesity, Alzheimer's disease and even COVID-19. The fact has led to a large-scale search for inhibitors of these enzymes. In total, several dozen promising molecules have been proposed, but not a single one has successfully passed clinical trials. The failures in clinical studies motivated in-depth fundamental studies of PLA2s. Here we review alternative ways to control sPLA2 activity, outside its catalytic site. The concept can be realized by preventing sPLA2 from attaching to the membrane surface; by binding to an external protein which blocks sPLA2 hydrolytic activity; by preventing sPLA2 from orienting properly on the membrane surface; and by preventing substrate binding to the enzyme, keeping the catalytic site unaltered. Evidence in the literature is summarized in the review with the aim to serve as a starting point for new types of sPLA2 inhibitors.

Pharmacokinetics and Tissue Distribution of Bee Venom-Derived Phospholipase A2 Using a Sandwich ELISA after Subcutaneous Injection of New Composition Bee Venom in Rats

Bee venom is a traditional drug used to treat the nervous system, musculoskeletal system, and autoimmune diseases. A previous study found that bee venom and one of its components, phospholipase A2, can protect the brain by suppressing neuroinflammation and can also be used to treat Alzheimer's disease. Thus, new composition bee venom (NCBV), which has an increased phospholipase A2 content of up to 76.2%, was developed as a treatment agent for Alzheimer's disease by INISTst (Republic of Korea). The aim of this study was to characterize the pharmacokinetic profiles of phospholipase A2 contained in NCBV in rats. Single subcutaneous administration of NCBV at doses ranging from 0.2 mg/kg to 5 mg/kg was conducted, and pharmacokinetic parameters of bee venom-derived phospholipase A2 (bvPLA2) increased in a dose-dependent manner. Additionally, no accumulation was observed following multiple dosings (0.5 mg/kg/week), and other constituents of NCBV did not affect the pharmacokinetic profile of bvPLA2. After subcutaneous injection of NCBV, the tissue-to-plasma ratios of bvPLA2 for the tested nine tissues were all <1.0, indicating a limited distribution of the bvPLA2 within the tissues. The findings of this study may help understand the pharmacokinetic characteristics of bvPLA2 and provide useful information for the clinical application of NCBV.

Development of a bis-pyrene phospholipid probe for fluorometric detection of phospholipase A2 inhibition

In this work, we report the design, synthesis, and application of a bis-pyrene phospholipid probe for detection of phospholipase A2 action through changes in pyrene monomer and excimer fluorescence intensities. Continuous fluorometric assays enabled detection of the activities of multiple PLA2 enzymes as well as the decrease in catalysis by PLA2 from honey bee venom caused by the inhibitor p-bromo phenacylbromide. Thin-layer chromatography and mass spectrometry analysis were also used to validate probe hydrolysis by PLA2. Mass spectrometry data also supported cleavage of the probe by phospholipase C and D enzymes, although changes in fluorescence were not observed in these cases. Nevertheless, the bis-pyrene phospholipid probe developed in this work is effective for detection of PLA2 enzyme activity through an assay that enables screening for inhibitor development.

The phospholipase A2 superfamily as a central hub of bioactive lipids and beyond

In essence, "phospholipase A₂" (PLA₂) means a group of enzymes that release fatty acids and lysophospholipids by hydrolyzing the sn-2 position of glycerophospholipids. To date, more than 50 enzymes possessing PLA₂ or related lipid-metabolizing activities have been identified in mammals, and these are subdivided into several families in terms of their structures, catalytic mechanisms, tissue/cellular localizations, and evolutionary relationships. From a general viewpoint, the PLA₂ superfamily has mainly been implicated in signal transduction, driving the production of a wide variety of bioactive lipid mediators. However, a growing body of evidence indicates that PLA₂s also contribute to phospholipid remodeling or recycling for membrane homeostasis, fatty acid β-oxidation for energy production, and barrier lipid formation on the body surface. Accordingly, PLA₂ enzymes are considered one of the key regulators of a broad range of lipid metabolism, and perturbation of specific PLA₂-driven lipid pathways often disrupts tissue and cellular homeostasis and may be associated with a variety of diseases. This review covers current understanding of the physiological functions of the PLA₂ superfamily, focusing particularly on the two major intracellular PLA₂ families (Ca²⁺-dependent cytosolic PLA₂s and Ca²⁺-independent patatin-like PLA₂s) as well as other PLA₂ families, based on studies using gene-manipulated mice and human diseases in combination with comprehensive lipidomics.

Response of gut microbiota and ileal transcriptome to inulin intervention in HFD induced obese mice

Inulin, as a dietary fiber, exerted prominent anti-obesity effects by modulating gut microbiota. However, the possible relationship and interplay of gut microbiome and function of distal intestine is still unclear now. This study aimed to investigate the possible targets of microbes and the related intestinal genes mediated by inulin. C57 BL/6 male mice were randomly allocated to chow diet (Chow) group, high-fat diet (HFD) group, and HFD supplemented with 3 % inulin (Inulin) group. Compared with HFD treatment, inulin supplementation significantly decreased the body weight, fat deposition, and fasting blood glucose level. In addition, mice treated with inulin had a remarkable alteration in the structure of cecal microbiota and transcriptomic profiling of ileum. In particular, inulin supplementation significantly reversed the HFD induced expression of Bacteroides, Allobaculum and nonrank_f_Bacteroidates_S24-7_group, and reversed the expression of genes belonging to phospholipase A2 (PLA2) family and cytochrome P450 (CYP450) family. In summary, inulin might alleviate HFD-induced fat deposition and metabolic disorders via regulating lipid metabolism of ileum, while the interaction between the sPLA2s and gut microbes might play important roles in the process.

Secretory Phospholipases A2, from Snakebite Envenoming to a Myriad of Inflammation Associated Human Diseases-What Is the Secret of Their Activity?

Secreted phospholipases of type A2 (sPLA2s) are proteins of 14-16 kDa present in mammals in different forms and at different body sites. They are involved in lipid transformation processes, and consequently in various immune, inflammatory, and metabolic processes. sPLA2s are also major components of snake venoms, endowed with various toxic and pharmacological properties. The activity of sPLA2s is not limited to the enzymatic one but, through interaction with different types of molecules, they exert other activities that are still little known and explored, both outside and inside the cells, as they can be endocytosed. The aim of this review is to analyze three features of sPLA2s, yet under-explored, knowledge of which could be crucial to understanding the activity of these proteins. The first feature is their disulphide bridge pattern, which has always been considered immutable and necessary for their stability, but which might instead be modulable. The second characteristic is their ability to undergo various post-translational modifications that would control their interaction with other molecules. The third feature is their ability to participate in active molecular condensates both on the surface and within the cell. Finally, the implications of these features in the design of anti-inflammatory drugs are discussed.

Identification of a Dual Inhibitor of Secreted Phospholipase A2 (GIIA sPLA2) and SARS-CoV-2 Main Protease

The development of novel agents to combat COVID-19 is of high importance. SARS-CoV-2 main protease (M^pro) is a highly attractive target for the development of novel antivirals and a variety of inhibitors have already been developed. Accumulating evidence on the pathobiology of COVID-19 has shown that lipids and lipid metabolizing enzymes are critically involved in the severity of the infection. The purpose of the present study was to identify an inhibitor able to simultaneously inhibit both SARS-CoV-2 M^pro and phospholipase A₂ (PLA₂), an enzyme which plays a significant role in inflammatory diseases. Evaluating several PLA₂ inhibitors, we demonstrate that the previously known potent inhibitor of Group IIA secretory PLA₂, GK241, may also weakly inhibit SARS-CoV-2 M^pro. Molecular mechanics docking and molecular dynamics calculations shed light on the interactions between GK241 and SARS-CoV-2 M^pro. 2-Oxoamide GK241 may represent a lead molecular structure for the development of dual PLA₂ and SARS-CoV-2 M^pro inhibitors.

Platelet extracellular vesicles and the secretory interactome join forces in health and disease

Extracellular vesicles (EVs) are small membrane-bound vesicles released by cells under various conditions. They are found in the extracellular milieu in all biological fluids. As the concentrations, contents, and origin of EVs can change during inflammation, the assessment of EVs can be used as a proxy of cellular activation. Here, we review the literature regarding EVs, more particularly those released by platelets and their mother cells, the megakaryocytes. Their cargo includes cytokines, growth factors, organelles (mitochondria and proteasomes), nucleic acids (messenger and non-coding RNA), transcription factors, and autoantigens. EVs may thus contribute to intercellular communication by facilitating exchange of material between cells. EVs also interact with other molecules secreted by cells. In autoimmune diseases, EVs are associated with antibodies secreted by B cells. By definition, EVs necessarily comprise a phospholipid moiety, which is thus the target of secreted phospholipases also abundantly expressed in the extracellular milieu. We discuss how platelet-derived EVs, which represent the majority of the circulating EVs, may contribute to immunity through the activity of their cargo or in combination with the secretory interactome.

Therapeutic and prophylactic effect of flavonoids in post-COVID-19 therapy

The high incidence of post-covid symptoms in humans confirms the need for effective treatment. Due to long-term complications across several disciplines, special treatment programs emerge for affected patients, emphasizing multidisciplinary care. For these reasons, we decided to look at current knowledge about possible long-term complications of COVID-19 disease and then present the effect of flavonoids, which could help alleviate or eliminate complications in humans after overcoming the COVID-19 infection. Based on articles published from 2003 to 2021, we summarize the flavonoids-based molecular mechanisms associated with the post-COVID-19 syndrome and simultaneously provide a complex view regarding their prophylactic and therapeutic potential. Review clearly sorts out the outcome of post-COVID-19 syndrome according particular body systems. The conclusion is that flavonoids play an important role in prevention of many diseases. We suggest that flavonoids as critical nutritional supplements, are suitable for the alleviation and shortening of the period associated with the post-COVID-19 syndrome. The most promising flavonoid with noteworthy therapeutic and prophylactic effect appears to be quercetin.

Secreted Phospholipases A2 - not just Enzymes: Revisited

Secreted phospholipases A₂ (sPLA₂s) participate in a very broad spectrum of biological processes through their enzymatic activity and as ligands for membrane and soluble receptors. The physiological roles of sPLA₂s as enzymes have been very well described, while their functions as ligands are still poorly known. Since the last overview of sPLA₂-binding proteins (sPLA₂-BPs) 10 years ago, several important discoveries have occurred in this area. New and more sensitive analytical tools have enabled the discovery of additional sPLA₂-BPs, which are presented and critically discussed here. The structural diversity of sPLA₂-BPs reveals sPLA₂s as very promiscuous proteins, and we offer some structural explanations for this nature that makes these proteins evolutionarily highly advantageous. Three areas of physiological engagement of sPLA₂-BPs have appeared most clearly: cellular transport and signalling, and regulation of the enzymatic activity of sPLA₂s. Due to the multifunctionality of sPLA₂s, they appear to be exceptional pharmacological targets. We reveal the potential to exploit interactions of sPLA₂s with other proteins in medical terms, for the development of original diagnostic and therapeutic procedures. We conclude this survey by suggesting the priority questions that need to be answered.

Secretory Phospholipase A2 Enzymes in Acute Lung Injury

The secretory phospholipase A2 (sPLA2) group of secreted enzymes hydrolyze phospholipids and lead to the production of multiple biologically active lipid mediators. sPLA2s and their products (e.g., eicosanoids) play a significant role in the pathophysiology of various inflammatory diseases, including life-threatening lung disorders such as acute lung injury (ALI) and the Acute Respiratory Distress Syndrome (ARDS). The ALI/ARDS spectrum of severe inflammatory conditions is caused by direct (such as bacterial or viral pneumonia) or indirect insults (sepsis) that are associated with high morbidity and mortality. Several sPLA2 isoforms are upregulated in patients with ARDS as well as in multiple ALI preclinical models, and individual sPLA2s exert unique roles in regulating ALI pathophysiology. This brief review will summarize the contributions of specific sPLA2 isoforms as markers and mediators in ALI, supporting a potential therapeutic role for targeting them in ARDS.

The atypical binding mechanism of second calcium on phospholipase A2 group IIE

Secreted phospholipase A2s (sPLA2s) are calcium dependent enzymes involved in various biological events such as lipid metabolism and inflammation. We previously identified the second calcium (Ca2) binding site of human sPLA2 Group IIE (hGIIE) by structural study and suggested that Asn21 act as the switch of Ca2 binding to modulate the enzymatic activity, but the detailed Ca2 binding mechanism is still unclear. Combined with enzymatic assay, model analysis and calcium binding affinity data for mutated hGIIE proteins, we herein further demonstrate that the flexibly bound Ca2 is essential for the catalysis of hGIIE, unlike the stable binding of Ca2 in hGIIA that replenishes the calcium in the typical loop during the reaction. The atypical Ca2 binding feature of hGIIE will provide a better understanding on the catalytic mechanism of hGIIE.

Short Linear Motifs Characterizing Snake Venom and Mammalian Phospholipases A2

Snake venom phospholipases A2 (PLA2s) have sequences and structures very similar to those of mammalian group I and II secretory PLA2s, but they possess many toxic properties, ranging from the inhibition of coagulation to the blockage of nerve transmission, and the induction of muscle necrosis. The biological properties of these proteins are not only due to their enzymatic activity, but also to protein–protein interactions which are still unidentified. Here, we compare sequence alignments of snake venom and mammalian PLA2s, grouped according to their structure and biological activity, looking for differences that can justify their different behavior. This bioinformatics analysis has evidenced three distinct regions, two central and one C-terminal, having amino acid compositions that distinguish the different categories of PLA2s. In these regions, we identified short linear motifs (SLiMs), peptide modules involved in protein–protein interactions, conserved in mammalian and not in snake venom PLA2s, or vice versa. The different content in the SLiMs of snake venom with respect to mammalian PLA2s may result in the formation of protein membrane complexes having a toxic activity, or in the formation of complexes whose activity cannot be blocked due to the lack of switches in the toxic PLA2s, as the motif recognized by the prolyl isomerase Pin1.

Serum Glycerophospholipid Profile in Acute Exacerbation of Chronic Obstructive Pulmonary Disease

Studies have shown that glycerophospholipids are involved in the pathogenesis of chronic obstructive pulmonary disease (COPD). This study adopted targeted metabolomic analysis to investigate the changes in serum glycerophospholipids in acute exacerbation of chronic obstructive pulmonary disease (AECOPD) and their differential expression in patients with different inflammatory subtypes. Patients with AECOPD admitted between January 2015 and December 2017 were enrolled, and their clinical data were collected. The patients' gender, age, body mass index, and lung function were recorded. Routine blood and induced sputum tests were performed. Liquid chromatography-mass spectrometry was used to detect the serum glycerophospholipid metabolic profiles and to analyze the metabolic profile changes between the acute exacerbation and recovery stages as well as the differences between different inflammatory subtypes. A total of 58 patients were hospitalized for AECOPD, including 49 male patients with a mean age of 74.8 ± 10.0 years. In the metabolic profiles, the expression of lysophosphatidylcholine (LPC) 18:3, lysophosphatidylethanolamine (LPE) 16:1, and phosphatidylinositol (PI) 32:1 was significantly reduced in the acute exacerbation stage compared to the recovery stage (P < 0.05). The three glycerophospholipids were used to plot the receiver operating characteristic curves to predict the acute exacerbation/recovery stage, and the areas under the curves were all above 70%. There were no differential metabolites between the two groups of patients with blood eosinophil percentage (EOS%) ≥2% and <2% at exacerbation. The expression of LPC 18:3, LPE 16:1, and PI 32:1 was significantly reduced in the acute exacerbation stage compared to the recovery stage in the inflammatory subtype with blood EOS <2% (P < 0.05). Abnormalities in the metabolism of glycerophospholipids may be involved in the onset of AECOPD, especially in the non-eosinophilic subtype.

A Representative GIIA Phospholipase A2 Activates Preadipocytes to Produce Inflammatory Mediators Implicated in Obesity Development

Adipose tissue secretes proinflammatory mediators which promote systemic and adipose tissue inflammation seen in obesity. Group IIA (GIIA)-secreted phospholipase A₂ (sPLA₂) enzymes are found to be elevated in plasma and adipose tissue from obese patients and are active during inflammation, generating proinflammatory mediators, including prostaglandin E₂ (PGE₂). PGE₂ exerts anti-lipolytic actions and increases triacylglycerol levels in adipose tissue. However, the inflammatory actions of GIIA sPLA₂s in adipose tissue cells and mechanisms leading to increased PGE₂ levels in these cells are unclear. This study investigates the ability of a representative GIIA sPLA₂, MT-III, to activate proinflammatory responses in preadipocytes, focusing on the biosynthesis of prostaglandins, adipocytokines and mechanisms involved in these effects. Our results showed that MT-III induced biosynthesis of PGE₂, PGI₂, MCP-1, IL-6 and gene expression of leptin and adiponectin in preadipocytes. The MT-III-induced PGE₂ biosynthesis was dependent on cytosolic PLA₂ (cPLA₂)-α, cyclooxygenases (COX)-1 and COX-2 pathways and regulated by a positive loop via the EP₄ receptor. Moreover, MT-III upregulated COX-2 and microsomal prostaglandin synthase (mPGES)-1 protein expression. MCP-1 biosynthesis induced by MT-III was dependent on the EP4 receptor, while IL-6 biosynthesis was dependent on EP3 receptor engagement by PGE₂. These data highlight preadipocytes as targets for GIIA sPLA₂s and provide insight into the roles played by this group of sPLA₂s in obesity.

miRNA/Target Gene Profile of Endothelial Cells Treated with Human Triglyceride-Rich Lipoproteins Obtained after a High-Fat Meal with Extra-Virgin Olive Oil or Sunflower Oil

SCOPE

The effects of triglyceride-rich lipoproteins (TRLs) on the miRNA expression of endothelial cells, which are very involved in atherosclerosis, according to the type of diet are not known.

METHODS AND RESULTS

The differences between the effects of TRLs isolated from blood of subjects after a high-fat meal with extra-virgin olive oil (EVOO) and sunflower oil (SO) on the microRNA-Seq profile related to atherosclerosis in human umbilical vein endothelial cells are analyzed. 28 upregulated microRNAs with EVOO-derived TRLs, which can regulate 22 genes related to atherosclerosis, are found. 21 upregulated microRNAs with SO-derived TRLs, which can regulate 20 genes related to atherosclerosis, are found. These microRNAs are mainly involved in angiogenesis, with a predominance of an anti-angiogenic effect with EVOO-derived TRLs. Other microRNAs upregulated with SO-derived TRLs are involved in cardiovascular diseases. Pathways for the target genes obtained from the upregulated microRNA with EVOO-derived TRLs are involved in lipid metabolism and inflammatory and defense response, while those with SO-derived TRLs are involved in lipid metabolic process.

CONCLUSION

EVOO-derived TRLs seem to produce a more atheroprotective profile than SO-derived TRLs. This study provides alternative mechanisms on the protective role of EVOO against the atherogenic process through microRNA regulation in endothelial cells.

Generation of a conditional transgenic mouse model expressing human Phospholipase A2 Receptor 1

The Phospholipase A2 Receptor 1 (PLA2R1) was first identified for its ability to bind some secreted PLA2s (sPLA2s). It belongs to the C-type lectin superfamily and it binds different types of proteins. It is likely a multifunctional protein that plays a role i) in inflammation and inflammatory diseases, ii) in cellular senescence, a mechanism participating in aging and age-related diseases including cancer, and iii) in membranous nephropathy (MN), a rare autoimmune kidney disease where PLA2R1 is the major autoantigen. To help study the role of PLA2R1 in these pathophysiological conditions, we have generated a versatile NeoR-hPLA2R1 conditional transgenic mice which will allow the specific expression of human PLA2R1 (hPLA2R1) in relevant organs and cells following Cre recombinase-driven excision of the NeoR-stop cassette flanked by LoxP sites. Proof-of-concept breeding of NeoR-hPLA2R1 mice with the ubiquitous adenoviral EIIa promoter-driven Cre mouse line resulted in the expected excision of the NeoR-stop cassette and the expression of hPLA2R1 in all tested tissues. These Tg-hPLA2R1 animals breed normally, with no reproduction or apparent growth defect. These models, especially the NeoR-hPLA2R1 conditional transgenic mouse line, will facilitate the future investigation of PLA2R1 functions in relevant pathophysiological contexts, including inflammatory diseases, age-related diseases and MN.

Secreted Phospholipase A2 Group X Acts as an Adjuvant for Type 2 Inflammation, Leading to an Allergen-Specific Immune Response in the Lung

Secreted phospholipase A₂ (sPLA₂) enzymes release free fatty acids, including arachidonic acid, and generate lysophospholipids from phospholipids, including membrane phospholipids from cells and bacteria and surfactant phospholipids. We have shown that an endogenous enzyme sPLA₂ group X (sPLA₂-X) is elevated in the airways of asthmatics and that mice lacking the sPLA₂-X gene (Pla2g10) display attenuated airway hyperresponsiveness, innate and adaptive immune responses, and type 2 cytokine production in a model of airway sensitization and challenge using a complete allergen that induces endogenous adjuvant activity. This complete allergen also induces the expression of sPLA₂-X/Pla2g10 In the periphery, an sPLA₂ found in bee venom (bee venom PLA₂) administered with the incomplete Ag OVA leads to an Ag-specific immune response. In this study, we demonstrate that both bee venom PLA₂ and murine sPLA₂-X have adjuvant activity, leading to a type 2 immune response in the lung with features of airway hyperresponsiveness and Ag-specific type 2 airway inflammation following peripheral sensitization and subsequent airway challenge with OVA. Further, the adjuvant effects of sPLA₂-X that result in the type 2-biased OVA-specific adaptive immune response in the lung were dependent upon the catalytic activity of the enzyme, as a catalytically inactive mutant form of sPLA₂-X does not elicit the adaptive component of the immune response, although other components of the immune response were induced by the inactive enzyme, suggesting receptor-mediated effects. Our results demonstrate that exogenous and endogenous sPLA₂s play an important role in peripheral sensitization, resulting in airway responses to inhaled Ags.

BoaγPLI: Structural and functional characterization of the gamma phospholipase A2 plasma inhibitor from the non-venomous Brazilian snake Boa constrictor

Plasma in several organisms has components that promote resistance to envenomation by inhibiting specific proteins from snake venoms, such as phospholipases A2 (PLA2s). The major hypothesis for inhibitor's presence would be the protection against self-envenomation in venomous snakes, but the occurrence of inhibitors in non-venomous snakes and other animals has opened new perspectives for this molecule. Thus, this study showed for the first time the structural and functional characterization of the PLA2 inhibitor from the Boa constrictor serum (BoaγPLI), a non-venomous snake that dwells extensively the Brazilian territory. Therefore, the inhibitor was isolated from B. constrictor serum, with 0.63% of recovery. SDS-PAGE showed a band at ~25 kDa under reducing conditions and ~20 kDa under non-reducing conditions. Chromatographic analyses showed the presence of oligomers formed by BoaγPLI. Primary structure of BoaγPLI suggested an estimated molecular mass of 22 kDa. When BoaγPLI was incubated with Asp-49 and Lys-49 PLA2 there was no severe change in its dichroism spectrum, suggesting a non-covalent interaction. The enzymatic assay showed a dose-dependent inhibition, up to 48.2%, when BoaγPLI was incubated with Asp-49 PLA2, since Lys-49 PLA2 has a lack of enzymatic activity. The edematogenic and myotoxic effects of PLA2s were also inhibited by BoaγPLI. In summary, the present work provides new insights into inhibitors from non-venomous snakes, which possess PLIs in their plasma, although the contact with venom is unlikely.

A Potential Role of Phospholipase 2 Group IIA (PLA2-IIA) in P. gingivalis-Induced Oral Dysbiosis

Porphyromonas gingivalis is an oral pathogen with the ability to induce oral dysbiosis and periodontal disease. Nevertheless, the mechanisms by which P. gingivalis could abrogate the host-microbe symbiotic relationship leading to oral dysbiosis remain unclear. We have recently demonstrated that P. gingivalis specifically increased the antimicrobial properties of oral epithelial cells, through a strong induction of the expression of PLA₂-IIA in a mechanism that involves activation of the Notch-1 receptor. Moreover, gingival expression of PLA₂-IIA was significantly increased during initiation and progression of periodontal disease in non-human primates and interestingly, those PLA₂-IIA expression changes were concurrent with oral dysbiosis. In this chapter, we present an innovative hypothesis of a potential mechanism involved in P. gingivalis-induced oral dysbiosis and inflammation based on our previous observations and a robust body of literature that supports the antimicrobial and proinflammatory properties of PLA₂-IIA as well as its role in other chronic inflammatory diseases.

Antimalarial Activity of Human Group IIA Secreted Phospholipase A2 in Relation to Enzymatic Hydrolysis of Oxidized Lipoproteins

The level of human group IIA secreted phospholipase A₂ (hGIIA sPLA₂) is increased in the plasma of malaria patients, but its role is unknown. In parasite culture with normal plasma, hGIIA is inactive against Plasmodium falciparum, contrasting with hGIIF, hGV, and hGX sPLA₂s, which readily hydrolyze plasma lipoproteins, release nonesterified fatty acids (NEFAs), and inhibit parasite growth. Here, we revisited the anti-Plasmodium activity of hGIIA under conditions closer to those of malaria physiopathology where lipoproteins are oxidized. In parasite culture containing oxidized lipoproteins, hGIIA sPLA₂ was inhibitory, with a 50% inhibitory concentration value of 150.0 ± 40.8 nM, in accordance with its capacity to release NEFAs from oxidized particles. With oxidized lipoproteins, hGIIF, hGV, and hGX sPLA₂s were also more potent, by 4.6-, 2.1-, and 1.9-fold, respectively. Using specific immunoassays, we found that hGIIA sPLA₂ is increased in plasma from 41 patients with malaria over levels for healthy donors (median [interquartile range], 1.6 [0.7 to 3.4] nM versus 0.0 [0.0 to 0.1] nM, respectively; P < 0.0001). Other sPLA₂s were not detected. Malaria plasma, but not normal plasma, contains oxidized lipoproteins and was inhibitory to P. falciparum when spiked with hGIIA sPLA₂ Injection of recombinant hGIIA into mice infected with P. chabaudi reduced the peak of parasitemia, and this was effective only when the level of plasma peroxidation was increased during infection. In conclusion, we propose that malaria-induced oxidation of lipoproteins converts these into a preferential substrate for hGIIA sPLA₂, promoting its parasite-killing effect. This mechanism may contribute to host defense against P. falciparum in malaria where high levels of hGIIA are observed.

Comparison of liver transcriptome from high- and low-intramuscular fat Chaohu ducks provided additional candidate genes for lipid selection

The meat quality of ducks is closely related to the intramuscular fat (IMF) content. This study explored the candidate regulatory genes of IMF formation and lipid deposition in Chaohu ducks. The IMF of breast muscle in 100 ducks was determined and statistically analysed by normal distribution test. Duck liver samples with high IMF (CH, n = 3) and low IMF (CL, n = 3) were selected for transcriptome analysis by RNA sequencing (RNA-Seq). The IMF was in accordance with normal distribution (T = 0.001, P = 0.999). The IMF from two tails of the normal distribution was significantly different with 2.9983% ± 0.3296% in the CH group and 1.1960% ± 0.1481% in the CL group (P < 0.0001). RNA-Seq revealed 147 differentially expressed genes, including 78 up-regulated and 69 down-regulated genes in both groups. Validation by qRT-PCR was in agreement with RNA-Seq (R ² = 0.838). Gene ontology analysis revealed that organophosphate catabolism, oxidation-reduction process, cellular lipid catabolism, lipid transport, lipid localisation, lipid biosynthesis and cellular lipid catabolism were involved in lipid metabolism. Meanwhile, Kyoto Encyclopedia of Genes and Genomes pathway analysis suggested that steroid hormone biosynthesis, ovarian steroidogenesis, alpha-linolenic acid metabolism, glycosylphosphatidylinositol anchor biosynthesis and linoleic acid metabolism were involved in lipid deposition, wherein the genes COMT, NT5E, PDE4D, PLA2G4F, A-FABP, ADRA2A, HSD17B2, PPP1R3C, PPP1R3B and NR0B2 were involved in lipid deposition. This study provided insights into the molecular mechanism for regulating lipid metabolism and identified candidate genes for selecting markers to control IMF formation in Chaohu ducks.

Small-molecule inhibitors as potential therapeutics and as tools to understand the role of phospholipases A2

Phospholipase A2 (PLA2) enzymes are involved in various inflammatory pathological conditions including arthritis, cardiovascular and autoimmune diseases. The regulation of their catalytic activity is of high importance and a great effort has been devoted in developing synthetic inhibitors. We summarize the most important small-molecule synthetic PLA2 inhibitors developed to target each one of the four major types of human PLA2 (cytosolic cPLA2, calcium-independent iPLA2, secreted sPLA2, and lipoprotein-associated LpPLA2). We discuss recent applications of inhibitors to understand the role of each PLA2 type and their therapeutic potential. Potent and selective PLA2 inhibitors have been developed. Although some of them have been evaluated in clinical trials, none reached the market yet. Apart from their importance as potential medicinal agents, PLA2 inhibitors are excellent tools to unveil the role that each PLA2 type plays in cells and in vivo. Modern medicinal chemistry approaches are expected to generate improved PLA2 inhibitors as new agents to treat inflammatory diseases.

Sea Anemone Toxins: A Structural Overview

Sea anemones produce venoms of exceptional molecular diversity, with at least 17 different molecular scaffolds reported to date. These venom components have traditionally been classified according to pharmacological activity and amino acid sequence. However, this classification system suffers from vulnerabilities due to functional convergence and functional promiscuity. Furthermore, for most known sea anemone toxins, the exact receptors they target are either unknown, or at best incomplete. In this review, we first provide an overview of the sea anemone venom system and then focus on the venom components. We have organised the venom components by distinguishing firstly between proteins and non-proteinaceous compounds, secondly between enzymes and other proteins without enzymatic activity, then according to the structural scaffold, and finally according to molecular target.

Respective contribution of cytosolic phospholipase A2α and secreted phospholipase A2 IIA to inflammation and eicosanoid production in arthritis

Phospholipase A₂s (PLA₂) play a key role in generation of eicosanoids. Cytosolic PLA₂α (cPLA₂α) is constitutively expressed in most cells, whereas IIA secreted PLA₂ (sPLA₂-IIA) is induced during inflammation and is present at high levels in the synovial fluid of rheumatoid arthritis patients. In mice, both cPLA₂α and sPLA₂-IIA have been implicated in autoimmune arthritis; however, the respective contribution of these two enzymes to the pathogenesis and production of eicosanoids is unknown. We evaluated the respective role of cPLA₂α and sPLA₂-IIA with regard to arthritis and eicosanoid profile in an in vivo model of arthritis. While arthritis was most severe in mice expressing both enzymes, it was abolished when both cPLA₂α and sPLA₂-IIA were lacking. cPLA₂α played a dominant role in the severity of arthritis, although sPLA₂-IIA sufficed to significantly contribute to the disease. Several eicosanoids were modulated during the course of arthritis and numerous species involved sPLA₂-IIA expression. This study confirms the critical role of PLA₂s in arthritis and unveils the distinct contribution of cPLA₂α and sPLA₂-IIA to the eicosanoid profile in arthritis.

Eicosanoids, prostacyclin and cyclooxygenase in the cardiovascular system

Eicosanoids represent a diverse family of lipid mediators with fundamental roles in physiology and disease. Within the eicosanoid superfamily are prostanoids, which are specifically derived from arachidonic acid by the enzyme cyclooxygenase (COX). COX has two isoforms; COX-1 and COX-2. COX-2 is the therapeutic target for the nonsteroidal anti-inflammatory drug (NSAID) class of pain medications. Of the prostanoids, prostacyclin, first discovered by Sir John Vane in 1976, remains amongst the best studied and retains an impressive pedigree as one of the fundamental cardiovascular protective pathways. Since this time, we have learnt much about how eicosanoids, COX enzymes and prostacyclin function in the cardiovascular system, knowledge that has allowed us, for example, to harness the power of prostacyclin as therapy to treat pulmonary arterial hypertension and peripheral vascular disease. However, there remain many unanswered questions in our basic understanding of the pathways, and how they can be used to improve human health. Perhaps, the most important and controversial outstanding question in the field remains; 'how do NSAIDs produce their much publicized cardiovascular side-effects?' This review summarizes the history, biology and cardiovascular function of key eicosanoids with particular focus on prostacyclin and other COX products and discusses how our knowledge of these pathways can applied in future drug discovery and be used to explain the cardiovascular side-effects of NSAIDs. LINKED ARTICLES: This article is part of a themed section on Eicosanoids 35 years from the 1982 Nobel: where are we now? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.8/issuetoc.

Pancreatic and mucosal enzymes in choline phospholipid digestion

The digestion of choline phospholipids is important for choline homeostasis, lipid signaling, postprandial lipid and energy metabolism, and interaction with intestinal bacteria. The digestion is mediated by the combined action of pancreatic and mucosal enzymes. In the proximal small intestine, hydrolysis of phosphatidylcholine (PC) to 1-lyso-PC and free fatty acid (FFA) by the pancreatic phospholipase A₂ IB coincides with the digestion of the dietary triacylglycerols by lipases, but part of the PC digestion is extended and must be mediated by other enzymes as the jejunoileal brush-border phospholipase B/lipase and mucosal secreted phospholipase A₂ X. Absorbed 1-lyso-PC is partitioned in the mucosal cells between degradation and reacylation into chyle PC. Reutilization of choline for hepatic bile PC synthesis, and the reacylation of 1-lyso-PC into chylomicron PC by the lyso-PC-acyl-CoA-acyltransferase 3 are important features of choline recycling and postprandial lipid metabolism. The role of mucosal enzymes is emphasized by sphingomyelin (SM) being sequentially hydrolyzed by brush-border alkaline sphingomyelinase (alk-SMase) and neutral ceramidase to sphingosine and FFA, which are well absorbed. Ceramide and sphingosine-1-phosphate are generated and are both metabolic intermediates and important lipid messengers. Alk-SMase has anti-inflammatory effects that counteract gut inflammation and tumorigenesis. These may be mediated by multiple mechanisms including generation of sphingolipid metabolites and suppression of autotaxin induction and lyso-phosphatidic acid formation. Here we summarize current knowledge on the roles of pancreatic and mucosal enzymes in PC and SM digestion, and its implications in intestinal and liver diseases, bacterial choline metabolism in the gut, and cholesterol absorption.

β-Lactones: A Novel Class of Ca2+-Independent Phospholipase A2 (Group VIA iPLA2) Inhibitors with the Ability To Inhibit β-Cell Apoptosis

Ca²⁺-independent phospholipase A₂ (GVIA iPLA₂) has gained increasing interest recently as it has been recognized as a participant in biological processes underlying diabetes development and autoimmune-based neurological disorders. The development of potent GVIA iPLA₂ inhibitors is of great importance because only a few have been reported so far. We present a novel class of GVIA iPLA₂ inhibitors based on the β-lactone ring. This functionality in combination with a four-carbon chain carrying a phenyl group at position-3 and a linear propyl group at position-4 of the lactone ring confers excellent potency. trans-3-(4-Phenylbutyl)-4-propyloxetan-2-one (GK563) was identified as being the most potent GVIA iPLA₂ inhibitor ever reported ( X_I(50) 0.0000021, IC₅₀ 1 nM) and also one that is 22 000 times more active against GVIA iPLA₂ than GIVA cPLA₂. It was found to reduce β-cell apoptosis induced by proinflammatory cytokines, raising the possibility that it can be beneficial in countering autoimmune diseases, such as type 1 diabetes.

Roles of secreted phospholipase A2 group IIA in inflammation and host defense

Among all members of the secreted phospholipase A₂ (sPLA₂) family, group IIA sPLA₂ (sPLA₂-IIA) is possibly the most studied enzyme. Since its discovery, many names have been associated with sPLA₂-IIA, such as "non-pancreatic", "synovial", "platelet-type", "inflammatory", and "bactericidal" sPLA_2. Whereas the different designations indicate comprehensive functions or sources proposed for this enzyme, the identification of the precise roles of sPLA₂-IIA has remained a challenge. This can be attributed to: the expression of the enzyme by various cells of different lineages, its limited activity towards the membranes of immune cells despite its expression following common inflammatory stimuli, its ability to interact with certain proteins independently of its catalytic activity, and its absence from multiple commonly used mouse models. Nevertheless, elevated levels of the enzyme during inflammatory processes and associated consistent release of arachidonic acid from the membrane of extracellular vesicles suggest that sPLA₂-IIA may contribute to inflammation by using endogenous substrates in the extracellular milieu. Moreover, the remarkable potency of sPLA₂-IIA towards bacterial membranes and its induced expression during the course of infections point to a role for this enzyme in the defense of the host against invading pathogens. In this review, we present current knowledge related to mammalian sPLA₂-IIA and its roles in sterile inflammation and host defense.

Lipid Droplets in Cancer: Guardians of Fat in a Stressful World

Cancer cells possess remarkable abilities to adapt to adverse environmental conditions. Their survival during severe nutrient and oxidative stress depends on their capacity to acquire extracellular lipids and the plasticity of their mechanisms for intracellular lipid synthesis, mobilisation, and recycling. Lipid droplets, cytosolic fat storage organelles present in most cells from yeast to men, are emerging as major regulators of lipid metabolism, trafficking, and signalling in various cells and tissues exposed to stress. Their biogenesis is induced by nutrient and oxidative stress and they accumulate in various cancers. Lipid droplets act as switches that coordinate lipid trafficking and consumption for different purposes in the cell, such as energy production, protection against oxidative stress or membrane biogenesis during rapid cell growth. They sequester toxic lipids, such as fatty acids, cholesterol and ceramides, thereby preventing lipotoxic cell damage and engage in a complex relationship with autophagy. Here, we focus on the emerging mechanisms of stress-induced lipid droplet biogenesis; their roles during nutrient, lipotoxic, and oxidative stress; and the relationship between lipid droplets and autophagy. The recently discovered principles of lipid droplet biology can improve our understanding of the mechanisms that govern cancer cell adaptability and resilience to stress.

Selectivity of phospholipid hydrolysis by phospholipase A2 enzymes in activated cells leading to polyunsaturated fatty acid mobilization

Phospholipase A₂s are enzymes that hydrolyze the fatty acid at the sn-2 position of the glycerol backbone of membrane glycerophospholipids. Given the asymmetric distribution of fatty acids within phospholipids, where saturated fatty acids tend to be present at the sn-1 position, and polyunsaturated fatty acids such as those of the omega-3 and omega-6 series overwhelmingly localize in the sn-2 position, the phospholipase A₂ reaction is of utmost importance as a regulatory checkpoint for the mobilization of these fatty acids and the subsequent synthesis of proinflammatory omega-6-derived eicosanoids on one hand, and omega-3-derived specialized pro-resolving mediators on the other. The great variety of phospholipase A₂s, their differential substrate selectivity under a variety of pathophysiological conditions, as well as the different compartmentalization of each enzyme and accessibility to substrate, render this class of enzymes also key to membrane phospholipid remodeling reactions, and the generation of specific lipid mediators not related with canonical metabolites of omega-6 or omega-3 fatty acids. This review highlights novel findings regarding the selective hydrolysis of phospholipids by phospholipase A₂s and the influence this may have on the ability of these enzymes to generate distinct lipid mediators with essential functions in biological processes. This brings a new understanding of the cellular roles of these enzymes depending upon activation conditions.

Cell surface nucleolin interacts with and internalizes Bothrops asper Lys49 phospholipase A2 and mediates its toxic activity

Phospholipases A2 are a major component of snake venoms. Some of them cause severe muscle necrosis through an unknown mechanism. Phospholipid hydrolysis is a possible explanation of their toxic action, but catalytic and toxic properties of PLA2s are not directly connected. In addition, viperid venoms contain PLA2-like proteins, which are very toxic even if they lack catalytic activity due to a critical mutation in position 49. In this work, the PLA2-like Bothrops asper myotoxin-II, conjugated with the fluorophore TAMRA, was found to be internalized in mouse myotubes, and in RAW264.7 cells. Through experiments of protein fishing and mass spectrometry analysis, using biotinylated Mt-II as bait, we found fifteen proteins interacting with the toxin and among them nucleolin, a nucleolar protein present also on cell surface. By means of confocal microscopy, Mt-II and nucleolin were shown to colocalise, at 4 °C, on cell membrane where they form Congo-red sensitive assemblies, while at 37 °C, 20 minutes after the intoxication, they colocalise in intracellular spots going from plasmatic membrane to paranuclear and nuclear area. Finally, nucleolin antagonists were found to inhibit the Mt-II internalization and toxic activity and were used to identify the nucleolin regions involved in the interaction with the toxin.

Discovery of a Series of Indole-2 Carboxamides as Selective Secreted Phospholipase A2 Type X (sPLA2-X) Inhibitors

In order to assess the potential of sPLA₂-X as a therapeutic target for atherosclerosis, novel sPLA₂ inhibitors with improved type X selectivity are required. To achieve the objective of identifying such compounds, we embarked on a lead generation effort that resulted in the identification of a novel series of indole-2-carboxamides as selective sPLA2-X inhibitors with excellent potential for further optimization.

A Snake Venom-Secreted Phospholipase A2 Induces Foam Cell Formation Depending on the Activation of Factors Involved in Lipid Homeostasis

MT-III, a snake venom GIIA sPLA₂, which shares structural and functional features with mammalian GIIA sPLA₂s, activates macrophage defense functions including lipid droplet (LDs) formation, organelle involved in both lipid metabolism and inflammatory processes. Macrophages (MΦs) loaded with LDs, termed foam cells, characterize early blood vessel fatty-streak lesions during atherosclerosis. However, the factors involved in foam cell formation induced by a GIIA sPLA₂ are still unknown. Here, we investigated the participation of lipid homeostasis-related factors in LD formation induced by MT-III in macrophages. We found that MT-III activated PPAR-γ and PPAR-β/δ and increased the protein levels of both transcription factors and CD36 in macrophages. Pharmacological interventions evidenced that PPAR-γ, PPAR-β/δ, and CD36 as well as the endoplasmic reticulum enzymes ACAT and DGAT are essential for LD formation. Moreover, PPAR-β/δ, but not PPAR-γ, is involved in MT-III-induced PLIN2 protein expression, and both PPAR-β/δ and PPAR-γ upregulated CD36 protein expression, which contributes to MT-III-induced COX-2 expression. Furthermore, production of 15-d-PGJ₂, an activator of PPARs, induced by MT-III, was dependent on COX-1 being LDs an important platform for generation of this mediator.

Macrophages regulate lung ILC2 activation via Pla2g5-dependent mechanisms

Group V phospholipase A₂ (Pla2g5) is a lipid-generating enzyme necessary for macrophage effector functions in pulmonary inflammation. However, the lipid mediators involved and their cellular targets have not been identified. Mice lacking Pla2g5 showed markedly reduced lung ILC2 activation and eosinophilia following repetitive Alternaria Alternata inhalation. While Pla2g5-null mice had Wt levels of immediate IL-33 release after one Alternaria dose, they failed to upregulate IL-33 in macrophages following repeated Alternaria administration. Unexpectedly, while adoptive transfer of bone marrow-derived (BM)-macrophages restored ILC2 activation and eosinophilia in Alternaria-exposed Pla2g5-null mice, exogenous IL-33 did not. Conversely, transfers of Pla2g5-null BM-macrophages reduced inflammation in Alternaria-exposed Wt mice. Mass spectrometry analysis of free fatty acids (FFAs) demonstrated significantly reduced FFAs (including linoleic acid (LA) and oleic acid (OA)) in lung and BM-macrophages lacking Pla2g5. Exogenous administration of LA or LA+OA to Wt mice sharply potentiated IL-33-induced lung eosinophilia and ILC2 expansion in vitro and in vivo. In contrast, OA potentiated IL-33-induced inflammation and ILC2 expansion in Pla2g5-null mice, but LA was inactive both in vivo and in vitro. Notably, Pla2g5-null ILC2s showed significantly reduced expression of the FFA-receptor-1 compared to Wt ILC2s. Thus, macrophage-associated Pla2g5 contributes significantly to type-2 immunity through regulation of IL-33 induction and FFA-driven ILC2 activation.

Extracellular vesicles and their content in bioactive lipid mediators: more than a sack of microRNA

Extracellular vesicles (EVs), such as exosomes and microvesicles, are small membrane-bound vesicles released by cells under various conditions. In a multitude of physiological and pathological conditions, EVs contribute to intercellular communication by facilitating exchange of material between cells. Rapidly growing interest is aimed at better understanding EV function and their use as biomarkers. The vast EV cargo includes cytokines, growth factors, organelles, nucleic acids (messenger and micro RNA), and transcription factors. A large proportion of research dedicated to EVs is focused on their microRNA cargo; however, much less is known about other EV constituents, in particular, eicosanoids. These potent bioactive lipid mediators, derived from arachidonic acid, are shuttled in EVs along with the enzymes in charge of their synthesis. In the extracellular milieu, EVs also interact with secreted phospholipases to generate eicosanoids, which then regulate the transfer of cargo into a cellular recipient. Eicosanoids are useful as biomarkers and contribute to a variety of biological functions, including modulation of distal immune responses. Here, we review the reported roles of eicosanoids conveyed by EVs and describe their potential as biomarkers.

Phospholipases: An Overview

Phospholipases are lipolytic enzymes that hydrolyze phospholipid substrates at specific ester bonds. Phospholipases are widespread in nature and play very diverse roles from aggression in snake venom to signal transduction, lipid mediator production, and metabolite digestion in humans. Phospholipases vary considerably in structure, function, regulation, and mode of action. Tremendous advances in understanding the structure and function of phospholipases have occurred in the last decades. This introductory chapter is aimed at providing a general framework of the current understanding of phospholipases and a discussion of their mechanisms of action and emerging biological functions.

Possible Role of Phosphatidylcholine and Sphingomyelin on Fumonisin B1-mediated Toxicity

A major corn-related mycotoxin, fumonisin B1 (FB1), continues to attract attention of researchers as well as risk-assessors due to the diverse toxicological characteristics, including distinct target tissues in different animal species and opposite susceptibility in males and females in mice and rats. More than thirty years passed since the structure identification as a sphingoid-like chemical, but the causal mechanism of the toxicity remains obscure in spites of extensive studies. Considerable amounts of knowledge have been accumulated on the biochemical/toxicological actions of FB1, but the influence on lipid dynamics and mobilization in the body has not been focused well in relation to the FB1-mediated toxicity. Considerable influences of this toxin on mobilization of sphingolipids and phospholipids and also on adaptive changes in their compositions in tissues are implicated from recent studies on FB1-interacting ceramide synthases. Accumulated patho-physiological data also suggest a possible role of hepatic phospholipid on FB1-mediated toxicity. Thus, a mechanism of FB1-mediated toxicity is discussed in relation to the mobilization of phospholipids and sphingolipids in the body in this context.

Structural basis for functional selectivity and ligand recognition revealed by crystal structures of human secreted phospholipase A2 group IIE

Secreted phospholipases A₂s (sPLA₂s) are involved in various pathological conditions such as rheumatoid arthritis and cardiovascular disease. Many inhibitors were developed and studied in clinical trials, but none have reached the market yet. This failure may be attributed to the lack of subtype selectivity for these inhibitors. Therefore, more structural information for subtype sPLA₂ is needed to guide the selective inhibitor development. In this study, the crystal structure of human sPLA₂ Group IIE (hGIIE), coupled with mutagenesis experiments, proved that the flexible second calcium binding site and residue Asn21 in hGIIE are essential to its enzymatic activity. Five inhibitor bound hGIIE complex structures revealed the key residues (Asn21 and Gly6) of hGIIE that are responsible for interacting with inhibitors, and illustrated the difference in the inhibitor binding pocket with other sPLA₂s. This will facilitate the structure-based design of sPLA₂'s selective inhibitors.

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.