The Involvement of Phospholipases A2 in Asthma and Chronic Obstructive Pulmonary Disease

The increased morbidity, mortality, and ineffective treatment associated with the pathogenesis of chronic inflammatory diseases such as asthma and chronic obstructive pulmonary disease (COPD) have generated much research interest. The key role is played by phospholipases from the A2 superfamily: enzymes which are involved in inflammation through participation in pro- and anti-inflammatory mediators production and have an impact on many immunocompetent cells. The 30 members of the A2 superfamily are divided into 7 groups. Their role in asthma and COPD has been studied in vitro and in vivo (animal models, cell cultures, and patients). This paper contains complete and updated information about the involvement of particular enzymes in the etiology and course of asthma and COPD.


Introduction
Both asthma and COPD are airway diseases characterized by impaired airflow in the respiratory tract, chronic airway inflammation, as well as symptoms such as coughing, dyspnea, and wheezing. Intensive studies focused on the pathogenesis of these conditions implicate, among others, the group of phospholipases A 2 , which possess enzymatic and nonenzymatic properties. This paper presents general information about phospholipases and details the current knowledge about particular phospholipases A 2 involved in asthma and COPD in human and animal models. The data regarding interactions between members of this superfamily is summarized, as well as the role of these enzymes in exacerbations of inflammatory diseases.

Phospholipases
Phospholipases are enzymes that hydrolyze phospholipids. The main substrates for these enzymes are glycerophospholipids which contain glycerol with a saturated fatty acid in the sn-1 position and an unsaturated fatty acid in the sn-2 position. The phospholipases responsible for hydrolysis of glycerophospholipids are divided into two groups: acylhydrolases and phosphodiesterases. The first group comprises phospholipase A 1 (PLA 1 ) and A 2 (PLA 2 ), which hydrolyze the ester bond at the sn-1 and sn-2 positions, respectively. The second group comprises phospholipase C (PLC) which cleaves the glycerol-phosphate bond, and phospholipase D (PLD), which liberates phosphatidic acid and alcohol (Figure 1). Phospholipase B shares both the properties of PLA 1 and PLA 2 .
The structure, function, and catalytic mechanism of the enzyme determine its place within the phospholipase A 2 superfamily, be it secretory PLA 2 (sPLA 2 ), cytosolic PLA 2 (cPLA 2 ), Ca 2+ -independent phospholipase A 2 (iPLA 2 ), PAF acetylhydrolases (PAF-AH), or lysosomal PLA 2 (LPLA 2 ). The latest classification, based on genetic structure, divides these enzymes into groups from I to XVI (in each one, the enzyme is represented by a capital letter) [1]. The characteristic features of each group are presented in Table 1. Table 2 includes information about the mechanism of action and function of particular subgroups of PLA 2 s concerning physiology and pathophysiology.

Asthma and COPD
Currently about 300 million people worldwide suffer from asthma, and in 2025, this number is expected to grow by another 100 million. Annually, about 250 000 people die from asthma [2]. Asthma is defined according to the GINA (Global Initiative for Asthma) [3] as a chronic airway inflammatory disease in which many cells and cellular elements are involved. Chronic inflammation is a cause of bronchial hyperresponsiveness, leading to recurrent episodes of wheezing, dyspnea, chest tightness, and coughing, occurring particularly at night or dawn. This is usually accompanied by episodes of diffuse bronchial obstruction of varying severity, which often subside spontaneously or with treatment.
According to GOLD (The Global Initiative for Chronic Obstructive Lung Diseases) [6], COPD is characterized by a progressive and poorly reversible airflow limitation caused by both small airway diseases (airway inflammation and destruction) and parenchymal destruction (loss of alveolar attachment and decrease of elastic recall). Also, other extrapulmonary effects, such as weight loss, nutritional abnormalities, skeletal muscle dysfunction influence the severity of the disease. Apart from the genetic background (hereditary alpha-1 antitrypsin deficiency) [7] cigarette smoke is a crucial environmental factor in COPD development [8]; it is responsible for airway inflammation and further oxidant/antioxidant imbalance (oxidative stress) causing amplification of lung inflammation.  established that primary human lung mast cells constitutively  express mRNA for the IB, IIA, IID, IIE, IIF, III, V, X, XIIA, and XIIB sPLA 2 groups and stimulation with anti-IgE antibodies can induce their secretion [10]. Hence sPLA 2 proteins are believed to belong to preformed mediators which are stored in mast cells granules. Cells stimulation by anti-IgE antibodies causes degranulation of mast cells, and sPLA 2 appears in the early phase of allergic reaction. Muñoz et al. have shown that sPLA 2 V is not expressed in eosinophils in detectable amounts. However exogenous hPLA 2 V can activate eosinophils, inducing the liberation of arachidonic acid (AA) and LTC 4 production [11]. Increased cPLA 2 phosphorylation and cPLA 2 activity was observed in eosinophils of asthmatics after allergen challenge [12].

Analysis of Phospholipases A 2 Involvement in Asthma and COPD
Alveolar macrophages and neutrophils play a crucial role in the pathophysiology of COPD [13,14]. Human macrophages express cPLA 2 IVA, iPLA 2 VIA, and several sPLA 2 s (IIA, IID, IIE, IIF, V, X, and XIIA, but not group IB and III enzymes). Higher expression of sPLA 2 IIA is observed after LPS treatment [15]. Neutrophils stimulated in vitro by the tripeptide formyl-Met-Leu-Phe (fMLP) demonstrate mRNA and protein expression of sPLA 2 V and sPLA 2 X, where the sPLA 2 V protein is found in azurophilic and specific granules, and sPLA 2 X is found only in azurophilic granules. GIB, GIIA, GIID, GIIE, GIIF, GIII, and GXII sPLA 2 s are undetectable. Cell activation by fMLP or zymosan results in the release of GV but not GX sPLA 2 [16].
The BALF of patients with COPD demonstrates a threeto fivefold higher activity of PLA 2 s in comparison to a control BALF but the protein level shows no difference [17]. No differences in sPLA 2 IIs serum levels exist between healthy smokers and nonsmokers. However, significantly greater levels of this enzyme are found in the BALF of smokers compared with nonsmokers [18]. Among sPLA 2 s, sPLA 2 IID is also considered as a molecule involved in the course of COPD. A change of Gly80Ser in the sPLA 2 IID protein may be associated with body weight loss in patients suffering from COPD [19]. sPLA 2 IID can be also involved in control of inflammation by inhibition of CD4+, CD8+ T cells proliferation and induction of regulatory T cell differentiation [20]. Cigarette smoke extract (CSE) can induce the production of cytosolic phospholipase A 2 in human pulmonary microvascular endothelial cells [21]. Moreover oxidative stress can increase the activity of cPLA 2 by promoting its phosphorylation [22]. cPLA 2 also participates in phosphodiesterase 4 signaling, whose inhibition attenuates neutrophilic inflammation in COPD [23]. The increased values of PLA 2 VII in patients with longstanding pulmonary hypertension (severe complication in COPD) are related to severe endothelial dysfunction [24]. sPLA 2 V plays a different role in the activation of eosinophils and neutrophils. Hence, its involvement in the pathogenesis of asthma and COPD can vary. Exogenous sPLA 2 V can activate the production of AA and leukotrienes in both cell types. However, LTB 4 is preferentially produced in neutrophils, and LTC 4 in eosinophils [11]. The sPLA 2 V-induced activation of neutrophils in contrast to eosinophils requires the presence and activation of cPLA 2 [25]. The inhibition of cPLA 2 may be more effective in diseases where neutrophils  play a crucial role because they indirectly inhibit also the function of sPLA 2 .

Role of PLA 2 s in Asthma and COPD
The proposed mechanism of action of phospholipases A 2 (PLA 2 s) in inflammatory diseases includes the liberation of arachidonic acid, generation of lysophospholipids, interaction between enzymes belonging to the A 2 superfamily, surfactant degradation, release of cytokines, and the impact on immunological and inflammatory cells (dendritic cells, Tcells, and leukocytes) [26].

The Enzymatic
Activity of PLA 2 s. The enzymatic properties of PLA 2 s refer to their phospholipase, lysophospholipase, transacylase, adiponutrin-like, triglyceride lipase, peroxiredoxin 6, and acyl-ceramide synthase activities. Phospholipases A 2 play a pivotal role in eicosanoid production because they hydrolyze the ester bond at the sn-2 position of the glycerophospholipid membrane, releasing arachidonic acid (AA) and lysophospholipids [27]. Arachidonic acid plays a dual role. It can act as a signaling molecule that regulates the activity of protein kinase C (PKC) and phospholipase C , influences Ca 2+ concentration, and acts as an endogenous ligand for PPAR receptors [28,29]. AA is also a precursor of lipid inflammatory mediators (eicosanoids). In cyclooxygenase (COX) pathways, it is transformed to prostaglandins and thromboxane while in lipoxygenase (ALOX) pathways, it is converted to leukotrienes. These molecules are responsible for bronchial constriction, increased vessel permeability, and inflammatory cell recruitment [30]. AA is also a substrate for resolvins and lipoxins (LXs) which have anti-inflammatory properties. Lipoxins can block granulocyte chemotaxis, migration, degranulation, oxidative burst, cytokine-mediated signaling in eosinophils, and secretion of cytokines from bronchial epithelial cells [31]. Several independent studies have reported that significantly lower levels of LXs are observed in severe asthmatics compared to patients with nonsevere asthma [32,33]. Resolvins demonstrate endogenous anti-inflammatory, proresolving, antifibrotic, antiangiogenic, anti-infective, and antihyperalgesic activity [31].
Among cytosolic phospholipases A 2 , it has been well documented that cPLA 2 IVA (cPLA 2 ) plays an important role in eicosanoid production. In patients with inherited cPLA 2 deficiency (loss-of-function mutations in both cPLA 2 alleles), a widespread decrease in eicosanoid concentrations has been observed [34]. S111P, R485H, and K651R mutations in PLA2G4A gene are thought to play a crucial role in this condition. The functional consequences of localized mutations concerning cPLA 2 catalytic activity, Ca 2+ recruitment, and affinity for the phospholipid membrane have been confirmed in vitro and in cell culture [35]. In patients with severe asthma, the microsatellite fragments (T) n and (CA) n in the promoter region of cPLA 2 gene (PLA2G4A) are shorter in comparison to healthy subjects [36]. In addition, asthmatic patients with shorter microsatellite sequences demonstrate greater expression of cPLA 2 mRNA, cPLA 2 protein, PGE 2 and 15-HETE, but not LTC 4 [37]. cPLA 2 participates in intracellular signaling, leading to allergeninduced production of inflammatory cytokines in the PBMC of asthmatics [38]. Hallstrand et al. [39] identified increased expression of three cPLA 2 s, including cPLA 2 , cPLA 2 , and cPLA 2 in induced sputum cells from subjects with asthma and exercise-induced bronchoconstriction. Both cPLA 2 and cPLA 2 enzymes also participate in eicosanoids biosynthesis [40,41]. Increased cPLA 2 expression and subsequent PGE 2 production are present in the asthma phenotype. The therapeutic decision to inhibit cPLA 2 in asthmatics may be unclear when considering the role of PGE 2 in airway inflammation. There is some evidence that PGE 2 can act as bronchodilator, as well as an inhibitor of both allergeninduced bronchoconstriction and inflammatory mediators production [42]. It should be noticed that PGE 2 acts through four different types of receptors (EP 1 , EP 2 , EP3, and EP 4 ). Changes in expression and combination of receptor subtypes actions may affect the action of PGE 2 giving it proinflammatory or bronchoprotective outcomes [43][44][45]. The pleiotropic properties of PGE 2 make it difficult to establish the direct impact of PGE 2 deficiency which appears as a consequence of cPLA 2 inhibition [46]. Moreover, although cPLA 2 is a major enzyme, it is not the only one providing substrates for eicosanoids synthesis; hence it cannot be excluded that other existing pathways can also perform this function.  sPLA 2 s and arachidonic acid accumulate in the BALF of asthmatics after allergen challenge [47,48]. Despite being specific to the sn-2 bond, sPLA 2 s play more of a supporting role in AA liberation. Only sPLA 2 V and sPLA 2 X can efficiently interact and hydrolyze phospholipids from the outer surface of the cell membrane [9]. In acute and chronic animal asthma models, a deficit of sPLA 2 X diminishes the features of asthma (eosinophilia, airway hyperresponsiveness to methacholine, airway remodeling, eicosanoids, and Th2 cytokine production) [49].
Hallstrand et al. [50] showed that the expression of sPLA 2 X predominates in the airway epithelium, and both sPLA 2 X and sPLA 2 IIA are the main phospholipases produced by BALF cells. The activity of the sPLA 2 V protein was found to be greatly lowered and undetectable. They have suggested that sPLA 2 X is most important among secretory phospholipases. Only sPLA 2 X, not sPLA 2 IIA, is correlated with asthma features such as lung function, recruitment of neutrophils in asthmatics [50]. sPLA 2 X is responsible for production of cysteinyl leukotrienes (cysLTs) which are proinflammatory in asthma and can be responsible for observable features of asthma. Moreover, the level of prostaglandin E 2 (PGE 2 ) is also connected with sPLA 2 X, which can be explained by the fact that sPLA 2 X increases activity of cPLA 2 IV which in turn leads to production of PGE 2 . These results are consistent with earlier studies by the same authors in which gene expression of sPLA 2 X and sPLA 2 XII was demonstrated to be elevated in induced sputum cells of patients with asthma. The level of sPLA 2 X in induced sputum cells supernatant increased after exercise challenge among asthmatics with exercise-induced bronchoconstriction (EIB) [39]. Lai et al. [51] have confirmed the involvement of sPLA 2 X. They demonstrated that recombinant sPLA 2 X caused AA release and rapid onset of cysLT synthesis in human eosinophils.
Limited information suggests a possible anti-inflammatory role of sPLA 2 X. However in asthma, sPLA 2 X facilitates the polarization toward proasthmatic M2-macrophage phenotype [52]. It is possible that in a proinflammatory environment, that the sPLA 2 X propeptide is more rapidly converted to an active form that might influence the Th1/Th2 balance [53]. All these factors may suppress its anti-inflammatory action.
Other sPLA 2 s (IIA, IID, IIE) contain a heparin-binding domain which allows these enzymes to be taken into the cells and further directed to compartments enriched in AA and enzymes responsible for eicosanoid production [54].
In spite of the fact that several studies have confirmed the participation of iPLA 2 [55] and iPLA 2 [56] in AA release and eicosanoid production, there is no data indicating that these enzymes play a direct role in asthma. By the induction of Ca 2+ influx they can influence the translocation and activity of Ca 2+ -dependent PLA 2 s isoforms.
Group VII and VIII PAF-AH hydrolyze the short sn-2 residue of PAF (platelet activating factor). As they lack activity against membrane phospholipids with long-chain sn-2 residues, they are unable to release arachidonic acid from membrane phospholipids [57]. They exhibit pro-and antiinflammatory properties. On the one hand, they inactivate PAF-the proinflammatory mediator-by hydrolyzing it to inactive acetate and lysolipid but on the other hand, they assist in the generation of lysophospholipids and fatty acid hydroperoxides [4]. Stafforini et al. [58] have established that asthmatics have a decreased level of PAF-AH, and that asthma incidence and severity correlate to PAF-AH deficiency in the Japanese population. Also some PAF-AH gene polymorphisms (Ile198Thr and Ala379Val variants) are known to be a risk factors for developing atopy and asthma [59]. Despite positive effects in animal models [60], administration of human recombinant PAF-AH (rPAF-AH) does not reduce both early and late phase of asthmatic response in mild asthmatics challenged with allergens [61].
The enzymatic activity of PLA 2 s embraces also lysophospholipid generation. Lysophospholipids are biologically active molecules acting through specific receptors. They are a precursor of platelet activating factor (PAF) and lysophosphatidic acid (LPA). LPA is involved in cell adhesion, motility, and survival. In animal models, lysophospholipid receptors are required for proper development and function of the cardiovascular, immune, respiratory, and reproductive systems [62]. Lysophosphocholine and polyunsaturated fatty acids, including AA, can activate cPLA 2 and 5-lipoxygenase by increasing Ca 2+ and inducing cPLA 2 phosphorylation, which then leads to LTB 4 biosynthesis [25]. Lysophospholipid has nonspecific cytotoxic effect that depends on its concentration (critical micelle concentration). At concentration below their unspecific cytotoxic effect lysophospholipids can induce apoptosis by interrupting the synthesis of phosphatidylcholine [63].
Phospholipases A 2 activity is also connected with disturbed lipid homeostasis in the lung. Asthma and other inflammatory lung diseases are characterized by impaired surfactant function [64]. Secretory phospholipases degrade phosphatidylcholine (PC), the main component of the surfactant responsible for maintenance of small airway patency. The generation of lysophospholipids and free fatty acids by sPLA 2 -mediated PC hydrolysis has been implicated in small airway closure in asthma. sPLA 2 action is enhanced by eosinophilic lysophospholipases that use lysophospholipids as a substrate [65][66][67][68]. The presence of iPLA 2 proteins in alveolar macrophages suggests that they might play a role in surfactant degradation [69].
It should be mentioned that some PLA 2 s are involved in antibacterial defense thanks to their ability to hydrolyze the lipids of the bacterial membrane. sPLA 2 s IIA, V, X, and IB demonstrate bactericidal activity against gram-positive pathogens but the most effective is sPLA 2 IIA. Group XII can directly kill E.coli, unlike the other sPLA 2 s that require cofactors [70]. This property of phospholipases can be important in bacterial exacerbations of asthma and COPD.

Nonenzymatic
Activity of PLA 2 s. The secretory forms of many PLA 2 s exert a range of actions in airway inflammation. Apart from their enzymatic activity, they can act as extracellular mediators involved in chemotaxis, cytokine production, and induction of cellular signaling pathways.
Mammalian N-type receptors have been identified for sPLA 2 IB and IIA, X and M-type receptors for sPLA 2 IB, IIA, IIE, IIF, V, and X [71]. N-type like receptors are present in lungs whereas M-type receptors have been identified in lung and myeloid cells [72]. The binding of sPLA 2 s to their M-type receptor deactivates their enzymatic properties [73]. sPLA 2 s are stored in intrinsic mast cell granulates and are released after cell activation by IgE and non-IgE stimuli [9]. After exocytosis, they can act in both autocrine and paracrine manners. By interacting with heparan sulphate proteoglycans and M-type receptors, they can induce PGD 2 and LTC 4 production and stimulate the subsequent degranulation of mast cells [74]. Granata et al. [17] delivered an evidence that sPLA 2 s can act as proinflammatory connections between mast cells and macrophages in the airway. They suggest that the activation of macrophages by sPLA 2 s leads to production of proinflammatory cytokines which sustain the inflammatory and immune response, chemokines responsible for recruitment of monocytes and neutrophils, as well as destructive lysosomal enzymes, NO, PGE 2 , and metalloproteinases connected with airway remodeling [17]. The sPLA 2 s induce -glucuronidase release and production of IL-6 from human lung macrophages [75]. They influence the migration and adhesion of neutrophils as well as the release of elastase [76,77]. In eosinophils, sPLA 2 IA and IIA stimulate -glucuronidase release and cytokine production (IL-6, IL-8) by AA and lysophospholipid generation, by interaction with membrane peptidoglycans via their heparin-binding site, and through binding with specific M-type or N-type receptors [78]. The functions of sPLA 2 s receptors require further studies because there are still some missing or unequivocal information [52].

5.3.
Crosstalk between PLA 2 s. The phospholipases can cooperate in mechanism leading to eicosanoid production. sPLA 2 and cPLA 2 interaction is quite well documented [79,80]. The effect of group IIa and V PLA 2 s on H 2 O 2 -induced AA release is dependent upon the presence of cPLA 2 and the activation of PKC and ERK1/2 in murine mesangial cells. Offer et al. [81] have described negative feedback between sPLA 2 and cPLA 2 in eicosanoid production. sPLA 2 activation induces production of bronchoconstrictor cysteinyl leukotrienes and suppresses cPLA 2 expression and the subsequent production of bronchodilator PGE 2 . Recently it has been established that in human eosinophils, sPLA 2 initiates Ser(505) phosphorylation of cPLA 2 and stimulates leukotriene synthesis through involvement of p38 and JNK MAPK, cPLA 2 , and 5lipoxygenase activation, which may be an important process also in airways of asthmatics [51]. Also in bone-marrowderived mast cells, sPLA 2 mediates the selective release of AA by binding M-type receptors and then inducing MAPK signaling pathways that lead to cPLA 2 activation [82].

PLA 2 s in the Exacerbation of Disease.
Another aspect of phospholipases and the asthma/COPD relationship is the participation of these enzymes in the pathogenetic mechanisms of disease exacerbation caused by bacterial factors. This role relates to increased expression of selective PLA 2 s, modulation of their activity and involvement in cellular signaling. Elevated cPLA 2 expression was found in primary human lung macrophages after LPS treatment [15,83]. LPS stimulates expression of cPLA 2 and COX-2 in macrophages, leading to increased production of AA and PGE 2 [83]. LPS treatment was also followed by rapid changes in cPLA 2 phosphorylation [84,85]. This is one of the mechanisms of regulating enzyme activity [86]. The LPS-phosphorylated form of cPLA 2 is present in induction of iNOS and TNFexpression [87,88] and metalloproteinase production [89]. Selective sPLA 2 contributes to LPS-intracellular signaling in liver macrophages [84,90,91].
In mice with LPS-induced lung inflammation, the expression of sPLA 2 X remains the same before and after treatment. In this study, increased expression of sPLA 2 IID and sPLA 2 V has been observed, as well as decreased sPLA 2 IIE and sPLA2IIF levels in the lungs. In rats, sPLA 2 IIA was seen to have the highest expression after LPS administration [92]. In msPLA 2 X −/− mice with knock-in of human sPLA 2 X (hsPLA 2 X), allergen-induced inflammatory cell recruitment into airways (eosinophils) was restored, as well as hyperresponsiveness to methacholine. The application of specific hsPLA 2 X inhibitor (RO 061606) significantly attenuates airway inflammation symptoms, mucous secretion, and hyperresponsiveness [93]. In sPLA 2 V −/− knock-out mice, sPLA 2 V has been proven to play a role in the development of lung injury and neutrophilic inflammation after bacterial stimulus (LPS) [94]. In addition, sPLA 2 V was seen to be connected with regulation of cell migration and generation of airway hyperresponsiveness after ovalbumin challenge [95]. In a murine allergen-challenged asthma model, administration of rPAF-AH is effective in blocking late-phase pulmonary inflammation [60].

The Clinical Significance of Studying the Participation of PLA 2 s in Airway Inflammatory Diseases
Taking into consideration the severe asthma phenotype, the difficulties related to obtain asthma control utilizing currently 8 Mediators of Inflammation available treatments and the progressive character of inflammation in patients with COPD that increases the morbidity, it seems reasonable to study the differences in pathogenesis of the diseases conditions, especially in relation to possible new therapies and drugs. The PLA 2 s are an interesting object of study for several reasons. The superfamily of these enzymes contains approximately 30 members that have similar and isoform-specific properties. It has been confirmed that they are strictly connected with inflammation. The inhibitors of particular PLA 2 s show the positive effect in treatment of inflammatory diseases [96] and they inhibit allergic reaction in vitro [38]. The cPLA 2 that evolved together with receptors for eicosanoids, present only in vertebrate, seems to play crucial role in course of inflammation. Its inhibitors such as efipladib [97] and ecopladib [98] successfully inhibit inflammation in rheumatoid arthritis and osteoporosis. The inhaled form of cPLA 2 inhibitor, the PLA-950, is considered as potential new treatment in asthmatic patients as well as other PLA 2 s can influence the function of cPLA 2 or have similar effects. Recent studies report positive results of a preclinical evaluation of a cPLA 2 inhibitor [99]. The studies and analysis of protein involved in regulation of particular sPLA 2 involved in inflammatory diseases could result in finding new target for drugs. Since 1980, it has been known that glucocorticoids (GCs) can inhibit the activity of PLA 2 [100]. The underlying mechanism concerns induction of mRNA and protein expression of lipocortin 1 (annexin 1) and the PLA 2 inhibitory protein [101][102][103][104]. The structure, function, and mechanism behind the anti-inflammatory action of annexin 1 have been well described elsewhere [105]. Glucocorticoids can also suppress the production of sPLA 2 IIA by blocking mRNA synthesis and posttranslational expression in rats [106]. It is questionable whether therapeutic doses of glucocorticoids have sufficient power to satisfactorily inhibit the activity of PLA 2 . Juergens et al. [107] demonstrated that topical GCs at therapeutically relevant concentration (10 −8 M) inhibit the spontaneous activity of cPLA 2 in the range of 8.6-17.3% depending on the type of GC. They suggest also that this effect may appear as a consequence of a decreased ability to binding the receptors by GCs present in airway in subtherapeutical doses. Although it has been established that treatment with GCs can indirectly inhibit cPLA 2 and AA-derivates production resistance to GCs in patients with asthma and COPD could also be problematic. Moreover the GCs have systemic effects and long-term application can cause the side effects. The approach to attack the inflammation process more precisely and downstream (inhibition the eicosanoids production) seems to be rationale.
Another aspect regarding annexin 1 and PLA 2 s is their cell-specific manner of interactions [105]. Kwon et al. [108] demonstrated that cleavage of annexin 1 causes phosphorylation of cPLA 2 during mast-cell activation. Hence it is not clear whether GCs-induced expression of annexin always leads to inhibition of cPLA 2 activity. Posttranslational changes can dramatically influence the primary protein function. As previous studies indicate that GCs can stimulate expression of cPLA 2 in amnion fibroblast it cannot be excluded that in some specific circumstances GCs may directly induce cPLA 2 [109,110].

Conclusions
Previous studies confirm the involvement of phospholipases A 2 in asthma and COPD although there are some gaps relating to the roles of specific enzymes. The participation of PLA 2 in asthma pathogenesis has been better investigated. The diagnostic problems concerning the overlap syndrome that shares the features of asthma and COPD demand further studies on the pathogenesis of these diseases. The phospholipases A 2 through their involvement in the course of inflammation seem to be important aspects of this investigation. As they demonstrate pro-and anti-inflammatory properties, a detailed analysis of their role should act as a focus for further studies intended to bring new insights into the pathogenesis of the diseases and identify targets for new drugs.
Data from studies focused on role of PLA 2 s in inflammatory diseases facilitate the understanding of molecular aspects of inflammation. It can be observed that cPLA 2 plays a main role in eicosanoid production and other PLA 2 s may influence their activity thanks to enzymatic properties or act as regulators of inflammation through their nonenzymatic activity. The pleiotropic properties of single phospholipase and their differential expression in many cells confirm that this is well-organized network of interaction, and further studies focused on this aspect may provide more useful knowledge. A comparison of how this network works in different inflammatory diseases, as well as in healthy subjects may indicate a key molecule, whose activity or presence will be a diagnostic parameter or whose activation or inhibition will have therapeutic value.
Asthma and COPD are heterogeneous diseases and current treatment gives only the possibility to obtain the phenotype of well-controlled diseases. Analysis of data regarding the involvement of PLA 2 s in course of diseases arises the concept to use combined therapy rather than the treatment based on inhibition of one of them. The results from preclinical studies of cPLA 2 inhibitors are promising but clinical trials will give concrete knowledge about the effectiveness and possible side effects.