Effects of rolipram and siguazodan on the human isolated bronchus and their interaction with isoprenaline and sodium nitroprusside

Clinical relevance of the relaxant effects of roflumilast on human bronchus: potentiation by a long-acting beta-2-agonist

Roflumilast is an oral, add-on option for treating patients with severe COPD and frequent exacerbations despite optimal therapy with inhaled drugs. The present study focused on whether this phosphodiesterase 4 inhibitor and its active metabolite roflumilast N-oxide affect the tone of human bronchial rings. We also investigated the interactions between roflumilast, roflumilast N-oxide and the long-acting β₂ -agonist formoterol with regard to the relaxation of isolated human bronchial rings at basal tone or pre-contracted with histamine. Our results demonstrated for the first time that at a clinically relevant concentration (1 nm), roflumilast N-oxide and roflumilast induce a weak relaxation of the isolated human bronchus either at resting tone (22% and 16%, respectively) or even weaker on pre-contracted bronchus with histamine (7% and 5%, respectively). In addition, the combination of formoterol with roflumilast or roflumilast N-oxide is more potent than each component alone for relaxing pre-contracted isolated bronchi - the apparent pD2 of formoterol was significantly reduced for the threshold concentration of 1 nm of the phosphodiesterase 4 inhibitors by a factor of 2.4 for roflumilast N-oxide and 1.9 for roflumilast. The full inhibition of phosphodiesterase 4 activity is achieved at 100 nm but this high concentration only caused partial relaxations of the human bronchi. At a clinically relevant concentration, these oral phosphodiesterase 4 inhibitors are not effective direct bronchodilators but could enhance the efficacy of inhaled long-acting β2-agonists.

Phosphodiesterase type 4 inhibition enhances nitric oxide- and hydrogen sulfide-mediated bladder neck inhibitory neurotransmission

Nitric oxide (NO) and hydrogen sulfide (H₂S) play a pivotal role in nerve-mediated relaxation of the bladder outflow region. In the bladder neck, a marked phosphodiesterase type 4 (PDE4) expression has also been described and PDE4 inhibitors, as rolipram, produce smooth muscle relaxation. This study investigates the role of PDE4 isoenzyme in bladder neck gaseous inhibitory neurotransmission. We used Western blot and double immunohistochemical staining for the detection of NPP4 (PDE4) and PDE4A and organ baths for isometric force recording to roflumilast and tadalafil, PDE4 and PDE5, respectively, inhibitors in pig and human samples. Endogenous H₂S production measurement and electrical field stimulation (EFS) were also performed. A rich PDE4 and PDE4A expression was observed mainly limited to nerve fibers of the smooth muscle layer of both species. Moreover, roflumilast produced a much more potent smooth muscle relaxation than that induced by tadalafil. In porcine samples, H₂S generation was diminished by H₂S and NO synthase inhibition and augmented by roflumilast. Relaxations elicited by EFS were potentiated by roflumilast. These results suggest that PDE4, mainly PDE4A, is mostly located within nerve fibers of the pig and human bladder neck, where roflumilast produces a powerful smooth muscle relaxation. In pig, the fact that roflumilast increases endogenous H₂S production and EFS-induced relaxations suggests a modulation of PDE4 on NO- and H₂S-mediated inhibitory neurotransmission.

Novel relaxant effects of RPL554 on guinea pig tracheal smooth muscle contractility

BACKGROUND AND PURPOSE

We investigated the effectiveness of RPL554, a dual PDE3 and 4 enzyme inhibitor, on airway smooth muscle relaxation and compared it with that induced by salbutamol, ipratropium bromide, glycopyrrolate or their combination on bronchomotor tone induced by different spasmogenic agents.

EXPERIMENTAL APPROACH

Guinea pig tracheal preparations were suspended under 1 g tension in Krebs-Henseleit solution maintained at 37°C and aerated with 95% O2 /5% CO2 and incubated in the presence of indomethacin (5 μM). Relaxation induced by cumulative concentrations of muscarinic receptor antagonists (ipratropium bromide or glycopyrrolate), β2 -adrenoceptor agonists (salbutamol or formoterol), PDE3 inhibitors (cilostamide, cilostazol or siguazodan) or a PDE4 inhibitor (roflumilast) was evaluated in comparison with RPL554. Maximal relaxation was calculated (% Emax papaverine) and expressed as mean ± SEM.

KEY RESULTS

Bronchomotor tone induced by the various spasmogens was reduced by the different bronchodilators to varying degrees. RPL554 (10-300 μM) caused near maximum relaxation irrespective of the spasmogen examined, whereas the efficacy of the other relaxant agents varied according to the contractile stimulus used. During the evaluation of potential synergistic interactions between bronchodilators, RPL554 proved superior to salbutamol when either was combined with muscarinic receptor antagonists.

CONCLUSIONS AND IMPLICATIONS

RPL554 produced near maximal relaxation of highly contracted respiratory smooth muscle and provided additional relaxation compared with that produced by other clinically used bronchodilator drugs. This suggests that RPL554 has the potential to produce additional beneficial bronchodilation over and above that of maximal clinical doses of standard bronchodilators in highly constricted airways of patients.

Phosphodiesterase 4 inhibitors modulate beta2-adrenoceptor agonist-induced human airway hyperresponsiveness

Chronic exposure of human isolated bronchi to beta2-adrenergic agonists, especially fenoterol, potentiates smooth muscle contraction in response to endothelin-1 (ET-1), a peptide implicated in chronic inflammatory airway diseases. 5'-Cyclic adenosine monophosphate (cAMP) pathways are involved in fenoterol-induced hyperresponsiveness. The present study investigated whether chronic elevation of intracellular cAMP by other pathways than beta2-adrenoceptor stimulation provokes bronchial hyperresponsiveness. Samples from eighteen human bronchi were sensitized to ET-1 by prolonged incubation with 0.1 microM fenoterol (15 h, 21 degrees C), or, under similar conditions, were incubated with a selective type-3 phosphodiesterase inhibitor (1 microM siguazodan), two selective type-4 phosphodiesterase inhibitors (0.1 microM rolipram and 0.1 microM cilomilast), a combination of fenoterol and rolipram (0.1 microM each) or of fenoterol and cilomilast (0.1 microM each). Rolipram and cilomilast, but not siguazodan, induced hyperresponsiveness (p < 0.01 and p < 0.05 vs. paired controls, respectively) similar to the fenoterol effect. Fenoterol-induced bronchial hyperresponsiveness was significantly enhanced by coincubation with cilomilast (p < 0.05 vs. fenoterol alone) but not with rolipram. Our results suggest that prolonged activation of intracellular cAMP through phosphodiesterase 4 inhibition induces hyperresponsiveness to ET-1 in human isolated bronchi. However, differences in subcellular localization of phosphodiesterase 4 may provoke divergent responsiveness patterns when human bronchi are continuously exposed to selective phosphodiesterase inhibitors with or without beta2-adrenergic agonists.

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.

Bronchodilator and anti-inflammatory activities of glaucine: In vitro studies in human airway smooth muscle and polymorphonuclear leukocytes

1. Selective phosphodiesterase 4 (PDE4) inhibitors are of potential interest in the treatment of asthma. We examined the effects of the alkaloid S-(+)-glaucine, a PDE4 inhibitor, on human isolated bronchus and granulocyte function. 2. Glaucine selectively inhibited PDE4 from human bronchus and polymorphonuclear leukocytes (PMN) in a non-competitive manner (Ki=3.4 microM). Glaucine displaced [3H]-rolipram from its high-affinity binding sites in rat brain cortex membranes (IC50 approximately 100 microM). 3. Glaucine inhibited the spontaneous and histamine-induced tone in human isolated bronchus (pD2 approximately 4.5). Glaucine (10 microM) did not potentiate the isoprenaline-induced relaxation but augmented cyclic AMP accumulation by isoprenaline. The glaucine-induced relaxation was resistant to H-89, a protein kinase A inhibitor. Glaucine depressed the contractile responses to Ca2+ (pD'2 approximately 3.62) and reduced the sustained rise of [Ca2+]i produced by histamine in cultured human airway smooth muscle cells (-log IC50 approximately 4.3). 4. Glaucine augmented cyclic AMP levels in human polymorphonuclear leukocytes challenged with N-formyl-Met-Leu-Phe (FMLP) or isoprenaline, and inhibited FMLP-induced superoxide generation, elastase release, leukotriene B4 production, [Ca2+]i signal and platelet aggregation as well as opsonized zymosan-, phorbol myristate acetate-, and A23187-induced superoxide release. The inhibitory effect of glaucine on superoxide generation by FMLP was reduced by H-89. 5. In conclusion, Ca2+ channel antagonism by glaucine appears mainly responsible for the relaxant effect of glaucine in human isolated bronchus while PDE4 inhibition contributes to the inhibitory effects of glaucine in human granulocytes. The very low PDE4/binding site ratio found for glaucine makes this compound attractive for further structure-activity studies.

Selective phosphodiesterase inhibitors for the treatment of bronchial asthma and chronic obstructive pulmonary disease

Theophylline is commonly used in the treatment of obstructive airway diseases. The identification and functional characterization of different phosphodiesterase (PDE) isoenzymes has led to the development of various isoenzyme-selective inhibitors as potential anti-asthma drugs. Considering the distribution of isoenzymes in target tissues, with high activity of PDE3 and PDE4 in airway smooth muscle and inflammatory cells, selective inhibitors of these isoenzymes may add to the therapy of chronic airflow obstruction. However, initial data from clinical trials with selective PDE3 and PDE4 inhibitors have been somewhat disappointing and have tempered the expectations considerably since these drugs had limited efficacy and their use was clinically limited through side effects. The improved understanding of the molecular biology of PDEs enabled the synthesis of novel drugs with an improved risk/benefit ratio. These 'second generation' selective drugs have produced more promising clinical results not only for the treatment of bronchial asthma but also for the treatment of chronic obstructive pulmonary disease.

Modulation of human airway smooth muscle proliferation by type 3 phosphodiesterase inhibition

Elevation in cell cAMP content can inhibit mitogenic signaling in cultured human airway smooth muscle (HASM) cells. We studied the effects of the type 3-selective phosphodiesterase inhibitor siguazodan, the type 4-selective phosphodiesterase inhibitor rolipram, and the nonselective inhibitor 3-isobutyl-1-methylxanthine (IBMX) on proliferation of cultured HASM cells. At concentrations selective for the type 3 phosphodiesterase isoform, siguazodan inhibited both [3H]thymidine incorporation (IC50 2 microM) and the increase in cell number (10 microM; 64% reduction) induced by platelet-derived growth factor-BB (20 ng/ml). These effects were mimicked by IBMX. At concentrations selective for type 4 phosphodiesterase inhibition, rolipram was without effect. A 20-min exposure to siguazodan and rolipram did not increase whole cell cAMP levels. However, in HASM cells transfected with a cAMP-responsive luciferase reporter (p6CRE/Luc), increases in cAMP-driven luciferase expression were seen with siguazodan (3.9-fold) and IBMX (16.5-fold). These data suggest that inhibition of the type 3 phosphodiesterase isoform present in airway smooth muscle results in inhibition of mitogenic signaling, possibly through an increase in cAMP-driven gene expression.

Modulation of spasmogen-stimulated Ins(1,4,5)P3 generation and functional responses by selective inhibitors of types 3 and 4 phosphodiesterase in airways smooth muscle

1. The effects of isoenzyme-selective inhibitors of phosphodiesterases PDE3 and PDE4 on cyclic AMP concentration, two indices of phosphoinositide hydrolysis, and contractile responses to spasmogens have been investigated in bovine tracheal smooth muscle (BTSM). 2. Neither the PDE3-selective inhibitor ORG 9935, nor the PDE4-selective inhibitor rolipram increased cyclic AMP levels in BTSM. However, rolipram addition in the presence of PDE3 inhibition (ORG 9935; 1 microM) concentration-dependently (-log EC50 (M), 6.55+/-0.15; n = 3) increased cyclic AMP levels to about 70% of the maximal response to the beta-adrenoceptor agonist isoprenaline. 3. Rolipram per se inhibited histamine-stimulated [3H]-inositol (poly)phosphate ([3H]-InsP(X)) accumulation by > 80% (-log EC50 (M), 6.92+/-0.11; n = 3). Although ORG 9935 (1 microM) had little effect on histamine-stimulated [3H]-InsP(X) accumulation alone it greatly facilitated the inhibitory action of rolipram (-log EC50 (M), 8.82+/-0.39; n = 3). The effects of PDE3 and/or PDE4 inhibition on [3H]-InsP(X) accumulation stimulated by muscarinic acetylcholine (mACh) receptor activation were less marked. However, combined PDE3/4 inhibition significantly decreased this response at a submaximal concentration of mACh receptor agonist (carbachol; 1 microM). 4. The greater-than-additive effect of combined PDE3/4 inhibition was also observed at the level of contractile responses to histamine and carbachol. In experiments designed to investigate the effects of PDE3 and/or 4 inhibitors on the carbachol-mediated phasic contraction, additions of rolipram (10 microM) or ORG 9935 (1 microM) were without effect, whereas added together the inhibitors caused a significant (P < 0.01) 40% reduction in the peak phasic contractile response. 5. The effect on contraction correlated with a substantial inhibitory effect of PDE3/4 inhibition on the initial increase in inositol 1,4,5-trisphosphate (InsP3) accumulation stimulated by spasmogen. Thus, in the presence of ORG 9935 (1 microM) rolipram concentration-dependently inhibited carbachol-stimulated InsP3 accumulation by > or = 50% (-log EC50 (M), 6.77+/-0.21; n = 4). 6. Carbachol (100 microM) addition caused a rapid decrease (by 67% at 10 s) in BTSM cyclic AMP level in the presence of PDE3/4 inhibition. However, omission of Ca2+ from the incubation medium prevented the carbachol-evoked decrease in cyclic AMP and this coincided with a greater inhibition (> or = 80%) of the carbachol-stimulated InsP3 response. 7. These data indicate that combined PDE3 and PDE4 inhibition has greater-than-additive effects on second messenger and functional responses to spasmogens in BTSM. Furthermore, the ability of PDE3/4 inhibition significantly to attenuate mACh receptor-mediated contractile responses, may be, at least in part, attributed to an effect exerted at the level of InsP3 generation.

The effect duration of selective phosphodiesterase inhibitors in the guinea pig

The beta-adrenoceptor agonists, isoprenaline, salbutamol and salmeterol, the non-selective phosphodiesterase (PDE) isoenzyme inhibitors, theophylline, trequinsin; the PDE3 isoenzyme inhibitor, milrinone; the PDE3/4 isoenzyme inhibitor, benzafentrine; and the PDE4 isoenzyme inhibitors, denbufylline, nitraquazone, RP 73401, Ro-20-1724, rolipram and tibenelast all induced concentration-dependent reversal of prostaglandin F2alpha-induced contraction of guinea-pig superfused trachea in vitro. The relaxant response of the non-selective PDE isoenzyme inhibitor trequinsin was slow in onset and demonstrated very slow recovery, similar to that observed with the long-acting beta2-adrenoceptor agonist, salmeterol and the PDE4 inhibitor, RP 73401. The relaxant agonists also significantly reversed bombesin-induced bronchospasm in anaesthetised guinea-pigs and there was a highly significant correlation between the ability of drugs to reverse PGF2alpha-induced contraction of guinea-pig isolated trachea in vitro and bombesin-induced bronchoconstriction in vivo. Furthermore, both salmeterol and trequinsin demonstrated long lasting bronchodilator responses consistent with the in vitro data. These results show that PDE isoenzyme inhibitors demonstrate different pharmacodynamic profiles that is not determined by PDE4 inhibitory potency and indicate that other factors may be important in this regard.

Functional and biochemical evidence for diazepam as a cyclic nucleotide phosphodiesterase type 4 inhibitor

1. The responses of the electrically-driven right ventricle strip of the guinea-pig heart to diazepam were recorded in the absence and in the presence of different selective cyclic nucleotide phosphodiesterase (PDE) inhibitors. 2. Diazepam, at concentrations ranging from 1 microM to 100 microM, was devoid of effect on the contractile force in this preparation. 3. Conversely, diazepam (5 microM-100 microM) produced a consistent positive inotropic response in the presence of a concentration (1 microM), that was without effect in the absence of diazepam, of either of the selective PDE 3 inhibitors milrinone or SK&F 94120, but not in the presence of the selective PDE 4 inhibitor rolipram. 4. This effect of diazepam was not gamma-aminobutyric acid (GABA)-dependent, since it was neither mimicked nor potentiated by GABA, and was not affected by either a high concentration (5 microM) of the antagonists of the benzodiazepine/GABA/channel chloride receptor complex, picrotoxin, flumazenil and beta-carboline-3-carboxylic acid methyl ester (betaCCMe), or by the inverse agonists, beta-carboline-3-carboxylic acid N-methylamide (betaCCMa) and methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM, 0.1 microM). Furthermore, a specific antagonist of the peripheral benzodiazepine receptors, PK 11195 (5 microM), did not influence the effect of diazepam. 5. Biochemical studies with isolated PDEs, confirmed that diazepam selectively inhibits type 4 PDE from guinea-pig right ventricle rather than the other PDEs present in that tissue. The compound inhibited this enzyme in a non-competitive manner. Diazepam was also able to inhibit PDE 5, the cyclic GMP specific PDE absent from cardiac muscle, with a potency close to that shown for PDE 4. 6. Diazepam displaced the selective type 4 PDE inhibitor, rolipram from its high affinity binding site in rat brain cortex membranes, and also potentiated the rise in cyclic AMP levels induced by isoprenaline in guinea-pig eosinophils, where only type 4 PDE is present. 7. The PDE inhibitory properties of diazepam were shared, although with lower potency, by other structurally-related benzodiazepines, that also displaced [3H]-rolipram from its high affinity binding site. The order of potency found for these compounds in these assays was not related to their potencies as modulators of the GABA receptor through its benzodiazepine binding site. 8. The pharmacological and biochemical data presented in this study indicate that diazepam behaves as a selective type 4 PDE inhibitor in cardiac tissue and this effect seems neither to be mediated by the benzodiazepine/GABA/channel chloride receptor complex nor by peripheral type benzodiazepine receptors.

Effects of phosphodiesterase inhibitors and salbutamol on microvascular leakage in guinea-pig trachea

The aim of this study was to investigate the effects of selective phosphodiesterase inhibitors and their combination with salbutamol on antigen-induced microvascular leakage in the trachea. In actively sensitized anaesthetized guinea-pigs, the non-selective phosphodiesterase inhibitor theophylline (100 mg/kg p.o.) and the selective phosphodiesterase type 4 inhibitor Ro 20-1724 (30 mg/kg p.o.) inhibited antigen-induced microvascular leakage (-73.8% and -44.1%, respectively) as demonstrated by a reduced extravasation of plasma proteins measured by the use of Evans blue dye. No significant reduction in microvascular leakage was seen with (a) the selective phosphodiesterase type 4 inhibitor rolipram (10 mg/kg p.o.), (b) the selective phosphodiesterase type 3 inhibitors milrinone (30 mg/kg p.o.) and SK and F 94-836 (30 mg/kg p.o.) or (c) the selective phosphodiesterase type 1/5 inhibitor zaprinast (30 mg/kg p.o.). Neither Ro 20-1724 nor rolipram and theophylline inhibited microvascular leakage induced by either substance P or histamine. Pretreatment with aerosolized salbutamol (10 microg/ml) potentiated the inhibitory effects of theophylline (-49.8% at 30 mg/kg p.o.) and Ro 20-1724 (-52.6% at 10 mg/kg p.o.) versus antigen-induced microvascular leakage. Furthermore, a significant inhibitory effect of rolipram (10 mg/kg, p.o.) was obtained following pretreatment with this concentration of aerosolized salbutamol. Even at higher concentrations (0.3-2 mg/ml) salbutamol did not augment the corresponding inhibitory effects of rolipram and Ro 20-1724 versus microvascular leakage induced by either histamine or substance P. Theophylline had no effect versus substance P-induced microvascular leakage, but did inhibit it significantly (P < 0.05) after pretreatment with aerosolized salbutamol (0.3 mg/ml). The potentiation by salbutamol of the inhibitory effects of both non-selective and selective phosphodiesterase type 4 inhibitors versus antigen-induced microvascular leakage probably results from a synergistic reduction in the release of anaphylactic mediators.

Phosphodiesterase IV inhibitors synergistically potentiate relaxation induced by forskolin in guinea-pig trachea

1. Beta-adrenoceptor receptor agonists are the principal bronchodilator agents used in the treatment of bronchial asthma. However, the regular use of beta-adrenoceptor agonists in asthmatic patients is likely to increase asthma severity because of a defective beta-adrenoceptor function. Bronchodilators that bypass this defective function are therefore needed. 2. Our objectives in this study were: (i) to assess the effects of an agent that directly activates adenylate cyclase (forskolin) on guinea-pig tracheal smooth muscle; (ii) to study the interactions between selective cyclic nucleotide phosphodiesterase (PDE) inhibitors and forskolin by measuring isometric tension; and (iii) to compare these results with the interaction between PDE inhibitors and terbutaline, a beta-adrenoceptor agonist. 3. The relaxant effects of forskolin alone, which is now under development as a new bronchodilator for bronchial asthma therapy, were slightly weaker than those of terbutaline on guinea-pig tracheal smooth muscle. 4. Both denbufylline and Ro 20-1724, cyclic nucleotide PDE IV inhibitors, synergistically increased the relaxant effects of forskolin and terbutaline, while other PDE isozyme inhibitors (amrinone, vinpocetine and zaprinast) had only a minor influence. 5. In conclusion, a good synergistic interaction between forskolin and PDE IV inhibitors, especially denbufylline, may provide a means for bypassing beta-adrenoceptors. Thus, the combination of forskolin and PDE inhibitors would become useful in the treatment of bronchial asthma.

Effects of fenspiride on human bronchial cyclic nucleotide phosphodiesterase isoenzymes: functional and biochemical study

We have investigated the role of human bronchial cyclic nucleotide phosphodiesterases in the effects of fenspiride, a drug endowed with bronchodilator and anti-inflammatory properties. Functional studies on human isolated bronchi showed that fenspiride (10(-6)-3 x 10(-3) M, 30 min) induced a shift to the left of the concentration-response curves for isoprenaline and sodium nitroprusside with -logEC50 values of 4.1+/-0.1 (n = 7) and 3.5+/-0.2 (n = 8), respectively. Biochemical studies were carried out on three human bronchi in which separation of cyclic nucleotide phosphodiesterase isoenzymes was performed by ion exchange chromatography followed by determination of phosphodiesterase activity with a radioisotopic method. Phosphodiesterase 4 (cyclic AMP-specific) and phosphodiesterase 5 (cyclic GMP-specific) were the major phosphodiesterase isoforms present in the human bronchial tissue. The presence of phosphodiesterase 1 (Ca2+/calmodulin-stimulated), phosphodiesterase 2 (cyclic GMP-stimulated) and, in two cases, phosphodiesterase 3 (cyclic GMP-inhibited) was also identified. Fenspiride inhibited phosphodiesterase 4 and phosphodiesterase 3 activities with -logIC50 values of 4.16+/-0.09 and 3.44+/-0.12, respectively. Phosphodiesterase 5 activity was also inhibited with a -logIC50 value of approximately 3.8. Fenspiride (< or = 10(-3) M) produced less than 25% inhibition of phosphodiesterase 1 and phosphodiesterase 2 activities. In conclusion, fenspiride is an effective inhibitor of both cyclic AMP and cyclic GMP hydrolytic activity in human bronchial tissues and this action may contribute to its airway effects.

Regulation of cGMP by soluble and particulate guanylyl cyclases in cultured human airway smooth muscle

Although guanosine 3',5'-cyclic monophosphate (cGMP) acts as a relaxant second messenger, the regulation of intracellular cGMP has not been comprehensively studied in human airway smooth muscle. We studied the production of cGMP by cultured human airway smooth muscle cells (HASMC) after stimulation with activators of soluble guanylyl cyclase [sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP)] and particulate guanylyl cyclase [atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), and Escherichia coli heat stable enterotoxin (STa)]. cGMP was measured by enzyme-linked immunosorbent assay. Both SNP (10(-6) to 10(-3) M) and SNAP (10(-6) to 10(-3) M) caused concentration-dependent elevation of cGMP in the presence of the nonselective phosphodiesterase (PDE) inhibitor 3-isobutyl-1-methylxanthine (10(-3) M), with cGMP increasing 6- and 15-fold in response to SNP and SNAP, respectively, at the highest concentration tested (10(-3) M). The increases in cGMP in response to SNP (5 x 10(-5) M) and SNAP (10(-5) M) were inhibited by hemoglobin (Hb; 5 x 10(-5) M), a nitric oxide scavenger, and methylene blue (MB; 5 x 10(-4) M), an inhibitor of guanylyl cyclase. cGMP accumulation after SNAP was abolished by both Hb and MB. The response to SNP was inhibited by 79% with Hb and was abolished with MB. ANP, BNP, and CNP (10(-9) to 10(-5) M) + phosphoramidon (10(-6) M) caused a concentration-dependent elevation in cGMP with an order of potency ANP > BNP > CNP. cGMP formation in the presence of the highest concentration of the most potent natriuretic peptide (10(-5) M ANP) was two- to threefold greater than with the highest concentration of SNAP. The increase in cGMP seen with natriuretic peptides was similar in the presence or absence of phosphoramidon, a neutral endopeptidase (NEP) inhibitor, suggesting that NEP is not playing a role in modulating the effect of natriuretic peptides in HASMC. STa (400 IU/ml) had no effect on cGMP levels. SNAP- and ANP-induced cGMP accumulation was increased by the selective type V PDE inhibitors SKF-96231 and zaprinast, suggesting that type V PDE is responsible for cGMP breakdown in HASMC. These results suggest that cultured HASMC contain both soluble and particulate guanylyl cyclases. The order of potency of the natriuretic peptides ANP > BNP > CNP suggests that type A particulate membrane-bound guanylate cyclase predominates.

Effects of SCA40 on human isolated bronchus and human polymorphonuclear leukocytes: comparison with rolipram, SKF94120 and levcromakalim

1. SCA40 (0.1 nM-0.1 mM) produced concentration-dependent suppression of the spontaneous tone of human isolated bronchus (-log EC50 = 6.85 +/- 0.09; n = 10) and reached a maximal relaxation similar to that of theophylline (3 mM). The potency (-log EC50 values) of SCA40 compared to other relaxants was rolipram (7.44 +/- 0.12; n = 9) > SCA40 > or = levcromakalim (6.49 +/- 0.04; n = 6) > SKF94120 (5.87 +/- 0.10; n = 9). 2. When tested against the activity of the isoenzymes of cyclic nucleotide phosphodiesterase (PDE) isolated from human bronchus, SCA40 proved highly potent against PDE III (-log IC50 = 6.47 +/- 0.16; n = 4). It was markedly less potent against PDE IV (4.82 +/- 0.18; n = 4) and PDE V (4.32 +/- 0.11; n = 4). 3. Human polymorphonuclear leukocytes (PMNs) stimulated with N-formylmethionyl-leucyl-phenylalanine (FMLP) produced a concentration-dependent superoxide anion generation and elastase release. SCA40 (1 nM-10 microM) produced a concentration-related inhibition of FMLP (30 nM approximately EC50)-induced superoxide production (-log IC50 = 5.48 +/- 0.10; n = 6) and elastase release (-log IC50 = 5.50 +/- 0.26; n = 6). Rolipram was an effective inhibitor of superoxide generation and elastase release (-log IC50 values approximately 8) while SKF94120 and levcromakalim were scarcely effective. 4. FMLP (30 nM) and thimerosal (20 microM) induced leukotriene B4 production and elevation of intracellular calcium concentration in human PMNs. The production of leukotriene B4 was inhibited by SCA40 in a concentration-related manner (-log IC50 = 5.94 +/- 0.22; n = 6) but SCA40 was less effective against the elevation of intracellular calcium. Rolipram was an effective inhibitor of leukotriene B4 synthesis (-log IC50 approximately 7) and intracellular calcium elevation (-log IC50 approximately 6) while SKF94120 and levcromakalim were scarcely effective. 5. It is concluded that SCA40 is an effective inhibitor of the inherent tone of human isolated bronchus. The bronchodilatation produced by SCA40 appears mainly related to PDE inhibition since the potency of SCA40 as a relaxant of human isolated bronchus was found to be close to its potency as inhibitor of PDE III activity isolated from human bronchus. In addition, SCA40 exhibited inhibitory effects on human PMN function stimulated by FMLP. These effects may be related to the ability of SCA40 to inhibit PDE IV from human PMNs while the contribution of PDE V inhibition is uncertain. We found no evidence of a role for levcromakalim-sensitive plasmalemmal K+-channels in human PMNs.

Effects of RP 73401, a novel, potent and selective phosphodiesterase type 4 inhibitor, on contractility of human, isolated bronchial muscle

1. The aim of this study was to investigate the smooth muscle relaxant effects of the novel, selective phosphodiesterase (PDE) type 4 inhibitor, RP 73401 in comparison with the classical PDE 4 inhibitor, rolipram, the non-selective PDE inhibitor, theophylline and the beta-adrenoceptor agonist, isoprenaline on the human, isolated bronchus. 2. At resting tone, the rank order of potency (pD2) for the relaxants was RP 73401 > or = rolipram > or = isoprenaline >> theophylline. In terms of maximum relaxation produced (Emax) the PDE 4-selective inhibitors were similar, but the maximal effects (70-75% of theophylline, 3 mM) were lower than that observed with isoprenaline (98% of theophylline, 3 mM) or theophylline itself (100%). 3. On the human isolated bronchus pre-contracted with acetylcholine (ACh, 0.1 or 1.0 mM), the rank order of potency remained the same. The maximal responses to RP 73401 and rolipram were however markedly reduced (Emax 39.9-46.6%) compared with isoprenaline (Emax 79-85%). 4. In tissues pre-contracted with ACh (0.1 mM), RP 73401 and rolipram (10(-9)-10(-7) M) significantly and concentration-dependently increased tissue sensitivity to isoprenaline. RP 73401 and rolipram were similar in potency. Both selective PDE 4 inhibitors also significantly increased the maximal relaxant effects of isoprenaline. These effects were not observed with the PDE 3 inhibitor, siguazodan. 5. In terms of retention by tissues (an index of duration of action), the onset of action of RP 73401 (2.11 +/- 0.53 min) and rolipram (1.70 +/- 0.45 min) was significantly slower than that of isoprenaline (0.33 +/- 0.06 min) or theophylline (1.17 +/- 0.25 min). The retention of RP 73401 (89.0 +/- 21.9 min) on the human isolated bronchial tissues after washing was however dramatically longer than that of rolipram (18.3 +/- 4.5 min), theophylline (3.43 +/- 0.58 min) or isoprenaline (2.81 +/- 0.31 min). 6. These data indicate that RP 73401 is a potent and long acting relaxant of human bronchial muscle in vitro. RP 73401 is more potent than the classical PDE 4-selective inhibitor rolipram and the non-selective PDE inhibitor theophylline and is retained in bronchial tissue for a much longer period of time.

Salbutamol potentiates the relaxant effects of selective phosphodiesterase inhibitors on guinea pig isolated trachea

The ability of low concentrations of salbutamol to potentiate the relaxant effects of the phosphodiesterase (PDE) inhibitors, rolipram, Ro 20-1724 (PDE type IV inhibitor), siguazodan and milrinone (PDE type III inhibitor) was studied on guinea pig isolated trachea. These PDE inhibitors were strong relaxants of guinea pig trachealis under basal tone, but had only a weak activity on tissues precontracted with histamine (10(-5) M). In both cases, PDE type IV inhibitors showed a relaxant effect composed of two phases. The first phase represented 20 and 40% and the second, 90 and 140%, respectively, of relaxation of basal tone and histamine-induced tone. A second characteristic of PDE type IV inhibitors was the very fast and partially reversible relaxation observed at concentrations greater than 3 x 10(-8) M (for histamine-induced tone) at the first addition of inhibitor, followed by a residual relaxant activity. The latter relaxant effect was stable at concentrations of 3 x 10(-8)-10(-5) M and was equivalent to a 20% relaxation (for histamine-induced tone). In the presence of low concentrations (10(-9) and 10(-8) M) of salbutamol, there was a significant concentration-dependent potentiation of the effects of PDE inhibitors on trachea precontracted with histamine. Salbutamol, at a concentration of 10(-9) M, potentiated the effects of PDE inhibitors between 1.4- and 3.6-fold. In the presence of salbutamol 10(-8) M, the potentiation was more marked for siguazodan (37.9-fold), milrinone (11.0-fold) and Ro 20-1724 (14.5-fold) than for rolipram (4.3-fold). These results suggest that low concentrations of salbutamol can potentiate the relaxant effects of both PDE type III and PDE type IV inhibitors. Thus, PDE type IV inhibitors, which have antiinflammatory properties, could also provide adequate bronchodilation when used in combination with lower than usual doses of beta 2-agonists.

Inhibition of bronchospasm and ozone-induced airway hyperresponsiveness in the guinea-pig by CDP840, a novel phosphodiesterase type 4 inhibitor

1. The activity of CDP840, a novel, potent and selective cyclic nucleotide phosphodiesterase type 4 (PDE 4) inhibitor, was evaluated in guinea-pig models (in vitro and in vivo) of bronchospasm, ozone-induced airway hyperresponsiveness (AHR) and non-cholinergic bronchoconstriction. Comparisons were made with (i) other PDE 4 inhibitors: CT1731 (S-enantiomer of CDP840), rolipram, RP73401 and (ii) the clinically used agents salbutamol and theophylline. 2. CDP840 relaxed isolated trachea, under basal tone (EC50 4.5 +/- 1.1 microM) being 17 fold less potent than rolipram (EC50 0.26 +/- 0.13 microM) but attaining the same Emax (83 +/- 6% of the response to 300 microM papaverine). 3. CDP840 relaxed tracheae pre-contracted with carbachol (IC25 39 +/- 9 microM) and histamine (IC25 4 +/- 1 microM) producing monophasic curves. Stereoselectivity was not observed with CT1731 against either carbachol (IC25 33 +/- 11 microM) or histamine (IC25 17 +/- 10 microM). Aminophylline was 1.6 fold (carbachol) and 11 fold (histamine) less potent than CDP840. Rolipram and RP73401 produced tri-phasic relaxation curves but were of similar potency (at the IC25 level) to CDP840 against carbachol (rolipram 18 +/- 5 microM, RP73401 39 +/- 1 microM) whereas against histamine they were approximately 20 fold more potent (rolipram 0.2 +/- 0.1 microM, RP73401 0.2 +/- 0.1 microM). In producing > 30% (carbachol) and > 60% (histamine) relaxation these inhibitors had similar potency and were poor compared to salbutamol. 4. Pre-incubation with CDP840 (10 microM) did not antagonize histamine-induced contraction of isolated trachea; however, it did cause a slight potentiation of the subsequent relaxation to salbutamol (IC50 23 +/- 1 to 15 +/- 2 nM). 5. Pretreatment (1 h) with either CDP840 (1 mg kg-1, i.p. or 3 mg kg-1, i.v.) or rolipram (1 mg kg-1, i.p.) did not bronchodilate or antagonize bronchospasm due to inhaled histamine in anaesthetized, ventilated guinea-pigs. Salbutamol (1 mg kg-1, i.p.) did not bronchodilate but caused a parallel 7 fold rightward shift in the histamine dose-response curve. 6. Stimulation of the vagus nerve in the presence of atropine resulted in a frequency-related bronchoconstriction. CDP840 and rolipram (i.v.) inhibited the response being approximately equipotent (EC50 approximately 10 micrograms kg-1). Neither drug inhibited bronchospasm to inhaled substance P. 7. CDP840 (1-10 micrograms kg-1 i.p.) dose relatedly inhibited ozone-induced bronchoconstriction. CT1731 (1 mg kg-1), rolipram (1 mg kg-1), RP73401 (10 micrograms kg-1) and aminophylline (10 mg kg-1) had no effect. Ozone-induced AHR to inhaled histamine was inhibited by CDP840 in a dose-related manner, 10 micrograms kg-1 abolishing the AHR. This effect was stereoselective as CT1731 was approximately 30 fold less potent than CDP840. Rolipram was approximately 100 fold less potent and RP73401 and aminophylline had no effect. CDP840 was orally active being approximately 10 fold less potent compared to i.p. administration. 8. CDP840 is a poor spasmolytic and anti-spasmogenic agent in response to exogenous mediators; however, it potently inhibits vagally mediated non-cholinergic bronchoconstriction and ozone-induced AHR to histamine. It is possible that regulation of cyclic AMP by PDE 4 contributes to neuronal sensitivity in the airways. Furthermore, CDP840 may suppress AHR without being an overt bronchodilator. Such a profile of activity may have therapeutic benefit in airways diseases such as asthma.

Involvement of cyclic AMP in the effects of phosphodiesterase IV inhibitors on arachidonate release from mononuclear cells

The effects of selective phosphodiesterase inhibitors, cyclic AMP (cAMP) elevating agents and stable analogues of cyclic nucleotides, on the release of arachidonate induced by N-formyl-Met-Leu-Phe (fMLP) were investigated on human peripheral blood mononuclear cells. The selective phosphodiesterase IV inhibitors, rolipram and Ro 20-1724, and the non-selective phosphodiesterase inhibitor, theophylline, elicited a concentration-dependent inhibition of arachidonate release (EC50 = 1.3 x 10(-6) M, 3.2 x 10(-6) M and 3.7 x 10(-4) M respectively). The selective phosphodiesterase III inhibitor, milrinone (10(-5) M), only caused a slight effect while the phosphodiesterase V inhibitor, zaprinast (10(-5) M), the beta 2-adrenoceptor agonists, salbutamol and fenoterol (10(-5) M), failed to inhibit arachidonate release. Forskolin (10(-5) M) and N6,2'-O- dibutyryladenosine 3':5'-cyclic monophosphate (db-cAMP), 10(-3) M) elicited a moderate inhibition. Forskolin increased the effects of rolipram and Ro 20-1724 (EC50 = 4.5 10(-7) M and 4 x 10(-7) M respectively). Incubation of the cells with rolipram (10(-8) to 10(-5) M), Ro 20-1724 (10(-8) to 10(-5) M, forskolin (10(-5) M) or salbutamol (10(-5) M) alone, induced a moderate increase or no increase at all in intracellular cAMP. However, in the presence of forskolin, rolipram (10(-8) to 10(-6) M) and Ro 20-1724 (10(-8) to 10(-6) M) induced significant and concentration-dependent increase in intracellular levels of cAMP. These results suggest that the potent inhibition of arachidonate release from mononuclear cells by selective phosphodiesterase IV inhibitors may be due to increases in discrete pools of intracellular cAMP.

Airway smooth muscle relaxation

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Isoenzyme-selective cyclic nucleotide phosphodiesterase inhibitors: effects on airways smooth muscle

Cyclic nucleotide phosphodiesterase (PDE) isoenzymes (I-V) have been demonstrated in airways smooth muscle of several species including man. Theophylline is a non-selective inhibitor of PDE and is a potent relaxant of airways smooth muscle but its use is limited by its toxicity. Consequently, research into new, isoenzyme-selective PDE inhibitors is seen as important. The potential airways smooth muscle relaxant effects of these drugs is discussed in this review. Cyclic AMP PDE (types III and IV) inhibition produces greater relaxation than cyclic GMP PDE (types I and V) inhibition. No PDE II-selective inhibitors have been described. Airways smooth muscle relaxation in vitro, is greater with PDE IV than PDE III inhibitors in guinea-pig and bovine airways whereas PDE III is more important in porcine airways. Both cyclic AMP PDEs are important in human airways. PDE III or IV inhibition can produce additive effects and can augment isoprenaline actions. PDE V inhibition augments sodium nitroprusside-induced effects. There are no reported interactions between cyclic AMP and cyclic GMP PDE inhibitors. In vivo, cyclic AMP PDE inhibitors are more potent bronchodilators than cyclic GMP PDE inhibitors. PDE IV inhibitors have less cardiovascular side-effects. Topical administration may further increase efficacy and selectivity. Clinically PDE III inhibition improves lung function but also affects cardiovascular parameters. Inhaled PDE III/IV inhibitors produce bronchodilation without marked side effects. Potent, selective PDE IV inhibitors are currently being evaluated. In conclusion, isoenzyme-selective PDE inhibitors, especially PDE IV, may be useful airways smooth muscle relaxants in the treatment of lung disorders such as asthma.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-inflammatory and bronchodilator properties of RP 73401, a novel and selective phosphodiesterase type IV inhibitor

1. We have investigated the effects of RP 73401, a novel, potent and highly selective cyclic nucleotide phosphodiesterase (PDE) type IV inhibitor, in guinea-pig and rat models of bronchoconstriction and allergic inflammation. In some models, the effects of RP 73401 have been compared with those of the standard PDE type IV inhibitor, rolipram. 2. RP 73401 (0.4-400 micrograms kg-1, intratracheally (i.t.) on lactose) inhibited antigen-induced bronchospasm in previously sensitized conscious guinea-pigs (ID50: 7 +/- 1 micrograms kg-1) and in anaesthetized rats (ID50: 100 +/- 25 micrograms kg-1). Rolipram inhibited the antigen-induced bronchospasm in guinea-pigs with an ID50 of 5 +/- 1 micrograms kg-1. In guinea-pig bronchoalveolar lavage (BAL) fluid, total inflammatory cell and eosinophil numbers were reduced by RP 73401 (ID50s: 3.9 +/- 0.8 micrograms kg-1 and 3.2 +/- 0.7 micrograms kg-1, respectively). In the rat, inflammatory cell numbers are less affected. Only the highest dose of RP 73401 (400 micrograms kg-1) significantly inhibited eosinophil influx (41 +/- 16% inhibition). 3. RP 73401 (0.02-100 micrograms kg-1, i.v.) inhibited PAF-induced bronchial hyperreactivity to bombesin in the anaesthetized guinea-pig (ID50: 0.09 +/- 0.03 micrograms kg-1) and inhibited (0.4-40 micrograms kg-1, i.t.) histamine-induced airway microvascular leakage in the anaesthetized guinea-pig by approximately 60% at all doses. 4. RP 73401 relaxed guinea-pig isolated trachea under basal tone (EC50: 9 nM) and when precontracted with histamine (IC50: 2 nM), methacholine (IC50: 29 nM) or leukotriene D4 (LTD4, IC50: 4 nM). 5. RP 73401 (0.4-100 microg kg-1, i.t.) inhibited bronchospasm induced by histamine (ID.%: 34 +/- 6 microg kg-1), methacholine (ID50: 66 +/- 12 pg kg-1) and LTD4 (ID50: <4 microg kg-1) in the anaesthetized guinea pig.Against these same bronchoconstrictors, rolipram (i.t.) had ID5o values of 44 +/- 4, 72 +/- 18 and<4 pg kg- respectively. RP 73401 (4 and 40 pg kg-, i.t.) increased the magnitude and duration of bronchodilatation produced by salbutamol in the anaesthetized guinea-pig. At doses producing significant bronchodilatation, RP 73401 was without effect on heart rate or blood pressure in the anaesthetized guinea-pig. RP 73401 (0.01 -0.25 mg kg-1, i.v.) did not affect heart rate and produced only a small fall in blood pressure in the anaesthetized rat.6. These data demonstrate that RP 73401 and rolipram inhibit antigen- and mediator-induced bronchospasmin guinea-pigs with the same potency. Furthermore, RP 73401 administered directly into the airways, protects against allergic airway inflammation. These results indicate the importance of PDE IV in regulating smooth muscle and inflammatory cell activity. At doses suppressing the inflammatory response in the lung, RP 73401 had little effect in the cardiovascular system. RP 73401 may have a role as a bronchodilator and, more importantly, as a prophylactic anti-inflammatory agent in the treatment of asthma.

Beta-adrenoceptors, cAMP and airway smooth muscle relaxation: challenges to the dogma

beta-Adrenoceptor agonists are assumed to induce airway smooth muscle relaxation through the cAMP-protein kinase A (PKA) phosphorylation cascade system. This traditional second messenger paradigm of beta-adrenoceptor agonist action is deeply engrained, but in this article Theodore Torphy reviews recent observations that force a re-examination of the dogma. For example, cAMP can activate protein kinase G as well as PKA, and this unanticipated dual action may contribute to the relaxant activity of cAMP. Other studies suggest that beta-adrenoceptor agonists can induce relaxation by a cAMP-independent mechanism involving a direct coupling of the beta-adrenoceptor to Ca(2+)-dependent K+ channels. Consequently, it is possible that multiple cAMP-dependent pathways act in concert with cAMP-independent pathways to mediate bronchodilation in response to beta-adrenoceptor agonists.

Cyclic nucleotide phosphodiesterases in the human lung

Although theophylline has been used in the treatment of lung diseases, particularly bronchial asthma, since the nineteenth century, the mechanisms underlying its effectiveness remained poorly understood until quite recently. The identification of cyclic nucleotide phosphodiesterase (PDE)--the enzyme responsible for breaking down cyclic AMP and cyclic GMP within cells--as a target for methylxanthines such as theophylline led to a research effort that has resulted in the characterization of multiple forms of the PDE enzyme and the development of selective inhibitors for some of these forms. Using these drugs, it has been possible to identify the PDE "isoenzymes" in a number of tissues and cells and to demonstrate the functional effects of the inhibition of different PDEs upon these tissues. Studies on the smooth muscle of human airways and pulmonary arteries have identified isoenzyme-selective PDE inhibitors that are effective broncho- and vasorelaxants in vitro, and it is hoped that these agents may be effective in relieving airway obstruction and pulmonary hypertension in patients. In addition, selective inhibitors of certain PDE isoenzymes suppress the proinflammatory functions of a range of immune cells, including the lung mast cell and the alveolar macrophage. Selective inhibitors of PDE isoenzymes are beginning to undergo clinical trials for the treatment of asthma. The advancing understanding of the PDE distribution in the lung and the ever more precise characterization of distinct enzyme proteins should allow the development of site-selective drugs for the treatment of lung diseases, while minimizing the systemic side effects associated with nonselective PDE inhibitors such as theophylline.