Effects of selective inhibition of PDE4 and PDE7 on airway reactivity and cough in healthy and ovalbumin-sensitized guinea pigs

Recent Developments and Future Perspectives of Purine Derivatives as a Promising Scaffold in Drug Discovery

Numerous purine-containing compounds have undergone extensive investigation for their medical efficacy across various diseases. The swift progress in purine-based medicinal chemistry has brought to light the therapeutic capabilities of purine-derived compounds in addressing challenging medical conditions. Defined by a heterocyclic ring comprising a pyrimidine ring linked with an imidazole ring, purine exhibits a diverse array of therapeutic attributes. This review systematically addresses the multifaceted potential of purine derivatives in combating various diseases, including their roles as anticancer agents, antiviral compounds (anti-herpes, anti-HIV, and anti-influenzae), autoimmune and anti-inflammatory agents, antihyperuricemic and anti-gout solutions, antimicrobial agents, antitubercular compounds, anti-leishmanial agents, and anticonvulsants. Emphasis is placed on the remarkable progress made in developing purine-based compounds, elucidating their significant target sites. The article provides a comprehensive exploration of developments in both natural and synthetic purines, offering insights into their role in managing a diverse range of illnesses. Additionally, the discussion delves into the structure-activity relationships and biological activities of the most promising purine molecules. The intriguing capabilities revealed by these purine-based scaffolds unequivocally position them at the forefront of drug candidate development. As such, this review holds potential significance for researchers actively involved in synthesizing purine-based drug candidates, providing a roadmap for the continued advancement of this promising field.

Rolipram and pentoxifylline combination ameliorates the morphological abnormalities of dorsal root ganglion neurons in experimental diabetic neuropathy by reducing mitochondrial dysfunction and apoptosis

Diabetic neuropathy (DN) is the most prevalent complication of diabetes. Pharmacological treatments for DN are often limited in efficacy, so the development of new agents to alleviate DN is essential. The aim of this study was to evaluate the effects of rolipram, a selective phosphodiesterase-4 inhibitor (PDE-4I), and pentoxifylline, a general PDE inhibitor, using a rat model of DN. In this study, a diabetic rat model was established by i.p. injection of STZ (55 mg/kg). Rats were treated with rolipram (1 mg/kg), pentoxifylline (100 mg/kg), and combination of rolipram (0.5 mg/kg) and pentoxifylline (50 mg/kg), orally for 5 weeks. After treatments, sensory function was assessed by hot plate test. Then rats were anesthetized and dorsal root ganglion (DRG) neurons isolated. Cyclic adenosine monophosphate (cAMP), adenosine triphosphate (ATP, adenosine diphosphate and mitochondrial membrane potential (MMP) levels, Cytochrome c release, Bax, Bcl-2, caspase-3 proteins expression in DRG neurons were assessed by biochemical and ELISA methods, and western blot analysis. DRG neurons were histologically examined using hematoxylin and eosin (H&E) staining method. Rolipram and/or pentoxifylline significantly attenuated sensory dysfunction by modulating nociceptive threshold. Rolipram and/or pentoxifylline treatment dramatically increased the cAMP level, prevented mitochondrial dysfunction, apoptosis and degeneration of DRG neurons, which appears to be mediated by inducing ATP and MMP, improving cytochrome c release, as well as regulating the expression of Bax, Bcl-2, and caspase-3 proteins, and improving morphological abnormalities of DRG neurons. We found maximum effectiveness with rolipram and pentoxifylline combination on mentioned factors. These findings encourage the use of rolipram and pentoxifylline combination as a novel experimental evidence for further clinical investigations in the treatment of DN.

Modulation of Human Dendritic Cell Functions by Phosphodiesterase-4 Inhibitors: Potential Relevance for the Treatment of Respiratory Diseases

Inhibitors of phosphodiesterase-4 (PDE4) are small-molecule drugs that, by increasing the intracellular levels of cAMP in immune cells, elicit a broad spectrum of anti-inflammatory effects. As such, PDE4 inhibitors are actively studied as therapeutic options in a variety of human diseases characterized by an underlying inflammatory pathogenesis. Dendritic cells (DCs) are checkpoints of the inflammatory and immune responses, being responsible for both activation and dampening depending on their activation status. This review shows evidence that PDE4 inhibitors modulate inflammatory DC activation by decreasing the secretion of inflammatory and Th1/Th17-polarizing cytokines, although preserving the expression of costimulatory molecules and the CD4+ T cell-activating potential. In addition, DCs activated in the presence of PDE4 inhibitors induce a preferential Th2 skewing of effector T cells, retain the secretion of Th2-attracting chemokines and increase the production of T cell regulatory mediators, such as IDO1, TSP-1, VEGF-A and Amphiregulin. Finally, PDE4 inhibitors selectively induce the expression of the surface molecule CD141/Thrombomodulin/BDCA-3. The result of such fine-tuning is immunomodulatory DCs that are distinct from those induced by classical anti-inflammatory drugs, such as corticosteroids. The possible implications for the treatment of respiratory disorders (such as COPD, asthma and COVID-19) by PDE4 inhibitors will be discussed.

Transient receptor potential ankyrin 1 (TRPA1) modulators: Recent update and future perspective

The transient receptor potential ankyrin 1 (TRPA1) channel is a non-selective cation channel that senses irritant chemicals. Its activation is closely associated with pain, inflammation, and pruritus. TRPA1 antagonists are promising treatments for these diseases, and there has been a recent upsurge in their application to new areas such as cancer, asthma, and Alzheimer's disease. However, due to the generally disappointing performance of TRPA1 antagonists in clinical studies, scientists must pursue the development of antagonists with higher selectivity, metabolic stability, and solubility. Moreover, TRPA1 agonists provide a deeper understanding of activation mechanisms and aid in antagonist screening. Therefore, we summarize the TRPA1 antagonists and agonists developed in recent years, with a particular focus on structure-activity relationships (SARs) and pharmacological activity. In this perspective, we endeavor to keep abreast of cutting-edge ideas and provide inspiration for the development of more effective TRPA1-modulating drugs.

Advances in the development of phosphodiesterase 7 inhibitors

Phosphodiesterase 7 (PDE7) specifically hydrolyzes cyclic adenosine monophosphate (cAMP), a second messenger that plays essential roles in cell signaling and physiological processes. Many PDE7 inhibitors used to investigate the role of PDE7 have displayed efficacy in the treatment of a wide range of diseases, such as asthma and central nervous system (CNS) disorders. Although PDE7 inhibitors are developed more slowly than PDE4 inhibitors, there is increasing recognition of PDE7 inhibitors as potential therapeutics for no nausea and vomiting secondary. Herein, we summarized the advances in PDE7 inhibitors over the past decade, focusing on their crystal structures, key pharmacophores, subfamily selectivity, and therapeutic potential. Hopefully, this summary will lead to a better understanding of PDE7 inhibitors and provide strategies for developing novel therapies targeting PDE7.

Pathophysiology, Therapeutic Targets, and Future Therapeutic Alternatives in COPD: Focus on the Importance of the Cholinergic System

Chronic obstructive pulmonary disease (COPD) is a progressive disease characterized by airway limitation and changes in airway structure. It has a high global burden of mortality and morbidity. The etiology of COPD is complex, but exposure to tobacco smoke and other inhaled lung oxidants are major risk factors. Both pharmacological and non-pharmacological approaches are used to manage COPD, but there remains an urgent unmet need for drugs that can modify the course of the disease. This review focuses on the role of acetylcholine and other components of the pulmonary cholinergic system in the pathogenesis of COPD, and the inhaled pharmacological agents that target it. In addition to its role as a neurotransmitter, acetylcholine regulates diverse aspects of COPD pathogenesis including bronchoconstriction, airway remodeling, mucus secretion and inflammation. Inhaled antimuscarinic drugs are a key component of therapy for COPD, as monotherapy or in combination with inhaled β2 agonists or corticosteroids. We review the evidence supporting the use of current anticholinergic agents in COPD and preview novel drugs targeting the cholinergic system and agents from other classes in clinical development, such as phosphodiesterase-4 inhibitors and monoclonal antibodies targeting inflammatory mediators.

Rolipram and pentoxifylline combination ameliorates experimental diabetic neuropathy through inhibition of oxidative stress and inflammatory pathways in the dorsal root ganglion neurons

Diabetic neuropathy (DN) is the most challenging microvascular complication of diabetes and there is no suitable treatment for it, so the development of new agents to relieve DN is urgently needed. Since oxidative stress and inflammation play an essential role in the development of DN, clearance of these factors are good strategies for the treatment of this disease. According to key role of cyclic adenosine monophosphate (cAMP) in the regulation of oxidative stress and inflammatory pathways, it seems that phosphodiesterase inhibitors (PDEIs) can be as novel drug targets for improving DN through enhancement of cAMP level. The aim of this study was to evaluate the effects of rolipram, a selective PDE4 inhibitor, and pentoxifylline, a general PDE inhibitor on experimental model of DN and also to determine the possible mechanisms involved in the effectiveness of these agents. We investigated the effects of rolipram (1 mg/kg) and pentoxifylline (100 mg/kg) and also combination of rolipram (0.5 mg/kg) and pentoxifylline (50 mg/kg), orally for five weeks in rats that became diabetic by STZ (55 mg/kg, i.p.). After treatments, motor function was evaluated by open-field test, then rats were anesthetized and dorsal root ganglion (DRG) neurons isolated. Next, oxidative stress biomarkers and inflammatory factors were assessed by biochemical and ELISA methods, and RT-PCR analysis in DRG neurons. Rolipram and/or pentoxifylline treatment significantly attenuated DN - induced motor function deficiency by modulating distance moved and velocity. Rolipram and/or pentoxifylline treatment dramatically increased the cAMP level, as well as suppressed DN - induced oxidative stress which was associated with decrease in LPO and ROS and increase in TAC, total thiol, CAT and SOD in DRG neurons. On the other hand, the level of inflammatory factors (TNF-α, NF-kB and COX2) significantly decreased following rolipram and/or pentoxifylline administration. The maximum effectiveness was with rolipram and/or pentoxifylline combination on mentioned factors. These findings provide novel experimental evidence for further clinical investigations on rolipram and pentoxifylline combination for the treatment of DN.

The effects of BRL-50481 on ovalbumin-induced asthmatic lung inflammation exacerbated by co-exposure to Asian sand dust in the murine model

Asian sand dust (ASD), which mainly originates in China and Mongolia in the spring and blows into Korea, can exacerbate respiratory and immunological diseases. This study aims to observe effects of co-exposure to ASD on ovalbumin (OVA)-induced asthmatic lung inflammation and of treatment with a phosphodiesterase 7 (PDE7) inhibitor in a mouse model. The challenge with OVA increased airway hyperresponsiveness (AHR) and inflammatory cell infiltration into the lung tissue. Interleukin (IL)-13, tumor necrosis factor-alpha, monocyte-protein-1, mucin, and antigen-specific IgE and IgG1 production increased in mouse serum. The co-exposure of ASD significantly exacerbated these effects in this asthma model. Notably, the administration of a PDE7 inhibitor, BRL-50481 (BRL), significantly reduced AHR, infiltration of inflammatory cells into the lungs, and the levels of type 2 T helper cell-related cytokines, antigen-specific immunoglobulins, and mucin. Thus, the administration of BRL ameliorated OVA-induced allergic asthmatic responses exacerbated by co-exposure to ASD. This study suggests that PDE7 inhibition can be a therapeutic strategy for inflammatory lung diseases and asthma via the regulation of T lymphocytes and reduction of IL-13, and, consequently, mucin production.

New Avenues for Phosphodiesterase Inhibitors in Asthma

Introduction

Phosphodiesterases (PDEs) are isoenzymes ubiquitously expressed in the lungs where they catalyse cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (GMP), which are fundamental second messengers in asthma, thereby regulating the intracellular concentrations of these cyclic nucleotides, their signaling pathways and, consequently, myriad biological responses. The superfamily of PDEs is composed of 11 families with a distinct substrate specificity, molecular structure and subcellular localization. Experimental studies indicate a possible role in asthma mainly for PDE3, PDE4, PDE5 and PDE7. Consequently, drugs that inhibit PDEs may offer novel therapeutic options for the treatment of this disease.

Areas Covered

In this article, we describe the progress made in recent years regarding the possibility of using PDE inhibitors in the treatment of asthma.

Expert Opinion

Many data indicate the potential benefits of PDE inhibitors as an add-on treatment especially in severe asthma due to their bronchodilator and/or anti-inflammatory activity, but no compound has yet reached the market as asthma treatment mainly because of their limited tolerability. Therefore, there is a growing interest in developing new PDE inhibitors with an improved safety profile. In particular, the research is focused on the development of drugs capable of interacting simultaneously with different PDEs, or to be administered by inhalation. CHF 6001 and RPL554 are the only molecules that currently are under clinical development but there are several new agents with interesting pharmacological profiles. It will be stimulating to assess the impact of such agents on individual treatable traits in specially designed studies.

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.

Inhibition of phosphodiesterase suppresses allergic lung inflammation by regulating MCP-1 in an OVA-induced asthma murine model with co-exposure to lipopolysaccharide

Objective

Methods

Results

Conclusion

Role of Phosphodiesterase 7 (PDE7) in T Cell Activity. Effects of Selective PDE7 Inhibitors and Dual PDE4/7 Inhibitors on T Cell Functions

Phosphodiesterase 7 (PDE7), a cAMP-specific PDE family, insensitive to rolipram, is present in many immune cells, including T lymphocytes. Two genes of PDE7 have been identified: PDE7A and PDE7B with three or four splice variants, respectively. Both PDE7A and PDE7B are expressed in T cells, and the predominant splice variant in these cells is PDE7A1. PDE7 is one of several PDE families that terminates biological functions of cAMP—a major regulating intracellular factor. However, the precise role of PDE7 in T cell activation and function is still ambiguous. Some authors reported its crucial role in T cell activation, while according to other studies PDE7 activity was not pivotal to T cells. Several studies showed that inhibition of PDE7 by its selective or dual PDE4/7 inhibitors suppresses T cell activity, and consequently T-mediated immune response. Taken together, it seems quite likely that simultaneous inhibition of PDE4 and PDE7 by dual PDE4/7 inhibitors or a combination of selective PDE4 and PDE7 remains the most interesting therapeutic target for the treatment of some immune-related disorders, such as autoimmune diseases, or selected respiratory diseases. An interesting direction of future studies could also be using a combination of selective PDE7 and PDE3 inhibitors.

The future of bronchodilation: looking for new classes of bronchodilators

Available bronchodilators can satisfy many of the needs of patients suffering from airway disorders, but they often do not relieve symptoms and their long-term use raises safety concerns. Therefore, there is interest in developing new classes that could help to overcome the limits that characterise the existing classes.At least nine potential new classes of bronchodilators have been identified: 1) selective phosphodiesterase inhibitors; 2) bitter-taste receptor agonists; 3) E-prostanoid receptor 4 agonists; 4) Rho kinase inhibitors; 5) calcilytics; 6) agonists of peroxisome proliferator-activated receptor-γ; 7) agonists of relaxin receptor 1; 8) soluble guanylyl cyclase activators; and 9) pepducins. They are under consideration, but they are mostly in a preclinical phase and, consequently, we still do not know which classes will actually be developed for clinical use and whether it will be proven that a possible clinical benefit outweighs the impact of any adverse effect.It is likely that if developed, these new classes may be a useful addition to, rather than a substitution of, the bronchodilator therapy currently used, in order to achieve further optimisation of bronchodilation.

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.

Phosphodiesterase 4 and 7 inhibitors produce protective effects against high glucose-induced neurotoxicity in PC12 cells via modulation of the oxidative stress, apoptosis and inflammation pathways

Diabetic neuropathy (DN) is the most common diabetic complication. It is estimated diabetic population will increase to 592 million by the year 2035. This is while at least 50-60% of all diabetic patients will suffer from neuropathy in their lifetime. Oxidative stress, mitochondrial dysfunction, apoptosis, and inflammation are crucial pathways in development and progression of DN. Since there is also no selective and effective therapeutic agent to prevent or treat high glucose (HG)-induced neuronal cell injury, it is crucial to explore tools by which one can reduce factors related to these pathways. Phosphodiesterase 4 and 7 (PDE 4 and 7) regulate oxidative damage, neurodegenaration, and inflammatory responses through modulation of cyclic adenosine monophosphate (cAMP) level, and thus can be as important drug targets for regulating DN. The aim of this study was to evaluate the protective effects of inhibitors of PDE 4 and 7, named rolipram and BRL5048, on HG-induced neurotoxicity in PC12 cells as an in vitro cellular model for DN and determine the possible mechanisms for theirs effects. We report that the PC12 cells pre-treatment with rolipram (2 μM) and/or BRL5048 (0.2 μM) for 60 min and then exposing the cells to HG (4.5 g/L for 72 h) or normal glucose (NG) (1 g/L for 72 h) condition show: (1) significant attenuation in ROS, MDA and TNF-a levels, Bax/Bcl-2 ratio, expression of caspase 3 and UCP2 proteins; (2) significant increase in viability, GSH/GSSG ratio, MMP and ATP levels. All these data together led us to propose PDE 4 and 7 inhibitors, and specifically, rolipram and BRL5048, as potential drugs candidate to be further studied for the prevention and treatment of DN.

Novel butanehydrazide derivatives of purine-2,6-dione as dual PDE4/7 inhibitors with potential anti-inflammatory activity: Design, synthesis and biological evaluation

A novel butanehydrazide derivatives of purine-2,6-dione designed using a ligand-based approach were synthesized and their in vitro activity against both PDE4B and PDE7A isoenzymes was assessed. The 7,8-disubstituted purine-2,6-dione derivatives 31, 34, 37, and 40 appeared to be the most potent PDE4/7 inhibitors with IC₅₀ values in the range of that of the reference rolipram and BRL-50481, respectively. Moreover, docking studies explained the importance of N-(2,3,4-trihydroxybenzylidene)butanehydrazide substituent in position 7 of purine-2,6-dione core for dual PDE4/7 inhibitory properties. The inhibition of both the cAMP-specific PDE isoenzymes resulted in a strong anti-TNF-α effect. Compounds 31, 34, and 37 in the in vivo study in rats with LPS-induced endotoxemia decreased the maximum concentration of this proinflammatory cytokine by 53, 84 and 88%, respectively.

Inhibitors of phosphodiesterases in the treatment of cough

A group of 11 enzyme families of metalophosphohydrolases called phosphodiesterases (PDEs) is responsible for a hydrolysis of intracellular cAMP and cGMP. Xanthine derivatives (methylxanthines) inhibit PDEs without selective action on their single isoforms and lead to many pharmacological effects, e.g. bronchodilation, anti-inflammatory and immunomodulating effects, and thus they can modulate the cough reflex. Contrary, selective PDE inhibitors have been developed to inhibit PDE isoforms with different pharmacological effects based on their tissue expression. In this paper, effects of non-selective PDE inhibitors (e.g. theophylline) are discussed, with a description of other putative mechanisms in their effects on cough. Antitussive effects of selective inhibitors of several PDE isoforms are reviewed, focusing on PDE1, PDE3, PDE4, PDE5 and PDE7. The inhibition of PDEs suggests participation of bronchodilation, suppression of TRPV channels and anti-inflammatory action in cough suppression. Selective PDE3, PDE4 and PDE5 inhibitors have demonstrated the most significant cough suppressive effects, confirming their benefits in chronic inflammatory airway diseases associated with bronchoconstriction and cough.

Intensity of swimming exercise influences tracheal reactivity in rats

Studies that evaluate the mechanisms for increased airway responsiveness are very sparse, although there are reports of exercise-induced bronchospasm. Therefore, we have evaluated the tracheal reactivity and the rate of lipid peroxidation after different intensities of swimming exercise in rats. Thus, male Wistar rats (age 8 weeks; 250–300 g) underwent a forced swimming exercise for 1 h whilst carrying attached loads of 3, 4, 5, 6 and 8% of their body weight (groups G3, G4, G5, G6 and G8, respectively; n=5 each). Immediately after the test, the trachea of each rat was removed and suspended in an organ bath to evaluate contractile and relaxant responses. The rate of lipid peroxidation was estimated by measuring malondialdehyde levels. According to a one-way ANOVA, all trained groups showed a significant decrease in the relaxation induced by aminophylline (10⁻¹²–10⁻¹ M) (pD2=3.1, 3.2, 3.3, 3.3 and 3.2, respectively for G3, G4, G5, G6 and G8) compared to the control group (pD2=4.6) and the E_max values of G5, G6, G8 groups were reduced by 94.2, 88.0 and 77.0%, respectively. Additionally, all trained groups showed a significant increase in contraction induced by carbachol (10⁻⁹–10⁻³ M) (pD2=6.0, 6.5, 6.5, 7.2 and 7.3, respectively for G3, G4, G5, G6 and G8) compared to the control group (pD2=5.7). Lipid peroxidation levels of G3, G4 and G5 were similar in both the trachea and lung, however G6 and G8 presented an increased peroxidation in the trachea. In conclusion, a single bout of swimming exercise acutely altered tracheal responsiveness in an intensity-related manner and the elevation in lipid peroxidation indicates a degree of oxidative stress involvement.

A short review on structure and role of cyclic-3',5'-adenosine monophosphate-specific phosphodiesterase 4 as a treatment tool

Cyclic nucleotide phosphodiesterases (PDEs) are known as a super-family of enzymes which catalyze the metabolism of the intracellular cyclic nucleotides, cyclic-3',5'-adenosine monophosphate (cAMP), and cyclic-3',5'-guanosine monophosphate that are expressed in a variety of cell types that can exert various functions based on their cells distribution. The PDE4 family has been the focus of vast research efforts over recent years because this family is considered as a prime target for therapeutic intervention in a number of inflammatory diseases such as asthma, chronic obstructive pulmonary disease, and rheumatoid arthritis, and it should be used and researched by pharmacists. This is because the major isoform of PDE that regulates inflammatory cell activity is the cAMP-specific PDE, PDE4. This review discusses the relationship between PDE4 and its inhibitor drugs based on structures, cells distribution, and pharmacological properties of PDE4 which can be informative for all pharmacy specialists.

PDE4 and PDE5 regulate cyclic nucleotide contents and relaxing effects on carbachol-induced contraction in the bovine abomasum

The effects of various selective phosphodiesterase (PDE) inhibitors on carbachol (CCh)-induced contraction in the bovine abomasum were investigated. Various selective PDE inhibitors, vinpocetine (type 1), erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA, type 2), milrinone (type 3), Ro20-1724 (type 4), vardenafil (type 5), BRL-50481 (type 7) and BAY73-6691 (type 9), inhibited CCh-induced contractions in a concentration-dependent manner. Among the PDE inhibitors, Ro20-1724 and vardenafil induced more relaxation than the other inhibitors based on the data for the IC₅₀ or maximum relaxation. In smooth muscle of the bovine abomasum, we showed the expression of PDE4B, 4C, 4D and 5 by RT-PCR analysis. In the presence of CCh, Ro20-1724 increased the cAMP content, but not the cGMP content. By contrast, vardenafil increased the cGMP content, but not the cAMP content. These results suggest that Ro20-1724-induced relaxation was correlated with cAMP and that vardenafil-induced relaxation was correlated with cGMP in the bovine abomasum. In conclusion, PDE4 and PDE5 are the enzymes involved in regulation of the relaxation associated with cAMP and cGMP, respectively, in the bovine abomasum.

cAMP-specific phosphodiesterase inhibitors: promising drugs for inflammatory and neurological diseases

INTRODUCTION

PDEs are key enzymes in the adenosine and guanosine cyclic nucleotides (cAMP and cGMP) signaling cascade. Their inhibition increases cyclic nucleotide levels inside the cell. Thus, pharmacological modulation of PDE activity can have profound effects on the function of cells and organ systems throughout the body.

AREAS COVERED

Among the large PDE families, only PDE4, PDE7 and PDE8 are cAMP-specific hydrolyzing enzymes. cAMP is an important second messenger not only by its involvement in a vast number of physiological processes but also by activation of protein kinase A, exchange protein activated by cAMP (Epac) and cAMP response element-binding (CREB) or cyclic nucleotide-gated channels. Clearly, such enzymes represent ideal drug targets for the pharmacological treatment of many pathologies. The discovery and development of small molecules targeting cAMP-specific PDEs reported in the last 5 years is the focus of the present review.

EXPERT OPINION

The first PDE4 inhibitors recently reached the market, having avoided, by different strategies, their dose-limiting side effects (after more than two decades of drug development). Meanwhile, new cAMP-specific PDE7 and PDE8 inhibitors emerged as effective and safe drugs for severe unmet diseases. The therapeutic potential of these inhibitors will be tested in the near future, as many of these drug candidates are ready to start clinical trials.

Theophylline inhibits the cough reflex through a novel mechanism of action

Background

Theophylline has been used in the treatment of asthma and chronic obstructive pulmonary disease for more than 80 years. In addition to bronchodilator and anti-inflammatory activity, clinical studies have suggested that theophylline acts as an antitussive agent. Cough is the most frequent reason for consultation with a family doctor, and treatment options are limited. Determining how theophylline inhibits cough might lead to the development of optimized compounds.

Objective

We sought to investigate the inhibitory activity of theophylline on vagal sensory nerve activity and the cough reflex.

Methods

Using a range of techniques, we investigated the effect of theophylline on human and guinea pig vagal sensory nerve activity in vitro and on the cough reflex in guinea pig challenge models.

Results

Theophylline was antitussive in a guinea pig model, inhibited activation of single C-fiber afferents in vivo and depolarization of human and guinea pig vagus in vitro, and inhibited calcium influx in airway-specific neurons in vitro. A sequence of pharmacological studies on the isolated vagus and patch clamp and single-channel inside-out experiments showed that the effect of theophylline was due to an increase in the open probability of calcium-activated potassium channels. Finally, we demonstrated the antitussive activity of theophylline in a cigarette smoke exposure model that exhibited enhanced tussive responses to capsaicin.

Conclusion

Theophylline inhibits capsaicin-induced cough under both normal and “disease” conditions by decreasing the excitability of sensory nerves through activation of small- and intermediate-conductance calcium-activated potassium channels. These findings could lead to the development of optimized antitussive compounds with a reduced side effect potential.