Selective inhibition of phosphodiesterase type IV suppresses the chemotactic responsiveness of rat eosinophils in vitro

Inhibition of Phosphodiesterase-4 in Psoriatic Arthritis and Inflammatory Bowel Diseases

Phosphodiesterases (PDEs) are a heterogeneous superfamily of enzymes which catalyze the degradation of the intracellular second messengers cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Among PDEs, PDE4 is the most widely studied and characterized isoenzyme. PDE4 blocking can lead to increased levels of intracellular cAMP, which results in down-regulation of inflammatory responses by reducing the expression of tumor necrosis factor (TNF), interleukin (IL)-23, IL-17, interferon-γ, while increasing regulatory cytokines, such as IL-10. Therefore, PDE4 has been explored as a therapeutic target for the treatment of different chronic inflammatory conditions such as psoriatic arthritis (PsA) and inflammatory bowel disease (IBD). PsA shares clinical, genetic, and pathogenic features with IBD such as ulcerative colitis (UC) and Crohn’s disease (CD), and enteropathic spondyloarthritis (eSpA) represent a frequent clinical evidence of the overlap between gut and joint diseases. Current therapeutic options in PsA patients and underlying UC are limited to synthetic immunosuppressants and anti-TNF. Apremilast is an oral PDE4 inhibitor approved for the treatment of active PsA patients with inadequate response to synthetic immunosuppressants. The efficacy and a good safety profile observed in randomized clinical trials with apremilast in PsA patients have been confirmed by few studies in a real-life scenario. In addition, apremilast led to significant improvement in clinical and endoscopic features in UC patients in a phase II RCT. By now there are no available data regarding its role in eSpA patients. In view of the above, the use of apremilast in eSpA patients is a route that deserves to be deepened.

Synergistic effect of phosphodiesterase 4 inhibitor and serum on migration of endotoxin-stimulated macrophages

Macrophage migration is an essential step in host defense against infection and wound healing. Elevation of cAMP by inhibiting phosphodiesterase 4 (PDE4), enzymes that specifically degrade cAMP, is known to suppress various inflammatory responses in activated macrophages, but the role of PDE4 in macrophage migration is poorly understood. Here we show that the migration of Raw 264.7 macrophages stimulated with LPS was markedly and dose-dependently induced by the PDE4 inhibitor rolipram as assessed by scratch wound healing assay. Additionally, this response required the involvement of serum in the culture medium as serum starvation abrogated the effect. Further analysis revealed that rolipram and serum exhibited synergistic effect on the migration, and the influence of serum was independent of PDE4 mRNA expression in LPS-stimulated macrophages. Moreover, the enhanced migration by rolipram was mediated by activating cAMP/exchange proteins directly activated by cAMP (Epac) signaling, presumably via interaction with LPS/TLR4 signaling with the participation of unknown serum components. These results suggest that PDE4 inhibitors, together with serum components, may serve as positive regulators of macrophage recruitment for more efficient pathogen clearance and wound repair.

TAS-203, an oral phosphodiesterase 4 inhibitor, exerts anti-inflammatory activities in a rat airway inflammation model

Cyclic adenosine monophosphate (cAMP) is a key intracellular second messenger, which is degraded by phosphodiesterase 4 (PDE4). PDE4 suppresses cAMP levels, and thus stimulates the activity of inflammatory cells. Therefore, PDE4 has been considered as a therapeutic target for airway inflammatory diseases including asthma and chronic obstructive pulmonary disease (COPD). Roflumilast, an approved PDE4 inhibitor, has been shown to have clinical benefits in COPD. However, central nervous system-related side effects including nausea and vomiting have limited the therapeutic index of roflumilast. Moreover, although airway mucus hypersecretion is the characteristic feature, which is associated with the severity and prognosis, the inhibitory effect of roflumilast on sputum production is limited to a minority of patients. In this study, we demonstrate the inhibitory effects of TAS-203, which is an orally active PDE4 inhibitor associated with a lowered emetic effect, on airway inflammation and mucus hypersecretion. A cell-based assay showed TAS-203 treatment suppressed epidermal growth factor (EGF)-induced mucin MUC5AC expression. TAS-203 also suppressed monocyte chemoattractant protein-1 (MCP-1), interleukin (IL)-5 and IL-13 production in a Sephadex-induced airway inflammation model, and the number of infiltrating cells in bronchoalveolar lavage (BAL) fluid. TAS-203 caused marked reduction of goblet cell hyperplasia in a histopathological analysis of airway epithelium. Furthermore, TAS-203 suppressed 5-hydroxytryptamine (5-HT)-induced airway hyperresponsiveness (AHR). In addition, we preliminarily confirmed TAS-203 prevents airway MUC5AC production in BAL fluid, and shows lower specific airway resistance (sRaw) in a cigarette smoke-induced COPD-like model. Our data suggest that TAS-203 might be useful in the treatment of airway inflammatory disease.

PDE4 Inhibition and Inflammatory Bowel Disease: A Novel Therapeutic Avenue

BACKGROUND

In the last few decades, a better knowledge of the inflammatory pathways involved in the pathogenesis of Inflammatory Bowel Disease (IBD) has promoted biological therapy as an important tool to treat IBD patients. However, in spite of a wider spectrum of biological drugs, a significant proportion of patients is unaffected by or lose their response to these compounds, along with increased risks of infections and malignancies. For these reasons there is an urgent need to look for new pharmacological targets. The novel Phosphodiesterase 4 (PDE4) inhibitors have been recently introduced as new modulators of intracellular signals and gene transcription for the treatment of IBD.

AIM

To discuss and describe the state of the art of this new class of compounds in the IBD field, with particular attention to apremilast.

METHODS

Published articles selected from PubMed were comprehensively reviewed, with key words including apremilast, inflammatory disease, IBD, psoriasis, psoriatic arthritis, pathogenesis, therapies, and treatment.

RESULTS

PDE4 inhibitors generate elevated intracellular levels of cyclic Adenosine Monophosphate (cAMP), that consequently down-regulate the release of pro-inflammatory cytokines in the mucosa of IBD patients. The newly developed apremilast is one of these drugs and has already been approved for the treatment of dermatologic/rheumatologic inflammatory conditions; studies in psoriasis and psoriatic arthritis have in fact demonstrated its clinical activity. However, no clinical trials have yet been published on the use of apremilast in IBD.

CONCLUSION

In light of the similarity of pro-inflammatory signaling pathways across the gut, the skin, and joints, apremilast is likely supposed to show its efficacy also in IBD.

The potential role of phosphodiesterase inhibitors in the management of asthma

Asthma is a chronic inflammatory condition characterised by reversible airflow obstruction and airway hyperreactivity. The course of the illness may be punctuated by exacerbations resulting in deterioration in quality of life and, in some cases, days lost from school or work. That asthma is common and increasingly prevalent magnifies the importance of any potential economic costs, and promoting asthma control represents an important public health agenda. While lifestyle changes represent a valuable contribution in some patients, the majority of asthmatic patients require therapeutic intervention. The recognition of the role of inflammation in the pathogenesis of asthma has led to an emphasis on regular anti-inflammatory therapy, of which inhaled corticosteroid treatment remains the most superior. In selected patients, further improvements in asthma control may be gained by the addition of regular inhaled long-acting beta(2)-adrenoceptor agonists or oral leukotriene receptor antagonists to inhaled corticosteroid therapy. However, a significant minority of patients with asthma remain poorly controlled despite appropriate treatment, suggesting that additional corticosteroid nonresponsive inflammatory pathways may be operative. Furthermore, some patients with asthma display an accelerated decline in lung function, suggesting that active airway re-modeling is occurring. Such observations have focused attention on the potential to develop new therapies which complement existing treatments by targeting additional inflammatory pathways. The central role of phosphodiesterase (PDE), and in particular the PDE4 enzyme, in the regulation of key inflammatory cells believed to be important in asthma - including eosinophils, lymphocytes, neutrophils and airway smooth muscle - suggests that drugs designed to target this enzyme will have the potential to deliver both bronchodilation and modulate the asthmatic inflammatory response. In vivo studies on individual inflammatory cells suggest that the effects are likely to be favorable in asthma, and animal study models have provided proof of concept; however, first-generation PDE inhibitors have been poorly tolerated due to adverse effects. The development of second-generation agents such as cilomilast and roflumilast heralds a further opportunity to test the potential of these agents, although to date only a limited amount of data from human studies has been published, making it difficult to draw firm conclusions.

Olprinone and colforsin daropate alleviate septic lung inflammation and apoptosis through CREB-independent activation of the Akt pathway

Olprinone, a specific phosphodiesterase III inhibitor, and corforsin daropate, a direct adenylate cyclase activator, are now being used in critical conditions. We investigated whether their therapeutic use provides protection against septic acute lung injury (ALI) and mortality. Polymicrobial sepsis was induced by cecal ligation and puncture (CLP) in BALB/c mice. Olprinone or colforsin daropate was continuously given through an osmotic pump that was implanted into the peritoneal cavity immediately following CLP. These treatments prevented the ALI development in CLP mice, as indicated by the findings that severe hypoxemia, increased pulmonary vascular permeability, and histological lung damage were strikingly remedied. Furthermore, continued administration of olprinone or colforsin daropate suppressed apoptosis induction in septic lungs and improved the survival of CLP mice. Olprinone and corforsin daropate enhanced Akt phosphorylation in septic lungs. Wortmannin, which inhibits the Akt upstream regulator phosphatidylinositol 3-kinase, abrogated the protective effects of olprinone and corforsin daropate on sepsis-associated lung inflammation and apoptosis. In vivo transfection of cyclic AMP response element binding protein (CREB) decoy oligodeoxynucleotide failed to negate the abilities of these agents to increase Akt phosphorylation and to inhibit IκBα degradation in septic lungs. These results demonstrate for the first time that CREB-independent Akt-mediated signaling is a critical mechanism contributing to the therapeutic effects of olprinone and corforsin daropate on septic ALI. Moreover, our data also suggest that these cyclic AMP-related agents, by blocking both nuclear factor-κB activation and apoptosis induction, may represent an effective therapeutic approach to the treatment of the septic syndrome.

Phosphodiesterase 4B is essential for T(H)2-cell function and development of airway hyperresponsiveness in allergic asthma

BACKGROUND

Cyclic AMP (cAMP) signaling modulates functions of inflammatory cells involved in the pathogenesis of asthma, and type 4 cAMP-specific phosphodiesterases (PDE4s) are essential components of this pathway. Induction of the PDE4 isoform PDE4B is necessary for Toll-like receptor signaling in monocytes and macrophages and is associated with T cell receptor/CD3 in T cells; however, its exact physiological function in the development of allergic asthma remains undefined.

OBJECTIVES

We investigated the role of PDE4B in the development of allergen-induced airway hyperresponsiveness (AHR) and T(H)2-driven inflammatory responses.

METHODS

Wild-type and PDE4B(-/-) mice were sensitized and challenged with ovalbumin and AHR measured in response to inhaled methacholine. Airway inflammation was characterized by analyzing leukocyte infiltration and cytokine accumulation in the airways. Ovalbumin-stimulated cell proliferation and T(H)2 cytokine production were determined in cultured bronchial lymph node cells.

RESULTS

Mice deficient in PDE4B do not develop AHR. This protective effect was associated with a significant decrease in eosinophils recruitment to the lungs and decreased T(H)2 cytokine levels in the bronchoalveolar lavage fluid. Defects in T-cell replication, T(H)2 cytokine production, and dendritic cell migration were evident in cells from the airway-draining lymph nodes. Conversely, accumulation of the T(H)1 cytokine IFN-γ was not affected in PDE4B(-/-) mice. Ablation of the orthologous PDE4 gene PDE4A has no impact on airway inflammation.

CONCLUSION

By relieving a cAMP-negative constraint, PDE4B plays an essential role in T(H)2-cell activation and dendritic cell recruitment during airway inflammation. These findings provide proof of concept that PDE4 inhibitors with PDE4B selectivity may have efficacy in asthma treatment.

Apremilast: a novel PDE4 inhibitor in the treatment of autoimmune and inflammatory diseases

Phosphodiesterase 4 (PDE4) is a key enzyme in the degradation of cyclic adenosine monophosphate and is centrally involved in the cytokine production of inflammatory cells, angiogenesis, and the functional properties of other cell types such as keratinocytes. In this review article, apremilast, a novel small molecule inhibitor of PDE4, is introduced. Apremilast has profound anti-inflammatory properties in animal models of inflammatory disease, as well as human chronic inflammatory diseases such as psoriasis and psoriatic arthritis. Apremilast blocks the synthesis of several pro-inflammatory cytokines and chemokines, such as tumor necrosis factor alpha, interleukin 23, CXCL9, and CXCL10 in multiple cell types. In contrast to the biologics, which neutralize pro-inflammatory mediators at the protein level, apremilast modulates production of these mediators at the level of mRNA expression. Apremilast also interferes with the production of leukotriene B4, inducible nitric oxide synthase, and matrix metalloproteinase and reduces complex inflammatory processes, such as dendritic cell infiltration, epidermal skin thickening, and joint destruction. As this novel PDE4 inhibitor interferes with several key processes of inflammation, it may emerge as a promising new drug for the treatment of chronic inflammatory diseases such as those of the skin and the joints.

Cyclic AMP enhances resolution of allergic pleurisy by promoting inflammatory cell apoptosis via inhibition of PI3K/Akt and NF-kappaB

Selective and timely induction of apoptosis is an effective means of resolving inflammation. The effects and putative mechanisms by which cyclic AMP (cAMP) modulates leukocyte apoptosis in vivo are still unclear. The present study aims at identifying intracellular pathways underlying the ability of cAMP elevating agents to resolve eosinophilic inflammation in a model of allergic pleurisy in mice. Ovalbumin (OVA) challenge of immunized mice induced eosinophil recruitment that peaked at 24h and persisted till 48h. Treatment with the PDE4 inhibitor rolipram, cAMP mimetic db-cAMP or adenylate cyclase activator forskolin, at 24h after antigen-challenge resulted in profound resolution of eosinophilic inflammation, without a decrease of mononuclear cell numbers. There was a concomitant increase in number of apoptotic cells in the pleural cavity. The effects of rolipram and db-cAMP were inhibited by the PKA inhibitor H89. Inhibition of PI3K/Akt or NF-kappaB induced resolution of inflammation that was associated with increased apoptosis. OVA-challenge resulted in a time-dependent activation of Akt and NF-kappaB, which was blocked by treatment with rolipram or PI3K/Akt pathway inhibitors. Thus, cAMP elevating agents resolve established eosinophilic inflammation by inducing leukocyte apoptosis. Mechanistically, the actions of cAMP are dependent on PKA and target a PI3K/Akt-dependent NF-kappaB survival pathway.

Anti-inflammatory activity in the aqueous crude extract of the leaves of Nidularium procerum: A bromeliaceae from the Brazilian coastal rain forest

Nidularium procerum LINDMAN, a common bromeliaceae from the Brazilian flora, remains poorly studied regarding its chemical and pharmacological properties. We have recently published that N. procerum has potent analgesic and anti-inflammatory activities. In the present work, we have investigated potential mechanisms involved in the anti-inflammatory effects of N. procerum aqueous extract on lipopolysaccharide (LPS)-, platelet activating factor (PAF)- or formyl-methionyl-leucyl-phenylalanine (fMLP)-induced pleurisy models of inflammation. We found that the aqueous extract of N. procerum leaves (leaf aqueous extract; LAE) inhibits the neutrophil migration, production of inflammatory cytokines interleukin-1 and -6 (IL-1 and IL-6) and the generation of prostaglandin E2 (PGE2) in LPS-induced pleural inflammation in mice. Such inhibitory effect of N. procerum on PGE2 generation was tightly correlated to the inhibition of formation of new cytoplasmic lipid bodies within recruited leukocytes. N. procerum also blocked the in vivo neutrophil influx induced by injection of PAF or fMLP into the mouse pleural cavity and directly inhibited PAF-induced neutrophil chemotaxis in vitro. The data obtained in this study indicate that N. procerum LAE exerts its anti-inflammatory effects by interfering with the capacity of the host to respond to injury at different levels. Among the different functions affected by N. procerum LAE, lipid body formation, PGE2 and cytokine production and neutrophil chemotaxis are readily evidenced in relevant surrogate models. The N. procerum bioactive profile makes it an attractive candidate for future development as a drug or phytomedicine.

Selective PDE4 inhibitors as potent anti-inflammatory drugs for the treatment of airway diseases

Phosphodiesterases (PDEs) are responsible for the breakdown of intracellular cyclic nucleotides, from which PDE4 are the major cyclic AMP metabolizing isoenzymes found in inflammatory and immune cells. This generated greatest interest on PDE4 as a potential target to treat lung inflammatory diseases. For example, cigarette smoke-induced neutrophilia in BAL was dose and time dependently reduced by cilomilast. Beside the undesired side effects associated with the first generation of PDE4 inhibitors, the second generation of selective inhibitors such as cilomilast and roflumilast showed clinical efficacy in asthma and chronic obstructive pulmonary diseases trials, thus re-enhancing the interest on these classes of compounds. However, the ability of PDE4 inhibitors to prevent or modulate the airway remodelling remains relatively unexplored. We demonstrated that selective PDE4 inhibitor RP 73-401 reduced matrix metalloproteinase (MMP)-9 activity and TGF-beta1 release during LPS-induced lung injury in mice and that CI-1044 inhibited the production of MMP-1 and MMP-2 from human lung fibroblasts stimulated by pro-inflammatory cytokines. Since inflammatory diseases of the bronchial airways are associated with destruction of normal tissue structure, our data suggest a therapeutic benefit for PDE4 inhibitors in tissue remodelling associated with chronic lung diseases.

Inhibitory effects on human eosinophil chemotaxis in vitro by BAY 41-2272, an activator of nitric oxide-independent site of soluble guanylate cyclase

This study was designed to investigate the effects of the 5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-pyrimidin-4-ylamine (BAY 41-2272) on formyl-methionyl-leucyl-phenylalanine (fMLP; 10(-7)M)-induced human eosinophil chemotaxis, cyclic guanosine-3',5'-monophosphate (cGMP) and cyclic adenosine-3',5'-monophosphate (cAMP) levels. Human eosinophils were pretreated or not with 3-isobutyl-l-methyl-xanthine (IBMX; 500microM), and then exposed to BAY 41-2272 (0.1-10.0microM) for either short (10min) or prolonged (90min) time periods. Exposition of eosinophils with BAY 41-2272 for either 10min or 90min markedly inhibited the eosinophil chemotaxis, independently of IBMX pretreatment. Inhibition of fMLP-induced eosinophil chemotaxis by BAY 41-2272 (in absence of prior treatment with IBMX) was about of the same irrespective if cells were exposed for 10min or 90min with this compound. In IBMX-pretreated eosinophils, the inhibition of fMLP-induced chemotaxis by BAY 41-2272 in the 10-min exposure protocols was even higher in comparison with the 90-min protocols. Incubation of IBMX-treated eosinophils for 90min with BAY 41-2272 resulted in 2.0-2.5 times higher levels of cGMP and cAMP compared with the 10-min protocols. The BAY 41-2272-induced cGMP increases were abolished by pre-incubation of eosinophils with the soluble guanylate cyclase inhibitor 1H-[1,2,4]-oxidiazolo[4,3-a] quinoxalin-1-one (ODQ). No eosinophil toxicity was observed in any experimental condition, according to 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyl tetrazolium bromide (MTT) assay. Our findings show that inhibitory effects of fMLP-induced human eosinophil chemotaxis by BAY 41-2272 at short-term or prolonged exposition time are accompanied by significant elevations of cGMP and cAMP, but we could not detect a clear correlation between chemotaxis inhibition and elevation of cyclic nucleotide levels.

PPAR-gamma modulates allergic inflammation through up-regulation of PTEN

The ligand-activated nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) has been shown to regulate cell activation, differentiation, proliferation, and/or apoptosis. PPARgamma is also associated with anti-inflammatory responses. However, the signaling mechanism remains elusive. We have used a mouse model for asthma to determine the effect of PPARgamma agonists, rosiglitazone or pioglitazone, and PPARgamma on allergen-induced bronchial inflammation and airway hyperresponsiveness. Administration of PPARgamma agonists or adenovirus carrying PPARgamma cDNA (AdPPARgamma) reduced bronchial inflammation and airway hyperresponsiveness. Expression of PPARgamma was increased by ovalbumin (OVA) inhalation, and the increase was further enhanced by the administration of the PPARgamma agonists or AdPPARgamma. Levels of IL-4, IL-5, IL-13, and eosinophil cationic protein were increased after OVA inhalation, and the increased levels were significantly reduced by the administration of PPARgamma agonists or AdPPARgamma. The results also showed that the administration of PPARgamma agonists or AdPPARgamma up-regulated phosphatase and tensin homologue deleted on chromosome ten (PTEN) expression in allergen-induced asthmatic lungs. This up-regulation correlated with decreased phosphatidylinositol 3-kinase activity as measured by reduced phosphorylation of Akt. These findings demonstrate a protective role of PPARgamma in the pathogenesis of the asthma phenotype through regulation of PTEN expression.

PDE4 inhibitors as new anti-inflammatory drugs: effects on cell trafficking and cell adhesion molecules expression

Phosphodiesterase 4 (PDE4) is a major cyclic AMP-hydrolyzing enzyme in inflammatory and immunomodulatory cells. The wide range of inflammatory mechanisms under control by PDE4 points to this isoenzyme as an attractive target for new anti-inflammatory drugs. Selective inhibitors of PDE4 have demonstrated a broad spectrum of anti-inflammatory activities including the inhibition of cellular trafficking and microvascular leakage, cytokine and chemokine release from inflammatory cells, reactive oxygen species production, and cell adhesion molecule expression in a variety of in vitro and in vivo experimental models. The initially detected side effects, mainly nausea and emesis, appear at least partially overcome by the 'second generation' PDE4 inhibitors, some of which like roflumilast and cilomilast are in the later stages of clinical development for treatment of chronic obstructive pulmonary disease. These new drugs may also offer opportunities for treatment of other inflammatory diseases.

PDE4-regulated cAMP degradation controls the assembly of integrin-dependent actin adhesion structures and REF52 cell migration

Plating of REF52 cells onto extracellular matrix components leads to the formation of integrin-dependent actin adhesion microspikes. We show that the formation of these structures is sensitive to chemical agents that regulate cAMP levels, such as forskolin and IBMX. In particular, by using the specific inhibitor rolipram, we identify the PDE4 family of cAMP-specific phosphodiesterases as critical regulators of this process. The effect of PDE4 on microspike formation is mediated by actions exerted through the activation of PKA - rather than through the alternative cAMP effector, Epac. We provide evidence that peripheral microspikes are RhoA-, ROCK- and myosin-dependent, and that this pathway is suppressed by PDE4 inhibition. In addition, PDE4 inhibition impairs cell locomotion that requires dynamic protrusion and retraction of peripheral spike structures. Our data demonstrate that PDE4 activity is a key modulator of integrin-induced actin assembly at the cell periphery which, in turn, controls cell migration.

Increased levels of cyclic adenosine monophosphate contribute to the hyporesponsiveness of mast cells in alloxan diabetes

In this study, we investigated the influence of intracellular cyclic adenosine monophosphate (cAMP) changes on the rat mast cell hyporesponsiveness following immunological and non-immunological stimuli. Compared with mast cells from normal rats, those recovered from 21-day diabetic animals showed a significant augmentation in the intracellular levels of cAMP, in directly correlated with secretion of lower amounts of histamine after stimulation with antigen, bradykinin and compound 48/80 in vitro. Incubation of normal mast cells with selective inhibitors of phosphodiesterase type 4 (PDE 4) rolipram, NCS 613 and RP 73401, or the cell permeable analogue N6-2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (db cAMP), led to a decrease of histamine secretion in vitro. However, the effectiveness of either NCS 613 or db cAMP in inhibiting antigen-induced degranulation is comparable in both normal and diabetic mast cells. We suggest that (a) there is a close correlation between higher levels of intracellular cAMP and hyporesponsiveness of diabetic mast cells, phenomena probably associated with a reduction in the expression and/or activity of PDE 4 and that (b) the mechanism of cAMP-mediated down-regulation of mast cell function is saturated in diabetic rats.

Allergen challenge alters lymphocyte phosphodiesterase activity in horses with heaves

Heaves is an allergic airway disease in horses characterised by reversible airway obstruction, bronchial hyperresponsiveness and airway inflammation associated with a Th(2) response. Cyclic nucleotide-dependent signalling pathways can regulate lymphocyte function. In this study, we examined lymphocyte PDE activity comparing horses with heaves to healthy control animals. Total PDE activity and the effects of isoenzyme selective inhibitors were measured before, 5 and 24 h after the start of a 7 h allergen challenge. Allergen challenge had no effect on either total cAMP PDE activity or its inhibition by the PDE4 selective inhibitor, rolipram, and the non-selective PDE inhibitor, theophylline. In contrast, the PDE3 selective inhibitor, quazinone, caused significantly greater inhibition of cAMP PDE activity before challenge in the heaves susceptible group. Additionally, total cGMP PDE activity was significantly lower 24 h after the start of challenge in the heaves affected group (11+/-2 and 21+/-3 pmol/min/mg for heaves and control animals, respectively) and the PDE5 selective inhibitor, zaprinast, caused significantly less inhibition in the heaves group at this time point. The functional significance of these findings was explored by examining the effect of PDE3, PDE4 and PDE5 selective inhibitors on mitogen-induced mononuclear cell proliferation before and 24 h after the start of allergen challenge. Proliferation decreased after challenge in the heaves group (stimulation index=328+/-110 and 200+/-72 before and after challenge, respectively) whilst remaining constant in the control group (stimulation index=161+/-13 and 183+/-45 before and after challenge, respectively). However, all three PDE inhibitors caused a similar amount of inhibition at each time point and the effect of a combination of a PDE3 and a PDE5 inhibitor was simply additive in both groups. These results suggest differences in the control of lymphocyte PDE activity in horses with heaves.

β2-Integrin adhesion caused by eotaxin but not IL-5 is blocked by PDE-4 inhibition and β2-adrenoceptor activation in human eosinophils

We investigated the effect and mechanism(s) of PDE-4 treatment with concurrent beta2-adrenoceptor stimulation on human eosinophil adhesion mediated by beta2-integrin in vitro. Eosinophils were pretreated with either rolipram, a PDE-4 inhibitor, alone or combined with salmeterol, a beta2-adrenoceptor agonist, before activation with either eotaxin or IL-5. Beta2-integrin mediated adhesion was assessed as adherence to BSA, an established surrogate for ICAM-1. Rolipram caused progressive blockade (77.7 +/- 6.2%) of adhesion elicited by eotaxin. Maximal blockade of IL-5-activated adhesion by rolipram was substantially less (29.9 +/- 5.2%). Salmeterol + rolipram synergistically enhanced the blockade of eotaxin-activated adhesion. Eotaxin also caused approximately 50% increase in surface CD11b expression, which was blocked additively by rolipram + salmeterol. By contrast, CD11b upregulation caused by IL-5 was not blocked by rolipram + salmeterol. Rolipram also attenuated cPLA2 phosphorylation caused by eotaxin but did not block IL-5-induced phosphorylation. We conclude that rolipram blocks expression of CD11b and inhibits cPLA2 phosphorylation in human eosinophils, thus blocking eotaxin-induced adhesion of beta2-integrin. IL-5-induced adhesion likely utilizes a different upstream mechanism in regulation of integrin adhesion.

Cyclic AMP-mobilizing agents and glucocorticoids modulate human smooth muscle cell migration

Hyperplasia and cell migration of smooth muscle are features of both airway and pulmonary vascular diseases. The precise cellular and molecular mechanisms that regulate smooth muscle migration in the lungs remain unknown. In this study, we examined the effect of cAMP-mobilizing agents and steroids on smooth muscle cell migration. Platelet-derived growth factor (PDGF), transforming growth factor-alpha, vascular endothelial growth factor, and basic fibroblast growth factor significantly stimulated cell migration in pulmonary vascular smooth muscle (PVSM) cells. Airway smooth muscle (ASM) migration was also stimulated by PDGF, transforming growth factor-alpha, and basic fibroblast growth factor, but vascular endothelial growth factor was without effect. Interestingly, the smooth muscle mitogen thrombin did not stimulate migration of either cell type. Agents capable of elevating intracellular cAMP inhibited basal (unstimulated) cell migration in both cell types, whereas their effects on PDGF-stimulated migration were more variable. Prostaglandin E2, salmeterol, and the phosphodiesterase type 4 inhibitor cilomolast inhibited basal ASM and PVSM migration by 30-60%. Prostaglandin E2 and cilomolast also inhibited PDGF-stimulated migration of ASM and PVSM cells, but salmeterol was without effect. Preincubation of ASM cells with dexamethasone or fluticasone inhibited basal and PDGF-stimulated migration, and enabled an inhibitory effect of salmeterol on PDGF-induced cell migration. Steroids alone did not stimulate cAMP production or cAMP/PKA-dependent gene transcription (CRE-Luc activity), but slightly augmented salmeterol-stimulated CRE-Luc activity. Collectively, these findings demonstrate that cAMP-mobilizing agents and steroids modulate human smooth muscle cell migration, likely by distinct mechanisms.

Inhibitory effects of glucocorticoids on rat eosinophil superoxide generation and chemotaxis

Eosinophil infiltration into inflammatory tissues and the subsequent release of inflammatory mediators are the hallmarks of several inflammatory allergic diseases. Although there have been a considerable number of publications on anti-inflammatory effects of glucocorticoids, little is known about whether glucocorticoids affect the activation of eosinophils directly. We studied the effects of three glucocorticoids, mometasone furoate, dexamethasone and beclomethasone dipropionate, on superoxide generation and the chemotaxis of rat eosinophils. Highly purified rat eosinophils were treated for 6 h with mometasone furoate, dexamethasone or beclomethasone dipropionate. Eosinophils were stimulated with phorbol myristate acetate (PMA) for superoxide generation, while for induction of chemotaxis, platelet-activating factor (PAF) or leukotriene B(4) (LTB(4)) was used. None of the glucocorticoids used in the present study caused significant suppressive effects on superoxide generation induced by PMA. On the other hand, both PAF- and LTB(4)-induced migration of rat eosinophils were inhibited in a concentration-dependent manner by glucocorticoids. Mometasone furoate showed a significant effect at concentrations higher than 10(-11) M. Dexamethasone and beclomethasone dipropionate also caused a significant inhibition at concentrations higher than 10(-8) and 10(-7) M, respectively. These results indicated that the anti-inflammatory effects of glucocorticoids were mediated by direct inhibition of eosinophil migration. Furthermore, mometasone furoate was suggested to be more useful than the other drugs in the treatment of allergic diseases responsible for eosinophil chemotaxis.

Involvement of PTEN in airway hyperresponsiveness and inflammation in bronchial asthma

Phosphatase and tensin homologue deleted on chromosome ten (PTEN) is part of a complex signaling system that affects a variety of important cell functions. PTEN blocks the action of PI3K by dephosphorylating the signaling lipid phosphatidylinositol 3,4,5-triphosphate. We have used a mouse model for asthma to determine the effect of PI3K inhibitors and PTEN on allergen-induced bronchial inflammation and airway hyperresponsiveness. PI3K activity increased significantly after allergen challenge. PTEN protein expression and PTEN activity were decreased in OVA-induced asthma. Immunoreactive PTEN localized in epithelial layers around the bronchioles in control mice. However, this immunoreactive PTEN dramatically disappeared in allergen-induced asthmatic lungs. The increased IL-4, IL-5, and eosinophil cationic protein levels in bronchoalveolar lavage fluids after OVA inhalation were significantly reduced by the intratracheal administration of PI3K inhibitors or adenoviruses carrying PTEN cDNA (AdPTEN). Intratracheal administration of PI3K inhibitors or AdPTEN remarkably reduced bronchial inflammation and airway hyperresponsiveness. These findings indicate that PTEN may play a pivotal role in the pathogenesis of the asthma phenotype.

Phosphodiesterase 4 inhibitor cilomilast inhibits fibroblast-mediated collagen gel degradation induced by tumor necrosis factor-alpha and neutrophil elastase

Tissue destruction, resulting in emphysema, can be a consequence of several pathologic processes. The current study evaluated the effects of the phosphodiesterase (PDE)4 inhibitor, cilomilast, and other PDE inhibitors on the ability of fibroblasts to degrade extracellular matrix. Using the three-dimensional collagen gel culture system, fibroblasts (HFL-1) were cultured with tumor necrosis factor (TNF)-alpha, known to induce matrix metalloproteinase (MMP) release, and/or neutrophil elastase (NE), which can induce MMP activation. On Day 4, gels containing TNF-alpha and NE were significantly degraded (20.8 +/- 2.9% of original collagen content). Cilomilast (10 micro M) inhibited this degradation (84.4 +/- 8.4%). Amrinone, a PDE3 inhibitor, and zaprinast, a PDE5 inhibitor, had no effect. Gelatin zymography and immunoblotting revealed that fibroblasts cultured with TNF-alpha released increased amounts of latent MMP-1 and -9. The addition of NE resulted in the conversion of MMP-1 and -9 to their active forms, indicative of collagen degradation. Cilomilast inhibited the release of MMP-1 and -9, as well as conversion of MMP-1 to its active form. Using real-time PCR analysis, cilomilast's effect on MMP-1 release was not associated with the proteinase's mRNA expression, suggesting that the inhibition of release is regulated at the post-transcriptional level. These results suggest that cilomilast may be a potentially effective therapeutic agent in diseases characterized by excessive tissue destruction, such as emphysema.

PDE4 inhibitors attenuate fibroblast chemotaxis and contraction of native collagen gels

Therapies that mitigate the fibrotic process may be able to slow progressive loss of function in many lung diseases. Because cyclic adenosine monophosphate is known to regulate fibroblasts, the current study was designed to evaluate the activity of selective phosphodiesterase (PDE) inhibitors on two in vitro fibroblast responses: chemotaxis and contraction of three-dimensional collagen gels. Selective PDE4 inhibitors, rolipram and cilomilast, each inhibited the chemotaxis of human fetal lung fibroblasts (HFL-1) toward fibronectin in the blindwell assay system (control: 100% versus cilomilast [10 microM]: 40.5 +/- 7.3% versus rolipram: [10 microM] 32.1 +/- 2.7% cells/5 high-power fields; P < 0.05, both comparisons). These PDE4 inhibitors also inhibited contraction of three-dimensional collagen gels (control: 100% versus cilomilast: 167.7 +/- 6.9% versus rolipram: 129.9 +/- 1.9% of initial size; P < 0.05, both comparisons). Amrinone, a PDE3 inhibitor, and zaprinast, a PDE5 inhibitor, had no effect in either system. Prostaglandin E(2) (PGE(2)) inhibited both chemotaxis and gel contraction, and the PDE4 inhibitors shifted the PGE(2) concentration-dependence curve to the left in both systems. The inhibition of endogenous PGE(2) production by indomethacin diminished the effects of the PDE4 inhibitors in both chemotaxis and gel contraction, consistent with the concept that the PDE4 inhibitory effects on fibroblasts are related to the presence of cyclic adenosine monophosphate in the cells. In summary, these in vitro results suggest that PDE4 inhibitors may be able to suppress fibroblast activity and, thus, have the potential to block the development of progressive fibrosis.

Platelet-activating factor drives eotaxin production in an allergic pleurisy in mice

1. The activation of eosinophils via G-protein-coupled seven transmembrane receptors play a necessary role in the recruitment of these cells into tissue. The present study investigates a role for PAF in driving eotaxin production and eosinophil recruitment in an allergic pleurisy model in mice. 2. The intrapleural injection of increasing doses of PAF (10(-11) to 10(-9) moles per cavity) induced a dose- and PAF receptor-dependent recruitment of eosinophils 48 h after stimulation. 3. Intrapleural injection of PAF induced the rapid (within 1 h) release of eotaxin into the pleural cavity of mice and an anti-eotaxin antibody effectively inhibited PAF-induced recruitment of eosinophils. 4. Eosinophil recruitment in the allergic pleurisy was markedly inhibited by the PAF receptor antagonist UK-74,505 (modipafant, 1 mg kg(-1)). Moreover, recruitment of eosinophils in sensitized and challenged PAF receptor-deficient animals was lower than that observed in wild-type animals. 5. Blockade of PAF receptors with UK-74,505 suppressed by 85% the release of eotaxin in the allergic pleurisy. 6. Finally, the injection of a sub-threshold dose of PAF and eotaxin cooperated to induce eosinophil recruitment in vivo. 7. In conclusion, the production of PAF in an allergic reaction could function in multiple ways to facilitate the recruitment of eosinophils -- by facilitating eotaxin release and by cooperating with eotaxin to induce greater recruitment of eosinophils.

Modulation of eotaxin formation and eosinophil migration by selective inhibitors of phosphodiesterase type 4 isoenzyme

1. This study was undertaken to investigate the possible contribution of the blockade of eotaxin generation to the anti-eosinophilotactic effect of phosphodiesterase (PDE) type 4 inhibitors. In some experiments, the putative synergistic interaction between PDE type 4 inhibitors and the beta2-agonist salbutamol was also assessed. 2. Sensitized guinea-pigs aerosolized with antigen (5% ovalbumin, OVA) responded with a significant increase in eotaxin and eosinophil levels in the bronchoalveolar lavage fluid (BALF) at 6 h. Eosinophil recruitment was inhibited by both PDE type 4 inhibitors rolipram (5 mg kg(-1), i.p.) and RP 73401 (5 mg kg(-1), i.p.) treatments. In contrast, only rolipram inhibited eotaxin production. 3. Sensitized rats intrapleurally challenged (i.pl.) with antigen (OVA, 12 microg cavity(-1)) showed a marked eosinophil infiltration at 24 h, preceded by eotaxin generation at 6 h. Intravenous administration of a rabbit anti-mouse eotaxin antibody (0.5 mg kg(-1)) significantly reduced allergen-evoked eosinophilia in this model. 4. Local pretreatment with rolipram (40 microg cavity(-1)) or RP 73401 (40 microg cavity(-1)) 1 h before challenge reduced eosinophil accumulation evaluated in the rat pleural effluent, but only the former was active against eotaxin generation. The inhibitors of PDE type 3 (SK&F 94836) and type 5 (zaprinast) failed to alter allergen-evoked eosinophil recruitment in rats. 5. Local injection of beta2-agonist salbutamol (20 microg cavity(-1)) inhibited both eosinophil accumulation and eotaxin production following pleurisy. The former was better inhibited when salbutamol and rolipram were administered in combination. 6. Treatment with rolipram and RP 73401 dose-dependently inhibited eosinophil adhesion and migration in vitro. These effects were clearly potentiated by salbutamol at concentrations that had no effect alone. 7. Our findings indicate that although rolipram and RP 73401 are equally effective in inhibiting allergen-induced eosinophil infiltration only the former prevents eotaxin formation, indicating that PDE 4 inhibitors impair eosinophil accumulation by mechanisms independent of eotaxin production blockade.

Evaluation of signal transduction pathways in chemoattractant-induced human monocyte chemotaxis

The intracellular signaling pathways involved in human monocyte chemotaxis toward a variety of chemoattractant molecules were evaluated using selected pharmacological agents. Neither phosphatidylinositol-3-kinase (P13K) or extracellular signal-regulated kinase (ERK) activity were required for monocyte migration toward monocyte chemoattractant protein-1 (MCP-1), RANTES (Regulated on Activation, Normal T cell Expressed and Secreted), macrophage inflammatory protein-1alpha (MIP-1alpha) or formyl-Met-Leu-Phe (fMLP), since pretreatment with wortmannin or LY294002, or with PD098059, had no effect on the chemotactic response. Addition of forskolin and IBMX significantly attenuated chemotaxis to each of these chemoattractants and was reversed by co-treatment with Rp-cAMP, a competitive inhibitor of cAMP-dependent protein kinase A. Incubation with the protein kinase C (PKC) inhibitor GF109203X-HCl (GF109) did not affect monocyte migration, but pretreatment of monocytes with PMA significantly impaired the response to each of these chemotactic agents. Inhibition by PMA was reversed by co-treatment with GF109, implying that heterologous PKC activation is capable of desensitizing chemokine and fMLP-induced monocyte chemotaxis. These results help to define the signalling pathways involved in human monocyte chemotaxis and suggest pharmacological approaches to evaluating the cross-desensitization of chemoattractant-induced leukocyte migration.

Neuropeptide-induced chemotaxis of eosinophils in pulmonary diseases

Eosinophilic lung diseases include various disease entities, and the incidence of pulmonary infiltration with eosinophilia is on the rise. Because eosinophils, well known as inflammatory cells, respond to peripheral neuropeptides in vitro and in vivo, and these peptides are also present in human airway nerves, their interactions are thought to play a major role in the initiation and perpetuation of inflammatory lung diseases. This article reviews the current literature on eosinophil biology and interactions of these cells with the neuroendocrine system. Also, implications of tachykinins and other neuropeptides in eosinophilic pulmonary diseases is discussed based on recently investigated mechanisms. Eosinophils and sensory nerves most likely influence each other in a two-directional way in the pathogenesis of pulmonary diseases. Although release of sensory neuropeptides is involved in most conditions of airway hyperresponsiveness, increased bronchial resistance, and lung eosinophilia, the role of these nervous system-derived mediators in pulmonary diseases may be underestimated.

Cutting edge: lipoxin (LX) A4 and aspirin-triggered 15-epi-LXA4 block allergen-induced eosinophil trafficking

Tissue eosinophilia prevention represents one of the primary targets to new anti-allergic therapies. As lipoxin A4 (LXA4) and aspirin-triggered 15-epi-LXA4 (ATL) are emerging as endogenous "stop signals" produced in distinct pathologies including some eosinophil-related pulmonary disorders, we evaluated the impact of in situ LXA4/ATL metabolically stable analogues on allergen-induced eosinophilic pleurisy in sensitized rats. LXA4/ATL analogues dramatically blocked allergic pleural eosinophil influx, while concurrently increasing circulating eosinophilia, inhibiting the earlier edema and neutrophilia associated with allergic reaction. The mechanisms underlying this LXA4/ATL-driven allergic eosinophilia blockade was independent of mast cell degranulation and involved LXA4/ATL inhibition of both IL-5 and eotaxin generation, as well as platelet activating factor action. These findings reveal LXA4/ATL as a novel class of endogenous anti-allergic mediators, capable of preventing local eosinophilia.

Phosphodiesterase 4 (PDE4) inhibitors in asthma and chronic obstructive pulmonary disease (COPD)

Phosphodiesterases (PDE) are a family of enzymes responsible for the metabolism of the intracellular second messengers cyclic AMP and cyclic GMP. PDE4 is a cyclic AMP specific PDE that is the major if not sole cyclic AMP metabolizing enzymes found in inflammatory and immune cells, and contributes significantly to cyclic AMP metabolism in smooth muscles. Based on its cellular and tissue distribution and the demonstration that selective inhibitors of this isozyme reduce bronchoconstriction in animals and suppress the activation of inflammatory cells, PDE4 has become an important molecular target for the development of novel therapies for asthma and COPD. This chapter will review the evidence demonstrating the ability of PDE4 inhibitors to modify airway obstruction, airway inflammation and airway remodelling and hyperreactivity, will present some preliminary findings obtained with theses compounds in clinical trials and and will discuss experimental approaches designed to identify novel compounds that maintain the beneficial activity of the initial selective PDE4 inhibitors but with a reduced tendency of elicit the gastrointestinal side effects observed with this class of compounds.

VCAM-1 contributes to rapid eosinophil accumulation induced by the chemoattractants PAF and LTB4: evidence for basal expression of functional VCAM-1 in rat skin

The aim of the present study was to investigate the role of the adhesion pathway alpha4 integrins/vascular cell adhesion molecule type 1 (VCAM-1) in rapid eosinophil accumulation induced by the chemoattractants PAF and LTB4. For this purpose we have used an in vivo model of local 111In-eosinophil accumulation to quantify eosinophil accumulation induced by intradermal administration of platelet-activating factor (PAF) and leukotriene B4 (LTB4) in rats. Initial experiments carried out over 4 hr demonstrated that intravenous administration of an anti-VCAM-1 monoclonal antibody (mAb; 5F10) or an anti-alpha4 integrin mAb (TA2) caused a significant reduction in PAF- or LTB4-induced 111In-labelled eosinophil accumulation. Time-course experiments demonstrated that the anti-VCAM-1 mAb was effective at suppressing early phases of the 111In-labelled eosinophil accumulation induced by PAF and LTB4 (e.g. within the first 60 min). In contrast, 111In-labelled eosinophil accumulation induced by these chemoattractants was unaffected by the local administration of the transcriptional inhibitor actinomycin D, suggesting a role for basally expressed VCAM-1. Indeed, basal expression of VCAM-1 in rat skin sites was demonstrated by the localization of intravenously administered radiolabelled mAb. The localization of the radiolabelled antibody was not altered in skin sites injected with PAF or LTB4. Finally, the inhibitory effects seen with the anti-VCAM-1 mAb were enhanced when the antibody was co-injected into rats with an anti-intercellular adhesion molecule-1 (ICAM-1) mAb (1A29). The combination of these two mAb also caused a significant inhibition of PAF-induced oedema, as quantified by the local accumulation of 125I-labelled human serum albumin. The results indicate a role for alpha4 integrins/VCAM-1 and ICAM-1, in PAF- and LTB4-induced eosinophil accumulation in vivo and suggest that basally expressed VCAM-1 may have a functional role in rapid accumulation of eosinophils induced by chemoattractants.

Phosphodiesterase 4-dependent regulation of cyclic AMP levels and leukotriene B4 biosynthesis in human polymorphonuclear leukocytes

Several selective phosphodiesterase 4 inhibitors were found to be potent inhibitors of the N-formyl-Met-Leu-Phe (fMLP)-induced leukotriene B4 biosynthesis by human polymorphonuclear leukocytes with IC50s in the nanomolar range (0.09-26 nM). The rank order of potency was 6-(4-pyridylmethyl)-8-(3-nitrophenyl)quinoline (RS-14203) > 3-benzyl-5-phenyl-3H-imidazo[4,5-c][1,8]naphthyridin-4(5H)-one (KF18280) > 8-aza-1-(3-nitrophenyl)-3-(4-pyridylmethyl)-2,4-quinazoline dione (RS-25344) > 3-cyclo-pentyloxy-N-[3,5-dichloro-4-pyridyl]-4-methoxybenzamide (RP-73401) > R-rolipram > R-4-[2-(3-cyclopentyloxy-4-methoxyphenyl)-2-phenylethyl] pyridine (CDP840)> S-rolipram. Isoproterenol (IC50 = 350 nM) and prostaglandin E2 (IC50 = 59 nM) also suppressed leukotriene B4 biosynthesis. Inhibitors of the phosphodiesterase 1 (8-methoxymethyl-1-methyl-3-(2-methylpropyl)xanthine (8-MeOMe-IBMX)), phosphodiesterase 2 (erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA)), phosphodiesterase 3 (quazinone and milrinone) and phosphodiesterase 5 (zaprinast and dipyridamole) had no inhibitory effects on the fMLP-induced leukotriene B4 biosynthesis (IC50s > 20 microM). All phosphodiesterase 4 inhibitors caused an accumulation of cellular cyclic AMP to 140-185% over the basal level of fMLP-treated control cells, comparable to that observed with high concentrations of isoproterenol and prostaglandin E2. In contrast, the complete inhibition of leukotriene B4 production by 5-lipoxygenase and 5-lipoxygenase-activating protein (FLAP) inhibitors had no effect on cyclic AMP levels. Phosphodiesterase 1, 2, 3 and 5 inhibitors had little effect on the level of cellular cyclic AMP (89-126% of the basal cyclic AMP level). Dose-dependencies for R-rolipram, RS-14203 and CDP840 indicated that the maximal accumulation of cyclic AMP occurred at concentrations of phosphodiesterase 4 inhibitors higher than those required for the inhibition of leukotriene B4 production. The presence of a mixture of 8-MeOMe-IBMX, EHNA, milrinone and zaprinast to inhibit phosphodiesterase 1, 2, 3 and 5 had little effect on the dose-dependence of R-rolipram for the inhibition of leukotriene B4 biosynthesis or cyclic AMP accumulation. These data demonstrate that selective phosphodiesterase 4 inhibitors can inhibit the fMLP-induced leukotriene B4 biosynthesis in human polymorphonuclear leukocytes with a potency similar or greater than that of potent 5-lipoxygenase or FLAP inhibitors. This inhibition is accompanied by small variations in the levels of cellular cyclic AMP and appears to proceed independently of the other phosphodiesterases.

Effect of selective phosphodiesterase inhibitors on the rat eosinophil chemotactic response in vitro

In the present study, we have performed a comparative analysis of the effect of selective inhibitors of phosphodiesterase (PDE) type III, IV and V on eosinophil chemotaxis triggered by platelet activating factor (PAF) and leukotriene B4 (LTB4) in vitro. The effect of the analogues N6-2'-O-dibutyryladenosine 3':5'cyclic monophosphate (Bt2 cyclic AMP) and N2-2'-O-dibutyrylguanosine 3':5' cyclic monophosphate (Bt2 cyclic GMP) has also been determined. The eosinophils were obtained from the peritoneal cavity of naive Wistar rats and purified in discontinuous Percoll gradients to 85-95% purity. We observed that pre-incubation of eosinophils with the PDE type IV inhibitor rolipram suppressed the chemotactic response triggered by PAF and LTB4' in association with an increase in the intracellular levels of cyclic AMP. In contrast, neither zaprinast (type V inhibitor) nor type III inhibitors milrinone and SK&F 94836 affected the eosinophil migration. Only at the highest concentration tested did the analogue Bt2 cyclic AMP suppress the eosinophil chemotaxis, under conditions where Bt2 cyclic GMP was ineffective. We have concluded that inhibition of PDE IV, but not PDE III or V, was able to block the eosinophil chemotaxis in vitro, suggesting that the suppressive activity of selective PDE IV inhibitors on tissue eosinophil accumulation may, at least, be partially dependent on their ability to directly inhibit the eosinophil migration.

Secretoneurin, a Novel Neuropeptide, Is a Potent Chemoattractant for Human Eosinophils

Secretoneurin (SN), a 33-amino acid neuropeptide, is derived from secretogranin II that is released from sensory afferent C-fibers by capsaicin. Described functions of secretoneurin include chemotaxis of monocytes and endothelial cells, and inhibition of endothelial cell proliferation. Inhibition of monocyte chemotaxis by staurosporine indicated involvement of specific signaling pathways. We have tested effects of SN, substance P (SP), and interleukin-8 (IL-8) on eosinophil migration in modified Boyden chambers including signaling mechanisms of neuropeptide and cytokine stimulation of human eosinophils. Experiments showed SN as eosinophil chemoattractant comparable in its potency to IL-8. Checkerboard analysis, usage of a specific anti–SN-antibody, and receptor desensitization experiments confirmed the chemotactic activity. Preincubation of the cells with effective concentrations of staurosporine or tyrphostin-23 showed no effect, whereas treatment with wortmannin (WTN) or 3-isobutyl-1-methylxantin (IBMX) completely blocked SN-induced migration. Additionally, experiments ruled out tyrphostin-23- and WTN-sensitive signaling pathways for SP-induced chemotaxis of eosinophils. We conclude that SN-stimulated human eosinophil chemotaxis is mediated via a unique and specific signal transduction pathway that involves activation of phosphodiesterases and WTN-sensitive enzymes, ie, phospholipase D and phosphatidylinositol-3-kinase. In contrast, we report that activation of the latter and tyrosine kinases is required for SP-induced chemotaxis of eosinophils.

Secretoneurin, a Novel Neuropeptide, Is a Potent Chemoattractant for Human Eosinophils

Secretoneurin (SN), a 33-amino acid neuropeptide, is derived from secretogranin II that is released from sensory afferent C-fibers by capsaicin. Described functions of secretoneurin include chemotaxis of monocytes and endothelial cells, and inhibition of endothelial cell proliferation. Inhibition of monocyte chemotaxis by staurosporine indicated involvement of specific signaling pathways. We have tested effects of SN, substance P (SP), and interleukin-8 (IL-8) on eosinophil migration in modified Boyden chambers including signaling mechanisms of neuropeptide and cytokine stimulation of human eosinophils. Experiments showed SN as eosinophil chemoattractant comparable in its potency to IL-8. Checkerboard analysis, usage of a specific anti–SN-antibody, and receptor desensitization experiments confirmed the chemotactic activity. Preincubation of the cells with effective concentrations of staurosporine or tyrphostin-23 showed no effect, whereas treatment with wortmannin (WTN) or 3-isobutyl-1-methylxantin (IBMX) completely blocked SN-induced migration. Additionally, experiments ruled out tyrphostin-23- and WTN-sensitive signaling pathways for SP-induced chemotaxis of eosinophils. We conclude that SN-stimulated human eosinophil chemotaxis is mediated via a unique and specific signal transduction pathway that involves activation of phosphodiesterases and WTN-sensitive enzymes, ie, phospholipase D and phosphatidylinositol-3-kinase. In contrast, we report that activation of the latter and tyrosine kinases is required for SP-induced chemotaxis of eosinophils.