Section Review: Cardiovascular & Renal: Cyclic nucleotide phosphodiesterases as therapeutic targets in cardiovascular diseases

The Complexity and Multiplicity of the Specific cAMP Phosphodiesterase Family: PDE4, Open New Adapted Therapeutic Approaches

Cyclic nucleotides (cAMP, cGMP) play a major role in normal and pathologic signaling. Beyond receptors, cyclic nucleotide phosphodiesterases; (PDEs) rapidly convert the cyclic nucleotide in its respective 5′-nucleotide to control intracellular cAMP and/or cGMP levels to maintain a normal physiological state. However, in many pathologies, dysregulations of various PDEs (PDE1-PDE11) contribute mainly to organs and tissue failures related to uncontrolled phosphorylation cascade. Among these, PDE4 represents the greatest family, since it is constituted by 4 genes with multiple variants differently distributed at tissue, cellular and subcellular levels, allowing different fine-tuned regulations. Since the 1980s, pharmaceutical companies have developed PDE4 inhibitors (PDE4-I) to overcome cardiovascular diseases. Since, they have encountered many undesired problems, (emesis), they focused their research on other PDEs. Today, increases in the knowledge of complex PDE4 regulations in various tissues and pathologies, and the evolution in drug design, resulted in a renewal of PDE4-I development. The present review describes the recent PDE4-I development targeting cardiovascular diseases, obesity, diabetes, ulcerative colitis, and Crohn’s disease, malignancies, fatty liver disease, osteoporosis, depression, as well as COVID-19. Today, the direct therapeutic approach of PDE4 is extended by developing allosteric inhibitors and protein/protein interactions allowing to act on the PDE interactome.

Selective changes in cytosolic β-adrenergic cAMP signals and L-type Calcium Channel regulation by Phosphodiesterases during cardiac hypertrophy

Background In cardiomyocytes, phosphodiesterases (PDEs) type 3 and 4 are the predominant enzymes that degrade cAMP generated by β-adrenergic receptors (β-ARs), impacting notably the regulation of the L-type Ca2+ current (ICa,L). Cardiac hypertrophy (CH) is accompanied by a reduction in PDE3 and PDE4, however, whether this affects the dynamic regulation of cytosolic cAMP and ICa,L is not known. Methods and Results CH was induced in rats by thoracic aortic banding over a time period of five weeks and was confirmed by anatomical measurements. Left ventricular myocytes (LVMs) were isolated from CH and sham-operated (SHAM) rats and transduced with an adenovirus encoding a Förster resonance energy transfer (FRET)-based cAMP biosensor or subjected to the whole-cell configuration of the patch-clamp technique to measure ICa,L. Aortic stenosis resulted in a 46% increase in heart weight to body weight ratio in CH compared to SHAM. In SHAM and CH LVMs, a short isoprenaline stimulation (Iso, 100 nM, 15 s) elicited a similar transient increase in cAMP with a half decay time (t1/2off) of ~50 s. In both groups, PDE4 inhibition with Ro 20-1724 (10 μM) markedly potentiated the amplitude and slowed the decline of the cAMP transient, this latter effect being more pronounced in SHAM (t1/2off ~ 250 s) than in CH (t1/2off ~ 150 s, P < 0.01). In contrast, PDE3 inhibition with cilostamide (1 μM) had no effect on the amplitude of the cAMP transient and a minimal effect on its recovery in SHAM, whereas it potentiated the amplitude and slowed the decay in CH (t1/2off ~ 80 s). Iso pulse stimulation also elicited a similar transient increase in ICa,L in SHAM and CH, although the duration of the rising phase was delayed in CH. Inhibition of PDE3 or PDE4 potentiated ICa,L amplitude in SHAM but not in CH. Besides, while only PDE4 inhibition slowed down the decline of ICa,L in SHAM, both PDE3 and PDE4 contributed in CH. Conclusion These results identify selective alterations in cytosolic cAMP and ICa,L regulation by PDE3 and PDE4 in CH, and show that the balance between PDE3 and PDE4 for the regulation of β-AR responses is shifted toward PDE3 during CH.

Resveratrol enhances the inotropic effect but inhibits the proarrhythmic effect of sympathomimetic agents in rat myocardium

Background

Resveratrol is a cardioprotective agent with known antiarrhythmic effects that has recently been shown to inhibit phosphodiesterase (PDE) enzyme activity. Thus, it is possible that resveratrol increases the inotropic effect of sympathomimetic agents, as PDE inhibitors do but, unlike other PDE inhibitors, its effect may not be accompanied by proarrhythmia due to its antiarrhythmic action. This work is aimed to test this hypothesis.

Methods

This is an “in vitro” concentration-response relationship study. The effects of noradrenaline, tyramine and isoproterenol, alone or in combination with either resveratrol or with the typical PDE inhibitor 3-isobutylmethylxantine (IBMX), were studied in electrically driven strips of right ventricle or in the spontaneously beating free wall of the right ventricle of rat heart in order to investigate inotropic or proarrhythmic effects respectively. Also, the effects of resveratrol or IBMX on the sinoatrial node rate were examined in the isolated right atria of rat heart.

Results

Resveratrol (10 µM and 100 µM) produces a leftward shift in the concentration-response curves for the contractile effects of noradrenaline, tyramine or isoproterenol and reduces the –log EC₅₀ values of these three agents. IBMX produces similar effects. The spontaneous ventricular beating rate was increased by all three compounds, an effect that was further enhanced by the addition of IBMX. In contrast, resveratrol (100 µM) abolished the effects of these sympathomimetic agents on the ventricular rate. Resveratrol (1–100 µM) had no effect on the sinoatrial node rate, while IBMX produce a concentration dependent sinoatrial tachycardia.

Discussion

Taken together, the finding, indicate that resveratrol, like the PDE inhibitor IBMX enhances the contractile effects of sympathomimetic agents but, in contrast to IBMX, it does not enhance their proarrhythmic effect or produce sinoatrial tachycardia. This is most probably consequence of the antiarrhythmic effect of resveratrol which protect against the proarrhythmic effects resulting from PDE inhibition.

Angiotensin-converting enzyme inhibition prevents myocardial infarction-induced increase in renal cortical cGMP and cAMP phosphodiesterase activities

We investigated whether myocardial infarction (MI) enhances renal phosphodiesterases (PDE) activities, investigating particularly the relative contribution of PDE1-5 isozymes in total PDE activity involved in both cGMP and cAMP pathways, and whether angiotensin-converting enzyme inhibition (ACEi) decreases such renal PDE hyperactivities. We also investigated whether ACEi might thereby improve atrial natriuretic peptide (ANP) efficiency. We studied renal cortical PDE1-5 isozyme activities in sham (SH)-operated, MI rats and in MI rats treated with perindopril (ACEi) 1 month after coronary artery ligation. Circulating atrial natriuretic peptide (ANP), its second intracellular messenger cyclic guanosine monophosphate (cGMP) and cGMP/ANP ratio were also determined. Cortical cGMP-PDE2 (80.3 vs. 65.1 pmol/min/mg) and cGMP-PDE1 (50.7 vs. 30.1 pmol/min/mg), and cAMP-PDE2 (161 vs. 104.1 pmol/min/mg) and cAMP-PDE4 (307.5 vs. 197.2 pmol/min/mg) activities were higher in MI than in SH rats. Despite increased ANP plasma level, ANP efficiency tended to be decreased in MI compared to SH rats. Perindopril restored PDE activities and tended to improve ANP efficiency in MI rats. One month after coronary ligation, perindopril treatment of MI rats prevents the increase in renal cortical PDE activities. This may contribute to increase renal ANP efficiency in MI rats.

Temporal and spatial regulation of cAMP signaling in disease: role of cyclic nucleotide phosphodiesterases

Since its discovery, cAMP has been proposed as one of the most versatile second messengers. The remarkable feature of cAMP to tightly control highly diverse physiological processes, including metabolism, homeostasis, secretion, muscle contraction, cell proliferation and migration, immune response, and gene transcription, is reflected by millions of different articles worldwide. Compartmentalization of cAMP in space and time, maintained by mainly phosphodiesterases, contributes to the maintenance of equilibrium inside the cell where one signal can trigger many different events. Novel cAMP sensors seem to carry out certain unexpected signaling properties of cAMP and thereby to permit delicate adaptations of biologic responses. Measuring space and time events with biosensors will increase our current knowledge on the pathophysiology of diseases, such as chronic obstructive pulmonary disease, asthma, cognitive impairment, cancer, and renal and heart failure. Further insights into the cAMP dynamics will help to optimize the pharmacological treatment for these diseases.

Role of membrane microdomains in compartmentation of cAMP signaling

Spatially restricting cAMP production to discrete subcellular locations permits selective regulation of specific functional responses. But exactly where and how cAMP signaling is confined is not fully understood. Different receptors and adenylyl cyclase isoforms responsible for cAMP production are not uniformly distributed between lipid raft and non-lipid raft domains of the plasma membrane. We sought to determine the role that these membrane domains play in organizing cAMP responses in HEK293 cells. The freely diffusible FRET-based biosensor Epac2-camps was used to measure global cAMP responses, while versions of the probe targeted to lipid raft (Epac2-MyrPalm) and non-raft (Epac2-CAAX) domains were used to monitor local cAMP production near the plasma membrane. Disruption of lipid rafts by cholesterol depletion selectively altered cAMP responses produced by raft-associated receptors. The results indicate that receptors associated with lipid raft as well as non-lipid raft domains can contribute to global cAMP responses. In addition, basal cAMP activity was found to be significantly higher in non-raft domains. This was supported by the fact that pharmacologic inhibition of adenylyl cyclase activity reduced basal cAMP activity detected by Epac2-CAAX but not Epac2-MyrPalm or Epac2-camps. Responses detected by Epac2-CAAX were also more sensitive to direct stimulation of adenylyl cyclase activity, but less sensitive to inhibition of phosphodiesterase activity. Quantitative modeling was used to demonstrate that differences in adenylyl cyclase and phosphodiesterase activities are necessary but not sufficient to explain compartmentation of cAMP associated with different microdomains of the plasma membrane.

PDEs1-5 activity and expression in tissues of cirrhotic rats reveal a role for aortic PDE3 in NO desensitization

Liver cirrhosis is associated with increased nitric oxide (NO) production in the vasculature. We have previously demonstrated that aorta from rats with liver cirrhosis have a reduced relaxant response to NO donors that is corrected by DMPPO, a PDE5-specific inhibitor. Vasodilator responses to DMPPO itself were also reduced in rings from cirrhotic rats. These results supported previous suggestions that upregulation of PDE5 in liver cirrhosis might contribute to renal sodium retention, and consequently modulate vascular reactivity in the context of increased NO production (Tahseldar-Roumieh et al. in Am. J. Physiol. Heart Circ. Physiol. 290, H481-H488, 2006). Here, we investigated the possible alteration in activity and expression of cyclic nucleotide phosphodiesterase PDE1-PDE5 in kidney and vascular tissues in rats 4 weeks after bile duct ligation. The kidney of rats with cirrhosis had increased activity of PDE1 and PDE4 but not PDE5, and increased expression of PDE1A. Unexpectedly and interestingly, there was no change in cirrhotic aorta PDE5, but an increase in PDE3 and PDE4 activity associated with increased expression of PDE3A and PDE3B. Cilostamide, a specific PDE3 inhibitor, corrected the decreased response to an NO donor in isolated aorta from cirrhotic rats, suggesting that the difference in response to NO donors was due to differences in PDE3-induced hydrolysis of cGMP or to cGMP-induced inhibition of PDE3, rather than to differences in PDE5 contribution. In conclusion, these changes in PDE isozymes could greatly contribute to NO desensitization and to the regulation of vascular and renal function in liver cirrhosis.

Decreased expression and activity of cAMP phosphodiesterases in cardiac hypertrophy and its impact on beta-adrenergic cAMP signals

RATIONALE

Multiple cyclic nucleotide phosphodiesterases (PDEs) degrade cAMP in cardiomyocytes but the role of PDEs in controlling cAMP signaling during pathological cardiac hypertrophy is poorly defined.

OBJECTIVE

Evaluate the beta-adrenergic regulation of cardiac contractility and characterize the changes in cardiomyocyte cAMP signals and cAMP-PDE expression and activity following cardiac hypertrophy.

METHODS AND RESULTS

Cardiac hypertrophy was induced in rats by thoracic aortic banding over a time period of 5 weeks and was confirmed by anatomic measurements and echocardiography. Ex vivo myocardial function was evaluated in Langendorff-perfused hearts. Engineered cyclic nucleotide-gated (CNG) channels were expressed in single cardiomyocytes to monitor subsarcolemmal cAMP using whole-cell patch-clamp recordings of the associated CNG current (I(CNG)). PDE variant activity and protein level were determined in purified cardiomyocytes. Aortic stenosis rats exhibited a 67% increase in heart weight compared to sham-operated animals. The inotropic response to maximal beta-adrenergic stimulation was reduced by approximately 54% in isolated hypertrophied hearts, along with a approximately 32% decrease in subsarcolemmal cAMP levels in hypertrophied myocytes. Total cAMP hydrolytic activity as well as PDE3 and PDE4 activities were reduced in hypertrophied myocytes, because of a reduction of PDE3A, PDE4A, and PDE4B, whereas PDE4D was unchanged. Regulation of beta-adrenergic cAMP signals by PDEs was blunted in hypertrophied myocytes, as demonstrated by the diminished effects of IBMX (100 micromol/L) and of both the PDE3 inhibitor cilostamide (1 micromol/L) and the PDE4 inhibitor Ro 201724 (10 micromol/L).

CONCLUSIONS

Beta-adrenergic desensitization is accompanied by a reduction in cAMP-PDE and an altered modulation of beta-adrenergic cAMP signals in cardiac hypertrophy.

The flavonoid dioclein is a selective inhibitor of cyclic nucleotide phosphodiesterase type 1 (PDE1) and a cGMP-dependent protein kinase (PKG) vasorelaxant in human vascular tissue

The inhibitory effect of the flavonoid dioclein was assessed on purified vascular cyclic nucleotide phosphodiesterase isoforms (EC 3.1.4.17, PDE1-5) in comparison with 8-methoxymethyl-isobutylmethylxanthine (8-MM-IBMX) and vinpocetine which are currently used as PDE1 inhibitors. The mechanism underlying the vasorelaxant effect of dioclein was investigated in human saphenous vein. Dioclein inhibited PDE1 more selectively than vinpocetine and 8-MM-IBMX, with IC(50) values of 2.47+/-0.26 and 1.44+/-0.35 microM, respectively in basal- and calmodulin-activated states. Dioclein behaved as a competitive inhibitor for cGMP hydrolysis by PDE1 in basal- and calmodulin-activated states (K(i)=0.62+/-0.14 and 0.55+/-0.07 microM, respectively), indicating this inhibitory effect to be independent of calmodulin interactions. In addition, dioclein induced a concentration-dependent relaxation of human saphenous vein which was independent on the presence of functional endothelium (EC(50) values of 7.3+/-3.1 and 11+/-2.7 microM, respectively with and without endothelium). 8-MM-IBMX relaxed human saphenous vein with an EC(50)=31+/-16 microM, whereas vinpocetine did not cause any vasorelaxation at concentrations up to 100 microM. Rp-8-pCPT-cGMPS, which inhibits cGMP-dependent protein kinase (PKG), blocked the vasodilator effect of dioclein, whereas H-89, which is a cAMP-dependent protein kinase (PKA) inhibitor, had a minor inhibitory effect. Our data show that dioclein is a potent calmodulin-independent selective inhibitor of PDE1 and that inhibition of PDE1 is involved in the PKG-mediated vasorelaxant effect of dioclein in human saphenous vein. Furthermore, dioclein may represent a new archetype to develop more specific PDE1 inhibitors.

Compartmentation of cAMP signaling in cardiac myocytes: a computational study

Receptor-mediated changes in cAMP production play an essential role in sympathetic and parasympathetic regulation of the electrical, mechanical, and metabolic activity of cardiac myocytes. However, responses to receptor activation cannot be easily ascribed to a uniform increase or decrease in cAMP activity throughout the entire cell. In this study, we used a computational approach to test the hypothesis that in cardiac ventricular myocytes the effects of beta(1)-adrenergic receptor (beta(1)AR) and M(2) muscarinic receptor (M(2)R) activation involve compartmentation of cAMP. A model consisting of two submembrane (caveolar and extracaveolar) microdomains and one bulk cytosolic domain was created using published information on the location of beta(1)ARs and M(2)Rs, as well as the location of stimulatory (G(s)) and inhibitory (G(i)) G-proteins, adenylyl cyclase isoforms inhibited (AC5/6) and stimulated (AC4/7) by G(i), and multiple phosphodiesterase isoforms (PDE2, PDE3, and PDE4). Results obtained with the model indicate that: 1), bulk basal cAMP can be high ( approximately 1 microM) and only modestly stimulated by beta(1)AR activation ( approximately 2 microM), but caveolar cAMP varies in a range more appropriate for regulation of protein kinase A ( approximately 100 nM to approximately 2 microM); 2), M(2)R activation strongly reduces the beta(1)AR-induced increases in caveolar cAMP, with less effect on bulk cAMP; and 3), during weak beta(1)AR stimulation, M(2)R activation not only reduces caveolar cAMP, but also produces a rebound increase in caveolar cAMP following termination of M(2)R activity. We conclude that compartmentation of cAMP can provide a quantitative explanation for several aspects of cardiac signaling.

Study of the mechanisms involved in the vasorelaxation induced by (-)-epigallocatechin-3-gallate in rat aorta

This study investigated several mechanisms involved in the vasorelaxant effects of (-)-epigallocatechin-3-gallate (EGCG). EGCG (1 microM-1 mM) concentration dependently relaxed, after a transient increase in tension, contractions induced by noradrenaline (NA, 1 microM), high extracellular KCl (60 mM), or phorbol 12-myristate 13-acetate (PMA, 1 microM) in intact rat aortic rings. In a Ca2+ -free solution, EGCG (1 microM-1 mM) relaxed 1 microM PMA-induced contractions, without previous transient contraction. However, EGCG (1 microM-1 mM) did not affect the 1 microM okadaic acid-induced contractions. Removal of endothelium and/or pretreatment with glibenclamide (10 microM), tetraethylammonium (2 mM) or charybdotoxin (100 nM) plus apamin (500 nM) did not modify the vasorelaxant effects of EGCG. In addition, EGCG noncompetitively antagonized the contractions induced by NA (in 1.5 mM Ca2+ -containing solution) and Ca2+ (in depolarizing Ca2+ -free high KCl 60 mM solution). In rat aortic smooth muscle cells (RASMC), EGCG (100 microM) reduced increases in cytosolic free Ca2+ concentration ([Ca2+]i) induced by angiotensin II (ANG II, 100 nM) and KCl (60 mM) in 1.5 mM CaCl2 -containing solution and by ANG II (100 nM) in the absence of extracellular Ca2+. In RASMC, EGCG (100 microM) did not modify basal generation of cAMP or cGMP, but significantly reversed the inhibitory effects of NA (1 microM) and high KCl (60 mM) on cAMP and cGMP production. EGCG inhibited the enzymatic activity of all the cyclic nucleotide PDE isoenzymes present in vascular tissue, being more effective on PDE2 (IC50 approximately 17) and on PDE1 (IC50 approximately 25). Our results suggest that the vasorelaxant effects of EGCG in rat aorta are mediated, at least in part, by an inhibition of PDE activity, and the subsequent increase in cyclic nucleotide levels in RASMC, which, in turn, can reduce agonist- or high KCl concentration-induced increases in [Ca2+]i.

A specific pattern of phosphodiesterases controls the cAMP signals generated by different Gs-coupled receptors in adult rat ventricular myocytes

Compartmentation of cAMP is thought to generate the specificity of Gs-coupled receptor action in cardiac myocytes, with phosphodiesterases (PDEs) playing a major role in this process by preventing cAMP diffusion. We tested this hypothesis in adult rat ventricular myocytes by characterizing PDEs involved in the regulation of cAMP signals and L-type Ca2+ current (I(Ca,L)) on stimulation with beta1-adrenergic receptors (beta1-ARs), beta2-ARs, glucagon receptors (Glu-Rs) and prostaglandin E1 receptors (PGE1-Rs). All receptors but PGE1-R increased total cAMP, and inhibition of PDEs with 3-isobutyl-1-methylxanthine strongly potentiated these responses. When monitored in single cells by high-affinity cyclic nucleotide-gated (CNG) channels, stimulation of beta1-AR and Glu-R increased cAMP, whereas beta2-AR and PGE1-R had no detectable effect. Selective inhibition of PDE3 by cilostamide and PDE4 by Ro 20-1724 potentiated beta1-AR cAMP signals, whereas Glu-R cAMP was augmented only by PD4 inhibition. PGE1-R and beta2-AR generated substantial cAMP increases only when PDE3 and PDE4 were blocked. For all receptors except PGE1-R, the measurements of I(Ca,L) closely matched the ones obtained with CNG channels. Indeed, PDE3 and PDE4 controlled beta1-AR and beta2-AR regulation of I(Ca,L), whereas only PDE4 controlled Glu-R regulation of I(Ca,L) thus demonstrating that receptor-PDE coupling has functional implications downstream of cAMP. PGE1 had no effect on I(Ca,L) even after blockade of PDE3 or PDE4, suggesting that other mechanisms prevent cAMP produced by PGE1 to diffuse to L-type Ca2+ channels. These results identify specific functional coupling of individual PDE families to Gs-coupled receptors as a major mechanism enabling cardiac cells to generate heterogeneous cAMP signals in response to different hormones.

Phosphodiesterase 5 (PDE 5) inhibitors for the treatment of male erectile disorder: Attaining selectivity versus PDE6

The role of phosphodiesterase type 5 (PDE5) in the mechanism of male erection has been well understood, and several drugs inhibiting this enzyme are being used for the treatment of erectile dysfunction (ED). Discovery of inhibitors with improved selectivity versus other PDE isozymes could lead to drugs with improved safety profile. Achievement of selectivity versus PDE6, co-inhibition of which results in disturbances of color perception, remains the most challenging aspect of current drug discovery programs. The present review describes several case studies, where significant (>100 fold) selectivity versus PDE6 has been attained via investigation of structure-activity relationships (SAR). Special attention is given to the chemical routes leading to novel chemotypes and allowing efficient exploration of their SAR's. Strategies for attaining inhibitor selectivity discussed below may be applicable for other drug discovery programs.

Association of phosphodiesterase 4D gene with ischemic stroke in a Pakistani population

BACKGROUND AND OBJECTIVES

Identification of STRK1 locus by the deCODE group followed by the discovery of phosphodiesterase 4D (PDE4D) gene in strong association with ischemic stroke patients has provided useful insights toward understanding the genetic etiology of the disease. In this study, we aimed at investigating the association between 3 polymorphisms of the PDE4D gene and ischemic stroke in the Pakistani population.

METHODS

Three polymorphisms in PDE4D gene were analyzed in 200 patients of ischemic stroke and 250 controls of Pakistani origin using polymerase chain reaction-restriction fragment length polymorphism method. Data were coded and entered in SPSS Windows (version 12.0). Odds ratios and 95% CIs were calculated using multivariate logistic regression analysis.

RESULTS

Marker SNP83(rs966221) was found significantly associated with ischemic stroke on univariate and multivariate analysis (P<0.005; odds ratio, 1.64 [1.13 to 2.40]). Haplotype analysis for markers in linkage disequilibrium failed to show any association with the disease.

CONCLUSIONS

The association of PDE4D variation with ischemic stroke extends to the Pakistani population and supports a role for phosphodiesterases in stroke pathogenesis.

Cyclic nucleotide phosphodiesterase (PDE) superfamily: a new target for the development of specific therapeutic agents

Cyclic nucleotide phosphodiesterases (PDEs), which are ubiquitously distributed in mammalian tissues, play a major role in cell signaling by hydrolyzing cAMP and cGMP. Due to their diversity, which allows specific distribution at cellular and subcellular levels, PDEs can selectively regulate various cellular functions. Their critical role in intracellular signaling has recently designated them as new therapeutic targets for inflammation. The PDE superfamily represents 11 gene families (PDE1 to PDE11). Each family encompasses 1 to 4 distinct genes, to give more than 20 genes in mammals encoding the more than 50 different PDE proteins probably produced in mammalian cells. Although PDE1 to PDE6 were the first well-characterized isoforms because of their predominance in various tissues and cells, their specific contribution to tissue function and their regulation in pathophysiology remain open research fields. This concerns particularly the newly discovered families, PDE7 to PDE11, for which roles are not yet established. In many pathologies, such as inflammation, neurodegeneration, and cancer, alterations in intracellular signaling related to PDE deregulation may explain the difficulties observed in the prevention and treatment of these pathologies. By inhibiting specifically the up-regulated PDE isozyme(s) with newly synthesized potent and isozyme-selective PDE inhibitors, it may be potentially possible to restore normal intracellular signaling selectively, providing therapy with reduced adverse effects.

Phosphodiesterase 4D is required for beta2 adrenoceptor subtype-specific signaling in cardiac myocytes

beta adrenoceptor (betaAR) signaling is finely regulated to mediate the sympathetic nervous system control of cardiovascular function. In neonatal cardiac myocytes, beta1AR activates the conventional Gs/cAMP pathway, whereas beta2AR sequentially activates both the Gs and Gi pathways to regulate the myocyte contraction rate. Here, we show that phosphodiesterase 4D (PDE4D) selectively impacts signaling by beta2AR in neonatal cardiac myocytes, while having little or no effect on beta1AR signaling. Although beta2AR activation leads to an increase in cAMP production, the cAMP generated does not have access to the protein kinase A-dependent signaling pathways by which the beta1AR regulates the contraction rate. However, this restricted access is lost in the presence of PDE4 inhibitors or after ablation of PDE4D. These results not only suggest that PDE4D is an integral component of the beta2AR signaling complex, but also underscore the critical role of subcellular cAMP regulation in the complex control of receptor signaling. They also illustrate a mechanism for fine-tuned betaAR subtype signaling specificity and intensity in the cardiac system.

Comparative study of the vasorelaxant activity, superoxide-scavenging ability and cyclic nucleotide phosphodiesterase-inhibitory effects of hesperetin and hesperidin

This study investigated the vasorelaxant activity, superoxide radicals (O2(*-))-scavenging capacity and cyclic nucleotide phosphodiesterase (PDE)-inhibitory effects of hesperidin and hesperetin, two flavonoids mainly isolated from citrus fruits. Hesperetin concentration-dependently relaxed the isometric contractions induced by noradrenaline (NA, 1 microM) or by a high extracellular KCl concentration (60 mM) in intact rat isolated thoracic aorta rings. However, hesperetin (10 microM-0.3 mM) did not affect the contractile response induced by okadaic acid (OA, 1 microM). Mechanical removal of endothelium and/or pretreatment of aorta rings with glibenclamide (GB, 10 microM), tetraethylammonium (TEA, 2 mM) or nifedipine (0.1 microM) did not significantly modify the vasorelaxant effects of this flavonoid. Hesperetin (10 microM-0.1 mM) did not affect the basal uptake of (45)Ca(2+) but decreased the influx of (45)Ca(2+) induced by NA and KCl in endothelium-containing and endothelium-denuded rat aorta. Hesperetin (10 microM-0.1 mM) did not scavenge O2(*-) generated by the phenazine methosulfate (PMS)-reduced beta-nicotinamide adenine dinucleotide (NADH) system. Hesperetin (0.1 mM) significantly reversed the inhibitory effects of NA (1 microM) and high KCl (60 mM) on cyclic nucleotide (cAMP and cGMP) production in cultured rat aortic myocytes. Hesperetin preferentially inhibited calmodulin (CaM)-activated PDE1 and PDE4 isolated from bovine aorta with IC(50) values of about 74 microM and 70 microM respectively. In contrast, the 7-rhamnoglucoside of hesperetin, hesperidin (10 microM-0.1 mM), was inactive in practically all experiments, although it inhibited basal and cGMP-activated PDE2 isolated from platelets (IC(50) values of 32+/-4 microM and 137+/-34 microM respectively). These results suggest that the vasorelaxant effects of hesperetin are basically due to the inhibition of PDE1 and PDE4 activities.

Negative feedback exerted by cAMP-dependent protein kinase and cAMP phosphodiesterase on subsarcolemmal cAMP signals in intact cardiac myocytes: an in vivo study using adenovirus-mediated expression of CNG channels

Intracardiac cAMP levels are modulated by hormones and neuromediators with specific effects on contractility and metabolism. To understand how the same second messenger conveys different information, mutants of the rat olfactory cyclic nucleotide-gated (CNG) channel alpha-subunit CNGA2, encoded into adenoviruses, were used to monitor cAMP in adult rat ventricular myocytes. CNGA2 was not found in native myocytes but was strongly expressed in infected cells. In whole cell patch-clamp experiments, the forskolin analogue L-858051 (L-85) elicited a non-selective, Mg2+ -sensitive current observed only in infected cells, which was thus identified as the CNG current (ICNG). The beta-adrenergic agonist isoprenaline (ISO) also activated ICNG, although the maximal efficiency was approximately 5 times lower than with L-85. However, ISO and L-85 exerted a similar maximal increase of the L-type Ca2+ current. The use of a CNGA2 mutant with a higher sensitivity for cAMP indicated that this difference is caused by the activation of a localized fraction of CNG channels by ISO. cAMP-dependent protein kinase (PKA) blockade with H89 or PKI, or phosphodiesterase (PDE) inhibition with IBMX, dramatically potentiated ISO- and L-85-stimulated ICNG. A similar potentiation of beta-adrenergic stimulation occurred when PDE4 was blocked, whereas PDE3 inhibition had a smaller effect (by 2-fold). ISO and L-85 increased total PDE3 and PDE4 activities in cardiomyocytes, although this effect was insensitive to H89. However, in the presence of IBMX, H89 had no effect on ISO stimulation of ICNG. This study demonstrates that subsarcolemmal cAMP levels are dynamically regulated by a negative feedback involving PKA stimulation of subsarcolemmal cAMP-PDE.

Sildenafil alters calcium signaling and vascular tone in pulmonary arteries from chronically hypoxic rats

Sildenafil, a potent type 5 nucleotide-dependent phosphodiesterase (PDE) inhibitor, has been recently proposed as a therapeutic tool to treat or prevent pulmonary artery hypertension (PAHT). We thus studied the effect of sildenafil on both the calcium signaling of isolated pulmonary artery smooth muscle cells (PASMCs) and the reactivity of pulmonary artery (PA) obtained from chronic hypoxia (CH)-induced pulmonary hypertensive rats compared with control (normoxic) rats. CH rats were maintained in an hypobaric chamber (50.5 kPa) for 3 wk leading to full development of PAHT. Intracellular calcium concentration ([Ca2+]i) was measured in PASMCs loaded with the calcium fluorophore indo 1. Unlike in control rats, sildenafil (10–100 nM) decreased the resting [Ca2+]ivalue in PASMCs obtained from CH rats. In PASMCs from both control and CH rats, sildenafil concentration dependently inhibited the [Ca2+]iresponse induced by G-coupled membrane receptor agonists such as angiotensin II and phenylephrine but had no effect on the amplitude of the [Ca2+]iresponse induced by caffeine. Sildenafil (0.1 nM–1 μM) concentration dependently reduced basal PA tone that is present in CH rats and relaxed PA rings precontracted with phenylephrine in both control and CH rats. These data show that sildenafil is a potent pulmonary artery relaxant in CH rats and that it normalizes CH-induced increases in resting [Ca2+]iand basal tone. Consequently, pharmacological inhibition of sildenafil-sensitive PDE5 downregulates the Ca2+signaling pathway involved in this model of pulmonary hypertension.

Analysis of the effects of phosphodiesterase type 3 and 4 inhibitors in cerebral arteries

Inhibitors of phosphodiesterases 3 and 4, the main cyclic AMP (cAMP) degrading enzymes in arteries, may have therapeutic potential in cerebrovascular disorders. We analysed the effects of such phosphodiesterases in guinea pig cerebral arteries with organ bath technique and cyclic nucleotide assays. Guinea pig and human cerebral arteries were used for phosphodiesterase assays. Cilostazol (6-[4-(1-cyclohexyl-1H-tetrazol-5-yl)butoxy]-3,4-dihydro-2(1H)-quinolinone), a phosphodiesterase 3 inhibitor, was compared to conventional phosphodiesterase 3 and 4 inhibitors. Phosphodiesterases 3 and 4 were the major contributors to total cAMP hydrolysis in the arteries examined. The phosphodiesterase 3 inhibitors additionally attenuated cyclic GMP (cGMP) hydrolysis, but relaxant responses were not dependent on an intact endothelium or on the nitric oxide-cGMP pathway. Conversely, the phosphodiesterase 4 inhibitor used was endothelium-dependent and affected by cGMP levels. This suggests that phosphodiesterase 3 inhibitors are still effective under conditions with possible dysfunctional nitric oxide-cGMP pathway, such as in ischemic stroke or cerebral vasospasm.

Cyclic AMP compartmentation due to increased cAMP-phosphodiesterase activity in transgenic mice with a cardiac-directed expression of the human adenylyl cyclase type 8 (AC8)

Hearts from AC8TG mice develop a higher contractility (LVSP) and larger Ca2+ transients than NTG mice, with (surprisingly) no modification in L-type Ca2+ channel current (ICa,L) (1). In this study, we examined the cardiac response of AC8TG mice to beta-adrenergic and muscarinic agonists and IBMX, a cyclic nucleotide phosphodiesterase (PDE) inhibitor. Stimulation of LVSP and ICa,L by isoprenaline (ISO, 100 nM) was twofold smaller in AC8TG vs. NTG mice. In contrast, IBMX (100 microM) produced a twofold higher stimulation of ICa,L in AC8TG vs. NTG mice. IBMX (10 microM) increased LVSP by 40% in both types of mice, but contraction and relaxation were hastened in AC8TG mice only. Carbachol (10 microM) had no effect on basal contractility in NTG hearts but decreased LVSP by 50% in AC8TG mice. PDE assays demonstrated an increase in cAMP-PDE activity in AC8TG hearts, mainly due to an increase in the hydrolytic activity of PDE4 and PDE1 toward cAMP and a decrease in the activity of PDE1 and PDE2 toward cGMP. We conclude that cardiac expression of AC8 is accompanied by a rearrangement of PDE isoforms, leading to a strong compartmentation of the cAMP signal that shields L-type Ca2+ channels and protects the cardiomyocytes from Ca2+ overload.

Effect of sildenafil on cyclic nucleotide phosphodiesterase activity, vascular tone and calcium signaling in rat pulmonary artery

(1) Sildenafil (viagra) is a potent PDE5 inhibitor and thus a relaxant drug in corpus carvernosum smooth muscle. In the present work, we evidenced the presence of PDE5 isozyme and investigated the effect of sildenafil on the specific cyclic nucleotide phosphodiesterase (PDE) activity, smooth muscle tone and calcium signaling in the rat main pulmonary artery (MPA). (2) The PDE activity was measured in cytosolic and microsomal fractions. Total cAMP and cGMP-PDE activities were mainly present in the cytosolic fraction. Sildenafil (0.1 micro M) reduced by 72% cGMP-PDE activity, whereas zaprinast (10 micro M), a relatively selective PDE5 inhibitor, reduced this activity by 63%. Sildenafil (0.1 micro M) also inhibited significantly (22%) the cAMP-PDE activity. (3) Western blot analysis revealed the expression of PDE5 mainly in the cytosolic fraction of MPA. Sildenafil concentration-dependently inhibited (IC(50)=3.4 nM) the activity of MPA PDE5 partially purified by HPLC. (4) Sildenafil (0.1 nM-50 micro M) concentration-dependently relaxed MPA rings precontracted with phenylephrine (0.5 micro M). The potency of sildenafil (IC(50)=11 nM) was similar to that of a nitric oxide donor, sodium nitroprusside, but higher than that of zaprinast (IC(50)=600 nM). The vasorelaxant effect of sildenafil was not altered by endothelium removal or in the presence of KT 5823 (1 micro M) and H89 (1 micro M), potent inhibitors of PKG and PKA, respectively. (5) In isolated MPA myocytes, which had been loaded with the calcium fluorophore indo-1, sildenafil (10-100 nM) antagonized ATP- and endothelin-1-induced calcium oscillations but had no effect on the transient caffeine-induced [Ca(2+)](i) response. (6) This study demonstrates the presence of a functional and highly sildenafil-sensitive PDE5 isozyme in rat MPA. Inhibition of this isozyme mainly accounts for the potent pulmonary vasodilator action of sildenafil, which involves alteration in the inositol triphosphate-mediated calcium signaling pathway.

The phosphodiesterase 5 inhibitor sildenafil has no effect on cerebral blood flow or blood velocity, but nevertheless induces headache in healthy subjects

Cyclic nucleotides are important hemodynamic regulators in many tissues. Glyceryl trinitrate markedly dilates large cerebral arteries and increases cGMP. Here, the authors study the effect of sildenafil, a selective inhibitor of cGMP-hydrolyzing phosphodiesterase 5 on cerebral hemodynamics and headache induction. Ten healthy subjects were included in a double-blind, placebo-controlled crossover study where placebo or sildenafil 100 mg (highest therapeutic dose) were administered on two separate days. Blood velocity in the middle cerebral artery (Vmca) was recorded by transcranial Doppler, and regional cerebral blood flow in the perfusion area of the middle cerebral artery (rCBFmca) was measured using single photon emission computed tomography and xenon inhalation. Radial and temporal artery diameters were studied using high-frequency ultrasound. Blood pressure and heart rate were recorded repeatedly. Headache responses and tenderness of pericranial muscles were scored verbally. Sildenafil caused no significant changes in rCBFmca, Vmca, or in temporal or radial artery diameter, but heart rate increased and diastolic blood pressure decreased significantly compared to placebo. Despite the lack of cerebral arterial dilatation, sildenafil caused significantly more headache than placebo. The present results show that sildenafil 100 mg does not dilate cerebral or extracerebral arteries but nevertheless causes headache, which may be attributed to nonvascular mechanisms.

Characterisation of cyclic nucleotide phosphodiesterase isoforms in the media layer of the main pulmonary artery

Cyclic nucleotides are involved in the control of pulmonary vascular tone. In the present study, we measured the cyclic nucleotide specific phosphodiesterase (PDE) activity in the media of bovine isolated main pulmonary artery (MPA). Total cAMP- and cGMP-PDE activities were measured in microsomal and cytosolic fractions. Both cyclic nucleotides were hydrolysed in these subcellular fractions at consistently higher rate in the cytosolic than in the microsomal fraction. Using different classes of PDE modulator, at least four PDE isoforms (PDE1, 3, 4 and 5) were identified in these fractions. PDE3 (cilostamide-sensitive), PDE4 (rolipram-sensitive) and PDE5 (zaprinast- and DMPPO-sensitive) isoforms appeared as the main isozymes implicated in the cAMP and cGMP hydrolytic activities. Calcium-camodulin stimulated PDE activity (PDE1) was mainly present in the cytosolic fraction. PDE2, although present, had a lower hydrolytic activity since addition of its specific inhibitor, erythro-9-(2-hydroxy-3nonyl)adenine (EHNA), to a combination of inhibitors of PDE3, 4 and 5 produced no further significant reduction in the enzymatic activity. Resolution of PDE activities from the cytosolic fraction using anion exchange chromatography confirmed this finding. Functional experiments performed in endothelium-denuded rings of rat MPA revealed that all specific PDE inhibitors used relaxed precontracted vascular smooth muscle preparations in a concentration-dependent manner. The rank order of potency was cilostamide >zaprinast>rolipram>>EHNA. The present study demonstrates the presence in the smooth muscle cells-containing layer of MPA of PDE1, 3, 4 and 5 isoforms and suggests that PDE3, 4 and 5 are the main enzymes involved in the control of vascular tone.

Expression and role of phosphodiesterase 6 in the chicken pineal gland

The chicken pineal gland is directly photosensitive, with light causing an inhibition of melatonin synthesis. A possible role of phosphodiesterase 6 (PDE6, the primary effector of retinal phototransduction) in mediating this response was investigated. RT-PCR, DNA sequencing and northern blots revealed the presence of RNA encoding both catalytic and regulatory subunits of PDE6 in the chicken pineal gland. Both rod and cone forms of PDE6 subunits mRNA were detected. The concentration of the transcripts encoding PDE6 catalytic subunits peaked at night. Western blot analysis of chicken pineal proteins with an antibody directed against the catalytic subunits of bovine rod PDE6 identified a single immunoreactive protein of 97 kDa. Anion exchange chromatography of chicken pineal soluble proteins revealed a peak of PDE6 activity that accounted for about 30% of cyclic GMP-hydrolysis. In cultured chick pineal glands, arylalkylamine N-acetyltransferase (AA-NAT), the rate-limiting enzyme of melatonin synthesis, was protected from inhibition by light when selective PDE5/6 inhibitors (zaprinast, DMPPO) were added to the culture medium. PDE5/6 inhibitors did not affect AA-NAT activity in the dark. In contrast, a general PDE inhibitor (IBMX) increased AA-NAT in a light-independent manner. Together, the data indicate that rod and cone forms of PDE6 are expressed in chick pineal cells and that this enzyme plays a role in the inhibition of melatonin synthesis by light.

Cyclic GMP regulation of the L-type Ca(2+) channel current in human atrial myocytes

1. The regulation of the L-type Ca(2+) current (I(Ca)) by intracellular cGMP was investigated in human atrial myocytes using the whole-cell patch-clamp technique. 2. Intracellular application of 0.5 microM cGMP produced a strong stimulation of basal I(Ca) (+64 +/- 5 %, n = 60), whereas a 10-fold higher cGMP concentration induced a 2-fold smaller increase (+36 +/- 8 %, n = 35). 3. The biphasic response of I(Ca) to cGMP was not mimicked by the cGMP-dependent protein kinase (PKG) activator 8-bromoguanosine 3',5' cyclic monophosphate (8-bromo-cGMP, 0.5 or 5 microM), and was not affected by the PKG inhibitor KT 5823 (100 nM). 4. In contrast, cGMP stimulation of I(Ca) was abolished by intracellular perfusion with PKI (10 microM), a selective inhibitor of the cAMP-dependent protein kinase (PKA). 5. Selective inhibition of the cGMP-inhibited phosphodiesterase (PDE3) by extracellular cilostamide (100 nM) strongly enhanced basal I(Ca) in control conditions (+78 +/- 13 %, n = 7) but had only a marginal effect in the presence of intracellular cGMP (+22 +/- 7 % in addition to 0.5 microM cGMP, n = 11; +20 +/- 22 % in addition to 5 microM cGMP, n = 7). 6. Application of erythro-9-[2-hydroxy-3-nonyl]adenine (EHNA, 30 microM), a selective inhibitor of the cGMP-stimulated phosphodiesterase (PDE2), fully reversed the secondary inhibitory effect of 5 microM cGMP on I(Ca) (+99 +/- 16 % stimulation, n = 7). 7. Altogether, these data indicate that intracellular cGMP regulates basal I(Ca) in human atrial myocytes in a similar manner to NO donors. The effect of cGMP involves modulation of the cAMP level and PKA activity via opposite actions of the nucleotide on PDE2 and PDE3.

The role of cGMP hydrolysing phosphodiesterases 1 and 5 in cerebral artery dilatation

The aim was to investigate the presence and activity of cGMP hydrolysing phosphodiesterases in guinea pig basilar arteries and the effect of selective and non-selective phosphodiesterase inhibitors on cerebral artery dilatation involving the nitric oxide (NO)-guanosine cyclic 3'5-monophosphate (cGMP) pathway. Immunoreactivity to phosphodiesterases 1A, 1B and 5, but not phosphodiesterase 1C was found in fractions of homogenised cerebral arteries eluted by high-pressure liquid chromatography (HPLC). Both the phosphodiesterase 1 inhibitor 8-methoxymethyl-1-methyl-3-(2methylpropyl)-xanthine (8-MM-IBMX) and the phosphodiesterase 5 inhibitors zaprinast and dipyridamole induced dilatation of cerebral arteries. The dilatory response to 8-MM-IBMX was reduced by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10 microM) and endothelial removal and restored by sodium nitroprusside (0.1 microM) pretreatment, indicating a close relation to the nitric oxide-cGMP pathway. The responses to zaprinast and dipyridamole, however, were not only moderately affected, but also restored by sodium nitroprusside (0.1 microM) pretreatment. At high concentrations, the dilatory effects of zaprinast and dipyridamole were partly caused by cGMP-independent mechanisms. Targeting the phosphodiesterases present in cerebral arteries, with selective inhibitors or activators of phosphodiesterase, may be a possible new way of treating cerebrovascular disease.

Expression of different phosphodiesterase genes in human cavernous smooth muscle

PURPOSE

Knowledge of intracellular signal propagation in smooth muscle tone regulation is of major importance in the understanding of the physiology of penile erection, and the development of new and selective pharmacological agents for the treatment of related disorders. Since phosphodiesterases (PDE) are key enzymes of the signaling pathway, we elucidate their presence and potential functional relevance in human cavernous tissue.

MATERIALS AND METHODS

To identify PDE messenger RNA in human cavernous tissue, we constructed primers for 14 published PDE isoforms. Expression of the genes was then analyzed by reverse transcriptase polymerase chain reaction under standard conditions and by subsequent sequencing.

RESULTS

Messenger RNA was detected in human corpus cavernosum for the human phosphodiesterase isoenzymes and isoforms PDE1A, PDE1B, PDE1C, PDE2A, PDE3A, PDE4A, PDE4B, PDE4C, PDE4D, PDE5A, PDE7A, PDE8A and PDE9A.

CONCLUSIONS

A total of 13 PDE genes were expressed in human cavernous tissue, indicating a role of these enzymes in penile erection regulation. The intracellular mechanisms of hydrolyzing cyclic adenosine monophosphate and cyclic guanosine monophosphate by PDEs are more complex than assumed previously. These findings open up new possibilities in the development of drugs for the treatment of erectile dysfunction.

Role of cGMP-inhibited phosphodiesterase and sarcoplasmic calcium in mediating the increase in basal heart rate with nitric oxide donors

Nitric oxide (NO) donors increase heart rate (HR) through a guanylyl cyclase-dependent stimulation of the pacemaker current I(f), without affecting basal I(Ca-L). The activity of I(f)is known to be enhanced by cyclic nucleotides and by an increase in cytosolic Ca(2+). We examined the role of cGMP-dependent signaling pathways and intracellular Ca(2+)stores in mediating the positive chronotropic effect of NO donors. In isolated guinea pig atria, the increase in HR in response to 1-100 micromol/l 3-morpholino-sydnonimine (SIN-1; with superoxide dismutase, n=6) or diethylamine-NO (DEA-NO, n=8) was significantly attenuated by blockers of the cGMP-inhibited phosphodiesterase (PDE3; trequinsin, milrinone or Ro-13-6438, n=22). In addition, the rate response to DEA-NO or sodium nitroprusside (SNP) was significantly reduced following inhibition of PKA (KT5720 or H-89, n=15) but not PKG (KT5728 or Rp-8-pCPT-cGMPs, n=16). Suppression of sarcoplasmic (SR) Ca(2+)release by pretreatment of isolated atria with ryanodine or cyclopiazonic acid (2 micromol/l and 60 micromol/l, n=16) significantly reduced the chronotropic response to 1-100 micromol/l SIN-1 or DEA-NO. Moreover, in isolated guinea pig sinoatrial node cells 5 micromol/l SNP significantly increased diastolic and peak Ca(2+)fluorescence (+13+/-1% and +28+/-1%, n=6, P<0.05). Our findings are consistent with a functionally significant role of cAMP/PKA signaling (via cGMP inhibition of PDE3) and SR Ca(2+)in mediating the positive chronotropic effect of NO donors.

Adenosine A(2A) and A(2B) receptors mediated nitric oxide production in coronary artery endothelial cells

The present study further examined the functional presence and the signal transduction mechanism(s) for adenosine A(2A) and A(2B) receptors through nitric oxide (NO) and the guanosine 3', 5'-cyclic monophosphate (cGMP) pathway in cultured porcine coronary artery endothelial cells (PCAEC). The application of adenosine receptor agonists, NECA, CGS-21680 and CAD between 10(-7) and 10(-4) M, enhanced the production of NO (measured as nitrite) in a dose-dependent manner. On the basis of EC(50) values, these agonists showed the following order of potency: NECA>CGS-21680>CAD. This order appears to be of the A(2) adenosine receptor subtype. Similarly, the same concentrations of adenosine agonists evoked the production of cGMP in a dose-dependent manner, exhibiting a rank order that is similar to that of NO production. NO synthase inhibitor, N-nitro-L-arginine methylester (L-NAME, 10(-5) M), inhibited the production of NO and cGMP, which was reversed by L-arginine (10(-4) M). Selective A(2A) adenosine receptor antagonists, ZM-241385 and SCH-58261, at 10(-7) M, significantly inhibited the effects of CGS-21680, but only partly inhibited the effect of NECA on NO and cGMP production. Along with the earlier molecular evidence from this laboratory [Am. J. Physiol. 279 (2000) H650], the present data further support the presence of both A(2A) and A(2B) receptors in PCAEC. These results further support that coronary endothelial cells express functional A(2A) and A(2B) adenosine receptors, leading to GMP production through the NO-synthase-linked mechanism. This is the first direct evidence where an A(2B) adenosine receptor has been linked to NO production in cultured endothelial cells and could play a role in coronary artery physiology and pathophysiology.

Characterization of cyclic nucleotide phosphodiesterase isoforms associated to isolated cardiac nuclei

The identity and location of nuclear cyclic nucleotide phosphodiesterases (PDE) has yet to be ascertained. Intact cardiac nuclei and subnuclear fractions from ovine hearts were isolated to determine cAMP-specific PDE activity which was 3-fold greater than that of cGMP PDE, the latter being insensitive to Ca-calmodulin and zaprinast. Specific hydrolytic activities of the cardiac nuclear envelopes (NE) were similar to those measured in the corresponding intact nuclei, thus suggesting that most PDE activity is associated with the nuclear membrane. Moreover, the main hydrolytic activities in cardiac nuclei were attributed to PDE4 (56%) and PDE3 (44%). The pharmacological sensitivity of each isoform in terms of IC(50), K(m) and K(i) values was typical of previously characterized cardiac PDE 3 and 4 isoforms. PDE2 (cGMP-stimulated PDE) represented a minor component (8-9%) of total hydrolytic activity. Solubilization of nuclear envelopes and HPLC separation also yielded rolipram-sensitive PDE activities. Upon 1% Triton X-100 extractions, the presence of PDE3 and PDE4 was revealed in a low speed, nucleopore complex-enriched, P1 pellet. In addition, Western blot analysis demonstrated the presence of PDE4B and PDE4D subtypes in the nuclei as well as enrichment in NE. However, in the same preparations, the presence of PDE4A could not be ascertained. Altogether, these results suggest an intrinsic and predominant association of these nuclear PDEs with the NE and much likely with nucleopore complexes.

Comparative involvement of cyclic nucleotide phosphodiesterases and adenylyl cyclase on adrenocorticotropin-induced increase of cyclic adenosine monophosphate in rat and human glomerulosa cells

The present study investigated the role and identity of cyclic nucleotide phosphodiesterases (PDEs) in the regulation of basal and ACTH-stimulated levels of intracellular cAMP in human and rat adrenal glomerulosa cells. Comparative dose-response curves indicated that maximal hormone-stimulated cAMP accumulation was 11- and 24-fold higher in human and rat cells, compared with cAMP production obtained in corresponding membranes, respectively. Similarly to 3-isobutyl-1-methyl-xanthine, 25 microM erythro-9-[2-hydroxy-3-nonyl]adenine (EHNA, a specific PDE2 inhibitor), caused a large increase in ACTH-stimulated cAMP accumulation; by contrast, it did not change cAMP production in membranes. Moreover, in membrane fractions, addition of 10 microM cGMP inhibited ACTH-induced cAMP production, an effect completely reversed by addition of 25 microM EHNA. These results indicate that PDE2 activity is involved in the regulation of cAMP accumulation induced by ACTH, and suggest that ACTH inhibits this activity. Indeed, time-course studies indicated that ACTH induced a rapid decrease in cGMP production, resulting in PDE2 inhibition, which in turn, contributed [with adenylyl cyclase (AC) activation] to an accumulation in cAMP for 15 min. Thereafter, cAMP content decreased, because of cAMP-stimulated PDE2, as confirmed by measurement of PDE activity that was activated by ACTH, but only after a 10-min incubation. Hence, we demonstrate that the ACTH-induced increase in intracellular cAMP is the result of a balance between activation of AC and direct modulation of PDE2 activity, an effect mediated by cGMP content. Although similar results were observed in both models, PDE2 involvement is more important in rat than in human adrenal glomerulosa cells, whereas AC is more stimulated in human than in rat glomerulosa cells.

Molecular biological characterization of phosphodiesterase 3A from human corpus cavernosum

The hydrolysis of the second messenger cyclic AMP (cAMP) by phosphodiesterase 3 (PDE3) is known to play an important regulatory role in the context of relaxation of cavernous smooth muscle of the penis. Thus, we investigated the PDE3A isoform from penile cavernous tissues of male patients with and without symptoms of erectile dysfunction at the molecular biological level. As revealed by reverse transcriptase polymerase chain reaction, of all tissues of the urogenital tract analyzed the expression of the PDE3A gene was highest in the corpus cavernosum. However, significant differences in the levels of gene expression were not found between the two subgroups of patients. Also, the determined nucleotide sequences of the cloned penile PDE3A cDNAs of all patients were absolutely identical. Surprisingly, some deviations could be detected in the cDNA sequences of PDE3A from human myocard and platelets. The data obtained indicate that neither the expression levels nor the sequence deviations of PDE3A are the main reasons for erectile dysfunction in men.

Characterization of the cyclic nucleotide phosphodiesterase subtypes involved in the regulation of the L-type Ca2+ current in rat ventricular myocytes

The effects of several phosphodiesterase (PDE) inhibitors on the L-type Ca current (I(Ca)) and intracellular cyclic AMP concentration ([cAMP]i) were examined in isolated rat ventricular myocytes. The presence of mRNA transcripts encoding for the different cardiac PDE subtypes was confirmed by RT-PCR. IBMX (100 microM), a broad-spectrum PDE inhibitor, increased basal I(Ca) by 120% and [cAMP]i by 70%, similarly to a saturating concentration of the beta-adrenoceptor agonist isoprenaline (1 microM). However, MIMX (1 microM), a PDE1 inhibitor, EHNA (10 microM), a PDE2 inhibitor, cilostamide (0.1 microM), a PDE3 inhibitor, or Ro20-1724 (0.1 microM), a PDE4 inhibitor, had no effect on basal I(Ca) and little stimulatory effects on [cAMP]i (20-30%). Each selective PDE inhibitor was then tested in the presence of another inhibitor to examine whether a concomitant inhibition of two PDE subtypes had any effect on I(Ca) or [cAMP]i. While all combinations tested significantly increased [cAMP]i (40-50%), only cilostamide (0.1 microM)+ Ro20-1724 (0.1 microM) produced a significant stimulation of I(Ca) (50%). Addition of EHNA (10 microM) to this mix increased I(Ca) to 110% and [cAMP]i to 70% above basal, i.e. to similar levels as obtained with IBMX (100 microM) or isoprenaline (1 microM). When tested on top of a sub-maximal concentration of isoprenaline (1 nM), which increased I(Ca) by (approximately 40% and had negligible effect on [cAMP]i, each selective PDE inhibitor induced a clear stimulation of [cAMP]i and an additional increase in I(Ca). Maximal effects on I(Ca) were approximately 8% for MIMX (3 microM), approximately 20% for EHNA (1-3 microM), approximately 30% for cilostamide (0.3-1 microM) and approximately 50% for Ro20-1724 (0.1 microM). Our results demonstrate that PDE1-4 subtypes regulate I(Ca) in rat ventricular myocytes. While PDE3 and PDE4 are the dominant PDE subtypes involved in the regulation of basal I(Ca), all four PDE subtypes determine the response of I(Ca) to a stimulus activating cyclic AMP production, with the rank order of potency PDE4>PDE3>PDE2>PDE1.

Inhibitory effects of rolipram on partially purified phosphodiesterase 4 from rat brains

Several previous studies have demonstrated that the phosphodiesterase 4 selective inhibitor rolipram affects cellular function at a much lower concentration than the reported Ki value for phosphodiesterase 4 inhibition. In this study, we examined the inhibitory effect of rolipram on rat brain phosphodiesterase 4 to determine the heterogeneity of the enzyme activity. Partial purification of various phosphodiesterases from the rat brain was performed by anion-exchange chromatography. The eluant was pooled into four fractions, two of which manifested cAMP-selective phosphodiesterase activity that was blocked by 10 microM of rolipram, indicating the presence of phosphodiesterase 4 in these fractions. The IC50 of rolipram (racemate) of these two fractions was 492 and 79 nM, respectively. The R-(-)-enantiomer of rolipram inhibited the cAMP-phosphodiesterase activity in the latter fraction 10 times more than did S-(+)-rolipram, and the inhibition of the former fraction was less stereospecific. Dixon plot analysis revealed that the rolipram enantiomers inhibited the cAMP-phosphodiesterase in the latter fraction in a multiphasic manner, with two Ki values, one at the micromolar level and the other at the sub-micromolar level, respectively, for both of the enantiomers. These results suggest that there is a heterogeneity for phosphodiesterase 4 in the rat brain, and some of the phosphodiesterase forms are sensitive to rolipram.

Phosphodiesterase type 4 that regulates cAMP level in cortical neurons shows high sensitivity to rolipram

To characterize the role of phosphodiesterase type 4 (a cAMP-specific and rolipram-sensitive phosphodiesterase) among phosphodiesterases in the regulation of the intracellular cAMP level in cortical neurons, we investigated the effects of phosphodiesterase inhibitors on the intracellular cAMP levels in primary cultured rat cortical neurons. Selective inhibitors of phosphodiesterase type 4 and type 2 significantly enhanced beta-adrenoceptor-mediated cAMP increase. Selective inhibitors of phosphodiesterase type 1, type 3 and type 5/6 had no effect on the cAMP level. Rolipram enhanced the beta-adrenoceptor-mediated cAMP increase in cortical neurons, astrocytes and vascular smooth muscle cells at different minimum effective concentrations (10, 100 and 1000 nM, respectively). These findings indicate that phosphodiesterase type 4, showing a high-sensitivity to rolipram, plays a major role in regulating cAMP in the cortical neurons, and that rolipram at low doses enhances the intracellular cAMP increase in the cortical neurons selectively.

Muscarinic regulation of the L-type calcium current in isolated cardiac myocytes

Muscarinic agonists regulate the L-type calcium current in isolated cardiac myocytes. The second messengers pathways involved in this regulation are discussed briefly, with particular emphasis on the involvement of cAMP and cGMP pathways.