Absence of muscarinic cholinergic airway responses in mice deficient in the cyclic nucleotide phosphodiesterase PDE4D

Theophylline-Induced Relaxation Is Enhanced after Testosterone Treatment via Increased KV1.2 and KV1.5 Protein Expression in Guinea Pig Tracheal Smooth Muscle

Theophylline is a drug commonly used to treat asthma due to its anti-inflammatory and bronchodilatory properties. Testosterone (TES) has been suggested to reduce the severity of asthma symptoms. This condition affects boys more than girls in childhood, and this ratio reverses at puberty. We reported that guinea pig tracheal tissue chronic exposure to TES increases the expression of β₂-adrenoreceptors and enhances salbutamol-induced K⁺ currents (IK⁺). Herein, we investigated whether the upregulation of K⁺ channels can enhance the relaxation response to methylxanthines, including theophylline. Chronic incubation of guinea pig tracheas with TES (40 nM, 48 h) enhanced the relaxation induced by caffeine, isobutylmethylxanthine, and theophylline, an effect that was abolished by tetraethylammonium. In tracheal myocytes, chronic incubation with TES increased theophylline-induced IK⁺; flutamide reversed this effect. The increase in IK⁺ was blocked by 4-aminopyridine by ~82%, whereas iberiotoxin reduced IK⁺ by ~17%. Immunofluorescence studies showed that chronic TES exposure increased the expression of K_V1.2 and K_V1.5 in airway smooth muscle (ASM). In conclusion, chronic exposure to TES in guinea pig ASM promotes upregulation of K_V1.2 and K_V1.5 and enhances theophylline relaxation response. Therefore, gender should be considered when prescribing methylxanthines, as teenage boys and males are likely to respond better than females.

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.

Phosphodiesterase 4B inhibition: a potential novel strategy for treating pulmonary fibrosis

Patients with interstitial lung disease can develop a progressive fibrosing phenotype characterised by an irreversible, progressive decline in lung function despite treatment. Current therapies slow, but do not reverse or stop, disease progression and are associated with side-effects that can cause treatment delay or discontinuation. Most crucially, mortality remains high. There is an unmet need for more efficacious and better-tolerated and -targeted treatments for pulmonary fibrosis. Pan-phosphodiesterase 4 (PDE4) inhibitors have been investigated in respiratory conditions. However, the use of oral inhibitors can be complicated due to class-related systemic adverse events, including diarrhoea and headaches. The PDE4B subtype, which has an important role in inflammation and fibrosis, has been identified in the lungs. Preferentially targeting PDE4B has the potential to drive anti-inflammatory and antifibrotic effects via a subsequent increase in cAMP, but with improved tolerability. Phase I and II trials of a novel PDE4B inhibitor in patients with idiopathic pulmonary fibrosis have shown promising results, stabilising pulmonary function measured by change in forced vital capacity from baseline, while maintaining an acceptable safety profile. Further research into the efficacy and safety of PDE4B inhibitors in larger patient populations and for a longer treatment period is needed.

Homeostatic glucocorticoid signaling in airway smooth muscle: A roadmap to asthma pathogenesis

Homeostasis is the self-regulating process by which the body maintains internal stability within a narrow physiological range (i.e., "normality") as it dynamically adjusts to disruptive influences. Thus, whereas homeostasis maintains bodily health, disrupted homeostasis at the tissue or systemic level leads to disease. Airway smooth muscle (ASM) is the pivotal site of disrupted homeostasis in asthma. While extensive research has greatly expanded our understanding of ASM behavior under pro-asthmatic conditions, the cellular signaling mechanisms that underlie ASM homeostasis under these conditions remain elusive. Based on a broad collection of published studies, a homeostasis mechanism intrinsic to ASM and exhibited under inflammatory and non-inflammatory pro-asthmatic conditions is identified herein. Central to this mechanism is the novel unifying concept that the pro-asthmatic-exposed ASM can independently generate its own active glucocorticoid (i.e., cortisol), produce its own newly activated glucocorticoid receptors for the steroid, and, accordingly, use this molecular strategy to homeostatically prevent induction of the asthmatic state. This article addresses the experimental evidence that underlies the proposed homeostatic glucocorticoid signaling mechanism in ASM, followed by a discussion and depiction of the feed-forward and feedback intrinsic ASM signaling circuitry that constitutes the homeostatic state. The proposed mechanism offers a practical roadmap for future basic and translational research aimed at identifying potential key site(s) of disrupted ASM homeostasis leading to asthma.

Modulation of IL-4/IL-13 cytokine signaling in the context of allergic disease

Aberrant activation of CD4 T_H2 cells and excessive production of T_H2 cytokines such as IL-4 and IL-13 have been implicated in the pathogenesis of allergic diseases. Generally, IL-4 and IL-13 utilize Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathways for induction of inflammatory gene expression and the effector functions associated with disease pathology in many allergic diseases. However, it is increasingly clear that JAK/STAT pathways activated by IL-4/IL-13 can themselves be modulated in the presence of other intracellular signaling programs, thereby changing the overall tone and/or magnitude of IL-4/IL-13 signaling. Apart from direct activation of the canonic JAK/STAT pathways, IL-4 and IL-13 also induce proinflammatory gene expression and effector functions through activation of additional signaling cascades. These alternative signaling cascades contribute to several specific aspects of IL-4/IL-13-associated cellular and molecular responses. A more complete understanding of IL-4/IL-13 signaling pathways, including the precise conditions under which noncanonic signaling pathways are activated, and the impact of these pathways on cellular- and host-level responses, will better allow us to design agents that target specific pathologic outcomes or tailor therapies for the treatment of uncommon disease endotypes.

Clinical Implication of Phosphodiesterase-4-Inhibition

The pleiotropic function of 3′,5′-cyclic adenosine monophosphate (cAMP)-dependent pathways in health and disease led to the development of pharmacological phosphodiesterase inhibitors (PDE-I) to attenuate cAMP degradation. While there are many isotypes of PDE, a predominant role of PDE4 is to regulate fundamental functions, including endothelial and epithelial barrier stability, modulation of inflammatory responses and cognitive and/or mood functions. This makes the use of PDE4-I an interesting tool for various therapeutic approaches. However, due to the presence of PDE4 in many tissues, there is a significant danger for serious side effects. Based on this, the aim of this review is to provide a comprehensive overview of the approaches and effects of PDE4-I for different therapeutic applications. In summary, despite many obstacles to use of PDE4-I for different therapeutic approaches, the current data warrant future research to utilize the therapeutic potential of phosphodiesterase 4 inhibition.

Transforming Growth Factor-β1 Decreases β2-Agonist-induced Relaxation in Human Airway Smooth Muscle

Helper T effector cytokines implicated in asthma modulate the contractility of human airway smooth muscle (HASM) cells. We have reported recently that a profibrotic cytokine, transforming growth factor (TGF)-β1, induces HASM cell shortening and airway hyperresponsiveness. Here, we assessed whether TGF-β1 affects the ability of HASM cells to relax in response to β₂-agonists, a mainstay treatment for airway hyperresponsiveness in asthma. Overnight TGF-β1 treatment significantly impaired isoproterenol (ISO)-induced relaxation of carbachol-stimulated, isolated HASM cells. This single-cell mechanical hyporesponsiveness to ISO was corroborated by sustained increases in myosin light chain phosphorylation. In TGF-β1-treated HASM cells, ISO evoked markedly lower levels of intracellular cAMP. These attenuated cAMP levels were, in turn, restored with pharmacological and siRNA inhibition of phosphodiesterase 4 and Smad3, respectively. Most strikingly, TGF-β1 selectively induced phosphodiesterase 4D gene expression in HASM cells in a Smad2/3-dependent manner. Together, these data suggest that TGF-β1 decreases HASM cell β₂-agonist relaxation responses by modulating intracellular cAMP levels via a Smad2/3-dependent mechanism. Our findings further define the mechanisms underlying β₂-agonist hyporesponsiveness in asthma, and suggest TGF-β1 as a potential therapeutic target to decrease asthma exacerbations in severe and treatment-resistant asthma.

Hyperinsulinemia promotes heterologous desensitization of β2 adrenergic receptor in airway smooth muscle in obesity

β-Adrenergic receptor (β-AR) agonists are the most common clinical bronchodilators for asthma. Obesity influences asthma severity and may impair response to β-AR agonists. Previous studies show that in obese mice, hyperinsulinemia plays a crucial role in β-AR desensitization in the heart. We therefore investigated whether insulin promotes β-AR desensitization in airway smooth muscle (ASM) and compromises airway relaxation responsiveness to β-AR agonists. We found that human ASM cells and mouse airway tissues exposed to insulin exhibit impaired β₂ AR-induced cAMP accumulation and airway relaxation. This impaired relaxation is associated with insulin-induced phosphorylation and expression of phosphodiesterase 4D (PDE4D) through transactivation of a G protein-coupled receptor kinase 2 (GRK2)-dependent β₂ AR-G_i -ERK1/2 cascade. Both acute and chronic pharmacological inhibition of PDE4 effectively reversed impaired β₂ AR-mediated ASM relaxation in an obesity mouse model induced by a high fat diet. Collectively, these findings reveal that cross talk between insulin and β₂ AR signaling promotes ASM β₂ AR desensitization in obesity through upregulation of PDE4D phosphorylation and expression. Our results identify a novel pathway of asthma pathogenesis in patients with obesity/metabolic syndrome, in which the GRK2-mediated signaling can be a potential therapeutic modality to prevent or treat β₂ AR desensitization in ASM. Moreover, PDE4 inhibitors may be used as efficacious therapeutic agents for asthma in obese and diabetic subjects.

A pathophysiological role of PDE3 in allergic airway inflammation

Phosphodiesterase 3 (PDE3) and PDE4 regulate levels of cyclic AMP, which are critical in various cell types involved in allergic airway inflammation. Although PDE4 inhibition attenuates allergic airway inflammation, reported side effects preclude its application as an antiasthma drug in humans. Case reports showed that enoximone, which is a smooth muscle relaxant that inhibits PDE3, is beneficial and lifesaving in status asthmaticus and is well tolerated. However, clinical observations also showed antiinflammatory effects of PDE3 inhibition. In this study, we investigated the role of PDE3 in a house dust mite-driven (HDM-driven) allergic airway inflammation (AAI) model that is characterized by T helper 2 cell activation, eosinophilia, and reduced mucosal barrier function. Compared with wild-type (WT) littermates, mice with a targeted deletion of the PDE3A or PDE3B gene showed significantly reduced HDM-driven AAI. Therapeutic intervention in WT mice showed that all hallmarks of HDM-driven AAI were abrogated by the PDE3 inhibitors enoximone and milrinone. Importantly, we found that enoximone also reduced the upregulation of the CD11b integrin on mouse and human eosinophils in vitro, which is crucial for their recruitment during allergic inflammation. This study provides evidence for a hitherto unknown antiinflammatory role of PDE3 inhibition in allergic airway inflammation and offers a potentially novel treatment approach.

Roflumilast treatment inhibits lung carcinogenesis in benzo(a)pyrene-induced murine lung cancer model

Roflumilast, a potent and selective inhibitor of phosphodiesterase-4 (PDE4), has been used in treatment of COPD. PDE4 inhibitor is associated with inhibition of chronic airway inflammation, oxidative stress, and mesenchymal markers in B(a)P-induced lung tumors. The aim of this study was to assess whether roflumilast alone or added to inhaled budesonide might have dose-dependent inhibition on lung carcinogenesis induced by carcinogen B(a)P in mice. Female A/J mice were given a single dose of benzo(a)pyrene. Administration of roflumilast (1mg/kg or 5mg/kg) via oral gavage and aerosolized budesonide (2.25mg/ml) began 2 weeks post-carcinogen treatment and continued for 26 weeks. Tumor load was determined by averaging the total tumor volume in each group. Benzo(a)pyrene induced an average tumor size of 9.38 ± 1.75 tumors per mouse, with an average tumor load of 19.53 ± 3.81mm³. Roflumilast 5mg/kg treatment decreased (P < 0.05) tumor load per mouse compared to the B(a)P group. Roflumilast 5mg/kg treatment significantly increased the levels of cAMP in tumors with adjacent lung tissues (P < 0.05). The expression level of PDE4D gene was decreased by roflumilast 5mg/kg treatment, significantly (P < 0.05). Compared to the B(a)P exposure group, expression levels of HIF-1α and VEGFA were attenuated by roflumilast 5mg/kg treatment (P < 0.05). High-dose roflumilast can attenuate lung carcinogenesis in B(a)P-induced murine lung cancer model. The chemopreventive effect of roflumilast might be associated with inhibition of increased cAMP-mediated inflammatory process and markers of angiogenesis in tumor tissues.

Exploring the origin of phosphodiesterase inhibition via proteochemometric modeling

A proteochemometric study of a set of phosphodiesterase 4B and 4D inhibitors sheds light on the origin of their inhibition and selectivities.

Genetic Understanding of Stroke Treatment: Potential Role for Phosphodiesterase Inhibitors

Phosphodiesterase (PDE) gene family is a large family having at least 21 genes and multiple versions (isoforms) of the phosphodiesterase enzymes. These enzymes catalyze the inactivation of intracellular mediators of signal transduction such as cAMP and cGMP and therefore, play a pivotal role in various cellular functions. PDE inhibitors (PDEI) are drugs that block one or more of the five subtypes of the PDE family and thereby prevent inactivation of the intracellular cAMP and cGMP by the respective PDE-subtypes. The first clinical use of PDEI was reported almost three decades ago. Studies later found the ability of these compounds to increase the levels of ubiquitous secondary messenger molecules that can cause changes in vascular tone, cardiac function and other cellular events and thus these findings paved the way for their use in various medical emergencies. PDEs are found to be distributed in many tissues including brain. Therefore, new therapeutic agents in the form of PDEI are being explored in neurodegenerative diseases including stroke. Although studies have revealed their use in cerebral infarction prevention, their full-fledged application in times of neurological emergency or stroke in specific has been very limited so far. Nevertheless, recent investigations suggest PDE4 and PDE5 inhibitors to play a vital role in mitigating stroke symptoms by modulating signaling mechanisms in PDE pathway. Further, extensive research in terms of their pharmacological properties like dosing, drug specific activities, use of simultaneous medications, ancillary properties of these compounds and studies on adverse drug reactions needs to be carried out to set them as standard drugs of use in stroke.

Aberrant DNA Methylation of Phosphodiesterase [corrected] 4D Alters Airway Smooth Muscle Cell Phenotypes

Airway hyperresponsiveness (AHR) is a hallmark feature in asthma characterized by exaggerated airway contractile response to stimuli due to increased airway sensitivity and chronic airway remodeling. We have previously shown that allergen-induced AHR in mice is associated with aberrant DNA methylation in the lung genome, suggesting that AHR could be epigenetically regulated, and these changes might predispose the animals to asthma. Previous studies demonstrated that overexpression of phosphodiesterase 4D (PDE4D) is associated with increased AHR. However, epigenetic regulation of this gene in asthmatic airway smooth muscle cells (ASMCs) has not been examined. In this study, we aimed to examine the relationship between epigenetic regulation of PDE4D and ASMC phenotypes. We identified CpG site-specific hypomethylation at PDE4D promoter in human asthmatic ASMCs. We next used methylated oligonucleotides to introduce CpG site-specific methylation at PDE4D promoter and examined its effect on ASMCs. We showed that PDE4D methylation decreased cell proliferation and migration of asthmatic ASMCs. We further elucidated that methylated PDE4D decreased PDE4D expression in asthmatic ASMCs, increased cAMP level, and inhibited the aberrant increase in Ca(2+) level. Moreover, PDE4D methylation reduced the phosphorylation level of downstream effectors of Ca(2+) signaling, including myosin light chain kinase and p38. Taken together, our findings demonstrate that gene-specific epigenetic changes may predispose ASMCs to asthma through alterations in cell phenotypes. Modulation of ASMC phenotypes by methylated PDE4D oligonucleotides can reverse the aberrant ASMC functions to normal phenotypes. This has provided new insight to the development of novel therapeutic options for this debilitative disease.

The Role of Protein Kinase A in Anxiety Behaviors

This review focuses on the genetic and other evidence supporting the notion that the cyclic AMP (cAMP) signaling pathway and its mediator, the protein kinase A (PKA) enzyme, which respond to environmental stressors and regulate stress responses, are central to the pathogenesis of disorders related to anxiety. We describe the PKA pathway and review in vitro animal studies (mouse) and other evidence that support the importance of PKA in regulating behaviors that lead to anxiety. Since cAMP signaling and PKA have been pharmacologically exploited since the 1940s (even before the identification of cAMP as a second messenger with PKA as its mediator) for a number of disorders from asthma to cardiovascular diseases, there is ample opportunity to develop therapies using this new knowledge about cAMP, PKA, and anxiety disorders.

PDK1/Akt/PDE4D axis identified as a target for asthma remedy synergistic with β2 AR agonists by a natural agent arctigenin

BACKGROUND

Asthma is a heterogenetic disorder characterized by chronic inflammation with variable airflow obstruction and airway hyper-responsiveness. As the most potent and popular bronchodilators, β2 adrenergic receptor (β2 AR) agonists bind to the β2 ARs that are coupled via a stimulatory G protein to adenylyl cyclase, thereby improving cAMP accumulation and resulting in airway smooth muscle relaxation. We previously demonstrated arctigenin had a synergistic function with the β2 AR agonist, but the target for this remained elusive.

METHOD

Chemical proteomics capturing was used to enrich and uncover the target of arctigenin in human bronchial smooth muscle cells, and reverse docking and molecular dynamic stimulation were performed to evaluate the binding of arctigenin and its target. In vitro enzyme activities and protein levels were demonstrated with special kits and Western blotting. Finally, guinea pig tracheal muscle segregation and ex vivo function were analysed.

RESULTS

Arctigenin bound to PDK1 with an ideal binding free energy -25.45 kcal/mol and inhibited PDK1 kinase activity without changing its protein level. Additionally, arctigenin reduced PKB/Akt-induced phosphorylation of PDE4D, which was first identified in this study. Attenuation of PDE4D resulted in cAMP accumulation in human bronchial smooth muscle. The inhibition of PDK1 showed a synergistic function with β2 AR agonists and relaxed the constriction of segregated guinea pig tracheal muscle.

CONCLUSIONS

The PDK1/Akt/PDE4D axis serves as a novel asthma target, which may benefit airflow obstruction.

Identification and Characterization of Baicalin as a Phosphodiesterase 4 Inhibitor

Asthma is a chronic inflammatory disease of lung airways, and pharmacological inhibitors of cyclic adenosine monophosphate-specific phosphodiesterase 4 (PDE4) have been considered as therapeutics for the treatment of asthma. However, development of PDE4 inhibitors in clinical trials has been hampered because of the severe side effects of non-selective PDE4 inhibitors. Here, screening of a plant extract library in conjunction with dereplication technology led to identification of baicalin as a new type of PDE4-selective inhibitor. We demonstrated that while rolipram inhibited the enzyme activity of a range of PDE4 subtypes in in vitro enzyme assays, baicalin selectively inhibited the enzyme activity of PDE4A and 4B. In addition, baicalin suppressed lipopolysaccharide-induced TNF-α expression in macrophage where PDE4B plays a key role in lipopolysaccharide-induced signaling. Furthermore, baicalin treatment in an animal model of allergic asthma reduced inflammatory cell infiltration and TNF-α levels in bronchoalveolar lavage fluids, indicating that the antiinflammatory effects of baicalin in vivo are attributable, in part, to its ability to inhibit PDE4.

MEK Inhibitors Reverse cAMP-Mediated Anxiety in Zebrafish

Altered phosphodiesterase (PDE)-cyclic AMP (cAMP) activity is frequently associated with anxiety disorders, but current therapies act by reducing neuronal excitability rather than targeting PDE-cAMP-mediated signaling pathways. Here, we report the novel repositioning of anti-cancer MEK inhibitors as anxiolytics in a zebrafish model of anxiety-like behaviors. PDE inhibitors or activators of adenylate cyclase cause behaviors consistent with anxiety in larvae and adult zebrafish. Small-molecule screening identifies MEK inhibitors as potent suppressors of cAMP anxiety behaviors in both larvae and adult zebrafish, while causing no anxiolytic behavioral effects on their own. The mechanism underlying cAMP-induced anxiety is via crosstalk to activation of the RAS-MAPK signaling pathway. We propose that targeting crosstalk signaling pathways can be an effective strategy for mental health disorders, and advance the repositioning of MEK inhibitors as behavior stabilizers in the context of increased cAMP.

Phosphodiesterase inhibitors as therapeutics for traumatic brain injury

Developing therapeutics for traumatic brain injury remains a challenge for all stages of recovery. The pathological features of traumatic brain injury are diverse, and it remains an obstacle to be able to target the wide range of pathologies that vary between traumatic brain injured patients and that evolve during recovery. One promising therapeutic avenue is to target the second messengers cAMP and cGMP with phosphodiesterase inhibitors due to their broad effects within the nervous system. Phosphodiesterase inhibitors have the capability to target different injury mechanisms throughout the time course of recovery after brain injury. Inflammation and neuronal death are early targets of phosphodiesterase inhibitors, and synaptic dysfunction and circuitry remodeling are late potential targets of phosphodiesterase inhibitors. This review will discuss how signaling through cyclic nucleotides contributes to the pathology of traumatic brain injury in the acute and chronic stages of recovery. We will review our current knowledge of the successes and challenges of using phosphodiesterase inhibitors for the treatment of traumatic brain injury and conclude with important considerations in developing phosphodiesterase inhibitors as therapeutics for brain trauma.

Genome-wide interaction study of gene-by-occupational exposure and effects on FEV1 levels

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a complex disease characterized by impaired lung function and airway obstruction resulting from interactions between multiple genes and multiple environmental exposures. Thus far, genome-wide association studies have largely disregarded environmental factors that might trigger the development of lung function impairment and COPD, such as occupational exposures, which are thought to contribute to 15% to 20% of the COPD prevalence.

OBJECTIVES

We performed a genome-wide interaction study to identify novel susceptibility loci for occupational exposure to biological dust, mineral dust, and gases and fumes in relation to FEV1 levels.

METHODS

We performed an identification analysis in 12,400 subjects from the LifeLines cohort study and verified our findings in 1436 subjects from a second independent cohort, the Vlagtwedde-Vlaardingen cohort. Additionally, we assessed whether replicated single nucleotide polymorphisms (SNPs) were cis-acting expression (mRNA) quantitative trait loci in lung tissue.

RESULTS

Of the 7 replicated SNPs that interacted with one of the occupational exposures, several identified loci were plausible candidates that might be involved in biological pathways leading to lung function impairment, such as PCDH9 and GALNT13. Two of the 7 replicated SNPs were cis-acting expression quantitative trait loci associated with gene expression of PDE4D and TMEM176A in lung tissue.

CONCLUSION

This genome-wide interaction study on occupational exposures in relation to the level of lung function identified several novel genes. Further research should determine whether the identified genes are true susceptibility loci for occupational exposures and whether these SNP-by-exposure interactions consequently contribute to the development of COPD.

Constitutively active signaling by the G protein βγ-subunit mediates intrinsically increased phosphodiesterase-4 activity in human asthmatic airway smooth muscle cells

Signaling by the Gβγ subunit of Gi protein, leading to downstream c-Src-induced activation of the Ras/c-Raf1/MEK-ERK1/2 signaling pathway and its upregulation of phosphodiesterase-4 (PDE4) activity, was recently shown to mediate the heightened contractility in proasthmatic sensitized isolated airway smooth muscle (ASM), as well as allergen-induced airway hyperresponsiveness and inflammation in an in vivo animal model of allergic asthma. This study investigated whether cultured human ASM (HASM) cells derived from asthmatic donor lungs exhibit constitutively increased PDE activity that is attributed to intrinsically upregulated Gβγ signaling coupled to c-Src activation of the Ras/MEK/ERK1/2 cascade. We show that, relative to normal cells, asthmatic HASM cells constitutively exhibit markedly increased intrinsic PDE4 activity coupled to heightened Gβγ-regulated phosphorylation of c-Src and ERK1/2, and direct co-localization of the latter with the PDE4D isoform. These signaling events and their induction of heightened PDE activity are acutely suppressed by treating asthmatic HASM cells with a Gβγ inhibitor. Importantly, along with increased Gβγ activation, asthmatic HASM cells also exhibit constitutively increased direct binding of the small Rap1 GTPase-activating protein, Rap1GAP, to the α-subunit of Gi protein, which serves to cooperatively facilitate Ras activation and, thereby, enable enhanced Gβγ-regulated ERK1/2-stimulated PDE activity. Collectively, these data are the first to identify that intrinsically increased signaling via the Gβγ subunit, facilitated by Rap1GAP recruitment to the α-subunit, mediates the constitutively increased PDE4 activity detected in asthmatic HASM cells. These new findings support the notion that interventions targeted at suppressing Gβγ signaling may lead to novel approaches to treat asthma.

The effect of the novel phosphodiesterase-4 inhibitor MEM 1414 on the allergen induced responses in mild asthma

Background

Inhaled allergen challenge is a standard method to study airway responses to inflammatory provocation and evaluate the therapeutic potential of novel anti-inflammatory compounds in asthma. MEM 1414 is a novel oral PDE4 inhibitor with high affinity and selectivity creating the potential for an improved side effect profile vs non-selective PDE inhibitors. We evaluated the tolerability and effect of MEM 1414 on airway responses in mild asthmatics.

Methods

A randomised double blind placebo controlled cross over study in two centres, in which sixteen steroid naïve atopic asthmatics were challenged with inhaled allergen. Subjects were dosed with MEM 1414 (600 mg) or placebo, twice daily orally for 7 days. Allergen challenge was performed on day 6 (2 hours post-dose), and methacholine responsiveness was measured 24 hours post allergen (day 7). Biomarkers of drug effects using ex vivo LPS stimulation of whole blood production of interleukin (IL)-6 and leukotriene (LT)-B4 and fractional exhaled nitric oxide (FeNO) were measured on day 6 (0, 2 and 8 hours post-dose). Plasma pharmacokinetics were measured on days 1, 6 and 7. The primary endpoint was the effect on late asthmatic response to allergen.

Results

Treatment with MEM 1414 abrogated the late phase response with a mean difference in FEV₁ (LAR 3–10 hours) of 104 ml (25%) vs placebo (p < 0.005), with no effect on the early response. Biomarker responses were also attenuated with MEM 1414 treatment with reductions in LPS-stimulated whole blood assays for TNFα at 8 hours (p < 0.03) and LTB₄ at 24 hours (p = 0.0808) with no change in the IL-6 response. The MEM 1414 treatment phase was associated with higher incidence of nausea (6/16 MEM 1414 vs 2/16 placebo) and vomiting (3/16 vs 0/16 placebo).

Conclusions

Oral MEM 1414, a novel PDE4 inhibitor, significantly reduces the late response following inhaled allergen challenge. MEM 1414 also inhibited whole blood assays of cytokine production from inflammatory cells. MEM 1414 was associated with a typical adverse event profile of PDE4 inhibitors, namely nausea and vomiting although these were mild side effects.

Trial registration number

Current controlled trials ISRCTN48047493.

Cyclic nucleotide phosphodiesterases: important signaling modulators and therapeutic targets

By catalyzing hydrolysis of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), cyclic nucleotide phosphodiesterases are critical regulators of their intracellular concentrations and their biological effects. As these intracellular second messengers control many cellular homeostatic processes, dysregulation of their signals and signaling pathways initiate or modulate pathophysiological pathways related to various disease states, including erectile dysfunction, pulmonary hypertension, acute refractory cardiac failure, intermittent claudication, chronic obstructive pulmonary disease, and psoriasis. Alterations in expression of PDEs and PDE-gene mutations (especially mutations in PDE6, PDE8B, PDE11A, and PDE4) have been implicated in various diseases and cancer pathologies. PDEs also play important role in formation and function of multimolecular signaling/regulatory complexes, called signalosomes. At specific intracellular locations, individual PDEs, together with pathway-specific signaling molecules, regulators, and effectors, are incorporated into specific signalosomes, where they facilitate and regulate compartmentalization of cyclic nucleotide signaling pathways and specific cellular functions. Currently, only a limited number of PDE inhibitors (PDE3, PDE4, PDE5 inhibitors) are used in clinical practice. Future paths to novel drug discovery include the crystal structure-based design approach, which has resulted in generation of more effective family-selective inhibitors, as well as burgeoning development of strategies to alter compartmentalized cyclic nucleotide signaling pathways by selectively targeting individual PDEs and their signalosome partners.

Effects of inactivated Bordetella pertussis on phosphodiesterase in the lung of ovalbumin sensitized and challenged rats

This paper indicated that inactivated Bordetella pertussis (iBp) can enhance the lung airway hyperreactivity of the rats sensitized and challenged with OVA. The mechanisms were involved in the upregulation of cAMP-PDE activity and PDE4A, PDE4D, and PDE3 gene expression in the lungs. But only PDE4 activity was different between the OVA and OVA+iBp groups, and PDE4D expression was significantly increased in iBp rats alone. So, our data suggested that cosensitization with OVA and iBp affects lung airway reactivity by modulating the lung cAMP-PDE activity and PDE4D gene expression.

Novel drug targets for asthma and COPD: lessons learned from in vitro and in vivo models

Asthma and chronic obstructive pulmonary disease (COPD) are highly prevalent respiratory diseases characterized by airway inflammation, airway obstruction and airway hyperresponsiveness. Whilst current therapies, such as β-agonists and glucocorticoids, may be effective at reducing symptoms, they do not reduce disease progression. Thus, there is a need to identify new therapeutic targets. In this review, we summarize the potential of novel targets or tools, including anti-inflammatories, phosphodiesterase inhibitors, kinase inhibitors, transient receptor potential channels, vitamin D and protease inhibitors, for the treatment of asthma and COPD.

Advances in targeting cyclic nucleotide phosphodiesterases

Cyclic nucleotide phosphodiesterases (PDEs) catalyse the hydrolysis of cyclic AMP and cyclic GMP, thereby regulating the intracellular concentrations of these cyclic nucleotides, their signalling pathways and, consequently, myriad biological responses in health and disease. Currently, a small number of PDE inhibitors are used clinically for treating the pathophysiological dysregulation of cyclic nucleotide signalling in several disorders, including erectile dysfunction, pulmonary hypertension, acute refractory cardiac failure, intermittent claudication and chronic obstructive pulmonary disease. However, pharmaceutical interest in PDEs has been reignited by the increasing understanding of the roles of individual PDEs in regulating the subcellular compartmentalization of specific cyclic nucleotide signalling pathways, by the structure-based design of novel specific inhibitors and by the development of more sophisticated strategies to target individual PDE variants.

Arrestin-dependent localization of phosphodiesterases

Many G-protein-coupled receptors trigger the synthesis of cAMP in order to transduce signals from the membrane into the cell cytoplasm. As stimulation of each receptor type results in a specific physiological outcome, compartmentalization of proteins that make, break, and are activated by cAMP underpin receptor-specific responses. Until 2002, it was thought that static compartmentalization of phosphodiesterase 4 (PDE4), conferred by N-terminal targeting sequences, was one way to shape intricate cAMP gradients that formed after receptor activation. Discovery of the PDE4-β-arrestin complex represented a major breakthrough in cAMP signaling, as it spurred the initial realization that PDE4s could be transported to sites of high cAMP to orchestrate destruction of the second messenger at the same time as the receptor's signal to the G-protein is silenced. This chapter charts the scientific process that led to the discovery and characterization of the PDE4-β-arrestin interaction and discusses the known functions of this signaling complex.

Clinical and molecular genetics of the phosphodiesterases (PDEs)

Cyclic nucleotide phosphodiesterases (PDEs) are enzymes that have the unique function of terminating cyclic nucleotide signaling by catalyzing the hydrolysis of cAMP and GMP. They are critical regulators of the intracellular concentrations of cAMP and cGMP as well as of their signaling pathways and downstream biological effects. PDEs have been exploited pharmacologically for more than half a century, and some of the most successful drugs worldwide today affect PDE function. Recently, mutations in PDE genes have been identified as causative of certain human genetic diseases; even more recently, functional variants of PDE genes have been suggested to play a potential role in predisposition to tumors and/or cancer, especially in cAMP-sensitive tissues. Mouse models have been developed that point to wide developmental effects of PDEs from heart function to reproduction, to tumors, and beyond. This review brings together knowledge from a variety of disciplines (biochemistry and pharmacology, oncology, endocrinology, and reproductive sciences) with emphasis on recent research on PDEs, how PDEs affect cAMP and cGMP signaling in health and disease, and what pharmacological exploitations of PDEs may be useful in modulating cyclic nucleotide signaling in a way that prevents or treats certain human diseases.

Structural basis for the design of selective phosphodiesterase 4B inhibitors

Phosphodiesterase-4B (PDE4B) regulates the pro-inflammatory Toll Receptor -Tumor Necrosis Factor α (TNFα) pathway in monocytes, macrophages and microglial cells. As such, it is an important, although under-exploited molecular target for anti-inflammatory drugs. This is due in part to the difficulty of developing selective PDE4B inhibitors as the amino acid sequence of the PDE4 active site is identical in all PDE4 subtypes (PDE4A-D). We show that highly selective PDE4B inhibitors can be designed by exploiting sequence differences outside the active site. Specifically, PDE4B selectivity can be achieved by capture of a C-terminal regulatory helix, now termed CR3 (Control Region 3), across the active site in a conformation that closes access by cAMP. PDE4B selectivity is driven by a single amino acid polymorphism in CR3 (Leu674 in PDE4B1 versus Gln594 in PDE4D). The reciprocal mutations in PDE4B and PDE4D cause a 70-80 fold shift in selectivity. Our structural studies show that CR3 is flexible and can adopt multiple orientations and multiple registries in the closed conformation. The new co-crystal structure with bound ligand provides a guide map for the design of PDE4B selective anti-inflammatory drugs.

Tiotropium sustains the anti-inflammatory action of olodaterol via the cyclic AMP pathway

Mesenchymal cells (fibroblasts) of the airway wall respond to cholinergic stimulation by releasing pro-inflammatory and chemotactic cytokines and may thus contribute to chronic inflammation of the lung. Here, we studied the anti-inflammatory potential of olodaterol, a long acting β2-adrenergic receptor agonist, and tiotropium, a long-acting muscarinic receptor antagonist, and whether they interact at the level of the cyclic AMP dependent signaling pathway. Pulmonary fibroblasts of asthmatic (n = 9) and non-asthmatic (n = 8) subjects were stimulated with the muscarinic receptor agonist carbachol and interleukin-1β (IL-1 beta) in presence or absence of tiotropium or olodaterol alone, or their combination. We also measured cAMP levels and phosphorylation of the cAMP response element binding protein (CREB). As single components, carbachol, olodaterol and tiotropium did not affect IL-6 and IL-8 release. Carbachol concentration-dependently enhanced the production of IL-1β-induced IL-6 and IL-8, which was blocked by the simultaneous addition of tiotropium. The combination of olodaterol plus tiotropium further reduced IL-6 and IL-8 release. Olodaterol induced cAMP and the phosphorylation of CREB, an effect counteracted by carbachol, but rescued by tiotropium. We conclude that olodaterol plus tiotropium cooperate to decrease the inflammatory response in pulmonary fibroblasts in vitro.

RGS5 gene and therapeutic response to short acting bronchodilators in paediatric asthma patients

Short-acting β2-adrenergic receptor agonists are commonly used bronchodilators for symptom relief in asthmatics. Recent evidence demonstrated that prolonged exposure of cultured airway smooth muscle cells to β2 agonists directly augments procontractile signaling pathways with the change in expression of regulator of G protein signaling 5 (RGS5). The aim of this study was to test whether genetic variants in RGS5 gene affect the response to short acting β2-agonists. Bronchodilator responsiveness was assessed in 137 asthmatic children by % change in baseline forced expiratory volume in 1 sec (FEV1 ) after administration of albuterol. The analyses were performed in patients with FEV1 /FVC ratio below 0.9 (FVC-forced vital capacity, n = 99). FEV1 % change adjusted for baseline FEV1 values was significantly different between genotypes of rs10917696 C/T polymorphism (P = 0.008). The association remained significant with inclusion of age, sex, atopy, parental smoking, and controller medications into multivariate model (P = 0.005). We also identified additive effect on the treatment outcome with previously published genetic variant G/A rs1544791 in phosphodiesterase 4 (PDE4D) gene. Carriers of two risk alleles (C and G) had adjusted mean % FEV1 change value 4.6 ± 1.3, while carriers of one and none of the risk alleles had 8.1 ± 0.7% and 13.5 ± 2.4%, respectively, P = 0.001. Our work identifies a new genetic variant in RGS5 demonstrating additive effect with PDE4D, both implicated in modulation of asthma treatment.

Epigenetic alterations by DNA methylation in house dust mite-induced airway hyperresponsiveness

Asthma is one of the most prevalent chronic lung diseases, affecting 235 million individuals around the world, with its related morbidity and mortality increasing steadily over the last 20 years. Exposure to the environmental allergen, house dust mite (HDM), results in airway inflammation with a variable degree of airway obstruction. Although there has been much experimental work in the past using HDM challenge models to understand mechanistic details in allergic inflammation and airway hyperresponsiveness (AHR), there has been no study on reprogramming of lung or airways mediated through epigenetic mechanisms in response to an acute HDM exposure. Male mice, 6 weeks of age, were administrated HDM extracts or saline at Days 1, 14, and 21. Exposure of mice to HDM extracts caused significant airway inflammation and increased AHR. These HDM-challenged mice also exhibited a change in global DNA methylation as compared with saline-exposed (control) mice. Next, by employing methylation-sensitive restriction fingerprinting, we identified a set of genes, showing aberrant methylation status, associated with the HDM-induced AHR. These candidate genes are known to be involved in cAMP signaling (pde4 d), Akt-signaling (akt1 s1), ion transport (tm6 sf1, pom121l2, and slc8a3), and fatty acid metabolism (acsl3). Slc8a3 and acsl3 were down-regulated, whereas pde4 d, akt1 s1, tm6 sf1, and pom121l2 were up-regulated in the mice exposed to HDM. Hence, our results suggest that HDM exposure induces a series of aberrant methylated genes that are potentially important for the development of allergic AHR.

Genetics of onset of asthma

PURPOSE OF REVIEW

Most asthma starts early in life. Defining phenotypes of asthma at this age is difficult as many preschool children have asthma-like respiratory symptoms. This review discusses progress in defining early wheezing phenotypes and describes genetic factors associated with the age of onset of asthma.

RECENT FINDINGS

Latent class analyses confirmed transient and persistent wheezing phenotypes, and identified a novel intermediate-onset wheezing phenotype that was strongly associated with atopy and asthma at age 8 years. However, no single cross-sectional or longitudinal definition of respiratory symptoms in childhood strongly predicts asthma later in life. Genome-wide association (GWA) studies have identified a locus on chromosome 17q12-21 (encoding ORMDL3 and GSDMB) as a risk factor for predominantly childhood-onset asthma, but not for atopy, and overall not for adult-onset asthma. Other loci found by GWA studies appear to increase asthma risk both in children and adults. Atopy genes do not explain early-onset asthma.

SUMMARY

Although most asthma starts early in life, no valid test is able to identify asthma at that age period. GWA studies have provided more insight into the unique and common genetic origins of adult-onset and childhood-onset asthma. The 17q12-21 locus is predominantly associated with childhood-onset asthma.

PDE4 as a target for cognition enhancement

INTRODUCTION

The second messengers cAMP and cGMP mediate fundamental aspects of brain function relevant to memory, learning, and cognitive functions. Consequently, cyclic nucleotide phosphodiesterases (PDEs), the enzymes that inactivate the cyclic nucleotides, are promising targets for the development of cognition-enhancing drugs.

AREAS COVERED

PDE4 is the largest of the 11 mammalian PDE families. This review covers the properties and functions of the PDE4 family, highlighting procognitive and memory-enhancing effects associated with their inactivation.

EXPERT OPINION

PAN-selective PDE4 inhibitors exert a number of memory- and cognition-enhancing effects and have neuroprotective and neuroregenerative properties in preclinical models. The major hurdle for their clinical application is to target inhibitors to specific PDE4 isoforms relevant to particular cognitive disorders to realize the therapeutic potential while avoiding side effects, in particular emesis and nausea. The PDE4 family comprises four genes, PDE4A-D, each expressed as multiple variants. Progress to date stems from characterization of rodent models with selective ablation of individual PDE4 subtypes, revealing that individual subtypes exert unique and non-redundant functions in the brain. Thus, targeting specific PDE4 subtypes, as well as splicing variants or conformational states, represents a promising strategy to separate the therapeutic benefits from the side effects of PAN-PDE4 inhibitors.

Quercetin acutely relaxes airway smooth muscle and potentiates β-agonist-induced relaxation via dual phosphodiesterase inhibition of PLCβ and PDE4

Asthma is a disease of the airways with symptoms including exaggerated airway narrowing and airway inflammation. Early asthma therapies used methylxanthines to relieve symptoms, in part, by inhibiting cyclic nucleotide phosphodiesterases (PDEs), the enzyme responsible for degrading cAMP. The classification of tissue-specific PDE subtypes and the clinical introduction of PDE-selective inhibitors for chronic obstructive pulmonary disease (i.e., roflumilast) have reopened the possibility of using PDE inhibition in the treatment of asthma. Quercetin is a naturally derived PDE4-selective inhibitor found in fruits, vegetables, and tea. We hypothesized that quercetin relaxes airway smooth muscle via cAMP-mediated pathways and augments β-agonist relaxation. Tracheal rings from male A/J mice were mounted in myographs and contracted with acetylcholine (ACh). Addition of quercetin (100 nM-1 mM) acutely and concentration-dependently relaxed airway rings precontracted with ACh. In separate studies, pretreatment with quercetin (100 μM) prevented force generation upon exposure to ACh. In additional studies, quercetin (50 μM) significantly potentiated isoproterenol-induced relaxations. In in vitro assays, quercetin directly attenuated phospholipase C activity, decreased inositol phosphate synthesis, and decreased intracellular calcium responses to Gq-coupled agonists (histamine or bradykinin). Finally, nebulization of quercetin (100 μM) in an in vivo model of airway responsiveness significantly attenuated methacholine-induced increases in airway resistance. These novel data show that the natural PDE4-selective inhibitor quercetin may provide therapeutic relief of asthma symptoms and decrease reliance on short-acting β-agonists.

Selective fluorogenic chemosensors for distinct classes of nucleases

NUCLEASE SENSOR TRIO: Fluorogenic DNA sensors were developed for distinct classes of nucleases: 3'-exonucleases, 5'-exonucleases, and endonucleases. The highly selective sensors, built from very small modified DNA oligomers containing the unnatural fluorescent base pyrene, and employing thymine as a quencher, were found to function in a variety of complex biological media.

Identification of novel mutations confirms PDE4D as a major gene causing acrodysostosis

Acrodysostosis is characterized by nasal hypoplasia, peripheral dysostosis, variable short stature, and intellectual impairment. Recently, mutations in PRKAR1A were reported in patients with acrodysostosis and hormone resistance. Subsequently, mutations in a phosphodiesterase gene (PDE4D) were identified in seven sporadic cases. We sequenced PDE4D in seven acrodysostosis patients from five families. Missense mutations were identified in all cases. Families showed de novo inheritance except one family with three affected children whose father was subsequently found to have subtle features of acrodysostosis. There were no recurrent mutations. Short stature and endocrine resistance are rare in this series; however, cognitive involvement and obesity were frequent. This last finding is relevant given PDE4D is insulin responsive and potentially involved in lipolysis. PDE4D encodes a cyclic AMP regulator and places PDE4D-related acrodysostosis within the same family of diseases as pseudohypoparathyroidism, pseudopseudohypoparathyroidism, PRKAR1A-related acrodysostosis and brachydactyly-mental retardation syndrome; all characterized by cognitive impairment and short distal extremities.

Novel 5,6-dihydropyrazolo[3,4-E][1,4]diazepin-4 (1H)-one derivatives for the treatment of asthma and chronic obstructive pulmonary disease

This application claims dihydropyrazolodiazepinones as phospho-diesterase 4(PDE4) inhibitors for the treatment of asthma and chronic obstructive pulmonary disease. The compounds are shown to be potent inhibitors of PDE4B2, but no other biological data are provided. Thus, it is not clear whether these compounds provide any advantage over previously described PDE4 inhibitors or whether the issues frequently associated with PDE4 inhibitors have been addressed.

Novel cAMP signalling paradigms: therapeutic implications for airway disease

Since its discovery over 50 years ago, cAMP has been the archetypal second messenger introducing students to the concept of cell signalling at the simplest level. As explored in this review, however, there are many more facets to cAMP signalling than the path from Gs-coupled receptor to adenylyl cyclase (AC) to cAMP to PKA to biological effect. After a brief description of this canonical cAMP signalling pathway, a snapshot is provided of the novel paradigms of cAMP signalling. As in the airway the cAMP pathway relays the major bronchorelaxant signal and as such is the target for frontline therapy for asthma and COPD, particular emphasis is given to airway disease and therapy. Areas discussed include biased agonism, continued signalling following internalization, modulation of cAMP by AC, control of cAMP degradation, cAMP and calcium crosstalk, Epac-mediated signalling and finally the implications of altered genotypes will be considered. LINKED ARTICLES This article is part of a themed section on Novel cAMP Signalling Paradigms. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.166.issue-2.

A new model of Pde4d deficiency: genetic knock-down of PDE4D enzyme in rats produces an antidepressant phenotype without spatial cognitive effects

Phosphodiesterases (PDEs) are a superfamily of intracellular second messenger cyclic nucleotide hydrolyzing enzymes composed of 12 families. The Pde4 family has been implicated in depression and cognition, and PDE4 inhibitors have been evaluated as antidepressants and possible cognitive enhancers. Pde4d(-/-) mice show an antidepressant phenotype and learning enhancement on some tests, but not others as do mice treated with PDE4 inhibitors. Here, we report for the first time the behavioral phenotype of a new Pde4d knock-down (KD) rat model of PDE4D deficiency. Consistent with other data on PDE4D deficiency, Pde4d KD rats showed depression resistance in the Porsolt forced swim test and hyperreactivity of the acoustic startle response with no differential response on prepulse inhibition, suggesting no sensorimotor gating defect. Pde4d KD rats also exhibited a small exploratory activity reduction but no difference following habituation, and no enhanced spatial learning or reference memory in the Morris water maze. A selective improvement in route-based learning in the Cincinnati water maze was seen as well as enhanced contextual and cued fear conditioning and a more rapid rate of cued extinction from their higher freezing level that declined to wild-type (WT) levels only after ∼20 extinction trials. The rat model confirms Pde4d's role in depression but not in spatial learning or memory enhancement and shows for the first time higher fear conditioning and altered extinction compared with controls. The new model provides a tool by which to better understand the role of PDE4D in neuropsychiatric disorders and for the development of alternate treatment approaches.

Discovery of a novel orally active PDE-4 inhibitor effective in an ovalbumin-induced asthma murine model

Phosphodiesterase-4 (PDE-4) is responsible for metabolizing adenosine 3',5'-cyclic monophosphate that reduces the activation of a wide range of inflammatory cells including eosinophils. PDE-4 inhibitors are under development for the treatment of respiratory diseases such as asthma and chronic obstructive pulmonary disease. Herein, we report a novel PDE-4 inhibitor, PDE-423 (3-[1-(3-cyclopropylmethoxy-4-difluoromethoxybenzyl)-1H-pyrazol-3-yl]-benzoic acid), which shows good in vitro and in vivo oral activities. PDE-423 exhibited in vitro IC(50)s of 140 nM and 550 nM in enzyme assay and cell-based assay, respectively. In vivo study using ovalbumin-induced asthmatic mice revealed that PDE-423 reduced methacholine-stimulated airway hyperreactivity in a dose-dependent manner by once daily oral administration (ED(50)=18.3 mg/kg), in parallel with decreased eosinophil peroxidase activity and improved lung histology. In addition, PDE-423 was effective in diminishing lipopolysaccharide-induced neutrophilia in vivo as well as in vitro. Oral administration of PDE-423 (100 mg/kg) had no effect on the duration of xylazine/ketamine-induced anesthesia and did not induce vomiting incidence in ferrets up to the dose of 1000 mg/kg. The present study indicates that a novel PDE-4 inhibitor, PDE-423, has good pharmacological profiles implicating this as a potential candidate for the development of a new anti-asthmatic drug.

Selective PDE inhibitors as novel treatments for respiratory diseases

Phosphodiesterases (PDEs) are a family of enzymes which catalyse the metabolism of the intracellular cyclic nucleotides, c-AMP and c-GMP that are expressed in a variety of cell types and in the context of respiratory diseases, It is now recognised that the use of PDE3, PDE4 and mixed PDE3/4 inhibitors can provide clinical benefit to patients with asthma or chronic obstructive pulmonary disease (COPD). The orally active PDE4 inhibitor Roflumilast-n-oxide has been approved for treatment of severe exacerbations of COPD as add-on therapy to standard drugs. This review discusses the involvement of PDEs in airway diseases and various strategies that are currently being pursued to improve efficacy and reduce side-effects of PDE4 inhibitors, including delivery via the inhaled route, mixed PDE inhibitors and/or antisense biologicals targeted towards PDE4.

Overview of animal models of asthma

Asthma is an inflammatory disease characterized by airways obstruction, airways hyperresponsiveness, excessive mucous secretion and cough. Guinea pig airways display many anatomical, physiological and pharmacological attributes of human airways, making this species ideal for modeling the asthmatic condition. This unit provides an overview of animal models of asthma, including definitions, descriptions of available animal models, and discussion of numerous critical issues to consider before designing a model to study this complex disease.

G Protein βγ-subunit signaling mediates airway hyperresponsiveness and inflammation in allergic asthma

Since the Gβγ subunit of Gi protein has been importantly implicated in regulating immune and inflammatory responses, this study investigated the potential role and mechanism of action of Gβγ signaling in regulating the induction of airway hyperresponsiveness (AHR) in a rabbit model of allergic asthma. Relative to non-sensitized animals, OVA-sensitized rabbits challenged with inhaled OVA exhibited AHR, lung inflammation, elevated BAL levels of IL-13, and increased airway phosphodiesterase-4 (PDE4) activity. These proasthmatic responses were suppressed by pretreatment with an inhaled membrane-permeable anti-Gβγ blocking peptide, similar to the suppressive effect of glucocorticoid pretreatment. Extended mechanistic studies demonstrated that: 1) corresponding proasthmatic changes in contractility exhibited in isolated airway smooth muscle (ASM) sensitized with serum from OVA-sensitized+challenged rabbits or IL-13 were also Gβγ-dependent and mediated by MAPK-upregulated PDE4 activity; and 2) the latter was attributed to Gβγ-induced direct stimulation of the non-receptor tyrosine kinase, c-Src, resulting in downstream activation of ERK1/2 and its consequent transcriptional upregulation of PDE4. Collectively, these data are the first to identify that a mechanism involving Gβγ-induced direct activation of c-Src, leading to ERK1/2-mediated upregulation of PDE4 activity, plays a decisive role in regulating the induction of AHR and inflammation in a rabbit model of allergic airway disease.

β2-Agonists upregulate PDE4 mRNA but not protein or activity in human airway smooth muscle cells from asthmatic and nonasthmatic volunteers

β(2)-Adrenergic receptor (β2AR) agonists induce airway relaxation via cAMP. Phosphodiesterase (PDE)s degrade and regulate cAMP, and in airway smooth muscle (ASM) cells PDE4D degrades cAMP. Long-acting β(2)-agonists are now contraindicated as monotherapy for asthma, and increased PDE4D has been speculated to contribute to this phenomenon. In this study we investigated the expression of PDE4D in asthmatic and nonasthmatic ASM cells and its regulation by formoterol and budesonide. Primary ASM cells from people with or without asthma were stimulated with transforming growth factor (TGF)-β(1), formoterol, and/or budesonide. PDE4D mRNA was assessed by real-time PCR, or PCR to assess splice variant production. PDE4D protein was assessed by Western blotting, and we investigated the effect of formoterol on cAMP production and PDE activity. Interleukin (IL)-6 was assessed using ELISA. PDE4D mRNA was dose dependently upregulated by formoterol, with a single splice variant, PDE4D5, present. Formoterol did not induce PDE4D protein at time points between 3 to 72 h, whereas it did induce and increase IL-6 secretion. We pretreated cells with actinomycin D and a proteasome inhibitor, MG132, and found no evidence of alterations in mRNA, protein expression, or degradation of PDE4D. Finally PDE activity was not altered by formoterol. This study shows, for the first time, that PDE4D5 is predominantly expressed in human ASM cells from people with and without asthma and that formoterol does not upregulate PDE4D protein production. This leads us to speculate that continual therapy with β2AR agonists is unlikely to cause PDE4-mediated tachyphylaxis.

Regulation of murine cardiac function by phosphodiesterases type 3 and 4

Cyclic nucleotide phosphodiesterases (PDEs) encompass a large group of enzymes that regulate intracellular levels of two-second messengers, cAMP and cGMP, by controlling the rates of their degradation. More than 60 isoforms, subdivided into 11 gene families (PDE1-11), exist in mammals with at least six families (PDE1-5 and PDE8) identified in mammalian hearts. The two predominant families implicated in regulating contraction strength of the heart are PDE3 and PDE4. Studies using transgenic models in combination with family-specific PDE inhibitors have demonstrated that PDE3A, PDE4B, and PDE4D isoforms regulate cardiac contractility by modulating cAMP levels in various subcellular compartments. These studies have further uncovered contributions of PDE4B and PDE4D in preventing ventricular arrhythmias.

Phosphodiesterases as targets for modulating T-cell responses

The cAMP-protein kinase A (PKA) signaling pathway is strongly involved in the regulation and modulation of immune responses, and cAMP is the most potent and acute inhibitor of T-cell activation. Thus, cAMP levels in the cell must be tightly regulated. Cyclic AMP-specific phosphodiesterases (PDEs) provide the only mechanism for degrading cAMP in cells, thereby functioning as key regulators of signaling. To obtain a complete immune response with optimal cytokine production and T-cell proliferation, ligation of both the T-cell receptor (TCR) and the CD28 receptor is required. However, engagement of the TCR in primary T cells is followed by rapid cAMP production in lipid rafts and activation of the cAMP- PKA-Csk pathway inhibiting proximal T-cell signaling. In contrast, TCR/CD28 costimulation leads to the recruitment of a PDE4/β-arrestin complex to rafts in a phosphatidylinositol 3-kinase (PI3K)-dependent manner, resulting in the downregulation of cAMP levels. Thus, the activities of both PKA and PDE4 seem to be important for regulation of TCR-induced signaling and T-cell function. The use of selective inhibitors has revealed that PDEs are important drug targets in several diseases with an inflammatory component where immune function is important such as asthma, chronic obstructive pulmonary disease (COPD), cardiovascular diseases, and neurological disorders. PDEs are also interesting drug targets in immunosuppression following transplantation and for modulation of immune responses.

Phosphodiesterase inhibitors in the treatment of inflammatory diseases

Phosphodiesterase 4 (PDE4) belongs to a family of enzymes which catalyzes the breakdown of 3, 5'-adenosine cyclic monophosphate (cAMP) and is ubiquitously expressed in inflammatory cells. There is little evidence that inflammatory diseases are caused by increased expression of this isoenzyme, although human inflammatory cell activity can be suppressed by selective PDE4 inhibitors. Consequently, there is intense interest in the development of selective PDE4 inhibitors for the treatment of a range of inflammatory diseases, including asthma, chronic obstructive pulmonary disease (COPD), inflammatory bowel disease, and psoriasis. Recent clinical trials with roflumilast in COPD have confirmed the therapeutic potential of targeting PDE4 and recently roflumilast has been approved for marketing in Europe and the USA, although side effects such as gastrointestinal disturbances, particularly nausea and emesis as well as headache and weight loss, may limit the use of this drug class, at least when administered by the oral route. However, a number of strategies are currently being pursued in attempts to improve clinical efficacy and reduce side effects of PDE4 inhibitors, including delivery via the inhaled route, development of nonemetic PDE4 inhibitors, mixed PDE inhibitors, and/or antisense biologicals targeted toward PDE4.

Phosphodiesterase type 4D gene polymorphism: association with the response to short-acting bronchodilators in paediatric asthma patients

Short-acting b2-adrenergic receptor agonists are commonly used bronchodilators for symptom relief in asthmatics. The aim of this study was to test whether genetic variants in PDE4D gene, a key regulator of b2-adrenoceptor-induced cAMP turnover in airway smooth muscle cells, affect the response to short-acting b2-agonists. Bronchodilator responsiveness was assessed in 133 asthmatic children by % change in baseline forced expiratory volume in one second (FEV₁) after administration of albuterol. The analyses were performed in patients with airway obstruction (FEV₁/FVC ratio below 90%, n = 93). FEV₁  % change adjusted for baseline FEV₁ values was significantly different between genotypes of rs1544791 G/A polymorphism (P = 0.006) and −1345 C/T (rs1504982) promoter variation (P = 0.03). The association remained significant with inclusion of age, sex, atopy, and controller medication into multivariate model (P = 0.004 and P = 0.02, resp.). Our work identifies new genetic variants implicated in modulation of asthma treatment, one of them (rs1544791) previously associated with asthma phenotype.

Phosphodiesterases in endocrine physiology and disease

The cAMP-protein kinase A pathway plays a central role in the development and physiology of endocrine tissues. cAMP mediates the intracellular effects of numerous peptide hormones. Various cellular and molecular alterations of the cAMP-signaling pathway have been observed in endocrine diseases. Phosphodiesterases (PDEs) are key regulatory enzymes of intracellular cAMP levels. Indeed, PDEs are the only known mechanism for inactivation of cAMP by catalysis to 5'-AMP. It has been suggested that disruption of PDEs could also have a role in the pathogenesis of many endocrine diseases. This review summarizes the most recent advances concerning the role of the PDEs in the physiopathology of endocrine diseases. The potential significance of this knowledge can be easily envisaged by the development of drugs targeting specific PDEs.