Phosphodiesterase 1 Upregulation in Pulmonary Arterial Hypertension

Phosphodiesterase in heart and vessels: from physiology to diseases

Phosphodiesterases (PDEs) are a superfamily of enzymes that hydrolyze cyclic nucleotides, including cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Both cyclic nucleotides are critical secondary messengers in the neurohormonal regulation in the cardiovascular system. PDEs precisely control spatiotemporal subcellular distribution of cyclic nucleotides in a cell- and tissue-specific manner, playing critical roles in physiological responses to hormone stimulation in the heart and vessels. Dysregulation of PDEs has been linked to the development of several cardiovascular diseases, such as hypertension, aneurysm, atherosclerosis, arrhythmia, and heart failure. Targeting these enzymes has been proven effective in treating cardiovascular diseases and is an attractive and promising strategy for the development of new drugs. In this review, we discuss the current understanding of the complex regulation of PDE isoforms in cardiovascular function, highlighting the divergent and even opposing roles of PDE isoforms in different pathogenesis.

Capillary leak and endothelial permeability in critically ill patients: a current overview

Capillary leak syndrome (CLS) represents a phenotype of increased fluid extravasation, resulting in intravascular hypovolemia, extravascular edema formation and ultimately hypoperfusion. While endothelial permeability is an evolutionary preserved physiological process needed to sustain life, excessive fluid leak-often caused by systemic inflammation-can have detrimental effects on patients' outcomes. This article delves into the current understanding of CLS pathophysiology, diagnosis and potential treatments. Systemic inflammation leading to a compromise of endothelial cell interactions through various signaling cues (e.g., the angiopoietin-Tie2 pathway), and shedding of the glycocalyx collectively contribute to the manifestation of CLS. Capillary permeability subsequently leads to the seepage of protein-rich fluid into the interstitial space. Recent insights into the importance of the sub-glycocalyx space and preserving lymphatic flow are highlighted for an in-depth understanding. While no established diagnostic criteria exist and CLS is frequently diagnosed by clinical characteristics only, we highlight more objective serological and (non)-invasive measurements that hint towards a CLS phenotype. While currently available treatment options are limited, we further review understanding of fluid resuscitation and experimental approaches to target endothelial permeability. Despite the improved understanding of CLS pathophysiology, efforts are needed to develop uniform diagnostic criteria, associate clinical consequences to these criteria, and delineate treatment options.

The role of vasoactive intestinal peptide in pulmonary diseases

Vasoactive intestinal peptide (VIP) is an abundant neurotransmitter in the lungs and other organs. Its discovery dates back to 1970. And VIP gains attention again due to the potential application in COVID-19 after a research wave in the 1980s and 1990s. The diverse biological impacts of VIP extend beyond its usage in COVID-19 treatment, encompassing its involvement in various pulmonary and systemic disorders. This review centers on the function of VIP in various lung diseases, such as pulmonary arterial hypertension, chronic obstructive pulmonary disease, asthma, cystic fibrosis, acute lung injury/acute respiratory distress syndrome, pulmonary fibrosis, and lung tumors. This review also outlines two main limitations of VIP as a potential medication and gathers information on extended-release formulations and VIP analogues.

Mesenchymal stem cell-derived extracellular vesicles prevent the formation of pulmonary arterial hypertension through a microRNA-200b-dependent mechanism

BACKGROUND

Bone marrow mesenchymal stem cell-derived extracellular vesicles (BMSC-EVs) have been highly studied with their critical roles as carriers of therapeutic targets such as microRNAs (miRNAs) in the treatment of human diseases, including pulmonary arterial hypertension (PAH). Herein, we tried to study the potential of BMSC-EVs to deliver miR-200b for the regulation of macrophage polarization in PAH.

METHODS

Rat models of PAH were induced with monocrotaline treatment, followed by miR-200b expression detection in lung tissues, pulmonary artery smooth muscle cells (PASMCs) and macrophages. miR-200b-containing BMSCs or miR-200b-deficient BMSCs were selected to extract EVs. Then, we assessed the changes in rats with PAH-associated disorders as well as in vitro macrophage polarization and the functions of PASMCs after treatment with BMSC-EVs. Moreover, the interaction between miR-200b, phosphodiesterase 1 A (PDE1A) was identified with a luciferase assay, followed by an exploration of the downstream pathway, cAMP-dependent protein kinase (PKA).

RESULTS

miR-200b was reduced in lung tissues, PASMCs and macrophages of rats with PAH-like pathology. BMSC-EVs transferred miR-200b into macrophages, and subsequently accelerated their switch to the M2 phenotype and reversed the PAH-associated disorders. Furthermore, miR-200b carried by BMSC-EVs induced PKA phosphorylation by targeting PDE1A, thereby expediting macrophage polarization.

CONCLUSION

Our current study highlighted the inhibitory role of BMSC-EV-miR-200b in PAH formation.

Prostacyclin mimetics inhibit DRP1-mediated pro-proliferative mitochondrial fragmentation in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare cardiopulmonary disorder, involving the remodelling of the small pulmonary arteries. Underlying this remodelling is the hyper-proliferation of pulmonary arterial smooth muscle cells within the medial layers of these arteries and their encroachment on the lumen. Previous studies have demonstrated an association between excessive mitochondrial fragmentation, a consequence of increased expression and post-translational activation of the mitochondrial fission protein dynamin-related protein 1 (DRP1), and pathological proliferation in PASMCs derived from PAH patients. However, the impact of prostacyclin mimetics, widely used in the treatment of PAH, on this pathological mitochondrial fragmentation remains unexplored. We hypothesise that these agents, which are known to attenuate the proliferative phenotype of PAH PASMCs, do so in part by inhibiting mitochondrial fragmentation. In this study, we confirmed the previously reported increase in DRP1-mediated mitochondrial hyper-fragmentation in PAH PASMCs. We then showed that the prostacyclin mimetic treprostinil signals via either the Gs-coupled IP or EP2 receptor to inhibit mitochondrial fragmentation and the associated hyper-proliferation in a manner analogous to the DRP1 inhibitor Mdivi-1. We also showed that treprostinil recruits either the IP or EP2 receptor to activate PKA and induce the phosphorylation of DRP1 at the inhibitory residue S637 and inhibit that at the stimulatory residue S616, both of which are suggestive of reduced DRP1 fission activity. Like treprostinil, MRE-269, an IP receptor agonist, and butaprost, an EP2 receptor agonist, attenuated DRP1-mediated mitochondrial fragmentation through PKA. We conclude that prostacyclin mimetics produce their anti-proliferative effects on PAH PASMCs in part by inhibiting DRP1-mediated mitochondrial fragmentation.

Phosphodiesterase 4B activation exacerbates pulmonary hypertension induced by intermittent hypoxia by regulating mitochondrial injury and cAMP/PKA/p-CREB/PGC-1α signaling

Proliferation of smooth muscle cells, oxidative stress, and pulmonary vasoconstriction resulting from intermittent hypoxia (IH) facilitate pulmonary hypertension (PH) in patients with obstructive sleep apnea. The role of Phosphodiesterase 4 B (PDE4B) in PH has not yet been established. Herein, we investigated whether PDE4B inhibition ameliorates experimental PH by modulating cAMP signaling. We performed an integrative analysis of PDE4B expression in Gene Expression Omnibus datasets, experimental IH-induced rat PH samples, and IH-induced pulmonary arterial smooth muscle cells (PASMCs). PDE4B expression was modulated using siRNA in vitro and a specific adeno-associated virus serotype 1 in vivo. In the databases of mouse models of IH-induced and sustained hypoxia-induced PH and in a rat model of six weeks of IH, the expression of PDE4B was up-regulated. Inhibition of PDE4B attenuated IH-induced pulmonary vascular remodeling and right ventricular hypertrophy. Our results also showed that PDE4B deficiency inhibited IH-induced proliferation of PASMCs with less mitochondrial reactive oxygen species and mitochondrial damage. Meanwhile, IH induced an increase in ATF4, which positively regulated the expression of PDE4B through transcription, and inhibition of ATF4 exerted effects similar to those of PDE4B inhibition. Mechanistically, downregulating the expression of PDE4B resulted in the activation of the cAMP/PKA/p-CREB/PGC-1α pathway in PASMCs after IH. Taken together, our present study provides evidence that inhibition of PDE4B attenuates IH-induced PH by regulating cAMP signaling.

Construction of a diagnostic signature and immune landscape of pulmonary arterial hypertension

Background

Molecular biomarkers are widely used for disease diagnosis and exploration of pathogenesis. Pulmonary arterial hypertension (PAH) is a rapidly progressive cardiopulmonary disease with delayed diagnosis. Studies were limited regarding molecular biomarkers correlated with PAH from a broad perspective.

Methods

Two independent microarray cohorts comprising 73 PAH samples and 36 normal samples were enrolled in this study. The weighted gene co-expression network analysis (WGCNA) was performed to identify the key modules associated with PAH. The LASSO algorithm was employed to fit a diagnostic model. The latent biology mechanisms and immune landscape were further revealed via bioinformatics tools.

Results

The WGCNA approach ultimately identified two key modules significantly associated with PAH. For genes within the two models, differential expression analysis between PAH and normal samples further determined nine key genes. With the expression profiles of these nine genes, we initially developed a PAH diagnostic signature (PDS) consisting of LRRN4, PI15, BICC1, PDE1A, TSHZ2, HMCN1, COL14A1, CCDC80, and ABCB1 in GSE117261 and then validated this signature in GSE113439. The ROC analysis demonstrated outstanding AUCs with 0.948 and 0.945 in two cohorts, respectively. Besides, patients with high PDS scores enriched plenty of Th17 cells and neutrophils, while patients with low PDS scores were dramatically related to mast cells and B cells.

Conclusion

Our study established a robust and promising signature PDS for diagnosing PAH, with key genes, novel pathways, and immune landscape offering new perspectives for exploring the molecular mechanisms and potential therapeutic targets of PAH.

Heart Failure with Preserved Ejection Fraction and Pulmonary Hypertension: Focus on Phosphodiesterase Inhibitors

Pulmonary hypertension (PH) is common in patients with heart failure with preserved ejection fraction (HFpEF). A chronic increase in mean left atrial pressure leads to passive remodeling in pulmonary veins and capillaries and modest PH (isolated postcapillary PH, Ipc-PH) and is not associated with significant right ventricular dysfunction. In approximately 20% of patients with HFpEF, "precapillary" alterations of pulmonary vasculature occur with the development of the combined pre- and post-capillary PH (Cpc-PH), pertaining to a poor prognosis. Current data indicate that pulmonary vasculopathy may be at least partially reversible and thus serves as a therapeutic target in HFpEF. Pulmonary vascular targeted therapies, including phosphodiesterase (PDE) inhibitors, may have a valuable role in the management of patients with PH-HFpEF. In studies of Cpc-PH and HFpEF, PDE type 5 inhibitors were effective in long-term follow-up, decreasing pulmonary artery pressure and improving RV contractility, whereas studies of Ipc-PH did not show any benefit. Randomized trials are essential to elucidate the actual value of PDE inhibition in selected patients with PH-HFpEF, especially in those with invasively confirmed Cpc-PH who are most likely to benefit from such treatment.

Vinpocetine is the forthcoming adjuvant agent in the management of COVID-19

Vinpocetine (VPN) is an alkaloid derivative of vincamine inhibits phosphodiesterase type 1 that increase cyclic guanosine monophosphate and cyclic adenosine monophosphate. VPN have anti-inflammatory and antioxidant effects with suppression release of pro-inflammatory cytokines. Moreover, VPN mitigates oxidative stress (OS) and inflammatory reactions through inhibition of mitogen-activated protein kinase (MAPK) signaling pathway. Therefore, VPN may decrease hyper-inflammation-induced acute lung injury in COVID-19 through modulation of NF-κB pathway. Taken together, VPN has pulmonary and extra-pulmonary protective effects against COVID-19 through mitigation of OS and hyperinflammation. In conclusion, VPN has noteworthy anti-inflammatory and anti-oxidant effects through inhibition of NF-κB/MAPK signaling pathway so, it may reduce SARS-CoV-2-induced hyper inflammatory and OS.

Vinpocetine (VPN) is an alkaloid from vincamine with a potent anti-inflammatory and antioxidant effects. VPN has the possibility of inhibiting substances that cause inflammation and oxidative stress and as a result, may be beneficial in COVID-19 treatment. Due to the anti-inflammatory effect of VPN, acute lung injury in COVID-19 may reduce as a result of the inhibition of agent that causes lungs inflammation in COVID-19. VPN may have potential to reduce difficulty in breathing and damage to the lungs. Conclusively, VPN when administered with other therapy may improve the outcome of treatment of COVID-19.

Molecular Signatures of Diabetic Kidney Disease Hiding in a Patient with Hypertension-Related Kidney Disease: A Clinical Pathologic Molecular Correlation

The Kidney Precision Medicine Project (KPMP) seeks to establish a molecular atlas of the kidney in health and disease and improve our understanding of the molecular drivers of CKD and AKI. Herein, we describe the case of a 66-year-old woman with CKD who underwent a protocol KPMP kidney biopsy. Her clinical history included well-controlled diabetes mellitus, hypertension, and proteinuria. The patient's histopathology was consistent with modest hypertension-related kidney injury, without overt diabetic kidney disease. Transcriptomic signatures of the glomerulus, interstitium, and tubular subsegments were obtained from laser microdissected tissue. The molecular signatures that were uncovered revealed evidence of early diabetic kidney disease adaptation and ongoing active tubular injury with enriched pathways related to mesangial cell hypertrophy, glycosaminoglycan biosynthesis, and apoptosis. Molecular evidence of diabetic kidney disease was found across the nephron. Novel molecular assays can supplement and enrich the histopathologic diagnosis obtained from a kidney biopsy.

PDE1 inhibitors: a review of the recent patent literature (2008-present)

INTRODUCTION

: PDE1 has been demonstrated to be a potential drug target for a variety of diseases, such as Alzheimer's disease and cardiovascular disease. In the past decades, numerous PDE1 inhibitors with structural diversities have been developed and patented by pharmaceutical companies, providing drug candidates for exploring novel disease indications of PDE1.

AREA COVERED

: This review aims to provide an overview of PDE1 inhibitors reported in patents from 2008 to present.

EXPERT OPINION

: Among current PDE1 inhibitors, only a few of them showed high selectivity over other PDEs, which might cause severe side effects in clinic. The development of highly selective PDE1 inhibitors is still the "top priority" in the following research. The selective recognition mechanism of PDE1 with inhibitors should be further elucidated by X-ray crystallography in order to provide evidences for the rational design of selective PDE1 inhibitors. In addition, PDE1 inhibitors should be applied in the different clinical indications beyond CNS diseases.

Acute Hemodynamic Effects and Tolerability of Phosphodiesterase-1 Inhibition With ITI-214 in Human Systolic Heart Failure

BACKGROUND

PDE1 (phosphodiesterase type 1) hydrolyzes cyclic adenosine and guanosine monophosphate. ITI-214 is a highly selective PDE1 inhibitor that induces arterial vasodilation and positive inotropy in larger mammals. Here, we assessed pharmacokinetics, hemodynamics, and tolerability of single-dose ITI-214 in humans with stable heart failure with reduced ejection fraction.

METHODS

Patients with heart failure with reduced ejection fraction were randomized 3:1 to 10, 30, or 90 mg ITI-214 single oral dose or placebo (n=9/group). Vital signs and electrocardiography were monitored predose to 5 hours postdose and transthoracic echoDoppler cardiography predose and 2-hours postdose.

RESULTS

Patient age averaged 54 years; 42% female, and 60% Black. Mean systolic blood pressure decreased 3 to 8 mm Hg (P<0.001) and heart rate increased 5 to 9 bpm (P≤0.001 for 10, 30 mg doses, RM-ANCOVA). After 4 hours, neither blood pressure or heart rate significantly differed among cohorts (supine or standing). ITI-214 increased mean left ventricular power index, a relatively load-insensitive inotropic index, by 0.143 Watts/mL²·10⁴ (P=0.03, a +41% rise; 5-71 CI) and cardiac output by 0.83 L/min (P=0.002, +31%, 13-49 CI) both at the 30 mg dose. Systemic vascular resistance declined with 30 mg (-564 dynes·s/cm-⁵, P<0.001) and 90 mg (-370, P=0.016). Diastolic changes were minimal, and no parameters were significantly altered with placebo. ITI-214 was well-tolerated. Five patients had mild-moderate hypotension or orthostatic hypotension recorded adverse events. There were no significant changes in arrhythmia outcome and no serious adverse events.

CONCLUSIONS

Single-dose ITI-214 is well-tolerated and confers inodilator effects in humans with heart failure with reduced ejection fraction. Further investigations of its therapeutic utility are warranted. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03387215.

Microvascular Sex- and Age- Dependent Phosphodiesterase Expression

Objective: The cyclic nucleotide second messengers, cAMP and cGMP, are pivotal regulators of vascular functions; their cellular levels are tightly controlled by the cyclic nucleotide hydrolases, phosphodiesterases (PDE). Biologic sex and age are recognized as independent factors impacting the mechanisms mediating both vascular health and dysfunction. This study focused on microvessels isolated from male and female rats before (juvenile) and after (adult) sexual maturity under resting conditions. We tested the hypothesis that sexual dimorphism in microvascular PDE expression would be absent in juvenile rats, but would manifest in adult rats.

Methods: Abdominal skeletal muscle arterioles and venules were isolated from age-matched juvenile and adult male and female rats under resting conditions. Transcripts of five PDE families (1–5) associated with coronary and vascular function with a total of ten genes were measured using TaqMan real-time RT-PCR and protein expression of microvessel PDE4 was assessed using immunoblotting and immunofluorescence.

Results: Overall expression levels of PDE5A were highest while PDE3 levels were lowest among the five PDE families (p < 0.05) regardless of age or sex. Contrary to our hypothesis, in juveniles, sexual dimorphism in PDE expression was observed in three genes: arterioles (PDE1A, female > male) and venules (PDE1B and 3A, male > female). In adults, gene expression levels in males were higher than females for five genes in arterioles (PDE1C, 3A, 3B, 4B, 5A) and three genes (PDE3A, 3B, and 5A) in venules. Furthermore, age-related differences were observed in PDE1-5 (in males, adult > juvenile for most genes in arterioles; in females, adult > juvenile for arteriolar PDE3A; juvenile gene expression > adult for two genes in arterioles and three genes in venules). Immunoblotting and immunofluorescence analysis revealed protein expression of microvessel PDE4.

Conclusion: This study revealed sexual dimorphism in both juvenile and adult rats, which is inconsistent with our hypothesis. The sex- and age-dependent differences in PDE expression implicate different modulations of cAMP and cGMP pathways for microvessels in health. The implication of these sex- and age-dependent differences, as well as the duration and microdomain of PDE1-5 activities in skeletal muscle microvessels, in both health and disease, require further investigation.

Role of phosphodiesterase 1 in the pathophysiology of diseases and potential therapeutic opportunities

Cyclic nucleotide phosphodiesterases (PDEs) are superfamily of enzymes that regulate the spatial and temporal relationship of second messenger signaling in the cellular system. Among the 11 different families of PDEs, phosphodiesterase 1 (PDE1) sub-family of enzymes hydrolyze both 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) in a mutually competitive manner. The catalytic activity of PDE1 is stimulated by their binding to Ca²⁺/calmodulin (CaM), resulting in the integration of Ca²⁺ and cyclic nucleotide-mediated signaling in various diseases. The PDE1 family includes three subtypes, PDE1A, PDE1B and PDE1C, which differ for their relative affinities for cAMP and cGMP. These isoforms are differentially expressed throughout the body, including the cardiovascular, central nervous system and other organs. Thus, PDE1 enzymes play a critical role in the pathophysiology of diseases through the fundamental regulation of cAMP and cGMP signaling. This comprehensive review provides the current research on PDE1 and its potential utility as a therapeutic target in diseases including the cardiovascular, pulmonary, metabolic, neurocognitive, renal, cancers and possibly others.

Phosphodiesterase Inhibitors in Acute Lung Injury: What Are the Perspectives?

Despite progress in understanding the pathophysiology of acute lung damage, currently approved treatment possibilities are limited to lung-protective ventilation, prone positioning, and supportive interventions. Various pharmacological approaches have also been tested, with neuromuscular blockers and corticosteroids considered as the most promising. However, inhibitors of phosphodiesterases (PDEs) also exert a broad spectrum of favorable effects potentially beneficial in acute lung damage. This article reviews pharmacological action and therapeutical potential of nonselective and selective PDE inhibitors and summarizes the results from available studies focused on the use of PDE inhibitors in animal models and clinical studies, including their adverse effects. The data suggest that xanthines as representatives of nonselective PDE inhibitors may reduce acute lung damage, and decrease mortality and length of hospital stay. Various (selective) PDE3, PDE4, and PDE5 inhibitors have also demonstrated stabilization of the pulmonary epithelial-endothelial barrier and reduction the sepsis- and inflammation-increased microvascular permeability, and suppression of the production of inflammatory mediators, which finally resulted in improved oxygenation and ventilatory parameters. However, the current lack of sufficient clinical evidence limits their recommendation for a broader use. A separate chapter focuses on involvement of cyclic adenosine monophosphate (cAMP) and PDE-related changes in its metabolism in association with coronavirus disease 2019 (COVID-19). The chapter illuminates perspectives of the use of PDE inhibitors as an add-on treatment based on actual experimental and clinical trials with preliminary data suggesting their potential benefit.

Discovery of catalytic-site-fluorescent probes for tracing phosphodiesterase 5 in living cells

Small molecule fluorescent probes provide a powerful labelling technology to enhance our understanding of particular proteins. However, the discovery of a proper fluorescent probe for detecting PDE5 is still a challenge due to the highly conservative structure of the catalytic domain in the phosphodiesterase (PDE) families. Herein, we identified probes based on the key amino residues in the ligand binding pocket of PDE5 and catalytic-site-fluorescent probes PCO2001–PCO2003 were well designed and synthesized. Among them, PCO2003 exhibited extraordinary fluorescence properties and the ability to be applied to PDE5 visualization in live cells as well as in pulmonary tissue slices, demonstrating the location and expression level of PDE5 proteins. Overall, the environment-sensitive “turn-on” probe is economical, convenient and rapid for PDE5 imaging, implying that the catalytic-site-fluorescent probe will have a variety of future applications in pathological diagnosis as well as drug screening.

To enhance the understanding of PDE5 as the drug target. Herein, we designed catalytic-site-fluorescent probes that can be applied to PDE5 visualization in live cells and tissue slices, implying the potential in diagnosis and drug screening.

Vascular Smooth Muscle Remodeling in Conductive and Resistance Arteries in Hypertension

Cardiovascular disease is a leading cause of death worldwide and accounts for >17.3 million deaths per year, with an estimated increase in incidence to 23.6 million by 2030. ¹ Cardiovascular death represents 31% of all global deaths ² -with stroke, heart attack, and ruptured aneurysms predominantly contributing to these high mortality rates. A key risk factor for cardiovascular disease is hypertension. Although treatment or reduction in hypertension can prevent the onset of cardiovascular events, existing therapies are only partially effective. A key pathological hallmark of hypertension is increased peripheral vascular resistance because of structural and functional changes in large (conductive) and small (resistance) arteries. In this review, we discuss the clinical implications of vascular remodeling, compare the differences between vascular smooth muscle cell remodeling in conductive and resistance arteries, discuss the genetic factors associated with vascular smooth muscle cell function in hypertensive patients, and provide a prospective assessment of current and future research and pharmacological targets for the treatment of hypertension.

Validation of Phosphodiesterase-10 as a Novel Target for Pulmonary Arterial Hypertension via Highly Selective and Subnanomolar Inhibitors

Pulmonary arterial hypertension (PAH) causes pathological increase in pulmonary vascular resistance, leading to right-heart failure and eventual death. Previously, phosphodiesterase-10 (PDE10) was reported to be a promising target for PAH based on the studies with a nonselective PDE inhibitor papaverine, but little progress has been made to confirm the practical application of PDE10 inhibitors. To validate whether PAH is ameliorated by PDE10 inhibition rather than other PDE isoforms, here we report an integrated strategy to discover highly selective PDE10 inhibitors as chemical probes. Structural optimization resulted in a PDE10 inhibitor 2b with subnanomolar affinity and good selectivity of >45 000-fold against other PDEs. The cocrystal structure of the PDE10-2b complex revealed an important H-bond interaction between 2b and Tyr693. Finally, compound 2b significantly decreased the arterial pressure in PAH rats and thus validated the potential of PDE10 as a novel anti-PAH target. These findings suggest that PDE10 inhibition may be a viable treatment option for PAH.

Phosphodiesterases as therapeutic targets for respiratory diseases

Chronic respiratory diseases, such as chronic obstructive pulmonary disease (COPD) and asthma, affect millions of people all over the world. Cyclic adenosine monophosphate (cAMP) which is one of the most important second messengers, plays a vital role in relaxing airway smooth muscles and suppressing inflammation. Given its vast role in regulating intracellular responses, cAMP provides an attractive pharmaceutical target in the treatment of chronic respiratory diseases. Phosphodiesterases (PDEs) are enzymes that hydrolyze cyclic nucleotides and help control cyclic nucleotide signals in a compartmentalized manner. Currently, the selective PDE4 inhibitor, roflumilast, is used as an add-on treatment for patients with severe COPD associated with bronchitis and a history of frequent exacerbations. In addition, other novel PDE inhibitors are in different phases of clinical trials. The current review provides an overview of the regulation of various PDEs and the potential application of selective PDE inhibitors in the treatment of COPD and asthma. The possibility to combine various PDE inhibitors as a way to increase their therapeutic effectiveness is also emphasized.

The Regulation of Pulmonary Vascular Tone by Neuropeptides and the Implications for Pulmonary Hypertension

Pulmonary hypertension (PH) is an incurable, chronic disease of small pulmonary vessels. Progressive remodeling of the pulmonary vasculature results in increased pulmonary vascular resistance (PVR). This causes secondary right heart failure. PVR is tightly regulated by a range of pulmonary vasodilators and constrictors. Endothelium-derived substances form the basis of most current PH treatments. This is particularly the case for pulmonary arterial hypertension. The major limitation of current treatments is their inability to reverse morphological changes. Thus, there is an unmet need for novel therapies to reduce the morbidity and mortality in PH. Microvessels in the lungs are highly innervated by sensory C fibers. Substance P and calcitonin gene-related peptide (CGRP) are released from C-fiber nerve endings. These neuropeptides can directly regulate vascular tone. Substance P tends to act as a vasoconstrictor in the pulmonary circulation and it increases in the lungs during experimental PH. The receptor for substance P, neurokinin 1 (NK1R), mediates increased pulmonary pressure. Deactivation of NK1R with antagonists, or depletion of substance P prevents PH development. CGRP is a potent pulmonary vasodilator. CGRP receptor antagonists cause elevated pulmonary pressure. Thus, the balance of these peptides is crucial within the pulmonary circulation (Graphical Abstract). Limited progress has been made in understanding their impact on pulmonary pathophysiology. This is an intriguing area of investigation to pursue. It may lead to promising new candidate therapies to combat this fatal disease. This review provides a summary of the current knowledge in this area. It also explores possible future directions for neuropeptides in PH.

Roles of A-Kinase Anchoring Proteins and Phosphodiesterases in the Cardiovascular System

A-kinase anchoring proteins (AKAPs) and cyclic nucleotide phosphodiesterases (PDEs) are essential enzymes in the cyclic adenosine 3′-5′ monophosphate (cAMP) signaling cascade. They establish local cAMP pools by controlling the intensity, duration and compartmentalization of cyclic nucleotide-dependent signaling. Various members of the AKAP and PDE families are expressed in the cardiovascular system and direct important processes maintaining homeostatic functioning of the heart and vasculature, e.g., the endothelial barrier function and excitation-contraction coupling. Dysregulation of AKAP and PDE function is associated with pathophysiological conditions in the cardiovascular system including heart failure, hypertension and atherosclerosis. A number of diseases, including autosomal dominant hypertension with brachydactyly (HTNB) and type I long-QT syndrome (LQT1), result from mutations in genes encoding for distinct members of the two classes of enzymes. This review provides an overview over the AKAPs and PDEs relevant for cAMP compartmentalization in the heart and vasculature and discusses their pathophysiological role as well as highlights the potential benefits of targeting these proteins and their protein-protein interactions for the treatment of cardiovascular diseases.

Pulmonary vasodilator therapy in tetralogy of Fallot with pulmonary atresia and major aortopulmonary collaterals: case series and review of literature

We present the use of pulmonary vasodilators in three adult patients with unrepaired tetralogy of Fallot, pulmonary atresia, aortopulmonary collaterals, and segmental pulmonary arterial hypertension. Patients improved by 1-2 NYHA classes with modest exercise-tolerance increase, and remained stable without side effects during 2.5, 10, and 14 years. Literature review revealed five studies with pulmonary vasodilators in heterogeneous, mostly repaired patient populations.

PDE1A inhibition elicits cGMP-dependent relaxation of rat mesenteric arteries

BACKGROUND AND PURPOSE

PDE1, a subfamily of cyclic nucleotide PDEs consisting of three isoforms, PDE1A, PDE1B and PDE1C, has been implicated in the regulation of vascular tone. The PDE1 isoform(s) responsible for tone regulation is unknown. This study used isoform-preferring PDE1 inhibitors, Lu AF58027, Lu AF64196, Lu AF66896 and Lu AF67897, to investigate the relative contribution of PDE1 isoforms to regulation of vascular tone.

EXPERIMENTAL APPROACH

In rat mesenteric arteries, expression and localization of Pde1 isoforms were determined by quantitative PCR and in situ hybridization, and physiological impact of PDE1 inhibition was evaluated by isometric tension recordings.

KEY RESULTS

In rat mesenteric arteries, Pde1a mRNA expression was higher than Pde1b and Pde1c. In situ hybridization revealed localization of Pde1a to vascular smooth muscle cells (VSMCs) and only minor appearance of Pde1b and Pde1c. The potency of the PDE1 inhibitors at eliciting relaxation showed excellent correlation with their potency at inhibiting PDE1A. Thus, Lu AF58027 was the most potent at inhibiting PDE1A and was also the most potent at eliciting relaxation in mesenteric arteries. Inhibition of NOS with l-NAME, soluble GC with ODQ or PKG with Rp-8-Br-PET-cGMP all attenuated the inhibitory effect of PDE1 on relaxation, whereas PKA inhibition with H89 had no effect.

CONCLUSIONS AND IMPLICATIONS

Pde1a is the dominant PDE1 isoform present in VSMCs, and relaxation mediated by PDE1A inhibition is predominantly driven by enhanced cGMP signalling. These results imply that isoform-selective PDE1 inhibitors are powerful investigative tools allowing examination of physiological and pathological roles of PDE1 isoforms.

A comprehensive review on the potential therapeutic benefits of phosphodiesterase inhibitors on cardiovascular diseases

Phosphodiesterases are a group of enzymes that hydrolyze cyclic nucleotides, which assume a key role in directing intracellular levels of the second messengers' cAMP and cGMP, and consequently cell function. The disclosure of 11 isoenzyme families and our expanded knowledge of their functions at the cell and molecular level stimulate the improvement of isoenzyme selective inhibitors for the treatment of various diseases, particularly cardiovascular diseases. Hence, future and new mechanistic investigations and carefully designed clinical trials could help reap additional benefits of natural/synthetic PDE inhibitors for cardiovascular disease in patients. This review has concentrated on the potential therapeutic benefits of phosphodiesterase inhibitors on cardiovascular diseases.

Novel selective PDE type 1 inhibitors cause vasodilatation and lower blood pressure in rats

BACKGROUND AND PURPOSE

The PDE enzymes (PDE1-11) hydrolyse and thus inactivate cyclic nucleotides and are important in the regulation of the cardiovascular system. Here,we have investigated the effects on the cardiovascular system, of two novel selective PDE1 inhibitors, Lu AF41228 and Lu AF58027.

EXPERIMENTAL APPROACH

We used rat mesenteric small arteries (internal diameters of 200-300 μm), RT-PCR and measured isometric wall tension. Effects of Lu AF41228 and Lu AF58027 on heart rate and BP were assessed in both anaesthetized and conscious male rats.

KEY RESULTS

Nanomolar concentrations of Lu AF41228 and Lu AF58027 inhibited PDE1A, PDE1B and PDE1C enzyme activity, while micromolar concentrations were required to observe inhibitory effects at other PDEs. RT-PCR revealed expression of PDE1A, PDE1B and PDE1C in rat brain, heart and aorta, but only PDE1A and PDE1B in mesenteric arteries. In rat isolated mesenteric arteries contracted with phenylephrine or U46619, Lu AF41228 and Lu AF58027 induced concentration-dependent relaxations which were markedly reduced by inhibitors of guanylate cyclase, ODQ, and adenylate cyclase, SQ22536, and in preparations without endothelium. In anaesthetized rats, Lu AF41228 and Lu AF58027 dose-dependently lowered mean BP and increased heart rate. In conscious rats with telemetric pressure transducers, repeated dosing with Lu AF41228 lowered mean arterial BP 10-15 mmHg and increased heart rate.

CONCLUSIONS AND IMPLICATIONS

These novel PDE1 inhibitors induce vasodilation and lower BP, suggesting a potential use of these vasodilators in the treatment of hypertension and vasospasm.

The Changing Landscape of Pulmonary Arterial Hypertension in the Adult with Congenital Heart Disease

Pulmonary arterial hypertension associated with congenital heart disease (PAH-CHD) is a common type of pulmonary arterial hypertension (PAH) and a frequent complication of congenital heart disease (CHD). PAH-CHD represents a heterogeneous patient population and it is important to distinguish between the underlying cardiac defects considering the prognostic and therapeutic implications. Improved interventional techniques have enabled repair or palliation of most cardiac defects, though a substantial number of patients remain at high risk for PAH after closure. Traditionally, the treatment and management of PAH-CHD patients has been limited to palliative and supportive care, and based on expert opinion rather than clinical trials. Recently, however, the availability of advanced PAH-specific treatment has opened up a new field for the clinical management of this condition. Nevertheless, there is limited evidence on the optimal therapeutic approach for PAH-CHD. Herein, we discuss the current and novel therapeutic options for PAH-CHD as well as highlight several challenges in the clinical management at present.

Pharmacological Profile of GPD-1116, an Inhibitor of Phosphodiesterase 4

We have previously reported that GPD-1116, an inhibitor of phosphodiesterase (PDE) 4, exhibits anti-inflammatory effects in a model of cigarette smoke-induced emphysema in senescence-accelerated P1 mice. In the present study, we further characterized the pharmacological profile of GPD-1116 in several experiments in vitro and in vivo. GPD-1116 and its metabolite GPD-1133 predominantly inhibited not only human PDE4, but also human PDE1 in vitro. Moreover, GPD-1116 was effective in several disease models in animals, including acute lung injury, chronic obstructive pulmonary disease (COPD), asthma and pulmonary hypertension; the effective doses of GPD-1116 were estimated to be 0.3-2 mg/kg in these models. With regard to undesirable effects known as class effects of PDE4 inhibitors, GPD-1116 showed suppression of gastric emptying in rats and induction of emesis in dogs, but showed no such suppression of rectal temperature in rats, and these side effects of GPD-1116 seemed to be less potent than those of roflumilast. These results suggested that GPD-1116 could be a promising therapeutic agent for the treatment of inflammatory pulmonary diseases. Furthermore, the inhibitory effects of GPD-1116 for PDE1 might be associated with its excellent pharmacological profile. However, the mechanisms through which PDE1 inhibition contributes to these effects should be determined in future studies.

Cyclic nucleotide phosphodiesterases in heart and vessels: A therapeutic perspective

Cyclic nucleotide phosphodiesterases (PDEs) degrade the second messengers cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), thereby regulating multiple aspects of cardiac and vascular muscle functions. This highly diverse class of enzymes encoded by 21 genes encompasses 11 families that are not only responsible for the termination of cyclic nucleotide signalling, but are also involved in the generation of dynamic microdomains of cAMP and cGMP, controlling specific cell functions in response to various neurohormonal stimuli. In the myocardium and vascular smooth muscle, the PDE3 and PDE4 families predominate, degrading cAMP and thereby regulating cardiac excitation-contraction coupling and smooth muscle contractile tone. PDE3 inhibitors are positive inotropes and vasodilators in humans, but their use is limited to acute heart failure and intermittent claudication. PDE5 is particularly important for the degradation of cGMP in vascular smooth muscle, and PDE5 inhibitors are used to treat erectile dysfunction and pulmonary hypertension. There is experimental evidence that these PDEs, as well as other PDE families, including PDE1, PDE2 and PDE9, may play important roles in cardiac diseases, such as hypertrophy and heart failure, as well as several vascular diseases. After a brief presentation of the cyclic nucleotide pathways in cardiac and vascular cells, and the major characteristics of the PDE superfamily, this review will focus on the current use of PDE inhibitors in cardiovascular diseases, and the recent research developments that could lead to better exploitation of the therapeutic potential of these enzymes in the future.

[Phosphodiesterase-5 inhibitors for the treatment of pulmonary arterial hypertension]

In experimental and clinical cardiology, phosphodiesterase type 5 (PDE-5) inhibitors have brought scientific interest as a therapeutic tool in pulmonary arterial hypertension (PAH) management in recent years. Phosphodiesterases are a superfamily of enzymes that inactivate cyclic adenosine monophosphate and cyclic guanosine monophosphate, the second messengers of prostacyclin and nitric oxide. The rationale for the use of PDE-5 inhibitors in PAH is based on their capacity to overexpresss the nitric oxide pathway pursued inhibition of cyclic guanosine monophosphate hydrolysis. By increasing cyclic guanosine monophosphate levels it promotes vasodilation, antiproliferative and pro-apoptotic effects that may reverse pulmonary vascular remodeling. There is also evidence that these drugs may directly enhance right ventricular contractility through an increase in cyclic adenosine monophosphate mediated by the inhibition of the cyclic guanosine monophosphate -sensitive PDE-3. Sildenafil, tadalafil and vardenafil are 3 specific PDE-5 inhibitors in current clinical use, which share similar mechanisms of action but present some significant differences regarding potency, selectivity for PDE-5 and pharmacokinetic properties. Sildenafil received approval in 2005 by the Food and Drug Administration and the European Medicines Agency and tadalafil in 2009 by the Food and Drug Administration and the European Medicines Agency for the treatment of PAH in patients classified as NYHA/WHO functional class II and III. In Mexico, sildenafil and tadalafil were approved by Comisión Federal de Protección contra Riesgos Sanitarios for this indication in 2010 and 2011, respectively.

Pulmonary arterial hypertension associated with tetralogy of Fallot

Pulmonary arterial hypertension (PAH) is a common postoperative complication in patients with congenital heart disease (CHD). Although the recent clinical classification of pulmonary hypertension divided PAH associated with CHD (PAH-CHD) into several subclasses, the anatomical and hemodynamic features of postoperative PAH-CHD vary enormously. Therefore, it is still difficult to obtain clinical evidence supporting the indication of pulmonary vasodilators for PAH-CHD. We often encounter patients with PAH occurring after surgical treatment of tetralogy of Fallot (TOF), especially patients with major aortopulmonary collateral arteries (MAPCAs). PAH might be caused by pulmonary agenesis, hypoplasia and/or thrombosis, inadequate closure of the ventricular septal defect, relief of the pulmonic stenosis, or an excessively large prior systemic-to-pulmonary shunt. Moreover, patients with TOF and MAPCAs who are diagnosed as inoperable because of the presence of PAH show similar hemodynamic and clinical features to patients with Eisenmenger syndrome. The MAPCAs in these patients usually show hypoplastic and abnormal arborization. Based on our experience, we believe that PAH-targeted therapies are effective in some patients with PAH occurring after surgical treatment of TOF and MAPCAs, especially as an adjunct to percutaneous pulmonary angioplasty. To help classify patients with PAH associated with TOF, especially with MAPCAs, we propose several new subclassifications: "PAH due to hypoplastic pulmonary arterial beds", "PAH due to abnormal pulmonary arborization", or "segmental PAH associated with CHD." A multicenter registry of patients using a unified protocol is essential to explore the indications and efficacy of pulmonary vasodilators for postoperative PAH-CHD.

The mechanistic basis of prostacyclin and its stable analogues in pulmonary arterial hypertension: Role of membrane versus nuclear receptors

Pulmonary arterial hypertension (PAH) is a progressive disease of distal pulmonary arteries in which patients suffer from elevated pulmonary arterial pressure, extensive vascular remodelling and right ventricular failure. To date prostacyclin (PGI2) therapy remains the most efficacious treatment for PAH and is the only approved monotherapy to have a positive impact on long-term survival. A key thing to note is that improvement exceeds that predicted from vasodilator testing strongly suggesting that additional mechanisms contribute to the therapeutic benefit of prostacyclins in PAH. Given these agents have potent antiproliferative, anti-inflammatory and endothelial regenerating properties suggests therapeutic benefit might result from a slowing, stabilization or even some reversal of vascular remodelling in vivo. This review discusses evidence that the pharmacology of each prostacyclin (IP) receptor agonist so far developed is distinct, with non-IP receptor targets clearly contributing to the therapeutic and side effect profile of PGI2 (EP3), iloprost (EP1), treprostinil (EP2, DP1) along with a family of nuclear receptors known as peroxisome proliferator-activated receptors (PPARs), to which PGI2 and some analogues directly bind. These targets are functionally expressed to varying degrees in arteries, veins, platelets, fibroblasts and inflammatory cells and are likely to be involved in the biological actions of prostacylins. Recently, a highly selective IP agonist, selexipag has been developed for PAH. This agent should prove useful in distinguishing IP from other prostanoid receptors or PPAR binding effects in human tissue. It remains to be determined whether selectivity for the IP receptor gives rise to a superior or inferior clinical benefit in PAH.

Phosphodiesterase-1 Inhibitory Activity of Two Flavonoids Isolated from Pistacia integerrima J. L. Stewart Galls

Pistacia integerrima is one of twenty species among the genus Pistacia. Long horn-shaped galls that develop on this plant are harvested and used in Ayurveda and Indian traditional medicine to make "karkatshringi", a herbal medicine used for the treatment of asthma and different disorders of respiratory tract. However, until now, the molecular mechanisms of action of "karkatshringi" and its chemical characterization are partially known. This study deals with the isolation and characterization of the active constituents from the methanolic extract of P. integerrima galls and it was also oriented to evaluate in vitro and in silico their potential enzymatic inhibitory activity against phosphodiesterase-1 (PDE1), a well-known enzyme involved in airway smooth muscle activity and airway inflammation. Our results showed that the methanolic extract of P. integerrima galls and some of its active constituents [naringenin (1) and 3,5,7,4'-tetrahydroxy-flavanone (2)] are able in vitro to inhibit PDE1 activity (59.20 ± 4.95%, 75.90 ± 5.90%, and 65.25 ± 5.25%, resp.) and demonstrate in silico an interesting interaction with this enzymatic site. Taken together, our results add new knowledge of chemical constituents responsible for the biological activity of P. integerrima and contextually legitimate the use of this plant in folk medicine.

Inhalable delivery of AAV-based MRP4/ABCC4 silencing RNA prevents monocrotaline-induced pulmonary hypertension

The ATP-binding cassette transporter MRP4 (encoded by ABCC4) regulates membrane cyclic nucleotides concentrations in arterial cells including smooth muscle cells. MRP4/ABCC4 deficient mice display a reduction in smooth muscle cells proliferation and a prevention of pulmonary hypertension in response to hypoxia. We aimed to study gene transfer of a MRP4/ABCC4 silencing RNA via intratracheal delivery of aerosolized adeno-associated virus 1 (AAV1.shMRP4 or AAV1.control) in a monocrotaline-induced model of pulmonary hypertension in rats. Gene transfer was performed at the time of monocrotaline administration and the effect on the development of pulmonary vascular remodeling was assessed 35 days later. AAV1.shMRP4 dose-dependently reduced right ventricular systolic pressure and hypertrophy with a significant reduction with the higher doses (i.e., >10¹¹ DRP/animal) as compared to AAV1.control. The higher dose of AAV1.shMRP4 was also associated with a significant reduction in distal pulmonary arteries remodeling. AAV1.shMRP4 was finally associated with a reduction in the expression of ANF, a marker of cardiac hypertrophy. Collectively, these results support a therapeutic potential for downregulation of MRP4 for the treatment of pulmonary artery hypertension.

Extending the translational potential of targeting NO/cGMP-regulated pathways in the CVS

The discovery of NO as both an endogenous signalling molecule and as a mediator of the cardiovascular effects of organic nitrates was acknowledged in 1998 by the Nobel Prize in Physiology/Medicine. The characterization of its downstream signalling, mediated through stimulation of soluble GC (sGC) and cGMP generation, initiated significant translational interest, but until recently this was almost exclusively embodied by the use of PDE5 inhibitors in erectile dysfunction. Since then, research progress in two areas has contributed to an impressive expansion of the therapeutic targeting of the NO-sGC-cGMP axis: first, an increased understanding of the molecular events operating within this complex pathway and second, a better insight into its dys-regulation and uncoupling in human disease. Already-approved PDE5 inhibitors and novel, first-in-class molecules, which up-regulate the activity of sGC independently of NO and/or of the enzyme's haem prosthetic group, are undergoing clinical evaluation to treat pulmonary hypertension and myocardial failure. These molecules, as well as combinations or second-generation compounds, are also being assessed in additional experimental disease models and in patients in a wide spectrum of novel indications, such as endotoxic shock, diabetic cardiomyopathy and Becker's muscular dystrophy. There is well-founded optimism that the modulation of the NO-sGC-cGMP pathway will sustain the development of an increasing number of successful clinical candidates for years to come.

AAV delivery of tumor necrosis factor-α short hairpin RNA attenuates cold-induced pulmonary hypertension and pulmonary arterial remodeling

Cold temperatures are associated with increased mortality and morbidity of cardiovascular and pulmonary disease. Cold exposure causes lung inflammation, pulmonary hypertension (PH), and right ventricle hypertrophy, but there is no effective therapy because of unknown mechanism. Here, we investigated whether RNA interference silencing of tumor necrosis factor (TNF)-α decreases cold-induced macrophage infiltration, PH, and pulmonary arterial (PA) remodeling. We found for the first time that continuous cold exposure (5.0°C) increased TNF-α expression and macrophage infiltration in the lungs and PAs right before elevation of right ventricle systolic pressure. The in vivo RNA interference silencing of TNF-α was achieved by intravenous delivery of recombinant AAV-2 carrying TNF-α short hairpin small-interfering RNA 24 hours before cold exposure. Cold exposure for 8 weeks significantly increased right ventricle pressure compared with the warm controls (40.19±4.9 versus 22.9±1.1 mm Hg), indicating that cold exposure caused PH. Cold exposure increased TNF-α, interleukin-6, and phosphodiesterase-1C protein expression in the lungs and PAs and increased lung macrophage infiltration. Notably, TNF-α short hairpin small-interfering RNA prevented the cold-induced increases in TNF-α, interleukin-6, and phosphodiesterase-1C protein expression, abolished lung macrophage infiltration, and attenuated PH (26.28±1.6 mm Hg), PA remodeling, and right ventricle hypertrophy. PA smooth muscle cells isolated from cold-exposed animals showed increased intracellular superoxide levels and cell proliferation along with decreased intracellular cGMP. These cold-induced changes were prevented by TNF-α short hairpin small-interfering RNA. In conclusions, upregulation of TNF-α played a critical role in the pathogenesis of cold-induced PH by promoting pulmonary macrophage infiltration and inflammation. AAV delivery of TNF-α short hairpin small-interfering RNA may be an effective therapeutic approach for cold-induced PH and PA remodeling.

Ion channels and transporters as therapeutic targets in the pulmonary circulation

Pulmonary circulation is a low pressure, low resistance, high flow system. The low resting vascular tone is maintained by the concerted action of ion channels, exchangers and pumps. Under physiological as well as pathophysiological conditions, they are targets of locally secreted or circulating vasodilators and/or vasoconstrictors, leading to changes in expression or to posttranslational modifications. Both structural changes in the pulmonary arteries and a sustained increase in pulmonary vascular tone result in pulmonary vascular remodeling contributing to morbidity and mortality in pediatric and adult patients. There is increasing evidence demonstrating the pivotal role of ion channels such as K(+) and Cl(-) or transient receptor potential channels in different cell types which are thought to play a key role in vasoconstrictive remodeling. This review focuses on ion channels, exchangers and pumps in the pulmonary circulation and summarizes their putative pathophysiological as well as therapeutic role in pulmonary vascular remodeling. A better understanding of the mechanisms of their actions may allow for the development of new options for attenuating acute and chronic pulmonary vasoconstriction and remodeling treating the devastating disease pulmonary hypertension.

Inhibition of phosphodiesterase 2 augments cGMP and cAMP signaling to ameliorate pulmonary hypertension

BACKGROUND

Pulmonary hypertension (PH) is a life-threatening disorder characterized by increased pulmonary artery pressure, remodeling of the pulmonary vasculature, and right ventricular failure. Loss of endothelium-derived nitric oxide (NO) and prostacyclin contributes to PH pathogenesis, and current therapies are targeted to restore these pathways. Phosphodiesterases (PDEs) are a family of enzymes that break down cGMP and cAMP, which underpin the bioactivity of NO and prostacyclin. PDE5 inhibitors (eg, sildenafil) are licensed for PH, but a role for PDE2 in lung physiology and disease has yet to be established. Herein, we investigated whether PDE2 inhibition modulates pulmonary cyclic nucleotide signaling and ameliorates experimental PH.

METHODS AND RESULTS

The selective PDE2 inhibitor BAY 60-7550 augmented atrial natriuretic peptide- and treprostinil-evoked pulmonary vascular relaxation in isolated arteries from chronically hypoxic rats. BAY 60-7550 prevented the onset of both hypoxia- and bleomycin-induced PH and produced a significantly greater reduction in disease severity when given in combination with a neutral endopeptidase inhibitor (enhances endogenous natriuretic peptides), trepostinil, inorganic nitrate (NO donor), or a PDE5 inhibitor. Proliferation of pulmonary artery smooth muscle cells from patients with pulmonary arterial hypertension was reduced by BAY 60-7550, an effect further enhanced in the presence of atrial natriuretic peptide, NO, and treprostinil.

CONCLUSIONS

PDE2 inhibition elicits pulmonary dilation, prevents pulmonary vascular remodeling, and reduces the right ventricular hypertrophy characteristic of PH. This favorable pharmacodynamic profile is dependent on natriuretic peptide bioactivity and is additive with prostacyclin analogues, PDE5 inhibitor, and NO. PDE2 inhibition represents a viable, orally active therapy for PH.

Cyclic nucleotide-based therapeutics for chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) defines a group of chronic inflammatory disorders of the airways that are characterised by a progressive and largely irreversible decline in expiratory airflow. Drugs used to treat COPD through actions mediated by cyclic AMP (cAMP) are restricted to long-acting and short-acting β2-adrenoceptor agonists and, in a subset of patients with chronic bronchitis, a phosphodiesterase 4 inhibitor, roflumilast. These agents relax airway smooth muscle and suppress inflammation. At the molecular level, these effects in the airways are mediated by two cAMP effectors, cAMP-dependent protein kinase and exchange proteins activated by cAMP. The pharmacology of newer agents, acting through these systems, is discussed here with an emphasis on their potential to interact and increase therapeutic effectiveness.

Structural and functional prevention of hypoxia-induced pulmonary hypertension by individualized exercise training in mice

Pulmonary hypertension (PH) is a disease with a poor prognosis characterized by a vascular remodeling process and an increase in pulmonary vascular resistance. While a variety of reports demonstrated that exercise training exerts beneficial effects on exercise performance and quality of life in PH patients, it is not known how physical exercise affects vascular remodeling processes occurring in hypoxia-induced PH. Therefore, we investigated the effect of individualized exercise training on the development of hypoxia-induced PH in mice. Training effects were compared with pharmacological treatment with the phosphodiesterase 5 inhibitor Sildenafil or a combination of training plus Sildenafil. Trained mice who received Sildenafil showed a significantly improved walking distance (from 88.9 ± 8.1 to 146.4 ± 13.1 m) and maximum oxygen consumption (from 93.3 ± 2.9 to 105.5 ± 2.2% in combination with Sildenafil, to 102.2 ± 3.0% with placebo) compared with sedentary controls. Right ventricular systolic pressure, measured by telemetry, was at the level of healthy normoxic animals, whereas right heart hypertrophy did not benefit from training. Most interestingly, the increase in small pulmonary vessel muscularization was prevented by training. Respective counterregulatory processes were detected for the nitric oxide-soluble guanylate cyclase-phosphodiesterase system. We conclude that individualized daily exercise can prevent vascular remodeling in hypoxia-induced PH.

Gene-centric meta-analysis in 87,736 individuals of European ancestry identifies multiple blood-pressure-related loci

Blood pressure (BP) is a heritable risk factor for cardiovascular disease. To investigate genetic associations with systolic BP (SBP), diastolic BP (DBP), mean arterial pressure (MAP), and pulse pressure (PP), we genotyped ~50,000 SNPs in up to 87,736 individuals of European ancestry and combined these in a meta-analysis. We replicated findings in an independent set of 68,368 individuals of European ancestry. Our analyses identified 11 previously undescribed associations in independent loci containing 31 genes including PDE1A, HLA-DQB1, CDK6, PRKAG2, VCL, H19, NUCB2, RELA, HOXC@ complex, FBN1, and NFAT5 at the Bonferroni-corrected array-wide significance threshold (p < 6 × 10(-7)) and confirmed 27 previously reported associations. Bioinformatic analysis of the 11 loci provided support for a putative role in hypertension of several genes, such as CDK6 and NUCB2. Analysis of potential pharmacological targets in databases of small molecules showed that ten of the genes are predicted to be a target for small molecules. In summary, we identified previously unknown loci associated with BP. Our findings extend our understanding of genes involved in BP regulation, which may provide new targets for therapeutic intervention or drug response stratification.

Pharmacologic treatments for pulmonary hypertension: exploring pharmacogenomics

Pulmonary hypertension (PH) is a disease with multiple etiologies and is categorized into five broad groups. Of these groups, pulmonary arterial hypertension (PAH) is the most studied and, therefore, all of the currently available drug classes (prostacyclin analogs, endothelin receptor antagonists and phosphodiesterase type 5 inhibitors) were developed to treat PAH. Thus, limited treatment data exist for the less-studied non-PAH forms of PH. Pharmacogenomics can be a tool to better understand the pathways involved in PH, as well as to improve personalization of therapy. However, little pharmacogenomic research has been carried out on this disease. New treatments for PH are on the horizon, deriving from both repurposed currently available drugs and novel therapeutics.

Inhibition of phosphodiesterase-1 attenuates cold-induced pulmonary hypertension

Chronic exposure to cold caused pulmonary arterial hypertension (cold-induced pulmonary hypertension [CIPH]) and increased phosphodiesterase-1C (PDE-1C) expression in pulmonary arteries (PAs) in rats. The purpose of this study is to investigate a hypothesis that inhibition of PDE-1 would decrease inflammatory infiltrates and superoxide production leading to attenuation of CIPH. Three groups of male rats were exposed to moderate cold (5±1°C) continuously, whereas 3 groups were maintained at room temperature (23.5±1°C, warm; 6 rats/group). After 8-week exposure to cold, 3 groups in each temperature condition received continuous intravenous infusion of 8-isobutyl-methylxanthine (8-IBMX) (PDE-1 inhibitor), apocynin (NADPH oxidase inhibitor) or vehicle, respectively, for 1 week. Cold exposure significantly increased right-ventricular systolic pressure compared with warm groups (33.8±3.2 versus 18.6±0.3 mm Hg), indicating that animals developed CIPH. Notably, treatment with 8-IBMX significantly attenuated the cold-induced increase in right ventricular pressure (23.5±1.8 mm Hg). Cold exposure also caused right-ventricular hypertrophy, whereas 8-IBMX reversed cold-induced right ventricular hypertrophy. Cold exposure increased PDE-1C protein expression, macrophage infiltration, NADPH oxidase activity, and superoxide production in PAs and resulted in PA remodeling. 8-IBMX abolished cold-induced upregulation of PDE-1C in PAs. Interestingly, inhibition of PDE-1 eliminated cold-induced macrophage infiltration, NADPH oxidase activation, and superoxide production in PAs and reversed PA remodeling. Inhibition of NADPH oxidase by apocynin abolished cold-induced superoxide production and attenuated CIPH and PA remodeling. In conclusion, inhibition of PDE-1 attenuated CIPH and reversed cold-induced PA remodeling by suppressing macrophage infiltration and superoxide production, suggesting that upregulation of PDE-1C expression may be involved in the pathogenesis of CIPH.

Treating pulmonary arterial hypertension: current treatments and future prospects

Pulmonary arterial hypertension (PAH) consists of a group of heterogeneous but distinct disorders characterized by complex proliferation of the pulmonary vascular endothelium and progressive pulmonary vascular remodeling that leads to right ventricular failure and death. Over the past two decades, significant advances in our understanding of the pathobiology of PAH have led to the development of several therapeutic targets in this disease. Besides conservative therapeutic strategies such as anticoagulation and diuretics, the current treatment paradigm for PAH targets the mediators of the three main biologic pathways that are critical for its pathogenesis and progression: endothelin receptor antagonists inhibit the upregulated endothelin pathway by blocking the biologic activity of endothelin-1; phosphodiesterase-5 inhibitors prevent breakdown and increase the endogenous availability of cyclic guanosine monophosphate, which signals the vasorelaxing effects of the downregulated mediator nitric oxide; and prostacyclin derivatives provide an exogenous supply of the deficient mediator prostacyclin. In addition to these established current therapeutic options, a large number of potential therapeutic targets are being investigated. These novel therapeutic targets include soluble guanylyl cyclase, phosphodiesterases, tetrahydrobiopterin, 5-hydroxytryptamine (serotonin) receptor 2B, vasoactive intestinal peptide, receptor tyrosine kinases, adrenomedullin, rho kinase, elastases, endogenous steroids, endothelial progenitor cells, immune cells, bone morphogenetic protein and its receptors, potassium channels, metabolic pathways, and nuclear factor of activated T cells. This review provides an overview of the current therapeutic options and potential therapeutic targets for PAH.