Phosphodiesterase 4B is essential for T(H)2-cell function and development of airway hyperresponsiveness in allergic asthma

Targeting pro-inflammatory T cells as a novel therapeutic approach to potentially resolve atherosclerosis in humans

Atherosclerosis (AS), a leading cause of cardio-cerebrovascular disease worldwide, is driven by the accumulation of lipid contents and chronic inflammation. Traditional strategies primarily focus on lipid reduction to control AS progression, leaving residual inflammatory risks for major adverse cardiovascular events (MACEs). While anti-inflammatory therapies targeting innate immunity have reduced MACEs, many patients continue to face significant risks. Another key component in AS progression is adaptive immunity, but its potential role in preventing AS remains unclear. To investigate this, we conducted a retrospective cohort study on tumor patients with AS plaques. We found that anti-programmed cell death protein 1 (PD-1) monoclonal antibody (mAb) significantly reduces AS plaque size. With multi-omics single-cell analyses, we comprehensively characterized AS plaque-specific PD-1+ T cells, which are activated and pro-inflammatory. We demonstrated that anti-PD-1 mAb, when captured by myeloid-expressed Fc gamma receptors (FcγRs), interacts with PD-1 expressed on T cells. This interaction turns the anti-PD-1 mAb into a substitute PD-1 ligand, suppressing T-cell functions in the PD-1 ligands-deficient context of AS plaques. Further, we conducted a prospective cohort study on tumor patients treated with anti-PD-1 mAb with or without Fc-binding capability. Our analysis shows that anti-PD-1 mAb with Fc-binding capability effectively reduces AS plaque size, while anti-PD-1 mAb without Fc-binding capability does not. Our work suggests that T cell-targeting immunotherapy can be an effective strategy to resolve AS in humans.

Topical Application of a PDE4 Inhibitor Ameliorates Atopic Dermatitis through Inhibition of Basophil IL-4 Production

Phosphodiesterase 4 inhibitors have been approved for the treatment of atopic dermatitis. However, the cellular and molecular mechanisms underlying their therapeutic effect remain to be fully elucidated. In this study, we addressed this unsolved issue by analyzing the action of difamilast, a novel phosphodiesterase 4 inhibitor, on an oxazolone-induced skin allergic inflammation commonly used as a mouse model of atopic dermatitis. Topical application of difamilast ameliorated skin inflammation in association with reduced IL-4 expression even when the treatment commenced 4 days after the initiation of oxazolone challenge, showing its therapeutic effect on atopic dermatitis. IL-4-deficient mice displayed milder skin inflammation than did wild-type mice, and the difamilast treatment had little or no further therapeutic effect. This was also the case in mice depleted of basophils, predominant producers of IL-4 in the skin lesion, suggesting that difamilast may act on basophils. Notably, basophils accumulating in the skin lesion showed highly upregulated expression of Pde4b encoding the B subtype of the phosphodiesterase 4 family. Difamilast suppressed IL-4 production from basophils activated in vitro, at least in part, through inhibition of ERK phosphorylation. Taken together, difamilast appeared to ameliorate atopic dermatitis inflammation through the suppression of basophil IL-4 production in the skin lesion.

Dysregulated Cyclic Nucleotide Metabolism in Alcohol-Associated Steatohepatitis: Implications for Novel Targeted Therapies

BACKGROUND

Cyclic nucleotides are second messengers, which play significant roles in numerous biological processes. Previous work has shown that cAMP and cGMP signaling regulates various pathways in liver cells, including Kupffer cells, hepatocytes, hepatic stellate cells, and cellular components of hepatic sinusoids. Importantly, it has been shown that cAMP levels and enzymes involved in cAMP homeostasis are affected by alcohol. Although the role of cyclic nucleotide signaling is strongly implicated in several pathological pathways in liver diseases, studies describing the changes in genes regulating cyclic nucleotide metabolism in ALD are lacking.

METHODS

Male C57B/6 mice were used in an intragastric model of alcohol-associated steatohepatitis (ASH). Liver injury, inflammation, and fibrogenesis were evaluated by measuring plasma levels of injury markers, liver tissue cytokines, and gene expression analyses. Liver transcriptome analysis was performed to examine the effects of alcohol on regulators of cyclic AMP and GMP levels and signaling. cAMP and cGMP levels were measured in mouse livers as well as in livers from healthy human donors and patients with alcohol-associated hepatitis (AH).

RESULTS

Our results show significant changes in several phosphodiesterases (PDEs) with specificity to degrade cAMP (Pde4a, Pde4d, and Pde8a) and cGMP (Pde5a, Pde6d, and Pde9a), as well as dual-specificity PDEs (Pde1a and Pde10a) in ASH mouse livers. Adenylyl cyclases (ACs) 7 and 9, which are responsible for cAMP generation, were also affected by alcohol. Importantly, adenosine receptor 1, which has been implicated in the pathogenesis of liver diseases, was significantly increased by alcohol. Adrenoceptors 1 and 3 (Adrb), which couple with stimulatory G protein to regulate cAMP and cGMP signaling, were significantly decreased. Additionally, beta arrestin 2, which interacts with cAMP-specific PDE4D to desensitize G-protein-coupled receptor to generate cAMP, was significantly increased by alcohol. Notably, we observed that cAMP levels are much higher than cGMP levels in the livers of humans and mice; however, alcohol affected them differently. Specifically, cGMP levels were higher in patients with AH and ASH mice livers compared with controls. As expected, these changes in liver cyclic nucleotide signaling were associated with increased inflammation, steatosis, apoptosis, and fibrogenesis.

CONCLUSIONS

These data strongly implicate dysregulated cAMP and cGMP signaling in the pathogenesis of ASH. Future studies to identify changes in these regulators in a cell-specific manner could lead to the development of novel targeted therapies for ASH.

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.

Novel Anti-Inflammatory Approaches to COPD

Airway inflammation, driven by different types of inflammatory cells and mediators, plays a fundamental role in COPD and its progression. Neutrophils, eosinophils, macrophages, and CD4+ and CD8+ T lymphocytes are key players in this process, although the extent of their participation varies according to the patient's endotype. Anti-inflammatory medications may modify the natural history and progression of COPD. However, since airway inflammation in COPD is relatively resistant to corticosteroid therapy, innovative pharmacological anti-inflammatory approaches are required. The heterogeneity of inflammatory cells and mediators in annethe different COPD endo-phenotypes requires the development of specific pharmacologic agents. Indeed, over the past two decades, several mechanisms that influence the influx and/or activity of inflammatory cells in the airways and lung parenchyma have been identified. Several of these molecules have been tested in vitro models and in vivo in laboratory animals, but only a few have been studied in humans. Although early studies have not been encouraging, useful information emerged suggesting that some of these agents may need to be further tested in specific subgroups of patients, hopefully leading to a more personalized approach to treating COPD.

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.

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.

PDE4B Is a Homeostatic Regulator of Cyclic AMP in Dendritic Cells

Chronic decreases in the second messenger cyclic AMP (cAMP) occur in numerous settings, but how cells compensate for such decreases is unknown. We have used a unique system-murine dendritic cells (DCs) with a DC-selective depletion of the heterotrimeric GTP binding protein Gαs-to address this issue. These mice spontaneously develop Th2-allergic asthma and their DCs have persistently lower cAMP levels. We found that phosphodiesterase 4B (PDE4B) is the primary phosphodiesterase expressed in DCs and that its expression is preferentially decreased in Gαs-depleted DCs. PDE4B expression is dynamic, falling and rising in a protein kinase A-dependent manner with decreased and increased cAMP concentrations, respectively. Treatment of DCs that drive enhanced Th2 immunity with a PDE4B inhibitor ameliorated DC-induced helper T cell response. We conclude that PDE4B is a homeostatic regulator of cellular cAMP concentrations in DCs and may be a target for treating Th2-allergic asthma and other settings with low cellular cAMP concentrations.

Transcriptional changes in dendritic cells underlying allergen specific induced tolerance in a mouse model

To investigate food allergy-tolerance mechanisms induced through allergen-specific immunotherapy we used RNA-Sequencing to measure gene expression in lymph-node-derived dendritic cells from Pru p 3-anaphylactic mice after immunotherapy with glycodendropeptides at 2 nM and 5 nM, leading to permanent tolerance and short-term desensitization, respectively. Gene expression was also measured in mice receiving no immunotherapy (anaphylaxis); and in which anaphylaxis could never occur (antigen-only). Compared to anaphylaxis, the antigen-only group showed the greatest number of expression-changes (411), followed by tolerant (186) and desensitized (119). Only 29 genes changed in all groups, including Il12b, Cebpb and Ifngr1. The desensitized group showed enrichment for genes related to chronic inflammatory response, secretory granule, and regulation of interleukin-12 production; the tolerant group showed genes related to cytokine receptor activity and glucocorticoid receptor binding, suggesting distinct pathways for similar outcomes. We identified genes and processes potentially involved in the restoration of long-term tolerance via allergen-specific immunotherapy, representing potential prognostic biomarkers.

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.

Ligustrazine Inhibits Lung Phosphodiesterase Activity in a Rat Model of Allergic Asthma

Objectives

This study sought to examine whether ligustrazine was capable of inhibiting phosphodiesterase (PDE) activity and improving lung function in a rat model of asthma.

Methods

Rats were initially sensitized using ovalbumin (OVA) and then were challenged daily with aerosolized OVA beginning 14 days later (30 min/day) to generate a rat model of asthma. Changes in airway function following methacholine (MCh) injection were evaluated by monitoring lung resistance (R_L) and dynamic lung compliance (C_dyn) values using an AniRes2005 analytic system. In addition, serum IgE was measured via ELISA, while PDE expression was evaluated via qPCR and western blotting. Key Findings. Ligustrazine significantly impaired allergen-induced lung hyperresponsivity and inflammation in this asthma model system. Ligustrazine treatment was also associated with reduced expression of PDEs including PDE4 in the lungs of these rats.

Conclusions

Ligustrazine suppresses airway inflammation and bronchial hyperresponsivity in this rat model system, and these changes are associated with decreased PDE expression at the protein and mRNA levels.

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.

Assessment of PDE4 Inhibitor-Induced Hypothermia as a Correlate of Nausea in Mice

Simple Summary

Type 4 cAMP-phosphodiesterases (PDE4s) comprise a family of four isoenzymes, PDE4A to D, that hydrolyze and inactivate the second messenger cAMP. Non/PAN-selective PDE4 inhibitors, which inhibit all four PDE4 subtypes simultaneously, produce many promising therapeutic benefits, such as anti-inflammatory or cognition- and memory-enhancing effects. However, unwanted side effects, principally, nausea, diarrhea, and emesis, have long hampered their clinical and commercial success. Targeting individual PDE4 subtypes has been proposed for developing drugs with an improved safety profile, but which PDE4 subtype(s) is/are actually responsible for nausea and emesis remains ill-defined. Based on the observation that nausea is often accompanied by hypothermia in humans and other mammals, we used the measurement of core body temperatures of mice as a potential correlate of nausea induced by PDE4 inhibitors in humans. We find that selective inactivation of any of the four PDE4 subtypes did not change the body temperature of mice, suggesting that PAN-PDE4 inhibitor-induced hypothermia (and hence nausea in humans) requires the simultaneous inhibition of multiple PDE4 subtypes. This finding contrasts with prior reports that proposed PDE4D as the subtype mediating these side effects of PDE4 inhibitors and suggests that subtype-selective inhibitors that target any individual PDE4 subtype, including PDE4D, may not cause nausea.

Abstract

Treatment with PAN-PDE4 inhibitors has been shown to produce hypothermia in multiple species. Given the growing body of evidence that links nausea and emesis to disturbances in thermoregulation in mammals, we explored PDE4 inhibitor-induced hypothermia as a novel correlate of nausea in mice. Using knockout mice for each of the four PDE4 subtypes, we show that selective inactivation of individual PDE4 subtypes per se does not produce hypothermia, which must instead require the concurrent inactivation of multiple (at least two) PDE4 subtypes. These findings contrast with the role of PDE4s in shortening the duration of α₂-adrenoceptor-dependent anesthesia, a behavioral surrogate previously used to assess the emetic potential of PDE4 inhibitors, which is exclusively affected by inactivation of PDE4D. These different outcomes are rooted in the distinct molecular mechanisms that drive these two paradigms; acting as a physiologic α₂-adrenoceptor antagonist produces the effect of PDE4/PDE4D inactivation on the duration of α₂-adrenoceptor-dependent anesthesia, but does not mediate the effect of PDE4 inhibitors on body temperature in mice. Taken together, our findings suggest that selective inhibition of any individual PDE4 subtype, including inhibition of PDE4D, may be free of nausea and emesis.

Synthesis and in vitro evaluation of anti-inflammatory, antioxidant, and anti-fibrotic effects of new 8-aminopurine-2,6-dione-based phosphodiesterase inhibitors as promising anti-asthmatic agents

Phosphodiesterase (PDE) inhibitors are currently an extensively studied group of compounds that can bring many benefits in the treatment of various inflammatory and fibrotic diseases, including asthma. Herein, we describe a series of novel N'-phenyl- or N'-benzylbutanamide and N'-arylidenebutanehydrazide derivatives of 8-aminopurine-2,6-dione (27-43) and characterized them as prominent pan-PDE inhibitors. Most of the compounds exhibited antioxidant and anti-inflammatory activity in lipopolysaccharide (LPS)-induced murine macrophages RAW264.7. The most active compounds (32-35 and 38) were evaluated in human bronchial epithelial cells (HBECs) derived from asthmatics. To better map the bronchial microenvironment in asthma, HBECs after exposure to selected 8-aminopurine-2,6-dione derivatives were incubated in the presence of two proinflammatory and/or profibrotic factors: transforming growth factor type β (TGF-β) and interleukin 13 (IL-13). Compounds 32-35 and 38 significantly reduced both IL-13- and TGF-β-induced expression of proinflammatory and profibrotic mediators, respectively. Detailed analysis of their inhibition preferences for selected PDEs showed high affinity for isoenzymes important in the pathogenesis of asthma, including PDE1, PDE3, PDE4, PDE7, and PDE8. The presented data confirm that structural modifications within the 7 and 8 positions of the purine-2,6-dione core result in obtaining preferable pan-PDE inhibitors which in turn exert an excellent anti-inflammatory and anti-fibrotic effect in the bronchial epithelial cells derived from asthmatic patients. This dual-acting pan-PDE inhibitors constitute interesting and promising lead structures for further anti-asthmatic agent discovery.

Ablation of PDE4B protects from Pseudomonas aeruginosa-induced acute lung injury in mice by ameliorating the cytostorm and associated hypothermia

Pseudomonas aeruginosa is a frequent cause of hospital-acquired lung infections characterized by hyperinflammation, antibiotic resistance, and high morbidity/mortality. Here, we show that the genetic ablation of one cAMP-phosphodiesterase 4 subtype, PDE4B, is sufficient to protect mice from acute lung injury induced by P aeruginosa infection as it reduces pulmonary and systemic levels of pro-inflammatory cytokines, as well as pulmonary vascular leakage and mortality. Surprisingly, despite dampening immune responses, bacterial clearance in the lungs of PDE4B-KO mice is significantly improved compared to WT controls. In wildtypes, P aeruginosa-infection produces high systemic levels of several cytokines, including TNF-α, IL-1β, and IL-6, that act as cryogens and render the animals hypothermic. This, in turn, diminishes their ability to clear the bacteria. Ablation of PDE4B curbs both the initial production of acute response cytokines, including TNF-α and IL-1β, as well as their downstream signaling, specifically the induction of the secondary-response cytokine IL-6. This synergistic action protects PDE4B-KO mice from the deleterious effects of the P aeruginosa-induced cytostorm, while concurrently improving bacterial clearance, rather than being immunosuppressive. These benefits of PDE4B ablation are in contrast to the effects resulting from treatment with PAN-PDE4 inhibitors, which have been shown to increase bacterial burden and dissemination. Thus, PDE4B represents a promising therapeutic target in settings of P aeruginosa lung infections.

Novel pharmacological therapies for the treatment of bronchial asthma

Asthma has long been recognised as a chronic inflammatory disease of the airways, often in response to inhaled allergens prompting inappropriate activation of the immune response. involving a range of cells including mast cells, Th2 lymphocytes and eosinophils and a wide range of inflammatory mediators. First-line therapy for treatment of persistent asthma involves the use of inhaled corticosteroids (ICS) in combination with inhaled β2-agonists enabling both the control of the underlying airways inflammation and a reduction of airway hyperresponsiveness. However, many patients remain symptomatic despite high-dose therapy. There is therefore a continued unmet clinical need to develop specifically new anti-inflammatory therapies for patients with asthma, either as an add-on therapy to ICS or as replacement monotherapies. The success of fixed dose combination inhalers containing both a bronchodilator and an anti-inflammatory drug has also led to the development of "bifunctional" drugs which are molecules specifically designed to have two distinct pharmacological actions based on distinct pharmacophores. In this review we will discuss these different pharmacological approaches under development for the treatment of bronchial asthma and the available pre-clinical and clinical data.

Fermented Red Ginseng Alleviates Ovalbumin-Induced Inflammation in Mice by Suppressing Interleukin-4 and Immunoglobulin E Expression

Ginseng (the root of Panax ginseng Meyer) has been reported to have many biologic therapeutic effects, including anti-inflammatory properties, and ginsenosides are considered as one of the factors responsible for these therapeutic effects. To improve their therapeutic action, probiotic bacteria are used to ferment and chemically transform ginsenosides in red ginseng (RG). In this study, we aimed to investigate the beneficial effects of RG fermented by probiotic bacteria (FRG) against ovalbumin (OVA)-induced allergic rhinitis in a mouse model. We induced the mouse model via OVA inhalation; experimental results revealed increased immunoglobulin E (IgE) and interleukin (IL)-4 levels, leading to Th2-type cytokine response. The mice with induced allergy were then orally administered RG and FRG over 2 weeks, as a result of which, IL-4 and IgE levels in bronchoalveolar lavage fluid, nasal fluid, and serum were found to be ameliorated more effectively by FRG than by RG, suggesting that FRG has better immune regulatory effects than RG. FRG also downregulated immune cell levels, such as those of eosinophils and basophils, and significantly decreased the thickness of OVA-induced respiratory epithelium compared to RG. Collectively, the results showed that FRG treatment alleviates inflammation, thereby extending a protective effect to mice with OVA-induced inflammatory allergic rhinitis.

The cAMP-phosphodiesterase 4 (PDE4) controls β-adrenoceptor- and CFTR-dependent saliva secretion in mice

Saliva, while often taken for granted, is indispensable for oral health and overall well-being, as inferred from the significant impairments suffered by patients with salivary gland dysfunction. Here, we show that treatment with several structurally distinct PAN-PDE4 inhibitors, but not a PDE3 inhibitor, induces saliva secretion in mice, indicating it is a class-effect of PDE4 inhibitors. In anesthetized mice, while neuronal regulations are suppressed, PDE4 inhibition potentiates a β-adrenoceptor-induced salivation, that is ablated by the β-blocker Propranolol and is absent from homozygous ΔF508-CFTR mice lacking functional CFTR. These data suggest that PDE4 acts within salivary glands to gate saliva secretion that is contingent upon the cAMP/PKA-dependent activation of CFTR. Indeed, PDE4 contributes the majority of total cAMP-hydrolytic capacity in submandibular-, sublingual-, and parotid glands, the three major salivary glands of the mouse. In awake mice, PDE4 inhibitor-induced salivation is reduced by CFTR deficiency or β-blockers, but also by the muscarinic blocker Atropine, suggesting an additional, central/neuronal mechanism of PDE4 inhibitor action. The PDE4 family comprises four subtypes, PDE4A-D. Ablation of PDE4D, but not PDE4A-C, produced a minor effect on saliva secretion, implying that while PDE4D may play a predominant role, PDE4 inhibitor-induced salivation results from the concurrent inactivation of multiple (at least two) PDE4 subtypes. Taken together, our data reveal a critical role for PDE4/PDE4D in controlling CFTR function in an in vivo model and in inducing salivation, hinting at a therapeutic potential of PDE4 inhibition for cystic fibrosis and conditions associated with xerostomia.

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

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

Coupling sparse Cox models with clustering of longitudinal transcriptomics data for trauma prognosis

Background

Longitudinal gene expression analysis and survival modeling have been proved to add valuable biological and clinical knowledge. This study proposes a novel framework to discover gene signatures and patterns in a high-dimensional time series transcriptomics data and to assess their association with hospital length of stay.

Methods

We investigated a longitudinal and high-dimensional gene expression dataset from 168 blunt-force trauma patients followed during the first 28 days after injury. To model the length of stay, an initial dimensionality reduction step was performed by applying Cox regression with elastic net regularization using gene expression data from the first hospitalization days. Also, a novel methodology to impute missing values to the genes selected previously was proposed. We then applied multivariate time series (MTS) clustering to analyse gene expression over time and to stratify patients with similar trajectories. The validation of the patients’ partitions obtained by MTS clustering was performed using Kaplan-Meier curves and log-rank tests.

Results

We were able to unravel 22 genes strongly associated with hospital’s discharge. Their expression values in the first days after trauma showed to be good predictors of the length of stay. The proposed mixed imputation method allowed to achieve a complete dataset of short time series with a minimum loss of information for the 28 days of follow-up. MTS clustering enabled to group patients with similar genes trajectories and, notably, with similar discharge days from the hospital. Patients within each cluster have comparable genes’ trajectories and may have an analogous response to injury.

Conclusion

The proposed framework was able to tackle the joint analysis of time-to-event information with longitudinal multivariate high-dimensional data. The application to length of stay and transcriptomics data revealed a strong relationship between gene expression trajectory and patients’ recovery, which may improve trauma patient’s management by healthcare systems. The proposed methodology can be easily adapted to other medical data, towards more effective clinical decision support systems for health applications.

Insight into Inhibitory Mechanism of PDE4D by Dietary Polyphenols Using Molecular Dynamics Simulations and Free Energy Calculations

Phosphodiesterase 4 (PDE4), mainly present in immune, epithelial, and brain cells, represents a family of key enzymes for the degradation of cyclic adenosine monophosphate (cAMP), which modulates inflammatory response. In recent years, the inhibition of PDE4 has been proven to be an effective therapeutic strategy for the treatment of neurological disorders. PDE4D constitutes a high-interest therapeutic target primarily for the treatment of Alzheimer's disease, as it is highly involved in neuroinflammation, learning ability, and memory dysfunctions. In the present study, a thorough computational investigation consisting of molecular docking, molecular dynamics (MD) simulations, and binding free energy calculations based on the linear response approximation (LRA) method was performed to study dietary polyphenols as potential PDE4D inhibitors. The obtained results revealed that curcumin, 6-gingerol, capsaicin, and resveratrol represent potential PDE4D inhibitors; however, the predicted binding free energies of 6-gingerol, capsaicin, and resveratrol were less negative than in the case of curcumin, which exhibited the highest inhibitory potency in comparison with a positive control rolipram. Our results also revealed that the electrostatic component through hydrogen bonding represents the main driving force for the binding and inhibitory activity of curcumin, 6-gingerol, and resveratrol, while the van der Waals component through shape complementarity plays the most important role in capsaicin's inhibitory activity. All investigated compounds form hydrophobic interactions with residues Gln376 and Asn602 as well as hydrogen bonds with nearby residues Asp438, Met439, and Ser440. The binding mode of the studied natural compounds is consequently very similar; however, it significantly differs from the binding of known PDE4 inhibitors. The uncovered molecular inhibitory mechanisms of four investigated natural polyphenols, curcumin, 6-gingerol, capsaicin, and resveratrol, form the basis for the design of novel PDE4D inhibitors for the treatment of Alzheimer's disease with a potentially wider therapeutic window and fewer adverse side effects.

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.

The regulatory role of SFRP5/WNT5A axis in allergic rhinitis through inhibiting JNK pathway activation and lowering mucin generation in human nasal epithelial cells

Allergic rhinitis (AR) is tightly associated with type 2 inflammation. SFRP5 combined with WNT5A mainly inhibits chronic inflammatory response, atherosclerosis, and other metabolic disorders. However, the effect of SFRP5/WNT5A axis on recombinant human interleukin-13 (rhIL-13)-induced inflammation has not been studied. In this study, we aimed to investigate whether secreted frizzled-related protein 5 (SFRP5) could modulate the production of cytokines relevant to eosinophil infiltration and mucin secretion through blocking the activation of Wnt family 5A (WNT5A) signaling pathway. A mouse model of AR demonstrated low expression of SFRP5 and high expression of WNT5A, and indicated that the number of eosinophil and goblet cells was increased, concomitant with elevated IL-13, colony stimulating factor 2 (CSF2), chemokine ligand 11 (CCL11), Mucin 4, and Mucin 5AC levels. Furthermore, lentivirus-SFRP5 overexpression up-regulated the expression of SFRP5 but down-regulated WNT5A level, and inhibited the activation of JNK pathway via decreasing p-JNK1/2 (Thr183/Tyr185) and p-c-Jun (Ser73) protein expressions in rhIL-13-treated human nasal epithelial cells (HNEpCs). Noticeably, SFRP5 overexpression markedly reduced rhIL-13-induced inflammatory protein and mucin generation through lowered CSF2, CCL11, Mucin 4, as well as Mucin 5AC levels. Taken together, these findings confirmed the regulatory role of SFRP5/WNT5A axis in rhIL-13-mediated inflammatory response in HNEpCs.

Current insights on clinical efficacy of roflumilast for treatment of COPD, asthma and ACOS

Phosphodiesterase-4 inhibitors (PDE4) are of great interest for the treatment of airway inflammatory diseases due to its broad anti-inflammatory effects. Roflumilast is a selective PDE4 inhibitor that inhibits pulmonary and systemic inflammation and rallies symptoms in airway diseases. Asthma and COPD are common chronic airway inflammatory diseases having incompletely illustrious pathophysiology and clinical manifestations. Recently, the condition called Asthma- COPD Overlap (ACO) has been evolved having the overlapping symptoms of both diseases. The newly discovered PDE4 inhibitor, roflumilast has exposed its potential in the treatment of Asthma, COPD and ACOS. Its mechanism of action in airway inflammatory diseases are said to be exerts by elevating intracellular cAMP and shows its anti-inflammatory action. Roflumilast, a promising therapeutic approach in inflammatory airway diseases, has many significant outcomes. In this review, we have provided various promising clinical evidences of roflumilast in COPD and asthma. However, there is no published clinical evidence to date for the role of roflumilast in ACOS. Nevertheless, there are therapeutic mechanisms that provide a reference for clinical application for ACOS.

NCS 613, a Potent PDE4 Inhibitor, Displays Anti-Inflammatory and Anti-Proliferative Properties on A549 Lung Epithelial Cells and Human Lung Adenocarcinoma Explants

Chronic inflammation is a deleterious process occurring in several pulmonary diseases; it is a driving force promoting tumorigenesis. By regulating local cyclic nucleotide concentration, cyclic nucleotide phosphodiesterases (PDE) govern important biological processes, including inflammation and proliferation. The aim of this study was to investigate the anti-inflammatory and anti-proliferative effects of NCS 613, a specific PDE4 inhibitor, on TNFα-treated human lung adenocarcinoma cell line (A549) and on human lung adenocarcinoma explants. PDE4 isoforms and inflammatory pathways mediated by p38 MAPK, ERK1/2, and IκBα were analyzed by Western blot and immunostainings. Proliferation were performed using [³H]-thymidine incorporation under different experimental conditions. TNFα-stimulation increased p38 MAPK phosphorylation and NF-κB translocation into the nucleus, which was abolished by NCS 613 treatment. Concomitantly, NCS 613 restores IκBα detection level in human adenocarcinoma. An IC₅₀ value of 8.5 μM was determined for NCS 613 on anti-proliferative properties while ERK1/2 signaling was down-regulated in A549 cells and lung adenocarcinoma explants. These findings shed light on PDE4 signaling as a key regulator of chronic inflammation and cancer epithelial cell proliferation. It suggests that PDE4 inhibition by NCS 613 represent potential and interesting strategy for therapeutic intervention in tackling chronic inflammation and cell proliferation.

Phosphodiesterase-4 enzyme as a therapeutic target in neurological disorders

Phosphodiesterases (PDE) are a diverse family of enzymes (11 isoforms so far identified) responsible for the degradation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) which are involved in several cellular and biochemical functions. Phosphodiesterase 4 (PDE4) is the major isoform within this group and is highly expressed in the mammalian brain. An inverse association between PDE4 and cAMP levels is the key mechanism in various pathophysiological conditions like airway inflammatory diseases-chronic obstruction pulmonary disease (COPD), asthma, psoriasis, rheumatoid arthritis, and neurological disorders etc. In 2011, roflumilast, a PDE4 inhibitor (PDE4I) was approved for the treatment of COPD. Subsequently, other PDE4 inhibitors (PDE4Is) like apremilast and crisaborole were approved by the Food and Drug Administration (FDA) for psoriasis, atopic dermatitis etc. Due to the adverse effects like unbearable nausea and vomiting, dose intolerance and diarrhoea, PDE4 inhibitors have very less clinical compliance. Efforts are being made to develop allosteric modulation with high specificity to PDE4 isoforms having better efficacy and lesser adverse effects. Interestingly, repositioning PDE4Is towards neurological disorders including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), multiple sclerosis (MS) and sleep disorders, is gaining attention. This review is an attempt to summarize the data on the effects of PDE4 overexpression in neurological disorders and the use of PDE4Is and newer allosteric modulators as therapeutic options. We have also compiled a list of on-going clinical trials on PDE4 inhibitors in neurological disorders.

Advances in the Development of Phosphodiesterase-4 Inhibitors

Cyclic nucleotide phosphodiesterase 4 (PDE4) specifically hydrolyzes cyclic adenosine monophosphate (cAMP) and plays vital roles in biological processes such as cancer development. To date, PDE4 inhibitors have been widely studied as therapeutics for the treatment of various diseases such as chronic obstructive pulmonary disease, and many of them have progressed to clinical trials or have been approved as drugs. Herein, we review the advances in the development of PDE4 inhibitors in the past decade and will focus on their pharmacophores, PDE4 subfamily selectivity, and therapeutic potential. Hopefully, this analysis will lead to a strategy for development of novel therapeutics targeting PDE4.

Glucagon reduces airway hyperreactivity, inflammation, and remodeling induced by ovalbumin

Glucagon has been shown to be beneficial as a treatment for bronchospasm in asthmatics. Here, we investigate if glucagon would prevent airway hyperreactivity (AHR), lung inflammation, and remodeling in a murine model of asthma. Glucagon (10 and 100 µg/Kg, i.n.) significantly prevented AHR and eosinophilia in BAL and peribronchiolar region induced by ovalbumin (OVA) challenge, while only the dose of 100 µg/Kg of glucagon inhibited subepithelial fibrosis and T lymphocytes accumulation in BAL and lung. The inhibitory action of glucagon occurred in parallel with reduction of OVA-induced generation of IL-4, IL-5, IL-13, TNF-α, eotaxin-1/CCL11, and eotaxin-2/CCL24 but not MDC/CCL22 and TARC/CCL17. The inhibitory effect of glucagon (100 µg/Kg, i.n.) on OVA-induced AHR and collagen deposition was reversed by pre-treatment with indomethacin (10 mg/Kg, i.p.). Glucagon increased intracellular cAMP levels and inhibits anti-CD3 plus anti-CD28-induced proliferation and production of IL-2, IL-4, IL-10, and TNF- α from TCD4⁺ cells in vitro. These findings suggest that glucagon reduces crucial features of asthma, including AHR, lung inflammation, and remodeling, in a mechanism probably associated with inhibition of eosinophils accumulation and TCD4⁺ cell proliferation and function. Glucagon should be further investigated as an option for asthma therapy.

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.

Anti‑inflammatory effect of ciclamilast in an allergic model involving the expression of PDE4B

The present study aimed to investigate the potent inhibitory effects and possible biochemical basis of the novel phosphodiesterase 4 (PDE4) inhibitor ciclamilast, which is a derivative of piclamilast (RP 73401), on PDE4 and allergic inflammation. Ciclamilast was orally administered to allergic rats, their lungs and bronchoalveolar lavage fluid (BALF) were harvested, and their levels of inflammation and goblet cell hyperplasia, particularly cAMP‑PDE activity, and expression and distribution of PDE4 subtypes were determined. The results suggested that oral administration of ciclamilast significantly reduced the total leukocyte number and eosinophil number in BALF and suppressed lung histology changes, including the infiltration of inflammatory cells into the perivascular and peribronchial spaces, structural changes and goblet cell hyperplasia. For eosinophil infiltration, ciclamilast exhibited improved selectivity compared with piclamilast. Furthermore, ciclamilast significantly inhibited the upregulated activity of cAMP‑PDE and showed improved selective inhibition of the protein expression of PDE4B than piclamilast in a dose‑dependent manner. The mRNA expression of PDE4D was significantly increased in allergic rats, but PDE4B was not. PDE4B was mainly distributed in the cytoplasm, whereas PDE4D was mainly distributed in the cell membrane. The improved anti‑inflammatory activity of ciclamilast compared with piclamilast may be due to its higher level of inhibition of the activity, mRNA and protein expression of PDE4, particularly its effect on PDE4B.

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.

Phosphodiesterase 4B plays a role in benzophenone-3-induced phototoxicity in normal human keratinocytes

Benzophenone-3 (BP-3), which is extensively used in organic sunscreen, has phototoxic potential in human skin. Phosphodiesterase 4B (PDE4B) has a well-established role in inflammatory responses in immune cells. Currently, it is unknown if PDE4B is associated with BP-3-induced phototoxicity in normal human keratinocytes (NHKs). We found that BP-3 significantly increased PDE4B expression in ultraviolet B (UVB)-irradiated NHKs. Notably, BP-8, a sunscreen agent that shares the 2-hydroxy-4-methoxyphenyl methanone moiety with BP-3, also upregulated PDE4B expression in NHKs. Upon UVB irradiation, BP-3 upregulated the expression of pro-inflammatory factors, such as prostaglandin endoperoxide synthase 2, tumor necrosis factor α, interleukin 8, and S100A7, and downregulated the level of cornified envelope associated proteins, which are important in the development of the epidermal permeability barrier. The additive effects of UVB-activated BP-3 on the expression of both pro-inflammatory mediators and cornified envelope associated proteins were antagonized by treatment with the PDE4 inhibitor rolipram. The BP-3 and UVB co-stimulation-induced PDE4B upregulation and its association with the upregulation of pro-inflammatory mediators and the downregulation of epidermal differentiation markers were confirmed in a reconstituted three dimensional human epidermis model. Therefore, PDE4B has a role in the mechanism of BP-3-induced phototoxicity.

Phosphodiesterase 4B negatively regulates endotoxin-activated interleukin-1 receptor antagonist responses in macrophages

Activation of TLR4 by lipopolysaccharide (LPS) induces both pro-inflammatory and anti-inflammatory cytokine production in macrophages. Type 4 phosphodiesterases (PDE4) are key cAMP-hydrolyzing enzymes, and PDE4 inhibitors are considered as immunosuppressors to various inflammatory responses. We demonstrate here that PDE4 inhibitors enhance the anti-inflammatory cytokine interleukin-1 receptor antagonist (IL-1Ra) secretion in LPS-activated mouse peritoneal macrophages, and this response was regulated at the transcriptional level rather than an increased IL-1Ra mRNA stability. Studies with PDE4-deficient macrophages revealed that the IL-1Ra upregulation elicited by LPS alone is PKA-independent, whereas the rolipram-enhanced response was mediated by inhibition of only PDE4B, one of the three PDE4 isoforms expressed in macrophages, and it requires PKA but not Epac activity. However, both pathways activate CREB to induce IL-1Ra expression. PDE4B ablation also promoted STAT3 phosphorylation (Tyr⁷⁰⁵) to LPS stimulation, but this STAT3 activation is not entirely responsible for the IL-1Ra upregulation in PDE4B-deficient macrophages. In a model of LPS-induced sepsis, only PDE4B-deficient mice displayed an increased circulating IL-1Ra, suggesting a protective role of PDE4B inactivation in vivo. These findings demonstrate that PDE4B negatively modulates anti-inflammatory cytokine expression in innate immune cells, and selectively targeting PDE4B should retain the therapeutic benefits of nonselective PDE4 inhibitors.

Pharmacophore Based Virtual Screening Approach to Identify Selective PDE4B Inhibitors

Phosphodiesterase 4 (PDE4) has been established as a promising target in asthma and chronic obstructive pulmonary disease. PDE4B subtype selective inhibitors are known to reduce the dose limiting adverse effect associated with non-selective PDE4B inhibitors. This makes the development of PDE4B subtype selective inhibitors a desirable research goal. To achieve this goal, ligand based pharmacophore modeling approach is employed. Separate pharmacophore hypotheses for PDE4B and PDE4D inhibitors were generated using HypoGen algorithm and 106 PDE4 inhibitors from literature having thiopyrano [3,2-d] Pyrimidines, 2-arylpyrimidines, and triazines skeleton. Suitable training and test sets were created using the molecules as per the guidelines available for HypoGen program. Training set was used for hypothesis development while test set was used for validation purpose. Fisher validation was also used to test the significance of the developed hypothesis. The validated pharmacophore hypotheses for PDE4B and PDE4D inhibitors were used in sequential virtual screening of zinc database of drug like molecules to identify selective PDE4B inhibitors. The hits were screened for their estimated activity and fit value. The top hit was subjected to docking into the active sites of PDE4B and PDE4D to confirm its selectivity for PDE4B. The hits are proposed to be evaluated further using in-vitro assays.

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.

Asthma Pharmacogenomics: 2015 Update

There is evidence that genetic factors are implicated in the observed differences in therapeutic responses to the common classes of asthma therapy such as β2-agonists, corticosteroids, and leukotriene modifiers. Pharmacogenomics explores the roles of genetic variation in drug response and continues to be a field of great interest in asthma therapy. Prior studies have focused on candidate genes and recently emphasized genome-wide association analyses. Newer integrative omics and system-level approaches have recently revealed novel understanding of drug response pathways. However, the current known genetic loci only account for a fraction of variability in drug response and ongoing research is needed. While the field of asthma pharmacogenomics is not yet fully translatable to clinical practice, ongoing research should hopefully achieve this goal in the near future buttressed by the recent precision medicine efforts in the USA and worldwide.

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.

Cross-talk between PKA-Cβ and p65 mediates synergistic induction of PDE4B by roflumilast and NTHi

Phosphodiesterase 4B (PDE4B) plays a key role in regulating inflammation. Roflumilast, a phosphodiesterase (PDE)4-selective inhibitor, has recently been approved for treating severe chronic obstructive pulmonary disease (COPD) patients with exacerbation. However, there is also clinical evidence suggesting the development of tachyphylaxis or tolerance on repeated dosing of roflumilast and the possible contribution of PDE4B up-regulation, which could be counterproductive for suppressing inflammation. Thus, understanding how PDE4B is up-regulated in the context of the complex pathogenesis and medications of COPD may help improve the efficacy and possibly ameliorate the tolerance of roflumilast. Here we show that roflumilast synergizes with nontypeable Haemophilus influenzae (NTHi), a major bacterial cause of COPD exacerbation, to up-regulate PDE4B2 expression in human airway epithelial cells in vitro and in vivo. Up-regulated PDE4B2 contributes to the induction of certain important chemokines in both enzymatic activity-dependent and activity-independent manners. We also found that protein kinase A catalytic subunit β (PKA-Cβ) and nuclear factor-κB (NF-κB) p65 subunit were required for the synergistic induction of PDE4B2. PKA-Cβ phosphorylates p65 in a cAMP-dependent manner. Moreover, Ser276 of p65 is critical for mediating the PKA-Cβ-induced p65 phosphorylation and the synergistic induction of PDE4B2. Collectively, our data unveil a previously unidentified mechanism underlying synergistic up-regulation of PDE4B2 via a cross-talk between PKA-Cβ and p65 and may help develop new therapeutic strategies to improve the efficacy of PDE4 inhibitor.

Regulatory T-cells and cAMP suppress effector T-cells independently of PKA-CREM/ICER: a potential role for Epac

cAMP signalling is both a major pathway as well as a key therapeutic target for inducing immune tolerance and is involved in Treg cell (regulatory T-cell) function. To achieve potent immunoregulation, cAMP can act through several downstream effectors. One proposed mechanism is that cAMP-mediated suppression, including immunosuppression by Treg cells, results from activation of PKA (protein kinase A) leading to the induction of the transcription factor ICER (inducible cAMP early repressor). In the present study, we examined CD4(+)CD25(-) Teff cell (effector T-cell) and CD4(+)CD25(+) Treg cell immune responses in Crem (cAMP-response-element modulator) gene-deficient mice which lack ICER (Crem(-/-)/ICER-deficient mice). ICER deficiency did not significantly alter the frequency or number of Treg cells and Teff cells. Treg cells or a pharmacological increase in cAMP suppressed Teff cells from Crem(+/+) and Crem(-/-)/ICER-deficient mice to an equivalent degree, demonstrating that ICER is dispensable in these functions. Additionally, activating the cAMP effector Epac (exchange protein directly activated by cAMP) suppressed Teff cells. Treg cells expressed low levels of all cyclic nucleotide Pde (phosphodiesterase) genes tested, but high levels of Epac. These data identify ICER as a redundant mediator of Treg cells and cAMP action on Teff cells and suggest that Epac may function as an alternative effector to promote cAMP-dependent Teff cell suppression.

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.

Antipruritic mechanisms of topical E6005, a phosphodiesterase 4 inhibitor: inhibition of responses to proteinase-activated receptor 2 stimulation mediated by increase in intracellular cyclic AMP

BACKGROUND

Phosphodiesterase 4 (PDE4), which catalyses the conversion of cyclic adenosine 3',5'-monophosphate (cAMP) to 5'-AMP, plays a critical role in the pathogenesis of inflammatory disorders. Pruritus is the main symptom of dermatitides, such as atopic dermatitis, and is very difficult to control. Recent studies have shown that the activation of proteinase-activated receptor 2 (PAR2) is involved in pruritus in dermatoses in humans and rodents.

OBJECTIVE

To investigate the inhibitory effect of E6005, a topically effective PDE4 inhibitor, on PAR2-associated itching in mice.

METHODS

Mice were given an intradermal injection of SLIGRL-NH2 (100 nmol/site), a PAR2 agonist peptide, into the rostral part of the back. E6005 and 8-bromo-cAMP were applied topically and injected intradermally, respectively, to the same site. Scratching bouts were observed as an itch-related behavior, and firing activity of the cutaneous nerve was electrophysiologically recorded. Keratinocytes were isolated from the skin of neonatal mice and cultured for in vitro experiments. The concentrations of cAMP and leukotriene B4 (LTB4) were measured by enzyme immunoassay. The distribution of PDE4 subtypes in the skin was investigated by immunostaining.

RESULTS

Topical E6005 and intradermal 8-bromo-cAMP significantly inhibited SLIGRL-NH2-induced scratching and cutaneous nerve firing. Topical E6005 increased cutaneous cAMP content. Topical E6005 and intradermal 8-bromo-cAMP inhibited cutaneous LTB4 production induced by SLIGRL-NH2, which has been shown to elicit LTB4-mediated scratching. E6005 and 8-bromo-cAMP inhibited SLIGRL-NH2-induced LTB4 production in the cultured murine keratinocytes also. PDE4 subtypes were mainly expressed in keratinocytes and mast cells in the skin.

CONCLUSIONS

The results suggest that topical E6005 treatment inhibits PAR2-associated itching. Inhibition of LTB4 production mediated by an increase in cAMP may be partly involved in the antipruritic action of E6005.

Attenuation of TNF production and experimentally induced inflammation by PDE4 inhibitor rolipram is mediated by MAPK phosphatase-1

BACKGROUND AND PURPOSE

3',5'-Cyclic nucleotide PDE4 is expressed in several inflammatory and immune cells, and PDE4 catalyses the hydrolysis of cAMP to 5'AMP, down-regulating cAMP signalling in cells. MAPK phosphatase-1 (MKP-1) is an endogenous p38 MAPK signalling suppressor and limits inflammatory gene expression and inflammation. In the present study, we investigated the effect of a PDE4 inhibitor rolipram on MKP-1 expression and whether MKP-1 is involved in the anti-inflammatory effects of rolipram.

EXPERIMENTAL APPROACH

The effect of rolipram on TNF production was investigated in J774 mouse macrophage cell line and in primary mouse peritoneal macrophages (PM) from wild-type (WT) and MKP-1(-/-) mice. We also investigated the effect of rolipram on carrageenan-induced paw inflammation in WT and MKP-1(-/-) mice.

KEY RESULTS

MKP-1 expression was enhanced by rolipram, by a non-selective PDE inhibitor IBMX and by a cAMP analogue 8-Br-cAMP in J774 cells and in PM. Enhanced MKP-1 mRNA expression by rolipram was reversed by a PKA inhibitor. Rolipram, IBMX and 8-Br-cAMP also inhibited TNF production in activated macrophages. Accordingly, rolipram inhibited TNF production in PMs from WT mice but, interestingly, not in PMs from MKP-1(-/-) mice. Furthermore, rolipram attenuated carrageenan-induced paw inflammation in WT but not in MKP-1(-/-) mice.

CONCLUSIONS AND IMPLICATIONS

PDE4 inhibitor rolipram was found to enhance the expression of MKP-1, and MKP-1 mediated, at least partly, the anti-inflammatory effects of PDE4 inhibition. The results suggest that compounds that enhance MKP-1 expression and/or MKP-1 activity hold potential as novel anti-inflammatory drugs.

Phospholipase cε, an effector of ras and rap small GTPases, is required for airway inflammatory response in a mouse model of bronchial asthma

Background

Phospholipase Cε (PLCε) is an effector of Ras and Rap small GTPases and expressed in non-immune cells. It is well established that PLCε plays an important role in skin inflammation, such as that elicited by phorbol ester painting or ultraviolet irradiation and contact dermatitis that is mediated by T helper (Th) 1 cells, through upregulating inflammatory cytokine production by keratinocytes and dermal fibroblasts. However, little is known about whether PLCε is involved in regulation of inflammation in the respiratory system, such as Th2-cells-mediated allergic asthma.

Methods

We prepared a mouse model of allergic asthma using PLCε^+/+ mice and PLCε^ΔX/ΔX mutant mice in which PLCε was catalytically-inactive. Mice with different PLCε genotypes were immunized with ovalbumin (OVA) followed by the challenge with an OVA-containing aerosol to induce asthmatic response, which was assessed by analyzing airway hyper-responsiveness, bronchoalveolar lavage fluids, inflammatory cytokine levels, and OVA-specific immunoglobulin (Ig) levels. Effects of PLCε genotype on cytokine production were also examined with primary-cultured bronchial epithelial cells.

Results

After OVA challenge, the OVA-immunized PLCε^ΔX/ΔX mice exhibited substantially attenuated airway hyper-responsiveness and broncial inflammation, which were accompanied by reduced Th2 cytokine content in the bronchoalveolar lavage fluids. In contrast, the serum levels of OVA-specific IgGs and IgE were not affected by the PLCε genotype, suggesting that sensitization was PLCε-independent. In the challenged mice, PLCε deficiency reduced proinflammatory cytokine production in the bronchial epithelial cells. Primary-cultured bronchial epithelial cells prepared from PLCε^ΔX/ΔX mice showed attenuated pro-inflammatory cytokine production when stimulated with tumor necrosis factor-α, suggesting that reduced cytokine production in PLCε^ΔX/ΔX mice was due to cell-autonomous effect of PLCε deficiency.

Conclusions

PLCε plays an important role in the pathogenesis of bronchial asthma through upregulating inflammatory cytokine production by the bronchial epithelial cells.

Current and novel bronchodilators in respiratory disease

PURPOSE OF REVIEW

β2-Agonists and muscarinic antagonists are widely used to treat asthma and chronic obstructive pulmonary disease (COPD), and a number of novel drug targets are being investigated for potential clinical utility. This review will summarize current developments in the field.

RECENT FINDINGS

The clinical effectiveness of a number of once a day inhaled β2-agonists and muscarinic antagonists is a major advance providing sustained bronchodilation in asthma and COPD. The identification of novel targets (e.g. bitter taste receptor TASR2), the demonstration of clinical effectiveness of others [e.g. phosphodiesterase (PDE)3/4] and exploring the potential of inverse agonists/biased agonists are evidence of continuing interest in the development of novel bronchodilators.

SUMMARY

Novel long-acting β2-agonists (e.g. indacaterol, vilanterol, olodaterol and carmoterol) and muscarinic antagonists (e.g. tiotropium, aclidinium, glycopyrronium and umeclidinium bromide) document sustained bronchodilation and their combination provides additional benefits over monotherapy. Not surprisingly, inhaled long-acting β2-agonist and long-acting muscarinic antagonists remain the drugs of choice for maintenance bronchodilation. However, there is a continued interest in developing novel bronchodilators illustrated by the clinical effectiveness of long acting mixed PDE3/4 inhibitors, vasointestinal peptide adenylyl cyclase agonists and inverse agonists/biased agonists for the β2-adrenoceptor, and the identification of intracellular (e.g. Rho kinase, exchange proteins activated by cyclic AMP) and cell surface (e.g. TAS2R, natriuretic peptide receptor) targets.

Mice deficient in phosphodiesterase-4A display anxiogenic-like behavior

RATIONALE

Phosphodiesterases (PDEs) are a super family of enzymes responsible for the halting of intracellular cyclic nucleotide signaling and may represent novel therapeutic targets for treatment of cognitive disorders. PDE4 is of considerable interest to cognitive research because it is highly expressed in the brain, particularly in the cognition-related brain regions. Recently, the functional role of PDE4B and PDE4D, two of the four PDE4 subtypes (PDE4A, B, C, and D), in behavior has begun to be identified; however, the role of PDE4A in the regulation of behavior is still unknown.

OBJECTIVES

The purpose of this study was to characterize the functional role of PDE4A in behavior.

METHODS

The role of PDE4A in behavior was evaluated through a battery of behavioral tests using PDE4A knockout (KO) mice; urine corticosterone levels were also measured.

RESULTS

PDE4A KO mice exhibited improved memory in the step-through-passive-avoidance test. They also displayed anxiogenic-like behavior in elevated-plus maze, holeboard, light-dark transition, and novelty suppressed feeding tests. Consistent with the anxiety profile, PDE4A KO mice had elevated corticosterone levels compared with wild-type controls post-stress. Interestingly, PDE4A KO mice displayed no change in object recognition, Morris water maze, forced swim, tail suspension, and duration of anesthesia induced by co-administration of xylazine and ketamine (suggesting that PDE4A KO may not be emetic).

CONCLUSIONS

These results suggest that PDE4A may be important in the regulation of emotional memory and anxiety-like behavior, but not emesis. PDE4A could possibly represent a novel therapeutic target in the future for anxiety or disorders affecting memory.

Discovery of triazines as selective PDE4B versus PDE4D inhibitors

In this study we report a series of triazine derivatives that are potent inhibitors of PDE4B. We also provide a series of structure activity relationships that demonstrate the triazine core can be used to generate subtype selective inhibitors of PDE4B versus PDE4D. A high resolution co-crystal structure shows that the inhibitors interact with a C-terminal regulatory helix (CR3) locking the enzyme in an inactive 'closed' conformation. The results show that the compounds interact with both catalytic domain and CR3 residues. This provides the first structure-based approach to engineer PDE4B-selective inhibitors.

PDE inhibitors currently in early clinical trials for the treatment of asthma

INTRODUCTION

PDE inhibitors could be useful in the treatment of asthma because of their bronchodilator and/or anti-inflammatory activities. Recently, some selective PDE3, PDE4 and PDE3/4 inhibitors have been shown to have beneficial effects in patients with asthma suggesting that such drugs may offer novel therapeutic options for the treatment of this disease.

AREAS COVERED

The authors describe the main PDE families that could be involved in asthma as well as the PDE inhibitors that have been evaluated for the treatment of asthma.

EXPERT OPINION

Although the potential therapeutic utility of PDE inhibitors has been demonstrated in various animal models of asthma, their clinical efficacy have been restricted by the dose-limiting side effects; no PDE inhibitor has yet been approved for the treatment of patients with asthma. Although new PDE inhibitors have been synthesised, most data are from cellular and tissue-level studies with human trials still on the horizon. Apparently, only CHF 6001, an inhaled PDE4 inhibitor, and RPL554, a dual PDE3/4 inhibitor, are still under clinical development. Further data from these new drugs are eagerly anticipated to better understand where these drugs might stand in the future treatment of asthma.