Cysteinyl leukotrienes in asthma: old mediators up to new tricks

The cysteinyl leukotrienes have long been suspected to play a role in the pathogenesis of asthma. This speculation was based largely on their release in human lung following antigen challenge as well as their potent bronchoconstrictor activity. However, there is increasing evidence that the cysteinyl leukotrienes also produce several pro-inflammatory effects and alter the activity of neuronal pathways in the airways. Douglas Hay, Theodore Torphy and Bradley Undem review these recent data and discuss the therapeutic possibilities of cysteinyl leukotriene receptor antagonists and 5-lipoxygenase inhibitors.

Characterization of two human cAMP-specific phosphodiesterase subtypes expressed in baculovirus-infected insect cells

Recombinant baculoviruses were constructed to express cDNAs encoding two distinct subtypes of human cAMP-specific phosphodiesterase (hPDE4A and hPDE4B). Infection of Spodoptera frugiperda insect cells with the appropriate recombinant baculoviruses resulted in high level production of biologically-active protein as measured by enzymatic activity and immunoblotting using subtype-specific anti-hPDE4 antisera. Both recombinant proteins showed catalytic activity with a low Km (approximately 3 microM) for cAMP (with no cGMP hydrolyzing activity) and were inhibited by R-rolipram with apparent Kis of 0.38 and 0.25 microM, respectively. The recombinant enzymes also contained saturable, stereoselective and high-affinity rolipram-binding sites (Kd approximately 2 nM). Thus, insect cell-derived hPDE4s possess kinetic properties analogous to native enzymes as well as to recombinant enzymes produced in yeast.

Inhibitors of phosphodiesterase IV (PDE IV) increase acid secretion in rabbit isolated gastric glands: correlation between function and interaction with a high-affinity rolipram binding site

In this report, we describe the ability of selective inhibitors of phosphodiesterase (PDE) isozymes to increase aminopyrine accumulation in rabbit isolated gastric glands. Aminopyrine accumulation in the presence of histamine was increased by the nonselective PDE inhibitor isobutylmethylxanthine (EC50 = 4.8 microM) and by two selective PDE IV inhibitors, rolipram and Ro 20-1724 (EC50 = 0.013 and 0.07 microM, respectively) but not by selective PDE III inhibitors (siguazodan and SK&F 94120) or by a selective PDE V inhibitor (zaprinast). These results suggest that PDE IV is an important regulator of acid secretion in response to histamine. One of the more fascinating properties of PDE IV is the expression of a high-affinity binding site for [3H]-rolipram in addition to cAMP catalytic activity. Although agents that inhibit PDE IV catalytic activity also appear to bind to the high-affinity rolipram-binding site, the rank-order potencies of compounds for these two effects are poorly correlated. Also, certain pharmacological actions of PDE IV inhibitors appear to be related to an interaction with this binding site. In this study, we observed that the ability of PDE IV inhibitors to enhance acid secretion was not associated with their ability to inhibit PDE IV catalytic activity but did show a strong correlation with their ability to compete for [3H]-rolipram binding. Furthermore, we were able to detect [3H]-rolipram binding sites in gastric glands that had characteristics similar to those of the [3H]-rolipram binding sites in rat brain microsomes and human recombinant PDE IV.

The ability of phosphodiesterase IV inhibitors to suppress superoxide production in guinea pig eosinophils is correlated with inhibition of phosphodiesterase IV catalytic activity

Elevation of cyclic AMP (cAMP) content inhibits eosinophil function. Because phosphodiesterase IV (PDE IV) appears to be the major PDE isozyme present in eosinophils, inhibitors of this isozyme should suppress eosinophil activation. Previous studies on PDE IV have revealed that this enzyme possesses both cAMP catalytic activity that is inhibitable by rolipram, a prototypical PDE IV inhibitor, and a high-affinity binding site for rolipram. The function of this high-affinity rolipram binding site relative to the inhibitory action of compounds is not clear because the rank order potency of PDE IV inhibitors for competing with [3H]-rolipram binding is distinct from that for inhibiting cAMP hydrolysis. Consequently, the present experiments were carried out to fulfill the following objectives: 1) to determine whether PDE IV inhibitors suppress eosinophil function and, if so, 2) to establish a correlation between this functional activity and inhibition of PDE IV catalytic activity or interaction with the high-affinity rolipram binding site. Various PDE inhibitors produced approximately 60% maximal inhibition of formylmethionine-leucine-phenylalanine-induced superoxide anion production, so that IC30 concentrations were used as a basis to compare the potency of various PDE inhibitors. Selective PDE IV inhibitors were the most potent compounds tested. PDE inhibitors selective for other isozymes were devoid of activity or considerably less potent.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitors of CoA-independent transacylase block the movement of arachidonate into 1-ether-linked phospholipids of human neutrophils

The enzyme CoA-independent transacylase (CoA-IT) has been proposed to mediate the movement of arachidonate between phospholipid subclasses and influence the formation of arachidonic acid metabolites and platelet-activating factor. To substantiate the critical role of CoA-IT, we have developed two structurally diverse inhibitors of CoA-IT activity, SK&F 98625 [diethyl 7-(3,4,5-triphenyl-2-oxo-2,3-dihydro-imidazole-1-yl)heptane phosphonate] and SK&F 45905 [2-[2-(3-4-chloro-3-(trifluoromethyl)phenyl)-ureido]-4- (trifluoromethyl)phenoxy]-4,5-dichlorobenzenesulfonic acid]. These compounds were tested for their capacity to block microsomal CoA-IT activity using two assay systems, the transacylation of 1-alkyl-2-lyso-sn-glycero-3-phosphocholine (GPC) and the transfer of [14C]arachidonate from 1-acyl-2-[14C]arachidonoyl-GPC to lyso-PE. Both SK&F 98625 and SK&F 45905 inhibited CoA-IT activity (IC50s 6-19 microM) in these two assays. In contrast, SK&F 98625 or SK&F 45905 had little or no effect on other lipid-modifying activities, including CoA-dependent acyltransferase or acetyltransferase. Kinetic analysis revealed that both SK&F 98625 and SK&F 45905 interact directly with the enzyme and prevented the acylation of lysophospholipids in a competitive manner. In intact human neutrophils, both SK&F 98625 and SK&F 45905 completely blocked the movement of [3H]arachidonate from 1-acyl-linked phospholipids into 1-alkyl-2-arachidonoyl-GPC and 1-alk-1'-enyl-2-arachidonoyl-GPE. In contrast, these compounds did not inhibit the incorporation of free arachidonic acid into cellular lipids indicating that they did not alter CoA-dependent acyl transferase activities in the intact cell.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphodiesterase IV inhibitors as therapy for eosinophil-induced lung injury in asthma

Asthma is a complex, multifactorial disease that is underpinned by airway inflammation. A variety of cytotoxic substances are released into the airway from infiltrating inflammatory cells, especially the eosinophil. These cytotoxic substances, including reactive oxygen metabolites, produce damage to the airway epithelium, a histologic feature of chronic asthma. Damage to the airway epithelium, in turn, is thought to be a major factor responsible for the development of airway hyperreactivity, a hallmark of asthma. One notable molecular target for novel antiasthmatic drugs is the cyclic AMP-specific phosphodiesterase (PDE) or PDE IV. This isozyme is the predominant form of cyclic nucleotide PDE activity in inflammatory cells. Thus, in view of the putative role of cyclic AMP as an inhibitory second messenger in these cells, PDE IV inhibitors have been shown to suppress inflammatory cell activity. The purpose of the present experiments was to examine the effect of the PDE IV inhibitor, R-rolipram, on three key functions of the guinea pig eosinophil: a) superoxide anion (O2-) production, b) adhesion to human umbilical vein endothelial cells (HUVECs), and c) infiltration into the airway. R-rolipram-elevated eosinophil cyclic AMP content (EC50 = 1.7 microM) and inhibited fMLP-induced O2- production in a concentration-dependent manner (IC50 = 0.3 microM). In contrast, neither siguazodan, a PDE III inhibitor, nor zaprinast, a PDE V inhibitor, had an appreciable effect. R-rolipram (30 microM) also reduced by 25 to 40% the adhesion of eosinophils to HUVECs stimulated with phorbol myristate acetate or tumor necrosis factor-alpha, particularly under conditions in which both cell types were simultaneously exposed to the PDE IV inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

A Candida albicans cyclic nucleotide phosphodiesterase: cloning and expression in Saccharomyces cerevisiae and biochemical characterization of the recombinant enzyme

We have cloned a Candida albicans gene, which encodes a cyclic nucleotide phosphodiesterase (PDEase), by complementation in a Saccharomyces cerevisiae PDEase-deficient mutant. The deduced amino acid sequence is similar to that of the low-affinity PDEase of S. cerevisiae (PDE1) and the cyclic nucleotide PDEase (PD) of Dictyostelium discoideum. Biochemical analysis of recombinant protein produced in S. cerevisiae indicated that the enzyme behaves as a PDE1 homologue: it hydrolyses both cAMP (Km = 0.49 mM) and cGMP (Km = 0.25 mM), does not require divalent cations for maximal activity and is only moderately inhibited by millimolar concentrations of standard PDEase inhibitors. Based on these data, we designate the C. albicans we have cloned, PDE1. Low-stringency genomic Southern blots showed cross-hybridization between C. albicans PDE1 and DNA from Candida stellatoidea, but not with DNA from S. cerevisiae or several closely related Candida species.

Comparison of phosphodiesterase III, IV and dual III/IV inhibitors on bronchospasm and pulmonary eosinophil influx in guinea pigs

Selective inhibition of phosphodiesterase (PDE) isozymes has been shown to inhibit inflammatory cell function and relax airway smooth muscle and, thus, may be useful in the therapy of asthma. In guinea pigs sensitized to ovalbumin (OA), the effects of three PDE inhibitors were compared: siguazodan (PDE III selective, IC50 = 0.7 microM), rolipram (PDE IV selective, IC50 = 0.8 microM) and zardaverine (dual PDE III/IV, IC50S = 2.5 microM and 1.1 microM, respectively) against histamine-, leukotriene (LT) D4- and OA-induced bronchospasm in vitro and in vivo. Rolipram or zardaverine (0.1-10 microM), but not siguazodan, inhibited OA-induced contraction of the isolated trachea in a concentration-dependent manner. Rolipram or siguazodan alone (10 microM) were ineffective against histamine- or LTD4-induced contractions. Zardaverine alone (10 microM) or the combination of rolipram and siguazodan (10 microM each) markedly antagonized the contractions elicited by both spasmogens. In anesthesized, ventilated guinea pigs, the i.v. ID50S against OA-induced bronchospasm were: rolipram = 0.2 mg/kg, siguazodan > 10 mg/kg and zardaverine = 2.4 mg/kg. When administered at doses up to 7.5 mg/kg, i.v., rolipram or siguazodan were markedly less effective (i.e., < or = 50% inhibition) than zardaverine (ID50S = 2.4 and 1.7 mg/kg, respectively) at blocking exogenous histamine- or LTD4-induced bronchospasm. However, when administered in combination with siguazodan (5.4 mg/kg, i.v.), rolipram (0.4-5.4 mg/kg) abolished histamine- and LTD4-induced bronchoconstriction. In conscious guinea pigs, zardaverine (5 mg/kg, intragastrically (i.g.) or the combination of rolipram and siguazodan (5 mg/kg each) were substantially more effective than rolipram or siguazodan alone at inhibiting aerosol histamine- or LTD4-induced bronchospasm. In the same animals, rolipram or zardaverine (5 mg/kg, i.g.) but not siguazodan (5 mg/kg, i.g.) markedly inhibited aerosol OA-induced bronchoconstriction. The OA-induced pulmonary eosinophil infiltration in these animals was attenuated by all treatments with zardaverine producing the greatest degree of inhibition. These results indicate that 1) PDE IV inhibitors but not PDE III inhibitors are effective at blocking antigen-induced bronchospasm, 2) compounds that selectively inhibit either PDE III or PDE IV are poor inhibitors of bronchoconstriction elicited by exogenously administered spasmogens, and 3) the combined inhibition of both PDE III and PDE IV isozymes acts in an additive or synergistic manner to inhibit bronchospasm in the guinea pig.

Differential antagonism of airway contractile responses to prostaglandin (PG)D2 and 9 alpha, 11 beta-PGF2 by atropine, SK&F 88046 and SQ 29,548 in the guinea pig

PGD2, the predominant prostanoid released from activated human lung mast cells, is metabolized to 9 alpha, 11 beta-PGF2 by an 11-ketoreductase. Both prostanoids contract mammalian airway smooth muscle. In the present study, aerosol administration of PGD2 or 9 alpha, 11 beta-PGF2 (five puffs of 10-50 micrograms/ml) to anesthetized, spontaneously breathing guinea pigs produced significant increases in airway resistance and decreases in dynamic lung compliance. The changes in airway resistance and dynamic lung compliance induced by 50 micrograms/ml were reduced approximately 60% and 25%, respectively, by pretreatment with atropine (1 mg/kg, i.v., -10 min). Pretreatment with the TxA2 receptor antagonist SK&F 88046 (N,N'-bis[7-(3-chlorobenzene aminosulfonyl)-1,2,3,4- tetrahydroisoquinolyl]disulfonylimide) (5 mg/kg, i.v., -10 min), nearly abolished the changes in airway resistance and dynamic lung compliance that were elicited by both agonists. Pretreatment with a TxA2 synthase inhibitor, CGS 13080 (10 mg/kg, i.v., -10 min), had no effect on PGD2- or 9 alpha, 11 beta-PGF2-induced bronchoconstriction, suggesting that these prostanoids did not provoke the release of TxA2. In vitro, PGD2, 9 alpha, 11 beta-PGF2 and a TxA2 mimic, U-44069, produced concentration-dependent contractions of the guinea pig isolated trachea with pD2s of 6.4, 6.0 and 7.2, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The crystal structure, absolute configuration, and phosphodiesterase inhibitory activity of (+)-1-(4-bromobenzyl)-4-(3-(cyclopentyloxy)- 4-methoxyphenyl)-pyrrolidin-2-one

Chiral HPLC resolution of the phosphodiesterase IV (PDE IV) inhibitor rolipram (1) provided (-)-1, and this enantiomer was converted into its 1-(4-bromobenzyl) derivative, (+)-2. X-ray structural analysis of (+)-2 established the absolute configuration as R, which provides the first direct evidence for a previously assumed assignment of configuration. The crystal structure of (+)-2 and the PDE inhibitory activity of both enantiomers of 2 are discussed in the context of a previously proposed topological model.

Association between leukotriene B4-induced phospholipase D activation and degranulation of human neutrophils

We have explored the role of phospholipase D (PLD) activation in leukotriene B4 (LTB4)-induced Ca2+ mobilization and degranulation of human neutrophils. Stimulation of [3H]alkyl-acyl-phosphatidylcholine-labeled neutrophils with LTB4 resulted in a rapid accumulation of [3H]alkyl-phosphatidic acid (PA) as well as a somewhat slower accumulation of [3H]alkyl-diglyceride (DG). In the presence of ethanol, PLD catalyzed a transphosphatidylation reaction in which LTB4 increased [3H]alkyl-phosphatidylethanol formation and simultaneously decreased LTB4-induced PA and DG accumulation. This pattern of lipid metabolism is consistent with the conclusion that LTB4 stimulates PLD activity in human neutrophils. Additional studies in which the extracellular and intracellular concentrations of Ca2+ were varied indicated that maximal LTB4-induced PLD activation was dependent upon Ca2+ and potentiated by inhibitors of protein kinase C. The time-course and concentration-response curves for LTB4-induced PLD activation were different from those for LTB4-induced Ca2+ mobilization, as measured by fura-2 fluorescence. On the other hand, the concentration-response curve for LTB4-induced PLD activation was similar to that for LTB4-induced degranulation. Preincubation of the cells with ethanol inhibited LTB4-induced PA and DG accumulation, as well as degranulation, suggesting that one or both of these metabolites were important for this response. In contrast, ethanol had no effect on LTB4-induced Ca2+ mobilization. Propranolol, an inhibitor of phosphatidate phosphohydrolase, abolished DG accumulation in response to LTB4 but had no effect on degranulation, suggesting that PA is more important than DG as a mediator of degranulation. Taken collectively, these data indicate that LTB4-induced activation of PLD in human neutrophils is mediated by a Ca(2+)-dependent mechanism, but not by protein kinase C. In addition, PLD activation in these cells may induce degranulation, but not Ca2+ mobilization.

Influence of isoproterenol and phosphodiesterase inhibitors on platelet-activating factor biosynthesis in the human neutrophil

Increasing cellular levels of cAMP inhibit eicosanoid production in the human neutrophil; however, little is known about the effects of cAMP on platelet-activating factor (PAF) biosynthesis in this cell. In the current study, the beta-adrenergic receptor agonist isoproterenol, alone or in combination with the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX), was used to increase cAMP in neutrophils. The incorporation of [3H]acetate into PAF and the synthesis of leukotrienes in response to ionophore A23187 were significantly inhibited by 10 microM isoproterenol. The inhibitory effect on PAF was potentiated by the addition of 10 microM IBMX. The effects of IBMX were mimicked by rolipram, an inhibitor of the cAMP-specific phosphodiesterase IV. Mass spectrometric analysis of the PAF molecular species in stimulated neutrophils indicated that the combination of isoproterenol and IBMX inhibited (&gt; 50%) ionophore- and fMLP-induced production of PAF. To better understand the mechanism involved in the inhibition of PAF formation, the major biosynthetic steps were examined in the presence and absence of a maximally effective concentration of isoproterenol and IBMX. Isoproterenol alone or in the presence of IBMX had no measurable effect on the ionomycin-induced increase in cytosolic calcium concentration, as assessed by fura-2 fluorescence. Treating intact neutrophils with a combination of isoproterenol and IBMX did not inhibit acetyltransferase activity when assayed in a subsequent broken cell preparation. Finally, increasing cellular cAMP with these drugs did not influence the ability of the neutrophil to catabolize PAF. Phospholipase A2-like activity was assayed in the whole cell by measuring the mobilization of phospholipase A2 products, PAF, lyso PAF, and arachidonic acid, from cellular phosphoglycerides. Treatment of neutrophils with isoproterenol and IBMX significantly reduced the production of lyso PAF and PAF from 1-alkyl-2-arachidonoyl sn-glycero-3-phosphocholine. Similarly, increasing cellular levels of cAMP inhibited the cell's ability to mobilize arachidonic acid upon cell activation. These data suggest that increasing cellular levels of cAMP leads to the inhibition of PAF and leukotriene biosynthesis, at least in part, by regulation of phospholipase A2 activity.

Inhibition of antigen-induced bronchoconstriction and eosinophil infiltration in the guinea pig by the cyclic AMP-specific phosphodiesterase inhibitor, rolipram

Selective inhibition of the low Km cyclic AMP-specific phosphodiesterase has been shown to inhibit inflammatory cell function and relax airway smooth muscle. These studies were conducted to characterize the bronchodilator and anti-inflammatory activity of rolipram, an archetypical cyclic AMP-specific phosphodiesterase inhibitor, in in vitro and in vivo guinea pig airway models. In isolated tracheal rings from ovalbumin (OA)-sensitive guinea pigs, both R- and S-enantiomers of rolipram (1 microM) significantly antagonized OA-induced contractions. In contrast, neither enantiomer at concentrations up to 1 microM significantly inhibited histamine- or LTD4-induced contractions. In superfusion and mediator release experiments, both enantiomers of rolipram significantly reduced antigen-induced prostaglandin D2 release, but had minimal effect on histamine release. In anesthetized, ventilated OA-sensitive guinea pigs, racemic rolipram or enantiomers reduced OA-induced bronchoconstriction with ID50 values of approximately 0.25 mg/kg i.v. Histamine- and leukotriene D4-induced bronchoconstriction were not affected by doses of rolipram which abolished the response to OA. Higher doses (3-10 mg/kg) reduced histamine-, but not the leukotriene D4-induced bronchoconstriction. In conscious OA-sensitive guinea pigs, intragastric pretreatment with rolipram dose-dependently reduced both the OA-induced decreases in specific conductance as well as the corresponding pulmonary eosinophil influx as assessed by both bronchoalveolar lavage and histological evaluation. Therefore, rolipram produces significant inhibition of antigen-induced bronchoconstrictor and inflammatory responses, thus providing strong evidence that this pharmacological approach may be of significant therapeutic value in allergic asthma.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of isoproterenol and phosphodiesterase inhibitors on platelet-activating factor biosynthesis in the human neutrophil

Increasing cellular levels of cAMP inhibit eicosanoid production in the human neutrophil; however, little is known about the effects of cAMP on platelet-activating factor (PAF) biosynthesis in this cell. In the current study, the beta-adrenergic receptor agonist isoproterenol, alone or in combination with the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX), was used to increase cAMP in neutrophils. The incorporation of [3H]acetate into PAF and the synthesis of leukotrienes in response to ionophore A23187 were significantly inhibited by 10 microM isoproterenol. The inhibitory effect on PAF was potentiated by the addition of 10 microM IBMX. The effects of IBMX were mimicked by rolipram, an inhibitor of the cAMP-specific phosphodiesterase IV. Mass spectrometric analysis of the PAF molecular species in stimulated neutrophils indicated that the combination of isoproterenol and IBMX inhibited (> 50%) ionophore- and fMLP-induced production of PAF. To better understand the mechanism involved in the inhibition of PAF formation, the major biosynthetic steps were examined in the presence and absence of a maximally effective concentration of isoproterenol and IBMX. Isoproterenol alone or in the presence of IBMX had no measurable effect on the ionomycin-induced increase in cytosolic calcium concentration, as assessed by fura-2 fluorescence. Treating intact neutrophils with a combination of isoproterenol and IBMX did not inhibit acetyltransferase activity when assayed in a subsequent broken cell preparation. Finally, increasing cellular cAMP with these drugs did not influence the ability of the neutrophil to catabolize PAF. Phospholipase A2-like activity was assayed in the whole cell by measuring the mobilization of phospholipase A2 products, PAF, lyso PAF, and arachidonic acid, from cellular phosphoglycerides. Treatment of neutrophils with isoproterenol and IBMX significantly reduced the production of lyso PAF and PAF from 1-alkyl-2-arachidonoyl sn-glycero-3-phosphocholine. Similarly, increasing cellular levels of cAMP inhibited the cell's ability to mobilize arachidonic acid upon cell activation. These data suggest that increasing cellular levels of cAMP leads to the inhibition of PAF and leukotriene biosynthesis, at least in part, by regulation of phospholipase A2 activity.

Identification, characterization and functional role of phosphodiesterase isozymes in human airway smooth muscle

In the present study phosphodiesterase (PDE) isozymes in human airway smooth muscle were isolated, identified and characterized, and the functional roles of these isozymes in intact bronchi were evaluated by using isozyme-selective PDE inhibitors. PDE isozymes in human trachealis were isolated by using a combination of DEAE-Sepharose and calmodulin-Sepharose affinity chromatography, and were identified based upon their kinetic characteristics as well as their sensitivity to allosteric modulators and isozyme-selective PDE inhibitors. By using this approach, six distinct isozymes were identified: two calmodulin-stimulated PDEs (PDE I alpha and PDE I beta), cyclic GMP (cGMP)-stimulated PDE (PDE II), cGMP-inhibited PDE (PDE III), cyclic AMP (cAMP)-specific PDE (PDE IV) and cGMP-specific PDE (PDE V). PDEs III and IV were the major cAMP-hydrolyzing enzymes present, whereas PDEs I alpha, I beta and V accounted for most of the cGMP-hydrolytic activity. In carbachol-precontracted small (< 0.5-2 mm diameter) or large (4-15 mm diameter) human bronchus, zaprinast (10 nM-30 microM), the selective PDE V inhibitor, was without marked relaxant activity (< 13%), whereas rolipram (30 microM), the selective PDE IV inhibitor, produced approximately 25% relaxation in both preparations. Siguazodan was a significantly more effective relaxant than zaprinast or rolipram in large bronchus, producing a maximum relaxation of 77 +/- 15% at a concentration of 30 microM, whereas in small bronchus 30 microM siguazodan elicited 20 +/- 6% relaxation. Similar results were obtained in large bronchi contracted with leukotriene (LT) D4 (0.1 microM). The ability of isozyme-selective PDE inhibitors to potentiate agonist-induced relaxation was studied in LTD4-contracted large bronchi. Siguazodan (10 microM), but not rolipram (10 microM) or zaprinast (10 microM), potentiated the relaxant response in LTD4-contracted large bronchus to isoproterenol, a beta adrenoceptor agonist thought to induce relaxation via a cAMP-mediated mechanism. In contrast, zaprinast (10 microM), but not siguazodan (10 microM), potentiated relaxation induced by sodium nitroprusside, a nitrovasodilator that relaxes airway smooth muscle via a cGMP-mediated mechanism. The most striking observation from functional studies was that the combination of rolipram and siguazodan produced a much greater relaxation of small or large human bronchi than either agent alone, indicating an interaction between PDE III and PDE IV inhibitors that was at least additive and, in some cases, synergistic.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of selective phosphodiesterase type IV inhibitor, rolipram, on fluid and cellular phases of inflammatory response

The antiinflammatory activity of rolipram, a selective inhibitor of the cyclic AMP-specific phosphodiesterase (PDE IV), was studied. Rolipram did not inhibit 5-lipoxygenase activity but did inhibit human monocyte production of leukotriene B4 (LTB4, IC50 3.5 microM). Likewise, murine mast cell release of leukotriene C4 and histamine was inhibited. In vivo, rolipram inhibited arachidonic acid-induced inflammation in the mouse, while the low Km-cyclic-GMP PDE inhibitor, zaprinast, did not inhibit. Rolipram had a modest effect on LTB4 production in the mouse, but markedly reduced LTB4-induced PMN infiltration. Beta-adrenergic receptor activation of adenylate cyclase was important for rolipram antiinflammatory activity since beta blockade abrogated arachidonic acid-induced inflammation. Thus, the antiinflammatory profile of rolipram is novel and may result from inhibition of PMN function and perhaps vasoactive amine release and leukotriene biosynthesis. These actions may be dependent upon endogenous beta-adrenergic activity and are likely mediated through inhibition of PDE IV.

A low-Km, rolipram-sensitive, cAMP-specific phosphodiesterase from human brain. Cloning and expression of cDNA, biochemical characterization of recombinant protein, and tissue distribution of mRNA

We have isolated cDNA clones from human frontal cortex cDNA libraries that encode a unique subtype of the low-Km, cAMP-specific phosphodiesterases (PDEs IV). The 564-amino acid sequence of the protein (human brain PDE IV (hPDE IVB)) shows significant homology to a PDE IV subtype expressed in human monocytes (hPDE IVA), particularly within the approximately 300-amino acid PDE IV catalytic domain. The degree of protein sequence identity is much greater between hPDE IVB and a homolog derived from rat brain (92% over 562 amino acids) than between hPDE IVB and hPDE IVA (76% over 538 amino acids), suggesting a greater subtype-specific versus species-specific conservation of protein sequence. Analysis of the distribution of hPDE IVB mRNA expression revealed a restricted pattern, with an approximately 4-kilobase mRNA detected in brain, heart, lung, and skeletal muscle and not in placenta, liver, kidney, or pancreas. An additional approximately 5-kilobase hPDE IVB-related mRNA species was detected in brain tissue. Recombinant hPDE IVB displayed all of the expected kinetic characteristics for a PDE IV, including sensitivity to the isozyme-selective inhibitor rolipram (Ki = 0.085 microM). Scatchard analysis of (R)-[3H]rolipram binding data suggested the presence of two noninteracting high affinity rolipram-binding sites (Kd = 0.4 and 6 nM) or a negatively cooperative interaction among multiple binding sites.

Biochemical characteristics and cellular regulation of phosphodiesterase IV

Considerable interest has been generated in the potential utility of phosphodiesterase (PDE) IV inhibitors as a novel class of anti-asthmatic agents. Because a detailed understanding of the molecular and biochemical characteristics of any molecular target of interest provides a key ingredient for rational drug design, we cloned a cDNA encoding a PDE IV (hPDE IV) from a human monocyte library and expressed, purified and characterized the recombinant gene product. Purified hPDE IV has kinetic characteristics consistent with native PDE IV isolated from tissue sources. In addition, it is inhibited by rolipram (Ki = 60 nM) and other archetypical PDE IV-selective inhibitors. Purified hPDE IV also contains a high affinity binding site for rolipram (Kd = 2 nM), although the precise relationship between this site and the cAMP catalytic site is not clear. In other studies in which the regulation of PDE IV expression was examined in U937 cells, a human monocytic cell line, prolonged treatment with salbutamol was shown to induce an increase in the activity of PDE IV. This up-regulation of PDE IV activity appears to be mediated by cAMP and occurs at the transcriptional or pretranscriptional level. As a consequence of PDE IV up-regulation, the sensitivity of U937 cells to the inhibitory effects of adenylyl cyclase activators on cell function is greatly diminished. If such regulation of PDE IV occurs in inflammatory cells in vivo, it could have implications for the therapeutic use of beta-adrenoceptor agonists. Specifically, induction of PDE IV activity in asthmatics being treated with beta-adrenoceptor agonists could result in a heterologous desensitization of inflammatory cells to endogenous anti-inflammatory agents (e.g., epinephrine, prostaglandin E2).

Stimulation of beta adrenoceptors in a human monocyte cell line (U937) up-regulates cyclic AMP-specific phosphodiesterase activity

Experiments were conducted using undifferentiated U937 cells, a human monocytic cell line, to establish an in vitro model to examine the hormonal regulation of the cyclic AMP (cAMP)-specific phosphodiesterase (PDE IV). Standard chromatographic techniques, coupled with the use of inhibitors and activators that are selective for various phosphodiesterase (PDE) isozymes, were used to establish the PDE isozyme profile in supernatant fractions of U937 cells. When PDE activity was assessed using 1 microM [3H]cAMP as a substrate, 70 to 90% of the total U937 cell supernatant activity in the major peak eluting from anion-exchange columns was inhibited by 30 microM rolipram, a selective inhibitor of PDE IV. The remaining activity was nearly abolished by 10 microM siguazodan or 10 microM cyclic GMP (cGMP,) selective inhibitors of the cGMP-inhibited PDE. Kinetic analyses of the enzyme activity contained within this major peak of PDE activity revealed a cAMP Km = 3 microM and a rolipram Ki = 0.5 microM, values characteristic of PDE IV. Additional studies revealed the presence of a small amount of Ca++/calmodulin-stimulated PDE, but no cGMP-stimulated PDE or cGMP-specific PDE activity. In an effort to induce PDE activity in intact U937 cells by producing a sustained increase in cAMP content, cells were treated for 4 hr with salbutamol (1 microM), rolipram (30 microM) or a combination of both agents. The combination of salbutamol and rolipram produced a 2- to 3-fold increase in PDE activity in U937 cells; when used alone, rolipram was without effect whereas salbutamol induced an increase that was approximately one-half of that observed with the combination. Isozyme isolation and characterization revealed that the overall elevation of cellular PDE activity could be accounted for by a 2- to 3-fold increase in the Vmax of PDE IV with no change in its Km. The induction of PDE IV by salbutamol was: 1) concentration- and time-dependent; 2) detectable only after prolonged (2-4 hr) agonist exposure; 3) preceded by an increase in cAMP content and an activation of cAMP-dependent protein kinase; 4) mimicked by 8-bromo-cAMP and prostaglandin E2; 5) reversible within 3 hr of salbutamol removal; and 6) abolished by cycloheximide or actinomycin D. Collectively, these results indicate that the major PDE isozyme in the soluble fraction of U937 cells is PDE IV and that the activity of this enzyme is increased markedly in cells after prolonged exposure to agents that increase cAMP content.

SK&F 104353, a selective leukotriene receptor antagonist, inhibits leukotriene D4- and antigen-induced bronchoconstriction in cynomolgus monkeys

The ability of SK&F 104353 to prevent and reverse leukotriene (LT) D4- and antigen (Ag)-induced bronchoconstriction was examined in anesthetized, spontaneously breathing cynomolgus monkeys. Aerosol administration of LTD4 (10 micrograms/ml; 20 breaths) produced a sustained increase in pulmonary resistance and decrease in dynamic lung compliance. Aerosolized SK&F 104353 (150 breaths, 0.3 or 4.4 mg/ml) administered 15 min prior to LTD4 challenge antagonized these changes in a dose-dependent manner. When given intravenously 6 min after LTD4, SK&F 104353 (5 mg/kg) rapidly and completely reversed the ongoing bronchoconstriction. In mepyramine-pretreated (2 mg/kg i.v.) monkeys sensitive to aerosolized Ascaris suum Ag, intravenously administered SK&F 104353 (5 mg/kg) substantially reversed, but did not abolish, Ag-induced bronchoconstriction when administered 12 min after the Ag challenge. In contrast, SK&F 104353 (5 mg/kg i.v.) did not reverse Ag-induced bronchoconstriction in animals that had not been pretreated with mepyramine. Similar results were obtained when SK&F 104353 (20 mg/kg i.v.) was administered (as a pretreatment) 5 min prior to Ag under these conditions. Thus, SK&F 104353 reduced Ag-induced bronchoconstriction in mepyramine-pretreated monkeys, but had little effect in the absence of mepyramine. The data suggest that LTs, in addition to histamine, play a role in allergic bronchoconstriction in cynomolgus monkeys.

Agonist-related differences in the relationship between cAMP content and protein kinase activity in canine trachealis

We investigated the relationships between relaxation, cyclic AMP (cAMP) accumulation and cAMP-dependent protein kinase (cAMP-PK) activity in canine tracheal smooth muscle. In time course and concentration-response studies, forskolin and isoproterenol elicited relaxation of isolated trachealis strips that was accompanied by an increase in cAMP content and an activation of cAMP-PK. Although these results were consistent with the proposal that cAMP is a second messenger mediating relaxation of airway smooth muscle, close inspection of the data revealed a discrepancy in the relationship between cAMP accumulation and relaxation. To induce equivalent degrees of tracheal relaxation, forskolin generated greater increments in cAMP accumulation than did isoproterenol. On the other hand, the activation state of cAMP-PK correlated reasonably well with relaxation regardless of which agonist was used. Further analysis of the data revealed that the apparent disparity between cAMP accumulation and relaxation could largely be explained at the level of the relationship between cAMP content and cAMP-PK activity: compared to isoproterenol, forskolin induced greater increases in cAMP accumulation to achieve the same activation state of cAMP-PK. These observations lend support to the proposal that in canine trachealis, various components of the cAMP/cAMP-PK cascade exist in distinct subcellular compartments such that not all of the cAMP generated in response to forskolin has access to its target enzyme, cAMP-PK.

Preliminary identification and role of phosphodiesterase isozymes in human basophils

We attempted to identify and establish the role of cyclic nucleotide phosphodiesterase (PDE) isozymes in human basophils by using standard biochemical techniques as well as describing the effects of isozyme-selective and nonselective inhibitors of PDE. The nonselective PDE inhibitors, theophylline and 3-isobutyl-1-methylxanthine, inhibited anti-IgE-induced release of histamine and leukotriene C4 (LTC4) from basophils. This inhibition was accompanied by elevations in cAMP levels. Rolipram, an inhibitor of the low Km cAMP-specific PDE (PDE IV), inhibited the release of both histamine and LTC4 from activated basophils and increased cAMP levels in these cells. In contrast, mediator release from basophils was not inhibited by either siguazodan or SK&F 95654, inhibitors of the cGMP-inhibited PDE (PDE III) or zaprinast, an inhibitor of the cGMP-specific PDE (PDE V). SK&F 95654 failed to elevate basophil cAMP in these experiments whereas zaprinast induced significant increases in cAMP content. The inhibitory effect of rolipram on mediator release was potentiated by siguazodan or SK&F 95654, but not by zaprinast. SK&F 95654 also enhanced the ability of rolipram to increase cAMP content. Forskolin, a direct activator of adenylate cyclase, inhibited IgE-dependent release of mediators from basophils and increased cAMP levels in these cells. These effects were enhanced by rolipram, but not by SK&F 95654 or zaprinast. The cell permeant analog of cAMP, dibutyryl cAMP, inhibited mediator release from these cells, a property not shared by either dibutyryl-cGMP or sodium nitroprusside, an activator of soluble guanylate cyclase. The presence of both PDE III and PDE IV was confirmed by partially purifying and characterizing PDE activity in broken cell preparations. Overall, these data lend support to the hypothesis that cAMP inhibits mediator release from basophils and suggest that the major PDE isozyme responsible for regulating cyclic AMP content in these cells is PDE IV, with a minor contribution from PDE III. However, the finding that zaprinast caused increases in cAMP without inhibiting mediator release indicates that cAMP accumulation is not invariably linked to an inhibition of basophil activation.

Preliminary identification and role of phosphodiesterase isozymes in human basophils

We attempted to identify and establish the role of cyclic nucleotide phosphodiesterase (PDE) isozymes in human basophils by using standard biochemical techniques as well as describing the effects of isozyme-selective and nonselective inhibitors of PDE. The nonselective PDE inhibitors, theophylline and 3-isobutyl-1-methylxanthine, inhibited anti-IgE-induced release of histamine and leukotriene C4 (LTC4) from basophils. This inhibition was accompanied by elevations in cAMP levels. Rolipram, an inhibitor of the low Km cAMP-specific PDE (PDE IV), inhibited the release of both histamine and LTC4 from activated basophils and increased cAMP levels in these cells. In contrast, mediator release from basophils was not inhibited by either siguazodan or SK&F 95654, inhibitors of the cGMP-inhibited PDE (PDE III) or zaprinast, an inhibitor of the cGMP-specific PDE (PDE V). SK&F 95654 failed to elevate basophil cAMP in these experiments whereas zaprinast induced significant increases in cAMP content. The inhibitory effect of rolipram on mediator release was potentiated by siguazodan or SK&F 95654, but not by zaprinast. SK&F 95654 also enhanced the ability of rolipram to increase cAMP content. Forskolin, a direct activator of adenylate cyclase, inhibited IgE-dependent release of mediators from basophils and increased cAMP levels in these cells. These effects were enhanced by rolipram, but not by SK&F 95654 or zaprinast. The cell permeant analog of cAMP, dibutyryl cAMP, inhibited mediator release from these cells, a property not shared by either dibutyryl-cGMP or sodium nitroprusside, an activator of soluble guanylate cyclase. The presence of both PDE III and PDE IV was confirmed by partially purifying and characterizing PDE activity in broken cell preparations. Overall, these data lend support to the hypothesis that cAMP inhibits mediator release from basophils and suggest that the major PDE isozyme responsible for regulating cyclic AMP content in these cells is PDE IV, with a minor contribution from PDE III. However, the finding that zaprinast caused increases in cAMP without inhibiting mediator release indicates that cAMP accumulation is not invariably linked to an inhibition of basophil activation.

Coexpression of human cAMP-specific phosphodiesterase activity and high affinity rolipram binding in yeast

Studies by various investigators have demonstrated that the low Km, cAMP-specific phosphodiesterase (PDE IV) is selectively inhibited by a group of compounds typified by rolipram and Ro 20-1724. In addition to inhibiting the catalytic activity of PDE IV, rolipram binds to a high affinity binding site present in brain homogenates. Although it has been assumed that the high affinity rolipram-binding site is PDE IV, no direct evidence has been produced to support this assumption. The present studies were undertaken to determine whether the rolipram-binding site is coexpressed with PDE IV catalytic activity in Saccharomyces cerevisiae genetically engineered to express human recombinant monocytic PDE IV (hPDE IV). Expressing hPDE IV cDNA in yeast resulted in a 20-fold increase in PDE activity that was evident within 1 h of induction and reached a maximum by 3-6 h. The recombinant protein represented hPDE IV as judged by its immunoreactivity, molecular mass (approximately 88 kDa), kinetic characteristics (cAMP Km = 3.1 microM; cGMP Km greater than 100 microM), sensitivity to rolipram (Ki = 0.06 microM), and insensitivity to siguazodan (PDE III inhibitor) and zaprinast (PDE V inhibitor). Saturable, high affinity [3H] (R)-rolipram-binding sites (Kd = 1.0 nM) were coexpressed with PDE activity, indicating that both binding activity and catalytic activity are properties of the same protein. A limited number of compounds were tested for their ability to inhibit hPDE IV catalytic activity and compete for [3H](R)-rolipram binding. Analysis of the data revealed little correlation (r2 = 0.35) in the structure-activity relationships for hPDE IV inhibition versus competition for [3H] (R)-rolipram binding. In fact, certain compounds (e.g. (R)-rolipram Ro 20-1724) possessed a 10-100-fold selectivity for inhibition of [3H] (R)-rolipram binding over hPDE IV inhibition, whereas others (e.g. dipyridamole, trequinsin) possessed a 10-fold selectivity for PDE inhibition. Thus, although the results of these studies demonstrate that hPDE IV activity and high affinity [3H](R)-rolipram binding are properties of the same protein, they do not provide clear cut evidence linking the binding site with the PDE inhibitory activity of rolipram and related compounds.