Cyclic Nucleotide Phosphodiesterase Isoenzymes Research Articles

Enhancement of amrinone-induced positive inotropy in rabbit papillary muscles with depressed contractile function: effects on cyclic nucleotide levels and phosphodiesterase isoenzymes.

The inotropic activity of amrinone and its effects on cyclic nucleotide levels in rabbit papillary muscles with normal and depressed contractile function have been compared. The effects of amrinone on the cyclic (c) AMP hydrolytic activity of cyclic nucleotide phosphodiesterase (PDE) isoenzymes were also examined. Amrinone (2.4 x 10(-4) - 1.2 x 10(-3) M) produced a relatively weak (maximal increase 11%) positive inotropic effect in papillary muscles stimulated at the near optimal stimulation frequency of 1 Hz. In contrast, large positive inotropic responses (maximal 138-200%) were obtained with amrinone in papillary muscles in which contractile force had been depressed by: (a) lowering stimulation frequency to 0.4 Hz, (b) reducing extracellular Ca2+ concentration from 2.5 x 10(-3) M to 6.3 x 10(-4) M, (c) prior addition of sodium pentobarbitone (6.5 x 10(-4) M). The EC50 values for amrinone under conditions (a), (b), and (c) were 3.0 x 10(-3), 2.6 x 10(-3), and 2.8 x 10(-3) M, respectively. Force-frequency curves in rabbit papillary muscles were compared at normal (2.5 x 10(-3) M) and low (6.3 x 10(-4) M) extracellular Ca2+ concentration. Contractions at low frequencies of stimulation (less than 0.4 Hz) were less sensitive to removal of extracellular Ca2+ than higher stimulation rates indicating that in the former situation, recycling of intracellular Ca2+ is more important for maintaining contractile force.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical distribution of cyclic nucleotide phosphodiesterase (PDE) isoenzymes in the human vagina: A potential forensic value?

Objectives Phosphodiesterase (PDE) isoenzymes are key proteins involved in the maintenance of the normal function of various tissues of the human body including those of the male and female urogenital tract. More recently, PDEs and their main substrates, cyclic GMP and cyclic AMP, have also been assumed to play a crucial role in the control of the human vagina. In order to elucidate the potential significance of phosphodiesterases as marker proteins in female genital organs, it was the aim of the present study to evaluate by means of immunohistochemistry the distribution of cGMP- and cAMP-PDE isoenzymes in specimens of the human vagina. Methods Conventional immunohistochemical techniques (double antibody technique, laser fluorescence microscopy) were applied to sections of the human vaginal wall in order to evaluate the presence of the PDE isoenzymes 1, 2, 3, 4, 5 and 10. Results Immunoreactivities (IR) specific for PDE1 (cAMP/cGMP-PDE, Ca 2+/Calmodulin-dependent), PDE2 (cAMP-PDE, cGMP-dependent) and PDE5 (cGMP-PDE) were exclusively registered in the smooth musculature of vaginal arterial vessels, whereas no signals were detected in non-vascular tissue. IR indicating the expression of the cAMP-degrading PDE4 was mainly observed in the vaginal epithelium. Vaginal epithelial cells also presented immunosignals specific for PDE3 (cAMP-PDE, inhibited by cGMP) and PDE10 (dual substrate PDE), nevertheless, these stainings were less abundant than those related to the PDE4. IR for PDE10 was also registered in inflammatory cells located in the subepithelial region of the vaginal wall. Conclusion Our study revealed the presence of IR specific for PDE1, PDE2, PDE4, PDE5 and PDE10 in sections of the human vagina and demonstrated that these enzymes are not evenly distributed in the tissue. Especially, the prominent expression of the cyclic AMP-PDE4A in the vaginal epithelium may give hint to a potential significance of this isoenzyme as a forensic marker protein. The findings give a rationale to investigate further as to whether the immunohistochemical detection of PDE4 may represent a new forensic tool in order to identify human vaginal epithelial cells.

In vitro effects of PDE5 inhibitors sildenafil, vardenafil and tadalafil on isolated human ureteral smooth muscle: a basic research approach

Cyclic nucleotide phosphodiesterase (PDE) isoenzymes are key proteins regulating intracellular cyclic nucleotide turnover and thus smooth muscle tension. Several in vitro studies have indicated that the cyclic GMP and cyclic AMP-mediated signaling may play a role in the control of human ureteral muscle. The aim of the present study was to evaluate the functional effects of PDE5 inhibitors sildenafil (Sil), vardenafil (Var) and tadalafil (Tad), as well as nitric oxide (NO)-donating agent sodium nitroprusside (SNP) and non-selective muscarinic antagonist butylscopolamine (BSC) on the tension induced by KCl and the turnover of cyclic nucleotides in isolated human ureteral smooth muscle. In vitro relaxant responses of human ureteral smooth muscle to the PDE5 inhibitors mentioned above were investigated using the organ bath technique. Cyclic nucleotides cAMP and cGMP were determined by means of specific radioimmunoassay following incubation of the tissue with Sil, Var, Tad and SNP. The tension induced by KCl of the ureteral tissue was dose dependently reversed by the drugs with the following rank order of efficacy: SNP > Var >or= Sil > Tad > BSC. R(max) values ranged from 25 +/- 9% (SNP) to 5 +/- 3% (BSC). Relaxant responses were paralleled by threefold to fourfold increase in tissue levels of cGMP. Our results indicate that PDE5 inhibitors can reverse the tension of isolated human ureteral smooth muscle via cGMP-mediated pathways. Nevertheless, further studies are indicated in order to evaluate as to whether there might be a use for PDE5 inhibitors in the treatment of ureteral stone disease.

Role of cyclic nucleotide phosphodiesterase isoenzymes in contractile responses of denuded rat aorta related to various Ca2+ sources.

We have examined the cyclic nucleotide phosphodiesterase isoforms (PDE) involved in the contractile response of rat aorta to different agonists and different experimental procedures for use in functional studies. The inhibitory effect of AAL 05 on the different PDEs isolated from bovine aortic smooth muscle was examined. Compound AAL 05 appeared to be a selective PDE3 inhibitor. We analyzed the ability of the non-selective inhibitor IBMX (3-isobutyl-1-methylxanthine) and the isoenzyme selective inhibitors nimodipine (type 1), AAL 05 (6-(N-methyl-N-cyclohexyl butyl carboxamide) quinolin-2-one) and SK&F 94120 (5-(4-acetamidophenyl) pyrazin-2(1H)-one; type3), rolipram (type4) and zaprinast (type5) to affect the contractile responses of denuded rat aortic rings to KCl (80 mM) and noradrenaline (NA, 1 microM) in the presence or absence of extracellular Ca2+. Rolipram (10-100 microM) and zaprinast (1-100 microM) failed to relax the aortic strips, but IBMX (0.1-30 microM), nimodipine (1 fM10 microM), AAL 05 (0.01-100 microM) and SK&F 94120 (0.1-100 microM) produced a concentration-dependent relaxation or inhibition of contractile responses to the different agonists, but the pIC50 obtained for each inhibitor was different depending on the experimental procedure. Except for nimodipine (a Ca2+ channel blocker), all the PDE inhibitors showed the following rank of potency: pIC50 on NA-induced contractions in Ca2+-free medium > pIC50 on NA-induced contractions in Ca2+-containing solution > pIC50 on depolarizing solution-induced contraction. This ranking apparently depends on the differences in the Ca2+ sources. We obtained a good correlation between the pKi of PDE3 inhibitors in biochemical studies and the pIC50 on NA-induced contraction in Ca2+-free medium. In conclusion, PDE1 and PDE3 isoenzymes play an important role as modulators of rat aortic smooth muscle contractility regardless of the experimental procedure used. Since intracellular mechanisms are more dependent on PDE activity, experimental procedures performed in absence of extracellular calcium are the most suitable for analyzing the modulatory role of PDE inhibitors.

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

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

New imidazo[1,2- a]pyrazine derivatives with bronchodilatory and cyclic nucleotide phosphodiesterase inhibitory activities

New imidazo[1,2- a]pyrazine derivatives have been synthesized either by direct cyclization from pyrazines or by electrophilic substitutions. The presence of electron donating groups on position 8 greatly enhances the reactivity of the heterocycle towards such reactions on position 3 of the heterocycle. The activities of these derivatives in trachealis muscle relaxation and in inhibiting cyclic nucleotide phosphodiesterase (PDE) isoenzyme types III and IV have been assessed. All compounds demonstrated significantly higher relaxant potency than theophylline. All the derivatives were moderately potent in inhibiting the type IV isoenzyme of PDE but only those with a cyano group on position 2 were potent in inhibiting the type III isoenzyme.

Identification and function of cyclic nucleotide phosphodiesterase isoenzymes in airway epithelial cells.

Epithelial cells actively participate in inflammatory airway disease by liberating mediators such as arachidonate metabolites and cytokines. Inhibition of phosphodiesterases (PDEs) may be a useful anti-inflammatory approach. The PDE isoenzyme pattern and the effects of PDE inhibition on mediator generation were analyzed in primary cultures of human and porcine airway epithelial cells (AEC) and in the bronchial epithelial cell line BEAS-2B. PDE4 and PDE5 were detected in lysates of all cell types studied. In primary cultures of human AEC, the PDE4 variants PDE4A5, PDE4C1, PDE4D2, and PDE4D3 were identified by polymerase chain reaction analysis. Evidence of the recently described PDE7 was obtained by rolipram- insensitive cyclic adenosine monophosphate (cAMP) degradation, and its presence was verified by the demonstration of PDE7 messenger RNA. Primary cultures of human airway epithelium also expressed PDE1. Enhanced epithelial cAMP levels, induced by forskolin and PDE4 inhibition, increased formation of prostaglandin E2 (PGE2), but not of interleukin (IL)-8 or 15-hydroxyeicosatetraenoic acid (15-HETE) in airway epithelial cells. Increased cyclic guanosine monophosphate levels in these cells provoked by sodium nitroprusside and the PDE5 inhibitor zaprinast reduced the PGE2 synthesis, whereas 15-HETE and IL-8 formation were unchanged. The data suggest that PDE isoenzymes are important in airway inflammation and that PDE inhibitors exert anti-inflammatory effects by acting on AEC.

Cyclic Nucleotide Phosphodiesterase (PDE) Isoenzymes in the Human Detrusor Smooth Muscle: I. Identification and Characterization

Phosphodiesterases (PDEs) are key enzymes involved in the regulation of intracellular cyclic nucleotide metabolism. The aim of the present study was to identify and to characterize the PDE isoenzymes present in the human detrusor smooth muscle. Human detrusor PDE isoenzymes were separated by Q-Sepharose anion exchange and calmodulin-agarose affinity chromatography and characterized upon their kinetic characteristics and their sensitivity to allosteric modulators and inhibitors. All five presently known PDE isoenzyme families were identified: one high-affinity, low-Km calcium/calmodulin-stimulated PDE I with a slight preference for cGMP over cAMP, one cGMP-stimulated PDE II, one cGMP-inhibited PDE III, one cAMP-specific PDE IV and one cGMP-specific PDE IV. All five known PDE isoenzyme families exist in human detrusor smooth musculature. The kinetic characteristics, together with functional in vitro studies, suggest that the PDE I may be of importance in the intracellular regulation of the human detrusor smooth muscle tone.

Cyclic Nucleotide Phosphodiesterase (PDE) Isoenzymes in the Human Detrusor Smooth Muscle: II. Effect of Various PDE Inhibitors on Smooth Muscle Tone and Cyclic Nucleotide Levels In Vitro

Phosphodiesterases (PDEs) regulate intracel- lular cyclic nucleotide metabolism and, thus, contrac- tion and relaxation of smooth musculature. The aim of the present study was to evaluate the functional effects of isoenzyme-selective inhibitors and their effects on cyclic nucleotide levels in the human detrusor smooth muscle. In addition, the functional relevance of the cAMP versus the cGMP pathways in the regulation of the detrusor smooth muscle tone was assessed. Relax- ant responses to various PDE inhibitors, forskotin and sodium nitroprusside (SNP) were investigated in vitro using a standard organ bath setup. Cyclic nucleotide levels were measured after incubation with the same substances using cAMP and cGMP radioimmuno- assays (RIAs). Significant relaxant responses were only induced by non-selective PDE inhibition, the PDE I inhibitor vinpocetine and the adenylate cyclase ac- tivator forskolin. Relaxant responses to these substan- ces were paralleled by increases in cyclic nucleotide levels. Our data suggest that the cAMP pathway and calcium/calmodulin-stimulated PDE (PDE I) may be of functional importance in the regulation of the hu- man detrusor smooth muscle tone in vitro.

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 −6–3×10 −3 M, 30 min) induced a shift to the left of the concentration–response curves for isoprenaline and sodium nitroprusside with −log EC 50 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 (Ca 2+/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 −log IC 50 values of 4.16±0.09 and 3.44±0.12, respectively. Phosphodiesterase 5 activity was also inhibited with a −log IC 50 value of ∼3.8. Fenspiride (≤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.

Role of Phosphodiesterase 4 Isoenzyme in Alkaline Phosphatase Activation by Calcitonin in Porcine Kidney LLC-PK1 Cells

To confirm the intracellular signal transduction in regulation of alkaline phosphatase (ALP) activity by calcitonin in kidney tubular cells, effects of several inhibitors of cyclic nucleotide phosphodiesterase (PDE) isoenzymes and cyclic AMP-dependent protein kinase (PKA) on the action of salmon calcitonin in porcine kidney tubular epithelial cells LLC-PK1 were examined. A confluent culture of LLC-PK1 cells was treated with calcitonin and inhibitors in Dulbecco’s modified Eagle’s medium supplemented with 0.1% bovine serum albumin, and intracellular cyclic AMP content and ALP activity were measured after incubation for 30 min and 48 hr, respectively. Calcitonin and PDE 4 inhibitors increased cyclic AMP level and ALP activity in the cells, and PDE 4 inhibitors synergistically potentiated the effects of calcitonin. Calcitonin induced ALP activation by treatment for the first 1 hr, as well as continuous treatment for 48 hr, while it never increased the enzyme activity just after 1-hr exposure. Rolipram, an inhibitor of PDE 4 isoenzyme, induced ALP activation by itself and in combination with calcitonin by only a long term treatment (48 hr). The activation of ALP by calcitonin and rolipram each alone and in combination was completely abolished by a PKA inhibitor, H-89. These results confirm that calcitonin induces ALP activation through the cyclic AMP-PKA pathway and that PDE 4 isoenzyme is closely associated with the calcitonin-receptor system and plays a major role in hydrolysis of cyclic AMP produced in the kidney tubular cells.

Effects of SCA40 on bovine trachealis muscle and on cyclic nucleotide phosphodiesterases

While UK-93,928 (1-[[3-(6,9-dihydro-6-oxo-9-propyl-1H-purin-2-yl)-4-ethoxyphenyl] sulfonyl]-4-methylpiperazine; 5 nM–5 μM) was devoid of relaxant activity, benzafentrine, isoprenaline, levcromakalim and SCA40 (6-bromo-8-methylaminoimidazo[1,2- a]pyrazine-2-carbonitrile) each relaxed histamine (460 μM)-precontracted bovine isolated trachealis. Each of these relaxants was antagonised by a K +-rich (80 mM) medium. Except in the case of levcromakalim, nifedipine (1 μM) offset this antagonism. Charybdotoxin (100 nM) antagonised isoprenaline in a nifedipine-sensitive manner but did not antagonise SCA40 or benzafentrine. Iberiotoxin (100 nM) did not antagonise SCA40. Acting on tissue precontracted with carbachol, SCA40 potentiated isoprenaline but did not potentiate sodium nitroprusside. While levcromakalim (1 and 10 μM) induced hyperpolarisation, SCA40 (1 and 10 μM) induced little change in the membrane potential of bovine trachealis. In trachealis preloaded with 86Rb + , levcromakalim (1 and 10 μM) promoted efflux of the radiotracer while SCA40 (1 and 10 μM) had no effect. Tested as an inhibitor of isoenzymes of cyclic nucleotide phosphodiesterase, SCA40 was most potent against the type III, less potent against the type IV and least potent against the type I isoenzyme. It is concluded that neither inhibition of phosphodiesterase type V nor the promotion of BK Ca channel opening explains the tracheal smooth muscle relaxant activity of SCA40. This compound relaxes bovine tracheal smooth muscle mainly by inhibiting phosphodiesterase isoenzyme types III and IV.

Characterization of the Isoenzymes of cyclic nucleotide phosphodiesterase in human platelets and the effects of E4021

In extracts of human platelets, three isoenzymes of cyclic nucleotide phosphodiesterase (PDE), namely, PDE2, PDE3, and PDE5, were identified; activities of PDE1 and PDE4 were not detected. In human platelets, the cGMP-hydrolytic activity was about six times higher than the cAMP-hydrolytic activity, and PDE5 and PDE3 are the major phosphodiesterase isoenzymes that hydrolyze cGMP and CAMP, respectively. PDE5 exhibited organ-specific expression in humans, and platelets were among the tissues richest in PDE5. A novel inhibitor of PDE5, sodium 1-[6-chloro-4-(3,4-methylenedioxybenzyl)aminoquinazolin-2-yl] piperidine-4-carboxylate sesquihydrate (E4021), was a potent and highly selective inhibitor of human platelet PDE5. However, E4021 (up to 10 μM) did not inhibit 9,11-epithio-11,12-methano-thromboxane A 2-induced platelet aggregation, in vitro. E4021 plus SIN-1 (3-morpholino-sydnonimine), at concentrations that had little effect individually, inhibited aggregation. These results suggest the unique distribution of phosphodiesterase isoenzymes in human platelets and the PDE5 inhibitors might be useful as a new class of antiplatelet drugs.

Cyclic nucleotide phosphodiesterase (PDE) isoenzymes in the human detrusor smooth muscle. II. Effect of various PDE inhibitors on smooth muscle tone and cyclic nucleotide levels in vitro.

Phosphodiesterases (PDEs) regulate intracellular cyclic nucleotide metabolism and, thus, contraction and relaxation of smooth musculature. The aim of the present study was to evaluate the functional effects of isoenzyme-selective inhibitors and their effects on cyclic nucleotide levels in the human detrusor smooth muscle. In addition, the functional relevance of the cAMP versus the cGMP pathways in the regulation of the detrusor smooth muscle tone was assessed. Relaxant responses to various PDE inhibitors, forskolin and sodium nitroprusside (SNP) were investigated in vitro using a standard organ bath setup. Cyclic nucleotide levels were measured after incubation with the same substances using cAMP and cGMP radioimmunoassays (RIAs). Significant relaxant responses were only induced by non-selective PDE inhibition, the PDE I inhibitor vinpocetine and the adenylate cyclase activator forskolin. Relaxant responses to these substances were paralleled by increases in cyclic nucleotide levels. Our data suggest that the cAMP pathway and calcium/calmodulin-stimulated PDE (PDE I) may be of functional importance in the regulation of the human detrusor smooth muscle tone in vitro.

Cyclic nucleotide phosphodiesterase (PDE) isoenzymes in the human detrusor smooth muscle. I. Identification and characterization.

Phosphodiesterases (PDEs) are key enzymes involved in the regulation of intracellular cyclic nucleotide metabolism. The aim of the present study was to identify and to characterize the PDE isoenzymes present in the human detrusor smooth muscle. Human detrusor PDE isoenzymes were separated by Q-Sepharose anion exchange and calmodulin-agarose affinity chromatography and characterized upon their kinetic characteristics and their sensitivity to allosteric modulators and inhibitors. All five presently known PDE isoenzyme families were identified: one high-affinity, low-Km calcium/calmodulin-stimulated PDE I with a slight preference for cGMP over cAMP, one cGMP-stimulated PDE II, one cGMP-inhibited PDE III, one cAMP-specific PDE IV and one cGMP-specific PDE IV. All five known PDE isoenzyme families exist in human detrusor smooth musculature. The kinetic characteristics, together with functional in vitro studies, suggest that the PDE I may be of importance in the intracellular regulation of the human detrusor smooth muscle tone.

Separation and characterisation of cyclic nucleotide phosphodiesterases from the lacrimal, Harderian and zygomatic glands of the rabbit

To investigate the activity profile of cyclic nucleotide phosphodiesterase (PDE) isoenzymes and the effects of isoenzyme selective inhibitors in the superior and inferior lacrimal glands, Harderian gland, and zygomatic gland of the rabbit. Protein fractions extracted from crude homogenates on an anion exchange column were examined for PDE activity using an HPLC method for detecting nucleotides. The superior and inferior lacrimal glands had identified PDE activity profiles. PDE I was the major type of activity and there was also a minor PDE III peak of activity. The main activity detected in the lipid secreting Harderian gland was PDE II and for the mucus secreting zygomatic gland PDE III. All glands contained PDE IV activity. The kinetics of the peak enzyme activities were examined and found similar, but not identical to the kinetics for PDE activities obtained from other tissues. Inhibitors of specific PDE classes and the general PDE inhibitor, IBMX, were tested on the peak enzyme activities. Activities designated by their substrate specificity or co-factor modification were most strongly inhibited by the corresponding class selective inhibitor. For example, PDE I activity in the lacrimal gland was most strongly inhibited by nicardipine. All activities were inhibited by IBMX. The superior and inferior lacrimal glands of the rabbit have the same PDE profile and this differs from the PDE subtypes detected in the mucus secreting zygomatic gland and the lipid secreting Harderian gland.

Isoenzymes of cyclic nucleotide phosphodiesterase in the human aorta: characterization and the effects of E4021

In extracts of the human aorta, five isoenzymes of cyclic nucleotide phosphodiesterase, namely, phosphodiesterase I, phosphodiesterase II, phosphodiesterase III, phosphodiesterase IV and phosphodiesterase V, were identified exclusively in the cytosolic fraction, and no phosphodiesterase activity was detected in the particulate fraction. Phosphodiesterase V and phosphodiesterase I were the major cGMP-hydrolyzing enzymes in the human aorta. A novel vasorelaxant, sodium 1-[6-chloro-4-(3,4-methylenedioxybenzyl)aminoquinazolin-2-yl]piperidine-4-carboxylate sesquihydrate (E4021), relaxed prostaglandin F 2α-precontracted strips of human pulmonary artery with an ED 50 value of 0.5 μM. E4021 potently and highly selectively inhibited the activity of phosphodiesterase V from human aorta with a K i value of 2.4 nM. These results suggest that there is a unique distribution of phosphodiesterase isoenzymes in the human aorta and that inhibitors of phosphodiesterase V might be useful as a new type of vasodilator in the treatment of clinical disorders.

Isozyme selective inhibition of cGMP-stimulated cyclic nucleotide phosphodiesterases by erythro-9-(2-hydroxy-3-nonyl) adenine

Erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA), a potent inhibitor of adenosine deaminase (ADA), was tested as an inhibitor of the soluble cyclic nucleotide phosphodiesterase (PDE) isoenzymes from pig and human myocardium. Four soluble PDE activities were resolved from human papillary muscle extracts using anion exchange chromatography (DEAE Sepharose CL-6B). These activities were designated PDE I–IV according to the nomenclature of Beavo. PDE I was stimulated by Ca 2+-calmodulin and PDE II by cGMP (1 μM). PDE III was inhibited by cGMP (1 μM) as well as SK&F 94120, and PDE IV by both rolipram and Ro 20–1724. Enzyme kinetics and inhibition constants were similar with the PDE isoenzymes from pig heart. However, porcine myocardium lacked Ca 2+-calmodulin-stimulated soluble PDE I activity. The present data reveal that EHNA exerted a concentration-dependent inhibition of the cGMP-stimulated PDE II (cGs-PDE) ( ic 50: 0.8 μM (human), 2 μM (pig)) but did not inhibit the other PDE isoenzymes ( ic 50 > 100 μM). These findings indicate that EHNA is a potent and, as far as cytosolic PDEs are concerned, selective inhibitor of cGMP-stimulated PDEs. The compound may lend itself for the rational design of other isozyme selective PDE II inhibitors and for examining the specific biological functions of cGs-PDEs. EHNA may be used in systems in which inhibition of ADA is of no concern. Conversely, dual inhibition of both ADA and cGs-PDE by EHNA may cause accumulation of two inhibitory metabolites, adenosine and cGMP, which may act in synergy to mediate diverse pharmacological responses, including antiviral, antitumour and antiarrhythmic effects.

Diversity in Cyclic Nucleotide Phosphodiesterase Isoenzyme Families

Diversity in Cyclic Nucleotide Phosphodiesterase Isoenzyme Families

Cyclic nucleotide phosphodiesterase isoenzyme activities in human alveolar macrophages.

Alveolar macrophages and their precursors, the monocytes are involved in airway inflammation in asthma. An increase in intracellular cAMP by PDE inhibitors is known to suppress macrophage and monocyte functions. A comparison of the PDE-isoenzyme profiles of human alveolar macrophages from normal and atopic donors and of human peripheral blood monocytes might form a basis to differentially affect functions of these cells by PDE inhibitors. The study compares the PDE isoenzyme activity profiles of human alveolar macrophages from normal and atopic asthmatic donors and human peripheral blood monocytes. In addition, the effect of in vitro maturation of monocytes on their PDE isoenzyme profile is studied. Macrophages were purified (95-97%) by adherence to plastic, and blood monocytes were purified (88%) by counter-current elutriation. PDE isoenzyme activity profiles were investigated using isoenzyme selective inhibitors and activators. In macrophages substantial PDE I activity, which was significantly higher than PDE III-V activity was detected and PDE II was absent. PDE III was membrane-bound whereas PDE I, IV and V were soluble. No difference was found between alveolar macrophages of normal donors and atopic asthmatics. Monocytes exclusively contained PDE IV but their in vitro maturation led to a PDE isoenzyme profile similar to that of alveolar macrophages. These results indicate that human monocytes and alveolar macrophages are distinct targets for the effects of selective PDE inhibitors while alveolar macrophages from normal and atopic individuals appear to be equally sensitive.