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The Proceedings of the American Thoracic Society 4:659-666 (2007)
© 2007 The American Thoracic Society
doi: 10.1513/pats.200707-103TH
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Future Treatment to Lessen Exacerbations of Chronic Obstructive Pulmonary Disease

Alan R. Leff1,2 and Nilda M. Muñoz1

Departments of 1 Medicine, 2 Pediatrics, Pharmacology and Physiology, and Anesthesia and Critical Care, University of Chicago, Chicago, Illinois

Correspondence and requests for reprints should be addressed to Alan R. Leff, M.D., Department of Medicine, University of Chicago, 5841 South Maryland Avenue, Chicago, IL 60637. E-mail: aleff{at}medicine.bsd.uchicago.edu

ABSTRACT

Therapies currently used to reduce exacerbations of chronic obstructive pulmonary disease (COPD) are compounds used almost entirely for asthma therapy. A notable exception is tiotropium, a long-acting parasympatholytic agent. This compound and its precursor, iprotropium, are only occasionally used for asthma therapy. Likewise, leukotriene-modifying drugs are used occasionally for the treatment of COPD. In neither circumstance is there agency-approved indication for these particular cross-over therapies, but the use of long-acting β2-adrenergic compounds and high-solubility inhaled steroids is a mainstay for therapy in both asthma and COPD. Similarly, theophylline, although less often used for either process, is therapeutically applicable to both asthma and COPD. Although overlap syndromes point to the occurrence of a common pathway in some cases, the inflammatory process for asthma and chronic obstructive pulmonary disease (COPD) differs substantially in most cases. Hence, the application of therapies designed to relax airway smooth muscle and ameliorate asthmatic inflammation lacks a therapeutic rationale for a disease characterized by predominant neutrophilic inflammation occurring in the small airways and alveoli. By definition, COPD is poorly reversible airflow obstruction; hence, the use of drugs designed to relax airway smooth muscle is somewhat counterintuitive and does not address the pathophysiological process of the disease.

Key Words: chronic obstructive pulmonary disease • annexin-1 • HIV-TAT • secretory group V phospholipase A2 • neutrophils

Unlike most cases of asthma, COPD is progressive, especially in more advanced states. This progression of airflow obstruction is generally attributed to an inflammatory process originating from either the vascular (1) and/or epithelial side (2) of the small airways of the lung. This was discussed extensively in the proceedings of the AstraZeneca COPD Symposium held on April 25 and 26, 2006, in Lund, Sweden (see Proc Am Thorac Soc 2006;3:665–736).

Current therapies have been shown in some cases to reduce COPD exacerbations, but, unlike asthma, no therapy has been designed specifically to ameliorate the frequency of COPD exacerbations. Omalizumab, which reduces the exacerbations in allergic asthma by targeting circulating immunoglobulin E (IgE) (3), and bronchial thermoplasty (4), which decreases airway smooth muscle mass (5), both have been shown to reduce asthma exacerbations in subjects with either allergic asthma or more advanced persistent asthma. Although omalizumab and thermal bronchoplasty are not applicable in the treatment of COPD, they reveal a parallel need in the approach to prevent exacerbations of COPD, that is, to develop therapies that are disease-specific antiinflammatory therapies and pathophysiologically relevant modalities for COPD. This approach requires basic research into the mechanisms of pathogenesis that promote the inflammatory process of COPD. Understanding cell–cell signaling in the inflammatory process of COPD requires further understanding of signal transduction in inflammatory cells—from upstream activation by proinflammatory agents to translation of irreversible damage to airways by effector cells.

In this rendition of a pathway to specific, pathogenetically based reduction of airway injury, it will be assumed that blockade of the inflammatory process is a helpful rather than harmful process. A potential argument can be made to the contrary, that is, that inflammation is protective against the pathogens and other external agents that otherwise would be even more destructive. There are no definite data to suggest that this is the case. Antiinflammatory therapies not specifically designed for COPD, such as inhaled corticosteroids, reduce exacerbations of COPD (6), with only a slight increase in the incidence of pulmonary infections, for example, pneumonias (7).

PATHOGENESIS OF NEUTROPHILIC INFLAMMATION

Irritant stimuli attract in nonspecific fashion the migration of polymorphonuclear leukocytes (PMNs) in both infectious and noninfectious disease processes. Cigarette smoking, the predominant cause of COPD, is such a stimulus. The precise mechanism of neutrophil chemotaxis still is not elucidated fully, but a sequence of intracellular events is known to mediate the process. Intervention at any of these steps will prevent the migration of granulocytes into sites of inflammation (8–11). Although the most convincing work in this area has been done in eosinophilic granulocytes, some of the same processes are shared by neutrophils (PMNs). At least five separate processes are required for granulocyte migration to a targeted site (Table 1). After laminar flow is disrupted by selectins in the circulation of small vessels, activated granulocytes begin to roll along the capillary wall (11). The next step is firm adhesion to the endothelial wall, which in PMNs appears to be mediated solely by β2-integrins on the neutrophil surface. In neutrophils, β2-integrins are constitutively expressed, although further up-regulation occurs during cell activation (Figure 1A, top). Up-regulation of β2-integrin (CD11b/CD18) in PMNs requires a conformational change/avidity in this integrin (Figure 1A, middle) to allow for binding to the endothelial counterligand, intercellular adhesion molecule-1 (ICAM-1), an immunoglobulin supergene that resides on the endothelial surface and that itself must be up-regulated. Before up-regulation, surface β2-integrin migrates within the inflammatory cell surface membrane, so that this integrin is clustered in one portion of the cell (focal clustering) (Figure 1A, bottom). This allows the rolling cell to "stick" to its counterligand, as clustering increases affinity (Figure 1B). The bound cell is pulled out through the junctions of the endothelial membrane into the airway within about 30 minutes by progressive integrin ligation (11) Thus, the process is continuous and self-renewing. The self-renewing component refers to the persistent ability of granulocytes to readhere to interstitial extracellular matrix protein (e.g., fibronectin [12]) and to its counterligand expressed on airway smooth muscle, CD4+ cells, and epithelial cells. This route of molecular adhesion augments the secretory capacity of eosinophils and neutrophils to release granular proteins that are destructive to airway tissues, for example, major basic protein, which destroys epithelial cells and neutrophilic antiproteases, which disrupt the alveolar matrix in COPD.


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  		TABLE 1. REQUIREMENTS FOR β2-INTEGRIN LIGATION

 

Figure 1
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  		Figure 1. (A) β2-Integrin activation for adhesion. Top: Up-regulation of cell surface CD11b expression. Middle: Conformational change/avidity of CD11b. Bottom: Focal clustering/affinity of CD11b to amplify "stickiness" while rolling. (B) Localization of CD11b on the eosinophil surface. Naive eosinophils were transduced with HIV-TAT–dominant negative Ras protein (TAT-dnRas) before activation with IL-5, eotaxin, N-formyl-methionine-leucine-phenylalanine (fMLP), or phorbol myristate acetate (PMA). Note that CD11b is dispersed for cells treated with TAT-dnRas; PMA, which bypasses the Ras pathway, is not affected by TAT-dnRas. Reprinted by permission from Reference 18.

 
Table 1 summarizes five essential steps in PMN adhesion based on studies of PMNs and other cells that rely on β2-integrin for cell migration. In eosinophils, corticosteroids block only step 4, but this is sufficient to block almost completely eosinophil adhesion in vitro in human cells (13, 14) and in vivo in murine models (14).

Other interventions that block phosphorylation of the intracellular phospholipase A2 (group IVa PLA2, less specifically referenced as cytosolic PLA2) also block β2-integrin adhesion, and dephosphorylation of this protein is associated with de-adhesion from endothelial ligands (15). De-adhesion is an obviously essential step, lest granulocytes be attached forever to the endothelial membrane. The extent to which interventions block each of these processes differs somewhat among granulocytes, each of which has different phosphorylation processes. Hence, knowledge of signal transduction in one cell cannot be applied generally to all cells—even those sharing the same integrins. Because the most comprehensive data for granulocytes are derived from eosinophils, these cells are the major granulocytes from which therapeutic approaches based on previously published observations will be suggested. The caveat, of course, is that activation and inhibition of these processes, even for a specific pathway, vary among inflammatory cells.

HIV-TAT PROTEINS AND RELATED THERAPIES PROXIMAL TO gIVaPLA2 PHOSPHORYLATION

The HIV-1 transactivator gene product, TAT, has been shown to be a regulator of transcription in latent HIV and contains no elements for genomic incorporation (16). As such, these TAT proteins added exogenously to culture (17) or freshly isolated cells (18), as well as in vivo (19, 20), are taken up rapidly by cells. TAT is an 86–amino acid protein made from two exons of 72 and 14 amino acids (16, 21). Dowdy and coworkers (16, 21) improved the delivery of TAT protein by constructing fusion proteins between several polypeptides and proteins and a short (11-amino acid) region of the TAT protein referred to as the protein transduction domain (Figure 2A). The desired denatured protein tagged onto the TAT vector is transduced more efficiently directly into cells, where it unfolds and is expressed as an active enzyme or inhibitor (Figure 2B). An essential and valuable component of TAT protein treatment is that it does not require cell replication. Most work has used transduction of dominant negative proteins (Figure 1B), which can inhibit intracellular processes within minutes (18–20). The efficiency of transduction in vitro approximates 100% with as little as 100 nM TAT protein (18–20). Inhibition of extracellular signal-regulated kinase (ERK)-1/2 signaling is established within 10 minutes (Figures 2C and 2D). High molecular mass proteins (greater than 100 kD) can be introduced into cells with TAT protein (16, 21). Transduction of dominant negative Ras protein into primary isolates of human eosinophils (18) blocks substantially or completely the β2-integrin adhesion caused by cytokines or chemokines, which correlated with phosphorylated ERK-1/2, an essential step in gIVaPLA2 activation (Figure 3). Alternative gIVaPLA2 phosphorylation pathways (e.g., phosphatidylinositol 3-kinase [PI3-K]) are blocked in vitro and in vivo by TAT-{Delta}p85, an 85-kD dominant negative form of Class IA PI3-K protein (20). This alternative pathway was established with fully mature animals because genomic deletion of PI3-K is a lethal knockout (22).


Figure 2
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  		Figure 2. Purification and function of TAT protein. (A) Structure of TAT-Ras fusion protein. Six histidine residues and the 11–amino acid TAT peptide precede the NH2 terminus of the Ras protein. The 11 amino acids of TAT are the protein transduction domain. (B) Transduction of TAT-dnRas into isolated eosinophils as assessed by Western blot analysis. TAT-dnRas is fully incorporated into the cell within 20 minutes in vitro. (C) Time-dependent effects of 100 nM TAT-dnRas on IL-5–stimulated extracellular signal-regulated kinase (ERK)-1/2 phosphorylation. Eosinophils were treated with 100 nM TAT-dnRas for the indicated times and stimulated with IL-5 (10 ng/ml). Cell lysates were loaded onto the sodium dodecyl sulfate–polyacrylamide gel and probed with antibody directed against phosphorylated ERK-1/2 (top) and with total ERK-1/2 antibody (bottom) to demonstrate equal loading in all lanes. (D) Concentration-dependent effects of TAT-dnRas on IL-5–stimulated ERK-1/2 phosphorylation. ERK-1/2 phosphorylation was measured as described above. Reprinted by permission from Reference 18.

 

Figure 3
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  		Figure 3. Effects of TAT-dnRas on eosinophil adhesion. Cells were treated with 100 nM TAT-dnRas or vehicle control (cont) (100 nM TAT-vehicle) before activation with IL-5 (10 ng/ml), eotaxin-1 (100 ng/ml), 10–6 M N-formyl-methionine-leucine-phenylalanine (fMLP), or 1 nM phorbol myristate acetate (PMA). Eosinophil adhesion was assessed by measuring the residual eosinophil peroxidase activity in treated cells, using a microplate reader. *P < 0.05 vs. positive cont and TAT-vehicle. Reprinted by permission from Reference 18.

 
Both TAT–dnRas transduction and modest concentrations of corticosteroid block physiological activation of gIVaPLA2, the former by preventing phosphorylation and the latter by blocking translocation of cytosolic gIVaPLA2 to the nucleus of eosinophils (Table 1 and Figure 4). Interestingly, neither agent blocks up-regulation of surface CD11b expression, the only active neutrophil integrin. This is a potentially exciting finding, because it suggests that therapies can be targeted downstream, possibly even to specific sites without causing global inhibition of essential inflammatory responses that are protective.


Figure 4
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  		Figure 4. Effect of fluticasone propionate (FP) on stimulated cytosolic group IVa phospholipase A2 (gIVaPLA2). (A) Negative control; (B) unstimulated control; (C) eosinophils stimulated with 2 x 10–6 M A23187 (positive control); (D) IL-5–stimulated eosinophils; (E) IL-5 plus 10–7 M FP; (F) eotaxin-stimulated eosinophils; (G) eotaxin plus 10–7 M FP. Cytosolic gIVaPLA2 is equally distributed in the cytosol (B) and translocated to the nuclear membrane in response to IL-5 (D) and eotaxin (F). Pretreatment of eosinophils with FP blocked the translocation of cytosolic gIVaPLA2 to the perinuclear membrane (E and G). Reprinted by permission from Reference 13.

 
The extent to which these observations apply to PMNs and therapy for inflammation in COPD remains to be elucidated. However, the technology allows for selective blockade of regional inflammatory processes and should with appropriate modification be easily adapted to antiinflammatory technologies for COPD.

ROLE OF THERAPIES DISTAL TO gIVaPLA2 TRANSLOCATION

Cytosolic gIVaPLA2 hydrolyzes the membrane phospholipids at the sn-2 position to release free fatty acids and lysophospholipids, which eventually lead to the production of arachidonic acid metabolites and the lyso form of platelet-activating factor (PAF), respectively (Figure 5). A substantial literature documents the roles of arachidonate metabolites in inflammation. These include 5-lipoxygenase (leukotriene B4 [LTB4] and cysteinyl leukotrienes) and cyclo-oxygenase (thromboxanes and prostaglandins) products. In airway disease, only cysteinyl leukotrienes (LTC4, LTD4, and LTE4) have been shown to cause even moderate airway disease; accordingly, arachidonate metabolites per se appear to play a rather limited role in airway inflammation. However, PAF has been demonstrated as the essential factor in both eosinophil (23, 24) migration in a mouse model of asthma and neutrophil migration in a mouse model of acute respiratory distress syndrome (25). Intracellular PAF exists in equilibrium with lyso-PAF, which is an inactive form. The phosphorylation and migration of cytosolic gIVaPLA2 to the nuclear membrane result in the production of PAF (26), which has been shown to be essential to the maintenance of eosinophil adhesion in rodent asthma models (27). PAF receptor knockout and pharmacologic blockade with late-generation PAF inhibitions block both eosinophil migration in allergen-challenged allergic mice and neutrophil migration caused by hydrochloric and oleic acids (23, 25). As noted above, inhibition of gIVaPLA2, which is mediated by either a Ras-dependent or PI3-K-dependent pathway, blocks phosphorylation of gIVaPLA2 (see above). Hence, even if β2-integrins are up-regulated, granulocytes cannot adhere unless intracellular PAF concentrations are maintained or up-regulated.


Figure 5
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  		Figure 5. Cell activation by cytokine, chemokine, and G protein–coupled receptor agonist–induced β2-integrin adhesion. Ras is the upstream pathway, which initiates the activation of extracellular signal-regulated kinase (ERK)-1/2 and subsequently the gIVaPLA2 pathway. The alternative pathway for induction of β2-integrin adhesion is phosphatidylinositol 3-kinase (PI3-K). Activated gIVaPLA2 hydrolyzes the nuclear phosphatidylcholine-rich membrane, causing the generation of lysophospholipids and free fatty acids including arachidonic acid. The inactive lyso-PAF is converted to active-form PAF by acetyltransferase, which is crucial in increasing the affinity of cell β2-integrin for its counterligand. AA = arachidonic acid; COX = cyclo-oxygenase; IP3 = inositol triphosphate; JAK2 = Janus kinase 2; 5-LOX = 5-lipoxygenase; LTA4/LTB4/LTC4 = leukotriene A4/B4/C4; MAPK = mitogen-activated protein kinase; MEK = MAPK/ERK kinase; PAF = platelet-activating factor; PC = phosphatidylcholine; PGs = prostaglandins; PIP2 = phosphatidylinositol diphosphate; PLC = phospholipase C; TBX = thromboxane.

 
The long-ignored by-product of PLA2 hydrolysis, PAF, now appears to be an essential regulator of integrin adhesion, as is gVIIaPLA2 (PAF-acetyl hydrolase), which back-converts PAF into lyso-PAF (28). It now appears that the intracellular PAF receptor is the critical regulator. Hence the process of inflammatory cell activation with PAF, which may not be important in granulocyte inflammation, is now the final common pathway of integrin adhesion. This would seemingly explain the disappointing results in prior therapeutic trials of PAF antagonists in human asthma. Application of the demonstration that PAF receptor knockout and inhibition prevent granulocyte adhesion and tissue infiltration is obvious, although details on how to effect this process require further elucidation.

ANNEXIN-1

Corticosteroids promote transcription of annexin-1 in eosinophils (Figure 6) (14). Although the role of annexin-1 has not yet been elucidated in PMNs, this protein is also up-regulated in these cells in the activated state (29). In eosinophils, β2-integrin adhesion is blocked by long-term (24-h) incubation with 10–8 to 10–6 M fluticasone propionate (13, 14). Immunocytochemical staining reveals that after annexin-1 synthesis by corticosteroid, this protein is transported to both the nucleus and outer plasma membranes, although the outer plasma membrane transport appears to be the critical factor in the blockade of eosinophil β2-integrin adhesion (Figure 6A). This effect is mimicked by administration of a peptide spanning the first 24 amino acids of annexin-1, termed peptide Ac2-26 (Figure 6B) (14). The fact that annexin-1 and its NH2-terminus-derived peptide cause detachment of adherent eosinophils indicates that controlled activation of adherent cells is occurring. There currently are no published reports of the ability of annexin-1 to block β2-integrin adhesion in PMNs. However, annexin-1 is synthesized by PMNs (29). The value of administration of annexin-1, or its mimetic fragment, which exist in nature and thus should not be immunogenic, has not been evaluated. The discovery of annexin-1 drug is likely another potential therapeutic strategy, perhaps modulatory rather than fully inhibitory, for patients with intercurrent illness that is promoting COPD exacerbation.


Figure 6
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  		Figure 6. Effects of fluticasone propionate (FP) and Ac2-26, a long fragment of annexin-1. (A) Representative histogram of annexin-1 expression in eosinophils. (B) Composite data demonstrating inhibition of eosinophil adhesion to counterligand in vitro, caused by administration of Ac2-26. Anti-N19 = antibody to a shorter fragment of annexin-1 NH2 terminus–derived peptide. FL = fluorescence intensity. Reprinted by permission from Reference 42.

 
SECRETORY PLA2

Mammalian secretory PLA2s are small molecular mass enzymes (10–14 kD, mostly) that are secreted ubiquitously as multiple, diverse isoforms by many species to the extracellular medium as fully active enzymes in response to cell activation (30). In contrast to the 85-kD intracellular PLA2 (cytosolic gIVaPLA2), secretory PLA2s act from the outside in. Eosinophils and neutrophils contain group IIa PLA2, a secretory enzyme with no established physiological function in airway disease (31, 32). For many years, gIIaPLA2 was not distinguishable from the much more active gVPLA2, which is not contained in eosinophils but is expressed in neutrophils (33), airway smooth muscle (34), macrophages (35), epithelial cells (32, 36), and T cells (37). Extensive structure–function studies have established that secretory gVPLA2 contains a considerable number of tryptophan residues, which play a major role in binding of this enzyme to zwitterionic membranes, most notably phosphatidylcholine bilayers (38, 39).There is no receptor for gVPLA2; the predilection of gVPLA2 for outer membrane hydrolysis is due solely to its putative interfacial binding surface located at Trp-31 (W31); mutation of W31 to alanine reduces the activity of gVPLA2 (31, 32, 38, 39). Figure 7 demonstrates the close homology between gIIaPLA2 and gVPLA2 (40). Accordingly, gVPLA2 has approximately 50-fold the hydrolytic capacity for phosphatidylcholine-rich membrane compared with gIIaPLA2, its close homolog, in cell-free systems (30, 38–40).


Figure 7
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  		Figure 7. Putative structures of two highly homologous 14-kD secretory PLA2 isoforms. gVPLA2 has a 50-fold hydrolytic capacity for phosphatidylcholine-rich membrane compared with gIIaPLA2. W31 is the critical interfacial binding site of gVPLA2. The molecules are oriented with their (putative) interfacial binding surfaces facing the viewer. Two mutated surface tryptophans of gVPLA2 are shown in red and labeled. Aliphatic side chains are shown in yellow, aromatic side chains in green, cationic side chains in blue, and anionic side chains in pink. Polar side chains and the peptide backbone are shown in white. Reprinted by permission from Reference 39.

 
gVPLA2 causes direct hydrolysis of the outer plasma membranes of mammalian cells, thus generating lysophospholipids and free fatty acids including arachidonic acid, which in turn leads to eicosanoid biosynthesis. Both gIIaPLA2 and gVPLA2 are transported into the cytosol of PMNs and eosinophils by anionic heparan sulfate proteoglycan (31, 36, 38) located on the cell surface membrane. Unlike gVPLA2, gIIaPLA2 has low activity on outer phosphatidylcholine-rich membranes but has a strong hydrolytic preference for phosphatidylserine and phosphatidylethanolamine, located in the inner plasma membranes of inflammatory cells (30). After intracellular uptake by heparan sulfate proteoglycan, gIIaPLA2 is degraded to avoid extensive lipolytic damage of the outer plasma membrane. By contrast, gVPLA2 on intracellular uptake hydrolyzes further the intracellular phosphatidylcholine-rich nuclear membrane, adding more arachidonate to the intracellular content, in addition to that taken up by the cell by external hydrolysis of outer membrane. gVPLA2 also activates 5-lipoxygenase in granulocytes through gIVaPLA2-dependent and -independent pathways (31, 32, 36). Within 5 minutes, secretion of small amounts of LTB4 is apparent in PMNs; this LTB4 then serves as an autocrine activator of PMN function, and within 15 minutes there is a further threefold increase in LTB4, suggesting that gIVaPLA2 activation is required for the augmented synthesis of LTB4 in PMNs (36, 38). It thus appears that many, if not all, airway inflammatory activities attributed to gIIaPLA2 (once referenced as secretory PLA2 [sPLA2]) are probably a function of gVPLA2. The biochemical distinction between these two homologous isoforms was performed in large part by Cho and others (31, 32, 38, 39), and the generation of monoclonal antibody (mAb) to separate the functions of these two isoforms by Muñoz and coworkers (41). mAb MCL-3G1 has nearly complete specificity for gVPLA2 (31, 32, 41) and has substantiated the concept that gVPLA2 is the active secretory PLA2 with potential pathophysiological significance in both asthma and COPD.

On the basis of the observation of the high extracellular lipolytic capacity of gVPLA2, its intracellular activity, and its insignificant presence in PMNs and eosinophils, Muñoz and coworkers postulated that gVPLA2 might be the intercellular messenger protein between epithelium and PMN activation through the cascade described above (32). Endogenously secreted gVPLA2, brought about by selective stimulation of epithelial cells cocultured with eosinophils by endothelin-1, causes activation of eosinophils that is blocked by both pharmacologic inhibitors of gIVaPLA2 and MCL-3G1, an mAb directed against gVPLA2 (32). In these studies, secreted gVPLA2 from activated epithelial cells was shown to be translocated to the surface membrane of adherent eosinophils (Figure 8). Ligand binding of β2-integrin of eosinophils to ICAM-1 on epithelial cells also was demonstrated. This serves to bring these cells into direct proximity, magnifying by several logs the efficacy of the stimulus compared with measurable concentrations in vitro.


Figure 8
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  		Figure 8. (A–C) Transcellular migration of group V phospholipase A2 (gVPLA2) from activated epithelial cells (EPI) to adherent eosinophils (EOS). Release of gVPLA2 (arrows) caused the activation of eosinophil secretion of leukotriene C4. ET-1 = endothelin-1. Bottom: Higher magnification of boxed area in (C). Red arrow indicates secreted gVPLA2. Reprinted by permission from Reference 32.

 
As gVPLA2 can be inhibited nonspecifically by orally administered compounds that block gIIaPLA2, there is ample justification for an efficacy trial to determine whether these compounds can prevent exacerbations of COPD. Current studies are in progress to determine whether this is the critical enzyme mediating both neutrophil and eosinophil activation in vivo.

CONCLUSIONS

There currently are no drugs designed to prevent exacerbations of COPD. Despite vast differences in pathophysiology, therapeutic agents for this syndrome are virtually the same as for asthma, which is largely a disease of allergy, eosinophilic inflammation, and airway smooth muscle contraction. The treatment benefits of inhaled corticosteroids (ICS) are marginal and do not prevent progression of the disease with exacerbations. No mechanism or rationale by which ICS might actually ameliorate COPD has been suggested, because ICS stimulate PMNs and delay apoptosis.

Novel therapies can be directed specifically to pathways mediating airway inflammation that characterizes COPD, but the rationale for these therapies is obtained, at least in part, from data derived from homologous ligands and signaling pathways in eosinophils. There currently are no therapies to prevent up-regulation of β2-integrins on PMNs, which are, to a large degree, constitutively up-regulated. Nonetheless, surface expression of β2-integrin alone, even in the activated state, will not mediate granulocyte adhesion. Blockade of phosphorylation of the 85-kD gIVaPLA2, an intracellular PLA2, blocks eosinophil adhesion, even in the up-regulated β2-integrin adhesion molecule. The ERK-1/2 cascade has been shown to be the upstream pathway by which cytokines and chemokines initiate the adhesion process.

These examples cite just three potential approaches to novel therapies for preventing exacerbations of COPD. Each is designed to meet specifications of the PMNs, and the assumption is that blockade of augmented neutrophilic inflammation occurring with COPD exacerbations will be a beneficial process. There is no way of knowing whether any of these approaches will work, but the time has come to approach the inflammatory component of COPD in a manner tailored to the nature of the syndrome, rather than merely transposing therapies from asthma, which has a wholly different pathophysiology than COPD.

FOOTNOTES

Conflict of Interest Statement: A.R.L. does not have a commercial interest in AstraZeneca. He attended the 2006 Lund Conference and received an honorarium of $1,850 for his presentation. N.M.M. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript.

(Received in original form July 20, 2007; accepted in final form July 20, 2007)

REFERENCES

  1. Taraseviciene-Stewart L, Douglas IS, Nana-Sinkam PS, Lee JD, Tuder R, Nicolls MR, Voelkel NF. Is alveolar destruction and emphysema in chronic obstructive pulmonary disease an immune disease? Proc Am Thorac Soc 2006;3:687–690.[Abstract/Free Full Text]
  2. Henson PM, Vandivier RW, Douglas IS. Cell death, remodeling, and repair in chronic obstructive pulmonary disease. Proc Am Thorac Soc 2006;3:713–717.[Abstract/Free Full Text]
  3. Busse W, Corren J, Lanier BQ, McAlary M, Fowler-Taylor A, Cioppa GD, van As A, Gupta N. Omalizumab, anti-IgE recombinant humanized monoclonal antibody, for the treatment of severe allergic asthma. J Allergy Clin Immunol 2001;108:184–190.[CrossRef][Medline]
  4. Cox G, Thomson NC, Rubin AS, Niven RM, Corris PA, Siersted HC, Olivenstein R, Pavord ID, McCormack D, Chaudhuri R, et al. Asthma control during the year after bronchial thermoplasty. N Engl J Med 2007;356:1327–1337.[Abstract/Free Full Text]
  5. Danek CJ, Lombard CM, Dungworth DL, Cox PG, Miller JD, Biggs MJ, Keast TM, Loomas BE, Wizeman WJ, Hogg JC, et al. Reduction in airway hyperresponsiveness to methacholine by the application of RF energy in dogs. J Appl Physiol 2004;97:1946–1953.[Abstract/Free Full Text]
  6. Calverley PMA, Anderson JA, Celli B, Ferguson GT, Jenkins C, Jones PW, Yates JC, Jorgen B. Salmeterol and fluticasone propionate and survival in chronic obstructive pulmonary disease. N Engl J Med 2007;356:775–789.[Abstract/Free Full Text]
  7. Celli BR, Barnes PJ. Exacerbations of chronic obstructive pulmonary disease. Eur Respir J 2007;29:1224–1238.[Abstract/Free Full Text]
  8. Henson PM, Vandivier RW, Douglas IS. Cell death, remodeling, and repair in chronic obstructive pulmonary disease? Proc Am Thorac Soc 2006;3:713–717.[Abstract/Free Full Text]
  9. Di Stefano A, Caramori G, Ricciardolo FL, Capelli A, Adcock IM, Donner CF. Cellular and molecular mechanisms in chronic obstructive pulmonary disease: an overview. Clin Exp Allergy 2004;34:1156–1167.[CrossRef][Medline]
  10. Drost EM, MacNee W. Potential role of IL-8, platelet-activating factor and TNF-{alpha} in the sequestration of neutrophils in the lung: effects on neutrophil deformability, adhesion receptor expression, and chemotaxis. Eur J Immunol 2002;32:393–403.[CrossRef][Medline]
  11. Leff AR, Hamann KJ, Wegner CD. Inflammation and cell–cell interactions in airway hyperresponsiveness. Am J Physiol Lung Cell Mol Physiol 1991;260:L189–L206.[Abstract/Free Full Text]
  12. Muñoz NM, Rabe KF, Neeley SP, Herrnreiter A, Zhu X, McAllister K, Mayer D, Magnussen H, Galens S, Leff AR. Eosinophil VLA-4 binding to fibronectin augments bronchial narrowing through 5-lipoxygenase activation. Am J Physiol 1996;270:L587–L594.[Medline]
  13. Myo S, Zhu X, Myou S, Meliton AY, Liu J, Boetticher E, Lambertino AT, Xu C, Muñoz NM, Leff AR. Additive blockade of β2-integrin adhesion of eosinophils by salmeterol and fluticasone propionate. Eur Respir J 2004;23:511–517.[Abstract/Free Full Text]
  14. Sun JG, Deng YM, Wu X, Tang HF, Deng JF, Chen JQ, Yang SY, Xie QM. Inhibition of phosphodiesterase activity, airway inflammation and hyperresponsiveness by PDE4 inhibitor and glucocorticoid in a murine model of allergic asthma. Life Sci 2006;79:2007–2085.
  15. Zhu X, Muñoz NM, Kim KP, Sano H, Cho W, Leff AR. Cytosolic phospholipase A2 activation is essential for β1 and β2-integrin–dependent adhesion of human eosinophils. J Immunol 1999;163:3423–3429.[Abstract/Free Full Text]
  16. Ho A, Schwarze SR, Mermelstein SJ, Waksman G, Dowdy SF. Synthetic protein transduction domains: enhanced transduction potential in vitro. Cancer Res 2001;61:474–477.[Abstract/Free Full Text]
  17. Ma M, Nath A. Molecular determinants for cellular uptake of Tat protein of human immunodeficiency virus type 1 in brain cells. J Virol 1997;71:2495–2499.[Abstract]
  18. Myou S, Zhu X, Boetticher E, Myo S, Meliton A, Lambertino A, Muñoz NM, Leff AR. Blockade of focal clustering and active conformation in β2-integrin-mediated adhesion of eosinophils to intercellular adhesion molecule-1 caused by transduction of HIV TAT–dominant negative Ras. J Immunol 2002;169:2670–2676.[Abstract/Free Full Text]
  19. Myou S, Zhu X, Myo S, Boetticher E, Meliton AY, Liu J, Muñoz NM, Leff AR. Blockade of airway inflammation and hyperresponsiveness by HIV-TAT–dominant negative Ras. J Immunol 2003;171:4379–4384.[Abstract/Free Full Text]
  20. Myou S, Leff AR, Myo S, Boetticher E, Tong J, Meliton AY, Liu J, Muñoz NM, Zhu X. Blockade of inflammation and airway hyperresponsiveness in immune-sensitized mice by dominant-negative phosphoinositide 3-kinase–TAT. J Exp Med 2003;198:1573–1582.[Abstract/Free Full Text]
  21. Ford KG, Souberbielle BE, Darling D, Farzaneh F. Protein transduction: an alternative to genetic intervention? Gene Ther 2001;8:1–4.[CrossRef][Medline]
  22. Okkenhaug K, Vanhaesebroeck B. New responsibilities for the PI3K regulatory subunit p85 {alpha}. Sci STKE 2001;65:PE1.
  23. Nagase T, Ishii S, Katayama H, Fukuchi Y, Ouchi Y, Shimizu T. Airway responsiveness in transgenic mice overexpressing platelet-activating factor receptor: roles of thromboxanes and leukotrienes. Am J Respir Crit Care Med 1997;156:1621–1627.[Abstract/Free Full Text]
  24. Ishii S, Nagase T, Shindou H, Takizawa H, Ouchi Y, Shimizu T. Platelet-activating factor receptor develops airway hyperresponsiveness independently of airway inflammation in a murine asthma model. J Immunol 2004;172:7095–7102.[Abstract/Free Full Text]
  25. Nagase T, Uozumi N, Ishi S, Kume K, Izumi T, Ouchi Y, Shimizu T. Acute lung injury by sepsis and acid aspiration: a key role for cytosolic PLA2. Nat Immunol 2000;1:42–46.[CrossRef][Medline]
  26. Sano A, Muñoz NM, Sano H, Choi J, Zhu X, Leff AR. Inhibition of cPLA2 translocation and LTC4 secretion by fluticasone propionate in exogenously activated human eosinophils. Am J Respir Crit Care Med 1999;159:1903–1909.[Abstract/Free Full Text]
  27. Myou S, Sano H, Fujimura M, Zhu X, Kurashima K, Kita T, Nakao S, Nonomura A, Shioya T, Kim KP, et al. Blockade of eosinophil migration and airway hyperresponsiveness by cPLA2-inhibition. Nat Immunol 2001;2:145–149.[CrossRef][Medline]
  28. Zhu X, Lambertino AT, Houghton TJ, McGilvra JD, Xu C, Rawal VH, Leff AR. Structural determinants of blockade of eosinophil activation, adhesion and secretion by synthetic analogs of phomactin. Life Sci 2003;73:3005–3016.[CrossRef][Medline]
  29. Perretti M, Flower RJ. Annexin-1 and the biology of the neutrophil. J Leukoc Biol 2004;76:25–29.[Abstract/Free Full Text]
  30. Tatulian SA. Toward understanding interfacial activation of secretory phospholipase A2 (PLA2): membrane surface properties and membrane-induced structural changes in the enzyme contribute synergistically to PLA2 activation. Biophys J 2001;80:789–800.[Medline]
  31. Muñoz NM, Kim YJ, Meliton AY, Kim KP, Han SK, Boetticher E, O'Leary E, Myou S, Zhu X, Bonventre JV, et al. Human group V phospholipase A2 induces group IVA phospholipase A2–independent cysteinyl leukotriene synthesis in human eosinophils. J Biol Chem 2003;278:38813–38820.[Abstract/Free Full Text]
  32. Muñoz NM, Meliton AY, Lambertino A, Boetticher E, Learoyd J, Sultan F, Zhu X, Cho W, Leff AR. Transcellular secretion of group V phospholipase A2 from epithelium induces β2-integrin–mediated adhesion and synthesis of leukotriene C4 in eosinophils. J Immunol 2006;177:574–582.[Abstract/Free Full Text]
  33. Degousee N, Ghomashchi F, Stefanski E, Singer A, Smart BP, Borregaard N, Reithmeier R, Lindsay TF, Lichtenberger C, Reinisch W, et al. Group IV, V, and X phospholipases A2s in human neutrophils: role in eicosanoid production and gram-negative bacterial phospholipid hydrolysis. J Biol Chem 2002;277:5061–5073.[Abstract/Free Full Text]
  34. Masuda S, Murakami M, Mitsuishi M, Komiyama K, Ishikawa Y, Ishii T, Kudo I. Expression of secretory phospholipase A2 enzymes in lungs of humans with pneumonia and their potential prostaglandin-synthetic function in human lung-derived cells. Biochem J 2005;387:27–38.[CrossRef][Medline]
  35. Shirai Y, Balsinde J, Dennis EA. Localization and functional interrelationships among cytosolic group IV, secreted group V, and Ca2+-independent group VI PLA2 in P388D1 macrophages using GFP/RFP constructs. Biochim Biophys Acta 2005;1735:119–129.[Medline]
  36. Muñoz NM, Boetticher E, Sperling AI, Kim KP, Meliton AY, Zhu X, Lambertino A, Cho W, Leff AR. Quantitation of secretory group V phospholipase A2 in human tissues by sandwich enzyme-linked immunosorbent assay. J Immunol Methods 2002;262:41–51.[CrossRef][Medline]
  37. Ho JC, Arm JP, Bingham CO III, Choi A, Austen KF, Glimcher LH. A novel group of PLA2s preferentially expressed in type 2 helper T cells. J Biol Chem 2001;276:18321–18326.[Abstract/Free Full Text]
  38. Kim KP, Rafter JD, Bittova L, Han SK, Snitko Y, Muñoz NM, Leff AR, Cho W. Mechanism of human group V phospholipase A2 (PLA2)–induced leukotriene biosynthesis in human neutrophils: a potential role of heparan sulfate binding in PLA2 internalization and degradation. J Biol Chem 2001;276:11126–11134.[Abstract/Free Full Text]
  39. Han SK, Kim KP, Koduri R, Bittova L, Muñoz NM, Leff AR, Wilton DC, Gelb MH, Cho W. Roles of Trp31 in high membrane binding and proinflammatory activity of human group V phospholipase A2. J Biol Chem 1999;274:11881–11888.[Abstract/Free Full Text]
  40. Cho W. Structure, function, and regulation of gVPLA2. Biochim Biophys Acta 2000;1488:48–58.[Medline]
  41. Muñoz NM, Kim KP, Han SK, Boetticher E, Sperling AI, Sano H, Zhu X, Cho W, Leff AR. Characterization of monoclonal antibodies specific for 14-kDa human group V secretory phospholipase A2 (hVPLA2). Hybridoma 2000;19:171–176.[CrossRef][Medline]
  42. Liu J, Zhu X, Myo S, Lambertino AT, Xu C, Boetticher E, Muñoz NM, Sano M, Cordoba M, Learoyd J, et al. Glucocorticoid-induced surface expression of annexin 1 blocks β2-integrin adhesion of human eosinophils to intercellular adhesion molecule 1 surrogate protein. J Allergy Clin Immunol 2005;115:493–500.[CrossRef][Medline]



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Erratum: Future Treatment to Lessen Exacerbations of Chronic Obstructive Pulmonary Disease
Proceedings of the ATS, February 15, 2008; 5(2): 283 - 284.
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