Phosphodiesterase isozymes: molecular targets for novel antiasthma agents

Bronchodilatory and anti-inflammatory properties of inhaled selective phosphodiesterase inhibitors in a guinea pig model of allergic asthma

In a guinea pig model of allergic asthma, we investigated the effects of the selective phosphodiesterase inhibitors rolipram (phosphodiesterase 4-selective), Org 9935 (phosphodiesterase 3-selective) and Org 20241 (dual phosphodiesterase 4/phosphodiesterase 3-selective), administered by aerosol inhalation in approximately equipotent bronchodilatory doses, on allergen-induced early and late asthmatic reactions, airway hyperreactivity and airway inflammation. Using ovalbumin-sensitized non-challenged animals, different nebulizer concentrations of each inhibitor were tested for their protective effects against histamine-induced bronchoconstriction. Inhalation of 2.5 mM rolipram, 100 mM 4,5-dihydro-6-(5,6-dimethoxybenzo[b]thien-2-yl-5-methyl-3(2H)pyridazinone (Org 9935) and 10 and 100 mM N-hydroxy-4-(3,4-dimethoxyphenyl)-thiazole-2-carboximidamide HCl (Org 20241) provided a similar, 1.8-fold (P<0.01), 2.0-fold (P<0.05), and 1.8- and 1.9-fold (P<0.05) protection, respectively. The duration of these bronchoprotective effects were different, the rate of decline being faster with rolipram and the lower Org 20241 concentration than with Org 9935 and the higher concentration of Org 20241. All compounds strongly protected against the immediate allergen-induced bronchoconstriction and significantly (P<0.05) diminished the overall early asthmatic reaction from 0 to 6 h following allergen-provocation. The severity of the late asthmatic reaction was also significantly inhibited by rolipram (P<0.05) and Org 9935 (P<0.05). Allergen-induced airway hyperreactivity to inhaled histamine after the early reaction, at 6 h after ovalbumin challenge, was strongly reduced by rolipram (P<0.05) and completely prevented by the two other phosphodiesterase inhibitors; in addition, airway hyperreactivity after the late asthmatic reaction, at 24 h, was abolished in all treatment groups. Bronchoalveolar lavage performed at 24 h after allergen challenge revealed no inhibition of eosinophil infiltration in the rolipram-treated animals, whereas inhalation of Org 9935 and the higher-but not the lower-concentration of Org 20241 strongly reduced the influx of these cells. Eosinophil peroxidase activity in the lavage fluid tended to be diminished in all treatment groups but significance was not reached with the exception of the lower concentration of Org 20241. Infiltration of lymphocytes and macrophages was significantly inhibited by Org 9935 only (P<0.05 and P<0.01, respectively), whereas neutrophil influx was not significantly affected. The results indicate that inhalation of phosphodiesterase 3-, phosphodiesterase 4- and dual phosphodiesterase 3/phosphodiesterase 4-selective inhibitors afford protection against acute histamine- and allergen-induced bronchoconstriction and prevent the development of airway hyperreactivity both after the early and late asthmatic reaction predominantly through inhibition of phosphodiesterase 4; in contrast, for significant reduction of eosinophil infiltration, both phosphodiesterase 3 and phosphodiesterase 4 inhibition seems to be required.

Purification and characterization of the human PDE4A catalytic domain (PDE4A330-723) expressed in Sf9 cells

The human PDE4A catalytic domain (PDE4A330-723) expressed in Sf9 cells was found to be heavily phosphorylated on both serines of the conserved SPS motif by mass spectrometric analysis. The purified protein exists as a tetramer at a concentration approximately 1 mg/ml from light scattering measurement and has a Km of 2 microM in hydrolyzing cAMP. In comparison, a partially purified PDE4A330-723 expressed in Escherichia coli has an apparent Km of 10 microM. The EC50 values for the Mg2+- or Co2+-mediated cAMP hydrolysis between the two enzymes differed by less than twofold. In addition, both enzymes exhibit similar sensitivities toward inhibition by a diverse set of inhibitors. Together with the fact that its adjacent peptide was covalently labeled by an electrophilic cAMP analogue, these results support that the SPS motif is not part of but is positioned near the active site. An efficient purification protocol that provides a highly purified PDE4A catalytic domain suitable for crystallization study is described.

The phosphodiesterase 4 inhibitor roflumilast is effective in the treatment of allergic rhinitis

BACKGROUND

The beneficial effects of phosphodiesterase 4 (PDE4) inhibitors in allergic asthma have been shown in previous preclinical and clinical studies. Because allergic rhinitis and asthma share several epidemiologic and pathophysiologic factors, PDE4 inhibitors might also be effective in allergic rhinitis.

OBJECTIVE

The main objective of this study was to investigate the efficacy of oral roflumilast (500 microg/day) in allergic rhinitis.

METHODS

In a randomized, placebo-controlled, double-blinded, crossover study, 25 subjects (16 male, 9 female; median age, 28 years) with histories of allergic rhinitis but asymptomatic at screening received roflumilast (500 microg once daily) and placebo for 9 days each with a washout period of at least 14 days in between treatment periods. In each of the treatment periods, controlled intranasal allergen provocation with pollen extracts was performed daily beginning the third day of treatment, each time approximately 2 hours after study drug administration. Five and 30 minutes after each allergen provocation, rhinal airflow was measured by means of anterior rhinomanometry and the subjective symptoms obstruction, itching, and rhinorrhea were assessed by means of a standardized visual analog scale.

RESULTS

Rhinal airflow improved almost consistently during the 9 days of roflumilast treatment, and it was significantly higher at study day 9 on roflumilast in comparison with placebo, a result also found for itching and rhinorrhea. With respect to the subjective obstruction score, a significant difference in comparison with placebo could be demonstrated within 4 days.

CONCLUSION

This study shows that a PDE4 inhibitor, roflumilast, effectively controls symptoms of allergic rhinitis. Thus PDE4 inhibitors might be a future treatment option not only in allergic asthma but also in allergic rhinitis or the combination of the 2 diseases.

New clinical applications of xanthine derivatives: modulatory actions on leukocyte survival and function

The use of theophylline in the treatment of obstructive pulmonary diseases has diminished with the advent of new medications. However, its use as a second-line bronchodilator has been reconsidered in recent years. Theophylline is reported to have immunomodulatory actions that may account for its clinical effectiveness in the control of airway inflammation. Theophylline, even at low plasma concentrations, inhibits the late asthmatic reaction following allergen challenge. The apparent suppression of airway inflammation by theophylline reinforces findings from in vitro experiments (including our recent studies). Its immunomodulatory actions include inhibition of cytokine synthesis and release, inhibition of inflammatory cell activation, and acceleration of granulocyte apoptosis. On the basis of these findings, theophylline has been re-evaluated as a key drug for the long-term management of bronchial asthma, and new applications are proposed for the clinical use of xanthine derivatives. Here, we review some recent advances in the understanding of pharmacological actions and new applications of xanthine derivatives.

Dissecting the cofactor-dependent and independent bindings of PDE4 inhibitors

Type 4 phosphodiesterases (PDE4s) are metallohydrolases that catalyze the hydrolysis of cAMP to AMP. At the bottom of its active site lie two divalent metal ions in a binuclear motif which are involved in both cAMP binding and catalysis [(2000) Science 288, 1822-1825; (2000) Biochemistry 39, 6449-6458]. Using a SPA-based equilibrium [(3)H]rolipram binding assay, we have determined that Mg(2+), Mn(2+), and Co(2+) all mediated a high-affinity (K(d) between 3 and 8 nM) and near stoichiometric (R)-rolipram binding to PDE4. In their absence, (R)-rolipram binds stoichiometrically to the metal ion-free apoenzyme with a K(d) of approximately 150 nM. The divalent cation dose responses in mediating the high-affinity rolipram/PDE4 interaction mirror their efficacy in catalysis, suggesting that both metal ions of the holoenzyme are involved in mediating the high-affinity (R)-rolipram/PDE4 interaction. The specific rolipram binding to the apo- and holoenzyme is differentially displaced by cAMP, AMP, and other inhibitors, providing a robust tool to dissect the components of metal ion-dependent and independent PDE4/ligand interactions. cAMP binds to the holoenzyme with a K(s) of 1.9 microM and nonproductively to the apoenzyme with a K(d) of 179 microM. In comparison, AMP binds to the holo- and apoenzyme with K(d) values of 7 and 11 mM, respectively. The diminished Mg(2+)-dependent component of AMP binding to PDE4 suggests that most of the Mg(2+)/phosphate interaction in the cAMP/PDE4 complex is disrupted upon the hydrolysis of the cyclic phosphoester bond, leading to the rapid release of AMP.

Adenosine 3',5'-cyclic monophosphate (cAMP)-dependent inhibition of IL-5 from human T lymphocytes is not mediated by the cAMP-dependent protein kinase A

IL-5 is implicated in the pathogenesis of asthma and is predominantly released from T lymphocytes of the Th2 phenotype. In anti-CD3 plus anti-CD28-stimulated PBMC, albuterol, isoproterenol, rolipram, PGE2, forskolin, cholera toxin, and the cAMP analog, 8-bromoadenosine cAMP (8-Br-cAMP) all inhibited the release of IL-5 and lymphocyte proliferation. Although all of the above compounds share the ability to increase intracellular cAMP levels and activate protein kinase (PK) A, the PKA inhibitor H-89 failed to ablate the inhibition of IL-5 production mediated by 8-Br-cAMP, rolipram, forskolin, or PGE2. Similarly, H-89 had no effect on the cAMP-mediated inhibition of lymphocyte proliferation. Significantly, these observations occurred at a concentration of H-89 (3 microM) that inhibited both PKA activity and CREB phosphorylation in intact cells. Additional studies showed that the PKA inhibitors H-8, 8-(4-chlorophenylthio) adenosine-3',5'-cyclic monophosphorothioate Rp isomer, and a myristolated PKA inhibitor peptide also failed to block the 8-Br-cAMP-mediated inhibition of IL-5 release from PBMC. Likewise, a role for PKG was considered unlikely because both activators and inhibitors of this enzyme had no effect on IL-5 release. Western blotting identified Rap1, a downstream target of the cAMP-binding proteins, exchange protein directly activated by cAMP/cAMP-guanine nucleotide exchange factors 1 and 2, in PBMC. However, Rap1 activation assays revealed that this pathway is also unlikely to be involved in the cAMP-mediated inhibition of IL-5. Taken together, these results indicate that cAMP-elevating agents inhibit IL-5 release from PBMC by a novel cAMP-dependent mechanism that does not involve the activation of PKA.

Novel selective PDE4 inhibitors. 2. Synthesis and structure-activity relationships of 4-aryl-substituted cis-tetra- and cis-hexahydrophthalazinones

A series of 4-aryl-substituted cis-4a,5,8,8a-tetra- and cis-4a,5,6,7,8,8a-hexahydro-2H-phthalazin-1-ones with high inhibitory activity toward cAMP-specific phosphodiesterase (PDE4) was synthesized. To study structure-activity relationships various substituents were introduced to the 2-, 3-, and 4-positions of the 4-phenyl ring. Substitution at the 4-position of the phenyl ring was restricted to a methoxy group, probably due to unfavorable steric interactions of larger groups with the binding site. The introduction of many alkoxy substituents including distinct ring systems and functional groups was allowed to the 3-position. It was found that in general the cis-4a,5,8,8a-tetrahydro-2H-phthalazin-1-ones are more potent than their hexahydrophthalic counterparts, the best activity residing in (4-imidazol-1-yl-phenoxy)butoxy analogue 16o (pIC(50) = 9.7).

Novel selective PDE4 inhibitors. 1. Synthesis, structure-activity relationships, and molecular modeling of 4-(3,4-dimethoxyphenyl)-2H-phthalazin-1-ones and analogues

A number of 6-(3,4-dimethoxyphenyl)-4,5-dihydro-2H-pyridazin-3-ones and a novel series of 4-(3,4-dimethoxyphenyl)-2H-phthalazin-1-ones were prepared and tested on the cGMP-inhibited phosphodiesterase (PDE3) and cAMP-specific phosphodiesterase (PDE4) enzymes. All tested compounds were found to specifically inhibit PDE4 except for pyridazinone 3b, which showed moderate PDE4 (pIC(50) = 6.5) as well as PDE3 (pIC(50) = 6.6) inhibitory activity. In both the pyridazinone and phthlazinone series it was found that N-substitution is beneficial for PDE4 inhibition, whereas in the pyridazinone series it also accounts for PDE4 selectivity. In the phthalazinone series, the cis-4a,5,6,7,8,8a-hexahydrophthalazinones and their corresponding 4a,5,8,8a-tetrahydro analogues showed potent PDE4 inhibitory potency (10/11c,d: pIC(50) = 7.6-8.4). A molecular modeling study revealed that the cis-fused cyclohexa(e)ne rings occupy a region in space different from that occupied by the other fused (un)saturated hydrocarbon rings applied; we therefore assume that the steric interactions of these rings with the binding site play an important role in enzyme inhibition.

Administration of pentoxifylline during allergen sensitization dissociates pulmonary allergic inflammation from airway hyperresponsiveness

Asthma, a chronic inflammatory disease characterized by intermittent, reversible airflow obstruction and airway hyperresponsiveness (AHR), is classically characterized by an excess of Th2 cytokines (IL-13, IL-4) and depletion of Th1 cytokines (IFN-gamma, IL-12). Recent studies indicating an important role for Th1 immunity in the development of AHR with allergic inflammation suggest that Th1/Th2 balance may be important in determining the association of AHR with allergic inflammation. We hypothesized that administration of pentoxifylline (PTX), a phosphodiesterase inhibitor known to inhibit Th1 cytokine production, during allergen (OVA) sensitization and challenge would lead to attenuation of AHR in a murine model of allergic pulmonary inflammation. We found that PTX treatment led to attenuation of AHR when administered at the time of allergen sensitization without affecting other hallmarks of pulmonary allergic inflammation. Attenuation of AHR with PTX treatment was found in the presence of elevated bronchoalveolar lavage fluid levels of the Th2 cytokine IL-13 and decreased levels of the Th1 cytokine IFN-gamma. PTX treatment during allergen sensitization leads to a divergence of AHR and pulmonary inflammation following allergen challenge.

Differential inhibition of equine neutrophil function by phosphodiesterase inhibitors

Neutrophils are recruited to the lungs of horses with chronic obstructive pulmonary disease (COPD) and exhibit increased activity after antigen challenge, which may contribute to inflammation and lung damage. Inhibition of phosphodiesterase isoenzymes (PDEs) has been shown to attenuate human neutrophil functions including superoxide production, leukotriene (LT)B4 biosynthesis, enzyme and chemokine release. As equine neutrophils contain predominantly the isoenzyme, PDE4, the present study was undertaken to investigate the effects of rolipram, a PDE4 inhibitor, on equine neutrophil function. For comparison, the effects of the nonselective PDE inhibitor, theophylline, were examined. Cells from both normal horses and COPD horses in remission were used. Superoxide production was significantly inhibited by both rolipram [32.2 +/- 2.6 vs. 10.1 +/- 1.1 nmol/10(6) cells and 49.8 +/- 6.8 vs. 22.7 +/- 2.2 nmol/10(6) cells for normal and COPD susceptible horses, respectively, in response to 10(-7) M human recombinant (hr) C5a] and theophylline (19.0 +/- 0.6 vs. 10.2 +/- 0.6 nmol/10(6) cells and 24.3 +/- 2.1 vs. 10.7 +/- 0.9 nmol/10(6) cells for normal and COPD susceptible horses, respectively, in response to 10(-7) M C5a). However, superoxide production induced by serum treated zymosan was inhibited only by theophylline (10(-3) M). Neither hrC5a- nor platelet activating factor (PAF)-induced neutrophil adherence to fibronectin coated plastic was reduced by rolipram (10(-5) M). These results demonstrate that the effects of PDE inhibitors on equine neutrophils are both stimulus and function dependent. The PDE4 inhibitors may reduce neutrophil activation in vivo in horses with COPD.

Urodilatin, a natriuretic peptide stimulating particulate guanylate cyclase, and the phosphodiesterase 5 inhibitor dipyridamole attenuate experimental pulmonary hypertension: synergism upon coapplication

In a model of acute pulmonary hypertension in intact rabbits, we investigated the vasodilatory potency of intravascularly administered urodilatin, a renal natriuretic peptide type A known to stimulate particulate guanylate cyclase. Urodilatin infusion was performed in the absence and presence of the phosphodiesterase (PDE) type 5 inhibitor dipyridamole. Stable pulmonary hypertension was evoked by continuous infusion of the thromboxane mimetic U46619, resulting in approximate doubling of the pulmonary artery pressure (PAP). When infused as sole agents, both urodilatin and dipyridamole dose-dependently attenuated the pulmonary hypertension, with doses for a 20% decrease in PAP being 30 ng/kg min for urodilatin and 10 microg/kg min for dipyridamole. A corresponding decrease in systemic arterial pressure (SAP) was noted to occur in response to both agents. Sequential intravenous administration of a subthreshold dose of dipyridamole (1 microg/kg min), which per se did not affect pulmonary and systemic hemodynamics, and a standard dose of urodilatin (30 ng/kg min) resulted in a significant amplification of both the PAP and the SAP decrease in response to the natriuretic peptide. At the same time, manifold enhanced plasmatic cyclic guanosine monophosphate (cGMP) levels were detected. Aerosolized dipyridamole also dose-dependently attenuated pulmonary hypertension, with only 1 microg/kg min being sufficient for a 20% decrease in PAP, with no SAP decline. Preceding administration of subthreshold aerosolized dipyridamole (50 ng/kg min) did, however, cause only a minor amplification of the pulmonary vasodilatory response to a subsequently infused standard dose of urodilatin. In conclusion, this is the first study to show that urodilatin does possess vasodilatory potency in the pulmonary circulation, and enhanced plasma levels of cGMP and synergy with the PDE5 inhibitor dipyridamole both strongly suggest that this effect proceeds via guanylate cyclase activation. The effect of infused urodilatin is, however, not selective for the pulmonary vasculature, as the systemic vascular resistance declines in a corresponding fashion.

Hypoxic vasoconstriction of rat main pulmonary artery: role of endogenous nitric oxide, potassium channels, and phosphodiesterase inhibition

This study investigated the influence of NO, potassium (K+) channel blockade, and the phosphodiesterase inhibitors (PDEIs) theophylline (non-selective PDEI), siguazodan (PDE3I), rolipram (PDE4I), and zaprinast (PDE5I) on rat isolated main pulmonary artery hypoxic (95% N2 and 5% CO2) vasoconstriction. Hypoxic vasoconstriction increased by 27% (p < 0.01) in the presence of the NO synthase inhibitor L-NAME (10(-4) M), and by 15% (p < 0.05) in the presence of the K(ATP) channel blocker glibenclamide (10(-6) M), without potentiation by the combination of these two drugs. Hypoxic vasoconstriction decreased by 28% (p < 0.01) in presence of the Kv,-voltage-dependent channel blocker 4-aminopyridine (10(-3) M), whereas the other K+ channel blockers, charybdotoxin (BKCa, large-conductance Ca2+-sensitive K+ channels) and apamin (SKCa, small-conductance Ca2+-sensitive K+ channels) had no effect. The nonselective PDEI theophylline induced a concentration-dependent relaxation (pD2 = 4.05, Emax = 90% [expressed as a percentage of maximal relaxation induced by papaverine 10(-4) M]). Among the selective PDEIs, siguazodan was significantly (p < 0.01) more efficient than rolipram and zaprinast (Emax values were 84%, 67%, and 58%, respectively) and significantly (p < 0.05) more potent than zaprinast (pD2 values were 6.48, 6.34, and 6.16 for siguazodan, rolipram, and zaprinast). Glibenclamide and L-NAME significantly (p < 0.05) shifted the concentration-response curve (CRC) for zaprinast to the right, and L-NAME shifted the CRC significantly to the right for siguazodan. In the presence of L-NAME, glibenclamide had no effect on the CRC of zaprinast. We conclude that (a) NO exerts a permanent inhibitory effect against hypoxic vasoconstriction that might be mediated in part by an activation of K(ATP) channels; (b) a 4-aminopyridine-sensitive K+ channel is involved in vasoconstriction under hypoxic conditions; (c) PDEs 3 and 5 are the predominant PDE isoforms in rat pulmonary artery relaxation; and (d) NO and K(ATP), but neither BK(Ca), SK(Ca), nor Kv channels, are involved in the relaxant effect of PDEIs.

The next generation of PDE4 inhibitors

A number of highly potent PDE4 inhibitors are being developed for the treatment of asthma, chronic obstructive pulmonary disease, rheumatoid arthritis, multiple sclerosis and Crohn's disease. Cilomilast (Ariflo, SB 207499, SmithKline Beecham), the most advanced member of the class in Phase III clinical trials, was reported to have a limited therapeutic window. Other inhibitors with improved profiles in preclinical models are entering into (or are in) clinical trials. The recent developments in understanding PDE4 catalysis, inhibitor binding and their emetic response should facilitate the design of the next generation of PDE4 inhibitors.

Cilomilast, a selective phosphodiesterase-4 inhibitor for treatment of patients with chronic obstructive pulmonary disease: a randomised, dose-ranging study

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a common, progressive respiratory disease that causes great morbidity and mortality despite treatment. There is evidence for airway inflammation in COPD. Cilomilast is an orally active, potent, selective phosphodiesterase type 4 inhibitor, which in vitro can affect cells thought to be of clinical importance in COPD. Our aim was to assess the safety, efficacy, and dose response of cilomilast in the treatment of patients with this disease.

METHODS

We did a 6-week, randomised, dose-ranging study in 424 patients with COPD (forced expiratory volume in 1 s [FEV(1)] 46.8% of predicted, FEV(1)/forced vital capacity [FVC] 54.6%, and postsalbutamol reversibility 5.4%). We randomly assigned individuals at 60 European centres to receive cilomilast 5 (n=109), 10 (n=102), or 15 (n=107) mg twice daily, or placebo (n=106). The main outcome measure was trough FEV(1) before and after use of a bronchodilator. Analyses were by intention to treat.

FINDINGS

Cilomilast 15 mg twice daily significantly improved FEV(1) compared with placebo (mean 130 mL vs -30 mL [95% CI 90-240] at week 6, p<0.0001). FVC and peak expiratory flow were also improved (p=0.001 and p<0.0001, respectively). Quality of life measures did not differ significantly between the groups. There were no significant differences in serious adverse events between the groups.

INTERPRETATION

Cilomilast 15 mg twice daily might be an effective maintenance treatment for COPD. Further clinical studies are underway.

Does sildenafil also improve breathing?

Sildenafil is being used by a number of patients with erectile dysfunction. Some of these patients also may have concomitant COPD. The effect of sildenafil on lung function is not known. Two patients with severe COPD and erectile dysfunction reported that their dyspnea improved when they took oral sildenafil for erectile dysfunction. Spirometry performed in these patients revealed an improvement in FEV(1) by 24% and 12%. This suggests that, in COPD patients, oral sildenafil does not have any deleterious effect on pulmonary function, and in some patients it may produce a modest improvement in FEV(1).

Cilomilast: a second generation phosphodiesterase 4 inhibitor for asthma and chronic obstructive pulmonary disease

Cilomilast (Ariflo, SB-207499) is an orally-active, second generation phosphodiesterase (PDE) inhibitor that may be effective in the treatment of asthma and chronic obstructive pulmonary disease (COPD). It has high selectivity for the cyclic AMP-specific, or PDE4, isoenzyme that predominates in pro-inflammatory and immune cells and is ten-fold more selective for PDE4D than for PDE4A, B and C. In vitro, cilomilast suppresses the activity of many pro-inflammatory and immune cells that have been implicated in the pathogenesis of asthma and COPD and is highly active in animal models of these diseases. Cilomilast demonstrates a markedly improved side effect profile over the archetypal PDE4 inhibitor, rolipram, which has been attributed to its inability to discriminate between the high affinity rolipram binding site and the catalytic domain of the enzyme, and the fact that it is negatively charged which at physiological pH should limit its penetration in to the CNS. In humans cilomilast is rapidly absorbed after oral administration, providing dose-proportional systemic exposure up to 4 mg, completely bioavailable, has a half-life of approximately 7 h and is subject to negligible first pass hepatic metabolism. Cilomilast is extensively metabolised with decyclopentylation, acyl glucuronidation and 3-hydroxylation of the cyclopentyl ring representing the principal routes. Most of the drug is excreted in the urine (approximately 90%) and faeces (6 - 7%) with unchanged cilomilast accounting for less than 1% of the administered dose. Cilomilast has been evaluated in Phase I, Phase II and Phase III trials and dose-response experiments have demonstrated a clinically significant increase in lung function and a perceived improvement in quality of life in patients with COPD. Trials of cilomilast in asthma have been less impressive although a trend towards improved lung function has been reported. Cilomilast is safe and well-tolerated at doses up to 15 mg in both short- and long-term dosing trials with a low incidence of adverse effects. No evidence for drug-drug interactions with commonly prescribed medications for COPD and asthma such as digoxin, corticosteroids, salbutamol, theophylline or warfarin has been found. Moreover, the pharmacokinetics of cilomilast are essentially the same in smokers and non-smokers, indicating that no dose adjustments of cilomilast will be required in patients with COPD. Thus, cilomilast displays a promising clinical profile in the treatment of inflammatory airway diseases, in particular COPD and the results of further Phase III trials are awaited with interest.

Bioavailability of the oral selective phosphodiesterase 4 inhibitor cilomilast

STUDY OBJECTIVE

To determine the absolute bioavailability of cilomilast, and assess the effects of food, dosing time, and coadministration of antacid agents on its bioavailability and pharmacokinetics in healthy volunteers.

SETTING

Clinical pharmacology unit.

DESIGN

Five prospective pharmacokinetic studies: one single-blind, dose-escalating, placebo-controlled trial; four open-label, randomized studies.

SUBJECTS

Ninety-six healthy adult volunteers who were nonsmokers.

INTERVENTION

In the first study, four subjects received intravenous cilomilast 1, 2, and 4 mg. In the second study, 16 subjects received oral cilomilast 15 mg or intravenous cilomilast 4 mg. In the other three studies, a total of 76 subjects were given single oral 15-mg doses; one study compared its effects in fed versus fasted subjects, one looked for differences of morning versus evening dosing, and one examined coadministration with aluminum hydroxide-magnesium hydroxide.

MEASUREMENTS AND MAIN RESULTS

After intravenous administration of cilomilast, plasma concentrations increased in an approximately dose-proportional manner; the half-life, approximately 6.5 hours, was dose independent. Cilomilast clearance and volume of distribution were small. After oral dosing, the absolute bioavailability was consistently close to 100%. Absorption was slower in fed subjects than in fasted (median 2-hr delay in time to reach maximum plasma concentration, average 39% reduction in maximum plasma concentration), but the area under the concentration-time curve from time zero to infinity (systemic availability) was unaffected. Pharmacokinetic parameters were not influenced by time of dosing or coadministration of antacid.

CONCLUSION

The absolute bioavailability of oral cilomilast was 100%; it was not adversely affected by time of dosing or coadministration with food or antacid.

The anti-inflammatory interactions of epinephrine with human neutrophils in vitro are achieved by cyclic AMP-mediated accelerated resequestration of cytosolic calcium

This study was designed to evaluate the effects of epinephrine (0.01-1 microM) on superoxide production by, and release of elastase from human neutrophils activated with the chemotactic tripeptide, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) (1 microM) in vitro, and to relate alterations in these responses to changes in adenosine 3,5' cyclic monophosphate (cAMP) and cytosolic free Ca(2+). Cyclic AMP, superoxide production and elastase release were measured by radioimmunoassay, lucigenin-enhanced chemiluminescence, and a colorimetric procedure respectively. Cytosolic Ca(2+) fluxes were measured by fura-2 spectrofluorimetry in combination with radiometric procedures that enable distinction between net efflux and influx of the cation. Epinephrine treatment of neutrophils resulted in increased cAMP and dose-related inhibition of both superoxide production and elastase release, which was potentiated by the type 4 phosphodiesterase inhibitor, rolipram, and attenuated by propranolol, but not by selective beta(1)-, alpha(1)- or alpha(2)-adrenoreceptor antagonists. Although epinephrine did not affect the FMLP-activated abruptly-occurring increase in fura-2 fluorescence intensity, indicating no effects on the release of Ca(2+) from neutrophil intracellular stores, this agent accelerated the rate of decline in fluorescence in the setting of decreased efflux and a reduction in store-operated influx of Ca(2+). These effects of epinephrine on the clearance of Ca(2+) from the cytosol of FMLP-activated neutrophils were attenuated by propranolol, and are compatible with enhancement of the activity of the cAMP-dependent Ca(2+) sequestering/resequestering endo-membrane Ca(2+)-ATPase. We conclude that epinephrine down-regulates the pro-inflammatory activities of neutrophils by cAMP-mediated enhancement of the clearance of cytosolic Ca(2+).

Molecular cloning, genomic positioning, promoter identification, and characterization of the novel cyclic amp-specific phosphodiesterase PDE4A10

We describe the cloning and expression of HSPDE4A10, a novel long form splice variant of the human cAMP phosphodiesterase PDE4A gene. The 825 amino acid HSPDE4A10 contains a unique N terminus of 46 amino acids encoded by a unique 5' exon. Exon-1(4A10) lies approximately 11 kilobase pairs (kb) downstream of exon-1(4A4) and approximately 13.5 kb upstream of the PDE4A common exon 2. We identify a rat PDE4A10 ortholog and reveal a murine ortholog by nucleotide sequence database searching. PDE4A10 transcripts were detected in various human cell lines and tissues. The 5' sequence flanking exon-1(4A10) exhibited promoter activity with the minimal functional promoter region being highly conserved in the corresponding mouse genomic sequence. Transient expression of the engineered human PDE4A10 open reading frame in COS7 cells allowed detection of a 121-kDa protein in both soluble and particulate fractions. PDE4A10 was localized primarily to the perinuclear region of COS7 cells. Soluble and particulate forms exhibited similar K(m) values for cAMP hydrolysis (3-4 microM) and IC(50) values for inhibition by rolipram (50 nM) but the V(max) value of the soluble form was approximately 3-fold greater than that of the particulate form. At 55 degrees C, soluble HSPDE4A10 was more thermostable (T(0.5) = 11 min) than the particulate enzyme (T(0.5) = 5 min). HSPDE4A10 and HSPDE4A4B are shown here to be similar in size and exhibit similar maximal activities but differ with respect to sensitivity to inhibition by rolipram, thermostability, interaction with the SRC homology 3 domain of LYN, an SRC family tyrosyl kinase, and subcellular localization. We suggest that the unique N-terminal regions of PDE4A isoforms confer distinct properties upon them.

Effects of phosphodiesterase inhibitors on hypoxic pulmonary vasoconstriction. Influence of K(+) channels and nitric oxide

We studied the relaxant effects of the cyclic nucleotide phosphodiesterase inhibitors theophylline (non-selective), rolipram (type IV, 3',5'-cyclic monophosphate (cAMP)-specific) and zaprinast (type V, 3',5'-cyclic monophosphate (cGMP)-specific) on the hypoxic vasoconstriction in the isolated perfused rat lung and the involvement of K(+) channels and nitric oxide (NO) in these effects. K(+) channels were inhibited by glibenclamide, charybdotoxin, apamin and 4-aminopyridine and nitric oxide synthase by L-N(G)-nitroarginine methyl ester (L-NAME). Hypoxic ventilation produced a significant pressure response. L-NAME and 4-aminopyridine increased this response. Rolipram, zaprinast and theophylline shared the ability to oppose the hypoxic pulmonary vasoconstriction. The order of potency was zaprinast>rolipram>theophylline. Glibenclamide partially inhibited the relaxant effects of rolipram and theophylline. Charybdotoxin inhibited the dilator response to rolipram. Apamin inhibited partially the vasodilation induced by rolipram and zaprinast. 4-Aminopyridine inhibited partially the relaxant effects of theophylline. L-NAME failed to block the effects of the three compounds. These data illustrate different pharmacological profiles according to the phosphodiesterase inhibitors and support the potential interest of selective inhibitors as relaxant agents in pulmonary vessels.

Dual effect of cAMP on the writhing response in mice

The intraperitoneal injection of agents that increase the intracellular level of cyclic AMP (cAMP), reduced significantly the number of writhes induced by acetic acid and zymosan in mice. However, dibutyryl cyclic AMP (Db-cAMP) induced a dual response: (a) low doses caused antinociception, and (b) a high dose potentiated the nociceptive effect of a low concentration of acetic acid. High doses of Db-cAMP also reversed the antinociceptive effect of dexamethasone and the depletion of resident peritoneal cells. We also demonstrated that a low dose of Db-cAMP, forskolin or dexamethasone inhibited the production of tumor necrosis factor-alpha and interleukin-1 beta by macrophages stimulated by zymosan. In conclusion, this study suggests that cAMP has a dual effect in the writhing model: an antinociceptive effect due to its modulatory action on resident peritoneal cells, thus, reducing the synthesis of mediators involved in the nociceptive response, and a nociceptive effect by directly sensitizing the nociceptive neuron.

Drug treatment of airway inflammation in asthma

Several methods are available for assessing drug effects on airway inflammation and the antiinflammatory effects of drugs for asthma. Cromolyn and theophylline are well-established drugs for the treatment of asthma, and each has antiinflammatory properties. Drugs in development include those aimed at inhibiting inflammatory mediators and immunoglobulin E function; clinical studies, however, have been conducted largely in patients with moderate to severe asthma.

Novel drugs for treating asthma

The health burden of asthma is increasing globally at an alarming rate, providing a strong impetus for the development of new therapeutics, particularly drugs that may prevent development of the disease. Currently available inhaled bronchodilators and anti-inflammatory drugs are effective in most asthmatic patients, but this palliative therapy requires long-term daily administration. Despite considerable efforts by the pharmaceutical industry, it has been difficult to develop novel therapeutic agents, the leukotriene antagonists being the only new class of asthma treatments to be licensed in the past 30 years. It is clearly important to understand more about the underlying mechanisms of asthma and about how currently used drugs work before rational improvements in therapy can be expected. There are numerous therapies in clinical development that combat the inflammation found in asthma, specifically targeting eosinophils, IgE, adhesion molecules, cytokines (interleukin-4, -5, -13) and chemokines, inflammatory mediators, and cell signaling (kinase inhibitors). In particular, there is the obvious need for new therapy for severe asthma that is poorly controlled by high-dose corticosteroids as well as agents to counter acute emergency asthma. A long-term goal is to develop disease-modifying immunotherapy that could be introduced in childhood to alter the natural history of asthma. Thanks to the extensive efforts of the pharmaceutical industry, we can expect the introduction of a range of novel therapies for asthma in the near future.

New perspectives in asthma treatment

The recent advances in the knowledge of the basic mechanisms underlying asthmatic inflammation have significantly contributed to the delineation of new therapeutic perspectives for asthma. There are currently three main approaches to the development of novel antiasthma treatments: 1) improvement in existing classes of drugs 2) identification of new compounds able to interfere with the complex network of proinflammatory mediators, cytokines, chemokines, and adhesion molecules involved in the pathogenesis of asthma 3) utilization of new forms of immunotherapy aimed at blocking the unbalanced Th2 response which characterizes the pathophysiology of asthma. Such a remarkable expansion in available therapeutic options will probably allow us, over the next decade, to treat asthma by more selectively targeting the pathogenetic events responsible for this widespread airway disease.

CGS 21680, dibutyryl cyclic AMP and rolipram attenuate the pro-inflammatory interactions of the Pseudomonas aeruginosa -derived pigment, 1-hydroxyphenazine, with human neutrophils

The effects of the intracellular adenosine 3':5' cyclic monophosphate (cAMP)-elevating agents, CGS 21680 (0.01- 1 microM) and rolipram (0.01-1 microM), as well as those of dibutyryl cAMP (0. 05-4 mM) on the pro-inflammatory interactions of the P. aeruginosa -derived pigment, 1-hydroxyphenazine (1-hp, 3.1 and 12.5 microM), with human neutrophils have been investigated in vitro. Ca(2+)fluxes in FMLP-activated neutrophils were measured using a fura-2/AM spectrofluorimetric procedure, while a colourimetric method was used to measure release of the primary granule enzyme, elastase, from the cells. Treatment with 1-hp resulted in delayed clearance of Ca(2+)from the cytosol of N -formyl- L -methionyl- L -leucyl- L -phenylalanine (FMLP, 1 microM)-activated neutrophils and increased release of elastase. All 3 test agents caused dose-related antagonism of 1-hp-mediated potentiation of elastase release from activated neutrophils, which was associated with restoration of Ca(2+)homeostasis. These observations demonstrate the potential of cAMP-elevating agents, acting on Ca(2+)clearance mechanisms in activated neutrophils, to attenuate the potentially harmful pro-inflammatory effects of 1-hp.

Effects of therapeutic doses of albuterol on beta2-adrenergic receptor density and metabolic changes

Beta2-agonist drugs at inhaled supratherapeutic doses or when given orally or parenterally alter peripheral lymphocyte beta2-adrenoceptor density (betaAR) and have demonstrable metabolic effects. However, it is not known whether these changes occur at therapeutic inhaled doses. We therefore studied the effects of therapeutic doses of inhaled albuterol in five asthmatic subjects (mean age 23.0+/-2.4 years) and six normal subjects (mean age 28.3+/-3.3 years). Subjects were studied in a randomized, double-blind protocol in which each subject received either inhaled albuterol (270 microg four times daily) for 2 weeks followed by placebo or vice versa in two sequential 2-week periods separated by a 2-week washout period. In the asthmatics, baseline FEV1 increased significantly (p < 0.05) after 2 weeks of inhaled albuterol treatment compared to the initial visit and after 2 weeks of placebo (mean FEV1: 3.2 L+/-0.7 L, 2.9 L+/-0.5 L, and 3.0 L+/-0. 7 L, respectively). Baseline peripheral lymphocyte betaAR was not significantly different (p > 0.05) between the asthmatic (mean: 757+/-176) and normal subjects (mean: 732+/-251). However, in neither group was there any significant change (p > 0.05) in betaAR or plasma potassium, insulin, or glucose, either acutely or after 2 weeks of albuterol therapy. The present study confirms that there is no difference in peripheral lymphocyte betaAR between asthmatic and normal subjects and also shows that at therapeutic doses of inhaled albuterol, there are no significant changes in betaAR or metabolic effects.

Accelerated calcium influx and hyperactivation of neutrophils in chronic granulomatous disease

The relationship between activation of NADPH-oxidase, alterations in membrane potential and triggering of Ca2+ fluxes in human phagocytes has been investigated using neutrophils from four subjects with chronic granulomatous disease (CGD). Cytosolic Ca2+ and membrane potential were measured by spectrofluorimetry, and net efflux and influx of Ca2+ by radiometric procedures. Exposure of normal neutrophils to the chemotactic tripeptide, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP; 1 microM) was accompanied by an abrupt increase in cytosolic Ca2+ coincident with membrane depolarization and efflux of the cation. These events terminated at around 30 s after the addition of FMLP and were followed by membrane repolarization and store-operated influx of Ca2+, both of which were superimposable and complete after about 5 min. Activation of CGD neutrophils was also accompanied by an increase in cytosolic Ca2+, which, in spite of an efficient efflux response, was prolonged in relation to that observed in normal cells. This prolonged increase in cytosolic Ca2+ in activated CGD neutrophils occurred in the setting of trivial membrane depolarization and accelerated influx of Ca2+, and was associated with hyperactivity of the cells according to excessive release of elastase and increased activity of phospholipase A2. Treatment of CGD neutrophils with the type 4 phosphodiesterase inhibitor, rolipram (1 microM) restored Ca2+ homeostasis and attenuated the increase in elastase release. These findings support the involvement of NADPH-oxidase in regulating membrane potential and Ca2+ influx in activated neutrophils, and may explain the disordered inflammatory responses and granuloma formation which are characteristic of CGD.

Phthalazine PDE4 inhibitors. Part 2: the synthesis and biological evaluation of 6-methoxy-1,4-disubstituted derivatives

This communication describes the synthesis and in vitro evaluation of a novel and potent series of phosphodiesterase type IV (PDE4) inhibitors. The compounds described present substituents in position 4 of the phthalazine ring to replace the commonly observed cyclopentyloxy moiety of rolipram analogues. Preliminary evidences of reduced side effects compared to standards and improved pharmacokinetic properties for selected derivatives are also reported.

Synthesis, structure-activity relationships, and pharmacological profile of 9-amino-4-oxo-1-phenyl-3,4,6,7-tetrahydro[1,4]diazepino[6, 7,1-hi]indoles: discovery of potent, selective phosphodiesterase type 4 inhibitors

The synthesis, structure-activity relationships, and biological properties of a novel series of potent and selective phosphodiesterase type 4 (PDE4) inhibitors are described. These new aminodiazepinoindoles displayed in vitro PDE4 activity with submicromolar IC(50) values and PDE4 selectivity vs PDE1, -3, and -5. Specifically, one compound (CI-1044, 10e) provided efficient in vitro inhibition of TNFalpha release from hPBMC and hWB with IC(50) values of 0.34 and 0.84 microM, respectively. This compound was found to exhibit potent in vivo activity in antigen-induced eosinophil recruitment in Brown-Norway rats (ED(50) = 3.2 mg/kg po) and in production of TNFalpha in Wistar rats (ED(50) = 2.8 mg/kg po). No emetic side effects at therapeutic doses were observed in ferrets.

The effect of selective and non-selective phosphodiesterase inhibitors on allergen- and leukotriene C(4)-induced contractions in passively sensitized human airways

Non-selective inhibitors of cyclic nucleotide phosphodiesterase (PDE) block allergen-induced contraction of passively sensitized human airways in vitro by a dual mechanism involving a direct relaxant effect on smooth muscle and inhibition of histamine and cysteinyl leukotriene (LT) release from airways. We investigated the effects of non-selective PDE inhibitors and selective inhibitors of PDE3 and PDE4 in order to determine the involvement of PDE isoenzymes in the suppression of allergic bronchoconstriction. Macroscopically normal airways from 76 patients were sensitized with IgE-rich sera (>250 u ml(-1)) containing specific antibodies against allergen (Dermatophagoides farinae). Contractile responses of bronchial rings were assessed using standard organ bath techniques. Passive sensitization caused increased contractile responses to allergen, histamine and LTC(4). Non-selective PDE inhibitors (theophylline, 3-isobutyl-1-methylxanthine [IBMX]), a PDE3-selective inhibitor (motapizone), PDE4-selective inhibitors (RP73401, rolipram, AWD 12-281) and a mixed PDE3/4 inhibitor (zardaverine) all significantly relaxed inherent bronchial tone at resting tension and to a similar degree. Theophylline, IBMX, zardaverine and the combination of motapizone and RP73401 inhibited the contractile responses to allergen and LTC(4). Pre-treatment with motapizone, RP73401, rolipram or the methylxanthine adenosine receptor antagonist, 8-phenyltheophylline, did not significantly decrease responses to either allergen or LTC(4). We conclude that combined inhibition of PDE3 and PDE4, but not selective inhibition of either isoenzyme or antagonism of adenosine receptors, is effective in suppressing allergen-induced contractions of passively sensitized human airways. The relationship between allergen- and LTC(4)-induced responses suggests that PDE inhibitors with PDE3 and PDE4 selectivity are likely to act in part through inhibition of mediator release and not simply through direct relaxant actions on airway smooth muscle.

Update on pharmacologic therapy for chronic obstructive pulmonary disease

As described throughout this article, significant improvements continue to occur in the pharmacologic management of COPD. These improvements range from improved medication targeting to better understanding of mechanisms of action, to better delivery of medications, to lower side effects. New areas of pharmacologic intervention, if not ready for use today, hold great promise for the not-too-distant future. In addition to the many agents described here, multiple mediator antagonists and anti-inflammatory agents are also under investigation for use in COPD. Interestingly, repair of alveolar tissue may be possible. Indeed, preliminary animal studies suggest that retinoic acid may be able to induce regeneration of lung alveoli. Overall, more effort is needed to broaden awareness and provide for the appropriate diagnosis of COPD, better explain pharmacologic therapies for COPD, simplify and disseminate guidelines, and highlight key differences between asthma and COPD, including their treatment strategies. As interest in COPD continues to grow, future updates on COPD management will continue to add new pharmacologic options for this devastating and preventable disease.

Expression, purification, refolding, and characterization of recombinant human interleukin-13: utilization of intracellular processing

Interleukin-13 (IL-13) is a pleiotropic cytokine that elicits both proinflammatory and anti-inflammatory immune responses. Recent studies underscore its role in several diseases, including asthma and cancer. Solution studies of IL-13 and its soluble receptors may facilitate the design of antagonists/agonists which would require milligram quantities of specifically labeled protein. A synthetic gene encoding human IL-13 (hIL-13) was inserted into the pMAL-c2 vector with a cleavage site for the tobacco etch virus (TEV) protease. Coexpression of the fusion protein and TEV protease led to in vivo cleavage, resulting in high levels of hIL-13 production. hIL-13, localized to inclusion bodies, was purified and refolded to yield approximately 2 mg per liter of bacteria grown in minimal media. Subsequent biochemical and biophysical analysis of both the unlabeled and (15)N-labeled protein revealed a bioactive helical monomer. In addition, the two disulfide bonds were unambiguously demonstrated to be Cys29-Cys57 and Cys45-Cys71 by a combined proteolytic digestion and mass spectrometric analysis.

Phosphodiesterase activity in neutrophils from horses with chronic obstructive pulmonary disease

Neutrophils are recruited to the lungs of horses with chronic obstructive pulmonary disease (COPD) and exhibit increased activity after antigen challenge. Phosphodiesterase type4 (PDE4) inhibitors have been shown to attenuate human neutrophil activation. The aim of this study was to establish the PDE isoenzyme profile of equine neutrophils using isoenzyme selective inhibitors to determine if these compounds should be evaluated in horses with COPD. Total cAMP and cGMP dependent PDE activity was no different in neutrophils from normal (156.2+/-7.1 and 6.8+/-0.6 pmol/min/mg for cAMP and cGMP, respectively) and COPD susceptible horses (146.0+/-10.2 and 5.5+/-0.6 pmol/min/mg for cAMP and cGMP, respectively). The PDE4 inhibitors, CDP840 and rolipram, caused significant, concentration related and almost complete inhibition of PDE activity (IC(50) values=8.8+/-0.1 x 10(-9) and 7.3+/-0.2 x 10(-9)M for CDP840; 1.2+/-0.1 x 10(-6) and 1.1+/-0.1 x 10(-6)M for rolipram in normal and COPD susceptible horses, respectively). The inhibitory effects of the mixed PDE3/ PDE4 inhibitor, zardaverine were of similar magnitude and potency to rolipram. However, the limited inhibitory effects of the PDE3 inhibitor, siguazodan, suggest that zardaverine is acting primarily via PDE4 inhibition. These results indicate that PDE4 is the predominant isoenzyme present in the equine neutrophil and inhibition of PDE activity using selective PDE4 inhibitors may, therefore, modulate equine neutrophil activation in horses with COPD.

Cyclic nucleotide phosphodiesterases: relating structure and function

Cyclic nucleotide phosphodiesterases (PDEs) comprise a superfamily of metallophosphohydrolases that specifically cleave the 3',5'-cyclic phosphate moiety of cAMP and/or cGMP to produce the corresponding 5'-nucleotide. PDEs are critical determinants for modulation of cellular levels of cAMP and/or cGMP by many stimuli. Eleven families of PDEs with varying selectivities for cAMP or cGMP have been identified in mammalian tissues. Within these families, multiple isoforms are expressed either as products of different genes or as products of the same gene through alternative splicing. Regulation of PDEs is important for controlling myriad physiological functions, including the visual response, smooth muscle relaxation, platelet aggregation, fluid homeostasis, immune responses, and cardiac contractility. PDEs are critically involved in feedback control of cellular cAMP and cGMP levels. Activities of the various PDEs are highly regulated by a panoply of processes, including phosphorylation events, interaction with small molecules such as cGMP or phosphatidic acid, subcellular localization, and association with specific protein partners. The PDE superfamily continues to be a major target for pharmacological intervention in a number of medically important maladies.

The synthesis and biological evaluation of a novel series of phthalazine PDE4 inhibitors I

This communication describes the synthesis and in vitro evaluation of a novel and potent series of phosphodiesterase type IV (PDE4) inhibitors. The compounds described represent conformationally constrained analogues of RP 73401, Piclamilast. Preliminary evidences of reduced side effects of II compared to standards are also reported.

Sub-family selective actions in the ability of Erk2 MAP kinase to phosphorylate and regulate the activity of PDE4 cyclic AMP-specific phosphodiesterases

Expressed in intact cells and in vitro, PDE4B and PDE4C isoenzymes of cyclic nucleotide phosphodiesterase (PDE), in common with PDE4D isoenzymes, are shown to provide substrates for C-terminal catalytic unit phosphorylation by the extracellular signal-regulated kinase Erk2 (p42(MAPK)). In contrast, PDE4A isoenzymes do not provide substrates for C-terminal catalytic unit phosphorylation by Erk2. Mutant PDE4 enzymes were generated to show that Erk2 phosphorylation occurs at a single, cognate serine residue located within the C-terminal portion of the PDE4 catalytic unit. PDE4 long-form isoenzymes were markedly inhibited by Erk2 phosphorylation. The short-form PDE4B2 isoenzyme was activated by Erk2 phosphorylation. These functional changes in PDE activity were mimicked by mutation of the target serine for Erk2 phosphorylation to the negatively charged amino acid, aspartic acid. Epidermal growth factor (EGF) challenge caused diametrically opposed changes in cyclic AMP levels in COS1 cells transfected to express the long PDE4B1 isoenzyme compared to cells expressing the short PDE4B2 isoenzyme. We suggest that PDE4 enzymes may provide a pivotal point for integrating cyclic AMP and Erk signal transduction in cells with 4 genes encoding enzymes that are either insensitive to Erk2 action or may either be activated or inhibited. This indicates that PDE4 isoenzymes have distinct functional roles, giving credence to the notion that distinct therapeutic benefits may accrue using either PDE4 subfamily or isoenzyme-selective inhibitors.

Apparent involvement of the A(2A) subtype adenosine receptor in the anti-inflammatory interactions of CGS 21680, cyclopentyladenosine, and IB-MECA with human neutrophils

This study was undertaken to identify the adenosine receptor (AR) subtypes which down-regulate the proinflammatory activities of human neutrophils, as well as the involvement of adenosine 3',5'-cyclic monophosphate (cAMP) and its relationship to cellular handling of Ca(2+) in mediating these effects. Neutrophils were treated with varying concentrations (0.01-1 microM) of AR agonists operative at A(1) (N(6)-cyclopentyladenosine, CPA), A(2A) (2(4-[(2-carboxyethyl)phenyl]ethylamino)-5'-N-ethylcarboxamidoadenosi ne, CGS 21680), and A(3) (N(6)-(3-iodobenzyl-5'-N-methylcarbamoyladenosine, IB-MECA) receptors, after which they were activated with the chemoattractant, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP, 1 microM). Intracellular cAMP, superoxide, and elastase were assayed using radioimmunoassay, lucigenin-enhanced chemiluminescence (LECL), and colorimetric procedures, respectively, while changes in the concentrations of cytosolic Ca(2+) were monitored by fura-2-based spectrofluorimetry. CGS 21680, at all concentrations tested, inhibited superoxide production in a dose-related manner, while CPA and IB-MECA were effective only at the highest concentrations tested (0.5-1 microM). The release of elastase from activated neutrophils was also inhibited by all three AR agonists, but was more sensitive to CGS 21680 and IB-MECA than was superoxide production. The inhibitory effects of all 3 agonists on superoxide production and elastase release were associated with accelerated clearance of Ca(2+) from the cytosol of activated neutrophils, and were effectively neutralized by pretreatment of the cells with the highly selective A(2A)R antagonist, ZM 241385 (4-(2-[7-amino-2-(2-furyl)[1, 2,4]triazolo[2,3-a][1,3,5]triazin-5yl amino]ethyl)phenol). Increased cAMP was detected in neutrophils treated with CGS 21680 and IB-MECA (1 microM). These data support the involvement of the A(2A)R subtype in the suppression of superoxide production and degranulation by activated human neutrophils, probably by cAMP-mediated alterations in Ca(2+) handling.

Phosphodiesterase inhibitors and forskolin Up-regulate arginase activity in rabbit alveolar macrophages

Alveolar macrophages (AMsmall ef, Cyrillic) express considerable arginase activity which can be modulated by various mediators. As inhibitors of phosphodiesterase (PDE) play an increasing role in the treatment of chronic inflammatory and obstructive airway disease, we tested whether PDE inhibitors affect arginase activity in AMsmall ef, Cyrillic. Isolated rabbit AMsmall ef, Cyrillic were cultured for 20 h in the absence or presence of bacterial lipopolysaccharides (LPS) and/or different test substances. Thereafter arginase activity was determined by measuring the formation of [(3)H]-L-ornithine during 1 h incubation with [(3)H]-L-arginine. Lipopolysaccharide-enhanced (0. 01-5 microg/ml) maximal arginase activity by about 2.5-fold. The non-selective PDE inhibitor IBMX and the PDE4 selective inhibitor rolipram (each up to 30 microM) caused a 2.4-fold increase in arginase activity, and these effects were additive to those of LPS. The PDE3-selective inhibitor siguazodan had only marginal effects. Forskolin (10 microM) also enhanced arginase activity in the absence and presence of LPS. The effect of forskolin was almost prevented by cycloheximide (30 microM) and largely attenuated by the protein kinase A inhibitor KT 5720 (300 nM). In conclusion, inhibition of the cAMP-specific PDE4, like direct activation of adenylyl cyclase, causes an up-regulation of arginase activity in rabbit AMsmall ef, Cyrillic.

The cAMP-specific phosphodiesterase PDE4A5 is cleaved downstream of its SH3 interaction domain by caspase-3. Consequences for altered intracellular distribution

The unique N-terminal region of the cAMP-specific phosphodiesterase PDE4A5, which confers an ability to bind to certain protein SH3 domains, is cleaved during apoptosis in both Rat-1 fibroblasts and PC12 cells. Cleavage was abolished by the caspase-3-selective inhibitor, z-DEVD-CHO but not the caspase-1 selective inhibitor, z-YVAD-CHO. Caspase-3 treatment of PDE4A5, expressed either transiently in COS cells or generated in vitro by coupled transcription translation, generated a similar cleavage product of 100 kDa compared with the native 110-kDa PDE4A5. This product could be detected immunochemically with an antibody raised to a C-terminal PDE4A5 peptide but not an antibody raised to the N terminus of PDE4A5, indicating that caspase-3 caused N-terminal cleavage of PDE4A5. Deletion of the putative caspase-3 cleavage site, (69)DAVD(72), in PDE4A5, or generation of either the D72A or the D69A mutants, ablated the ability of caspase-3 to cause cleavage. The N-terminal truncate PDE4A5-DeltaP3 was engineered to mimic the caspase-cleaved product of PDE4A5. This showed altered catalytic activity and, unlike PDE4A5, was unable to interact with the SH3 domain of the tyrosyl kinase, LYN. Although both PDE4A5 and PDE4A5-DeltaP3 were localized at cell cortical regions (ruffles), the distinct perinuclear association noted for both PDE4A5 and LYN was not seen for PDE4A5-DeltaP3. Staurosporine-induced apoptosis caused a marked redistribution of PDE4A5 but not PDE4A8 in stably transfected Rat-1 cells. The PDE4-selective inhibitor, rolipram together with the adenylyl cyclase activator forskolin, caused a synergistic increase in the apoptosis of Rat-1 cells. Overexpression of PDE4A5 in Rat-1 cells protected against staurosporine-induced apoptosis in contrast to overexpression of PDE4A8, which potentiated apoptosis. PDE4A5 may be the sole PDE4 family member to provide a substrate for caspase-3 cleavage and this action serves to remove the SH3 binding domain that is unique to this isoform within the PDE4A family and to alter its intracellular targeting.

Chronic obstructive pulmonary disease: emerging therapies

Despite the high prevalence of and mortality from chronic obstructive pulmonary disease, extensive research on the underlying pathophysiology and specific therapeutics for this disease is, relatively, in its infancy. Several novel molecular targets are being investigated as potential treatments for the disease. The most exciting new class of compounds is the phosphodiesterase 4 inhibitors; Ariflo (SB 207499)-a member of this class, and the most advanced in development (Phase III)-was reported recently to have significant clinical efficacy in patients with chronic obstructive pulmonary disease. Phosphodiesterase 4 inhibitors, such as Ariflo, possibly represent the most important advance in pulmonary medicine in recent years.

Anti-inflammatory and analgesic effects of the phosphodiesterase 4 inhibitor rolipram in a rat model of arthritis

There has been much interest in strategies which modulate tumour necrosis factor-alpha (TNF-alpha) levels and/or function in rheumatoid arthritis. The elevation of intracellular levels of cyclic AMP in leukocytes by phosphodiesterase 4 inhibitors is accompanied by significant inhibition of the production of TNF-alpha. Nevertheless, these drugs may enhance the hyperalgesia induced by a range of inflammatory mediators, including TNF-alpha. In the present study, we examined the effects of the phosphodiesterase 4 inhibitor rolipram on the local inflammatory infiltrate and hyperalgesia in a rat model of adjuvant-induced arthritis. Rolipram (3 mg/kg) was administered by oral gavage from day 10 to 14 after disease induction. Pretreatment with rolipram abrogated oedema formation and significantly inhibited hyperalgesia. Histopathological analysis revealed a marked inhibition of cellular influx as well as bone and cartilage destruction. Serum and local TNF-alpha levels were suppressed in treated animals whereas there were little changes in interleukin-1beta levels. Although cyclic AMP elevating agents may affect nociceptor threshold to increase the hyperalgesic responses acutely, they also possess significant anti-inflammatory activity, which may hinder local mediator release and/or action. The anti-inflammatory effects of rolipram predominate during this chronic arthritis model in the rat.

New directions in allergic diseases: mechanism-based anti-inflammatory therapies

Advances in our understanding of allergic inflammation have led to the development of several novel anti-inflammatory drugs that target specific aspects of the inflammatory process. These treatments are based on improvements in existing therapies or on a better understanding of the cellular and molecular mechanisms involved in atopic diseases. Although most attention has been focused on asthma, treatments that inhibit the atopic disease process would have application to all atopic diseases, which often coincide. Specific agents that are now in development for the treatment of allergic inflammation include inhibitors of eosinophilic inflammation (eg, anti-IL-5, CCR3 antagonists, and very late antigen 4 inhibitors), drugs that may inhibit allergen presentation, and inhibitors of T(H)2 cells. More general anti-inflammatory approaches include novel cortico-steroids, phosphodiesterase inhibitors, and mitogen-activated protein kinase inhibitors. Most of the new therapies in development are aimed at inhibiting or suppressing components of the allergic inflammatory response, but in the future, there are possibilities for development of preventive and curative treatments.

Absence of muscarinic cholinergic airway responses in mice deficient in the cyclic nucleotide phosphodiesterase PDE4D

Muscarinic cholinergic signaling plays an essential role in the control of the normal airway functions and in the development of pulmonary pathologies including asthma. In this paper we demonstrate that the airways of mice deficient in a cAMP-specific phosphodiesterase (PDE4D) are no longer responsive to cholinergic stimulation. Airway hyperreactivity that follows exposure to antigen was also abolished in PDE4D(-/-) mice, despite an apparently normal lung inflammatory infiltration. The loss of cholinergic responsiveness was specific to the airway, not observed in the heart, and was associated with a loss of signaling through muscarinic receptors with an inability to decrease cAMP accumulation. These findings demonstrate that the PDE4D gene plays an essential role in cAMP homeostasis and cholinergic stimulation of the airway, and in the development of hyperreactivity. In view of the therapeutic potentials of PDE4 inhibitors, our findings provide the rationale for novel strategies that target a single PDE isoenzyme.