Phosphodiesterase 7A: a new therapeutic target for alleviating chronic inflammation?

Neuronal lack of PDE7a disrupted working memory, spatial learning, and memory but facilitated cued fear memory in mice

BACKGROUND

PDEs regulate cAMP levels which is critical for PKA activity-dependent activation of CREB-mediated transcription in learning and memory. Inhibitors of PDEs like PDE4 and Pde7 improve learning and memory in rodents. However, the role of PDE7 in cognition or learning and memory has not been reported yet.

METHODS

Therefore, we aimed to explore the cognitive effects of a PDE7 subtype, PDE7a, using combined pharmacological and genetic approaches.

RESULTS

PDE7a-nko mice showed deficient working memory, impaired novel object recognition, deficient spatial learning & memory, and contextual fear memory, contrary to enhanced cued fear memory, highlighting the potential opposite role of PDE7a in the hippocampal neurons. Further, pharmacological inhibition of PDE7 by AGF2.20 selectively strengthens cued fear memory in C57BL/6 J mice, decreasing its extinction but did not affect cognitive processes assessed in other behavioral tests. The further biochemical analysis detected deficient cAMP in neural cell culture with genetic excision of the PDE7a gene, as well as in the hippocampus of PDE7a-nko mice in vivo. Importantly, we found overexpression of PKA-R and the reduced level of pPKA-C in the hippocampus of PDE7a-nko mice, suggesting a novel mechanism of the cAMP regulation by PDE7a. Consequently, the decreased phosphorylation of CREB, CAMKII, eif2a, ERK, and AMPK, and reduced total level of NR2A have been found in the brain of PDE7a-nko animals. Notably, genetic excision of PDE7a in neurons was not able to change the expression of NR2B, BDNF, synapsin1, synaptophysin, or snap25.

CONCLUSION

Altogether, our current findings demonstrated, for the first time, the role of PDE7a in cognitive processes. Future studies will untangle PDE7a-dependent neurobiological and molecular-cellular mechanisms related to cAMP-associated disorders.

Circ_0091702 relieves lipopolysaccharide (LPS)-induced cell injury by regulating the miR-182/PDE7A axis in sepsis

Circular RNA (circRNA) plays an important role in the progression of sepsis. Circ_0091702 has been found to be an important regulator of sepsis progression, so its role and mechanism in sepsis progression deserve to be further explored. LPS could suppress cell viability, while enhance cell apoptosis and inflammation to induce cell injury. Circ_0091702 was downregulated in LPS-induced HK2 cells, and its overexpression alleviated LPS-induced cell injury. MiR-182 could be sponged by circ_0091702. Moreover, miR-182 inhibitor could relieve LPS-induced cell injury, and its overexpression also reversed the inhibition of circ_0091702 on LPS-induced cell injury. PDE7A was a target of miR-182, and its expression was reduced in LPS-induced HK2 cells. Additionally, silencing of PDE7A reversed the suppressive effect of circ_0091702 on LPS-induced cell injury. Our data suggested that circ_0091702 sponged miR-182 to regulate PDE7A, thereby alleviating LPS-induced cell injury in sepsis.

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

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

Phosphodiesterase 7 Regulation in Cellular and Rodent Models of Parkinson's Disease

Parkinson's disease is characterized by a loss of dopaminergic neurons in the ventral midbrain. This disease is diagnosed when around 50% of these neurons have already died; consequently, therapeutic treatments start too late. Therefore, an urgent need exists to find new targets involved in the onset and progression of the disease. Phosphodiesterase 7 (PDE7) is a key enzyme involved in the degradation of intracellular levels of cyclic adenosine 3', 5'-monophosphate in different cell types; however, little is known regarding its role in neurodegenerative diseases, and specifically in Parkinson's disease. We have previously shown that chemical as well as genetic inhibition of this enzyme results in neuroprotection and anti-inflammatory activity in different models of neurodegenerative disorders, including Parkinson's disease. Here, we have used in vitro and in vivo models of Parkinson's disease to study the regulation of PDE7 protein levels. Our results show that PDE7 is upregulated after an injury both in the human dopaminergic cell line SH-SY5Y and in primary rat mesencephalic cultures and after lipopolysaccharide or 6-hidroxydopamine injection in the Substantia nigra pars compacta of adult mice. PDE7 increase takes place mainly in degenerating dopaminergic neurons and in microglia cells. This enhanced expression appears to be direct since 6-hydroxydopamine and lipopolysaccharide increase the expression of a 962-bp fragment of its promoter. Taking together, these results reveal an essential function for PDE7 in the pathways leading to neurodegeneration and inflammatory-mediated brain damage and suggest novel roles for PDE7 in neurodegenerative diseases, specifically in PD, opening the door for new therapeutic interventions.

Exposure of trophoblast cells to fine particulate matter air pollution leads to growth inhibition, inflammation and ER stress

Ambient air pollution is considered a major environmental health threat to pregnant women. Our previous work has shown an association between exposure to airborne particulate matter (PM) and an increased risk of developing pre-eclamspia. It is now recognized that many pregnancy complications are due to underlying placental dysfunction, and this tissue plays a pivotal role in pre-eclamspia. Recent studies have shown that PM can enter the circulation and reach the human placenta but the effects of PM on human placental function are still largely unknown. In this work we investigated the effects of airborne PM on trophoblast cells. Human, first trimester trophoblast cells (HTR-8/SV) were exposed to urban pollution particles (Malmö PM2.5; Prague PM10) for up to seven days in vitro and were analysed for uptake, levels of hCGβ and IL-6 secretion and proteomic analysis. HTR-8/SVneo cells rapidly endocytose PM within 30 min of exposure and particles accumulate in the cell in perinuclear vesicles. High doses of Prague and Malmö PM (500-5000 ng/ml) significantly decreased hCGβ secretion and increased IL-6 secretion after 48 h exposure. Exposure to PM (50 ng/ml) for 48h or seven days led to reduced cellular growth and altered protein expression. The differentially expressed proteins are involved in networks that regulate cellular processes such as inflammation, endoplasmic reticulum stress, cellular survival and molecular transport pathways. Our studies suggest that trophoblast cells exposed to low levels of urban PM respond with reduced growth, oxidative stress, inflammation and endoplasmic reticulum stress after taking up the particles by endocytosis. Many of the dysfunctional cellular processes ascribed to the differentially expressed proteins in this study, are similar to those described in PE, suggesting that low levels of urban PM may disrupt cellular processes in trophoblast cells. Many of the differentially expressed proteins identified in this study are involved in inflammation and may be potential biomarkers for PE.

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.

Deducting MicroRNA-Mediated Changes Common in Bronchial Epithelial Cells of Asthma and Chronic Obstructive Pulmonary Disease-A Next-Generation Sequencing-Guided Bioinformatic Approach

Asthma and chronic obstructive pulmonary disease (COPD) are chronic airway inflammatory diseases that share some common features, although these diseases are somewhat different in etiologies, clinical features, and treatment policies. The aim of this study is to investigate the common microRNA-mediated changes in bronchial epithelial cells of asthma and COPD. The microRNA profiles in primary bronchial epithelial cells from asthma (AHBE) and COPD (CHBE) patients and healthy subjects (NHBE) were analyzed with next-generation sequencing (NGS) and the significant microRNA changes common in AHBE and CHBE were extracted. The upregulation of hsa-miR-10a-5p and hsa-miR-146a-5p in both AHBE and CHBE was confirmed with quantitative polymerase chain reaction (qPCR). Using bioinformatic methods, we further identified putative targets of these microRNAs, which were downregulated in both AHBE and CHBE: miR-10a-5p might suppress BCL2, FGFR3, FOXO3, PDE4A, PDE4C, and PDE7A; miR-146a-5p might suppress BCL2, INSR, PDE4D, PDE7A, PDE7B, and PDE11A. We further validated significantly decreased expression levels of FOXO3 and PDE7A in AHBE and CHBE than in NHBE with qPCR. Increased serum miR-146a-5p level was also noted in patients with asthma and COPD as compared with normal control subjects. In summary, our study revealed possible mechanisms mediated by miR-10a-5p and miR-146a-5p in the pathogenesis of both asthma and COPD. The findings might provide a scientific basis for developing novel diagnostic and therapeutic strategies.

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

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

Epac Function and cAMP Scaffolds in the Heart and Lung

Evidence collected over the last ten years indicates that Epac and cAMP scaffold proteins play a critical role in integrating and transducing multiple signaling pathways at the basis of cardiac and lung physiopathology. Some of the deleterious effects of Epac, such as cardiomyocyte hypertrophy and arrhythmia, initially described in vitro, have been confirmed in genetically modified mice for Epac1 and Epac2. Similar recent findings have been collected in the lung. The following sections will describe how Epac and cAMP signalosomes in different subcellular compartments may contribute to cardiac and lung diseases.

MicroRNA-712 restrains macrophage pro-inflammatory responses by targeting LRRK2 leading to restoration of insulin stimulated glucose uptake by myoblasts

Chronic inflammatory diseases such as insulin resistance, Type 2 diabetes, neurodegenerative diseases etc., are shown to be caused due to imbalanced activation states of macrophages. MicroRNAs which are transcriptional/post-transcriptional regulators of gene expression drive several pathophysiological processes including macrophage polarization. However the functional role of microRNAs in regulating inflammation induced insulin resistance is ill defined. In our current study we observed that the expression of miR-712 was reduced in macrophages exposed to LPS and IFN-γ. Ectopic expression of miR-712 in RAW 264.7 mouse macrophages impaired the expression of iNOS protein and secretion of pro-inflammatory cytokines such as TNF-α, IL-6 and IFN-β which in turn led to improved insulin stimulated glucose uptake in co-cultured L6 myoblasts. Mechanistically, we identified that miR-712 targets the 3'UTR of a potent inflammatory gene LRRK2 and dampens the phosphorylation of p38 and ERK1/2 kinases. Taken together, our data underscore the regulatory role of miR-712 in restoring insulin stimulated glucose uptake by myoblasts through down-regulating macrophage mediated inflammatory responses.

The cAMP Pathway as Therapeutic Target in Autoimmune and Inflammatory Diseases

Nucleotide signaling molecules contribute to the regulation of cellular pathways. In the immune system, cyclic adenosine monophosphate (cAMP) is well established as a potent regulator of innate and adaptive immune cell functions. Therapeutic strategies to interrupt or enhance cAMP generation or effects have immunoregulatory potential in autoimmune and inflammatory disorders. Here, we provide an overview of the cyclic AMP axis and its role as a regulator of immune functions and discuss the clinical and translational relevance of interventions with these processes.

PDE7 inhibitor TC3.6 ameliorates symptomatology in a model of primary progressive multiple sclerosis

BACKGROUND AND PURPOSE

cAMP plays an important role in the transduction of signalling pathways involved in neuroprotection and immune regulation. Control of the levels of this nucleotide by inhibition of cAMP-specific PDEs such as PDE7 may affect the pathological processes of neuroinflammatory diseases like multiple sclerosis (MS). In the present study, we evaluated the therapeutic potential of the selective PDE7 inhibitor, TC3.6, in a model of primary progressive multiple sclerosis (PPMS), a rare and severe variant of MS.

EXPERIMENTAL APPROACH

Theiler's murine encephalomyelitis virus-induced demyelinated disease (TMEV-IDD) is one of the models used to validate the therapeutic efficacy of new drugs in MS. As recent studies have analysed the effect of PDE7 inhibitors in the EAE model of MS, here the TMEV-IDD model was used to test their efficacy in a progressive variant of MS. Mice were subjected to two protocols of TC3.6 administration: on the pre-symptomatic phase and once the disease was established.

KEY RESULTS

Treatment with TC3.6 ameliorated the disease course and improved motor deficits of infected mice. This was associated with down-regulation of microglial activation and reduced cellular infiltrates. Decreased expression of pro-inflammatory mediators such as COX-2 and the cytokines, IL-1β, TNF-α, IFN-γ and IL-6 in the spinal cord of TMEV-infected mice was also observed after TC3.6 administration.

CONCLUSION

These findings support the importance of PDE7 inhibitors, and specifically TC3.6, as a novel class of agents with therapeutic potential for PPMS. Preclinical studies are needed to determine whether their effects translate into durable clinical benefits.

Phosphodiesterase 7 inhibition induces dopaminergic neurogenesis in hemiparkinsonian rats

Parkinson's disease is characterized by a loss of dopaminergic neurons in a specific brain region, the ventral midbrain. Parkinson's disease is diagnosed when approximately 50% of the dopaminergic neurons of the substantia nigra pars compacta (SNpc) have degenerated and the others are already affected by the disease. Thus, it is conceivable that all therapeutic strategies, aimed at neuroprotection, start too late. Therefore, an urgent medical need exists to discover new pharmacological targets and novel drugs with disease-modifying properties. In this regard, modulation of endogenous adult neurogenesis toward a dopaminergic phenotype might provide a new strategy to target Parkinson's disease by partially ameliorating the dopaminergic cell loss that occurs in this disorder. We have previously shown that a phosphodiesterase 7 (PDE7) inhibitor, S14, exerts potent neuroprotective and anti-inflammatory effects in different rodent models of Parkinson's disease, indicating that this compound could represent a novel therapeutic agent to stop the dopaminergic cell loss that occurs during the progression of the disease. In this report we show that, in addition to its neuroprotective effect, the PDE7 inhibitor S14 is also able to induce endogenous neuroregenerative processes toward a dopaminergic phenotype. We describe a population of actively dividing cells that give rise to new neurons in the SNpc of hemiparkinsonian rats after treatment with S14. In conclusion, our data identify S14 as a novel regulator of dopaminergic neuron generation.

SIGNIFICANCE

Parkinson's disease is a neurodegenerative disorder characterized by the loss of dopaminergic neurons in the ventral midbrain. Currently, no cure and no effective disease-modifying therapy are available for Parkinson's disease; therefore, an urgent medical need exists to discover new pharmacological targets and novel drugs for the treatment of this disorder. The present study reports that an inhibitor of the enzyme phosphodiesterase 7 (S14) induces proliferation in vitro and in vivo of neural stem cells, promoting its differentiation toward a dopaminergic phenotype and therefore enhancing dopaminergic neuron generation. Because this drug is also able to confer neuroprotection of these cells in animal models of Parkinson's disease, S14 holds great promise as a therapeutic new strategy for this disorder.

Silencing phosphodiesterase 7B gene by lentiviral-shRNA interference attenuates neurodegeneration and motor deficits in hemiparkinsonian mice

Different studies have suggested that the nucleotide cyclic adenosine 3', 5'-monophosphate can actively play an important role as a neuroprotective and anti-inflammatory agent after a brain injury. The phosphodiesterase 7 (PDE7) enzyme is one of the enzymes responsible for controlling specifically the intracellular levels of cyclic adenosine 3', 5'-monophosphate in the immune and central nervous systems. Therefore, this enzyme could play an important role in brain inflammation and neurodegeneration. In this regard, using different chemical inhibitors of PDE7 we have demonstrated their neuroprotective and anti-inflammatory activity in different models of neurodegenerative disorders, including Parkinson's disease (PD). In the present study, we have used the toxin 6-hydroxydopamine and lipopolysaccharide to model PD and explore the protective effects of PDE7B deficiency in dopaminergic neurons cell death. Lentivirus-mediated PDE7B deprivation conferred marked in vitro and in vivo neuroprotection against 6-hydroxydopamine and lipopolysaccharide toxicity in dopaminergic neurons and preserved motor function involving the dopamine system in mouse. Our results substantiate previous data and provide a validation of PDE7B enzyme as a valuable new target for therapeutic development in the treatment of PD.

Comparative assessment of PDE 4 and 7 inhibitors as therapeutic agents in experimental autoimmune encephalomyelitis

BACKGROUND AND PURPOSE

PDE4 inhibition suppresses experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). However, side effects hinder PDE4 inhibitors clinical use. PDE7 inhibition might constitute an alternative therapeutic strategy, but few data about the anti-inflammatory potential of PDE7 inhibitors are currently available. We have used the EAE model to perform a comparative evaluation of PDE4 and PDE7 inhibition as strategies for MS treatment.

EXPERIMENTAL APPROACH

Two PDE7 inhibitors, the sulfonamide derivative BRL50481 and the recently described quinazoline compound TC3.6, were assayed to modulate EAE in SJL mice, in comparison with the well-known PDE4 inhibitor Rolipram. We evaluated clinical signs, presence of inflammatory infiltrates in CNS and anti-inflammatory markers. We also analysed the effect of these inhibitors on the inflammatory profile of spleen cells in vitro.

KEY RESULTS

TC3.6 prevented EAE with efficacy similar to Rolipram, while BRL50481 had no effect on the disease. Differences between both PDE7 inhibitors are discussed. Data from Rolipram and TC3.6 showed that PDE4 and PDE7 inhibition work through both common and distinct pathways. Rolipram administration caused an increase in IL-10 and IL-27 expression which was not found after TC3.6 treatment. On the other hand, both inhibitors reduced IL-17 levels, prevented infiltration in CNS and increased the expression of the T regulator cell marker Foxp3.

CONCLUSIONS AND IMPLICATIONS

These results provide new information about the effects of Rolipram on EAE, underline PDE7 inhibition as a new therapeutic target for inflammatory diseases and show the value of TC3.6 to prevent EAE, with possible consequences for new therapeutic tools in MS.

Inhibition of endogenous phosphodiesterase 7 promotes oligodendrocyte precursor differentiation and survival

During the development of the central nervous system (CNS), oligodendrocyte precursors (OPCs) are generated in specific sites within the neural tube and then migrate to colonize the entire CNS, where they differentiate into myelin-forming oligodendrocytes. Demyelinating diseases such as multiple sclerosis (MS) are characterized by the death of these cells. The CNS reacts to demyelination and by promoting spontaneous remyelination, an effect mediated by endogenous OPCs, cells that represent approximately 5-7 % of the cells in the adult brain. Numerous factors influence oligodendrogliogenesis and oligodendrocyte differentiation, including morphogens, growth factors, chemotropic molecules, extracellular matrix proteins, and intracellular cAMP levels. Here, we show that during development and in early adulthood, OPCs in the murine cerebral cortex contain phosphodiesterase-7 (PDE7) that metabolizes cAMP. We investigated the effects of different PDE7 inhibitors (the well-known BRL-50481 and two new ones, TC3.6 and VP1.15) on OPC proliferation, survival, and differentiation. While none of the PDE7 inhibitors analyzed altered OPC proliferation, TC3.6 and VP1.15 enhanced OPC survival and differentiation, processes in which ERK intracellular signaling played a key role. PDE7 expression was also observed in OPCs isolated from adult human brains and the differentiation of these OPCs into more mature oligodendroglial phenotypes was accelerated by treatment with both new PDE7 inhibitors. These findings reveal new roles for PDE7 in regulating OPC survival and differentiation during brain development and in adulthood, and they may further our understanding of myelination and facilitate the development of therapeutic remyelination strategies for the treatment of MS.

Reduction of microglial activity in a model of multiple sclerosis by dipyridamole

Background

Despite extensive and persistent activation of microglia in multiple sclerosis (MS), microglia inhibitors have not yet been identified for treatment of the disorder. We sought to identify medications already in clinical use that could inhibit the activation of microglia. On the basis of the reported inhibitory effects of dipyridamole on phosphodiesterase activity that result in the production of various anti-inflammatory outcomes, we selected it for study. Dipyridamole is used clinically for secondary prevention in stroke. In this study, dipyridamole was examined using microglia in culture and in the mouse model of MS, experimental autoimmune encephalomyelitis (EAE).

Results

We found that dipyridamole attenuated the elevation of several cytokines and chemokines in human microglia caused by Toll-like receptor stimulation. Morphological characteristics of activated microglia in culture were also normalized by dipyridamole. In mice, dipyridamole decreased the clinical severity of EAE and reduced microglial activity and other histological indices of EAE in the spinal cord.

Conclusions

Dipyridamole is an inhibitor of microglia activation and may have a role in MS and other neurological conditions to attenuate microglial activity.

Combined use of pharmacophoric models together with drug metabolism and genotoxicity "in silico" studies in the hit finding process

In this study we propose a virtual screening strategy based on the generation of a pharmacophore hypothesis, followed by an in silico evaluation of some ADME-TOX properties with the aim to apply it to the hit finding process and, specifically, to characterize new chemical entities with potential to control inflammatory processes mediated by T lymphocytes such as multiple sclerosis, systemic lupus erithematosus or rheumatoid arthritis. As a result, three compounds with completely novel scaffolds were selected as final hits for future hit-to-lead optimization due to their anti-inflammatory profile. The biological results showed that the selected compounds increased the intracellular cAMP levels and inhibited cell proliferation in T lymphocytes. Moreover, two of these compounds were able to increase the production of IL-4, an immunoregulatory cytokine involved in the selective deviation of T helper (Th) immune response Th type 2 (Th2), which has been proved to have anti-inflammatory properties in several animal models for autoimmune pathologies as multiple sclerosis or rheumatoid arthritis. Thus our pharmacological strategy has shown to be useful to find molecules with biological activity to control immune responses involved in many inflammatory disorders. Such promising data suggested that this in silico strategy might be useful as hit finding process for future drug development.

NCS 613 exhibits anti-inflammatory effects on PBMCs from lupus patients by inhibiting p38 MAPK and NF-κB signalling pathways while reducing proinflammatory cytokine production

Systemic lupus erythematosus (SLE) is a polymorphic and multigenic autoimmune disease that evolves into progressive and chronic inflammation of multiple joints and organs. Phosphorylation and activation of p38 MAPK, along with the resulting overproduction of interleukin (IL)-1β, IL-6, and tumour necrosis factor (TNF)-α is a hallmark of inflammatory disorders. Here, we investigated the anti-inflammatory pathway modulated by NCS 613, a specific PDE4 inhibitor, on human peripheral blood mononuclear cells (PBMCs) from 5 healthy donors and 12 SLE patients. PDE4 subtypes, p38 MAPK, and IκBα protein levels were analyzed by Western blot, while NF-κB and PDE4B immunostaining was assessed in control and lipopolysaccharide (LPS) -pretreated PBMCs. Proinflammatory cytokines were quantified by ELISA, while IL-1β mRNA was resolved by RT-qPCR. NCS 613 treatment decreased PDE4B and upregulated PDE4C in human PBMCs from healthy donors and SLE patients. LPS stimulation increased p38 MAPK phosphorylation and NF-κB translocation to the nucleus, which was abolished by NCS 613 treatment. Concomitantly, NCS 613 restored IκBα detection levels in human PBMCs from both healthy donors and SLE patients. This compound also abolished LPS-induced inflammation in PBMCs by reducing IL-6, IL-8, and TNF-α cytokines. NCS 613 is a small molecule displaying anti-inflammatory properties that may provide an alternative or complementary strategy for SLE management.

Effect of phosphodiesterase 7 (PDE7) inhibitors in experimental autoimmune encephalomyelitis mice. Discovery of a new chemically diverse family of compounds

Phosphodiesterase (PDE) 7 is involved in proinflammatory processes, being widely expressed both on lymphocytes and on certain brain regions. Specific inhibitors of PDE7 have been recently reported as potential new drugs for the treatment of neurological disorders because of their ability to increase intracellular levels of cAMP and thus to modulate the inflammatory process, as a neuroprotective well-established strategy. Multiple sclerosis is an unmet disease in which pathologies on the immune system, T-cells, and specific neural cells are involved simultaneously. Therefore, PDE7 inhibitors able to interfere with all these targets may represent an innovative therapy for this pathology. Here, we report a new chemically diverse family of heterocyclic PDE7 inhibitors, discovered and optimized by using molecular modeling studies, able to increase cAMP levels in cells, decrease inflammatory activation on primary neural cultures, and also attenuate the clinical symptoms in the experimental autoimmune encephalomyelitis (EAE) mouse model. These results led us to propose the use of PDE7 inhibitors as innovative therapeutic agents for the treatment of multiple sclerosis.

Phosphodiesterase inhibitors in inflammatory bowel disease

Inflammatory bowel disease (IBD) is fundamentally a relapsing and remitting disease appearing in forms of ulcerative colitis (UC) or Crohn's disease (CD) with a non-well-known etiology. With the hope to prevent adverse drug events and to increase the efficacy of therapies for IBD, in the recent years, other than new monoclonal antibodies such as infliximab, the novel phosphodiesterase inhibitors (PDEIs) have been introduced. Among PDE4Is, rolipram, OPC-6535, mesopram, roflumilast and tetomilast have shown beneficial effects in experimental colitis. Unfortunately until now, human studies have not been successful in showing significant superiority of PDE4Is in the treatment of IBD. Parallel with discovery of PDE4Is and their anti-inflammatory properties, inhibiting other PDE isoenzymes in immune and proinflammatory cells is on the way. PDE7Is have shown synergistic effect with PDE4Is and they may act similar to PDE3Is in experimental settings. Sildenafil as the PDE5I has shown good effects in experimental colitis by balancing oxidant-antioxidant status. Although the present data about PDE superfamily and their specific roles in gastrointestinal tract is limited but inhibitors of PDE4, PDE5 and PDE7 seem good candidates as the next generation of effective drugs. The synergistic anti-inflammatory effect of PDE4Is and PDE7Is is also important.

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.

Phosphodiesterase 7 inhibition preserves dopaminergic neurons in cellular and rodent models of Parkinson disease

Background

Phosphodiesterase 7 plays a major role in down-regulation of protein kinase A activity by hydrolyzing cAMP in many cell types. This cyclic nucleotide plays a key role in signal transduction in a wide variety of cellular responses. In the brain, cAMP has been implicated in learning, memory processes and other brain functions.

Methodology/Principal Findings

Here we show a novel function of phosphodiesterase 7 inhibition on nigrostriatal dopaminergic neuronal death. We found that S14, a heterocyclic small molecule inhibitor of phosphodiesterase 7, conferred significant neuronal protection against different insults both in the human dopaminergic cell line SH-SY5Y and in primary rat mesencephalic cultures. S14 treatment also reduced microglial activation, protected dopaminergic neurons and improved motor function in the lipopolysaccharide rat model of Parkinson disease. Finally, S14 neuroprotective effects were reversed by blocking the cAMP signaling pathways that operate through cAMP-dependent protein kinase A.

Conclusions/Significance

Our findings demonstrate that phosphodiesterase 7 inhibition can protect dopaminergic neurons against different insults, and they provide support for the therapeutic potential of phosphodiesterase 7 inhibitors in the treatment of neurodegenerative disorders, particularly Parkinson disease.

Harnessing the clinical efficacy of phosphodiesterase 4 inhibitors in inflammatory lung diseases: dual-selective phosphodiesterase inhibitors and novel combination therapies

Phosphodiesterase (PDE) 4 inhibitors have been in development as a novel anti-inflammatory therapy for more than 20 years, with asthma and chronic obstructive pulmonary disease (COPD) being primary indications. Despite initial optimism, only one selective PDE4 inhibitor, roflumilast (Daxas (®)), has been approved for use in humans and available in Canada and the European Union in 2011 for the treatment of a specific population of patients with severe COPD. In many other cases, the development of PDE4 inhibitors of various structural classes has been discontinued due to lack of efficacy and/or dose-limiting adverse events. Indeed, for many of these compounds, it is likely that the maximum tolerated dose is either subtherapeutic or at the very bottom of the efficacy dose-response curve. Thus, a significant ongoing challenge that faces the pharmaceutical industry is to synthesize compounds with therapeutic ratios that are superior to roflumilast. Several strategies are being considered, but clinically effective compounds with an optimal pharmacophore have not, thus far, been reported. In this chapter, alternative means of harnessing the clinical efficacy of PDE4 inhibitors are described. These concepts are based on the assumption that additive or synergistic anti-inflammatory effects can be produced with inhibitors that target either two or more PDE families or with a PDE4 inhibitor in combination with other anti-inflammatory drugs such as a glucocorticoid.

New classes of PDE7 inhibitors identified by a fission yeast-based HTS

Studies of the phosphodiesterase PDE7 family are impeded by there being only one commercially available PDE7 inhibitor, BRL50481. The authors have employed a high-throughput screen of commercial chemical libraries, using a fission yeast-based assay, to identify PDE7 inhibitors that include steroids, podocarpanes, and an unusual heterocyclic compound, BC30. In vitro enzyme assays measuring the potency of BC30 and 2 podocarpanes, in comparison with BRL50481, produce data consistent with those from yeast-based assays. In other enzyme assays, BC30 stimulates the PDE4D catalytic domain but not full-length PDE4D2, suggesting an allosteric site of action. BC30 significantly enhances the anti-inflammatory effect of the PDE4 inhibitor rolipram as measured by release of tumor necrosis factor alpha from activated monocytes. These studies introduce several new PDE7 inhibitors that may be excellent candidates for medicinal chemistry because of the requirements for drug-like characteristics placed on them by the nature of the yeast-based screen.

A review of the herbal phosphodiesterase inhibitors; future perspective of new drugs

Phosphodiesterase inhibitors (PDEIs) are a class of drugs that are widely used because of their various pharmacological properties including cardiotonic, vasodilator, smooth muscle relaxant, antidepressant, antithrombotic, bronchodilator, antiinflammatory and enhancer of cognitive function. In the recent years, interest in drugs of plant origin has been progressively increased. Some pharmacologically active substances that come from plants demonstrate PDEI activity. They mainly belong to alkaloids, flavonoids, and saponins. In this review, studies on herbal PDEI were reviewed and their possible therapeutic applications were discussed. Screening plants for PDE inhibitory activity may help to develop standardized phytotherapeutic products or find new sources for new lead structures with PDEI pharmacological activity. The studies discussed in this paper are mainly in vitro and for more reasonable and conclusive results, it is required to conduct in vivo and finally human and clinical tests.

Phosphodiesterase genes and antidepressant treatment response: a review

Depression results in a tremendous burden to individuals suffering from the disorder and to the global health economy. Available pharmacologic treatments for depression target monoamine levels and monoamine receptors. However, delayed onset of effect, partial or inadequate treatment response, and side-effects are significant limitations of current therapies. The search for a better understanding of mechanisms of depression and for new treatment targets has turned attention to intracellular mediators. Phosphodiesterases (PDEs) are enzymes that break down the intracellular second messenger mononucleotides cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Recent data from animal and human studies indicate that PDEs may play a role in depression and in related stress conditions. PDE genes have been linked directly to depression and to other genes associated with psychiatric disorders.

Cyclic nucleotide phosphodiesterase profiling reveals increased expression of phosphodiesterase 7B in chronic lymphocytic leukemia

Cyclic nucleotide phosphodiesterase (PDE) isoforms can influence disease pathogenesis and be novel therapeutic targets. Because lower cAMP levels may contribute to the decreased apoptosis that occurs in chronic lymphocytic leukemia (CLL), we assessed the expression levels of PDE isoforms in peripheral blood mononuclear cells (PBMC) of healthy adults and patients with CLL. We found a unique PDE mRNA signature in CLL: higher levels than in normal PBMC of PDE7B (increased approximately 23-fold) and lower levels of PDE3B, 4D, 5A, and 9A mRNA (each decreased approximately 30-fold). Increased PDE7B mRNA in CLL correlates with a 10-fold-higher expression of PDE7B protein and results in an increased contribution of PDE7 to total PDE activity. Consistent with the higher level of PDE7B expression, inhibitors of PDE7 (BRL-50481, IR-202) and a dual PDE4/PDE7 inhibitor (IR-284) selectively increase apoptosis in CLL cells compared with normal PBMC or B cells. Apoptosis of CLL cells promoted by inhibitors of PDE7 and PDE4/7 is attenuated by PKA inhibition, occurs via a mitochondrial-dependent process, and is associated with increased cAMP accumulation and down-regulation of the antiapoptotic protein survivin and of PDE7B. The increase in PDE7B expression and PDE7 inhibitor-promoted apoptosis implicates PDE7B as a drug target in CLL. Our findings identify a unique PDE signature in CLL and illustrate the utility of broad analyses of PDE isoform expression in human disease.

Stereoelectronic properties of spiroquinazolinones in differential PDE7 inhibitory activity

A detailed computational study on a series of spiroquinazolinones showing phosphodiesterase 7 (PDE7) inhibitory activity was performed to understand the binding mode and the role of stereoelectronic properties in binding. Our docking studies reproduced the essential hydrogen bonding and hydrophobic interactions for inhibitors of this class of enzymes. The N1 proton of the quinazolinone scaffold was involved in H-bonding to an amide side chain of the conserved glutamine residue in the active site. The central bicyclic ring of the molecules showed hydrophobic and pi-stacking interactions with hydrophobic and aromatic amino acid residues, respectively, present in the PDE7 active site. The docked conformations were optimized with density functional theory (DFT) and DFT electronic properties were calculated. Comparison of molecular electrostatic potential (MEP) plots of inhibitors with the active site of PDE7 suggested that the electronic distribution in the molecules is as important as steric factors for binding of the molecules to the receptor. The hydrogen bonding ability and nucleophilic nature of N1 appeared to be important for governing the interaction with PDE7. For less active inhibitors (pIC(50) < 6.5), the MEP maximum at N1 of the spiroquinazolinone ring was high or low based on the electronic properties of the substituents. All the more active molecules (pIC(50) > 6.5) had MEP highest at N3, not N1. Efficient binding of these inhibitors may need some rearrangement of side chains of active-site residues, especially Asn365. This computational modeling study should aid in design of new molecules in this class with improved PDE7 inhibition.

Advantageous toxicity profile of inhaled antisense oligonucleotides following chronic dosing in non-human primates

TPI ASM8 and TPI 1100 are two products containing modified phosphorothioate antisense oligonucleotides (AONs), which are undergoing development for the treatment of asthma and chronic obstructive pulmonary disease (COPD), respectively. TPI ASM8 is comprised of two AONs, one targeting the human chemokine receptor 3 (CCR3) and the other targeting the common beta-chain of the IL-3/IL-5/GM-CSF receptors. TPI 1100 is also a dual-AON compound targeting the phosphodiesterase (PDE) 4 and 7 isotypes. For both products, the AONs are present in a 1:1 ratio by weight. Both products will be administered by inhalation to patients, and TPI ASM8 is currently undergoing Phase 2 clinical trials. As part of the safety assessment of both products, the toxicity and disposition (i.e., pharmacokinetics of the AON components in plasma and tissues) were investigated in 14-day inhalation studies in monkeys at doses ranging from 0.05 to 2.5mg/kg/day. Results indicated that both products were safe and well tolerated at all dose levels. Reversible treatment-related alterations were only observed at the high dose levels tested and were limited to changes in the respiratory tract which were characterized primarily by the presence of alveolar macrophages in the absence of a generalized inflammatory response. Plasma pharmacokinetic profiles showed very low plasma concentrations, and no plasma accumulation was observed after repeated doses. While significant amounts of the AONs of both TPI ASM8 and TPI 1100 were measured in trachea and lung, only limited amounts of the AONs could be measured in kidney and liver, which, in combination with the low plasma level data, is indicative of very low systemic exposure. Taken together, these results demonstrate that these two new AON-based products are safe and that delivery via the inhaled route achieves localized deposition in the pulmonary tract with very limited systemic exposure and reduced toxicity compared to other routes of AON administration.

Purification of recombinant human phosphodiesterase 7A expressed in Dictyostelium discoideum

Phosphodiesterase plays an important role in regulating inflammatory pathways and T cell function. The development of phosphodiesterase 7 inhibitor may give better efficacy profile over phosphodiesterase 4 inhibitors. However, the recombinant phosphodiesterase 7 is required in large quantity for high-throughput screening of new drugs by in vitro enzymatic assays. In the present study, recombinant human PDE7A1 was expressed in Dictyostelium discoideum under the control of constitutively active actin-15 promoter. The cytosolic localization of the expressed protein was confirmed by immunofluorescence studies. Upto 2 mg of recombinant protein was purified using His-Tag affinity column chromatography followed by ion-exchange Resource Q column purification. The recombinant protein expressed in D. discoideum followed Michaelis-Menten kinetics similar to the protein expressed in mammalian system and showed no major changes in affinity to substrate or inhibitors. Thus, our study clearly demonstrates a robust expression system for successful bulk production of pharmacologically active isoform of human PDE7A1 required for high-throughput assays.

The molecular basis for different recognition of substrates by phosphodiesterase families 4 and 10

Phosphodiesterases (PDEs) are key enzymes that control the cellular concentrations of the second messengers cAMP and cGMP. The mechanism for selective recognition of substrates cAMP and cGMP by individual PDE families remains a puzzle. To understand the mechanism for substrate recognition by PDE enzymes, the crystal structure of the catalytic domain of an inactive D201N mutant of PDE4D2 in complex with substrate cAMP has been determined at 1.56 A resolution. The structure shows that Gln369 forms only one hydrogen bond with the adenine of cAMP. This finding provides experimental evidence against the hypothesis of two hydrogen bonds between the invariant glutamine and the substrate cAMP in PDE4, and thus suggests that the widely circulated "glutamine switch" model is unlikely the mechanism for substrate recognition by PDEs. A structure comparison between PDE4D2-cAMP and PDE10A2-cAMP reveals an anti configuration of cAMP in PDE4D2 but syn in PDE10A2, in addition to different contact patterns of cAMP in these two structures. These observations imply that individual PDE families have their characteristic mechanisms for substrate recognition.