Novel alternative splice variants of cGMP-binding cGMP-specific phosphodiesterase

Bifunctional Sildenafil Diazeniumdiolates Acting as Phosphodiesterase 5 Inhibitors and Nitric Oxide Donors- Towards Wound Healing

Inefficient wound healing poses a global health challenge with a lack of efficient treatments. Wound healing issues often correlate with low endogenous nitric oxide (NO) levels. While exogenous delivery with NO-releasing compounds represents a promising therapeutic strategy, controlling the release of the highly reactive NO remains challenging. Phosphodiesterase 5 (PDE5) inhibitors, like sildenafil, have also been shown to promote wound healing. This study explores hybrid compounds, combining NO-releasing diazeniumdiolates with a sildenafil-derived PDE5 inhibitor. One compound demonstrated a favorable NO-release profile, triggered by an esterase (prodrug), and displayed in vitro nanomolar inhibition potency against PDE5 and thrombin-induced platelet aggregation. Both factors are known to promote blood flow and oxygenation. Thus, our findings unveil promising prospects for effective wound healing treatments.

PDE-Mediated Cyclic Nucleotide Compartmentation in Vascular Smooth Muscle Cells: From Basic to a Clinical Perspective

Cardiovascular diseases are important causes of mortality and morbidity worldwide. Vascular smooth muscle cells (SMCs) are major components of blood vessels and are involved in physiologic and pathophysiologic conditions. In healthy vessels, vascular SMCs contribute to vasotone and regulate blood flow by cyclic nucleotide intracellular pathways. However, vascular SMCs lose their contractile phenotype under pathological conditions and alter contractility or signalling mechanisms, including cyclic nucleotide compartmentation. In the present review, we focus on compartmentalized signaling of cyclic nucleotides in vascular smooth muscle. A deeper understanding of these mechanisms clarifies the most relevant axes for the regulation of vascular tone. Furthermore, this allows the detection of possible changes associated with pathological processes, which may be of help for the discovery of novel drugs.

The Role of PDE8 in T Cell Recruitment and Function in Inflammation

Inhibitors targeting cyclic nucleotide phosphodiesterases (PDEs) expressed in leukocytes have entered clinical practice to treat inflammatory disorders, with three PDE4 inhibitors currently in clinical use as therapeutics for psoriasis, psoriatic arthritis, atopic dermatitis and chronic obstructive pulmonary disease. In contrast, the PDE8 family that is upregulated in pro-inflammatory T cells is a largely unexplored therapeutic target. It was shown that PDE8A plays a major role in controlling T cell and breast cancer cell motility, including adhesion to endothelial cells under physiological shear stress and chemotaxis. This is a unique function of PDE8 not shared by PDE4, another cAMP specific PDE, employed, as noted, as an anti-inflammatory therapeutic. Additionally, a regulatory role was shown for the PDE8A-rapidly accelerated fibrosarcoma (Raf)-1 kinase signaling complex in myelin antigen reactive CD4⁺ effector T cell adhesion and locomotion by a mechanism differing from that of PDE4. The PDE8A-Raf-1 kinase signaling complex affects T cell motility, at least in part, via regulating the LFA-1 integrin mediated adhesion to ICAM-1. The findings that PDE8A and its isoforms are expressed at higher levels in naive and myelin oligodendrocyte glycoprotein (MOG)_35–55 activated effector T (Teff) cells compared to regulatory T (Treg) cells and that PDE8 inhibition specifically affects MOG_35–55 activated Teff cell adhesion, indicates that PDE8A could represent a new beneficial target expressed in pathogenic Teff cells in CNS inflammation. The implications of this work for targeting PDE8 in inflammation will be discussed in this review.

Identification of murine phosphodiesterase 5A isoforms and their functional characterization in HL-1 cardiac cell line

Phosphodiesterase 5A (PDE5A) specifically degrades the ubiquitous second messenger cGMP and experimental and clinical data highlight its important role in cardiac diseases. To address PDE5A role in cardiac physiology, three splice variants of the PDE5A were cloned for the first time from mouse cDNA library (mPde5a1, mPde5a2, and mPde5a3). The predicted amino acidic sequences of the three murine isoforms are different in the N-terminal regulatory domain. mPDE5A isoforms were transfected in HEK293T cells and they showed high affinity for cGMP and similar sensitivity to sildenafil inhibition. RT-PCR analysis showed that mPde5a1, mPde5a2, and mPde5a3 had differential tissue distribution. In the adult heart, mPde5a1 and mPde5a2 were expressed at different levels whereas mPde5a3 was undetectable. Overexpression of mPDE5As induced an increase of HL-1 number cells which progress into cell cycle. mPDE5A1 and mPDE5A3 overexpression increased the number of polyploid and binucleated cells, mPDE5A3 widened HL-1 areas, and modulated hypertrophic markers more efficiently respect to the other mPDE5A isoforms. Moreover, mPDE5A isoforms had differential subcellular localization: mPDE5A1 was mainly localized in the cytoplasm, mPDE5A2 and mPDE5A3 were also nuclear localized. These results demonstrate for the first time the existence of three PDE5A isoforms in mouse and highlight their potential role in the induction of hypertrophy.

Design of novel β-carboline derivatives with pendant 5-bromothienyl and their evaluation as phosphodiesterase-5 inhibitors

New derivatives with the tetrahydro-β-carboline-imidazolidinedione and tetrahydro-β-carboline-piperazinedione scaffolds and a pendant bromothienyl moiety at C-5/C-6 were synthesized and tested for their ability to inhibit PDE5 in vitro. The following SAR can be concluded: The tetracyclic scaffold is essential for PDE5 inhibition; the ethyl group is the most suitable among the adopted N-substituents on the terminal ring (hydantoin/piperazinedione); the appropriate stereochemistry of C-5/C-6 derived from the aldehyde rather than C-11a/C-12a derived from tryptophan appears crucial for inhibition of PDE5; surprisingly, derivatives with the hydantoin terminal ring are more active than their analogs with the piperazinedione ring; the selectivity versus PDE5 relative to PDE11 with cGMP as a substrate is mainly a function of the substitution and stereochemistry pattern of the external ring, in other words of the interaction with the H-loop residues of the isozymes. Thirteen derivatives showed PDE5 inhibitory activity with IC(50) values in the range of 0.16-5.4 µm. Compound 8 was the most potent PDE5 inhibitor and showed selectivity towards PDE5 versus other PDEs, with a selectivity index of 49 towards PDE5 rather than PDE11 with cGMP as the substrate.

Identification of cytosolic phosphodiesterases in the erythrocyte: a possible role for PDE5

Background

Within erythrocytes (RBCs), cAMP levels are regulated by phosphodiesterases (PDEs). Increases in cAMP and ATP release associated with activation of β-adrenergic receptors (βARs) and prostacyclin receptors (IPRs) are regulated by PDEs 2, 4 and PDE 3, respectively. Here we establish the presence of cytosolic PDEs in RBCs and determine a role for PDE5 in regulating levels of cGMP.

Material/Methods

Purified cytosolic proteins were obtained from isolated human RBCs and western analysis was performed using antibodies against PDEs 3A, 4 and 5. Rabbit RBCs were incubated with dbcGMP, a cGMP analog, to determine the effect of cGMP on cAMP levels. To determine if cGMP affects receptor-mediated increases in cAMP, rabbit RBCs were incubated with dbcGMP prior to addition of isoproterenol (ISO), a βAR receptor agonist. To demonstrate that endogenous cGMP produces the same effect, rabbit and human RBCs were incubated with SpNONOate (SpNO), a nitric oxide donor, and YC1, a direct activator of soluble guanylyl cyclase (sGC), in the absence and presence of a selective PDE5 inhibitor, zaprinast (ZAP).

Results

Western analysis identified PDEs 3A, 4D and 5A. dbcGMP produced a concentration dependent increase in cAMP and ISO-induced increases in cAMP were potentiated by dbcGMP. In addition, incubation with YC1 and SpNO in the presence of ZAP potentiated βAR-induced increases in cAMP.

Conclusions

PDEs 2, 3A and 5 are present in the cytosol of human RBCs. PDE5 activity in RBCs regulates cGMP levels. Increases in intracellular cGMP augment cAMP levels. These studies suggest a novel role for PDE5 in erythrocytes.

Feedback control through cGMP-dependent protein kinase contributes to differential regulation and compartmentation of cGMP in rat cardiac myocytes

RATIONALE

We have shown recently that particulate (pGC) and soluble guanylyl (sGC) cyclases synthesize cGMP in different compartments in adult rat ventricular myocytes (ARVMs).

OBJECTIVE

We hypothesized that cGMP-dependent protein kinase (PKG) exerts a feedback control on cGMP concentration contributing to its intracellular compartmentation.

METHODS AND RESULTS

Global cGMP levels, cGMP-phosphodiesterase (PDE) and pGC enzymatic activities were determined in purified ARVMs. Subsarcolemmal cGMP signals were monitored in single cells by recording the cGMP-gated current (I(CNG)) in myocytes expressing the wild-type rat olfactory cyclic nucleotide-gated (CNG) channel. Whereas the NO donor S-nitroso-N-acetyl-penicillamine (SNAP) (100 μmol/L) produced little effect on I(CNG), the response increased 2-fold in the presence of the PKG inhibitors KT5823 (50 nmol/L) or DT-2 (2 μmol/L). The effect of KT5823 was abolished in the presence of the nonselective cyclic nucleotide PDE inhibitor 3-isobutyl-1-methylxantine (IBMX) (100 μmol/L) or the selective cGMP-PDE5 inhibitor sildenafil (100 nmol/L). PKG inhibition also potentiated the effect of SNAP on global cGMP levels and fully blocked the increase in cGMP-PDE5 activity. In contrast, PKG inhibition decreased by ≈50% the I(CNG) response to ANP (10 and 100 nmol/L), even in the presence of IBMX. Conversely, PKG activation increased the I(CNG) response to ANP and amplified the stimulatory effect of ANP on pGC activity.

CONCLUSIONS

PKG activation in adult cardiomyocytes limits the accumulation of cGMP induced by NO donors via PDE5 stimulation but increases that induced by natriuretic peptides. These findings support the paradigm that cGMP is not uniformly distributed in the cytosol and identifies PKG as a key component in this process.

Phosphodiesterase 5 restricts NOS3/Soluble guanylate cyclase signaling to L-type Ca2+ current in cardiac myocytes

Endothelial nitric oxide synthase (NOS3) regulates the functional response to beta-adrenergic (beta-AR) stimulation via modulation of the L-type Ca(2+) current (I(Ca)). However, the NOS3 signaling pathway modulating I(Ca) is unknown. This study investigated the contribution of soluble guanylate cyclase (sGC) and phosphodiesterase type 5 (PDE5), a cGMP-specific PDE, in the NOS3-mediated regulation of I(Ca). Myocytes were isolated from NOS3 knockout (NOS3(-/-)) and wildtype (WT) mice. We measured I(Ca) (whole-cell voltage-clamp), and simultaneously measured Ca(2+) transients (Fluo-4 AM) and cell shortening (edge detection). Zaprinast (selective inhibitor of PDE5), decreased beta-AR stimulated (isoproterenol, ISO)-I(Ca), and Ca(2+) transient and cell shortening amplitudes in WT myocytes. However, YC-1 (NO-independent activator of sGC) only reduced ISO-stimulated I(Ca), but not cardiac contraction. We further investigated the NOS3/sGC/PDE5 pathway in NOS3(-/-) myocytes. PDE5 is mislocalized in these myocytes and we observed dissimilar effects of PDE5 inhibition and sGC activation compared to WT. That is, zaprinast had no effect on ISO-stimulated I(Ca), or Ca(2+) transient and cell shortening amplitudes. Conversely, YC-1 significantly decreased both ISO-stimulated I(Ca), and cardiac contraction. Further confirming that PDE5 localizes NOS3/cGMP signaling to I(Ca); YC-1, in the presence of zaprinast, now significantly decreased ISO-stimulated Ca(2+) transient and cell shortening amplitudes in WT myocytes. The effects of YC-1 on I(Ca) and cardiac contraction were blocked by KT5823 (a selective inhibitor of the cGMP-dependent protein kinase, PKG). Our data suggests a novel physiological role for PDE5 in restricting the effects of NOS3/sGC/PKG signaling pathway to modulating beta-AR stimulated I(Ca), while limiting effects on cardiac contraction.

ABCD of the phosphodiesterase family: interaction and differential activity in COPD

Phosphodiesterases (PDEs) are important enzymes that hydrolyze the cyclic nucleotides adenosine 3'5'-cyclic monophosphate (cAMP) and guanosine 3'5'-cyclic monophosphate (cGMP) to their inactive 5' monophosphates. They are highly conserved across species and as well as their role in signal termination, they also have a vital role in intra-cellular localization of cyclic nucleotide signaling and integration of the cyclic nucleotide pathways with other signaling pathways. Because of their pivotal role in intracellular signaling, they are now of considerable interest as therapeutic targets in a wide variety diseases, including COPD where PDE inhibitors may have bronchodilator, anti-inflammatory and pulmonary vasodilator actions. This review examines the diversity and cellular localization of the isoforms of PDE, the known and speculative relevance of this to the treatment of COPD, and the range of PDE inhibitors in development together with a discussion of their possible role in treating COPD.

Myocardial phosphodiesterases and regulation of cardiac contractility in health and cardiac disease

Phosphodiesterase (PDE) inhibitors are potent cardiotonic agents used for parenteral inotropic support in heart failure. Contractile effects of these agents are mediated through cAMP-protein kinase A-induced stimulation of I (Ca2+) which ultimately results in increased Ca(2+)-induced sarcoplasmic reticulum Ca(2+) release. A number of additional effects such as increases in sarcoplasmic reticulum Ca(2+) stores, stimulation of reverse mode Na(+)-Ca(2+) exchange, direct or cAMP-mediated effects on sarcoplasmic reticulum ryanodine receptor, stimulation of the voltage-sensitive sarcoplasmic reticulum Ca(2+) release mechanism, as well as A(1) adenosine receptor blockade could contribute to positive inotropic responses to PDE inhibitors. Moreover, some PDE inhibitors exhibit Ca(2+) sensitizer properties as they could increase the affinity of troponin C Ca(2+)-binding sites as well as reduce Ca(2+) threshold for thin myofilament sliding and facilitate cross-bridge cycling. Inotropic responses to PDE inhibitors are significantly reduced in cardiac disease, an effect largely attributed to downregulation of cAMP-mediated signalling due to sustained sympathetic activation. Four PDE isoenzymes (PDE1, PDE2, PDE3 and PDE4) are present in myocardial tissue of various mammalian species, of which PDE3 and PDE4 are particularly involved in regulation of cardiac myocyte contraction. PDE cAMP-hydrolysing activity is preserved in compensated cardiac hypertrophy but significantly reduced in animal models of heart failure. However, clinical studies have not revealed any changes in distribution profile as well as kinetic and regulatory properties of myocardial PDEs in failing human hearts. A reduction of PDE inhibitors-induced contractile responses in heart failure has therefore been ascribed to reduced cAMP synthesis due to uncoupling of adenylyl cyclase from beta-adrenoreceptor. In cardiac myocytes, PDEs are targeted to distinct subcellular compartments by scaffolding proteins such as myomegalin, mAKAP and beta-arrestins. Over subcellular microdomains, cAMP hydrolysis by PDE3 and PDE4 allows to control the activity of local pools of protein kinase A and therefore the extent of protein kinase A-mediated phosphorylation of cellular proteins.

The emerging role for type 5 phosphodiesterase inhibition in heart failure

Patients with heart failure (HF) due to left ventricular (LV) systolic dysfunction have abnormal endothelium-dependent, nitric oxide-cyclic guanosine monophosphate-mediated vasodilation in the pulmonary and skeletal muscle vasculature. Therefore, inhibition of type 5 phosphodiesterase (PDE5), the principle enzyme responsible for cyclic guanosine monophosphate catabolism in the lungs and skeletal muscle, has been targeted in an effort to counteract vasoconstriction that contributes to increased right and LV afterload in HF. The efficacy of PDE5 inhibition in the treatment of pulmonary arterial hypertension has led to the investigation of its potential utility in the treatment of HF patients with secondary pulmonary hypertension. Moreover, recent preclinical studies suggest direct myocardial effects of PDE5 inhibition that may counteract beta-adrenergic, hypertrophic, and pro-apoptotic signaling, three critical pathways in the development of LV dysfunction. This review outlines both the underlying rationale and the results of initial studies of the therapeutic effects of PDE5 inhibition in HF.

Compartmentation of cyclic nucleotide signaling in the heart: the role of cyclic nucleotide phosphodiesterases

A current challenge in cellular signaling is to decipher the complex intracellular spatiotemporal organization that any given cell type has developed to discriminate among different external stimuli acting via a common signaling pathway. This obviously applies to cAMP and cGMP signaling in the heart, where these cyclic nucleotides determine the regulation of cardiac function by many hormones and neuromediators. Recent studies have identified cyclic nucleotide phosphodiesterases as key actors in limiting the spread of cAMP and cGMP, and in shaping and organizing intracellular signaling microdomains. With this new role, phosphodiesterases have been promoted from the rank of a housekeeping attendant to that of an executive officer.

Phosphodiesterase-5 isoforms: differential cyclic guanyl monophosphate binding and cyclic guanyl monophosphate catalytic activities, and inhibitory effects of sildenafil and vardenafil

PURPOSE

We determined the differential cyclic guanyl monophosphate catalytic and cyclic guanyl monophosphate binding activity of phosphodiesterase-5 isoforms and the inhibitory effects of sildenafil (Pfizer, New York, New York) and vardenafil (Bayer Pharmaceutical Research, Wuppertal, Germany).

MATERIALS AND METHODS

Coding sequences of the human phosphodiesterase-5 isoforms A1, A2 and A3 were cloned into pBlueBac4.5/V5-His (Invitrogen, Carlsbad, California), which allows the tagging of histidines at the carboxyl terminal of the expressed protein. Isoforms were expressed with the Bac-N-Blue baculoviral system and purified with the ProBond system. Expression clones were identified by polymerase chain reaction using vector and phosphodiesterase-5 specific primers. Purified proteins were verified by Western blotting. Purified proteins were analyzed for cyclic guanyl monophosphate catalytic and cyclic guanyl monophosphate binding activity, and used to determine the differential potencies of the phosphodiesterase-5 selective inhibitors sildenafil and vardenafil.

RESULTS

Cloning and expression of phosphodiesterase-5A1 to A3 isoforms in the baculoviral system resulted in the isolation of purified isoform proteins. Mean cyclic guanyl monophosphate catalytic activity (K(m)) +/- SD was 4.76 +/- 0.37, 4.52 +/- 0.09 and 11.39 +/- 0.22 microM for A1 to A3, respectively. Mean cyclic guanyl monophosphate binding activity (K(d)) was 3.24 +/- 0.47, 1.95 +/- 0.60 and 1.70 +/- 0.47 microM for A1 to A3, respectively. Mean IC(50) of sildenafil against phosphodiesterase-5A1 to A3 was 1.20 +/- 0.34, 2.83 +/- 0.56 and 2.28 +/- 0.38 nM, respectively. Mean IC(50) of vardenafil against phosphodiesterase-5A1 to A3 was 0.41 +/- 0.15, 0.23 +/- 0.08 and 0.45 +/- 0.06 nM, respectively.

CONCLUSIONS

Phosphodiesterase-5A1 and A2 had similar K(m) values, while phosphodiesterase-5A3 had a much higher K(m) and, thus, lower cyclic guanyl monophosphate catalytic activity. Phosphodiesterase-5A2 and A3 had similar K(d) values, while phosphodiesterase-5A1 had higher K(d) and, thus, lower cyclic guanyl monophosphate binding activity. Vardenafil was more potent (3 to 12-fold) than sildenafil for inhibiting the catalytic activity of all 3 human phosphodiesterase-5 isoforms with phosphodiesterase-5A2 showing the highest differentiation (12-fold).

Cyclic guanosine monophosphate compartmentation in rat cardiac myocytes

BACKGROUND

Cyclic guanosine monophosphate (cGMP) is the common second messenger for the cardiovascular effects of nitric oxide (NO) and natriuretic peptides, such as atrial or brain natriuretic peptide, which activate the soluble and particulate forms of guanylyl cyclase, respectively. However, natriuretic peptides and NO donors exert different effects on cardiac and vascular smooth muscle function. We therefore tested whether these differences are due to an intracellular compartmentation of cGMP and evaluated the role of phosphodiesterase (PDE) subtypes in this process.

METHODS AND RESULTS

Subsarcolemmal cGMP signals were monitored in adult rat cardiomyocytes by expression of the rat olfactory cyclic nucleotide-gated (CNG) channel alpha-subunit and recording of the associated cGMP-gated current (ICNG). Atrial natriuretic peptide (10 nmol/L) or brain natriuretic peptide (10 nmol/L) induced a clear activation of ICNG, whereas NO donors (S-nitroso-N-acetyl-penicillamine, diethylamine NONOate, 3-morpholinosydnonimine, and spermine NO, all at 100 micromol/L) had little effect. The ICNG current was strongly potentiated by nonselective PDE inhibition with isobutyl methylxanthine (100 micromol/L) and by the PDE2 inhibitors erythro-9-(2-hydroxy-3-nonyl)adenine (10 micromol/L) and Bay 60-7550 (50 nmol/L). Surprisingly, sildenafil, a PDE5 inhibitor, produced a dose-dependent increase of I(CNG) activated by NO donors but had no effect (at 100 nmol/L) on the current elicited by atrial natriuretic peptide.

CONCLUSIONS

These results indicate that in rat cardiomyocytes (1) the particulate cGMP pool is readily accessible at the plasma membrane, whereas the soluble pool is not; and (2) PDE5 controls the soluble but not the particulate pool, whereas the latter is under the exclusive control of PDE2. Differential spatiotemporal distributions of cGMP may therefore contribute to the specific effects of natriuretic peptides and NO donors on cardiac function.

Cyclic nucleotide phosphodiesterases as targets for treatment of haematological malignancies

The cAMP signalling pathway has emerged as a key regulator of haematopoietic cell proliferation, differentiation and apoptosis. In parallel, general understanding of the biology of cyclic nucleotide PDEs (phosphodiesterases) has advanced considerably, revealing the remarkable complexity of this enzyme system that regulates the amplitude, kinetics and location of intracellular cAMP-mediated signalling. The development of therapeutic inhibitors of specific PDE gene families has resulted in a growing appreciation of the potential therapeutic application of PDE inhibitors to the treatment of immune-mediated illnesses and haematopoietic malignancies. This review summarizes the expression and function of PDEs in normal haematopoietic cells and the evidence that family-specific inhibitors will be therapeutically useful in myeloid and lymphoid malignancies.

Effect of sildenafil on gastric emptying in healthy adults

BACKGROUND AND AIM

Phosphodiesterase type 5 hydrolyzes and inactivates cyclic guanosine monophosphate produced by the nitric oxide-stimulated guanylate cyclase. Sildenafil is a potent, reversible, and highly selective inhibitor of this phosphodiesterase. It causes smooth muscle relaxation by increasing intracellular concentrations of cyclic guanosine monophosphate. The aim of this study was to test the hypothesis that sildenafil alters gastric emptying and the intragastric distribution of food in healthy adults.

METHODS

Nine normal subjects (mean age 28 years, range 25-33) were given a placebo or a tablet of sildenafil (50 mg) at different times along with radio-opaque markers. A gastric emptying scan was used to calculate the t(1/2) for gastric emptying (the time taken for the initial radioactivity to fall by 50%). Intragastric food distribution was also assessed using the gastric emptying scan to calculate proximal gastric emptying t(1/2), the proximal volume (the highest activity value in the proximal stomach at any time point in the study), and the distal volume (the highest activity value in the distal stomach at any time point in the study. Gastric emptying of an indigestible solid meal was assessed by calculating gastric clearance of radio-opaque markers.

RESULTS

Sildenafil did not change total gastric emptying or gastric clearance of radio-opaque markers. It shortened the proximal T(1/2), decreased proximal volume, and significantly increased distal volume.

CONCLUSION

Sildenafil alters the intragastric distribution of food rather than causing gastric stasis.

Intracellular targeting of phosphodiesterase-4 underpins compartmentalized cAMP signaling

The phosphodiesterase-4 (PDE4) enzyme belongs to a family of cAMP-dependent phosphodiesterases that provide the major means of hydrolyzing and, thereby, inactivating the key intracellular second messenger, cAMP. As such, PDE4s are central to the regulation of many diverse signaling processes that allow cells to respond to external stimuli. Four genes (4A, 4B, 4C, and 4D) encode around 20 distinct isoform members of the PDE4 family. Each isoform is characterized by a unique N-terminal region. PDE4s are multidomain metallohydrolases with each domain serving particular roles allowing them to be targeted to varying regions and organelles of intracellular space and regulated in distinct fashions by phosphorylation and protein-protein interaction. Although identical in catalytic function, each isoform locates to distinct regions within the cell so as to create and manage spatially distinct pools of cAMP. The multiplicity of partners associating with members of the four gene PDE4 family places these enzymes in key regulatory positions, permitting them to channel complex biological signals via fundamental signaling cohorts such as G-protein-coupled receptors (GPCRs), arrestins, A-kinase-anchoring proteins (AKAPs), and tyrosyl family kinases. The cAMP cascade has long been linked to cellular growth and embryogenesis and with this comes the implication that PDE4 may play considerable roles in the regulation of progeny development in maturing cells and tissues.

Type 5 phosphodiesterase inhibition in heart failure and pulmonary hypertension

The availability of selective inhibitors of the cyclic guanosine monophosphate (cGMP)-specific type 5 phosphodiesterase (PDE5) has created increasing interest in unlocking the therapeutic potential of PDE5 inhibition in cardiovascular diseases that are marked by dysfunction of nitric oxide (NO)-cGMP signaling. Pulmonary arterial hypertension (PAH) and heart failure (HF) are characterized by pulmonary arterial vasoconstriction that is thought to be caused by relative deficiencies of vasodilators such as NO and exaggerated production of vasoconstrictors such as endothelin. PDE5 is abundant in the pulmonary vasculature where it catabolizes cGMP, the second messenger of NO. Inhibition of PDE5 has been shown to lower pulmonary vascular resistance in PAH and HF by augmenting local cGMP. This review outlines the therapeutic potential of PDE5 inhibition for the treatment of PAH and HF.

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.

Cyclic GMP-specific phosphodiesterase 5 regulates growth and apoptosis in pulmonary endothelial cells

Sustained increases in intracellular cGMP concentrations ([cGMP]i) inhibit cell growth and induce apoptosis. We now report that a cGMP-specific phosphodiesterase, PDE5, plays a dominant role in regulating [cGMP]i transitions that inhibit cell growth and control susceptibility to apoptosis in pulmonary endothelium. Atrial natriuretic peptide (ANP) activates guanylyl cyclase A/B and induces a rapid [cGMP]i rise 2-5 min after its application, in both pulmonary arterial endothelial cells (PAECs) and pulmonary microvascular endothelial cells (PMVECs). However, increased [cGMP]i in PAECs is transient and decays within 10 min due to cytosolic PDE5 hydrolytic activity. Increased [cGMP]i in PMVECs is sustained for >3 h due to the absence of PDE5. Indeed, at any ANP concentration, the sustained (30 min) [cGMP]i rise is greater in PMVECs than in PAECs, unless PAECs are also treated with the PDE5 inhibitor zaprinast. Using RT-PCR, Western blot analysis, immunoprecipitation, and DEAE chromatography, we resolved the expression and activity of PDE 5A1/A2 only in PAECs. Similarly, PDE5 expression was restricted to extra-alveolar endothelium in vivo. ANP induced growth inhibition and apoptosis in PMVECs, but similar effects were not seen in PAECs unless ANP treatment was combined with zaprinast. ANP blocked the VEGF-induced proliferation and migration in PMVECs. Collectively, these data suggest that PDE5-regulated [cGMP]i controls endothelial cell growth and apoptosis, representing a mechanism of heterogeneity between two endothelial phenotypes.

The cGMP-binding, cGMP-specific phosphodiesterase (PDE5): intestinal cell expression, regulation and role in fluid secretion

The expression and regulation of the cGMP-binding, cGMP-specific phosphodiesterase, PDE5, was studied in intestinal cells. Both PDE5A1 and PDE5A2 splice forms were cloned from the cDNA prepared from human colonic T84 cells, and PDE5 activity was dependent on increases in intracellular cGMP levels which correlated with increased phosphorylation of the enzyme. PDE5 expression was monitored in different regions of the gastrointestinal tract and nearly 50% of the phosphodiesterase activity in the duodenum, jejunum, ileum and colon was inhibited by sildenafil citrate. Administration of the stable toxin to intestinal loops resulted in activation of PDE5. Inhibition of PDE5 by sildenafil citrate led to fluid accumulation in loops, suggesting a possible explanation for the side effect of diarrhoea observed in individuals administered sildenafil citrate. Our results therefore represent the first study on the expression and regulation of PDE5 in intestinal tissue, and indicate that mechanisms to control its activity may have important consequences in intestinal physiology.

Tissue expression, distribution, and regulation of PDE5

Phosphodiesterase 5 (PDE5) has been identified in many species. The three isoforms, PDE5A1, PDE5A2, and PDE5A3, differ only in their N-terminal sequence. PDE5A1 and PDE5A2 are ubiquitous, but PDE5A3 is specific to smooth muscle. The initial three exons (A1-A3-A2) of PDE5A, located on chromosome 4q26, are alternative first exons encoding the isoform-specific sequences. The PDE5A promoter overlaps with the A1-specific exon, while the PDE5A2 promoter is located between the A3- and A2-specific exons. Both respond to cyclic guanosine monophosphate (cGMP) or cyclic adenosine monophosphate (cAMP) stimulation. The PDE5A2 promoter contains an Sp1-binding sequence critical for basal and cGMP/cAMP-inducible promoter activities. PDE5A is induced by adjacent sequences (enhancers) containing Sp1-binding sites. The potential role of PDE5A promoters in the tachyphylaxis effect of PDE5 inhibitors is currently being investigated. Preliminary data suggest that hypoxia might down-regulate PDE5A promoters, implying an involvement of PDE5 in stuttering priapism.

Expression of PDE5 splice variants during ontogenesis of chick dorsal root ganglia

Cyclic GMP (cGMP)-binding cGMP-specific phosphodiesterase (PDE5) activity was found in chick dorsal root ganglia (DRG). PDE5 expression was studied at different stages of development: in embryonic day 10 (E10) and E18 embryos and in 5-day post-hatching chick (P5). The presence of PDE5 was suggested by the ion exchange chromatography elution profile in E18 DRG extracts, where cGMP-specific hydrolytic calmodulin-independent activity was found; in other stages, this activity coeluted with the PDE1 calmodulin-stimulated isoform characterized previously. Inhibition studies supported the hypothesis that the newly identified PDE activity belongs to the PDE5 isoform. Western blot analysis using a PDE5-specific antibody was also carried out and revealed the presence of three specific immunoreactive bands with apparent molecular weights of 98, 93, and 86 kDa, corresponding to the three described splice variants (PDE5A1, PDE5A2, and PDE5A3). The expression in DRG of the three PDE5 isoforms was also confirmed by RT-PCR. Developmental regulation of PDE5 was revealed by the immunoblot analysis at different stages; expression was very low at E10 but an overall substantial increase occurred between E10-18 (about 12-fold, considering the three PDE5 isoforms together). Differences were revealed, however, when a single PDE5 isoform was considered. PDE5A1 and PDE5A3 showed an increase at all stages although more pronounced between E10-18, whereas PDE5A2 underwent a marked increase (about 38-fold) in the first period and remained nearly constant between E18 and P5. This is the first evidence of PDE5 in sensory neurons, and the distinct temporal expression patterns of enzyme isoforms may indicate different physiologic roles in developing and mature chick DRG.

Selective reversal of hyperglycemia-evoked gastric myoelectric dysrhythmias by nitrergic stimulation in healthy humans

Acute hyperglycemia disrupts gastric myoelectric rhythm in healthy humans. Defective nitrergic function is a factor in animal models of diabetic gastropathy. We tested participation of nitrergic pathways in hyperglycemia-evoked myoelectric dysrhythmias and compared their role in preventing dysrhythmic actions of experimental motion sickness. Twelve healthy volunteers underwent electrogastrography (EGG) with and without intravenous 20% dextrose to produce plasma glucoses of 250 mg/dl. EGG continued for 2 h after oral nitroglycerin (9 mg) or the cyclic GMP-specific phosphodiesterase inhibitor sildenafil (100 mg). In separate studies, 12 volunteers underwent circular vection (60 degrees /s) without and 90 min after nitroglycerin (9 mg) or sildenafil (100 mg) with concurrent EGG. Hyperglycemia decreased recording time in normal rhythm, increased tachygastria more than 3-fold, and decreased power of the dominant frequency (P < 0.05). Nitroglycerin and sildenafil reversed effects of hyperglycemia, improving normal rhythm, decreasing tachygastria (both P < 0.05), and blunting power decreases. Neither agent affected EGG rhythm during euglycemia. Vection decreased time in normal rhythm and increased tachygastria (P < 0.05). However, nitroglycerin and sildenafil did not reverse dysrhythmic effects of vection (P = N.S.). In conclusion, administration of a nitric oxide (NO) donor or an inhibitor of cyclic GMP-selective phosphodiesterase reverses the dysrhythmic effects of hyperglycemia on gastric myoelectric activity in healthy humans. These agents have no effect on dysrhythmias during motion sickness. These findings are consistent with selective impairment of nitrergic function in this model of diabetic gastropathy and suggest that NO donors and other agents that increase NO activity may be useful for treating diabetic dysrhythmias.

mRNA expression patterns of the cGMP-hydrolyzing phosphodiesterases types 2, 5, and 9 during development of the rat brain

Recent evidence indicates that cGMP plays an important role in neural development and neurotransmission. Since cGMP levels depend critically on the activities of phosphodiesterase (PDE) enzymes, mRNA expression patterns were examined for several key cGMP-hydrolyzing PDEs (type 2 [PDE2], 5 [PDE5], and 9 [PDE9]) in rat brain at defined developmental stages. Riboprobes were used for nonradioactive in situ hybridization on sections derived from embryonic animals at 15 days gestation (E15) and several postnatal stages (P0, P5, P10, P21) until adulthood (3 months). At all stages PDE9 mRNA was present throughout the whole central nervous system, with highest levels observed in cerebellar Purkinje cells, whereas PDE2 and PDE5 mRNA expression was more restricted. Like PDE9, PDE5 mRNA was abundant in cerebellar Purkinje cells, although it was observed only on and after postnatal day 10 in these cells. In other brain regions, PDE5 mRNA expression was minimal, detected in olfactory bulb, cortical layers, and in hippocampus. PDE2 mRNA was distributed more widely, with highest levels in medial habenula, and abundant expression in olfactory bulb, olfactory tubercle, cortex, amygdala, striatum, and hippocampus. Double immunostaining of PDE2, PDE5, or PDE9 mRNAs with the neuronal marker NeuN and the glial cell marker glial fibrillary acidic protein revealed that these mRNAs were predominantly expressed in neuronal cell bodies. Our data indicate that three cGMP-hydrolyzing PDE families have distinct expression patterns, although specific cell types coexpress mRNAs for all three enzymes. Thus, it appears that differential expression of PDE isoforms may provide a mechanism to match cGMP hydrolysis to the functional demands of individual brain regions.

Adenosine receptors and phosphodiesterase inhibitors stimulate Cl- secretion in Calu-3 cells

We investigated cystic fibrosis transmembrane conductance regulator (CFTR) activation by clinically used phosphodiesterase inhibitors (PDEis) in Calu-3 cell monolayers alone and in combination with A2B adenosine receptor stimulation. This receptor pathway has previously been shown to activate wild-type and mutant CFTR molecules. Several PDEis, including milrinone, cilostazol (Pletal), papaverine, rolipram, and sildenafil (Viagra), produced a short circuit current (Isc) that was glibenclamide-sensitive, achieving 20-85% of forskolin-stimulated Isc. Papaverine, cilostazol, and rolipram also augmented both the magnitude and the duration of Isc following low dose stimulation of adenosine receptors with Ado (0.1-1.0 microM, P < 0.01). Subsequent studies demonstrated that very low concentrations of cilostazol or papaverine (approximately 1/2 peak serum concentrations) were sufficient to activate Isc, and both agents markedly augmented Ado-stimulated Isc (1 microM, P < 0.01). Our results provide evidence that select PDEis, at concentrations achieved as part of systemic therapies, can activate CFTR-dependent Isc in Calu-3 cell monolayers. These studies also indicate that PDEis have the capacity to augment an endogenous CFTR-activating pathway in an "in vivo"-like model system, and supports future investigations of these agents relevant to cystic fibrosis.

Diagnosis and treatment of chronic gastroparesis and chronic intestinal pseudo-obstruction

Chronic gastroparesis and CIP are debilitating disorders that are difficult to treat with currently available therapies. Failure of proper migration and differentiation of enteric neurons or ICC can result from specific genetic mutations and lead to phenotypes of CIP with or without concomitant gastroparesis. Intestinal dysfunction in diabetes may reflect a depletion of NO production (and perhaps other neurotransmitters or modulators), which is manifest as a syndrome of gastroparesis, diarrhea, or constipation in individual patients. As the key molecular changes underlying these disorders are defined, clinicians will begin to understand their precise etiology and rational medical therapy may become possible. In the future, testable hypotheses regarding the etiology of other functional bowel disorders (e.g., functional dyspepsia, irritable bowel syndrome, and so forth) may be developed.

Effects of sildenafil (viagra) on human myocardial contractility, in vitro arrhythmias, and tension of internal mammaria arteries and saphenous veins

Sildenafil (Viagra) has been proved effective in the therapy for erectile dysfunction. Cardiovascular adverse effects are a matter of continuous debate. The aim of the study was to investigate effects of sildenafil on isolated human cardiovascular tissue directly. Isometric force of contraction was determined in isolated, electrically stimulated (1 Hz, 37 degrees C) human right atrial and left ventricular muscle strips. Vascular tension was determined in rings of human internal mammaria arteries and saphenous veins. Sildenafil (0.0001-10 microM) neither in human atrium (n = 12) nor in failing (n = 8) or nonfailing (n = 5) ventricle exerted a significant inotropic response. Furthermore, no effect on isoprenaline-elicited arrhythmias was observed. Neither addition of isoprenaline (0.1 microM) nor addition of the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP) (100 microM) affected myocardial contractility in the presence of sildenafil (10 microM). In precontracted arteries and veins, addition of sildenafil (0.1-10 microM) led to pronounced vasorelaxation (maximal 35.5 +/- 2.2% and 45.6 +/- 6.3%, respectively, in the presence of 10 microM sildenafil). In the presence of SNAP (0.03 microM), this effect was markedly increased in arteries (72.4 +/- 10.1%, n = 4, P < 0.02) as well as in veins (73.5 +/- 6.3%, n = 6, P < 0.02). Sildenafil exerts potent vasodilatory actions but has no direct influence on human myocardial contractility or proarrhythmic effects in vitro.

Isolation of two isoforms of phosphodiesterase 5 from rat penis

Inhibition of cGMP-specific phosphodiesterase type 5 (PDE5) has been shown to improve penile erection in patients with erectile dysfunction. We have reported previously the cloning of three PDE5 isoforms from human penile tissues. Here we report the cloning of two PDE5 isoforms from rat penile tissues. The similarity between rat and human PDE5A1-specific sequences were 68 and 88% at the nucleotide and amino-acid levels, respectively. Like the bovine and canine PDE5A1 sequences, the rat PDE5A1 sequence lacks the polyglutamine tract that appears to be unique to the human PDE5A1 sequence. The similarity between rat and human PDE5A2-specific sequences were 64 and 100% at the nucleotide and amino-acid levels, respectively. The equivalent of human PDE5A3-specific sequence was identified in the rat PDE5A gene; however, repeated efforts to clone the putative rat PDE5A3 isoform were not successful. Expression of PDE5A1 and A2 mRNA in various tissues was examined by Northern blotting and reverse transcription-polymerase chain reaction. Results from the two experimental procedures were largely in good agreement and indicated that PDE5A1 and A2 mRNA were expressed in a tissue-specific manner with PDE5A2 being the dominant isoform. International Journal of Impotence Research (2003) 15, 129-136. doi:10.1038/sj.ijir.3900983

Inhibition of cyclic GMP hydrolysis with zaprinast reduces basal and cyclic AMP-elevated L-type calcium current in guinea-pig ventricular myocytes

(1) Cyclic GMP (cGMP) has been shown to be an important modulator of cardiac contractile function. A major component of cGMP regulation of contractility is cGMP-mediated inhibition of the cardiac calcium current (I(Ca)). An under-appreciated aspect of cyclic nucleotide signalling is hydrolysis of the cyclic nucleotide (i.e., breakdown by phosphodiesterases (PDEs)). The role of cGMP hydrolysis in regulating I(Ca) has not been studied. Thus the purpose of this study was to investigate if inhibition of cGMP hydrolysis can modulate I(Ca) in isolated guinea-pig ventricular myocytes. (2) Zaprinast, a selective inhibitor of cGMP-specific PDE (PDE5), caused a significant increase in cGMP levels in myocytes, but was without affect on basal or beta-adrenergic stimulated cAMP levels (consistent with its actions as a specific inhibitor of PDE5). (3) Zaprinast inhibited I(Ca) that was pre-stimulated with cAMP elevating agents (isoproterenol, a beta-adrenergic agonist; or forskolin, a direct activator of adenylate cyclase). The effect of zaprinast was greatly reduced by KT5823, an inhibitor of cGMP-dependent protein kinase (PKG). (4) Zaprinast also significantly inhibited basal I(Ca) when perforated-patch or whole-cell recording with physiological pipette calcium concentration (10(-7) M) was used. However, this effect was not observed when using standard calcium-free whole-cell recording conditions. (5) These results indicate that inhibition of cGMP hydrolysis can decrease both basal and cAMP-stimulated I(Ca). Thus, cGMP hydrolysis may likely be an important step for physiological modulation of I(Ca). This regulation may also be important in disease states in which cGMP production is increased and PDE5 expression is altered, such as heart failure.

Phosphodiesterase inhibitors are neuroprotective to cultured spinal motor neurons

We have previously reported that cyclic guanosine-3',5'-monophosphate (cGMP) protects spinal motor neurons against acute reactive oxygen species (ROS)-induced toxicity but not against chronic ROS-induced or glutamate (Glu)-induced toxicity. In this study, we investigated the effects of phosphodiesterase (PDE) inhibitors on the survival of cultured spinal motor neurons. Selective PDE5 inhibitors (dipyridamole, T-1032, and zaprinast) as well as a nonselective PDE inhibitor (aminophylline) protected motor and nonmotor neurons against both acute ROS-induced and chronic Glu-induced neurotoxicity, whereas selective inhibitors of PDE1-4 offered no protection. 8-Bromo-cGMP (8br-cGMP), a cGMP analogue, protected both motor and nonmotor neurons against acute ROS-induced toxicity but protected only nonmotor neurons against chronic Glu-induced toxicity. This neuroprotection was blocked by KT5823, a cGMP-dependent protein kinase (PKG) inhibitor. Immunohistochemical staining confirmed that PDE5 and PKG are located in almost all rat lumbar spinal neurons. Furthermore, semiquantitative analysis of the immunostaining intensity revealed that PDE5 was more abundant in motor neurons than in nonmotor neurons. Our results suggest that this difference in the amount of PDE5 may be responsible for the vulnerability of motor neurons to chronic excitotoxicity. In addition, the results of this study raise the possibility that PDE5 inhibitors might be used as a treatment for amyotrophic lateral sclerosis.

Acute and chronic effects of T-1032, a novel selective phosphodiesterase type 5 inhibitor, on monocrotaline-induced pulmonary hypertension in rats

We examined the hemodynamic property of T-1032 (methyl 2-(4-aminophenyl)-1,2-dihydro-1-oxo-7-(2-pyridylmethoxy)-4-(3,4,5-trimethoxy-phenyl)-3-isoquinoline carboxylate sulfate), a novel selective phosphodiesterase type 5 (PDE5) inhibitor, and evaluated the chronic effect of T-1032 on cardiac remodeling and its related death in monocrotaline (MCT)-induced pulmonary hypertensive rats. T-1032 (1, 10, 100 micro g/kg, i.v.) significantly reduced mean arterial pressure (MAP) and right ventricular systolic pressure (RVSP) without a change in heart rate. The change in RVSP was more potent than that in MAP with 1 micro g/kg T-1032 treatment (RVSP: -8.2+/-1.2%, mean arterial pressure: -5.7+/-1.2%), and reductions in RVSP and MAP reached a peak at doses of 1 and 10 micro g/kg, respectively. In contrast, nitroglycerin (0.1, 1, 10 micro g/kg, i.v.) and beraprost (0.1, 1 micro g/kg, i.v.) did not cause a selective reduction in RVSP at any dose. When T-1032 (300 ppm in diet) was chronically administered, it delayed the death, and significantly suppressed right ventricular remodeling (T-1032-treated: 0.318+/-0.021 g, control: 0.401+/-0.013 g, p<0.05). Our present results suggest that T-1032 selectively reduces RVSP, and resulting in the suppression of right ventricular remodeling with a delay of the death in MCT-induced pulmonary hypertensive rats.

Type V phosphodiesterase expression in cerebral arteries with vasospasm after subarachnoid hemorrhage in a canine model

Cyclic GMP (cGMP) mediates smooth muscle relaxation in the central nervous system. In subarachnoid hemorrhage (SAH), decreases in intrinsic nitric oxide (NO) cause cerebral vasospasms due to the regulation of cGMP formation by NO-mediated pathways. As phosphodiesterase type V (PDE V) selectively hydrolyzes cGMP, we hypothesized that PDE V may function in the initiation of vasospasm. This study sought to identify the altered PDE V expression and activity in the vasospastic artery in a canine SAH model. We also used this system to examine possible therapeutic strategies to prevent vasospasm. Using a canine model of SAH, we induced cerebral vasospasm in the basilar artery (BA). Following angiographic confirmation of vasospasm on day 7, PDE V expression was immunohistochemically identified in smooth muscle cells of the vasospastic BA but not in cells of a control artery. The isolation of PDE enzymes using a sepharose column confirmed increased PDE V activity in the vasospastic artery only through both inhibition studies, using the highly selective PDE V inhibitor, sildenafil citrate, and Western blotting. Preliminary in vivo experiment using an oral PDE V inhibitor at 0.83 mg kg(-1) demonstrated partial relaxation of the spastic BA. PDE V activity was increased from control levels within the BA seven days after SAH. PDE V expression was most prominent in smooth muscle cells following SAH. These results suggest that clinical administration of a PDE V inhibitor may be a useful therapeutic tool in the prevention of vasospasm following SAH.

Application of molecular biology to impotence research

To encourage further application of molecular biology in impotence research, we have compiled a list of techniques that have been or can be used in such endeavors. While by no means complete or perfect, the list encompasses both some of the most commonly used (such as RT-PCR) and some of the most promising (such as gene chip) methods. All three levels of the gene expression hierarchy, namely, DNA, RNA, and protein, are represented in the discussion. Whenever possible, each technique is discussed with references relevant to impotence research. Interested readers therefore can trace the original or the most recent research protocols for more detailed information.

Light-induced changes in glutamate release from isolated rat retina is regulated by cyclic guanosine monophosphate

Isolated rat retina was preloaded with [(14)C]glutamate and subsequently superfused to follow release of glutamate (Glu). After 20 min of superfusion in the dark, exposure of the [(14)C]Glu preloaded rat retina to a single train of white light pulses reduced Glu efflux significantly in the absence as well as in the presence of low (4 microM) and high (0.5 mM) concentrations of the Glu uptake inhibitor trans-L-pyrrolidine-2,4-dicarboxylate (t-PDC). The dark-light response was the highest in the presence of 4 microM t-PDC by establishing a plateau at 75% +/- 7% of the tonic Glu release in the dark (100%). Displaying transient to saturating responses with increasing relative luminance, time series of four trains of white light pulses arrived at a plateau of 85% +/- 10%. The cyclic guanosine monophosphate (cGMP) phosphodiesterase inhibitor Zaprinast (200 microM) antagonized the effect of the light series, leading to a plateau of 115% +/- 9%. Exposure of the retina to the guanylyl cyclase inhibitor LY83583 (30 and 100 microM) showed fast, transient responses characterized by peaks at 90% +/- 1% and 80% +/- 3%, respectively.

Activation of phosphodiesterase 5 and inhibition of guanylate cyclase by cGMP-dependent protein kinase in smooth muscle

The regulation of cGMP-specific phosphodiesterase (PDE) 5 and soluble guanylate cyclase (GC) by cGMP- and cAMP-dependent protein kinases (PKG and PKA respectively) was examined in gastric smooth muscle. The NO donor, sodium nitroprusside (SNP), stimulated PDE5 phosphorylation and activity, which was blocked by the selective PKG inhibitor, KT5823, resulting in an elevation of cGMP levels. Activation of PKA either directly by Sp-5,6-dichloro-1-beta-d-ribofuranosyl benzimidazole 3',5'-cyclic monophosphothioate, or via isoproterenol- and forskolin-dependent increase in cAMP, also caused an increase in PDE5 phosphorylation and activity, but only in the presence of cGMP; consistent with the dependence of PDE5 phosphorylation and activity on cGMP binding to allosteric sites in the regulatory domain of PDE5. The selective PKA inhibitors, myristoylated protein kinase inhibitor and H-89, blocked the increase in PDE5 phosphorylation and activity induced by PKA. SNP also stimulated soluble GC phosphorylation and activity. KT5823 abolished phosphorylation and augmented soluble GC activity, implying feedback inhibition of soluble GC by PKG-dependent phosphorylation. Phosphorylation by PKG was direct and could be induced in vitro. Activation of PKA had no effect on soluble GC. Thus cGMP levels are regulated by PKG- and PKA-dependent activation of PDE5 and PKG-specific inhibition of soluble GC.

Cardiac phosphodiesterase 5 (cGMP-specific) modulates beta-adrenergic signaling in vivo and is down-regulated in heart failure

Recent studies implicate increased cGMP synthesis as a postreceptor contributor to reduced cardiac sympathetic responsiveness. Here we provide the first evidence that modulation of this interaction by cGMP-specific phosphodiesterase PDE5A is also diminished in failing hearts, providing a novel mechanism for blunted beta-adrenergic signaling in this disorder. In normal conscious dogs chronically instrumented for left ventricular pressure-dimension analysis, PDE5A inhibition by EMD82639 had modest basal effects but markedly blunted dobutamine-enhanced systolic and diastolic function. In failing hearts (tachypacing model), however, EMD82639 had negligible effects on either basal or dobutamine-stimulated function. Whole myocardium from failing hearts had 50% lower PDE5A protein expression and 30% less total and EMD92639-inhibitable cGMP-PDE activity. Although corresponding myocyte protein and enzyme activity was similar among groups, the proportion of EMD82639-inhibitable activity was significantly lower in failure cells. Immunohistochemistry confirmed PDE5A expression in both the vasculature and myocytes of normal and failing hearts, but there was loss of z-band localization in failing myocytes that suggested altered intracellular localization. Thus, PDE5A regulation of cGMP in the heart can potently modulate beta-adrenergic stimulation, and alterations in enzyme localization and reduced synthesis may blunt this pathway in cardiac failure, contributing to dampening of the beta-adrenergic response.

Identification and regulation of human PDE5A gene promoter

PDE5A gene encodes type 5 phosphodiesterase (PDE5), the principal cGMP-catalyzing enzyme in the penis and the primary target of sildenafil (Viagra). We have isolated a 3.7-kb DNA fragment that contains the human PDE5A gene promoter. The DNA fragment contains a sequence of 234 nucleotides at its 3' end that corresponds to most of the untranslated region of the PDE5A1 mRNA. The remaining 3.5-kb upstream flanking sequence contains no apparent TATA box but has several sequences that resemble binding sequences for transcription factors such as androgen receptor (AR), AP1, AP2, AP4, Sp1, MyoD, Myc, and CArG. In search of promoter activities, we used a luciferase reporter system to examine 10 DNA fragments that cover various regions of the 3.7-kb fragment. We found that a full basal promoter activity was confined to a 139-bp region that includes 78 bp of the PDE5A1-specific first exon. A lesser basal promoter activity was still detectable in a 94-bp fragment that contains the same 78-bp PDE5A1-specific exon plus 16 bp of upstream sequence. Either the 139-bp or the 94-bp promoter fragment responded minimally to cAMP or cGMP (2 mM) stimulation. Longer fragments that contain either a 308-bp 5' extension (from the 138-bp fragment) or a 156-bp 3' extension (all exon sequence) responded at higher levels to cAMP and cGMP stimulation. The 5' and 3' extensions cooperated with each other to provide the highest level of responses to cAMP and cGMP stimulation. DNase I footprint analysis identified four AP2- and two Sp1-binding sites in the 5' extension and four Sp1-binding sites in the 3' extensions. Cyclic AMP and cGMP had similar stimulatory effects on the PDE5A promoter.

Characterization and effects of methyl-2- (4-aminophenyl)-1, 2-dihydro-1-oxo-7- (2-pyridinylmethoxy)-4-(3,4, 5-trimethoxyphenyl)-3-isoquinoline carboxylate sulfate (T-1032), a novel potent inhibitor of cGMP-binding cGMP-specific phosphodiesterase (PDE5)

An isoquinolone derivative, methyl-2-(4-aminophenyl)-1, 2-dihydro-1-oxo-7-(2-pyridinylmethoxy)-4-(3,4, 5-trimethoxyphenyl)-3-isoquinoline carboxylate sulfate (T-1032), was found to be a novel potent inhibitor of cyclic GMP (cGMP)-binding cGMP-specific phosphodiesterase (PDE5). We investigated the inhibitory effects of T-1032 on six PDE isozymes isolated from canine tissues. T-1032 specifically inhibited the hydrolysis of cGMP by PDE5 partially purified from canine lung, at a low concentration (IC(50) = 1.0 nM, K(i) = 1.2 nM), in a competitive manner. In contrast, the IC(50) values of T-1032 for PDE1, PDE2, PDE3, and PDE4 were more than 1 microM. T-1032 also inhibited PDE6 from canine retina with an IC(50) of 28 nM, which is of the same order of magnitude as the IC(50) of sildenafil. cGMP hydrolytic activities of two alternative splice variants of canine PDE5 expressed in COS-7 cells were inhibited by this compound to a similar extent. T-1032 increased the intracellular concentration of cGMP in cultured rat vascular smooth muscle cells in the presence and absence of C-type natriuretic peptide, an activator of membrane-bound guanylate cyclase, whereas the compound did not change cyclic AMP levels. These data indicated that T-1032, which belongs to a new structural class of PDE5 inhibitors, is a potent and selective PDE5 inhibitor. This compound may be useful in pharmacological studies to examine the role of a cGMP/PDE5 pathway in tissues.

Cyclic nucleotide phosphodiesterases: relating structure and function

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

Isolation and characterization of two novel phosphodiesterase PDE11A variants showing unique structure and tissue-specific expression

cDNAs encoding a novel phosphodiesterase, phosphodiesterase 11A (PDE11A), were isolated by a combination of reverse transcriptase-polymerase chain reaction using degenerate oligonucleotide primers and rapid amplification of cDNA ends. Their catalytic domain was identical to that of PDE11A1 (490 amino acids) reported during the course of this study. However, the cDNAs we isolated had N termini distinct from PDE11A1, indicating two novel N-terminal variants of PDE11A. PDE11A3 cDNA encoded a 684-amino acid protein including one complete and one incomplete GAF domain in the N-terminal region. PDE11A4 was composed of 934 amino acids including two complete GAF domains and shared 630 C-terminal amino acids with PDE11A3 but had a distinct N terminus containing the putative phosphorylation sites for cAMP- and cGMP-dependent protein kinases. PDE11A3 transcripts were specifically expressed in testis, whereas PDE11A4 transcripts were particularly abundant in prostate. Recombinant PDE11A4 expressed in COS-7 cells hydrolyzed cAMP and cGMP with K(m) values of 3.0 and 1.4 microm, respectively, and the V(max) value with cAMP was almost twice that with cGMP. Although PDE11A3 showed the same K(m) values as PDE11A4, the relative V(max) values of PDE11A3 were approximately one-sixth of those of PDE11A4. PDE11A4, but not PDE11A3, was phosphorylated by both cAMP- and cGMP-dependent protein kinases in vitro. Thus, the PDE11A gene undergoes tissue-specific alternative splicing that generates structurally and functionally distinct gene products.

Insulin restores neuronal nitric oxide synthase expression and function that is lost in diabetic gastropathy

Gastrointestinal dysfunction is common in diabetic patients. In genetic (nonobese diabetic) and toxin-elicited (streptozotocin) models of diabetes in mice, we demonstrate defects in gastric emptying and nonadrenergic, noncholinergic relaxation of pyloric muscle, which resemble defects in mice harboring a deletion of the neuronal nitric oxide synthase gene (nNOS). The diabetic mice manifest pronounced reduction in pyloric nNOS protein and mRNA. The decline of nNOS in diabetic mice does not result from loss of myenteric neurons. nNOS expression and pyloric function are restored to normal levels by insulin treatment. Thus diabetic gastropathy in mice reflects an insulin-sensitive reversible loss of nNOS. In diabetic animals, delayed gastric emptying can be reversed with a phosphodiesterase inhibitor, sildenafil. These findings have implications for novel therapeutic approaches and may clarify the etiology of diabetic gastropathy.

Identification of human PDE7B, a cAMP-specific phosphodiesterase

We isolated a human cAMP-specific phosphodiesterase (PDE7B) cDNA from human caudate nucleus. The human PDE7B was composed of 450 amino acid residues with a molecular mass of 51,835 Da. The deduced amino acid sequence of human PDE7B was 64.1% identical to that of human PDE7A (67.1% identity in the catalytic region). Northern blot analysis demonstrated that PDE7B transcripts were abundantly expressed in the putamen, caudate nucleus, and heart followed by skeletal muscle, pancreas, and occipital pole. Recombinant PDE7B expressed in transfected COS-7 cells had a low cAMP K(m) value of 0. 13 microM, which is similar to the K(m) value of recombinant human PDE7A expressed in transfected COS-7 cells. Interestingly, the relative V(max) value of recombinant PDE7B was half to one-third of recombinant PDE7A. The PDE7B activity was inhibited by dipyridamole and SCH51866, with IC(50) values of 1.1 microM and 1.5 microM, respectively. Thus, the PDE7B exhibited unique tissue distribution in humans and kinetic profiles. Human PDE7B showed the lowest K(m) values compared to the other cAMP-hydrolyzing PDEs which have been reported to be expressed in the brain. Therefore, human PDE7B may be involved in the control of cAMP-mediated neural activity and cAMP metabolism in the brain.

Immunohistochemical localization of cGMP-binding cGMP-specific phosphodiesterase (PDE5) in rat tissues

We raised a polyclonal antibody against maltose binding protein fusion human cGMP-binding, cGMP-specific phosphodiesterase (PDE5) produced in E. coli. This antibody immunoreacted specifically with recombinant human and rat PDE5 proteins expressed in transfected COS-7 cells and with a native form of PDE5 in extracts of rat platelets, lung, and cerebellum. Immunohistochemical analysis showed that the anti-PDE5 antibody detected immunoactive materials in Purkinje cell layers of the cerebellum, proximal renal tubules, collecting renal ducts, and epithelial cells of pancreatic ducts in rats. Reverse transcriptase-polymerase chain reaction analysis demonstrated that PDE5 transcripts are also present in rat cerebellum, kidney, and pancreas. Here we described a cell-specific localization of PDE5 in various rat tissues, suggesting the possibility of the presence of a cGMP/PDE5 pathway in these tissues.

Identification of three alternative first exons and an intronic promoter of human PDE5A gene

In the accompanying paper we present evidence for the existence of three PDE5A isoforms that differed only in the 5' end of the mRNAs. In this paper we present evidence that the three isoform-specific 5' ends were encoded by three alternative first exons that were arranged in the order of A1-A3-A2. Because the isoform-specific mRNAs could be transcribed from individual promoters, DNA fragments of the two intronic regions (A1-A3 and A3-A2) were tested for possible promoter activities. The intron between A1- and A3-specific exons did not exhibit any promoter activities even in smooth muscle cells that expressed the A3 isoform (see accompanying paper). In contrast, the intron between A3- and A2-specific exons had promoter activities in PDE5A2-expressing COS-7 and smooth muscle cells. This intronic promoter was bound by transcription factors AP-2 and Sp1, but not by AP-1, as shown by DNase I footprint analysis. However, the sequence bound by AP-2 (5'-GGGAAACGCTCGCGGGAGAGTTGG) is unusual in that it bears little resemblance to the consensus AP-2-binding sequence.

Expression of three isoforms of cGMP-binding cGMP-specific phosphodiesterase (PDE5) in human penile cavernosum

Inhibition of cGMP-specific phosphodiesterase type V (PDE5) has been shown to improve penile erection in patients with erectile dysfunction. We report here the cloning of three PDE5 isoforms from human penile tissues. Two of the isoforms were identical to PDE5A1 and PDE5A2, respectively, which had been isolated from nonpenile tissues. The third isoform was novel and hence called PDE5A3. The deduced amino acid sequence of PDE5A3 was the same as the C-terminal 823-residue sequence of PDE5A1 and PDE5A2. While PDE5A1 and A2 isoforms were expressed in all tissues examined, the A3 isoform was confined to tissues with a smooth muscle or cardiac muscle component. When expressed in COS-7 cells, PDE5A1, A2, and A3 isoforms had similar cGMP-catalytic activities with K(m) of 6.2, 5.75, and 6.06 microM, respectively. Their cGMP-catalytic activities were inhibited by zaprinast with IC(50) values of 3.2 microM, 1.3 microM, and 1.6 microM, respectively, and by sildenafil with IC(50) of 28, 14, and 13 nM, respectively.

Characterization and phosphorylation of PDE10A2, a novel alternative splice variant of human phosphodiesterase that hydrolyzes cAMP and cGMP

We have isolated a novel alternative splice variant of human cAMP- and cGMP-hydrolyzing phosphodiesterase (PDE10A2) from human fetal lung. The N-terminal sequence of human PDE10A2 differed from that of human PDE10A1 reported previously. PDE10A1 and PDE10A2 expressed in COS-7 cells have cGMP K(m) values of 14 and 13 microM, low cAMP K(m) values of 0.28 and 0.22 microM, and high cAMP K(m) values of 0.96 and 1.1 microM, respectively, at high concentrations of cGMP and cAMP. PCR analysis demonstrated that both PDE10A1 and PDE10A2 transcripts are present in various human tissues and that PDE10A2 transcripts are a major form in some human tissues. The unique N-terminus of PDE10A2 has a putative phosphorylation site by cAMP-dependent protein kinase (cAK), but PDE10A1 does not. The recombinant PDE10A2 protein is preferentially phosphorylated by cAK, although the recombinant PDE10A1 protein is not phosphorylated by cAK.

Cloning and characterization of a novel human phosphodiesterase that hydrolyzes both cAMP and cGMP (PDE10A)

cDNA encoding a novel phosphodiesterase (PDE) was isolated from a human fetal lung cDNA library and designated PDE10A. The deduced amino acid sequence contains 779 amino acids, including a putative cGMP binding sequence in the amino-terminal portion of the molecule and a catalytic domain that is 16-47% identical in amino acid sequence to those of other PDE families. Recombinant PDE10A transfected and expressed in COS-7 cells hydrolyzed cAMP and cGMP with Km values of 0.26 and 7.2 microM, respectively, and Vmax with cGMP was almost twice that with cAMP. Of the PDE inhibitors tested, dipyridamole was most effective, with IC50 values of 1.2 and 0.45 microM for inhibition of cAMP and cGMP hydrolysis, respectively. cGMP inhibited hydrolysis of cAMP, and cAMP inhibited cGMP hydrolysis with IC50 values of 14 and 0.39 microM, respectively. Thus, PDE10A exhibited properties of a cAMP PDE and a cAMP-inhibited cGMP PDE. PDE10A transcripts were particularly abundant in the putamen and caudate nucleus regions of brain and in thyroid and testis, and in much lower amounts in other tissues. The PDE10A gene was located on chromosome 6q26 by fluorescent in situ hybridization analysis. PDE10A represents a new member of the PDE superfamily, exhibiting unique kinetic properties and inhibitor sensitivity.