Dual expression and differential regulation of phosphodiesterase 3A and phosphodiesterase 3B in human vascular smooth muscle: implications for phosphodiesterase 3 inhibition in human cardiovascular tissues

PDE3A Is a Highly Expressed Therapy Target in Myxoid Liposarcoma

Liposarcomas (LPSs) are a heterogeneous group of malignancies that arise from adipose tissue. Although LPSs are among the most common soft-tissue sarcoma subtypes, precision medicine treatments are not currently available. To discover LPS-subtype-specific therapy targets, we investigated RNA sequenced transcriptomes of 131 clinical LPS tissue samples and compared the data with a transcriptome database that contained 20,218 samples from 95 healthy tissues and 106 cancerous tissue types. The identified genes were referred to the NCATS BioPlanet library with Enrichr to analyze upregulated signaling pathways. PDE3A protein expression was investigated with immunohistochemistry in 181 LPS samples, and PDE3A and SLFN12 mRNA expression with RT-qPCR were investigated in 63 LPS samples. Immunoblotting and cell viability assays were used to study LPS cell lines and their sensitivity to PDE3A modulators. We identified 97, 247, and 37 subtype-specific, highly expressed genes in dedifferentiated, myxoid, and pleomorphic LPS subtypes, respectively. Signaling pathway analysis revealed a highly activated hedgehog signaling pathway in dedifferentiated LPS, phospholipase c mediated cascade and insulin signaling in myxoid LPS, and pathways associated with cell proliferation in pleomorphic LPS. We discovered a strong association between high PDE3A expression and myxoid LPS, particularly in high-grade tumors. Moreover, myxoid LPS samples showed elevated expression levels of SLFN12 mRNA. In addition, PDE3A- and SLFN12-coexpressing LPS cell lines SA4 and GOT3 were sensitive to PDE3A modulators. Our results indicate that PDE3A modulators are promising drugs to treat myxoid LPS. Further studies are required to develop these drugs for clinical use.

Phosphodiesterase 4D contributes to angiotensin II-induced abdominal aortic aneurysm through smooth muscle cell apoptosis

Abdominal aortic aneurysm (AAA) is a permanent expansion of the abdominal aorta that has a high mortality but limited treatment options. Phosphodiesterase (PDE) 4 family members are cAMP-specific hydrolyzing enzymes and have four isoforms (PDE4A-PDE4D). Several pan-PDE4 inhibitors are used clinically. However, the regulation and function of PDE4 in AAA remain largely unknown. Herein, we showed that PDE4D expression is upregulated in human and angiotensin II-induced mouse AAA tissues using RT-PCR, western blotting, and immunohistochemical staining. Furthermore, smooth muscle cell (SMC)-specific Pde4d knockout mice showed significantly reduced vascular destabilization and AAA development in an experimental AAA model. The PDE4 inhibitor rolipram also suppressed vascular pathogenesis and AAA formation in mice. In addition, PDE4D deficiency inhibited caspase 3 cleavage and SMC apoptosis in vivo and in vitro, as shown by bulk RNA-seq, western blotting, flow cytometry and TUNEL staining. Mechanistic studies revealed that PDE4D promotes apoptosis by suppressing the activation of cAMP-activated protein kinase A (PKA) instead of the exchange protein directly activated by cAMP (Epac). Additionally, the phosphorylation of BCL2-antagonist of cell death (Bad) was reversed by PDE4D siRNA in vitro, which indicates that PDE4D regulates SMC apoptosis via the cAMP-PKA-pBad axis. Overall, these findings indicate that PDE4D upregulation in SMCs plays a causative role in AAA development and suggest that pharmacological inhibition of PDE4 may represent a potential therapeutic strategy.

Effects of a Phosphodiesterase inhibitor on the Browning of Adipose Tissue in Mice

Cilostazol is a selective inhibitor of phosphodiesterase type 3 (PDE3) that increases intracellular cyclic adenosine monophosphate (cAMP), which plays a critical role in the development of the beige phenotype and the activation of its thermogenic program in white adipose tissue (WAT). We investigated the metabolic effects of PDE3B inhibition with cilostazol treatment in the adipose tissue of high-fat diet (HFD)-fed mice. Seven-week-old male C57BL/6J mice were randomly assigned to either the cilostazol or control group. The control group was divided into two groups: the chow diet and HFD. The expression of uncoupling Protein 1 (UCP1) and other brown adipocyte markers was compared. In the HFD-fed cilostazol group, C57BL/6J mice displayed improvements in systemic metabolism, including improved glucose tolerance and lipid profile, but only modest effects on body weight were observed. In the visceral WAT of HFD-fed cilostazol-treated mice, cAMP/protein kinase A (PKA) signaling pathways were activated, resulting in the “browning” phenotype, smaller fat deposits, and enhanced mRNA expression of UCP1 and other brown adipocyte markers. PDE3B appears to be an important regulator of lipid metabolism, insulin sensitivity, and thermogenic programs in adipose tissues. An increase in intracellular cAMP via PDE3B inhibition with cilostazol treatment promoted the browning of visceral WAT.

Nitric oxide signalling in the brain and its control of bodily functions

Nitric oxide (NO) is a versatile molecule that plays key roles in the development and survival of mammalian species by endowing brain neuronal networks with the ability to make continual adjustments to function in response to moment-to-moment changes in physiological input. Here, we summarize the progress in the field and argue that NO-synthetizing neurons and NO signalling in the brain provide a core hub for integrating sensory- and homeostatic-related cues, control key bodily functions, and provide a potential target for new therapeutic opportunities against several neuroendocrine and behavioural abnormalities.

Identification and functional study of genetic polymorphisms in cyclic nucleotide phosphodiesterase 3A (PDE3A)

Phosphodiesterase 3A (PDE3A) is an enzyme that plays an important role in the regulation of cyclic adenosine monophosphate (cAMP)-mediated intracellular signaling in cardiac myocytes and platelets. PDE3A hydrolyzes cAMP, which results in a decrease in intracellular cAMP levels and leads to platelet activation. Whole-exome sequencing of 50 DNA samples from a healthy Korean population revealed a total of 13 single nucleotide polymorphisms including five missense variants, D12N, Y497C, H504Q, C707R, and A980V. Recombinant proteins for the five variants of PDE3A (and wild-type protein) were expressed in a FreeStyle 293 expression system with site-directed mutagenesis. The expression of the recombinant PDE3A proteins was confirmed with Western blotting. Catalytic activity of the PDE3A missense variants and wild-type enzyme was measured with a PDE-based assay. Effects of the missense variants on the inhibition of PDE3A activity by cilostazol were also investigated. All variant proteins showed reduced activity (33-53%; p < .0001) compared to the wild-type protein. In addition, PDE3A activity was inhibited by cilostazol in a dose-dependent manner and was further suppressed in the missense variants. Specifically, the PDE3A Y497C showed significantly reduced activity, consistent with the predictions of in silico analyses. The present study provides evidence that individuals carrying the PDE3A Y497C variant may have lower enzyme activity for cAMP hydrolysis, which could cause interindividual variation in cAMP-mediated physiological functions.

Expression of Recombinant Phosphodiesterases 3A and 3B Using Baculovirus Expression System

Background

Phosphodiesterase 3A (PDE3A) and phosphodiesterase 3B (PDE3B) play a critical role in the regulation of intracellular level of adenosine 3´,5´-cyclic monophosphate (cyclic AMP, cAMP) and guanosine 3´,5´-cyclic monophosphate (cyclic GMP, cGMP). Subsequently PDE3 inhibitors have shown to relax vascular and inhibit platelet aggregation in cardiovascular disease.

Objectives

In this study, our aim was to establish a method of expression for the recombinant human PDE3A and PDE3B proteins in insect cells using baculovirus expression system in order to investigate the activity of the expressed PDE3A and PDE3B proteins.

Materials and Methods

The full length human PDE3A and PDE3B cDNA were cloned into recombinant baculovirus and transfected into the SF9 insect cells. Recombinant proteins were collected at 48 h, 60 h, 72 h, and 84 h post transfection. Transfection of recombinant baculovirus was verified by the morphological changes of the SF9 cells. Expression of human PDE3A and PDE3B was detected by using RT-PCR and western blot, respectively. The ¹²⁵I RIA method was used to determine the level of adenosine 3´,5´-cyclic monophosphate cAMP and cGMP, correspondingly. The activity of the expressed PDE3A and PDE3B proteins were investigated by cAMP and cGMP dsgradation with or without addition of milrinone, a potent and selective PDE inhibitor.

Results

Recombinant human PDE3A and PDE3B proteins were stably expressed in SF9 cells and could be detected by distinct morphological changes in the SF9 cells, RT-PCR, and western blot at 48 h post-transfection. The molecular weights of the recombinant PDE3A and PDE3B molecular weights proteins were about 120 KDa and 135 KDa, respectively. Results of ¹²⁵I RIA assay showed that the levels of cAMP and cGMP were significantly decreased after incubation with the expressed PDE3A and PDE3B proteins. Furthermore, degradation of cAMP and cGMP through the activity of PDE3A and PDE3B was suppressed following to the addition of milrinone.

Conclusions

Recombinant human PDE3A and PDE3B could be expressed in SF9 cells using baculovirus expression system, and thus provides the basic material for studying human PDE3A and PDE3B activity.

Expression and function of phosphodiesterases (PDEs) in the rat urinary bladder

Background

It has been shown that hosphodiesterases (PDEs) play an important role in mediating the smooth muscle tone of rat urinary bladder. However, the gene expression profiles of them were still unknown.

Methods

Urinary bladder Strips were obtained from both neonatal and adult Sprague-Dawley rats. RT-PCR/western blot and organ bath were used to measure the expression and function of PDEs.

Results

Adult rat urinary bladder expressed various PDE mRNA with the following rank order: PDE5A ≈ PDE9A ≈ PDE10A > PDE2A ≈ PDE4A ≈ PDE4D > PDE4B ≈ PDE3B ≈ PDE8B ≈ PDE7A ≈ PDE7B > PDE1A. PDE1B, PDE1C, PDE3A, PDE4C, PDE8A, and PDE11A were not detected. Of interest, the mRNA and protein of PDE3A were significantly decreased in adult rat urinary bladder compared to neonatal rat urinary bladder. Cilostamide, a specific inhibitor for PDE3, significantly inhibited the amplitude and frequency of carbachol-enhanced phasic contractions of neonatal rat bladder strips by 38.8% and 12.1%, respectively. Compared to the neonatal rat bladder, the effect of cilostamide was significantly blunted in adult rat urinary bladder: the amplitude and frequency of carbachol-enhanced phasic contractions were decreased by 13.4% (P < 0.01 vs neonatal rat bladder) and 4.4%, respectively. However, the mRNA and the protein levels of PDE3B were similar between neonatal and adult rat bladder.

Conclusion

We found that several PDE isoforms were expressed in the rat urinary bladder with distinct levels. Moreover, we showed that the function of PDE3 was blunted in adult rat bladder likely due to the decreased expression of PDE3A.

Distinct phosphodiesterase 5A-containing compartments allow selective regulation of cGMP-dependent signalling in human arterial smooth muscle cells

Cyclic GMP (cGMP) translates and integrates much of the information encoded by nitric oxide (NO^·) and several natriuretic peptides, including the atrial natriuretic peptide (ANP). Previously, we reported that integration of a cGMP-specific cyclic nucleotide phosphodiesterase, namely phosphodiesterase 5A (PDE5A), into a protein kinase G (PKG)- and inositol-1,4,5-trisphosphate receptor (IP₃R)-containing endoplasmic reticulum (ER) signalosome allows localized control of PDE5A activity and of PKG-dependent inhibition of IP₃-mediated release of ER Ca²⁺ in human platelets. Herein, we report that PDE5A integrates into an analogous signalosome in human arterial smooth muscle cells (HASMC), wherein it regulates muscarinic agonist-dependent Ca²⁺ release and is activated selectively by PKG-dependent phosphorylation. In addition, we report that PDE5A also regulates HASMC functions via events independent of PKG, but rather through actions coordinated by competitive cGMP-mediated inhibition of cAMP hydrolysis by the so-called cGMP-inhibited cAMP PDE, namely phosphodiesterase 3A (PDE3A). Indeed, we show that ANP increases both cGMP and cAMP levels in HASMC and promotes phosphorylation of vasodilator-stimulated phospho-protein (VASP) at each the PKG and PKA phospho-acceptor sites. Since selective inhibition of PDE5 decreased DNA synthesis and chemotaxis of HASMC, and that PDE3A knockdown obviated these effects, our findings are consistent with a role for a PDE5A-PDE3A-PKA axis in their regulation. Our findings provide insight into the existence of distinct "pools" of PDE5A in HASMC and support the idea that these discrete compartments regulate distinct cGMP-dependent events. As a corollary, we suggest that it may be possible to target these distinct PDE5A-regulated pools and in so-doing differentially impact selected cGMP-regulated functions in these cells.

Multiple Genetic Associations with Irish Wolfhound Dilated Cardiomyopathy

Cardiac disease is a leading cause of morbidity and mortality in dogs and humans, with dilated cardiomyopathy being a large contributor to this. The Irish Wolfhound (IWH) is one of the most commonly affected breeds and one of the few breeds with genetic loci associated with the disease. Mutations in more than 50 genes are associated with human dilated cardiomyopathy (DCM), yet very few are also associated with canine DCM. Furthermore, none of the identified canine loci explain many cases of the disease and previous work has indicated that genotypes at multiple loci may act together to influence disease development. In this study, loci previously associated with DCM in IWH were tested for associations in a new cohort both individually and in combination. We have identified loci significantly associated with the disease individually, but no genotypes individually or in pairs conferred a significantly greater risk of developing DCM than the population risk. However combining three loci together did result in the identification of a genotype which conferred a greater risk of disease than the overall population risk. This study suggests multiple rather than individual genetic factors, cooperating to influence DCM risk in IWH.

The Influence of Known Genetic Variants on Subclinical Cardiovascular Outcomes in Childhood

Background—

Genome-wide association studies have identified single-nucleotide polymorphisms (SNPs) for subclinical cardiovascular outcomes in adults. We examined the influence of these variants on the same outcomes in childhood.

Methods and Results—

In a population-based prospective cohort study among 4137 children, we examined the associations of SNPs, individually and incorporated in genetic risk scores, which were identified in adults for cardiac (2 SNPs for left ventricular end-diastolic diameter and 5 SNPs for aortic root diameter) and blood pressure outcomes (29 SNPs for systolic and diastolic blood pressure, 22 SNPs for mean arterial pressure, and 10 SNPs for pulse pressure) with the same outcomes in children (median age of 6.0 years [95% range, 4.5–8.7]). Weighted and unweighted risk scores for aortic root diameter were associated with childhood aortic root diameter (difference per additional average risk allele 0.09 mm [95% CI: 0.05, 0.13]). Weighted and unweighted risk scores for pulse pressure were associated with childhood pulse pressure (difference per additional average risk allele 0.22 mm Hg [95% CI: 0.08, 0.35] and 0.18 mm Hg [95% CI: 0.05, 0.31], respectively), but not with childhood systolic or diastolic blood pressure or mean arterial pressure. The risk scores for blood pressure and mean arterial pressure were not associated with any of the childhood blood pressure outcomes.

Conclusions—

Genetic risk scores based on SNPs for aortic root diameter and pulse pressure in adults are associated with the same outcomes in children. SNPs related to cardiovascular outcomes in adulthood at least partly influence cardiovascular development from early life onwards.

Metabolic effects of newly synthesized phosphodiesterase-3 inhibitor 6-[4-(4-methylpiperidin-1-yl)-4-oxobutoxy]-4-methylquinolin-2(1H)-one on rat adipocytes

Background

Clinical use of selective PDE3 inhibitors as cardiotonic agents is limited because of their chronotropic and lipolytic side effects. In our previous work, we synthesized a new PDE3 inhibitor named MC2 (6-[4-(4-methylpiperidin-1-yl)-4-oxobutoxy]-4-methylquinolin-2(1H)-one) which produced a high positive inotropic action with a negative chronotropic effect. This work was done to evaluate the effects of MC2 on adipocytes and compare its effects with those of amrinone and cilostamide.

Methods

Preadipocytes were isolated from rat adipose tissue and differentiated to adipocyte in the presence of cilostamide, amrinone or MC2. Lipolysis and adipogenesis was evaluated by measuring glycerol level and Oil Red O staining, respectively. Adipocyte proliferation and apoptosis were determined with MTT assay and Annexin V/PI staining, respectively.

Results

Differentiation to adipocyte was induced by amrinone but not by cilostamide or MC2. Basal and isoproterenol-stimulated lipolysis significantly increased by cilostamide (p < 0.05). Similarly, amrinone enhanced the stimulated lipolysis (p < 0.01). On the other hand, MC2 significantly decreased both adipogenesis (p < 0.05) and stimulated lipolysis (p < 0.001). Also, incubation of differentiated adipocytes with MC2 caused the loss of cell viability, which was associated with the elevation in apoptotic rate (p < 0.05).

Conclusion

Our data indicate that selective PDE3 inhibitors produce differential effects on adipogenesis and lipolysis. MC2 has proapoptotic and antilipolytic effects on adipocytes and does not stimulate adipogenesis. Therefore, in comparison with the clinically available selective PDE3 inhibitors, MC2 has lowest metabolic side effects and might be a good candidate for treatment of congestive heart failure.

Novel PDE4 inhibitors derived from Chinese medicine forsythia

Cyclic adenosine monophosphate (cAMP) is a crucial intracellular second messenger molecule that converts extracellular molecules to intracellular signal transduction pathways generating cell- and stimulus-specific effects. Importantly, specific phosphodiesterase (PDE) subtypes control the amplitude and duration of cAMP-induced physiological processes and are therefore a prominent pharmacological target currently used in a variety of fields. Here we tested the extracts from traditional Chinese medicine, Forsythia suspense seeds, which have been used for more than 2000 years to relieve respiratory symptoms. Using structural-functional analysis we found its major lignin, Forsynthin, acted as an immunosuppressant by inhibiting PDE4 in inflammatory and immune cell. Moreover, several novel, selective small molecule derivatives of Forsythin were tested in vitro and in murine models of viral and bacterial pneumonia, sepsis and cytokine-driven systemic inflammation. Thus, pharmacological targeting of PDE4 may be a promising strategy for immune-related disorders characterized by amplified host inflammatory response.

β-Adrenergic cAMP signals are predominantly regulated by phosphodiesterase type 4 in cultured adult rat aortic smooth muscle cells

BACKGROUND

We investigated the role of cyclic nucleotide phosphodiesterases (PDEs) in the spatiotemporal control of intracellular cAMP concentrations in rat aortic smooth muscle cells (RASMCs).

METHODOLOGY/PRINCIPAL FINDINGS

The rank order of PDE families contributing to global cAMP-PDE activity was PDE4> PDE3  =  PDE1. PDE7 mRNA expression but not activity was confirmed. The Fluorescence Resonance Energy Transfer (FRET)-based cAMP sensor, Epac1-camps, was used to monitor the time course of cytosolic cAMP changes. A pulse application of the β-adrenoceptor (β-AR) agonist isoproterenol (Iso) induced a transient FRET signal. Both β(1)- and β(2)-AR antagonists decreased the signal amplitude without affecting its kinetics. The non-selective PDE inhibitor (IBMX) dramatically increased the amplitude and delayed the recovery phase of Iso response, in agreement with a role of PDEs in degrading cAMP produced by Iso. Whereas PDE1, PDE3 and PDE7 blockades [with MIMX, cilostamide (Cil) and BRL 50481 (BRL), respectively] had no or minor effect on Iso response, PDE4 inhibition [with Ro-20-1724 (Ro)] strongly increased its amplitude and delayed its recovery. When Ro was applied concomitantly with MIMX or Cil (but not with BRL), the Iso response was drastically further prolonged. PDE4 inhibition similarly prolonged both β(1)- and β(2)-AR-mediated responses. When a membrane-targeted FRET sensor was used, PDE3 and PDE4 acted in a synergistic manner to hydrolyze the submembrane cAMP produced either at baseline or after β-AR stimulation.

CONCLUSION/SIGNIFICANCE

Our study underlines the importance of cAMP-PDEs in the dynamic control of intracellular cAMP signals in RASMCs, and demonstrates the prominent role of PDE4 in limiting β-AR responses. PDE4 inhibition unmasks an effect of PDE1 and PDE3 on cytosolic cAMP hydrolyzis, and acts synergistically with PDE3 inhibition at the submembrane compartment. This suggests that mixed PDE4/PDE1 or PDE4/PDE3 inhibitors would be attractive to potentiate cAMP-related functions in vascular cells.

PDE5 Inhibitors as Potential Tools in the Treatment of Cystic Fibrosis

Despite great advances in the understanding of the genetics and pathophysiology of cystic fibrosis (CF), there is still no cure for the disease. Using phosphodiesterase type 5 (PDE5) inhibitors, we and others have provided evidence of rescued F508del-CFTR trafficking and corrected deficient chloride transport activity. Studies using PDE5 inhibitors in mice homozygous for the clinically relevant F508del mutation have been conducted with the aim of restoring F508del-CFTR protein function. We demonstrated, by measuring transepithelial nasal potential difference in F508del mice following intraperitoneal injection of sildenafil, vardenafil, or taladafil at clinical doses are able to restore the decreased CFTR-dependent chloride transport across the nasal mucosa. Moreover, vardenafil, but not sildenafil, stimulates chloride transport through the normal CFTR protein. We developed a specific nebulizer setup for mice, with which we demonstrated, through a single inhalation of PDE5 inhibitors, local activation of CFTR protein in CF. Significant potential advantages of inhalation drug therapy over oral or intravenous routes include rapid onset of pharmacological action, reduced systemic secondary effects, and reduced effective drug doses compared to the drug delivered orally; this underlines the relevance and impact of our work for translational science. More recently, we analyzed the bronchoalveolar lavage of CF and wild-type mice for cell infiltrates and expression of pro-inflammatory cytokines and chemokines; we found that the CFTR activating effect of vardenafil, selected as a representative long-lasting PDE5 inhibitor, breaks the vicious circle of lung inflammation which plays a major role in morbi-mortality in CF. Our data highlight the potential use of PDE5 inhibitors in CF. Therapeutic approaches using clinically approved PDE5 inhibitors to address F508del-CFTR defects could speed up the development of new therapies for CF.

Phosphodiesterases Regulate BAY 41-2272-Induced VASP Phosphorylation in Vascular Smooth Muscle Cells

BAY 41-2272 (BAY), a stimulator of soluble guanylyl cyclase, increases cyclic nucleotides and inhibits proliferation of vascular smooth muscle cells (VSMCs). In this study, we elucidated mechanisms of action of BAY in its regulation of vasodilator-stimulated phosphoprotein (VASP) with an emphasis on VSMC phosphodiesterases (PDEs). BAY alone increased phosphorylation of VASP(Ser239) and VASP(Ser157), respective indicators of PKG and PKA signaling. IBMX, a non-selective inhibitor of PDEs, had no effect on BAY-induced phosphorylation at VASP(Ser239) but inhibited phosphorylation at VASP(Ser157). Selective inhibitors of PDE3 or PDE4 attenuated BAY-mediated increases at VASP(Ser239) and VASP(Ser157), whereas PDE5 inhibition potentiated BAY-mediated increases only at VASP(Ser157). In comparison, 8Br-cGMP increased phosphorylation at VASP(Ser239) and VASP(Ser157) which were not affected by selective PDE inhibitors. In the presence of 8Br-cAMP, inhibition of either PDE4 or PDE5 decreased VASP(Ser239) phosphorylation and inhibition of PDE3 increased phosphorylation at VASP(Ser239), while inhibition of PDE3 or PDE4 increased and PDE5 inhibition had no effect on VASP(Ser157) phosphorylation. These findings demonstrate that BAY operates via cAMP and cGMP along with regulation by PDEs to phosphorylate VASP in VSMCs and that the mechanism of action of BAY in VSMCs is different from that of direct cyclic nucleotide analogs with respect to VASP phosphorylation and the involvement of PDEs. Given a role for VASP as a critical cytoskeletal protein, these findings provide evidence for BAY as a regulator of VSMC growth and a potential therapeutic agent against vasculoproliferative disorders.

Targeting phosphodiesterases in anti-platelet therapy

There are two primary modes of platelet inhibition: blockade of membrane receptors or neutralization of intracellular pathways. Both means of inhibition have proven benefits in the prevention and resolution of atherothrombotic events. With regard to intracellular inhibition, phosphodiesterases (PDEs) are fundamental for platelet function. Platelets possess several PDEs (PDE2, PDE3 and PDE5) that catalyze the hydrolysis of cyclic adenosine 3'-5'-monophosphate (cAMP) and cyclic guanosine 3'-5'-monophosphate (cGMP), thereby limiting the levels of intracellular nucleotides. PDE inhibitors, such as cilostazol and dipyridamole, dampen platelet function by increasing cAMP and cGMP levels. This review focuses on the roles of PDE inhibitors in modulating platelet function, with particular attention paid to drugs that have anti-platelet clinical indications.

Mammalian Cyclic Nucleotide Phosphodiesterases: Molecular Mechanisms and Physiological Functions

The superfamily of cyclic nucleotide (cN) phosphodiesterases (PDEs) is comprised of 11 families of enzymes. PDEs break down cAMP and/or cGMP and are major determinants of cellular cN levels and, consequently, the actions of cN-signaling pathways. PDEs exhibit a range of catalytic efficiencies for breakdown of cAMP and/or cGMP and are regulated by myriad processes including phosphorylation, cN binding to allosteric GAF domains, changes in expression levels, interaction with regulatory or anchoring proteins, and reversible translocation among subcellular compartments. Selective PDE inhibitors are currently in clinical use for treatment of erectile dysfunction, pulmonary hypertension, intermittent claudication, and chronic pulmonary obstructive disease; many new inhibitors are being developed for treatment of these and other maladies. Recently reported x-ray crystallographic structures have defined features that provide for specificity for cAMP or cGMP in PDE catalytic sites or their GAF domains, as well as mechanisms involved in catalysis, oligomerization, autoinhibition, and interactions with inhibitors. In addition, major advances have been made in understanding the physiological impact and the biochemical basis for selective localization and/or recruitment of specific PDE isoenzymes to particular subcellular compartments. The many recent advances in understanding PDE structures, functions, and physiological actions are discussed in this review.

Decreased cGMP level contributes to increased contraction in arteries from hypertensive rats: role of phosphodiesterase 1

Recent evidence suggests that angiotensin II (Ang II) upregulates phosphodiesterase (PDE) 1A expression. We hypothesized that Ang II augmented PDE1 activation, decreasing the bioavailability of cyclic guanosine 3' 5'-monophosphate (cGMP), and contributing to increased vascular contractility. Male Sprague-Dawley rats received mini-osmotic pumps with Ang II (60 ng·min(-1)) or saline for 14 days. Phenylephrine (PE)-induced contractions were increased in aorta (E(max)168% ± 8% vs 136% ± 4%) and small mesenteric arteries (SMA; E(max)170% ± 6% vs 143% ± 3%) from Ang II-infused rats compared to control. PDE1 inhibition with vinpocetine (10 μmol/L) reduced PE-induced contraction in aortas from Ang II rats (E(max)94% ± 12%) but not in controls (154% ± 7%). Vinpocetine decreased the sensitivity to PE in SMA from Ang II rats compared to vehicle (-log of half maximal effective concentration 5.1 ± 0.1 vs 5.9 ± 0.06), but not in controls (6.0 ± 0.03 vs 6.1 ± 0.04). Sildenafil (10 μmol/L), a PDE5 inhibitor, reduced PE-induced maximal contraction similarly in Ang II and control rats. Arteries were contracted with PE (1 μmol/L), and concentration-dependent relaxation to vinpocetine and sildenafil was evaluated. Aortas from Ang II rats displayed increased relaxation to vinpocetine compared to control (E(max)82% ± 12% vs 445 ± 5%). SMA from Ang II rats showed greater sensitivity during vinpocetine-induced relaxation compared to control (-log of half maximal effective concentration 6.1 ± 0.3 vs 5.3 ± 0.1). No differences in sildenafil-induced relaxation were observed. PDE1A and PDE1C expressions in aorta and PDE1A expression in SMA were increased in Ang II rats. cGMP production, which is decreased in arteries from Ang II rats, was restored after PDE1 blockade. We conclude that PDE1 activation reduces cGMP bioavailability in arteries from Ang II, contributing to increased contractile responsiveness.

Role of phosphodiesterases in adult-onset pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by increased mean pulmonary artery pressure (mPAP) due to vasoconstriction and structural changes in the small pulmonary arteries (PAs); proliferation of pulmonary artery smooth muscle cells (PASMCs) contributes to the remodeling. The abnormal pathophysiology in the pulmonary vasculature relates to decreased cyclic nucleotide levels in PASMCs. Phosphodiesterases (PDEs) catalyze the hydrolysis of cAMP and cGMP, thereby PDE inhibitors are effective in vasodilating the PA and decreasing PASMC proliferation. Experimental studies support the use of PDE3, PDE5, and PDE1 inhibitors in PAH. PDE5 inhibitors such as sildenafil are clinically approved to treat different forms of PAH and lower mPAP, increase functional capacity, and decrease right ventricular hypertrophy, without decreasing systemic arterial pressure. New evidence suggests that the combination of PDE inhibitors with other therapies for PAH may be beneficial in treating the disease. Furthermore, inhibiting PDEs in the heart and the inflammatory cells that infiltrate the PA may offer new targets to reduce right ventricular hypertrophy and inhibit inflammation that is associated with and contributes to the development of PAH. This chapter summarizes the advances in the area and the future of PDEs in PAH.

cGMP-dependent protein kinases and cGMP phosphodiesterases in nitric oxide and cGMP action

To date, studies suggest that biological signaling by nitric oxide (NO) is primarily mediated by cGMP, which is synthesized by NO-activated guanylyl cyclases and broken down by cyclic nucleotide phosphodiesterases (PDEs). Effects of cGMP occur through three main groups of cellular targets: cGMP-dependent protein kinases (PKGs), cGMP-gated cation channels, and PDEs. cGMP binding activates PKG, which phosphorylates serines and threonines on many cellular proteins, frequently resulting in changes in activity or function, subcellular localization, or regulatory features. The proteins that are so modified by PKG commonly regulate calcium homeostasis, calcium sensitivity of cellular proteins, platelet activation and adhesion, smooth muscle contraction, cardiac function, gene expression, feedback of the NO-signaling pathway, and other processes. Current therapies that have successfully targeted the NO-signaling pathway include nitrovasodilators (nitroglycerin), PDE5 inhibitors [sildenafil (Viagra and Revatio), vardenafil (Levitra), and tadalafil (Cialis and Adcirca)] for treatment of a number of vascular diseases including angina pectoris, erectile dysfunction, and pulmonary hypertension; the PDE3 inhibitors [cilostazol (Pletal) and milrinone (Primacor)] are used for treatment of intermittent claudication and acute heart failure, respectively. Potential for use of these medications in the treatment of other maladies continues to emerge.

Design, synthesis and pharmacological evaluation of 6-hydroxy-4-methylquinolin-2(1H)-one derivatives as inotropic agents

Selective PDE3 inhibitors improve cardiac contractility and may be used in congestive heart failure. However, their proarrhythmic potential is the most important side effect. In this research we designed, synthesized and evaluated the potential cardiotonic activity of thirteen PDE3 inhibitors (4-[(4-methyl-2-oxo-1,2-dihydro-6-quinolinyl)oxy]butanamide analogs) using the spontaneously beating atria model. The design strategy was based on the structure of cilostamide, a selective PDE3 inhibitor. In each experiment, atrium of reserpine-treated rat was isolated and the contractile and chronotropic effects of a synthetic compounds were assessed. All experiments were carried out in comparison with IBMX, amrinone and cilostamide as standard compounds. The results showed that, among the new compounds, the best pharmacological profile was obtained with the compound 6-[4-(4-methylpiperazine-1-yl)-4-oxobutoxy]-4-methylquinolin-2(1H)-one, 4j, which displayed selectivity for increasing the force of contraction (165 +/- 4% change over the control) rather than the frequency rate (115 +/- 7% change over the control) at 100 microM and potent inhibitory activity of PDE3 with IC(50) = 0.20 microM.

Milrinone enhances relaxation to prostacyclin and iloprost in pulmonary arteries isolated from lambs with persistent pulmonary hypertension of the newborn

Prostacyclin is a pulmonary vasodilator and is produced by prostacyclin synthase and stimulates adenylate cyclase (AC) via the prostacyclin receptor (IP) to produce cAMP. Forskolin is a direct stimulant of AC. Phosphodiesterase 3 hydrolyzes cAMP and is inhibited by milrinone.

OBJECTIVE

To characterize the prostacyclin-AC-cAMP pathway in the ovine ductal ligation model of persistent pulmonary hypertension of the newborn (PPHN).

SETTING

University-based laboratory animal facility.

SUBJECTS

Lambs delivered to time-dated pregnant ewes.

INTERVENTIONS

Fifth generation pulmonary arteries (PA) and lung parenchyma were isolated from control fetal lambs (n = 8) and fetal lambs with PPHN induced by antenatal ductal ligation (n = 9). We studied relaxation responses to various agonists (milrinone, forskolin, prostacyclin, and iloprost, a prostacyclin analog) that increase cAMP in PA after half-maximal constriction with norepinephrine and pretreatment with propranolol +/- indomethacin. Lung protein levels of prostacyclin synthase, IP, AC2, and phosphodiesterase 3A were analyzed by Western blot and cAMP by enzyme-linked immunoassay.

MAIN RESULTS

Milrinone relaxed control and PPHN PA and pretreatment with indomethacin significantly impaired this response. Relaxation to milrinone, prostacyclin, and iloprost were significantly impaired in PA from PPHN lambs. Pretreatment with milrinone markedly enhanced relaxation to prostacyclin and iloprost in PPHN PA, similar to relaxation in control PA. Relaxation to forskolin was similar in control and PPHN PAs indicating normal AC activity. Protein levels of prostacyclin synthase and IP were decreased in PPHN lungs compared with control, but AC2, cAMP, and phosphodiesterase 3A remained unchanged.

CONCLUSIONS

Prostacyclin and iloprost are dilators of PAs from PPHN lambs and their effect is enhanced by milrinone. This combination therapy may be an effective strategy in the management of patients with PPHN.

Intravenously administered phosphodiesterase 4 inhibitors dilate retinal blood vessels in rats

In the present study, we examined effects of intravenously administered inhibitors of phosphodiesterase 4 (rolipram and 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (Ro-20-1724)) and non-selective inhibitor of phosphodiesterases (theophylline) on diameter of retinal blood vessel and fundus (retinal/choroidal) blood flow in rats. Male Wistar rats (8- to 10-week-old) were treated with tetrodotoxin (50 microg/kg, i.v.) to eliminate any nerve activity and prevent the eye movement under artificial ventilation. Methoxamine was used to maintain adequate systemic circulation. Ocular fundus images were captured with an original high-resolution digital fundus camera for small animals. Diameters of retinal blood vessels contained in the digital images were measured using image-processing softwares on a personal computer. Fundus blood flow was measured using a laser Doppler flow meter. Both rolipram (0.01-10 microg/kg/min, i.v.) and Ro-20-1724 (0.01-10 microg/kg/min, i.v.) increased diameters of retinal blood vessels in a dose-dependent manner without significant effect on systemic blood pressure, heart rate and fundus blood flow. The effects of phosphodiesterase 4 inhibitors on retinal arterioles were greater than those on retinal venules. Similarly, theophylline (0.1-10 mg/kg/min, i.v.) dilated retinal blood vessels, whereas it decreased blood pressure and increased heart rate markedly. These results suggest that phosphodiesterase 4 contributes to maintenance of retinal vascular tone. Inhibitors of phosphodiesterase 4 could be considered as a candidate for therapeutic drugs to treat diseases associated with disorders of retinal circulation without severe cardiovascular side-effects.

Synergy between natriuretic peptides and phosphodiesterase 5 inhibitors ameliorates pulmonary arterial hypertension

RATIONALE

Phosphodiesterase 5 (PDE5) inhibitors (e.g., sildenafil) are selective pulmonary vasodilators in patients with pulmonary arterial hypertension. The mechanism(s) underlying this specificity remains unclear, but studies in genetically modified animals suggest it might be dependent on natriuretic peptide bioactivity.

OBJECTIVES

We explored the interaction between PDE5 inhibitors and the natriuretic peptide system to elucidate the (patho)physiological relationship between these two cyclic GMP (cGMP)-regulating systems and potential of a combination therapy exploiting these cooperative pathways.

METHODS

Pharmacological evaluation of vascular reactivity was conducted in rat isolated conduit and resistance vessels from the pulmonary and systemic circulation in vitro, and in anesthetized mice in vivo. Parallel studies were undertaken in an animal model of hypoxia-induced pulmonary hypertension (PH).

MEASUREMENTS AND MAIN RESULTS

Sildenafil augments vasodilatation to nitric oxide (NO) in pulmonary and systemic conduit and resistance arteries, whereas identical vasorelaxant responses to atrial natriuretic peptide (ANP) are enhanced only in pulmonary vessels. This differential activity is mirrored in vivo where sildenafil increases the hypotensive actions of ANP in the pulmonary, but not systemic, vasculature. In hypoxia-induced PH, combination of sildenafil plus the neutral endopeptidase (NEP) inhibitor ecadotril (which increases endogenous natriuretic peptide levels) acts synergistically, in a cGMP-dependent manner, to reduce many indices of disease severity without significantly affecting systemic blood pressure.

CONCLUSIONS

These data demonstrate that PDE5 is a key regulator of cGMP-mediated vasodilation by ANP in the pulmonary, but not systemic, vasculature, thereby explaining the pulmonary selectivity of PDE5 inhibitors. Exploitation of this mechanism (i.e., PDE5 and neutral endopeptidase inhibition) represents a novel, orally active combination therapy for pulmonary arterial hypertension.

cAMP-Specific Phosphodiesterase-4 Enzymes in the Cardiovascular System

Cyclic AMP regulates a vast number of distinct events in all cells. Early studies established that its hydrolysis by cyclic nucleotide phosphodiesterases (PDEs) controlled both the magnitude and the duration of its influence. Recent evidence shows that PDEs also act as coincident detectors linking cyclic-nucleotide- and non-cyclic-nucleotide-based cellular signaling processes and are tethered with great selectively to defined intracellular structures, thereby integrating and spatially restricting their cellular effects in time and space. Although 11 distinct families of PDEs have been defined, and cells invariably express numerous individual PDE enzymes, a large measure of our increased appreciation of the roles of these enzymes in regulating cyclic nucleotide signaling has come from studies on the PDE4 family. Four PDE4 genes encode more than 20 isoforms. Alternative mRNA splicing and the use of different promoters allows cells the possibility of expressing numerous PDE4 enzymes, each with unique amino-terminal-targeting and/or regulatory sequences. Dominant negative and small interfering RNA-mediated knockdown strategies have proven that particular isoforms can uniquely control specific cellular functions. Thus the protein kinase A phosphorylation status of the beta(2) adrenoceptor and, thereby, its ability to switch its signaling to extracellular signal-regulated kinase activation, is uniquely regulated by PDE4D5 in cardiomyocytes. We describe how cardiomyocytes and vascular smooth muscle cells selectively vary both the expression and the catalytic activities of PDE4 isoforms to regulate their various functions and how altered regulation of these processes can influence the development, or resolution, of cardiovascular pathologies, such as heart failure, as well as various vasculopathies.

Expression and activity of cGMP-dependent phosphodiesterases is up-regulated by lipopolysaccharide (LPS) in rat peritoneal macrophages

It has been shown that cyclic GMP (cGMP) modulates the inflammatory responses of macrophages, but the underlying molecular mechanisms are still poorly understood. Looking for proteins potentially regulated by cGMP in rat peritoneal macrophages (PMs), in this study we analyzed expression and activity of cGMP-hydrolyzing and cGMP-regulated phosphodiesterases (PDEs). It was found that freshly isolated peritoneal exudate macrophages (PEMs) express enzymes belonging to families PDE1-3, PDE5, PDE10, and PDE11. Analysis of substrate specificity, sensitivity to inhibitors, and subcellular localization showed that PDE2 and PDE3 are the main cGMP-regulated PDE isoforms in PEMs. The profile of PDE expression was altered by maintaining PEMs in culture and treatment with bacterial endotoxin (LPS). After 24 h culture, PDE5 was not present and the levels of PDE2, PDE3, and PDE11 were markedly decreased. However, their expression and activity was recovered after treatment of cultured cells with LPS. A similar pattern of changes was observed for the expression of TNFalpha, but not for guanylyl cyclase A (GC-A). LPS up-regulated PDE expression also in resident peritoneal macrophages (RPMs), although not all PDEs present in PEMs were detected in RPMs. Taken together, our results show that in rat PMs expression of cGMP-dependent PDEs positively correlates with the activation state of cells. Moreover, the fact that most of these PDEs hydrolyze also cAMP indicates that cGMP can play a role of potent regulator of cAMP signaling in macrophages.

Cyclic Nucleotide Phosphodiesterases: Molecular Regulation to Clinical Use

Cyclic nucleotide phosphodiesterases (PDEs) are enzymes that regulate the cellular levels of the second messengers, cAMP and cGMP, by controlling their rates of degradation. There are 11 different PDE families, with each family typically having several different isoforms and splice variants. These unique PDEs differ in their three-dimensional structure, kinetic properties, modes of regulation, intracellular localization, cellular expression, and inhibitor sensitivities. Current data suggest that individual isozymes modulate distinct regulatory pathways in the cell. These properties therefore offer the opportunity for selectively targeting specific PDEs for treatment of specific disease states. The feasibility of these enzymes as drug targets is exemplified by the commercial and clinical successes of the erectile dysfunction drugs, sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra). PDE inhibitors are also currently available or in development for treatment of a variety of other pathological conditions. In this review the basic biochemical properties, cellular regulation, expression patterns, and physiological functions of the different PDE isoforms will be discussed. How these properties relate to the current and future development of PDE inhibitors as pharmacological agents is especially considered. PDEs hold great promise as drug targets and recent research advances make this an exciting time for the field of PDE research.

Natriuretic peptides and nitric oxide stimulate cGMP synthesis in different cellular compartments

Cyclic nucleotide-gated (CNG) channels are a family of ion channels activated by the binding of cyclic nucleotides. Endogenous channels have been used to measure cyclic nucleotide signals in photoreceptor outer segments and olfactory cilia for decades. Here we have investigated the subcellular localization of cGMP signals by monitoring CNG channel activity in response to agonists that activate either particulate or soluble guanylyl cyclase. CNG channels were heterologously expressed in either human embryonic kidney (HEK)-293 cells that stably overexpress a particulate guanylyl cyclase (HEK-NPRA cells), or cultured vascular smooth muscle cells (VSMCs). Atrial natriuretic peptide (ANP) was used to activate the particulate guanylyl cyclase and the nitric oxide donor S-nitroso-n-acetylpenicillamine (SNAP) was used to activate the soluble guanylyl cyclase. CNG channel activity was monitored by measuring Ca2+ or Mn2+ influx through the channels using the fluorescent dye, fura-2. We found that in HEK-NPRA cells, ANP-induced increases in cGMP levels activated CNG channels in a dose-dependent manner (0.05-10 nM), whereas SNAP (0.01-100 microM) induced increases in cGMP levels triggered little or no activation of CNG channels (P < 0.01). After pretreatment with 100 microM 3-isobutyl-1-methylxanthine (IBMX), a nonspecific phosphodiesterase inhibitor, ANP-induced Mn2+ influx through CNG channels was significantly enhanced, while SNAP-induced Mn2+ influx remained small. In contrast, we found that in the presence of IBMX, both 1 nM ANP and 100 microM SNAP triggered similar increases in total cGMP levels. We next sought to determine if cGMP signals are compartmentalized in VSMCs, which endogenously express particulate and soluble guanylyl cyclase. We found that 10 nM ANP induced activation of CNG channels more readily than 100 muM SNAP; whereas 100 microM SNAP triggered higher levels of total cellular cGMP accumulation. These results suggest that cGMP signals are spatially segregated within cells, and that the functional compartmentalization of cGMP signals may underlie the unique actions of ANP and nitric oxide.

Effects of a phosphodiesterase 3 inhibitor, olprinone, on rhythmical change in tension of human gastroepiploic artery

The gastroepiploic artery, used widely as a conduit in coronary artery bypass grafting, has high vasospasticity. The aims of this study were to examine the vasorelaxant effects of three phosphodiesterase 3 (PDE3) inhibitors, olprinone, milrinone and amrinone, on isolated gastroepiploic arterial preparations in comparison with a calcium channel blocker diltiazem, and to confirm the mRNA expression of PDE3A isoenzyme using reverse transcription-polymerase chain reaction (RT-PCR) in the human gastroepiploic artery isolated from stomach removed in cancer surgery. In endothelium-denuded gastroepiploic arterial preparations, phenylephrine (100 microM) produced spontaneous, rhythmical changes in tension consisting of repeated contraction and relaxation. Olprinone at a concentration of 10 microM (n=6) significantly inhibited the frequency (2.7+/-1.1 times/30 min vs. 6.2+/-0.7 times/30 min in the vehicle group), maximum tension (1.7+/-0.6 g vs. 3.6+/-0.6 g in the vehicle group) and minimum tension (0.6+/-0.2 g vs. 1.7+/-0.3 g in the vehicle group) of rhythmical changes. Such potency is comparable to that of diltiazem, but is stronger than milrinone and amrinone. RT-PCR using PDE3A- or PDE3B-specific oligonucleotide primer demonstrated the existence of PDE3A sequence in the gastroepiploic artery. These results suggest that olprinone, a potent PDE3A inhibitor, would be suitable for protecting against perioperative spasm during coronary artery bypass graft surgery.

Optical biosensor provides insights for bradykinin B2receptor signaling in A431 cells

The spatial and temporal targeting of proteins or protein assemblies to appropriate sites is crucial to regulate the specificity and efficiency of protein-protein interactions, thus dictating the timing and intensity of cell signaling and responses. The resultant dynamic mass redistribution could be manifested by label free optical biosensor, and lead to a novel and functional optical signature for studying cell signaling. Here we applied this technology, termed as mass redistribution cell assay technology (MRCAT), to study the signaling networks of bradykinin B(2) receptor in A431 cells. Using MRCAT, the spatial and temporal relocation of proteins and protein assemblies mediated by bradykinin was quantitatively monitored in microplate format and in live cells. The saturability to bradykinin, together with the specific and dose-dependent inhibition by a B(2) specific antagonist HOE140, suggested that the optical signature is a direct result of B(2) receptor activation. The sensitivity of the optical signature to cholesterol depletion by methyl-beta-cyclodextrin argued that B(2) receptor signaling is dependent on the integrity of lipid rafts; disruption of these microdomains hinders the B(2) signaling. Modulations of several important intracellular targets with specific inhibitors suggested that B(2) receptor activation results in signaling via at least dual pathways - G(s)- and G(q)-mediated signaling. Remarkably, the two signaling pathways counter-regulate each other. Several critical downstream targets including protein kinase C, protein kinase A, and epidermal growth factor receptor had been identified to involve in B(2) signaling. The roles of endocytosis and cytoskeleton modulation in B(2) signaling were also demonstrated.

Vascular smooth muscle cell phenotype-dependent phosphodiesterase 4D short form expression: role of differential histone acetylation on cAMP-regulated function

Sustained activation of adenylyl cyclase in vascular smooth muscle cells (VSMCs) results in the activation of a series of complex regulatory systems designed to desensitize these cells to further cAMP-mediated events. Although an increase in phosphodiesterase (PDE) 4-mediated hydrolysis of cAMP forms an integral part of this desensitization program in both "contractile/quiescent" and "synthetic/activated" VSMCs, distinct PDE4D gene variants coordinate these events in these phenotypically distinct cells. Using a combination of pharmacological, biochemical, and molecular biological approaches, and both in vivo and in vitro systems, we have identified the molecular basis underlying this VSMC phenotype-selective expression of PDE4D in response to cAMP-elevating agents in these cells. Thus, whereas the protein kinase A/cAMP response element-binding protein/cAMP response element signaling cascade regulates PDE4D expression in each VSMC phenotype, elevated levels of histone acetylation of the intronic promoter regulating PDE4D1 and PDE4D2 expression allows selective cAMP-mediated induction of expression of these PDE4D variants in synthetic/activated VSMCs. In contrast, the newly described EPAC1/Rap1A cAMP-dependent signaling cascade plays no role in regulating PDE4D expression in either VSMC phenotype. Our data are presented in the context of PDE4-mediated desensitization to cAMP-elevating agents in VSMCs and with the recognition that cAMP-elevating agents are being considered as adjunctive pharmacotherapy in percutaneous coronary interventions, including stenting.

Cardiovascular implications in the use of PDE5 inhibitor therapy

Cardiovascular smooth muscle cells (SMCs) exist as resting or activated cells. Resting SMCs produce contractile proteins and are nearly transcriptionally inactive; activated SMCs are transcriptionally active and are involved in pathological processes such as atherosclerosis. Soluble guanylate cyclase, protein kinase G, and protein kinase A are present in SMCs, but their levels can be decreased in activated cells. Phosphodiesterase 3 (PDE3) activity is abundant in cardiovascular tissues; both PDE3A and PDE3B are involved in cyclic adenosine monophosphate (cAMP) hydrolysis in these tissues. Cyclic-AMP-hydrolyzing PDE activities are altered during the phenotypic transition of SMCs from the resting to the activated phenotype. Similar changes have been observed in cyclic guanosine monophosphate cGMP-hydrolyzing PDEs, although the impact of these alterations on PDE5 inhibitor-mediated effects requires further study. This report presents the changes in PDE expression that accompany phenotypic modulation of SMCs and discusses the potential impact of these events on PDE5-mediated cell functions.

The phosphodiesterase 3 inhibitor cilostazol dilates large cerebral arteries in humans without affecting regional cerebral blood flow

Cilostazol, an inhibitor of phosphodiesterase (PDE) type 3, is used clinically in peripheral artery disease. PDE3 inhibitors may be clinically useful in the treatment of delayed cerebral vasospasm after subarachnoid hemorrhage. The authors present the first results on the effect of cilostazol on cerebral hemodynamics in normal participants. In this double-blind, randomized, crossover study, 200 mg cilostazol or placebo was administered orally to 12 healthy participants. Cerebral blood flow was measured using 133Xe inhalation and single photon emission computerized tomography. Mean flow velocity in the middle cerebral arteries (VMCA) was measured with transcranial Doppler, and the superficial temporal and radial arteries diameters were measured with ultrasonography. During the 4-hour observation period, there was no effect on systolic blood pressure (P = 0.28), but diastolic blood pressure decreased slightly compared with placebo (P = 0.04). VMCA decreased 21.5 +/- 5.7% after cilostazol and 5.5 +/- 12.2% after placebo (P = 0.02, vs. placebo), without any change in global or regional cerebral blood flow. The superficial temporal artery diameter increased 17.6 +/- 12.3% (P < 0.001 vs. baseline) and radial artery diameter increased 12.6 +/- 8.6% (P < 0.001 vs. baseline). Adverse events, especially headache, were common. The findings suggest that cilostazol is an interesting candidate for future clinical trials of delayed cerebral vasospasm.

Nitroprusside stimulates mitochondrial aconitase gene expression through the cyclic adenosine 3',5'-monosphosphate signal transduction pathway in human prostate carcinoma cells

BACKGROUND

Mitochondrial aconitase (mACON), an iron-requiring enzyme, is a major target of nitric oxide (NO) in cells, which causes the oxidant-mediated disruption of the [4Fe-4S] prosthetic group of the enzyme. In this study, the effect of NO on mACON enzymatic activity and gene expression were investigated.

METHODS

Three NO generators, sodium nitroprusside (SNP), S-nitoso-N-acetylpenicillamine (SNAP), and 3-morpholinosydnonimine (SIN) were used to determine the regulation of mACON enzymatic activity by NO. The effect of SNP on mACON, which modulates citrate secretion and cellular bioenergetics in PC-3 cells, was investigated by determining the effect of SNP on mACON gene expression using Western blot and transient gene expression assays.

RESULTS

SNP upregulated mACON enzymatic activity and gene expression in PC-3 cells. However, treating cells with other NO generators, SNAP and SIN, resulted in decreased mACON enzymatic activity. The addition of ascorbic acid to the SNP treatment resulted in a decrease in mACON enzymatic activity and gene expression. Our results showed that both SNP and dibutyryl-cAMP increased the mACON promoter activity 2-fold while the effect was blocked by adding H-89. Mutation of the cAMP response element (CRE) to the AGAGCT abolished the activating effects of SNP and dibutyryl-cAMP on mACON promoter activity.

CONCLUSIONS

These results establish the function of nitroprusside as a signaling molecule for mACON gene expression through the cAMP signal transduction pathway in human prostatic carcinoma cells.

Differential regulation of mesangial cell mitogenesis by cAMP phosphodiesterase isozymes 3 and 4

Mesangial cell (MC) mitogenesis is regulated through "negative cross talk" between cAMP-PKA and ERK signaling. Although it is widely accepted that cAMP inhibits mitogenesis through PKA-mediated phosphorylation of Raf-1, recent studies have indicated that cAMP-mediated inhibition of mitogenesis may occur independently of Raf-1 phosphorylation or without inhibiting ERK activity. We previously showed that MCs possess functionally compartmentalized intracellular pools of cAMP that are differentially regulated by cAMP phosphodiesterases (PDE); an intracellular pool directed by PDE3 but not by PDE4 suppresses mitogenesis. We therefore sought to determine whether there was a differential effect of PDE3 vs. PDE4 inhibitors on the Ras-Raf-MEK-ERK pathway in cultured MC. Although PDE3 and PDE4 inhibitors activated PKA and modestly elevated cAMP levels to a similar extent, only PDE3 inhibitors suppressed MC mitogenesis (-57%) and suppressed Raf-1 kinase and ERK activity (-33 and -68%, respectively). Both PDE3 and PDE4 inhibitors suppressed B-Raf kinase activity. PDE3 inhibitors increased phosphorylation of Raf-1 on serine 43 and serine 259 and decreased phosphorylation on serine 338; PDE4 inhibitors were without effect. Overexpression of a constitutively active MEK-1 construct reversed the antiproliferative effect of PDE3 inhibitors. PDE3 inhibitors also reduced cyclin A levels (-27%), cyclin D and cyclin E kinase activity (-30 and -50%, respectively), and induced expression of the cell cycle inhibitor p21 (+90%). We conclude that the antiproliferative effects of PDE3 inhibitors are mechanistically related to inhibition of the Ras-Raf-MEK-ERK pathway. Additional cell cycle targets of PDE3 inhibitors include cyclin A, cyclin D, cyclin E, and p21.

Phosphodiesterases in the vascular system

Cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) are second messengers involved in the intracellular signal transduction of a variety of extracellular stimuli in several tissues. In the vascular system, these nucleotides play important roles in the regulation of vascular tone and in the maintenance of the mature contractile phenotype in smooth muscle cells. Given that cyclic nucleotide signaling regulates a wide variety of cellular functions, it is not surprising that cyclic nucleotide phosphodiesterases (PDEs). In paticular, the accumulating data showing that there are a large number of different PDE isozymes have triggered an equally large increase in interest about these enzymes. At least 11 different gene families of PDEs are currently known to exist in mammalian tissues. Most families contain several distinct genes, and many of these genes are expressed in different tissues as functionally unique alternative splice variants. This article reviews many of the important aspects about the structure, cellular localization, and regulation of each family of PDEs. Particular emphasis is placed on new information obtained in the last few years about vascular disease. The development of novel methods to deliver more potent and selective PDE inhibitors to individual cell types and subcellular locations will lead to new therapeutic uses for this class of drugs in diseases of the vascular system.

Cyclic nucleotide phosphodiesterase activity, expression, and targeting in cells of the cardiovascular system

Cyclic AMP (cAMP) and cGMP regulate a myriad of cellular functions, such as metabolism, contractility, motility, and transcription in virtually all cell types, including those of the cardiovascular system. Considerable effort over the last 20 years has allowed identification of the cellular components involved in the synthesis of cyclic nucleotides, as well as effectors of cyclic nucleotide-mediated signaling. More recently, a central role for cyclic nucleotide phosphodiesterase (PDE) has also been elaborated in many cell types, including those involved in regulating the activities of the cardiovascular system. In this review, we introduce the PDE families whose members are expressed in cells of the cardiovascular system including cardiomyocytes, vascular smooth muscle cells, and vascular endothelial cells. Because cell behavior is a dynamic process influenced by numerous factors, we will attempt to emphasize how changes in the activity, expression, and targeting of PDE influence cyclic nucleotide-mediated regulation of the behavior of these cells.

Cyclic GMP phosphodiesterases and regulation of smooth muscle function

Cyclic GMP (cGMP) made in response to atrial natriuretic peptide (ANP) or nitric oxide (NO) is an important regulator of short-term changes in smooth muscle tone and longer-term responses to chronic drug treatment or proliferative signals. The ability of smooth muscle cells (SMCs) to utilize different combinations of phosphodiesterase (PDE) isozymes allows cGMP to mediate these multiple processes. For example, PDE5 as a major cGMP-hydrolyzing PDE effectively controls the development of smooth muscle relaxation. In order for contraction to occur, PDE5 is activated and cGMP falls. Conversely, blockade of PDE5 activity allows the relaxation cycle to be prolonged and enhanced. A recently shown direct activation of PDE5 by cGMP binding to the GAF A domain suggests that this regulatory site might be a target for new drug development. The calcium surge associated with vasoconstrictor initiated contraction also activates a calcium/calmodulin-dependent PDE (PDE1A). Together, PDE5 and PDE1A lower cGMP sufficiently to allow contraction. Longer term, both PDE5 and PDE1A mRNA are induced by chronic stimulation of guanylyl cyclase. This induction is a major cause of the tolerance that develops to NO-releasing drugs. Finally, high levels of cGMP or cAMP also act as a brake to attenuate the proliferative response of SMCs to many mitogens. After vessel damage, in order for SMC proliferation to occur, the levels of cGMP and cAMP must be decreased. In humans, this decrease is caused in large part by induction of another Ca2+/calmodulin-dependent PDE (PDE1C) that allows the brake to be released and proliferation to start.

Alterations in EDHF-type relaxation and phosphodiesterase activity in mesenteric arteries from diabetic rats

In isolated superior mesenteric artery rings from age-matched control rats and streptozotocin (STZ)-induced diabetic rats, we investigated the role of cAMP in endothelium-derived hyperpolarizing factor (EDHF)-type relaxation. The ACh-induced EDHF-type relaxation was significantly weaker in STZ-induced diabetic rats than in control rats, and in both groups of rats it was attenuated by 18alpha-glycyrrhetinic acid (18alpha-GA), an inhibitor of gap junctions, and enhanced by IBMX, a cAMP-phosphodiesterase (PDE) inhibitor. These enhanced EDHF-type responses were very similar in magnitude between diabetic and age-matched control rats. The EDHF-type relaxation was enhanced by cilostamide, a PDE3-selective inhibitor, but not by Ro 20-1724, a PDE4-selective inhibitor. The expression levels of the mRNAs and proteins for two cAMP PDEs (PDE3A, PDE3B) were significantly increased in STZ-induced diabetic rats, but those for PDE4D were not. We conclude that the impairment of EDHF-type relaxations in STZ-induced diabetic rats may be attributed to a reduction in the action of cAMP via increased PDE activity.

Phosphodiesterase 3 activity is reduced in dog lung following pacing-induced heart failure

We hypothesized that decreases in expression and/or activity of cAMP-specific phosphodiesterases (PDE) contribute to protective adaptations observed in lung after heart failure. In this study, we compared PDE activity in lung parenchyma isolated from control dogs and those paced to heart failure by assaying cyclic nucleotide hydrolysis in fractions of homogenate supernatant eluted from DEAE-Trisacryl columns. Cyclic nucleotide hydrolysis due to PDE3, PDE4, and PDE5 isoforms was predominant in both control and paced groups. The ratio of PDE3 activity to total cAMP PDE activity was decreased in the paced group compared with control (P < 0.05), whereas PDE4 or PDE5 activity ratios were not different between the two groups. With the use of RT-PCR, message expression for PDE3A or PDE3B did not differ between the two groups. Cilostamide, a selective PDE3 inhibitor, and forskolin, a nonspecific agonist for adenylyl cyclase, both inhibited thapsigargin-induced increases in endothelial permeability in control lung. We conclude that PDE3 activity, but not mRNA expression, is reduced in lung from dogs paced to heart failure, a change that could contribute to heart failure-induced attenuation of the lung endothelial permeability response to injury.

Vascular smooth muscle cell phosphodiesterase (PDE) 3 and PDE4 activities and levels are regulated by cyclic AMP in vivo

Prolonged incubation of several cell types, including cultured vascular smooth muscle cells (VSMC), with cyclic AMP-elevating agents increases cAMP phosphodiesterase (PDE) activity and levels. In this work, we describe for the first time an increase in arterial VSMC cAMP PDE activity and levels caused by cAMP-elevating agents when these agents are administered to rats in vivo. Injections of rats with dibutyryl cAMP (dbcAMP) or forskolin increased both PDE3 and PDE4 activities in aortic and femoral artery VSMC. Consistent with the idea that cAMP-elevating agents increased PDE3 and PDE4 activities by acting directly on VSMC, local delivery of dbcAMP or forskolin to femoral arteries using a pluronic gel-based approach increased femoral artery VSMC PDE3 and PDE4 activities to levels similar to those observed after injection of these agents. Consistent with a role for de novo mRNA and protein synthesis in the cAMP-elevating agent induced increase in PDE3 and PDE4, 1) systemic administration of forskolin increased PDE3A, PDE3B, and PDE4D mRNA levels in aortic VSMC and femoral artery VSMC, 2) local delivery of dbcAMP increased PDE3A, PDE3B, and PDE4D3 protein levels in femoral artery VSMC, and 3) local administration of either actinomycin D or cycloheximide attenuated the effect of dbcAMP. In addition, our results indicate that the PDE3 and PDE4 variants increased by cAMP-elevating agents in arterial VSMC in situ were distinct from those elevated by these agents in cultured arterial VSMC. Consistent with the effect of increased VSMC cAMP PDE on blood vessel function, inhibition of PDE3 and PDE4 activities potentiated the relaxant effect of forskolin in dbcAMP-treated femoral artery rings to a greater extent than in untreated control blood vessels. We propose that our findings are consistent with the concept that cAMP regulates VSMC cAMP PDE activity and levels in vivo and that VSMC phenotype influences the choice of cAMP PDE variant that is elevated. Our findings are discussed in the context that agents aimed at specific PDE3 or PDE4 variants could perhaps allow greater control of cAMP-mediated regulation of VSMC behaviors that are phenotype-dependent.

Reduced phosphodiesterase 3 activity and phosphodiesterase 3A level in synthetic vascular smooth muscle cells: implications for use of phosphodiesterase 3 inhibitors in cardiovascular tissues

Vascular smooth muscle cells (VSMC) in situ function to control contraction and are said to express a contractile phenotype. However, during development or in response to vascular damage, VSMC proliferate and express a more synthetic phenotype. A survey of literature values for contractile and synthetic VSMC phosphodiesterase (PDE) 3 and PDE4 activities identified a marked difference in the PDE3 and PDE4 activities of these cells. In this study, a comparison of PDE3 and PDE4 activities in contractile and synthetic VSMC demonstrates that a reduced PDE3/PDE4 activity ratio in synthetic VSMC correlates with a reduced PDE3 activity and is associated with marked reductions in PDE3A mRNA and protein levels. Because we show that similar reductions in PDE3 activity and PDE3A levels occur upon culture of human aortic VSMC and that this phenomenon associates with the phenotypic switch that occurs to VSMC in response to vascular damage, our findings are presented in the context that PDE3 inhibition might be expected to selectively alter functions of contractile VSMC.

Altered phosphodiesterase 3-mediated cAMP hydrolysis contributes to a hypermotile phenotype in obese JCR:LA-cp rat aortic vascular smooth muscle cells: implications for diabetes-associated cardiovascular disease

Cardiovascular diseases represent a significant cause of morbidity and mortality in diabetes. Of the many animal models used in the study of non-insulin-dependent (type 2) diabetes, the JCR:LA-cp rat is unique in that it develops insulin resistance in the presence of obesity and manifests both peripheral and coronary vasculopathies. In this animal model, arterial vascular smooth muscle cells (VSMCs) from homozygous obese (cp/cp) rats, but not from age-matched healthy (+/+ or + /cp, collectively defined +/?) littermates, display an " activated" phenotype in vitro and in vivo and have an elevated level of cAMP phosphodiesterase (PDE) activity. In this report, we confirm that cp/cp rat aortic VSMCs have an elevated level of PDE3 activity and show that only particulate PDE3 (PDE3B) activity is elevated. In marked contrast to results obtained in + /? VSMCs, simultaneous activation of adenylyl cyclase and inhibition of PDE3 activity in cp/cp VSMCs synergistically increased cAMP. Although PDE3 inhibition did not potentiate the antimigratory effects of forskolin on +/? VSMCs, PDE3 inhibition did markedly potentiate the forskolin-induced inhibition of migration of cp/cp-derived VSMCs. Although PDE3 activity was elevated in cp/cp rat aortic VSMCs, levels of expression of cytosolic PDE3 (PDE3A) and PDE3B in +/? and cp/cp VSMCs, as well as activation of these enzymes following activation of the cAMP-protein kinase A signaling cascade, were not different. Our data are consistent with an increased role for PDE3 in regulating cAMP-dependent signaling in cp/cp VSMCs and identify PDE3 as a cellular activity potentially responsible for the phenotype of cp/cp VSMCs.

PKA-dependent activation of PDE3A and PDE4 and inhibition of adenylyl cyclase V/VI in smooth muscle

Regulation of adenylyl cyclase type V/VI and cAMP-specific, cGMP-inhibited phosphodiesterase (PDE) 3 and cAMP-specific PDE4 by cAMP-dependent protein kinase (PKA) and cGMP-dependent protein kinase (PKG) was examined in gastric smooth muscle cells. Expression of PDE3A but not PDE3B was demonstrated by RT-PCR and Western blot. Basal PDE3 and PDE4 activities were present in a ratio of 2:1. Forskolin, isoproterenol, and the PKA activator 5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole 3',5'-cyclic monophosphate, SP-isomer, stimulated PDE3A phosphorylation and both PDE3A and PDE4 activities. Phosphorylation of PDE3A and activation of PDE3A and PDE4 were blocked by the PKA inhibitors [protein kinase inhibitor (PKI) and H-89] but not by the PKG inhibitor (KT-5823). Sodium nitroprusside inhibited PDE3 activity and augmented forskolin- and isoproterenol-stimulated cAMP levels; PDE3 inhibition was reversed by blockade of cGMP synthesis. Forskolin stimulated adenylyl cyclase phosphorylation and activity; PKI blocked phosphorylation and enhanced activity. Stimulation of cAMP and inhibition of inositol 1,4,5-trisphosphate-induced Ca(2+) release and muscle contraction by isoproterenol were augmented additively by PDE3 and PDE4 inhibitors. The results indicate that PKA regulates cAMP levels in smooth muscle via stimulatory phosphorylation of PDE3A and PDE4 and inhibitory phosphorylation of adenylyl cyclase type V/VI. Concurrent generation of cGMP inhibits PDE3 activity and augments cAMP levels.

Cyclic nucleotide phosphodiesterase 1C promotes human arterial smooth muscle cell proliferation

Proliferation of arterial smooth muscle cells (SMCs) is a key event in the formation of advanced atherosclerotic lesions and restenosis after angioplasty. Cyclic nucleotides (cAMP and cGMP) inhibit arterial SMC proliferation, and elevation of cyclic nucleotides reduces neointimal formation after angioplasty in animal models. Degradation of cAMP and cGMP is catalyzed by cyclic nucleotide phosphodiesterases (PDEs). One of these, PDE1C, hydrolyzes cAMP and cGMP and is expressed in proliferating human SMCs but is absent in quiescent human aorta. Thus, PDE1C expression is low in cultured human SMCs made quiescent by attaching to fibrillar collagen type I. After release from the fibrillar collagen, PDE1C expression is induced and associated with traverse through S-phase of the cell cycle. Further, PDE1C is expressed in vivo in human fetal aorta containing proliferating SMCs, but not in newborn aorta in which SMC proliferation has ceased. Inhibition of PDE1C in SMCs isolated from normal aorta or from lesions of atherosclerosis using antisense oligonucleotides or a PDE1 inhibitor results in suppression of SMC proliferation. In conclusion, PDE1C expression is a marker of human SMC proliferation ex vivo and in vivo. Inhibition of PDE1C leads to inhibition of human SMC proliferation. Because PDE1C is absent in quiescent SMCs, PDE1C inhibitors may target proliferating SMCs in lesions of atherosclerosis or restenosis.

Molecular pathways of cyclic nucleotide-induced inhibition of arterial smooth muscle cell proliferation

Cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) are second messengers involved in the intracellular signal transduction of a wide variety of extracellular stimuli. These signals regulate many biological processes including cell proliferation, differentiation, migration, and apoptosis. Recently, significant progress has been achieved in the molecular basis underlying cyclic nucleotide regulation of cell proliferation. This review summarizes our knowledge of the signaling pathways regulated by cyclic nucleotides in arterial smooth muscle cells.